UNIVERSITY OF ILLINOIS LIBRARY AT UP°" 'MA-CHAMPAION OLOGY NOTICE: Return or renew all Library Materials! The Minimum Fee for each Lost Book is $50.00. The person charging this material is responsible for Digitized by the Internet Archive in 2016 https://archive.org/details/geologyoftarrant313wint 6 t 3 7 3D tO ON A NEW EXOGYRA FROM THE DEL RIO CLAY AND SOME OBSERVATIONS ON THE EVOLUTION OF EXOGYRA IN THE TEXAS CRETACEOUS 1 By Emil Bose Nearly twenty years ago attempts were made to subdivide the Texas Cretaceous, basing stratigraphical zones on the occurrence of oysters, especially Gryphaeas and Exogyras. That such a subdivision must be doomed to failure will be evident to any paleontologist on account of the extreme variability of oysters, Exogyra included. But these at- tempts are interesting, in so far as they showed that Ex- ogyras occur in most of the Cretaceous beds of Texas and that all these may be related to each other. Exogyras occur practically from the lowest stratum of the Trinity form- ation, which corresponds to the Aptian, to the highest Cre- taceous, the Navarro beds; which in their upper part, the higher Escondido beds, certainly represent the Maestrich- tian. In order to show the evolution of Exogyra in the Texas Cretaceous a thorough collection of specimens of this genus in the different beds and a redescription of the known species would be absolutely necessary; first, because many forms are still undescribed; and second, because in most of the described species the development from the smallest to the mature individuals has not been sufficiently taken into account. The very small specimens are often the most important ones, because their ornamentation is frequently Qiuite different from that of the full grown individuals and demonstrates from which forms in lower beds the species has branched off. Often the ornamentation on the very first part of the beak of mature specimens shows also this original ornamentation, but generally the beak has been corroded by the movement of the shell in the water or by the grinding effect of sand in currents. In these cases the beak will appear smooth, although the younger specimens show a decided ornamentation. In Exogyra the evolution 4 1 The manuscript for this paper was submitted in June, 1919: the bulletin was issued in September, 1919. (Ed.) 4 University of Texas Bulletin of the beak is of an importance similar to that of the suture and the smaller whorls in the ammonites. More than twelve years ago, when I described the fauna of the Cerro de Muleros near Ciudad Juarez, Chihuahua, Mexico, I felt convinced that most of the Texas Exogyras had developed from a common tribe, but at that time I did not have enough material and there seemed to exist serious gaps which in part have been filled since that date. One of them especially was between the Vraconnian and the highest Cenomanian; or, using local terms, between the uppermost Edwards limestone and the Buda limestone. This latter one has been recently filled through a discovery made by Mr. W. R. Cartledge, who found a new Exogyra in the upper part of the Del Rio beds in the region near the quick- silver deposits of the Terlingua district; a species which will be described farther on. I do not propose to prove that the evolution of the Texan Exogyras was entirely continuous, because my material is still very incomplete; but I wish to open a road for some- body else who may want to demonstrate in what manner Exogyra developed in Texas during the Cretaceous. It will probably be found that such an evolution existed and was at least partly parallel to the development of this genus in southern Europe and northern Africa; possibly in the later stages also in Asia. Thus the content of the following paper will be merely a sketch, but it may point out a way for a monographicai description of the Cretaceous species of Exogyra in Texas.’ The oldest species of Exogyra in the Texas Cretaceous seemingly occurs in the lower part of the Trinity formation, the Basement sands or Travis Peak formation of Travis County. This species has been described, although net fig- ured, by Cragin 1 as Exogyra Hilli. He asserts that it has also been found in Arkansas, where it was described by R. T. Hill . 2 It is a small form somewhat similar in out- 1 F. W. Cragin, A contribution to the invert. Paleontol. of the Texas Cretaceous. 4th An. Rep. Geol. Surv. Texas, 1893, p. 186. 2 R. T. Hill, The Mesozoic geology of southwestern Arkansas. An. Rep. Geol. Surv. Arkansas, 1888, vol. 11, p. 131 (under the name of Ostrea Franklini ), pi. 5, fig. 1-10 (not pi. 5, fig. 11-18; pi. 6, fig. 19-27; pi. 7, fig. 28-30). On a New Exogyra from Del Rio Clay 5 line to immature specimens of Ex. texana , with 5 to 8 radial folds on the anterior slope, a distinct umbonal ridge, and a steep anterior slope. The upper valve is practically smooth. This form seems to be intimately related to Exogyra Bous- singaulti d’ Orb. 1 which occurs approximately in the cor- responding horizon of Europe. A similar form has been found in the Aptian of San Juan Raya, Puebla, Mexico. This species seems to have branched off into several forms in the next higher division of the Trinity formation, some of which have been described and very imperfectly figured by Cragin as Ex. pauper cula 2 3 and Ex. weather for densis.^ These species are quite frequent in the Alternating beds (Glenrose), the middle and upper part of the Trinity form- ation. Both seem to be related to Ex. Hilli and Ex. Bous- singaulti, although the distinguishing feature in Ex. pau- percula is that the beak becomes free from the rest of the shell as in Ex. arietina. Ex. paupercula has only 2 to 4 irregularly-topped, angular, radial folds on the lower valve, while the upper valve seems to be smooth. I have not been able to see the original specimens. Much more similar to the Ex. Boussingaulti group is the Ex. weather fordensis (pi. 1, fig. 1, 2) with a strong um- bonal ridge, 6 to 12 oblique plications on the anterior slope, and a greater number of narrow, subradiate, or curved pli- cations on the posterior slope. The upper valve is smooth, but the margin is often scalloped corresponding to the end- ing of the ribs on the lower valve. This is, at least, what I take to be Ex. weather fordensis, a species which has not been very well figured. In the collection of the University of Texas exists a number of specimens collected by Taff at one quarter of a mile west of Weatherford, labeled E. Boussingaulti d’Orb. This species certainly is very similar to the French form and a near rela- tive of it, and at the same time also of Ex. Hilli. It does iA.d’ Orbigny, Voy. dans l’Amerique merid. t. Ill, 4me part, Pal., p. 91, pi. 18, fig. 20; pi. 20, fig. 8, 9. Idem, Paleont. frang., Terr. Cret. t. Ill, p. 702, pi. 468. 2 Cragin, loc. cit., p. 186, pi. 30, fig. 7, 8. 3 Idem, ibidem, p. 188, pi. 45, fig. 7-10. 6 University of Texas Bulletin not seem possible to prove that it is the type of Ex. weather- fordensis but it appears at least to be very similar to the specimens described and figured by Cragin ; and it certainly proves that a very near relative of Ex. Boussingaulti lived in the Texas sea at about the epoch of the European species. The specimens from a place four miles west of Montell, also cited by Cragin, may belong to the same species, but they are mainly upper valves, and not very characteristic. These last two species seem to grow larger than Ex. Hilli and to a certain degree lead over to Ex. texana and Ex. arietina. The first of these two species is found well de- veloped in the Walnut clays, the base of the Fredericksburg formation. This species has been described and figured by several authors, first by Roemer , 1 then by Conrad, Gabb, Coquand, White, Hill and Vaughan, and by myself . 2 The species is nearly related to Ex. flabellata Goldfuss of the Cenomanian of Europe, but it is in general broader, the ribs are more numerous, and the ridge is nearer to the anterior side ; the European species is generally a little younger than Ex. texana , although this latter passes through quite a num- ber of horizons. In the Walnut clay it is associated with Engonoceras, Schloenbachia group of Sch. Belknapi, and Schloenbachia group of Sch. acutocarinata, and these beds probably represent the Vraconnian or the Albian. It is found also in the Comanche Peak limestone and the Ed- wards limestone; both still belonging to the Vraconnian or Albian. At the Cerro Muleros it occurs throughout the whole Vraconnian. It should not be overlooked that the Comanche Peak lime- stone seemingly contains another species of Exogyra, di- rectly derived from the main tribe and exceedingly similar to Ex. Boussingaulti; it is distinguished from Ex. texana by its smooth upper valve, is not very frequent, and I have not seen more than a very few specimens. Ex. texana is certainly derived from the tribe of Ex. Boussingaulti represented by Ex. weatherfordensis , but the younger species grows much broader, the umbonal ridge 1 Roemer, Kreidebild. v. Texas, 1852, p. 69, pi. 10, fig. la-le. 2 Bbse, Cerro de Muleros, Bol. Inst. geol. de Mexico, 25. P. 112, pi. 20, fig. 14-16; pi. 21, fig. 1-11; pi. 22, fig. 1-9. On a New Exogyra from Del Rio Clay 7 moves nearer to the anterior margin, which becomes ex- ceedingly steep, while the posterior slope becomes flattened or even concave. The upper valve develops a great number of somewhat irregular radial ribs, the umbonal ridge be- comes very pronounced and the anterior slope quite steep. A conscientious study of the forms from different horizons may show that even within the species a certain develop- ment takes place, in so far as the umbonal ridge is nearer to the anterior margin in the older specimens than in the younger ones, and that the ribs grow coarser in the indi- viduals found in the higher horizons. Ex. texana nearly always occurs in great numbers and with it begins the rich development and subdivision of the principal tribe. Before we go any farther we shall have to mention an- other form developed during thq Albian or the Vraconnian and apparently the ancestor of several younger species. This is the form described by Cragin 1 as Ex. plexa. Under this name Cragin seems to have united at least two differ- ent species; I refer his name to one of these which looks entirely like an enlarged juvenile specimen of Ex. arietina (compare the description of this species given below). The exact types could not be found, but there is sufficient ma- terial from the original localities. (Compare pi. 1, figs. 3, 4.) I regard as the type the specimen figured by Cragin in his figures 3, 5, 6 (not 4). It is entirely covered with fine radial ribs which cross the prominent umbonal ridge obliquely as in the juvenile specimens of Ex. arietina. The specimens occur in the bed of Ex. texana below the Kiami- tia clays on the Texas and Pacific railroad, three miles west of Benbrook. The whole shell is spirally curved similar to the young Ex. arietina although the size is much larger. The beak is still pressed down against the body of the shell, but a further spiral development would detach the beak from the rest of the valve. This species has probably developed from the group of Ex. Boussingaulti (Ex. weatherfordensis) losing the thick 1 Cragin, loc. cit., p. 187, pi. 30, fig. 3-6. 8 University of Texas Bulletin folds and developing fine ribs, but retaining the high um- bonal ridge. In the same strata we find another species, of which a specimen not very characteristic has been illustrated by Cragin in his fig. 4. The upper part (about 15 mm. in height) is practically of the same form and ornamentation as Ex. plexa typ. but from there on it begins to develop on the anterior side four to five strong radial folds begin- ning near the umbonal ridge and going down obliquely with the ridge to the antero-inferior margin. They are much stronger and sharper than shown in Cragin’s figure and are covered by fine radial ribs. They are fainter on the mould and there appear smooth. As our material is not sufficient to allow a complete description we shall designate the species as Ex. nov. sp. aff. plexa. (PI. 1, fig. 5). Ex. plexa seems to lose the fine ribs on the lower margin in larger specimens, as is shown by an individual from the original locality. This feature is still more evident in larger specimens found at the base of the Fort Worth limestone in Duck Creek, Grayson County. This is evidently a younger form of the same group, but possibly a different species or variety. It grows much larger than the type, shows ap- proximately the same ornamentation on the umbonal region, but becomes entirely smooth on the inferior margin. Another form from the Kiamitia clays found on little Mineral Creek, north of Pottsboro, Grayson County, shows an ornamentation very similar to that of Ex. plexa on the umbonal region, but develops a rather deep furrow along the umbonal ridge on the posterior side and several obtuse folds covered with fine radial ribs on the anterior side near the antero-inferior margin. It is most probably a descend- ant of Ex. nov. sp. aff. plexa, mentioned above (PI. 1, fig. 6.) About the development of Exogyra in the Georgetown formation, i. e., the lower and middle part of the Cenoman- ian, little is known. There is a large species frequently found in this forma- tion and it has generally been called Ex. americana or Ex. Walkeri. It was originally described by Marcou as Gry- phaea sinuata var. americana, and Cragin cites it as Ex. On a New Exogyra from Del Rio Clay 9 americana Marcou. Unfortunately, only very large speci- mens are described and figured, but the individual illus- trated by Marcou shows that the younger specimens must have strong, fold-like, radial ribs in the umbonal region. Therefore I presume that this broad and flat species with its obtuse ridge near the anterior margin developed from a broad, coarsely-ribbed group, probably one derived from Ex. texana . Exogyra becomes exceedingly frequent on top of the Georgetown formation in the Del Rio clay which represents part of the upper Cenomanian. The principal species is Ex. arietina Roem. which we have redescribed farther on. It is evidently a descendent of Ex. plexa; it retains the ornamentation of this species and its form on the umbonal region and in the very young indi- viduals, but later on becomes entirely smooth and its beak becomes detached because the whole valve coils spirally. A second species is Ex. Cartledgei nov. sp., described be- low. It certainly was derived from Ex. nov. sp. aff. plexa , developing the strong radial ribs still more, while the beak became somewhat detached from the rest of the shell by the coiling of the valve. The strong umbonal ridge is still in existence, but the fine ribs on the beak were lost ; or at least are not preserved on the specimens I have in hand. This species grows much larger than either Ex. nov. sp. aff. plexa or Ex. arietina. Cragin 1 described another species from the Del Rio clay which he called Ex. Drakei. Unfortunately his figures are very deficient, but his originals show that the species is entirely different from Ex. Cartledgei. It is covered with irregular but strong ribs on the lower valve, not really coiled, but rather bent over to one side, as shown in Cragin’s figure 11. The upper valve is very similar to that of Ex. arietina and Ex. Cartledgei. In the next higher horizon, the Buda limestone and the corresponding strata of the Cerro de Muleros, which, ac- cording to the echinoid fauna described by Whitney, and iCragin, loc. cit., p. 184, pi. 29, fig. 8-11. 10 University of Texas Bulletin the ammonites, represents the very uppermost part of the Cenomanian, several Exogyras occur which are larger than most of those in beds below, with only the possible excep- tion of Ex. americana. The species found in the Buda limestone is Ex. Clarki Shatt., 1 but the specimens figured by Shattuck represent only medium-sized individuals and the species should be re- described and figured. It is a very broad and not very thick species very similar to Ex. americana; the medium- sized specimens show rather strong radial ribs, while the mature specimens are almost smooth. Very juvenile speci- mens do not seem to have been found. The species evi- dently is a direct descendent of the older Ex. americana. In the corresponding strata of the Cerro de Muleros an Exogyra is found in great numbers, which I took formerly to be identical with Ex. Clarki and which on account of its great similarity with Ex. ponderosa I described as Ex. pon- derosa var. Clarki. 2 The medium-sized specimens of this species really are extremely similar to Ex. Clarki while the full grown individuals are entirely different. I therefore rename the species from the Cerro de Muleros and call it Exogyra Whitneyi in honor of Prof. F. L. Whitney, whose beautiful studies about the echinoid and mollusk fauna of the Buda limestone have given us the first idea of its rich fauna and its real age. I have figured especially the juvenile and medium-sized specimens of Ex. Whitneyi in the work cited above. If we compare figs. 5, 6, 7, 11 on plate 26 with specimens of Ex. plexa, we can find nearly no difference. Comparing figs. 4, 8, 10, 12 on the same plate with Ex. Cartledgei and Ex. Drakei we see at once that the similarity is extremely great, although the beak is not quite as much coiled spirally as in Ex. Cartledgei. The upper valve figured in fig. 9 of the same plate is very similar to that of Ex. Cartledgei. The mature forms are entirely different from the younger 1 Shattuck, Buda Limestone, Bull. U. S. Geol. Surv. no. 205. 1903. p. 22, pi. 10, 11. 2 E. Bose, Cerro d£ Muleros, p. 115, pi. 23, fig. 17; pi. 24, fig. 6; pi. 25, fig. 8; pi. 26, fig. 4-11. On a New Exogyro, from Del Rio Clay 11 ones ; the ribs mostly are destroyed by erosion and the shell becomes entirely smooth, the beak detached from the body. It brings to mind at once the elongate varieties of Ex. yon- derosa but notwithstanding the great similarity between the two species I have become convinced that they should be separated specifically on account of the somewhat different form of the younger specimens, the generally broader shape of the mature Ex. yonderosa, and the extremely different age of the beds in which both species occur. Those small individuals from Cerro de Muleros which I have taken to be juvenile forms of Ex. Whitneyi show an astounding similarity to a small Exogyra extremely fre- quent in the Mainstreet limestone of Denison. This form has been frequently cited under the name of Exogyra arie- tina, but is easily distinguished from it by its rather strong ribs and the form of the beak pressed against the body of the shell. The real Ex. arietina occurs in a somewhat higher horizon of the same locality ; that is to say, in the Grayson Marls. The similarity between the small Exogyra of the Mainstreet limestone and the small individuals from the red sandstone of Cerro Muleros is so great that I have become somewhat doubtful if these latter forms are really the ju- venile forms of Ex. Whitneyi and not perhaps a different species identical with or very similar to the small Exogyra in the Mainstreet limestone, although they certainly occur together with Ex. Whitneyi in the red sandstone of Cerro Muleros. It is of course possible that the small Exogyra of the Mainstreet limestone is at the same time a prede- cessor of Ex. Whitneyi and of Ex. arietina. A species very nearly related to Ex. Whitneyi is Ex. ferox, if it is not only a variety. Ex. ferox was described by Cragin 1 ; unfortunately his figures are so deficient that one cannot get an adequate idea of the shape, and the upper valve of the original has been lost. The lower valve is very similar to that of the mature Ex. Whitneyi, but is still more elongate; no closer comparison can be made before the ju- 1 Cragin, loc. cit., p. 185, pi. 32, fig. 1; pi. 33, fig. 5; pi. 34, fig. 1; pi. 36, fig. 6. 12 University of Texas Bulletin venile stages of Ex. ferox have been found and described. The species was found in the so-called lower Cross Timber (Woodbine) sands, which correspond in age probably to the Buda limestone; at least, they also belong in their lower part to the upper Cenomanian. It is difficult to say to what group belongs the form cited by Cragin 1 as Ex. columbella Meek. It certainly has noth- ing to do with the type of that species. The specimen which came from the lower Cross Timber sands of Timber Creek, two miles below the Dallas-Lewisville Road, Denton County, is so much corroded that the surface appears nearly smooth, but on close inspection one can easily see that it had been covered by thick, rounded, rather strong ribs. It might be a very young individual belonging to the group of Ex. Clarki. From the next higher beds, the Eagle Ford shales, which correspond to the Turonian, very few fossils have been de- scribed in Texas, and among these only one Exogyra is cited under the name of Ex. columbella Meek. This is a rather small form with thin shell and covered by small, quite regular, radial ribs, which bifurcate at the umbonal ridge. It seems to be very possible that this species is a branch of the Ex. Clarki group, if it is not directly derived from Ex. arietina through the so-called Ex. columbella Cragin. This may only be decided when larger collections in the Eagle Ford shales or the upper part of the Wood- bine sands shall have been made. In Colorado a large species, Ex. suborbiculata Lam., occurs, which as Stanton justly remarks, is intimately related to the European group of Ex. columba, but this larger form has not yet been found in Texas. Also in the next higher formation, the Austin Chalk, very few Exogyras are known, although they can be found in great numbers in it. The Austin Chalk corresponds in its lower part to the Emscherian, in its middle to the lower Santonian, and in its upper part to the middle Santonian. I have not seen any Exogyra in the lower part, but it is Cragin, loc. cit., p. 184. On a New Exogyra from Del Rio Clay 13 possible that Ex. laeviuscula Roemer or a related form oc- curs there, as it certainly does in the middle portion. This very characteristic form is entirely smooth, but if the younger specimen figured by Roemer in PI. 9, fig. 3c, really belongs to this species, we might suppose that it is derived from Ex. nov. sp. aff. plexa through Ex. Cartledgei and Ex. columbella Cragin (not Meek) having lost entirely the finer ribs. An undescribed and unstudied small Exogyra is very fre- quent in the middle part of the Austin Chalk (zone of Mortoniceras texanum) on the Rio Grande. In the upper part of the Austin Chalk near Austin we find a great number of a large Exogyra which commonly has been called Ex. ponderosa, although it is specifically quite different. It has a broad and not very convex lower valve, with a rounded ridge and an extremely steep slope on the anterior margin, and is very similar to the large specimens of Ex. Clarki and to a certain degree to Ex. amer- icana. These species with very low right valves probably form an independent branch and are derived from Ex. tex- ana. I have not seen any of this tribe in higher strata of Texas, but a near relative, Ex. tamulica Stol., appears in the higher Senonian of India. The Exogyras of the higher strata of Texas, the Taylor marls (upper Santonian), Navarro beds (Campanian) and the higher Escondido beds (Maestrichtian) are very little known, practically only two species having been described : Ex. ponderosa Roem. from the Taylor marls and Ex. costata Say from the Navarro beds, which seems to continue into the base of the higher Escondido beds. Exogyra ponderosa has been first and very well described and figured by Roemer. 1 In recent years it has been re- described and figured by Stephenson.- His figures are very characteristic but unfortunately he has not tried to describe and figure the development of the species from the Roemer, Kreidebild. v. Texas, p. 71, pi. 9, fig. 2. 2 L. W. Stephenson, Cret. dep. on the Eastern Gulf region. U. S. Geol. Surv. Prof. Paper 81, 1914, p. 46, pi. 13, fig. 5-7; pi. 14; pi. 15, fig. 1-3. 14 University of Texas Bulletin youngest to the mature individuals. Roemer mentions that specimens about 2.5 cm. long show distinct, unequal, radial folds which begin to grow indistinct near the margin of the valve. Stephenson's PL 13, fig. 5 shows clearly this kind of ribs on the beak of a medium-sized specimen. If we imagine this beak detached from the valve and in the form of a young specimen, it would have exactly the shape and ornamentation of a young specimen of our young Ex. Whit- neyi from the Cerro de Muleros, and be extremely similar to the young of Ex. arietina and to the mature specimens of Ex. plexa. Stephenson (loc. cit. p. 49, pi. 15, fig. 4; pi. 16, fig. 1, 2) has described a number of shells as Ex. pon- derosa var. erraticostata Steph. It will be rather difficult to sustain this variety because the figure of Roemer's type shows very similar ribs and thus should be part of this variety. Ex. costata has been quite frequently described and fig- ured ; recently Stephenson 1 has very fully described the ma- ture specimens and also has illustrated these profusely. Unfortunately also in this case we lack the exact knowledge of the ornamentation of very young specimens. The species is possibly derived from Ex. ponderosa or at least from a form of which Ex. ponderosa is a branch, but this cannot be proven at the present time. Specimens should be espe- cially studied in the zone where Ex. ponderosa and Ex. cos- tata appear to occur together and where the real antecessor of the latter species may be found. The preceding sketch of the evolution of Exogyra in the Texas Cretaceous necessarily has to be deficient, incomplete and in a great part hypothetical, but at least it shows that all the species, even the largest which are practically smooth, came originally from a rather small costate form; and that the great diversity of forms in the upper strata is simply due to the subdivision of a tribe represented at the base by forms that are intimately related to each other and at the same time to Ex. Boussingaulti of the European Aptian. It shows also that some of the large species in the Stephenson, loc. cit. n. 50 p 1 . 16. fig. 3, 4; pi. 17, fig. 1, 2; pi. 18; pi. 19, fig. 1-4; pi. 20 fig. 1. On a New Exogyra from Del Rio Clay 15 higher horizons may not be intimately related, notwith- standing the very similar shape, but rather be convergent forms. A monograph of the Texas Cretaceous Exogyras would probably show a still much greater variety of forms which were derived from the same original tribe, and at the same time it would not at all be difficult to demonstrate that in Europe, Northern Africa and Asia quite a similar evolution has taken place. 16 University of Texas Bulletin Probable relationships of the species of Exogyra in Texas. On a New Exogyra from Del Rio Clay 17 DESCRIPTION OF SPECIES Exogyra Cartledgei nov. sp. Pl. I, fig. 7-13; PL II, fig. 1-4; Pl. III, fig. 1-8. Shell medium-sized, very thick, elongate to sub-oval, some- what oblique up to the beak, which is spirally coiled down- ward and outward. Inferior valve. Shape very variable, elongate to obliquely suboval up to the beak, strongly convex, the highest part forming an obtuse, curved, umbonal ridge which follows approximately the middle line of the height of the shell, and which disap- pears toward the inferior margin of the valve. The slope toward the anterior margin is sometimes much steeper than toward the posterior side. Beak generally spirally twisted or coiled downward and outward; sometimes pressed against the body of the shell, sometimes almost entirely free in the shape of a ramshorn. The beginning of the beak is never free, but always pressed against the shell, which shows that in the juvenile stage the beak was not detached from the rest of the valve and that the development in the form of a ramshorn is the latest stage caused by the spiral coiling of the valve during the later stages. The point of the beak often shows a scar, due to its having been attached to some small object, such as shells, etc. The ornamentation consists of about fifteen coarse long- itudinal ribs which on each of the slopes (anterior and posterior) are nearly parallel on the upper half of the valve. The series on the anterior side is not parallel to that on the posterior one, but forms an angle of about 40 degrees. On the umbonal ridge the two series are united by an inter- vening space covered by intercalated, bifurcating ribs. The ribs on the anterior side form a wide angle with the axis of the umbonal ridge but on the last part of the beak they 18 University of Texas Bulletin become nearly parallel to the ridge. The opposite side of the beak always appears to be entirely smooth, which prob- ably is in part due to the state of preservation. The ribs are crossed by lines of growth and by strong lamellae which give them a scaly aspect. The lines of growth and lamellae cover also the beak. The ligamental groove is generally spirally curved, deep, broad, triangular, very long to very short, according to the shape of the beak, limited on both sides by a ridge. Below the groove on the posterior side is a shelf-like fold finely crenulated, on the anterior side a similar one but rounded and less distinct. The shell outside of these ridges is also finely crenulated along the upper part of the animal cavity, the crenulation becoming very faint on the lower half until it disappears, entirely. The muscular impression is deep and very near the posterior margin. The cavity often ex- tends somewhat into the beak. Upper valve. Rather thick, slightly convex to flat, operculiform, sub- ovate with a nearly flat spiral twist, the beak being near the margin. Beak very little prominent, nearly pressed down to the rest of the shell. Sometimes there is a very obtuse, spirally curved umbonal ridge which disappears to- ward the postero-inferior margin. On the posterior side right near the beak is a distinct depression. On a well preserved specimen the ornamentation consists of numerous concentric growth lines and lamellae which cover the whole surface. The lamellae are not of circular form, but show an angular prolongation on the umbonal ridge. Where this is absent the lamellae follow a more or less elliptical course. Fine radiating ribs are visible on the postero-superior part of the shell in the region close to the beak. The margins are distinctly crenulated. The ligamental groove is mostly broad and flat, seldom narrow and deep ; in the first case strongly spirally curved, in the second case much less so. In the first case, the lig- amental groove is almost parallel to the superior margin; in the second case it nearly forms a right angle with it. On a New Exogyra from Del Rio Clay 19 This seemingly depends on the thickness of the valve. To- ward the interior and posterior side of the groove, a striated protuberance elevates itself more or less highly ; it is oppo- site the depression formed by the striated shelf and cren- ulated margin of the lower valve, and probably fits into it. The muscular impression is deep and near the posterior side, far below the region of the beak. Relation to other species: Ex. Cartledgei has a certain similarity to Ex. arietina, but its strong ribs and large size make it easy to distinguish the two. It probably has been derived from the same tribe, that of Ex. plexa , or a similar form, as has been explained in the first chapter of this paper. Occurrence: The species has been found very frequently in the Del Rio clay in a horizon about 10 to 30 feet below the Buda limestone. The Del Rio clay has at this place a thickness of 120 feet or more. It is associated with Nodosaria tex- ana, which occurs in abundance above it, Gryphaea sp., En- allaster cf. bravoensis, and Hemiaster sp. According to Dr. Udden, Exogyra arietina is rare at this locality but was noted at a level not far from the middle height of the Del Rio clay. Locality: Reed Plateau, point almost exactly one mile south from the Chisos Mining Company’s mine, in Brewster County, Texas. Exogyra arietina Roemer PL IV, fig. 1-18; PI. V, fig. 1-23. 1852. Ferd. Roemer, D'e Kreidebildungen von Texas und Hire or- ganischen Einschliisse. Bonn. P. 68, PI. 8, fig. 10. Roemer’s description of this species is very careful and his illustrations are quite good, but figures of the juvenile stages of the species are lacking, as these were not given overmuch importance by the paleontologists of that time. 20 University of Texas Bulletin Roemer remarks that the surface of the lower valve in the region of the beak is covered by delicate longitudinal striae interrupted by the lamellae of growth and which gen- erally can be seen only in the more juvenile specimens, the region of the beak being more or less corroded in the larger individuals. A study of well preserved specimens of Ex. arietina of different ages shows at once that Roemer is absolutely cor- rect in his description, but also that the development of the species shows three clearly marked stages. Leaving aside the protoconch which is of the size of about a common pinhead, the first stage of development (PI. V, fig. 7-10) has the following character: In shells up to about 3 mm. in length, the surface does not show a trace of ribs, even where not the slightest corrosion has taken place ; it is only covered by rounded, concentric, relatively broad and not very distinct folds and the growth lines. At this size, the posterior side of the shell is distinctly flat with the beak pressed against the rest of the valve; only the very first part of the beak in a length of 0.5 to 1.0 mm. elevates itself a little above the surface of the shell. The umbonal ridge is relatively sharp and high and reaches from the beak to the postero-inferior margin. The anterior side forms an angle of about 50 degrees with the posterior side, and is rounded in height as well as in width. This angle between the two sides causes the prominent umbonal ridge. The outline of the valve is triangular-suboval at this stage. The second stage is represented by specimens of a length of about 10 mm. or a little more (PL V, fig. 11-16). In these individuals the shell of the first part of the beak, up to about 3 mm. from its point, is of course smooth, but on the next wrinkles of growth, fine radial ribs appear sud- denly in the number of about 30 to 35. They are very dis- tinct on the anterior side, the umbonal ridge, and the greater part of the posterior side, but become indistinct in this lat- ter region on the surface near the end of the beak. The ribs reach higher on the anterior than on the posterior side, and pass obliquely over the umbonal ridge. The lamellae On a New Exogyra from Del Rio Clay 21 of growth begin to develop, interrupting the ribs and im- parting to them the aspect of roof tiles. The umbonal ridge is as prominent as in the preceding stage at least in the umbonal region, but toward the post- ero-inferior region it becomes rounded and less distinct. The shape of the shell begins to change. It has no longer the triangular form but begins to coil spirally. In connec- tion with this circumstance the growth lines and lamellae no longer form a perfect elliptical curve, but begin to show in their course a distinct protuberance or tongue-like pro- longation on the umbonal ridge. The next stage represents the beginning of the mature development (PI. IV, fig. 10-15; PL V, fig. 1-3). The ribs disappear about as suddenly as they began, the shell becomes smooth and is only covered by lines of growth and lamellae which appear more distinct the more the shell grows. They no longer form a simple curve, but are rather wavy, especial- ly on the posterior side and a little less on the anterior side, showing a pronounced tongue-like prolongation or protu- berance in their outline on the umbonal ridge. The wavy appearance of the lamellae on both sides corresponds to the development of shallow furrows (PL V, fig. 4, 17), one more distinct on the anterior side and one generally less so on the posterior side. The shape of the shell now changes very rapidly, coiling spirally so that the umbonal region becomes twisted and de- tached from the rest of the valve. Exceptionally it can be observed that very faint and some- what irregular longitudinal ribs appear again on larger shells up to a distance of about 35 mm. from the beak, measured along the umbonal ridge (PL V, fig. 17)*. In the last stage of mature specimens the shell attains its characteristic shape similar to a ramshorn, as described by Roemer (PL IV, fig. 1-9, 16-18; PL V, 4-6, 17). The opercular upper shell does not change essentially (PL IV, fig. 4; PL V, fig. 16, 18-23). It appears to have the same character from the size of about 2 mm. to the largest mature forms with a length of 25 mm. and more. The valve is sometimes nearly flat, always with a rather deep 22 University of Texas Bulletin depression on the posterior side near the spirally coiled beak, the point of which is pressed down against the sur- face of the shell. Sometimes this valve is entirely oval, especially in immature individuals ; in other specimens it is distinctly spirally coiled, developing a relatively high um- bonal ridge. The ornamentation of the surface consists only of spiral lines of growth and lamellae. Only the superior margin of the umbonal region is finely crenulated. Traces of fine crenulation show sometimes on the inferior margin. The interior of the lower valve does not change mater* ially from the immature stage to the well developed spec- imen. The ligamental groove is always very narrow and deep, spirally coiled, and follows the superior margin. A faintly crenulated ridge is below it, the margin on the upper half of the cavity being always slightly crenulated. The cavity continues into the beak, more or less. The muscular impression is near the posterior side and close to the region of the beak. The interior of the upper valve does not change materially from the immature stages to the final development of the species. The ligamental groove is very long, very narrow and deep, spirally coiled, follows the superior margin of the valve, and obliquely crosses the spiral lamellae of growth. The space between the groove and the superior margin is finely crenulated. The muscular impression is strong and exactly under the umbo, as has already been observed by Roemer. Occurrence : Del Rio clay. Locality of the specimens studied: Shoal Creek, Austin, Texas. EXPLANATIONS OF PLATES Plate I Fig. 1, 2... Exogyra weatherfordensis Cragin. — Glenrose formation. One-fourth of a mile west of Weatherford, Parker County, Texas. Page 5 Fig. 3, 4 . . . Exogyra plexa Cragin. — From bed with Exo- gyra texana below the Kiamitia clays. Texas and Pacific Railway, three miles west of Benbrook, Tarrant County, Texas. Page 8 Fig. 5 Exogyra nov. sp. aff. plexa Crag. From bed with Exogyra texana below the Kiamitia clays. Texas and Pacific Railway, three miles west of Benbrook, Tarrant County Page 8 Fig. 6 Exogyra sp. aff. plexa Crag. — Kiamitia c by. Little Mineral Creek, north of Pottsboro, Grayson County, Texas. Fig. 7-13 .. .Exogyra Cartledgei nov. sp. — Del Rio clay. Reed Plateau, about one mile from the Chisos Mining Company’s mine in Brewster County, Texas Page 17 Fig. 7-9, 11-13, beaks of the lower shell showing the dif- ferent stages of development. Fig. 10, Lig- amental groove of a large and slender speci- men. Plate I Plate II Fig. 1-4 . . . Exogyra Cartledgei nov. sp. — Del Rio clay. Reed Plateau, about one mile south from the Chisos Mining Company's mine, in Brewster County, Texas Page 17 Fig. 1 . . large slender shell, lower valve. • Fig. 2 . . inside of same. Fig. 3 . . broad adult shell with coiled beak. Fig. 4. .inside of same. Plate II Plate III Fig. 1-8 . . Exogyra Cartledgei nov. sp. — Del Rio clay. Reed Plateau about one mile from the Chisos Min- ing Company's mine, in Brewster County, Texas Page 17 Fig. 1 . . upper valve. Fig. 2 . . inside of the same. Fig. 3, 6, 7 . . surface of upper valves. Fig. 4, 8. .inside of upper valves. Fig. 5 . . inside of lower valve showing a strongly curved beak and a corresponding ligamental groove. Plate III Plate IV Fig. 1-18. . .Exogyra arietina Roemer. — Del Rio clay. Shoal Creek, at Austin, Texas Page 17 Fig. 1-3 . . adult normal specimen shown in three positions. Fig. 4-6 . . adult normal specimen shown in three positions. Fig. 7-9.. adult normal specimen shown in three positions. Fig. 10-12 . . young normal specimen shown in three positions. Fig. 16-18. .adolescent stage shown in three positions. Plate IV < I . ' Plate V Fig. 1-23 . . . Exogyra arietina Roemer. — Del Rio clay. Shoal Creek at Austin, Texas. Fig. 1-3. .young normal specimen shown in three positions. Fig. 4. .. .young individual showing a strong spiral groove. Fig. 5.. . .aberrant adult specimen with ex- ceptionally coiled beak. Fig. 6.. . .aberrant adult specimen with strongly coiled beak. Fig. 7.. . .very young specimen, natural size. Fig. 8... . the same, strongly amplified, show- ing a smooth surface on the greater part of the shell, ribs beginning to appear at the mar- gin. Fig. 9. . . . very young specimen, natural size. Fig. 10.. . .the same, strongly amplified, show- ing the smooth surface of the shell at this stage of develop- ment. Fig. 11.. . .very young specimen, natural size. Fig. 12, 13 . the same, strongly amplified to show the ornamentation. The shell is smooth on the point of the beak, and develops radial ribs farther down. Fig. 14 ... . very young specimen, natural size. Fig. 15, 16. the same, strongly amplified to show the ornamentation. The shell is smooth on the point of the beak, and develops radical ribs farther down. Fig. 17. . . . adult specimen twice amplified to show the ornamentation on the point of the beak, and its simi- larity with that of the small in- dividuals illustrated in fig. 11- 16. Fig. 18-23. upper valves of small specimens. The slit apparently limiting the umbo in figure 19 is due to frac- turing and is not natural. Plate V n it u i ■ !ff;m!!;ii' fit B96-819-6m University of Texas Bulletin No. 1931: June 1, 1919 THE GEOLOGY OF TARRANT COUNTY By W. M. WINTON AND W. S. ADKINS BUREAU OP ECONOMIC GEOLOGY AND TECHNOLOGY J. A. Udden, Director DIVISION OP ECONOMIC GEOLOGY J. A. Udden, Head of the Division Published by the University Six Times a Month, and Entered as Second-Class Matter at the Postoffice at Austin, Texas, Under the Act of August 24, 1912. GEOLOGY The benefits of education and of useful knowledge, generally diffused through a community, are essential to the preservation of a free govern- ment. Sam Houston Cultivated mind is the guardian genius of democracy .... It is the only dictator that freemen acknowl- edge and the only security that free- men desire. Mirabeau B. Lamar Page LIST OF ILLUSTRATIONS . 5 GENERAL DESCRIPTION OF THE AREA 7 PHYSIOGRAPHY AND TOPOGRAPHY 9 Topographic Divisions of Tarrant County 9 Black Prairie 9 Ea'stern Cross Timbers 10 Grand Prairie 11 Western Cross Timbers 12 Drainage. . * 12 Geological Map 14 Type Localities in Tarrant County 15 FOSSILS AS HORIZON MARKERS : 16 Mode of Preservation 16 Possibility of Recurrent Horizons 18 Utility of Fossils in Interpreting Well Logs 19 Table of Identification Values of Comanchean and Cretaceous Fossils 21 THE GEOLOGICAL SECTION 24 Description of Formations 25 Pennsylvanian . 25 Comanchean 25 Trinity Division 25 Trinity (Basement) Sands 26 Glenrose Limestone 26 Paluxy Sands 26 Fredericksburg Division 26 Washita Division 33 Kiamitia Marl . . 33 Duck Creek Formation 39 Fort Worth Formation 51 Denton Marl 58 Weno Formation 61 Pawpaw Formation 67 Mainstreet Formation # 69 Grayson Marl 72 Woodbine Formation 74 Upper Cretaceous 82 Eagleford Shales 82 Cenozoic and Recent 84 ECONOMIC GEOLOGY. Resources of Location 84 85 4 University of Texas Bulletin Page Resources of Soil 87 Resources of Plant and Animal Life 88 Resources of Crude Material 89 Limestone Industries 89 Gravel and Sand 91 Clay Industries 92 Possibilities of Oil and Gas 95 Water Resources 97 DIP, ALTITUDES, WELL LOGS, ETC 100 Dip, 100 Altitudes in Tarrant County 101 Precise Levels in Tarrant County 102 Description of New Magnetic Station 107 Log of Well at Polytechnic, Texas 107 Log of well near Mansfield, Texas 115 INDEX 119 TOPOGRAPHIC MAP OP THE T. C. U. VICINITY 122 GEOLOGICAL MAP OF TARRANT COUNTY 122 LIST OF ILLUSTRATIONS FIGURES Pag© Fig. 1. Columnar Section of the Frederickbui g Limestone in the Valley of the West Fork of the Trinity River near the Lake Worth Dam 31 Fig. 2. Columnar Section of the Kiamitia Formation in Cut on the Azle Road, eight miles* northwest of Fort Worth 36 Fig. 3. Columnar Section of the Duck Creek Formation in Cuts near Forest Park, Fort Worth 41 Fig. 4. Columnar Sections of the Fort Worth Limestone. A. On Sycamore Creek, northwest corner of Glenwood Park. B. Eastward facing Exposure in a run one-half mile east of Texas Christian University and one-half mile south of Forest Park, Fort Worth .53 Fig. 5. Columnar Section of the Denton, Weno and Pawpaw formations on Sycamore Creek, 3 miles southwest of Fort Worth 63 Fig. 6. Columnar Section of Portions of the Woodbine Forma- tion in Cuts of the Rock Island Railway between Tarrant Station and the Tarrant-Dallas County Line 79 PLATES (Inside back cover) Plate 1. Goodland Limestone (top of Fredericksburg Division) at the Lake Worth Dam, 8 miles northwest of Fort Worth. Plate 2. Fig. 1. Top of Goodland (Fredericksburg) Lime- stone, looking east from near Benbrook. Figure 2. Goodland Limestone, Stove Foundry Road, 4 miles west of Fort Worth. Plate 3. Fig. 1. Top of the Goodland Limestone, looking east from near Benbrook. Fig. 2. Terraces in the Fredericksburg Division. Fig. 3. Terraces in the Basal Washita Division. Plate 4. Fig. 1. Base of the Fort Worth Limestone, which un- derlies the business section of the city of Fort Worth. Fig. 2. Gate posts and flower beds in Forest Park, ibuilt of 6 University of Texas Bulletin the large Ammonite, Desmoceras brazoense, of the Duck Creek Limestone. Plate 5. Pig. 1. The large Ammonite, Schloenbachia species J., which characterizes the Fort Worth Limestone. Pig. 2. Illustration of the terms “cast” (left) and “mold” (right) . Plate 6. Fort Worth Limestone in Excavation at the northwest corner of Eighth and Houston streets. THE GEOLOGY OF TARRANT COUNTY BY W. M. WTNTON AND W. S. ADKINS 1 GENERAL DESCRIPTION OF THE AREA Tarrant County is in the third tier of counties of the east central province of Texas, and is included within the belt of densest population in the state. The estimated population of the county, January, 1919, is about 148,000, of which 130,000 is concentrated in the city of Fort Worth. This city, like the cities of Dallas, Waco, Austin, and San Antonio, lies on the outcrop of the calcareous formations of the Cretaceous system. Lime- stone areas have always been the areas of the greatest industrial development and its accompaniment of concentrated popula- tion; and of limestone areas those of the Cretaceous have in the past been the most favorable. Many writers have commented on the curious relationship between centers of civilization and the outcrops of Cretaceous rocks. In fact, even today, a map of the world showing the areas of greatest human development would bear a striking resemblance to the map of the world ’s out- crops of Cretaceous rocks. Many explanations have been at- tempted of this suggested connection. The simple facts seem ample. Cretaceous limestones furnish an abundant water supply, a firm substratum, break down into rich soil, furnish material for the construction of roads and buildings, and by their mode of weathering furnish a land surface which is a perfect com- promise between the level surface most favorable to the develop- ment of elaborate transportation, and the rolling surface most favorable for perfect drainage. Tarrant County epitomizes in a way the agricultural indus- tries of the state. The western part of the county is in the rolling short-grass prairie region of West Texas, which is typical grazing land; while the eastern part of the county is made up of timbered country and bottom lands, including a typical cotton- farming country. In a biological sense the county lies at the junction of the humid and semi-arid divisions of the Lower Austral life zone. Its location implies a great mixture of wild life, both plant and animal; and such a condition exists. Be- 1 The order of names does not in any way indicate seniority. Ms. accepted June 1, 1919, published March 1920. 8 Umversity of Texas Bulletin sides this, the county lies at what might be considered the junc- tion of life zones in a north-south distribution; that is, it con- tains life forms which belong both to the sub-tropical area and to the warmer temperate zones. There is probably no other region in the state which shows such a variety of wild life, especially of plant life, exhibiting a blending of semi-arid with humid forms and temperate with sub-tropical forms. Tarrant County lies roughly between longitude W. 97° 1.8' and longitude W. 97° 32.6', and latitude N. 32° 33.3' and lati- tude N. 32° 59.3', giving it an area of about 903 square miles. The magnetic declination at the station of the United States Coast -and Geodetic Survey on the Texas Christian University campus at Fort Worth is 9° 27.4' east. On the ordinary pocket compass used by hunters, boy scouts, and field geologists, reading to a minimum of two degrees, the declination is ten degrees to the east. That is, when the pocket compass is held so that the needle points to 10° east, the zero or north mark of the compass is pointing to the true north. The entire county is covered by rocks belonging to a single geological age — the Cretaceous, about equally divided between lower Cretaceous, or more properly Comanchean, and Upper Cretaceous. The underlying rocks dip gently toward the south- east. The rocks are hard chalky limestones, soft limestones, marls, and red sandstones. The dip of the strata gives, in gen- eral, long gentle slopes on the southeast side of the uplands, where the surface of the ground approximates the dip of the underlying rocks, and it gives rather abrupt slopes on the north- west side of such uplands, Avhere the successive ledges of the different formations emerge from below the surface. This is the so-called “cuesta” type of topography. Despite its recogniz- able nature, with the gentle dip plains on one side and steep bluffs on the other side, the fact must be kept in mind that in many cases the “dip plains” are not true dip plains, and the abrupt bluffs are not always the “ends” of formations. This statement is made here because many writers in discussing this feature of North Texas topography have taken rather too liter- ally the proposition that this cuesta type of topography indi- cates exactly the position, thickness, and attitude of the forma- tions. The Geology of Tarrant County 9 PHYSIOGRAPHY AND TOPOGRAPHY The underlying geological formations, aside from climatic factors, are the most important natural features in determining the configuration of a region, and therefore, also, its possibili- ties for cultivation and its suitability for a dense population, location of large cities, and other cultural developments. The area included in Tarrant County illustrates this intimate relation between the geology of a country and its surface features. A complexity of surface features is possible with a combination of alternate hard and soft strata, an even dip, and a well developed drainage. These factors result in a striking diversity of land forms and a pleasing variety of scenery. The highest point in the county is in the western part, where an elevation of 1050 feet above sea level is reached. The lowest point is where the Trinity River passes out of the county to the east. This latter point has an elevation of 450 feet, giving the entire county a maximum relief of 600 feet. In general this is represented by a gradual slope to the east, broken by the west- ward facing escarpments. The escarpments are steep and con- spicuous, but the much longer and gentler eastern slopes are not so readily noticed. The trip from Fort Worth to Dallas by the automobile pike is decidedly downhill in its entirety, the fall being about 160 feet in a distance of a little more than thirty miles ; but because of the several conspicuous escarpments which must be ascended in traveling east, the average individual fancies that he is traveling mostly up hill. TOPOGRAPHIC DIVISIONS OP TARRANT COUNTY The area included within Tarrant County consists of four broad belts, two prairie strips alternating with two sandy strips or “ cross timber” zones. These are as follows, from east to west: the Black Prairie, the Eastern Cross Timbers, the Grand Prairie, and the Western Cross Timbers. The Black Prairie has only a small part of the lower and western portion of its great area in Tarrant County. This black land prairie is underlain by the whole Cretaceous series, above 10 University of Texas Bulletin the Woodbine sand 1 . Due to the dip of the strata toward the Gulf Coast, this is the lowest of the belts in altitude, but the highest in the geological series. It is a gently rolling slope with a treeless surface. The soil is black, waxy, and carbonaceous. It is deep and of a superior grade. Because of the deep soil, the cuesta topography is not prominent, but even in the soft marly shales, as in the eastern part of Tarrant County, the escarpment and dip plains are recognizable. The Eagleford subdivision of the Black Prairie is separated from the Austin chalk subdivision by the prominent Austin chalk escarpment which extends for hundreds of miles across Texas parallel to the general direction of outcrop of the strata, and is finely ex- posed in White Cliff on the Fort Worth-Dallas pike, a few miles west of Dallas. This westward-facing escarpment overlooks the successive strips of Eagleford prairie, which arise from under it, and ascending westward divide the prairie by small crests which are themselves miniature escarpments. These correspond to the subdivisions of the Eagleford formation. Approaching Fort Worth from the east, these rise in altitude until just east of Arlington the top of the Woodbine sand emerges from underneath the basal member of the Eagleford shales. The Eastern Cross Timbers are underlain by a homogeneous strip of red sandstone composing the Woodbine formation; and are heavily timbered with black jack oaks and post oaks. The exposure of the Woodbine formation is an important catchment area for water, as noted by Dr. Hill, furnishing artesian water in areas far to the east of Tarrant County where this sand is deep * underground. A conspicuous feature of the rock under the Cross Timbers is its tendency to form large lens-like masses and to show cross bedding. These features should be considered very cautiously by prospective oil drillers and are explained and discussed under the section on the Woodbine formation At the western border of the Cross Timbers where the limestone emerges, an interesting feature is the string of small ‘ ‘ islands 9 9 or outliers of the red sandstone. These form the numerous “ Brushy Knobs”, seen in this strip from the Red River to the Brazos. Some of 1 The formations referred to in this discussion are subsequently more fully described under the section on Geology. The Geology of Tarrant County 11 these ‘‘knobs” are distinctly peak-like, and are possibly due to lenticular masses in the sandstone. The Grand Prairie has a surface which is varied correspond- ing to the diverse groups of rock strata underlying it. The columnar section (fig. 1-6) indicates roughly a series of lime- stone layers alternating with marl members. The limestones weather out as upland surfaces which are more or less flat, ex- cept for the effects of erosion, while the softer marl groups break down more readily under weathering and are exposed as slopes connecting the levels of the limestones above and below. This pro- duces a terrace effect which is one of the features of the region. The limestones do not always or even usually weather out into dip plains whose surfaces are entirely upon a single stratum. This sort of plain is rare, despite frequent reference to such occurrences in the geological literature of this' region The most common upland slope is an erosion slope dipping in the direc- tion of the greatest dip of the underlying strata but also slanting off towards the drainage and consequently not lying entirely on one stratum, but including many successive strata. The state- ment that the cuesta type of topography prevails must be ac- cepted with reserve so far as Tarrant County is concerned. The Grand Prairie has two areally prominent members, the Mainstreet limestone and the Fort Worth limestone. These to- gether make up 80 per cent of the total area ; and the other mem- bers of the series form essentially narrow strips connecting these two with the adjoining areas and with each other. For instance, the Grayson marl connects the eastern prairie strip, the Main- street limestone, with the Woodbine sand. Although fifty feet thick, the Grayson is an inconspicuous strip areally (exaggerated in mapping) and the formation is very rarely exposed or entirely free from overwash. The Mainstreet with the same thickness forms a broad upland many miles wide. At many places the Denison beds, the Denton, Weno, and Pawpaw formations, form a sharp, even slope connecting the Mainstreet limestone upland of the eastern side with the Fort Worth limestone upland of the western side. Yet the thickness of the Denison beds far exceeds the combined thickness of the Mainstreet and Fort Worth lime- stones. 