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Thornburgh, Hubert Robert A petrographic description of the igneous rocks of the Cisco Buttes, Cisco, California, with a study of the character of the contact relations 1922 BIBLIOGRAPHIC RECORD TARGET University of California at Berkeley Library Master negative storage number: 03-67.58 (national version of the master negative storage number: CU SN03067 .58) GLADIS NUMBER: 1847773373 FORMAT : BK AD:990922/FZB LEVEL:D BlT:am DCF:a (0CSC:4 MOD: FlL:7 UD:030606/PT CP:cau L:eng INT: GPC: BI1O: F1C: CON: ARCV: PC: PD:1922/ REP: CP1: FSI: T1.C: 11: 040 CUScCU 090 SbDISS.THORNBURGH.GEOL 1922 100 1 Thornburgh, Hubert Robert. 245 12 A petrographic description of the igneous rocks of the Cisco Buttes, Cisco, California, with a study of the character of the contact relations 260 $c1922, 300 [vl], 176 leaves : ill., col. maps ;:$c29 cm. 502 Thesis (B.S. in Geology)-University of California, Berkeley, January- May, 1922. 610 20 University of California, Berkeley.$bDept. of Geology and Geophysics$SxDissertations. 690 0 Dissertations, Academic$xUCB$xGeology$y1921-1930 Microfilmed by University of California Library Photographic Service, Berkeley, CA FILMED AND PROCESSED BY LIBRARY PHOTOGRAPHIC SERVICE, UNIVERSITY OF CALIFORNIA, BERKELEY, 94720 DATE: 7/03 REDUCTION: 10 X PM-1 3%:"x4” PHOTOGRAPHIC MICROCOPY TARGET NBS 1010a ANSI/ISO #2 EQUIVALENT 10 Eh = = EA I 22 w fi | | = la 122 =’ pr ke i fu, iF E22 lis pe rg ly gl H 's he oo” — b alt 1 8 i. le le iv. j&. IB: i" sui gt cl tot le 18) 2, [0 16 6 16/2 ulin DISS THORN Bu KGH | Geo L : 192 A EARLT | A PETROGRAPHIC DESCRIPTION of the IGNEOUS ROCKS OF THE CI3CC BUTTES Cisco, California with a study of the CHARACTER OF THE CONTACT RELATICHNS LIBRARY COPY RS. D~.~ Jenuary-liay, 1922 H. R. Thornburgh TABLE OF CONTENTS SUBJECT PAGE Letter of Submittal Acknowledgements 1. Introduction ====-=--e---e=--cemcecs-s-ssoo-o-===- l A. Purposes of thesis B., Accomplishments 1. Benefit derived -2., Conclusions drawn II. Problem statement: Field work . Problem statement -----==--=-e-ee--eenc--m- 2 1. A careful petrographic description 2. Character of contacts B. Field work 1. History of area, showing reasons ----- 2-2 for study 2. Notes and collecticns e. Character of notes taken -------- Z=4 b. Character of collestion ---==----- 4 C. Future work on the are ~-=====-=rece=e-=== 4-5 111. The Area: Geology A. loeation «---===r==sssccceccccsasasnc-ecace. 5 B., TOpOZraphy =======-erssmsscccscssemnmmeeeee. 5 (Index map; and Cisco Area map )---==-=---- 58, C. Geology l. Sediments -==--cec-receccccncccccnncen- 6 2. Intrusives -=-=seccccmcccccncccnccccnnen- 6-7 (Sketeh areal maps: different men) - 6a 2, Structure -==-=ccccccccccacnceccnnn—- 7 IV, The Problem A. 3ubdivisiong -=---cccccccmccnrncnncccrmrer-- 8 B. Collection of data 1. Unpacking and labelling of specimens-- 8 2. Grinding ¢?f sections -»»-=~=ovrr=en==- 9 32 Thin section study ==-=ee-emccccccc-- 9-10 4, 3psecimen drawing ----==-=r-eceeecan-- 10-11 5. Ileasurement of drawings -----======-- 11-12 6. Computation of composition ---»=vn-~~- 12-17 (Mineral table and feldspar diagresm)- 1l4a 7. 3ummery =----=-==ss-cecccecccaccssce-- 17-18 C. Formulation of results l1. Oxide variation curves -~-====-===eme= 18-19 (The curves) =-==-=m-memmececcccccc-een= 18a 2. Percentage contour maps -=====m==m===- 19-22 (The mips ) ==-==--==--s-cmermcmmme—n—— 22a TABLE OF CONTENTS (Continued) (Page) V. Conclusions A. 3ubdivisions -=------eo cmmcmeeeeeoo 22 B. llineral and specimen peculiarities ----- 22-25 C. Magma relationships: contacts l. General ~c-cccecm eee 25 2. Oxide variation curve results ----- 25=27 5. Percentage contour curve results -- 27-29 Yi. VW00AS' Hotes > Cisco Region and bec:zuse this eliminated the time and ex®» specimens for thin section study in the Universi- ; . : ; ; pense necessary in doing the field work, Im addition, it ty of California, : offered a problem along magmatic lines, which was interest- Thanks are also extended to Dr. Louder- | ing. back for a discussion of methods of graphical ACCOMPLISHIERTS rotrayal of rock types; and to Inst 0 p J ypes 7 ngrugtor intrinsic value of the petro- ) graphic descriptions, and the conclusions reached (if Irrespective of the llorse, for valuable criticisms and suggestions 83 19 neihods or precesiure smi nesms OF ex. there is any value in them) the main purposescvofithis Pressing the regulls, thesis have already been accomplished. The work did all that was expected in familiarizing the author with the microscope and its use. It is believed that some facility has been acquired in the methods of mineral iden- tification and in the manipulation of the microscope. Aside from this, there are a few broad facets which have been ascertained concerning the rocks of the Cisco Region; and which have been stated under the heading of Conclusions. Page 2 Page 3 PROBLEM STATENENT: FIELD WORK ( : that there were places in the intrusives where contacts PROBLEM STATEIENT were s0 sharp that they could be covered by the hand, This thesis has two immediate purposes: (I) The ; while in the same region and locality there were con- trographic description of an as- WAN SIS Srsvele Tree P tects which were almost entirely gradational, Both lutonies, and (2) The determi- SoTSee lisevim Eee! types seemed to occur in this small area immediately nation of the character of the contacts between the vari- : abound Cisco. lected portion of the Cisco area; in : Se FOSk ¥Ypes n= wsler P Professor Woods became interested in this phase of im i icini of the Cisco Buttes. Vie Lumsdints vical or un the problem, and after securing the consent of Lindgren, ipti to be found under the Data, while Sa¢ Nescrinviony are made a visit to the locality during the month of July ] 2 th ontects have been explained in the jae CresScier oy Ms 0 2 in 1904 or Ob. The month was spent in 2 general study Sonslasion, of tiiis phase of the problem in this region; in the col- Ee lection of the excellent series of rocks now in posses- RX ! ield work was done by the author. Prof. Rpg of %ae fie 7 = sion of Department of Ceology of the University, =nd in Ww i I i ork and collected the specimens some Pedy S10 ths fre 7 : P the taking of notes which were somewhat fragmentary be- 8g0. A short history of the reasons for this field : : : bluse 2¢ y cause they were to be merely guides to Prof. Woods in work, will explain its peculiarities of character and hence . : : the writing up of the region. the erratic relationship of this thesis to the original 3 _ eo . : = P : The first difficulty which was incountered is shown ork. * ¥ rr - 1 : . - w in Prof, Woods' notes after the preliminary reconnais- m : . Yi > he s The Cisco area is in the east central part of © ; sance: "Unable to map on present scale." (His base map 1 which was mapped for the U.S5.G.5. by Soliaz Mmimngls, ¥ P . was the U.3.G.5. Topographic sheet.) Irrespective of this wi : 4 1900. The Cisco Buttes Waldemar Lindgren shortly after h the entire collection is referred to this map. the contact between the mein Batholithiec intrusive : a Bes CHARACTER OF NOTES 3 K de and the Carboniferous and Jura- BESS Of the Slierrs heva 2 THe notes are quite brief; in facet too brief for i mel re now greatly metamorphosed. SriSy Ssulnamis, Rule sre z y P them to be of much value to any but the original author, w i hi ee, Lindgren came to the conclu-- While working in this ares, 5 in a description of the petrology of the region. Thus 3 i ather remarkable, for the fact Sion knsy the reglon Wes » we have the peculiar situation of a somewhat detailed col- Page 4 lection of rocks referred to a very general location map. This trouble is further aggrevated by the charac- ter of the work done here. The local peculiarities of the rock nave been noticed in great detail in thin sec- tion study, while the original specimen is only hazily - located relatively. This explains one discrepancy and lack of consistancy in the relation of petrographic minuteness of deseription to areal generalties. The method of location of the specimen was to divide the Base llap into a series of squares, which were re- ferred to by number and letter along the sides of the lap A specimen was located by placing a dot in the index gquare and giving its number and letter, CHARACTER OF COLLECTION The collection, as mentioned above, is in excellent condition. Every specimen is quite fresh as regards surface alteration, The suite of rocks is comppésed by about 96 specimens, but some of these have unfortu- nately been lost during transportation and later hand- ling. They have in & measure lost their value, how- ever, because of the lack of an accurate reference map, but as = series of hand specimens they are excellent, FUTURE WORK The region would very easily repay careful study in the future. Some very interesting things could be geen in this series, and no doubt some important con- clusions could be made by one highly trained in petro- graphy. The character of alteration in particular would repay study; as all gradations between quite fresh and quite altered rocks occur here, The schists of the Cisco "Tongue" which extends out into the intru- sives, when studied in relation to the intrusives them- selves, would easily yield important results. However, future work should be based on a more ac- curate location map and on field work done by the one who studies the future collections. THE AREA: GEQIOGY AB mentioned above, Ciseo is in the East Central portion of the Colfax Quadrangle. It is on the line of the Southern Pacific Railroad where it crosses the Sierra levadas in the vicinity of Lake Tahoe. Cisco is but a small mountain village of the typical railroad type. TOPOGRAPHY The general charscter of the topography can be seen from the sketch map of the region. Because of the large contour interval, the rugged character of the topography is not apparent from the map. There are two Césco Buttes; the Horth and South Buttes. These are shown well on the sketch map. Both Buttes are immediately to the west of the station of Cisco. THE CISCO AREA Showing small area covered by the 3howing location and general geology. report; and general topography » 2 0 ZN Ermgran : Gap #* | 0 é 3 | MILES GEOLCGICAL LEGEND Brown: Tongue of metamorphozed sediments Red: Granodiorite of sierra llevada Intrusion lage © GEOLOGY The formations of the region consist of three main divisions; (I) The older Carboniferous sediments of the Blue Canyon Formation, (2) The younger Juratrias sedi- ments of the Sailor Canyon Formation, and (3) The plu- tonies of the Sierra llevada Batholithie intrusion. SEDIMENTS The Blue Canyon Formation consists of fissile clay slates and quartzitic sandstone, with lenses of chert and limestone in this locality. In the vicinity cf the contact with the intrusives this has become metamorphosed by contact action and is ncw chiefly a mica schist, The Sailor Canyon Formation consists of Calcare- ous clay slates with some limestone, It also has suf- fered contact metamorphism, and as it constitutes in the main the "Tongue" of sediments which extends out into the main mass of the intrusives, it has suffered marked con- tact action, which has converted it into mica schists and hornfels. INTRUSIVES However, the intrusives are most important here. The general character of the mass of intrusives, in its central portions, is that of Granodiorite. In the vicin- ity of the contact with the sediments however, border zones are occasionally found. To the e=st of Cisco, on the east side of the Tongue, the granodiorite changes merely to a quartz diorite as a border facies, as is shown by specimens 70 and 72 of this description. On the west, in the vicinity UNIVERS rtp ———e—— ITY OF CALIFORNI LINDGREN'S MAP A 28 29 30 NI o> WOOD3' MAP 30 30 Q R $ N @ 0 0 Q Q THE AUTHOR'S LAP ith = (2, Page 7 of Cisco Buttes, there appear to be quite a variety of basic zones in the vicinity of the contact. This immedi- ate area is the one studied in the main here. Following references to the area, mean this particular side. Lindgren had the zonal arrangment:of the intrusives on this side arranged in the following order as the sediments are approached: Granodiorite, gabbro, grano- dorite with lenses of peridotite next to the contact and on the north fsce of North Cisco Butte. Prof, Woods, in his map, showed the granodiorite grading to gabbro and then to peridotite lens south of the South Butte also. Illy results seem to indicate that this supposed peridotite mass is in reality a body of hornblendite. The map sketches show the various contacts as worked out by the different men. STRUCTURE As to the structure here; the sediments are highly schistose, with schistosity parallel in the main to the stratification; and with both dipping steeply east in a nearly vertical attitude. The intrusive contact is in general almost vertical also, but it differs from the sed- iments in that it strikes slightly east of north while the sediments strike to the west north. THE PROBLEM The study of the problem naturally fell under several different steps. The different steps whieh were meade were ag follows: (A) COLLECTION OF DATA (I) The specimens were unpacked and labelled (2) Thin sections were made of the specimens to be studied. (2) In each section the minerals were determined, textures were worked out, and the peeuliarities of the roek and its name were compiled. (4) A drawing of a portion of the section was made (56) This drawing was accurately measured. (6) From the data obtained, the mineral composi- tion was worked out; and from this, the chemical per- centage was figured. 7) The specimens were written up and a summary for each made. These seven steps produced the data, upon which the conelusions were to rest. ; (B) SYNTHESIS OF RESULTS (I) Oxide variation curves were plotted (2) "Percentage contour maps" were made for each (3 ) General conclusions were drawned. UNPACKING AND LABELLING This work was done in part by the author; tho the majority of it was done by the Department. The press of other business set this work aside to a large ex- tent, so thet delay resulted, whieh prohibited speedy work in preparation of thin sections. GRINDING OF SECTIONS Due to the lack of availability of Prof. Woods’ notes at the time, the majority of the sections had to be made before the localityes of the different speci- mens could be determined. As a result, certain general types of specimens were ground, so as to cover the en- tire area, and a chance taken that some of the specimens 80 chosen would cone within the area to be later studied. The arrival of the notes soon after made selection of specimens possible. Thirty-three sections were made in all; but only nineteen were written up. The remaining fourteen are either non-igneous, or else are igneous rocks lying outside of the area here reported on, In the labelling and grinding of sections, the facilities of the Department were utilized. - THIN SECTION STUDY THis is ofeourse the most important part of the work, The accuracy with whieh the different minerals were determined; and the textures worked out determins to a large extent the validity of the conelusions drawn. The detailed descriptions of each 8pecimen, found on later pages, will speak for themselves as to the time, carefulness, and labor required in working out the see- tions. It was at this time that the second ang third pur- poses of the thesis were sceomplished: that is; familiar- ity with the microscope and its manipulation was ob%ain- ed, and a certain degree of facility in the identifica- tion of minerals wes secured. Page IC This stage of the work absorbed most of the time spent on the thesis. DRAVING As the sections were worked out, drawings were made using the Camera Lucida, Difficulty was experienced in fitting the Camera to the eyepiece ¢f the microscope, but finally a makeshift was rigged up whieh allowed the use of the Camera on the eyepieces available. These drawings were made using the low power ob- Jeetive and the high power eyepiece with one of the lenses removed. The drawings are an attempt to graph- ically and quantitatively show the minerals and textures present. They are thot to be fairly representative. The method of construction was to find a spot in the section which seemed to contain the minerals of the slide in their representative proportions. When this was im- possible, the drawings were partially "idealized" so as to include all of the minerals making up an appreciable percentage of the roek, in of course, their proper pro- portions. The success with whieh representative spots were selected is shown in part by the close agreement in per- centage composition of the other oxides, in two differ- ent specimens which happen to contain the same percent- age of silica. The oxide variation curves bring this point out well. Difficulty was experienced in many cases in trying to represent by a single sharp line the boundary between Pagell Page 12 two minerals which closely resembled each other, This To one experienced in the use of the planimeter, and the difficulty was aggravated by the haziness of the image shortcuts possible in its use, its value to the petro- produced by the forced removal of one of the lenses of grapher is clearly seen, It should be used to = greater . the eyepiece. This was a source of inaccuracy. extent. The beauty of the use of the drawing measured by the MEASURELENT CF DRAWING planimeter is the obsolute accuracy of the results; grant- Several methods have been proposed and used by dif- ed, th:t minerals are properly determined and the sketch ferent authors for the determination of proportions of properly made; and with all of this accuracy but a small mineral constituents in a slide. The two main classes amount of time is required. It thus combines two most of measurements are: (I) Estimation of percentages by desirable features; accurate results in a2 very short time. the use of special ruled eyepieces or mechanical stages The main drawback to its use is the chance that the par- (2) Estimation by the construction of accurate drawings, ticular section chosen will not be representative of the made to scale, usually by the use of the Camera Lucida; slide as a whole. This varies with the judgement of this drawing being later measured by one means Or another. the user. I strongly advocate the second method. It is simple, As to the details of the measurement and computa- and possesses the highest degree of accuracy. The rela- tion of the section, the following is an explanation, tive size of the grains has absolutly no influence on the First, the entire circular field if view of the draw- accuracy of the results, 2s it has in the first case. ing was measured by the polar planimeter. The plani- With a fresh rock showing clearly defined minerals, a meter used on this work was a "Fixed arm" instrument, sketeh made by use of the Camera is & simple matter which measuring Fousre inches directly, and was an ideal type takes very little time. And the sketeh is an absolutely for this class of work. The area was of course the accurate record of the proportions of the minerals present difference between the final and initial readings. The in the particmlar spot sketched. actual area is totally unimportant, as the relative areas After the sketeh is once made, again different authors : are the things sought. S50 the figure representéng the advise different methods of proceedure in its measurement. entire area of the field was obtained. Of all different methods, I believe the use of the | Next, all of the eorystals of the same mineral were planimeter is again the most logical and satisfactory. measured in a similar manner, This figure was set There seems to be a prejudice against its use among geolo- ; down. This process was repeated for all of the minerals gists; probably resulting from the fact that the instru- present in the slide. ment itself is hardly known by them. Page I3 The results for the different