Shorter Contributions to General Geology 1958 GEOLOGICAL SURVEY PROFESSIONAL PAPER 334 Tflz'y Prqfessimal Paper way pué/z's/zea’ as yeparate cflapters A—H UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1962 UNITED STATES DEPARTMENT OF THE INTERIOR STEWART L. UDALL, Secretary GEOLOGICAL SURVEY Thomas B. Nolan, Director For sale by the Superintendent of Documents, US. Government Printing Off-lee Washington 25, DC. (A) (B) (C) (D) (E) (F) (G) (H) CONTENTS §E75 Pt v. 33¢ EARTH SCIENCES LIBRARY [The letters in parentheses are those used to designate the separate chapters] Tables for the calculation of lead isotOpe ages, by L. R. Stieff, T. W. Stern, Seiki Oshiro, and F. E. Senftle ____________ Fossils of the Littleton formation (Lower Devonian) of New Hampshire, by A. J. Boucot and Robert Arndt __________ Tri10bites of the Upper Cambrian Dunderberg shale, Eureka district, Nevada, by Allison R. Palmer _________________ Late Paleozoic Gastropoda from northern Alaska, by Ellis Y. Yochelson and J. Thomas Dutro, Jr ___________________ Upper Cretaceous Pelecypods of the genus I noceramus from northern Alaska, by David L. Jones and George Gryc _____ Ammonites of Early Cretaceous age (Valanginian and Hauterivian) from the Pacific Coast States, by Ralph W. Imlay- Dispersion characteristics of montmorillonite,kaolinite, and illite clays in waters of varying quality, and their control with phosphate dispersants, by B. N. Rolfe, R. F. Miller, and I. S. McQueen ___________________________________ Geology of southeastern Ventura basin, Los Angeles County, California, by E. L. Winterer and D. L. Durham ________ 184 III U. S. GOVERNMENT PRINTING OFFICE: 1962 0 -58l734 Page 1 41 53 111 149 167 229 275 Tables for the Calculation of Lead Isotope Ages f 5 éég‘ZOLOGICAL SURVEY/EROFESSIONAL PAPER 334-A Tnis report concerns woré done on oenalf of Me U. S. Atomic Energy Commission and is pnélisfiea’ witn tne permission of Me Commission 8M6 A (/Géyr‘eée/ *49'75 éflé , \1. 335’ EARTH SGIENCES LIBRARY «W *\ g ,V‘,‘ .. Tables for the Calculation * of Lead Isotope Ages By L. R. STIEFF, T. W. STERN, SEIKI OSHIRO, and F. E. SENFTLE SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY GEOLOGICAL SURVEY PROFESSIONAL PAPER 334—A Tao/es for t/ze calculation of geologic age using t/ze atomic ratios of Pbm/Um, Pbm/Um, Pb207/Pb206, anaI P bml Th2”. T/zis report concerns woré done on oe/za/f of t/ze U. S. Atomic Energy Commission anaI is pno/z's/zea' wit/z tne permission of t/ze Commission UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1959 UNITED STATES DEPARTMENT OF THE, INTERIOR FRED A. SEATON, Secretary GEOLOGICAL SURVEY Thomas B. Nolan, Director The U. S. Geological Survey Library has cataloged this publication as follows: Stieif, Lorin Rollins, 1920— Tables for the calculation of lead isotope ages, by L. R. Stiefi' [and others] Washington, U. S. Govt. Print. 03., 1959. iv, 40 p. diagrs., tables. 30 cm. (U. S. Geological Survey. Pro- fessional paper 334—A. Shorter contributions to general geology) “Tables for the calculation of geologic age using the atomic ratios of Pb206/U238, Pb207/U235, Pb207/Pb206, and Pb208/Th232.” Bibliography : p. 7. 1. Lead—Isotopes. 2. Isotopes—Tables, etc. 3. Geological time I. Title. (Series: U. S. Geological .Survey. Professional paper 334—A. Series: U. S. Geological Survey. Shorter contributions to general geology) 550.1 For sale by the Superintendent of Documents, U. S. Government Printing Office Washington 25, D. C. — Price 35 cents (paper copy) CONTENTS Page Abstract ___________________________________________ . 1 Sample age ~calculation——Continued Introduction _______________________________________ 1 Pbm/Um age method __________________ Methods of computation _____________________________ 3 PbW/U”5 age method ___________________ The N .1/ N , relation _____________________________ 3 Pb207/Pbm age method __________________ The N2o7/Nm relation ____________________________ 4 PbW/Th232 age method _________________ Sample age calculation __________________ , ___________ 5 Literature cited ___________________________ Correction for original common lead _______________ 6 Tables for the calculation of lead isotope ages __________ ILLUSTRATIONS FIGURE 1. Atomic ratio N d/N ,, plotted against the age, 1, showing the plus and minus tolerance curves ___________________ 2. Atomic ratio N207/N209 plotted against the age, 1, showing the plus and minus tolerance curves _________________ TABLES TABLE 1 Physical constants used in calculation of tables _________________________________________________ 2 Errors in t produced by uncertainties in the physical constants used In calculation __________________ 3. Range and interval of t _______________________________________________________________________ 4. Decay constants Ai1(y 1) _____________ , ________________________________________________________ III Page coxrslxlqca 9:020:19 IV paw wggzflny LETTER SYMBOLS decay constant age, in millions of years half life number of atoms number of atoms of daughter products number of atoms of parent present—day atomic ratio of U238 to U235 year atomic ratio SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY TABLES FOR THE CALCULATION OF LEAD ISOTOPE AGES By L. R. STIEFF, T. W. STERN, SEIKI OSHIRO, and F. E. SENFTLE ABSTRACT Tables are presented for calculating geologic age by using the atomic ratios of Pbm/Um, Pb207/U235, Pb207/Pb205, and Pb208/Th232. Tables of values of N d/N ,, and t are given for the age equation Nd... .- N,_exPM 1 where k is the decay constant, t is age, in millions of years, N a is the number of atoms of daughter products, and N p is the number of atoms of parent. Values for Nm/Nm and t are also given in tabular form for the age equation M: exphmt— 1 N zoo Ic(exp)\mt— 1) where N207 and N205 are the number of atoms of radiogenic Pb”? and Pbm, respectively, and where k, the present-day atomic ratio of U238 to U235, is taken as 137.7. The half lives (T) of U233, U235, and Th232 used in the calculations are: T235=4.51><10° years, Tm=7.13><108 years, T232=1.42><10‘° years. The tables cover selected values of t from 1 to 6,000 million years (6X109 years) at intervals of t ranging from 1 to 15 million years. Only the calculated errors in 25 resulting from experi— mental uncertainties in the determinations of the decay con- stants and relative abundance of U238 and U235 have been in- cluded. An example is given for a hypothetical geologic age calculation by use of these tables. INTRODUCTION Although lead isotope age calculations are in general not difficult to make, both graphs and nomographs are available in the literature to simplify these computa- tions. Holmes (1931, p. 208) published in “The Age of the Earth” a graphical solution of the age equation involving total lead, uranium, and thorium. Eight years later Wickman (1939, p. 6) published several nomographs that gave ages in millions of years equiva- lent to the weight ratios of Pbm/Um, Pb207/Pb206, and Pom/Th”? More recently, Kulp and others (1954, p. 345) have prepared nomographs of the three age ratios mentioned above as well as the ratios of Pbm/U”5 in terms of numbers of atoms rather than in weight percent. During the course of geochronological studies made by the U. S. Geological Survey it was found desirable to have age equivalents for the various lead isotope ratios at smaller intervals and over a greater range of time than could be obtained from the references men- tioned above. Initially, these tables were calculated for the atomic ratios of Pbm/U233, Pb207/U235, Pb207/Pbm, and l"b"’°8/Th232 at intervals of t of 1 million years from 1 million years to 6,000 million years. The tables in this paper are an abridgment of the original tables. The calculations were carried to 6,000 million years, an age greater than the probable age of the earth, so that speculative calculations could be made. They are being published because it has been found that for certain types of analysis of isotopic age data these tables are more satisfactory than the published nomo- graphs.‘ For example, the tables offer greater accuracy and ease of manipulation than the nomographs in making repeated solutions of the age equations. Such repeated calculations are particularly useful in evaluat— ing different geologic processes which have produced discordant ages. The general form of the age equations used to com- pute the tables was developed by Kovarik (1931, p. 73), Keevil (1939, p. 195), and others. Solutions were obtained for equations of the form N d ——= — 1. N, expxt The equation - N22: £32351: N206 k (eXPMsst — 1) was solved by iteration. It is important to note that the ratios of N d/N, and N207/N206 in the present tables are given as ratios of number of atoms of daughter (N d) to number of atoms of parent (Np), and number of atoms of Pb207 (N207) t0 Pb206 (N205) and not in terms ~ of Weight percent. The authors wish to express their appreciation to F. W. Reilly and D. B. Rock of the Computer Branch for their aid in the operation of the computer, and also 1 2 SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY to Raynor L. Duncomb, Julena S. Duncomb and G. M. Clemence, of the U. S. Naval Observatory, for their cooperation and help in preparing the tables for printing. This work is part of a program being con- ducted by the U. S. Geological Survey on behalf of the Division of Research of the U. S. Atomic Energy Commission. The half lives, decay constants, and ratio of Um/U235 used in the calculations are shown in table 1, along with those used by Wickman and by Kulp and others. The values used in this paper were chosen for the following reasons. Fleming and others (1952, p. 642) discuss in some detail the earlier work on the determination of the half life of U235. The weighted average of all previous measurements is numerically the same as their value with a slightly larger probable error. The half- life data of Fleming and others was therefore chosen for these calculations. These authors have also dis- cussed the past determinations of the half life of U238. From their “best values” a half life of (4.51:!:0.007) X 109 years has been calculated. More recently Kovarik and Adams (1955, p. 46) have redetermined three of their original specimens. Their newest value, (4507:]: 0.009)><109 years, lies within the limits of error of the “best value” calculation of Fleming and others. In view of the small differences in half lives, as well as the differences in probable error, a value of (4.51 $0.01) X 109 years was therefore chosen. TABLE 1.—-Physical constants used in calculation of tables Kulp and others, 1954 Wickman, 1939 Nucllde This paper U238 _______________________________ 1 T=(4.51;1: 0.01) X 10°y A: 1.5359X10‘10y‘1 U235 _______________________________ 1 T: (7.13:1:0.16)X103y X=9.72m)< 10—1014—l Th7“2 ______________________________ 2 T=(1.42i0.07)><101°y >\=4.88.3><10‘“y—I Atomic ratio Um/U235 _______________ 3 137.7:I:0.32 T= (4.49:1:0.01)><10°y T=4.56><10°y >\= 1.541 X 10‘1°y‘l )‘= 1.52 X 10—101;—1 T= (7.13:1:0.16)><103y T=7.14><103y )\=9.722>< 10—101]—1 T: (1.39 :I: 0.02) X 10101] A=4.987X 10—1131—l 137.7:1:0.5 >.=9.72><10-wy-l T=1.39X 10mg i=4.99><1o-uy-I 139.04: 1.0 1 Fleming and others, 1952, p. 642. 1 Senftle, Farley, and Lazar, 1956, p. 1629. 3 Senftle, Stieff, Cuttitta, and Kuroda, 1957, p. 189. Kovarik and Adams (1938, p. 413) have also deter- mined the half life of Th”? as (1.391.03)X101° years. In their very thorough and excellent paper they deter- mined in addition the branching ratio of Bi”. Recently this branching ratio and the half life of thorium have been redetermined by Senftle, Farley, and Lazar (1956). Using a pulse-counting technique they obtained a branching ratio 7.4 percent higher than that obtained by Kovarik and Adams. Although the half life as determined by Kovarik and Adams does not directly depend on the branching ratio of Bi” the half life, ’ was determined from the basic alpha-count data. In spite of the careful alpha-counting techniques used by Kovarik and Adams, the differences in the branching ratio of Bi212 raise some questions on the earlier Th”? half-life determinations. Also, their calculations de- pended on the existence of radioactive equilibrium between Th232 and Th228 based on the age of the thorite and the assumption that the daughter products were undisturbed by processes of alteration and weathering. Senftle, Farley, and Lazar, however, have shown that even for a specimen of fresh thorite chosen because it showed no signs of alteration, the Ra"’24 was 9.5 percent less than the equilibrium amounts; this implies a loss of its parents Th"’28 and Ram. The tendency of radio.- genic daughter products to migrate has beenpointed out in detail by Rosholt (1958). Hence, the value of the half life (1.42:|:0.07)><101° years as determined by Senftle and others was used, even though the quoted percent of error is somewhat larger than that of Kovarik and Adams. The determination of the atomic ratio Nzgg/N235 has been discussed by Fleming and others (1952, p. 642). They observe that a mean value of 137.7 “falls within the limits of error of all values reported.” Kulp and others (1954, p. 345) used a value of 137.7:t0.5. More recently Senftle, Stieff, Cuttitta, and Kuroda (1957, p. 190) have shown an average value of 137.7:1: 0.32 for 13 uranium specimens. This value with its somewhat smaller probable error has been used for these calculations. In general, the ratios in the tables are given to four significant places, a value somewhat better than can be justified by present physical measurements and analytical methods. The remaining two numbers in smaller type have been included because of their usefulness in certain theoretical calculations. ’ Corre- sponding to each ratio a value of t plus or minus the error may be read from the tables or may be directly interpolated as a first approximation if the exact value of the ratio desired is not found. The limits of error for t shown in the tables have been calculated by using only the limits of experimental error reported for TABLES FOR THE CALCULATION OF LEAD ISOTOPE AGES . 3 the determinations of the decay constants and the abundance ratios, and the error term has been rounded to the nearest 0.1 million years. The error calculations are treated more fully in the section “Methods of computation.” TABLE 2.—Errors in t produced by' uncertainties in the physical constants used in calculation Errors in calculation of various ages, both in millions of years Age method 100 500 , 1,500 2,500 4,500 6,000 Pbm/U”8 _______________________________________ i0. 22 :t 1. 11 i3. 33 :I: 5. 54 j: 9. 98 i 13. 30 Pb207/U235 _______________________________________ i 2. 24 :I: 11. 22 $33. 66 :l: 56. 10 :l; 100. 98 j; 134. 69 PbW/Pbm ______________________________________ :1: 57. 18 :l: 63. 95 i 82. 21 i 102. 38 i: 146. 50 :1: 181. 65 Pbm/Th“2 ______________________________________ :t 4. 93 :1: 24. 65 :l: 73. 94 :t 123. 24 j: 221. 83 j; 295. 77 Table 2 lists for several different t’s the limits of error might be obtained for the same value of t. Admittedly, in the age calculations resulting from the uncertainties in the physical constants used. This table shows that the limits of error in calculated age for the Pb‘m/U238 method are less than the limits of error for the other three methods. The selection of intervals of t (table 3) was determined in part by the limits of error for the TABLE 3.—Range and interval of t Range (years) Interval (years) 1x10° to 500x10° 1x10° 500x10° to 1,500x10° 2x10° 1,500x10° to 2,500x10° 5x10° 2,500>< 10° to 4,500>< 10° 10x10° 4,500>< 10° to 6,000>< 10° 15><1O° Pbm/U238 method. In spite‘of the larger errors inherent in the other methods, the same interval of t has been used for all four tables in order that equivalent ratios the intervals chosen for the abridged tables are smaller that the uncertainties in the calculated ages introduced by the most precise analytical techniques currently available. However, improvements in the quantitative determination of lead, uranium, thorium, and isotopic abundance may ultimately permit the measurement of small differences in age (1 to 2 million years) of radio- active minerals from rocks of Cambrian age or younger. METHODS OF COMPUTATION THE Nd/Np RELATION For the purpose of programing this work for the digital computer, the general form of the age equation was used, N W:=R=expMIt—1 (1) where i=1, 2, 3 and j =1, 2, 3. The values of the decay constants with their limits, Mi, used for these calculations are shown in table 4. ‘ TABLE 4.—Decay constants Mi(y") x x plus error x minus error U133>\11= 1.5369X 10-10 U2357\21= 9.72m X 10—10 ThmMI= 4.8813X10‘ll K12: 1.5335X 10—‘0 X22: 9.5032 X 10"" X32 = 4.6520 )(10'11 X13= 1.5403X 10—10 K23=9.9447X 10‘” >\33=5.1344>< 10‘ll \ In computing expx,It—1 the exponential series was expanded ' x2 :63 n=1 7t! ”—1 n (n—l)! 13:77! the series. N 0 round off was used in the evaluation and the maximum error in expat it can be shown to be less than 5X10‘5. The problem of calculating the errors in the ages due and the recursion was/used to evaluate to the uncertainties in the decay constants was simpli- fied in the following graphical treatment shown in figure 1. By virtue of the geometry in figure 1, t1N= t3M= t20 where t2 is the age for a plus error in )\ and t3 is the age for a minus error in )\. Therefore, , expxtlt1—1= exthz— 1 (3a) and exletl— 1 =expk13t3— 1. (3b) 4 SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY FIGURE 1.—-Atomlc ratio N a/N, plotted against the age, t, showing the plus and minus tolerance curves. Simplifying and taking logarithms, x,,t,=>\,,t2 (4a) and x,,t,=)\,3t3. (4b) Also it is evident from figure 1 that MN=t1—t3 and N0=t2—t1. Thus, by the substitution the error in the age, MN and N0, can be simply evaluated in a con- venient form, h M, )\ N0=t1(>\~i‘—1) [I If new, more nearly accurate, values of the decay constants become available, it is a simple matter to obtain the corrected age from the tables. For example, suppose the half life of the Th232 is changed from 1.42zt 0.O7><1010 years to 1.45;{:0.02X101° years. Calcu- lated in this way using T instead of )\, the new value of the age, tl’ say, will be (5a) and ’ (5b) ,_1.45 t1_ t‘ _ 1.42 Similarly, t2’ and t3’ will be t,__1.47 t1 2 _ 1.42 and t,_1.43 t1. 3 “ 1.42 Then, if one assumes an experimental ratio of Nm/Nm of (0.050023), the corresponding value of 131 (NM/N232 table) is 1,000><106 years. The new half—life value would yield tl’, t2", and t3’ ages of 1,021><106 years, 1,035X106 years, and 1,007><106 years, respec- tively. Thus, the tables can still be used even if new values of the half lives are redetermined at a later date. THE Nm/Nm RELATION The general equation, &_ __ expkzlt—l (6) N20,,— ‘k1(exp>\,,t—1)’ was used for computing the szm/Pb206 table. The value, k1, used for the UmlU235 atomic ratio was 137.7 :l:0.32 where kg and k3 designate the abundance ratios with the plus and minus tolerances, respectively. TABLES FOR THE CALCULATION OF LEAD ISOTOPE AGES 5 As in the Nd/Np relation previously described, the calculation of limits of error in the age due to uncertain- ties in the decay constants has been simplified for programing on the digital computer. By use of a similar graphical argument as shown in figure 2, it can be seen that expMItl—l ,expxgztz—l = = (7a) k1 (eprlltlnl) k2 (exphlztz—l) and x )x t—l ex )\ t—l e P 21 1 = P 23 3 (7b) =k1 (expxlltl—l) k3 (expxlata—if However, unlike the previous solution, the equations (7a, b) have no direct solution for £2 and t3 and an iterative-approximation method had to be used. The left-hand sides of the equations can be evaluated. The right—hand sides are quotients of infinite series in t2 and t3. An initial guess was made for t; or £3, as the case may be, and a test for equality was made. Succes— sive approximations were made to the i values until equality was obtained. For the particular case where tl=t2=t3=0, the ratio R is indeterminate. However, by using L’Hospital’s ule an approximate but quite accurate value of R can ”207 ”206 R3 - 0.0470 R, = 0.0459 R2 = 0.0449 be obtained. Hence, the limits of the ratios as t1, t2, and t3—>0, are R,=0.045936, R2=0.0449, and R3 =0.0470. Thus, radiogenic lead being formed at the present time should and does have a Nam/N206 ratio between 0.045 and 0.047, a value very close to the experimentally observed value. From the age tables it can be seen that below an age of 56><106 years, the Pb'm/Pb206 method has errors that are larger than the calculated value of 23. As has been mentioned, this error is due only to the uncertain- ties in the physical constants used in the calculations. It is shown in figure 2 for an age t, (which is less than 56><106 years) that the horizontal line (a—b) between the ages representing the plus and minus tolerances does not intersect the upper curve on the positive side of the coordinates because of the flatness of the curves in this region. Also, this “flatness” and the round—off error cause oscillation of approximately 0.1 to 1.0 million years in the quoted error in t for ages less than 400 million years, and small irregularities in the 5th and 6th places of the Nan/N206 ratio for the range from 0 to 50 million years. SAMPLE AGE CALCULA TION A hypothetical uraninite gave the following chemical data: U=43.646 percent, Pb=7.532 percent, Th=5.201 FIGURE 2.—Atomic ratio N201/N206 plotted against the age, t, showing the plus and minus tolerance curves. 485342 0—59—2 6 \ SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY percent. For an exact age solution in terms of numbers of atoms it is not necessary to convert these data from the chemical to physical scale of atomic weights by multiplying these values by the conversion factor 1.0002783 given by Nier (1950). This conversion factor cancels out in the lead-uranium ratio age calculations. However, for an exact age solution, it is necessary to use the calculated physical atomic weight of the lead based on the isotopic composition of the sample being dated rather than the physical atomic weight of average common lead, 207.282. The physical atomic weight of this hypothetical radiogenic lead is obtained by multi- plying the four lead atom percent abundances by the respective physical atomic weights for the individual lead isotopes. Using the isotopic atomic masses given by Sullivan (1957), 204.0368, 206.039, 207.041, and 208.041, the calculated atomic weight of the radiogenic lead in the uraninite is 206.32. The weight percent of lead corrected for this small factor is: 207.282 7.532XW Failure to correct for differences in atomic weight will result in errors of approximately 0.2 to 0.5 percent in the calculated lead-uranium and lead-thorium ages depending on the atomic weight of the lead in the radioactive mineral and the physical constants used in the calculation. Isotopic analyses, in atom percent, of lead in uraninite and asso- ciated hypothetical galena Lead in— ‘ Associated Uranimte hypothetical galena Pb?“ ___________________________ 0. 1957 1. 43o Pb206 ___________________________ 81. 173 , 23. 307 Pb207 ___________________________ 8. 642 23. 277 Pbm ___________________________ 9. 984 51. 987 The presence of lead originally deposited (common lead) with the uraninite and not produced by the radio- active decay of the uranium or thorium in the mineral - is indicated by 0.195, percent Pb?04 in the isotopic analysis of the lead extracted from the uraninite. Pb204 is the only isotope of lead not known to be pro— duced by radioactive decay. The isotopic analysis of the hypothetical galena associated with the uraninite is assumed to approximate closely the isotopic com— position of the nonradiogenic lead originally deposited with the uraninite. As this galena also contains Pb206, Pb“, and Pb“, it is necessary to correct the uraninite lead before the age calculations can be made. CORRECTION FOR ORIGINAL COMMON LEAD The correction for the original common lead may be made in the following way: 1. Using Pb204 as the “index” of the amount of original lead present, a factor proportional to the amount of Pb204 present in the uraninite (0.1957) com- pared to the Pb2°4 in the galena (1-435) is obtained. 0.1957 1 .435 =0.13623 2. This factor, when multiplied by the percent abundances of the lead isotopes in the associated galena, will give the proportional amounts of szo“, Pbm, Pb”, and Pb208 originally present in the uraninite. Pbm:1.435X0.13623=0.1957 Pb2°°=23.305X0.13628=3.176 Pbm7=23.277X0.13628=3.177 Pb2°8=51.981X0.13628=7.084 3. The isotopic analysis of the lead, in atom percent, from the uraninite is then corrected for the original lead present. Pbm Pbm Pbm Pbm Isotopic analysis of uran- inite lead ____________ 0. 1957 81. 17s 8. 647 9. 984 Isotopic analysis of origi- nal lead present _______ —. 1957 ——3. 17° —3. 177 -7. 084 Radiogenic lead pro- duced by U+Th ______ 0. 000 78. 007 5. 470 2. 900 PbmlUm AGE METHOD . The Pbm/U”8 age is obtained by first multiplying the weight percent (chemical scale) of total lead by the corrected percent of radiogenic Pb206 produced by the uranium and dividing by the weight percent (chemical scale) of total uranium multiplied by the atom percent abundance of U238, that is 7 .567X78.002 ‘divided by 43.643X99.273. It is then necessary to convert this weight ratio into an atomic ratio by dividing the physical atomic weight of the uranium, 238.103, by the physical atomic weight of the lead, 206.32; that is, 238.103 m=1.1540' As Avagadro’s number would appear in both the denominator and numerator, it can be canceled out TABLES FOR THE CALCULATION OF LEAD ISOTOPE AGES 7 without altering the numerical value of the ratio Nd/Np. The age calculation thus becomes 7.567X 78.002 —— 1.1 =o.1572. 43.6...><99.273>< 54° ° N 2011/ N233: From the tables read 950:1;2.1 million years. Pb’W/Um AGE METHOD Similarly, the Pb2°7/U”5 age is obtained by multi- plying the chemical weight percent of total lead by the corrected atom percent abundance of radiogenic Pb” and dividing by the chemical weight percent of total uranium multiplied by the atom percent abundance of U“. The conversion factor of weight to atom percent, 1.1540, is used to change the lead-uranium ratio to an atomic ratio. The Pb2°7/U236 age thus becomes 7. 5__6_7><5. _4_7o_ N207/N235= 43 648><0 720—9 ><1.1540=1.518,. From the tables read 950:1:21.3 million years. PbW/Pbm AGE METHOD The age calculated from the Pb2°7/Pb206 ratio may be obtained directly from the isotopic composition of the remaining radiogenic Pb“ and Pb”. The Pb2°7/Pb2°6 age thus becomes 5. 47° N.../N...=7—8' 00 =0.07013. From the tables read 950:1;719 million years. Pbm/Thm AGE METHOD The Pbm/Th232 age is obtained by multiplying the total chemical weight percent of lead by the atom per- cent abundance of remaining radiogenic Pb2°5 and divid- ing by the total chemical weight percent of thorium times 100. This ratio is converted to an atomic ratio by using the following factor: 232.111 2(JG.—32_1'1250°' The Pbm/Th232 age thus becomes 7.567X2.900 N zoa/N 2:12=———5.20l X 100 X1.1250= 0.04747 From the tables read 950i46.8 million years. Physical isotopic masses were calculated from data given by Huizenga (1955) and by Sullivan (1957). LITERATURE CITED Fleming, E. H, Jr. ,Ghiorso, A. and Cunningham, B. B. 1952, The specific alpha-activities and half- lives of U234, U235, and U9“: Phys. Rev., v. 88, p 642— 652. Holmes, Arthur, 1931, Radioactivity and geological time, pt. 4 of The age of the earth: Natl. Research Council Bull. 80, p 124—459. Huizenga, J. R., 1955, Isotopic masses A>201: Physica, v. 21, p. 410-424. Keevil, N. B., 1939, The calculation of geological age: Am. Jour. Sci., v. 237, p. 195—214. Kovarik, A. F., 1931, Calculating the age of minerals from radio- activity data and principles, pt. 3 of The age of the earth: Natl. Research Council Bull. 80, p. 73-123. Kovarik, A. F. and Adams, N. L, Jr., 1938, The disintegration constant of thorium and the branching ratio of thorium C: ‘ Phys. Rev., v. 54, p. 413—421. ———— 1955, Redetermination of the disintegration constant of U233: Phys. Rev., v. 98, p. 46. Kulp, J. L., Bate, G. L., and Broecker, W. S., 1954, Present status of the lead method of age determination: Am. Jour. Sci., v. 252, p. 345365. Nier, A. 0., 1950, A redetermination of the relative abundances of the isotopes of carbon, nitrogen, oxygen, argon, and potassium: Phys. Rev., v. 77, p. 789. Rosholt, J. N., 1958, Radioactive disequilibrium studies as an aid in understanding the natural migration of uranium and its decay products: United Nations Internat. Conf. Peace- ful Uses of Atomic Energy, 2d, Geneva, 1958, Proc., v. 2, Survey of raw material resources, p. 230236. Senftle,‘F. E., Farley, T. A., and Lazar,‘ N., 1956, Half-life of Th5” and the branching ratio of Bi”: Phys. Rev., v. 104, 'p. 1629. Senftle, F. E., Stiefi', L. R., Cuttitta, Frank, and Kuroda, P. K., 1957, Comparison of the isotopic abundance of U235 and U238 and the radium activity ratios in Colorado Plateau uranium ores: Geochim. et Cosmochim. Acta, v. 11, p. 189—193. Sullivan, W. H., 1957, Trilinear chart of nuclides: U. S. Govern- ment Printing Oflice, Washington 25, D. C. Wickman, F. E. 1939, Some graphs on the calculation of geo— logical age: Sveriges Geol. Undersokning Arsbok, v. 33, no. 7, p. 1— 8. TABLES F OR THE CALCULATION OF LEAD ISOTOPE AGES [Numbers above tables are the ages, in millions of years, that are given on each page] TABLES FOR THE CALCULATION OF LEAD ISOTOPE AGES 11 1-50 Geologic age, in millions of years, calculated from the atomic ratios of indicated isotopes NZOG/N238 N207/N235 N207/N206 Nzos/Nzaz Age Age A e Age Ratio Number Error Ratio ‘ Number Error Ratio Number Error Ratio Number Error of + .7 of of + of + years - years — years '- years "' 0.000153 1 0.0 0.000972 1 0.0 0.045955 1 55.8 0.000048 1 0.0 0.000307 2 0.0 0.001945 2 0.0 0.045974 2 55.2 0.000097 2 0.1 0.000461 3 0.0 0.002920 3 0.1 0.045993 3 55.2 0.000146 3 0.1 0.000614 4 0.0 0.003895 4 0.1 0.046012 4 55.2 0.000195 4 0.2 0.000768 5 0.0 0.004871 5 0.1 0.046030 5 55.1 0.000244 5 0.2 0.000922 6 0.0 0.005849 6 0.1 0.046049 6 55.1 0.000292 6 0.3 0.001075 7 0.0 0.006828 7 0.2 0.046063 7 55.1 0.000341 7 0.3 0.001229 8 0.0 0.007807 8 0.2 0.046087 8 55.1 0.000390 8 0.4 0.001383 9 0.0 0.008787 9 0.2 0.046106 9 55.1 0.000439 9 0.4 0.001537 10 0.0 0.009768 10 0.2 0.046124 10 55.1 0.000488 10 0.5 0.001691 11 0.0 0.010750 11 0.2 0.046143 11 56.6 0.000536 11 0.5 0.001845 12 0.0 0.011733 12 0.3 0.046162 12 56.7 0.000585 12 ' 0.6 0.001998 13 0.0 0.012717 13 0.3 0.046181 13 57.7 0.000634 13 0.6 0.002153 14 0.0 0.013702 14 0.3 0.046200 14 56.7 0.000683 14 0.7 0.002307 15 0.0 0.014688 15 0.3 0.046219 15 56.6 0.000732 15 0.7 0.002462 16 0.0 0.015674 16 0.4 0.046237 16 55.6 0.000781 16 0.8 0.002615 17 0.0 0.016662 17 0.4 0.046256 17 56.5 0.000829 17 0.8 0.002769 18 0.0 0.017651 18 0.4 0.046275 18 56.6 0.000878 18 0.9 0.002924 19 0.0 0.018642 19 0.4 0.046294 19 55.8 0.000927 19 0.9 0.003077 20 0.0 0.019633 20 0.4 0.046313 20 56.9 0.000976 20 1.0 0.003232 21 0.0 0.020624 21 0.5 0.046337 21 56.3 0.001025 21 10 0.003386 22 0.0 0.021616 22 0.5 0.046361 22 56.3 0.001073 22 1.1 , 0.003540 23 0.1 0.022609 23 0.5 0.046380 23 56.4 0.001122 23 . 1.1 0.003694 24 0.1 0.023605 24 0.5 0.046399 24 56.6 0.001171 24 1.2 0.003849 25 0.1 0.024600 25 0.6 0.046417 25 56.1 0.00122 0 25 1.2 0.004002 26 0.1 0.025597 26 0.6 0.046436 26 56.9 0.001269 26 13 0.004157 27 0.1 0.026595 27 0.6 0.046455 27 56.4 0.001317 ' 27 1.3 0.004312 28 0.1 0.027593 28 0.6 0.046474 28 56.0 0.001366 28 1.4 0.004466 29 0.1 0.028592 29 0.7 0.046493 29 56.3 0.001416 29 1.4 0.004620 30 0.1 0.029593 30 0.7 0.046513 30 56.5 0.0014651 30 1.5 0.004775 31 0.1 0.030594 31 0.7 0.046532 31 56.2 0.001514 31 15 0.004930 32 0.1 0.031597 32 0.7 0.046551 32 56.0 0.001563 32 1.6 0.005033 33 0.1 0.032600 33 0.7 0.046570 33 56.6 0.001611 33 1.6 0.005238 34 0.1 0.033605 34 0.8 0.046589 34 56.4 0.001660 34 17 0.005393 35 0.1 0.034609 35 0.8 ‘ 0.046607 35 56.1 0.001709 35 1.7 0.005547 36 0.1 0.035616 36 0.8 0.046626 36 56.4 0.001758 36 1.8 0.005702 37 0.1 0.036622 37 0.8 0.046645 37 56.2 0.001807 37 ‘ 1.8 0.005857 38 0.1 0.037632 38 0.9 0.046664 38 56.1 0.001855 38 1.9 0.00601 0 39 0.1 0.038641 39 0.9 0.046682 39 56.8 0.001904 39 1.9 0.006165 40 0.1 0.03965 1 40 0.9 0.046701 40 56.5 0.001953 40 2.0 0.006320 41 0.1 0.040662 41 0.9 0.04672 0 41 56.4 0.002003 41 2.0 0.006475 42 0.1 0.041674 42 0.9 0.046739 42 56.3 0.002052 42 2.1 0.006629 43 0.1 0.042687 43 1.0 0.046758 43 56.6 0.002100 43 2.1 0.006784 44 0.1 0.043702 44 1.0 0.046777 44 56.5 0.002149 44 2.2 0.006939 45 0.1 0.044716 45 1.0 0.046796 45 56.3 0.002198 45 2.2 0.007093 46 0.1 0.045732 '46 1.0 0.046815 46 56.6 0.002247 ' 46 2.3 0.007249 47 0.1 0.046749 47 1.1 0.046834 47 56.2 0.002296 47 2.3 0.007404 48 0.1 0.047767 ‘ 48 1.1 - 0.046853 48 56.1 0.002345 48 2.4 0.007558 49 0.1 0.048787 49 1.1 0.046872 49 56.5 0.002393 . 49 2.4 0.007713 50 0.1 0.049807 50 1.1 0.046891 50 56.5 0.002442 50 2.5 12 SHORTER CONTRHHMHONS TO GENERAL GEOLOGY 51-100 Geologic age, in millions of years, calculated from the atomic ratios of indicated isotopes N206/N238 N207/0V235 N207/N206 N208/N232 Age A e A e Age . Ratio Number Error Ratio Number Error Ratio Number Error Ratio Number Error of + of i of + Of i years - years years — years 0007868 51 01 0050829 51 11 0046910 51 566 0002492 51 2 0008022 52 01 0051850 52 12 0046929 52 567 0002541 52 2 0008178 53 01 0052873 53 12 0046948 53 564 0002590 53 2 0008333 54 01 0053897 54 12 0046967 54 564 0002638 54 2 0008488 55 01 0054922 55 12 0046986 55 565 0002687 55 2 0008643 56 01 0055947 56 3 0047005 56 564 0002736 56 1 0008798 57 01 0056976 57 3 0047024 57 565 0002785 57 2 0008953 58 01 0058003 58 3 0047043 58 565 0002835 58 2 0009108 59 01 0059032 59 3 0047062 59/ 565 0002883 59 2 0009263 60 01 0060063 60 3 0047081 60 566 0002932 60 3 0009418 61 01 _ 0061093 61 0047100 61 566 0002981 61 3 0009573 62 01 0062125 62 0047119 62 567 0003030 62 3 0009728 63 01 0063159 63 0047138 63 568 0003079 63 3 0009884 64 01 0064193 64 0047157 64 567 0003128 64 3 0010038 65 01 0065228 65 0047176 65 569 0003177 65 1 0010194 66 01 0066264 66 0047196 66 568 0003226 66 0010350 67 01 0067301 67 0047216 67 566 0003275 67 0010505 68 02 0068339 68 0047243 68 567 0003324 68 0010660 69 02 0069378 69 0047264 69 568 0003373 69 0010815 70 02 0070418 70 0047284 70 569 0003421 70 0010971 71 02 0071459 71 0047301 71 567 0003471 71 0011126 72 02 0072501 72 0047322 72 568 0003520 72 0011281 73 02 0073545 73 0047344 73 569 0003569 73 0011437 74 02 0074589 74 0047361 74 569 0003618 74 0011592 75 02 0075634 75 0047383 75 569 0003667 75 0011748 76 02 0076681 76 0047401 76 569 0003715 76 0011904 77 02 0077727 77 0047418 77 568 0003765 77 0012058 78 02 0078775 78 0047443 78 510 0003814 78 0012214 79 02 0079825 79 , 0012370 80 02 0080875 80 0012526 81 02 0081926 81 0012681 82 02 0082979 82 0012837 83 02 0084032 83 0012993 84 02 0085086 84 0013148 85 02 0086142 85 0013304 86 02 0087198 86 0013460 87 02 0088255 87 0013615 88 02 0089315 88 0013771 89 02 0090374 89 0013927 90 02 0091434 90 0014082 91 02 0092496 91 0014238 92 02 0093558 92 0014395 93 02 0094621 93 0014551 94 02 0095687 94 0014706 95 ‘02 0096753 95 0014862 96 02 0097819 96 0015019 97 02 0098887 97 0015174 98 02 0099956 98 . 0015330 99 02 0101025 99 0015487 100 02 0102096 100 0047462 79 510 0003863 79 0047479 80 569 0003912 80 0047498 81 569 0003960 81 0047520 82 510 0004010 82 0047538 83 510 0004059 83 0047557 84 569 0004108 84 0047579 85 511 0004157 85 0047598 86 510 0004205 86 0047616 87 569 0004255 87 0047640 88 511 0004304 88 0047658 89 510 0004353 89 . 0047677 90 511 0004402 90 0047700 91 512 0004451 91 0047719 92 512 0004500 92 0047735 93 511 0004549 93 0047755 94 511 0004598 94 0047778 95 513 0004647 95 0047798 96 513 0004696 96 0047815 97 512 0004745 97 0047838 98 513 0004794 98 0047857 99 513\ 0004843 99 0047874 100 512 0004892 100 45-9??? PP??? MMMMM MMMMM MMMMM .NNNNN .NNNNN NNN.N!—' Hr‘r‘r‘r‘ l—‘l—‘k—‘l—‘b‘ PHI-'3‘!“ 1-‘1-‘3—‘1—‘1‘ 1-‘1-‘3‘42—‘r‘ l—‘l—‘l—‘I—‘r‘ OommN‘N00mm‘bhwwmlvHHoO-OommN-N00mmlflb&ww“WWW“:OQQmW'NV00m NNNNN l—ll-‘l—‘r—‘O 00000 0000000 mmmflfl \INO‘O‘O‘ O‘U‘IU'ILHU'I m-b-hh-b #55559? PP??? 101-150 TABLES FOR THE CALCULATION OF LEAD ISOTOPE AGES Geologic age, in millions of years, calculated from the atomic ratios of indicated isotopes 485342 O—59~——3 N206/W238 N207/0V235 N207/N206 N208/N232 Age Age A Age Ratio Number Error Ratio Number Ratio Number Error Ratio Number of of of + of years years 'years — years 0015642 8101 0103168 101 23 0047898 101 514 0004942 101 50 0015798 102 0104242 102 23 0047918 102 515 0004990 102 50 0015955 103 0105316 103 23 0047936 103 513 0005039 103 51 0016110 104 0106391 104 23 0047959 104 515 0005088 104 51 0016267 105 0107466 105 24 0047976 105 513 0005138 105 52 0016423 106 0108543 106 24 0047997 106 514 0005187 106 52 0016580 107 0109622 107 24 0048015 107 513 0005236 107 53 0016735 108 0110701 108 24 0048038 108 515 0005284 108 53 0016892 109 0111782 109 24 0048057 109 514 0005334 109 54 0017048 110 0112862 110 25 0048077 110 514 0005383 110 54 0017204 111 . 0113945 111 25 0048098 111 515 0005432 111 55 0017361 112 . 0115028 112 25 0048116 112 514 0005481 112 55 0017517 113 03 0116113 113 25 0048137 113 515 0005530 113 56 0017673 114 03 0117199 114 26 0048159 114 517 0005579 114 56 0017830 115 03 0118285 115 26 0048177 115 516 0005628 115 57 0017986 116 03 0119372 116 26 0048198 116 516 0005678 116 57 0018142 117 03 0120461 117 26 0048220 117 517 0005727 117 58 0018299 118 03 0121551 118 26 0048238 118 516 0005775 118 58 0018457 119 03 0122643 119 27 0048255 119 514 0005824 119 59 0018614 120 03 0123734 120 27 0048274 120 514 0005874 120 59 0018769 121 03 0124827 121 27 0048298 121 516 0005923 121 50 0018926 122 03 0125922 122 27 0048317 122 515 0005972 122 50 0019083 123 03 0127016 123 28 0048336 123 515 0006022 123 51 0019239 124 03 0128111 124 28 0048358 124 516 0006070 124 51 0019396 125 03 0129210 125 28 0048378 125 516 0006119 125 52 0019553 126 03 0130309 126 28 0048397 126 516_ 0006168 126 52 0019709 127 03 0131407 127 28 0048419 127 517 0006218 127 53 0019866 128 03 0132508 128 29 0048439 128 517 0006267 128 53 0020023 129 03 0133609 129 29 0048458 129 516 0006315 129 54 0020179 130 03 0134711 130 29 0048480 130 517 0006365 130 54 0020336 131 03 0135815 131 29 0048500 131 518 0006414 131 55 0020493 132 03 0136921 132 50 0048521 132 518 0006463 132 ,55 0020650 133 03 0138026 133 50 0048540 133 517 0006513 133 56 0020807 134 03 0139133 134 50 0048560 134 518 0006561 134 56 0020964 135 03 0140241 135 50 0048581 135 518 0006610 135 57 0021121 136 03 0141350 136 51 0048601 136 518 0006660 136 57 0021277 137 03 0142460 137 51 0048623 137 519 0006709 137 58 0021434 138 03 0143572 138 51 0048644 138 519 0006758 138 58 0021592 139 03 0144684 139 51 0048662 139 518 0006808 139 59 0021748 140 03 0145797 140 51 0048685 140 550 0006856 140 59 0021905 141 03 0146911 141 52 0048705 141 519 0006905 141 10 0022063 142 03 0148027 142 52 0048723 142 518 0006955 142 10‘ 0022219 143 03 0149143 143 52 0048746 143 550 0007004 143 10 0022376 144 03 0150261 144 52 0048767 144 581 0007053 144 11 0022534 145 03 0151380 145 53 0048786 145 500 0007102 145 11 0022691 146 03 0152499 146 53 0048806 146 580 0007151 146 12 . 0022848 147 03 0153621 147 53 0048827 147 500 0007200 147 12 0023005 148 03 ' 0154742 148 53 0048848 148 501 0007250 148 13 0023163 149 03 0155865 149 53 0048867 149 501 0007299 149 13 0023320 150 03 0156989 150 54 0048888 150 580 0007348 150 14 14 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 151-200 Geologic age, in millions of years, calculated from the atomic ratios of indicated isotopes \OOJCDKIKI O‘O‘U'IU'I-b AUWNN HI—‘OOQ \OUJCDNN O‘O‘U'IU'I-b Nzos/Nzas Nzo7/N235 N207/N206 Nzos/N232 Age A A Age Rado Number Enor Rado Number Enor Rado Number Enor Rado Number Eran of + of _ of + of + years - years years -' years " 0023478 151 03 0158116 151 14 0048908 151 5&0 0007397 151 14 0023635 152 03 0159241 152 14 0048928 152 5&0 0007446 152 15 0023792 153 03 0160369 153 14 0048950 153 5&1 0007495 153 15 0023950 154 03 0161497 154 15 0048969 154 5&0 0007545 154 16 0024107 155 03 0162627 155 15 0048990 155 5&1 0007594 155 16 0024264 156 03 0163758 156 15 0049012 156 5&2 0007642 156 17 0024422 157 03 0164890 157 15 0049031 157 5&1 0007692 157 17 0024579 158 04 0166023 158 15 0049053 158 5&2 0007741 158 18 0024736 159 04 0167157 159 16 .0049075 159 5&3 0007791 159 18 0024894 160 04 0168293 160 16 0049095 160 5&2 0007840 160 19 0025052 161 04 0169429 161 16 0049114 161 5&2 0007888 161 19 0025209 162 04 0170566 162 16 0049136 162 5&3 0007938 162 &0 0025366 163 04 0171706 163 17 0049158 163 5&4 0007987 163 &0 0025524 164 04 0172844 164 17 0049178 164 5&3 0008037 164 &1 0025682 165 04 0173985 165 17 0049198 165 5&3 0008086 165 &1 0025839 166 04 0175127 166 17 0049220 166 5&4 0008135 166 &2 0025997 167 04 0176269 167 17 0049240 167 5&3 0008184 167 &2 0026155 168 04 0177414 168 18 0049260 168 5&3 0008233 168 &3 0026312 169 04 0178560 169 18 0049282 169 5&4 0008283 169 &3 0026470 170 04 0179707 170 18 0049303 170 5&5 0008332 170 &4 0026629 171 04 0180853 171 18 0049321 171 5&3 0008381 171 8 0026786 172 04 0182002 172 19 0049344 172 5&4 0008430 172 & 0026944 173 04 0183151 173 19 0049364 173 5&4 0008479 173 & 0027102 174 04 0184302 174 19 0049384 174 5&4 0008529 174 & 0027260 175 04 0185453 175 19 0049405 175 5&4 0008578 175 & 0027417 176 04 0186607 176 19 0049428 176 5&5 0008627 176 & 0027576 177 04 0187762 177 40 0049447 177 5&4 0008676 177 & 0027734 178 04 0188917 178 40 0049468 178 5&4 0008725 178 & 0027891 179 04 0190073 179 40 0049490 179 5&6 0008775 179 & 0028049 180 04 0191231 180 40 0049511 180 586 0008824 180 8 0028207 181 04 0192387 181 41 0049531 181 5&5 0008874 181 & 0028365 182 04 0193549 182 41 0049553 182 5&6 0008923 182 9 0028523 183 04 0194710 183 41 0049574 183 5&6 0008971 183 9 0028681 184 04 0195871 184 41 0049595 184 5&6 0009021 184 9 0028839 185 04 0197034 185 42 0049616 185 5&6 0009070 185 9 0028997 186 04 0198199 186 42 0049638 186 5&7 0009120 186 9 0029155 187 04 0199364 187 42 0049659 187 5&7 0009169 187 9 0029315 188 04 0200531 188 42 0049677 188 5&6 0009218 188 9 0029472 189 04 0201698 189 42 0049700 189 5&7 0009267 189 9 0029631 190 04 0202867 190 43 0049720 190 5&7 0009317 190 9 0029789 191 04 0204036 191 43 0049741 191 5&7 0009366 191 9 0029947 192 04 0205207 192 43 0049762 192 5&7 0009415 192 9 0030105 193 04 0206379 193 43 0049784 193 5&8 0009464 193 9 0030264 194 04 0207554 194 44 0049804 194 5&7 0009513 194 9 0030422 195 04 0208729 195 44 0049826 195 5&8 0009563 195 9 0030580 196 04 ' 0209904 196 44 0049848 196 5&8 0009612 196 9 0030739 197 04 0211081 197 44 0049868 197 588 0009662 197 9 0030896 198 04 0212259 198 44 0049891 198 509 0009711 198 9 0031055 199 04 0213438 199 45 0049912 199 5&9 0009760 199 9 0031214 200 04 0214617 200 45 ‘0049932 200 5&8 0009809 200 9 TABLES FOR THE CALCULATION OF LEAD ISOTOPE AGES 15 201-250 Geologic age, in millions of years, calculated from the atomic ratios of indicated isotopes N206/N238 N207/4V235 Nzo7/N206 NZOB/N232 Age A e A e ' Age Rado Number Enor Rado Number Enor Rado Number Enor Rado Number Enor of + of i of + of + years — years years - years _ 0031373 201 04 0215800 201 45 0049952 201 588 0009859 201 99 0031530 202 04 0216982 202 45 0049976 202 590 0009908 202 100, 0031690 203 05 0218166 203 46 0049995 203 589 0009958 203 100 0031849 204 05 0219350 204 46 0050015 204 588 0010006 204 101 0032007 205 05 0220536 205 46 0050038 205 590 0010056 205 101 0032166 206 05 0221722 206 46 0050058 206 589 0010105 206 102 0032325 207 05 0222913 207 46 0050079 207 589 0010155 207 102 0032432 208 05 0224101 208 47 0050103 208 591 0010204 208 103 0032641 209 05 0225291 209 47 0050124 209 591 0010253 209 103 0032800 210 05 0226484 210 47 0050145 210 590 0010302 210 104 0032958 211 05 0227676 211 47 0050167 211 591 0010352 211 104 0033117 212 05 0228870 212 48 0050188 212 591 0010401 212 105 0033276 213 05 0230066 213 48 0050209 213 591 0010451 213 105 0033435 214 05 0231263 214 48 0050230 214 591 0010500 214 105 0033594 215 05 0232460 215 48 0050251 215 591 0010549 215 106 0033754 216 05 0233660 216 48 0050271 216 590 0010598 216 106 0033913 217 05 0234858 217 49 0050292 217 590 0010648 217 10] 0034071 218 05 0236060 218 49 0050315 218 592 0010697 218 107 0034230 219 05 0237262 219 49 0050337 219 592 0010747 219 108 0034389 220 05 0238466 220 49 0050358 220 592 0010795 220 108 0034547 221 05 0239669 221 50 0050381 221 593 0010845 221 109 0034707 222 05 0240875 222 50 0050401 222 592 0010894 222 109 0034866 223 05 0242083 223 50 0050422 223 592 0010944 223 110 0035024 224 05 0243291 224 50 0050445 224 593 0010993 224 110 0035183 225 05 0244500 225 50 0050467 225 593 0011043 225 111 0035343 226 05 0245711 226 51 0050487 226 592 0011091 226 111 0035503 227 05 0246922 227 51 0050508 227 593 0011141 227 112 0035661 228 05 0248134 228 51 0050531 228 594 0011190 228 112 0035821 229 05 0249348 229 51 0050551 229 593 0011240 229 113 0035980 230 05 0250564 230 52 0050573 230 593 0011290 230 113 0036139 231 05 0251779 231 52 0050595 231 594 0011338 231 114 0036298 232 05 0252998 232 52 0050617 232 594 0011388 232 114 0036458 233 05 0254216 233 52 0050637 233 594 0011437 233 115 0036616 234 05 0255436 234 53 0050661 234 595 0011487 234 115 0036776 235 05 0256658 235 53 0050682 235 595 0011536 235 116 0036935 236 05 0257879 236 53 0050704 236 595 0011585 236 116 0037095 237 05 0259103 237 53 0050725 237 595 0011634 237 117 0037254 238 05 0260328 238 53 0050747 238 595 0011684 238 117 0037414 239 05 0261554 239 54 0050768 239 595 0011734 239 118 0037574 240 05 0262780 240 54 0050789 240 595 0011783 240 118 0037732 241 05 0264008 241 54 0050812 241 596 0011833 241 119 0037892 242 05 0265238 242 54 0050833 242 595 0011881 242 119 0038052 243 05 0266469 243 55 0050855 243 596 0011931 243 120 0038211 244 05 0267701 244 55 0050877 244 596 0011980 244 120 0038370 245 05 0268934 245 55 0050900 245 597 0012030 245 121 0038530 246 05 0270168 246 55 0050921 246 597 0012080 246 121 0038690 247 05 0271403 247 55 0050942 247 596 0012128 247 122 0038850 248 05 0272639 248 56 0050963 248 596 0012178 248 122 0039010 249 06 0273873 249 56 0050985 249 596 0012227 249 123 0039169 250 06 0275116 250 56 0051008 250 597 0012277 250 123 16 SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY 251-300 Geologic age, in millions of years, calculated from the atomic ratios of indicated isotopes Nzoe/sta Nzoz/N235 Nzov/N206 N208/N232 Age A A e Age Ratio Number Error Ratio Number Ratio Number Error Ratio Number Error of + of i of + of years " years years - years ‘ 0039329 251 06 0276357 251 56 0051029 251 597 0012327 251 124 0039489 252 06 0277599 252 57 0051051 252 597 0012375 252 124 0039648 253 06 0278841 253 57 0051074 253 598 0012425 253 125 0039807 254 0.6 0280084 254 5.7 0051096 254 59.8 0012474 254 12.5 0039968 255 0.6 0.281330 255 5.7 0.051117 255 59.7 0.012524 255 12.6 0040129 256 06 0282575 256 5.7 0051137 256 59.7 0012574 256 12.6 0040288 257 06 0283825 257 58 0051161 257 598 0012623 257 127 0040448 258 06 0285072 258 58 0051182 258 598 0012672 258 127 0.040608 259 0.6 0286322 259 5.8 0051204 259 59.8 0.012721 259 12.8 0040767 260 0.6 0.287574 260 5.8 0.051227 260 59.8 0012771 260 12.8 0040927 261 06 0288825 261 59 0051249 261 599 0012821 261 129 0041087 262 06 0290078 262 59 0051271 262 599 0012870 262 129 0041246 263 06 0291335 263 59 0051295 263 600 0012919 263 130 0041408 264 0.6 0.292590 . 264 5.9 0.051314 264 59.9 0.012969 264 13.0 0041568 265 06 0293847 265 59 0051336 265 599 0013018 265 131 0041728 266 06 0295106 266 60 0051358 266 599 0013068 266 151 0041887 267 06 0296365 267 60 0051382 267 600 0013117 267 132 0042048 268 06 0297625 268 60 0051403 268 600 0013166 268 132 0.042208 269 0.6 0298889 269 6.0 0.051425 269 60.0 0.013216 269 13.3 0.042367 270 06 0.300152 270' 6.1 0051449 270 60.1 0.013265 270 13.3 0042529 271 0.6 0.301416 271 6.1 0051469 271 600 0013315 271 13.4 0.042689 272 0.6 0302681 272 6.1 0051491 272 60.0 0.013365 272 13.4 0.042849 273 0.6 0303948 273 6.1 0051513 273 60.0 0.013414 273 13.5 0043009 274 0.6 0.305216 274 6.1 0051536 274 60.]. 0.013463 274 13.5 0043170 275 06 0306486 275 62 0051557 275 600 0013513 275 136 0043329 276 06 0307757 276 62 ‘ 0051581 276 601 0013562 276 136 0043490 277 0.6 0.309030 277 6.2 ' 0051603 277 60.2 0.013612 277 137 0043650 278 0.6 0.310302 278 6.2 0.051625 278 60.2 0.013662 278 13.7 0043812 279 0.6 0.311577 279 6.3 0.051646 279 60.1 0.013710 279 13.8 0.043971 280 06 0312852 280 6.3 0.051670 280 60.2 0.013760 280 13.8 0044132 281 06 0314128 281 63 0051691 281 601 0013810 281 139 0044293 282 06 0315407 282 63 0051713 282 602 0013859 282 139 0044452 283 0.6 0316687 283 6.4 0051737 283 60.3 0013909 283 14.0 0044613 284 06 0317968 284 64 0051759 284 603 0013958 284 140 0.044775 285 0.6 0319249 285 6.4 0.051779 285 60.2 0.014007 285 14.0 0044935 286 06 0320532 286 64 0051802 286 602 0014057 286 141 0045095 287 06 0321817 287 64 0051825 287 603 0014107 287 141 0045256 288 06 0323102 288 65 0051847 288 603 0014156 288 142 0045416 289 06 0324390 289 65 0051871 289 604 0014206 289 142 0045577 290 06 0325678 290 65 0051892 290 603 0014255 290 143 0045738 291 06 0326967 291 65 0051914 291 603 0014304 291 143 0045900 292 0.6 0.328258 292 66 0051936 292 60.3 0014354 292 14.4 0.046059 293 0.6 0329549 293 6.6 0051960 293 60.4 0.014404 _ 293 14.4 0.046220 294 0.7 0330844 294 6.6 0.051982 294 60.4 0.014453 294 14.5 0.046381 295. 07 0332138 295 6.6 0.052004 295 60.4 0014502 295 14.5 0046541 296 07 0333433 296 66 0052028 296 605 0014552 296 146 0046702 297 07 0334729 297 67 0052050 297 605 0014602 297 146 0046863 298 07 0336027 298 67 0052072 298 605 0014651 298 147 0. 047024 299 0.7 0337327 299 67 0.052095 299 60.5 0.014701 299 14.7 0047185 300 07 0338627 300 67 0052117 300 605 0014751 300 148 301-350 TABLES FOR THE CALCULATION OF LEAD ISOTOPE AGES 17 Geologic age, in millions of years, calculated from the atomic ratios of indicated isotopes Nzoe/sts N207/4V235 N207/N206 Nzos/N232 ' Age A A e Age Ratio Number Error Ratio Number Ratio Number Error Ratio Number Error of + of of + of + years - years years " years " 0047347 301 07 0339930 301 68 0052139 301 605 0014799 301 148 0.047507 302 0.7 0341234 302 6.8 0.052162 302 60.5 0.014849 302 14.9 0047668 303 07 0342537 303 68 0052185 303 606 0014899 303 149 0.047829 304 07 0.343843 304 6.8 0.052207 304 60.6 0.014949 304 15.0 0047990 305 0.7 0345151 305 6.8 0052230 305 60.6 0.014998 305 15.0 0048151 306 0.7 0346459 306 6.9 0052253 306 60.6 0.015047 306 15.1 0048313 307 07 0347769 307 69 0052274 307 606 0015097 307 151 0048474 308 07 0349080 308 69 0052297 308 606 0015147 308 152 0048634 309 07 0350393 309 69 0052321 309 607 0015196 309 152 0048796 310 07 0351705 310 Z0 0052343 310 607 0015246 310 153 0048958 311 0.7 0.353022 311 7.0 0052365 311 60.7 0015295 311 15.3 0049118 312 0.7 0354336 312 7.0 0.052389 312 60.7 0.015344 312 15.4 0.049280 313 0.7 0.355654 313 7.0 0.052411 313 60.7 0.015394 313 15.4 0049441 314 07 0356973 314 Z0 0052434 314 608 0015444 314 155 0049601 315 0.7 0358293 315 7.1 0.052458 315 60.8 0.015494 315 15.5 0049764 316 07 0359613 316 Z1 0052479 316 608 0015543 316 156 0049925 317 07 0360935 317 Z1 0052502 317 608 0015592 317 156 0050086 318 07 0362259 318 Z1 0052525 318 608 0015642 318 157 0050247 319 07 0363584 319 Z2 0052548 319 608 0015692 319 157 0050409 320 07 0364911 320 Z2 0052570 320 608 0015741 320 158 0050570 321 07 0366238 321 Z2' 0052594 321 609 0015791 321 158 0050732 322 07 0367568 322 Z2 0052616 322 609 0015840 322 159 0050894 323 07 0368898 323 Z2 0052638 323 609 0015890 323 159 0051055 324 0.7 037022 8 324 7.3 0.052661 324 60.9 0015940 324 16.0 0.051216 325 0.7 0.371561 325 7.3 0.052685 325 61.0 0.015989 325 16.0 0051378 326 0.7 0.372896 326 7.3 0052708 326 61.0 0016039 326 16.1 0.051540 327 0.7 0374231 327 7.3 0052730 327 610 0016088 327 16.1 0051701 328 07 0375567 328 Z4 0052753 328 610 0016138 328 162 0051863 329 07 0.376905 329 7.4 0.052776 329 61.0 0.016187 329 16,2 0052025 330 07 0378244 330 Z4 0052799 330 610 0016237 330 163 0.052185 331 0.7 0379584 331 7.4 0052823 331 61.1 0.016287 331 16.3 0052348 332 07 0380928 332 Z5 0052845 332 611 0016337 332 164 0052510 333 07 0382270 333 Z5 0052868 333 611 0016386 333 164 0.052672 334 0.7 0.38361 5 334 7.5 0.052891 334 61.1 0016435 334 16.5 0052833 335 0.7 0384959 335 7.5 0052914 335 61.1 0.016485 335 16.5 0.052995 336 0.7 0386306 336 7.5 0052937 336 61.1 0016535 336 16.6 0.053158 337 0.7 0387654 337 7.6 0052959 337 61.1 0016585 337 16.6 0.053319 338 0.7 0.389004 338 7.6 0052983 338 61.2 0016634 338 16.7 0.053481 339 08 0.390356 339 7.6 0053006 339 612 0016683 339 16,7 0053643 340 0,8 0.391708 340 7.6 0053029 340 61.2 0016733 340 16.8 0053804 341 08 0393062 341 Z7 0053053 341 612 0016783 341 168 0053967 342 0.8 0.394416 342 7.7 0.053075 342 61.2 0016833 342 16.9 0.054129 343 0.8 0.395773 343 7.7 0.053098 343 61.2 0.016882 343 16.9 0054290 344 08 0397131 344 Z7 00531227 344 612 0016931 344 ,170 0.054452 345 0.8 0398489 345 7.7 0.053145 345 61.3 0.016981 345 17.0 0054615 346 0.8 0399849 346 7.8 0.053167 346 61.3 0.017031 346 17.1 0.054778 347 08 0401211 347 78 0053190 347 61.2 0.017081 347 17.1 0054939 348 0.8 0.402574 348 7.8 0.053214 348 61.3 0017131 348 17.2 0.055101 349 0.8 0.403939 349 7.8 0.053238 349 61.3 0.017180 349 17.2 0055263 350 08 0405303 350 Z9 0053261 350 613 0017229 350 1Z3 18 SHORTER CONTRHHMHONS TO GENERAL GEOLOGY 351-400 Geologic age, in millions of years, calculated from the atomic ratios of indicated isotopes NZOé/NZSB N207//N235 N207/N206 Nzos/N232 Age A e Age Age Ratio Number Error Ratio Number Error Ratio Number .Error Ratio Number Error of + of + of : + of + years - years _ years 3 - years ‘ — 0.055426 351 0.8 0.406671 351 7.9 0.053283 351 61.4 0.017279 351 17.3 0.055588 352 0.8 0.408040 352 7.9 0.053307 352 61.4 0.017329 352 17.4 0.055750 353 0.8 0.409408 353 7.9 0.053330 353 61.4 0.017379 353 17.4 0.055912 354 0.8 0.410780 354 7.9 0.053354 354 61.4 0.017428 354 17.5 0.056075 355 0.8 0.412151 355 8.0 0.053376 355 61.4 0.017478 355 17.5 0.056237 356 0.8 0.413524 356 8. 0.053400 356 61.4 0.017527 356 17.5 0.056399 357 0.8 0.414900 357 8. 0.053424 357 61.5 0.017577 357 17.6 0.056561 358 0.8 0.416276 358 8. 0.053447 358 61.5 0.017627 358 17.6 0.056724 359 0.8 0.417655 359 8. 0.053470 359 61.5 0.017677 359 17.7 0.056887 360 0.8 0.419032 360 8. 0.053493 360 61.5 0.017726 360 17.7 0.057049 361 0.8 0.420413 361 8. 0.053517 361 61.6 0.017776 361 17.8 0.057211 362 0.8 0.421794 362 8. 0.053541 362 6L6 0.017826 362 17.8 0.057374 363 0.8 0.423178 363 8. 0.053564 363 61.6 0.017875 363 17.9 0.057536 364 0.8 0.424562 364 8. 0.053587 364 61.6 0.017925 364 17.9 0.057699 365 0.8 0.425947 365 8. 0.053610 365 61.6 0.017974 365 18.0 0.057862 366 0.8 0.427333 366 8. 0.053633 366 61.6 0.018024 366 18.0 Q058023 367 Q8 Q428722 367 Q058187 368 Q8 Q430110 368 Q058350 369 Q8 Q431501 369 Q058511 370 Q8 Q432895 370 Q053653 367 617 Q018074 367 181 Q053680 .368 616 Q018124 «368 181 Q0537o4 369 616 Q018174 369 182 Q053729 370 617 Q018223 370 182 mmmm mun-b h-h-bmw wwmmm NNi—Iy—u—I hip—loco 8058674 371 Q8 Q434289 371 8 Q053752 371 617 Q018272 371 183 Q05883e '372 Q8 Q435683 372 8 Q053774 372 616 Q018322 372 183 Q059001 373 Q8 Q437080 373 8 Q053793 373 617 Q018373 373 184 Q059162 374 Q8 Q438477 374 8 Q053823 374 618 Q018423 374 184 Q059325 375 Q8 Q439876 375 8 Q053846 375 618 Q018473 375 185 8059489 376 Q8 Q441277 376 8 Q053869 376 618 Q018522 376 185 Q059651 377 Q8 Q442680 377 8 Q053893 377 618 Q018572 377 186 Q059814 378 Q8 Q444082 378 8 Q053917 378 619 Q018622 378 186 Q059977 379 Q8 Q445436 379 85 Q05394o 379 618 Q018672 379 187 Q06014o 380 Q8 Q446892 380 85 Q053964 380 618 Q018722 380 187 8060303 381 Q8 Q4483o1 381 85 Q0539a7 381 619 Q01877o 381 188 Q060466 382 Q8 Q449708 382 86 Q054011 382 619 Q018820 382 188 Q060628 383 Q8. Q451119 383 86 Q054036 383 619 Q018870 383 189 Q060792 ‘384 Q9 Q45253o 384 86 Q054053 384 619 Q018920 384 189 Q060955 385 Q9 Q453943 385 86 Q054032 385 619 8018970 385 190 Q061113 386 Q9 Q455356 386 87 Q054106 386 620 Q019019 386 190 Q061281 387 Q9 Q456771 387 87 Q05413o 387 620 Q019069 387 191 Q061444 388 Q9 Q458190 388 87 Q054154 388 620 Q019119 388 191 Q0616oe 389 Q9 Q459609 389 87 Q054177 389 620 Q019169 389 192 8061770 390 Q9 Q461028 390 88 Q054202 390 620 Q019219 390 192 Q061934 391 Q9 Q462449 391 88 Q054225 391 620 Q019269 391 193 Q062097 392 Q9 Q463870 392 88 Q054248 392 620 Q019313 392 193 Q062260 393 Q9 8465294 393 88 Q054273 393 621 Q019367 393 194 Q062423 394 Q9 Q466713 >394 88 Q054297 394 621 Q019417 394 194 Q062587 395 Q9 Q468147 395 89 Q0543zo 395 621 Q019467 395 195 Q062759 396 Q9 Q469575 396 89 Q054344 396 621 Q019517 396 195 Q062913 397 Q9 Q471004 397 89 Q054363 397 622 Q019566 397 196 Q063077 398 Q9 Q472435 398 89 Q054392 398 622 Q019616 398 196 Q063241 399 Q9 Q473866 399 90 8054415 399 622 Q019666 399 197 Q063403 400 Q9 Q4753oo 400 90 Q054440 400 622 Q019716 400 197 TABLES FOR THE CALCULATION OF LEAD ISOTOPE AGES 401-450 19 Geologic age, in millions of years, calculated from the atomic ratios of indicated isotopes Nzoc/sts NzoL/NZBS N207/N206 Nzos/N232 Age A A Age Rado Number Enor Rado; Number Enor Rado Number Enor R800 Number EUOI of + of ‘ i of + of + years - years years " years _ 0063568 401 09 0.476737 401 90 0054463 401 62.2 0019766 401 198 0063731 402 09 0478171 402 90 0054487 402 622 0019815 402 198 0063894 403 09 0479608 403 90 0054512 403 62.3 0019865 403 199 0064057 404 09 0481049 404 91 0054536 404 62.3 0019915 404 199 0064222 405 09 0482489 405 91 0054559 405 623 0019965 405 200 0064384 406 09 0483930 406 91 0054584 406 623 0020015 406 200 0064548 ‘407 09 0485374 407 91 0054608 407 624 0020065 407 201 0064713 408 09 0486820 408 92 0054631 408 62.3 0020114 408 201 0064875 409 09 0488265 409 92 0054656 409 62.4 0020164 409 202 0065039 410 09 0489712 410 92 0054680 410 624 0020214 410 20.2 0065204 411 09 0491160 411 92 0054703 411 623 0020264 411 203 0065367 412 09 0492610 412 92 0054728 412 624 0020314 412 203 0065530 413 09 0494063 413 93 0054753 413 625 0020363 413 204 0065694 414 09 0495516 414 93 0054776 414 62.4 0020413 414 20.4 0065859 415 09 0496971 415 93 0054800 415 62.5 0020463 415 205 0066021 416 09 0498427 416 93 0054825 416 625 0020513 416 20.5 0066185 417 09 0499885 417, 94 0054849 417 625 0020563 417 20.6 0066350 418 09 0501344 418 94 0054873 418 62.5 0020612 418 20.6 0066513 419 09 0502804. 419 94 0054898 419 626 0020662 419 20.7 0066677 420 09 0504267 420 94 0054922 420 62.6 0020712 420 207 0066842 421 09 0505729 421 94 0054945 421 625 0020762 421 208 0067005 422 09 0507192 422 95 0054970 422 626 0020812 422 208 0067169 423 09 0508658 423 95 0054994 423 626 0020862 423 209 0067334 424 09 0510126 424 95 0055018 424 62.6 0020911 424 20.9 0067498 425 09 0511595 425 95 0055042 425 62.6 0020961 425 210 0067661 426 09 0513065 426 96 0055068 426 627 0021011 426 210 0067826 427 09 0514537 427 ” 96 0055091 427 627 0021061 427 210 0067990 428 09 0516009 428 96 0055116 428 627 0021111 428 211 0068153 429 10 0517485 429 96 0055141 429 62.7 0021160 429 211 0068318 430 10 0518960 430 96 0055165 430 62.7 0021210 430 212 0068482 431 10 0520437 431 97 0055189 431 627 0021260 431 212 0068646 432 10 0521917 432 97 0055214 432 628 0021310 432 213 0068811 433 10 0523398 433 97 0055238 433 628 0021360 433 213 0068975 434 10 0524878 ”434 97 0055262 434 62.8 0021410 434 21.4 0069138 435 10 0526361 435. 98 0055288 435 62.9 0021459 435 21.4 0069304 436 10 0527845 436 98 0055311 436 628 0021509 436 215 0069468 437 10 0529333 437 98 0055336 437 628 0021559 437 215 0069632 438 10 0530821‘ 438 98 0055361 438 629 0021609 438 216 0069797 439 10 0532309 439 99 0055385 439 62.9 0021659 439 21.6 0069961 440 10 0533800 440 99 0055410 440 62.9 0021708 440 217 0070125 441 10 0535291 441 99 0055434 441 62.9 0021758 441 217 0070290 442 10 0536784 442 99 0055459 442 62.9 0021808 442 218 0070454 443 10 0538278 443 99 0055483 443 62.9 0021858 443 218 0070619 444 10 0539774 444 100 0055508 444 63.0 0021908. 444 21.9 0070783 445 10 0541275 445 100 0055533 445 630 0021957 445 219 0070948 446 10 0542773 446 100 0055557 446 630 0022007 446 22.0 0071113 447 10 0544273 447 100 0055581 447 '630 0022058 447 22.0 0071277 448 10 0545774 448 101 0055607 448 63.1 0022108 448 22.1 0071441 449 10 0547277 449 101 0055632 449 63.1 0022158 449 22.1 0071607 450 10 0548782 450 101 0055655 450 63.0 0022208 450 22.2 2O SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 451-500 Geologic age, in millions of years, calculated from the atomic ratios of indicated isotopes N206/N238 N207/N235 N207/N206 N208/N232 Age Age A 6 Age ' Ratio Number Error Ratio Number Error Ratio Number Error Ratio Number Error of + of i of + of — years " years years - years 0.071771 451 1.0 0.550289 451 10.17 0.055681 451 63.1 0.022257 451 22.2 0.071935 452 1.0 0.551797 452 10.1 0.055706 452 63.1 0.022307 452 22.3 0.072101 453 1.0 0.553307 453 10.2 0.055730 453 63.1 0.022357 453 22. 3 0.1072266 454 1.0 0.554818 454 10.2 0.055754 454 63.1 0.022407 454 22.4 0.072430 455 1.0 0.556330 455 10.2 0.055780 455 63.2 0.022457 455 22.4 0.072595 456 1.0 0.557843 456 10.2 0.055804 456 63. 2 0.022506 456 22.5 0.072761 457 10 0.559360 457 10.3 0.055828 457 63.1 0.022556 457 22.5 0.072926 458 1.0 0.560875 458 10.3 0.055853 458 63.2 0.022606 458 22.6 0.073091 459 1.0 0.562392 459 10.3 0.055878 459 63.2 0.022656 459 22.6 0.073256 460 1.0 0.563913 460 10.3 0.055902 460 63.2 0.022707 460 22.7 0.07342 0 461 1.0 0.565433 461 10.3 0.055928 461 63.2 0.022756 461 22.7 0.073585 462 1.0 0.566957 462 10.4 0.055953 462 63.3 0.022806 462 22.8 0.073751 463 1.0 0.568481 463 10.4 0.055977 463 63.2 0.022856 463 22.8 0.073915 464 1.0 0.570007 464 10.4 0.056003 464 63.3 0.022906 464 22.9 0.074080 465 1.0 0.571533 465 10.4 0.056028 465 63.3 0.022956 465 22.9 0.074246 466 10 0.573060 466 10.5 0.056052 466 63. 3 0.023006 466 23.0 0.07441 1 467 1.0 0.574592 467 10.5 0.056077 467 63. 3 0.023055 467 23.0 0.074576 468 1.0 0.576123 468 10.5 0.056102 468 63. 3 0.023105 468 23.1 0.074741 469 1.0 0.577656 469 10.5 0.056127 469 63. 4 0.023 56 469 23.1 0.074906 470 1.0 0.579191 470‘ 10.5 0.056152 470 63.4 0.023 07 470 23.2 0.075072 471 1.0 0.580727 471 10.6 0.056177 471 63.4 0.023257 471 23.2 0.075237 472 1.0 0.582264 472 10.6 0.056202 472 63. 4 0.023306 472 23.3 0.075403 473 LO 0.583803 473 10.6 0.056226 473 63. 4 0.023356 473 23.3 0.075567 474 1.1 0.585343 474 10.6 0.056252 474 63.4 0.023406 474 23.4 0.075732 475 1.1 0.586885 475 10.7 0.056278 475 63.5 0.023456 475 23.4 0.075898 476 1.1 0.588429 476 10. 7 0.056302 476 63.5 0.023506 476 23.5 0.076063 477 1.1 0.589974 477 10.7 0.056328 477 63.5 0.023556 7 477 23.5 0.076229 478 1.1 0.591520 478 10.7 0.056352 478 63.5 0.023606 478 23.6 0.076394 479 1.1 0.593069 479 10.7 0.056378 479 63. 5 0.023656 479 23.6 0.076560 480 1.1 0.594617 480 10.8 0.056402 480 63. 5 0.023706 480 23.7 0.076725 481 1.1 0.596168 481 10.8 0.056428 481 63.6 0.023756 481 23.7 0.076890 482 1.1 0.597722 482 10.8 0.056454 482 63.6 0.023806 482 23.8 0.077057 483 1.1 0.599276 483 10.8 0.056478 483 63.6 0.023855 483 23.8 0.077221 484 1.1 0.600832 484 10.9 0.056504 484 63. 6 0.023906 484 23.9 0.077388 485 1.1 0.602389 485 10.9 0.056528 485 63. 6 0.023956 485 23.9 0.077553 486 1.1 0.603947 486 10.9 0.056554 486 63.7 0.024006 486 24.0 0.077718 487 1.1 0.605507 , 487 10.9 0.056580 487 63.7 0.02405 6 487 24.0 0.077884 488 1.1 0.607069 488 11.0 0.056605 488 63. 7 0.024105 488 24.1 0.078050 489 1.1 0.608632 489 11.0 0.05663 0 489 63. 7 0.024155 489 24.1 0.078215 490 1.1 0.610197 490 110 0.056656 490 63. 8 0.024206 490 24.2 0.078381 491 1.1 0.611761 491 11.0 0.056680 491 63.7 0.024256 491 24.2 0.078547 492 11 0.613330 492 11.0 0.056706 492 63.8 0.024306 492 24. 3 0.078713 493 1.1 0.614898 493 11.]. 0.056731 493 63.8 0.024355 493 24.3 0.078878 494 1.1 0.616469 494 1] 1 0.056757 494 63.8 0.024405 494 24.4 0.079044 495 1.1 0.618043 495 11.1 0.056782 495 63.8 0.024455 495 24.4 0.07921 0 496 1.1 0.619617 .496 11.1 0.056807 496 63.8 0.024506 496 24.5 0.079376 497 1.1 0.621191 497 11.2 0.056833 497 63.9 0.024556 497 24.5 0.079542 498 1.]. 0.622767 498 11.2 0.056858 498 63.9 0.024606 498 24. 5 0.079708 499 1.1 0.624346 499 11.2 0.056883 499 63.9 0.024655 499 24. 6 0.079873 500 1.1 0.625927 500 11.2 0.056910 500 63.9 0.024705 500 24.6 TABLES FOR THE CALCULATION 502-600 OF LEAD ‘IS‘OTOPE AGES 21. Geologic age, in millions of years, calculated from the atomic ratios of indicated isotopes N206/N238 NZOL/N235 N207/N206 Nzos/stz Age Age A e Age Ratio Number Error Ratio Number Error Ratio Number Error Ratio Number Error of + of _ of + of + years - , years years — years " 0080206 502 L1 0629090 502 113 0056960 502 659 0024806 502 247 0080538 504 L1 0632262 504 1L3 0057011 504 640 0024905 504 248 0080870 506 L1 0635436 506 1L4 0057062 506 640 0025006 506 249 0081202 508 L1 0638621 508 114 0057113 508 64.0 0025106 508 250 0081534 510 L1 0641809 510 1L4 0057165 510 64.1 0025205 510 25.1 0081868 512 L1 0645005 512 115 0057215 512 641 0025306 512 252 0082200 514 L1 0648207 514 1L5 0057267 514 64.2 0025406 514 253 0082532 516 L1 0651415 516 1L6 0057319 516 64.2 0025506 516 254 0082866 518 L1 0654627 518 116 0057369 518 64.2 0025606 518 25.5 0083198 520 L2 0657850 520 11.7 0057422 520 64.2 0025706 520 256 0083532 522 L2 0661075 522 1L7 0057473 522 643 0025806 522 257 0083864 524 L2 0664306 524 1L8 0057525 524 643 0025907 524 258 0084197 526 L2 0667547 526 118 0057577 526 64.4 0026006 526 25.9 0084531 528 L2 0670792 528 1L8 0057628 528 64.3 0026107 528 26.0 0084864 530 L2 0674043 530 1L9 0057680 530 644 0026207 530 26.1 0085198 532 L2 0677303 532 119 0057732 532 644 0026307 532 252 0085531 534 L2 0680568 534 120 0057784 534 645 0026407 534 263 0085865 536 L2 0683837 536 120 0057836 536 645 0026507 536 26.4 0086199 538 L2 0687116 538 12.1 0057888 538 64.6 0026608 538 26.5 0086532 540 L2 0690399 540 121 0057941 540 646 0026709 540 26.6 0086866 542 L2 0693688 542 122 0057993 542 647 0026808 542 207 0087202 544 L2 0696984 544 122 0058044 544 646 0026909 544 258 0087535 546 L2 0700288 546 123 0058097 546 647 0027010 546 269 0087870 548 L2 0703595 548 12.3 0058149 548 647 0027109 548 210 0088204 550 L2 0706911 550 12.3 0058202 550 648 0027210 550 211 0088538 552 L2 0710233 552 124 0058255 552 648 0027309 552 212 0088873 554 L2 0713561 554 124 0058307 554 648 0027410 554 213 0089208 556 L2 0716895 556 125 0058360 556 649 0027511 556 214 0089544 558 L2 0720240 558 12.5 0058412 558 64.9 0027610 558 215 0089878 560 L2 0723585 560 12.6 0058465 560 64.9 0027711 560 216 0090213 562 L2 0726939 562 126 0058518 562 65.0 0027812 562 217 0090548 564 L3 0730301 564 127 0058571 564 65.0 0027911 564 218 0090883 566 L3 0733669 566 127 0058625 566 65.1 0028012 566 219 0091218 568 L3 0737042 568 127 0058678 568 65.1 0028112 568 28.0 0091555 570 L3 0740425 570 128 0058730 570 65.1 0028213 570 28.1 0091890 572 L3 0743810 572 128 0058784 572 3651 0028313 572 202 0092226 574 L3 0747203 574 129 0058837 574 652 0028413 574 283 0092561 576 L3 0750605 576 129 0058891 576 652 0028514 576 284 0092896 578 L3 0754012 578 13.0 0058945 578 653 0028615 578 285 0093234 580 L3 0757425 580 13.0 0058997 580 65.3 0028714 580 286 0093569 582 L3 0760847 582 151 0059051 582 653 0028815 582 287 0093906 584 13 0764272 584 151 0059104 584 653 0028916 584 288 0094241 586 L3 0767706 586 152 0059159 586 65.4 0029016 586 289 0094577 588 L3 0771147 588 13.2 0059213 588 65.5 0029116 588 250 0094915 590 L3 0774595 590 132 0059266 590 655 0029216 590 291 0095251 592 L3 0778049 592 153 0059320 592 655 0029318 592 202 0095587 594 L3 0781509 594 153 0059374 594 655 0029419 594 203 0095925 596 L3 0784976 596 13.4 0059427 596 656 0029519 596 29.4 0096261 598 L3 0788450 598 13.4 0059482 598 65.6 0029620 598 29.5 0096598 600 L3 0791929 600 13.5 0059536 600 65.6 0029720 29.6 600 22 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 602-700 Geologic age, in millions of years, calculated from the atomic ratios of indicated isotopes N206/N238 N207/4V235 N207/N206 Nzos/N232 Age A A Age Ratio Number Error Ratio Number Error Ratio Number Error Ratio Number Error of + of _ of + of + years years years — years _ 0096936 602 L3 0795417 602 135 0059590 602 657 0029820 602 297 0097273 604 L3 0798911 604 136 0059644 604 657 0029921 604 298 0097611 606 L3 0802413 606 136 0059698 606 657 0030021 606 299 0097947 608 L3 0805921 608 136 0059754 608 658 0030122 \608 300 0098285 610 L4 0809436 610 137 0059808 610 658 0030223 610 301 0098623 612 L4 0812957 612 137 0059862 612 658 . 0030323 612 302 0098961 614 L4 0816486 614 138 0059917 614 659 0030424 614 303 0099299 616 L4 0820020 616 138 ‘0059971 616 659 0030525 616 304 0099636 618 L4 1 0823562 618 139 0060026 618 660 0030624 618 305 0099974 620 L4 0827113 620 139 0060081 620 660 0030725 620 306 0100313 622 14 0830667 622 140 0060136 622 660 0030825 622 307 0100650 624 L4 0834231 624 140 0060191 624 661 0030926 624 308 0100990 626 L4 0837801 626 140 0060246 626 661 0031027 626 309 0101327 628 L4 0841377 628 141_ 0060301 628 661 0031127 628 3L0 0101666 630 L4 0844961 630 141 0060356 630 661 0031228 630 3L1 0102005 632 L4 0848552 632 142 0060411 632 662 0031329 632 3L2 0102344 634 L4 0852150 634 142 0060467 634 662 0031429 634 3L3 0102682 636 L4 0855754 636 143 0060523 636 663 0031530 636 3L4 0103022 638 L4 0859365 638 143 0060577 638 663 0031631 638 3L5 0103360 640 L4 0862985 640 144 0060634 640 664 0031732 640 3L5 0103700 642 L4 0866611 642 144 0060689 642 664 0031834 642 3L6 0104039 644 L4 , 0870242 644 145 0060744 644 664 0031934 644 3L7 0104379 646 L4 0873884 646 145 0060800 646 664 0032035 646 3L8 0104719 648 L4 0877529 648 145 0060855 648 664 0032136 648 3L9 0105058 650 L4 0881183 650 146 0060912 650 665 0032236 650 320 0105398 652 L4 0884846 652 146 0060967 652 665 0032337 652 321 0105738 654 L5 0888513 654 147 0061023 654 666 0032437 654 322 0106077 656 L5 0892189 656 147 0061080 656 666 0032538 656 323 0106418 658 L5 0895872 658 148 0061135 658 666 0032639 658 324 0106757 660 L5 0899561 660 148 0061192 660 667 0032739 660 325 0107097 662 L5 0903257 662 149 0061249 662 667 0032841 662 326 0107439 664 15 0906963 664 149 0061304 664 667 0032942 664 327 0107778 666 L5 0910673 666 149 0061361 666 668 0033042 666 328 0108120 668 L5 0914392 668 150 0061417 668 668 0033143 668 329 0108459 670 LS 0918117 670 150 0061474 670 669 0033243 670 330 0108800 672 L5 0921850 672 151 0061531 672 669 0033344 672 331 0109142 674 L5 0925591 674 151 0061587 674 669 0033446 674 332 0109482 676 15 0929339 676 152 0061644 676 610 0033546 676 ‘333 0109824 678 L5 0933094 678 152 0061701 678 610 0033648 678 334 0110165 680 L5 0936855 680 153 0061758 680 610 0033749 680 335 0110506 682 L5 0940627 682 153 0061815 682 611 0033850 682 336 0110848 684 L5 0944403 684 153 0061872 684 611 0033951 684 337 0111189 686 L5 0948186 686 154 0061929 686 611 0034051 686 338 0111531 688 L5 0951979 688 154 0061986 688 612 0034152 688 339 0111872 690 15 0955778 690 155 0062044 690 612 0034254 690 340 0112214 692 LS 0959585 692 155 0062101 692 613 0034354 692 341 0112557 694 L5 0963397 694 156 0062158 694 613 0034455 694 342 0112898 696 L5 0967220 696 156 0062216 696 613 0034557 696 343 0113240 698 L5 0971047 698 157 0062273 698 613 0034657 698' 344 0113583 700 L6 0974883 700 157 0062331 700 614 0034758 700 345 TABLES FOR THE CALCULATION OF LEAD ISOTOPE AGES 702-800 23 Geologic age, in millions of years, calculated from the atomic ratios of indicated isotopes NZOG/NZSB Nzo7/N235 Nzo7/N206 ”ms/”232 Age Age A Age Ratio Number Error Ratio Number Error Ratio Number Error Ratio Number Error 0f + of __ of + of _ years "' years years — years 0.113925 702 1.6 0.978729 702 15.8 0.062389 702 67.4 0.034859 702 34.6 0.114268 704 1.6 0.982578 704 15.8 0.062446 704 67.4 0.034960 704 34.7 0.114609 706 16 0.986437 706 15.8 0.062505 706 67.5 0.035061 706 34.8 0.114952 708 1.6 0.990304 708 15.9 0.062563 708 67.6 0.035162 708 34.9 0.115295 710 1.6 0.994176 710 15.9 0.062620 710 67.6 0.035263 710 35. 0 0.115638 712 L6 0.998057 712 16 0 0.062678 712 67.6 0.035364 712 35.1 0.115981 714 1.6 1.001947 . 714 16.0 0.062737 714 67.6 0.035466 714 35.2 0.116325 716 1.6 1.005842 716 16.1 0.062794 716 67.6 0.035567 716 35.3 0.116667 718 1.6 1.009744 718 16.1 0.062853 718 67.7 0.035669 718 35.4 0.117011 720 1.6 1.013659 720 16.2 0.062911 720 67.7 0.035769 720 35.5 0.117354 722 1.6 1.017577 722 162 0.062970 722 67.8 0.035871 722 35.6 0.117697 724 1.6 1.021502 724 16.2 0.063028 724 67.8 0.035971 724 35.7 0.118042 726 1.6 1.025439 726 16.3 0.063086 726 67. 8 0.036072 726 35.3 0.118385 728 1.6 1.029379 728 16.3 0.063145 728 67.9 0.036174 728 35.9 0.118729 730 1.6 1.033328 730 16.4 0.063204 730 67. 9 0.036274 730 36.0 0.119073 732 1.6 1.037288 732 16.4 0.063263 732 68.0 0.036376 732 36.1 0.119416 734 1.6 1.041251 734 16.5 0.063322 734 68.0 0.036477 734 36.2 0.119741 736 1.6 1.045224 736 16.5 0.063381 736 68.0 0.036578 736 36.3 0.120105 738 L6 1.049203 738 16. 6 0.063440 738 68.1 0.036679 738 36.4 0.12 0449 740 1.6 1.053191 740 16.6 0.063499 740 68.1 0.036780 740 36.5 0.120795 742 1.6 1.057189 742 16.7 0.063557 742 68.1 0.036881 742 36.6 0.121139 744 1.6 1.061191 744 16.7 0.063617 744 68.1 0.036983 744 36.7 0.121484 746 1.7 1.065203 746 16. 7 0.063676 746 68.2 0.037084 746 36.8 0.121829 748 1.7 1.069223 748 16.8 0.063735 748 68.2 0.037186 748 36.9 0.122173 750 1.7 1.073249 750 16.8 0.063795 750 68.3 0.037288 750 37.0 0.122518 752 17 1077288 752 16.9 0.063855 752 68.3 0.037388 752 37.1 0.122863 754 1.7 1.081328 754 16.9 0.063914 754 68.3 0.037490 754 37.2 0.123208 756 1.7 1.085377 756 17 0 0.063974 756 68.4 0.037590 756 37.3 0.123553 758 1.7 1.089439 758 17. 0 0.064034 758 68. 4 0.037692 758 37.4 0.123898 760 1.7 1.093504 760 17.1 0.064094 760 68. 4 0.037794 760 37.5 0.124244 762 1.7 1.097578 762 17 1 0.064154 762 68.5 0.037894 762 37.6 0.124589 764 1.7 1.101661 764 17.1 0.064214 764 68.5 0.037996 764 37.7 0.124934 766 1.7 1.105752 766 17.2 0.064275 766 68.6 0.038098 766 37.8 0.125283 768 1.7 1.109849 768 17.2 0.064333 768 68.6 0.038198 768 37. 9 0.125628 770 17 1.113957 770 17.3 0.064394 770 68.6 0.038300 770 38.0 0.125974 772 1.7 1.118071 , 772 17.3 0.064454 772 68.7 0.038401 772 38.1 0.126320 774 1.7 1.122190 774 17.4 0.064514 774 68.7 0.038502 774 38.2 0.126665 776 1.7 1.126322 776 17.4 0.064576 776 68.8 0.038605 776 38.3 0.127012 778 L7 1.130459 778 17 5 0.064636 778 68. 8 0.038706 778 38.4 0.127359 780 1.7 1.134607 780 17.5 0.064696 780 68.8 0.038807 780 38.5 . 0.127705 782 1.7 1.138763 782 17.5 0.064757 782 68. 9 0.038909 782 38. 5 0.128052 784 1.7 1.142923 784 17.6 0.064818 784 68. 9 0.039010 784 38.6 0.128398 786 1.7 1.147094 786 17.6 0.064879 786 68. 9 0.039112 786 38. 7 0.128746 788 1.7 1.151270 788 17.7 0.064939 788 68.9 0.039212 788 38.8 0.129093 790 1.8 1.155459 790 17.7 0.065000 790 69.0 0.039314 790 38.9 0.129440 792 1.8 1.159653 792 17.8 0.065061 792 69.0 0.039416 792 39.0 0.129787 794 1.8 1.163857 794 17.8 0.065123 794 69.1 0.039517 794 39.1 0.130135 796 1.8 1.168070 796 17.9 0.065183 796 69.1 0.039618 796 39.2 0.130483 798 1.8 1.172287 798 17. 9 0.065244 798 69.1 0.039720 798 39.3 0.130829 800 1.8 1.176515 800 18.0 0.065306 800 69.2 0.039821 800 39.4 24 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 802-900 Geologic age, in millions of years, calculated from the atomic ratios of indicated isotopes Nzoe/sts N207/N235 N207/N206 NZOS/N232 Age A A 5 Age Ratio Number Error Ratio Number Error Ratio Number Error Ratio Number Error of + of _ of + of i 5 years — years years - years 0131177 802 18 1180752 802 180 0065368 802 692 0039923 802 395 0.131525 804 18 1.184996 804 18.0 0065429 804 69.2 0.040025 804 39.6 0131872 806 18 1189248 806 181 0065491 806 693 0040126 806 397 0132220 808 18 1193510 1808 181 0065553 808 693 0040228 808 398 0.132568 810 18 1197777 810 18.2 0.065615 810 69.4 0.040329 810 39.9 0132917 812 18 1202055 812 18.2 0065676 812 694 0040431 812 400 0133266 814 18 1206341 814 18.3 0065738 814 694 0040533 814 401 0133614 816 18 1210636 816 18.3 0065800 816 695 0040634 816 402 0.133962 818 18 1214937 818 18.4 0.065862 818 69. 5 0040736 818 40.3 0134311 820 18 1219249 820 184 0065924 820 69.5 0040837 820 40.4 0.134660 822 18 1223569 822 18.4 0.065986 822 69.5 0.040938 822 40.5 0.135009 824 1.8 1227894 824 185 0066048 824 69.6 0.041040 824 40.6 0135357 826 18 1232233 826 18.5 0066111 826 696 0041141 826 407 0135706 828 18 1236576 828 18. 6 0.066174 828 69.7 0.041243 828 40.8 0136056 830 18 1240929 830 18.6 0066236 830 697 0041346 830 409 0.136405 832 18 1245290 832 18.7 0066298 832 69.7 0.041447 832 41.0 0136753 834 18 1249659 834 187 0066362 834 698 0041549 834 411 0137104 836 19 1.2 54037 836 18.8 0.066424 836 69.8 0.041650 836 412 0137453 838 19 1258423 838 188 0066487 838 69.9 0041752 838 413 0137803 840 19 1262819 840 18.8 0.066550 840 169.9 0.041854 840 414 0.138153 842 1.9 1.267223 842 18.9 0.066612 842 69.9 0041955 842 415 0.138501 844 1.9 1271635 844 18.9 0066676 844 70.0. 0.042057 844 416 0138852 846 19 1276058 846 190 0066739 846 700 0042159 846 417 0139201 848 19 1280486 848 19.0 0066803 848 701 0042260 848 418 0.139554 850 1.9 1284925 850 19.1 0.066865 850 70.1 0.042362 850 419 0.139904 852 19 1289373 852 19.1 0066929 852 70.1 0042463 852 42.0 0.140253 854 19 1293826 854 19.2 0066993 854 70.1 0042566 854 42.1 0140605 856 1.9 1298291 856 19.2 0.067055 856 70.1 0.042668 856 42. 2 0.140955 858 19 1302766 858 19.3 0067120 858 70.2 0.042770 858 42.3 0.141304 860 19 1307246 860 19. 3 0.067184 860 70.3 0.042872 860 42.4 0.141656 862 19 1311735 862 19.3 0.067247 862 70.3 0.042974 862 42.5 0.142 007 864 19 1316237 864 19.4 0.06731 1 864 70.3 0.043075 864 42.6 0.142359 866 19 1320745 866 19.4 0067375 866 70.4 0.043177 866 42.7 0.142710 868 19 1.325260 868 195 0067439 868 70.4 0.043279 868 42.8 0143061 870 19 1329788 870 19.5 '0067503 870 704 0043380 870 42.9 0.143413 872 19 1.334321 872, 19.6 0.067567 872, 70. 5 0.043482 872 43.0 0143763 874 19 1338864 874 19.6 0.067632 874 70. 5 0.043584 874 43.1 0.144116 876 19 1343416 876 19.7 0.067696 876 70.5 0043687 876 43.2 0.144467 878 1.9 1.347976 878 19.7 \ 0067760 878 70.6 0.043789 878 43.3 0.144819 880 2.0 1352546 880 19.7 0.067825 880 70.6 0.043890 880 43.4 0145172 882 80 1357126 882 19.8 0067889 882 706 0043992 882 43.5 0145523 884 2.0 1361713 884 19.8 0067954 884 70.7 0044095 884 43.6 0145875 886 80 1366308 886 19.9 0068019 886 707 0044196 886 43.7 0.146228 888 2.0 1.370912 888 19.9 0068084 888 70.8 0.044298 888 43.8 0146580 890 80 1375528 890 20.0 0068149 890 70.8 0044399 890 439 0.146933 892 2.0 1.380152 892 20. 0 0.068214 892 70.8 0.044501 892 44.0 0.147285 894 2.0 1384783 894 20.1 0.068279 894 70.9 0.044604 894 44.1 0147637 896 20 1389426 896 201 0068344 896 709 0044705 896 442 0147992 898 20 1394075 898 20.2 0068409 898 70.9 0044808 898 443 0.148344 900 2.0 1398732 900 20.2 0.068474 ' 900 71. 0 0.044911 900 44.4 902-1000 TABLES FOR THE CALCULATION OF LEAD ISOTOPE AGES 25 Geologic age, in millions of years, calculated from the atomic ratios of indicated isotopes Nzos/Nzas N207/N235 Nzo7/N206 Nzos/stz Age A A Age Ratio Number 2 Ratio Number Error Ratio Number Error Ratio Number Error of of i of + of + years years years — years 0148695 902 20 1403404 902 202 0068541 902 710 0045012 902 445 0149049 904 20 1408079 904 203 0068606 904 711 0045114 904 446 0149402 906 20 1412767 906 203 0068672 906 711 0045215 906 44.7 0149756 908 20 1417465 908 204 0068737 908 711 0045318 908 448 0150109 910 20 1422169 910 204 0068803 910 712 0045420 910 44.9 70150463 912 20 1426881 912 205 0068869 912 712 0045521 912 450 0150817 914 20 1431607 914 205 0068934 914 712 0045624 914 451 0151170 916 20 1436339 916 206 0069001 916 713 0045726 916 452 0151526 918 20 1441078 918 20.6 0069066 918 713 0045827 918 45.3 0151879 920 20 1445831 920 20.6 0069133 920 713 0045931 920 45.4 0152232 922 20 1450591 922 207 0069199 922 714 0046032 922 455 0152587 924 20 1455353 924 207 0069265 924 714 0046135 924 455 0152942 926 21 1460142 926 208 0069332 926 714 0046237 926 45.6 0153295 928 21 1464927 928 20.8 0069399 928 715 0046338 928 457 0153650 930 21 1469722 930 209 0069465 930 715 0046441 930 45.8 0154004 932 21 1474533 932 209 0069532 932 716 0046543 932 459 0154360 934 21 1479348 934 210 0069598 934 716 0046645 934 400 0154715 936 21 1484172 936 210 0069665 936 716 0046747 936 401 0155069 938 21 1489006 938 210 0069732 938 716 0046849 938 46.2 0155425 940 21 1493850 940 211 0069799 940 717 0046952 940 46.3 0155780 942 21 1498706 942 211 0069866 942 717 0047055 942 464 0156135 944 21 1503566 944 212 0069933 944 717 0047156 944 465 0156491 946 21 1508441 946 212 0070001 946 718 0047259 946 46.6 0156846 948 21 1513320 948 213 0070068 948 718 0047361 948 [46.7 0157202 950 21 1518213 950 213 0070135 950 719 0047463 950 46.8 0157557 952 21 1523116 952 214 0070203 952 719 0047565 952 469 0157913 954 21 1528023 954 214 0070271 954 720 0047667 954 410 0158270 956 21 1532944 956 215 0070338 956 720 0047769 956 411 0158625 958 21 1537874 958 215 0070406 958 72.0 0047873 958 47.2 0158982 [960 21 1542813 960 215 0070474 960 72.1 0047974 960 47.3 0159337 962 21 1547763 962 216 0070542 962 721 0048077 962 414 0159695 964 21 1552720 964 216 0070610 964 721 0048180 964 415 0160052 966 21 1557689 966 217 0070678 966 722 0048281 966 416 0160407 968 21 1562665 968 217 0070747 r968 72.2 0048384 968 417 0160765 970 22 1567654 970 218 0070814 970 722 0048485 970 418 0161121 972 22 1572651 972 218 0070883 972 72.3 0048588 972 419 0161478 974 22 1577656 974 219 0070952 974 723 0048691 974 480 0161836 976 22 1582677 976 219 0071020 976 72.3 0048793 976 481 0162192 978 22 1587702 978 219 0071089 978 72.4 0048896 978 482 0162549 980 22 1592736 980 220 0071158 980 724 0048999 980 483 0162907 982 22 1597785 982 220 0071227 982 72.5 0049100 982 404 0163264 984 22 1602840 984 221 0071296 984 72.5 0049203 984 405 0163622 986 22 1607905 986 221 0071364 986 725 0049305 986 486 0163980 988 22 1612980 988 222 0071433 988 72.6 0049407 988 48.7 0164338 990 22 1618067 990 222 0071503 990 726 0049510 990 48.8 0164696 992 22 1623161 992 223 0071572 992 72.6 0049612 992 409 0165054 994 22 1628263 994 223 0071641 994 727 0049716 994 490 0165412 996 22 1633384 996 224 0071711 996 72.7 0049818 996 491 0165771 998 22 1638507 998 22.4 0071780 998 72.7 0049920 998 49.2 0166129 1000 22 1643640 1000 22.4 0071850 1000 72.8 0050023 1000 49.3 26 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 1002-1100 Geologic age, in millions of years, calculated from the atomic ratios of indicated isotopes Nzoc/Nzas [1207/4123S N207/N206 Nzos/stz Age Age A e Age Ratio Number Error Ratio Number Error Ratio Number Error Ratio Number Error of + of _ of + of + years - years years -' years "’ 0.166487 1002 2.2 1.648789 1.002 22.5 0.071920 1002 72.8 0.050126 1002 49. 4 0.166846 1004 2.2 1.653941 1004 22.5 0.071989 1004 72.8 0.050227 1004 49. 5 0.167203 1006 2.2 1.659107 1006 22.6 0.072060 1006 72. 9 0.050330 1006 49. 6 0.167563 1008 2.2 1.664284 1008 22. 6 0.072129 1008 72.9 0.050432 1008‘ 49. 7« 0.167922 1010 2.2 1.669469 1010 22.7 0.072199 1010 73.0 0.050535 1010 49.8 0.168282 10.12 2.2 1.674662 1012 22.7 0.072269 1012 73.0 0.050639 1012 49.9 0.168640 1014 2.2 1.679872 1014 22.8 0.072340 1014 ‘ 73.1 0.050740 1014 50.0 0.168999 1016 2.3 1.685084 1016 22.8 0.072410 1016 73.1 0.050843 1016 50.1 0.169359 1018 2.3 1.690309 1018 _ 22.8 0.072480 1018 73.1 0.050946 1018 50.2 0.169719 1020 2.3 1.695548 1020 22.9 0.072551 1020 73.2 0.051048 1020 50.3 0.170078 1022 2.3 1.700791 1022 22.9 0.072622 1022 73.2 0.051151 1022 50.4 0.170438 1024 2.3 1.706049 1.024 23.0 0.072692 1024 73.2 0.051253 1024 50.5 0.170797 1026 2.3 1.711315 1026 23.0 0.072763 1026 73.3 0.051356 1.026 50.6 0.171158 1028 2.3 1.716592 1028 23.1 0.072834 1028 73. 3 0.051460 1.028 50.7 0.171518 1030 2.3 1.721878 1030 23.1 0.072905 1030 73.4 0.051561 1030 50.8 0.171877 1.032 2.3 1.727178 1032 23.2 0.072976 1032 73.4 0.051664 1032 50.9 0.172238 1034 2.3 1732483 1034 23.2 0.073047 1034 73.4 0.051767 1034 51.0 0.172598 1036 2.3 1.737801 1.036 23.2 0.073119 1036 73.5 0.051869 1036 51.1 0.172959 1.038 2.3 1.743129 1038 23.3 0.073190 1038 73.5 0.051972 1038 51.2 0.173320 1040 2.3 1.748471 1040 23.3 0.073261 1040 73. 5 0.052074 1040 51.3 0.173680 1042 2.3 1.753819 1042 23.4 0.073333 1042 73.6 0.052177 1042 51.4 0.174041 1044 2.3 1.759177 1044 23. 4 0.073404 1044 73.6 0.052281 1044 51.5 0.174402 1046 2.3 1.764548 1046 23 5 0.073476 1.046 73.6 0.052383 1.046 51.6 0.174764 1048 2.3 1.769929 1048 23.5 0.073547 1048 73.7 0.052486 1048 51.7 0.175125 1050 2.3 1.775320 1050 23.6 0.073619 1050 73.7 0.052589 1050 51.8 0.175485 1052 2.3 1.78072 1 1052 23.6 0.073692 1052 73.8 0.052691 1052 519 0.175847 1054 2.3 1.786132 1054 23.7 0.073764 1054 73.8 0.052794 1054 52.0 0.176208 1056 2.3 1.791553 1.056 23.7 0.073836 1056 73.8 0.052896 1056 52.]. 0.176570 1058 2.3 1.796988 1058 23. 7 0.073908 1058 73. 9 0.052999 1058 52. 2 0.176932 1060 ‘ 2.4 1.802431 1060 23.8 0.073980 1060 73.9 0.053103 1060 52.3 0.177293 1062 2.4 1.807885 1062 23.8 0.074053 1062 73.9 0.053205 1062 . 52.4 0.177655 1064 2.4 1.813351 1064 23.9 0.074125 1064 74.0 0.053308 1064 52.5 0.17801 6 1066 2.4 1.81882 5 1066 23.9 0.074198 2 1066 74.0 0.05341 1 1066 52.5 0.178380 1068 2.4 1.824310 1.068 24.0 0.074270 1068 74. 0 0.053513 1068 52. 6 0.178742 1070 2.4 1.829808 1070 24.0 » 0.074343 1.070 74.1 0.053616 1070 52. 7 0.179104 1.072 2.4 1.835315 1072 24.1 0.074416 1072 74.1 0.053719 1072 52.8 0.179466 1074 2.4 1.840831 1074 24.1 0.074489 1074 74.2 0.053823 1074 52.9 0.179830 1076 2.4 1.846363 1076 24.1 0.074562 1076 74.2 0.053926 1076 53.0 0.180192 1078 2.4 1851902 1078 24.2 0.074636 1078 74.2 0.054028 1078 53.1 0.180556 1080 2.4 1.857451 1080 24.2 0.074708 1.080 74.2 0.054131 1080 53.2 0.180918 1082 2.4 1.863012 1082 24.3 0.074782 1082 74.3, 0.054234 1082 53.3 0.181281 1084 2.4 1.868587 1.084 24.3 0.074856 1084 74.4 0.054336 1084 53.4 0.181645 1086 2.4 1.874168 1086 24.4 0.074929 1.086 74.4 0.05444 0 1086 53.5 0.182008 1088 2.4 1.879760 1088 24. 4 0.075002 1088 74. 4 0.054542 1088 53.6 0.182372 1090 2.4 1.885368 1090 24. 5 0.075076 1090 74. 4 0.054646 1090 53.7 0.182735 1092 2.4 1.890980 1092 24.5 0.075150 1092 74.5 0.054749 1092 53.8 0.183099 1094 2.4 1.89660 6, 1094 24.5 0.075224 1094 74.5 0.054851 1094 53.9 0.183463 1096 2.4 1.902248 1096 24.6 0.075298 1096 74.6 0.054955 1096 54.0 0.18382 5 1098 2.4 1.907894 1098 24. 6 0.075372 1.098 74. 6 0.055058 1098 54.1 0.184190 1.100 2.4 1.913552 1100 24.7 0.075446 1.100 74.6 0.055160 1100 54.2 TABLES FOR THE CALCULATION OF LEAD ISOTOPE AGES 1102-1200 27 Geologic age, in millions of years, calculated from the atomic ratios of indicated isotopes Nzoo/sts N201121235 N207/N206 N208/N232 Age A A 6 Age Ratio Nuggber Iii-tor Ratio Nugnfber Error Ratio Nugifber Eiror Ratio Nugnfber Eior years — years - years ‘- years - 0184554 1102 24 1919225 1102 247 0075521 1102 74.7 0055263 1102 543 0184918 1104 24 1924905 1104 248 0075595 1104 747 0055367 1104 544 0185283 1106 \25 1930598 1106 248 0075669 1106 747 0055470 1106 54.5 0185648 1108 25 1936302 1108 249 0075744 1108 74.8 0055573 1108 54.6 0186011 1110 25 1942016 1110 249 0075819 1110 74.8 0055675 1110 547 0186376 1112 25 1947741 1112 250 0075893 1112 748 0055779 1112 548 0186740 1114 25 1953480 1114 250 0075969 1114 749 0055882 1114 549 0187106 1116 25 1959227 1116 250 0076043 1116 74.9 0055984 1116 550 0187471 1118 25 - 1964985 1118 251 0076118 1118 749 0056089 1118 551 0187836 1120 25 1970758 1120 25.1 0076193 1120 75.0 0056191 1120 552 0188201 1122 25 1976537 1122 252 0076269 1122 750 0056294 1122 553 0188567 1124 25 1982333 1124 252 0076344 1124 751 0056398 1124 554 0188931 1126 25 1988138 1126 253 0076420 1126 75.1 0056500 1126 55.5 0189297 1128 25 1993953 1128 25.3 0076495 1128 75.2 0056603 1128 55.6 0189661 1130 25 1999777 1130 254 0076571 1130 752 0056707 1130 55.7 0190029 1132 25 2005615 1132 254 0076646 1132 752 0056810 1132 558 0190394 1134 25 2011466 1134 254 0076722 1134 752 0056914 1134 559 0190759 1136 25 2017325 1136 255 0076799 1136 75.3 0057016 1136 560 0191126 1138 25 2023197 1138 25.5 0076874 1138 75.3 0057119 1138 561 0191492 1140 25 2029084 1140 25.6 0076951 1140 754 0057223 1140 562 0191859 1142 25 2034978 1142 256 0077027 1142 754 0057325 1142 563 0192224 1144 25 2040884 1144 257 0077103 1144 754 0057430 1144 564 0192591 1146 25 2046803 1146 257 0077180 1146 755 0057533 1146 565 0192959 1148 25 2052732 1148 25.8 0077256 1148 755 0057636 1148 566 0193325 1150 25 2058672 1150 25.8‘ 0077333 1150 756 0057739 1150 567 0193690 1152 26 2064629 1152 259 0077410 1152 756 0057843 1152 568 0194059 1154 26 2070591 1154 259 0077486 1154 756 0057945 1154 569 0194425 1156 26 2076567 1156 259 0077563 1156 757 0058049 1156 57.0 0194793 1158 26 2082554 1158 26.0 0077640 1158 757 0058152 1158 57.1 0195161 1160 26 2088556 1160 26.0 0077717 1160 757 0058256 1160 57.2 0195528 1162 26 2094564 1162 26.1 0077794 1162 758 0058359 1162 5Z3 0195896 1164 26 2100590 1164 26.1 0077872 1164 758 0058462 1164 574 0196263 1166 26 2106624 1166 262 0077949 1166 759 0058565 1166 57.5 0196632 1168 26 2112667 1168 26.2 0078026 1168 75.9 0058669 1168 57.6 0196999 1170 26 2118727 1170 263 0078104 1170 75.9 0058772 1170 57.7 0197366 1172 26 2124797 1172 263 0078182 1172 76.0 0058876 1172 5Z8 0197736 1174 26 2130878 1174 263 0078259 1174 76.0 0058978 1174 5Z9 0198103 1176 26 2136974 1176 264 0078338 1176 76.1 0059082 1176 500 0198471 1178 26 2143077 1178 264 0078416 1178 761 0059186 1178 581 0198840 1180 26 2149193 1180 265 0078494 1180 761 0059288 1180 502 0199208 1182 26 2155323 1182 265 0078572 1182 762 0059393 1182 583 0199577 1184 26 2161464 1184 266 0078650 1184 76.2 0059497 1184 504 0199945 1186 26 2167616 1186 26.6 0078729 1186 76.2 0059599 1186 505 0200314 1188 26 2173780 1188 26.7 0078808 1188 76.3 0059703 1188 506 0200683 1190 26 2179961 1190 267 0078886 1190 763 0059806 1190 507 0201052 1192 26 2186146 1192 267 0078965 1192 764 0059909 1192 558 0201422 1194 26 2192346 1194 268 0079043 1194 764 0060013 1194 589 0201791 1196 27 2198562 1196 26.8 0079123 1196 764 0060117 1196 590 0202160 1198 27 2204786 1198 269 0079202 1198 765 0060220 1198 59.1 0202531 1200‘ 27 2211023 1200 26.9 4 0079280 1200 765 0060324 1200‘ 59.2 28 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 1202-1300 Geologic age, in millions of years, calculated from the atomic ratios of indicated isotopes N206/N238 N207/0V235 N207/N206 NZOB/N232 Age A e Age Age Ratio Number Error Ratio Number Error Ratio Number Error Ratio Number Error of + of i of + of + years — years years — years ‘ 0202899 1202 27 2217275 1202 210 0079360 1202 765 0060427 1202 593 0203268 1204 27 2223534 1204 210 0079440 1204 766 0060531 1204 594 0203640 1206 27 2229809 1206 211 0079518 1206 766 0060633 1206 595 , 0204009 1208 27 2236095 1208 211 0079598 1208 767 0060738 1208 595 0204379 1210 27 2242392 1210 212 0079678 1210 767 0060842 1210 596 0204751 1212 27 2248701 1212 212, 0079757 1212 767 0060945 1212 597 0205120 1214 27 2255027 1214 212 0079838 1214 768 0061048 1214 598 0205490 1216 27 2261361 1216 213 0079918 1216 768 0061152 1216 599 0205862 1218 27 2267705 1218 213 0079997 1218 768 0061256.1218 600 0206231 1220\ 27 2274067 1220 214 0080078 1220 769 0061360 1220 601 0206603 1222 27 2280439 1222 214 0080158 1222 769 0061463 1222 602 0206974 1224 27 2286824 1224 215 0080238 1224 769 0061566 1224 603 0207345 1226 27 2293221 1226 215 0080319 1226 710 0061670 1226 604 0207716 1228 27 32299630 1228 216 0080399 1228 710 0061773 1228 605 0208088 1230 27 2306051 1230 216 0080479 1230 710 0061878 1230 606 0208460 1232 27 2312482 1232 216 0080560 1232 711 0061982 1232 607 0208830 1234 27 2318934 1234 217 0080642 1234 711 0062085 1234 608 0209203 1236 27 2325392 1236 217 0080722 1236 712 0062189 1236 609 0209575 1238 27 2331860 1238 218 0080803 1238 712 0062291 1238 610 0209945 1240 27 2338347 1240 218 0080885 1240 713 0062395 1240 611 0210319 1242 28 2344844 1242 219 0080965 1242 713 0062500 1242 612 0210690 1244 28 2351355 1244 219 0081047 1244 713 0062603 1244 613 0211062 1246 28 2357878 1246 280 0081129 1246 714 0062707 1246 614 0211435 1248 28 2364412 1248 280 0081210 1248 714 0062811 1248 615 0211806 1250 28 2370959 1250 281 0081292 1250 714 0062914 1250 616 0212181 1252 28 2377523 1252 281 0081373 1252 715 0063019 1252 617 0212553 1254 28 2384092 1254 281 0081455 1254 715 0063122 1254 618 0212924 1256 28 2390678 1256 282 0081538 1256 715 0063226 1256 619 0213298 1258 28 2397279 1258 282 0081620 1258 716 0063330 1258 620 0213671 1260 28 2403892 1260 283 0081702 1260 716 0063433 1260 621 0214045 1262 28 2410516 1262 283 0081784 1262 717 0063537 1262 622 0214417 1264 28 2417156 1264 284 0081867 1264 717 0063642 1264 623 0214790 1266 28 2423804 1266 284 0081950 1266 718 0063745 1266 624 0215165 1268 28 2430469 1268 285 0082032 1268 718 0063849 1268 625 0215538 1270 28 2437145 1270 285 0082115 1270 718 0063952 1270 626 0215911 1272 28 2443833 1272 285 0082198 1272 719 0064056 1272 627 0216286 1274 28 2450534 1274 286 0082280 1274 719 0064161 1274 628 0216658 1276 28 2457254 1276 286 0082364 1276 719 0064264 1276 629 0217033 1278 28 2463980 1278 287 0082447 1278 700 0064368 1278 610 0217407 1280 28 2470720 1280 287 0082530 1280 780 0064472 1280 611 0217780 1282 28 2477473 1282 288 0082614 1282 780 0064576 1282 612 0218156 1284 28 2484244 1284 288 0082697 1284 701 0064681 1284 613 0218530 1286 29 2491026 1286 289 0082781 1286 781 0064785 1286 614 0218905 1288 29 2497817 1288 289 0082864 1288 781 0064888 1288 615 0219279 1290 29 2504627 1290 289 0082949 1290 782 0064992 1290 616 0219653 1292 29 2511448 1292 290 0083033 1292 783 0065095 1292 617 0220030 1294 29 2518281 1294 290 _ 0083116 1294 783 0065199 1294 618 0220405 1296 29 2525129 1296 291 0083200 1296 783 0065305 1296 619 0220779 1298 29 2531988 1298 291 0083285 1298 784 0065408 1298 640 0221155 1300 29 2538864 1300 292 0083369 1300 784 0065512 1300 601 TABLES FOR THE CALCULATION OF LEAD ISOTOPE AGES 1302-1400 29 Geologic age, in millions of years, calculated from the atomic ratios of indicated isotopes N206/N238 N207x/N235 N207/N206 Nzoa/stz Age A e Age Age Ratio Number Error Ratio Number Error Ratio Number Error Ratio Number Error of + of _ of + of years — years years ‘- years "' 0221530 1302 29 2545752 1302 202 0083454 1302 704 0065616 1302 642 0221906 1304 29 2552653 1304 203 0083538 1304 785 0065719 1304 643 0222281 1306 29 2559564 1306 203 0083623 1306 705 0065825 1306 644 0222656 1308 29 2566495 1308 204 0083708 1308 785 0065928 1308 645 0223034 1310 29 2573437 1310 204 0083793 1310 706 0066032 1310 646 0223408 1312 29 2580388 1312 204 0083878 1312 706 0066136 1312 647 0223786 1314 29 2587360 1314 205 0083963 1314 706 0066239 1314 648 0224161 1316 29 2594338 1316 205 0084049 1316 707 0066345 1316 649 0224538 1318 29 2601335 1318 206 0084134 1318 707 0066449 1318 650 ‘0224914 1320 29 2608345 1320 206 0084219 1320 708 0066552 1320 651 0225290 1322 29 2615367 1322 207 0084305 1322 708 0066657 1322 652 0225667 1324 29 2622403 1324 207 0084391 1324 709 0066760 1324 653 0226044 1326 29 2629455 1326 208 0084477 1326 709 [0066865 1326 654 0226421 1328 29 2636516 1328 208 0084562 1328 789 0066970 1328 655 0226798 1330 29 2643593 1330 208 0084648 1330 709 0067073 1330 656 0227175 1332 30 2650684 1332 209 0084735 1332 700 0067177 1332 657 0227552 1334 30 2657792 1334 209 0084821 1334 700 0067283 1334 658 0227931 1336 30 2664906 1336 300 0084907 1336 701 0067386 1336 659 0228308 1338 30 2672041 1338 300 0084993 1338 701 0067490 1338 600 0228686 1340 30 2679188 1340 301 0085080 1340 701 0067594 1340 651 0229064 1342 30 2686349 1342 301 0085167 1342 702 0067698 1342 662 0229440 1344 30 2693522 1344 302 0085254 1344 702 0067804 1344 653 0229820 1346 30 2700714 1346 302 0085340 1346 703 0067907 1346 604 0230196 1348 30 2707915 1348 302 0085428 1348 703 0068011 1348 605 0230575 1350 30 2715129 1350 303 0085515 1350 703 0068116 1350 665 0230954 1352 30 2722362 1352 303 0085602 1352 704 0068219 1352 656 0231332 1354 30 2729607 1354 304 0085690 1354 704 0068325 1354 657 0231711 1356 30 2736863 1356 304 0085777 1356 704 0068428 1356 658 0232090 1358 30 2744136 1358 305 0085864 1358 705 0068533 1358 669 0232467 1360 30 2751424 1360 305 '0085953 1360 705 0068637 1360 610 0232847 1362 30 2758724 1362 306 0086040 1362 706 0068740 1362 611 0233226 1364 30 2766041 1364 306 0086128 1364 706 0068846 1364 612 0233604 1366 30 2773370 1366 307 0086217 1366 706 0068951 1366 613 0233984 1368 30‘ 2780711 1368 307 0086304 1368 707 0069054 1368 614 0234363 1370 30 2788072 1370 307 0086393 1370 707 0069159 1370 615 0234744 1372 30 2795445 1372 308 0086481 1372 707 0069263 1372 616 0235122 1374 30 2802831 1374 308 0086570 1374 708 0069368 1374 617 0235502 1376 31 2810232 1376 309 0086658 1376 708 0069472 1376 618 0235882 1378 31 2817649 1378 309 0086747 1378 709 0069576 1378 619 0236262 1380 31 2825076 1380 310 0086836 1380 709 0069680 1380 680 0236643 1382 31 2832521 1382 310 0086925 1382 709 0069786 1382 681 0237022 1384 31 2839981 1384 311 0087014 1384 800 0069889 1384 602 0237401 1386 31 2847454 1386 311 0087104 1386 800 0069994 1386 683 0237783 1388 31 2854939 1388 311 0087193 1388 801 0070098 1388 684 0238163 1390 31 2862445 1390 312 0087282 1390 801 0070203 1390 605 0238543 1392 31 2869960 1392 312 0087372 1392 801 0070308 1392 686 0238924 1394 31 2877491 1394 313 0087462 1394 802 0070412 1394 607 0239306 1396 31 2885039 1396 313 0087551 1396 802 0070516 1396‘ 688 0239687 1398 31 2892600 1398 314 0087641 1398 802 0070621 1398 609 0240068 1400 31 2900174 1400 314 0087731 1400 803 0070726 1400 600 30 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 1402-1500 Geologic age, in millions of years, calculated from the atomic ratios of indicated isotopes NZOG/NZBS N207x/N235 N207/N206 N208/N232 Age Age Age Age Ratio Number Error Ratio Number Error Ratio Number Error Ratio Number Error of + of It of + of + years years years -' years " 0240448 1402 31 2907767 1402 315 0087822 1402 803 0070830 1402 691 0240831 1404 31 2915372 1404 315 0087911 1404 804 0070934 1404 692 0241211 1406 31 2922991 1406 316 0088002 1406 804 0071039 1406 693 0241594 1408 31 2930630 1408 316 0088092 1408 804 0071144 1408 694 0241975 1410 31 2938278 1410 316 0088183 1410 805 0071248 1410 695 0242357 1412 31 2945941 1412 317 0088274 1412 805 0071353 1412 696 0242738 1414 31 2953624 1414 317 0088365 1414 806 0071458 1414 '697 0243121 1416 31 2961315 1416 318 0088456 1416 806 0071562 1416 698 0243503 1418 31 2969024 1418 318 0088547 1418 806 0071667 1418 699 0243886 1420 314 2976750 1420 319 0088638 1420 807 0071771 1420 700 0244268 1422 32 2984489 1422 319 0088729 1422 807 0071876 1422 701 0244652 1424 32 2992244 1424 320 0088820 1424 807 0071980 1424 702 0245034 1426 32 3000015 1426 320 0088912 1426 808 0072085 1426 703 0245415 1428 32 3007800 1428 320 0089004 1428 808 0072190 1428 704 0245800 1430 32 3015597 1430 321 0089095 1430 808 0072295 1430 705 0246181 1432 32 3023411 1432 321 0089188 1432 809 0072399 1432 706 0246566 1434 32 3031245 1434 322 0089279 1434 809 0072504 1434 707 0246948 1436 32 3039090 1436 322 0089372 1436 810 0072609 1436 708 0247332 1438 32 3046949 1438 323 0089464 1438 810 0072714 1438 709 0247715 1440 32 3054829 1440 323 0089557 1440 811 0072819 1440 710 0248099 1442 32 3062719 1442 324 0089649 1442 811 ’0072924 1442 711 0248432 1444 32 3.070625 1444 32.4 0.089742 1444 811 0073029 1444 712 0248866 1446 3.2 3.078552 1446 32.4 0089835 1446 812 0073134 1446 713 0249250 1448 32 3086486 1448 325 0089928 1448 81.2 0073237 1448 714 0.249634 1450 32 3094438 1450 32.5 0090021 1450 81.2 0.073343 1450 715 0250019 1452 32 3102410 1452 326 0090113 1452 813 0073448 1452 716 0250401 1454 32 3110393 1454 326 0090208 1454 813 0073552 1454 717 0250787 1456 32 3118389 1456 327 0090300 1456 813 0073657 1456 718 0251172 1458 32 , 3126410 1458 327 0090394 1458 814 0073762 1458 719 0251557 1460 32 3134440 1460 328 0090487 1460 814 0073867 1460 720 [10251941 1462 32 3142484 1462 328 0090581 1462 815 0073972 1462 721 0252325 1464 32 3150548 1464 329 0090675 1464 815 0074076 1464 _722 0252711 1466 33 3158626 1466 329 0090769 1466 816 0074182 1466 723 0253095 1468 33 3166718 1468 329 0090864 1468 816 0074287 1468 724 0253480 1470 33 3174830 1470 330 0090958 1470 816 0074391 1470 725 0253866 1472 33 3182954 1472 330 0091052 1472 817 0074496 1472 726 0254251 1474 33 3191094 1474 331 0091147 1474 817 0074601 1474 727 0254638 1476 33 3199248 1476 331 0091241 1476 817 0074706 1476 728 0255022 1478 33 3207423 1478 332 0091336 1478 818 0074811 1478 729 0255409 1480 33 3215611 1480 332 0091430 1480 818 0074915 1480 730 0255796 1482 33 3223814 1482 333 0091525 1482 818 0075021 1482 731 _ 0256181 1484 33 3232037 1484 333 0091621 1484 819 0075126 1484 732 0256569 1486 33 3240273 1486 333 0091715 1486 819 0075230 1486 733 0256954 1488 33 3248523 1488 334 0091811 1488 820 0075335 1488 734 0257340 1490 33 V 3256795 1490 334 0091907 1490 .820 0075440 1490 735 0257728 1492 33 3265079 1492 335 0092002 1492 820 0075546 1492 735 0258113 1494 33 3273379 1494 335 0092098 1494 821 0075651 1494 736 0258500 1496 33 3281698 1496 336 0092194 1496 821 0075755 1496 737 0258887 1498 33 3290029 1498 336 0092290 1498 822 0075861 1498 738 0259274 1500 33 3298375 1500 337 0092386 1500 822 0075966 1500 739 TABLES FOR THE CALCULATION 1505-1750 OF LEAD ISOTOPE AGES 31 (Ecologic age, in nfillions of years, calculated fronithe atonfic ratios of indicated isotopes ,Nzoo/sts N207/4V235 N207/N206 N208/N232 A i A Age Ratio Ratio Number Error Ratio Number Error Ratio Number Error of of + of + years _ years -' years " 0260243 33 3319322 1505 338 0092626 1505 823 0076229 1505 742 0261211 33 3340369 1510 339 0092868 1510 824 0076491 1510 744 0262180 34 3361520 1515 340 0093111 1515 825 0076754 1515 747 0263151 34 3382772 1520 341 0093354 1520 826 0077017 1520 749 0264120 34 3404125 1525 342 0093598 1525 827 0077279 1525 752 0265094 34 3425585 1530 343 0093842 1530 828 0077542 1530 754 0266067 34 3447149 1535 344 0094088 1535 829 0077806 1535‘ 757 0267039 34 3468821 1540 346 0094335 1540 830 0078068 1540 759 0268013 34 3490599 1545 347 0094582 1545 831 0078331 1545 762 0268989 34 3512473 1550 348 0094829 1550 832 0078595 1550 764 V 0269964 34 3534463 1555 349 0095078 1555 833 0078857 1555 767 0270941 35 3556557 1560 350 ' 0095328 1560 834 0079121 1560 769 0271917 35 3578761 1565 351 0095578 1565 835 0079384 1565 711 0272895 35 3601073 1570 352 0095830 1570 836 0079649 1570 734 0273872 35 3623489 1575 353 0096082 1575 837 0079912 1575 736 0274852 35 3646019 1580 355 0096335 1580 838 0080176 1580 719 0275833 35 3668656 1585 356 0096588 1585 839 0080439 1585 701 0276814 35 3691406 1590 357 0096843 1590 840 0080702 1590 704 0277796 35 3714269 1595 358 0097098 1595 841 0080966 1595 706 0278777 35 3737235 1600 359 0097355 1600 842 0081230 1600 709 0279761 36 3760320 1605 360 0097612 1605 843 0081494 1605 791 0280745 36 3783516 1610 361 0097870 1610 843 0081758 1610 794 0281729 36 3806823 1615 362 0098128 1615 844 0082022 1615 796 0282714 36 3830246 1620 364 0098388 1620 845 0082286 1620 799 0283702 36 3853778 1625 365 0098648 1625 846 0082550 1625 801 0284688 36 3877430 1630 366 0098910 1630 847 0082814 1630 804 0285676 36 3901198 1635 367 0099172 1635 848 0083078 1635 806 0286663 36 3925082 1640 368 0099435 1640 849 0083343 1640 808 0287653 36 3949079 1645 369 0099699 1645 850 0083608 1645 811 0288642 37 3973190 1650 310 0099964 1650 851 0083873 1650 813 0289632 37 3997424 1655 311 0100230 1655 852 0084137 1655 816 0290624 37 4021775 1660 313 0100496 1660 853 0084401 1660 818 0291616 37 4046244 1665 314 0100764 1665 854 0084666 1665 821 0292610 37 4070834 1670 315 0101032 1670 855 0084931 1670 823 0293602 37 4095538 1675 316 0101301 1675 856 0085196 1675 826 0294598 37 4120370 1680 317 0101571 1680 857 0085460 1680 828 0295592 37 4145318 1685 318 0101843 1685 858 0085725 1685 831 0296589_ 37 4170392 1690 319 0102114 1690 859 0085990 1690 833 0297584 38 4195587 1695 300 0102388 1695 860 0086255 1695 836 0298584 38 4220898 1700 381 0102660 1700 861 0086521 1700 838 0299581 38 4246342 1705 303 0102935 1705 862 0086786 1705 840 0300580 38 4271905 1710 384 0103211 1710 863 0087051 1710 843 0301581 38 4297593 1715 385 0103487 1715 864 0087317 1715 845 0302580 38 4323407 1720 306 0103765 1720 865 0087583 1720 848 V0303581 38 4349342 1725 387 0104043 1725 866 0087849 1725 850 0304584 38 4375408 1730, 308 0104322 1730 867 0088114 1730 853 0305588 38 4401602 1735 389 0104602 1735 868 0088380 1735 855 0306591 39 4427922 1740 390 0104883 1740 869 0088645 1740 858 0307595 39 4454374 1745 392/ 0105165 1745 810 0088910 1745 860 0308599 39 4480945 1750 393 0105448 1750 811‘ 0089176 1750 863 32 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 1755-2000 Geologic age, in millions of years, calculated from the atomic ratios of indicated isotopes Nzoe/sts N207/N235 N207/N206 N208/N232 Age A e Age Age Ratio Number Error Ratio Number Error Ratio Number Error Ratio Number Error of + of _. of + of + years "‘ years years - years " 0309606 1755 39 4507653 1755 394 0105732 1755 872 0089442 1755 865 0310614 1760 39 4534493 1760 ,395 0106016 1760 873 0089708 1760 808 0311621 1765 39 4561462 1765 396 0106302 1765 874 0089974 1765 870 0312630 1770 39 4588554 1770 397 0106588 1770 875 0090240 1770 873 0313637 1775 39 4615787 1775 398 0106877 1775 876 0090506 1775 875 0314648 1780 39 4643153 1780 399 0107165 1780 877 0090772 1780 877 0315658 1785 40 4670650 1785 401 0107454 1785 878 0091038 1785 800 0316671 1790 40 4698282 1790 402 0107744 1790 879 0091305 1790 802 0317682 1795 40 4726043 1795 403 0108036 1795 800 0091572 1795 885 0318696 1800 40 4753945 1800 404 0108328 1800 801 0091839 1800 887 0319708 1805 40 4781984 1805 405 0108622 1805 802 0092104 1805 890 0320723 1810 40 4810156 1810 406 0108916 1810 803 0092371 1810 892 0321739 1815 40 4838468 1815 407 0109211 1815 884 0092637 1815 895 0322756 1820 40 4866913 1820 408 0109507 1820 885 0092904 1820 897 0323771 1825 40 4895498 1825 410 0109805 1825 806 0093170 1825 900 0324789 1830 '41 4924230 1830 411 0110103 1830 887 0093437 1830 902 0325807 1835 41 4953097 1835 412 0110403 1835 808 0093704 1835 905 0326827 1840 41 4982106 1840 413 0110703 1840 809 0093971 1840 907 0327848 1845 41 5011250 1845 414 0111004 1845 890 0094238 1845 910 0328867 1850 41 5040542 1850 415 0111307 1850 891 0094505 1850 912 0329890 1855 41 5069976 1855 416 0111609 1855 892 0094772 1855 914 50330911 1860 41 5099554 1860 417 0111914 1860 893 0095039 1860 917 0331935 1865 41 5129275 1865 419 0112219 1865 894 0095306 1865 919 0332959 1870 41 5159136 1870 420 0112525 1870 895 0095575 1870 922 0333984 1875 42 5189152 1875 421 0112833 1875 896 0095842 1875 924 0335009 1880 42 5219307 1880 422 0113141 1880 897 0096109 1880 927 0336035 1885 42 5249613 1885 423 0113451 1885 898 0096377 1885 929 0337062 1890 42 5280068 1890 424 0113761 1890 899 0096644 1890 932 0338089 1895 42 5310664 1895 425 0114073 1895 900 0096913 1895 934 0339119 1900 42 5341414 1900 426 0114385 1900 901 0097180 1900 937 0340147’1905 42 5372315 1905 427 0114699 1905 902 0097448 1905 939 0341179 1910 42 5403365 1910 429 0115013 1910 903 0097717 1910 942 0342209 1915 42 5434568 1915 430 0115329 1915 904 0097984 1915 944 0343241 1920 43 5465915 1920 431 0115645 1920 905 0098252 1920 946 0344274 1925 43 5497425 1925 432 0115963 1925 906 0098520 1925 949 0345308 1930 43 5529084 1930 433 0116282 1930 907 0098788 1930 951 0346341 1935 43 5560898 1935 434 0116602 1935 908 0099056 1935 954 .0347377 1940 43 5592872 1940 435 0116922 1940 909 0099324 1940 956 0348411 1945 43 5624987 1945 436 0117245 1945 910 0099593 1945 959 0349450 1950 43 5657274 1950 438 0117567 1950 911 0099862 1950 961 0350488 1955 43 5689710 1955 439 0117891 1955 912 0100130 1955 904 0351525 1960 43 5722310 1960 440 0118217 1960 913 0100398 1960 906 0352564 1965 44 5755066 1965 441 0118543 1965 914 0100668 1965 909 0353604 1970 44 5787976 1970 442 0118870 1970 915 0100936 1970 971 0354645 1975 44 5821053 1975 443 0119199 1975 916 0101205 1975 974 0355685 1980 44 5854291 1980 444 0119529 1980 917 0101473 1980 976 0356728 1985 44 5887691 1985 445 0119859 1985 918 0101742 1985 979 0357771 1990 44 5921252 1990 447 0120191 1990 919 0102010 1990 901 0358816 1995 44 5954970 1995 448 0120524 1995 920 0102279 1995 903 0359859 2000 44 5988862 2000 449 0120858 2000 921 0102549 2000 906 2005-2250 TABLES [FOR THE CALCULATION OF LEAD ISOTOPE AGES 33 Geologic age, in millions of years, calculated from the atomic ratios of indicated isotopes Nzoa/Nus LN207/N7-35 N207/N206 NZOB/N232 Age Age A e Age Ratio Number Ratio Number Error Ratio Number Error Ratio Number Error of of ‘1‘. 0f + 0f years years years "' years " 0360905 2005 44 0022918 2005 450 0121193 2005 922 0102818 2005 988 0361951 2010 45 0057140 2010 451 0121530 2010 923 0103087 2010 991 0362998 2015 45 0091526 2015 452 0121867 2015 924 0103356 2015 993‘ 0364047 2020 45 0126076 2020 453 0122205 2020 925 0103626 2020 996 0365094 2025 45 0160799 2025 454 0122545 2025 926 0103895 2025 998 0366144 2030 45 0195695 2030 456 0122886 2030 927 0104166 2030 1001 0367194 2035 45 0230758 2035 457 0123228 2035 928 0104435 2035 1003 0368245 2040 45 0265992 2040 458 0123571 2040 929 0104704 2040 1006 0369296 2045 45 0301391 2045 459 0123916 2045 '930 0104974 2045 1008 0370349 2050 45 0336972 2050 400 0124261 2050 931 0105243 2050 1011 0371403 2055 46 0372720 2055 401 0124607 2055 932 0105514 2055 1013 0372458 2060 46 0408648 2060 402 0124955 2060 933 0105783 2060 1015 0373511 2065 46 0444749 2065 403 0125305 2065 934 0106053 2065 1018 0374569 2070 46 0481019 2070 405 0125654 2070 935 0106322 2070 1020 0375624 2075 46 0517473 2075 406 0126006 2075 936 0106593 2075 1023 0376682 2080 46 0554104 2080 407 0126358 2080 937 0106863 2080 1025 0377742 2085 46 0590912 2085 408 0126711 2085 938 0107133 2085 1028 0378799 2090 46 0627904 2090 409 0127067 2090 ‘939 0107402 2090 1030 0379859 2095 46 0665064 2095 410 0127423 2095 940 0107674 2095 1033 0380921 2100 47 0702414 2100 411 0127779 2100 941 «0107944 2100 1035 0381982 2105 47 0739946 2105 412 0128138 2105 942 0108214 2105 1038 0383043 2110 47 0777662 2110 413 0128498 2110 943 0108486 2110 1040 0384109 2115 47 0815561 2115 415 0128858 2115 944 0108756 2115 1043 0385172 2120 47 0853638 2120 416 0129220 2120 945 0109026 2120 1045 0386236 2125 47 0891908 2125 417 0129584 2125 946 0109296 2125 1048 0387303 2130 47 0930364 2130 418 0129948 2130 947 0109568 2130 1050 0388368 2135 47 0969005 2135 419 0130314 2135 948 0109838 2135 1052 0389436 2140 47 1007839 2140 400 0130681 2140 949 0110108 2140 1055 0390504 2145 48 1046852 2145 401 0131049 2145 950 0110380 2145 1057 0391573 2150 48 1086061 2150 482 0131419 2150 951 0110652 2150 1000 0392643 2155 48 1125465 2155 404 0131789 2155 952 0110922 2155 1002 0393714 2160 48 1165058 2160 485 0132161 2160 953 0111194 2160 1005 0394783 2165 48 1204844 2165 406 0132535 2165 955 0111465 2165 1007 0395857 2170 48 1244819 2170 487 0132909 2170 956 0111738 2170 1010 0396930 2175 48 1284996 2175 488 0133285 2175 957 0112008 2175 1012 0398005 2180 48 1325365 2180 489 0133661 2180 958 0112279 2180 1015 0399078 2185 48 1365933 2185 490 0134040 2185 959 0112551 2185 1017 0400154 2190 49 1406698 2190 491 0134419 2190 900 0112822 2190 1000 0401231 2195 49 1447655 2195 493 0134800 2195 901 0113095 2195 1002 0402307 2200 49 1488819 2200 494 0135182 2200 902 0113366 2200 1005 0403387 2205 49 1530185 2205 495 0135565 2205 903 0113637 2205 1087 0404464 2210 49 1571751 2210 496 0135951 2210 904 0113909 2210 1009 0405546 2215 49 1613518 2215 497 0136336 2215 905 0114181 2215 1092 0406625 2220 49 1655485 2220 498 0136723 2220 906 0114453 2220 1094 0407706 2225 49 1697660 2225 499 0137112 2225 907 0114724 2225 1097 0408788 2230 49 1740041 2230 500 0137502 2230 908 0114996 2230 1099 0409873 2235 50 1782628 2235 502 0137893 2235 909 0115269 2235 1102 0410956 2240 50 1825426 2240 503 0138286 2240 910 0115540 2240 1104 0412041 2245 50 1868422 2245 504 0138679 2245 911 0115814 2245 1107 0413125 2250 50 1911637 2250 505 2250 912 0116087 2250 1109 0139075 34 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 2255-2500 Geologic age, in millions of years, calculated from the atomic ratios of indicated isotopes Nzoe/sts [‘1207/N235 N207/N206 NZOB/N232 Age A A e Age Ratio Number Error Ratio Number Error Ratio Number Error Ratio Number Error of + of 21'. of + of + years ' years years -- years " 0414211 2255 00 195506 2255 ‘506 0139472 2255 913 0116360 2255 1112 0415300 2260 00 199870 2260 507 0139869 2260 914 0116632 2260 1114 0416336 2265 00 004254 2265- 508 0140269 2265 915 0116904 2265 1117 0417477 2270 00 008660 2270 509 0140669 2270 976 0117176 2270 1119 0418565 2275 00 013088 2275 511 0141071 2275 97.7 0117450 2275 1121 0419658 2280 01 017537 2280 512 0141474 2280 918 0117722 2280 1124 0420747 2285 01 022008 2285 513 0141879 2285 919 0117995 2285 1126 0421840 2290 01 026501 2290 514 0142285 2290 900 0118267 2290 1129 0422932 2295 01 031014 2295 515 0142693 2295 901 0118540 2295 1101 0424026 2300 01 035551 2300 516 0143102 2300 902 0118813 2300 1104 0425121 2305 01 040110 2305 517 0143512 2305 983 0119086 2305 1106 0426217 2310 01 044691 2310 518 0143923 2310 984 0119359 2310 1109 0427313 2315 01 049294 2315 519 0144337 2315 985 0119632 2315 114.1 0428409 2320 01 053919 2320 521 0144751 2320 98.6 0119907 2320 114.4 0429509 2325 02 058567 2325 522 0145167 2325 987 0120180 2325 1146 0430608 2330 02 063238 2330 523 0145584 2330 908 0120453 2330 1149 0431707 2335 02 067932 2335 524 0146003 2335 909 0120727 2335 1101 0432807 2340 02 072649 2340 525 0146423 2340 900 0121001 2340 1104 0433910 2345 02 077387 2345 526 0146844 2345 991 0121274 2345 1106 0435012 2350 02 082150 2350 527 0147267 2350 993 0121548 2350 1108 0436116 2355 02» 086936 2355 528 0147691 2355 993 0121822 2355 1101 0437219 2360 02 091745 2360 500 0148118 2360 995 0122095 2360 1163 0438325 2365 02 096577 2365 501 0148544 2365 996 0122369 2365 1106 0439430 2370 03 001433 2370 502 0148973 2370 997 0122643 2370 1108 0440537 2375 03 006312 2375 503 0149403 2375 908 0122916 2375 1111 0441643 2380 03 011216 2380 504 0149835 2380 909 0123191 2380 1113 0442752 2385 03 016143 2385 505 0150268 2385 1000 0123464 2385 1116 0443862 2390 03 021095 2390 506 0150703 2390 1001 0123739 2390 1118 0444971 2395 03 026070 2395 537 ‘0151139 2395 1002 0124010 2395 1101 0446082 2400 03 031069 2400 539 0151577 2400 1003 0124288 2400 1103 0447193 2405 03 036093 2405 540 0152016 2405 1004 0124562 2405 1106 ' 0448307 2410 03 041142 2410 541 0152456 2410 1005 0124837 2410 1108 0449419 2415 04 046216 2415 542 0152899 2415 1006 0125113 2415 1100 0450535 2420 04 051313 2420 54.3 0153341 2420 1007 0125387 2420 1103 0451648 2425 04 056436 2425_ 54.4 0153787 2425 1008 0125661 2425 1105 0452765 2430 04 061584 2430 545 0154234 2430 1009 0125936 2430 1108 0453882 2435 04 066756 2435 546 0154682 2435 1010 0126210 2435 1200 0454998 2440 04 071955 2440 548 0155132 2440 1011 0126485 2440 1203 0456117 2445 04 077177 2445 549 0155583 2445 1012 0126760 2445 1205 0457236 2450 04 082426 2450 550 0156036 2450 1013 0127036 2450 1208 0458357 2455 04 087700 2455 501 0156490 2455 1014 0127310 2455 1210 0459479 2460 05 093000 2460 502 0156945 2460 1015 0127585 2460 1213 0460602 2465 05 098327_2465 55.3 0157403 2465 1016 0127860 2465 1215 0461723 2470 05 1003677 2470 554 0157862 2470 1018 0128137 2470 1218 0462849 2475 05 1009055 2475 55.5 0158322 2475 1019 0128411 2475 1220 0463972 2480 05 1014460 2480 507 0158784 2480 1020 0128687 2480 1223 0465097 2485 05 1019890 2485' 558 0159248 2485 1021 0128963 2485 1225 0466224 2490 05 1025347 2490 509 0159713 2490 1022 0129239 2490 1227 0467352 2495 05 1030830 2495 560 0160180 2495 1023 0129515 2495 123.0 0468478 2500 05 1036340 2500‘ 561 0160649 2500 1024 0129790 2500 1202 2510-3000 TABLES FOR THE CALCULATION OF LEAD IS‘OTOPE AGES 35 Geologic age, in millions 'of years, calculated from the atomic ratios of indicated isotopes Nzoc/sts N207/N235 N207/N206 Nzos/Nzaz Age Age A 6 Age Ratio Number Error Ratio Number Error Ratio Number Error Ratio Number Error of of of + of + years years —' years *' years " 0470737 2510 56 1047442 2510 553 0161591 2510 1026 0130341 2510 1237 0472999 2520 56 1058650 2520 555 0162539 2520 1028 0130893 2520 1242 0475266 2530 56 1069970 2530 558 0163493 2530 1030 0131444 2530 1247 0477535 2540 56 1081399 2540 510 0164455 2540 1032 0131997 2540 1252 0479806 2550 57 1092940 2550 512 0165423 2550 1034 0132550 2550 1257 0482083 2560 57 1104594 2560 514 30166397 2560 1036 0133104 2560 1252 0484363 2570 57 1116361 2570 517 0167378 2570 1038 0133657 2570 1257 0486644 2580 57 1128244 2580 519 0168367 2580 1041 0134210 2580 1212 0488933 2590 57 1140243 2590 501 0169361 2590 1043 0134763 2590 1217 0491222 2600 58 1152358 2600 503 0170363 2600 1045 0135317 2600 1252 0493515 2610 58 1164593 2610 556 0171372 2610 1047 0135871 2610 1257 0495813 2620 58 1176947 2620 558 0172387 2620 1049 0136428 2620 1292 0498113 2630 58 1189421 2630 590 0173409 2630 1051 0136982 2630 1296 0500418 2640 59 1202019 2640 592 0174439 2640 1053 0137537 2640 1301 0502726 2650 59 1214737 2650 595 0175475 2650 1055 0138092 2650 1306 0505037 2660 59 1227581 2660 597 0176519 2660 1057 0138647 2660 1311 0507352 2670 59 1240550 2670 599 0177570 2670 1050 0139203 2670 1316 0509671 2680 59 1253646 2680 601 0178628 2680 1052 0139760 2680 1321 0511992 2690 50 1266870 2690 604 0179694 2690 1054 0140316 2690 1326 0514318 2700 50, 1280222 2700 606 0180767 2700 1056 0140874 2700 1331 0516647 2710 50 1293706 2710 608 0181847 2710 1058 0141430 2710 1336 0518931 2720 50 1307321 2720 610 0182935 2720 1010 0141988 2720 1341 0521316 2730 51 1321069 2730 613 0184030 2730 1012 0142546 2730 1346 0523656 2740 51 1334953 2740 615 0185133 2740 1014 0143103 2740 1351 0526000 2750 51 1348970.2750 617 0186244 2750 1017 0143661 2750 1356 0528349 2760 51 1363125 2760 619 0187361 2760 1019 0144219 2760 1351 0530698 2770 51 1377417 2770 622 0188488 2770 1051 0144778 2770 1355 0533052 2780 52 1391851 2780 624 0189622 2780 1003 0145338 2780 1310 0535410 2790 52 1406426 2790 626 0190764 2790 1005 0145896 2790 1315 0537771 2800 52 1421141 2800 628 0191913 2800 1057 0146456 2800 1300 0540137 2810 52 1436002 2810 631 0193071 2810 1059 0147016 2810 1305 0542506 2820 53 1451006 2820 633 0194236 2820 1091 0147575 2820 1390 0544878 2830 53 1466159 2830 635 0195410 2830 1094 0148136 2830 1395 0547254 2840 53 1481459 2840 637 0196592 2840 1096 0148695 2840 1400 0549634 2850 53 1496908 2850 640 0197782 2850 1098 0149257 2850 1405 0552017 2860 53 1512508 2860 642 0198980 2860 1100 0149818 2860 1410 0554406 2870 54 1528260 2870 644 0200186 2870 1102 90150381 2870 1415 0556796 2880 54 1544167 2880 646 0201402 2880 1104 0150942 2880 1420 0559190 2890 54 1560229 2890 649 0202626 2890 1106 0151503 2890 1425 0561588 2900 54 1576447 2900 651 0203858 2900 1109 0152065 2900 1430 0563993 2910 55 1592826 2910 653 0205097 2910 1111 0152627 2910 1435 0566397 2920 55 1509361 2920 655 0206347 2920 1113 0153192 2920 1439 0568805 2930 55 1526061 2930 658 0207605 2930 1115 0153754 2930 1444 0571216 2940 55 1542923 2940 650 0208873 2940 1117 0154317 2940 1449 0573635 2950 55 1559949 2950 652 0210148 2950 1119 0154880 2950 1454 0576055 2960 56 1577143 2960 654 ~ 0211432 2960 1121 0155445 2960 1459 0578479 2970 56 1594502 2970 656 0212726 2970 1124 0156008 2970 1454 0580907 2980 56 1112034 2980 659 0214028 2980 1126 0156572 2980 1459 0583339 2990 56 1129737 2990 611 0215340 2990 1128 0157138 2990 1414 0585775 3000 57 1147610 3000 613 0216660 3000 1130 0157704 3000 1419 36 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 3010-3500 Geologic age, in millions of years, calculated from the atomic ratios of indicated isotopes 3500 1219 Nzoc/sts N207/4N235 N207/N206 Nzos/Nzaz Age A e Age Age Ratio Number Error Ratio Number Error Ratio Number Error Ratio Number Error of + of _ of of 2'. years " years years -' years 0588213 3010 67 1165661 3010 615 0217991 3010 1132 0158268 3010 1404 0590656 3020 67 1183885 3020 618 0219330 3020 1154 0158833 3020 1409 0593103 3030 67 1802289 3030 600 0220678 3030 1137 0159399 3030 1494 0595553 3040 67 1820874 3040 602 0222037 3040 1159 0159966 3040 1499i 0598006 3050 68 1039637 3050 684 0223404 3050 1141 0160531 3050 1504 0600464 3060 68 1058586 3060 607 0224782 3060 1143 0161098 3060 1508 0602928 3070 68 1077718 3070 609 0226168 3070 1145 0161665 3070 1513 0605393 3080 68 1097040 3080 691 0227564 3080 1147 0162233 3080 1518 0607862 3090 69 1916550 3090 693 0228971 3090 1150 0162800 3090 1523 0610335 3100 69 1936248 3100 696 0230387 3100 1152 0163368 3100 1528 . 0612811 3110 69 1956141 3110 698 0231814 3110 1154 0163936 3110 1533 0615292 3120 69 1976227 3120 700 0233249 3120 1156 0164504 3120 1538 0617777 3130 69 1996510 3130 702 0234696 3130 1158 0165072 3130 1543 0620266 3140 10 2016992 3140 705 0236152 3140 1160 0165642 3140 1548 0622757 3150 10 2037671 3150 707 0237619 3150 1163 0166211 3150 1553 0625255 3160 10 2058555 3160 709 0239095 3160 1165 0166780 3160 1558 0627752 3170 10 2079641 3170 711 0240583 3170 1167 0167349 3170 1563 0630256 3180 11 2100935 3180 714 0242081 3180 1169 0167920 3180 1568 0632765 3190 11 2122437 3190 .716 0243589 3190 1111 0168490 3190 1513 0635275 3200 11 2144146.3200 718 0245108 3200 1113 0169060 3200 1517 0637791 3210 11 2166070 3210 720 0246638 3210 1116 0169631 3210 1502 0640310 3220 11 2188206 3220 723 0248178 3220 1118 0170203 3220 1507 0642833 3230 12 2210561 3230 725 0249729 3230 1180 0170774 3230 1592 0645360 3240 12 2233133 3240 727 0251292 3240 1182 0171346 3240 1597 0647891 3250 12 2255924 3250 729 0252865 3250 1184 0171917 3250 1602 0650425 3260 12 2278940 3260 752 0254449 3260 1107 0172489 3260 1607 0652965 3270 13 2502179 3270 754 0256044 3270 1189 0173062 3270 1612 0655506 3280 13 2525646 3280 736 0257651 3280 1191 0173635 3280 1617 0658052 3290 13 2349344 3290 758 0259270 3290 1193 0174208 3290 1622 0660600 3300 13 2373270 3300 741 0260900 3300 1195 0174782 3300 1627 0663155 3310 13 2397432 3310 743 0262541 3310 1198 0175354 3310 1652 0665714 3320 14 2421829 3320 745 0264193 3320 1200 0175928 3320 1657 0668276 3330 14 2446465 3330 747 0265857 3330 1202 0176502 3330 1642 0670843 3340 14 2471342 3340 750 0267533 3340 1204 0177077 3340 1646 0673412 3350 14 2496460 3350 752 0269221 3350 1206 0177651 3350 1651 0675985 3360 15 2521826 3360 754 0270921 3360 1209 0178226 3360 1656 0678564 3370 15 2547438 3370 756 0272633 3370 1211 0178802 3370 1661 0681148 3380 15 2573301 3380 758 0274356 3380 1213 0179377 3380 1666 0683733 3390 15 2599418 3390 761’ 0276093 3390 1215 0179955 3390 1611 0686323 3400 15 2625787 3400 763 0277841 3400 1217 0180530 3400 1616 0688916 3410 16 2652416 3410 765 0279602 3410 1219 0181106 3410 1651 0691513 3420 16 2679303 3420 767 0281376 3420 1222 0181683 3420 1686 0694114 3430 16 2106455 3430 710 0283162 3430 1224 0182260 3430 1691 0696721 3440 16 2133873 3440 712 0284961 3440 1226 0182839 3440 1696 0699330 3450 16 2161555 3450 714 0286772 3450 1228 0183415 3450 1701 0701944 3460 17 2189511 3460 716 .0288596 3460 1251 0183992 3460 1706 0704561 3470 17 2817737 3470 719 0290434 3470 1233 0184571 3470 1711 0707183 3480 17 2846241 3480 721 0292284 3480 1255 0185148 3480 1715 0709808 3490 17 2875024 3490 703 0294148 3490 1257 0185727 3490 1720 0712439 3500 18 2904086 3500 785 0296024 0186307 3500 1725 TABLES FOR THE CALCULATION OF LEAD ISVOTOPE AGES 3510-4000 Geologic age, in millions of years, calculated from the atomic ratios of indicated isotopes NZOG/sts Nzom/N235 N207/N206 N208/N232 Age Age A e Age Ratio Number Error Ratio Number Error Ratio Number Error Ratio Number Error of + of + of + of years - years . — years -' years 0.715073 3510 7.3 29.33434 3510 78.8 0.297914 3510 124.2 0.186885 3510 173.0 0.717712 3520 18 29.63065 3520 79.0 0.299817 3520 124.4 0.187466 3520 173.5 0720353 3530 7.8 29.92990 3530 79.2 0.301735 3530 124.6 0.188045 3530 174.0 0.722997 3540 7.8 30.23203 3540 79.4 0.303666 3540 124.8 0.188625 3540 174.5 0.725648 3550 7.9 30.53715 3550 79.7 0.305610 3550 125.0 0.189206 3550 1750 0728304 3560 1 3084526 3560 799 0307568 3560 1253 0189785 3560 1755 0730961 3570 1 3115633 3570 801 0309540 3570 1255 0190366 3570 1760 0733623 3580 1 3147048 3580 803 0311527 3580 1257 0190947 3580 1765 0736292 3590 8 3178766 3590 806 «0313526 3590 1259 0191530 3590 1710 0738961 3600 0741637 3610 0744316 3620 0746998 3630 0749686 3640 0752377 3650 0755070 3660 0757770 3670 0760474 3680 0763182 3690 0765894 3700 0768610 3710 0771329 3720 0774056 3730 0776784 3740 0779517 3750 0782254 3760 0784996 3770 0787740 3780 0790439 3790 9° 0090.00.00.00 9090909000 mmmmm 90.90.0090 ooooooooo m\l\l\l\l O‘O‘O‘O‘O‘ U1U1U'IU'I-b Daub-Db) uwumm NNNI—H—J r—H—Iooo OO~O\O\0 0793244 3800 8 3921365 3800 853 0359001 3800 1306 0203806 3800 1873 0796001 3810 8 3960652 3810 855 0361342 3810 1308 0204393 3810 1818 0798764 3820 8 4000318 3820 857 0363698 3820 1311 0204982 3820 1883 0801530 3830 8 4040375 3830 859 0366073 3830 1313 0205571 3830 1888 0804301 3840 8 4080820 3840 862 0368463 3840 1315 0206159 3840 1893 0807077 3850 8 4121664 3850 864 0370871 3850 1317 0206748 3850 1898 0809857 3860 8 4162907 3860 866 0373296 3860 1320 0207336 3860 1903 0812641 3870 8. 4204549 3870 868 ,0375739 3870 1322 0207927 3870 1908 0815430 3880 8 4246602 3880 811 0378199 3880 1324 0208517 3880 1913 0818222 3890 8 4289062 3890 813 0380677 3890 1326 0209108 3890 1918 0821018 3900 8 4531940 3900. 815 0383173 3900 1329 0209697 3900 1923 0823817 3910 8 4575238 3910 817 0385688 3910 1351 0210288 3910 1927 0826623 3920 8 4418953 3920 880 0388220 3920 1353 0210879 3920 1952 0829432 3930 8 4463101 3930 882 0390770 3930 1355 0211470 3930 1957 0832247 3940 0835065 3950 0837887 3960 0840715 3970 0843546 3980 0846382 3990 0849221 4000 0000.00.00.00 .0090 3210798 3600 808 0315542 3600 1262 0192112 3600 1715 3243143 3610 ‘810 0317570 3610 1264 0192694 3610 1780 3275800 3620 812 0319614 3620 1266 0193276 3620 1785 3508779 3630 815 0321672 3630 1268 0193859 3630 1789 3542078 3640 817 0323745 3640 1210 0194441 3640 1794 3575705 3650 819 0325833 3650 1213 0195023 3650 1799 3409660 3660 821 0327936 3660 1215 0195607 3660 1804 3443945 3670 824 0330053 3670 1217 0196192 3670 1809 3478567 3680 826 0332186 3680 1219 0196777 3680 1814 3513523 3690 828 0334334 3690 1282 0197359 3690 1819 3548826 3700 850 0336497 3700 1284 0197944 3700 1824 3584473 3710 853 0338676 3710 1286 0198529 3710 1829 3620464 3720 855 0340871 3720 1288 0199114 3720 1854 3656811 3730 857 0343080 3730 1290 0199699 3730 1859 3693509 3740 859 0345306 3740 1293 0200287 3740 1844 3130569 3750 842 0347548 3750 1295 0200872 3750 1849 3167992 3760 844 0349806 3760 1297 0201459 3760 1854 3805776 3770 846 0352080 3770 1299 0202044 3770 1858 3843933 3780 848 0354371 3780 1302 0202631 3780 1863 3882459 3790 850 0356678 3790 1304 0203218 3790 1868 4507675 3940 884 0393333 3940 1358 0212061 3940 1942 4552689 3950 886 0395925 3950 1340 0212653 3950 1947 4598144 3960 889 0398532 3960 1342 0213245 3960 1952 4644037 3970 891 0401155 3970 1344 0213838 3970 1957 4690383 3980 893 0403799 3980 1347 0214431 3980 1962 4137178 3990 895 0406461 3990 1349 0215023 3990 1967 4184434 4000 898 0409143 4000 1351 0215616 4000 1972 38 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 4010-4500 Geologic age, in millions of years, calculated from the atomic ratios of indicated isotopes Nzos/sts [1207/4135 N207/N206 Nzoa/stz Age A e A e Age Ratio Number Error Ratio Number Error Ratio Number Error Ratio Number Error of + of _ of + of + years ' years years - years " 0852067 4010 09 4032153 4010 900 0411844 4010 1353 0216210 4010 197.7 0854915 4020 09 4880331 4020 902 0414564 4020 1356 0216803 4020 198.2 0857765 4030 09 4928987 4030 904 0417306 4030 1358 0217397 4030 198.7 0860626 4040 90 4978112 4040 90.7 0420064 4040 1360 0217994 4040 199.2 0863486 4050 90 5027722 4050 90.9 0422845 4050 1362 0218587 4050 199.6 0866352 4060 90 5077817 4060 911 0425646 4060 1365 0219183 4060 2001 0869224 4070 90 5128396 4070 913 0428465 4070 1367 0219776 4070 2006 0872099 4080 90 5179474 4080 916 0431306 4080 1369 0220372 4080 201.1 0874978 4090 91 5231046 4090 918 0434167 4090 1372 0220969 4090 201.6 0877861 4100 91 5283127 4100 920 0437050 4100 137.4 0221563 4100 202.1 0880750 4110 91 5535717 4110 922 0439952 4110 1316 0222160 4110 2026 0883644 4120 91 5588816 4120 925 0442875 4120 1318 0222758 4120 2051 0886540 4130 92 5442438 4130 927 0445821 4130 1381 0223355 4130 2056 0889443 4140 92 5496579 4140 92.9 0448787 4140 1303 0223952 4140 2041 0892347 4150 92 5551254 4150 93.1 0451776 4150 1305 0224550 4150 2046 0895257 4160 92 5606464 4160 954 0454786 4160 1307 0225147 4160 2051 0898172 4170 92 5662207 4170 956 0457817 4170 1390 0225745 4170 2056 0901092 4180 93 5118501 4180 958 0460870 4180 1392 0226343 4180 2061 0904017 4190 93 5175338 4190 940 0463945 4190 1394 0226942 4190 2065 0906946 4200 93 5832736 4200 94.2 0467043 4200 1396 0227542 4200 2010 0909879 4210 93 5890696 4210 945 0470163 4210 1399 0228142 4210 2015 0912817 4220 94 5949215 4220 947 0473306 4220 1401 0228741 4220 2000 0915759 4230 94 6008312 4230 949 0476472 4230 1403 0229341 4230 2005 0918705 4240 94 6067980 4240 951 0479660 4240 1406 0229941 4240 2090 0921655 4250 94 6128238 4250 954 0482873 4250 1408 0230542 4250 2095 0924613 4260 94 6189085 4260 956 0486107 4260 1410 0231142 4260 2100 0927571 4270 95 6250519 4270 958 0489367 4270 1412 0231745 4270 2105 0930537 4280 95 6512560 4280 960 0492649 4280 1415 0232345 4280 2110 0933506 4290 95 6575201 4290 96.3 0495955 4290 1417 0232948 4290 2115 0936480 4300 95 6438459 4300 96.5 0499286 4300 1419 0233549 4300 2120 0939459 4310 96 6502336 4310 967 0502640 4310 1422 0234150 4310 2125 0942441 4320 96 6566830 4320 969 0506020 4320 1424 0234753 4320 2150 0945430 4330 96 6631962 4330 912 0509423 4330 142.6 0235356 4330 2155 0948422 4340 96 6697722 4340 974 0512851 4340 142.8 0235960 4340 2159 0951420 4350 96 6164132 4350 97.6 0516304 4350 143.1 0236563 4350 2144 0954419 4360 97 6031191 4360 918 0519784 4360 1453 0237167 4360 2149 0957428 4370 97 6898897 4370 901 0523286 4370 1455 0237771 4370 2154 0960438 4380 97 6967272 4380 903 0526816 4380 1458 0238375 4380 2159 0963453 4390 97 7036308 4390 985 0530371 4390 1440 0238980 4390 2164 0966472 4400 98 7106025 4400 987 0533953 4400 1442 0239584 4400 2169 0969496 4410 98 7176425 4410 990 0537561 4410 1444 0240190 4410 2114 0972527 4420 98 7247503 4420 992 0541193 4420 1447 0240796 4420 217.9 0975562 4430 98 7519284 4430 994 0544853 4430 1449 0241402 4430 218.4 0978598 4440 98 7591758 4440 99.6 0548541 4440 145.1 0242007 4440 218.9 0981642 4450 99 7464949 4450 99.9 0552255 4450 145.4 0242614 4450 219.4 0984690 4460 99 7538854 4460 100.1 0555996 4460 1456 0243221 4460 2199 0987743 4470 9.9 7613473 4470 100.3 0559763 4470 1458 0243828 4470 2204 0990800 4480 9.9 7688829 4480 100.5 0563560 4480 146.0 0244435 4480 2208 0993862 4490 10.0 7164914 4490 100.8 0567383 4490 146.3 0245044 4490 2213 0996930 4500 100 7841750 4500 1010 0571234 4500 146.5 0245651 4500 2218 TABLES FOR THE CALCULATION OF LEAD ISOTOPE AGES 4515-5250 39 Geologic age,in minions ofyears, caleulated fronrthe atonfic ratios of indicated isotopes Nzos/Nzas N207/N235 Nzo7/N206 Nzos/stz Age 7 A e A e Age Ratio Number Error Ratio Number Error Ratio Number Error Ratio Number Error of + of __ of + of 1 years " years years - years 1001538 4515 100 795840 4515 1013 0577064 4515 1409 0246564 4515 2226 1006158 4530 100 807678 4530 1017 0582959 4530 1412 0247475 4530 2233 1010789 4545 101 819688 4545 1020 0588917 4545 1415 0248389 4545 224 1015429 4560 101 831876 4560 1023 0594943 4560 1419 0249304 4560 2248 1020080 4575 101 844243 4575 1027 0601034 4575 1402 0250220 4575 2255 1024745 4590 102 856790 4590 1030 0607190 4590 1406 0251134 4590 2203 1029416 4605 102 809524 4605 1033 0613418 4605 1409 0252051 4605 2210 1034100 4620,102 802443 4620 1037 0619712 4620 1493 0252967 4620 2217 1038795 4635 103 895553 4635 1040 0626076 4635 1496 0253887 4635 2205 1043499 4650 103 908854 4650 1043 0632511 4650 1500 0254805 4650 2292 1048218 4665 103 922351 4665 1047 0639014 4665 1503 0255723 4665 2300 1052944 4680 104 936047 4680 1050 0645592 4680 1507 0256643 4680 2307 1057683 4695 104 949943 4695 1054 0652241 4695 1510 0257564 4695 2314 1062431 4710 104 904045 4710 1057 0658965 4710 1513 0258486 4710 2322 1067192 4725 105 918352 4725 1000 0665762 4725 1517 0259407 4725 2329 1071963 4740 105 992870 4740 1004 0672634 4740 1520 0260330 4740 2337 1076746 4755 105 1007602 4755 1007 0679582 4755 1524 0261252 4755 2344 1081538 4770 106 1022550 4770 1010 0686608 4770 1527 0262175 4770 2351 1086344 4785 106 1037718 4785 1014 0693710 4785 1531 0263100 4785 2359 1091157 4800 106 1053107 4800 1017 0700892 4800 1534 0264026 4800 2306 1095986 4815 107 1008723 4815 1001 0708152 4815 1538 0264951 4815 2314 1100823 4830 107 1004569 4830 1004 0715494 4830 1541 0265879 4830 2301 1105671 4845 107 1100647 4845 1007 0722917 4845 1545 0266806 4845 2308 1110532 4860 108 1116963 4860 1091 0730422 4860 1548 0267734 4860 2396 1115402 4875 108 1133516 4875 1094 0738010 4875 1552 0268662 4875 2403 1120283 4890 108 1150314 4890 1097 0745683 4890 1555 0269592 4890 2411 1125177 4905 109 1107358 4905 1101 0753441 4905 1559 0270521 4905 2418 1130084 4920 109 118A652 4920 1104 0761283 4920 1502 0271451 4920 2425 1135001 4935 109 1202202 4935 1107 0769214 4935 1506 0272383 4935 2433 1139928 4950 110 1220007 4950 1111 0777233 4950 1509 0273316 4950 2440 1144866 4965 110 1238075 4965 1114 0785341 4965 1513 0274247 4965 2448 1149817 4980 110 1256409 4980 1118 0793539 4980 1516 0275182 4980 2455 1154777 4995 111 1215011 4995 1121 0801829 4995 1500 0276115 4995 2402 1159751 5010 111 1293888 5010 1124 0810210 5010 1503 0277050 5010 2410 1164737 5025 111 1313040 5025 1128 0818684 5025 1507 0277985 5025 2417 1169733 5040 112 1332474 5040 1131 0827252 5040 1590 0278921 5040 2405 1174743 5055 112 1352195 5055 1134 0835915 5055 1594 0279858 5055 2492 1179759 5070 112 1312204 5070 1138 0844678 5070 1597 0280795 5070 2499 1184791 5085 113 1392508 5085 1141 0853536 5085 1601 0281734 5085 2507 1189836 5100 113 1413110 5100 1144 0862491 5100 1604 0282673 5100 2514 1194887 5115 113 1434013 5115 1148 0871550 5115 1608 0283613 5115 2521 1199953 5130 114 1455226 5130 1151 0880708 5130 1611 0284553 5130 2529 1205033 5145 114 1416748 5145 1155 0889966 5145 1615 0285493 5145 2536 1210122 5160 114 1498588 5160 1158 0899330 5160 1618 0286436 5160 2544 1215222 5175 115 1520748 5175 1101 0908798 5175 1622 0287377 5175 2551 1220333 5190 115 1543233 5190 1105 0918373 5190 1625 0288319 5190 2558 1225459 5205 115 1506049 5205 1108 0928053 5205 1629 0289263 5205 2506 1230598 5220 116 1509200 5220 1111. 0937839 5220 1632 0290207 5220 2513 1235744 5235 116 1612692 5235 1115 0947739 5235 1636 0291154 5235 2501 1240905 5250 116 1636527 5250 1118 0957747 5250 1639 0292100 5250 2508 40 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 5265-6000 Geologic age, in millions of years, calculated from the atomic ratios of indicated isotopes N206/N238 Nzoz/N235 N207/N206 N208/N232 Age Age A 6 Age Ratio Number Error Ratio Number Error Ratio Number Error Ratio Number Error of + of _ 0f + 0f - years - years years — years 1246076 5265 117 1660713 5265 1181 0967868 5265 1643 0293046 5265 2595 1251259 5280 117 1685255 5280 1185 0978103 5280 1646 0293992 5280 2603 1256457 5295 117 1710157 5295 1188 0988449 5295 1650 0294939 5295 2610 1261664 5310 118 1735424 5310 1192 0998913 5310 1653 0295890 5310 2618 1266883 5325 118 1761064 5325 1195 1009496 5325 1657 0296838 5325 2625 1272116 5340 118 1787079 5340 1198 1020194 5340 1660 0297788 5340 2632 1277361 5355 119 1813477 5355 1202 1031014 5355 1664 0298738 5355 2640 1282616 5370 119 1840262 5370 1205 1041955 5370 1667 0299689 5370 2647 1287885 5385 119 1867440 5385 1208 1053018 5385 1611 0300642 5385 2655 1293166 5400 120 1895020 5400 1212 1064205 5400 1614 0301595 5400 2662 1298453 5415 120 1923002 5415 1215 1075518 5415 1618 0302547 5415 2669 1303764 5430 120 1951398 5430 1219 1086958 5430 1681 0303501 5430 2617 1309080 5445 121 1980208 5445 1222 1098527 5445 1685 0304456 5445 2684 1314411 5460 121 2009442 5460 1225 1110223 5460 1689 0305413 5460 2692 1319752 5475 121 2039108 5475 1229 1122054 5475 1692 0306369 5475 2699 1325105 5490 122 2069207 5490 1232 1134017 5490 1696 0307324 5490 2706 1330471 5505 122 2099750 5505 1235 1146115 5505 1699 0308282 5505 2714 1335850 5520 122 2130740 5520 1239 1158347 5520 1703 0309240 5520 2721 1341243 5535 123 2162185 5535 1242 1170715 5535 1706 0310201 5535 2729 1346645 5550 123 2194094 5550 1245 1183227 5550 1710 0311160 5550 2736 1352062 5565 123 2226469 5565 1249 1195876 5565 1713 0312119 5565 2743 1357491 5580 124 2259323 5580 1252 1208669 5580 1717 0313080 5580 2751 1362931 5595 124 2292657 5595 1256 1221606 5595 1720 0314042 5595 2758 1368385 5610 124 2326480 5610 1259 1234687 5610 1724 0315005 5610 2765 1373851 5625 125 2360802 5625 1262 1247918 5625 1727 0315968 5625 2713 1379330 5640 125 2395627 5640 1266 1261296 5640 1731 0316932 5640 2780 1384823 5655 125 2430965 5655 1269 1274825 5655 1735 0317896 5655 2788 1390327 5670 126 2466820 5670 1212 1288506 5670 1738 0318862 5670 2795 1395843 5685 126 2503202 5685 1216 1302343 5685 1742 0319829 5685 2802 1401373 5700 126 2540120 5700 1219 1316335 5700 1745 0320794 5700 2810 1406915 5715 127 2517578 5715 1282 1330485 5715 1749 0321763 5715 2817 1412469 5730 127 2615590 5730 1286 1344797 5730 1752 0322730 5730 2825 1418041 5745 127 2654157 5745 1289 1359264 5745 1756 0323699 5745 2832 1423620 5760 128 2693290 5760 1293 1373900 5760 1759 0324669 5760 2839 1429214 5775 128 2733001 5775 1296 1388700 5775 1763 0325639 5775 2847 1434819 5790 128 2713292 5790 1299 1403668 5790 1767 0326609 5790 2854 1440439 5805 129 2814179 5805 1303 1418805 5805 1710 0327581 5805 2862 1446073 5820 129 2855662 5820 1306 1434111 5820 1714 0328554 5820 2869 1451718 5835 129 2897756 5835 1309 1449591 5835 1717 0329528 5835 2816 1457377 5850 130 2940470 5850 1313 1465247 5850 1781 0330500 5850 2884 1463050 5865 130 2983809 5865 1316 1481078 5865 1784 0331474 5865 2891 1468733 5880 130 3027788 5880 1319 1497092 5880 1788 0332450 5880 2899 1474434 5895 131 3012409 5895 1323 1513282 5895 1791 0333427 5895 2906 1480143 5910 131 3117686 5910 1326 1529659 5910 1795 0334404 5910 2913 1485867 5925 131 3163631 5925 1330 1546222 5925 1799 0335381 5925 2921 1491604 5940 132 3210249 5940 1333 1562972 5940 1802 0336359 5940 2928 1497355 5955 132 3257554 5955 1336 1579912 5955 1806 0337338 5955 2936 1503120 5970 132 3305550 5970 1340 1597041 5970 1809 0338317 5970 2943 1508897 5985 133 3354252 5985 1343 1614366 5985 1813 0339298 5985 2950 1514686 6000 133 3403672 6000 1346 1631891 6000 1816 0340279 6000 2958 U. 5, GOVERNMENT PRINTING OFFICE: 1959 0—485342 Fossils of the Littleton Formation (Lower Devonian) of New Hampshire GEOLOGICAL SURVEY PROFESSIONAL PAPER 3,34—B Fossils of the Littleton Formation (Lower Devonian) of New Hampshire By A. J. BOUCOT and ROBERT ARNDT GEOLOGICAL SURVEY PROFESSIONAL PAPER 334—B UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1960 UNITED STATES DEPARTMENT OF THE INTERIOR FRED A. SEATON, Secretary GEOLOGICAL SURVEY Thomas B. Nolan, Director For sale by the Superintendent of Documents, U.S. Government Printing Oflice Washington 25, DC. — Price 25 cents (paper cover) CONTENTS Page Abstract ___________________________________________ 41 Introduction _______________________________________ 41 Age of the Littleton formation ________________________ 41 Geology of the Devonian fossil—collecting locality on Dal- ton Mountain ____________________________________ 43 Stratigraphy of the Littleton formation on Dalton Mountain ________________________________________ Systematic paleontology _____________________________ Summary __________________________________________ Selected references __________________________________ Index _____________________________________________ ILLUSTRATIONS [Plates 1—3 follow index] PLATES 1, 2. Brachiopods from the Littleton formation. 3. Brachiopods and other fossils from the Littleton formation. FIGURE 3. Index map showing quadrangles cited in text _______ 4. Geologic map and cross-section of area adjacent to the Devonian fossil-collecting locality, Dalton Mountain, Whitefield quadrangle, N.H ____________________ TABLES TABLE 1. Distribution of fauna from the Littleton formation of New Hampshire and the Moose River sandstone (upper part) of northern Maine ______ u, ______________ III Page 45 46 50 50 51 42 44 43 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY FOSSILS OF THE LITTLETON FORMATION (LOWER DEVONIAN) OF NEW HAMPSHIRE BY A. J. BOUCOT AND ROBERT ARNDT ABSTRACT Reexamination and study of fossils collected from 3 localities in New Hampshire show the presence of the brachiopods Amphi‘ gcnia and In‘oderomu'ia cf. E. arcuata at 2 of the localities. The evidence suggests a correlation of the containing strata with the Camden chcrt (Lower Devonian) of Tennessee. All the fossils are from slightly metamorphosed (chlorite zone) strata of the Littleton formation in northern New Hampshire. Fossils from highly metamorphosed (sillimanite zone) rocks correlated with the Littleton formation are determined to be of post-Early Ordovician age. Several thousand feet of unfossilif— erous post—Silurian rocks, below the fossiliferous strata (Little- ton formation) in the Littleton quadrangle. are present in part of the adjoining Whitefield quadrangle. The absence of these strata in part of the Whitefield quadrangle may be due to nondeposition or to erosion prior to deposition of strata of Camden age. INTRODUCTION The slightly metamorphosed fossiliferous beds of the Littleton formation crop out in the Littleton, Moosi- lauke, and Whitefield quadrangles of northwestern New Hampshire (fig. 3). Devonian fossils were first reported from this area by F. H. Lahee (1912). A previous study of the fauna by Cleaves (Billings and Cleaves, 1934) concluded that the strata which yielded the fossils are of Oriskany age. Restudy of the fossils available to Cleaves, plus those obtained from a new locality located by Arndt in the IVhitetield quadrangle (collected by Boucot and others) demonstrates that the faunas are of Camden rather than of Oriskany age.1 The locality in the Whitefield quadrangle was visited in the summer of 19-19 by M. P. Billings, K. Fowler— Billings, and the authors. The Littleton formation is the only formation in New Hampshire which has yielded generically identi— fiable fossils of Early Devonian age. All the speci- 1The‘Camden chert. in Boucot‘s opinion. is of Early Devonian age. as It is a correlative at least of part of the lower Emsian portion of the standard section for the Devonian in the Rhineland. Em'yspirifcr atlantzcus of the Littleton formation and the Moose River sandstone (upper part) is very similar to Euryapirifer hercyniae (Giebel) which characterizes the lower Emsian. mens are slightly metamorphosed. The Littleton has well-developed slaty cleavage and porphyroblasts of pyrite with pressure shadows of fibrous quartz (often in the beaks of the brachiopods). Metamorphism renders the specific identification of the fossils difficult. The nearest. fossiliferous beds of similar age are to the northeast in Somerset County, Maine (upper part of the Moose River sandstone). The following fossil-collecting localities are cited in text : 1. Pageau Farm (Tip Top Hill, loc. 8 of Billings and Cleaves, 193-1), Littleton quadrangle, Grafton County, N.H. USGS SD—3247. . Mormon Hill (loc. 11 of Billings and Cleaves, 1934), Littleton quadrangle, Grafton County, N.H. 3. Mount Clough, Moosilauke quadrangle, County, N.H. 4. Dalton Mountain, Whitefield quadrangle, Coos County. N.H. USGS SD—3248. Two and threequarters miles northwest of Whitefield, or one-half of a mile N. 10° E. of knob 2,000 feet elevation on northeast end of Dal- ton Mountain. (See fig. 4.) [O Grafton AGE OF THE LITTLETON FORMATION The fossils identified in the faunas collected from the Littleton formation and also the ones that are com- mon to the upper part of the Moose River sandstone are shown on table 1. Inspection of table 1 indicates that the faunas from the Pageau Farm, Mormon Hill, and Dalton Mountain are very similar and therefore are concluded to be of the same age. The forms common to both the faunas of the Littleton formation and that of the upper part of the Moose River sandstone sug- gests that these two units are of the same age. The presence of Awmlrégem'a in three of the above mentioned faunas indicates that they are to be corre— lated with the zone of A7n79higem'a which elsewhere in North America (Cloud, 1942, p. 77; Cooper, 1942, chart) is thought to be restricted to strata of Onondaga age. In addition, the presence of highly convex speci- 41 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 72° 73” r FOSSILIFEROUS LOCALITIES 1 Pageau Farm 2 Mormon Hill 3 Mount Clough 4 Dalton Mountain é Burlington St J ohnsbury MgNTPELIER ‘-— CHAMPLAIN ’ Woodsvillé) i l R 7'” 3 .. \.- ,. J / f" " Rutland LL/ 43° - —.._..—.-—_ I l 7—--—- I O Bennington -—_..—.-_..—.._ ..__..._ __ _ .. — .. 43° 71° /' 73" FIGURE 3.~Index map showing quadrangles cited in text. 40 Miles l FOSSILS OF THE LITTLETON FORMATION, NEW HAMPSHIRE 43 TABLE 1.—Dtstribution offauna from the Littleton formation of New Hampshire and the Moose River sandstone (upper part) of northern Maine Locality Fossil Species com- Known stratigraphic range Dalton l’ageau Mormon mon to Moose Mount Mountain Farm Hill River sand- Clough stone (upper part) Unidentified orthoid brachiopod--- _ _ _ _ ________ X __________________________ Rhtpidometloides musculosa solaris _____ X X ________ X ________ Late Early Devonian. Costelltrostra sp ______________________ X __________________________________ Late Early Devonian. Atrypa “reticularis” ,,,,,,,,,,,,,,,,,,,,,,,,,, X _ _ _ _ ; - - _ X ________ Silurian and Devonian. Eurysptrtfer of. E. atlanttcus __________________ X X X ........ Late Early Devonian. Brachysptrifer of. B. perimele ,,,,,,,,,, X ________________ X ________ Late Early Devonian. Prototeptostrophz'a of. P. blatnvillet ______________ X X X ________ Schuchertella? sp ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, X X ________ Silurian to Mississippian. Leptaena ”rhombotdalts” ______________________ X X X ________ Ordovician to Mississippian. ”Chonetes” of. “C.” nectus ____________ X X. ,,,,,,,, X ________ Late Early Devonian. Eodevonaria cf. E. arcuata ____________ X X X X ________ Late Early Devonian. Amphigem'a of. A. parva ______________ X X ________ X _________ Late Early Devonian. Prionothyrts? sp _____________________________ X ........ X ________ Late Early Devonian. Brachiopod? __________________________________________________________ >< Unidentified pterineoid pelecypod _____________ X ________ X ________ Pelecypod, unidentified _______________ X ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, Tentaculites sp ______________________________________ X __________________ Ordovician to Devonian. mens of E odeoonaria, and spiriferoids similar to Euryspz'rifer attentions- are suggestive of a post-Cris- kany age since these forms have not previously been reported from strata of Oriska‘ny age or older. The faunules obtained from the Littleton formation in the Littleton and “7hitefield quadrangles occur in structurally isolated synclines from which the strata cannot be traced directly into the adjacent highly meta- morphosed rocks with which they have been correlated. At Mount Clough (fig. 3, 100. 3) two specimens were obtained from the metamorphic rocks correlated with the unmetamorphosed Littleton formation (Billings and Cleaves, 1985, p. 530—536). Both specimens were identified as brachiopods by Cleaves, and the better specimen (pl. 3, fig. 26) as “Spirifer sp. indet.” The better specimen was probably a coarsely plicated bivalve, but no basis for reliable phyletic assignment, much less a generic assignment, exists. It is Boucot’s opinion, after studying various faunas of early Paleo- zoic age from the northern Appalachians, that the specimens probably are brachiopods rather than pelecy- pods, although this opinion cannot be proved on a mor- phologic basis. If the specimens are brachiopods or pelecypods, it is probable that the containing beds are of post-Early Ordovician age. In Boucot’s opinion the better specimen could be assigned to any coarsely plicate brachiopod, including forms such as Platystro- phia and Howettetla. More detailed assignment of the strata must be based on stratigraphic sequence and lithologic simi- larity rather than on any fossil evidence. As recognized by Billings and Cleaves (1935, p. 534), these specimens from Mount Clough were not suffi- ciently diagnostic to date the enclosing rocks. They assigned the rocks to the Littleton formation on the basis of stratigraphic position and lithologic character. Because beds of massive gray sandstone at locality 2 are very poorly exposed, no attempt was made to deter- mine their stratigraphic position within the sandy member. Cobbles of quartzite of the type found in the Albee formation are present in an outcrop of con— glomerate that is approximately 250 feet west of local- ity 2 (fig. 4). Their large size suggests that the con— glomerate lies relatively close to the contact with the Albee formation. The relation of bedding to cleavage indicates that a syncline lies to the southeast as at 10- cality 2. GEOLOGY OF THE DEVONIAN FOSSIL-COLLECTING LOCALITY ON DALTON MOUNTAIN Fossils of Camden age are found in two exposures on the northwest limb of the Dalton Mountain subsidi- ary syncline (fig. 4) (Billings, 1955). The rocks at both exposures are slaty sandstone of the Littleton for- mation. At locality 1, which has yielded the most fos- sils and from which all the described material has come, the strata lie between 65 and 170 feet above the base of the sandstone, depending on whether the beds are repeated by folding or dip uniformly toward the southeast, with no minor folding. Field data indicate the presence of some minor folding, but its extent is undetermined because of the small size and scattered 44 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY / 055% / A e / // 0a / nmwww / mm who / // t k // “e /// e \ ’/ 4’04 j \ ‘ ’ git ’7 /Fe‘ds me D / D ' | / // ‘ gr 4 \"m \_Quavtzmc 50 /-’ 55 -' / ‘ r In alhc f, E Pel(lspam‘c/// // e w I E;\ g /’ 45 Femsuam: r9, 2 w Senuhr VQuartzose /y/ n‘ m 4 _ » 1; E / Oa / \ / O _. Quartzmr .— a ‘ yew“, 1 / Auarlzose SEW!“ Measured” 50 89mm '\ /Quavtzmc “ 55 ) section "A ,« //55 -' / I 3/ / Sencmc‘ MeaSUrEU \Sem/mc o ..... or / section “B" __ M 22“ «=50 70 // senc.m%adouavxz.x.c y EXPLANATION // VSencrIIc V ‘ DI ”l § / Oa % Fossfliferous locality} ® 4 ., *4 C E / ‘Quanzmc thtleton formatlen l g / // :/ / / ,, 30% // 5‘3““? _‘V 3"? D' , l E i / g. Sencmc 55 0a L 3 ‘ V. V / 4 1 8 ‘ v Albee formation a , I l / f'"\ O l 52 . . \ Fo — _ _ __.. 4/ (/ é. . a g ssnhferous locallty 2 \\ contact 20 y A “Fem am \ so] Dashed where m/erred //// p o 100 200 300 400 500 600 700 300 900 1000 Feet \ N, \ 50145 A, Strike and dip ataxia! plane 0! fold ’ and plunge of was 30 ,4 , Strike and dip of beds E 90 i ,Hi ‘ Strike of vertical beds x 20 1 x ‘. L J Fossilulerous locality 1 sum: and am of cleavage WV Schlst Slate Sandstone Conglomerate FIGURE 4.—Geologic map and cross section of area adjacent to the Devonian fossil locality, Dalton Mountain, Whitefield: quadrangle, New Hampshire. nature of the outcrops of essentially massive, Slaty Section A of figure 1, sandstone. General structural relations are shown Extensive covered zone Feet in the cross section (fig. 4). Conglomerate _________________________________________ 2 N t] fl (H 1 t1 b, f 1 L‘ t1 t f 1 Quartz“ --------------------------------------------- 11/2 . 0r 1 0. OCM‘y , 1e dse 0 tie file on Olma— Gap and lateral Offset ________________________________ 2 tion conSISts of quartz-pebble conglomerate, gray Conglonlerate _________ 2 quartzite, and Clark-g *ay Slaty sandstone that lie on the Covered zone _________________________________________ 15 Albee formation. The contact between the formations Albee formatlon “““““““““““““““““““““ " is not exposed, but at one place it occurs Within a Section, B of figure 4 Feet COVBI‘ed zone 15 feet wide. The character of the base Conglomerate _________________________________ ___ 1 ' u . , _ V _____________________ 1" 0f the Littleton formation 18 suggested in two sections 131’ ————————————————————————————— ) _ d _ 1 .1 f 1 b d 1 . 1 1. Gray sandstone _______________________________________ 3 measure aCIOSS tie st11 [Wingella(Paraimz'ngella) -> Irvingella (lrvz'ngella) might be included in one lineage by as— summing reduction in the length of the frontal area and gradual decrease in the taper of the glabella for these three taxa with long arcuate palpebral lobes. This lineage could be contrasted with one from Dan- derbergm -> E lburgia -> E lrvinia in which the posterior glabellar furrows are first deepened, and then con— nected across the top of the glabella. These three genera have similar pygidia. In addition, Dunder- bergz’a and E lburgz'a share a bluntly pointed anterior TRILOBITES OF THE UPPER CAMBRIAN margin and marginal furrow; and, E lbtwgz’a, on the basis of observation of specimens from California, has free cheeks indistinguishable from those of E lm'm'a. Alternative possibilities might be to derive E Zm'm'a from E lvim'ella’ by gradual reduction in length of the palpebral lobe or to group the genera with noticeably arcuate palpebral lobes and transglabellar posterior furrows together in one subfamily (that is, E Zvim'ella, E lm'm'a, Irvingella) and leave the genera with simple palpebral lobes (Dunderbergiw, Elbm‘gia‘) in a sec- ond subfamily. Obviously, more information about the genera of the Elviniidae is needed before an acceptable subfam- ily classification can be prepared. Perhaps studies of the faunas of the Dunderberg shale elsewhere in the Great Basin will provide this information. Genus DUNDERBERGIA Walcott, 1924 Text figure 9 Dunderbergia Walcott, 1924, p. 56; 1925, p. 84; Resser, 1935, p. 23; Raymond, 1937, p. 1112; Kobayashi, 1938, p. 181; Shimer and Shrock, 1944, p. 625; Palmer, 1954, p. 760. Type species.—0repicephalus (Loganellus) m'tz'dus Hall and Whitfield, 1877, p. 212, pl. 2, fig. 8. I)iagnosis.——Elviniidae with prominent subquadrate glabella; glabellar furrows hardly visible. Length of palpebral lobe about 1/3 to 14 length of glabella in- cluding occipital ring. Line connecting midlengths of palpebral lobes crosses glabella just posterior to junc- tion of second glabellar furrows with dorsal furrow. Anterior margin and marginal furrow commonly come to a blunt point on axial line instead of form- ing an even curve. Thorax includes either (or both) segments with pleural spines short, laterally directed, or long, backwardly directed. Pygidium subsemicircular in outline, widest at anterolateral corners. Border narrow, of nearly constant width. Axial lobe promi- nent, subparallel sided, bluntly rounded posteriorly. Pleural lobes nearly flat. Modification of this diagnosis from that given ear- lier (Palmer, 1954) results from a consideration of the characters of the genera assigned to the Elviniidae. Description.—Medium-sized trilobites, probably few longer than 40 mm. Form of entire exoskeleton un- known. Cephalon subsemicircular in outline, moder- ately to strongly arched transversely and longitudi- nally. Cranidium exclusive of posterior limbs sub- quadrate in outline, anterior margin commonly bluntly pointed. Glabella prominent, elevated above brim and cheeks, tapered slightly forward, bluntly rounded or truncate anteriorly. \Vidth just anterior to occipital furrow nearly equal to length exclusive of occipital ring. Three pairs of shallow glabellar furrows may be present. Posterior pair generally with bigenicu- DUNDERBERG SHALE , EUREKA DISTRICT, NEV. 65 FIGURE 9.—Partial reconstruction of Dundarbergia polybothra n. 81)., about X 8. late form. Occipital furrow always moderately deep, particularly at distal ends. Occipital ring with low median node adjacent to occipital furrow. Dorsal furrow deep at sides of glabella; shallow across front. Border distinct, moderately to strongly convex; length one—half or slightly leSS than that of brim. Marginal furrow deep, generally comes to blunt point on axial line. Brim gently to moderately convex. Fixed cheeks gently to moderately convex, horizontal or slightly upsloping; width about one-third basal glabellar width. Palpebml lobes semicircular in outline, mod- erately well defined by shallow palpebral furrow; width one—third or slightly more that of cheek; length about 1A; to 14 length of glabella including occipital ring. Ocular ridges generally Visible, anterior mar- gin best defined. Posterior limbs sharply pointed, length (transverse) generally slightly greater than basal glabellar width. Marginal furrow on posterior limb broad, deep; broadens laterally. Anterior course of facial suture slightly divergent from palpebral lobe to marginal furrow; turns inward across border, cuts anterior margin at point slightly less than one-half distance from anterolateral corners of cranidium to axial line. Connective sutures convergent posteriorly, not meeting on axial line. Rostral suture beneath midlength (sagittal and exsagittal) of border (fig. 8C). Posterior course of facial suture divergent-sinuous. 66 Free cheek with well—defined continuous lateral and posterior marginal furrows; posterior marginal fur- row generally deepest. Border narrow. Ocular plat- form gently convex, twice or more width of border. Genal spine short, sharply pointed, tip on some spe— cies curved slightly inward; length generally less than axial length of glabella on associated cranidium. Hypostome and rostrum not known. Form of thorax unknown. Thoracic segments of the same species with pleural spines either short, sharp, and directed laterally; or long, slender, and directed posteriorly. Width (transverse) of pleurae, from dor- sal furrow to geniculation, between 1 and 2 times width of axial ring. Pygidium short and wide, nearly flat except for prominent axial lobe. Axial lobe with 1 or 2 promi— nent ring furrows and with blunt indistinct posterior termination near inner margin of border. A low poorly defined median ridge connects axial lobe with border. Border well defined along all of margin ex- cept directly on axial line; width about half greatest width of pleural platform. A slight median inden— tation of margin may be present. Surface of exoskeleton variously ornamented. Ex- ternal surface of cranidium and cheeks entirely smooth, partly or wholly granular, or coarsely pitted. Sur- face of mold of cranidium and checks ornamented with either pits or fine pits interspersed with coarse gran- ules. Fine—granular and coarse-pitted ornament not apparent on surface of mold. Ornamentation of surface of thoracic segments comparable to that of cheeks and cranidium. Pygidium with top surface of axial lobe and border always bearing granules. Border generally also with prominent terrace lines. Pleurae either smooth, coarsely (but weakly) pitted, or granular. Surface of mold generally finely pitted. Discussion.—Walcott (1924, p. 56) proposed Dander- bergia to include Crepicephalus (Loganellus) nitidas Hall and Whitfield and gave a brief diagnosis of the genus. Other brief mentions of some of the character— istics of Dunderbergia were given by Walcott (1925, p. 83), Raymond (1937, p. 1112) and Kobayashi (1938, p. 181). A more detailed description of the genus was given by Palmer (1954, p. 760) and is repeated with only slight modification here. Thirteen species, besides the type species, have been assigned to Dunderbergia. These were Urepicephalus (Loganellus) macalosus Hall and Whitfield, (‘repicephalas (Loganellus) simulator Hall and Whitfield, Crepicephalus (Loganellus) granulosus Hall and Whitfield, Ptychaspis pustulosa Hall and Whitfield, Ptychoparia suada Wal- cott, and Dunderbergia halli Resser assigned by Resser (1935, p. 23, 24); Danderbergia? declivita (Miller, 1936, p. 30); Crepicephalus (Loganellus) anytas Hall and SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY Whitfield (Resser, 1937, p. 9) ; Danderbergia vermontensis (Raymond, 1937, p. 1120); Dunderbergia canadensis, D. conveza, and D. quadrata assigned by Kobayashi (1938, p. 181, 182) who included the latter two species along with D. pustalosa Hall and Whitfield, D. maculosa (Hall and Whitfield), and D. granalosa (Hall and Whitfield) in a new subgenus, Megadunderbergia; and Dunderbergia variagranala (Palmer, 1954, p. 761). Wilson (1948, p. 33) considered Dunderbergia? de- clivita Miller a synonym of Deadwoodia daris (Walcott). Wilson, (1951, p. 636) also removed Danderbergia suada (Walcott) from the genus and considered it a senior synonym of Dellea wilbernsensis Wilson (1949, p. 35). Shaw (1952, p. 475) pointed out that Dunderbergia vermontensis Raymond is a young individual of Mete— oraspislminuta (Raymond). A review of the 11 other species during this study shows that only D. nitida (Hall and Whitfield), D. anyta (Hall, and Whitfield), D. quadrata Kobayashi, and D. variagranula Palmer are recognizable species remaining in Dunderbergia. Of the seven other species, D. simulator (Hall and Whit- field) was considered a synonym of D. nitida (Hall and Whitfield) by Walcott (1884, p. 57), was later resur- rected by Resser (1935, p. 24), and is here, again, con- sidered a synonym of D. nitida. D. granalosa (Hall and Whitfield) is removed from Danderbergia and assigned to the new genus Elbargia. D. halli Resser is based on a pygidium correctly assignable to Housia (p. 75) ; and D. macalosa (Hall and Whitfield) (pl. 5, fig. 5), D. pastulosa (Hall and Whitfield) (pl. 5, fig. 8), D. cana- densis Kobayashi and D. convexa Kobayashi are based on such poor material that the specimens, though probably belonging to Dunderbergia, cannot be assigned with confidence to any of the species of the genus here recognized and are considered indeterminate. The names should be restricted to the type specimens. Because D. macalosa (Hall and Whitfield), the type species of Megadunderbergia Kobayashi, is considered an indeterminate species, the subgenus also must be considered indeterminate. No subgenera of Dander- bergia are recognized in this paper. Species presently assigned to Dunderbergia: Dundbergeria anyla (Hall and Whitfield) bigranulosa n. sp. nitida (Hall and Whitfield) polybolhra n. sp. quadrata Kobayashi variagranula Palmer maculosa (Hall and Whitfield) pustulosa (Hall and Whitfield) canadensis Kobayashi convexa Kobayashi Restricted to holotype Dunderbergia bigranulosa n. :1). Plate 5, figures 10—13, 15—23 I)iagnosis.—Members of Dunderbergia with exter— nal surface of cephalon bearing low scattered coarse TRILOBITES OF TIIE UPPER CAMBRIAN granules on brim, fixed cheeks, posterior limbs, and ocular platforms; fine close-spaced granules on bor- der, top of glabella, and outer margins of palpebral lobes. Surface of mold shows position of coarse gran- ules; surface beneath fine—granular areas is finely pit- ted. Pygidium with fine granules on border and top of axial lobe; scattered low coarse granules on pleu— ral platforms. Discussion.—Some variation in degree of expres- sion and detailed distribution of the coarse granules was observed within collections of D. bigranulosa. On some specimens the coarse granules are only apparent after the specimen has been lightly whitened and ob- served with low oblique lighting (pl. 5, fig. 13). On specimens from USGS collection 795, associated with D. nitida (Hall and Whitfield), the coarse granules are exceptionally prominent (pl. 5, figs. 10, 11), and in this way resemble the coarse granules of D. vari— agranula Palmer; however, the border and glabella have the fine granules characteristic of D. bigranulosa. Two types of free cheeks, perhaps indicating di- morphism within the species, have been found in col— lections of D. bigranulosa and D. variagranula. On one type, the border broadens slightly anterior to the base of the genal spine and it is distinctly flattened. On the other type, the border maintains an even width and it is gently convex (cf. pl. 5, figs. 16, 17). An unusual, apparently pathologic, pygidium is present in USGS collection 2295—CO (pl. 5, fig. 23). This specimen includes two distorted thoracic seg- ments that have their right pleurae free and their left pleurae fused with each other and the remainder of the pygidium. Occurrence: Abundant, lower 40 ft of Dunderberg shale; unit A. USGS colln. 795—00, 2294—00, 2295—00. Figured specimens: Holotype cranidium, USNM 136847, USGS colln. 2295. Paratypes: Cranidium, USNM 136848a, USGS colln. 2295—00; cranidia, USNM 136846a, b, USGS colln. 795—00; cranidium, USNM 136849b, USGS colln. 2294—00; free cheeks, USNM 136848b,c, USGS colln. 2295—00; free cheek, USNM 136849a, USGS colln. 2294—00; pygidia, USNM 136848d—f, USGS colln. 2295—00; pygidium, USNM 1368490, USGS colln. 2294—00. Dunderbergia nitida (Hall and Whitfield) Plate 4, figures 14—21, 23, 24 Crepicephalus (Loganellus) nitidus Hall and Whitfield, 1877, p. 212, pl. 2, fig. 8. Orepicephalus (Loganellus) simulator Hall and Whitfield, 1877, p. 218, pl. 2, figs. 16—18. Ptychoparia nitidus (Hall and Whitfield). 57. Dunderbergia nitida (Hall and Whitfield). Walcott, 1924, p. 56, pl. 11, fig. 2; 1925, p. 84, pl. 16, fig. 4; Shimer and Shrock, 1944, pl. 264, fig. 29. Dunderbergia simulator (Hall and Whitfield). p. 24. Walcott, 1884, p. Resser, 1935, DUNDERBERG SHALE, EUREKA DISTRICT, NEV. 67 Diagnosis—Members of Dunderbergia with exter- nal surface of exoskeleton smooth except for top of axial lobe and border of pygidium which bear fine close-spaced granules and border of free cheek which has terrace lines. Surfaces of molds of all parts of exoskeleton are finely pitted. Discussion—This species is the most common spe- cies of Dunderbergia in the collections studied. Some cranidia from USGS collection 2300—CO have rare low barely discernible coarse granules on the brim, suggesting that D. nitida may have been derived from a form like D. bigranulosa through the loss of the fine granules on the border and glabella. The holotype of this species was not designated by Hall and Whitfield. Two specimens in the type col— lection have handwritten labels bearing the original name pasted on the rock. One, USNM 24572b, a mold, (pl. 4, fig. 16) is the specimen cited by Walcott (1925, p. 132, fig. 5) as an “original type specimen.” The illustration given by Walcott is not of this specimen, nor is it of the other with the handwritten label. The second specimen, USNM 24572, preserves enough of the external surface (pl. 4, fig. 15) to show that it was for the most part smooth. Inasmuch as \Valcott did not designate holotypes of the other species in his 1925 paper, Walcott’s cited comment is interpreted here to mean only that he was illustrating one of the original types. Because the illustration does not con- form to either of the labeled specimens, Walcott’s com- ment is not considered a valid citation of a lectotype for D. nilida, and the specimen bearing USNM 24572 and the handwritten label “U. (L.) nitidus” is here designated as lectotype of the species. The pygidium illustrated for D. nitida by Walcott (1925, pl. 16, figs. 6, 7) and Shimer and Shrock (1944, pl. 264, fig. 30) is a Housia pygidium (p. 75; pl. 7, fig. 8). Occurrence: Common, from 50—200 ft above the base of the Dunderberg shale; units B, C. USGS colln. 789—00, 795— CO, 864—00, 872—00, 873-00, 953—00—955—00, 2295—00—— 2302—00. Figured specimens: Lectotype cranidium, USNM 24572. Paratype cranidium, USNM 24572b. Plesiotypes: Cranidium, holotype of D. simulator (Hall and Whitfield), USNM 24575; cranidia, USNM 136838b, c, USGS colln. 2300—00; free cheeks, USNM 136838d, f, USGS colln. 2300-00; free cheek, USNM 136839, USGS colln. 873—00; pygidia, USNM 1368383, e, USGS colln. 2300—00. Dunderbergia polybothra n. sp. Plate 5, figures 1—4, 6, 7, 9, 14 Diagnosis.—Members of Dunderbergia with surfaces of all parts of exoskeleton except top of axial lobe and border of pygidium bearing coarse pits. Pits most apparent on border of cephalon, top of glabella, and axial parts of thoracic. segments; visible on other parts 68 SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY of exoskeleton only on exceptionally well—preserved specimens. Top of axial lobe and border of pygidium bear close-spaced granules. Surfaces of molds of all parts of exoskeleton are finely pitted. Discussion—This distinctive species is known from only two collections, Where it is the only species of Dunderbergia present. It differs from all other spe- cies in the genus by having a pitted surface. Occurrence: Moderately common, about 40 ft above base of Dunderberg shale, unit B. USGS colln. 1297—00, 2296—00. Figured specimens: Holotype cranidium, USNM 136845, USGS colln. 2296—00. Paratypes, cranidium, free cheeks, tho- racic segments, and pygidium, USNM 136844a-f, USGS colln. 2296-00. Dunderbergia variagranula Palmer Plate 4, figures 22, 25, 26, 28, 29 Dunderbergia variagrenula Palmer, 1954, p. 761, pl. 88, fig. 7. Diagnosis—Members of Dunderbergia with exter- nal surfaces of all parts of exoskeleton bearing scat- tered coarse granules. Surfaces of molds of all parts of exoskeleton also bearing scattered coarse granules. Discussion—In view of observations made on rea- sonably abundant material of this species in the Eu- reka district, the only illustrated specimen from Texas now retained in this species is the holotype (Palmer, 1954, pl. 88, fig. 7). The other three illustrated speci— mens may represent a species not known in the Eureka district. One difference was noted between the holotype and the Nevada specimens. Coarse granules are rare on the posterior limbs of the few specimens of D. vari- agranula from Nevada that have the limbs preserved. The posterior limbs of the holotype bear abundant coarse granules. Unfortunately, not enough speci- mens are known from either area to determine if this is a consistent difference. Because the distribution of coarse granules on other parts of the cranidium is somewhat variable among cranidia in a single collec— tion, the Texas and Nevada specimens are here con- sidered to be most likely conspecific. D. quadrata Kobayashi (pl. 4, fig. 27) is represented by a single cranidium that has coarse granular orna- ment on both the external surface and the surface of the mold. Fine granules are also present on the bor- der. These are characteristic features of D. varia- granula. However, the cranidium of D. quadratic is three times larger than any cranidia of D. uariagran- uia known, has a much more prominent glabella, and appears to have a relatively shorter frontal area and broader border. Although D. variagranula may be a synonym of D. guadrata, more knowledge of D. quad- rata is desirable before suppressing D. uariagranula. A single small cranidium from USGS collection 2302 (pl. 4, fig. 26) is tentatively referred to D. varia- granula. It conforms to the species in all respects except that the border bears only close-spaced fine granules. Also, it occurs with D. nitida, about 120 feet higher than any collection in which granular spe- cies of Dunderbergia are common. This certainly in- dicates that the granular and smooth forms of Dun- derbergia have a nearly common range in time. How- ever, the abundance of granular species in the rela- tively common limestones of the lower Dunderberg, where smooth forms of Dunderbergia are rare, and the reverse situation in the relatively rare limestones of the middle shaly part of the Dunderberg may in- dicate that the granular and smooth forms have dif- ferent facies preferences. Occurrence: Moderately common, 50—75 ft above the base of the Dunderberg shale; units B, C. USGS colln. 809—00, 873—00, 952—00, 2297—00, 2298-00. Figured specimens: Plesiotypes—cranidium and free cheek, USNM 136840a, b, USGS colln. 2297—00; cranidium, USNM 136841, USGS colln. 2298—00; crandium, USNM 136842, USGS colln. 2302—00; pygidium, USNM 136843, USGS colln. 809—00. Genus ELBUBGIA n. gen. Text figure 10 Type species.—0repicephalus (Loganellus) granu- losus Hall and Whitfield, 1877, p. 214, pl. 2, figs. 2, 3. Diagnosis.—Elviniidae with cranidium having pal- pebral lobes about one-third length of glabella in- cluding occipital ring, and with posterior pair of gla- bellar furrows deep, bigeniculate, connected by a shal— low furrow across top of glabella. Second glabellar furrows also conspicuous, only slightly curved. Ante- rior glabeller furrows only conspicuous on mold. Pygidium and free cheeks not distinguishable from E Zuinia. FIGURE 10.—Partial reconstruction of Elburgia quinneneis Resser, about X 6. Description.~—Medium to large trilobites (as much as 90 mm in total length). Outline of cranidium, ex— clusive of posterior limbs, subquadrate; anterior mar— TRILOBITES OF TIIE UPPER CAMBRIAN DUNDERBERG SHALE, EUREKA DISTRICT, NEV. 69 gin evenly rounded or bluntly pointed. Glabella prominent, elevated above cheeks, tapered forward, bluntly rounded or truncate anteriorly; with just an- terior to occipital furrow about equal to length ex- clusive of occipital ring. Three pairs of glabellar furrows present. Anterior pair shallowest, short; mid- dle pair moderately deep, reach about three-fourths distance to axial line; posterior pair deep, bigenicu- late, connected across top of glabella by shallow fur- row. All furrows more conspicuous on mold. Oc- cipital furrow broad, deep. Occipital ring with low median node adjacent to occipital furrow. Dorsal furrow deep at sides and anterolateral corners of glabella, shallow across axial line. Border distinct, moderately to strongly convex, length one-half or slightly less that of brim. Marginal furrow broad, deep, with slight tendency to come to a blunt point on axial line. Brim gently to moderately convex. Fixed cheeks gently to moderately convex, nearly hori— zontal. Width slightly less than one-half basal gla- bellar width. Palpebral lobes moderately arcuate in outline; width about one-third width of cheek; length about one—third length of glabella including occipital ring. Palpebral furrow broad, well defined. Ocular ridges visible but not prominent; anterior margin best defined. Posterior limbs sharply pointed, length (transverse) equal to or slightly greater than basal glabellar width. Marginal furrow on posterior limb broad, deep, broadens laterally. Anterior course of facial suture only slightly divergent from palpebral lobes to marginal furrow; turns inward across border; cuts anterior margin and becomes submarginal at point slightly less than one-half distance from anterolateral corner of cranidium to axial line. Posterior course of facial suture divergent sinuous. Hypostome rostrum and thoracic segments not known. Free cheek and pygidium same as Elvim'a (cf. figs. 10. 11). Discussions—This genus includes, at present, two species whose cranidial shape and stratigraphic ranges are intermediate between those of Dunderbergz’a and Elvim'a. The form of the preglabellar area is char- acteristic of Dunderbergz'a, and the posterior glabellar furrows connected across the glabella are characteris— tic of Elvinia. These characters combined, plus the general prominence of all glabellar furrows, are the distinguishing characteristics of the species of El- burgia. Species differentiation in Elburgia, as in Dunder- bergz'a, is primarily based on the nature of the exter- nal surface and the surface of the mold of the cranid- ium. Two cranidia representing this genus, but identified as EZm’m’a sp., were figured by Palmer and Hazzard (1956, pl. 1, figs. 1, 2) from the Cornfield Springs and Nopah formations in California. Elburgia granulosa (Hall and Whitfield) Plate 6, figures 16, 17, 19 Crepicephalus (Loganellus) granules-us Hall and Whitfield, 1877, p. 214, pl. 2, figs. 2, 3. Ptychoparz'a granulosus (Hall and Whitfield). 57. Dunderbergia granulasa (Hall and Whitfield). 24. Dunderbergia (Megadunderbergia) granulosa (Hall and Whit- field). Kobayashi, 1938, p. 181. Walcott, 1884, p. Resser, 1935, p. Diagnosis—Members of Elburgia with cranidium having external surface and surface of mold, exclusive of furrows and palpebral lobes, thickly covered with coarse granules. Discussion—No further comments on the character of this species have been published since the original description by Hall and Whitfield, though Walcott, Resser, and Kobayashi successively transferred it to three different genera or subgenera. Kobayashi (1938) included granulosa with Dunderbergia pustulo‘sa (Hall and Whitfield) in a new subgenus, Megadunderbergia. The holotype of the type species of M egadunderbergz'a (D. pustulosa) is here considered (p. 66) an inde- terminate specimen of Dunderbergz'a. Thus, Mega- dmederbergz'a is also indeterminate, and the identifi- able species assigned to it require reassignment. E. granulosa, with its conspicuous Elm'mL-like glabellar furrows, does not fit the present concept of Dunder— bergia and is here designated as the type species of E lburgia (see generic discussion). It is easily dis- tinguished from the only other species presently as- signed to the genus E. quinnensz's (Resser) by the coarse granular nature of the external surface and the surface of the mold of the cranidium. Occurrence: Rare, 45—70 ft above base of Dunderberg shale; unit B. USGS colln. 795—00; 2297—00. Figured specimens: Holotype cranidium. USNM 24573. Plesiotypes: Cranidium, USNM 136857, USGS colln. 2297—00; cranidium, USNM 136856, USGS colln. 795—00. Elburgia quinnensis (Resser) Plate 6, figures 11—13, 15 Taenicephalus quinnensis Resser, 1942b, p. 105, pl. 21, figs. 18, 23. Diagnosis—Members of Elburgia with external sur— face of cranidium nearly smooth. Lateral parts of brim and of posterior limbs with numerous close- spaced low granules visible only when specimen is whitened and viewed in extreme oblique lighting. Brim also bears scattered low coarse granules, also barely visible. Surface of mold with numerous fine pits most noticeable on brim and cheeks. Positions of coarse granules may be indicated by low elevations 70 with terminal pits slightly larger than those on other parts of cranidium. Discussion—This species was described by Resser (1942, p. 105) as Taem'cephalus quinnensz's from a small collection of unknown stratigraphic position collected by J. E. Spurr While on reconnaisance in Nevada in 1899. Although the prominent glabellar furrows are reminiscent of Taem'cephalus, the facial sutures do not cut the margin near the axial line as they seem to do in that genus, and no true species of Taem'cephalus have the posterior pair of glabellar furrows connected across the glabella. Furthermore, this species is associated with a species of Sigmocheilus n. gen., a genus characteristically found in beds older than those bearing E lm'xnia. Taem'cephalus is known only from beds younger than those bearing E lm’m’a. Free cheeks and pygidia associated with cranidia of this species in the lower part of the Nopah formation, California, are virtually indistinguishable from those of E lvim'a. A pygidium and free cheek, probably of E lburgia guirmensis, were figured by Resser from the small type collection from the Quinn Canyon Range, Nev. Occurrence: Moderately rare, 70—100 ft above base of Dun— derberg shale; unit B. USGS colln. 2298—00, 2299—00, 2300— 00. Outside the Eureka district, this species has been recog- nized in collections from the Nopah formation in California and in Dunderberg equivalents in the Las Vegas quadrangle, Nevada. Figured specimens: Holotype exfoliated cranidium, USNM 1088383, USNM loc 7j; Dunderberg(?) shale, Quinn Canyon Range, Nev. Paratype, cranidium, on same block as holotype, with external surface preserved. Plesiotypes: Cranidium, USNM 136855, USGS colln. 2298—00; cranidium, USNM 136438, USGS colln. 2299—00. Genus ELVINIA Walcott, 1924 Text figure 11 Elm’m‘a Walcott, 1924, p. 56; 1925, p. 88; Bridge and Girty, 1937, p. 252; Kobayashi, 1938, p. 179; Shimer and Shrock, 1944, p. 625. Moosia Walcott, 1924, p. 59; 1925, p. 106. Diagnosis.——Elviniidae with posterior glabellar fur- rows connected across glabella forming single arcuate furrow of nearly even depth. Other glabellar furrows rarely apparent. Palpebral lobes arcuate, length about one-third that of glabella including occipital ring. Width of fixed cheeks between 2/5 and 1/2 basal glabel— lar width. Anterior margin of cranidium evenly curved. Marginal furrow appears nearly straight in dorsal view. Anterior course of facial sutures nearly straight forward from palpebral lobes. Free cheek with short sharp genal spine diverging from general curvature of cheek margin. Ocular platform broad, separated from moderately to strongly convex border by broad deep marginal furrow, con— nection between lateral and posterior marginal furrows shallow. SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY Pygidium subsemicircular in outline, widest at ante- rior margin. Border narrow, of nearly constant width. Axial lobe prominent, subparallel sided, bluntly rounded posteriorly. Pleural lobes nearly flat. FIGURE 11.—Partlal reconstruction of Elvinia, roemeri (Shumard), about X 3. Discussion—Bridge and Girty (1937, p. 252; pl. 69, figs. 1—21) described the genus in detail and illustrated specimens from many parts of the United States. The inclusion of E. granulata (Resser) in the genus re- quires the following slight modification in the other- wise excellent characterization given by Bridge and Girty: Frontal area with length (sagittal) of border equal to or less than length (sagittal) of brim. Ex- ternal surface smooth or granular. Species differentiation in E lvim'a is here based pri— marily on the nature of the surface of the cranidium and secondarily on the character of the frontal area. The inadequacy of minor variations of cranidia] pro- portion for species difl’erentiation within E l’uim'a has already been treated by Bridge and Girty (1937) and Frederickson (1949). Elvinia roemeri (Shumard) Plate 6, figure 7 Dikelocephalus roemeri' Shumard, 1861, p. 220, 221. Crepz'cephalus (Loganellus) um'sulcatus Hall and Whitfield, 1877, p. 216, pl. 2, fig. 22. Ptychoparia matheri Walcott, 1912, p. 268, pl. 44, figs. 15~17. Elvinia roemeri (Shumard). Walcott, 1924, p. 56, pl. 11, fig. 3; 1925, p. 88, pl. 17, figs. 9—13; Bridge, 1933, p. 232, pl. 2, figs. 17—19; Miller, 1936, p. 30, pl. 8, fig. 36; Bridge and Girty, 1937, p. 251, pl. 69, figs. 1—22; Shimer and Shrock, 1944, pl. 264, figs. 34—37; Wilson, 1949, p. 38, pl. 10, figs. 5, 9, 10, 12, 13: Frederickson, 1949, p. 352, pl. 69, figs. 19* 21; Lochman, 1950, pl. 47, figs. 21-23; Wilson, 1951, p. 642, pl. 92, figs. 18—22; Nelson, 1951, p. 775, pl. 107, fig. 8; Bell, and others, 1952, p. 183, pl. 30, figs. 1a—d. Moosia grandz’s Walcott, 1924, p. 59, pl. 14, fig. 9; 1925, p. 107, pl. 23, figs. 20, 21. TRILOBITES OF THE UPPER CAMBRIAN DUNDERBERG SHALE, EUREKA DISTRICT, NEV. 71 Elvinia tetonensis Resser, 1937, p. 12. Elvinia texana Resser, 1938, p. 30. Elvinia shumdrdi Resser, 1938, p. 30; Shimer and Shrock, 1944, pl. 264, figs. 41, 42. Elvinia bridgei Resser, 1938, p. 31; 1942b, p. 97, pl. 18, figs. 28—31; pl. 19, figs. 1—5. Elvini'a missouriensis Resser, 1938, p. 31; 1942b, p. 96, pl. 18, figs. 13—17. Elvinia dakotensis Resser, 1938, p. 32. Elvini'a utahensz‘s Resser, 1938, p. 32; 1942b, p. 95, pl. 18, figs. 5, 6. Elvinia gregalis Resser, 1942b, p. ‘97, pl. 18, figs. 28—31. Elvini'a, longa Resser, 1942b, p. 97, pl. 18, figs. 24—27. Elvinia vagans Resser, 1942b, p. 98, pl. 19, figs. 6—9. Elvinia brevifrons Resser, 1942b, p. 98, pl. 19, figs. 10—14. Elvini'd matheri' (Walcott). Shimer and Shrock, 1944, pl. 264, fig. 40. Diagnosis.——Specimens of E lnim'a with smooth ex- ternal surface of crandium. Brim generally moder— ately convex; length (sagittal) nearly twice that of border. Discussion—This species has been discussed or i1- lustrated perhaps more than any other Upper Cam- brian species. Orepicephalus (Loganellus) unisuled- tus, described by Hall and Whitfield (1877) from the Eureka district, was shown by Bridge and Girty (1937) to be a synonym of E. roemeri. Later, Resser (1937, 1938, 1942) described many new species of El- m’nia. Except for E. granulatd Resser and E. rende- manni Resser, and E. hamburgensis (Resser), origi- nally described as Pdrdirpingelld hamburgensis (Res- ser, 1942) and transferred to Elnini’d by Kobayashi (1954, p. 34), all other species assigned by Resser to Elmim'a are now considered synonyms of E. roemeri (Shumard). Frederickson (1949) discussed much of the synonymy, and those species that he did not return to E. roemem’ are here returned. E lcinia utaherwis was used by Resser twice, both times cited as a new species (1938, p. 32; 1942, p. 95). Both holotypes are conspecific with E. roemeri'. Occurrence: Rare, upper Dunderberg shale (units 0, D) and lower part of overlying Windfall formation. USGS colln. 789—00, 864—00; 955—00; 2302—00. Figured specimen: Cranidium, USNM 136851, USGS colln. 789—00. Elvinia granulata Besser Plate 6, figure 4 Elvinu granuldta Resser, 1942b, p. 96, pl. 18, figs. 11, 12. Elvind ruedemanni Resser, 1942b, p. 95, pl. 18, figs. 7—10; Fisher and Hanson, 1951, pl. 1, figs. 1, 2. ?I’araircingella hamburgensis Resser, 1942b, p. 27, pl. 4, figs. 23, 24. Diagnosis—Members of E Zpini'a with external sur- face of cranidium, exclusive of furrows and palpebral lobes, covered with low granules. Brim generally flat or concave in longitudinal profile. axial length about equal to that of border. Discussion—Two species described by Resser (1942), E. granulatd and E. medemanni are indistinguishable from each other and represent a distinct species of E lm'nia. E. granuldta' is chosen as the name for the species even though E. medemanm' has page prefer- ence (p. 96 vs. p. 95) because its holotype is a much more complete specimen. A third species, Elvinia hamburgensis (Resser) (pl. 6, fig. 5), may also be con- specific with E. granulatd, but the granules on the glabella are much broader and have peculiar pologo- nal outlines. Certain identity cannot be established because too few specimens assignable to E. granulata are known to determine the amount of variability of surface granulation within the species. Occurrence: Rare, upper Dunderberg shale (unit D), Eu— reka, Nev.; Galway limestone of Fisher and Hanson (1951), near Saratoga Springs, N.Y. Figured specimen: Holotype cranidium, USNM 108815, USNM 100. 63. Elvinia‘l sp. Plate 6, figure 6 A single cranidium from a collection intermediate in stratigraphic position between the known occur- rences of Elburgia granulosd (Hall and Whitfield) and Elvinz'd granuldta (Resser) is also intermediate in morphology between the two species and cannot be assigned clearly to either genus. Perhaps, if more material becomes available, it can be shown to repre— sent a new genus intermediate between E lburgi'd and EZ/vini'a. In any event, this specimen emphasizes the close morphologic relationship of the two genera. The glabella has three pairs of conspicuous glabel— lar furrows, the posterior pair connected across the top of the glabella by a shallow furrow, a character- istic feature of the species of E Zburgid. The frontal area, the granular surface, and the overall form of the crandium are for the most part like those of E lm'nia granulata. Occurrence: Rare, about 90 ft above base of Dunderberg shale; unit B. USGS colln. 2300—00. Figured specimen: Cranidium, USNM 136850. Genus ELVINIELLA n. gen. T ype species.—Elvim§ella laem's Palmer, n. sp. Didgnosis.—Elviniidae with cranidium bearing conspicuous posterior glabellar furrows connected across glabella, other glabellar furrows hardly visible. Border and marginal furrow with tendency to come to blunt point on axial line. Fixed cheeks broad. Palpe- bral lobes long, strongly arcuate; length about one— half that of glabella including occipital ring. Ante- rior course of facial sutures nearly straight forward from palpebral lobes. Other parts of exoskeleton not known. 72 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY Descriptiorl.—Generally small trilobites probably not exceeding 15 mm in total length. Cranidium, only known part. Outline, exclusive of posterior limbs, subquadrate; anterior margin tending to come to a blunt point on axial line. Glabella prominent, tapered forward, straight sided, bluntly rounded an- teriorly. “'idth just anterior to occipital furrow slightly less than length exclusive of occipital ring. Only posterior glabellar furrows well defined; deep along flanks of glabella, connected across top of gla- bella by shallow furrow, not connected to dorsal fur- row. Occipital furrow broad, deep; deepest at distal ends. Occipital ring with median node adjacent to occipital furrow. Dorsal furrow broad, deep slong sides of glabella and at anterolateral corners, some- what shallower across axial line. Border distinct, gently convex, separated from brim by a distinct change in slope and a broad marginal furrow that tends to come to blunt point on the axial line. Brim gently convex; length (sagittal) slightly more than that of border. Fixed cheeks broad, gently to mod- erately convex, nearly horizontal; width slightly greater than one-half basal glabellar width. Palpe— bral lobes, long, slender, broadly arcuate, situated slightly below general level of cheek; line connecting anterior tips crosses glabella nearly at anterior mar- gin. Width of palpebral lobes slightly less than one— fourth width of cheek; length about one—half length of glabella including occipital ring. Palpebral fur- row broad, shallow, well defined. Ocular ridges low, barely apparent. Posterior limbs relatively short, length (transverse) slightly less than basal glabellar width. Marginal furrow of posterior limb broad, deep. Anterior course of facial suture straight for— ward from palpebral lobe to marginal furrow; turns inward across border and appears to become almost immediately submarginal. Posterior course diver- gent sinuous. Dz’scussioraaThis genus is proposed to include nine cranidia from collections in the middle part of the Dunderberg shale. Although more than one species may be represented, only the type species is described because even it is represented by only a few specimens and the significance of the variant forms, represented by single specimens, cannot be certainly determined. Elwiniella most nearly resembles Elm'm'a among de- scribed genera, particularly in the shape of the gla- bella. It is easily distinguished from Elvinia, 110w- ever, by the long, slender palpebral lobes and the bluntly pointed anterior margin. The form of the frontal area indicates possible relationships to Duri- derbergia and Elburgz'a and the long palpebral lobes indicate possible affinities with Iroingella. The pos- sible significance of these relationships in the family classification has already been discussed (p. 64). Elviniella laevis n. sp. Plate 6, figures 8—10, 14 Description—The description presented for the genus covers most of the characteristics of this spe- cies. The external surface of the cranidium is virtu- ally smooth; however, whitened specimens observed in oblique lighting show faint irregular anastamosing or reticulate markings on the posterior part of the cheek and terrace lines along the anterior margin of the border. Discussion—Two specimens differ from the holo- type in features that may be significant. One (pl. 6, fig. 8) has a much more definitely pointed anterior margin, a suggestion of a low median boss on the brim, distinctly roughened cheeks posterior to the midlength of the palpebral lobes, and the posterior glabellar furrow is deepest on the axial line. The second variant specimen (pl. 6, fig. 14) differs from the holotype by having a distinctly shorter and broader frontal area and by having the line connect- ing the anterior tips of the palpebral lobes passing slightly anterior to the glabella, thus also giving the ocular ridges the appearance of being directed outward and forward from the anterior end of the glabella. As both variants occur at about the same strati- graphic level and are each associated with forms vir- tually like the holotype, they may merely indicate that there is more variation in shape of specimens of this species than in those of such possibly related genera as Dunderbergz’a and E lvim'a. Occurrence: Rare, 60—150 ft above base of Dunderberg shale; units B, C. USGS colln. 