12 University of Texas Bulletin The Western Cross Timbers and the adjoining rocks to their east are complicated by the greatly dissected headwaters of the Trinity River. This dissected lowland is likewise composite, and is underlain by three groups of strata in addition to the river alluvium. The three groups are timbered but are very dissimilar in the rock composing them. The upper and eastern strip is the Walnut formation, which is conspicuous by the great amount of slabs composed entirely of Grypheas, a-fossil oyster-like shell. The region is considerably dissected into steep hills, deep laterals of the Trinity River, with frequent waterfalls, cliffs and small rapids. It is well timbered with post-oak, black-jack oak, and water oak. Next underlying it geologically, and farther west, is a strip of Paluxv sand. This weathers into flat bottom lands of dull reddish sand. The Glen- rose limestone, which is westward and immediately under the Paluxv sand, is not exposed at the surface in Tarrant County. Throughout the four great belts of country above described, there are two types of gravel, an upland and a lowland type, and probably several stages of alluvium. These two gravels are recognized commercially as “pit” (upland) and “stream” (lowland). In these gravels are found the few fossils of the Pleistocene age which are known for this region, such as mam- moths, and a few others. DRAINAGE Tarrant County is drained entirely by the Trinity River. The Clear Pork of the Trinity, arising in Johnson County near the Noland’s River divide (Brazos drainage) passes northeast to join at Fort Worth the main branch of the Trinity, the West Pork, which rises in Wise County. These two forks drain the entire western half of the county, and the east half is drained by smaller laterals of the Trinity, such as Sycamore, and Big and Little Fossil creeks. The Trinity descends from an elevation of 1050 feet at the southwest corner of the county to 450 feet at the Tarrant-Dallas County line, giving a drop of 600 feet in 40 miles, or 15 feet per mile. Much of this drop is almost in the strike, for where the river runs directly across the outcrops of the formations near Fort Worth, the rock strata are The Geology of Tarrant County 13 dipping eastward about ten times as fast as the river. The result is that the river in passing eastward crosses successively younger formations until northeast of Arlington it has passed into the Eagleford shales. The drop of the Trinity River is rather even across Tarrant County where throughout its course it has a timbered lowland alluvial floodplain, increasing in width to five miles at the eastern border. The floodplain is bordered by Goodland and Duck Creek escarpments capped by Goodland and Fort Worth uplands west of Fort Worth, and east of Fort Worth by Weno and Pawpaw escarpments capped by Mainstreet uplands. In the southwest part of the county the Clear Fork of the Trinity passes through a Goodland floodplain as described, but in the northwest the West Fork cuts down a much dissected head- waters region. To the east the alluvial floodplain is bordered by Cross Timbered Woodbine sands. The strata of Tarrant County have suffered erosion from the Trinity drainage according to their hardness and other char- acteristics so that the topography of the areas bordering the river valley shows three general types: (a) Dissected Head- waters; (b) Dissected Uplands; (c) Cross Timbered Bottom Lands. These types have distinct individualities, divide the county into natural regions by producing each a different topog- raphy and scenery, and have differing possibilities of develop- ment. Dissected Headwaters of the Trinity : — This is an area of about one-sixth that of the county, on the upper course of the West Fork. The inequalities in hardness and composition of the underlying Walnut clays and shell marl produce a very rough and precipitous headwaters region whose aspect is totally different from that of the uplands. The laterals of the Trinity run mostly in deeply cut narrow valleys which are tortuous and carry swift streams during the rainy season. The hills make indented and irregular ridges converging towards the river valley and to the east capped by Goodland limestone. From the top of the Goodland escarpment are broad vistas of this dissected timbered landscape ascending toward the west and uncovering in its turn the underlying sandy land of the Western Cross Timbers. (See page 26.) 14 University of Texas Bulletin Dissected Uplands : — These strips of upland prairie, mainly underlain by the Fort Worth and Mainstreet limestones (page 51) are topographic units over the whole Cretaceous area in North Central Texas, where their direction of outcrop is a little east of north. It is notable that several railroads ap- proaching Fort Worth from the north and south have found at the same time an even gradient and a firm substratum by running in the strike of these formations. It has been mentioned that while the outcrops of these up- land limestones and their interbedded marl formations conform in general to the cuesta type of topography, it is nearly always with modification due to erosion slope toward the drainage bot- toms. The uplands are covered with ‘young’ stream valleys cutting their way into the original dip plains or their remnants and producing a rolling topography. This upland dissection is active and rapid in Tarrant County, while in the adjoining counties of the Cretaceous strip the exposures seem rarer. As the Trinity cuts across these limestones it produces the con- spicuous escarpments which border its valley for over half its course in the county. The city of Fort Worth owes its favor- able location to the Fort Worth limestone escarpment as ex- posed along the south bank of the Trinity and its resulting good drainage and broad outlook over the adjacent valley. Although the Trinity is a small stream at low water there has been considerable lateral swing as evidenced by the comparatively broad valley, the bordering escarpments, the fluviatile shell de- posits, and other features. GEOLOGICAL MAP Because of the lack of an areal map which is reliable enough to be used as a base for geological mapping, our base map is composite and contains certain errors which affect the exact- ness of the formation contacts. In general it may be pointed out that the formations most nearly follow the roads as mapped, although even sight compass intersections show the roads to be slightly mislocated in places. In addition an even degree of refinement has been attempted over the whole area, and this has necessitated a simplification of the geology at places where more detail could have been shown. On the map the finest pen The Geology of Tarrant County 15 line drawn represents a width of 106 feet, and at many places the geology can be mapped more closely than this. It is hoped that there may be produced an areal map on which the known detail of Tarrant County geology can be represented. Tarrant County has been more worked than any other county in the North Texas Comanchean, except Grayson County. It is the scene of investigations by Hill, Taff, Leverett, and others. Part of the county or all of it is included in the following maps. 1892 *Taff and Leverett: Cretaceous Area North of the Colorado River. 3rd Annual Report, Texas Geological Survey. 1898 *Hill: Black and Grand Prairies of Texas. 21st Annual Report, Part VII, U. S. G. S. 1898 Reconnaissance Map, U. S. G. S., Fort Worth Sheet. 1912 J. B. Hawley, Topographical map of the Lake Worth region. 1913 J. C. Tra villa: Road map of Tarrant County. 1916 *Geological Map of Texas; Udden, Baker and Bose. Bureau of Economic Geology and Technology, University of Texas, Bulletin 44. (Third edition, 1919). Missouri, Kansas and Texas Railway of Texas. Contour map of 4 square miles southeast of Fort Worth, Texas. 1918-19 Corps of Engineers, U. S. Army. Progressive Military Map, Advance Sheet 487 N, II & IV. TYPE LOCALITIES IN TARRANT COUNTY Within this county are found the type localities of many of the species described by Cragin and Clark. For convenience of reference there is here given a list of these localities, the original terminology being quoted: Epiaster elegans var. praenuntius Cragin 1 Comanche Peak, Ben- brook. Epiaster hemiasterinus Cragin 1 Grayson marl, 6 miles east of Fort Worth. Heterodiadema ornatum Clark 2 Washita group, Fort Worth. Leptarbacia argutus Clark 2 Washita group, Fort Worth. *Geological map. Bragin, 4th Ann. Rept. Tex. Geol. Surv., 1893. 2 Clark and Twitchell, U. S. G. S., Mon. LIV., 1915. 16 University of Texas Bulletin Ophioglypha texana Clark 3 Denton marl, 6 miles north of Fort Worth, on the banks of Lit- tle Fossil Creeek. Astarte acuminata Cragin 1 Weno marl, 3 y 2 miles east of Fort Worth. Vola bellula Cragin 1 Half mile above T. P. bridge on Sycamore Creek, near Fort Worth. Exogyra plexa Cragin 1 T. P. Ry., 3 miles east of Benbrook, 20 feet below the top of a bed of Exogyra tex- ana. Stearnsia robbinsi White 3 Little Fossil Creek, 6 miles north of Fort Worth. Dalliconcha invaginata White 3 Same. Cinulia tarrantensis Cragin 1 Top of Exogyra Texana bed, T. & P. Ry., 2 y 2 miles east of Ben- brook, with Tylosto- ma mutabilis and Cylindrites formosus. Cylindrites formosus Cragin 1 Same. Trichotropis shumardi Cragin 1 E. texana beds, iy 2 miles east of Ben- brook. Neritopsis tramitensis Cragin 1 Woodbine sands, top, Bear Creek, Tarrant County, near Dallas County line. These localities are all still recognizable. The type localities of the Fort Worth limestone (Hill 4 ) are practically obliterated by overwash and by street grading. FOSSILS AS HORIZON MARKERS It is desirable to place on record here certain observations regarding the range of the fossils found in the formations ex- H^ragin, 4th Ann. Rept. Tex. Geol. Surv., 1893. 3 Hill, Bull. Geol. Soc. Amer., 5, 1893, p. 328. * Hill, Amer. Jour. Sci., 1888; and 21st Ann. Rept., U. S. G. S., Pt. VII, 1901, pp. 259-61. The Geology of Tarrant County 17 posed in this county, and to indicate so far as practicable the relative utility of different species as horizon markers, including the mode of preservation of the fossils, and the possibility of recurrent horizons. In Tarrant County the limestones and interbedded marls fol- low each other in alternating beds, so that the whole geological column presents a remarkable uniformity. In the first place, the formations alternate between harder and softer groups of rocks, so that each limestone formation is overlain by a soft marly or clay formation. For example, the Goodland limestone is overlain by the Kiamitia marl; then comes the Duck Creek limestone, overlain by the Duck Creek marl ; then the Fort Worth limestone, overlain by the Denton shell marl ; then the Weno limestone and marl, overlain by the Pawpaw clay; then the Mainstreet limestone, overlain by the Grayson marl. In the second place, within a formation are alternating lime and marl strata. With such a confusing similarity of strata some means of locating the exact geological level is necessary other than that of a mere inspection of the rock. This is furnished by certain of the fossils contained in the beds. Of course some fossils run throughout the series or through considerable portions of it, and therefore are worthless as horizon markers. Of these practi- cally nothing will be said in this paper. Certain others are strictly limited in their range and occur only at particular levels. These are key fossils, or horizon markers. If their range of occurrence in Tarrant County is roughly less than ten feet vertically, the range, in this paper, will be called the zone of occurrence. If it is two vertical feet or less, it will be referred to as a restricted zone. If it is more than ten feet, but of limited range, it will be referred to as a horizon. Some fossils have zones in which they are particularly abundant, lying within horizons in which they occur, but less abundantly. Some fossils appear in re- current zones, that is, zones between which the fossils in ques- tion have never been found, even after considerable search, although admittedly they might occur there. It seems likely that many fossils now known only at certain levels will be found more widely distributed; and that the main reliance is to be placed upon their zones of abundance as here outlined. 2— Tarrant 18 University of Texas Bulletin MODE OF PRESERVATION Fossils in this region have been found in the following modes of preservation : (a) In the condition of lime compounds, as aragonite, and calcite. This is the most common mode. There are two condi- tions: The original shell material may be replaced by lime, preserving the original appearance and the material may be either indurated or chalky ; or the original shell may be present, sometimes with the nacre and lustre of the living form. (b) In the condition of iron compounds, as pyrite, hematite, or limonite. (c) In the condition of silica, as in some fossilized or opal- ized wood fragments and sandstone fossils. (d) In the condition of mud casts, consisting of compacted marl, often yellowish, and differing from ordinary shells in appearance, usually casts of the interior of the original shell. These casts are especially prevalent in the Goodland limestone, but are common also in the Washita division. The impressions may be internal, as casts; or external, as moulds. If the original shell is replaced by iron oxide it is then called an iron pseudomorph. Sometimes, but rarely, calcareous shells are colored pinkish. POSSIBILITY OF RECURRENT HORIZONS Certain species which are doubtfully recurrent will be men- tioned. The matter of recurrent forms is at present debatable, and we confine ourselves to bare facts. To establish recurrence in a given region, a fossil must occur in certain zones and not between these, and it must be proven that the recurrent zones contain the same species. If these things are true, there was at intervals a presumable migration of the species in and out of the region to one or more “reservoirs” in other regions. In practice it is essential not to confuse fossils from different levels by supposing them to indicate the same level. The chief recurrent forms are: (a) Kingena wacoensis and other species. In Tarrant County, these brachiopods have been found in only four zones: base of the Duck Creek limestone; Lower Kingena zone and upper Kingena zone of the Duck Creek marl ; and base of the Mainstreet The Geology of Tarrant County 19 limestone. Of these, the Kingena zone near the base of the Main- street limestone is the Kingena zone of the literature, and is stated to lie at the top of the Georgetown limestone at George- town, Austin, and other Central Texas localities. At Blum, in Hill County, near the Brazos River, brachiopods occur near the top of the Gryphea and Ostrea conglomerate of the Denton formation, and at the classic locality on Duck Creek north of Denison and other places on the Red River they occur at the base of the Hamites zone in association with fossils of this zone. The Mainstreet zone extends from the Red River to the Rio Grande, according to Hill. The Duck Creek marl zones -extend for miles in every direction from Fort Worth, but have not yet been found at the Red River. We know of no occurrences be- tween the zones above mentioned. For practical purposes, it can be said of the Kingenas, first, that they are not confined to one zone; and second, that there are probably several species of brachiopods in these zones. (b) Ostrea carinata Lamarck. The taxonomy is again con- fused here and the Texas material requires critical study and comparison with European individuals. This is one of the two or three species still remaining from a large number of species formerly thought to be common to the Texas and European Cretaceous. The zones of recurrence of this species have been so greatly extended that they are only doubtfully recurrent, yet between these zones these forms have not yet been found in the Texas region. In Europe where the species ranges widely in the Cenomanian it is not considered to be recurrent. (c) Gervilliopsis invaginata (White.) The situation is es- sentially the same as for Ostrea carinata. (d) Exogyra americana Marcou. This large conspicuous oyster occurs near the top of the Duck Creek limestone near Denison (Dr. Boese) and persistently in the top of the Fort Worth limestone in Tarrant County and other places. It has so far not been found elsewhere. UTILITY OF FOSSILS IN INTERPRETING WELL RECORDS All of the following fossils are of much practical importance, since even from minute fragments such as are found in well drill- 20 University of Texas Bulletin ing, the level may be determined always approximately, and sometimes with exactness. These levels have been carefully checked and their sequence verified in the field in numerous local- ities and over wide areas. Where there is variation within Tar- rant County, this is stated under the discussion of the fossil horizon. These key fossils will be seen to unequal advantage in well washings. If, as sometimes estimated, the largest compact fragment likely to be found in a standard rotary drill cutting is about 5/8 of an inch, it is evident that some fossils will survive the drilling process intact, while others will be ground to un- recognizable fragments. Fossils will survive because of their small size, as some of the small pvrite fossils mentioned in this paper; or because of their hardness, as certain Grypheas; or because of both, as Kingena; or because of their abundance, as some of the Grypheas in the shell marls; or for other reasons. With the number of key fossils cited in this paper, it is believed that a sufficient sample of one or a combination of several fossils can be had from practically any level of the Washita division, to determine the level. To assist in the certainty of these determinations, the value of the fossils for locating specific levels has been designated in the following table of identification values. The list as given in this table is incomplete and subject to re- vision. As in the European section the ammonites and echinoids are most reliable for determination of stratigraphic level and other fossils are variable in value. Certain associations and zones of abundance are valuable, as has been explained, if recur- rences of the same fossil are carefully distinguished from each other. (See page 18). In the following list, the fossils are arranged within each formation, in the order of their occurrence, from top to bottom. 1 1 In this table fossils which are most likely to be found and which have not been found at other levels than those indicated are marked with two asterisks. (**) Fossils which are less likely to be found, but which identify the level indicated within narrow limits, are marked with one asterisk. (*) Fossils occurring in zones of abundance or other fossils occurring in zones important for locating stratigraphic levels, are left with- out asterisk. The Geology of Tarrant County 21 TABLE OF IDENTIFICATION VALUES OF COMANCHEAN AND CRETA- CEOUS FOSSILS 1 Eagleford : **Ostrea belliplicata, gastropods, fish teeth and bones. Schloenbachia sp. P. *Acanthoceras swallovi (Shumard). Woodbine : * Conglomerate of Ostrea soleniscus, Ostrea carica, Barbatia micron- ema(?), Exoygra sp., Aguilera cumminsi, Cerithium, fish ver- tebrae, and teeth. Dexter sands: no fossils observed. Grayson Marl: *Exogyra sp. 1. *Gryphea mucronata Gabb. *Exogyra sp. 2 and Exogyra arietina Roemer. Pecten subalpina (abundant), Cyphosoma, Hemiaster calvini, etc. Mainstreet Limestone: Leiocidaris (highest). **Turrilites brazoensis Shumard. **Kingena wacoensis Roemer ( ? ) . Schloenbachia sp. O., aff. inflata. *Exogyra arietina Roemer. Ostrea quadriplicata Shumard (highest). *Holectypus sp., aff. limitis Boese. Ostrea carinata Lamarck. Pachymya austinensis Shumard * Pecten cleburnensis Adkins and Winton (sp. 1). Pecten sp. 2. Pawpaw Clay: Hemiaster sp. 1; Nautilus sp. 1. **Pyrite fauna: Baculites sp.; Scaphites hilli Adkins and Winton (sp. A); Hamites tenawa Adkins and Winton; Enallaster sp. 1; Salenia sp. 1; Trochosmilia sp. 1; Turrilites worthensis Adkins and Winton (sp. A) and spp.; Mortoniceras sp. A; Acanthoceras sp. A. * Starfish zone: Metopaster hortensae Adkins and Winton; Comp- tonia sp.;* other starfishes. Nodosaria texana Conrad. Fish teeth, vertebrae, plates. Enallaster sp. 3; aff. bravoensis Boese. Weno Limestono and Marl: “Quarry group”: Ostrea quadriplicata, Ostrea carinata (abun- dant). Gryphea washitaensis (abundant), Homomya sp. 1 These and other key fossils are described and figured in: Adkins and Winton, Univ. of Texas Bull. 1945. 22 University of Texas Bulletin ♦Pentagonaster texensis Adkins and Winton (sp. 1). Schloenbachia spp. L-M. ♦Engonoceras sp. 1 *Nodosaria texana Conrad. Venericardia sp. 1, Corbula spp. 1-2, Turritella sp. 1. ♦Cervilliopsis invaginata (White). ♦Pecten georgetownensis Kniker (?), Turritella sp. 2, Remondia (?) acuminata Cragin, Hamites sp. B, Cottaldia sp. 1. Denton Marl: ♦♦Gryphea washitaensis (abundant). Ostrea carinata (abundant). Protocardia sp., Trigonia sp. Fort Worth Limestone: *Enallaster longisulcus Adkins and Winton (sp. 2). ♦Nerinea sp. 1. ♦Exogyra americana Marcou. Ostrea carinata Lamarck. *Hemiaster elegans Shumard (abundant). ♦♦Pecten bellula Cragin,, ♦Schloenbachia sp. K (size of austinensis Lasswitz). ♦♦Holaster simplex Shumard (abundant). ♦Pecten sp. 3. Schloenbachia sp. I. Duck Creek Marl and Limy Marl: * Upper Kingena zone. Upper Gastropod zone: Cerithium, Turritella, Pleurotomaria^ Gyrodes ( ? ) . Schloenbachia sp. I. ♦Pecten wrightii Shumard. ♦♦Lower (Main) Kingena zone. *Goniophorus sp. I. * Crania rp. 1. ** Hamites tanima Adkins and Winton; Hamites spp. D-G. ♦Pinna sp. 1. ♦Scaphites worthensis Adkins and Winton (sp. B). Lower Gastropod Horizon: Cerithium, Lunatia, Cinulia. Turbo. Nerinea sp. aff. pellucida Cragin, Schloenbachia sp. Duck Creek Marly Lime and Limestone: ♦Schloenbachia sn. I-T. aff. trinodosa Boese. * Schloenbachia sp. G. ♦Schloenbachia sp. F. ♦Desmoceras sp. B (“brazoensis”, “graysonense”?). ♦Desmoceras sp. A. ♦In'oceramus comancheanus, I. munsoni. ♦♦Hamites comanchensis Adkins and Winton (sp. A); H. nokoni& The Geology of Tarrant County 23 Adkins and Winton (sp. B); H. fremonti Marcou (sp. C); H. spp. H-J. Kiamitia Marl: ** Gryphea navia Hall. Gryphea washitaensis (lowest). Pholadomya sp. ♦Exogyra plexa Cragin (highest). ♦Schloenbachia belknapi Marcou (highest). ♦Fecten irregularis Boese (highest). ♦Schloenbachia acutocarinata Shumard (highest). ♦Exogyra texana Roemer (highest). Cyprimeria sp. 1. Fredericksburg Division : Cyprimeria sp. 1. *Schloenbachia sp. near belknapi. Schloenbachia acutocarinata Shumard *Diplopodia taffi. Cragin. ♦♦Coral syndrome: Parasmilia sp., Trochosmilia sp. ♦Holectypus sp. ♦Enallaster texanus Roemer (abundant). *Hemiaster sp. near whitei Clark. ♦♦Salenia mexicana. Upper level. Exogyra plexa Cragin (small form). ** Syndrome of Chondrodonta sp. aft. munsoni (Hill), Pecten ir- regularis (Boese), Cinulia, Lima, Pinna sp. near comancheanus Cragin, etc. *Engonoceras sp. aff. pi'edernale von Buch. ♦Exogyra plexa Cragin (large form). * *Schloenbachia acutocarinata (Shumard) (abundant). Pholadomya sancti-sabae Roemer (abundant). .Gryphea maxcoui Hill and Vaughan (abundant). ♦Schloenbachia sp. A. ♦Gryphea marcoui (Upper Conglomerate). Exogyra texana (Upper Horizon, abundant). Salenia sp. (lower level). Protocardia filosa (Conrad). Cerithium bosquense Shumard. Natica sp. aff. pedernalis Roemer. Walnut conglomerate and clay: ♦Schloenbachia acutocarinata Shumard (lowest) Enallaster sp., Turritella sp. ♦Gryphea marcoui conglomerate. Paluxy sands: No fossils noted in Tarrant County. 24 University of Texas Bulletin THE GEOLOGICAL SECTION The marine formations found in Tarrant County, as already stated, are those of the Cretaceous System. In addition there are alluvial and terrace deposits of the Cenozoic. In the fol- lowing table these formations are listed in order, the oldest foimations being placed at the bottom of the table. In the second column is given the probable equivalence of the terms here used as applied to other sections in Central Texas, as given in Bulletin 44 of the Bureau of Economic Geology. Of the formations here listed, the oldest actually exposed at the surface in Tarrant County is the Paluxy. The older formations, how- ever, are penetrated in well drilling. Table OF GEOLOGIC FORMATIONS' OF TARRANT COUNTY 1 Tarrant County Section. Cenozoic and Recent Eagleford Woodbine Gray son ) Mainstreet^ Pawpaw Weno Denton Fort Worth \ Duck Creek j Kiamitia J Edwards 'j Comanche Peak l Goodland J Walnut Paluxy Glen’ose Trinity Pennsylvanian Central Texas Section. Cenozoic and Recent. Eagleford , Buda ( ? ). .Del Rio. Georgetown. Peak. Walnut. Paluxy. Glenrose. Travis Peak. ^Edwards. jComanche Tn this tabulated statement of formations the Woodbine of Northern Texas appears as the equivalent of the Buda of Central Texas. Although in accordance with present usage, the authors wish to express reserve with regard to the equivalence of the Woodbine in the Central .Texas section. The Geology of Tarrant County 25 DESCRIPTION OF FORMATIONS. PENNSYLVANIAN Knowledge of the composition and exact horizons of the Pennsylvanian strata beneath Tarrant County is very defective and awaits further drilling and especially a careful and intelli- gent recording cf the well logs. The Tucker’s Hill well, drilled in East Fort ‘Worth in 1892. apparently penetrated at 1120 feet a series of alternating clays and sandstones; the ‘Polytechnic’ well went out of “dark brown shale and sand” at 1200 feet; the record for 1200-1297 feet is missing ; 1297-1416 feet is recorded as “blue shale”. From logs of other wells it is known that the base of the Trinity is red sandstone and the top of the Pennsyl- vanian at Fort Worth is bluish to black shales so that the parting between the Comanchean and the Pennsylvanian sediments in the Polytechnic well possibly lay in the gap in the log, sum- marized. above. DIP OP THE PENNSYLVANIAN ROCKS A contouring of the basal Trinity does not, of course, give information which determines the attitude of the underlying Paleozoic rocks, since the two systems are unconformable. Well data show an eastward dip of the base of the Trinity sand, and an eastward dip of the underlying Pennsylvanian strata has been assumed. In addition there appears to be a large depres- sion, possibly synclinal, in the Pre-Comanchean strata under Tarrant County. (See page 97). COMANCHEAN TRINITY DIVISION 1 The Trinity Division consists in Tarrant County of the fol- lowing formations, beginning at the bottom: Trinity (Base- ment) sands, Glenrose limestone, Paluxy Sands. The Basement sands are underlain by the Pennsylvanian, and the Paluxy Hn this paper we follow the terminology of Hill, who established the accepted classification of the Texas Comanchean and mimed its divisions and formations. 26 University of Texas Bulletin sands are overlain by the Walnut formation of the Fredericks- burg Division of the Comanchean. TRINITY (BASEMENT) SANDS. The Trinity (Basement) sand, not exposed at the surface in Tarrant County, is an important reservoir for artesian water under the Black and Grand Prairies, as fully explained by Hill. It contains at least three important artesian levels under this area and is probably about 120 feet thick. Underneath Fort Worth it is penetrated at the depths of from 1025 to 1150 feet. GLENROSE LIMESTONE. Proceeding southward from southern Oklahoma, the Antlers or basal Cretaceous sand, is described as being split into two sandy formations by an intervening wedge-shaped limestone mass which thus occupies a place between the two sands. It increases in thickness southeastward. This limestone is the Glenrose formation. It is not exposed at the surface in Tarrant County, but has been penetrated by wells at various points in the county. It is stated by Hill to be about 470 feet thick under Fort Worth and to increase in thickness southeastward at the rate of 8 or 9 feet per mile. Underneath Fort Worth it occurs at depths of about 500-1025 feet. PALUXY SANDS. This sand, the westernmost outcropping formation in the county, is exposed in the valley of the West Fork, in the north- west corner of the county. It is an artesian water reservoir and consists of alternating layers of rather unconsolidated sands and compact clay, the formation being iron-stained but free from gypsum, and its water of a correspondingly good quality. On exposure -the material is seen to be poorly consolidated, and readily disintegrated; it contains rounded concretions and phos- phate nodules. The Paluxy sand is about 100 feet thick and contains three principal artesian layers. It is poor in fossils. FREDERICKSBURG DIVISION. The Fredericksburg division consists in north-central Texas The Geology of Tarrant County 27 of four groups of strata : Edwards limestone, Comanche Peak limestone, Goodland limestone, and Walnut shell conglomerate and clays. Since the limits of each of these divisions are still being studied, the formations will be discussed together. Brief Diagnosis : Underlying the narrow but very easily recognizable outcrop of brownish shelly Kiamitia marl in Tar- rant County is 117 feet of white, chalky, rather pure limestone and interbedded whitish marl, which makes the bluffs of the Clear Pork between Port Worth and Benbrook, and is exposed over a considerable area along the two forks of the Trinity. Beneath this whiter rock is a bluish shell conglomerate which is the top of the Walnut formation. Under the conglomerate is a series of marls, unconsolidated sand and shell conglomerates ex- tending about 100 feet down to the easily recognized Paluxy sand. A characteristic sequence of fossils in these sediments is noted in the following discussion. Lithology: The upper 16 feet of the Fredericksburg Division at Port Worth is a hard, resistant, crystalline, rather unfossilif- erous limestone which forms a protective cap for the underlying, more chalky limestones. This has been considered the northern attenuated portion of the Edwards and Comanche Peak forma- tions, which thicken rapidly toward the south, forming below the Brazos the substratum of the Lampasas Cut- Plain. Tat! records from Benbrook a rudistid in the upper four feet of the Fredericksburg; these fossils and an abundance cf flinty masses characterize the Edwards limestone farther south. Below the upper 16 feet is a series of softer, chalky limestones and light straw-colored marls extending from a point which will be defined as the top occurrence of Schloenbachia sp. aff. belknapi Marcou, downward to the top of a prominent blackish- blue, hard shell conglomerate made almost entirely of the oyster Gryphea marcoui Hill and Vaughan. This conglomerate lies 117 feet below the base of the Kiamitia marl, the Fredericksburg- Washita contact, which is easily recognized in Tarrant County. The basal part of the limestone above the conglomerate contains considerable yellowish-brown marl. The basal contact is sharply defined. The limestone contains a characteristic sequence of 28 University of Texas Bulletin fossils, which is invariable over a wide area. These fossils are, in part, beginning at the top : — 1. Schloenbachia sp. near belknapi (Marcou). 2. Schloenbachia acutocarinata (Shumard). 3. Diplopodia taffi Cragin. 4. Coral syndrome: Paiasmilia, Trochosmilia. 5. Holectypus sp. 6. Enallaster texanus Roemer. 7. Hemiaster sp. near whitei Clark. 8. Salenia mexicana. Upper level. 9. Exogyra plexa Cragin. Small form. 10. Syndrome of Chondrodonta sp. aff. munsoni (Fill), Lima, Pecten irregularis Boese. 11. Engonoceras sp. 12. Schloenbachia acutocarinata (Shumard), abundant. 13. Pholadomya sancti-sabae Roemer, abundant. 14. Gryphea marcoui Hill and Vaughan, abundant. 15. Schloenbachia sp. 16. Schloenbachia sp. (6"). 17. Turritella sp., abundant. 18. Gryphea marcoui. Upper conglomerate. 19. Exogyra texana, Upper horizon, abundant. 20. Salenia sp., Lower level. 21. Protocardia filosa Conrad. 2 2. Natica pedernalis Roemer. The foregoing white limestone portion of the Fredericksburg Division is exposed in a vertical section at the north end of the Lake Worth dam; good exposures occur on the Azle road 9 miles northwest of Fort Worth, where practically the whole thickness is seen underlying a nearly complete section of the Kiamitia marl ; on the Stove Foundry road, half way between Fort Worth and Benbrook, where the upper third is well ex- posed; on the Weatherford, Granbury, and Plover roads; and elsewhere in the area mapped. The formation is very fossilifer- ous, most of the fossils being mud casts. The cut in the hill at the north end of the Lake Worth dam sections the upper part of the Fredericksburg division, com- monly assigned to the Goodland limestone, and continues down- wards to the top of the bluish-gray Walnut shell conglomerate. The Geology of Tarrant County 29 LAKE WORTH SECTION OF THE FREDERICKSBURG DIVISION Feet. Inches. Duck Creek Limestone 40 (The lower two feet of this limestone is the Hamites ledge.) Kiamitia marl: Brown marl containing Gryphea navia and Exogyra plexa, forming grassy slope above cliff. .31 6 Fredricksburg Division: 9. Chalky limestone, sparsely fossiliferous 26 9 This contains the following strata: 9h. Massive limestone in 4 layers 6 feet. 9g. Marly fragmented limestone 8 9f. Blue marl 1 9e. Three marl layers interbedded with thin limestone layers 3 9d. Fragmented limestone 4 • 9c. Blue marl with 2 limy layers 2 9b. Chalky limestone. Echinoid zone. ... 2 9a. Blue marl 0.75 These strata are rather barren in the upper 16 feat but contain especially in the lower part: Hemiaster whitei, Enallaster texanus, Diplopodia taffi, Schloenbachia sp. aff. belknapi, S. acutocarinata, Cinulia, Lima, Pecten irregularis, Gryphea mar- coui, Exogyra texana, Pinna sp. aff. comancheanus, Cyprimeria, Lunatia, Parasmilia, Trochosmilia and many other fossils. 8. Massive chalky limestone 5 3 This massive and distinct band contains: Hemiaster whitei, Lima wacoensis, Lima sp, Enal- laster texanus, Pecten subalpina, P. irregularis, Exogyra texana, E. plexa, Engonoceras, Schloen- bachia acutocarinata, S. sp. aff. belknapi, Tylos- toma sp. 7. Blue calcareous marl 5 6 This distinct marl band is conspicuous (Plate 1), and contains: Turritella, Pholadomya, Lima, Trigonia, Cyprimeria, Exogyra plexa, Enallaster texanus. 6. Massive chalky limestone 13 0 Hemiaster whitei, Hemiaster sp, Gryphea marcoui, Lima wacoensis, Schloenbachia acutocarinata, sheets of celestite. 30 University of Texas Bulletin Feet. Inches. 5. Blue marl 7 0 Hemiaster, Lima, Pecten irregularis, Enallaster texanus and many other fossils. 4. Chalky limestone 10 0 The bottom of this layer is about at the level of the approach to the dam. 3. Massive impure fragmented chalky limestone, marly at the base 43 0 1. Massive chalky limestone overlying the Walnut shell conglomerate and seen in the channel below the dam 5 0 Total 117 0 Walnut Conglomerate: Massive blue gray shell conglomerate composed mainlj of Gryphea marcoui shells 5 0 The Fredericksburg limestone can be studied to advantage on the steep slopes of the valley of the West Fork, just north- east of the Lake Worth dam, where its fossil sequence is excel- lently displayed. The following series of levels holds for any locality in Tarrant County within narrow limits, and may be used at Lake Worth, Mary’s Creek north of Benbrook, Bear Creek southwest of Benbrook, Azle Road sections northwest of Fort Worth, and Stove Foundry Road sections along the Texas and Pacific track between Fort Worth and Benbrook. DISTANCE OF FREDERICKSBURG FOSSIL HORIZONS AND ZONES OF ABUNDANCE BELOW THE TOP OF THE FREDERICKSBURG LIMESTONE, IN TARRANT COUNTY Feet. Fossils sparse Corals: Parasmilia, Trochosmilia Diplopodia Salenia (upper level) Trichotropis shumardi Exogyra plexa Lima (abundant) Ostrea sp. aff. munsoni Schloenbachia belknapi Hemiaster sp. (small) Salenia (lower level) Protocardia filosa Exogyra texana Natica pedernalis 0-16 23 24 26 27 28 28 28 40 36 55 57 40-57; 90-100 110 1. Columnar section of the Fredericksburg limestone in the valley of the West Fork of the Trinity River near the Lake Worth Dam. The upper half of the section is seen in Plate 1. The numbers refer to corresponding strata described on pp. 29-32. Vertical scale, y 8 inch=l foot. 32 University of Texas Bulletin The portion of the Fredericksburg Division lying between the limestone just described and the Paluxy sand below, consists of alternating conglomerate and sand layers totalling about 100 feet iu thickness. This series of strata constitutes the prom- inent escarpment seen below the Fredericksburg limestone on the Azle road, two miles east of Azle, on the Weatherford road near the county line, and elsewhere in the northwest corner of Tarrant County. The topmost impervious conglomerate pro- tects the underlying unconsolidated sands from weathering, and thus gives to the whole escarpment a resistant appearance. In fact the cap conglomerate breaks off and strews the sides of the hills with fossiliferous slabs and debris. This topmost layer sometimes weathers unevenly, and small hard caps remain, forming the Walnut peaks seen near Azle. The shell conglom- erate outcrops around Lake Worth, where it is seen at the small exposure just below the dam and for several miles up the river. This basal Fredericksburg belongs to the Walnut formation, but the upper contact will not be defined here. SECTION OF THE LOWER PORTION OF THE FREDERICKSBURG DIVISION, ON AZLE ROAD, TWO MILES EAST OF AZLE TARRANT COUNTY, TEXAS Thickness in feet. Brown limy marl with Gryphea marcoui, Turritella, Exogyra texana, Enallaster, Natica 20 Blue-black shell conglomerate, containing Gryphea marcoui (in great numbers), Trigonia, Pecten subalpina, Pecten sp., Exogyra texana and spp., Cyprimeria, Turritella, Enallaster texanus, Remondia (?), Lunatia sp 5 Unconsolidated sand, slightly yellow stained, containing ferrugi- nous fragments. No fossils noted 7 5 Arenaceous reddish limestone and shell conglomerate, contain- ing Gryphea marcoui, Turritella sp., Enallaster texanus, Exogyra texana 25 Paluxy sand. The upper conglomerate of the Walnut, a mass of Gryphea marcoui shells, is seen in the east bank of Lake Worth at the Nine-mile bridge, just opposite the bathing beach. It should be especially noted that there is another conglomerate having the same sequence of lithology and of fossils, lying stratigraphi- callv 20 feet above this level and easily confused with it. The Geology of Tarrant County 33 FAUNA OF THE GOODLAND LIMESTONE Hemiaster whitei Clark Hemiaster sp. Enallaster texanus (Roemer) Holectypus planatus Roemer Salenia mexicana S'chlueter Diplopodia taffi Cragin Cypho.soma" texana Goniopygus sp. Engonoceras sp. S’chloenbachia spp. Schloenbachia acutocarinata S'numard) Turritella seriatim-granulosa Roemer Turritella sp. Cinulia tarrantensis Cragin Trichotropis shumardi Cragin Cylindrites formosus Cragin Cerithium bosquense Shumard Tylo.stoma chihuahuense Boese Tylostoma tumidum? S’humard Lunatia pedernalis Roemer Nerinea sp. Neritina sp. Rostellaria subfusiformis Conrad Turbo sp. Homomya sp. Pinna sp. aff. comancheanus (Cragin) Protocardia texana (Conrad Protocardia filosa (Conrad) Isocardia sp. Oyprimeria texana (Roemer) Pecten occidentalis ? (Conrad) Pecten irregularis (Boese) Pecten subalpina Boese) Exogyra texana Roemer Exogyra plexa Cragin (Boese) Exogyra sp. aff. plexa Boese Gryphea marcoui Hill & Vaughan Pholadomya sancti-sabae Roemer Ostrea sp. aff. johannae Choffat Lima wacoensis Roemer Trigonia sp. Tapes sp. Corbula sp. Schloenbachia sp. aff. belknapi (Marcou) crustacean claws Trochosmilia texana (Conrad) Parasmilia austinensis Roemer FAUNA OF THE WALNUT FORMATION. Exogyra texana Roemer Exogyra weatherfordensis Cragin Enallaster texanus (Roemer) Remondia ? sp. Gryphea marcoui Hill & Vaugban Salenia sp. aff. mexicana Turritella sp. Pecten irregularis (Boese) Triginia sp. Schloenbachia acutocarinata (Shumard) Holectypus sp. aff. planatus WASHITA DIVISION The Washita Division of the Comanchean Cretaceous is very fully developed in Tarrant County, and includes the following formations beginning at the base : Kiamitia, Duck Creek, Fort Worth, Denton, Weno, Pawpaw, Mainstreet, Grayson, and Woodbine. 1 KIAMITIA MARL Brief Diagnosis : The Kiamitia formation is a brownish yel- low, slightly calcareous marl, with scattered limestone, shelly and flaggy bands and abundant deposits of oyster shells, mostly Gryphea navia. It is 27 feet thick at Fort Worth. It weathers out usually into a narrow hillside slope which lies above the glaring white Fredericksburg limestone and below the scarp produced by the basal Duck Creek limestone. The outcrops are *The inclusion of the Woodbine in the Washita Division is tenta- tive on the part of the authors. 3— Tarrant 34 University of Texas Bulletin usually grassy and poorly exposed, and due to their situation are often contaminated by gravel deposits. The limits of the formation are sharply defined in Tarrant County. Description of Localities : This formation skirts the western edge of the Black Prairie at the foot of its escarpment and forms a narrow sloping strip often less than 50 feet wide. Due to its narrowness and to the close affinities of the formation with the Fredericksburg strata (page 27) it has not been sep- arately mapped ; but it may be projected on the map by cutting off a hair-line strip from the east border of the Fredericksburg Division as mapped. The formation decreases in thickness and in shelliness southward. At Shawnee Creek, Denison, it is over 60 feet thick and has prominent bands of hard shell conglom- erate distributed through most of its thickness. In Tarrant County the shell bands have disappeared and the shells are pres- ent in smaller amounts in the loose limy layers and the interbed- ded marls. On the Noland’s River, southeast of Blum, the forma- tion is 19 feet thick and very similar to its outcrops in Tarrant County. The constant features, from the Red River to the Brazos, according to Hill, are a basal member which is cal- careous and argillaceous and contains quantities of shell frag- ments ; the upper part of the formation is a series of calcareous laminated blue clays which turn brownish-black upon weath- ering, interstratified layers of indurated calcareous clay (e. g., stratum 15 below) and laminated sandstone flags (strata 2, 4, 7, 17). The flags are somewhat calcareous and the whole forma- tion shows iron discoloration. South of the Brazos the forma- tion is attenuated, and near Round Rock is stated to be an “earthy, blue, marly, rather hard limestone” at the base of the Georgetown limestone. (Hill). In Tarrant County there are two general types of Kiamitia exposure, the hillside and the upland type, of which the latter is very rare and exceptional. If the overlying Duck Creek lime- stone has been leveled or brought to a very gentle grade over a considerable area, the Kiamitia will form a gentle slope back- ward from the resistant underlyiug Fredericksburg rocks and will produce the upland type of exposure. This sort of outcrop is seen at the western edge of Duck Creek uplands, hence its The Geology of Tarrant County 35 rarity. The best examples are along the Azle road near Lake Worth. On the prevailing hillside outcrops exposures are pro- duced in stream cuttings but they are very inconsecutive. The exposures lying near the main drainage lines are usually partly overlain by terrace gravel deposits. However, the present day lateral drainage is rapidly cutting into the uplands and the headwaters of these valleys show uncontaminated Kiamitia exposures. Nearly a complete exposure, lacking the upper contact, is seen on the Azle road, about 6 miles northwest of Fort Worth and 2 y 2 miles northeast of Lake Worth, at the point where the road sections the Kiamitia marl and passes down thru the Good- land escarpment. SECTION OF KIAMITIA MARL, AZLE ROAD, SIX MILES NORTHWEST OF FORT WORTH 18-19 17 16 15 14 13 12 11 10 9 8 7 5-6 4 3 2 1 A' Height from Thickness bottom of section Feet In. From Brown marl. Gryphea navia ... .20' Hard shelly limestone . ..19'9" Very fossiliferous bluish marl “E. plexa zone” T 19' Fractured limestone, double band with central marl layer 18' Bluish fossiliferous marl 16' Hard coarse grained limestone, blue upon fracture 14'4" Blue marl 14' Hard shelly limestone 13'6" Blue marl 13' Blue shaly marl 12'10" Brownish marl, bluish before weathering . 12' Brown sandy flag ll'lO" Blue marl, more compressed at top 6 '6" Light colored soft sandy flag. . . . 6'4" Blue marl 5' Light colored soft sandy flag. . . . 4'10" Brown laminated clayey marl, blue on fresh exposure Fredericksburg limestone. (Upper 2 feet of Kiamitia concealed by soil overwash). To 25' 20 ' 19'9" 19' 18' 16' 15'4" 14' 13'6" 13' 12 ' 10 " ll'lO" 6 ' 6 " 6'4" 5' 4'10" 8 4 6 6 2 10 2 4 2 4 2 10 36 University of Texas Bulletin These several members in the Azle section may be arranged in three groups that can be distinguished and described as below : 18-19 17 Ife 15 r* 13 \Z 1 1 '§ 8 7 5-6 4- 3 2 Fig. 2. Columnar section of the Kiamitia formation in cut on Azle road, eight miles northwest of Fort Worth. The numbers refer to corresponding strata described on pp. 35-7. Vertical scale, V 8 inch — = 1 foot. Basal portion ( strata 1-6) : Approximately the lower half of the formation is a clay-marl which is bluish or bituminous on fresh exposure and extensively laminated; is brown on weathering, breaks into cuboidal chunks, indurates locally in thin layers, and at places is sandy. Hill notes the following features of this portion : It is a dark blue clay resting directly upon the smooth surface of the white Fredericksburg limestone; at a level of 5 feet above the base is a persistent band of gray indurated limy clay (2) ; at places it is variably arenaceous in the basal portion and some layers very near the base are sandy ; near Aledo (Parker County) there is a basal layer of laminated, sandy, very calcareous and argillaceous material which contains The Geology of Tarrant County 37 large quantities of shell fragments. This argillaceous portion at the Brazos is not more than 5 feet thick. The Fredericksburg-Kiamitia contact is lithologically the most contrasting and abrupt change in the series. It is seen to advantage at the Marine Creek crossing of the Azle Road. Here the blue, closely laminated, flaky Kiamitia marl lies directly upon the flat but irregular and lumpy surface of the limestone. In stream cuts the marl may be removed exposing the limestone. At localities nearer Fort Worth a finely fragmental shell de- posit was noted just over this limestone; and at the Texas Pacific Railroad crossing of the Clear Fork is a six inch slightly shelly, blue marl stratum at the base of the Kiamitia. As noted later the fossils are mainly continuous across this contact. Middle portion ( strata 7-17) : This limestone portion is topographically and paleontologically the most interesting part of the formation. It consists of six thin limestone layers or flaggy, sandy layers, alternating with blue and brown calcareous, laminated, and in part carbonaceous, clay. Three of these layers (7, 9, 17) are calcareous sandstone flag layers each 2 or 3 inches thick; of the other three layers 13 is a hard, coarse-grained limestone, 11 and 15 are soft marly-chalky limestones. All of the layers are fossiliferous, and the formation, in richness of fossils, is quite the reverse of the description of Taff. The faun# is, however, poor in ammonites and echinoids. Upper portion ( strata 18-19) : This is a clay marl, brown, non-laminated and sparsely shelly, without the extensive con- glomerate sheets which are so prominent in the upper Kiamitia of the Red River section. Gryphea navia and G. corrugata were noted in this portion. Palentology : Although the Kiamitia formation has been placed in the Washita division it has strong paleontological affinities with the Fredericksburg, as shown by the following table: 38 University of Texas Bulletin Fossils' of the Kiamitia marl, at Fort Worth, Texas. Formation or formations in which fossil is found, indicated by aster- isk in column opposite fossil named. Fredericks- Kiamitia Duck Washita burg Gryphea navia Hall Avicula leveretti Cragin Schloenbachia sp. (belknapi?) Ostrea sp. Exogyra texana Roemer * Pecten irregularis Boese * Exogyra plexa Cragin * Schloenbachia acutocarinata Shumard * Isocardia sp. * Homomya sp. * Trigonia sp. * * Pecten subalpina ? Boese * Protocardia texana (Conrad) * Cyprimeria sp. * Gryphea washitaensis Hill Gryphea corrugata Say Creek Kiamitia Fauna (Forms known to occur only in the Kiamitia) Members of Azle section preceding, in which fossil is found Pinna sp 3 Gryphea navia Hall 1-19 The typical G, navia is very abundant in the middle third of the formation at Fort Worth, though it forms thick conglom- erates in the upper portion on the Red River. It is a massive imbricated shell, usually with a twisted beak. Schloenbachia acutocarinata, Exogyra plexa (plicate and non-plicate forms), and Pecten irregularis were not seen above the stratum 16. Exogyra plexa is limited to this layer. “16” is a very fossiliferous layer. Below it the fossils de- crease in number and in the lower third of the formation are rare. Schloenbachia acutocarinata and Exogyra texana were not observed in the basal Duck Creek limestone as at the Red River. The Geology of Tarrant County 39 DUCK CREEK FORMATION. The Duck Creek formation at Fort Worth is divisible into four lithological and palentological members beginning at the top: (1) Kingena member — the Duck Creek Marl. (2) Scaphites member — the Duck Creek Limy Marl. (3) Schloenbachia sp. (aff. trinodosa) member, — the Duck Creek Marly Lime. (4) Desmoceras member — the Duck Creek Limestone. DUCK CREEK MARL AND LIMY MARL These groups in Tarrant County consist of a series of pre- vailingly light colored yellowish-gray marls containing thin seams of impure fragmental chalky limestone. The marl is recognizable in the landscape as a gently sloping shelf or terrace lying at the base of the escarpment produced by the overlying Fort Worth limestone and sloping to the outcrop of a lime- stone layer which lies at the base of the Marl (stratum 17). Be- low this layer, which in stream cuts forms the edge of the marl* shelf, the slope is steep and is continuous with that the the Duck Creek limestone escarpment below. The top of the Duck Creek limestone is a persistent grayish, usually lichen-incrusted band, Outcropping below the edge of the shelf in the face of the es- carpment. The outcrop of these strata is generally narrow and lies along the rim of the main escarpment as seen near the Texas Christian University at Fort Worth, and therefore its soil value is almost negligible. At places, however, it weathers into a brownish-yellow hillside slope devoid of rock and is then indis- tinguishable from the Fort Worth upland except for a slight topographic break at their junction. The series is 34% feet thick near Fort Worth. It is characterized by the following well defined sequence of fossils: Pleurotomaria austinensis zone Upper Kingena zone Pecten wrightii zone Upper Gastropod horizon Globiconcha (?), Turritella, Diplopodia zone Fusus, Cerithium Lower (Main) Kingena zone Goniophorus sp. zone Crania sp. zone Limonite fossil (Lower Gasteropod) zone, Scaphites sp B (top) Gerontic Ammonite zone Hamites spp. Pinna sp. 40 University of Texas Bulletin Description of Localities: The Duck Creek Marl and Limy Marl are distinct from the overlying Fort Worth limestone and the underlying Duck Creek limestone, both lithologically and paleontologically, and have as much justification for ranking as a separate formation as either of them. If they are to be placed with either it should be with the Fort Worth limestone, since f ft fie faunal changes are very abrupt at the end of the Duck dreek limestone, The Fort Worth-Duck Creek contact as here described and mapped, following the most frequent usage in the literature, is totally arbitrary. It is debatable if it would not be much better to place this contact below the abundant Kingena zone and the horizon of Pecten bellula or lower, so as to partition the ammon- ites and echinoids more accurately. Such a contact would be as well warranted lithologically and topographically as the present one, and more consistent paleontologically; but since the forma- tions are of only local application, no insistence is placed on this matter of contact. There is a clear and mappable topographic break above the stratum 24, so that the overlying Fort Worth limestone, even if thin, makes a continuous miniature escarp- ment in the landscape. The only other consistent topographic break is at stratum 17, which is resistent to erosion and caps the underlying Duck Creek escarpment; 17 forms conspicuous horseshoe bend outcrops in runs, while 24 fails to withstand erosion. In this group of strata the limestone beds are soft, chalky and fractured, and the marls are yellowish, water-bear- ing and very calcareous. Due to the thinness and softness of the limestone bands these degrade rapidly and so produce no conspicuous surface features. Only the Duck Creek stratum 21 is noticeably sandy and flaggy. The limestones and marls grade into each other, and locally there is slight lateral replacement. The Duck Creek marl is typically exposed in the run above the first turn of the street car track north of Texas Christian University, and in the cut of the military road nearby. Fig. 3. Columnar section of the Duck Creek formation in cuts near Forest Park, Fort Worth. The numbers refer to cor- responding strata described on pp. 42-4. Vertical scale, Vs inch — 1 foot. 42 TJmversity of Texas Bulletin SECTION OF THE DUCK CREEK MARL, ON BOTH SIDES OF RUN SOUTHEAST OF FIRST TURN OF STREET CAR TRACK, % MILE NORTH OF TEXAS CHRISTIAN UNI- VERSITY AND 3 Yz MILES SOUTHWEST OF FORT WORTH. Altitude of top of Duck Creek Marl 680 feet. Thickness Feet Inches Fort Worth Limestone. 