minerals were added to- gether, and if the original area did not check to with- in 50, the drawing was remeasured. It is absurdly easy to get an accuracy of 5% with the planimeter. By far the majority of the sections measured checked within 0.1. The drawings shown are approximately 10 square inehes in area; so that the sum total of the individual arees checked within I/20 square inches with the total area measured direetly. This is 2 high degree of accura- ey and can be obtained with no trouble at all. The particular planime¥er used happened to read directly to hundredths of an inch, so that in the oxide percentage ("Composition") sheets, given after the descrip- tion of each specimen, the column headed "Areas" give the area of each mineral in the sketch to hundredths of an ineh. Thus the serpentinized augite of specimen I, con- stitutes 4.16 souare inches in the drawing for that speci- men. COMPUTATION (F COMPOSITION CBrtain assumptions are made when this proceedure is used to get the composition of the rock. These as- sumptions are discussed below, The next step might be to reduce these figures pro- portionately so as to make the total 100, The resul% ing: figures would then express the volume composition of the specimen in terms of the different minerals, However, the volume composition is not the thing which is wanted. The percent composition by weight is the thing desired. If the volume were reduced to a I00% Page basis, the next step would be to multiply the volume <3 8 P Ad oA percentage of the mineral by its Gravity) and the re- Aust, sulting figures obtained for the different minerals would express their relative weights. llevertheless, & step can be eliminated, if the en o 2 2 A a "Areas" are direetly multiplied by the Gravity; without A reducing to a IUU% basis by volume first. The result- ing figures for any two minerals are in the ratio of their reppective weights in the specimen. "Gr" column 3s, Y, 2 hiked i in the Composition sheet gives the gravity of the minerals, and "Wt." column gives the proportionate weights. In the next column these figures are reduced to a I0U% weight basis by simple proportion. This last column, "Wt B", gives the percent by weight of the mineral in the specimen. After the mineral composition of the specimen is obtained, the next step is to try to figure the chemical composition in terms of the oxides present in the rock. To do this, a definite composition must be assign- ed to all niperals whieh appear in appreciable quanti- ties in the rock. It is an accepted facet that many minerals are impure, and that the character and amount of impurity varies from place to place over the surface of the globe. Also, some minerals eontain different elements whieh isomorphously replace each other. In other words, no definite composition can be assigned many minerals. The variable oharaister of the composition however, is nt¢t as serious as it first ap- pears to be. MINERALS Quartz Biotite Magnetite Titanite Tremolite Actinolite Hornblende Engstatite Hypersthene Diopside Diallage Augite Chlinochore Gehlenite Olivene Zoisite Antigorite 310p ALgO03 FepOz FeO Cal 1ig0 K,0 Napg0 HO 100 20 38 56 39 54 49 55 52 50 al 20 40 MINERAL COMPOSITION 19 10 OR +~ 0 CI 18 26 34 16 69 0 OO == OO OO NO O TABLE OF 31 16 el 10 42 I 29 14 14 i2 25 17 20 43 25 I0 4,5 0.5 (T1105 = 41 ) 25 23 11 32 23 21 16 15 2 A 3 HOH HF OH ~ Iv 280 2.70 1 2.60 fy goclase Ande sre 62 0 Labradorie UNIVERSITY OF CAL IFORNIA ~S07 17 par Con Diagram 0 x0 40 position 5S peal 5 Grav: Ys 4. Os) so 60 NAN 0 Lime LE Zod (4 By lowe | ae § Ls \ - | /1 444-444 Page 15 The reason for this is that in the first place the figures obtained for % mineral composition are sub- jeet to seversl sources of error themselves, Certain assumptions are made which may invalidate the accuracy to some extent. The upshot of this is, that if care and judgement are used in selecting analyses of minerals which may be reasonably expected to represent an aver- age; there is a constant accuracy thruout; which is all thet can be hoped for in any proceedure. The average character of the mineral compositions assumed was secured by averaging together several dif- ferent analyses by several different analysts made upon the same mineral from different parts of the world. This data was obtained from Dana's 3ystem of Mineralogy. In averaging these figures, radical extremes were neglected. Hence, the probability is that the figures are fairly re- presentative. It is definitely a fact that there is a consistant degree of accuracy thruout. The accompanying table shows the analyses of these minerals, stated in terms of the nine most important oxides of the earth's erust, which practically completely make up the minerals. This is the table used in the further proceedure, A special sheet has been made for the feld- spars, giving in graphical form the composition and spe- cifie gravity. Now ifca given mineral contains 50% silica, and that mineral occurs to the extent of 30% in the rock, (figures by weight), then that mineral contributes (20) x 650) /% or 156 silica to the rock; and so on for the Page 16 other oxides making up the minerals. The weight of the mineral is simply distributed proportionately over the oxides which make up the mineral. 30 on, for all of the minerals in a rock. Hence, the silica content of a rock is simply the sum of tie silicas contributed by each com=- ponent minersl, This is the method used in the computa- tion of chemical composition of the specimens. In all of these computations, the slide rule was used. However, there is still considerable labor in- volved in the computations. These particular composi- tions have this advantage; they check themselves to a large extent, so that speed is possible. As to the mature of the assumptions mentioned above, they are easily stated. This whole proceedure assumes that the figures obtained by the measurement of the draw- ing are representative of composition of large masses of the rock from which the specimen came in the field. This is not true unless all stages in the securing of the figures have been representative; that is: (I) The hand specimen taken in the field must be representative of the mass as found in place over large areas. (2) The particular chip taken from the specimen, for the construction of the section, must be representas tive of the specimen. (2) The particular sliee of the thin seetion must berepresentitive of the e¢hip; that is, the proportional areas of the different minerals in the section must re- present accurately the proportional volume of the mineral chip. Page 17 (4) The particular area of the sedtion used in the making of the drawing with the Camera Lucida, must contain the minerals in their eorrect proportions. (5) Finally, all of the minersls concerned must be correctly determined, the drawing be correctly made and measured, and the mineral percent composition correctly & rf A Arg Blulul Ti pan Ro figured. It is highly improbably thet all of these conditions are fulfilled; so that it is clearly seen thet there is a consistant accuracy all of the way thru in assuming a definite mineral composition, . Furthermore, the error made by the assumption of the particular mineral composi- tion is decreased, due to the limited occurrence of the mineral in the slide. If the mineral constitutes only 10% of the entire rock, then the error resulting from this assumed composition is only one tenth of that origin- ally made. 50, by the use of the Camera Lueidza, the plani- meter, and the slide rule, a consistantly accurate analysis; both minersl and chemical, can be made. This has been done for each of the nineteen specimens of the thesis. SUMMARY This material, having been written up, was abstract- ed to gain its most importent points, These points were placed in the Summary sheet. This sheet shows the speci- men texture, structure, mineral composition, method of alteration, (by arrows pointing to secondary products), peculiarities, (under remarks); and finally the name. OXIDE Page 18 As mentioned above, this stage completes the col- lection of data; all further work done is & study of the facts collected, and constitutes an snnlysis,( or rather) I a synthesis, of the material at hand. VARIATION CURVES THese curves are an attempt to show graphically how the different. oxides in the different specimens vary in relation to each other. The diagrams show accurately by means of the black straight line segments, and gen- erally by means of the brown smooth curve, how one oxide varies in relation to another thruout the entire nine- teen specimens. These curves are based upon the oxide percentage composition of the several specimens. Since there are nine different oxides in each speeci- men, there are thirty-six different ways in which the oxides may be plotted against each other. However, this is unnecessary. Une series of curves, with each other oxide plotted against silica, is sufficient to bring out the characteristies of the oxide variations thruout the series, As to the method of construction of the curves, each point marked by a small circle in each diagram represents a specimen, The silica percent is taken as the vertical axis. Thus specimen I is found to contain 48% silica and 12% alumina and is placed at thie intersection of these two lines in the diagram, It will be observed that there is absolutely no arrangement of the specimens as to space occurrence; the positions on the eurve being plotted en- tirely independent of all factors except the one of chemi- 0 C22 BPR, ALUMINA - SILICA Ei OXIDE VARIATION Q CURVE - 62 X Q 2X 2% 8 NN aN aN 5 2 XN Str Naa) Ans OS 3 ~ 167, 2 - 147 < “vm LIME -SILICA Q OXIDE VARIATION - 10} 3 - CURVE a A % —- 67 { N - 42 Sei TT 27 : o 2 NR NN Se § 8 Silla (50) Ass 3 ¥ NN x NY [ERRIC OXOF -S/L/cA -19% Q eS ONDE VARIATION COVE ~ OZ 1 S EA 3 “ez N N 2 8 -72 : — = as N Silex (S510) J Als : 8 - 167 - 14% rez 8 FLIROUS ONDE - SULICA > OXIDE VARIATION CVE - 107, Q LV _en QD ol T -47 } -2% NN . 8 Sra) Silica 1 NN N PTAGNESIA - SILICA OXIDE VARIF TION 3 A 3 8 § 0 X X S 3 CURVE - #2 J T N \ QL - 47 3 - 7 s \ L : RN Sis (50) § Ax § : —- x aS 0p SILICA NS QNDE VARIATION CURVE oe H 8 8 Silica (5/4) X Ans R, ! iy LO[ASH — SILICA ONDE VATATION UvE Se RN AN] 0 5 hea (STB) | Ans \ Axls ro Na SI) (Hz <3 oT S. WATER - SILICA NO ONDE VARIATION CURVE “22 QT = ke. = : Silica (574) SAX cal composition, Wheat do these diagrams show? Take the alumina-silica curve. This diagram shows that for a range of from about 50 to 75% silica in a roek of this Ciseo area, the content of alumina is near- ly constant, tho there is apparently a maximum of alumina usually found when the roek contains around 70% silica. It shows that as the rocks of the region become more basic, in the neighborhood of a 44% siliea content, there is a sudden decrease in the alumina content of the roek, and that this alumina content decreases rapidly with increas- ing basicity. This is, I believe, a somewhat unusual faet, and brings to light immediately the fact, that there is something peculiar about the most basic rocks of the region, irrespective of where they occur. It will be noticed all thru the curves that that specimen containing 29% siliea is apparently very erratic. This is fouhd to be specimen 35, and on investigation it is seen that it contains some very peculiar minerals. This at once throws some doubt upon its correctness of character, or else points out that it is a very peculiar type. Hence, in constructing the general eurves, it has been to a large extent ignored. fortunately, it does not come within the area studied. And so on, for the other curves. What they show will be discussed under eonelusions. PERCENTAGE CUNTCUR LAPS S50 far as the author is aware, this scheme of repre- senting graphically the composition in relation to the Page 20 areal distribution, is new. Hence, & measure of origi- nality is elaimed for it. The construction of this mep grew out of an attempt to show in some graphical manner the way in which the various oxides varied across the contact. Because of the meagerness of the data from which the sections would have had to be constructed, it suddenly was seen that & clearer idea of variation could be shown by the contour method than by the section method. As to how the map is constructed, first, an enlarg- ed map of the area to be studied is made. This area is outlined on the general topographic sketch map. Upon this enlargement the positions of the different specimens are plotted, as they occur in the field. A percentage contour map is a contour map of the area in question, in which the contour represent equal- ities in oxide percentage com osition, rather than heights above sea level. The sea level of the map would be those specimens containing none of the oxide in question. In other words, all that is done is to replace heights in feet by composition in percent. A separate mep is required for each oxide. Thus, if the drawing is correct, it should be possi- ble to go into the field, and from a study of location, predict what the, say, silica content is by noting what "gontours" the specimen falls between. As to what the map shows; it is a graphical represen- tation of the variation of the various oxides , with change in position within the intrusive mass. Page 21 Share are some very important properties which this map possesses, and certain limitations which must be kept in mind during its construction. The same limita- tions as to construction hold for this type of map &s hold for any other; the greater the number of points ae- curately located, the greater is the chance that the map will accurately represent the true state of affairs, These particular maps have been constructed on rather slim data: but they ate probably no more misleading than simple profiles would be under the same circumstances. Thus the exact construction of the contour, as shown, is probably open to considerable doubt; yet, it is confi- dently believed that they represent , with a fair degree of accuracy, the way in which the oxides actually vary. Also in their construetion, it must be kept in mind that the forms, are not the same as with ordinary contour maps; since they are not determined by the same processes. To- pographie contour maps show forms which are determined by the drainage features; the fall in surface being in the direction of the @grainaze lines. However, with this kind of a map, the location of the high points, the "hills" are determined by a local excess of that particular oxide in the magma, and the forces which cause variations in components of & magma are complex indeed and in general not related to a single broad faet, such &s a drainage system. Of all of the different types of topographje forms found in nature, probably the one most closely resembling the "magmatic forms" is the glacial type of topography. Page 22 In order to be useful, maps of this type should be constructed from actual chemical analyses of rocks; these rocks being more or less regularly distributed over the area studied. The maps would then represent quite accurate- ly the true state of affairs for the different chemical components, llaps of this sort are ideal for the study of grada- tional contacts, or for the study of areas containing both types of cantauts. They bring out vividly and graphically just how the constituent varies over the area in question. Low, rolling topography points to gradations in composition; while abrupt, precipitous to- pogrephy points to rapid sha instantaneous variation in composition, The first is charaeteristic of gradational contacts, and the second is characteristic of contacts between different types of rocks. The first type would point to differentiation of a single magma; the second to intrusion of one magma by another, A map has been drawn for each oxide shown in the Uxide Variation curves. I think that they are self- explanatory to a large extent, Thus, to sum up; the original problem part of the work was to study the character of the contac¥s in the region. To do this, specimens were taken, sections made and worked out, the composition, both mineral and chemical, was figured, and two sets of drawings made; one showing the relations of one oxide to another, the other showing the variation of a single oxide with re- spect to its position in the field. From this, conclusions have been drawn. SRETCH TOROGRAFNIC MAE 5920 i (Based on thin MAP GEOLOGY section study ) i Metomorphozed Sedien’s LIEN) 27 28 29 30 SILICA ( 310g ) PERCENTAGE CONTOUR MAP A 29 20 ALUMINA (A1,05) PERCENTAGE CONTOUR VAP y - yr { { | { J { I ; | : 1 Tr] cn i : i + + } Emo ITAGE CONTOUR IAPR FERROUS OXIDE LIME ( Ca0) PERCENTAGE CONTOUR PERCENTAGE CONTOUR MAP MAP < 3 x o i HH | Bw I E fr F CA UNIVERSITY O HHH rH | { +5 +4 +4 3 HHH i + { MAGNESIA PERCENTAGE CONTOUR 27 28 29 30 VERAL AID SPECIIEN PECULIARITIES CONCLUSIONS Conclusions to be drawn concerning the rocks of the Cisco area, may be divided into two main groups: (I) Those related to the individual specimens alone: considering each specimen only as a study in petrography, and ignoring entirely its relation to others or its own aresl distribution, (2) Those conclusions reached from a study of the re- lation of one specimen to znother, as to its character and distribution. kiost of the conclusions coming under the first heading have been summed up in the individual summaries for each individual specimen. For convenience; the main points of these will be repeated here. The minor points can be found by glancing thru the individual deseriptions. (I) THere is a very general and pronounced tendency for the feldspars to show zonal growths, and to show grada- tions from the more calcic plagioclases in the nuclei to the varieties containing more soda at the borders. In other words, there has been a gradual shift in conditions while the feldspars were crystellizing, which hes caused the serie: to shift from the anorthite end to the albite end. In a few cases this range is considerable. Practically all of the individuals of this area show this tendency clearly. (2) There is a rather characteristic presence of the rhombic pyroxenes in most of the specimens, this pyroxene Page 24 grading to olivene in places. It is apparent that there is but a slight equilibrium change needed to produce olivene in these immediate rocks; and further, it is seen that this change from rhombie pyroxene to olivene occurs by gradation rather than by sudden jump. (See conclusions below.) (3) With only one or two exceptions, there has been a crystallization of the monoelinie aluminous pyroxene about the rhombic pyroxenes as a nucleus. This seems to be a general rule; elosely resembling the gradations in the feld- spars. There is this difference however, in the latter the gradation was due to isomorphie growth, while in the former it was probably only the crystallization of a crystal about a mineral grain which merely served as a nucleus; as of bio- tite around magnetite. (4) There is a definite series of individuals which points out clearly the stages in the alteration of pyroxene to hornblende. (5) Cceasionally there is shown the growth of amphi- bole as a border zone about a pyroxene center, (6) There is a very characteristic development of fine magnetite (?) rods occuring in oriented sets within the aluminous pyroxenes, and the relative variety of grain magnetite 2c an inclusion in the same pyroxene. (7) There is & characteristic growth of the biotite about large grains of segnetibe. (8) There is a very notable absence of the alkali feldspars in the rocks studied; even in the most types, re- presented by specimens 70 and 72. OXIDE VARIATICN CURVES (9) The fact that most of the quartz present in the specimens shows an apparent biaxial character and a good de- velopment of fracturing points to erushing stresses which have acted on the region since intrusion and solidification, (IC) The presence of tale, serpentine, and chlorite as the common mode