952—00, 954—C0, 2301—00. Figured specimens: Holotype cranidium, USNM 136854, USNM colln. 952—00; Elvim‘ella 312., USNM 136852, USGS colln. 954—CO; Elvim‘ella 81)., USNM 136853, USGS colln. 2301— CO. Genus IRVINGELLA Ulrich and Resser, 1924 Irvingella Ulrich and Resser (in Walcott), 1.024, p. 58; Walcott and Resser, 1924, p. 10; Walcott, 1925, p. 97; Resscr, 1938, p. 33; 1942b, p. 3, 13; Shimer and Shrock, 1944, p. 627; Kobayashi, 1954, p. 34. Irvz‘ngella (Parairm'ngella) Kobayashi, 1938, p. 175. Parairvingella Resser, 1942b, p. 4, 25. Irvingella (Irvingellina) Kobayashi, 1938, p. 175. Type species.—lrvingella major Ulrich and Resser (in ll’alcott), 1924, p. 58, pl. 10, fig. 3. Diagnosis.—E1viniidae with prominent subquadrate glabella, broadly rounded anteriorly. Posterior gla- bellar furrows connected across glabella, forming single deep furrow; junctions of lateral parts with furrow across top generally slightly angular. Mid- dle pair of glabellar furrows generally visible at sides of glabella. Frontal area short, less than one-fourth length of glabella including occipital ring. Fixed cheeks moderately broad; width between palpebral and TRILOBITES OF THE UPPER CAMBRIAN DUNDERBERG SHALE, EUREKA DISTRICT, NEV. 73 dorsal furrows slightly more than one-third width of glabella just anterior to occipital furrow. Palpebral lobes long, slender, depressed below general level of cheek; length about two-thirds length of glabella in- cluding occipital ring. Posterior limbs short, steeply depressed. Free cheek narrow. Border broader than ocular platform except posterolateral to eye. Genal spine moderately long, continues curvature of border. Pygidium subtrapezoidal in outline broadest at or near anterior margin, with prominent axial lobe crossed by 1 or 2 deep ring furrows; length of axial lobe about three-fifths length of pygidium. Distinct border generally present. Pleural lobes narrower than axial lobe. Discussion—Historically, Irvingella has been con- sidered a member of the Komaspidae (Kobayashi, 1935, 1954; Hupé, 1953, 1955; Lochman, 1954); how- ever, the determination of critical features of the Komaspidae is questioned below, and Irvingella is here placed in the Elviniidae. Kormpz's typa Kobay- ashi, the type species of Kmnaspis and the Koma- spidae, is represented by a single poorly preserved cranidium from beds of Middle Cambrian age in Korea. The cranidium is somewhat similar in shape to cranidia of Irvingella (Paraireingell‘a), but noth- ing is known of the free cheeks or pygidium or of the critical anterior course of the facial suture of this species. Furthermore, nearly all the other species assigned to the Komaspidae are from beds of Late Cambrian age in North America. Because of the poor quality and inadequate knowledge of the mor— phology of the holotype and only specimen of If. typa, its relationships to the North American genera are at best tentative, and the characteristics of the Koma- spidae, which must ultimately be based on this speci- men are, at least for the present, not determinable. Ulrich and Resser (in VValcott, 1925) have given an adequate description of Irvingella. Kobayashi (1938) proposed two subgenera, Parairvingella and Irvingellz'na, for forms with a distinct brim and bor- der, and with the front of the glabella overhanging the frontal area, respectively. Resser (1952) raised Parairvingella to generic rank and suppressed Irwin- gellimz as a synonym of I reingella based on distorted specimens. VVestergard (1947) described a species of Irvingella from Sweden showing gradation from forms characteristic of Parairoingella to forms char- acteristic of Irvingella. Lochman (1953) following \Vestergard’s suggestion has considered Parairvz'n- gella a synonym of Irvingella. In the Eureka dis— trict, forms of Irvingell‘a with brim and border pres— ent are found in the uppermost parts of the Dunder- berg shale whereas forms without a divided frontal 507219 0—59—3 area are known certainly only from the basal beds of the overlying Windfall formation. Parairrvingella, as a subgenus of I rvingella, is a rec- ognizable taxon apparently occurring in slightly older rocks than the much more widesread I rvingella (Ir'vz'rzgella) species. It is used here in the sense orig- inally intended by Kobayashi. Subgenus IRVINGELLA (PARAIRVINGELLA) Kobayashi Type species.—0hariocephalm? tumz'frons VValcott (not Hall and Whitfield) 1884, p. 61, pl. 10, fig. 16 (renamed Irvingella (Paraz'rvingella) angustilimbatus by Kobayashi, 1938, p. 175. Diagnosis.—-Species of I r'vi’ngella with a well—devel— oped border on the adult cranidium. Discussion.—Two species are recognized within this subgenus. Neither is represented by abundant mate- rial, but the differences shown are considered sig- nificant. Irvingella (Parairvingella) angustilimbatus Kobayashi Plate 6, figures 2, 3 Chariocephalus? tumifrons Walcott (not Hall and Whitfield) 1884, p. 61, pl. 18, fig. 16. Irvingella (Parairvingella) angustilimbatus Kobayashi, 1938, p. 175. Parairvingella anyustilimbatus (Kobayashi), p. 26, pl. 4, figs. 18-22. Parairvmgella intermedia Resser, 1942b, p. 27, pl. 4, figs. 25—31. Resser, 1942b, Diagnosis.—Members of Parairvingella with axial length of border greater than that of brim; axial length of frontal area on small cranidia (length 7 mm) about one-sixth length of glabella not including occipital furrow, axial length of frontal area in larger specimens proportionately greater. Ocular ridges di- rected nearly straight laterally from anterolateral cor- ners of glabella. Discussion.—This species is represented by seven cranidia showing the features given in the diagnosis. Resser-’5 statement that brim and border of Para- irm’ngella intermedia are subequal in length is not correct. The border is distinctly longer (sagittal) than the brim, and the species is not distinguishable from I. (P.) angustilimbatus. All the cranidia now assigned to this species come from old collections whose stratigraphic position within the Dunderberg shale is not exactly known. However, the associated trilobites indicate that l. (P.) angustilimbatus comes from the upper limestone beds of the Dunderberg shale. Occurrence: Rare, upper part of the Dunderberg shale; unit D. Figured specimen: Holotype cranidium, USNM 24643, USNM 10c. 63. Plesiotype cranidium, USNM 108672, USNM 10c. 62. 74. SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY Irvingella (Parairving‘ella) eurekensis (Resser) Plate 6, figure 1 Parairvingella eurckensis Resser, 1942b, p. 26, pl. 4, figs. 15—17. Diagnosis—Members of Pamimingella with sub- equally divided frontal area; axial length of frontal area on small cranidia (about 5 mm) about one-fourth axial length of glabella exclusive of occipital ring. Ocular ridges directed anterolaterally from anterolate— ral corners of glabella. Discussion—This species is represented by only two cranidia, both from old collections and thus only ap- proximately located stratigrphically within the Dun- derberg shale. Both specimens are small, that is, axial length of cranidium less than 5 mm. They might, at first glance, merely seem to represent small specimens of I. (P.) angustilimba‘tus. However, the axial length of the frontal area is proportionately greater than that of the smallest specimen of I. (P.) angustih’m— batus (cranidial length 7 mm). Ontogenetic studies of most ptychoparioid trilobites show that the axial length of the frontal area generally increases with increasing size, and this is apparently true for the seven cranidia assigned to I. (P.) angustilimbatus. It therefore seems improbable that the small speci- mens of I. (P.) eurekeasis with the relatively long frontal area could be conspecific with I . (P.) angus— tilimbaz‘us. This species shows some similarity to one of the variants of Elvim'ella‘ Zaevis n. sp. (pl. 6, fig. 14) from beds slightly lower in the Dunderberg shale. It dif- fers from that specimen, however, principally by lack- ing the distinctly pointed anterior margin and having a subparallel-sided glabella. The series of forms oc- curring in apparent stratigraphic succession, begin- ning with E lvim'ella laem's in the middle Dunderberg shale and progressing through the variant just men- tioned to lrvingella (Pamimingella) eurekensz’s and I . ( P.) angustilimbatus in the upper beds of the Dun- derberg shale, and finally to Irvingella (Irvingella) major in the basal beds of the overlying Windfall formation is suggestive evidence for close genetic re- lationships between E lvim'ella and I rvz'ngella (p. 64). Occurrence: Rare, upper Dunderberg shale; unit D. USGS colln. 789—00. Figured specimen: USNM loc. 61. Holotype cranidium, USNM 108668, Family HOUSIIDAE History—This family name has been used by Hupé (1953, 1955) and Lochman (1956) to include only the genus Housz'a. Two of the genera here proposed, Prehousia and Pamhousia, are added to the family and the diagnosis is modified accordingly. Diagnosis.—Cranidium with glabella tapered for- ward, well to poorly defined at sides by dorsal fur- row, less well defined across front. Depressions tend to be developed in dorsal furrow at anterolateral cor- ners of glabella. Glabellar furrows weak or absent. Palpebral lobes situated anterior to midlength of glabella and generally close to glabella, poorly de- fined on external surface. Facial sutures (fig. SB, D) intramarginal three-fourths or more distance from an- terolateral corners of cranidium to axial line. Rostral suture, if present, nearly marginal. Rostrum appar- ently present only in older genera; younger genera with median suture across doublure. Pygidium with length generally less than width. Border broad, poorly defined, of nearly constant width. Axial lobe prominent, tapered posteriorly, generally bears two or more ring furrows; width 1A3 to 14 width of pygidium. I)2'scussion.—The anteriorly situated generally poorly defined palpebral lobes on the cranidium and the border of nearly constant width on the pygidium are the most distinctive characters of members of this family. The other features in the diagnosis are shared to some extent with the Pterocephaliidae, and it is probable that the two families are closely related. In addition to the genera given above, the follow- ing genera or species may also belong to the Housiidae: Morosa, from the Dunderberg fauna (p. 98); “Apr- Zaspis” tumifm’ns Resser, from pre-Dunderberg rocks in eastern Nevada and western Utah and the May- nardville limstone member of the Nolichucky shale in Tennessee; and possibly Acmcephalaspis from the Upper Cambrian of Kazakhstan, Russia (Ivshin, 1956), and Ullaspis from the late Middle Cambrian of Sweden (VVestergard, 1948). Genus HOUSIA Walcott Text figure 12 Dolichom‘etopus (H 0mm) Walcott, 1916, p. 374. Housia Walcott, 1924, p. 57; 1925, p. 93; Shimer and Shrock, 1944, p. 625; Wilson, 1951, p. 642; Lochman, 1956, p. 456. T ype species—Dolichometopus (Housia) lValcott, 1916, p. 374, pl. 65, figs. 1—1e. Diagnosis.—Housiidae reaching perhaps 60 mm in length, with cranidium having brim and anterior part of glabella depressed. Border at a distinct angle to brim; length (sagittal) slightly less than that of brim. Fixed cheek composed almost completely of flaplike palpebral lobe that is situated adjacent to dorsal furrow anterior to midlength of glabella. Doublure of cephalon crossed by median suture. Free cheek with moderately broad slightly convex border. Lateral and posterior marginal furrows mod- erately deep, not connected, disappearing near base of genal spine. Genal spine short or long. Thorax with 10 to 11 thoracic segments. Axial lobe prominent. Pleural spines short, posteriorly directed. ’UdWO TRILOBITES OF THE UPPER CAMBRIAN Pygidium transversely subovate in outline. Axial lobe prominent, well defined, extends to inner edge of broad, poorly defined border. Border maintains nearly constant width. FIGURE 12.—Partial reconstruction of Housia ovata n. sp., about X 3. Description—The genus has been well described by Walcott (1925) and \Vilson (1951). Discussion—Howie is found over most of North America in beds of the E lvim'a zone. The depressed brim and anterior part of the glabella and the ex- tremely narrow fixed cheeks of the cranidium are the most distinctive features of the genus. In addi— tion, species of H ousz’a characteristically show unusual variation in the character of the anterior part of the pygidium. Commonly, the last thoracic segment is incompletely separated from the pygidium so that some pygidia have anterolateral spines, some have a thoracic segment developed on one pleural lobe and not on the other (pl. 7, fig. 6, developed left pleuron broken off), and some pygidia have no anterolateral spines. The retention of the last thoracic segment in the pygidium on some specimens causes a super- ficial resemblance of this genus to Proceratopyge. Whitehouse (1939) believed that the genera were synonyms. Both \Vilson (1951) and Lochman (1956) have given good reasons for considering Housia as a distinct genus perhaps not even closely related to Proceratopg/ge. An additional and perhaps more im- portant reason than those given by “'ilson and Loch- 1nan is that the spine-bearing anterior pygidia] seg— ment of Proccratopyge is a fundamental part of the pygidium whereas that segment in Housia is prima- rily a thoracic segment that has not been detached in normal fashion into the thorax. There islittle evi- dence for or against the suggested relationship of Housia to the asaphidae by Wilson (1951). DUNDERBERG SHALE, EUREKA DISTRICT, NEV. 75 Housia halli (Resser) Plate 7, figure 8 Crepicephalus (Loganellus) maculosus Hall and Whitfield 1877 (part), p. 215, pl. 2, fig. 26. Dunderbergia hallr‘ Resser, 1935, p. 23. Discussion—The single pygidium originally as- signed to Orcpicephalus (Loganellus) maculosus by Hall and Whitfield and later made the type of a new species in Dunderbergz'a by Resser represents a spe- cies of H ousia whose pygidium differs from the pygid- ium of H. ovate n. sp. by being relatively broader and by having a proportionately wider border. It is asso- ciated with cranidia of Bynumina globosa (VValcott) and probably came from limestones near the top of the Dunderberg shale. The pygidium does not differ significantly from those assigned to H. cam/ma (VValcott) and H. cana- dcnsis (Walcott). \Vhen cranidia and free cheeks of H. ham are found, it may prove to be a synonym of 1 of those 2 species. Occurrence: Rare, uppermost(?) Dunderberg shale; unit I)(?). Figured specimen: Holotype pygidium, USNM 90670. Housia ovata, n. sp. Plate 7, figures 1—7, 9 Dz'agnosz's.—Members of Housia with free cheeks having gently curved lateral margin and long, slender genal spine. Pygidium with length (sagittal) about two—thirds width. External surface of brim on cepha- lon, ocular platform of free cheek, and axial lobe and pleural furrows of pygidium coarsely pitted. I)iscussi0nv.—Cranidia alone cannot be used satis- factorily for identification of species of H ousz'a ; how- ever, the combined features of the cephalon and pygid- ium of this species distinguish it from the other spe- cies in the same genus. H. canadensz's (VValcott) and H. vacrm‘a (VValcott) have pygidia with length (sag— ittal) only about one-half width. The free cheeks of H. sacrum and H. canadensz's have short genal spines. The pygidia in the type lot of H. warm are distorted, but seem to have a shape intermediate between that of II. mama and H. (mam. The free cheek of H. varro has a strongly curved lateral margin. A short genal spine is present on some specimens whereas others seem to lack a genal spine. H. halli (Resser) is rep- resented only by a pygidium that may be conspecific with either H. canadensz's or H. vacmm. 'lransitory pygidia of [1.00am show that retention of pa1tially developed thoracic segments with the pygidium is even more marked in the meraspid stage than in the adult. Several specimens of transitory pygidia in collection 955—CO have 3 to 5 almost com- pletely developed thoracic segments (pl. 7, figs. 4, 9). 76 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY On all of these specimens, the grooves between the anterior segments of the transitory pygidium are less pronounced than those adjacent to the segment that will become the last segment of the thorax. The rela- tively poor differentiation of the anterior segments on the transitory pygidium is an unusual feature, be- cause these segments are imminent thoracic segments and should be most nearly ready to be detached from the pygidium. Two features are of importance for indicating the meraspid development of H. ovate: the last incipient thoracic segment on each transitory pygidium is dis- tinctly macropleural, and the smallest transitory py- gidium (pl. 7, fig. 9) has the greatest number (5) of incipient thoracic segments. The macropleural seg- ment does not advance forward in the incipent thorax, indicating that it is probably truly the last thoracic segment. Thus, adults may also have the last tho- racic segment macropleural. It is also probable that the transitory pygidium of meraspid stage 0 has 10 to 11 partially developed thoracic segments fused with the pygidium and that during development these are successively shed forward into the thorax. Similar development has been shown for Macropyge gladiator Ross from the Lower Ordovician (Ross, 1951) and Ceraum'nella type Cooper from the Middle Ordovician (VVhittington and Evitt, 1954). Occurrence: Moderately common, about 200 ft or more above base of Dunderberg shale; unit C. USGS colln. 789— 00, 864—00, 872*CO, 955—00. Figured specimens: Holotype cranidium, USNM 136863, USGS colln. 872—00. Paratypes: Free cheek and pygidia, USNM 136864a—c, USGS colln. 872—00; cranidium, adult py- gidium, and transitory pygidia, USNM 136865a—d, USGS colln. 955—00. Genus PARAHOUSIA n. gen. Text figure 13 Type specz‘es.——Paml¢ousia constrict’a n. sp. Diagnosis.—Housiidae with frontal area short; length slightly less than one—half that of glabella. Marginal furrow shallow. Length (sagittal) of bor— der almost twice length of brim. Palpebral lobes prominent, situated close to glabella and anterior to glabellar midlength. Palpebral furrow hardly visible. Fixed cheek narrow; width about one-fifth basal gla- bellar width. Free cheek with conspicuous lateral and posterior marginal furrows that disappear near base of long slender genal spine and are not connected. Pygidium strongly arched in transverse profile. Axial lobe prominent, extended to inner edge of poorly defined depressed border. Description—Generally small trilobites (length probably less than 20 mm) with cranidium subtrape- zoidal in outline, gently arched transversely and longi- FIGURE 13.—Partlal reconstruction of Parahouaia constricta n. sp., about X 8. tudinally. Anterior margin bluntly pointed. Gla- bella well defined by dorsal furrow, tapered strongly forward, slightly constricted between palpebral lobes, bluntly rounded anteriorly. Glabellar furrows hardly visible. Occipital furrow shallow, with sinuous course. Occipital ring broadest on axial line, with low median node. Frontal area short; length slightly less than one-half of glabella. Brim flat. Border slightly con— vex; length (sagittal) almost twice that of brim. Fixed cheeks narrow; width about one-fifth basal gla- bellar width. Palpebral furrow hardly visible. Pos- terior limbs tapered to a blunt tip; length (transverse) slightly less than basal glabellar width. Posterior marginal furrow moderately deep. Anterior course of facial suture slightly divergent forward from palpebral lobe to marginal furrow, then turned abruptly inward across border to cut an- terior margin at axial line. Submarginal course not known. Free cheek with border, at anterior margin, well defined by moderately deep lateral marginal furrow; breadth about one-half breadth of ocular platform. Lateral marginal furrow disappears posteriorly near base of genal spine. Posterior marginal furrow mod- erately deep at junction with posterior limb, disap- pears laterally near base of genal spine; not con- nected with lateral marginal furrow. Genal spine moderately long, slender; length slightly less than length (exsagittal) of ocular platform. Pygidium subsemicircular in outline, moderately to strongly arched transversely. Axial lobe prominent; three shallow ring furrows generally visible. Pleural platforms triangular, gently arched, crossed by 3 or 4 broad shallow pleural furrows that do not extend onto border. Border poorly defined, depressed, broadest at TRILOBITES OF THE UPPER CAMBRIAN anterolateral corners of pygidium, narrowed slightly on axial line. Posterior edge smooth. Except for border of cheek and muscle scar areas, external surfaces of most parts of cephalon are cov- ered with coarse pits. External surface of axial lobe and pleural platforms on pygidium with hardly visi- ble coarse pits. Border of free cheek, genal spine, and anterolateral corners of pygidium with prominent ter- race lines. Discussion—This genus is closely related to H ousia with which it is associated. It has an almost identical glabellar shape, anteriorly placed palpebral lobes, and nearly identical free cheek. It differs from Housia by having broader fixed cheeks, a less depressed fron- tal area with proportionately broader border, and less sharply pointed posterior limbs on the cranidium. The pygidium has a depressed rather than nearly horizontal border. Parahousia constricta n. sp. Plate 7, figures 16—18 Diagnosis.—This is the only species presently known in Parahousz'a and its characteristics are described un- der the genus. Discussion—This species is unlike any other spe- cies in the Dunderberg fauna. Its present known range is limited to the upper part of the Dunderberg shale. Occurrence: Moderately common, 190—220 ft above base of Dunderberg shale; unit 0. USGS colln. 955—00, 2302—00. Figured specimens: Holotype cranidium, USNM 136870. Paratypes, free cheek and pygidium, USNM 136871a, b. All from USGS colln. 955—00. Genus PREHOUSIA n. gen. Text figure 14 Type species.—Prehousia alum n. sp. Diagnosis.—Housiidae with frontal area short; length (sagittal) slightly more than one-half that of glabella. Border well defined, slightly convex; length (sagittal) between 1/2 and 5% that of brim. Palpebral lobes scarcely defined by palpebral furrow, situated anterior to glabellar midlength; length (exsagittal) between 14 and 1/2 that of glabella. Fixed cheeks narrow; width one-fifth or less basal glabellar width. Facial sutures cut anterior margin nearly at axial line. Free cheek with well—defined border. Lateral and posterior margin furrows joined, not noticeably ex— tended onto base of genal spine. Genal spine slender, tapered to sharp point; length less than greatest length of pleural platform. Pygidium transversely subovate in outline; breadth greater than twice length. Axial lobe prominent, tapered posteriorly, merged with inner part of bor- DUNDERBERG SHALE, EUREKA DISTRICT, NEV. 77 der; breadth one-third to slightly less than one-fourth greatest breadth of pygidium. Border moderately broad, separated from pleural platform only by grad- ual change in slope; maintains nearly constant width. External surface smooth, pitted, or finely granular in axial region. FIGURE 14.—Partial reconstruction of Prehousia alata n. sp., about X 5. Description—Small to medium-sized trilobites (length of largest specimens about 50 mm). Cepha- lon subsemicircular in outline, moderately arched transversely and longitudinally. Cranidium subtrape- zoidal in outline with slightly pointed anterior mar- gin. Glabella well defined by shallow dorsal furrow of nearly constant depth; straight sided, tapered for- ward, bluntly rounded or truncate anteriorly. Gla- bellar furrows generally not apparent. Occipital fur- row shallow, straight. Frontal area divided into dis- tinct brim and border by shallow to moderately deep margin furrow that may develop a slight posterior median inbend or become perceptibly shallower on axial line. Border gently convex; length (sagittal) between 1/2 and 34 that of brim, greatest on axial line. Brim gently convex. Fixed cheeks narrow; palpebral lobes hardly defined by palpebral furrow; low ocular ridges may be present. Width of cheek one—fifth or less basal glabellar width. Palpebral lobes situated anterior to glabellar midlength; length (exsagittal) between 14 and 1/2 that of glabella; width from one- half to slightly greater than width of cheek. Poste- rior limbs elongate triangular in outline; length 78 (transverse) about equal to basal glabellar width; tips bluntly pointed. Anterior course of facial suture slightly divergent forward from anterior end of palpebral lobe to mar- ginal furrow, then curved sharply onto and across border to cut anterior margin nearly at axial line. Posterior Course of facial sutures divergent-sinuous. Free cheek with gently to moderately curved lat- eral margin. Genal spine slender, tapered to sharp point; length less than that of ocular platform. Bor- der well defined, gently convex; width at anterior margin of cheek between 1/2 and 5% width of ocular platform. Lateral and posterior margin furrows of about equal depth, joined but not extended notice- ably onto base of genal spine. Pygidium transversely subovate in outline. Width greater than twice length. Axial lobe well defined, bears 2 or 3 shallow ring furrows; width from one- third to slightly less than one-fourth greatest width of pygidium; length about two—thirds that of pygid- ium; posterior end merges with inner part of border. Border differentiated from pleural platforms only by gradual change in slope. Width nearly constant. Pleural platforms crossed by 2 or 3 shallow pleural furrows. Posterior margin smooth. External surface finely pitted, smooth, or finely granular in axial regions. Discussion—This genus is widespread in rocks of latest Dresbach age in the Great Basin. A species of this genus was illustrated as n. gen. aff. Aphelaspis (Palmer and Hazzard, 1956, pl. 1, fig. 3). The type species and another undescribed form occur in the upper part of the Lincoln Peak formation in the southern Snake Range, White Pine County, Nev. (Drewes and Palmer, 1957). The genus is based on the species from the Snake Range rather than on the one from the Eureka district because of the avail- ability of more abundant and better quality material of the Snake Range species. Prehousia, as its name implies, is related to Housz'a and occurs consistently in beds older than those bear- ing species of Housia. The subtrapezoidal shape to the cranidium, palpebral lobes placed anteriorly and close to the glabella, and the pygidium with poorly defined border of nearly constant width all empha— size relationships to IIousia. The downsloping rather than depressed frontal area, slightly broader fixed cheeks and straight-sided well-defined glabella all serve to distinguish the genus from Housia. The Shape of the glabella, course of the facial sutures, and shape of the pygidium, indicate aflinities to Aphelaspis. These relationships are the principal reason for con— sidering the Housiidae to be closely related to the Pterocephaliidae of which Aphelaspz's apparently is the ancestral genus. SHORTER CONTRIBUTIONS 'TO GENERAL GEOLOGY Prehousz'a differs from Parahousia by having the glabella straight sided rather than constricted between the palpebral lobes, the brim longer (sagittal) than the border on the cranidium, the pygidium trans- versely subovate in outline rather than subsemicircu- lar, and the border of the pygidium nearly horizontal rather than depressed. Prehousia alata n. sp. Plate 7, figures 10, 12, 13 Diagnosis.——Members of Prehonsia with length of border (sagittal) only slightly greater than one—half length of brim. Palpebral lobes short, narrow; length slightly less than one-third length of glabella; Width about one-half width of fixed cheek. Pygidium with tendency for border to develop alae at anterolateral margins. Width of axial lobe nearly one—third width of pygidium. External surface apparently smooth ex- cept for low fine granules on axial part of glabella. Discussion—Specimens of this species are abundant at three localities in the Snake Range, White Pine County, Nev. The species differs from P. semicircu- laris n. sp. by having smaller palpebral lobes, a broader brim, a broader axial lobe on the pygidium, and slightly alate anterolateral pygidial margins. Occurrence: Common, 130—146 ft below top of Lincoln Peak formation, southern Snake Range, White Pine County, Nev. USGS colln. 1197—CO, 1436—C0, 1441—00. Figured specimens: Holotype cranidium, USNM 136866. Paratypes, free cheek and pygidium, USNM 136867a, b. All from USGS colln. 1441—00. Prehousia semicircularis n. sp. Plate 7, figures 11, 14, 15, 19 Diagnosis—Members of Prehousia with length of border (sagittal) about three-fourths length of brim; palpebral lobes relatively large; length slightly less than one—half that of glabella; width slightly greater than width of fixed cheek. Pygidium with evenly rounded anterolateral corners; width of axial lobe slightly less than one-fourth that of pygidium. Ex- ternal surface smooth on all parts. Discussion—The distinctions between this species and P. claim n. sp. are given in the discussion of P. alata. Occurrence: Moderately rare, lower 20 ft of Dunderberg shale; unit A. USGS colln. 2294—00. Holotype cranidium, USNM 136868. All from Figured specimens: l’aratypes, free cheek and pygidia, USNM 136869a-c. U SGS colln. 2294—00. Family OLENIDAE Burmeister Henningsmoen (1957, p. 94) gives a detailed discus— sion of the characteristics of trilobites assignable to this family and points out that the included trilobites TRILOBITES OF THE UPPER CAMBRIAN are so varied that an objective diagnosis is virtually impossible. Most of the features considered essential to an olenid by Henningsmoen (1957, p. 95) are pres- ent on the trilobites discussed below. Subfamily OLENINAE Diagu0858.—“Olenids with free cheeks with straight spine confluent with course of lateral margin or de- viating only very slightly outwards.” (Hennings- moen, 1957, p. 96.) Discussion—Two closely related species of olenid trilobites, 0Zenus? wilsom' Henningsmoen and 0. .9 gran- ulatus n. sp. are present in the Dunderberg fauna. They differ from typical olenids by having a distinct junc- ture of the facial suture with the anterior margin of the cranidium and by having only 2 distinct ring fur- rows and 1 pair of pleural furrows on the pygidium. The cranidial shape, as noted by Henningsmoen (1957, p. 112) for 0.? wilsom', is rather more like Parabolina than Oleuus. The free cheek of 0.? wilsom', has char- acteristics more like 0leuu8 than Paraboh'na. Pygidia of both species have fewer axial and pleural furrows and a slightly less rounded posterior margin than pygidia characteristic of either 0Zeuus or Paraboliua. Perhaps the two species here described represent a new olenid genus unknown in the extensively devel- oped olenid faunas of western Europe. Olenus? wilsoni Henningsmoen Text figure 15; plate 6, figures 18, 20—22 Paraboliuella incerta (Rasetti). figs. 18—22. Oleuus? wilsom’ Henningsmoen, 1957, p. 111, text fig. 117. Wilson, 1954, p. 280, pl. 26, Diagnosis.—Members of 0Zeuus? with length (sag- ittal) of frontal area about one-third or slightly more than length of glabella exclusive of occipital ring. Length of border one—half or slightly more than length of brim. Palpebral lobes small, situated ante- rior to glabellar midlength. Width of fixed cheek slightly less than one—third basal glabellar width. Free cheek with obtuse inner spine angle. Facial su— ture cuts anterior margin at slight angle at point in front of anterolateral corner of glabella. Pygidium without marginal spines. Length (sagittal) slightly less than one-third width. Axial lobe with one ring furrow; pleural lobes with one pleural furrow. Ex- ternal surfaces of all parts smooth. D2'scussz'ou.—This species differs from all known Oleuus species in the combination of features given in the diagnosis. It is most similar to 0.? granulatus n. sp., differing primarily by having a smooth rather than granular surface on the cranidium. Occurrence: Moderately rare, 30—90 ft above base of Dun- derberg shale; units A, B. USGS colln. 2295-00(‘?), 2296— CO. 2297—C0, 2299—00, 2300—00. DUNDERBERG SHALE, EUREKA DISTRICT, NEV. 79 FIGURE 15.—Partia1 reconstruction of Olenus? wilsom Henningsmoen, about X 12. Figured specimens: Plesiotypes—cranidia and pygidium, USNM 136858a, b, USGS colln. 2300—00; cranidium and free cheek, USNM 136859a, b, USGS colln. 2297—00. Olenus’l granulatus n. sp. Plate 6, figures 23—27 Diagnosis.—Members of Oleuus? with length (sagit- tal) of frontal area about one-third length of glabella exclusive of occipital ring. Length (sagittal) of bor- der slightly more than one-half length of brim. Palpebral lobes small, situated anterior to glabellar midlength. Width of cheek slightly more than one- fourth basal glabellar width. External surface of most of cranidium covered with fine granules. Pygidium transversely subovate in outline. Length about one-third width. Axial lobe prominent, bear- ing distinct articulating furrow and one ring furrow; subquadrate in outline; length about three-fourths that of pygidium. Pleural lobes nearly flat, crossed by one deep furrow diverging backward from anterior mar- gin. Border narrow, poorly defined, not crossed by pleural furrow. Lateral margin of pygidium sharply rounded. Posterior margin gently curved away from pygidium from lateral margin to point behind dorsal furrow, then gently curved towards pygidium to axial line producing a distinct angulation on margin di- rectly behind dorsal furrows on each side of axial lobe. External surface covered with low fine gran- ules. Discussion—This species differs from all described species of Oleuus by having a granular external sur- face. The transverse pygidium with only one ring furrow distinguishes it from all species except 0.? wilsom' Henningsmoen. Occurrence: Moderately rare, 70—90 ft above base of Dun- derberg shale; unit B. USGS colln. 795—00, 2299—00, 2300- C0. Figured specimens: Holotype cranidium, USNM 136861, USGS colln. 2300-00. Paratypes: Cranidium, USNM 136862, 80 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY USGS colln. 795—00; pygidium, USNM 136860, USGS colln. 2299—00. Family PTEROCEPHALIIDAE History—Contents of a taxon bearing this name have been discussed by only two authors. Kobayashi (1935, p. 230) proposedithe Pterocephaliinae as a sub- family of the Ptychopariidae. As in the Elviniidae, the genera grouped by Kobayashi seem to have little real relationship. Lochman (1956, p. 458, 459) pre- sented a new combination of genera under this name that includes many of the trilobites grouped here in the subfamilies Aphelaspidinae and Pterocephaliinae. No statement of the family characteristics of the Pterocephaliidae was given by Lochman, however; it is not possible, therefore, to determine her grounds for the family grouping. Diagnosis—The Pterocephaliidae as used here in- cludes genera that share, in addition to stratigraphic and geographic continuity, the following distinguish- ing morphologic features: Cranidium with glabella tapered forward, generally well defined at sides and anterolateral corners by dorsal furrows, anterior end less well defined; glabellar furrows generally poorly defined—when distinct, generally broad, rarely, if ever, deep and narrow; dorsal furrows with tendency to develop depressions at anterolateral corners of gla- bella; border generally moderately broad and with breadth distinctly greater than distance from upper surface to lower surface of doublure; palpebral lobes generally well defined, subcentrally located; posterior limbs slender, sharply pointed. Facial sutures intra— marginal three—fourths or more distance from ante— rolateral corners of cranidium to axial line (fig. 8A,E). Rostral suture, if present, nearly marginal. Rostrum apparently present only in older genera; most younger genera with median suture across doublure. Pygidium with broad border and doublure; width of axial lobe generally one—fourth or leSS that of pygidium; two or more ring furrows generally present; border poorly defined, generally noticeably narrower on axial line. Discussion.——Of the features listed above, the shape of the cranidium posterior to the front of the gla- bella and the course of the facial suture have been of primary importance in relating the genera of the Pterocephaliidae. Few North American genera from beds older than the Aphelaspis zone or younger than the EZ/vz'nia/ zone and few genera of any age outside North America have a glabellar shape of the type described above. Pterocephalops (Rasetti,1944) from a boulder in the Levis conglomerate in eastern United States, fllaladioidella from the Upper Cambrian of Manchuria, and [Vericia from the late Middle Cam— brian of Sweden—genera not known from the Great Basin—are most likely to be representatives of this family. Grénwalh’a from the late Middle Cambrian of Sweden may also belong to the Pterocephaliidae. The Pterocephaliidae of this study are grouped into two subfamilies, the Aphelaspidinae and Pterocepha- liinae, that are distinguished primarily on character- istics of the border of the cranidium and secondarily on characteristics of the pygidium and free cheeks. Whether these taxa represent families or subfam- ilies is an unanswerable question. They are here con- sidered as subfamilies to emphasize their many com- mon features that seem to show real genetic relation- ships, while still permitting recognition of the distinc- tive features that separate the generic groupings. Subfamily APHELASI’IDINAE n. subfamily Diagnoisis.—Pterocephaliid trilobites with border on cephalon well—defined, commonly convex; less com- monly flat or slightly concave. Pygidium with border subequal in width to greatest width of pleural plat- form. Discussion—This subfamily includes the American genera Aphelaspis, Labiostm'a, Litoicephalus, and Tamara, and possibly also Maladioidella from the Upper Cambrian of Manchuria. Nericia as repre— sented by its type species, N. quinquedentata Wester- gard from the late Middle Cambrian of Sweden, has a cranidium strikingly similar to that of Labiostria, but differs in having relatively smaller palpebral lobes. The pygidium has a much narrower border than any of the species of the Aphelaspidinae. Nari- cia septemdentata Westergard, also from the late Mid- dle Cambrian of Sweden, has a frontal area on the cranidium and border on the cheek much like Ptero- cephalia, but an entirely different pygidium. Al- though the species assigned to Nerz’cia seem referable to the Pterocephaliidae, they do not seem to belong to either of the subfamilies here described. Labiosz‘ria as originally constituted (Palmer, 1954), included three species, the type species, L. conceivi- marginatus, L. platifrons, and L. sigmoidalis. L. platifram is tentatively aSSigned here to T aenm-a n. gen., and L. sigmoidalis, with its concave cranidial border, is removed from both the genus and the sub- family and related to Sigmocheilus n. gen. in the Pterocephaliinae. Aphelaspis, the oldest genus in the subfamily, rep— resents perhaps the root stock of both the Aphelas— pidinae and Pterocephaliinae. Although its cephalic border is distinct, it lacks the well—defined marginal furrow characteristic of the other genera in the sub- family. The pygidium also is relatively smaller and has fewer segments than pygidia in the younger genera. Létocephalus and Teenom, as elements of the Dun- derberg fauna, are discussed below. TRILOBITES OF THE UPPER CAMBRIAN DUNDERBERG SHALE, EUREKA DISTRICT, NEV. 81 Trilobites of the Aphelaspidinae are the dominant elements of the trilobite faunas of the Aphelaspis zone. In the Dunderbergia and Elvim'a zones, they are subordinate in numbers of species to trilobites of the Pterocephaliinae and Elviniidae. Genus LITOGEPHALUS Resser, 1937 Text figure 16 Litocephalus Resser, 1937, p. 17 ; Palmer, 1956a, p. 608. Pterocephalina Resser, 1938, p. 42. Type species.—Dicellocephalus m'clzmondensis Wal- cott, 1884, p. 41, pl. 10, fig. 7 (=Dz'kellocephalus bila- batus Hall and Whitfield, 1877, p. 226, pl. 2, fig. 36). Daignosis.—Aphelaspidinae with cephalon having border well defined by deep marginal furrow. Thorax with pleural spines of most segments long, slender, backwardly directed. Pygidium with border concave; posterior margin with deep median notch reaching nearly to posterior end of axial lobe. Figure Iii—Reconstruction of Litocephalua bilobatus (Hall and Whitfield), about X 2. Description—Medium to large trilobites (up to about 85 mm in length) with exoskeleton elongate subovate in outline; widest about on line through occipital ring. Cephalon subsemicircular in outline with prominent posteriorly directed genal spines. Cranidium, exclusive of posterior limbs, elongate rectangular in outline, moderately arched transversely and longitudinally, moderately to strongly rounded at anterior margin. Glabella distinct, well defined, straight sided, tapered slightly forward, bluntly rounded or truncate anteriorly; commonly featureless, though traces of three pairs of slightly arcuate gla- bellar furrows may be seen on exfoliated specimens. Dorsal furrows deepest along side and at anterolateral corners of glabella, shallow on midline. Occipital ring with small median node. Occipital furrow mod- erately shallow, straight. Brim and border present, separated by a narrow marginal furrow. Brim flat. Border in profile arched up sharply from marginal furrow, then gently arched or flat to anterior margin; length (sagittal) from slightly more than one-half to about equal that of brim. Fixed cheeks nearly flat, slightly upsloping; width about one-third basal gla- bellar width. Palpebral lobes arcuate in form, mod- erately well defined by shallow palpebral furrow. Oc- ular ridges generally distinct. Posterior limbs narrow, sharp pointed; length (transverse) about equal to basal glabellar width. Facial sutures diverge slightly to moderately for- ward from palpebral lobes until reaching marginal furrow, turn sharply inward to cut anterior margin near point directly in front of anterolateral corners of glabella, and continue submarginal nearly to axial line where they curve sharply backward across doublure outlining edge of triangular or subtrape- zoidal rostrum. Posterior course divergent-sinuous. Hypostome elongate subovate in outline, strongly arched transversely and longitudinally. Anterolateral corners extended into short depressed pointed alae. Border narrow, distinct, present only along sides. Anterior lobe of central body not clearly differenti- ated from posterior lobe. Free cheek with long, slender, sharply pointed an- terior projection resulting from partly intramarginal anterior course of facial suture. Border separated from ocular platform by a narrow marginal furrow; profile similar to that on border of cranidium. Lat- eral and posterior marginal furrows of about equal depth; they join at genal angle and extend for a short distance onto genal spine as a shallow pointed depression. Infraocular ring present between eye surface and ocular platform. Thorax probably composed of 13 segments. Axial lobe distinct, elevated above nearly flat pleural lobes. Pleural furrow of each segment broad, shallow, lo- cated at, or slightly anterior to, midlength (exsaggi- tal) of segment, not extended to thoracic tip. Pleu- 82 SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY ral spines on all but perhaps last two thoracic seg- ments are long, slender, turned sharply backward from proximal portion of pleuron; length about equal to width (transverse) of proximal portion. Pygidium wide, short, much smaller than cephalon. Axial lobe prominent, elevated above pleural plat- forms; 4 or 5 distinct axial rings and a bluntly pointed terminal part present; posterior margin of first seg- ment distinctly separated on medial line from fused part of articulating half ring of second segment. Pleural platforms gently arched, downsloping; broad, shallow pleural furrows of 4 or 5 segments present, extending nearly across border. Border slightly con— cave, greatest width about equal to that of pleural platform; inner margin marked by narrow shallow straight furrow extending from tip of axial lobe to anterolateral corner of pygidium; lateral margin a broad curve extending from anterolateral corner of pygidium to base of prominent posterior medial notch near tip of axial lobe. Discussiom—Litocephalus is a distinctive genus characterized principally by the combination of a well—defined border and deep marginal furrow on the cephalon and by a deep median notch in the posterior margin of the pygidium. Three species of the genus are here recognized, based principally on consistent differences in the external surface of the cephalic bor— der. The species have short and apparently mutually exclusive stratigraphic ranges within that of the genus. Litocephalus bilobatus (Hall and Whitfield) Plate 7, figures 24~27 Dikellocephalus bilobatus Hall and Whitfield, 1877, p. 226, pl. 2’ fig. 36. Dicellocephalus richmondensis Walcott, 1884, p. 41, pl. 10, fig. 7. Litocephalus richmondensis (Walcott). Resscr, 1937, p. 17. Pterocephalina bilobata (Hall and Whitfield). Resser, 1942b, p. 77, pl. 14, figs. 39~43. Litocephalus bilobatus (Hall and Whitfield). 608—610, pl. 73, figs. 1—6, 8. Palmer, 1956a, p. Diagnosis.~Members of Litocephalus with cranidium and free cheek having external surface of border smooth. Length (sagittal) of border about three-fourths that of brim. Facial suturescut anterior margin between point directly in front of anterolateral corners of glabella and axial line. Pygidium with surface of axial rings smooth. Discussion—The type lot of Litocephalus bilobaz‘us comes from an unknown stratigraphic position within the Dunderberg shale and contains only pygidia of this species. Study of the Dunderberg shale fauna shows that 3 species of Litocephalus are present, and, for 2 of these, isolated pygidia cannot be certainly distinguished. Furthermore, pygidia of these two species are not distinguishable from the type of L. bélobatus. Fortunately, on the same pieces of rock with the type pygidium and its counterpart, speci- mens of Morosa longispina n. sp. and Dzmderbergia cariagranula Palmer are present. Only 1 of the 2 species of Litocephalus in the stratigraphically con- trolled collections is associated with M. longispina and I). vafiagranula, and that one is here considered as L. bilobatus. This indicates that L. bilobatus comes from the lower part of the Dunderberg shale in the Eureka district rather than from the upper part as stated earlier (Palmer, 1956a, p. 610). The conclu- sion is supported by the association of the specimens illustrated in 1956 (op. cit.) with Dunderbergia poly- bothra n. sp., known from only 1 collection in the measured section about 40 feet above the base of the Dunderberg shale. Cranidia of L. bilobatus are distinguished from those of L. cerruculapeza n. sp. and L. granulomar- ginatus n. sp. by having a smooth external surface on the border. They are further distinguished from L. verruculapeza by having relatively large palpebral lobes. Pygidia of L. bilobatus cannot be distinguished with certainty from those of L. granulomarginatus, but lack the paired granules on each axial ring that characterize pygidia of L. cerruculapeaa. Occurrence: Common, 50—70 ft above base of Dunderberg shale; unit B. USGS colln. 809—00, 2297—00, 2298—00. Figured specimens: Plesiotypes, cranidium, free cheek, pygidium, and thoracic segment, USNM 128324a, b, d, e, USGS colln. 1297—00. Litocephalus granulomarginatus n. sp. Plate 8, figures 14, 17, 18, 24 [Magnesia—Members of Litocephalus with cranid- ium having border moderately arched in longitudinal profile and covered with low fine granules. Border of cheek also covered with low fine granules. Length of border (sagittal) slightly less than three-fourths length of brim. Length of palpebral lobes about one- half length of glabella exclusive of occipital ring. Facial suture cuts anterior margin between point di- rectly in front of anterolateral corners of glabella and axial line. Pygidium with surface of axial rings smooth. Discussion—Except for the fine-granular border on the cephalon, this species is like L. bilobatus (Hall and thitfield). The larger palpebral lobes and the absence of scattered coarse granules on the border of the cranidium and the absence of paired granules on the axial rings of the pygidium distinguish this spe— cies from L. cerruculapeza n. sp. Rare, 80—100 ft above base of Dunderberg shale; unit B. USGS colln. 795—CO, 2300—00. Figured specimens: Holotype cranidium, USNM 136883, USGS colln. 795—00. Par-atypes, pygidium and free cheek, USNM 1368843, b, USGS colln. 2300—00. Occurrence: TRILOBITES OF THE UPPER CAMBRIAN DUNDERBERG Litocephalus verruculapeza n. sp. Plate 8, figures 12, 13, 15, 16, 19, 20 I)iagnosis.—Specimens of Litocephalus with cranid- ium having border nearly equal in length to brim, flattened in profile, and bearing scattered coarse gran— ules. Palpebral lobes small, situated about opposite second glabellar furrow; length about one—third or less that of glabella exclusive of occipital ring. Fa- cial suture cuts anterior margin almost directly in front of anterolateral corners of glabella. Pygidium with pair of coarse granules on each of first four axial rings. Discussion—The small palpebral lobes, the scat- tered coarse granules on the border of the cranidium, and the paired granules on the axial rings of the pygidium distinguish this species from the other known species of Lz'tocephalus. Occurrence: Moderately rare, 70—80 ft above base of Dun- derberg shale; unit B. USGS colln. 2299—00. Figured specimens: Holotype cranidium, USNM 136881. I’aratypes, cranidium, pygidia, and free cheeks, USNM 136882 a—e. All from USGS colln. 2299—00. Genus TAENORA n. gen. Text figure 17 Type species—Tuenora empamsa n. sp. Diagnosis—Aphelaspidinae with cranidium having well-defined flat or slightly concave border of nearly constant breadth. Fixed cheeks flat, horizontal, width less than one-third basal glabellar width. Anterior course of facial suture moderately divergent forward from palpebral lobe to marginal furrow, intramargi- nal along most of anterior margin, cuts anterior margin nearly imperceptibly near axial line. Free cheek with moderately broad flat or slightly concave border; lateral and posterior marginal fur— rows joined at base of genal spine, extended for short distance onto spine. Genal spine relatively short; length less than that of ocular platform. Pygidium transversely subovate in shape with poorly defined flat or concave border, with or without slight me- dian indentation. Axial lobe prominent, merged pos- teriorly with inner part of border. All furrows on pygidium shallow. Descriptiomv.—Medium to large trilobites (up to about 70 mm in length). Cranidium gently to mod- erately arched transversely and longitudinally, broadly rounded anteriorly. Glabella well defined at sides and anterolateral corners by shallow dorsal furrow, poorly defined across front; straight sided, tapered forward, bluntly rounded anteriorly. Three pairs of shallow glabellar furrows may be visible; posterior pair bigeniculate and on some specimens also bifur— cate forming Y—shape with posterior branch of Y most SHALE, EUREKA DISTRICT, NEV. 83 FIGURE 17.—Partlal reconstruction of Taenora ewpansa n. sp., about X 3. deeply impressed; anterior pairs of glabellar furrows straight. Occipital furrow moderately deep, straight, shallowest on axial line. Occipital ring gently arched (sagittally), with small median axial node. Frontal area divided into well-defined brim and border by shallow evenly curved marginal furrow. Border broad, flat, or slightly concave near anterior margin, horizontal or slightly downsloping, of nearly constant breadth. Brim flat or gently convex; length (sagit- tal) about equal to or less than that of border. Fixed cheeks flat, horizontal; width about 1/3 to 14 basal glabellar width. Distinct ocular ridges present. Pal- pebral lobes well defined by shallow palpebral fur— rows, situated opposite or slightly posterior to mid- length of glabella; length (exsagittal) 1/2 to 1/3 length of glabella. Width about one—half width of fixed cheek. Posterior limbs slender, tapered to sharp point; length (transverse) about equal to basal gla- bellar width. Anterior course of facial suture divergent forward from anterior end of palpebral lobe to marginal fur- row, then curved slightly inward and crossing border nearly to anterior margin; intramarginal from that point nearly to axial line. Junction with anterior margin hardly noticeable. Posterior course divergent- sinuous. Free cheek with gently convex lateral margin; genal spine short, flattened in cross section, tapered rapidly to sharp point; length less than that of ocu- lar platform. Lateral and pogterior marginal fur- rows joined and extended slightly onto base of genal spine. Pygidium transversely subovate in outline with prominent axial lobe bearing 2 or 3 shallow ring fur- rows. Axial lobe tapered posteriorly, merged with 84: SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY inner part of border or with poorly defined ridge that extends to margin; length slightly more than three- fourths length of pygidium. Border flat or slightly concave, poorly defined; may have distinct median indentation. Pleural platforms with 2 or 3 shallow pleural furrows. External surfaces of all known parts smooth. Discussion—The most distinctive feature of trilo- bites of this genus is the form of the border on the cranidium. Taenora differs from Labio‘stria, which is here restricted to forms with a convex cranidial border like that of L. concemimarginatus Palmer, and Litotcephalus by having a flat or slightly concave somewhat downsloping border of nearly constant breadth on the cranidium. The fact that trilobites with this sort of border differ in relative breadth of border, size of palpebral lobes, impression of glabel- lar furrows, shape of genal part of free cheek and of posterior margin of pygidium indicates that the flat border may be a subfamily rather than a generic character. Until more species of this type are known, they are being included in the Aphelaspidinae. Labiostm'a platifmns Palmer from the Upper Cam— brian of central Texas is tentatively referred to this genus. Taenora expanse. n. sp. Plate 7, figures 20—23 Diagnosis—Members of Taenom with length (sag- ittal) of border almost twice that of brim. Palpebral lobes relatively short. about one-third length of gla- bella. Glabella with moderately well defined gla- bellar furrows. posterior pair on many specimens Y—shaped. Free cheek with border moderately broad, well defined, distinctly narrowed near base of genal spine. Pygidium short, wide; with distinct median indentation. Dismtssi0fl.—This species differs from all other spe- cies in the fauna by having a nearly flat cranidial bor- der of almost constant width and approximately hori- zontal fixed cheeks. The relatively wide border on the cranidium, shape of the genal part of the free cheek, and median indentation in the pygidium dis- tinguish this species from T”? platifrons (Palmer). Two fragmentary cranidia, one each from USGS col— lections 795—(‘0 and 2298—00 seem to belong to Tamara, but cannot certainly be assigned to this species. Occurrence: Rare, 70(?)—150 ft above base of Dunder- berg shale; units B(?), C. USGS colln. 954—CO, 2301—00, ?75)5—CO, ?2298—CO. Figured specimens: Holotype crandium, USNM 136872, USGS colln. 954—00. I’aratypes: Pygidium, USNM 136874, USGS colln. 954—00; cranidium and free cheek, USNM 136873 a, b, USGS colln. 2301—00. Subfamily PTEROCEPHALIINAE I)iagnosis.—Pterocephaliid trilobites with border of cranidium generally broad, concave, and longer (sag- ittal) than brim. Border of free cheek generally broad, concave. Pygidium with broad, poorly de- fined border on most species. Discussion—This subfamily includes at present only the North American genera Pterocephalia, Uemuolim- bus, and Sigmocheilus. Similar foreign trilobites that may have some affinities with this subfamily are Nem'cia, septcm/dentata \Vestergard (p. 80) from the late Middle Cambrian of Sweden, and possibly Dikelo- cephalites flabelliformés Sun, from the Upper Cam- brian of China. The latter species is too poorly known, however, for adequate determination of its systematic position. Anechocephalu‘s n. gen. (p. 92) may also belong to this subfamily. Pterocephalinid trilobites are distinctive elements of the Dunderberg fauna and its correlatives over most of the Great Basin. They are not known from beds older than the post-Aphelaspz's zone nor younger than the EZm'm'a zone. Genus CERNUOLIMBUS n. gen. Text figure 18 Type species.——(76m,u0limbue orygmatos Palmer n. sp. Diagnosis.—Pterocephaliinae with cranidium having distinct brim and border; axial length of border equal to or slightly greater than axial length of brim; border generally downsloping. Anterior branches of facial suture cut anterior margin at distinct angle at a point slightly more than three-fourths distance from ante- rolateral corner of cranidium to axial line. Free cheek with long genal spine and well-defined generally concave border. Lateral marginal furrow continuous with posterior marginal furrow. Breadth of border varies from one—fourth to slightly less than greatest breadth of ocular platform. _ Pygidium subovate to subsemicircular in outline; axial lobe reaching more than three-fourths total axial length of pygidium, bearing 2 to 5 distinct ring fur- rows. Pleurae with 2 to 4 low pleural ribs extending nearly to margin. Border not clearly differentiated from pleural platform, concave, widest at anterolat- eral corners, tapers gradually posteriorly, narrowest on axial line. I)escrépflour—Medium-sized trilobites (probably averaging 40 mm or less in total length) with cepha- lon subsemicircular in outline, moderately arched transversely and longitudinally. bearing long genal spines extending nearly straight back from posterolat- eral corners. Border well defined by shallow margi- TRILOBITES OF THE UPPER CAMBRIAN FIGURE 18.——Partial reconstruction of Cemuolimbus orygmatos n. 51)., about X 4. nal furrow. Eyes prominent, at or slightly below level of top of glabella. Cranidium with somewhat pointed anterior margin resulting from facial sutures cutting margin at a dis- tinct angle near the axial line. Glabella well defined, straight sided, tapered slightly forward, bluntly rounded or truncate anteriorly. Glabellar furrows hardly visible. Occipital furrow straight, moder- ately deep. Occipital ring with low median node. Dorsal furrows deep at sides and anterolateral cor— ners of glabella, shallow across front. Frontal area subequally divided into brim and border, or with bor- der slightly longer (sagittal) than brim. Border downsloping, with anterior margin slightly flexed up- ward; flexure distinctly anterior to midlength (sagit- tal) of border. Brim gently arched in longitudinal profile. Fixed cheeks upsloping from dorsal furrow; width between palpebral and dorsal furrows slightly less than one-half basal glabellar width. Ocular ridges moderately well defined, directed obliquely backward from slightly behind anterolateral corners of glabella. Palpebral lobes prominent, well defined by shallow arcuate palpebral furrow; width about one-half width of cheek between dorsal and palpebral furrows; length about one—half length of glabella ex— clusive of occipital ring. Posterior limbs slender, sharply pointed; length (transverse) about equal to basal glabellar width. Anterior course of facial su— ture slightly divergent from anterior end of palpebral lobe to marginal furrow, then turned diagonally in- ward and forward across border to cut anterior mar— gin slightly more than three-fourths distance from 507219 O—59——4 DUNDERBERG SHALE, EUREKA DISTRICT, NEV. 85 anterolateral corner of cranidium to axial line. Pos- terior course divergent-sinuous. Free check with long, slender genal spine continu- ing curvature of margin. Border well defined, gen— erally concave. Lateral and posterior marginal fur- rows connected but not continuous posterolaterally onto genal spine. Pygidium with axial lobe prominent, narrow, tap- ered posteriorly, bearing 2 to 5 distinct ring furrows. Length about three-fourths axial length of pygidium. Pleurae with 1 to 4 low pleural ridges extending nearly to margin. Border not clearly defined, con— cave, widest at anterolateral corner, tapered backward to axial line. Hypostome, rOstrum, and thoracic segments not known. Discussion—This genus seems to be ancestral to Pterooephalz’a and Sigmocheilus. Cranidia can be most easily recognized by their pointed anterior mar- gin and flat or slightly arched downsloping border that, is only slightly longer (sagittal) than the brim. The free cheeks have the lateral and posterior margi- nal furrows characteristically connected and not ex- tending onto the genal spine. Pygidia are most eas- ily recognized by the combined features of an evenly rounded posterior margin and a border that is rela— tively narrower than that of other genera in the sub- family. Cernuolimbus depressus n. sp. Plate 8, figures 9, 10 Diagnosis.—Members of Uernuolz'mbus with exter- nal surface of cranidium coarsely pitted; border downsloping, continuing slope of brim, tapered to a point laterally. Facial sutures nearly meeting on axial line giving pointed anterior margin to cranid- ium. Marginal furrow on mold bears single row of granules. Discussion—This species is represented by four cranidia. No other parts are known. The character of the border is the most striking feature that distin— guishes it from 0. orygmatos n. sp. and 0. semigmmo- laws n. sp. Occurrence: Rare, 50—60 ft above base of Dunderberg shale; unit B. USGS colln. 2297—00. Figured specimens: Holotype cranidium, USNM 136879. Paratype cranidium, USNM 136880. Both from USGS colln. 2297—CO. Cernuolimbus orygmatos n. sp. Plate 8, figures 1, 3, 5, 8, 11 Ding/nos{ax—Members of Uermwlimbus with exter- nal surfaces of all parts coarsely pitted. Border of cranidium slightly downsloping from marginal fur- row, nearly flat or slightly turned up at anterior mar- gin. Pygidium with subsemicircular outline; 4 well— 86 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY defined ring furrows; anterior 4 or 5 axial rings each bear a pair of coarse granules. Discussion—The distinctive coarse pitted surface serves to distinguish this species from C’. semigrauu— Zosus n. sp. It differs from 0. depressus n. sp. by hav- ing a relatively longer frontal area and less—pro- nounced lateral taper to the border Of the cranidium. Occurrence: Common, 30—50 ft above base of Dunderberg shale; units A, B. USGS colln. 2295—00, 2296—00. Figured specimens: Holotype cranidium. USNM 136875. Paratypes, free cheek and pygidia, USNM 136876a—c. All from USGS colln. 2295~CO. Cernuolimbus semigranulosus n. sp. Plate 8, figures 2, 4, 6, 7 Diagnosis—Members of Oer’nuolz'mbus with border nearly flat or slightly turned up at anterior margin; generally downsloping from marginal furrow. Ex- ternal surface of cranidium smooth except for tops of palpebral lobes and glabella which are thickly cov- ered with small granules. Free cheek with close- spaced fine granules on genal spine; breadth Of border equal to or only slightly less than greatest breadth of ocular platform. Pygidium transverse in outline with scattered barely visible fine granules over most of surface. Axial lobe with two moderately well defined ring furrows. Discussion—This species differs from both Oar-nua- Zimbus depress-us n. sp. and 0. org/gmutos n. sp. by having a fine—granular rather than coarse-pitted sur— face ornament. It difiers further from 0. depressus by having a much less laterally tapered and down- sloping border on the cranidium, and from 0. orygma— tos by having a relatively wide border on the free cheek. The pygidium of (l. semigranulosus lacks the distinct granules on the axial rings characteristic of U. orygmatos, and also has only 2 rather than 4 or 5 distinct ring furrows. Its outline is proportionately shorter and wider than that of 0. oirygmatos. Occurrence: Moderately common, lower 20 ft of Dunder- herg shale; unit A. USGS colln. 2294-00. Figured specimens: Holotype cranidium, USNM 136877. Paratypes, pygidium and free cheek, USNM 13687821, b. All from USGS colln. 2294—00. Genus PTEROCEPHALIA Roemer, 1849 Text figure 19 Pterocpehalia Roemer, 1849, p. 421; 1852, p. 92; Bridge in Bridge and Girty, 1937, p. 247; Shimer and Shrock, 1944, p. 631; Palmer, 1954, p. 751. Type species.—Pterocepiz(Ilia sanctisabae Roemer, 1849, p. 421. Diagnosis.—Pterocephaliinae with cranidium having border broad, concave, scarcely differentiated from brim. Length of border (sagittal) greater than three times length of brim. Junction of facial sutures with anterior margin generally imperceptible. Facial su- tures submarginal beneath part of anterior margin to axial line, then turn abruptly backward to form me- dian suture across doublure. Free cheek with broad concave border, slightly raised above level of ocular platform at marginal furrow. A low ridge parallels entire lateral margin nearly to tip of genal spine at distance about one- fourth width Of border from lateral margin. Genal spine moderately long, broad and flat at base, tapered to sharp slender point. Some thoracic segments with long broad backswept pleural tips. Pygidiuin subquadrate to subovate in outline with well-defined axial lobe bearing 4 to 8 visible ring furrows. Border not differentiated from pleural plat— form gently arched, crossed by 3 to 5 pleural ridges that extend onto but not across border. Border broad, concave, with slight to moderate median indentation. Edge smooth. External surface of exoskeleton generally with close-spaced fine granules in axial region. Borders of cranidium, free cheek and pygidium, and tips of pleu- rae of thorax generally with prominent terrace lines. FIGURE 19.——Partia1 reconstruction of Pterocephalia sanctiaabae Roemer, about X 2. Description—Medium to large trilobites (length up to about 70 mm) with large cephalon and pygid- ium. (‘eplialon with broad slightly concave border scarcely differentiated from brim on cranidium, with inner margin slightly raised above ocular platform TRILOBITES OF THE UPPER CAMBRIAN on free cheek. Length of border (sagittal) on cranid- ium is greater than 3 and up to 9 times that of brim. Low ridge present on border of nearly all free cheeks and many cranidia parallel to and about one-fourth breadth of border from margin. Genal spines broad, flattened, tapered to a sharp point. Glabella straight sided, tapered forward, truncate to bluntly rounded anteriorly, generally less than one-half length (sagit— tal) of cranidium. Dorsal furrows deep at sides and anterolateral corners of glabella, shallow across front. Three pairs of moderately deep glabellar furrows present on some species. Occipital furrow straight, deep adjacent to dorsal furrow, shallow across axial line. Occipital ring with low median node. Fixed cheeks broad, upsloping from dorsal furrows; width about one-half basal glabellar width. Ocular ridges generally well developed. Palpebral lobes moderately long, curved, midlength situated slightly posterior to midlength of glabella; length (exsagittal) about one- half length (sagittal) of glabella; breadth (trans- verse) nearly one—half breadth of fixed cheek. Palpe— bral furrow moderately deep, arcuate. Posterior limbs slender; length (transverse) slightly greater than basal glabellar Width. Anterior course of facial suture slightly to mod- erately divergent forward from palpebral lobe until onto border, then curved broadly across border to cut anterior margin- nearly imperceptibly and continue submarginally to axial line where it turns abruptly backward as median suture across doublure. Poste- rior course of facial suture divergent, sinuous. Entire thorax not known. Some thoracic segments with long broad pleural spines directed posteriorly. Pygidium with elongate subquadrate to transversely subovate outline. Axial lobe well defined, tapered posteriorly to a blunt point at inner edge of broad border, generally continued across border as a narrow ridge. Four to eight ring furrows visible. Pleurae not clearly divided into border and pleural platform. Pleural platform generally slightly arched, crossed by 3 to 5 well—defined pleural ridges. Border broad, slightly concave; broadest posterior and posterolate— ral to tip of axial lobe. Margin with slight to mod- erate median indentation. Edge smooth. External surfaces of border of cephalon, distal parts of thoracic pleurae, and border of pygidium generally with well-developed terrace lines. Axial region of exoskeleton generally with close—spaced fine granules. Scattered large granules on the border may be pres— ent or absent within a suite of cranidia of a single species. Hypostome not known. Discussion—Bridge (1937, p. 246—250) discussed Pterocephalia and the species included in the genus to that time. He recognized three species, P. samtisabae DUNDERBERG SHALE, EUREKA DISTRICT, NEV. 87 Roemer, P. asiatz’ca (Walcott), and P. occidens Wal- cott. Kobayashi (1936), unknown to Bridge, had placed P. asiatica in Paracoosz'a. The types of this species are incomplete. The cranidium shows promi- nent bumps on the fixed cheeks adjacent to the dorsal furrow and just anterior to its junction with the oc- cipital furrow. The pygidium has short broad spines along the margin. These features are here considered sufficient to exclude asiatica from Pterocepkalia. Resser (1938) placed specimens of P. sanctisabae illustrated by Bridge from various localities in the United States in 9 species of which 7 were new. On the basis of material from Oklahoma, Frederickson (1949) placed three of Resser’s species in synonymy with P. sanctisabae. Lochman (1950) grouped three more of Resser’s species together under the name P. bridgei and considered this species distinguishable from P. sanctisabae by having a proportionately shorter frontal area on the cranidium. Wilson (1951), though not mentioning Resser’s 1938 paper, included all the specimens illustrated by Bridge (1937) in the synonymy of P. sanctisabae, thus implying that all the species recognized by Resser in 1938 are synonyms of P. sanctisabae. Part of the confusion in the taxonomy of speci- mens assigned to Pterocephalz’a results from the fact that specimens well—enough preserved to study are relatively rare, and few collections have sufficient in- dividuals to permit adequate determination of infra- specific variation in the cranidial proportions that have been used for specific differentiation. Thus, Lochman’s recognition of two species of Ptemcephalz’a based solely on differing proportions between the length (sagittal) of the frontal area and the length of the glabella has an inadequate statistical basis. All the types and topotypes of the species of Ptero- cephalic recognized by Resser (1938) and regrouped by Lochman have been examined in the course of this study. For all the cranidia under 15 mm in length, no significant differences are observable in the length of the frontal area compared to the length of the glabella. Only 6 cranidia longer than 15 mm are present. These are distributed among four of the species recognized by Resser and include a cranidium of P. bridgei. Although there is variation in the relative lengths of the frontal areas compared to gla- bella lengths from slightly less than 1.5: 1 to 2: 1, and specimens representing P. bfidgei and P. sanctisabae are nearly at opposite extremes, no sample has more than 2 of the large cranidia and determination of the significance of the variation in the proportion cited is not possible. lomparison of the variation of cranidial characters with size in Cambrian trilobites indicates that there is more apparent variation among larger specimens than among smaller specimens 88 SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY (Palmer, 1958). Until more is known of the varia- tion of cranidial proportions within a single popula- tion of P. sanctisabac, the characterization of P. bridgci by Lochman is considered inadequate for its separation from P. sanctisabae and all species of Pterocephalz'a listed by Resser (1938) are here con- sidered synonyms Of P. sanctisaba'c. P. o‘ccz'de'ns VValcott is represented by a single small exfoliated cranidium (pl. 9, fig. 21) from an unknown level within the Dunderberg shale. It could repre- sent either P. conccwa n. sp. or P. elongata n. sp. Because of this, the species is here considered to be indeterminate and the name should be restricted to the holotype. Ptcrc‘cephalz'a cf. P. occidens from Texas (Palmer, 1954) is more like P. concava n. sp. than any of the other species of Ptcroccphalia here recognized and should now be designated Pterocephalz‘a cf. P. con- cava Palmer. Pterocephalia concava n. sp. Plate 9, figures 1—6, 9—12 ?Ptcroccphalm cf. P. occidens Walcott, Palmer, 1954, p. 752, pl. 86, figs. 9, 10; pl. 87, figs. 1, 2. Diagnosis.—Specimens of Pterocephalz’a with shal- low glabellar furrows. Border of cranidium and free cheek generally with low scattered coarse granules. Length (sagittal) of border increases from 3 to greater than 5 times that of brim from small (4—5 mm long) to large (14 mm long) mature cranidia. Some thoracic segments, perhaps all, with long broad flattened backwardly directed pleural tips. Breadth (transverse) of pleural tips greater than breadth (exsagittal) of proximal part of pleuron. Pygidium transversely subovate in outline, with slight median inbend in posterior margin. Axial lobe with 4 to 5 distinct ring furrOWS. Pleural lobes crossed by 2 or 3 distinct pleural ridges. Breadth of border increases relative to breadth of pleural plat- form, and border becomes more concave with increas— ing size. Discussion—This species, which occurs in pre- Elvim‘a zone beds, is most similar to P. sawctz’sabac from the Elvinia zone. It differs principally by hav— ing less conspicuous glabellar furrows, fewer distinct ring furrows and pleural ridges on the pygidium, and a strikingly different development of the mature speci- mens. Small mature specimens of P. (,‘O’IIc'a‘Ufl (cranid— ial length 4—5 mm) are similar to forms of comp- parable size in Uermuolz'mbus and Sig/Inoc/Icilus, differing principally in the absence of clear distinction between the brim and border. Large specimens re- semble P. sanctisabde. Small mature specimens of P. sanctisabac, however, look virtually like the large specimens of P. sawctisabae (cf. pl. 9, figs. 1, 3, 4, 7). The change in form of mature specimens of P. con- cava with increasing size emphasizes the relationships of Ptcroccphalz'a, to Cemuolz'mbus and Sigmocheilus. The comparative mature development of P. concave and P. sanctisabac may be strong evidence indicating that P. concaca is one of the earliest species of Ptero- cephalic. P. concaca differs from P. clongata n. sp. prima- rily by having a transverse rather than elongate sub- quadrate form to the pygidium and by having a less well-marked median indentation of the posterior margin. Occurrence: Moderately common, 50—60 ft above base of Dunderberg shale; unit B. USGS colln. 809—00, 2297—00. Specimens are questionably assigned to this species from USGS colln. 795—00. Figured .s'pccimcns: Holotype cranidium, U SNM 136887, USGS colln. 2297—00. Paratypes: Cranidia, USNM 136888a—c; free Cheek, USNM 1368888; pygidia, USNM 136888d, f—h; tho- racic segment, USNB 1368881 All from U SGS colln. 2297—010. I’terocephalia elongate. n. sp. Plate 9, figures 14—20 Diagnosis—Members of Ptcrocephalia with shal- low glabellar furrows. Length (sagittal) Of border between 3 and 5 times length of brim. Pygidium with elongate subquadrate outline. Great- est breadth near posterior margin. Sides straight, nearly parallel or slightly diverging posteriorly. Pos- terior margin nearly straight, with slight median in- dentation. _ Axial lobe with «1 or 5 distinct ring furrows. J unc- tion of lateral and posterior margins strongly rounded. Two or three distinct pleural ridges parallel lateral margin of pygidium. A narrow ridge continues pos- teriorly from tip of axial lobe across border to pos- terior margin. Hypostome and thoracic segments not known. Discussion—The shape of the pygidium Of this species is its most distinctive feature. Isolated cranidia and free cheeks cannot be distinguished with certainty from those of P. concava. The cranidium of P. clongata differs from that of P. smactz'sabac by having less conspicuous glabellar furrows, a some- what more concave border, and a straighter poste- rior margin. ()ccurrcncc: Moderately common, 80—100 ft above base of Dunderberg shale; unit B. USGS colln. 873—00, 2300-00. Figured specimens: Holotype cranidium, USNM 136891, USGS colln. 873—00. Paratypes: Pygidium, USNM 136892, USGS colln. 873—00: cranidium, free cheeks, and pygidia, USNM 1368932140, USGS colln. 2300—00. Pterocephalia sanctisabae Roemer Plate 9, figures 7, 8, 13 Pterocephalia sanctisabae Roemer, 1849,:p. 421; 1852, p. 92, pl. 11, figs. 1 a—d; Bridge, 1933, p. 232, pl. 2, figs. 26, 27; TRILOBITES OF THE UPPER CAMBRIAN Kobayasni, 1936, p. 172, pl. 21, figs. 10—12; Bridge, in Bridge and Girty, 1937, p. 246, pl. 67, figs. 1 a—d; pl. 68, figs. 7—43; Shimer and Shrock, 1944, pl. 266, figs. 35—37,- Wilson, 1949, p. 42, pl. 10, figs. 1&3; Frederickson, 1949, p. 355, pl. 69, figs. 1—4; (?) Wilson, 1951, p. 647, pl. 91, fig. 24. Conocephalites (Pterocephalus) laticeps Hall and Whitfield, 1877, p. 221, pl. 2, figs. 4—7. Dikellocephalus multicinctus Hall and Whitfield, 1877, p. 226, pl. 2, fig. 37. Pterocephalz‘a dakotensis Resser, 1938, p. 39. Pterocephalia bridgez’ Resser, 1938, p. 40; Lochman, 1950, p. 334, pl. 47, figs. 14—18. Pterocephalia oriens Resser, 1938, p. 40. Pterocephalia potosiensz’s Resser, 1938, p. 40. Pterocephalia ulrz’chi Resser, 1938, p. 41. Pterocephalia silvestrz's Resser, 1938, p. 41. Pterocephalia deckeri Resser, 1938, p. 41. Diagnosia—Members of Pterocep/Lalia with moder- ately deep glabellar furrows. Length (sagittal) of border on cranidium between 5 and 9 times length of brim on mature specimens. Free cheek with breadth of border four or more times breadth of ocular platform at anterior margin. Pygidium transversely subovate in outline, with at least 6 distinct ring furrows on axial lobe and with 4 or 5 distinct pleural ridges on pleural lobes. Pos—_ terior‘margin with slight median indentation. Discussion—This species is a distinctive element of the E Zvim’a fauna over most of the United States. Its complicated nomenclatural history has been reviewed in the discussion of the genus. The extremely broad border on the cephalon, conspicuous glabellar furrows, and the many conspicuous ring furrows and pleural ridges on the pygidium are the distinctive specific features. Occurrence: Rare, 140 ft or more above base of Dunder- berg: shale; unit 0. USGS colln. 2301—00, 2302-00. Figured specimens: Plesiotypes—cranidium and free cheek, USNM 13688921, b, USGS colln. 2302—00; pygidium, USNM 1368.90, USGS colln. 2301—00. Genus SIGMOCHEILUS n. gen. Text figure 20 Type species.—Simnockeilus serratus n. sp. Diagnosz's.———Pterocephaliinae with generally well— defined border on cranidiuin. Length of border (sag- ittal) between 1.5 and 3 times greater than that of brim. Border generally concave in profile with great— est depth near its midlength (sagittal). Facial su— tures cut anterior margin at slight angle between point opposite anterolateral corners of glabella and axial line. Free cheeks with long genal spine and well-defined concave border. Lateral and posterior marginal fur- rows barely connected. Lateral marginal furrow shallowest; posterior marginal furrow continues onto genal spine. Breadth of border less than greatest breadth of ocular platform. DUNDERBERG SHALE, EUREKA DISTRICT, NEV. 89 Pygidium subquadrate to transversely subovate in outline, greatest width about opposite posterior end of axial lobe. Axial lobe prominent, bears 4 or 5 ring furrows; tapered to a blunt point at inner edge of border. Border and pleural platform not clearly differentiated; 3 to 5 pleural ridges generally appar— ent, geniculated at boundary between pleural plat— form and border. Lines connecting geniculations roughly outline triangular pleural platforms. Pleural ridges continued onto but not across border. Border concave, posterior margin evenly rounded, nearly straight, or with slight median indentation. Edge smooth or with short broad spines. FIGURE 20.—Partial reconstruction of Sigmocheilus eerratus, n. sp.. about X 3. Description.—-Medium-sized trilobites (probably averaging 40 mm or less in length) with cephalon subsemicircular in outline, moderately arched trans- versely and longitudinally, bearing long genal spines extending nearly straight back from posterolateral corners. Border well-defined to poorly defined on cranidium and 011 free cheek by shallow marginal furrow. Lateral marginal furrow barely connected to posterior marginal furrow. Eyes prominent, at or slightly below level of top of glabella. Cranidinm with anterior margin evenly rounded. Glabella well-defined, dorsal furrow deep at sides and 90 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY anterolateral corners, shallow across bluntly rounded front. Glabellar furrows shallow, posterior pair bi— geniculate to slightly Y—shaped with posterior arm of Y most strongly developed. Occipital furrow straight, deepest adjacent to dorsal furrow. ()ccipital ring with low median node centrally located. Border concave in longitudinal profile, deepest part Of concavity near midlength (sagittal). Length (sagittal) of border 1.5 to 3 times that Of brim. Marginal furrow shallow; junction between brim and border generally marked by contrast between strong veination or granulation Of brim and nearly smooth surface of border. Inner margin of border sometimes slightly raised above ad- jacent. brim surface. Fixed cheeks horizontal or up— sloping. Ocular ridges low, extending backward to palpebral lobe from a point slightly posterior to anterolateral corners of glabella. Width of fixed cheek slightly more than one-third basal glabellar width. Palpebral lobes well defined by arcuate palpe- bral furrow; width about two—fifths width Of fixed cheek; length between 2/5 and 1/2 length of glabella. Posterior limb slender, sharply pointed; length (transverse) slightly less than basal glabellar width. Anterior course of facial suture slightly divergent forward from palpebral lobe onto border, then curved sharply inward acr0ss border to cut anterior margin between a point directly anterior to anterolateral cor— ner of. glabella and axial line; suture then submar- ginal to axial line and turned backward across doublure as median suture. Rostrum apparently ab- sent. Posterior course of facial suture divergent- sinuous. Free cheek with long tapered genal spine. Border concave. well—defined to poorly defined along lateral margin by marginal furrow; breadth slightly less than greatest breadth Of ocular platform. Shallow lateral marginal furrow not clearly connected to deep poste- rior marginal furrow. Pygidium with axial lobe prominent, narrow, tapered posteriorly to inner edge of border; 4 or 5 ring furrows generally Visible; length (sagittal) be- tween 1/2 and 34 length of pygidium. Pleurae with 3 to 5 low pleural ridges extending laterally across poorly defined pleural platform and then turning backward onto, but not across, border at an angle of between 30° to 45° with axial line. Border concave. Posterior margin broadly rounded, nearly straight, or with slight median indentation. Edges smooth or with short broad spines. Hypostome and thoracic seglnents not known. External surface of cranidium generally partly cov- ered with low small granules. External surfaces of other parts smooth or granular. Surface of molds of all parts smooth. Discussion. Species Of this genus are most likely to be confused with those of Ccrnuolimbus or early forms of Pterovcephalia. Cranidia can be most easily recognized by a distinct concave border that is up to 3 times longer (sagittal) than the brim. Free cheeks are characterized principally by having the border concave and narrower than the ocular platform. Pygidia of S. gram and S. utahensis resemble those Of early species of Pterocephalia and can only be certainly assigned to Sigmocheilus when they are associated with the characteristic cranidium. Later pygidia with scalloped or spinose margins are dis- tinctive Of Sigmocheilus. Resser (1912, p. 76—79) included in a genus P256740- ccplzalz’m four new species, P. Momma, P. notha, P. pay/072.27pemis. and P. grata besides the type species, P. bilobata (Hall and Whitfield). Pterocephalina has since been shown to be a synonym of Litocephalus. and P. bilobata to be properly Liz‘ocephalus bilobatus (Palmer, 1956a). Of the remaining species, all but P. temoma belong to Sigmocheilus. P. texamz was stated to come from the VVilberns formation (Resser, 1942, p. 77) in Texas. An insolu— ble residue Of a part of the limestone piece bearing the holotype pygidium contained Angulotmta triangu- larz's Palmer, and fragmentary specimens of Aphe- Iaspis are present adjacent to the pygidium. These associated fossils show that the holotype came from the Aphelaspis zone of the Riley formation. The pygidium is probably that Of a species of Labéostm’a. Wilson (1954, p. 271) figured two fragmentary cranidia and referred them tO Pterocephalina cf. P. gram Resser. These cranidia represent an indetermi- nate species of Sigmochez'lus. Iddingsia? quinnensis Resser (1942, p. 88, pl. 16, figs. 39—11) is known only from cranidia. It defi- nitely represents a species of Sigmocheflus, but its relationships to the species here described will not be known until its pygidium is described. Sigmocheilus grata (Resser) Plate 9, figures 22, 23, 26, 27 Pferoccphalina gram Resser, 1942b, p. 78, pl. 15, figs. 3—6. Diagn(Mia—Specimens of Sigmocheilm with length of border (sagittal) between 2 and 3 times length Of brim. Brim nearly flat. Fixed cheeks upsloping from dorsal furrow. External surface of border smooth or with few scattered low coarse granules. Remainder of surface of cranidium, exclusive of furrows, covered with low fine granules. Free cheek with moderately well defined lateral marginal furrow. External surface smooth except for low veination. TRILOBITES OF THE UPPER CAMBRIAN Pygidium with poorly defined border moderately expanded posterolaterally, posterior margin broadly rounded or straight, with slight median indentation on some specimens. Edge smooth. Two or three low pleural ridges Visible. Discussion—This species may require redefinition and subdivision when more is known of the associ- ated cranidia, pygidia, and cheeks of early species of Sigmacheilus. The present collections contain slightly differing forms, but there are not enough specimens to establish certainly limits of variation of the dif- fering features within a population. In this paper, 8. grate includes forms with a smooth cranidial bor- der, forms with a few low scattered granules on the border, and forms with slightly to moderately flared pygidial borders. Occurrence: Moderately common, 50—80 ft above base of Dunderberg shale; units B and C. USGS colln. 952—00, 2297— CO—2299—CO. Figured specimens: Plesiotypes—cranidium, pygidium, and free cheek, USNM 138895a—c, USGS colln. 2299—00; pygidium, USNM 136894, USGS colln. 952—00. Sigmocheilus pogonipensis (Resser) Plate 10, figures 4—7 Ptcroccphalinu pogom‘pensis Resser, 1942b, p. 78, pl. 15, figs. 1, 2. Diagnosis—Specimens of Sigmochcilus with cranid- ium having brim strongly convex and border strongly concave. Length of border (sagittal) about 1.5 times length of brim. Front of glabella well defined be- cause of arching of brim. Fixed cheeks upsloping from dorsal furrow. External surface of cranidium, exclusive of furrows and border, covered with low coarse granules. Free check with poorly defined strongly concave border. Lateral marginal furrow hardly visible; posterior marginal furrow deep. Pygidium with transverse subovate outline. Axial lobe about three-fourths length (sagittal) of pygidium. Border not clearly defined. Pleurae crOSsed by 4 or 5 prominent pleural ribs; lateral parts bear prominent terrace lilies. Margin bears six pairs of short asym- metrical spines. I)2'scussz'(m.—The strongly arched brim on the cranidium and short asymmetrical marginal spines 011 the pygidium are the most distinctive characteristics of this species. The holotype is from an unknown position within the Dunderberg shale in the W'hite Pine district, Nevada. Occurrence: Moderately common, 140—150 ft above base of Dunderberg shale: unit 0. USGS colln. 954—00, 2301—00. Figured specimens: Paratypes—cranidium, free cheek, and pygidium, USNM 136900a—c, USGS colln. 2301—00; cranidium, USNM 136901, USGS colln. 954—00. DUNDERBERG SHALE, EUREKA DISTRICT, NEV. 91 Sigmocheilus serratus n. sp. Plate 10, figures 1-3 Diagnosis—Members of Sigmocheilus with cranid- ium having length of border (sagittal) about 1.5 times length of brim. Brim gently to moderately convex, border moderately concave. Fixed cheeks upsloping. External surface of top of glabella with close-spaced fine granules. Free cheek with poorly defined moderately concave border. Surface of ocular platform with moderately prominent veination; border with moderately promi- nent terrace lines. Pygidium transversely subovate in outline. Axial lobe about three—fourths length (sagittal) of pygidium. Border not defined. Pleurae crossed by 3 or 4: low pleural ridges. Posterior margin bears 5 or 6 pairs of broad rapidly tapered sharp marginal spines; the pair nearest axial line generally shorter than the re- maining pairs. Pleurae with numerous terrace lines. Discussion—Jrhe relatively subdued convexity and concavity of the brim and border on the cranidium and the more prominent marginal spines on the pygid— ium distinguish this species from S. polgom'pensis. Isolated cranidia resemble those of S. gram but have a relatively broader brim. Occurrence: Moderately common, 190—220 ft above base of Dunderberg shale; unit C. USGS colln. 789—00, 864—00, 878- CO, SSS—CO, 2302—CO. Figured specimens: Holotype cranidium, USNM 13689821, USGS colln. 955—00. Par-atypes: Pygidium, on same block as cranidium, USNM 136898b, USGS colln. 955—00; free cheek, USNM 136899, USGS colln. 864—00. Sigmocheilus utahensis (ReSser) Plate 9, figures 24, 25, 28 Ptcrocephalinn utarhensis Resser, 1942b, p. 79, pl. 15, figs. 7—11. DiagnMia—Specimens of Sigmocheflus with cranid— ium having border poorly defined by shallow marginal furrow. Length of border (sagittal) about 1.5 times that of brim. Brim gently convex and border gently concave. Glabella with moderately deep glabellar furrows. Fixed cheeks nearly horizontal. External surface of all but border of cranidium and furrows covered with close-spaced moderately coarse granules. Border with well-defined terrace lines. Free cheek with poorly defined concave border. Pleural platform bears scattered coarse granules on external surface. Pygidium with poorly defined border expanded pos- terolaterally and with moderately deep median inden- tation in margin. Two or three low pleural ridges generally visible. Surface of axial lobe and pleural platform seems to be roughened on larger specimens. Hypostome and thoracic segments not known. 92 SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY Discussion—This species is the oldest of the four species here assigned to Sigmachez’lus. The poorly de— fined border and coarse—granular surface on the cepha- lon and the deep indentation in the posterior margin of the pygidium are its most distinctive features. The holotype is from the Orr formation, Fish Springs Range, Utah. Occurrence: Rare, 30—50 ft above base of Dunderberg shale; unit B. USGS colln. 795—00, 2296—00. Figured specimens: Plesiotypes—small cranidium, USNM 136897, USGS colln. 795—C0; free cheek and pygidium, USNM 13689621, b, USGS colln. 2296-00. PTYCHOPARIODEA UNASSIGNED Species and genera are not assigned to families in this paper if they are either well represented, but un- like any other trilobites in the collection; represented by small numbers of specimens, generally only cra— nidia; or are nearly featureless. If a stable family classification of Cambrian trilobites is to be developed, it must be built from groupings of two or more genera in which at least some of the species are well repre- sented by cranidia, pygidia, and free cheeks. Mono- typic families, families of superficially similar trilo— bites from rocks having no paleogeographic or stratigraphic continuity, or families for trilobites that are inadequately known do not contribute to stability. Genus ANECHOCEPHALUS n. gen. DiagnoSis.—Pteroceplialiidaei with cephalon having short frontal area. Brim nearly vertical; border slightly arched, subequal in length (sagittal) to brim, nearly horizontal. Fixed cheeks elevated; width about one-third basal glabellar width. Palpebral lobes raised above level on top of glabella; length (exsagittal) about two-thirds length of glabella; width about two- thirds that of fixed cheeks; midlength situated poste- rior to glabellar midlength. Pygidium subquadrate in outline with short poste- riorly tapered axial lobe; border downsloping, poorly defined, broad, flat, with broad deep median notch in posterior margin. Description—Small pterocephaliid? trilobites (total length probably about 15 mm). Cranidium with gla- bella well defined at sides and anterolateral corners, poorly defined on axial line; glabellar furrows shal- low; occipital furrow deep, of nearly constant depth. Occipital ring gently arched along axial line, with low median node near anterior margin. Frontal area short; length (sagittal) about one-third length of glabella; subequally divided into well—defined brim and border. Brim nearly vertical, continuing forward curvature of glabella. Border gently convex, nearly horizontal, tapered slightly laterally. Fixed cheeks elevated; width about one—third basal glabellar width. Palpe- bral lobes large, situated slightly above level of top of glabella; length (exsagittal) about two-thirds length of glabella; width about, two-thirds that of fixed cheek; midlength situated posterior to glabellar midlength; line connecting posterior ends passes just in front of occipital furrow. Posterior limbs slender, shape not known. Anterior course of facial sutures directed nearly straight forward from palpebral lobes to marginal furrow, then turned abruptly inward across border to cut anterior margin in front of gla- bella. Ventral course not known. Posterior course not known. Free cheek, thoracic segments, and hypostome not known. Pygidium subquadrate in outline. Axial lobe well defined, tapered posteriorly to inner edge of border; bears 2 or 3 shallow ring furrows; length about one— half and width about one—third that of pygidium. Pleural platforms nearly flat, horizontal, crossed by 2 or 3 shallow pleural furrows that extend slightly onto border. Border broad, flat, downsloping, differ— entiated from brim only by change in slope. Posterior margin with broad deep median notch not reaching to end of axial lobe. External surface of border of cranidium covered with distinct terrace lines. Remainder of cranidium, except for glabellar and occipital furrows, bears low coarse imperfect reticulate ornament. External sur- face of pygidium smooth except for transverse row of three low coarse evenly spaced granules near posterior margin on each side of median notch. Discussion—This genus is represented by 3 cranidia and 3 pygidia of a single species from 1 collection. It is not referable to any described genus, and has dis- tinctive enough features to warrant description even though represented by a small sample. The associa~ tion of cranidium and pygidium is not certain, but it seems probable because these are the only unassigned parts of a pterocephaliid? trilobite in the collection from the type locality. Except for the frontal area, this genus has several characters of the Pterocepha- liinae—prominent posteriorly placed palpebral lobes on raised fixed cheeks, poorly defined border, and curved pleural furrows extending onto the border of the pygidium. The subequally divided frontal area with a nearly vertical brim and a narrow border that is convex instead of concave upward is unlike that of any pterocephalinid. Anechocephalus trigranulatus n. sp. Plate 8, figures 21—23 Description~1n the absence of other species of Anechocephalus, the generic description is also a de— scription of this species. The characteristics that will probably be most important in differentiating this species from any subsequently described are the reticu— TRILOBITES OF THE UPPER CAMBRIAN late surface ornament of the cranidium and the dis- tinctive rows of coarse granules near the posterior margin of the pygidium. Occurrence: Rare, 70—80 ft above base of Dunderberg shale; unit B. USGS colln. 952—00. Figured specimens: Holotype cranidium, USNM 136885. Paratypes, cranidium and pygidium, USNM 136886a, b. All from USGS colln. 952—00. Genus BYNUMIELLA Resser Type species.—Bymamiella typicalis. Resser, 1942b, p. 57, pl. 10, figs. 1, 2. Diagnosis.—“Small trilobites with a tapering gla- bella without furrows. Dorsal and occipital furrows are well defined. The simple brim varies in width, but tends to extend forward in the middle causing the anterior outline of the cranidium to project.” (Resser, 1942, p. 57.) Discussion—A single species from the lower part of the Dunderberg shale is tentatively assigned to this genus. Bynumz'ella is based on two species repre- sented by only a few imperfectly preserved cranidia from beds of F ranconia or Trempeleau age in the Canadian Rockies. Although the Dunderberg species seems to conform reasonably well to the generic diag- nosis, the differences between this species and the Canadian species in both morphology and stratigraphic position indicate that another generic assignment may eventually result for the Dunderberg species when more is known about the relationships of the small smooth trilobites. Bynumiella? acuminata n. sp. Text figure 21; plate 10, figures 9, 10 Description—Small trilobites (length of cranidium about 3 mm) with cranidium subtriangular in outline, moderately arched transversely, gently arched longi— tudinally, sharply pointed at anterior margin. Gla- bella poorly defined by shallow dorsal furrow, straight sided, tapered forward, bluntly rounded anteriorly. Glabellar furrows not apparent. Occipital furrow deep adjacent to dorsal furrow, shallow on axial line. Occipital ring widest on axial, line, with low median node near anterior edge. Frontal area short, with straight shallow marginal furrow separating down- sloping brim and border; length slightly less than one-third length of glabella. Border flat, sharply pointed on axial line, tapered rapidly to point before reaching anterolateral corners of cranidium; length (sagittal) almost twice length of brim. Fixed cheeks moderately narrow, flat, downsloping; width slightly less than one-third basal glabellar width. Palpebral lobes hardly differentiated from cheek; situated slightly anterior to glabellar midlengtli; lateral mar- gin gently curved outward, only slightly interrupting DUNDERBERG SHALE, EUREKA DISTRICT, NEV. 93 gentle inward curve of facial suture. Posterior limbs subtriangular; length (transverse) about three—fourths basal glabellar width. Posterior marginal furrow broad, shallow, straight. Anterior course of facial suture nearly straightforward from palpebral lobes, sharply curved inward before reaching marginal fur- row, and continuing in straight line across border to cut anterior margin at distinct angle nearly at axial line. Posterior course divergent outward from palpe- bral lobe, nearly straight until across posterior margi- nal furrow, then curved backward to posterior margin. External surface of occipital ring and posterior part of posterior limbs with many low coarse granules on some specimens, smooth or only faintly granular on others. External surface of remainder of cranidium smooth. Free cheek with narrow poorly defined border. Ocular platform broad, smooth. Genal spine short. FIGURE 21.—Partial reconstruction of Bynumiella! acuminata n. 81)., about X 20. Discussion—This species differs from B. typicalz's Resser and B. briscoensis Resser by having a smooth rather than coarsely pitted external surface of the brim and cheeks and scattered coarse granules near the posterior margin of the cranidium, a somewhat more truncate anterior end to the glabella, a more sharply pointed anterior margin on the cranidium, and an occipital furrow that is deeper near the dorsal furrow and shallower on the axial line. No other known species in the Dunderberg fauna is likely to be confused with this one. Occurrence: Moderately common, about 40 ft above base of Dunderberg shale; unit B. USGS colln. 795—00, 2296—00. Figured specimens: Holotype cranidium, USNM 136903, USGS colln. 2296—00. Paratype free cheek, USNM 136904, USGS colln. 2296—C0. Genus BYNUMINA Resser Bynuminu Resser, 1942, p. 58. Type speciex.—Byrlmnz'rm meiam Resser, 1942b, p. 58, pl. 10, figs. 18—22. [)2'agnosis.—Cranidiuin without distinct furrows on ‘ external surface. Anterior margin broadly rounded. No apparent border. Palpebral lobes small, situated 94 SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY anterior to midlength of cranidium. Posterior course of facial suture diverges at nearly right angle to axial line just behind palpebral lobe, then curves broadly to posterior margin. Free cheek subtriangular in outline, with rounded genal angles. Pygidium simple, without distinctive generic fea- tures. Description—Small nearly featureless trilobites (probably not much more than 10 mm in total length) with cranidium subtrapezoidal in outline, moderately arched transversely and longitudinally, without dis— tinct external furrows. Exfoliated specimens have well-defined anteriorly tapered glabella, slightly rounded at front. Last two pairs of glabellar fur- rows, when present, strongly curved posteriorly. Oc- cipital furrow deep, straight. Occipital ring narrow, tapered laterally. Frontal area length slightly greater than one-third that of remainder of cranidium; shal— low marginal furrow when present, separates brim and border of nearly equal length. Posterior limbs broad (exsagittal), shorter (transverse) than basal glabellar width, bluntly rounded or pointed at tips; marginal furrow only apparent near dorsal furrow. Anterior course of facial suture straight forward or slightly convergent, from palpebral lobes to anterolat- eral corners of cranidium, then curved gently inward to cut anterior margin imperceptibly about in front of anterolateral corners of glabella. Posterior course nearly straight laterally directly behind palpebral lobe, then curved broadly ot posterior margin. Free cheek subtriangular in outline, without well- defined border. Eye small. Genal spines absent, genal angles strongly rounded. Pygidium subsemicircular in outline; axial lobe not distinctly differentiated on external surface; border not apparent. 011 exfoliated specimens, axial lobe tapers backward nearly to posterior margin, not well defined by dorsal furrow, bears up to five shallow ring furrows. First two axial segments more distinctly developed than more posterior segments in some species. External surfaces of all parts smooth. Discussion—Neither Resser (1942) when he pro- posed this genus for B. caclam Resser and B. missouri- emis Resser from the Davis formation of Missouri, nor Wilson (1951) when he added B. terrcnda Wilson from the Ore Hill limestone member of the Gatesburg formation in Pennsylvania and compared it with the type species seems to have recognized that the types of the Missouri species are exfoliated cranidia. Re- examination of the type lots of B. caelam and B. mis— souricmix has turned up one cranidium in each lot that retains its exoskeleton. The appearance of these cra- nidia is much like that of B. terrenda (Wilson, 1951, pl. 89, fig. 10) and quite unlike the exfoliated speci- mens. The gently rounded anterior margin, absence of a distinct cranidial border, and strongly divergent pos- terior course of the facial sutures on the cranidium distinguish species of this genus from other nearly featureless trilobites. A single distinct species, B. glo- bosa (Walcott), represents this genus in the Dunder— berg fauna. The descriptions of the free cheek and pygidium are based on material from the Davis formation in Mis— souri. Bynumina globosa (Walcott) Plate 10, figure 8 Agra/alas? globosus Walcott, 1884, p. 61, pl. 9, fig. 23. Kingstom‘a globosar (Walcott), Resser, 1936, p. 24. Diagnosis.—Specimens of Bynumina with cranidium having glabella nearly parallel sided, subquadrate in outline; anterior part somewhat elevated above adja- cent cheeks. Thoracic segments, free cheeks, and py— gidium not known. Discussion—The distinct, although not clearly de— fined subquadrate glabella, is the principal feature distinguishing this species from others in Bynumina. Its relations to the older genus Kingstom'a cannot be determined until more is known of these nearly fea- tureless trilobites. Occurrence: Moderately common, upper Dunderberg shale; unit D. USNM 10c. 61. Figured specimen: 61. Cranidium, USNM 136902, USNM 10c. Genus CHEILOCEPHALUS Berkey Chrc'iloccphalus Berkey, 1898, p. 290; Palmer, 1954, p. 757. Pseudolisunia Kobayashi, 1935, p. 162; Shimer and Shrock, 1944, p. 621. The fragmentary material from the Dunderberg shale does not add any new information to the descrip— tion of this genus already presented (Palmer, 1954). Cheilocephalus spp. Plate 10, figures 13, 14 Discussion—Two cranidia and a pygidium from three different collections represent this rare but dis— tinctive genus in the Dunderberg shale. None of the specimens are completely preserved. The two cranidia have a distinctive coarse granular external surface and are perhaps referable to (llzcz'locephalus buttsi Resser (Resser, 1942, p. 36, pl. 11, fig. 6; Wilson, 1951, p. 631, pl. 91, fig. 13). This species is known from only two cranidia in the Ore Hill limestone member of the Gatesburg formation in central Pennsylvania. The pygidium is exfoliated so that, although it has a shape characteristic of pygidia of several species of TRILOBITES‘ OF THE UPPER CAMBRIAN DUNDERBERG SHALE, EUREKA DISTRICT, NEV. 95 Cheilocephalus, its external surface and thus its aflini— ties are not known. Reference of the Dunderberg material to new or described species must await more complete informa- tion about the morphology of associated cranidia and pygidia. Occurrence: Rare, Dunderberg shale; units B, C. USGS colln. 864—00, 872—00, 2299—C0. Figured specimens: Cranidium, USNM 136907, USGS colln. 864—C0; pygidium, USNM 136908, USGS colln. 2299—00. Genus DOKIMO CEPHALUS Walcott Dokimocephalus Walcott, 1924, p. 55; 1925, p. 83; Shimer and Shrock, 1944, p. 623; Frederickson, 1948, p. 800; Wilson, 1949, p. 36. Type species.—Ptychopcria? 1884, p. 49, pl. 10, figs. 8, 8a—b. Discussion—On the basis of relatively abundant material in Oklahoma and Texas, Frederickson (1948) and Wilson (1949) gave detailed descriptions of this genus. Only 2 imperfect cranidia and 1 free cheek represent the genus in the Dunderberg faunas. Dokimocephalus resembles Iddingsia in having a prominent glabella with deep posteriorly directed gla- bellar furrows. It differs from Iddiugsia primarily in having the border greatly extended anteriorly. pernasutus Walcott, Dokimocephalus pernasutus (Walcott) Plate 11, figures 18, 20 Ptychopari'a? pernasutus Walcott, 1884, p. 49, pl. 10, figs. 8, 8a—b. Dokimocephalus pcrnasutus (Walcott). Walcott, 1924, p. 55, pl. 11, fig. 1; 1925, p. 84, pl. 16, figs. 29—31. Z’Dokimocephalus gregori Walcott, 1925, p. 84, pl. 16, figs. 32—33; Shimer and Shrock, 1944, pl. 264, figs. 38, 39. Diagnosis—Members of Dokimocephalus with border forming a pointed snout with concave sides and with tip curved down at end. Discussion—This species is represented by 2 frag— mentary cranidia and 1 free cheek that are inadequate for the preparation of a description of the species characteristics. Neither cranidium has its fixed cheeks, lateral margins, or external surface preserved. The free cheek is also exfoliated. Only one cranidium, the holotype, retains the distinctive pointed snout. D. gregom' VValcott, from Missouri, may be conspe- cific with D. pcrnasutus. It has a nearly identical shape to the border and differs only slightly in observ- able proportions of other cranidial features. Until better material of I). pernasum is obtained, such a synonymy cannot be definitely established. Occurrence: Rare, upper beds of Dunderberg shale; unit D. USNM loc. 61. Figured specimens: Holotype cranidium, USNM 2460821. Paratype free cheek, USNM 24608b. Genus IDDINGSIA Walcott Iddiugsic Walcott, 1924, p. 58; 1925, p. 97; Shimer and Shrock, 1944, p. 627. Bell, and others, 1952, p. 184. T ype species.—Ptychoparéa similz's Walcott, 1884, p. 52, pl. 10, fig. 10. Diagnosis.—Cranidium with prominent glabella bearing 1 or 2 pairs of deep glabellar furrows. Frontal area expanded anteriorly, length between .1/2 and 2/3 that of glabella; subequally divided into brim and border. Fixed cheeks generally upsloping, narrow; eye ridges prominent; palpebral lobes well defined, strongly bowed. Posterior limbs narrow (exsagittal) tapered to sharp point. Free cheek with deep lateral and posterior marginal furrows and long posterolaterally directed cylindrical genal spine. Pygidium transverse subtriangular in outline. Axial lobe prominent, slightly tapered, reaching to inner edge of poorly defined narrow border that is nearly absent on axial line. Description—Medium to large trilobites (up to about 90 mm in length) with cranidium bearing prom- inent glabella well defined by dorsal furrow that is deep at sides, slightly bowed outward, and deep or shallow across front of glabella. One or two pairs of short deep posteriorly directed glabellar furrows always present. Occipital furrow broad, deep, deep- est adjacent to dorsal furrow. Occipital ring gener- ally with median node, rarely with median spine. Frontal area long (sagittal); length about two-thirds that of glabella; subequally divided into downsloping to depressed brim and gently downsloping to horizon- tal, concave, flat, or slightly arched border by shallow marginal furrow or sharp change in slope. Marginal furrow generally comes to blunt point on axial line. Fixed cheeks upsloping to elevated, bearing distinct posterolaterally directed eye ridges; width between 1A), and 1/2 that of glabella. Palpebral lobes strongly bowed, well defined by deep palpebral furrow; length between 14:, and 1/2 that of glabella; width 1/3 to 14 that of fixed cheeks. Posterior limbs narrow (exsagit- tal), dominated by broad deep posterior marginal furrow; tapered to sharp point; length (transverse) slightly less than basal glabellar width. Anterior course of facial suture divergent from palpebral lobe to inner edge of border, then angled inward across border to cut anterior margin in front of fixed cheek. Posterior course strongly divergent- sinuous. Free cheek subtriangular in outline with broad flat or slightly arched border well defined by deep lateral marginal furrow. Lateral marginal furrow may or may not be connected to deep posterior marginal fur— row. Genal spine long, large, cylindrical, straight, or 96 slightly curved, directed posterolaterally at slight an- gle to margin of check. Pygidium transversely subtriangular in outline; axial lobe prominent, gently tapered posteriorly, bluntly rounded, extended to inner edge of border. Three or four distinct ring furrows present. Pleural platforms flat or slightly arched, bearing 1 or 2 shal- low pleural furrows. Border narrow, poorly defined, tapered towards axial line, nearly absent behind axial lobs. Thoracic segments and hypostome not known. Discussion.——lddingsz'a was proposed by Walcott (1924, 1925) to include Ptychoparia similis Walcott and Ptychopam‘a sz'rmih's robusta \Valcott known only from cranidia in collections from the Eureka district, Nevada. A brief statement of the generic character- istics was given at that time. No subsequent descrip— tion of the genus has been presented until now. Mean- while, Kobayashi (1938) added I. concava and Resser (1942a) added nine new species, I. alpersensis, I. (ma— timz, I. bicz'ncta, I. ems.9z'nmrginata, I. missoum'ensis, I. nevadensz's, I. simplicims, I. utahensz's, and I 9 quin- nensis. Wilson (1949) proposed a new genus, Planta- spella, typified by I. (matina, to include five of Resser’s species that differed from I. similis (Walcott) by pos- sessing an occipital spine, shallow glabellar furrows, and “a much more flattened and laterally expanded border and brim which lack the convexity of those Iddz'ngsia.” Later, Wilson (1951) reported intergra- dation of features formerly thought to be distinctive of I ddé’ngsia or Plataspella but continued to recognize Plataspella, as a distinct genus. Bell, F eniak, and Kurtz (1952, p. 184) concluded that “the characters used by Wilson to separate Plataspella from I ddingsia are not generically significant * * *” and made Plata- spella. a subjective junior synonym of Iddingsia. Lochman (1953) concurred with this conclusion. Since then, one additional species, I. occidentalis Deland and Shaw (1956), has been added to the genus. To prepare a description of I ddingsz'a. and determine its characteristics, type material for all the species assigned to Iddz'ngxm except I. occidentalis Deland and Shaw has been reexamined. In this complex of trilobites, the texture of the external surface of the cranidium, as in the Elviniidae, is the most reliable primary feature for difl“erentiation of species. “lithin any one collection, all cranidia have the same external surface texture. None of the collections are large enough to provide adequate statistical basis for many of the slight difiereiices in shape cited as distinctive for various species of the genus. Although some of the characters given by \Vilson for Plataspella do not seem important as generic characters, there is a group of trilobites, including P. (”Latina (Resser), that lack conspicuous glabella furrows and differ among them- ‘SI-IORTER CONTRIBUTIONS TO GENERAL GEOLOGY selves in surface texture. They also generally have an occipital spine and nearly horizontal fixed cheeks. In the light of what has been learned during this study about the taxonomic importance of shape and surface texture in the better represented trilobite groups in the Dunderberg shale, the trilobites resembling P. anatina (Resser) and bearing the characters cited above are here considered to represent a separate genus from those resembling I. similz's. Only I ddingsia is repre— sented in the Dunderberg faunas. As now constituted, Iddz'ngsia, includes four de- scribed species with the following primary distinguish- ing external textural characters on their cranidia: I. similis (VValcott), top of glabella and occipital ring covered with close-spaced moderately coarse granules, fixed cheeks and frontal area smooth; I. robusta (VVal- cott) (syn. I. nevadensis Resser), entire cranidium covered with close-spaced generally small granules of several sizes; I. utahensis Resser, surface of entire cranidium smooth though top of glabella faintly rough- ened; I . missouriensis Resser (syn. I. crassz'marginata Resser), glabella and occipital ring covered with low coarse granules, frontal area covered with close-spaced fine pits, fixed cheeks with both fine pits and low coarse granules. Precise stratigraphic placement of I. utahensis and I. missoum'ensis within the E lm’m’a fauna is not yet known. I. similis occurs with other trilobites known only in association with Irvingella (Irvingella) major Ulrich and Resser in the basal beds of the Windfall formation which overlies the Dunderberg shale. Id- dingsM mbusta is associated with trilobites known only in association with Kindbladia, and [Wingella (Pamz'r- oingella) in the upper beds of the Dunderberg shale. The specimen identified by Bell, Feniak, and Kurtz as I. similis (1952, pl. 30, fig. 4b) may represent a fifth species of I ddingsz'a characterized by an occipital spine. The other specimen identified as I. similz's by Bell, Feniak, and Kurtz (1952, pl. 31, fig. 2) repre- sents a species of Plataspella. Species relationships of the remaining specimens of I ddingsia illustrated by Bell, Feniak, and Kurtz (1952), I. nevadensis illus- trated by Wilson (1949), and I. occidentalis Deland and Shaw (1956) cannot be made without knowledge of their external surface textures. Iddingsia concava Kobayashi is represented by a single specifically inde— terminate cranidium. I 7 guinnensis Resser belongs to Sigmocheilm n. gen. (p. 90). Iddingsia robusta (Walcott) Plate 11, figures 13—16 l’fychoparia similia robustus Walcott, 1884, p. 53, pl. 1, figs. 9, 9a. 1ddingsia robusta (Walcott). 1041. [ddmgsia nevadensis Resser, 1942b, p. 85, pl. 16, figs. 15-17. Walcott, 1924, p. 97, pl. 16, figs. TRILOBITES‘ OF THE UPPER CAMBRIAN Diagnosis—Members of I ddz'ngsz'a with dorsal fur— row generally shallow across front of glabella. Length of frontal area slightly greater than one-half length of glabella. Brim and border separated by abrupt change in slope. Border nearly flat, slightly down- sloping. Fixed cheeks upsloping; width about one- third basal glabellar width. Occipital ring with low median node. External surface covered with close- spaced generally small granules of several sizes. Some of the granules along brim arranged in rows parallel- ing veination. Discussion—This species is represented only by cra- nidia. It differs from I . similz's (Walcott) from the overlying Windfall formation by having a granular rather than smooth surface on the brim and border. Exfoliated specimens of the two species cannot be identified or differentiated with certainty. Iddz'ngsia neoadensis Resser is represented by one nearly completely exfoliated specimen that retains a small piece of the granular external surface of its border, and is not significantly diflerent in any respect from I . robusta. Occurrence: The holotype is associated with Bynumina globosa (Walcott), a species known only from the upper beds (unit D) of the Dunderberg shale. Figured specimens: Holotype cranidium USNM 24609, USNM 10c. 61; plesiotype cranidium, USNM 136924, USNM loc. 62; I. ncvadens'is holotype, USNM 108796, USNM Ice. 61. Genus KINDBLADIA Frederckson, 1948 Kimlblatliu. Frederickson. 19-18. 1). 802. T ype species.—Berkcia wiehitaensis Resser, 1942b, p. 93, pl. 15, figs. 31, 33. Discussion—A good description of this genus was given by F rederickson (1948) on the basis of abundant material from the Honey Creek formation in Okla- homa. The genus is represented in the Dunderberg shale by a single species, If. afinis (Walcott), known only from cranidia. Resser (1942a, p. 7) included K. afinis in Berkeia without stating reasons why he had changed his earlier assignment of the species (Resser, 1937, p. 14) to Iddz'ngsz'a. This species and most of the other species assigned to Ber/rem by Resser (1942b) differ from the type species of Ber/hem, B. typica Resser, by having more strongly arched and upsloping fixed cheeks and by having three shallow depressions in the marginal furrow. F rederickson (1948) included species with these characters in his new genus Kindbladia. This genus can be distinguished from all others in the Dun- derberg fauna by its prominent anteriorly tapered glabella, strongly rounded in front and bearing two deep pairs of glabellar furrows; deep dorsal furrow; narrow upsloping convex fixed cheeks; and short sub- equally divided frontal area with three shallow de- pressions in the marginal furrow. DUNDERBERG SHALE, EUREKA DISTRICT, NEV. 97 Kindbladia affinis (Walcott) Plate 11, figures 17, 19, 20 Ptychoparz'a (Euloma?) afiim’s Walcott, 1884, p. 54, pl. 10, fig. 12- Iddingsia afiim‘s (Walcott). Resser, 1937, p. 14. Berkeia afiinis (Walcott). Resser, 1942a, p. 7. Berkeia comes Resser, 1942b, p. 90, pl. 15, figs. 18—21. Berkeia nevadensis Resser, 1942b, p. 91, pl. 15, figs. 26, 27. Diagnosis—Members of Kindbladia with occipital ring bearing median node rather than median spine. I)escm'pf2'0n.—Small to medium—sized trilobites (probably about 20 mm in total length) with cranid— ium having prominent anteriorly tapered glabella, strongly rounded in front, with slight keel on axial line. Two pairs of short deep glabellar furrows gen- erally present; posterior pair strongly curved back— ward. Dorsal furrow deep around entire glabella. ()ccipital ring well defined by deep occipital furrow; bears prominent median node. Frontal area short; length about two-fifths that of glabella; subequally divided by deep marginal furrow into brim and bor- der both moderately to strongly convex and slightly downsloping on axial line. Marginal furrow broadly curved in dorsal view; depressions in marginal furrow shallow, most apparent on exfoliated specimens. Fixed cheeks moderately to strongly arched, upsloping from dorsal furrow, narrow; width slightly less than one- fourth basal glabellar width. Palpebral lobes well defined by palpebral furrow; width slightly more than one-half that of cheek; length about two-fifths that of glabella. Posterior limbs tapered to a point laterally, downsloping; length (transverse) slightly less than basal glabellar width. Posterior marginal furrow deep, nearly straight. Anterior course of facial su- ture slightly divergent forward from palpebral lobes to marginal furrow, then curved strongly across bor- der and apparently submarginal to axial line. Poste- rior course divergent, sinuous. External surface cov- ered with fine close-spaced granules. Thoracic segments, free cheeks, pygidium, and hy— postome not known. Discussion—Nearly all the cranidia of Kindbladia aflfm's and those in the type lots of the other species of Kindblaa’ia are exfoliated. This tends to emphasize the depth of all the furrows and limits comparison of the described species. One of the rare specimens of K. afinz’s retaining its external surface is illustrated (pl. 11. fig. 17). No consistent distinction can be made between the specimens, mostly exfoliated, in the type lots of If. afim’s, Berklcia. nevadenwis Resser, and B. comes Resser. They are here considered conspecific, and represent a species differing from K. w'z'chitaensis (Resser) and K. retum (Resser) by lacking an occipital spine. Occurrence: Moderately rare, 230 ft or more above base of Dunderberg shale; unit D. USGS colln. 2303—00. 98 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY Figured specimens: Holotype cranidium, USNM 24642, USNM 10c. 65. Plesiotype, USNM 136925, USNM loc. 61. Holo- type of K. nevadensis (Resser), USNM 108788a, USNM 10c. 61. Genus MINUPELTIS n. gen. Type species.—Mz'nupeltis conservator n. sp. Diagnosis—Small trilobites with subquadrate cra- nidium having glabella well defined only at sides; not defined across front. No distinct glabellar furrows. Occipital furrow straight, deepest on axial line. Fron— tal area with moderately well defined strongly arched (sagittal) border; inner part nearly horizontal, outer part nearly vertical. Fixed cheeks gently arched, down- sloping; palpebral lobes small about opposite glabel— lar midlength. Posterior limbs short; length about two-thirds basal glabellar width. Anterior course of facial sutures straight forward from palpebral lobes to marginal furrow, curved inward across border to cut anterior margin in front of glabella. Description—Small trilobites (total length proba- bly less than 10 mm). Cranidium subquadrate in outline, gently arched transversely and longitudinally. Glabella prominent, well defined at sides by shallow dorsal furrow, not defined across front. Sides slightly bowed. Glabellar furrows not apparent. Occipital furrow straight, narrow, deepest on axial line. Fron— tal area downsloping; length (sagittal) slightly less than one-half length of glabella, subequally divided into brim and border. Border well defined by broad shallow marginal furrow; strongly arched in profile, inner part nearly horizontal, outer part nearly verti— cal. Brim not differentiated from front of glabella. Fixed cheeks gently arched, downsloping; width about one-third basal glabellar width. Palpebral lobes hardly differentiated from cheek, situated about Oppo- site glabellar midlength; length about one-third that of glabella. Posterior limbs short, bluntly pointed; length (transverse) about two-thirds basal glabellar width. Posterior median furrow straight, shallow. Anterior course of facial suture nearly straightfor- ward from palpebral lobes to marginal furrow, then curved abruptly inward across border to cut anterior margin between axial line and point OppOsite ante- rolateral corner of glabella. Posterior course of facial suture divergent from palpebral lobe, slightly bowed outward. Free cheek, hypostome, thoracic segments, and pygidium not known. External surface of all parts smooth, shiny on well— preserved specimens. Discussion—This distinctive trilobite is moderately common in the lowest collection from the Dunderberg shale. It does not resemble closely any described Up— per Cambrian trilobite from western North America, or any other trilobite from the Aphewspis, Dunder— bergia, or E lvz'm'a faunas. The overall form of the cranidium, except for the anterior course of the facial sutures, is similar to that of simple Lower Cambrian ptychoparioids like Crassifimbrd (Palmer, 1958) ; hence the species name, conservator. The subequally divided frontal area, slightly bowed sides to the glabella, and small poorly defined centrally located palpebral lobes indicate possible affinities to solenopleurid trilobites, such as species of Parasolenopleura (Westergard, 1953). leimopeltis differs from similar Lower Cam- brian trilobites primarily by having the facial sutures cutting the anterior margin nearer the axial line; it differs from similar solenopleurid forms by having the front of the glabella not defined and by having the border strongly arched in longitudinal profile. Minupeltis conservator n. sp. Plate 10, figures 11, 12 Description—This is the only species presently known in Minupeltz's, and the description of the genus also gives the characters of the species. Disei,¢ssi0a.—One cranidium in the type lot (pl. 10, fig. 12) is an unusual pathologic specimen on which the right side is not so well developed as the left. This is particularly noticeable on the posterior limb and at the right anterolateral corner of the cranidium. Occurrence: Moderately common, lower 20 ft of Dunder- berg shale; unit A. USGS colln. 2294—00. Figured specimens: Holotype cranidium. USNM 136905, USGS colln. 2294—00. Paratype pathologic cranidium, USNM 136906, USGS colln. 2294—00. Genus MOROSA n. gen. Text figure 22 Type species.——Morosa longispina n. sp. I)iagnosis.—Housiidae? with axial length of frontal area slightly less than one—third glabellar length. Frontal area subequally divided into well-defined brim and border. Border tapered laterally to a point just before reaching anterolateral corner of cranidium. Anterior margin in front view nearly horizontal; course of marginal furrow in front view strongly bowed upward. (n‘rlabella well defined. Glabellar fur- rows hardly visible. Fixed cheeks narrow, gently arched upward, nearly horizontal; width slightly less than one-fourth basal glabellar width. Palpebral lobes prominent, situated anterior to midlength of gla- bella. ()ccipital ring with prominent median node. Free cheek with narrow border. Marginal furrow distinct at anterior margin, disappears posteriorly. Gena] spine broad at base, flat, tapered to sharp point. Inner and outer margins straight. Pygidium with prominent axial lobe extending to inner edge of moderately .wide, slightly concave, poorly TRILOBITES OF THE UPPER CAMBRIAN DUNDERBERG SHALE, EUREKA DISYI‘RICT, NEV. 99 defined border that maintains nearly constant Width along entire pygidial margin. External surface of exoskeleton except areas of muscle attachment covered with distinct pits. Sur— faces of pleural lobes and axial lobe of pygidium also bear low fine granules. Surface of mold smooth or pitted. Marginal parts of cephalon and pygidium with prominent terrace lines. FIGURE 22.——Partia1 reconstruction of Morosa longispina n. sp.. about X 15. Description—Generally small trilobites (length probably less than 20 mm) with cranidium having well-defined straight-sided anteriorly tapered glabella, truncate anteriorly. Dorsal furrow deepest at sides and anterolateral corners of glabella, somewhat shal- lower across front. Occipital furrow straight, deep— est at side of glabella, shallow on axial line. Occipital ring with prominent median node. Glabellar furrows generally not apparent. Frontal area short, depressed; length (sagittal) slightly less than one—third glabellar length. Border well defined, downsloping. tapered laterally to a point just before reaching the ante- rolateral corners of the cranidimn. Course of mar- ginal furrow when viewed from the front, strongly bowed upward. Length (sagittal) of border slightly greater than length of brim. Fixed cheeks narrow, gently arched upward. nearly horizontal. \Vidth slightly less than one—fourth basal glabellar width. Short poorly defined eye lines present. Palpebral lobes well defined by nearly straight shallow palpebral furrow; width slightly more than one-half width of fixed cheek; length slightly less than one-half length of glabella. Posterior limbs slightly backswept; slightly shorter (transverse) than basal glabellar width. Posterior marginal furrow deep. Facial su- tures divergent anteriorly from palpebral lobe almost to marginal furrow, then curved sharply inward across marginal furrow and border to cut anterior margin near, but not at, axial line. Submarginal course not known. Thoracic segments and hypostome unknown. Free cheek with ocular platform well defined along anterolateral and posterior margins, merges poste- rolaterally with genal spine. Border narrow; width at anterior margin between 1/3 and 14 width of ocular platform. Lateral marginal furrow distinct but shal— low at anterior margin, disappears posteriorly. Pos— terior marginal furrow deep at junction with posterior limb, disappears laterally. Genal spine broad at base, flat, tapered to a sharp point. Outer and inner mar- gins straight. Length about two-thirds length of ocu- lar platform. Pygidium with prominent posteriorly tapered axial lobe bearing three conspicuous ring furrows and ex- tending to inner edge of poorly defined border. Pleu- ral platform triangular, crossed by 1 or 2 pleural fur- rows that do not extend onto border. Border slightly concave, maintains nearly constant width along pygid- ial margin. Posterior margin smooth. Surfaces of all known parts of exoskeleton except muscle-scar areas on cranidium are covered with nu- merous distinct pits of variable size. Prominent ter- race lines on margins of cephalon and pygidium. Pleural platform and axial lobe of pygidium with low poorly defined granules. Discussion—This distinctive genus is represented by only a single rather common species that has no apparent ancestors or descendants in the Dunderberg shale fauna. It may belong to the Housiidae because of the anteriorly placed palpebral lobes on the cranid- ium and the even width of the pygidial border. How- ever, the character of the frontal area and the dis— tinct palpebral furrows are not typical of the family, and the genus is not here assigned to any family or subfamily. Morosa longispina n. sp. Plate 10, figures 15—17 Diagnoses—As this is presently the only described species of Momsa, the diagnOsis is the same as that for the genus. Discussion.—~The range of this abundant, species is sufiiciently restricted to mark a distinctive faunal sub- zone within the Dunderberg shale. A second species of this genus is known, but not yet described, from the basal beds of the Nopah formation in California. It differs from HI. lowgz’spina principally in having 100 much shorter genal spines and a relatively broader free cheek. Occurrence: Abundant, 40—100 ft above base of Dunder- berg shale; unit B. USGS colln. 795-00, 873—00, 2296—00, 2298—00—2300-00. Figured specimens: Holotype cranidium, USNM 136909, USGS colln. 2299—00. Paratypes, pygidium and free cheek USNM 13691021, b, USGS colln. 2299—00. Genus OLIGOMETOPUS Resser Oligometopus Resser, 1936, p. 28. Type species.—Ptychopariu (Solencpleura?) brevi- ceps VValcott, 1884, p. 49, pl. 10, fig. 9. Diagnosis—Small trilobites with cranidium having well—defined anteriorly tapered glabella reaching to marginal furrow. Border straight, thickened, nearly vertical. Fixed cheeks moderately arched, slightly downsloping; width about one-half basal glabellar width. Palpebral lobes small, narrow. situated below level of cheek about on line through glabellar mid- length. Posterior limbs short; length (transverse) less than basal glabellar width. External surface of cranidium covered with low coarse granules. Free cheek, hypostome, thorax, and pygidium not known. Description—Small trilobites (length of cranidium about 4 mm) with cranidium subquadrate in outline, anterior margin nearly straight. Glabella prominent, well defined by broad dorsal furrow. straight sided, tapered forward, bluntly rounded anteriorly, extended to marginal furrow. Three pairs of broad shallow glabellar furrows visible. Occipital furrow deep, deepest, adjacent to dorsal furrow. Occipital ring broken on known specimens, shape not known. Fron- tal area made up entirely of narrow border that is thickened and nearly vertical along entire anterior margin. Fixed cheeks broad, moderately arched up— ward, slightly downsloping; width about one-half basal glabellar width. Low ocular ridges extend obliquely outward and backward from junction of glabella with marginal furrow. Palpebral lobes well defined, small, situated below general level of cheek about on line through glabellar midlength: length about one—third that of glabella; width about one-fifth that of cheek. Posterior limbs short, bluntly termi— nated; length (transverse) less than basal glabellar width. Posterior marginal furrow broad, deep, straight. External surface of all parts except bor— der and furious covered with low coarse granules. Border bears conspicuous terrace lines. Anterior course of facial suture slightly conver- gent forward from palpebral lobe to marginal fur- row, then turned abruptly inward and nearly straight across border to cut anterior margin near anterolateral corners of cranidium. Posterior course directed lat— erally in a broad curve to posterior margin. SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY No other parts of exoskeleton known. Discussion—This rare genus seems to have aflinities to asiatic genera, such as Chuangz'a and Pagodia, which also have broad fixed cheeks and a glabella that reaches to, or nearly to, the marginal furrow. Oli- gometopus differs from the asiatic genera either in the shape of the glabella or of the frontal area. No American or other foreign genera can be easily con- fused with OZ-igoonetopus. The placement of this genus in a family and adequate comparison with known genera must await knowledge of other parts of the exoskeleton. Oligometopus breviceps (Walcott) Plate 10, figures 19, 20 Piychoparia (Solenopleuro?) breviceps Walcott, 1884, p. 49, pl. 10, fig. 9. ()ligometopus brem‘ceps (Walcott). Stcnelymus breviceps (Walcott). Resser, 1936, p. 29. Raymond, 1937, p. 1101. Discussion-.—Raymond’s reference of this species to Stenciymus seems to have been based on inadequate knowledge of the holotype. The shapes of the fixed cheeks, glabella, and frontal area are unlike those in Stenelj/mus. Recently, Lochman (1953, p. 888) con- sidered Stenclymus a synonym of Genevievella, a genus that is entirely unlike Oligmncz‘cpus in its critical diagnostic features. Besides the holotype, only one other cranidium of ()Zigometopus is known. This specimen shows that the species had a granular external cranidial surface rather than a smooth surface as stated by “’alcott. The holotype, which has most of its external surface damaged, shows the g‘anules on the posterior limbs. Occurrence: Rare, 140 ft or more above base of Dunder- berg shale; units C, D. USGS colln. 954—00. Figured specimens: Holotype, USNM 24577, USNM loc. 62. Plesiotype cranidium, USNM 136913, USGS colln. 954—00. Genus PINCTUS Wilson Type species—Pinctus lutus \Vilson, 1951, p. 646, pl. 93, figs. 1—4. 15. Description—This genus was described by Wilson (1951, p. 646). (i‘ranidium small and bluntly triangular in shape, moderately convex with well-developed furrows. Glabella very long, prom- inent, convex, and quadrate with three pairs of well-impressed oblique furrows; occipital ring posteriorly extended at axis. Brim reduced and depressed; border prominent, widely arcu- ate, and considerably tapered; brim: border ratio about 1 or less. Fixed cheeks downsloping, moderately wide (ratio 2 or less) ; palpebral lobes small and thin, slightly anterior; poste- rior limbs broad and extended. Facial suture intramarginal almost to axis, beginning to di- verge already just behind anterolateral corner, indenting but slightly at each end of palpebral lobe, and sweeping outward behind it enough to give cranidium a wide base. TRILOBITES OF THE UPPER CAMBRIAN DUNDERBERG SHALE, EUREKA DISTRICT, NEV. Pinctus? spp. Plate 10, figures 18, 21 Three small cranidia represent two species of a trilobite possibly related to Pincutus Zdtus Wilson. The cranidia are characterized by a prominent gla- bella; small anteriorly placed palpebral lobes; broad arched horizontal or slightly downsloping fixed cheeks; and a well—defined border about equal in length (sag- ittal) to the brim. Two of the cranidia, from USGS collection 952—CO, have the palpebral lobes distinctly defined, distinct glabellar furrows, and a border that is of nearly constant width across much of the front of the cranidium. The third cranidium, from USGS collection 953—CO, has undefined palpebral lobes, shal- low, hardly apparent glabellar furrows, and a border that tapers rapidly laterally from the axial line, much like that of Morosa longispind n. sp. Both species differ from Pinctus Zatus in having smooth rather than fine-granular external surfaces and in having broader and shorter glabellas. Certain generic and specific identification of these trilobites must await more knowledge of the small trilobites in the Dunderberg and related faunas. Occurrence: Rare, 60—120 ft above base of Dunderberg shale; units, B, C. USGS colln. 952—00, 953—00. Figured specimens: Cranidium, USNM 136911, USGS colln. 952—00; cranidium, USNM 136912, USGS colln. 953—00. Genus PSEUDOSARATOGIA Wilson 1951 Pseudosaratogid Wilson, 1951, p. 647. Type species.—Pseudosarat0gz'a magna Wilson, 1951, p. 648, pl. 94, figs. 9~16. Diagnosis.—Elviniidae? with flaring frontal area on cranidium; axial length of border about one—half or less axial length of brim. Discussion—A complete description of this genus was given by Wilson (1951). Specimens of Pseudo- 8drdtoge’a are rare in the Dunderberg shale and do not provide any new information concerning the mor- phology of the genus. The two species here described have a rounded glabellar front and nearly horizontal cheeks, similar to Pseudosaratogia lam Wilson from the Ore Hill limestone member of the Gatesburg for- mation in central Pennsylvania. This species was considered a somewhat aberrant form by lVilson (1951). The palpebral lobes are also somewhat smaller than those of the Pennsylvania species. Nevertheless, the overall characteristics of the cranidia are more suggestive of I’seudosawztogm than other genus. Pseudosaratogia leptogranulata n. sp. Plate 11, figure 10 Diagncafe—Specimens of Paeudosarutogz’a with cranidium bearing prominent glabella that is bluntly 101 rounded anteriorly. Marginal furrow deep, narrow. Axial length of border slightly more than one-half that of brim. External surface exclusive of furrows and palpebral lobes covered with fine granules. Sur- face of mold pitted. Discussion—This species is represented by six cranidia in USGS collection 954—00. It is most simi- lar to Pseu-dosaratogi‘a lam Wilson (1951) but differs by having a more prominent glabella, a deep margi- nal furrow, and finer granular ornament present only on the external surface of the cranidium. Two cra- nidia in USGS collection 953—CO have the same shape as P. Zeptogranulata, but one is nearly smooth and the other has distinct and abundant coarse and fine granules on its external surface. The specimens are questionably assigned to this species. Occurrence: Rare, 120—150 ft above base of Dunderberg shale; unit 0. USGS colln. 953—CO(?), 954—00. Figured specimen: Holotype cranidium, USNM 136922, USGS colln. 954—00. Pseudosaratogia abnormis Palmer n. sp. Plate 11, figure 11 Diagnosis—Specimens of Pseudosarato-gz'a with ax- ial length of border about one—third that of brim; border separated from brim by abrupt change in slope; length (exsagittal) of palpebral lobes about one-third length of glabella exclusive of occipital ring; surface of cranidium covered with moderately coarse granules. Discussion—A single cranidium from a collection about 60 feet above that bearing P. Zeptogranulata n. sp. has the characteristic flared frontal area, nar- row upturned border separated from the brim more by a change in slope than by a marginal furrow, nar- row fixed cheeks, posteriorly placed palpebral lobes and granular external surface characteristic of species of Pseudosaratogz'a. It lacks conspicuous glabellar furrows, it has a shorter palebral lobe, and the gla- bella is more strongly arched longitudinally than any of the Pennsylvania species described by Wilson (1951). This species differs from P. Icptogranulata by hav- ing shorter (sagittal) border, less well-incised margi- nal furrow, and stronger surface granulation. Occurrence: Very rare, about 220 ft above base of Dunder- berg shale; unit C. USGS colln. 955—00. Figured specimen: Holotype cranidium, USNM 136923. Genus and species undetermined 1 Plate 11, figures 2, 5, 6 Two cranidia from USGS collection 2297—CO rep- resent a trilobite unlike any other described from the Dunderberg or related faunas. It is characterized by low cranidial relief; a nearly parallel-sided squarely 102 truncate glabella bearing three pairs of broad short deep slotlike glabellar furrows that are isolated from the dorsal furrows; an anteriorly flared frontal area with a narrow border of nearly constant width; and wide fixed cheeks bearing large well-defined arcuate palpebral «lobes. A third cranidium (pl. 11, fig. 5) in this collection probably is congeneric and perhaps conspecific with the forms described above. It differs from them prin- cipally by having the glabellar furrows marked by broad and shallow rather than deep depressions. Proposal of new names is deferred until more ma- terial can be obtained to determine more clearly the relationships of these cranidia. Occurrence: Rare, 50—60 ft above base of Dunderberg shale; unit B. USGS colln. 2297-00. Figured specimen: Cranidia, USNM 136915a—c. Genus and species undetermined 2 Plate 11, figure 1 A cranidium from USGS collection 2295—CO rep— resents a species that is most similar to genus and species undetermined 1. This species is characterized by low relief on the cranidium, an expanded frontal area with a narrow raised border, a straight-sided slightly tapered truncate glabella, and broad fixed cheeks bearing large well-defined arcuate palpebral lobes. It differs from genus and species undetermined 1 by having a raised rather than flattened border, an anteriorly tapered glabella, and somewhat more pos- teriorly placed palpebral lobes. Occurrence: Rare, 40—50 ft above base of Dunderberg shale; unit A. USGS colln. 2295—00. Figured specimen: Cranidium, USNM 136914. Genus and species undetermined 3 Plate 11, figure 3 An incomplete but distinctive elongate pygidium from USGS collection 2297—CO cannot be assigned to any described trilobite from the Dunderberg fauna. It has a long slender well-defined axial lobe bearing 8 ring furrows becoming shallower posteriorly; elon- SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY gate downsloping pleural lobes bearing 6 shallow pleural furrows; and a narrow concave poorly de- fined border. The posterior margin is curved sharply upward and inward to the axial line forming an in- verted V when viewed from the rear. This pygidium shows mOst similarity to that of Cliffiu Zutagenae (\Vilson) from the Ore Hill lime- stone member of the Gatesburg formation in central Pennsylvania. It differs by possessing a narrow bor- der and by lacking median nodes on each segment of the axial lobe. Occurrence: Very rare, 50—60 ft above base of Dunder- berg shale; unit B. USGS colln. 2297-00. Figured specimen: Pygidium, USNM 136916. LOCALITY INFORMATION The collections referred to in this paper are cata- logued under 1 of 2 sets of numbers except for the collections studied by Hall and thitfield (1877). These were listed only as coming from the Eureka district without more precise locality data. They have never been given locality numbers. Many of the collections obtained from the Eureka district before 1900 are listed in the US. National Museum locality catalogue. Specimens from these collections bear green paper circles with handwritten locality numbers. Collections since 1939 by the U.S. Geological Sur- vey are listed by collection number in the USGS Cambriail—Ordovician locality catalogue. Specimens from these collections bear orange paper circles or rectangles with machine-printed collection numbers. USGS collection numbers referred to in the text bear the suffix “—CO” to differentiate them from a parallel series of numbers in the Silurian—Devonian (suffix “—SD”) locality catalogue. Unless otherwise indicated in the list below, the collections are from the Eureka mining district, Eu- reka County, Nev. Most of the geographic features that are referred to in the locality descriptions are shown on the Eureka and Pinto Summit (15-minute) quadrangles. Exact location of the measured section is shown in figure 6. USGS collection Locality description and collector USGS collection Locality description and collector 789—00 ,,,,,,,,, From limestone in the Dunderberg shale, about 200 ft above the Hamburg dolomite. In place. 2,050 ft S. 18 E. of the Hamburg shaft. Elev 8,025. Josiah Bridge, 1939. 795—C0 ,,,,,,,,, Near base of Dunderberg shale on road to Catlin shaft, about 250 ft from New York Canyon road. In place. 760 ft S. 29 E. of the Catlin shaft. Elev 7,480 ft. Josiah Bridge, 1939. 809—C0 __________ Southwest slope of Hoosac Mountain, east of the high pinnacle of Hamburg dolomite. East of spring in tributary of Secret Canyon. In place. 4,980 ft S. 5 E. of the Windfall shaft. Elev 8,075 ft. Josiah Bridge, 1939. North side of Widewcst Canyon. 900 ft N. 55 E. of Cyanide shaft. Elev 6,470 ft. Josiah Bridge, 1939. 864700 ,,,,,,,,, TRILOBITES OF THE UPPER CAMBRIAN DUNDERBERG SHALE, EUREKA DISYI‘RICT, NEV. 103 USGS collection Locality description and collector USGS collection Locality description and collector 872—CO _________ 873—CO _________ 952—00 _________ 953—00 _________ 954—CO _________ 955—CO _________ 1197—00 ________ 1297—CO ________ 1436—CO ________ 1441-CO ________ 2294—CO ________ Dump of prospect 1,350 ft N. 64 W. of USMMl 10, near Bullwhacker mine. (Northern 1 of 2 prospects close together.) Elev 6,327 ft. Josiah Bridge, 1939. Dump of prospect 1,300 ft S. 74 W. of USMMl 10 (near Bullwhacker mine). Elev 6,365 ft. Josiah Bridge, 1939. Dunderberg shale section, extending east of prospect pits, 500 ft north of Windfall shaft, Windfall Canyon, 67 ft above base of Dunderberg shale. A. R. Palmer and A. B. Shaw, 1951. Same locality as 952; 121 ft above base of Dunderberg shale. A. R. Palmer and A. B. Shaw, 1951. Same locality as 952; 144 ft above base of Dunderberg shale. A. R. Palmer and A. B. Shaw, 1951. Same locality as 952; 215 ft above base of Dunderberg shale. A. R. Palmer and A. B. Shaw, 1951. Nevada, White Pine County, Wheeler Peak quadrangle. Cambrian section on south side of the south fork of Lincoln Canyon, at junction with north end of Johns “’ash, irregular to nodular limestone with shale partings; 150 ft below top of Lincoln Peak formation. A. R. Palmer 1952. East side of Sierra Canyon, first baked shale outcrop seen after entering from the south. Josiah Bridge, 1939. Nevada, White Pine County, Wheeler Peak quadrangle. North trending canyon just below Johns Wash limestone, sec. 23, T. 12 N., R. 69 E. on south line of section at elev 7,080 ft. A. R. Palmer; 1953. Nevada, White Pine County, Wheeler Peak quadrangle. Cambrian section on south side of south fork of Lincoln Canyon at junction with the north end of Johns Wash; 150 it below top of Lincoln Peak formation. A. R. Palmer, 1953. Windfall Canyon section, north side of spur due east of New Windfall shaft, about 12 ft above Hamburg dolomite; 2-in. lime- stone bed. A. R. Palmer and R. J. Ross, 1957. 2295-CO ________ 2296—CO ________ 2297—00 ________ 2298—C0 ________ 2299—CO ________ 2300*C0 ........ 2301—CO ________ 2302—CO ,,,,,,,, 2303—CO ________ USNM locality 73 ______________ 61 ,,,,,,,,,,,,,, 62_,-,, ,,,,,,,,, 63 ,,,,,,,,,,,,,, 65 ,,,,,,,,,,,,,, Windfall Canyon section, about 30 ft above Hamburg dolomite; 8-in. limestone bed. A. R. Palmer and R. J. Ross, 1957. Windfall Canyon section, about 40 ft above Hamburg dolomite; 6-in. limestone bed. A. R. Palmer and R. J. Ross, 1957. Windfall Canyon section, about 55 ft above Hamburg dolomite; 2 ft below top of 10-ft limestone unit. A. R. Palmer and R. J. Ross, 1957. Windfall Canyon section, about 70 ft above Hamburg dolomite; 1-ft limestone bed. A. R. Palmer and R. J. Ross, 1957. Windfall Canyon section, about 77 ft above Hamburg dolomite; 2 ft above base of unit of 1- to 3-in. fine-grained limestone beds that crop out sporadically for about 20—25 ft. A. R. Palmer and R. J. Ross, 1957. Windfall Canyon section, about 90 ft above Hamburg dolomite; 10 ft below top of highest limestone in middle of Dunder- berg shale. A. R. Palmer and R. J. Ross, 1957. Windfall Canyon section, about 195 ft above Hamburg dolomite; 3-in. limestone bed. A. R. Palmer and R. J. Ross, 1957. Windfall Canyon section, about 75 ft below top of Dunderberg shale. A. R. Palmer and R. J. Ross, 1957. Windfall Canyon section, about 40 it below top of Dunderberg shale. A. R. Palmer and R. J. Ross, 1957. Limestones at the north end of the Quinn Canyon Range, 1 mile (1.6 km) northwest of the Italian Ranch foothills, Nye County, Nev. J. E. Spurr, 1899. A little south of the Hamburg mine, Eureka County, Nev. C. D. Walcott, 1882. In canyon just north of Adams Hill. Walcott. 1880. At the base of the Pogonip limestone north- east of Adams Hill. C. D. Walcott, 1880. Limestone 011 the east side of Sierra Canyon, opposite Pinnacle Peak. Arnold. Hague and J. P. Iddings, 1880. C. D. 1 U.S. mineral marker. REFERENCES CITED Barrande, Joachim, 1846, Note preliminaire sur le systeme silu- rien et les trilobites de Boheme: Leipzig. Bell, W. 0., Feniak, O. W., and Kurtz, V. E., 1952, Trilobites of the Franconia formation, southeast Minnesota: Jour. Paleontology, v. 26, no. 2, p. 175—198. Belt, Thomas, 1867, On some new trilobites from the Upper Cambrian rocks of North Wales: Geol. Mag, v. 4, p. 29-1— 295. Berg, R. R., 1953, Franeonian trilobites from Minnesota and Wisconsin: Jour. Paleontology, v. 27, no. 4, p. 553—568. Ber-key, C. P., 1898, Geology of the St. Croix Dalles: Am. Geol- ogist, v. 21, p. 270—294. Bridge, Josiah, 1933, in, Sellards, E. H., Adkins, W. S., and I’lummer, F. 1%., The geology of Texas, v. 1, Stratigraphy: Texas ['niv. Bull. 3232, p. 231—234. 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INDEX [Italic numbers indicate descriptions] A Page abnormis, Pseudosaralogia ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 101: pl. 11 Acknowledgments ........................................................... 55 Acrocephalaspis ............................................................. 74 acuminala, Bynurm‘ella. _. ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 55, 93; pl. 10 acutus, Homagnostus.._. .............................................. 62 Pseudaanostus _____ aflim’s, Kindbladia. Agnostus ________________________________ 56, 97—98; pl. 11 62, 63 cyclopwe ................... 6'1 pisifarmis ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 62-63 obesus ________________________________________________________________ 6‘9, m alata, Prehousia __________________________________________________________ 77, 78; pl. 7 alpersensis, Iddinasia ......................................................... 96 anatina, Iddingsz'u ____________________________________________________________ 96 Plataspella ............................................................. 96 Anechocephalus. . ________________________________ 84, 92 trigranulams. _ _ _ . Angulotreta triangular”: ,,,,,,,,,,,,,,,,,,, 90 angustilimbatus, Irvinqella (Parafm‘ngella) ....... .. 73, 74; pl. 6 anyta, Dunderbergia ____________________________________ 66 Crepicephalus (Logamllus) ________________________________________________ 66 Aphelaspidinae ______________________________________________________ 80—81 . 82—84 Aphelaspis ________________________________________________________ 56, 64, 78, 80, 90 tumi/rons,. _____________________________________________________________ 74 Aphelaspis zone____ 90 asiah’ca, Pterocephalia ________________________________________________________ 87 Maladiodes _______________________________________________________________ 64 B Baum bibullatus ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 63 Bell, W. C., quoted .......................................................... 96 Berkeia _______________________________________________________________________ 97 comes __________________________________________________________________ 97 nevadertsis _________ 97 typica .................................................................... 97 wichitaensis, . . . _ . ____________________________________________________ 97 bibullatus, Baum. _ _ _ ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 63 bicincta, Iddingsia, ,,,,, ... ______ 96 bigranulosa, Dunderbergia_ . . 56, 60, 6‘6—67; pl. 5 bilobata, Pterocephalina..._ . 90 bilobatus, Dikellocephalus ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 81 Litocephalus ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 58, 81, 82, 90; pl. 7 Brachiopods ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 55, 56 breviceps, ()ligometopas ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 100; pl. 10 Ptychoparia (Solenopleura) ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 100 bridyei, Pterocephalz‘a_. ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 87, 88 briscoensis, Bynumiella buttsi, Cheilocephalus Bynmneilla. . ________ acuminata ________________ briscoensis ________________ typicalis _________________________________________ 93 Bynumina ___________________________________ . 93—94 caelata ________________________ glabosa ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 56, 75, 94; pl. 10 mmsouricnsis _____________________________________________________________ 94 terremia ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 94 C caelata, Bymum‘na. _ .... ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 93, 94 canadensis. Dunderbergia..., ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 66 Housia ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, _ 75 Catlin member of the Windfall formation __________________________ Ceraurinella typo . . _ ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 76 Cernuolimbus ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 57, 58, 60, 86—85, 88, 90 depressus ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 86, 86; pl. 8 orygmatos. _ _ . ......................... . ...... 56, 60. 84. 86—86; pl. 8 semioranulasus. ....................................... 85, 86; pl. 8 Chariocephalus._ . _ . _ ............................. 64 tumijrons ................................................. 73 Cheilocephalus .......................... 94, 95 butlsh _ . , . ........................................ 94 spp ............................................. . . 94—96;]1l. 10 Chuartgz'a ...................................................................... 100 Page Clifi’a latagenae. _ .......................................................... 102 Collecting localities, description ___________________________________________ 102—103 Collectors, names ...................................................... 53, 102—103 comes, Berkeia ________________________________________________________________ 97 communis, Pseudagnostus ________________ Conaspis .................................. concava, Iddingsia._ Pterocephalia.___ . _ conservator, Minupeltis crmstricta, Parahausia ...... 76, 77, pl. 7 camera, Dunderbergia ________________________________________________________ 66 convezimarqinams, Labiosm’a ............................................... , 80, 84 Crassifimbra . , ............................................................... 9S crassimargz'rtata, Iddingsia _______ . 96 Crepicephalus (Loganellus) anytus ........................................... 66 granulosus ....................... maculosus _______________________ nitidus.._ . . simulator. . _ unisculcatus . cyclopyge, Agnostus ........................................................... D Davis formation, Missouri ____________________________________________________ 56, 94 Deadwoodia duris ........................................................... 66 declivita, Dunderbergia ,,,,,,,,,, 66 Dellea wilbernsensis .................................................... _ ,,,,,, 66 depressus, Cemuolimbus ................................................ _ 85, 86; pl. 8 Dicellocephalus richmortdmsia ................................................. 81 Dikellocephalus bilobatus. . . _ . . . 81 Dikelocephalites flabellz‘formis. . . 84 Dokimocephalus_._. _ 95 gregori _____ .. 95 pernasutus ______________ . 95; pl. 11 Dolichomelopus (IIousia) varro ................................................ 74 Dunderbcrg shale, description ________________________________________________ 55—56 lithic units ____________________________________________________________ 55—56, 57 measured section ......................................................... 55 Dunderbergia ________________________________ 56, 57, 58, 60, 64, 65—66, 67, 68, 69, 72, 75 anyta _____________________________________________________________________ 66 bigranulasa ___________________________________________________ 56, 60, (76—67; pl. 5 canadensis ....... 66 camera .......... 66 declivita _________________________________________________________________ 66 granulosa 66 halli, 66 macalosa. 66 nitida .................................................. 56, 60, 66, 67, 68; pl. 4 polybothra ______________________________________________ 60, 65, 66, (77—68, 82; pl. 5 pustulosa _________________________________________________________________ 66, 69 quadrata ____________________________________________________________ 66, 68; pl. 4 simulator _________________________________________________________________ 66, 67 suada _____________________________________________________________________ 66 variagranula __________________________________________________ 66, 67, 68, 82; pl. 4 vermontensis .............................................................. 66 Dunderbergia zone ____________________________________________________________ 56, 81 Drumaspis _____________________________________________________________ 64 duris, Deadwoodia.,._ 66 E Elburgia ..................................................... 64, 65, 66, 68—69, 71, 72 granulata . . _ _ ...... 59 granulosa._ 6.9, 71; pl. 6 quinnensis. ._ _______________________________ 68, 09« 70; pl. 6 elongata, Pteracephalia ______________________________________________ 60, 88; pl.9 Elvim'a _________________________________________________ 56, 64, 65, 68, 69, 70, 71, 72, 89 granulata ........................................................... 70, 71; pl, 6 ham/)urgensis ___________________________________________________________ 71; pl. 6 reudemanni _______________________________________________________________ 71 roemen' ______________________________________________________________ 70—71; pl. 6 utahertsis ............................... 108 INDEX Page K Page Elvim'u zone ........................................................ 56, 75, 80, 81, 84 Kindbladia ___________________________________________________________________ 96, 97 Elviniella ........................................................... 64, 65, 71—72, 74 affim's777 . 5697-98; p]. 11 laevz‘s ____________________________________________________________ 71, 72, 74; pl. 6 retusa ..... 97 Elviniidae _____________________________________________ 59, 60, 64—65, 66—74, 80, 81, 96 wichitaemis ................................................... 97 eurekensz's, Irvingella (Parairvingella) ________________________________________ 74; pl. 6 Kingstonia _________________________________________________________ 94 expansa, Tamara ....................................................... 83, 84; pl. 7 Komaspidue ............................................................... 73 F Komaspis typa .............................................................. 73 Kurtz, V. E., noted _______________________________________________________ 96 Feniak, 0. W., quoted _______________________________________________________ 96 q flabelliformis, Dikelocephalites ................................................. 84 L G Labiostrw ____________________________________________________ 80, 84, 90 , , convezimarginatus.7 .7 80, 84 Generw groupmgs .......................................................... 58 1,1,”,me _________________________ 7_ 80,84 Genemevella.7.777777777777777 _______________________________________________ 100 sigmoidalis _______________________ 80 Gengs and specms undetermined 1 .................................. 101—102; pl. 11 laem's, Elz-iniella ______________________________________________________ 71179,”; p]. 6 "‘ lata, Pseudosaratogia _______________________________________ 101 3'“ "‘_‘"j"", """""""""""""""""""""""""" 102" pl. 11 latagenae, C'lifia _____________________________________________________________ 102 Geographic distrlbutlon, Dunderberg shale. Mus, Pinctus _______________________________________________________________ 100,101 Geragnostmae """""""""" “ leptogranulata, Pseudosaratogia ___________________________________________ 101; pl. 11 Gerognostus """""" Lincoln Pgak formation, Snake Range, Nev ______________________________ 56,78,103 gladmfor, Macrom/ae .......................................................... 76 Limamonella ___________ 56 glandzforme, Pholacroma """""""""""""""""""""""""""""" 63 List of collections _______________ 102—103 ”10°03“, BMW”? ************************************************ 56’ 75' 94" pl- 10 Litocephalus7 7. 7 56, 57, 58, 30, 81—82, 90 WWW”, Emmy” *********************************************************** 59 bilobatus ________________________________________________ 5s, 81, 32, 90; pl. 7 Elvima7 ”””””””””””””””””””””””””””””””” 70’ “QDL 6 granulomarginatus ______________________ 77.. 58, 82; pl. 8 oranulatus, Qlenus“: ................................................... 79-50: pl. 6 verruculapm ______ 7 ______________________________________________ 58782, 83,. p]. 8 granulomawmatus, szocephalus ......................................... 58, 82: pl- 8 (Logamllus) (mums, Crepicephalus ___________________________________________ 66 granulosa, Punderbergza" ‘ 66 granulosus, Crepicephalus _______________________________________________ 66 Elburgta77777 """""""""""" ’" 69' 71; pl. 6 maculoxus, Crepicephalus _______________________________________________ 66, 75 aranuloaus, Crepifephalus (Loganellu3)77 66 Midas, Crew-“Mam ________________________________________________ 65 66,67 grata,-Pteroce7)hal1na """""" ’ """ ” “’ 90 simulator, Crepicephalus ________________________________________________ 66 S‘FMDChF'm """"""""""""""""""""""""""""""" 90—91“ p]. 9 unisculcatus, Crepicephalum 71 We?” Dok'mocephalus ***************************************************** 95 10779731177741, Morosa ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 56, 82, 98, 99—100, 101; pl. 16 Gronwallia __________________________________________________________________ 80 H . M halli, Dunderbergz‘a ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 66 Macropyge gladiator": """""""""""""""""""""""""""""" 76 [Iousia _________________________________________________________________ 75; 91- 7 maculosa, Dundejberma. 7 ..................................................... 66 Hamburg dolomite ___________________________________________________________ 53 maculosus, Crepzcepholus (Loganellus) ......................................... 66. 75 hamburgemz’s, Elvim‘u ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 7 ,,,,,,, 71; pl. 6 maonu, Paieudosaratagzm ” """"""""""""""""""""""""""" 101 Parairvingella ______________ 71 major, Irrmqella """"""""""""""""""""""""""""""""""" 72 Henningsmoen, Gunnar, quoted77 _________________________________________ 79 ' (Irvzngellay """"""" 74' 96 Homagnostus _______ _ 62—63 Maladzoidella7 80 acutus ____________________ 62 Malad'zm-deau 64 obesus ______________ 56—57, 62, 6‘3,- pl. 4 ““mcm- » 6" “Ml-mus _____________________________________ 7 ______________ 56’ 62, 63; pl, 4 Meandunderheram7777 777777777 7 --------------------------------------------- 66. 69 Housia __________________________________________________________ 64, 67, 74—75, 77, 73 Mfteom?” ”mm" ********************************************************* 66 wmdmsi, ______________________________________________________________ 77 75 Mmupeltzs 77777777777777777777777777777777777777777777777777777777777777777 98 halli ___________________ 7 ___________________________ 7 ___________________ 75; pl. 7 . conservalor77777 ..................................................... 98: pl. 10 mmfifl ______________________________________________ 56’ 75—70; D]. 7 minufa,'Me.teoraspts. 7 7 ————————————————————————————————————————————————————— 66 vacuum. 75 mzssourtensts, Bynummm... ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 94 varro 777777777777777777 75 Iddmgxia777 .......................................................... ; 96 (llousia) varro, Dolichometopus ,,,,,,,, 7 ,,,,,,,,,,,,, 74 Momsa-fj """" "’ '4'98'99 Housiidae _______________________ _ 64’ 74' 7548’ 98, 99 longtspma 77777777777777777777777777777777777777777777 56.82.98.99-100. 101; pl. 10 Hypostomes, characteristics ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 60 \7 unidentified ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 60—61; pl. 11 ‘ Nericz’tL _ 7 ................................................................. 80 I quinrluidentata ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 7 ,,,,,,, 7. 80 Iddingsia ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 95—96, 97 septemdentata ........................................................... 80. 84 alpersemz's77 ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 96 nezradensis, Ber/coin ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 97 anatina _________ 7 7 ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 96 Iddingsia_777 7 ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 96. 97 bicincla ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 96 nilida, Dunderbergia ____________________________________________ 56, 60, 66. 67, 68: pl. 4 concam ,,,,,,,,,,,,,,,,,,,,,,, 77 7 ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 96 nitidus, (Yrepicephalus (Loganellus)777 ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 65, 66, 67 crassimarginutm ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, Nopah formation 7 7 ___________________ 99 misseurz‘ensis7 notha, Pterocephalma ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 90 neradensis7 7 occidentalis _______________ 7 ,,,,,,, 0 qurinnemis ,,,,,,,,,,,,,,,, 7 ,,,,,,, 77 ,7 90, 96 obesus, Agnostus pisz’formis_7 7 ................................................. 6?, 6’3 robusta ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 77 ,,,,,, 56, 96—97; pl. 11 Homagnosms .................................................. 56—57, 62, 63; pl. 4 similz‘s ______ 7 ,,,,,,,,,,,,,,,,,,,,, 77 96, 97 occidens, Pterocephalm ........................................................ 87, 88 simpliCifas ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 77__ 96 occidenmlis, Iddingsia ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 96 illahensis ,,,,,,,,,,,,,,,,,, 7 ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 96 016nidne. 7 7 7 7 7 7 ......................... 7 777777777777777777777777777777777777 78—79 intermedia, Parain'ingella ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 73 Oloninue ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 79 Irringella 7777777777777777777777777777777 7 77777777777777777777777 60,64, 65, 72—73, 74 Olenus 77777777777777777777 7 777777777 777777 7 7777777777777777777777777 56, 79 Irvingella (Irvingella). ,,,,,,,,,,,,,,,,,,,,,,,, 64, 73 granulatus ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 79‘80; pl. 6 major77777 777777777 wilsomfi 7777777777777777777777777777777777777777777777777777777 79; pl. 6 major 77777 7 77777777777 7 Oligameropus7 777777 100 (Irvingella), Irvingellm ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 7 64,73 brez'iceps7 7 ,,,,,, - 100; pl- 10 major, Irringella ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 77 74,96 Ontogeny, discussion 777777777777777777777777777 7 7 75776783 Irrimella (I’aruirringella) 7 . _ 7777777777777 7 77777777777777777777777777777 56, 64, 73, 96 Ore Hill limostone member or (latosburg formation 77777777 7 77777777777777777 94, 102 angustilimbatus 77777777 7 7 7 7 777777777777777777777777777777777777 73, 74; pl. 6 Ornament-anon, kinds_ 7 77777777777777777777777777777777777777777777777777777 59. 60 eurekemis 77777777777777777777777777777777777777777777777777777777 74; pl. 6 Orr formation 7777777777777777777777777777777777777777777777777 7 777777777777 56. 92 suecica 777777777777777777777777777777777777777777777777777777777777777 57 orygmatos, Cemuolimbus, 7777777777777777777777777777777777777 56. 60, 81. 85-86; pl. 8 Irvingellina 7777777777777777777 77 7777777777777777777777777777777777777777777 7, 7 ovum. Housia 777777777777777777777 7 777777777777777777777777777777777 56, 75776: pl. 7 INDEX 109 P Page R Pagodia ..................................................................... 100 Pag" Parabolina... _» 7 79 Ranges of trilobites in Dunderberg shale ____________________________________ 56, 57 Parabolinoididae __________ 54 Resser, 0- E., quoted —————————————————————————————————————— 93 Paracoosia ______ __ 87 retusa, Kindbladia .............................. 97 pamhomia __________ 74, 73.77, 78 rendemtmni, Elvinia .................. 71 constricta. _ _ __ ,, 55’ 75‘ 77; pl. 7 richmondensis, Dicellocephalus _________ 81 puraim-ngem ________________________________________________________________ 73, 74 robusta, Iddinysia ............................................... 56, 96—97; pl. 11 hamburgensis _____________________________________________________________ 71 Ptz/chozoaria similis ........................................................ 96 intermedia ________________________________________________________________ 73 roemeri, Elvinia ......................................................... 70—71; pl. 6 (Paraimingella) angustilimbatua, Irvinoella .............................. 73, 74; pl. 6 eurekensis, Irvingella _________________________________________________ 74; pl. 6 S Irvingella, . , ....................................................... 5664,7196 sanctisabae, Pterocephalia _________________________________________ 86, 87, 88—89; pl. 9 suecz‘ca, Irzringellai ................................. 57 semicircularis, Prehousia .................................................... 78; pl. 7 Parasolenoplema --------------------------------------------- 98 semigranulosus, Cernuolimbus ___________________________________________ 85, 86; pl. 8 pernasutus, Dokimocephflus. 96; pl. 11 aeptemdentata, Nen’cia _________________________________________________________ 80, 84 Ptychoparia ----------------------------------- - 95 serratus, Siymocheilus _________________________________________ 56, 60, 61,89,91; pl. 10 Phalacromu ..... , . 63 Sigmocheilus .................... 70, 80,84, 85, 88, 89—90, 91, 92, 96 ylandi/ormc ————————————————————————————————————————————————————————————— 63 grata _______________________________________ 90—91,- pl. 9 SD ---------------------------------------------------------------------- 631‘DL4 pogonipensis. __._ ,_ 60,91; pl. 10 Phalacrominae—w ——————————————————————————————————————————————————————————— 63 serratus__ _ 56, 60, 61,89, 91,- pl. 10 Pinctus ——————————————————————————————————————————————————————————————————————— 100 utahensis ....... ._ 90, 91—92; pl. 9 WW -------------------------------------------------------------------- 100.101 sigmoidalia, Labiostria _________________________________________________________ 80 SM) ------------------------------------------------------------------ 101; D1- 10 similz’s, Iddingsia _______________________________________________________ ._ 96, 97 pisiformis, Agnostusi ............. 62—63 Ptychoparia _______________________________________________________________ 95, 96 chews, Agnostusir .7 69,63 robusta, Ptychoparia _____________________________________________________ 96 Plataspella ------- 96 simplicitas, Iddingsia ....... 96 a"“”"“~—-» 95 simulator, Crepicephalus (Loganellus).-. 66 platifrons, Labiostria ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 80, 81 Dundgrbewia ___________________________________________________________ 66, 67 T057107“ ---------------------------------------------------------------- 84 (Solenopleaura) breviceps, Ptychoparia _________________________________________ 100 pogoninpensis, Pterocephalina ................................................. 90 Species characters ____________________ Sigmochezlus ....................................................... 60, 91; pl. 10 Stenelymus _________________________ polybathra, Dunderbergiah ................................... 60, 65, 66, 67—68. 82; pl. 5 Stratigraphy, Dunderberg shale. Post-Aphelaspis zone ........................................................ 56. 84 Preh ousia _______________________________________________________________ 64, 74, 77—76 alata --------- >— 7178; FL 7 suecica, Irvingella (Parairvingella) _____________________________________________ 57 semicircularus --------------- , '7 78; D1- 7 Suprageneric groupings _________________ 58—59 Preparation of specimens for study? 7 .. 55 Sutures, ventral cephalic_ _ _ V ________ 54, 74, 80 Principles of classification ,,,,,,,,,,,,,,,,,,,, , ,,,,,,,,,,,,,,,,,,,,,,,,,,, 57—59, 92 Proceratopyge ................................................................. 75 T r P e a n t s ____________________________________________________ 6 ; 1.4 23:22:33)” 5:51. _g _ 08 u ______________________________________________________ I67), 62 “”559?de -------------------------------------------------------------- 64' 70 acutus __________________________________________________________________ 62; p], 4 quinnensis ------------------------------------------------------------- 70 communis ______________________________________________________________ 61'. p]. 4 Taenora ————————————————————————————————————————————————————— 80, 83-84 ”0,0,,ng _ V _ __________________________________________ 6,; pl, 4 expansa ------------------------------------------------------------ 83, 84: pl. 7 Pseudosaratogiai 101 platifnms ' ‘ ‘ 84 abnormis. 7 101'. p]. 11 Terms, morphologic _____ __ 59, 60 lata __________________________________________ > __ 101 terrenda, Bynumina.._. 94 leptomnulm ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, V 101.. p], 11 lemma, Pterocephalina——.— 90 magna ____________________________________________________________________ 101 triangularis, Angulotreta. _ . ............. 90 Ptemcephalia 777777777777777777777777777777777777777777 56, 64y 80Y g1, 85, 56-88, 89, 90 tleTa’fl’U/latu8y AnEChocephalu-B -------------------------------------------- 92—93? D]. 3 asiatica _________________________________________________________________ 87 tumidosus, Homagnostus ............................................. 56, 62, 6‘3: D1. 4 bridge: 77777777777777777777777777777777777777777777777777777777777777777777 87, 88 tumifrons, Aphelaspis ......................................................... 74 concava _________________________________________________________________ 88,- pl. 9 Chariocephalus ........................................................ 73 elongata ,,,,,,,,,,,,,, V VVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVV 60, 88; mg t1/Pa. Cerauriflella -------------------- 76 accidens ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 87, 88 Komasl’is ------------ 73 sanclisabae , _ _ ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 86, 87, 88—89; pl. 9 tummy 3571:9171 ----------- 97 Ptemcephaliidae.., 59, 60, 74, 78, 80, 81—92 typical“, Bynumiella ---------------------------------------------------------- 93 Ptcrocephaliinao. _ 60,80,81,84.S5—92 Pterocephalina. , , 90 U bilobata _________________________________________________ 90 Ullagpis ____________________________________________________ 74 grata ------------------------------------------------------------------- 90 unisculcatus, Crepicephalus (Loganellus) 71 notha ----- 90 utahensis, Elvinia ______ 71 pogom’n pensis ___________________________________________________________ 90 Iddingsia ___________ _ _ -96 tezzma .................................................................. 90 Sigmochez'lus _________________________________________________ 90, 91432,” pl. 9 Pterocephalops .............................................................. 80 Plychaspis pustulosa ________________________________________________________ 66 V Ptyilzf'fitlzga “mfg-t1}? """""""""""""""""""""""""""""" 95 vacuna, I Iousia ................................................................ 75 """ variagranula, Dunderbergz'a,__._....._............................ 66, G7, 6‘3, 82; pl. 4 robusta _________ 96 . l -4 (Solenopleura) breniceps_ 100 varro, D0l70h0m€t0p118 (Ilousm) ______________________________________________ i I Iousm _________________________________________________________________ 45 suada _________________________ _ 66 . . 66 Ptychoparioidea ________________ _ 64—102 vermontensls, Blenderbema """"""""""""""""""""""" 8283 l 8 pustulasa, Dunderberyia ____________________________________________________ 66, 69 vermculapeza, thocephalus .......................................... 58, 7 , D - Ptychaspis ________________________________________________________________ 66 \‘v Q 11‘ichitaensis, Berkeia __________________________________________________________ 97 quadrata, Dunderbergz'a __________________________________________________ 66, 68; pl. 4 Kindbladia ___________ 97 quinnensis, Elburgia __________________________________________________ 68, 69—70; pl 6 wilbernsensis, Dellea ..... 6‘5 Iddingsz'a ......................................... Wilson, J. L., quoted ........................................................ 96, 100 Taenicephalus.. u'z’lsoni, OIemls ....................................................... ._. 79: DL 5 quinquedentata, Nericia ________________________________________________________ 80 Windfall formation ............................................... 53Y 56. 61, 73. 74v 97 PLATES 4—1 1 FIGURES 1, 2. 3, 4. 7—9. 10712. 13. 14—21, 23, 24. 22, 25, 28, 29. 26. 27. PLATE 4 Homagnostus tumidosus (Hall and Whitfield) (p. 63), X 10. 1. Cephalon, USNM 136831a, USG-S colln. 2299—CO. 2. Pygidium, USNM I36831b, USGS colln. 2299—C0. Pseudagnostus communis (Hall and Whitfield) (p. 61), X 10. 3. Cephalon, USNM 136832a, USGS colln. 2299‘CO. 4. Pygidium, USNM 136832b, USGS colln. 2299—C0. . Pseudagnostus prolongus (Hall and Whitfield) (p. 61). 5. Cephalon, X 10, USNM 136833a, USG-S colln. 23017CO. 6. Pygidium, X 8. USNM 136833b, USGS colln. 23014CO. Homagnostus obesus (Belt) (p. 63), X 10. 7. Cephalon, USNM 136834a, USGS colln. 2296700 showing finely pitted outer surface. 8. Pygidium, USNM 136834b, USGS colln. 229€rCO. 9. Cephalon, USNM 136835, USGS colln. 2295—CO. Pseudagnostus? aculus (Kobayashi) (p. 62), X 10. 10. Leetotype pygidium, NMC 11996, from so-called Parabolinella limestone, east of Harrogate, British Columbia, Canada. Specimen figured. by Kobayashi (1938, pl. 16, fig. 18). 11. Pygidium, USNM 136836a, USG-S colln. 2297700, showing muscle scars. 12. Pygidium, USNM 136836b, USGS colln. 2297»CO. Phalacroma? sp. (p. 63), X 10. Cephalon, USNM 136837, USGS colln. 2300—CO. Dunderbergia nilida (Hall and Whitfield) (p. 67). 14. Pygidium, X 4, USNM 136838a, USGS colln. 2300—00. 15. Lectotype cranidium, X 3, USNM 24572, Dunderberg shale, Eureka, Nev. 16. Paratype cranidium, X 3, USNM 24572b, Dunderberg shale, Eureka, Nev. 17. Cranidium, holotype of D. simulator (Hall and Whitfield), X 1, USNM 24575, Dunderberg shale, Eureka, Nev. 18. Latex cast of exfoliated cranidium, X 3, USNM 136838b, USGS colln. 2300*C0. 19. Stereogram of cranidium, X 4, USNM 1368380, USGS colln. 2300400. 20. Latex cast of underside of right free cheek showing form of doublure, X 3, USNM 136839, USGS colln. 873—CO. 21. Latex cast of right free cheek, X 3, USNM 136838d, USGS colln. 2300—CO. 23. Pygidium, X 3, USNM 136838e, USGS colln. 2300~CO. 24. Exfoliated right free cheek showing fine-pitted surface, X 4, USN M 136838f, USGS colln. 2300—CO. Dunderbergia uariagmnula Palmer (p. 68). 22. Stereogram 0f eranidium, X 4, USNM 136840a, USGS colln. 2297—CO. 25. Cranidium, X 4, showing coarse granules on surface of internal mold of glabella, USNM 136841, USGS colln. 2298—CO. 28. Pygidium, X 4, USNM 136843, USGS colln. 809—CO. 29. Free cheek, X 4, USNM 136840b, USGS colln. 2297eCO. Dunderbergia variagranula? Palmer (p. 68), X 8. Cranidium, questionably assigned to this species, USNM 136842, USGS colln. 2302—00. Dunderbergia quadrata Kobayashi (p. 68), X 2. Cranidium, NMC 11962, west of Harrogate, British Columbia, Canada. GEOLOGICAL SURVEY AGNOSTIDAE AND ELVINIIDAE GEOLOGICAL SURVEY PROFESSIONAL PAPER 334 PLATE 5 ELVINIIDAE PLATE 5 FIGURES 1—4, 6, 7, 9, 14. Dunderbergia polybothra n. sp. (p. 67). 1. Cranidium, X 3, USNM 136844a. 2, 3. Free cheeks, X. 4, USNM 136844b, c. 4, 7. Thoracic segments, X 3, USNM 136844d, e. 6. Pygidium, X 3, USNM 136844f. 9. Stereogram of holotype cranidium, X 4, USNM 136845. 14. Detail of top surface of glabella and occipital ring, of cranidium in fig. 1, X 10. All specimens from USGS colln. 2296—00. 5. Dunderbergia maculosa (Hall and Whitfield) (p. 66), X 1. Holotype cranidium, USNM 24617 Dunderberg shale, Eureka district, Nevada. 8. Dunderbergia pustulosa (Hall and Whitfield) (p. 66), X 1. Holotype cranidium, USNM 24579 Dunderberg(?) shale, White Pine district, Nev. 10—13, 15—23. Dunderbergia bigranulosa n. sp. (p. 66). 10. Cranidium, X 4, USNM 136846a, USGS colln. 795—CO. 11. Exfoliated cranidium, X 3, USNM 136846b, USGS colln. 795—00. 12. Stereogram of holotype cranidium, X 3, USNM 136847, USGS colln. 2295—00. 13. Detail of surface of brim and border of cranidium in fig. 19, X 10. 15. Free cheek, x 4, USNM 136848b, USGS colln. 2295—09. 16. Free cheek, X 4, USNM 136849a, USGS colln. 2294—00. 17. Free cheek, X 5, compare border with fig. 16, USNM 136848c, USGS colln. 2295—00. 18. Cranidium, X 4, USNM 136848a, USGS colln. 2295—00. 19. Cranidium, X 4, USNM 136849b, USGS colln. 2294—00. 20. Pygidium, X 4, USNM 1368490, USGS colln. 2294-00. 21, 22. Pygidia, X 4, USNM 136848d, e, USGS colln. 2295—CO. 23. Pathologic pygidium with partly attached, distorted thoracic segments, X 3, USNM 136848f, USGS colln. 2295—00. FIGURE 1. 2, 3. 11—13, 15. 16, 17, 19. 18, 20—22. 23—27. PLATE 6 Irvingella (Pamirvingella) eurekensz’s (Resser) (p. 74), X 3. Stereogram of holotype cranidium, USNM 108668, USNM 100. 61. Irvingella (Parairvingella) angustilimbatus Kobayashi (p. 73), X 2. 2. Stereogram of small plesiotype cranidium for comparison with I. (P.) eurekensis, USNM 108672, USNM 100. 62. 3. Large cotype cranidium, USNM 24643, USNM loc. 63. . Elvim'a granulata Resser (p. 71), X 2. Stereogram of holotype cranidium, USNM 108815, USNM 100. 63. . Elvim'a hamburgensis (Resser) (p. 71), X 2. Holotype cranidium, USNM 108669, USNM 100. 61. . Elvim’a? sp. (p. 71), X 3. Cranidium, USNM 136850, USGS colln. 2300—00. . Elvim’a roemeri (Shumard) (p. 70), X 2. Cranidium, USNM 136851, USGS colln. 789-00. . Elvim‘ella sp. (p. 72), X 4. 8. Stereogram of cranidium, USNM 136852, USGS colln. 954—CO. 14. Cranidium, USNM 136853, USGS colln. 2301-00. . Elvim’ella laevis n. gen., n. sp. (p. 72), X 4. 9. Stereogram of holotype cranidium, USNM 136854a, USGS colln. 952—CO. 10. Latex cast of posterior part of holotype cranidium USNM 136854b. Elburgia quirmensis (Resser) (p. 69). 11. Stereogram of exfoliated holotype cranidium, X 3, USNM 10883851, USNM loc. 7j. 12. Cranidium on same block as holotype, X 3. 13. Cranidium, x 4, USNM 13685521, USGS colln. 2298—00. 15. Exfoliated cranidium, X 3, USNM 136855b, USGS colln. 2298-CO. Elburgia granulosa (Hall and W'hitfield) (p. 69), X 3. 16. Cranidium, USNM 136856, USGS colln. 795—CO. 17. Cranidium, USNM 136857, USGS colln. 2297-00. 19. Stereogram of holotype cranidium, USNM 24573, Dunderberg shale, Eureka district, Nevada. Olenus? wilsom' Henningsmoen (p. 79), X 5. 18. Cranidium, USNM 136858a, USGS colln. 2300—00. 20. Cranidium, USNM 136859a, USGS colln. 2297—00. 21. Free cheek, USNM 136859b, USGS colln. 2297—00. 22. Pygidium, USNM 136858b, USGS colln. 2300—C0. Olenus? granulatus n. sp. (p. 79). 23. Pygidium, >< 5, USNM 136860, USGS colln. 2299—00. 24. Stereogram of holotype cranidium, X 5, USNM 136861, USGS colln. 2300-00. 25. Detail of surface, holotype cranidium, X 15. 26. Cranidium, USNM 136862, USGS colln. 795-C0. 27. Detail of surface of pygidium, X 15. GEOLOGICAL SURVEY PROFESSIONAL PAPER 334 PLATE 6 ELVINIIDAE AND OLENIDAE GEOLOGICAL SURVEY PROFESSIONAL PAPER 334 PLATE 7 HOUSIIDAE AND APHELASPIDINAE PLATE 7 FIGURES 1—7, 9. Hausia ovata n. sp. (p. 75). 1. Stereogram of holotype cranidium, X 2, USNM 136863, USGS colln. 872—CO. 2. Free cheek, X 1, USNM 136864a, USNM 100. 60. 3. Cranidium, X 4, for comparison with cranidium of comparable size for Parahousia constn’uta n. sp. (fig. 16), USNM 13686521, USGS colln. 955—00. 4, 9. Transitory pygidia, X 15, USNM 136865b,c, USGS colln. 955—CO. 5. Exfoliated pygidium, X 2, USNM 136864b, USGS colln. 872—CO. 6. Pygidium showing uneven development of left and right pleural lobes, X 3, USNM 136864c, USGS colln. 872—CO. 7. Pygidium, X 4, USNM 136865d, USGS colln. 955—CO. 8. Housia halli (Resser) (p. 75), X 2. Holotype pygidium, USNM 90670, Dunderberg shale, Eureka district, Nevada. 10, 12, 13. Prehousia alata n. gen., n. sp. (p. 78). 10. Stereogram of holotype cranidium, X 3, USNM 136866. 12. Free cheek, X 2, USNM 136867a. 13. Pygidium, X 2, USNM 136867b. All specimens from USGS colln. 1441—00, Lincoln Peak formation, Snake Range, Nev. 11, 14, 15, 19. Prehousia semicircularis n. gen., n. sp. (p. 78). 11. Holotype, small cranidium, X 8, USNM 136868. 14. Pygidium showing posterior margin, X 3, USNM 136869a. 15. Free cheek, X 4, USNM 136869b. 19. Fragmentary pygidium showing anterolateral margin, X 3, USNM 1368690. All specimens from USGS colln. 2294—00. 16—18. Parahousz’a constricta n. gen., n. sp. (p. 77), X 4. 16. Stereogram of holotype cranidium, USNM 136870. 17. Free cheek, USNM 136871a. 18. Pygidium, USNM 136871b. All specimens from USGS colln. 955—00. 20—23. Taenora erpansa n. gen., n. sp. (p. 84). 20. Stereogram of holotype cranidium, USNM 136872, USGS colln. 954—00. 21. Free cheek, X 2, USNM 136873a, USGS colln. 2301—CO. 22. Pygidium, X 2, USNM 136874, USGS colln. 954—00. 23. Small cranidium, X 5, USNM 136873b, USGS colln. 2301—00. 24—27. Litocephalus bilobalus (Hall and Whitfield) (p. 82), X 2. 24. Stereogram of cranidium, USNM 128324a. 25. Free cheek, USNM 128324b. 26. Pygidium, USNM 128324d. 27. Thoracic segment, USNM 128324e. All specimens from USGS colln. 1297—00. FIGURES 1, 3, 5, 8, 11. 2, 4, 6, 7. 12, 13, 15, 16, 19, 20. 14, 17, 18, 24. 21—23. PLATE 8 Cemuolz'mbus orygmatos n. gen., 1). sp. (p. 85). 1. Stereogram of holotype cranidium, X 2, USNM 136875. 3. Pygidium X 2, USNM 136876a. 5. Detail of external surface of right posterior limb of holotype, X 10. 8. Free cheek, X 2, USNM 136876b. 11. Pygidium, X 3, USNM 136876c. All from USGS colln. 2295—00. Cemuolimbus semigranulosus n. gen., n. sp. (p. 86). 2. Stereogram of holotype cranidium, X 3, USNM 136877. 4. Pygidium, X 3, USNM 136878a. 6. Detail of external surface of back of glabella of holotype, X 10. 7. Free cheek, USNM 136878b. All from USGS colln. 2294-00. . Cernuolimbus depressus n. gen., 11. sp. (p. 85), X 3. 9. Stereogram of holotype cranidium, USNM 136879. 10. Cranidium, USNM 136880. Both from USGS colln. 2297—00. Litocephalus verruculapeza n. sp. (p. 83). 12. Stereogram of holotype cranidium, X 3, USNM 136881. 13. Detail of cranidial border X 3, USNM 136882a. 15. Free cheek showing shape of anterior part of doublure, X 2, USNM 136882b. 16. Free cheek, X 3, USNM 136882c. 19, 20. Pygidia, x 3, USNM l36882d, e. All from USGS colln. 2299—CO. Litocephalus granulomarginatus n. sp. (p. 82). 14. Detail of border of holotype, X 5. 