3. Soft chalky limestone; Pecten bellula, Pleuroto- maria austinensis 6 2. Marl. Pecten bellula < 6 1. Soft fragmental limestone. Pecten bellula 6 Duck Creek Marl: 24. Soft marl with chalky limestone fragments. Kingena (Upper) horizon in lower half. Pecten wrightii zone 3 6 23. Soft chalky limestone. Kingena (Upper) horizon. P. bellula. Forms a slight terrace. . . 4 22. Marl. Upper gastropod horizon. Turritella, Ceri- thium, Fusus, Gyrodes (?) 2 8 21. Soft sandy limestone flag. Diplopodia zone 3 20. Marl. Pecten bellula 3 9 19. Soft chalky limestone. Lower (Main) Kingena zone 1 18. Straw colored marl 5 16-17. Laminated limestone, gray and iron-stained. indurated locally, rather unfossiliferous, making ‘horseshoe’ bends where the streams cut through It, and everywhere forming the cap of the Duck Creek escarpment or at least a break in the topo- graphy 4 (The section is continued in the cut of the military road through the Duck Creek escarp- ment, y± mile north of the University). 16-17. Laminated gray indurated limestone, capping the crest of the escarpment. Kingena may usually be found just above it 4 13-15. Marl. Gryphea corrugata, Hemiaster elegans, Schloenbachia sp. I, Goniophorus sp 3 12. Crumbling, marly limestone. Pinna sp. 1 2 11. Limy straw-yellow marl. Limonite fossil horizon (Lower gastropod horizon): Nerinea sp. near pellucida Cragin, Lunatia, Cinulia, Cerithium, Turbo 1 The Geology of Tarrant County 43 Thickness Feet Inches 9-10. Crumbling chalky very marly limestone Crania sp. 1. Hamites spp 2 7.8. Straw colored marl 2 6. Chalky or bluish impure limestone 2 Limestones and marls continue downward to the Hamites zone in the bed of the run. SECTION OF THE DUCK CREEK FORMATION IN THE RUN FROM SOUTHEAST CORNER OF FOREST PARK TO THE FRISCO SHOPS. LOCALITY, 3 MILES SOUTHWEST OF FORT WORTH AND V 2 MILE NORTH EAST OF TEXAS CHRISTIAN UNIVERSITY. Altitude of lower Kingena Zone at second turn of car track, 640 feet. Thickness Feet Inches Scaphites member (Limy Marl) : 17. Gray indurated Limestone 2 16. Calcareous marl 2 13-15. Two equal limy ledges with thin interbedded marl layers . 3 12. Calcareous marl 2 7-11. Three thin limstone ledges and two thicker marl layers . 5 6. Compacted, closely bedded, impure limestone.... 4 Schloenbachia sp. (trinodosa?) Member. (Marly Lime) : 5. Compact limestone 1 0 Calcareous marl 6 4. Compact limestone in four equal layers with inter- bedded thin marl. 4 3. Compactly bedded, lumpy, in part “fucoidal” lime- stone mixed with bluish marl 7 Desmoceras member (Limestone) : 2. Bluish very impure limestone, slightly marly at top, but becoming more compact toward base and usually weathering into smooth cliff faces 12 1. Harder limestone with iron nodular inclusions. Hamites zone. 2 (The members 1-2 are well exposed along the drive-way in the park near the east entrance). 44 University of Texas Bulletin Paleontology : Of the fossil zones to be mentioned, the Diplo* podia zone (21), -the Turrilites" zone (19), the Crania zone (10), the Hamites spp. zone (11) and the Pinna zone (6) will be less easily located by the fossils than the others; however, they are easily located by their levels. The other zones, are conspicuous. The most dependable fossil, both in the field and in well borings, for locating the Duck Creek Marl is the Lower Kingena (19). The marl above this Kingena zone contains frequent P eaten bel- lula f which in the Fort Worth limestone is sparse. The portion of the marl below the Kingena zone is harder to diagnose; it con- tains considerable numbers of Gryphea corrugaia and other un- distinctive fossils.. The most conspicuous associations or synd- romes of fossil are the upper and lower gastropod horizons, each containing several genera. It may be mentioned that iron pseudo- morphs range considerably in the Duck Creek marl. The fauna of the Duck Creek, marl is essentially a shallow water fauna and has been stated to represent a shallowing and oscillating ocean bottom. The frequent turning of some shells, as Gryphea wash- itaensis, convex side upward is stated to indicate a bottom dis- turbed by local currents, and there are evidences that some other shells were washed into their place of deposition. FOSSIL ZONES AND HORIZONS Upper Kingena Zone : This zone containing many small rounded brachiopods at present referred to the genus Kingena lies in stratum 23 and the lower half of 24, about 7 feet above the main Kingena zone. It is thicker than the main Kingena zone, and the Kingenas, are much sparser than in the main zone. Between the two zones no Kingenas have been found in situ, though washed down individuals are abundant to below the indurated ledge 17. Upper Gastropod Zone: This zone, which contains among other genera Cerithium, Turrit ella, Gyrodes (?), and Pleuroto- maria austinensis, occurs in stratum 22, where the gastropods are abundant, and in 23-24 where they are sparse. This zone is apparently the lowest range of Pleurotoniaria austinensis Shumard, of which smooth individuals showing only the fii*st four or five whorls are found. It is a zone of abundance of The Geology of Tarrant County 45 Turritella sp., which is also abundant in the lower Kingena zone. The Gyrodes (?) sp. has not yet been found elsewhere by us. Diplopodia Zone: There is a zone of abundance of Diplopodia in the arenaceous limy flag ]aver 21. These slabs also contain plates and fragments of Hemiaster and other echinoids, Pecten subdlpina and Lima. Lower (Main) Kingena Zone: This abundant brachiopod zone, occupying stratum 19, is about a foot thick. The material above and below it does not contain brachiopods. This is a soft chunky, limestone layer which weathers into scattered irregular angular fragments with intervening projecting harder masses. A square meter of area at one locality contained 260 brachiopods of various sizes and shapes and of probably several species. This is one of the most persistent, easily located, and important hori- zons in the series and has been traced for miles in both directions from Fort Worth. Kingenas occur at the following levels, so far as known to us : (1) Mainstreet limestone, an extensive horizon near middle. Some of the individuals are much larger than any found at lower levels and are intermingled with those of smaller size and of various shapes, probably referable to several species. This is the horizon most frequently mentioned in the literature. (2) Denton marl, top: on the Noland’s River near Blum. These individuals were mostly of large size. (3) Duck Creek marl: Upper Kingena zone. Tarrant County. (4) Duck Creek marl: Lower (Main) Kingena zone, Tarrant County. (5) Duck Creek Limestone, base. In Grayson County these brachiopods of the smaller size occur within 10 feet of the top of the Kiamitia conglomerate in association with Exogyra plexa Cragin, Schloenbachia belknapi Marcou and in Tarrant County they were found at this level in association with Salenia sp., Plicatula sp. and fish teeth. Turrilites sp. A single individual of a vertically ribbed species was found in the lower Kingena zone (19). This is the only turrilite known to us below the base of the Pawpaw in the North Texas sec- tion. In the European and Mexican sections Turrilites is well represented in the Vraconien. 46 University of Texas Bulletin Goniophorus sp. This level is characterized by a very restricted zone of a few inches thickness, containing great numbers of a minute salenid, % inch in diameter, which lias a star-shaped apical system and narrow linear sutures. Crania sp. A zone of Crania sp. 1 is contained in stratum 10; the species ia % distinctive but rare, having yet been found nowhere else in the series. Hamites spp. Several small species of Hamites and related genera, quite dis- tinct from the species of large Hamites in the basal Duck Creek limestone, have not been found so far outside stratum 10. These individuals are rather rare. Pinna sp. 1. A zone of Pinna sp. with fine concentric and spined imbrications occurs in stratum 6. It is rare and distinctive, but ranges somewhat. Lower Gastropod Horizon. This is an aggregation of peculiar small iron stained mud casts and iron pseudomorphs, occurring in strata 9-11. It includes Lunatia, Cinulia, Cerithium, Turbo, Nerinea sp. near pellucida Cragin, Schloenbachia sp., Hamites sp., and S^caphites sp. (top). Most of these fossils are less than 1 cm. in diameter. They are fairly abundant. This limonite fauna occurs at the Red River. Scaphites sp. B. This small gerontic ammonite of which usually only the coiled end is preserved, practically characterizes the Duck Creek Limy Marl member. In its upper range it is associated with the iron stained fossils of the lower Gastropod horizon. (Strata 9-11). The Geology of Tarrant County 47 The following additional species, which range into the Fort Worth limestone, will also be mentioned here: Pecten bellula Cragin This fine ribbed pecten begins near the main Kingena zone (19) and is frequent up to the base of the Fort Worth limestone and present to the top stratum (33) of this formation. Pleurotomaria austinensis Shumard This gastropod has not been found by us below the Lower Kin- gena zone (19) of the Duck Creek Marl; it ranges into the base of the Fort Worth limestone where a fine individual with the body volution and the ornamentation was found. The last two volutions and the markings are usually absent. Hemiaster elegans Shumard This echinoid ranges from stratum 12 of the Duck Creek marl to high in the Fort Worth limestone, where it has a zone of abundance in the upper part of the formation. Holaster simplex Shumard — low individuals The low flat bottomed Holasters range from the indurated ledge (17) of the Duck Creek Marly Lime to the base of the Fort Worth limestone and are abundant between the two Kingena layers. They are mud casts, rarely with a calcareous test, are usually iron stained and faintly tuberculated. Holaster simplex Shumard — tall individuals These tall and top heavy Holasters range from stratum 20 of the Duck Creek marl to near the top of the Fort Worth lime- stone, being more abundant in a zone near the top of their range. Pecten wrighti Shumard This strongly ribbed pecten begins at stratum 22 of the Duck Creek marl and is abundant in 23-24. Thereafter it is sparse and disappears high in the Fort Worth limestone. More than one species may be involved in this range. A similar Pecten occurs in the basal Mainstreet limestone. Schloenbachia sp. I. This ammonite begins at the lower Kingena zone and ranges into the base of the Fort Worth limestone. 48 University of Texas Bulletin Gryphea corrugata Say. This Kiamitia and Duck Creek Gryphea is conspicuous in all the Washita strata below the indurated ledge (17) of the Duck Creek Limy Marl, and is probably absent above that point. DUCK CREEK MARLY LIME AND LIMESTONE Brief Diagnosis: The basal part of the Duck Creek formation is a series of compact soft impure limestone strata, thicker bedded than the Fort Worth limestone and with less interbedding. It produces in Tarrant county the steep escarp- ment at the west edge of the Fort Worth uplands, but almost never itself forms uplands. The series is bounded above by the Duck Creek Limy Marl and below by the Kiamitia marl, and in Tarrant County is 27 feet thick. This portion of the Duck Creek formation is characterized by a remarkable sequence of ammonite zones which locate with exactness the various levels in the formation. The sequence is divisible into four groups, in part overlapping: 1. above, Bchloenbachia spp. of the rostrata type; 2. Schlo enbachia spp. of the inftata type; 3. Desmoceras horizon ; 4. Hamites spp. horizon, at the base of the formation. Fossils collected by Shumard in the Duck Creek limestone of Grayson county, near Preston on the Red River, were described in 1858 by Marcou, who referred the beds to the Gault. The formation was first named by Hill, who described its lithologic peculiarities, mentioned some of its striking fossils, and defined it so as to include the marly strata lying between the limestone proper and the overlying Fort Worth limestone. The Fort Worth limestone in the old sense as used by Taff and others included the whole Duck Creek formation and at times various other formations. Descriptions of Localities : Good localities will often be found in stream beds cutting down through the Duck Creek es- carpment at the west edge of the Fort Worth uplands. The nar- row strip occupied by this member is usually rocky, grassy and marked at the top by isolated clumps of shrubs and trees. TJerraee topography is often present; and in case the Fort Worth limestone scarp is recognized the underlying terrace is the Duck Creek (Kingena) marl; the next underlying scarp is that The Geology of Tarrant County 49 of the Duck Creek with the limestone at its base ; and the terrace beneath is the Kiamitia clay which makes usually a gentle slope downward to the Goodland limestone outcrop. The Duck Creek limestone is prevailingly an escarpment forming rock ; very rarely is a Duck Creek upland present, and then it is of limited area and forms a transitional slope to the underlying Goodland escarpment. Such an upland is seen on the Azle road northeast of the upper lake. More often the limestone forms a divide, but in this case it is usually capped by the harder Fort Worth limestone, as on the Arlington Heights divide. Sections of the Duck Creek escarpment are well exposed in Forest Park. Several good localities lie near the Azle road about two miles northeast of the upper lake. Northeast of Moslah Temple on this road eight and one-half miles northwest of Fort Worth is an extensive exposure of the ammonite zones of the lower Duck Greek. This portion also forms the rim of an amphitheater- like depression on the headwaters of Marine Creek, Azle road, nine miles northwest of Fort Worth. Three and a half miles southwest of the court-house the formation is well exposed in Forest Park, where complete sections may be seen along a line from the park entrance to the Frisco shops; stream cuts a half mile west of the University also afford good exposures of the basal Duck Creek. The uplands around Plover and Primrose are well exposed. Those southwest of Benbrook are poor. The Duck Creek limestone interbedded with marl forms steep rocky slopes of hard terraced material which for a few miles southwest of Fort Worth makes a conspicuous escarpment bordering the broad alluvial river bottom; this escarpment with the Fort Worth prairies above is seen with striking effect from Benbrook. 4— Tarrant 50 University of Texas Bulletin SECTION OP DUCK CREEK LIMESTONE IN FOREST PARK NEAR EAST ENTRANCE, EAST SIDE OF DRIVEWAY. (Cemented Upland Gravel and cross-bedded sand at top of section.) Thickness Feet Inches 3. White limestone mixed with marl, containing Schloenbachia sp. H., Pecten subalpina, Lima, Plioatula, etc 4 2. White limestone and interbedded marl, containing Desmoceras sp. and Schloenbachia spp. aff. S. inflata. The Desmoceras is more abundant in the basal strata (B) 12 1. Harder massive grayish limestone, containing Ham- ites spp., Plicatula sp., and Pecten subalpina. . . 2 This stratum is seen along the driveway south of the other locality. The Kiamitia formation is not clearly exposed at this locality. A similar section is to be seen in the first run west of the University, while in the run from the Frisco shops the whole Duck Creek formation above the middle of the Democeras hori- zon, and most of the Fort Worth limestone are exposed. Paleontology : The Duck Creek ammonite series is one of the paleontological landmarks of the Washita division. The Duck Creek limestone is nearly constant in thickness at least from Woodville, Oklahoma, to Georgetown, Texas, and probably farther. The contained ammonite sequence is very widely dis- tributed, possibly world-wide. A portion of this zonal sequence follows, beginning at top : Schloenbachia sp. H., aff. trinodosa Boese. Schloenbachia spp. F-G, inflata group. Desmoceras sp. B. Desmoceras sp. A. Schloenbachia sp. E. aff. elobiense Szajnocha Schloenbachia belknapi Marcou. Inoceramus comancheanus Cragin, I. munsoni Cragin. Hamites spp. and other gerontic am- monites. The Geology of Tarrant County 51 FOSSILS OF THE DUCK CREEK FORMATION. Ostrea subovata ( ?) Shumard. Ostrea sp. Gryphea corrugata Say. Gryphea washotaensis Hill Pecten texanus Roemer. Pecten subalpina Boese. Pecten bellua Gragin Pecten wrightii Shumard Pecten sp. Pinna sp. Lima wacoensis Roemer Inoceramus comancheanus Cragin Inoceramus munsoni Cragin Trigonia sp. Pholadomya sp. Gyrodes sp. (?) Turritella sp. Pleurotomaria austinensis Shumard. Fusus sp. Cerithium sp. Crania sp. Nerinea sp. Turbo sp. Lunatia sp. Schloenbachia spp. Schloenbachia belknapi Marcou Hamites fremonti (?) Marcou. Hamites spp. Scaphites sp. Turrilites sp. Desmoceras spp. Kingena wacoensis (?) (Roemer). Kingena spp. Diplopodia sp. Hemiaster white! Clark Hemiaster sp. Holaster simplex Shumard. Hemiaster elegans Shumard Salenia sp. Callianassa sp. Fish teeth. FORT WORTH FORMATION. Brief Diagnosis : The Fort Worth formation includes a series of limestone and marl layers, each less than one foot thick, al- ternating rather regularly with each other. The limestones are chalky and dead white, or are indurated, bluish interiorly and stained superficially with yellow or brown iron smears. The strata underlie broad stretches of upland grazing and farming country composed of a black soil, and in stream beds weather into small cliff faces with shelf-like projecting limestone layers. The formation is thirty feet thick in Tarrant County. It contains numerous characteristic fossils, such as Pecten bellula, Holaster simplex, Hemiaster elegans, Exogyra americana, Schloenbachia sp. J, and may be identified by the following sequence of fossil zones beginning at top : Enallaster sp. Ostrea carinata Lamarck. Exogyra americana Marcou. Hemiaster elegans Shumard. Pecten bellula Cragin. Schloenbachia spp. of inflata type size of austinensis Lasswitz. Holaster simplex Shumard. Schloenbachia sp. J. Pleurotomaria austinensis Shumard. A nearly complete exposure of the Fort Worth limestone and the overlying Denton Marl is seen on the west bank of Sycamore Creek about 1% miles above its mouth. The limestone is ex- posed at several isolated localities, particularly the cliff along the creek at the southwest corner of Glenwood Park, which gives the following section: 52 University of Texas Bulletin Feet Inches 33. Miarl, limy at top 3 32. Soft impure limestone. Enallaster sp. 2 3 3 31. Chalky limestone 10 30. Marl. Nerinea sp 8 2 9. Limestone in 4 equal layers with thin marl inter- bedding . 2 28. Loose crumbly limestone.... 1 27. Solid, hard, yellow stained limestone 1 8 26. Marl 1 6 25. Limestone in 4 equal layers with slight marl in- terbedding, but the bedding somewhat irregular near base 2 6 24. Compact coarse grained limestone, iron stained and locally sparingly flinty 1 3 23. Limestone, concretionary and fucoidal at top, fol- lowed by compressed marl (2"), limestone (3") and compressed marl (2"). 1 3 22. Coarse limestone, fucoidal at base 1 20-21. Coarse grained fucoidal limestone with marl at top 1 5 19. Lumpy fucoid layer . . . 2 19. Brown marl. 1 17-18. Chalky limestone with very calcareous coarsely laminated marl at base. . 1 3 16. Chalky concretionary limestone 8 15. Brownish marl 8 14. Chalky concretionary limestone 5 13. Brownish marl 5 12 Hard, fine-grained, compact, slightly shelly lime- stone, semi-crystalline and iron stained at base. . 7 11. Blackish marl, brown or weathering. Lima, Holaster, Schloenbachia sp. J 6 10. Irregular, chalky limestone, Schloenbachia sp J. . 4 9. Closely laminated calcareous marl, slaty color, speckled; Holaster simplex, Pecten bellula, Hem- iaster elegans 5 8. Limestone, slightly lumpy or irregularly bedded. . 7 7. Laminated marl 3 6. Limestone, irregularly bedded 8 5. Laminated marl . 6 4. Limestone, irregularly bedded 1 10 TOTAL.... 30 1 The basal layers are not exposed here. The whole Denton marl, showing its usual character, thickness and fossils, is exposed in several places between Belzise Terrace and Sycamore Creek. BT : -'i A B Fig. 4. Columnar sections of the Fort Worth limestone. A. On Sycamore Creek, northwest corner of Glenwood Park, Fort Worth. The Denton marl immediately overlies stratum 33. B. Eastward facing exposure in a run y 2 mile east of Texas Christian University and y 2 mile south of Forest Park, Fort Worth. The numbers refer to corresponding strata described on pp. 52-4. Vertical scale, V 8 inch = 1 foot. 54 University of Texas Bulletin Description of Localities : This formation in the restricted sense adopted by Hill occupies a strip of variable width running through the middle of Tarrant County from north to south. The type localities, % mile east of the Texas & Pacific Railway sta- tion, Port Worth, and on the river bank just north of the Court- house are now almost obliterated, the former by erosion, the latter by grading and overwash. There has been some variation in the nomenclature of this formation, but as eventually defined, it ‘ ‘ consists of a group of impure white limestones, very slightly arenaceous, regularly banded in persistent layers averaging nearly a foot in thickness and alternating very regularly with similar layers of marly clay. The limestones and marls occur in strata 4 or 5 inches to 2 or more feet in thickness. The marly layers alternate with the hard limestones in bands ranging from thin laminae to beds 6 inches or more thick.” “Paleontologi- cally the formation may be defined as the horizon of Ammonites leonensis and E piaster elegans.” With little variation, the following sections may be taken as typical for Tarrant County : SECTION OF FORT WORTH LIMESTONE, EASTWARD FACING EXPOSURE IN RUN V 2 MILE EAST OF TEXAS CHRISTIAN UNIVERSITY, 3 MILES SOUTHWEST OF FORT WORTH, TEXAS. Altitude, top of exposure, 685 feet. Feet Inches 25. Three thin limestone bands with 2 interbedded marl layers 2 2 24. Laminated marl, with a 3" limy hand in center. . 1 6 22-23. Limestone in 4 equal layers interbedded with thin much compressed limy marl 2 21. Marl . 6 18-20. Limestone in 3 laminated equal layers inter- bedded with thin, much compressed limy marl. .1 8 18. Marl 6 16-17. Limestone. Laminated marl ...... ... ... 2 Limestone. ' " 6 i5i -mm 8 14. Limestone . . . ; . . . . . 6 13. Marl 10 12. Limestone ... 8 8-11. Blue marly Limestone 1 6 4- 7. Laminated marl 3 3. Limestone 5 The basal strata 1-2 are exposed in the bend of the stream just north of this locality. The Geology of Tarrant County The formation is thus composed of a series of alternating beds of soft chalky limestone and calcareous marl. It differs from the upper Duck Creek beds in that there is a regular alternation of lime and marl, no bed in general is more than 1 foot thick, and the limestone strata indurate, especially in eastward facing exposures and form projecting ledges, the softer marl having eroded away. The marl layers are compactly laminated and very limy and grade evenly into the limestone, so that the exact limits are undefined even though they appear definite due to tfie weathering of the marl and the shelf -like projection of the lime- stone. In addition the hard layers vary slightly in thickness even in the same cliff face due to their being composed of un- even flaky accretions of calcareous material cemented together by limy marl. The contact of the Fort Worth limestone and the Denton marl is well shown at a point y 2 mile south of the Frisco track and 4y 2 miles southwest of Fort Worth. Denton Marl Feet 3. Shell conglomerate of Gryphea washitaensis, con- taining Ostrea carinata. Pecten subalpina, etc.. 1 2. Bluish clay with innumerable Gryphea washit- aensis adults and larvel stages 16 1. Brown sandy marl with many sandstone flags. ... 8 25 Fort Worth Formation: 33. Straw-colored calcareous marl with limy fragments. Enallaster sp. E. texanus, Nautilus texanus, Pecten subalpina, Schloenbachia sp. I, Holaster simplex, Hemiaster elegans, Lima sp. .......... 3 32. Three limy strata with interbedded thin mart layers 2 Ihe lower Fort Worth strata are excellently exposed along this run. Essentially the same sequence is seen north of the Frisco track, 3 miles north of Denison and along the Red River in Cooke • County and elsewhere. ' ; • i-xr' V/: .'■> UIJ* inmtl Ihe base of the Fort Worth limestone is well exposed at the following locality: 56 University of Texas Bulletin FORT WORTH AND DUCK CREEK FORMATIONS AT FIRST TURN OF CAR TRACK % MILE NORTH OF THE UNIVER- SITY AND 3 y 2 MILES SOUTHWEST OF FORT WORTH, TEXAS. Elevation at base of Fort Worth limestone, 680 feet. Fort Worth Formation: Feet Inches 3. Soft chalky limestone. Pecten bellula Cragin, Pleurotomaria austinensis Shumard 6 2 . Marl. Pecten bellula 0 1 . Limestone. Pecten bellula 6 Duck Creek Marl: 34. Soft straw marl with chalky limestone fragments. Upper Kingena zone in lower half; Pecten wrightii 3 6 23. Soft chalky limestone. Kingena, upper zone. Pecten bellula. Forms a slight terrace . 4 22. Marl. Gasttopod zone: Globiconcha (?), Tur- ritella, Cerithium, Fusus, Pleurotomaria 2 8 21. Soft flaggy arenaceous limestone. Diplopodia zone. Hemiaster plates 3 20. Marl. Pecten bellula 3 2 19. Soft, chalky limestone. Lower (Main) Kingena zone. Turrilites sp 1 18. Marl ■ 5 16-17. Laminated gray limestone, ironstained, locally indurated, rather unfossiliferous, making ‘horse- shoe’ bends in streams 4 The rest of the Duck Creek formation is exposed in the run north of this locality. It is seen that the upper contact of the formation is unmis- takeable, and that the lower contact as here placed, leaves the Fort Worth limestone about 30 feet thick in Tarrant County. Paleontology : The Fort Worth limestone contains certain diagnostic fossil zones, some of which are, beginning at the top : Zone of Enallaster sp. In the uppermost stratum (33) are two or three species of Enallaster, of which one, an elongated low species occurring at this level at Denison, Fort Worth, Blum and elsewhere has not been seen at any other level. The Geology of Tarrant County 57 Exogyra americana Marcou. This large characteristic oyster occurs in a restricted vertical zone (25-27) where it is abundant and easily recognized. It usually fails to weather out cleanly. It occurs at this level from the Red River to the Brazos; Dr. Boese has also found it near the top of the Duck Creek limestone in Grayson County. Ostrea carinata (?) Lamarck. Fossils ordinarily referred to this species are much more widely distributed in the Texas Coman- chean than has been suspected. This species is widely ranging and one of its zones of abundance is in the top of the Fort Worth limestone (28-29). The following occurrences are known to us: (1) Buda limestone, Austin, Texas (Whitney). (2) Base of Mainstreet limestone, Fort Worth and Denton, Texas, below the Pachymya zone. (3) Pawpaw clay, Fort Worth, Texas, and elsewhere. (4) Quarry limestone, Gainesville and Denton, Texas, abundant. (5) Top of Weno limestone, Fort Worth, Texas. (6) Denton marl, top. Conglomerate of Gryphea washitaensis and Ostrea carinata, widespread in north Texas (Hill’s member i in 21 Ann. Rept. pt. 7, U. S. G. S., pp. 270-71 and elsewhere). (7) Fort Worth Limestone, top, zone below Exogyra americana, Gaines- ville, Fort Worth and Krum, Texas, and elsewhere. (8) Basal Fort Worth Limestone (1) Fort Worth, Texas. The positive identification of the individuals awaits comparison with European material. It may be mentioned that two cross- sections are prevalent; a triangular one and a semi-elliptical one. Hemiaster elegans Shumard. This echinoid begins in stratum 11 of the Duck Creek Marl and ranges upward to the top of the Fort Worth Limestone, with a zone of abundance in strata 22-24. There is con- siderable variation among individuals referred to this species, some being larger, broader and much flatter than others. Schloenbachia sp. J. This species ranges from the base of the Fort Worth Limestone to the top. It is most abundant in a broad zone near the base (1-5). Holaster simplex Shumard. Tall, top-heavy individuals referred to this species range from the indurated ledge (17) of the Duck Creek Limy Marl to the top of the Fort Worth, being most abundant near the middle of the limestone (22-24). 58 University of Texas Bulletin Peeten wrighti Shumard. This peculiar Peeten ranges from the Lower Kingena zone (19) of the Duck Creek Marl to the middle of the Fort Worth and is most abundant just below the base of the Fort Worth limestone. Peeten bellula Cragin. This characteristic fine-ribbed Peeten ranges from the lower Kin- gena zone (19) to the top of the Fort Worth, and is most abundant in the upper part of the marl. FAUNA OF THE FORT WORTH LIMESTONE Gryphea washitaensis Hill Exogyra americana Marcou Ostrea subovata? Shumard Ostrea carinata ? Lamarck Ostrea sp. Plicatula spp. Peeten subalpina (Boese) Peeten wrighti (Shumard) Peeten bellula (Cragin) Pinna sp. Trigonia sp. Pachymya sp. Pteria sp. Remondia ? robbinsi (White) Tapes sp. Protocardia texana (Conrad) Lima wacoensis Roemer Lima sp. Pholadomya shattucki Boese Turritella marnochi White Turritella seriatim-granulosa ? Roemer Pleurotomaria austinensis Shumard Cinulia sp. aff. tarrantensis Cragin Nautilus texanus Shumard Schloenbachia spp. Enallaster sp. Enallaster texanus (Roemer) Holaster simplex Shumard Hemiaster elegans Shumard Hemiaster sp. aff. whitei Clark Epiaster aguilerae Boese Ophioglypha texana Clark Trochosmilia sp. Serpula sp. Lamna sp. fucoid masses DENTON MARL Brief Diagnosis : The Denton marl is a very shelly blue- grayish marl formation, 25 feet thick in Tarrant County, lying between the Fort Worth limestone below and the Weno marl above. It is characterized by a great abundance of the oyster- lake shells of Gryphea washitaensis , which especially near the top of the marl make a conglomerate containing - also shells of Ostrea carinata. Lithology: The Denton shell marl is a shallow water deposit and. has the texture and appearance of sediments deposited in modern seashore mud flats. If is excessively shelly, the shells being mainly,; adults and various young stages of the oyster, Gryphea washitaensis Hill; * ~ ^ ^ ’ The mass of the material is a flaky, non-arenaceous, laminated The Geology of Tarrant County 59 bluish-gray calcareous marl, having considerable plasticity. The basal part of the formation is somewhat sandier, flaggy and less fossiliferous. The top of the marl is a bedded conglomerate of the Gryphea shells, which is usually slabby and breaks off into considerable sheets. The top of the formation is exposed % mile southeast of Our Lady of Victory Academy, Fort Worth, between the Missouri, Kansas and Texas Railway and the Inter, national and Great Northern Railway tracks; on Sycamore Creek, in the bluff below the Houston and Texas Central Rail- way bridge and at the waterfall just east of the International and Great Northern Railway track, both localities 4 miles south- east of Fort Worth; at points 1 and 2 miles southeast of Haslet and elsewhere. The top of the formation does not make a con- spicuous topographic break as in Grayson County, where it forms a surface shelf at its outcrops. The base of the formation is exposed at a point % mile southeast of the Frisco track and 5 miles southwest of Fort Worth, and elsewhere. SECTION OF DENTON MARL AT BLUFF 100 YARDS NORTH OF THE HOUSTON AND TEXAS CENTRAL RAILWAY BRIDGE ACROSS SYCAMORE CREEK, 4 MILES SOUTHEAST OF FORT WORTH, TEXAS. Weno: Feet Inches 3. Limestone . . . 1 2. Marl 1 6 1. Limestone • 1 Denton : 3. Unfossiliferous marl above, followed by Grypbea washitaensis Shell Conglomerate, two layers separated by a thin marly stratum and con- taining Ostrea carinata, Pecten subalpina, Trigonia, Plicatula, etc 5 2. Blue shelly hiarl with inconspicuous, scattered con- glomerate layers ..... 2 1 6 1. Brown, sandy marl with a few thin, sandstone flags. Enallaster, Pecten, Plicatula, Lima. . . 1. 6 60 University of Texas Bulletin Feet Inches Fort Worth: 33. Very calcareous marl with Enallaster sp., Nautilus texanus, Hemiaster elegans, Pecten subalpina . . 3 2 2-32. Alternating limestone and marl layers 20 (The lower portion of the Denton and the Fort Worth limestone are seen farther down Sycamore Creek) . Paleontology : The Denton marl has few restricted fossils and none that are absolutely distinctive, so far as now known. The fauna is marked by the abundance of Gryphea washitaensis and by the practical absence of ammonites and echinoids. (a) Association of Trigonia, Proto car dia, Tapes. This loose association of pelecvpods occurs in the lower, more arenaceous part of the Denton marl stratum. It is an aggregation which is easily recognized, though no one species is limited to this forma- tion. (b) Association of Ostrea carinata and Gryphea ivashitacn- sis. Succeeding the uppermost strata containing Hemiaster elegans — the top of the Fort Worth limestone — are marly strata containing increasing numbers of Gryphea washitaensis and scattered individuals of Ostrea carinata. In Tarrant County this shelly marl culminates (stratum 3) in two thin slabby lay- ers of shell conglomerate composed almost entirely of Grypheas but containing frequent Ostrea carinata , and Pecten subalpina, Plicatula sp. and other fossils. Gryphea washitaemis Hill ranges from the lower Duck Creek limestone to basal Mainstreet limestone. Its zone of great- est abundance is in the upper 10 feet of the Denton marl. Below this point, in both the Denton and the Fort Worth formations, it is scattered but frequent; while in the Weno and Pawpaw it becomes gradually sparser and in Tarrant County has not been found above the basal Mainstreet. Ostrea carinata occurs sparsely throughout the upper 10 feet of the Denton; it is locally abun- dant in the conglomerate slabs at the top of the Denton, though not so abundant as at the Red River. This is the main zone of this oyster always referred to in the literature; the other oc- currences have been noted elsewhere (p. 57). The association of these two species as a persistent shell con- The Geology of Tarrant County 61 glomerate makes a sheet of rock that extends throughout North Central Texas at this horizon, and is a paleontological land- mark in the Washita division. As stated it is thicker and more prominent as a topographic factor at the Red River; at Fo*t Worth the conglomerate is only 1 foot thick and rarely with- stands erosion, although it marks the soil along its outcrop with scattered, very easily recognizable shelly slabs. On Noland’s River, near Blum, the Denton is much reduced and the con- glomerate has entirely lost its slabby character, being only a loose, slightly calcareous and uncemented shell marl containing Gryp'hea washitaensis and a few Ostrea carinata. Farther south it is supposed to form a portion of the Georgetown limestone. FOSSILS OF THE DENTON MARL Leiocidaris hemigranosus (?) Shum- Nautilus texanus Shumard. ard. Lima wacoensis Roemer. Ostrea carinata (?) Lamarck. Protocardia sp. Gryphea washitaensis Hill. Trigonia sp. Ostrea marcoui Boese. Ostrea quadriplicata Shumard. Pecten subalpina Boese. Plicatula sp. Pecten texanus Roemer. WENO FORMATION Brief Diagnosis : The Weno formation consists of a series of limestones and brown or yellow calcareous marls containing seams of limestone or ironstone, lying above the Gryphea con- glomerate of the top of the Denton marl, and below the Paw- paw clays. It is 67 feet thick on Sycamore Creek near Fort Worth and nearly twice as thick at the Red River. In Tarrant County it is reduced in thickness but it is not in any way ‘ ‘ con- solidated” (with the adjoining formations) as has been claimed. It is abundantly fossiliferous. The top limit on the Red River is the Quarry Limestone group, but at Fort Worth this group is reduced and is recognizable only with difficulty; the contact in Tarrant County is placed at the junction of the white chalky Weno limestone below and brown sandy clay containing pyrite fossils, are described later (p. 67). The Denison and Gainesville sections of the Weno are essentially similar to each other. As we go south from the Red River the Weno thins, and becomes more calcareous and somewhat less fossiliferous. The nacreous and chalky fossils seen at the Red River and their ironstone casts and molds become rarer in southern Cooke County and are 62 University of Texas Bulletin absent in this form at Fort Worth. The separate members of the Weno also seem to thin towards the south. As noted for the Pawpaw marls (p. 68), the ironstone seams of the Bed Biver section are replaced in Tarrant County, espe- cially north of the Trinity, by great amounts of jasper-like peb- bles. The Weno appears prevailingly as a yellow marl with chalky limestone layers. Description of Localities : On the east bank of the upper half of Sycamore Creek, which runs nearly in the strike, there is exposed for several miles a continuous section, from the Gervil- liopsis ledge at the top of the lower third of the Weno, upwards to the base of the Mainstreet limestone. In addition, the pit at the Cobb Brick Yards, an exposure on Sycamore Creek % mile below the brickyards and two exposures near the Houston & Texas Central Bailway bridge across the Sycamore Creek show the basal third of the Weno and most of the Denton marl. These localities are rich in fossils; and the whole landscape reveals the very intimate relations between the topography and the underlying geological structure. The diagrammatic terrace features correspond accurately to the formations beneath them, and represent from bottom to top : (a) the top of the lower half of the Weno limestone, usually an inconspicuous terrace; (b) the top of the Weno limestone producing the first main terrace; (c) the second terrace, composed of the limestone cap over the Paw- paw clay; and (d) an erosion slope, often terrace-like, which rep- resents the Mainstreet limestone capping the hill. In the portion of Sycamore Creek which runs nearly in the strike, the Gervil- liopsis ledge forms the bed of the creek. South from Sycamore Creek the Weno-Pawpaw strip narrows and follows the edge of the reduced Mainstreet upland, close to the west border of the Cross Timbers, leaving the county west of Burleson. The out- crops are here covered with Woodbine and Mainstreet overwash. Northwards from upper Sycamore Creek the Weno-Pawpaw strip widens to about 3 miles and spreads 6ver the uplands along the tributaries of Sycamore Creek. The cliffs of the two forma- tions, with the Mainstreet upland above, border the river valley near Biver crest for several miles east of Fort Worth just as the Duck Creek and Goodland escarpments do in the western part Fig. 5. Columnar section of the 'Denton, Weno fend Pawpaw formations on Sycamore Creek, 3 miles southeast of Fort Worth. The numbers refer to corresponding strata described on pp. 58-69. Vertical scale, y 8 inch = 1 foot. 64 University of Texas Bulletin of the county. North of the Trinity the strip widens, is gently sloping and, due to overwash, is mapable with difficulty. Lower Weno: The Weno begins with two layers of chalky limestone separated by a marl layer and lying just above the Denton shell marl. Prom the base of these two layers to the base of a hard white limestone stratum containing clumps and scattered individuals of Gervilliopsis invaginata (White) is a layer of gray-blue or slate-colored, slightly laminated, jointed argillaceous marl, sometimes called a ‘pipe clay.’ It is rather fossiliferous and contains two fossils which especially distinguish it: a species of Turritella and Pecten sp. aff. georgetownensis Kniker, which differs from that species in having split ribs on only the right valve. This pipe clay is well exposed on the northeast bank of Sycomore Creek, 150 yards north of the Hous- ton and Texas Central Railway bridge, where the upper Denton marl is also seen. The bluish Denton marl becomes less shelly near its top, and is abruptly followed by the two thin ledges, each about 8 inches thick and lying 1 foot apart. The pipe- clay is capped by a thin ledge of fragmented chalky limestone, locally slabby and indurated. The lower Weno is 15 feet thick on Sycamore Creek. Middle Weno ; The Gervilliopsis ledge, which is a persistent and reliable stratigraphic marker in the county,' forms the bed of Sycamore Creek in its middle portion, where it runs almost in the strike, and elsewhere very consistently forms the resist- ent shelf of small, waterfalls, such as those at the crossing of the Houston & Texas Central and the International & Great North- ern tracks and at the crossing of the International & Great Northern track over Sycamore Creek, both about 4 miles south- east of Fort Worth. The ledge is often indurated and fucoidal and is the base of a group of marly limestones which extend upwards for about 34 feet to the top of a chalky limestone layer which often makes a subsidiary terrace. At the brickyards 1% miles southeast of Gainesville, the Gervilliopsis ledge is a blue- gray loosely compacted marl 1 foot thick, containing great num- bers of Gervilliopsis and other fossils and lying 39 feet below the top of the Quarry limestone group. In the branch of Duck Creek 1 mile north of the Union Station, Denison, the layer is also well developed. The Geology of Tarrant County 65 Upper Weno: The upper 18 feet lies between the subsidiary terrace in the Weno and the base of the Pawpaw marls. It con- sists of ichalky white limestone and its upper limit is distinct, since the overlying brown marl washes away and leaves the top of the Weno limestone as a projecting shelf or terrace. Paleontology : The following is a brief summary of the Weno fossil sequence: Pawpaw clay: Py rite fossil zone (p. 69). Weno limestone and marl. 8. Nautilus sp., Homomya; Ostrea carinata (abundant). These species and others characterize the uppermost Weno Lime- stone. Certain of them occur in the basal Mainstreet lime- stone. The Ostrea carinata is conspicuous and abundant; its other occurrences have been noted (p. 57). 6-7. Nodosaria texana Conrad. The Weno occurrence of this fossil protozoon is in a narrow zone about 19 feet below the top of the Weno. Nodosaria also occurs in the base of the Pawpaw in North Texas; in the Denison Beds at Cerro de Muleros; and in the Del Rio Clays, in association with Exogyra arietina Roemer in South Texas 5. Gervilliopsis invaginata (White) The main zone of occurrence of this fossil is at the top of the ‘pipeclay’. Its other occurences have been noted. 1-4. Turritella sp., Pecten sp. near georgetownensis, Remondia acuminata Cragin. These species are frequent in the basal part of the Wenu pipeclay, where there exists a considerable fossil sequence that will not be discussed here. Denton marl: Gryphea washithensis (abundant) and Ostrea car- inata. &— Tarrant 66 University of Texas Bulletin FOSSILS OF THE WENO FORMATION IN TARRANT COUNTY (PAR- TIAL LIST) Trochosmilia sp. Hemiaster calvini Hemiaster sp. Enallaster bravoensis Enallaster texanus ? Holaster sp. Cottaldia sp. Leiocidaris hemigranosa Nodosaria texana Pentagonaster sp. Trochosmilia sp. Turritella sp Cinulia sp. Anchura sp. Turbo sp. Trochus sp. Schloenbachia sp. Schl. sp. like inflata Hamites sp. Engonoceras sp. Nautilus texanus Homomya sp. Pecten subalpina Pecten texanus Plicatula sp. Corbula sp. Tapes sp. Nucula sp. Astarte acuminata Protocardia sp. Ostrea quadriplicata Ostrea carinata Gryphea washitaensis Trigonia sp. Gervilliopsis invaginata Ostrea sp. near marcoui Lima sp. Lamna sp. Oxyrhina sp. Weno Pawpaw Mainstreet Grayson Buda 5(! ' $ * * * * * * * * * * * 5$C *}« * * * * * * * * * * The Geology of Tarrant County 67 PAWPAW FORMATION Brief Diagnosis : This formation on Sycamore Creek consists of 23 feet of brown arenaceous clay, lying below the hard, white Mainstreet limestone, and above the softer chalky lime- stone which forms the cap of the Weno formation. This brown clay contains sandy slabs in its basal half and carries a charac- teristic assortment of fossils. On account of its totally different color, hardness and composition, it should be easily recognized and separated from the adjoining formation in well drilling. Due to its increment in thickness northwards it is about 27' thick at the Denton-Tarrant County Line, while at the Tar- rant- Johnson County line it is about 12 feet thick. The pre- vailing texture is sandy, the soil is acidic, the vegetation sparse; the slopes are variable, sometimes gentle but usually steep, mak- ing a narrow outcrop and good exposures. There is a sudden and marked increase in the amount of ironstone fragments in the Pawpaw northwards from the Trinity. The prevailing as- pect of the formation, aside from this red material, is brown sandy-flaggy. The Pawpaw contains characteristic and unmis- takable fossils. At the Pawpaw pit of the Cobb brickyards, Fort Worth, the total section is exposed, and shows a resistant, firm ironstained brown clay with ironstone, bituminous arenaceous and limy seams. Description of Localities : There are numerous localities in Tarrant County, lying above the terrace formed by the top of the Weno limestone and weathering into a steep barren slope filled with sandy flags and limestone fragments. Such slopes in stream cuttings often recede considerably from the face of the Weno terrace and form extensive amphitheatre-like basins whose sides are continuous exposures of the whole Pawpaw and whose floors along the streamlets contain fine concentrations of the small fossils which occur near the base of the clay. Such lo- calities occur along the middle and upper portions of Sycamore creek especially near the International and Great Northern rail- way bridge and thence northwards to the river; along the Trinity valley southeast of Riverside; at several localities southeast of Haslet; near Watauga; and near the Cleburne road 68 University of Texas Bulletin south of Fort Worth. The localities are just underneath the western border of the Mainstreet limestone and naturally are contaminated with rock and fossils from that formation. SECTION OF PAWPAW CLAYS ON SYCAMORE CREEK NEAR THE HOUSTON AND TEXAS CENTRAL RAILWAY, 4 MILES SOUTHEAST OF FORT WORTH, TEXAS: Feet 4. Brown slabby argillaceous thin limestone layers with considerable interbedded marl and scattered jasper pebbles. Nautilus sp. Hemiaster sp., Pec- ten subalpina; Plicatula sp 13 3 Brown clay with scattered flags. Turrilites sp 6 2. Sandy flagstone, fragile, containing Metopaster sp. 1. Brown clay with pyrite and other fossils 3 23 SECTION EAST OF KELLER ROAD, 1 MILE SOUTH OF HASLET, TEXAS: (Mainstreet limestone forms thin cap of hills around amphitheater.) 3-4. Brown clay with flaggy and slabby dimension layers and great quantities of ironstone pebbles. Few fossils 22 8 2. Flaggy layer 4 1. Brown clay with pyrite fossils 4 27 From these sections the increment in thickness towards the Red River is visible within Tarrant County. PALEONTOLOGY 3-4. Nautilus sp. and Hemiaster sp. The upper portion of the formation, especially the upper 5 feet contains a small species of Nautilus and a rotund bulky species of Hemiaster. The middle part of the formation contains Nautilus sp. near texanus, Pecten subatpina, Plica- tula, etc. Inches The Geology of Tarrant County 69 2. Metopaster sp. A thin flaggy stratum about 4 feet above the base of the Pawpaw contains the starfish Metopaster sp., which so far has not been found elsewhere and may prove to be narrowly limited. The zone also contains other species of starfish. 1. ‘Pyrite Fossil Zone’. Approximately the lower 8 feet of the clay contains an assort- ment of iron pseudomorphs and other fossils which is dis- tinctive and includes the following: Turrilites sp. Schloenbachia sp. Scaphites sp. A. Hamites sp. Area sp. Engonoceras sp. Cinulia sp. Enallaster sp. Salenia sp. Fish teeth and vertebrae. Baculites sp: Flickia sp. Acanthoceras sp. Mortoniceras spp. The zone is present at this level at all localities in Tarrant County. The Turrilites are distinctive, and none has been found by us below the Pawpaw except a solitary vertically ribbed species in th« Main Kingena zone of the Duck Creek marl. For brevity we call this a pyrite fauna; some fossils are pyrite, some hematite and some limonite. MAINSTREET FORMATION Brief Diagnosis : The Mainstreet limestone, the second most important upland forming rock in Tarrant County, underlies a belt of irregular width just west of the Eastern (Woodbine) Cross Timbers. Its outcrop is a dissected dip plain modified by erosional slope towards the stream valleys, and is essen- tially similar to the Fort Worth limestone prairie. The Gray- son marl lies between it and the Woodbine Cross Timbers, and the brown Pawpaw clays underlie it. It is thus sharply limited both above and below and should be recognizable in well drill- ing. It is characterized by the sequence of fossils listed later. The Mainstreet limestone totals about 50 feet in thickness at Fort Worth. Lithology : The formation with little variations from top to bottom, is composed of regularly alternating strata of straw- colored marl and chalky, or hard fairly pure limestone. The bands do not usually exceed one foot in thickness and the 70 University of Texas Bulletin formation has a deceptive similarity to the Fort Worth lime- stone. Description of Localities: This limestone forms conspicuous and extensive uplands. In general appearance these are much like those formed by the Fort Worth limestone. The uplands of the Mainstreet limestone extend from one end of the county to the other in a north south line passing east of Fort Worth. The extensive and gently rolling area between the Burleson and the Cleburne roads in the southern part of the county is underlain by this formation. Good exposures may be seen along Sycamore creek, from the region of the Glen Garden country club southeast: in the stream cuts between Seminary hill and Crowley; along the road from the Burleson pike to Crowley, where almost the entire thickness is passed through; near Keller, and other parts of the county. The lowest strata are well exposed in Sycamore Creek about one half mile north of Crowley. This part of the formation is highly fossiliferous, Holectypus limitis (?) and P achy my a sp. aff. austinensis being especially abundant. Turrilites brazoensis which ranges throughout the formation occurs here, but is more abundant higher up, as in the exposures along Deer Creek between Burle- son and Crowley. The upper portions of the formation are well exposed at various places along the Keller road, especially just south of Keller. The upper portion may be seen also at the crossing of the Mansfield road and the Cleburne-Fort Worth interurban rail- way. Paleontology : The Mainstreet limestone can be identified and its levels distinguished by means of the fossil sequence, which in part is as follows : Leiocidaris sp. Rarely spines of this echinoid are seen high in the Mainstreet formation. Cyphosoma and other echinoids are as- sociated with it. It lies nearly at the top under the level of Exogyra sp. 2 which occurs in the basal chalky marl of the Grayson formation. Turrilites brazoensis Shumard. The upper ten feet or so of the The Geology of Tarrant County 71 Mainstreet formation is rather barren; below this, Turrilites ap- pears and ranges downward as low as the Holectypus zone, which is about eight feet above the base of the ‘formation. The greatest abundance of Turrilites is about eighteen feet below the top of the formation. It may be seen in greatest abundance at the Deer Creek crossing of the Cleburne interurban. Kingena wacoensis? Roemer. This distinctive large brachiopod is not found outside of the Mainstreet limestone except possibly in the Denton marl of the southern section. A zone of great abundance and almost the highest occurence is about 20 feet above the base of the formation; the lower limit is the base of the forma- tion itself. Scliloenbachia sp. O, like inflata. Throughout the Mainstreet. Exogyra arietina Roemer. This tall spired Exogyra begins about the middle of the Mainstreet limestone and ranges upward into the basal Grayson. Ostrea quadriplicata Shumard. This characteristic fossil of the Denton, Weno and Pawpaw formations has not been seen above the basal Mainstreet, where it is rare. Holectypus limitis (?) Boese. Large sized Holectypus are abun- dant in a zone about eight feet above the base of the Mainstreet formation. Ostrea carinata Lamarck. One of the numerous but distinctive occurences of this striking oyster is a stratum in the basal Main- street limestone. This and the following zone may be seen along the Cleburne road. Pachymya sp. aff. austinensis Shumard,. A narrow zone of this fos- sil characterizes the base of the Mainstreet, where numerous well preserved individuals occur. We have seen it elsewhere only in the middle of the Weno limestone. FOSSILS OF THE MAINSTREET FORMATION (PARTIAL LIST) Ostrea sp., aff. marcoui Boese Ostrea carinata (?) Lamarck. Ostrea quadriplicata Shumard Lopha sp. Ostrea subovata Shumard. Exogyra arietina Roemer. Exogyra sp. Gryphea sp. Pecten texanus Roemer Pecten subalpina Boese Pecten wrightii Shumard Pecten roemeri Hill Pecten spp. Spondylus cragini Whitney. Lima wacoensis Roemer. Protocardia vaughani Shat.tuck. Pholadomya shattucki Boese. Ptychomya ragsdalei Cragin Pachymya sp. aff. austinensis Shumard Homomya sp. Barbatia Simondsi Whitney Trigonia sp. Schloenbachia sp. aff. inflata. Turrilites brazoensis Shumard. Turrilites sp. Nautilus texanus Shumard. Nautilus hilli Shattuck. Kingena wacoensis (?) Roemer. Cyphosoma volanum Cragin. Holectypus limitis (?) Boese. Enallaster bravoensis Boese. Enallaster sp. Hemiaster sp. Leiocidaris sp. aff. hemigranosus Shumard. 