of alteration points very strongly to alter- ation by hydrothermal action, The specimens show but very little, if any, alteration which may be ascribed to weather- ing processes. The specimens are remarkably fresh in this respect. Uther more minor conclusions may be found under the individual deseriptions. MAGMA QELATIONSEIPS: CONTACTS THis is the broadest aspect of the problem. It is seen that the rocks of the Cisco region, in the immediate vieinity of the Cisco Buttes, make up & uniform basic series. It will be noted that there is a general absence of the peridotite found by Prof. Woods in the southern part of 3 theeres, and but a limited occurrence of the peridotite to the north, on the north slope of North Cisco Butte. Around the South Butte, the roek is apparently not a peridotite; the evidence of the thin section study seems to point to a hornblendite, rather than a peridotite, with the presence of rhombie pyroxene rather than olivene. These different nomenclatures will be seen on the sketches illustrating areal distribution of the roek types. The alumina silice curve shows: A uniform alumina — i Page 26 content with silica range 46% to 80h, with a slight maximum around 65% - 705: then a sudden drop in alumina content from 465 to 426 silica, with decreasing alumina as silica decreas- es. These excessively low values for alumina are found to be in the hornblendite area to the south of South Butte. It might be remarked in passing, that specimen number 35, (the "eratic”)lies on the approximate continuation of the main curve to the left in practically all of the different graphs. This single speeimen may represent the normal continuance of of the main type of more acid magma, while the sharp breakaway represents some later differentiated intrusiwas. The line-silieca curve shows a similar variation. Irom 70% to 80% there is 2 uniformly low content of lime; this content rises uniformly between 50% and 706, reaching an apparent maximum at about 50% silica, then a gradational decrease with decrease in silica which would apparently take it thru the "erratic" but at 46% silica there is a sudden break and the lime suddenly increases, reaching a second maximum at about 425, from where it appears to straighten out and continue rather uniformly. The sudden break again comes in the specimens from the hornblendite area. The Ferric oxide-silica curve shows & uniform slow rise in iron content with decrease in silica, from 805 to 550% ; then a slow decrease of 3light amount to 465, and then e sudden and rapid rise in iron content continuing to 328%. The ferrous oxide-silica curve is similar in character; but more uniform. Here the iron increases uniformly from nothing at 77% to zbout &h at 48% silica and then more rapid- ly to 427 and again less rapidly from here to 38%. Page 27 The increase in iron is seen tc largely take the place of the decrease in alumina, The magnesia silica curve shows an increase in magnesia by uniform stages from 75% silica to 48% siliea; where a maxi- mum oceurs, then a decline to 465, with a sudden rise to a second maximum at 420, followed by a decline in magnesia from 42% to 28h. The soda, potash and water curves are rather smooth and uniform in character. It appears in all of these curves, that the specimens con- taining between 42% and 46) silica , are of a peculiar charac- ter, and in general of different character than the other speci- mens. This conclusion is bourne out by the percentage con- tour curves. These curves in general, point out the really notable de- gree of accuracy with which compositions can be figured, by use of drawing and planimeter. In several cases, as bouble lines show, two individuals have ha! the same composition in both silica and another oxide, There #s a variation of only a few percent, one way or the other, in all cases. This speaks well for carefulness, judgement of representative areas, and identi- fication of minerals. It is a general check upon the accura- ey of the work as a whole, PERCENTAGE CONTUUR GRAPHS The silica contours show gentle gradations of silica in the northern portion of the area, with increase in silica as gabbro to north and sediments to east are left behind, The contours follow in a general manner the contacts. To the south, there is 2 steep valley in the vicinity of the horn- Page 28 blendite area with a sudden rise again further south; the contours here being transverse to the contact with the sediments. In the northern part, changes are even and uniform: in the southern part, they are sudden and rapid. The northern part appesrs to sug est a silica content deter- mined by distance from contact. The alumina contours seem to show a distribution in all parts, irrespective of the contact, again, there is the gentle gradational change to the north; with the sud- den predipitous change to the south, around the hornblendite area, The calcium curve seems to show a uniform character over most of the area, To the north, the lime content is possibly a funetion of the distance from the contact, while to the south, it is irrespective of contacts. Here again, in the southern portion, there is a sudden variation in con- tent inthe vicinity of the hornblendite, tho not so marked as in the other specimens, The magnesium curve is also quite irrespective of the contacts. It seems to show rather sudden gradations in both north and south areas, in the vieinity of the contaets., In the vicinity of the hornblendite, there is 2 very sud- den increase in magnesia however, which is not found to the north. The ferric iron seems to show in & rather marked manner, the relation to the sediments. As to whether there is any real relationship between the two cannot be told; but its presence is suspected. Here again, the area shows uniform gradations with the exception of the hornblend- Page 29 ite area, where there is 2 very sudden increase in iron con- tent. Ferrous iron seems more independent of the contacts. It shows uniform veriations except for the southern portion, where there are sudden changes in the vieinity of the horn- blendire. It would aspear from these curves, that there is gentle "percentage topography" around the vicinity of Horth Cisco Butte. Jince two different rocks are here in contact the actual contact is very probably gradational. There are sudden complex breaks, or "precipitous pre- centage topography" just south of the South Butte. Here different rocks are also in contact; and .the sudden nature of the variations points to sharp contacts. In particular, the eontact between the hornblendite and the norite of this area, is marked by very sudden changes in magma composition. Thus, by figuring the specimen composition, and by plotting the results graphically, 1 believe I have been able to show that both kinds of contacts exist in the atea; even, gradational contacts, and sudden sharp contects., In spite of the meagerness of the date, the main conclusions 8till have a reasonable foundation of fect. Accurate chemical analyses, plotted in this way, would do much to furnish additional data upon which more definite conglusions could be atated with a sreater degree of confi=- dence. Page 30 2 WOOUDS' NOTES | ( In part only) | : (I) Coarse grained igneous phase from SE face of true summit of Cisco Butte (2) Finer grained basic igneous phase from 3E face of outlying 3W pseudosummit of Cisco Butte (32) Igneous phase from the very summit of South Cisco Butte (22) Igneous phase from the north face of Cisco Butte at 6250 (25) Phase of the peridotite at this same exact snot THE DATA (referring to specimen 23, described as "Peculiar white | : = == eontact body.") (28) Gabbro dicrite phase from 3W progiontory of Southern Cisco Butte (89) Uoarse grained hornblendic feldspar phase, small body in coarse peridotite phase (40-41) Adjacent phases in sm=1l bodies of coarse peridotite phases (42-43) Closely adjacent phases within a few feet of the contact with the older sedimentary formation ( an acid igneous schist a. t. p. (44-45) Closely adjacent phases a few yards from the sedi- mentary contact (66) Phases of gabbro in smell lens between peridotite and sediments (66) Phase of igneous complex in contaet zone between gabbro : and peridotite typical of large bodies; but there are many other variants (69) A loose phase of the peridotite mass from out the square 30 € (70) Normel phase of the granodiorite (?) in situ at big | bend in road E of Cisco Ba . (72) Phase of granodiorite fro: loose boulder nearby 70 (83) Igneous phase at the contact ( with the sediments) SPECIIEN Page Z1 1 e SUMMARY TEXTURE: lledium to fine grained STRUCTURE: lleainly normel order; some diabasic order present CUNPOSITICH ; (1) Mineral: | (Primary) (3econdary) Augite (107) Antigorite (373) Feldspar (16 Chlorite (9%) Biotite (150) llagnetite Hypersthene (15) Hornblende (120) Kaolin (2) Chemical: 5i0g==mmn-- 487 a0 ===-==m- 127 AlsOn- a 125% gl ==m-emea 147, Pes0-----~ 3 K,0 =--=---- 17% Fel “------ 7% N80 -====-=- 17 Hob ——————— 2 REMARKS : Plagi.clase range: Labradorite 45-55 to Oligoclase 70-30 ? Faint red tinge of Augite due to growth about mbic pyroxene? Chlorite a narrow fringe about Augite secondary hornblende, irregular similar occurrence. Numerous magnetite rod inclusions in the Augite Veins of Chlorite cut all of tie individuals i — pre gr fd —— — COPD No Nt Set ect Sa St er ® VALE: AUGITE BICOTITE HCRNBLENDE DICRITE OX RX NX X NO PRC IMEN 1 LEGEND Feldspar Lugite Augite altering to Serpentine Biotite Chlarite Altered Feldspar SJecondary Hornblende Rhombic Pyroxene Page 23 SPEC IMEN 1. TEXTURE A... S——————————— This slide shows a holocrystalline phane-ocrystalline medium to fine grained texture. Locally it is ophiftic diabasic, a few of the feldspars being poikilitically in- cluded in the pyroxene and its alteration products. The biotite also notably included poikilitieally both pyroxene and feldspar. In one or two cases, hornblende included pyroxene and feldspar, tho the primary char:zcter of the hornblende is doubtful. The normal order of separation of Rosenbusch is not followed, part of the feldspar at least crystallizing simaltaneously with the biotite and the pyroxene. PRIMARY MINERALS Feldspar is present, tho to somewhat limited extent. It was found to be biaxial, and with smell two V. The sign of this individusl was foudd to be positive. On an individ- nal showing a good Bxg figure in convergent light, a 300° extinction angle between the fast direction and the 010 cleavage was found. This indigates a I=bradorite of about 45-55 eomposition., On another individual,showing an optic axial figure, 2V was found to be close to 90°, making the sign uncertain, -This showed a 62° extinction angle, anf indicates an Andesine of about 60-40 composition. By the use of the "Statistical method" of maximum extinction, a 15° extinction was found, which corresponds to an Cligo- clase of about 70-30 composition. The habit of the segond individual was equant to irregular in outline, while the habit 0f the third was prismatic and tabular, showing abundant albite striations. The cleavage of the feldspsr was not apparent. In reflected light the individuals =2ppeared an icy white, while in fransmitted light they were colorless. There seems to be a tendency for distinet prismatic habit, tho this is somewhat curtailed by the limited room for crystallization, A few of the individuals show a good lath shaped habit, and these in particular show the twinning after the albite law; but the majority of the individuals are equant te intersticial in habit and mode of occurrence, Those individuals which ha as poikilitically included crystals are of equant habit, for the Host part. The feld- spars as a whole make up but a minor portion of the rock. Polysynthetic albite twinning is common in the lath shaped individuals, and is occasionally so wven with the equant individuals, tho the common rule of twinning in the latter is the presence of only a few broad albite lemellae. The rock seems to be on the boundary line &s far as texture goes, between that of the normal order and that of the diabasic order, siice both types of feldspsr are seen to oceur. Possibly 1/7 of the individuals show szlteration by kaolinization, these masses appear snowy white and translucent in reflected light 2nd a dirty gray in transmitted light. Feldspar is small in occureence. No distinct tyve of sssoce- iation is visible. Monoclinic pyroxene, probably augite, is the most abundant constituent of the rock, It shows high relief, high double refractimn, very good prismatic cleavaze well developed in few but very sharp cleavage lines, and i: the end sections the 88° cleavage is well brought out. The mineral is a very pale watery greenish in color. Besides the prismatic cleavage, there is a strong tendency to part at an angle of about 70° to the cleavage. Locally this parting is very distinct. When tested in convergent light, a biaxial figure was obtained, which proved to be positive when tested with the quartz wedge. 2V was smell. Extincti n angles were measured between the slow direction and the prismatic cleavage, and were found to range ( in approximately side sections) from 40° to 559 This points to a typical Augite aB the particular pyroxene. The general habit is equant and pseudo-hexagonal in end sectians, and long prismatic in side sections. The end sections seem to show the best automprphism, tho the extreme baisc character of the rock and the consequent abundance of this particular mineral makes for hypautomorphic outlines in general. Notwithstand- ing this fact, there are regular outlines to the individuals in zeneral. The color is a pale greenish blue, occasion- ally a non-pleochroic very faint reddish tinge (iton con- tent?). The end sectiins show very well indedd, the augite method of twinning, the lamellae locally branching out and fadipg away. As to primary inclusions, magnetite in definite- ly primary and unaltered pyroxene is rare, tho a few notable grains occur locally. By far most of the pyroxene is altered Page 35 when it contains magnetite; the magnetite here being in 8trings and seams of fine granular magnetite; mainly par- allel to the elongatiin of the fibres and to the principal cleavage. A few of the augite cyystals show much larger included grains of macnetite, tho this is relatively rare, A second alteration product is secondary hornblende, w.ich occurs as flakes and spots of distinctly darker color and very pronounced pleochroism, with extinctian angles ranging from 0° to 15°, These flakes are in the main bounded by sharp cleavage cracks, and in the end sections are very clearly seen; the transition from pyroxene to amphibole cleavage being very strikingly brought out. The hornblende is characteiized by a distinetly bluish tinge, and by a blue- green pleochroism very marked in character snd intensity. The occurrence is mainly as long flakes in the main mass of the augite, but quite charscteristically it also occurs as a very irregular broad border around the augite crystals. This border is quite irregular in width, and is entirely absent in placed, giving the secondary hornblende a patched appearance. The third method of alteration is to chlorite which occurs as a narrow persistant band or fringe around most of the individuals. The mineral called chlorite may include small patches of both antigorite and secondary horn- blende, since all have practical ly the same color and occur toeally in quite 8 complex mixture of minerals. Locally the augite conteins minute rods of magnetite which seem to be oriented into two sets; the rods of one set being parallel to (1) Page 37 each other and to the prismatic cleavage; while the other set 15 inclined to the first at a high angle. This method of inclusion is of only local occurrence however, and is not nearly so abundant in this individual as with some of the other rocks of this suite. Rhombie pyroxene, probably hypersthene, is present to a very limited amount. The sign test on the individual was indistinct. It had a peculiar fracture, and a zood to poor cleavage of rectangular character. The fracture made the minerzl resemble olivene in general appearence, It has & high index of rafraction.. It shows the beginnings of & somewhat mesh-like alteration structure. Its main dis- tinguishing identifying mark however, is its rose-blue pleochroism, which is so distinctive for the rhombic pyrox- enes. This pleochroismis very chi racteristic for the in- dividual, Of the one main crystal, and the three of four smell ones, all seem to be embedded in an altered mess of very highly confused aggregates of minute flakes ang scales of highly doubly refracting minerals, containing secondary magnetite abundantly in fine grained locally abundant dense aggregates. The primary mineral contained a few large grains of primary magnetite ineluded in it. It is possible that the embedding mass of flakes is the remnant of a surrounding augite individual, since alteration to parallel (fibres) or bastite would be expected if the embedding mesg were Lo be derived from the rhombic pyrosmene itself. This is a pos=- sibility on}y, however. Biotite is generally quite =bundant. It shows the basal cleavage very perfectly =nd abundantly. The cleavage lines are not continuous, but are in the main very distinct and sharp gashed, all of the cashes being very clearly par- allel to each other. The pleochroism is very intense and characteristic, Extineticn is parallel. The mineral shows 8 light honey-yellow normal to the c2eavage, while it is a deep golden brown parallel to the ckeavage; the absorption being almost complete in this direction. The mein mass of The biotite shows this brownish tinge, but a few of the individuals show with somewhat greener tinces, =nd one or tvo are very distinctly and definitely green in color, When the stage is turned so there is maximum absorption in the biotite, the individual seems to have a very characteristic crumpled wayyssilky appearance, which is almost enough of it- self tc determine the mineral. The main mass of the bictite is brown, but some @f it is green. The general occurrence is as small tabular shreads and flaked prisms. of irregular outline; a few poikilitically including both altered pyroxene and altered feldspar. The individuals are extinsively dis- tributed, tho small in size. The biotite here includes but little if any magnetite, and herein differs from most of the specimens in this suite. It is associated with the mono- clinic pyroxene, which seems to be about contemporaneous with it in crystallization. ALTERATICN The main type of alteration is very notable, and is that of the pyroxené to antigorite and magnetite. About half of these altered masses resemble bastite in appearance, being made up of parallel aggregates of highly doubly refracting fibres, with streams of secondary magnetite along the seams. The other half consists of confused non-parallel aggregates of about the same apnearanee as to fineness of fibre and double refractian. This has been called antigorite after pyroxene. Another typicel type of alteration is of the pyroxene to secondary hornblende, This is next in abundance to serpcm- tinization, It is quite noticeable. Ilost of the hornblende, if not all of it, has been formed by this process of alteration. The shreads show a blue-green pleochroism, ahd an extinction angle of 129-14%, The distinct blue of the hornblende is the distinguishing feature. This method of alteration is not s0 complete as is the first. A third methcd is from pyrox- ene to chlorite. This is still more limited in character. As mentioned sbove, the mass of flakes (anticorite?) surrounding the enstatite may be derived by its alteration, but possibly it may be derived from a once-surrounding border of augite to the enstatite. Approximately half of the feldspar has been altered by kaolinization. | Lagtly, there are some veins of chlorite which cut across the feldspars aud also acrossithe other individuals, occasion- ally cutting even these altered