17. Stereogram of holotype cranidium, X 2, USNM 136883, USGS colln. 795—CO. 18. Pygidium, X 2, USNM 136884a, USGS colln. 2300—00. 24. Free cheek, X 2, USNM 136884b, USGS colln. 2300—00. Anechocephalus trigranulatus n. gen., n. sp. (p. 92), X 5. 21. Pygidium, USNM 1368863.. 22. Stereogram of holotype cranidium, USNM 136885. 23. Cranidium, USNM 136886b. All from USGS colln. 952—00. GEOLOGICAL SURVEY PROFESSIONAL PAPER 334 PLATE 8 ,4? " 22 PTEROCEPHALIINAE, APHELASPIDINAE, AND ANECHOCEPHALUS GEOLOGICAL SURVEY PROFESSIONAL PAPER 334 PLATE 9 PTEROCEPHALIINAE PLATE 9 FIGURES 1—6, 9—12. Pterocephalia concava n. sp. (p. 88). 7, 8, 13. 14—20. 21. 22, 23, 26, 27. 24, 25, 28. . Stereogram of holotype cranidium, X 2, USNM 136887. . Large incomplete cranidium, X 1, USNM 1368883. . Medium-sized cranidium, X 3, USNM 136888b. Small cranidium, X 4, USNM 1368880. Small pygidium, X 3, USNM 136888d. Free cheek, X 1,USNM 136888e .Latex cast of large pygidium, X 1, USNM 136888f. 10, 11. Medium- sized pygidia, X 2, USNM 136888g, h. 12. Left pleuron of thoracic segment, X 2, USNM 1368881. All from USGS colln. 2297—CO. Pterocephalia sanctisabae Roemer (p. 88). 7. Cranidium, X 3, for comparison with comparable-sized cranidium of P. concava n. sp. (fig. 3), USNM 136889a, USGS colln. 2302—00. 8. Pygidium, X 3, USNM 136890, USGS colln. 2301—00. 13. Free cheek, X 2, USNM 136889b, USGS colln. 2302—00. Pterocephalia elongata n. sp. (p. 88) X 3. 14. Stereogram of holotype cranidium, USNM 136891, USGS colln. 873—00. 15. Freecheek, USNM 1368939., USGS colln. 2300—00. 16. Cranidium, USNM 136893b, USGS colln. 2300—00. 17. Pygidium, USNM 136892, USGS colln. 873-00. 18, 19. Pygidia, USNM 1368930, (1, USGS colln. 2300—00. 20. Free cheek showing shape of anterior part of doublure, USNM 136893e, USGS colln. 2300-00. Pterocephalz'a occidens (Walcott) (p. 88), X 4. Holotype cranidium, USNM 24613, USNM 100. 61. Sigmocheilus gram (Resser) (p. 90). 22. Pygidium, X 3, USNM 136894, USGS colln. 952-00. 23. Pygidium, X 3, USNM 13689521, USGS colln. 2299—00. 26. Free cheek, X 3, USNM 136895b, USGS colln. 2299-00. 27. Stereogram of cranidium, X 3, USNM 136895c, USGS colln. 2299—00. Sigmocheilus utahensis (Resser) (p. 91). 24. Pygidium, X 5, USNM 136896a, USGS colln. 2296-C0. 25. Free cheek, X 3, USNM 136896b, USGS colln. 2296-00. 28. Stereogram of small cranidium, X 4, USNM 136897, USGS colln. 795—CO. ngfiP‘gP-wtov—a FIGURES 1—3. 11, 12. 13, 14. 15—17. 18, 21. 19, 20. PLATE 10 Sigmocheilus serratus n. gen., n. sp. (p. 91), X 3. 1. Stereogram of holotype cranidium USNM 13689821, USGS colln. 955—CO. 2. Free cheek, USNM 136899, USGS colln. 864-CO. 3. Pygidium, on same block as holotype, USNM 136898b, USGS colln. 955—00. . Sigmocheilus pogonipensis (Resser) (p. 91), X 3. 4. Stereogram of characteristic cranidium, USNM 136900a, USGS colln. 2301-CO. 5. Latex cast of pygidium, USNM 136900b, USGS colln. 2301—00. 6. Cranidium showing shape of anterior margin, USNM 136901, USGS colln. 954—00. 7. Free cheek, USNM 1369000, USGS colln. 2301-00. . Bynumina globosa (VValcott) (p. 94), X 10. Stereogram of nearly perfect cranidium, USNM 136902, USNM 10c. 61. . Bynumiella? acuminata n. sp. (p. 93), X 8. 9. Stereogram of holotype cranidium, USNM 136903. 10. Silicified free cheek, USNM 136904. Both from USGS colln. 2296—CO. Minupeltis conservator n. gen., n. sp. (p. 98), X 8. 11. Stereogram of holotype cranidium, USNM 136905. 12. Assymetrical cranidium with poorly developed right side, USNM 136906. Both from USGS colln. 2294—00. Cheilocephalus spp. (p. 94), X 3. 13. Cranidium, USNM 136907, USGS colln. 864—00. 14. Pygidium, USNM 136908, USGS colln. 2299—CO. Morosa longispina n. gen., n. sp. (p. 99), X 6. 15. Stereogram of holotype cranidium, USNM 136909. 16. Pygidium, USNM 13691021. 17. Free cheek, USNM 136910b. All from USGS colln. 2299—CO. Pinctus? spp. (p. 101), X 10. 18. Latex cast of cranidium, USNM 136911, USGS colln. 952—CO. 21. Latex cast of cranidium, USNM 136912, USGS colln. 953—CO. Oligometopus breviceps (Walcott) (p. 100), X 8. 19. Stereogram of holotype cranidium, USNM 24577, USNM 100. 62. 20. Cranidium, USNM 136913, USGS colln. 954—00. GEOLOGICAL SURVE PROFESSIONAL PAPER 334 PLATE 10 «w» a,» q, PTEROCEPHALIINAE AND UNASSIGNED GENERA GEOLOGICAL SURVEY PROFESSIONAL PAPER 334 PLATE 11 UNASSIGNED GENERA AND HYPOSTOMES FIGURES 1. 2, 5, 6. 4, 7—9, 12. 10. 11. 13—16. 17, 19, 20. 18, 21. PLATE 1 1 Genus and species undetermined 2 (p. 102), X 5. Cranidium, USNM 136914, USGS colln. 2295—00. Genus and species undetermined 1 (p. 101), X 5. 2. Cranidium, USNM 13691521. 5. Cranidium questionably assigned to this species, USNM 136915b. 6. Cranidium, USNM 1369150. All from USGS colln. 2297—00. . Genus and species undetermined 3 (p. 102), X 5. Pygidium, USNM 136916, USGS colln. 2297—00. Hypostomes (p. 60), X 5. 4. Hypostome, type C, USNM 136917, USGS colln. 2294—00. 7. Hypostome, type B, USNM 136918, USGS colln. 2295—00. 8. Hypostome, type E, USNM 136919, USGS colln. 2296—C0. 9. Hypostome, type D, USNM 136920, USGS colln. 2301—00. 12. Hypostome, type A, USNM 136921, USGS colln. 2302—00. Pseudosaratogia leptogranulata n. sp. (p. 101), X 2. Stereogram of holotype cranidium, USNM 136922, USGS colln. 954—00. Pseudosaratogia abnormis n. sp. (p. 101), X 3. Stereogram of holotype cranidium, USNM 136923, USGS colln. 955—00. Iddingsz'a robusta (Walcott) (p. 96). 13. Stereogram of holotype cranidium, X 2, USNM 24609, USNM 100. 61. 14. Detail of right anterolateral corner of cranidium in fig. 16, X 5. 15. Cranidium, holotype of I. nevadensz‘s Resser, X 2, USNM 108796, USNM 100. 61. 16. Cranidium preserving part of external surface, X 2, USNM 136924, USNM 10c. 62. Kindbladia afiinis (VValcott) (p. 97). 17. Stereogram of cranidium with external surface preserved, X 5, USNM 136925, USNM 100. 62. 19. Cranidium, holotype of K. nevadensis Resser, X 4, USNM 108788a, USNM loc. 61. 20. Holotype, cranidium, X 4, USNM 24642, USNM 100. 65. Dokimocephalus pernasutus (Walcott) (p. 95), X 1. 18. Holotype cranidium, USNM 24608a. 21. Paratype free cheek, USNM 24608b. Both from USNM Ice. 61. U.S. GOVERNMENT PRINTING OFFICE: 1960 0 -507219 Late Paleozoic Gastropoda from Northern Alaska GEOLOGICAL SURVEY PROFESSIONAL PAPER 334—D Late Paleozoic Gastropoda from Northern Alaska By ELLIS L. YOCHELSON and J. THOMAS DUTRO, JR. SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY GEOLOGICAL SURVEY PROFESSIONAL PAPER 334—D Descriptions and i/[mtratiom 0f34 .rpecies and I flew genus, wit/z érief discussion of t/zeir ytrdti- grap/iic sigmficaflce UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1960 UNITED STATES DEPARTMENT OF THE INTERIOR FRED A. SEATON, Secretary GEOLOGICAL SURVEY Thomas B. Nolan, Director For sale by the Superintendent of Documents, US. Government Printing Office Washington 25, D.C. - Price 50 cents (paper cover) CONTENTS Page Page Abstract ___________________________________________ 111 Systematic paleontology _____________________________ 131 Introduction _______________________________________ 111 Superfamily Bellerophontacea ____________________ 131 Stratigraphic distribution of the gastropods ____________ 113 Superfamily Euomphalacea ---------------------- 133 R k 't ________________________________ 113 Superfamily Pleurotomariacea ____________________ 135 00 um s _____ , Superfamily Platyceratacea ______________________ 140 Fauna] zones """""""""""""""""" 115 Superfamily Microdomatacea _____________________ 141 Stratigraphic diStribUt/ion ------------------------ 115 Superfamily Anomphalacea _______________________ 142 Lower Mississippian undifferentiated __________ 115 Superfamily Neritacea ___________________________ 142 Upper Mississippian _________________________ 118 Superfamily Murchisoniacea ______________________ 144 Permian ___________________________________ 118 Superfamily Loxonematacea ______________________ 144 Ecological and paleogeographical data _________________ 119 Superfamily Subulitacea ------------------------- 144 General considerations _______________________________ 121 Class Scaphopoda ““““““““““““““““ 144 , . , References cited ____________________________________ 145 Register of localities _________________________________ 122 Index _____________________________________________ 147 ILLUSTRATIONS [Plates follow p. 148] PLATES 12, 13, and 14. Late Paleozoic Gastropoda. Page FIGURE 23. Index map of northern Alaska ________________________________________________________________________ 112 24. Mississippian stratigraphic nomenclature and faunal zones _______________________________________________ 114 25. Ranges of gastropod species __________________________________________________________________________ 120 26. Schematic representation of terms for direction of growth lines ___________________________________________ 121 27. Fossil-collecting localities in parts of the Misheguk Mountain quadrangle (A), the Noatak quadrangle (B), the Point Hope quadrangle (C), and the Howard Pass and Misheguk Mountain quadrangles (D), Alaska ________ 123 28. Fossil—collecting localities in parts of the Killik River and Chandler Lake quadrangles (A), and the Chandler Lake and Philip Smith Mountains quadrangles (B), Alaska ____________________________________________ 124 29. Fossil-collecting localities in parts of the Demarcation Point and Table Mountain quadrangles, Alaska and adja- cent parts of Canada (A), and the Sagavanirktok and Mount Michelson quadrangles, Alaska (B) ___________ 125 TABLE Page TABLE 1. Distribution and number of Late Paleozoic gastropods in northern Alaska ___________________________________ 116 III 3.". I K, Ii. .1 ‘ SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY LATE PALEOZOIC GASTROPODA FROM NORTHERN ALASKA by ELLIS L. YOCHELSON and J. THOMAS DUTRO, Jr. ABSTRACT Late Paleozoic gastropods from northern Alaska occur in rocks of both Mississippian and Permian age; most of the fossils studied came from the Mississippian. Although the gastropods are of use for dating the rocks only in the broadest terms, locally they are useful in establishing informal fauna] zonation. 0n the basis of predominant occurrence of certain gastropods, it is possible to distinguish rocks of Early Mis- sissippian, Late Mississippian, and Permian age. Two divi~ sions, based on the distribution of gastropods, are distinguished in the Upper Mississippian. One collection, consisting entirely of specimens of Glabrocz‘ngulum and Trepospira, may indicate the presence of rocks of Pennsyl 'anian age. Occurrence and distribution data are summarized in tabular form. The gastropod faunule is composed primarily of euomphala- ceans, platycerataceans, pleurotomariaceans, neritaceans, and bellerophontaceans, in that order of abundance. There is no indication that a distinct boreal fauna is represented. Many of the specimens are poorly preserved, though some well-pre- served shells occur, particularly among the pleurotomariaceans. Thirty-four species are recognized in the systematic treat- ment; nine of these are formally named as new species and one is referred to a previously described species. One new pleurotomariacean genus, Nodospira, is described. At least two other new genera may occur in the faunule but specimens are too incomplete for adequate taxonomic description. The occurrence of two scaphopod specimens is reported. Most of the fossils were collected from the Brooks Range during fieldwork in connection with geologic investigations of Naval Petroleum Reserve No. 4 and adjacent areas. Some earlier collections from northern Alaska were restudied. INTRODUCTION This study deals primarily with specimens collected from 1944 to 1953 during the geologic exploration of Naval Petroleum Reserve No. 4. This is one of a series of papers by members of the U.S. Geological Survey planned to describe the various groups of Pale- ozoic fossils collected in northern Alaska. Mackenzie Gordon, Jr. (1957) has completed a study of the Mis— sissippian cephalopods. Work on certain other fos- sil groups is in progress. The philosophy that has guided this work was ex- pressed by J . Brookes Knight (1953, p. 84) who, in describing a poorly preserved Permian gastropod fauna from Mexico, remarked: “* * * a collection of fossils from beds in a region previously unstudied may tell us much, even though the specimens themselves are too poorly preserved to warrant detailed descrip- tions or naming of species.” Most of the fossil gas- tropods from northern Alaska are poorly preserved; nevertheless, their study contributes to our under— standing of the classification and geographic distri- bution of Paleozoic gastropods. In addition, it pre- sents detailed information useful in regional strati- graphic studies. Mississippian gastropods were first collected from the Brooks Range by Philip S. Smith in 1911 (Smith, 1913). George H. Girty listed gastropods from north- ern Alaska in several U.S. Geological Survey Bulle- tins, but did not describe any of the species. Most of his identifications are summarized in a single chart (Smith and Mertie, 1930, facing p. 182). Specimens identified by Girty were reexamined during the pres- ent investigation. A few dozen specimens were col- lected by A. G. Maddren, J. M. Jessup, and G. L. Harrington during the geologic reconnaissance of the Alaska-Canada boundary (Maddren, 1912, p. 297— 314). Finally, several gastropods were obtained by E. de K. Leflingwell (1919) from the Canning River district. The paleontologic literature of Alaska is well in- dexed. Dutro (1956) compiled an annotated bibliog- raphy of Alaskan Paleozoic paleontology; in addition, Alaska is included in the excellent “Arctic Bibliog- raphy” (U.S. Department of Defense, 1953—57). Neither of these sources records late Paleozoic gastro- pods from Alaska. About half a dozen papers illus- trate a few specimens from other parts of the Arctic, but all figures examined are small-size reproductions of poorly preserved specimens. These few specimens are either unnamed or are compared with species de- scribed from western Europe. 111 SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY 112 .38: :08 85885 no nousflfiwg 38889.58.» was goo.— naEEmmEEE no #3 333:0 383.88% “mm 8: .mm 8N 38w: MO 82302 6N3 5 3 69:38 weanwnuuau M5393 difid 8.55.8: no man: Navaldw 5:55 9:: .mw: amm: 8888.8: anogflcam 88388.: 838.8: 38.28: mo @833 we :8: 35889594 mo @233 Mo :8: 3m8§oan< //II |\\\\ \ cofifia €335 we mobaso mo :8: 8w889an< 838 :«EEwflwflS Mo @2350 \ In \ Illll.\ om©\ szEpoz 5:6 85:8 5. 9. 9 ’lLlnl} EV mwm mmDOE _ _ 8:2 co: , : \ \ \ owe: owe /°E nov: 03: omv: umm: com: 500: ave: 0mm: LATE PALEOZOIC GASTROPODA FROM NORTHERN ALASKA C. C. Branson’s bibliographic index of Permian fos- sils described through 1941 (Branson, 19-18) aids a search of the literature for previously named species. Mississippian fossils, on the other hand, have not been systematically indexed for many years. To the best of the writers’ knowledge, the last major papers deal- ing with gastropods of Mississippian age or early Carboniferous, are those of Koninck (1881, 1883). Literature describing American Mississippian gastro- pods is scant. The Brooks Range physiographic province includes several distinct groups of mountains extending from near the 165th meridian eastward to the Canadian boundary. For most of its length the range lies es- sentially along the 68th parallel, forming the back- bone of Alaska and constituting the divide for drain— age to the Pacific and Arctic Oceans. Eastward from the 150th meridian the range makes a crescentic bend northeastward until the mountain front is only about 25 miles south of the Arctic coast. The regional set- ting and topography were described in detail by Smith and Mertie (1930) and summarized by Payne and others (1951). The index map (fig. 23) shows the quadrangles from which gastropod specimens were collected. The topography of the Brooks Range has been ex— tensively modified by glacial action. Glaciers are not now common, but the climate remains severe. The isolated position of the region has complicated and handicapped fossil collecting. Many collections were backpacked by geologists from the collecting locali— ties and cached in places accessible by airplane. This necessarily limited the number and size of the fossil collections. A few of the localities were visited more than once; most have been only casually sampled. More than customary acknowledgment is due the fieldmen because fieldwork in northern Alaska is rig— orous and requires physical efi’ort not normally asso- ciated with fossil collecting. Members, or former members, of the U.S. Geological Survey who collected fossil material on which this paper is based are: A. L. Bowsher, IV. P. Brosgé, R. M. Chapman, R. L. Det- terman, J. T. Dutro, Jr., Allen Feder, IV. A. Fischer, George Gryc, C. J. Gudim, A. S. Keller, B. H. Kent, C. E. Kirschner, A. H. Lachenbruch, M. D. Mangus, R. H. Morris, W. ‘V. Patton, Jr., H. N. Reiser, E. G. Sable, I. L. Tailleur, and R. F. Thurrell, Jr. Dr. J. Brookes Knight, Smithsonian Institution, re- tired, examined some of the specimens and made per- tinent taxonomic suggestions. Photographs were taken by Nelson \V. Shupe, US. Geological Survey. 113 STRATIGRAPHIC DISTRIBUTION OF THE GASTROPODS The assemblage of gastropod genera dates the rocks as late Paleozoic, but the gastropods themselves are of little value in correlating individual stratigraphic units with rock sequences in regions outside Alaska. “Vith the exception of Portloclciella sp., Rhineo- derma? sp., and Turbonellina? law, n. sp., no genera or species thought to be limited to rocks of Mississip- pian age are known. No species or genera diagnostic of Permian age were identified. On the other hand, fieldwork has demonstrated that some of the gastropods are useful, locally, in provid- ing supplementary evidence that helps determine the position of certain rock units. Units currently rec- ognized in northern Alaska are discussed below on the basis of distribution of the gastropods. ROCK UNITS Rocks of late Paleozoic age in northern Alaska can be assigned to at least six formations. The Missis- sippian system, represented largely by a complex ar- ray of carbonate facies, is divided into two major parts. The nomenclature of Mississippian rock units in the central Brooks Range (fig. 2-1) has been re- vised by Bowsher and Dutro (1957, p. 3—7). The lower part, essentially a black shale with a sandstone member at the base and argillaceous limestone beds near the top, is designated as the Kayak shale. The upper part, the Lisburne group, consists of the lVachs- muth limestone below and the Alapah limestone above. Elsewhere in northern Alaska, the Lisburne group has been subdivided into several formations, not as yet formally published. The approximate limits of the Mississippian outcrop belt are shown in figure 23. No rocks of undoubted Pennsylvanian age are known from northern Alaska. A carbonate rock sequence in the eastern Brooks Range, lying above the Alapah limestone, may represent some part of the Pennsyl- vanian system. Fossils are rare in these rocks and no gastropods have been collected from them. The Permian is represented by three quite different formations, each of which represents a predominantly elastic facies. The approximate limits of outcrop of these units are shown in figure 23. The Sadlerochit formation of Permian and Early Triassic age in the eastern Brooks Range was first defined as the Sad- lerochit sandstone by Leflingwell (1919, p. 103). Its fauna was studied by Girty and, although the forma- tion was originally called Pennsylvanian, it was Girty who recognized affinities with faunas now considered to be of Permian age (Smith, 1939, p. 32). The Sik- sikpuk formation of Permian(?) age in the central Brooks Range was described recently by W. W. Pat- 114 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY GROUP 1 FORMATION MEMBER FAUNAL ZONE Alapah limestone Upper limestone \ Cher! nodule C ', ,, “' stn'at ' (Schwetjolf) Fine-grained limestone Light-gray limestone Lithostrotiomlm? 5p. Chen-shale k \ W“ Banded limestone T Gmialitex trenistn'a Phillips ' Sciophyllum lambarti Harker and Madmen Plnty limestone Eumetnla 042st (Hall) Dark limestone V\ Lithoxtrotwn eff. L. asiaticum (Yabe and Hayasaka)‘ Shaly limestone K\ 3 N. (Naticopsis) suturt’comfita Yochelson and Dutro" Lisbume group Wachsmuth limestone Banded Chen-limestone Bruhythyris suborbwuiam (Han), Dolomite Spin'fer lenuicostalus (Hall) Lighbg-ray limestone Crinoidal limestone Shaly limestone “Zaphrentis” konimki s. l. Milne Edwards and Haime' 400 Kayak shale Red limesmne Upper black shale C'ryptoblastus aff. C. p’isum (Meek and Wonhen) Argillaceous limesmne Lepmm analoga (Phillips). Lower black shale Basal sandstone Scalan'tuha 5% ‘ Gastropod bearing. FIGURE 24.—Misslssippian stratigraphic nomenclature and funnel zones in the Shainln Lake area, central Brooks Range (modified from Bowsher and Dutro, 1957). LATE PALEOZOIC GASTROPODA FROM NORTHERN ALASKA ton, Jr. (1957, p. 41—43). It is essentially a fine- grained clastic facies of the Sadlerochit formation. In some areas a minor amount of silicification is re- corded. The third formation of Permian age, as yet unnamed, is a thick sequence of sandstone, quartzose limestone, shale, chert, and conglomerate that crops out extensively in the western part of the Brooks Range. This unit has produced the greatest variety of Permian fossils in northern Alaska and is correla- tive, in part, with the Sadlerochit and Siksikpuk formations. FAUNAL ZONES Mississippian collections yielding gastropods are listed in table 1 according to the faunal zones from which they were collected. These faunal zones were established by Bowsher and Dutro (1957, p. 5 and 6). Gastropods were collected from zones characterized by Scalarituba sp., Leptaena analoga (Phillips), “Zaphrentz's” konincki Milne Edwards and Haime (sensu lato), Brachythg/m's suborbiculam's (Hall), N. (Natz'copsz's) sutum’compta Yochelson and Dutro, Lithostrotz‘on cf. L. asidticum (Yabe and Hayasaka), and Gom'atites crenistria Phillips (fig. 24 and table 1). Gastropods were the basis for the erection of one of the faunal zones of Bowsher and Dutro. The fauna of the Naticopsis howi Dawson zone (Bowsher and Dutro, 1957, p. 6) is essentially limited to gastropods. The species referred to as N. howi by Bowsher and Dutro is described in this paper as Naticopsz's (Nati- copsis) sutum'compta, n. sp., and the name of the zone is changed accordingly. By an analysis of the cephalopods of the Gom'atites crem’stm’a zone, these beds have been correlated with the latest Middle Viséan and early Upper Viséan by Gordon (1957, p. 15 and table 2). Regarding the cephalopod faunule, Gordon states (1957, p. 15) : In the British section, forms identical with and closely re- lated to the Alaskan species of the black chert and shale mem- ber are distributed through stratigraphic thicknesses of 150 to nearly 400 feet. In the northern Alaska section, the fossils are limited to the lower 60 feet of the black chert and shale member. Goniatites suggesting three different subzones (B2, Fla and Plc) have been found at roughly the same strati- graphic level but each in a difierent river valley. Whether this means that the ranges of certain goniatite genera are somewhat telescoped in the Alaskan section, or whether the black chert and shale member transgresses the section rather irregularly, is not determinable on the basis of present evi- dence. No faunal zones have been set up, as yet, for the Permian system in Alaska. The gastropod Slim-parol— Zus (Euomphaius) alaskensz's, n. sp. is commonly found in the lower part of the Siksikpuk formation, but has also been found in the other two Permian formations. 115 Several informal faunal zones have been distinguished in Dutro’s research on the younger Permian, particu- larly in the unnamed rocks of the western Brooks Range. The only zone pertinent to this gastropod study is one characterized by Licharewz'a, a spiriferoid brachiopod that is of widespread occurrence in the upper Permian of Russia and parts of Europe and Asia. The gastropod Mourlom’a? reloba, n. sp. oc- curs in this Zone in northern Alaska. Stratigraphic position was assigned to the individ- ual collections either by the collector or by Dutro. Dutro based certain of the assignments on observa— tions made during fieldwork, knowledge of the lithol- ogy and regional stratigraphy, study of the general aspect of the fauna, and position of the collection within measured sections. These assignments are used in placing collections in the faunal or rock units listed in table 1. “Vithin each unit, collections are listed in numerical order. Principal causes of uncertainty as to stratigraphic placement of collections are increasing stratigraphic refinement as the fieldwork progressed, incomplete stratigraphic sequences, and poor preservation of fos- sils. Collections from measured type sections, or from closely associated sections on which considerable reli- ance as to correct stratigraphic assignment can be placed, are indicated by reference to footnote 1 pre- ceding the locality number. STRATIGRAPHIC DISTRIBUTION LOWER MISSISSIPPIAN UNDIFFERENTIAT’ED The Lower Mississippian rocks of northern Alaska include the Kayak shale and the ‘Vachsmuth limestone, each of which contains three faunal zones (fig. 24). The few snails collected from these zones provide, in themselves, no basis for distinguishing any one zone from another. Accordingly, most collections from 10- calities other than type sections are treated as Lower Mississippian undifferentiated. The most important difference between the Lower and Upper Mississippian gastropod faunules is the apparent abundance of platycerataceans in the earlier beds compared with a virtual absence in the later beds. This may be simply a matter of facies, Platy- ceras apparently being able to live only on pelmato— zoan echinoderms (Bowsher, 1955). Suitable habi- tats for crinoids apparently were few in Late Mis- sissippian seas of northern Alaska. Most platycera- tid specimens occur in dark bioclastic limestone con— taining much crinoidal debris. Platyceratids do occur in Permian rocks and, rarely, in the Upper Mississip- pian of this region. Their presence is not, in itself, an index of an Early Mississippian age. 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OEWI Z6614 £8881 L816 ZLZS 9101 MOI l 99811 19816 I I?!“ I OSII’I I 6LLZI 25s 3553901158 :chEHe nnEuEec one“ one“ getahmess 93.:me 5:388. :oSnEHoH 5E9? coaaHanfioEuH: 9 552% ”8.5.5.5 $393355 8 ”1:585 2 45wa :Efiuonfi UoEnn gees—cam ”3&wame 1mHmm1HH>H .naEEmewH 2 15H SHEEN. SHED Uwaflenooloagmwaz nan—WE memIoads go .19qu N 1910111 ‘ 605530015355: 3:32 Him .33 3:53 Eon—WERE 635300]:unan 3223: .E floaaetwg oweuefisl 8H5 use $a§3§ HES £3392?»ng mam—SH. 118 T urbanellina? lata, n. sp. is found only in rocks of Early Mississippian age. Several other species are known from single specimens and little reliance can be placed on them for stratigraphic determinations. Anematim rocky/montanum (Shimer) is more com- mon in the Lower Mississippian than in the Upper Mississippian. Euomphalaceans, mostly indeterminate as to genus and species, are more common in the Lower Mississippian; bellerophontaceans, also mostly inde- terminate as to species, are less abundant. Pleuro- tomareans are less common and individual specimens are smaller in the Lower Mississippian than in the Upper Mississippian. Finally, neritaceans are much rarer in the Lower Mississippian than in later beds. UPPER MISSISSIPPIAN Naticopsis and Lithostrotion zones—Collections from the Natlcopsz's zone of the Upper Mississippian Alapah limestone, constitute a gastropod faunule composed primarily of large neritaceans and large bellerophontaceans. Most specimens are steinkerns in a blocky black limestone matrix. One specimen of Anematz'na and an indeterminate euomphalacean were also collected from rocks of this zone. The Lithostrotion zone yields a more diversified gastropod faunule. Nearly half the specimens are euomphalaceans, a considerable number of which can- not be assigned to genus with any degree of confi- dence. Several specimens are identified as Straparol— lus (Euomphalus) brooksensz’s, n. sp. Other gastro- pods from this zone are single specimens of Portlock- fella? sp., Rhineodema? sp., Anomphalus sp., an in- determinate murchisoniacean, and an indeterminate neritacean. Two specimens each of Ammatlna and an indeterminate species of pleurotomariacean com- plete the faunule. Neither zone can be distinguished solely on the basis of gastropod species present, although collec— lections from the Lithostrotion zone show more taxo- nomic variety than those from the Naticopsis zone. In addition, many of the species and genera found in these two zones also occur in rocks of Early Missis— sippian age. Among these are Bellerophon sp., Ane- matz'na rockymontamum (Shimer), Straparollus (Eu- omplzalus) brooksensls, n. sp., and, tentatively, Natlcopsis (Natlcopsis) sutum'compt‘a, n. sp. Never- theless, fieldwork has demonstrated that the dark matrix and large size of the specimens from the Natlcopsls zone are distinctive. Certain collections from among those listed in table 1 as “Naticopsis or Lithostrotion zones” seem more likely to represent the Natlcopsis zone. In this cate— gory are USGS (U.S. Geological Survey) localities SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY 11799 and 13287. On much less certain grounds, col- lections from USGS localities 976 and 5430 may also represent the Naticopsis zone. Other collections can- not be assigned to either zone with any degree of confidence. Goniatites zone and probable Goniatites zone—This assemblage, dominated by the large pleurotomaria- ceans Bembewia? inumbllicata, n. sp. and Nodospira ornala, n. gen., n. sp., is the most distinctive of the gastropod faunules studied. With the exception of Euphemltes and Loam/mama, of which one and two specimens, respectively, occur in the Lower Mississip- pian, all specifically identifiable gastropods from rocks assigned to this zone are limited to it. Within. this zone, cephalopods and gastropods occur together at USGS localities 11828, 11865, and 12084. These gastropod studies suggest strongly that the collections listed as “probable Gonlatz'tes zone” in table 1 should be referred to that zone without question. Neilsom'a? sp. and Euphemz'tes sp. occur in both sets of collections, along with Nodospz'm omata, n. sp. and Bembemla? inumbilicata, n. sp. In addition, Mom'- lom'a mlnuta, n. sp. is present in collections question- ably referred to the Goniatltes zone and may be rep- resented by a steinkern in a collection definitely from the G'om'atites zone. Upper Mississippian undifierenliated.—All speci— mens referred to this listing are exceedingly poorly preserved. No significant stratigraphic statement can be made on the basis of the available material. PERM IAN Euomphalaceans constitute nearly two-thirds of the Permian gastropod assemblage. Pleurotomariaceans, most of which are indeterminate as to genus and spe- cies, comprise much of the remainder but they are widely distributed and occur in nearly as many col- lections as the euomphalaceans. Several indetermi- nate bellerophontaceans and Platycems complete the assemblage. The presence of Platyceras in beds of Permian age indicates that, in Alaska, the genus can- not be used as a guide to the Mississippian. The euomphalacean species appear to be relatively reliable guide fossils to the Permian rocks. Two of these species, Straparollus (Euomphalus) alaslcensis, n. sp. and Amphis'oapha (Cyllcioscapha) grada, n. sp. are described. Among the pleurotomariaceans, Mom"- lom'a? reloba, n. sp. is the most common species. Many kinds of pleurotomariaceans seem to be repre- sented in the poorly preserved material from the Per- mian of northern Alaska. The gastropods suggest faunal relationships among the Siksikpuk, Sadlerochit, and unnamed Permian LATE PALEOZOIC GASTROPODA FROM NORTHERN ALASKA formations. Straparollus (Euomphalus) alas/70671858, n. sp. occurs in all three formations, and Amphiscapha (Uylécioscapha) grader, n. sp. is present in the latter two. Finally, Mom'lom'a? reloba, n. sp. occurs in the unnamed formation, is tentatively identified in collec- tions from the Siksikpuk formation, and may be pres- ent in the Sadlerochit formation. USGS locality 14174, assigned to the Siksikpuk . formation on the basis of rock type, is atypical. The collection consists of two specimens of Glabrocingulum‘ (Glabroci’ngu-Zum) sp. and one specimen of Trepospir‘a (Trepospira) sp. Except for one questionable occur- rence, Trepospim is unknown in Permian faunas else- where in the world. Furthermore, the specimens of Glabrocingulum differ from Permian species known from the southwestern United States and other well— known areas of Permian exposures. It may be that this collection is actually of Pennsylvanian age. More fieldwork in northern Alaska and additional collec— tions are needed to confirm the presence of Pennsyl- vanian rocks. Known ranges of the more significant species are shown in figure 25. ECOLOGICAL AND PALEOGEOGRAPHICAL DATA Representatives of five superfalnilies—euomphala- ceans, platycerataceans, pleurotomariaceans, nerita- ceans, and bellerophontaceans, in that order of abun- dance-comprise virtually all the gastropods studied. The groups are represented by nearly equal numbers of specimens, with the euomphalaceans being perhaps half again as abundant as the bellerophontaceans. Although many of the pleurotomariaceans are poorly preserved, this group has considerably more generic diversity than the others. Individual collections show little taxonomic variety. Less than 10 percent of the collections contain more than three taxa. This lack of diversification may re— flect the small amount of collecting or it may, in part, reflect a time of unfavorable or relatively uniform en- vironment. For example, fossils of Lower Mississip- pian strata of the western United States have been collected for nearly 100 years, but relatively few gas- tropods are known. It could be more than coincidence that both regions were the sites of predominantly clas- tic limestone deposition during the late Paleozoic. lcologic and paleogeographic inferences drawn from this study are listed below. Further work is needed before the generalizations can be applied to upper Paleozoic gastropods from other regions. These inferences involve examination of other fossil groups in the late Paleozoic faunas of the region. Docu- mentation of some of the statements must necessarily 507218 0—60—2 119 await the publication of research by other specialists. 1. Platyceras commonly occurs here in crinoidal lime- stone. This partially supports the hypothesis con- cerning life relationships of platyceratids on pelma- tozoan calyxes (Bowsher, 1955). . In the Lower Mississippian where Platycems is common, the associated gastropods show less vari— ety than in the Upper Mississippian. This sug- gests that areas of limestone deposition favorable for crinoids were unfavorable for most benthonic gastropods. 3. Straparollus occurs in limestone, sandstone, silt- stone, and shale. This suggests that species of this genus had considerable ecologic tolerance. 4. Although large gastropods (an inch or more in height) are not confined to the coarse elastic facies, they are the only snails that have been collected from rocks of this facies. These large gastropods apparently lived in a zone of heavy surf, the prob- able sedimentary depositional environment of the coarse elastic material. Some of the large shells occur in a siliceous conglomeratic matrix contain— ing pebbles half an inch in diameter. 5. Cephalopods are rarely associated with the gastro- pods; the 2 groups occur together at only 6 locali- ties. Corals and gastropods also appear to be nearly mutually exclusive, although details of coral distri- bution have not been published as yet. On the other hand, except. in the N aticopsis sutm‘icmpta zone, gastropods are commonly associated with nu- merous taxonomically diversified brachiopods. Ap- parently environments favorable for diversified brachiopod faunas afforded optimum conditions for abundant gastropods. Conversely, it seems that only certain kinds of gastropods were able to live in en— vironments well suited for corals and cephalopods. 6. In the N aticopsis suturicompta zone, except for one collection, fossil assemblages consist entirely of gas- tropods. There is no obvious explanation for this apparent exclusion of other fossil invertebrates. Mississippian collections include genera known to be common in the lower Carboniferous elsewhere in the world. Heretofore they have not been reported from the American Arctic, and knowledge of their stratigraphic occurrence and geographic. distribution fills an important gap in our information on paleogeo- graphic distribution. There is no evidence at the family level, and most probably none at the generic level, that any of the groups is conspicuously present or absent because of cold—water conditions. So far as can be interpreted from this study, a boreal marine invertebrate fauna did not exist in Mississippian time. 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X {13255 , 13245><>< {3%, 13222 / 68'30’ A 13246 13242 1 u /) 13535 13223 1323112773 I 6 X{ X {3337 x 13232 x 13238 13258 13225 r '0 | _, g r { ll \\/\ 0 U HOWARD PASS \ Fauna Creek MISHEGUK o / MOUNTAIN w / 011711 RIVER 0 e “In 0 ‘ ° V O D FIGURE 27.—Fossil-collecting localities ln parts of the Misheguk Mountain quadrangle (A), the Noatak quadrangle (B), the Point Hope quadrangle (0), and the Howard Pass and Misheguk Mountain quadrangles (D), Alaska. 124 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 153° 152° X 12348 A CASTLE 68°30‘ MOUNTAIN \ < )\ I \ K/ Kr \ M \ D \ w >\(11799 Q 10862 x 14174" >i «2 11814 14150 x 1 27§ §< 11815 14151 \ x 11816 X 12779 x 14992 3292 12342 14152 Chandler ’ Lake KILLIK RIVER I CHANDLER LAKE A 151° 148° \ & 4: > 68°30' l )r . Nemushuk Imam 3169 I 1409 Lake 3107 4 3171 3087 ‘8; 3110 ”Max 3172 X 12355 3087a 13164 30§9>< 3173 14984 3091 />< 3170 x 3272 La X 3113 3088 3100 3115 3167 3247>< 3186 3182 /\‘ 11324 3098 14965 / / X3279 CHANDLER LAKE PHILIP SMITIFI MOUNTAINS B FIGURE 28.——Fossil-collecting localities in parts of the Killik River and Chandler Lake quadrangles (A) and the Chandler Lake and Philip Smith Mountains quadrangle-s (B), Alaska. 69°30’ FIGURE 29.—-Fossil-collectlng localities in parts of the Demarcatlon Point and Table Mountain quad- rangles, Alaska, and adjacent parts of Canada (A) and the Sagavanirktok and Mount Michelson LATE PALEOZOIC GASTROPODA FROM NORTHERN ALASKA 147° 142° 69° DEMARCATION POINT CA ADA >\408a>< / | 1008 1004 x 994 ”a 1009 989ax Xngg Jomc’ xx 983,?” } 1010 R / >5 TABLE MOUNTAIN 146° 145° (m SHUBLIK \ MOUNTAINS WELLER ‘5‘: MOUNT 7 / SAGAVANIRKTOK 1 .JJ ) ”x é a: X MOUNT MICHELSON L SALISBURY C quadrangles, Alaska (B). 125 126 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY Register of localities Locality N 0. Field No. Collector, year of collection, and description of locality Stratigraphic position and age USNM 3087 F 7 of 11 June ______ Bowsher, A. L., Dutro, J. T., Jr., Gudim, C. J.; 1949; Dark limestone member, Alapah F 1 of 13 June Chandler Lake quadrangle; Shainin Lake area, limestone Lithostrotion afl’. L. F 3 of 16 June southwest corner of ridge, top of Sugarloaf Hill; lat asiaticum zone; Upper Missis- 68°19’20” N., long 150°55’30” W.; measured sec- sippian. tion J, 84.5~93.3 ft above base of Alapha limestone. 3087a F 1 of 16 June ______ Bowsher, A. L., Dutro, J. T., Jr., Gudim, C. J.; 1949; Shaly limestone member, Ala- same locality as 3087; 49 ft above base of Alapah pah limestone; Naticopsz's sut- limestone. uricompta zone; Upper Missis- sissippian. 3088 F 5 of 24 July _______ Bowsher, A. L., Dutro, J. T., Jr., Gudim, C. J.; 1949; Shaly limestone member, Alapah Chandler Lake quadrangle; Nanushuk Lake area, limestone; Naticopsis suturi- along west side of main ridge southeast of lake; lat compta zone; Upper Mississip- 68°22’20” N., long 150°29’34” W., 80 ft above base pian. of Alapah limestone. 3089 F 2 of 27 August____ Bowsher, A. L., Dutro, J. T., Jr.; 1949; Philip Smith Crinoidal limestone member, Mountains quadrangle; Itkillik Lake area, north Wachsmuth limestone; “Za— slope of hill about 11,100 ft .S. 85° E. of Itkillik Lake phrentis” kom'ncki zone; Lower camp; lat 68°24’15” N., long 149°43’20” W.; 139— Mississippian. 145 ft above base of Wachsmuth limestone. 3091 F 1 of 3 June _______ Bowsher, A. L., Dutro, J. T., Jr.; 1949; Chandler Lake Crinoidal limestone member, . quadrangle; Shainin Lake area, top of lower massive Wachsmuth limestone; “Za- clifl', southwest slope of Mount Wachsmuth; lat phrentz’s” kom'ncki zone; Lower 68°18’50” N., long 150°55'25” W.; measured section Mississippian. I, 141.6—148 ft above base of Wachsmuth limestone. 3095 F 3 of 22 June ______ Bowsher, A. L., Dutro, J. T., Jr.; 1949; Chandler Lake Argillaceous limestone member, quadrangle; Shainin Lake area, head of small creek Kayak shale; Leptaena analoga about 14,700 ft. S. 8° E. of Shainin Lake camp; lat zone; Lower Mississippian. 68°16’25” N. long 150°57’25”W.; 720—777 ft above base of Kayak shale. 3098 F 1 of 22 June ______ Bowsher, A. L., Dutro, J. T., Jr., Gudim, C. J.; Feder, Crinoidal limestone member, A.; 1949; Chandler Lake quadrangle; Shainin Lake Wachsmuth limestone; “Za- area, north side of first valley south of Pinnacles; lat phrentz’s” konincki zone; Lower 68°17’ N., long 150°55’15” W., 187—198 ft above Mississippian. base of Wachsmuth limestone. 3100 F 2 of 20 August__-_ Bowsher, A. L., Dutro, J. T. Jr.; 1949; Philip Smith Crinoidal limestone member, Mountains quadrangle; Itkillik Lake area, 8,500 ft Wachsmuth limestone “Za- S. 40° E. of Itkillik Lake camp; lat 68°23’15” N., phrentis” kom'ncki zone; Lower long 149°45’50” W.; 73—75 ft above base of Wachs- Mississippian. muth limestone. 3107 F 2 of 21 July ______ Bowsher, A. L., Dutro, J. T., Jr., Gudim, C. J.; 1949; Crinoidal limestone member, Chandler Lake quadrangle; Nanushuk Lake area, Wachsmuth limestone; “Za- south side of ridge, 10,000 ft N. 12° W. of Nanushuk phrentis” kom'ncki zone; Lower Lake camp; lat 68°25’10” N., long 150°30’15” W. Mississippian. 3110 F 6 of 23 July _______ Bowsher, A. L., Dutro, J. T., Jr., Gudim, C. J.; 1949; Crinoidal limestone member, Chandler Lake quadrangle; Nanushuk Lake area, Wachsmuth limestone; “Zaph- 6,800 ft east of Nanushuk Lake camp; lat 68°23’30” rentis” kom'ncki zone; Lower N., long 150°26’20” W. Mississippian. 3113 F 3 of 3 August _____ Bowsher, A. L., Dutro, J. T., Jr.; 1949; Chandler Lake Banded limestone member, Wach- quadrangle; Shainin Lake area, south face of Sugarloaf smuth limestone; Brachythyris Hill; lat 68°18’50" N., long 150°55’35” W.; 957 ft suborbicularis zone; Lower Mis- above base of Wachsmuth limestone. sissippian. 3115 F 1 of 12 July ....... Bowsher, A. L., Dutro, J. T., Jr.; 1949; same locality as Banded limestone member, Wach- 3113; 845—849 ft above base of Wachsmuth limestone. smuth limestone; Brachythyris suborbiculan's zone; Lower Mis- sissippian. 3164 F 2 of 24 July _______ Bowsher, A. L., Dutro, J. T., Jr., Gudim, C. J.; 1949; Shaly limestone member, Alapah Chandler Lake quadrangle; Nanushuk Lake area, limestone; Naticopsis suturi- about 1,800 ft S. 34°E. of Nanushuk Lake camp; lat compta zone; Upper Missis- 68°23’10” N., long 150°28’45” W.; lower 30 ft of sippian. Alapah limestone. 3167 F 6 of 24 July _______ Bowsher, A. L., Dutro, J. T., Jr., Gudim, C. J.; 1949; Dark limestone member, Alapah Chandler Lake quadrangle; Nanushuk Lake area, limestone; Lithostrotion afi. L. about 6,900 ft S. 6° W. of Nanushuk Lake camp; lat asiaticum zone; Upper Mis- 68°22’15” N., long 150°29’35” W.; 97—113 ft above sissippian. ’ base of Alapah limestone. 3169 F 1 of 28 August__-- Bowsher, A. L., Dutro, J. T., Jr., Gudim, C. J.; 1949; Dark limestone member, Alapah Philip Smith Mountains quadrangle; Itkillik Lake limestone; Lithostrotion all. L. area, about 13,900 ft N.60° E. of Itkillik Lake camp; asiaticum zone; Upper Mis~ lat 68°25’25” N., long 149°43’40” W.; 86.3 ft above sissippian. base of Alapah limestone. 3170 F 1 of 23 July _______ Bowsher, A. L., Dutro, J. T., Jr., Gudim, C. J.; 1949; Shaly limestone member, Alapah Chandler Lake quadrangle; Nanushuk Lake area, limestone; Naticopsis suturi- about 2,500 ft N. 65° E. of Nanushuk Lake camp; lat compta zone; Upper Missis- 68°23’40” N., long 150°28’ W.; about 60 ft above sippian. base of Alapah limestone. LATE PALEOZOIC GASTROPODA FROM NORTHERN ALASKA Register of localities—Continued 127 Locality No. Field N o. Collector, year of collection, and description of locality Stratigraphic position and age USNM 3171 3172 3173 3182 3186 3188 3247 3272 3279 USGS 7118b (Green) USGS 406 408a 960 971 972 975 976 979 982 987 989a F 4 of 11 August___- F 3 of 23 August---- F 2 of 25 August---- F 1 of 26 July _______ F 4 of 7 August _____ F 5 of 7 August _____ F 6 of 6 July__--_-__ F 3 of 24 August---- F 1 of 20 June _______ 19D _______________ 11 Md 26__-__--__-- 11 Md 28a__--______ 12 Md 31 ___________ 12 Md 40 ___________ l2 Md 41_---_---_-_ 12 Md 44 ____________ 12 Md 46 ___________ 12 Md 49 ____________ 12 Md 53 ----------- 12 Md 59 ___________ 12 Md 61 ___________ Bowsher, A. L., Dutro, J. T., Jr.; 1949; Philip Smith Mountains quadrangle; Itkillik Lake area, about 13,600 ft N. 60° E. of Itkillik Lake camp; lat 68°20’25” N., long 149° 43’0‘5” W.; 63 ft above base of Alapah limestone. Bowsher, A. L., Dutro, J. T., Jr.; Gudim, C. J.; 1949; same locality as 3171; about 140 ft above base of Alapah limestone. Bowsher, A. L., Dutro, J. T., Jr., Gudim, C. J.; 1949; Philip Smith Mountains quadrangle; Itkillik Lake area, about 12,200 ft N. 65° E. of Itkillik Lake camp; lat 68°25’12” N., long 149°43’10” W.; float at base of section. Bowsher, A. L., Dutro, J. T., Jr.; 1949; Chandler Lake quadrangle; Nanushuk Lake area, about 6,900 ft S. 6° W. of Nanushuk Lake camp; lat. 68°22’25” N., long 149°43’40” W.; 80 ft above base of Alapah lime- stone. Bowsher, A. L., Gryc, G., Fischer, W.; 1949; Chandler Lake quadrangle; Shainin Lake area, near south end of Sugarloaf Hill; lat 68°19’25” N., long 150°55’30” W.; 172 ft above base of Alapah limestone. Bowsher, A. L., Gryc, G., Fischer, W.; 1949; same locality as 3186; 0.3 ft above locality 3186. Bowsher, A. L., Dutro, J. T., Jr.; 1949; Chandler Lake quadrangle; Shainin Lake area, about 8,000 ft S. 32° W. of Shainin Lake camp; lat 68°17’45” N., long 150°56’30” W.; 795.3—798 ft above base of Kayak shale. Bowsher, A. L., Dutro, J. T., Jr.; 1949; Philip Smith Mountains quadrangle; Itkillik Lake area; lat 68°25’30” N., long 149°42’40” W.; 91 ft above base of Alapah limestone. Bowsher, A. L.; 1950; Chandler Lake quadrangle; upper Alapah Creek, about 600 ft S. 80° E. of Alapah Creek camp; lat 68°10’18” N., long 150°46’20” W.; lower 44 ft of Wachsmuth limestone: Lcfiingwell, E. de K.; 1908; Mount Michelson quad- rangle, Ikiakpaurak valley; approximate lat 69°28’ N., long 145°50’ W. Maddren, A. G.; 1911 ; International Boundary Survey; about 4 mi south of east camp on Joe Creek of Firth River; lat 68°53’40” N., long 140°57’30” W. Maddren, A. G.; 1911; International Boundary Survey; about 2 mi west of west camp on Joe Creek; lat 68°57’ N., long 141°22’30” W. Jessup, J. M.; 1912; International Boundary Survey; west side of You Creek, north end of ridge; lat 68°44’ N., long 141°04’25” W. Jessup, J. .M.; 1912; International Boundary Survey; northeast slope of main fork of Incog Creek; lat 68°46’30” N., long 140°56” W. Jessup, J. M.; 1912; International Boundary Survey; northeast slope of main fork of Incog Creek, near head of creek; lat 68°47’10” N., long 140°57’55” W. Jessup, J. M.; 1912; International Boundary Survey; southwest slope of Turner Mountain; lat 68°48’50” N., long 140°56'W. Maddren, A. G.; 1912; International Boundary Survey; west end of Turner Mountain, on east slope of upper afoulevard Creek; lat 68°49’50” N., long 140°58’35” Harrington, G. L.; 1912; International Boundary Sur- vey; mountain spur 2% mi southeast of Joe Creek camp; lat 68°53’40” N., long 140°56’ W. Jessup, J. M.; 1912; International Boundary Survey; 1 mi south of Joe Creek and %-, mi east of 141st meridian; lat 68°54’30” N., long 140°59’30” W. Maddren, A. G.; 1912; International Boundary Survey; 1%,, mi west of 141st meridian, south of Joe Creek; lat 68°55’ N., long 141°03’ W. Maddren, A. G.; 1912; International Boundary Survey; north bank of Joe Creek, %' mi west of 141st meridian; lat 68°55’30” N., long 141°02’ W. Shaly limestone member, Alapah limestone; Naticopsis suturi- compta zone; Upper Missis- sippian. Dark limestone member, Alapah limestone; Lithostrotion afl". L. asiaticum zone; Upper Mis- s1ssippian. Crinordal limestone member, Wachsmuth limestone; “Zaph- rentis” konmcki zone; Lower Mississippian. Shaly limestone member, Alapah limestone; Naticopsis suturi- compta zone; Upper Mississip- pian. Dark limestone member, Alapah limestone; Lithostrotion afl'. L. asiaticmn zone; Upper Missis- sippian. Dark limestone member, Alapah limestone; Lithostrotion afl‘. L. asiaticum zone; Upper Missis- sippian. Argillaceous limestone member Kayak shale; Leptaena analoga zone; Lower Mississippian. Dark limestone member, Alapah limestone; Lithostrotion aff. L. asiaticum zone; Upper Missip- pian. Shaly limestone member(?) , Wachsmuth limestone; “Zap- hrentis” Iconincki zone; Lower Mississippian. Sadlerochit formation; Permian. Alapah limestone(?), Lisburne group; Upper Mississippian (1’) . Permian(?). Permian(?). Lisburne group; Upper Mississip- pian. Alapah limestone, Lisburne group; Upper Mississippian. Alapah limestone, Lisburne group; Upper Mississippian. Alapah limestone, Lisburne group; Upper Mississippian. Permian(?). “Pennsylvanian shales” (of Mad- dren) ; Permian(?). “Pennsylvanian shales” (of Mad- dren); Permian(?). “Pennsylvanian shales” (of Mad- dren); Permian(?) 128 SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY Register of localities—Continued Locality No. Field No. Collector, year of collection, and description of locality Stratigraphic position and age USGS 994 12 Md 66 ___________ Harrington, G. L.; 1912; International Boundary Alapahlimestone,Lisburnegroup; Survey; ridge north of Joe Creek, from bed above Upper Mississippian. reddish—weathering slaty limestone; lat 68°56’ 10” N., long 140°57’15" W. 996 12 Md 68 ___________ Jessup, J. M.; 1912; International Boundary Survey; Alapahlimestone,Lisburnegroup; east slope of gulch north of Joe Creek, about % mi Upper Mississippian. egst of 14151; meridian; lat 68°56’10” N., long 140°58' 997 12 Md 69 ___________ Jessup, J. M.; 1912; same locality as 996; about 250 ft Alapahlimestone,Lisburnegroup; north of 996, along strike. Upper Mississippian. 1004 12 Md 76 ___________ Maddren, A. G.; 1912; International Boundary Alapahlimestone,Lisburnegroup; Survey; northwest corner of limestone outcrop west Upper Mississippian. (ééTub Mountain; lat 68°58’50” N., long 141°06’35” 1008 12 Md 79 ___________ Harrington, G. L. ; 1912; International Boundary “Artinskian limestone” (of Mad- Survey; south side Joe Creek, about 6% mi west of dren); Permian. 14lst meridian; lat 69°56’30" N., long 141°18’ W. ' 1009 12 Md 80----..______ Harrington, G. L.; 1912; same locality as 1008; about “Artinskian limestone” (of Mad- iio mi west. dren); Permian. 1010 12 Md 81 ___________ Jessup, J. M.; 1912; International Boundary Survey; “Artinskian limestone” (of Mad- north side Joe Creek valley about 7% mi west of dren), Permian. 141st meridian; lat 68°56’ N., long 141°21’ W. 1014 12 Md 85 ___________ Jessup, J. M.; 1912; International Boundary Survey; Alapah limestone(?), Lisburne north slope of gulch on ‘vest side Clarence River, group; Upper Mississippian. about 1% mi west of 141813 meridian; lat 69°25’ N., long 141°04’ W. 1015 12 Md 85a __________ Harrington, G. L.; 1912; same locality as 1014, from Alapah limestone(?), Lisburne talus below outcrop. group; Upper Mississippian. 9184 45 AKr 58 __________ Kirschner, C. E. ; 1945; Killik River quadrangle; east Alapahlimestone,Lisburnegroup; bank of Okpikruak River, 16% mi S. 4° W. from Upper Mississippian. forks of Killik River; lat 68°34’30” N., long. 153°31’ W. 9186 45 AGr l ___________ Gryc, G.; 1945; Chandler Lake quadrangle; bluffs Lisburne group; Lower Missis- west of northernmost tip of Chandler Lake; lat sippian(?). 68°17’30” N., long 152°36’ W. 9187 45 AGr 2 ___________ Gryc, G.; 1945; Chandler Lake quadrangle; bluffs Alapah limestone(?), Lisburne west of northernmost tip of Chandler Lake; lat group; Upper Mississippian. 68°17’ N., long 152°36' W. 10862 49 APa 384 _________ Patton, W. W., Jr.; 1949; Chandler Lake quadrangle; Alapah limestone; Gom'atites cren- cutbank on north side of Monotis Creek; lat 68°22’» istria zone; Upper Mississip- 35” N., long 152°54’ W.; from limestone bed over- pian. lying chert-shale member of Alapah limestone. 10868 49 ATr 399 _________ Tailleur, I. L.; 1949; Killik River quadrangle; cutbank Alapah limestone Gom'atites cren- on east side of Middle Fork of Okpikruak River; lat istria zone; Upper Mississip- 68°33’ N., long 153°31’ W.; near top of Alapah lime- pian. stone. 10870 48 ASa 47 __________ Sable, E. G., Lachenbruch, A. H.; 1948; Mount Michel— Lisburne group; Upper Mississip— son quadrangle; north slope of Kikittut Mountain pian. about 1 mi west of Hulahula River; lat 69°28’ N., long 144°25’ W. 11785 50 ABe 201 _________ Brosgé, W. P.; 1950; Philip Smith Mountains quadran- Siksikpuk formation; Permian(?). gle; Galbraith Lake area; approximate lat 68°29’ N., long 149°13’ W.; about 560 ft above base of Siksikpuk formation. 11786 50 ABe 200 _________ Brosgé, W. 1).; 1950; same locality and level as 11785-- Siksikpuk formation; Permian(?). 11799 50 ARr 49 __________ Reiser, H. N.; 1950; Chandler Lake quadrangle; Sik- Alapah limestone (middle part); sikpuk River area; approximate lat 68°20’ N., long Upper Mississippian. 151°50’ W.; about 800 ft above base of Alapah lime- stone. 11807 50 ABe 115 _________ Reiser, H. N.; 1950; Chandler Lake quadrangle; Chan- Wachsmuth limestone; Lower dler Lake area, about 10,000 ft S. 85° E. of astronom- Mississippian. ical point on Little Chandler Lake; lat 68°16’40” N., long 152°36’50” W.; 280 ft above base of Wachsmuth limestone. 11808 50 ABe 44 __________ Brosgé, W. P.; 1950; same locality as 15408; 575 ft Wachsmuth limestone; Lower above base of Wachsmuth limestone. Mississippian. 11814 50 AKe 238 __________ Keller, A. S.; 1950; Chandler Lake quadrangle; cutbank Siksikpuk formation; Permian(?). on east side of Skimo Creek, a tributary of Tiglukpuk Creek; lat 68°17’ N., long 151°53’ W.; basal 60 ft of Siksikpuk formation. 11815 50 AKe 240 _________ Keller, A. S.; 1950; same locality as 11814,- possibly Siksikpuk formation;Permian(?). slightly different stratigraphic level. 11816 50 AKe 242__-_,____ Keller, A. S.; 1950; same locality as 11814; possibly Siksikpuk formation; Permian(?). slightly different stratigraphic level. 11823 50 AKt 329 ......... Kent, B. H.; 1950; Howard Pass quadrangle; station K Unnamed Permian formation (‘1); 280; lat 68°36’ N., long. 158°22’ W.; in structurally complex area, stratigraphic position unknown. Permian(?). LATE PALEOZOIC GASTROPODA FROM NORTHERN ALASKA Register of localities—Continued 129 Locality No. Field No. Collector, year of collection, and description of locality Stratigraphic position and age USGS 11828 11843 11858 11861 11865 11867 11890 12084 12340 12342 12348 12355 12700 12701 12709 12773 12779 12785 12788 12798 13215 13216 13219 13222 13225 13228 13231 50 ATr 45 __________ 50 ATr 189 _________ 50 ASa 227 _________ 50 ASa 235 _________ 5O ASa 150 _________ 5O ASa 236 _________ 50 AMg 149 ________ F3 of 12 June _______ 50 ACh 41 __________ 50 AKe 226 _________ 46 ATh 8 ___________ 50 ABe 112 _________ 11 AS 46 ___________ 11 AS 51 ___________ 50 ADu 16 __________ 51 ATr 14 ___________ 51 ABe 5 ___________ 11AS 77 ___________ 5O ADu 77 _________ 50 ADu 44 _________ 51 ARr 100 _________ 51 ART 101 _________ 51 ARr 84 __________ 51 ARr 107 _________ 51 ATr 1 ___________ 51 ATr 10 __________ 51 ATr 346 _________ Tailleur, I. L.; 1950; Howard Pass quadrangle; Etivluk River valley; lat 68°35’ N., long 156°38’ W. Tailleur, I. L.; 1950; Howard Pass quadrangle; Ipnavik River valley; lat 68°35’ N., long 157°29’ W. Sable, E. G.; 1950; Misheguk Mountain quadrangle; station Sa 350, Utukok River valley; 2 mi north of west fork of Utukok River; lat 68°34’40” N., long 161°10’30” W. Sable, E. G.; 1950; Misheguk Mountain quadrangle; 2,800 ft southeast of locality 11858; lat 68°34’20” N., long 161°10’ W. Sable, E. G.; 1950; Misheguk Mountain quadrangle; station Sa 249, head of west fork of Utukok River; lat 68°34’40” N., long 161°16’50” W. Sable, E. G.; 1950; Misheguk Mountain quadrangle; station Sa 350(15), north side of Kogruk Mountain, Utukok River valley; about 400 ft south of locality 11861; lat 68°34’20” N., long 161°10’ W. Mangus, M. D.; 1950; Misheguk Mountain quadrangle; divide between Iligluruk Creek and Kugururok River; lat 68°34’ N., long 161°20’30” W. Bowsher, A. L., Grye, G.; 1950; Chandler Lake quad- rangle; Anaktuvuk River valley; 1,500 ft east of Kanakutk Lake; lat 68°18’ N., long 151°21’ W. Chapman, R.; 1950; Killik River quadrangle; Colam- nagavik River valley; lat 68°35’ N., long 154°32’ W. Keller, A. S.; 1950; Chandler Lake quadrangle; 100 ft south of locality 11814; lat 68°17’ N., long 151°53’ W.; upper 75 ft of Alapah limestone. Thurrell, R.; 1946; Killik River quadrangle; upper Oolamnagavik River valley; lat 68°35’ N., long 154°32’ W. Gudim, C. J; 1950; Philip Smith Mountains quadrangle; Galbraith Lake area; approximate lat 68°28’30” N., long 149°21’ W.; about 60 ft above base of Alapah limestone. Smith, P. S.; 1911; Misheguk Mountain quadrangle; central Noatak River valley; cutbank on south side of river; approximate lat 68°01’ N., long 159°02’ W. Smith, P. S.; 1911; Misheguk Mountain quadrangle; central Noatak River valley, cutbank on north side of river; approximate lat 68°07’48” N., long 159°53’ W. Dutro, J. T., Jr.; 1950; Misheguk Mountain quad- rangle; Nimiuktuk River valley; lat 68°22’18” N., long 159°53’45” W. Tailleur, I. L.; 1951; Howard Pass quadrangle; Ipnavik River valley; approximate lat 68°22’ N., long 157°28’ W. Brosgé, W. P.; 1951; Chandler Lake quadrangle; Monotis Creek section; lat 68°20’ N., long 152°50’15” W. upper 100 ft of Alapah limestone. Smith, P. S.; 1911; Noatak quadrangle; lower Noatak River valley; approximate lat 67°14’30” N., long 162°30’ W. Dutro, J. T., Jr.; 1950; Misheguk Mountain quad- rangle; Nimiuktuk River valley; lat 68°16’23” N., long 159°57’36” W. Dutro, J. T., Jr.; 1950; Misheguk Mountain quad- rangle; Nimiuktuk River valley; lat 68°24’ N., long 159°53’ W. Reiser, H. N.; 1951; Howard Pass quadrangle; station 79d, Kiligwa River valley; lat 68°39’ N., long 158°38’ W. Re7i3er, H. N.; 1951; same locality as 13215; station e. Reiser, H. N.; 1951; Howard Pass quadrangle, Kiligwa River valley; lat 68°35’ N., long 158°20’ W. Reiser, H. N.; 1951; Howard Pass quadrangle; same locality as 13219. Tailleur, I. L.; 1951; Howard Pass quadrangle; Ipnavik River valley, lat 68°21’ N., long 157°18’ W. Tailleur, I. L.; 1951; Howard Pass quadrangle; Ipnavik River valley; lat 68°22’30” N., long 157 15’ W. Tailleur, I. L.; 1951; Howard Pass quadrangle; Kuna River valley; lat. 68°22’ N., long 157°42’ W. Lisburne group; Gom’atites aren- istrz’a zone; Upper Mississip- pian. Lisburne group(?); Lower Mis- sissippian. Lisburne group (lower forma- tion) ; Lower Mississippian. Lisburne group (lower forma- tion); Lower Mississippian. Lisburne group (upper forma- tion); Upper Mississippian. Lisburne group (lower forma- tion; Lower Mississippian. Lisburne group (lower forma- tion) ; Lower Mississippian. Chert-shale member, Alapah lime- stone; Gom’atites cremistria zone Upper Mississippian. Alapah limestone(?); Upper Mis- sissippian (‘3). Alapah limestone; Upper Mis- sissippian. Alapah limestone (?) ; Upper Mis- sissippian (?). Shaly limestone member, Alapah limestone; Naticopsis suturi- compta zone; Upper Missis- sippian. Lisburne group (lower forma- tion?) ; Lower Mississippian. Lisburne group; Lower Missis- sippian. Lisburne group (lower forma- tion) ; Lower Mississippian. Lisburne group; Lower Missis- sippian. Chert-shale member, Alapah lime- stone; G’oniatites crenistria zone; Upper Mississippian. Lisburne group; Lower Missis- sippian. Lisburne group; Lower Missis- sippian. Lisburne group; Lower Missis- sippian. Unnamed. Permian formation; Permian. Unnamed. Permian formation; Permian. Kayak sha1e(?); Leptaena analoga zone(?) ; Lower Mississippian. Kayak shale(?); Scalarituba zone(?); Lower Mississippian. Lisburne group; Lower Missis- sippian. Lisburne group; Lower Missis- sippian. Kayak shale; Leptaena analoga zone; Lower Mississippian. 130 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY Register of localities—Continued Locality No. Field No. Collector, year of collection, and description of locality Stratigraphic position and age USGS 13232 51 ATr 347 _________ Tailleur, I. L.; 1951; same locality as 13231 ___________ Lisburne group; Lower Missis- s1pp1an. 13234 51 ATr 350 _________ Tailleur, I. L.; 1951; same locality as 13231--__________ Lisburne group; Lower Missis- s1pp1an. 13235 51 ATr 351 _________ Tailleur, I. L.; 1951; same locality as 13231____________ Lisburne group; Lower Missis- s1pp1an. . 13236 51 ATr 352 _________ Tailleur, I. L.; 1951; same locality as 13231 ___________ Lisburne group; Lower Missis- s1pp1an. 13237 51 ATr 353 _________ Tailleur, I. L.; 1951; same locality as 13231 ___________ Lisburne group; Lower Missis- s1ppian. 13238 51 ATr 354 _________ Tailleur, I. L.; 1951; same locality as 13231_________ __- Kayak shale(?); Leptaena analoga zone; Lower Mississippian. 13240 51 ATr 392 _________ Tailleur, I. L.; 1951; Howard Pass quadrangle; Kiligwa Lisburne group; Lower Missis- River valley; lat 68°32’ N.; long 158°51’ W. sippian. 13241 51 ATr 393 _________ Tailleur, I. L.; 1951; same locality as 13240 ___________ Lisburne group; Lower Missis- s1pp1an. 13242 51 ATr 394 _________ Tailleur, I. L.; 1951; same locality as 13240--__________ Lisburne group; Lower Missis- s1pp1an. 13245 51 ATr 406 _________ Tailleur, I. L.; 1951; Howard Pass quadrangle; Kiligwa Kayak shale(?); Scalam’tuba River valley; lat 68°33’ N.; long 158°53’ W. zone(?); Lower Mississippian. 13246 51 ATr 412 _________ Tailleur, I. L.; 1951; Howard Pass quadrangle; Kiligwa Lisburne group; Upper Missis— River valley; lat 68°30’30” N.; long 158°48’ W. sippian(?). 13247 51 ATr 162 _________ Reiser, H. N.; 1951; Howard Pass quadrangle; Kiligwa Kayak sha1e(?); Leptaena ana- River valley; lat 68°33’ N.; long 158°54’ W. loga zone; Lower Mississippian. 13252 51 ATr 323 _________ Tailleur, I. L.; 1951; Howard Pass quadrangle; station Kayak shale(?); Leptaena ana- T—91, Kiligwa River valley; lat 68°25’ N.; long loga zone(?); Lower Missis- 158°26’ W. sippian. 13254 51 ATr 328 _________ Tailleur, I. L.; 1951; Howard Pass quadrangle; station Lisburne group; Lower Missis- T—92, Kiligwa River valley; lat. 68°25’ N.; long sippian. 158°27’ W. 13255 51 ATr 329 __________ Tailleur, I. L.; 1951; same locality as 13254 ___________ Lisburne group; Lower Missis- s1 plan. 13258 51 AKt 124 _________ Kent, B. H.; 1951; Howard Pass quadrangle; Kuna Kayrak shale; Leplaena analoga River valley; lat 68°22’ N., long 157°42’ W. zone(?); Lower Mississippian. 13278 50 ABe 31 __________ Brosgé, W. P.; 1950; Chandler Lake quadrangle; Wachsmuth limestone; Brachy- Chandler Lake area; lat 68°18’30” N.; long thyris suborbicularis zone; 152°40’30” W.; section B-20, 40 ft above base of Lower Mississippian. Wachsmuth limestone. 13286 50 ABe 43 __________ Brosgé, W. P.; 1950; Chandler Lake quadrangle; Wachsmuth limestone; Brachy— 11,000 ft N. 86° E. of astronomical point on Little thyris suborbicularis zone(?); Chandler Lake; lat 68°17’ N.y long 152°36’30” W.; Lower Mississippian. about 500-550 ft above base of Wachsmuth lime- stone. 13287 50 ABe 45 ___________ Brosgé, W. P.; 1950; same locality as 13286; from float Alapah limestone(?); Naticopsz's about 800 ft above base of Lisburne group (may be suturicompta zone or Lithoslro- basal Alapah limestone). tion zone; Upper Mississippian. 13288 50 ABe 46 __________ Brosgé, W. P.; 1950; same locality as 13286; from Alapah limestone; Lithostrotion about 200 ft above base of Alapah limestone. aff. L. asiaticum zone; Upper Mississippian. 13292 50 ABe 117 _________ Gudim, C. J., Reiser, H. N.; 1950; Chandler Lake Wachsmuth limestone; Lower quadrangle; 5 mi west of Little Chandler Lake, from Mississippian. southern Lisburne klippe; lat 68°18’ N., long 152°45’ W.; about 250 ft above base of Wachsmuth lime- stone. 14035 50 ARr 18 __________ Reiser, H. N.; 1950; Philip Smith Mountains quad- Alapah limestone (upper part?); rangle; Galbraith Lake area; lat 68°29’ N.; long Upper Mississippian. 149°13’ W., possibly from upper part of formation. 14074 49 AMg 91 _________ Mangus, M. D.; 1949; Howard Pass quadrangle; Wachsmuth limestone; “Zaph- about 5 mi east of Howard Pass Lake; lat 68°12’ N.y rentis” kom’ncki zone(?); Lower long 156°38’ W. Mississippian. 14097 49 ALa 5 ___________ Lachenbruch, A. H.; 1949; Howard Pass quadrangle; Wachsmuth limestone; Lower Etivluk River valley, cutbank in Fay Creek, 5 mi Mississippian. west of Etivluk River; lat 68°20’ N., long 156°53’ W. 14099 50 ARr 23 __________ Reiser, H. N.; 1950; Philip Smith Mountains quad- Siksikpuk formation (basal part); rangle; Galbraith Lake area; lat 68°29’ N.; long Permian(?). 149°13’ W.; basal bed of Siksikpuk formation. 14150 53 APa 105 _________ Patton, W. W., Jr., Bowsher, A. L., 1953; Chandler Chert-shale member(?); Alapah Lake quadrangle; cutbank near head of Kiruktagiak limestone; Gom'atites crenistria River; lat 68°20’30” N.; long 152°54’ W.; top of zone; Upper Mississippian. ' Alapah limestone. 14151 53 ABC ____________ Patton, W. W., Jr., Bowsher, A. L. ; 1953; same locality Chert-shale(?) member; Alapah as 14150. limestone; Goniatites crem'sm'a zone; Upper Mississippian. 14152 53 APa 122 _________ Patton, W. W., Jr., 1953; same locality as 11814 ______ Siksikpuk fqgmation (basal part); Permian(. . 14169 53 ASa 43 __________ Sable, E. G.; 1953; Misheguk Mountain quadrangle; Unnamed Permian formation; Nuka River valley; lat 68°39’30” N.; long 159°16’ W. Permian. LATE PALEOZOIC GASTROPODA FROM NORTHERN ALASKA Register of localities—Continued 131 Locality No. Field No. Collector, year of collection, and description of locality Stratigraphic position and age USGS 14174 49 ATr 449A ________ Tailleur, I. L.; 1949; Chandler Lake quadrangle; rubble Siksikpuk(?) formation; Per- west of Kiruktagiak River; lat 68°23’ N ., long mian(?). 152°54' W. _ . 14947 53 ATr 79 __________ Tailleur, I. L.; 1951; Misheguk Mountain quadrangle, Lisburne group; Upper M1s51s- Nuka River valley; lat 68°36’ N., long 159°18' W. sippian(?). 14954 F4 of 2 June ________ Bowsher, A. L.; 1950; Chandler Lake quadrangle; Banded limestone member, Shainin Lake area; lat 68°19’21” N., long 150°55’ W. Wachsmuth limestone; Brachy- thyris suborbicularis zone; Lower Mississippian. 14965 F3 of 10 June _______ Bowsher, A. L.; 1950; Chandler Lake quadrangle; Crinoidal limestone member, Shainin Lake area; lat 68°19’20” N., long 150°53’30” Wachsmuth limestone; “Za- W. phrentis” kom'ncki zone; Lower Mississippian. 14984 50 ABe 22 __________ Brosgé, W. P.; 1950; Philip Smith Mountain quad- Alapah limestone (lower part) rangle; Galbraith Lake area; lat 68°26’ N ., long Upper Mississippian. 149 22’ W. 14992 50 ABe 3 ___________ Brosgé, W. P.; 1950 ; Chandler Lake quadrangle; Anak- Alapah limestone (lower part); tuvuk River valley; lat 68°16’30” N., long 151°34’ W. Upper Mississippian. 15408 50 ABe 33 __________ Brosgé, W. P. ; 1950; Chandler Lake quadrangle; Alapah limestone; Naticopsis su- Chandler Lake area; lat 68°17’ N., long 152°36’30” turicompta zone; Upper Missis- W.; from section B—17. sippian. 15430 47 AGr 182 _________ Gryc, G.; 1947; Mt. Michelson quadrangle; Canning Alapah limestone; Upper Missis- River area; lat 69°17’ N., long 145°59’ W. sippian. 15453 53 ASa 247 _________ Sable, E. G.; 1953; Point Hope quadrangle; Cape Siksikpuk formation;Permian(?). Lisburne area, north side of Lisburne Hills; lat 68°49’ N., long 165°58’ W. 15455 53 ABo 18 __________ Bowsher, A. L.; 1953; Point Hope quadrangle; Cape Lisburne group; Upper Missis- Lisburne area; approximate lat 68°52’ N., long sippian. 166°08’ W. 15813 51 ADt 147 _________ Detterman, R. L.; 1951; Philip Smith Mountains Sadlerochit formation (basal quadrangle; Lupine River; lat 68°49’ N., long part); Permian. 148°22’30” W. 15817 51 AKe 162 _________ Keller, A. S.; 1951; Philip Smith Mountains quad- Sadlerochit formation; Permian. rangle; Ribdon River, about 3 mi southwest of Elusive Lake; lat 68°40’10” N., long 148°27’45” W.; 100 ft above base of Sadlerochit formation. 15826 52 AMo 5 __________ Morris, R. .; 1952; Sagavanirktok quadrangle; Sadlerochit formation; Permian. Kemik Creek; lat 69°20’30” N., long 147°02’ W.; 10 ft above base of Sadlerochit formation. 15829 52 AMo 37 _________ Morris, R. H.; 1952; Mt. Michelson quadrangle; Cache Sadlerochit formation (basal Creek, Canning River; lat 69°28’ N., long 145°49’ W. part); Permian. SYSTEMATIC PALEONTOLOGY Class GASTROPODA Superorder PROSOZBRANCHIA Order ARCHAEOGASTROPODA Superfamily BELLEROPHONTACEA Family SINUITIDAE Subfamily EUPHEMITINAE Genus EUPHEMITES Warthin, 1930 Euphemites sp. Plate 12, figures 2—4 Discussion—Several specimens retain patches of shell showing the spiral lirae characteristic of the genus. One specimen has at least 18 lirae from one umbilicus to near the selenizone; all other specimens are less complete and lirae cannot be counted. The selenizone is relatively Wide and slightly depressed. At least the first third of the body whorl is sec— ondarily smoothed by a thin inductural layer or lay- ers. Most specimens are of uniform size, about 12 mm across the axis of ceiling. All are regularly and smoothly coiled. 507218 O—60—-—3 Steinkerns, or internal fillings of the shells, have been referred to this species in one instance. These steinkerns are of the same general size and shape and occur in the same collection as identifiable specimens of E uphemz'tes. To check this identification, an artifi- cial steinkern was prepared by removing the shell from a specimen. This steinkern and the naturally occur- ring ones all show slightly wider umbilici with steeper walls than do steinkerns referred to Bellerophmt. Illustrated specimens.—USNM 13650751, 136507b; USGS 10- cality 12084. Occurrence and abundance—Lower Mississippian undifferen- tiated: USGS locality 12340, two. Alapah limestone: USGS 10- cality 12084, nine. Family BELLEROPHONTIDAE Subfamily BELLEROPHONTINAE Genus BELLEROPHON Montfort, 1808 Bellerophon sp. Plate 12, figures 5—9 Discussion.—Bellerophontacean steinkerns are com- mon; three of these retain patches of shell showing 132 growth lines and a selenizone characteristic of Bel- lerophon. Other steinkerns were identified as Bel- lerophon by comparison with these three specimens. Most identifications of steinkerns as Bellerophon were based on the character of the umbilical openings. Among the Alaskan specimens at least, the umbilical openings are relatively narrower and have more arched walls and a slightly less abrupt juncture of side and umbilical opening than in umbilici in steinkerns re- ferred to Euphemites. It is to be emphasized that these are not characters of the shell; there is sug- gestive evidence that the shell itself may have been anomphalous. Some of the steinkerns that exceed the size of the largest known specimens of Euphemites are called Bellerophon sp. even though the umbilical characters of the steinkern are not certainly known. Although some specimens are well rounded along the dorsum, having only a faint ridge at the position of the selenizone, others have flattened sides and a more prominent crestlike dorsum. In several, the dor- sum is wide and depressed in the center. It is pos— sible that these bellerophontaceans with flattened sides represent another taxon. Until better specimens are obtained so that this hypothesis can be tested, all the material is assigned to one species with some of the specimens presumed to have been compressed during deformation of the enclosing strata. Several of the specimens are quite large for the genus; such an individual, measuring over 70 mm across the aperture, is shown on plate 12, figure 9. The only described American late Paleozoic species that approaches this size is the poorly known Bel- lercphon giganteus Worthen. Slightly larger speci— mens of Bellerophon have been illustrated by K0— ninck (1883) from the Carboniferous of Belgium. In most cases steinkerns are of little use in paleon- tology and, indeed, specific identification of them can often do more harm than good. It may well be that several biologic species are included here under Bel— lerophzm sp. However, inasmuch as many of these specimens come from a single stratigraphic unit, it seems reasonable to conclude that these specimens be- long to a single species. The occurrence of bellero- phontacean steinkerns of this sort has been shown to be a good field guide to rocks of the lower part of the Alapah limestone and its equivalents. Because of the occurrence of similar steinkerns in both older and younger rocks in northern Alaska, caution is urged in their use for age determination. At best, these steinkerns should be used only to supplement more positive evidence of the age of a rock unit. SHORTER CONTRIBUTIONS T0 GENE-RAH GEOLOGY Illustrated specimens.——USNM 136508a, 136508b, USNM 10‘ cality 3088; USNM 136509, USGS locality 11799; USNM 136510, USGS locality 15408. Occurrence and abundance—Lower Mississippian undifferen- tiated: USGS locality 11807, one; 11808, one; 13234, one; 13235, one. Alapah limestone: USGS locality 976, eight; 13287, four; 15408, two; USNM locality 3088, nine; 3172, one. Upper Mississippian undifferentiated: USGS locality 11799, four. Subfamily KNIGHTITINAE Genus KNIGHTITES Moore, 1941 Subgenus RETISPIRA Knight, 1945a Knightites (Retispira?) sp. Plate 12, figure 1 Discussion—Identification is based on a single in- complete Mississippian specimen, showing spiral lirae and a raised selenizone. Uncertainty as to identifica- tion arises from two sources. First, the specimen is so incomplete that apertural characters, particularly the presence or absence of a ridge on the floor of the aperture, cannot be determined. Second, there is a slight chance that the specimen may be a pleuroto- mariacean, genus indeterminate, with the upper part of the shell destroyed. Orienting plate 12 with the left margin, downward shows the basis for this pos- sible identification. A second small poorly preserved specimen, of ques- tionable Permian age, is more certainly referable to the subgenus. It cannot be determined if it is con- specific with the other specimen, and it is too poorly preserved to be illustrated or treated separately. Illustrated specimen—USNM 136506, USGS locality 11843. Occurrence and abundance—Lower Mississippian undifferen- tiated: USGS locality 11843, one. ?Permian: USGS 408a, one. INDETERMINATE BELLEROPHONTACEANS Discussion—In addition to the material discussed above, other poorly preserved and indeterminate speci- mens may represent this superfamily. For a few of them, however, it is possible to assay a generic assign- ment. Collections not commented upon below can be determined only to the superfamily level. Occurrence and abundance—Kayak shale: USGS locality 13245, may be Euphemltes sp.; 13258, one, may be a Bellero- phon, matrix differs from that yielding Bellerophcn sp. Wachs- muth limestone: USNM locality 3115, one, may be a Bellero- phcn, matrix differs from that yielding Bellercphon sp. Lower Mississippian undifferentiated: USGS locality 11867, not a Bellerophon, in gross form this specimen resembles Sinultina Knight, 1945a. Alapah limestone: USGS locality 406, one; 1004, six; 14151, one; 14992, one. Upper Mississippian undif- ferentiated: USGS locality 975, eight, slight indication this may be Bellercphon sp.; 996, one, slight indication this may be Bellerophcn sp.; 10870, one. Sadlerochit formation: USGS locality 7118b (green), one, probably a bellerophontid, form approaches Bellerophon sp., but collection is known to be of LATE PALEOZOIC GASTROPODA FROM NORTHERN ALASKA Permian rather than Mississippian age. Unnamed Permian formation: USGS locality 11823, one, similar to Bellerophou sp., but collection is known to be of Permian rather than Mis— sissippian age. Superfamily EUOMPHALACEA Family EUOMPHALIDAE Genus STRAPAROLLUS Montfort, 1810 Subgenus EUOMPHALUS Sowerby, 1814 Straparollus (Euomphalus) brooksensis Yochelson and Dutro, n. sp. Plate 12, figures 15, 20—23 Description.—Low-spired euomphalids having a sharp upper angulation and rounded umbilical whorls; juvenile whorls well rounded and discoidal, sutures impressed only in this growth stage; mature shell low spired with body whorl embracing penultimate whorl at periphery; upper whorl surface flattened, inclined upward nearly 10° from horizontal in early growth stages, nearly horizontal to upper shoulder at ma- turity; upper shoulder angulated in most growth stages but not bearing a carina, the angulation be- coming less distinct with age so that large specimens show a differentiation of upper and outer whorl faces but no sharp angulation; outer whorl face distinctly arched with periphery near midwhorl, becoming steeper and with a lower periphery in the gerontic stage; basal whorls well rounded in all growth stages, the profile following the arc of a circle from outer whorl face to umbilicus; umbilical sutures distinct; growth lines gently prosocline on upper whorl sur— face, gently prosocline to orthocline from upper an- gulation to periphery, seemingly gently prosocline be- low on outer whorl face, on basal whorl surface and up into umbilicus. Discussions—The low spire, relatively large size, and rounded umbilical whorls differentiate Straparollus (Euomphalus) brookseusis from other Alaskan Eu- omphalidae. Several specimens bridge the gap from the discoidal earliest stages to the low-spired adult. In View of the long stratigraphic range of this form, it may very well be that more than one species is included. The number of specimens is so small and preservation is such that attempts to differentiate Lower Mississippian from Upper Mississippian forms have been unsuccessful. Pending study of additional specimens, it is assumed that this is a single species. Several incomplete specimens have been tentatively referred to the species. These are indicated by the reference to footnote 2 in the proper column of the distribution chart (table 1). Numerous low—spired euomphalids with rounded whorls have been named, particularly in European literature. Until these named forms have been sys- 133 tematically restudied, no comparison between them and S. (E uomphalus) brooksensis is warranted. Illustrated spectmens.—Holotype: USNM 136515, USNM locality 3186; paratypes: USNM 136514, USGS locality 11890, and USNM 136513, USGS locality 13235. Measurements.——Measurements of the illustrated specimens (in mm) are given below: Height of Width of Specimen Height Width aperture aperture USNM 136513 __________ 5. 4 13. 0 _____________ 136514 __________ 1 23 41. 7 14. 6 1 16 136515 __________ 10. 7 21. 0 _____________ 1 Estimated. Occurrence and abundance—Wachsmuth limestone: USNM locality 3107, one; 3091, cf. one. Lower Mississippian undif- ferentiated: USGS locality 11890, one; 13235, two; 13240, cf. one. Alapah limestone: USN M locality 3087, two: 3186, one. Straparollus (Euomphalus) alaskensis Yochelson and Dutro, n. sp. Plate 12, figures 10—14, 16-19 Descriptiou.—Very low spired euomphalids with nearly vertical umbilical walls; sutures distinct, rela- tively deep in early growth stages; nucleus and ju- venile whorls discoidal with rounded whorls, the up- per angulation being poorly developed on largest juvenile whorl; mature whorl produced downward slightly so that it embraces penultimate whorl above midwhorl; upper whorl surface distinctly flattened, inclined 50—100 from horizontal to a sharp, distinct, noncarinate outer angulation, the inclination of the upper whorl face increasing with age; outer whorl face inclined outward and downward following a con- cave outward curve for the upper one-third of face, the lower edge of the curve being at the periphery, below which the outer whorl face is inclined inward 20°—30° from vertical for most of distance below the periphery, curving more strongly near base; basal whorl face distinctly flattened, set ofl’ from the um- bilicus by a sharp circumbilical angulation in all ex- cept the late mature and gerontic stages; umbilical walls turning abruptly from circumbilical angulation to nearly vertical; umbilicus wide and relatively deep for size and height of shell; growth lines gently proso— cline from suture to upper angulation, on outer whorl face very gently opisthocline to periphery, there turn— ing to prosocline and continuing straight down the lower part of the face across the base and into the umbilicus. Discussion.—-The nearly vertical walls of the um- bilicus readily distinguish Straparollus (Euomphalus) alas/censis from other known Permian species. The umbilical walls are even steeper than those of S. (Euomphalus) Zecicarz'uatus Yochelson from the mid— dle Permian of the southwestern United States (1956. 134 p. 217). Most cross sections do not appear to show the two shell layers characteristic of the family (Knight, 1934, pl. 26), but they can be observed on a few of the well—preserved specimens. The seeming lack of an outer shell layer, coupled with the poor development of the upper angulation in the earlier growth stages, suggested at first that specimens were only subinternal molds, that is, specimens lacking the outer shell layer. Subsequent finding of large speci- mens with a reasonably well developed upper angula- tion ruled out this possibility. As in the case of other species described herein, some poorly preserved specimens have been tentatively referred to this species. These are distinguished by reference to footnote 2 in the appropriate column of the distribution chart (table 1). Illustrated locality 11823; Paratypes: 1365110, USGS locality 11814. M easurements.—Measvrements of three of the illustrated specimens (in mm) are given below: specimens.—-—Holotype: USNM 136512, USGS USNM 1365119., 136511b, and Height of Width of Specimen Height Width aperture aperture USNM 136511b _________ 6.0 14. 1 _____________ 1365110 _________ 6.0 13. 9 5.0 5. 1 136512 __________ 12 27. 7 9. 1 8. 8 Occurrence and abundance—Siksikpuk formation: USGS locality 11785, six; 11814, twelve; 11816, seven; 14099, four; 14152, nine; 11786, cf. three; 15453, cf. four. Sadlerochit formation: USGS locality 15813, one. Unnamed Permian formation: USGS locality 11823, one. ?Permian2 USGS 10- cality 982, one. Straparollus (Euomphalus) sp. Plate 12, figures 24—26 Discussion—A third species of Euomphalus in the Alaskan collections differs from the other two in be- ing discoidal, with the earliest whorls depressed rather than low spired. The upper whorl surface is dis- tinctly inclined upward to a carina on the outer angulation. The outer whorl face is slightly crushed in the specimen, but it appears to be arched outward to the periphery, located below midwhorl, and then less strongly curved inward to a basal angulation. Below this angulation, the basal whorl surface is flat- tened, except near the wide shallow umbilicus. The umbilical walls are steep, but no circumbilical angula- tion is present; the juncture with the basal surface is smoothly rounded. Growth lines are orthocline on the upper surface, essentially radial from the suture. On the outer whorl face they are gently opisthocline to the periphery, prosocline below, and finally straight, gently prosocline on the basal surface. It does not seem appropriate to give a formal name to this single specimen. In some respects, particu- SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY larly in the character of the umbilicus, this species is similar to Straparollus (Euomphalus) wateriformis (Koninck) from the Tournaisian of Belgium, but in that species the base is distinctly wider than the up- per surface. A second incomplete small specimen has been tentatively referred to this species. Illustrated specimen.—USNM 136516, USGS locality 14954. Occurrence and abundaiice.——Wachsmuth limestone: USGS locality 14954, one. Alapah limestone: USGS locality 997, cf. one. Genus AMPHICAPHA Knight, 1942 Subgenus CYLICIOSCAPHA Yochelson, 1956 Amphiscapha (Cylicioscapha) grade. Yochelson and Dutro, n. sp. Plate 12, figures 27—29 Description.—Discoidal euomphalids with a shelf on outer whorl face and a prominent basal angulation; juvenile whorls rounded, depressed slightly below gen- ~ eral upper surface of shell; sutures impressed in all growth stages; upper whorl surface distinctly in- clined, following a curve gently concave upward from suture to a carinate angulation at the outer edge of upper surface; outer whorl face inclined outward and strongly downward below sharp carina for about one- third of its total width, then bending abruptly to nearly horizontal for a short distance, next abruptly flexed downward forming a step in the profile of the outer whorl face; below this step the outer whorl face is gently arched outward for a short distance to the periphery which is located just below midwhorl; be- low the periphery the face steadily curves inward to the base, there being some evidence that in later growth stages a shallow groove and essentially vertical seg- ment of the face occur just above the basal angulation; basal angulation distinct, slightly more than 90°, non- carinate; basal whorl surface flattened, nearly hori- zontal, curving gently inward as umbilicus is ap- proached, then bending more abruptly into nearly vertical-walled wide umbilicus without, however, de- veloping a circumbilical angulation; growth lines Orthocline, radial from suture across inner half of up- per whorl face, then gently curving prosocline to an- gulation, being nearly straight opisthocline on upper part of outer whorl face, but straight gently proso- cline below the shelf, across the base, and into the umbilicus. Discussion—The characteristic “step” on the outer whorl face readily distinguishes members of this sub- genus from specimens of Euomphalus. In detail, Amphiscapha (Cylicioscapha) grade is discoidal, rather than low spired as are Straparollus (E uompha- lus) brooksensis and S. (Euomphalus) alaskensts. In basal view it is most similar to S. (E uomphalus) sp., LATE PALEOZOIC GASTROPODA FROM NORTHERN ALASKA but the basal angulation of that species is sharper and the basal whorl surface somewhat more inclined. A. (Cg/liciosmpha) grada lacks the nodes or rugo- sities on the upper angulation that are characteristic of other described species of the subgenus. Illustrated specimen—Holotype: USNM 136517, USGS 10- cality 11823. Measurements.——Measurements of the illustrated specimen (in mm) are as follows: height, 5.1; width, 16.2; height of aperture, 5.2; and width of aperture, 5.0. Occurrence and abundance—Sadleroohit formation: USGS locality 15829, one. Unnamed Permian formation: USGS 10- cality 11823, three. INDETERMINATE EUOMPHALAGEAN S Discussion—As in the case of the bellerophonta- ceans, many specimens referable to this superfamily are poorly preserved, but most of these are relatively more poorly preserved than are the bellerophonta- ceans. Accordingly, for less than one—third of these specimens is it possible to express an opinion as to what species they represent. Occurrence and abundance—Kayak shale: USGS locality 13219, one; 13245, one; 13247, one. Wachsmuth limestone: USNM locality 3100, one; 3279, six, may be Straparollus (Eu- omphnlus) brooksensis; USGS locality 13286, one; 14074, one, may be a distinct species from any described or discussed above. Lower Mississippian undifferentiated: USGS locality 11807, one; 11858, one; 11861, one, may be Straparollus (Eu- omphalus) brooksensis; 12701, one; 12785, three; 13234, two; 13241, one; 14097, two, may he Straparollus (Euomphalus) brooksensis. Alapah limestone: USNM locality 3087a, one; 3167, one; 3169, one; 3188, two; USGS locality 976, four, may be Straparollus (Euomphalus) brooksensls; 1015, one, may be Straparollus (Euomphalus) brookscnsis; 12355, one; 14151, two; 15430, two, may be Stravparollus (Euomphalus) brook— sensis; 15455, one, may be Strapnrollus (Euomphnlus) brook- sensis. Upper Mississippian undifferentiated: USGS locality 971, one; 11799, one may be Straparollus (Euomphalus) brook- sensis. Siksikpuk formation: USGS locality 11815, two. Sad- lerochit formation: USGS locality 1010, three. Unnamed Per- mian formation: USGS locality 13215, one, may be Straparol- lus (Euomphalus) alaske’nsis. ?Permian: USGS locality 989a, one. Superfamily PLEUROTOMARIACEA Family SINUOPEIDAE Subfamily TURBONELLININAE Genus RHINEODERMA Koninck, 1883 Rhineoderma? sp. Plate 12, figure 34 Discussion—A single specimen is questionably re- ferred to this genus. The specimen is compressed and its original shape cannot be determined. There is some indication that the peripheral selenizone acted as a zone of weakness during compression, because growth lines are prosocline from suture to edge of specimen and are seemingly orthocline below. The specimen is phaneromphalous. The upper surface is ornamented 135 by spiral lirae, six major ones being present with finer lirae intercalated. The ornament and the pre- sumed low-spired conical shape suggest a possible ref- erence to th’neoderma. Illustrated specimen—USNM 136520, USNM locality 3167. Occurrence and abundance.——Alapah limestone: USNM lo— cality 3167, one. Genus TURBONELLINA Koninck, 1881 Turbonellina? lata Yochelson and Dutro, n. sp. Plate 12, figures 30—33 Description—Beehiveshaped phaneromphalous gas— tropods with a strong circumbilical angulation; nu- cleus and earliest whorls planispiral, more mature whorls moderately high spired; sutures distinct, slightly impressed; outer whorl face inclined outward and strongly downward, gently arched throughout its 'length, the flattened nearly horizontal base being set off from the outer whorl face by a relatively narrow well-rounded periphery, the angle between outer face and base approximately 60°; narrowly phanerom- phalous, with steeply inclined circumbilical walls, the umbilicus being set off by a sharp circumbilical an- gulation; growth lines on upper part of outer whorl surface prosocline, nearly 15° from vertical, their course below not certainly known, but seemingly with a sinus on the periphery; shell polished and unornamented. Discussion—This species has a flattened nucleus and general whorl shape similar to that of the type species Turbonellina Zepida (Koninck) from the Viséan of Belgium. It differs in being smooth rather than elab- orately ornamented. In addition, there is some ques- tion as to the course of the growth lines in T.? latta. Until better specimens are available, the generic place- ment of the species must be questioned. Illustrated snecimens.——Holotype: USNM 136518, USGS locality 13235; paratype: USNM 136519, USGS locality 13234. Measuremanta—Measurements of the illustrated specimens (in mm) are given below: Specimen Height Width USNM 136518 __________________________ 4.0 5. 2 136519 __________________________ 10 10 Occurrence and abundance—Kayak shale: USN M locality 3095, one. Lower Mississippian, undifferentiated: USGS locality 13234, two; 13235, one. Family RAPHISTOMATIDAE Subfamily LIOSPIRINAE‘ Genus TREPOSPIRA Ulrich and Scofleld, 1897 Subgenus TREPOSPIRA Ulrich and Scofield, 1897 Trepospira (Trepospira) sp. Plate 13, figures 1—3 Discussion—A single specimen referable to this subgenus has been found in the Siksikpuk formation. 136 It is low spired and has a sharp keel. Ornament con- sists of short lirae radial from the suture. Unfortu— nately, most of the rest of the shell surface is lacking and details of the selenizone and other ornament can- not be determined. It appears likely that the shell is missing from the base and that the specimen origi— nally had the umbilicus filled with callus. Illustrated specimen.—USNM 136522, USGS locality 14174. Occurrence and abundance—Siksikpuk formation: USGS 10- cality 14174, one. Subgenus ANGYOMPHALUS Cossmann, 1915 Trepospira. (Angyomphalus?) sp. Plate 12, figures 35, 36 Discussion—A second species of Trepospira, from the Mississippian, appears to have a true umbilicus. The single specimen is a juvenile and cannot be con- trasted with the preceding species except in the char- acter of the umbilicus. Illustrated specimcu.—USNM 136521, USGS locality 11843. Occurrence and abundance—Lower Mississippian undifferen- tiated: USGS locality 11843, one. Family EOTOMARIIDAE Subfamily EOTOMARIINAE Tribe MOURLONIDES Genus MOURLONIA Koninck, 1883 MourIOnia minuta Yochelson and Dutro, n. sp. Plate 13, figures 4, 5 Description.—Turbiniform gastropods with colabral ornament and a wide raised selenizone on the periph— ery; nucleus unknown; body whorl embracing penul— timate whorl at lower edge of selenizone; upper whorl surface inclined outward and downward, slightly more arched near the selenizone, below which the whorl surface curves more strongly inward than above so that the upper whorl surface is distinctly more in- clined toward vertical than the lower; base anom- phalous; growth lines prosocline from suture, ap- proximately 30° from the vertical, proceeding straight for most of the distance across the upper surface, curving more strongly backward near the selenizone, opisthocline below the selenizone for a short distance then turning to nearly orthocline; selenizone rela— tively wide, unbordered, raised slightly above the gen- eral level of the whorl surface, and bearing numerous lunulae; narrow parietal inductura in the upper part of the columellar lip; colabral ornament consisting of low rounded lirae above selenizone, somewhat weaker below, the interspaces being twice the width of the lirae. Discussion—The relatively wide raised selenizone distinguishes Mourlom’a minuta from other pleuroto- SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY mariaceans in the Alaskan faunas. The ornament appears to be somewhat finer than that of other species having strong colabral ornament. This slight differ- ence may be a reflection of the small size of the speci- mens of M. minuta, compared to the other pleuro- tomariaceans described. Mourlom’a minuta appears to be slightly higher spired with less well rounded whorls than other spe- cies referred to ZlIourZom'a. More significantly, the selenizone of this species is also relatively wider than that of other species currently placed in the genus. Further study of additional material may show that this represents a distinct genus. Illustrated specimeu.—Holotype: USNM 136523, USGS 10- cality 11865. M casuremcuts—Measurements of the illustrated specimen (in mm) are as follows: height, 9; width, 8.6; height of aper- ture, 5.4; and width of aperture, 5. Occurrence and abundance—Alapah limestone: USGS locality 11865, seven. Mourlonia? reloba Yochelson and Dutro, n. sp. Plate 13, figures 6—9 Descriptiara—Turbiniform gastropods with globose whorls and a narrow, bordered selenizone at periph- ery; shell moderately high spired; whorls embracing at upper edge of selenizone, the line of contact lower- ing very slightly with increasing maturity; sutures gently impressed; whorls well rounded from suture to peripheral selenizone, being somewhat less rounded below; anomphalous; growth lines orthocline at su- ture but, after leaving suture, prosocline, about 30° from vertical along upper whorl face to near edge of selenizone where they bend a little more strongly backward, below selenizone opisthocline for a short distance then turning to gently prosocline and pro- ceeding straight to base of columella; selenizone rela— tively narrow, with closely spaced lunulae, and bor- dered by lirae; a narrow parietal inductura present on upper part of columellar lip, unknown below; colabral or\nament of strong lirae above selenizone, slightly finer below, with fine colabral lirae inter- calated near the columella, the ornament becoming less prominent with age. Discussiou.——M0urlom'a? reloba differs from other pleurotomariacean species described herein in having a narrow, bordered selenizone at the periphery and a globose whorl profile. The strong colabral ornament is not an important taxonomic character as several unrelated pleurotomariacean lineages possess similar ornamentation. Specimens from localities 11816 and 15453, are poorly preserved; these have been referred tentatively to the species. LATE PALEOZOIC GASTROPODA FROM NORTHERN ALASKA The Mourlom'a‘l reloba form of shell with its nar- row selenizone and globose whorls may be a distinct phylogenetic line. A Mississippian specimen in the U.S. National Museum collections, from near Fort Gibson, Okla, is remarkably similar to the specimens illustrated. Revision of the genus must be delayed, however, until more well—preserved specimens are at hand. No previously described Permian pleuroto- mareans are known that are comparable to 211.? reloba. Illustrated specimens.—Holotype: USNM 136525, USGS local- ity 14169; paratype: USNM 136524, USGS locality 14169. Measurements.~—Measurements of the illustrated specimens (in mm) are given below: Height of Width of Specimen Height Width aperture aperture USNM 136524 __________ 1 37 29 1 22 17 136525 __________ 1 20 17. 0 1 14 11. 9 1 Estimated. Occurrence and abundance—Unnamed Permian formation: USGS locality 14169, four. Siksikpuk formation: USGS locality 11816, cf. one; 15453, cf. one. NODOSPIRA Yochelson and Dutro, n. gen. Type species.—Nodospira ornate Yochelson and Dutro, n. sp. Diagnosia—Moderately high spired ornamented pleurotomariaceans with a bordered peripheral seleni- zone and well-rounded whorls; shell moderately high spired, the body whorl embracing the penultimate whorl at the lower edge of the selenizone; whorls relatively well rounded, with periphery near mid- whorl; concave selenizone on periphery bordered by strong flanges; distinct colabral lirae. Discussion—The genus Mourlom'a Koninck appears to be much in need of revision for, as presently in— terpreted, it includes species from Middle Ordovician through Permian in age. Nodo‘spira is proposed in an attempt to separate some species from the Mour— lom'a complex. The well-rounded whorls and the selenizone bordered by distinct strong flanges serve to distinguish Nodospira from Maurlouia. The colabral lirate ornament of this genus is similar to that of Ptychomphalin‘a Fischer, which has been placed, per- haps improperly, in the synonymy of Mourlout'a. Nodospira differs from Ptychomphaliua in having the selenizone at midwhorl rather than below, and in having well—rounded whorls. In the literature examined, no species have been found that can be referred to this genus. Maurlom'a- like forms occur in most Mississippian faunas. That no previously described species can be attributed to this genus is a reflection of the inadequacy of pub— lished illustrations and a lack of comparative mate- rial for study. 137 Nodospira ornata Yochelson and Dutro, n. sp. Plate 13, figures 14—17 Description—Conical pleurotomariaceans with strong subsutural protuberances and pronounced co- labral lirae; earlier whorls unknown; shell moder- ately high spired with body whorl embracing penulti- mate whorl at lower edge of selenizone; upper whorl surface distinctly arched from suture, turning abruptly to horizontal at periphery and forming a relatively wide flange marking the upper border of the selenizone; below the selenizone the whorl surface is well curved, the profile following a curve nearly the arc. of a circle; anomphalous; outer lip gently prosocline almost to selenizone, then sweeping strongly opisthocline for a short distance below selenizone and then swinging to distinctly prosocline on most of basal surface; columellar lip reflexed with a thin, nar- row inductura; selenizone concave between strong bor- dering flanges; ornament of strong colabral lirae on upper whorl surface in all growth stages known, the lirae somewhat finer below the selenizone; strong closely spaced, elongate, subsutural protuberances pe- riodically interrupting the smooth profile of the upper whorl surface. Diseussion.——-The presence of the subsutural pro- tuberances immediately distinguishes Nodospira 0r- ual‘a from other large pleurotomariaceans. In addi- tion, the selenizone is wider than in Mourlom'a? reloba, and is raised. Colabral lirae are thicker than on Bembemia? iuumbilicata, and the gross shape differs, with the body whorl of this species embracing higher on the penultimate whorl. These same features, and the lack of an umbilicus, distinguish N. amata from new genus? B. Illustrated speeimens.——Holotype: USN M 136528, USGS local- ity 14150; paratype: USNM 136529, USGS locality 14150. Measuremerits—Measurements of the illustrated specimens (in mm) are given below: Height of Width of Specimen Height Width aperture aperture USNM 136528 __________ 32 27. 3 18. 7 l5. 4 136529 __________ 57 51 1 37 28 1 Estimated. Occurrence and abundance.—Alapah limestone: USGS locality 14150, six; 12340, twenty-two; 12348, ten. Genus SPIROSCALA Knight, 1945 cf. Spiroscala sp. Plate 13, figure 10 Discussion.—Two specimens are tentatively referred to this genus. The first shows a conical, relatively high spired form with a peripheral flangelike seleni- zone. The second specimen, not illustrated, is mashed 138 and incomplete, but shows an eavelike overhang of the selenizone and an absence of ornament near the suture. Lack of ornament distinguishes these specimens from a Mississippian form in the collections referred to Phym-atoplcura. Illustrated specimenr.—USNM 136526, USGS locality 1008. Occurrence and dbundarice—Sadlerochit formation: USGS locality 1008, one; 15826, one. Tribe EOTOMARII'DES Genus BEMBEXIA Oehlert, 1888 Bembexia? inumbilicata Yochelson and Dutro, n. sp. Plate 13, figures 30, 31 Description—Large conical anomphalous gastro— pods with bordered selenizone forming periphery; earlier whorls unknown; sutures impressed; body whorl embracing penultimate whorl below periphery; upper whorl surface inclined outward approximately 35° from vertical and gently inflated, turning abruptly to horizontal and forming the upper bordering flange of the selenizone at the periphery; whorl profile below selenizone inclined steeply downward for approxi- mately one—half of its length, then curving more strongly inward to the anomphalous base; concave selenizone located on the periphery between strong bordering flanges7 the upper flange overhanging the lower; lunulae faint; growth lines prosocline from suture, approximately 20°, bending more abruptly backward just above the selenizone, below the seleni- zone opisthocline for a short distance then curving to prosocline, about 20° from vertical, and continuing straight downward; columellar lip with a narrow in— ductura; ornament of impressed growth lines alone. Discussion.—Bem.bem'al iuumbilz'cata appears to be most similar, superficially, to Tropédostrophd Long— staff, 1912, but lacks both an umbilicus and pitting in the shell. It differs from Bernbem’d Zarteti (Munier— Chalmas), the type species, in being higher spired and in having the upper flange of the selenizone, rather than the lower flange, at the periphery. Because the significance of these differences cannot now be evalu— ated, generic placement of the species is questioned. In addition to gross shape, Bembem'd? inumbz’licuta differs from Alaskan specimens referred to Mourlom‘a in lacking strong colabral ornament. It lacks nodes on the upper surface as are found in Nodes-Mm 0r— rzata. The species is most similar in shape to speci— mens referred to as New genus? 13., and at one time the two forms were confused. They differ however in the nature of the umbilicus, 3.? éuumbilicata being clearly anomphalous. SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY The spire of the holotype is incomplete and the aperture is slightly crushed. No meaningful meas- urements of the species can be presented. Illustrated specimenr.—Holotype: USNM 136536, USGS 10- cality 10862. Occurrence and abundance—Alapah limestone: USGS 10- cality 10862, two; 12779, three; 14151, one; 12342, one. Genus GLABROCINGULUM Thomas, 1940 Subgenus GLABROCINGULUM Thomas, 1940 Glabrocingulum (Glabrocingulum) 51). Plate 13, figures 11—13 Discussion—This species is represented by two specimens from the Siksikpuk formation. They are moderately low spired, conical, and have the seleni- zone located at the periphery. The upper whorl sur- face bears a row of coarse nodes at the suture and at least three rows of fine nodes. The narrow seleni- zone is concave and bordered by sharp lirae. The arched basal surface bears at least seven spiral carinae, all of which are noded. The base is anomphalous. The species does not warrant specific naming in View of the small number of specimens available. Illustrated specimen.—USNM 136527, USGS locality 14174. Occurrence and abundance.—Siksikpuk formation: USGS locality 14174, two. Subfamily NEILSO‘NIINAE Genus NEILSONIA Thomas, 1940 Neilsonia'! sp. Plate 13, figure 25 Discussiou.——Two collections from northern Alaska contain small, moderately high spired pleurotomari- ceans. All are poorly preserved, but enough remains of the shell to show the main features. The upper surface is distinctly inclined, but little arched. The selenizone forms the outer whorl face and is nearly vertical, the lower edge being at the periphery. The selenizone proper is concave and distinctly bordered. Below the selenizone the basal whorl surface is nearly straight, inclined inward for a distance about the width of the selenizone, at which place there is a distinct though slight angulation, below which the basal whorl surface curves inward and strongly downward. The base is anomphalous. The columel- lar lip is slightly reflexed. The upper whorl surface appears to have strong colabral ornament. N0 speci- men is complete enough to show all the details given above, and a formal name does not appear justified. Illustrated specimen.—USNM 136533, USGS locality 9184. Occurrence and abundances—Alapah limestone: USGS lo— cality 9184, fifty; 10868, twenty five. LATE PALEOZOIC GASTROPODA FROM NORTHERN ALASKA Family PORTLOCKIELLIDAE Genus PORTLOCKIELLA Knight, 1945 Portlockiella? sp. Plate 13, figures 18, 19 Discussion—A single specimen is questionably placed in this genus. It is a low—spired, relatively wide form. The specimen is either narrowly phaner- omphalous or pseudoumbilicate. Ornament consists of five widely spaced, low, spiral carinae. A selenizone probably occurs just below the last carina, below mid- whorl, but just above the periphery. Growth lines, however, are not clear. On the base, below this pre- sumed selenizone, ornament consists of revolving lirae, the exact number not determinable. Illustrated specimen—USNM 136530, USNM locality 3167. Occurrence and abundance—Alapah limestone: USNM lo- cality 3167, one. Family GOSSELETINIDAE Subfamily GOSSELETININAE Genus GOSSELETINA Fischer, 1885 Gosseletina? sp. Plate 13, figures 20, 21 Discussion—A single specimen is characterized by a narrow selenizone high on the whorl, a distinctive feature of Gosseletina. The selenizone is concave and strongly bordered. Below the selenizone the whorl is ornamented by numerous spiral lirae. VVhorls are moderately rounded and the specimen is relatively high spired for a pleurotomariacean. Except in the position of the selenizone, none of the features de— scribed are found on the low-spired smooth type spe- cies of Gosseletina. It may be that this form repre- sents a new genus but, as with many of the specimens discussed, formal systematic treatment must be de- ferred until more specimens are available. Illustrated specimen.—USNM 136531, USGS locality 13236. Occurrence and abundance—Lower Mississippian undifferen— tiated: USGS locality 13236, one. Family PHYMATOPLEURIDAE Genus PHYMATOPLEURA Girty, 1939 Phymatopleura sp. Plate 13, figures 22—24 Discussion—A single well preserved specimen of Phymatopleura was collected from the Lower Missis- sippian. It shows the characteristic conical shape with a narrow, bordered, peripheral selenizone. The flat- tened base is ornamented by six revolving lirae. Or— nament of the upper whorl surface is unusual in showing pronounced ontogenetic change. The penulti- mate whorl and earlier whorls bear five sharp spiral 139 lirae. The body whorl, on the other hand, is smooth except for growth lines and a noded subsutural lira. Illustrated specimen—USNM 136532, USGS locality 13234. Occurrence and abundance—Lower Mississippian undifferen- tiated: USGS locality 13234, one. Family uncertain New genus? A Plate 13, figures 26—28 Discussion—A new genus of pleurotomariaceans may occur in the Wachsmuth limestone. It is repre- sented by a single distorted specimen and, therefore, the taxon is not formally named. The specimen does show several interesting morphological details. The shell is conical and moderately 10w spired, and has a peripheral selenizone located well below mid- whorl. Sutures are distinct and impressed. Because of distortion the shape of the upper whorl surface cannot be determined with certainty, but it appears to have been essentially flattened from near the su- ture almost to the selenizone. The selenizone is nar- row, raised and rounded, strongly convex outward. Below the periphery, the basal surface bends sharply inward. The base is anomphalous. Ornament con- sists of two elements, a series of short lirae normal to the suture and fine threads normal to the growth lines. The intersections of these two sets form a reticulate pattern on the upper whorl surface. Growth lines are prosocline, about 30°, curving back more strongly near the selenizone. Below the selenizone, growth lines are orthocline, abruptly curving to pro- socline on the base. In gross shape the specimen re- sembles Phymatopleura, but the convex selenizone of this specimen is distinctive. It is possible that this convexity is a result of distortion; more specimens are needed to determine this point. Phylogenetic po- sition of this form within the Pleurotomariacea is most uncertain. Illustrated specimen—USNM 136534, USGS locality 3110. Occurrence and abundance—Wachsmuth limestone: USNM locality 3110, one. New genus? 3 Plate 14, figures 26, 27 Discussion—Two specimens from the unnamed Per- mian formation, may represent another new genus. One specimen is exceedingly fragmentary. The sec- ond, illustrated, was partially cleaned from a very resistant matrix. This specimen is incomplete and the body whorl has been offset by a small fracture. The specimens are quite similar to Bembem’a? in- unzbilicata. They appear to be slightly lower spired, and have the body whorl embracing lower on the penultimate whorl. As there are only slight differ- 140 ences between the two forms, incomplete specimens could be readily confused. They differ in that this form has a depression in the base. Unfortunately, it cannot be determined if a true umbilicus is present. There is some similarity to the Mississippian genus Tropidostropha Longstaff, 1912, but comparisons must be delayed until more complete specimens are avail- able. So far as is known, this occurrence is unique in the Permian. Illustrated specimeu.—USNM 136551, USGS locality 13215. Occurrence and abundance—Unnamed Permian formation: USGS locality 13215, two. INDETERMINATE PLEUROTOMARIACEANS Discussion—Numerous poorly preserved specimens can be referred to the Pleurotomariacea. Some few can be placed questionably in the taxa previously de- scribed. Others appear to represent additional genera and species too poorly preserved to discuss in detail. Still others are so incomplete that they cannot be placed in any taxon satisfactorily. Occurrence and abundance—Kayak shale: USGS locality 13222, one, identification as pleurotomariacean uncertain. VVachsmuth limestone: USNM locality 3173, three, two genera present, one with spiral orna- ment suggestive of Bhirzeoderma? sp., the other mod- erately high with a conical shape and possibly a genus not otherwise recorded in the fauna. Lower Missis- sippian undetermined: USGS locality 11807, one, may be Phg/rnatopleura sp., 12700, one, pleurotomariacean; 12701, three, with spiral ornament suggestive of Bkz’ucoderma? sp.; 12785, three, moderately low spired and ornamented by spiral lirae, possibly a genus not otherwise recorded in the fauna; 13234, one, identifi— cation as pleurotomariacean uncertain; 13235, two, two genera present, one a pleurotomariacean, the other, so incomplete that identification as pleurotomariacean is uncertain; 13236, one, identification as pleurotomaria- cean uncertain. Alapah limestone: USNM locality 3167, five, two genera present, similar, respectively, to those listed for USNM locality 3173; USGS locality 1014, one, with spiral ornament suggestive of Rhineo- dcrma? sp.; 12084, two, may be Mourlom'a minuta. Upper Mississippian undifferentiated: USGS locality 972, one, conical with sutures little impressed and or- namented by spiral lirae, possibly a genus not other- wise recorded in the fauna. ?Upper Mississippian: USGS locality 14947, thirteen, moderately high spired with a peripherial selenizone and colabral ornament, may be a genus not otherwise recorded in the fauna. Siksikpuk formation: USGS locality 15453, one, pleu- rotomariacean with spiral ornament on base. Sad- SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY lerochit formation: USGS locality 7118b green, three, possibly Mourlom'a? rcloba; 1009, one, pleurotomaria- cean; 1010, one, may be cf. Spiroscala sp.; 15817, one, doubtfully Mourlouia? reloba. Unnamed Permian formation: USGS locality 11823, one moderately high spired with a concave selenizone near periphery, and spiral lirae on base, possibly a genus not otherwise recorded in the fauna; 13216, one, may be Mourlom'a? rcloba. Permian: USGS locality 982, one, pleuroto- mariacean; 987, four, two genera present, one moder- ately high spired with a vertical outer whorl face, a selenizone at the juncture of upper and outer whorl faces, and spiral ornament, and may be a genus not otherwise recorded in the fauna, the other, identifica- tion of pleurotomariacean uncertain. Superfamily PLATYC‘ERATAGEA Family HOLOPEIDA'E Genus YUNNANIA Mansuy, 1912 Yunnania sp. Plate 13, figure 29 Discussion—One specimen is placed in this genus. It is moderately high spired with the upper whorl surface flattened, inclined outward and downward; su— tures are not impressed. The outer whorl face is nearly vertical, and the basal surface is flattened, in- clined inward and more strongly downward. The specimen is anomphalous. Ornament consists of spiral lirae on all three whorl faces, there being at least ten on the body whorl. The specimen is a steinkern re— taining only one small patch of shell which does not show growth lines. It may be that this species is actually a pleurotomariacean, but slight evidence sug- gests that the outer lip did not possess a slit. Illustrated specimen—USNM 136535, USGS locality 12785. Occurrence and abundance—Lower Mississippian undifferen- tiated: USGS locality 12785, one. Family PLATYCERATIDAE Genus PLATYCERAS Conrad, 1840 Subgenus PLATYCERAS Conrad, 1840 Platyceras (Platyceras) .sp. Plate 14, figure 28 Discussiou.—The genus Platyccras has been divided into several subgenera (Knight, Batten, and Yochel— son, in press), the typical subgenus being restricted to those forms which have at least the earliest whorls in cont act. This feature can be shown with certainty only for two collections of specimens, one from the Lower Mississippian and one from the Upper Mississippian. Except for the earlier whorls, the specimens are poorly LATE PALEOZOIC GASTROPODA FROM NORTHERN ALASKA preserved and in other respects are similar to those identified as Platycerus (Orthouyc/Lz'a) sp. As used here, the grouping of Platycems (Platycems) sp. prob- ably has no biologic meaning. Numerous species of Platycems have been described, particularly from rocks of Mississippian age, but no synthesis of the family has been attempted. Individ- ual variation is great and definitive work on Platy- cems should properly discuss the host echinoderms of the several species. Additional species names would only further complicate study of this family. Illustrated specimen—USNM 136552, USGS locality 14035. Occurrence and abundance—Lower Mississippian undifferen- tiated: USGS locality 11807, three. Upper Mississippian un- differentiated: USGS locality 14035, five. Subgenus ORTHONYCHIA Hall, 1843 Platyceras (Orthonychia) sp. Plate 14, figures 17—19 Discussion.—Orthonychia differs from the typical subgenus of Platycems in having all growth stages, including the earliest, out of contact so that a mature specimen does not complete as much as one whorl. Specimens in nine of the collections preserve the ear- liest whorls, and in six others enough of the shell is preserved to indicate that it is unlikely that the early growth stages were coiled. Other incomplete speci- mens have been referred to this taxon as a conven- ience rather than having them listed separately as indeterminate platycerataceans. Most of the specimens are tubelike, but a few are flattened, patelliform. None of the specimens is well enough preserved to warrant detailed description; al- most all lack the aperture. A detailed study of the shape of the apertures of some specimens might reveal information about. the host echinoderms (Bowsher, 1956), but poor preservation makes this extremely un- likely. The platyceratids show considerable individual vari- ation because of their life attachment to echinoderm calices. Variation results from the orientation of the gastropod on the calyx and the shape of the tegmen. Little is known of specific limits of platyceratids. The grouping used here probably does not reflect a bi- ologically valid species. Orthonychz’a is of little value in dating rocks because it is known from beds of Devonian through Permian age. Illustrated specimens.——USNM 13654421, 136544b, USNM lo- cality 3089; USNM 136545, USGS locality 9186. Occurrence and abundance—Kayak shale: USNM locality 3095, three; 3247, three; USGS locality 13231, six; 13238, two; 13252, two; 13258, two. Wachsmuth limestone: USNM local- ity 3089, thirty three; 3100, one; 3113, one; 3173, two; 3279, 141 two; USGS locality 14965, two. Lower Mississippian undif- ferentiated: USGS locality 9186, one; 12773, one; 12785, two; 12798, one; 13225, one; 13228, one; 13232, two; 13236, one; 13237, two; 13254, four; 13292, one. Upper Mississippian un- differentiated: USGS locality 14984, one. Sadlerochit forma- tion: USGS locality 1009, two. ?Permian: USGS locality 960, one 979, one. Superfamily MICRODOMATACEA Family ELASMONEMATIDAE Genus ANEMATINA Knight, 1933 Anematina rockymontanum (Shimer) Plate 14, figures 10—16 Lou-enema rockymoutauum Shimer 1926, Canada Geol. Survey Museum Bull. 42, p. 81—82, pl. 4, figs. 9a, b; 10. Description.—High-spired subtrochiform gastropods with a flattened outer whorl face; in early growth stages sutures distinct and impressed; outer whorl face straight, little arched in juvenile stages, with increas- ing age developing a low spiral ridge at suture, below which the whorl face is slightly concave to near mid- whorl, becoming slightly convex to the periphery lo- cated low on the whorl, the overall face being strongly inclined downward; in maturity the whorl face gently but distinctly arched; below the periphery the whorl curving strongly and rather abruptly inward to base in early growth stages, the base itself being flattened to about 10° or 15° from horizontal, becoming slightly arched and less clearly set off from the upper whorl face with increasing maturity; base probably anom- phalous but, doubtfully, minutely phaneromphalous; growth lines on outer whorl face straight, prosocline at about 15°, crossing periphery and forming a wide shallow sinus on the base; columellar lip not re- flexed; ornamented by numerous spiral lirae which are finer than the fine growth lines, the lirae becom- ing more obscure with increasing size; shell thin. Discwsz'on.——The flattened outer whorl face and flat- tened base of the early growth stages, combined with the large size, mark this as a distinct species. The type species, Auemaz‘ina prouta’na (Hall), is charac- terized by extremely small size and by rounded whorls in all growth stages. Anematz'na rockymontanum (Shimer) seems to be closely related to A. lagueal‘a (Koninck) from the Viséan of Belgium, but differs in lacking a spiral ridge on the base. Through the kindness of Dr. Hans Frebold, Chief of the Section of Stratigraphic Palaeontology, Geo- logical Survey of Canada, we were able to examine H. W. Shimer’s original specimens of Loxouema rocky— mo‘ntanum (Shimer, 1926, p. 81). Geological Survey of Canada No. 5093 is the holotype, the original of 142 Shimer’s figures 9a and 9b. Geological Survey of Canada No. 5093a is a figured paratype, the original of Shimer’s figure 10. The specimens were numbered some years after the original description was pub- lished. Four additional specimens are included in 5093. They are poorly preserved but may belong to this species. Shimer also studied two specimens from lot 5095, an associated locality. These are so poorly preserved that they cannot be referred even question- ably to this species. With the exception of one natu- ral cross section, all of Shimer’s specimens were bro— ken from limestone. There is no doubt that the specimens from northern Alaska are conspecific with Shimer’s species. The close similarity between the types and the Brooks Range material is illustrated on plate 14. Unfortu- nately, many of the Alaskan specimens have been dis- torted. Others are incomplete or are steinkerns. This less well preserved material is only tentatively re- ferred to the species. Small steinkerns of Anematim can be separated from those of Lowortema by two characters. First, the more angular whorl face and flattened base are reflected in the steinkern; the profile of Lomoucma is relatively well rounded. Second, the Aucmatiua shell is thinner than that of Lowouema. This feature re- sults in a relatively smaller gap between whorls of the steinkern. In the holotype, the outer whorl face is flattened and set off rather abruptly from the flattened basal whorl surface. The slightly larger paratype, on the other hand, has a somewhat more rounded body whorl with the outer and basal faces distinctly arched and not so clearly separated. Although the whorl profiles of mature specimens of Lama/mama and Anematiua are not too dissimilar, the growth lines are fundamentally different. Poorly preserved specimens of the two genera could be confused. Illustrated specimens.—Holotype: G80 5093; paratype: GSC 5093a; hypotype: USNM 136542, USGS locality 13288; hypo- type: USNM 136543, USGS locality 11808. Measurements.—Measurements of the illustrated specimens (in mm) are given below: M M M GSC 5093 ______________________________ 20. 5 1 10 5093a ___________________________________ 1 14 USNM 136542 __________________________ 1 26 1 12 136543 __________________________ 1 14 5. 9 1 Estimated. Occurrence and abundance.—Wachsmuth limestone: USNM locality 3098, one; 3173, cf. one; USGS locality 13278, one. Lower Mississippian undifferentiated: USGS locality 11808, two; 12785, one; 12701, cf. one. Alapah limestone: USNM locality 3182, one, 3272, one; USGS locality 13288, one; 9187, cf. two. SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY Anematina’l sp. Discussiou.—Ten high—spired specimens listed below are questionably placed in Aucmatt'na because of the poor quality of preservation. In spite of the present uncertainty it seems reasonable to suggest that fur- ther collecting will indicate that only a single species of the genus is present in Mississippian rocks of northern Alaska. Occurrence and abundance—Lower Mississippian undifieren- tiated: USGS locality 13242, one. Alapah limestone: USNM locality 3167, one; USGS locality 1014, one. Upper Mississip- pian undifferentiated: USGS locality 975, seven. Superfamily ANOMPHALACEA Family ANOMPHALIDAE Genus ANOMPHAL‘US Meek and Worthen, 1867 Anomphalus sp. Plate 14, figures 7—9 Discussiou.——One small well-preserved rotelliform gastropod is placed in this genus. The shell surface is typically polished and smooth except for two faint spiral lirae near the suture. Sutures are impressed. Growth lines are gently opisthocline on the upper surface to nearly halfway between suture and periph- ery, where they swing backward becoming distinctly prosocline on the lower part of the outer whorl face. The umbilicus is relatively wide and seemingly with- out any sort of an inductural constriction or filling, although preservation is such that the possibility of a pseudoumbilicate condition cannot be ruled out. The species lacks the short radial ornament at the suture which apparently characterizes Anomphahts ucrvicnsis Koninck, from the Lower Carboniferous of Belgium. Illustrated spectmcu.——USNM 136547, USNM locality 3167. Occurrence and abundance.—Alapah limestone: USNM lo- cality 3167, one. Super-family NERITACEA Family NERITOPSIDAE Subfamily NATIGOPSINAE Genus NATICOPSIS M’Coy, 1844 Subgenus NATIGOPSIS M’Coy, 1844 Naticopsis (Naticopsis) suturicompta Yochelson and Dutro, n. sp. Plate 14, figures 20—25 Description—Well-rounded neritopsids with orna- ment on a subsutural ramp developed in intermediate growth stages; sutures distinct, becoming more im- pressed with age; shell low spired, the body whorl embracing the penultimate whorl above the periphery; whorls relatively well rounded, “apple shaped,” a nar- row subsutural ramp in all intermediate growth stages, followed by a smooth curve which near the LATE PALEOZOIC GASTROPODA FROM NORTHERN ALASKA periphery approaches the arc of a circle, and a slight elongation of the whorl below the periphery; growth lines straight, gently prosocline from suture to colu- mella; inductura and other apertural features un- known; ornamented by distinct subsutural lirae which appear after the earliest growth stages, coincidentally with the development of the subsutural ramp, and disappear at maturity simultaneously with disappear- ance of the ramp. Discussion—The subsutural ornament‘ 0f Naticop- sis (Naticopsis) sutnricompta is similar to that of species referred to N. (Jedria) Yochelson, 1953. The relatively high-spired, elongate shape of the latter, however, is quite distinct from the well—rounded “ap- ple shape” of the typical subgenus. As closely as can be determined, this combination of well-rounded whorls and subsutural ornament is confined to this spe- cies. Certain American and Belgian species approach the shape of N. (N atieapsis) sntum'compta, but orna- ment either is not present or was overlooked and not figured by earlier workers. This species characterizes the “Natioopse’s howi zone” of Dutro and Bowsher (1957) and is the same form referred to by them. Partially exfoliated specimens show the presence of two shell layers. They also show, on the inner layer, growth lines parallel to those on the outer layer. These lines have not been observed on silicified speci- mens from the Permian of west Texas. Rather, the inner shell layer of those forms is characterized by structures essentially normal to the growth lines. As with most of the gastropods from northern Alaska, preservation of specimens presents problems with the taxonomic treatment. The type of this spe- cies and a few other smaller specimens show the char- acteristic ornament. Most of the specimens do not preserve the early whorls or, if they are present, they are partially exfoliated or are steinkerns. However, in these specimens the shape of the mature body whorl agrees closely with the type. The alternatives of re- garding these less well preserved specimens as a sepa- rate species or only tentatively comparing them to this species have been considered but rejected, and all Up- per Mississippian specimens of fair preservation are placed in one species. Several specimens from the Lower Mississippian are tentatively referred to the species. These are all small nearly globular shells possessing subsutural ornament but lacking a subsutural ramp. Some neritacean spe- cies are known to undergo considerable ontogenetic. change. Further collections may show that the ma- ture stage of these Lower Mississippian forms distin- 143 guishes them from the Upper Mississippian species. If they do represent another species, it would indicate that ornament alone is an unreliable criterion for iden- tification of poorly preserved or immature specimens. Illustrated speeimens.—Holotype: USNM 136549, USGS local- ity 9187; paratypes: USNM 136548, USNM locality, 3088; and USNM 136550, USNM locality 3170. Measurements.—Measurements of the illustrated specimens (in mm) are given below: Height 0/ Width of Specimen Height Width aperture aperture USNM 136548 __________ l 55 55 47 43 136549 __________ 26 24 20 1 6 136550 __________ 1 25 26 20 18 1 Estimated. Occurrence and abundance—Lower Mississippian undifferenti- ated: USGS locality 11808, cf. one; 12701, cf. one; 13240, of. two. Alapah limestone: USNM locality 3088, twenty; 3164, one: 3170, two; 3171, one; 3182, cf. one; USGS locality 9187, three; 12355, three; 15430, one; 994, of. one. Upper Missis- sippian undifferentiated: USGS locality 11799, three. Naticopsis (Naticopsis) sp. Plate 14, figure 5 Discussion—A single small specimen from the Mis— sissippian Lisburne group differs from juvenile speci- mens of Naticopsis (Naticopsis) suturicompta. It is markedly higher spired, and has an elongate, poorly rounded body whorl with the periphery well below midwhorl. No subsutural ramp is developed. The specimen has fainter subsutural ornament than is characteristic of N. (Naticopsis) sntum’eompta, but this may be a feature of immaturity. The specimen is too poorly preserved to warrant a formal specific name. Illustrated specimen—USNM 136540, USGS locality 13235. Occurrence and abundance—Lower Mississippian undifferen- tiated: USGS locality 13235, one. INDETERMINATE NERITACEANS Discussion—As with most of the other superfam— ilies treated herein, there are some specimens referable to the superfamily that are quite poorly preserved. Unlike the material from the other groups, most of these are not steinkerns, but are either distorted speci- mens or juveniles. It seems probable that most of these specimens are referable to Naticopsis in the broad sense. Specific identification is not possible. Occurrence and abundance—Kayak shale: USGS locality 13247, one. Wachsmuth limestone: USGS locality 13286, one. Lower Mississippian undifferentiated: USGS locality 12701, eight; 12709, one; 12785, three; 12788, one; 13234, one; 13235, one; 13254, one; 13255, one. Alapah limestone: USGS local- ity 976, one; 997, one; USNM locality 3167, one. ?Upper Mis- sissippian: USGS locality 13246, one. 144 Order MESOGASTROI’ODA Superfamily MURCHISONIACEA Family MURCHISONIIDAE Genus MURCHISONIA Archiac and Verneuil, 1841 cf. Murchisonia sp. Plate 14, figure 1 Discussion—A single specimen is tentatively re- ferred to this genus, as used in the broadest sense. The specimen is high spired, has impressed sutures and apparently well—rounded whorls. There is a spiral lira below the periphery forming what appears to be the lower border of a gently concave selenizone. The specimen is exceedingly poorly preserved, but it is unique in the fauna and has been figured. A second, even more poorly preserved specimen is questionably placed in this taxon. Illustrated specimen—USNM 136537, USGS locality 13240. Occurrence and abundance—Lower Mississippian undifferen- tiated: USGS locality 13240, one. Alapah limestone: USGS locality 9184, cf. one. Family PLETHO‘SI’IRIDAE Subfamily PITHODEINAE Genus PLATYZONA Knight, 1945 Platyzona sp. Plate 14, figure 2 Discussion—This species, identified from a single specimen, is not named. The specimen is fairly well preserved, but is incomplete. The shell is moderately high spired. Sutures are impressed and whorls are relatively broad and well rounded, being flattened near the suture. A broad concave selenizone is located on the periphery. Growth lines on the upper whorl sur— face are prosocline, sweeping backward from the su- ture to the selenizone. Below the selenizone they are gently opsithocline for about the upper third of the lower whorl surface. Details of the aperture and base are unknown. Illustrated specimen—USNM 136538, USGS locality 13246. Occurrence and abundance.~—?Upper Mississippian: USGS locality 13246, one. INDETERMINATE MURGHISONIACEANS Discussion—F our specimens are placed in this grouping. The first is a steinkern retaining patches of shell. The other three are incompletely silicified shells. Occurrence and abundance—Lower Mississippian undifferen- tiated: USGS locality 13240, one, whorls ornamented by sew eral spiral lirae; more angular than cf. Murchisonia sp. Ala- pah limestone: USNM locality 3167, one, may show evidence of a selenizone; 3272, two, may show evidence of a selenizone. SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY Superfamily LOXONEMATAGEA Family LOXONEMA'I‘IDAE Genus LOXONEMA Phillips, 1841 Loxonema sp. Plate 14, figure 6 Discussion—Specimens referred to this species are typical of the genus. They are exceedingly high spired, have deep sutures and well—rounded whorls. Growth lines are arcuate, forming a wide, quite shal- low sinus, the most posterior portion of which is near midwhorl. This sinus distinguishes the specimens from those called cf. Murchisonz'a sp. All the speci— mens are small and it is assumed that they are im— mature. Illustrated spectmens.—USNM 136541, USGS locality 11828. Occurrence and abundance.—Alapah limestone: USGS 10- cality 11828, three. INDETERMINATE LOXO‘NEMATACEANS Discussion—Specimens placed here are poorly pre- served steinkerns. It should be pointed out that ref— erence to cf. Murchisonia sp. would be nearly as fea— sible, because either of these fundamentally difierent shells, when exfoliated, produce almost identical stein- kerns. Occurrence and abundance—Lower Mississippian undifferen- tiated: USGS locality 9186; two, possibly Lowonema; 13235, five, four to five times size of specimens of Lea-enema sp.; Alapah limestone: USGS locality 976, seven, doubtfully Loam- nema. Order NEOGASTROPODA Superfamily SUBULITACEA Family SUBULITIDAE Subfamily SOLENISCINAE Genus IANTHINOI’SIS Meek and Worthen, 1866 Ianthinopsis’! sp. Plate 14, figure 3 Discussion—Two specimens from the Lower Mis— sissippian show the low-spired subglobular shape char- acteristic of some of the soleniscinids. They are ques- tionably placed in Ianthinopsis, this being the most common upper Paleozoic genus. Neither shows fea— tures of the columellar lip, critical for more exact placement. The specimens are in part exfoliated; the rest of the shell has been recrystallized. Illustrated spectmen.—USNM 136539, USGS locality 12785. Occurrence and abundance—Lower Mississippian undifferen- tiated: USGS locality 11867, one; 12785, one. Class SCAPHOPODA Genus indeterminate Plate 14, figure 4 Discussion—A single, incomplete scaphopod is pres- ent in the collection from USGS locality 13246. Faint LATE PALEOZOIC GASTROPODA FROM NORTHERN ALASKA traces of annular growth lines can be seen, but if other ornament was originally present, it is not preserved. The specimen does not warrant description and is in- cluded here only because Mississippian scaphopods are relatively rare and occurrences should be recorded. A second specimen from USGS locality 13240 seems to lack transverse ornament, and in that respect is simi- lar to Plagioglypta Pilsbry and Sharp (1897). Illustrated specimen.—USNM 136546, USGS locality 13246. Occurrence and abundance—Lower Mississippian undifferen- tiated: USGS locality 13240, one. ?Upper Mississippian: USGS locality 13246, one. REFERENCES CITED Archiac, E. J. A. d’, and Verneuil, E. P., 1841, Note sur le genre Murchisonia,: Soc. géol. France Bull., lst ser., v. 12, p. 154—160. Bowsher, A. L., 1955, Origin and adaptation of platyceratid gastropods: Kansas Univ. Paleont. Contr. Mollusca, Art. 5, p. 1—11, pls. 1, 2. _ 1956, The effect of the crinoid host on the variability of Permian platyceratids, in Yochelson, E. L., Permian Gastropoda of the southwestern United States; [pt. 1.]: Am. Mus. Nat. History Bull, v. 110, art. 3, p. 261—263. Bowsher, A. L., and Dutro, J. T., Jr., 1957, The Paleozoic section in the Shainin Lake area, central Brooks Range, Alaska: U. S. Geol. Survey Prof. Paper 303—A. Branson, C. C., 1948, Bibliographic index of Permian inverte- brates: Geol. Soc. America Mem. 26. Conrad, T. A., 1840, Third annual report on the palaeontologi- cal department of the Survey: New York Geol. Survey Ann. Rept. 4, p. 199—207. Cossmann, Maurice, 1915, Essais de paléoconchologie comparée: Paris, v. 10, [1916]. Cox,-'L. R., 1955, Observations on gastropod descriptive termi— nology: Malacological Soc. London Proc., v. 31, pts. 5 and 6, p. 190—202. Dutro, J. T., Jr., 1956, Annotated bibliography of Alaskan Paleozoic paleontology: U. S. Geol. Survey Bull. 1021—H, p. 253-287. Fischer, Paul, 1885, Manuel de conchyliologie et de paleon— tologie conchyliologique, ou histoire naturelle des mollus- ques vivants et fossiles, fasc. IX: Paris, p. 785—896. Girty, G. H., 1939, Certain pleurotomariid gastropods from the Carboniferous of New Mexico and Texas: Washing- ton Acad. Sci. Jour., v. 24, no. 1, p. 21—36. Gordon, Mackenzie, Jr., 1957, Mississippian Cephalopoda from northern and eastern Alaska: U. S. Geol. Survey Prof. Paper 283. Hall, J. W., 1843, Geology of New York, pt. 4, comprising the survey of the fourth geological district: Albany, Charles Van Benthuyson and Sons. Knight, J. B., 1933, The gastropods of the St. Louis, Missouri, Pennsylvanian outlier; V. The Trocho-Turbinidae: Jour. Paleontology, v. 7, no. 1, p. 30—58, pls. 8—12. ______ 1934, The gastropods of the St. Louis, Missouri, Pennsylvanian outlier; VII. The Euomphalidae and Platy- ceratidae: Jour. Paleontology, v. 8, no. 2, p. 139-166, pls. 20—26. 145 __ 1941, Paleozoic gastropod genotypes: Geol. Soc. America Spec. Paper 32. 1942, Four new genera of Paleozoic Gastropoda: Paleontology, v. 16, no. 4, p. 487—488. 1945a, Some new genera of the Bellerophontacea: Paleontology, v. 19, no. 4, p. 333—340, pl. 49. 1945b, Some new genera of Paleozoic Gastropoda: Paleontology, v. 19, no. 6, p. 573—587, pls. 79, 80. 1953, Gastropoda, in Cooper, G. A. and others, Per- mian fauna at El Antimonio, western Sonora, Mexico: Smithsonian Misc. Colln., v. 119, no. 2, p. 83—90, pls. 24, 25. Knight, J. B., Batten, R. L., and Yochelson, E. L., 1960, Paleo« zoic Gastropoda, m Treatise on invertebrate paleontology; pt. I. Gastropoda: Geol. Soc. America. (In press) Koninck, L. G. de, 1881, Faune du calcaire carbonifere de la Belgique, 3e partie, Gastéropodes: Mus. royal d’Histoire nat. Belgique Annales, Ser. Paléont., t. 6. 1883, Faune du calcaire carbonifere de la Belgique, 4e partie, Gastéropodes (suite et fin.) : Mus. royal d’His- toire nat. Belgique Annales, Ser. Paléont., t. 8. Leflingwell, E. de K., 1919, The Canning River region, north- ern Alaska: U. S. Geol. Survey Prof. Paper 109. Longstaff, J. D., 1912, Some new Lower Carboniferous Gas- teropoda: Geol. Soc. London Quart. Jour., v. 68, p. 295— 309, pls. 27~30. M’Coy, Frederick, 1844, A synopsis of the characters of the Carboniferous limestone fossils of Ireland: Dublin, Mc- Glashon and Gill. Maddren, A. G., 1912, Geologic investigations along the Canada- Alaska boundary: U. S. Geol. Survey Bull. 520—K. Mansuy, Henri, 1912, Etude géologique du Yun-nan oriental, 2e partie, Paléontologie: Indochine Service géol. Mém., v. 1, 1, fasc. 2. Meek, F. B., and Worthen, A. H., 1866, Descriptions of inverte- brates from the Carboniferous system, in Illinois Geol. Survey v. 2, Paleontology, p. 143—410, pls. 14—32. 1867, Contributions to the paleontology of Illinois and otherwestern states: Acad. Nat. Sci. of Philadelphia Proc. for 1866, p. 251—275. Montfort, Pierre Denys de, 1808, Conchyliologie systématique, et classification méthodique des coquilles; offrant leurs figures, leur arrangement générique, leurs description ca- ractéristiques, leurs noms; ainsi que leur synonymie en plusieurs langues; tome 1. Coquilles univalves, cloisonnées: Paris, F. Schoell. _ 1810, Conchyliologie syste’matique, et classification méthodique des coquilles; offrant leurs figures, leur ar- rangement géniérique, leurs descriptions caracte’ristiques, leurs noms; ainsi que leur synonymie en plusieurs langues; tome 2. Coquilles univalves, non cloisonnées: Paris, F. Schoell. Moore, R. C., 1941, Upper Pennsylvanian gastropods from Kan- sas: Kansas Geol. Survey Bull. 38, pt. 4, p. 121-163, pls. 1—3. Oehlert, D. P., 1888, Descriptions de quelques epéces dévo- niennes du department de la Mayenne: Soc. d’Etudes Sci- entiflques d’Angers Bull. 1887, p. 65—120, pls. 6—10. Patton, W. W., Jr., 1957, A new upper Paleozoic formation, central Brooks Range, Alaska: U. S. Geol. Survey Prof. Paper 303—3. Payne, T. G., and others, 1952, Geology of the Arctic slope of Alaska: U. S. Geol. Survey Oil and Gas Inv. Map, OM— 126, 3 sheets. J our. J our. J our. 146 Phillips, John, 1841, Figures and descriptions of the Paleozoic fossils of Cornwall, Devon, and West Somerset; Observed in the course of the Ordinance Geological Survey of that district: London, Longman, Brown, Green and Longmans. Pilsbry, H. A., and Sharp, B., 1897, Scaphopoda (part), in Tryon, G. W., Manual of conchology: Acad. of Nat. Sci. of Philadelphia, Conchological Section, ser. 1, v. 17, pt. 65, p. 1—80. Shimer, H. W., 1926, Upper Paleozoic faunas of the Lake Min- newanka section, near Banff, Alberta: Canada Dept. of Mines, Geol. Survey Mus. Bull. No. 42, p. 1—84, pls. 1—8. Smith, P. S., 1913, The Noatak-Kobuk region, Alaska: U. S. Geol. Survey Bull. 536, p. 75—78. __ 1939, Areal geology of Alaska: Prof. Paper 192. Smith, P. S., and Mertie, J. B., Jr., 1930, Geology and mineral resources of northwestern Alaska: U. S. Geol. Survey Bull. 815. Sowerby, James, 1814, Mineral conchology of Great Britain, nos. IX and X, or colored figures and descriptions of those remains of testaceous animals or shells, which have been preserved at various times and depths in the earth: Lon- don, v. 1. U. S. Geol. Survey SHORTER CONTRIBUTIONS TO GENERAD GEOLOGY Stehli, F. G., 1957, Possible Permian climatic zonation and its implications: Am. Jour. Sci., v. 255, p. 607—618. Thomas, E. G., 1940, Revision of the Scottish Carboniferous Pleurotomariidae: Geol. Soc. Glasgow, v. 20, pt. 1, p. 30— 72. Ulrich, E. 0., and Scofield, W. H., 1897, The Lower Silurian Gastropoda of Minnesota, in Geology of Minnesota: Minn. Geol. and Nat. Hist. Survey, final rept. 3, pt. 2, p. 8137— 1081, pls. 61—82. U. S. Department of Defense, 1953—1957, Arctic bibliography: v. 1—7. Warthin, A. S., Jr., 1930, Micropaleontology of the Wetumka, Wewoka, and Holdenville formations: Oklahoma Geol. Survey Bull. 53. Yochelson, E. L., 1953, chriar a new subgenus of Naticopsis: Washington Acad. Sci. Jour., v. 43, p. 65. __ 1956, Permian Gastropoda of the southwestern United States; [pt.] 1. Euomphalacea, Trochonematacea, Pseudo~ phoracea, Anomphalacea, Craspedastomatacea, and Platy- ceratacea: Am. Mus. Nat. History Bull, v. 119, p. 173— 276, pls. 9—24. Page Acknowledgment _______________________________ 113 Alapah limestone ..................... 113, 116, 117, 118 alaskensia, Straparollus (Euomphalus) ___________ 115, 116,117,118,119,133,134, pl. 12 Amphiscapha ................................... 121 (Cylicioscapha) grada_.__ 116,117,118,119,134,p1 12 analoga, Leptaena .......... 115 Anematina laqueata ........ 141 proutana _______________ 141 rockymomanum ............. 116, 117,118,141,p1. 14 sp ________________________________ 116,117,118,14£ (Angyomphalus), Trepaspim. _ 116, 117, 136, pl. 12 Anomphalidae _______________ 142 Anomphalus nerviensis. 142 Sp __________________________ 116 117,118, 142,1)1 14 asiaticum, Lithoatrotion .......................... 115 Bellerophon gigameua ___________________________ 132 sp __________________________ 116,117,118,131,p1.12 Bellerophontaceans ___________________ 116, 117, 118, 119 Bellerophontidae, _ _ . . _ 131 Bellerophontinae _______________________________ 131 Bembezia inumbilicata. . 116, 117, 118,137, 138, 139, pl. 13 larteti _______________________________________ 138 Brachythyris suborbicularis ______________________ 115 zone ......................... __ 115,116 Brooks Range._ _______________________ 111,113,115 brooksensis, Straparollus (Euomphalus) __________ 116, 117,118,133,134,p1. 12 Canning River district _________________________ 111 crateriformia, Straparollus (Euomphalus) ....... 134 crem’stria, Goniatites ____________________ 115 (Cylicioscapha) grada, Amphiscapha _____________ 116, 117,118,119,134,p1. 12 Elasmonematidae ____________________________ 141—142 Eotomarlidae _____ _ _ - 136 Eotomariinae ___________________________________ 136 Euomphalaeeans _____________________ 116, 117, 118, 119 Euomphalidae.... . 133 Euomphalus ____________________________________ 134 (Euomphalus), Straparollus. _ _ _ ____ 116,117,134,p1. 12 alaskemis, Straparollus ___________________ 115,116, 117,118,119,133,134,p1. 12 brooksemis, Straparollus .................. 116,117, 118,133,134, pl. 12 crateriformis, Straparollus ___________________ 134 levicarinatus, Straparollus ___________________ 133 Euphemites Sp ______________ 116, 117, 118, 131, 132, pl. 12 Euphemitinae __________________________________ 131 giganteus, Bellerophon ........................... 132 Glabrocingulum (Glabrocingulum) sp _________ 116,117, 119,138,p1. 13 (Glabrocinaulum), Glabrocingulum ............ 116,117, 119,138,111. 13 Gom’atites crem‘stria _____________________________ 115 zone _______________ __. ....... 115,117,118 Gordon, .11., Mackenzie, quoted. 115 Gosseletina Sp ______________________ 116,117,139,p1. 13 Gosseletinidae __________________________________ 139 Gosseletininae ____________ 139 grada, Amphiscapha (Cylicioscapha) _ _ ._ 116, 117, 118,119,134, pl. 12 INDEX [Italic numbers indicate descriptions] Holopeidae ____________________________ howi, Naticopsis, __ Naticopsis zone ___________________ 115, 117, 118, 143 Ianthinopsis Sp _____________________ 116, 117, 144, pl. 14 inumbilicata, Bembezia _______________________ 116, 117, 118, 137, 138, 139, pl. 13 (Jedria), Naticopsis ............................. 143 Kayak Shale ______________________________ 113,115,116 Knight, J. Brookes, quoted... 111 Knightites (Retispira) Sp_. ________ 116,117,132,p1. 12 Knightitinae ____________ 132 konimki, Zaphrentis ____________________________ 115 luqueata, Anematina ____________________________ 141 larteti, Bemberia ................................ 138 late, 7urbonellina__ _ 113,116,117,118, 135, pl. 12 lepidu, Turbonellina.. 135 Leptaena analogu. _ . 115 zone ...................................... 115, 116 levicarinatus, Straparollus (Euomphalus) ________ 133 Licharewia _____________________________ 115 Liospirinae . . _ 135 Lisburne group 113 Lithostrotion asiaticum __________________________ 115 zone .............................. 115, 116, 117, 118 Lozonema rockymontanum ______________________ 141 Sp ______________________ 116,117,118,142,144,pl. 14 Loxonemataeeans._ _____________________ 116, 117 Loxonematidae _________________________________ 144 minute, Mourlom'a _________ 116, 117, 118, 136, 140, pl. 13 .Mourlom’a ____________________________________ 137, 138 minuta _________________ 116, 117, 118, 136, 140, p]. 13 reloba ....... 115,116,117,118,119,136,137,140,p1.13 Murchixonia Sp ..................... 116, 117, 144,111. 14 Murchisoniaceans ........................ 116,117, 118 Murchisoniidae _________________________________ 144 Naticopsinae ___________________________________ 142 Naticopsis howi, . 115 (Jedria) .......... 143 (Naticopsis) suturicompta _____ 115, 116, 117,118, 142 Sp .......................... 116,117,143,p1.14 suturicompta ................................ 119 zone .............. 115,116,117,118,119,143 (Naticopsis), Naticopsis. ________ 116, 117, 143, pl. 14 suturicompta, Naticopsis ...... 115, 116, 117, 118, 142 Naval Petroleum Reserve No. 4 ................ 111 Neilsom'a Sp .................... 116,117,118,138,p1. 13 Neilsonilnae_. 138 Neritaceans __________________________ 116,117, 118, 119 Neritopsldae ................................... 142 nerviensis, Anomphalus _________________________ 142 New genus A _______________________ 116,117,139,p1. 13 B _______ 116,117, 139, pl. 14 Nodospira ______________________________________ 137 ornata __________________ 116,117,118,137,138,pl. 13 Opisthocline, defined ___________________________ 121 ornate, Nodospira ___________ 116,117,118,137,138,pl. 13 Orthocline, defined _____________________________ 121 (Orthonychia), Platyceraa ........... 116, 117, 141, pl. 14 Page Pelmatozoan calyxes .......................... . 119 echinoderms___. 115 Phymatopleum Sp __________ 116, 117, 138, 139, 140, pl. 13 Phymatopleuridae .............................. 139 Pithodeinae ______________ . 144 Plagiaglypta. _ 145 Platycems ________ _ 115,116,117, 118,119,140 (Orthonychia) Sp ________________ 116,117,141, pl. 14 (Platyceras) sp _________ 115, 116, 117, 118, 140, pl. 14 (Platyceras), Platyceras. . 115,116,117,118,140,p1. 14 Platycerataeeans _____________________________ 115, 119 Platyceratidae____ 140 Platyzona sp ....................... 116, 117, 144, pl. 14 Plethosplridae __________________________________ 144 Pleurotomariaceans _______ 116, 117, 118,119, 122 Portlockiella sp ....... .. 113,116,117,118,1.39,p1. 13 Portlockiellidae_. 139 Prosocline defined ..................... 121 proutana, Anematina __________________ 141 Ptychomphalina _________________________________ 137 Raphistomatidae. . 135 reloba, Mourlom'a-... 115, 116, 117, 118, 119, 136, 137, 140, pl. 13 (Retispira), Knightiiea .............. 116,117,132,p1. 12 Rhineoderma Sp ________ 113,116,117,118,135,140,p1. 12 rockymontanum, Anematinanh 116, 117, 118, 141, pl. 14 Lozonema _____________________________ 141 Rugose corals _______ 111 Sadlerochit formation _____________ 113, 115, 117,118,119 Scalarituba sp ________________________ 115 Zone _____________________________ 115,116 Scaphopod, genus indet ________ 116,117,144,p1. 14 Siksikpuk formation ______________ 113,115,117,118,119 Sinuitidae ______________________________________ 131 Sinuopeidae. .._ ...... . 135 Soleniscinae __________________________ 144 Spiroscala Sp ..... __ 116, 117, 137, 140, pl. 13 Steinkerns ______________________________________ 118 Straparollu: __________________________________ 119, 121 (Euomphalus) alaskensis ____________________ 115, 116,117,118,119,133,134,111. 12 brooksensis ......... 116, 117,118, 183, 134, pl. 12 crateriformis ____________________________ 134 levicarinatua ____________________________ 133 sp ________________ 116,117,134,p1.12 suborbicularis, Brachythyris... 115 Subulitidae _______________ 144 suluricompta, Naticopsis ........................ 119 Naticopsis (Naticopsis) ________ 115,116,117, 118, 142 Trepospira (Angyomphalus) sp _____ 116,117,136,p1. 12 (Trepoepira) Sp ____________ 116, 117, 119, 135, pl. 13 (Trepaspira), Trepospira. .. 116, 117, 119,135, pl. 13 Tropidostrapha __________________________________ 140 Turbonellina lam ___________ 113, 116,117,118,135, pl. 12 lepida ___________ 135 Turbonellininae ___________________ 135 Viséan formation _______________________________ 115 Wachsmuth limestone ____________________ 113,115, 116 Yunnania Sp _______________________ 116, 117, 140,131. 13 Zaphrentis kam’ncki _____________________________ 115 zone ______________________________________ 115, 116 147 PLATES 12 —14 FIGURE 1. 2—4. 5‘9. 10—14.‘ 16~19. 15, 20—23. 24~26. 27—29. 30—33. 34. 35—36. PLATE 12 Knightz'tes (Retispira?) sp. (p. 132) Oblique top view, X 2; USNM 136506, from USGS 100. 11843, Lower Mississippian. Euphemites Sp. (p. 131) 2. Oblique front view, X 2; USNM 136507a, from USGS loc. 12084, Gom‘atites zone, Alapah limestone. Oblique top view and side view, respectively, X 2; USNM 136507b, from USGS loc. 12084, Gom'atites zone, Alapah limestone. Bellerophon sp. (p. 131) 5. Side View of small steinkern, X 2; USNM 136508a, from USNM 100. 3088, Naticopsis zone, Alapah limestone. 6. Front View showing selenizone, X 2; USNM 136509, from USGS 100. 11799, Naticopsv's zone, Alapah limestone. 7, 8. Side and top views, respectively, of a steinkern, X 1; USNM 136508b, from USNM loc. 3088, Naticopsis zone, Alapah limestone. 9. Top view of a large steinkcrn, X 1; USNM 136510, from USGS 100. 15408, Naticopsz's zone, Alapah limestone. Straparollus (Euomphalus) alaskensis Yochelson and Dutro, n. Sp. (p. 133) 10. Section showing two shell layers, X 2; paratype, USNM 136511a, from USGS loc. 11814, Siksikpuk formation. 11. Slightly oblique side View, X 2; paratype, USNM 13651lb, from USGS loc. 11814, Siksikpuk formation. Straparollus (Euomphalus) alaskensis Yochelson and Dutro, n. Sp, (p. 133) 12—14. Side, top, and basal views, respectively, X 2; paratype, USNM 1365110, from USGS loc. 11814, Siksikpuk formation. 16—19. Side, apertural, basal, and top views, respectively, X 1; holotype, USNM 136512, from USGS 10c. 11823, unnamed Permian formation(?). Straparollus (Euomphalus) brooksensis Yochelson and Dutro, n. Sp. (p. 133) 15, 20. Basal and top views, respectively, of small specimen, X 2; paratype, USNM 136513, from USGS loc. 13235, Lower Mississippian. 21. Apertural view, X 1; paratype, USNM 136514, from USGS 100. 11890, Lower Mississippian. 22, 23. Side and top views, respectively, X 2; holotype, USNM 136515, from USNM 100. 3186, Lithostrotion zone, Alapah limestone. Straparollus (Euomphalus) sp. (p. 134) Top, basal, and apertural views, respectively, X 2; USNM 136516, from USGS loc. 14954, Brachythyris zone, Wachsmuth limestone. Amphiscapha (Cylz'cioscapha) grada Yochelson and Dutro, n. Sp. (p. 134) Side, top, and basal views, respectively, X 2; holotype, USNM 136517, from USGS loc. 11823, unnamed Permian formation(?). Turbonellina? lata Yochelson and Dutro, n. Sp. (p. 135) 30—32. Side, basal, and oblique top views, respectively, X 2; holotype, USNM 136518, from USGS loc. 13235, Lower Mississippian. 33. Basal view, X 4; paratype, USNM 136519, from USGS 100. 13234, Lower Mississippian. Rhineoderma? sp. (p. 135) Top view, X 2; USNM 136520, from USNM loc. 3167, Lilhostrotz’on zone, Alapah limestone. Trepospira (Angyomphalus?) Sp. (p. 136) Top and basal views, respectively, X 4; USNM 136521, from USGS loc. 11843, Lower Mississippian. GEOLOGICAL SURVEY PROFESSIONAL PAPER 384 PLATE 12 32 LATE PALEOZOIC GASTROPODA FIGURES 1—3. 4~5. 6—9. 10. 11—13. 14—17. 18, 19. 20, 21. 2244. 25. 26~28. 29. 30~31. PLATE 13 Trepospira (Trepospira) sp. (p. 135) Basal, top, and side views, respectively, X 1; USNM 136522, from 100. USGS 14174, Siksikpuk(?) formation. Mourlom'a minuta Yochelson and Dutro, n. sp. (p. 136) Side, and top views, respectively, X 2; holotype USNM 136523, from USGS 100. 11865, Lisburne group (upper formation). Mourlom’a? reloba Yochelson and Dutro, n. sp. (p. 136) 6, 7. Side and basal views, respectively, X 1; paratype, USNM 136524, from USGS 100. 14169, unnamed Permian formation. 8, 9. Top and adapertural views, respectively, X 2; holotype, USNM 136525, from USGS 100. 14169, unnamed Permian formation. cf. Spiroscala sp. (p. 137) Side view, X 2; USNM 136526, from USGS 100. 1008, Sadlerochit(?) formation. Glabrocingulum (Glabrocingulum) Sp. (p. 138) Top, adapertural, and basal views, respectively, X 2; USNM 136527, from USGS 100. 14174, Siksikpuk formation. Nodospira ornata Yochelson and Dutro, n. sp. (p. 137) 14—16. Top, apertural, and basal views, respectively, X 1; holotype, USNM 136528, from USGS 100. 14150, Gom‘atites zone, Alapah limestone. 17. Apertural view, X 1; paratype, USNM 136529, from USGS 10c. 14150, Goniatz’tes zone, Alapah limestone. Portlockiella? sp. (p. 139) Adapertural and top views, respectively, X 3; USNM 136536, from USNM Ice. 3167, Lithostrotion zone, Alapah limestone. Gosseletina? sp. (p. 139) Basal and side views, respectively, X 2; USNM 136531, from USGS 100. 13236, Lower Mississippian. Phymatopleura sp. (p. 139) Adapertural, top, and basal views, respectively, X 3; USNM 136532, from USGS 100. 13234, Lower Mississippian. Neilsom'a? sp. (p. 138) Side View, X 4; USNM 136533, from USGS 100. 9184,, Alapah limestone. New genus? A (p. 139) Adapertural, basal and top views, respectively, X 4; USNM 136534, from USNM 10c. 3110, “Zaphrentis” zone Wachsmuth limestone. Yunnama sp. (p. 140) Adapertural View of steinkern, X 6; USNM 136535, from USGS loc. 12785, Lower Mississippian. Bembexia? inumbilicata Yochelson and Dutro, n. sp. (p. 138) Apertural and side views, respectively, X 1; Holotype: USNM 136536, from USGS 100. 10862, Goniatz‘tes zone, Alapah limestone. GEOLOGICAL SURVEY PROFESSIONAL PAPER 334 PLATE 13 30 LATE PALEOZOIC GASTROPODA FIGURE 1. 2. 3. 17—19. 20-25. 26, 27. 28. PLATE 14 cf. Murchisonia sp. (p. 144) Side view, X 4; USNM 136537, from USGS 10c. 13240, Lower Mississippian. Platyzona sp. (p. 144) Side view, X 2; USNM 13658, from USGS loc. 13246, probably Upper Mississippian. lanthirwpsis? sp. (p. 144) Side view, X 2; USNM 13659, from USGS 10c. 12785, Lower Mississippian. Scaphopod, genus indeterminate (p. 144) Side view, X 2; USNM 136546 from USGS loc. 13246, probably Upper Mississippian. Naticopsis (Naticopsis) sp. (p. 143) Side view, X 2; USNM 136540 from USGS 100. 13235, Lower Mississippian. Lozonema sp. (p. 144) Side View, showing growth lines, X 4; USNM 136541, from USGS loc. 11828, Gom'atz'tes zone, Lisburne group. . Anomphalus sp. (p. 142) Adapertural, top, and basal views, respectively, X 3; USNM 136547, from USNM 100. 3167, Lithrostrotion zone, Alapah limestone. . Anematina rockymontanum (Shimer) (p. 141) 10, 12, 13. Two side and basal views, respectively, X 2; holotype, GSC 5093, from Lower Mississippian of Lake Min- newanka Alberta. 11. Side View, X 2; paratype, GSC 5093a, from Lower Mississippian at Lake Minnewanka, Alberta. 14. Adapertural View, X 2; USNM 136542, from USGS 100. 11808, Lower Mississippian. 15, 16. Adapertural and apertural views, respectively, X 2; USNM 136543, from USGS 100. 13288, Lithostrotion zone, Alapah limestone. Platyceras (Orthonychia) sp. (p. 141) 17. Side view, X 1; USNM 136544a, from USNM 100. 3089, “Zaphrentis” zone, Wachsmuth limestone. 18. Side view, X 1; USNM 136545, from USGS 100. 9186, Lower Mississippian. 19. Side View, X 1; USNM 136544b, from Ice. 3089, “Zaphrentz's” zone, Wachsmuth limestone. Naticopsis (Naticopsis) suturicompta Yochelson and Dutro, n. sp. (p. 142) 20, 21. Enlargement showing shell layers, and adapertural View, respectively, X 4 and X 1; paratype: USNM 136548, from USNM loc. 3088, Naticopsis zone, Alapah limestone. 22—24. Side, apertural, and top views, respectively X 1; holotype, USNM 136549, from USGS 100. 9187, Alapah limestone(?). 25. Adapertural view, X 1; paratype, USNM 136550 from USNM loc. 3170, Naticopsis zone, Alapah limestone. New genus? B (p. 139) Basal and side views, respectively, X 1; USNM 136551, from USGS loc. 13215, unnamed Permian formation. Platyceras (Platyceras) sp. (p. 140) Top view showing early whorls, X 4; USNM 136552, from USGS loc. 14035, Upper Mississippian. U. 5. GOVERNMENT PRINTING OFFICE : 1960 0 -507218 GEOLOGICAL SURVEY PROFESSIONAL PAPER 334 PLATE 14 27 LATE PALEOZOIC GASTROPODA ”3.; 35%»? Upper Cretacwus Pelecypods . of the Genus [Imemmm V from Northern Alaska ”Qflf [GEOLOGICAL SURVEVE/PROFESSIONAL PAPER 334-E Upper Cretaceous Pelecypods of the Genus [mtemmm from Northern Alaska By DAVID L. JONES and GEORGE GRYC SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY GEOLOGICAL SURVEY PROFESSIONAL PAPER 334—E A dercrz'ptz'm affive specter w/tz'c/z are important guz’a’efosrz'ly t0 tfie Upper Cretaceous rocér of t/ze Midwestern interior of Nort/z flmeriw and nart/zerfi fl/méa UNITED STATES GOVERNMENT PRINTING OFFICE7 WASHINGTON :1960 UNITED STATES DEPARTMENT OF THE INTERIOR FRED A. SEATON, Secretary GEOLOGICAL SURVEY Thomas B. Nolan, Director For sale by the Superintendent of Documents, US. Government Printing Office Washington 25, D. C. — Price 45 cents (paper cover) CONTENTS Page Page Abstract _____________________________________________ 149 Age and correlation _________________________________ 152 Introduction ________________________________________ 149 Geographic distribution _____________________________ 153 Cretaceous rocks ___________________________________ 149 Systematic descriptions _____________________________ 158 Upper Cretaceous rocks ______________________________ 150 Literature cited _____________________________________ 162 Nanushuk group (part) _________________________ 150 Index _____________________________________________ 165 Colville group _________________________________ 150 ILLUSTRATIONS [Plates 15—23 follow page 167] PLATE 15. Inaceramus (lnoceramus) dunveganensis McLearn. 16. 17. 18. 19. 20. 21. 22. 23. FIGURE 3 3 3 3 TABLE 1. 2. O. 1. 2. 3. Inoceramus (Inoceramus) dunveganensis McLearn. Inoceramus (Inoceramus) dunveganensis McLearn. Inaceramus (Inoceramus) dunveganensis McLearn and Inoceramus aff. I. (Inoceramus) cuvierz’i Sowerby. Inoceramus aff. I. (Inaceramus) cuvierii Sowerby, Inoceramus (Inoceramus) dunveganensis McLearn, Inoceramus (Mg/ti- loides) labiatus (Schlotheim), and Inoceramus (Sphenooeramus) steenstrupi de Loriol. Inoceramus (Mytiloides) labiatus (Schlotheim) and Inoceramus (Inoceramus) dunveganensz’s McLearn. Inaceramus (Inoceramus) dunveganensis McLearn and Inocemmus (Sphenoceramus) patootensis de Loriol. Inoceramus (Sphenoceramus) patootensz‘s de Loriol. Inoceramus (Sphenocemmus) steenstrupi de Loriol and Inoceramus (Sphenoceramus) patootensis de Loriol. Page Diagrammatic sections showing terminology and relationship of Cretaceous lithologic units in northern Alaska__ 151 Age of formations and fossil sequence __________________________________________________________________ 153 Correlation of Cretaceous formations __________________________________________________________________ 154 Index map of the Colville River region showing Inoceramus-bearing localities _______________________________ 155 TABLES Geographic distribution of Inoceramus in northern Alaska ________________________________________________ 156 Inoceramus-bearing localities in the Upper Cretaceous rocks of the Colville River region _____________________ 156 III SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY UPPER CRETACEOUS PELECYPODS OF THE GENUS INOCERAMUS FROM NORTHERN ALASKA By DAVID L. JONEs and GEORGE GRYC ABSTRACT Upper Cretaceous rocks in the Colville River region of northern Alaska contain a fauna consisting of five species of Inoceramus, all of which are known from other localities, either in the United States, Canada, Europe, or elsewhere. Associated fossils include a small number of pelecypod species, a few species of gastropods, and several species of ammonites. The species of Inoceramus range in age from Cenomanian to late Santonian or early Campanian, but none are of Coniacian age. Upper Cretaceous rocks in the Colville River region are divided into three formations, which are, in ascending order, the Ninuluk, the Seabee, and the Schrader Bluff. Inoccramus (Inoccramus) (lmwcganensis McLearn, of Cenomanian age, is abundant in the Ninuluk formation. Inoceramus (Mytiloidcs) labiatus (Sehlotheim) and I. aff I. (Inoceramus) czmicrii Sowerby occur in the lower part of the Seabee formation of early Turonian age. Inoceramus aff. I. (I.) cum’erii occurs alone in the upper part of the Seabee. which probably is of middle to late Turonian age. There is no evidence that this species extends into the Coniacian in northern Alaska. The Barrow Trail member of the Schrader Bluff formation contains Inoccmm'us (Sphenoceramus) partootcnsis de Loriol and I. (S.) steenstrupi de Loriol, both of late Santonian to early Campanian age. The precise age of the lower and upper mem- bers of the Schrader Bluff formation is not certain. INTRODUCTION Before 1943 the geology of northern Alaska was known only from exploratory and reconnaissance surveys. Schrader (1902 and 1904) made the first geologic traverse of the region and mapped the geology along the Anaktuvuk and lower Colville Rivers. Later Collier (1906), Lefiingwell (1919), and Smith and Mertie (1930) made major contributions to the geology of northern Alaska. These studies indicated the presence of extensive deposits of fossiliferous Creta— ceous rocks, but little stratigraphic detail was recorded and few fossils were collected. Several occurrences of Inocemmus are noted in the reports of Schrader, Leflingwel], and Smith and Mertie. In 1943 the US. Geological Survey renewed its mapping activities in northern Alaska in support of the US. Navy’s program to explore Naval Petroleum Reserve N0. 4 and determine the petroleum possibilities of the region. This program began in 1944 and was suspended in 1953. The Survey cooperated in all the geologic aspects, including detailed and semidetailed mapping of nearly all the bedrock exposures. Many Cretaceous fossils from several hundred localities were collected. Several species of Inocemmus and the gen- eral sequence of Cretaceous faunas were reported by Gryc, Patton, and Payne (1951). This study of the subfamily Inoceraminae from northern Alaska is based on collections made from 1944 through 1953. The collectors include: Robert S. Bickel, William P. Brosgé, Robert. R. Coats, Robert L. Detterman, Robert E. Fellows, George Gryc, Charles E. Kirschner, Allan N. Kover, Richard G. Ray, Karl Stefansson, Lawrence A. Warner, and Edward J. VVebber. The stratigraphic relationships, locality descriptions, and positions of localities on figure 31 have been prepared primarily by William P. Brosgé, Robert L. Detterman, George Gryc, and Charles L. Whittington. In the following text, Jones discusses the fossils and interregional correlations. Gryc describes the formations and their stratigraphic relations. CRETACEOUS ROCKS Upper Cretaceous rocks were first recognized and mapped in northern Alaska along the Anaktuvuk River by Schrader. The age of these rocks was determined from the presence of the ammonite Scaphites and several pelecypods, including Inocemmus (Schrader, 1904, p. 80). Smith and Mertie (1930) added descrip- 149 150 tions of the lithologic characteristics and distribution of the Upper Cretaceous rocks but did not define formations. After the US. Navy began its oil exploration pro- gram in the Arctic, detailed stratigraphic information was rapidly accumulated and a formational nomen- clature was developed. In May 1951, Gryc, Patton, and Payne published the first formal definitions and descriptions of Upper Cretaceous formations in northern Alaska. A summary of the geology of the Arctic Slope and further stratigraphic details were published by Payne and others later that year. In February 1956, Gryc and others revised the strati— graphic terminology for the Mesozoic sequence in the Colville River region (fig. 30). In November 1956, Sable extended the use of part of this terminology to northwestern Alaska. Upper Cretaceous rocks and Lower Cretaceous rocks of Albian age, constitute a stratigraphic sequence that rests with marked angular discordance on older Creta- ceous (Neocomian, Okpikruak formation) and pre- Cretaceous rocks. Lower Cretaceous rocks (fig. 30) include up to 12,000 feet of predominantly marine shale, and up to 1,000 feet of graywacke sandstone. The Tuktu forma- tion (Albian) is overlain to the south by the nonmarine Chandler formation and to the north by the pre- dominantly marine Grandstand formation. The con- tact of the Tuktu with the overlying units is marked by white quartz in the sandstone. The Lower Creta- ceous formations defined in the outcrop belt cannot be readily distinguished lithologically in the subsurface of the coastal plain. Thus two subsurface units, the Oumalik and Topagoruk formations have been defined (Robinson, and others, 1956). UPPER CRETACEOUS ROCKS NANUSHUK GROUP (PART) The position of the Lower Cretaceous-Upper Creta- ceous contact in northern Alaska has been in question for several years. The next, highest readily mappable unit above the ridge-forming Lower Cretaceous Tuktu formation is the black shale of the Upper Cretaceous Seabee formation, which overlies the coarser sedi- mentary rocks of the Ninuluk formation or, to the south, the Niakogon tongue of the Chandler formation. Because of the apparent depositional continuity from the Tuktu to the base of the Seabee, this sequence was defined as the Nanushuk group (Gryc and others 1951, p. 162). In 1954 Imlay and Reeside (p. 243) stated, SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY At the top of the Nanushuk group in the foothills of the Brooks Range abundant Inoceramus have been found in marine intercalations in the Niakogon tongue of the Chandler forma- tion. The common species include I. athabaskcnsis McLearn and I. dmweytmensis McLearn. These have been identified elsewhere in Alaska in the lower part of the Upper Cretaceous sequence * * *. These “marine intercalations” have since been de- fined by Detterman (1956, p. 241, 242) as the Ninuluk formation of Late Cretaceous age. At the type locality it is 657 feet thick. In the northern part of the outcrop area and in the subsurface of the coastal plain the Ninuluk formation overlies beds of the Grandstand formation which contain a Lower Cretaceous micro— fauna. In these areas the Lower Cretaceous-Upper Cretaceous contact can be determined. However, in the southern part of the outcrop area, the Ninuluk formation overlies nonfossiliferous beds of the Chandler formation and the lower limit of the Upper Cretaceous sequence is indeterminate. Imlay (1960) has described the Lower Cretaceous megafauna and Tappan (written communication) is studying the microfauna. The megafossils are commonly associated with red-weathering conglomeratic sandstone. Sable (1956) applied the name Nanushuk group to rocks in northwestern Alaska but stated that precise correlations with the formations of the Colville River region cannot be made. Sable described two forma- tions, the Kukpowruk and the Corwin, in the Utukok- Corwin area (fig. 30) and gives the age as “late Early and Late Cretaceous, not older than middle Albian” (Sable, 1956, p. 2641). COLVILLE GROUP The Colville group unconformably overlies the Nanu- shuk group. \Vhittington states (1956, p. 244), The group consists of a sequence of intertonguing marine and non-marine rocks and is about 5,500 feet thick in the type section. Northward and eastward non-marine become thinner and tend to disappear. Rock types include clay shale, claystone, silt shale. siltstone. sandstone, conglomer- ate, bentonite, tuff, coal, clay ironstone, and limestone * * * Bentonite and tuff are much more prevalent than in the Nanushuk group. The Seabee formation, about 1,500 feet thick at the type locality, marks the base of the Colville group. It is divided into two units: an unnamed member and the Ayiyak member (Detterman, 1956). The unnamed member is characterized by thick units of black, oil- shale which, when weathered, commonly splits into paper-thin sheets. Fossiliferous, thin beds, lenses, and units UPPER CRETACEOUS PELECYPODS OF THE GENES INOC'ERAMUS FROM NORTHERN ALASKA Utukok-Corwin area (after Sable, 1956) Colville River Region (modified from Gryc and others, 1956) South<——— Arctic foothills ———) North Arctic coastal plain k Kogosukruk tongue Sentinel Hill member of Schrader Bluff formation Schrader - Prince Barrow Trail member Prmce Creek of Schrader Blufi Bluff g formation formation 0 m 0 s Creek _ formation a g Tuluvak d 3 tongue Rogers Creek H E member of E 0 formation Schrader Bluff 0 s formation 0 3.. a . \2 // Ay1yak member / Seabee \ // . formation Unnamed member of Seabee formation a-UNCONFOPMITL/ AUNCONFORMITY Nggggfign Ninuluk a Corwm Chandler /l// Ninuluk formation formation g IL formation /_/ _ g 3 formation ,1, Z a: K1111k Grandstand < ‘5 tongue formation Z Kukpowruk Topagoruk formation Tuktu formation formatlon (subsurface) to ? é fr 8 e Torok and Fortress Oumalik E . . ' D Torok and Fortress Mountaln format10ns formation s Mountaln formations (subsurface) § 3 WM Lower Cretaceous(?) Okpikruak Okpikruak and Upper formation formation Jurassic(?) rocks undifferentiated FIGURE 30.—Diagrammatic sections showing terminology and relationship of Cretaceous lithologlc units in northern Alaska. 151 152 concretions of limestone are common. Fossils are also common in the shale but are mostly crushed and poorly preserved. The sandy beds in the upper part of the formation contain a similar, but more limited fauna and were defined as the Ayiyak member by Detterman in 1956. The marine Schrader Bluff formation (approxi— mately 2,300 ft. thick) overlies the Seabee formation with apparent unconformity. The Schrader Bluff has been divided into three members, the Rogers Creek, Barrow Trail, and Sentinel Hill (Gryc and others, 1951, p. 166; thittington, 1956, p. 250—251). Fossils have been found in all three but are abundant only in the middle member and are commonly associated with a very fine grained tuffaceous sandstone. The Prince Creek formation is the approximate nonmarine equivalent of the Schrader Bluff and probably part of the upper part of the Ayiyak member of the Seabee formation. The Prince Creek is about 1,700 feet thick and is subdivided into the Tuluvak tongue and the Kogosukruk tongue, which is the top unit in the Upper Cretaceous sequence in northern Alaska. East of the Anaktuvuk-Colville Rivers, the Upper Cretaceous is unconformably overlain by the Tertiary Sagavanirktok formation (Gryc and others, 1951, p. 167). \Vest of the Anaktuvuk-Colville Rivers, no Tertiary beds have been identified and the Gubik formation of Pleistocene age unconformably overlies the Cretaceous. The Gubik also extends to the east where it overlies the Sagavanirktok formation. AGE AND CORRELATION The species of [flocemmus collected from the Colville River region are known also from Alberta, British Columbia, and other parts of Canada, as well as from the western interior of the United States. Several of the species also occur in England, Greenland, and northern Europe, and one species, I. (Mg/triloides) labiatus, has worldwide distribution. The number of species of [nocemmus found in northern Alaska is very small compared with that found in Cretaceous rocks of the same age in the western interior of the United States and in southern Canada. Likewise, many of the ammonites that characteristically are associated with the extensive Inocemmws faunas of the western interior are missing in northern Alaska. lwocermmm (lnoccmmus) (hm- vcgammis is typically a northern species. The south— ern known limit of this species is in Montana. 1710067“ SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY amus (Mytiloides) labiatus is known throughout the world, and is not indicative of any faunal province. Inocemmus (Sphenocemmm) pat‘ootensis and I. (8.) steenstmopz' are both northern species, occurring in Canada, the western interior of the United States, Greenland, England, Germany, and elsewhere. I . (1.) cum‘em’i has a wide distribution, but seems most typically to be a northern species. Although the [nocemmus fauna from the Colville River region has strong affinities with the western interior of the United States and Canada, and with the faunas of northern Europe, it shows very little relationship to the [nocemmus of the Indo—Pacific faunal province, known from southwestern Alaska, Vancouver Island, British Columbia, California, Japan, and elsewhere. With exception of l. Zabz’aéus and possibly I . cuvierii, no species of lnoceramus from northern Alaska is known to occur in the Indo—Pacific Province. The oldest species of Inocemmus known from the Upper Cretaceous rocks of the Colville River region is I. dunvegammis McLearn, s. l., which occurs in the Ninuluk formation. As herein interpreted, this species ranges from late Albian to late Cenomanian (fig. 31). No ammonites have been found in the Colville River region in association with I. dumieganensis, so it is impossible to determine precisely the upper and lower age limits of the Ninuluk formation, or to locate the Lower and Upper Cretaceous boundary in this area. The Ninuluk is probably nearly equivalent to the Belle Fourche shale of the western interior of the United States and the Dunvegan formation of British Columbia, both of which are believed to be Ceno- manian in age (fig. 32). The Seabee formation, which unconformably over- lies the Ninuluk formation, contains a fauna consist- ing of Inocemmus (Mytz’loides) Zabiatus (Schlot- heim), I. aft”. [. (1.) mmierii Sowerby, Watz'nocems sp., Scaphz'tes sp., and Borissialcocems (Borissjako- cams) sp. I. labirttus seems to be restricted to rocks of early Turonian age. In the western interior of the United States, this species is very abundant in the Pfeifer shale member of the Greenhorn limestone, and also occurs in the overlying Fairport chalky member of the Carlile shale (zone of Collingnonioems wooll- gam‘) (William A. Cobban, oral communication.) I. cum’em'i Sowerby in England ranges from about middle North America, I. aff. I. cuniem’i ranges from the zone of Collignom‘cems hyatti to the zone of Scaphz'tes Turonian to late Santonian. In UPPER CRETACEOUS PELECYPODS OF THE GENCS INOCERAMUS FROM NORTHERN ALASKA Age of formations Fossil sequence E m ‘2 3 European stages Rock units a a Maestrichtian ? 7.12.4 5 Sentinel Hill '5; No fossil evidence for late member . Campanian E Campaman age 3 7 Ex: . .E to E Barrow Trail Inoce’ramus patoote'mn's and 5 member Inoceramua steenstrum' E 94 B Santonian c: (5 Rogers Creek a member No fossil IeVidence for early 5 Santoman age § :> s 3 § 0 5 7 . . . i No fossil evidence for Coniacian age Coniacian _7 ”J b D 0 L11 0 < E4 H a: , Imceramus aft. 1. cumenz, Turonian Seabee formation Wattaocerus sp.. Scaphites sp. and Borissjakocems sp. Inacera‘mus labiatus Q4 D ' O Cenomaman 5 Ninuluk formation Inocemmus dunveganensis M D I ‘3 7 z ? . ; Grandstand formation 5 - Topagoruk § Albian formation as (subsurface) f1 Oumalik formation g (subsurface) ? ? FIGURE 31.—Age of formations and fossil sequence. corveme‘s (middle to late Turonian), but has not been found above the T uronian. The genus Watz'no- cams is restricted to the lower Turonian according to “'I'ight (1957, p. 11416). Morrow (1935, p. 465) re- ports species of Borissjakocems from the Graneros shale (late Cenomanian) and the Blue Hill shale member of the Carlile shale (early Turonian) in Kansas. All this evidence indicates that the un- named member of the Seabee formation is probably early Turonian, and is a correlative of the upper part of the Greenhorn limestone and possibly the lower part of the Carlile shale of the western interior. If this correlation is correct, I. curriem'i may have a slightly lower range in North America than it does in Europe. 527586 0 - so - 2 153 The Ayiyak member of the Seabee formation con- tains only Inocemmus afl. I . cuviem'i, and is probably the correlative of the upper part of the Carlile shale (late Turonian). There are no indications that the upper part of this member extends into the Coniacian. The Schrader Bluff formation overlies the Seabee formation with apparent conformity, but strata of Coniacian age may be missing and an unconformity may separate the two formations. In northeastern British Columbia, McLearn and Kindle (1950) re- port a faunal sequence consisting of Watz'nocems of. W. coloradoense Henderson and Inocemmus labiatus from the Smoky group, followed by I . pontom’ and Scaphites oentm’cosus in the Kotaneelee formation, with I . cf. I . tuberculatus W’oods (equals I . steenstrupz’ de Loriol) in the upper part of the formation. This faunal sequence is similar to that of the Colville River region, except that the Scaphz'tes oentm'cosus fauna has not been found in northern Alaska. The age of Scaphz'tes ventricosus in the western interior of the United States is about middle Coniacian, and the absence of this species in the Colville River region suggests that some Coniacian strata may be miss- ing. The upper limit of the Seabee formation is not known, and no diagnostic fossils are known from the Rogers Creek member of the Schrader Bluff forma- tion. Either one, or both, of these units may be, in part, of Coniacian age. The Barrow Trail member of the Schrader Bluff formation contains Inocemmus (Sphenocemmus) patootensis de Loriol and I. (8.) steenstrum’ de Loriol of middle Santonian to early Campanian age. These two species are also known from Canada, Greenland, England, Germany, and elsewhere. No fossils are available to date the overlying Sentinel Hill member. The Schrader Bluff is probably Santonian to early Campanian in age, and is nearly equivalent to the upper part of the Niobrara formation, the Telegraph Creek formation, the Eagle sandstone, and possibly the lower part of the Pierre shale of the western in— terior of the United States. GEOGRAPHIC DISTRIBUTION The occurrence by locality and formation of the species of Inoccmmus described in this report is shown on table 1. The general position of each locality is shown on figure 33. Detailed descriptions of the localities, as well as stratigraphic data, are given in table 2. 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V r H K .. / \ 233. r A, \ \ a . \ a A. \ q , «=3 .../ . x / 2/ x. .V \.\ w w b ' KM, 1 K x 53:30.2 . ., .. ,.\ wk; a 5:5, n. .. ._ ‘./ .\ 1 K n. \ a /.. \ k ..\) / a. N .. ...l \W. .. k \ . L w\ ‘ A m / m w . an: 2&3 ummfi bmamfl Q2 5?va 0mm: 156 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY TABLE 1.—Geographic distribution of Inoceramus in northern USGS Mesozoic locality (fig. 33) Alaska [X indicates present] I. (Inocera- I. (Myti- I. afinl.‘ I. (Spherio- I. (Spheric- mus) dun- loldes) (1.) cuvzerii ceramus) ceramus) veganensis labiatus patootensis steenstrupi XXXXXXXXXXXXXXXXXXXXXXX TABLE 2.—Inoceramus-bearing localities in the Upper Creta- ceous rocks of the Colville River region USGS Meso- Field No. Stratigraphic Locality, lithology, and collector zoic loc. position (fig. 33) Ninuluk formation, 657 ft thick at type locality 20465. . . 45AWa97._.. Basal part of Colville River, south bank, lat 69°04’30” formation. N., long 153°41’ W. Sandstone and conglomerate. ' Collector, W. A. Warner, 1945. 20466. . . 45AWa82.... 10 ft above base. Killik River, northeast bank about 10 miles upstream from Colville River, lat 68°59’ N., long 153°36’30” W. Same locality as 24629. Collector, W. A. Warner, 1945. 20467.. . 45AWa122. .. Basal part of Colville River, south bank, lat 69°08’ N., formation. long 153°18’ W. Same locality as 25148. Sandstone float. Collector. W. A. Warner, 1945. 20468. . 45AWa123A. 10 ft above base Colville River, south bank, same locality as 20467. 1945. Collector, W. A. Warner, TABLE2.—Inoceramus-bearing localities in the Upper Cretaceous rocks of the Colville River region—Continued USGS Meso- Field No. Stratigraphic Locality, lithology, and collector zoic loc. position (fig. 33) Ninuluk formation, 657 f t thick at type locality—Continued 20475. . . 45AKr155. . . 420 it above Colville River, south bank, lat 69°08’ N., base. long 153°18' W. Collector, C. E. Kirschner, 1945. 20476. . . 45AKr162. . . Basal 100 it of Colville River, south bank; lat 69°09’ N., formation. long 153°15’ W. Sandstone. Collector, C. E. Kirschner, 1945. 20418... 46ARy100B. 600—650 it Weasel Creek, 2.5 miles southwest of below top. confluence with Maybe Creek, lat 69°13’ N., long 153°58’ W. Cut bank on east side of stream, poorly exposed massive to slabby sandstone, 50A60 it thick. Collector, R. G. Ray, 1946. 20419.. 46ARy125E . Probably same On an unnamed stream 1.6 miles south- as 20418. east of its confluence with Maybe Creek, lat 69°15’30” N., long 153°33’ W. Cut bank on northeast side of stream imperfectly exposing about 100 ft of sandstone with subordinate shale and Coal. Fossils occur in talus. Col- lector, R. G. Ray, 1946, 25148.. . 47ADt107. .. 100 ft above Colville River, south bank, lat 69°08’ N., base. long 153°18" W. Thin-bedded sand- stone. Collector, R. L. Dettcrman, 1947. 25154. . 47ADt158 .. Near base of On ridge south of tributary of Ninuluk formation. Creek, lat 69°11’ 51.. long 153°02’ W. Sandstone and conglomerate. Collec- tor, R. L. Detterman, 1947. 25155.. . 47ADt163 . . . Basal part of Colville River, north bank, lat 69°13’30” formation. N., long 153°03’ W. Interbedded sand- stone, siltstone, and clay shale. Col. lector, R. L. Dettcrman, 1947. 25140. .. 48ADt215. . . Basal 100 ft Chandler River, east hank, lat 68°49’15" of formation. N., long 151°57’30” W. Sandstone and conglomerate. Collector, R. L. Detter- man, 1948. 24264... 52AB145 _____ Basal part of On ridge west of Ayiyak River, lat formation 68°57’30” N., long 152°28' W. Green to yellow-red sandstone. Collector, R. S. Bickel, 1952. 24268... 52AB1181.... Near base of Anaktuvuk River, lat 68°55’ N., long formation. 151°11’30” W. Collector, R. S. Bickel, 1952. 24276 ._ 52ADt32..._ Base of forma- Wolverine Creek, east bank of east fork, tion. lat 68°45’ N., long 152°22’ W. Massive conglomerate and sandstone. Col- lector, R. L. Detterman, 1952. 24278 ._ 52ADt74..._ Middle of for- On ridge top, lat 68°59'30” N., long mation. 152°51’ W. Medium-bedded, salt- and-pepper sandstone. Collector, R. L. Detterman, 1952. 24283. . 52ADt102.. 100—150ft above On ridge south of Ayiyak River, lat base. 68°55’ N., long 152°23’ W. Medium- bcdded gray sandstone. Collector, R. L. Detterman, 1952. 24284. 52ADt155A. Basal 100 ft of Anaktuvuk River, west bank, lat formation. 68°56’30” N., long 151°10’30" W. Sand- stone and conglomerate. Collector, R. L. Dettcrman, 1952. 24285. . 52AI)t168. .. Basal part olfor- Anaktuvuk River, west bank, lat 68°51’ mation. N., long 151°09’ W. Thick-bedded sandstone. Collector, R. L. Detter- man, 1952. 24300 _ . 52ADt230. .. Basal part of for- On hillside about 1 mile from Small trib- mation. utary of Ninuluk Creek, lat 69°05’30" N., long 152°38’ W. Thin-bedded greenish sandstone. Collector, R. L. Detterman, 1952. UPPER CRETACEOUS PELECYPODS OF THE GENUS INOCERAJIUS FROM NORTHERN ALASKA TABLE 2.—Inoceramus—bearing localities in the Upper Cretaceous rocks of the Colville River region~Continued 157 TABLE 2,—Inoceramus-bearing localities in the Upper Cretaceous rocks of the Coluille River region—Continued 527586 0 - so - 3 USGS (154190? Field No. Stratigraphic Locality, lithology, and collector Meso- Field No. Stratigraphic Locality, lithology, and collector zoic loc. position zoic loc. position (fig. 33) (fig. 33) Ninuluk formation, 675 ft thick at type locality—Continued Seabee formation, Unnamed member, 250-1,250 ft thick—Continued 24271. _. 52AB1273___. Lower part of On ridge east of small tributary of Fossil 26568. .. 52AB133._.. Nearcontact with Ayiyak River, east bank, lat 68°53’ N., formation. Creek, lat 69°07’ N., long 152°36’ W. Ayiyak mem- long 152°30’30” W. Bentonitic clay Thin-bedded green sandstone. Col- ber. shale and green sandstone. Collector, lector, R. S. Bickel, 1952. R. S. Bickel,1952. 24629... 53ADt62..__ Basal 10 it of Killik River, northeast bank, about 10 26569.__ 52AB1259____ 400-450 ft below On small tributary of Chandler River, formation. miles upstream from Colville River, top. lat 69°02’15” N., long 151°58’ W. Ben- lat 69°59’ N., long 153°36’ W. Thick- tonitic black paper shale and limestone bedded, ferruginous sandstone. Col- concretions. Collector, R. S. Bickel, lector, R. L. Detterman, 1953. 1952. 24630.. _ 53ADt84. . . . Basal 10 ft of Colville River, north bank, about 4miles formation. downstream from Killik River, lat 69°04’ N., long 153052, W. Thick- Seabee formation, Ayiynk member, 360 ft thick at type locality bedded ierruginous sandstone and con- glomerate, same as 24629. Collector, . o , R. L. Detterman. 1953. 26533... 47AWb264.. 130 ft below top.. Nanushuk River, west bank, lat 69 04 N., long 150°50’ W. Interbedded sand- stone, siltstone, silt, and clay shale. Seabee formation, Unnamed member, 2.50-1.250 ft thick Collecmv E- 15 WW”, 1947- 24632 . ._ 53ADtllfi. . . 300 it below top._ Nanushuk River, west bank, lat 68°50’30” N., long 150°32’30” W. Greenish-yel- 19435... 44110525.... 375-5501t above Bluff on north side Colville River at low sandstone and conglomerate. 001- base. Umiat Mtn., lat 69°23’30” N., long lector, R. L. Detterman, 1953. 152° W. Dark fossiliferous shale with dark fossiliferous calcareous concre- tions and many light-colored benton- Schrader Blufl‘ formation, Barrow Trail member, 700-900 ft thick ite laminae and thin beds. Forms con- zrlgzusulzgack Chfi' Collector, R' R' 19434... 44AC522.... 325—355 it below Colville River, south side, prominent 20424... 46ASt3 ...... Same as 19435... Location and lithology same as 19435. ‘0‘" blufi “ear mm" mm 7 "me: 53m!" Collector K Stefansson 1946 west of Umlat Mtn., lat 69 29 IV" ' ' ' ' long. 152°15" W. Seven-inch con~ 20413... 46ARy6Sa... 180 it below top__ Maybe Creek, north bank, 3.75 miles glomerate and 25—foot tufiaceous sand- above mouth 0‘ September Creek, lat stone. Collector, George Gryc, 1944. 69°19 N" long 154°]? W- 171°“ 0f 20461... 45AGr195... 250—350 it above Chandler River, west bank at mouth of gray-brown fine-grained calcareous base. Kutchik River, lat 69°19’ N ., long sandstone. Collector, R. G. Ray, 1946. 151025, W. Tuflaceous sandstone. 20413. ._. 46A Ry68b... 180 it below top__ Location and lithology same as 46- Collector, George Gryc, 1945. ARV68a~ Collectorv R- G Ray, 1946- 20462... 45AGr200_.- 200—300 it above Chandler River,westbank,1at69°20’ N., 20420... 4641137131... 255—265 it below Maybe Creek, north bank, 1.5 miles base. long 151°25'w_ Light bufl' sandstone. top. above mouth of Anak Creek, lat 69°16’ Collector, George Gryc, 1945, N., long 153047, W- Dark-gray lime- 20463. ._ 45AGr201. .. Same as above. Same as above. stone concretions in black shale. 001‘ 20481_ . . 45AFSllfif... Upper 600 ft _____ Anaktuvuk River, east bank at Schrader lector, R. G. Ray, 1946. Bluff, lat 69°10’ N., long 150° W. 26545. .. 47AWb63. ._ About 850 ft be- Nanushuk River, west bank, lat Tuflaceous sandstone and siltstone. low top. 68°50’30” N., long 150°33’ W. Benton- Collector, R. E. Fellows, 1945. “if clayshale andlimestom wnCIetionS- 20493... 45AF529 _____ Exact position Anaktuvuk River, east bank, lat 68°29’ Collector, E- J' Webber, 1947' not known. N., long 151°17’ W. Collector, R. E. 26549. . 47AWb177.. About 1,100 ft Nanushuk River, west bank, lat 69°03’ Fellows, 1945. below t011 N., long 150°51’ W. Black paper shale 26498. . . 