72 University of Texas Bulletin GRAYSON MARL Brief Diagnonsis : The Grayson marl in Tarrant county is exposed either as a steep narrow marl band lying against the western margin of the Woodbine Cross Timbers or as a gentle slope connecting the Woodbine sands with the Mainstreet up- land. In either case it is at nearly all places covered with over- wash and vegetation. Exposures are more rare than in any other Comanchean formation. The marl is yellowish-brown and locally contains pyrite seams and fossils, gypsum, and inter- spersed thin limestone bands. The formation is about 50 feet thick at its outcrops near Fort Worth. ^Descriptions of Localities : The best and most accessible localities are a cliff one mile east, and a small divide about two uiiles southeast of Burleson, just outside of Tarrant county. The slopes of the Woodbine hills just west and northwest of Burleson also bear isolated exposures of the Grayson marl. The Texas and Pacific railway cut. one-fourth mile east of Handley exposes the middle portion of the formation, as do small stream cuts one mile west of Handley. SECTION OP THE GRAYSON MARL, 2 MILES SOUTHEAST OF BURLESON, JOHNSON COUNTY. Feet 3. Yellowish calcareous marl, sparsely fossiliferous 12 2. Shelly limestone band 1 1. Yellowish calcareous marl, with gypsum, pyrite and limonite. Gryphea mucronata, Exogyra sp., Pecten subalpina, Hemi- aster calvini, Enallaster sp., Turrilites sp., Lima sp., Engon- oceras sp., abundant small pyrite fossils *...15 (Top and base of Grayson marl not exposed here). No locality clearly showing the Grayson- Woodbine contact has yet come to light in Tarrant county. This contact has been claimed by Taff to be unconformable at the locality on the Red River in Cooke county, which is now much obscured by Wood- bine overwash. The Grayson marl locality just east of Burleson is rich in Pecten subalpina, Lima sp., Gryphea mucronata, and •contains Cyphosoma volanum, Hemiaster calvini f Enallaster bravoensis and Engonoceras. The Geology of Tarrant County 73 None of these exposures shows the entire thickness of the Grayson marl. In the cliff east of Burleson about 50 feet is ex- posed, reaching not quite to the Grayson- Woodbine contact; while between, the bottom of the exposure and the Mainstreet limestone near Village Creek there is at least 20 more feet of basal Grayson. Part of these basal strata are seen at the locality 2 miles southeast of Burleson. At Handley likewise, the Grayson is probably about 70 feet thick, and here as usually the upper part is mantled by Woodbine overwash, a sandy, red, timbered soil whose , presence everywhere makes the Grayson ap- pear abnormally thin. Perhaps the completest exposure known is in a tall bluff 3 miles ESE. of the bridge of the Fort Worth-Denton road over Denton Creek, east of Roanoke, Texas. This shows an appar- ently conformable contact of the Grayson with the overlying Woodbine, and also the contact with the underlying Mainstreet limestone. The .Grayson here is 75.2 feet thick. GRAYSON MARL NEAR ROANOKE, TEXAS WOODBINE: Red ledge, forming crown of hill. Feet GRAYSON: Soft gray marl containing eleven limestone ledges, each 3 to 12 inches thick, the uppermost lying in contact and conformable with the base of the Woodbine. Lima sp., Protocar dia sp., (same as the Weno sp.), Cidarid spines (very large), zone of Hemiaster calvini and Enallaster bravoensis (10 feet below top), Schloenbachia sp., Gyprimeria sp., Gryphea mucronata (scarce), Pecten texanus (abundant), PUcatula (abundant), Scaphites ? sp 37.8 Yellowish limonite stained marl. Rich in Gryphea mucronata. Turrilites (small sp.), no other ammonites seen; no echinoids seen. Pecten texanus, less abundant than above 15.2 Soft gray marl. Fossils scarce, mostly Engonoceras sp., Gryphea mucronata and flattened Exogyra arietina. A number of red ironstone seams weathering out black 22.2 MAINSTREET LIMESTONE: Top: Kingena sp. very abundant. This locality is noticeably more calcareous than those farther west. 74 University of Texas Bulletin SEQUENCE OF GRAYSON FOSSILS The following paleontological sequence is taken from the Bur- leson, Roanoke and Denison localities : WOODBINE: Ostrea carica and spp. Seen at Burleson and else- where immediately overlying the Grayson. GRAYSON: a. Zone of abundance of Hemiaster calvini and Enallaster bravo- ensis about 10 feet below top. Associated fossils: Pecten sub- alpina, Pecten texanus, Lima sp., Protocard'ia sp., Cyprimeria sp. b. Zone of Acanthoceras sp. and Tissotia ? sp. 20-30 feet below top. Associated fossils: Gyphosoma volanum, Pachymya sp., Proto- car dia texana, Turrilites (small sp., ranges down to Pawpaw). c. Zone of abundance of Gryphea mucronata. Associated fossils: Pecten texanus, P. sp. aff. subalpina, Inoceramus sp. 45 feet below top of Grayson. d. Exogyra sp. 1. Associated with Pectens, Gryphea and Lima. 45-55feet below top. e. Engonoceras sp. About 65 feet below top. f. Association of Nautilus, Enallaster bravoensis, Enallaster sp. near texanus, Holectypus limitis, Gryphea mucronata, a salenid, Pec- ten, Lima and other pelecypods. g. Exogyra arietina and sp. This zone lies just beneath the preced- ing, at the base of the Grayson. Turrilites sp. is abundant in both layers. The zone is underlain by Mainstreet limestone containing abundant Kingena. Brief Diagnosis : The Woodbine formation is a series of sandy ; iron stained, argillaceous clay strata and ironstone; which weathers into low rolling hills with open glades and flats of bottom land. The outcrop, which covers roughly the eastern third of Tarrant county, is heavily timbered with black jack FOSSILS OF THE GRAYSON MARL Gryphea sp. like corrugata Say. Gryphea mucronata Gabb. Exogyra spp. 1-3. Exogyra arietina Roemer. Exogyra sp. like texana Roemer. Pecten subalpina (Boese). Turrilites spp. 1-2. Area sp. Lima sp. Gyphosoma volanum Cragin. Ostrea sp. Anomia sp. Plicatula spp. Protocardia sp. Tapes sp. Pholadomya shattucki Boese. T'rigonia sp. Cerithium sp. Cinulia pelletti Whitney. Turritella sp. Hemiaster calvini Clark. Enallaster bravoensis Boese. WOODBINE FORMATION The Geology of Tarrant County 75 oak and post oak, and is known as the Eastern (Upper) Cross Timbers. The soil is sandy, red, and acidic, and is suitable for special purposes as fruit growing. The outcrop forms the catchment area for the Woodbine artesian reservoir whose water bearing sands dip eastward, underlying at an increasing depth a large area in north central Texas. The Woodbine has been divided into two divisions, the lower (Dexter) sands and the upper (Lewisville) beds. The latter are locally fossiliferous. The series has been considered about 300 feet thick between Handley and Arlington. R. T. Hill 1 gives the following excellent description of the Woodbine formation: “The rocks of the Woodbine formation are largely made up of ferruginous, argillaceous sands, char- acterized by intense brownish discoloration in places, which are accompanied by bituminous laminated clays. These sands, like those of the Trinity division, are unconsolidated in places, but differ from them by containing a greater proportion of iron and other mineral salts, which materially influence the char- acter of the waters derived from them. The sand, which in the unoxidized substructure are usually white and friable contain particles of iron occurring with glauconite and pyrite. These minerals oxidize toward the superficies, and their solutions con- solidate the more porous beds of sand into dark brown siliceous iron ore, occuring in immense quantities in certain localities. Other beds of sand break down into deep loose soils. These support a vigorous timber growth.’’ Description of Localities : The Woodbine sands are poorly exposed in Tarrant county due to the small, inconsecutive sec- tions, the softness of the strata and the consequent very general overwash, and the extensive timbering. The best series of ex- posures is along the road east of Birdville, and the Rock Island railway cuts east of Tarrant station. The basal contact of the Woodbine was not anywhere seen with clearness, altho localities near Burleson and Handley have the basal part poorly exposed. The upper contact with the Eagle Ford shales is seen in Taff’s ’Hill, 21st Ann. Rept. U. S. ( G. S., part 7, p. 294. 76 University of Texas Bulletin locality on Bear Creek, % of a mile west of the Tarrant-Dallas county line and 2 y 2 miles northeast of Tarrant. A few basal strata are visible in cuts of the Fort Worth-D alias interurban, 2 miles east of Handley. An excellent section of part of the Woodbine formation near the base is seen at the pit of the Acme brick yards, Denton, Texas. This section is forty-two feet deep, and is strongly acidic in all of its material. The alternation of argillaceous bands with pure sandstone beds is striking. There is a perceptible stratification, apparently with conformable members, except at the top. Here there is either the end of a lenticular mass or the beds represent the foreset laminae of strong cross bedding. The former is the more likely, especially since about a mile distant and in the plane of the cut, a similar group of beds is shown whose dip is strongly against that of the beds, suggesting the other edge of the lenticular mass. SECTION IN THE PIT OF THE ACME BRICK YARDS, DENTON, TEXAS: Feet 5. Lenticular mass, four members, overlain by a red sandy clay 15 4. Light colored limonitic argillaceous member 7 3. Red sandstone 5 2. Light colored limonitic argillaceous member 1 1. Grayish sandy argillaceous member, containing several bands of almost black sandstone 14 42 A 25 foot boring at this point penetrated the Grayson marl. / SECTION OF WOODBINE EAST OF TARRANT STATION (The following section is seen south of the railroad below the first bridge west of the county line.) Feet Inches 27. Sandstone ledge, locally a shell conglomerate, con- taining Barbatia micronema Meek, Ostrea soleniscus Meek, Ostrea carica Cragin, Ostrea sp., Exogyra sp., and other Lewisville fossils. The upper portion is indurated, laminated and espe- cially fossiliferous. Exposed in three cuts nearest The Geology of Tarrant County 77 Feet Inches the Tarrant-Dallas County line. This is the top of the Woodbine and is overlain hy Eagleford shale. Between the two localities it has locally a dip of 2 1/2° East, but this reduces at most places to about 1/2° East 7 26. Light yellowish sand with limonitic stain, usually unconsolidated and containing Ostrea sp. (with large attachment scar) 5 25. Arenaceous yellow-brown shales containing Ostrea sp 8 24. Three ironstone bands interbedded with bluish sandy shale . 2 23. Thin bedded closely laminated shale with dimension layers of iron stained red shale, and containing gypsum, limonite and oyster shells (O. carica). The lower 10 feet is especially fossiliferous 22 (The section in the cuts west of this locality exposes all of the foregoing members, and in addition in a deep run about a mile east of Tarrant, the following section is exposed.) 22. Bluish red shale with limonite stain and abundant gypsum. Ostrea carica is rare in the top 20 21. Loosely laminated thin bedded brown shale, weathering to a rough faced cliff 5 20. Compact laminated brown shale forming a smooth cliff face, .i 2 19. Three thin red ironstone layers with interbedded compact blue clay 4 18. Bluish limonitic shale... 12 (There is a break in the section at this point. A cut of the Rock Island Railway 1/2 mile east of Tarrant exposes the following section.) 16. Thin bedded red sandstone, no fossils seen. Minor faulting present. Gypsum present. Dip is 2 degrees east in the west end of the cut, and straightens out to 1 degree in the east end. . . .10 15. Blue shales containing gypsum and lignite seams. No fossils 12 It is doubtful if many of these members are continuous over great areas. There is a break in the section near Tarrant sta- tion. There is a middle sandstone member of the Woodbine formation which consists of massive red sandstone, and which seems extensive. Its structure is complicated by lenticular 78 University of Texas Bulletin masses and by sharp reversals of dip. About 2 miles west of Tarrant station at the crossing of the Arlington-Grapevine road and the Rock Island railway, is a massive sandstone ledge. A cut of the railway 2 miles west exposes a similar sandstone ledge. Cuts along the first parallel road north of the Rock Island railway, from Birdville to the county line and a few cuts south of the railway expose the lower half of the Woodbine formation. There is locally at least a basal sandstone which forms the resistant cap of certain “ Brushy Knobs.” For ex- ample, on the knob 2 miles northwest of Burleson, the basal strata of the Woodbine are seen to be in part a sandy shale and in part a red sandstone whose massive fragments are scat- tered over the crest of the hill. At Burleson this stratum* is fos- siliferous. The Woodbine formation in the Liggett-Tarrant section thus seems to consist of three red sandstones and two interbedded series of blue shales with various other lithologic features. Ex- tensive cross bedding and some evidence of large lenticular masses were seen in this section. Sharp reversals of dip and rapid tapering of small lenses so as to simulate angular non- conformity within the formation were seen. Dip and thickness : The apparent local dip of the Woodbine varies greatly, due to two factors, cross bedding and lenticular masses. An estimated thickness between Handley and Arlington of 300 feet has been given by Hill. This is based on a dip of 40 feet per mile of the overlying and underlying strata, but this estimate is probably too low. The uniform maximum dip of the Washita division east of Fort Worth is 2 degrees southeast, and the measured dip of the Eagle Ford and Austin chalk west of Dallas approximate 1 degree southeast A From numerous observations Tarrant and *The minor faulting of the Austin chalk often obscures its general dip, but the following data indicate the mean maximum dip to be about 1 degree near Dallas:* White Rock cliff, cut on Fort Worth pike, 5 miles west of Dallas, 1 degree dip, direction 260 degrees from magnetic north. South end of Oak Cliff viaduct, 1 degreen 20 minutes, dip in direction 215 degrees from magnetic north. Missouri, Kansas & Texas Railway cut, 1 mile north of Union Terminal Dallas, 1 degree dip, direction 110 degrees from magnetic north. Fig. 6. Columnar section of portion of Woodbine formation in cuts of Rock Island railway between Tarrant station and the Tarrant-Dallas county line. The numbers refer to correspond- ing strata described on pp. 76-7. Vertical scale, % inch 1 foot. 80 University of Texas Bulletin Dallas counties we place the mean maximum dip of the Wood- bine at 1 Y 2 degrees southeast, which counting reversals of dip would mean a thickness of 350 feet for the formation. DIPS OF WOODBINE STRATA IN TARRANT AND DALLAS COUNTIES 1. Road due east from Birdville: Angle of dip Direction in degrees ° ' from magnetic north 3 30 90 1 20 82 5 114 (lenticular mass) 1 30 196 1 245. 2. Rock Island Rail- way cuts 2 miles east of Tarrant station : 2 3. Bear creek, 2 miles north west of Tarrant station: 4. 1/2 miles south- west of Grapevine: 1-3 30 80 30 80 110 (with reversals) Structure : The main relief features of the Woodbine strip of cross timber land are produced by the alternating harder and softer strata. This gives an obscured “euesta” topography, especially near the outcrops of the middle and upper massive sandstones, both of which make small ridges in the landscape. The outcrop of the latter may be seen along the Rock Island railway between Irving and Tarrant station. Certain harder ironstone ledges cap the summits of numerous “Brushy Knobs” which form outlying strips of islands often parallel to the west- ern border of the main Woodbine formation. Certain notably sharp peaks within the outcrop are likely due to lenticular masses of iron ore. The cross bedding and consequent divergence of dip is one of the most striking structural features of the Woodbine sands and is purely local in extent and not indicative of underlying dis- turbances of economic importance. Very striking reversals of dip within short distances are common features of the Woodbine The Geology of Tarrant County 81 formation. If the contacts of the Woodbine in north Texas are conformable as reported, then these variations of dip within the formation must straighten ont at the contacts. Such twisted strata overlain by evenly dipping beds are seen in many places. Even more deceptive are the numerous steep or gentle len- ticular masses which are underlain and may be overlain by evenly dipping strata. These are not to be confused with “domes” and indicate no underlying structure of importance, as detailed in the discussion on possibilities of oil and gas. A lens- shaped mass with its slopes will often closely resemble a dome, especially if the mass is not penertated by a cutting revealing the undisturbed strata beneath. These lenses are of variable size, often many hundred feet across. Small scale faulting was seen at many places. The shallow- ness of the deposition is indicated by included masses, as for instance an irregular limestone mass of about two cubic feet surrounded by a sandstone cyst and completely imbedded in the Woodbine formation. Vertical joint planes running in the di- rection of the strike were seen in the middle sandstone near Tarrant station. Minerals: The Woodbine sands contain immense quantities of low grade iron oxides which make up the bulk of the strata at certain levels and at others merely impregnate or discolor the sandstone. At a few levels and locally as in the basal ar- gillaceous sand, the iron is extremely low in percentage, but such material burns to a red brick. A nearly stainless stratum outcrops near Mansfield.. Gypsum is present as broken sheets and .fragments at certain levels, as in the upper third of the formation, and contributes an unpleasant element to the water from this level. Scattered fragments of gypsum are seen at practically all levels of the Woodbine formation which were examined by us. Lignite is present in the blue shale below the middle sandstone, and may be seen in the Rock Island railway cut east of Tarrant station, where there are several seams each less than one inch thick, and of no commercial importance. Wood occurs in three forms, silicified, lignitized, and practically un- altered. So far no other plant remains occur in Tarrant county although they are reported in abundance along the Red River. t— Taft-ant 82 University of Texas Bulletin Desert varnish is a thin enamel-like incrustation which sometimes forms on the face of sandstone exposures, especially if the sandstone is rich in iron. The conditions necessary are that the sandstone shall contain a large quantity of absorbed water to- gether with a considerable amount or iron (or manganese) salts and that there shall be an uninterrupted arid spell of many weeks. The eapilliary movement of the water brings to the surface the dissolved salts of iron and deposits them in a thin crust which is reddish or yellowish if there is little organic matter and increasingly greenish with the increased amounts of organic substances which can reduce the iron oxides. A truly remarkable exhibition of this phenomenon was observed by the writers in an isolated block of Woodbine sandstone two miles southeast of Denton, Texas. Following the very long arid spell of 1918, the “varnish” had formed in an excavated pit about twelve feet across and about seven feet deep. The excavation faced towards the southwest and the entire surface, including furrows and grooves made by the picks, was covered with a thin enameled surface of greenish color, averaging about 1/16 of an inch in thickness. The green color was spotted with darker green and blacks, the whole giving the effect of the rarest Turkish tile. Fossils of the Woodbine formation: The following fossils were reported by Hill in the 21st Ann. Rept., U. S. G. S., part 17, pages 314-318: Ostrea soleniscus Meek. Ostrea carica Cragin. Exogyra columbella Meek. Modiola filisculpta Cragin. Aguilera cumminsi White. Cytherea leveretti Cragin. Trigonarca siouxensis H. & M. Area gallieni variety tramitensis Cragin. Barbatia micronema Meek. Pteria salinensis White. Turritella coalvillensis Meek. Turritella renauxiana Cragin. Cerithium interlineatum Cragin. Natica tramitensis Cragin. Nerita sp, Cragin. Scaphites sp. Hill. Crab sp. Plants spp. UPPER CRETACEOUS EAGLEFORD SHALES Brief Diagnosis: The Eagle Ford Shales, the easternmost formation in Tarrant County, outcrops in two small areas which are separated by the alluvial Trinity River valley. The first The Geology of Tarrant County 88 area extends from near the northeast corner of the county along an irregular line through Grapevine and thence southeast to the Dallas county line near Liggett, where the contact runs nearly south, remaining within Tarrant county and about *4 mile west of the county line. The formation outcrops in small runs into the Trinity almost at the point where the Rock Island railway crosses the Tarrant-Dallas county line. The contact likewise runs along a stream, Tradinghouse creek, just east of Arlington. The second area is a roughly triangular strip covering the south- east corner of the county. The formation consists of blackish and bluish shales, with seams of arenaceous and shelly limestone, and weathers into a black, waxy, carbonaceous, treeless, rolling upland soil. The formation is stated to be about 500 feet thick between Arlington and the White Rock escarpment west of Dal- las; of this thickness about half occurs in southeastern Tarrant county. Description of Localities: The Bear Creek locality is stated by Taff and Shuler to show the contact between the Woodbine and the basal Eagleford shales. The contact is excellently exposed in a small run . and in railway cuts at the point where the Rock Island railway crosses the Tarrant-Dallas county line. Here the Eagleford is a characteristic laminated blue shale with a few arenaceous thin ledges near the base. Acanthoceras swallovi (Shumard) is found in the basal three feet. The Eagleford formation conformably overlies the Woodbine, whose top stratum is a laminated sandstone in most places composed almost entirely of masses of nacreous shells. The upper contact of the Eagleford shales does not occur in Tarrant county but is finely exposed at the White Rock escarpment, 5 miles west of Dallas, and in the hills south of the Arcadia Park stop on the Dallas interurban. At these localities are found many shark teeth and vertebrae, Schloenbachia spp., Ostrea belliplicata Shu- mard, Inoceramus sp., gastropods and pelecypods. There are slight variations in dip in the Eagleford shales but it is doubtful if these in Tarrant county indicate any struc- tures of economic importance in the Eagleford or the under- lying Woodbine formations; while the slight disturbances farther east may be connected with the local small scale faulting so prevalent in the Austin chalk. 84 University of Texas Bulletin CENOZQIC AND RECENT The Cenozoic and recent deposits in Tarrant County are made up, as previously noted, of gravels. The gravels are readily divided into the upland deposits and the lowland deposits, — known to the trade as “pit” gravels and “stream” gravels. The distribution and physical appearance of these is discussed on page 91. Besides the physical appearance, the fossils of the two gravels are of interest. In both cases the fossils originate — except for the rare vertebrate forms, — in older formations. The lowland gravels contain the fossils of the beds through which the streams pass, being predominantly of the upper part of the geological section in the south and east and of the lower part of the section in the west and north. The upland gravels contain fossils which are consistently of the Fredericksburg formations. In both types of gravel certain fossils are readily recognized, the various species of Grypheas and the small sea urchin, Hemiaster, being well preserved, although badly worn. The few vertebrate remains which have been found occur in the upland gravels. Among these are the Mammoth (Elephas im- perator) of which a splendid tusk and a few teeth are on ex- hibition in the Carnegie Library at Fort Worth; a mastodon; Elephas, small species, and Megatherium, bothfrom a gravel pit in the river bank one mile east of the Court House, where many Pleistocene fossils have been found; and a small horse, believed to be Equus francisii, of which only the teeth have been found. Shells of clams (Quadrula spp.), snails and other fresh water invertebrates are common just below the Lake Worth dam, on the uplands and elsewhere. The distribution of the upland gravels indicates that they may be older than the Pleistocene, but the authors have not entered into the broad problems connected with these deposits. ECONOMIC GEOLOGY The nature of the underlying rocks of Tarrant county, deter- mines to a great extent its natural resources and possibilities and indicates its logical line of future development. Geology The Geology of Tarrant County 85 explains many of the resources and natural advantages of a region, and among them the following: (1) Resources of location: Substratum, drainage, accessibility, varieties of topography, scenery. (2) Resources of soil: Adaptability to different kinds of use; farm land, grazing land, etc. (3) Resources of native or importable plant and animal life,. (4) Resources of crude material: Building material, road ma- terial, minerals, oil and gas, artesian water. RESOURCES OF LOCATION Excavation and foundations. The question of the safety hardness, resistance, and thickness of the underlying rocks bears directly upon excavation for deep foundations of large buildings, or for pipe lines, drainage lines, sewers, cuts, dams, bridges and other structural works. This question is of significance where, as under Fort Worth, a rather thin cap rock is succeeded by a marl member which not only is soft but is water bearing and caves readily. The solid Fort Worth limestone under the business district of the city averages about 25 feet in thickness. If this is not mostly excavated out for basements and sub-basements, it of course affords a firm substratum for buildings up to a certain size, depending upon the amount of the excavation. When this 25 feet of limestone is penetrated a marl mixed with insecure thin limy ledges and extending downward for about 15 feet is en- countered. This level may be instantly recognized by the abundant brachiopod, Kingena, which the excavation will reveal. Then comes a limy ledge about 7 feet thick with considerable marl material intermixed. This ledge has firmness enough for many building purposes. Underneath is a series of limy and marl layers of increasing firmness and compactness, which after 11 feet below the ledge are quite compact and afford an excellent foundation. The sec- tion may be seen in Plate 6, and is exposed at several places near the court house. The marlier layers have a certain water content which will depend somewhat on whether their outcrops west and north of 86 University of Texas Bulletin the site of excavation have a favorable catchment area or not. If they are narrow or built over or paved, or slope sharply to the west, less water will seep under the foundation. The foundations of numerous buildings in Fort Worth have penetrated these strata to different depths. An example is the foundation of the W. T. Waggoner office building whose exca- vation (May 1919) sectioned at Eighth and Houston streets about two feet of soil, then penetrated the typical thin bedded Fort Worth limestone, which towards the base was bluish, cal- careous and very hard. The interbedding was a hard calcareous marl. The excavation for concrete piles was continued to stratum 1 which lay at a distance of 28 feet below the level of the side- walk. In general it is inadvisable to base heavy buildings on marl. Roads and railroads. Roads in many parts of the county have a naturally firm sub-stratum-, as over portions of the Fort Worth and Mainstreet uplands. The Woodbine roads often have a natural base, and along the eastern border the Eagle Ford over- wash forms a clay binder for the sand and makes an excellent natural roadbed. The railroads running in the strike of the Comanchean for- mations often lie on limestone strata, as the Frisco on the min- eralized ledge (17) of the- Duck Creek formation, southwest of Fort Worth. The Misouri, Kansas and Texas and the Interna- tional and Great Northern run successively on the Fort Worth limestone, the Weno limestone and the Mainstreet limestone south of Fort Worth. The Santa Fe south of Fort Worth in Tarrant County runs on the Mainstreet limestone. Railroad cuttings across the strike follow more or less the * ‘ cuesta ’ ’ slopes, as the Texas and Pacific to the west and the Interurban to Dallas. Drainage. The streams have cut back the softer materials from the adjoining harder formations producing small and poor exposures of the marly material. This is especially true of the Grayson marl, where good exposures are rarely found, and which only exceptionally weathers as a divide, such as that southeast of Burleson, or in stream cuts descending from the Woodbine for- mation. The softer nature of the Grayson marl is attested by the The Geology of Tarrant County 87 disproportionate number of graveyards scattered throughout its outcrop across Tarrant county. Certain railroads run on drainage divides, as the Fort Worth and Denver City Railway, which north of Fort Worth follows the divide between the West Fork and the Denton Fork of the Trinity. Slumping and side-slip of strata on the edge of uplands result in virtual reversals of dip and in two known places blocks of Fort Worth limestone have been undermined by the Trinity. RESOURCES OF SOIL No soil map of Tarrant county has appeared, but analagous conditions resulting from the same types of geology may be seen in the maps of Grayson and Travis counties. The county contains soil areas which follow closely the outcrop of the geo- logical formations as mapped here, and these may be roughly- divided as follows: (1) Uplands : The Fort Worth and Mainstreet uplands have been stated to possess such shallow soil that they are suitable only for grazing. However over great stretches, notably the dip plain area north of Fort Worth, which Hill calls the type of the Black Prairie, the soil and subsoil are deep and are used for large scale farming. The exposures of the Fort Worth limestone southwest of the city are extensively used for graz- ing. These uplands drain quickly, even after heavy rains, and in general artificial water basins must be constructed if a per- manent water supply is desired. This portion of the county is dissected by streams cutting down to the Trinity, especially near the western prairie border, and is rolling or slightly hilly and almost treeless. Practically the same conditions hold for the Mainstreet upland except that near its eastern border there is a considerable mixture of red sandy soil from Woodbine overwash. The two uplands are at many places connected by a fairly even grassy slope obscuring the intervening formation and making the two areas practically one topographic unit. (2) River Bottom. The untimbered portion of the alluvial Trinity River valley is wide enough in many places to permit 88 University of Texas Bulletin of considerable cultivation and in the central and western part of the county i s not subject to serious overflow. In the eastern part of the county a system of levees exists. The river alluvium is deep and has at many places a gravel and sand foundation which is exploited commercially, as at the Rock Island pits near Birdville. This material is transported by the stream for con- siderable distances as seen by the Fredericksburg fossils occur- ring in gravel deposits near Dallas. The numerous Exogyra texana and Grypkea mwcoui in these gravels come mostly from strata below and outcropping west of the white Goodland lime- stone. As the river cuts thru the Woodbine cross timbers the ^oil deposits gather sandy acidic components, so that this por- tion of the bottom land like the Woodbine is used for fruit growing. (3) Woodbine Gross Timbers : This strip of red sandy acidic soil is still densely timbered with black jack and post oak, but contains natural glades and artificially cleared areas. The soil is suitable for many purposes, especially fruit growing, peaches, peanuts, and to a less extent cotton, corn and to- bacco. However its limitations should be clearly noticed if loss is to be avoided in the selection of crops. The Fort Worth region has been agriculturally, first a cattle raising country, and second a grain and cotton country. Without doubt its diverse soils are suited to a variety of profitable special products whose exploitation is only a matter of study and experiment. The main cotton belt at present is the outcrop of Eagle Ford (and to a less extent the Woodbine also) in the eastern part of the county. RESOURCES OF NATIVE OR IMPORTABLE PLANT AND ANIMAL LIFE As already stated the county lies at the junction of the humid (eastern) and the semi-arid (western) divisions of the Lower Austral Zone, and it has accordingly a mixture of temperate and subtropical wild life. This is seen clearly in the mammals, birds, insects, and in the plants. Subtropical and temperate zone birds live side by side in the upper Trinity valley, as noted The Geology of Tarrant County 89 bv Bendire. The county lies on the northern range of certain subtropical insects and other invertebrates. Finally the same situation is true of other vertebrates. A plant zone map of Texas as indeed of most of the United States will correspond broadly to a map of the underlying geo- logical systems. Hill and others have recognized that the vari- ous divisions of the Texas Oomanchean and Cretaceous carry their own peculiar or at least prevailing flora; and the pheno- menon of timber belts which characterize certain formations has long been known. This correspondence extends for some plants to the minute subdivisions of geological formations. There are certain plants which occur either largely or ex- clusively upon certain types of topography regardless of the underlying geological formation. 1) UPLAND PLANTS Centaurea americana. Helianthus annuus. Helianthus maximiliani. Lindheimera texana. Castilleja purpurea. Linum lewisii. Linum arkansana. Polygala alba. Croton texensls. Euphorbia marginata. Baptisia bracteata. Psoralea hypogaea. Callirhoe digitata. Megapterium missouriense. Phellopterus macrorhizus. Eustoma russellanium. Amsonia texana. Quamasia hyacinthea. Cooperia drummondi. S'isyrhinchium amoenum. Lesquerella gracilis. Draba cuneifolia. Neptunia lutea. (2) ESCARPMENT PLANTS Yucca arkansana (mainly on Fredericksburg limestone). Androstephium ceruleum (mainly on Duck Creek limestone). Erythronium albidum coloratum (mainly on Duck Creek limestone). Aragallus lamberti. (3) LOWLAND PLANTS Smilax bona-nox. Viola obliqua. Clematis simsii. Viola raflnesquii Cnidosculus texanus. Oraetegus mollis. (4) PLANTS OF THE WOODBINE SANDSTONE BELT Quercus marylandicus the “Black Jack” oak is the characteristic tree of the “lower cross timbers.” Pentstemon australis. Houstonia minima. RESOURCES OF CRUDE MATERIAL LIMESTONE INDUSTRIES. When mention is made of the resources suggested by the geology of a region, the average layman assumes at once that reference is made to mining possibilities and to oil and other 90 University of Texas Bulletin so-called mineral resources. Often a region has undeveloped resources in its rocks which are of more permanent value than even fairly rich mineral deposits in the popular sense. Limestone industries are many, and much depends on the various factors of the quality of the limestone, the presence or absence of other substances besides the calcium carbonate which makes up the bulk of all limestone, transportation fa- cilities, accessibility to a market, fuel, labor, etc. Examples of limestone industries are: quarries, cement plants, carbon- dioxide gas plants, rock crushers and lime kilns.. The limestones in Tarrant county which offer possibilities in the opinion of the writers are as follows : the Mainstreet lime- stone, which is fifty feet thick; the Weno limestone, which is twenty feet thick; the Duck Creek limestone, which is thirty feet thick; and the Coodland limestone which is a little more than one hundred feet thick. The areal extent of each of these at the surface can be seen on the map. Unfortunately very little exploitation of these various lime- stones has been carried beyond the experimental stage. Even in the simple matter of crushed rock for road metal, the writers lack any practical data based on industrial experience, as Tar- rant county has the crushed rock for its roads shipped from another county. The following considerations govern the limestones of * the county: Only one, the Weno limestone offers possibilities for the establishment of quarries. This excellent material is rather limited. The rock, however, seems to cleave well and should be adapted to .exploitation as a good grade of building stone. It is white in color, fine grained in texture, does not contain enough iron to be likely to develop wall stains, and as noted above cleaves well, with the cleavage planes clean and parallel. Blocks to a maximum thickness of eighteen inches should be Readily obtained and with a length of six feet and a breadth of three feet. As this limestone is in many places covered with other formations or otherwise in a condition to make a quarry impracticable, the following localities are suggested to ^prospectors : the area north of Polytechnic especially in the region near the Texas and Pacific tracks, the bluffs along Syca- The Geology of Tarrant County 91 more creek especially in the neighborhood of the crossing of the loop road about a mile after it leaves the Burleson road. A considerable area of this limestone is exposed along the Keller road about four miles north of Fort Worth, but much of the exposure is overlain by a thick blanket of soil. The Mainstreet limestone is the best exposed over a large area, but is massive, breaking into angular fragments and con- siderably iron stained. In the opinion of the writers, however, this limestone should be entirely satisfactory for erushed rock. It i,s remarkably uniform through a considerable thickness, and this is a quality desirable in crushed rock. The Fort Worth limestone and the Duck Creek limestone contain much marl in the form of beds alternating with the limestone. In the present stage of development of the limestone industries these two limestones are not likely to be worth exploiting as long as there is such a large supply of much higher grade material. The Goodland limestone offers, apparently, more possibilities. The map indicates the great area covered by this formation. The region around Benbrook is especially rich "in good exposures of this limestone. The most conspicuous single exposure of this limestone is in the bluff at the north end of the Lake Worth dam. In fact the use of this limestone in connection with the construction of this dam seems to be the only extensive ex- periment which has been made in its exploitation. The Goodland limestone is almost pure calcium carbonate, and offers possibilities for exploitation in many ways : lime kilns, carbon dioxide plants, cement plants (using the Kiamitia clays immediately overlying the Goodland limestone). For practical purposes the supply may be considered as inexhausti- ble and many excellent exposures occur near the city of Fort Worth. GRAVEL AND SAND There are two types of gravel in Tarrant county : (a) River gravel, lowland, rounded, clean, little cementing or adhering of sand or clay. (b) Pit gravel, upland, angular, cemented with matrix of poorly assorted particles of sand, clay, rock materials, etc., of various sizes. 92 University of Texas Bulletin The lowland gravel occurs at or near the present level of the drainage at many places even up the small laterals. The up- land gravel is widely distributed and is worked commercially. There are considerable deposits along the whole course of the Trinity particularly the Clear Fork, on the" south side of the Arlington Heights divide, on the hills around the Texas Chris- tian University, on the Rock Island railway south of Birdville, and along Sycamore Creek, Big and Little Bear Creeks apd Big and Little Fossil Creeks. SAND : The river sands are impure, being mixed with clay, gravel and calcareous particles and fragments. The purest sands are probably in the upper part of the Woodbine near Mans- field. This is a round-grained sand, and has some iron stain. Extensive sands occur in the Walnut and Paluxy formations west and northwest of Fort Worth. MINERALS : The following have been found in Tarrant County: Calcite, aragonite; pyrite, hematite, limonite; celes- tite ; gypsum ; radidlarian ooze ; desert varnish. In addition gilsonite in the Trinity sand, and lignite in the Woodbine occur in non- workable amounts. Apparently none is of economic importance. CLAY INDUSTRIES Probably the purest clays in the county are those of the Pawpaw and Woodbine formations; which, so far as known, have not been tested except for brick. There are also clay members in the Paluxy sand. These clays are iron stained and somewhat impure, but should be suitable for tile, crockery, earthenware, and certain other clay products. The Athens Pottery Company at Fort Worth ships in its clay. The availability of clay for commercial use depends somewhat upon the price of fuel and the conditions of transportation. Factories will locate in a great rail center like Fort Worth and ship in their raw material. Hence it is extremely desirable to use all possible local raw material, and to make special investigations to find which are suitable. There has apparently been little testing and no ex- ploitation in Tarrant county but the favorable combination of The Geology of Tarrant County 93 materials found here makes a greater future development of certain clay industries seem very probable. BRICK The general requirements for the location of a brickyard are accessibility to transportation, to fuel, to suitable market, to water, and to crude material as described. The crude material should be present in large quantities ; should be accessible with- out great amounts of excavation ; should be free from overlying soil or undesirable rock formations which would require re- moval; should be capable of proper drainage; and should be of a certain quality or purity, especially as regards shell material or other calcareous inclusions. Evidently several formations exposed in Tarrant county fit these conditions, especially the following: Eagle Ford shales, Woodbine sands (basal part), Pawpaw clays, Weno marl, Kiamitia marl Paluxy sands, Walnut clays. These are exploited so far at only five places in Tarrant county, but it will be useful to refer to the nearly similar conditions found in the same formations in adjoining counties. In this connection attention is called to the interesting geological possibilities of brick yards to students or others doing paleontological work, since in brick- yards marl formations, otherwise poorly exposed, are well sec- tioned. As the pits deepen the question of drainage becomes more pressing. Many pits are pumped, a proceedure involving ex- pense and often delay. It might be practicable in some pits to resort to the drainage device used at times by the American Expeditionary Forces in France, in which a lower lying dry sand was reached by boring and the drainage emptied automati- cally into this sand. In the Washita divisions, certain levels of the Paluxy sand might be drilled to ; and above the Washita, certain of the Woodbine sands. CLAYS OF THE WOODBINE SANDS Acme Brick yards, one mile south of Denton, Texas: The material used is mainly a whitish arenaceous clay layer whose base lies within 25 feet of the bottom of the Woodbine forma- tion. This layer is nearly 30 feet thick and is overlain by a 94 University of Texas Bulletin lenticular mass of red sandstone which is dragged back from the top preceding excavation of the material. This whitish ma- terial is semi-consolidated in places and weathers nearly white with little iron stain. The “red clay” burnt alone gives a non- spotted building brick; the white material alone gives a cream colored brick; while the two mixed give a spotted de luxe brick which is sorted. J ohnson Station, Tarrant County : This brick yard uses material from the lower third of the Woodbine sands. Kennedale, Tarrant county : two brickyards use the middle part of the Woodbine sands. Brambleton, Tarrant county: this brickyard uses middle Woodbine material. CLAYS OF THE PAWPAW AND WENO FORMATIONS The Cobb Brick yards, Fort Worth, use two sources of sup- ply, the basal Weno marl and the Pawpaw clay. The pit in the Weno near Sycamore Creek exposes nearly the basal third of the marl, including the Gervilliopsis layer. The marl after weathering, is grayish-blue, putty colored and is only slightly shelly. The few Gryphea , Gervilliopsis and other shells present after screening are burned with the mixture and reduce to in- significant friable limy spots. This Weno marl burns at about 1700° F to a variety of red bricks, which are sorted. The upper Pawpaw marl east of Sycamore Creek is used to produce a red building brick which burns at about 1700°F. The clays of the Pawpaw formation in Tarrant County offer many advantages for brickmaking. They are particularly free from shells, ob- viating screening, as is necessary in certain clays of the Weno deposits. The formation has in the basal portion small pyrite fossils whose contained sulphur might be a disadvantage, but the total amount of this material is small. The Pawpaw formation is a homogeneous clay or shale prac- tically free from calcareous shells, about 23-27 feet thick. It is capped at most places by Mainstreet limestone which would have to be blasted or stripped back. This Mainstreet cap at places disintegrates so that the stripping is easier; however, at such places it contaminates by percolation the underlying clay to a depth of 3 feet or more. The drainage of Pawpaw localities The Geology of Tarrant County 95 is almost invariably good, since they lie on hillsides. For the same reason a gravity haul to a plant located so as to utilize also the underlying Weno marl is practicable. The amount of ma- terial is unlimited, since it is necessary only to follow the line of outcrop. This 23-27 feet of Pawpaw is underlaid by an amount of Weno limestone which it would be impracticable to remove, in order to expose the underlying Weno marl. It should be noted that north of the Trinity, the Pawpaw contains immense amounts of siliceous fragments resembling jasper, which will probably require screening; this material is absent south of the Trinity. Finally, in Tarrant County the forma- tion is accessible to railroads. BRICKYARDS 1 % MILES SOUTHEAST OF GAINESVILLE, TEXAS The pit of the Gainesville Brick Co. exposes the Weno forma- tion from the Quarry limestone group, which is well developed on the south rim of the pit down to the basal third of the formation, about 20 feet below the Gervilliopsis layer. The Weno is about 75 feet thick and the depth of the pit practically the same. A water well nearby penetrated the Denton marl and the Fort Worth limestone. A “buff marl” layer, free from shells and lying about 2 feet below the Gervilliopsis layer burns to a clear buff brick and is much fayored. If the material is excessively shelly it is dis- carded. Much material from the upper part of the pit also was discarded on account of the abundant ironstone. The burn- ing temperatures vary from 1700°F. to 1800°F., and the bricks are sorted. The plant uses the dry moulding process, is equipped to burn lignite and coal, and has a capacity of 40,000 bricks per day. CLAYS OF THE PALUXY SANDS One brickyard north of the Texas & Pacific Railway on the White Settlement road 15 miles west of Fort Worth, uses the material from the upper part of the Paluxy formation, which burns to a red building brick. POSSIBILITIES OF OIL AND GAS A bulletin on the geology of any of the counties of North Texas would be incomplete and unsatisfactory without a dis- 96 University of Texas Bulletin cussion of the possibilities of petroleum. Mr. E. W. Shaw, of the U. S. Geological Survey, included Tarrant County in his study of the natural gas resources of parts of North Texas, (U. S. G. S. Bulletin 629), including a structural maj of the outcrop of certain limestone ledges in the area south and west of Benbrook. It was his opinion that notwithstanding the fact that oil and gas showings in water wells of the southern part of Tarrant County are frequent it is likely that the accumula- tions of petroleum products in the rocks underlying this county has escaped. The writers of this bulletin are inclined to agree with this general view. We do not pretend to have thoroughly investigated all the structural possibilities in the county, and it is of course possible that structures favorable for the con- centration and retention of oil or gas may exist. How T ever, we have seen no such structures, and the probable occurrence of a large syncline in the^ Paleozoic rocks in this region is es- pecially unfavorable. In Tarrant County, as in many other counties of North Texas, considerable exploratory drilling has been carried on in the area covered by the Woodbine formation. The red sand- stone which makes up the formation, is extremely interesting and complex. Its exact thickness is not known, and a complete recorded section does not exist. It is much cross bedded and its dip changes with frequent and startling suddenness. Above all else, it has extremely deceptive structural features in the shape of lens-like masses. Some cf these are quite extensive, and might very well be mistaken for “domes” suggesting a corresponding structure in the underlying rocks and, of course, the possibility of concentration of petroleum. A careful study of one of these bodies has been made by the winters. Unfor- tunately this body does not occur in Tarrant County, but it is so perfectly exposed and the arguments of the writers are so well illustrated that attention is called to one of these bodies in the Acme Brick Yards at Denton, Texas, In the westward facing out of the pit, a little more than forty feet of the Wood- bine formation is exposed. The upper fifteen feet is made up of a iens-like mass, containing four members. The lens shape is due to sharply dipping members in the bed. The dip here The Geology of Tarrant County 97 is mainly south. About a thousand yards north of the pit in the cut of the Missouri. Kansas and Texas Kailway is an ex- posure of the rocks in the plane of the pit, in which the mem- bers dip in the opposite direction. In both cases, the under- lying: rocks are horizontal. This pseudo “dome” then is esti- mated to have had an original depth of from sixty to seventy feet and a diameter of nearly a mile, and without the under- lying horizontal beds so well exposed, this “dome” might have been discovered and exploited by some inexperienced pefson. The Bend and the Ellenburger formations, if present under- neath Tarrant County, are deeply buried. The Bend has not been reached in the Polytechnic well at 4380 feet according to Dr. Udden. A sample said to be from this well from “below 4,000 feet” (depth not stated, possibly near 4,600 feet) is a hard black shale lacking fossils; and a sample claimed to be from “about 4,600 feet” is likewise black shale, probably not Bend, but resembles somewhat the black shale above the Bend, in the opinion of Dr. Udden. Comparison of wells at George- town, Gatesville, Myra, and Muenster with those in Tarrant County would appear to indicate a considerable depression, possibly synclinal, of the Trinity, and the Bend and Ellen- burger if present, under the Fort Worth region; there is also a feeble reflection of this depression in the overlying Coman- chean formations. The following table gives approximate data for contouring the base of the Trinity sand in Tarrant County; it indicates that the base of the Trinity here dips almost east at the rate of about 48 feet per mile. WELL Altitude BASE OF TRINITY See of well Depth Altitude page Tucker’s Hill Well . . . . 650 1120 - 495 25 Polytechnic Well 1250? - 600? 25,107 Mansfield Well 1678 -1078 115 Grapevine Well 1720? -1120? 7— Tarrant 98 University of Texas Bulletin WATER RESOURCES The water supply of Tarrant County is derived from (a) streams, (b) artesian wells, (c) dug wells and (d) seepage springs; of these the first two named produce the greater part of the supply. The various city reservoirs on the two forks of the Trinity, especially the Lake Worth reservoir, have been widely discussed and will not be treated here. The problem of impounded water is in Tarrant County mainly an engineering problem, since a supply is assured. Much water is still derived from artesian sources, mainly by pumping. The principal ar- tesian reservoirs under Tarrant County are the Woodbine, which is a shallow source of water underlying the strip of country east of Handley; the Paluxy reservoirs, which underly the whole County except a small area in the northwest corner; and the Trinity reservoir, which underlies the whole county. Since all these reservoirs dip to the southeast they increase in depth, and the pressure of their waters increases, going either south or east. Accordingly, as younger strata come in on top of them towards the east border of the county they will be overlain at increasing depths, as seen in the following table of approx- imate depths. This table gives the approximate depths at which the various artesian water reservoirs occur in Tarrant County. The points taken to illustrate these depths to the various water reservoirs are Mansfield, Texas, the Texas and Pacific Railway Station at Arlington, Texas (elevation 616 feet), the Central Fire Station, Fort Worth, Texas (elevation 620 feet), The Polytechnic and the Tucker’s Hill wells, East Fort Worth (elevation 650 feet). The figures are only approximate. The notation of Dr. R. T. Hill is used, the shallowest horizon in each formation being listed first and the deepest last. Trinity 1 is the main Trinity reser- voir. The Geology of Tarrant County 99 o ,£ < E- 32 “ 42 University of Texas Bulletin No. 1931 a • o ,a ? " si LIBRARY OF THE UNIVERSITY OF ILLINOIS University of Texas Bulletin No. 1931 Plate 2. Fig. 1. Airplane view of top of Goodland limestone, Benbrook, Texas. (Locality described by Taff.) Plate 2. Fig. 2. GoodJpnd Hmestone. '’"eve Foundry Poa'U 4 miles west of Fort Worth. The base of the telephone pole is the Upper Salenia horizon. LIBRARY OF THE UNIVERSITY OF ILLINOIS University of Texas Bulletin No. 1931 Plate 3. Fig. 1. Top of Goodland (Fredericksburg) limestone, looking east from near Benbrook. Plate 3. Fig. 2. Terrace in the Fredericksburg division. The top terrace is the top of the Goodland. Plate 3. Fig. 3. Terraces in the basal Washita Division. The bottom terrace is the top of the Goodland limestone, and the top two are the Duck Creek limestone and marl. LIBRARY OF THE UNIVERSITY OF ILLINOIS University of Texas Bulletin No. 1931 Plate 4. Fig. 1. Base of Fort Worth limestone, which underlies the business section of the City of Fort Worth. On Main Street, the base of the limestone is about 30 feet underground. The limestone is underlain by the less resistant Duck Creek marl. Plate 4. Fig. 2. Gate posts and flower beds in Forest Park, built of the large ammonite, Desmoceras brazoense. ,r ' V. & i LIBRARY OF THE UNIVERSITY OF ILLINOIS University of Texas Bulletin No. l'J31 Plate 5. Fig. 1. The large ammonite, Schloenbachia sp. J., which characterizes the Fort Worth limestone. Plate 5. Fig. 2. Illustration of the terms “cast” (left) and “mold” (right). LIBRARY OF THE UNIVERSITY OF ILLINOIS University of Texas Bulletin No. 193J Plate 6. Fort Worth limestone, in excavation at northwest corner of 8th and Houston sts., Fort Worth. Excavations for buildings in the main business district pass into or entirely through the Fort Worth limestone. LIBRARY OF THE UNIVERSITY OF ILLINOIS HJN4 1973 University of Texas Bulletin No. 1932: June 5, 1919 The Geology and Mineral Resources of Bexar County By E. H. SEIXARDS BUREAU or ECONOMIC SEOIOOY SND TECHNOLOGY t „ TT _ DIVISION OF ECONOMIC 'GEOLOGY J. A. UDDEN, Director of the Bureau and Head of the Division PUB V P S ” E "A Y THE UN1VERS ITY six times a month, and entered as SECOND-CLASS MATTER AT THE POSTOFFICE AT AUSTIN. TEXAS. UNDER THE ACT OF AUGUST 24, 1912 geology The benefits of education and of useful knowledge, generally diffused through a community, are essential to the preservation of a free govern- ment. Sam Houston Cultivated mind is the guardian genius of democracy. . . It is the only dictator that freemen acknowl- edge and the only security that free- men desire. Mirabeau B. Lamar 2. x, /W£* o ) ^ Y 3 CONTENTS r * fN.