masses of antigorite. SPECIIEN I We Oxide percentages wt. i liineral Areag Grd Wt. | 5 310, [A1:0,|Fe;0, | FeO [Cal] igh £0 [Ne20[H20 Serpentinized AUGITE 416 3.3) 1372] 26.8] 18.4 | 1.8 243] 7.8] B45 0.4 BIOTITE 192] 2/9Q 556] 14.9 6.4 2.8 2.4 0,7 10,1] 1.5]0,7 (0.1 FELDSPAR 220 | 2.64 585] 15.7 9.4 38 0.3 0.9] 0,310.3 |1.4 Oligoclase 70-20 Fresh------ 150 Altered----- 70 HURIVBLENDE 136| B.8 435) 11.79 42.6 | I.2 0.8 19 | 1.4) 1.310.2 [0.2 |O.1 (Secondary?) CHICRITE 182 2.7 329 8.8 2.01 1.6 32 1.1 AUGITE 114 3.2] 376] 10.1 5.0 0.5 0,9 | 2.0({ 1.8 0,1 HYPER3ITHENE 22 | 3.45 76 2.0 X.o0 Ou. : 0.41 0.1] 0.4 279 |ILW.CHl 47,8 | 11.8 2.5 ree FT 8 TET. (IT. Totgl: 100.0 Adjusted: 48% | 12% | #5 wl j12%) 145) 15 (1% | 2% 0% o3sg SPECIMEN 2 Page 41 A ——— SULMARY TEXTURE: liedium even grained granitic STRUCTURE: Normal order; one or two diabasic ophitic areas CUMPOSITICN : (1) Mineral: (Primary) (secondary) Feldspar (350) ——————=Kaolin Augite (zB) Hornblende Hornblende (115) Chlorite (47%) Biotite (117) llagnetite Antigorite (2) Chemical: 310, ~=--~-~ 50% Cal -==---- 115 AlgBg---m--- 147, MgO =------ -10% FeoOp-=n--~-- 47 Ko0 =-=-==- 15 Feb =------- 6 N8s0 ~----e- = HpO0 -=----- 1% REMARKS (1) Plagioclase range: Andesine 60-40 to Cligoclase 70-20 (£) Undulatory extinetion in feldspars present but not marked. (2) Feldspars contain some inclusions (4) Chlorite veinlets thru feldspars ‘etermined by cleavige ahd boundaries (5) Thread of isotropic material along chore of chlorite veinlets (6) Augite shows parting tendency parsllel to (100) (7) Narrow fringe of fibrous Chlorite end Antigorite about the Augites (8) Augites cut by chlorite veinlets and filled with flaked alteration products. (9) Widespread magnetite rod inclusions in Augite (10) Zornblende shows speckled extinction due to =slteration (11) Biotite is in Xenomorphic aggregates. AUCITE BICOTITE HOXNBLENDE DICRITE 00Ce®®0O SPECIMEN LEGEND Feldspar Augite Biotite Hormblende Chlorite Kaolinized Feldspar lagnetite Page 42 Page 43 SPECI MEN 2 shaded appearance when seen in ordinary light. But these TEXTURE inclusions of alteration produets do not alter the sharp This specimen is holocrystallline phanerocrystalline complete character of the extimetion. Approximately one- medium even grained granitic in texture. Locally one or fifth of the feldspar is keolinized, this zone of alter- two augite individuals show the diabasic ophitic texture, ation being charscteristically in the very center apparent- where they include small feldspar individuals. As a | ly of the crystal. The feldspars show sbundant fractures general rule, the normal order of separation is followed. and seams which have been filled with chlorite; the seams The augite individuals are slightly larger than the other | appearing to follow the boundaries of the crystals, and constituents, being about one and one-half times as large | also the direction of best cleavage. Under crossed nicols as the feldspar crystals. be these chloritic seams are seen to be nade uf of fimecgrains and very short flakes of chlorite; but the most remarkable PRIMARY I'INERALS | and noticeable thing is the fact that there seens to be a With the feldspar present, cleavage is localily well central core, or thread of isotro ic material along the cen- developed, ti0 as & rule this is generally not the case. ( ter of these seams. These were examined to see if they might The habit of the individuals is mainly, (approximately not be cracks filled with canada balsam, but they did not 4/5) lathshaped to prismatic, with the ends interrupted a i i seem to be different in ordinary light from the resé of the and jagged. The remaining portion is in the main somewhat vein material. The feldspar is seen to contain most of the intersticial in habit. Broad albite lamellae is the gen- grains and rods of apatite also, The usual rule of twinning eral rule of twinning; tho a few of the individuals show was a few broad lamellae of albite striations; snd these abundant polysynthetic twinning. The polysynthetic type when tested by the Method of "Maximum Extinction" showed of twinning is seen best on those individuals showing the : | angles such as ; 0°, 49 0° 20° 20° 10°, OF, 4°, g0 | lath-shape. Zonal growths are not apparent in the feld- This gives a maximum of around 20°, and points tu an spars, unless the individuals are seen between crossed Andesine of 60-40 composition. A few individuals were tested nicols and near the extinction positicn; where the zonal ; in convergent light, and two which showed a good optic axis character is shown by undulatory extinetion., This undulatory | figure and angle of 2V of around 90°, showdd a 10° extinction. extinction is present, but is marked only in 2 few in- The sign was possibly on the plus side of the 90° 2Vv, Dhis dividuals. The feldspar shows innumerable inclusions of ( corresponds to an Oligoclase andesine of 70-30 composition. fine zrains, flakes, and specks, giving it a stippled and (2) Page 45 Augite is present. It is distinctly automorphic in outline. In convergent iigzht, the value of 2V was secn to be about 60°; the sign of the mineral being positive. The double refraction and the relief were hich, and the color pale, pointing to a pyroxene or amphibole. There was a peculiar tendency for parting parallel to(l00), as was shown by the very distinct straight fractures along this direc- tion, The angle between (ec) and the cleava-e, vhen measured, wes; 20°, 40°, 45°, 50°, 45°, This makes the pyroxene Augite., The individuals were definitely automorphic in out- line, the of course there were loecdl irregularities around the borders. The individuals were showt and long prismatic in habit, and quite irregular in size. There was a very faint yellowish greenish tinge and very faint pleochroism, almost invisible. The larger individuals locally ophitically in- clude small feldspar grains in one or two cases. End sections seem to be common in the rock. These show the 88° cleavae very well, and also the tendency to part parallel to (100). There is commonly & narrow, continuous fringe of chlorite (possibly some antisorite) about the entire individuals, same of this material being quite fibrous. All of the augite individuals show speckled extinction, due to alteration pro- ducts. Veins of chlorite cutting across and passing thru the individuals are quite corion, There seem to be red flakes and sceles in the cleavage planes of the augite. There is a noticeable beginning of alteration of some of the augite to secondary hornblende, as is shown by the deeper color, the Page 46 marked greater cleavage angle, and the pronounced pleochroism, This type of alteration is best seen in the end sections, hhere the prismatic cleavage is so well exposed; tho it is 2l1so visible in the side sections, where the secondary hornblende appears as flakes and shreads in the augite. There are irregular patches of hornblende around the sgédes of the augite individuals. Rod inclusions, arrange8 in the usual characteristic two sets, are also characteristically pres- ent and widespread, tho they are not thickly accumulated except in three or four cases, which are quite distinct and characteristic. These rods are probably macnetite, one set being parallel to the prismatic cleavage, end the other at an angle to the first. A few of the individuals are altered. completely to a mass of irregular dendritic secon- dary magnetite arranged in dense aggregateg, these being surrounded by and embedded in a radiating =nd confused ag- gregate of doubly refracting flakes of high double refraction. These altered ing#ividuals show the characteristic greenish fringe of chlorite encircling them, Primary magnetite seems to be rarely present. Hornblende is present, and closely resembles the augite in color and index of refraction. It is distin- guished from the augite however, by its pleochrcic character and slightly smaller individual size. A few of the in- dividuals are present in end section, and these show the 1240 cleavage wery well, The pleochroism is yellow to pale green, The common habit is small stout prismetic and guite automorphic. All of the individuals show speckled extinc- tion. They seem to be passing into chlorite locally. It would be di¥ficult to state whether the horblende is primaty or secondary, but the best probability is that it is primary; because of the charscteristically smaller size of the in- dividuals showing the hornblende characters. There is con- sistantly shown an extinction sn2le measured on side sections of from 0° to 10°, Cleavage is marked and perfect. Ch, is negative and Chy positive. 2V could not be measured. Both index and double refraction were found to be high. The creater absorption was seen tv be roughly parallel to the cleavage. The hornblende is apparently embedded mainly in the feldspar, which accounts for its automorphic appearance, All of the individuals show highly speckled extinctian. In ordinary light, they resemble the chlorite in (he seams and veins thruout the feldspar, except for the pleochroisnp, which is locally rarked, tho faint in color. Cn close in- spection the hornblende is seen to possess very good cleavage. The magnetite of the rock is closely associated with these individuals of hornblende. Biotite is also present. It is distinctly red’'ish in e¢olor, The pleoch-oism and double refraction are well seen, Parallel extinction, with greatest ( almost complete) ab- sorption parallel to the cleavage is characteiistic. The index of refraction seems’ to be high, The individuals are not automorohic in outline, but seem to be mostly xeno- morphic aggregates, small, but widely scattered thruout the rock. Jocaily they seem to take the place of the feldppar Page 47 and are here secn to be the matrix in which the augite is embedded, It is thus the poikilitic host for pyroxene and amphibole, being intersticial in character. The relation is not truly poikilitic however, for the individuals which seem to make up the host of biotite are seen not to be one con- tinuous individual, but an aggregate of different individuals. It is typically asscciated with the ferromagnesians., Cleav~- age is present. llagnetite is also present, Its mode of occurrence is as small grains, mostly in the augite. A very slight amount of it seems to be primary, most of it appearing as irregualsr dendritic aggregates, which are most probably secondary in character. Chlotite veinlets and seams are the most characteristic alteration product of the rock, These are marked and common. They seem to follow the lines of cleavage where they cut across the feldspars, and commonly they follow the boundaries of the individuals. The alteration of pyroxene to masses o€ chlorite and secondary hornblende is next in abundance. A few of the individuals of pyroxene have been completely replaced by magnetite and antigorite, and these show the narrow fringe of chlorite around the border quite characteristiecally. The feldspar is but little altered. As usual, the augite is the most sensitive mineral tow- ard alteration, SPECIMEN 2 Oxide percentages Vt o |B - llineral Area Cr,| Wt.| % [5105 |A1,0.| Pe 0, | FeO| CaO] ligO[Ko0 | Na20|H20 FELD3PAR Andesine 65-35 470 2.67 1255( 34,7] 20,5 | B,7 | 0.5 2.7 | 0.8]0,5 2,8 Fresh---454 Altered--16 AUGITE 416) 3.2] 13712) 38.04 I9.,0 | 1.9 3447.6 [5.7 0.4 BICTITE 129 2,99 403 11.lp 4.9] 2.1) 1.8 | 0.610,1 11,1 {0.50.1 HCRNBLENDE (Primvary--89( 129) Z2.2] ¢13( 1.41 4.4] 1.1] 0.8 | 1.81.4 11.3|0.,2 10,2 (0. Jecondary40 CHLORITE BO 2,7] 138] 3.8] 1.3 | 0.7 1.4 0.5 MAGNETITE 71 Bed 28 1.0 Cal [| 0.3 | ICC OI", T [TZ ET 2.8 [G.I IT BI IC. BIT. 2 (ET IT.0 Tota 101.6 Adjysted: 506 | 14% 4% 6h (115 (10% { 18 | 3% | 16 6% essed NAME: SPECIMEN Ie SUITIARY TEXTURE: Uneven medium to fine grained granitic STRUCTURE: Normal order of separation. COMPOSITION : (I) Mineral; (Primary) (Secondary) Feldspar (46h) = Kaolin Augite (265) = Chlorite (II}) Biotite (50) Antigorite Apatite llagnetite Enstatite (0.3%) (2) Chemical: 310p==m=mmmm= 51% Caf-=-=mmnn- 11% AB, remem 16 Eg0sneevcn-n 107 Fe50z==---==-- 2h KoO--mmmmmmm 0% Fel-=-mmmmeu= 4% Nao0==mm-mmm- 3% HoQ~mm-mmmmm 2% REI’ARKS : (I) Plagioclase range: Labradorite 45 - 55 to Oligoclase 80 - 20. (2) Undulatory extinction distinct and marked (2) linerals frectured: chlorite veins thru fresh rock: both indicate crushing stresses (4) Enstatite occurs es a mucleus szbout which augite has grown (5) Granular magnetite, but especially rod magnetite, included in the augite in two sets (6) Rod inelusions occasionally found in zones of growth only (7) An alteration fringe about augite (8) Biotite occurs as sbundant irregular distributed small individuals (9) Biotite the host for large magnetite grains (IC) Roek notably fresh AUGITE BICTITE DIOSITE Page 51 SPEC I MEN LEGEND Feldspar Augite Biotite Chlotite Enstatite Ilagnetite Page be SPECINEN 12 URE TEX This slide shows a holocrystalline phanerocrystalline uneven medium to fine grained granitic texture. The normal order of separation is followed. The pyroxenes are large and quite automorohic, while the feldspars, tho gutomorphic to some extent, are much less s@ than the pyroxene. The feldspars are also of much smaller size than the pyroxene in- dividuals. PRIIARY MIN RALS FPeldspar constitutes about half of the rock. In the complete absense of cuartz it is the entire colorless constituent of the rock. Low double refraction, low in- dex of refraction. cleavage, hiaxial character, 8ll point to a feldsper. Then optic axial figures ( convergent light) were tested, they were found to be in the main positive, tho a few showed negative sigh. However, 8ll showed a very large 2¥V, epproaching 90° in size. Extinction angles measured on these individuals were 209, 18°, 25° , and 289; showing quite a variation in composition. In the main these angles point to an .ndesine around 65-35 in composition, By the method of equal extinctiun, the angle between the cleavage and the (a) direction was found to vary as: 0°, 20, 30°, 20°, 15°, and 0°, These point to a variation from Cligocalse 80-20 to Labradorite 45-55. The feldspars con- stitute the "base" in which the ferromagnesians are embedded, There are two main types of cccurrence. One is short lathshaped (12) Page 53 to prismatic, while the other is intersticial, xenomorphiec, or equant. The minute veinlets and seams of secondary minerals complicate the appearance of the habit of the feldspar as seen between crossed nicols. In general the individuals are approximately half the size of the pyroxenes. The lath shaped individuals show the albite striations usuallv broad and simple, tho occasionglly nolysynthetic and fine. Carlsbad twinning is very rarely present. The xenomorphiec individuals show the albite twinning also, tho only very simply. The perfect cleavage is quite apparent in the in- dividuals. As a general rule, the extinetion is undulatory, the inner and outer portions of the same individual differ- ino occasionally as much as 20° in extinction angle. Some of the crystals z&8re bent and fractured, especially where they are cut by the secondary veinlets. This fracturing is an indication of crushing stresses, as is the presence of distinct veinlets thruout a rock otherwise hardly altered at all. The feldspar is quite fresh, only the beginnings of kaolinization being visible. Augite is present next in abundance. The index and relief are high, the cleavege perfect and distinet fracturing almost resembling cleavage is abundant. The mineral is & very pale whitish green and is not pleochroic. @n an inclined figure the mineras was found to be biaxial, 2V around 60° or better, and the extinction ancle a maximum of 45°. Some angles measured were 450, 45°, 259, 359, 40°, and 21°. The maximum angle is thus around 45°, so that the mineral is possibly & diallage in part, or an augite close to a diallage in com- position, The habit is from equant to distinctly prismatic, tho in detail the outline is irregular. The cleavage, tho perfect, is usually in but a few lines, but these few cleav- age lines sre very sharp and clear. There seems to be a second less perfect cleavage or good fracture, being more perfect when it cwvosses the first at & low angle, and more of a fracture at high angles. The color is a pale green. There are a few twinning lamellae present. The extinction is in general rather sharp buththere are also many minute scales of differing extinction angle present, which gives to the main individual a slightly spotted appearance, This is very probably due to the beginning of alteration Ato secondary hornblende. Vhere the individuals re notably altered, there: is a highly speckled extinction, tho in general the extinction is parallel in the different individuals. Inclusions dre distinctive and of several kinds. One variety is very dis- tfinctive, and is & center of enstatite, abcut which the mineral has gwown. However, this is but a rare occurrence, being found in only three or four individuals. Another in- clusion is the presence of small aggregates of small granular grains of magnetite, these being occasionally replaced by a few larger grains. However, the most charscteristic in- clusion is very fine needle-likemagnetite, the minute needles or rods being parallel to the prismatic cleavage. There is occasionally another set of these rods, 211 parallel to each other, and i clined to the first set. These are very fine in size, and very numerous in occurrence. They are generally scattered thruout the mass of the crystal in which they occur, tho occasionally they are limited to a narrow zone or band having the same crystal-like form as the individual in which they are embedded, and suggesting a zonal band or growth. Occasionally they occur as very fine short needles, almost submicroscopic in size, irregularly scattered tihruout the crystal, giving it a shaded stippled appearance when seen with the low power. Almost evepy grain is fringed with a narrow zone waich seems to be an alteration product of some sort, probably chlorite and antigorite mixed. Rarely the entire éndividual is replaced. When it is, the resulting product shows practically parallel extinction =nd a very fine fibrous appearance. lo convergent light figure was obtainable on these small individuals, the result being merely an indistinct blur. The alteration product found in the fringes is generally granular or short flaky. It differs from the border to the biotite, these being more shreaded and fibrous, The fracture sesms throut the augite often contain brown flakes, especially in the vicinity of the magnetite grains, Locally, bictite occurs as a fringe for the augite. Augite is associated with both biotite and magnetite. Biotite is noticeably present. Its usualy distinctive optical properties were observed, the bleochroism of honey yellow to deep brown, parallel extinction and perfect cleavage being quite distinetive., The ususl mode of oceurrence is as irregular, shreaded small individuals, abundantl- scattered thruout the area of the rock. Ione of the individuals are large. The color is a deep brown. A few of the Chlorite (12) | Page 56 &~ individuals, so called, mey be in reality a green biotite. This possibility is strensthened by the apparentlyomere pronounced pleochroism in some of the blue individuals. The biotite is the host for large grains of magnetite. Cecasionally the biotite is altered to orobhably chlorite, which occurs as a deep green, pleochroic fringe around the biotite. It is associated with the magnetite and the auzite, and is apparently xenomorphic towards the latter. % Apatite is noticeably present. It shows parallel extinction, index higher than for feldspar, and is colorless and clear, being not at all altered, The usual mode of oceurrence is as fine grains and shreads, and as needles with very long gevelopment. These are scattered sparingly thruout the mass of the rock. They can be scen only under the intermediate power. A rhombic pyroxene, enstatite, i: also sparingly present. It is biaxial positive, showing parallel extinction. The index is greate: than for the monoclinic pyroxene. It is a light green in color parallel to the best cleavage, snd & faint pink normal to thid direction. It was recognized entirely by its pinkish pleochroism and its characteristic occurrence =s 2 neucleus about which the monoclinic pyrox- ene has grown, This tatter fact seems to be quite consist- ant for all of the individuals where rhombic pyroxene is sgerce,i.e., it occurs in these cases as a neucleus about wnich the monoclinic pyroxene has grown. Only twee small individuals were found in the rock, both being neuclei. (12) Page 57 ALTERATION Chlorite scems to be the most charscteristic mineral produced by alteration. It is sorewhat abundant. The rain mode of occurrence is as a fringe about the augite. ILoeally chlorite, ( or antigorite) completely replaces the latter; this is seen to be the case especially in the ind iviSunls Bhowing aggregates of granular magnetite. It also seems to Occur more rarely as a pseudomorphiafter biotite; it being e& deep bluish greeh here. The most typical occurrence is as irregular patches and veinlets thruout the mein mass of the rock, especially in the feldspar. The individuals show low double refraction, =n index around that for pyroxene (2?) and a bluish green(perallel to elongation) light greenish yellow(normel to elongation) pleochroism. Ch, could hot be tested reliably. Thus chlorite is the most characteristic alteration product. But the beginnings of alteration of the augite are visible. Furthermore, this is not the usual mode of alter- ation for specimens in this suite, which is to hornblende. The feldspar is barely kaolinized in spots and patches, The biotite is generally fresh. Wath the exception of slter- ation to chlorite, which is locally complete, the roek is in general quite fresh. SPECIMEN I2 Uxide percentages Wt. a Ilineral Areas Cr. % 10, AloO, FepOz | FeO [Cal | 1ig0| X20 FELDSPAR Andesine 607 | 2.67 46,0 g7.6 11.0 | 0.5 B.710.5] 0.5 65-35 AUGITE 283 | 2.3 z5. 