47AWb136. . Lower 120 it ..... Nanushuk River, northeast bank, lat and limestone concretions. Collector, 68°59’15” N., long 150°42’ W. Lami- E.J.Webber,1947. hated, tufiaceous sandstone. Collec- 26560. _. 49A Bel ..... 255465 it below lat 69°16’ N., long 153°47’ W. Same as tor, E. J. Webber, 1947. top. 20420. Collector.W.P.Brosgé.1949. 26504... 47ADt293... 220ftbelowtop.. Colville River, south bank about 3.6 26563 .. 51AGr34. . .. 60—100 it below ’I‘uluga River, east fork, north bank, lat miles southwest of Umiat, lat 69°20’30” top. 68°50’45” N., long 151°25’ W. I ime- N., long 152°15’ W. Tufl'aoeous sand- stone concretions in shale. Collector, stone. Collector, R. L. Detterman, G. Gryc, 1951. 1947_ 26565 .. 52ADt57. . ._ 160 it below top__ Ayiyak River, east bank, lat 68°51’30” 26508 .. 48ADt387... 80150 ft above Chandler River, east bank, lat 69°12’15” N., long 152°36’ W. Interbedded silty base. N., long 151°26’30” W. Tuf‘iaceous shale, clay shale, siltstone, and sand- sandstone, siltstone, and clay shale. stone. Collector, R. L. Detterman, Collector, R. L. Detterman, 1948. 1952- 26509 48ADt410 540—600 ft above Chandler River, east bank, lat 69°13’ N., 26566'" 52AD‘61~~ 130“ below $011. Ayiyak River, east bank, lat 68°52’ N., base. long 151°25’30” W. ’I‘ufiaceous silt- long 152°33’30” W. Siitstone, silty stone, silty shale, clay shale. Collec- shale and clay shale. Collector, R. L. tor, R. L. Detterman, 1948. Detterman, 1952. 26511... 48ADt449. .. 900—1040 ft Chandler River, west bank at the junc- 24641... 52AB131 ..... 20—30 it below Ayiyak River, east bank, lat 68°52’30" above base. tion of Kutchik River, lat 69°19’15” top. N., long 152°32’ W. Bentonitie clay N.,long151°25’ W. Siltstone and silty shale and thin, green sandstone. Col- shale. Collector, R. L. Detterman, lector, R. S. Biekel, 1952. 1948. 158 TABLE 2.-—Inoceramus-bearing localities in the Upper Cretaceous rocks of the Colm'lle River region—Continued Egg: Field No. Stratigraphic Locality. lithology, and collector zoic 10c. position (fig. 33) Schmder Blufl' formation, Barrow Trail member, 700-900 ft thick—Continued 26515.. 52ADt175 .. 500—520 ft above Outpost Mtn.,north side, about1.5 miles base. west of Tuluga River, lat 69°10’30” N., long 151°08’45” W. Tufiaceous sandstone. Collector, R. I]. Detter- man, 1952. 26516_ 52ADt176.. 55()—5601't above Outpost Mtn., about 1 mile southwest base. of 26515, lat 69°09’30” N., long 151°10’ W. Tufiaceous sandstone. Collector, R. L. Detterman, 1952. 26518_ . 52AB1194.._. 6701‘t above Outpost Mtn., south side, about 1 mile base. southwest of 26515, lat 69°09’ N ., long 151°09’ W. Tufiaceous sandstone and siltstone. Collector, R. S. Bickel, 1952. 26519_ . 52AB1195.... 630 ft above Outpost Mtn., about 0.3 mile west of base. 26518, lat 69°09’ N., long 151°10’ W. Tufiaceous siltstonc. Collector, R. S. Bickcl, 1952. 26521_.. 52AB1197.... 430—450 ft above Outpost Mtn., about 0.5 mile west of base. 26518, lat 69°09’ 51., long 151°10’45” W. Tufiaceous siltstone. Collector, R. S. Bickel, 1952. 26525.. 52AB1202__.. 430—450 ft above Outpost Mtn., lat 69°09’15” N., long base. 151°14’30” W. Tufiaceous sandstone and siltstone. Collector, R. S. Bickcl, 1952. 26526_. 52ABl203.... 500—530 it above Outpost Mtn., lat 69°09’30” N., long base. 151°13’30” W. Tufiaceous sandstone. Collector, R. S. Bickcl, 1952. SYSTEMATIC DESCRIPTIONS Class PELECYPODA Family ISOGNOMONIDAE Iredale Subfamily INOCERAMINAE Zittel, 1881 Genus INOCERAMUS Sowerby, 1814 1814. Inoceramus Sowerby, Annals Philosophy, p. 448. Type species: Inocemmus cuvierii Sowerby, 1814. (International Commission on Zoological Nomenclature decision pending.) Subgenus INOGERAMUS Type species: I nocemmus cuvierii Sowerby, 1814. Inoceramus afl’. I. (Inoceramus) cuvierii Sowerby, 1814 Plate 18, figure 3; plate 19, figures 1, 5. 1814. Inoccramus cuvierii Sowerhy, Annals Philosophy, p. 448. 1912. Inoceramus lamarcki var. mwiert Sowerby. Woods, Paleontographical Soc. v. 65, p. 307—327, pl. 53, fig. 7; text figs. 78—83. (See Woods’ paper for complete synonymy 11p to 1912.) ?1930. Inoccramus allant Warren, Research Council Alberta, Rept. 21, app., p. 62, pl. 3, fig. 1. Shell equivalve, very inequilateral, subquadrate, moderately inflated, height 1 greater than length; 1Height is measured from the dorsal margin to the ventral margin; length is measured from the anterior margin to the posterior margin; width is measured normal to the plane of the valves. SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY beaks anterior, incurved; hinge line moderately long, forming angle greater than 90° with anterior margin; posterodorsal area compressed to form wing; anterior margin truncated, straight to concave, and may extend anteriorly beyond position of beaks; ventral margin broadly rounded; posterior margin slightly rounded. Ornamentation consists of rounded, fairly prominent, unsymmetrically curved, concentric ribs which are marked by more than one growth line. This type of concentric ribbing that carries multiple growth lines was named Anwachsreifen (growth bands) by Heinz (1928b, p. 1—39). Woods (1912, p. 307—327) has shown that [macera- mus cuvierii varies greatly in the prominence of the concentric ribs, the degree of convexity of the valves, the size of the posterior wing, and the angle formed between the hinge line and the anterior margin. Most of the northern Alaskan specimens are poorly pre- served and fragmentary, but they agree with Woods” illustrations of I. cuvierii in general outline and convexity of the valves, the presence of the posterior wing, and in the Amoachsreifen type of ornamenta- tion. The specimen illustrated by Warren (1930, p. 62, pl. 3, fig. 1) as I. allam’ has not been examined by the writer, but as Warren’s figure agrees very well in general shape and outline with Woods’ (1912, p. 315, text fig. 73) illustration of the type of I. cuvierii, it is tentatively regarded as a synonym of I. cuvierii. lVarren’s species seems to have less prominent orna- mentation, but this probably is not significant. Inocemmus afl’. I. cuvierii is reported by Cobban (oral communication) from the Carlile shale (upper Turonian) of the western interior of the United States. According to Donovan (1953, p. 93; 1954, p. 17), poorly preserved specimens with ornamentation said to be similar to that of I. cuvierii occur in deposits of Turonian age in Greenland. There is no evidence that I. afl". I. cuvierii extends above the Turonian in North America or Greenland. The range of Inoceramus cuvierii in England is, according to Woods (1912, p. 332), from the zone of Terebmtulina lam (middle Turonian) to the zone of Illz'cmster corangm'num (lower Santonian). In north- ern Alaska, I . aff. I. cuciem'i occurs with I. labiatus in the upper part of the unnamed member of the Seabee formation, and it is found along throughout the overlying Ayiyak member. The age of I. Zabz’atus is probably early Turonian, so possibly the lowest limit of I. cuvierii is slightly lower in northern Alaska than it is in England. The Ayiyak member is prob- ably late Turonian in age and possibly, in part, early Coniacian, but no fossils are present to establish a more precise age. UPPER CRETACEOUS FELECYPODS OF THE GERUS INOCERAJIUS FROM NORTHERN ALASKA Number of specimens: 33 (mostly fragments). Figured specimens: USNM2 129226, 129227, 129228. Localities: Unnamed and Ayiyak members of Seabee for- mation; USGS Mesozoic locs. 20413, 24632, 26533, 26560, 26563, 26569. Inooeramus (Inoceramus) dunveganensis McLearn, 1926 Plate 15, figures 1—13; plate 16, figures 1—5; plate 17, figures 1—5; plate 18, figures 1, 2, 4; plate 19, figures 2, 4; plate 20, figures 2, 3, 6; plate 21, figures 1—4, 6. 1926. Inoceramus dzmveganensis McLearn, Canada Dept. Mines, Geol. Ser. 45, Bull. 42, p. 122, pl. 20, fig. 5. 1930. Inoceramus mcconnelli Warren, Research Council Al- berta, Rept. 21, app., p. 60, pl. 4, figs. 1—3. 1931. Inoceramns nahwisi McLearn, Royal Soc. Canada Proc. & Trans, ser. 3, v. 25, p. 7, pl. 2, fig. 1. 1943. Inoceramus athabaskensis McLearn. The Canadian Field Naturalist, v. 57, p. 44. 1943. Inoceramus nahwisi var. goodrichensis McLearn, idem, p. 45. ‘21943. Inoceramus nahwisi var. moberlicnsis McLearn, idem, p. 46. 1945. Inoceramus athabaskensis McLearn, Canada Geol. Survey Paper 45—27, pl. 2, fig. 10; pl. 5, fig. 1; pl. 6, fig. 1. 1945. Inoccramns dunvcganensis McLearn, idem, pl. 2, fig. 11; pl. 4, figs. 1, 2. 1945. Posidonomya nahwisi (McLearn), Canada Geol. Sur- vey Paper 44—17, pl. 9, figs. 1, 2; pl. 10, fig. 1. 1945. Posidonomya nahwisi var. goodrichensis (McLearn), idem, pl. 10, fig. 3; pl. 11, figs. 4, 5. ?1945. Posidonomya nahzcisi var. moberliensis (McLearn), idem, pl. 10, fig. 7. 1945. Inoceramns dunvegancnsis var. mcconnelli Warren, McLearn, idem, pl. 3, fig. 2. Shell equivalve( ?), very inequilateral, height greater than length, slightly oblique, moderately con- vex; anterior margin nearly straight to broadly rounded, compressed in some specimens to form an- terior wing; ventral margin broadly and regularly rounded; posterior margin slightly rounded; postero- dorsal area compressed to form wing; hinge line short to moderately long, formng angle of more than 90° with anterior margin; ornamentation consists of coarse, distantly spaced, rounded, irregular, concentric ribs which are generally more prominent on anterior and posterior parts of the valves than on central portion, where ribs may be completely lacking. Growth axis forms angle of 80° to 90° with hinge line. The posterior adductor muscle scar is slightly behind the median line of the valves. (See pl. 15, figs. 6, 8, 12, 13; pl. 16, figs. 3, 5; pl. 21, fig. 2.) The anterior adductor muscle scar is not visible; ap- parently, this muscle was greatly reduced in size. A series of disconnected attachment scars extends in a broad curve from near the posterior adductor muscle '-‘ United States National Museum. 159 scar to the anterior part of the umbo. The purpose of these attachment scars is not known, but presum— ably they served as attachments for the mantle. MacLearn’s and VVarren’s original descriptions of lnooeramus dunveganensis, I. athabaskensis, I . nah- wisi and its varieties, and I. mcconnelli were based on very few specimens. The much larger collections from northern Alaska, consisting of 107 specimens, show that the holotypes of their species are only isolated examples of one variable species, and that transitions exist between all the holotypes, except possibly for I . nahioisi moberliensis. Therefore, all these specimens are included under the oldest name, I . dunveganensis McLearn. This species is actually not as variable as many other species of Inoceramus. The main variations observed in I. dunveganensis s. l. are: Height of valves: The specimens range in height from 1 inch to more than 15 inches and distinct size groups cannot be recognized. This range in size seems to be a normal characteristic of I noceramus, and differentiation of species on the basis of size alone is not valid. Ratio of length of hinge line to height of valve: This ratio ranges from about 0.2 to more than 0.4, (pl. 16, figs. 2, 5; pl. 17, fig. 2) but clearly defined groups with either a short hinge line (near 0.2) or a moderately long hinge (near 0.4) are not recogniz- able. Ratio of width of valve to height of valve: The width and height of the valves cannot be measured accurately because complete specimens are rarely pre- served. However, approximate measurements show a transition between specimens with a ratio of width to height of about 0.5 to specimens with a ratio of about 0.8. None of the specimens have a ratio of 1.0 or greater. Degree of rounding of the anterior margin and presence of an anterior icing: These features cannot be measured accurately and expressed numerically. The curvature of the anterior margin is extremely variable, not only among specimens, but also in the growth stages of an individual. During early growth stages, the anterior margin is nearly straight, trun- cated, and forms an angle of about 90° with the hinge line (pl. 15, figs. 1—10). After a height of 1 to 2 inches or more, the anterior marginal area be- comes flat. and new shell material is added to form a broadly rounded skirt (pl. 15, fig. 13; pl. 16, figs. 3, 5). In some specimens this skirt is very wide and projects anteriorly beyond the beaks to form an anterior wing (pl. 20, fig. 6; pl. 21, fig. 1, 6); in other specimens the skirt is narrow and no wing is 160 formed (pl. 18, figs. 1, 2; pl. 20, fig. 2). Thus, the degree of development of the anterior wing is vari- able, and its presence or absence is not of specific importance in this species. Ornamentation: The ornamentation consists of rounded, concentric ribs which generally are more prominent on the anterior and posterior sides than on the central part of the valve (pl. 15, fig. 13; pl. 17, fig. 1; pl. 20, fig. 6). However, in some specimens the ribs formed during early growth stages continue without diminishing in prominence across the central part of the valve, and only those ribs formed in later growth stages are interrupted (pl. 15, fig. 12; pl. 16, fig. 5). Other specimens lack ribs when small, but develop them as the shell becomes larger. I nocemmus mcconnelli Warren, which is similar in shape and outline to I. dunoeganensis s. l., has this type of ornamentation. Obliquity of the calms: The angle between the hinge line and the axis of growth (the line connecting the point of maximum curvature of successive con- centric ribs) ranges from about 80° to 90° in all of the specimens studied, including the holotypes of McLearn’s Inoceramus dunveganensis, I. athabasken- sis, I. narhwisz' and I. nahwisz' goodrichensz's, and of Warren’s I. mcconnelh'. However, I. nahwisi mober- 12.671858 has a growth angle of about 60° during its early stages, and an even smaller angle in later stages (pl. 21, figs. 3, 4). None of the specimens from northern Alaska have as s‘mall an angle, so it cannot be shown that the specimens with large angles are transitional into those with smaller angles. Therefore, I. nahwixi moberlieasis is only tentatively regarded as a synonym of I. dunnveganemix. If this oblique type can be shown to have stratigraphic significance, the name probably should be retained. In northeastern British Columbia, McLearn and Kindle (1950, p. 82, 84, 93) report the occurrence of Inoccmmus mhwisi goodm'che'nsia in the Goodrich formation, and the ammonite Neogastroplz'tes, of latest Albian or earliest Cenomanian age (see Reeside, 1957, table 1, opposite p. 540). I. dunveganemis s. s., I. athabaskensis. and I. mccmmelli occur in the Dun- Vegan formation in northeast British Columbia in as- sociation with ammonite Dumwgamocems (see Mc— Learn and Kindle, 1950, p. 99; McLearn, 1943, fig. 1), which, according to Reeside (1957, table 1, opposite p. 540), is restricted to the upper Cenomanian. As the author can find no morphologic basis for separat- ing any of these species, I. dunveganensis is interpreted as ranging in age from late Albian to middle or late Cenomanian. SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY I. dunweganensis occurs in the western interior of Canada, in the Ninuluk formation of northern Alaska, and also in the sandy beds that are equivalent to the Mowry shale of Montana (J. B. Reeside, Jr., oral communication). One questionable occurrence is also reported in the Kuskokwim region of Alaska (USGS Mes. loc. 19388). Number of specimens: 107. Figured Specimens: USNM 129210, 129211, 129212, 129213, 129214, 129215, 129216, 129217, 129218, 129219, 129220, 129221, 129222, 129223, 129224, 129225. Plastotypes CGS3 6106, 6344, 8937, 8945, 8938, 9710, 9713, 9811, 9813, 9816, 9817. Plastotype Univ. Alberta CT 417, CT 418. Localities: Ninuluk formation, USGS Messazoic locs. 20418, 20419, 20465, 20466, 20467, 20468, 20475, 20476, 20488, 24264, 24267, 24268, 24271, 24276, 24278, 24283, 24284, 24285, 24300, 24629, 24630, 25140, 15148, 15154, 25155. Subgenus MYTILOIDES Brongniart, 1822 Type species: Inocemmus labiatus (Schlotheim). Inoceramus (Mytiloides) labiatus (Schlotheim), 1813 Plate 19, figure 3; plate 20, figures 1, 4, 5. 1813. Ostracites Iabiatus Schlotheim, Leonard, Taschenbuch fiir Mineralogie, v. 7, p. 93 (flde Woods, 1911, p. 281). (For synonymy to 1911, see Woods, 1911, p. 281). Shell mytiliform, nearly equivalve, moderately in- flated, extremely inequilateral, oblique, height much greater than length; beaks anterior, slightly incurved; hinge line short to medium in length and generally forms an angle of less than 90° with anterior margin; anterior margin broadly rounded, posterior margin nearly straight. Ornamentation consists of low, fairly regular, rounded, concentric ribs. I-nocemmus labiatus s. l. is found throughout the world in deposits of Turonian age. Specimens show much variation in the length of the hinge line, the angle formed between the anterior margin and the hinge line, the convexity of the valves, and the degree of posterior obliquity. Unfortunately, no worldwide study of this species has been made in suflicient detail to ascertain if geographic or stratigraphic subspecies exist. Seitz (1935) recognized five subspecies of I. labiatus, but the validity of his work is questioned because none of his published samples contains more than eight specimens, which is not a sufficient number to show adequately the range of variation. According to Woods (1911, p. 283), [nocemmus Iabiatus in England is found mainly in the zone of Ehynchonella curiem'i (early Turonian), but it also occurs in the zone of Terebmtulina lam (late Turo- nian). In Germany Heinz (1928a, pl. 3) and Andert 3Geological Survey Canada. UPPER CRETACEOUS PELECYI’ODS OF THE GENUS INOOERAMUS FROM NORTHERN ALASKA (1934, p. 41) record I. labiatus only from the lowermost Turonian beds. This species is also common in the uppermost part of the Greenhorn limestone and its equivalents in the western interior of the United States where, according to Cobban and Reeside (1952, p. 1018), it occurs with the early T uronian ammonites Thomasites and Vascoceras. Thus, I. labiatus is a Turonian species, and perhaps is confined to lower Turonian beds, but such a restricted range has not been conclusively proved. Number of specimens: 54. Figured specimens: USNM 129229, 129230, 129231. 129232. Localities: Unnamed member of Seabee formation; USGS Mesazoic locs. 19-135, 20413, 20420, 20424, 24641, 26545, 26549, 26560, 26563, 26565, 26566, 26568. Subgenus SPHENOCERAMUS Boehm, 1915 Type species: Iuoceramus cardissoides Goldfuss, 1836. Inoceramus (Sphenoceramus) patootensis de Loriol, 1883 Plate 21, figure 5; plate 22, figures 1—3; plate 23, figure 3. 1877. Inoccramus lobatus Goldfuss, Schiilter, graphica, v. 24, p. 275, pl. 39, figs. 1, 2. Palaeonto- 1883. Inoccramus patootensis de Loriol, Medd. on Gronland, v. 5, no. 4, p. 211. 1918. Inoceramus patootcnsis de Loriol, Ravn, Medd. om Gronland, v. 56, p. 337, pl. 5, fig. 1; pl. 6, figs. 1—2. 1929. Inoceramus lundbreckensis )IcLearn, Canada Nat. Mus. Bull. 58, p. 77, pl. 15, fig. 4; pl. 16, fig. 2. 1936. Iuoccramus paiootensis de Loriol forma typica Beyen- burg, Deutsche geol. Gessell. Zeitschr., v. 88, no. 2, p. 107. (See Beyenburg’s 1936 paper for more com- plete synonymy up to 1936.) 1936. Inoceramus patootcnsis de Loriol var. augusta Beyen- burg, idem, p. 110, pl. 25, fig. 4. 1953. Inoccramus (Sphcuoccranms) patootensis de Loriol, Donovan, Medd. om Griinland, v. 3, no. 4, p. 95. 1955. Inoceramus Iobutus (Ioldfuss, Cobban, Billings G901. Soc. Guidebook, 6th annual field cont, p. 207, pl. 4. Shell equivalve(?), very inequilateral, moderately inflated, oblique, divided into a V—shaped, inflated, anterior part and a compressed, sharply distinct, posterodorsal wing; height much greater than length; hinge line moderately long, forming an angle of 90° or more with anterior margin; beaks anterior, sharply pointed; anterior margin straight, long, truncated; a shallow furrow extends obliquely from behind beaks to posteroventral margin; posterior side of furrow bounded by an oblique, narrow ridge or line of nodes. Ornamentation on V—shaped portion consists of con- centric ribs of two sizes: small, closely spaced, rounded ribs, and larger, distantly spaced, very irregular ribs; concentric ribs have unsymmetrical curvature where they cross the posterior furrow; ornamentation on wing less prominent and more regular than on 161 V—shaped part; small, radial riblets may occur on inflated, central part of valve; nodes formed along anterior margin, on ridge bordering the furrow, and along dorsal margin of posterior wing. Inocemmus patooteusis has been identified by many writers as I. lobatus Goldfuss, but their interpretation of I . lobatus was based upon specimens illustrated by Sehll‘iter (1877, pl. 39, figs. 1, 2), not by Goldfuss (1836, pl. 110, fig. 3). Goldfuss based I. lobatus on one small, crushed, apparently juvenile specimen, and it is ques- tionable whether this species is recognizable. Schliiter’s specimens are well preserved and adequately illus- trated, and there is little question about the identity of his species. A comparison of a plaster cast of Goldfuss’ type with specimens very similar to Schliiter’s types indicates that the two species are probably distinct. The distinction between I. lobatus Schlfiter and I. lobaius Goldfuss was previously pointed out by Stolley (1916, p. 72—73), Heinz (1928a, p. 79), Riedel (1931, p. 653), Beyenburg (1936, p. 107), and others. Heinz first recognized that I . lobaius Schliiter and I . patooteusis de Loriol are identical, and he applied de Loriol’s name to Schliiter’s species. Beyenburg (1936, p. 107—111) split Iuocemmus pa- tooteusis into five varieties, as follows: I. patooteusis forma typica; media Beyenburg; angusta Beyenburg; Zingua Goldfuss; and cancellata Goldfuss. Of these varieties, augusta is unnecessary as it falls within the range of variation of I. patooteusis. On the other hand, I. Zingua seems to be distinct from I. patooiensis as its ribbing is regular throughout. The variety media seems to be more closely associated with I. Ziugua than with I. paiootensis, and I. can- cellai‘us may fall within the range of variation of I. cardissoides Goldfuss. A study of large collections of I. patootcusis and I. liuguu may indeed show a transition between the two species. So far, this transition has not been demon- strated so it seems best to keep the two species separate. If a transition is shown to exist, the name I. partooteusis must be rejected as a synonym of I. Zingua; Beyen- burg’s designation of I. Iiugua as a variety of I. patootensis was done without regard for priority of names. If I. cancellartus is also found to fall within the range of variation of I. pavtooteusis, the name I. cancellatus should have priority over I. lingua as it has line precedence (Goldfuss, 1836, p. 113). Inoceramus patooteusis is common in northern Europe, Greenland, and the western interior of North America. According to Woods (1912, p. 302), in England this species probably occurs in the zone of Actinocamaw quadratus (early Campanian). Riedel (1931, p. 653) reports that in Germany this species 162 has a range from late Santonian to early Campanian. In North America, Cobban (1955, p. 207) has shown that I. patootensz’s (equals 1. Zobatus) is an excellent guide fossil to the uppermost part of the Colorado shale, the Telegraph Creek formation, and the Eagle sandstone. Its range is through the ammonite zones of Desmoscaphites erdmanm', Desmoscaphites basslem', and Scaphites hippocrepis (middle Santonian through early Campanian). Thus, on the basis of the presence of I . patootensz's, the age of the Barrow Trail member of the Schrader Bluff formation is between middle Santonian to early Campanian. Number of specimens: 20. Figured spccimcns: USNM 129233, 129234, 129235, 129236; National Museum Canada 9037. Localities: Barrow Trail member of Schrader Bluff forma- tion; IYSGS Mesozoic locs. 19434. 20461, 20462, 20463, 20481, 26498, 26508. 26509, 26511, 26515, 26516, 26518, 26519, 26521. 26525. Inoceramus (Sphenoceramus) steenstrupi de Loriol, 1883 Plate 19. figure 6: plate 23. figures 1. 2. 1883. Inoccramus stccnstrupi (le Loriol, Medd. om Gronland, v. 5, no. 4, p. 211. 1912. Inoccramus tuberculatus \Voods. Paleontographical Soc., v. 65, p. 302, pl. 54. fig. 8; text fig. 59. 1918. Inoccramus sfccnsfrupi (le Loriol, Ravn. Medd. om Griinland, v. 56, p. 336, pl. 5, fig. 2. 1931. Inoccramus stccnstrupi de Loriol, Riedel. I’reussische geol. Landesanstalt Jahrb., v. 51, p. 660. (See Riedel's paper for complete synonymy up to 1931.) 1953. Inoccramlls (Sp/wizoccramus) stccnstrupi (le Loriol, Donovan. Medd. om Griinland, v. 3, no. 4, p. 95. The specimens of Inocemmus steenstrupi from northern Alaska are fragmentary and the identifica~ tion of this species is based on the characteristic tuberculate ornamentation. Ravn (1918, p. 336—337) described topotype material from Patoot, Greenland, as follows: Shell very large. slightly convex, very inequilateral. Height greater than length. Ornamentation consists of numerous strong. but comparatively narrow, concentric ribs, separated by rather wide interspaces. steeper than the dorsal slope. The ventral slope of the ribs In the middle part of the shell the ribs are crossed by radial furrows. so that the ribs appear to consist of rows of tubercles; in the spaces between the ribs these furrows are indistinct or quite absent. The northern Alaska specimens clearly show the strong concentric ribs and the tubercles on the central part of the valve. Although none of the specimens are complete and nothing is known about the hinge line or the general shape and outline of the valves, the name lnocemmus sfecm-tmpé can be applied to these fragments with reasonable assurance on the basis of the tubercles alone. No other species is known SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY to have this type of ornamentation so prominently developed. The degree of development of the tubercles on I. steenstrupi is variable; some specimens have very large, protruding tubercles (pl. 23, fig. 1), but others have small and inconspicuous tubercles (pl. 19, fig. 6; pl. 23, fig. 2). Possibly a transition exists between I . steenstrupi with tubercles and I . patootensz’s with- out tubercles, but large collections of each species must be studied before this question can be answered. IVoods (1912, p. 302) states that Inoceramus tuber— culatus \Voods (equals I . steenstrupi) occurs in Eng- land in the zone Actinocamax quadratus (early Cam— panian) along with l. lobatus (equals I . patootensis). In Germany Riedel (1931, p. 626) indicates that I. steenstmpi occurs stratigraphically below I . patooten- sis in beds of Santonian age. In Greenland and northern Alaska, I. patootensz's and I. stéenstrupz' occur together (see Ravn, 1918, p. 336—337) and are, at least in part, of the same age. Thus, the range of I. steemfrupi is probably about the same as the range of I. patootemz’s, that is, from middle Santonian to early Campanian. Number of specimens: 8. Figured spccimens: {ISNM 129237, 129238, 129239. Localitics: Barrow Trail member of Schrader Bluff forma- tion; USGS Mesozoic locs. 20481, 20493, 26498, 26504, 26521, 26526. LITERATURE CITED Andert. Hermann, 1934, Die Kreideablagerungen zwischen Elbe und Jeschken. pt. 3 Die Fauna der obersten Kreide in Sachsen. Boehmen und Schlesien: Preussische geol. Landesanstalt Abh., i'eue Folge, no. 159. p. 1—477, 19 pls. Arkell, \V. J., Kummel. Bernhard. and Wright. C. \V. Mesozoic Ammonoidea in Joint Committee on Invertebrate Paleon- tology, Treatise on Invertebrate Paleontology, part L— )Iollusca 4: Geol. Sec. America and Univ. Kansas Press. Beyenburg, Edmund, 1936, Neue Fossilfunde aus dem I'ntersenon der Westfalischen Kreide: Deutsche geol. Gesell. Zeitschr., v. 88. no. 2. p. 104-115, 2 pls. Cobban. W. A., 1955, Some guide fossils from the Colorado shale and Telegraph Creek formation, northwestern Montana: Billings Geol. Soc, Guidebook, 6th annual field cont, p. 198—207, 4 pls. ()obhan, W. A.. and Reeside, J. B., Jr., 1952, Correlation of the Cretaceous formations in the western interior of the l'nited States: Geol. Soc. America Bull.. v. 63. p. 1011—1044. Collier, A. J., 1906. Geology and coal resources of the Cape Lisburne region. Alaska: INS. Geol. Survey Bull. 278 p. Detterman. R. I... 1956. New and redefined nomenclature of Nanuslluk group: Am. Assoc. Petroleum Geologists 3111]., v. 40, no. 2. p. 233—244. Donovan, D. T., 1953. The Jurassic and Cretaceous strati- graphy and paleontology of Trail (3, East Greenland: )Iedd. om Gronland. v. 111. no. 4, p. 1—150, 25 pls. 1954, Upper Cretaceous fossils from Traill and Geo- graphical SOciety (")er, East Greenland: )Iedd. om Grou- land, v. 72, no. 6, p. 1—33, 3 pls. LITERATURE CITED Goldfuss, G. A., 1836, Petrefacta Germaniae, v. 2. Gryc, George, 1951, "Paleontology,” in T. G. Payne and others, Geology of Arctic Slope If. S. Geol. Survey Oil and Gas Inv. Map OM 126. Gryc, George, Patton, W. W., and Payne, T. G., 1951, Present Cretaceous stratigraphic nomenclature of northern Alaska: Washington Acad. Sci. Jour., v. 41, no. 5. Gryc, George, and others, 1956, Mesozoic sequence in Colville River region, northern Alaska: Am Assoc. Petroleum Geologists Bull., v. 40, n0. 2, p. 209—254. Heinz, Rudolf, 1928a, Das Inoceramen-Profil der oberen Kreide Liineburgs:Niedersiichsische geol.Ver. [Hannover] Jahrb., no. 21, p. 65-81, 2 pls. 1928b, L'eber die bisher wenig beachtete Skulptur der Inoceramen—Shale: Hamburg min—geol. Staatsinst. Mitt., no. 10, p. 1—39. , Imlay, R. W., 1960, Lower Cretaceous megafossils from northern Alaska: US Geol. Survey Prof. Paper 335, 74 p. Imlay, R. W., and Reeside, J. B., Jr. 1954, Correlation of the Cretaceous formations of Greenland and Alaska: Geol. Soc. America Bull, v. 65, p. 233—246. Lefl‘ingwell, E. de K., 1919, The Canning River Region, north- ern Alaska: US. Geol. Survey Prof. Paper 109, 251 p. De Loriol, Percival, 1883, Om Fossile Saltvandsdyr fra Nordgronland: Medd. om Gronland, v. 5, no. 4, p. 203—213. McLearn, F. H., 1943, Trends in some Canadian Cretaceous species of Inoceramus: The Canadian Field Naturalist, v. 57, p. 36—46, 1 fig. McLearn, F. H., and Kindle, E. D., 1950, Geology of north- eastern British Columbia: Canada Geol. Survey Mem. 259, 236 p., 16 figs, maps. Morrow, A. L., 1935, Cephalopods from the Upper Cretaceous of Kansas: Jour. Paleontology, v. 9, no. 6, p. 463—473, pls. 49—53, text figs. 1—8. Payne, T. G. and others, 1951, Geology of Arctic Slope of Alaska: U.S. Geol. Survey Oil and Gas Inv. Map, OBI—126. Ravn, J. P. J., 1918, De marine Kridtaflejringer i Vestgronland 0g deres Fauna: Medd. om Griinland, v. 56, p. 313—336, 5 pls. 527586 0 - 60 - 4 163 Reeside, J. B., Jr., 1957, Paleoecology of the Cretaceous seas of the western interior of the United States: Geol. Soc. America Mem. 67, p. 505—542, 21 figs. Riedel, Leonhard, 1931, Zur Stratigraphie und Faciesbildung im Oberemscher am Siidrande des Beckens von munster: Preussische geol. Landesanstalt Jahrb., v. 31, p. 605—713, 8 pls., 6 text figs. Robinson, F. M., Rucker, F. P., and Bergquist, H. R., 1956, Two subsurface formations of Early Cretaceous Age: Am. Assoc. Petroleum Geologists Bull., v. 40, no. 2, p. 223—233. Sable, E. G., 1956, New and redefined Cretaceous formations in western part of northern Alaska: Am. Assoc. Petroleum Geologists Bull., v. 40, no. 11, p. 2635—2643. Schliiter, Clemens, 1877, Zur Gattung Inoceramus: Palaeonto- graphica, v. 24, p. 248—290. 4 pls. Schrader, F. C., 1902, Geological section of the Rocky Moun- tains in northern Alaska: Geol. Soc. America Bull., v. 13, p. 233—252. 1904, A reconnaissance in northern Alaska: U.S. Geol. Survey Prof. Paper 20, 139 p. Seitz, Otto, 1935, Die Variabilitiit des Inoceramus labiatus v. Schloth.: Preussische geol. Landesanstalt Jahrb., v. 55, no. 1 (fiir 1934), p. 429—474, 5 pls., 9 figs., 9 diagrams. Smith, P. S., and Mertie, J. B., Jr., 1930, Geology and mineral resources of northwestern Alaska: US. Geol. Survey Bull. 815. 351 p. Stolley, Ernst, 1916, New Beitriige Zur Kenntnis der nord- deutschen oberen Kreide, I—IV: Niedersachsische geol. Ver. [Hannover] Jahrb., p. 69—108, 5 pls. Warren, P. S., 1930, New species of fossils from Smoky River and Dunvegan formations, Albert: Alberta Research Council Geol. Survey Rept. 21, p. 57—68, 5 pls. Woods, Henry, 1911, A monograph of the Cretaceous Lamelli- branchia of England, v. 2, pt. 7, Inoceramus: Palaeonto- graphical Soc., v. 64, p. 261—284, pls. 45—50. 1912, A monograph of the Cretaceous Lamellibranchia of England, v. 2, pt. 8, Inoccmmus: Palaeontographical Soc., v. 65, p. 285—340, pls. 51—54. Whittington, C. L., 1956, Revised stratigraphic nomenclature of Colville group: Am. Assoc. Petroleum Geologists Bull., v. 40, no. 2, p. 244—253. a? kflm A inwa- gig Page Actinocamat quadratus... _________________ 161, 162 allam‘, Inoceramus. .. Anak Creek area. . ..._ Anaktuvuk River area... __________ 149, 152, 156, 157 Anwachsreifen (growth bands) ................ 158 Arctic Slope, geology __________________________ 150 athabaskenais, Inoceramus _______________________ 150, 159,160; pls. 15-17, 19 Ayiyak River area ____________________________ 156, 157 bassleri, Desmoscaphites _________________________ 162 Belle Fourche shale, stratigraphic relations.... 152 Barissiakocems, occurrence ____________________ 152, 153 cancellalus, Inaceramus. . 161 cardiaroidea, Irwceramur ____________ _ 161 Carlile shale, Blue Hill shale member.. _ 153 Fairport chalky member ......... _ 152 fossil content .............................. 158 Chandler formation, Niakogon tongue _________ 150 stratigraphic relations _____________________ 150 Chandler River area ________________________ 156, 157 Collignanicerar hyam' ......................... 152 woollgari ___________________________________ 152 coloradoenxe, Watinocerar.. _____ 153 Colorado shale, fossil content ________________ 162 Colville River area.. . _._.. 149, 150,152,153.156—158 coranguin um, Micraater ________________________ 158 corvemis, Scaphites .................... 153 Corwin formation, of Sable .................... 150 cuvierii, Inoceramus ___________________ .. ______ 153, 156 Inoceramus (Inoceramus) _______ 152,158; pls. 18,19 Rhymlwmlla _______________________________ 160 Desmoscaphites basalen‘ __________________________ 162 erdmanm’ ___________________________ ..__._ 162 dunveganemis, Inoceramus __________ .__ 150,160 Inoceramus (Inoceramus)... 152.156,!59; pls. 15—21 Dunvegan formation, fossil content... 160 stratigraphic relations __________ . . 152 Dunveganocems, occurrence _____________ 160 Eagle sandstone, fossil content ______________ ____ 162 stratigraphic relations. . . . 153 erdmanni, Deamnacaphites.... 162 Fossil Creek area _______________________________ 157 Fossil localities _______________ 156-158, 159, 160,161, 162 Geology of northern Alaska, history ____________ 149 goodrichemis, Incceramus nahwisi... 159, 160; pls. 19, 21 Grandstand formation, stratigraphic relations. .. 150 Graneros shale, fossil content ___________________ 153 Grecnhorn limestone, Pfeifer shale member _____ 152 Gubik formation, stratigraphic relations.. ._ . .._ 152 hippocrepia, Scaphitea _________________________ 162 hyatti, Collig'noniceraa _____________________ ..._ 152 Indo-Paciflc fauna] province ____________________ 152 Inoceraminae, subfamily, fossil collections ______ 149 Inoceramus allam' ........ 158 associated ammonites. 152 athabaskemia ____________ 150, 159,160; pls. 15—17, 19 cancellatus ........... 161 cardisroider ______________________________ 161 cuvierii ................................... 153, 156 INDEX [Italic numbers indicate descriptions] Page Inoceramur—Continued dunveganemia ______________ 150, 160 from Cretaceous rocks 149, 150, 152, 153, 156—158 holotypes ................................. 159, 160 (Im‘ceramua) cuvierii ___________ 152,168; pls. 18,19 dunveqammis __________ 152, 156,169; pls. 15—21 labiatua _______________________ ... 153,158,161 lamarcki ____________ 158 lirwua .............. 161 lobatua..._ _____ 161, 162 lundbreckenaic. ..- 161; pl. 22 mccmnelli ........ 159,160; pl. 16 (Mytiloidea) labiatus ________ 152,156,160; pls. 19,20 nahwisi ................ 159, 160; pls. 15, 18, 19, 21 qoodrichmsia _______________ 159, 160; pls. 19, 22 moberh‘ensis ____________________ 159, 160; pl. 21 patootensis .................................. 162 pontom' ____________________________________ 153 (Sphenoceramua) patootensis._.. 152, 153, 156,161; pls. 21—23 stemstrupi _____________ 153, 156,162. pls. 19, 23 steemlrupz'. - 152, 153. 156 tuberculatus __________________ .._ 153,162 (Inoceramus) cuvierii, Immerumus .......... 152, I58; pls. 18,19 dunveqanensie, Inoceramus __________________ 152, 156, 159; pls. 15—21 Killik River area _____________________________ 156, 157 Kotaneelee formation, fossil content.. 153 Kukpowruk formation, of Sable ...... Kuskokwim region ...... 160 Kutchik River area ...... 157 labiatus, Inoceramua ______________________ 153, 158, 161 Inoceramus (Mytiloide8)_._- 152, 156, 160; pls. 19, 20 Ostracz‘tes ____________________ 160 lamarcki, Inoceramus 158 lata, Terebralulina _____ lingua, Inoceramua. . . lobatus, Inoceramus _________________________ 161, 162 lundbreckensis, Inoceramus _________________ 161; pl. 22 Maybe Creek area ............................ 156, 157 mccmmelli, Inoceramus ................. 159,160; pl. 16 Megafauna, Lower Cretaceous.._.______..; ..... 150 M icraster coranguinum ......................... 158 Microfauna, Lower Cretaceous. ....... 150 moberliensia, Inoceramus nahwisi ................ 159, 160; pl. 21 Mowry shale, fossil content ..................... 160 (Mytiloidesl labiatus, Inoceramus ................ 152, 156,160; pls. 19, 20 Nanushuk group, defined ........... 150 Nanushuk River area. . . _. . 157 Naval Petroleum Reserve No. 4.- . 149 nahwisi goodrichensz’s, Inoceramus .............. 159, 160; pls. 19,21 Inoceramus ............... 159,160; pls. 15,18, 19,21 moberliemia, Inoceramus ........... 159, 160; pl. 21 Posidonomya ............................... 159 Neogartropliier, occurrance .......... 160 Ninuluk Creek area ..................... 156 Ninuluk formation, fossil content. . 152,156—157,160 stratigraphic relations ____________________ 150, 152 O Page N in brara formation, stratigraphic relations ..... 153 Okpikruak formation, stratigraphic relations... 150 Oatracites labiutua ............................ . 160 Oumalik formation, stratigraphic relations. - 150 Outpost Mountain area ........................ 158 patootensis, Inoceramus _________________________ 162 Inoceramus (Sphenoceramus) ................ 152, 153, 156, 161; pls. 21-23 Pierre shale, stratigraphic relations ............. 153 pontom', Inoceramus ............................ 153 Poaidonomya nahwisi ........................... 159 Prince Creek formation, Kogosukruk tongue... 15% stratigraphic relations ........ . 152 Tuluvak tongue ........................... 152 quadrants, Actinocamaz ...................... 161, 162 Rhynchonella cuvierii ............................ 160 Sagavanirktok formation, stratigraphic rela- tions .............................. 152 Scaphites corvemis. 153 hippocrepis. . 162 occurrance .......................... 149, 152, 162 ventricosus __________________________________ 153 Schrader Bluff formation, Barrow Trail mem- ber __________________ 152, 153, 157—158, 162 fossil content ........................ 157, 158, 162 Rogers Creek member ................... 152, 153 Sentinel Hill member... . 152, 153 stratigraphic relations ..... . 152,153 Seabee formation, Ayiyak member .............. 150, 152, 153, 157, 158, 159 fossil content .................... 152, 157, 158, 161 stratigraphic relations ........... 150, 152, 153, 158 unnamed member ............ 150,153, 157,159, 161 September Creek area .......................... 157 (Sphenocemmus) patootemis, Inoceramus ........ 152, 153, 156,161; pls. 21—23 153, 156,162; pls. 19,23 _.- 152, 153, 156 steenstmpi, Inoceramus.. steenstrupi, Inoceramaa ........... Inoceramus (Sphmocemmus).. 153, 156,162; pls. 19,23 Stratigraphic terminology ...................... 150 Telegraph Creek formation, fossilcontent ....... 162 stratigraphic relations ................. Terebratutina late _________ Thomasiter, occurrance ........... Topagoruk formation, stratigraphic relations... 150 tuberculatus, Inoceramus ...................... 153, 162 Tuku formation, stratigraphic relations _________ 150 Tuluga River area .............................. 157 Umiat Mountain area ......................... 157 Utukok-Corwin area .......................... 150 Vascoceras, occurrance ............ 161 ventricosus, Scaphitea ............. 153 Watinoceras coloradoense ........................ 153 occurrance ............................. 152, 153 Weasel Creek area... 156 Wolverine Creek area. . . _ 156 woollgari, Collingnoniceras ..................... 152 165 PLATES 15—23 PLATE 15 [All figures natural size] FIGURES 1—13. Inoceramus (Inocemmus) dunveganensis McLearn (p. 159) 1. . Left valve, plesiotype USNM 129218. From USGS Mesozoic 100. 24268. . Left valve, I. alhabaskensis McLearn, plastoplesiotype, CGS 9811; McLearn, 1945, Paper 45—27, plate 2, Right valve, plesiotype USNM 129217. From USGS Mesozoic 100. 24268. figure 10. From Dunvegan formation, Monkman Pass, British Columbia. . Left valve, plesiotype USNM 129219. From USGS Mesozoic 10c. 20475. . Left, right, and posterior views, plesiotype USNM 129220. From USGS Mesozoic 100. 24630. . Right, anterior, and left views, plesiotype USNM 129221. From USGS Mesozoic 10c. 24630. . Right valve (‘3), I. nahwz’si McLearn, 1944, Paper 44—17, plate 9, figure 1, CGS 9705. From Shaftebury formation, east of Cache Creek, Peace River, Alberta. . Left valve, I. dunveganensis McLearn, plastoplesiotype, CGS unfigured specimen. From Dunvegan forma- tion, Peace River, opposite mouth of Spirit River, Alberta. . Left valve, plesiotype USNM 129222. From USGS Mesozoic loc. 20465. GEOLOGICAL SURVEY PROFESSIONAL PAPER 334 PLATE 15 12 IN OCERAM US ( IN OCERAM US) DUN VEGANENSIS MCLEARN PLATE 16 [All figures natural size except as indicated on plate] FIGURES 1—5. Inoceramus (Inoceramus) dunveganensis McLearn (p. 159) 1. Right valve, 1. mcconnelli Warren, plastocotypo, Univ. Alberta CT. 417. From Dunvegan formation north bank Peace River, sec. 3, T. 80, R. 3, Alberta. 2. Right valve, I. athabaskensis McLearn, plastoholotype, CGS 8937. From La Biche shale, Athabaska River, about 2% miles below Stony Rapids, Alberta. 3. Right valve, plesiotype USNM 129210. From Colville River region, locality unknown. Left valve, I. mcconnelli Warren, plastocotype, Univ. Alberta CT. 418, localtiy as in figure 1. 5. Right valve, plcsiotype USNM 129213. From USGS Mesozoic 100. 20475. t“ GEOLOGICAL SURVEY PROFESSIONAL PAPER 334 PLATE 16 INOCERAMUS (INOCERAMUS) DUNVEGANENSIS MCLEARN FIGURES 1A5. PLATE 1 7 [All figures natural size except as indicated on plate] Inoceramus (Inoceramus) dunveganensis McLearn (p. 159) 1. 9"?“59 Right valve, 1. athabaslcensz's McLearn, plastoparatype, CGS 8938; McLearn, 1945, Paper 45—27, plate 6, figure 1. From La Biche shale, west bank of Athabaska River, just above Stony Rapids, Alberta. Right valve, plesiotype USNM 129223. From USGS Mesozoic 100. 25140. Right valve, plesiotype USNM 129224, From USGS Mesozoic Ice. 2427]. Left valve, plesiotype USNM 129225. From ITSGS Mesozoic 100. 20467. Right valve, [. d’zmveganensis McLearn, plastoholotype, CGS 6106; McLearn, 1945. Paper 45—27, plate 4, figure 1. From Dunvegan formation, north bank of Peace River, about 6 miles west of mouth of Riviére du Brulé, British Columbia. GEOLOGICAL SURVEY PROFESSIONAL PAPER 334 PLATE 17 5 INOCERAM US (INOCE'RAM US) DUN VEGANENSIS MCLEARN PLATE 18 [All figures natural size] FIGURES 1, 2, 4. Inocemmus (Inoceramus) dunveganensis McLearn (p. 159) 1. Right valve, I. dunveganensis McLearn, unnamed variety, piastohypotype, CGS 9816; McLearn, 1945, Paper 45—27, plate 4, figure 2. 2. Right valve, plesiotype USN M 129214. From USGS Mesozoic loc. 24271. 4. Right valve (‘3), Inoceramus nahiwsi McLearn, plastoholotype, CGS 6344; McLearn, 1944, Paper 4447, plate 10, figure 1. From Shaftsbury formation, Peace River, British Columbia. 3. Inoceramus aff. I. (Inoceramus) cuvierii Sowerby (p. 158) Right valve of specimen, USN M 129226. From USGS Mesozoic 100. 26533. GEOLOGICAL SURVEY PROFESSIONAL PAPER 334 PLATE 18 4,9 - «£6 INOCERAMUS (INOCERAMUS) DUNVEGANENSIS MCLEARN AND INOCERAMUS AFF. I. (INOQERAMUS) CUVIERII SOWERBY FIGURES 1, 5. 2, 4. PLATE 19 [All specimens natural size] Inoceramus aff. I. (Inoceramus) cuvierii Sowerby (p. 158) 1. Right valve of specimen, USN M 129227. From USGS Mesozoic loc. 20413. 5. Left valve of specimen, USN M 129228. From USGS Mesozoic loc. 24632. Inoceramus (Inoceramus) dunveganensis McLearn (p. 159) 2. Right valve, Inoceramus nahwisi McLearn, var. goodrichensis McLearn, plastoplesiotype CGS 9713; McLearn 1944, Paper. 44~17, plate 11, figure 4. From first sandstone of the Sikanni formation, Cypress and Halfway, British Columbia. 4. Left valve (2’), Inocemmus athabaskensis McLearn, plastohypotype, CGS 9817; McLearn, 1945, Paper 45—27, plate 5, figure 1. From Dunvegan formation, locality unknown. Inoceramus (Mytiloides) labiatus (Sehlotheim), (p. 160) Right valve, plesiotype USNM 129229. From USGS Mesozoic 100. 24641. Inoceramus (Sphenoceramus) steenstrupi de Loriol (p. 162) Left valve, plesiotypo USN M 129239. From USGS Mesozoic 100. 20481. GEOLOGICAL SURVEY PROFESSIONAL PAPER 334 PLATE 19 INOCERAM US AFF. I. (INOCERAM US) CU VIERII SOWERBY, INOCERAMUS (INOCE'RAM US) DUNVEGANE’NSIS MCLEARN, INOCERAMUS (MYTILOIDES) LABIATUS (SCHLOTHEIM), AND INOCERAMUS (SPHENOCERAMUS) STEENSTRUPI DE LORIOL PLATE 20 [All figures natural size] FIGURES 1, 4, 5. Inocemmus (Alytiloides) labiatus (Schlotheim) (p. 160) 1. Right valve, plesiotype USN M 129230. From USGS Mesozoic loc. 26545. 4. Right valve, plesiotype USN M 129231. From USGS Mesozoic loc. 20420. 5. Right valve, plesiotype USN M 129232. From USGS Mesozoic loc. 24641. 2, 3, 6. Inoceramus (Inoceramus) dunveganensis McLean) (p. 158) 2. Right valve, plesiotype USN M 129215. From USGS Mesozoic 100. 24283. 3. Right valve, Inoceramus dunveganensis McLearn, plastoplesiotype, CGS 9813; McLean), 1945, Paper 45427, plate 2, figure 2. From Dunvegan formation, British Columbia. 6. Left valve, plesiotype USNM 129216. From USGS Mesozoic 100. 24630. PROFESSIONAL PAPER 334 PLATE 20 GEOLOGICAL SURVEY INOCERAMUS (MYTILOIDES) LABIATUS (SCHLOTHEIM) AND INOCERAMUS (INOCERAM US) DUN VEGANENSIS MCLEARN PLATE 21 [All figures natural size] FIGURES 1—4, 6. Inoceramus (Inoceramus) dunveganensis McLearn (p. 158) 1. Left valve, plesiotype USNM 129211. From USGS Mesozoic 100. 20468. 2. Right valve, plesiotype USNM 129212. From USGS Mesozoic 100. 20476. 3. Left valve, Inoceramus nahwisi moberliensis McLearn, plastoholotype CGS 8945; McLearn, 1944, Paper 44—17, plate 10, figure 7. From the Goodrich formation, Cool Creek, south of Peace River Canyon, British Columbia. 4. Left valve, Inocemmus nahwisi moberliensis McLearn; unfigured plastoparatype CGS 8945; location as above. 6. Right valve, Inoceramus nahwisi McLearn goodrichensis McLearn, plastoplesiotype CGS 9710; McLearn, 1944, Paper 44—17, plate 2, figure 5. From Sikanni formation, talus in creek, Sikanni Chief River, 3 miles east of highway bridge. 5. Inoceramus (Sphenoceramus) patootensis de Loriol (p. 161) Left valve, plesiotype USNM 129235. From USGS Mesozoic 100. 26498. GEOLOGICAL SURVEY PROFESSIONAL PAPER 334 PLATE 21 INOCERAMUS (INOCERAMUS) DUNVEGANENSIS MCLEARN AND INOCERAMUS (SPHENOCERAMUS) PATOOTENSIS DE LORIOL PLATE 22 [All figures natural size except as noted on plate] FIGURES 1—3. Inoceramus (Sphenoceramus) patootensis de Loriol (p. 161) 1. Rubber cast of right valve, plesiotype USNM 129233. From USGS Mesozoic 10c. 26509. 2. Right valve, Inoceramus lundbreckensis McLean], plastoholotype, Natl. Mus. Canada 9037. From Alberta shale, 50 feet from top, Crowsnest River, Alberta. 3. Right valve, plesiotype USNM 129234. From USGS Mesozoic 100. 26509. GEOLOGICAL SURVEY PROFESSIONAL PAPER 334 PLATE 22 INOCERAMUS (SPHENOCERAM US) PATOOTENSIS DE LORIOL PLATE 23 [All figures natural size] FIGURES 1, 2. Inoceramus (Sphenoceramus) steenstrupi de Loriol (p. 162) l. Fragment, valve unknown, plesiotype USNM 129238. From USGS Mesozoic loc. 26504. ‘2. Right valve (?), plesiotype USNM 129237. From USGS Mesozoic 100. 20493. 3. Inoceramus (Sphenocemmus) patootensis de Loriol Right valve, plesiotype USNM 129236. From USGS Mesozoic loc. 20461. GEOLOGICAL SURVEY PROFESSIONAL PAPER 334 PLATE 23 INOCERAMUS (SPHENOCERAMUS) STEENSTRUPI DE LORIOL AND INOCERAMUS (SPHENOCERAMUS) PATOOTENSIS DE LORIOL U.S. GOVERNMENT PRINTING OFFICE: 1960 O - 527586 Ammonites of Early Cretaceous A ge' (Valanginian and Hauterivian) from The Pacific Coast States ”W" 3‘ 'j :f‘lnf/ / § “"C"""E"6L0GICAL SURVI‘E'X‘E’ROFESSIONAL PAPER 334-1? Ammonites of Early Cretaceous Age (Valanginian and Hauterivian) from The Pacific Coast States By RALPH W. IMLAY SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY GEOLOGICAL SURVEY PROFESSIONAL PAPER 334—F T/ze ammom'te succession provides correlations wit/z- z'rz toe Paczfic Coast States and wit/z ot/zer areas. T/zz's suggests t/zat Cretaceous strata 1'72 California and Oregon rest a'z'scon/ormaobl on jarassz'e strata UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1960 UNITED STATES DEPARTMENT OF THE INTERIOR FRED A. SEATON, Secretary GEOLOGICAL SURVEY Thomas B. Nolan, Director For sale by the Superintendent of Documents, US. Government Printing Office Washington 25, D.C. - Price $1.25 (paper cover) CONTENTS Page Page Abstract ___________________________________________ 167 Faunal zones and correlations—Continued Introduction _______________________________________ 167 Hollisites dichotomus _____________________________ 176 Biologic analysis ____________________________________ 168 Hamlin-Broad zone of Anderson __________________ 178 Stratigraphic summary ______________________________ 169 Hertleinites agm‘la _______________________________ 180 Faunal zones and correlations ________________________ 171 Comparisons with other faunas _______________________ 181 Kilianella crassiplicata ___________________________ 171 Ecologic considerations ______________________________ 182 Sarasinella hyatti _______________________________ 172 Geographic distribution ______________________________ 183 Homolsomites mutabilis __________________________ 174 Summary of results _________________________________ 190 Olcostephanus pecki _____________________________ 175 Systematic descriptions ______________________________ 194 Wellsia aregonensis ______________________________ 176 References _________________________________________ 221 IVeusia packardi ________________________________ 176 'Index _____________________________________________ 225 ILLUSTRAITONS [Plates 24—43 follow index] PLATE 24. Hoplocrioceras. 25. Hoplocrioceras, Anahamulina, Hypophylloceras, and Shasticrioceras. 26. Crioceratites and Acrioceras. 27. Homolsomites. 28. Homolsomites. 29. Olcostephanus. 30. Olcostephanus. 31. Olcostephanus, Spitidiscus, Durangites, and Polyptychites. 32. Neocraspedites and Wellsia. 33. Simbz’rskites and Wellsia. 34. Hertleim‘tes. 35. Hértleim'tes and Hollisiles. 36. Hollisites. 37. Hollisites. 38. Hollisites. 39. Thurmannicems. 40. Thurmanniceras and Hertleim’tes. 41. Hannaites and Neocomites. 42. Kilianella, Speetoniceras, Sarasinella, and Acanlhodiscus. 43. Hertleinites. Page FIGURE 34. Index map of Early Cretaceous localities in northwestern Washington ____________________________________ 191 35. Index map of Early Cretaceous localities in southwestern Oregon ______ . ___________________________________ 192 36. Index map of Early Cretaceous localities in northern California ___________________________________________ 193 TABLES TABLE 1. Ammonite genera in the Valanginian and Hauterivian beds of the Pacific Coast States, showing biological re- lationships, relative numbers available for study, and ages represented ________________________________ 168 2. WOrld ranges of certain Early Cretaceous ammonites present in Oregon and California ____________________ 172 3. Zonal distribution of Valanginian and Hauterivian ammonites in Washington, Oregon, and California _________ 173 4. Geographic distribution of the Early Cretaceous (Valanginian—Hauterivian) ammonites in the Pacific Coast States __________________________________________________________________________________________ 184 CHART CHART 1. Correlation of Early Cretaceous (Valanginian—Hauterivian) faunas in the Pacific Coast States ............. In pocket III SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY AMMONITES OF EARLY CRETACEOUS AGE (VALANGINIAN AND HAUTERIVIAN) FROM THE PACIFIC COAST STATES By RALPH W. IMLAY AB STRACT Study of the ammonites in the earliest Cretaceous of Cali- fornia, Oregon, and Washington has made possible the recog- nition of 4 ammonite zones in beds of Valanginian age and 5 ammonite zones in beds of Hauterivian age. These zones pro— vide general correlations with the Valanginian and Hauterivian stages in other parts of the world and detailed correlations along the Pacific coast. These correlations are strengthened by the associations of the Valanginian‘ ammonites with the Valanginian pelecypod Buchia crassicollis (Keyserling) and by the absence of earlier Cretaceous species of Buchia that occur from Washington northward to Alaska. 0n the basis of such associations, the oldest Cretaceous beds exposed in California and Oregon are considered to be not older than Valanginian and probably not older than middle Valanginian. Failure to find in California certain ammonite zones of late Valanginian to early Hauterivian age that are present in‘ south- western Oregon may be explained by nondeposition, slow de- position, unfavorable facies, inadequate collections, or some combination of these possibilities. The Valangin‘ian-Hauterivian ammonites found in the Pacific Coast States have a local aspect, owing to the presence of genera not yet found elsewhere, or only rarely elsewhere, and to the absence of genera that are common elsewhere. Pro— vincial genera include Wellsia, Hanmites, Hollisites, and Her- tleim‘tcs. Besides these gen‘era Shasticriooeras has been found elsewhere only in British Columbia and Japan, and Homol- somitcs, only in British Columbia and Greenland. The absence of such ammonites as Rogersites, Valangim‘tes, Distoloce'ras, and Leopoldm is in contrast to their abundance in the Medi- terranean province, and Mexico. With these exceptions the Valanginian ammonites from the Pacific coast show aflinities more strongly with ammonites in the Mediterranean province than with northern Eurasia, and the Hauterivian ammonites show affinities mostly with ammonites in northern Eurasia. INTRODUCI‘ION This study of the Early Cretaceous (Valanginian— Hauterivian) ammonites from the Pacific Coast States is based primarily on collections at. the California Acad— emy of sciences described in 1938 by Frank M. Ander— son and on collections made by members of the Geological Survey since 1890. It includes, also, a few specimens from several universities. Special thanks for assistance or loan of specimens are due V. S. Mal- lory, of the University of Washington, Wyatt Durham, of the University of California at Berkeley, W. P. Po~ penoe, of the University of California at Los Angeles, Michael Murphy, of the University of California at Riverside, Calif, and Leo Hertlein and Dallas Hanna, of the California Academy of Sciences in San Fran- cisco. Larry Lucas, of Agness, Oreg., contributed sev- eral excellently preserved ammonites. The description of the Valanginian-Hauterivian am- monities from the Pacific coast is a byproduct of paleon- tological assistance to Francis Wells and associates of the Geological Survey in compiling the geologic map of Oregon. Some of the problems involved included demarcation of the J urassic-Cretaceous boundary, eval- uation of the age significance of the fossils in the map- pable units above and below that boundary, and determination of which species would be useful to field geologists for mapping purposes. It was found that only species of the pelecypod Buckie (hitherto generally called Aucella) occurred in sufficient numbers and places to be useful in mapping or in drawing a boundary be- tween Jurassic and Cretaceous rocks. Determination of the ages of the mappable units, however, in terms of European stages involved detailed studies of the am- monites as well as of the species of Buchia. The evidence furnished by the ammonites was par- ticularly pertinent because many field parties in Alaska had found the same species of Buckie in the same rela— tive stratigraphic positions as on the west coast, but had not found any associated ammonites. Consequently, determination of the ages of the species of Buckie in Alaska had to be made on the assumption that the spe- cies had the same ranges as in Eurasia. That assump— tion could now be tested by studying the ammonites found in the Pacific Coast States. It seems fitting, 167 168 therefore, to publish descriptions of the ammonites and interpretations of their significance to supplement those already presented concerning Buehia (Imlay, 1959, p. 164—166). Abbreviations appearing in the text and ontable 5 include UW for the University of Washington, CAS for the California Academy of Sciences, UCLA for the University of California at Los Angeles, and USGS Mes. 100. for U.S. Geol. Survey Mesozoic locality. The number 9.3.54.6 represents a field locality of Peter Misch of the University of Washington. BIOLOGIC ANALYSIS The Va]anginian-Hauterivian ammonites from the Pacific coast that have been examined during prepara- tion of this paper number about 470 specimens. Their distribution by genera», subfamilies, and families and the known ages of the genera on the Pacific coast are shown in table 1. For purposes of this analysis the TABLE 1.—Ammon.ite genera in the Valanginian and H aateri'vian beds of the Pacific Coast States, showing biological relation- ships, relative numbers ai‘vailable for study, and ages repre- sented Number Family Subfamily Genus of speci- Stages mens Phylloceratidae ,,,,,, Phylloceratinae_ __ Phi/llapachyceras . . 45 V and H Hypophylloceras_ . . 5 H Lytoceratidae ........ Lytoceratinae ..... Lytoceras .......... 15 V and H Bochianitidae ........ Bochianitinae..... Bochianites ,,,,,,,, 3 V Ancyloceratidae ______ Criooeratinae ...... Crioceratites _______ 14 V and H Hoplocrioceras _____ 13 H Shasticrioceras _____ 4 H Ilemihoplitidae ______ Ancyloceratinae... Acrioceras ......... 4 H Pseudo- 2 H thurmannia?. Ptychoceratidae _________________________ Anahamulina . , _, , 1 H Craspeditidae ________ Tolliinae ,,,,,,,,,, Homolsomites ______ 100 V Olcostephanidae ..... Olcostephaninae ,. Olcostephanus ,,,,, 25 V and H Polyptychitinae... Palyptz/chites ,,,,,, 2 V N eocraspedites ..... 6 V Wellsia ,,,,,,,,,,,, 90 H Hertleinites. . . . . 9 H Simbirskitinae. ,. Simbirskites ....... 50 H Speetoniceras . 1 H Hollisites. . . 14 H Berriasellidae ________ Neocomitinae ..... Neocamites?_ . 2 V Thurmanniceras... 32 V Hannaites_ ,,,,,,,, 11 H Kilianella _________ 4 V Sarasihella ________ 15 V Acanthodiacus _____ 1 V Holcodiscidae ........ ., .................. Spitidisc’us ________ 2 H ranges of the genera within, or beyond, the Valangin- iau-Hauterivian stages are not shown, but are discussed herein in the section dealing with correlation. The table shows that the Berriasellidae is the domi- nant family in the Valanginian on the Pacific coast and is represented mostly by Thurmamzieems, Sarasinella, and Kiliamella. The family is represented in the Hauterivian by only one genus, Hammm'tes, which to date has been found solely in Oregon. This genus shows some resemblance to Leopoldia, which occurs characteristically in beds of early Hauterivian age SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY throughout the Mediterranean region. The fact that only one specimen of Acanthodisous has been found on the Pacific coast is likewise a contrast with the Mediter- ranean region. The family Olcostephanidae is dominant in the Hau- terivian beds of the Pacific coast, where it is repre- sented by the genera Olcostephanas, Wellsia, H ertlei/ni- tcs, Simbirskites, Speetonieeras, and H ollisites. The family is less well represented in the Valanginian beds by the genera Olcostephanus, Polyptychites, and Neo- oraspedites. All the occurrences of' Olcostephanus ex- cept one are from the upper part of the Valanginian. The absence of other genera of the Olcostephaninae is in contrast with the abundance of that subfamily in the Valanginian of the Mediterranean region and partic- ularly of the Mexican area. The family Ancyloceratidae occurs in fair abundance only in the Hauterivian beds. Two specimens belong- ing to Orioceratites have been found below the Hauteri- vian near the top of the occurrence of Buchia crassieol- lis (Keyserli'ng). Otherwise all occurrences of Orio- eeratites, H oplocrioceras, and Aeriocems are from Hauterivian beds. The genus Shastieriocems is repre- sented in the Pfauterivian by only a few specimens from the zone of H ertleinites agaila. The families Lytoceratidae and Phylloceratidae are fairly well represented throughout the Valanginian- Hauterivian beds. The Bochianitidae is represented by one genus, Boehianites, found only at one locality in Tehama County, Calif, in beds of late Valanginian age. The Hemihoplitidae is possibly represented by two specimens that are questionably assigned to Pseudoth-ur— ma/m'a. These could belong to the genus H oplocm'o- cams. The Ptychoceratidae is represented by one spec- imen of the genus Anahamulina in the zone of H ertlein— ites aguila. This occurrence is unusually low for the genus. To the Craspeditidae is assigned the genus H omolsomites because it has strong constrictions on its intermediate and outer whorls, and pinched primary ribs on its intermediate whorls similar to those of the genus Tollia. Except for these features it shows con— siderable resemblance to N eoeraspedites, which Wright (1957, p. L348) places in the Olcostephanidae. The Holcodiscidae is poorly represented by the genus Spiti- discus in the Hauterivi an of Oregon. Of the genera mentioned above, Wellsia, Hertlein— Vites, H olh'sites, and H annai'tes have not been recorded outside of California and Oregon. Shasticrioceras has been recorded from Washington, British Columbia, and Japan. H omolsomites has been recorded from Wash- ington, British Columbia, and Greenland. The other genera have been found in many parts of the world. AMMONITES OF EARLY CRETACEOUS AGE FROM THE PACIFIC COAST STATES STRATIGRAPHIC SUMMARY The Valanginian sequence in both California and Oregon has certain lithologic features that permit rather easy recognition. It consists mostly of units of olive-gray to dark-gray slightly sandy siltstone and silty claystone interbedded with thinner units of gray to greenish-gray sandstone that may be thin bedded or massive and that are locally pebbly. The siltstone units generally contain thin interbeds of sandstone and in places contain limestone lenses and concretions. The base of the Valanginian sequence in both States is marked at many places by a massive conglomeratic sandstone or conglomerate that rests on Late Jurassic (Portlandian) beds. The Valanginian sequence as a whole is characterized by the robust pelecypod Buckie cressz'collz's (Keyserling), occurring in such large numbers that it constitutes an important litho- logic feature and may be used for mapping purposes. The Valanginian in Oregon forms the middle part of the Myrtle formation at its type locality on Myrtle Creek as mapped by Diller (1898) and the upper part of the Knoxville formation in the Riddle quadrangle as mapped by Diller and Kay (1924). The generalized section along the South Umpqua River just south of Days Creek in Douglas County from top to bottom is as follows: Section of Veleugum‘eu beds eloug west side of South Umpqua River in NW1/1 sec. 15, T. 30 8., R. J, W. [Measured by Home Dole, Dallas Peck, Len, Ramp, and R. W. Imlay] Feet Siltstone, slightly sandy, olivegray; contains Otcosteph- anus peckt Imlay, n. sp., 85 ft. below top; Buckie cresstcollis (Keyserling) occurs rarely throughout____ 141 Sandstone, massive, fine-grained, silty, dark-greenish- gray; contains an abundance of Buchie cressicollts (Keyserling). Olcostepheuus peckt Imlay, n. sp., ob- tained 15 ft. above base of unit ______________________ 75 Siltstone dominant, medium-gray; some beds sandy; includes a few beds of medium- to fine-grained dark- greenish-gray sandstone from 8 to 14 in. thick; some limestone lenses and concretions occur in siltstone. Contains Buckie cressicollis (Keyserling) throughout; Olcostepheuus peckt Imlay, n. sp., obtained 41, 52, and 87 ft. below top of unit; Homolsomttes steutom’ (Mc- Lellan) obtained 87 ft. below top of unit ____________ 114 Sandstone, medium-fine— to fine-grained, silty, dark-green- ish-gray; no Buckie noted __________________________ 46 Total thickness of Valanginian beds ______________ 376 The Valanginian is probably absent in the area. imme- diate east and southeast of Roseburg, Oreg., although J. S. Diller and his assistants obtained collections of the Valanginian fossil Buckie euessicollz's (Keyserling) from five localities Within that area. This occurrence is questioned becaused subsequent search has not yielded any specimens of Buckie; because the rocks from which 169 this genus was reported resemble the Dothan forma- tion according to Francis Wells and Hollis Dole; and because the Whitsett limestone lentils of Diller (1898), which are younger than the Dothan-like rocks, have furnished an ammonite that resembles immature speci- mens of Dureugz'tes. (See pl. 31, figs. 11, 12.) The Valanginian sequences exposed on Cow Creek below Riddle and on Myrtle Creek in Douglas County, Oreg., were not measured, but appear to be similar in lithology and in thickness to that on the South Umpqua River near Days Creek. Westward in Oregon the Va- langinian sequences thicken considerably, but careful measurements of them have not been made. At the head of the road along Foggy Creek, in sec. 16, T. 32 S., R. 10 W., Coos County, the conglomeratic part of the Valanginian is about 1,000 feet thick and the overlying siltstone-claystone part is many hundreds of feet thick (oral communication from Francis Wells, March 1958). In the Port Orford quadrangle the Valanginian appears to be at least as thick. The Valanginian sequence in California crops out discontinuously in the Coast Ranges from Santa Bar- bara County on the south to the Trinity River, in cen- tral Trinity County, on the north (Anderson, 1938, p. 49—55) and ranges in thickness from a few hundred to 1,500 feet or more. It was included by Stanton (1895, p. 11, 17, 18 [1896]) in the upper part of the Knoxville formation, whose top as then defined coincided with the upper limit of the sandy beds containing Buckie Guessi— collis (Keyserling). It was included by Anderson (1902, p. 43—47; 1933, p. 311—326; 1938, p. 44—48) in his Paskenta group. Anderson intended, apparently, that his Paskenta group should include all the Early Cretaceous beds containing Buckie, and he consistently correlated it with the Valanginian stage of Europe. Unfortunately, in its type area near Paskenta, Te- hama County, the Paskenta group was extended up- ward by Anderson above the beds bearing Buckie cressz'collz's (Keyserling) to include several thousand feet of shale and siltstone from which he recorded Bu- ckie at several levels. These records are possibly mis- identifications of I uoceremus or Aucellz'ue, as the writer has discussed in another paper (Imlay, 1959, p. 164), and are from beds of Hauterivian or later ages. Unfor- tunately, also, all the beds near Ono, in Shasta County, that Anderson (1938, p. 46—49) referred to his Pas- kenta group are younger than Valanginian and have not furnished a single specimen of Buckie. As this last fact was admitted by Anderson (1938, p. 47) and as he states, also, that the boundary between his Pas- kenta and Horsetown groups (1938, p. 42, 43, 46, 62) is mainly paleontological, his Paskenta group does not appear to be either a mappable unit or a faunal unit. 170 The writer believes that the term Paskenta formation may be useful if redefined to include only the alternat- ing sandstones and shales characterized by Buchiu wussicollis (Keyserling), but that must await detailed mapping. Beds of Hauterivian age in California have been identified faunally at only three places. The southern- most occurrence is on the eastern part of the Wilcox Ranch, in western Tehama County, where ammonites of middle to late Hauterivian age, described herein, have been obtained in the lower 500 feet of shales over- lying the beds containing Buchiu crassicollis (Keyser- ling). These shales were included by Anderson (1938, p. 46) in the upper part of his Paskenta formation and by Stanton (1895, p. 18 [1896]) in the lower part of the Horsetown formation. They were described by An- derson as being clay shales that contain some thin beds of limestone and sandstone. A second occurrence of Hauterivian rocks in Cali- fornia is near Ono in western Shasta County. These have been recently described by Murphy (1956, p. 2103— 2113) and are included in his Rector formation and the lower part of the Ono formation. These include at least 800 feet of sandstone, conglomerate, and mudstone that have little in common lithologically with equiva— lent beds in western Tehama County. The upper part of the sequence includes the Hertleiuites wgutila zone (Murphy, 1956, p. 2113), which is herein considered to be of late Hauterivian age. The lower part of the sequence includes some of the fossils in Hamlin-Broad zone of Anderson (1938, p. 47), which was based on ammonites found from 4 to 6 miles southwest of Ono below the Roaring River tongue of the Ono formation. This zone is of middle to late Hauterivian age. A third occurrence of Hauterivian rocks in California is on and near the Clements Ranch on Redding Creek, in the central part of Trinity County (Anderson, 1938, p. 50). The fossils found there suggest a correlation with beds in Shasta County that were placed by Ander- son (1938, p. 47) in his Hamlin-Broad zone. The preservation and lithologic characteristics of the fossils indicate that the beds are probably lithologically simi- lar to the early and middle Hauterivian beds of Oregon. Thicknesses are at least 600 feet. (Anderson, 1938, p. 203). The Hauterivian sequence in Oregon differs from that in California by being much sandier and probably much thicker. The best exposed sections that have been found are on Cow Creek near Riddle, in Douglas County; on the South Umpqua River near Days Creek, in Douglas County; on the Foggy Creek road, in Coos County; on the south bank of the Rogue River 11/2 miles below Agness, in Curry County; and in the SHORT‘ER CONTRIBUTIONS TO GENERAL GEOLOGY Waldo-Cave Junction area, in Josephine County. At none of these places is the entire Hauterivian repre- sented. The section exposed along the South Umpqua River just south of Days Creek is one of the best ex- posed and from top to bottom is as follows: Partial section of Hauterivian beds along the west side of the South Umpqua River in N W14 sec. .15, SW14 sec. 1,7, and Ell/2 sec. .9, T. ‘30 8., R. 1, W., Douglas County, Oreg. [Measured by Hollis Dole, Dallas Peck, Len Ramp, and R. W. Imlayi] Feet Siltstone, sandy, massive, dark-greenish-gray; grading into silty sandstone, weathers spheroidally; contains many small fossiliferous limestone concretions. Well- sia packardi (Anderson) obtained. 120 and 180 ft below top of unit: Hana/(lites riddleusis (Anderson) obtained 140 ft below top; Wellsia oregoueusis ( Ander- son) obtained 190 ft below top. Fault truncates top of unit _____________________________________________ 210+ Sandstone, silty, very fine-grained, dark-greenish-gray; some limestone concretions present __________________ 95 Sandstone, massive, in beds 12 to 20 ft thick separated by some lenses of siltstone from several inches to sev- eral feet thick; contains many fossiliferous limestone lenses. Sandstone constitutes about 90 percent of unit. Wood fragments and pelecypods scattered throughout unit. Huuuaites riddleusis (Anderson) and Wellsia oregoneusis (Anderson) obtained at top of unit. H. truncate Imlay, n. sp., and Wellsiu oregoueusis (An- derson) obtained 70 ft below top ____________________ 128 Total exposed thickness of Hauterivian beds ______ 433 This section is entirely of early Hauterivian age. A similar section of the same age is exposed in the bed of Cow Creek about a quarter of a mile below the bridge at the town of Riddle, in Douglas County. At the bridge itself is exposed 15 feet of massive gray sandstone that has furnished the ammonites Simbirskites and Hol- lisites, of middle Hauterivian age. Beds of sandstone and sandy siltstone occurring in the creek above the bridge for at least a mile are assigned a middle Haute- rivian age on the basis of stratigraphic position, but have furnished only one ammonite, Lytocems aulueum Anderson. These beds are repeated by gentle folding and cannot be measured, but are probably some hun- dreds of feet thick. A poorly exposed, discontinuous sequence of early and middle Hauterivian age occurs on the side of the road up Foggy Creek in T. 32 S., R. 10 W., Coos County. The exposures consist of soft massive greenish-gray sandstone and siltstone that weather in a spheroidal manner. Along the road Simbimkites (USGS Mes. 100. 25211) was obtained four-tenths of a mile above the junction with the Eden Valley road; Huumuites rid— dlensis (Anderson) (USGS Mes. 10c. 25212) was ob- tained 1 miles from the junction; Wellsia oregonensz's (Anderson) (USGS Mes. 100. 25213) was obtained 1.3 AMMONITES 0F EARLY CRETACEOUS AGE FROM THE PACIFIC COAST STATES miles from the junction; and Buckie cressicollz's (Key— serling) (USGS Mes. loc. 25196) was obtained 1.5 mile from the junction. The beds at the last three mentioned localities have a southeast dip and are presumably over- turned. The beds containing Simb’irs/cz'tes have a north- west dip and are presumably not overturned. The thickness of the beds containing Wellsz'e and H enmites is at least 400 feet and may be much thicker. The thick— ness of the younger beds containing Simbirslc‘ites can- not be estimated because of poor exposures. Beds of middle Hauterivian age are well exposed on the south side of the Rogue River about 11/2 miles below Agness, Curry County. They consist mostly of greenish-gray sandstone and siltstone that weather to brownish spheroidal masses. Their thickness is ap— parently some hundreds of feet, but cannot be measured because of folding and faulting. Fossils of middle Hauterivian age have been found from 100 to 200 feet above exposures of serpentine and 100 feet or less above beds containing Buckie cressz'collis (Keyserling), of Valanginian age. Beds of early Hauterivian age have not been identified faunally, and there is less than 100 feet of beds that could be of that age. The jumbled character of the exposures suggest that the middle Hauterivian beds are in fault contact with the Valan- ginian beds. Beds of middle to late Hauterivian age crop out in the Takilma-Waldo-Cave Junction area, T. 40 S., R. 8 W., in the southernmost part of Josephine County, Oreg. The oldest beds rest on Late Jurassic rocks (Galice formation) and are lithologically similar to the early and middle Hauterivian beds elsewhere in south- western Oregon. They have furnished fragments of pelecypods and gastropods but no ammonites. Else- where in the same area fossils have been obtained (USGS Mes. locs. 3339, 2166) that are probably of late Hauterivian and Barremian age, as discussed herein under the heading H ertlez'm'tes egulz'e zone. The thick- ness of the Cretaceous beds in the area is unknown. FAUNAL ZONES AND CORRELATIONS KILIANELLA CRASSIPLICATA This is a provisional zone (table 3) representing the lower third to fourth of the sandy beds bearing Buckie cressicollis (Keyserling) in Tehama County, Calif. It is characterized by the species Kilienelle cressz'plicete (Stanton) and Tkurmennicems celifomi— cum (Stanton). This zone is considered provisional because it is based on only three collections. One of these (USGS Mes. locs. 1001 and 1095), containing both of the character- istic species, was made, according to Stanton (1895, p. 171 17, 77, 82 [1896]), on McCarthy Creek about half a mile east of the buildings of the Henderson Ranch and from 1,500 to 2,000 feet below the top of the Buckie- bearing beds. Its location, based on the generalized geologic map published by Anderson (1933, p. 314), is near the base of the Buckie beds in the NW14 sec. 29, T. 24 N., R. 6 W. From the same location on McCarthy Creek was obtained the specimen of Kilienelle messi- plz'cete (Stanton) illustrated by Anderson (1938, pl. 83, figs. 3, 4). Another collection (Mes. 100. 5339), containing Kili- enelle cressiplicete (Stanton) and Lytoceres seturnele Anderson, was made one-third of a mile west of the Wilcox Ranch buildings in the NW% sec. 4, T. 24 N., R. 6 W. Its stratigraphic position, based on the map published by Anderson (1933, p. 314), is considerably below the middle of the Buckie cressicollz's beds. It should be about 500 feet above the base of those beds if their thickness is 1,500 feet, as stated by Anderson (1933, p. 321). Of the three species of ammonites found in the Kili- enelle oressiplicete zone, Lyteceres seturnele Anderson ranges considerably higher (Anderson, 1938, p. 47 ) into beds containing the middle Hauterivian ammonite Simbz'rske'tes. Kilienelle cressiplicete (Stanton) and Tkurmevmiceres celiform'cum (Stanton) have not been found, however, above the lower third of the Buckie cressicollz's beds. If these species ranged higher they should have been found in some of the many collections made from higher parts of the Buckie cressicollz‘s beds in Oregon and California. Anderson (1933, p. 321) inferred that the type specimens of these species were obtained about 1,300 feet above the base of the Buckie cressz'collis beds, but he evidently misunderstood the statements published by Stanton (1895, p. 77, 82 [1896]). The specimen described herein as Kilienelle cf. K. besez'm'ei Spath, obtained from Strawberry Canyon in Berkeley Hills, Alameda. County, Calif, is reported by Anderson (1938, p. 53) to be from the lower beds of his Paskenta group. If so, it and the other fossils men- tioned by Anderson may belong in the zone of Kilienella wessiplz'cete. Other fossils that may belong in the Kilienelle ores- sz'plicete zone include 24 species obtained by Stanton (1895, p. 14 [1896]) from northern Tehama County about half a mile and a little north of west of Stephen- son’s Ranch houses near the Cold Fork of Cottonwood Creek (USGS Mes. 100. 1069). These were listed or described by Stanton under the following names: Pentacm'nes sp. Rhynchonelle sp. Terebretula oeliform'ce Stanton 172 Terebratula sp. Ostrea sp. cf. 0. skidgatensis Whiteaves Lima multilineata Stanton Spondylas fragilis Stanton Aucella orassicollis Keyserling Myoconoha americana Stanton Area tea‘trina Stanton Peotunoulus? ovatua Stanton Leda glabra Stanton Opts californica Stanton Cyprina occidentalis Whiteaves Astarte caltfo'rm'ca Stanton Soleourtus? dubius Stanton Corbula filosa Stanton Helcion granulatus Stanton Fissu‘rella bipanctata Stanton Pleurotvomarr‘a sp. Tu/rritella sp. Oerithiam sp. Belemnites impressus Gabb Concerning the above fossils, the association of Buchia erassicolhk (Keyserling) needs confirmation, as the collections from locality 1069 now on hand do not contain that species. According to Stanton’s notebook, dated October 6—8, 1893, the fossils listed were obtained from several hundred feet of beds. The stratigraphi— cally lowest collections consisted of several poorly pre— served specimens of Buchia, Pleuromgz/a ?, and Pecten? ; about 40 feet higher were obtained rhynchonellid brachiopods and pectens; and about 260 feet still higher were obtained the remainder of the fossils. An excel— lent collection of Buchia crassioollz's (Keyserling) was made in a ravine about 200 yards west of Stephenson’s ranch houses (USGS Mes. 100. 1071) in beds which Stanton considered to be a few hundred feet lower than those at Mesozoic locality 1069. Stanton noted that the beds under discussion were all part of a conformable sequence and belonged in the upper part of the Knox— ville formation as then defined. The beds were later examined by Anderson (1938, p. 43, 113, 119) who con- cluded that the fossils at Mesozoic locality 1069 were obtained near the base of his Paskenta group. The age of the beds characterized by Kilianella orassiplicata is considered middle Valanginian (chart 1), although both Kilianella and Thurmanm'ceras have a considerably longer range. (See table 2.) This age assignment is based on the close resemblance of Kilianella crassiyflioafa (Stanton) to K. roubaudi (d’Orbigny) (Sayn, 1907, p. 47, pl. 6, figs. 9, 10a, b), from the middle Valanginian of France; on the con— siderable resemblance of the inner whorls of Thurman— m'eeras californicum (Stanton) to T. pertransz'ens (Sayn) , from the middle Valanginian of France (Sayn, 1907, pl. 5, fig. 10) and Argentina (Leanza, 1945, p. 64, pl. 10, figs. 5—7) ; on the resemblance of the largest whorls of T. caliform'cum to the large whorls of T. SHOR’TER CONTRIBUTIONS TO GENERAL GEOLOGY TABLE 2.——World ranges of certain Early Cretaceous ammonites present in Oregon and California [An arrow indicates that the genus ranges higher than the Barremian stage] Genus Berriasian Valanginian Hauterivian Barremian Phyllop achyceras ________ Hypophylloceras _________ Bochianites _____________ Crioceratites ____________ H oplocrioceras __________ S hasticrioceras __________ A crioceras ______________ Pseudothurmannia _______ ? A nahamulinm - _ Homolsomites- _ _ _ _? |||.|" “l” w S peetoniceras ___________ Simbirskites ____________ N eocomites _____________ Thurmannz'ceras _________ ? K 1' lianella .............. ? S arasr‘nella _____________ A canthodiscus ___________ ?__ S pitidiscus _____________ novihispanz'cum Imlay (1937, pl. 78, fig. 8, pl. 79, fig. 6), from the middle Valangini‘an of Mexico; on the fact that Thurmannz'ceras attained its greatest development in the middle Valanginian and Kilianella in the middle and upper Valanginian; on the fact that the associated pelecypod Buchia crassioallis (Keyserling) attained the climax of its development during middle and late Valanginian times; on the absence of any species of ammonite or of Buchia indicative of the early Va- langinian; and on the position of the beds containing Kilianella crassiplieata some hundreds of feet below other beds of late Valanginian age. All these considerations strongly favor a middle Valanginian age for the Kilianella crassiplz’cata zone, but do not exclude the possibility that the zone is of early Valanginian age. The best evidence that the zone is not older than the middle Valanginian consists of the abundance of Buchia crassicollis (Keyserling) and the absence of such species as B. sublaemis (Keyserling) and B. eolgensie (Lahusen) that are recorded from beds of early Valanginian age in the Boreal region. SARASINELLA HYA'I‘TI This is another provisional zone (table 3) that prob- ably represents part of the beds between the Kilianella orassiplicata zone and the H omolsomz'tes mutabilis zone. It has not been identified in California. In Oregon it has been found near Riddle (USGS Mes. 100. 26405), near Bald Mountain (USGS Mes. 10c. 2107, 2136) in Curry County, and near the forks of Elk River (USGS Mes. locs. 4384, 4386, 4391) in Curry County. On Elk River Sarasz'nella hyatte' (Stanton) was found one-fifth AMMONITES or EARLY CRETACEOUS AGE FROM THE PACIFIC COAST STATES 173 TABLE 3.—Zonal distribution of Valanginian and Hauterivian ammonites in Washington, Oregon, and California Berri- Valanginian Hauterivian Barre- asian mian and of and Simbirskites 311‘. S. elatus No fossil evidence No {05311 ev1dence Thurmanniceras californicum, Kilianella craosiplicata, and Saraainella Imam Olcostephanus pecki Homolsomites stantoni Wellsia oregonensis Wellsia packardi dichotomus HamlinfiBroad zone Anderson Hertleinites aauila Shasticriaceras panientz Homalsomites mutabilis Hollisites Phyllopachyceras trinitense (Anderson) ___________ of. P. trinitense (Anderson) _________________ umpquanum (Anderson) ___________________ cf. P. umpquanum (Anderson) ______________ Hypophylloceras aff. H. onoense (Stanton) ________ Lytoceras aulaeum Anderson ____________________ saturnale Anderson ________________________ cf. L. traski Anderson _____________________ Bochianites paskentaensis Anderson ______________ Crioceratites latus (Gabb) ______________________ of. C. yollabollium (Anderson) ______________ cf. C. tehamaensis (Anderson) _______________ sp. indet _________________________________ Hoplocrioceras remondi (Gabb) __________________ cf. H. remondi (Gabb)__--__ ________________ duncanense (Anderson) ____________________ sp. indet _________________________________ Shasticrioceras afl‘. S. whitneyi Anderson _________ of. S. poniente Anderson ___________________ ‘— 5p _______________________________________ ?_ Acrioceras voyanum Anderson ___________________ of. A. voyanum Anderson _________________ vespertinum (Anderson) ____________________ hamlini (Anderson) _______________________ Pseudothurmannia? russelli (Anderson) ___________ ?jupiter (Anderson) _______________________ Anahamulina wilcoxensis Imlay, n. sp ____________ Homolsomites mutabilis (Stanton) _______________ stantoni (McLellan) _______________________ Olcostephanus pecki Imlay, n. sp ________________ cf. 0. pecki Imlay, n. sp ___________________ 4.— popenoei Imlay n. sp ______________________ ‘— cf. 0. quadriradiatus Imlay _________________ (—1? Polyptychites trichotomus (Stanton) ______________ s _______________________________________ P Neocraspedites giganteus Imlay, n. sp ____________ Wellsia oregonensis (Anderson) __________________ packardi (Anderson) _______________________ ? vigorosa I mlay, n. sp _______________________ ?__? Hertleinites aguila (Anderson) __________________ signalis (Anderson) ________________________ Simbirskites broadi Anderson ___________________ lecontei (Anderson) ________________________ sp. juv. afl'. S. elatus (Trautschold) __________ sp. juv. afl”. S. progrediens Lahusen __________ cf. H. lucasi Imlay ________________________ dichotomus Imlay, n. sp ____________________ inflatus Imlay, n. sp _______________________ Speetoniceras agnessense Imlay, n. sp ____________ Neocomites? cf. N. indicus Uhlig _________________ _? Thurmanniceras californicum (Stanton) __________ wilcoxi (Anderson) ________________________ ?_ jenkinsi (Anderson) _______________________ stippi (Anderson) _________________________ sp. juv. cf. T. etippi (Anderson) ____________ Hannaites riddlensis (Anderson) _________________ truncatus Imlay, n. sp _____________________ Kilianella crassiplicata (Stanton) ________________ cf. K. besairiei Spath ______________________ ?_‘ 174 SHORT‘ER CONTRIBUTIONS T0 GENERAL GEOLOGY TABLE 3.—Zonal distribution of Valanginian and Hauterivian ammonites in Washington, Oregon, and California—Continued Berri- as1an Barre- mien Valanginian Hauterivian No fossil evidence N o fossxl ev1dence ifomicum, Kilianella crussiplicata, and Samsinella Matti Homolsomites mutabilix pecki and Homolsamites stantom’ Wellsia oregonensis dichotomus and Simbirskites afl. S. elatus zone of Hertleim‘tes aauila Shasticrioceras ponimte Thurma'lmiceras cal Olcostephanus Wellsia packardi Hamlin—Broad Anderson Hollisites Sarasinella densicostata Imlay, n. sp _____________ of. S. densicostata Imlay, n. sp ______________ cf. 8'. subspinosa (Uhlig) ___________________ hyatti (Stanton) ___________________________ cf. S. hyatti (Stanton) _____________________ angulata (Stanton) ________________________ cf. 8. angulata (Stanton) ___________________ sp _______________________________________ Acanthodiscus sp. juv. afl'. A. subradiatus Uhlig- _- Spitidiscus oregonensis Imlay, n. sp ______________ of a mile up the South Fork at a position that is esti- mated to be 500 feet below the beds containing H omel- somites mutabili; (Stanton) at Mesozoic localities 2154 and 4390. This is the only place Where the relative stratigraphic positions of the two species has been determined. As both of the provisional zones of Kilianella massi- plicata and Samsimlla hyatti underlie the Homols‘o- mites mutabilis zone, there is no assurance that one zone is younger than the other. The matter cannot be settled until more ammonites are found and relative strati- graphic positions are determined. The assumption that the Samsinella hyatti zone is the younger is based on the resemblance of its characteristic species to S. densi- costata Imlay, n. sp., in the Homolsomites mutabilis zone and the fact that Samsinella hyatti (Stanton) was found closer stratigraphically to the H omolsomites mutabilis zone than was Kilianella crassiplicata (Stanton). HOMOLSOMIT ES MUTABILIS This zone (table 3) is characterized by the ammonites Homolsomitcs mutabilis (Stanton), Poly/ptychitc‘s trichotomus (Stanton), Neocmspedites giganteus .Im- lay, n. sp., Thurmannicercm jenkinsi (Anderson), T. stippi (Anderson), Samsinella angulata (Stanton), S. densicostata Imlay, n. sp., Bochiamites pasken‘taensis Anderson, and Acanthodiscuw aff. A. subradiams Uhlig. It has been identified only in Tehama County, Calif, and in Curry County, Oreg. In Tehama County it occurs in the upper part of the range of Buckie crassi— collis (Keyserling) and is represented by many collec- tions (USGS Mes. locs. 1009, 1010, 1087, 1088, 1091, 1093, 2266). These were obtained, according to Stan- ton, near the upper limit of the Buchia-bearing beds. Anderson (1933, p. 321, 322) notes that the collections were made from 1,200 to 1,300 feet above the base of the Buchia crassicollis beds, which according to him are about 1,500 feet thick. The H omolsomites muta- bilis zone in Curry County, Greg, has been identified definitely only near the Forks of the Elk River (USGS Mes. locs. 2154, 4390, 4393, 6142), where its stratigraphic position relative to the top or bottom of the Buckie crassicollis beds is unknown. The age of the H omolsomites mutabilis zone is mid- dle or late Valanginian age on the basis of the ranges of the ammonite genera present. (See table 2.) The presence of Samsinella, Polyptychites, and Homolso- mites implies that the zone is not younger than Valanginian. The presence of Acanthodiscus and Neocmspedites indicates an age not older than the middle Valanginian. In fact these genera strongly favor a late Valanginian age because Acanthodiscus reached its climax in the early Hauterivian and N 60- cmspedites in the late Valanginian. Also the presence of the uncoiled ammonite Uriocemtites (USGS Mes. loc. 1009), is strong evidence that the age of the zone is not older than late Valanginian because the genus oc- curs typically in rocks of Hauterivian and Barremian ages (Sarkar, 1955, p. 25, 33; Wright, 1957, p. 1208). The genus Homolsomites is of unknown value at pres- ent for close dating of the beds in which it occurs, be- cause it has been found at only a few places in Cali- fornia, Oregon, Washington, and Greenland (Imlay, AMMONITE S 1956, p. 1146). In Greenland, however, it is associated with ammonites that Donovan (1953, p. 135, 136; 1957, p. 149) considers to be of late Valanginian age. Comparisons by species favors a late Valanginian or a late middle Valanginian age for the H om-olsomites mutabilis zone. H omolsomz'tes mutabilis (Stanton) is closely similar to H. paucicostatus (Donovan) (1953, p. 110—112, pl. 23, figs. 1a, b), from beds of probable late Valanginian age in East Greenland. Polyptychites trichotom/us (Stanton) resembles P. ramulicosta A. Pavlow (1892, p. 481, pl. 8, figs. 10a, b, pl. 15, figs. 6a, b), from the late middle Valanginian at Speeton, Eng- land. Neocraspedites giganteus Imlay, n. sp., resem- bles N. flexicosta (Von Koenen) (1902, p. 74, pl. 5, figs. 14—16), from the late Valanginian of Germany. Thur- manm'oems jenkinsz' Anderson resembles T. durazmmse Gerth (1925, p. 97, pl. 4, figs. 1, 1a; Leanza, 1945, table opposite p. 96), from the late Berriasian of Argentina. Samsz'nella angulata (Stanton) is closely similar to S. trezamnsz's (Sayn) (1907, p. 34, pl. 3, figs. 20, 25a, b), from the middle Valanginian of France. Amntho- discus sp. juv. aff. A. radians Uhlig resembles a species from the late Valanginian of India much more than any of the species from the early Hauterivian of Europe. The H omolsomites mutabilis zone in Oregon has fur- nished few mollusks other than ammonites and Buc‘hia crassz'collz's (Keyserling). I nocemmus cf. I . vallejo— ensis Anderson occurs at Mesozoic localities 2154, 2156, 4390, 4393, and 4394 on Elk River. Acroteuthz's sp. and T urbo? cf. T. morganensz‘s Stanton occur at Mesozoic locality 2154. In contrast, in Tehama County, Calif. between McCarthy Creek and Elder Creek, the H omol- som/ites mutabilis zone has furnished a large molluscan fauna that has been described by Stanton (1895 [1896]) under the following names : Buchia crassicollis (Keyserling) (Mes. locs. 1071, 1087, 1091, 1093, 1095) Anomia sen csccns Stanton (Mes. locs. 1009, 1087) Aviculw (Owytoma) whiteavesi Stanton (Mes. Ice. 1093) Piano sp. (Mes. 100. 1093) Area tehamaensis Stanton (Mes. 10c. 1093) Nucula gabbi Stanton (Mes. Ice. 1088) Leda glabra Stanton (Mes. loos. 1069, 1093) Astarte corrugata Stanton (Mes. loc. 1093) Astarte trapezoidah‘s Stanton (Mes. 100. 1088) Dentalium califormcum Stanton (Mes. 10c. 1093) Turbo trilinea‘tus Stanton (Mes. 100. 1088) Turbo? humerosus Stanton (Mes. 10c. 1088) Hypsipleura gregaria Stanton (Mes. 10c. 1093) Cerithium strigosum Stanton (Mes. 100. 1093) Belemm‘tes impressus Gabb (Mes. locs. 1088, 1093) Belemm'tcs sp. (Mes. 100. 1093) OLCOSTEPHANUS PECKI This zone has been identified definitely only near Days Creek and Myrtle Creek, in Douglas County, OF EARLY CRETACEOUS AGE FROM THE PACIFIC COAST STATES 175 ()reg., but probably is represented in northwestern Washington. Its stratigraphic position in the upper part of the Buchia crassz'collis beds directly beneath beds containing early Hauterivian ammonities has been determined only on the South Umpqua River near its junction with Days Creek. At this place a sequence nearly 1,900 feet thick, involving beds of Portlandian, Valanginian, and Hauterivian ages, was measured by Hollis Dole, Dallas Peck, Len Ramp, and R. W. Imlay. The beds assigned to the Valanginian are about 375 feet thick and are characterized by the presence of the pelecypod Buchia orassicollis (Keyserling) in their upper 330 feet. They have furnished the ammonite Olcostephanus pee/vi Imlay, n. sp., at four levels from 73 feet to 291 feet above their base, and a single specimen of the ammonite H omolsomites stqmtom' (McLellan) at 73 feet above their base. Other mollusks present in- clude Lytocems cf. L. satumale Anderson, Phyllocems of. P. tz'z'm'tense Anderson, belemnite fragments, and Pleuromya, E ntolz'um, and Inocemmus. The presence of the zone of Olcostephanus peckz’ in northwestern Washington is indicated by two fragments probably belonging to that species that were obtained 3 miles east of Glacier, Wash. (Washington Univ. loc. VVA538), in association with H omolsomites stantom' (McLellan) and Buchia crassz'collis (Keyserling). This occurrence is similar to that on the South Umpqua River, Oreg., just discussed, where the same species of ammonites and Buchia are likewise associated (USGS Mes. loc. 26788). These associations indicate that the beds containing H omolsomdtes stamtom' (McLellan) on Spieden Island belong in the Oloostephanus pecki zone. The ammonite, ()lcostephomus pecki Imlay, n. sp., differs from most described species of Olcostephanus by having closely spaced ribs and by lacking umbilical tu- bercles except on its innermost whorls. In these re- spects it greatly resembles 0. jeannoti (d’Orbigny) (1841, p. 188, pl. 56, figs. 3—5), from the latest Valangin- ian and early Hauterivian of France. By comparison 0. peeled could be of either age. A Valanginian age is shown, however, by its association with the Valanginian pelecypod Buchia cmssz'collis (Keyserling) and by the fact that its highest occurrence is about 85 feet below a thick sequence of beds containing ammonities of early Hauterivian age. As the zones of Olcostephanus peckz’ and H omolso- mites mutabilis have not been found in a single section, their relative stratigraphic positions have not been de— termined. However, a higher stratigraphic position for the Olcostep/Lanus pee/62' zone is indicated by its po— sition at the very top of a Valanginian sequence near Days Creek, Oreg., whereas the H omolsomz'tes mutabilis zone in California and Oregon occurs at least several 176 hundred feet below the top of the Valanginian beds containing Buohz’a Massicollis (Keyserling). The pos- sibility that the two zones reflect environmental differ- ences rather than time differences is discounted because the sedimentary rocks present in the zones have the same lithologic characteristics and contain an abun- dance of the same species of Buchia. Combined with this, the fact that the characteristic species of one zone have not been found in the other implies that they 0c- cupy somewhat different positions. The zone of Olcostephanus pecki may still be found in California in the uppermost part of the range of Buchz'a crassicollis (Keyserling) above the H omolso— mites mutabilis zone. If Anderson’s data (1933, p. 321, 322) are correct, this zone in Tehama County is over- lain by 200 to 300 feet of beds containing Buahia cras- sicollis (Keyserling), which could account for the 0. pecki zone. Against this possibility is the record by Anderson (1938, p. 46, 164, 165) of certain fossils from the lower part of the shaly sequence overlying the beds containing Buchia cmssicollis (Keyserling) in abun- dance. The fossils (CAS 100. 33502) were assigned by Anderson to N eocomz'tes jen/cz'nsz’ Anderson, Thur- manm'w paskentae Anderson, Subastem'a sp., Berm‘asella crassiplicata (Stanton), and to two species of Aucella (now called Buckie). The ammonites have been exam- ined by the writer and are herein referred to T hurman- m'cems jenlcinsz' (Anderson), T. sp. juv. cf. T. stippz' (Anderson), Polyptychz'tes sp. juv. (see pl. 31, fig. 14), and Kiliarnella sp. As all these are characteristic of the H omolsomc'tes murtabilis zone, the zone of Olcoste- phanus pecki may be still higher stratigraphically, or may not be represented by sediments. WELLSIA OREGONENSIS This zone is characterized by the ammonites Wellsia oregonensis (Anderson). Other ammonites in the zone include Phyllocems trinitense Anderson, P. umpqua- num Anderson, Lytocemw aulaeum Anderson, Spitidis— Gus orego’nensis Imlay, n. sp., Hammites riddlenszls (Anderson), H. truncate Imlay, n. sp., and Uriocem- tites latum (Gabb). All these except Wellsia oreganen- 82's (Anderson) range into the overlying zone of Wellsz'a packardi, and the species of Spitidiscus ranges still higher into the zone characterized by Simbz'z-s/cites. Associated with these ammonites are many species of pelecypods and some gastropods, belemnites, and crustaceans. Described pelecypods include Periplo- mya tm’m’tensis Anderson, Periplomya reddingensis Anderson, Pleumomya papymcea (Gabb), Trigom'a [sag/amt Anderson, and Entolz'um operculz'formc's (Gabb). The pelecypod genera Astarte, Trigom'a, Owytoma, Solecumtus, Cercomya, and Mytilus are rep- SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY resented by undescribed species. Pleu'romya and Entolium are represented by many more individuals than the other genera. The interesting feature con— cerning the pelecypods is that not a single species occurs in the older beds containing Buchia, crassicollis (Key- serling) but that the range of many of the species ex- tends higher into beds of middle Hauterivian age. The zone of Wellsia oregonemis has been identified only in southwestern Oregon. Most of the occurrences of Wellsz'a oregonemis (Anderson) are near Days Creek and Riddle in Douglas County, but the species has been found at one place in Coos County. All its occurrences in Douglas County are in gray siltstone and greenish- gray sandstone directly overlying gray sandstone con— taining Buchia crassicollis (Keyserling). On the South U mpqua River near Days Creek, W. oregonensis (An- derson) has been collected from 58—243 feet above the top of the beds containing Buckie. On the Foggy Creek road in Coos County, W. oregoflensis (Anderson) was collected (Mes. loc. 25213) 400 feet below Hannaites riddlensis (Anderson) (USGS Mes. 100. 25212) and 1,200 feet above the top of conglomeratic beds contain- ing Buckie crassicollae (Keyserling), which are about 1,000 feet thick. WELLSIA PACKARDI This zone (table '3) is characterized by the ammonite Wellsia packardz' (Anderson) and has been found only in Douglas County, Ore., near Days Creek and Riddle. It is considered provisional because its relative position above W. oregmwnsz's (Anderson) has been established only in one sequence and because the associated mega- fossils belong to the same species as those in the W. oregonensis zone. Differentiation of the two zones was indicated by collecting along the South Umpqua River near Days Creek which showed that W. packafl'dd oc— curred stratigraphically higher than W. oregmwmz's and ranged from 253 to 413 feet above the beds contain- ing Buckia crassicollz's (Keyserling). Some of the collections (USGS Mes. locs. 718, 1243, 1252) made between 1890 and 1900 on Cow Creek below Riddle contain both Wellsia oregonensz's and W. packardi. These collections were not made stratigraphically, how- ever. The fact that the specimens of W. packardi in these collections are browner and generally more crushed than the specimens of W. oregonensis suggests that the species were obtained in different beds. HOLLISITES DICHOTOMUS This zone, identified only in southwestern Oregon, is characterized by the ammonites H ollisites dichotomus Imlay, n. sp., Speetonicems agnessense Imlay, n. sp., Simbimkites afi'. S. elatus (Trautschold), and Simbz'rs— kites afl'. S. progrediem Lahusen. Associated with AMMONITES OF EARLY CRETACEOUS AGE FROM THE PACIFIC COAST STATES these species are others that range upward from older Hauterivian beds in Oregon, including Phyllopachy- cams tn’niteme (Anderson), P. umpguanum Anderson, Hanmites riddlensis (Anderson), Lytocems aulaeum Anderson, and Spitz'dz'scm oregonemis Imlay, n. sp. Also, associated with these species are others that are similar to, or identical with species in California in the middle Hauterivian Hamlin-Broad zone of Anderson and the late Hauterivian Hertleim'tes aguila zone. These species include Acriocems coycm’um Anderson, A. of. A. voyanum Anderson, Hoplocriocems cf. H. remondz’ (Gabb), and Hollisites Zucasz' Imlay, n. sp. The pelecypods found with these ammonites include Plewromg/a papymcea (Gabb) (USGS Mes. locs. 1245, 25214), Trigonia [mg/mm Anderson (USGS Mes. locs. 1243, 25214), T rigonia cf. T. lama Gabb (USGS Ice. 1245), Entolium sp. (USGS Mes. loc. 24449), 1720067"- amus sp. (USGS Mes. loc. 24449). In addition to these pelecypods, a subcircular Inocemmus similar to the Albian species I. anglicus Woods occurs at USGS Mesozoic localities 2093, 3352, 25210, and 25215, The H ollz'sz'tes dichotomus zone has been identified in Douglas County near Riddle (USGS Mes. locs. 1251, 1245, 25210) and is probably present on the South Umpqua River below the bridge at the mouth of Days Creek (UCGS Mes. locs. 3352 in part). In Curry County it occurs at several places near Agness (USGS Mes. locs. 2078, 2080, 2093, 25214, 25215, 25216, and 26879). In Coos County a large collection was made near the Foggy Creek Road USGS Mes. locs. 25211, 24449). The stratigraphic position of the H ollz'sz'tes dichoto- mus zone relative to the Wellsz'a packardi zone has been determined only in Cow Creek at the town of Riddle, Douglas County. Collections containing both Wellsia packardi (Anderson) and W. oregonensés (Anderson) USGS Mes. locs. 718, 1252, 25208) have been obtained from a couple hundred feet of beds about a quarter of a mile below the bridge across Cow Creek at Riddle. A collection containing Hollisz'tes dichotomus Imlay, n. sp., and Simbirskites sp. juv. aff. S. claims (Tram- schold) was obtained from 15 feet of gray sandstone exposed at the west end of the bridge across Cow Creek (USGS Mes. loc. 1251). The thickness of the beds between these collections cannot be accurately deter— mined because of minor folding and faulting, but, ac- cording to Stanton’s notes of October 23, 1894, and the writer’s own observations, the collections at Mesozoic locality 1251 are only slightly higher stratigraphically than the others. Another locality where the relative stratigraphic po- sitions of Simbz'rskites and Wellsia oregoncnsz's has been determined is on the Foggy Creek road in Coos 177 County. Numerous specimens of Simbirskz'tes and other ammonites were obtained on the west side of the Foggy Creek road about a quarter of a mile above its junction with the Eden Valley road (USGS Mes. loc. 25211). Specimens of Hannaz'tes m’ddlensz's Anderson (Mes. loc. 25212) were obtained 1 mile upstream from the junction; Wellsia oregonensis (Anderson) (Mes. loc. 25213) was obtained 1.3 miles upstream and Buchia cratesiaollis. (Keyserling) was obtained 1.5 miles upstream. According to Francis Wells (oral com- munication, March 1958) the collection containing Simbz'rskz'tes was apparently obtained 3,000 feet higher stratigraphically than that containing Hannaz'tes rid- dlensis (Anderson) and 3,400 feet above that contain- ing Wellsz'a oregonensis (Anderson). He considers that a thickness of 3,000 feet between the first 2 col- lections probably includes repetition of beds by fault- ing or folding, but that the fossil collections are in correct stratigraphic sequence. The Hollisites dichotomm zone has not been identi- fied in California. The possibility that it is equivalent to part of Hamlin-Broad zone of AnderSOn (1938, p. 47—49) in Shasta and Tehama Counties, Calif, is un- likely because most of the ammonites that have been found in it belong to different species than those in Anderson’s (Hamlin-Broad zone and it includes a num- ber of ammonite species that range up from the Wellsia packardz'. zone, but are not known from California. The age of the Simbimlcites dichotomus zone is indi- cated as middle to early late Hauterivian on the basis of the presence of the ammonite Simbirskites, of the resemblance of the genus Hollisites to Speeton-z'cems and on the presence of the genus Speetom'cems itself. At Speeton, England, Simbz‘mkites is recorded by Spath (1924, p. 76, 77) as ranging from the beds containing Subastz'eria sulcosa (Pavlow) into the beds containing Simibz'rskites progredicus Lahusen and to be most abundant in the upper part of its range. Sim- bimkites in northern Germany (Von Koenen, 1902, p. 420, 433; Stolley, 1908, p. 145, 151) and in Russia (A. Pavlow, 1892, p. 558, 559; 1901, p. 46, 47) is reported to occur a little above the middle of the Hauterivian. The range of Speetonicems in Europe is similar to that of Simbz'rs/cites. At Speeton, England, Speetom'cems has been found only in the lower part of the range of Simbi/rskites (Spath, 1924, p. 76, 77), but in Russia the genus is reported to occur in the upper part of the range of Simbz'rskites (Spath, 1924, table 3, faces p. 80). If the Hollisz'tes dichotomrus zone in Oregon is older than beds in California that contain Sz'mbirskites broadi Anderson, it may reasonably be correlated with the lower part of the range of Simbirs/cites in Europe. 178 HAMLIN—BROAD ZONE 0F ANDERSON Some beds characterized by species of the ammonites Simbirskites, Hoplocriocems, A cflocems, and Uriocem— tites were named by Anderson (1938, p. 47, 48) the Hamlin-Broad zone after the specific names of two am- monite species, Aspinocems hamliml Anderson and Simbz'rskites broadz' Anderson. He included in his zone the fossils from CAS localities 1665, 113, and nearby places from 3 to 6 miles southwest of Ono in Shasta County. He states on page 47 that the fossils at local- ity 113 were obtained 450 feet below a conglomerate marking the base of his Horsetown group and were more than 1,000 feet above the base of the Cretaceous section. On pages 122, 147, 154, 208, he states that the fossils were collected 500 feet below the conglomerate and on page 111 ‘he states they were collected 600 feet below the conglomerate. On table 2 opposite page 44 he indicates that locality 113 has B and 0 subdivisions. The probable explanation for these discrepancies is that the fossils in CA8 locality 113 were collected from 3 places near each other and from an interval ranging from 450 to 600 feet below the conglomerate. This par- ticular conglomerate was named the Roaring River tongue of the Ono formation by Murphy (1956, p. 2108, 2111). The stratigraphic position of the Hamlin-Broad zone according to Anderson (1938, table 2, p. 47—49, 64) is definitely below beds containing H ertlez'm’tes agm'la (Anderson). However, Michael Murphy, pale- ontologist at the University of California at Los Angeles, has found Simbirs/cites broadi Anderson asso- ciated with Hertleim'tes dgm'lu (Anderson) southwest of Ono, Calif. Furthermore, concerning CAS locality 113, he states (written communication, Jan. 9, 1959) : There are two fossil zones at the head of Mitchell Creek west of the road * * *. You may recall that Anderson indicated the specimens he collected came from 450 to 600 feet below a conglomerate and that he gave all specimens the same locality number CAS 113. This apparently was standard procedure with him. He regarded his localities as areas from which he collected fossils and paid little attention to whether or not all the specimens at a particular locality came from the same stratigraphic position. Murphy’s fieldwork shows, therefore, that one species, Simbirslcites broadi Anderson, that Anderson consid- ered characteristic of his Hamlin-Broad zone actually occurs in, or ranges into the H ertleim'tes aguila zone. He indicates, however, that some of the species from Anderson’s Hamlin-Broad zone are from beds older than those containing H ertlez'm'tes aguila. (Anderson). This conclusion seems reasonable considering that most of the ammonites from CAS localities 1665 and 113 have not been found with Hertlez'm'tes aguc'la (Anderson). SHOR‘TER CONTRIBUTIONS TO GENERAL GEOLOGY The fossils from CAS locality 1665 described or listed by Anderson are as follows : N eocomites russelli Anderson (1938, p. 201) Crioceras dumnense Anderson (Anderson, 1938, p. 201) Urioceras latum Gabb (1938, p. 200) Criocems cf. 0. nolam’ Kilian (Anderson, 1938, p. 48) H oplocm'oceras remondi (Gabb) (Anderson, 1938, p. 202) H oplocrioceras sp. (Anderson, 1938, p. 47) Spiticeras duncammse Anderson (1938, p. 160) Pleuromya papyra‘cca Gabb (Anderson, 1938, p. 115) Pholadomya Clementine Anderson (1938, table 2) Of these species the writer assigns N eo‘comites msselli Anderson questionably to Pseudothumannm, 01600674“ duncanense Anderson is considered a synonym of Orio— cemtites lam (Gabb), and Spiticems dumaneme An- derson belongs to the genus H oplocm'ocems. The rea- sons for these assignments are discussed herein under the description of the species. The fossils from CAS locality 113 described or listed by Anderson are as follows : Lytoceras satumale Anderson (1938, p. 47) Lytocems aulaeum Anderson (1938, p. 147) Subastieria cha/nchelulu Anderson (1938, p. 156) Si/mbirskites (broadi Anderson (1938, p. 155) Polyptychites lecontei Anderson (1938, p. 154) Polyptychitcs hesperius Anderson (1938, p. 154) Urioceras latum Gabb (Anderson, 1938, p. 200) Aspinocems hamlim’ Anderson (1938, p. 207) Anahamulina vespcrtina Anderson (1938, p. 219) Aoroteuthis shastensis Anderson (1938, p. 226) Ostrea indigena. Anderson (1938, p. 108) Plicatula onocnsis Anderson (1938, p. 111) Venus collim‘um Anderson (1938, p. 111) The fossils from CAS locality 113B described or listed by Anderson are as follows : Thurmmmm jupiter Anderson (1938, p. 162) Phylloccras occidentalc Anderson (1938, table 2) Lytoccras traski Anderson (1938, table 2) Acrotcuthis impressa (Gabb) (Anderson, 1938, table 2) .11 odiolus (moensis Anderson (1938, table 2) The fossils from CAS locality 113C described or listed by Anderson are as follows : Discohelim planigyrm‘dcs Hanna in Anderson (1938, p. 128) Area temrma Stanton? Anderson (1938, table 2) Trigoma cf. T. kayana Anderson (1938, table 2) Of the ammonites from CAS locality 113, 113B, and 113C the writer considers that Subastiem'a chanchelula Anderson is an immature specimen of Simbirskites broadi Anderson; Polyptychites lecontei Anderson is assigned to the genus Simbz'rskites and is probably a synonym of Ammonites traslci Gabb, which Shimizu (1931, p. 15) designated as the type of Californicerw; Polyptychites hespem’us Anderson probably belongs to the genus H ollisites Imlay (1957, p. 276) ; Uriocems latum Gabb belongs to Urioc'eratz'tes; Aspinacems hamlim' Anderson and Amhamulina vespertz'na Ander- AMMONITES OF EARLY CRETACEOUS AGE FROM THE PACIFIC COAST STATES son belong to Am'ioceras; and _ Thumannz'a jrwpz'ter Anderson probably belongs to Pseudothcnrmannia. The reasons for these assignments are discussed herein under the description of the species. The Hamlin-Broad zone of Anderson is possibly rep- resented at one place in Tehama County where T. W. Stanton, James Storm, and J. S. Diller made a large collection (USGS Mes. loc. 1092) on the Wilcox Ranch. Stanton states in his notebook, dated October 16, 1893, that the collection was made from 50 to 200 feet above the sandy beds containing Bun/Lia crassicollis (Keyser- ling). The fossils at this locality, listed by Stanton (1895, top of p. 18 [1896]), have been restudied and are as follows: Hypophyllocerars cf. H. onocnsc (Stanton) Lytoceras aulaeum Anderson Orioceratites cf. 0. tehamacnsis (Anderson) Anahamnlina wilcomcnsis Imlay, n. sp. H ertleinites pecki Imlay, n. sp. H ollisites lncasi Imlay Hollisites inflatns Imlay, n. sp. Shasticrioceras sp. Acroteuthis sp. Plcnromya papyracea‘ Gabb Plicatnla variata Gabb Entolium? operculiformis (Gabb) Parallelodon cf. P. breweriana (Gabb) Tessarolaz bicarinata (Gabb) Potamides diadema Gabb Ampullina cf. A. avellana Gabb Concerning the preceding fossils, a position in the Hertleinites agm'la zone rather than in the Hamlin- Broad zone is indicated by the particular species of gastropods, by the resemblance of the fragment of H y- pophyllocems to H. omense (Stanton) and by the presence of the genus Hertlez‘nites and Shasticrioceras. The genus H olZz'sites, however, has not been previously found in the Hertlez‘m'tes agmlla zone and is common in Oregon in beds containing Simbirskz'tes. In 1900 Stanton made additional collections on the Wilcox Ranch. According to his notes of September 3d and 4th he made several collections over a distance of about a mile at a stratigraphic position from 400 to 500 feet above the sandy beds containing Buchia crassi- collis (Keyserling). He assumed that the fossiliferous beds were the same in which he collected in 1893 at Mesozoic locality 1092. His collections, however, con- tain different species, particularly Hertlez‘m‘tes agmlla Anderson and Inoceramus ovatoides Anderson, than he obtained in 1893; so the probabilities are that they were obtained from a slightly higher stratigraphic position. The fossils obtained in 1900 will be listed and further discussed under the description of the H ertlez‘nites agm'la zone. Considering the reported differences in the strati- 179 graphic intervals from which collections were made and the differences in faunal characteristics of the fossil collections made in 1893 with those made in 1900, the probabilities are that the fossils collected in 1893 (USGS Mes. loc. 1092) are slightly older than those collected in 1900 (USGS Mes. locs. 2267—2269), or rep- resent mixture from different levels and are in part from the Hertleinites agm'la zone. If the Hamlin- Broad zone of Anderson is not represented, there is only a slight thickness of beds above the Buckie crassicolh's beds to account for the early and middle Hauterivian zones that are so richly developed in southwestern Oregon. The matter can only be settled by additional fieldwork. Another area in California that may contain beds slightly older than H ertleinites aguila zone is on the Clements Ranch in the valley of Bedding Creek, Trinity County. A collection made near the building of the Clements Ranch by James Storr (USGS Mes. loc. 4415) contains the following described species: “Phylloceras” trinitense Anderson Criooeratites latum Gabb Plcnromya papyracea Gabb Gom‘omya vespera Anderson Pinna pontica- Anderson Entolium? operculiformis (Gabb) The following species are listed or described by An- derson (1938) from about the same place (CAS Ice. 1691) : Pleuromxya papyracea Gabb (Anderson, 1938, p. 118) Periplomya trinitense Anderson (1938, p. 118) Periplomya reddingcnsis Anderson (1938, p. 118) Goniomya vespem Anderson (1938, p. 117 ) Pholadomya altiumbonata Anderson (1938, p. 116) Pholadomya Clementine Anderson (1938, p. 116) “Venus” collinium Anderson (1938, p. 111) “Syncylonema.” opercnliformis (Gabb) (Anderson, 1938, p. 200) In addition Anderson reports the following species from a nearby area: “Phylloceras” trinitense Anderson (1938, p. 200) “Grim-ems" latnm Gabb (Anderson, 1938, p. 200) “Hoplocm‘oceras” yollabollium Anderson (1938, p. 203) The last mentioned species is reported to have been obtained about 600 feet below the beds exposed at the Clements Ranch buildings and to be similar to Oriocem- tites bedem’ (Gerth) from Argentina. Most of these species occur in the Hamlin-Broad zone of Anderson at CAS localities 113 and 1665 in Cali- fornia. The presence of “Phyllocems” trinitense An— derson might be taken as evidence for correlation with the early or middle Hauterivian of Oregon. However, the collections from the Clements Ranch do not contain certain species of Astarte, Solecurtus, Arcom/ya, Omy- toma, and Tm’gom‘a that are common in the Hauterivian 180 beds in Oregon and do contain species of Pholadmya and Gom‘omxya not known in Oregon. Also, the speci- mens of Uriooeratz'tes in Oregon appear to differ a little from Orioceratites latum (Gabb), which species occurs in California both in the Hamlin-Broad zone of An- derson and in the H ertleimltes agm'la zone. The age of beds at CAS localities 113 and 1665 near Ono, Calif, is either late middle or late Hauterivian on the basis of the association of the ammonites H oplocri- 006mg, Acrioceras, and Simbz'rslcites. (See table 2.) The resemblance of Hollisites to Speetom'ceras and of N eocomz'tes russelli Anderson to Pseudothummmia. also indicates such an age. HERTLEINITES AGUILA This zone was established by Murphy (1956, p. 2113, 2114) for essentially the same beds that Anderson (1938, table 2, faces p. 44, 64) included in his Ono zone. Murphy lists the following species: Entolium operculiformis (Gabb) Gom‘omya vespera (Anderson) Periplomya tri'nite'nse Anderson Nucum gabbi Stanton Inoceramus ovatoidcs Anderson Pirmo pontioa Anderson Parallelodon breweriana (Gabb) Plicatula variant Gabb Pholadomya altiumbomta Anderson Pleuromya papyracea Gabb Potamides diadcma, Gabb Turbo festival’s Anderson Palamede perforate (Gabb) Tessarolaw bicarmata (Gabb) “Ncocraspeditea” agm’la Anderson Lytoceras aulaeum Anderson Shasticrioccras sp. indet. Aoroteuthis aboriginalis Anderson Anderson lists most of these species and in addition the following: Modiolus omensis Anderson (1938, p. 114) Astarte oalifornica Stanton (Anderson, 1938, p. 64) Pholadomya Clementine Anderson (1938, p. 116) Corbula filosa Stanton (Anderson, 1938, p. 64) Dentalium caliform’cum Stanton (Anderson, 1938, p. 126) Ampullina avellana Gabb (Anderson, 1938, p. 64) N crime archimcdi Anderson (1938, p. 64) Clicocolus indubitus Anderson (1938, p. 121) Lytoccras traslci Anderson (1938, pp. 64, 146) Phylloceras occidentalc Anderson (]938, pp. 64, 139) Hoploorioccras rcmondi (Gabb) (Anderson, 1938, p. 201) H oploorioceras onocnse Anderson (1938, p. 202) Urioceras latum Gabb (Anderson, 1938, p. 200) “Neocragpcditcs” rectoris Anderson (1938, p. 157) A croteuthis (mocnsis Anderson (1938, p. 227) Aeroteuthis kerncnsis Anderson (1938, pp. 64, 227) The collections of the Geological Survey made by T. W. Stanton near Ono, Calif, contain most of the species listed by Murphy and Anderson. One of the SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY most interesting additions is Hypophylloceras atf. H. onoense (Stanton) (USGS Mes. loos. 2223, 2225). Other collections made by Stanton on the Wilcox Ranch, in Tehama County, Calif, show the existence of the H ertleim'tes aguila zone in that area. These col- lections were made according to Stanton’s notes of Sep- tember 3 and 4, 1900, from 400 to 500 feet above the top of the sandy beds containing Buckie crassicollz's (Keyserling). In addition to the common pelecypods and gastropods characteristic of the zone, they include the following: Lytoceras aulaeum Anderson (Mes. loc. 2267) Lytoceras cf. L. traski Anderson (Mes. 10c. 2268) H ertleinites aguila (Anderson) (Mes. 10c. 2267 ) H oploorioceras remomli (Gabb) (Mes. 10c. 2268) Acrioceras cf. A. voyanum- Anderson (Mes. loc. 2269) At Mesozoic locality 2269 Stanton found a small spec- imen of Inoceramus ovato’ides (equals I . colonicus An‘ derson) Which he mistook for Awella (now called Bus/Lia). Its shape is similar to that of Buckie piochiz' (Gabb), but its nacreous shell layer is unlike that of any Buckie. The species is fairly common in the H ert- Zeim'tes aguila zone near Ono, Calif, as well as in the overlying Shasticrioceras poniente zone (Murphy, 1956, fig. 6, p. 2114), but has not been recorded from the Hamlin—Broad zone of Anderson. The H ertleim'tes aguila zone is possibly represented in southwestern Oregon about 4 miles south of Cave Junction by a. collection (USGS Mes. loc. 3339) con- taining the following fossils: I noceramus ovatoides Anderson (abundant) Trigom‘a of. T. leana Gabb (abundant) Entolium operculiformis (Gabb) I’Icuromya sp. Astartc sp. Protocardia sp. Den talium sp. Simbirskites? sp. The ammonite referred questionably to Simbirskz'tes is small and fragmentary but suggests a middle to late Hauterivian age. The occurrence of Inoceramus o'va— toides Anderson in abundance suggests an age as young as the H ertleim'tes aguila zone, because the species has not been identified in older beds in California. About 5 miles south of Cave Junction another col- lection (Mes. loc. 2166) contains the following species: I noccramus ovatoidcs Anderson Plcuromya papyracca Anderson Trigom’a cf. T. lama Gahh Trigonia kayan-a Anderson Mcckiar sp. Nucula sp. Gom‘omya sp. Entolium. opcrculifomzis (Gabb) Corbula sp. AMMONITES OF EARLY CRETACEOUS AGE FROM THE PACIFIC COAST STATES Solecurtus sp. Acrioceras? sp. Shasticrioceras cf. S. pom‘enie Anderson Concerning the age significance of the above fossils, the presence of Shasticrioceras similar to S. pom’ente Anderson is strong evidence that the fossiliferous beds belong in the Shasticriocems pom‘en-te zone (Murphy, 1956, p. 2113), although the genus has been recorded in the underlying Hertleim'tes agm'la zone. lnocemm'us ovatoides Anderson has been recorded from both of these zones (Murphy, 1956, fig. 6, p. 2114) but not higher or lower. Trigom'a kaycma Anderson occurs in Oregon in beds of early to middle Hauterivian age. In California it is recorded by Anderson (1938, p. 108) from beds probably as low as the H ertleim'tes agm'la zone. It is recorded by Murphy (1956, p. 2116) as be— ing particularly abundant in the lower part of his Gab- biocems wintum'um zone of early Aptian age. The holotype specimen of Trigonia hag/(ma Anderson was obtained near Ono, Calif, at an unknown stratigraphic position. Apparently this species has a much longer stratigraphic range than the Showtimiocems poniente zone. The beds in California included in the H ertleim'tes aguz'la zone were considered by Anderson (1938, table 2, faces p. 44, 64) to be not younger than early Haute- rivian because of the presence of ammonites that he as- signed to Neocraspedz'tes, Hoplocm'ocems, and Uria- cems and because he considered (1938, p. 47) the ammonites from the underlying Hamlin-Broad zone of Anderson to be Valanginian. The writer interprets the age significance of the ammonites in these zones some- what differently as discussed herein. The only fossils in the H ertlenites aguz'la zone that have much significance in intercontinental correlation are the ammonites H ertleim'tes (equals Neom'aspedites of Anderson), Simbirskites, Hoplocm'ocems, and 07-5- ocemtites (equals Uriocems of Anderson). Of these, Hertleim'tes has not been recorded outside of Cali- fornia, but its resemblance to the late Hauterivian genus Oraspedodiscm may indicate a similar age. Sim— bz'rskz'tes is a characteristic Hauterivian genus. H oplo- cm'ocems at Speeton, England, ranges from the zone of Simbirskites progredicus through the Hauterivian (Spath, 1924, p. 78). \Vright (1957, p. 208) indicates that the genus occurs likewise in the Barremian. The genus is mostly recorded, however, from the late Haute- rivian corresponding to the European zone of Pseudo— thurmanm'a angulz'costata. Uriocemtites is recorded as ranging through the Hauterivian and Barremian (Sarkar, 1955, p. 25) but it is mostly recorded from the Hauterivian. In summation the evidence from the am- monites favors a. Hauterivian rather than a Barremian 181 age and a late Hauterivian rather than an early Hau- terivian age. A late Hauterivian age assignment is supported, also, by the relative stratigraphic position of the Hertlez'nites aguila zone above beds containing Simbirskites and be- low beds containing Pulchellia and Ancylocems. As previously mentioned Simbirskites is mostly recorded as from beds of middle or late middle Hauterivian age. The Barremian age of the overlying Shasticriocems poniente zone is definite, considering that Pulchellia oc- curs at one place in the lower part of the zone and Amyloceras is common in the upper part. The genus Pulckellz'a ranges through the Barremian, but most of its occurrences are from the early Barremian. As Amyloceras ranges from late Barremian into early Aptian, its occurrence above Pulchellia in California is normal. COMPARISONS WITH OTHER FAUNAS The ammonite faunules in beds of Valanginian and Hauterivian ages in the Pacific Coast states have a pecu- liar local aspect owing to the fact that some of the com- mon genera present have either not yet been found else- where, or rarely elsewhere, and to the fact that some genera that are common in other parts of the world are either unknown or are rare in these States. There ap- pears to be a commingling of local, or provincial, genera with others that are common either in the Mediter- ranean province or in‘northern Europe. Interestingly, resemblance with ammonites of Valanginian age in Mex— ico are no greater than with those in India or in south- ern France, and the Hauterivian ammonites of the Pa- cific coast are much more similar to those of England, northern Germany, and central Russia than to those of Mexico. (See chart 1). Unfortunately, for compara- tive purposes ammonites of these ages from Alaska and Canada are unknown or undescribed. The affinities of the Valanginian ammonites from Oregon and California are predominantly with am- monites of the Mediterranean province. Comparable species of the genera Kilianella, Sarasz'nella, Thumman— nicems, Acanthodiscus, Neocomitesfl Olcostephcmus, and Bochianites occur in various parts of that province, particularly in India, southern France, and Switzer- land. Some affinities with ammonites of central and northern Europe are suggested, however, by the pres- ence of species of N eocraspedites and Polyptychites sim- ilar to species in northern England and northern Germany. Also, the genus Homolsomz'tes, known else- where only in Washington, British Columbia, and Greenland, probably belongs to the boreal subfamily Tolliinae. In contrast with the Valanginian beds in most parts of the world the Valanginian of the west 182 coast has furnished very few species of the subfamily Olcostephaninae. This scarcity is surprising, consider- ing the abundance of that subfamily in Mexico. The absence in Oregon and California of such typical Valanginian genera as Rogersc'tes, Valanginites, Dis- tolocems, or even typical species of N eonomz'tes, is striking and needs a special explanation. Such differences may be due in part to inadequate collecting, to the fact that beds containing an abun- dance of Buchia seldom contain many ammonites, to provincial preferences of certain genera and families of ammonites, or to time differences of the faunules com- pared. Considering that in the Valanginian beds only the zone of H omolsomz'tes mutabilis has furnished even a moderate number of ammonites, the environmental factor is probably very important. If certain genera did not inhabit the waters where Buchia lived in abun- dance, they may still have lived offshore in slightly deeper waters. If so, their shells should at times have been washed inshore among the Buchia beds. The im- portance of this factor relative to the others listed can only be settled by additional collecting. The affinities of the Hauterivian ammonites of Ore- gon and California are mostly with those of northern Europe, rather than with southern Europe, and par- ticularly are with those in northern England, northern Germany, and central Russia. These affinities are shown by the presence of the genera Hoplocriocems, Speetom'cems, and Simbz'rskites and by the resemblance of the west coast genera H ollisites and H ertleim'tes to Speetom'cems and Uraspedodiscus, respectively. The species of Uriocemtz'tes, Acm’oceras, Amhamulina, Olcostephanus, and Spitidiscus in Oregon and Cali— fornia may be compared to species in either northern or southern Europe. Other affinities with the Hauterivian of Europe are furnished by the resemblances of the west coast genera H annaites and Wellsia to Leopoldia and N eocmspedz'tes, respectively. A contrast with the Hauterivian in most parts of Eurasia and the Mediter- ranean region in general, including Mexico, is furnished by the absence of such genera as Leopoldia, Accmtho- discus, and Distolocems. A contrast with northern Eu- rope is furnished by the absence of Lyticocems. These differences with Hauterivian ammonite as— semblages in other parts of the world are difficult to explain by facies control, or inadequate collecting, or SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY time differences of the ammonite faunules compared, as was suggested for the Valanginian ammonites of the Pacific coast. The chances of future collections resolv- ing the differences are not very great, because ammonites in beds of Hauterivian age in both Oregon and Cali- fornia are moderately abundant at many levels and are associated with a normal marine, shallow—water assem- blage of pelecypods, gastropods, and crustaceans. Evidently facies control of Hauterivian ammonites of the Pacific coast does not appear to be very important. In particular the presence of Lytocem‘s and the pkg/Zlo- cemtz'ds throughout the Hauterivian beds show that the ammonites of the open sea entered freely into the areas where these beds now crop out. These considerations plus the presence of such genera as Wellsia, H amuu'tes, H ollz'sites, and H ertlez'nites show that the Hauterivian ammonite assemblage on the Pacific coast has certain local peculiarities that distinguish it from assemblages of that age in other continents or even in Mexico. ECOLOGIC CONSIDERATIONS Acceptable conclusions concerning the characteristics of the sea that covered parts of the Pacific coast during Valanginian and Hauterivian times cannot be drawn until much more lithologic, stratigraphic, and paleon- tologic data are obtained. In the meantime some facts that may be useful in making interpretations concerning temperature, depth of water, and habitats are given. The genus Bucha'a was the dominant benthonic or- ganism during Valanginian time in the Pacific coast region. It existed in enormous numbers in silty, sandy, and pebbly beds, but was locally rare in such beds. It disappeared abruptly at the end of the Valanginian. With the disappearance of Buchia, many pelecypod genera that had been rare in the Pacific coast region became common. These include in particular such genera as Periplomg/a, Pleuromya, Cercomg/a, Trigom'a, Owytoma, E ntolium, Solecurtus, and Mytilus. Associ- ated with these are some crustaceans and many wood fragments. There are few records of corals, echinoderms, or of the pelecypod family Ostreidae in the Valanginian and Hauterivian beds of the Pacific coast. The pelecypod I nocemmus is rare in California below the zone of Hertleim'tes aguz’la. In Oregon many ex- amples of I nocemmus have been found in various parts AMMONITES OF EARLY CRETACEOUS AGE FROM THE PACIFIC COAST STATES of the Valanginian-Hauterivian sequence. The ex- amples from the Valanginian beds are generally asso- ciated with ammonites in beds that contain only a few specimens of Buckie. Inocemm/ws has not yet been found in beds containing Buckie in abundance. Beds containing abundant Buckie contain few speci- mens of other benthonic pelecypods. The long—ranging ammonites, the phylloceratids and Lytocems, occur throughout the Valanginian-Haute- rivian sequence, but the phylloceratids are uncommon below the uppermost Valanginian. The short-ranging ammonites of the Valanginian beds show affinities both with the Mediterranean region and with the northern Europe, but not particularly with Mexico. Many of the short-ranging ammonites of the Haute- rivian beds show affinities with ammonites of that age in England, northern Germany, Japan, and central Russia and little at all with the Hauterivian ammonites of Mexico. The Hauterivian beds contain several ammonite ge— nera that have not yet been found outside the Pacific coast region, although they do resemble certain genera of that age elsewhere. Both the Valanginian and the Hauterivian beds are characterized by an absence of certain ammonite genera that are common in beds of those ages in many parts of the world. From these data certain broad generalizations may be drawn. For example, the presence of the thin— shelled ammonites, the phylloceratids and Lytooems, in fair abundance suggests that the Valanginian and Hauterivian marine waters along the Pacific coast were connected broadly with the main ocean immediately to the west. The affinities of many of the other ammonites with ammonites in distant parts of the world such as Japan, the Russian platform, Germany, England, India, and the Caucasus, implies marine connections 'northward, westward, and southward. The lack of any close affinities with Valanginian and Hauterivian faunas in Mexico is rather surprising and suggests the presence of some kind of a barrier, either physical or environmental or both. Perhaps the abundance of Buckia in the Valanginian beds of the west coast and its absence in Mexico reflect an environmental barrier. The affinities with Eurasia and the lack of them with 183 Mexico are suggestive that major currents in the northern part of the Pacific Ocean were similar to those existing today. The data should be considered, also, in terms of cer- tain events that affected large parts of the world dur- ing Early Cretaceous times. These include the near extinction of ammonites in Barremian time (Arkell, 1949, p. 412), the general disappearance of the pelecypod Buckia near the end of Valanginian time (Pavlow, 1907, p. 84 and facing table) except for a few stragglers locally in the Hauterivian in Europe (Woods, 1905, p. 71; Wollemann, 1900, p. 56—59; Pav- low, 1907, p. 79; Sokolov and Bodylevsky, 1931, p. 118), and the Arctic Ocean becoming much more restricted during Hauterivian to early Aptian times than it had been previously in the Cretaceous or in the Jurassic. The evidence for such restriction consists of the ab- sence, with possibly one exception, of sedimentary beds of Hauterivian to early Aptian ages in the lands adja- cent to the present Arctic Ocean (Mayne, 1949, p. 242; Imlay and Reeside, 1954, p. 241). The exception may exist in northwest Canada near the Arctic Ocean (J elet— sky, 1958, p. 9—15). Elsewhere near the present Arctic Ocean, Valanginian beds are overlain directly by Aptian, or Albian, beds. The northernmost records of marine beds of Hauterivian and Barremian ages in Europe are in the Russia platform, northern Germany, and northern England. In the Pacific Ocean area the northernmost records are in Japan and in southern- most British Columbia. Some of the items mentioned above, such as the ex- tinction of Buchz’a and the near extinction of ammonites are probably related in some way to restriction of the Arctic Ocean during middle Early Cretaceous time. The provincial aspect of the Valanginian—Hauterivian ammonites may be similarly related, but their con- spicuous lack of affinities with ammonites of the same ages in Mexico suggests that provincialism was also re— lated to some kind of barrier in Central America sepa- rating the Atlantic and Pacific Oceans. Further in- terpretations do not seem warranted at present. GEOGRAPHIC DISTRIBUTION The occurrences by area and locality of the fossils described herein is shown in table 4. The general posi- tion of each locality is shown on figures 34—36. De- 184 SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY TABLE 4—Geograph1'c distribution of the Early Cretaceous [localities 1069, 1071, 2156, 4394, and 25215, discussed in the text, do not contain ammonites, but are included in this table in order to show their OREGON Shasta series (lower part) Myrtle formation (middle and upper parts) 5 67 8 UWA536 McLellan UWA538 1 7273 McLellan 26789 Phyllapachvcema triniteme (Anderson) _____ cf. P. trinitense (Anderson) ___________ umpqmmum (Anderson) _____________ cf. P. umpquanum (Anderson) ________________ Hypophylloceras afi. H. 0mm: (Stanton) ________________________ Lytoocms autumn Anderson _____________________________________ satumale Anderson ______________ cf. L. traaki Anderson __________ Bochiunites paskmtaensia Anderson Crioceratites lama (Gabb) ........................................ cf. (0. yollabollium) (Anderson) ______________________________ of. (C. lehamaemis) (Anderson). _ sp. indet _______________________ Hoplocn'oceraa remondi (Gabb). cl. H. remondi (Gabb) _______________________________________ dumamme (Anderson) ______________________________________ sp. indet _________________________________ Shadicriocems off. S. whitmvi Anderson. ________ of. S. ponimte Anderson- 51) ............................... Acrioceras voyamtm Anderson ____________________________________ cf. A. uoyanum Anderson. - respertimtm (Anderson)_. hamlim’ (Anderson) .............. Pseudothurmunnia? ruuelli (Anderson) jupiter (Anderson) ........................................... Amhamulina wilmemis Imlay, n. sp. Homolaamites mutubilis (Stanton). . atantom' (McLellan) .................. Olcostephanus packi Imlay, n. Sp ................................. cf. 0. peckz' Imlay, n. sp ...................................... popenoei Imlay, n. sp. _ .. cf. 0 quadriradiatus Imlay. __ Poll/surchilea trichotomua (Stanton) Neocraapedites giganteua Imlay, n. sp ............................. Wellsia oregmmis (Anderson) .. ...... packardi (Anderson). . . .. ........ vigorosa Imlay, n. sp. _ . Hertleim’tes aguila (Anderso ............. gecki. Imlay, n. sp ............................................ Sim skim broadi Anderson. ........ loco/Mei (Anderson) .......................... sp. juv. afi. S. claws (Trautschold) ......... ._ sp. juv. off. S. proorediem Lahusen ........................... spp. juv ..................................................... Simbirskites? sp ........ Hollicites lucaai Imlay_. cf. H. lucaai Imlay... dichotomus Imlay, n. sp sp. juv. cf. H. dichotomus Imlay, n. sp ........................ inflows Imlay, n. sp .................. Spcetoniceras agnessenae Imlay, n. sp ........ .__. Neocomites? cf. N. 1111116113 Uhllg _____________ __.. Thurmannicems californicum (Stanton) .......................... wilcozi (Anderson) ........................................... jenkimi (Anderson).. .............. stippi (Anderson)... .. _ ...... sp.juv.cf. T.st1'pp1( _ . Hematite: riddlemis (Anderson) ................... truncatus Imlay, n. sp ........................................ Kilianella crassiplicata (Stanton). . ...... ...... cf K besairiez Spath ................ Sarasinella densicostota Imlay, n. sp ............... cf. S. denaicoatata Imlay, n. sp ................................ cf. S. 81103111710811 (Uhlig) ..................................... 111111111 (Stanton) ......... cf. S. Matti (Stanton). ungulata (Stanton) ______ cf. S. 1111911111111 (Stanton)...‘. ................................. Acamhodiacus sp. juv. off. A. subradiatus Uhlig. Spatidiscue oregmnsia Imlay, n. sp.....____._._.._.....____.__... _. .. .. _. ._ .. ._ .. ._ .. .. .. .. .. .. .. .. .. .. ._ .. .. ._ .. .. .. .. .. .. .. .. X .. ._ .. .. .. .. .. .. 22.2....i.I:iii...::IIS€IZIZI.:"""""" vlclv ..... I.III...I:I:I.22:12:...I:::I:S€:.II:: AMMONITES 0F EARLY CRETACEOUS AGE FROM THE PACIFIC COAST STATES 185 (Valanginian-Hauterivian) ammonites in the Pacific Coast States approximate geographic postion. Numbers 1—29 refer to numbers in flgs. 34436. Higher numbers are Geological Survey Mesozoic locality numbers] OREGON—Continued CALIFORNIA Shasta series (lower part)—Continued Myrtle formation (middle and upper parts) Ono formation (part) Paskenta formation of Anderson 9 10 11 12 13 1415 16 1718 19 20 21 22 23 24 25 26 27 28 29 ‘ hi— § 53 m s— a: M V‘ 186 tailed descriptions of the individual localities are given in the following table. Abbreviations used in the list include Univ. Wash. for the University of Washington, SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY UCLA for the University of California at Los Angeles, and Calif. Acad. Sci. for the California Academy of Sciences. No. on flgs. 34—36 Geological Survey Mesozoic localities Collector’s fleld numbers Localities of other institutions Collector, year of collection, description of locality, stratigraphic assignment, and age 5 17273 1681 25207 3352 25192 25193 25194 25197 25198 25199 25200 25201 25202 9.3.54.6 ____________ Sta. 10C ___________ Sta. 10E ,,,,,,,,,,, Sta. 10F ,,,,,,,,,,, Sta. 11 plus 20 ,,,,,, Sta. 11 plus 30 ....... Sta. 11A ,,,,,,,,,,, Univ. Wash. WA 535- Univ. Wash. WA 536- Univ. Wash. WA 538- Geology students at University of Washington, 1954. Spieden Blufi on northwest side of Spieden Island, San Juan County, Wash. Spieden formation of McLellan (1927). Valanginian. Mallory, V. S., 1955. Spieden Bluff on northwest end of Spieden Island, San Juan County, Wash. Spieden formation of McLellan (1927). Valanginian. McLellan, R. D., 1922425. From shales and sandstones near base of conglomeratic sequence at foot of Spieden Bluff on north side of Spieden Island, San Juan County, Wash. Spie- den formation of McLellan (1927). Valanginian. Landes, Henry, 1955; 3 miles east of Glacier in north center of sec. 3, T. 39 N., R. 7 E., Whatcom County, Wash. Nooksack group as used by Danner (1958), upper part. Valanginian. Erdman, C. E., 1936. Argillite on left bank of north fork of Nooksack River 2.1 miles below bridge in north center of sec. 3, T. 39 N., R. 7 E., Whatcom County, Wash., Nooksack group as used by Danner (1958), upper part. Valanginian. Misch, Peter, 1954. Hard black siltstone. Skyline Ridge trail near section line in north center of sec. 11, T. 39 N., R. 7 E., 2%. miles east of Glacier Creek bridge, Whatcom County, Wash., Nooksack group as used by Danner (1958), upper part. Valanginian. McLellan, R. D., 1922~24. Road cut on south bank of Nook— sack River about 2 miles east of Glacier in sec. 5, T. 39 N., R. 7 E., Whatcom County, Wash., Nooksack group as used by Danner (1958), upper part. Valanginian. Diller, J. S., 1895; 2 miles east of Myrtle Creek, Douglas County, Oreg. Valanginian. Imlay, R. W., and Dole, H. M., 1954. East side of Days Creek in NW% sec. 8, T. 30 S., R. 3 W., Douglas County, Oreg. Hauterivian. Diller, J. S., 1905. Month of Days Creek on the South Umpqua River, Douglas County, Oreg. Hauterivian. Imlay, R. W., Dole, H. M., and Peck, D. L., 1954; 108 ft above top of 3d conglomerate on west side of South Umpqua River in W1/2 sec. 16, T. 30 S., R. 4 W., Douglas County, Oreg. Valanginian. Same as 100. 25192 except 119 ft above 3d conglomerate. anginian. Imlay, R. W., Dole, H. M., and Peck, D. L., 1954. From upper part of beds containing Buchia crassicollis (Keyserling) on east side of South Umpqua River in WVz sec. 16, T. 30 S., R. 4 W., Douglas County, Oreg. Valanginian. Same as loc. 25192 except 291 ft above 3d conglomerate. anginian. Same as loc. 25192 except 434 ft above 3d conglomerate. Haute- rivian. Same as Ice. Hauterivian. Same as ice. Hauterivian. Same as 10c. Hauterivian. Same as loc. Hauterivian. Val— Val— 25192 except 504 ft above 3d conglomerate. 25192 except 619 ft above 3d conglomerate. 25192 except 629 ft above 3d conglomerate. 25192 except 669 ft above 3d conglomerate. AMMONITES 0F EARLY CRETACEOUS AGE FROM THE PACIFIC COAST STATES 187 No. on G§31r°5e1§al Collector's field numbers Localities of other Collector, year of collection, description of locality, stratigraphic assignment, and age figs. 34—36 Mesozoic institutions localities 5 25203 Sta. 11A plus 20”-- ____________________ Same as 10c. 25192 except 689 ft above 3d conglomerate. Hauterivian. 5 25204 _________________________________________ Imlay, R. W., Dole, H. M., and Peck, D. L., 1954. Sandy shale containing Wellsw oregonensis (Anderson) on east side of South Umpqua River in W}§ sec. 16, T. 30 S., R. 4 W., Douglas County, Oreg. Hauterivian. 5 25205 _______________________________________ Same as Ice. 25204 except near top of exposed sequence. Hauterivian. 5 25206 I54—7—22A _________ - A _ - _ _ _ . A Imlay, R. W., Dole, H. M., and Peck, D. L., 1954. North end of bridge across river at town of Days Creek, SEV4 sec. 9, T. 30 S., R. 4 W., Douglas County, Oreg. Hauterivian. 5 26252 ___________________ A A AA_ A . A A _ A Beason, John, and others, 1956. From South Umpqua River in SE% sec. 16, T. 30 S., R. 4 W., Douglas County, Oreg. Hau- terivian. 5 26257 ___A . . . _ ,.__A _ ,,,,,,,,,,,,,,,,,, A Beason, John, and others, 1956. Same as 10c. 25206. Hauterivian. 5 26787 __-_ . . . _ , _ _ , A A A A A A A__ Imlay, R. W., Imlay, M. J., and Imlay, R. L., 1957. Same as 10c. 25192 except 73 ft above 3d conglomerate. Valanginian. 5 26788 I57—8—12A_A_A_ A - AA A A _ A A A A _ Same as 100. 26787 except 119 ft above 3d conglomerate. Val- anginian. 5 26789 ____ . _ _ A A_ _ AAA A _ A A _ Imlay, R. W., and Peterson, Norman, 1957. Same as loc. 25192 except 175 ft above 3d conglomerate. Valanginian. 5 26790 ____ A . _ . _ A A A A. A A _ _ A A A Imlay, R. W., Imlay, M. J., and Imlay, R. L., 1957. About 119 ft above 3d conglomerate on east side of South Umpqua River, in W% sec. 16, T. 30 S., R. 4 W., Douglas County, Oreg. Val- anginian. 6 1245 W-, ._ . -._ . _ AA A A A A _ A A A A Stanton, T. W., 1894; 1% miles N. 10° W. of Fiddle, Douglas County, Oreg. Hauterivian. 7 26405 ____ _ A A A 1 AAA A ,,,,,,,,, A Brown, W. Q., 1893(7). About 2 miles west of Riddle in SWMNWl/fi sec. 16, T. 30 S., R. 6 W., Douglas County, Oreg. Valanginian. 8 718 __-- _ A., . _ A AA‘ AA A _ A A A A A A _ Becker, G. F., 1890. At Riddle, Douglas County, ()reg. Hauteri- vian. 8 724 A"--. , . . A _ AAA A A _ A A Samedataasloc.718. 726 718b-.. , - . A A A A A A A Same data as 100. 718. 8 905 __._ A A A . A A A A _ Brown, W. Q., 1891. Bank of Cow Creek just below town of Riddle, Douglas County, Oreg. Hauterivian. 8 1243 151_A _ , . A _ _ A _AA A A Stanton, T. W., 1894. 1A mile south of bridge across Cow Creek at Riddle, Douglas County, Oreg. Hauterivian. 8 1251 148 _______________ A A A A AAAAA Stanton, T. W., 1894. At west end of bridge across Cow Creek at Riddle, Douglas County, Oreg. Hauterivian. 8 1252 149 AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA Stanton, T. W., 1894. West bank of Cow Creek 400 yd below bridge at Riddle, Douglas County, Oreg. Hauterivian. 8 1823 _ - _ - _ AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA Rice, Claude. 1898. Near Riddle, Douglas County, Oreg. Haute— rivian. 8 25208 I57—7—21A AAAAAAAAAAAAAAAAAAAAAAAAAAAAAA Imlay, R. W., Dole, H. M., and Peck, D. L., 1954; 1A mile below bridge (northeast) across Cow Creek at Riddle near center of sec. 24, T. 30 S., R. 6 W., Douglas County, Oreg. Hauterivian. 9 1826 ___________________________________________ Brown, W. Q., 1898. Jerry Creek near Riddle in SVVMSEl/Q of sec. 22, T. 30 S., R. 6 W., Douglas County, Oreg. Hauterivian. 9 25210 _________________________________________ Imlay, R. W., and Dole, H. M., 1954. }4—1 mile above bridge at Riddle in northern part of sec. 26, T. 30 S., R. 6 W., Douglas County, Oreg. Hauterivian. 10 3923 6812 AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA Storrs, James, 1906. South line of sec. 31, T. 30 S., R. 5 “7., IA mile southeast of Ashes Ranch houses, Douglas County, Oreg. Hauterivian. 11 24449 FGW—5l _______________________________ Wells, F. G., Dole, H. M., 1951. Sec. 8, T. 32 S., R. 10 W., Coos County, Oreg. Hauterivian. 527569 0—60———2 188 SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY No. on Ggglflgal Collector’s fleld numbers Localities of other Collector, year of collection, description of locality, stratigraphic assignment, and age flgs.34—36 Mesozoic institutions localities 11 25211 I54«8—4A __________ ,_ __________________ Imlay, R. W., Wells, F. G., Dole, H. M., and Peck, D. L., 1954. Massive green sandstone on west side of road along Foggy Creek in NW1/48WV4 sec. 8, T. 32 S., R. 10 W., Coos County, Oreg. Same as loc. 24449. Hauterivian. 11 25212 __________________________________________ Imlay, R. W., Wells, F. G., Dole, H. M., and Peck, D. L., 1954. On Foggy Creek road 1 mile upstream from Eden Valley road in SELQ sec. 8, T. 32 S., R. 10 W., Coos County, Oreg. Haute- rivian. 11 25213 ________________________________________ Imlay, R. W., Wells, F. G., Dole, H. M., and Peck, D. L., 1954. On Foggy Creek road in northeast corner sec. 17, T. 32 S., R. 10 W., Coos County, Oreg. Hauterivian. 12 25214 ________________________________________ Imlay, R. W., and Dole, H. M., 1954. On road from Powers to Agness in north-central part of sec. 7, T. 35 S., R. 11 W., Curry County, Oreg. Hauterivian. 13 2078 8—9-99 ________________________________ Diller, J. S., 1899. Trail on south side of Rogue River 1 mile west of mouth of Illinois River, Curry County, Oreg. H auterivian. 13 2080 8—11—99 _______________________________ Diller, J. S., 1899. Sandstone 1% miles below Agness on south side of Rogue River, Curry County, Oreg. Hauterivian. 13 2093 0—37-99_‘____' _________________________ Diller, J. S., 1899. Left bank of Rogue River 11/4 miles below Agness, Curry County, Oreg. Hauterivian. 13 25215 ________________________________________ Imlay, R. W., 1954. At mouth of small creek just upstream from serpentine on north side of Rogue River about 1V2 miles below Agness in NE. corner of sec. 11, T. 35 S., R. 12 W., Curry County, Oreg. Hauterivian. 13 25216 ________________________________________ Imlay, R. W., and Dole, H. M., 1954. 100—200 ft above ser- pentine on south side of Rogue River 1% miles below Agness, Curry County, Oreg. Valanginian. 13 26450 ________________________________________ Lucas, Larry. South side of Rogue River 1% miles below Agness, Curry County, Oreg. Hauterivian. 14 26879 _______________________________________ Stringer, Calvin, 1957. About % mile southwest of Agness and y. mile south of section boundary in north central part of sec. 13, T. 35 S., R. 12 W., Curry County, Oreg. Hauterivian. 15 25275 _________________________________________ Peck, D. L., and Baldwin, E. M., 1954. East bank of Illinois River }4 mile above mouth of Lawson Creek, SE12 sec. 29, T. 35 S., R. 11 W., Curry County, Oreg. Valanginian. 16 2154 5446 ___________________________________ Diller, J. S, 1900. Elk River between the forks and the mouth of Blackberry Creek, Curry County, Oreg. Valanginian. 16 2155 5447 ___________________________________ Diller, J. S., 1900. Elk River below the mouth of Blackberry Creek, Curry County, Oreg. Valanginian. 16 2156 5448 ___________________________________ Diller, J. S., 1900. North Fork of Elk River 1 mile above the forks, Curry County, Oreg. Valanginian. 16 4384 8—4 ___________________________________ Storrs, James, 1907. y. mile above the forks of Elk River in the South Fork, Curry County, Oreg. Valanginian. 16 4386 8—3 ___________________________________ Storrs, James, 1907. % to 1 mile above the forks of Elk River on the South Fork, Curry County, Oreg. Valanginian. 16 4390 8—9 ___________________________________ Storrs, James, 1907. V3 mile below the forks of Elk River, Curry County, Oreg. Valanginian. 16 4391 8—10 __________________________________ Storrs, James, 1907. About 200 yd above the forks of Elk River on the North Fork, Curry County, Oreg. Valanginian. 16 4393 8—13 ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, Storrs, James, 1907. Fossils from loose pieces in the North Fork of Elk River about 11/6 miles above the forks, Curry County, Oreg. Valanginian. 16 4394 S—14 __________________________________ Storrs, James, 1907. Float }é—% mile above forks of Elk River in bed of North Fork, Curry County, Oreg. Valanginian. 16 6142 70970 _________________________________ Diller, J. S., 1909. From boulder at forks of Elk River in stream- bed, Curry County, Oreg. Valanginian. 17 2117 C—l37—99-----,___ ______________________ Diller, J. S., 1899. From big slide on Sixes River opposite mouth of Dry Creek, Curry County, Oreg. Valanginian. AMMONITES 0F EARLY CRETACEOUS AGE FROM THE PACIFIC COAST STATES 189 No figs. . on 34—36 Geological Survey Mesozoic localities Collector’s field numbers Localities or other institutions Collector, year of collection, description of locality, stratigraphic assignment, and age 17 18 19 19 20 21 21 21 22 22 22 22 22 22 23 24 25 25 26 26 2119 25217 2107 2136 2166 3339 4415 1062 2222 2223 2224 2225 1071 1009 1087 C—143—99 ______________________________ C—88—99 __________________________ , VVVVV 5269 ___________________________________ 5549 _______________ - - ,,,,,,,,,,,,,,,,,,, 6690_-____--_------ ,,,,,,,,,,,,,,,,,,,, S—2l __________________________________ Calif. Acad. Sci. 1691- UCLA 2816____.---- Calif. Acad. Sci. 1353_ ____________________ Calif. Acad. Sci. 113- ____________________ Calif. Acad. Sci. 1665- 69, 69a, 69b, 72 ,,,,,,,,,,,,,,,,,,,,,,,,, 15 ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, Sta. 90 _________________________________ Divelbise, 1899?. From gravel of Sixes River near Dry Creek, Curry County, Oreg. Valanginian. Peck, D. L., 1954. Along beach V4 mile north 01 Rocky Point and 2 miles south of Port Orford in NWV; sec. 15, T. 33 S., R. 15 W., Curry County, Oreg. Hauterivian. Diller, J. S., 1899. Point on ridge ‘A mile S. 10° W., from Bald Mountain, Curry County, Oreg. Valanginian. Diller, J. S., 1899. South end of Bald Mountain, Curry County, Oreg. Valanginian. Diller, J. S., 1900. Simmons Cut, 3 miles north of Waldo, Josephine County, Oreg. Hauterivian or Barremian. Diller, J. S., and Storrs, James, 1905. A deep cut, 4 miles north of Waldo, that drains from Logan Mine to Illinois River, Josephine County, Oreg. Hauterivian. Storrs, James, 1907. Calcareous nodules in shale and sandstone 100 yds. south of Clements house in Valley of Redding Creek, Trinity County, Calif. Hauterivian. Anderson, F. M., 1929. From Clements Ranch on Indian Creek 4 miles east of Douglas City, Trinity County, Calif. Haute- rivian. Rodda, Peter, 1953. Hard sandy dark-gray mudstone. Bed of Redding Creek just north of junction with Panwauket Gulch on section line between secs. 28 and 29, T. 32 N., R. 9 W., Trinity County, Calif. Hauterivian. Storrs, James, 1893. From Eagle Creek between its mouth and Ono, Shasta County, Calif. Hauterivian. Stanton, T. W., 1900. On stage road 1 mile east of Ono, Shasta County, Calif. Hauterivian. Stanton, T. W., 1900. Near mouth of Byron Creek (now called Rector Creek) at Ono, Shasta County, Calif. Hauterivian. Stanton, T. W., 1900. On North Fork of Cottonwood Creek 200—400 yd above bridge at Ono, Shasta County, Calif. Hauterivian. Stanton, T. W., 1900. On North Fork of Cottonwood Creek between Ono bridge and Eagle Creek, Shasta County, Calif. Hauterivian. Anderson, F. M., and Hanna, G. 1)., 1928. On highway grade near bridge about }4 mile south of Ono, Shasta County, Calif. Hauterivian. Anderson, F. M. Head of North Fork of Mitchell Creek 315-4 miles southwest of Ono, Shasta County, Calif. Hauterivian. Anderson, F. M., 1929. From Duncan Creek 1 mile north of Maxey’s house, Shasta County, Calif. Hauterivian. Diller, J. S., Storrs, James, and Stanton, T. W., 1893. About V2 mile west-northwest of Stephenson’s Ranch houses of 1893 and 11/; miles west-southwest of Pettyjohn’s houses. North- central part of sec. 30, T. 27 N., R. 7 W., Tehama County, Calif. Valanginian. Diller, J. S., Storrs, James, and Stanton, T. W., 1893. About 200 yds. west of Stephenson's Ranch houses on Cold Fork of Cottonwood in sec. 30, T. 27 N., R. 7 W., Tehama County, Calif. Valanginian. Diller, J. S., and Storrs, James, 1893. About halfway between the Lowry and Wilcox Ranch houses. South—central part of sec. 28, T. 25 N., R. 6 W., Tehama County, Calif. Valangin- ian. Diller, J. S., Storrs, James, and Stanton, T. W., 1893. Same as loc. 1009. 190 SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY Geological Survey Mesozoic localities No. on figs. 34—36 Localities of other institutions Collector’s field numbers Collector, year of collection, description of locality, stratigraphic assignment, and age 26 1088 Sta. 91 ____________ 27 1010 16 and 17 __________ 27 1091 Sta. 94 ____________ 27 1092 Sta. 95 ____________ 27 27 1093 2265 27 2266 2267 27 2268 27 2269 27 5339 28 1001 28 1095 98 _________________ 28 Calif. Acad. Sci. 144- 28 Calif. Acad. Sci. 33502. 29 26404 Diller, J. S., Storrs, James, and Stanton, T. W., 1893. About % mile north of Wilcox Ranch houses in south-central part of sec. 33, T. 25 N., R. 6 W., Tehama County, Calif. Valangin- lan. Diller, J. S., and Storrs, James, 1893. About }.’1 mile northwest of Shelton’s Ranch houses in north-central part of sec. 9, T. 24 , N., R. 6 W., Tehama County, Calif. Valanginian. Stanton, T. W., Diller, J. S., and Storrs, James, 1893. About % mile east of Wilcox Ranch houses in NE. corner sec. 4, T. 24 N., R. 6 W., Tehama County, Calif. Valanginian. Stanton, T. W., Diller, J. S., and Storrs, James, 1893; }é—% mile northeast of Wilcox Ranch houses on road from 'Lowry’s Ranch to Paskenta in SE. corner sec. 33, T. 25 N., R. 6 W., Tehama County, Calif. Hauterivian. Stanton, T. W., and Storrs, James, 1893. Same as 100. 1010. Stanton, T. W., 1900. South-central part of sec. 28, T. 25 N., R. 6 W., Tehama County, Calif. Hauterivian, Stanton, T. W., 1900. Same as loc. 1091. . Stanton, T. W., 1900. 400—500 feet higher stratigraphically tha 10c. 2266. K934 mile north of loo. 2266 in SE. corner sec. 33, T. 25 N., R. 6 W., Tehama County, Calif. Hauterivian. Stanton, T. W., 1900. Concretions in shale at same level as 100. 2267. About 974 mile southeast of Wilcox Ranch houses in east-central part of sec. 4, T. 24 N., R. 6 W., Tehama County, Calif. Hauterivian. Stanton, T. W., 1900. Same as 100. 2268 except 8 ft. lower stratigraphically. Hauterivian. Storrs, James, 1908; }{; mile west of Wilcox Ranch houses in NWV4 sec. 4, T. 24 N., R. 6 W., Tehama County, Calif. Valan- ginian. Diller, J. S., and Storrs, James, 1893; }é mile east of Henderson’s house on upper road leading from Paskenta to Lowry’s Ranch. NW}£ sec. 29, T. 24 N., R. 6 W., Tehama County, Calif. Valanginian. Stanton, T. W., and Storrs, James, 1893; 1,500—2,000 ft below top of beds containing Buchia crassicollis (Keyserling). Same as 100. 1001. Valanginian. Collector unknown. From south bank of McCarthy Creek oppo- site Burt’s Ranch house in NE}{; sec. 29, T. 24 N., R. 6 W., Tehama County, Calif. Valanginian. Anderson, F. M., 1,200 ft southeast of Burt’s Ranch house on McCarthy Creek in SE% sec. 29, T. 24 N., R. 6 W., Tehama County, Calif. Valanginian. This locality was listed by An- derson (1938) as 2398 and 3398. Lawson, A. C., 1894. From mouth of Strawberry Canyon near Berkeley, Alameda County, Calif. Valanginian. SUMMARY OF RESULTS The Early Cretaceous (Valanginian-Hauterivian) ammonites from the Pacific coast discussed herein in- clude 26 genera and 65 species. Of these 65 species, 13 are described as new. Of the 26 genera, 4 were de- scribed as new in a preliminary paper (1957, p. 275— 277) published during the course of this study. During the Valanginian the family Berriasellidae was dominant in numbers and genera, and the Olcoste- phanidae was of secondary importance. During the Hauterivian the Olcostephanidae was dominant, and the Ancyloceratidae was of secondary importance. Of somewhat lesser importance are the Phylloceratidae and Lytoceratidae. The Bochianitidae, Hemihoplitidae, Ptychoceratidae, and Holcodiscidae are represented by only a few specimens. The Craspeditidae is probably represented by the genus H omolsomz'tes, which occurs locally in fair abundance in the upper Valanginian. AMMONITES OF 123“ EARLY CRETACEOUS AGE FROM THE PACIFIC COAST STATES 122D 121D 49 —_‘¥ ‘,%‘¥ _ _7 _ __ _g A N A_l_) A ____.-__———- WASHINGTONO’W Glacieroz < W H A T C 0 M \ \ 10 o 10 20 30Miles 1 G _/ N |_L_i_‘__g_l_.__J_.—L___J “Q ( _______——————-—-——I_ i 0 K A N O G A _ by Friday Harbor / Winthropo S K A G I T \K (A A V > /\i 489* JiAiM SNOHOMISH H - I Everett < _____ _ 1 _ g _+i \ c H E L A N J EFFERSON ‘ __ ——_—_——‘2\ \ Seattle /\\ K 1 N G ,/ ‘ \ fl ‘ v\ t \\ ’ K 1 T T I TA S \\ "X “\\____ FIGURE 34.—Index map of Early Cretaceous localities in northwestern Washington. The Valanginian beds are considered to include four ammonite zones. From oldest to youngest these zones are represented by the species Kilianella omssz'plicata (Stanton), Samsinella hyatti (Stanton) , H omolsomz'tes mutabilis (Stanton), and Olcostephanus pecki Imlay, n. sp. The lower two zones are provisional because they are based on only a few collections. The zone of Olcostephanus peckz' is of late Valan- ginian age because it directly underlies lower Hauteriv- ian beds, because it occurs at the top of the range of the Valanginian species, Buchia crassicollis (Keyser- ling), and because the index species is similar to 0. jeamwti (d’Orbigny) which occurs in France in beds of late Valanginian to early Hauterivian age. The zone of H omolsomites mutabilis is considered to be late Valanginian because of the association of Acantlwdiscus, Neocmspedites, Uriocemtites, Samsz'n- ella, ahnd Polyptychites and because of its stratigraphic position in the upper part of the range of Buchz’a crossi— -collz's (Keyserling). The zones of Sarasz'nella hyatti and Kilianella massi- plicata are considered to be of middle Valanginian age on the basis of stratigraphic position below the zone of H omolsomites mutabilis, on the resemblances of Kilia- nella crassiplicata (Stanton) and its associate Thur/man- nicems caliform'cum (Stanton) to species of middle Valanginian age elsewhere, and on the presence of But-Ma crassicollis (Keyserling) rather than species of Buchia of Berriasian or early Valanginian age. The Hauterivian beds are considered to include five ammonite zones. From oldest to youngest these are designated as the Wellsia oregonensz's zone, W. packardi zone, Hollisites dichotomus zone, Hamlin-Broad zone of Anderson, and Hertleim'tes agm’la zone. Of these, only the zones of Wellsia oregonensz's and of Hertleim'tes aguz'la are well substantiated. The zone of Hertleimites aguila is considered to be late Hauterivian in age because of its stratigraphic position above beds containing the middle to late Hauterivian ammonite Simbirslcz'tes and below beds containing the Barremian ammonites Pulchellz'a and Amylocems. A Hauterivian rather than a Barremian age is indicated, also, by the presence of Uz'z'ocemtz'tes and Hoplocm'ocems, as most of the records of these genera are from beds of Hauterivian age. Futhermore, the resemblance of H ertleim'tes to Umpedodz'scus sug- gests a late Hauterivian age. The Hamlin-Broad zone of Anderson is either late middle, or late Hauterivian on the basis of the associ— , ation of the ammonites H oplocriocems, Acm'ocems, and 192 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 124° 123° l ! ORoseburg l | I (—1 D 0 U G L A s C O O S 430 Myrtle Creeko X3 I“ Is *4 ——_L‘_ | X7 QRiddle 5)PDays Creek L 9x 8 10 X LL‘fi OPowers l JJ | j Jrrr x17 r X11 1 “U L' r \ __JJ Port Orford I. l /L I_____,_,_r’_ g L— a 3> x16 1 F ’ —L"1—\_ r—J—F— fi—LJF'J— ('3 x19 / ~ l Agness 12 / '71 lgxcfila ) l 15 ~ X <~,_\_/) C U R R Y C} ) Grants PassO Gold Beach \/ J A C K S 0 N k—~—¢-\/ J O S E P H I N E O \W oMedford O \8 {Tl / > x) I 'Z > X2o / Waldoo oTakilma | 42" _ \A L“ __ OREGON __ C A L I F O R N I A 10 0 10 2'0 jOMiles I I I I I I I FIGURE 35.—Index map of Early Cretaceous localities in southwestern Oregon. Simbirs/cites, on the probability that N eocomites mssel- Zi Anderson and Thu/madam}; jupz'ter Anderson belong to the genus Pseudothur’mannia, and on the strati- graphic position of the zone below H ertleim'tes aguz'la. The zone of Hollisz'tes dichotomus is of middle to early late Hauterivian age, based on the presence of the ammonibe Simbirslcites and the resemblance of the genus H Ollisites t0 Speetonicems in Europe. The zone is not much younger than the zone of WeZLsia» packardz' and W. oregonensis, as it occurs only a little strati- graphically above these zones near Riddle, Oreg., and it contains a number of species that range upward from those zones. It is not identical with the Hamlin-Broad zone of Anderson because it has only a few ammonite species in common with that zone and none of the species that range upward from the Wellsia packardi zone have been found in the Hamlin—Broad zone. Fau- nally the Hollc'sites dichotomus zone appears to bridge an interval between those zones and consequently to correlate with the lower part of the range of Simbz'w- skites in Europe. The zones of Wellsia packm'di and W. oregonensis are considered to be of early Hauterivian age because of their stratigraphic position above beds containing the Valanginian Buchia crassicollz'a (Keyserling) and below beds containing the middle to late Hauterivian ammonite Simbz'rskites. The zones are not older than the Hauterivian because they contain the ammonite AMMONITES OF EARLY CRETACEOUS AGE FROM THE PACIFIC COAST STATES 193 124° 122° 120° 42° __ __ O__R E G 9_N __ __ __ __ __ 7 C A L I F 0 R N I A l a i ' I j ' I Ik ! “IL I . \ /“ ‘ I 7R [A] 3¢_________1 ___________ / \_.\ J T > \m ff ' 0| r\\/ I ll >| I L“ 2 ‘I 21 / l a: i X/j) o Redding ! o i :> I x22 _ _L___ :U U i / afifasm-w/fw E 7. Z > . "\x HI I x25 0 Red Bluff 43 L»/ \\ an _'L X26 / 2 \\ §27 oCorning / ' V‘I 28 ‘r_’ K | _______ A \ - A \\ If \ _______ ‘_ r” ' ,r’\\_ _I H-_-m_, ‘ // , H ___ \-\ #3:?“ l/ /—‘*‘ ( \‘ y &— Jl/ fP—l \___ 52 11’ ///’\\v/‘ S ,‘h “x i / , ‘ \VJ \ “PM ({ L \‘ \fiSacramghfo ’\ /// ‘ ‘ ”"’W A V” "’Z/— A \\ 2: 1 If ‘ /’/ //\\ ,_ I \‘ r Tp_/“/—\,.// ’ \__\ l K I \ // /~V‘<:/A)( \\ 1/ 3 \ 2 ‘ 29 L / SAN FRANCISCO XL ‘ /’/{ ,»/')\‘ //’N"‘ 10 0 1o 20 30 40 50 Miles V ' /’ \X ___|__—l_—J—.L__J—J / k / // \ _./——““ /// \ FIGURE 36.—Index map of Early Cretaceous localities in northern California. 194 Spitidz'scus. An age not younger than early Hauterivi- an is indicated by the resemblance of Wellsia, to N ea— cmspedites and of Hannaites to Leopoldia. The ammonites found in the Valanginian and Hau- terivian beds of the Pacific Coast States have a local aspect, owing to the presence of genera not found else- where and to the absence of genera that are common elsewhere. Provincial genera include Wellsz'a, Han- naz'tes, H ole'sz'tes, and H ertleinites. Besides these genera Shastiom'oceras has been found elsewhere only in British Columbia and Japan, and Homolsomites has been found elsewhere only in British Columbia and Greenland. Conspicuous by their absence are the am- monites Rogersites, Valanginites, and Distolocem‘s in the Valanginian and Leopoldz'a in the Hauterivian. The affinities of the Valanginian ammonites from the Pacific Coast States are predominantly with those of the Mediterranean province, as shown by comparisons of species of the genera Kilianella, Sarasz'mlla, Thur- ma'rmz'cems, Acanthodiscus, N eocomz'tefl, Olcoste- phanus, and Bochiam'tes. In contrast with the Mediter- ranean province, however, there is a striking scarcity of members of subfamily Olcostephaninae. Also, a central to northern Eurasian aspect is shown by the presence of Polyptychz'tes and N eocraspedites. The genus H omolsomz'tes is probably of boreal or northern Pacific origin. The affinities of the Hauterivian ammonites of the Pacific Coast States are mostly With those of northern Eurasia, particularly with those in northern England, northern Germany, and central Russia. A contrast with the Hauterivian in most parts of the world is fur- nished by the absence of Leopoldia, Acanthodiscus, and Distolocems and by the presence of the provincial gen- era Wellsz'a, H annaites, H ollz‘sz’tes, and H ertelez’m’tes. The oldest Cretaceous beds exposed in Oregon and California contain genera of ammonites and species of Buckie of Valanginian age. They have not yet fur- nished fossils of Berriasian age. As the Valanginian beds directly overlie beds of Late Jurassic (Portland- ian) age, a break in deposition is indicated. Such is supported by the common occurrence of a massive conglomerate at the base of the Cretaceous. In contrast, the oldest beds exposed in northwest Washington con- tain species of Buck/5a which have been identified by J. A. Jeletsky, of the Canadian Geological Survey, as being of Berriasian age (written communication from Wilbert R. Danner dated Oct. 2, 1957, concerning fossil identifications by J. A. J eletsky). The nature of the Jurassic-Cretaceous contact in all three States needs more investigation before the presence or absence of an unconformity can be established beyond doubt. SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY SYSTEMATIC DESCRIPTIONS Genus PHYLLOPACHYCERAS Spath, 1925 Phyllopachyceras trinitense (Anderson) Phyllocems tm‘m‘tense Anderson, 1938, Geol. Soc. America Spec. Paper 16, p. 140, pl. 55, figs. 3—6. This species is characterized by its stout whorls, by coarse, sparse ribbing that is continuous across the venter, and by a smooth area on the flanks near the umbilicus. It was recorded by Anderson (1938, p. 140) from Redding Creek, eastern Trinity County, Calif, and from the Riddle area, Douglas County, Oreg., in beds that he considered to represent the Valanginian stage of the Early Cretaceous. The Geological Survey collections from Douglas County, Oreg., that contain this species likewise contain other ammonites that the writer considers to be of early Hauterivian rather than Valanginian age, as discussed herein. In addition the species has been found in Coos County, Oreg., at Mes- ozoic locality 25211 and in Curry County, Oreg., at Mesozoic locs. 2080 and 2093 associated with ammonites of middle Hauterivian age. The species has not been identified definitely in beds that the writer considers to be of Valanginian age, although one fragment possibly belonging to the species was obtained with BucIm'a cras- sz'collis (Keyserling) at Mesozoic 100. 25193, near Days Creek, Douglas County. Associated with P. tfim‘teme (Anderson) at Mesozoic locs. 1243, 2080, 2093, and 25211 in southwest Oregon are some nearly smooth specimens of Phyllopachg/cems that differ from P. tm'm'tense only by having much weaker ribbing. They resemble P. trinitense in shape and in sparseness of ribbing and are probably only a variant. Localities: USGS Mesozoic locs. 718, 1243, 1252, 2080. 2093, 25206, 25211, 26257; GAS 10c. 1691. Phyllopachyceras umpquanum (Anderson) Ph‘ylloceras umpquanum Anderson, 1938, Geol. Soc. America Spec. Paper 16, p. 143, pl. 30, figs. 9, 10. Phyllocems oreganense Anderson, 1938, idem, p. 144, pl. 30, fig. 8. Phyllocems myrtlense Anderson, 1938, idem, p. 144, pl. 30, fig. 7. Phyllopachycems umpquanum (Anderson) differs from P. tm’m'tense (Anderson) by being more com— pressed, somewhat smaller, and by having finer, denser ribbing. It is associated with P. trim'teme (Ander— son) in beds of early and middle Hauterivian age in Oregon and has not been recorded from beds of Valanginian age. The holotype specimens of the three species P. urmp- ' quanum (Anderson), P. oregomnse Anderson, and P. myrtlense Anderson were obtained from a single local— AMMONITES OF EARLY CRETACEOUS AGE FROM THE PACIFIC COAST STATES ity 1 mile east of Riddle, Douglas County, Oreg. These species were distinguished from each other by trifling differences in whorl shape and in the size of the umbili- cus that were probably induced by compaction of sedi- ments. They do not appear to the writer to be worthy of even subspecific rank. Accordingly only the name of the first-mentioned species is considered to be valid. Localities: USGS Mes. locs. 718, 724, 726, 905, 1252, 24449, 25198, 25199, 25200, 25208, 25211, 25212, 26257. Genus HYPOPHYLLOOERAS Salfeld, 1927 Hypophylloceras afi‘. H. onoense (Stanton) Plate 25, figure 4 Some specimens of H ypophyllocems, associated with H ertleim’tes aguila (Anderson), differ from H. onoense (Stanton) (1895, p. 74 [1896]) by having a stouter whorl section, a broader venter, and slightly coarser ribbing. At a whorl height of 46 mm, the whorl thick— ness is 26 mm. On a specimen of H. onoense (Stan- ton) at the same whorl height. the whorl thickness is 23 mm. Similar specimens occur in Oregon in beds of early Hauterivian age. Figured specimen: USNM 129672. Localities: USGS Mes. locs. 1092, 1252, 2223, 2225, 25206. Genus LYTOGERAS Suess, 1865 Lytoceras aulaeum Anderson Lytoceras aulaeum Anderson, 1938, Geol. Soc. America Spec. Paper 16, p. 146, pl. 14, figs. 1—-4. This species is distinguished from L. satumle An- derson by its whorl sections being higher than wide and in certain details of the ornamentation that have been well described and illustrated by Anderson. The holo- type was recorded by Anderson (1938, p. 147) from California Academy Science locality 113, about 4 miles southwest of Ono, Shasta County, Calif. He mentions the occurrence of fragments as high as the lower beds of his Horsetown group. For the same area Murphy (1956, p. 2113) shows that L. aulaeum has a range co- extensive with that of “Neocmspedites” agm’la Ander— son. These occurrences in the writers opinion are of middle to late Hauterivian age. Farther south in the Paskenta area of Tehama County L. aulaeum occurs with “Neocmspedz'tes” aguz’la Anderson at Mesozoic locality 2267, which is about two- thirds of a mile northeast of the Wilcox Ranch build- ings and from 400 to 500 feet above the sandy beds con- taining Buchia crassioollz's (Keyserling). From the top of these sandy beds at Mesozoic locality 1091, Stan- 195 ton (1895, p. 17, 75, pl. 13, fig. 11 [1896]) obtained a specimen of Lytocems that has the whorl section and ornamentation characteristic of L. aulaeum, rather than of L. satmmale, as suggested by Anderson (1938, p. 145). This occurrence is of late Valanginian age. Stanton also obtained a specimen belonging to L. aulaeum from the base of the shales overlying the Buckie-bearing beds at a spot (USGS Mes. loc. 2265) about halfway between the Wilcox and Lowry Ranches. In southwestern Oregon, L. aulaeum Anderson has been obtained at Mesozoic localities 718, 1252 and 25210, near Riddle, Oreg., in association with other ammonites of early to middle Hauterivian age. On the basis of these occurrences, L. aulaeum An- derson ranges in age from late Valanginian to late Hauterivian and, therefore, overlaps the upper part of the range of L. satmmale Anderson. Localities: USGS Mes. 1005. 718, 1091, 1092, 1252, 2225, 2265, 2267, 25210; OAS 10c. 113. Lytoceras saturnale Anderson Lytoceras suturnale Anderson, 1938 Geol. Soc. America Spec. Paper 16, p. 145, pl. 13, fig. 1. Lytoceras saturnale is characterized by‘ its whorl sec- tions being much wider than high. Anderson (1938, p. 146) noted that the species “has a stratigraphic range throughout the Paskenta group in its type dis- trict, and has been found in the Cottonwood district at various levels in the same group.” The only specimens of L. satumale in the Geological Survey collections are from the sandy beds containing Baa/Lia, crmssicollis (Keyserling) in the Paskenta area between the Lowry and Wilcox Ranches, Teham'a County. One collection (Mes. 10c. 1087) was made near the top of these beds about 1 mile north of the Wilcox Ranch houses, and the other (Mes. 100. 5339) was made near the base of the sandy beds about one- third of a mile west of the Wilcox Ranch buildings. These collections are dated by other ammonites present as late and middle Valanginian respectively. Lytocerax saturnale Anderson is probably uncommon in the Cottonwood Creek area of Western Shasta County, considering that Murphy (1956, fig. 6) did not find any in that area after many months of careful searching and that Anderson (1938, p. 47) actually lists only two such occurrences. One of these» (Calif. Acad. Sci. 100. 113), from about 4 miles southwest of Ono, contains the ammonite Simbérskites of middle Hauterivian age. There is “no published evidence that L. satumale ranges as high as the zone of “Neocm‘spe- difes” aguila Anderson. 196 Genus CRIOCERATITES Léveiué, 1837 Crioceratites latus (Gabb) Plate 26, figures 6, 7 Crioceras latus Gabb, 1864, Paleontology Calif., v. 1, p. 76, pl. 14, fig. 25b, pl. 15, figs. 25, 25a. Gabb. Paleontology Calif., v. 2, p. 218, 1869. Orioceras latum Gabb. Anderson, 1938, Geol. Soc. America Spec. Paper 16, p. 200, pl. 55, fig. 1. Crioceras duneanense Anderson, 1938, Idem, p. 200, pl. 55, fig. 2. This species is assigned to Uriocemtites, as that genus is generally defined, on the basis of having crioceratid coiling, ribs of 2 sizes, and from 1 to 3 rows of tubercles on the major ribs. As the major ribs on 0. latus (Gabb) are separated by only from 3 to 5 ribs, the species might be assigned to the genus E mm'm'eems, which Sarkar (1955, p. 21, 74, 75) separates from Urioeeras on the basis of having much stronger trituberculation more major ribs, and fewer minor ribs. The tuberculation on 0. latum (Gabb) , however, is not as strong as on most species that Sarkar (1955, p. 7 5— 98) assigns to Emem'ciceras and is of nearly the same strength as that of the trituberculate Orioceratites mlani (Kilian) (1907, p. 224, pl. 4, figs. 3a, b; d’Orbigny, 1840, p. 459, pl. 113, figs. 1—4). Orioceras dime-enema Anderson was separated from 0’. Zatus (Gabb) by Anderson ( 1938, p. 201) because it was more tightly coiled and had more minor ribs be- tween major ribs. These differences seem minor, how— ever, when the holotype of 0'. dmwanense is compared 1 with the inner whorl of the holotype of 0. Zatus ( Gabb) (Anderson, 1938, pl. 55, fig. 1). At a comparable size both holotypes have from 4 to 5 minor ribs between major ribs and both have equally prominent triber- culation of the major ribs. Such close resemblances, plus Anderson’s record (1938, p. 201) that both species occur at the same place (Calif. Acad. Sci. 100. 1665), suggest rather strongly that 0. dumanese is only a variant of 0. lotus and is not worthy of even a sub- specific name. The occurrences of 0. latus (Gabb) recorded by An- derson (1938, p. 200) are mostly from the Cottonwood Creek area of Shasta County, Calif, in beds containing Simbirskites broadi Anderson and “Neocraspedites” aguila Anderson. The writer considers these to be of middle and late Hauterivian age respectively. Localities: CAS locs. 113, 1353, 1665; USGS Mes. Ice. 4415. Crioceratites cf. 0. tehamaensis (Anderson) One specimen from Tehama County consists of parts of two whorls similar to “Holeodiscus” tehamaensis Anderson (1938, p. 191, pl. 83, fig. 5). The largest part is similar to the adoral end of the holotype of “H.” tehamaensis, but differs by having more pronounced SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY tubercles and only one minor rib between major ribs. The smaller part has from 10 to 12 minor ribs between the major ribs. N onfigured specimen: USNM 129845. Locality: USGS Mes. Ice. 1092. Crioceratites cf. 0. yollabollium (Anderson) One specimen from the Riddle area in Oregon is probably identical with “H oploerioeeras” yollabollium Anderson (1938, p. 308, pl. 72, fig. 2) from Trinity County, Calif. The specimen from Oregon has from 2 to 4 minor ribs between major ribs. The major ribs bear pronounced umbilical tubercles and somewhat weaker lateral and ventral tubercles. Some of the minor ribs bear ventral tubercles, also. The holotype of Orioceratites yollabollium (Ander- son) has umbilical swelling and traces of lateral tuber— cles. As the venter is not preserved its characteristics are unknown. It does not sh(w rib bundling at the umbilical border in the manner characteristic of the genus H optoerioeems. N onfigured specimen: USN M 129841. Locality: USGS Mes. 10c. 1826. ,Crioceratites sp. indet. Plate 26, figures 1. 5 Orioceras lame Gabb. Stanton, 1895, U.S. Geol. Survey Bull. 133, p. 17, 18, &3 [1896]. The specimen, referred by Stanton to Orioceras lam; Gabb, was obtained at the top of the beds containing Buehia cras'sieollis (Keyserling) in association with other ammonites of late Valanginian age. It differs from 0. lame Gabb by having from 8 to 9 minor ribs instead of 3 to 5 minor ribs between the major ribs, by bifurcation of some of the minor ribs high on the flanks, by the major ribs bearing much weaker umbilical and lateral tubercles, and by the ribbing in general being finer, and more fiexuous. Its general appearance is similar to that of Orioeemiite‘s dwvali Léveillé as fig— ured by d’Orbigny (1842, pl. 113, fig. 1) from the Hauterivian of France. Figured specimen: USNM 23101. Localities: USGS Mes. Ice. 1009. Fragments probably be longing to the same species as the specimen illustrated were obtained in Oregon from beds of Valanginian age at Mes 10c. 25275 and of early Hauterivian age at. Mes. locs. 25198, 25199, and 26252. Genus HOPLOCRIOCERAS Spath, 1924 Hoplocrioceras remondi (Gabb) Plate 24, figures 1—4, 8, 9, 11, 12 Orioeeras ( ?Ancyloceras) remondi Gabb, 1864, Paleontology Calif., v. 1. p. 75, pl. 14, figs. 24, 24a. AMMONITES OF EARLY CRETACEOUS AGE FROM THE PACIFIC COAST Ancyloceras remondi Gabb, 1869, Paleontology Calif., v. 2, p. 138, pl. 23, fig. 17. Hoplocriocems remondi (Gabb). Anderson, 1938, Geol. Soc. America Spec. Paper 16, p. 201, pl. 62, figs. 1—3, 5 [not pl. 63, figs. 1, 2]. The Geological Survey collections contain six frag- mentary specimens of this species. The whorls are sub— quadrate in section, higher than wide. The dorsum and flanks are flattened. The venter is slightly convex on the inner whorls and is arched on adult whorls. The shell is ornamented with three rows of tubercles and with flexuous fasciculate ribs. The internal molds are marked in addition by shallow constrictions. The ribs on the dorsum are rather weak, arch forward strongly, and become faint at the umbilical edge. The ribs on the flanks arise in two’s, or rarely three’s, from umbilical tubercles or in part arise freely at the umbili- cal edge. They incline forward on the flanks in a gently flexuous manner and arch forward weakly on the venter. On the lower part of the flanks, the ribs are broad, low, and wider than the interspaces; on the middle of the flanks, they are sharp and narrower than the inter- spaces; on the upper part of the flanks and on the venter, they are broad, fairly strong and about as wide as the interspaces. Some ribs bifurcate high on the flanks or even on the venter. The shells are distinctly trituberculate, although one row situated on the flanks is so weak that neither Gabb nor Anderson mentioned its presence. On a small speci- men, such as shown on plate 24, figures 1, 3, the umbili- cal tubercles are blunt and low, give rise to 2 or 3 ribs, and are separated from each other by 1 to 3 flank ribs that arise freely. On this speciment nearly every rib bears a tiny tubercle along a zone slightly above the middle of the flanks. The ventral tubercles are blunt and low but are a little stronger than the umbilical tubercles. Most ventral tubercles mark the junction of two lateral ribs. Between adjoining ventral tubercles are from 1 to 4 ribs that are nontuberculate, or only weakly swollen. On larger septate whorls (pl. 24, fig. 8) the umbilical tubercles become more prominent and develop a for— ward twist. The lateral tubercles weaken and nearly disappear, but generally a few are present on some of the flank ribs that pass from the umbilical tubercles. Toward the aperture all ventral tubercles weaken gradually and all ribs tend to develop weak ventral tubercles. One large specimen (pl. 24, figs. 9, 12) is probably an adult Of the species. It shows parts of two inner whorls and nearly half a whorl of body chamber. On the body chamber the umbilical tubercles are distinct, but variable in strength; lateral tubercles are absent; STATES 1 97 and weak ventral tubercles are present only at the be— ginning of the body chamber. The resemblance of Hoplocm'ocems remondz’ (Gabb) to H. Zaeviusculum (Von Koenen) (1902, p. 350, pl. 28, figs. 4—6) from Germany was the basis for Anderson’s (1938, p. 201) generic assignment. The ribbing of the two species is closely similar. H. remo’ndi is differen— tiated by more open coiling, a higher whorl section, probably more fasciculate ribbing, and the presence of lateral tubercles. The presence of lateral tubercles does not bar an assignment to Hoploom‘ocems because other species with lateral tubercles were assigned by Spath (1924, p. 78) to H oplocriocems when he proposed the genus. H. remondz' (Gabb) also shows some resemblance to Pseudothurmanm'a mortilletz' (Pictet and Loriol) (1858, p. 21, pl. 4, figs. 2a—d) from Switzerland, but differs by having lateral tubercles and a rounded in- stead of a truncated venter. The presence of a rounded venter on H. remondi at all stages of growth bars any assignment to Pseudothurmannia, even though the adults of certain species of that genus, according to Sarkar (1955, p. 152), acquire rounded venters and lateral tubercles. Anderson (1938, p. 47, 202, 307) records H. remondz' (Gabb) from several stratigraphic levels in the Cotton— wood Creek area near Ono, Calif. One is in the zone of “Neocraspedites” aguila (CAS 100. 1353), which the writer considers of late Hauterivian age. Another is in the underlying zone of Sémbirskites broadz' (CAS 1665), which is of middle Hauterivian age. Anderson (1938, p. 307, pl. 62, fig. 6) also assigned to H. re'mondi (Gabb) a specimen from 1 mile east of Riddle, Greg, in beds containing “Lytz'coceras” packardi Anderson, which the writer considers to be of early Hauterivian age. This specific assignment is questioned. The Geological Survey collections contain H. remondz' from the “N eocmspedites” agm'la zone near Ono, Calif, and from the same zone on the eastern part of the Wilcox Ranch in the Paskenta area, California. Type: Plesiotypes USN M 129661, 129662, 129664. Localities: USGS Mes. lOC'S. 1062, 2225, 2268: CAS 100. 1353, 1665: UCLA 10C. 2816. Hoplocrioceras cf. H. remondi (Gabb) Plate 24, figures 5, 6 One specimen from Oregon is possibly an adult vari— ant of H. remondi (Gabb). It differs, however, from the adult specimens that Anderson (1938, pl. 62, figs. 2, 2a, pl. 63) assigns to that species by having finer ribbing on the flanks. The ribs arise singly or in pairs from pronounced umbilical tubercles, are flexu— 198 ous on the flanks, generally bifurcate indistinctly on the upper half of the flanks, become swollen or weakly tuberculate at the edge of the venter, and arch forward slightly on the venter. The surface of the flanks is covered, also, by flexuous striae that are stronger on the ribs than on the interspaces. No trace of lateral tubercles is visible. Figured specimen: USNM 129665. Locality: USGS Mes. Ice. 2080. Hoplocrioceras duncanense (Anderson) Plate 25, figures 1, 3, 8, 9 Spiticeras dimcanense Anderson, 1938, Geol. Soc. America Spec. Paper 16, p. 160, pl. 27, figs. 1, 2. fHoplocrioccras 041061186 Anderson, 1938, Idem, p. 202, pl. 53, fig. 3, 3a, b, pl. 61, fig. 4. It is astonishing that Anderson failed to recognize the resemblance of the holotype of this species to the specimens of Hoplocm'oceras that he identified from the same locality and from other localities near Ono, Calif. The presence of the rows of ventral tubercles that he described and illustrated should have barred an assignment to Spiticems, but. in addition the holo- type specimen bears a row of widely—spaced lateral tubercles a little above the middle of the flanks. One of these is evident near the middle of the lateral view published by Anderson, but under oblique lighting seven tiny lateral tubercles are visible. On the oppo- site side of the holotype, at least five lateral tubercles are visible. Anderson likewise failed to mention the presence of several shallow constrictions. H. dimcanense (Anderson) greatly resembles H. remondi (Gabb) in ornamentation. The holotype dif— fers from H. remondi by retaining ventral and lateral tubercles to a later growth stage, by its umbilical tubercles being separated by from 2 to 5 nontubercu- late ribs, by having 3 ribs in many rib bundles, and by having a much stouter, rounder whorl section. Whether these differences are actually of specific value cannot be determined until enough specimens are obtained to show the range of variation of the species. In addition to the holotype, one specimen (pl. 25, figs. 1, 3) having a similar stout whorl has been found in the zone of “Neocmspedites” aguila near Ono, Calif. Furthermore H. onoense Anderson (CAS 100. 