-'f _3 r Introduction Early settlements Acknowledgments Location with respect to major physiographic divisions Topography and drainage Climate and rainfall Balcones Escarpment Minor physiographic divisions The Glenrose hills The Edwards flint hills The Del Rio plain The Austin hills The Taylor-Navarro plain The Midway- Wilcox hills The Carrizo sand hills Stream terrace plains Stratigraphic geology The Pre-Cretaceous sediments Table of geologic formations The Mesozoic Comanchean Cretaceous Trinity Travis Peak formation Glenrose formation Fredericksburg Comanche Peak formation Edwards formation Washita Georgetown formation Del Rio formation Buda formation Upper Cretaceous Eagle Ford formation Austin formation Taylor formation Navarro formation The Cretaceous-Tertiary contact The Cenozoic Eocene Midway formation Wilcox formation Carrizo formation Pleistocene Uvalde formation Leona formation 7 7 8 TO 12 13 13 14 14 15 16 16 17 18 18 18 19 19 20 21 21 21 23 24 25 27 28 31 34 34 36 44 49 53 54 54 54 57 63 64 65 69 Contents Late Pleistocene Alluvial deposits 72 Cave deposits 73 Recent 74 Calcareous concretions 75 Structural geology 77 Location of principal faults 77 Structurally high areas 82 The Culebra structure 83 The San Antonio structure 84 The Alta Vista structure 85 The Geological Map 86 Index to levels on the Del Rio formation 87 Notes on exposures seen on the public roads, including Blanco, Bulverde, Nacogdoches, Austin, St. Hedwig, Pleasanton, Somerset, Pearsall, Castroville, Potranca Culebra, Bandera, Babcock and Fredericksburg roads. 90 Economic Geology 97 Artesian and other underground waters 97 Principles of artesian wells and ground-water ac- cumulation 98 Water of the Glenrose-Travis Peak formations 100 Water of the Georgetown-Edwards limestones 101. Areas of artesian flow 101 Water of the Del Rio and Buda formations 103 Water of the Eagleford and Austin formations 104 Water of the Taylor and Navarro formations 104 Water of the Tertiary formations 104 Springs 104 Warm sulphur water in the Comanchean limestones. . . .105 Source of hydrogen sulphide in underground waters. . .106 Cement 108 Clay 112 Building brick 112 Fuller’s earth 114 Bentonite 115 Concrete 116 Greensand 117 Lignite 118 Limestone 119 Lime 120 Building stone 121 Petroleum and Natural gas 121 The Alta Vista oil field 122 The Mission oil field 123 The Gas Ridge oil and gas field 123 The Somerset oil field 124 Contents The South Medina oil field 125 Relation of the Bexar County oil fields to structure 125 Quality of the Bexar County oil 127 General considerations 127 Road materials . 128 Well records 129 Wells entering the Pre-Cretaceous formations 129 Wells terminating in the Comanchean formations 135 Tabulated records 136 Logs and other data supplementary to the tab- ulated records 143 Wells terminating in the Upper Cretaceous 171 Index 199 ILLUSTRATIONS. Fig. 1. Fig. 2. Fig. 3. Fig. 4. Fig 5. Fig 6. Figures. Page Sketch map to show the location of Bexar County with respect to the major physiographic provinces of Texas 11 Sketch map to show the minor physiographic prov- inces in Bexar County . 15 Table of geologic formations and columnar section. . 20 Graphic representation of logs of wells arranged in order from northwest to southeast 78 Schematic representation of structure on an approx- imately north-south line through Bexar County. ... 79 Sketch map indicating the location of brick, cement and fullers earth plants, lime kilns, lignite mine, oil and gas fields, and areas of flowing artesian water 98 Plate. PI. 1. Pisolitic gravel in the Pleistocene as seen in pit ex- cavated for gravel road material near the Mission Loop Road south of San Antonio 72 Map. Geologic and structural map of Bexar County . . Inside back cover GEOLOGY AND MINERAL RESOURCES OF BEXAR COUNTY* BY E. H. SELLARDS Bexar Coujity is located in south-central Texas, about 125 miles from the Gulf Coast, and approximately an equal distance from the Mexican border. The adjoining counties are Kendall and Comal on the north, Guadalupe and Wilson on the east, Atascosa on the south, and Medina and Bandera on the west. San Antonio, the county-seat, is one of the large cities of the southwest part of the United States. The area of Bexar County is estimated at 1,268 square miles. The population, according to the latest census, that of 1913-1914, was 119,676. EARLY SETTLEMENTS In 1718 the Spanish established the mission of San Antonio de Valero and the Villa de Bexar near the headwaters of the San Antonio River and on the site of the present city of San Antonio. The principal natural advantage inducing settlement at this place was the existence of large springs which emerge at the head of the San Antonio River a few miles farther inland. The location for this setllement is said to have been pointed out to the Spaniards by the Frenchman, Saint Denis, as a suitable place for a city “in the most pleasant place” in the province of Texas.! Subsequently, between the years 1718 and 1731, there was built up by the Spanish, the several missions of which the ruins still remain. Of these, the mission of San Antonio de Valero, already noted, and Conception Mission are within the limits of the present city of San Antonio. The others are farther south, but all are within the valley of the San Antonio River, where water from the springs was available and was used in irrigation. The presence of these springs, giving rise to a per- manent flowing stream in a region otherwise lacking in surface water supplies, determined the original location of the city of San Antonio. fClark, Robert Carlton. The Beginnings of Texas. Univ. of Texas Bull. No. 98, p. 87, 1907. ♦Issued March, 1920. 8 University of Texas Bulletin Settlement by citizens of the United States began in Bexar County while Texas was still a Spanish province, although not until 1820 was official permission secured to establish an Ameri- can colony. Immigration from the United States continued and at the time of the declaration of independence of Texas, a con- siderable colony had been established. The historic associations of the city, especially those connected with the struggle for in- dependence from Mexico, center around the Alamo, built orig- inally as the chapel of the Mission of San Antonio de Valero, where in 1836 Colonel Travis and his small band of 182 follow- ers made their famous although unsuccessful stand against the army of Santa Anna. Since the acquisition of Texas by the United States, the military control of the southwest has in a measure centered in San Antonio, and at the present time the county is notable for the number of army camps and large military reservation that it contains. Fort Sam Houston, near the eastern limits of San Antonio, has for many years been the headquarters for the Southern Military Department. The Leon Springs military reservation is located in the northern part of the county. South of Leon Springs is the Camp Bullis reservation, now under lease by the Government. Adjoining Fort Sam Houston on the east, and partly within the city limits, is a large army training camp named in honor of Colonel W. B. Travis. Camp Stanley, a cavalry camp, is located in the Leon Springs reservation. Kelly field No. 1 and Kelly Field No. 2, both aviation camps, are lo- cated on the terrace plain about six miles southwest of the center of the city. Brooks Field, another aviation camp, is about eight miles south of San Antonio. Camp John Wise Balloon School is located just north of the city limits. ACKNOWLEDGMENTS An investigation of the geology of Bexar County was begun for the Bureau of Economic Geology by Mr. C. L. Baker, in 1917. The field notes made by Mr. Baker at that time have been available and have proved of much assistance in the subsequent field work in this county and in the preparation of this report. Geology and Mineral Resources of Bexar County 9 Dr. J. A. Udden, has also made notes at various times on this county, both on surface exposures and on cuttings from deep wells. These notes likewise have been made available and have been used in this report. In 1911 and again in 1918, Dr. L. W. Stephenson of the U. S. Geological Survey visited and made notes on the geology of Bexar County. A part of the data in Dr. Stephenson’s notes was incorporated by him in a paper on “The Camps Around San Antonio”, published on the reverse side of the topographic map of the San Antonio quadrangle, edition of 1919. The unpublished notes by Dr. Stephenson have very generously been placed at the disposal of the Bureau of Economic Geology by the Director of the United States Geo- logical Survey, and have added very materially to the data on this county. From Mr. Alexander Deussen many additional data have been secured, including well records collected by him in connection with a report on the water supply of Central Texas for the U. S. Geological Survey, as well as other data personally collected by himself. Brief reports on oil discoveries in Bexar County, made for the Bureau of Economic Geology by Mr. E. L. Porch, Jr., have been available and have supplied data utilized in this report. To Mr. R. M. Madison is due credit for many data on wells. To the Chamber of Commerce of San Antonio, to well drillers, and oil- and mineral-producing companies as well as to many other individuals, the writer is under obligations for courtesies and for data that have been contributed. The base maps which have been available in this county in- clude, first, a topographic map of the San Antonio quadrangle, by the United States Geological Survey. This quadrangle covers approximately one-half of the county. From the County En- gineer of Bexar County, Mr. A. C. Pancoast, was obtained a very carefully made road map of the county which has been of much service. In addition, maps of the military reservations were available in the offices of the War Department. The soil survey map of the San Antonio area made by the United States Bureau of Soils was likewise consulted. The published literature relating directly or indirectly to Bexar County, although not extensive, includes a number of papers that should be specially mentioned. The following list 10 University of Texas Bulletin contains the more important papers relating to this county, ar- ranged chronologically : A Partial Report on the Geology of Western Texas, consisting of a general Geological Report and a Journal of Geological Observations along the Routes traveled by the Expedition between Indianaola, Texas, and the Valley of the Nimbres, New Mexico, during the years 1855 and 1856; with an Appendix giving a detailed report on the Geology of Grayson County. By Prof. Geo. G. Shumard, Assistant State Geologist of Texas. Introduction by H. P. Bee, Commis- sioner of Insurance, Statistics and History. Austin, 1886. Report on the Brown Coal and Lignite of Texas, by Edwin T. Dumble. Second Annual Report, Texas Geological Survey, 1892. Geology of the Edwards Plateau and Rio Grande Plain adjacent to Austin and San Antonio, Texas, with reference to the occurence of Artesian waters, by Robert T. Hill and T. W. Vaughan.* U. S. ’ Geological Survey, 18th Ann. Rpt., Pt. II, pp. 193-321, 1898. Geography and Geology of the Black and Grand Prairies, Texas, with detailed descriptions of the Cretaceous formations and spe- cial reference to artesian waters, by R. T. Hill. U. S. Geol. Surv., 21st Ann. Rpt., Pt. VII, pp. 666, 80 figs., 1901. Soil Survey of the San Antonio Area, Texas, by Thomas A. Caine and W. S. Lyman. U. S. Dept. Agric., Bureau of Soils, 1904. Underground Waters of the Coastal Plain of Texas, by Thos. U. Taylor. U. S. Geol. Surv., Water Supply Paper No. 190, 1907. The Geology of the Artesian Water Supply of the San Antonio Area, by A. H. Muir. San Antonio, 1911. Geology and Underground Waters of the Southeastern part of the Texas Coastal Plain, by Alexander Deussen. U. S. Geol. Surv., Water Supply Paper No. 335, 1914. The Mineral Resources of Texas, by Win. B. Phillips. Bulletin of the University of Texas, No. 365, 1914. The Lower Eocene Floras of Southeastern North America, by E. W. Berry. U. S. Geol. Surv., Prof. Paper No. 91, 1916. Review of the Geology of Texas, by J. A. Udden, C. L. Baker, and Emil Bose. Bull. Univ. Texas, No. 44, 1916. LOCATION WITH RESPECT TO MAJOR PHYSIOGRAPHIC PROVINCES Two of the large physiographic provinces of the United States, namely the Gulf Coastal Plain and the Great Plains, extend into Bexar County. The Gulf Coastal Plain, in which the greater part of the county lies, reaches from Central America, bordering the Gulf of Mexico, to the Atlantic Ocean, there merging with the Atlantic Coastal Plain. The Great Plains, including several Geology and Mineral Resources of Bexar County 11 sub-divisions, extend from Mexico to the Arctic Ocean. In cen- tral and southern Texas the line dividing the Great Plains and the Gulf Coastal Plain is a pronounced southeast to south facing escarpment produced by faults and dips, and known as the Bal- cones Escarpment. This escarpment, coming into the state near Del Rio on the Rio Grande River, continues east to Medina County and there turns to the northeast, passing through Bexar County in a direction approximating 60 degrees east of north. Approximately seven-eighths of the county lies in the Gulf Coastal Plain southeast of the escarpment, while the remaining one-eighth, or about 150 square miles, lies to the northwest in the margin of the highlands known as the Edwards Plateau, which is the southernmost division in Texas of the Great Plains. The location of the county in the State, and with respect to these major physiographic divisions, is indicated on the ac- companying sketch map (fig. 1). Fig. 1. — Sketch map to show the location of Bexar County with respect to the major physiographic provinces of Texas. The shaded area indicates the location of Bexar County. 12 University of Texas Bulletin TOPOGRAPHY AND DRAINAGE The topographic and physiographic divisions in Bexar County are determined very largely by the geologic structure. The formations dip in general, and with some variations, to the south- east. This also is the direction of the average maximum surface slope, but as the rate of dip of the formations is more rapid than the surface slope, it follows that in passing to the southeast younger formations come successively into the . section. Each formation develops in the line of its outcrop a more or less well defined surface topography or topographic expression which is often very characteristic for that particular formation. The formations containing much hard rock resist decay and stand out as hills, often forming northwest-facing escarpments or “cuestas”. The softer and less resistant formations, on the other hand, produce either valleys or plains. The strike of the formations, as already indicated, is in general northeast-south- west. Accordingly, the topographic areas developed from these formations trend in a northeast-southwest direction across the county. In addition to topographic divisions dependent upon the surface outcropping of the formations, there is in this county a large development of flood plain stream deposits. These plains, some of which are extensive in area, cut across and cover over the successive formations, concealing the surface features that otherwise would have characterized the outcropping of the underlying rocks. The formations to which it is necessary to refer in this discussion of topography are more fully described in the section on Geology. They include formations of the Cre- taceous and Cenozoic systems. The surface drainage in Bexar County is to the south or south- east in the direction of average surface slope. The maximum elevation is at the northern part of the county and approximates or exceeds 1500 feet above sea level, while near the southern boundary of the county the elevation is 500 or 600 feet above sea level. The principal stream is the San Antonio Riverf which heads in this county and flows southeast to the Gulf at San Antonio Bay. Among smaller streams in the county, all of which flow directly or indirectly into the San Antonio River, are the Geology and Mineral Resources of Bexar County 13 following : Medina, Medio, Leon, Helotes, Salado, and Calaveras. Rio Cibolo forms a part of the northern and eastern boundaries of the county. With the exception of the San Antonio River and Salado Creek, which are supplied by large springs, all of these streams are in at least a part of their course intermittent, flowing for only a short time following rains. CLIMATE AND RAINFALL Bexar County is intermediate in location between the arid southwest and the much more moist climate of the Coastal Plains. The following data on temperature and rainfall are taken from reports of the United States Weather Bureau, and are based on the records from 1885 to 1903. The annual mean temperature at San Antonio as obtained from these records is 69 degrees F. The mean for the four seasons of the year is as follows: winter, 54; spring, 69; summer, 82; fall, 70. The maximum summer heat recorded within this period is 106 degrees F. The minimum winter temperature recorded is 4 degrees F. The annual mean rainfall for the same interval was 28.4 inches. This is distributed throughout the year on an average as follows: January, 1.7; February, 1.9; March, 1.8, April, 2.9; May 3.0; June, 2.7; July 2.6; August, 3.1; September, 3.4; October, 1.8; November, 1.8; December, 1.7. BALCONES ESCARPMENT A prominent topographic feature in this county, already re- ferred to, is the Balcones Escarpment which passes through the county in a northeast-southwest direction. To the northwest of this escarpment, the country is high, and in this county hilly; but to the southeast the land, although in places hilly; is on the average much lower in elevation, including also a larger amount of level land and flood plains. This escarpment enters the county at the west boundary a few miles north of the Culebra Road, and leaves at the big bend of the Cibolo in the northeast corner of the county. The hills of this escarpment are entered on the Bandera Road 18 miles from San Antonio; on the Fredericks- 14 University of Texas Bulletin burg Road, 16 miles; on tbe Blanco Road, 18 miles; and on tlie Bulverde Road, about 21 miles from San Antonio. This escarpment indicates the location of the first largo faults and dips of the Balcones fault zone. In the western part of Bexar County the escarpment is abrupt. In the eastern part of the county on the other hand the escarpment is not so pro- nounced, the Edwards Plateau rising more gradually from the lowlands. These differences in topography which indicate dif- ferences in the amount of faulting are more fully discussed in the section on structural geology. MINOR PHYSIOGRAPHIC DIVISIONS Several well characterized minor physiographic divisions are recognized in this county. These areas for the most part form belts which trend with the formations from which they are derived in a general northeast-southwest direction through the county. The names applied to these minor divisions indicate the formations from which they are chiefly derived. The loca- tion of these divisions is indicated on the sketch map (Fig. 2). The Glenrose Hills: That part of the county northwest of the Balcones Escarpment, forming the eastern margin of the Edwards Plateau, may be known as the Glenrose hills. The underlying formation, the Glenrose, has here been cut into by the headwaters of many small streams forming steep sloping hills and rock-filled stream channels. This formation includes alternating hard and soft layers which weather on the slopes to a succession of small benches giving the hillsides a characteristic terraced appearance. Each terrace or bench is as a rule small, corresponding to soft layers of from one to a few feet in thick- ness. The slopes thus come to present the appearance of having been cultivated, the rows of planting having seemingly followed the contours of the hill. The vegetation in this area is chiefly low trees and shrubs. The predominating small tree is the mountain cedar or juniper, although in addition there are many small oak and other shrubby trees. The maximum elevation in this area, which is also the maximum for the county, is perhaps somewhat more than 1500 feet above sea level. The range in Geology and Mineral Resources of Bexar County 15 elevation from the higher hills to the stream valleys is from 200 to 300 feet. The Edwards Flint Hills : Adjoining the Glenrose hills on the southeast is a belt of hilly country in which flint rock is ex- tremely abundant in the soils and surface debris. This area stands at a somewhat lower level than the Glenrose Hills. The / Fig. 2. — Sketch map to show the minor physiography divisions in Bexar County. prevailing rock is the Edwards limestone from wdiich the flints have been derived by weathering. The timber growth of this area is juniper and small oaks. The soils, especially those derived from the flinty phases of the limestone, are often red, 16 University of Texas Bulletin and the belt is known locally as the “red lands”. The area forms a narrow belt lying next to and southeast of the Balcones Escarpment. Near the west boundary of the county this belt narrows to such an extent as not to be appreciable. In the central and eastern part of the county, on the other hand, it enlarges to a belt of three or four miles in width, being approx- imately coincident with the surface exposures of the Edwards formation as indicated on the geologic map. The Peter Clausen ranch in the northeastern part of the county lies very largely within this belt. The Del Rio Plain: The soft materials of the Del Rio forma- tion, chiefly clays, weather rapidly when exposed at the surface, and the outcropping belt of this formation is repre- sented in the surface features by a valley or low plain. Lateral streams frequently follow the strike of this formation and for that reason the plain developed from this formation is fre- quently merged with or obscured by stream terrace deposits. At both the west and east boundaries of Bexar County the clays of this formation have but a limited surface outcropping and the plain developed from them is inconspicuous. In the central part of the county, however, particularly on the Bab- cock and Fredericksburg roads, the belt of exposures of this clay is much widened, representing here successive exposures of this formation, interrupted by occasional belts of exposures of the Buda limestine. The predominating timber growth on the Del Rio Plain is mesquite, while the intervening Buda limestone belts are characterized by a heavy growth of live oak. This belt is crossed on the Fredericksburg Road from 10 to 15 miles from San Antonio. The Austin Hills: In the central part of Bexar County are some belts of prominent hills trending northeast-southwest. These hills are conspicuous because of a heavy growth of live oak trees thus differing on the one hand from the prevailing mesquite growth of the plains, and on the other from the juniper of the hills of the Balcones Escarpment. These hills mark the outcropping belts of the hard rock or basal phase of the Austin formation, combined in some instances with the Buda and Eagle Ford formations. There are several of these belts of hills representing successive or repeated exposures of Geology and Mineral Resources of Bexar County 17 this phase of the formation. When followed to the southwest, these belts of hills are found to terminate, giving place to lower, mesquit.e-covered land. This limitation in this direction is due to the southwest plunge of the structures, as sub- sequently explained, by which this phase of the Austin forma- tion is carried below surface level. One belt of these hills in western Bexar County is seen lying between the C’astroville and Culebra roads. To the southwest, this belt of hills narrows and terminates in Medina County. To the northeast, on the other hand, the belt widens and forms the broad belt of hills of the west-central part of the county, entered on the Fredericksburg road about eight miles from San Antonio. A second belt of similar hills, originating near San Pedro Park in San Antonio, passes to the northeast. These hills, which approximately parallel the San Antonio- Austin Road, are crossed by the Perin-Beitel Road from Fratt to Wetmore. The Taylor-Navarro Plain: The relatively non-resistant strata of the late Cretaceous, including the upper part of the Austin and the Taylor and Navarro formations, form extensive plains. Much of this plain has subsequently become covered with terrace gravel deposits, and in places has been much cut into by stream erosion. However, it may be regarded as a single plain known as the Taylor-Navarro Plain. When not in- fluenced by terrace gravel deposits, the soils on this plain are black and in wet weather very sticky. The predominating timber growth is mesquite. This type of country includes a wide belt passing through the central part of the county. In addition to this main belt there are finger-like extensions of this plain to the northeast, lying between ranges of Austin Hills. One such extension of the plain is followed by the International and Great Northern Railroad from San Antonio. Another notable northeastward extension from the large plain is at the west side of the county on and near the Culebra Road. The plain is here gravel-covered, but is without doubt underlain, as indicated by well records, by the Taylor forma- tion. On the northwest the plain is limited by the foothills of the Balcones Escarpment where exposures are found of the Austin and older formations. To the southeast the plain ex- 2-Bex. 18 University of Texas Bulletin tends to the range of Austin Hills already referred to. When followed to the northeast the plain narrows and terminates within a few miles of Helotes Creek. To the southwest, on the other hand, it broadens and in Medina County coalesces with the larger plain beyond the termination of the belt of Austin Hills. The Midway -Wilcox Hills: The areas underlain by the Ter- tiary formations in this county are characterized by more sandy soils than those of the Cretaceous areas. The belt of country underlain by the Midway and Wilcox formations includes low hills together with areas of level lands. The predominating timber growth is mesquite. The soils derived from the Mid- way formation are brown or dark in color, while those from the Wilcox are distinctly sandy and frequently are red in color. The Carrizo Sand Hills : The surface exposures of the Car- rizo formation are characterized by low hills and very sandy soils. The vegetation on the hills is chiefly deciduous oaks. In Bexar County the sand hills of this belt occupy a limited area in the southern part of the county. Stream Terrace Plains : A prominent feature of the Coastal Plains part of the county is the river flood plains. These stream deposits are of different ages, from Pliocene or early Pleistocene to Recent. They are found likewise at different levels, and many of them have been cut into by erosion. Some of the larger plains are those on which Kelly and Brooks aviation fields are located. These plains are described in connection with the discussion of the Pleistocene geology. Geology and Mineral Resources of Bexar County 19 STRATIGRAPHIC GEOLOGY. The formations exposed at the surface in Bexar County are those of the Mesozoic and Cenozoic eras. The Mesozoic rocks of this county are those of the Lower and Upper Cretaceous (Comanchean and Cretaceous systems), this division of geo- logic time being well represented. The Cenozoic deposits are those of the Eocene, together with terrace deposits of the Pleistocene. For convenience of reference the formations found in the county are listed in the table which follows. Al- though not exposed at the surface, pre-Cretaceous formations are reached by deep wells in the northern part of Bexar County. PRE-CRETACEOUS Two of the wells of Bexar County of which records have been obtained have passed entirely through the Cretaceous formations and into older deposits. Of these two wells one is located on the Leon Springs Reservation north of the Balcones fault zone, while the other is on the Camp Bullis Reservation a few miles south of the first fault of that zone. Both wells were drilled in an effort to obtain an adequate water supply for the Leon Springs Government reservation, and in each of the wells the rocks lying next below the Cretaceous were found to be schists. In the well north of the Balcones fault zone the schists below the Comanchean formation were entered at about 1015 feet below the surface and were pene- trated 1500 feet, or to the total depth below the surface of 2500 feet. Among pebbles from the basal part of the Coman- chean in this well, Dr. J. A. Udden, who has studied the cuttings, recognizes pebbles resembling fragments of the Hickory formation of the Central Mineral region; also a few flint pebbles, dark in color and laminated like pebbles from the Bend series. With regard to the schists, he says, “Samples 45 to 49 inclusive (representing cuttings from the schists) are most probably pre-Carboniferous, and in my opinion they are identical with similar material described from below 1100 feet in the boring at Georgetown in Williamson County”. (MSS.) The second well reaching into the pre-Cretaceous, on the Camp Bullis Reservation, is south of the Balcones Escarpment and within the fault zone. In this well the schists were reached at the depth of 1790 feet and were penetrated 115 feet, or to the total depth below the surface of 1905 feet. With regard to the schists of this well, Dr. Udden, who has examined 20 University of Texas Bulletin TABLE OF GEOLOGIC FORMATIONS IN BEXAR COUNTY. Formation name Thick- ness o ‘o N o Pleistocene Flood- plain deposits 100-+- fl CD O Eocene Carrizo Wilcox Midway ? 600 -f- 200-t- Upper Cretaceous Navarro Taylor Austin Eagleford 450-+- 450-f- 350 35 W d o Washita Buda Del Rio Georgetown 65 70 50-f- Mesozoic • dS CD Fredericks- burg ! Edwards Comanche Peak 450 —f— 9 i a o D Trinity Glenrose Travis Peak 800-+- 1200 —|— Fig. 3. Table of Geologic formations together with graphic representa- tion of the Columnar section. Ktp, Travis Peak; Kgr, Glenrose; Ke, Edwards including Georgetown; Kdr, Del Rio; Kba, Buda; Kef, Eagleford; Ka, Austin Chalk; Kt. Taylor; Kn, Navarro; Em, Midway; Ew, Wilcox; PI, Pleistocene. Geology and Mineral Resources of Bexar County 21 the samples, states that the formation represented is probably the Packsaddle Schists of the Central Mineral Region. (Mss.) The logs of these two ^ells are given in the section on well records. How far to the east from the Balcones Escarpment these schists lie immediately below the Comanchean formations can be determined only by subsequent drilling. The fact that the schists have been found under the Comanchean at George- town and at San Antonio indicates that they underlie those formations through a considerable north and south distance along the Balcones fault zone. MESOZOIC COMANCHEAN CRETACEOUS The formations of the Comanchean series in this county are shown in the table on page 20. They are included on the Trinity, Fredericksburg and Washita divisions as there indicated. TRAVIS PEAK FORMATION The term Travis Peak formation has been applied by Hill to the lowermost rocks of the Cretaceous of south-central Texas. This formation represents in part at least the Trinity or Base- ment sands of northern Texas. Although not exposed at the surface, the Travis Peak formation is reached by some of the deep wells in the northern and north-central parts of the county. Records have been obtained of about six wells in the county which pass into or through this formation. The well of R. Mercke at Bulverde on the Cibolo River at the north line of the county, is reported by Hill and Vaughan* as reaching a depth of 361 feet. The surface exposure at this locality is the Glenrose formation, and on the basis of the log, Hill and Vaughan have regarded this formation as extending to the depth of 137 feet. From 147 feet to the bottom of the well, 361 feet, the formation is identified by them as Travis Peak. A well drilled on the Leon Springs Reservation in this county in 1909, starting in the Glenrose formation, passed entirely through the Travis Peak formation and into underlying schists. Samples of the cuttings from the well were submitted to the *18th Ann. Rept., pt. 2, U. S. Geol. Surv., p. 272, 1898. 22 University of Texas Bulletin Bureau of Economic Geology and were examined by Dr. J. A. Udden. A log of the well and supplementary data were sent to the Bureau by Mr. Alexander Deussen. The record from this well, which is of especial importance in determining the thick- ness of the Glenrose and Travis Peak formations, is given on a later page. Prom the surface to the depth of 1025 feet, the cuttings from this well are identified by Dr. Udden as Coman- chean. Mr. Alexander Deussen has assigned the strata from 535 feet to 1015 feet to the Travis Peak, . indicating for the formation a thickness of about 480 feet. The third well passing into this formation is also a Gov- ernment well located on the Camp Bullis Reservation, six miles south and one-half mile east of the well on the Leon Springs Reservation. In this well the combined thickness of the Glenrose and Travis Peak formations, including Basement sand, amounts to between 1200 and 1300 feet. A fourth well believed to enter or pass through the Travis Peak formation was drilled on the Waring Estate near the Bandera Road, seven and one-half miles northwest of San Antonio. Of this well there is preserved the driller’s log, but unfortunately no samples of the cuttings. A blue print record of the log of the well has been obtained from the Con- structing Quartermaster’s office at Fort Sam Houston. The data for the log were preserved and the blue print record made at the time the well was drilled by Mr. F. A. Gartner. In this well the Comanchean formations were entered at 400 feet from the surface. The well was drilled to the depth of 2853 feet, thus penetrating 2453 feet of Comanchean or older sediments. The Ridder well on the Medina River southwest of San An- tonio and the Kearney Pipe Line and Oil Company well south of Leon Creek, record of which is subsequently given, probably terminate in the Travis Peak formation. As indicated by the drillers’ logs and more particularly by the cutings from these wells, the Travis Peak formation under- lying Bexar County includes layers of limestone alternating with softer layers, chiefly of marly clays. The limestones, as indicated by the well on the Leon Springs Reservation, in- clude both ordinary and dolomitic layers, while the marly clays frequently contain pyrite. A phase of this formation is recorded in the logs as “red mud” or “red clay”. The samples of cuttings seem to indicate that the layers so recorded include Geology and Mineral Resources of Bexar County 23 rather soft calcareous clays or marls with, in some instances, a calcareous and • ferruginous cement, together with fine sands or silts. As this formation lies unconformably on the pre-Cretaceous, its thickness may be expected to vary exceedingly. Of the structure and rate of dip of the formation, very little can be determined from the scanty records now available. North of the Balcones fault zone it is to be expected that the formation will conform to the Glenrose and have a similar moderate southeast dip. In that part of the county within and east of the Balcones fault zone, it is to be expected that this forma- tion shares in the disturbed conditions common to the other formations of that belt, which are more fully described else- where. GLENROSE FORMATION The Glenrose formation of the Lower Cretaceous (Comanchean) age, is the oldest of the formations exposed at the surface in this county. This formation includes chiefly alternating layers of moderately hard and soft rocks. The harder ledges are chiefly limestone, as this formation contains almost no flint. Some of the limestone layers are fine-grained and quite hard, although as a rule the limestones of this formation are of but medium hardness. The marl layers of the formation are usually thin, being from a few inches to one or two feet thick, and rather soft. At the surface the marl layers, like the limestone ledges, are usually yellow. When buried within the earth, they may be at times gray or blue. The formation may usually be recognized by the characteristic succession of hard and soft strata, although in places the formation is more heavily bedded. Occasionally also, the heavy limestone ledges are honey-combed and under these conditions resemble the non-flinty ledges of the overlying Edwards formation. The examination of any considerable sec- tion, however, will usually afford a basis for separation from the Edwards formation. The marls of this formation have been used in road-making on some of the roads passing through this area where other ma- terials are not readily available. The calcium sulphate mineral, celestite, is occasionally found filling cavities in this formation, 24 University of Texas Bulletin and has been mined to a limited extent near Austin, in Travis County. The' sub-surface layers of the formation produce mod- erate supplies of water, and many of the wells yielding moderate supplies north of the Balcones fault zone terminate in this formation. Thickness : The fact that the base of the Glenrose formation is nowhere exposed in this county makes it impossible to measure the thickness of the formation from surface exposures. By combining surface exposures and well records, however, it is possible to determine the thickness of this formation probably within reasonably close limits. Perhaps the most trustworthy measurement of the thickness of the formation in this county is that obtained on the Leon Springs Military Reservation. In the deep well on the reservation, as already noted, the Glenrose is regarded as extending from the surface to a depth of 535 feet. In the hills near the well, the Edwards limestone is pro- visionally identified as coming into the section at about the 1420 foot level. The ground level at the well is about 1156 feet above sea level. Hence to the 535 feet of this formation penetrated in the well must be added between 265 and 315 feet exposed at the surface, making a total thickness for this formation of about 800 feet. This measurement, however, may include the equiva- lent of the Walnut clays and the Comanchean Peak limestone; which, however, are of limited development in this county. Physiographic expression: The alternately hard and soft strata of this formation gave rise in the early literature to the term ‘ ‘ alternating beds” as applied to the formation. This suc- cession of hard and soft layers occasions the characteristic ter- raced appearance already referred to as distinguishing the Glen- rose Hills. Common fossils: Among the fossils found in considerable abundance in the Glenrose, the most frequently met with are the gastropod Lunatia ( Tylostoma ) pedernalis and the bivalve Cyprinaf mediate. Neither of these, however, is confined to the Glenrose since both are found likewise in the Travis Peak forma- tion. COMANCHE PEAK FORMATION The Comanche Peak limestone has not been differentiated as Geology and Mineral Resources of Bexar County 25 a formation in this county, and in the mapping and in the measurement of sections it is included either with the Glenrose or with the Edwards. According to Hill and Vaughan this formation is present in the Austin quadrangle to the northeast of this county and likewise in the Uvalde quadrangle to the southwest, where it is a nodular, somewhat massive limestone, containing the oyster Exogyra texana. In these quadrangles the formation has a thickness of from 50 to 60 feet. Hence, although not yet differentiated, it is probably present also in Bexar County. EDWARDS FORMATION The Edwards formation consists chiefly of limestones. The rock of the formation as developed in this county is usually coarsely crystalline, although in this respect it is variable, some parts of the formation being particularly dense and of fine texture, approaching a lithographic stone in structure. Fre- quently both on surface exposures and deep within the earth, as indicated by well borings, the formation is profoundly honey- combed and cavernous. These openings in the rock, where ex- posed in quarrying the limestone, follow more or less the bedding planes and joint planes of the formation. The Edwards forma- tion is especially characterized by a great abundance of flints enclosed within the limestone. These flints are in the form of layers which lie parallel with the bedding planes, or replace for a considerable space the limestone layers of the formation. Some of the flint, however, is in the form of nodules, oval or flattened masses, or so-called “boulders” in the limestone. Upon the disintegration of the limestone, the flints remain on the surface in great profusion. Usually the Edwards limestone may be recognized by the presence of these flint masses both in the rock when seen in place, and in the residue. The soils derived from the flinty phase of the Edwards formation are prevailingly red, and the belt of country occupied is referred to locally as the “red lands.” In parts of this formation, however, the flints are less abundant and exposures may frequently be met with in which no flints are observed. In the absence of fossils some difficulty may be experienced in separating such exposures from 26 University of Texas Bulletin the hard phases of the Glenrcse on the one hand, and the Buda on the other. If in such exposures the texture is found to be coarsely crystalline, the rock may be quite definitely separated from the Buda, which never presents this appearance in this county. If, on the other hand, the rock is close-grained, dense and of fine texture, the separation from the Buda can perhaps be safely made only on the fauna. . Aside from the flint masses which it -contains, the Edwards limestone is for the most part a very pure calcium carbonate. It is also, as previously noted, a very dense, hard, partly crys- tallized limestone. These characteristics make it valuable for a number of purposes. Several quarries have been opened in this formation in Bexar County for the manufacture of lime. Bock from this formation is taken from a quarry at Beckman for use as rip-rap in Government work on the harbors of the Gulf coast. The hard, dense rock of the Edwards formation, when crushed, should afford material favorable for concrete, although so far as observed no part of the formation is being so used at the present time, owing perhaps to the abundance of concrete ma- terial in this county. This rock should be of service also in road-building. Upon partial decay the rock in places assumes a soft, spongy appearance/ This form of the rock has been used in road-building on the Bulverde and Blanco roads. Thickness : A full measure of the thickness of the Edwards formation has not been obtained from surface exposures in this county, but from well records the thickness of the formation is estimated to be between 400 and 500 feet. Physiographic Expression: The belt of country occupied by the Edwards formation is moderately to distinctly hilly, although in places there are areas of relatively level lands. The native vegetation is chiefly juniper and small oaks, including in places a limited amount of mesquite. The surface materials from the formation, as already noted, contain quantities of flint. The soils, especially those derived from the flinty phases of the formation, are characteristically red in color. The soil supports a good growth of grass and these lands form desirable ranch lands and are used chiefly for this purpose. Common fossils : Although not always abundant, several of Geology and Mineral Resources of Bexar County 27 the fossils of the Edwards formation are very unusual in ap- pearance. This is true in particular of the bizarre mollusks of the genera Radiolites, Monopleura , and Requienia. Surface exposures and local details: The surface exposures of the Edwards limestone form a belt varying in width, lying immediately south of the Glenrose area and hence at the north- ern margin of the Balcones fault zone. This belt is widest at the eastern margin of the county and narrows towards the west. Where crossed by the Bulverde Road, in the eastern part of the county, this belt of the Edwards formation, including possibly the Georgetown; has a width of over live miles. On the Blanco Road the belt is somewhat narrowed. At the Fredericksburg and Babcock road-crossing, the belt is further narrowed, and at the Bandera Road crossing has a width not exceeding one-half mile. At the pit of the San Antonio Lime Company, on the Fred- ericksburg Road 16 miles from San Antonio, the limestones of the Edwards formation are well stratified, consisting of layers of hard rock varying from a few inches to four or live feet in thickness. Some layers of the rock contain numerous small cavities produced by ground water. Flint layers are present usually lying parallel with the bedding planes, although flint concretions are seen, and occasionally flint deposits are found filling joint planes. The solution cavities . also are more or less lined with silica. The limestone rock is heavy and upon close examination is seen to be in places minutely banded. The right bank of Helotes Creek below the Bandera Road crossing affords a good exposure of this formation. The creek here follows on or near the main fault line separating the Glen- rose and the Edwards formations. GEORGETOWN FORMATION Lithologically the Georgetown formation if present in this area is very similar to the Edwards, and in the mapping and columnar section these formations are not separated. This treatment of the two formations has seemed the more necessary since in well logs there is almost no opportunity to separate them. An exposure which probably represents the Georgetown is seen on the Bandera Road, 17 miles from San Antonio. The 28 University of Texas Bulletin limestone’ rock exposed here, lying immediately below the Del Rio clay, is a very hard, close-grained rock, containing little or no flint. In the eastern part of the connty a similar rock is seen lying below the Del Rio on the Peter Clansen ranch, 1 y 2 mile north of the Nacogdoches Road. The Georgetown formation in the Colorado River section is reported to have a thickness of from 65 to 70 or 80 feet. In the Uvalde folio the formation is estimated by Yanghan to have possibly a thickness of 40 feet. These two formations, the Edwards and Georgetown, are of special economic importance in this connty as the chief large water-bearing formations of the area. DEL RIO FORMATION The Del Rio formation consists largely of clays which on surface exposure are usually yellow, but when encountered below the surface are usually blue in color. The clays of this formation contain in places great numbers of fossils, especially of the small oyster Exogyra arietina. Occasionally these shells are cemented together by calcareous or ferruginous cement forming indurated layers within the clay beds. The formation contains more or less iron sulphide as pyrite and in well cuttings the amount of pyrite is not infrequently found to be considerable. On the surface exposures gypsum in small quantities is not in- frequently observed in the clay. Thickness: No surface exposure has been found in this county in which the whole thickness of this formation can be measured. In the records of wells, however, the formation is quite uniformly reported as having a thickness of from 50 to 70 feet. Rarely does the reported thickness of the formation fall below or rise above these limits. In Bexar County this formation is quite generally known to the well drillers as the “mud hole” or the “second mnd”, cr the “big mud”. These names have origi- nated because of the character and position of the formation. It is known as the “mud hole” because the clay when churned up by the drill becomes mud. The term “second mud” is sometimes applied to it because a formation at a higher level, the Eagle- ford, frequently contains enough clay to cause cable tools to stick, and hence gives the formation the character of mud. The Geology and Mineral Resources of Bexar County 29 origin of the term ‘‘big mud” is similar. As the Del Rio forma- tion has a thickness of from 50 to 70 feet while the clayey phase of the Eagleford rarely exceeds 30 to 35 feet, the Del Rio has come come to be known as the “big mud”. Physiographic expression: The Del Rio formation, being chiefly a relatively non-resistant clay lying between relatively resistant limestones '(the. Georgetown-Edwards series below and the Buda limestone above), is found as a rule on surface ex- posures to occupy a valley, or the abrupt slope from an upland to the valley. The soils derived from this formation are black or brownish in color. The timber growth is chiefly mesquite, and frequently the Del Rio outcrop when in a valley may be followed by the dense growth of mesquite, differing in this respect from the mixed growth of timber, chiefly oak and juniper, found on the hard phases of the limestone formations. Common fossils : As already noted, the small oyster, Exogyra arietina , is a very characteristic index fossil of this formation, and its stratigraphic equivalents. This fossil is particularly abundant in the lower part of the formation. Near the top the deposits become relatively unfossiliferous. A fossil occasionally found in the upper part of the formation is the oyster, Gryphea mucronata. Lithologically, the beds change somewhat towards its upper limit, becoming more calcareous and including in places shelly lime rock. Near the contact with the Buda is seen occa- sionally a soft, light-colored phase of the formation superficially resembling in a degree the partially disintegrated phases of the Eagleford formation. Surface exposures and local details : The surface exposures of the Del Rio formation are found throughout a belt of country next south of the exposure of the Georgetown-Edwards forma- tions. The formation being thin, this belt of surface outcropping is relatively narrow, usually not exceeding a half mile. There are, however, some localities where the belt of surface exposures of this formation is widened, owing to minor faulting, which brings the formation successively to the surface. This belt of minor faulting is crossed on the Fredericksburg Road from 10.2 to 13.2 miles from San Antonio, and on the Babcock Road from 12 to 15 miles from San Antonio. Within this belt on the Fred- 30 University of Texas Bulletin ericksburg Road, owing to a combination of faulting and folding together with variations in surface level, the Del Rio formation shows itself in five successive belts as follows: First belt, from 10.2 to 10.3 miles from San Antonio; second belt, from 10.5 to 10.7 ; third belt, from 11.4 to 11.6 ; fourth belt, from 11.9 to 12.3 ; fifth belt, from 12.7 to 13.2 miles. On the Babcock Road, suc- cessive belts of this formation come in as follows : First belt, 12.05 to 12.1 miles from San Antonio; second belt, 12.4 -to 12.5; third belt, 12.6 to 12.7 ; fourth belt, 12.8 to 12.85 ; fifth belt, Valley of Leon Creek probably occupied chiefly by this forma- tion, about 13 to 13.5 miles. The formations alternating with the Del Rio in these ex- posures are the underlying Georgetown-Edwards and the over- lying Buda, including the Eagleford and a part of the Austin. As already stated, the successive exposures of the formation are due in part to faulting and in part to changes in the surface elevation. East of the Leon Springs Reservation in this county and also west of the . Bandera Road, this formation so far as observed appears as but a single belt with usually but few actual surface exposures. On the Blanco Road the belt is crossed, without any observed exposures immediately on the road, at about 12 miles from San Antonio. On the Bulverde Road, the Buda formation is well exposed at the foot of a north-sloping hill 13.5 miles from San Antonio. Although no exposures of the Del Rio clays are seen on the road, this formation may be expected to occupy the valley at the foot of this hill and to extend to the limestone hills which begin on this road at about 13 miles from San An- tonio. To the east of the Bulverde road the Del Rio formation has not been traced in detail, but is to be expected as a rela- tively narrow belt extending as mapped in a general northeast- ward direction to the county line at the Cibolo River. Near the county line an exposure is seen at a water-tank on the Clausen Ranch, 1% miles north of the Nacogdoches Road crossing of the Cibolo River. West of the Bandera Road exposures of this formation continue for two or three miles, beyond which the belt narrows and the formation in places is faulted out of sight. The Del Rio formation is extensively used in its belt of sur- Geology and Mineral Resources of Bexar County 31 face outcropping in the construction of ponds. On the Bandera Road a pond made from this formation is seen near Helotes Creek 17 miles from San Antonio. The clays of the formation are utilized in making a pond on the Clausen ranch, near' the east county line, 1^2 miles north of the Nacogdoches Road. At these localities the small fossil Exogyra arietina is extremely abundant. BUDA FORMATION I The Buda formation as developed in this county is quite uniformly a close-grained, dense, hard limestone. On surface exposures this rock is usually light-colored, or tinged with gray, yellow, or blue. As seen in well cuttings, the limestone is usually of light color, although a part of the formation fre- quently shows as a blue rock; Black specks in the limestone is a characteristic frequently referred to by drillers in describing the cuttings from wells. The change in sedimentation from the Del Rio to the Buda and from the Buda to the Eagleford formations appears to have been abrupt, there being little or no gradation between the formations. The hard limstone of the Buda formation lying between the softer rocks of the Del Rio and Eagleford forms a horizon both conspicuous and readily followed on the surface. The Buda limestone in this county is but little utilized at the present time. Its hardness and close texture indicate that as here developed the limestone would be suitable for concrete material. Thickness: Both in lithologic characteristics and in thickness the Buda formation is perhaps the least variable of the Creta- ceous formations as developed in this county. Well records indi- cate that the Buda limestone is here quite uniformly between 55 and 65 feet thick. Rarely is the formation reported to vary beyond these limits. Physiographic expression : In its surface exp'osures the Buda limestone appears as hard, thickly bedded rock. The surface is frequently rough owing to partial dissolution through the agency of surface waters. The soils derived from the formation are dark colored and usually relatively thin, including many rock fragments. When found capping hills the soils from the Buda 32 University of Texas Bulletin formation support a rather heavy growth of timber made up chiefly of oaks. In this respect, the Buda formation resembles the hard rock phases of the Austin formation. Common fossils: The Buda limestone on surface exposures; is usually found to contain fossils, sometimes in considerable num- ber. The shells of invertebrates have, however, for the most part been replaced or filled with a mineral deposit, probably usually calcite. Hence the fossils are seldom easily removed from the matrix, and are with difficulty used in identifying the formation. Thin sections of the rock have shown that in this formation are found numbers of foraminifera.