7517.8 | 1.8 2.2 tn, 1t5,4 CELORITE 143 | 2.7 10.80 3.6 { 1.8 2.9 BIOTITE 55 | 2.9 4.5 =.0 | 6.9 : GC. {0,2 0.5! 0.2 ENSTATITE Z| 3.1 0.3 0.2 C0.0 [BTl.2 (16.8 2.37 [A.2 (OU ORO. 4 OG. 7| 3 Total |ICI.5 Adjupted: 51% | 16h 2% 4h 111% 1100] 0% | #4 ~~ 8G 8%Bg Page 59 Page 60 SPECIMEN 22 SPECIMEN SUITIARY 22 TEXTURE: Uneven medium grained. STRUCTURE: Gabbro order of separation COMPOSITION: (I) Iineral; (Primary) (Secondary) Feldspar (370) EE (135) Diopside (3é&h0 Antigorite Biotite (7h) Iron stain Rhombie i (Olivene) (60) = Serpentine lagnetite (20) Apatite (2) Chemical: : LEGEND Si0p===m==-== 487 Caf-====mm== 120 — Al 0 ----=m- 150 1g0===-====~ 15% Feo 0fmw~---==~ 30 EcQevunnnen- : O Feldspar Pel-==-==----- 4% NEoO=m=m--=-- 2% Ho0 m———————— I} @ Diopside @ Olivene RELIARKS : ) Plagioclage range. Bytomnite to andesine @ Biotite ) Notable undulatory extinction ) Diopside shows fringe alteration to chlorite () Enstatite d serpentine ) liagnetite is the center about which biotite hes grown @ Chlorite ) DBiotite & border mineral to pyroxene ) Rhombic pyroxene is the center about which the @ Apatite 0 pside has grown J0livene present sparingly before it was altered to rpentine ) Apatite as long needles only ) Common mode of alteration is to chlorite; not to condary hornblende 0) Roek is notably fresh - a HO WOO IPODS MH NANE: DIOPSIDE CLIVENE GABBRO Page 61 SPECIIEN 22 TEXTURE This individual is as usual holoerystalline phanero- crystalline uneven medium grained, showing the gabbro tex- ture. Locally the individual is ophitic. The ferro- megnesians show the largest sized grain, the feldspars being somewhat smaller. The texture c=nnot be said to be diabasic, because the ferromegnesians are oo automorphic. PRIMARY MINERALS Feldspar is abumdant. It is reoognized by its low interference tint. (The seetion is thick, so the tints are high), The Becke test showed the inlex of refraction to be slightly above Qamada Balsam. The relief is low, In a2 few cases, the monoclinic form (really triclinic) was apparent. A good Bx, figure was obtained, =nd from this Ch, was found to be positive, and Chy; negative. The min- eral is biaxial , with small 2V for a feldspar. Undulatory extinction is very common, and varies from 18° on the border to 28° at the cernter. This corresponds to a Lebradorite on the outside to a Bytownite in the center, and proves the existance of zonal growths. There is an abundsnce of albite twinning present, also some carlsbad. Individuals vary in the twinning they show from simple ecarlsbad to occasionally polysynthetic 2lbite twinning. The most common habit is lathshaped; the most common habit next is tabular. zonal growths are very cormon, especially in the tesbular varieties, which show the growths in ordinary light as a result of differing degrees of alteration, Universally themineral : shows undulatory extinction, Good cleavage is apparent. Double refraction is low, The mineral is told mostly by its habit, interference tint, cleavage, twinninz, zonal growth, and definitly biaxial charscter. It is not limited in its associations, as it makes up the entire colorless mass of the transparent constituent. lath shaped indivia- uals show a maximum extinction angle measured on the albite twinning of around 259. hence some of these are very probably Andesine., Hence the range of minersls of the feldspar group is considerable, being from Andesine to on the border zones to Bytownite in the center. Diopside is the representative of the pyroxenes. The relief is high, the shigreen is high, showing the typical schiller structure. Color varies from & very pale grayish green to almost colorless. The mineral appears to be biaxial of very small 2V, The specimen upon vhich te test was made showed a hazy Bxg figure, slightly inclined. Both Ch and Ch, were found to be positive, The mineral is practically non- leochroic. The double refraction is fair. laximum extinction angles measured on the long prismatic individuals showing the prismatic cleavage varied from 359 to 30°, This, combined with the lack of color, makes it probaile that the mineral is diopside. It is characteristically and notably automorphic in outline, and is equant to short prismatic in pS (22) Page 63 habit. It characteristically shows a few twinning lamellse, the twinning being after the augite law. The individuals centain usually minute brownish flakes, which seem to be en alteration product probably an iron stain. These flakes or stains are commonest in fracture lines. There is very characteristically found a scaly and splintery fringe of secondary antigorite about the margins of the individuals. There is also some greenish chlotite mixed in with it. This indicates the high lig0 content in the pyroxene. Biotite is present also. It shows the usual perfect basal cleavage and persllel extinction, It varies i: color rom dark brown to black to 2 clear licht yellow. The basal sections are entirely a very dark baleckish brown, and non- pleochroic, The relief is high, and the double refraction variable. The ray parallel to the cleavage is the most strongly absorbed, and the absorption is almost complete. A convergent light figure is difficult to get on account Of the thickness of the slide, and the high 8bsorption in the basal section, The darkest individuals show = roughly irregular equant habit, while the side sections, showing the pleochroism, are elongated and lathshaped. The perfect cleavage in the side section, the parallel extinction, the characteristié pleochroism and absorption very directly and definitly determine the mineral. It is as easy tu recognise as is the feldspar, Itis characteristically associated with the dasnetite. which is often the center about which the biotite has grown. It is also associated with the pyroxene, occurring here as a border mineral. (22) Page 64 There is a rhombic pyroxene present to a slight amount. The presence is determined by the pale pink rose to colorless pleochroism. It otherwise has the appearances of the augite, It is present only very sparingly and always as a center to an augite individuals. It is thus a center of a zonal growth. Olivene was apparently present. It is now altered to serpentine however. In the individual present, a very ir- regular fracture system wos observed. No good cleavage is apparent, The individual seems almost entirely altered. It is now a mass of fine arsine dusty megnetite and doubly refracting individuals. The magnetite is disposed in ir- regulars cracks which run thru a very fine aggregate of doubly refracting flakes, scales and grains. The character- istic mesh structure of altered olivene is shown by the individual, It has been called olivene because of the mesh structure, the t pical adl3ociation with the only loeal aggregates of fine grained magnetite, the association with the rhombic pyroxene, and the irregular fracture system. Cpacue metallic rounded grains of magnetite were also present. It oceurs characteristically as & neucleus about which the biotite has grown. There seems tc be loeally an indigation that it has been formed from the alteration of olivene. Apatite occurs also in minute flaked scales and needles. It is colorless, has an index intermediate between feldspar end pyroxene. Parallel extinction was seen. The individuals penetrate into the pyroxene and extend out into the feldspar, They are very distinctly developed and are cuite automorphic in outline. Their very long lathshaped character is quite individual. ALTERATION Chlorite and antigorite seem to be the main alteration products. Both have a green cclor. There is no apparent cleavage present. Some of the individuals are quite distinetly pleochroic, tho rather faintly so. The common form is as ragged splintery aggregates, bordering the augite. There is low double refraction, I is higher than feldspar, Ch, is positive, (¢) being faint green to c@dorless, while ( (') is faint green. Some of the biotite is seen altering to this, as well as the augite. Thus the magnesium pyroxene is altering to serpentine and chlorite. DBiotite is altering to chlorite. The feldspars are hardly altered at ail, The rock is quite fresh for one of this suite. SPECIMEN 22 Oxide percentages wi . liinerals Areas | Gr. Vt. yo 510,| Alp0g| Fey0z FeO | CaO | MgO | Kpo0|NagOHoO FEID3PAR Labrad.-Bytownifle 479 2.71[1200 | 36.5ff 18.6] 11.0] 0.4 4.71 0.4] 0.4 1.4 20-70 DIOPSIDE 297 3.2 11870 | 36.1] 19.8 0.4 0.8] 0.7] 2.0f 7.6 CHLORITE 170 2.7 | 4b8 | 18,9 4,2 €el 4,7 1.7 BICTITE 81 2.9 225 6.6 2.81 1.8) 1.1 71 O.3) 0.1) Ou? O.2 OLIVENE 68 Z.25| 194 5.5 1.9 £3 1.3 MAGNETITE 11 5.1 55 1.5 1.0] 0.5 EN3TATITE 10 Sed 1 0.9 DD 0.1 0.2 2542 |100.0f 47.2] 15.0 2.9 2.9113.8{15.0] 0.7% 1.81.7 Total 108.7 Ad Justed 48% 155 | 26 |4% 125] 15% oh 1% 99 edsd SPECIMEN 3b AUNMARY TEXTURE: lledium grained STRUCTURE: A single universal, hence hypautomorphic COMPOSITION: (I) Ilineral: (Primary) (Secondary) Pyroxene or (Eornblend?) —(89)) — —s—-Hornblende Zoisite (10/0) ed llagnetite (Ij) (2) Chemical: §10p==-~==n== 39% Ca0--------- 135 Al 20x -—-——— I 3/0 gO Ne Sa VS. - IO ( Fe Og~-=====- 7% Kg0-m-mmmmmm 2 PGBs iocine 14% N320ceecnve- A REMARKS: I) No feldspar present 2) Rock extremely altered; recognition difficult 3) S5light pleochroism and psle color point to yroxene: other properties point to anphibole (2) Frayed needlelike development of hornblende notable 5) llottled extinction universal 6) Magnetite included in ferromagpesian abundantly nm) Zoisite presence is notable. It also contains argest magnetite grains. 8) Zoisite is stained brown in the vicinity of magnetite. CR ALTERED ZUISITE PYROCXENITE. ZOISITE HCRNBLEIDE: SPECIMEN 35 LEGEND Hornblende Zoisite llagnetite (Secondary?) Page 69 SPECIMEN 35 TEXTURE The specimen is holocrystalline phanerocrystalline medium grained hypautomorphic in texture. The section taken consists practically of a single mineral, which ac- counts for the hypoutomorphic texture. PRIMARY MINERALS Hornblende is present but it is difficult to state whether it is secondary or primary. It is very probably secondary. A few end sectimn show the characteristic 124° amphibole cleav:ige; Ch, is negative, 2V is apparently about 30°. The mineral is a very pale :reen, and is slightly pleochroic; end sections showing the direction bisecting the obtuse cleavage angle to be the lightest in color. 3ide sections show Ch, positive and parallel; or rather inclined to the cleavage at the amphibole angle. This extinction angle was found on measurement to range around 209-250, Angles measured were: 23°, 20°, 3°, 359(high n) 20°, 20°, 250, N is high, relief is high, and all of the properties check with an amphibole. Practically all od the individuals show the lack of deep color so characteristic of other specimens, yet the mineral is distinctly an amphibole. The mineral shows in particular a sedgy, frayed, needlelike development which was missing in the other specimens. This necdle-like develorment, the pele color, and the high extinction angle (for an amphibole) are all notable. There is not 2 single in- dividual present showing a sharp extinction and a pure (35) Page 70 interference color; all are densely speckled, showing a very mottled color between crossed nicols. All of the characteristics taken together seem to point to a horn- blende; but they seem also to point to a secondary origin for it. There are in addition a few simple broad twinning bands characteristically present in most of the individuals. This type of twinning is also characteristic of the pyroxenes. The individuals are are of rather uniform size. The habit is in genersl prismatic and automorphic; but in detail the outline is xenomorphic and irregular. The extreme flakyness and altered appearance of the rock make it & very hard one to work with, Note of the reactions are definite. 1Identi- fication is somewhat uncertain; but it is highly probable that the m neral is secondary hornblende, after a pyroxene. It is charecteristically filled with minute cub cal and rounded opagmne greins, which resemble magnetite in appesar- ance. All of the grsins are of about uniform size, and are very thickly speckeld thruout the individuals. Their outline is seen only under the hi~h power; under low power the hornblende simply seems to be "dotted" over the entire surface. Practical.!y all of the individuals show these inclusions. Locally there are larger grains, but these are much less in number, so that the content is about the game irrespective of the size of the inclusion. Zoigite is thought to be present. The cleavage is poor and not apparent. The index is slightly less than for hornblende, as shown by the Becke test. Fracture is ir- regular. The mineral has a faint green tinge. It is gray between crossed hicols thruout most of the revolution of the stage hut extinguishes irregularly four times per revolution. The mineral seems to be nearly Bxg in one section; whike the other large section present gives an indistinct inclaned figure, still it is dark gray between crossed nicols. The explanation is that the mineral is one of low double re- fraction. 2V seems to be very small; the individual may be a strained uniaxial. The sign is uncertain, but is probably negative. The mineral is distinctly and charascteristically associated with the magnetite present in the rock in apprec- iable grains. The low double refraction, the smail optic an gle and other characteristics mentioned seem to point to zoisite a8 the mineral present. The distinct, non-ap- parent cleavage is to be .oted. The mineral occurs in slight- ly larger size than the other individuals; and the two main ones seem to be automorphic toward the hornblende. The habit is ecuant in general, but very irregular in detail. There is 2 slight elongation in the direction of the most distinct fracturing. It is a deeper green in color then the hornblende, tho still it is light in color. None of the very fine grained imclusions are to be fond in it; instead, it is notably the host for much larger and more irregular grains of magnetite. It is characteristically stained a dark brown along the lines of fracture, especially in the vicinity of the magnetite. As mentioned above, the very peculiar blackish blue appearance when seen between crossed nicols is dee to the low birefringence. The darker green, the associa- tion with marnetite and the mr esence of the brown stain in Page 71 5) the fractures are distinguishing factors in the recognition of the mineral. Locally thruout the rock, much finer flakes and seales oceur, having the same charscteristics as the larger in- dividuals. They can be recognized at = glance when it is kept in mind that they are associgted with the brown stain in the hornblende. But a small percent occurs in this way, however. llagnetite is present, tho not abundantly. It is ap=- parent in large grains only in the zoisite, by wich tt is included, However, it is extensively present as very fine granules included in the hornblende. ALTERATION The rock is very extensively altered for one of this Buite., The extensive speckling and fl-kiness, combined with the locally complete seams and bands of agegregztes completely unoriénted, makes the determination of the rock uncertain, and difficult. If the section were seen between crossed nicols alone, it would seem as a great ma s of scales, flskes and fibres. These are gemerally grouped into groups which winthin themselves show parallel orientation optically; but locally the gromps are but confused aggregates, completely unoriented optically. The general appearance makes it appear extremely probab- le that the hornblende present is secondary after pyroxene; the sedgy character and lack of color especially pointing to this possibility. Page "72 SPECIIEN Zb Oxide percentages Wt. i llineral Areas Gr. | Wt. | 77 [3105 |Al.0x|Fes0, [FeO a0 | 120 | X20 |Nas0|H20 HORNBLENDE | 929 | 3.2|2000 | 89.0) 24,7] 8.9 6.2 {14,2[10,7/ 9.8] 1.5 1,8 ZOISITE 102 | 2.3] 720 | 10.1 4.0] 2.2 2.5 0.2 MAGNETITE 6 | B31]. 2 0.9 Jd 0.2] 0.2 2271. |{100,01 z5.7| 12.9 +6.5|12.2[17.2| 9.8( 1.8/2.0 Tetal 99.1 Ad jysted: 297 12% 7h | 145 | 13% | 105 2% | 27 esBd Page 74 SUMLARY TEXTURE: Iledium to fine grained STRUCTURE: Gabbro order COMPOSITION : (I) Iiiineral: (Primary) (Secondary) Feldspar Augite =~ (Chlorite and Antigorite) tion Iron stain Biotite llagnetite (2) Chemical: 310---===m=- 45% BB0= nv mm men 107 ( ALoOQ.