1353) probably is a synonym of H. dancer/tense, judging by its broad whorl section and by the features mentioned by Anderson (1938, p. 202). Types: Plesiotype, USNM 129674; holotype, GAS 8810. Localities: USGS Mes. 10c. 2224; CAS Ice. 1665. SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY Genus SHASTICRIO‘CERAS Anderson, 1938 Shasticrioceras afl’. S. Whitneyi Anderson Plate 25, figures 7, 10 One specimen of Shastioi'iocems from the H ertlein- ites aguila zone is illustrated to prove that the genus occurs as low as that zone. The specimen greatly resembles S. whitneyi Anderson (1938, p. 205, pl. 58, fig. 1) in lateral View and may be a variant of that species. It differs, however, by having a less distinctly truncated venter, by having rather weak, ventral tubercles that become indistinct adorally, and by its ribs arching forward on the venter instead of crossing the venter transversely. Both this specimen and the holotype of S. whitneyi differ from S. poniente Ander— son and S. hespem’wm Anderson in lateral view by having a more open coil and by their flank ribs being straighter, more widely spaced, and a little less regular in strength. Only one other specimen of Shmtiom‘ocems has been recorded from the Hertleinites aguila zone (Murphy, 1956, p. 2114). That specimen, according to Murphy (oral communication 1958), resembles S. iohz'meyi Anderson in its open coil but is otherwise not particularly different from S. poniente Anderson. Figured specimen: USNM 129673. Locality: USGS Mes. Ice. 2225. Genus ACRIOCERAS Hyatt, 1900 Acrioceras voyanum Anderson Plate 26, figures 2—4 Acriocerars voyanum- Anderson, 1938, Geol. Soc. America Spec. Paper 16, p. 206, pl. 59, fig. 1. One ammonite from Oregon, consisting of a shaft and a recurved limb, is nearly identical in shape and ornamentation with the holotype of A. voyanum Anderson. It differs by being a little smaller and by the shaft bearing prominent comma—shaped tubercles on the edge of the dorsum and a row of weak tubercles on each side of the venter. Anderson mentions the presence of a few tubercles 011 the shaft but he does not state their position. His illustration, however, indicates the presence of tubercles at the edge of the dorsum such as occur on the specimen from Oregon. The holotype was obtained from the Cottonwood Creek area of Shasta County, Calif, at an unknown stratigraphic position. Anderson (1938, p. 206, 304) considered that the characteristics of the concretion in which the ammonite was partly enclosed indicated AMMONITES 0F EARLY CRETACEOUS AGE FROM THE PACIFIC COAST STATES a position from or just above his Ono zone, which is herein referred to as the H ertleinites aguila zone fol- lowing the usage of Murphy (1956, p. 2113). Con- firmation of a position as low as that zone is furnished by the occurrence of Acm'ocemw ooyamwn Anderson in Oregon in association with the middle Hauterivian ammonite Simbirskites described herein. Also, a frag- ment possibly belonging to A. ray/(mum Anderson (see pl. 24, figs. 7, 10) was obtained at USGS Mes. 100. 2269 only 8 feet below an occurrence of Hertleim'tes agm'la, (Anderson). In general appearance, A. voyammi Anderson is simi— lar to A. maheswam'ae Sarker (1955, p. 108, pl. 8, fig. 17) from the Barremian of France. Types: Plesiotype USNM 129862; holotype, Univ. Calif. Berkeley 110. Localities: USGS Mes. 10c. 24449. A specimen possibility belonging to this species was obtained at USGS Mes. loc. 2269. Acrioceras vespertinum (Anderson) Plate 26, figures 11—14 Anahamulina vespertina Anderson, 1938, Geol. Soc. America Spec. Paper 16, p. 219, pl. 23, figs. 3, 3a. The shaft of this species bears three rows of tuber- cles. All ribs on each side of the venter bear weak tubercles arranged in a row. The major ribs bear prominent tubercles at the edge of the dorsum and near the middle of the flanks. These ribs are separated by 1 to 3 minor ribs that are nontuberculate except on the venter. On the recurved limb only lateral and dorsal tubercles are Visible and these are weaker than on the shaft. This species has much coarser ribbing than either A. rvoyanum Anderson or A. hamlini (Anderson). Its ribbing compares in coarseness to that on some speci- mens of Acriocems figured by Sarkar (1955, pl. 6, fig. 8, pl. 7, fig. 5, pl. 9, fig. 12) from the Neocomian of France. The specimen of A. tabarelli (Astier) fig- ured by Uhlig (1883, pl. 28, fig. 2) from the Barremian of the Carpathian Mountains is comparable to A. [vespertinrum in size and coarseness of ornamentation, but differs by its flank ribs inclining forward less strongly and by having fewer minor ribs. Type: Holotype Calif. Acad. Sci. 8915. Locality: Calif. Acad. Sci. loc. 113. Acrioceras hamlini (Anderson) Plate 26, figures 8—10 Aspimocems hamlim‘ Anderson, 1938, Geol. Soc. America Spec. Paper 16, p. 207, pl. 60, figs. 1, 2. This species, known only by the holotype, was made the type of a new genus by Anderson on the basis of 199 the absence of tubercles and the presence of alternating simple and forked ribs. Actually the holotype does bear tubercles and is so similar to Acriocems cog/(mum Anderson in shape and ornamentation that the two species may reasonably be placed in the same genus. The most conspicuous difference is the greater breadth and strength of the ribs on A. lzamliml. Most of the holotype specimen of A. hamlini is much worn. The shell is fairly well preserved only at two small places on the venter. At both places weak ventral tubercles are discernable. On the left side of the venter, 6 consecutive ribs bear tiny tubercles; and on the right side, 4 consecutive ribs bear tubercles. On the right flank at one spot where some of the shell is preserved, two of the ribs bear distinct tubercles a little above the middle of the flanks. Elsewhere on the flanks faint swellings are visible on the worn ribs along the same zone. The dorsal edges of the flanks are so much worn that neither the presence or absence of tubercles can be proved. However, the ribs at the dorsal edge are twisted in a comma-shaped manner very much as in a specimen of A. voya/mwn from Oregon (pl. 26, figs. 2, 4)——this feature suggests that originally umbilical tubercles or swellings were present on the shell. The general appearance of A. hamlim' (Anderson) is similar to A. muckleae Sarkar (1955, p. 109, pl. 9, fig. 3), from the Neocomian of France. Its apparently weaker tuberculation is at least in a part a result of corrosion. A. hamlim' (Anderson) is considered to be of mid— dle Hauterivian age because of its association with Simbirs/cites. Type: Holotype Calif. Acad. Sci. 8879. Locality: Calif. Acad. Sci. 100. 113. Genus PSEUDOTHURMANNIA Spath, 1923 Pseudothurmannia? russelli (Anderson) Neocomitcs russclli Anderson, 1938, Geol. Soc. America Spec. Paper 16, p. 165, pl. 27, figs. 3, 3a. The holotype of this species has not been located in the collections of the California Academy of Sciences, and consequently its proper generic assignment remains in doubt. Judging from Anderson’s description and illustra- tions the holotype of “N eocomites” msselli Anderson has ribbing similar to that of Pseudothurma’n/nia angu- licostata (d’Orbigny) (1841, p. 146, pl. 46, figs. 3, 4). That species differs apparently by having a truncated venter, ventral tubercles along the edge of the venter, and a Wider umbilicus. Those differences may be re— lated, however, to the size and growth stages of the specimens compared. In this regard, Sarkar (1955, p. 151, 152) points out that the adult whorls of certain species of Pseudothurmannia, as illustrated by Sarasin 200 and Schondelmayer (1901, pl. 10, figs. 1, 2, 6, pl. 11, fig. 4), acquire a rounded whorl section and loose the ven— tral tubercles. Wright (1955, p. 564) notes that P. masemz's (Torcapel) (1884, p. 137, 138, pl. 6) likewise has a rounded instead of an angulated venter. The general appearance of these species is similar, there— fore, to that of “N.” russelli Anderson. An assignment of “N.” mselh’ to Pseudothurmannia rather than to Thurmannicems or N eocomitcs seems reasonable on the basis of its association with H oplo- crioceras, which did not appear in Europe until late middle Hauterivian time, whereas Thurmamicems and N cocomites are not known later than early Hauterivian. The correct generic identification of “N.” msselli, must await the discovery of specimens that show the inner whorls. Locality: Calif. Acad. Sci. loc. 1665. Pseudothurmannia? jupiter (Anderson) Thurmanm‘a jupiter Anderson, 1938, Geol. Soc. America Spec. Paper 16, p. 162, pl. 31, fig. 1. Anderson’s illustration of the holotype of this species is about one-half natural size, and consequently the rib- bing appears to be much denser than in reality. Actu- ally the inner whorls bear ribbing only slightly closer spaced than the ribbing on Pseudothumunmia? russellz' Anderson (1938, p. 165, pl. 27, figs. 3, 3a). As the other characteristics of the inner whorls of P.? jupiter ap- pear closely similar to those of R? msselli, the two species are possibly identical. This cannot be proved, or rejected, until the growth stages of P. '4 jupz'ter are better known. The characteristics of the ornamentation on the large outer whorl of P.? jupiter (Anderson) were not fully described by Anderson. Most of the ribs begin singly at weak umbilical tubercles, a few arise in pairs from the tubercles, and a few branch indistinctly low on the flanks. They are slightly swollen on the edge of the venter, but not tuberculate. They cross the venter nearly transversely without reduction in strength. On the flanks the ribs are sickle—shaped and variable in strength. From 7 to 8 weak constrictions are present. Lateral tubercles are not present. Type: Holotype Calif. Acad. Sci. 8792. Locality: Calif. Acad. Soc. 10c. 113B. Genus ANAHAMULINA Hyatt, 1900 Anahamulina wileoxensis ‘Imlay, n. sp. Plate 25, figures 2, 5, 6 The species is represented by two straight fragments of a shaft that probably belong to' a single individual. The largest fragment is mostly sutured, but at its an- SI-IORT‘ER CONTRIBUTIONS TO GENERAL GEOLOGY terior end it includes a little of the body chamber, which is crushed laterally. The uncrushed sutured part is nearly circular in section, is a little higher than wide, and is less convex on the dorsum than on the ventor. The shell is marked by fine ribs of somewhat irregular strength that are strongest on the venter. The ribs arch forward weakly on the dorsum, incline forward strongly on the flanks, and arch forward moderately on the venter. The venter bears several pronounced con- strictions that fade out dorsally near the middle of the flanks. Each constriction is followed anteriorly by a slightly swollen rib. The suture line is highly frilled. The first lateral lobe is irregularly bifid and a little longer than the ven- tral lobe. The second lateral lobe is trifid and is much shorter than the first lateral lobe. The dorsal lobe is trifid and terminates in a long slender point. A. rwz'lcowensz's resembles the finely ribbed nontubercu— late species that Gignoux (1920, p. 128, 129) places in the group of “H axmxulina” subcylz'ndm’ca d’Orbigny. Its ribbing in particular is similar to that of A. paxillosa (Uhlig) (1883, p. 94, pl. 14, figs. 3, 5, 6), from the Bar— remian of the Carpathian Mountains. It differs from that species by its shaft tapering less gradually, and in that respect bears a closer resemblance to another speci- men of Anahamuh’na figured by Uhlig (1883, pl. 13, fig. 1). A. wilcowensis appears to have more numerous and more pronounced constrictions on its venter than the other species of Anahamulina that have been de- scribed. Type: Holotype USNM 129671. Locality: USGS Mes. Ice. 1092. Genus HOMOLSOMITES Crickmay 1930 Homolsomites mutabilis (Stanton) Plate 28, figures 1—22 Olcostephanus (Slmbirsk'ltes) mutabllls Stanton, 1895, US. Geol. Survey Bull. 133, p. 77—78, pl. 15, figs. 1—5 [1896]. Subcraspcdltes? mutabllls (Stanton). Spath, 1923, Geol. Soc. London Quart. Jour., v. 79, pt. 3, no. 313, p. 306. Dichotomltes mutabllls (Stanton). Anderson, 1938, Geol. Soc. America Spec. Paper 16, p. 160. chhotomltes tehamaensis Anderson, 1938, Idem, p. 158, pl. 28, fig. 2, pl. 30, fig. 6. chhotomltes gregerseml Anderson, 1938, Idem, p. 158, 159, pl. 28, figs. 3, 4. chhotomltes burgerl Anderson, 1938, Idem, p. 159, pl. 28, fig. 5. Homolsoml‘tes mutabllls (Stanton). Imlay, 1956, Jour. Pale- ontology v. 30, no. 5, p. 1144, 1145. The specimens of H omolsomz'tes described by Stanton and Anderson were obtained from the same small ex- posures on a hill northwest of the houses of the Shelton Ranch, about 5 miles north of Paskenta, Tehama County, Calif. (Mes. locs. 1010 and 1093). Both Stanton and Anderson collected about 40 specimens. AMMONITES 0F EARLY CRETACEOUS AGE FROM THE PACIFIC COAST STATES Stanton noted variations in the ornamentation of the specimens that he examined, but concluded that the specimens all belonged to a single variable species. An- derson assigned the specimens that he examined to 4 species of which 3 were described as new. The 40 specimens available to Stanton have been divided by the writer into 4 lots based on coarseness of ribbing and number of ribs. Each lot contains 1 or 2 specimens that might nearly as well have been placed in another lot, although the differences between the most finely ribbed and the most coarsely ribbed speci- mens are rather striking. One lot contains seven spec~ imens that agree with the definition and illustration of “Dickotomites” tehamaensis Anderson (1938, p. 158, pl. 28, fig. 2). These specimens are finely and densely ribbed, secondary ribs outnumber primary ribs about 5 to 1, and the ribs fade out rapidly adorally on the lower part of the body chamber. A second lot contains 17 specimens, including 2 specimens illustrated by Stanton (1895, pl. 15, figs. 3—5 [1896]). These agree with the definition and illustra- tion of “Dichotomz'tes” burgem‘ Anderson ( 1938, p. 159, pl. 28, fig. 5). Their ribbing is slightly coarser and sparser, than in “D.” tehumaensis, and the secondary ribs outnumber the primary ribs about 4 to 1 0n the larger whorls and 3 t0 1 on the smaller whorls. A third lot contains 12 specimens, including 1 illus- trated by Stanton (1895, pl. 15, figs. 1, 2 [1896]). These agree with the definition and illustrations of “Dichoto- mites” gregersem' Anderson (1938, p. 158, pl. 28, figs. 3, 4). They differ from “D.” burgeri by having slightly coarser and sparser ribbing. The secondary ribs out- number the primary ribs 3 to 1 on the larger whorls and 2 to 1 on the smaller whorls. These specimens include the lectotype of H omolsomz'tes mutabilis (Stanton) that was selected by Anderson (1938, p. 160) . A fourth lot contains five specimens that are charac- terized by being still coarser and sparser ribbed than the specimens in the other lots and by having fewer secondary ribs. These coarsely ribbed specimens are herein given the subspecific name crassicostatus under the species H. mutabilis (Stanton), and the specimen shown on plate 28, figures 3, 4, is designated the type of the subspecies. In conformity with this usage “Dichotomz'tes” burgem' Anderson and “D.” tehamaemis Anderson are likewise considered subspecies of H. mm- tabih's that are finer ribbed than the typical subspecies mutabilis, but are connected with it by many transitions. The suture line of H. mutabilis Stanton is character- ized by having long, nearly symmetrical lobes. The first lateral lobe is appreciably longer than the ventral and second lateral lobes. The second lateral saddle is nearly as broad as the first lateral saddle. 201 The various species of H omolsomites, from Washing- ton, British Columbia, and Greenland have been listed by the writer (1956, p. 1144) recently under a discussion of the characteristics of the genus. Of these species H. stantom' (McLellan), from Washington and British Columbia, has fine, dense ribbing similar to that of H. mutabilz's tehamaensz's Anderson, but is distinguished by a more narrowly rounded venter and consequently by a subtriangular rather than an elliptical cross sec- tion. H. paucicostatus Donovan (1953, p. 110—112, pl. 23, figs. 1a, b), from Greenland, was considered by its author to be a variety of H. gregersem' (Anderson), difiering only by having fewer ribs. H. paucicostatus does not, however, have fewer ribs than some of the typical specimens of H. mutabilis of which H. gregersem' (Anderson) is a synonym. H. paucicostatus (Dono- van) is possibly difierentiated from H. mutabilis (Stan— ton) by a more narrowly rounded venter and weaker ribbing. Types: Lectotype of H. mutabilis mutabilis Stanton, USNM 23089a; plesiotypes, USNM 129689, 129691, 129693. Holotype of H. mutabilis crassq‘costatus Imlay, n. subsp., USNM 129690; paratype, USNM 129692. Plesiotypes of H. mutabilis burgeri (Anderson), USNM 230891), c, 129688a—c. Plesiotypes of H. mutabilis tehamaensis (Anderson), USNM 129687, 129694. Localities: All the California specimens of H. mutabilis (Stan— ton) in the Geological Survey are from USGS Mes. loc. 1093 (equals 1010'). In Oregon 2 typical specimens of H. mutabilis were found at Mes. Ice. 2154 and 2 specimens of the subSpecies tehamaensis at Mes. 100. 4390. Some ammonites from Mes. locs. 1088 and 1091 that Stanton (1895, p. 17 [1896]) referred to H. mutabilis (Stanton) are herein described under Ncocras- pedites giganteus Imlay, n. sp. Homolsomites stantoni (McLellan) Plate 27, figures 1—16 Holcodiscus? stantoni McLellan, 1927, Washington Univ. Pub. in Geology, v. 2, p. 115, pl. 12, figs. 3—5. Homolsomites poeciloohotomus Crickmay, 1930, Canada Natl. Mus. Bull. 63, Geol. Ser. 51, pp. 63, 64, pl. 21, figs. 1—4. Hmnolsomitcs stantom‘ (McLellan). Imlay, 1956, Jour. Pale- ontology, v. 30, pp. 1143—1146, pl. 120. One large adult of Homolsmm’tes stantoni (McLel- lan) has been found on the South Umpqua River in southwestern Oregon, in association with Olmste- phtmus pecké Imlay, n. sp., about 257 feet below the top of the beds containing Buchc'a crassz'collz's (Keys— erling). This adult specimen appears so different from the small immature type specimens (see pl. 27, figs. 8, 9, 11—13) described by McLellan (1927, p. 115, pl. 12, figs. 3—5) that identification would not have been possible without breaking the adult specimen enough to show the characteristics of inner whorls. These revealed that the specimen during growth passed through the various changes in ornamentation and 202 shape as illustrated recently by Imlay (1956). The identification became positive after the acquisition of additional topotype specimens and of plaster casts of the type specimens furnished through the courtesy of V. Standish Mallory and Warren S. Drugg, of the University of Washington at Seattle. The innermost exposed whorl of the specimen from the South Umpqua River shows ribbing comparable in coarseness to the small type specimens. Its pri- mary ribs incline forward on the flanks and are slightly stronger than its secondary ribs. Secondary ribs arise in pairs between the lower fourth and lower third of the flanks. Many of the secondary ribs branch again between the middle and upper third of the flanks. All secondary ribs incline forward strongly on the upper parts of the flanks and arch forward on the venter, and are not reduced in strength on the venter. These small whorls bear 7 or 8 weak forwardly inclined constrictions per whorl. On specimens larger than the types, the primary ribs become more prominent than the secondary ribs, acquire a pinched appearance, and then gradually fade on the penultimate and body whorls. The ribbing on the venter remains fairly strong even on the adult body chamber, as shown on the large specimen from the South Umpqua River, in which the body chamber occupies three-fourths of a whorl. The specimens of H. stantom' (McLellan) now avail- able show some variation in ribbing. The type speci- mens and some others (pl. 27, figs. 9, 13, 15) have about 4 secondary ribs for each primary rib and are similar in this respect to H. mutabilis burgem' Ander- son. Others have about 5 secondary ribs for each pri- mary (pl. 27, figs. 3, 4) and are similar in this respect to H. mutabilis tehamaemis Anderson. H. stantom' differs, however, from H. mutabilis (Stanton) and its subspecies by having a more narrowly rounded venter, a smaller umbilicus, less pinched primary ribs, and more common furcation low on the flanks on immature specimens. It appears, also, to attain a much larger Size. The distinctions between Homolsomites stantom' (McLellan) and Wellsia oregonensz's (Anderson) are described under the description of the latter. H. stantom' (McLellan) shows some resemblance to Neocraspedz‘tes carterom' (d’Orbigny) (1841, p. 209, pl. 61, figs. 1—3), from the lower Hauterivian of France. It difl'ers by lacking swollen primary ribs near the umbilical margin by having more distinct furcation points from which the secondary ribs arise in pairs rather than in bundles, by having a more nar- rowly rounded venter, and by the primary ribs being rather prominent on the small and intermediate size SHORT‘E'R CONTRIBUTIONS TO GENERAL GEOLOGY whorls and then fading uniformly on the penultimate and body whorls instead of near the medial parts of the flanks. Types: Holotype Univ. Wash. 15001; paratype, Univ. Wash. 15002; plesiotypes, Univ. Wash. 12763-12767 ; plesiotypes, USNM. 129695, 129696. Localities: USGS Mes. locs. 17273, 26788; Univ. Washington locs. WA 535, 536, 538; field number 9.3.54.6 of Peter Misch. Genus OLCOSTEPHANUS Neumayr, 1875 Olcostephanus pecki Imlay, n. sp. Plate 29, figures 1—5, 7—9; plate 30; plate 31, figure 7 This species is represented by 6 nearly complete speci- mens and by 16 fragments. The shell is stout and moderately involute. The body whorl is ovate in sec- tion, nearly as high as wide, overlaps about three-fifths of the penultimate whorl, and attains its greatest thick- ness at the umbilical edge. The flanks are gently con- vex, and the venter is evenly arched. The umbilicus is moderately narrow, its wall is fairly high and vertical, its edge is evenly rounded. On the largest specimens the body chamber represents nearly one whorl. The aperture is marked by a pronounced forwardly inclined swelling, followed by a deep constriction, which is fol— lowed in turn by a moderately strong swelling. These swellings are a little stronger than those on the aper- tures figured by Baumberger (1908), pl. 28, fig. 2; 1910 pl. 32, fig. 1). The ribs on the smallest whorls (pl. 29, figs. 3, 4) are fine and closely spaced. They incline backward on the umbilical wall, incline forward on the flanks, and cross the venter transversely. The ribs on the umbilical wall are a little stronger than the ribs on the flanks and bear distinct, small conical tubercles at the umbilical edge. From these tubercles pass pairs of ribs. Most pairs are separated by a single rib that arises freely along the zone of tuberculation. In addition the smallest whorls bear pronounced forwardly inclined constrictions that may truncate some of the ribs. The ribs on the larger whorls become progressively stronger and more widely spaced during growth and are moderately strong at the anterior end of the adult body chamber. Faintly, the ribs begin low on the um- bilical wall, incline backward to the umbilical edge. incline forward gently on the flanks, and cross the venter transversely. Most of the primary ribs bifurcate just above the umbilical edge into 2, or rarely 3 secondary ribs. A few secondary ribs branch again higher on the flanks. Most paired ribs are separated by single ribs that arise freely at or near the zone of furcation. The furcation points are slightly swollen but are not tuber- culated. Each whorl bears 5 or 6 weak constrictions, AMMONITES 0F EARLY CRETACEOUS AGE FROM THE PACIFIC COAST STATES and the innermost whorls bear the strongest constric- tions. Accurate measurements cannot be made because all the specimens have been crushed. The suture line is of the olcostephanid type, as described by Uhlig (1903, p. 84, 86, pl. 18, figs. 2e). The lobes are deep and frilled. The saddles are high and not divided by a secondary lobe. Discussion: This species is characterized by lacking distinct umbilical tubercles except on its innermost whorls, and by having closely spaced ribs that branch by twos and threes near the umbilical edge. Many species of Olcosteplumus have ribbing comparable in density to 0. pee/vi Imlay, n. sp., but most of them have distinct umbilical tubercles from which pass bundles of 4 or 5 secondary ribs. Probably the most similar species is 0. jeamwti (d’Orbigny) (1841, p. 188, pl. 56, figs. 3—5), from the late Valanginian and early Haute— rivian of France. It resembles 0. pecki in degree of involution, rib ranching, density of ribbing, and ab- sence of tubercules. It difi'ers by being much smaller and more compressed. Another similar species is 0. geei Spath (1939, p. 26, pl. 7, figs. 6a—c) , from the Valan- ginian of the Salt Range of India. It differs from 0. pee/lei by being stouter and by having coarser ribbing. O. frequens Zwierzycki (1.914, p. 51, pl. 6, figs. 1—5, 10, 11, 14, 15), from east Africa, has ribbing on its outer whorl similar to that on 0. pecki, but its inner whorls are strongly tuberculate, and it is much more evolute. Olcostephanus pecki and 0. jeamwz‘i (d’Orbigny) are similar to some species of H olcodiscus, such as H. uhligi Karakasch (1907, p. 113, pl. 9, figs. 19a, b), from the Crimea, in such features as their rib pattern and their lack of umbilical tubercles on adult whorls. Spath (1939, p. 12) considered that O. jeannoti belonged to a group transitional from Olcostephanus to Holcodiscus. That genus differs from Olcostephamis, however, by being more evolute, by having stronger constrictions, and by its ribs generally branching higher on the flanks. Distribution: Olcostephanus pee/ti has been identified definitely only near Days Creek, Douglas County, Ore. At that place it has been collected throughout 218 feet of beds in the upper part of the sandy unit characterized by an abundance of Buchia crassicollis (Keyserling). The highest occurrence of 0. pecki is 85 feet below the highest occurrence of B. crassicollis and 143 feet below the lowest occurrence of Wellsia oregonensie (Ander- son). Fragments of Olcostegmanus that may belong to O. pecki have been found with H o-In‘OZsom-ites stantoni (McLellan) 3 miles east of Glacier, lVaslr, in the north center of sec. 3, T. 31 N., R. 7 E. (Univ. Washington colln. [see pl. 29, fig. 6] WA 538). 203 Types: Holotype USNM 129848; paratypes USNM 129846, 129847a—c, 129849. Localities: USGS Mes. locs. 25192—25194, 25197, 26787-26790. A fragment probably belonging to 0. pecki was found at Mes. 10c. 1681. The species is named in honor of Dallas L. Peck, of the US. Geological Survey. Olcostephanus popenoei Imlay, n. sp. Plate 31, figures 1—3 This species is represented by a single small speci- men that possesses well-developed lateral lappets. The body chamber occupies about four-fifths of a whorl. The whorl is subquadrate in section and slightly higher than wide. As it is somewhat crushed laterally, the width was probably originally as great as the height. The coiling appears to be fairly evolute for the genus. The ornamentation is similar to that on the inner whorls of 0. pecki Imlay, n. sp. It differs by having fewer intercalated ribs, weaker and sparser primary ribs, and weaker umbilical tubercles. Pronounced con— strictions occur at both ends of the body chamber. On the right side of the shell the lateral lappet is pro- longed about 8 mm beyond the final constriction. Discussion: If it were not for the presence of lateral lappets, the holotype of this species might have been considered an immature specimen of 0. pecki Imlay, n. sp., although it exhibits minor differences in shape and ornamentation. The presence of lateral lappets shows that it is an adult and that it differs from 0. pecki in aperatural characteristics as well in its vastly different size. Perhaps these species represent another case of dimorphism (see discussion by Callomon, 1957, p. 62; Arkell, 1957, p. 87 —90), but this cannot be proved. Also, the fact that O. popenoei is represented in available 001- lections by only 1 specimen, whereas 0. pecki is repre— sented by many, suggests that the 2 species are not dimorphic. The presence of lateral lappets in 0. popcnoei does not place that species in a separate genus from 0. pecki al- though a simple, sinuous apertural constriction is more common in Olcostephamus. Examples of typical 0200— stephamzs that have lappets have been illustrated by Spath (1939, pl. 1, 3a, 8a, pl. 2, fig. 2a, pl. 19, fig. 6a). The species is named in honor of W. Parkison Popenoe, 0f the University of California at Los Angeles. Type: Holotype USNM 129863. Locality: USGS Mes. 100. 26790. Olcostephanus cf. 0. quadriradiatus Imlay Plate 31, figure 10 One external mold of an ammonite from a locality near Port ()rford, (he, has a rib pattern similar to that of Olcostephanus rather than Polyptychites. In par- ticular, the ribbing may be compared to that on the body 204 whorls of 0. guadriradiatus Imlay (1938, p. 554, pl. 5, figs. 1, 2) , 0. astiem'formis (Bose) (1923, p. 72, pl. 1, figs. 1—4), 0. astierianus (d’Orbigny) (1840, p. 115, pl. 28, figs. 1, 2), and 0. singularis (Baumberger) (1908, p. 3, pl. 26, fig. 5). All these species are from beds of early Hauterivian age. The ammonite from Oregon bears very strong, widely spaced umbilical tubercles, from which pass bundles of 4 to 5 ribs that incline forward on the flanks. Generally one rib in each bundle bifurcates on the middle third of the flanks. Most rib bundles are separated by 1 or 2 ribs that arise freely on the flank above the zone of tuberculation. The ammonite was collected from thick-bedded sand- stone some hundreds of feet above beds containing Buchia crassicollis (Keyserling). On the basis of stratigraphic position, it should be of Hauterivian age. Figured specimen, USNM 129861. Locality: USGS Mes. 10c. 25217. Genus POLYPTYCHITES Pavlow, 1892 Polyptychites trichotomus (Stanton) Plate 31, figures 13, 15 Olcostephcmus (Polyptychites) trichotomus Stanton. Stanton, 1895, U.S. Geol. Survey Bull. 133, p. 78, pl. 16, fig. 1, [1896]. Dichotomites trichotomous (Stan-ton). Anderson, 1938, Geol. Soc. America Spec. Paper 16, p. 159. This species was compared by Stanton with Poly- ptychites polyptg/chus (Keyserling) (Pavlow, 1892, pl. 15 (8), figs. 2a, b), but that species differs by having umbilical tubercles, sharper ribs, and more frequent rib branching. In these respects P. trichotomm shows much more resemblance to P. mmulicosta, Pavlow (1892, p. 481, pl. 8 (5), fig. 10a, b, pl. 15 (8), figs. 6a, b), from the middle Valanginian beds at Speeton, England, or to P. densicosta Pavlow (1914, p. 26, pl. 5, figs. 3a—c), from the Valanginian of Russia. It appears to be more evolute than those European species, but that appear- ance may be a result of crushing. Its assignment to Dichotomites by Anderson cannot be maintained be- cause Dichotomites has fairly regular rib bifurcation from umbilical swellings or tubercles. Type: Holotype USNM 23090. Locality: USGS Mes. 100. 1087. Genus NEOCRASPEDITES Spath, 1923 Neocraspedites giganteus Imlay, n. sp. Plate 32, figures 1—6 Desmoceras? sp. Stanton, 1895, U.S. Geol. Survey Bull. 133, p. 77, [1896]. Six specimens of this species were obtained from a locality near the top of the beds bearing Buc/u'a crassi- SHORT‘ER CONTRIBUTIONS TO GENERAL GEOLOGY collis (Keyserling) in the Paskenta area, Tehama County, Calif. On the smallest specimen (pl. 32, fig. 1) the whorl section is subovate and a little wider than high. On the other specimens the whorl section is subtrapezoidal and much higher than wide and attains its greatest thickness near the umbilical edge. The flanks on the smallest specimen are gently convex. On the larger specimens the flanks are flattened and converge slightly toward a broadly arched venter. The umbilicus is narrow. The umbilical wall on the smallest specimen is steeply inclined and rounds evenly into the flanks. On all larger specimens the umbilical wall is vertical and rounds abruptly into the flanks. The body chamber is unknown. The ribbing on the smallest specimen (pl. 32, fig. 1) consists of strong primary ribs that incline forward to the lower third of the flanks, where about half of them bifurcate into higher, sharper secondary ribs. Other ribs arise simply along the zone of furcation. All secondary ribs curve backward slightly on the middle of the flanks and then curve forward strongly on the upper part of the flanks and on the venter. All ribs cross the venter, but some are slightly reduced in strength. Several very weak constrictions are present. The ribbing on a somewhat larger specimen (pl. 32, fig. 4) is similar to that just described except that fewer ribs bifurcate on the lower third of the flanks and most ribs bifurcate a little above the middle of the flanks. The ribbing is distinctly stronger near the umbilicus and venter than on the middle of the flanks. On a slightly larger specimen (pl. 32, fig. 2) the lower part of the flank bears about 18 primary ribs that are distinct near the umbilicus, but broaden and become indistinct near the middle of the flanks. The upper third of the flanks and the venter are marked by fine ribs that are closely spaced and forwardly curved and appear to arise in bundles from the primary ribs. On the largest well-preserved specimen, which is the holotype (pl. 32, figs. 3, 5, 6), the rib pattern is similar. The primary ribs are rather weak but are still strongest near the umbilicus. They incline forward, broaden, and pass indistinctly near the middle of the flanks into numerous sharp secondary ribs that curve forward on the flanks and arch forward gently on the venter. The ribs attain their greatest strength on the venter. The species probably attained a diameter at least three times as large as that of the holotype specimen as figured. The ventral part of that specimen was orig- inally attached to parts of two outer whorls that are much crushed. The innermost of these two whorls is septate and bears ornamentation on its venter a little coarser than that on the figured holotype. The outer— AMMONITES OF EARLY CRETACEOUS AGE FROM THE PACIFIC COAST STATES most whorl, represented only by the lower part of the flank, bears traces of broad, low primary ribs. The suture line is imperfectly preserved and cannot be traced accurately. The holotype of this species greatly resembles Neo- cmspedz'tes flewicosta (Von Koenen) (1902, p. 74, pl. 5, figs. 14—16), from the late Valanginian of Germany. It appears to have slightly weaker primary ribs near the umbilicus and slight-1y stronger secondary ribs. Types: Holotype USNM 23088; paratypes USNM 129833a, b, 129834. Localities: USGS Mes. loc. 1009. 1087, 1088, and 1091. Genus WELLSIA Imlay, 19-57 This genus was originally defined (Imlay, 1957, p. 275) as follows: Wellsia bears many resemblances to the genus Neocmspedites (Spath, 1923, p. 17) based on Oraspedites semilaem’s Von Koenen (1902, p. 80, pl. 5, figs. 8—10). It differs by its ribs being arched forward more strongly on the venter and some- what reduced in strength along the midventral line, by its umbilical swellings disappearing at an earlier growth stage, by its venter being more narrowly rounded, and by its umbili- cus being slightly smaller. The type species is designated as Wellsia oregonensis (Anderson) (1938, p. 159, pl. 30, fig. 5). The genus likewise includes W. packardi (Anderson) ( 1938, p. 164, pl. 31, figs. 2—5). It is named in honor of Francis G. Wells of the U.S. Geo- logical Survey in recognition of his important contributions to the geologic knowledge of Oregon and California. Wellsia has been found only in Oregon in beds of early Hauterivian age directly overlying beds containing the pelecypod Aucella crassicollis Keyserling and the ammonites Olcoste- phanus, Samsinella, and Thurmanniceras. Wellsia oregonensis (Anderson) Plate 32, figures 7-20 Dichotomites oregonensis Anderson, 1938, Geol. Soc. America, Spec. Paper 16, p. 159, pl. 30, fig. 5. The species is represented in the collections of the Geological Survey by 40 specimens that show the vari- ous growth stages. The holotype is an immature specimen. Its description by Anderson is accurate except for failure to mention the presence of several weak constrictions on the internal mold. The larger specimens show that during growth the whorl shape changes from subtrapezoidal to subtrigonal; the rib- bing fades first near the middle of the flanks, then near the umbilicus, and finally in the venter; and the point of rib branching rises during growth from a place near the middle of the flank to about two-thirds of the height of the flank and gradually becomes less distinct. As the ribbing fades the surface of the shell becomes marked by faint forwardly inclined striae that are not evident on the internal mold. On the adult 205 body chamber (pl. 32, figs. 18—20) the ornamentation consists only of striae that are faintly visible under oblique lighting. One feature described by Anderson is the weaking of the ribs along the midline of the venter. Such weakening is evident on all interal molds at all stages of growth. However, small specimens that bear some shelly material (pl. 32, fig. 9) do not show weakening of the ribs on the venter. Larger septate specimens that bear some shell material (pl. 32, figs. 12, 13) do show a little weakening of the ribs on the venter. An incomplete body chamber, representing about two-thirds of a whorl, is present on the largest known specimen of N. mega/name's (pl. 32, figs. 18—20). The beginning of the body chamber is indicated by traces of the suture line at the point indicated on the illus- tration. The part of the body chamber nearest the aperture appears to be slightly retracted from the remainder of the shell, but this effect is probably related to a small fault induced by lateral compression. The suture line of W. oregommis (Anderson) could be traced only on an immature specimen at a diameter of 21 mm. It is characterized by slender symmetrical lobes and relatively broad saddles. The first lateral lobe is a little longer than the ventral lobe. The general plan of the suture line is similar to that of a small speci— men of Neocmspedites figured by Von Koenen (1902, p. 6, fig. 18a, 19) but differs by having more auxiliary lobes on the flanks. The suture line also resembles that of H omolsomdtes except that the second lateral saddle is not nearly as wide as the first lateral saddle. Immature specimens of Wellsz’a oregonensis (Ander- son), such as the holotype, differ from Neocmspedites stantom' Imlay, n. sp., at a comparable size by having a smaller umbilicus, a more narrowly rounded venter, slightly weaker primary ribs, and less flexuous ribbing near the middle of the flanks. During growth the dif— ferences between the species become more conspicuous as W. oregonensz's acquires a subtrigonal whorl section and loses most of its ribbing. The immature specimens of W. olregonemis (Ander- son) show considerable resemblance to small specimens of Homolsomz’tes stantom' (McLellan), as figured by Imlay (1956, pl. 120, figs. 1—5) but differ by having weaker primary ribs that fade earlier, more secondary ribs for each primary rib, less distinct furcation points, weakening of the ribs on the venter, rib branching gen- erally above rather than below the middle of the flanks. and a somewhat wider umbilicus. The adult specimens of W. oregonensis differ from those of H. stam‘om‘ by lacking ribs on the venter and by having a somewhat wider umbilicus. The small septate specimens of W. oregonensis (An- 206 derson) are similar in appearance to those of N eocms— pedites complamtus (Von Koenen) (1902, pl. 6, figs. 18a, b) at a comparable size but differ by having a nar- rower venter and a smaller umbilicus. All specimens of W. oregonensis (Anderson) have been collected in southwestern Oregon from siltstone and sandstone directly overlying sandy beds containing Buchia crassicollis (Keyserling) . On Days Creek, Douglas County, the species has been collected from 58 to 243 feet above the top of the beds containing B. cras— sicollis (Keyserling). Types: Holotype Calif. Acad. Sci. 8779; plesiotypes USNM 129675—129679. Localities: USGS Mes. locs. 718, 905, 1243, 1252, 1823, 25198—- 25200, 25204, 25206, 25208, 25213, 26252. Wellsia packardi (Anderson) Plate 33, figures 26—31 Lyticocems packardi Anderson, 1938, Geol. Soc. America Spec. Paper 16, p. 164, pl. 31, figs. 2, 5 [not 3 and 4]. This species is represented in the Geological Survey collections by 42 specimens. It differs from W. are- gonemis (Anderson) by having thicker and more prom- inent ribs and by retaining those ribs to a much larger growth stage. As in W. oregonensis the ribs on internal molds arch forward strongly on the venter and weaken along the midventral line. This weakening varies con- siderably from one specimen to another and is least con- spicuous wherever shell layers are preserved. The suture line, drawn from an immature specimen, at a whorl height of 12 mm, is essentially the same as on W. oregonensis (Anderson), previously described. Discussion: Among European species, W. packardi shows some resemblance to Neocmspedites carterom' (d’Orbigny) (1841, p. 209, pl. 61, figs. 1—3), from the lower Hauterivian of France. It differs by having a slightly smaller umbilicus, by the adult whorls lacking swollen primary ribs near the umbilical margin, by the ribs weakening along the midline of the venter, and by the venter being more narrowly rounded. Anderson’s assignment of W. packardi to the genus Lyticocems is not tenable because Lyticocems is evolute rather than involute and bears ventral tubercles during most of its growth, and because its ribbing does not fade out on the flanks. W. packardi shows much greater resemblance to the genus Leopoldia (d’Orbigny, 1942, pl. 23, pl. 25, figs. 3, 4; Baumberger, 1906, pls. 4—9 [in part] ; Imlay, 1938, pl. 12, figs. 1—4), but it lacks a completely smooth midventral area and ventral tuber— cles, and its suture line does not have the unsymmetrical first lateral lobe that is characteristic of Leopoldia. Immature specimens of W. packardi (Anderson) bear a strong resemblance in rib pattern on both flanks and SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY venter to Leo-poldia jodmiensis (R. Douville), as figured by Roman (1933, p. 12, pl. 1, figs. 4, 4a), but they have a smaller umbilicus and a more narrowly rounded ven- ter and lack umbilical tubercles, and the midventral area is not entirely smooth. As the holotype of L. jodariensis has continuous ribs across the venter, accord- ing to Roman (1933, p. 12), it probably resembles N. packardi considerably more than the specimen figured by Roman. Distribution: In a section measured in 1954 near Days Creek, Douglas County, Ore., W. packardi was found stratigraphically higher than W. oregonensis in a se- quence from 253 to 313 feet above the top of beds con- taining Buchia crassicollis (Keyserling). Most of the specimens of W. packardi had undergone more crush- ing than the specimens of W. oregonensis and had weathered to a browner color. Older collections, made during the years from 1890 to 1900 from several hun— dred feet of beds exposed along Cow Creek near the town of Riddle, Douglas County, contain both species apparently associated. Examination of the collections USGS (Mes. locs. 718, 1243, and 1252) shows, however, that the specimens of W. packardi are more crushed than the specimens of W. oregonemis and weather much browner. These differences suggest, therefore, that the two species actually occur at slightly different stratigraphic positions, as they do on Days Creek. Wellsia packardi has been found only in southwest- ern Oregon. Its absence in northern California prob- ably has stratigraphic significance. Types: Plesiotypes USNM 129666—129668; holotype, CAS 8738. Localities: USGS Mes. locs. 718, 726, 1243, 1252, 3352, 3923, 25201, 25202, 25203, 25207. Wellsia vigorosa Imlay, n. sp. Plate 33, figures 19-22, 25 Lyticocems packard/i Anderson, 1938, Geol. Soc. America Spec. Paper 16, p. 164, pl. 31, figs. 3, 4 [not 2 and 5]. Four specimens in the survey collections greatly re- semble the paratype of “Lg/ticocems” packardi Ander- son, which diflers from the holotype of “Lyticocems” packardi Anderson by having a less narrowly rounded venter, flatter flanks, and much more prominent ribs that are only slightly reduced in strength along the mid ventral line even on internal molds. Owing to the prominence of the ribbing on the venter, the chevronlike arrangement of the ribbing is much more conspicuous than in the holotype of Wellsia pack‘ardi. These differ- ences seem great enough to justify assigning the four specimens as well as the paratype of Lyticocems pack- ardi to a new species. W. vigorosa has been found only near the town of AMMONITES 0F EARLY CRETACEOUS AGE FROM THE PACIFIC COAST STATES Riddle, Ore. The specimens in the Geological Survey collections are from several hundred feet of beds that have furnished many specimens of W. oregonemz's (An- derson) and of W. packardz‘ (Anderson). The speci- mens weather to a dark brown, as do the specimens of W. packamdz’, and presumably come from the same beds as that species rather than from the beds containing W. oregonensis. It is possible, of course, that they are from a different stratigraphic position than either of those species. Types: Holotype USNM 129669; paratypes, USNM 129670a, b. Locality: USGS Mes. Ice. 1252. Genus HERTLEINITES Imlay, 1958 The genus was originally described (Imlay, 1957, p. 275) as H ertleim‘a, but as that name had been used pre- viously (Marks, p. 457, 1949), it was changed to H ert- leim'tes (1958, p. 1032). The original description is as follows: This genus has a moderately compressed shell, subquadrate whorl section, and a moderately arched venter. The umbilicus widens during growth from fairly narrow to fairly wide. The umbilical wall is low and vertical. The ornamentation consists of strong primary ribs that curve backward on the umbilical wall, curve forward on the lower two-fifths of the flanks and then divide into two weaker secondary ribs that continue the forward inclination of the prim—’ary ribs. One, or both, sec- ondary ribs of each pair bifurcate between the middle and the upper third of the flanks. A few ribs begin freely near the middle of the flanks. The ribs continue across the venter with out diminution in strength and with a gentle forward arching. Many shallow constrictions occur on each whorl. The suture line is characterized by having long, rather slender lobes. Neocraspedites aguila Anderson (1938, p. 156, pl. 25, figs. 1—3, pl. 68, fig. 4) is designated as the genotype species. The genus, also, includes H. rectom’s (Anderson) (1938, p. 157, pl. 23, fig. 2) and H. signalis (Anderson) (1938, p. 157, pl. 26, fig. 1). The genus is named in honor of Leo G. Hertlein of the Cali- fornia Academy of Sciences. Hertleim‘a [now Hertleim’tes] is distinguished from Neocras- pedites in which its species were placed by Anderson (1938, p. 156, 157) by its shell being much more evolute in the adult, by its ribs persisting on the middle of the flanks, and by its ribs arching forward much less strongly on the venter. H ertle- im‘a differs from Oraspedodiscus Spath (1924, p. 77) by becom- ing more evolute during growth, by its venter remaining mod- erately broad in the adult instead of becoming narrow, by re- taining ribbing on its flanks in the adult, and by the ribs being much less strongly arched on the venter. Hertleim‘a has been found only in California associated with species of Hoplocm'oceras a few hundred feet above beds con- taining Simbirskites of middle Hauterivian age and many hun- dreds of feet below an occurrence of the Barremian ammonite Pulchellia. Its age is considered to be only slightly younger than that of Simbirskites and, therefore, late Hauterivian. Such features of Hertleim'tes as degree of involution, rib pattern, and persistence of contrictions suggest that it is more closely related to Oraspedodiscus than to Neo- cmspedites. It is placed accordingly in the Simbirskit- 207 inae rather than the Polyptychitinae, but its systematic position is not considered to be definitely established. Hertleinites aguila (Anderson) Plate 34, figures 1—7 Neocraspedites aguila Anderson, 1938, Geol. Soc. American Spec. Paper 16, p. 156, pl. 25, figs. 1—3, pl. 68, fig. 4. Four specimens of this species are on hand. One of these (pl. 34, fig. 6) has a crushed outer whorl that is similar in size and appearance to the holotype and an inner whorl that is exceptionally well preserved. This inner whorl at a diameter of 48 mm has a whorl height of 22 mm, a whorl thickness of 19 mm and an umbilical width of 11 mm. The whorls are subquadrate in section and embrace about three-fourths of the pre- ceding whorls. The flanks are flattened below but round evenly above into a moderately arched venter. The umbilical wall is low and vertical and rounds abruptly into the flanks. The primary ribs are sharp and fairly widely spaced. They curve backward on the umbilical wall, incline forward gently on the flanks, and bifurcate at about two-fifths of the height of the flanks. Gen- erally one rib of each pair of secondary ribs bifurcates again near the middle of the flanks. A few ribs arise freely near the middle of the flanks. The secondary ribs arch forward weakly on the venter. Secondary ribs outnumber the primary ribs a little more than 3 to l. The whorl bears six weak constrictions. The outer whorl of the specimen under discussion (pl. 34, fig. 6) compares in size with the outer whorl of the holotype (pl. 34, fig. 2). On these whorls the ribbing differs from that just described by the furcation points being less distinct and by most of the secondary ribs bifurcating at, or a little above, the middle of the flanks. The secondary ribs outnumber the primary ribs nearly 4 to 1. Weak constrictions are present. On the outer whorl of a still larger specimen (pl. 34, figs. 1, 7), the zone of furcation of the primary ribs be- comes still less distinct and furcation of the secondary ribs occurs between the middle and the upper three- fifths of the flanks. Secondary ribs outnumber the primary ribs more than 4 to 1. Several weak constric— tions are present. The body chamber occupies about half of a whorl. The dimensions of the holotype as listed by Anderson need correction. The greatest diameter is about 85 mm, the whorl height is about 42 mm, and the umbilical width is 41 mm. The holotype is so crushed that its thickness cannot be estimated. The suture line, drawn from the specimen shown on plate 34, figure 7, at a whorl height of 46 mm, is char- acterized by long, slender lobes and saddles. The ven— tral lobe is the longest, and the other lobes are progres- 208 sively shorter. The first lateral lobe is irregularly trifid. The specimens that Stanton (1896, p. 18) identified as Olcostephamus aims/702' (Gabb) during his fieldwork in California in 1893 and 1894 belong to Neocmspedites aguila Anderson. This mistake in identification was recognized by Stanton in 1900 when he examined the holotype of Gabb’s species and is discussed herein under the description of Simbirskites lecontei (Anderson). The holotype of Neocmspedz'tes rectom's Anderson (1938, p. 157, pl. 23, fig. 2) (see this paper, pl. 40, figs. 8, 10) is comparable in size to the small whorl of N. agm'la (pl. 34, fig. 6). It differs by having a stouter whorl sec: tion, stronger and fewer primary ribs, and about four secondary ribs for each primary rib. H ertleim'tes agm'la (Anderson) was assigned to N eo- craspedites by Anderson (1938, p. 157) on the basis of its resemblance to Omspedz'tes temuis Von Koenen (1902, p. 76, pl. 6, figs. 1—3, pl. 13, figs. 1a, b), which Spath (1924, p. 76, 87) assigned to Neocmspedites. The re— semblance is apt in regard to degree of involution, gen- eral rib pattern, and sutural pattern. H. aguz'la Ander- son differs, however, by having a much stouter whorl section, a moderately instead of a narrowly rounded venter, a vertical instead of a steep umbilical wall, and by its ribbing remaining fairly strong on the flanks during growth instead of fading. H. agm'la differs even more from other European species that have been assigned to Neocmspedz’tes (Von Koenen, 1902, pl. 5, figs. 5—16, pl. 6, figs. 18, 19; d’Orbigny, 1942, pl. 61, figs. 1—3; Neumayr and Uhlig, 1881, pl. 26, fig. 2; Danford, 1906, pl. 10, fig. 1) by being much more evolute, by retaining ribbing on the middle of the flanks, by its ribs being weakly instead of strongly arched forward on the venter, and by the persistence of constrictions on adult whorls. The fact that Hertleimltes aguc’la, (Anderson) re- sembles 1V. tenm's (Von Koenen) more than the other species of the genus may have stratigraphic significance, considering that N. term-2's is recorded (Von Koenen, 1902, p. 76, 418) as probably from the middle Hauteriv- ian zone of Uraspedoddscm phillipsi, whereas the other species are recorded from beds of middle Valanginian to early Hauterivian age (Von Koenen, 1902, p. 418). On the basis of stratigraphic position, Hertleinites aguila (Anderson) cannot be as old as the middle Hau— terivian beds characterized by Simbz'rs/cz'tes and is therefore younger than any of the European species of Neocrwspedites except possibly N. tenm's (Von Koenen). H ertleim'tes agm'la, also shows resemblance in ribbing, coiling, and whorl shape to European species of the genus Umspedodz'seus of middle to late Hauterivian age (Von Koenen, 1902, pl. 37, figs. 1, 2, pl. 38, fig. 4; SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY Neumayr and Uhlig, 1881, pl. 15, figs. 7a—c; Weerth, 1884, pl. 4, figs. 2a, b, 3; Pavlow, A, 1901, pl. 3, figs. 2, pl. 4, figs. 2, 3, pl. 6, figs. la—d, pl. 7, figs. 2a-c, 3a—c) . Small specimens of Uraspedodiscus greatly resemble small specimens of the several species from California that Anderson assigned to N eocraspedites, except that their primary ribs generally terminate in tiny tubercles, the secondary ribs are more strongly arched on the venter, more secondary ribs arise freely on the flanks, and the whorls are generally more compressed. During growth the. species of Oraspedodiscus become more and more compressed, the venter becomes very narrowly rounded, the ribs disappear from the middle of the flanks and finally from the umbilical region, but the umbilicus re— mains narrow to fairly narrow. The change in whorl section of 0. discofalcatus (Lahusen) from moderately compressed to strongly compressed, as illustrated by A. Pavlow (1892, pl. 18 (11), fig. 2b; 1901, pl. 6, fig. 10), is in striking contrast to the whorl section of the species of H ertleimites. Type: Holotype Calif. Acad. Sci. 8769; Plesiotypes, USNM 129654—129656. Localities: USGS Mes. locs. 2222, 2223, 2225, 2267; CAS 10c. 1353. Hertleinites pecki Imlay, n. sp. Plate 35, figures 1, 3—5, plate 43, figures 1—3 Two specimens of this species were obtained by Stan- ton (Mes. loc. 1092) on the eastern part of the Wilcox Ranch, Tehama County, Calif, at a position from 50 to 200 feet above the sandy beds containing Buchia emissi- collie (Keyserling). Another specimen was obtained about 3 miles to the south and probably somewhat higher stratigraphically (U. C. Berkeley B—5089). The holotype (pl. 35, figs. 4, 5) shows the features of two whorls. The inner whorl at a diameter of 82 mm has a whorl height of 39 mm, a whorl thickness of 31 mm, and an umbilical width of 18 mm. The whorl is subquadrate in section and embraces about three- fourths. The flanks are flatened. The venter is evenly rounded. The umbilicus is fairly narrow; its wall is low, vertical, and rounds abruptly into the flanks. The primary ribs are broad and fairly closely spaced. They curve backward on the umbilical wall, curve forward on the flanks, and bifurcate at about two—fifths of the height of the flanks into sharper secondary ribs. Gren- erally one rib of each pair bifurcates again above the middle of the flanks. A few ribs arise freely near the middle of the flanks. Secondary ribs outnumber the primary ribs about 4 to 1. The ribs arch forward gently on the venter. Weak constrictions are present. The outer whorl of the holotype is much crushed lat— erally but embraces about three-fifths of the preceding AMMONITES 0F EARLY CRETACEOUS AGE FROM THE PACIFIC COAST STATES whorl. It bears moderately prominent primary ribs that curve backward on the umbilical wall, incline for- ward on the flank and bifurcate near the middle of the flanks. A few secondary ribs arise freely on the flanks, and some secondary ribs bifurate on the upper parts of the flanks. Secondary ribs outnumber the primary ribs about 3 to 1. On the venter all ribs arch forward weakly. Several weak constrictions are present. A larger specimen associated with the holotype shows parts of two whorls. It is much worn, but reveals some- what coarser ornamentation. As it is entirely septate and has an estimated diameter of 210 mm, the adult of the species must have been at least 300 mm in diameter. The suture line is similar to that of H ertleim'tes agm’la (Anderson), differing mainly by the first lateral and external lobes being nearly equally long. A specimen (pl. 43, figs. 1—3) in the University of California collections at Berkeley shows the last sep- tate whorl and fragments of the body chamber. The septate part of the specimen is comparable in size and ornamentation to the holotype but appears to have a smaller umbilicus. This difference is due mainly to deformation of the specimens and is not considered to be of specific importance. Compared with H ertleim'tes aquila (Anderson), this species is more compressed, its flanks are flatter, its umbilicus is smaller on its inner whorls, and its ribv bing is weaker and denser on its inner whorls but sparser on its outer whorls. Compared with “Neo- craspedz’tes” sigmlis Anderson (1938, p. 157, pl. 26, fig. 1), this species has a narrower umbilicus, flatter flanks, and much sharper secondary ribs. Its inner whorls compared with the holotype of H. rectom's (Anderson) (1938, p. 157, pl. 23, fig. 2) are more compressed, bear finer ribbing, and have fewer secondary ribs per primary rib. This species is named in honor of Joseph H. Peck, Jr., of the University of California at Berkeley. Types: Holotype USNM 129835; paratype, USNM 130023; paratype, U. 0. Berkeley 12120. Localities: USGS Mes. Ice. 1092. U. S. Berkeley 100.. B—5089. Genus SIMEBIRSKITES Pavlow, 1891 Simbirskites broadi (Anderson) Plate 33, figures 16—18 Simbirskites broadi Anderson [part], 1938, Geol. Soc. America Spec. Paper 16, p. 155, pl. 22, figs. 2, 3, not pl. 28, figs. 1, 1A. 7Subastieria. chamhelula Anderson, 1938, idem, p. 156, pl. 22, figs. 4, 5. The original description of the holotype is accurate, except for the statement concerning the lateral tuber- 209 cles. These arise near the top of the lower third of the flanks instead of near the middle. Also, the ribs arch forward gently on the venter. The specimen that Anderson figured as a paratype of S. broadi on his plate 28, figures 1, 1a (see this paper, pl. 33, figs. 1, 14, 15) is much more compressed than the holotype and has weaker tuberculation. It more likely represents an immature stage of Simbz'rskites lecontei (Anderson) (1938, p. 154, pl. 22, fig. 1, pl. 23, fig. 1). However, the specimen that Anderson named Subastiem'a chanchelula (see this paper, pl. 33, figs. 23, 24) compares very closely in whorl shape and orna— mentation with the inner whorls of S. broadz' and probably represents an immature stage of that species. These probabilities are strengthened by the fact that all the specimens in question were obtained from a single locality. S. broadi was compared by Anderson (1938, p. 155) with S. dechem' Pavlow [not Roemer] (A. Pavlow, 1892, pl. 18, (11), figs. 4—6; Spath, 1924, p. 77) from England. Both species have a similarly depressed whorl section, but S. broadi has finer, denser ribbing. Some specimens of Simbirslcites from Russia described by A. Pavlow (1901, p. 69, pl. 1, figs. 4—6) as S. deckem' Lahusen have ribbing that is only a little coarser than on S. broadi. Type: Holotype Calif. Acad. Sci. 8784. Locality: Calif. Acad. Sci. loc. 113. Simbirskites lecontei (Anderson) Plate 33, figures 1, 14, 15 Polyptychites leoontei Anderson, 1938, Geol. Soc. America Spec. Paper 16, p. 154, pl. 22, fig. 1, pl. 23, fig. 1. Simbirskites broadi Anderson [part], 1938, idem, pl. 28, figs. 1, 1A, [not pl. 22, figs. 2, 3]. Anderson says that tubercles are not present on the type specimens of P. leconteé, but examination of his specimens shows that small tubercles are present at the ends of the primary ribs at about one-third of the height of the flanks. They are visible, also, on the original illustration of the paratype (Anderson, 1938, pl. 23, fig. 1). The small ammonite that Anderson (1938, pl. 28, figs. 1, 1A) assigned to his species Simbz'rskz'tes broadz‘ has a compressed whorl shape much more similar to that of S. lecontei (Anderson) than to that of the holotype of S. broadi (Anderson). Its identification definitely with S. lecontei must await the discovery of other specimens of intermediate sizes. The assignment of S. Zecontei (Anderson) to Sim- bz'rs/cz'tes rather than Polyptychites is based on rib branching by threes and fours from tubercles that arise 210 a little below the middle of the flanks from prominent primary ribs. On Polyptychites the tubercles are situ- ated at or near the umbilicus, and rib branching com- monly occurs at several different heights on the flanks. Among European species, S. imierse‘lobatus (Neu- mayr and Uhlig) (1881, p. 19, pl. 17, figs. 1, 1a) com- pares with S. lecontei' (Anderson) in degree of involu- tion, whorl shape, and strong forward curvature of the ribbing on its flanks, but appears to have somewhat sparser ribbing. “Ammonites” tmwki (Gabb) (1864, p. 63, pl. 11, fig. 10, pl. 12, fig. 11) was considered by Anderson (1938, p. 154, 155) to be similar to his species “Polyptychites” lecontei Anderson. Similarities include the suture lines, subcircular whorls that embrace about one—half of the preceding whorls, mode of rib branching, shape of umbilicus, and probably umbilical tubercles. In his original description, Gabb does not mention the pres— ence of tubercles on Ammonites traslci, but later (1869, p. 137) he mentions that the Late Cretaceous Ammo— m'tes frotermos Gabb “is nearly a miniature of A. traski', in general appearance * * *.” As A. fratemus (equals Uanwdocems fraternum) bears prominent tubercles, it seems probable that the holotype of A. traski also was tuberculate. In particular the characteristics of the suture line of “A.” traski Gabb (1864, pl. 12, fig. 11) confirm the close relationship of that species with “Polyptychites” [econ- tez' (Anderson) and show that the similar appearing “Neocmspedites” agm'la Anderson (1938, pl. 25, fig. 2, pl. 68, fig. 4) is not closely related. Bearing on the identity of Ammonites traslci (Gabb) is a statement that T. W. Stanton made in his notebook on September 24, 1900, after examining the holotype of that species. He said, “Saw the figured type of Amm. Mask-ii Gabb and found it very different from the Horsetown form I have been identifying with it.” The specimens that Stanton had been identifying with Ammonites traski Gabb are herein identified with “Neocmspedites” aguila Anderson. This species differs from the holotype of A. traski (Gabb) (1864, pl. 11, , fig. 10), as illustrated, by having a slightly compressed instead of a subcircular whorl section, by its whorls embracing three-fifths instead of one—half of the pre- ceding whorls, and by having many more primary ribs on whorls of comparable size. Although Anderson maintains that “Amanom'tes” traski Gabb is a distinct species from “Polyptyehz'z‘ex” lecontei Anderson, his reasons for separating them are not made clear. As the holotype of A. fraskz' was de— stroyed in the San Francisco fire of 1906, the specific identity of that species may never be firmly established. The evidence discussed above indicates, however, that SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY A. traslci Gabb belongs in the same genus as Sim- bz'rslcites lecontei (Anderson) and is possibly identical. Types: Holotype Calif. Acad. Sci. 8762; paratype, Calif. Acad. Sci. 8763. Locality: Calif. Acad. Sci. 10c. 113. Slmblrskites sp. juv. at. S. elatus (Trautschold) Plate 33. figures 10, 11 One small specimen has a broadly depressed whorl similar to that of the innermost whorl of the holotype of Simbz'rskites broadi Anderson (see pl. 33, fig. 16) but differs by developing bifurcating ribs. The smallest part of the specimen has trifurcating ribs, but adorally bifurcating ribs become more common. A crushed frag- ment of a still larger whorl of the same ammonite shows that bifurcation continues as the dominant mode of rib branching. Prominent. tubercles occur at about two- fifths of the height of the flanks. This small specimen resembles the immature speci- mens of S. dechem' (Lahusen) as figured by A. Pavlow (1901, pl. 1, figs. 6a, b) but differs by developing bi- furcating ribs. It is likewise similar to an immature specimen from Speeton, England, that A. Pavlow ( 1892, p1. 18(11), fig. 5; 1901, p. 68) assigns to Simbz'rskites elatus (Trautschold), but differs by having considera- bly denser ribbing. It is similar to S. elatus, however, in the development of bifurcating ribs after an early stage in which trifurcating ribs predominate. Figured specimen: USNM 129680. Locality: USGS Mes. Ice. 1251. Simbirskites sp. juv. at. S. progredlens (Lahusen) Plate 33, figures 2, 3, 8, 9 Eight fragments from one locality in Oregon resem- ble immature specimens of S. progredz'ens (Lahusen) as figured by A. Pavlow (1892, pl. 18(11), fig. 15; 1901, pl. 2, figs. 50, d). Their ornamentation is possibly a little sharper than that of S. prog‘rediens and in that respect they show some resemblance to S. ooncz'mms Phillips, as figured by A. Pavlow (1891, pl. 18(11), fig. 16). That species, however, develops rib furcation by twos, whereas on the Oregon specimen furcation oc— curs mostly by threes. Figured specimens: USNM 129681. Locality: USGS Mes. 10c. 25211 (equals 24449). Slmblrskites app. juv. Plate 33, figures 4—7, 12, 13 Associated with the coarsely ribbed specimens re- ferred to Simbirski'tes sp. juv. aff. progrediem (Lahu- sen), shown on plate 33, figures 2, 3, 8, 9, are many other immature ammonites that appear to belong to the same AMMONITES 0F EARLY CRETACEOUS AGE FROM THE PACIFIC COAST STATES genus, but they differ by being much finer ribbed. These can be arranged roughly into three groups based on fineness of ribbing and number of secondary ribs. All three groups .have the same shape, the same general rib pattern, and numerous constrictions. In the group with the coarsest ribbing, the secondary ribs arise in pairs from prominent tubercles at the ventral ends of the primary ribs. A few ribs arise singly low on the flanks or are indistinotly connected with a tubercle. In the group with next finest ribbing, secondary ribs arise mostly in pairs from the lateral tubercles, but some arise in threes and many ribs arise freely low on the flanks. In the group with finest ribbing, most second- ary ribs arise by threes from very weak lateral tubercles, and most bundles of ribs are separated by a single rib that begins low on the flank. On the basis of the material on hand, it is impossible to be certain whether these three groups are distinct species or are merely variants of a single species. They are illustrated to show that considerable variation may occur in Simbirskites at a single locality. Figured specimens: USN M 129682. Genus HOLLISITES Imlay, 1957 The original description of this genus (Imlay, 1957, p. 276) is as follows: This genus has a stout to fairly stout shell, moderately evolute coiling, regular bifurcating ribs on its inner whorls, virgatoid ribs on its outer whorls, and a suture line characterized by a fairly wide first lateral lobe. H. lucaxi Imlay, n. sp.. is desig- nated as the genotype. Immature specimens of Hollisitcs have perisphinctoid ribbing similar to that on small specimens of the genus Spectoniccras (Spath, 1924, p. 76) from England (Danford, 1906, pl. 12, fig. 3) and Russia (M. Pavlow, 1886, pl. 1, figs. 4, 5; A. Pavlow, 1892, p1. 15(8), figs. 3a—c; pl. 18(11), figs. 12, 14), differing mainly by losing their lateral tubercles at a very small size. Adult specimens of Hollisites differ from the adults of Spectoniccras (M. Pavlow, 1886, pl. 1, fig. 1, pl. 2, figs. 1a, b ;.A. Pavlow, 1892, pl. 18(11), fig. 13a ; Karakasch, 1907, pl. 13, fig. 4a) by being more involute, by acquiring weaker, denser, virgatoid ribbing, and by lacking tubercles at the points of rib furcation. The branching of the ribs at various heights above and below the middle of the flanks is in striking contrast to the regular bifurcation of the ribs on the adults of Spectoniceras. Among Eurasian species Hollisites probably includes “Sim- birskites” auerbachi Eichwald (1868, p. 1092, pl. 34, figs. 9(3—d; Karakasch, 1907, p. 130, pl. 13, figs. la, b, 5a, b, pl. 24, figs. 30, 31) from the Crimea and “Perisphinctcs” kocncni Neumayr and Uhlig (1881, p. 18, pl. 21, figs. 1, 1a) from Germany. Hollisitcs is named in honor of Hollis M. Dole, State Geologist of Oregon. Hollisitcs has been found in Oregon associated with the. am- monite Simbirskites of middle Hauterivian age. In California it occurs with, or slightly below, Hertlcinites aguila (Anderson) of late Hauterivian age. The large fragment named Polypty- chi/tea hespcrius Anderson (1938, p. 154, pl. 24, figs. 1, 2) prob- ably belongs to Hollisites and was found at the same locality 52.7569 0—60——3 211 as Simbirskitcs broadi Anderson (1938, p. 155, pl. 22, figs. 2, 3). Judging from these occurrences, Hollisites is of middle to late Hauterivian age. Immature specimens of Hollisites may be distin- guished from Thummannicems of similar size by their convex instead of flattened venter, by their ribs arching forward on the venter instead of crossing the venter transversely, and by their many shallow constrictions. Adult specimens of Hollisites show some resemblances in rib pattern to adult specimens of Hertleim'tes but dif- fer by having stouter whorls, more evolute coiling, much stronger and sparser ribbing, and a broader first lateral lobe. Immature specimens of the two genera differ in many respects, as shown on plate 38, figures 1—10 and plate 40, figures 8, 10. Hollisites lucasi Imlay Plate 35, figure 2: plate 36; plate 38, figures 2, 5; plate 37, fig- ures 1, 2, 11—13 Hollisitcs Iucaai Imlay, 1957, Jour. Wash. Acad. Sci, v. 47, no. 8, p. 276, figs. 1, 2. The original description of this species is as follows: The holotype is entirely septate and the body chamber is un- known. At the beginning of the outermost whorl of the holo- type the whorl section is ovate and as wide as high. At the adoral end the whorl is a little wider than high. The outer whorl embraces about half of the preceeding whorl. The flanks are gently convex and the venter is evenly rounded. The um— bilicus is moderate in width and fairly shallow. The umbilical wall is vertical, fairly low, and rounds abruptly into the flanks. The ribbing on a small specimen and on the inner whorls of a paratype is perisphinctoid. The primary ribs curve backward on the. umbilical wall. incline forward on the flanks, and bi- furcate regularly at the middle of the flanks. The secondary ribs incline forward more strongly than the primary ribs and arch forward gently on the venter. The furcation points are swollen but not tuberculate. Toward the adoral end the ribbing tends to become flexuous and at two places is virgatomous. Constrictions are common. The ribbing on the outer whorl of the paratype, just men- tioned, and on the holotype is mostly virgatomous. The pri- mary ribs bifurcate at about two-fifths of the height of the flank and then the posterior rib of each pair of secondary ribs bifurcates again at about three-fifths of the height of the flanks. The secondary ribs are appreciably weaker than the primary ribs. are inclined forward more strongly on the flanks, and arch forward gently on the venter. Eight constrictions occur on half a whorl. Toward the adoral end of the holotype more of the secondary ribs bifurcate above the middle of the flank and some secondary ribs arise freely near the middle of the flanks. The holotype at a diameter of 170 nun has a whorl height of 67 mm, a whorl thickness of 69 mm, and an umbilical width of 58 mm. The suture line greatly resembles that of Hcrtleinifcx aguila Anderson (1938. pl. 25. fig. 2. pl. 68. fig. 4) in general plan. It differs mainly by having a broader first lateral lobe. H. lucasi Imlay, n. sp., greatly resembles “Simbirskitcs” aucrbachi Eichwald (Karakasch, 1907. p. 130, pl. 13, figs. 1a, b, 5a. b) from the (‘rimea in plan of ribbing and in suture line. It differs by having more virgatomous ribs and a somewhat 212 broader venter. Its rib pattern is similar to that of “Peri- sphinctes" Icoenem: Neumayr and Uhlig (1881, p. 18, pl. 21, figs. 1, 1a) from Germany, but it differs by having much stouter whorls and broader sutural lobes. Hollisites lucasi Imlay, n. sp. is named for Larry Lucas of Agness, Oreg., who collected the holotype specimen on the south side of the Rogue River 11/2 miles below Agness, Curry County, Oreg. Its age is probably middle Hauterivian because from the same general location have been found specimens of Hannaitcs riddlensis (Anderson), Shnbirskites?, and Hoplocrioceras. The paratypes were obtained at USGS Mesozoic locality 1092 in association with, or just below, Hertleim'a [=Hertleim‘tes] agm‘la (Anderson) which is considered to be of late Hauterivian age. Typos: Plastoholotype, USNM 129045; paratypes, USNM 129044. The holotype specimen is the property of Larry Lucas at Agness, Oreg. Localities: USGS Mes. loc. 1092, 26450, and questionably at 25214. Hollisites dichotomus Imlay, n. sp. Plate 38, figures 6, 7 This species is represented by one internal mold of a medium-sized specimen that probably is not an adult. The whorls are subquadrate in section, a little higher than wide, and embrace about two-fifths of the pre- ceding whorl. The flanks are flattened below and round evenly above into a gently convex venter. The umbilicus is fairly wide, the umbilical wall is low and vertical, and the umbilical edge is abruptly rounded. The body chamber is represented on the holotype by half a. whorl but is incomplete. The ribbing of the inner whorls of the holotype, as exposed in the umbilicus, consist of fine moderately spaced primary ribs that are radial on the umbilical wall, incline forward on the lower half of the flanks, and divide into two secondary ribs at, or just below, the umbilical seam. Several weak constrictions are present. On the largest whorl of the holotype the ribs branch a little above the middle of the. flanks and the furcation points are merely swollen. The holotype at a diameter of 38 mm has an umbili- cal width of 12 mm, a whorl height of 14 mm, and a probable whorl width of 12 mm. This species greatly resembles the immature speci- men of “Simbirskites” auterbachi (Eichwald) figured by Karakasch (1907, pl. 13, figs. 1a, b) from the Cri— mea. It differs apparently by its ribs bifurcating slightly higher on the flanks. Speetom'cems inversum (A. Pavlow (1892, p. 508, pl. 18 (11), figs. 14a, b) from England has much coarser ribbing and a more rounded whorl section. The ribbing on H. dichoto- mus Imlay is similar to that on the specimens of H. lucasi Imlay at a comparable size, but differs by being coarser, more widely spaced, and more strongly arched forward on the venter. ‘ SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY Type: Holotype, USNM 129659. Locality: USGS Mes. loc. 1251. Hollisites sp. juv. cf. H. dichotomus Imlay, n. sp. Plate 38, figures 3—5, 8—10 Nine external molds of immature specimens bear ribbing similar to that exposed in the umbilicus of II. dichotomus Imlay, n. sp., and possibly belong to that species. The whorls are ovate in section and broader than high. They are smooth to a diameter of about 7 mm. Then ribbing appears abruptly and becomes fairly strong in one—fourth of a whorl. The primary ribs begin singly low on the umbilical wall, trend radially to the umbilical edge and incline forward nearly straight to the middle of the flanks, where most of them divide into two slightly weaker secondary ribs. The latter arch forward strongly on the upper part of the flanks and on the venter and are not. reduced in strength along the midventral line. lVeak tubercles are present at the points of rib furcation. Several weak constrictions are present. Figured- specimcn: USNM 129657. Locality: USGS Mes. Inc. 2078. Hollisites inflatus Imlay, n. sp. Plate 37, figures 1, 3, 4, 6 The species is represented by 1 specimen consisting of parts of 3 septate whorls. The whorls are ovate in section and broader than high and become more depressed during growth. The flanks round evenly into a broadly convex venter. The umbilicus is mod— erate in width. The umbilical wall is low and vertical at base and rounds rather abruptly into the flanks. The body chamber is unknown. The ribs are strong, incline forward gently on the flanks, and arch forward slightly on the venter. On the smallest known whorl the primary ribs bifurcate near the middle of the flanks into slightly weaker sec— ondary ribs. The furcation points are swollen, but not tuberculate. On the next larger whorl, rib branch— ing occurs by threes and twos just below the middle of the flanks, and the primary ribs are appreciably stronger than the secondary ribs. The next larger whorl is not well enough preserved to show the sec- ondary ribs, but does show prominent primary ribs that. curve backward on the umbilical wall and incline forward on the flanks. Constrictions are numerous and pronounced. The suture line is only partly preserved but appears to be essentially the same as in H. Zucasi Imlay. The smaller whorl of H. inflatus Imlay, n. sp., may be compared with Speentonicems subz'n’versus (A. Pav- AMMONITES OF EARLY CRETACEOUS AGE FROM THE PACIFIC COAST STATES low) (1892, pl. 18 (11), figs. 13a, b), from Speeton, England. It differs by having finer denser ribbing and a more depressed whorl section and by lacking tubercles at the ends of the primary ribs. The fragment of a large ammonite that was named Polyptychz'tes hesperius Anderson (1938, p. 154:, pl. 24, figs. 1, 2) possibly belongs to the genus H Ollisites, as it shows some resemblances both to II. inflatus Imlay, n. sp., and to H. Zucasz' Imlay. It appears to differ from both species by its primary ribs being strongly swollen near the umbilicus and branching mostly on the lower fifth to fourth of the flanks. Some ribs bifurcate again near the middle of the flanks, and some arise singly low or near the middle of the flanks. H. inflatus differs from H. Zucasi by having a much wider whorl section and stronger, sparser ribbing. Type: Holotype USN M 129839. Locality: USGS Mes. 10c. 1092. Genus SPEETONICERAS Spath, 1924 Speetoniceuras agnessense Imlay, n. sp. Plate 42, figures 6, 9, 10, 15, 17 Only one specimen of this species is known. It. shows parts of four whorls including the adoral end of the body chamber. The whorls are depressed ovate in sec- tion, wider than high, and embrace about two-fifths of the preceding whorl. The flanks and venter are gently convex. The umbilicus is fairly wide, the umbilical wall is low and vertical, and the umbilical shoulder is evenly rounded. The body chamber is incomplete at its adapical end, but includes at least two-fifths of a whorl. The two inner whorls, shown in the umbilicus, bear strong, widely spaced, forwardly inclined primary ribs that begin low on the umbilical wall and terminate ven- trally in tubercles at the line of involution of the suc- ceeding whorl. The penultimate whorl bears sharp, moderately spaced primary ribs that. incline forward on the lower two-fifths of the flanks and terminate in weak radially elongate tubercles. From these arise pairs of sharp secondary ribs that trend radially near the middle of the flanks and then strongly forward on the upper part of the flanks and on the venter. On the body chamber the ribbing becomes much stronger and sparser. The primary ribs are swollen at the furcation points, which become lower adorally. The last three ribs bor- dering the aperture are a little higher than the others and do not fork at all. The secondary ribs arch for- ward considerably on the venter without reduction in strength. The holotype at its anterior end has a whorl height of 20.5 mm and a whorl width of 22 mm measured in the interspaces. The penultimate whorl has a whorl 213 height of 12.5 mm and a whorl width of 15 mm. The body whorl has an umbilical width of 23 mm at an esti- mated diameter of 60 mm. The suture line is not well preserved. This species is characterized by a. marked increase in the coarseness of its ribbing between the penultimate and body whorls. It is distinguished from most species of Speefom'cems by having finer ribbing on its inner whorls and by being less evolute. Probably the most similar species is S. subinversum (M. Pavlow) as fig- ured by A. Pavlow (1892, p. 507, pl. 18 (11), figs. 12a, b, 13a, b) from Speeton, England. The Oregon species is readily distinguished, however, by the finer ribbing of its inner whorls. S. agnessense Imlay, n. sp., is assigned to Speetoni— Gems rather than to H oliisites because of the persistence of its lateral tubercles and by the development of high, sharp, widely spaced ribs that bifurcate regularly below the middle of the flank. Type: Holotype USNM 129658. Locality: USGS Mes. 100. 26879. Genus NEOCOMITES Uhlig, 1905 Neocomites? cf. N. indicus Uhlig Plate 41, figures 2, 6 Two fragmentary ammonites have characteristics similar to those of N. indim/s Uhlig (1910, p. 262-264, pl. 89, figs. 3-6), from the Valanginian of India. On the smaller specimen (pl. 41, fig. 2) the outer whorl em- braces about one-third the preceding whorl. The umbil- ical wall is vertical. The flanks are flattened in their lower half but converge above toward the venter. The venter is narrow and flattened. The ribs begin at the line of involution, incline backward on the umbilical wall, and pass into tubercles of varying prominence on the umbilical edge. On the flanks the ribs are high, thin, slightly flexuous, and forwardly inclined. They arise from the umbilical tubercles singly or in pairs. Commonly the. bundles of paired ribs are separated by 1 or 2 single ribs. About two-thirds of the ribs bifur- cate on the flanks at heights varying from just below to a little above the middle. Near the anterior end of the specimens, bundling of the ribs at the umbilicus becomes more common. All ribs terminate ventrally in blunt tubercles that bound a smooth midventral area. No lateral tubercles are evident. Constrictions are fairly common. The larger specimen (pl. 41, fig. 6) shows bundling of the ribs at prominent umbilical tubercles. Between suc— cessive bundles occur from 1 to 3 single ribs that are merely swollen at the umbilical edge. Rib branching on the flanks is not evident. 214 These specimens from Oregon resemble N. indicus Uhlig in their high narrow ribs, the bundling of the ribs at umbilical tubercles, and the presence of con- strictions. The venter is not sufficiently exposed to show if the cross section is wedge shaped as in N. indicus or is elliptical. Another Indian species, N. theodom‘i (Oppel) (Uhlig, 1910, p. 260—262, pl. 89, figs. 1, 2), is likewise similar but has finer ribbing and less frequent rib bundling at the umbilicus. Both these Indian species were referred questionably by Spath (1939, p. 76, 78, pl. 14, figs. 7a, b) to his genus Parandiceras (1939, p. 76), from which they differ by their ribs being more flexuous and irregularly branched on the flanks and rather commonly arising in pairs from umbilical tubercles. Spath (1939, p. 77) consid- ers both species as intermediate in character between Parandicems and Calliptychocems Spath (1924, p. 88; Uhlig, 1910, p. 251, pl. 87, figs. 2a—c). The species of Calliptychocems (Uhlig, 1910, p. 250—255, pl. 86, figs. 1, 2, pl. 87, figs. 1—4, pl. 90, figs. 3, 7) possess bundled ribs at the umbilicus, as in the specimens from Oregon, but differ from them by having an oblique instead of a vertical umbilical wall, somewhat weaker ribbing that tends to weaken even more on the body chamber, and weaker lateral tubercles on the adult whorl. The Oregon specimens herein compared to N coco-m- ites indicus Uhlig likewise show a general resemblance in shape and ribbing to Sarmz'nella trezanensis Lory (Sayn, 1907, p. 34, pl. 3, figs. 25a, b; Baumberger, 1923, p. 307, pl. 8, figs. 2—4), from the middle Valanginian of France and Switzerland, but lack lateral tubercles on their inner whorls. Figured specimen: ITSNM 129858. Localities: USGS Mes. locs. 2117, 2119, Oregon. Genus THURMANNICERAS Cossmann, 1901 Thurmanniceras californicum (Stanton) Plate 39, figures 11—15 Desmoceras californ-icum Stanton, 1895, US. Geol. Survey Bull. 133, p. 76, 77, pl. 15, figs. 6, 7 [1896]. The original description and illustrations of this species are fairly accurate but do not depict all the features that can be seen on the type specimens. As mentioned by Stanton, there are three unfigured frag- ments that probably belong to the same individual ammonite as the figured holotype. Illustrations of these clearly show that the species belongs in the Neo- comitinae. In particular, the largest fragment (pl. 39, figs. 11, 13), which is part of the body chamber, resembles the largest whorls of Thumnanniccras novi- hispaniomn (lmlay) (1937, pl. 78, fig. 8, pl. 79, fig. 6), from the Valanginian of eastern Mexico. The smaller fragments (pl. 39, figs. 12, 14, 15) greatly resemble SHORT‘ER CONTRIBUTIONS TO GENERAL GEOLOGY Thumnannicems pertramz'em (Sayn), as figured by Leanza (1945, p. 64, pl. 10, figs. 5—7) from the Valanginian of Argentina. Most of the specimens from southern France that Sayn (1907, p. 43, 44, pl. 4, fig. 14, pl. 5, figs. 10—11, 15-17) described under the name of T. pertmmiem are too small for comparisons, but. the largest specimen illustrated by Sayn on his plate 5, figure 10, certainly bears a strong resemblance to the specimens from Argentina and to the smaller specimens of T. califomi- (rum (Stanton). All these specimens have a similar evolute form, elliptical whorl shape, numerous for- wardly inclined constrictions, and fine, dense, for- wardly inclined ribbing that during growth tends to fade out on the lower and middle parts of the flanks. As a result the furcation, points of the ribs are rather indistinct 011 the body whorl and the penultimate whorl. On the (‘alifornia specimens the furcation of ribs on the upper third of the flanks can be observed at. only a few places. The secondary ribs outnumber the pri- mary ribs more than 2 to 1 and arise either freely, or are indistinctly connected with the primary ribs along a zone a little above the middle of the flanks. The ribs are weakly swollen 011 the edge of the umbilicus and are slightly reduced in strength on the venter. The whorl section becomes subtrapezoidal on the body chamber. On the basis of the material on hand, T. califor- m'oum (Stanton) appears to differ from T. pcrtramiens (Sayn), from France, by being more evolute and by having finer ribbing. The specimens from Argentina assigned to T. pertramiens by Leanza are closer to T. oaliform'cum in these respects than to the types of T. pertmmz'em from France and could very well belong to the same species, as T. caliform'cum. Such an identi- fication must await the finding in California of addi- tional specimens showing the early growth stages of T. califomicum. Associated with the holotype of T. caliform'cum (Stanton) is a small specimen that Stanton (1895, p. 17 [1896]) referred to Hoph'tes dillem’ Stanton. It belongs to Thu/rinamzinems, however, and probably is an immature representative of T. californicum. Typc: Holotype ITSNM 23087. Locality: USGS Mes. Inc. 1001. Thurmanniceras wilcoxi (Anderson) Plate 40. figures 3—5 L’Vencmspeditcs tL‘iIf‘OII‘i Anderson. 1938. Geol. Soc. America Spec. Paper 16, p. 158, pl. 26, fig. 2, pl. 27, fig. 4. Anderson failed to mention in his original descrip- tion that the dorsum of the inner whorl of the holotype AMMONITES 0F EARLY CRETACEOUS AGE FROM THE PACIFIC COAST STATES bears an imprint of a flattened venter which is bor- dered on both sides by single rows of weak tubercles. (See pl. 40, fig. 3.) The presence of such a. venter bars an assignment to N eocmspedites, but favors an assign- ment to the Neocomitidae. In fact, the lateral appear— ance and the character of the ribbing is rather similar to that of Thurmanniceraw califomécum (Stanton) (il- lustrated herein on pl. 39, fig. 15). The species are dis— tinguishable easily, however, by their whorl sections, which on T. caiifornicmn is elliptical and compressed and on T. Wilson is subquadrate and stout. The holotype of T. mam (Anderson) was obtained in. shales in the eastern part of the Wilcox Ranch well above the standy beds containing Buchia crawsicollz's (Keyserling), according to Anderson (1938, p. 158). It seems improbable, however, that the holotype was ob— tained as high stratigraphically as the specimen (Mes. loc. 2267) of “Neocraspedz’z‘es” agm’la Anderson (see pl. 34, fig. 6) that Stanton obtained on the same ranch 400 to 500 feet above the beds containing Buchz'a crtwsicollis (Keyserling). Typo: Holotype Calif. Acad. Sci. 8771. Thurmanniceras jenkinsi (Anderson) Plate 40. figures 1, 2, 6, 7, 9 Neocomitcs jenkinsi Anderson. 1938. Geol. Soc. America Spec, Paper 16, p. 165, pl. 29, fig. 1. ?.Yc0(-omitcs m’ocmnicnsis Anderson, 1938. idem, p. 166, pl. 83, figs. 2. 2a. The collections of the Geological Survey contain three specimens that are definitely assigned to this spe- cies. In addition, 9 immature or fragmentary speci- mens from Mesozoic locality 1091 (equals 2266) and 1 from Mesozoic locality 1093 probably belong to the species. The three largest specimens, including the holotype, are much crushed laterally, but probably had a shape similar to that of the smaller specimen shown on plate 40, figures 1, 2. This specimen has a stout whorl section, about two- thirds as wide as high. Its whorls overlap about one— half. Its umbilicus is moderate in width, and its um- bilical wall is inclined. It bears lateral tubercles on an inner whorl exposed in the umbilicus. It also bears ventral tubercles bordering a. smooth midventral area at diameters less than 27 mm. At diameters greater than 27 mm, the ribs cross the venter transversely with slight weakening. Tubercles are not present on the three larger specimens. All the specimens have the same kind of fairly thick low closely spaced fasciculate ribs. The ribs all begin singly, low on the umbilical wall, are faintly swollen at the edge of the umbilicus, are rather strongly flex- uous on the flanks, and cross the venter transversely 215 with only slight reduction in strength along the mid- ventral line. A few of the ribs bifurcate between the lower third and the middle of the flanks. More than half of the ribs bifurcate between the middle and the upper third of the flanks. About one-third of the ribs do not bifurcate. 0n the internal mold the ribs appear to be fine, but where the shell is preserved they are a little wider than the interspaces. All ribs become wider ventrally. A number of weak constrictions oc- cur on each whorl, and are strongest on the inner whorl of the smallest. specimen. The suture line, as preserved on a plaster replica of the holotype, has a slender, trifid, symmetrical first lateral lobe. This species is placed in Thurm-anniceras rather than Neocomites because it lacks umbilical tubercles, has an oblique instead of a. vertical umbilical wall, has a gently rounded rather than a truncated venter, except on immature specimens, does not have rib furcation at the umbilical edge, does have rib bifurcation mostly above the middle of the flanks, does not have a smooth midventral area except at a, very small size, and does have constrictions even on large, adult whorls. The presence of a slender, symmetrical first lateral lobe shows that it does not belong to Lyticoceras. Among foreign species the most similar are Thur- mrmnicems dumznense (Gerth) (1925, p. 97, pl. 4, figs. 1, 1a) and T. discoidalis (Gerth) (1925, p. 18, pl. 5, figs. 3, 3a), from the Berriasian of Argentina (Leanza, 1945, p. 65—67, table opposite p. 96). Of these, T. discoidalz‘s is most. similar to T. jenki/nsz' (Anderson), differing mainly by having coarser, sparser ribbing. Both of the Argentine species, as illustrated by Gerth, have a smooth midventral area, but Leanza (1945, p. 66) says that this feature is confined to the internal mold and that wherever the shell is preserved on the venter, the ribs are not interrupted but only weakened. Another Argentine species with fasciculate ribbing similar to T. jenkz'nsi is N eocomites wichmanm' Leanza (1945, p. 61, pl. 12, figs. 2, 3), from the lower to middle Valanginian. This species, however, has umbilical and ventral tubercles, a truncated venter, and a smooth mid- ventral area. Among species of Thummaniceras from California, the most similar is T. califomicum (Stanton), rede- scribed herein, which is more evolute, has much coarser primary ribs, fewer secondary ribs, and much less dis— tinct bifurcation points. Another similar species is “N eoomnites” pmeneocom— icmz’s Burckhardt (1912, p. 193, 194, pl. 45, figs. 14, 16—18, 20—23), from the Berriasian of eastern Durango, Mexico. The holotype of this species, compared with T. jenkimz' at a similar size (pl. 40, fig. 6), differs by being more involute and by having sharper, less flexu- 216 ous ribbing. As in T. jenkinsi the lack of umbilical and ventral tubercles, the oblique umbilical wall, and the continuation of ribs across the venter suggest ge- neric reference to Thurmanniceras, or perhaps Submar- manm‘a, rather than Neocomites. T. jenkimi is recorded by Anderson (1933, p. 322; 1938, p. 165) from California Academy Science 10- cality 33502 (equals 2398 of Anderson) on McCarthy Creek, Tehama County, at a stratigraphic position stated to be about 2,400 feet above the base of the Cretaceous. The associated species according to An- derson include Thurmanm'a paekentae Anderson (1938, p. 162), Subastieria chanchelula Anderson (1938, p. 156), and Bewiasella crassz'ph'cata (Stan- ton) (Anderson, 1938, p. 164). The specimen that Anderson assigned to Sub— astiem‘a is herein referred to Polyp‘tychites (pl. 31, fig. 14). The specimen described as Thurmanm'a padre??— tae Anderson is possibly an immature example of Thurmannicems stippz' (Anderson). The specimen referred to Berriasella cmssiplz'cota (Stanton) is a small fragment of a whorl of Kilianella. It is not the same as the specimen of Kilianella crassiphcata (Stan— ton) figured by Anderson (1938, pl. 83, figs. 3, 4) and cannot be identified specifically. Types: Holotype, Calif. Acad. Sci. 8775. 23223. 129859, 129860. Localities: U SGS Mes. 33502. Plesiotypes, 1' SNM locs. 1088, 1091, 2154; (‘AS 100. Thurmanniceras stippi (Anderson) Plate 39, figures 14), 8—10 Neocomitcs stippi Anderson, 1938. Geol. Soc. America Spec. Paper 16, p. 166, pl. 29, fig. 2. Three specimens of this species have been found in southwestern Oregon. The coiling is fairly evolute. The whorls are subquadrate in section, wider than high. The flanks are nearly flat. The venter is narrow, flat— tened in the young and gently convex in the adult. The umbilical wall is low and steep. Only the beginning of the body chamber is preserved. The immature whorls, exposed in the umbilicus (pl. 39, figs. 4, 10), have high, sharp, slightly flexuous K271i- (mella-like ribs of which all begin singly at the um- bilicus. Some bifurcate at or near the line of involu- tion and are swollen at the furcation points. During growth, bifurcation of the ribs just above the middle of the flanks becomes rather common. On the penultimate whorl (pl. 39, figs. 5, 8, 9) the ribs begin singly at the umbilicus, about two-thirds of them bifurcate above the middle of the flanks, and all terminate ventrally in elongate tubercles that are weakly connected across the venter. On the septate part of the body whorl and on the SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY body chamber, the ribs are thick, closely spaced, and gently flexuous. They all begin singly near the um- bilicus and are swollen at the umbilical edge; a few bifurcate indistinctly low on the flanks, and about. two- thirds of them bifurcate above the middle of the flanks. The ribs are very thick and slightly swollen at the edge of the venter and are only slightly reduced along the midventral line. Several weak constrictions are present. The suture line on the holotype (Anderson, 1938, pl. 29, fig. 2) has a long, slender, trifid first lateral lobe, which shows clearly that the species does not belong to Lyficocems. The immature specimen that Anderson (1938, p. 162, pl. 29, figs. 3—6) named Thurmamn'a. pas/centae has rib- bing similar to the inner whorls of T. stippz' Ander- son and possibly belongs to that species. Its reference to Thumwmnicems (‘ossmann (replacing Thurmnnia and ’l'ILm-m/mm'tes of authors) rather than Neocomz‘tes is justified by the presence of constrictions, the lack of umbilical tubercles, the lack of rib branching at the umbilical edge, the uniform bifurcation of ribs a little above the middle of the flanks, and the presence of swellings at the furcation points. For the same reasons, Neocomz'tes stippi Anderson is herein assigned to Thurmannicems, but that species in addition develops a venter on its outer two whorls that resembles T/zurmanniceras rather than Neocomites. Its venter during growth becomes slightly convex in- stead of truncated, and its ribs are only slightly weak— ened on the venter instead of being terminated by a smooth midventral area. Anderson (1938, p. 166) records Thurmannicems .s-fippi from the south bank of McCarthy Creek in his zone M which he says is about 1,300 feet above the base of the Cretaceous sequence and about 1,000 feet below the beds containing “Neocomites” jenkinsz' Anderson. 'l‘ypcs: Plesiotypes I’S‘Nll’l 129836, 129837a, b. Holotype, C'alif. Amid. Sci. 10465. Localiticx: YSGS Mes. locs. 1091, 2154, and 25216; CAS loc. 144. Genus HANNAITES Imlay, 1957 The original description of this genus (Imlay, 1957, p. 275) is as follows: Hmmm'tcx is characterized by fairly tight coiling of whorls of small to medium size; a compressed, subquadrate whorl sec- tion: a truncated venter: a vertical umbilical wall; flexuous ribs that tend to fade out on the lower parts of the flanks; strong forwardly arched ribs on the venter; backwardly in- clined umbilical tubercles: spirally elongated ventral tubercles at, the ventral shoulder: a body chamber that tends to retract from the remainder of the shell; many shallow constrictions; appreciable variation in the strength of ribs and tubercles; and a fairly short, narrow, slightly asymmetrical first lateral lobe. AMMONITES OF EARLY CRETACEOUS AGE FROM THE PACIFIC COAST STATES The type species is Hannaitcs riddlensis (Anderson) (1938, p. 167, pl. 30. figs. 1—4). Honnaifcs greatly resembles Lcopoldia (Baumberger, 1906, p. 28—47) in, lateral view, but differs by having a flatter venter, sharply defined ventral shoulders, continuous strong ribbing across the venter. considerable variation in the strength of its ornamentation. the presence of constrictions in adults, and the tendency of its body chamber to become scaphitoid. Also, the suture line appears to have a much narrower first lateral lobe than that of Lcopoldia. Hmmaz‘tcs is named in honor of G. Gallas Hanna of the Cali- fornia Academy of Sciences. Hannaitcs has to date been found only in Oregon in beds of early to middle Hauterivian age. Hannaites riddlensis (Anderson) Plate 41, figures 5, 7—16 Neocomitcs riddlcnsis Anderson, 1938, Geol. Soc America Spec. Paper 16, p. 167, pl. 30, figs. 1—4. Six specimens of this species in the Geological Survey collections have furnished much data concerning its characteristics. The shell is compressed, much higher than wide, subquadrate in section. The flanks and venter are flattened, but the venter becomes less flattened during growth. The inner whorls are strongly involute and the body whorl tends to become scaphitoid. The umbilicus is narrow, except on the body whorl, its wall is fairly low and vertical, its edge is abruptly rounded. The smallest available specimen (pl. 41, figs. 10, 11) at a whorl height of 5 mm bears straight, ‘low forwardly inclined primary ribs of variable strength. Some of them divide into two equally strong secondary ribs near the middle of the flanks. A few secondary ribs arise freely on the upper part of the flanks. All ribs terminate on the ventral shoulder in tubercles of variable strength which are connected across the venter by broad low ribs that are as strong as the ribs on the flanks. Two shallow constrictions are present. The next larger size, represented by the small speci— men illust 'ated by Anderson (1938, pl. 30, fig. 4), is fairly smooth on the lower part of the flanks and has weak ribs on the upper part of the flanks that terminate in small tubercles bordering a flattened, nearly smooth venter. A little larger specimen (pl. 41, figs. 14, 15) is very similar in shape and ornamentation to small specimens of Leopoldia such as L. flemuosar Imlay (1938, pl. 11, figs. 5, 6) except for the presence of ribbing across the venter. The umbilical edge bears backvardly inclined nodes that become strong during growth. From these arise faint, forwardly inclined striae that. become stronger ventrally, recurve near the middle of the flanks, and then pass a little above the middle into thick forwardly inclined ribs. These terminate on the ventral shoulder in prominent, spirally elongated tubercles. 217 The tubercles are connected across a slightly convex venter by broad, forwardly arched ribs that are nearly as strong as the flank ribs. The ribs and the tubercles are slightly variable in strength. Several shallow con- strictions are present. Still larger specimens have been illustrated by An- derson (1938, pl. 30, figs. 1—3). These show the same features as just described, but have even stronger con- strictions and more variable ribbing. An even larger specimen (pl. 41, figs. 5, 12, 13, 16), probably an adult, shows traces of tightly coiled, weakly ribbed inner whorls in its umbilicus but con- sists mostly of a body chamber more than half a whorl in length. This body chamber is marked by fairly strong backwardly inclined umbilical nodes from which arise 1 or 2 low, weak ribs that incline gently forward on the flanks. Other weak ribs arise low on the flanks. A little above the middle of the flanks, all these recurve slightly and pass into stronger ribs that may remain single or may bifurcate. All these ribs terminate on the ventral shoulder in weak spirally elongate tubercles that are connected across the venter by gently arched ribs that are not reduced in strength. Both ribs and tubercles vary somewhat in strength. A number of constrictions are present. The suture line can be seen on one specimen (pl. 41, figs. 14, 15) but cannot be traced in detail. The first lateral lobe is moderately slender and slightly asym- metrical, and its inner branch is more strongly devel- oped than its outer branch. It is not nearly as stout, or as asymmetri :al, as the first lateral lobe of Leopoldia (Baumberger, 1906, p. 43, fig. 25) on a specimen of comparable size. [Ian‘naifes riddle/mix was compared by Anderson (1938, p. 167) with Neocomites monflmus (Uhlig), from the Valanginian of India, but the latter is much less involute, has stronger ribbing on the lower part of its flanks, and has a smooth midventral area. N. neo- comiemifomnis Uhlig (1902, p. 54, pl. 3, figs. 1, 2) from the Carpathian Mountains has ribbing on the flanks similar to that of II. riddlemis but differs in the same manner as N. montcmus. I]. riddlemis resembles species of the genus Leopoldia (Baumberger, 1906, p. 28~47, pls. 4—10 [in part]) much more than Neocomitex in such features as its strongly embracing whorls, the tendency for its ribbing to be faint on the lower part of the flanks and the spiral elongation of its ventral tubercles. For example, the specimen shown on plate 41, figures 14, 15, greatly re- sembles some immature specimens of Leopoldz’a from Mexico (Imlay, 1938, pl. 11, figs. 5, 6, pl. 12, figs. 1—4). I]. riddlemis differs, however, from all described species of Leopoldia by having a sharply defined ventral shoul- 218 der, continuous strong ribbing across the venter, and a more slender first lateral lobe. Typo: Plesiotypes I'SNM 129850429853. Localities: USGS Mes. locs. 12-13, 1252, 2093, 25199, 25202, and 25212. Hannaites truncatus Imlay, n. sp. Plate 41, figures 1, 3, 4 Only the adoral end of the body chamber of this species is known. The whorl section is subquadrate. It is 34 mm high and 20 mm thick. The flanks are flattened below, and inclined gently above to a mod- erately narrow, nearly flat, distinctly shouldered ven- ter. The umbilical wall is vertical, and its edge is rather sharp. From weak tubercles on the edge of the umbilical wall arise 1 or 2 faint ribs that incline for— ward on the flanks, recurve near the middle of the flanks, and pass into 1, or 2 much stronger, narrower ribs on the upper third of the flanks. These ribs at the umbilical shoulder bear low. spirally elongated tu— bercles that are continued weakly across the interspaces between the ribs. The tubercles are also connected across the venter by thick ribs that arch forward and are a. little stronger than the flank ribs. The rib nearest the aperture is much stronger on the flanks than the other ribs, is preceded by a constriction, and is fol— lowed by a sinuous margin that probably represents the margin of the aperture. H. frunoatus is easily distinguished from H. riddlen- sis (Anderson) by having much coarser, sparser rib- bing, and a more compressed whorl section. Typc.‘ Holotype USNM 129840. Locality: ITSGS Mes. loo. 25198. Genus KILIANELLA Uhlig, 1905 Xilianella crassiplicata (Stanton) Plate 42, figures 1—5, 7 Hoplitcs crassiplicatus Stanton, 1895, 11.8. Geol. Survey Bull. 133, p. 81—82, pl. 18, fig. 8, [1896]. Bcrriasclla cf. B. crassiplicuta 1938 (Stanton). Anderson, Geol. Soc. America Spec. Paper 16, p. 163, 164, pl. 83, figs. 3, 4. This species is represented in the Geological Survey collections by 2 specimens that show parts of 2 whorls. The whorls are compressed, higher than wide and are probably only slightly distorted. The outer whorl embraces about one—fourth of the preceding whorl. The body chamber is incomplete, but includes about one-fifth of the outer whorl. The inner whorl bears six pronounced constrictions. Its primary ribs are prominent, fairly closely spaced, and nearly radial. They start. at. the umbilicus, be— come high and narrow as they pass over the umbilical SHORT‘ER CONTRIBUTIONS TO GENERAL GEOLOGY wall, and generally bifurcate at, or just below, the line of involution with the outer whorl. The bifurcation points are marked by blunt swellings. On the outer whorl the contrictions are less pro- nounced. The primary ribs trend radially across the lower three-fifths of the flanks, then recurve backward, and then sharply forward. On the septate part of the whorl a secondary rib arises from the anterior side of each primary rib at the point where the primary rib curves backward. On the body chamber the secondary ribs are indistinctly joined with the primary ribs and at least one secondary rib arises freely below the middle of the flanks. All ribs terminate ventrally in elongated swellings of variable strength that incline forward and bound a smooth midventral area. The suture line is rather simple. The ventral lobe is a little longer than the first lateral lobe, which is stocky and slightly asymmetrical. The auxiliary lobes de- scend abruptly toward the umbilical seam. Stanton’s illustration of the holotype is fairly ac- curate, but he failed to note that the ribs are swollen ventrally and at the furcation points, or that constric- tions are present. These omissions probably misled Illilig (1910, p. 171), who assigned the specimen ques- tionably to T lilo/momma (now Thumnannicems). K 272'— (meila crus-xiplimrta (Stanton) actually bears consider- able resemblance to some of the specimens of K. rou- bumli (d’Orbigny) as figured by Sayn (1907, p. 47, pl. 6, figs. 9, 10a, b). It appears to have flatter flanks and a higher whorl section. The similarly compressed K. Zepfoxomu. Uhlig (1910, p. 232, pl. 82, figs. 3a, b), from India, has finer and more flexuous ribs. K. pewiptychus Uhlig (1902, p. 41, pl. 4, figs. 4—7; 1910, p. 229, pl. 82. figs. 2a—c) has more flexuous ribs that bifurcate lower on the flanks and has a stouter whorl section. 'I'ypcx: Holotype I'SNM 23094; plesiotype I‘SNM 129684. Localiticx: I'SGS Mes. loos. 1001 and 5339. Kilianella cf. K. besairiei Spath Plate 42, figure 8 One specimen bears unforked ribs similar to, but weaker than, those on K. besairie’i Spath (1939, p. 96, pl. 16, figs. 4a, b, 5a—c; Besairie, 1936, p. 138, pl. 24, fig. 13). The ribs are gently flexuous, are sharp on the lower part of the flanks and broaden ventrally. Some become very broad on the upper part of the flanks. One constriction is present. The venter is not pre- served. This specimen was mentioned by Lawson (1914, p. 8) and Anderson (1938, p. 53). Figured spcm’men: I'SNM 129683. Locality: L’SGS Mes. loc. 26404. AMMONITES 0F EARLY CRETACEOUS AGE FROM THE PACIFIC COAST STATES Genus SARASINELLA Uhlig, 1905 Sarasinella densicostata Imlay, n. sp. Plate 42, figure 25 One laterally crushed specimen is characterized by fine, dense ribs that rarely bifurcate on the flanks. The shell is fairly evolute. The inner whorls are poorly preserved but show the presence of sharp, closely spaced trituberculate ribs that incline slightly forward. Nearly half of the outer whorl belongs to the body chamber, which is mainly complete. The ribs on the outer whorl are sharp, closely spaced, and gently flex- uous. About half of them arise singly from weak elongate umbilical tubercules and the remainder arise by twos or threes from slightly stronger umbilical tubercules. On the septate part of the outer whorl, 1 rib in 4 bifurcates on the upper part of the flank. On the body chamber only two ribs bifurcate high on the flanks. The points of furcation are slightly swollen but not tuberculate. All ribs incline forward on the edge of the venter and terminate in elongate tubercles. Weak constrictions are present on the inner whorls and on the septate part of the outer whorl. The ribs near the anterior end of the body chamber bend forward in a manner suggestive of the base of a lateral lappet. The suture line is poorly preserved. The ribs on the outer whorl are as closely spaced as on S. hyatti (Stanton) at a comparable size but are sharper and rarely fork on the flanks. None of the described European or Asiatic species have nearly as fine and dense ribbing. Type: Holotype USNM 129855. Locality: USGS Mes. Ice. 2154. Sarasinella cf. S. subspinosa (Uhlig) Plate 42, figure 16 Two crushed specimens from a single locality in southwestern Oregon resemble S. subspinosa (Uhlig) (1910, p. 239, pl. 90, figs. 4a—c) in most particulars. The inner whorls of the smaller specimen bear constric- tions and sharp, rather widely spaced trituberculate ribs. Some of the ribs are simple, and others fork high on the flanks. The forked ribs bear rather strong tubercles at the furcation points, wherease the simple. ribs generally bear weak tubercles along the zone of furcation. The ventral terminations of the ribs are swollen, incline forward, and border a smooth mid- ventral area. On the largest. whorls of the same speci- men, the umbilical tubercles are strong and give rise to pairs of flexuous ribs of which one generally forks fairly high on the flanks and is slightly swollen at the furcation point. The larger specimen bears ornamentation similar to that on the outer whorl of the smaller specimen. Most 219 ribs arise in pairs from prominent umbilical tubercles, nearly half bifurcate high on the flank, all are strongly flexuous, and all bend forward sharply at the edge of the venter where they are strongly swollen. The mid- ventral area is marked by weak continuations of the ribs. Several constrictions are present. The smaller specimen very much resembles a speci- men figured by Spath (1939, p. 100, pl. 16, figs. 2a, b) and has much sparser ribbing than S. (mgulata (Stan- ton), described herein. The larger specimen may be compared with the outer whorl of the holotype of S. subspinom (Uhlig) (1910, p. 239, pl. 90, figs. 4a~c). It differs by its ribs rising more commonly in pairs from the umbilical tubercles, by having more forked ribs on the flanks, and by lacking a smooth midventral area. The bundling of ribs at the umbilical tubercles is similar to that on the much larger outer whorl of S. moi/limos (Uhlig) (1910, p. 238, pl. 81, figs. 3a—d). The Oregon specimens probably represent. a distinct species but should not be given a name until better material is available. Figurcll spccimcn.‘ I'SNM 129856a, b. I.o('(IIiI]/: l'sus Mes. 100. 2154. Sarasinella hyatti (Stanton) Plate 42. figures 19—24 Hopiites hyatti Stanton, 1895, RS. Geol. Survey Bull. 133, p. 79,1)1. 16, fig. 2 [1896 |. This species is represented by the holotype, which shows a complete body chamber, by another fragment of a body chamber, and by 3 smaller specimens, of which 2 (pl. 42, figs. 19, 24) are considered to be micro- morphs. ()ne of these has a well—developed lateral lappet and is probably an adult. The other shows the base of a lateral lappet. All the specimens are more or less crushed. Allow- ing for crushing, the whorls are subquadrate in section and a little higher than wide and embrace about two- fifths of the preceding whorl. The flanks are flattened below and converge above to a moderately narrow, nearly flat venter. The umbilicus is fairly wide; its wall is low and vertical. The body chamber occupies slightly more than half a whorl. On the small specimens the septate whorls have high thin ribs that incline backward on the umbilical wall, incline forward on the lower part of the flanks, recurve just above the middle, and then incline forward to the venter. Most of the ribs bifurcate at or a little above the middle of the flanks. A few ribs arise above the middle of the flanks. The ribs are swollen at the edge of the umbilicus are swollen to weakly tuberculate at the bifurcation points on the flanks and bear distinct ventral tubercles. The venter is smooth on the internal 220 molds and is crossed by weak continuations of the ribs wherever the shell is preserved. On each whorl 4 to 6 weak constrictions occur. The inner whorls of the holotype, partly exposed in the umbilicus, bear closely spacedsharp ribs that in- cline forward and bear three rows of weak, persistent tubercles. The penultimate whorl bears fine, closely spaced gently flexuous ribs that begin at weak umbilical swellings and terminate ventrally in slightly stronger swellings that incline forward. About half of the ribs remain single, and half bifurcate at about three-fifths of the height of the flanks. The midventral area is marked by weak continuations of the ribs. At the beginning of the body chamber, the ribbing changes considerably. The umbilical swellings become more pronounced and give rise to pairs of thick flex- uous ribs, of which one or both bifurcate on the upper part of the flanks. Toward the aperture the ribs be— come broader, lower, and more distantly spaced. Weak constrictions are visible. on the penultimate whorl and on the posterior part of the body chamber. One con- striction occurs at the adoral end of the body chamber preceding a pronounced lateral lappet. The suture line is too poorly preserved to be repro- duced or described. The body chamber of S. hyatti (Stanton) is similar to that of S. cautleyi (Oppel), figured by Uhlig (1910, p. 242, pl. 84, figs. 2a—c), but its penultimate whorl has finer more flexuous ribs that branch more frequently on the flanks and that do not arise in bundles from prom- inent umbilical tubercles. S. campylotowus (Uhlig) (1902, p. 49, pl. 4, figs. 1—3; Sayn, 1907, pl. 5, figs. 12) likewise has a similar body chamber but is distinguished from S. hyatti by coarser, sparser ribbing and more pronounced umbilical and ventral tubercles. S. cm- bigua (Uhlig) (1902, p. 45, pl. 6, figs. 3—6) is more in- volute than S. hyatti, has sparser ribbing, and more single ribs. Type: Holotype USNM 23091; plesiotypes USNM 129842— 129844. Locality: USGS Mes. locs. 2107, 2136, 4384. 4386, and 26405. Sarasinella angulata (Stanton) Plate 42, figures 11—14 Hoplites angulatus Stanton. 1895 U.S. Geol. Survey Bull. 133. p. 80, 81. pl. 18, figs. 3, 4 [1896]. The original description failed to mention the pres- ence of constrictions or of lateral nodes. These are well shown on the holotype in its umbilicus and near the beginning of its outer whorl. ()n most of the outer whorl, the furcation points of the ribs near the middle of the flanks are marked only by swellings. All the tubercles are variable in strength within the rows. The SHORT‘ER CONTRIBUTIONS T0 GENERAL GEOLOGY ventral tubercles are more uniform in strength than the others and become more so during growth. The lateral and umbilical tubercles are generally much stronger on every second or third rib than on the intervening ribs. On the outer septate whorl of the type specimens, the prominent umbilical tubercles generally mark the union of 2 lateral ribs, of which 1 remains single and 1 bifur- cates at or above the middle of the flank. The suture line cannot be accurately traced. S. angulata (Stanton) is closely similar in dimen- sions and ornamentation to S. tree/anemia (Sayn) (1907, p. 34, 35, pl. 3, figs. 20, 25a, b, pl. 4, fig. 15), from the middle Valanginian of France but, appears to have slightly coarser and denser ribbing. Type: Holotype I'SNM 23093: plesiotype I'SNM 129660. Locality: [YSGS Mes. locs. 1093 and 4393. Genus ACANTHODISCUS Uhlig, 1905 Acanthodiscus sp. juv. afl’. A. subradiatus Uhlig Plate 42. figure 18 One small external mold from Oregon is 28 mm in diameter and has an umbilical width of 12 mm. The outer whorl overlaps about two-fifths of the preceding whorl. The inner whorls exposed in the umbilicus bear sharp forwardly inclined primary ribs that terminate in prominent lateral tubercles along the line of involu- tion. The outermost whorl bears about 33 sharp pri- mary ribs that begin at the edge of the umbilicus, are slightly swollen on the umbilical wall, incline forward gently on the flanks, and terminate a little above the middle of the flanks in more or less prominent conical tubercles. From most of these tubercles arise 2, or less commonly 3, broad secondary ribs that. incline forward sharply and terminate ventrally in conical tubercles. At a few lateral tubercles only single secondary ribs arise. The union of the secondary ribs with the tu- bercles becomes indistinct anteriorly on the outer whorl. The presence of ventral tubercles can be observed at only one place near the anterior end of the specimen. This small Acanthodz‘scus from Oregon is difficult to compare with the large adult. specimens of the genus that have been described. It shows considerable re- semblance, however, to an immature specimen from In- dia (Uhlig, 1910, p. 214, pl. 26, figs. 3a—c) that is about one whorl larger and has attained slightly sparser and coarser ribbing. Both of these specimens resemble A. submdiatus Uhlig (1910, p. 208, pl. 23, figs. 1a, b, pl. 26, fig. 1), from the Valanginian of India, in their large number of primary ribs, their small number of second- ary ribs, and the appearance of trituberculation at a small size. They are differentiated readily by this com- bination of characters from the described European AMMONITES OF EARLY CRETACEOUS AGE FROM THE PACIFIC COAST STATES species of Acanthodz’scug. (See Neumayr and Uhlig, 1881, p. 165—166, pl. 34, figs. 2, 3, pl. 55, fig. 2; Baum- berger, 1906, p. 8—28, pls. 14—18 [in part].) Figured specimen: USNM 129685. Locality: USGS Mes. loc. 2154. Genus SPITIDISCUS Kilian, 1910 Spitidiscus oregonensis Imlay, n. sp. Plate 31, figures 4—6, 8, 9 The shell is small, compressed, and moderately in— volute but becomes less involute during growth. The whorls are elliptical in section, higher than wide, and embrace about three-fifths of the preceding whorl. The flanks are weakly convex. The venter is highly arched. The umbilicus is moderately narrow; the umbilical wall is low and vertical and rounds abruptly into the flanks. The ornamentation consists of 5 or 6 weak, flexuous constrictions and of many low flexuous ribs. Most ribs begin weakly on the umbilical wall. Others arise at various heights on the flanks either freely or indis— tinctly united with longer ribs. All incline forward on the lower part. of the flanks, curve forward more strongly on the upper parts of the flanks, and arch for- ward gently on the venter. They become broader and a little stronger ventrally and vary somewhat in strength on the venter. Tubercles are not present. The holotype at a diameter of 28 mm has a whorl height of 13 mm, an estimated whorl thickness of 10 mm, and an umbilical width of 6 mm. The paratype (pl. 31, figs. 4—6) has a whorl height of 15 mm and a whorl thickness of 12 nnn. Both specimens have been compressed a little laterally. This species is similar in shape and ornamentation to Spitz'dismm intermedius (d’Orbigny) (1841, p. 128, pl. 38. figs. 5, 6; Kilian, 1907, p. 265, pl. 5, fig. 7), from the Hauterivian of France, but. has weaker constric- tions and ribbing and is probably more involute. Types: Holotype USNM 129697; paratype USNM 129698. Localities: USGS Mes. 100. 718 and 25211. REFERENCES Anderson, F. M., 1902. Cretaceous deposits of the Pacific Coast: Calif. Acad. Sci. I'roc., 3d ser., v. 2, 126 p., illus. 1933, Jurassic and Cretaceous divisions in the Knoxville- Shasta succession of California: Mining in California, v. 28, p. 311—328. 5 figs... 2 pls.. correlation table. —-——— 1938, Lower Cretaceous deposits in California and Oregon: Geol. Soc. America Spec. Paper 16, 339 p., 84 pls., 3 figs. Arkel, W. J., 1949, Jurassic ammonites in 1949: Science Progress, no. 147, p. 401—417, 1 pl., 4 text figs. 1957, Jurassic ieology of the World: 806 p., 46 pls., 102 figs, 28 tables. London, Oliver and Boyd Ltd. 221 Ernst, 1903~10, Fauna der untern Kreide in Schweizer. palaeont. Gesell. Baumberger, Westschweizerischen J ura : Abh., v. 30—36, 33 pls. 1923, Beschreibung zweier Valangien-Aminoniten, nebst Bemerkungen iiber die Fauna ties Gemsmiittli-Horizontes von Sulzi im Justital: Eclogae geol. Helvetiae, v. 18, no. 2, p. 307, pl. 8. Besaire, Henri, 1936, Recherches géologiques a Madagascar, Premiere suite, La Géologie du Nerd-Quest: Acad. 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The cephalopoda of the Neocomian belemnite beds of the Salt Range: I’aleontologia Indica. new ser.. v. 25, men]. 1, 15-1 p.. 25 pls. Tel-rains 1946. Preliminary notes on the Cretaceous ammonite faunas of East, Greenland: Meddel. om Gronland. v. 132, no. 4.)). 1—11. 1947. Additional observations on the invertebrates (chiefiy ammonites) of the Jurassic and Cretaceous of East 1reenland. I. The Ilcctoroccras fauna of S. W. Jameson Land: Meddel. om Gronland, v. 132. no. 3. p. 1—70. pls. 1A5. 8 text figs. 1 table. 1952, Additional observations on the invertebrates (chiefly ammonites) of the Jurassic and Cretaceous of East Greenland. 11. Some Infra—\‘alanginian ammonites from AMMONITES OF EARLY CRETACEOUS AGE FROM THE PACIFIC COAST STATES Lindemans Fjord, Wollaston Forland; with a note on the base of the Cretaceous: Meddel. om Gryinland, v. 133, no. 4, p. 1—40, pls. 1—4. 1 text fig. 1 table. Stanton, T. W., 1895. Contributions to the Cretaceous Paleon- tology of the Pacific Coast—The fauna of the Knoxville beds: [T.S. Geol. Survey Bull. 133. 132 p., 20 pls. [Issued Feb. 3, 1896, not 1895]. Stolley, Ernst. 1908, Die Gliederung der norddeutschen unteren Kreide: (‘entralbL Mineralogie, Geologie 11. I’alaeontolgie, 1908. p. 107—124, 140—151. 162—175. 211—220. 242—250. —— 1937, Die Gliderung (ler norddeutschen marinen I'nter- neocoms: Centralbl. Mineralogie, Geologie u. l’alneontologie, 1937, Abt. B. p. 43-1—4536, 497—506. Torcapel, M. A., 1884, Quelques fossiles nouveaux (le l’t'rgonien du Languedoc: Soc. Etude Sci. Nat. Ninles Bull. nos. 9 and 11. p. 109—110. 133—141, pls. 1—9. llhlig, Victor, 1883, Die (‘ephalopodenfauna der \Vernsdorfer Schichten: K. Akad. \\'iss.. math.-naturw. KL, Denkschr. v. 46, 1). 1—166 (128—290). 32 pls. 1902, I‘ber die Cephalopoden den Teschener und (lro- dischter Schichten: K. Akad. Wiss. Wien.. nult.h.-naturw. K1,, I)enkschr.. V. 72. X7 1).. 9 pls. 1903—10. The fauna of the Spiti shales: Paleontolgia Indica. 15 set, v. 4, 395 p.. 93 pls. Weaver, Charles. 1931. Paleontology of the Jurassic and ("re- taceous of west central Argentina: Washington L'niv. Mem. at. Seattle, V. 1, 469 1)., 62 pls. 223 Weerth, 0., 1884. Die Fauna des Neocomsandsteins im Teuto- burger Walde: I’aleont. Abh., v. 2, no. 1, 77 p., 11 pls. Windhausen, Anselmo, 1918, Lineas generales de la estrati— grafia del Neocomiano en la Cordillera Argentina: Acad. Nae. Ciene. Bol. V. 18. Woods, 1899—1913, A monograph Lamellibranchia of England: 2 v., 9 parts, illus. tographical (London) Sou, V. 53—66. Wollemann, A., 1900, Die Bivalven deutschen 11nd hollandischen Neocoms: Landesanstalt Abh., neue Folge, no. 31. of the Cretaceous Paleon- Henry, und Gastropoda des Preuss. geol. Wright, C. W.. 1955, Notes on Cretaceous Ammonites. II. The phylogeny of the Desmocerataceae and the Hoplitaceae: Annals and Mag. Nat. History, ser. 12, V. 8, p. 561—575. Wright, C. W.. in. Arkell, W. J.. Kummel. Bernhard, and “'right. C. \V., 1957. Mesozoic Ammonoidea: Treatise on Invertebrate Paleontology, part L. Mollusca 4, 490 1)., illus. Zonov, N. T.. 1937. The stratigraphy of the Jurassic and lower Neocomian of the central parts of the East-European plat- form in. Geological investigations of agricultural ores I'SSR: Sci. Inst. Fertilizers and Insecto—fungicides Trans, no. 142, p. 32-43. Zwierzycki, Joseph. 191-1. Die cephalopoden-fauna der Ten- daguruschichten in Deutsch—Ostafrika: Archiv fiir Bion- tologie, v. 3, no. 4, pt. 3, p. 7—96, 10 pls. A Page aboriginalis, Acroteuthis _______________________ 180 Acanthodiscus ....... 168, 174, 181, 182, 191, 194, 220, 221 submdiatus ______________ 174, 175, 184. 220, pl. 42 Acrioceras __________ 168, 172, 178, 179, 180, 182, 191, 198 hamlini ____________________ 173, 184, 199, pl. 26 maheswariae ________ 199 muckleae ................................ 199 tabarelli.... .............. 199 vespertinum... ..... 173, 184, 199, pl. 26 voyanum.. . 173, 177, 180, 184, 198, pl. 26 sp ________________________________________ 181 Acroteuthis aboriginalia..._ 180 impressa .............. 178 kernensia .......................... 180 onoensis ................................ 180 shastemis _______________________________ 178 51) ......... 175, I79 agnessense, Speetoniceras... 173, 176, 184, ZIS, pl. 42 aguila, lIertlez‘m'tes ...... 168, 173, 178, 179, 180, 184, 192, 195, 199, £07, 209, 211, 212, pl. 34 Neocraspedites .. 180, 195, 196, 197, 198, 207, 210, 215 alliumbonata, Pholadomya ................... 179, 180 ambigua, Sarasinella ......................... 220 amm‘cana, .Myoconcha ...... ... 172 Ammonite fauna, comparison with other faunas ............................ 181 ocologic considerations __________________ 3182—183 geographic distribution. .. 184—185 long ranging.. ...... 183 short ranging ....... 183 summary of results ..... ... .. . 190 Ammonite genera of Pacific Coast States. . ' 168 Ammonites fraternus .......................... 210 truski __________________________________ 178, 210 Ampullina avellana ........................ 179. 180 Anahamulina... . ________________ 168, 172. 182, 200 parillosa ................................ 200 ziespertina ................................ 178, 199 wilcoIensz's. 173, 179, 184, 200, pl. 25 Ancyloceras" 181, 191 remondi ________________ . 197 (Ancyloceras) remondi, Crioceras ,,,,,,,,,,,,,, 196 Aneyloceratidae __________________________ 168, 190 Ancyloceratinae ............................. 168 anglicus, Inoceramus ___________________________ 177 angulata, Sarasinella.... 174, 175, 184, 219, 220, pl. 42 angulatus, Iloplites ___________________________ 220 angulicostata, Pseudothurmannia ____________ 181, 199 Anemia senescens. . , 175 Aptian age ______ 181 Aptian time_. 183 Area tehamaensts 175 tel'trina _________________________________ 172, 178 archimedi, Nerinea ____________________________ 180 Arcomya ______________________________________ 179 Arctic Ocean ________________________________ 183 Aspinoceras hamlim‘ _______________________ 178, 199 Astarte _____________________________________ 176, 179 californica. 172, 180 corrugata. . . . _ 175 trapezoidalis. . 175 SD ...................................... 180 astierianus, Olcostephanus. _ . . _ . . . _. . _. . ._ . . _'. 204 astieriformis, Olcostephanus ___________________ 204 Atlantic Ocean _____________________________ 183 Aucella _______________________________ 167, 176, 180 crassicollis .............................. 172, 205 INDEX [Italic numbers indicate descriptions] Page Aucellina _________________________ 169 auerbachi, Simbirskites ____________________ 211, 212 aulaeum, Lytocerus ____________________________ 170, 173, 176, 177, 178, 179, 180, 184,195 avellana, Ampullina ___________________ 179,180 Avicula (OIytoma) whiteavesi ................. 175 B Bald Mountain __________________________ 172 Barremian age... 171, 173,174,181 Barremian time. .. .. 183 bedm', Crioceralites... __ 179 Belemnite fragments" _____________________ 175 Belemnites impressus . . . . _________________ 172, 175 SI) .............................. 175 Berriasella crassiplicata.. .._._._._.. ... 176, 216,218 Berriascllidae .............................. 168, 190 Berriasian age .......................... 173, 191, 194 hesairiei, Kilianella ...... 171, 173, 184, 218, pl. 42 bicarinaia, Tessarolaz .................... 179,180 Biologic analysis, . . . .. .. 168 bipunctata, Fissurella._ ...... 172 Bochiam'tes. .. .. .. ... 168, 172, 181, 194 paskentaensia ...................... 173, 174, 184 Bochianitidae ............................ 168, 190 Bochianitinae ............... . .............. 168 Boreal region ................................. 172 breuveriana, Parallelodtm .............. _.._ 179, 180 hroadi, Simbirskites ............................ 173, 177, 178, 184, 196, 197, 209, 211, pl. 33 Is‘uchia ....................................... 167, 168, 172, 175, 176, 180,182, 183, 191, 194 crassicollis ............ .... 168, 169, 170, 171, 172, 174, 175, 176, 177, 179, 180, 186, 190, 191, 192, 195, 196, 201, 203, 204, 206, 208, 215. piochii ..................................... 180 sublaevis ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 172 volgensis. . 172 burgeri, Dichotomites _________________________ 200 llomolsamites mutabilis . . 202 Burt’s Ranch _________________________________ 190 C californica, Astarte ,,,,,,,,,,,,,,,,,,,,,,,,,,, 172, 180 ()pis ______________________________________ 172 Terehratulu ,,,,,,,,,,,,, 171 Californicems ______________ 178 californ-icum, Dentalium ___________________ 175, 180 Desmoceras ______________ 214 ’I‘hurmamzicems_.___....... ............. _. 171, 172, 173, 184, 191, 214, 215, pl. 39 Calliptychaceras ............. . . 1.. 214 campylotorus, Sarasinella Ca nadoceras fratermmt. . . cartenmi, Neocmspedites.. cautleyi, Sarasinella ________ Cave Junction ............... Cercomya .................... Cen'thium strigosum ......................... 175 sp .................................. 172 chanchelula, Subastieria ________________ 178, 209, 216 clementina, Pholadomya. . . _ ___________ 178, 179, 180 Clements Ranch ........................ 170, 179, 189 Chisocolus indubiius. _.. 180 collinium, Venus ....... _ 178,179 colonicus, Inoceramus ________ 180 Page Comparisons with other faunas _____________ 181—182 complanatus, Neocraspedites ___________________ 206 concinnus, Simbirskites _________ 210 Corals ....................................... 182 Corlmla filosa ............................ 172,180 sp ......................... Correlations and fauna] zones_. corrugata, Astarte _______________ Cottonwood Creek __________________ 171, 189, 195, 196 Cow Creek ......... 169, 170, 177, 187, 206 Craspedites semilaevis _______ 205 tenuis ......... . 208 Craspeditidae. .. _ 168,190 Craspedodiscus._ 181, 182, 191,207,208 discofalcatus. . . 208 phillipsi __________________________________ 208 crassicollis, Aucella ......................... 172,205 Buchia ......................... I68, 169, 170, 171, 172, 174, 175, 176, I77, 179, 180, 186, 190, 191, 192, 195, 196, 201, 203, 204, 206, 208, 215 crassicostatus, Homolsomitea mutabilis .......... 201 crassiplz'cata, Berriaaella __________ .-.. 176,216,218 Killianella ................... 171, 172,173,174,184,191,216,218,pl. 42 crassiplicalus, Hoplites ........... 218 Cretaceous ammonites, range... . 172 Cretaceous time._.. Crioceras ............ duncanenae ............................. 178, 196 latum .......................... 178, 179, 180, 196 lutus._ 196 nolam'. 178 (Ancylocems) remondi ........ 196 Crioceratinac .................... 168 Crioceratites._ 168, 172, 174, 178, 180, 181, 182, 191, 196 bederi.. 179 196 .......................... 176, 180 lotus ....................... 173, 184, 196’, pl. 26 nolam' ................................... 196 tehamaensis ................... 173, 179, 184, 1.96 yollabollium ........................ 173, 184, 196 sp. indet ............... .. 173, 184, 196, pl. 26 cruasensis, Pseudothurmannia ................ 200 Crustaceans .......... _ 182 Cyprina occidentalis... ............... 17 2 D Days Creek.. 169, 170, 175, 176, 177, 186, 194, 203, 206 decheni, Simbirakites ........................ 209, 210 densicosta, Polyptychltes ....................... 204 Sarasinella .................. 174, 184, 21.9, pl. 42 Dentalium califarnicum ..................... 175, 180 sp ................................. 180 Desmoceras californicum ............. 214 sp .................. diadema, Potamides. Dichotomites ........................... burgeri... gregersem mutabilis ............................... 200 oreganensi3.. ______ 205 tehamaensis ........... 200 trichotomous .............................. 204 diuhotomus, IIollisiles. . . 173, 176, 184, 192, 212, pl. 38 Simbirskitea ............................... 177 225 226 Page dilleri, Hoplites _______________________________ 214 discofalcutus, Craspedodiscus _________________ 208 Discoheliz jilunigyroides ______________________ 178 discoidalis, Thurmanniceras ___________________ 215 Distoloceras _________________________________ 182, 194 Distribution, geographic ................... 183—190 Dothan formation ________ . 169 dubius, Salecurtus._ . 172 Duncan Creek ..... - 189 duncanense, Crioceras ....................... 178, 196 Hoplocrioceras _____________ 173, 184, 198, pl. 25 Spiliceras ............................. 178, 198 Durangites ____________________________________ 169 duraznense, Thurmanniceras ________________ 175,215 duvali, Crioceratiles ........................... 196 E Eagle Creek _________________ 189 Echinoderms. .. . 182 Ecologic considerations _____________________ 182—183 elatus, Simbirskites.. 173, 176, 177, 184, 210, pl. 33 Elder Creek... . 175 Elk River _____ 172,188 Emericicerax... 196 Entolium ................ 175, 176, 182 aperculiformix ...................... 176, 179, 180 Sp ........................................ 177 F Fauna] zones and correlations ............. 171—181 festivius, Turbo ............ 180 filosa, Carhula. . .. 172,180 Fissurella hipunctuta. . 172 fiezicostu, Neocraspetlites ____________________ 175, 205 flexuosa, Leopoldia ....................... .. . 217 Foggy Creek ................................ 169 Foggy Creek road .......... 170 fragilis, Spondylus ......................... 172 fraternum, Crmadocems ..................... 210 fraternus, Ammom’tex ................... 210 frequens, Olcostephanus ....................... 203 (1 gabbi, Nucula ................. . 175,180 Gabhioceras wintunium zone 181 Galiee formation .......... 171 Gastropods ....... . 182 geei, Olcostephanus ........................... 203 Geographic distribution .................... 1837 190 giganteus, Neocraspedites. 173, 174, 175, 184, 204, pl. 32 glabra, Leda .............................. 172, 175 Goniomya .................................. 180 vespera ............................... 179, 180 SD ......... . 180 yramtlatus, Helcion. . . . 172 gregaria, Ilypsipleura. . 175 gregersem‘, Dichotomiles ...................... 200 11 Hamlin-Broad zone of Anderson ______________ 170, 173,177,178,179,180,181,191,192 hamlini,/1crioceras ............. 173, 184, 199, pl. 26 Aspinnceras ........... Hamulina xzzhcylindrica. I Iammz'tes ................. ... 168,171,182,194, 216‘ riddlmsz's ................................. 170, 173, 176, 177, 184, 212, 217, 218, pl. 41 truncate __________________________________ 176 truncatus .................. 173, 184, 218, pl. 41 Ilautcrivian age ....... 171,174,175,176, 179,180,181 lIauterivian ammonites, affinities ............ 182 facies control ............................ 182 zonal distribution 173 llauterivian rocks in California.. 170 llauterivian sequence in Oregon. . 170 llauterivian time ............................ 183 Ilelcion granulatus._ ........................ 172 llemihoplitidae .......................... 168,190 Henderson Ranch. _ ......................... 171 IIertleim'a ................................. 207,212 IN DEX Page Hertleim‘tes ............................ 168, 179, 181 , 182,191,194,207, 208,211, pl. 34 aguila .............. 168,173,178,179,18{),184,192, 195, 199, 207, 209, 211, 212, pl. 34 zonei... 170,171,177,179,180,181,182,191,199 lucasi .................................... 211 pecki ............. 179, 184, 208, pls. 35, 43 rectan's. . . ...................... 207,209 signalis. .. . 173,207 hespen‘um, Shasticrioceraa. . _ _. _. 198 hesperius, Polyptychites. . 178,211,213 lloleodiseidae .............................. 168, 190 Holcodiscus, . . 203 stantoni... 201 tehamaensis ............................... 196 uhligi ..................................... 203 Hollisz‘tes .............................. 168, 170,177, 178,179,180,182,192,194, 211, 213 dichotomus. . 173,176,184,192,212, pl. 38 zone.. ................. 177, 191 inflatus .................. 173,179,184, 212, pl. 37 lucasi .............................. 173, 177, 179, 184, 211, 212, pls. 35, 36, 37, 38 Homolsomites ....... 168, 172, 174, 181, 190, 194,200, 205 mutabilis ........................... 173, 174, 175, 184,191, 200, 201, 202, pl. 28 burgeri ................................ 202 craxsicostatus ..... 201 mutabilis ...... ... 201 tehumaenxis... . .......... ._ . 201,202 zone ....... 172, 174, 175, 176, 182, 191 paucicostatus. .......................... 175, 201 poecilorhotomus ........................... 201 stantoni ............................ 169, 173, 175, 184, 201, 203,205, pl, 27 IIoplites angulatus ........................... 220 crassiplicatus ............................ 218 dilleri .................................... 214 hyatti. .................................... 219 Hoplocrioceras ........................ 168, 172, 178, 180,181, 182,191, 196,198, 200,207,212 duncanense . ., ............. 173,184, 198, pl. 25 laeviusculum .............................. 197 onoenxe ................................. 180, 198 remondi ............................ 173, 177,178, 180, 184,196,197,198, pl. 24 yollabollium ........................... 179, 196 sp ....................................... 178 sp. indet ......... . 173, 184 llorsetown formation“ ... 170 llorsetown group.... . 169,195 humerosus, Turbo ............................. 175 hyatti, lloplites ................................ 219 Sarasinellu.. 172, 173, 174, 184, 191, 219, pl. 42 Ilypophylloceras .................... 168, 172, 179, 195 anaemia .............. 173,179,180,184,I95, pl, 25 IIupsipleum gregarin .......................... 175 I Illinnis River .............................. 188,189 impressa, Acmteulhis. . . 178 impressus, Bele‘mnites... .................... 172, 175 Indian Creek ................................. 189 indicus, Neocomites ............ 173, 184, 2I3, pl. 41 indigena, Ostrea ............................... 178 indubitus, Clisocolus . . ..................... 180 inflatus, IIollisites ............ 173,179,184, 212,111.37 Inoceramus. ................... 169,175,177,182,183 anylirus. ........... 177 colonirus... 180 oziatoides _. ...... 179,180,181 Ivallejoensis ................................ 175 sp ........................................ 177 intermedius, Spilidiscus, _ .................... 221 inverselobatus, Simhirekites .................... 210 inversum, Speetoniceras ....................... 212 J jeannoti, Olcoslephanus ............... 175,191,203 Page jeukinsi, Neocomitea ..................... 176, 215, 216 Thurmmmicems. 173, 174, 175, 176,184, 915, pl. 40 Jerry Creek .................................. 187 jadariemix, Leopoldia ......................... 206 jupiter, Pseudolhurmannia .............. 173,184,200 Thurmannia... . . . ._ ......... 178, 179,192,200 Jurassic rocks, Late ..... 171 K kayana, Trigom'a ................ 176, 177, 178,180,181 kernensis, Acroteuthis ......................... 180 Kilianella. .............. 168, 172, 181, 194, 216, 218 besairie .............. 171,173,184, 218, pl. 42 crassiplicata ............................. 171, 172, 173, 174,184,191, 216, 218, pl. 42 zone ................................. 178 leptosoma. . 218 peziptychus. . . 218 rouhaudi. . . 172,216 172 Knoxville formation ...................... 169, 172 koenem‘, Perisphinctes.. .................. 211,212 L laeviusculum, Haplocrioceras .................. 197 latum, Crioceras. . ......... 178, 179, 180, 196 Crioceratilea. ...... 176, 180 lotus, Cn'ocems .............................. 196 Crioceratites .................. 173, 184, 196, pl. 26 leana, Trigonia ............................. 177, 180 lecontei, Palyptychites ....................... 178,209 Simoirskites .......... 173, 184, 208, 209, 210, pl. 33 Leda glahra ............................... 172, 175 Leopoldia ........... . 168, 182, 194,206, 217 flewosa ......... 217 jodariensis ...... 206 leptosama, Kilianella .......................... 218 Lima multilineula... 172 Lowry Ranch ............................ 190,195 lucasi, Hertleim'tea ............................ 211 IIollisites ................................. 173, 177,179,184,211,212, pls. 35, 36, 37, 38 Lyticoceras .................................. 182, 215 packardi ............................... 197, 206 Lytoceras ..................... . . 168, 182, 183, 195 aulaeum. ... 170,173,176,177,178,179,180,184,195 saturnale....... ..... 171,173,175,178,184,195 traski .......................... 173, 178, 180, 184 Lytoceratidae ............................ 168, 190 Lytoccratinae. , . .. 168 M McCarthy Creek ........................... 171,175 maheswariae, Acrioceras ....................... 199 Aleekia sp ..................................... 180 Mitchell Creek..1 ........................ 178, 189 Jfodiolua onoensis .......................... 178, 180 montanus, Neocomitea ........................ 217 marganensis, Turbo ........................... 175 mortilleti, I’seudothurmannia. 197 muckleae, Acrioceras ......................... 199 multilinealu, Lima ........................... 172 mutabilis. ................................. 201 burgeri, Homolsomiles .................... 202 crassicostatus, Homolsomiles ......... 201 Dichotamites , _ ...................... 200 IIomnlsomitea .......... 173, 174, 175, 184, 191, 200,202,131. 28 lIomolsomites mutabilis ................. 201 mum/Jill's, IIomolsomiles ................... 201 Olcostephanus (Simbirxkz’tes) . . _ . . ........_ 200 Subcraspedites ............................ 200 tehamaeneix, Homolsomites ............... 201 .Vyoconcha americana ........................ 172 Myrtle Creek ........................ 169,175, 186 Myrtle formation ..................... 169 myrtlense, Phylloceras ........................ 194 Mytilus ..................................... 176, 182 N Page neocomiensifarmis, Neocomitea ________________ 217 neocomiensis, Neocomites ___________ 215 Neocamites..._ 168, 172, 181, 182, 194, 200, 213, 215, 216 indicus... __________________ 173,184,213, pl. 41 jenkinsi ............................. 176, 215, 216 montanua _______________________________ 217 neocomiensia ______ 215 neocomiensiformis _______________________ 217 praeneocomiensis ........................ 215 russelli ........................ 178, 180, 192, 199 stippL. ________ 216 theodorii ________________ 214 wichmanm’ 215 Ncooo mitidae . . 215 N cocomitinae, ................... 168 Neocraspeditea ................................ 168, 172, 174, 181, 182, 191, 194, 204, 205, 207, 208,215 aguila ________ 180, 195, 196, 197, 198, 207, 210, 215 carteroni ______________________________ 202, 206 complanatus ______ 206 flezicosta ................................ 175, 205 oiganteus" 173, 174, 175, 184, £04, p1.32 oreganensis . . __________________ 205 rectoris..._ 180, 208 signalis. ______________________________ 209 stanttmi. ______________________________ 205 tennis ........... 208 wilcaIi ________ 214 Nerinea archimedi. 180 nolam‘, Crioceras.. 178 Crioceratites... 196 Nooksack group ............ 186 Nooksack River .............. 186 novihispanicum, Thurmunniceras 172,214 Nucula gahbi ................... 175, 180 sp .............. 180 0 occidentale, Phyllacema ______________________ 178, 180 occidentulis, Cyprina ......................... 172 Olcostephanidae __________________________ 168, 190 Olmstephaninac ............................ 182, 194 Olcostephanus _______ 168, 172, 175, 181, 182, 194, 203, 205 astierianus.... 204 astieriformis... _ 204 frequens ______ _ 203 geei _____ _... __ 203 jeannoti ________________________ 175, 191, 203 pecki ...................................... 169, 173, 175,176, 184,191, 201, 209, 1115 29, 30, 31 zone ...... 175 popenoei ___________________ 173, 184, 203, pl. 31 quadriradiutus ________________ 173, 184, 203, pl. 31 singularis _________________________________ 204 traski ................................. . 208 (Polyptychites) trichotomua. _ 204 (Simbirskites) mutabilis _ 200 Ono formation ........... . 170 onoense, Hoplocn'oceras ___________________ 180, 198 Hypophylloceras ______ 173, 179, 180, 184, 195, pl. 25 onoensis, Acroteuthis __________________________ 180 Modiolus ______________________________ 178, 180 Plicatula ________________________________ 178 operculz‘formis, Entolium ________________ 176, 179, 180 Syncylrmema ......... _ 179 Opir califomica ________ - 172 oregonense, Phyllocems... . 194 oregonenxis, Dichotomites... ____ 205 Neocraspedites ____________________________ 205 Spitidiscus ............ 174, 176, 177, 184, 221, pl. 31 W'ellsia ........................ 170, 173,176, 177, 184, 187, 191, 192, 202, 203, 205, 207, pl. 32 Ostrea indigena _______________________________ 178 skidgatensis _______________________ . 172 Ostreldac _____________________________ .. . 182 avatoides, Inocemmus. 119, 180, 181 ovatus, Pectunculus ________________ 172 Oil/tome _____________________ __ 176, 179, 182 (OJ’ytoma) whiteavesi, Aviculina ............... 175 INDEX p Page Pacific Ocean ................................. 183 packardi, Lyticoceras ________________________ 197, 206 Wellsia _______ 170, 173, 176, 184, 205, 206, 207, pl. 33 ........... 180 176, 177, 178, 179, 180 Palamede perforata._ papyracea, Pleuramya... Parallelodon breweriana ___________________ _ 179, 180 Parundiceras ________________ 214 Paskenta formation ___________ 170 Paskenta group .................... 169, 170, 171, 172 paskentae, Thurmanniceras _________________ 176, 216 paskentaemis, Bochianites .............. 173, 174, 184 paucicostatus, Homolsomitea ________________ 175, 201 paxillosa, Anahamulina _______________________ 200 pecki, Hertleinites _______ 179, 184, 208, 1315.35, 43 Olcostephanus ________________________ 169, 173, 175, 176, 184, 191, 201, 202, pls. 29, 30, 31 Peotens _______________________________________ 172 Pectunculus ovatus ______________________ ___ 172 Pelecypods ................................ 176, 182 Pentacrinus sp _______________________________ 171 per/cram, Palamede __________________________ 180 Periplomya ................................. 182 reddmgensis ___________________________ 176, 179 trinitensis __________________________ 176, I79, 180 Periaphinctes komeni _____ _. 211,212 pertramiens, Thurmannicerus. 172,214 pexiplychua, Kilianella ...... _ 218 philhpsi, Craspedodiscuc ____________________ 208 Pholadomua ................................ 180 altiumbonata __________________________ 179, 180 clementina ......................... 178, 179, 180 Phyllaceras myrtlense ........................ 194 occidentale ............................ 178, 180 oregonense .............. 194 trinitense _______________ 173, 175, 176, 177, 179, 194 umpquanum _____________ 176, 194 Phylloccratidae._ ._ 168,180 Phylloceratids._ 182, 183 Phylloceratinao _____________________________ 168 Phyllopachyceras ______________________ 168, 172, 194 trinitense _____________________________ 184, 194 umpquanum .................... 173, 177, 184, 194 Pimm pumice ______________________________ 179, 180 SD ————————————————————— 175 piochii, Buchia 180 planigyroides, Discohelix 178 Pleuromya ................. 172, 175, 176, 182 papyracea. . , . 176, 177, 178, 179, 180 Pleurotomaria sp. . .. 172, 180 Plicatula anaemia ........................... 178 variata _________________________________ 179, 180 paecilochotomus, Homolsomitea _______________ 201 Polyptychites .................................. 168, 172, 174, 181, 191, 194, 203,204, 209, 216 densicosta ................................ 204 hesperius ...................... 178,211,213 lecontei ___________________________ 178, 209 polyptychus. 204 ramulicosta .................. , __ 175, 204 lrichotomus. _ _ __ _ 173, 174, 175, 184, 204, pl. 31 sp ______________________________________ 173, 184 sp. juv ____________________________________ 176 (Polyptychites) trichotamus, Olcostephanus ..... 204 Polymychitinao ___________________________ 168, 207 polyptychus, Polyptychites ____________ 204 poniente, Shasticrioceras _____________ 173, 181, 184, 198 ___________ 179, 180 _ 173, 184, 205, pl. 31 pontica, Pinna __________ popenoei, Olcostephanus Portlandian age ____________________________ 175, 194 Port Orford quadrangle _______________________ 169 Potamides diadema __________________________ 179, 180 praeneocomiensis, Neacomites __________________ 215 progredicus, Simbirskites. ,. _______________ 177, 181 progrediens, Simbirskz‘tes ,,,,,, 173, 176, 184, 210, pl. 33 Pratocardia sp _______________________________ 180 Paeudothurma7mia._ 168,172,178,179,180,192,197,199 angulicostala ____________ 181, 199 cruasenaia ............................... 200 227 Pseudothurmannia—Continued Page jupiter .............................. 173, 184,200 mortilleti _________________________________ 197 russelli ________________________ 173, 184, 199, 200 Ptychoceratidae ........................... 168, 190 Pulchellia .............................. 181, 191, 207 Q quadriradiatus, Olcoatephanus _____ 173, 184, 203, pl. 31 R ramulicosta, Polyptychitea .................. 175, 204 Rector Creek ____________ 189 Rector formation ______ 170 rectorix, Hertleim‘tea ________________________ 207,209 Neocraapedites .......................... 180, 208 Redding Creek ______________________ 170,179, 189, 194 reddingensis, Periplomya ___________________ 176,179 remondi, Ancyloceras ________________________ 197 Crioceras (Ancylaceras). . _ _ _______ _...... 196 Hoplocrioceras ___________________________ 173, 177,178,180,184,196,197,198, pl. 24 Rh ynchonella sp ____________________ 171 Rhynchonellid brachiopods ......... 172 Riddle quadrangle ..... riddlemia, Hannaitex... 173, 176, 177,184. 212, 217, 218. [11. 41 Roaring River tongue of Ono formation _____ 170, 178 Rogersitea __________________________________ 182, 194 Rogue River ______________________ 170, 171. 188, 212 roubaudi, Killianella ________________________ 172,218 russelli, Neocomites. _ 178,180,192, 199 Pseudathurmannia__ _________ 173, 184, 199, 200 S Sarasinella .......... 168, 172, 174, 181, 191, 194, 205,219 ambigua __________________________________ 220 angulata ______________ 174, 175, 184, 219, 290, 1'11. 42 campy/1010111.! _____________________________ 220 cautleyi ............ 220 densicoatata .................. 174, 184, 219, pl. 42 hyatti _____________ 172,173, 174,184,191, 219, pl. 42 aubspinasa ____________________ 174,184, 219, pl. 42 trezanensis ___________________ . 175,214, 220 variam. . . ..... 219 Sp _________________________ 174,184 saturnale, Lytoceras_, 171,173, ”5,178,184,195 semilaenis, Craspedites _________________________ 205 senescens, Anemia ___________________________ 175 shastemis, Acroteuthis ________________________ 178 Shasticrioceras ______________ 168, ”2,179,181,194, 198 hesperium ________________________________ 198 poniente _______________________ 173, 181, 184, 198 zone ___________________ 180,181 ulhitneyi ............... 173, 184, 198, pl. 25 Sp _______ 173,179,184 sp. lndet... 180 Shelton Ranch , _ . _ _. _______ 190,200 signalis, Hertleim’tes. __. 173,207 Neocraspedites ___________________________ 209 Simbirskites... . 168,170,171,172,176,177,178,179,180, 181,182,191,192,195,199, 207, 208,209, 211 , 212 auerhachi ____________________________ 211,212 broadL. . , 173,177,178,184,196,191, 209, 211, pl. 33 concimms _________________________________ 210 _____________________ 209, 210 dichotomus ______________________________ 177 elatus ________________ 173, 176, 177,184, 910, pl. 33 inverselobalua ______________________________ 210 lecontei ................... 173,184,208,209, pl. 33 progredicus _____________________________ 177, 18] progrediens _______________ 173,176,184,210, pl. 33 Sp ________________ 173,180,184 spp. .............. 173,184,210, pl. 33 (Simbirskites) mutabilis, 0lcostephanus......,_ 200 Simbirskltinae ________________________ 168,207 ainaularis, Olcoslephanus _____________________ 204 228 Sixes River ___________________ skidgatensis, Ostrea Solecurtus, 1 1 11 1. ............... 176, 179, 182 dubiua __________________________________ 172 sp ........................................ 181 South Umpqua River __________ 169,170,175,176,177, 186, 201, 202 Speetom'ceras , 1 _____ 168,172, 177, 180,182, 192,211,213 agnessense ________________ 173, 176, 184, 213, pl. 42 inversum __________________ 212 subinversus11 1 ,,,,,,,, 212,213 Spieden formation ............. 186 Spiticeraa ____________________________________ 198 duncanense ......................... 178, 198 SpitidiacuL 1 .................. 168, 176, 182, 194, 221 inlermedius _______________________________ 221 oreoonemis ........... 174,176, 177,184,221, pl. 31 Spomiylua fragilis ,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 172 atantom‘, Holcodiacua .......................... 201 Homolsomites ______________ 169, 173,175, 184, 20], 203,205, pl. 27 Neocraspedites ............................ 205 Stephenson’s ranchhouses _________ 171, 172, 189 atippi, Neocomites ___________ 216 Thurmanm'ceras ______ 173,174,176,184, 216‘, pl. 39 Stratigraphic summary _____________________ 169—171 atrigosum, Cerithium ________________________ 175 Subastieria .............................. 1 _ 216 ch unchelula. ...................... 178, 209, 216 sulcosa _______________ 177 sp __________________ 176 Subcraspediten mutabilis. 200 aubcylindrica, Hamulina, 1 11 200 subimersm, Speetoniceras. 1 212,213 aublaeuis, Buchia ______________________ 1.1. 172 subradiatus, Acamhodiacus. . __ 174, 175, 184, 220. pl. 42 subspinosa, Sarasimlla1_11 1-. 174, 184, 219, pl. 42 Subthurmamaia ______________________________ 216 aulcosa, Subuslieria ...................... .1. 177 Summary of results _______ Symylomma operculifarmia ___________________ 179 Systematic descriptions _____________________ 194—221 ’I‘ tnbarelli, Acrioceraa, __________________________ 199 Takilma—Waldo—Cavc Junction area __________ 171 INDEX Page tehamaensis, Area ,,,,,,,,,,,, 111 11 1 1 1,, 175 Crioceratiles ,,,,,,,,,,,,,, .1. 1 173, 179, 184, 1572’ Dichotomites ,,,,,,,,,,, . . 111 1 11 1 . 1 200 Holcodiscus __________ 196 Ilomolsomites mutabilis, ................ 201, 202 tennis, Craspedites, .1111. 1 , 208 Neocmspedites. 1.1 1 208 Terebratula califomirm, 1 171 sp _____________________ .._1._,.1.1_..1. 172 Tessarolar bicarinata ______________________ 179, 180 textrimz, Arca ______________________________ 172, 178 theadorii, Neocomites ________________________ 214 Thurmanm’a ______________________________ 216, 218 jupiler __________________________ 178, 179, 192, 200 Thurmanniceras _________ 168, 172, 181,194, 200, 205, 211,214, 215, 218 califomicum ______________________________ 171, 172, 173, 184,191, 21.4, 215, pl. 39 discaidulis ____________ 215 duraznense _____________________________ 175, 215 jenkinsi ___________ 173, 174, 175,176, 184, 915, pl. 40 novihispanicum. ........................ 172, 214 paskentae ............................. 176, 216 pertramienr ............................ 172, 214 etippi ................ 173, 174, 176, 184, 216, pl. 39 wilchL. ____________________ 173, 184, 214, pl. 40 Thurmumtites 1 1 1 11111 216 Tollia.,,.,111_. 168 Tolliinae ,,,,,,,,,,,, . 1. 1111. 168,181 trapezoidalis, Astana, 175 traski, Ammonites__11_ 1 ,,,,,,,,,,,,,,,,,,, 178, 210 Lytaceras ...................... 1 173, 178, 180, 184 Olcoslephanue ,,,,,,,,,,,,,,,,,,,,,,,,,,, 208 lrezanensis, Sarasinella 11111111111111 , 175, 214, 220 trichotomoua, Dirhotomilea ,1_, 1 1 ,, 204 trichotomus, Olcostephanus (Polyptychites) 11111 204 Palyptychites _________ 173, 174, 175, 184, 20.5, pl. 31 Trigonia ,,,,,,,,,,,,,,, .1. 1 . 1 176, 179, 182 kayana, , 176,177,178,180,181 team: ___________________________ 177, 180 trilineatus, Turbo,__1 ______________________ 175 trinitense, PhylloceraL 1 1 1. 1 1 173, 175, 176, 177, 179, 194 Phyllopachyceras 11111111111111111111 184, 194 trinitensis, Periplomya 111111111111111111 176,179,180 Trinity River 11111111111111111111111111111111 169 truncata, Hannaites 11111111111111111111111111 176 truncatus, Hannaites 1111111111111 173, 184, 218, pl. 41 Page Turbo festivius 1111111111111111111111111111111 180 humerosus111 175 morganensis 11111111111111111111111111111 175 trilineatus. _ _ 175 Turritella sp 111111111111111111111111111111 172 U uhligz‘, Holcodiscus 11111111111111111111111111111 203 umpquanum, Phylloceras 11111111111111111111 176, 194 Phyllopachuceras 11111111111111111 173, 177, 184,194 V Valanginian age _____________________ 172, 174, 175, 182 Valanginian ammonites, zonal distribution... _ 173 Valanginian beds 11111111111111111111111111111 171 Valanginian-Hauterivian ammonites, number of specimens 1111111111111111111111 168 Valanginites 1111111111111 _ __ 182,194 vallejoensis, Inocemmus 1111111111111111111111 175 varians, Sarasinella ____________________________ 219 variata, Plicatula 1111111111111111111111111111 179, 180 Venus collinium_111 ..................... 178, 179 vespera, Goniomya 111111111111111111111 179,180 vespertina, Anahamulina 11111111111111111111 178, 199 vespertinum, Acrioceras __________ 173, 184, 199, pl. 26 vigorosa, Wellsia ________________ 173, 184, 206', pl. 33 volgensia, Buckie" 172 vaganum, Acrioceras. 173, 177, 180, 184, 198, 199, pl. 26 W Waldo-Cave Junction area ____________________ 170 Wellsia 1111111111111111111111 . 168, 171, 182, 194.205 oregnnensi3111. 11111111111 170, 173, 176, 177, 184, 187, 191, 192, 202, 203, 2‘06. 207, pl. 32 packardi1111 170, 173, 176, 184, 205, 206, 207, pl. 33 zone 1111111111111111111111111111 177, 191, 192 vigorosa _____________________ 173, 184, 206, pl. 33 whiteavesi, Avicula (Ozytoma) 111111111111111111 175 whitneyi, Shasticrioceras 1111111111 173, 184, 198, pl. 25 Whitsett limestone lentils _____________________ 169 wichmanni, Neacomites 111111111111111111111111 215 Wilcox Ranch11 170,171, 179, 181), 189, 190, 195, 208. 215 wilcozensis, Anahamulina1111 173, 179, 184, 200, pl. 25 wilcozi, Neacraspeditea 1111111111111111111111111 214 Thurmanniceras 1111111111111 173, 184, 214, pl. 40 Y yollahollium, Crioceratites ________________ 173, 184,196 Iloplocrioceras 111111111111111111111111111 179, 196 PLATES 24—43 PLATE 24 [All figures natural size] FIGURES 1—4, 8, 9, 11, 12. Hoplocrioceras remondi (Gabb) (p. 196). 1—4. Ventral and lateral views of plesiotypes, USNM 129664a, b from USGS Mes. loc. 2225. 8. Plesiotype, USNM 129662 from USGS Mes. loc. 1062. Specimen crushed laterally. 9, l2. Plesiotype, UCLA type collection from UCLA 10c. 2816. Shows nearly complete adult body chamber. 11. Plesiotype, USNM 129661 from USGS Mes. Ice. 2268. Shows change from fine, dense ribbing of inner whorls to coarser, variably-spaced ribbing of outer whorls. 5, 6. Hoplocrioceras cf. H. remondi (Gabb) (p. 197). Lateral and ventral views of specimen, USNM 129665 from USGS Mes. Ice. 2080. 7, 10. Acrioceras cf. A. voyanum Anderson (p. 199). Lateral and ventral views of specimen, USNM 129663 from USGS Mes. 100. 2269. PROFESSIONAL PAPER 334 PLATE 24 GEOLOGICAL SURVEY H OPLOCRI O CERAS GEOLOGICAL SURVEY PROFESSIONAL PAPER 334 PLATE 25 10 HOPLOCRIOCERAS, ANAHAMULINA, H YPOPH YLLOCERAS, AND SHASTICRIOCERAS PLATE 25 [All figures natural size unless otherwise indicated] FIGURES 1, 3, 8, 9. Hoplocrioceras duncanense (Anderson) (p. 198). 1, 3. Plesiotype, USNM 129674 from USGS Mes. loc. 2224. 8, 9. Holotype, CAS 8810 from CAS 100. 1665. Note presence of lateral tubercles. 2, 5, 6. Anahamulina wilcozensis Imlay, n. sp. (p. 200). Suture line (X 2), ventral and lateral views of holotype, USNM 129671 from USGS Mes. loc. 1092. 4. Hypophylloceras afi. H. onoense (Stanton) (1). 195). Specimen, USNM 129672 from USGS Mes. 100. 2223. 7, 10. Shasticrioceras aff. S. whitneyi Anderson (p. 198). Ventral and lateral views of specimen, USNM 129673 from USGS Mes. 100. 2225. FIGURES 1, 5. 8—10. 11—14. PLATE 26 [All figures natural size] Crioceraliles sp. indet. (p. 196). Lateral and ventral Views of specimen, USNM 23101 from USGS Mes. 100. 1009. Proves occurrence of the genus in beds of Valanginian age. Acrioceras voyanum Anderson (p. 198). 2, 3. Lateral and ventral views of internal mold of plesiotype, USNM 129862 from USGS Mes. 100. 24449. 4. Lateral View of rubber cast from external mold of same specimen shown in figs. 2 and 3. . Crioceratites talus (Gabb) (p. 196). Ventral and lateral views of holotype of Crioceras duncanense Anderson, CAS 8873 from CA8 [00. 1665. This spec- imen is considered herein to be an immature representative of Crioceratites talus (Gabb). Acrioceras hamlim' (Anderson) (p. 199). Lateral and ventral Views of holotype, CAS 8879 from CAS 100. 113. Acrioceras vespertz'num (Anderson) (p. 199). Lateral and ventral views of holotype, CAS 8915 from CAS 100. 113. GEOLOGICAL SURVEY PROFESSIONAL PAPER 334 PLATE 26 \ “Ill CRIOCERA TI TES AN D A CRIOCERAS 527569 O—60————4 GEOLOGICAL SURVEY PROFESSIONAL PAPER 334 PLATE 27 H OM OLS OM I TES PLATE 27 [All figures natural size unless otherwise indicated] FIGURES 1—16. Homolsomites stantom’ (McLellan) (p. 201). l, 2, 5. Suture line (X2), cross section, and lateral view of adapical end of body chamber of a large specimen, University Washington 12763 from U.W. loc. WA535. 6, 7. Lateral and ventral views of part of penultimate whorl of same specimen shown in figure 1. 3, 4, l0. Lateral and cross sectional views of plesiotype, USNM 129696 from U.W. loc, WA 536. 8, 9. Ventral and lateral VieWs of paratype, U.W. 15002 from north shore of Spieden Island, Wash. 11—13. Ventral, apertural, and lateral views of holotype, U.W. 15001 from north shore of Spieden Island, Wash. 14~16. Suture line (X2) at whorl height of 28 mm on specimen shown in figs. 15 and 16. Fig. 15 shows coarse ornamentation of inner whorl comparable to that shown on figs. 4 and 9. Fig. 16 shows about one- quarter of the adult body whorl. Another half whorl of the body chamber is preserved, but is not shown because it is crushed and is similar to the part illustrated. Plesiotype, USNM 129695 from USGS Mes. 100. 26788. PLATE 28 [All figures natural size unless otherwise indicated] FIGURES 1—4. Homolsomites mutabilis crassicostatus Imlay, n. subsp. (p. 201). l, 2. Paratype, USNM 129692 from USGS Mes. Ice. 1010. 3, 4. Holotype, USNM 129690 from USGS Mes. 100. 1093. 5—11. Homolsomites mutabilis mutabilis (Stanton) (p. 201). 5, 6. Plesiotype, USNM 129693 from USGS Mes. loc. 2154. 7, 11. Lateral view and suture line (X 2) of lectotype, USNM 230893 from USGS Mes. 100. 1010 (lectotype selected by Anderson, 1938, p. 160). 8. Plesiotype, USNM 129691 from USGS Mes. 100. 1010. 9, 10. Plesiotype, USNM 129689 from USGS Mes. Ice. 1010. 12—17. Homolsomites mutabilis burgem' (Anderson) (p. 201). 12. Plesiotype, USNM 23089b from USGS Mes. Ice. 1010. 13, 16, 17. Plesiotypes, USNM l29688a—c from USGS Mes. 100. 1093. 14, 15. Plesiotype, USNM 23089c from USGS Mes. loc. 1010. Notes that plesiotypes shown in figs. 12, 14, and 15 are part of the original types of H. mutabilis (Stanton). 18—22. Homolsomiles mutabilis tehamaensis (Anderson) (p. 201). 18, 19. Holotype, CAS 5943 from CAS 10c. 1343. 20, 21. Plesiotype, USNM 129687 from USGS Mes. Ice. 1093. 22. Plesiotype, USNM 129694 from USGS Mes. 10c. 4390. GEOLOGICAL SURVEY PROFESSIONAL PAPER 334 PLATE 28 H OM OLSOMI TES PROFESSIONAL PAPER 334 PLATE 29 GEOLOGICAL SURVEY {1.}??? y,l‘v'l.. \va ‘ ”a"; 1 I. y i t :3, £9 +5 OLCOSTE'PH AN US PLATE 29 [All figures natural size unless otherwise indicated] FIGURES 1—5, 7—9. Olcostephanus pecki Imlay, n. sp. (p. 202). 1, 2, 5, 9. Lateral View, sutur line (X 2), cross section, and ventral View of paratype, USNM 1298473 from USGS Mes. loc. 25193. 3, 4. Lateral views of two small whorls of a single specimen showing tubercles and rib branching. Paratype, USNM 129849 from USGS Mes. 10c. 26790. 7. Lateral view of an aperture. Paratype, USNM 129847b from USGS Mes. loc. 25193. 8. Holotype, USNM 129848 from USGS Mes. 10c. 25192. Note fine ribbing on an inner whorl. The specimen includes parts of another fourth of a whorl. 6. Olcostephanus cf. 0. pecki Imlay, n. sp. (p. 203). Fragment of an inner whorl showing dense ribbing and tubercles. This was associated with a fragment of an outer whorl bearing ribbing as coarse as on the adoral end of the specimen shown on fig. 8. University Washington 100. WA538. PLATE 30 [Figure natural size] FIGURE 1. Olcostephanus pecki Imlay, n. sp. .(p. 202). Largest known specimen of species showing body chamber (about four-fifths of a whorl). Paratype, USNM 129846 from USGS Mes. 100. 26789. GEOLOGICAL SURVEY PROFESSIONAL PAPER 334 PLATE 30 OLCOSTEPHAN US GEOLOGICAL SURVEY PROFESSIONAL PAPER 334 PLATE 31 13 14 OLCOSTEPHANUS, SPITIDISCUS, DURANGITES, AND POLYPTYCHITES FIGI'RES 1—3. 4—6, s, 9. ‘1 11,12. l3, l5. l4. PLATE 31 [All figures natural size unless otherwise indicated] Olcostephanus popenoei lmlay, n. sp. (p. 203). Ventral and lateral views of holotype, USNM 129863 from USGS Mes. 100. 26790. Spitidiscus oregonensis lmlay, n. sp. (p. 221). 4—6. Lateral and ventral views of paratype, USNM 129698 from USGS Mes. 100. 718. 8, 9. Lateral and ventral views of holotype, USNM 129697 from USGS Mes. 100. 718. . Olcostephanus pecki lmlay. n. sp. (p. 202). Paratype, USNM 1298470 from USGS Mes. loc. 25193. Compare ribbing with that shown in figs. 1 and 8 on pl. 29. . Olcostephanus cf. 0. quadriradiatus lmlay (p. 203). Specimen, USNM 129861 from USGS Mes. loc. 25217. Durangites sp. juv. (p. 169). Specimen, 129686 from USGS Mes. 10c. 2026. Presented as evidence that the Whitsett limestone lentils of Diller (1898) near Roseburg, Oreg., are of Late Jurassic rather than of Cretaceous age. Polyptychites lrichotomus (Stanton) (p. 204). Lateral views of crushed holotype, USN M 23090 from USGS Mes. 100. 1087. Polyptychites sp. juv. (p. 176). Lateral view (X 3) of rubber cast of external mold from CAS 10c. 33502. Plaster replica, USN M 129699. PLATE 32 [All figures natural size unless otherwise indicated] FIGURES 176. Neocraspedites giganleus Imlay, n. sp. (p. 204). 1. Paratype, USNM 129834 from USGS Mes. 10c. 1088. Shows development of ribbing on an immature specimen. 2y 4. Lateral views of specimens somewhat larger than that shown in fig. 1 to illustrate development of flexuous ribbing. Paratypes. USNM 12983321, b from USGS Mes. Ice. 1091. 3, 5, 6. Cross section, ventral, and lateral views of holotype, USNM 23088 from USGS Mes. loc. 1009. The speci- men ineludes fragments of a still larger whorl (not shown). 7—20. Wellsia oregonensis (Anderson) (p. 205). 7y 8. Small plesiotype, USNM 129679a from USGS Mes. loc. 25198. Shows ribbing on an internal mold. 9. Plesiotype, USNM 129679b from USGS Mes. 100. 25198. Shows ribbing on shell. 10. Plesiotype, USNM 129677 from USGS Mes. 100. 25199. 11, 17. Suture line (X 2) drawn at whorl height of 11 mm on left side of specimen shown in fig. 17. Pleisiotype, USNM 129678 from USGS Mes. 10c. 1253. 12—14. Plesiotype, USNM 129676a from USGS Mes. loc. 25204. 15, 16. Lateral and cross sectional view of plesiotype, USNM 129676b from USGS Mes. 100. 25204. 18720. Ventral and lateral views of plesiotype, USNM 129675 from USGS Mes. 100. 1252. Beginning of body chamber is indicated by an arrow. GEOLOGICAL SURVEY PROFESSIONAL PAPER 334 PLATE 32 19 NEOCRASPEDITES AND WELLSIA GEOLOGICAL SURVEY PROFESSIONAL PAPER 334 PLATE 33 SIMBIRSKITES AND WELLSIA FIGURES 1, 14, 15. 2, 3, 8,9. 4—7, 12, 13. 10, 11. 16—18. 23, 24. 19—22, 25. 26—3 1. PLATE 33 [All figures natural size unless otherwise indicated] Simbirskites lecontei (Anderson) (p. 209). CAS 8785 from CAS 113. The specimen illustrated is a paratype 0f Simbirskites broadz’ Anderson, but is herein assigned to S. lecontei (Anderson). Simbirskites sp. juv. 2111'. S. progrediens (Lahusen) (p. 210). Specimens, USNM 129681 from USGS Mes. 10c. 25211. Simbirskites spp. juv. (p. 210). Specimens, USNM 129682 from USGS Mes. 10c. 25211. Simbirskites sp. juv. afl'. S. elatus (Trautschold) (p. 210). Specimen, USNM 129680 from USGS Mes. 10c. I251. Simbirskites broadi Anderson (p. 209). Lateral, cross sectional, and ventral views of holotype, (TAS 8784 from OAS [00. 113. “Subastieria” chanchelula Anderson (p. 209). Holotype, CAS 8791 at. CAS ICC. 113. The specimen illustrated probably represents an immature stage of Simbirskites broadi Anderson. Wellsia vigorosa Imlay, n. sp. (p. 206). 19, 20. Holotype, USNM 129669. 21, 25. Paratype, 129670a. 22. Paratype, 129670b. All types from USGS Mes. 100. 1252. Wellsz'a packardi (Anderson) (p- 206). 26. Suture line drawn at whorl height of 10 mm on plesiotype, USNM 129667 from USGS Mes. 10c. 25202. 27. Plesiotype, USNM 129668 from USGS Mes. 10c. 718. 28—31. Plesiotypes, USNM 129666 from USGS Mes. 100. 1252. PLATE 34 [All figures natural size} FIGURES 1~7. Hertleim'tes aguila (Anderson) (p. 207). 1, 5, 7. Ventral view, suture line drawn at whorl height of 46 mm, and lateral View of plesiotype, USNM 129654 from USGS Mes. 100. 2223. 2, 3. Holotype, CAS 8769 at CAS 100. 1353. Fig. 2 represents a rubber cast made from an external mold. Fig. 3 shows the internal mold oriented in the same manner as fig. 2. 4. Rubber cast of an external mold of plesiotype, USNM 129655 from USGS Mes. 100. 2222. 6. Internal mold showing ribbing of inner whorls. Plesiotype, USNM 129656 from USGS Mes. loc. 2267. GEOLOGICAL SURVEY PROFESSIONAL PAPER 334 PLATE 34 H ER TLEI N I TES WHENWNQQOE QZ< WHENZNHHNNWE mm HBdJHm vmm Mfimm>MDm J 195:3, .N .mc .mm .3 :o 550% mm as: 235w .omwwm .02 .mvE mUmD EC: mwoma EZwD 69220: we :53 $55.59“ 9:». 2235.4 .23” .3 >515 .363: mmfifizem .N 4 9.555% 885%.— hflamzw 05.2.3“ 53: wm Hakim WHHNWNNQOE mm MEANAW vmm mummdwm Qm>mDm 4<0Hmv040m0 GEOLOGICAL SURVEY PROFESSIONAL PAPER 334 PLATE 37 H OLLI SI TES PLATE 37 [All figures natural size] FIGURES l, 3, 4, 6. Hollisites inflatus Imlay, n. sp. (p. 212). Two inner whorls of holotype, USNM 129839 from USGS Mes. Ice. 1092. Fig. 4 shows cross section drawn near adoral end of whorl shown in figs. 3 and 6. The specimen is represented, also, by a larger septate whorl that is not figured. 2, 5. Hollisites lucasi Imlay (p. 211). 2. Whorl section of holotype, USNM 129045 from USGS Mes. loc. 26450. Drawn near adoral end. Other views of holotype shown on pl. 35, fig. 2, and pl. 36, figs. 1, 2. 5. Ventral view of holotype near adoral end, by comparison with apcrtural View on pl, 36, fig. 2, shows marked increase in thickness of shell. 533 Eng co Elm film .35 E Escam wane 3 mfimcec «Ea sauces,» E 3:86 E Eon? 5:5 05 :o wins: 97H .33 .03 .82 mUmD So...“ awwamd EZwD 59320: «c @503 355; «Ea Esaad .ANAN .5 dw .c Cad—EH 33:39:83 «$3333 .h ”w . .wsgwfigfiwam‘ Ho 2259me :«8m :0 gang 83883 mien: one :2fi3E:waE 9: 3 wEBC .38 .92 .32 mOmD Ea: nmwmfi EZmD ,mcwEEomm Am XV awao gonna a mo 33> Ehooag .3 Am XV $3 :59: a we @503 $555 was .933 .m J .Am XV $8 $325.. Sauces Ho 32> :233 .m .8 Xv emu”. .529: “0 95¢; ESE; «Ed 1239— .v hm .G3 .3 .mm d 82:; «32:35.8». .E can .>:.n A? 3:33: .oTw rmin N9: .92 .32 wOwD Ea: 35mg SZwD .mwazaahdm .E—fioafl FEE—.5 @983qu ion .2 c5“ _ .35 E mtg—3 $5: :o «5898 minor 25 302 £886on cwfimépfivwfikofi: 5:5 :aEm “o :owaaenvfiaso @595 fig .5 Eu: .283 £E§§ «HT: .N 4 was»: 33535 023.553 via—a: cs} 3.5:: wit—m: :«J mm HB - . _ Thurmanmcems . . ‘ . Kzlmnella crassmlzcata N t ’d t'f‘ d Polyptychites bullatus keyserrlmgi Thurmanmcems thurmanm Neocomztes wichmanm’ P 01W tych ites sp. and 0 1 en 1 1e 91- and (not zoned) . . . H Eurypty'chites diplommus . _ Thurmanmceras calzformoum a . ? ? Thurmanmcems pertranszens v Tolypecems marcoui ' ' i 3 Absent Pseudogamie/ria Lower . Platylenticems heteropleurum undulato- Not identified Platylenticems gemili plzcatzlis ? 7 7 7 Tollia pug/em" . 2 O S . . d . S 't' hl' . i ' submmdm- Tome toll;- Spiticems “”0921: “mm m “63:: u 1‘” Not identified Not identified Berriasian r) 7 S b and d ”3::qu Subthurmannia boissiem‘ Cuyamceras transgrediens Subthurmanma densistriatus , - ' ‘ ' u or ‘t i - - Subcmspedites stenomphalus (Continental depos1ts only) stenogfgzmlu? Thurmannicems S ‘t' and Z' Y . . Buchw Cf' 8' okenszs Subcmspedites cf 51 subpressuilus Hectoroqems SROCWSPRWOS aff. T. m zcems negro l Argentzmcems nodulifemm Subthurmanma tenochz ’ . ' ' ' . " ’ 1600’”. boissieri and and Subcmspedztes (Pameraspedztes) Pretollw Subcmspedites Neocosmoceras egregium Spiticems zirkeli spasskenszs magma spasskenszs 527569 0 - 60 (In pocket) Dispersants GEOLOGICAL SURVEY'PROFESSIONAL PAPER 334-G Prepared in cooperation wwz'tfl Colorado State University BERKELEY H$fiéRY w u; uBRARY Dispersion Characteristics of Montmorillonite, Kaolinite, and Illite Clays in Waters of Varying Quality, and Their Control with Phosphate Dispersants By B. N. ROLFE, R. F. MILLER, and I. s. MCQUEEN SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY GEOLOGICAL SURVEY PROFESSIONAL PAPER 334—G Prepared in cooperation wit/z Coloraa’o State University UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1960 UNITED STATES DEPARTMENT OF THE INTERIOR FRED A. SEATON, Secretary GEOLOGICAL SURVEY Thomas B. Nolan, Director For sale by the Superintendent of Documents, US. Government Printing Office Washington 25, DC. - Price 40 cents (paper cover) CONTENTS “3° Results and discussion—Continued Page Abstract- — —* --------------------------------------- 229 Sodium illite in hard water _______________________ 241 Introduction ....................................... 229 Calcium illite in hard water ______________________ 243 Personnel ...................................... 230 Volclay in distilled water ________________________ 243 Acknowledgments ............................... 230 Volclay in medium-hard water ____________________ 243 Materials ------------------------------------------ 231 Kaolinite (78.8 percent sodium saturated) in distilled Clay minerals __________________________________ 231 water _______________________________________ 245. Phosphate dEflOCCUIentS ------------------------- 231 Kaolinite (78.8 percent sodium saturated) in medium- Waters ---------------------------------------- 231 hard water ___________________________________ 246 Methods ------------------------------------------- 233 Illite (78.8 percent sodium saturated) in distilled Water synthesis ................................ 233 water _______________________________________ 245 Exchange complex saturation 0f clays ----------------- 233 Illite (7 8.8 percent sodium saturated) in medium- Treatment with deflocculents _____________________ 234 hard water ___________________________________ 243 Hydrometer analysis ———————————————————————————— 234 Summary of conclusions _____________________________ 248 RESUME and discussion ——————————————————————————————— 234 Properties of clay minerals, by B. N. Rolfe ____________ 248 Sodium montmorillonite in distilled water __________ 235 Kaolinite ______________________________________ ~ 249 Calcium montmorillonite in distilled water _________ 235 Montmorillonite ________________________________ 249 Sodium montmorillonite in soft water _____________ 237 Illite __________________________________________ 250 Calcium montmorillonite in 50“ water ------------- 237 Discussion of the hydrometer method, by I. S. McQueen- 250 Sodium montmorillonite in hard water ............. 237 Advantages of the hydrometer method ____________ 251 Calcium montmorillonite in hard water ------------ 237 Disadvantages of the hydrometer method __________ 251 Sodium kaolinite in distilled water ———————————————— 239 Theory of clay mineral behavior in dilute suspensions, by Calcium kaolinite in distilled water _______________ 239 R. F. Miller ______________________________________ 252 Sodium kaolinite in 50” water -------------------- 239 Factors that control the degree of dispersion _______ 252 Calcium kaolinite in soft water ___________________ 241 Dispersion and clay minerals _____________________ 254 Sodium kaolinite in hard water ——————————————————— 241 Mechanism of dispersion control __________________ 255 Calcium kaolinite in hard water —————————————————— 241 Tables of data and dispersion indices __________________ 255 Sodium illite in distilled water -------------------- 241 Filter—loss test of clay suspensions, by I. S. McQueen---- 269 Calcium illite in distilled water ___________________ 241 Selected references __________________________________ 270 Sodium illite in soft water _______________________ 241 Index _____________________________________________ 273 Calcium illite in soft water _______________________ 241 ILLUSTRATION S Page FIGURE 37. Dispersion characteristics of sodium— and calcium-saturated montmorillonite in distilled (A and B) and soft water (0 and D) _______________________________________________________________________________________ 236 38. Dispersion characteristics of sodium— and calcium-saturated montmorillonite in hard water ___________________ 238 39. Dispersion characteristics of sodium- and calcium-saturated kaolinite in distilled water ______________________ 239 40. Dispersion characteristics of sodium- and calcium-saturated kaolinite in soft water __________________________ 240 41. Dispersion characteristics of sodium— and calcium-saturated kaolinite in hard water _________________________ 242 42. Dispersion characteristics of sodium- and calcium-saturated illite in distilled water __________________________ 243 43. Dispersion characteristics of sodium— and calcium-saturated illite in soft water _____________________________ 244 44. Dispersion characteristics of sodium— and calcium-saturated illite in hard water _____________________________ 245 45. Dispersion characteristics of Volclay in distilled and medium-hard water ___________________________________ 246 46. Dispersion characteristics of kaolinite (78.8 percent sodium saturated) in distilled and medium-hard water- _ _ _ 247 47. Dispersion characteristics of illite (78.8 percent sodium saturated) in distilled and medium-hard water ________ 247 48. Nature of zone measured by a hydrometer____7 ________________________________________________________ 251 m TABLE MHHD—‘b—‘r—‘b—‘I—‘D—‘b—‘H OCDWKIQO‘VPOJNHO oooqcapngsoarow . Properties of the Hydrometer data Hydrometer data: Hydrometer data Hydrometer data . Hydrometer data . Hydrometer data . Hydrometer data . Hydrometer data . Hydrometer data . Hydrometer data. . Hydrometer data . Hydrometer data: . Hydrometer data . Hydrometer data . Hydrometer data . Hydrometer data . Hydrometer data . Hydrometer data . Results of filter-loss tests _____________________________________________________________________________ CONTENTS TABLES phosphate deflocculents used in the study _______________________________________________ : Montmorillonite and sodium tripolyphosphate __________________________________________ Montmorillonite and sodium hexametaphosphate _______________________________________ : Montmorillonite and sodium hexametaphosphate plus sodium carbonate ___________________ : Kaolinite and sodium tripolyphosphate ________________________________________________ : Kaolinite and sodium hexametaphosphate _____________________________________________ : Kaolinite and sodium hexametaphosphate plus sodium carbonate _________________________ : Illite and sodium tripolyphosphate ____________________________________________________ : Illite and sodium hexametaphosphate _________________________________________________ : Illite and sodium hexametaphosphate plus sodium carbonate _____________________________ : Volclay and sodium tripolyphosphate _________________________________________________ :, Volclay and sodium hexametaphosphate _______________________________________________ Volclay and tetrasodium pyrophosphate _______________________________________________ : Kaolinite and sodium tripolyphOSphate ________________________________________________ : Kaolinite and sodium hexametaphOSphate _____________________________________________ : Kaolinite and tetrasodium pyrophosphate _____________________________________________ : Illite and sodium tripolyphosphate ____________________________________________________ : Illite and sodium hexametaphosphate _________________________________________________ : Illite and tetrasodium pyrophosphate _________________________________________________ Page 232 256 257 258 259 260 261 262 263 264 265 265 266 p 266 267 267 268 268 269 270 SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY DISPERSION CHARACTERISTICS OF MONTMORILLONITE, KAOLINITE, AND ILLITE CLAYS IN WATERS OF VARYING QUALITY, AND THEIR CONTROL WITH PHOSPHATE DISPERSANTS By B. N. ROLFE, R. F. MILLER, and I. S. MCQUEEN ABSTRACT This study is concerned with the dispersion characteristics of montmorillonite, kaolinite, and illite clay minerals in waters of different hardness and the relation of these characteristics to the control of canal seepage by artificial sedimentation. The effect of dehydrated sodium phosphates on dispersion was also investi- gated. The importance of recognizing colloidal suspensions as ternary systems (colloid, water, ionized salt) is emphasized. Representative samples of montmorillonite, kaolinite, and illite clays, were saturated with either calcium or sodium and then pre- pared as 1 percent suspensions in distilled, hard, and soft waters. This provided extreme clay-water environments with respect to an investigation of the control of dispersion through the injection of sodium polyphosphate-type dispersants. Intermediate condi- tions were also provided by using a water of intermediate quality between hard and soft extremes. A native montmorillonite clay was selected for use as the prototype of calcium-sodium exchange relation and was replicated on the kaolinite and illite clays. The dispersion characteristics of the clay minerals under the preceding environments are involved in sediment transport in natural streams and play a decisive role in sediment-lining procedures. The deflocculents used in the investigation were sodium tripoly— phosphate (Na5P3010), tetrasodium pyrophosphate (Na4P207), so- dium hexametaphosphate (NaP03),., and sodium hexametaphos- phate plus soda ash (N a2003) in a 50—50 by weight mixture. The deflocculents varied in dispersion efficiency depending upon the interaction of the clay-water-phosphate systems. These variations were related to dissociation of sodium and length of polymer chains. .A specific deflocculent for each clay, water, ionized salt system was indicated by the data. The percentage of dispersion was measured by sensitive hy- drometers, reading from 0—10 grams of colloid per liter. This instrument gave generally acceptable results, except where con- ditions did not conform to the limitations imposed by basic theories of hydrometer analysis. The greatest source of trouble was in montmorillonite suspensions which produced anomalous increases in the hydrometer readings. This was attributed to consolidation of uniformly sized particles in the hydrometer jar, producing a greater apparent specific gravity in the zone meas- ured by the hydrometer. The increase was usually accompanied by phenomena similar to gelation. As an aid in comparing the many hydrometer analyses (con- sisting of 3,156 hydrometer readings), the index of dispersion con- cept was introduced. This value totals selected ordinates under a dispersion curve and compares the sum to a base value obtained by the same method for selected ordinates under a standard curve representing sodium—saturated clays in distilled water. Thus, for each clay mineral there is a standard value against which all deflocculating treatments may be compared. The results indicate the importance of understanding the chem- istry of the ternary system (clay, water, ionized salt). The-de- pendence of dispersion on the interaction of these three factors is great. Each clay-mineral group has specific properties and char- acteristics in the system. Not only does montmorillonite show the greatest colloidal yield but it is the most responsive to changes in chemical environment. It is far more difficult to sodium saturate a calcium clay than a hard calcium water. Although repulsion between like negative surfaces is the basis of dispersion, the location, source and amount of negativity of the various clay minerals determine the best deflocculent for effecting dispersion. The general implications of the study have a bearing on several fields of sedimentation. With respect to sediment lining of canals, theinvestigation indicated the relative superiority of mont- morillonite-type clays for the penetration and filling of small voids. With respect to filling of joints, cracks, burrows, and other relatively large openings, kaolinite and illite clays may be suitable as mortaring agents. INTRODUCTION Irrigation is practiced in areas Where precipitation is insufficient to produce a profitable crop. It is also used to a limited extent where supplemental applica- tions of water are needed to offset irregularities in rainfall distribution. More than 100 million acre-feet of water is diverted annually for irrigation purposes in the 17 Western States (exclusive of Alaska). The amount of water that reaches the user is reduced during transport by a minimum of 25 percent (Dirmeyer, 1955). Most of this loss may be attributed to seepage from unlined canals. In addition to the actual decrease in available water supply, there is the problem of damage to cropland adjacent to seeping irrigation canals, such as waterlogged soil, drowned crops, and zones of salt accumulation. Investigation has there- fore been centered on possible means of decreasing the losses. Canal seepage has been diminished by treating the leaking bed material to reduce itftpermeability. These treatments consist of lining the canals with materials 229 230 such as concrete, plastics, bentonite, and asphalt membranes, and compacted earth. The cost of such treatment ranges from $0.15 to $5 per square yard of canal bed. None of these treatments has satisfactorily supplied a low-cost canal lining. Sediment lining seems to offer great promise, and the present investigation is the outgrowth of the need for low-cost canal lining. Canal lining by sedimentation is very appealing because little special equipment is required. Sediment lining of canals was originally a natural phenomenon connected with the early history of irrigation farming. Irrigation waters were first di- verted directly from natural streams. The spring floodflows at the start of the growing season normally carried enough suspended sediment to serve as a natural seepage control through sedimentation. The only drawback to this means of seepage control was its transient stability. Clear irrigation water, diverted during the middle and latter parts of the season broke up the sediment cake and carried it away in suspension. As irrigation progressed the installation of reservoirs as sources of irrigation waters terminated the favorable natural sedimentation of former years by intercepting the sedimenting material. An artificially introduced sedimenting material should be more stable than the temporary sediment cake of the past. Seepage control by sedimentation probably could be improved, either by increasing the stability or toughness of the filter cake at the surface of the bed material, or by adding a fine-grained sediment below the bed surface as a void filler. If the sedimenting material is to be used as a void filler below the surface of the canal bed, it should be transportable by the canal water. This imposes certain limits on the size and transportability of the particles. The particles probably should be colloidal in size (less than 1 micron in diameter), and the chem- istry of the clay-water system should be controlled so that the particles do not coagulate and form clumps of particles that will not enter the soil voids. A native Wyoming bentonite that apparently conforme‘d to the above requirements was used for sediment lining by the US. Bureau of Reclamation on its Kendrick project at Casper, Wyo. This was a bentonitic clay that had a median particle diameter of 0.5. micron. It was found early in the work at Kendrick, however, that this bentonite was equally responsive to both flocculating and dispersing environments. If the canal waters were of such a chemical quality as to promote floc formation, the transport of the introduced sedi— menting material was shortlived. The bentonite sus- pension failed to cover the desired extent in the canal because the particles generally precipitated a short distance from the starting point. Also, flocs of SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY bentonite with a sedimentation diameter larger than the desired 0.5 micron were formed; these would not penetrate the voids of canal-bed material. There seemed to be a need for a dispersing medium or chemical control to insure the suspension of bentonite in. differing canal waters. It was at this stage in the sediment-lining investigation that the Geological Survey was approached on the subject of a possible cooperative project with Colorado Agricultural and Mechanical College. The transport of sediment by water may be influenced by the kind of sediment and the chemical quality of the water. Therefore a basic study into the dispersion characteristics of several clay minerals in waters of differing chemical quality was of mutual interest to the Geological Survey and to investigators into canal lining by sedimentation. The need for chemical additives to maintain a dispersion medium led to discussionswith represent- atives from chemical companies. The several phos- phate deflocculents available seemed to offer the greatest promise of success so the study was designed to investigate these in conjunction with the ternary system (clay, water, ionized salt). PERSONNEL The investigation was made by the Geological Survey in cooperation with Colorado Agricultural and Mechan- ical College, now Colorado State University. The investigation was started in 1954 at Colorado Agricul- tural and Mechanical College, where laboratory space was provided for the Geological Survey, and was com- pleted in 1956 in the soils laboratory of the Geological Survey at the Denver Federal Center. The investi- gation by Geological Survey personnel was under the administrative direction of R. W. Davenport, cnief Technical Coordination Branch succeeded by C. C. McDonald, chief General Hydrology Branch, and under the supervision of H. V. Peterson, project hydrologist and later branch area chief, General Hydrology Branch, Denver, Colo. B. N. Rolfe, soil scientist, was in immediate charge of the investigation until his resignation in 1956. Reuben F. Miller, soil scientist, and I. S. McQueen, hydraulic engineer, assisted in the research and completed the report. A0 KNO WLEDGMENTS There were many formal and informal conferences during the study. The names that follow are those of people who contributed much to the study but any omissions do not imply lesser contributions by others to the overall problem. The writers are indebted to many faculty members at Colorado State University, espe- DISPERSION CHARACTERISTICS, MONTMORILLONITE, KAOLINITE, ILLITE CLAYS cially to Dr. D. F. Peterson, R. D. Dirmeyer, Jr., R. B. Curry, and Dr. M. L. Albertson of the Civil Engineer- ing Department, to Dr. R. S. Whitney of the Soils Department, and Dr. C. G. H. Johnson of the Chemistry Department. Valuable counsel was received also from Dr. S. R. Olsen and Dr. C. V. Cole of the regional phos- phate laboratory of the Agricultural Research Service, US. Department of Agriculture, stationed at Colorado State University. Several chemical companies were generous with time, data, and suggestions. Representing the companies were R. P. Gates, Victor Chemical Works; Clark Sum- ner, A. R. Maas, R. N. Thompson and W. C. Bennett, Calgon, Inc.; and John Deming, L. V. Sherwood and R. A. Ruehrwein, Monsanto Chemical Co. These men contributed very helpful counsel and furnished supplies of deflocculents for the testing program. The clay companies were also generous with time, data, and samples. Paul Bechter, American Colloid Co., supplied samples as well as technical information. Messrs. S. C. Lyons and R. E. Lehman of Georgia Kao- lin Co. helped by furnishing pertinent data on the kao— lin used in the investigation. For the Baroid Co., Messrs. Huebotter, Neznayko, Weintritt, and the late F. J. Williams offered technical advice and information on many aspects of the study. The writers also wish to acknowledge the fine cooper- ation given by Engineering Laboratories Division of the US. Bureau of Reclamation at Denver, Colo. Messrs. Hunter, Jones, Mielenz, and the late M. E. King were always gracious in exchanging ideas and informa- tion during the course of the investigations. MATERIALS CLAY MINERALS The materials used were components of the ternary system; clays, water, and ionizable salts. The clays used were: 1. Kaolinite, supplied by Georgia Kaolin Co., Dry Branch, Ga. 2. Montmorillonite, trade name “Volclay” supplied by American Colloid Co., Belle Fourche, S. Dak. 3. Illite, an illite-bearing shale from Fithian, Ill. A discussion of clay mineral properties by B. N. Rolfe is presented on p. 248. PHOSPHATE DEFLOGCULENTS Three phosphate deflocculents were selected for the investigation. Each was studied to determine its effect on the control of dispersion in the different clay-water systems utilized in the experiments. The various phosphates have several common prop- erties, but differ in efficiency as to specific reactions (Chu 231 and Davidson, 1955; Tchillingarian, 1952; Whitehouse and Jeffrey, 1955; Wintermyer and Kinter,1955). The results of this investigation indicate only the relative ca- pabilities of three phosphate reagents, all of which were dehydrated sodium phosphates, in dispersing three dif- ferent types of clay minerals. The chemical composi- tion and general characteristics of the compounds used are given in table 1. ' There is apparently some confusion concerning phos- phate nomenclature. The terms in this report are those in common usage in the phosphate industry. The term. “molecularly dehydrated phosphates” refers to certain complex salts formed by the high temperature dehydra- tion of monosodium orthophosphate, disodium ortho- phosphate, or an intermediate mixture. The phosphates differ significantly in P205 content, chemical formula, and atomic arrangement. As is shown in table 1, so- dium tripolyphosphate, tetrasodium pyrophosphate, and sodium hexametaphosphate are separate entities and represent distinct phosphate salts with individually dif- ferent characteristics. Table 1 was compiled from literature furnished by Victor Chemical Works and Calgon, Inc. There has been no effort to edit these statements. The writers have merely arranged the information for easy compara- tive reading. Sodium tripolyphosphate and sodium hexametaphos- phate were used during both years of the study whereas tetrasodium pyrophosphate was used only during the second year. A 50—50 mixture, by weight, of sodium hexametaphosphate and soda ash (Na2C03) was tried during the first year of the study. This was done in response to a suggestion by personnel at Calgon, Inc., on the basis of their experience in the paper industry with dispersing kaolinite clays. WATERS The chemical quality of the waters used in the study varied greatly with respect to hardness (calcium, mag- nesium content). The relative amounts of the metallic ions, calcium, magnesium, and sodium are of para- mount importance to the dispersion characteristics of the various clay minerals. Two prototype waters, a hard and a soft water, were selected from a table of representative irrigation waters described in the US. Department of Agriculture Salinity Handbook (Ri- chards, and others, 1954). This was in accord with the objective of the work for the first year wherein end- member relations such as sodium- versus calcium satu- rated clays were to be studied. The plan for the second year decided upon by inter— ested parties in conferences held at Fort Collins in early 1955 was to study the dispersion characteristics of a clay commercially available in water of intermediate SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 232 .2238 3858 _ .muozuoa woo“ mnmm $80.5 m8: .858 music .8“ amqowfiunoo $88808 8882 88 2585 £898w8 88 >20 .88 8888:. .wntgoausnaE £888 82»; dais $8.5m .8 .598 8 898 .88 888R £20m 808 833 Bed mnobm £25 .86 .muammsaov 8m .8315 88388 035 wagflooazd .MoEa :05 .mfiaotom 883 ~3.588 28m 48 8.5“ 3888 8,888.8 some «Tex .wEm 88 82888 88 803.353 838888 85 -38 8 8288.