* Lithologically the formation may be in a measure recognized by its uniformly close-grained*, dense structure, although similar dense masses of rock are found also at places in the Georgetown and Edwards formations, and less distinctly so in the hard rock phases of the Austin formation. The position of the Buda limestone, lying between the lithologically very different Del Rio and Eagleford formations, assists materially in locating this formation on sur- face exposures and in well drillings determines its position definitely. Surface exposures and local details : The Buda formation in Bexar County comes to the surface in a relatively narrow belt having a general northeast-southwest trend. On the Bulverde Road the rocks of this formation are exposed near the base of a north-sloping hill about 13.5 miles from San Antonio. The for- mation here dips into the hill under the Eagleford and Austin formations, the belt of exposed rock being narrow. So far as observed the rocks of the Buda are not again exposed on this road. To the east of the road the line of outcropping of this formation has not been traced in detail although it is known to continue in a general northeast direction to the county line. A small anticline in this formation is observed at the Salado Creek crossing of the Blanco Road. Just above this crossing as much as 35 or 40 feet of the Buda formation is exposed in the right bank of the stream. Downstream the Buda disappears be- neath the Eagleford and Austin formations within about one- fourth mile below the road crossing. When followed upstream *U. S. Geol. Surv., 18th. An. Rpt. pt. 2, p. 228, 1898. Geology and Mineral Resources of Bexar County 33 the rocks of the Buda formation are found likewise to dip below the stream level, giving place to the Eagleford and Austin formations in the stream banks. However, the Buda reappears in this stream within about three-fourths or one mile further upstream, indicating a relatively limited development of the v/est slope of the anticline. On the Blanco Road the Buda is exposed at the Salado Creek crossing, and again between eleven and one- half and twelve miles from San Antonio. On the Fredericksburg and Babcock roads the Buda formation is found to share in the minor faulting which, as already men- tioned, brings these thinner formations repeatedly to the surface. On the Fredericksburg Road the Buda formation is first met with lying below the Eagleford formation a short distance beyond the Lockhill-Selma Cross-road, about 10.1 miles from San Antonio. It is last seen on this road at the Bacon Ranch cross- road, 12.7 miles from San Antonio. On the Babcock road the formation appears at intervals from 12 to 12.9 miles from San Antonio. On both of these roads this formation alternates by changes in surface elevation and by faulting with the Del Rio and other formations. The belt of Buda exposures may be seen at intervals as far west as the Hoffman Ranch, about three miles west of Helotes Creek. Beyond this place the belt of Buda exposures narrows and the formation shows but limited exposures to the Medina County line. The place of the formation below the surface is recorded in well records throughout most of the central part of the county. From its surface exposures the formation dips with variations due to faulting and folding toward the south and southeast. At the northern limits of the city of San Antonio this formation may be expected at from 300 to 350 feet beneath the surface, depending upon variations in surface elevation. At the southern city limits, six miles farther south, owing to steep dips and faults, this formation lies much deeper and is there encountered in well drilling at between 1200 and 1300 feet. A few miles farther south, near the Chavanneux Cross-road, it is found by well drilling to be buried to a depth of 1600 or 1700 feet. 3-Bex. 34 University of Texas Bulletin UPPER CRETACEOUS The Upper Cretaceous series is well represented in the Bexar County section. The formations in order, beginning with the oldest, are: Eagleford, Austin, Taylor and Navarro. EAGLEPOBD FORMATION The Eagleford formation as developed in Bexar County includes a very characteristic series of calcareous and more or less sandy shales. The rock is granular in appearance, and breaks horizontally into thin slabs, giving a flaggy appearance. With this light-colored flaggy rock are found frequently layers of much harder indurated clay-lime rocks. These interpolated layers frequently have a thickness of from one-half to one foot or more and are probably continuous over considerable areas. The formation is to some extent bituminous and when encoun- tered in drilling is frequently of a dark color. It also contains sufficient clay material in parts of the formation to cause the tools to stick more or less in drilling. For this reason the forma- tion is sometimes known to the drillers as the “first mud” (the Del Bio formation being the “second mud”). To most of the drillers in the central part of Bexar County this formation is known as the “lignite”. This name, although scarcely justified by the characteristics of the formation, is firmly fixfed in the nomenclature of the drillers of this county. It is not to be con- fused, however, with the true lignite deposits which are found in much later formations (Tertiary) not represented in the central and northern parts of the county. Thickness: The Eagleford formation is relatively thin in Bexar County. Practically all well records place the thickness of this formation at from 30 to 35 feet. In a few records this thickness is exceeded slightly, while in others the thickness is recorded as less, the formation being recorded as absent in a few wells. With regard to the reported absence of the formation in wells, it is not impossible that occasionally a well is so located with respect to a fault that this formation is missed in drilling. Such would be the case if the well were located at a place where the Austin formation is faulted against the Buda formation. On Geology and Mineral Resources of Bexar County 35 the other hand, the apparent thinness and possibly the supposed absence of the formation may also be due to local induration in the formation so that it is not recognized in drilling. Two ex- posures have been found in the county in which it is believed that the full thickness of this formation is shown. Both of these exposures are on Salado Creek near the Blanco Road crossing, one below and one above the crossing. In these exposures the base of the formation, resting upon the Buda limestone, is defi- nitely limited. The top of the Eagleford where this formation passes into the Austin formation is much less definitely marked. It appeared to the writer, however, that not more than about 30 or 35 feet of the exposure at these localities can be referred to the Eagleford formation. Physiographic expression: The exposures of the Eagleford are scarcely extensive enough to develop well marked topographic features. However, as the formation is softer and less resistant than either the Buda below or the lower part of the Austin above, the formation when exposed on relatively level land is usually represented by a slight although more or less well- marked valley. On steep hill slopes the rocks of this formation, though in themselves characteristic by their lithologic characters, do not notably affect the surface features. Common fossils: Among the characteristic fossils which may be frequently utilized in identifying the Eagleford formation are plant stems and fragments, fish scales and shark’s teeth. As developed in Bexar County, the formation is rather more lacking in plant remains than at some other localities. Fish scales and teeth are occasionally present, although rarely abundant. However, the lithologic characters of this formation are so distinctive that little or no difficulty will be experienced in locating the formation on surface exposures. In well drillings likewise the place of the formation is readily recognized by its place between the Austin and the Buda formations. Surface exposures: As the Eagleford is the. thinnest of the formations recognized in Bexar County, the surface exposures are correspondingly limited. The belt of surface exposures of this formation is closely associated with the belt of exposures of the Buda formation already described. On the Bulverde Road 36 University of Texas Bulletin it is found exposed, as already noted, with and just above the Buda formation at about 13.5 miles from San Antonio. On the Blanco Road are found the exposures of the full thickness of this formation on Salado Creek which have previously been mentioned, and also an exposure in the road on the hill beyond the creek. An isolated exposure of this formation is seen also on a small stream on the Lockhill-Selma Road, slightly south of west of the Blanco Road crossing on Salado Creek. On the Fredericksburg and Babcock roads the formation is first crossed at about 10 and 11 miles respectively from San Antonio. In the western part of the county the formation is found in a narrow belt too limited to map except by exaggeration. Exposures may be seen on Canyon Creek on the Hoffman Ranch, within a few miles of the west boundary line of the county. In its sub-surface position, the Eagleford formation partakes of the general southward dip, passing under the later formations The depth at which it may be expected from the surface may be deduced from the structural contour map accompanying this report, on which the actual level of the top of the Del Rio forma- tion is indicated. The stratigraphic interval from the top of the Del Rio to the base of the Eagleford is about 60 or 65 feet. AUSTIN FORMATION The Austin formation includes a thick deposit of limestone, chalk, and marl. The lower beds of the formation are hard limestones. Higher up the formation passes into a more chalky and as a rule softer phase, while near the top the deposits be- come chalky marls. The formation is stratified and consists in places of alternating harder and softer beds, which on weather- ing give a banded appearance, in some instances not entirely un- like that of some exposures of the Glenrose formation. On sur- face exposures the rocks of this formation are prevailingly creamy yellow, while in sub-surface exposures the rock is either blue, white, or yellow. In drilling, the cuttings from the upper part of this formation, including perhaps one or two hundred feet, as they come to the surface are blue in color and resemble a clay or mud and are in some instances so recorded in the drillers * logs. At lower Geology and Mineral Resources of Bexar County 37 levels the formation is white or yellow in color and is usually somewhat harder than near the top. This phase of the forma- tion is often referred to as the “ Magnesian” rock, although so far as known, it is a calcium carbonate. Beneath the “ magne- sian ” phase of the formation are the harder limestone layers al- ready referred to, often described in well logs as blue, gray, white, or yellow limestones. The chalk rock of the Austin formation is used near San An- tonio in the manufacture of portland cement. The harder lime- stones from the lower part of the formation are used for con- crete. The formation yeilds moderate supplies of water, although frequently containing more or less hydrogen sulphide gas. The oil of the Alta Vista and Mission fields is from this formation. Thickness: The thickness of the Austin formation is difficult of exact measurement either on surface exposures or from well records. No ^locality has been found in the county where the full thickness of the formation can be measured at the surface. On the other hand, in the well logs it is extremely difficult if not impossible to determine the level at which the drill passes from the Taylor to the Austin formation. The most trustworthy measurements of the formation are those obtained from wells known to be located near the contact line on the surface of the Austin and Taylor formations together with data from >vells passing entirely through the whole Upper Cretaceous. Of a number of wells so located, the following may be cited as afford- ing the most trustworthy records available. The average ob- tained from these wells indicates a thickness of between 300 and 400 feet. The Government well at the old target range, now the aviation post, on the Austin Road, 6 miles from San Antonio, is probably located within the belt of Taylor exposures but quite near the Taylor- Austin contact. In the bed of Salado Creek about one mile northeast of the well and at a level approximately 75 feet lower, is an exposure placed by Dr. Stephenson as the probable Taylor-Austin contact. Judging from the surface exposures at the well and from this exposure in the stream bed it is probable that as much as 50 or 75 feet of the deposits at the well are to be referred to the Taylor formation. In this well the base of the Austin was recognized at the depth of 353 feet. 38 University of Texas Bulletin In the log this interval is divided up as follows: “Soil, 2 feet; yellow and blue clay and soft limestone or shale, 218 feet; and chiefly hard limestones, light gray, blue-gray, and white, 133 feet”. On the basis of the data given above, it is probable that between 275 and 300 feet of this interval is to be referred to the Austin formation, representing the full thickness of the forma- tion at that place. A well on the Waring estate near the Bandera Road, 7% miles from San Antonio, is believed to be located within the belt of surface exposures of the Austin formation or with only a thin covering of the Taylor. In this well there is recorded beneath the surface soil and gravel, 145 feet of “blue clay”, and 155 feet of yellow, white, and blue limestones, giving a total of 300 feet, all of which with the possible exception of some clays near the surface is to be referred to the Austin forma- tion. A well drilled at Schertz on the Cibolo River is also near the contact line of the Austin-Taylor 1 formations. A short dis- tance upstream from this well are found surface exposures of the Austin formation, while immediately downstream are ex- posures of the Taylor formation. In this well there are recorded 14 feet of yellow clays, 215 feet of blue clay, and 149 feet of magnesian and other limestones. This would seem to indicate a possible thickness of 378 feet for the Austin. However, upon other data it is suspected that a fault or a very steep dip passes immediately north of this well ; that is between the well and the exposures of the Austin formation. If this is true, only a part of the 229 feet of yellow and blue “clays” of this record is to be referred to the Austin formation. A well at the residence of A. E. Goforth on the Culebra Road, 18 miles northwest of San Antonio, appears to be located near the contact line of the Austin-Taylor formations. In this well the base of the Austin was recognized at the depth of 349 feet, all of which apparently, aside from the surface materials, is to be referred to the Austin formation. From these records it appears that the Austin formation in Bexar County in its belt of surface exposures, approximates 300 feet in thickness. From the record of a considerable number of wells drilled south of the belt of surface exposures it appears probable that the formation thickens toward the south. Among Geology and Mineral Resources of Bexar County 39 the wells which indicate a thickening of the limestones southward are the following : City water supply wells on Market Street in San Antoino, hard rock above the base of the Austin about 380 feet; City water supply 'well near Conception Mission in south San Antonio, magnesian and other limestones, 417 feet, with blue clays above; Hoffheintz well, southwest city limits, mag- nesian and other limestones, exclusive of overlying blue clay, 310 feet; Hill and Roby well, 7 miles south of San Antonio, magnesian and other limestones, exclusive of overlying clay, 480 feet. In the Benke well on the Culebra Road near the west county line, limestone above the Eagleford are reported through an interval of 485 feet, which if referable in full to the Austin, represents the maximum recorded thickness of the formation in the county. With due allowance for the indefinite record afforded by the well logs, it appears that the harder limestones of this formation vary in thickness. In the columnar section the thickness of 350 feet is assigned to the formation, which is probably an average, being neither the maximum nor the mini- mum thickness in the county. Physiographic expression: The Austin formation appears on surface exposures under two different phases corresponding to the hard and soft rocks of the formation. The limestones of the lower part of the formation, when exposed, usually make up ranges of hills having a northeast-southwest trend. On these hills the soils are thin and contain considerable rock debris. The timber growth includes a preponderance of oaks with relatively little mesquite. This phase of the formation where exposed usually forms a conspicuous feature of the landscape and the belt of the hills may often be seen and its trend across the county mapped, at a distance of some miles. The softer rocks of the upper part of the Austin formation, however, present on surface exposures entirely different topographic features. The country underlying the exposures of this part of the formation is usually gently rolling with rounded hills and gentle slopes. The native timber is largely mesquite. The soils are black and at the present time the lands are largely cleared for agricultural purposes. This physiographic development corresponds to the upper 150 or 200 feet of the formation as now delimited. 40 University of Texas Bulletin Common fossils: The Austin formation is highly fossiliferous and a large number of species of marine invertebrates is included in the fauna. Among conspicuously abundant fossils of the lower limestones of the formation are the oysters, Gryphea aucella and Exogyra laeviuscula. These fossils are particularly abundant in certain layers of the limestones of the Austin forma- tion. One of the best exposures showing these fossils is found in the rock quarry near the north side of San Pedro Park where the fossil horizon includes a ledge of rock from one to two feet thick, lying five or six feet above the base of the exposure. A similar fossiliferous ledge appears in the Ling Quarry at the west side of San Antonio River at the north city limits, lying near the base of the exposure. From a well drilled nearby, it is known that the base of the Austin formation at this place lies about 100 feet below the bed of the river, hence unless affected by concealed faulting the horizon of these fossils at this place is between 100 and 125 feet above the base of the formation. A notable exposure of a similar fossiliferous bed of the Austin formation is seen in the bluffs on Leon Creek near the Bandera Road crossing. The upper beds of the formation contain considerable numbers of the large oyster, Exogyra ponderosa* found also in the Taylor formation. This oyster is believed not to extend its range be- low the softer beds of the upper part of the formation, being apparently absent from the hard limestones of the lower beds. This fossil is found in the upper part of the formation at many localities. At the Bandera Road crossing on Leon Creek, the species seems to extend its range downward to the top of the hard limestones of the formation and to within a few feet of the level of the Gryphea bed. Surface exposures and local details: Surface exposures of the Austin formation are found throughout a broad belt having a northeast-southwest trend across this county. The Austin belt is somewhat interrupted in part by surface erosion and in part by terrace deposits, but more especially by faulting and folding *The Exogyra of the Austin formation, according to Bose is specifically distinct from E. ponderosa of the Taylor formation. Univ. Texas Bull., No. 1902, 1919. Geology and Mineral Resources of Bexar County 41 by which other formations are interpolated into the belt of country otherwise occupied chiefly by this formation. On the line across the Austin formation in the eastern part of the county marked by the Bulverde and Perrin-Beitel roads, there are two distinct belts of Austin. The northern belt of Austin exposures is crossed on the Bulverde Road from 1% miles north of Wet- more to Wetmore; the southern belt is crossed on the Perin- Beitel Road from about 1% miles south of Wetmore to Pratt station on the Austin Road. On the Blanco Road extending due north from San Antonio, are likewise found two belts of the Austin formation. On this road, however, the northern belt is found to be much wider than on the Bulverde Road, having a width of about five miles. The southern belt on the other hand is much narrowed, having a width probably of scarcely more than a mile. This southern belt, as indicated in the mapping, passes below the surface within the city of San Antonio, giving place to the Taylor formation. The broad belt of surface exposures of the Austin formation is crossed on the Culebra Road from Leon Creek to about 18% miles from San Antonio. From surface exposures it is known that the Taylor formation lies on this road both at the south- eastern and at the southwestern boundaries of the Austin ex- posures. The evidence relating to structure of these formations is more fully presented subsequently. The high lands of the central part of this belt present surface exposures that on litho- logic characters must be placed as well down in the Austin formation. The Potranca Road which branches off from the Culebra Road at the Leon Creek crossing, and runs slightly south of west, affords for some miles exposures which are prob- ably near the top of the Austin, many of them containing an abundance of Exogyra ponderosa. However, from about Medio Creek to the county line, this road in places affords exposures including the Gryphea zone that are to be referred to the lower half of the Austin formation. In its sub-surface position, this formation presents the char- acteristics of the other formations of this part of the state. In general the dip is to the south or southeast. The southernmost well in this coufity in which the formation has been definitely 42 University of Texas Bulletin recognized, is that on the J. K. Lamb property 16 miles south and 2% miles east of San Antonio. At this place the top of the formation lies approximately 1600 feet below the surface. To the southeast the formation lies somewhat deeper. From the log of the Bradley and Winters well at Saspamco it appears that the formation at the county line on the Goliad Road altho not reached must lie at least 2500 feet from the surface. The rock bluffs and cliffs at the west side of Brackenridge Park in San Antonio are composed of this formation and afford good exposures of the heavy limestones. The Ling rock quarry just across the city limits at the north side of the park, is opened up also in the Austin formation. In a well drilled at the north city limits in Brackenridge Park, in 1918, a log of which is given elsewhere, the Eagleford shales were recognized at the depth of 101 feet. It is thus seen that the exposures iir Brackenridge Park and in the rock quarry north of the park lie within the lower part of the Austin and represent the formation from about 100 to 140 or 150 feet above its base. The rock as seen at these exposures is light-colored or tinged with yellow; it is evenly bedded, consisting of layers from six inches to several fe$t in thickness. Pyrite nodules originally on the limestone have be- come oxidized and are represented by spots or nodules of rusty- colored iron oxide. Near the base of the section at the quarry is a layer in which a small Gryphea is very abundant. At the west limits of Alamo Heights, overlooking the valley of Olmos Creek, there is a bluff into which a quarry has formerly been opened, representing a phase of the Austin formation similar to that seen in Brackenridge Park. The Gryphea layer at this exposure lies 45 feet or more above the stream bed, indicating that the section here affords an exposure lying a little lower in the forma- tion than the exposures at Brackenridge Park. Immediately west of the West Texas Military Academy, a little more than a mile north of the north city limits of San Antonio, is another west-facing bluff, exposing a similar section of the Austin forma- tion. The exposures of this formation at the cement plant two miles north of the city limits are described elsewhere. At San Pedro Park are seen exposures of the hard limestones of the Austin formation from which springs emerge. The exposures Geology and Mineral Resources of Bexar County 43 here described lie within and represent an upthrust block of the Austin formation which forms the range of Austin Hills indi- cated on the sketch map (Fig. 2). The southernmost exposure seen of this belt of Austin is found near the intersection of Zal- zamora and Ruiz streets in west San Antonio, where a much later phase of the formation is seen, consisting of soft marly rock. To the northeast, exposures of this belt of the Austin formation may be seen to the county line at the Austin Road crossing on the Cibolo River. Particularly good exposures -are seen at the cross- ing of the Austin Road on Salado Creek, and at the Perin-Beitel Road crossing of a tributary entering from the east. On these exposures Baker has made the following notes : When fresh the chalk has a light bluish-gray color while on weathered exposures it is light yellowish-buff, passing upward, upon weathering, to a brown substance resembling marl. It is much jointed in very irregular fashion and breaks often with a semi-con- choidal fracture. Nodules of pyrite are present which weather to limonite. Some beds of the rock are slightly more indurated than others and so stand out more prominently on exposed surfaces. This rock forms the bed rock at Fratt. Near the mouth of the small creek tributary to Salado Creek and heading northeast of Fratt, the dip (probably not true dip) is 1° S 65° E. About one-fourth mile downstream and about 200 yards above the junction with Sal- ado Creek, the dip (perhaps not maximum) is 4° to the south. In the soft chalk rock of the Austin formation at the crossing of the Perrin-Beitel Road near Fratt, Stephenson has noted the presence of the following fossils (Mss. notes) : Scaphites sp., Placenticeras sp., and a large Baculites. In the more indurated rocks of this formation about one mile farther west, he notes the presence of the following fossils: Exogyra laeviuscula, Avicula?, Pecten sp., Liopsifka elegantula (Roemer) ?, Barbatia sp. Exposures in the large belt of the Austin formation passing through the county north of San Antonio are too numerous to receive separate description. This belt of the Austin is crossed by all roads running north and northwest from San Antonio. At the Leon Creek crossing on the Bandera Road are seen good bluffs exposing the hard limestones of the formation including in some layers an abundance of fossils. Other good bluffs are seen 44 University of Texas Bulletin at the first and second crossings of the Culebra Creek on the Culebra Road. At the Salado Creek crossing of the Bulverde Road, the bluffs seen at the right are a part of the limestones of the Austin formation and represent the west margin of the block originating in San Antonio. TAYLOR FORMATION The Taylor formation includes chiefly marls and calcareous clays. In surface exposures and to the depth affected by weathering, the clays are yellow, although where unaffected by weathering they are for the most part blue in color. As a water-bearing formation, the Taylor is of but slight importance as the marls and clays are too close in texture to carry large quantities of water. The bentonite deposits of this county probably lie within the Taylor formation. The fuller’s earth deposits are either near the top of this formation or in the next later formation, the Navarro. The gas of the Gas Ridge field is probably from this formation, while the oil of the Somer- set field appears to be either from this or from the Navarro formation, or possibly in part from the Midway. Thickness : A measurement of the thickness of the Taylor formation is extremely difficult. No surface exposures found in Bexar County are adapted to that purpose while in well records, it is difficult to determine from logs or from cuttings, the depth at which the formation is either entered or passed through. In the Terrell well six miles south of San Antonio there was assigned to this formation by Hill and Vaughan* a thickness of about 400 feet. In the Alta Vista oil Fields the combined thickness of the Navarro and Taylor formations, if present, apparently does not exceed six or seven hundred feet, although here a part of the Navarro may have been removed by erosion.** In the Kearney test well for oil south of Leon Creek, the combined thickness of the Navarro and Taylor formations may be as much as 900 feet. In the columnar section, this formation has been *Hill, R. T. and Vaughan, T. W., 18th Ann. Rept. U. S. Geol. Surv., Part II. **Record of Elder-Wolf well. Geology and Mineral Resources of Bexar County 45 assigned a thickness of 450 feet which may be regarded as an average thickness where the formation is fully developed. In the Mathey well of the Bexar Petroleum Company the Ter- tiary as noted subsequently under the discussion of the thickness of the Midway formation, appears to extend to the depth of between 1340 and 1402 feet,- while the Austin formation accord- ing to the driller was entered at 1892 feet and continued to the bottom of the well 2025 feet. If this is true there remains for the Taylor and Navarro formations at this place a combined thickness of not more than 552 feet. The reduced thickness of these formations may of course be accounted for by possible erosion from the top since the Tertiary-Cretaceous contact is very probably an erosion unconformity. Samples of cuttings from this well from 1938 feet and below submitted by the driller and examined by Dr. J. A. Udden apparently represent the Austin formation. Bitty sio graphic expression: Much of the area underlain by the Taylor formation in this county consists of a level plain often gravel covered by terrace deposits. When subjected to stream erosion, the hills formed from the Taylor marls are rounded, with moderate slopes. The soils derived from this formation are black and in wet weather very' sticky. The prevailing timber growth is mesquite. Common fossils: The lower part of the Taylor formation contains an abundance of the large oyster, Exogyra ponderosa , which is also present as already noted in the upper part of the Austin formation. The Taylor formation may be separated from the Austin probably within approximate limits upon litho- logic characters, particularly by the presence of an increased clay ingredient. From the overlying Navarro formation it may be separated probably also within approximate limits. Glauconite is usually more or less abundant in the Navarro, while it is present in much smaller quantities, if at all, in the Taylor. The following notes on the Taylor formation have been made by Stephenson (manuscript notes) : — Taylor marl, consisting of weathered greenish-gray, calcareous clay, is poorly exposed in the west-facing slope of Salado Creek at 46 University of Texas Bulletin the crossing of the Seguin Road about four miles north by east of the post-office building at San Antonio. The thickness exposed is about 10 feet. It is overlain by a Pleistocene gravel bed and the latter is overlain by sandy loam. The Pleistocene is 15 or 20 feet thick. On the east-facing slope of Salado Creek Valley about x one mile above the crossing of the Missouri, Kansas and Texas Railroad, the following section is exposed along a private roadway or trail: Section Feet Pleistocene: 3. Yellow sandy clay loam with lines of pebbles at irregular intervals . 15 2. Bed of gravel with chiefly flint pebbles and cobbles 8 (Unconformity) Cretaceous (Taylor): 1. Gray calcareous clay or shale with a few poorly preserved fossils 6 From the Taylor (layer No. 1) 'obtained the following fossils (Collection No. 182): Hamulus onyx Morton Ostrea plumbsa Morton Anomia argentaria Morton Paranomia sp. Pecten sp. (small) Liopistha (Cymella) bella (Conrad)? Bluff on Salado Creek, left bank, 3 % miles due east of Alamo Heights, Bexar County, Texas. Section Feet Pleistocene: Irregularly bedded loam and calcareous sand and gravel. The sand and gravel are ex- tremely calcareous in places, consisting chiefly of a spongy mass of lime. In places the chief matrix of the gravel is spongy lime. Frequently pebbles are noticed with concentric layers of lime about them . .1 20 (Unconformity) Cretaceous (Taylor): Gray (greenish gray to yellow where weath- ered) calcareous shaly clay carrying a Geology and Mineral Resources of Bexar County 47 few poorly preserved fossils. The shale contains occasional seams of gypsum. . . .25 The fossils collected include: Lima (young individual) Pecten (small) Two feet of relatively soft bluish-gray chalk is exposed in the bed of Salado Creek, about a half mile above the preceding. The following poorly preserved fossils were obtained (Collection No. 184) : Inoceramus sp. Ostrea plumosa Morton Placenticeras sp. Crustacean (fragment) This locality is one mile below the crossing of the Austin Road. The rock is probably at the extreme top of the Austin chalk. Surface exposures and local details: Surface exposures of the Taylor formation are found in successive belts which extend in a general northeast to southwest direction across the county. Owing to structural features subsequently to be described, the belts of exposures of the Taylor formation in part surround Austin exposures. The northernmost belt of Taylor is that which lies on the north side of the Austin exposures on the Culebra Road. The Taylor in this belt extends north to within a mile or less of the Balcones escarpment. Exposures represent- ing this formation may be seen on the property of H. Wehmeyer, H. Mossman, and R, Brown, north of the Culebra Road. Ex- posures may be seen also farther east on the Hoffman Road on the property of R. Brown and G. Wehmeyer, where the clays are utilized in making ponds. At many of these exposures, particu- larly those on the Brown and Wehmeyer properties, the fossil Exogyra ponderosa is abundant. This belt of Taylor apparently terminates somewhat east of the Hoffman Road at the north turn north of the Steubing cross-road. A large area of Taylor exposures lies south of the main Austin exposures. At the west county line these exposures are found north of the Castroville Road, and extending northeast, lying somewhat south of, and approximately paralleling the Potranca Road to the Leon Creek crossing. East of Leon Creek the Taylor is seen on the Culebra Road at a cut in the road 8 miles from 48 University of Texas Bulletin San Antonio. At about this place, the Taylor belt is divided by a southward projecting nose of Austin exposures. On the Fredericksburg Road, marls containing Exogyra ponderosa are seen from 9.3 to 9.7 miles from San Antonio. In the city of San Antonio, the Taylor exposures are again divided by a southward projecting nose of the Austin formation. The western area of Taylor marl is interpreted as crossing the Bandera and Fredericksburg roads at from 2.6 to 6.6 and from 2.5 to 5.4 respectively miles from San Antonio. This Taylor belt may be expected to narrow farther to the east, and probably does not extend as far as the east county line. The oyster, Exogyra ponderosa, is found in clays resembling the Taylor on the slope to the alluvial plain of the Cibolo on the Nacogdoches road about 15 miles from San Antonio. In the western part of San Antonio are seen several exposures which are referred more or less definitely to the Taylor forma- tion. One of these is seen in the cut on the Fredericksburg road at the crossing of a small stream about two miles from the Court- house. Another is seen at the Culebra Road crossing of the same stream a little farther south. In neither of these exposures are fossils found and the reference to the Taylor formation is on the lithology. A similar exposure of yellow clay is seen on the same creek still further south, at the crossing of the old Castroville Road near itg union with Zalzamora Street. The southernmost belt of Taylor exposures in this county is that which extends from San Anotnio northeastward to the county line. Exposures of the Taylor of this area may be seen at a cut in the public road on River Avenue, at the north city limits, and again on the Austin road opposite the Aviation Post about 6 miles from San Antonio. At neither of these exposures so far as observed are fossils found and the identification is chiefly on lithologic characters. The belt of the Taylor marls is here narrow as the Austin formation is exposed a short dis- tance to the north, while fossils indicating the Navarro are found not far to the south of these localities. To the east of Sal ado Creek the Taylor formation lies south of and approxi- mately parallel to the Austin road, to the county line. Geology and Mineral Resources of Bexar County 49 NAVARRO FORMATION The Navarro formation includes chiefly deposits of clay and marl although in parts of the formation, particularly toward the upper limits, there are layers of well indurated lime rocks and in places limestone ledges. Lithologically the formation on sur- face exposures resembles the Taylor. In the Navarro, however, is found considerable glauconite which is frequently in such abundance as to give a greenish tinge to the clays and shales of the formation. Within the formation, probably in its upper part, is a green glauconitic sandstone, often met with in drilling and usually recorded in the well logs as “green marl”. At the surface exposures on Leon Creek, this stratum has a thickness of from 12 to 15 feet. The water supply in the Navarro, as in the Taylor, is very limited, the marls and clays containing but little water. The greensands of the formation contain a limited amount of potash and phosphate, which at the present time is not utilized. The oil of the Somerset field, as already stated, is obtained either from this formation or from near the top of the Taylor forma- tion. Thickness: The thickness of the Navarro formation is difficult to determine, since in well logs and cuttings the transition from this formation to the underlying Taylor is not sufficiently well marked to be easily recognized. In a well on the property of J. K. Lamb, south of the Medina River, samples from which were examined by Dr. J. A. Udden, a thickness of about 1000 feet was provisionally assigned to these two formations. On the Ritter property on Medina River near the Frio road, the strati- graphic interval between the top of the Del Rio formation and the uppermost green sands assumed to lie near the top of the Navarro formation, is apparently between 1250 and 1300 feet. Assigning approximately 400 feet as the combined thickness of the Austin, Eagleford and Buda formations, there is an indi- cated thickness for the Taylor and Navarro formations of 850 or 900 feet at that place. Approximately the same thickness is indicated by the Kearney well and well of the Superior Oil Company. On the basis of this somewhat indefinite data, the -I thickness of the formation is given in the columnar section at 4-Bex. 50 University of Texas Bulletin about 450 feet. However, it is necessary to consider in these measurements the apparently great thickness of the Tertiary in the Mathey well and the correspondingly reduced thickness of the Navarro-Taylor. (p. 45.) Physiographic expression: The belt of country underlain by the Navarro formation presents surface features not unlike those of the Taylor marl. The slopes of the hills developed from this formation are possibly somewhat more abrupt than are those from the Taylor formation, due probably to the presence of the indurated limy layers of the Navarro formation. The soils are black and the prevailing timber growth is mesquite. Common fossils: The Navarro formation contains rather more fossils than does the Taylor formation. The large oyster, Exogyra costata , is abundant in this formation. Two other oysters, Gryphea vesicularis and Alectryonia larva, are listed by Hill and Vaughan* as common in this formation. Surface exposures and local details : The Navarro formation has been recognized at surface exposures in a belt of country passing across the county from northeast to southwest imme- diately south of the southernmost belt of Taylor marl. In the western part of the county, this formation is seen exposed on the Castroville Road, at the crossing of a small creek about 1% miles from the county line and again at the top of the hill about 2 miles from the county line. The fossil, Exogyra costata, is very abundant at each of these exposures. Another exposure probably to be referred to the Navarro is found near and stratigraphically above the fuller’s earth beds north of the Cas- troville Road 17% miles from San Antonio. About one mile south of the Castroville Road, on the Cagnon cross road 14 miles from San Antonio, is an exposure on the hill slope containing many shells of E. costata. At the north side of the Castroville Road, 9 miles from San Antonio, is seen an exposure made by an excavation for a pond. The yellow clay of this exposure contains E. costata. On the Culebra Read five miles from San Antonio is an exposure which is to be referred either to this formation or to the Taylor marl, containing an abundance of E. costata. On the Austin Road opposite the Country Club Austin Quadrangle, page 5, 1902. Geology and Mineral Resources of Bexar County 51 grounds at the north limit of the city of San Antonio is an ex- posure -containing many E. costata which is probably to be re- ferred to this formation. An exposure of the Navarro is seen in the cut made by the Camp Travis switch north of the Seguin Road near the east city limits of San Antonio. A series of good exposures of the Navarro formation is seen on Leon Creek from the Castroville to the Pearsall Road cross- ings. About one-eighth mile below the Castroville Road cross- ing on the right bank of the stream is a bluff exposing clays and limestone ledges of the Navarro formation. The clays on surface exposure are dun-colored. A well dug nearby, how- ever, shows that the unweathered clays are blue. The harder ledges in this exposure are frequently concretionary. The dip as observed at this exposure, in the direction about due north- west, is about 7 degrees. About 30 or 35 feet of the formation is seen at this exposure, overlaid by terrace gravel deposits. At the north side of the Castroville Road in the right bank of a small tributary entering Leon Creek from the southwest, about one-eighth mile from Leon Creek, exposures are seen of a glauconitic sandstone horizon. The glauconitic sandstone at this exposure dips rapidly to the northwest. In the right bank of Leon Creek south of Kelly Field, from three-fourths to one mile above the Pearsall Road crossing, is a bluff of the Navarro formation. The exposure here includes 70 or 80 feet of calcareous clays which are yellow on exposure. The bedding planes here are obscure, but the dip in the strata is apparently to the northwest. On the left bank of the stream in Kelly Field, an excavation made for a sewage disposal tank exposes thin-bedded clays, blue in color or partially oxidized yellow. The dip as seen in this pit in the direction 30 degrees west of south, amounts to about 7 degrees. Overlying the clays at this exposure are the gravel terrace deposits. This exposure is interpreted as lying lower in the Navarro formation than the exposure seen at the Castro- ville Road crossing, the dip being as noted to the southwest. About one and a half miles upstream from this exposure is a 52 University of Texas Bulletin bluff on the right side of the stream. The following section is- seen near the middle of this bluff: — Feet Heavy gravel deposits at the top of the bluff . .16 Calcareous clays weathering yellow 30 Glauconitic sands, harder ledges at top and base , . 