===--~-- 13 MgO-===mmmm--m 9% Fes0r---=-== 9 KoO-==-==mmmmm 17% Fel---=-mmm- 165 Na&pQmmmmmmmmm Zh REMARKS: (I) A local fine grained "basic" segregation present Plagioclase range slight: practically andesine- radorite Undulatory extenction universal in feldspar Feldspar locally bent and crushed Augite most extensively altered Augite locally indented to contain hypersthene grains, there are not a center about which former have grown Augite includes magnetite, hypersthene does not Biotite crystalized about magnetite bunches and grains Biotite also occurs @&s a "border" mineral *to hyper- ene occasionally )) llagnetite rods in augite are characteristic ) Roeks one of freshest of suite HH OO~NISs OO dhOID AUGITE EYPERSTHENE BIOTITE DICSITE SPECIMEN 28 LEGUED Feldspar Alugite Hypersthene Biotite llagnetite Page 76 SPECIMEN 38 TEXTURE The specimen is holoerystalline hhanerocrystalline medium to fine grained. The ferromagnesians are automorphic to hypsutomorphic in outline. The feldspars are notably lathshaped and automorphic, giving the rock the Gabbro texture. There is a noticeable segregaticn of more basic material in a small occurrence in the slide. It is much fi= finer crained than the rest of the Fock; feldspars are ab- sent; there is an abundance of magnetite, while the pyrox- enes and amphiboles are equigranular pansautomorphiec, PRIMARY MINERALS Among the essentisl minerals, feldspars are prominent. Altho hypsutomdrphic, they have an automorphic sppearance being commonly lath-shaped in outline. Most of the individ- nals are twinned after the albite law; usually poly- synthetically. Practically all of the individuals show undulatory extineticn; and hence zonal growths are probably present the not apparent. Loeslly the feldspar laths are slightly bent and contorted, tho this is not the general case. The twinning, low index, undulatory extinction, color. and habit made recognition under the microscope easy. By using the method of maximum extineti.n angles in the zone normal to the albite twinning lamellsze in conjuncticn with the extinction esncle in sections normal to the optic axis; the feldspar was found to be approximately &n Andesine-Labradorite. Page 77 (38) There is only the beginning of alteration present in the feldspar. Augite is the next most common constituent. It is also hypautomorphic, but has the szme appearance of auto- morphism &s has the feldspar. As is apparently typieal with these rocks, the augite seems to be the most sensitive mineralsand is hence the first indicator of alteration. Here there are seams and flakes of an unidentifiable alter- ation product, giving the individual a corroded appearznce in the extinction position. Fine needle-like rod inclus- ions of probably magnetite seem to be very charactsristic. These are approximately in parallel orientation, and in a few orientations of the augite seem to be arranged in two planes inclined to each oth er. There are 2lso longer end more continuous seams of yellowish stain thruout the grains. The individuals are twinned in a few cases; loe=lly poly- synthetically, but usually as a few isolated striations. The yellowish stains seem to be common around the border of the augite individuals. The augite locally is indented and irregular in loutline, and occasiona’!ly is seen to con- tain pertially grains of the more automorpi:ic hypersthene. The color is normally & transparent grayish green, shagreen is high 2nd relief sharp. It is biaxial positive with in- clined extinetion of about 54 degrees maximum between slow direction and cleavaze. Hypersthene is the third constituent present in abundance. It is characterised by noticeably automorphic boundaries, and is more automorphic than is the augite. It Page 78 (38) occurs as platy to lathshspéd individuals. It is commonly associated with the magnetite, tho it rarely includes the latter, as does the augite. This minerals also shows the beginning of alteration by the presence of = few broad bands of yellow stain. It shows characteristically a pleochroic scheme of (a) reddish orange, (¢) grayish green. Chp and Ch, are both negative, double refraction is fairly high. Parallel extinction, automorphic outline snd pleo- chroic scheme are the signposts to the gecognition of this mineral. Biotite occurs =s a characterizing assessory. It shows the characteristic parallel extinction, perfect basal cleavage and =21lmost complete absorption parsllel to the cleavage. It is maikly brown in color, tho there is = small amount of the sree bic ite present. It is apparently uniaxial negative, with high double refraction. It is chars acteristically irregular and corroded in appearance. It also typieally includes bunches of magnetite. It seems to be automorphic towards all but the magnetite and enstatite and is found as a border to the latter occasionally, lMagnetite is present as a minor accessory. It is included by the biotite in large irregular masses, and oc- casionally by the augite in this manner also; tho its presence &s fine rods in the latter are most char:cteristiec. It is of course opaque and shows 2 metallic shimmer in re- flected light. ALTERATICN This specimen is probably one of the freshest of its type in the suite of rocks studied here. Only the be- ginnings of alteration are visible. 3ince this is the case, it is somewhat important &s an indicator of the ease wiih which the various minerals here undergo alteration. Augite is apparently the easiest mine 21 to alter. The beginning of the alteration to fine flaky rasses of doubly refracting mineral aggregates is visible here. The enstatite is but slightly zltered; the only signs beins the formatiin of a few cracks stained = pale yellow, possibly by iron oxide, Kaolinizaticn is but incipient with the feldspars as there is but a sprinkling of cloudy keolin in finely divided ccndition thruout a few individuals of feldspar. There are yellow stains from light to ~rominent thruout the rock in general along lines of = parent fract- ure but these are especially prominent in the ferromag- nesians. 3PEC 3 ILIEN 8 Uxide percentages Vt, liineral Area ar. Wt. | 7% |pi6, RI-O. Fes0, FeO [a0 |lig0|Ko0 Nal 2 2-3 YZ ’ 2 2 PELDSPAR (Andes-Lab.) Fresh----490B 498 | 2.691340 | 29.4| 22.2 10. 0.8 4,0 0.8/0.8] 2.8 Altered-- 8p AUGITE 2900a|l 2.3 960| 28.8 14.1] 1.7 2.5 5.6 4.0 HYPERSTHENE | I50a| 2.45 517 | 15.8 7.8 0.2 3.0 0.2 3.3 BIOTITE 65a | 2,9] 189| B.% 2.2 1.4 0.91!0.5 0.5 MAGNETITE ves | 5.1 | zag! 11.4 7.91! 2.8 7594000.0| 46.8 12.7 9.6] 2.6 9.5 8.6[0.8] 2.8 rotal] I0IL.2 Adjusted: ash | 135| 9 | 104 104 9h| 14 | Zo | | 08 938d 29 SPECIMEN SPECIMEN 39 TEXTURE: Coarse uneven grained STRUCTURE: Pseudoporphyritic granitic COMPOSITION : (1) Mineral; (Primary) (Secondary) Hypersthene (177) Hornblende (147) Hornblende (26%) Antigorite Diopside (Ij) saussurite Titanite (2%) Feldspar (4050 Magnetite (2) Chemical: | 510 -=-==mmm- 450 Ca0----==-== 12% : : AloBpmmmmmmmm 16% Mglm-=-m==== 9% LEGEND ) FesOp=mmmm==- Zo KgO-=nmnnn~ 27 | _—_— Higher nunnus 10% N5z0me-re-== 2% | Pi0p===-==== A Hypersthene @ Primary Hornblende REMARKS: ¥) Secondary Hornblende (I) Rock very intensely altered: original texture very difficult to make out : © Diopside (2) Peculiar border of hypersthene notable | (z) Hypersthene does not show rose pleochroism Titanite | (4) A border of hornblende about hypersthene which is the potEiLieis host for feldspar | (O Feldspar 5) Hypersthene has altered to antigorite rather than to bastite | } (6) PFeldspar fresh in "sieve holes"; altered otherwise (7) Hornblende contains the swall amount of magnetite of | { the rock (8) Titanite (?) In large masses, showing corroded outline (9) Illagnetite rare (IC) Hypersthene but slightly altered: is extraordinary, since all other minerals show effects of alteration very narkedly p— ry NORITE Page 88& SPECIMEN 39 The specimen shows a coarse uneven grained liolo- crystalline phanerocrystalline pseudoporphyritic geanitic texture. The alteration of the specimen is so intense that the original texture as well as composition of the minerals was very difficult to make out. The rock is extremely altered. PRIMARY MINERALS There is a single large crystal present, which seems to be very much larger in size than the surrounding .nes. It is not altered at all. It has been called hypersthene. As to optieal properties, the cleavage is good, tho not per- fect, in one direction; and indistinet in the direction ner- mal to the cleavage of the first. Parallel extinetion is present. The mineral is distinetly pleochroic. In convergent light a Bxg figure is obtained. 2v is appatently moderate in size. Ch, is positive, while Chy is negative. Parallel to (e¢) the color is & light green; parallel to (b) it is a darker brownish green. The absorption is notable; (b) be- ing greater than (ec). Un the basis of the negative character of the mineral, paresllel extinction and absorption just op- posite to the hornblende extinetion scheme, the mineral has been called hypersthene. It does not show the red pleochroism so characteristic in the hypersthene of this suite of rocks; but the stronger absorption normel to the cleavage is to be noted. In the genersl outline, the habit is automorphic; Page 84 but in detail, the edges are secon to have a very frayed appearance just before the surrounding zone of hornblende is reached. This outer boundary of the hypersthene is marked by a difference in relief; the surrounding material having slightly lower index of refraction, The hypersthene and the hornblende are in cikystallographic intergrowth; or rather, they are similarly oriented optically. The hypers=- thene giant crystal seems to be a neucleus €dr the growth of the hornblende. There is one other smaller detatched patch of hypers- thene present. It is a single grain, completely embedded in a confused aggregate of doubly refracting minerals of very fine dimemsions. Its light color, negative character, and characteristic associaticn with the brown stains in the frec- ture lines are the distinguishing features in i$$ reco=nition. This fracture thruout the transparent mineral, stained brown, seems to be a distinguishing feature for the hypers- thene present. The mineral is associated with the hornblende, for which it seems to serve as a neucleus of condensation, or rather crystallization. It has an equant habit. Alteration in the large individual was not observed, but i» the smaller individual, alteration is to a confused mags of fibres, thAsher than to bastite, the usual mode of alteration here. Feldspar is present. It seems to ofcur in two main differing ways: (1) as large, generally intensely altered (29) Page 85 messes, and (2) as minute clear grains, embedded in the "sieve" holes in the the hornblende surrounding the hypersthene crystal, These small grains are not in the main altered, tho a few are. The usual habit is quant; tho at the same time somewhat xenomorphic., There is no twinning visible. As scen by the Becke method, the mineral has low index and low relief; higher than C:nada Balsam, It shows alteration to such an extent that only cone or two in- dividuals gave a figure which could be distinguished in convergent light. It was seen to be biaxial with very wide axial anzle. The mineral rain tested was probably positive. Cleavage is perfect. The grains are t.o small to get a reliable figure on, and the sltered masses are opaque to the convergent light. However, the mineral is certainly a feldspar. Its association points to a Plagioclase; and the proximity to & 2V of 90°, combined with the positive character and as:ociation, points to a Bytownite. This is merely estimate however, In the 34tered portions, the feldspar is now a confused ag-regate of minute low doubly re- fracting grains and flakes, containing a few flakes of higher double refraction. The areas are now clouded and flaked so ‘as to be translucent. The unaltered portions show minute greins and flaked of kasolin(%) included. Hornblende seems to be present, both as a primary con- stituent and as an alteration product. The primary material forms a zone or belt around the hypersthene. This is very characteristiecally the howt for feldspar (see sketch). This host relationship is very characteristic. The hornblende has Page 86 (29) & paler and somewhat less brownish green cclor than has the enstatite. The border shows parzllel extinction. The index of refraction is less than with the enstatite, as shown by the aBecke test. On other grains, the extinction angle was found to be around 15°-20°, the grains showing ‘the same color and appearance i. ordinary light as this border zone. 2V is about 60°; Chy is negative and Ch, positive. Cleavage, tho present, is not apparent except upon close inspection with the high power. The inclusions of feldspar in the hornblende are SO abundant and uniform in size as to giv eht hornblende & porous look in ordinary light, it appears as a sieve. The relation of the hornblende and feldspar is typically dia- bag&c ophitiec. This type of hornblende is peesent in two places in the slide, and in both is the host for feldspar: while the hypersthene, about which the hornblende is grown, is singularly fresh from inclusions of feldspar. This horn- blende gives a sharp extinction and rather a pure interference color; and is hence probably primary. Locally it contains & few small grains of magnetite. Secondary hornblende is also present. This is scatter- ed thruout the pseudogroundmass of confused alteration pro- ducts #f the feldsper:; and occurs as frayed crystals of greenish hue showing perfect prismatic cleavage. It is pleo- chroic; (e¢) being a dark green, (a') a light green. Ch, is negative, Ch, positive; and the extinction angles run: 120, 159, 0°, 5°, 149, 80. The remnants are always embedded in this frayed confused aggregate, so that its relation to the other minerals present eannot be made out. The individ- vals vary much in size; from minute flakes to large "worl eaten" (39) Page 87 individuals, which have all the a)pearances of being remnants of alteration. They show speckled interference color, and somewhat irregular extinction. No twinning lamellae =2Te present. The greenish shrcaded appearance is characteristic. The brownish, irregular, fading stains are =lso present. Diopside is also present. It resembles the secondary hornblende when seen in ordinarly light, but it has a higher extinction angle. There are two isolated small grains present. Titanite (7?) seems to be represented quite noticeably here. The individuals seem to show parallel extinction. The mineral is biaxial, 2V beinz large. Double refracticn is notably very high, being quite a little higher than for hornblende. In ordinary light the mineral shows great relief, standing out very distinctly as compared with the other minerals present. It is white or very pale yellow in color. Cleavace seems to be somewhat indistinct or not apparent; fracture being the most common. Absorption is (e) greater then (b), the mineral showing pleochroism, It is now a very irregular ap earing ragged individual of de- tatched grains showing a very corroded appearance, which is emohasized by the presence of cleava~-e. These cleavage lines have been the seat of alteration, an opaque very fine mater- ial having been deposited in the fracture and cleavage lines, giving the mineral the appearance of an aggregate of detatched grains. The cleavageis fairly good, tho not weil developed. The high double refraction, pleochroism , the Page 88 (39) index of refraction and the color paint tc titanite as being the mineral, lMagnetite is sparingly present, occurring as a few isolated grains in the hornblende. ALTERATION The hypersthene is hardly altered at all in this specimen, which is rather noteworthy. The feldspar alter- ation is quite notable and complete. Where it is surround- ed by the hornblende it has apparently been protected from alteration and is therefore fresh; tho most of the feldspar present is completely altered. This altered mass con- stitutes almost & "groundmass"” in which the surrounding material seems to be embedded. It is seen under the high power to be an agecregate of low doubly fefracting grains and flakes, but nothing else could be made out. They are not oriented, but are matted .and interwoven in oceurrence. The secondary hornblende is notably fresh. Diopside present is probably only the remnants of more extensive crystals which have been altered ( serpentinization?). The rock is dis- finely fractured, and two of these fractures are minute vein- lets containing secondary flakes znd scales of probably calcite. The specimen is extremely altered for this suite of rocks. SPECIMEN 29 Oxide percentages Wt. liineral Arees|Gr. | Wt. | % | 5105 |A1,0;|Feg0z [FeO | CaO | 1ig0 | K,0|Nay0| Ti04H0 FELD3PAR Bytownite( ?) 544 |2,.72|1480 [40.5 20.2] 12.00 0,8 5.1 0.8 0.80 1.6 20-80 HCRNBLENDE Primary---3.5| 4565 |Z.2 |1455 [39.8 15.5)! 4.00 2.8) 6,4 ¢,4 4.4 0.3] 0.8 0.4 Secondary-100 HYPERSTHENE 178 |Z.45| 615 [16.8 8,7 z.5! 0,8 35.9 TITANITE 19 [2.5 67 | 1.9 0.6 0.6 0.8 DIOPSIDE iz 3.2 28 | 1,0 0. 0.4 0.8 6 2655 [100.0 45.21 17.5 2.0 9.9. 11.9 9.3 1.6] 2.4 0.80.4 Totaly 102%.6 Adjystead: 45% | 165 | 26 | 10% |126| of | 2% | 25 | 1% 68 °3BJ SPECIIEN 40 SUIIARY TEXTURE: Very coarse grained STRUCTURE: Poikilitic COMPUSITICH : (I) liineral: (Primary) (Secondary) Hornblende (605%) Saussuritized feldspar Diopside (31%) Bastite Enstatite llagnetite llagnetite Hornblende (75) Chlorite (2) Chemical: 510p===m=mmu- 43% Ca0-m=mmmmmm 16) ( AL 0z--m---- 7h MgO--~~--=--= 14% Fe 0p===mm=== 60 KoO-=meommmm- % Pel-z----cnx- 12% NapO-=~- + X09 I : | i | | i I i i» oO 0g Oo I | | | I 1 I 1 ! 4 DO FH Hs ( IEGEND 3 2 : - Plagioclase range: DBytownite Z0-70 to Andesine 65-35 Undulat tory extinction marked Abundance of carlsbad and pericline twinning, but absence of albite twinning Feldspar shows peculiar mosaic texture Two sets of magnetite rods found in the Augite llassive magnetite also present in the Augite liagnetite rods locally in zonal arrangment Augite seems to be xenomorphic toward enstatite, the latter does not occur 2s a nucleus about which augite has grown Rutile or titanite inelusion in the Augite? Actinolite present(?) Enstatite associated with grains ¢f magnetite But beginnings of ¢ alteration of augite seen Roek quite distinetly fresh of this suite FPeldspar eet St er J 2 ee Augite Enstatite 000 IHagnetite bond Fo ONO B NHR - IDO HH 4 ~~ ct TD HH HO Page 135 SPECIMEN 66 TEXTURE To. This specimen exibits a texture which may be described a8 holocrystalline phanerocrystalline granitic medium to fine grained. The ferromagnesians present are slightly the larger crystals, but between crossed nicols there is an apparent approach to a pan-hypautomorphic condition which results in giving the rock a granulitic appearance. Practically all of the individuals are hypautomorphic to automorphic in outline. PRIMARY MINERALS There is appgarantly & complete absence of quartz, but plagioclase feldspar is abundan ly present. The gener=1 habit of the feldppar is fine grsined equant. A few of the feldspars are tabular to short prismatic. Very few of the lathshaped forms are presen’. The feldpsars are xenomorphic when in con- tact with the other consitiuents, but hypsutomorphic tov par- tially automorphic when they abutt against ea h other. They are in general of uniform size, slightly smaller than the other con- stituents, and present almost a mosaic appearance between crossed nicols because of the aggregationazl mode of occurrence, Twinning is abundant and of various kinds; the carlsbad twin- ing by far predominating. Albite twinning is =1so present, but is comparatively rare; and when it is present the individuals show & "wedging out" set of striations. Periecline twinning is also distinct and occurs as frequently, if not more so, than the abbite striations. About 4/5 of the feldspar individuals show the carlsbad twinning, while probably 1/5 shows the peri- cline twinning. (56) Page 13 The mosaic texture of the aggregates of feldsper is particular- ly noticeable where the latter occurs intersticially. The feldspar is all remarkably 'resh, is practically unaltered; and appears almost as clear quartz in ordinary light. Its cleavage is not strikingly asparent, even tho the entire rock is somewhat fractured. The identification of the feldsyars was made entirely by the use of individuals showing an optic axial figure in convergent polarized light, as the albite twinning was hardly present. The index was uniformly higher in ell cases than for Balsam. When extinction angles were measured on optic axial figure crystals, the extincting angles were found to range from 35° to 70° on the various individuals, which shows a range in composition from Bytownite to an Andesine. Thus, compositions were Andesine (65-35); andesine (55-45); labradorite (44-56); Labradocrite-bytownite (30-70) and bytownite. The optic angle 2V was very nearly 90° in most cases tested Augite is the next most abundant mineral present. It is pale green in color, A fairly good cleavage is visible on the side sections. The individuals are shout prismatic in habit, The end sections which are occasionally present show the 880 pyroxene cleavace very well, and usually also some twinning dtemellae. These lamellae are inclined tu be simple, tho a few ‘are rcpeated. The individuals are automorphic in general out- line tho in detail they have a ragged, irregular, and rounded appearance. 