— 88 88 H .oaanmmosn team do: .88 8o8a8$ EonmoEH a .w 8328 meanwnflom 08388 838 on. 3 3 I \A 883 82.0 o .5 ..... a moms/C -aowEaxw: 8=€om $888 8% 81838 maid—flaw $88898 23x3 £88888 his £58— 883 8888 m8 .ouanmmonaohhm .8888 .82qu man: .8“ 0.88 888853 88 -8983 :mE 8 838.38 m8 .858 -mio 88qu as S Nam -88? #85868 .888 9:58 8828 888 8888 80338 3 03 8:803:88 ”$8332. 88 88.888 88m £2883 23: w. on A896»: 6983883 madam .5“ .8389 £88838 8wa N .3 $8928 mwsafigow .moom: ea .8 S m cm. ......... ow. ..... o .3 -88 50$qu -053 88608508 Amen—among 6:8 mange .9580 888a $853888 $838008 23 wd 68880838 -xwa .wfimhvmmmu his 6.88.3: Jan 88qu NA ‘ 8&8 .893 8 .9588 :38 8”. 6883885 888986 .8883 ”£5868 Sfinmongmoaia «am an .Amfi8oo3805 Adam Q30 88 8888.598 mm 9: .83 95.868 .888 88 38% 4888888 88 8888 :38— m: on .83: .Sdnamonm 83% .8“ 8383$88fi8 .583 w .m 8838 mwsmmnflow .8 hoes ea .8 S E on 89% .vmuvaom w Sm ..... sommnaz 4209.5 888% Ahoy 832cm 3.3m 9.88 u88n .88an 3:8 mewD g a 8 Ma 8838 8383288 8:838 S .3585 888898 32925 .88 83 do: 8280qu .88 no am 88888 82880 .533 38.8 88 E 5:328 85» 2: 5 88 3:388:38 £21323 2: .3 83.88.5'4 884B DISPERSION CHARACTERISTICS, MONTMORILLONITE, KAOLINITE, ILLITE CLAYS quality. A Wyoming bentonite (Volclay) and water from the Tri—County Canal in central Nebraska, were selected as prototypes for the clays and waters used during the second year’s investigation. Distilled water was the first aqueous medium in which the various clays were dispersed. Any addition of deflocculent to such a clay-water system would merely serve to counter the influence of any hard (Ca++ or Mg++) ions in exchange positions on the clay. Under such a premise, a sodium-saturated clay in distilled water should represent maximum dispersion potential, and the dispersion index discussed later is based on this condition. The composition of the hard water was selected from a field prototype to represent an extreme in flocculating effect. The synthetic model contained the following in milliequivalents per liter: Calcium, 17; magnesium, 8; and sodium, 17. This is an admittedly unusual water because of its high electrolyte content and high cal- cium, magnesium values. Anions were not regarded as significant during the design stage of this study but proved to be, as will be described later. The soft water, as with the hard water, was selected from a field prototype to represent the other extreme in waters. The synthetic model contained the follow- ing, in milliequivalents per liter: Calcium, 3; mag— nesium, 2; and sodium, 15.5. This is a highly sodic water and is probably an end member in the range that might be expected in irrigation waters. Water from the Tri-County Canal in central Nebras- ka was selected as a prototype for the study because its chemical compositon fell midway between those of the hard and soft waters. The synthetic model contained the following, in milliequivalents per liter: Calcium, 6.2; magnesium, 3.6; and sodium, 6.3. METHODS WATER SYNTHESIS The synthetic waters of varying degrees of hardness were assembled in the laboratory by adding the proper amounts of calcium, magnesium, and sodium salts to distilled water. As indicated previously, there was a different experimental procedure for each year of study. This was true for the clays and waters. It is, therefore, convenient to discuss the water synthesis in chrono- logical order. ’ The analyses of the waters for 1954—55 have been reported in the previous section. Only the sources of the cations are noted here. Sodium was derived from reagent grade sodium chloride (NaCl); calcium from reagent grade calcium sulfate (CaSO4-2H20) ; and magnesium from reagent grade magnesium sulfate (MgSO4'7H20) . 530716 0—60—2 233 During the second year (1955—56) the sodium ions were derived from reagent grade sodium chloride. However, to provide calcium, calcium chloride was used instead of calcium sulfate in order to avoid the possible formation of an insoluble precipitate as occurred in the investigation of the hard water. EXCHANGE COMPLEX SATURATION OF CLAYS The clay minerals were treated to saturate their exchange complexes with either calcium or sodium or a combination of the two. In the first year’s investiga- tion the clay minerals were made homoionic with respect to calcium and sodium. In the second year the clays were ionically adjusted to simulate the exchange complex of a native Wyoming bentonite (Volclay). Homoionic clays were prepared as follows: 1. 10-gram portions of air-dry clay were placed in 100 milliliter glass centrifuge tubes. 2. 100 milliliters of 1 N calcium acetate or sodium chloride were added and mixed with the clay. 3. The centrifuge tubes were placed in beakers containing water and warmed gently overnight on a hot plate. 4. The suspensions were then centrifuged and the supernatant liquid decanted. 5. The above procedure was repeated three times. 6. The clays were washed three times with distilled water, centrifuged and decanted between each washing. 7. The washed clays were transferred into hydrometer jars and filled to 1 liter with the proper aqueous medium. During the second year’s investigation, instead of using homoionic clays, the cation-exchange complex of Volclay was used as a prototype from which calcium- sodium percentages were calculated. As presented in the American Colloid Co. Circular, Data No. 202, the ionic content of Volclay (per 100 grams) is as follows: Mlllkquivalenla Sodium ____________________________________________ 85. 5 Calcium ___________________________________________ 22. 0 Magnesium ________________________________________ 1. 0 Total __________________________________ 108. 5 In calculating the percentage of saturation with respect to calcium and sodium, magnesium was grouped with calcium. Therefore, the sodium saturation is equal to 85.5——:-108.5><100 or 78.8 percent, and the calcium saturation is 100 percent minus 78.8 percent or 21.2 percent. The percentage of exchangeable cations was simulated on the kaolinite and illite as follows: 1. Homoionic sodium and calcium clays were prepared as described previously. 2. Instead of transferring the clays to hydrometer jars (step 6), they were air—dried and stockpiled. 234 3. 7.88 grams of air—dry sodium clay was mixed with 2.12 grams of calcium clay. 4. The mixtures (10 grams) were put into hydrometer jars which were filled to 1 liter with the desired water. TREATMENT WITH DEFLOCCULENTS The phosphate deflocculents were added progressively in small increments to each clay-water system to determine the quantity producing the maximum dispersion. The dispersion attained in a phosphate- distilled water medium was considered the maximum obtainable for each type of clay. The increments of phosphate were added to the system at the end of each hydrometer test sequence, stirred, and allowed to soak for about 20 hours. The hydrometer procedure was followed and the phosphate addition repeated. The time required to attain maximum dispersion varied with the clay-water system and took as long as 3 weeks in the calcium-clay hard- water system. The possible effect of the time element on the validity of the results was recognized but the described procedure was adopted because of the space limitations of the laboratory and the time allotted to the study. The objection to this method was the possibility of the phosphate reverting to P04 ionization products of phosphoric acid an orthophosphate in the time elapsed during the experiment. However, some checks that were made using single optimum applications of phosphates to clay—water systems, showed no appreciable differences in the results. Also, the temperatures involved in the study were of such a range as to restrict reversion to a minimum. The latter statement agrees with published statements by phosphate manufacturers. The method described above was followed during both years of the investigation. It proved expedient and allowed for a greater number of tests than would have been possible otherwise. HYDROMETER ANALYSIS The hydrometer test procedures used were patterned after standard wet mechanical analysis methods with modifications to adapt them to the objectives of this investigation (see the section “Discussion of the hy- drometer method”). The procedure was as follows: 1. 10 grams of air-dry colloid was placed in each hydrometer cylinder. 2. Each cylinder was filled to the 1 liter mark with either dis- tilled water or previously prepared synthetic water. The mixture was allowed to stand for 24 hours with occasional mixing. 3. A cylinder was filled with the same water as that used in the test, to act as a check on temperature and other effects. 4. The hydrometer was inserted into the check cylinder, and the reading recorded. SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 5. The samples were thoroughly mixed for a period of 1 minute by one of the following methods: a. The hydrometer cylinder was covered with the palm of the hand and the suspension mixed by vigorous end—over-end shaking of the cylinder. b. A mixing tool was inserted (a large rubber stopper fixed to the end of a glass rod) into the cylinder and moved rapidly up and down. . A clock or stopwatch was started as the mixing was stopped. . The hydrometer was carefully inserted into the suspension. 8. The percentage of clay in suspension was read and recorded 1 minute and 4 minutes after mixing. 9. The hydrometer was placed in the check cylinder and the observed reading recorded, thereby accounting for changes in temperature and electrolyte effects. This value was applied to the readings in the sample as a correction. 10. Additional readings were made on the sample and the check cylinder 19, 60, 435, and 1,545 minutes after mixing. 11. Specified amounts of deflocculent were added to the sample and to the check cylinder and steps 4 through 10 were repeated. NC» The hydrometer used was an ultrasensitive instru- ment that measures 10 grams of soil per liter at maxi- mum reading. This instrument was used to enable work in the same range of concentration (about 1 percent) as was used in field experiments on sediment lining. When the salt concentration in the water was high and the amount of deflocculent was large, readings were beyond the range of the sensitive hydrometer and it was necessary to use a standard hydrometer calibrated to 60 grams of suspended material per liter. RESULTS AND DISCUSSION Many attempts have been made to devise a universal means of comparing the results from hydrometer tests and from other methods of mechanical analysis. Where large numbers of analyses were made, no rapid visual method of comparing the results was available. The primary deterrent was the lack of a suitable standard of comparison. In the present investigation, interest centered on the relative efficiency of the various phosphate defloccu- lents. By adoption of one set of data as a standard of comparison, the relative dispersion characteristics of one clay in different phosphate-water systems could be evaluated. The numerical relation between the stand- ard and the individual set of data is referred to as “the index of dispersion.” The data for sodium-saturated clays in distilled water with no deflocculent were selected as the standard of comparison for computation of dispersion indices. Each sequence of tests on each clay type started with no deflocculent added. Because there was a sequence for each of three types of deflocculent using distilled water, this provided 3 runs on each clay that were duplicates, that is the same amount of clay dis- DISPERSION CHARACTERISTICS, MONTMORILLONITE, KAOLINITE, ILLITE CLAYS persed in identical liquid media. This provided a usable standard with several advantages: 1. There were duplicate tests that could be averaged. 2. Sodium-saturated clays in distilled water represent near optimum dispersion. 3. The aqueous medium is salt free and does not introduce any extraneous electrolytic effects into the system. 4. The individual size distribution curves for a given clay were similar. Therefore the standard should be reproducible. In the test procedure used, hydrometer readings were made 1, 4, 19, 60, 435, and 1,545 minutes after mixing the sample. As the grain-size distribution for all samples of a given type of clay was presumably the same, the sum of these readings would represent the relative dispersion of the sample. The average of the sum of the readings for 3 runs on each sodium-saturated clay in distilled water with no deflocculent was used as a standard or 100 percent dispersion. For Volclay, a montmorillonite—type clay, the average sum was 532; for kaolinite it was 453; and for illite it was 395. The dispersion indices were computed as in the following example. For calcium-saturated Volclay in distilled water with 0.5 grams per liter of sodium tripolyphosphate added, the corrected hydrometer readings at the specified times were 90, 83, 69, 52, and 41 percent of dispersed weight. The total is 404 and the dispersion index is 404+532X100=75.9 percent. Thus each test run was compared on a percentage basis with the standard for the type of clay being tested. The computation of dispersion indices requires that there be no missing data. The hydrometer readings in the standard at 1, 4, 19, 60, 435, and 1,545 minutes must be matched by readings at the same time intervals in the hydrometer run being studied. However, 1 or more of these readings were omitted during several tests, the reasons being time, expediency and apparent end to sequence. Examination of the data and the laboratory procedures used indicated that the missing readings lay within narrow definable limits and could be supplied with reasonable accuracy by extrapolation and interpolation. The following criteria were followed in substituting for missing data: 1. Missing values were assumed to be equal to or less than those preceding them in a series. 2. Incomplete curves were compared with complete size distri- bution curves in the same system and the missing data was chosen to make their curve shapes conform. 3. Notes on original data sheets such as references to clear surface breaks and floc formation, were used as guides in determining the extrapolated values. 4. Dispersion indices for a given system were plotted and any significant deviation from a norm was rechecked. The results of the hydrometer analyses are presented in the section “Tables of Data and Dispersion Indices” 235 in tables 2 through 19 and are summarized for discussion in figures 1 to 11. Figures 1 to 11 are graphs of the dispersion indices versus the amount of deflocculent as listed in the tables of base data. The dispersion indices are plotted as ordinates with the abscissa of the point being the amount of deflocculent. Both are on linear scales as indicated. All graphs are labeled to indicate the colloid, type of water and ion saturation. The deflocculent used is indicated by the type of line in the individual graphs. The line coding used con- sistently through all of the summary curves is as follows: Sodium tripolyphosphate Sodium hexametaphosphate Sodium hexametaphosphate plus sodium carbonate — — — —- — .— Sodium tetrapyrophosphate SODIUM MONTMORILLONITE IN DISTILLED WATER Sodium montmorillonite was in a well-dispersed state when at equilibrium with distilled water (fig. 37A). This was in accord with dispersion theories (See section “Theory of clay-mineral behavior in dilute suspen- sion”, by R. F. Miller.) in that there is no electrolyte contribution from the water and the inherent negativity of the montmorillonite particles is at equilibrium with sodium, the least opposing cation to dispersion. The introduction of phosphate deflocculents into the system increased the index of dispersion beyond that of the standard. There was little difference among the three reagents in their effect on percentage of dispersion. The improvement in dispersion of the system was probably due to sequestration of multivalent cations still present on the sodium saturated clay surfaces. The energy relations between ions and surfaces preclude the complete replacement by mass action of multiva- lent ions by sodium. Sequestration reduces this diffi- culty and increases the degree of sodium saturation. It is also possible, but less likely, that dispersion may have been improved by increasing the negativity of the montmorillonite particles by phosphate anion adsorption to clay edges. CALCIUM MONTMORILONITE IN DISTILLED WATER The calcium montmorillonite was in a flocculent state when at equilibrium with the distilled water (fig. 37B). Unlike sodium saturation, calcium satura- tion may be completely effected by mass action. Thus, the exchange complex of the clay was probably 100 percent calcium and these closely held, divalent ions decreased the intensity of the clay negativity. The particles could then approach each other to the point where attractive forces become effective, thereby inducing floc formation and more rapid settling velocities. 236 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY A. Sodium- saturated clay B. Calcium-saturated clay 120 100 ii 0 80 E Z 9 60 (I) 0: Lu 3; — 4 D O 20 0 0 0.05 0.1 0 0.5 l 1.5 2 GRAMS DEFLOCCULENT C D 120 :‘< \\ 100 \ fl —---u ———=- X Lu 80 Q E Z 9 60 U) 0: Lu CL 1’ 4o 0 20 0 0 0.05 0.1 0 0.5 1 1.5 2 Sodium tripolyphosphate GRAMS DEFLOCCULENT EXPLANATION Sodium hexametaphosphate Sodium hexametaphosphate plus sodium carbonate FIGURE 37.—Dispersion characteristics of sodium- and calcium-saturated montmorillonite in distilled and soft water. A, B, distilled water; C, D, soft water. DISPERSION CHARACTERISTICS, MONTMORILLONITE, KAOLINITE, ILLITE CLAYS The introduction of phosphate deflocculents into this system improved dispersion. The slope of the index curve was greatest up to 70 percent; beyond this point there was a smaller increase in dispersion per unit weight of deflocculent. This point of maximum efficiency (70 percent) corresponds to 5 percent defloc- culent per unit weight of clay. At the 70 percent dispersion index there was little difference among the dispersants. Below this point, the reagents in the order of their efficiency in increasing the percentage of dispersion were: Sodium hexameta- phosphate, sodium hexametaphosphate plus sodium carbonate, and sodium tripolyphosphate. Beyond the 70 percent dispersion index, sodium tripolyphosphate had a slight advantage over the other two. The greater efficiency of sodium hexametaphosphate up to the 70 percent dispersion index was probably a function of its long chain polymer structure. Because the calcium montmorillonite-distilled-water system represented a high degree of neutralization of clay nega- tivity, long chain hexametaphosphate polymeric anions could probably get closer to the clay edges than in other systems. Such contact may have facilitated the adsorption of these anions to the clay particle by con- tact with exposed positive charges (Al+++) at these edges. This could improve dispersion by increasing the negative charge of the clay particles and by facilitat- ing sequestration of the tightly bound Ca++ ions. The apparent supremacy of sodium tripolyphosphate above the 70 percent index may be attributable to its greater supply of dissociated Na+. Displacement of Ca++ by Na+ is by mass action and it may require more Na+ in this range than can be supplied by the hexametaphosphate. Sequestration facilitates disper- sion but a calcium-saturated system also requires mass action displacement by sodium. SODIUM MONTMORILLONITE IN SOFT WATER Sodium montmorillonite was in a semidispersed state when at equilibrium with soft water (fig. 37 0'). The system seemed dispersed because of the turbidity throughout the hydrometer columns. However, a clear—water break soon developed at the surface (before a 24-hour period) and indicated that maximum dis- persion had not been attained. Apparently, the ion concentration about each clay particle permissible for maximum dispersion had been exceeded and consoli- dation had taken place wherein porous flocs of material were compressed, leaving clear water at the surface. The introduction of phosphate deflocculents into this system did not improve dispersion; in fact, the depth of clear—water breaks increased directly with the amount of defiocculent added. This was probably due to 237 electrolytic concentrations and compression of the dif- fuse cloud of cations about the clay particles. Sodium tripolyphosphate and the mixture of hexametaphos- phate plus sodium carbonate was least detrimental to dispersion in this system. CALCIUM MONTMORILLONITE IN SOFT WATER The calcium montmorillonite was flocculated when at equilibrium with the soft water (fig. 37 D). This system showed properties similar to that of the calcium montmorillonite in distilled water. The high electro- lyte content of the soft water apparently served to repress the dispersive tendency of the montmorillonite clay. Introduction of phosphate deflocculents into this system improved dispersion. The phosphate disper- sants ranked in efficiency in the order of possible dis- placement of calcium by sodium as follows: sodium tripolyphosphate, sodium hexametaphosphate, and sodium hexametaphosphate plus sodium carbonate. Sodium tripolyphosphate with the highest percent sodium per unit weight of salt was superior. This system contained hard (calcium) clays requiring mass- action displacement by sodium ions. SODIUM MONTMORILLONITE IN HARD WATER The sodium montmorillonite at equilibrium in hard water (fig. 38A) was in a semiflocculent state. The dispersion index at zero deflocculent was 80 and was. accompanied by a clear-water break at the surface. This system could be better described as a high floc. Calcium ions apparently displaced sodium from ion exchange surfaces, reducing the negativity of the mont- morillonite particles and compressing the diffuse outer layer of associated cations. The introduction of phosphate defiocculents into this system improved dispersion only slightly. This was probably due to the increase in electrolyte content from the added dispersant counteracting any possible benefit from replacing Ca++ ions with Na+ ions. CALCIUM MONTMORILLONITE IN HARD WATER The calcium montmorillonite in hard water (fig. 383) was in a flocculent state at equilibrium. Introduction of phosphate deflocculents improved dispersion up to a maximum at 30- percent deflocculent per weight of clay. Dispersant addition not only increased disper- sion but caused the formation of a white precipitate. Analysis of the precipitate by X-ray diffraction and spectrography indicated that it was a complex of gypsum and phosphate. The formation of this precipitate may be explained by review of the electrolyte content of the system. The 238 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY Al Sodium-saturated clay 120 100 fi ’1‘”— / "\ / ’~\‘ ‘ uxJ so & \ /// 4/ ’ I “ ~ E ’ ,,/ z V C_) 60 (I) CE Lu [1 Q 40 D 20 O , 0 1 2 3 4 5 6 GRAMS DEFLOCCULENT B. CalciumAsaturated clay 120 100 1 E _ _ Q 80 f / — \ \\ \‘ Z //// \- —— —— A‘ Z // / O 60 /A 7/ <7) ,’ E / // g) 40 /,é// O \— 7 _ _/ 20 O O 1 - 2 3 4 5 6 GRAMS DEFLOCCULENT EXPLANATION Sodium tripolyphosphate Sodium hexametaphosphate Sodium hexametaphosphate plus sodium carbonate FIGURE 38.~Dlsperslon characteristics of sodium- and calcium-saturated montmorillonlte in hard water. anions of the calcium and magnesium salts in the hard trolyte in the form of phosphate deflocculents possibly water were sulfate (SOD. The composition of the water caused the system to exceed the solution limit of the was such that the solubility product of gypsum (CaSO4- gypsum-phosphate complex, thereby causing it to pre- 2H20) was close to its limit. The addition of elec- cipitate. The complex may be the result of the affinity DISPERSION CHARACTERISTICS, MONTMORILLONITE, KAOLINITE, ILLITE CLAYS of the phosphate polyanions for Ca++ ions causing them to be carried down with the calcium sulphate. The re- moval of Ca++ ions from the system by sequestration and precipitation apparently softened the water and improved the dispersion. Sodium tripolyphosphate seemed most eflicient, probably because of its greater content of dissociated sodium concurrent with its sequestering capacity. The dissociated sodium is needed to replace exchangeable calcium from the clay. Dehydrated sodium phosphates are poor sources of sodium for displacement of calcium from exchange surfaces by mass action. SODIUM KAOLINITE IN DISTILLED WATER Sodium kaolinite was dispersed when at equilibrium with distilled water (fig. 39A). The addition of phos- phate deflocculents improved dispersion probably by sequestering any stray multivalent cations still in the system and by increasing clay negativity through sorption onto clay edges. CALCIUM KAOLINITE IN DISTILLED WATER Calcium kaolinite was flocculated when at equilibrium with distilled water (fig. 393). The phosphate de- A. Sod iu m - saturated Clay 120 239 flocculents improved dispersion in the following order: Sodium hexametaphosphate, then sodium car- bonate plus sodium hexametaphosphate, and last, sodium tripolyphosphate. The superiority of the sodium hexametaphosphate treatments indicates that increased negativity from adsorption of polyanions helped increase the dispersability of kaolinite in this system above the dispersion attainable from Ca++ ion sequestation alone SODIUM KAOLINI’I‘E IN SOFT WATER Sodium kaolinite was partly flocculated when at. equilibrium with soft water (fig. 40A). This was probably due to the effect of the high salt content and the 5 milliequivalents per liter of Ca++ plus Mg++ in the soft water. Addition of phosphate deflocculents to the sytem increased dispersion. The order of efficiency of the three reagents was: Sodium hexametaphosphate plus sodium carbonate, sodium tripolyphosphate’, and last, sodium hexametaphosphate. The fact that the degree of dispersion was greater in the two alkaline sys- tems indicates that dissociation of OH‘ ion from alumi- na sheets increased the negativity of clay particles. The superiority of sodium hexametaphosphate bufi'ered by 8. Calcium-saturated clay r—h— —_ 100 k \ \\ \\ U I! II DISPERSION INDEX 8 8 ‘5 V 1“ 20 0 0.05 0.1 0 0.5 l 1.5 2 GRAMS DEFLOCCULENT EXPLANATION Sodium tripolyphosphate Sodium hexametaphosphate Sodium hexametaphosphate plus sodium carbonate FIGURE 39.'—Dlspersion characteristics of sodium- and calcium-saturated kaolinite in distilled water. 240 120 100 DISPERSION INDEX DISPERSION INDEX 80 6O 40 20 120 100 SHORTER CONTRIBUTIONS ’1‘0 GENERAL GEOLOGY A. Sodium-saturated clay /— _.—_—___/._..,-=. T:_‘—.:‘__—_:___ I / /I / /// /// ’,/7 // I 0.5 1 1.5 GRAMS DEFLOCCULENT B. CaIcium-saturated clay / ‘L‘ ‘ \ L Sodium tripolyphosphate 0.5 l GRAMS DEFLOCCULENT EXPLANATION Sodium hexametaphosphate 1.5 Sodium hexametaphosphate plus sodium carbonate FIGURE 40,—Dlspersion characteristics of sodium- and calcium saturated kaolinlte in soft water. DISPERSION CHARACTERISTICS, MONTMORILLONITE, KAOLINITE, ILLITE CLAYS sodium carbonate indicates that increased negativity from adsorption of polyanions also was effective in dispersing the system. CALCIUM KAOLINITE IN SOFT WATER Calcium kaolinite was flocculated when at equilib- rium with soft water (fig. 40B). Phosphate defloc- culents increased dispersion in the following order: Sodium tripolyphasphate, sodium hexametaphosphate, and sodium hexametaphosphate plus sodium carbonate. The reaction order indicates that sequestration of Ca++ ions and replacement of these ions with monovalent N a+ ions was effective in dispersing this system. SODIUM KAOLINITE IN HARD WATER Sodium kaolinite was flocculated when at equilibrium with hard water (fig. 41A). The introduction of phosphate deflocculents into the system caused a gradual increase in degree of dispersion. The increase in dispersion was coincident with formation of a precipitate similar to that formed in montmorillonite- hard-water system, that is, a complex of gypsum and phosphate. There was little difference between the reagents with respect to dispersion efficiency. The sodium tripoly- phosphate, however, produced a slightly higher index than the other two, reflecting its greater capacity for sequestering Ca‘H’ ions. The high electrolyte content of this system apparently prevented it from attaining as high a degree of dispersion as existed in the standard sodium kaolinite distilled water system. CALCIUM KAOLINITE IN HARD WATER Calcium kaolinite was flocculated when at equilibrium with hard water (fig. 413). Both clays and water were dominated by the calcium ion and the environment was especially conducive to flocculation. The introduction of phosphate deflocculents improved dispersion coincident with the formation of a gypsum- phosphate precipitate. Sodium tripolyphosphate was most efficient, followed by the sodium hexametaphos- phate-sodium carbonate mixture with sodium hexametaphosphate last. The superiority of the two alkaline buffered dispersants over acid sodium hexametaphosphate indicates that the negativity of kaolinite may have been increased in the alkaline sys- tems by dissociation of OH‘ ions in the alumina sheet. SODIUM ILLITE IN DISTILLED WATER Sodium illite was dispersed when at equilibrium with distilled water (fig. 42A). The colloidal yield of the dispersed standard was only 25 percent, that is, only 530716 0—60—e3 241 one-fourth of the mass had a diameter of less than one micron. The introduction of phosphate deflocculents into the system increased dispersion. This was probably due to sequestration of any stray multivalent ions still present. There was little or no difference in efficiency between the phosphates. CALCIUM ILLITE IN DISTILLED WATER Calcium illite was flocculated when at equilibrium with distilled water (fig. 423). Phosphate defloccu- lents did not improve dispersion in this system. SODIUM ILLITE IN SOFT WATER Sodium illite had a dispersion index of a little more than 60 percent when at equilibrium with soft water (fig. 43A). This decrease of dispersion in distilled water must be attributed to the high salt content of the soft water and the effecl of the divalent ions, Ca++ and Mg++, in the water. The introduction of phosphate deflocculents into the system produced an increase in degree of dispersion. Only treatments containing long chain polymers (hexa- metaphosphates) progressively improved dispersion, indicating benefits from increased negativity from adsorption of long chain polyanions to clay surfaces. The ineffectiveness of sodium tripolyphosphate indi- cates little benefit to the system by the sequestration mechanism. The increase in dispersion efficiency of sodium tripolyphosphate, after this chemical became more concentrated in the system, cannot be explained on the basis of available data. CALCIUM ILLITE IN SOFT WATER The calcium illite was in a flocculent condition when at equilibrium with soft water (fig. 433). The addi- tion of phosphate reagents did not materially increase the dispersion of the system. This indicates that it is impractical to improve the dispersibility of a calcium- saturated clay by the use of sequestering agents. The relative efficiencies of the deflocculents in this system were the same as those observed when sodium-saturated illite was studied in the soft water. The similarity between curves in both systems indicates the same factors were effective with both the sodium- and calcium—saturated clays in the soft water. SODIUM ILLITE IN HARD WATER Sodium illite in hard water (fig. 44A) was flocculent and showed a dispersion index of slightly more than 40 percent when at equilibrium with hard water. This system exhibited dispersion characteristics similar to those of the sodium illite in soft water, indicating the 242 DISPERSION INDEX DISPERSION INDEX 120 100 80 60 4o 20 120 100 on O 03 0 J5 O 20 SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY A. Sodium-satu rated clay Sodium tripolyphosphate GRAMS DEFLOCCULENT Sodium hexametaphosphate EXPLANATION / 1/ x I” / / / / / / I’ / [V / ”/ /c._‘_‘_'_‘;/ r, L 0 1 2 3 4 5 GRAMS DEFLOCCULENT B. CaIcium-saturated clay I <\ / \\ / \\ // /"\ ‘~\ 1/ / \ \\\ 7/ / —‘ \ x \\ /: / _\ \\ N / / / \ ‘ £4 0 l 2 3 4 5 Sodium hexametaphosphate plus sodium carbonate FIGURE 41.~—DIspersion characteristics of sodium- and calcium-saturated kaollnite in hard water. DISPERSION CHARACTERISTICS, MONTMORILLONITE, KAOLH‘IITE, ILLITE CLAYS A. Sodium— saturated clay 243 B. Calcium-saturated clay 120 100 (I) O DISPERSION INDEX 8 8 20 ‘ s\ .hfg——— \ \ L’ / / 0 0 0.05 0.1 0 0.5 l 1.5 2 GRAMS DEFLOCCULENT EXPLANATION Sodium tripolyphosphate Sodium hexametaphosphate Sodium hexametaphosphate plus sodium carbonate FIGURE 42.——Disperslon characteristics of sodium- and calcium-saturated illite in distilled water. prevailance of similar factors in both systems. Ap- parently, long chain polymers were most effective in dispersing the system. The initial depression of disper- sion in the sodium tripolyphosphate system could be related to an increase in the salt concentration without benefit from polyanion adsorption. CALCIUM ILLITE IN HARD WATER Calcium illite at equilibrium with hard water (fig. 443) was flocculated. The increase in dispersion index through use of phosphate reagents was small, from about 20 percent to between 40 and 50 percent. Large quantities of the dispersants had to be added before dispersion was improved. The superiority of sodium tripolyphosphate at this point indicates that availability of N aJr ions for displacement of Ca++ ions and ability to sequester Ca.++ ions were most effective in improving dispersion. The data further indicate that it is im- practical to attempt to disperse a calcium-saturated system with phosphate dispersants. ' The illite and kaolinite used in the following phases of the study were treated to simulate ion saturation on a Wyoming bentonite sold by American Colloid Co. as Volclay. Circular 202 of this company indicates that the relative sodium and calcium plus magnesium percentages in Volclay are 78.8 and 21.2 respectively. The dispersion characteristics of the above-treated clays were examined in distilled water and in a syn— thetic water of medium hardness, based on a prototype water from the Tri-County Canal system in central Nebraska. This water contained 6.2, 3.6, and 6.3 milliequivalents per liter respectively of calcium, mag- nesium, and sodium. VOLCLAY IN DISTILLED WATER Volclay was dispersed when at equilibrium with dis- tilled water (fig. 45A). Not only was the water rela- tively free from cations but the exchangeable cations were in such proportion as not to effectively reduce the negativity of the montmorillonite particles. The addition of phosphate deflocculents did not im- prove dispersion. The increase in electrolyte content probably counteracted any possible benefit by seques- tration or polyanion adsorption. VOLCLAY IN MEDIUM-HARD WATER The dispersion index of the native montmorillonite medium hard water system (fig. 453) was about 75 per 244 SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY A. Sodium-saturated clay 120 Calgon _’_.___—____-——-— ”—— /---— _——— I sod‘Laih——“ _— caIgOL‘ 1' — ' , - 100 / ———— 40 DISPERSION INDEX 20 0 0 0.5 l 1.5 2 GRAMS DEFLOCCULENT B, Calcium-saturated clay 120 100 80 DISPERSION INDEX O 0.5 I 1.5 2 GRAMS DEFLOCCULENT EXPLANATION Sodium tripolyphosphate Sodium hexametaphosphate Sodium hexametaphosphate plus sodium carbonate FIGURE 43,—Diaperslon characteristics of sodium- and calcium-saturated lllite In soft water. DISPERSION INDEX DISPERSION INDEX 120 100 80 60 40 20 120 100 0) O 05 0 ¢ 0 20 DISPERSION CHARACTERISTICS, MONTMORILLONITE, KAOLINITE, ILLITE CLAYS A. Sodium-saturated clay A I r /, x / A" / / / / / l / / / [L’A / / \\‘/ /// m. ______ / o 1 2 3 4 5 ' 6 GRAMS DEFLOCCULENT B. Calcium-saturated clay / " ‘ — ~ ‘ o .— —— N \ 4/ “"’"‘/’\.‘§ I \ ‘ ’// \ ~u/ / _. ’- d "d’ ngh/ r O 1 2 3 4 5 6 GRAMS DEFLOCCULENT EXPLANATION Sodium tripolyphosphate Sodium hexametaphosphate Sodium hexametaphosphate plus sodium carbonate FIGURE 44.—Dlsperslon characteristics of sodium- and calcium-saturated illlte in hard water. 245 246 A. Distilled water SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY B. Medium-hard water 120 100 é,— 80 60 40 DISPERSION INDEX 20 0 0.05 0.1 0 0.5 l 1.5 2 GRAMS DEFLOCCULENT EXPLANATION Sodium tripolyp hosp hate Sodium hexametaphosphate Tetrasodium pyrophosphate FIGURE 45,—Disperslon characteristics of Volclay in distilled and medium-hard water. cent when at equilibrium. This was probably due to the flocculating effect of the divalent cations and the salt content of the water. The introduction of phosphate deflocculents into the system improved dispersion. This may be attributed to displacement of multivalent ions by monovalent Na+ ions, and sequestration of the multivalent ions. There was little difference between the deflocculents with res- pect to dispersion efficiency; but the dispersants did rank in the order of their sodium composition per unit weight, as follows: 1. tetrasodium pyrophosphate, 2. so— dium tripolyphosphate, 3. hexametaphosphate. KAOLINITE (78.8 PERCENT SODIUM SATURATED) IN DISTILLED WATER This kaolinite was dispersed when at equilibrium with distilled water (fig. 46A). Again the environment was conducive to dispersion. The introduction of phosphate deflocculents into the system did little to increase dispersion. The slight in- crease may be attributed to sequestration of divalent cations and possibly polyanion adsorption to clay edges The latter possibility is remote because physicochemical consideration of the system indicate that the phosphate anions would have some difficulty in approaching the clay particles when the latter were surrounded by diffuse clouds of Na+ ions; the more diffuse the clouds of ions about the particles the more difficult the approach of negative ions to the clay surface. KAOLINITE (78.8 PERCENT SODIUM SATURATED) IN MEDIUM-HARD WATER The dispersion index of this system (fig. 46B) was 40 percent when at equilibruim. The electrolyte and di— valent cation content of the water was sufficient to partly flocculate the system. The introduction of phosphate deflocculents into the system improved dispersion. The partly flocculated system apparently allowed the approach of polyanions to the clay surfaces. This hypothesis is supported by the order of efficiency of the reagents, namely, sodium hexametaphosphate, sodium tripolyphosphate, tetra- sodium pyrophosphate. The above order is that of de- creasing length of polymer chain, which characteristic is related to efficiency in dispersing kaolinite through increasing the negativity of the clay by adsorption of polyanions to exposed edges. ILLITE (78.8 PERCENT SODIUM SATURATED) IN DISTILLED WATER The illite was dispersed when at equilibrium with dis- tilled water (fig. 47A). However, it must be remem- bered that only 30 percent of the material was less than 1 micron in diameter when fully dispersed. DISPERSION INDEX DISPERSION CHARACTERISTICS, MONTMORILLONITE, KAOLINITE, ILLITE CLAYS A. Distilled water 8. Medium~hard water 120 fl??- -—-_ £__—=~A--.\_:‘ 100 ,' 3—, —.‘—<.—_:— ‘ H I/ / // V 4/ 4/ 8° /' / / a, ’ // 6O 40 20 0 0 0.05 0.1 O 0.5 1 1.5 GRAMS DEFLOCCULENT EX P LA N AT I O N Sodium tripolyphosphate Sodium hexametaphosphate Tetrasodium pyrophosphate FIGURE 46,—Dlspersion characteristics of kaolinlte (78.8 percent sodium saturated) in distilled and medium—hard water. A. Distilled water 8. Medium-hard water 120 I \_: I///—— -EéF ____ ‘/ 100 \ - -— - V 1" ’ 7 I ” ’/ / / I x / r’ /\ / LIJ 80 I, , I O / ‘/ ‘ .2. / ./ / — —- _V Z I/ O 60 l‘ 27) I Q: LIJ ,l “L / ‘2 40 I o J 20 0 O 0.05 0.1 O 1 2 3 Sodium tripolyphosp hate GRAMS DEFLOCCULENT EXPLANATION Sodium hexametaphosphate Tetrasodium pyrophosphate FIGURE 47,—Dispersion characteristics of lllite (78.8 percent sodium saturated) in distilled and medium-hard water. 247 248 The addition of phosphate deflocculents into the sys- tem did not materially increase the dispersion. There was no marked difference among the reagents with respect to dispersion efficiency ILLITE (78.8 PERCENT SODIUM SATURATED) IN MEDIUM-HARD WATER The illite was flocculated when at equilibrium with medium-hard water (fig. 47B). The data indicate that the degree of flocculation was not as great as in the cal- cium-illite hard-water system. The addition of phosphate deflocculents into the sys- tem increased dispersion. Sodium tripolyphosphate was better than sodium hexametaphosphate and tetraso- dium pyrophosphate was the least eflicient. The order of the dispersants probably reflects the relative efficiency of the dispersants as sequestering agents. Tetrasodium pyrophosphate was superior only in systems where so— dium was needed to displace Ca++ ions from exchange surfaces, which was apparently not needed in this system. SUMMARY OF CONCLUSIONS 1. It is not practical to attempt to disperse calcium- saturated clays with hexametaphosphate, tripolyphos- phate, or tetrasodium pyrophosphate. 2. Only clays that are easily dispersed in distilled water without the use of deflocculents should be used for sediment lining of canals if control 'of dispersion is a requirement. 3. Hexametaphosphate, tripolyphosphate, and tet- rasodium pyrophosphate can control the degree to which clay particles are dispersed in waters varying in hard- ness (calcium and magnesium content) if the total salt content is not excessive. 4. The mechanism whereby the phosphate defloccu— lents disperse clay suspensions is probably a function of either divalent ion sequestration or increasing the neg— ative charge of clay particles by adsorption of poly- anions, or both. 5. Montmorillonite clays are apparently the best source of colloidal particles for sediment lining of canals if control of dispersion and penetration of small voids are required. 6. Tripolyphosphate was the most efficient dispers— ing agent for control of montmorillonite dispersion in waters of low to medium hardness. 7. Sodium hexametaphosphate was generally supe- rior for dispersion of kaolinite The kaolinite tested was, however, easily dispersed by all the phosphate dispersants tested. 8. Illite was difficult to disperse and keep in sus- pension. When sodium saturated, however, it formed SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY asticky paste, which may make it useful for filling cracks and large voids. 9. If the electrolyte (salt) content of the canal water is too high it may prevent the dispersion of clays even with the use of phosphate dispersants. 10. The point of complete sequestration of calcium and magnesium by phosphate dispersants was measured by using dye indicators normally used for calcium and magnesium determinations. However, the quantities of sequestering agent required for practical dispersion of clay in canal waters seldom coincided with total sequestration. The only practical method found for determining the quantity of sequestering agent required is to add different quantities to samples of fresh water and measure dispersion with a hydrometer. Fresh water is specified because the chemical composition of a stream varies with time, or calcium may precipitate out as calcium carbonate as the water becomes stagnant and cause an underestimation of the quantity of se— questering agent needed. The effects of organic matter dissolved in the water would also express itself and could be compensated for. PROPERTIES OF CLAY MINERALS By B. N. ROLFE This section of the report discusses the clay minerals used in the investigation. It is not intended as a primer on clay mineralogy but as background material for a better understanding of the experimental data. The reader is referred to Grim (1953) for a more detailed treatment of the subject. A discussion of the behavior of clay minerals in suspensions is presented in the section “Theory of Clay Mineral Behavior in Dilute Suspen- sions” by R. F. Miller. As the present study was designed to investigate basic dispersion characteristics of colloidal clays, it seemed expedient to simplify the problem by restricting the study to monomineralic clays. Therefore, three representative clay minerals were selected for the inves- tigation of the dispersion characteristics of possible sedimenting materials. Clay minerals are usually classified on the basis of structure and composition. Structurally, two units are included in the atomic lattices of most clay minerals. One unit is comprised of two sheets of closely packed oxygen or hydroxyl ions between which aluminum and, less frequently, magnesium or iron atoms are embedded in octahedral coordination, that is, each metallic atom is equidistant from six oxygen or hydroxyl ions. This arrangement of sheets will hereinafter be referred to as the octahedral unit. DISPERSION CHARACTERISTICS, MONTMORILLONITE, KAOLINITE, ILLITE CLAYS The second unit is built of silica tetrahedrons in which a silicon atom is equidistant from four oxygen or hydroxyl ions. The silicon atoms apparently lie in a a plane and form a hexagonal network. This sheet arrangement will be hereinafter referred to as the tetra- hedral unit. These two units form the building blocks for the formation of clay minerals. Classification is based on the arrangement of these units and on deviations from modal atomic composition. The three main types of clay minerals will be discussed, in relation to the clay . materials used during the investigation. KAOLINITE Kaolinite is the most prominent member of the kaolin group of clays among which are kaolinite, dickite, nacrite and halloysite. Clays in this group are called 1:1 layer minerals because unit cells are composed of one tetrahedral unit joined to one octahedral unit. There is little or no atomic substitution in the units, and kaolinite may be regarded as consisting of model sheet units of silica tetrahedra and alumina octahedra. Because of the dimensional similarity between struc- tural units along the a and b crystallographic axes, unit cells of octahedra and tetrahedra are readily formed and are fairly stable. Substitution of one ion for another, called isomor- phous substitution in clay mineralogy, is rare in the kaolinite minerals and the kaolinite clays are generally electrostatically neutral. Charge deficiencies at the broken edges of the a and 1) planes are both negative and positive. Anionic deficiencies along these broken edges are the probable sources of anion attraction and probably are the point of phosphate ion adsorption as is explained later. Slight irregularities in the cation composition of kaolinite, as well as cationic deficiencies at broken edges, may be sources of positive charge deficiencies. The cation exchange capacity of kaolinite minerals generally ranges from 3 to 15 milliequivalents per 100 grams of kaolinite material. Kaolinite minerals generally occur in the upper size diameters of clays. They may be found as discrete particles with diameters as large as 20 microns but the median diameter is generally about 1 micron. The specific dispersion characteristics of kaolinite are dis- cussed on page 254 but deflocculation is probably ef- fected by increasing clay negativity via anion sorption of complex polyphosphates along the broken edges. MONTMORILLONITE Montmorillonite is the dominant member of the montmorillonite group of clay minerals, among which are montmorillonite, beidellite, hectorite, saponite 530716 0—60—4 249 and nontronite. The clay used in the present study is commonly called bentonite and occurs abundantly in some parts of Western United States. The high- swelling bentonite, produced extensively in Wyoming, is usually composed mostly of sodium montmorillonite together with traces of cristobalite and volcanic ash, and it has the ability to absorb large quantities of water. The montmorillonite group of clay minerals is classified as 2:1 layer minerals—the unit cells are composed of two tetrahedral units enclosing a single octahedral unit. Isomorphous substitution is common. to both units. This substitution phenomenon results in an imbalance of charge within the montmorillonite lattice and is characteristic of the mineral. Sub- stitution in either unit may be partly compensated by substitution in the other unit. However, substitutions in the montmorillonite lattice yield a net negative charge on the lattice. This negative charge is balanced by exchangeable cations, such as Ca++ or Na+, adsorbed between the layers and around their edges. Discrete montmorillonite particles grow by con- tinuous extension along the a and b axes and by stacking in the c direction. Bonding between unit cells is weak by comparison with kaolinite and is the reason for the small size of discrete montmorillonite particles, generally under 0.5 micron in diameter. Only cation exchange is assumed to take place on the planar surfaces of the montmorillonite particles whereas both cation and anion exchange occur at the edges. The probable ratio of planar to edge surfaces may be indicated by cation-anion exchange capacity ratios of 6.7 to 1.0. A similar comparison for kaolinite shows a ratio of 0.5 to 1.0 (cation exchange capacity divided by anion exchange capacity) (Kelley, 1948). While the edge surface in kaolinite is more important than planar surfaces as a source of charge, the reverse is true in montorillonite. However, the greater total surface exposed by the smaller montmorillonite particles balances their comparative anion exchange capacities on a gravimetric basis. That is, 1 gram of mont- morillonite, which has about an acre of total surface area, may have the same anion exchange capacity as a gram of kaolinite, in spite of the dominance of edge surfaces in the kaolinite. The montmorillonite minerals are highly responsive to chemical environments, probably because of their colloidal size and structural peculiarities. A stable dispersion of this type mineral produces a high colloidal yield. It is likely that provision of a proper sodium environment is sufficient to enhance the inherent negativity of the montmorillonite particles to a point of adequate dispersion. 250 ILLITE Illite includes a broad group of micalike clay minerals which to date have not been subdivided. Illites, like micas and montmorillonites are 2:1 layer minerals; that is, two silica tetrahedra units enclose one octahedral unit. Illites, however, differ from the mica minerals in several ways: in illites one-sixth of the Si+Ur++ ions are replaced by A1+++ ions whereas in true micas one-fourth of the Si++++ ions are so replaced; the unbalanced cation deficiency is less, being 1.3 per unit cell as contrasted to 2.0 in micas; less potassium is adsorbed in interface position in illites but some Ca++ and Mg++ ions are adsorbed. Particles of illite generally are small, less than 1 to 2 microns. This may be attributed to weaker bonding brought about by less fixed K+ in interface positions. Illites generally as the fine-grained component of marine shales and are not as free from mineral contamin- ation as the other two clay groups. Whereas the kaolinite and montmorillonite minerals used in the present study may be considered monomineralic, the illitic mineral is polymineralic, because of its intimate mixture with shale fragments. The previously mentioned cation deficiency gives illite a weak negative charge, as indicated by its cation exchange capacity of but 1040 milliequivalents per 100 grams. Anion exchange occurs at edge surfaces, and the ratio of cation to anion exchange capacities is approximately 2.3 to 1.0 (Kelley, 1948). One may postulate that dispersion characteristics of illite are somewhere between those of kaolinite and montmoril- lonite. If so, it should be possible to effect moderate deflocculation of illite particles by anion adsorption at clay edges and by increasing inherent negativity through replacement of adsorbed Ca++ and Mg++ ions by Na+ ions. DISCUSSION OF THE HYDROMETER METHOD By I. S. MCQUEEN The hydrometer has been used extensively as a means of determining the particle-size distribution of soils and sediments. Like most methods of wet mechanical analysis, the hydrometer method is based on Stokes’ law, defined in 1845 by Sir ‘George Stokes, a British mathematician and physicist. Stokes’ law states that the terminal fall velocity of a solid spherical particle in quiet water is defined by the following relation: 210—170 2 V—§ gr M Where V=velocity of fall in centimeters per second g=acceleration due to gravity (981 centimeters per second squared) SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY r=radius of particle in centimeters p=density of particle in grams per cubic centi- meter po=density of fluid in grams per cubic centimeter t=viscosity of fluid in poises (dyne-second per square centimeter) If a point is chosen at a given depth, H (centimeters), and time, 1! (minutes), after mixing in a column of uniform spherical particles dispersed in water (for which p0=1), the above expression can be solved for the diameter of the coarsest particle remaining in suspension at the given depth and time. Substituting V: 61:13 and 7': go for time in minutes and diameter of particle in millimeters, gives: 30H]; d=\/9: (p—1)t There are several requirements in any method that uses Stokes’ law to determine the diameter of particles: 1. The depth of fall, H, must be defined and measurable. 2. The density and viscosity of the fluid must be constant and known. The specific gravity of the particles must be known. The particles should be spherical. . The concentration of particles in suspension should be low enough to minimize the interference between particles yet high enough to produce measurable differences in the specific gravity of the suspension. 6. The particles must be completely dispersed as discrete par- ticles and must remain so throughout the test. ones» In standard hydrometer analysis methods, these conditions are all assumed to have been met. Krynine (1941, p. 477) describes the theory of grain-size measurement with a hydrometer as follows: Since at the start of the hydrometer test the suspension is thoroughly mixed there are, at each horizontal section of the graduate, particles of all sizes present in the given sample in their natural concentration. As sedimentation proceeds, all grains of a given diameter settle with equal velocity; hence their concentration at all horizontal sections of the graduate is the same. Owing to the limited supply of particles from above, coarser particles gradually fall out. Thus at a given time mo- ment there are at a given horizontal section of the graduate, particles finer than a given diameter only, though in their natural concentration. A hydrometer consists of a hollow glass chamber or bulb, weighted at the bottom and having a graduated stem at the top. It has a constant mass, and when placed in a liquid it sinks until it displaces its own weight of liquid. In conventional hydrometer analyses the depth of fall of a particle is assumed to be the distance from the water surface to the center of the hydrometer bulb. The hy- drometer, however, does not measure the specific grav— DISPERSION CHARACTERISTICS, MONTMORILLONITE, KAOLINITE, ILLITE CLAYS ity of the fluid or suspension at a point (Puri, 1949, p. 245). It averages the specific gravity in a zone, the nature of which depends upon the shape and depth of submergence of the hydrometer. This characteristic of the hydrometer may bring errors into an analysis. ADVANTAGES OF THE HYDROMETER METHOD Two important advantages of the hydrometer method over other types of wet mechanical analysis are its con- venience and the rapidity with which observations can be made. Results are available as soon as the settling time for the smallest size fraction to be determined has passed. There is no problem of evaporating large num- bers of samples to dryness. Each point on the size dis- tribution curve, or each size fraction to be determined, merely requires that a reading be made of the hydrom- eter at a specified time. There is also a saving in space and equipment, because the hydrometer method does not require the pipette rack, drying oven, balance, and evaporating dishes that are used in the pipette method. Another advantage of the hydrometer method is that the sample remains intact. There is no removal of parts of the sample as the test proceeds. This makes it pos- sible to use the same sample for successive increments of deflocculents, resulting in a saving in time and material and eliminating some inaccuracies resulting from differ- ences in samples. It is not necessary to prepare and disperse a separate sample for each increment of defloc— culent. In the present work it was desirable and im- portant that the sample remain intact so that successive amounts of deflocculent could be added to the same sample. If it had been necessary to use separate samples, small differences among samples possibly could have masked the efiects of the deflocculent. DISADVANTAGES OF THE HYDROMETER METHOD The theory of hydrometer analyses assumes that the density of the suspension is being measured at a point. Actually, the hydrometer averages the specific gravity in a zone. If the specific gravity varied uniformly through the measured zone, the value at the center of the zone and the average value would coincide. This is generally true with materials that have a Wide distribution of grain sizes in suspension. In suspensions with a narrow range of grain size the aver- age density through the measured zone may not be the same as the density at the center of the hydrometer. The exact nature of the zone measured by a given hydrometer can be determined by a simple experiment. From a balance, suspend a hydrometer in a hydrometer jar or cylinder. Gradually fill the hydrometer jar with water and record the weight of the hydrometer and the 251 depth of submergence at small intervals. Curve (1 of figure 48A is a plot of the data that may be obtained from such an experiment. The relative buoyancy of the hydrometer at each horizontal section will be a func- tion of the rate of change of hydrometer weight with depth of submergence and hence will be a function of the slope of curve a. Curve b of figure 48A is derived from curve a 1 and represents the relative buoyancy of the fluid on the hydrometer at each horizontal section. 40. a Immediately Iner/ mmnl 1? 3°“ \ x _ dBentonite clays .— § — =1" 10" \ \ _ _ _ \ \ L1 25- “ ---- x \ e z \ “- thersettlinl, \ l E g 15- nerves '3'!!! ‘ ‘ 5 20_ ‘E 01mm we | +- D ‘ I g In I - l s 5 2° ' l 15- d b After settling. wide ' l E 2: range oi grain size “ l ‘6‘ E 25- '. | 10— 3 l I K \ 35- a 0 100 1.000 1.0062 A SPECIFIC GRAVITY 8 FIGURE 48.—Nature oi zone measured by a hydrometer. A, diagrammatic repre- sentation of zone 1 measured by hydrometer: B, hypothetical curves illustrating different types of suspensions. Figure 483 represents the theoretical distribution of specific gravities of different types of suspensions in a hydrometer jar. Curve (1 shows a suspension immed- iately after mixing. Curve b represents a material with a wide range of grain sizes after a period of settling. On this curve, if the specific gravities are averaged over the zone measured by the hydrometer, a value is obtained that is very near the value at the depth of the center of the hydrometer bulb. Curve 0 represents a material with a verry narrow range of grain sizes. If the particles are discrete they all have about the same settling velocity and clear solution is left above them. If the hydrometer measured the specific gravity at a fixed point, the readings would change from max- imum to a minimum almost immediately as the last particles pass the measuring point. However, as the hydrometer measures a zone and also sinks deeper as 'the particles settle, it takes an appreciable time interval 1 Curve b of figure 48A represents the cosine of the angle between curve a and the I-axis plotted against the depth. Curve b also corresponds to the shape of the hy- drometer used and defines the zone measured by it. 252 for the readings to change and the grain size distribu- tion curve may be distorted. The materials used in this investigation tend toward narrow ranges of grain sizes, and hence may have distorted grain size distri- bution curves. Montmorillonite clays seem to be special in that, under certain conditions, they do not settle as discrete particles but form loose floc structures that undergo consolidation. This condition is repre- sented by curve d and the anomalous results obtained from it are discussed more fully in the section on tables of data and dispersion indices. The behavior of the hydrometer in suspensions with a narrow range of grain sizes is the principal disadvan- tage in the method. This disadvantage was mini- mized in the current investigations, because it was not pertinent to determine the grain size of discrete particles. The purpose of the investigation was to measure differences in dispersion characteristics and the hydrometer method proved to be well suited for this purpose. THEORY OF CLAY MINERAL BEHAVIOR IN DILUTE SUSPENSIONS By R. F. MILLER The primary objectives of a canal sedimenting program are to transport the clay material by canal waters to the areas where seepage losses occur and to allow the clay material to penetrate and seal the openings through which seepage takes place. The efficiency of clay transport and penetration is a function of the effective size of the clay materials. The effective size of clay particles suspended in water may vary with the type of clay and the chemical environment in the water system. One of the objectives of this investigation was to study the dispersion characteristics of three basic types of clay minerals in waters of different chemical compo- sition. These characteristics are a function of physico- chemical reactions in the clay-water system. A brief review of the interactions operative in a clay—water system follows. It is presented here as a guide to evaluating the observations on clay-water systems noted during the study. The dispersion of clays in water involves the separa- tion of the clays into their finest discrete particles and maintaining them in suspension. Clays that are dis- persed can be transported more easily by water and can penetrate small voids more readily. A dispersed clay-water system is related to the physical law that like charges repel and unlike charges attract. There are many theories on the mechanism of dis- persion. The discussion that follows is a composite of SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY these theories that explains the observations made during this investigation. The various clay minerals are negatively charged to some degree. The mechanism of the dispersion of clay particles in water is a function of this negative charge. The literature on clay minerals generally attributes the negative charge on the surface of clay particles to isomorphous substitution, dissociation of lattice hy- droxyl (OH‘) ions, and anion adsorption. Isomorphous substitution is the substitution of ions of similar size for each other during the formation of the crystal lattice of a clay mineral. An example of isomorphous substitution is the substitution of divalent magnesium (Mg++) ions for trivalent aluminum (Al+++). This type of substitution results in an imbalance of positive and negative charges within the structure of a clay particle yielding a cation deficiency and a negative charge expressed at the surface. The intensity of this negative charge is proportional to the amount of cation deficiency resulting from isomorphous substitution. This influences the number of cations that are adsorbed to each clay particle to balance the negative charge. Isomorphous substitution is discussed in more detail by Marshall (1949), Grim (1953), and Kelly (1948). Dissociation of lattice OH' ions as a source of nega- tive charge for clay particles is summarized by Russell (1950, p. 117) as “Negative charges developed by hy— drogen ions dissociating from hydroxyls attached to silicon atoms at the broken edges of oxygen sheets, which compose the clay mineral.” This reaction can be written, Si——OH+H20—>Si—O'+H30+. It only occurs appreciably under neutral or alkaline conditions, and the more alkaline the conditions the greater is the negative charge developed. Anion adsorption is the electrostatic attraction of negatively charged anions to positively charged cations exposed at the broken edges of clay particles. This reaction adds to the total negative charge expressed at the surface of clay particles, if the adsorbed anion is more highly charged than the attracting cation. This source of charge is. discussed in more detail by Ruehr- wein (1953) and Olphen (1950). FACTORS THAT CONTROL THE DEGREE OF DISPER- SION If negatively charged clay particles and distilled water were the only components of a clay-water system, the system would be easy to understand. The nega— tively charged particles would repel each other and dis- perse throughout the system, since like charges repel. Also, since water molecules tend to be positive at one end and negative at the other, they could be expected to orient themselves about the charged clay particles DISPERSION CHARACTERISTICS, MONTMORILLONITE, KAOLINITE, ILLITE CLAYS in concentric shells. The water shells could act as barriers between particles and the net result would probably be a dispersed system. However, a clay- water system is not this simple, for water contains salts in solution which ionize into positively charged cations such as calcium (Ca++), magnesium (Mg++), and sodium (N a+), and negatively charged anions such as chloride (01'), sulfate (804"), and phosphate (PO4““). These charged ions react with the clay, the water, and each other and complicate clay disper- sion. The maintenance of a dispersed system or a degree of dispersion in a complex clay, water, ionized salt system may be described as control of repelling and attracting forces. These forces are affected by: 1. The negative charge of the clay particle. 2. The valence or negative charge carried by the anions in the solution. 3. The valence or positive charge carried by the cations in the solution. . The concentration of the cations in solution. Hydration of ions in solution. The mobility of the cations in solution. Osmotic pressure differences in the clay-water system. 5'99"!“ Any one or all of these factors could influence dispersion when a clay is placed in a canal water in a sediment- lining operation. A discussion of each of the above factors follows: Negative charge on the surface of clay particles—The. negative charge on the surface of clay particles provides a repellent force between clay particles but also attracts, and holds the exchangeable cations. The quantity of exchangeable cations associated with a clay particle is directly proportional to the negative charge of the par- ticle. The clays in order of magnitude of the negative charge expressed at their surfaces are: (a) montmoril- lonitc, (b) illite, (c) kaolinite. To illustrate the magni- tude of the attractive force that may be expressed on a single clay surface, Kelley (1948) estimates that a mont- morillonite-type clay (ben tonite) with plate dimensions of 1 p X 0.4 It could have about 600,000 exchangeable monovalent ions per lattice layer. This type of clay would have an exchange capacity of approximately 1 milliequivalent per gram of clay and l milliequivalent of a monovalent ion such as sodium, contains 6.023 X 1020 ions. Valence of the negative ions (anions).——The negative valency of the anions in solution in a complex clay, water, ionized salt system may affect the control of dispersion in the system. Polyvalent anions may replace anions with less charge from anion exchange 253 positions at the broken edges of clay particles, thus increasing the negative charge. Multivalent anions may add a negative charge to a clay particle but no charge is added by monovalent anions. Only part of the negative charge associated with a multivalent anion is used by attraction to the exposed cation. The increase in dispersion potential of a clay-water system through the absorption of nega- tively charged ions on the clay particle is roughly pro- portional to the unused valency of the anions. For example, much more negative charge would be added to a clay surface by the adsorption of a long chain polyanion of high negative valence than by the adsorp- tion of a simple anion, such as orthophosphate (PO4"‘). Valence of the positive ions (cations).—The positive valency of the cations is also an important factor in the control of dispersion in a clay, water, ionized salt system. The cations attracted to a negatively charged clay particle form a positively charged shell or cloud around each clay particle. The attracted cations tend to form two layers about each particle, a closely held inner layer and a more loosely held or diffuse outer layer. The diffuseness or depth of the outer layer or cloud of cations is related to the charge or valency of its component cations. Multivalent cations are more strongly at- tracted to the clay than are monovalent cations; there- fore, an outer shell of monovalent cations is more diffuse than one of multivalent cations. This results in a shell or barrier of positively charged monovalent ions at greater distance from the clay particle than when multivalent cations comprise the shells. The shells of positively charged ions surrounding each clay particle in a clay-water system tend to repel one another. Therefore, the diffuseness of the outer ring of associated cations is an important factor in the control of clay dispersion in a clay, water, ionized salt system. Generally, the greater the diffuseness of the clouds of cations about each clay particle in the system. the greater the dispersion in the system. Concentration of the cations in solution.~The concen- tration of the cations in solution in a clay-water system is another of the factors that controls the depth of the diffuse shell of cations that surround a clay particle. Increasing the concentration of positively charged ions crowds more cations into the zone between clay particles and, in effect, helps to neutralize the negative charge of a clay particle closer to the particle. This in turn decreases the diameter, or depth of the shells of positive ions surrounding the clay particles. Thus, dispersion in a clay, water, ionized salt system may be reduced by decreasing the diameter of the repelling shells of cations about each clay particle. through increased cation concentration. ' 254 Conversely, Bolt,2 found that dispersion of the sys- tem may be obtained even if Ca++ or Mg++ are the dominant ions, but that the concentration of these ions in the system must be much more dilute to achieve dispersion than is necessary when Na+ is the predomi- nant ion in solution. Hydration of cations in solution—The hydration of cations in solution is the result of electrostatic attraction of concentric shells of dipole water molecules about each cation. These shells of dipole water molecules vary in depth with the size, valency, and mobility of the cations. If cations become hydrated the shells of water may affect the efficiency of their positive charge, for the intensity of an electrostatic charge varies inversely with the square of the distance from the source of the charge. For example, if two cations of equal charge were hydrated to different degrees, the cation with the smaller shell of attracted water would be the more efficient in neutralizing the negative charge of a clay particle in a clay-water system. Thus, hydration along with valency and concentration may affect the diffuse cloud of cations about each clay particle and affect control of dispersion. Mobility of the cations in solution—The mobility of the cations in solution in a clay-water system may also affect the diffuseness of the repelling shell or cloud of cations about each clay particle. The mobility of a cation in solution may be considered as the speed with which the cation moves or oscillates about in solution. A highly mobile cation such as sodium may not be as easily attracted to a negatively charged clay particle as a less mobile cation such as calcium or magnesium. Therefore, mobility could effect the efficiency with which a cation neutralized the negative charge of the clay particle. This may result in diffuse shells of cations about each of the clay particles and thus influence the control of dispersion in a clay-water system. Osmotic pressure—Osmotic pressure may aid in attaining dispersion in a clay-water system. The concentration of ions in the diffuse cloud of ions around each clay particle is greater than the con- centration of ions in the part of the solution not affected by electrostatic forces from the clay particles. There is a tendency for ions in solution to come to equilibrium and eliminate differences in concentration. While the two systems are attempting to reach equi- librium, convection currents may be set up which could aid the other forces in the system in attaining dispersion. This aid to dispersion would no longer exist after equilibrium had been attained. aBolt, G. H., 1954, Physico-chemieal properties of thelelectrlc double layer on planar surfaces: Ph. D. thesis, Cornell Univ., Ithaca, N.Y., 106 p. SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY Forces other than those mentioned here may be effective in controlling dispersion in a clay, water, ionized salt system, but those discussed are perhaps the most dominant interacting in the systems studied in these experiments. DISPERSION AND CLAY MINERALS Montmorillonite, “illite”, and kaolinite are the three dominant clay-mineral types that may be avail- able for sediment-lining operations. .Each of the above clays has associated with it some negative charge. The negative charge of clay particles affects the degree to which they may be dispersed in a clay- water system. As previously stated, three sources of negative charge on clay surfaces are isomorphous substitution (cationic deficiency), dissociation of lattice hydroxy (OH‘) ions, and anion adsorption. These sources of negative charge may be common to all types of clay but are effective to different degrees. M ontmorillonite-type clays .——Montmorillonite - t y p e clays are more highly charged and finer textured than the other two clays. Isomorphous substitution is the predominant source of the negative charge on montmorillonite-type clays. Grim (1953, p. 132) attributes about 20 percent of the exchange capacity to broken bonds. This includes possible negative charge from dissociation of lattice OH‘ ions, or adsorp- tion of high valence anions. Because of the more intense negative charge and finer texture associated with montmorillonite-type clays, a higher degree of dispersion is possible with them than with other types of clay. Kaolinite-typc clays.——The predominant source of negative charge on kaolinite-type clay minerals is un- satisfied chemical bonds at the broken edges, or from dissociation of H+ from exposed OH+ groups or the octahedral (alumina) sheet. The negative charge may also be increased through the adsorption of high valence negative ions to positive ions exposed at the broken edges. Since the anion exchange capacity of kaolinite particles is equivalent to the cation exchange capacity, it is logical that the dispersibility of kaolinite could readily be influenced by the valence of the anions injected into the clay-water system. Illite-type clays.—The dispersion characteristics of illite-type clays should be intermediate between those of montmorillonite- and kaolinite-type clays. The neg- ative charge on the surface of illite-type clays is the result of both isomorphous substitution and anion ad- sorption at the broken edges. Illite clays are generally components of shales and are less likely to be mono- mineralic than are montmorilloni’te and kaolinite de- posits, therefore, the characteristics of this type of material are more difficult to evaluate or predict. DISPERSION CHARACTERISTICS, MONTMORILLONITE, KAOLINITE, ILLITE CLAYS MECHANISM OF DISPERSION CONTROL Since a dispersed clay-water system may be more readily obtained with Na+ as the dominant cation in the system, most dispersion controls involve deactiva- tion or removal of Ca++ and Mg++ from the clay—water system and replacement with Na+ ions. Calcium and magnesium ions may be removed from a clay-water system by causing them to form insoluble precipitates and to settle out of the system. This may be accomplished by adding Na2003 to the system. For example, if calcium were in the system as CaSO4 and Na2003 were added to the system, the salts would react according to the following equation: H20+CaSO4+N842003 903003 + Nast4+H20 (insoluble precipitate) Since calcium is precipitated, no equilibrium could be maintained and most of the calcium could be removed from solution. The settling of the precipitate thus formed to the canal bottom could hinder the penetra~ tion and sealing action of clay. To avoid this it is pos- sible to cause the Ca++ and Mg++ ions to lose their entity as active cations by causing them to become part of a complex phosphate anion. This process is known as sequestration. Through the mechanism of sequestration, Ca++ and Mg‘r+ ions that can quite effectively neutralize the negative charge on clay particles and cause floccula- tion3 in a clay, water, ionized salt system lose their identity as cations and subsequently lose their positive charge by becoming part of a complex anion. Concurrent with the removal of calcium and mag- nesium from the solution as active ions, amounts of sodium from the sodium polyphosphates may be re- leased into the clay, water, ionized salt system. The amount of calcium that may be sequestered by a dehydrated sodium phosphate is related to the dis- sociation of Na+, and its replacement by Ca++ or Mg++. The dehydrated sodium phosphates do not dissociate completely when dissolved in water as do salts such as sodium chloride. Sodium chloride dissociates as follows: N aCl:N a+ + 01‘ All of the N a+ ions in sodium chloride immediately ionize and are available for reactions. According to Daugherty (1948) sodium hexametaphosphate ionizes or dissociates in two steps as follows: (N aPOahF—‘Z N a++ [N an—2(P03)nl— 3 Bolt (1954) presented evidence that the binding force among particles within a floc may be the attraction of positive ions exposed at broken edges to the negative surfaces, but that these attractive forces are too small to be effective until most of the negative charge on the clay surface has been equalized by the introduction of suffi- cient quantities of cations into the system. 255 and possibly a secondary ionization as follows: [N an—2(PO3)nl—:2 N a++ [N an-4(P03)n]" This dissociated sodium is available to react with the clay, water, ionized salt system. If Ca++ or Mg++ are present they replace the dissociated Na+ and the equi— librium reverses to form Ca Nan_2(P03),, or 2 Ca N an_4(P03)n. Which complex salt is formed is a func- tion of the concentration of Ca++ and Mg++ in the system. The other dehydrated sodium phosphates tested, dissociate and sequester in a similar manner. The net result is a more dispersed system through the mechanisms previously described. This may not always hold true, for if the initial salt concentration in the system is such that even the less effective Na+ ions neutralize the negative charge close to the clay sur- faces, the clay-water system will remain flocculated; as occurred in the soft water used in the first year’s study. Aside from the sequestration of Ca++ and Mg” as a part of complex anions, these anions affect the total negative charge on the clay particles in a clay, water, ionized salt system. As previously discussed, anions may be attracted to incompletely neutralized positive ions exposed at the broken edges of clay particles. If the absorbed negative ion is a long chain polyanion, it could be attracted to the clay particle by a fraction of its negative valency. The net result could be the addi- tion of a strong negative charge to the clay particle, thus increasing the dispersion potential of the system. This would increase the negative charge proportionately more for kaolinite than for montmorillonite. TABLES OF DATA AND DISPERSION INDICIES All of the base data obtained during this investiga- tion are contained in tables 2 to 19. Each table in- cludes the data for a specific combination of colloid and deflocculent. Soft water refers to a synthetic water having a content of calcium, magnesium, and sodium of 3, 2, and 15.5 milliequivalents per liter, respectively. Hard water refers to a synthetic water having a content of calcium, magnesium, and sodium of 17, 8, and 17 milliequivalents per liter, respectively. Ion saturation—This column designates the ion sat- uration on the colloid prior to its introduction into the system. Grams defiocculent.—The total amount of defloccu— lating chemicals in the system is listed for each hydrom- eter test run. Percent in suspension—In these columns are listed the amounts of colloid remaining in suspension at the given times following mixing as indicated by the hydrom- 256 eter reading corrected for the hydrometer reading in the check cylinder. These amounts are listed as per- centages of the colloid originally introduced into the system. With montmorillonite, these percentages oc- casionally exceed 100 because of the anomalous be- havior of this clay in dilute suspensions. The loose floc structure formed by some suspensions of montmoril- lonite seems to consolidate instead of settle as discrete particles. If the zone measured by the hydrometer is Within the consolidated portion of a cylinder of this suspension it will measure a higher concentration of clay than the original freshly mixed sample contained. Percentage values in parentheses were obtained by ex- trapolation. Approximate grain size being measured at each time in a normal hydrometer grain size analysis is: SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY Timeinmlnutes ................ Approximate grain size in microns ______________________ 1 37 4 19 19 9 60 5 435 2 These grain sizes have no literal significance in the cur- rent investigations and should be used only as a guide in plotting the hydrometer data for comparison purposes. The column headed “sum” is the sum of the percen- tages in suspension as listed in the preceding six columns. This sum was used in computing the disper- sion indices. Dispersion index.—This column lists a percentage comparison between the given sample run and a stand- ard. This is described and discussed in a previous section of this report. TABLE 2.—Hydrometer data: Montmorillcmite and sodium Iripolyphosphate l Percentage in suspension after settling for the number of minutes indicated Ion saturation Grams «Sum Dispersion deflecculent index 1 4 19 60 435 1,545 Distilled water Sodium _______________ 0. 0 91 90 86 92 90 90 539 100. 9 D0 _______________ ‘ . 025 98 96 96 99 98 97 584 109. 7 Do _______________ . l 101 99 99 99 100 96 594 111. 7 Calcium ______________ . 0 74 54 28 11 (4) (2) 173 32. 5 Do _______________ . 05 84 67 38 4 ( 2) (0) 195 36. 6 Do _______________ . 1 82 70 10 7 (3) (1) 173 32.5 Do _______________ . 3 80 72 46 34 24 (14) 270 50. 8 Do _______________ . 5 90 83 69 69 52 41 404 75. 9 Do _______________ 1. 0 87 86 86 85 82 73 499 93. 8 Do _______________ 1. 5 87 86 89 88 87 82 519 97. 6 Soft water Sodium _______________ 0. 0 102 102 106 100 103 (100) 613 115. 2 Do _______________ . 025 99 98 102 102 103 108 612 115. 0 Do _______________ . l 96 96 101 102 97 (97) 589 110. 7 Calcium ______________ . 0 74 54 34 8 .0 (0) 170 32. 0 Do _______________ . 025 81 65 44 15 (5) (3) 213 40. 0 Do _______________ . 1 82 66 47 7 (3) (l) 206 38. 7 Do _______________ . 5 83 71 68 54 34 (14) 324 60. 9 Do _______________ 1. 0 96 92 91 88 80 70 517 97. 2 Do _______________ l. 5 97 97 97 95 92 79 557 104. 7 Do _______________ 2. 0 91 91 91 91 89 1 86 539 101. 3 Hard water Sodium _______________ 0. 0 82 81 80 86 85 4 418 78. 6 Do _______________ . 05 88 88 88 89 (80) (18) 451 84. 8 Do _______________ . 1 84 86 86 84 (74) (6) 420 78. 9 Do _______________ . 5 85 85 85 86 (60) (2) 403 75. 8 Do _______________ 1. 0 82 82 79 82 (80) (5) 410 77. 1 Do _______________ 2. 0 85 85 76 76 83 (47) 452 85. 0 Do _______________ 3. 0 96 96 96 96 85 (11) 480 90. 2 Do _______________ 4. 0 94 94 94 94 89 52 517 97. 2 .0 80 72 1 0 (0) (0) 153 28. 8 . 025 84 72 1 (0) (0) (0) 157 29. 5 . 05 84 71 1 (0) (0) (0) 156 29.3 . 1 86 75 2 (l) (0) (0) 164 30. 8 .3 86 70 l (0) (0) (0) 157 29. 5 .5 85 73 13 (7) (0) (0) 178 33. 5 l. 0 80 75 64 24 12 (0) 255 47. 9 2. 0 82 78 79 74 55 37 405 76. l 3. 0 94 94 94 94 92 78 546 102. 6 1 At 4,31) minutes=7l percent; at 5,760 minutes=64 percent. DISPERSION CHARACTERISTICS, MONTMORILLONITE, KAOLINITE, ILLITE CLAYS 257 TABLE 3.—Hydrometer data: Montmorillom'te and sodium hezametaphosphate Percentage in suspension alter settling for the number of minutes indicated Ion saturation Grams Sum Dispersion deflocculent index 1 4 19 60 435 1, 545 Distilled water 0. 0 89 87 89 89 90 86 530 99. 6 . 025 98 96 99 97 97 95 582 109. 4 . 1 99 96 97 97 99 96 584 109. 8 . 0 72 51 26 10 (5) (0) 164 30. 8 . 05 75 69 42 26 (13) (0) 225 42. 3 . 1 78 65 48 36 (24) (12) 262 49. 2 . 3 82 70 60 50 36 (24) 322 60. 5 . 5 83 75 68 62 52 43 383 72. 0 1. 0 83 81 81 78 77 62 462 86. 8 l. 5 92 83 90 90 84 77 516 97. 0 Soft water Sodium _______________ 0. 0 98 97 100 93 99 (98) 585 110. 0 Do _______________ . 025 93 93 96 97 95 100 574 107. 9 D0 _______________ . 1 91 90 93 90 (80) (75) 519 97. 6 Calcium ______________ . 0 78 59 36 11 2 (1) 187 35. 2 Do _______________ . 025 81 66 45 11 (5) (1) 209 39. 3 Do _______________ . 1 84 69 48 6 (3) (O) 210 39. 5 Do _______________ . 5 86 76 67 58 8 (4) 299 56. 2 Do _______________ 1. O 94 83 78 79 58 53 445 83. 6 Do ............... 1. 5 99 99 88 86 73 61 506 95. 1 Do _______________ 2. 0 89 89 89 88 82 1 72 509 95. 7 Hard water Sodium _______________ 0. 0 85 85 85 85 79 34 453 85. 2 Do _______________ . 05 88 88 88 74 (70) (25) 433 81. 4 Do _______________ . 1 86 86 86 83 (80) (30) 451 84. 8 Do _______________ . 5 86 86 86 86 (80) (40) 464 87. 2 Do _______________ l. 0 82 81 82 80 (75) (25) 425 79. 9 Do _______________ 2. 0 86 86 86 86 (80) (40) 464 87. 2 Do _______________ 3. 0 96 96 96 96 85 (50) 519 97. 6 Do _______________ 4. 0 93 93 96 88 86 85 541 101. 7 Calcium ______________ . 0 92 82 8 2 (1) (0) 185 34. 8 Do _______________ . 025 92 l 8 5 (3) (0) 189 35. 5 Do _______________ .050 89 (75) 5 (3) (0) (0) 172 32. 4 Do _______________ . 1 94 74 4 (2) (0) (0) 174 32.7 Do _______________ .3 89 70 6 5 (3) (0) 173 32.5 Do _______________ .5 93 70 6 (3) (0) (0) 172 32.3 Do ............... 1. 0 94 84 21 8 (4) (0) 211 39. 7 Do _______________ 2. 0 98 90 77 58 12 (6) 341 64. 1 Do _______________ 3. 0 96 96 91 44 44 18 418 78. 6 Do _______________ 4. 0 75 75 74 74 68 8 374 70. 3 Do _______________ 5. 0 59 59 58 58 67 65 366 68. 8 I At 4,320 mlnutes=61 percent; at 5,760 minutes=58 percent. 258 SHORTER CONTRIBUTIONS ’1‘0 GENERAL GEOLOGY TABLE 4.—Hydrometer data: Montmorillom'te and sodium hezametaphosphate plus sodium carbonate Percentage in suspension after settling for the number of minutes indicated Ion saturation Grams Sum Dispersion deflocculent index 1 4 19 60 435 1,545 Distilled water Sodium _______________ 0. 0 88 88 89 88 88 89 530 99. 6 Do _______________ . 025 98 96 98 98 98 96 584 109. 8 Do _______________ . 1 98 97 97 98 98 96 584 109. 8 Calcium ______________ . 0 72 59 32 16 (8) (0) 187 35. 2 Do _______________ . 05 78 62 42 26 (13) (7) 228 42. 9 Do _______________ . 1 81 70 51 35 (18) (9) 264 49. 6 Do _______________ . 3 76 67 52 41 28 (20) 284 53. 4 Do _______________ . 5 89 81 69 59 49 37 384 72. 2 Do _______________ 1. 0 86 83 81 76 68 58 452 85. 0 Do _______________ 1. 5 87 85 86 85 82 76 501 94. 2 Soft water Sodium _______________ 0. 0 102 102 103 102 104 (102) 615 115. 6 Do _______________ . 025 98 98 102 104 101 108 611 114. 8 Do _______________ . 1 100 99 104 104 103 105 615 115. 6 Calcium ______________ . 0 76 57 33 12 0 (0) 178 33. 5 Do _______________ . 025 79 59 40 7 (4) (0) 189 35. 5 Do _______________ . 1 77 62 38 3 (2) (0) 182 34. 2 Do _______________ . 5 85 70 54 27 0 (0) 236 44 4 Do _______________ 1. 0 86 78 68 61 25 2 320 60. 2 Do _______________ 1. 5 95 95 91 88 76 60 505 94. 9 Do _______________ 2. 0 90 88 88 86 83 176 511 96. 1 Hard “(er Sodium _______________ 0. 0 86 86 86 91 4 (2) 355 66. 7 Do _______________ . 05 83 83 81 81 (7) (2) 337 63. 3 Do _______________ . 1 84 84 84 85 (12) (6) 355 66. 7 Do _______________ . 5 86 86 85 85 (20) (4) 366 68. 8 Do _______________ 1. 0 90 90 90 90 (40) (8) 408 76. 7 Do _______________ 2. 0 83 83 83 83 (60) (12) 404 75. 9 Do _______________ 3. 0 88 88 85 88 85 34 468 88. 0 Do _______________ 4. 0 93 91 85 82 75 0 426 80. 1 Calcium ______________ . 0 83 74 3 0 (0) (0) 160 30. 1 Do _______________ . 025 80 72 0 (0) (0) (0) 152 28. 6 Do _______________ .05 84 (73) 0 (0) (0) (0) 157 29. 5 Do _______________ . 1 82 75 0 (0) (0) (0) 157 29.5 Do _______________ .3 84 73 0 (0) (0) (0) 157 29.5 Do _______________ . 5 82 73 0 (0) (0) (0) 155 29. 1 Do _______________ 1.0 83 77 51 0 (0) (0) 211 39. 7 Do _______________ 2. 0 89 87 80 62 0 (0) 318 59. 8 Do _______________ 3. 0 100 100 90 76 56 0 422 79. 3 Do _______________ 4. 0 73 73 72 71 71 69 429 80. 6 Do _______________ 5. 0 59 59 57 57 68 68 368 69. 2 1 At 4,320 minutes=58 percent; at 5,760 minutes=55 percent. DISPERSION CHARACTERISTICS, MONTMORILLONITE, KAOLINITE, ILLITE CLAYS 259 TABLE 5.——Hydrometer data: Kaolim‘te and sodium tripolyphosphate Percentage in suspension after settling for the number of minutes indicated Ion saturation Grams Sum Dispersion deflocculent index 1 4 19 60 435 1,545 Distilled uter- Sodium _______________ 0 0 90 88 86 80 58 49 451 99. 6 Do _______________ 025 92 92 90 85 66 56 481 106. 2 Do _______________ 1 99 97 95 86 68 55 500 110. 4 Calcium ______________ 0 68 17 0 0 (0) (0) 85 18. 8 Do _______________ 05 80 64 14 5 (3) (2) 168 37. 1 Do _______________ 1 83 34 8 8 (4) (2) 139 30. 7 Do _______________ 3 75 30 26 21 16 (11) 179 39. 5 Do _______________ 5 85 74 64 55 39 29 346 76. 4 Do _______________ 1 0 90 88 83 73 57 45 436 96. 2 Do _______________ l 5 88 91 86 73 58 46 442 97. 6 Soft water Sodlum _______________ 0. 91 80 7 7 (6) (5) 196 43. 3 D0 _______________ . 025 95 92 30 6 (3) (0) 226 49. 9 Do _______________ 1 97 96 58 13 7 (4) 275 60. 7 Do _______________ 5 97 95 88 78 58 16 432 95. 4 Do _______________ 75 94 93 86 75 54 44 446 98. 5 Do _______________ 1 0 97 95 87 77 58 45 459 101. 3 Do _______________ 1 5 96 96 88 75 57 45 457 100. 9 Calcium ______________ 0 66 37 8 5 0 (0) 116 25. 6 Do _______________ 025 79 58 10 5 (0) (0) 152 33. 6 Do _______________ 1 70 56 12 4 (2) (1) 145 32. 0 Do _______________ 5 80 65 55 39 1 (0) 240 53. 0 Do _______________ l 0 96 93 84 71 54 49 447 98. 7 Do _______________ l 5 98 98 97 81 62 52 488 107. 7 Do _______________ 2 0 91 89 89 82 62 153 466 102. 9 Hard water Sodium _______________ 0. 0 70 27 0 (0) (0) (O) 97 21. 4 Do _______________ . 05 87 44 0 (0) (0) (0) 131 28. 9 Do _______________ . l 83 50 2 (0) (0) (0) 135 29. 8 Do _______________ .5 85 70 0 (0) (0) (0) 155 34. 2 Do _______________ 1. 0 82 75 0 (0) (0) (0) 157 34. 7 Do _______________ 2. 0 85 85 25 0 (0) (O) 195 43. 0 Do _______________ 3. 0 96 91 77 21 5 (3) 293 64. 7 Do _______________ 4. O 96 89 83 72 54 38 432 95. 4 Calcium ______________ . 0 89 37 3 2 (0) (0) 131 28. 9 Do _______________ . 025 93 48 4 (2) (0) (0) 147 32. 4 D0 _______________ . 05 97 63 4 (2) (0) (0) 166 36. 6 Do _______________ . 1 99 61 7 (4) (0) (0) 171 37.7 Do _______________ . 3 99 69 5 (3) (0) (0) 176 38. 8 Do _______________ . 5 99 78 4 (2) (0) (0) 183 40. 4 D0 _______________ 1. 0 97 81 4 2 (l) (0) 185 40. 8 Do _______________ 2. 0 97 97 59 10 2 (1) 266 58. 7 Do _______________ 3. 0 94 94 94 78 54 41 455 100. 4 1 At 4,320 minutes=45 percent; at 5,760 minutes=40 percent. 260 SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY TABLE 6.—Hydrometer data: Kaolim'te and sodium hezametaphosphate Percentage in suspension after settling for the number oi minutes indicated Ion saturation Grams Sum Dispersion deflocculent dex 1 4 19 00 435 1, 545 Distilled water Sodium _______________ 0. 0 91 90 88 79 63 55 466 102. 9 Do _______________ . 025 101 100 97 86 72 60 516 113. 9 Do _______________ . 1 100 99 96 88 73 60 516 113. 9 Calcium ______________ . 0 68 28 2 0 (0) (0) 98 21. 6 DO _______________ . 05 79 50 40 21 (10) (0) 200 44. 2 Do _______________ . 1 82 68 48 28 (15) (10) 251 55. 4 Do _______________ . 3 93 86 77 66 46 (35) 403 89. 0 DO _______________ . 5 93 91 85 74 55 40 438 96. 7 Do _______________ 1. 0 87 86 81 69 55 42 420 92. 7 Do _______________ 1. 5 95 93 88 76 52 41 445 98. 2 Soft water Sodium _______________ 0. 0 91 82 4 3 (2) (1) 183 40. 4 Do _______________ . 025 94 92 80 7 (5) (4) 282 62. 2 Do _______________ . 1 95 93 78 13 6 (5) 290 64. 0 Do _______________ . 5 93 91 87 78 34 4 387 85. 4 DO _______________ . 75 92 91 86 76 50 7 402 88 7 Do _______________ 1. 0 91 90 85 73 58 33 430 94. 9 DO _______________ l. 5 92 86 84 73 56 43 434 95. 8 Calcium ______________ . 0 50 34 12 7 2 (1) 106 23. 4 Do _______________ . 025 62 47 15 6 (3) (2) 135 29. 8 Do _______________ . 1 58 47 11 6 (4) (2) 128 28 2 DO _______________ . 5 67 59 51 39 3 (l) 220 48 6 Do _______________ . 0 91 87 83 70 54 35 420 92. 7 DO _______________ 1. 5 99 99 86 78 60 49 471 104. 0 Do _______________ 2. 0 88 87 85 76 60 1 50 446 98. 4 find water Sodium _______________ 0. 0 82 33 0 (0) (0) (0) 115 25. 4 Do _______________ .05 85 39 0 (0) (0) (0) 124 27. 4 Do _______________ . l 82 40 0 (0) (0) (0) 122 26. 9 Do _______________ .5 86 48 0 (0) (0) (0) 134 29. 6 DO _______________ 1. 0 82 50 2 (0) (0) (0) 134 29. 6 Do _______________ 2. 0 86 72 s (5) (3) (2) 176 38. 8 Do _______________ 3. 0 96 96 53 13 8 (6) 272 60. 0 DO _______________ 4. 0 90 83 83 67 10 5 338 74. 6 ' . 0 92 33 8 3 (2) (l) 139 30. 7 D . 025 99 61 8 4 (2) (0) 174 38. 4 .05 98 (61) 3 (2) (0) (0) 164 36.2 . 1 95 62 3 (2) (1) (0) 163 36.0 .3 98 59 7 6 (4) (2) 176 38. 8 .5 98 62 4 (3) (2) (1) 170 37. 5 1. 0 100 70 8 8 (7) (6) 199 43. 9 2.0 99 90 11 11 12 (12) 235 51. 9 3. 0 96 92 73 17 14 17 309 68 2 4. 0 75 75 72 30 8 10 270 59. 6 5. 0 57 57 56 56 13 12 251 55. 4 6. 0 45 44 43 43 40 6 221 48 8 1 At 4,320 minutessio percent; at 5,760 minutes=36 percent. DISPERSION CHARACTERISTICS, MONTMORILLONITE, KAOLINITE, ILLITE CLAYS 261 TABLE 7.—Hydrometer data: K aolinite and sodium hexametaphosphate plus sodium carbonate Percentage in suspension after settling for the number of minutes indicated Ion saturation Grams Sum Dispersion deflocculent index 1 4 19 60 435 1, 545 Distilled water Sodium _______________ 0 0 89 88 83 73 57 53 443 97. 8 Do _______________ 025 97 97 95 85 66 57 497 109. 7 Do _______________ 1 97 96 93 87 67 55 495 109. 3 Calcium ______________ 0 68 26 4 (2) (0) (0) 100 22. 1 Do _______________ 05 77 57 35 20 (10) (0) 199 43. 9 Do _______________ 1 82 66 47 33 (22) (11) 261 57. 6 Do _______________ 3 85 72 57 46 27 (18) 305 67. 3 Do _______________ 5 94 89 78 65 46 30 402 88. 7 Do _______________ 1 0 88 86 82 72 55 43 426 94. 0 Do _______________ 1 5 90 89 82 72 55 43 431 95. 1 Soft wnter Sodium _______________ 0. 0 96 78 2 0 (0) (0) 176 38 8 Do _______________ . 025 95 92 78 8 3 (0) 276 60. 9 Do _______________ . 1 95 93 79 6 0 (0) 272 60. 0 Do _______________ . 5 102 92 94 81 58 36 463 102. 2 Do _______________ . 75 95 93 92 80 59 46 465 102. 6 Do _______________ 1. 0 98 93 90 80 58 47 466 102. 9 Do _______________ 1. 5 97 95 90 80 60 47 469 103. 5 Calcium ______________ . 0 73 44 9 4 0 (0) 130 28 7 Do _______________ . 025 74 56 18 5 (0) (0) 153 33. 8 Do _______________ . 1 76 60 11 3 (0) (0) 150 33. 1 Do _______________ . 5 80 67 52 11 0 (0) 210 46. 4 Do _______________ 1. 0 89 75 63 55 42 30 354 78 1 Do _______________ 1. 5 96 95 85 76 55 42 449 99. 1 Do _______________ 2 0 97 91 88 74 57 147 454 100. 2 Hard water Sodium _______________ 0. 0 60 28 0 (0) (0) (0) 88 19. 4 Do _______________ .05 78 40 0 (0) (0) (0) 118 26.0 Do _______________ . 1 80 46 0 (0) (0) (0) 126 27. 8 Do _______________ . 5 84 68 0 (0) (0) (0) 152 33. 6 Do _______________ 1.0 83 69 1 (O) (0) (0) 153 33.8 Do _______________ 2. 0 81 79 34 (10) (0) (0) 204 45. 0 Do _______________ 3. 0 88 80 64 53 5 (0) 290 64. 0 Do _______________ 4. 0 91 90 82 72 46 16 397 87. 6 Calcium ______________ . 0 93 35 6 4 (3) (2) 143 31. 6 Do _______________ .025 90 52 3 (2) (1) (0) 148 32. 7 Do _______________ .05 91 (52) 3 (2) (1) (0) 149 32.9 Do _______________ . 1 90 69 5 (3) (1) (0) 168 37. 1 Do _______________ . 3 89 78 5 (3) (0) (0) 175 38. 6 Do _______________ . 5 90 80 4 (2) (0) (0) 176 38.8 Do _______________ 1. 0 89 87 23 0 (0) (0) 199 43. 9 Do _______________ 2. 0- 95 95 55 2 0 (0) 247 54. 5 Do _______________ 3. 0 100 100 95 65 6 0 366 80. 8 Do _______________ 4. 0 74 74 70 70 46 30 364 80. 4 Do _______________ 5. 0 61 61 57 57 50 36 322 71. 1 Do _______________ 6. 0 42 42 42 42 41 38 247 54. 5 1 At 4,320 minutes=36 percent; at 5,760 mmutes=30 percent. 262 SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY TABLE 8.—Hydrometer data: I llite and sodium tripolyphosphate Percentage in suspension after settling for the number of minutes indicated Ion saturation Grams Sum Dispersion deflocculent index 1 4 19 60 435 1, 545 Distilled water Sodium _______________ 0. 0 94 92 84 70 38 25 403 102. 0 Do _______________ . 025 96 95 91 78 46 31 437 110. 6 Do _______________ . 1 104 102 96 78 46 29 455 115. 2 Calcium ______________ . 0 19 14 8 0 (0) (0) 41 10. 4 Do _______________ . 05 26 18 12 4 (2) (0) - 62 15. 7 D0 _______________ . 1 32 24 16 12 (6) (4) 94 23. 8 Do _______________ . 3 28 20 14 9 4 (2) 77 19. 5 Do _______________ . 5 29 21 15 11 6 4 86 21. 8 Do _______________ 1. 0 28 18 14 9 6 0 75 19. 0 D0 _______________ 1. 5 29 22 18 11 8 6 94 23. 8 Soft water Sodlum _______________ 0. 0 90 89 62 16 (5) (2) 264 66. 8 Do _______________ . 025 93 91 77 24 6 (3) 294 74. 4 Do _______________ . 1 94 93 68 20 7 (4) 286 72. 4 D0 _______________ . 5 93 68 12 12 4 (2) 191 48. 4 D0 _______________ . 75 92 30 11 8 8 6 155 39. 2 D0 _______________ 1. O 92 37 19 17 15 10 190 48. 1 D0 _______________ 1, 5 93 93 86 68 39 23 402 101. 8 Calcium ______________ . 0 52 34 18 7 0 (0) 111 28. 1 Do _______________ . 025 63 44 20 5 (2) (1) 135 34. 2 Do _______________ . 1 58 42 21 3 (2) (0) 126 31. Do _______________ . 5 57 23 5 2 0 (0) 87 22. D0 _______________ 1. 0 54 12 5 4 4 8 87 22. Do _______________ 1. 5 72 57 44 32 21 19 245 62 Do _______________ 2. O 75 63 49 38 26 1 24 275 . 69 Hard water Sodium _______________ 0. 0 81 74 26 3 (2) (0) 186 47. 1 Do _______________ . 05 85 67 33 0 (0) (0) 185 46. 8 Do _______________ . 1 78 66 36 O (0) (0) 180 45. 6 Do _______________ .5 83 64 2 (0) (0) (0) 149 37. 7 D0 _______________ 1.0 80 65 1 (0) (0) (0) 146 37.0 Do _______________ 2. 0 85 37 0 (0) (0) (0) 122 30. 9 Do _______________ 3. O 88 80 32 13 0 (0) 213 53- 9 Do _______________ 4. 0 83 83 80 56 38 27 367 92. 9 Calcium ______________ . 0 43 39 9 2 (1) (0) \ 94 23. 8 Do _______________ .025 46 36 13 (6) (3) (1) 105 26. 6 Do _______________ .05 45 41 18 (9) (3) (2) 118 29.9 Do _______________ .1 46 41 18 (9) (3) (2) 119 30.1 Do _______________ .3 48 43 4 (2) (0) (0) 97 24. 6 Do _______________ .5 47 40 2 (1) (0) (0) 90 22. 8 Do _______________ 1. 0 44 38 0 0 (0) (0) 82 20. 8 Do _______________ 2. 0 48 45 3 2 0 (0) 98 24. 8 Do _______________ 3. 0 52 47 43 34 23 20 219 55. 4 I At 4,320 minutes=2l percent; at 5,760 minutes=20 percent. DISPERSION CHARACTERISTICS, MONTMORILLONITE, KAOLINITE, ILLITE CLAYS 263 TABLE 9.—-—Hydrometer data: I llite and sodium hexametaphosphate Percentage in suspension after settling for the number of minutes indicated Ion saturation Grams Sum Dispersion deflocculent index 1 4 19 60 435 1,545 Distilled water Sodium _______________ 0. 0 90 90 83 67 39 25 394 99. 7 Do _______________ . 025 98 96 91 74 44 29 432 109. 4 Do _______________ . 1 98 98 90 73 46 29 434 109. 9 Calcium ______________ . 0 31 21 8 0 (0) (0) 60 15. 2 Do _______________ . 05 26 18 12 7 (4) (2) 69 17. 5 D0 _______________ . 1 31 23 14 9 (5) (3) 85 21. 5 Do _______________ . 3 27 20 13 8 3 (2) 73 18. 5 Do _______________ . 5 28 22 14 8 4 1 77 19. 5 Do _______________ 1. 0 23 15 9 4 0 2 53 13. 4 Do _______________ 1. 5 28 22 15 10 5 1 81 20. 5 Soft water Sodium _______________ 0. 0 94 91 64 12 (4) (2) 267 67. 6 Do _______________ . 025 94 90 82 42 1 (0) 309 78. 2 Do _______________ . 1 93 90 84 52 5 (3) 327 82. 8 Do _______________ . 5 96 94 90 73 37 16 406 102. 8 Do _______________ . 75 94 92 91 71 38 23 409 103. 5 D0 _______________ 1. 0 97 96 91 73 36 24 417 105. 6 Do _______________ 1. 5 97 95 90 74 43 27 426 107. 8 Calcium ______________ . 0 58 37 18 8 0 (0) 121 30. 6 Do _______________ . 025 65 46 19 6 (0) (0) 136 34. 4 Do _______________ . 1 65 45 16 4 (0) (0) 130 32. 9 Do _______________ . 5 64 44 23 13 0 (0) 144 36. 4 Do _______________ 1. O 69 51 31 20 11 13 195 49. 4 Do _______________ 1. 5 77 60 41 29 22 19 248 62. 8 Do _______________ 2. 0 74 59 44 34 26 1 24 261 66. 1 Hard water Sodium _______________ 0. O 70 59 17 0 (0) (0) 146 37. 0 Do _______________ . O5 86 85 43 4 (2) (0) 220 55. 7 Do _______________ . 1 82 82 40 2 (1) (0) 207 52. 4 Do _______________ . 5 85 84 42 4 (2) (0) 217 54. 9 Do _______________ 1.0 81 78 16 8 (4) (0) 187 47. 3 Do _______________ 2. 0 86 86 33 14 (7) (4) 230 58. 2 Do _______________ 3. 0 99 96 69 16 11 (9) 300 75. 9 Do _______________ 4. 0 99 96 83 35 10 12 335 84. 8 Calcium ______________ . 0 42 39 9 0 (0) (0) 90 22. 8 Do _______________ . 025 47 39 20 2 (1) (0) 109 27. 6 Do _______________ .05 40 (35) 12 (4) (3) (2) 96 24. 3 Do _______________ . 1 38 33 9 (5) (0) (0) 85 21.5 D0 _______________ .3 40 34 8 2 (1) (0) 85 21.5 Do _______________ .5 42 40 2 (1) (0) (0) 85 21.5 Do _______________ 1. 0 45 40 14 0 (0) (0) 99 25. 1 Do _______________ 2.0 43 37 15 6 7 (6) 114 28. 9 Do _______________ 3. 0 49 43 36 10 10 10 158 40. 0 Do _______________ 4. 0 39 35 31 14 4 6 129 32. 7 Do _______________ 5. 0 43 35 31 25 19 12 165 41. 8 Do _______________ 6. 0 35 31 28 20 16 12 142 35. 9 1 At 4,320 minutes=22 percent; at 5,760 minutes=20 percent. 264 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY TABLE 10.—Hydrometer data: Illite and sodium hezametaphosphate plus sodium carbonate Percentage in suspension after settling for the number of minutes indicated Ion saturation Grams Sum Dispersion deflooculent index 1 4 19 60 435 1, 545 Distilled water Sodium _______________ 0. 0 93 92 83 64 37 23 392 99. 2 Do _______________ . 025 100 100 93 76 42 30 441 111. 6 Do _______________ . 1 100 99 93 73 43 28 436 110. 4 Calcium ______________ . 0 26 20 10 (5) (3) (0) 64 16. 2 Do _______________ .05 28 19 12 8 (5) (l) 73 18. 5 Do _______________ . 1 31 22 18 12 (8) (6) 97 24. 6 Do _______________ . 3 28 18 14 8 3 (2) 73 18. 5 Do _______________ . 5 29 20 16 11 8 3 87 22. 0 Do _______________ 1. 0 26 17 13 8 6 3 73 18. 5 Do _______________ 1. 5 25 17 13 9 7 4 75 19. 0 Soft water 0. 0 91 87 65 9 (0) (0) 252 63. 8 . 025 88 85 78 28 (0) (0) 279 70. 6 . 1 88 84 80 51 0 (0) 303 76. 7 . 5 91 88 85 66 18 2 350 88. 6 . 75 90 87 85 67 30 15 374 94. 7 1. 0 93 90 85 66 32 17 383 97. 0 1. 5 94 92 84 68 35 20 393 99. 5 .0 58 37 16 7 0 (0) 118 29. 9 .025 61 38 15 4 (0) (0) 118 29.9 .1 58 38 12 2 (0) (0) 110 27. 8 . 5 67 46 20 8 0 (0) 141 35. 7 1. 0 67 47 24 16 9 8 171 43. 3 1. 5 74 52 31 22 13 11 203 51. 4 2. 0 71 48 29 19 10 1 10 187 47. 3 Hard water 0. 0 76 70 24 0 (0) (0) 170 43. 0 . 05 80 78 40 0 (0) (0) 198 50. 1 . 1 78 74 47 0 (0) (0) 199 50. 4 .5 83 83 52 0 (0) (0) 218 55. 2 1.0 87 77 15 0 (0) (0) 179 45. 3 2.0 83 75 3 (0) (0) (0) 161 40. 8 3. 0 88 80 64 32 5 (0) 269 68. 1 4. 0 88 85 72 56 22 3 326 82. 5 .0 36 33 5 0 (0) (0) 74 18. 7 .025 34 3O 10 (2) (0) (0) 76 19.2 .05 35 (31) 8 (2) (0) (0) 76 19.2 . 1 35 32 20 10) (0) (0) 97 24. 6 .3 34 29 18 0 (0) (0) 81 20. 5 .5 37 31 11 (1) (0) (0) 80 20. 3 1.0 37 33 0 (0) (0) (0) 70 17. 7 2. 0 41 37 23 0 (0) (0) 101 25. 6 3. 0 50 46 40 29 17 5 187 47. 3 4. 0 46 40 32 24 14 7 163 41. 3 5. 0 49 39 34 27 20 10 179 45. 3 6. 0 32 32 32 24 15 5 140 35. 4 1 At 3,420 m1nutes=5 percent; at 5,760 m1nutes=4 percent. DISPERSION CHARACTERISTICS, MONTMORILLONITE, KAOLINITE, ILLITE CLAYS TABLE 11.—Hydrometer data: Volclay and sodium tripolyphosphate [Ion saturation 78.8 percent sodium] 265 Percentage in suspension after settling for the number of minutes indicated Grams Sum Dispersion deflocculent dex 1 4 19 60 435 1,545 Distilled water 0. 0 91 88 89 88 85 86 527 99. 1 . 025 92 92 92 95 87 84 542 101. 9 . O5 92 92 91 91 88 85 539 101. 3 . 1 91 89 91 93 85 86 535 100. 6 Synthetic Tri-County water 0. 0 98 98 100 90 (0) (0) 386 72. 6 . 05 95 92 91 88 (0) (0) 366 68. 8 . 1 98 98 94 87 46 3 426 80. 1 . 2 93 90 91 90 76 23 463 87. 0 . 3 97 94 92 91 77 59 510 95. 9 . 5 96 94 89 86 74 74 513 96. 4 . 75 92 89 88 90 (77) 68 504 94. 7 1. 0 93 90 . 90 88 84 74 519 97. 6 1. 25 94 92 91 91 90 80 538 101. l 1. 5 97 95 94 92 90 84 552 103. 8 1. 75 97 96 92 88 88 84 545 102. 4 2. 0 94 92 92 92 87 85 542 101. 9 TABLE 12,—Hydrometer data: Volclay and sodium hexametaphosphate [Ion saturation 78.8 percent sodium] Percentage in suspension after settling for the number of minutes indicated Grams Sum Dispersion deflocculent index 1 4 . 19 60 435 1,545 Distilled water 0. 0 91 90 88 88 87 87 531 99. 8 . 025 94 91 93 93 94 87 552 103. 8 . 05 93 90 93 93 92 87 548 103. 0 . 1 93 89 93 93 89 89 546 102. 6 Synthetic Tri-County water 0. 0 102 102 103 100 (0) (0) 407 76. 5 . 05 94 91 90 86 (0) (0) 361 67. 9 . 1 95 92 92 88 43 5 415 78. 0 . 2 95 93 90 88 83 8 457 85. 9 . 3 94 91 90 89 78 49 491 92. 3 . 5 92 92 89 85 80 66 504 94. 7 . 75 92 91 89 88 (84) 70 514 96. 6 1. 0 92 90 90 86 82 71 511 96. 0 1. 25 91 86 90 89 85 75 516 97. 0 1. 5 90 88 92 91 87 76 524 98. 5 1. 75 89 85 86 83 84 76 503 94. 5 2. 0 98 94 91 88 84 80 535 100. 6 266 SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY TABLE 13.—Hydrometer data: Volclay and tetrasodium pyrophosphate [Ion saturation 78.8 percent sodium] Percentage in suspension after settling for the number of minutes indicated Grams Sum Dispersion deflocculent index 4 19 60 435 1,545 Distilled water 0. 0 91 91 90 88 87 90 537 100. 9 . 025 95 93 93 93 94 86 554 104. 1 . 075 93 93 94 93 93 88 554 104. 1 . 1 93 92 94 92 89 90 550 103. 4 Synthetic 'l‘rI-Couniy water 0. 0 98 97 98 92 (0) (0) 385 72. 4 . 05 92 91 90 84 (0) (0) 357 67. l . 1 98 96 94 91 48 5 432 81. 2 . 2 94 91 90 86 79 41 481 90. 4 . 3 94 92 92 89 79 61 507 95. 3 . 5 94 92 91 90 89 79 535 100. 6 .75 91 89 89 91 (83) 72 515 96. 8 1. 0 94 92 92 91 90 80 539 101. 3 1. 25 97 95 94 90 91 85 552 103. 8 1. 5 95 92 90 87 90 85 539 101. 3 1. 75 98 94 92 90 89 85 548 103. 0 2. 0 94 92 92 91 92 89 550 103. 4 TABLE 14.——Hydromeier data: Kaolim'te and sodium tripolyphosphate [Ion saturation 78.8 percent sodium] Percentage in suspension after settling for the number of minutes indicated Grams Sum Dispersion deflocculent index 4 19 60 435 1, 545 Distilled water 0. 0 94 93 88 79 58 50 462 102. 0 . 025 96 95 94 84 59 48 476 105. 1 . 05 98 96 9'0 82 64 49 479 105. 7 . 1 97 95 93 83 59 50 477 105. 3 Synthetic Tri-County Inter 0.0 100 51 5 5 (0) (0) 161 35. 5 . 05 96 92 10 2 (0) (0) 200 44. 2 . 1 100 99 28 4 0 1 232 51. 2 . 2 97 96 61 6 2 (0) 262 57. 8 . 3 98 96 84 13 1 (0) 292 64. 5 . 5 98 96 89 75 (0) 362 79. 9 . 75 100 94 89 80 (42) 14 419 92. 5 1. 0 100 98 90 79 6 49 477 105. 3 1. 25 96 94 91 81 63 50 475 104. 8 1. 5 100 97 90 82 63 49 481 106. 2 1. 75 100 98 89 87 61 48 483 106. 6 2. 0 473 104 4 DISPERSION. CHARACTERISTICS, MONTMORILLONITE, KAOLINITE, ILLITE CLAYS TABLE l5.—Hydrometer data: Kaolim'te and sodium hemmetaphosphate [Ion saturation 78.8 percent sodium] 267 Percentage in suspension after settling for the number of minutes indicated Grams Sum Dispersion defloccuient , index 1 4 19 60 435 l, 545 Distilled wnter O. 0 91 90 84 80 56 50 451 99. 6 . 025 95 93 91 82 64 49 474 104. 6 . 05 93 91 91 81 63 51 470 103. 8 . 1 92 91 89 80 60 50 462 102. 0 Synthetic Til-County wate 0.0 100 64 6 4 (0) (0) 174 38. 4 . 05 95 92 11 2 (0) (0) 200 44. 2 . 1 100 96 21 6 0 (0) 223 49. 2 . 2 99 98 69 8 3 (0) 277 61. 1 . 3 97 94 86 16 1 (0) 294 64. 9 . 5 96 92 87 76 24 (6) 381 84. l . 75 95 93 90 76 (60) 48 462 102. 0 1. 0 94 90 86 74 59 47 450 99. 3 1. 25 94 91 87 76 62 50 460 101. 5 1. 5 94 92 88 78 62 49 463 102. 2 1. 75 96 90 84 72 58 47 447 98. 7 ‘ 2. 0 92 91 78 69 56 46 432 95. 4 TABLE Mir—Hydrometer data: Kaolim‘te and tetrtwodium pyrophosphate [Ion saturation 78.8 percent sodium] Percentage in suspension after settling for the number of minutes indicated Grams Sum Dispersion deflocculent index 1 4 19 60 435 1, 545 Distilled "tel- 0. 0 93 93 86 77 57 50 456 100. 5 . 025 95 93 89 71 64 48 460 101. 7 . 050 96 94 92 79 62 49 472 104. 2 . 1 93 91 90 79 59 51 463 102. 7 Synthetic Tri-County water 0.0 100 64 6 4 2 (0) 176 38. 8 .05 95 90 6 2 (0) (0) 193 42. 6 . 1 103 99 17 7 0 (0) 226 49. 9 . 2 99 97 32 2 2 (0) 232 51. 2 . 3 95 94 45 3 0 (0) 237 52. 3 . 5 98 97 86 15 l (0) 297 65. 6 .75 97 93 88 21 (11) 4 314 69. 3 1. 0 102 99 91 81 22 5 400 88. 3 1. 25 98 96 91 81 64 52 482 106. 4 1. 5 96 94 87 76 62 48 463 102. 2 1. 75 95 92 88 77 60 49 461 101. 8 2. 0 96 94 87 78 58 49 462 102. 0 268 SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY TABLE 17.——Hydrometer data: Illite and sodium tripolyphosphate [Ion saturation 78.8 percent sodium] Percentage in suspension after settling for the number oi minutes indicated Grams Sum Dispersion deflocculent index 4 19 60 435 1, 545 Distilled water 0. 0 94 90 81 64 38 28 395 100. 0 . 025 95 94 86 70 38 27 410 103. 8 . 05 97 93 83 67 40 25 405 102. 5 . 1 95 92 87 71 40 28 413 104. 6 Synthetic Tri-County water 0. 0 101 94 40 4 (0) (0) 239 60. 5 . 05 96 94 83 33 (3) (0) 309 78. 2 . l 100 96 88 30 2 (0) 316 80. 0 . 2 96 94 82 23 5 (0) 300 75. 9 . 3 97 95 75 3 1 (0) 271 68. 6 . 5 94 93 72 4 0 (0) 263 66. 6 . 75 94 90 75 10 (5) 0 274 69. 4 1. 0 98 92 80 59 6 0 335 84. 8 1. 25 96 92 79 66 40 25 398 100. 8 1. 5 95 90 80 66 40 28 399 101. 0 1. 75 98 92 78 61 40 26 395 100. 0 2. 00 96 89 76 67 40 31 399 101. 0 2. 25 100 96 84 70 51 35 436 110. 4 2. 50 100 98 90 77 50 36 451 114. 2 2. 75 96 95 90 73 50 38 442 111. 9 TABLE 18.—Hydrometer data: I llite and sodium hexametaphosphate [Ion saturation 78.8 percent sodium] Percentage in suspension after settling for the number at minutes indicated Grams ' Sum Dispersion deflocculent Index 4 19 60 435 1,545 Distilled water 0. 0 90 90 80 66 38 28 392 99. 2 . 025 95 91 85 71 42 26 410 103. 8 . 05 93 90 85 67 42 27 404 102. 3 . 1 92 89 83 68 39 28 399 101. 0 Synthetic Trl-County water 0. 0 102 97 43 4 (0) (0) 246 62. 3 .05 95 92 80 15 (0) (0) 282 71. 4 . 1 98 94 65 6 1 (0) 264 66. 8 . 2 99 88 76 6 3 (0) 272 68. 9 . 3 97 94 44 2 2 (0) 239 60. 5 . 5 94 91 47 4 0 (0) 236 59. 7 . 75 95 92 72 4 3 l 267 67. 6 1. 0 94 90 69 6 4 3 266 67. 3 1. 25 96 95 83 48 5 3 330 83. 5 1. 5 98 93 82 64 6 4 347 87. 8 1. 75 94 89 76 60 34 5 358 90. 6 2. 0 98 92 81 68 37 7 383 97. 0 2. 25 95 93 82 65 47 11 393 99. 5 2. 50 100 98 90 76 47 11 422 106. 8 2. 75 95 93 83 71 48 37 427 108. 1 DISPERSION CHARACTERISTICS, MONTMORILLONITE, KAOLINITE, ILLITE CLAYS TABLE 19n—Hydrometer data: I llite and tetrasodium pyrophosphate [Ion saturation 78.8 percent sodium] 269 Percentage in suspension after settling for the number of minutes indicated Grams Sum Dispersion deflocculent index 1 4 19 60 435 1,545 Distilled water 0. 0 94 94 84 66 38 30 406 102. 8 . 025 94 91 83 70 4O 26 404 102. 3 . 05 91 89 80 65 40 27 392 99. 2 . 1 94 84 82 66 40 29 395 100. 0 Synthetic 'l‘rl-County water 0. 0 97 91 33 4 (0) (0) 225 57. 0 . 050 96 93 83 24 (6) (0) 302 76. 4 . 1 101 100 81 11 1 (0) 294 74. 4 . 2 86 93 51 0 2 (0) 232 58. 7 . 3 97 91 21 0 —2 (0) 207 52. 4 . 5 96 90 2 0 0 (0) 188 47. 6 . 75 93 71 0 — 1 —3 —5 155 39. 2 1. 0 99 34 8 2 —4 —6 133 33. 7 1. 25 101 88 50 30 7 3 279 70. 6 l. 5 98 91 60 38 17 8 312 79. 0 1. 75 99 93 66 46 21 10 335 84. 8 2. 0 99 65 56 50 22 14 306 77. 5 2. 25 96 86 78 65 41 25 391 99. 0 2. 50 102 102 94 76 47 30 451 114. 2 2. 75 97 97 89 73 44 32 432 109. 4 FILTER-LOSS TEST OF CLA‘Y SUSPENSIONS By I. S. MCQUEEN A series of exploratory tests was conducted during the second year of the investigation to determine if there were significant differences in the sealing capacity of various clays with different deflocculents. A standard operating procedure in the oil-well drilling-mud industry known as the filter-loss test or “filtration” provides information on the ability of a slurry to retain water inside of a drill hole during drilling operations (American Petroleum Institute, 1950, p. 7). The sediment lining in a canal is analogous to the filter cake in a drill hole. The nature of the seal developed in a canal bottom by dispersed clays is not thoroughly understood. There are several possible mechanisms involved. Probably the seal easiest to develop is a surface seal or skin on the canal bottom. This type of seal, how- ever, would be subject to erosion and would therefore be extremely temporary. The seal most permanent would be achieved by material that penetrates the soil mass and fills its interstices. The filling of cracks and other flow channels is an important factor in canal- sealing. Probably all of the above mechanisms are involved in an effective seal. The filter-loss test procedure was designed to define differences in pore- sealing as well as the relative permeability of the filter cake. In the drill-mud filtration test, a quantity of 500 to 600 grams of mud is placed inside a cylinder on a disc of filter paper supported by a screen. The top of the cylinder is sealed and a pressure of 100 pounds per square inch is applied for 30 minutes. The character of the filter cake and the quantity of water extracted are measures of the effectiveness of the mud. The above procedure was modified for the current investi- gations because it was found that ordinary filter paper would not retain the dilute colloidal suspensions used. Test procedure—To retain colloidal-size particles an attempt was made to develop a barrier of greater depth and smaller pore size than ordinary filter paper. This was done by using glass beads, which are available in uniform sizes as small as 28 microns in diameter. In the chosen mixture 80 percent of the beads were between 20 and 70 microns in diameter. Uniform filter beds of these beads were formed by depositing a known weight of them in water on a filter paper in a Buechner funnel and consolidating the mass by alter- nately jarring the funnel and withdrawing the excess water with a partial vacuum. A filter paper was placed over the bed of beads to protect the bed from being disturbed by the suspensions being filtered and also to provide a means of removing the filter cake for testing the sealing brought about by particles that penetrated into the voids. Results of the filter-loss tests are shown in table 20. The first four columns of table 20 describe the 270 SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY TABLE 20.——Results of filter-loss tests . Prerun Cake de- After run Sample Colloid Deflocculent Water cubic cen- velopment cubic cen- timeters time in timeters per hour seconds per hour 1 Volclay _______ Sodium tripolyphosphate _______ Sy§tllii£a(t(i)c Tri-County with 447 7, 740 __________ a a 2 _____ do ________ Sodium hexametaphosphate __________ do _______________________ 473 8, 790 __________ 3 _____ do ________ Sodium tripolyphosphate _______ Synthetic Tri—County with NaCl- 411 7, 380 125 4 _____ do ________ Sodium hexametaphosphate __________ do _______________________ 415 9, 780 143 5 _____ do ________ Sodium tripolyphosphate _______ Natural Tri-County ___________ 493 7, 500 114 6 _____ do ________ Sodium hexametaphosphate __________ do _______________________ 522 8, 760 115 7 Illite _________ Sodium tripolyphosphate _______ Synthetic Tri—County with NaCl- 379 2, 100 (100 8 _____ do ________ Sodium hexametaphosphate __________ do _______________________ 286 600 356 9 _____ do ________ Tetra sodium pyrophosphate___ _ _____ do _______________________ 336 1, 680 293 suspension being tested. The next column shows the rate of movement of distilled water through the filter bed under a tension of 55 centimeters of water, prior to the application of the clay sample. The last column shows the rate of movement of distilled water through the filter bed under a tension of 55 centimeters of water, after application of the sample suspension and removal of the filter cake. This rate indicates the relative effectiveness of the suspension in sealing the soil matrix. The time required to develop the cake, by dewatering 100 cubic centimeters of the sample sus- pension with an applied tension of more than 800 centimeters, indicates the relative effectiveness of the sample in forming an impermeable cake. The following characteristics may be inferred from the limited data obtained. 1. The filter cake formed using Volclay with sodium hexametaphosphate was consistently less permeable than the cake formed with Volclay and sodium tripolyphosphate. 2. There was no difference between sodium hexameta- phosphate and sodium tripolyphosphate with Volclay in their “pore—sealing” ability. 3. The Volclay penetrated the filter bed and reduced its permeability to about one-third of its pre- treatment permeability. The effect of illite on the permeability of the filter bed was variable; ranging from an increase in permeability to a reduction to about one-fourth. The filter-loss experiments were discontinued because no well-defined differences in the effectiveness of the dispersants were evident and time would not permit a complete development of the method. Limitations on filter-loss tests—There are several serious limitations on the filter-loss test in its present- stage of development. It is difficult to achieve con— sistently uniform filter beds. At present, the difference in permeability of two freshly prepared filter beds may be as great as the difference in the change in permea- bility imposed on the filter beds by two samples with different deflocculating agents. The filter beds were not stable. One or two of them broke down and changed their basic permeability during the course of the tests. Sample 8 (table 20) is an example of this. The permea- bility of the filter bed increased 25 percent with the addition of the colloid. In this sample, the original packing of the beads seemed to be completely disturbed. Time would not permit further work on this filter-loss test to eliminate these limitations so the tests were discontinued. SELECTED REFERENCES American Petroleum Institute, 1950, Recommended practice for standard field procedure for testing drilling fluids (tenta- tive): Am. Petroleum Inst. Research Paper 29. Bell, R. N. , 1947, Hydrolysis of dehydrated sodium phosphates: Indus. and Eng. Chemistry, v. 39, p. 136—140. Chu, T. Y. and Davison, 0.T., 1955, Deflocculating agents for mechanical analysis of soils: Highway Research Board Bull. 95, Natl. Acad. Sci., Natl. Research Council, Pub. 343, p. 15-26. Daugherty, T. H., 1948, Sequestration, dispersion, and dilitancy— lecture demonstrations: Jour. Chem. Education, v. 25, p. 482-486. Dirmeyer, R. D., Jr., 1955, Report of sediment lining investiga- tions, fiscal years 1954—55: Colorado A & M College, Fort Collins, 0010., 150 p. Grim, R. E., 1953, Clay mineralogy: New York, McGraw-Hill Book 00., 384 p. Kelley, W. P., 1948, Cation exchange in soils: New York, Rein- hold Pub. Corp., 144 p. Krynine, D. P., 1941, Soil mechanics, its principles and structural applications: New York, McGraw-Hill Book Co., 511 p. Marshall, C. E., 1949, The colloid chemistry of the silicate min- erals: New York, Academic Press, 195 p. Olphen, H. Van, 1950, Stabilization of montmorillonite sols by chemical treatment, part 2. Effect of polymetaphosphates, sodium metasilicate, oxalate, citrate and orthophosphate on Na and Ca montmorillonite sols: Recuell des travaux chimiques des pays-has, v. 69, no. 9—10, p. 1313—1322, September-October. Puri, A. N., 1949, Soils: Their physics and chemistry: New York, Reinhold Pub. Corp., 550 p. DISPERSION CHARACTERISTICS, MONTMORILLONITE, KAOLINITE, ILLITE CLAYS Richards, L. A., and others, 1954, Diagnosis and improvement of saline and alkali soils: U.S. Dept. Agriculture, Agriculture Handbook no. 60, 160 p. Ruehrwein, R. A., 1953, The interactions of polyelectrolytes with clay suspensions: Monsanto Chemical 00., Central Research Dept. , Dayton, Ohio, 6 p. Russell, Sir John E., 1950, Soil conditions and plant growth: 8th ed., New York, Longmans, Green & 00., 635 p. Tchillingarian, G., 1952, Study of the dispersing agents: Jour. Sed. Petrology, v. 22, p. 229—233. 271 Whitehouse, U. G. and Jeffrey, L. M., 1955, Peptization resist- ance of selected samples of kaolinitic, montmorillonitic, and illitic clay materials: Clays and clay minerals, Natl. Acad. Sci., Natl. Research Council Pub. 395, p. 260—281. Wintermyer, A. M. and Kinter, E. B., 1955, Dispersing agents for particle-size analysis of soils: Highway Research Board Bull. 95, Natl. Acad. Sci., Natl. Research Council Pub. 343, p. 15—26. INDEX Page Anions, adsorption _________________________________________ 237, 241, 243,246, 252, 253 valence ................................................................... 253 Bentonite, dispersion, in distilled water _______________________________________ 243 dispersion, in medium-hard water. . . ________________________________ 243, 246 exchange complex ......................................................... 233 occurrence, Kendrick project, Casper, Wyo _______________________________ 230 Canal, irrigation, lining ................................................. 229, 230, 269 irrigation, lining, colloid size ............................................ 230, 252 lining, cost ___________________________________________________________ 230 natural sedimentation ____________________________________________ 230 Cations, behavior in solution ................................................. 253 concentration ............................................................. 253 effect of clay particles, .................................................. 237,246 hydration ................................................................ 254 mobility .................................................................. 254 sources ................................................................... 233 valenw ................................................................... 253 Clay minerals, classification __________________________________________________ 248 illite, cation exchange capacity ............................................ 250 dispersion, general characteristics ..................................... 254 in distilled water ........................................... 241, 246,248 in hard water ..................................................... 241 in medium-hard water ............................................ 248 in soft water ______________________________________________________ 241 structure ............................................................. 250 kaolinite, cation exchange capacity ..................................... 249,254 dispersion, general characteristics ..................................... 254 in distilled water _______________________________________________ 239,246 in hard water ..................................................... 241 in medium-hard water ............................................ 246 in soft water ____________________________________________________ 239,241 particle size ___________________________________________________________ 249 structure _____________________________________________________________ 249 montmorillonite, cation exchange capacity ______________________________ 249,254 dispersion, general characteristics ..................................... 254 in dilute suspensions .............................................. 256 in distilled water ............................................... 235, 237 in hard water ..................................................... 237 in soft water ...................................................... 237 249 249 249 Page Clay, water, ionized salt system ............................................ 230, 231 factors controlling dispersion. Clays, calcium-saturated ............................... 231, 233, 235, 237,239,241, 243 exchange complex ........................................................ 233 homoionic, preparation ................................................... 233 sodium-saturated _______________________________ 231, 233, 235. 237, 239, 241, 246, 248 Colorado State University .................................................. 230, 231 Dispersion index ................................................... 233, 237, 241, 246 computation ........................................................ 235, 256-269 Osmotic pressure ............................................................. 254 Phosphate deflocculents, efiect on illite _____________________________ 241, 243, 246, 248 efiect on kaolinite ______________ ..- 239, 241, 246, 248 montmorillonite. ___ 237, 238, 239, 243 Volclay..- ...... 243, 246 Stokes’ law. See Tests, hydrometer. Tests, conclusions .......................................................... 248, 270 filter-loss, limitations ___________________________________________________ 269, 270 procedure ............................................................ 269 results ................................................................ 270 Volclay, as a filter cake ............................................... 270 hydrometer, advantages and disadvantages _______________________________ 251 grain-size measurement ............................................... 250 possible source 01 error ................................................ 251 Stokes’ law used ...................................................... 250 results and discussion ..................................................... 234 treatment with deflocculents, temperature and time efiect ................ 234 x-ray analysis _____________________________________________________________ 237 Volclay. See Tests, filter-loss. Water, from Trl-County Canal, Nebr ______________________________________ 233, 243 hardness and softness determined ....................................... 231,255 sample prototype ....................................................... 233, 243 273 E 75' x94; ;#Z;:/ H Geology of Southeastern Ventura Basin Los Angeles County California GEOLOGICAL SURVEY PROFESSIONAL PAPER 334—H «gsm or 622% . 9y 7__ MAY 10 1962 x '4» \s ‘ ’7’ 8615ij $35: Geology of Southeastern Ventura Basin Los Angeles County California By E. L. WINTERER and D. L. DURHAM SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY GEOLOGICAL SURVEY PROFESSIONAL PAPER 334—H A stuaj/ of tee strutz'grup/ty, structure, and occurrence of oil in t/ze lute Cenozoic Veuturcz tam UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1962 UNITED STATES DEPARTMENT OF THE INTERIOR STEWART L. UDALL, Secretary GEOLOGICAL SURVEY Thomas B. Nolan, Director For sale by the Superintendent of Documents, US. Government Printing Office Washington 25, D.C. CONTENTS Abstract ___________________________________________ Introduction _______________________________________ Purpose and scope ______________________________ Fieldwork ______________________________________ Acknowledgments _______________________________ Geography __________________________________________ Climate _______________________________________ Vegetation _____________________________________ Santa Clara River ______________________________ Relief _________________________________________ Human activities _______________________________ Physiography ______________________________________ Structural and lithologic control of drainage ________ River terraces and old erosion surfaces ____________ Present erosion cycle ____________________________ Landslides _____________________________________ Stratigraphy _______________________________________ Pre-Cretaceous rocks ____________________________ Tertiary system ________________________________ Eocene series _______________________________ Fossils _________________________________ Age and correlation _____________________ Upper Eocene to lower Miocene ______________ Sespe(?) formation ______________________ Miocene series ______________________________ Topanga(?) formation ___________________ Mint Canyon formation _________________ Nomenclature ______________________ Distribution ________________________ General lithology ___________________ Thickness __________________________ Stratigraphic relations and age _______ Stratigraphy and lithology in mapped area _____________________________ Environment of deposition ___________ Modelo formation _______________________ Stratigraphy and lithology ___________ Fossils and age _____________________ Upper Miocene and lower Pliocene ____________ Towsley formation ______________________ Distribution ________________________ Distinction from Modelo formation- - _ Previous assignment ________________ Stratigraphy and lithology ___________ Santa Susana Mountains ________ San Fernando Pass and Elsmere Canyon area _________________ North of the San Gabriel fault- _ _ Subsurface development _________ Fossils _____________________________ Santa Susana Mountains ________ Elsmere Canyon region __________ North of San Gabriel fault _______ Environment suggested __________ Page 275 276 276 276 276 278 278 278 27 8 278 278 278 279 279 281 281 281 282 282 282 283 283 283 283 283 283 284 284 284 284 284 284 285 286 286 287 287 287 287 287 288 288 289 289 291 293 293 293 293 295 306 306 Stratigraphy—Continued Tertiary system—Continued Pliocene series ______________________________ Pico formation _________________________ Stratigraphy and lithology ___________ Newhall—Potrero area ____________ Newhall—Potrero oil field to East Canyon ______________________ Mouth of East Canyon to San Fer- nando Pass __________________ San Fernando Pass to San Gabriel fault ________________________ Santa Clara River to Del Valle fault ________________________ Del Valle fault to Holser fault___ _ Area north of Holser fault _______ Fossils _____________________________ Foraminifera ___________________ Megafossils ____________________ Upper Pliocene and lower Pleistocene _________ Saugus formation _______________________ Definition and subdivision ___________ Stratigraphy and lithology ___________ San Fernando Valley ____________ Area south of San Gabriel and H01- ser faults ____________________ Fossils _____________________________ Age of youngest formations of mapped area____ Towsley formation ______________________ Pico formation _________________________ Saugus formation _______________________ Quaternary system ______________________________ Pleistocene series ___________________________ Terrace deposits ________________________ Alluvium ______________________________ Turbidity current features in the Tertiary rocks____ ‘ Nature of turbidity currents _________________ Interrupted gradations ______________________ Angular fragments in sandstone ______________ Irregular contacts ___________________________ Intraformational breccias _______________ . _____ Current marks ______________________________ Slump structures and convolute bedding _______ Structure __________________________________________ Regional relations _______________________________ Structural history _______________________________ Pre-Late Cretaceous _________________________ Late Cretaceous and early Tertiary ___________ Early and middle Miocene ___________________ Late Miocene ______________________________ Pliocene and early Pleistocene(?) _____________ Pleistocene ________________________________ Late Pleistocene ____________________________ III Page 308 308 309 309 ~ 310 311 311 312 312 312 313 313 315 317 317 317 317 317 318 319 320 320 321 322 322 322 322 323 323 323 325 325 326 327 330 332 334 334 334 334 334 335 335 335 335 335 IV Structure—Continued Structural details _______________________________ Santa Susana Mountains and San Fernando Valley ___________________________________ Santa Clara River to San Gabriel fault ________ San Fernando Pass and Newhall area _________ San Gabriel fault to north edge of mapped area- - Geologic history ____________________________________ Occurrence of oil ____________________________________ Oil fields _______________________________________ Newhall ___________________________________ PLATE 44. 45. 46. 47. 48. 49. FIGURE 49. 50. 51. 52. 53. 54. 55. TABLE Pico Canyon area _______________________ De Witt Canyon area ___________________ Towsley Canyon area ____________________ Wiley Canyon area ______________________ Rice Canyon area _______________________ Page 335 335 336 336 337 337 340 340 340 341 342 342 342 342 Occurrence of oil—Continued Oil fields—Continued Newhall—Continued Tunnel area ____________________________ Elsmere area ___________________________ Whitney Canyon area ___________________ Newhall townsite _______________________ Placerita ___________________________________ Newhall-Potrero ____________________________ Del Valle __________________________________ Ramona ___________________________________ Castaic Junction ____________________________ Wildcat wells ___________________________________ Potential petroleum resources- ___________________ Selected references __________________________________ Index _____ ILLUSTRATIONS [Plates in pocket] Geologic map. Geologic sections. Stratigraphic sections in the Towsley forma- tion. Stratigraphic sections in the Pico formation. Distribution of Foraminifera in the Pico for- mation, Pico Canyon section. Distribution of Foraminifera in the Pico for- mation, Towsley Canyon, and other sections. Index map ______________________________ Erosion and river-terrace surfaces on the north side of the Santa Clara River ______ Concretionary sandstone unit in the Towsley formation ________________________ - - - _ - Contact of the Towsley formation with quartz diorite of the pre-Cretaceous base- ment complex _________________________ Large-scale sets of cross-strata in the lower part of the Pico formation ______________ The relation between contemporary deposits of the Saugus and Pico formations _______ Conglomerate, sandstone, and siltstone beds of the Pico formation ___________________ Fossils from Eocene rocks __________________ . Foraminifera from the Modelo formation- - - - . Foraminifera from the Towsley formation-___ . Fossils from the Towsley and Pico formations- . Geographic range of Recent species related to fossils from the Towsley formation ________ . Distribution of varieties of Calictmtharus humerosus (Gabb) _______________________ Page 277 280 290 292 294 309 311 FIGURE 56. 57. 58. 59. 60. 61. 62. 63. 64. 65. 66. 67. 68. TABLES Page 283 288 295 296 308 321 TABLE 7. 8. 9. 10. 11. Soft greenish—gray siltstone and fine-grained sandstone beds of the Sunshine Ranch member of the Saugus formation _________ Conglomeratic sandstone of the Saugus for- mation _______________________________ Sandstone and siltstone beds in the Towsley formation _____________________________ Types of deformation of sandstone-siltstone interface resulting from unequal loading, by which load casts are formed __________ Load casts in the Towsley formation _______ Load casts in the Towsley formation _______ Intraformational breccia in the Towsley formation _____________________________ Large angular erratic block of shale in the Towsley formation _____________________ Current bedding in the Towsley formation- _ Current lineations in the Towsley formation- Slump structure in the Towsley formation-- Paleogeography of beginning of late Miocene time __________________________________ Paleogeography of part of late Miocene (late Mohnian) time ------------------------ Oil- and gas-producing zones in four major fields west of Newhall ___________________ Oil —production statistics for period January 1* June 30, 1953 __________________________ Oil- and gas-producing zones in Del Valle field- List of wildcat wells including all known pros- pect wells drilled outside of productive oil fields prior to June 30, 1953 ______________ Fossil localities ----------------------------- Page 343 343 344 344 344 345 345 346 347 347 347 357 363 Page 318 319 326 326 327 328 328 329 331 333 333 339 339 Page 341 341 346 348 360 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY GEOLOGY OF SOUTHEASTERN VENTURA BASIN, LOS ANGELES COUNTY, CALIFORNIA By E. L. WINTERER and D. L. DURHAM AB STRACT The late Cenozoic Ventura basin, Ventura and Los Angeles Counties, Calif., is an elongate sedimentary trough which, to- gether with its deformed structures, trends approximately east- west. The mapped area of this report lies entirely within Los Angeles County. Most of the southeastern part of the Ventura basin is in the Santa Clara River watershed. 01d high-level erosion surfaces, some more than 3,000 feet in altitude, and younger, topo- graphically lower river—terrace surfaces and deposits are con- spicuous. The river valley is now partly filled with alluvium which is being dissected during the present cycle of erosion. Pre—Cretaceous basement rocks exposed in the San Gabriel Mountains are the oldest rocks in the area. These rocks include the fractured schist, gneiss, quartzite, and marble 0f the Placerita formation of Miller (1934) and also the somewhat gneissic Rubio diorite of Miller which intrudes them. Both of these rock units are intruded by quartz plutonites ranging in compo- sition from granite to quartz diorite. Outside the mapped area a large body of anorthosite and norite makes up part of the basement rocks. Within the mapped area, the oldest sedimentary rocks are well-indurated sandstone and siltstone containing a marine fauna indicative of a middle Eocene or early late Eocene age. Some wells in the area have penetrated several thousand feet of Eocene rocks. Some wells drilled near San Fernando Pass have penetrated varicolored unfossiliferous beds that overlie Eocene rocks and are overlain by upper Miocene marine strata. These vari- colored rocks have a thickness of nearly 2,000 feet but do not crop out in the area. They do not appear to interfinger with the overlying marine beds and are tentatively correlated with the Sespe formation of late Eocene to early Miocene age. Near the Aliso Canyon oil field, wells have been drilled through as much as 2,500 feet of strata; predominantly sandstone but including a layer of amygdaloidal basalt, correlated tentatively with the Topanga formation of middle Miocene age. Rocks representing the Luisian (middle Miocene) stage of Kleinpell overlie these strata. The nonmarine Mint Canyon formation of late Miocene age is present in the northeastern part of the area, north of the San Gabriel fault. This formation consists of fluviatile sandstone and conglomerate and lacustrine siltstone and tuff and has a thickness of at least 4,000 feet north of the mapped area. The marine Modelo formation, of late middle and late Miocene age, is exposed in the southwestern part of the area but is not present in the subsurface section east of Newhall and Saugus and is not recognized north of the San Gabriel fault. Westward from the town of Newhall, its thickness increases to at least 5,000 feet at the Ventura County line. The formation is chiefly siltstone, mudstone, and shale, but it also contains sandstone and conglomerate. The Towsley formation, of late Miocene and early Pliocene age, overlies and in places interfingers with the Modelo formation. Near Newhall and San Fernando Pass it overlaps the Modelo formation and lies directly on the Sespe(?) formation and on Eocene and pre-Cretaceous basement rocks. The formation ranges in thickness from about 4,000 feet in the southwestern part of the area to 0 Where it is overlapped by younger rocks to the east. In the Santa Susana Mountains it grades upward into the Pico formation. Beds assigned to the Towsley forma- tion rest unconformably on the Mint Canyon formation north of the San Gabriel fault. The Towsley formation consists chiefly of interfingering lentic- ular beds of sandstone, mudstone, and conglomerate. Clasts in the conglomerate beds are of rock types found to the east and northeast in the San Gabriel Mountains. Sandstone and conglomerate beds in the Santa Susana Mountains contain many sedimentary structures, including graded beds, load casts, intraformational breccias, current ripples and lineations, slump structures, and convolute bedding. At several localities graded sandy beds contain mixed assemblages of shallow— and deep- water mollusks, the latter representing depths of more than 600 feet. The sedimentary structures and fossils, taken together, indicate that marine turbidity currents were major factors in the transportation and deposition of the sediments that now constitute the Towsley formation. A study of the molluscan fauna of the Towsley formation indicates that the shallow-water species are allied to Recent faunas now living south of the lati- tude of the Ventura basin. The Pico formation, of Pliocene age, is distinguished from the Towsley formation largely by its soft olive-gray siltstone that generally contains small limonitic concretions. In the area near San Fernando Pass, the Towsley and Pico interfinger, but farther to the northeast there is an unconformity at the base of the Pico. Although the Pico is marine, it interfingers with brackish-water and nonmarine beds belonging to the basal part of the overlying Saugus formation. Near the west edge of the area it is at least 5,000 feet thick. Most of the sedimentary structures suggestive of turbidity currents found in the Towsley are also present in the lower part of the Pico in the Santa Susana Mountains. Abrupt lateral gradations from siltstone to sand- stone and conglomerate are common in the Pico. 275 276 Molluscan faunas of mixed depth assemblage in the Pico formation suggest turbidity currents as a mode of deposition. The southern affinities of the shallow-water species suggest that the surface water temperature in the Ventura basin during the Pliocene was somewhat warmer than that prevailing now in the Pacific Ocean near Ventura. The northern affinities of the deeper water species indicate that the water was cold enough at depth to accommodate them. The vertical sequence of fora- miniferal faunas suggests a gradual shoaling from water depths of about 2,500 feet in the deeper parts of the basin at the be- ginning to very shallow water depths at the close of Pico deposi- tion. Lateral changes in foraminiferal faunas, shown by the crossing of foraminiferal correlation lines (water-depth lines) by lithologic units deposited by turbidity currents (time lines), indicate that at any one time the water was shallowest near Newhall and became deeper toward the west. Turbidity cur- rents deposited coarse sand and gravel on this west-sloping bottom. The Pico formation grades upward and laterally into the Saugus formation, of Pliocene and early Pleistocene age, which consists of interfingering shallow-water marine, brackish-water, and nonmarine beds that in turn grade into exclusively non- marine beds. Sandstone, conglomerate, and reddish— and greenish-gray siltstone are characteristic of the formation. South of San Fernando Pass it is practicable to divide the Saugus formation into a lower member, the Sunshine Ranch member, characterized by greenish—gray siltstone beds, and an upper, coarser grained member. In this area the marine and brackish- water Sunshine Ranch member is separated from the upper nonmarine member by an unconformity. North and west of San Fernando Pass, the division of the Saugus formation into members is difficult, if not impossible. The thickness of the Saugus formation probably exceeds 7,000 feet in the west-central part of the area. Stream-terrace deposits of late Pleistocene age are very similar lithologically to parts of the Saugus formation. East of Saugus these deposits are as much as 200 feet thick and lie with marked unconformity on the Saugus formation. The Ventura basin is a narrow trough, filled with sedimentary rocks, whose axis approximately coincides with the Santa Clara River valley and the Santa Barbara Channel. The narrow troughlike form did not begin to develop until near the begin- ning of the Miocene epoch. Near the south margin of the Ventura basin the thick section of upper Cenozoic rocks has been thrust southward along the Santa Susana fault toward the older rocks of the Simi Hills. The southeastward—trending San Gabriel fault transects the northeastern part of the basin. Dis- similar facies in ‘the pre-Pliocene rocks on opposite sides of this fault indicate a long period of continued movement along it. The major folds and faults between the San Gabriel and Santa Susana faults trend northwestward; most of the faults are southward-dipping reverse faults. The first successful oil well in the area was completed in 1875. Most of the early development was in the Newhall oil field along the Pico anticline and near the southeast margin of the basin near the San Gabriel Mountains. Interest in the petroleum possibilities of the region was renewed with the discovery of the Newhall—Potrero oil field in 1937. Discovery of the Del Valle oil field (1940), Ramona oil field (1945), Castaic Junction oil field (1950), and a second period of development in the Placerita oil field (1948) followed. More than 80 million barrels of oil were produced from wells in the area, and at least 236 nonpro- ductive exploratory wells were drilled prior to June 30, 1953. SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY INTRODUCTION PURPOSE AND SCOPE The Ventura basin (fig. 49) has long been one of the important oil-producing districts of California. The eastern part of the basin includes some of the oldest oil fields in California and also several of those most recently discovered. Since 1937 several new fields have been discovered in the area and undoubtedly more oil remains to be found. The first work of the Geological Survey in this region was by Eldridge and Arnold (1907); Kew (1924) de- scribed part of the region studied by Eldridge and Arnold as well as much of the remainder of the Ventura basin. Since the publication of Kew’s report, and especially since 1937 when the Newhall-Potrero oil field was discovered, interest in the eastern part of the Ventura basin has steadily increased. The present report includes a small part of the area of Kew’s report but on the larger scale of 1:24,000 (pl. 44; fig. 49). Attention is focused particularly on the surface stratigraphy. Subsurface data were col- lected where available, but they are necessarily incomplete. FIELDWORK Fieldwork was begun by Winterer in the summer of 1949 and carried on a few days each month until the summer of 1950, after which work was more continuous. Durham joined the project in the summer of 1951 and fieldwork was completed in September 1952. The areas mapped by each author are shown on an index map on plate 44. T. R. Fahy assisted in the collection of most of the foraminiferal samples. The geology was mapped on aerial photographs, a few of which were 1:24,000 contact prints but most of which were 1: 10,000 enlargements. The data on the photographs were transferred to the topographic base map, which consists of enlargements of the following Geological Survey 6-minute quadrangle maps: Pico and Newhall and parts of Santa Felicia Canyon, Castaic, Saugus, Humphreys, and Sylmar, all in Los Angeles County. The stratigraphic sections of the Towsley formation (pl. 46) were measured with plane table and alidade; the stratigraphic sections of the Pico formation (pl. 47) were measured with tape and Brunton compass. ACKNOWLEDGMENTS Geologists on the staffs of oil companies operating in the region made much information available. Par- ticular acknowledgment is due to E. J. Bartosh of the Bankline Oil Co. ; T. L. Macleod of the Bell Petroleum GEOLOGY 0F SOUTHEASTERN VENTURA BASIN 120° 277 119° 118. 35'? Pt Conception NTA """ F odSunland ernan o S A BA EBA RA I I I I .............. ...... San Fernando Valley C194 ' 4, San Miguel “122 LOS ANGELES < 5 Island _ , 34° (“f/2 W wvAnacapa WSanm Monica Santa Rog) W Island Island P A ,’ O / Redondo Beach / m ) EXPLANATION Ventura basin Area shown on geologic map (pl.44) San Nicolas Island / San Pedro 0 O C’ 6 A Santa Barbarat9 N Island Santa Catalina Island 10 O 10 20 30 MILES L lllllllll I I I l FIGURE 49.—Index map, showing area of report and general outline of Ventura basin. 00. ; K. 8. Bishop and W. H. Corey of the Continental Oil 00.; R. S. Ballantyne, Jr., of the General Explo- ration Co. of California; D. B. Flynn, B. 0. Lupton, and V. M. Smith of the General Petroleum Corp.; Hunter Yarborough, Jr., of the Humble Oil and Re- fining 00.; W. McKersey, formerly of the Kern Oil 00., now with the Seaboard Oil 00.; G. P. Gariepy and R. 0. Shelton of the Ohio Oil 00.; Rollin Eckis, M. L. Natland, and W. T. Rothwell, Jr., of the Richfield Oil 00rp., L. S. Chambers of the Seaboard Oil 00.; V. L. Crackel and P. L. Hayes of the Southern California Petroleum Corp; 0. W. Gilbert, W. H. Holman, J. B. Long, and E. H. Rader of the Standard Oil Co. of California; J. W. Sheller of the State Exploration 00.; R. J. Hindle, J. S. Loofbourow, and Robert Maynard of the Sunray Oil Corp.; G. Y. Wheatley of the Superior Oil 00.; F. D. Bode of the Texas 00. ; R. F. Herron, formerly of the Texas 00., now with M. J. M. and M. Oil 00.; J. 0. Hazzard and G. H. Quick of the Union Oil Co. of California; and P. H. Gardett, consulting geologist. M. N. Bramlette, of Scripps Institute of Oceanog- raphy, who supervised the work in its early stages and who accompanied the authors in the field on several occasions, ofl’ered many valuable suggestions about strat— igraphic problems ,and examined several foraminiferal faunas. The micropaleontologic work was begun by Fahy and completed by Patsy B. Smith. Remains of a land mammal were identified by Remington Kellogg of the U.S. National Museum. The megafossils listed in this report were identified by W. P. Woodring, who was assisted by Ellen J. Trumbull and J. G. Vedder. 278 Woodring visited the field on several occasions to dis- cuss stratigraphic problems and also made a special study of the Calicantharus humerosus group. The courtesy of the Newhall Land and Farming Co. and of the many other land owners and residents in the region in granting access to their properties is gratefully acknowledged. GEOGRAPHY Most of the mapped area is in the eastern part of the Santa Clara River drainage basin. The south- eastern part of the area is in the part of the Los Angeles River drainage area called the San Fernando Valley. CLIMATE The eastern part of the Santa Clara River valley is a semiarid region having a mean annual rainfall of about 16 inches. The rain is seasonal——most of it falls during the winter months. Daily and seasonal records for the region show a wide temperature range. Temperatures on summer days often are above 100 °F and temperatures on winter nights sometimes fall a few degrees below freezing. VEGETATION The vegetation varies with the underlying rock, the altitude, and the orientation of the slope. Areas underlain by fine-grained rocks commonly develop a soil that supports grass, a sage community, and oak and California walnut trees. Sandstone and conglom- erate are commonly covered by the heavy brush locally called Chaparral, which is especially heavy on north slopes. Bigcone-spruce trees grow at higher altitudes in the vicinity of San Fernando Pass. SANTA CLARA RIVER The Santa Clara River flows from its source on the north side of the western San Gabriel Mountains to the coast south of Ventura. The drainage area upstream from the water-stage recording station at the US. Highway 99 bridge 4 miles west of Newhall is about 355 square miles. The largest tributaries are west of Highway 99; they enter the river from the north. These tributaries include Piru, Sespe, and Santa Paula Creeks, whose combined drainage area and discharge are much greater than that of the main river upstream from the mouth of Piru Creek. The Santa Clara River bed is commonly dry in summer. All its tributaries in the mapped area are intermittent streams. The average annual discharge of the river for the 16-year period from October 1929 to September 1945, as measured at the US. Highway 99 bridge water-stage recording station, was 19.7 cfs (cubic feet per second). The maximum discharge measured there during that SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY period was 24,000 cfs on March 2, 1938, during a time of severe flood in southern California. RELIEF The eastern Santa Clara River valley region is one of bold relief. In the mapped area, the highest alti- tude, 3,747 feet, is in the Santa Susana Mountains. The western San Gabriel Mountains rise to an altitude of 3,119 feet within the mapped area and to altitudes of more than 4,000 feet only a short distance farther east. The Santa Clara River descends from 1,385 to 805 feet in the mapped area. HUMAN ACTIVITIES San Fernando Pass is located at the west end of the San Gabriel Mountains and is a convenient geo- graphical boundary between them and the Santa Susana Mountains. The pass has been a natural entrance to the mountain-bordered Los Angeles region since early times. Evidence may still be seen of the pioneer wagon road through the pass. US. Highways 99 and 6, connecting Los Angeles with the San Joaquin Valley and the Mojave Desert, respectively, and the Southern Pacific railroad’s main line from Los Angeles to the San Joaquin Valley, now traverse the pass area. The Los Angeles Department of Water and Power aqueduct from Owens Valley, as well as several power lines and pipe lines, use the San Fernando Pass area as a con— venient gateway to the Los Angeles region. In addi— tion to the highways and railroad already mentioned, a highway and railroad follow the Santa Clara River valley to the coast. Ranch, oil field, and forestry roads provide access to most of the area. The towns of Newhall and Saugus, both along the Southern Pacific railroad, are the chief centers of popu- lation within the mapped area. The Santa Clara River valley, much of which is irrigated, supports farms, orchards, and cattle ranches. Numerous oil fields add to the economy of the region. PHYSIOGRAPHY The Santa Clara River follows the major structural depression of the region. The pattern of tributary streams and the shapes of the ridges are commonly de- termined by the varying resistance to erosion of the rocks. Old erosion surfaces and river terraces are conspic- uous. These may be conveniently divided into two groups: the older, topographically higher surfaces, rem- nants of which have been preserved in scattered local- ities; and the younger, topographically lower terrace surfaces, which are found along the Santa Clara River and its tributaries. The high surfaces extend to alti- tudes of more than 3,000 feet on the Santa Susana GEOLOGY OF SOUTHEASTERN VENTURA BASIN Mountains. The younger terrace surfaces are at alti- tudes as low as 900 feet along the river at the western border of the area and as high as 1,900 feet on the hills near the eastern border. Many small streams of the Santa Clara River drain- age have their sources near the crest of the Santa Susana Mountains. Some of these streams have been be- headed by other streams which originate on the oppo— site side of the mountains and are tributary to the San Fernando Valley drainage. Landslides are conspicuous. They are found in the Santa Susana Mountains on steep slopes underlain by shale and siltstone and in the northwestern part of the mapped area on high steep hills. STRUCTURAL AND LITHOLOGIC CONTROL OF DRAINAGE Because the Santa Clara River valley is developed more or less along the axial trend of the Ventura basin, the rocks exposed near the center of the valley are gen- erally younger and less resistant to erosion than are those nearer the basin margins. The structural de- pression of the basin, together with its attendant faults, folds, and the accumulation of easily eroded younger rocks near the center, is largely responsible for the po— sition of the valley. The pattern of the tributaries to the Santa Clara River in several parts of the mapped area is controlled by lithology and structure. Sedimentary rocks ex- posed on the northeastern flank of the Santa Susana Mountains have a strike nearly parallel to the trend of the mountains themselves. The thicker conglomerate and sandstone units are represented by strike ridges and the thicker siltstone units have been eroded to form the intervening valleys. Dip and antidip slopes are commonly almost equally steep so that the longitudi- nal or strike valleys are narrow canyons. Some major drainage lines, such as Pico Canyon, begin in amphi- theaters high on the north side of the main ridge of the Santa Susana Mountains, follow the strike for distances as much as 1 mile, and then alternately cut across the strike or follow it until they reach the lowland region west of N ewhall. The canyons are narrowest where they cut through strike ridges. Towsley Canyon, for example, is deepest and narrowest where it crosses a unit of hard sandstone and conglomerate with a se- quence of less resistant, finer grained rocks in the middle. The gorge crosses the resistant rocks, makes a right- angle bend to follow the softer intermediate beds along the strike for 400 feet, and then turns again at right angles to cross the remaining hard beds. The positions of several valleys seem to be deter- mined in part by the locations of major faults. In the northwestern part of the mapped area, San Martinez 279 Chiquito Canyon follows closely the trend of the Holser fault for about 2 miles before making a bend, crossing the fault, and joining the Santa Clara River. Simi- larly, the course of the upper part of San Martinez Grande Canyon may have been originally determined by the position of the nearby Del Valle fault. The canyon parallels this fault for nearly 2 miles before crossing it to join the Santa Clara River. RIVER TERRACES AND OLD EROSION SURFACES Several river-terrace levels and old erosion surfaces are exposed along the Santa Clara River and its trib- utaries. The hills north of the river between Bouquet Canyon and the eastern border of the mapped area are marked by remnants of seven distinct river terraces. Figure 50 shows diagrammatically the spatial distri- bution of these terrace remnants and their correla- tion. The terrace surfaces are formed on both river- terrace deposits and rock of the Saugus formation. The geologic map (pl. 44) shows the extent of river- terrace deposits but not necessarily the extent of sur- faces formed on these deposits. Inasmuch as the river-terrace remnants depicted on figure 50 have only a thin veneer of terrace deposits, the limits of the de- posits as shown on the map approximate closely the extent of the terrace surfaces as well. The lowest terrace surface is about 40 feet and the highest more than 400 feet above the present river bed. These ter- race surfaces are generally nearly planar with gentle slopes toward the river, but some steepen against the hills. The highest terrace surface extends back into the highlands up gently sloping valleys unrelated to the present drainage. Surfaces reconstructed from the remnants of various terrace levels slope in approx- imately the same direction as the present river valley. A comparison of the gradient of the river that formed the terraces with the gradient of the present river is difficult to make because of the limited extent and distribution and the possible deformation of these ter- race remnants; however, the gradients of the streams that formed the two highest terrace levels appear to have been flatter in this area than that of the present river (fig. 50). Remnants of an old erosion surface are found above the river terraces north of the Santa Clara River. This surface is on and near the tops of the highest hills and is as much as 520 feet above the present river bottom. South of the Santa Clara River, directly opposite the area of extensive terraces, only one terrace remnant is preserved. No correlation between it and those north of the river is apparent. Between Dry Canyon, just west of Bouquet Canyon, and Castaic Valley, no terraces are present along the north side of the central, alluvium-filled valley of the Santa Clara River. SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 280 .35. 25%;. an @886... 2a $93.3 So on. «o none .8. voted. on has .35 macaw anbmékoc one. .23 one a. 258 295 .S‘Ewfiu one 3 hgfiqflm 525m .3355. scuba”. ac mafia—9:8 can. .52.. on» $28: 83:5 on”. «o wave 2: 3.5.852 Hawks an”. 3 Eng 53°. 23 can .52. 23 Bob “7.053. 83:; 25 Ho «mg 25 353.59. .5923 new» .8 Swan. .899. 9: .53.. 95 @338 233 a man 23:38 :30 ms £05885 .mnnn. JESSE on: 8 #25 on» “not on» «o 8365... 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E, 88' \ ...\s a x 88 l I \l 13%». mulmhm.‘ ucouloml 00h «I | Dot” Com.” 1 l 00w.” A? _w>w_ $2.2 an... 9: w>onm 885m c285 Eo oomH coma "El/GT VHS 3A08V 1.33:4 NI ‘NOllV/GWE GEOLOGY OF SOUTHEASTERN VENTURA BASIN Remnants of several terrace and erosion surfaces are present east of Saugus and N ewhall, in La Placerita Canyon and along Newhall Creek. The most exten- sive of these surfaces is on the hills north and south of the lower part of La Placerita Canyon, where its lowest altitude is about 150 feet higher than the altitude of the adjacent canyon bottom. This surface increases in altitude to merge with an old erosion surface on the hills in the vicinity of the Placerita oil field. The highest part of this erosion surface has an altitude of over 1,900 feet, or more than 500 feet above the lowest part of the extensive surface. At its western end, the terrace surface is formed on a thick accumulation of river-terrace material but toward its eastern end it is underlain by only a thin mantle of terrace material covering rocks of the Saugus formation. This same surface is correlated with the extensive surface on the west side of the wide valley west of Newhall and Saugus and with surfaces of less extent near the Castaic Junction and Del Valle oil fields. In La Placerita Canyon, near US. Highway 6, the three lowest terrace levels are about 50, 125, and 175 feet above the adjacent canyon bottom. Along the Santa Clara River several somewhat similar terrace levels can be distinguished below extensive higher terraces. Just east of Saugus are remnants of two small valleys formed during an earlier cycle of erosion. The lower parts of these valleys are being destroyed by streams of the present erosion cycle, but their upper parts are still preserved. A nearly undissected erosion surface, cut on the crystalline rocks of the western flank of the San Gabriel Mountains in the vicinity of Elsmere Canyon, is a resurrected pre-Pliocene surface exposed by the recent removal of the sedimentary rock cover. The Santa Susana Mountains are made up of a con- tinuous northwestward-trending ridge with steep, deeply dissected flanks. The relatively narrow summit region has rounded knolls and gentle slopes; streams there have gentle gradients but steepen markedly Where they begin to descend the mountain flank. At one time these streams must have had gentle gradients throughout their length comparable to those now found along the uppermost parts of their courses. The crest of the Santa Susana Mountains is a remnant of the old surface across which they flowed. At the head of Rice Canyon, near the eastern end of the mountains at an altitude of 2,750 feet, boulders of granitic rocks rest on the Modelo formation. These boulders are the remains of a river—terrace deposit— the oldest such deposit recognized in the area. At other places on the flanks of the mountains, gently sloping bench areas and accordant ridge levels give 281 further evidence of the former existence of an old surface of erosion. PRESENT EROSION C YCLE The Santa Clara River is a graded stream. The river normally occupies only a comparatively narrow, sinuous channel, but during floods it may cover its entire flood plain. The Santa Clara River valley in this area and the val- leys that are tributary to it were alluviated just prior to the present cycle of erosion. The river and its tribu- taries now flow in channels that have been cut as much as 25 feet into the older alluvial deposits. At a point about 1 mile west of the Los Angeles-Ventura County line the Santa Clara River valley floor narrows abruptly. According to local residents, bedrock was exposed con- tinuously across the river channel at this point immedi- ately following a flood in 1938. Along the river between Bouquet Canyon and Castaic Creek, broad paired alluvial terraces are about 5 feet above the present river bed. This terrace level merges into the alluvium of the present river bottom both upstream and down- stream from the area of its distinct development. At the mouths of numerous small valleys and gullies, _ fans with comparatively steep slopes are forming on the surface of the older alluvium that veneers the floors of the Santa Clara River valley and its major tribu- taries. LANDSLIDES On the flanks of the Santa Susana Mountains and in the hills in the northwestern part of the area, the shale and siltstone of the Modelo and Pico formations are exposed in steep slopes. Soil creep, slumping, and landsliding are prevalent in these areas. Many of the hills near the Del Valle and Ramona oil fields have dip slopes that are especially susceptible to movements of the superficial rock and soil cover. This has been the source of much trouble in the maintenance of oil- well drill sites and roads. STRATIGRAPHY The area described in this report includes parts of three depositional provinces; each province has a dif- ferent geologic history, but the three are now crowded close together along faults of large displacement. Northeast of the San Gabriel fault a thick succession of pre-late Miocene nonmarine strata comprising the Vasquez and Mint Canyon formations overlies pre- Cretaceous igneous and metamorphic rocks. South- west of the fault, strata of roughly equivalent age are chiefly marine. The thick conformable upper Miocene, Pliocene, and lower Pleistocene section southwest of the fault is represented northeast of the fault by a 282 greatly thinned section that contains several uncon— formities. Within the province between the San Gabriel and Santa Susana faults, the formations of late Tertiary age thin markedly and become coarser grained toward the east, where successively younger formations rest directly on the lower Tertiary and pre—Cretaceous rocks of the San Gabriel Mountains. The Modelo and the Towsley formations and the lower part of the Pico formation were deposited in a marine environment, probably at depths greater than 600 feet. During deposition of the Pico the water became gradually shallower, and the overlying Saugus formation repre- sents chiefly nonmarine conditions. The contact be- tween the Pico and the Saugus, that is, the marine- nonmarine interface, rises stratigraphically toward the west. South of the Santa Susana fault system the strata of late Cenozoic age are thin or even absent in many places, although a very thick succession of Pliocene and Pleistocene strata is present in a narrow belt along the southern margin of the San Gabriel Mountains. PRE- CRETACEOUS ROCKS The San Gabriel Mountains consist of a complex assemblage of igneous and metamorphic rocks that constitute the oldest rocks in the mapped area. No attempt was made during fieldwork to distinguish units within these rocks for this report, and statements concerning them result from incidental observations made along their contacts with the younger sedimen— tary rocks, from brief reconnaissance trips into the San Gabriel Mountains, and from a perusal of published and unpublished maps and reports on the area. The oldest exposed rocks in the mapped area are assigned to the Placerita formation of Miller (1934) and consist of schist, gneiss, quartzite, and marble. This formation of metamorphosed sedimentary rocks has been intruded by the Rubio diorite of Miller (1934) which consists chiefly of hornblende and biotite dio- rite gneiss. In many places the diorite and metamor— phic rocks are so intimately associated that separation into mappable units is impossible. Miller (1934) in— cluded such mixed rocks in his San Gabriel formation (1931). These older rocks are intricately crumpled and fractured, but some of the marble units can be traced continuously for many hundreds of feet. At some places, particularly in the Grapevine Canyon area, dark mylonite is common. Plutonic igneous rocks that are probably much young- er than the Placerita formation of Miller (1934) and the Rubio diorite of Miller (1934) intrude the older formations. These younger rocks are medium to coarse SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY grained and range in composition from granite to quartz diorite. An important unit of the sequence of pre-Cretaceous crystalline rocks, present on the northeast side of the San Gabriel fault but not present in the mapped area, is a large body of anorthosite and norite containing irregular—shaped magnetite—ilmenite bodies. This oc— currence of the anorthosite-norite suite is unique in California, with the exception of a possible occurrence in a small area in or near the San Andreas fault zone more than 100 miles southeast, on the north side of Coachella Valley. The anorthosite-norite suite is easy to recognize as clasts in conglomerates, and its presence in a conglomerate is presumptive evidence of a San Gabriel Mountains provenance, even though by a circuitous and interrupted route. TERTIARY SYSTEM EOCENE SERIES Eocene rocks exposed in a small area in Elsmere Canyon are the oldest sedimentary rocks that crop out within the area shown on the geologic map. The possible Eocene age of these rocks was first realized by Homer Hamlin, who directed W. L. Watts to the out— crops. Watts (1901, p. 56—57) noted the resemblance of these rocks to sandstones of the Sespe district now assigned to the Domengine stage, but he apparently found no fossils. The rocks consist chiefly of light— to medium-gray well—indurated fine— to medium—grained sandstone that weathers grayish orange, interbedded with medium— to dark—gray siltstone that weathers light to moderate brown, and grayish—orange conglomeratic sandstone that weathers light gray. The coarser beds are gen— erally very thick bedded. Graded bedding is a prev- alent feature in the sandstone layers. In Elsmere Canyon the Eocene rocks are in fault contact with the pre-Cretaceous crystalline rocks and are overlain unconformably by rocks of early Pliocene age. Neither the base nor the top of the Eocene sequence is exposed. Many wells near N ewhall have penetrated Eocene rocks. One well, Continental Oil Phillips 1, was drilled about 6,500 feet through Eocene rocks (pl. 45) before reaching crystalline rocks. The dip of the beds in this well is mainly between 20° and 60°, but the possibility that reverse faults repeat parts of the succession makes it difficult to estimate the thickness of the sequence. Some of the more friable sandstone beds in Elsmere Canyon are saturated with tar, and heavy oil oozes from some fractures. Shows of oil in the Eocene rocks have been reported from many wells, and a few wells in Whitney Canyon have produced high—gravity light- green oil, apparently from Eocene rocks. GEOLOGY OF FOSSILS Fossils collected from outcrops in Elsmere Canyon and from cores of two wells, Union Oil Needham 3 in sec. 12, T. 3 N., R. 16 W., and North Star Mining and Development Shepard 1 in sec. 1, T. 3 N., R. 16 W., are listed in table 1. TABLE 1.—Foss1'ls from Eocene rocks [Identifications by Ralph Stewart] Locality (table 1]) Fossil F1 F2 F3 F4 F5 GASTROPODS Amamellma cf. A. clarki Stewart _______________________ c A; lajollaensis Stewart... ?Bomzelitz'a sp _____________________ Calyptmea of. C. diagoana (Conrad Conus 1emo11d1'1'? Gabb afl“. ?0. 11111116111 “Hendon” Turner, sm. me _________ Cylischnina cf. C.ta7111'lla (Anderson and Hanna). ?Diodora stillwateremz’s (Weaver and Palmer) Egmochilus afi E. elongatus (Weaver) ..... sp ______________________________________ Ficopsis cf F.remo7rd1'1' (Gabb) _________________________ Galeodaria? sp _________________________ ?Geganiu amoldi (Dickerson). Harp (1 sp __________________ Perissolaz? n. sp ___________ Pleurotomid ______ Sinum? s ?Solarz'ella dibitata Hanna_. ?Surculites sp _________________________ Tomatellaea aff. ?T. vacavillemz’s Palms .. Turritella sp ______________________________ SOAPHOPO D Dentalium sp ___________________________________________ PELE CYPODS Brachz'domes of. B. cowlitzmsés (Weaver and Palmer)... Corbula of. C'. parilis Gabb ............................. ?0. sp .................................................. C'uszn'daria n. Sp ........................................ 01111 of G.te111a Gabb.. ._ Jupitaria? sp ___________________ Macrocalliata of. M. horm’i (Gab M1ltha cf. M. gyrata (Gabb) .......... Nemocardium cf. N. linteum (Conrad) __________________ Ostraea sp ______________________________________________ ?Pitar califomianus (Conrad). .._ P. 11111184111118 (Conrad Plagiocardium (Schedocardia) of P. brewe Propeamussium sp ............. Saccella sp ............................................. Solen? sp ......... ?Spondz/lus sp ......... ?TTaras politus (Gabb). Tellimz of. T. longa Gabb_. __ of. T. soledadensis Hanna ........................... Teredo sp.? ............................................. Venericardia n. sp ...................................... ECHINOIDS Cassiduloid _________________________________________________ X _______________ Schizasterl....__.____.__._._.__.__...‘. ___________________________ X ..... ? Spatangoid _______________________________________________________ >< .......... AGE AND CORRELATION According to Stewart (written communication, 1952) : The fauna is comparable to that of the Santiago formation of the Santa Ana Mountains (Woodring and Popenoe, 1945) and is probably middle Eocene or lower part of the upper Eocene. This age determination agrees fairly well with that based on the Foraminifera, that is, the B—1 zone of Laiming reported from cores of some wells in this area. UPPER EOCENE 'I‘O LOWER MIOCENE SESPEU) FORMATION Numerous wells in the area between San Fernando Pass and Newhall have penetrated a sequence of un- SOUTHEASTERN VENTURA BASIN 283 fossiliferous light-gray, green, red, and bluish sandstone, siltstone, and claystone that does not crop out anywhere in the region (pl. 45, sections A—A’, B—B’). In wells that were drilled through this sequence the variegated beds directly overlie Eocene rocks. These beds of supposed continental origin are overlain in the Tunnel area of the Newhall oil field by lower Pliocene marine strata and farther west by marine strata representing the Delmontian and upper Mohnian stages of Kleinpell (1938). So far as the writers know, no evidence of interfingering between the variegated beds and the marine upper Miocene beds has been discovered. The sequence ranges in thickness from nearly 2,000 feet at the British American Oil Edwina 1 well in sec. 11, T. 3 N., R. 16 W., to 0 between the Tunnel area and Elsmere Canyon (pl. 45, section A—A’). In the past, these variegated beds have been corre- lated with the Mint Canyon formation of late Miocene age, but at least two considerations are opposed to this correlation. First, the apparent lack of interfingering with upper Miocene rocks and the absence of similar strata in a thick middle Miocene through lower Pliocene outcrop section suggest the beds are not only post— middle Eocene but pre-middle Miocene. Second, the lithology of the variegated beds, especially the presence of red beds and the bluish-green montmorillonitic clay, is not typical of the Mint Canyon formation; further— more, the Mint Canyon formation is exposed only north of the San Gabriel fault. Crowell (1952a, p. 2026— 2035) advanced several arguments in favor of a post- Mohnian right-lateral displacement of from 15 to 25 miles on the San Gabriel fault. If Crowell’s hypothesis is correct, the main area of deposition of the Mint Canyon formation during middle Miocene time would have been many miles to the northwest of Newhall. The stratigraphic relations and the lithology of the con- tinental beds make a correlation with the Sespe forma- tion of late Eocene to early Miocene age seem much more likely than a correlation with the Mint Canyon formation. MIOCENE SERIES TOPANGA (1) FORMATION In the hanging—wall block of the Santa Susana fault in the vicinity of the Aliso Canyon oil field, south of the area shown on the geologic map (pl. 44), a thickness of about 900 feet of light- to medium-brown thick- bedded fine- to medium-grained sandstone, with occa- sional thin lenses of pebble and cobble conglomerate, lies beneath shale of middle Miocene age. Locally, the upper part of the unit contains an amygdaloidal basalt flow. The Standard Oil of California Ward 3—1 well, about half a mile north of the area of outcrop of this sequence in sec. 27, T. 3 N., R. 16 W., penetrated a 284 thickness of about 2,500 feet of similar rocks, including at least one thin layer of amygdaloidal basalt. Both at the outcrop and in the well the unit is over- lain by rocks representing the Luisian stage (upper middle Miocene) of Kleinpell. Because of their strati- graphic position below upper middle Miocene rocks and because of the presence of a basalt flow, these beds are tentatively correlated with the Topanga formation of middle Miocene age. MINT CANYON FORMATION NOMENCLATURE Hershey (1902, p. 356—358) gave the name “Mellenia series” to the sequence of rocks that includes the Mint Canyon formation. Because the term Mellenia is not a place name, Kew (1924, p. 52) designated these rocks the Mint Canyon formation in recognition of their excellent development in the Mint Canyon region. Jahns (1939, p. 819) demonstrated that north of the area of this report the rocks that Kew named the Mint‘ Canyon formation consist of two formations rather than one ; he suggested that the lower part be called the Tick Canyon formation and the term Mint Canyon formation be retained for the upper beds. Only rocks from the upper part of the Mint Canyon formation as defined by Kew, and hence also from the Mint Canyon formation as restricted by Jahns, are exposed in the area shown on the geologic map (pl. 44). The older Tick Canyon formation of Jahns (1939) is not exposed, nor is it known to be present in the subsurface in the mapped area. DISTRIBUTION The Mint Canyon formation crops out on the north side of the Santa Clara River valley between Agua Dulce and Elizabeth Lake Canyons (outside the mapped area) and south of the valley between Sand Canyon and Honby (partly in the mapped area). It is not found south of the San Gabriel fault. Possible large right-lateral displacement along this fault (Crowell, 1952a) may explain the restriction of the known extent of the formation to the area north of the fault. GENERAL. LITHOLOGY The lithologic character of the Mint Canyon forma- tion has been discussed in detail by Kew (1924, p. 52—53) and Jahns (1940, p. 154—163). Jahns (p. 163) noted that “The beds in the lower half of the section are characteristically fine-grained, thin—bedded, and of variegated colors, whereas those higher up are more irregular, coarser, and subdued in color.” The con— glomerates are typically lenticular, cross-stratified, poorly sorted, and locally sandy. An abundance of gneiss, schist, and volcanic clasts is characteristic of the formation. Both well and poorly consolidated sand- SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY stones, which are arkosic and commonly cross-strati— fied, occur in the formation. Tan, gray, green, and pink siltstone and clay beds as well as white and gray vitric and crystal tufi' beds are interstratified with coarser deposits. Some fine-grained units grade later- ally into coarser grained beds; this gradation, together with the lenticular nature of the coarser grained beds, makes it difficult to trace lithologic units and horizons within the formation. Tufl’ beds are useful marker beds even though many of them are less than 4 feet thick. THICKNESS Jahns (1940, p. 162) ascribed an aggregate thick- ness of about 4,000 feet to the Mint Canyon formation in the Bouquet Canyon region. Oakeshott (1950, p. 53) reported the formation to be more than 2,400 feet thick in the area south of the Santa Clara River. A complete section is not exposed in the area shown on the geologic map. STRATIGRAPHIC RELATIONS AND AGE The first discovery of vertebrate remains in the Mint Canyon formation was made by Kew in 1919 during reconnaissance mapping Following the dis- covery of additional material, Maxson (1930) compared the fauna with those of other regions, and, after con— sidering the position of the Mint Canyon formation unconformably below marine strata regarded by Wood- ring (1930, p. 155) as the approximate equivalent of the Cierbo sandstone of northern California, he con- cluded that the Mint Canyon was deposited during approximately the middle part of the late Miocene. In a critical review of Maxson’s work, Stirton (1933, p. 569—576) differed with him on the identification of the mammalian forms and advocated an early Pliocene age for the fauna. Subsequent papers by Teilhard de Charden and Stirton (1934), Stirton (1936,- 1939), McGrew and Meade (1938), Lewis (1938), and Maxson (1938 a,b) have dealt with the paleontological aspect of the age of the Mint Canyon formation. As Reed and Hollister (1936, p. 40, 43) pointed out, the basic problem in the assignment of an age to the Mint Canyon fauna is the equivalence of the lower Pliocene of most vertebrate paleontologists and the upper Miocene of most California invertebrate paleontolo— gists. There are two major considerations in deter- mining the age of the Mint Canyon formation: (a) the occurrence of Hipparion in the Mint Canyon fauna, and (b) the occurrence of marine beds unconformably overlying the formation. The presence of Hippam'on indicates an early Pliocene age to many vertebrate paleontologists. Stirton (1933) adhered to this con- cept, but Maxson (1930), largely because of the strati— GEOLOGY 0F SOUTHEASTERN VENTURA BASIN graphic relationships of the Mint Canyon formation to the younger marine rocks, believed the range of the genus extends to the Miocene. Although Kew (1924, p. 52) recorded a marked un- conformity between the marine rocks and the Mint Canyon formation in Haskell Canyon, Stirton (1933, p. 569—576) and later Clements (1937, p. 215) indicated that the relationship is an interfingering or gradational one. Jahns (1939, p. 822) was able to demonstrate a distinct, though in places slight, angular discordance between the marine rocks and the Mint Canyon for- mation. He agreed with Eaton (1939, p. 534) that the Mint Canyon formation thins to the northwest by a loss of basal beds. Grant’s examination of additional collections of invertebrates from the marine rocks (Maxson, 1938a, p. 1716—1717) permitted a more exact determination than had previously been possible of their age as N eroly (uppermost Miocene). Kleinpell (1938, p. 71) referred meager foraminiferal faunas collected from the marine rocks to the Delmontian stage and agreed with the concept of the contemporaneity of the marine rocks and the Mint Canyon formation. Later, M. N. Bramlette I examined foraminiferal collections from the lower part of the marine sequence and considered the faunas as indicative of a late Mohnian (pre-Delmontian late Miocene) age. The Mint Canyon formation is undeniably older than marine rocks deposited during at least part of late Miocene time, based on the invertebrate time scale of California. Jahns (1940, p. 172) considered the Mint Canyon formation to be of late Miocene age, a desig- nation consistent with the stratigraphic position of the formation in the marine sequence. He also pointed out that the faunal gradation within the formation indicates that the deposition took place over a consid— erable time interval. The Mint Canyon formation (restricted) of Jahns (1939) unconformably overlies his Tick Canyon and older formations. Jahns (1940, p. 174—175) regarded his Tick Canyon formation as late early Miocene or possibly earliest middle Miocene in age. The Mint Canyon and Tick Canyon formations of Jahns (1939) overlie with pronounced unconformity beds called the Escondido series by Hershey (1902, p. 349—372), referred to the Sespe(?) formation by Kew (1924, p. 38—39), and named Vasquez series by Sharp (1935, p. 314) since Hershey’s term is pre— occupied. The Vasquez is of continental origin, is unfossiliferous, and has been tentatively referred to the Oligocene by Jahns (1940, p. 170—171). The Mint 1 Daviess, S. N., 1942. Contact relationship between Mint Canyon formation and upper Miocene marine beds in eastern Ventura basin, Los Angeles County, Califor- 1 la: Unpublished M. S. thesis, California Univ. at Los Angeles. 