12 Dark-colored clays 30 Light marly white clays 12 The dip at this exposure is to the west or southwest, amount- ing in places to as much as 4 degrees. Near the south end of the bluff, the glauconitic sandstone layer lies within about 15 or 18 feet of the top of the bluff, or directly under the gravel deposits. Near the north end, this horizon falls as low as about the middle of the exposure. In the bluffs between the Pearsall and Quintana Road crossings are seen similar exposures of the Navarro formation. In these exposures, however, the dip is in the opposite direction, or to the east or northeast. In this bluff, the glauconitic sandstone comes into the section near the north end of the bluff, where it lies from 90 to 100 feet above the stream. It drops rapidly and passes below water-level somewhat near the International and Great Northern Railway crossing close to the Quintana public road crossing. Baker has made the following notes on this exposure : At the south end of the International and Great Northern Rail- way bridge over Leon Creek is a blue-gray unctuous clay weather- ing yellow-brown, containing fossils and very small streaks of sand. At the south end of the Southern Pacific Railway bridge, just to the west, glauconitic sand containing small quartz pebbles is inter- bedded with sandy blue-gray clay. The dark green glauconitic sand containing small pebbles and fossils* notably sharks’ teeth, begins at the railroad bridges and extends up Leon Creek for about a mile. It dins 15° to the south. It probably represents the Na- varro formation. It is underlain by light gray limonite-stained sandy clay. These clays contain large gray sandstone concretions, some of which are very well indurated. The clays weather tawny (yellowish-brown). The clays pass downward into fine-grained, thin-bedded, ripple-marked, light gray sandstone. A layer con- Geology and Mineral Resources of Bexar County 53 .taining many black sharks’ teeth lies in the clay just above the sandstone. The thin sandstones are interbedded with the clays and the dip still continues. Lower down the clays are darker in color (greenish or olive) and are more argillaceous and unctuous. The dip flattens out northward. The structure revealed by these exposures is interpreted as a broad asymetrical anticline or tilted block, near the west side of which the gas wells west of Leon Creek are located. This structure, continued to the northeast, forms the Austin Hills elsewhere described. CRETACEOUS-TERTIARY CONTACT The contact line between the Cretaceous and the Tertiary as placed on the map is at best approximate in location, the surface being much obscured by Pleistocene gravels. At the west margin of the county the Tertiary apparently extends as indicated by sandy hills and occasional limestone' concre- tions, to the slight bluff overlooking the valley of the Medina River. On Leon Creek, the Navarro formation is observed to extend south as far as, or somewhat across, the International and Great Northern Railway. At the Pearsall Road crossing on the Medina River, however, the glauconitic sands which are provisionally placed as near the top of the Navarro formation, are encountered in drilling at from ICO to 200 feet below the surface. Accordingly, the eastern margin of the Cretaceous in this area between the Medina and Leon Creek in which the surface is terrace-covered, is provisionally mapped as approxi- mately paralleling the Galveston, Houston and San Antonio Railway. Between Leon Creek and the San Antonio River the contact is obscured by the Pleistocene gravels. Between the San Antonio River and Salado Creek the Tertiary repre- sented by the Midway formation extends north, reaching across the southeast corner of the city limits of San Antonio. Be- tween Salado and Rosillo Creeks the contact is again concealed by the flood plain. On Rosillo Creek .the Tertiary extends as far north at least as the St. Hedwig Public Road crossing and the Galveston, Houston and San Antonio Railway crossing, but probably does not extend much farther upstream. Prom 54 University of Texas Bulletin here to the east line of the county, owing to limited exposures, the contact is mapped approximately from the soil char- acteristics, those of the Tertiary being more sandy than the soils derived from the late Cretaceous formations. CENOZOIC EOCENE The Eocene formations recognized in this county are the Midway, Wilcox, and Carrizo, and posisibly outliers of the Mount Selman formation. MIDWAY The Midway formation of this county includes chiefly arenaceous clays in which are imbedded many concretions of sandy or limy rocks. The concretions are of various sizes from small concretions weighing only a few pounds, to those of large size, making up masses of rock of several tons weight. Thickness: The most reliable measurement of the thickness of the Midway formation obtained is that from the Mathey well drilled in 1919 near Losoya. The following data on this well have been kindly supplied by Messrs. H. L. Hamilton and W. L. Walker. STRATIGRAPHIC DATA FORM MATHEY WELL LOSOYA, TEXAS Horizon. Lignite cuttings .at 367, 560 and 590 feet. Wilcox. First fossils recovered, from cuttings, at 665-670 feet were: *Volutilithes limopsis Conrad Midway. Olivella mediavia Midway. Fossils found in core sample from 927 to 928 feet: Linthia alabamensis Clark Midway. Pecten alabamensis Midway. Fossil from cuttings, 1070-1090 feet: Cerithium mediaviae Midway. Fossils from cuttings at 1110, 1135, 1170, 1195, 1270 and 1340 feet all were characteristic Midway forms except a few that carry through to Cretaceous. Fossils from a core sample 1402-1406 feet, were the first to definitely establish the Cretaceous: Ammonite * Cretaceous. Cuspidaria Cretaceous. *A11 fossil identifications were checked by Dr. J. P. Smith. Geology and Mineral Resources of Bexar County 55 The top of the Midway horizon is somewhere between 590 and 665 feet deep. The bottom is between 1340 and 1402 feet. While there is no lithological suggestion of lower contact, it would ap- pear that the upper contact lies close to the 600-foot level. \ From these determinations it appears that the Midway at this place has a thickness of between 675 and 810 feet, and that the Midway and Wilcox have a combined thickness of between 1340 and 1402 feet. The record of a second well showing a great thickness of the Tertiary, the Sarah Smith No. 1 of W. C’. Stenbing, the data for which has been supplied by the United States Geological Survey, is given in the chapter on well records. Physiograhpic expression : The belt of country occupied by the Midway formation is for the most part moderately hilly, the hills having as a rule a southward slope which possibly in many instances approximates a dip slope. The soils derived from the formation are dark or brown in color and are more sandy than are the soils of the Cretaceous although less sandy than the soils of the Wilcox formation. The prevailing timber grown on the Midway hills is mesquite. Common fossils: Marine fossils are found in the Midway although rarely abundant. Of the mollusks the genus Veneri- cardia is the most abundantly represented. Surface exposures and local details: The Midway formation is well exposed in the cut made by the Missouri, Kansas and Texas Railway in the southeastern part of San Antonio. On fresh exposures the clays of the Midway at this cut are massive, much jointed and of medium hardness. On exposure they crumble to very small particles. The clays include numerous oval or flattened small concretions, frequently hollow, or con- taining hematite or other minerals. Venericardia was obtained from this section by Stephenson. (Mss. Notes). The following notes have been made by Mr. Baker, who first examined this exposure and recognized it as of the Midway formation : The Midway clays beneath the Uvalde in the new “Katy” cut through the hill in the eastern part of San Antonio are not ap- preciably sandy but are more weathered than in the lower-lying exposures of lower horizons. This weathering was to some extent 56 University of Texas Bulletin at least accomplished in pre-Uvalde times. The clays are irregu- larly mottled yellowish-brown and' light olive green with thin films of dendritic manganese oxide on joint planes, and an occasional small white nodule or concretion of CaC0 3 . The clays are much jointed. Among other exposures of the Midway noted by Baker are the following : Greenish drab unctuous clay, weathering yellow-brown with a few red limonit'e sandy (concretions and carrying Venericardia planicosta and a few other fossils as casts, is found in the gully east of ridge just below the junction of Salado and Rosilla creeks. In this gully are seen also the large yellow brown concretions, some of them with cone-in-cone structure. The Midway apparently carries marine fossils to its very top. Thus the highest beds a mile above the mouth of Comanche Creek (south of Alta Vista oil field) carrying the unctuous clay casts of Venericardia alticostata and other fossils. As usual the Midway here carries the brown limestone concretions. In the Alta Yista oil field very large concretions are exposed at the surface which with little doubt are Tertiary and prob- ably of the Midway formation. At the crossing* of the Gal- veston, Houston and San Antonio Railway on Rosilla Creek, east of San Antonio, exposures of the Midway clays are seen both in the stream bed and in the railway cut. In the dump from dug wells near this crossing were seen the massive clays of this formation, including numerous small concretions identi- cal with those of the Midway at the Missouri, Kansas and Texas Railyaw cut in San Antonio. On the Miedina River exposures recognized as Midway are found as far downstream as the Palo Alto Road crossing. The following section at this crossing is from notes made by Steph- enson : — Section in ravine near north end of bridge over Medina River, Palo Alto road: Feet Terrace deposit: 1. Yellowish sandy loam 18 2. Bed of coarse gravel i 2 Eocene (Midway): Geology and Mineral Resources of Bexar County 57 Hard, gray, earthy sandstone streaked with reddish limonitic iron ore. Shows faint cone-in-cone structure in the more earthy streaks 1 4. Dark gray, fineiy sandy, shaly clay .18 5. Ferruginous layer of fine earthy concretion- ary sandstone with some concretionary masses of hard limestone in center. Faint cone-in-cone structure noted in the more earthy portions. A few faint fossil impressions. Probably same as layer at bottom of bluff below Garza crossing 1-2 6. Dark gray, finely sandy, shaly clay 2 7. Concealed to water 1 5 -(- The lowest layer in the preceding section dips down to water- level within about 200 yards below the bridge. WILCOX FORMATION The Wilcox formation is well developed in this county and includes thinly laminated sands, sandstones, sand and limestone concretions, clays and lignites. The presence of sea shells in- dicates the marine origin of parts of the formation, while the lignite and land plants preserved in some of the shale indicate the lacustrine or near-shore origin of parts of the formation. Thickness: No data is at hand at present by which to approx- imately determine the thickness of this formation in Bexar County. A well drilled near the south county line at Saspamco starting at or near the top of the Wilcox, extended to a depth of 2500 feet. This well with little doubt passes through both the Wilcox and Midway and into the Cretaceous, but it is not possible from the log to determine the limitations of the sev- eral formations. A well drilled on the J. K. Lamb property in the southern part of the county starts near the top of the Wilcox. In this well the Eagleford formation, according to examination of the samples made by Dr. J. A. Udden, was probably reached at about 1900 feet (Mss. notes). Allowing for the Cretaceous, overlying the Eagleford, its usual thickness of about 1200 or 1300 feet, there remain 600 or 700 feet to be assigned to the Wilcox and Midway formations. Physiographic expression: The soils derived from the Wilcox formation are sandy and frequently of a red color. The coun- 58 University of Texas Bulletin try underlain by the formation becomes somewhat hilly and rough by the development of stream channels and valleys. The timber growth is mesquite in part, although deciduous oaks and other hardwood trees are found on the more sandy lands. Common fossils : The fossils of the Wilcox formation of this county as already indicated are in part marine invertebrates and land plants. Surface exposures and local details : In the bluffs west of the Pearsall Road crossing on the Medina River are numerous heavy limestone concretions. The cut made for the public road on this bluff exposes thinly laminated sands carrying plant fragments. These sands and concretionary limestones appear to represent the Wilcox formation. Similar laminated sands including limestone concretions are seen in he bluffs in the vicinity of Van Ormv. Good exposures of these sands are seen on the St. Anthony farm about three-fourths of a mile south of Van Ormy. Sandy lime concretions are seen here which measure as much as 35 feet in length by 15 feet in width and 8 feet or more in thickness. They are imbedded, finely- laminated, clayey sands. On the Gonzales Road, laminated micaceous sands of the Wilcox formation are seen on the slope to Saunders Creek, 131/2 miles east of San Antonio and thence in numerous ex- posures to the east county line. At the intersection of the Gonzales and Prie Roads about 17 miles from San Antonio, the dump from a dug well was found to contain typical sandy clays of the Wilcox formation including a few well preserved leaves. Thin lignite beds are reported in well logs of this part of the county. Much of the field work on the Wilcox formation in Bexar County was done by Mr. Baker, from whose notes the following observations are taken : On Losoya Creek, at concrete bridge on the Corpus Christi Road, the strata dip 3° S 60° E, which may not be the true dip. At the base of the section are thin alternating beds of loose brown sands and laminated clays overlain by brown, much cross-bedded sand- stone 3 feet, above which is mainly laminated sandy clay about 20 feet. The bottom of a small syncline is seen at the bridge, the axis Geology and Mineral Resources of Bexar County 59 of which trends northeast-southwest. The dip on the northwest limb runs up to 10° or more, but flattens rapidly. A splendid section of the Wilcox is exposed at the jog in the public road about three miles north of Elmendorf. The section is as follows: Brownish stained sands, weathering into “bad lands” 8 Laminated gray, medium-grained sands, weathering light brown with some thin interlaminae of yellow-brown clay 15 Gray drab, unctuous, structureless fire clay, passing downward into chocolate carbonaceous shale and finally into a good grade of lignite. The lignite has a minimum thickness of 2 feet with the base not exposed 6 Slightly laminated brownish-gray medium- grained micaceous sand with large flat- tened elliptical sandstone concretions at top and bottom 10 The observed dip in a direction about 20° south of east, ap- peared to be 7°, but flattened out toward the south. The lower Wilcox on Medina River at southern boundary of San Antonio topographic sheet, west-southwest of Earle, consists of medium-grained gray cross-bedded sands, with large sandstone con- cretions, weathering brown. In the bed of Comanche Creek a short distance above its junction with Leon Creek are many very large flattened sandstone concretions. Associated with these are inter- bedded brown sands and shaly gray sandy clay. The lower Wilcox at the bridge over Six Mile Creek, where crossed by old Espada Mission ditch, is medium-grained gray sandstone, somewhat cross- bedded, weathering brown and locally cemented into sandstone. Near mouth of first tributary on the west side of Calaveras Creek south of crossing of road running east-northeast of Elmendorf, are black and brown layers carrying carbonaceous materials in brown- ish laminated sands, with alum incrustations. Most of the 10-foot section is fine sand, some layers with an admixture of clay. The apparent dip here, possibly due to slumping, is about 5° to the east. Large ripple-marked flat blocks of brown sandstone occur in Cal- averas Creek bed in this locality. The sands are laminated and when fresh are light gray in color but are often stained with limonite. The Wilcox soils are light brick red and generally sandy. The sandstone layers in the Wilcox here are often cross-bedded and ripple-marked. When fresh, the sandstone is gray in color, but oxidation of the iron gives the brown most generally seen. Locally 60 University of Texas Bulletin they may be almost as hard as quartzite but they seem to be almost, if not quite, always local indurations' of a concretionary nature. At one place on Calaveras Creek about half a mile below the bridge before noted, ripple-marked and cross-bedded sandstone about 3 feet in thickness overlies large flattish concretionary masses cementing a conglomerate of light brown clay balls. Some have septarian structure and are seamed with crystalline calcite and cone-in-cone structure. These concretions contain marine Eocene fossils, carbonaceous fragments and grains of glauconite. In all respects they resemble the Wilcox concretions in Sabine-town bluff, this being the first locality of marine Wilcox found west of the Sabine basin. The concretionary layer is only about 4 feet above the bed of the creek. Below are 4 to 5 feet of loose laminated sands and above the sandstone layer overlying the concretions are about 20 feet of laminated gray clayey sands, limonite-stained and locally cemented. The latter are found in the bluff about 200 feet to the westward. The sandstone blocks between here and the bridge evidently belong to the same stratum, the one over the fossil-bearing concretions, only one large fossiliferous concretion being known to occur here. Nearly half a mile farther down is another 20 foot exposure of Wilcox. Here is about 5 feet of lavender carbonaceous sandy and unctuous clays at base, succeeded by cross-bedded, laminated sands with occasional thin laminae of clayey material for the next 10 feet. The upper five feet consists of two one-foot beds of gray clayey laminated sands separated and overlain by cross-bedded brown sands, the upper 2 feet of which is more consolidated and consists of a conglomeratic sandstone with small clay-iron-stone pebbles and small sharks’ teeth. This sandstone is also ripple-marked. Peb- bles of clay-iron-stone in such a formation mean little, for they are soon formed in consolidated condition along stream banks and ocean or lake littoral deposits. From this point on downstream to below the steel wagon bridge at Saspamco the banks sometimes 30 feet high are composed of alluvium of clayey sand. The first section on Parita Creek, V 2 mile above mouth, shows at base 6 feet of lavender, carbonaceous, cross-bedded, laminated, sandy clay, dipping upstream at an angle of about 10°, succeeded above by about 6 feet of laminated sand and being nearly horizon- tal. The whole section is prevailingly sandy, with indurated sand- stone layers both above and below. The first exposure on Parita Creek south of the bridge, about 4 miles northeast of Elmendorf (about 1-5 mile south of bridge) shows 9 feet of thinly interlaminated clay and sand layers. The sand layers are generally thicker than the clay layers, but few of the former are much thicker than an inch. The sand is brown, weathering gray when fresh. The clay laminae are gray when dry Geology and Mineral Resources of Bexar County 61 and lavender or light chocolate when wet. Sand is fine-grained and micaceous and some layers are 2 to 3 inches thick. The next three exposures downstream show substantially the same. The in- terbedding of sand and clay laminae still continues. Either one may sometimes be extremely thin, sometimes not much thicker than bristol board or thin cardboard. Light exposure about 1 mile be- low bridge shows above 10 feet of laminated, brown, fine-grained sands, with nodules arranged in thin layers of a whitish powdery substance, probably CaC0 3 . Below is 10 feet of mainly light gray, thinly-laminated, sandy clay but containing one 2 1 / z " layer of sand 2 y 2 feet above base. The clay member has three interlaminae of sand as was noted farther upstream. This exposure at junction of east tributary. One-half mile downstream below last 3 feet of rusty brown ripple and rill-marked irregular-bedded sandstone over- lies unconsolidated sands with interbedded laminae of clay. The next exposure downstream shows a good deal of cone-in-cone struc- ture in brown sandstone concretionary layers, interbedded with clayey sands. On Calaveras Creek, about 2 y 2 miles northeast of Elmendorf, and of Parita Creek, near the Bexar-Wilson county line, about y 2 mile north of southermost of two main road crossings in a northeasterly direction from Elmendorf, is exposed about 10 feet of light brown laminated sands. Next exposure, a mile farther upstream, has the usual interlaminated sands and clays with flattish sandstone con- cretions and selenite crystals 10 feet thick. Also a 7-foot exposure of the latter on road just east of bridge over Calaveras Creek 3 miles northeast of Elmendorf. The first exposure of any moment on the largest eastern tributary of Parita Creek, near the Bexar-Wilson county line, about y 2 mile above mouth of creek, consists of about 5 feet of thinly-laminated light chocolate clay, with very thin partings of light gray mica- ceous sand; above is 7 feet of thinly-laminated light gray clayey sand, seamed with limonite, and becoming sandier and less lami- nated in the upper 2 y 2 feet; capped by 8 feet of light gray, fine- grained sand weathering light brown with thin beds, especially at the top, of a white kaolin-appearing substance. The basal clays contain carbonaceous remains. The next exposure, at least 3/4 mile farther upstream, consists of the same sort of materials as the last and a recent well dug in the creek bed between the two shows about 10 feet of gray micaceous sandy clays and clayey sands. Under the last exposure noted lie brown concretionary sandstones some with cone-in-cone structure. These concretionary layers, as usual, are ripple-marked. Some of them are large flattened discs, gray in color when fresh, and hard as quartzite. The concretionary layers are interbedded with the usual clayey sands, which are lami- nated. Some of its larger concretions are probably cemented with sphaero-siderite. A conglomeratic concretionary layer, found at least 62 University of Texas Bulletin 1 y 2 miles upstream from the mouth of the largest eastern tribu- tary of Parita Creek, was composed of rolled iron-stone pebbles, shark’s teeth and oyster fragments. The latter may have come from the Cretaceous. Also worn fragments of other shells. As one goes upstream and consequently into lower strata, the beds become more clayey, ^becoming gray drab stained with oxide of manganese, and with small whitish soft, perhaps calcareous concretions. The following 1 notes on the Wilcox and other Cenozoic for- mations in Bexar County have been contributed by Dr. L. W. Stephenson : Medina River, a few hundred yards below the crossing of the Corpus Christi Road near Losoya, Bexar County, Texas, 13% miles south of the San Antonio postoffice building. Pleistocene: 2. Massive brown loam, becoming sandy and pebbly toward base and locally a basal bed of gravel reaching 3 or 4 feet in thickness. The material stands up in a vertical wall along the bluff like loess. 20-35 (Profound unconformity) Eocene (Wilcox?): 1. Gray to greenish gray, cross-bedded sand and sandstone. The sandstone consti- tutes local indurations of the sand. It is soft to very hard and is poorly ex- posed along the base of the bluff which is covered with talus 15-30 Faint banding is noticeable in layer No. 2, and about 10 feet below the top is a distinctly lighter band having a yellowish color. The bluff extends for. several hundred yards along the left bank. Earle, Texas, 11% miles due south of the San Antonio postoffice building. At the head of a gully on the east side of the road and south of Medina River, sandstone has been quarried for use in concrete work at the new bridge at Earle. The rock is the indurated portion of a greenish gray, cross- bedded, rather fine sand formation. It is not very well exposed, the slopes being covered with vegetation and rock debris. Unin- durated portions of the sand are exposed in the head of the gully proper. Thirty-five or forty feet of the rock and the unconsolidated Geology and Mineral Resources of Bexar County 63 sand is exposed. The rock rises nearly to the surface of the sur- rounding upland. Down the gully the rock and sand are overlain by Pleistocene sandy loam which rests unconformably against it. The sandstone contains large numbers of fossil leaves well preserved. As the rock does not split well the leaves are hard to get out in perfect condition. (Collection No. 181). I was informed of the where- abouts of the fossil plant locality just described by Mr. T. B. Apple- white, whose address is R. F. D. No. 7, Box 33, San Antonio, Texas. (The fossil leaves from this locality have been described by E. W. Berry in Prof. Paper 91, pp. 8-20, pis. 1-3, 1916). Corpus Christi Road, crossing of Losoya Creek, half a mile south tff Medina River crossing. Section Feet Surficial-alluvium : Reddish brown sandy loam with accumula- tion of pebbles at base in places. Con- tains land shells '. 4-15 (Great unconformity) Eocene (Wilcox?): Laminated, finely sandy, gray clay, and part- ings and thin layers of gray to brown- ish fine sand, some layers 6 or 8 inches thick. Some vegetable particles. Max.. 20 Layer of ferruginous earthy sandy lime- stone, apparently of concretionary origin, cemented, on top of which is a thin conglomeratic layer composed of coarse pebbles, most of which appear to be fine ferruginous sandstone and sandy iron carbonate concretions. Among those pebbles were collected a few poor prints of Venericardia. Also some silicified wood 1 Irregularly bedded sandstone and loose sand, some showing ripple marks, with subordinate gray laminated clay 4 CARRIZO FORMATION The Carrizo sandstone was named and described by Owen in the First Report of Progress of the Texas Geological Survey, published in 1889. The Carrizo formation of the Cambrian system exposed in the Carrizo Mountains of the Van Horn 64 University of Texas Bulletin Quadrangle, was named by Yon Streeruwitz in 1891. # If, there- fore, the Carrizo of the Eocene is recognized as of formation rank, the name as applied to this sandstone takes precedence over the Carrizo formation of the Cambrian. The Queen City member of the Wilcox formation, which is usually regarded as the northeast Texas equivalent of the Carrizo sandstone, was named by Kennedy in 1896. f The Carrizo sandstone is re- garded by some as a member of the Wilcox formation. A belt of sand hills extends across the southernmost part of Bexar County, representing country underlain either by the Carrizo sandstone or by very sandy phases of the Wilcox. This area is referred to locally as the ‘ ‘ sand hills ’ ’. The approximate location of this belt of country is indicated on the map. Some of the hills near the county line in the southwestern part of the county, thickly strewn with concretionary ironstone fragments, may represent outliers from the Mt. Selman forma- tion. PLEISTOCENE No marine formations are found in this county of later date than the Eocene period, the late Cenozoic being represented only by non-marine deposits, including river flood-plain, and to some extent chemically formed, sediments. Presumably, as indicated by the absence of marine formation, this area has been subjected to surface erosion during the latter part of the Tertiary and all of the Pleistocene. In this long interval there has been formed a complicated and extensive series of river flood plains. The earliest or oldest of these have themselves been more or less com- pletely destroyed and removed by erosion. Of those that remain some are as old as the early Pleistocene, or possibly older, while others were formed during the middle and latter part of the Pleistocene period. For a part only of this county are topographic maps available, and it has not been practicable to make a .detailed study of the successive flood plains. It is important, however, to indicate *Second Annual report of the Geol. Surv. of Texas, p. 683, 1890. fThe Eocene Tertiary of Texas east of the Brazos River. By Wm. Kennedy. Proc. Acad. Nat. Sci. Phila. for 1895, p. 135, 1896. Geology and Mineral Resources of Bexar County 65 the general characteristics of the flood plain deposits, and to map the larger areas. The flood-plain deposits of the county may be divided into two main groups, each of which is distinctive. The first of these groups includes the older and hence higher terraces of the county which are not obviously associated with the existing streams. The second group includes the low or late terraces whose rela- tion to existing streams is sufficiently evident. Data on which to determine the age of the older terraces are wanting, but they may safely be placed as early Pleistocene or older. The late terraces are recognized as belonging to the latter part of the Pleistocene period. The older and higher flood-plains, of which there are at least two and probably several, have some characteristics in common. As already stated they are not obviously associated with the existing streams. The sediments of these older terraces are locally more or less firmly cemented by calcium carbonate thus differing from the materials of the recent terraces, which are largely uncemented. Paleontologically, the older terraces pre- sent the negative characters of a complete or almost complete absence of fossils, while the more recent terraces contain fresh water land snails and in places vertebrate remains. Concretion- ary or pisolitic calcium carbonate pebbles subsequently more fully described, are occasionally found in the older flood-plains and in places are abundant, making up locally the greater part or all of the formation. UVALDE FORMATION AND UVALDE PLAIN (Pliocene or Pleistocene) The oldest and highest flood plain deposits of this area are probably contemporaneous in age with those which have else- where been referred to the Uvalde formation. The materials of this formation as developed in Bexar County include limestone and flint boulders often imbedded in a softer matrix of finer material, clay or silt, or in some instances soft calcareous ma- terial resembling caliche. Approaching the Balcones Escarp- ment, the limestone boulders, as would be expected, increase both in relative abundance and in size. Southward from this escarp- 5-Bex. 66 University of Texas Bulletin raent the relative amount of flint pebbles, although of smaller size, are in proportionately greater abundance. The flints of this formation were derived largely from the Edwards forma- tion The limestone boulders came originally from this or from other limestone formations, having been moved in many in- stances probably no great distance. Well to the south where this flood plain overlies Upper Cretaceous formations, there are undoubtedly extensive inclusions from these formations. Un- der these conditions the Uvalde may contain beds of clay and marly deposits which are with difficulty separated from the im- mediately underlying Upper Cretaceous formations. Many of the flint pebbles of this formation are coated with calcium car- bonate. The amount of this coating varies from mere films surrounding large flints to calcium carbonate concretions oi varying sizes around fragments of flints as a nucleus. These concretions are more fully described subsequently. The gradient of the streams being reduced in passing coastward from the hills, the coarse materials o'f all these flood plains grade to fine silts and loams which are non-resistant to erosion and are finally lost. The gravels of the Uvalde formation are utilized in road building and for concrete. Thickness: The Uvalde plain, being the oldest of the flood plains of this area, has been cut into and largely destroyed by erosion, and hence persists as hardly more than a remnant of its former extent. In thickness the formation probably varied greatly depending upon the irregularities of the top surface of the underlying formations. In those areas where the formation now persists there is observed a thickness varying from a few feet to as much probably as 70 feet, although more commonly the gravels of this formation are between 15 and 30 feet in thickness. Surface exposures and local details: Originally the Uvalde flood plain must have occupied an extensive area immediately south of the Balcones Escarpment, grading from very coarse materials near the hills to silts and loams farther south. The softer materials of the formation probably were first removed by erosion, the gravels and heavy conglomerates having been more persistent. Some of the areas occupied by this formation are indicated on the map, although for reasons elsewhere stated it has Geology and Mineral Resources of Bexar County 67 not been possible to represent all of the flood plains deposits of the county. The range of Austin Hills crossed on the Fredericksburg Road eight miles from San Antonio are overlaid by a remnant of the Uvalde formation. The formation is well exposed on this road 7.8 miles from San Antonio, where it consists of flint and hard limestone gravel imbedded in a chalky matrix. In a cut on the Altgelt-Wurtzbach road near its union with the Fred- ericksburg Road, 8.7 miles from San Antonio, is another good exposure of the formation. The lower part of the exposure here is chiefly very soft white marly material overlain by about eight feet of gravel including some very heavy limestone boulders. This area of the Uvalde formation continues with some interrup- tions as far to the southeast as the Waring estate between the Bandera and Culebra roads. The elevation of these exposures varies from about 1010 feet at the Fredericksburg Road crossing to 850 or 900 feet at the Waring estate. No fossils are known from the Uvalde gravels except possibly some invertebrates that have washed into the formation from the older formations. Physiographic expression : The Uvalde formation makes a plain now much cut into by erosion. The slope of this plain is more pronounced than that of the next later plain. Thus the Uvalde plain, if correctly identified, slopes south at the rate of about 20 feet per mile, while the lower plain on which Kelly field is located, slopes south at about 15 feet per mile. Locally the materials of this formation have become firmly cemented forming hard calcareous rocks. Under these conditions rocky thin soils are found, clothed with a mixed vegetation, chiefly oaks ; more commonly, especially toward the southern part of the area, occupied by the formation, the soils are very gravelly and the prevailing timber growth is mesquite. Surface exposures and local details: On the west side of Leon Creek west of San Antonio is found a considerable remnant of a flood plain which may be either an extension of the Uvalde plain or probably may be a plain at a slightly lower level. The plain here lies at the Castroville road crossing at an elevation of from 750 to 800 feet above sea level. To the south this plain 68 University of Texas Bulletin may be recognized to about the Frio Road crossing where it terminates by surface erosion although probably remnants may be found somewhat farther south. The plain may be traced to the north where it seems to pass without any very appreciable break onto the plain adjacent to Culebra Creek. On the up- lands between Medio and Potranca creeks are terrace plain rem- nants which apparently lie at about the same level, and origi- nally perhaps were parts of the same plain. At the north side of the Castroville Road, about one-fourth mile beyond Leon Creek, deep gullies have washed into the gravel beds of this plain, affording a good exposure. The formation here rests on the Navarro and the lower three feet in this exposure consists of a very heavy pebble conglomerate in which are found large masses of glauconitic sandstone de- rived from the Navarro formation. These green sandstones of the Navarro are now exposed as elsewhere noted in the same bluff. Above this level is seen white marly material. Near the top of the exposure pebble beds again come into the section. An exposure of gravel which is probably to be referred to the Uvalde formation is seen in a cut in the public road on New Braunfels Avenue, about 0.7 mile north of the north city limits of San Antonio. In this cut there are exposed about ten feet of clay, white chalky marl, and gravel. The gravel beds are strongly cross-bedded. The clay of this exposure, although probably included within the gravel series, closely resembles the clay of the Taylor formation which is exposed on River Avenue nearby. Similar gravel beds underlie the high lands north and northeast of Alamo Heights, lying at elevations of from 750 to 800 feet. Heavy gravel deposits overlie the highlands in the north- eastern part of the city of San Antonio and are well exposed in the cut made by the Missouri, Kansas and Texas Railway as well as in pits opened up for road material. The gravel beds at this exposure rest upon the Midway clays and are variable in thickness from a few feet to a maximum of 25 feet. The upper 3 or 4 feet are in places caliche cemented and form a very hard rock. At lower levels the gravel is less firmly cemented and is frequently cross-bedded. Lenses of clay like- Geology and Mineral Resources of Bexar County 69 wise are observed, one of which is a foot thick and 50 or 60 feet in lateral extent. Many of the flints are coated with a thin covering of calcium carbonate ; on some of the flints, especially the smaller ones, this coating is thicker and shows concentric or concretionary layers. Concretions consisting wholly of calcium carbonate, or with merely a nucleus of flint or other material, are present in this exposure, although not particularly abundant. In a pit opened for road material on the Sulphur Springs Road near this cut, the deposit consists almost wholly of small calcareous concretions. These are more fully described later in connection with the description of similar concretions from other localities. LEONA (?) FORMATION AITD PLAIN (Mid-Pleistocene ?) The term L'eona was proposed in 1900 by Dr. T. W. Vaughan, and was applied to a well developed flood plain in the Uvalde quadrangle lying at a lower level than the Uvalde plain* 5 In Bexar County there is a well developed flood plain which very possibly is contemporaneous in time with the flood plain to which the name Leona has been applied, and which is there- fore tentatively correlated with that formation. In Uvalde County, according to Vaughan, the position of the Leona formation is intermediate between that of the present flood plain and the Uvalde plain. In Bexar County .the conditions are more complicated, in that there are three Pleistocene flood plains, the Leona being intermediate between the older and the younger. The relation of the Leona flood plain to the existing streams is perhaps less obvious in Bexar than in Uvalde County. However, the writer offers the tentative suggestion that this flood plain as developed on the broad plains on which Kelly Field is located, is associated with the Leon Creek drainage. In the chapter on structure it is shown that the plunge of the structures underlying this area is to the southwest. Leon Creek in cutting across these structures has therefore tended to shift its course to the southwest. The effect of the south- *U. S. Geol. Surv., Uvalde Folio, p. 3, 1900. 70 University of Texas Bulletin west shifting is seen at the present time in the high bluffs of this creek all of which in this part of its course are found at the right, or southwest, side of the stream. The tentative explana- tion offered is that the Kelly Field plain as now developed was built up chiefly by Leon Creek or its predecessor which has gradually shifted and is still shifting its course in a south- westward direction. The plain east of San Antonio may in the same way be associated with the Salado Creek drainage. The high bluffs of the Salado, like those of the Leon, are on the right bank, the plain being entirely to the east of the stream. That the San Antonio River has taken so small a part in the development of this plain may be explained by the fact that its drainage system scarcely extends back to the Balcones escarpment and the flood waters which it carries are less ef- fective than are those of some of its tributaries. The materials of this formation are extensively used for road building. Water is obtained from the gravel beds of the forma- tion, chiefly through shallow dug wells. At the Castroville Road crossing on Leon Creek this plain stands at a level of from 700 to 710 feet above sea, or from 50 to 100 feet below the level of the plain on the west side of Leon Creek already described. The slope' of the plain is to the south or southeast and amounts to between ten and fifteen feet per mile. Its southern margin on the Somerset and Corpus Christi roads, six or seven miles south of San Antonio, ap- proximates six hundred feet above sea level. The part of this plain lying to the east of Salado Creek has a slope from north to south amounting to an average of about 15 feet per mile. The materials of this plain are largely gravel, and loam, although over a considerable area adjacent to the San Antonio River and Salado Creek, the deposits consist largely of con- cretionary calcite pebbles. At an excavation on the Quintana Road, 7 miles southwest of San Antonio, there is exposed of the formation 15 or 18 feet. The materials of the formation as seen in this exposure are stratified and consist of alternating layers of heavy gravel and calcareous sand. The deposits are here sufficiently well indurated to require blasting in working. Tliickness: Numerous pits for road material have been opened into gravel deposits of this plain. In these pits the Geology and Mineral Resources of Bexar County 71 formation as a rule has a thickness of from 20 to 30 feet. In some of the wells dug into these gravels they have been found to be from 40 to 45 feet thick. Since the gravel rests upon an eroded surface of the Upper Cretaceous and Tertiary forma- tions, they may be expected to vary greatly in thickness from place to place. Physiographic expression: The plain formed by these deposits has a very gradual south or southeast slope amounting on an average to about fifteen feet per mile. The soils include gravels and loams. The vegetation on the uncleared lands is chiefly mesquite. The elevation of this plain at its northern limit is about 750 feet while its gradual slope carries it to a level of about 650 or 600 feet at its southern limits. Common fossils : No fossils have been found by the writer in this formation, although the presence of vertebrates, particu- larly large proboscidians, has been reported from, excavations within the city of San Antonio. Inasmuch, however, as the locality in question is near the headwaters of the San Antonio River where this plain merges with the later Pleistocene alluvial plain, an exact record of the fossils in the excavation is necessary in order to make sure of their place in this, formation. In the absence of fossils the plain is referred doubt- fully to about the middle part of the Pleistocene period. This, reference is based on the fact that this plain lies above the late Pleistocene plain, to be described, and on the fact that the materials of the formation are not infrequently quite well cemented. Awaiting a more detailed study of these deposits, or the discovery of indigenous fossils, the age of the' formation can scarcely be more accurately determined. Surface exposures and local details : The largest continuous development of this plain is that extending from Leon Creek to the San Antonio River. The northern margin of this plain is found at the foot of the hills of the Austin and Taylor formations near or south of the Culebra Road. At its southern margin the plain terminates probably by surface erosion some six or seven miles south of San Antonio, although near the San Antonio River remnants of the plain, too limited to map, are found several miles forther to the south. Another large development of this plain is that found east of Salado Creek 72 University of Texas Bulletin and extending from just south of the Austin Road crossing to about the Goliad Road crossing. Good exposures of the gravels of this plain are afforded in the pits opened for road materials. In these pits the gravels are seen to be irregularly stratified or cross-bedded, often with alter- nated bands of coarser and finer materials. Most of the gravel is flint, although in this plain, as in the higher Uvalde plain, there are local areas in which the materials are made up en- tirely of small calcium carbonate concretions. On this plain such concretions are seen in numerous pits on the west side of the San Antonio River and on the east side of the Salado River. In the valley of the San Antonio River this plain apparently merges into the late Pleistocene and recent plains within the city of San Antonio. The concretionary gravels are subse- quently described. LATE PLEISTOCENE ALLUVIAL DEPOSITS . The flood plains here regarded as of late Pleistocene age are those which border on, and have an obvious relation to, the existing streams and which lie above the present flood plain. The most pronounced development of the plains of this kind are those of the Medina River. The inorganic materials of this plain are chiefly silts and loams. The maximum width of this late Pleistocene plain is found on the Medina west of the central part of the county where that river lies near the boundary between the Cretaceous and Tertiary deposits. Farther to the east where the river is cutting through the Tertiary formations, the plain, although conspicuous, is not as a rule so wide. The next best development of this plain is that which borders Salado Creek. Here also the maximum width of the plain is found where the creek is cutting through the soft upper Cretaceous formations, the Taylor and Navarro. In the Ter- tiary formations the plain is noticeably narrowed. On the San Antonio River there is but a slight development of this plain. Thickness: The late Pleistocene flood plain deposits attain a maximum thickness on the Medina River of about 50 feet. On the smaller streams they are of lesser development. Physiographic expression : The late Pleistocene plains are seemingly very level, although as a matter of fact they slope Univ. of Texas Bull. 1932. PI. I Pisolitic gravel in the Pleistocene as seen in pit excavated for road material near the Mission Loop Road south of San Antonio (See page 75). LIBRARY OF THE UNIVERSITY OF ILLINOIS Geology and Mineral Resources of Bexar County 73 very gradually downstream, the rate of slope amounting to about 15 feet per mile. The soils are calcareous loams, and the timber growth includes considerable hardwood deciduous trees. Common fossils: The late Pleistocene and the Recent deposits of this area are characterized by an abundance of the small land snail, Bulimulus dealbatus mooreanus* which is common throughout this region at the present time. The presence of this snail in the late Pleistocene deposits and its absence so far as observed in the older formations, suggests changed climatic or environmental conditions in the late Pleistocene. In addition to the land snails, proboscidian remains have been found in this formation at a number of localities. From the lower plain on the east side of Salado Creek, Baker secured the tooth of a mammoth, Elephas (Mss. notes). From the loam deposits at the Frio Road crossing on Medina River, Mr. C. H. Vogt collected some years ago a number of teeth of the elephant together with -other large bones probably of the same animal. Surface exposures and local details: The exposures of this late Pleistocene plain are found bordering all the larger streams lying from 25 to 35 feet above the present flood plain. The formation is readily recognized where typically developed by the presence of calcareous loams, containing a great abundance of the small land snail. In mapping, it has not been practicable on the scale used to represent this formation on the smaller streams, nor to show its full extent upstream. In all cases, however, it narrows in width and approaches and gradually merges into the present flood plain. Probably the maximum thickness of the formation # is seen on the Medina River near the Pleasanton Road crossing, where typical exposures are seen. CAVE DEPOSITS Numerous caves exist in the Cretaceous and Coman chean limestones of this county. One of these caves on the property of Mr. A. Friesenhahn, about 20 miles north of San Antonio, has been found to contain vertebrate fossils. The presence of *Kindly identified from Bexar County specimens by Dr. Paul Bartch. 74 University of Texas Bulletin fossils in this cave was discovered some years ago and a small amount of collecting from ‘the cave has been done by those locally interested. The entrance to this cave at the present time is through an opening extending vertically downward for about 25 feet. Formerly, however, there was another and dif- ferent opening through which the debris that partly fills the cave has been washed in. In addition to bones of small animals, this cave contains teeth and bones of the elephant. The sabre- tooth tiger has also been reported. With these bones there is associated a number of specimens of the land snail, Bulimulus dealbatus. The presence of this fossil suggests that the cave deposits probably are not older that the deposits of the Medina flood plain which this snail, so far as present observations have shown, first appears in the stratigraphic succession. The presence of the snail together with the elephant remains sug- gests that the cave deposits are probably contemporaneous with the flood plain deposits of the Medina river.* RECENT The Recent deposits of this area are chiefly those in the flood plains of the streams. Near the foothills of the Edwards Plateau, the streams, although for the most part intermittent in flow, have great volume and velocity for a short time following' heavy rains. For this reason the beds of the streams near the foothills contain a large amount of flint and limestone boulders and rock fragments, derived from the limestones of the Balconies fault zone and of the Edwards Plateau. In passing southward away from the foothills, the materials of the flood plains are found to contain relatively less of the heavy rocks and boulders and relatively more of the silts and clay loams derived from other formations through which the stream flows. In the southern part of the county the materials of the flood plain of the streams are chiefly silt, loam, and gravel. The gravel in the stream beds is relatively free from objection- able silt and for this reason is much used in road building especially in that part of the county just south of the Balcones escarpment where the largest bodies of clean gravel are found. Some of the higher flood plains are utilized in farming, since *Dr. O. P. Hay states that he has obtained sixteen species of fossils from this cave (Letter of Nov. 6, 1919). Geology and Mineral Resources of Bexar County 75 only occasionally are they overflowed. On the Medina River the high recent flood plain has frequently been utilized in pecan growing. In mapping, the flood plains of the streams have been in- cluded with the late Pleistocene flood-plain. The flood plains of all of the streams are narrow and could not well have been suc- cessfully represented on a map of the scale used for this report. CALCAREOUS CONCRETIONS OF THE PLEISTOCENE OF BEXAR COUNTY (PI. 1, p. 72) In connection with the description of the Pleistocene flood plain deposits it has been noted that calcareous concretions are present and in places are very abundant. Concretions of this nature are particularly numerous in the deposits referred to the Leona formation where they make up, over considerable area, the greater part of the formation, especially in areas adjacent to the San Antonio River and Salado Creek. Similar concretions are found locally in deposits that, judged by their present ele- vation above the stream levels, are to be referred to the Uvalde formation. In the literature the writer has been able to find only two references to these concretions, both of which unfortunately are merely abstracts of more extended papers. The earliest of these is a brief reference in an informal communication on various kinds of concretions made before the Geological Society of Washington at the meeting of January 25, 1911, by C. W. Hayes. The abstract of this paper given in Science is very brief, that part of it referring to the concretions from Bexar County being as follows : Calcite concretions from San Antonio, Texas. These occur in great abundance in the “tepetate” or “caliche,” a widespread chalky limestone formation, produced at or near the surface in semi-arid limestone regions by the ascent of w T ater through capillary action and evaporation with deposition of the dissolved salts. Ordinarily the deposit has a platy structure, but in places, as at San Antonio, it is strongly concretionary.* A paper on these concretions was read by Alexander Deussen at the California meeting of the Geological Society of America, *Sci. New Ser., Vol. XXXIII, p. 550, April 7, 1911. 76 University of Texas Bulletin 1915. The abstract of this paper, published in Volume 26, No. 4 of the Bulletins of the Geological Society of America is ^ery brief and does not include the author’s conclusions. However, in reply to an inquiry by the writer, Deussen has stated that his investigations led him to the conclusion that these concretions were formed from thermal springs.* The suggestion that these concretions were formed from thermal springs appeals to the writer as both reasonable and probable. It is probably not accidental that these concretions lie down stream from the location of the pronounced breaks or faults from which springs now issue supplying the present streams of San Antonio and Salado. It is true that these faults cross other creeks, as for instance Leon Creek, but in the case of Leon Creek the faults are so nearly sealed as to allow very little water to emerge at the surface, and on Leon Creek there is found no accumulation of these concretions such as are found near San Antonio and Salado Creeks. That the water of these .springs during the Pleistocene period was thermal or at least somewhat warmer than at present is probable. If the deep waters emerging at that time were thermal, the continued cir- culation of water through the rocks, emerging at the springs during and since the Pleistocene would tend to reduce both the temperature and the amount of solids carried in solution by the water. It may be noted in 'this connection that the waters of the Comanchean formations at the present time are found to be warm and to carry a heavy load of solids in solution in wells drilled a few miles southeast, that is down the dip, from the existing springs. The area occupied by these concretions includes a narrow belt on either side of the ‘San Antonio River for several miles south of San Antonio, and a much larger belt lying at the northeast side of the Salado Creek. This belt on Salado Creek has a width of two or three miles and extends for five or six miles south of the Seguin Road crossing. *Letter of August 18, 1919. Geology and Mineral Resources of Bexar County 77 STRUCTURAL GEOLOGY The formations in Bexar County, both those of the Cretaceous and Tertiary, dip toward the Gulf Coast. The rate of dip, however, is changed and the county is divided both structurally and physiographically into two very distinct provinces along the line already referred to, known as the Balcones Escarp- ment, which in this county faces south-southeast. The struc- tural conditions are very different in these two provinces. North of the Balcones Escarpment, the formations depart but little from the horizontal position, the rate of dip south of the Colorado River having been estimated by Hill and Vaughan to be not more than 10 feet per mile.* The structure in the coastal plains area of this county is much more complicated than is that north of the Balcones Escarpment, being affected both by faulting and by folding. At the inner or north margin of the Coastal Plains area are large faults, while farther to the south are other faults varying from small to .large, accompanied by folds. The downthrow in most, although not in all, of the faults, and in the largest faults, is to the southeast or coastal side. The structures are in some, perhaps all, instances asym- metrical, the longer slope being on the southeast side. The com- bined effect of faulting and dipping, although varying from place to place, results on the whole in carrying the formations rapidly to a lower level in passing toward the coast. The lines of faulting and folding in the coastal plains area either approximately parallel the main or first large fault of the Balcones fault zone, or they diverge to the south, and plunge to the southwest. The southwest plunge of the formations, as well as the divergence to the south from the line of the main fault, are possibly incident to the change of direction of the fault zone in this and the adjoining county, to which reference has already been made. LOCATION OF PRINCIPAL FAULTS The first large fault of the fault zone is that which brings the Edwards formation against the Glenrose. Helotes Creek at the Bandera Road crossing flows in this fault ; the downthrow side of the fault, the Edwards limestone, being exposed in the *U. S. Geol. Surv., 18th Ann. Rpt. Part 2, p. 258, 1898. 78 University of Texas Bulletin 0 • - G IT G 4j C S o S cd tyl o +-> o rn tj * sg-s ® .. be c$ g to P> c gS»S°«B - tfiS 2>o . +j ft a; d ^£<8 ^ C G - » t* CG +j ’3 h C J2, « CM ^ .53 O ° g § 2 ft o d V, 02 ZJ © .ft O > -H © ft ► ft © n a) V ft 02 O ^ © > ... a © 5 ft o ® d t ft d >> d S .22 aS S ft o> d i o P 2 £ ffl a ® O 5 ft a> ft > aS ID .. ft ft aS £ f-, O 3 p w © s* 2 § ft 02 02 o ft tt § 13 “- 1 rH fl is £ £ o ^ ft -*J ft 2 ft d ► * d o o 3 aS . t/2 ^ I bi) Ph fe ft d aS aS 02 .£ B! 3 2 ft ° 5 © o H- Z d ® 2 d 5 .