1.ey are the larger individuals of the rock. lagnetite rods, arganged in two sets, oceur as inclusions. Une set is situated with the rods lying apparently in the inter- Pace 127 section of the prismatic lines of cleavage; while the other set lies with the rods at the intersectidn of the basal and the side cleavages. llassive grains of magnetite are also present, When side sections of augite are visible these two sets of rods present a peculiar crossed hatched appear- ance in a narrow zone or line which was apparently at one time the outer shell of the crystal, but which was covered up by preceeding layers of augite material, so as to now appear as & narrow band on the inside of the crystal individual. The aagite 1s characteristically the host for minute grains and still morc minute rods of magnetite, which occur in such quantities as to meke the ausite seem almost flaked in places; tho it is loca ly clear. The augite is xenomorphic towards the automorphic grains of enstatite, which it poikilitically ineludes when the latter sre small; 2nd which it partially encloses when the latter are large. In seneral the augite is slightly fractured, “nd in the seams are yellow staing, es- pecially pronounced when the fracture is in the vicinity of magnetite grains. The augite is very locally and occas- icnally altered in‘o patéhes of chlotide which are a puch darker creen in appearance and which show a more noticeable pleochroism. A few augites show an abundant inclusion of very fine granular transparent mineral when viewed in ordinarly light; and which show with the Becke test a higher index than the augite. This inclusion may be rutile or titanite in a very fine state of subdivision. There is a little alteration of the augite to flakes, but these are not noticeable generally. Ch, and Ch, are positive, 2V is apparently small, ranging from 30° to 500, MN is high, cleavage is well developed and is clearly a pyroxene cleavaze, the color is & light ~reen or grayish green, the extinction =ngle on side sedtions of the highest interference colors and best developed prismatic cleavare is from 40° to 50°. All of which data point to augite as the particular pyroxene. There is an amphibole also present, tho i: minor am- ounts ( possibly 4% ). These individuals show a igh inter- ference color, small entinetion angle, and & minus sign. Identification is uncertain, but is probably actinolite. It is similar in appearance to the pyroxene in habit, cleavage and inclusions, tho it is a slightly deeper green in color end shows & slightly more proancunced pleochroism, The em- tinction angle on side sections ranges from 0° to 120, Enstatite is present as more or less automorphic equant grains. It is typleally associated with the sugite, by which it is partially included at times. A few individuals have a hypautomorphic relation to the augite, but the common relation is automorohic towards the more xenomorphic augite. It also occurs as somewhat granular clusters . If is characteristieally associated with segregations of magneiite, which here seem to be larger in grain than elsewhere in the rock. It typical- ly incluies these grains. Its apparent poor cleavage, abund- ant fracture and common staining, combine with its common association with magnetite, make the individuals somewhat resemble olivene, tho this is seen not to be the case on closer Ee Page 139 (67) inspection. It is characteristically corss-fractured and generally stained yellowish. In the vicinity of magnetite & grains the stain becomes a d:rk red at times, suggesting the magnetite TRUCTURE: Unequal granular granitic a - - COIMPCIITICN: (I) Mineral: (Primary) (3Bcondary) Feldspar (450) | Augite (265) —=Hornblende? Enstatite (185) llagnetite (1%) 2) Chemical: 310g==emmen—- 51% BBO mmm 14) AlnBresvnanas 16] Ber Ovo re ra 11} FegOr====mnm= Is KoQmmommmm mm Uo FeQ=-vvemeu-- 5% Hag0==vemme- 1 ElARKS : (I) Plagioclase renge; Labradorite to Byrownite (2) They seem peculiarly automorphic in outline (2) Carlsbad and pericline twinning abound; albite twinning is rare (4) Variation in iron content in enstatite? (5) llost of magnetite of rock associsted with enstatite (6) Enstatite occasionally the nucleus about whieh the augite has grown (7) Fracturing common (8) Two sets of rod inclusions present in augite (8) llagnetite as rounded grains in the enstatite, and as rods in the augite (IC) Augite the most sensitive mineral toward alteration (IL) Rock very fresh for one of tr is suite NALE: AUGITE ENSTATITE KHNCRITE SPECIIEN ®@O0® © O 67 LEGEND Feldspar Altered Feldspar Augite Enstatite lagnetite Page 142 Page 143 (67) SPECIMEN ( a” The feldspar is prectiically unaltered in this rock. Enstatite is notably present in this specimen. The TEXTURE common mode of oceurrence is as equ-nt 2rains, larger in This individual shows a texture which may be des- general than those of the feldspar. The usual occurrence is cribed as holoerystallind phanerocrystalline unequal as isolated grains; tho occasicnally = large individusl granular granitic. The normal order of separation of the will be cut by a fracture line and appear as an aggregate component minerals is followed, of grains. It has & higher relief than the feldspar, being ] about the same as augite. The double refraction is quite PRIMARY MINERALS high, probably as a result of a high content of iron. There is a feldspar present. It seems in the main " The individuals seem to show cleavage quite well developed to be optically negative with a 2V around 80°. Relief and s : in one direction, and less so normal to the first. Ex- index are low. The extinction angle measured on individ- tinction is parallel. The mineral is biaxial, and one uals giving an optic axial figure in convergent light ranged individual showing-& Bxg figure in convergent light gave ( from 420 to 729; those measured being 42°, 54° and 72°. : a negative test. 2V seemed to vary from individual, being This corresponds to a range from Labradorite to Bytownite. possibly 200 in one, and 70° in another. If this is sct- The cleavage is perfect, and apparently rhombohedral. It ually the case, it indivates a variation in the content of is very well developed. The habit is equant and tabular; : iron. The usual pleochroism was visible in most of the but very few, if any individuals show the lath shapes so specimens; cclof parallel to the best cleavage being a gommon in most orf the other specimens. The grains of feld- grass-green and normal to this a honey yellow or faint rose. spar are usua. ly much smaller in size than are those of the Wherever the mineral is fractured there is quite character- ferromagnesians. Inclusions are very rare; being at best istically present brown stains in the seams. liost of the a very few small flakes of magnetite, or liquid inclusions. megnetite in the rock ocewrs as an inclusion in, or closely The feldspars have an extremely peculisr automorphic a near- _ associated with the enstatite. In addition to the brownish ance when seen between crossed nicols. There is oract - bdo cally stains, the fracture seams are filled to varying degrees no albite twinning present; carlsbad twinning is very common; with & translucent gray to white kaolin-like material. The while pericline striations :re characteristically present more intemsely stained individuals appear somewhat yellow ( and resemble the twinning seen in calcite. The mineral is and vitreous. The mineral is associated with the magnetite definitely not calcite however, because of low double refrac- : tion and biaxial character. Page 145 (67) of the rock particularly, and also with the augite; for which it occasionally forms the neuclmsus about which growth has taken place. The augite is loeally indented to contain perfect enstatite grains. 3peckled interference colors are the usual thing. Augite is also present to quite an extent. The individ- uals whdch are present show the characteristic pyroxene prismatic cleavage, form, double refraction, index of re- fraction and lack of pleochroism. It has a pale green color in ordinary light, somewhat more intense and darker than the enstitite. It also has more perfect fracture and cleav- age. Extinction angles, measured as usual from the pris- matic dleavage to the slow direction of vibration, are as follows: 500, 35°, 27° 40°, and 30°, This points to augite as the particular pyroxene present. The general habit is short prismatic, and the individuals are usually the largest present in the rock. There are good auto- morphic boundaries, tho the edzes of the individuals are somewhat frayed in appearance. Fracturing and crushing have developed the cleavage to = high degree of visibility. The cleavage, tho being perfect, is develoned along but few lines as a rule, but these are very sharp and diéstinet; and give the individuals an appearence of several parallel lath- shaped individuals placed alongside of each other. TPracture is present, and tho irregular, is not so cormon as in the enstatite. It generally cuts the cleavage at a low angle, It has a high index, snd hence the relief is quite distinct, causing the mineral to stend out prominently. The light green c@lor also aids in making the mineral quite prominent. Practically all of the individuals show a few brownish flakes and stains, and are apparehtly arranged in variously oriented planes planes. A most characteristic feature is the loeal darkening in the green color where the material appears to heve a more pronounced fibrous chsracter. A few of the individuals show rather abundant inelusions of rods of magnetite(?) parallel to the cleavage for one .set, and at an angle to the first in another set, theitwo sets only usually being present. In addition to the rods, there are usually minute grains present also. The individuals are locally flaked with a translucent whitish k=olin materiel very finely subdividued; this flaking being loeally abundant in the fracture planes. Occasionally there are irregular streaks on the interior which show the rose pleochroism of rhombic pyroxene. The =ugite is associated with the enstatite, which is locally apparently intersticial between the augite grains, tho it is really more automorphic than the augite. Il: gnetite is present only in general in a smell quantity. However, il very definitely occurs in two very distinetive ways; one &s rounded grains in the enstatite mainly, while the other is as rods in the augite. It seems to have been the first individual to crystallize out, since it is in- clvded in 2]11 else. Page 146 Page 147 ALTERATICHN The rock scems to be very fresh for a specimen in this suite. It shows only the beginnings of 2lteration. The augite appears again tc be the most sensitive mineral in the section, as regards alteration, as it shows the flaky appearance resulting from partial alteration, probably into hornblende. Brown steins thru the enstatite are also quite noticeable. The feldspars arc practicaliy com- pletely fresh; hardly any alteration bein noticeable. The section is a very thick oney so that work was difficult. The feldspars whow colors of the second order. Ilineral \i . SPECIMEN 67 | Uxide percenta-es FELDSPAR Altered----40 AUGITE o {> A150; |pesOs 45,28 22.0 | 14,1] 0,4 26.50 I8,2 | 1.8 17.811 9.5 | 0,5 1.0 0.7 FILO BBY TIg.2 | XLT Totlal 100.7% 51% | Ieb 1% RQ tN be oS oO * ™N O 8¥T @o®Bd no Page 149 SPECIMEN 69 ATURE: Coarse to medium grained ICTURE : Peridotitic poikilitic relationship of minerals tm T om TRUC ION: . liineral: (Primary) (3econdary) Feldspar . = Jaussurite Diopside (30/6) — == Antigorite and Chlorite llagnetite (9) | ___ a= Serpentine Hornblende ( 617) Bagtite after Enstatite Chemical: Si00wneea mma 40% Ca0-~~==ve== 14% Afobne...ocau 6% REO vere 12} Feolnmmmmmmmm II} KoQ=-=n-mmmmme Io Feler-onncess 13% Bon0ewunnees I : H20==-mmmmm= Io (I) Feldspar completely s2ltered and small in amount. Labradorite (2) Diopside has altered to serpentine (3) Bastite after a rhombic pyroxene (4) Iliesh structure alteration of olivene seen (5) Hornblende slightly altered, while pyroxene is extensively altered DIC2SIDE HORNBLENDITE SPECIIEN LEGEND E) Hornblende ) Diopside, & llagnetite altering to serpentine Page 151 (69) Page 152 SPECIMEN 69 TEXTURE As shown in thin section, this is a holocrystalline phanerocrystalline coarse to medium grained rock. It shows the typical "poecilitie" texture of Harker; the crystals of gutomprphic to hypautomorphic feldspar beind embedded poikilitically in crystals of green hornblende. The rock thus shows the peridotitic texture. The mincral consitituents other than the hornblende show a rather even dévelopment of the crystals. PRIMARY MINETALS The feldspar is here & very minor constituent; nract- ically if not completely altered. It is now & mass of grayish white amorphous Or ncn-opsque material, closely resembling kaolin. Between cvpssed nicols, it is seen that there are many needle-like fibrous doubly refracting flakes scattered in varying orientations thruout the main mass of ¥aolin (?). The individuals are undoubtedly feldspar rem- nants. They are xenomorpiic and entirely intersticial; and probably constitute lass then 1% of the original material. On one s-ecimen an optic axis figure was obtained with poler- ized light. Un testing, this was found to be a-positive mineral, and the 42° extinction angle points to a Labradorite of a composition of about 45-55. Horhblende constitutes the main mass of the rock. If shows & 2rsss green~ yellowish ocreen-brownish zreen pleochroic scheme. It occurs in large individuals, which poikilitically include apparently all but the feldspars. It has apparently an automorphic to hypautomorphic outline, End sections show the 124° cleavage e¢specislly good in this specimen. Between crossed nicols, the hornblende is locally twinned, nut only intc a very few broad lamellae; and this is snnt common, The hornblende seems to vary greatly in size of individuals. 3ide sections show a 120-209 extinction angle. 2V is appatently very wide, and the index is high. The individuals are very slightly if at all altered; as there is sharp and complete extinction. Diopside is the pyroxene present, It is colorless to very pale green. Where it is included in the hornblende it is clearly automorphic, and occurs as equ=nt individuals. The cleavage is good, but not as ggod as with the horn- blende. Between cppssed nicold, the typical augite type of twinning is seen, The mineral is practically completely altered to a scaly aggregate of probably ahtigorite, as is the usual thing in these specimens. This scaly alteration is visible only between crossed nicols; but even in ordinary light the mineral has an altered, kaolinized look. It is optically plus, 2V is about 45°, and the maximum extinction angle is consistantly about 35°. The index is higher than the hornblende in which it is embedded. In addition to these minerals, there is appatently an amphibole presenti, 2V is about 70°, Chp is negative, and Chy positive. There is = pleochroism resembling enstatite; the slow direction making an angle ¢f from 20 to 30 degrees with the cleavige. The slow direction is a light green, (69) Page 153 while the fast direction is a pale rose. Cleav:ige is good and resembles the hornblende. The mineral is possibly about actinolite in composition, tho this is but an estimate. It is surrounded by 2 zone of secondary dusty magnetite, and between this zone and the hornblende is a seam of finely fibrous chrysotile, arrenged with the fibres nermal to the directicn of the crack, The main mineral is traversed by = Tew seams which are stained 2 pale yellow, In addition there seems to be one or two grains of olivene altering to the characteristic mesh structure serpen- tine. Inclusions of magnetite are characteristic here. ALTERATICHN were it not for the hornblende, the entire rock would seem to be extensively altered; while if the hornblende alone were considered, the rock would seen fairly fresh. As it is, the individual shows a rather peculiar combination of ex- tensive alteration and freshness. As mentioned above, the feldspars are practically completely altered and are how sirply a cloudy mass of dull grayish white specks, either isotropic or opaque; with a few scales of doubly refracting mineral embedded in the cloudy mass. The diopside is also extensively altered to an an- tigoritic aggregate of scales, showing an orientation in a rough way. The hornblende is very locally only altered around the borders to a latliice~structure serpentine, tho this is far from common. Page 154 (69) There are a few automorphic-like areas poikilitiecally included in the hornblende which are completely altered to serpentine and of which no trace of the original mineral remains, In these, there is an outer beopder of "dusty" magnetite of probably secondary origin, within which there is this mass of fibres, all practically parallel to one another, and which is very probably a bastite pseudomorph, after a rhombic pyroxene. These arcas are possibly three or four i» number. In addition there are probably as many areas with & similar ring of magnetite, similarly situated in the hor blende, in which there is simply a matt of very fine fibres of doubly refracting material, mixed with a few more scaly m@sses. The fibres are at ramdom orientation, and are almost submicroscopic in size, SPECIMEN 69 Oxide percentages Wt. lineral Areas| Gr, Wt, | 5 |piOg AIo0z Feo0z Fel Calf MgO |Ko0 Jos0 Ho0 HORNBLENDE 630] 3,2 12018 | 60.6 23.6) 61 | 4.2 (9.,M 7.3(6.6] 142/142, 0.6 DIUPSIDE Fresh----182| 209| 2.2 | 987 | 20.9[ 16.5] 0.3| 0.3 | 0.6 7.5 6.2 Altered--127 MAGNETITE 6} 5.1 31 9.4 6.0 1 2.9 : - $0%¢ |100.4| 40.1] 6.4] 11.0 032.204.8128 T.2| 1.2 G.¢ Total | I0IL3 od 7 Adjusted: 406 | eb | 11% | 134 140 13% 1% | 16 7% ~~ GGT @s8d Page 157 SPECIHEN 70 SPECIMEN 70 ( SUMMARY TEXTURE: Coarse grain 3TRUCTURE: Granitic; slight monzonitic relation CUMPCSITIOR : (I) Ilineral: (Primary) (Secondary) Quartz (455) Feldspar (50k) —=Kaolin Hornblende (Io) —=Chlorite Biotite (52) Rutile (15) LEGEND (2) Chemical: O Quattz 310z==-uns~- 772 CBO=-=----- 40 - ( All, ~-nvnen 12, HOw wee I O Feldspar PeoQfmmm=m=m lo Na20=-=-=-- 4/5 Foros mem 00 2 Os nian 0 - REMARKS ¢ (I) High silics content due to distance from the fs \ ] other specimens in the field gt (2) Quartz abundantly present, and shows negative ww crystals (2) Roek has been stained, es < 3 shown by apparently biaxial character of quartz, and by its fracturing (4) Illosaic relationship between quartz and feldspar (5)Plagioclase range; Bytownite 25-70 to Oligoclase 75-25 (6) High unduletory extinction, clear zonal growths (7) Inner zones of feldspar (the most calcic) are the most altered : (8) Hornblende is host for biotite, rutile =nd magnetite (9) Biotite is the host for magnetite (IC) Rutile is associated with the magnetite towsrds which it is xenomorphiec (II) liagnetite included by the biotite, but is on the boundary between the quartz and the feldspar ( (I2) Hornblende is notably altered, while feldspar is slightly altered, but apparently not to saussurite but to kaolin BIUTITE QUARTZ DICRITE Page 159 Page 158 (70) 5PECIIEN 70 { | the quartz crains are the poikilitic host for the feldspar; TEXTURE tho this is rare; and even when it is present, the tvo are 7 shows a h alline phanerocrystalline "he rock shows a holoecrystal Pp y not crystallog aphically interzrown. The quartz and feld- se grained granitic texture. There is a ; : medium to coarse grained g C | spar together, seen between crossed rnicold, has the appear- : 4 1 : pm * the monzonitic texture: a few of the : : : BSpLIeL deviant or ¥ ance almost of a coarse grained mosaic. feldspars having the same degree of automprphism &s the Peldspar is also abundantly present. It is of the quartz. plagioclase variety. It varies fro: stout prismetic to OT TAT MINERALS : A 2 : : PRIMARY MINERALS equant and granular in habit. A few of the individuals show nue is abund ntly oresent in this specimen. 1t et ha ra a longer prismatic development, and these latter show the 3 ol -pleochroic. The sign of : is srensverent, eclorless 21 mon+p 5 best albite striations; hence the probable habit is tabular. » - . 