285 Canyon formation also unconformably overlies Eocene sedimentary rocks and the crystalline basement com- plex, considered to be pre—Cretaceous. STRATIGRAPHY AND LITHOLOGY IN THE MAPPED AREA In the northeastern part of the mapped area, the Mint Canyon formation crops out in a predominantly fine- grained sequence of greenish-gray siltstone units and interstratified sandstone, conglomerate, and thin tuff beds. The formation has been compressed into a series of comparatively tight, nearly westward trending folds. Resistant sandstone and conglomerate beds form prom- inent hills and ridges; less resistant siltstone units form a more subdued topography that includes the hum- mocky landscape typical of landslide areas. Greenish-gray siltstone units include beds of mud- stone and claystone and thin beds of sandstone and tuff. The siltstone commonly has sharp contacts with interstratified sandstone and conglomerate, although at some places the contacts are gradational. Bedding in the siltstone is generally indistinct or contorted due to the folding of the beds. Gypsum, found along the bedding planes and in fractures, and small bits of carbonaceous matter are conspicuous in the siltstone. Fresh-water fossils are abundant in some horizons. The fresh-water gastropod Paludestrina imitator Pilsbry has been identified (Kew, 1924, p. 54) in the formation. The vitric and crystal tuff beds are massive and White to gray; they break with a blocky or conchoidal frac- ture. The tuffs are commonly finely laminated, cross- stratified, and ripple marked. Most of the sandstone beds are light tan or yellowish brown but some are greenish gray. They are arkosic, and generally poorly sorted, and show cross-stratifica- tion, channeling, and local erosion of beds. Pebbly sandstone beds and sandstone beds with pebble string- ers and lenses are common; the beds are from a few inches to several tens of feet thick. Pebble, cobble, and boulder conglomerates contain clasts that range from angular to well rounded, but the majority are subrounded. A count of 430 clasts from one pebble conglomerate showed the following percentages of rock types: Gneiss _________________________________________ 58. 5 Volcanic rocks __________________________________ 34. 8 Anorthosite (and related rocks) ___________________ 3. 0 Quartzite ______________________________________ 1. 4 Schist _________________________________________ . 2 Miscellaneous __________________________________ 2. 1 100. 0 The igneous and metamorphic rock types are like those found in the nearby San Gabriel Mountains and 286 Sierra Pelona. The volcanic rocks are similar to flows in the Vasquez, east and northeast of the area. The lithologic nature of the Mint Canyon formation in the mapped area is not characteristic of the entire formation in adjacent areas. The “light-gray to nearly white gravel interbedded with greenish clay or fine sand” (Kew, 1924, p. 52) in the upper part of the formation does not occur in significant amounts in the mapped area. A thickness of about 1,500 feet of the Mint Canyon formation is exposed in the mapped area. The base is not exposed. ENVIRONMENT OF DEPOSITION The Mint Canyon formation was deposited under subaerial conditions. The coarse, unsorted, and len- ticular sand and conglomerate beds appear to have been large alluvial fan deposits. Fresh-water lakes were present in the area concurrently with the develop- ment of the alluvial fans. Thick sections of siltstone with interstratified mudstone, tuff, sandstone, and conglomerate are lake deposits. The presence of fresh-water mollusks and of a turtle possibly related to Clemmys (Maxson, 1930, p. 82, 87) is evidence of a lacustrine environment during deposition of part of the formation. Maxson regarded the abundant re— mains of hypsodont horses, antelopes, camels, and rabbits as an indication that the vegetation of the region must have been at least as abundant as that supported by a semiarid region. The grazing types of mammals occupied grass-covered plains, while Pam- hippus, peccaries, and possibly the oreodonts and mastodons aPso found in the formation frequented wooded areas along streams and lakes. Axelrod (1940, p. 577—585) made a study of fossil plants from tufl’ beds of the Mint Canyon formation in the vicinity of Bouquet and Sand Canyons. He found elements in the flora indicative of at least four distinct habitats: rush- or reed-like plants suggestive of shallow lakes, desert scrub from the drier slopes of the lower basin, an oak assemblage from the savanna area surrounding the general basin and probably also from the borders of streams, and a woodland community found at higher altitudes and on cooler slopes. Comparison with similar modern floras indicates that the region had an annual rainfall of from 15 to 20 inches, that pre- cipitation was distributed as summer thundershowers and winter rains, and that temperatures were similar to those now prevailing in the region, except that the winters were slightly warmer. The source of a large part of the Mint Canyon sedi- mentary beds was probably to the east, where rocks similar to the types represented as clasts in conglom- erates of the Mint Canyon formation occur in the San Gabriel Mountains. Anorthosite and related rocks SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY present as clasts in the conglomerates of the Mint Canyon formation are especially indicative of an easterly derivation of the sediments, but the presence in some of the conglomerates of schist and sandstone clasts similar to the Pelona schist and sandstones of Eocene age in the mountainous region north of the Santa Clara River valley indicates a northerly source for part of the formation. During deposition of the Mint Canyon formation, the region was probably a large alluvium-covered valley or plain with scattered lakes, tree—bordered streams, and grass- and brush-covered alluvial—fan surfaces leading up to the adjacent mountainous areas. MODELO FORMATION The Modelo formation was named by Eldridge and Arnold (1907, p. 17—19), who described as typical its exposures in Hopper Canyon and at the head of Modelo Canyon in Ventura County. As originally defined, the formation consisted at the type area of from 1,700 to 6,000 feet of strata, divided into four members: a lower sandstone member, 200 to 2,000 feet thick; a lower shale member, 400 to 1,600 feet thick; an upper sandstone member, about 900 feet thick; and an upper shale member, estimated to be between 200 and 1,500 feet thick. Eldridge and Arnold described the formation as overlying a shale sequence correlated with the Vaqueros formation and underlying rocks of the Fernando group. Kew (1924, p. 55—69) redefined the Modelo formation to include the under- lying beds correlated by Eldridge and Arnold (1907) with the Vaqueros. As thus redefined, the Modelo formation at the type area consisted of five members: a lower shale member, a lower sandstone member (the basal unit as defined by Eldridge and Arnold), a middle shale member, an upper sandstone member, and an upper shale member. The aggregate thickness ‘ of this sequence was given by Kew as about 9,000 feet. . Hudson and Craig (1929) redefined and restricted the Modelo formation at the type area. They cor- related the lower shale, lower sandstone, and middle shale members of Kew’s Modelo formation with the Topanga formation, largely on paleontological evi— dence. They also excluded from their restricted Modelo the uppermost beds of Kew’s Modelo formation at the type area. The members of the Modelo formation at the type area are not recognizable in the Santa Susana Moun- tains. In the area included on the geologic map (pl. 44), the Modelo formation consists mainly of rocks that Kew (1924) mapped as a shale member of the Modelo. Strata mapped by him as an overlying sand- GEOLOGY 0F SOUTHEASTERN VENTURA BASIN stone member of the Modelo are included in the Towsley formation. Rocks of the Modelo formation crop out in a band along the crest of the Santa Susana Mountains and along the axis of the Pico anticline. Although the base of the formation is not exposed within the area shown on the geologic map (pl. 44), the Modelo formation rests unconformably on the Topanga(?) formation a short distance south of the mapped area in the Aliso Canyon oil field (White and others, 1952). The Modelo is present in the subsurface in all parts of the eastern Ventura basin except for the area northeast of the San Gabriel fault and the area east of a line ap- proximately through the towns of Newhall and Saugus. In the subsurface near N ewhall the Modelo formation wedges out and is overlapped by the Towsley formation. Westward from Newhall the thickness of the Modelo increases to at least 5,000 feet, but because no wells in the western part of the area have reached the base of the formation, the total thickness is not known. In the subsurface throughout most of the region the Modelo formation cannot consistently be differentiated from the overlying Towsley formation because of the lithologic similarity and lenticular nature of the sand- stone and conglomerate lenses in both formations. STRATIGRAPHY AND LI'IHOLOGY Near the crest of the Santa Susana Mountains, in the area of Aliso and Rice Canyons, a complete section of the Modelo formation is exposed. In Aliso Canyon (outside the mapped area), the Topanga(?) formation is overlain by a unit about 300 feet thick of gray to grayish-orange medium- to coarse-grained well-sorted sandstone with lenses of pebble- to cobble-conglom- erate. Above the basal sandstone of the Modelo a sequence of grayish-brown, brownish-gray, and grayish- , black, poorly indurated, thinly laminated to thin-bedded silty and sandy shale about 400 feet thick is overlain by about 800 feet of pale yellowish-orange hard platy, thinly laminated to thin-bedded cherty shale, clay shale, and porcellaneous shale. The upper part of the forma- tion, about 1,500 feet thick near Rice Canyon, con- sists chiefly of softer fine-grained rock. The siltstone, claystone, and mudstone are laminated to thick bedded, light brownish gray or grayish orange when fresh, medium brown when weathered. The thinly lami— nated, platy to punky silty shale is grayish brown to light brownish gray, grayish orange, pale red, or pale red purple. At many places fractures and bedding planes are encrusted with gypsum and coated with a yellow powdery mineral that is probably j arosite. Occasional beds of gray impure limestone, which commonly weathers pale yellowish orange and is prob- ably of concretionary origin, are interstratified in the 681734 0—612——2 287 shale. Elliposidal limy concretions, some more than 6 feet long, are scattered through the shale. At most places concretions are alined along definite horizons. Thin lenses and small nodules of nearly white phos- phatic material occur in the shale at several strati- graphic levels. The nodules commonly contain fish bones and scales. Layers of light-colored silty to coarse—grained sand- stone are interbedded in the shale at many places. The layers range from laminae to beds several feet thick. The sandstone beds are generally graded from coarse at the bottom to fine grained at the top and are like the sandstone beds in the overlying Towsley for- mation in every important respect. The upper part of the Modelo formation is exposed in a belt along the axis of the Pico anticline from East Canyon to Big Moore Canyon. In the vicinity of Rice Canyon a thickness of about 1,000 feet of Modelo formation is exposed below the Towsley formation. The lithology is similar to that of the upper part of the formation described above. Several deep exploratory wells that were drilled along the Pico anticline show that the thickness of the Modelo formation increases from about 3,000 feet at the crest of the Santa Susana Mountains to at least 5,000 feet near the axis of the anticline. FOSSILS AND AGE The only mollusks found in the Modelo formation are valves of a small Delectopecten. Fish bones and scales are common, especially in the more platy shales, and foraminifers are plentiful in some layers. The lower part of the Modelo formation in Aliso Canyon contains a foraminiferal fauna representative of the Luisian stage of Kleinpell (White and others, 1952). Forami- niferal faunas from several localities in the upper part of the Modelo formation in the Santa Susana Mountains region are given in table 2. The faunas that have any age significance seem to represent the Mohnian stage of Kleinpell, including the Bolivina hughesi zone, except for the faunas from localities f 10 and f11, between Rice and East Canyons, which may represent the Delmon- tian stage (Patsy B. Smith, oral communication, 1954). UPPER MIOCENE AND LOWER PLIOCENE TOWSLEY FORMATION DISTRIBUTION Along the north slopes of the Santa Susana Mountains the fine-grained sedimentary rocks of the Modelo for- mation are overlain by and interfinger with a sequence of light—colored sandstone, conglomerate, and inter— bedded brown-weathering mudstone beds. This se— quence was named the Towsley formation by the authors (1954) for its good exposures in the vicinity 288 TABLE 2 —~Foraminifera from M odelo formation [Identifications by Patsy B. Smith] Locality (table 11) Buggina of. B. subinequalis Kleinpell ________ Bolivian adrena striatella Cushman _ of. B. cuneiformis Kleinpell____ hootsi Rankin _________________ pseudobeyrichi Cushmam... pseudospissa KleinpelL _ _ pygmea Brady ________________ rankim’ Kleinpell ______________ _ sinuata Galloway and Wissler. _ woodrz’ngi‘.’ Kleinpell ____________________ Bulimina ovula pedroana Kleinpell __________ pagoda hebespmata R. E. and K. 0. Stewart _______________________________ rostrum H. B. Brady .................... cf. B. urigerz’naformis? Cushman and Kleinpell _____________________________ Bulimmellu curta Cushman _________________ subfusiformis Cushman .................. Cassidulina delicate Cushman ............... cf. C. limbata Cushman and Hughes- __. Cassidulinella renulinaformis N atland _______ Chilostomella grandis Cushman _________ Cibz'cides basilobus‘? (Cushman) _______ mckannai Galloway and Wissler. Discorbis valmonteensis Kleinpell _____ Epistominella bradyana (Cushman)__ of. E. elm Bandy ________________ subperum’ana (Cushman) _________ Epom’dea of. E. exigua (H. B. Brady) Globobulimz’na sp ______________________________________ Gyroidina rotundimargo R. E. and K. C. Stewart ___________________________________ Hopkinsina magnifica Bramlette ____________ Nom'on labmdoricum (Dawson)..__ Nom'onella miocenica Cushman .............. Um'gerz‘nu hootsi Rankin _____________________ subperegrma Cushman and KleinpelL... Valvulineria araucana (d’Orbigny) __________ califomica Cushman ____________________ Virgulina califomiensis Cushman ____________ califomiensis grandis Cushman and . Kleinpell ____________________________________________ X _______________ cornuta Cushman ______________________________________ X ..... X _____ of Towsley Canyon. The lithology and thickness of the Towsley formation change markedly from place to place so that the designation of a section truly typical of the formation as a whole is impossible. However, the section exposed along the north limb of the Pico anticline at Towsley Canyon is a representative one (pl. 46). At Towsley Canyon, the base of the Towsley formation is the base of the first unit of thick-bedded coarse-grained sandstone that lies above the typically fine-elastic rocks of the Modelo formation. The lower contact is not everywhere at the same stratigraphic horizon. The upper part of the Towsley formation closely resembles the lower part of the overlying Pico formation. The contact between the two is drawn at the base of the first conspicuous sandstone and con- glomerate unit below the lowest concretion-bearing olive—gray siltstone typical of the Pico formation. The upper contact too is not everywhere at the same stratigraphic horizon. In the area around Newhall and San Fernando Pass the Towsley formation over— laps the Modelo formation and rests on pre—Cretaceous crystalline rocks, on the Sespe(?) formation, and on Eocene rocks. Where it rests unconformably on older rocks, the basal part of the formation contains a shallow-water molluscan fauna. SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY In two small areas north of the San Gabriel fault, beds of siltstone and sandstone that rest unconformably on the Mint Canyon formation and are overlain uncon- formably by the Sunshine Ranch member of the Saugus formation are assigned to the Towsley formation. North of the belt of outcrops along the Santa Susana Mountains the Towsley formation can be traced in the subsurface by electric log correlations. The distinc- tiveness of the formation decreases as correlations are extended farther and farther from the belt of outcrops because numerous lenticular units of sandstone similar to those in the Towsley formation occur in the Modelo formation. DISTINCTION FROM MODELO FORMATION The many lenticular units of sandstone and conglom- erate in the Towsley formation distinguish it from the underlying lVIodelo formation. The base of the Towsley formation is much lower, stratigraphically, on the south limb of the Cat Mountain syncline than it is 1 or 2 miles farther north on the north limb of the Pico anti— cline. The interfingering between the Towsley and Modelo formations is particularly evident in the Vicinity of the headwaters of Rice Canyon. The position of the base of the Towsley formation in the upper reaches of Rice Canyon is more than 1,500 feet stratigraphi- cally below the horizon of the base of the Towsley on the north limb of the Pico anticline 1% miles to the north. Similarly, in the area between Little ‘Moore Canyon and Pico Canyon, along the Pico anticline, the base of the Towsley formation is at lower and lower stratigraphic horizons as the formation is traced west- ward. The thickness of the Towsley formation ranges from about 4,000 feet in the southwestern part of the mapped area to a thin edge where the formation is unconform- ably overlapped by younger strata in the eastern part of the area. PREVIOUS ASSIGNMENT In the Santa Susana Mountains, most of the strata assigned to the Towsley formation were mapped by Kew (1924) as a sandstone member of the Modelo for- mation; he included a few of the uppermost beds of the Towsley there in the overlying Pico formation. Kew included in the Pico most of the rocks in the eastern part of the area, near Elsmere Canyon, here assigned to the Towsley ; however, he assigned some of the higher beds to the Saugus formation. Oakeshott (1950) as- signed the beds of the Towsley in the eastern part of the area to the Repetto formation and distinguished two members: his basal Elsmere member, which in- cludes all the lower Pliocene in the vicinity of Elsmere Canyon, and a siltstone member, exposed in the two GEOLOGY 0F SOUTHEASTERN VENTURA BASIN small areas north of the San Gabriel fault. Willis (1952) included all the Pliocene strata in the eastern part of the area in the Pico and termed the lower parts of the sequence, which corresponds to the Towsley, the Repetto formation and the Repetto equivalent. Be- cause the type locality of the Repetto is in the Los Angeles basin, which was not connected with the Ven- tura basin during Pliocene time, and because the Tows— ley does not resemble the type Repetto lithologically, the term Repetto formation is not used for rocks de- scribed in this report. In the Santa Susana Mountains local names for the Towsley formation include: Elsmere, Delmontian sands, and Miocene—Pliocene transition zone. Productive intervals in the formation have been given local names in the various oil fields in the area (see p. 340—347). STRATIGRAPHY AND LITHOLOGY Santa Susana Mountains Relation to Modelo formation—The Towsley forma- tion is exposed in a continuous belt extending along the north slope of the Santa Susana Mountains to and beyond the west border of the area. Throughout this belt the Towsley overlies and interfingers with the Modelo formation and is overlain by the Pico formation along a gradational contact. The lithology and thick- ness of the Towsley at seven places is shown in the columnar sections on’ plate 46. The dashed lines between the columns indicate correlations based on the tracing in the field of mappable units. The strati— graphic relations of the Towsley in the Santa Susana Mountains area are also shown on plate 45. Fine-grained sedimentary rocks—Units of brown- weathering mudstone, siltstone, and shale make up the greater part of the Towsley formation, especially in the western and central parts of the mapped area. They are interbedded with lenticular units of sandstone and conglomerate as shown on the geologic map (pl. 44). The mapped units include many individual beds too thin or too limited in extent to be shown on the geologic map but whose lithology differs from that of the unit as a whole. In particular, beds and laminae of siltstone and mudstone are present in the sandstone and con- glomerate units. In the lower part of the formation the fine-grained rocks tend to be somewhat fissile, but at higher levels fissility is generally lacking. Fractures and bedding planes in the fine-grained rocks are commonly encrusted with gypsum crystals and lightly coated with films of jarosite(?). The general impermeability and high sulphate content of these rocks produce an unfavorable medium for plant growth. Belts conspicuously barren 289 of vegetation mark the outcrops of mudstone units in many areas. Ellipsoidal limy concretions similar to those in the Modelo formation are scattered sparcely in the mud- stone and, as in the Modelo, are generally alined along definite horizons. At many places bedding planes in the mudstone pass Without interruption through the concretions. The concretions are generally about a foot long, although a few are as much as 4 feet long. Occasional beds of hard fine-grained gray limestone that weathers yellowish gray are intercalated in the mud- stone. These beds, some of which may be traced for several hundred yards, are as much as 18 inches thick, but any one bed is generally of variable thickness. In some places the limestone beds contain foraminifers. Because of their similarity to the ellipsoidal concre- tions, the limestone beds are thought to be concretion- ary in origin rather than primary deposits. The most common fine-grained rock is massive light brownish-gray sandy mudstone that weathers a darker brown. In well cores this rock is generally dark greenish gray. Typically, the mudstone is poorly sorted. Mechanical analyses of representative samples showed medium and coarse silt (00156—00625 mm) to be the most abundant size classes. In most samples the clay fraction amounted to only about 5 percent by weight, but this low percent-age of clay may reflect incomplete dispersion of the samples rather than a real scarcity of material in this size. Fine—grained sand was present in all samples analyzed. Many hand speci- mens contain very coarse angular sand grains scattered in a muddy matrix. The lack of clear bedding in, and poor sorting of, the sandy mudstone may be due to the disturbance of the sediments by burrowing and mud— eating organisms at the time of deposition. Fossils are scarce in the mudstone. Foraminiferal faunas were meager, except for a few collected from the surfaces of concretions. Fish scales and fragments of fish bones are the most plentiful organic remains. Fossils may be scarce because conditions were not favorable for the development of a benthonic fauna. The gypsum and jarosite(?) on weathered surfaces might be interpreted as indicative of sulphurous bottom waters; however, the presence of benthonic Foraminifera in some of the limy concretions indicates that living conditions were suitable, at least at times. The fact that beds containing Foraminifera within concretions are generally not only barren outside the concretions but closely similar in appearance to most other barren mudstone beds suggests that Foraminifera were living on the bottom during deposition of the mud- stone, but that their remains were later destroyed. In places where the rocks are very poorly sorted and poorly bedded, mud-eating scavengers may have partly 290 destroyed the foraminiferal tests. Where the rocks are well bedded or where foraminiferal concretions are present, interstratal solution probably destroyed all calcareous shells except those protected within concretions. At a few places in the Towsley formation thin units of yellowish-gray shale with paper-thin laminations crop out. In these laminae fish bones and scales are abundant, and well-preserved mud pectens (Delecta- pecten sp.) are common. Sandstone and conglomerate—In many areas, the sandstone and conglomerate units are firmly cemented so that they produce bold topographic forms. Many streams have waterfalls in their courses where they cross these resistant units. The dense cover of brush that grows on most sandy slopes is nearly impenetrable in some areas, especially along the Santa Susana Mountains in the upper reaches of Towsley and Pico Canyons. Many of the sandstone and conglomerate units contain large concretions such as those shown in figure 51. Bedding planes pass through the concre- tions without interruption. Individual beds within these mappable units range from thin laminae to beds at least 5 feet thick. At many exposures single beds several feet thick pinch out completely in a few tens of feet. The beds of conglomerate tend to be the most variable in thickness. SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY Some of the mappable sandstone and conglomerate units can be traced laterally for only a few hundred yards. Others, like the resistant unit that is so well exposed north of the axis of the Pico anticline where Towsley Canyon narrows to a gorge, can be traced for several miles. Even this persistent unit is variable in both lithology and thickness from place to place. At the narrows in Towsley Canyon it is about 225 feet thick and consists largely of conglomerate. Clasts near the base of the unit are as large as 18 inches in diameter. One mile northwest of Towsley Canyon, near Little Moore Canyon, the unit is only a few feet thick and consists of sandstone. At Little Moore Canyon the unit thickens and coarsens abruptly again, then gradually thins toward Pico Canyon. South of the axis of the Pico anticline in Towsley Canyon the same unit consists of coarse-grained sandstone. The clasts of pebble or larger size in the conglomerate represent a great variety of rock types. At most places gneiss and leucocratic plutonic rocks constitute about 80 percent of the clasts. Dark volcanic rocks, chiefly andesite but representing a wide range in com- position, generally make up about 15 percent, and a host of other rock types, including quartzite, vein quartz, chert, aplite, gabbro, norite, and anorthosite, constitute the remainder. FIGURE 51.—Concretionary sandstone unit in the Towsley formation on the crest of the Santa Susana Mountains. GEOLOGY OF SOUTHEASTERN VENTURA BASIN The only place where anorthosite and norite crop out in the region of the Ventura basin is northeast of the San Gabriel fault in the San Gabriel Mountains, east and northeast of the easternmost outcrops of the Towsley formation. Gneiss and granitic rocks are exposed over extensive areas in both the San Gabriel Mountains and in the Traverse Ranges north of the eastern Ventura basin. Flows and sills of andesite lithologically similar to some of the clasts in the con- glomerate of the Towsley formation occur in the Vas- quez formation about 12 miles northeast of Newhall (Kew, 1924, p. 39). Many of the clasts in the Towsley formation are probably at least second generation, having been eroded from older conglomeratic forma— tions. The clasts show almost every degree of round- ing, although most rocks fall within Pettijohn’s rounded class (Pettijohn, 1949, p. 51—53). Boulders larger than 1 foot in diameter, although generally rare, are common in some places, as for ex- ample in the basal part of the conglomeratic unit that crops out at the narrows in Towsley Canyon. On the divide between Rice and Towsley Canyons 0n the south limb of the Oat Mountain syncline a bed con— taining many 3—foot boulders crops out near the base of the formation. Nearly all boulders consist of gneiss or light—colored plutonic rock. Beds of cobble con- glomerate occur throughout the Towsley formation in the Santa Susana Mountains, but boulder-bearing beds are confined chiefly to the area between Pico and Wiley Canyons, on the north limb of the Pico anticline, and to the area near the divide between Rice and Towsley Canyons, south of the axis of the anticline. This distribution is suggestive of a northern or northeastern source for the conglomerate. Graded bedding—The most prevalent sedimentary structure in the sandstone and conglomerate beds of the Towsley formation is graded bedding. Except for the lower part of the formation that rests uncon— formably on older rocks in the Vicinity of Elsmere Canyon, nearly all sandstone beds and most conglome- rate beds of the Towsley formation are graded. Gen— erally the grading is conspicuous, the contrast between average grain size at the base and at the top of most beds being marked. In some beds, however, the grading is obscure; these beds have a nearly uniform grain—size distribution through more than 90 percent of their thickness but show distinct grading in the uppermost parts. Other beds, thought to be ungraded when examined in the field, were found to be graded when sequences of samples from single beds were ana- lyzed in the laboratory. The relatively few ungraded sandstone beds are generally thin and contain evidence that reworking may have destroyed any original grading. 291 Typically, a graded bed is very poorly sorted, espe- cially in its lower part. The finest material is present throughout the entire thickness of such a bed, even in the coarsest basal part; the median diameter of the grains, however, decreases steadily from the base of the bed to the top. Near the top of many graded beds the sandstone grades into siltstone, and commonly the sequence continues to grade upward into claystone. This upward reduction in grain size near the top of a graded bed is accompanied by a steadily darkening color. Most commonly the contact of a graded bed with the overlying bed is distinct and abrupt. The interface between some beds is an even surface with no sign of any erosion or disturbance of the underlying bed. At many places where pebbles at the base of one graded bed rest directly on claystone of the underlying bed no evidence of channeling of the claystone can be detected. Where recent erosion stripped away part of the pebbly bed and exposed the surface of contact, the upper sur- face of the claystone is dimpled with the impressions of the eroded pebbles. At many places graded beds of sandstone contain angular fragments of finer grained rocks similar to the fine-grained strata interbedded with the sandstone. Most fragments are only an inch or two in diameter, but clasts with a diameter as great as 10 feet also occur (fig. 63). Carbonaceous material, commonly in the form of dark—brown or black angular fragments, is abundant in some beds. The fragments are generally arranged in laminae near the top of graded beds. Most fragments are sand or granule size, but pieces as large as 1 inch are present. The material has a low density and resembles charcoal. The angular shapes and charcoal- like appearance of the material suggest that it is burnt wood. According to Shepard (1951, p. 56—57), similar material has been found in Recent sand layers in one of the inner basins in the continental borderland ofl’ southern California. Other characteristic sedimentary structures in the Towsley strata in the Santa Susana Mountains area include load casts, small cut-and-fill structures, current ripples, slump structures, and convolute bedding. De- tailed descriptions of the sedimentary structures in the Towsley strata and a discussion of their origin and sig- nificance are given on pages 333—334. San Fernando Pass and Elsmere Canyon Area In the region southeast of Newhall, near San Fernando Pass and Elsmere Canyon, strata assigned to the Tows— ley formation include beds deposited in water shallower than that farther west Where the rocks of the Santa Susana Mountains proper were deposited. The for- mation thins eastward and northeastward, probably 292 partly because of successive overlap of lower parts of the formation by beds higher in the formation. An unconformity at the base of the overlying Pico forma- tion truncates strata of the Towsley formation near Elsmere and Whitney Canyons. From Whitney Canyon south to Grapevine Canyon the basal beds of the Towsley formation lie directly on pre-Cretaceous igneous and metamorphic rocks. The crystalline rocks near the contact generally show no evidence of pre-Towsley weathering. The degree of fracturing in the crystalline rocks is not perceptibly more intense near the contact than at places farther away. The surface of contact is jagged in detail but local relief on the surface is generally not greater than 1 or 2 feet. Viewed more broadly, the contact is very even. At most places the basal bed of the Towsley forma- tion is a well-indurated conglomerate containing, in addition to well—rounded clasts of a great variety of rock types, angular blocks of crystalline rock of very local derivation. In Elsmere Canyon the coarse basal beds are about 15 feet thick; in places in Grapevine Canyon the conglomerate or breccia is only a few inches thick and is overlain by fine-grained silty sandstone. In Whitney Canyon and on the divide between Whitney and Elsmere Canyons the entire exposed thickness of SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY the formation consists chiefly of conglomeratic sand— stone interbedded with relatively minor amounts of siltstone and mudstone. Figure 52 shows the basal part of the Towsley formation where it rests on quartz diorite on the divide between Elsmere and Whitney Canyons. The lowest part of the Towsley formation here consists of large, closely spaced blocks of quartz diorite. The interstices between blocks are filled with sand and rounded pebbles and cobbles of a variety of rock types. Lying above the basal rubble are lenticular beds of conglomerate and sandstone. The upper beds overlap the rubble and rest directly on the quartz dio- rite in the upper part of the figure. At some places, particularly in the area near the southeast corner of section 18, T. 3 N ., R. 15 W., mound-shaped lenses of light—gray hard calcareous fine-grained sandstone occur near the base of the formation. They are a few yards in diameter, as much as 10 feet thick, and interfinger with softer sandstone and pebbly sandstone beds. Erosion of the softer beds has left some of the hard lenses standing as prominent knobs. The lenses are generally very fossiliferous; specimens of Lucinoma (m- nulata (Reeve), identified by Winterer, are particularly abundant. In Elsmere Canyon the lower conglomeratic beds are overlain by a sequence about 150 feet thick of fossilif— FIGURE 52,—Contact of Towsley formation (Tt) with quartz diorite of Dre-Cretaceous basement complex (Bc) on ridge between Whitney and Elsmere Canyons. GEOLOGY OF SOUTHEASTERN VENTURA BASIN erous moderately indurated, poorly bedded sandstone, siltstone, mudstone, and occasional thin lenses of con- glomerate. The sandstone commonly contains con- cretions that are especially fossiliferous. The sequence is tar stained and has oil seeps. It has been productive in wells in the Elsmere, the Tunnel, and the Whitney Canyon areas, and in the Placerita field where it is known as the lower Kraft zone. This sequence of beds grades upward into a unit of moderate yellowish-brown to dark yellowish-brown massive sandy siltstone. This unit is about 150 feet thick at the place where the Whitney Canyon fault intersects Elsmere Canyon. It thins northeastward and pinches out near the divide between Elsmere and Whitney Canyons. The unit can be traced in the sub- surface, by means of drillers’ logs and electric logs,‘into the Tunnel area, where it is about 300 feet thick. An unconformity at the base of the overlying Pico forma- tion truncates the unit so that its original thickness cannot be measured at Elsmere Canyon. South and west of Elsmere Canyon the Towsley formation thickens markedly and the upper conglom- eratic beds interfinger with brown sandy siltstone and mudstone. In Grapevine Canyon the formation is at least 1,500 feet thick and consists of yellowish-brown mudstone, siltstone, and fine-grained sandstone inter— bedded with lenticular units of light-colored sandstone and conglomerate. In the area south of the Weldon syncline the beds of sandstone and conglomerate in the Towsley formation, excepting only the lowest, are similar in all important respects to the sandstone and conglomerate beds of the Towsley in the Santa Susana Mountains. The fine-grained beds are likewise very similar to those in the Santa Susana Mountains area. The increase in the thickness of the formation as it is traced westward may be due to the presence in the lower part of the formation of beds older than those resting on the crystalline rocks at the outcrops in Elsmere and Grapevine Canyons. The numerous faults in the San Fernando Pass area make correlations between various sedimentary units uncertain. In the area where the axis of the Weldon syncline crosses US. Highway 6,-the siltstone in the upper part of the Towsley grades northwestward in a very short distance into cross-stratified conglomerate and sandstone assigned to the Pico formation. The cross- stratification is very well exposed near San Fernando Pass (fig. 53). North Of the San Gabriel fault Beds assigned to the Towsley formation crop out north of the San Gabriel fault in sections 20 and 32, T. 4 N., R. 15 W. The correlation of these beds with the Towsley formation south of the fault is based on 293 lithologic similarity to the beds in Elsmere Canyon and on stratigraphic position. North of the fault the beds unconformably overlie the Mint Canyon formation and are in turn unconformably overlain by the Sunshine Ranch member of the Saugus formation. The rocks are chiefly light olive-gray, sparsely fossiliferous silty sandstone and sandy siltstone. Beds of light-colored fossiliferous pebbly sandstone are near the base of the formation. About 700 feet of Towsley strata are exposed in sec. 20, and a short distance beyond the east border of the area, in sec. 32, the formation is about 300 feet thick. Subsurface development The Towsley formation loses its identity as it is traced in the subsurface northward from the Santa Susana Mountains. Numerous lenses of sandstone and conglomerate occur in the Modelo formation as well as in the Towsley, and the fine-grained rocks in the lower part of the Towsley are not distinguishable from those of the Modelo, a combination of circumstances that makes the differentiation of the two formations in that area impracticable if not impossible. Valid correlations can be made from electric logs of wells drilled fairly close together, but in the absence of such data, correlations are best made on the basis of fora- miniferal faunas. Because of the highly competitive nature of the oil industry in this area, many operators find it inadvisable to release detailed subsurface infor- mation, especially details about foraminiferal corre- lations. Consequently, different species have been used by different paleontologists as index fossils for the same time-stratigraphic unit. Thus the top of the Miocene, as determined by different paleontologists, may vary as much as 1,000 feet in the same well. The correlations shown in the structure sections (pl. 45, sections A—A’ through F—F’) are therefore subject to the errors inherent in adjusting conflicting views. FOSSILS Santa Susana Mountains Foraminifera are relatively scarce in the Towsley formation in the Santa Susana Mountains. Forami- niferal faunas from localities in the Santa Susana Mountains as well as from Elsmere Canyon and from north of the San Gabriel fault are listed in table 3. The only mollusks found in the pelitic rocks of the Towsley formation in the Santa Susana Mountains are specimens of Delectopecten, generally with paired valves. These mud pectens are common in the fissile shale. Unidentifiable fragments of mollusks occur in many places in the sandstone and conglomerate, and at a few places whole shells occur. Collections from two locali- ties have been identified; the species are listed in table SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 294 .mmam ocnanuwm dam 5 my haanmm .m.D no .26 E $893 E5958 85 2: .8 tan .533 2: 5 «$5385 Ho meow oiowéuuaglfin ”359% GEOLOGY OF SOUTHEASTERN VENTURA BASIN 295 TABLE 3.—Foramim’fem from Towsley formation [Identifications by Patsy B. Smith] Locality (table 11) Els- Santa Susana Mountains mere North of San Can- Gabriel fault yon 1'28 f29 f30 {31 f32 f33 f34 f35 f36 f37 138 139 140 Angulogerina sp ................................................................ Bathysiphon sp _____________ Bolivina advena Cushman var.. hootsi Rankin ___________ imbricata Cushman var_. cf. B. imbricata Cushman ________________ piscifarmis Galloway and Morrey ....... pseudobeyrichi Cushman _________________ rankim‘ Kleinpell ,,,,, seminuda Cushman __________ smuata Galloway and Wissler. _ spissa Cushman _____________ tumida Cushman __________ Bulimina of. B. mica Seguenza pagoda Cushman var__ rostrum H. B. Brady _ subacummata Cushman Buliminella curta Oushman- elegamissima (d’ Orbigny) subfusiformis Cushman. _ Cassidulma califomica Cushman and Hughes. cushmam‘ R. E. and K. 0. Stewart ....... delicate Cushman ________________________ translucens Cushman and Hughes ________ Chilostomella sp ______________________ Cibicides basilobus (Cushman).._. lobatulus (Walker and Jacob) ____________ mckannai Galloway and Wissler. _ __.___. var. (flat) Cyclammina sp ____________________ Epistominella bradyana (Cushman)_. pacifica (Cushman) ____________ subperuvmna (Cushman) _ _ __ Epam'dcs peruviana (d’Orbigny) Frondicularia foliacea Schwager. _ Globigen’na spp ................ Globobulimma spp __.. _. Gyroidina altlformz's R. E. and . rotundimargo R. E. and K. 0 Stewart Nodosaria sp ___________________ Nonion cf. N. costifrrum (Cush cf. N. incisum (Cushman) _.__ s _______________________ p ........ Quinqueloculina sp ____________________ Rohulus cushmani Galloway and Wissler _____ Textularia sp ___________________________________ Trochammina pacifica Cushman ................... Uvigerina of. U. hispido—costata Cushman and Todd hootsi Rankin __________________________________ peregrine Cushman ...................... subperegrma Cushman and Kleinpell ..... Valvulineria araucana (d’Orbigny) ............. ornate Cushman _____________ Verneulz‘na sp ___________________ Virgulina californiensis Cushman ________________ califomiensz‘s grandis Cushman and Kleinpell ............................... 4. At a locality (F17) outside the area shown on the geologic map but near the top of the Towsley formation (see pl. 46) and along the line of the measured strati- graphic section between Tapo and Salt Canyons, fossils occur in several graded beds of pebbly sandstone interbedded with conglomerate. Fossils identified by Woodring and Trumbull from this locality (written communication, 1952), which have not been previously reported from the Ventura basin are: “Nassa” hamlz’m' Arnold, subsp. Fulgoram'a orgeonensis Dall Glyptostoma of. G. gabrz’elense Pilsbry Yoldia aff. Y. beringiana Dall Cyclocardia afl’. C. barbarensis (Stearns) Calyptogena lasia (Woodring) Elsmere Canyon region The fauna of the Towsley formation from the Elsmere Canyon area has been described or listed by a number of workers (Gabb, 1869, p. 49; Ashley, 1896, p. 337; Watts, 1901, p. 56; Eldridge and Arnold, 1907, p. 25; English, 1914, p. 203—218; Kew, 1924, p. 77-80; and Grant and Gale, 1931). No attempt was made to collect new material from the area during the course of the fieldwork for this report. Fossils are abundant in the lowest part of the formation, and especially abundant in concretions. The fossils are well preserved by the tar that impreg- nates the rocks. Paired pelecypod valves are very common at most localities, suggesting that the shells 296 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY TABLE 4.—Fossils from [Identified by W. P. Woodring, J. G. Vedder, and E. J. Trumbull, unless otherwise specified. Geographic and bathymetric data compiled by E. L. Winterer. AA, very orm; cf., similar form; sp., presumably Locality (table 11) Towsley formation Pico formation Santa Susana North of Mountains Sanstilgriel North of Santa Clara River valley au F16 F17 F18 F19 F41 F42 F43 F44 F45 F46 F47 F48 F49 F50 F51 F52 Bryozoa: Unidentified worn specimen .................................. X ........................................................................................ Brachiopods: Glottidia cf. 6'. albida (Hinds) ..................................................................... sp.R ................................................ Terebrutalia occidentalis Dall, including ............... X .............................................................................................. T. occidentalis obsoleta Dall. Chiton: Ischnochz’ton sp .................................................................................... R ................................................ Gastropods: Acmaea? cf. A. 'Im‘tra Eschscholtz ....................... X .............................................................................................. Solariella peramabilis Carpenter ............... afi. ................................ afl.R .......... ? ............ sp. __________________ afl. Calliostmna coalingense catotertm Woodrlng? ad. 0. coalingense Arnold ___________ . p.? 2 ..................... Tegula afi. T. ameotincta (Forbes) _______ gallina (Forbes)? _____________________ ligulata (Menke) ..................... Norrisia norrisi (Sowerby)? .............. Pamaulax gradatus (Grant and Gale) ..... Lacuna sp ________________________ _ Capulus? cf. C. culifomicus Dal] __________ Crepidula princeps Conrad _______________ (my: Sowerby ........................ aculeata (Gmelin) .................... Calyptrueu cf. 0. fastigiata Gould ......... filosa (Gabh) _____________________ Crucibulum cf. 0. spinosum (Sowuby)... C‘ruptonatica almtica Dali, medium-sized form. aleutica Dall, small form _____________ Nwerita reclusiana (Deshayes) ___________ Lunatic lewisii (Gould) .................. Sinum scopulowm (Conrad) ............. Turritella cooperi Carpenter, subsp ...... ganostomu hemohilli Applin .......... Aletes squamiaerus Carpenter ............ squamigerus Carpenter'h smooth form. Petaloctmchus montereyensis Dali ......... Unidentified Vermetid ................... “Cerithium” sp ______________ simplicus Grant and Gale? Bittium rugatum Carpenter .............. sp ................................... “Gyrineum” of. “G.” elsmerense English. mediocre lewisii Carson _______________ See footnotes. at end of table. x ...... 22:22: "isii‘ IIIIIZ "5E" x 7 ?R ........................ CLO ct __________________ cf.R afl __________________ R ________________________ A X ............ X CLR cf __________________ ""R """ x III: III: III __________ cf. _-_... __..-_ _____- C 7 ............ 'I R X .................. _._. ‘2 .................. R X __________________ R ________________________ GEOLOGY OF SOUTHEASTERN VENTURA BASIN Towaley and Pica formations abundant (more than 100); A abundant (50-100); C, common (10-50); R, rare (less than 10); x, occurrence in nonbulk collections; ?, doubtful occurrence; all, comparable similar form; ?sp., genus dou tf 1 locality (table 11)—Cont1nued 297 Present habitat Pioo formation—Continued North of Santa Clara River valley—Continued South of Santa Clara River valley Geographic range F59 F60 F61 F62 F76 F77 F78 F79 F80 F81 F82 Bathymetric data (depth in fathoms) sp. ____________ 'I ________ ? ______ cf. ____________________ cf. ........ sp. cf. X sp. __________________ III: "x" x x ____________________ X .................... X X X X X .............. cf. -..._- ______________ X -_____ cf. ____________ 'rcf. ...... cf. cf. ______ cf. cf. ______ cf. .................. sp. ....-. X ________________________ x .___.. III III: "of." III: S< """ 7 X ...... X X X X __________________ cf. .____. ___.._ ............ ?cf. ______ -..___ ____-. - Redondo, Calif, to Cape San Lucas, Baja Monterey Bay, Calif, to Magdalena Bay, Baja California (Hertlein and Grant, 1944, p. 14). San Francisco, Calif., to Cape San Lucas, Baja California (Hertlein and Grant, 1944,p. 129). Bering Sea to San Martin Island, Baja California (Burch, No. 57, p. 6).1 Forrester Island, Alaska, to San Diego, Calif. also Japan (Burch, No.58, p. 5).1 Extinct ___________________________________ Extinct __________________ Santa Barbara Islands, Calif, Margarita Island, lBaja (Burch, No. 57, p. 38).l San Francisco Bay, Calif., to Gulf of Cali- fornia (Burch, No. 57,, p. 35 ).1 Monterey, Calif, to Acapulco, Mexico (Burch, No. 57, p. 38).1 to Santa California Monterey, Calif., to Cedros Island, Baja California (Burch, No. 57, p. 34).1 Extinct ________________________ California (Burch, No.56, p.19).l Extinct ___________________________________ Monterey Calif, to Chile (Burch, No. 56,13,123.l PortHaiforld, Calif” to Chile (Burch, No. 56 Port Etches, Alaska, to Redondo Beach, ECalicf. (Burch, No. 56, 11.2 2.1) Xt ___________________________________ Trpini2dad, Calif. to Chile (Burch, No.56, Bering Sea to Washington and perhaps to southern California (Woodring and Bramlette, 1950, p. 72). Pt. Conception, Calif. to Tres Marias Island, Mexico (Burch, No. 56, p. 30) .1 Duncan Bay, British Columbia, to Todos Santos Bay lBaja California (Burch, No 56, p. 29 .1 Monterey, Calif. to Todos Santos Bay, Baja California (Burch No. 56, p. 32.) Monterey, Calif, to CedrosI Island oBaja Cali7f)ornia (T. cooperi) (Burch, .54 D Cape San Lucas, Baja California to Acapulco, Mexico (Woodring and Bramlette, 1950,p 8) Forrester Island, Alaska, to Peru (Burch, No. 54,p. 43).l Crescent City, Calif. (Burch, No. 54, p. 48)1 to Catalina Island, Calif. (Burch, No. 54, p. 45).1 San Pedro, Ca11f., to Todos Santos Bay, Baja California (Burch, No.54, p. 31). l Low water to 80 (Hertlein and Grant, 1 44, p. 14). 453,51 (Hertlein and Grant, 1944, p. 12‘7- Usually near lowtide mark, but 20 011 Monterey, Calif, and 75 off Redondo Beach, Calif. (Burch, No. 57,13 6). Alaska, 20—50; southern California (Burch No 58, p. 5),132—239 (Woodring, Bram. lette, and Kew, 1946, p. 90). Not uncommon in medium tidal zone (Burch, No. 57, p. 38) .1 At high-tide line and intertidal, on rocks (Vlgéodring, Bramlette, and Kew, 1946, p. . Shallow to moderate depths (Woodring and Vedder, written communication), gmmonly in rocky rubble (Burch, N o P3 Conimonly on kelp (Burch, No. 57, p. 20—25, off San Pedro, Calif. (Commensal on Pecten diegensz‘s Dall) (Burch, No. 56, p. 9) l Shallow (including estuaries) to moderate depths; 50 off Redlondo Beach, Calif. (Burch No., 56,p 12). Commonly on kelp holdfasts (Burch, No. 56,p .15 50—75 off Redondo Beach, Calif, 10—30 in Puget Sound (Burch, No. 56, p. 22).1 Shallow (including estuaries) to moderate depths 10—15 off Malaga Cove, Calif. (Burch, No. 56, p. 21).1 48-795 ofl California coast for C'. russa (Woodring, Bramlette, and Kew, 1946, p. 90), which Woodring (Woodring and Bramlette, 1950, p. 72) treats as 0. aleutoica. Shallow (including estuaries) to 25 (Burch, No. 56, p. 30). Common in estuaries, down to 25 off Monterey and Redondo Beach, Calif. (Burch, No. 56, p. 29, 30) .1 In bays and estuaries, lower limit not listed (Burch, No. 56, p. 32 ).1 10-50 011 Calif, 14—30 off Cedros Island, Baja California (Burch, No. 54, p. 47).1 Littoral to perhaps 20 ofl‘ Mlonterey, Calif. (Burch, No. 54, p.43). 20 011 )Monterey, Calif. (Burch, No. 54, 45 .1 p. 50—181 off California (Woodring, Bram~ lette, and Kew, 1946,p 90.) 298 SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY TABLE 4,—Fossils from Towsley Locality (table 11) Towsley formation Pico formation Santa Susana North of Mountains Sanf Gagoriel North of Santa Clara River valley an F16 F17 F18 F19 F41 F42 F43 F44 F45 F46 F47 F48 F49 F50 F51 F52 Gastropods —Continued Fusitriton oregonenxis (Redfield) _______________ x ____________ R .......... 311A ________________________________________ ?sp. ______ '2 Cymatid? ................................ Eulima cf. E, raymondi Rivers ___________ Pyramidella sp ___________________________ Turbom’lla sp ___________________________ Epitom'um hemphilli (Dall)?_ _ _ _ _ _._- __ _ Architectom'ca sp ________________________ Jaton of. J. festivus (Hinds) .............. Maxwellia gamma (Sowerby) ............. Tritonalia? sp ........................... Boreotrophon cf. B. stuarti (Smith) _______ B.? n. sp.? _______________________________ M uricid? _________________________________ Nucella elxmeremis (Grant and .Gale).___ Forrerz'u of. F. belcheri (Hinds) ________ .__ cf. F. magister (Nomland) ____________ Acamhina spiratu (Blainville), round- shouldered form. spirata (Blainville), angulate form. _. Mitrella carimzta gausapata (Gould) ______ of. M. tuberosa (Carpenter) __________ M.? sp ................................... Neptunea of. N. lyrata (Gmelin) __________ sp ................................... Plicifuaus sp _____________________________ Cglicantharus humerosus (Gabb), slender orm. humerasus (Gabb), intermediate form. humerosus (Gabb), typical form ...... of. C. humerosua (Gabb). _ _..- cf. 0. form (Carpenter) _____ cf. 0. form angulata (Arnold). kettlemanensis (Arnold) _____ Kelletia of. K. kelletii (Forbes) ............ Cantharus? of. C. elegans (Gray) _________ 0. sp ____________________________________ “Nessa" afi. “N." moraniana Martin __ hamlim’ Arnold _________________ of. N. mendicus Could ............... sp ................................... Barbarofuws afi. B. arnoldi (Cossmann)_. of. B. barbarensis (Trask) ____________ Fulgoruria oregonemis (Dall) _____________ Olivella pedroana (Conrad)- . _._-_ __ _. __ :- biplicata Sowerby .................... “ Cancellaria” afl’. “ C.” tritonidea Gabb-- n. sp.? of. “C.” tritom’dea Gabb ______ rapa perrim’ Carson .......... hemphilli Dall _______ amoldi Dall __________________________ See footnotes at end of table. GEOLOGY 0F SOUTHEASTERN VENTURA BASIN and Pico formations—Continued Locality (table 11)—Continued 299 Present habitat Pico formation—Continued North of Santa Clara River valley—Continued South of Santa Clara River valley F59 F60 F61 F62 F76 F77 F78 F79 F80 F81 F82 F85 Geographic range Bathymetric data (depth in fathoms) -MuguB Pribiloff Islands, Bering Sea, to Catalina Island, Calif. (Woodring, Bramlette, and Kew, 1946, p. 88). Probably close to E.cal1'forn1'ca which ranges from Santa Cruz Island, Calif. to Todos Santos Bay, Baja California (Burch, No 53, p. 16). Santa Barbara, Ca11f., to San Ignacio Lagoon, Baja California (Burch, No. 51, 6 Santa Barbara, Calif” to San Hipolito, Baja California (Burch, No.51, (1.36).! Extinct ______ y,C mon g Baja California 7(Burch, No. 51, p. 54). l Extinct ___________________________________ Monterey, Calif. to Socorro, Baja Cali- fornia (Burch, N0. 52, p. 9. Puget Sound to Socorro Island, Baja California (Burch, No. 52, p. 9).1 Forrester Island, Alaska to Salina Cruz, Mexico (Burch, No. 51, p. 14, 15).l Forrester Island, Alaska, to Gulf of California (Burch, No. 51, p. 16).1 ‘iéir“6sfééf 'Kr‘ét'i'cb’ciea'xi.‘ ‘éo' ‘ F€."1')'1i1'o§s',' Calif. (Burch, No. 50, p. 22).1 Circumboreal genus except for P. griseus, which was dredged ofl San Diego, Calif. (Burch, No. 50, p. 16—18).1 Extinct ___________________________________ Santa Barbara, Cal f. to San Qumtm Baly, Baja California (Burch, No. 50, 11)1 Gulf of):l California to Peru (Burch, No. 50, Kodiak Island, Alaska, to Magdalena Bay, Baja California (Burch, No. 51, p. 8).1 Monterey, Calif, to Cedros Island, Baja California (Burch, No. 50,p. 7, 8).1 Heceta Bank, Oregon, to San Diego, Calif. (Burch, No. 50, p. 9).1 Extinct _____________________________ Alaska to Cape San Lucas, Baja Calif (Burch, No. 49, p. 17, 21).1 Vancouver Island, 13. C., to Magdalena Bay)-Baja California (Burch, No. 49, 19 Extinct ___________________________________ d 80—1081 ofi California coast (Woodring, Bramlette, and Kew, 1946, p. 90). E.cal1fom1ca ranges from 20 to 75 (Burch, No.53, p.1 In almost all rocky localities; common on mudflats; as deep as 75 off Redondo Beach, Calif (Burch, No. 51, p. 36).1 Common in all rocky localities, in 30 off Catalina Island, Calif. (Burch, No.51, p. 36).1 50—202 off California (Woodring, Bram- lette, and Kew, 1946, p. 90); low tide to 25 in Alaska (Burch, No 51, p. 58).1 In bays and estuaries to 15 off Redondo Beach, Calif. (Burch, No. 51, p. 54).1 Shallow to moderate depths (Woodring and Vedder, written communication). Common on rocks between tides (Burch, No 52,1) .9).1 Common above hipgh- tide mark on rocks and pilings; estuaries on Mytilus beds (Burch, No. 52, p. 9).1 Commonly on rocky shores, not uncom- mon in 'bays on eel grass; 8 favorite habitat is on floating kelp; as deep as 35 at Catalina (Burch, No. 51, p. 15). 1 7—35 off southern California (Burch, No. 51, p. 16).1 755—958 off Pt. Pinos, Calif.; 0—50 in Alaskan waters (Burch, No. 50, p. 22; No. 51 ,p. 30).1 P. griseus in 414 and 636 off southern California coast (Burch, No. 50, p. 17). l Abundant between 10 and 35 off Radon- do, Newport, and Santa Monica, Calif. (Burch, No.50, p. 11).1 Shallow, including littoral, to moderate depths; as deep as 40 off Monterey, Calif. (Burch, No. 51, p. 8).1 15—108 (Burch, No. 50, p. 8).1 30—218 off California coast (Woodring, Bramlette, and Kew, 1946, p. 90). Shallow (including lagoons seasonally) to moderate depths; in 40 off Monterey, Calif. (Burch, No. 49,p .2.1)l Shallow (including lagoons seasonally) to moderate depths. Dredged in 25 off Redgnldo Beach, Calif. (Burch, No.49 p 20 300 SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY TABLE 4.—Fossils from Towsley Locality (table 11) Towsley formation Plco formation Santa Susana North of Mountains SanfGalgriel North of Santa Clara River valley au F16 F17 F18 F19 F41 F42 F43 F44 F45 F46 F47 F48 F49 F50 F51 F52 Gastropods—Continued Progabbia of. P. coopen‘ (Gabb) .................................................................... C .................. X ........................ Crawfordina cf. C.fugleri (Arnold) ........................................................................................................................... Admete of. A. gracilior (Carpenter) ................................... X .................... R ............................................... Genus califomicus Hinds ............................................. R .......... R .......... cf .......................................... Turn'cula? sp ____________________________ Antiplanes perversa (Gabb) _______________ sp ................................... Meguwrcula carpenteriana (Gabb) _______ afl. M. cooperz' (Arnold) ______________ Propebela sp ............................. Pceudomelatoma afi. P. semiinflata Grant and Gale ______ Crassispira? sp __________ Elaeocyma empyrosia (Da Ophiodermella afl. 0. quinquecincta (Grant and Gale) .............................. “Drzllia” cf. “D.” graciosana Arnold. Clavine? torrid, genus? ______________ Mangelia afl. M. variegata Carpenter _____ Glyphoatoma conradiana (Gabb) __________ Striaterebrum martini (English) ___________ Actetm afi. A. gramlior Grant and Gale... Acteocz'na cf. A. culcitellu (Gould) ________ Scaphander afi. S. jugularz‘s (Conrad). --. Bulla of. B. gouldiana Pilsbry ............ cf. B. punctulata (Adams) ........... Melampus cf. M. olivaceus Carpenter.-.. Glyplostoma cf. 0. gabrielense Pilsbry _____ Scaphopods: Dentalium neohexagonum Pilsbry and Sharp .................................. cf. D, pretioxum Nutmll .............. Cadulus sp _______________________________ Pelecypods: Acila castrmsis (Hinds) .................. castremis (Hinds), small form.. eemirostrata (Grant and Gale)_. Nuculana cf. N. hamata (Carpenter . of. N. leom‘na (Dall) ................. cf. N. extenuata (Dall) ............... Saccella taphria (Dall) .................... cf. S. orcum' (Arnold) cellulita (Dall) ..... Yoldz’a bermgilma Dall-_ ............ cooperi Gabb ......................... See footnotes at end of table. and- Pico formations—Continued GEOLOGY 0F SOUTHEASTERN VENTURA BASIN Locality (table 11)—Cont-1nued 301 Present habitat Pioo formation—Continued North of Santa Clara River valley—Continued South of Santa Clara River valley F79 F80 F82 F85 Geographic range Bathymetric data (depth in fathoms) F59 F60 F61 F62 F76 F77 F78 .................... ? ---___------_--_-- ...................................... x 1 ...... 7 ________________________ 22:22:31: 221:2"61'." 2:122:22: III: .............. x ______________ x x ...__. .__.__ .............. '1’ _____. ._.___ .__.__ .. .................... X ..._._ .__.._ ._ .............. sp. ..____ .____. ..-___ __ .............. sp. x x ...___ _. X X ........ cf. of. ........ "5'13." III: III: ______ X ......._ Monterey, Calif., toCoronados Islands, Baja California (Burch, No. 49, p. 6).1 Extinct. Possibly related to C'. craw- fordlana (Woodring and Bramlette, 1950, p.77), which ranges from Forrester Island, Alaska, to San Diego, Calif. (Burch, No. 49, p. 9.)1 Aleutian Islands to Todos Santos Bay, Baja California (Burch, No. 49, p 10, 11).1 Probably 1dentical with A. rhyasa (Woodring, Bramlette, and Kew, 1946, p. 90). Farallon Islands, Calif, to Ballenas Lagoon, Baja California (Burch, No. 48, p. 23).1 Alaska 'to San Diego, Calif. (Burch, No. 62, p. 15).1 Bodega Bay, Calif., to Cedros Island, Baja California (Burch, No. 62, p. 5). Extinct ____________________________________ Alaska to California (Woodring and Bramlette, 1950, p. 79). (Bu r,ch p. 8) l to Todos Santos Bay, Bajao Cali- fornia. Extinct ___________________________________ d Alaska to )Gulf of California (Burc , 62,1) San Pedro and Redondo Beach, Calif. (Burch, No 62, p. 24).1 Extinct _____________ Extinct(?) ................................ Alaska? to San Martin Island, Baja Cali- fornia (Burch, No. 47, p. 12).1 Extinct ___________________________________ Santa Barbara, Calif, to Mazatlan, Mexico (Burch, N0. 48, p. 2).1 Ensenada, Baja Czalilfornia, (Burch, No. 48, p.2 Monterey Bay (Salinas River), Calif. to Maiatllan, Mexico (Burch, No. 48, p. . Los Angeles region, Calif. (Burch, No. 4, p. 3, Oct. 7, 1941).1 to Peru Monterey, Calif. to Guacomayo, Colom- bia (Burch, No 46, p. 9). Forrester Island, Alaska to San Diego, Calif. (Burch, No. 46, p. 12).1 Sitka, Alaska, to Cedros Island, Baja California (Burch, No. 33, p. 8).1 Extinct ___________________________________ Puget Sound to Panama Bay (Burch, No.33, p. 11).1 Straits of Juan de Fuca to lat 35° N. (Burch, No. 33, p. 11).1 Sitka, Alaska (Burch, No. 33,1). 11).4 ...... Bodega Ba, Calif. (Burch, 0. 33p Extinct ___________________________________ Craig, 3:xgxlasklaBl to Puget Sound (Burch, 33,1310 Bering Sea to Anacapa Island, Calif. (Burch, No.33, p. 13).1 San Francisco, Calif, to Todos Santos 11tol Baja California 1:54;, Baja California (Burch, No. 33, p. l . 15—300 (Burch, No. 49, p. 6). C'. craw ordiana: 46—70 ofl California coast ( urch, No. 49, p. 9) I 20 (Burch, No. 49, p. 11) l to 81 (Wood- ring, Bramlette, and Kew, 1946, p. 90) ofi southern California coast. Far up in estuaries; down to at least 25 gigging open coast (Burch, No. 48, p. In 50—200 011 California coast (Burch. No. 62 ,.p 15). 15-50 (Burch, No. 62, p. 5).1 60—870 ofl California (Woodring and Bramlette, 1950, p. 80). Dredged from 25—50 (Burch, No. 62, p. 8 .1 Littoral to 50 (Burch, No. 62, p. 30).1 20—50 (Burch, No. 62, p.24).1 May be related to A. painei (Grant and Gale, 1931, p. 444), dredged in 30-50 off Catalina Island, Calif. (Burch, No. 47, p. 10).1 10-25 011 California coast (Burch, No. 47, p. 12, l3).1 Commonly in bays and sloughs; as deep as 25 off Catalina Island, Calif. (Burch, No. 48, p. 2).1 On mud flats in bays (Burch, No. 48, p. 11, 12).1 Air breathing. Land snail, usually in hilly areas (Burch, No. 4, p. 3, Oct. 7, 1 4 .1 5—100 011 California (Burch, No. 46, p. 9 .1 20—80 o)fl California coast (Burch, No. 46, p. 12 .1 15—233 ofl Caiifomia coast (Woodring, Bramlette, and Kew, 1946, p. 90). 25-1518110fl California (Burch, No.33, D 1521376631211 1l\/)Ionterey, Calif. (Burch, o 1569 1off Sitka, Alaska (Burch, No. 33, D. 1.) .3— 51 011‘ southern California (Burch, No. 33, p. 11).: 30-40 atl Craig, Alaska (Burch, No. 33, 1.0 152—1041 ofi Monterey, Calif. (Burch, No.33, p. 13 5—15 (Burch, No}. 33, p. 13).1 302 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY TABLE 4.—Foss1'ls from Towsley‘ Locality (table 11) Towsley formation Pico formation Santa Susana North of Mountains SanfGalliriel North of Santa Clara River valley au F16 F17 F18 F19 F41 F42 F43 F44 F45 F46 F47 F48 F49 F50 F51 F52 Pelecypods—Continued Tindan'a? sp _____________________________ Anadara camuloensis (Osmont). trilineata (Conrad) ___________________ trilineata (Conrad),s short form, of A. trilineata canalz‘x (Conrad) _ __ Anemia? sp __________________________ Pododeamua macroschiama (Deshayes).___ Volsella sp _______________________________ Pecten hemphilli Dall. sleamsii Dall _________________________ Aeguipeclen circularis (Sowerby) ......... circularis (Sowerby), small form ______ of. A. purpuratus (Lamarck) _________ Chlamys 13111111110113 hindsii (Carpenter). _ - opuntz’a (Dall) _______________________ Patinopecten healeyi .(Arnold) _ Lyropeoten cerrosemis (Gabb) Ostrea vespertina Conrad _________________ vespertina Conrad, strongly plicate ............................................................................................................. x Eucraggaltlelila aft. E. fluctuata (Carpenter). ................ X .............................................................................................. Cyclocardz'a afi. C". barbarensis (Stearns). ...... X ....-- -__..; cf.A X CLR CLAA X .................. cf. __________________ cf. 0. ventricasa (Gould)......._...-_. ....-. _.-....-__ ....-- -_..._ __-._._-._ __: ....... ‘.._1_____ —.-.._._-_ ....-- .....- ..' .................................. Examine:1113;233:315);::::::::::: :2: i ............ . .......... R .......... x __________________________________________ Lucim’sca nuttallii (Conrad) .................... X X Lucinoma cf. L. annulata (Reeve) .............. Parvilucz’na tenuisculpta (Carpenter) ................................. 01R .................... CLO ............ Sp. ? ........................ Miltha 1111111131 Dall .................................................. SD.R .............................................................................. Tellina 1'dae Dall _______________________________ X ............ ?R .............................................................................. Macoma of. M. calcarea (Gmelin) ........ ?sp. .......................................... R .................................................... X cf. M. calcarea (Gmelin), small form.. ...................................... 73p. ?sp.C R ............ sp. sp. ...... sp. ............ indentata Carpenter? ............................................. R .............................................................................. secta (Conrad) ....................................................................... CLR 7R ................................................ Apolymetis biangulata (Carpenter) ....... Spisula hemphilli (Dall)? ................. Schizothaerus nuttallii (Conrad) ________________ 'Icf. ................................ ?sp.R ‘?sp.R ?sp. .......................................... Dosim’a ponderosa (Gray), subsp ............... X ............ R sp. aff.R .......... X .................. ct? .................. Compsomyax subdiaphana (Carpenter). __ ...................... ?cf. R .......... R C ............ ‘?cf. X ............ ‘?sp. X Pachydesma crassatelloides (Conrad) ................................................ R ____________________________________________________ X [Tivela stultorum (Mawe)]. ' Macrocallistu aft. M squalma (Sowerby). ____________________________________________________________________ cf. __________________________________________ M. ?s Amiantw calloaa (Conrad) __ Chione femandoemis English _____________ X X Protothaca cf. P. staminea (Conrad) ____________ )< ...... ?sp. .................... R ______________________ sp. sp. ........................ See footnotes at end of table. GEOLOGY OF SOUTHEASTERN VENTURA BASIN and Pica formations—Continued 303 Locality (table ll)——Continued Present habitat Pico formation—Continued North of Santa Clara River valley—Continued South of Santa Clara River valley F59 F60 Geographic range Bathymetric data (depth in fathoms) X ______________________________________________________________________ .............. X X ....._ --.-.. --.... __._._ --...- ? 'Isp. ..___-__ 'I ...... . ..... X ____________________________________________ 'f 3 .............................................................. X ? .................................................. X cf. _..._--. ___._-.. III: III: 2222:: 'x" "6f.“ III: III: III: III: 222122 22222222 III: ‘P X cf. X X ____________ X X X ? ........ ‘SHfiifiéin Bering so}; ‘66 865613 233355; Baié' Califomia (Burch, No. 36, p. 3).1 Extinct ________________________ __ Extinct. Possibly related to P. aiegensis, which ranges from Monterey, Calif., to San Benito Islands, Baja California (Burch, No.35, p. 4).1 Monterey, Calif., to Peru (Burch, No. 35, p. 10).1 Some varieties living on South Am (Grant and Gale, 1931, p. 208—210). Alaska to San Diego, Calif. (Burch, No. ,1 _____ 0.... ____.___...._.._.___ __. Baja California and Gulf of California (Grant and Gale, 1931, p. 152). Santa Barbara Islands, Calif., to San Pedro, Calif. (Burch, No.39, p. 8).1 Santa Barbara Channel, Calif., to San Diego, Calif. (Burch, No. 39, p. 13).1 Belkoffski Bay, Alaska, to Coronados Islands, Baja California (Burch, No. 39, p. 14).1 Extinct(?) ................................. San Pedro, Calif., to Mazatlan, Mexico (Burch, No. 40, p. 6).1 Monterey, Calif., to Mazatlan, Mexico (Burch, No. 40, p. 6).1 Port Althorp, Alaska, to Coronados Islands, Baja California (Burch, No. 40, p. 7).1 Bering Sea to Coronados Islands, Baja California (Burch, No. 40, p. 8).‘ Gulf of California to Mazatlan, Mexico (Grant and Gale, 1931, p. 291). Santa Barbara Islands, Calif., to Newport, Calif. (Burch, No. 43, p. 6).1 Arctic Ocean to Monterey Bay, Calif. (Burch, no. 43, p. 11).1 ’ffié'ei'sb'dfia'ib"aéié'Ezii'iléifiifiiidiéfij' No.43, p. 15).1 Vancouver Island, British Columbia to Gulf of California (Burch, No. 43, p. 16).1 Santa Barbara, Calif., to Ensenada, Baja California (Burch, No. 43, p. 9).1 Redondo Beach, Calif., to Nicaragua (Burch, No. 44, p. 19).l Bolinas, Calif., to Scammons Lagoon, Baja California (Burch, No. 44, p. 22).1 Scammons Lagoon, Baja California, to Peru (7) (Woodring, Bramlette, and Kew, 1946, p. 88). Sannakh Islands, Alaska, to Todos Santos Bay, Baja California (Burch, No. 42, p. 1 1 Half Moon Bay, Calif., to Baja California (Burch, No.42, p. 6).1 Scammons Lagoon, Baja California, to Peru (Grant and Gale, 1931, p. 347). Santa Monica, Calif., to Gulf of Tehuan- - tepec (Burch, No. 42, p. 7).l Extinct ___________________________________ 681734 0—62—3 Aleutian Islands to San Quintin Bay, Baja California (Burch, No. 42, p. 13).1 A deepwater genus (Burch, No. 33, p. 14) On stones, pilings, etc., near low-tide line; as deep as 35 ofi Redondo Beach, Calif. (Burch, No. 36, p. 3).1 P. diegensia dredged in 14-266 off Call- fomia (Woodring, Bramlette, and Kew, 1946, p. 90). Sloughs to 25 (Burch, No. 35, p. 11).1 50 (one record) (Burch, No. 35, p. 6).1 25—30 off Catalina Island, Calif. (Burch, No. 39, p. 8).l 62—276 in Santa Barbara Channel (Wood- ring, Bramlette, and Kew, 1946, p. 90). 35—149 off Monterey, Calif. (Burch, No. 39, p. 14).! Upper reaches of bays down to 20 (Burch, 1 25 off southern California (Burch, No. 40, p. 7).1 f. annulata var. densilineata dredged from 8 to about 75 oil California (Burch, No. 40, p. 7).1 19 ofi)Monterey, Calif. (Burch, No. 40, p. 8 .1 In Newport Bay, Calif., and as deep as 50 off Redondo, Calif. (Burch, No. 43, p. 6).1 15—60 (Burch, N0. 43, p. 11).1 Lagoons (for example, Playa del Rey, Calif.) to as deep as 25 off Redondo Beach, Calif. (Burch, No. 43, p. 15).1 Bays, sloughs, and beaches. As deep as 25 off Redondo Beach, Calif. (Burch, No. 43, p. 16).1 Bays to as deep as 25 off Redondo Beach, Calif. (Burch, No. 43, p. 10).1 Immature in bays and lagoons, full- grown offshore in shallow water (Burch, No. 44, p. 20).1 Common in lagoons. Young living specimens in 20—25 off Redondo Beach, Calif. (Burch, No. 44, p. 20).1 1 (Burch, No. 42, p. 11).1 to 270 (Woodring, Bramlette, and Kew, 1946, p. 90) of! California. ‘ In surf (Burch, No. 42, p. 6).1 Just below low-tide line on sandy beaches, in surf (Burch, No. 42, p. 7 .1 304 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY TABLE 4,—Fossils from Towsley Locality (table 11) Towsley formation Pico formation Santa Susana North of Mountains San Gabriel fault North of Santa Clara River valley F16 F17 F18 F19 F41 F42 F43 F44 F45 F46 F47 F48 F49} F50 F51 F52 Pelecypods—Continued P. tenerrima (Carpenter) ................................................................. Psephidia lordi (Baird)? _________________ Petricala carditoides (Conrad)? ............ Trachycardium quadrayenarium (Conrad) , Laevicurdium of. L. substriatum (Conrad)- Pratulum centifilosum (Carpenter) _______ Chama pelludica Broderip? _______________ Paeudochama exogyra (Conrad)? __________ Gan" edemulu (Gabb) ..................... Mya aremm'a Linné? _____________________ Cryptomya califomica (Conrad) .......... Swan-malaria? of. S. nuttallii Conrad _____ Tagelua aubteres (Conrad)? ............... Panomya sp ............................. Corbula luleola Carpenter ................ (Iglrticorbula) gibbiformis Grant and a e. Solen cf. S. pem'm' Clark ................. Siliqua sp .............. Panope generosa Gould ................... Thracia trapezoideé Conrad _______________ Pandora punctuata Conrad ............... Cardiomya cf. 0. planetica Dall ........... Echinoids: Demiraster cf. D. diegoensis diegoensis __________________________________________ ew. D.? 51). indet _____________________ Briasopsz's pacifica (A. Agassiz)?_._- ..................................... Barnacles: Balunus cf. B. aquila Pilsbry__.. sp ............................. __ Mammal (identified by Remington Kell g) Illium of unidentified small cat __________ __________ cf.R ._..-_ _.._._ __._-. -_.... 7 -..._- -____- cf.>< I From unpublished minutes of the Conchological Society of Southern California, compiled by J. Q. Burch. 2 A smooth species unlike any described fossil of Recent trochid from Pacific coast. 3 Identified in the field by J. G. Vedder. GEOLOGY OF SOUTHEASTERN VENTURA BASIN and Pica formations—Continued 305 Locality (table ll)—Continued Present habitat Pico formation—Continued North of Santa Clara River valley—Continued South of Santa Clara River valley Geographic range Bathymetric data (depth in fathoms) F59 F60 F61 F62 F76 F77 F78 F79 F80 F81 F82 F85 ch ______ cf ________________________ cf. ........ of. Vancouver, British Columbia to Cape Littoral to 25 off Redlondo Beach, Calif ''''''''''' ' San Lucas, Baja California (Burch, No. (Burch, No 42, p 2,) 42, p 12 ................................................. ?sp. 3 Unalaska, Alaska, to Coronados Islands, 4—30 (Burch, No, 42, p, 16; No. 43, p_34).1 __________________ Baja California (Burch, No. 42, p. 16).! _______ x ______ ______ ______ -__.__ -_._._ -___._-. _..__-__ Vancouver Island, British Columbia, to Littoral to 40 (Burch, No.42, p, 19),1 """""""""""""" Magdalena Bay, Baja California (Burch, No. 42, p. 19).l of at ?sp. x of ______ cf ____________ sp. ................ Santa Barbara, Calif, to Todos Santos Upper reaches of estuaries to as deep as- Bay, lBaja California (Burch, No. 41, 75 off Redondo Beach, Calif (Burch, p. 21).1 No. 41, p. 21, 22).! _________________________________________ x .____. ....._._ ..._.... Point Mugu, Calif. to Acapulco, Mexico Common in sloughs and bays As deep """""" (Burch, No. 41, p. 26).1 as 25013 Redondo Beach, Calif (Burch, No.41, p. 26). 1 ______________ ‘Icf. .__... __-_._ ______ ? ..___. ..-.__ ‘? .__...__ ______._ Bodega Bay, Calif., to Baja CalifOrnia (Burch, No 41, p. 27) Oregon to Chile (Burch, No. 39, p. 18) 1.... Oregon to Panama (Burch, No. 39, p. 19).1 Redondo Beach, Calif, to San Diego, Calif. (Burch, No. 43, p. 22).1 Circumboreal, south to Vancouver Is- land(?); introduced into San Francisco Bay (Burch, No. 44, p. 26).1 Chicagofi Island, Alaska, to Topolo- bampo, Mexico (Burch, No. 44, p. 26).1 Monterey, Calif, to Magdalena Bay, Baja California (Burch, No. 43, p. 22). 1 Santa Barbara, Calif, to Panama (Burch, No. 43, p. 23).‘ Monterey, Calif, to Acapulco, Mexico (Burch, No. 44, p. 28). Extinct ___________________________________ _____ do...___.______-__________.._..._._____ Forrester Island, Alaska, to Scammons Lagoon, Baja California (Burch, No. 44, p. 29. Craig, Alaska, to Redondo Beach, Calif. (Burch, No. 45, p. 9).1 Vancouver Island, British Columbia, to Gulf of California (Burch, No. 38, p. 3).1 Bering Sea to Coronado Islands, Baja Cal« ifornia (Burch, No. 38, p. 13).1 Extinct ____________________________________ Off southern California; Gulf of California (Grant and Hertlein, 1938, p. 126). 16—108 off California (Woodring, Bram- lette, and Kew, 1946, p. 90). On rocks, pilings, etc. from just below low-tide mark to 25 off Redondo Beach, Calif. (Burch, No 39, p. 18).1 Intertidal (Burch, No. 39, p. 19).1 Shallow water, perhaps 15 off Redondo Beach, Calif. (Burch, No. 43, p. 22).1 Commonly on mud flats at low-tide line (Ricketts and Calvin, 1952, p. 303, 304). Common in bays and lagoons, but also alongopen coast (Burch, No. 44, p. 27). 1 Mainly estuarine and lagoonal (Burch, No. 43,1) 22.)1 Intertidal 1n bays (Burch, No. 43, p. 23).1 Littoral to 25 (Burch, No. 44, p. 29).l Deep mud, especially in lagoons and bays (Burch, No. 44, p. 30).1 16 (Woodn'ng, Bramlette, and Kew, 1946, p. 90) to 75 (Burch, No. 37, p. 13).1 Below lowest tide line to 25 off southern California (Burch, No 38. p. 3)1 35—202) ofi California (Burch, No. 39, p. 5 .1 20—780 (Woodring and Vedder, written communication, 1953). \ 306 have not been transported. Shark teeth, not noted in previous lists of fossils, are numerous at some places. North or San Gabriel fault Collections were made from two localities, F18 and F19, in the Towsley formation in sec. 20, T. 4 N., R. 15W. The species are listed in table 4. This list includes Norrisia norrisi (Sowerby)?, “Drillia” cf. “D”. gracio— sana Arnold, and Eucrassatella aff. E. fluctuate (Carpen- ter) not previously recorded from the Ventura basin (Vedder and Woodring, written communication, 1953). Kew (1924, 100. 3591) lists fossils collected from the Towsley formation in sec. 32, T. 4 N., R. 15 W. in- cluding the following speciesz: Ohione fernandoensis English, Phacoides annulatus Reeve (=Lucinoma an- nulata (Reeve)), P. nuttalli Conrad (=Lucz’nisca nut- talli (Conrad)), P. sanctaecrucis Arnold? (=?Miltha xantusi Dall), Tellina idae Dallff, Actaeon (Rectcxis) cf. A. punciocoelata Carpenter, Cancellaria elsmerensis English, Ofernandoensis Arnold (=?“0.” tritonidea var. femandoensz's Arnold), 0. tritom'dea Gabb, Columbella (Asiyris) cf. 0. tuberosa Carpenter (=Mifrella cf. M. tuberosa (Carpenter)), Mimi tristis Swainson, Nessa califomiana, Conrad (:?“N.” moraniana Martin), Natica recluziana Petit (=Neverita reclusiana (De- shayes)), Terebra simplex Cooper (=?Stri0terebrum pedrormum Dall), Trophosycon nodz‘ferum (Gabb) (=?T. ocoyana var. rug’modosa, Grant and Gale), T arm's (Bathytoma) cooperi Arnold (=Megasurcula coopem' (Arnold)), and Turm'tella cooperi Carpenter. About 1 mile east of the area shown on the geologic map (pl. 44), in sec. 27, T. 4 N., R. 15 W., Gale (Grant and Gale, 1931, p. 30) collected Patinopecten healeyz' var. lohri (Hertlein) and Trophosycon ocoyana (Conrad) from beds of lithology similar to those in sec. 32. Environment Suggested Attempts to define the environments that were occupied by fossil assemblages involve the assumption that the ecologic requirements of a species remain fairly constant through time, or that living close relatives of extinct species have habitats similar to those of their fossil relatives. It is further assumed that any physiological changes that develop in the species during the course of time will be reflected in some morphological change. That these assumptions ”may not be entirely valid is suggested by many in- stances in California and elsewhere of late Tertiary assemblages which contain at one locality and in one 2 The names in parentheses are translations by Winterer of the nomenclature used by Kew into more recently accepted terminology. SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY bed a mixture of species whose modern representa- tives live in habitats greatly different from one another. At many places a part of the mixing stems from the fact that remains of organisms that lived under many different ecologic conditions were transported and brought together after death. Just as streams carry plant remains from many different altitudes and deposit these remains together on a flood plain, so also waves and longshore currents and particularly submarine slides and turbidity currents may transport organic remains far from the places where the organisms lived. The opportunities for mixing of assemblages from various depths are especially favorable where sliding or turbidity currents are operative. It is well known that some animals that live in shallow water in northern regions are found only in deeper water in more southerly regions, owing, apparently, to the temperature requirements of the animals. The presence of shallow-water fossils in coarse—grained rocks has led some workers to conclude, sometimes incor- rectly, that the environment of deposition was neces— sarily in shallow water. Inferences about water temperatures that do not take into account the possible mixing of species from several depth zones are there- fore not realistic. Even after mixing of species from several depth zones is considered, some fossil faunas still show a residue of anomalous associations of species. Many of the anomalies can be understood by considering the variety of environments avail- able to marine organisms, even in shallow water. Such factors as salinity, exposure to waves, character of the bottom, and temperature, to mention but a few, vary irregularly within short distances along a coast. For example, the local upwelling of cold water, a very common phenomenon along the California coast, permits species generally found only in cool deep water to live locally in shallow water. The great variety of ecologic niches occupied by organisms within a small area and the possibility of faunas from several of these habitats being mixed mean that inferences about past environments must be based on communities rather than on selected individual species. As pointed out by Woodring and Trumbull who identified the collection (written communication, 1952), the fauna from locality F17 in the Santa Susana Moun- tains is a mixture of species whose modern representa- tives live in different depth zones. In table 4 the bathymetric distribution of the Recent forms is shown; 3 3 The data for both the bathymetric and geographic distribution of Recent forms were compiled by E. L. Winterer, who prepared the discussion of paleoecological interpretations, except where otherwise noted. GEOLOGY OF SOUTHEASTERN VENTURA BASIN the bathymetric range of mollusks from locality F17 is given in the table below: [Compiled by E. L. Winterer from data on referred fossils by Woodring and Trum- bull (written communication, 1952)] Water depth (feet) Mollusk Deep (more than 600)- Yoldia aff. Y. beringiana Dall Calyptogena lasia (Woodring) (related to C. pacifica) Solariella aff. S. peramabilis Carpenter Fusitriton oregonensis (Redfield) Barbarofusus afl‘. B. arnoldi (Cossmann) Cyclocardia afl". C. barbarensis (Stearns) Turritella cooperi Carpenter Kelletia cf. K. kelletii (Forbes) Tegula of. T. ligulata (Menke) Crepidula cf. 0. onyx Sowerby Neverita reclusiana (Deshayes) Aletes squamigerus Carpenter? Sacella taphria (Dall) Aequipecten circularis (Sowerby) Lucina excavata Carpenter Lucim'sca nuttalli (Conrad) Lucinoma cf. L. annulata (Reeve) Tellina idae Dall Schizothaerus nuttalli (Conrad) Corbula luteola Carpenter Ostrea vespertina Conrad Amiantis? of. A. callosa (Conrad) Terrestrial ___________ Glyptostoma cf. G. gabrz’elense Pilsbry Moderate (60—600, but ranging into deep). Moderate (60—600) _ _ _ _ Shallow (less than 60, but ranging into moderate). Shallow (less than 60)- According to Woodring and Trumbull (written com— munication, 1952), “The shallow-water species and those ranging from shallow water to moderate depths * * * are represented for the most part by a few in- complete or worn specimens. Other species, however, also are represented by a few incomplete or worn specimens.” The megafauna collected at locality F17 is obviously an assemblage of shells brought together after death; the presence of the shells in association with graded beds suggests that the agent of transpor- tation was a turbidity current. The depth of water at the site of deposition was probably in excess of 600 feet. The modern representatives of the molluscan assem- blage at locality F17 live either in shallow water or at moderate depths. Foraminiferal faunas from the Towsley formation of the Santa Susana Mountains contain such species as Bulimina ro'strata and Gyroidina rotundimargo, suggest- ing water depths of perhaps 3,000 feet. Forms such as Robulus cushmam' are known from Recent collections from depths as shallow as 100 feet, While Bulimina rostrata ranges downward to 11,000 feet. The modern representatives and relatives of the fauna of the Towsley formation in the Elsmere Canyon area live in shallow water or in water ranging from shallow to moderate depths. The abundance of paired 307 pelecypod valves and the stratigraphic position of the fossils, near the base of the formation where it rests unconformably on older rocks, seem to indicate that the shells were not transported far, if at all, from their life habitats, and that the water was shallow or only moderately deep during deposition of the fossiliferous part of the formation. One foraminiferal fauna from the Towsley formation at Elsmere Canyon (loc. f36) is difficult to evaluate bathymetrically. Depth ranges of some of the species in that fauna, based upon the range of closely allied modern forms living off California, are; Cassidulina translucens, 400—6,000 feet, Cibicides mckcmmn', 300— 3,330 feet, Epistominella pacified, 700—6,500 feet, and Uvigerina peregrine, 500—8,000 feet. Locality f36 is little more than 150 feet above the base of the formation and only 100—140 feet above numerous shallow-water mollusks. The fauna at locality F18, north of the San Gabriel fault near the base of the Towsley formation, consists of moderate—depth species such as Terebmtalt'a occi- dentalis, Calyptrea cf. 0. fastigiata, Turm'tella coopem‘ subsp, and Eucrassatella aff. E. fluctuate; species that range from shallow to moderate depths such as Acmaea? cf. A. mitm, Olivella cf. pedroana, and Trachycardt'um cf. T. quadragenarium; and shallow-water species such as Panope generosa?. At locality F19, severalhundred feet stratigraphically above locality F18, no strictly shallow-water species were collected. Species that range from shallow into moderate depths include Neverita reclusiana, Olivella pedroana, and Saccella cf. .8. taphm'a. Two species, Boreotrophon cf. B. stuarti and Oompsomyam? cf. 0. subdiaphana range from moderate depths into deep water. Foraminiferal faunas from localities f37 to f40 (close to locality F18) are dominated by species whose Recent relatives can nearly all be found at depths of from 500. to 1,000 feet. Some species, for example, Buliminella elegantt’ssima, range into quite shallow water, while several others range to depths of more than 3,000 feet. The geographic range of the Recent close relatives of the fossils found in the Towsley formation provides a basis for inferences about environments during the time the formation was being deposited. Table 5 shows the geographic affinities of fossils in the Towsley formation having living close relatives. The southern affinities of all the species collected from the Towsley formation that are confined strictly to a very shallow habitat are further emphasized by the fact that their modern relatives range at least as far 308 SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY TABLE 5.—Geogmphic range of Recent species related to fossils from the Towsley formation [Data compiled by E. L. Winterer] Locality Present status in relation to latitude of Ventura, Water depth Calif. Fossil Santa North Susana Elsmere of San Moun- Canyon Gabriel tains fault Turrttella of. T. gonostoma var. hemphz'lli Applln _____ X .......... Recent species and Recent relatives extinct, but now living farther south. Bim’um cf. B. asperum (Gabb) Ostrea vespertina Conrad ...... Miltha zantusi Dall ....... Lucina ercaoata Carpenter Spisula hemphilli (Dall)___. Dosim’a ponderosu (Gray). Amiantis callosu (Conrad) _____ Shallow or ranging from shal- low to moderate. Recent species and Recent relatives living at or near northern limits of their range. Neverita reclustamz (Deshayes) Mazwellia gamma (Sowerby) ._._ Kelletta cf. K. kelletiz' (Forbes). Tellina tdae Dall ____________________ Apolymetis biangulato (Carpenter) ________ Trachycardium quadragenarium (Conrad). Recent species extinct, but now living farther north Mya truncate Linné ______________________ Recent relative living at or near southern limits of its range. Megasurcula cf. M. carpenteriana (Gabb) ____________ Recent relative extinct, but now living farther south Elaeocyma aff. E. empyrosia (Dali) __________________ Recent relatives living at or near northern limits of their range. Eucrassatella afi. E. fluctuate (Carpenter) __ Cyclocardta aff. C. barbarensis (Stearns) ______________ Recent species and Recent relatives extinct, but now Moderate and deep living farther north. Cryptonatica aleutica‘? Dall ____________ Chlamys islzmdtcus hindsii (Carpenter) Macoma cf. M. calcarea (Gmelin).. Recent species and Recent relatives living at or near southern limits of their range. Calyptraea cf. 0. factigiata Oould.. Fusitritan oreganensis (Redfield). Yoldia beringianu Dall. _______ C’alpytogena lasia (Woodring)__ XXX south as Todos Santos Bay, Baja California. This range indicates that temperatures in shallow water during deposition of the Towsley formation were prob- ably several degrees warmer than they are at Ventura today. Mya truncate, however, which is in the shallow- Water assemblage at Elsmere Canyon and also at some other shallow-water Pliocene localities in California, does not range south of Puget Sound today. The anomalous occurrence of this circumboreal species in a “southern” fauna may have an explanation similar to that given for some of the anomalous associations recorded in late Tertiary floras. Axelrod (1941) re- viewed the floral problem and concluded that in the past some species may have had a tolerance for a broad range of environments, but that “ecotypes” adapted to certain of these environments may later have been eliminated. The modern representatives of the species may occupy a narrow ecologic niche greatly different from those occupied by some of the fossil members. Woodring (Woodring, Bramlette and Kew, 1946, p. 102; Woodring and Bramlette, 1950, p. 99) has warned against blind reliance on present geographic and bathy- metric distribution as an index to the environmental conditions under which a species may have lived in the past. PLIOCENE SERIES moo FORMATION Throughout most of the eastern Ventura basin the Towsley formation is overlain by the marine Pico for- mation. The Pico formation consists chiefly of light olive-gray and medium bluish- gray siltstone and fine- grained silty sandstone, containing small reddish—brown concretions, and light-colored sandstone and con- glomerate. In the western part of the area the sand- stone and conglomerate constitute a minor portion of the formation. In the easternmost part of the area the converse is true; there the formation consists largely of sandstone and conglomerate. The Pico formation is distinguished from the Towsley formation largely by the presence in the Pico of olive- gray soft siltstone that generally contains small limonite concretions. The lower part of the Pico very closely resembles the upper part of the Towsley formation; the contact is drawn at the base of the first prominent sandstone 0r conglomerate unit below the lowest bed of olive-gray concretion-bearing soft siltstone. The stratigraphic level of the contact is not exactly the same everywhere. In the area around San Fernando Pass the characteristic siltstone of the Pico formation is present only in minor amounts; there the base of the Pico is placed at the base of the sandstone and con- glomerate units that overlie the brown—weathering siltstone and fine-grained sandstone of the Towsley. The Towsley and Pico formations interfinger in the area near San Fernando Pass. At Elsmere and Whitney Canyons the base of the Pico formation is an unconformity. The Pico formation is entirely marine but interfingers at the top with normal marine, brackish—water, lagoonal, and nonmarine beds of the Sunshine Ranch member of the Saugus formation. Figure 54 illustrates dia- GEOLOGY OF SOUTHEASTERN VENTURA BASIN 309 PICO FORMATION SAUGUS FORMATION M a r i n e Brwagtlglsh Continental SEA LEVEL 2000 FEET Graded beds of sand and gravel with transported fauna Silt with an in-place fauna Sand and gravel deposited here later Gap in sedimentation Ungraded, poorly bedded, and cross- bedded sand and gravel with an in-place fauna Fluviatile sand and gravel Greenish-gray sill in lagoon FIGURE 54.—The relation between contemporary upper Pliocene deposits of the Saugus and the Pico formations. grammatically the conditions resulting in the contem- poraneous deposition of the marine Pico formation and the nonmarine Saugus formation. Minor fluctuations in the position of the shoreline together with the general retreat of the sea westward as the basin filled resulted in an interfingering relationship of the marine and nonmarine beds. In the western part of the area the Pico formation is about 5,000 feet thick; in the eastern part of the area, near the Placerita oil field, it is only a few hundred feet thick. STRATIGRAPHY AND LITHOLOGY Newhall-Potrero Area South of the Santa Clara River in the area between the Los Angeles-Ventura County line and the Newhall- Potrero oil field the Pico formation is 5,000 or more feet thick and consists chiefly of light olive-gray, gener- ally poorly bedded soft siltstone. Potrero Canyon, a broad lowland containing the Newhall—Potrero oil field, is formed in this soft siltstone. The siltstone generally contains many ellipsoidal concretions, most about 1 inch, but some as much as 6 inches in diameter. The concretions are dark yellowish orange and weather to light brown and moderate brown. The cementing material in the concretions is a car— bonate. Closely similar concretions occur in the Santa Barbara formation, of early Pleistocene age, in the Ventura region. In well cores the concretions in the Santa Barbara formation contain ankerite (Bailey, 1935, p. 492). Slopes developed on weathered siltstone of the Pico formation are commonly strewn with concretions. The siltstone contains Foraminifera but not in great abundance. A few hundred individuals can be recov— ered from an average 100 cc sample. Paired valves of small thin-shelled pelecypods, such as Yoldz’a scissurata and Macoma, and poorly preserved mollusks, as well as echinoid spines and external molds of echinoids, are scattered in the siltstone. Interbedded with the siltstone are layers a few inches thick of pale-olive fine—grained silty sandstone that weathers to a dark yellowish orange. In the lower part of the formation many of the sandstone beds are graded and closely resemble graded beds in the Towsley formation. In the upper part of the formation the beds of sandstone are commonly not noticeably graded. Occasional thin beds of grayish—olive brittle claystone are interbedded in the siltstone. In the lower third of the formation, units of light brownish-gray sandy mudstone that weather to a mod- erate brown alternate with units of siltstone. The brown-weathering jarositic mudstone is indistinguish— able from the mudstone in the upper part of the Towsley 310 formation (p. 289) with respect to lithology and weather- ing characteristics. Lenses of interbedded conglomerate and sandstone ranging in thickness from a few inches to as much as 500 feet are common in the lower half of the formation. These lenses tend to form bold topographic features, and a few can be traced for several miles; other lenses extend for less than 100 yards. Very abrupt lateral gradations from conglomerate to siltstone are common. At places a thickness of as much as 20 feet of sandstone and conglomerate grades laterally into siltstone in a distance of less than 20 yards. The conglomeratic lenses closely resemble the con- glomeratic units of the Towsley formation. The coarsest beds, consisting chiefly of cobbles, are generally several feet thick and nearly homogeneous in texture throughout their thickness. Beds consisting of pebbles and sand grains are commonly graded. Load casts are not uncommon in the graded beds, and at many places shallow channels were cut into the underlying beds. Sets of small—scale cross laminae, so common in the Towsley formation, are only in the lower beds in the Pico formation. Slump structures occur at a few places in the sandstone beds, but convolute bedding is not known. Beds containing small angular bits of charcoallike material are common, especially in the lower part of the formation. The sandstone and con- glomerate beds contain mollusks at many places, but the shells are generally concentrated in local lenses and pods. Paired pelecypod valves do not occur at these localities and many of the shells are broken or worn. Counts of pebbles from conglomerate beds at several places in the Pico formation in the mapped area showed that the conglomerate is very similar to that in the Towsley formation with respect to kinds of clasts and to their relative abundances (p. 290). In the uppermost parts of the Pico formation the olive-gray soft siltstone is more fossiliferous than similar rocks lower in the formation and is interbedded with nearly white or cream-colored massive thick- bedded conglomeratic sandstone and dusky-yellow silty sandstone. Paired valves of large pelecypods such as Sam'domus and Panope are not uncommon in the upper- most siltstone beds. The silty sandstone beds are very fossiliferous in some places, with Ostrea vespertina, Pecten hemphilli, P. stearnsii, and paired valves of Cyclo- cardz'a cf. 0. ventricosa especially abundant at some places. The beds of pebbly sandstone contain Den- draster, oysters, and pectens at many places (identi- fications by Winterer). Newhall-Potrero 011 field 170 East Canyon Eastward from the southeastern part of the Newhall- Potrero oil field the siltstone beds in the upper three- fifths of the Pico formation grade laterally into marine SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY sandstone and conglomerate beds which in turn grade into brackish-water and nonmarine beds of the Saugus formation. The contact between the two formations oc- curs at lower and lower stratigraphic levels eastward beyond Pico Canyon. Near the southeast end of the N ewhall-Potrero oil field the Pico formation is about 5,300 feet thick; 4 miles farther southeast, near East Canyon, the rocks assigned to it are only about 2,000 feet thick. The decrease in the thickness results wholly from lateral gradation in the upper part of the for- mation, as can be demonstrated by tracing several persistent units of conglomerate and sandstone east- ward from the oil field. These beds in the middle of the Pico near the oil field extend eastward into the Saugus. The mapping of these persistent units showed that the thickness of the part of the formation below the traced beds actually increases eastward, and that all the decrease in thickness of the formation as a whole takes place in its upper part. The most abrupt lateral graduation from siltstone to sandstone and conglomerate is at the southeast end of the Newhall—Potrero oil field, where a sequence of siltstone beds about 800 feet thick grades eastward into sandstone and conglomerate in a horizontal dis- tance of about 1,000 feet. The exposure in the transi- tion zone between the sandstone and conglomerate beds and the siltstone beds are sufficient to exclude the pos- sibility of major faulting. Many of the sandstone and conglomerate beds in the transition zone are graded. Figure 55 shows thick beds of conglomerate and sandstone alternating with thinner beds of dark-colored siltstone and fine-grained sandstone exposed near the southeast edge of the New- hall-Potrero oil field. The sandstone and conglomerate beds are graded, show marked changes of thickness, channel underlying beds, and contain slump struc- tures and angular siltstone fragments. The conglomer- ate grades upward without a break into-sandstone that contains scattered blocks of siltstone. The next over- lying bed likewise grades from conglomerate to sand; in fact, all the sandstone and conglomerate beds at this exposure are graded. Eastward the graded bedding in the transition zone becomes more obscure, and in a distance of about half a mile the beds show no grading and are slightly more conglomeratic. Scattered fragments of marine mol— lusks occur in the sandstone and conglomerate beds near the transition zone, but farther east fossils are lacking. Still farther east equivalent strata are mapped as part of the Saugus formation. The conditions of deposition are discussed on pages 309, 319, 320, and 325. In the area between Little Moore Canyon and San Fernando Pass, the upper part of the Pico formation is quite fossiliferous. At some places, especially in the GEOLOGY 0F SOUTHEASTERN VENTURA BASIN 311 FIGURE 55.—Conglomerate, sandstone, and siltstone beds of the Pico formation near the southeast end of the Newhall-Potrero oil field. Near right edge of photograph, a thick bed of conglomerate rests on an eroded surface; beds beneath the conglomerate are cut out to depths of at least 4 feet. Sandstone beds in the center have marked changes of thickness, a very characteristic feature of the beds in this area. structures are shown. more conglomeratic beds, the fossils are broken and worn, but at many places paired pelecypod valves are common. Near the mouth of Towsley Canyon several beds yield numerous specimens of a smooth form of Terebmtalia occidentalis (identified by Winterer). Mouth of East Canyon to San Fernando Pass Beginning at a point near the mouth of East Canyon, many tongues of sandstone and conglomerate appear in the Pico formation throughout its thickness. These tongues thicken eastward at the expense of the inter- vening units of siltstone and fine-grained sandstone. In the uppermost part of the formation near East Can- . yon some of the more sandy units are cross-stratified. Eastward large-scale cross-stratification appears in units progressively lower in the formation. At San Fernando Pass even the lowest part of the formation contains large—scale sets of cross—strata (fig. 53). The lower part of the formation consists of the typi- cal light olive-gray soft siltstone and fine-grained silty sandstone alternating with lenticular units of re- sistant conglomerate and sandstone. Graded bedding is prevalent in the coarse—grained units from East Can- yon to the divide between Gavin and Weldon Canyons. Megafossils are very abundant in some of the fine- In the upper left, conspicuous slump grained beds in the upper part of the formation and are locally abundant in a few conglomerate lenses. In the southeast corner of the mapped area (pl. 44), the Pico formation is represented by nearly White, very thick bedded conglomeratic sandstone and minor amounts of gray siltstone. Several 1- to 2-foot beds of reddish-brown to nearly black, hard fine- to coarse- grained sandstone in the upper part of the formation near San Fernando Pass consist almost entirely of magnetite and ilmenite with minor amounts of quartz, feldspar, red garnet, and zircon. San Fernando Pass to San Gabriel fault At San Fernando Pass, south of the Beacon fault, the cross-stratified conglomeratic beds in the lower part of the Pico formation interfinger with the brownish silt— stone beds of the Towsley formation. North of the Beacon fault an unconformity separates the two forma— tions. Near Elsmere Canyon the Pico formation con— sists almost entirely of lenticular units of cream-colored and yellowish—brown cross-stratified coarse-grained sandstone and light-brown conglomerate. The con— glomeratic beds in the lower part of the formation are tar soaked. The formation is about 1,000 feet thick in the Elsmere Canyon area. 312 In La Placerita Canyon the base of the Pico formation overlaps the Towsley formation and rests directly on the pre—Cretaceous crystalline rocks. The lower part of the Pico here consists chiefly of lenses of brownish- gray conglomerate and cross-stratified cream-colored pebbly sandstone With minor amounts of fine-grained sandstone and brownish-gray siltstone. In the upper part of the formation, conglomerate beds are less numer— ous and there are more beds of brownish-gray siltstone and silty sandstone. The upper part of the formation is best developed north of La Placerita Canyon, east of the Placerita oil field. Santa. Clara River to Del Valle fault The Pico formation is exposed north of the Santa Clara River in three fault blocks: one south of the Del Valle fault, a second between the Del Valle fault and the Holser fault, and a third north of the Holser fault. A thickness of about 6,000 feet of the Pico formation is exposed in the southward—dipping homocline on the south or hanging—wall side of the Del Valle fault. The gradational contact between the Pico and the under- lying Towsley formation is exposed for a short distance near the intersection of the county line and the trace of the fault. The lowest beds of the Pico formation con- sist of brown-weathering j arositic mudstone alternating with light-brown hard thick—bedded conglomeratic sandstone, light—brown and cream-colored thin-bedded friable fine- to coarse—grained silty sandstone, and light olive—gray siltstone. In the lower 2,000 feet of the formation the proportion of brown-weathering mudstone to olive-gray siltstone steadily decreases upward to zero. Lenses of sandstone and conglomerate occur throughout the formation, but they are most numerous in the middle part. Graded bedding is common in the sandstone. The lenses are locally very fossiliferous and the fossils are commonly worn and broken although some beds contain very well preserved specimens. Paired pelecypod valves do not occur in the coarse-grained beds but are very common in the siltstone. Throughout the formation the silt— stone contains Foraminifera and scattered generally poorly preserved mollusks and echinoids. The section exposed in this part of the area does not extend to the top of the Pico formation, although the conglomerate in the trough of the syncline near the county line is probably near the top of the formation. Del Valle fault to Holser fault The base of the Pico formation is not exposed in the area between the Holser and Del Valle faults. However the beds exposed immediately south of the trace of the Holser fault, in the steep amphitheater just west of the divide between Holser and San Martinez Chiquito SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY Canyons, are very similar in lithology to the lowest part of the Pico south of the Del Valle fault. These beds probably are Within 1,000 feet of the base of the forma- tion. In the area of the Ramona oil field a unit that constitutes the lower 2,000 feet of the Pico formation and that lies above the trace of the Holser fault consists chiefly of olive—gray siltstone with a few lenticular units of sandstone and conglomeratic sandstone and brown— weathering mudstone beds in its lower half. In the area near the county line a sequence of nearly white, very thick bedded sandstone and minor lenses of con- glomerate overlies the siltstone. Eastward from the county line, tongues of sandstone, which thicken and coarsen, appear in the Pico at pro- gressively lower stratigraphic levels. Beginning at about the east line of sec. 17, T. 4 N., R. 17 W., mollusks occur in abundance in many of the silty layers between the sandstone beds. The slender form of Caliccmtharus humerosus is very abundant in some beds. Near the divide between San Martinez Chiquito and San Martinez Grande Canyons, beds consisting almost wholly of closely packed shells of Ostrea vespertina var. sequens are interbedded with the sandstone and siltstone. The oyster reefs are traceable across San Martinez Chiquito Canyon and to the Holser fault. An oyster reef that crops out about 200 feet east of the Texas Malis 1 well in sec. 10, T. 4 N., R. 17 W., yielded a few horse teeth (loo. V84) that Chester Stock identified as Pliohippus (oral communication, 1950). East of San Martinez Chiquito Canyon the siltstone beds have a greenish-gray color, rather than the typical olive—gray color of the Pico formation. Beds of reddish-brown sandy claystone are intercalated with the greenish-gray siltstone beds and oyster reefs. Some of the sandstone beds contain numerous sand dollars. Although it is recognized that the red beds may represent nonmarine deposits and that the beds east of San Martinez Chiquito Canyon could be assigned to the Sunshine Ranch member of the Saugus formation, the prevalence of definitely marine fossils, such as Dendraster, at so many places is believed to be justification for including in the Pico formation all the beds below the'uppermost echinoid-bearing beds. Area north or Holser fault North of the Holser fault near the head of Holser Canyon the Pico formation consists of light-tan fine- to medium-grained sandstone and gray siltstone, with a minor amount of conglomerate. The sandstone is, for the most part, well bedded, individual beds being a few inches to several tens of feet thick. The silt~ stone contains thin hard limy beds and, on the north side of Holser Canyon near its head, both the siltstone and the hard limy beds contain abundant marine fossils. GEOLOGY 0F SOUTHEASTERN VENTURA BASIN Fossils are also present, but not abundant, in the sand- stone. FOSSILS Foramjnltera Several sections across the Pico formation were sampled systematically to determine the faunal succes- sion at various places in the eastern Ventura basin. Plate 47 shows four such sections in graphic form. Plates 48 and 49 show the fauna from each sample, 102 species from 343 localities. The locations of the sections are shown on the geologic map (pl. 44); the numbers at the ends of the traverse legs on the map correspond to the numbers on the columnar sections (pl. 47). At some places the traverse legs are tied by key beds; at other places, where key beds are lacking, the relative stratigraphic position of the partial sections was determined by projection of strike lines. The positions of the samples were determined in the field with tape and Brunton compass. Where no relatively fresh rock was at or near the surface, holes were dug with a hand auger to obtain less weathered material. Nearly all the faunas from Pico Canyon (pl. 48) were picked by T.R. Fahy. Identifications and abun- dance counts were made by Patsy B. Smith on both picked and unpicked material. Where Foraminifera were especially abundant, samples were split by hand, all specimens in a split fraction counted, and the totals multiplied by the number of splits. Temperature and depth information for Recent species was compiled and charted by Patsy B. Smith. The following fauna] and paleoecologic discussion in- volving Foraminifera is taken from written and oral communications from her (1953—1954). In the lower part of the Pico Canyon section are found Bolivina, pisciformis, B. seminuda, Bulimina sub- acuminata, Cassidulina cushmani, O. delicate, Oibz'c'ides mckarmai, Gyroidz’na rotundimargo, Epistominella pa- cifica, E. brcdyana, Um’gerina peregrina, and Bolivina argentea. Several species, including Cibicr'des mckan- ynai, Um'gerina, peregrina, and Epistommella pacifica, are present to the top of the section. Gyroidina rotundimargo is not present above sample fP66. Nonion pompilioides is not in the lower part of the section but is in samples fP59 through fP153. Cassidulirta limbata, occurs in sample fP98 and continues nearly to the top of the section. Gaudryina, arenaria, comes in abun- dantly near sample fP97. Angulogerina angulosa becomes abundant at sample fP120 and continues to the top. Cassidulina californica has its base at sample fP139. The succession in the Towsley Canyon section seems to be a rather compressed version of the Pico Canyon succession. Samples stratigraphically below number fT16 were nearly all barren. The base of the Pico 313 formation is near the horizon of sample fT14. Some of the species present in the lower part of the Pico Can- yon section, such as Bolivina seminuda, and Bulimina, subacuminata, do not occur in the Towsley Canyon section. Gyroidina rotundimargo and Cibicides melam- nai are present below sample fT32, and Bolivina argentea ranges from sample fT29 through fT35. Bolivina pisciformis, Um'gerina peregrina, and Epistomi- nella pacified are present throughout the section. Cassidulina limbata does not occur in the section, but Angulogerina angulosa, Nonion scaphum, and Buli- mma pagoda are present in the upper part of the column. The Gavin Canyon section, which includes only the upper part of the Pico formation, has even fewer species than the Towsley Canyon section. Cibicides mckarmafl} is absent and Nonion pompilioides occurs only in the lowest sample. The fauna is similar to that in the upper part of the Towsley Canyon section. The Weldon-Gavin Divide section, barren below sample fW16, contains a rather meager fauna, con- sisting chiefly of Epistominella pacified, E. subperu— viana, and Um'germa peregrine. The fauna resembles that in the Gavin Canyon section. All the foraminiferal species present in all sections also occur in Recent sediments, with the exception of Behring pisciformis. No foraminiferal species repre- sented is a guide fossil in any restricted sense. On the other hand, the assemblages have ecologic signifi- cance. The sequence of faunas in the Pico Canyon fora- miniferal section suggests a shallowing of the water during deposition of the Pico formation. However, the Pico formation in this area does not have the orderly progression of faunas indicative of a continu- ally shallowing sea that was inferred by Natland (1933, p. 225—230), Natland and Kuenen (1951, p. 76—107), and Bandy (1953b, p. 200—203) for the formation in the western part of the Ventura basin. In an efiort to determine the temperature and depth of water during the deposition of the Pico formation, comparison was made of the conditions under which the Pico foraminiferal species must have lived with those ofl’ the coast of California under which Recent forms of the same species now live. The temperature and depth information for Recent species compiled by Patsy B. Smith from Natland (1933), Crouch (1952), Butcher (1951), and Bandy (1953a) is given in column 0 on plates 48 and 49. The maximum and minimum temperatures and depths reported for Recent species in these sources are used as maximum and minimum ranges for the species on the checklist. No distinction was made in the studies between empty tests and live Foraminifera from the various depth and temperature regions. The possibility of shallow-water species being transported into much deeper water after death should 314 not be discounted when evaluating the depth and tem— perature ranges for Recent forms. The isopleth maps prepared by Butcher for population density of Gas- sidulina limbata are instructive in that they show the depth at which tests of that species are most abundant ofl“ San Diego. This depth is near the top of the total depth range of tests collected. The maximum and minimum depth and temperature ranges are plotted on plates 48 and 49, diagrams E and F, for species with five or more individuals in the sample. Samples with the largest faunas are plotted, and with few exceptions there is found to be a depth and temperature range common to all species plotted. The main exceptions to this common range are Nom'on pompilz'oides and Pullem'a bulloides, whose minimum. depths in the Eastern Pacific Ocean are reported to be 6,500 feet. They occur abundantly from sample fP59 to sample fP147 of the Pico Canyon section, as do 18 other species whose common depth is around 3,000 feet. The association of these two very deep-water forms with such forms as Cassidulma limbata, O. quadrata, Bulimina denudata, and Gaudryina arenaria is puzzling. It is possible that the shallow-water forms are not indigenous and that the tests were transported into deep water after the death of the animals. However, evidence that at least part of the Pico Canyon section was deposited in shallow water or water of moderate depth is furnished by the presence of a few paired valves of Schizothaerus, a shallow- to moderate-depth pelecypod, in the upper part of the section in geographic and stratigraphic positions close to the two deep— water species of Foraminifera. It is unlikely that the deep-water forms were reworked, as the sources of the Pico sediments lay generally to the east of the Pico Canyon section, and in that region there is no other evidence to indicate erosion in Pico time of deposits which would contain these two deep-water species. It seems more likely that Nom'on pompz'lioz'des and Pullem’a bulloides ranged into shallower water in this region during the Pliocene than they do today. N. pompilioides has been reported in Recent beach sands on the east coast of Japan in association with “Botalia” beccarii (Linné) var. (Harrington, 1955, p. 126). V Ignoring the few aberrant species, a range of probable water depth and temperature during deposition of the Pico Canyon section can be postulated (pl. 48 dia- grams E and F): Apparently, the water shallowed from a depth of 2,000~3,000 feet during deposition of the lower part of the section, to a depth of 600—1,600 feet during deposition of the upper part. The possible depth and temperature range indicated _ by the Towsley Canyon section is much greater than SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY that indicated by the Pico Canyon section (pl. 49, diagrams E and F), although it seems probable, from the geographic position of the Towsley Canyon section, that the water there would be shallower at any par- ticular time. During deposition of the Gavin Canyon section the water was probably never much deeper than 1,500 feet and may have been considerably shallower. The Gavin Canyon section, too, shows evidence of shallow- ing water and of increasing temperatures toward the top (pl. 49 diagrams E and F). The fauna in the Weldon—Gavin Divide section is too sparse to give significant information about depth and temperature of deposition, although the abundance of cross—stratified coarse sediments suggests a near- shore deposit. The Holser-Del Valle section is west and north of the previously discussed sections. It, like the Towsley Canyon section, shows wide and indefinite depth and temperature ranges. On plate 47, dashed lines are drawn between the four columnar sections to relate the highest or lowest occurrences of certain species. The solid double lines connect key horizons that can be correlated from one section to another. The correlations between sections were made by tracing a mappable conglomerate and sandstone unit as far as possible, offsetting a known stratigraphic distance to another mappable conglbmerate and sandstone unit, and then tracing it as far as possi- ble. This process was repeated as many times as nec- essary until the next section was reached. The correla- tion point then was located by compensating for the amount of stratigraphic offset made in tracing mappable lithologic units between the sections. The conglomerate and sandstone beds probably were deposited almost instantaneously by currents and they may therefore be treated as time lines. The crossing of faunal lines, marking depth of water, and time lines, represented by key beds between the Towsley Canyon and Pico Canyon sections, is interpreted to mean that the in- dividual beds were deposited on a slope that. extended from relatively shallow water at Towsley Canyon to relatively deep water at Pico Canyon. The range of depth of water represented by any foraminiferal sample in the sections shown on plate 47 can be approximated by an inspection of data on diagram F on plates 48 and 49. For the Pico, Towsley, and Gavin Canyon sections, the diagram shows a gen- eral trend from deeper water faunas at the base of the sections to shallower water faunas at the top. If a nearly uniform rate of shoaling is assumed for each section, a nearly straight line that stays always within the upper and lower depth tie lines can be drawn through the depth-range diagram (F of pls. 48. and 49) GEOLOGY OF SOUTHEASTERN VENTURA BASIN for each section. Using this line, an estimated depth for each sample can be inferred. The dotted lines on plate 47 connect points of equal depth facies as estimat- ed by this method. A crude parallelism with the dashed lines is at once apparent. It should be empha- sized, however, that no great confidence is placed on the exact position of the depth lines, and very little if any confidence is placed on the 1,500 and 2,000-foot lines, since the depth-range diagrams show no discern- ible trend in their middle portions. The angle at which the depth and faunal lines cross the lithologic lines changes gradually from a very large angle in the upper part of the Pico formation to a very small angle in the lowest parts of the formation. This change indicates that the difference in water ‘ depth between Towsley and Pico Canyons increased ‘ during the time of deposition of the Pico formation. At Pico Canyon the thickness of the Pico is about 5,000 feet; the depth of water at the beginning of deposition was probably about 2,500 feet. The amount of subsidence indicated is about 2,500 feet. At Towsley Canyon the thickness of the Pico formation is about 2,000 feet; if the estimate of 2,500 feet for the water depth at the beginning of deposition is correct, then there was no subsidence. Subsidence at Towsley Canyon at a later time, however, is necessary before deposition of the overlying Saugus formation. Megarossus Although megafossils are present in the siltstone in the lower part of the Pico formation, they are generally widely scattered and poorly preserved. Small pelecy- pods (identified by Winterer), including Ioldz‘a scissu- ram, Spisula, and Macoma?, seem to be the most com- mon forms. Several large faunas were collected from lenticular beds of sandstone and conglomerate in the lower part of the Pico formation north of the Santa Clara River. These collections (from 100. F41—48, F50, F51, F59, and F60) come from graded beds or from beds inti- mately associated with graded beds; the faunas prob- ably were transported to their place of final deposition by turbidity currents or submarine slides. The check- list (table 4) shows the species that occur at the various localities, which are listed in s'tratigraphic sequence. At localities F41, F43, and F44 blocks of fossiliferous rock were collected. The relative abundance of the species obtained from these bulk collections is shown on the checklist. The material at locality F49 occurred as float in a stream bottom and its true stratigraphic position could be anywhere between locality F42 and locality F50, although the distribution of shell frag- ments along the stream indicates that the material came from a horizon no lower than locality F46. 315 According to Woodring, Trumbull, and Vedder (written communications, 1952 and 1953), the following species from the Pico formation have not previously been reported from the Ventura basin: Crepidula cf. C. aculeata (Gmelin) Petaloconchus montereyensis Dall Eulima cf. E. raymondi Rivers “Gyrineum” mediocre lewisii Carson Neptunea cf. N. lyrata (Gmelin) Calicanlharus kettlemanensis (Arnold) “Nassa” hamlz’m’ Arnold Progabbla cf. P. cooperl (Gabb) Mangelia aff. M. variegata Carpenter Melampus cf. M. olivaceus Carpenter Nuculana cf. N. hamala (Carpenter) Nuculana cf. N. extenuata (Dall) Saccella cellulite (Dall) Pachydesma crassalelloides (Conrad) Macrocallisla cf. M. squalida (Sowerby) Cardlomya cf. C. planetica Dall Scaphander aff. S. jugularis (Conrad) was known previously only from Miocene rocks, and Brissopsis pacified, (A. Agassiz)? has not previously been reported from Tertiary rocks of the west coast. The uppermost few hundred feet of the Pico forma- tion are very fossiliferous at most places. Because the interfingering contact between the Pico and the Sun— shine Ranch member of the Saugus formation is time- transgressive, this fossiliferous zone, which Gale (Grant and Gale, 1931) termed the middle Pliocene San Diego zone, is not of the same age everywhere but rather represents a facies fauna. Collections were made from this so-called zone near San Fernando Pass (loc. F76) and near the mouth of Towsley Canyon (loc. F77— ,F81). Locality F61, near Val Verde Park, is in siltstone slightly below the upper fossiliferous zone of the Pico formation. According to Woodring and Vedder (written com- munication, 1953), Laevlcardium cf. L. substriatum (Conrad), from locality F80, has not previously been reported from the Ventura basin. Some of the collections from the lower part of the Pico are from localities where field evidence suggests deposition by turbidity currents, and these collections contain a mixture of species indicative of various depth zones (shallow, less than 60 feet; moderate, 60 to 600 feet; deep, more than 600 feet). Other collections from similar rocks consist of species that could have lived together in the same depth zone. Localities at which there is a mixture of species from different depth zones and localities at which there is no apparent mixing are listed below. Ecologic interpre- » tations for both groups were compiled by Winterer from data that includes reports of Woodring, Trumbull, and 316 Vedder, who identified the collections; all data in quo- tation marks are from Woodring and Vedder (written communication, 1953). Localities with species from difi'erent depth zones Locality Remarks F42 _______ Tegula gallina? suggests shallow water. Cyclocardia afl. C. barbarensis suggests moderate to deep water. The rest of the species live in moderate depths or range from shallow into moderate depths. ”A mixed ecologic facies is suggested by this fauna: shallow water and moderate depth.” F43 _______ “The air-breathing M alampus olivaceous lives above high tide level in the vegetation surrounding shallow bays and mud flats. The Pismo clam, Pachydesma crassatelloides, lives in surf. Cyclo- cardia cf. 0. barbarensis suggests a moderate to deep-water environment.” F44 _______ “A land snail, Glyptostoma sp., * * * is represented. Crepidula onyx, Mitrella carinata gausapata, Bulla cf. B. punctulata, Anadara camuloensis, Ostrea vespertina, Schizothaerus? sp., Protothaca tenerrima and Panope cf. P. generosa indicate shallow water to moderate depths. The majority of the species suggest moderate depths. Yoldia cf. Y. beringi- ana, Cyclocardia afl". C. barbarensis and Cardiomya cf. 0. planetica indicate moderate depths to deep water.” F45 _______ “Tegula ligulata, Crepidula cf. C. onyx, Acanthina spirata, Olivella pedroanaf, Bulla cf. B. gouldiana, Anadara camaloensis, Aequipecten afi'. A. circu- laris, Ostrea vespertina, Schizothaerus? sp., Dosinia ponderosa subsp., Amiantis cf. A. callosa, Pseudo- chama exogyra?, and Chama pellucida indicate shallow to moderate depths. The remaining mollusks suggest moderate depths, with the exception of Cyclocardia afi. C. barbarensis, which ranges into deep water. The echinoid Bris- sopsis pacifica has been recorded from depths of 120 to 4680 feet.” F48 _______ “Mitrella sp., Anadara cf. A. camuloensis, Ostrea vespertina indicate shallow water to moderate depths. Most of the species indicate moderate depths. Nuculana cf. N. hamata suggests mod- erate depths to deep water. Nuculana extenuata? and Yoldia cf. Y. beringiana suggest deep water. The only specimens of the living Nuculana exten- uata in the US. National Museum collections were dredged at a depth of 1,569 fathoms.” F49 _______ Shallow to moderate depths are indicated by Mitrella carinata gausapata, Dosinia cf. D. pon- derosa subsp.?, Protothaca tenerrina, and Gari edentula?. Cyclocardia cf. C. barbarensis sug- gests moderate depths to deep water. “The fauna suggests a mixed-depth facies of shallow, moderate-depth, and deep water. The major- ity of species indicate moderate depths.” F50 _______ “Shallow to moderate depths are indicated by the few species in this collection, other than Fusi- triton?, which suggests moderate depths to deep water.” F51 _______ “The majority of species indicate shallow to mod- erate depths with the exception of Yoldia ber- ingiana, which suggests deep water.” SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY Localities at which there is‘no apparent mixing of species from ' diflerent depth zones Locality Remarks F41 _______ This very large fauna “*** represent[s] a uniform moderate-depth environment within the range of 10 to 50 fathoms.” The cat bone from this locality seems no more anomalous than the chunks of wood that are in adjacent beds. F46 _______ “The meager fauna *** indicates moderate depth.” F47 _______ All the specimens in this collection are incomplete, immature, or worn. ”Shallow to moderate depths are indicated by the poorly preserved fauna.” F59 _______ “These species suggest shallow to moderate depth ranges.” F60 _______ ”The fossils in this collection indicate an environ- ment of shallow to moderate depths.” The same generalization holds for the geographic distribution of the modern representatives or close relatives of the species at localities F41 to F51, as for the fauna of the Towsley formation: the shallow-water species either include the latitude of Ventura in their; present range or are restricted to areas south of Ventura. All the exclusively shallow water species range south-’ ward at least as far as Todos Santos Bay, Baja Cali- fornia. This distribution suggest that surface water temperatures were slightly warmer than they are now at Ventura. L J The fact that all the species now extinct in the lat- itude of Ventura but living in areas north of Ventura are moderate—depth or deep-water species could be in- terpreted to mean that the water in the eastern Ventura basin was cold .enough at depth to allow these forms to range southward from their present habitats. The fossils from locality F61, near Val Verde Park, are interpreted by Woodring and Trumbull (written communication, 1952) as suggesting a moderate-depth facies of about 60 to 180 feet. 'The collections from localities F77 to F81 consist of species that live in water of moderate depths and species that live in water that ranges from shallow to moderate depths. According to Woodring and Vedder (written communication, 1953), Yoldia bering‘iana? from locality F81 indicates deeper water. Only one collection (from 100. F95) was made from a specific locality high in the Pico formation, but at several places, particularly around the northeast side of the Newhall-Potrero oil field, the beds in the upper part of the Pico stratigraphically higher than localities F77 to F81 commonly yield a fauna consisting chiefly of sand dollars, pectens, and oysters. This fauna is interpreted to represent a gradual shoaling of the water during deposition of the upper part of the Pico formation. GEOLOGY OF SOUTHEASTERN VENTURA BASIN UPPER PLIOCENE AND LOWER PLEISTOCENE SAUGUS FORMATION DEFINITION AND SUBDIVISION The marine Pico formation grades upward and later- ally into the Saugus formation, which comprises inter- fingering shallow-water marine, brackish-water, and nonmarine deposits that in turn grade upward and lat- erally into exclusively nonmarine beds. Conditions resulting in the contemporaneous deposition of the two formations are illustrated diagrammatically in figure 54. South of San Fernando Pass it is practicable to divide the formation into a lower member, termed the Sun- shine Ranch member, and an upper, coarser grained nonmarine member. A similar division was attempted for the formation north and west of San Fernando Pass but was finally abandoned as impractical or misleading. The Saugus formation was first described by Hershey (1902, p. 359—362) as the “Saugus division of the upper Pliocene series,” the name stemming from the exposures in Soledad Canyon not far from the town of Saugus. Eldridge and Arnold (1907, p. 22—28) restricted the term Saugus to the Pleistocene terrace deposits and applied the name Fernando formation to all the rocks younger than the Modelo formation and older than the Pleistocene terrace deposits in the Santa Clara River valley region. Kew (1924, p. 81), in raising the Fer- nando formation to group status, defined the Saugus formation as the upper part of the Fernando group that rests unconformably on the Pico formation in most places. Kew assigned to the Saugus many beds which are referred to the Pico in the present report. The term Sunshine Ranch was introduced as a for- mation name by J. C. Hazzard (Oakeshott, 1950, p. 59) for interfingering marine, brackish-water, and nonmarine beds lying above the Pico formation in the vicinity of the San Fernando Reservoir, a few miles south of the area shown on the geologic map (pl. 44). These beds were designated the Sunshine Ranch member of the Saugus formation by the authors (Winterer and Durham, 1958). At the type locality described by Hazzard the Sunshine Ranch member is about 3,000 feet thick and consists chiefly of interbed- ded “* * * gray, coarse—grained to pebbly, friable sandstone and gray to greenish-gray very fine grained sandstone, silty sandstone or sandy siltstone. These fine-grained greenish-gray beds are the most characteristic lithologic type in the formation. As a rule, their mere presence, even in thin beds, is indica- tive of their stratigraphic position. * * *” At the type locality marine fossils occur as high as the middle of the member. Oakeshott (1950, p. 59—61) adopted the name Sunshine Ranch for ”* * * upper Pliocene continental beds lying below the continental lower 317 Pleistocene Saugus formation and above marine beds commonly called Pico * * *” north of the San Fer- nando Pass in the vicinity of the Placerita oil field; he designated these beds as the uppermost member of the Pico formation. The Sunshine Ranch is here treated as the lower member of the Saugus formation. STRATIGRAPHY AND LITHOLOGY San Fernando Valley Both the Sunshine Ranch and the unnamed upper member of the Saugus formation are present in the San Fernando Pass area. Near the south end of the pass the Sunshine Ranch member is represented by a thickness of about 800 feet of greenish-gray soft silt- stone and fine-grained sandstone intercalated with light-gray sandstone and conglomeratic sandstone. Figure 56 shows an exposure of these beds in a road cut on US. Highway 99 (old road). Fossils are abundant at some horizons in the Sunshine Ranch member but generally the fauna at any one locality consists almost wholly of numerous individuals of one species. Three species of mollusks dominate the fauna in this area: Cryptomya caliform'ca, Ostrea vespertina, generally small individuals of the var. sequens, and a slender form of Oalicantharus humerosus. A few fragments of the echinoid Dendraster were noted at one locality (identifications by Winterer). The Sunshine Ranch member is separated by an unconformity from the upper member of the Saugus formation in the area east of US. Highway 99. The upper member consists mainly of lenticular beds of light-gray and brown sandstone and conglomerate intercalated with lesser amounts of reddish-brown sandy mudstone. West of Highway 99, where a fault separates the Sunshine Ranch member from the upper member of the Saugus, the younger bedsconsist chiefly of grayish-orange sandstone and light-gray conglom- erate. Some beds, especially in an area near the Santa Susana fault zone, are very firmly cemented by calcium carbonate. A thickness of about 1,500 feet of the upper member of the Saugus formation is exposed on the north limb of a syncline near the south end of San Fernando Pass. According to Oakeshott (1950, p. 62) the Saugus forma- tion (the unnamed upper member of this report) is at least 3,000 feet thick on the south limb of this syn- cline, the axial parts of which are covered by alluvium. Oakeshott also reported the finding of a horse tooth about 800 feet stratigraphically above the top of the Sunshine Ranch member of the Saugus. The tooth was tentatively identified by Stock as that of a Pleistocene horse. That the Saugus formation may be very thick in some places in this area is attested by evidence from Sunray 318 SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY FIGURE 56,—Soft greenish-gray siltstone and fine-grained sandstone beds of the Sunshine Ranch member of the Saugus formation exposed along U.S. Highway 99 south of San Fernando Pass. Oil Stetson-Sombrero well 1, drilled in sec. 21, T. 3 N., R. 15 W., about 100 yards east of the area shown on the geologic map (pl. 44) and about 300 yards north of Foothill Boulevard. This well entered the Saugus formation beneath a cover of alluvium and remained in the Saugus to the bottom of the hole at a depth of nearly 12,000 feet. The strata dip south at angles between 20° and 45°. . Area. south or San Gabriel and Holser faults Within the belt of outcrops extending in a large are from the Placerita oil field to the Del Valle oil field, the Saugus formation is not easily divided into members. In some parts of this area, such as the vicinity of Whitney Canyon, north of the Placerita oil field, south- west of Newhall, and near the Del Valle oil field, a two- fold division into a lower member characterized by numerous beds of greenish-gray siltstone and sandstone and an upper member that lacks the greenish beds would be possible; however, over most of the area of outcrop the upward change in lithology is very gradual and greenish-gray beds occur even in the uppermost exposed parts of the formation. For this reason, the Saugus is not subdivided in this area. The contact between the Saugus formation and the marine Pico formation is gradational and interfingering l in many places, the chief distinction between the two formations being a change in the color of the siltstone beds from olive gray or light bluish gray in the Pico to greenish gray in the Saugus. Near the southeast end of the Newhall-Potrero oil field the contact of the Saugus and Pico formations is, for a short distance, an angular udconformity. This unconformity can be traced for only about 2 miles as an angular discordance. In the vicinity of La Placerita Canyon also the Saugus formation rests nonconformably on the Pico formation. Elsewhere the contact is placed rather arbitrarily at the upper limit of the abundantly fossiliferous beds of the Pico formation. In the area south of the San Gabriel and Holser faults the Saugus formation consists of lenticular units of light-colored, loosely consolidated, poorly bedded, ill— sorted conglomerate (fig. 57), conglomeratic sandstone, and sandstone alternating with beds of greenish-gray siltstone, silty sandstone, and light-brown to moderate reddish-brown sandy siltstone and claystone. The pro- portion of greenish-gray beds is greater in the lower part and the proportion of reddish-brown beds is greater in the upper part of the formation. At a few places between Towsley Canyon and Newhall the lower part of the formation includes beds especially GEOLOGY 0F SOUTHEASTERN VENTURA BASIN 319 FIGURE 57.—Conglomeratlc sandstone of Saugus formation exposed along U.S. Highway 6 south of La Placerlta Canyon. rich in plant remains. These lignitic beds occur in units as much as 6 feet thick, but they are generally very lenticular and sandy. The clasts in the conglomerate beds of the Saugus formation are nearly all rounded to well rounded. Pebble counts made at several places show that the same rock types are represented in about the same abundance as in the conglomerate beds of the Pico formation. In fact, the variation within either for- mation is greater than the difference between the two formations. The average diameter of clasts decreases gradually from east to west. Near N ewhall, beds containing boulders are not common; near Pico Canyon, boulders are scarce, but cobbles are abundant; near the Del Valle oil field, cobbles are less common and most of the conglomerate beds contain pebble-size clasts. Because an unknown thickness of beds from the upper part of the Saugus formation has been removed by erosion, the original thickness of the formation is not known. In the area between the N ewhall-Potrero oil field and the syncline north of the Castaic Junction oil field, however, the Saugus formation is about 7,000 feet thick. FOSSILS In the area south of the Holser and San Gabriel faults, as well as in the San Fernando Valley, marine or 581734 0—62—4 brackish-water megafossils occur sparsely in the lower part of the formation. These consist mainly of Ostrea vespertina, var. sequens, Cryptomya caliform'ca, and Calicantharus humerosus, as well as fragments of un— identified naticids and fragments of Dendraster (iden- tifications by Winterer). In the area north of the Santa Clara River and south of the Holser fault, W. H. Corey (oral communication, 1951) collected horse teeth from the Saugus formation at localities which are shown on the geologic map (locs. V92 and V93). According to Corey, Chester Stock identified the teeth as probably belonging to Pliohippus. Two samples, stratigraphically only a few feet apart (locs. f90 and f91), were collected from greenish-gray siltstone in the Pico formation just below the base of the Saugus formation north of the N eWhall-Potrero oil field and were examined for microfossils. The lower sample contained an abundance of Nom'on soap/mm along with Rotalia sp., Gaudryina sp., and ostracodes. The higher sample contained only gastropods, ostracodes, a barnacle, and charaphytes. A sample collected higher in the formation (loc. f89), near the Castaic Junction oil field, contained fresh-water gastropods, ostracodes, and charaphytes. The mollusks and Foraminifera in the uppermost part of the Pico formation, which in many places inter- fingers with the Saugus formation, are interpreted as 320 indicating a shallow-water marine environment. The meager molluscan fauna from the lower part of the Saugus is suggestive of a shallow-water marine, or perhaps even an estuarine or lagoonal environment (fig. 54), as living Ostrea (related to 0. vespertina‘ seguens) and Oryptomya. califomz'ca have a wide sa- linity tolerance. Dendraster could also live in a some- what brackish-water environment. The microfauna from the Pico formation at locality f90, a short distance stratigraphically below the base of the Saugus, indicates shallow-water marine condi- tions. The fauna at locality f91, only a few feet higher stratigraphically, suggests a change to brackish- water conditions. The fauna from locality f89, in the Saugus formation, suggests a lacustrine environment. The upper part of the formation is unfossiliferous except for the horse teeth and presumably represents nonmarine deposition. The conglomeratic beds are doubtless stream deposits, and the unfossiliferous green- ish and reddish siltstone may represent lacustrine or flood plain deposits. AGE OF YOUNGEBT FORMATIONS OF MAPPED AREA Because of the gradational and interfingering rela- tion between each successive pair of the four youngest formations in the mapped area, the age assignment for each of the last three is dependent on the ages assigned to the adjacent formations. Marine fossils in the three youngest formations are better guides to depth or other facies than to precise ages. The guide lines for relative ages are furnished by the outcrops of thin graded conglomerate and sandstone beds which persist over long distances. Each of these beds was probably deposited quickly, almost instan- taneously, by a turbidity current. Using such a bed as a base line, it was found that the upper three-fifths of the Pico formation at the southeast end of the Ncwhall-Potrero oil field grades southeast into the lower part of the Saugus formation (cf. p. 310). Where persistent mappable graded beds were not found, or where the effect of faulting is complex or obscure, time lines are correspondingly uncertain. Both difficulties were encountered near San Fernando Pass. TOWSLEY FORMATION The oldest beds in the Towsley formation, which crop out near the crest of the Santa Susana Mountains, interfinger with the Modelo formation. A foraminiferal fauna from a bed in the Modelo about 50 feet strati- graphically below the base of the Towsley near Oat Mountain (10c. f12; see table 2) appears to represent the lower part of Kleinpell’s Mohnian stage (upper Miocene). The base of the Towsley formation on the south limb of the Pico anticline near East Canyon is SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY about 1,500 feet stratigraphically higher than at Oat Mountain, and foraminiferal faunas collected from the Modelo formation a short distance below the base of the Towsley formation there (loc. f10 and HI) suggest Kleinpell’s Delmontain stage (uppermost Miocene) for the basal beds of the Towsley at that place; the lower part of the formation in the Pico Canyon oil field area (100. f29—f32) yielded Foraminifera assigned to the Delmontian stage (Patsy B. Smith, written com- munication, 1953). The exact stratigraphic relation of the beds of the Towsley formation in Elsmere Canyon to the Towsley in the Santa Susana Moutains is not known because of the complex faulting near San Fernando Pass and the apparent thickening of the Towsley westward from near Elsmere Canyon. The horizon represented by the base of the Towsley formation where it rests uncon- formably on older rocks near Elsmere and Grapevine Canyons probably corresponds approximately with the horizon of the conglomeratic beds that crop out below the oil-stained sandstone in the road cuts at the junction of US. Highways 6 and 99. If this correla- tion is correct, the fossils at locality F16, near East Canyon in the middle of the Santa Susana Mountains section of the Towsley, are at very nearly this same horizon. The base of the Towsley formation at Tows- ley Canyon would be about 1,500 feet stratigraphically below this horizon. The position of the horizon of locality F17 with respect to the beds of the Towsley formation in Elsmere Canyon is even more uncertain, but it is probably slightly higher. The molluscan and echinoid fauna from the Towsley formation in the Elsmere Canyon area has long been regarded as indicating an early Pliocene age (English, 1914, p. 214; Grant and Gale, 1931, p. 29—32; Kew, 1924, p. 77—80; Woodring, 1938, p. 20). This age assignment is based on several facts: First, the fauna contains a large number of species not known in other parts of the California Coast Ranges from beds older than Pliocene. Second, the fauna includes such forms as Astrodapsis and Trophosycon, known elsewhere only in beds no younger than early Pliocene. Third, the fauna has a large number of species in common with the fauna of the Jacalitos formation of the Coalinga region and with the fauna of the lower part of the San Diego formation. The Jacalitos formation and also the lower part of the San Diego formation are probably considered early Plioaene in age (Woodring, Stewart, and Richards, 1940, chart facing p. 112). The Santa Susana Mountains localities both contain “Nessa” hamlim' and locality F17 yielded Acila semi- rostrata. These two species occur only in lower Pliocene strata outside the Ventura basin. Within the basin, A. semirostrata occurs well up in the Pico formation GEOLOGY OF SOUTHEASTERN VENTURA BASIN (loc. F52). Specimens of Turritella cooper-2', a species reported elsewhere from only two localities in beds older than Pliocene (Merriam, 1941, p. 118), were noted by Winterer about 1,000 feet above the base of the Towsley formation near Towsley Canyon. The boun- dary between the Pliocene and Miocene is probably, therefore, between the Turm'tella coopem' horizon and the beds (10c. f32) containing the foraminiferal fauna of Delmontain age near the Pico Canyon oil field, that is, in the interval from about 500 to 1,000 feet above the base of the Towsley at Towsley Canyon. This part of the formation contains few foraminifers. PICO FORMATION The Pico formation Within the mapped area un- doubtedly is entirely of Pliocene age in terms of the California subdivisions of the Cenozoic era. The beds along the northeast side of the N ewhall-Potrero oil field are probably the youngest in the formation and contain Patinopecten healeyi and Lyropecten cerrosensis, both of which occur in rocks no younger than Pliocene elsewhere in California. Just how much of the Pliocene is represented by the Pico formation is not known. The lower part of the formation, from which “Nessa” hamliml was collected, is regarded as lower Pliocene. Acila. semirostmta is known from a few localities in the lower part of Pliocene strata in the L05 Angeles basin (for example, Woodring, 1938, p. 28). In the Ventura basin, A. semirostrata occurs at least as high as the middle of the Pico forma- tion (100. F52). At all localities in the eastern Ventura basin where these two species are found, evidence of transportation after death indicates that the animals may have lived far from the places where their remains are found. The true depth facies of these two species is not known, although a moderate depth facies appears most likely. The strongly plicate variety of Ostrea cespertina, which occurs at localities in the uppermost part of the Pico formation, has not been found in association with either Acila semirostrata or “Nessa” hamlini. Although the presence of this form of 0. vespertina may suggest a late Pliocene age, correlations between fossil localities by means of key beds suggest that the stratigraphic range of the strongly plicate oyster partly overlaps the ranges of A. semirostrata and “N .” hamlz'm'. Table 6 shows the stratigraphic distribution of forms of Colic-anthems humerosus in the Pliocene rocks of the area. The table presents the result of a special study of the species by Woodring, who used University of California at Los Angeles collections as well as Geo- logical Survey collections. The form termed by Wood- ring as typical, which is strongly inflated and has a strong angular shoulder, occurs in the Towsley forma- formations. 321 TABLE 6.—Distribution of foams )of Calicantharus humerosus ( abb [Identification by W. P. Woodring] Form Locality (table 11) Formation Area Inter- mediate Slender Sunshine Ranch member of Saugus forma— tion. Santa Susana F87 Mountains. F86 South of San Fer- F85 nando Pass. South of Del Valle F49 fault. F50 Between Del Valle F69 Pico formation and Holser faults. F72 North of Holser F fault. F67 F Santa Susana Mountains. g3? Elsmere Canyon. F24 Towsley forma- F25 tion. Santa Susana F20 Mountains. F17 tion at Elsmere Canyon and in all except the uppermost part of the Pico formation. A form that Woodring called intermediate, which is moderately inflated, has a strong angular shoulder, and is more or less intergraded with the typical form, occurs in the Towsley and Pico The form that Woodring termed slender, which is round shouldered, occurs in the Pico formation and in the lower part of the Saugus formation. The different forms do not occur together except at one poorly described University of California at Los Angeles locality in the Towsley formation in Elsmere Canyon, where the typical and intermediate forms may occur together. The typical form has a somewhat longer stratigraphic range than Acila. semirostrata and “Nessa” hamlini, the intermediate form occurs in the upper part of the stratigraphic range of the typical form, and the slender form occurs mainly above both the other forms. Woodring (written communication, 1953) suggested that, “Inasmuch as the typical form occurs at Elsmere Canyon in an early Pliocene shallow-water association and the slender form occurs in the same kind of associa- tion in the late Pliocene part of the Pico formation, at least those two forms evidently are not ecologic varieties adapted to different environments * * *. The strati- graphic distribution strongly suggests a typical-inter- 322 mediate-slender chronologic lineage in decreasing age sequence.” Field evidence (Winterer) also suggests that the slender form may range into brackish-water deposits. At several places in the uppermost part of the Pico formation, or in the lower part of the Saugus formation, the slender form of Oalicantharus humerosus is asso- ciated with abundant Cryptomya californica, or with a small form of Ostrea, vespertina sequens. Paleontologic evidence may warrant a division of the Pliocene in the southwestern Ventura basin into the lower Pliocene, characterized by “Nessa.” hamlim' and Acila semirostrata, and the upper Pliocene, char- acterized by the strongly plicate form of Ostrea oes- pertina and the slender form of Calicantharus humerosus. SAUGUS FORMATION The Saugus formation interfingers with the upper Pliocene part of the Pico formation in the area south of the Holser fault. The Pliohippus teeth more than 1,000 feet above the base of the Saugus near the Del Valle oil field, where the base is relatively young with respect to the same horizon farther north or east, indicate a Pliocene age for at least the lower half of the Saugus formation. The horse tooth collected by Oakeshott from the upper member of the formation in the San Fernando Valley indicates that the upper member is in part of Pleistocene age. Near the town of Castaic, several miles north of the mapped area, W. H. Corey collected a Bison jawbone and teeth from reddish- brown clay beds near a large fault. The beds con- taining the vertebrate fossils dip about 30° and were tentatively assigned by Corey to the Saugus formation (oral communication). Chester Stock examined the material and told him that the Bison is a very late one, possibly even Recent. It may be that the dipping beds do not belong to the Saugus formation but are stream-terrace deposits of late Pleistocene age that were deformed during movements along the nearby fault. If, on the contrary, the beds containing Bison are with- in the Saugus formation, then the age range of that for- mation must be extended at least into the late Pleistocene. QUATEBNARY SYSTEM PLEISTOCENE SERIES TERRACE DEPOSITS Stream—terrace deposits are widely distributed in the Ventura basin but are most extensive near the town of Saugus and in the immediate vicinity of the Santa Clara River. The deposits consist of crudely stratified, poorly consolidated reddish-brown gravel, sand, and silt. In some areas where terrace deposits rest on the Saugus formation, the contact between the two units SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY is difficult to locate accurately because of the similarity of the gravels to loosely consolidated conglomerate beds in the Saugus formation. The extensive terrace deposits east of Saugus are as much as 200 feet thick. Farther west, near the Castaic Junction and Del Valle oil fields, the deposits are as much as 75 feet thick. At many places the former presence of a cover of gravel on stream terraces is in— dicated by isolated large boulders resting like glacial erratics on remnants of erosion surfaces. One notable occurrence of such residual boulders is at an altitude of 2,850 feet near the headwaters of Rice Canyon, where rounded granitic boulders as much as 2‘ feet in diameter are scattered on ridge tops on shale of the Modelo formation. ‘ The thick terrace deposits exposed in the vicinity of Saugus, near the Castaic Junction and Del Valle oil fields, and near the mouth of Potrero Canyon, are ap— parently remnants of a once continuous cover of allu- vium. The altitude of the base of this series of terrace deposits is about 150 feet above the Santa Clara River valley near the Del Valle oil field, but near Saugus, farther upstream, the base is lower than the present river bed. An erosion surface on this same series of terrace deposits likewise shows a lesser gradient than the present Santa Clara River valley. The down- stream divergence of the long profiles of the present Santa Clara River valley and the former valley is prob- ably due to broad warping after the formation of the terrace deposits. The terrace deposits are assigned a late Pleistocene age because they lie with marked unconformity on the Saugus formation, the upper part of which is of prob- able early Pleistocene age. At a few places faults of small displacement cut the higher terrace deposits, and the large terraces near the east end of the Del Valle oil field and just southwest of the Castaic Junction oil field may have been slightly folded; the terrace deposits are otherwise not obviously deformed. The oldest unde- formed rocks in the western part of the Ventura basin are assigned a late Pleistocene age on faunal evidence. The only faunal evidence for the age of the terrace deposits in the southeastern Ventura Basin is doubtful. A bison tooth was collected by Corey at an outcrop near the junction of Castaic Creek and the Santa Clara River (10c. V94). At this place terrace gravels lie unconform- ably on the Saugus formation. The tooth was collected at the surface of the Saugus outcrop, and Corey reported (oral communication, 1951) that he could not be cer- tain whether the tooth came from the Saugus formation or was washed from the over-lying terrace gravel. Chester Stock identified the tooth as belonging to a very late Pleistocene or even Recent Bison (See “Saugus formation” above). l GEOLOGY 0F SOUTHEASTERN VENTURA BASIN ALLUVIUM A blanket of alluvium covers the Santa Clara River valley floor and extends far up many of the tributary valleys. The present flood plain of the Santa Clara River is entrenched in this alluvial fill to a depth that ranges from about 20 feet near the Los Angeles—Ventura County line to about 5 feet near the eastern edge of the area shown on the geologic map (pl. 44). The deposits consist of poorly bedded, unconsolidated gravel, sand, and silt. TURBIDITY CURRENT FEATURES IN THE TERTIARY ROCKS The presence of graded sandstone and conglomerate beds in the Eocene rocks and in the Modelo, Towsley, and Pico formations has been noted in the discussions of the lithology of those formations, but the possible origin and significance of this prevalent sedimentary structure has not been discussed directly. Anomalous depth associations in the molluscan faunas from the. Towsley and Pico formations have been described also, and the suggestion has been made (p. 306 and 315) that turbidity currents may account for the mixed faunas. Analysis of foraminiferal faunas from the Pico forma- tion showed that a large part of that formation in the western half of the mapped area was deposited in water more than 600 feet deep, and that the depth may have been as much as 3,000 feet. However, siltstone beds containing deep-water Foraminifera are interstratified with beds of sandstone and coarse conglomerate. Un- less the Foraminifera have no depth significance, some mechanism of transportation must be found to explain the presence of large volumes of coarse material in deep water. Otherwise, a kind of “springboard tectonics” must be invented, alternately to raise the sea floor into the realm of strong wave and current action for depo- sition of the sandstone and conglomerate beds, and then to lower it again to depths at which the Foraminifera can live. Significantly, the sandstone and conglomer- ate beds in the midst of the deep-water siltstone contain sedimentary structures, notably size grading, that suggest turbidity currents as the probable agent of transportation of the sediments that formed these beds. NATURE OF TURBIDI'I‘Y CURRENTS A turbidity current, as the term is used in this report, is a sediment—laden current that flows in a body of standing clear water. It stays more or less segregated as a distinct layer because of a difference in density between the turbid water and the clear water. It is a special kind of density current. Depending on the difference in density, a turbidity current can flow along the top of, within, or along the floor of the body of standing water. A thin surface layer of sediment- 323 laden river water often extends for many miles out to sea opposite river mouths, even though the fresh water contains a greater concentration of suspended sediment than sea water (Scruton and Moore, 1953). Surface turbidity currents, or overflows, are driven mainly by winds and to a lesser extent by ocean currents and river flow. Overflows of turbid water occur in the upper part of Lake Mead, Ariz.-Nev., during late spring and early summer when, due to its lower salin- ity, the incoming Colorado River water is lighter than the surface water of the lake (Gould, 1951, p. 38, 39). Turbidity currents that flow at some intermediate level in a body of standing water are termed interflows; they can be produced in laboratory tank experiments and have been observed in Lake Mead (Gould, 1951, p. 39) but not in the sea. Turbidity currents that flow along the floor of a body of standing water have been investigated in the laboratory by Bell (1942a, b) and Kuenen (1937; 1938; 1951; Kuenen and Mig- liorini, 1950) and have been observed and studied in lakes (Gould, 1951, p. 38, 39). Turbidity currents flowing along the bottom have not been actually ob- served in the sea, although many writers have called upon marine turbidity currents to explain the deposi- tion of beds of sand (Shepard, 1951; Ericson, Ewing, and Heezen, 1951; 1952) or of graded beds of sand (Bramlette and Bradley, 1942; Kuenen, 1950, p. 367) in Recent deep-sea sediments. The presence of faunas consisting of shallow-water or mixed shallow- and deep- Water species of Foraminifera recovered from cores of Recent deep-sea sands has been ascribed to transpor- tation by turbidity currents (Phleger, 1951). The velocity of material in suspension in a flow is greatest at the nose of the current and the coarsest material in the flow at any one time is found there. As the head of the flow advances, the velocity is reduced owing to the resistance of the stagnant water and to dilution by mixing With clear water. A loss of velocity and turbulence leads to deposition of the coarsest material from the mixture at the head of the flow. Thus a horizontal grading is established. Behind the nose of the current the suspension is progessively more dilute and slower moving. A pronounced vertical gra- dient in both density and velocity can be observed in experimental flows. In flows containing a mixture of various sizes of grains, the vertical and horizontal ve- locity and density gradients caused corresponding aver- age grain-size gradients in the flows, and thus provide an explanation of the formation of graded beds by tur- bidity currents. Deposition is rapid enough to lay down and bury a mixture of particles of all sizes at the base of the flow before the current can Winnow out the finer particles. 324 Turbidity currents in Lake Mead (Gould, 1951) transport for great distances much of the finer material introduced at the head of the lake by the Colorado River. Many flows have travelled the entire length of the lake to the face of Hoover Dam, a distance of more than 70 miles, over an average bottom slope of from 3 to 5 feet per mile. The velocities of the flows, which transport chiefly clay-size material, range from about 1.0 foot per second near the upper end of Lake Mead to less than 0.25 foot per second farther down the lake. Measurements indicate that the flows are only a few feet thick and have a vertical density gradient. Effective differences in density measured in one flow ranged from 0.001 at the top to 0.200 at the bottom. Indirect evidence of the existence and importance of marine turbidity currents comes from several sources. Layers of sand interbedded with typical deep-water sediments have been observed in cores of Recent sediments recovered from deep water at a very large number of localities in many parts of the world (Shepard, 1951). Many of these areas are in middle and low latitudes where ice rafting of the sand is improbable. Some of the sand layers are well sorted and others are graded. Remains of shallow-water organisms, especially Foraminifera, are present in some layers. The sand layers are interbedded with deep— water sediments in some areas hundreds of miles from the nearest land or even from the nearest known appreciable submarine slope. The large number of cores from the North Atlantic obtained during cruises of the research vessel Atlantis show that coarse-grained sediments are distributed over thousands of square miles in deep ocean basins (Ericson, Ewing, and Heezen, 1952). The sand layers in the Atlantic range in thick- ness from thin films to beds several feet thick. Some of the cores were about 30 feet long and contained as many as 20 layers of sand. Many of the layers are graded from coarse clastics at the bottom to fine clastics at the top, with abyssal red clay at the top of some layers. Turbidity currents acting in conjunction with sub- marine slumping and sliding have been envoked as possible agents for the erosion of submarine canyons (Daly, 1936; Kuenen, 1950, p. 485—526; Woodford, 1951; Crowell, 1952b) and deep sea channels (Dietz, 1953; Ewing and others, 1953). Ludwick4 showed that in the San Diego trough, ofl” the coast of southern California, sand layers, although present in many parts of the trough, are most abundant near the outer part of submarine La Jolla Canyon. Near the distal part of the canyon, wide 4 Ludwick, J. C., 1950, Deep-water sand layers ofl' San Diego, California: Unpub- lished doctor‘s thesis, Scrlpps Inst. Oceanography. SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY shallow channels with gentle gradients have been found extending part way across the floor of San Diego trough. A fathogram (Menard and Ludwick, 1951, fig. 1) across one of these channels shows levees on both sides of it. Marine turbidity currents provide an explanation for the presence of layers of coarse—grained sediment in deep water, for their grading, for their alternation with typical deep-water sediments, for their abundance near the ends of submarine canyons, for their occurrence in depressions and below slopes, and for their content of the remains of displaced Recent shallow—water organisms. Many other theories have been advanced to explain the deep-water occurrences of sand, the most important of which are rafting by ice or floating vege- tation and transportation by wind and by currents in shallow waters during a time of drastic lowering of sea level. Doubtless ice rafting is an important agent in the transportation of coarse-grained material into deep water, especially in high latitudes; during the Pleisto- cene epoch this mechanism probably was of even greater importance and was effective in lower latitudes than it is today (Bramlette and Bradley, 1942, p. 4). However, it is difficult to see how this mechanism can produce well-sorted or graded beds; furthermore, the distribution of the rafted sediment or wind-blown sand would not have any special relation to the topography of the sea bottom. Sufiicient lowering of sea level to bring the sea bottom within the range of shallow-water currents, even if the mechanism responsible for such a IOWering were known, would not explain the layers of interstratified sand and fine-grained sediment contain- ing remains of deep-water F oraminifera. Evidence bearing on the existence and importance of marine turbidity currents is provided by phenomena associated with the Grand Banks earthquake of 1929 (Heezen and Ewing, 1952). Submarine cables lying downslope from the epicentral area, which was on the continental slope of Newfoundland, were broken in an orderly succession after the earthquake. The farthest cable was more than 300 miles from the epicenter, and the average slope of the sea floor below the epicentral area is 1°50’ ; many of the breaks were on a slope of less than 1°. Heezen and Ewing concluded that a large slide or slump was triggered by the earthquake and as the material moved down the slope it was converted into a turbidity current which broke the lower cables in succession. Because about a 200-mile length of the last cable was destroyed and buried deeply, it is reason— able to assume that the flow traveled even farther into the ocean basin. Heezen and Ewing (1952, p. 865~866) stated that deposits left by the flow are graded. Although earthquakes may initiate submarine slides or slumps that later are transformed into turbidity GEOLOGY 0F SOUTHEASTERN VENTURA BASIN currents, the flow might be triggered by other means. Shepard (1951, p. 58-59) reported that frequent surveys of the nearshore end of Scripps Canyon, which is a branch of submarine La Jolla Canyon, show that tributaries at the head of the canyon are constantly being filled with sand and then reopened. The fills contain an abundance of soft slimy decaying marine vegetation, which may make the sand less cohesive and more likely to slide down the canyon. The immediate cause of the slides is not known, although heavy storm waves may be an initiating force. Slides moving in canyons, if composed largely of incoherent sediment, may become transformed into turbidity currents by mixing with adjacent clear water. A flow of large vol- ume, moving down a steep canyon, may have sufficient momentum to spread far out onto the sea floor at the mouth of the canyon. The graded beds of sandstone in the Modelo, Towsley, and Pico formations exhibit characteristics that are suggestive of marine turbidity current deposits. The evenly graded beds are similar to those produced by Kuenen in tank experiments in which a quantity of material is introduced suddenly into the standing water. The beds that are nearly homogeneous throughout most of their thickness and that show grading only in their uppermost parts are similar to those produced (Kuenen and Menard, 1952, p. 83—96) in the laboratory by introducing the coarser material, not in one sudden slide, but in a continuous stream. In a small turbidity current induced by sudden introduction of material, the coarsest material is in the nose of the flow, owing to the greater velocities and turbulence prevailing there, and the average grain size gradually diminishes toward the tail of the flow. When a supply of sediment is fed continuously into the current, no such horizontal grain- size gradient Can be established; the current deposits an ungraded bed until the supply is cut off, at which time the horizontal gradient in the flow is established and vertical grading of the deposit begins. In nature a continuous feeding might result from a large slide originating over a large area (Kuenen and Menard, 1952, p. 94). Slumping of sediment that has accumu- lated for some distance along the headward parts of a submarine canyon appears to be a possible mechanism for maintaining continuous feeding. The greater than average thickness of most of the beds of sandstone in the Towsley formation that are graded only in their uppermost parts indicates that they were deposited by currents of large volume. A very well sorted supply of sediment also might lead to the near absence of grading, but the nearly homogeneous beds in the Towsley formation are commonly not sorted well enough to make this expla- nation the most likely. Many beds have uniform 325 grading from sand or coarser material at the base up into fine or very fine grained sand near the top; clay- stone rests abruptly on the fine sand with a smooth contact. The part of the bed that is normally repre- sented by siltstone in a bed perfectly graded from sandstone to claystone is missing. The sediment that would have formed the absent layers was probably carried past this site of deposition by currents at the tail of the turbidity current. The fact that beds with these layers missing generally contain sets of cross— laminae near their tops suggests reworking by currents. The next succeeding flow may have eroded the missing layers or may have followed so closely behind the first that its rapidly moving head overtook the dilute slow-moving tail of the first current and began depositing its load before the first bed was completed. A succession of flows following closely behind one another might be started by a succession of slumps on a submarine slope. Many thick beds of conglomerate are not graded. The larger the average clast size the less well developed is the grading. Ungraded beds of coarse conglomerate may represent deposits of undersea slides. INTERRUPTED GRADATIONS Although most beds grade upward into siltstone or even claystone, many consist only of sandstone and are overlain by another sandstone bed Whose base generally is not conspicuous because of the lack of a striking contrast in grain size or color across thecontact. The degree of induration is commonly the same in both beds and the contact is not necessarily a surface of fissility, as is the surfaCe between fine-grained and coarser beds. In some sandstone outcrops, however, graded bedding is conspicuous, and what may appear at a distance to be a single thick bed'of sandstone may prove to comprise several beds when examined closely. Within many graded beds the median grain size does not decrease upward in a uniform fashion. Thin dark streaks and wisps of micaceous silt (fig. 58) produce interruptions in the otherwise orderly sequence. The lower parts of graded beds are free of these fine laminae. The laminae may have been formed as a result of pulsations in the velocity or amount of turbu- lence in the current, although the common association of the laminae with sets of cross laminae suggests that they were formed by a current that moved its load at least partly by traction, rather than wholly in suspension. ANGULAR FRAGMENTS IN SANDSTONE A notable exceptionto uniform grading is the position of mudstone fragments that are commonly incorporated in the sandstone beds. These fragments are generally well up in a graded bed rather than at its base. In 326 SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY FIGURE 58,—Sandstone and siltstone beds in the Towsley formation, Santa Susana Mountains. The dark siltstone bed and the lighter colored siltstone bed with dark streaks and wisps of micaceous silt to the left of the 6-inch scale are channeled by the sandstone on which the scale rests. Angular clasts of siltstone lithologically identical with the dark siltstone bed that has been partially eroded are scattered in the channeling sandstone. some places they are scattered at various levels, but in other places they are chiefly at one level. Their low density and their slab shape probably combined to give the fragments a slow settling velocity as compared to igneous or metamorphic clasts of the same dimensions. The alinement of these fragments along fairly definite planes within a graded bed suggests that a layer of mudstone was broken up and carried away from its place of origin on the sea floor a very short distance upslope and that this erosion proceeded concurrently with, and perhaps because of, the passage of a‘turbid flow. The fragments thus may not even have been available for transport until the lower part of the graded bed had been deposited downslope. Intermittent ero- sion during passage of the current could have produced trains of fragments which would have been deposited in distinct layers a short distance downslope (fig. 62). IRREGULAR CONTACTS Many contacts between two graded beds, although abrupt, are irregular. In some places there is clear evidence of channeling of the underlying beds. Thin wisps and laminae in the channeled bed are truncated at the contact. Generally the channel extends only a few millimeters into the bed beneath, but deeper channels, such as the one illustrated in figure 58 are not rare. Irregularities in the shape of the surface of contact are generally not due to erosion of parts of the under- lying beds but rather to deformation of the interface during deposition, probably due to unequal loading. Figure 59 shows several varieties of such deformation. FIGURE 59.—Types of deformation of sandstone-siltstone interface, result- ing from unequal loading, by which load casts are formed: A, shallow depression; B, deep depression with narrow connection with overlying. bed; 0, isolated pocket in lower bed; D, depression modified to an asymmetrical form by slumping, perhaps due partly to the drag of the passing turbidity current, and by unequal loading. GEOLOGY OF SOUTHEASTERN VENTURA BASIN These features have been called load casts (Kuenen, 1953, p. 1048). The load casts are pockets of coarse- grained material projecting down into an underlying bed. Laminae in the bed beneath are not truncated as in an erosional channel but are bent around the pocket. The material in the pocket is generally markedly coarser than the material at the base of the overlying bed outside the pocket. This contrast is most notice- able where the overlying bed is pebbly. The material in the pockets generally grades evenly upward into the overlying material. Most of the casts are shallow depressions but some are much deeper and have a narrow connection with the overlying bed; in some places the pocket is isolated within the lower bed (fig. 59). Figure 60 shows load casts at the base of a bed of sandstone above siltstone beds. The attenuated form of the prongs of siltstone separating the load casts is evidence of the mobility of the substratum at the time of loading. Figure 61 shows load casts at the base of a sandstone bed that rests on siltstone. The siltstone has been eroded away so that the configuration of the lower surface of the load casts can be seen. The current that transported the material in the overlying bed must have distributed its load gently but unevenly on a very 327 plastic substratum, perhaps into small shallow original depressions. The weight of the unequally distributed material would cause it to sink in the underlying plastic mud wherever the larger, and therefore heavier, grains were concentrated. The coarsest material in a small turbidity current is at the nose of the current and would be the first to settle out. If the supply of new material is continuous, the sinking process is to a degree self—sustaining. The depth to which a pocket can grow is dependent on the strength of the substratum and the rate at which new material is supplied. A rapid supply, or a relatively stiff substratum, would cause the depression to be filled and a more equal load distri— bution to be developed before the pocket sank very deep. IN'TRAFORMATIONAL BRECCIAS Intraformational breccias are abundant throughout the Towsley formation (figs. 58, 62). The record of the formation of such breccias is preserved in the rocks. Deformed chips and slabs are common. Figure 58 shows a bed of coarse-grained sandstone containing siltstone fragments. In the center of the picture, the 2-inch layer of siltstone that underlies the sandstone has been eroded and the sandstone bed rests on a lower siltstone layer. The fragments in the sandstone bed are lithologically identical with the siltstone in the eroded FIGURE 60.—Load casts in the Towsley formation, Santa Susana Mountains. The small block of siltstone near the top margin of the photograph appar- ently has been completely detached from the parent bed below. 328 SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY FIGURE 61 .—Load casts developed on the basal surface of a sandstone bed in the Towsley formation, Santa Susana Mountains. The underlying slltstone bed has been eroded away. ”is t, FIGURE 62,—Intraformational breccia in the Towsley formation, Santa Susana Mountains. The siltstone blocks below the 6-inch scale have the same thickness and lithology as the undisturbed siltstone bed in the upper right corner of the photograph and were apparently derived from it. GEOLOGY OF SOUTHEASTERN VENTURA BASIN interval. The channeling sandstone bed actually underlies the siltstone for a distance of about 2 inches to the left of the broken end of the siltstone layer. The numerous dark laminae below the siltstone layer in the left half of the figure terminate against the sandstone— filled channel. The overhanging bed is bent downward slightly and was apparently the next unit that would have been eroded. Fragments in the sandstone were probably derived chiefly from a part of the siltstone layer that lies beyond the exposure shown on the photograph. The intraformational breccia shown on figure 62 has siltstone blocks scattered to the left of the parent layer that match it in thickness and lithology. A very large angular block of shale, more than 10 feet long in its largest exposed dimension (fig. 63) occurs with sandstone beds near the base of the Tows- ley formation. The block is exposed in the cut made for Standard Oil of California Brady Estates well 1, in sec. 13, T. 3 N., R. 17 W., near the summit of the Santa Susana Mountains. The base of the block lies a few inches above the base of a sandstone bed. Several other beds of sandstone and mudstone abut against higher parts of the shale block. Lack of deformation in beds adjacent to the block indicates that the upper part of the block projected above the sea floor and sediment filled in around it after the block arrived at 329 its final destination. The shale in the block is phos- phatic although no phosphatic shale in this part of the Towsley formation crops out nearby. The block therefore is not like those in the intraformational breccias described above for it does not have a nearby source. A unit of very similar phosphatic shale in the Modelo formation, a few hundred feet stratigraphically below the rocks in which the shale block occurs, crops out a few hundred feet to the south. The sandstone beds that enclose the shale block interfinger northward with phosphatic shale of the Modelo formation and are stratigraphic equivalents of the beds exposed near the axis of the Pico anticline, about 2 miles distant. Evidence from a study of the sedimentary structures indicates that the direction of transport of the sediment of the Towsley formation in this area was from the east or northeast. The nearest land in those directions during Towsley time probably was no closer than 5 miles. Regardless of actual source, however, the block must have travelled a considerable distance to reach its present site. Because the shale in the block is very brittle and crumbly, it is difficult to understand how such a large block, even if it were firmer and more cohesive at the time of its transportation, could survive a long journey along the sea floor. A very powerful current is needed to move an angular block of such large size, yet this current must be of such a nature FIGURE 63.—Large angular erratic block of shale in the Towsley formation, Santa Susana Mountains. 330 as to prevent the block from breaking as it moves along. Extrapolation of the results of laboratory experiments by Kuenen indicates that a large swift turbidity current of moderately high density could move the block by suspension. Because of the long distance to land, as compared to the distance to pos- sible submarine sources of phosphatic shale, it is more likely that the block was derived from a submarine source. The block was obviously coherent when eroded and transported. It may have been derived from some nearby submarine slide that involved a sequence of compacted beds thick enough to produce a block of this size. It is notable, however, that no other shale blocks of comparable dimensions were observed near this one or anywhere else in the Towsley or Pico formations. CURRENT MARK- Currents have left their impress on the rocks, not only in the form of cut-and-fill structures, but also as current bedding, current lineation, and ripple marks. A typical succession involving current bedding is illus- trated in figure 64. The base of the bed on which the scale rests is its coarsest part and the basal contact is irregular but very distinct. The middle part of the bed is banded by discontinuous streaks and wisps of dark silt and clay. Near the top of the bed are several small-scale lenticular trough sets of concave high—angle thin cross laminae (McKee and Weir, 1953, p. 381— 390). Resting with an abrupt contact on the sets of cross laminae is a band of dark siltstone and claystone. The contact between the siltstone and the underlying sandstone is wavy. The siltstone is thicker in the troughs of the waves than at the crests, and sets of cross laminae are either thin or missing under the wave troughs. In the sandstone bed that lies on the silt- stone band, the coarsest material lies in the wave troughs. These facts indicate that the wavy form is a primary feature and-is a cross section of a series of ripple marks. The average wavelength of ripples observed in the Towsley formation is about 10 inches. The apparent dip of the laminae is to the left in all beds shown in figure 64, but not all cross laminae are so regular. In some places beds containing cross lam— inae are slumped and contorted. Many determinations of the true dip of cross lam- inae in the Towsley formation were made and compared with the dip of the enclosing strata. Observations at numerous places from Rice Canyon westward to and beyond the border of the mapped area showed that the direction of current flow indicated by cross laminae is remarkably constant. Along the belt of outcrops 0n the north slope of the Santa Susana Mountains the SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY cross laminae were produced by currents flowing from the sector between east and northeast. In only one place, in a road cut in the Pico Canyon oil field area, was a bedding plane seen that had been stripped over a large enough area to show the pattern of the ripple marks. The current that produced the ripples flowed from the northeast. The persistence of the same direction of inclination of the cross laminae over such a large area and through— out the thickness of the formation can make the cross laminae useful in determining the direction of dip of beds penetrated by wildcat oil wells. It would be relatively easy to determine the direction of inclina- tion of cross laminae from a series of cores from wells in areas where the dip of the strata is known. The direction of cross-stratification, and hence the direction of currents, would probably be different in various parts of the eastern Ventura basin, but it should not be difficult to establish a pattern of variation. Because recovering well-oriented cores or measuring the direc- tion of dip with electrical devices is sometimes expen- sive and time-consuming, attention to cross-stratifica- tion in cores might be rewarding. The ripples and cross-stratification indicate currents that moved material by traction. The sets of cross laminae near the tops of many graded beds and the relative constancy of the direction of current flow indicated by the inclination of the cross laminae sug- gest that the dilute tail of the turbidity current that deposited a bed produced the ripples. The rather consistent direction of currents required to explain the uniformity of the direction of inclination of the cross laminae over a large area and through a consid- erable thickness of strata is not compatible with a shallow-water environment, where the direction of currents is generally subject to rapid shifting. In a basin deep enough to prevent normally fluctuating wind, wave, and tidal currents from stirring the sedi- ment on the bottom, turbidity currents originating along a submarine slope on a side of the basin could not only transport coarse—grained material into the basin, but could also produce a rather uniform orien- tation of directional features such as ripple marks. The existence of such a submarine slope during late Miocene time is suggested by subsurface data showing that both the Modelo and Towsley formations thin very markedly eastward toward N ewhall and Saugus from the intersection of US. Highway 99 with Pico Canyon. Structure section A—A’ (pl. 45) shows that this eastward thinning is so pronounced, especially in the Modelo formation, that it seems reasonable to assume that either a submarine slope against which the layers of basin sediment thinned existed in that area, or a very unequal rate of subsidence prevailed GEOLOGY OF SOUTHEASTERN VENTURA BASIN 331 ' FIGURE 64.