0D to be slightly biaxial; the mineral is positive; it appears 10 be E A medium to fine, generally polysynthetic 2lbite twinning 3 ra i iaxial. No cleavage is apparent; Rt 45 really s strained wniaxd g ? ? ils present. Carlsbad twinning is much less common, tho it cone! isible. It shows high r $0 ¥hers-is 2 coneholdal fraeWwre Vis " is present. Those tabul:=r feldspers showing equant in sec- ( ‘a1 tion is a thick one. interference colors, so that the sec tion ( being cut parsllel to 010 ) are locally quite char- The individuals sre xenomorphic, and the rains are as large acteristically seen to contain s& sharp, distinct, inner 3 onstituent. A few zonal growths are present. i : : as any other cons g crystal showing a much higher angle of extinction than the T rregular in occurrence, tho straight individually. : hese sre irreg ! outer one does. It usually shows undulaiory extincticn, r ‘hese g ths seemed to be cleava~e; Under the low poser dlese growihs S and is typically more clouded by alteration than the surround- der t high power they were seen to be surfaces of 2 : but under tne gn I 7 ing feldspar, when seen in ordinary light. There seems to i silo and often plenes containing negative | ; Bante imolasions P 2 be more or less of a sharp boundary between the two varieties. ; “he these negative crystals occur, the nlanes i . s : crystals. here thes € 2 ‘a the inner one, the extinction angle is around 20°; mek- i ( Th 8 )t abundant or continucus, a are guite distinct, They are no un ing it a Bytommite (25-75) while the mxtincticn angle on the hey & hars ristically present. They are an aid : bRé they are characteris ¥ pres y cuter one is around zero degrees; making it an Cligoclase A 4) 1ahiz 0 spar and the quartz. The in the distinguishing of the feldsp f e oi about 75-25 composition. The outer shell is app oximately 3 g , ; a se lines of inclusions quartz is very much fractured, and these lin 2/¢ the size of the inner one. lost of the feldspars how- iy ines ior is born out by the fact age bent. This strained condition J | ever do not show this zonal growth, but they do show undula- vc 3 Sv ly slightly biaxial. A few of . that the cuartz is apparently slightly tory extinction. llost of the feldspars are distinctly altered; Page 160 (70) these showing a proximately 1/3 the cloudy alteration to probably kaolin. Cthers of the feldspprs are distinctly fresh. Cleavage is not cenerally epparent, tho a slight cross fracturing is occasionally present. There are no noticeable inclusions except those due to alteration; this alteration differing for the zones of different composition. The feldspar is sssoueciated with the quartz, towards which it is automorphic to hypautomorphic. The feldspars have an index which is .igher than quartz, as shown by the Becke test. The composition seems to vary thruout the rogk. Thus on individuals showing optie exial figures in convergent light, extinction angles of 170, 570,650 etc were obtained, show- ing a varying composition of oligoclase-sndesine (65-35), andesine (60-40), oligoclase andesine (65-35) were obtained. Extinction angles measured on albite limell=e by the "Statistical method" vary from 0° to 89; pointing to an oligoclase of (75-25) composition. Hence this specimen - shows rather a variation in feldspar species than = con- stant single vargety. Hornblende is p esent to a minor amount. It is = deep greenish brown in color. Long prismatic occurrence is the typical habit. It is an amphibole because of the high relief, perfect cleavage and churacieristic 1240 cleavage angle in end sections, a few of which are present. It is the host for biotite, rutile, and magnetite. It is sparingly present; probably not exceeding 1%. A few of the individuals are but slightly altered, the most being very notably altered to a tr chlorite, probably chlinochore, giving a peculiar frayed Page 161 and shreaded appearance to the individuals. It is associated notably with biotite ( hence with the rutile) and with :ag- netite. 111 of the rutile present with the exception of one pateh is agsociated with the hornblende. Cn side sections there is a meximum inclined extinetiocn of 13° and s& pleochro- ism of (b) honey yellowish green, (e) =lmost blesck green; while on end sections the pleochroism is (b) almost black brownish green, (a) a light browhish green. Extinction is symmetrical in these sections. Biotite is also present sparingly. A deep brown is the common color. "hen seen in basal plates it is notably automorphic and hexagonal in appearsnce, and has a color best described as "dark dirty brown." When seen in side sec- tion, the perfect cleavage, parallel extinction 2nd charscter- istic pleochroism is present. It is the host for magnetite. A few shreads are often inecluied in the altering hornblende, towards which it is distinetly automorphic. It occurs both as a frayed automorphic individual, and as a more automorphic individual usually in isclated flakes. Cccasionally it is included by the hornblende, end when this i$ the case, it is usually shreaded in appearance. It varies from entirely fresh to ( in one specimen ) almost entirely altered to a chlorite, but a few remainin brown strips of biotite re- maining. The unaltered specimens show a honey yellow normal to the cleavage, and a dark brown parallel to the cleavage; while the more altered specimens show & yellowish green normal to the cleavage, and a bluish green parallel to it. 17. (70) Page 162 Rutile is notably present in this specimen, 2mount- ing to possibly a few tenths percent. It is automorphic, yellow in color, and granular. A few of the grains are rath- er large in size. Its index and double refraction are very | high. It is uniaxial and positive. It is associated with the magnetite, towards which it is xenomorphic. It is also associated with the biotite and somewhat with the hornblende. llegnetite occurs 21s0 in granular form. lost of the grains seem to be distinctly automorphic, being the most automorphic mineral in the slide. It is typically associated with the biotite, by which it is included. To 2 slizhtly less extent it is similarly related to the hornblende. It pro- bably makes up half a percent. A very few grains are scatter- ( ed around thruout the main mass of quartz and feldspar, and when thi: is the case, it is found to be on the boundary be- tween individuals, rather than included in any one of them, ALTERATICN The hornblende in this specimen is quite notably altered to probably a chlorite, as is the biotite. A few of the flakes of altered biotite closely resemble sgerine-augite. The feldspar, in spite of the extensive development of kaolin, shows but little development of the fine aggregates of doubly refracting needles present in other slides. The rock is in general cuite altered, tho apparently it is not. This i: due to the fact that the component minerals ( in the main show a2 high resistivity to alteration. The rock has been actéd upon by the same alterins forres as the others in the suite, but only a few minerals show this effect. ~ SPECIMEN 70 Oxide percentages Wt. Mineral Areas| Gr. | Wts} » 310, b£lp0z|Fegl,| Fel Calf Mel Nal Ko0| mid Quartz 50.6 | 2.65 | 134 |44.8| 44.5 Feldspar (Oligo-andes) | 55.4 | 2.66 | 147 |50,3|30.1| 12.6 3.5 4,0 Hornblende 1.0} 3,156 Z 1.1 1.4, O.6 O,59,1 0,0 10,3] 0,0{0.3 Biotite 2.5 | 2.90 10 | 3.4} 0.6 0.1 | 0.2 Rutile O.5 | 4.21 2 10,8 0.8 Totals 596 IU. 76e6|13.2 | U.b P.I|2.6| 0.6| 4.0/0.279.8 Grand| totall; [99.75 29T 838d Page 164 SPECIIIEN 72 SULIARY TEXTURE: Coarse to medium grained STRUCTURE: Gramitic; notmal order of separation CUMPOSITICN : (I) llineral: (Primary) (Secondary) Quartz (31%) Chlorite (2%) Feldspar— (570) Kaolin Biotite —( 840 llagnetite (20) Titanite (2) Chemical: 310p=mmmmm=m 705 ~~ C80--------- 3a 4120;------- 15) HgO-eme-om=s 25 Fes0x -—-— a Bo Ke 0 -————— Ik FeO-=--=--== I N8gO-------- 5/0 REMARKS : (I) Quartz and feldspar occur in fine grained xenomor- Fale aggregates; and hence show the mosaic texture High silica content due to distence from the other specimens in the field Plagioclase only seems to be present ) Felds ar: Oligoclase-Andesine 70-30 ) Rock subjected to crushing stresses, as is shown by arent biaxial character of quartz 3 But a small amount of magnetite included by the biotite ) Rutile presence notable ) PFeldspar show zénal alteration similar to type of vecimen 70; ? center being the most altered ) Undulatory extineton not marked here OS OI ec Ovid ah Page 165 SPECIIEN 72 LEGEND Quattz Feldspar Biotite Iagnetite Chlorite | Titanite Page 166 (72) SPECIMEN g2 4 by its biaxisl character, its undulsa tory extinetiocn, and TEXTURE sign; also twinning. By the method of maximum extinction This specimen is coarse crained to medium grained tngles measured ag: inst the .1lbite atriations, ani by the holoerystalline phanerocrystsalline graomitie in texture, use of "optic axial" sections, the feldspar was found to Tho there is generally » uniformity in size; still there be consist nily an Ulisoclsse-:ndesine of about 70-20 are local variations. In these both the quartz and the composition. Ca:lsbad twinning was present! locally; feldspar occur as fine grained xenomorphic agsregates. the polysynthetic twinning seemed to cecur especia ly on those feldspars showing the most =1lteration. nese latter PRIMARY MINERALS were lathshaped rather than tabular, ss were the others. Plagioclase alone seems to be present here as the representative of the feldspars. The usual texture is Guartz is the next importont constituent. It is hypautomorphic, with oceasicnal -utomorphic tabul r ! in general xenomorphic snd intersticial, Under convergent crystals. Decause of the predominance of the felds ar | light it appears to be slichtly biaxial, indicating { it seems to be quite utomorphie, but this a pearance is | strain. This is boutne out by the fact that it is locally deceptive. Fine alhite siriations ccecur on some, while | quite fractured. The individucls cf quartz are usus=lly others are a parently untwinned. Cleavage does not seem | large, but locally they seem to be small. They occur to be apparent. This is strange, 23 the quartz is notably | with the feldspar 2s small xenomorphic aggregates, fractured and its strained char cter is shown by its Biotite occurs as automorphic flakes nd segregstians apparently bisxinl charscter. Afew of the indiviiunls show : the majority of the individuwils showing a deep brown- honey- undulatory extinction; especially those which appear un- | yellow pleochroism with characteristic parallel extinction. twinned, Zonal gr wths are common, both cn the twinned arid | There mar be some green biotite present; tho this greenish the untwinned cryst: 1s. Tis is apparent in crdiinary light > : material closely resembles = chlorite. This latter pos- because of inclusions arranged in crystal faces, A ibility seems the most probable, as it does not have the clouded alteration to probably keclin is the common feature. perfect basal cheavize of the brdéwn variety; and as it Locally the altering feldspasrs are seen to contain flakes (or very similar material) occurs sparingly as = bo ‘der to of birefringent material, when viewed between crossei : the brown variety. There seems to be 2 sm=1l amount of y nicols. The feldspar was distinguished from the quartz magnetite 1ncluded in the biotite; the amount being very smail indeed. Page 168 (72) { Hagnetite is hardly present in this rock, tho as mentioned under blotite, it seems to be loeally included in arall grpain-like particles in the biotite. A trace of rutile was also found in this section. Ite lsck of cleav-ge, prle yellowish or pinkish eclor, automorpkic habit and its typleal ocecurrence ns a neucleus for the biotite 2ll point to thic particular mineral. Its high double re raciicn was determined by (1) lacing the stage in the extinction position and inserting the cuartsz wedge. The colors of the quartz c¢ uli be snsily seen thru it. (2) Hext ii was turned toc the 4.9 position and upon inserting the cuartz no colors at 211 could be seen. This { proves that the mineral actumlly has & high double refr- action and is not simply hizhly srbsorbast in ali directionms. ALTFERATILH The rock seems tc be somewhat sliered, Loeally the feldspars seem to be extensively alter i tov kmolin: with occasionally the production of doubly refracti g flakes of lower index than the feldsrar (?) . ‘48 mentione! under biotite, 'here seems to be mlteranticn of this mineral to & chlorite. Feldapar k.olinization seems tc proceed often from the center of the crystal. There 1: usurlly a definite can- ter of kaolin with i -repulayr branching spreading out thru the iddividual; renderi g it dul whitis. gray and opacue. SPECIMEN 72 Oxide percentages Wt. Mineral Area| Gr. Wt. jo p10, h1z0, FepOy [FeO (Cal [MgO | K,0 Nap} H20 FELDSPAR (Uligo-Andesine 570a | 2.66 | I515| 57.4: 85.0 13.7| 0.6 2.40.6] 0.65.2 70-30 QUARTZ 10a | 2.65] 820] 31.4] 31.0 BIOTITE 708 | 2.90] 203] 7. Z.3 1.5]; 1.2 |0.410.,1]0.8 0.3 MAGNETITE 9a. | 5,1 461 1. 1.2 10.5 CHLORITE 2% | 2.7 62! 2.4 o.8 0.4 0.8 OZ Teac | T00.4 70.1 15,61 5.0 0. 912Z.6/2.2] 0.9 B.2] 0.2 Total 101.7 Adjnsted: 70% | 15% | 3% 15) 36) 25| 1% 5% L 691 o&Bg Page 170 SP] Cc 1k EN 83 SPECI LEN 83 SUILIARY TEXTURE: Uneven medium grained 3TRUCTURE: Gabbroid to Diabasic CONSTRUCTION {I) llinersl: (Primary) (Secondary) Feldspar (46) Hornblende? Biotite (260) Iron stain . Augite 9/0) Enstatite—( 65) liagnetite (30) (2) Chemical: 510,-~=~~=~~ -53% Ca0--------- IC) LEGEND { AIpO0z-------- 14) Mg0----==--- 9 \ FecOrmmmmm-mm- 4% KpO=-mmmmmmm 1; FeQwwmwememmm- 50 Nagl-=emwmw=m- 4 Feldspar Biotite Augite | REMARKS: 3 Enstatite ; feldspar is entirely plagioclase | Undulatory extinction common, tho not exceed- Magnetite rly pronounced Plagioclase range: Cligockase, 70-30 to 80-20 Augite shows beginnings only of alteration Rod inclusions of magnetite in the Augite A border of green biotite or amphibole about augite Enstatite as grains and granular aggrepgatés Enstatite commonly include es much granuler magnetite Biotite occasionally grown about the enstatite ) Enstatite and biotite occasionally included by auzite A high content of magnetite Rock shows but slight alteration dH HOS IT oop E no HH Do Ho BICTITE ENSTATITE DIORITE m Pace 172 SPECIMEN 83 URE TEXTUR he This sléde shows a rock having a holoerystalline phanerocrystalline, uneven gabiroid to diabasit texture. The enstatite is granular znd automorphic, and much finer greined then the augite, which is larger, poorly tabular, and rarely the host for automorphic feldspar ckystals. Then the specimen is seen betw:-en crossed nicols the diabasic character of the texture is brought out by the automorphic appearance of the feldspar laths. PRIMARY IMINERALS Plaegioclase feldspar is present and makes up about half of the rock. The individuals are automorphic to hypautomorphic generally, and lath-shaped charccteristically. Albite twinning is cmmmon, and is usually of the broad sim- ple type; tho there are many individuals showing poly- synthetic =1lbite twinning. Carlsbad twinning is either spar- ingly present or (mest probably) entirely absent. Undula- tory extinctimn is common tho not exceedingly pronounced. , i,e; practicaily all individuals show undulatory extinction, but the inner and outer zones do not differ sc proncedly in extinction angle. There is slight evidence of bemding and and crushing of the feldspar, since many of the individuald are fractured and very slightly mispleced sc as to eppear bent. As no quartz is present, the feldspar is very easily recognizable between crossed nicols by the characteristic habit, color, and twinning. The feldspar is negative, and Page 173 on individuals showing an optic axis figure with polarized light the extinction angle varies from 75° to 90°, making the feldspar an oligoclase, varying in composition from 70-30 to 80-20 ( Albite-asnorthite) The Augite is present representing the monoclinic pyroxenes. It is light zreen in color; fairly distinetly automorphic in cutline, tho less so than the enstatite, which it occasionally includes. Twinning is common and character- istic, after apparently both the carlsbad 2nd slbite laws, In the sections showing the twinning, the 90° cleavage is very clearly brought out. The mineral shows the beginning only of alteration to the flaky aggregates sO character- istic in most of the specimens. It is the most altered of the minerals in she slide, and yet it is comparatively fresh. The inclusions are numerous (particularly so) and quite characteristic of the augite. There is an immense number of very fine needle-like rods, probably of magnetite, arranged very roughly in zones thruout the individual, These rods are almost submicwescopis in size and seem to be ar- ranged i. sets, the rods of each set being parallel and apparently lying along some crystal face. Under low power, this inelusion gives the augite & peculiar shoded appear- ance, very characteristic. There ar: approximately two sets probably lying along the prism faces. In addition to this inclusion, there is some massive magnetite sparingly in- cluded in the augite, tho nowhere nearly so common as with the rod inclusions. Page 174 (83) The augite also typically occurs as the center about which there is a border of either green biotite or amphibole; very probably the latter. There is but a partisl develop- ment of this zonal zrowth here however. The augite is com- monly in the vicinity of aggregates of magnetite. Enstaetite is present, and is quite automorphic and pleochroic. The grains are comparatively large, tho still mach smaller thin the other consitituents. It occurs as grains and granular aggregates. It commonly includes 'much massive magnetite, which ocecasiinelly forms the entire center of the cpystal. Also occasionally the enstatite is entirely included poikilitically within the biotite. Its usual occurrence is as an aggreg:ote of rather minute auto- morphic crystals. Its pleochroism is distinctive, the fast direction being a rose-pink, the slow direction a pale green. It is biaxial, of high axial angle, and positive in character. The fracture and cleavige is slight but distinct. Filling of the fracture by iron stain is common. The brown variety of biotite is common. Tho auto- morphic it is irregular in outline. It occasionally is the hogt for enst=tite, and is itself included occasionally | by auzite, as is the enstatite. It is usually in irregular | branching and stringy masses, tho occasicnalily it is in compact units of automorphic crystals. .8 menti ned above, there is a possibility that some of the gr-en material brodering the augite is green biotite, but from & consideration of order of crystallization it is highly improb=ble. llore likely the material is green hornblende. Page 175 (82) There is a rather high content of magnetite in this thin section. It is typieally included by both augite and biotite. It occurs in rekher large automorphic grains, ALTERATION The rock is but slightly altered; the feldspars being but hardly touched. As usual, the augite seems to be the most sensitive mineral 2nd shows the first signs of alteration. This type of alteration is by the formaticn of en aggregate of doubly refracting flakes of minerels thru- out the mass of the augite; visible only between crossed nicols., The greenish border found to the augzite ocecas- ionally ts usually mede up of this kipd of an agoregate, and hence is prodably altered augi‘e ‘rather than being primary hornblende or biotite. Locally there are hematite stzins, and flakes of & dark red color, also probably pronounced iron stain. This staining is mostly confined to the augite and (mainly) enstatite. SPECIMEN 83 Uxide percentages Sach Mineral Areas 0 ALo0z| FepOp Cal K,0 FELD3PAR Uligoclase 514 2.64 1368 JU.6] 0.5 2.8 Pb i10.5 "5-25 AUGITE z228 1.8 ly 2 BIOTITE 87 1,6} 1.4 10,1 0.4 ENSTATITE 59 0.2 0.1 MAGNETITE 18 LZ | 12.2 | 2.2 IC.: 0.9 1 [01.5 Adj 1456 | 4% 10% 15% by A 9LT o3sg END OF TITLE