—Current bedding in the Towsley formation Santa Susana Mountains. The bed on which the 3-inch scale rests and others below it have an irregular basal contact, coarser material at the base, discontinuous streaks and wisps of dark silt and clay in the middle part, and cross laminae near the top. 332 in two areas of equal depth on either side of the zone of thinning. The former possibility is consistent with the direction of the source of turbidity currents in- dicated by the inclination of the cross laminae. The geographic distribution of the lowest con- glomerate beds in the Towsley formation is not con- sistent with the source direction indicated by the study of crossbedding. The change in facies from the conglomerate and sandstone of the lowest beds of the Towsley along the crest of the Santa Susana Mountains to shale in beds of equivalent age in the Modelo for- mation farther northeast in the Rice Canyon area means that finer, rather than coarser grained rocks, occur to- ward the supposed source. The best examples of cur- rent bedding in this geographic and stratigraphic part of the Towsley formation definitely indicate a north- eastern source for the sediments. The conclusion seems warranted that gravel-loaded turbidity currents moved across a mud bottom for a mile or more without depositing coarse sediment and without leaving clear evidence of erosion. Channeling may have been oblit- erated from the structureless mudstone of the Modelo where not even bedding is apparent. The area of deposition of the Towsley may have been separated from the source area by a belt of mud. Though no evidence of erosion channels was seen in the field, the pronounced thinning of the Towsley and Modelo forma- tions toward the northeast, in the direction of N ewhall, may be partly due to penecontemporaneous erosion. That the same general source direction may have been predominant during deposition of the Pico forma- tion is indicated by the lateral change in foraminiferal faunas from deep-water types at the longitude of the Newhall-Potrero oil field to much shallower water types at the longitude of Towsley Canyon. Single mappable units of conglomerate and sandstone may be traced continously from the shallow- to the deep-water area. In the deep-water area, graded beds are preva- lent (fig. 54). Well-preserved current lineation was seen at only one place in the Towsley formation, probably because current lineations are not readily preserved in friable sandstones such as those in the Towsley. Figure 65 shows current lineation, a number of nearly parallel narrow low ridges, on the base of a block of sandstone removed from a sandstone bed overlying a layer of siltstone. The base of the sandstone bed in place also is marked by ridges like those in the figure. The ridges are casts of narrow grooves that score the upper part of the surface of the underlying siltstone layer. Be- cause the orientation of the lineation corresponds to the direction of current flow indicated by cross laminae in adjacent beds, the lineation is believed to have been produced by a current. Similar short, narrow, and SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY shallow grooves formed by sand grains rolling and sliding along the silty or clayey bottom of a present-day shallow stream near N ewhall were observed by the authors. Flow markings similar to those shown in figure 65 were described by Rich (1950, p. 717—741; 1951, p. 1~20) and by Kuenen (1953). SLUMP STRUCTURES AND CONVOLUTE BEDDIN'G The most common type of slump structure is post- depositional in origin; it generally involves more than one bed, and cross-stratification, where present, is equally well developed over troughs and crest of folds. Slump structures such as this are common in the Tows- ley formation. Figure 66 shows a slump structure that involves a sequence of beds about 8 feet thick. The mudstone bed probably provided the slipping base on which the slumping began. The light-colored banded rock is sandstone. The darker bands within the sandstone are discontinuous wisps of micaceous silt— stone. Two large prongs project up into the sandstone from the lower mudstone layer. Individual beds having only the middle parts crum- pled are rare in the Towsley formation, but folds truncated by the next overlying bed are more common. This feature, termed convolute bedding (Kuenen, 1952, p. 31), is commonly very difficult to distinguish from an ordinary slump structure. The folds in convolute bedding die out downward and the folding is confined to one bed; ideally, the folds of convolute bedding die out upward also. Convolute bedding has laminae that are commonly attenuated on the crests of the folds and thickened in the troughs, as in ordinary slump structures, but the sets of cross laminae commonly associated with the laminae near the top of the bed are generally more prevalent and thicker in the troughs than on the crests. Convolute bedding characteris- tically extends for considerable distances along a bed. The thickness of the bed, the steepness and asymmetry of folds within the bed, and the distance between the crests of the folds, as well as the relative width of the troughs and crests of the folds, remain constant. A particular pattern of crumpling may remain nearly the same for many yards along an exposure. One convoluted bed about 5 inches thick was traced for about 50 yards, showed no appreciable change in thick- ness, and retained a distinctive pattern of crumpling. Crumpling confined to the center of a bed is the result of movement that began and ceased during, not after, the deposition of the bed. If the top part of a crumpled bed is missing as a result of erosion, the dating of the movement is more uncertain. The crumpling of beds during deposition could be due to frictional drag of a current, but the currents producing the sets of cross laminae associated with the GEOLOGY OF SOUTHEASTERN VENTURA BASIN . 333 FIGURE (Hi—Slump structures in the Towsley formation, Santa Susana Mountains. The dark slltstone in the upper left tnmcates the contorted beds below. The lowest bed, at the extreme right edge of the figure, is mudstone. The dark, diamond-Shaped block of mudstone near the hammer was probably derived from the mudstone layer. 334 convolute bedding are probably not swift enough to accomplish the task. A more plausible explanation is that the deposition took place on a slope sufficiently steep to permit the water-saturated incoherent sand to continue to creep downslope even after deposition. The thin laminae of clay in the convoluted beds might be helpful in promoting the creep. STRUCTURE REGIONAL RELATIONS The Ventura basin is a deep narrow trough filled with a thick prism of sedimentary rocks of late Cenozoic age. The axis of the basin trends east-west and coin- cides approximately with the center of the Santa Clara River valley and Santa Barbara Channel. Although the Ventura basin has been an area of sub— sidence and accumulation of sediment since the be- ginning of the Tertiary period, the narrow troughlike form did not develop until near the beginning of the Miocene epoch. At that time the Oak Ridge uplift developed as a more or less linear positive element that bordered the Ventura basin on the south and ex- tended eastward from Oxnard through the Simi Hills to the north side of San Fernando Valley (fig. 49). Strata of late Cenozoic age thin toward this persistent high and are dissimilar on its north and south sides. The axis of the late Cenozoic trough north of the Oak Ridge high extends westward from the vicinity of Sunland (fig. 49) along the north edge of San Fernando Valley and through the Newhall-Potrero oil field to Piru. The narrow easternmost part of the basin is bordered on the north by highlands of pre—Cretaceous rocks of the San Gabriel Mountains. Near Newhall the trough increases in width, and its margin of crys- talline rocks trends northwestward near the trace of the San Gabriel fault. Farther west, the north border of the trough is ill defined, but the northward thinning of the upper Cenozoic section north of the Oak Canyon oil field indicates that the margin of the trough must have been only a short distance north of that area during Pliocene time and probably only 7 or 8 miles north of there during Miocene time. In the Ventura basin the tMiocene sea was, in general, more wide- spread than the Pliocene sea. Near the south margin of the Ventura basin the thick section of rocks of late Cenozoic age has been thrust southward along the Santa Susana fault toward the older rocks of the Simi Hills. The zone of thrust faulting extends northeastward, obliquely across the axis of the depositional trough near San Fernando Pass. The zone continues as a series of high—angle northward- dipping faults along which the pre—Cretaceous rocks of the San Gabriel Mountains are thrust southward over the nothern margin of the basin. SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY The San Gabriel fault zone transects the north- eastern part of the Ventura basin. This fault can be traced from the Frazier Mountain area, about 30 miles northwest of Saugus, to the eastern part of the San Gabriel Mountains, a distance of about 90 miles. Dis- similar facies in the pre-Pliocene rocks on opposite sides of the fault indicate a long history of continued movement. Evidence of 15 to 25 miles of right- lateral displacement along the fault after late Miocene time was presented by Crowell (1952a). Major folds and faults between the San Gabriel and Santa Susana fault zones trend northwestward. Most of the faults are southward—dipping reverse faults. STRUCTURAL HISTORY PRE-LATE CRETACEOUS During the course of field work no attempt was made to differentiate rocks unit within the crystalline complex. of the San Gabriel Mountains; therefore, no inferences are made regarding the structural history of these older rocks. LATE CRETACEOUS AND EARLY TERTIARY Cretaceous rocks are unknown in the area north of the Santa Susana fault, but their thickness (5,500zl: feet) in the nearby Simi Hills and their presence in wells immediately south of the fault suggest that the Creta- ceous sea may have covered at least part of the region north of the fault. Paleocene rocks likewise crop out in the Simi Hills and are reported from the Aliso Canyon oil field, just south of the Santa Susana fault. Paleocene rocks also crop out between branches of the‘ San Gabriel fault about 10 miles southeast of Newhall (Hill, 1930, pl. 15) and over a large area north of the San Gabriel fault near Elizabeth Lake Canyon and about 5 miles north of Castaic. Even if large lateral displacements have occurred along the San Gabriel fault, it is still probable that the southeastern Ventura basin was a depositional basin during Paleocene time. Eocene rocks exposed in Elsmere Canyon are at least in part equivalent in age to the Llajas formation of McMasters (1933) in Simi Valley. This formation rests with slight unconfromity on older beds in the Simi Valley area. In the region north of the Santa Susana fault a similar unconfromity may be present between crystalline rocks and rocks of Eocene age penetrated in Continental Oil Phillips 1 well. The Sespe formation is reported to rest conformably on the Llajas formation of McMasters (1933) in the Simi Valley (Stipp, 1943, p. 422), and no evidence was discovered to disprove a similar relationship between the Sespe(?) formation and marine Eocene rocks in the Newhall area. GEOLOGY OF SOUTHEASTERN VENTURA BASIN EARLY AND MIDDLE MIOCEN‘E Lower Miocene marine rocks are not known in the southeastern Ventura basin but they may have been present at one time. South of the Santa Susana fault, middle Miocene strata assigned to the Topanga for- mation rest with angular unconformity on the Llajas formation of'McMasters. The unconformity at the base of the Topanga formation is inferred to be associated with the beginning of the uplift of Oak Ridge and the Simi Hills. The most widespread unconformity in the Miocene section is at the base of the Modelo formation. In the Aliso Canyon oil field, the Modelo formation rests on Cretaceous and Eocene rocks; in the same area, but north of the Santa Susana fault zone, the Modelo for- mation rests unconformably on the Topanga formation. This unconformity, together with the southward thin- ning ,of the Modelo formation, suggests that the Oak Ridge-Simi area was a positive tectonic element at the time the Modelo formation was deposited. LATE MIOCE'N‘E Subsidence in the trough continued during the late Miocene, and the change from predominantly fine- grained clastic material in the Modelo formation to predominantly sandstone and conglomerate in the Towsley formation suggests the uplift of adjacent land areas to a higher altitude. The distribution of coarse anorthosite-bearing conglomerate in rocks of Kleinpell’s upper Miocene Mohnian stage northwest of Castaic was interpreted by Crowell (1952a) as suggestive of their derivation from a nearby area across (northeast of) the San Gabriel fault. The change from the finer grained rocks of the Modelo to the coarser grained rocks of the younger Towsley, especially considering the east- ern derivation of the material, may well be correlated with the beginning of important movement along the San Gabriel fault. The angular unconformity at the base of the upper Miocene Castaic formation of Oakeshott (1954) north of the San Gabriel fault records local, but intense, post- Mint Canyon (latest Miocene) deformation. The Whitney Canyon fault may have been active during late Miocene time also, but its “movement cannot be dated more precisely than post-Eocene and pre-Plicoene. .PLIOCENE AND EARLY PLEISTOCENE(?) , Lower Pliocene strata overlap older formations near the southeastern margin of the basin, but no unconform- ity separates Miocene and Pliocene rocks in its central part. Although subsidence continued in the central part of the basin during the Pliocene, the rate of sub- sidence was less than the rate of sedimentation. Un- conformities between the Pico and Towsley formations and between the Saugus and Pico formations near the margins of the basin reflect the tectonic activity in 581.734 0—62—5 335 these areas. That these disturbances also affected areas at some distance from the edges of the basin is indicated by the angular discordance between the Pico and Saugus formations southeast of the Newhall- Potrero oil field. Continued intermittent activity along the San Gabriel fault zone is inferred from the increased angularity of unconformities in areas near the fault. PLEISTOCENE After the deposition of the Saugus formation, which may include beds as young as late Pleistocene, the entire region was intensely deformed and the present structural features of the region were developed. The deformation in the mapped area cannot be dated pre- cisely, but presumably it is the same one that affected the Ventura region in the middle Pleistocene (Bailey, 1935, p. 491). LATE PLEISTOCENE The erosion surfaces and stream-terrace deposits that exist at various altitudes between the floor of the Santa Clara River valley and the top of the Santa Susana Mountains record continued vertical uplift of the entire region. The terrace surface that lies across the axis of the Del Valle anticline appears to have an exceptionally flat profile, rather than the valleyward— sloping profile that would be expected, suggesting that the fold is still being formed. Similarly, the profile of a terrace surface that lies across the axis of the syncline southwest of Castaic Junction oil field appears to be concave. Further evidence of continued tectonic activ- ity in the region is found in the displacement of terrace deposits by minor faults at several places. STRUCTURAL DETAILS SANTA SUSANA MOUNTAINS AN'D SAN FERNANDO VALLEY Faults.—The part of the Santa Susana Mountains shown on the geologic map (pl. 44) lies on the north or upthrown side of the Santa Susana fault. Southwest of the mapped area on the southwestern flank of the mountains, this fault has a very sinuous trace with an average trend of about N. 60° W- The fault south of San Fernando Pass that is labeled Santa Susana on the map does not have the general strike and low dip which are characteristic of the Santa Susana fault outside the area shown on the map. The northeast— ward-trending segment of the fault on the map is interpreted as a tear fault at the southeastern end of the Santa Susana fault proper. Southwest of the mapped area the Santa Susana fault commonly dips gently northward at the surface, although at some localities the fault surface is flat or even dips southward. At moderate depths the fault dips steeply to the north (pl. 45), but whether it con- 336 tinues to dip steeply at greater depth is uncertain. The dissimilarity of the stratigraphic sections on either side of the fault, as revealed at the surface and in wells, suggests that the rocks on opposite sides of the fault were deposited in areas remote from one another and were brought into closer proximity by movement on the Santa Susana fault. If this movement was, as believed, chiefly thrust rather than strike slip in char- acter, the fault surface must flatten northward at depth. Leach (1948) suggested 5 miles, and Hazzard (1944) a minimum of 1% miles of thrust movement on the Santa Susana fault. The zone of southward thrusting continues eastward along the south front of the San Gabriel Mountains as a series of reverse faults that bring rocks of pre- Cretaceous and Pliocene age into contact. The outlier of crystalline rocks east of Grapevine Canyon is prob- ably'a klippe related to the nearby thrust faults. The fault trending northwestward across Grapevine Canyon truncates a thick section of Pliocene rocks on the poorly formed eastward continuation of the Pico anticline. It is interpreted as a tear fault related to the faults along the south front of the San Gabriel Mountains. The Salt Creek fault (pl. 45), a reverse fault which dips steeply toward the northeast, truncates the west end of the Pico anticline. A horizontal component in the movement of this fault is demonstrated by right- lateral displacement of conglomerate beds of the Pico formation. Since no evidence was found that the fault continues north of Potrero Canyon, it is postulated that it may terminate there against an eastward-trending fault. Folds.—Eastward from Salt Canyon the general north- erly dip of the strata above the Santa Susana fault is disrupted by the Pico anticline and the parallel Oat Mountain syncline (pl. 45). The axial plane of the Pico anticline is nearly vertical in exposures in the canyon bottoms but dips southward in exposures high on the ridges. Subsurface information suggests that the axial plane dips steeply southward at depth. The rapid northward thickening of the Modelo formation near Rice and East Canyons greatly reduces the structural relief of the anticline in the subsurface. The asymmetric anticline in the subsurface in the N ew- hall-Potrero oil field (pl. 45 ) is represented at the surface in the central part of the field only by a broad structural terrace that changes toward the northwest to a north- westward—plunging nose. No unconformity is known which would explain the marked difference in surface and subsurface structure. The steep south limb of the anticline may have been caused by a fault in the subsurface. Although steep dips on the divide between Pico Canyon and Potrero Canyon and in the area southeast of the mouth of DeWitt Canyon may indicate SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY the presence of such a fault, no important displacement of beds was observed at the surface. SANTA CLARA RIVER TO SAN GABRIEL FAULT Faults—The Del Valle and Holser faults are two of the most important structural features north of the Santa Clara River in the western part of the area. The Del Valle fault trends eastward from the Los Angeles-Vent- ura County line for nearly 2 miles and turns southward before crossing San Martinez Grande Canyon. The eastward-trending part of the fault trace is a southward- dipping reverse fault (pl. 45); the southward-trending part of the fault trace is interpreted to be a tear fault. On the geologic map (pl. 44) these two segments are shown to be connected, but their true relationship is obscured in the field by landslides and creep. The Holser fault can be traced from near Piru Creek, several miles west of the Los Angeles-Ventura County line, to Castaic Creek. Subsurface information and conspicuous southward-dipping fractures in outcrops of the Saugus formation just east of the US. Highway 99 bridge over the Santa Clara River indicate that the fault extends eastward beneath the alluvium-covered river valley (pl. 45). The Holser fault is inferred to inter- sect the San Gabriel fault east of the town of Saugus. Subsurface data in the Del Valle and Ramona oil fields demonstrate that the Holser fault is a southward- dipping, rather sharply folded reverse fault (pl. 45). It is offset by cross—faulting in at least one place near the east boundary of sec. 9, T. 4 N., R. 17 W. Folds—Folds near the Ramona and Del Valle oil fields (pl. 45) have an east-west trend, plunge gently eastward, and have almost vertical axial planes. The east-west trend of the folds changes to a southeasterly trend near the Castaic Junction oil field. Folds south of the Holser fault between San Martinez Chiquito Canyon and Castaic Creek are more closely spaced near the fault. SAN FERNANDO PASS AND NEWHALL AREA Rocks of Pliocene age near Newhall and San Fer- nando Pass have a regional dip to the west; southward- dipping thrust and reverse faults have deformed these strata into gentle westward-plunging folds. “Legion fault” and “Beacon fault” are local names c0mmonly used by geologists for two of these faults. The Legion fault, the northernmost of the reverse faults (pl. 45), is named for its exposure behind the American Legion Hall, about 1 mile east of Newhall. The fault is mostly concealed by alluvium, but it is inferred to connect with a system of reverse faults exposed on the ridge south of Elsmere Canyon. The Beacon fault is named for its exposure near an airway beacon in San Fernando Pass. It is a thrust fault that dips about GEOLOGY 0F SOUTHEASTERN VENTURA BASIN 30° southward at the surface along the eastern part of its trace (pl. 45) but apparently steepens to the west. At its east end it is apparently parallel to the bedding of the strata and could not be traced. The Weldon fault, which parallels the Beacon fault to the south, does not steepen westward but rather flattens and the direction of its trace changes from west-northwest to nearly south. A klippe lies just west of the north—southward-trending part of the fault trace. The Weldon and Beacon faults are both be- lieved to steepen at depth. The pre-Pliocene stratig— raphy is very dissimilar in the subsurface on either side of the Weldon fault (pl. 45). Wells drilled south of the fault penetrate a thick section of the Modelo formation, whereas north of the fault the Modelo is very thin. This difference in thickness could be explained by the presence Of a strike-slip fault along which there has been considerable displacement, most probably left—lateral. Many small west-northwest- ward-trending faults, some of which have horizontal slickensides, are exposed in Weldon and Gavin Canyons; however, none of these faults appear to have sufficient displacement to explain the dissimilarity of rocks of pre-Pliocene age on either side of the Weldon fault. It is possible that different pre—Pliocene stratigraphic sequences may have been brought into juxtaposition along a strike-slip fault whose movement was chiefly of pre-Pliocene age. _ The nature and age of movements along the Whitney Canyon fault are not definitely known. No Eocene rocks are present east of this fault, but the Continental Oil Phillips 1 well (well 42 on pl. 44), which was drilled only 1,600 feet west of the surface trace of the fault, penetrated a very thick section of Eocene rocks between 1,300 and 7,911- feet (pl. 45). The difference in depth to crystalline rocks on opposite sides of the fault would indicate a vertical displacement of about 6,000 feet on the Whitney Canyon fault if the movement were entirely vertical. The base of the Pliocene section, however, has a vertical displacement of only about 400 feet across the fault, and, in a sense, opposite to the displacement of the top of the crystalline rocks. From this evidence it seems probable that the Whitney Canyon fault may have had at least two periods of activity: pre-Pliocene movement, which may have. been either dip-slip or strike-slip, and post—Pliocene move- ment, which was perhaps mainly dip-slip, as suggested by the similarity in thickness and facies of the rocks of Pliocene age on opposite sides of the fault. SAN GABRIEL FAULT TO NORTH EDGE OF MAPPED AREA Faults.»--The San Gabriel fault is a major right- lateral strike-slip fault that trends in a northwesterly direction across the'northeastern part of the mapped 337 area. The rock sequences of pre-Pliocene age on op- posite sides of the fault are quite dissimilar (pl. 45). The Miocene rocks south of the fault are chiefly marine, and those north of it are chiefly nonmarine. The Pliocene rocks, however, particularly the Saugus forma- tion, are similar on both sides of the fault. Although the postlate Miocene (Mohnian stage of Kleinpell) movement along the San Gabriel fault may have been large (Crowell, 1952a), the major movement occurred before the deposition of the Saugus formation. The trace of the fault through the Saugus is marked only by a zone where the beds have abnormally steep dips and relatively minor faults and fractures. Folds—South of the Santa Clara River, the Mint Canyon formation is compressed into a number of tight folds (pl. 45). East of US. Highway 6 these folds have a northwesterly trend, but west of the highway they trend nearly due west. This change in trend, to- gether with the poor correlation of the folds across the small valley west of US. Highway 6, suggests that a northeastward-trending fault may be present beneath the alluvium of the valley. Since no evidence of it was found in exposures of the Saugus formation, such a fault, if it exists, is pro-Saugus. The Saugus formation north of the San Gabriel fault is warped into a number of broad folds. The trend of some of the folds is at slight variance with the regional trend of folds in other parts of the mapped area. GEOLOGIC HISTORY Fundamental to an understanding of the Cretaceous and Tertiary history of almost any area in southern California is the realization that large lateral move- ments along faults can drastically alter the distribution of rock units, separating formerly contiguous rocks and placing together rocks originally deposited in different areas or even in different basins. The San Gabriel fault is apparently a strike-slip fault that has brought together two formerly distinct depositional provinces. The area northeast of the fault appears to have had a depositional history more or less independent of that of the area southwest of the fault until late Tertiary time, when movements along the fault began to bring the two areas into closer proximity. The earliest event in the region for which there is a record in the rocks was the deposition of the Placerita formation of Miller (1934) which was later intruded by the Rubio diorite of Miller (1934). Both of these formations were intruded before Late Cretaceous time by quartz plutonites. Late Cretaceous and Paleocene events are not re- corded in the mapped area, but marine deposits of those epochs in areas close by suggest that seas of these ages may have extended across the mapped area. 338 Middle or late Eocene seas undoubtedly covered the area south of the San Gabriel'fault, and in these seas were deposited several thousand feet of sandstone, silt- stone, and conglomerate. Graded beds suggest that turbidity currents may have been operative in tran- sporting and depositing sediment. In the Ventura basin deposition of nonmarine variegated strata of the Sespe(?) formation followed withdrawal of the Eocene sea. Whether a period of erosion intervened between the marine and nonmarine periods of deposition is not clear, nor is the time extent of the nonmarine deposition known. Beds of montmo- rillonitic clay in the nonmarine strata suggest volcanic activity accompanied by ash falls. During an unknown interval of time between the Paleocene and the beginning of the Miocene epoch, nonmarine deposits were laid down in the region north- east of the San Gabriel fault. These sediments, which now make up the Vasquez formation, include conglom- erates, derived in part from an anorthosite terrane, as well as lacustrine deposits, lava flows, and tufl" beds. The area of deposition of the Vasquez formation may have been separated from the area of deposition of the Sespe(?) formation by a ridge of pre-Cretaceous rocks, chiefly anorthosite. Sometime between the end of the deposition of the Sespe(?) formation and middle Miocene time a posi- tive element, the Oak Ridge-Simi Hills uplift, began to rise and to divide into two separate basins a former single area of accumulation of Cretaceous and early Tertiary sediment-s. The rocks in the uplifted area were folded and partly eroded before the deposition of the marine Topanga(?) formation in middle Miocene time, for the Topanga(?) formation rests unconform- ably on the older formations. Deformation northeast of the San Gabriel fault during the time between the end of deposition of the Vasquez formation and the early part of the Miocene epoch is recorded by the angular unconformity at the base of the Tick Canyon formation of Jahns (1939). The deformations in the Simi Hills area and in the area of deposition of the Vasquez formation may be re- lated to each other, but uncertainties about the age ranges of both the Sespe(?) and the Vasquez forma- tions and doubts concerning the exact ages of Jahns’ Tick Canyon formation and the Topanga(?) forma- tion makes a correlation of tectonic activity in the two regions dubious. Nonmarine conditions of deposition prevailed in the area northeast of the San Gabriel fault during deposition of the Tick Canyon formation of Jahns (1939). Lower Miocene marine deposits of the Va- queros formation near the fault a few miles north- west of Castaic indicate that the region southwest of SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY the fault was at least in part in a marine environment. However, early Miocene seas probably did not cover much of the mapped area. The generally coarse texture of the elastic material in the Topanga(?) formation suggests nearby land as source areas, but the local paleogeography of middle Miocene time is obscure. The sea probably covered the area now occupied by the Simi Hills, but deposi- tion there was very slow compared with that in the area now occupied by the Santa Monica Mountains to the south and the Ventura basin to the north. The middle Miocene sea extended eastward through the San Fernando Pass area at least as far as the present site of the town of Sunland, but how far the sea spread to the north is not known. Fine-grained marine rocks assigned to the Rincon formation, a part of which is equivalent in age to the Topanga(?) formation, are exposed about 15 miles northwest of outcrops of the Topanga(?) in the Santa Susana Mountains. The Topanga(?) may grade laterally into these finer grained beds in the subsurface. Minor eruptions of basalt accompanied deposition of the Topanga(?) in the area now occupied by Aliso Canyon. Deposition of the Topanga(?) formation was followed by tilting and erosion, at least in the Aliso Canyon area, that perhaps reflected renewed uplift in the Simi Hills area. Deposition may have been contin- uous in areas farther north in the Ventura basin. During late middle Miocene time the sea extended southward again into the Aliso Canyon area, where the sandstone at the base of the Modelo formation rep- resents near-shore deposits of this sea. Either the Luisian (late middle Miocene) sea was widespread and the Santa Susana Mountains area was far from land, or else nearby land areas were low lying, for the siliceous and organic shales of the lower part of the Modelo formation record slow deposition in an area receiving little land-derived detritus. Deposition of mud con- tinued in the Santa Susana Mountains area into late Miocene time, but the rate of deposition increased, and from time to time sand and gravel were swept into the basin by turbidity currents. The probable main geographic features of the region in the early part of late Miocene time are represented in figure 67. A moderately deep trough extended in an east—west direction along the general line of the Santa Clara River valley from at least as far west as the town of Ventura through the Fillmore and Piru areas into the Santa Susana Mountains and Newhall areas. South of this trough was the Oak Ridge-Simi Hills uplift, which, even if not actually emergent, was not an area receiving important amounts of sediment. North of the trough, perhaps 10 or 12 miles north of the Del Valle oil field, a land area (the Piru Mountains) was probably con- GEOLOGY 0F SOUTHEASTERN VENTURA BASIN 119°02’ 119° 50’ 40’ 30’ 118°28’ . \ Nonmarine basin / Castaic 7% \ 40’ — \ (Mint Canyon formation) «<$\\A;%N\\GABRIEL \\\\\\\\\\ MOUNTAINS 30’ — Marine basin (Modelo formation) 34°2o' >»__- ——’ 10 MlLES l i l \lx FIGURE 67.—Paleogeography of beginning of late Miocene time, eastern Ventura basin. tributing detritus to the northern part of the basin. A fairly steep submarine slope bordered the basin from the N ewhall area northward through Saugus, where the strike of the slope may have swung northwestward to become parallel to the present San Gabriel fault. Northwest of the San Gabriel fault pre-Cretaceous rocks, including anorthosite, were exposed on a land area. This mass possibly extended as far north as Castaic and perhaps connected with the land area rim- ming the basin of deposition on the north. On the north side of the ridge of crystalline rocks, in the same general area where the Vasquez formation was deposited at an earlier time, the fluviatile and laws- trine Mint Canyon formation was being deposited. The Mint Canyon basin may have drained southward into the Ventura basin or perhaps northwestward into the Cuyama Valley area. Movements along the San Gabriel fault apparently began at least as long ago as early late Miocene (Mohn- ian) time and influenced sedimentation during much of the later part of the Tertiary period. During later Miocene time, after deposition of the Mint Canyon for- mation, the sea spread northeastward across the former barrier between the Ventura and Mint Canyon basins of deposition (fig. 68). In the shallow basin northeast of the fault, sand and silt were deposited that now con— stitute the Castaic formation of Oakeshott (1954). Northwest of Castaic very coarse gneissic breccia accu- mulated, possibly as talus at the base of steep scarps along the San Gabriel fault. On the opposite side of the fault, and for many miles farther southeast, coarse gravel accumulated near the submarine slope leading from the shoreline near the fault into the deeper waters of the ancient Ventura basin. Occasionally sand and 581734 0—62—6 339 119° 02/ 11.9" 50’ 40’ 30’ 118°28’ \kaBgeccia l ‘ §\ Shallow water \ \ SAN GABRIEL \\\\\\\\\ M o u NTAI N s (Modelo formation) 34°20, — , / ’ I o 5 10 MILES \ . . . , “—J—‘—'—'—‘—J Shallow water \ \ I l | \ J FIGURE 68.—Paleogeography of part of late Miocene (late Mohnian) time, eastern Ventura basin. gravel were carried far out into the basin by undersea slides and turbidity currents. Through the remainder of the Miocene epoch, and probably through most of the Pliocene epoch as well, lateral movement along the San Gabriel fault continued. Vertical movements along this or other nearby faults kept the land area high enough so that coarse material was nearly always being brought to the sea by streams. Near the close of Miocene time the area close to the fault was probably uplifted sufficiently so that the Castaic formation of Oakeshott (1954) was partly eroded away, but in the central parts of the basin deposition was continuous. During the early Pliocene much of the marginal up- lifted area was resubmerged and the sea extended not only into the region northeast of the San Gabriel fault but also into the Elsmere Canyon area. The general pattern of deposition established in the late Miocene in the Ventura basin continued. Shallow—water deposits accumulated in the area around Newhall while deeper water deposits accumulated farther west. Turbidity currents were intermittently active in ’ transporting coarse material into deep water. Through Pliocene time the basin continued to subside, but the rate of sub— sidence was less than the rate of deposition and the basin gradually shallowed. Near the margins of the basin, shallow-water marine conditions of deposition gradually gave way to lagoonal and estuarine and finally to fluvi- atile conditions. The shore line of the basin of depo- sition was pushed farther and farther westward until fluviatile deposition prevailed over the entire area. Subsidence and deposition continued through the Plio- cene and into the early Pleistocene. Near the middle of the Pleistocene epoch the entire Ventura basin, along with the rest of coastal southern 340 California, was strongly compressed, and most of the present structural features of the area were produced. The main period of compression was apparently of short duration, although some deformation is probably going on in the region at present. Following this orogenic episode slow uplift of the re- gion began. Erosion surfaces were cut during the up- lift, and stream terrace gravels were deposited locally on these surfaces. OCCURRENCE OF OIL Early travelers in California found that the Indians were using oil and tar collected from many natural seepages near the present town of Newhall. By 1850, oil from seepages in Pico Canyon was being distilled at nearby San Fernando Mission to produce “burning oil” for illuminating purposes (Prutzman, 1913). After 1859 the numerous oil seepages in the area at— tracted the attention of persons familiar with petroleum development in Pennsylvania. As early as 1869—70, Sanford Lyon drilled a spring-pole hole to a depth of 140 feet near oil seeps on the axis of the Pico anticline in Pico Canyon. The well is reported to have flowed from 70 to 75 barrels of oil per day while being drilled (Standard Oil Co. of California, 1918), but the tools were lost in the hole and drilling was suspended. Not until 1875 was another attempt made to drill a well in the area. In that year C. C. Mentre drilled on the axis of the Pico anticline a spring-pole hole that had an initial daily production of 2 barrels of 32° Bé (Baumé) gravity oil at 30 feet (Orcutt, 1924, p. 65). This well is generally considered to mark the beginning of the California oil industry. After the successful completion of Mentre’s well, California Star Oil Works Co. was organized to develop the oil resources of the Pico Canyon area. This com— pany built the first oil refinery in California near New— hall in 1876. The refinery had a daily capacity of 20 barrels and the oil was hauled to it in wooden barrels. In 1877 steam-driven equipment was installed on well Pico 4 (Standard Oil Co. of California C.S.O.W. 4) and was used successfully to deepen the well from 370 to 610 feet.5 This first success with the use of steam- driven equipment marked the end of the spring-pole method of drilling in the area. The Pacific Coast Oil Co. was incorporated in 1879 and began operations in the Pico Canyon area where, by acquiring the holdings of the California Star Oil Works C0., it became the principal oil producer in the region. A new refinery with a greater capacity was built near Newhall and a 2-inch gravity pipeline, the 5 The names of operators and wells given in parentheses after the names of a few of the wells mentioned in the text refer to a later designation of the well where the well name or operator has been ofllcally changed. SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY first in California, was constructed to it from Pico Canyon. After the Newhall refinery was closed in 1883, the oil was shipped by rail to the Pacific Coast Oil Co.’s refinery at Alameda, near San Francisco. During 1884 and 1885 a combination 2- and 3-inch grav- ity pipeline was laid from Pico Canyon to a refinery at Santa Paula. Shortly afterward the line was extended to the seacoast at Ventura Where the oil was taken aboard ships for transit to San Francisco. Development of the oil resources of Pico Canyon, as well as those of adjacent areas to the east along the Pico anticline was actively carried out even though the market for the oil was limited. Walling reported (1934) that well Pico 2 was permitted to flow freely for about a year because the poor market did not warrant the marketing of the oil. Activity along the Pico anticline was greatest from 1875 to 1900. Exploration was begun in De Witt Canyon in 1882— 83, in Wiley Canyon prior to 1883, in Towsley Canyon prior to 1893, and in Rice and East Canyons in 1899. Development outside the Pico anticline area began in Elsmere Canyon in 1889, in Whitney Canyon in 1893, and in the Tunnel area in 1900. No new discoveries of importance were made until the Newhall-Potrero field was found in 1937. The major discoveries in the area from 1938 to 1953 were the Del Valle field in 1940, the Ramona field in 1945, the Placerita field in 1948, and the Castaic Junction field in 1950. The nomenclature used in this report for the various oil fields is similar to that used by the California Department of Natural Resources, Division of Oil and Gas. The small fields along the Pico anticline, together with those east and southeast of Newhall, are collec- tively called the Newhall field. The other fields are treated separately. The names of oil-producing zones used here conform with those used by most of the petroleum geologists who work in the region and with published reports. ’The oil-producing zones are listed in table 7 and the production statistics of the oil fields in the area are shown in table 8. The location of wells referred to in the text and of wildcat wells drilled prior to July 1953, whose locations are known to the authors, are shown on the geologic map (pl. 44). OIL FIELDS NEWHALL Newhall oil field is the term applied to a number of relatively small oil-producing areas on the northern flank of the Santa Susana Mountains along the Pico anticline and on the western flank of the San Gabriel Mountains east and southeast of Newhall. The earliest development in the Newhall field was along the Pico anticline with its many oil seepages. Attention was focused on a number of canyosn which afforded access through the rugged terrain to the axis of the anticline. GEOLOGY 0F SOUTHEASTERN VENTURA BASIN TABLE 7.—01.'l- and gas-producing zones in four major fields west of Newhall Field Age Ramona Del Valle Castaic Junction Newhall- Potrero Early Pliocene Sepulveda 20 Kinler Sepulveda Vasquez 13 Black Delmontian stage of Vasquez 1st Kleinpell Videgain 2d Kern Intermediate 3d Del Valle Del Valle Reservoir 10 Late Mohnian stage Anderson of Kleinpell Bering Reservoir 15 (53% Reservoir 21 7th Early Mohnian Barnes 9th stage of Kleinpell Lincoln PICO CANYON AREA The Pico Canyon area is located about 5 miles west of Newhall in secs. 1 and 2, T. 3 N., R. 17 W. With successive well completions, development gradually spread from its beginning near the oil seepages in the broken shales in the canyon bottom to the adjacent hillsides. Twelve wells were drilled south of the anti- clinal axis in Pico Canyon, but only 6 produced commer- cial quantities of oil, and these were soon abandoned because of 10W production. By the end of 1887, 31 wells had been drilled, of which 11 had been abandoned and the remaining 20 were producing an average daily total of 491 barrels of oil (Walling, 1934, p. 9). Sev- eral wells have been drilled in the area since 1902 ; how— ever, none of these newer wells has produced more than a few barrels per day. Wells C.S.O.W. (California Star Oil Works Co.) 12 and P.C.O. (Pacific Coast Oil Co.) 28 had the highest initial production records in the Pico Canyon area. Well C.S.O.W. 12, about 100 feet north of the axis, was completed at a depth of 1,400 feet in 1883 ; it produced 85 barrels of oil the first 24 hours. Well P.C.O. 28, 341 about 1,000 feet north of the axis of the Pico anticline, was completed at a depth of 1,610 feet in 1893; it pro- duced an average of 88 barrels per day during the first week. Sustained production showing a slow decline that is typical of the area is exemplified by well 0.8. O.W. 13, which was completed in 1884 at a depth of 1,500 feet and produced 80 barrels of oil per day. During March 1891, well 13 produced a daily average of only 16 barrels. Production was increased to 24 barrels a day after the well was cleaned out and placed on pump in May 1891, but by July 1893 production had declined again to only 15 barrels per day (Walling, 1934, p. 17). Approximately 80 wells were drilled in the area. Of these, 37 were still producing in 1934, with a daily average per well of 1.8 barrels of 38.2°API (American Petroleum Institute) gravity oil. In May 1940, 26 wells were producing only 50 barrels per day (Kew, 1943, p. 414). In 1953, a couple of wells were still pumping a few barrels of oil per day. The Pico Canyon area is at the west end of the north- westward-trending Pico anticline. Shale of the Modelo formation is exposed in places along the axis of the anticline east of the field, but all the wells in the field are spudded in the Towsley formation. The somewhat lenticular nature of the strata, together with faulting, makes the recognition of definite oil-producing zones in the Pico Canyon area difficult. However, Walling (1934, p. 15) recognized a top, central, and lower zone. The first wells were completed at depths of from 120 to 170 feet, depending on their structural position; they produced from the central zone. Although some oil was reported in the fractured shales, most of the central- zone production probably came from sandstone. Well C.S.O.W. 32 is the only one to produce oil from the lower zone. This well, which was drilled to a depth of 3,445 feet and was completed in 1905, produced from between 2,588 and 3,000 feet. As late as April 1917, it was still producing a daily average of 12 barrels of 33.6° Bé gravity oil, with 69 percent water. TABLE 8.—0il—production statistics for-period January 1 to June 30, 1953 [From: California State 011 and Gas Supervisor, 1953] Average Average production Acreage number Cumulative per well per produc- Field actual Production production, ing day (bbls) producing (bbls) June 30, 1953 Proved, Maximum wells (bbl) June 30, potential Oil Water 1953 Castaic Junction _______________________________________________________________ 10 278, 761 1, 112, 287 169. 9 l. 2 315 315 80 518,093 16, 485, 040 38. 8 61. 9 630 640 40 74. 017 6,205, 6 11. 8 12. 5 395 . 645 91 1,587, 141 30,184, 760 101. 8 6. 2 1,170 1,170 Placerita ..................... 326 1, 442, 314 19, 976, 443 25.0 9. 3 660 685 Ramona 1 ...................................................................... 122 545, 199 11,204,267 25. 1 4. 2 585 585 Total _____________________________________________________________________ 669 4, 445, 525 85, 168, 419 62. 3 15. 8 3, 755 4. 040 1 Only part of the Ramona field is within the area covered in this report. 342 In 1942, Standard Oil Co. of California drilled a deep test, P.C.O. 42, very near the axis of the anticline in the eastern part of the field. After penetrating the base of the Towsley formation, the well encountered steeply dipping fractured shales of the Modelo formation. The well bottomed at 8,758 feet in rocks assigned to the lower part of Kleinpell’s Mohnian stage. The few sand- stone beds encountered had low porosity. DE WITT CANYON AREA The De Witt Canyon area is about 2 miles east of Pico Canyon in the north half of sec. 7, T. 3 N ., R. 16 W. A total of 7 wells were drilled there near the axis of the Pico anticline between the years 1882 and 1897. The first well, Hardison and Stewart 1, was drilled on the south flank of the structure near the axis; it is reported to have been completed at a depth of 1,000 feet and to have produced 1 barrel per day of black 24.1° Bé gravity oil (Walling, 1934, p. 18). The deepest well, Hardison and Stewart 3, was drilled to a depth of about 1,600 feet and was abandoned, although some oil was reported. There is no record of any commercial pro— duction in the De Witt Canyon area. A deep test well, the Los Nietos Oil Odeen 1, was drilled about 1 mile southwest of the De Witt Canyon area on the south limb of the Pico anticline in 1951—52. The well, which was abandoned at a depth of 9,215 feet, bottomed in rocks assigned to the lower part of Kleinpell’s Mohnian stage. rowsmv CANYON AREA The Towsley Canyon area is about 3 miles southeast of Pico Canyon on the Pico anticline in the north half of sec. 17 and the south half of sec. 8, T. 3 N., R. 16 W. (pl. 45). The first well was drilled prior to 1893 by the Temple Oil Co., but it was abandoned without record. A number of shallow wells have been drilled since, none of which produced more than 30 barrels a day of low gravity oil. In 1929 Consolidated Oil Co. began one of the few attempts to find a deep producing zone along the Pico anticline. This well, which was later designated the Community Oil of Nevada 1, was drilled a short dis- tance north of the anticlinal axis; it was drilled to a depth of 5,225 feet, and for most of its depth the dips in cores were greater than 70°. The best oil show was in the interval between 3,915 and 3,990 feet, where a pumping test gave 20 to 75 barrels per day of 24° Bé gravity oil with 60 to 75 percent cut. In 1941—42 Barnsdall Oil Co., Bandini Petroleum Co., and Ambassador Oil Co., drilled a deep test, the Limbocher 1, on the south limb of the anticline. Oil sands were cored but in a formation test only a small amount of gassy mud was recovered. The well bot- tomed at 7,071 feet in steeply dipping shale beds of the SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY Modelo formation containing Foraminifera assigned to the lower part of Kleinpell’s Mohnian stage. Intermittent production has continued in the Towsley Canyon area to the present time. From January 1923 to January 1927 about 4,000 barrels was produced. During July 1935, 5 wells produced a daily average per' well of 1.9 barrels of 205° API gravity oil and 2.2 barrels of water (Walling, 1934, p. 21). WILEY CANYON AREA The Wiley Canyon area is on the Pico anticline about 1 mile east of Towsley Canyon in sec. 16, T. 3 N., R. 16 W. Oil development was begun by a Mr. Davis, who in 1868 leased Wiley Springs and collected seepage oil which he shipped to the Metropolitan Gas Works in San Francisco. Two tunnels were dug into the side of Wiley Canyon for distances of 300 and 400 feet in an attempt to obtain increased seepage production (Walling 1934), but these proved unsuccessful. The first well with a record of production was the Pacific Coast Oil well Wiley 4, which was placed on production May 31, 1884, and which pumped 2 barrels a day of 30° Bé gravity oil from a total depth of 1,275 feet. In 1909—10 Standard Oil Co. of California drilled the first two wells in the area to produce oil in commer- cial quantities. These wells, Wiley 18 and 19, were drilled about 200 feet south of the axis of Pico anticline and were completed at depths of 1,528 and 1,509 feet, respectively. Wiley 18 was completed in 1910 and pumped a daily average of 83 barrels during the first 8 days. This well was deepened in 1913 and when recompleted it pumped 89 barrels per day of 29° Bé gravity oil. The Wiley 19 had an initial production of 109 barrels a day, the highest in the area. The deepest well was Standard Oil of California Wiley 25, drilled in 1910—12 on the north flank of the anticline and abandoned at a depth of 3,835 feet. Of the 29 wells drilled in the Wiley Canyon area, 8 were still producing a daily average per well of 1.7 barrels of 282° API gravity oil and 3.7 barrels of water in 1934. Nearly all production in the area came from wells that are less than 2,900 feet deep and are near the axis of the Pico anticline. When shut down in 1940, 9 wells were producing less than 1 barrel a day per well. RICE CANYON AREA The Rice Canyon area had 10 productive acres on the Pico anticline 1 mile southeast of Wiley Canyon in sec. 22, T. 3 N., R. 16 W. The first well was drilled by Pacific Coast Oil Co. in 1899 to a depth of 550 feet. In 1900 it was producing 3 barrels a day. Ten wells were drilled, altogether, to depths ranging from 300 to 1,580 feet. All the wells are either on the axis GEOLOGY 0F SOUTHEASTERN VENTURA BASIN of Pico anticline or within a few hundred feet south of 1t. The deepest well, Inspiration Oil 1, was drilled by Rice Canyon Oil Co. in 1902; drilling was suspended at 1,580 feet because of mechanical difiiculties. More than 30 years later, the well was cleaned out; it pro— duced a daily average of 4.8 barrels of 25° API gravity oil and 48 barrels of water during July 1935 (Walling, 1934). Three wells were drilled on the Pico anticline in East Canyon, one-half mile southeast of Rice Canyon. The first, Occidental Petroleum 1, drilled by Bradshaw and Beville to a depth of 800 feet in 1899, had a good show of 18° Bé gravity oil near the bottom but was never pumped. There are no records of the sec- ond, Grapevine Cafion Oil 1. A deep test was made by General Petroleum Corp. with their Mendota 1 well in 1943. This well, which bottomed in rocks of the lower part of Kleinpell’s Mohnian stage at 6,834 feet, encountered no productive sands. TUNNEL AREA The Tunnel area, named for a former highway tunnel through San Fernando Pass, is about 2 miles southeast of Newhall, in sec. 13, T. 3 N., R. 16 W. and sec. 18, T. 3 N ., R. 15 W. Most of the production is obtained from sandstone and conglomerate beds of the Towsley formation, accumulation of oil being controlled by faulting and by the lenticularity of the beds. The first wells, Zenith Oil 1—5 (E. A. Clampitt Zenith 1‘5), were drilled along Newhall Creek from 1900 to 1902. They ranged in depth from 645 to 760 feet. Well 1 penetrated oil sand from 640 to 650 feet and produced about 7 barrels a day of 14° Bé gravity oil. Sixteen wells were drilled between 1900 and 1909 by small companies to depths ranging from 645 to 2,100 feet, all but 3 having total depths less than 1,000 feet. They had little or no oil production. Between 1922 and 1932, 9 wells were drilled by, or later acquired by, Southern California Drilling Co. The best initial pro- duction was 200 barrels a day of 195° Bé gravity oil with 10 percent water from Southern California Drill- ing Needham 1 (Airline Oil C. C. Herwick, Needham 1), which had a total depth of 1,952 feet. From 1929 to 1931, York-Smullin Oil Co. drilled 6 wells ranging in depth from 1,184 feet to 1,490 feet and with initial productions from 76 to 220 barrels of 19° to 227° Bé gravity oil per day. York-Smullin Oil 1, which was drilled to a depth of 1,490 feet, had the highest initial production of 220 barrels of 21.6° Bé gravity oil with 3.2 percent water. Several wells have been drilled through the Pliocene section into rocks of the Sespe(?) formation, where oil- stained sands occur throughout an interval of more than 343 300 feet. Southern California Drilling Needham 4 (Air- line Oil C. C. Herwick, Needham 4) penetrated the Sespe(?) formation; it was drilled in Eocene rocks from 2,747 feet to the bottom at 4,400 feet. Thirty-one wells were drilled in the area prior to 1943, 20 of which were producing 4 to 10 barrels per day of 16° to 22° API gravity oil. In the early 1950’s, several small operators, chiefly Morton and Dolley, entered the area and com- pleted a number of relatively shallow wells with modest records of low-gravity oil production. Morton and Dolley Hilty 1 and Needham 2 are examples of the later wells in the Tunnel area. Well Hilty 1, in sec. 12, T. 3 N., R. 16 W. was completed at a depth of 2,280 feet late in 1952; it flowed an estimated 135 barrels per day of 185° API gravity oil with 1.0 percent water. When put on pump several days later, it produced 33 barrels per day of 199° API gravity oil with 0.1 percent water. Well Needham 2, in sec. 12, T. 3 N., R. 16 W., was also completed late in 1952 and was drilled to a. depth of 1,578 feet. Several days after completion it was pumping 30 barrels per day of 190° API gravity oil with 2.0 percent water. ELSMEBE AREA The first successful drilling for oil in the eastern part of the Newhall field was in the Elsmere area about 1% miles southeast of Newhall in sec. 12, T. 3 N., R. 16 W. and sec. 7, T. 3 N., R. 15 W. The productive area covers about 60 acres in Elsmere Canyon and on the ridge south of the canyon. Rocks of the Towsley for— mation are at the surface; production is from the Towsley formation and possibly also from rocks of Eocene age, at depths of less than 1,500 feet. The oil accumulation is controlled by the lenticularity of the beds. The first well, Elsmere 1, was begun in 1889 by Pacific Coast Oil Co. Although it did not produce, oil shows were sufficiently good to encourage more drilling. Pacific Coast Oil Co. drilled 20 wells, 420 to 1,376 feet deep, in the Elsmere area before its holdings were acquired by Standard Oil Co. of California in 1902. The highest initial production was in Standard Oil of California Elsmere 2, which was completed in 1891 with a daily average production of 54 barrels per day during the first four days. Between 1900 and 1903, Alpine Oil Co. and Santa Ana Oil Co. drilled three wells each, to depths of 1,000 feet or less, in the Elsmere area; at least four of them produced some oil. From 1918 to 1920 E. A. and D. L. Clampitt drilled three wells to 660, 690, and 1,040 feet. The first two had initial productions of 15 barrels per day of 13° Bé gravity oil and 20 barrels per day of 14° Bé oil, respectively. The third produced heavy tar only. 344 Standard Oil Co. of California drilled two wells in 1916 and 1917 to depths of 1,611 and 691 feet; these wells had only poor oil shows. Republic Petroleum Corp. drilled wells Fink 3 and 4 in 1920 and 1921 as off- sets- to the north line of the E. A. and D. L. Clampitt property. Well Fink 3 was drilled to 1,242 feet; when completed it produced 25 barrels of 17° Bé gravity oil and 2.5 barrels of water a day. Fink 4, which was drilled to 1,383 feet, had no commercial oil production. Thirty-three wells were drilled in the field. Of these, six were still pumping in June 1949. The oil pro- duced varied from 14° to 16° API gravity. and averaged about 14.2° API gravity. WHITNEY CANYON AREA The Whitney Canyon area is )4 to 1% miles northeast of the Elsmere area in secs. 6, 7, and 8, T. 3 N., R. 15 W. The first well was drilled by Banner Oil Co. in 1893. It was completed at a depth of 850 feet with an initial production of about 100 barrels of oil per day. After a short time water broke in the hole and the well was shut down. A total of 13 wells were drilled by small companies between 1893 and 1933, but only four were drilled to a depth of more than 1,100 feet, the deepest being Southern Production Co. 1 (later Republic Pe- troleum Price 4), which was drilled to 2,842 feet in 1930~ 33. This well is of special interest as it produced oil of 27°API gravity and higher from rocks of Eocene age. Most of the wells have rather low production records of 14° to 17° Bé gravity oil. A deep wildcat well near Whitney Canyon, the Con- tinental Oil Phillips 1, drilled in sec. 6, T. 3 N., R. 15 W. (pl. 45), penetrated the entire thickness of rocks of Eocene age in this vicinity before being abandoned in crystalline rocks at 8,253 feet. NEWHALL rowsm: Recent exploration in the vicinity of Newhall resulted in the discovery of several new pools in that area. Late in 1948, the R. W. Sherman well Newhall-Com- munity 3—1 was completed in sec. 2, T. 3 N., R. 16 W., at a total depth of 5,846 feet, with a rated initial pro- duction of 265 barrels of oil per day from rocks of latest Miocene age (pl. 45). A total of 10 wells were drilled near the R. W. Sherman Newhall-Community 3—1 but none produced commercial quantities of oil. The Sherman well itself was subject to many production difficulties and was not commercially successful. In 1951, the Talisman Oil Braille 1, in sec. 1, T. 3 N., R. 16 W., was completed at a depth of 3,195 feet, with a rated initial production of 101 barrels per day. This new pool is in rocks of earliest Pliocene age (pl. 45). PLACERITA The Placerita field is about 1 mile northeast of Newhall and centers in sec. 31, T. 4 N., R. 15 W. The SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY field has had two periods of development; the first, and minor, period was from 1920 to 1933, the second after 1948. The first well in the field was Equity Oil Daisy 1 (York Oil York 1), drilled in 1920 to a depth of 975 feet. It was deepened to 1,394 feet in 1921, and in 1925 was producing 6 barrels a day of 14° Bé gravity oil. Four wells drilled during this first period (the deepest to 1,598 feet) were producing an average of 8.9 barrels a day of 118° Bé gravity oil with 18.8 percent water in April 1935. The second period of development of the Placerita field began in April 1948, when Nelson-Phillips Oil Kraft 1 (Tevis F. Morrow Kraft 1) was completed at a depth of 2,220 feet, flowing with a rated initial production of 60 barrels a day of 16-.4° API gravity oil from a sand between the depths of 585 and 718 feet (Moody, 1949, p. 819). This well marked the beginning of low-gravity production development in the southern part of the field. In February 1949, the northern or high-gravity part of the field was opened with the completion of Somavia and Yant Juanita 1, approxi- mately 1 mile north of Nelson-Phillips Kraft 1. This well produced 340 barrels a day of 228° API gravity oil from 100 feet of sand below 1,737 feet. The comple- tion of this well marked the beginning of the most spectacular townlot boom in California in 30 years. A highly subdivided area of 80 acres was opened to practically unrestricted drilling by a ruling of the California Superior Court which declared the State Well Spacing Act unconstitutional. Approximately 140 wells were drilled on about 60 acres, with a peak production of 28,950 barrels of oil a day being reached during September 1949. By the end of 1951, Tevis F. Morrow had purchased the three largest undeveloped holdings in the area and drilled 46 wells, most of which are in the part of the field which produced low-gravity oil. This completed development of the field. By the end of November 1951, the northern part of the field had produced 11,611,670 barrels of high-gravity oil as compared with 2,973,313 barrels of lower gravity oil produced in the southern part of the field. The oil in the Placerita field accumulated in a homoclinal structure bounded by the San Gabriel fault on the north and the Whitney Canyon fault on the east. The northern high-gravity oil-producing area is separated from the southern low-gravity area by a northwestward-trending normal fault of relatively small displacement. Two producing zones are recognized in the field, the lower and upper Kraft zones. The lower Kraft zone, which is unproductive in the southwestern part of the field, is in the Towsley formation of late Miocene and early Pliocene age. This zone is reported to have thick- nesses of 200 feet near the east margin and is 480 feet GEOLOGY 0F SOUTHEASTERN VENTURA BASIN thick in the northwestern part of the field (Willis, 1952, p. 38). The lower Kraft zone yields 20° to 25° API gravity oil in the northern high-gravity area, 16° API gravity oil in the southeastern part of the field, and 12° API gravity oil elsewhere. The upper Kraft zone in the Pico formation is of Pliocene age and pro- duces oil only in the southern part of the field where accumulation appears to be controlled largely by the lenticularity of the beds. The oil from this zone is of 10° to 12° API gravity. NEWHALL-POTRERO The Newhall-Potrero oil field is about 5 miles west of Newhall in secs. 25, 27, 35, and 36, T. 4 N., R. 17 W. The field was discovered by Barnsdall Oil Co. with the completion of well Rancho San Francisco 1 (Sunray Oil R.S.F. 1) in March 1937. The well was drilled to a depth of 6,472 feet and had an initial pro- duction per day of 208 barrels of 34° API gravity oil, with 4.0 percent water, and 500M cu ft of gas. It produced from 312 feet of oil sand between the depths of 6,160 and 6,472 feet. The Newhall-Potrero field has seven producing zones: the first, second, third, fifth, sixth, seventh, and ninth. The first zone is in rocks assigned to Kleinpell’s Delmontian stage. It is lenticular, has several mem- bers, and lenses out to the southwest in the vicinity of wells R.S.F. 89, 78, and 83. Its maximum thick- ness is 375 feet in the western part of the field. The second zone, which is also in rocks of the Del- montian stage, has a maximum thickness of 340 feet at the southeast end of the field and pinches out in a northerly direction near a line between wells R.S.F. 22, 11, 99, and 91. The, third zone, which is the most important oil- 'producing zone in the field, is also in rocks assigned to the Delmontian stage. It has a maximum thickness of 400 feet at the west end of the field and lenses out in an easterly direction. As of Dec. 31, 1951, a total of 56 wells had been drilled on leases of the Sunray Oil Corp., which produced oil from the combined first, second, and third zones. The cumulative production of these wells to that time was 19,451,000 barrels of oil averaging 35° API gravity. About two-thirds of this oil came from the third zone. The fifth zone, in rocks of the lowermost part of Kleinpell’s Delmontian stage or the uppermost part of his Mohnian stage, is at depths of from 8,000 to 10,300 feet. It was discovered in 1946 in Barnsdall Oil well R.S.F. 53—5 (Sunray Oil R.S.F. 53—5), which had an initial production of 533 barrels per day. The zone is more than 500 feet thick in the southeast-central part of the field. By the end of 1951, 31 wells had been completed in the fifth zone on Sunray Oil Corp. leases 345 with a cumulative production of 3,413,000 barrels of 25° to 40° API gravity oil. The gravity of the oil generally decreased down the flanks of the structure. The sixth zone, which is about 400 feet below the base of the fifth zone, is in rocks assigned to the upper part of Kleinpell’s Mohnian stage. It was discovered in 1945 in Barnsdall Oil well R.S.F. 44 (Sunray Oil R.S.F. 44), which reached a total depth of 11,229 feet and had an initial production of 530 barrels of oil and 590M cu ft gas per day. Cumulative production from the sixth zone as of December 31, 1951, was 1,594,000 barrels of oil. The seventh zone, Which is about 400 feet below the sixth zone, is believed to be in rocks of the lower part of Kleinpell’s Mohnian stage (Loofbourow, 1952). The only completed well in this zone at the end of 1951 was the discovery well, Barnsdall Oil R.S.F. 65—6 (Sunray Oil 65—6), which was completed in 1948 with a rated initial production of 431 barrels a day. Before the well was shut down, it produced 113,000 barrels of 30.5° API gravity oil. The ninth zone is the deepest producing zone in the field and is in rocks assigned to the lower part of Klein- pell’s Mohnian stage. The only well to produce from this zone, as of the end of 1951, was Barnsdall Oil R.S.F. 66 (Sunray Oil R.S.F. 66), completed late in 1948. The well penetrated 2,700 feet of rocks assigned to the ninth zone, of which 432 feet, between the depths of 13,936 and 14,501 feet, was open to produc— tion. It had produced 26,000 barrels of 24° to 28° API gravity oil by the end of 1951. The subsurface structure of the field is a long narrow northwestward-plunging asymmetrical anticline whose axis strikes N. 55° W. (pl. 45). At the surface, the structure is either not present or is obscured owing to the lack of exposures in siltstone of the Pico formation. There are numerous reverse crossfaults in the subsur- face section with displacements ranging from 50 to 300 feet, but these appear to have had little effect on the accumulation of oil. DEL VALLE The Del Valle oil field is north of the Santa Clara River, 8 miles northwest of Newhall, in secs. 16, 17, 20, and 21, T. 4 N., R. 17 W. The field was discovered in September 1940, when the R. E. Havenstrite Lincoln 1 (Union Oil Lincoln 1), was completed in the interval between 6,690 and 6,885 feet. The well had an initial production of 400 barrels of 58° API gravity oil with 1 percent water, and 11,000M cu ft of gas per day. It was recompleted in October to lower the gas-oil ratio and gave a rate of 875 barrels of 33° API gravity oil and 280M cu ft of gas per day. 346 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY TABLE 9.—0il- and gas-producing zones of Del Valle field [Modified from Nelson (1952)] Initial production API Zone Discovery well Date gravity Depth to zone Age 011 Gas (M (degree) (feet) (bbls. cu ft per per day) day) Sepulveda 20 _________ Standard Oil of California Sepulveda 20 ___________________________ 1951 __________ 1, 259 __________ 2870—3620 Early Pliocene. Kinler _________ ._.- Trigood Oil Kinler 1 ________________________________ 1950 140 .......... 22. 3 7128—7393 Delinontian. Sepulveda _____ ...- Standard 0110f California Sepulveda 3 _______ .._- 1942 707 .......... 35. 5 5040—5120 0 Vasquez 13-... .-.. Ohio Oil Vasquez 13 __________________________ _ 1945 400 264 36 5550—5645 Do Vasquez.-.. . Ohio Oil Vasquez 1 ........................ - 1941 1, 512 __________ 31. 4 5840—6193 Do Videgain ______ . R. E. Havenstrite (Union Oil) Lincoln 2.- 1940 3, 000 3,000 36 6037—6082 Do. Intermediate. . - Standard Oil of California Sepulveda 12-.. 1950 196 __________ 34.8 1 5751—7091 Do. Del Valle ______ - R. E. Havenstrite (Union Oil) Lincoln 1.. - 1940 400 11,000 58 6690—6885 D0. Anderson... . R. E. Havenstrite (Union Oil) Lincoln 15? .... 1947 310 .......... 43 7540—8150 Date Mohnian. Bering ................ R. E. Havenstrite (Union Oil) Barnes 2 ___________________________ 1943 972 580 44 7900—8065 Do. Lincoln ............... R. E. Havenstrite (Union Oil) Lincoln 15 _________________________ 1947 75 .......... 32 10, 110—10, 480 Early Mohnian. 1 Intermediate included in Vasquez 13 interval. The 11 oil and gas producing zones recognized in the field are tabulated in table 9. The field is on the Del Valle anticline, whose position in the subsurface closely corresponds to its surface location (pl. 45). The anticline, which trends in an easterly direction, plunges to the east except in sec. 17, Where 100 feet of closure is obtained. The structure is sharply terminated at the west against the Ramona anticline, probably by faulting. The oil accumulation is due to folding combined with faulting and to lentic— ularity of reservoir beds. The structure is also complicated by thrust faulting below the top of the Intermediate zone. The strata of Kleinpell’s Delmon- tian stage between the Videgain and Del Valle zones appear to merge into one almost continuous sand body east and southeast of the center of the field. RAM ONA Although the Ramona field is immediately adjacent to the western part of the Del Valle field, it is on a different structural feature and is considered a separate field. It is in sec. 18, T. 4 N., R. 17 W. and sec. 13, T. 4 N., R. 18 W. Part of the field is in Ventura County, west of the area covered in this report. The topography in the vicinity of the field is very rugged, so that many of the wells have been whipstocked to the proper subsurface position in order to avoid landslides and the roughest terrain. The field was discovered by the Texas Co. with its Kern 1, which was completed in 1945 in the Kern zone at 2,810 to 3,004 feet and which produced 196 barrels per day of 293° API gravity oil with 0.4 percent water, and 70M cu ft of gas per day. Shale and oil sand from 3,004 to 3,114 feet was plugged off but was left open in subsequent producing wells. The Black zone is in sandstone and conglomerate about 150 feet below the top of strata assigned to Kleinpell’s Delmontian stage and is 660 feet (well thick- ness) above the top of the Kern zone. It was dis- covered in 1946 by Bankline Oil Co. in Black 102 at a depth between 2,190 and 2,332 feet. This well had an initial production of 180 barrels per day of 26° API gravity oil. The zone usually is from 90 to 180 feet thick and is at depths of 2,220 to 2,680 feet. Wells pro- ducing form this zone have initial productions of from 120 to 180 barrels per day of 24° to 28° API gravity oil. The Kern zone, the first productive zone found in the field, varies in well thickness from 100 to 300 feet and is at depths of 2,000 to 4,000 feet. The first wells producing from this zone pumped from 25 to 200 barrels a day of 20° to 30° API gravity oil. After the Del Valle zone was discovered, however, dual Kern and Del Valle zone completions gave a better and more sus- tained production. These wells usually had initial productions of 50 to 400 barrels a day of 17° to 25° API gravity oil. In the easternmost part of the field, the Del Valle zone is cut out by the Holser fault and production is from sand of the Kern zone only. The Del Valle zone was discovered by Superior Oil Co. and British American Oil Producing Co. with their Black 1. The Del Valle zone has from 300 to 1,400 feet of oil-producing sandstone and conglomerate at depths of 3,000 to 6,000 feet. Superior Oil-British American Oil Producing Black 14, a deep test well that was completed in 1951, had an initial production of about 150 barrels per day of 20° API gravity oil from a sand of latest Miocene age that is duplicated below the Holser fault at depths from 7,680 to 7,800 feet. This well produced the first oil from below the Holser fault in the field. It also had favor— able production tests in the Bering zone above the Holser fault at 6,245 to 6,690 feet. The oil in the Ramona field has accumulated on the Ramona anticline, which is a drag fold developed on the upthrown block of the Holser fault. The anticline trends and plunges in a northeasterly direction. The north flank is narrow and locally steep, but the south flank, where most of the oil has accumulated, dips regularly at 45° to 50°. The structure is closed to the GEOLOGY 0F SOUTHEASTERN VENTURA BASIN north by the Holser fault and the northeasterly plunge of the anticline. The closure to the west is strati- graphic, for the producing zones lens out in that direc- tion. To the east the structure terminates against the Del Valle anticline, probably by faulting. CASTAIC JUNCTION The Castiac Junction field is 5 miles northwest of Newhall in secs. 23 and 24, T. 4 N., R. 17 W., and sec. 19, T. 4 N., R. 16 W”. It was discovered early in 1950 with the completion of Humble Oil and Refining Newhall Land and Farming 1. The well was completed in the interval 11,792 to 11,841 feet with a rated initial production of 161 barrels per day of 342° API gravity oil. This producing zone, Reservoir 21, is in rocks assigned to Kleinpell’s Mohnian stage. Late in 1-950, Humble Oil and Refining N. L. & F. 3 reached a new producing zone, Reservoir 10, at a depth of 9,745 to 9,880 feet, down structure from the first well. Reservoir 10 is in sand and conglomerate near the contact between Kleinpell’s Mohnian and Delmontian stages. Its thickness ranges from 95 feet in well N. L. & F. 3 to 221 feet in N. L. & F. 4. There is an apparent natural stratification of the gravity of oil in Reservoir 10, for structurally low wells produce 18.5° gravity oil whereas structurally higher wells produce oil of gravity as high as 21.3°. A third zone, Reservoir 15, in the upper part of Kleinpell’s Mohnian stage, was discovered by Humble Oil and Refining Co. in well N. L. & F. 6 in 1951. This zone was found at depths of 10,722 to 10,923 feet and produces 27° to 29° gravity oil. Early in 1952 a fourth zone was penetrated by Humble Oil and Refining N. L. & F. 8. This well had an initial production of 581 barrels per day from a depth of 11,080 feet. The field is developed on an anticlinal structure, the Del Valle nose, which plunges to the southeast (pl. 45). The axis of the structure has a pronounced shift to the north in the subsurface. Accumulation of oil is due either to pronounced cross faulting or to stratigraphic traps caused by the lenticular nature of the sands on the structure. WILDCAT WELLS Many wildcat wells have been drilled in the area. Table 10 lists 236 of these wells and such pertinent information concerning each well as was available to the authors. Many of the early wildcat wells in the region were drilled by small companies and little if any information on them is available. All the later 347 wildcat wells in the area on which drilling was completed before June 1, 1953, are included in the table. POTENTIAL PETROLEUM RESOURCES Rocks of Eocene age are present at depth over much of the area and are considered by many geologists to be a source of at least part of the oil that has accu- mulated in younger formations in the region. Some of the oil in the Whitney Canyon area, and possibly also in the Elsmere area, is from rocks of Eocene age. High-gravity oil obtained from schist of the basement complex in Placerita Canyon, east of the mapped area, is considered by Brown and Kew (1932) to have migrated from rocks of Eocene age. Several wildcat wells have been drilled to Eocene rocks in the mapped area, but as yet no production of importance has been obtained from them. Most of the sandstones of Eocene age which have been tested have shown both low porosity and low permeability. These char- acteristics, together with the great depth to possible reservoir rocks of Eocene age throughout most of the area, discourage exploration and may prevent Eocene rocks from becoming important oil producers in the near future. In view of nearby production from sandstone assigned to Kleinpell’s Luisian stage, rocks deposited during this stage should be considered as promising for future development. In the Aliso Canyon field, just south of the mapped area in the southeastern part of the Santa Susana Mountains, the Sesnon zone of Luisian age is one of the major petroleum-producing zones. In the Oakridge field, which is immediately southwest of the mapped area, sands of this age also have been productive. Wells in fields in the area covered in this report have yet to be drilled to depths great enough to test the oil possibilities of rocks of the Luisian stage. Wildcat wells have been drilled in nearly every section in the area. All of the conspicuous poten- tially productive structural features have been tested. In some cases wildcat wells did not provide'an adequate test of their site because they were not drilled deep enough. One notable part of the mapped area which has not been productive is north of the San Gabriel fault. Most of the wildcat wells drilled there were started in continental beds of the Saugus formation and were drilled to and bottomed in continental beds of the Mint Canyon formation. Marine rocks of late Miocene and early Pliocene age are found north of the fault but do not appear to be either source beds or reservoir rocks for petroleum. 348 SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY TABLE 10.—Wildcat wells, including all known prospect wells outside productive oil fields [Information presented in this table is the best available to the authors, but is not of uniform accuracy or quality. Elevation: gr, ground; (if, derrick floor; kb, kelly bushing] Num- Location Total ber Operator Well Year Elevation depth Geologic information (depths Oil and gas shows Remarks (depths (pl, drilled (feet) (feet) infect) (depths in feet) in feet) 44) Sec. T. N. R. W. 1 Abbe, Robert E _____ Montie 1 ...... 8 4 17 1951 1, 750 gr 4, 268 .............................. Formation test: Formerly: Brink- 3,200—3,833, re- man 011 Opera- covered mud tions Montie 1; and water. A. and P. Pevel. Montie 2 Aidlin, Joseph W., Atwood 1 _____ 1 10 3 16 1952 1,438 gr 6, 134 Top of the Mint Canyon Possible 011 shows Whipstock set at and Bering, R. E. formation 5,714. Bot- at 2,100 -2,500 in 1,965 and re- tomed in Mint Can on original hole. drilled to 2,600. formation Dip 10°—18 at ‘ 2,120—2,l29. 3 Airline Oil Co. and Needham 4.... 1 13 3 16 1930 1,796 3, 504 Pico formation and Sespe(?) No indication of Formerly South- ‘and Herwick, formation contact, 1,780: commercial oil ern California C.C. Sespe(?) formation and below 2,150. Drilling Need- Eocene contact, 27473:. ham 4. 4 Algord Oil Co ....... Shepard 5 ..... 1 1 3 16 1949 1,407 l, 225 .............................. Swabbed water Formerly M.G.N. wfith trace of Oil Shepard 5. o . 25 Alliance Oil Co ...................... 13 3 16 1901 ____________ 700:1: .............................. Penetrated some ‘ tar sands. 2 6 Anderson, P. B ______ 2 .............. 1 3 16 1929 1,253 1, 248 .............................. Soweto}; sand re- po e . 7 Anderson, W. 0. Anderson- I11 3 16 1944 1,530 4,736 Top of the Sespe(?) forma- ____________________ and J. 1., and Palmet To- tion, 4,270; top of the Del- Palmet, Inc. mato Can 1. montian stage of Klein- pell, 3,8003; 8 Apex Petroleum Weldon 1 _____ 24 3 16 1951 2,025 gr 4, 518 In Pliocene at 3,110; in rocks Formation tests: See pl. 45, section of the Delmontian stage of 4,1907 4,376, open D-D’. Kleinpell at 3,315. Good 20 min, re- 45° dips at 3,315 3,331; 35°— covered 1,100 ft 45° dips at 4,176—4,184. gassy, muddy water; 3,310— 3,417, recovered 520 ft gas-cut mud. 9 Ball, W. T ........... 1 ______________ 134 4 16 1932 1,250 3, 629 ______________________________ Few oil and gas shows reported. 2 10 B. and L. Drilling 1 .............. 14 3 16 1931 ____________ 1, 309 .............................. No oil or gas 00. shows reported. 11 Bankline Oil Co ..... The Newhall 131 4 16 1947—48 1,623 kb 9,906 Top of the Miocene, 7,760; .................... See 111.45, section Corp. 1. top of the Mohnian stage D-D’. of Kleinpell 9,110. Poor 52°-55° dips at 8,190-78,192; 36° dip at 9,374-9,376. 12 Barmore, Ned ....... Hays 1 ........ 136 4 16 ......... 1,335 2, 384 .................................................. 13 Barnsdall Oil Co., Limbocker 1.- 17 3 16 1941—42 1,6809: gr 7, 071 Bottomed in lower Moh- Oil sands at 1,488— See pl. 45, section Bandini Petro- nian stage of Kleinpell. 2,230, 4,040— C—C’. leum 00., and 4,136, and ambassador Oil 6,652—6,713. o. 14 Barnsdall Oil Co ..... 'I‘.I. 3: T. 1.... 1 30 3 15 1942 1,318 gr 8, 035 .................................................. 15 Beal, Carlton ........ Betsy Linda 1. l 1 3 16 1949 1,378 gr 2, 830 Pliocene and Eocene con- Swabbed and tact at 1,913. flowed fresh Water with some heav oil. 16 ..... do ............... Betsy Linda2. 1 1 3 16 1950 1,397 1, 262 .............................. Pumped 8 b is per day, 11.3° gravity, oil, 1 percent cut. 17 Bettymac 011 00.-.. Warren 1 ...... 1 1 3 16 1949 1,481 2, 650? Pliocene and Eocene con- .................... tact at 2,591. 18 ..... do ............... Braille 2 ....... l 1 3 16 19 Bevo Drilling 00.... Carter-Ear14-_ 5 3 15 220 Big 4 Oil Co ......... Brona 1 ....... 132 4 16 21 Brazell, James, Perkins 1 ...... 1 11 3 16 1,600 gr , Top of the Sespe(?) forma- .................... Trustee. tion, 4,380; in lower Del- montian, stage of Klein- , pell, 4,000. 22 British-American Edwina 1 ..... l 11 3 16 1940 1,6555: 6, 196 In lower Pliocene, 3,500; top Shows of tarry Oil Producing Co. of the Miocene, 36005:; oil, 4,200—5,982 top Sespe(?) formation, 4,103; top of the Eocene, 23 ..... d0 ............... Kinler-So. 16 4 17 1947-48 1,280 kb 6,857 Top of the Miocene, 5,500; Formation tests: Redrilled to 4,385. Cal. 1. Kaiser fault, 6,200. 5870-5305. open See pl. 45. sec- mln, re- tion F—F'. covered 246 ft gas-cut mud. =24 Buick Oil Co ........ 1 .............. 18 3 15 1918 ____________ 1,126 ______________________________ Some tar and 011 shows reported; excessive water. 7 25 ..... do ................ 2 .............. 1s 3 15 1913-19 ____________ 1, 485 __________________________________________________ Hole junked with lost tools 26 Bush, W. W ......... Perkins l ...... 1 11 3 16 1949-50 1,550 gr 5, 122 Top of the Delmontian Pumped very stage of Kleinpell, 4330:. small amount of 40° gravity oil, some gas. 3 27 California 011 00---- 1 .............. 18 3 15 1900 ____________ 1, 200 Drilling started in meta— .................... morphic rocks. I 28 ..... , do ............................... 15 3 16 ..................... 400 .................................................. 29 California Newhall 1 .............. s 3 15 1920-22 1,3503: 1,865 ______________________________ Some shows light Oil Co. 011 below 1,765. 30 Carter, W- J --------- Carter-E8112" 5 3 15 1948 ............ 653 In granitic rock at bottom... .................... 31 ..... do ............... Carter-Ear13.- 5 3 15 ..................... 1,038 In granitic rock at bottom..- .................... See footnotes at end of table. TABLE 10.—Wildcat wells, including all known prospect wells GEOLOGY 0F SOUTHEASTERN VENTURA BASIN outside productive oil fields—Continued 349 Num- Total ber Operator Well Year Elevation depth Geologic information (depths Oil and gas shows Remarks (depths l. drilled (feet) (feet) infect) (depths in feet) in feet) 3) n w 32 Chanselor—Canfleld Sanbornl _____ 16 1941 1,524 8,038? Top of the Mohnian stage .................... Midway Oil Co. of Klein 117130; in rocks e n 1 ' y - 2 33 Chamberlain, P000 2 ________ 15 1951 1,430 (if 1, 053+ Top of t eup er Kraft zone, .................... Chauncy w, 760;to p git e lower Kraft zone, 34 Clark, W. J .......... Conroy 2 ...... 16 ..................... 3,985 In11\217151_g ngényon formation, .................... 35 c. M. 151i 0g and Cook 1 ________ 16 1949 1,400 1,540 .............................. Swabbed water--.- Drill g o. 2 36 Community Oil Pro- 1 .............. 16 1920 1,214 227 .................................................. Water flowed over ducers of Calif. casltgs: made into wa r we . 237 ..... do ............................. 4 16 1920 1,214 255: ........... _--. 38 Continental Oil Co.- Braille 1 _______ 3 16 1951—52 1,324 kb 3,273 Top of the marine Miocene, Pumped 57 barrels 3,151; cored Eocene. in 18 hrs., 18. 3° gravity oil, 7 per- cent cut, 2-13—52; 16 bbls per day, 17.6° gravity oilt 125—12853“ 0“ , 39 ..... do ................ Braille 2 ....... 16 1951 1,308 3,648 In upper Pliocene, 3, 079— Pumped 30-40 ,425; top of the lower bbls per day Pliocene, 3, d320; top of the rate, 60 percent Braille sand, 3,420; top of cut. the Miocene (Eocene?), 3 520 ,hfttomelginSespeG) orma on or ocene 40 ..... do ............... Braille 3 ....... 16 1951—52 1,308 kb 3,835 Top of the Braille sand, Formation test: 3,345: in Eocene between 3 ,386—3,480, open 3,405—3,476. 2 hrs, strong blow 4 min, di- minishln gto dead, recovered 5419 ft d gassy, o ymu . 41 ..... do ............... Newhalll ..... 17 1938 1,591 2,616 In lower Pliocene, 1, 790: in .................... rocks of the Delmontian gtage of Kleinpell 1,870— 42 ..... do ............... Phillipsl ..... 15 1951—52 1,650gr 8,253 Pliocene and Eocene con- Plug, 1415; See pl. 45, section tact, 1,300; top of the pre- pumped water A—A’. Cretaceous crystalline with trace of rocks, 7,911. 011; tar shows at 400—600 and 31111336333 , 4. 43 ..... do ................ Phillips 2 ..... 6 3 15 1952 1,562 gr 1,814 .- 9 44 ..... do ............... Phillips 2A--.. 6 3 15 1952 1,550:l: 1, 060 .............................. Tested Kraft zone: com- pleted produc- ing 70 bbls per day gross in 7 hrs; 152 bbls per day 76 per- cent water, 2 it” 1.3% an one 45 C(ginth Petroleum Karen 1 ....... 16 1949 1,400? 2,005 P11080211; 68013: Eocene con- .................... o. c , . 2 46 --_.-do _______________ Thglvnpson 16 1949 1,673 kb 3,967 ’ 47 Corwln, W. T, Wegnerl ...... 16 McBeath, T. W. and Donley, Fred. 48 Crawford and Hiles.. Placerita 1..-- 4 15 1949 1,925 gr 3, 3m 49 Denison, Geo. A ..... 3 16 1924 1,400: 240 3 50 Dexter, George-- 4 16 1951—52 1,215 gr 1,684 51 Dividend Oil Co. . 3 l6 _____________________ 700 .- 52 Doc Oil Co .......... 4 15 ......... - 53 Downey Oil Corp.... 4 16 1938 ____________ 3,100 Bottomed in Towsley for- .................... mation. 1 3912(1))ng 500 dips - average — 54 Eagle 011 and Refln- 4 16 1949 1,285 6,236 Base of the Pliocene, 5,285; .................... ing Co. top of the Sespe(?go fo rma- tion, 6,210. dips, 6,090—6, 116; 18° dips, 6,116— ' 55 Edwards and Cole..- 1 .............. a 16 ............................. ' ...... - 4 56 Electrological Petro— Overman 1.... 3 16 1031 1,400: 1,070 .................................................. leum Corp. 57 Ellis, F. E ..... .. Lowe 1 ........ 4 16 1950 1,330 gr 3,445 Pico formation, 3,360 to Fox str‘llnggsssg! 0 cm. 0 san a , . 58 Enterprise Oil Co 1.. 3 16 1900 ............ i, 050:1: ........ . 2 59 ..... d ..- 2.. 3 16 1900 ............ 700 ______________________________ No 011 or gasd Junlgld $115131 1900‘]: encountere . an a an one 60 Fairfleld, F. E Reed-Ulrich 1. 4 16 1949 ............ 3,646 .................................................. i 61 Federal Oil C Oekgrove 1.--. 4 16 1949 1,417 l, 716 .- 62~ Fletcher, D. S. . Betsy Linda3- 3 16 1951 1,374 b 777 .-- See footnotes at end of table. 350 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY TABLE lO.—Wildcat wells, including all known prospect wells outside productive oil fields—Continued Num- Location Total ber Operator Well Year Elevation depth Geologic information (depths Oil and gas shows Remarks (depths (p1, drilled (feet) (feet) infeet) (depths in feet) in feet) 44) Sec. '1‘. N. R. W. 63 Frasier M. E ________ Ea ie 011- 124 3 15 1948—49 1,260 5,985 Top of the Miocene, 5,012; All sands very ’ Bg1shop 2 top of the Sespe(?) forma- tight. Forma- tion, 5,896. tion test: 5,856- 5,906, steady blow, 2 hrs, gas to surface in 55 min, blew 5 min and died. No oil. 1 64 Frasier, N.M ________ Gerard 1 ...... 1 31 4 16 ............................................................................... 1 65 Garllepp and Asso— l .............. 14 3 16 1933 2,3005: 1, 220 No oigeoir gas re- ciates. , DOT ~ 05 General Exploration N.L. & F. 1.-- 129 4 16 1951 1,415 gr 12, 47s Pico formation lithology at .................... See pl. 45, sections Co. of Calif. 7,526; top of the Delmon— A.A' and 1)— D', tian stage of Kleinpell, 9,540:l:; top of the Mohni- an stage of Beinpell, 11,060; bottomed in lower Mohnian stage of Klein- pell. Dips at 11,700- 11,800, 5°—10° to SW. 2 67 General Ex loratiou N.L. o F. 2--- '28 4 16 1953 1,365 gr 11,503 Top of the Miocene, 8,480- Plus 10,703; for- Co. of 0 8,520; top of the Mohnian mation tests: stage of Kleinpell, 9,480. 10,423—10 570 recovered salt water; formation tests: 11,433- 11,503, recovered salt water. 68 General Petroleum Bermite 1 _____ 125 4 16 1950 1,433 mat 5,043 Base of nonmarine section, Formation test: Corp, 3,500; top of the basement 4,968—5,043; open complex, 4,951. 2 hrs, recovered 1114191 tilt drilling 69 _____ do ............... Circle J—l ..... 126 4 16 1949 1,300 0,500 Top of the Miocene, 5,540; Swabbed salt top of the Eocene, 5,929 water with scum of oil. 70 _____ do ............... Circle J—2 ..... 126 4 16 1949-50 1,330 kb 6,112 In Saugus formation, 4,100— Formatlon test: Whipstock at 4,260; in upper Pliocene, 3,751—3,796 (re- 3,430; redrilled to 4,270—5,140; in Pliocene or drill); open 71/4 , 96. Miocene, 5,163—5,476; base- hrs., recovered ment complex at 5,570?. 157 it gassy mud with trace of tarry oil. 71 ..... do ............... H. &-M. 1.... 1 27 4 16 1949 1,199 kb 7,435 In Pliocene, 5020-5976; top ____________________ See pl. 45, section of the Delmontian stage 0—6”. of Kleinpeli, 6,410:l:; top of the Mohnian stage of Klein 11, 7,200:l:; top of the asement complex (green schist), 7,420. 72 ..... do ............... Mendota 1--.. 22 3 16 1943 1,325 gr 0334 Bottomed in lower Mohnian ____________________ stage of Kleinpell. 173 ..... do ............... N.L. & F. 3..- 120 4 17 1953 925 11, 497 Top of the Delmontian stage .................... , of Kleinpell, 5,680; fault between 6,480—7,380; Del- montian above fault; top of the Mohnian sta e of Kleinpell, 8,580; fa t at 8,900, Delmontian below fault; sand of the Delmon- tian stage of Kleinpell, 11,115—11,143. 74 ..... do ............... stabler 3 ...... 31 4 15 1919-20 1,450 2, e40 .............................. Few oil and gas shows reported, 1,800—2,100. 75 ..... do ............... Stabler 4 ...... 30 4 15 1919-20 1,605 3, 514 Bottomed in Mint Canyon Small 011 and gas See pl. 45, section formation. shows in shale, B—B’. , . 76 Gerard, P. M ........ Fisher- 6 3 16 1943 1,438 7,852 Top of the Delmontian stage .................... Week 1. of Beinpell, 6,010. 77 Grgfiegine Canon 1 ______________ 22 3 16 1901 ____________ 1, 3007 ______________________________ No 011 shows ...... o. 78 Gniberson Oil 0011).. Bailey 1 ....... 1 3 16 1949 1,640 g1- 3, 750 len; 033d Eocene con- .................... c , , . 279 Halfmoon Oil 00-... 1 .............. 6 3 16 1921 1,450 .- 80 Havenstrite Oil 00.. Vasquez 1 _____ 21 4 17 1941 1,102 7,102 ........................... 81 Hicks, H. O ......... Lillie 1 ........ 8 3 15 1930 1,000: ....... --__ 82 Higbrock Petroleum Broughton 1.. 1 28 4 16 1936 1,400 o, 284 Base of nonmarine rocks, N ohoil or gas orp. , s ows. 283 Howard Petroleum 1 ______________ l 11 3 10 1921-22 1,000? 005 ______________________________ N 0 oil or gas 00. shows reported. 84 Humble 011 and Re- N.L. dz F. 00. x 12 4 17 1950-51 1,007 kb 12, 744 Tap of the Delmontian stage Formation test: Plus 3,900; re- ing 00. B—i. of Kleinpell, 9,200; top of 740-905, open drilled to 4,452. the upper Mohnian stage 3% hrs., good See pl. 45, section of Kleinpell, 11,280. decreasing blow E— . 15 min. Swabbed mud and fresh water. 85 ..... do ............... Nip—.34: F. 00. 19 4 16 1951 1,150 gr 1,389 .................................................. See footnotes at end of table. GEOLOGY OF SOUTHEASTERN VENTURA BASIN TABLE 10.—Wildcat wells, including all known prospect wells outside productive oil fields—Continued 351 Num- Location Total ber Operator Well Year Elevation depth Geologic information (depths Oil and gas shows Remarks (depths (pl, drilled (feet) (feet) in feet) (depths in feet) in feet) 44) Sec. T. N. R. W. 86 Humble Oil and Re- N.L. 6: F. 00. 133 4 16 1952 1,278 12, 450 Top ofthe Delmontlan stage Formation test: See pl. 45, sections fining Co. E—l. of Klelnpell, 6,780; top of 8,220—8,311, AAA’ and 0-6". the upper Mo stage strong steady of Kleinpell, 9,250; top of blow, recovered the lower Mohnian stage water with of Kleinpell, 9,570. Slillght scum of o . 87 ngley and Mandel- 1 .............. 8 4 17 1952 1,625 gr 3, 251 .................................................. aum. 88 _____ do _______________ Exploration 1. 8 4 17 1952 1,625 gr .......................................................... 89 Kavenaugh 0., and Ramona Hills 8 4 17 1946 2,006 2,026 __________________________________________________ Wilhite, 1.. . 1. 90 Keck Inv. Co ________ Pena 1 ........ 18 4 17 1927 2,085 5, 128 Inlower Pliocene to bottom. .................... Del Valle fault, 2,205—2,270. 791 Keystone 011 and Hammon 3.... 8 3 16 1952 ............ l, 575 .................................................. Development Co. 92 L. & J. 01] Co ....... Clarella 1 ..... 31 4 15 1950 958 gr .................... 93 Larson, Ivar . 31 4 15 1949 1,700 gr 94 , . 32 4 15 1949 1,680 95 ..... do ______ - 32 4 15 1949 1,650 gr ______________ 96 Lockhart, L. M ...... l 2 3 16 1948—49 1,250? 5,423 InMiooene, 4,785; top of first Formation test. zone, 4,842. 5,199—5,218, o n 20 min.. me - um to steady blow, no gas, recovered 2,790 ft tgin, watery mu . 97 Los Nietos Co _______ Odeenl ....... 12 3 17 1951—52 2,800 gr 9,215 Bottomedin lower Mohnlan .................... See pl. 45 section stage of Kleinpell. D—D’. 98 Lytle Exploration N.L. & F. 1.-. 122 4 16 1949-50 1,175 9,735 Top of the P100 formation, .................... 00. 6,380; top of the Delmon- tiau stage of Kleinpell, 7,800; top of the upper glohnlan stage of Klelnpell. 99 McAdoo, Wm. G., 1 .............. 6 3 15 1925 1, 497 8955: ______________________________ Oil sands reported Could not shut 01! r. at 710-895. water. 100 McFann Drilling Co. Lottie B. ll 3 16 1949 1,385 ........................................... McFann 2. 101 Meyers 61 Wilhite.-. M. 6: W. 1.... 31 4 15 1949 1,575 652 ______________________________ Ballectlswfatefi' with spo o o . 102 Milham Exploration Conroyl ...... 111 4 16 1925 ............ 2,148 Base of the Saugus forma— .................... 00. tion, 930:. 103 Margan Petroleum Dunlap 1 ...... 31 4 15 1923-25 1, 550 1,300 ______________________________ Few small oil and orp. 104 Morrow, Tevis F._.. G.P.M. 17.... 31 4 15 ___________ _ 3 105 ..... do ........ . G.P.M. 26.... 31 4 15 1951 1,451 4,111 Bottom in Eocene ........... 106 ..... do ............... WF 38 ........ 31 4 15 ......... , 2,507 Pliocene and Eocene con- See pl. 45, section tact, 2,352. B—B’. 3107 Murphy, Dan.. ..... 1 .............. 14 3 16 ..................... ._ ..... __-- 108 Mutual Develop- Sanborn 1 ..... 6 3 16 1947 1, 542 6,415 . .-- ment Corp. 7109 ..... do ............... Sanborn 2 ..... 6 3 16 1948 1, 516 6,301 ______________________________ Formation test: 6,215—6,301, re- covered mud. 110 Nelson-Phillips Oil Swan-Fender 31 4 15 _______________________________________________________________________________ o. . 111 ..... do ............... Svgall-Ferrler 31 4 15 _________ .. ...- . 112 Newhall Land and County Line 132 4 17 1951—52 1,052 kb 10, 798 Spud in Pliocene; top of the Two formation See pl. 45, section Farming Co. 1. Miocene 2,150:i:; 2,500:|:, tests at 9,700 F-F’. fault; Pliocene below fault; tailed. top of the Miocene, 3,8005: top of the Mohnlan stage of Kleinpell 6,900:l:; top of the lower Mohnlan stage of Kleinpell, 9,500:l:. 113 NeWhalI Mt. 011 CO. 1 .............. 21 3 16 _____________________ 1,800 ______________________________ No 011 shows reported. 114 Newhall Refining Clampltt 13 3 16 1952 1,377 gr 1,958 .................................................. Formerly Morton Co. Com- and Dolle munity 1. Clampitt om- munlty 1. 115 North Star Mining Shepard 1 ..... 1 1 3 16 1930-31 1,360 2, 291 Pliocene and Eocene con- Oil sands reported Formerly National 80nd Development tact, 1,9305; between 850— Securities Oil 1. o. . 116 Cakes, R. F., Luf 1 ........ 12 3 16 1949 1 288 4,31 _______________ Coombs, E. E., ge ' gr 2 and others. 117 Occidental 1 .............. 22 3 16 1922 ............ 876 ______________________________ Good show 18° Be Originally drilled Petroleum Corp. gravity oil by Bradshaw 6: reported at Beville in 1899? bottom original Deepened from hole. Second 650 to 876 in 1922 hole produced by Occidental 350—500 bbls per Petroleum Corp. day water with maximum of 2 b11118 per day 01 . 118 ..... do ............... 1 ______________ 31 4 15 1922 1,375 605 . -— See footnotes at end of table. SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY TABLE 10.—Wildcat wells, including all known prospect wells outside productive oil fields—Continued Num- Location Total ber Operator Well Year Elevation depth Geologic information (depths Oil and gas shows Remarks (depths (pl. drilled (feet) (feet) in feet) (depths in feet) in feet) 44) Sec. T. N. R. W. 119 Ohio Oil Co _________ Mable S. 10 4 17 1950 1,180 gr 5,875 Bottomed in Miocene ........................... Redrilledfrom 3,476 Henderson 1. to 5,875. i 120 Ora Negro 1 .............. 14 3 16 1932 1,800 700 .................................................. Development Corp. 2121 Padua Oil Co ........................ 24 3 16 1900 ............ 1,200 .............................. A little oil near surface. 2 122 Patton Brown 1 ______ 18 3 15 1950 ____________ 755 .. ________ Transportation and Associates. 123 P100 Dome Oil Co... 1 .............. 14 3 16 1929 1,600:i: 918 ______________________________ No 011 or gas . reported. 2124 Pioneer Petroleum 1 .............. 14 3 16 1930 1,550 2, 840 .............................. N0 011 or gas 0., . reports . 2125 Portland Oil Co _____________________ 31 4 15 1902 ____________ 800 __ .-- 126 Provost, R. A., and Protrans 1.-.. 125 4 16 1950 1,540 gr 1,120 ___ Associates. 127 _____ do _______________ Protrana 2. . ._ 1 25 4 16 1950 1,571 gr 3, 652 ______________________________ Gas shows, 3.260— 3,280; sands wet from 3,280 to bottom. 128 Provost, Wm. H., P.D.S.1_.... 1 3 16 1953 1,399 gr 1,180 ...- _ Could not shut Jr. 011 water. Formerly P.D.s. Oil P.D.S. 1. 129 Rafglet Oil 02. and Dorothy 1 ..... 32 4 15 1949 1,575 gr 1,649 11 , e . 130 Republic Petroleum Amet 1 ________ l 12 3 16 1921 1,494 215 .......... .-._ o. 131 ..... do ............... Banner 2 ______ 6 3 15 1919-20 1,756 1,692 ..-. Formerly Tunnel Petroleum 3. 132 ..... do ............... Fink 4 ________ 12 3 16 1921 1,4803: 1,383 _ 133 _____ do _______________ Price 4 ________ 6 3 15 1930—33 1,476 2,342 Pliocene and Eocene con- Initial production, Formerly tact, 1,174. 2 bbls per day Southern 20° gravity Production 1. (API), from Eocene rocks. 134 ..... do _______________ Price 5 ________ 6 3 15 1934-35 1,475 1,812 ______________________________ 011 shows reported between 650—1,100. 135 _____ do _______________ Yankee 6 3 15 1900 ____________ 705 ______________________________ Some 011 reported. Formerly Yankee Doodle 1. Doodle Oil 1. 136 Richfleld Oil Corp... Briady Estate 13 3 17 1949. 3,388 kb 2, 748 ..... 137 _____ d0 ________________ Shepard 1 _____ i 1 3 16 1921-23 1,525 1, 600 .............................. Oil shows reported at 800 and 1,400. 138 ..... do ............... T.I. & T. 1.... I 19 3 15 1943-44 1,321 8, 207 Continental sedimentary .................... rocks to bottom?. 139 ..... do ............... Watson 1_____. 13 3 16 1949 1,702 gr 4,000 InPliocene,0—3,400; in rocks 011 sand cored See pl. 45, section of the Delmontian stage of 316563.641. B-B’- Kleinpell, 3,692—4,000. 140 Rocco, Robert s ..... D. dz 0. 1 _____ 1 36 4 16 1949-50 1,342 4, 015 Pliocene and Eocene con- Flowed 35 bbls tact, 3,722, per day water with trace of oil. 141 Rothschild, Harry s- Barbour 1 _____ 16 4 17 1952—53 1,197 kb 5, 753 ______________________________ Formation test: 5,530—5,642, open 40 min gas in 5 min, strong decreas- ing blow, re- covered 370 ft gas-cut mud, - no oil. 142 Rothschild Oil 00... Phillips 2 ...... 7 3 15 1950 1,465 3,000 Pliocene and Eocene con- POOI‘ 011581111 in tact, 972. core, 925-927. 143 ..... do ............... Pleasant 31 4 15 _______________________________________________________________________________ Community 144 ————— d0 ——————————————— Ramona Com- 8 4 17 1952 1,710 (if 4, 078 .................................................. munity 1. 145 ..... do ............... Wickham- 32 4 15 1951 1,300 gr 1, 652 .................................................. Ferrler 1. 1 140 Safe Oil Co ________________________ i 12 3 16 1901 ____________ 1,00%: ______________________________ Small amount of heavy tar. a 147 San Fernando Oil & 1 ______________ 13 3 16 1919.20 1,40%: 1,245 ____________ . _________________ Oil sand reported Could not exclude Gas Co. at 1,240. water 148 San Gabriel Oil 00.. San Gabriel 1, 32 4 15 _______________________________________________________________________________ 149 Schroeder Oil Syn--- Daugherty 1.. 4 3 16 1922—23 1,321 2, 785 ______________________________ No oi: tar gas re— por e . 150 Seaboard 011.00 ..... Daugherty 1-. 9 4 17 1952 1,241 kb 6,017 In rocks of the Delmontian No 011 shows ...... stage of Kleinpell, 5,057— 5,140; in Pliocene, 5,157— 151 ..... do ............... Evans 1 ....... 23 3 16 1945 1,733 gr 992 .................................................. 152 ----- d9 ............... Evans 1-A.... 23 3 16 1945-46 1,783 gr 8,209 Top of the Mohnian stage .................... See 91545. 8801:1011 of Kleinpell, l,150:|:; top of 3-3 - the lower Mohnian stage of Kleinpell, 2,500; top broccia, 5,310. 153 ..... do ............... Mission Land 1 25 3 16 1946 1,430 gr 9, 528 Top of the Mohnian stage ..... Do. 8-1. of Kleinpell, 1,450; lower See footnotes at end of table. Pliocene, 2,900—3,045. GEOLOGY OF SOUTHEASTERN VENTURA BASIN TABLE 10.—Wildcat wells, including all known prospect wells outside productive oil fields—Continued 353 Num- Location Total _ ber Operator Well Year Elevation depth Geologic information (depths Oil and gas shows Remarks (depths (pl, drilled (feet) (feet) infect) (depths in feet) in feet) 44) Sec. T. N. R. W. 154 Seaboard Oil Co ..... Mission Land 1 25 3 16 1947 1,410 4, 202 ..... 8—2. 155 Section 31 Petroleum ______________ 31 4 15 1930 1,475:t 2,008 Pliocene and Eocene con- No 011 or gas re- rp, tact, 1,000:i:; bottomed in ported. granitic locks. 156 Seigenberg, Horton Warren 1 ...... l 1 3 16 1930 1, 448 __________ Also called Shell- and Rodgers. 1lnar Oil Warren 157 Serago Oil Co ....... Yeager Com— 30 4 15 ............................................................................... munity 1. 158 Shafler Tool Works._ Shafier 6 ______ 1 36 4 16 _______________________________________________________________________________ 159 Shallow Field Oil Co. 1 ______________ l 12 3 16 1921 1,400:|: 1, 140 .............................. Oil shows re- ported, 1,115- 1,11). 1 160 Shell Oil Co ......... 1 ______________ l4 3 16 __________________ ._ .................... 161 ..... do ............... Daugherty 1.- 9 4 17 1938 1,342 gr 2,220 __. See 111745, section 162 ..... do ............... Mission 2—1... 125 3 16 1941-42 1,505 6, 978 Top of the lower Mohnian .................... See pl. 45, section stage of Kleinpeli, 2,090; B—B’. to of the Luisian stage of einpell, 6,400; top of the Topanga formation, 6,590. 163 Sherman, R. W__..._ Newhall l 2 3 16 1949 1,335 gr 5,891 .-.. lCommunity 164 ..... do ............... Newhall 1 2 3 16 1949 1,335 961 .. gimmunity 165 ..... do ............... Newhall I 2 3 16 1949-60 1,260 5, s45 .............................. 2-11—49, 300 bbls Redrilled to 5,687. Community per day gross, See 131. 45, sec- 3'1- 90 percent cut; tion A-A’. 27-12-49, flowed average 520 bbls per day net 011, 30—50 percent cut; 3-19—49, flowed estimated, 47 bbls per day net, 40° gravity, 85 percent out. 166 Signal Oil and Gas Signal-Need- 1 13 3 16 1945 1,604 4,997 Top oithe Delmontian stage .................... Co. am 1. of Kleinpell, 2,400; top of the Sespe(?) formation, 3,3; top of the Eocene, 167 Skinner, L. V., L. V. Skin- 6 3 15 ._-_ ..... Corwin Tom, and ner’s Ann 1 Beck, fired. 168 Southern California Handy 1 ...... 18 4 17 1942 1,590 5. 973 Petroleum Corp. 169 ..... o ............... Kinler 113-1.--- 16 4 17 1951 1,226 kb 8, 590 In rocks of the Delmontian Formation test; See pl. 45, seetion stage of Kleinpell between 6,565—6,720,ia11ed. F—F’. top of Miocene and strati- graphic level 01’ Intermedi- ate zone, 6990—7,013; in Del- montian between strati- graphic levels oi Interme- diate zone and Del Valle _ zone, 7,650—8,410. 170 ..... do ..... . ......... Lassalle 44-1.. 1 2 3 16 1943 1, 6,073 Base Pliocene, 5165 .............................. 171 ..... do ............... N.L. 6; F 2... ‘20 4 17 1951 1,052 (11 10,719 Top of the Miocene, 3,4743; .................... top of the Mohnian stage of Kleinpell 6840?; below fault—in rocks of the Del- montian stage of Kleinpell, 7,010—9,160, top of the up- gr Mohnian stage of einpell, 9,300; top of the e , . 172 ..... do ............... Vazquez 13-2.- 17 4 17 __ p6 ’ 173 StEmfiard Oil Co. of Bobier 1 _______ 15 4 17 ..................... a . 174 ..... do ............... Brady 2—1 ..... 13 3 17 1944 3,429 (if 9, 576 __________________________________________________ See pl. 45, section D—D’. Con- tacts in well projected from western Gulf Brady Estates 1 (well 233, this table). 175 ..... do ............... Brady 2-1A--. 13 3 17 _ .................... 176 ..... do ............... Elsmere 1 ..... 7 a 15 1889 1,465 1, 375 ______________________________ Numerous small Drilled b Pacific shows of black Coast 11 Co. all down to 940; Abandoned show of green while drilling. oil at 1,020; small amount (1)1 gas, 1,020- 177 ..... do ............... Elsmere 3 ..... 7 3 15 1891 1,457 555 ______________________________ Few shows of oil Drilled b Pacific and tar. Coast 11 Co. Could not shut off water at 384. See footnotes at end of table. SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY TABLE 10.—Wildcat wells, including all known prospect wells outside productive oil fields—Continued Num- Location Total be: Operator Well Year Elevation depth Geologic information (depth 011 and gas shows Remarks (depths (p1. drilled (feet) (feet) in feet) (depths in feet) in feet) 44) Sec. T. N. R. W. 178 Standard 011 00. of Elsmere 4 ..... 7 3 15 1891-92 1,625 705 .............................. Few small shows Drilled by Pacific Calii. of oil. Coast Oil Co. 179 _____ do _______________ Elsmere 8 ..... 7 3 15 1899 1,555 500 .................................................. Drilled 1) Pacific Coast 11 00. Could not shut off water. 180 _____ do _______________ Elsmere 11.... 7 3 15 1819360 1,514 700 .................................................. Do. 181 _____ do ............... Elsmere 12.... 7 3 15 1900 1,604 1, 225 .............................. Little 011 show. ... Drilled by Pacific Coast Oil Co. Abandoned be- cause of water and loose gravel. 132 _____ do ............... Elsmere 14..-. 7 3 15 1900 1,589 490 .............................. Produced very Drilled by Pacific little oil. Coast Oil Co. 183 _____ do ............... Elsmere 19.-.. 7 3 15 1900-01 1,596 848 .................................................. Drilled by Pacific Coast Oil 00. Could not shut off water. 1 184 _____ do ............... Newman 1 ..... l9 3 15 1899—1900 ............ 700 .................................................. Drilled b Pacific Coast 11 Co. 185 .-.-_do ............... N.L. & F. 00. 119 4 17 1944—45 1,665 df 5,034 .................................................. 3—2. 186 ..... do ............... N311:é & F. 00. 120 4 17 1945 1,547 d1 5, 224 ... ............................................... 187 ..... do _______________ N .L. &F. 00. 134 4 16 1947—48 1,232 df 9,296 T01) of the P100 formation, ____________________ 5-1. 5,000:1:; top of the Delmon- tian stage of Kleinpell, 6,190:1:; top of the upper Mohnian stage of Klein- pe11, 7,750: 188 _____ do ............... N.L. 61 F. Co. 1 34 4 16 1949 1,264 df 1,000 .................................................. 5—2. 189 ..... do ............... N523. & F. 00. 1 34 4 16 1949 1,252 7, 792 Base of the Pliocene, 5,440... .................... See pl. 45, section . A—A’. 190 ..... do ............... N.L. 8: F. 00. 1 19 4 16 1951—52 1,264 df 13, 255 .............................. Formation test: 6—52—19. 12535—12800, no goo . 191 ..... do ............... N.7Li 6: F. Co. 135 4 17 1952-53 1,519 9, 327 ...... -.- -- -_ ---- 192 ..... do ............... P.C.0. 42 ..... 1 3 17 1942 2,293 di 8,258 ........ -.. .......... 193 ..... do ............... Ward 3—1 ...... 127 3 16 1944—45 2,759 di 10,363 Top of the lower Mohnian, .................... 1,500; top of the Sesnon zone, 9,730. 194 St. Anthony Oil (LaSalle) 1.... 10 3 16 1941 1,480 5,416 Top of the Delmontian stage .................... Corp. of Kleinpell, 3,158; top of the upper Mohnian stage ‘ of Klelnpell, 4,293. 195 St. Bernard Oil 00.. 1 .............. 18 3 16 1903 196 St. Helens Petro- Ladd 1 ........ 7 4 17 1949 leum Corp. 197 Stine, Sabasta and Bailey 2 l 3 16 1952 Ackland. 198 _____ do ............... Henderson 1 . _ 1 3 16 ............................................................................... 199 Sunray Oil Corp ..... NOW 1 ....... 126 4 17 1945 1,269 9,046+ First zone, 6,700; 2nd zone, .................... 6,925; 3rd zone, 7,225. 200 _____ do ............... R.S.F. 103- -.- 1 34 4 17 1952 1,183 kb 9,483 In Pliocene, 1,640—6,040; in Two tests with See pl. 45, section Delmontian stage of Klein- slight gas. E—E’. pell, 6,280—7,972; in upper Mohnian stage of Klein- pell, 8,000—9.480; base 3rd zone equivalent, 7,607. 201 Superba Petroleum 1 .............. 11 3 16 1932 1,800:l: .......................................................... orp. 202 Superior Oil Co ...... Bonelli14—23.- 123 4 16 1951 1,254 8,969 Top of the Miocene, 6,750; No oil shows ...... Whipstock set, upper Mohnian stage of 5281; redrilled to Kleinpell, 7,922; gneiss 8070. See pl. 45, and schist at 8,515 (8002 in section C—C’. redrill). 203 ..... do ............... L.A. Homes 1. 136 4 16 1949—50 1,348g1' 5,399 Base of the Saugus forma- .................... tlon, 3,325; in Pico forma- tion 4,250—4,430; top of the Eocene, 4,687. 204 ..... do ............... N .L.&F. 37—8. 1 8 4 16 1951 1,060 gr 13, 303 Top of the Delmontian .................... See pl. 45, section stage, 10,100; top of the D—D’. upper Mohnian stage of Kleinpell, 11,355; top, of the lower Mohian stage of Klenpell, 12,250. 205 ..... do ............... N.L.&F. 48—21 1 21 4 16 1952 1,175 kb 13, 553 Top of the Delmontian .................... stage of Kleinpell, 8,333; in Mohnian(?) stage of Kleinpell, 10,300—10,310; in good Mohnian stage of Kleinpell at 10,550. 2206 Talisman Oil Co ..... Morrison 1.... 1 1 3 16 1952 1,450 df 161 .................................................. Suspended at 161. 207 Terminal Drilling Independent- 1 24 4 16 1949 1,381 gr 1, 922 Saugus formation and Mint .................... Co. Chiggia 1. Canyon formation con- See footnotes at end of table. tact, 1,282. GEOLOGY 0F SOUTHEASTERN VENTURA BASIN TaBLE 10.—Wlldcat wells, including all known prospect wells 355 outside productive oil fields—Continued Num- Location Total . bez- Operator Well Year Elevation depth Geologic information (depth Oil and gas shows Remarks (depths (p1, drilled (feet) (feet) in feet) (depths in feet) in feet) 44) Sec. T. N. R. W. 208 Terminal Drilling Phillips 1 _____ 12 3 16 1950 1,397 kb 1, 350 Top of the upper Kraft zone, 01] and tar shows Co. 850; top of the lower Kraft in cores at 410— zone, 1,100; top of the 430, 639—665, and Eocene(?), 1,320. 1,334—1,350; for- mation test: 2, re- covered 440 ft mud, gas, and , water 209 _____ do _______________ Thompson 1- - 1 36 4 16 1949 1,664 3, 990 210 The Texas 00. .. Bonelli 1 ...... 1 l3 4 16 1952 1,265 gr 1, 502 - 211 _____ Deaton 1 ...... 7 4 17 1945 1,300 4,803 Top of the Miocene, 1,995; I Abandoned. top of the Mohnlan stage tion, 41 bbis of Kleinpell 4,782; Kern per day, 36.0 sand, 2,597—2,805; top of percent cut. the Del Valle sand, 3,320. Malls 1 ........ 10 4 17 1947—48 - Newhall A—l 1 9 4 16 1952 Newhali B—1-- 1 11 4 16 1953 N.L.F. 2 ...... 1 21 4 17 1945 870(7) gr 8, . Whitnah 1..-. 14 3 16 1941 ,928 gr 4, In Pliocene, 2,700~3,800; in She rocks of the Delmontian in Sespe(?) for- stage of Kleinpell 3,900— matlon. 4,400; top of the upper Mohnfan stage of Klein- pell, 4,400; top of the Sespe(?) formation, 4,452. 2217 Trigood Oil Co ...... Southern 16 4 17 1950 1,160 gr 8, 359 __________________________________________________ Redrilled from Calif. Pe- 5750-7589. troleum Kinler 2. 218 Tune] 01] Co ....... (Needham) 1.. 1 13 3 l6 ......... 1,650 df 219 T.W.A. Oil Co ...... Newhall 1 ..... 1 15 4 17 1925 963 220 Union 011 Co. of Needham 1. -. 13 3 16 1951 1,775 gr 4, 008 Pliocene and Delmontian Calif. contact, 1,700; probably in Sespe(?) formation, 2,010-2,525; top of the Eocene, 3,850:I:. 221 _____ do ............... Needham 2.... 1 12 3 16 1951—52 1,560 gr 1, 805 .............................. Produced 17 bbls per day, 31.3° gravity 011, 12.0 percent cut on 11—19—52. Shut 222 ..... do ............... Needham 3--. 1 l2 3 16 1952 1,500: 4,031 Base of the Pliocene, 1,805; .................... See pl. 45, section Sespe(?) formation and B—B’. Eocene contact, 1,880:iz; bottom in Eocene. 223 ..... do ............... Newhall 1 20 4 17 1942 946 7, 004 .................................................. Land dz Fanning 1. 224 ..... do ............... Newhall— 1 15 4 16 1926-26 1,199 5, 893 In Mint Canyon formation, .................... Baugus 1. 2,625—5,893. 225 ..... do ............... Union-Ffr- 1 31 4 16 1951-52 1,530 gr 11, 549 .................................................. guson . 226 Universal Consoli- Phillips 1. .... 1 2 3 16 1949 1,260 5, 264 Bottomed in Sespe(‘?) for- Formation test: dated Oil Co. mation. 5,196—5,264, re- covered two stands gassy drilling fluid. 227 Von Glahn Oil Co.-- Lassale 1 ...... 10 3 16 ......... 1,500 df ........ Top of the Miocene, 4,800:l:; .................... Also called Mutual top of the Sespe(?) for- Development mation, 7,980. Lassale 1. 228 Watkins, Jack ....... Braille 1 ....... 1 2 3 16 ........................................................... 229 ..... do ............... Legion 1 ...... 1 3 16 1952—53 1,338 kb 3, 231 Base of the Pliocene, 2,8905: top of the Sespe(‘?) for- mation, 2,990; robably some rocks of De montian stage of Kleinpell between. 1 230 ..... do ............... Needham 2—2 . 1 12 3 16 1953 1.661 kb 1, 848 .............................. Completed on pump 2—27—53; 40 bbls per day, 21.6° gravity 011% 8.8 percent cu . 231 Watkins, Jack ....... Thompson 1.. 12 3 16 1952—53 1,568 kb 2,163 Bottomed in Sespe(?) for- Plug at 2,137; 15 mation. barrels per day, 16° gravity oil, 19 percent cut on 1-4—53; sanded up abandoned 232 West Coast Devel- Broughton 2.. 1 27 4 16 ............................................................................... opment Go. See footnotes at end of table. 581734 0 ~62 -7 356 SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY TABLE 10.—Wildcal wells, including all known prospect wells outside productive oil fields—Continued Num- Location Total bet Operator Well Year Elevation depth Geologic infigngion (depth Oil and gas shows Remarks (depths ee , drilled (feet) (feet) (depths in feet) in feet) 44) Sec. '1‘. N. R. W. “ 233 Western Gulf Oil Co. Brady Estate 13 3 17 1943 3,460 at 9,807 Spud in lower Mohnian ____________________ 1. stage of Kleinpell; top of the Luislan stage of Klein- peli, 1,770; top of the Topanga(?) formation, 2,230; Santa Susana fault, 2,505; lower Mohnian stage of Kleinpell, 2,505- 2,650; small fault, 2,650; rocks of the Delmontian stage of Kleinpell below fault; Brady fault, 5,100; Pliocene, 5,100—7,300; mp of the Delmontian stage of Kleinpell, 7,300; top of the lower Mohnian stage of Kleinpell, 8,510; top of the Luisian stage of Klein- pell, 8,690. 234 Willard, R. D ....... Phillips 3 _____ 12 3 16 1950 1,406 kb 931 .............................. Oil sand at 810; pumped water “filth trace of o . 1235 YojungNapoleon Oil (7) ..... 5 3 16 ......... ____ .-_ ...... .- .... o. 236 Young, Boy W., Inc. Walker 1 ______ I 11 4 16 1941? 1,2503: 9, 981 Saugus formation and Mint ____________________ See pl. 45, section Canyon formation oon- C—C’. tact, 2,937; bottom in Mint Canyon formation. I Profected section (within boundaries of land grants). 1 We 1 not shown on geologic map, plate 44. GEOLOGY 0F SOUTHEASTERN VENTURA BASIN SELECTED REFERENCES Ashley, G. H., 1896, The Neocene stratigraphy of the Santa Cruz Mountains of California: California Acad. Sci. Proc., ser. 2, v. 5, p. 273—367. Axelrod, D. I., 1940, Mint Canyon flora of southern California, a preliminary statement: Am. Jour. Sci., ser. 5, v. 238, p. 577—585. —— 1941, The concept of ecospecies in Tertiary paleobotany: Natl. Acad. Sci. Proc., v. 27, p. 545—551. Bailey, T. L., 1935, Lateral change of fauna in the lower Pleisto- cene: Geol. Soc. America Bull., v. 46, p. 489—502. Bandy, O. L., 1953a, The frequency distribution of Recent Foraminifera off California, in Ecology and paleoecology of some, California Foraminifera, pt. 1: Jour. Paleontology, v. 27, p. 161—182. V 1953b, Foraminiferal evidence of subsidence rates in the Ventura basin, in Ecology and paleoecology of some Cali- fornia Foraminifera, pt. 2: Jour. Paleontology, v. 27, p. 200—203. Barton, C. L., and Sampson, N. N., 1949, Placerita oil field: California Oil Fields, v. 35, no. 3, p. 5—14. Bell, H. S., 1942a, Density currents as agents for transporting sediments: Jour. Geology, v. 50, p. 512—547. 1942b, Stratified flow in reservoirs and its use in preven- tion of silting: U.S. Dept. Agriculture Misc. Pub. 491, p. 1—46. Bramlette, M. N., and Bradley, W. H., 1942, Geology and biol- ogy of North Atlantic deep-sea cores between Newfound- land and Ireland: U.S. Geol. Survey Prof. Paper 196, pt. 1, p. 1—34. Brown, A. B., and Kew, W. S. W., 1932, Occurrence of oil in metamorphic rocks of San Gabriel Mountains, Los Angeles County, California: Am. Assoc. Petroleum Geologists Bull., v. 16, p. 777—785. Butcher, W. S., 1951, Foraminifera, Coronado Bank and vicin- ity, California: Scripps Inst. Oceanography Submarine Geology Rept. 19, 8p. California State Oil and Gas Supervisor, 1953, Summary of operations, California oil fields, in Thirty-ninth Annual Report: v. 39, no. 1, Jan—June, 1953. Clements, Thomas, 1937, Structure of southeastern part of Tejon quadrangle, California: Am. Assoc. Petroleum Geologists Bull., v. 21, p. 212—232. Crouch, R. W., 1952, Significance of temperature on Forami- nifera from deep basins off southern California coast: Am. Assoc. Petroleum Geologists Bull., v. 36, p. 807—843. Crowell, J C , 1952a, Probable large lateral displacement on San Gabriel fault, southern California: Am. Assoc. Petro- leum Geologists Bull., v. 36, p. 2026—2035. 1952b, Submarine canyons bordering central and southern California: Jour. Geology, v 60, p. 58—83. Daly, R. A., 1936, Origin of submarine “canyons”: Am. Jour. Sci., ser. 5, v. 31, p. 401—420. Dietz, R. S., 1953, Possible deep-sea turbidity current channels in the Indian Ocean: Geol. Soc. America Bull., v. 64, p. 375—378. Driggs, J. L., and Sampson, N. N., 1951, Ramona oil field: California Oil Fields, v. 37, no. 1, p. 5—12. Eaton, J. E., 1939, Ridge basin, California: Am. Assoc. Petro- leum Geologists Bull., v. 23, p. 517—558. Eldridge, G. H., and Arnold, Ralph, 1907, The Santa Clara Valley, Puente Hills, and Los Angeles oil districts, southern California: U. S. Geol. Survey Bull. 309, 266 p. 357 Ellzey, B. V., 1921, First driller and first well in West: The Oil Weekly, v. 23, Nov. 19. English, W. A., 1914, The Fernando group near Newhall, Cali- fornia: California Univ. Dept. Geol. Sci. Bull., v. 8, p. 203—218. Ericson, D. B., Ewing, Maurice, and Heezen, B. G., 1951, Deep-sea sands and submarine canyons: Geol. Soc. America Bull., v. 62, p. 961-966. 1952, Turbidity currents and sediments in North Atlantic: Am. Assoc. Petroleum Geologists Bull., v. 36, p. 489—511. Ewing, Maurice, Heezen, B. G., Ericson, D. B., Northrop, John, and Dorman, James, 1953, Exploration of the northwest Atlantic mid-ocean canyon: Geol. Soc. America Bull., v. 64, p. 865—868. Gabb, W. M., 1869, Cretaceous and Tertiary fossils, in Paleon- tology: California Geol. Survey, v. 2, 299 p. Gould, H. R., 1951, Some quantitative aspects of Lake Mead turbidity currents: Soc. Econ. Paleontologists and Mineral- ogists Spec. Pub. 2, p. 34—52. Grant, U. S. IV, and Gale, H. R., 1931, Pliocene and Pleistocene Mollusca of California: San Diego Soc. Nat. History Mem., v. 1, 1,036 p. Grant, U. S. IV, and Hertlein, L. G., 1938, The West American Cenozoic Echinoidea: California Univ. at Los Angeles Pub. in Math. and Phys. Sci., v. 2. Harrington, G. L., 1955, Bathymetric position of some California Pliocene Foraminifera: Cushman Found. Foram. Research Contr., v. 6, p. 125—127. Hazzard, J. C., 1944, Some features of the Santa Susana thrust vicinity of Aliso Canyon field, Los Angeles County, Cali- fornia [abs.]: Am. Assoc. Petroleum Geologists Bull., v. 28, p. 1780—1781. Heezen, B. C., and Ewing, Maurice, 1952, Turbidity currents and submarine slumps, and the 1929 Grand Banks earth- quake: Am. Jour. Sci., ser. 5, v. 250, p. 849—873. Hershey, O. H., 1902, Some Tertiary formations of southern California: Am. Geologist, v. 29, p. 349—372. Herltein, L. G., and Grant, U. 8., IV, 1944, The Cenozoic Brach- iopoda of western North America, California Univ. at Los Angeles Pub. in Math. and Phys. Sci., v. 3. Hill, M. L., 1930, Structure of the San Gabriel Mountains north of Los Angeles, California: California Univ. Dept. Geol. Sci. Bull., v. 19, p. 137—170. Hodges, F. C., and Murray-Aaron, E. R., 1943, Newhall- Potrero, Aliso Canyon, Del Valle, and Oak Canyon fields: California Oil Fields, v. 29, no. 1, p. 5—29. Hudson, F. S., and Craig, E. K., 1929, Geologic age of the Modelo formation, California: Am. Assoc. Petroleum Geo- logists Bull. 5, p. 509—518. Jahns, R. H., 1939, Miocene stratigraphy of the easternmost Ventura Basin, California, a preliminary statement: Am. Jour. Sci., v. 237, p. 818—825. 1940, Stratigraphy of easternmost Ventura basin, California: Carnegie Inst. Washington Pub. 514, p. 145—194. Kew, W. S. W., 1924, Geology and oil resources of a part of Los Angeles and Ventura counties, California: U. S. Geol. Survey Bull. 753, 202 p. 1943, Newhall oil field: California Div. Mines Bull. 118, p. 412—416. Kleinpell, R. M., 1938, Miocene stratigraphy of California: Tulsa, Okla., Am. Assoc. Petroleum Geologists, 450 p. Kuenen, P. H., 1937, Experiments in connection with Daly’s hypothesis on the formation of submarine canyons: Leidsche Geol. Mededeel. 8, p. 327—351. 358 Kuenen, P. H., 1938, Density currents in connection with the problem of submarine canyons: Geol. Mag., v. 75, p. 241—249. 1950, Marine geology: New York, John Wiley and Sons, 568 p. 1951, Properties of turbidity currents of high density: Soc. Econ. Paleontologists and Mineralogists Spec. Pub. 2, p. 14-33. 1952, Paleogeographic significance of graded bedding and associated features: Koninkl. Nederlandsch Akad. wetensch. Proc., ser. B, v. 55, p. 28-36. 1953, Significant features of graded bedding: Am. Assoc. Petroleum Geologists Bull., v. 37, p. 1044—1066. Kuenen, P. H., and Menard, H. W., 1952, Turbidity currents, graded and nongraded deposits: Jour. Sedimentary Petrol- ogy, v. 22, p. 83-96. Kuenen, P. H., and Migliorini, C. I., 1950, Turbidity currents as a cause of graded bedding: Jour. Geology, v. 58, p. 91—127. Leach, C. E., 1948, Geology of Aliso Canyon oil field, California, in Structure of typical American oil fields: Tulsa, Okla., Am. Assoc. Petroleum Geologists, V. 3, p. 24—37. Lewis, G. E., 1938, Commentary on McGrew and Meade’s paper: Am. Jour. Sci., ser. 5, v.36, p. 208—211. Loofbourow, J. S., Jr., 1952, Newhall-Potrero oil field: AAPG— SEPM—SEG Guidebook, Joint Ann. Mtg. , Los Angeles, Calif. , March 1952, p. 52—56. McGrew, P.O., and Meade, G. E., 1938, The bearing of the Valentine area in continental Miocene-Pliocene correlation: Am. Jour. Sci., ser. 5, v. 36, p. 197—207. McKee, E. D., and Weir, G. W., 1953, Terminology for strati- fication and cross-stratification in sedimentary rocks: Geol. Soc. America Bull., v. 64, p. 381—390. McMasters, J. H., 1933, Eocene Llajas formation of California [abs]: Geol. Soc. America Bull., v. 44, pt. 1, p. 217—218. Maxson, J. H., 1930, A Tertiary mammalian fauna from the Mint Canyon formation of southern California: Carnegie Inst. Washington Pub. 404, p. 77—112. 1938a, Miocene-Pliocene boundary [abs]: Am. Assoc. Petroleum Geologists Bull., v. 22, p. 1716—1717. 1938b, Geologic age of earliest North American Hipparion fauna [abs.]: Geol. Soc. America Bull., v. 49, p. 1916—1917. Menard, H. W., and Ludwick, J. C., 1951, Applications of hydraulics to the study of marine turbidity currents: Soc. Econ. Paleontologists and Mineralogists Spec. Pub. 2, p. 2—13. Merriam, C. W., 1941, Fossil turritellas from the Pacific coast of North America: California Univ. Dept. Geol. Sci. Bull., v. 26, p. 1—214. Miller, W. J., 1931, Anorthosite in Los Angeles County, Cali- fornia: Jour. Geology, v. 39, no. 4, p. 331—344. 1934, Geology of the western san Gabriel Mountains of California: California Univ. at Los Angeles Pub. in Math. and phys. Sci., v. 1, p. 1—114. Moody, G. B., 1949, Developments in California in 1948: Am. Assoc. Petroleum Geologists Bull., v. 33, p. 805—826. Natland, M. L., 1933, The temperature- and depth-distribution of some Recent and fossil Foraminifera in the southern California region: Scripps Inst. Oceanography Bull., Tech. Ser., v. 3, p. 225—230. SHORTER CONTRIBUTIONS T0 GENERAL GEOLOGY Natland, M. L., and Kuenen, P. H., 1951, Sedimentary history of the Ventura basin, California, and the action of turbidity currents: Soc. Econ. Paleontologists and Mineralogists Spec. Pub. 2, p. 76—107. Nelson, L. E., 1948, Preliminary report on Ramona field, Los Angeles and Ventura Counties, California: Am. Assoc. Petroleum Geologists Bull., v. 32, p. 1658—1663. 1952, Del Valle and Ramona oil fields: AAPG—SEPM— SEG Guidebook, Joint Ann. Mtg., Los Angeles, Calif., March 1952, p. 57—63. North, Edward, 1890, The Pico Canyon oil fields: California Mining Bur. Ann. Rept. 10, p. 283—298. Oakeshott, G. B., 1950, Geology of Placerita oil field, Los Angeles County, California: Calif. Jour. Mines and Geology, v. 46, p. 43—79. —-——— 1954, Geology of the western San Gabriel Mountains: California Div. Mines Bull. 170, map sheet 9. Oldroyd, I. S., 1924, 1927, The marine shells of the west coast of North America: Stanford Univ. Pub. Geol. Sci., v. 1, 247 p.; v. 2, 640 p. Orcutt, W. W., 1924, Early oil development in California: Am. Assoc. Petroleum Geologists Bull., v. 8, p. 61—72. Phleger, F. B., 1951, Displaced Foraminifera faunas: Soc. Econ. Paleontologists and Mineralogists Spec. Pub. 2, p. 66—75. Prutzman, P. W., 1904, Production and use of petroleum in California: California Mining Bur. Bull. 32, p. 9—237. 1913, Petroleum in southern California: California Mining Bur. Bull. 63, 430 p. ' Reed, R. D., and Hollister, J. S., 1936, Structural evolution of southern California: Tulsa, Okla., Am. Assoc. Petroleum Geologists, 157 p. Rich, J. L., 1950, Flow markings, groovings, and intrastratal crumplings as criteria for recognition of slope deposits, with illustrations from Silurian rocks of Wales: Am. Assoc. Petroleum Geologists Bull., v. 34, p. 717-741. —— 1951, Three critical environments of deposition, and criteria for recognition of rocks deposited in each of them: Geol. Soc. America Bull., v. 62, p. 1—20. Ricketts, E. F., and Calvin, J ., 1952, Between Pacific tides: 3d ed., Stanford, Calif., Stanford Univ. Press, 502 p. Scruton, P. L., and Moore, D. G., 1953, Distribution of surface turbidity off Mississippi delta: Am. Assoc. Petroleum Geol- ogists Bull., v. 37, p. 1067—1074. Sharp, R. P., 1935, Geology of Ravenna quadrangle, California [abs]: Pan—Am. Geologist, v. 63, p. 314. Sheldon, D. H., and Havenstrite, R. E., 1941, Development of Del Valle oil field: Oil and Gas Jour., v. 40, p. 43-44. Shepard, F. P., 1951, Transportation of sand into deep water: Soc. Econ. Paleontologists and Mineralogists Spec. Pub. 2, p. 53—65. Sherman, R. W., 1943, Del Valle oil field: California Div. Mines Bull. 118, p. 408—411. Standard Oil Co. of California, 1918, The birth of an industry: Standard Oil Bull. (Calif), August 1918. Stipp, T. F., 1943, Simi oil field: California Div. Mines Bull. 118, p. 417—423. Stirton, R. A., 1933, Critical review of the Mint Canyon Plio- cene mammalian fauna and its correlative significance: Am. Jour. Sci., ser. 5, v. 26, p. 569—576. ——— 1936, Succession of North American continental mam- malian faunas: Am. Jour. Sci., ser. 5, v. 32, p. 161—206. GEOLOGY OF SOUTHEASTERN VENTURA BASIN Stirton, R. A., 1939, Significance of Tertiary mammalian faunas in holartic correlation with especial reference to the Pliocene in California: Jour. Paleontology, v. 13, p. 130—137. Tarbet, L. A., 1942, Geology of Del Valle oil field, Los Angeles fCounty, California: Am. Assoc. Petroleum Geologists Bull., V. 26, p. 188—196. Teilhard de Chardin, Pierre, and Stirton, R. A., 1934, A cor- relation of some Miocene and Pliocene mammalian as- semblages in North America and Asia, with discussion of the Mio—Pliocene boundary: California Univ. Dept. Geol. Sci. Bull., v. 23, p. 277—290. Union Oil Co. 1935, Yarns of yesterday: Union Oil Bull., Oct. 1935, p. 32. Vander Leek, Lawrence, 1921, Petroleum resources of California with special reference to unproved areas: California Mining Bur. Bull. 89, p. 1—186. Walling, R. W., 1934, Report on Newhall oil field: California Oil Fields, v. 20, p. 5—57 [1936]. Watts, W. L., 1897, Oil and gas yielding formations of Los Angeles, Ventura, and Santa Barbara Counties, pt. 1: California Mining Bur. Bull. 11, 94 p. 1901, Oil- and gas-yielding formations of California: California Mining Bur. Bull. 19, 236 p. White, R. T. , and others, 1952, Cenozoic correlation chart across eastern Ventura basin: Pacific Section, Am. Assoc. Petroleum Geologists. 359 Willis, Robin, 1952, Placerita oil field: AAPG—SEPM—SEG Guidebook, Joint Ann. Mtg, Los Angeles, Calif., March 1952, p. 32—41. Winterer, E. L., and Durham, D. L., 1954, Geology of a part of the eastern Ventura basin, Los Angeles, County: California Div. Mines Bull. 170, map sheet 5. 1958, Geologic map of a part of the Ventura basin, Los Angeles County, California: U.S. Geol. Survey Oil and Gas Inv. Map CM 196. Woodford, A. 0., 1951, Stream gradients and Monterey sea valley: Geol. Soc. America Bull., v. 62, p. 799—852. Woodring, W. P., 1930, Age of the Modelo formation in the Santa Monica Mountains, California [abs]: Geol. Soc. America Bull., v. 41, p. 155. 1938, Lower Pliocene mollusks and echinoids from the Los Angeles basin: U.S. Geol. Survey Prof. Paper 190, 67 p. Woodring, W. P., and Bramlette, M. N., 1950, Geology and paleontology of the Santa Maria district, California: U.S. Geol. Survey Prof. Paper 222, 185 p. Woodring, W. P., Bramlette, M. N., and Kew, W. S. W., 1946, Geology and paleontology of the Palos Verdes Hills, Cali- fornia: U.S. Geol. Survey Prof. Paper 207, 145 p. Woodring, W. P., Stewart, Ralph, and Richards, R. W., 1940, Geology of the Kettleman Hills oil field, California: U.S. Geol. Survey Prof. Paper 195, 170 p. Yarborough, H. E., and Bear, T. L., 1952, Castaic Junction field: AAPG—SEPM—SEG Guidebook, Joint Ann. Mtg, Los Angeles, Calif., March 1952, p. 47—51. 360 TABLE 11.——Fossil localities SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY [Number, this report: F, megaiossil locality; i, Foraminifera locality; V, vertebrate locality. Altitude from topographic base of geologic map, pl. 44] Number Altitude , (feet) Collector Date Description This report USGS Field EOCENE SERIES F1 1 ___________________________ Kew loo. 4 ...................... Kew ........................................ Elsmere Canyon. F2 __________________ 18294a .................................. Winterer, Durham, Fahy ......... 1952 Core from Union Oil Needham 3 NE. cor. sec. 12, T. 3 16 W. (projected), at well depth 2269-2289 ft. F3 __________________ 182940 _______________________________________ do ............................. 1952 Core from Union Oil Needham3 N E cor. sec. 12, T. 3 N. R. 16 W. (projected), at well depth 2742-2753 ft. F4 ______________________________________________________________ Kew, Driver ______________________ 1931? Core from North Star RMining and Development Shepard 21()s5e(i‘t’ l, T. 3 N. .16 W. (projected), at well depth F5 ................................................................... do ............................ 1931? Core from North Star Mining and Development Shepard 1, sec. 1, T. 3 N., R. 16 W. (projected), at well depth UPPER MIOCENE Modelo formation 16 ..................................................... 2165 Winterer, Durham, Bramlette_... 1952 East Clalrgygzn, 11.310 it S. and 3,000 ft W. of lat 34°22’, ong i7 ............................. Rice Canyon 8 ........ 2190 ..... do ............................. 1952 East Calgygzn, 11,490 it S. and 3,060 it W. of lat 34°22’, ong 11 1‘8 ............................. Rice Canyon7 ......... 2210 ..... do ............................. 1952 East Clalxgygzn, 11 5,70 ft S. and 3,070 ft W. of lat 34°22’, ong 1‘9 ............................. Rice Canyon 6 ........ 2320 _____ do ............................. 1952 East Cargygn, 11,830 ft S. and 2,960 ft W. of lat 34°22’, ong 11 2' no ............................ Rice Canyon 5 ........ 2350 _____ do _____________________________ 1952 Ezlast Claigyaon, 11,830 ft S. and 3,090 ft W. of lat 34°22’, ong 1 ill ............................ Rice Canyon 1A ...... 2470 Winterer, Durham ________________ 1951 East Calnygn, 11,800 it S. and 3, 380 it W. of lat 34°22’, 0111: 11 £12 .................................................... 3475 Winterer, Durham, Bramlette___. 1951 SW. of Towsley Canyon, 530 ft S. and 10. 040 ft W. of lat 34°20’, long 118°34’ UPPER MIOCENE AND LOWER PLIOCENE Towsley fonmtion £15 .................................................... 1600 Winterer .......................... 1953 Towslely10 Canyon, 4, 600 it S. and 3, 450 ft W. of lat 34°22’, on 8° F16 ................. 16842 JCH 343-.. ........... 2085 Hazzard _____________________________________ Ealsltstanyon, 10,150 it S. and 690 it W. of lat 34 22’, long F17 1 ................ 18208 M 200 ................. 850 Winterer, Woodring _______________ 1950 S0111t8h3side of Santa Clara Valley, Ventura COunty, on north-south ridge midway between Tapo Canyon and Los Angeles-Ventura County line, about 1. 75 miles S. 4° W. from intersection of county line and State Route 126, and 0.57 mile S. 58" E. from top of Hill 1988, Santa Susana quadrangle (1: 62, 500.) F18 ................. 18436 M 500 ................. 1525 Durham __________________________ 1951 S113.of1111801;é)y,8,550 it S. and 3,090 ft W. of lat 34°26’, on F19 ................. 18437 M 501 _________________ SE ogr Honby, 7, 880 it s and 2, 800 it W. of lat 34°26’, long 118° 28’. F20 ........................... SOC—F3 .............. S. of Gavin Canyon, 10,850 it S. and 9,620 ft W. of lat 34°22’, long 118°30 ’. F21 I __________________________ USGS 4401 ___________ Elsmere Canyon F22 Kew loo. 7 ............ Elsmere Canyon, 2, 700 ft S. and 9,870 ft W. of lat 34°22’. long 118° 8’. CIT 1539 .............. Do. UCLA L2056- ' Do. UCLA L 242.. Do. UCLA 3319 ........... North side or Elsmere Canyon, probably near Standard 0110f Calimeia Elsmere 1. UCLA 3322 ........... North side of Elsmere Canyon, probably near Standard Oil of California Elsmerel F 219B ................ 1975 Winterer, Bramlette ______________ 1951 Picosc%nyon,, 9, 560 it s. and 8,100 ft W. of lat 34°24! ions 11 F 222 .................. 1915 _____ do ____________________________ 1951 P1100 Calnsygéll, 10,810 ft S. and. 8, 650 It W. of let 34°24’, ongl F 223 _________________ 1950 _____ do ____________________________ 1951 Pico Canyon, 10, 820 ft 6. and 8,400 ft W. or lat 3024’, long 118°36’. F 224. ................ 2110 ..... do ____________________________ 1951Pilco Canygn, 10 520 it a and 7,760 ft W. of lat 34°24’, ong 118° 6’ 1‘ 224.4 ................ 2125 ..... do ____________________________ 1951 Pilco canyon, 10,400 it s. and 7,630 ft W. 0112:: 34°24’ ong F 140 ................. 2460 Winterer __________________________ 1950 SW. of Salt Can anoyon, 11,700 It s. and 1,930 ft W. of lat 34°24’, long 118 F 147- ................ 2190 ..... do ............................ 1950 SW. of Salt Can anyon, 10,440 it s. and 2,110 ft W. of lat 34°24’, long 11840 F 148- ................ 2225 ..... do ____________________________ 1950 SW. of Salt Can noyon, 10,340 ft 8. and 2,110 ft W of lat 34°22’, long 11840 a I SEPM ................ 1570 Bramlette ................................... Ellsmere0 Canyon, 4, 310 it S. and 8,800 ft W. 01' lat 34 22 ong 118° 28’. RR 2 ................. 1400 Winterer, Durham ................ 1953 SE. of 1Horéisay,, 7, 880 II: S. and 2,640 ft W. of lat 34°26' ong RR 3 ................. 1400 ..... do ____________________________ 1953 SE. ongr 1312173 , 7 810 it s. and 2,690 ft W. of lat 34°26’, ong 118 RR 4 ................. 1400 ..... do ............................ 1953 811? oflflsoggy, 7, 700 it s. and 2,710 ft W. of Int 34°26’. Eong RR 5 ................. 1400 ..... do- ........................... 1953 1 of 1llionby, 4, 440 it s. and 2,770 It W. of lat 3026’. ong See footnotes at end of table. GEOLOGY 0F SOUTHEASTERN VENTURA BASIN TABLE 11.—-—Fossil localities—Continued 361 Number Altitude Collector Date Description ee This report USGS Field PIJOCENE Pica formation F41- 18097 M 205 ................. 2000 Winterer .......................... 1950 S. of San Martinez Grande lCanyon, 2, 590 it S. and 10,040 ft W. of lat 34°26', long 118 F42. 18435 M 304 _________________ 2125 ..... do ............................ 1951 S. 01 San Martinez Grands Canyon, 2, 640 ft 8. and 9, 510 ft W. of lat 34°26’, long 118°40’. F43 2 ................ 18283 M 300 ........................... Winterer, Durham ................ 1951 North side Santa Clara River valley, Ventura County, 5,550 ft northwestward along Los Angeles-Ventura County line from intersection of county line and State Route 126, thence 780 it southwestward at right angle Santa Susana quadrangle (1: 62 ,.500) On W. slope of small hill bordering large eastwest closed basin. F44 1 ________________ 18432 M 301 ................................ do ............................ 1951 North side of Santa Clara River valley, Ventura County, 5, 460 ft northwestward along Los Angeles-Ventura County line from the intersection of the line and State Route 126, thence 640 ft southwestward at right angle. F331 same low hill and about 150 ft east-southeast 0 oc 1650 ..... do ............................ 1951 W. of San Martinez Grande Canyon, 5,000 ft S. and 9, 680 ft W. of lat 34°26’, long 118°40'. M 207 ................. 1510 Winterer .......................... 1051 W of San Martinez Grands Canyon, 6, 340 ft S. and 7, 840 ft W. of lat 34°26’, long 118 M 211 ................. 1180 ..... do ............................ 1951 W of San Martinez Grande8 Canyon, 6,850 ft S. and 4,440 ftW. oflat34° 26’, long118° 40'. M 210 ................. 1080 ..... do ____________________________ 1951 W. of San Martinez Grands Canyon, 7,400 ft S. and 5, 420 ft W. of lat 34°26’, long 118°40'. M 1982*. ............... 1000 Winterer, Woodring .............. 1950 W. of San Martinez Grande Canyon 7 ,230ft S and 8,750 ft. W. of lat 34°26’, long 118°40’. loat. M 198 .......... .. ..... dn ............... 1950 North side Santa Clara River valley, Ventura County, 2,925 feet northwestward along Los Angeles-Ventnra Couity line from intersection of county line and State Route 126, thence 200 it southwestward at right angles along ridge top. M 208 ................. 1285 Winterer .......................... 1951 W. of San Martinez Grands Canyon, 7, 380 it S. and 7, 800 ft W. of lat 34°26', long 118°40’. MNLF 180 ........... 1200 Durham, Fahy ................... 1951 North side Santa Clara River valley, Ventura County, 5,000 ft N. 52° W. of intersection of Los Angeles-Ventura County line and State Route 126; from sandstone at shag bend in bottom oi south-draining canyon. NLF 177. 1951 294 it . and 32 ft W. ofloc. F52. 1951 196 ft S. and 38 it E. of ice. F52. 1951 In siltstone immediately above sandstone of 100. F52. 1951 36ft N. and 44 ft E. of 100. F52. 1951 93ft N. and 46 it E. of loo. F52. do . 1951 232 it N. and 96 it E. of Ice. F52. Winterer .......................... 1951 W of San Martinez Grande Canyon, 7, 940 ft S. and 5,500 ft W. of lat 34°26’, long 118° 40’. 1075 ..... do ....................... . ..... 1950 San Martinez Grande Canyon, 6, 490 ft S. and 1, 720 it W. of lat 34°26’, long 118° 40’. 1400 ..... do ............................ 1950 W of San Martinez Chiqulto Canyon, 3, 750 It S. and 9,710 ft W. oflat34° 26’, longll 8° 38. 1775 Durham, Winterer ................ 1952 Holser Canyon, 4, 220 ft N. and 8, 880 ft W. of lat 34°26’, long 118°40’. 2075 Stiles .............................. 1952 Hiflser Canyon, 4, 880 ft N. and 8, 880 ft W. of lat 34°26’, on 118° 40’. ............... do.......-....--...--.._..-.-__ 1952 In tributary to up er part of San Martinez Chlquito Canyon, 1,150 ft .and 75 it E. of NW. corner sec. 8, T. N, R. 17 W. Castaic quadrangle. 1375 ..... do...., ........................ 1952 S. of San Martinez Chi uito Canyon, 3, 700 It N and ' 9,.860ftW oflat34° 26’, ong 118 1525 ..... do ............................. 1952 W. of San Martinez Chiquito Canyon, 3, 560 ft N. and 9,100 ft W. of lat 34°26’, long 118° 38’ 2200 Cooper, Kelley .................... 1938 Holser Canyon, 5, 400 it N. and 8, 690 ft W. of lat 34°26’, long 118 40. F68 ........................... UCLA 8118 ........... 885 ______________________________________________ W. of San Martinez Grande Canyon, 9, 000 ft 5 and 3,190 ftW. oflat34°26’ 1,0ng11 8° 40’. F69 ........................... UCLA L349 ___________ 1535 Brown ______________________________________ W of San Martinez Chiquito Canyon, 1, 890 ft N and E,9 780 ft W of let 34°26’, long 118° 38’ F70 ........................... UCLA L355 ___________ 1550 _____ do _______________________________________ of San Martinez Chiqulto Canyon, 1, 820 ft N and E5,7001'1‘. W. of lat 34°26’, long 118° 38. F71 ........................... UCLA L351 ___________ 1510 _____ do ______________________________________ N. ’01 San Martinez Grande Canyon, 780 ft N. and 888 ft . W. of lat 34° 26’, long 118° 40’. F72 --------------------------- CKL22 ............... 1750 Cooper, Kelley .................... 1938 W of San Martinez Chiquito Canyon, 2, 000 ft N. and 9, 600 ft W. of lat 34°26’, long 118°3 F73 ........................... UCLA L347 ........... 1250 Brown ______________________________________ San Martinez Chiquito Canyon, 190 ft S. and 9 370 ft W of lat 34°26’, long 118°38’. F74 ----------------- 1290 Woodring; Winterer _______________ 1950 San Martinez, Chiquita Canyon, 3,570 ft N. and 5,900 ft W. of lat 34° 26’, long 118° 3’.8 F75 ----------------- 1450 Brown ...................................... E. of San Martinez Chifiu uito Canyon, 3,740 ft N. and _ 3, 820 it W. of lat 34°26’, ong118°3 F76 ----------------- 1850 Wmterer .......................... 1951 sari Fernando Pass, 9, 94311 S,gand 2,980 ft W. oi lat 34°22, long 118° 30’. F77 ----------------- 1525 ..... do _____________________________ 1951 Towslely Canyon 2 400 it s and 8 000 It W. oflat 34° 22', long 118° 3’ F78 ................. 1530 _____ do _____________________________ 1951 Ttlzuwsley Canyon, 2, 220 it s and 8,150 it W. of lat 34° 22’ ong 118 32’. F79 ................. 1535 _____ do _____________________________ 1951 Towsieyso Canyon, 2 080 it s. and 8 190 ft W. of lat 34° 22' ong 11°32'. F80 ----------------- 1530 ..... do ............................. 1951 Triowsleys Canyon, 1 ,850 It s. and 8,910 ft W of lat 34° 22' ong132'. F81 ................. 1560 _____ do ............................. 1951 Towsley Canyon, 1,800 it s and 8,62011: W. oust 34° 22’. lon 118 32’. F82 ................. 1600 Winterer, Durham ................ 1952 P100 gCanyon, 6, 500 it s and 1 540 it W. of lat 34" 24'- See footnotes at end of table. long 118° 36’. 362 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY TABLE 11,—Fossil localities—Continued Number Altitude (feet) Collector Date Description This report UBGS Field PLIOCENE—Continued Plco formation—Continued F83 ___________________________ UCLA L1085 .......... 1510 O’Flynn, Paschal"-.. ........... 1938 Towslefi Caéyou, 2,090 it s. and 9,070 ft W. of lat 34° 22', ans V84 ........................... V2 .................... 1450 Corey ....................................... E. of San Martinez Chiquita Canyon, 3,900 ft N. and 4, 300 ft W. of lat 34° 26’, long 118° 38’. F95 ___________________________ M 600 _________________ 1300 Vedder, Durham .................. 1954 North edge of Newhall- Pottero oil field, 11, 700 it s. and 8,500 ft W. of lot 34° 26’, long 118° 36’ UPPER PLIOCENE AND LOWER PLEISTOCENE Saugus formation F85 ___________________________ M 507 ................. 1470 Winterer, Durham, Cloud, Wood- 1953 Grapevine Canyon, 2,100 it 8. and 6, 890 it W. of lat 34° ring, Bramlette. 20’, long 118 °28’ F86 ........................... UCLA L364 ........... 1625 Kew ........................................ N332: 239vf319§1§383n§°n"9' 710 ft S. and 2, 370 it W. of lot ong F87 ........................... UCLA L1088 .......... 1425 O’Flynn, PaSChall ................ 1938 N 3&(239Y51ey11083nyon, 10,680 ft 8. and 860 it W. 0! lat ong I88 ............................ F 180 .................. 925 Winterer .......................... 1950 E.1 of gelgovaglle, 5, 500 ft S. and 690 ft W. of lat 34° 26’, ong 1’89 ............................ F 181A ________________ 1250 Winterer, Bramlette .............. 1950 Potrenigaxégon, 11,740 ft 5. and 7, 880 ft W. of lat 34° 26’, ong 190“.-. ....................... F 181B ................ 1250 ..... do ............................. 1950 Potter? learziiyon, 11,740 it B. and 7, 880 ft W. oflat 34° 26', oug V91 ___________________________ V 1 .................... 1025 Corey ....................................... NlE. of 1113861 Valle, 1, 400 ft 8. and 4,050 ft W. of lat 34° 26’, ongl V92 ........................... V 3 .................... 1200 ..... do ....................................... NE. oflgglavme, 850 ft 8. and 2,280 ft W. of lot 34° 26’, ong V93 ___________________________ V 4 ____________________ 1200 ..... do ....................................... W. of Castaic Station, 4,030 ft N. and 560 It W. of let 34° 26’, long 118° UPPER PLEISTOCENE V94 ........................... V 12 ................... 985 Corey ....................................... SW. of Castalc Station, 1,510 ft 8. and 8, 700 it W. of let 34° 26’, long 118° 36’. 1 Locality in area but not shown on geologic map (1)]. 44) because location is uncertain. 2 Locality outside of map area. Pale A l Acamhina spirata .......................... 298, 316 Acila castrensis ..... 300 semirostrata ................. 300, 320, 321, 322 Acknowledgments .......................... 276—278 Acmaea mitm... _ _ - 307 Acteocina calcitella ___________________________ 300 Actaean (Rectazia) punctocoelata ______________ 306 Admete gracilior ______________________________ 300 Aeguipecten circularis .................. 302, 307, 316 purpuratus ______________________________ 302 Aletes squamigerus. ________________________ 296, 307 Aliso Canyon area, geologic history ........... 338 Modelo formation ........................ 287 Aliso Canyon oil field, Topanga formation- . ._ 284 Alluvium ____________________________________ 323 Amaurellma clarki. .......................... 283 lajollaensis ________________________________ 283 Amiantis callosa .................... 302, 307, 308, 316 Anadara camuloenais ________________________ 302,316 trilineata _________________________________ 302 canalis ............................... 302 Anguloyerina angulosa. ______________________ 313 sp. ______________________________________ 295 Anemia sp __________________ . _________________ 302 Anorthosite ................................ 282, 291 Antiplanea peruersa ........................... 300 sp. ...................................... 300 Apolymetis biangulata _______________________ 302, 308 Architectonica sp .............................. 298 A86 odapsis .................................. 320 B Baagina tubinegualis. ........................ 288 Balanus agaila _______________________________ 304 Barbarofusus arnoldi ________________________ 298,307 barbaremis ................................ 298 Bathyaiphon sp ............................... Beacon fault .......................... Beacon fault area, Pico formation ............ Big‘Moore Canyon, Modelo formation ....... 287 Bison _________________________________________ 322 Bittium asperum ______________________________ 308 rugatum __________________________________ 296 sp ........................................ 296 Bolivina advena _______________________________ 295 advena striatella __________________________ 288 argentea __________ ._ 313, pl. 47 cuneiformis _______________________________ 288 hootsi ___________________________________ 288, 295 hugheai zone .............................. 287 imbricata ................................. 295 pisciformis _______________________ 295, 313, pl. 47 pseudobzyrichi __________________________ 288, 295 pseudospiasa ______________________________ 288 pygmea ___________________________________ 288 ramkim _________________________________ 288, 295 seminuda _______________________________ 295, 313 sinuata _________________________________ 288, 295 apissa ____________________________________ 295 tumida ___________________________________ 295 woodringi _________________________________ 288 Bomtelitia sp ................................. 283 Boreatrophon. _ _ ____________________________ 298 atuarti .................................. 298,307 Bouquet Canyon, erosion and river-terrace surfaces near ______________________ 280 Brachidomea cowlitzemis ...................... 283 Breccias, intraformational, turbidity current feature _________________________ 327—330 Briuopais pacifica ...................... 304, 315, 316 INDEX Page Bulimina dmudata ........................... 314 etma ..................................... 295 ovula pedroana ............................ 288 pagoda ........................ 295, 313 hebespmata ........................... 288 rostrata ............................. 288, 295, 307 subacummata. __________ 295, 313 unigerinaformis ........................... 288 Bulimmella curta ........................... 288, 295 eleganlissima“ .............. 295, 307 aubfusiformis ........................... 288, 295 Bulla goaldiana ............................. 300,316 punctulata .............................. 300, 316 C Cadulua sp ................................... 300 Calicantharus fortis ........................... 298 fortis angulata ............................ 298 humerosus ...... 298, 312. 317, 319, 321, 322 kettlemanensia __________________________ 298,315 Callioatoma coalingeme ........................ 296 coalingeme catoteran 296 sp ........................................ 206 Calyptoae’na lasia ................... 295, 302, 307, 308 Caluptraea dieaoana. 283 fastmata ............................ 296, 307, 308 filosa ..................................... 296 Cancellaria amaldi.- 298 elsmeremis .............................. 306 femandoemis ............................. 306 hemphillz‘. . . . . 298 rapa perrini .............................. 298 tritonidea ............................... 298,306 C’anlharus elegam. 298 sp ........................................ 298 Capulue califomicus .......................... 296 Cardiomya planetica. . _ . ".304, 315,316 Cassidulina califomica _______________________ 295,313 cushmani ___________________________ 295, 313, pl.47 .288, 295, 313, pl. 47 limbata ______________________________ 288, 313,314 guadrata ............................... 314, pl. 47 tramlucem .................. 295, 307 Cam'dulinella rmulinaformis .................. 288 Casaidulnid 283 Castaic Junction 01] field, oil occurrence ..... 341, 347 production ............................... 341 Casts. See Load casts. Cerithium simplicus ........................... 296 sp ........................................ 296 Chama pelludica ............................. 304, 316 Chilostomella grandis.. .. 288 sp ........................................ ‘ 295 Chime fernandomais _________________________ 302,306 or. . 1 4- .1. M 302308 opuntia ................................... 302 Cibicides basilobus ............................ 288, 295 mckamzai. _ .288, 295, 307,313 Clavine ...................................... 300 C' , __ 286 Climate ...................................... 278 Calumbella (Asturis) tuberosa ................. 306 Compsomyaz subdiaphana .................... 302, 307 Conglomerate, Towsley formation, Santa Susana Mountains .............. 290—291 Contacts, irregular, turbidity current fea- tures ____________________________ 326—327 Conus califomicus ____________________________ 300 remomiii .................................. 283 warreni ___________________________________ 283 Convolute bedding, turbidity current fea- ture ............................. 332-334 Page Corbula luteola .............................. 304,307 parilis. ...... 283 ( Varicorbula) gibbiformts. . 304 sp .................... 283 C‘raasispira sp.. .. 300 C‘rawfordi‘na fugteri. - . 300 Grepidula aculeata" .- 296, 315 mm: .......... 296,307,316 princeps. ______________ ._ 296 Cretaceous structural history. 334 C‘rucibulum spinowm ________________ 296 C‘ryptomya califomfca. 304, 317,319, 320,322 C‘rypto'natica alemica ........................ 296,308 Current marks, turbidity current features.-.- 330— 332,333 Cmpidaria .................................... 283 Cyclammina sp ..... ._ 295 Cyclacardia barbarensis.. 295,302, 307, 308. 316 ventricasa _________ .... 302,310 Cylichnma tamilla. . 283 sp. . _ . 283 Cymatid ..................................... 298 D De Witt Canyon area, 011 occurrence ......... 342 Del Valle fault ............................... 336 Del Valle fault to Holser fault, stratigraphy and lithology of the Pico forma- tion ............................ 311, 312 Del Valle oil field, landslides- pretiosum ............................. 300 sp ................ 283 Diodora atillwatere’nsis 283 Discorbis valmo’ntemsis ...... ...- 288 Dosim‘a ponderosa ______________________ 302,308,316 Drainage, structural and iithologic control..-- 279 Drilia graciosrma ............................ 300,306 E East Canyon area, Modelo formation ......... 287 Pico formation .......................... 310, 311 to San Fernando Pass, stratigraphy and lithology of the P100 formation. . . . 311 Ectfnochilus elongatus ................... -. 283 SD .......................... .- 283 Elaeocyma empyroeia ..... 300, 308 Elsmere area, 011 occurrence ...... .. 343 Elsmere Canyon area, Eocene rocks.. fossils in Towsley formation... Towsley formation ................. 291, 292, 293 See also San Fernando Pass and Elsmere Canyon area. Environment of deposition, Towsley forma- tion ________________ .- 306—308 Eocene, upper, to lower Miocene. .. 283 Eocene series, description ....... 282-283 fossil localities __________ _ 360 structural history.-. 334 Epistominella bradyaua-.. 288, 295,313, pl. 47 war __________________ ____ 288 pacifica.. . 295, 307, 313 aubperuviana ....................... 288, 295, 313 ’4‘ " ' hemphilli - 298 363 364 Pale Epcmides erioua ............................... 288 perum'ana ....... 295 Erosion cycle, present ........................ 281 Erosion surfaces, old, description and distri- bution .......................... 279-281 Eucraasatella fluctuata .............. 302, 306, 307, 308 Eulima raymcmdi ........................... 298, 315 F Faults ________________________________ 335-336, 337 Ficopsie remon zi ............................. 283 Fieldwork ____________________________________ 276 Folds ....................................... 336, 337 Foraminifera, Modelo formation .............. 288 Pico formation ........... 313—315,323; pls. 47,48 Towsley formation 295 Forren'a belcheri ............................... 298 magister. . _-- . __________ 298 Fossil localities. . . _______________ 360-362; pl. 47 Fossils, environment suggested for Towsley formation _______________________ 306—308 Eocene rocks _____________________________ 283 Mint Canyon formation ____________ 284—285, 286 Modelo formation ______________________ 287. 288 Pico formation .................... 296—305, 309, 310, 311, 312, 313-316, 321—322; pls. 47, 48. Saugus formation _______________ 317, 319—320, 322 terrace deposits..- Towsley formation. 289, 290, 292, 293—308, 320—321 Frondz‘cularia foliacea ......................... 295 Fulgoraria oregonemis. Fusitriion ___________________________________ 316 oregonemis .......................... 298, 307, 308 Galeodaria sp ................................. 283 Gari ede'ntula ............................... 304, 316 Gaudryina armaria. sp ........................................ Geoania arnoldi ............................... Geography. ._.- Geologic history. . Globigerina spp ............................... Globobalimina sp. Glottidia albida SD Graded bedding, Towsley formation, Santa Susana Mountains ............... 291 Grand Banks earthquake, turbidity current features ........................... 324 Grapevine Canyon, Towsley formation ..... 292, 293 Gyrineum elesmerense _________________________ 296 mediocre lewisz'i. rotundimargo .............. 288,295 307 313, pl 47 H Harpa sp 283 Hipparion 284 Holser and San Gabriel faults, area south, stratigraphy and lithology of the Saugus formation ............... 318—319 Holser fault 336 Holser fault area, stratigraphy and lithology of the Pico formation ........... 312, 313 Hop/cinema magnifica ....................... 288 Hopper Canyon, Modelo formation..- ...... 286 Human geography ............................ 278 I Iachnochiton sp ............................... 296 J Jaton festivus ................................ 298 Jupitan’a sp 283 K Kellefia kelletii .......................... 298, 307. 308 INDEX Page L La J olla Canyon, turbidity current features. 324, 325 La Placerita Canyon, Saugus formation ...... 319 terrace levels near ........................ 281 Lacuna sp .................................... 296 Laericardium substriatum .................. 304, 315 Lake Mead, turbidity currents. ...... 323, 324 Landslides ................................ 279, 281 Legion fault. ................................ 336 Lithology, Pico formation .................. 309—313 Towsley formation ..................... 289—293 Load casts, turbidity current feature- _ 326—327, 328 Lucina ezcavata ........................ 302,307, 308 Lucinoma annulata ................. 292,302, 306,307 Luscinisca nuttallii ..................... 302, 306,307 Lunatic lewisii _________ 296 Lyropecten cerrosensia ....................... 302, 321 M Macoma .................................... 309,315 calcarea _________________________________ 302, 308 indentata. ____________ 302 secta .................................. 302 Macrocallista homii ........................... 283 squalida ................ 302, 315 sp ........................................ 302 Mangelia narieoata .......................... 300,315 Mazwellia gemma ................ 298,308 Megafossils, Pico formation ................ 315—316 Megasurcula carpenteriana .................. 300,308 cooperi ........................ 300, 306 Melampus oliraceas .................... 300,315,316 Milt/1a zantusi .......................... 302, 306, 308 Mint Canyon formation, correlated with Sespe formation ........................ 283 description ............................... 284 environment of deposition__ 286 geologic history ........................... 339 nomenclature ............................. 284 relation to Towsley formation .......... 288,293 stratigraphic relations and age .......... 284—285 stratigraphy and lithology in mapped area ............................ 285—286 structural details ......................... 337 Miocene, upper, fossil localities ............... 360 and lower Pliocene, fossil localities ...... 360—362 Towsley formation ................. 287—308 Miocene paleogeography ...................... 339 Miocene series, Mint Canyon formation..__ 284—286 Modelo formation ...................... 286—287 Topanga formation .................... 283—284 Miocene structural history- 335 Mitra trish's ................................... 306 Mitrella carinata gausapata .................. 298,316 tuberosa ............. sp ...................................... 298, 316 Modelo Canyon, Modelo formation ........... 286 Modelo formation, age ........... 287 description ............................... 286 fossil localities ............................ 360 geologic history... 338 relation to Towsley ............. 287, 288,289,293 stratigraphy and lithology ............... 287 structural history ......... 335 turbidity current features ....... 325, 3.39, 330, 332 M uricid ...................................... 298 Mya arenaria. 304 truncata .................................. 308 lilyltha gyrata. ............................... 283 N Nana califomiana ............................ 306 hamlim’ _____ 298, 315, 320, 321,322 subsp ................................. 295 mendicue ................................. 298 moram’ana. - 298, 306 sp ........................................ 298 N atica reclusiana ............................. 306 Nelson, L. E., clted.. 346 Nemocardiam Linteam ......................... 283 Page Neptuna lyrata .............................. 298, 315 5D .......... 298 Neverita reclusiana .................. 298,306, 307, 308 Newhall, Calif, population center of area ..... 278 Newhall area, structural details- ......... 336 oil occurrence.. ........................... 344 Newhall oil field, oil occurrence and pro- duction ......................... 340—344 Newhall-Potrero area, stratigraphy and lithol- ogy of the Pico formation ........ 309-310 Newhall- Potrero oil field, production. ._ 341 oil occurrence ............................ 341,345 to East Canyon, stratigraphy and lithol- ogy of the Pico formation ........ 310—311 Nodosarz’a sp .................................. 295 Nom'on coatiferum ............................. 295 incisam ....... 295 labradoricum .............................. 288 pompilioides ............................. 313, 314 scophum.__. .313, 319 sp .......... 295 Nonitmella miocenica .......................... 288 Norrisia norrisi. . . .296, 306 Norlte ..................................... 282,291 Nucella elsmerensis ........................... 298 Nuculana extenuata. .300, 315, 316 hamata .................................. 300, 316 leonina ................................... 300 0 Oak Ridge-Simi Hills uplift, geologic history. 338 Oat Mountain syncline, Towsley formation.. 291 Oil occurrence, history ........................ 340 oil fields ............ .340—347 potential resources. .. 347 wildcat wells. .. .347, 348-356 011 production ................................ 341 011 shows, Eocene rocks in Elsmere and Whit- ney Canyons ..................... 282 Olivella biplicata .......... 298 pedroana .............. .298, 307, 316 Ophiodermella quinquecinto._.. 300 Ostrea uespertina. 302, 307, 308, 310, 316, 317, 319, 321, 322 vespertina sequena-.. .312, 320, 322 sp .................. 283 P Pachydesma crassatelloides ................ 302, 315, 316 Paleocene structural history .................. 334 Paleogeography .......... 338. 339 Paladestrina imitator .......................... 285 Pandora punctuata ............................ ' 304 Panomz/a 51).... 304 Panope ....................................... 310 generosa ............................. 304, 307, 316 Parahippus ........... 286 Parvilucina tenuiscalpta ....................... 302 Patinopecten healem' ......................... 302, 321 healeyi lohri... 306 Pecten hemphilli ............................ 302, 310 steamsz’i ................................ 302, 310 Perissolaz ............... 283 Petaloconchua montereyensis ................. 296, 315 Petricola carditoides ........................... 304 Phacoides annulatus. . 306 nuttallii ................................... 306 aanctaccmsis .............................. 306 Physiography .................. 278-282 Pico anticline, Modelo formation ............. 287 Towsley formation ....................... 288 Pico Canyon, current marks.. 330 major drainage line ................... 279 Towsley formation ....................... 290 Pico Canyon area, oil occurrence. Pico formation, age ..................... cross-strata ....................... description ................... Foraminifera, depth significance--. fossils .................................. 296-305, 309, 310, 311, 312, 313-316, 321—322; pls. 47, 48. Page Pico formation—Continued stratigraphy and lithology .............. 309-313 structural history ......... . - 335 turbidity current features ................. 325 Pitar califomianus ............................ 283 urasanus ................................. 283 Placerita Canyon. See La Placerita Canyon. Placenta formation, geologic history .......... 337 oldest exposed rocks ____________ 282 Placerita oil field, 011 occurrence ............ 344—345 production ............................... 341 Plagiocardium (Schedocardiu) brewerii. 283 Pleurotomid .................................. 283 Pleistocene, upper, fossil localities ____________ 362 Pleistocene series, alluvium ___________________ 323 terrace deposits ........................... 322 Plicifuaus sp __________________________________ 298 Pliocene, upper, and lower Pleistocene, Saugus formation ............... 317-320 Pliocene series, Pico formation ________________ 308 Pliocene structural history ____________________ 335 Pliohippus ______________________________ 312, 319, 322 Pododesmus marcoochisma _____________________ .302 Pomaular madam: .......... 296 Population centers of area .................... 278 Potrero area. See Newhall-Potrero area. Pratulum centifiloaum ________________________ 304 Pre-Cretaceous rocks ......................... 292 Progabbz'a caoperi ........................... 300, 315 Propeamussium sp ____________________________ 283 Propebela sp.....--.-._--.._.. ................ 300 Protothaca slammed ___________________________ 302 tenerrima _______________________________ ' 304, 316 Psephidia lordi ................................ 304 Paeudochama erogyra ________________________ 304, 316 Pseudomelatama aemiinflata ___________ _ 300 Pullema bulloides _____________________________ 314 Pyramidella sp ................................ 298 Q Quaternary system, Pleistocene series ....... 322—323 Quartz diorite, pre-Cretaceous_.. _ 292 Quinqueloculina sp ___________________________ 295 R Ramona oil field, landslides ..... -.-- 281 oil occurrence ......... 341, 346-347 production. ______ 341 References ____________ -- 357—3 59 Relief ................ - - - - 278 Repetto formation ............ 288-289 Rice Canyon, Modelo formation 287 remains of river~terrace deposits. 281 Towsley formation ........... 288 Rice Canyon area, oil occurrence. 342 Rincon formation, geologic history.- 338 River terraces, description and distribution. 279—281, pl. 44 Robulus cushmam' .......................... 295, 307 Rotalta beccarii-. 314 SD. ...................... 319 Rubio diorite, geologic history. _- 337 intrudes Placerita formation .............. 282 S Sacella cellulita- - - _______________ 300, 315 taphria- . _ - . 300, 307 sp ________________________ 283 Salt Creek fault- __________________________ 336 San Diego trough. turbidity current features" 324 San Fernando Pass and Eismere Canyon area, stratigraphy and lithology of the Towsley formation ______________ 291—293 San Fernando Pass area, Saugus formation-. 317—318 Pico formation . . - - _________________ 294 structural details _______________________ 336—337 San Fernando Pass to San Gabriel fault, stra- tigraphy and lithology of the Pico formation ....................... 311—312 INDEX Page San Fernando Valley, stratigraphy and lithol- ogy of the Saugus formation---- 317—318 structural details _______________________ 335-336 San Gabriel and Holser faults, area south, stra- tigraphy and lithology of the Sau- gus formation ___________________ 318—319 San Gabriel fault, anorthosite-norite suite near- 282 geologic history ........................... 337 relation to Ventura basin. 334 structural history _________________________ 335 San Gabriel fault area, fossils in Towsley for- mation _____________________ 296—305, 306 geologic history.-. Pico formation ......................... 311—312 stratigraphy and lithology of the Towsley formation ......................... structural details. . . San Gabriel formation ..................... San Gabriel Mountains, anorthosite, norlte, gneiss, and granitic rocks _________ 291 pre-Cretaceous rocks ...................... 282 Sandstone, Towsley formation, Santa Susana Mountains ..................... 290-291 Sandstone beds, angular fragments, turbidity current feature ................. 325-326 Sanguinolmia nuttallii .......... »- 304 Santa Clara River, geography. .. 278 present erosion cycle ...................... 281 relation to river terraces and old erosion surfaces ............... 279, 280, 281, pl. 44 Santa Clara River to Del Valle fault. strati- graphy and lithology of the Pico formation ......................... 312 Santa Clara River valley, alluvium ___________ 323 fossils in Pico formation _________________ 296-305 structural details ......... 336 terrace deposits ....... 322 Santa Susana fault, description ............. 335, 336 Topanga formation ....................... 283 Santa Susana Mountains, landslides .......... 281 Modelo formation ........................ 287 relation to drainage of area ........ ...- 279 structural details _______________ -- 335—336 Towsley formation, fossils ______________ 293-305 occurrence .............. 287, 288, 289, 290, 291, 293,326, 327, 328, 329,330, 331, 332, 333, 334 stratigraphy and lithology .......... 289—291 Saugus, Calif, population center of area 278 terrace deposits... - - 322 Saugus formation, age ...... 322 deflmtion and subdivision 317 fossils ................. -- 317,319—320, 322 La Placenta Canyon..- ______ 319 relation to Pico formation. . . relation to Towsley formation- stratigraphy and lithology.- structural details ....... 337 structural history. 335 Saxidomua ---------- 310 Scaphander jugularis 300, 315 Schizaster ........ 283 Sch:zothaerua-. 314, 316 nuttallfi --------------------------------- 302, 307 Scope of report ............................... 276 Scripps Canyon, turbidity current features." 325 Sedimentary rocks, fine-grained, Towsley for- mation, Santa Susana Mountains. 289 Sespe formation, description and age .......... 283 geologic history ---------------- 337 relation to Eocene rocks ------------------ 334 relation to Towsley formation ------------ 288 Siliqua sp ------------------------------------- 304 Simi Hills, geologic history ------------------- 338 See also Oak Ridge-Simi Hills uplift ______ Sinum ecopulosum 296 sp ---------------------------------------- 283 Slump structures, turbidity current fea- tures ........................... 332—334 Smith, Patsy B., fossils identified ...... .-.. 288, 295 365 Page Salariella dibitata ------------------------------ 283 peramabiliL 296, 307 Salem perrim. . 304 SD --------- 283 Spatangoid. . - . 283 Spiwla...- 316 hemp“. ..... 302, 308 Spmdulua sp .......... . 283 Stewart, Ralph, fossils identified. 283 quoted ..................... 283 Stratigraphy, depositional provinces. 281—282 Pico formation ............... 309-313 pre-Cretaceous rocks. .. 282 Quaternary system- Tertiary system_-.- _-.- 282-322 Towsley formation. - . .- 289-293, pl. 46 turbidity current features in Tertiary rocks --------------------------- 323-334 Striaterebrum martini. . 300 pedroanum ----- .. 306 Structure, details. 335—337 history ------- 334—335 regional relations. - 334 Surculitea sp .................................. 283 T Tagelus subterea- ---------- 304 Taras politus. . - .......... 283 sp ........................ 283 Tegula aureotmcta. . ------------ 296 gallma ---------------- 296, 316 ligulata. ........ 296, 307, 316 Tellina idae .- 302, 306,307,308 longa ................. 283 soledademis- ---------- 283 Terebra simpler“. ........ 306 Terebratalia occidentalzs. .... 296,307,311 Teredo sp ------------------------------------- 283 322 structural history ......................... 335 Tertiary structural history ................... 334 Tertiary system, age of youngest formations of mapped area ................... 320—322 Eocene series ........................... 282-283 Miocene series .......................... 283—287 Pliocene series .......................... 308—316 turbidity current features ............... 323-334 upper Miocene and lower Pliocene ...... 287—308 upper Pliocene and lower Pleistocene... 317—320 Teztularia sp ........................... .--- 295 Thracia trapezoidea .................... 304 Tick Canyon formation, geologic history.. 338 relation to Mint Canyon formation.. 285 Tindaria sp ----------------------------------- 302 Tiaela stultorum. See Pachydeama cras- aatellofdea _________________________ 302 Topanga formation, description. .. 283—284 geologic history ............. 338 relation to Modelo formation. . 286,287 structural history... 335 Tomatellaea vucavillensis- . 283 Towsley Canyon, description. 279 Towsley formation ....................... 288, 290, 291 Towsley Canyon area, oil occurrence ......... 342 Towsley formation, age ............. .. 320-321 distinction from Modelo formation ...... 288 distribution .................... -- 287-288 --.- .. 360-362 288, 289, 290, 292, 320—321 previous assignment .................... 288—289 relation to Modelo formation. . 287,288, 289, 293 relation to Pico formation ......... 308,311, 312 stratigraphy and lithology-- 289-293, pl. 46 structural history ............. 335 turbidity current features ......... 325, 326, 327, 328, 329, 330, 331, 332, 333, 334 Trachycardium quadragenarium ........ 304, 307, 308 Tritonalia sp ................. 298 Trochammma pacifica ......................... 296 366 Page Trophoayco'n .................................. 320 nodiferum ................................. 306 ocoyana _____ . 306 ruainodoso ............................ 306 Trumbull, E. 1., fossils identified ___________ 296—305 Tunnel area, oil occurrence ___________________ 342 Turbidity current features, angular gragments in sandstone .................... 825—326 current marks ........ 330-332 interrupted gradations ____________________ 325 intraformational breccias _______________ 327—330 irregular contacts ....... 326—327 nature .................................. 323-325 slump structures and convulute bedding ________________________ 332—334 Turbonilla sp _________________________________ 298 Turriculo sp __________________________________ 300 Turria (Bathvtoma) cooperi- 306 Turritella cooperi ___________________ 296, 306, 307, 321 gonostoma hemphilli ..................... 296, 308 sp ________________________________________ 283 INDEX Page U Uvigerina hispido-costata ...................... 295 boom. _ . 288, 295 peregrina. 295, 307, 313, pl. 47 subperigrina ............................ 288, 295 V Valoulineria umucaua _______________________ 288, 295 caliform'cu .............. - .................. 2 88 ornate .................................... 295 Vasquez formation, geologic history ._ 337 Vedder, J. G., fossils identified ............. 296-305 with Woodrlng, W. P., quoted ........... 316 Vegetation ............ 278 Venericardia __________________________________ 283 Vemeulina sp ________________________________ 295 Virgulimz califomiensis, _ 288,295 califor’niensis grandis .................... 288, 295 comma ................................... 288 Volaella sp .................................... 302 Page W Weldon fault ................................. 337 Weldon syncline, Towsley formation _________ 293 Whitney Canyon, oil from Eocene rocks ...... 282 Towsley formation ................. 292, 293 Whitney Canyon area, oil occurrence ......... 344 Whitney Canyon fault ....................... 337 Wildcat wells .................. 347,348,356 Wiley Canyon area, oil occurrence ............ 342 Woodring, W. P., and Vedder, .T. G., quoted. 316 fossils identified ____________________ 296-305, 321 Y Yoldia beringiuna _______ '_ ....... 295, 300, 307, 308, 316 cooperi ____________________________________ 300 scissurota ............................... 309, 315 UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY PROFESSIONAL PAPER 554—1-1 PLATE 44 R. 18 W. R. 17 W. 34°26’ ' 7'" ""BasegHQIser-Del Val Map symbol WUOUU> OZEF‘FR‘HHIEQ’TI 11> B OUJ>N<><€7UOTI 0 DD EE FF GG HH 1 I J] KK LL MM NN 00 PP QQ RR 55 TT UU vv ww xx YY ZZ AAA BBB CCC DDD EEE Foramin'ifera sectio’ " 118°42’ Wells mentioned in text or used in constructing structure sections, but not listed on wildcat table Operator Breckenridge, B. B. Hardison and Stewart do. Humble Oil and Refining Co. do. do. do. do. do. do. Hurley-Kelley Morton and Dolley Newhall Land and Farming Co. Ohio Oil Co. do. Republic Petroleum Corp. Somavia and Yant Southern California Drilling Co. Southern California Petroleum Co. Standard Oil Co. do. do. do. do. do. do. do. do. do. do. do. Sunray Oil Co. do. do. do. do. do. do. do. do. do. do. do. do. do- Texas Co. Trigood Oil Co. Union Oil Co. do. do. do. do. do. do. do. do. York Oil Co. Base map by Topographic Division U. 8. Geological Survey 32' R.16 W. 30’ R. IS W. 118°28' .gi’ 4Q' 38/ 3.17 w. 36’ R.16 w. . . , 34' ’ ..... _' V.‘ ‘y Castaic ....... _ ..... . g. H . ‘ I ..j ‘ _ 4 g , . , 34°26’ EXPLANAT SEDIMENTARY ROCKS ION Qal or reddish-br A Alluvium Clay, silt, sand, and gravel, unconsolidated; gray, light-brown, own Qt Upper Pleistocene and Recent Terrace deposits Clay, silt, sand, and gravel, unconsolidated or poorly con- solidated; gray, light-brown, or reddish—brown QTs ' QTsu Tsr OUATERNARY /\ 118°40’ Well Field Reno 1 Placerita No. 1 De Witt Canyon area of Newhall field No. 3 do. Newhall Corp. 1 Castaic Junction NLF 1 do. NLF 2 do. NLF 3 do. NLF 5 do. NLF 6 do. NLF 8 d0. Orduno 1 Ramona Hilty 1 Newhall Socal 2 Del Valle Vasquez 1 do. Vasquez 13 do. Fink 3 Whitney Canyon area of Newhall field Juanita Placerita Needham 1 Tunnell area of Newhall field Vasquez 4 Del Valle Blair 7 do. C.S.O.W. 2 Pico Canyon area of Newhall field C.S.O.W. 12 do. C.S.O.W. 13 do. C.S.O.W. 32 do. Elsmere 2 Elsmere area of Newhall field Sepulveda 12 Del Valle Sepulveda 20 do. Wiley 4 Wiley Canyon area of Newhall field Wiley 18 do. Wiley 19 do. Wiley 25 do. RSF 1 Newhall-Potrero RSF 9-3 do. RSF 11 do. RSF 22 do. RSF 44 do. RSF 53-5 do. RSF 65-6 do. RSF 66 do. RSF 78 do. RSF 83 do. RSF 89 do. RSF 91 do. RSF 97-7 do. RSF 99 do. Kern 1 Ramona Kinler Del Valle Barnes 1 do. Barnes 2 do. Barnes 3 do. Barnes 4 do. Barnes 7 do. Lincoln 1 do. Lincoln 2 do. Lincoln 16 do. Lincoln 18 do. No. 1 Tunnel area of Newhall field On or near structure section B-B’ A-A’ A—A' E—E’ E—E’ E— , E—E’ E-E’ E- . E— i 34°20’ R.I7 W. 4: /\ 118°36’ TRUE NORTH APPROXIMATE MEAN DECLINATION. 1960 GEOLOGIC MAP OF PART R.16 VII. \/‘l :3 ' «42A . \ . / . OF THE VENTURA BASIN, LOS ANGELES‘ COUNTY, CALIFORNIA 1 V2 118°40’ 118°35’ 118°30’ Art \\ ) L \ Durham 34°25' Winterer 118°40’ 34°20' Durham \/ / 34°2o' 118°35’ 118°30' INDEX MAP SHOWING AREAS MAPPED BY AUTHORS SCALE 1:24 000 O 1MILE CONTOUR INTERVALS 5 AND 25 FEET DATUM IS MEAN SEA LEVEL 34°25’ a]. 34 °20’ h 22' U.) 118°28’ Strike and dip of overturned beds Pliocene and lower Pleistocene A Pliocene A Upper Miocene and lower Pliocene Upper Miocene Eocene Strike and dip of beds Horizontal beds Saugus formation North of San Fernando Pass: brown, reddish—brown, and tan sandstone and conglomerate; reddish—brown mudstone; and greenish-gray sandstone, QTs. South of San Fernando Pass: upper unnamed member, brown, reddish-brown, and tan sandstone and conglomerate, QTsu. Sunshine Ranch member, greenish-gray siltstone with intercalated sandstone and conglomerate, Tsr. Interfingers with upper part of Pico formation Pico formation Light oliveugray and bluish-gray siltstone and fine-grained sandstone, light-brown and gray sandstone and conglomerate, Tp. Dominantly siltstone or very fine grained sandstone, Tps. Dominantly sandstone or conglomerate, Tpc. Upper part interfingers with Saugus formation and lower part with Towsley formation. Mappable lithologic units within the formation do not occur in any fixed stratigraphic position Towsley formation Brown siltstone and mudstone, light—brown and gray sand- stone and conglomerate, Tt. Dominantly siltstone or mud- stone unit, Tts. Dominantly sandstone or conglomerate unit, TtC. Upper part interfingers with Pico formation and lower part with Modelo formation. Mappable lithologic units within the formation do not occur in any fixed stratigraphic position 3 Modelo formation Brown or gray siltstone, mudstone, and siliceous shale with minor amounts of light-brown or gray sandstone and some light-gray limestone. Upper part interfingers with Towsley formation t Tmc Mint Canyon formation Greenish-gray or light-brown siltstone and mudstone; light- brown or gray sandstone and conglomerate. Tuff beds, t Tsc Siltstone, sandstone, and conglomerate IGNEOUS AND METAMORPHIC ROCKS Basement complex Includes schist, gneiss, quartz, and marble; hornblende and biotite diorite gneiss," and plutonic igneous rocks ranging in composition from granite to quartz diorite Geologic boundary or position of mapped bed Dashed where approximately located _iiz_u_ _ _...7.. D . Fault, showing dip Dashed where approximately located or inferred; dotted where concealed; queried where doubtful. U, upthrown side; D, downthrown side L —— “- fl Fault, showing relative movement Dashed where approximately located or inferred; dotted where concealed .4 Thrust fault , Dashed where approximately located or inferred; dotted where concealed. T on upper plate , i--' __ ........ Anticline Showing trace of axial plane and direction of plunge of axis. Dashed where approximately located; dotted where concealed ,_ * ___ ........ Syncline Showing trace of axial plane and direction of plunge of axis. Dashed where approximately located; dotted where concealed +__ Overturned anticline Showing trace of axial plane and direction of dip of limbs. Dashed where approximately located; dotted where concealed __H______. ......... Overturned syncline Showing trace of axial plane and direction of dip of limbs. Dashed where approximately located; dotted where concealed 75 _|_ 2I—‘I2 o 90 _ -+— . Well being drilled Strike of vertlcal beds 4:» Figure .90 on up side of beds Dry hole 6 Producing oil well TERTIARY PRE-TERTIARY Location of measured section ad of the Towsley formatlon Number referred to in text + 5 Apparent dip of beds, Shut~1n 011 well strike undetermined + F24 Abandoned oil well X . . if M f I 1 1 ega OSSI oca 1ty Producing gas well xf35 x Microfossil locality V84 Vertebrate fossil locality ,fP18 fPl ”’7 Location of foraminiferal sec- t10n showmg sample numbers Abandoned oil well converted to water well ; Abandoned oil well converted to water drive well 15’ Dry hole converted to water drive well Well data as of March 1951, Note: See table 10 for data on numbered wells. INTERIOR—GEOLOGICAL SURVEY, WASHINGTON. D. 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V! $1 "‘ E 3 41 "‘ H -- ._. 917 311113 V M M N 0 M 08; .N I M a“ .N 1‘ .M 99 ,N , , . > 13 K . 11 a III 1 44 - , m 3 3 co , , ° M 0‘59 N M e99 N M 0179 N M 318 N ' ‘M 099 N ' M alB-‘N ' 'M asQ'N V H- 1729 HEIdVd WVNOISSHdOHd ‘ : AHAHHS ’IVOIOO'TO'HD HOIHELLNI 31-1.]. :10 lNEIWlHVdHG SELLVLS GELLINH UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY 1 Ridge between Tape and Salt Canyons west of mapped area in sec. 31, T. 4 N., R. 17 W, (pro- jected). and secs. 5 and 6, T. 3 N., R. 17 W. (projected) —‘ Fossil-bearing locality F17 2 Pico Canyon North limb of Pico anticline Base of Towsley formation . FEET —O — 500 --IOOO —1500 3 Towsley Canyon North limb of Pico anticline soaoooaa 'o’uéé o.qpa.999.v‘.’o.o,<9. 9.0 co 0000000009 oqoooyo go o ulqggg 605a cocoa noooag Base of Towsley formation 34'20' ’- PROFESSIONAL PAPER 534-H PLATE 46 118°35’ I EXPLANATION Towsley formation Fault 4 i————l See plate44 also for locations of sections 4 Wiley Canyon North limb of Pico anticline B o°o°o°a° 0° 099309, EXPLANATION LITHOLOGIC SYMBOLS Shale Siltstone North limb of Pico anticline North limb of Oat Mountain Sandstone poDOODOOOOI 0 can Conglomerate 6 Rice Canyon syncline Base of Towsley formation INDEX MAP SHOWING LOCATIONS OF MEASURED SECTIONS 7 Rice Canyon (Ith 0/0 . 81c cor,- ever (on Modelo formation STRATIGRAPHIC SECTIONS IN THE Modelo formation Modelo formation TOWSLEY FORMATION, VENTURA BASIN, LOS ANGELES COUNTY, CALIFORNIA 581734 0 -62 (In pocket) South limb of Oat Mountain synclin‘e V' 1 UNITED STATES DEPARTMENT OF THE INTERIOR R .. GEOLOGICAL SURVEY P OFESSIgfifiEPgPER 554 H Pico Canyon Faunal samples fPl—fP169 EXPLA N ATI O N LITHOLOGIC SYMBOLS Sample numbers; other sam- ples indicated by short lines between numbers Siltstone Two legs of measured section showing amount of overlap Sandstone Solid line Section measured, samples col- lected, and lithology described in detail Dashed line Measured section extended by means of information on geo- logic map Foraminitera correlation Correlation by lithology and interval Correlation between sections made by beginning at one section and tracing a mappab/e lithologic unit as far as possible, offsetting a known stratigraphic distance to another mappable lithologic unit, tracing it as far as posszb/e, and repeating this procedure as many times as necessary until the next section is reached, and then locating the correlation point by compensating for the amount of stratigraphic offset made in tracing mappab/e litho- logic units between the sections 0.0.0U30......OOOOOOOOOOIOOOIOICOO Weldon‘Gavin Divide ' Estimated depth of deposition Faunal samples le—fW51 Based on ecological data on foramin/I'era ofiaobnlflal'o 000069011 a°ll°l° Towsley Canyon Gavin Canyon Faunal samples le—fTGO Faunal samples le—fR33 not 000 O a o a o 0 0 00000 9 D Doanoo Pico formation AI—Saugus formation ____ Towsley formation ESTIMATED OIOIOIOOIOOOIOOOOOICO0.00... Towsley formation —I— Pico formation Gavin Canyon Weldon-Gavin Divide SEA LEVEL Basin of marine deposition 1t— Pico formation —— —— — —— —— Pico Canyon l _ _. __ __ ——Towsley Canyon _______\____s_ ___.' Basin floor CORRELATION A l I. l Towsley formation Near sho e SEA LEVEL ' Basin of marine deposition Basin floor Nonmarir.e deposits SEA LEVEL . .. . Basin floor I I I /? .. ' H l 2 MILES J DIAGRAMMATIC LONGITUDINAL SECTIONS NEAR THE EASTERN END OF THE VENTURA BASIN DURING DEPOSITION OF THE PICO FORMATION l. Basin at time represented by correlation A 2. Basin at time represented by correlation B 3. Basin at time represented by correlation C Towsley formation +Pico formation STRATIGRAPHIC SECTIONS IN THE PICO FORMATION SHOWING POSITIONS OF FORAMINIFERAL SAMPLES VENTURA BASIN, LOS ANGELES COUNTY, CALIFORNIA o 1 2 MILES‘ I I J 581734 0 —62 (In pocket) (3391:3081 111) 29- O VSLISS NOILOEIS NOANVO 001d ‘NOLLVWHOH 001d EIHL NI VHEIJINIWVHOJ .tIO NOILHHIHLSIG 1112198 '8 KSIEd £9 119113 pue suoneounuepl ‘0001' z z 7 II I II fi—I I I 1000!. Z Z z Z A 1 1 1 1 I 1 1 1 I I I 1 1 1 .0009 :. 10009 10009 ~\— NH 10009 s e '53011 91130110er 'saun an K pazoauuoa 918 safiuex uowwoa o swono q 3 q I000p _..s H x ”H 100017 11; pasn Iou mq :1 pue 3 qzoq uo panoId 91911901190 euwelofiqs pue st1 9111 faBuex uowmoa sq; unmm an 01 paumsse 51 uomsodap Joq1dapaq1‘deper aIdwes ewes sq; 111 3931121 ‘ A U I . 10009 77; ~ . 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