§ c -R d 9 ® I o * >> fe I 'd ft ® ft 80 University, of Texas Bulletin left bank of the stream. The following data afford an approxi- mate estimate as to the amount of throw of this fault: The surface elevation at the deep well on the Leon Springs Reservation is about 1156 feet above sea level. In this well the pre-Cretaceous schists were entered at the depth of 1015 feet or at the actual level of about 140 feet above sea. The elevation of the second deep well located on the Camp Bullis Reservation about six miles farther south, is less definitely known, but is probably about 1050 feet above sea. In this well, which is one or two miles east of the first or main fault of the Balcones fault zone, the pre-Cretaceous schists were entered -at the depth of 1799 feet, or at the actual level of about 750 feet below sea. The difference in elevation of the top surface of the schist at these two localities, amounting to about 890 feet, is doubtless due in part to irregularities of the top surface of the schists, but a part and probably the greater part of this difference in elevation is ac- counted for by faulting, since the wells, as already stated, are separated by the large fault of the Balcones fault zone. A second and probably more nearly exact measurement of the throw of this first large fault is obtained by comparing the records of these two wells. At the Leon Springs well the Glen- rose formation rises in the hills to an elevation of 1350 feet or more above sea. In the well on the Camp Bullis reservation this formation is first recognized by characteristic fossils at the depth of 584 feet below the surface, or at the elevation of about 466 feet above sea level. There is therefore an interval of be- tween 600 and 800 feet representing the downthrow of this fault, together with dips incidental to the faulting. South of the first large fault are numerous others, small and large. The amount of throw of these faults varies from a few feet to between 400 and 500 feet; the downthrow of some of the faults is to the north side but the usual downthrow and the maximum downthrow is to the south side. A study of the well records indicates that in addition to numerous small faults there are several heavy faults or narrow zones of multiple faulting. One of these faults or fault zones passes north of and approxi- mately parallels the Castroville Road west of San Antonio and in some way seems to involve the formation of the basin of El- mendorf Lake and possibly also of West End Lake. Well records in the vicinity of Elmendorf Lake in particular are very Geology and Mineral Resources of Bexar County 81 unusual and discordant, giving results that can be accounted for only by complicated faulting, breaking, and displacement of the formations. Across this zone of faulting there is a change of level in the formations, as indicated by well records, amount- ing to about 400 feet within a mile or less. In the western part of the county this fault zone may be located both by topography and surface exposures. The line of hills seen north of the Cas- troville Road in the western part of the county is formed from the Austin formation. The more or less dissected plain crossed by the Castroville Road lies chiefly on the Navarro formation. Exposures near the fault line are seen on the Masterson ranch north of the Castroville Road on Lucas Creek. A large fault with the usual northeast- southwest trend passes through the northwestern part of San Antonio. This fault is readily located by topography, surface exposures, and well rec- ords. From San Antonio to the east county line the upthrow of this fault brings the Austin formation to the surface while on the downthrow side is the Taylor formation. The surface topography revealing the upthrow side is the range of Austin Hills extending northeast from San Antonio. The exposures which reveal the fault have already been mentioned and include the exposures of the Austin formation seen in Brackenridge Park at the north city limits, and on Salado Creek and trib- utaries at the Austin Road crossing already described. The exposures of the Taylor formation on the downthrow side of the fault are seen on River Avenue. An approximate measurement of the amount of throw of this fault is obtained from two wells in the northeastern part of San Antonio. In a well located in Brackenridge Park at the north city limits, the Comanchean was reached at the actual level of 554 feet above sea. In the well drilled for Fort Sam Houston water supply, on Hackberry Street, about one mile farther south, these formations were entered at the actual level of 124 feet above sea. There is thus a drop in elevation of 430 feet within a mile. Whether this change in level is due to a single large fault, or to a succession of smaller faults, or to combined faulting and dipping, has not been determined. Near the southern limits of San Antonio is another zone of 6-Bex. 82 University of Texas Bulletin faults or rapid dips where, as indicated by well records, the formations pass in going southeast to a level about 350 feet lower in a distance of three-fourths of a mile or less. North of the fault zone the Comanchean is entered at from 900 to 950 feet from the surface, while south of the fault zone these formations are entered at from 1200 to 1250 feet from the surface. This zone of faulting is located chiefly by wells the location of which is indicated by map entries — 322 and — 338 (north of the fault), and — 680 and — 679 (south of the fault). These several fault lines do not seem to be continuous as equally strong faults entirely across the county. On the con- trary, some of them appear to pass from strong dips into faults and again into dips or a succession of small faults, a few of which have been located either by exposures or by well Records, but many of which are obscured at the surface. At least two small faults cross the Fredericksburg Road within two or three miles south of the main Balcones fault. One of these may be seen in a cut in the San Antonio and Aransas Pass Railway about 14 miles north of San Antonio. The trend of this fault at this exposure is north 30° east. The upthrow m this instance is at the south side, the Buda formation at the south side of the fault being thrown against the Eagleford formation at the north or downthrow side. Faults near the Austin Road crossing on Salado Creek have already been described. In the cut made by the Southern Pacific branch line to Camp Travis, near the east limits of San Antonio, is a fault which trends about north 50° east. The downthrow of this fault is probably to the south. Two wells drilled at Conception Mission indicate the location of a small fault having a downthrow to the south of about 50 feet. A small fault or very abrupt dip is seen at an exposure on the Pleasanton Road, eight miles south of San Antonio and near the southern margin of the Alta Vista oil field. The trend is here north 60° east. STRUCTURALLY HIGH AREAS Associated with and more or less definitely limited by the faults are well marked structurally high areas, lifted blocks, or Geology and Mineral Resources of Bexar County 83 folds, the location of which is recognized both on surface ex- posures and on well records. Three such pronounced structures • have been recognized in the north part of the county, which for convenience of reference may be known as the Culebra, San Antonio and Alta Vista structures. Aside from or within these larger structures are smaller structures, the location of which requires more detailed mapping than is attempted in this report. In the southern part of the county it becomes difficult to interpret structural conditions, owing to the few well records and limited surface exposures available. It seems probable, however, that another structure similar to those described is found south of the Medina River, its position being indicated by the J. K. Lamb well, elsewhere described. THE CULEBRA STRUCTURE The first of the pronounced high areas -is a relatively broad structure, the axis of which lies some six miles south of the Balcones Escarpment. This high area is recognized both on surface exposures and on well records. On the crest of this structure in the western part of the county the Austin forma- tion lies at the surface, while both to the north and south the Taylor formation lies at the surface. The structure is equally well indicated by well records. The actual level of the Del Rio formation on the north side of this structure near the west county line is about 150 feet above sea (well of J. Benke). The same formation three miles southeast of this place lies about 300 feet higher (well of H. Uhl). The axis of the structure ap- pears to lie another one or two miles farther south and hence somewhat higher than in the Uhl well. At the east side of the structure the Del Rio has again dropped to about 170 feet above sea level (well at fuller’s earth plant). Several well records are available on and near the Culebra Road, which crosses this structure obliquely in passing from the west county line to San Antonio. The axis of the structure is crossed on this road about 14 miles northwest of San Antonio. Here the Del Rio forma- tion lies at the actual level 730 feet above sea (well of Mrs. A. Voight). Passing southeast, this formation drops down to 170 feet above sea level in a distance of six miles (well of A. Skolout). Beyond this well to the southeast is the fault with 84 University of Texas Bulletin a downthrow of as much as 400 feet to which reference was , made earlier in this paper. It is difficult to determine whether this structurally high area represents an anticline in the usual sense of the term, or a fault block. If the latter, the block is limited at either side not by a single large fault, but by a succession of small or step faults. That there are faults at the north side of the area with the downthrow to the northwest is shown by the fault already referred to seen in the railway cut near the north side of the structure. It is probable that this structurally high area is produced by a combination of faulting and folding. The wells from which data have been obtained and used in mapping this structure include those indicated by map entries 150, 360, 369, 455, 496, 555, 730, 715, 685, 560, 545, 580, 492, 270, 188, 170, 85, 16. / THE SAN ANTONIO STRUCTURE A second notably high area having a northeast- southwest trend passes through the northwestern corner of the city of San Antonio. From San Antonio northeast the surface exposures on this structure are those of the Austin formation, forming the range of Austin Hills already described. Near the western limits of San Antonio, owing to the southwest plunge the Taylor comes to lie on the structure while exposures probably of the Navarro are seen at the north side on the Culebra Road, 5.4 miles from San Antonio. From near, the west limits of San Antonio to Leon Creek the structure is concealed by the flood-plain deposits, and when again seen at and beyond Leon Creek, the Taylor formation has been car- ried by the southwest plunge below the surface, the exposures being largely if not entirely those of the Navarro formation. The gas field west of Leon Creek appears to be located within this structure. Beyond Medina Creek the structure has not been located either by surface exposures or by well records, and it is not known whether it flattens out or its position is merely in doubt from lack of suitable data. The best exposures of this structure are those seen in the right bank of Leon Creek which crosses the structure south of Geology and Mineral Resources of Bexar County 85 Kelly Field from the Castroville to the Quintana Road crossings. At the Castroville Road and for at least two miles farther down Leon Creek, the dips are to the northwest. From near or west of the Pearsall Road to the Quintana Road, the dips, often strong, are to the southeast. A green glauconitic sandstone ledge which serves as a horizon marker in these sections is seen both at the west and the east sides, but is wanting on account of erosion from the central part of the structure at the Leon Creek crossing. The exposures east of San Antonio which best locate this high area are seen on the Perin-Beitel Road from Fratt to Wetmore. At Fratt, exposures are seen on this road which probably represent the upper marly phase of the Austin formation. On the hills one and a half miles north of Fratt are seen exposures representing the hard limestones of the lower half of the Austin formation, while in the valley next northwest of these hills are exposures of either the upper part cf the Austin or the Taylor formation. Near Elmendorf Lake at the west limits of San Antonio, this stricture is interrupted by a break or fault in which the formations are displaced as much as about 400 feet. The wells by which this structure is located include those in dica:ed by map entries 250, 485, 568, 317, 306, and 69. THE ALTA VISTA STRUCTURE Three of the oil fields of Bexar County, namely the Alta Vista, Mission, and Somerset fields, are so placed with respect to pre- vailing structural lines in this county as to suggest that they are possibly located on the same structure. If this is true, in this structure as in the two already described, there is a dis- tinct southwest plunge. The heavy oils of the Alta . Vista and Mission field s are obtained from the Austin formation at the actual level of from 450 to 550 feet below sea level. In the Sommerset field the lighter oils are obtained from either the Taylor __o r the Navarro formations at the actual level of from 400 to 700 feet below sea. To the northeast of Salado Creek, this structure, if we may rely on the rather limited well records available, turns more to the north, resembling in this respect the Culebra structure. It seems also to be interrupted near the 86 University of Texas Bulletin Seguin Road crossing by a fault. On this, however, the well records available are limited, and the mapping of this break is provisional. It is similar, however, to the interruption of the San Antonio structure already described. See wells No. 57, p. 138; 94, p. 140; 120, p. 165; 124, p. 167; and 160, p. 197. THE GEOLOGIC MAP On the geologic map are represented the surface exposures of the formations of this county in such detail as is practicable on a map of this scale. One of the problems to be met in mapping this area is the disposition to be made of the flood-plain de- posits which more or less completely mantle the whole of the coastal plains division of the county. Since the chief object of this report is to describe the general geology, these flood-plain deposits have been disregarded in mapping, except where suf- ficiently well developed to completely obscure the underlying formations over considerable areas. The low and relatively recent flood-plains have been shown where best developed bor- dering the larger water courses; of the next older and higher deposits, the Leona formation, there have been shown on the map the large areas lying southwest, south, and southeast of San Antonio ; of the highest plain, referred to the Uvalde forma- tion, there have been shown some areas in which the formation occupies uninterruptedly several square miles. All of these flood plains are more extensive than is here shown. Because of the presence of these surface materials, the boundary between the successive marine formations is neces- sarily placed in parts of the county on data from limited ex- posures, supplemented by well records. Where the surface is entirely obscured, the approximate boundary of the underlying marine formations has in some instances been indicated by broken lines, the data for placing the boundary being obtained chiefly from well records. As information is- accumulated on the geology of this and the adjoining counties, the boundary lines of the formations can be more exactly determined. In mapping structure the Del Rio has been used as a key horizon and the contours are drawn as on the top surface of this formation. In using well records and reducing elevations Geology and Mineral Resources of Bexar County 87 to sea level it has been necessary to determine the approximate surface level of the wells from the topographic map. In that part of the county for which there is no topographic map the elevations for wells near the public roads have been obtained from the profiles of public roads made by the County Engineer of Bexar County, kindly made accessible for this purpose. In a few wells not on the area topographically mapped and remote from the public roads, an estimate of the elevation has been secured by data showing the level to which the artesian water of the Georgetown-Edwards formations will rise in wells. The static head of this water brings it to an actual level usually between 665 and 685 feet above sea, affording an approximate basis for estimating the surface elevation at the well. These methods of determining levels have introduced a possible small error. A much larger possible error is found in the well records themselves. As t is well known, many well records afford only approximate data as to the depth at which formations are entered. While the wells of Bexar County afford unusually reliable data, yet it has been found in a number of instances that two logs of the same well, derived from different sources, differ to some extent. However, the limit of error both from approximate levels and from well logs, when carefully checked,, is not large as compared to the contour interval of 100 feet used' in making the sub-structure map. INDEX TO LEVELS ON THE DEL RIO FORMATION The numbers entered on the geologic map give the level of th e top of the Del Rio formation ^a bove or below sea, the levels below sea being indicated by a minus sign preceding the num- ber. In the following list the map entry numbers are ar- ranged serially and for each entry there is given the name of the owner of the well and also the number which will serve as an index reference to the more complete data given in the chapter on well records. The question mark following certain of the numbers on the map indicates that the record is in doubt, the level of the Del Rio having been in some instances estimated from the level at which some of the overlying formations were reached. 88 University of Texas Bulletin Map Entry Owner Well Number Number* 5 Southern Ice Co Ill 6 Bexar County Courthouse 17 16 F. Masterson well 80 25 Geunther Milling Co 41 • 30 Roy Hearne 51 60 Lone Star Brewing Co 7 6 69 Government well, Hackberry St 45 7 4 Artesian Ice Co 8 82 Southwestern Land Corporation 114 -82 T. F. Brady 22 85 Medina Fullers Earth Co 82 88 Salado Water Supply Co 98 88 Soutliwester Land Corporation 113 90 Geo. Brackenridge 23 -100 G. F. Trice 133 -110 H. Van Dale 136 115 H. Heine 54 —115 San Antonio Steam Laundry 105 —120^ Shattuck well 109 150 Mrs. Kate Benke 14 120 Roy Hearne 52 170 A. Skolaut 110 188 Ed Peffman 88 -190 J. H. Quinn 90 200 Mrs. Mackintosh 7 6 210 Paul Hartman . . , 50 213 St. Louis College 97 215 Southern Pacific Ry. Schertz (Guadalupe Co) -215 Oscar Kreutch 71 226 Roy Hearne . 33 227 H. Brendle 24 237 Chas. Matyear 81 239 J. D. Stephenson 116 —245 Community well, Cuppers Lane 31 250 Ross Davis 32 254 M. K. T. Ry., Landa 86 257 A. Koeps 70 260 Ed. E. Basse 55 260 L. M. Hubble 64 270 Chas. Hease 75 -270 S. A. and A. P. Ry 100 -280 Collins Gardens . 30 -285 H. J. Ackerman 3 306 H. Benz 15 *The wells to which these numbers refer are described on pages 129 to 197. Gfeology and Mineral Resources of Bexar County 89 Map Entry Owner Well Number Number -310 Acme Irrigation Co 4 -315 R. H. Hofheintz 59 317 Government well. Aviation post 44 -320 D. G. Allen 6 —322 Artesian Water Co 11 -323 J. H. Terrell 125 -328 D. J. Allen 7 —338 Steves Garden 118 -339 Gates and Co 40 350 Southern Pacific Ry 112 -350 Glen Carney 26 353 Dickenson well 33 -355 Dr. Sullivan 122 360 N. Kallison 63 367 H. H. Statte 115 369 Mrs. C. Hoffman 58 -36 9 Lady of the Lake Academy 72 -405 L. S. Toft 130 -410 C. C. Clamp 27 -415 West Gardendale 140 -418 H. Herff 56 435 H. Schumeier 108 440 J. Locke 75 449 H. Prinz 89 -453 J. T. Blank 15 455 H. Uhl . . .134 460 Waring Estate 139 470 Chris Weir 142 470 Hohnenberger well 62 —472 W. F. Leigler 74 485 Alex Lorenz 77 4 92 H. Steubing 117 496 A. E. Goforth 43 497 San Antonio City well 113 498 Joe Friesenhahn 39 520 O. J. Worsbach 144 54 5 A. Boerman 20 555 J. Widener 141 560 D. Boerman 21 568 F. Grote 46 580 E. J. Altgelt 11 620 H. Bruhn 25 655 Jud Harrison 49 -679 San Antonio City Water Supply 101 680 August Rumper . . 95 -680 R. Tommins 131 685 Pete Tezel 128 90 University of Texas Bulletin Map Entry Owner Well Number Number 715 Louis Tezel 127 730 A. Voight 138 735 E. J. Altgelt . . . . 10 -750 Terrell Hot Wells 124 -800 Wolfe & Elder 160 —816 A. J. Ridder 93 -841 Kearney Oil & Pipe Line Go 67 -870 Hot Wells Hotel 63 -880 Wm. Voght 137 —888 Superior Oil Co 123 —888 Anton Ripps 94 —915 Holz well 60 —920 Medina Oil Co 83 950 H. T. Biering 16 —1000 Perrinot well 156 -1005 Winters and Kreugel 143 1050 Government well, Camp Bullis 2 —1070 Hill and Roby 51 —1130 Steves well 120 —1380 Townsite well 132 -1500 J. K. Lamb 149 -1685 Blue Wing Club well 19 —1827 Mathey well 151 NOTES ON EXPOSURES SEEN ON THE PUBLIC ROADS It has seemed worth while to place on record here certain data accumulated in connection with the field work and used in the preparation of the geologic and other maps. These notes were for the most part taken while traveling the several main roads of the county, and for convenience of reference are reported in the order of roads out from San Antonio to the north, east, south, and west. Mileage in all instances refers to distance from the Court House in San Antonio. Presented in this form the notes will perhaps be of service to the people of the county who travel these roads, as well as to the large number of visitors who come each year to this part of the State. Blanco Road: The Blanco Road runs approximately due north from San Antonio to the county line. From the Bexar County court-house this road lies within the valley of the San Antonio River for a distance of about 1.4 miles. Underlying the stream deposits of this valley at this crossing is chiefly the Taylor forma- tion. In the western part of San Antonio, from 1.4 to 2.5 miles Geology and Mineral Resources of Bexar County 91 from the courthouse, the road passes over the San Antonio struc- ture previously described; the formation, beneath the surface grav- els, being the Austin chalk. From 2.5 to 3.7 miles is a gravel- covered and partially gravel-filled valley, the underlying formation being probably the Taylor as indicated by exposures on other roads. Between 3.7 to 4.7 miles from San Antonio this road passes onto the large zone of exposures of the Austin formation and continues chiefly or entirely on this formation to the valley of Salado Creek, about 10 miles from San Antonio. . In the bluffs of Salado Creek, the Austin, Eagleford, and Blida formations are exposed as al- ready described. These formations are again seen on the hill north of Salado Creek. Exposures of the Del Rio were not observed on this road but the formation is crossed over probably between 11 and 12 miles out from San Antonio, its zone of outcropping being represented by a valley beyond which are seen the Georgetown- Edwards limestones. The Glenrose formation comes in on this road about 19 miles from San Antonio. For the first 18 or 19 miles north of San Antonio, the water sup- plies are obtained chiefly from the Georgetown-Edwards limestones, which are reached at depths varying from 600 to 700 feet in San Antonio to surface exposures north of the north fork of Salado Creek. Beyond about 19 miles from San Antonio, the wells enter the Glenrose-Travis Peak formations. Bulverde Road: The Bulverde Road passes northeast from San Antonio to Wetmore, thence approximately north to the county line. From the courthouse to the north city limits, this road lies in the valley of San Antonio Creek. Near the north city limits it crosses the zone of faulting elsewhere described and passes onto exposures of the Austin formation. At the north side of the road about 6 % miles from San Antonio is a deep sink hole in the Austin chalk. From Wetmore to the top of the range of hills 1 V 2 miles north, the road again crosses the Austin exposures. At the north slope of this hill, as already noted, are exposures of the Eagleford and Austin formations, beyond which are the hills of the Georgetown- Edwards formations. The' Glenrose-Edwards contact is apparently crossed about 21 1 /£ miles from San Antonio. Nacogdoches and Austin roads: The Nacogdoches and Austin roads almost parallel the structural lines in this county. The Nacog- doches road which branches from the Bulverde Road one mile south of Wetmore affords exposures of the Austin formation. The Austin road lies toward the south side of the structurally high area described as the San Antonio structure. From the county line at Selma to Salado Creek the exposures seen on this road are chiefly, if not entirely, those of the Austin formation. Beyond the valley of 92 University of Texas Bulletin Salado Creek to the city limits are exposures some of which may represent the Taylor formation. St. Hedwig Road: The St. Hed.wig Road runs about due east from' San Antonio. In the eastern part of San Antonio this road crosses the high gravel deposits mapped as the Uvalde formation. The valley of the Salado at this crossing includes alluvial deposits referred to the late Pleistocene flood-plain. About % mile east of the crossing on Salado Creek the road ascends a pro- nounced terrace and passes onto the very level plain referred to the Leona formation, which continues to the break to Rosillo Creek, where exposures are seen of the Midway formation. The gravels of this formation as seen in the exposures on this terrace are largely pisolitic. Prom Rosillo Creek to the east county line the exposures on this road are interpreted as representing the Tertiary forma- tions. The contact line between the Midway and Wilcox formations is placed about 14 miles from San Antonio. Pleasanton Road: The Pleasanton Road runs about due south from San Antonio. For the first six miles from San Antonio this road passes over the level plain of the Leona formation. The gravels of this formation east of the Pleasanton Road near the San Antonio River are chiefly pisolitic, while west of this road they are largely flint pebbles deposits. The formations underlying the plain as indicated by well records are the Taylor and Navarro, with prob- ably more or less of the Tertiary toward the southern part of the plain. About seven miles from San Antonio the road passes onto the Midway formation. Near the Alta Vista oil field, about 8 V 2 miles from San Antonio, is the fault in the Tertiary formations to which reference has been made. From near Mitchell’s Lake to about three miles beyond the Medina River, the exposures on this road are mapped as Wilcox. Within about 4 miles of the county line, the road enters the belt of sand hills representing the Carrizo formation. Somerset Road: The Somerset Road runs in a general south- west direction from San Antonio into Atascosa County. From San Antonio to Leon Creek the road passes over the Pleistocene plain (Leona formation). The surface elevation rises very gradually to near the middle of the plain, and again drops gradually toward Leon Creek. Near this creek, the road descends to a lower plain forming a well marked terrace. Flowing artesian water is obtained on this road from the Georgetown-Edwards limestones which are reached at a depth of from 900 to 1000 feet, the top of the Coman- chean being reached at about 850 to 900 feet. However, the water from these formations, from about six or seven miles from San Anto- nio on to the southwest as far as tests have been made, is a warm sulphur water not desirable for drinking purposes, although used Geology and Mineral Resources of Bexar County 93 to some extent for irrigation. From Leon Creek to the Medina River is a plain which is gravel-covered. The timber growth is chieflly mesquite. In the bed of the Medina River are seen large concretions of the Tertiary formations. The late terrace deposits of the Medina River valley at this crossing have a thickness of as much as 50 feet. They consist of loams in which are found many land snails, chiefly Bulimuliis. On the south side of the Medina, this plain continues for about one mile, beyond which to the county line the road passes over the Tertiary. Beyond Somerset are sev- eral exposures of thinly laminated sands of the Wilcox formation. Pearsall (Frio) Road: The Pearsall Road runs southwest from San Antonio. From San Antonio to Leon Creek this road leads across the level plain on which Kelly, Field is located, mapped as the Leona formation. The gravel, silt, and loam deposits of this plain have a depth of from 25 to 50 feet and are utilized in places for road material. The native vegetation, now largely cleared, is mesquite. The formation underlying the plain is probably chiefly Navarro as indicated by exposures on Leon Creek. The Coman- chean is reached in wells drilled in this plain on the Pearsall Road at between 900 and 950 feet, being one or two hundred feet nearer the surface here than on the CastroviUe Road two or three miles northwest. This difference is due to structural features elsewhere described. Artesian water is obtained in these deep wells from the Georgetown-Edwards formations which are reached at about 1050 feet, and are penetrated in drilling a variable depth. In some of the wells on the lower lands the artesian water flows at the surface, although in wells located on higher lands the water is non-flowing. In the bluffs of Leon Creek at the Pearsall Road crossing are ex- posures of the Navarro formation elsewhere described. From Leon to Medina Creek the road passes over rolling lands with gravelly soils indicating remnants of flood-plain deposits. The underlying formation is largely concealed but is probably the Navarro forma- tion. From Media Creek to the Medina River, on this road, is a late Pleistocene flood-plain deposit, mapped as the Medina flood- plain. From the Medina River to the county line, this road passes over the Tertiary probably chiefly, or entirely, on the Wilcox forma- tion. In the cut in the public road west of the Medina, are ex- posures of the Wilcox already described. Castroville Road: The Castroville Road (West Commerce Street, in San Antonio) passes to the south of the termination of the range of Austin Hills, originating in San Antonio. By turning north on Zalzamora Street, a distance of about one-half mile, an exposure of the upper part of the Austin formation may be seen. On the other hand, by turning south on West 19th Street an exposure of what is probably the Taylor formation may be seen near the east 94 University of Texas Bulletin end of Elmendorf Lake. After passing Elmendorf Lake the road goes onto a level plain representing the Leona formation, which continues to Leon Creek. Well records indicate that the base of the Upper Cretaceous lies at a depth of between 1050 and 1100 feet from the surface. Hence, as the flood-plain deposits are only from 25 to 50 feet deep, the formation on this part of the plain , next below the Pleistocene is probably the Navarro. Water is obtained on this plain from shallow wells entering the Pleistocene and from deep wells entering the Comanchean formations. The deep wells give artesian water, which rises to within from 25 to 50 feet of the surface, depending upon the elevation at the well. Near Leon Creek the road passes down to a lower and later small terrace bordering the present stream. The gravels of this late terrace and of the stream bed are used in road construction. At the Leon Creek crossing on this road are seen exposures of the Navarro formation elsewhere described. Beyond the creek the road passes onto the high terrace mapped as Uvalde formation. From Leon Creek to Media Creek the exposures are chiefly of these high terrace deposits. This formation, however, is thin and small streams have cut through in places to the underlying clays, probably of the Navarro formation, as indicated by an exposure seen in a small stream channel about one mile beyond Leon Creek in which many Exogyra costata are found. The timber growth of this upland is chiefly mesquite with some oak on lands underlaid by caliche-ce- mented terrace gravels. The water supply here is chiefly from deep wells entering the Comanchean limestones. The top of the Coman- chean on this plain is reached at a depth of about 575 feet and the water-bearing limestones at about 700 feet from the surface. (Well of A. Skolout). From Media Creek to the county line this road passes over an undulating country in which the chief timber growth is mesquite, and which is underlaid throughout probably by the Navarro forma- tion. At the surface are found remnants of gravel terrace deposits which were formerly perhaps extensive, having been largely re- moved by erosion. Turning south on the Cagnon cross road about one mile there is seen at the slope to the valley of the Medina River an exposure of yellow clay containing many Exogyra costata. To the north of the Castroville Road and near the Cagnon cross road is the fuller’s earth plant elsewhere described. To the north from this road, near the west line of the county, may be seen tbe pronounced range of Austin Hills while to the south a few miles is seen the broad valley of the Medina River. One of the lines of heavy faulting approximately parallels this road from near the Leon Creek crossing to the county line separating the dissected plain over which the road passes from the Austin Hills to the north. Potranca Road: From Leon Creek to the west county line, the Geology and Mineral Resources of Bexar County 95 Potranca Road lacks but little of paralleling the structural lines of the Cretaceous formations. The road runs a few degrees south of west while the lines of structure are more nearly due southwest. For somewhat less than a mile beyond Leon Creek the road leads across a hill formed of Austin chalk. Beyond, for about one and a half miles, is a broad valley covered by gravel deposits. Although not shown on the map, this terrace plain extends north to Culebra Creek and possibly represents the location of a former valley. From this valley to the county line the road lies continuously on the Upper Cretaceous formations with frequent exposures. For the most part the soft marly phases of the Austin are represented, the •oyster. Exogyra ponderosa being very abundant, although at the Media Creek crossing and at several places beyond there are seen the hard limestones of the Austin formation. The vegetation in- cludes a dense growth of live oak on many of the hills, and mes- quite in the valleys. Culebra Road: The Culebra Road extends northwest from San Antonio. On this road 5.4 miles from San Antonio, exposures are seen at the south of the road containing Exagyra costata, probably indicating the Navarro formation. At the Zalzamora Creek crossing are seen exposures of the Austin formation, while at a somewhat higher level on the hill slope facing the valley of Leon Creek is an exposure 8.7 miles out, interpreted as representing the Taylor formation. Beyond the Leon Creek crossing for about 8 miles, aside from surface materials, the underlying formation is the Austin chalk. In this part of its course the road passes over the struc- turally high /area elsewhere described. For the last 3 or 4 miles before reaching the county line, the road passes over a high gravel- surfaced plain, underlaid, as indicated by well records, by the Taylor formation. The Bandera Road: This road extends northwest from San An- tonio. In a stream bed % mile north of the Bandera Road, 5 miles from San Antonio, is an exposure of yellow clay containing E. pon- derosa, probably representing the Taylor formation. From 6.6 miles to about 13.6 miles, the exposures on this road aside from surface materials are those of the Austin formation. At the Leon Creek crossing are the bluffs of this formation with an abundance of fos- sils to which reference has previously been made. From 13.6 to about 15 miles is relatively level land in which are occasional ex- posures of the Buda limestone, the Eagleford shales being ob- scured. At 15.5 miles, the Del Rio is seen exposed at a pond in a stream bed M mile north of the road; this formation is again seen near Helotes Creek. At the Helotes Creek crossing the Edwards formation lies at the surface, while beyond this crossing the road passes over the Glenrose formation to the county line. The large 96 . University of Texas Bulletin fault of the Baleones fault zone is crossed on this road at Helotes Creek. Babcock Road: Although lying close to and paralleling the Ban- dera and Fredericksburg roads, the Babcock Road affords a few exposures that should be mentioned. At 5.4 miles from San An- tonio on a small tributary to Martinez Creek is seen an exposure of yellow clay containing E. ponderosa and probably representing the Taylor formation. From 5.8 miles to 10 miles the exposures aside from surface materials are chiefly those of the upper part of the Austin formation, including possibly some exposures of the lower part of the Taylor formation. The hard limestones repre- senting the lower part of the Austin are first seen on this road 10.7 miles from San Antonio. The Eagleford and Buda formations are first seen on a small stream 11 miles out. The Del Rio is first seen on this road about 12 miles from San Antonio, and from 12 to 13 miles the road passes over repeated exposures of the Buda and Del Rio formations, the alternating exposures being due apparently chiefly to small faulting. At the Leon Creek crossing on this road is seen the flint-bearing phase of the Edwards formation. Beyond the crossing for a mile or so the Del Rio continues to be seen occasionally and is used in the construction of a pond near the Hausman cross road 14.8 miles from San Antonio. The limestone hills of the Edwards formation where crossed by this road are two or three miles wide, beyond which the road passes onto the Glen- rose formation. Fredericksburg Road: From San Antonio the Fredericksburg Road runs west of north to the county line, and thence to Fred- ericksburg. Within the city of San Antonio, at a distance of from 1.5 to 2.5 miles from the court-house, this road crosses the struc- turally high area elsewhere described as the San Antonio structure. Although not seen immediately on this road, Austin exposures have been seen both north and south of the road. A cut in the public road at a stream crossing about one mile from the north city limits affords an exposure of yellow clay in which no fossils were found but which on lithologic appearance would seem to represent the Taylor formation. Beyond this stream for several miles is a broad valley the surface of which is gravel covered. This valley is probably underlaid by either the TaylQr or the Austin formation. From 5.4 miles to 9.3 miles, the exposures, except those of the Uvalde gravels, are interpreted as representing the Austin forma- tion. From 9.3 to 9.7 miles are exposures of yellow clays contain- ing E. ponderosa, apparently representing the Taylor formation. From 9.7 to 10 miles exposures of the Austin formation are con- tinuous. The hard limestones of the lower part of the Austin are first see.n on this road at 10 miles from San Antonio, where Geology and Mineral Resources of Bexar County 97 they are underlaid by the Eagleford shales. From 10 miles to 13 miles from San Antonio this road crosses the belt of repeated ex- posures of the Buda and Del Rio and other formations to which reference has already been made, the succession of exposures being due in part to small faulting and in part to folding. At the Leon Greek crossing and for a mile or so beyond exposures are seen of the Edwards formation. About 16 miles from San Antonio the road passes onto the Glenrose formation and continues chiefly or entirely on that formation to the county line. ECONOMIC GEOLOGY The mineral resources of Bexar County include artesian and other ground waters, cement, concrete, clay, fuller’s earth, greensand, lignite, limestone, petroleum, natural gas, and road materials. On the accompanying map is shown the location of some of the principal mineral deposits of the county (Fig. 6). ARTESIAN AND OTHER UNDERGROUND WATER SUPPLIES The underground waters are one of the very valuable natural resources of Bexar County. In parts of the county flowing artesian wells of large volume are secured. In some other areas non-flowing waters are secured from wells of moderate depth ; while in some limited areas difficulty has been met with in secur- ing sufficient water. The relation of the geology to the water supply is very close, some of the formations containing but little water, while others afford an abundant supply. The principal water-bearing formations are the Glenrose-Travis Peak limestones, the Georgetown-Edwards limestones, the limestones of the Austin formation, and the sands and sandstones of the Tertiary formations. The formations in which the water supply is frequently found to be limited are the Del Rio, Buda, Eagle- ford, Taylor, and Navarro, and the upper part of the Austin in which the rocks are of such close texture as to retain and yield very little water. Since the formations pass through the country, as already explained, in belts having a general northeast-southwest direction, it follows that the county divides itself, with respect to water supplies, into similar belts, depend- ing upon the character of the underlying formations reached by wells. 7-Bex. 98 University of Texas Bulletin PRINCIPLES OF ARTESIAN WELLS AND GROUND-WATER • ACCUMULATION Since the principles underlying the accumulation of ground waters, including flowing artesian wells, have been fully set forth in numerous publications, they need not be discussed Fig. 6. Sketch map indicating the brick, cement and fuller’s earth plants, lime kilns, lignite mine, oil and gas fields and areas of flow- ing artesian water. Geology and Mineral Resources of Bexar County 99 here. It is therefore sufficient to state that for the coastal plains area of this county the principal intake area for the ground water is through the surface exposures of the forma- tions on their outcropping margins, chiefly south of the Balcones Escarpment. The flowing artesian waters obtained from the Georgetown-Edwards limestones enter those formations chiefly within a few miles of the Balcones Escarpment. The pores and cavities in the rock become completely filled with water up to limits which vary appreciably between dry and wet seasons. In the case of some of the formations, especially the limestones referred to, the pores and cavaties are so numerous that the quantity of water contained in the forma- tion is very great, so that the supply is not appreciably affected by pumping. With regard to the artesian waters, the conditions are ad- mirable for securing flowing wells from the water-bearing strata where the elevation is not greater than the effective head of the water. Thus water entering the Georgetown- Edwards formation follows the dip of the formation through the cavities and openings of the limestones to a lower level, and when tapped by wells will rise in the boring. The height to which the water will rise, however, varies with the seasons. Thus, following a long period of dry weather or a succession of dry seasons, the water line has been known to drop at San Antonio to the actual level o f 659 feet ab ove sea. On the other hand, following extremely wet seasons, the water has been known to rise to the level of 694 feet above sea, giving a maximum recorded variation of 36 f eet. # As a rule, the static head of the water varies between seasons within much smaller limits. At San Antonio, the static head of the water of the Georgetown-Edwards formations is close to an average of 670 feet above sea level. While exact measurements are not available, the water of these formations seem to be under a very close approximation to this same static head throughout the county. The only departure that would be expected from this head is that due to the friction of flow through the rock, which apparently is not great in this formation. *Records supplied by San Antonio Water Supply Company. 100 University of Texas Bulletin Water obtained from the Austin formation has been found to be under a static head in this area which differs more or less from the Edwards formation. Water obtained from the Travis Peak formation, where reached by wells in the coastal plain, has been found to be under a greater static head than is greater than that of the overlying formations. This fact is indicated by water obtained in the Waring well, subsequently described (No. 139, of the section on well records). WATER OF THE GLENROSE-TRAVIS PEAK LIMESTONES The Glenrose formation, as shown on the geologic map, and as stated in the discussion of the geology, lies at or near the surface in that part of the county north of the Balcones escarpment. Although not exposed at the surface, the Travis Peak formation underlies the Glenrose and is reached by some of the deeper wells. In the Glenrose formation water is usually found in sufficient quantity for household and stock purposes within the moderate depth of 200 or 300 feet. A few wells Jiave failed to get water in the Glenrose, and some have obtained a moderate supply by going through the Glenrose into the Travis Peak formation beneath, while two wells within this area, one on the Leon Springs Reservation and one on Camp Bullis Reservation, have passed entirely through the Travis Peak formation without securing a supply of water sufficient for the needs of the Government camps. The wells passing through these two formations encountered a succession of hard and soft limestones, marls, clays, and sands. East of the Balcones Escarpment these formations pass by faulting and dipping to a much lower level and are overlaid by later formations. At the Waring estate, about eight miles northwest of San Antonio, a deep well has been drilled through the overlying formations, and into, if not through the Travis Peak. In this well water is said to have been obtained at the depth of 2699 feet. This water is probably from sands near the base of the Travis Peak, or the equivalent of the Trinity sands farther north. The water rose to within about 46 feet of the surface or to about the actual level of 874 feet above sea. From the record secured in this well, it Geology and Mineral Resources of Bexar County 101 seems probable that the Travis Peak formation in this imme- diate area may be found to give an important water supply, the artesian head of which is much higher than that of the later formations. WATER OF THE GEORGETOWN-EDWARDS LIMESTONES The Georgetown-Edwards limestones afford the largest reser- voirs for underground waters of any of the formations of this area. The surface outcropping of these formations which is their intake area, forms a relatively narrow belt lying immediately south of the Baleones Escarpment and forming the line of hills elsewhere described as the Edwards Flint hills. Within the area in which these formations lie at the surface they supply non-artesian water to wells at the moderate depth of from 100 to 300 feet. Farther to the south and south- east these limestones pass under later impervious formations and the cavities of the limestones, becoming filled, contain very large quantities of water, which by reason of the eastward dip of the formations is under pressure and hence becomes ar- tesian water. AREA OF ARTESIAN FLOW The area of flowing wells from the Georgetown-Edwards lime- stones is indicated on the accompanying map (Fig. 6). Toward the north the flowing area is limited by the increased elevation of the country, the land rising to a level higher than the static head of the artesian water. To the south, on the other hand, the limitation of this belt for practical purposes is due in part to the increased depth of the water-bearing formations, but more particularly to a change in the quality of the water. South of the area indicated on the map, the water of these formations con- tains hydrogen sulphide gas, and also increases notably in tem- perature, becoming a warm sulphur water. The amount of salts in solution likewise increases until the water becomes undesir- able for household use. WELLS LOCATED IN THE AREA OF SURFACE EXPOSURES OF THE GEORGETOWN-EDWARDS FORMATION Wells located immediately south of the Baleones main fault line and within the area of surface exposures of the Georgetown- 102 University of Texas Bulletin . Edwards formations encounter in drilling chiefly hard lime- stones, with, in places, layers or masses of flint. Records of several wells within this area have been obtained in which the depth varies from 100 to about 300 feet. The water obtained is usually sufficient to supply household and ranch purposes. The Government test well on the Bacon Ranch in the Camp Bullis Reservation passed entirely through these limestones as well as the Glenrose and Travis Peak formations beneath, with- out getting sufficient water to supply the Government camps. NON FLOWING ARTESIAN WELLS OF THE GEORGETOWN -EDWARDS FORMATIONS’ Immediately north of the belt of flowing artesian wells is an- other belt in which artesian water is obtained from those forma- tions, but in which it is non-flowing because of the increased elevation of the ground. Since this belt of country lies to the north of the flowing artesian belt and hence nearer the surface outcropping of the formations the formations are reached and the artesian water obtained at a more shallow depth than farther south. FLOWING ARTESIAN WELLS' OF THE GEORGETOWN-EDWARDS FORMATIONS The number of flowing wells within the artesian belt ob- taining water from the Edwards and Georgetown limestones is so large that it is impracticable to record more than a relatively small number of them. The succession of formations in these wells, however, is very definite and by reference to the map a reasonably definite idea may be obtained of the formations to be expected in drilling in any part of the flowing area. Most of this flowing area lies within the natural divisions of the county designated as stream terrace deposits and Taylor- Navarro Plain (Fig. 2). The succession of formations to be expected in a well within this area therefore is about as follows trorn the surface to the artesian water horizon.- 1. Surface materials, soils, gravel, and other terrace deposits, variable, although of moderate thickness. 2. Clays, marls, and shales representing either the Taylor forma- Geology and Mineral Resources of Bexar County 103 tion or the combined Navarro and Taylor formations; thickness variable with the location from a few hundred to one thousand or more feet. 3. Soft marl and chalk beds passing below into harder lime- stones representing the Austin formation; thickness, between 300 and 400 feet. Some of the light-colored limestones near the middle of this formation are called “magnesian” by the drillers in this county. The limestones near the base of the formation are often quite indurated. Some water usually containihg more or less hy- drogen sulphide gas is often obtained in the Austin formation. 4. Dark colored calcareous shales, more or less sticky in drilling, representing the Eagleford formation, and commonly known in this county as the “lignite” or as the “first mud;” thickness from 30 to 40 feet. 5. A uniformly very hard limestone often characterized by black specks, representing the Buda formation; thickness quite uniformly from 60 to 65 feet. 6. Clay usually blue or yellow in color and often containing small twisted “ram’s horn” shells; thickness in this county qidte uniformly from 65 to 70 feet. This formation, the Del Rio clay, is very generally referred to by the drillers as the “mud hole” or as. the “big mud” or as the “second mud.” 7. The Georgetown and Edwards limestones lie immediately be- neath the clays of the Del Rio formation. After reaching the lime- stone the drilling is continued until a sufficient quantity of water is obtained. In some wells the drilling is continued into these forma- tions for only a few feet while in other wells it is continued to a considerable depth. In general, it is reported that the amount of water secured is increased with increased depth in these formations. WATER OF THE DEL RIO AND BUDA FORMATIONS The Del Rio and Buda formations supply relatively little water. The Del Rio consists of clays chiefly while the Buda is a close-grained limestone, neither being sufficiently porous to be well adapted as water reservoirs. A few strong flowing wells are reported as terminating in the Buda formation. Probably, however, in these instances the drill enters fracture zones in the rock, the water obtained being derived from the underlying water-bearing limestones. These formations, however, par- ticularly the Del Rio, form the overlying impervious stratum which confines the artesian waters within the Georgetown- Edwards limestones. 104 University of Texas Bulletin WATER OF THE EAGLEFORD AND AUSTIN FORMATIONS As a water-bearing rock, the Austin formation is somewhat unreliable. A considerable number of wells have obtained good water in moderate quantities from this formation, but on the other hand, a large number of wells drilled into this formation have secured water containing too much hydrogen sulphide gas to be desirable. The formation contains con- siderable quantities of pyrite and doubtless the hydrogen sulphide in the water is incident to the oxidation of the pyrite. The water is obtained chiefly from the limestones of the lower part of the formation. The Eagleford formation, which lies below the Austin, is relatively thin in this county and consists of calcareous shales. It contains as a rule relatively little water. WATER OF THE TAYLOR AND NAVARRO FORMATIONS The Taylor and Navarro formations, which consist chiefly of compact marls, clays, and shales, nearly a thousand feet in thickness, are essentially non-water-bearing. Wells drilled through these formations in the Leon Creek gas field, the Alta Vista and the Somerset oil fields, report very little water until within the middle or lower part of the Austin formation. There are, therefore, very few water wells terminating in these forma- tions. WATER OF THE TERTIARY FORMATIONS The sand lenses which are often numerous in the Tertiary formations afford moderate supplies of good water. Wells terminating in these formations supply water in sufficient quantities for household purposes at Somerset, Elmendorf, and elsewhere in the southern part of the county. For the record of numerous wells in this county, see the section on well records. SPRINGS The permanent surface waters of this county are derived from springs, the largest springs of the county being those in Geology and Mineral Resources of Bexar County 105 San Antonio at the headwaters of the San Antonio River, and on the Salado River a few miles east of San Antonio, and in San Pedro Park. These springs are located near fault lines and without doubt are supplied from the underground artesian reservoir, the water escaping to the surface through breaks in the rock incident to faulting. The following observations have been recorded, which seemingly establish the connection between the artesian reservoir and the water from these springs : “A few years ago a series of stakes was driven in the still waters of the head lake (of San Antonio River) and the height of the water marked thereon. The artesian wells were then all turned on and let run for twenty-four hours. The level of the water in the head lake or pond of the river had fallen 2 inches. The wells were then checked and in about one day the water in the head lake was at its former level. Then again the artesian wells were by survey connected in a system of levels. An excavation was made on the land of the observer below the water line. It was possible by observing the height of the water in this hole to obtain the height of water in any artesian well in the city”.* WARM SULPHUR WATER IN THE COMANCHEAN LIMESTONES Numerous wells drilled in Bexar County have shown that from a few miles south of San Antonio the water obtained from the Georgetown-Edwards limestones is warm sulphur water. The transition from non-sulphur to sulphur water in these formations, in passing to the south, is probably not as abrupt as some of the well records seem to indicate. The somewhat gradual transition from, the non-sulphur to the sulphur water areas is indicated by the slightly sulphurous waters of several wells near the dividing line between the two areas. No very satisfactory explanation has been offered to ac- count for this change from non-sulphur to sulphur water in these formations. However, in passing to the south or south- *The Water Powers of Texas, by Thofnas U. Taylor. U. S. Geol. Surv., Water Supply and Irrigation Paper No. 105, p. 25, 1904. 106 University of Texas Bulletin east, the water-bearing formations drop rapidly to lower levels and hence are more deeply buried beneath the surface It is reasonable to assume also that there is less circulation of water in these formations where deeply buried than in the same formations lying near the surface, especially within the general region of the location of fissure springs which probably have permitted the escape of water and consequently circula- tion in the formations since as early at least as sometime in the Pleistocene period. The boundary line of the sulphur water area conforms in general with the lines of structure, and is ap- proximately coincident with one of the lines of heavy faulting. Increased depth and increased chemical activity together with reduced circulations may account for an increased temperature in these waters. SOURCE OP HYDROGEN SULPHIDE IN UNDERGROUND WATER The probable sources of the hydrogen sulphide in ground waters may be summarized as follows: The decay of organic matter , containing sulphur; the reaction of organic matter upon sulphides or sulphates ; the reaction of acids upon sulphides ; the partial oxidation of sulphides. Hydrogen sulphide is formed during the decay of both animal and vegetable matter, and is obviously a possible source of hydrogen sulphide in underground waters. The hydrogen sulphide found in shallow waters in particular is doubtless very frequently from organic sources. Thorpe states that the decay of organic matter in contact with sulphates results in the formation of H 2 S. # The reaction in this case probably results from reducing properties of decaying organic matter, the sulphates being first reduced to sulphides according to the fol- lowing reaction: Na 2 S0 4 + C 2 (carbon of organic matter) =2C0 2 -|-Na 2 S. The sulphide is then acted upon by the car- bonic acid to form H 2 S as follows: Na 2 S-f-H 2 C0 3 = H 2 S+Na 2 C0 3 . The reaction of organic matter upon the suphides is regarded by Van Hise as another important source of HoS in underground water.! The formation of hydrogen sulphide as a result of action of *Dictionary of Chemistry, Vol. Ill, p. 697, 1900. fA Treatise on Metamorphism, Mon. XLVII U. S. Geol. Surv., p. 1112, 1904. Geology and Mineral Resources of Bexar County 107 acids upon metallic sulphides is - one of the most familiar of laboratory experiments. This suggests the possibility of the formation of this gas as the result of the action of acids upon metallic sulphides contained in the rocks. Sulphides, especially those of iron, are widely scattered in the earth’s crust and occur in sufficient quantity to account for the formation of H 2 S gas in water. Hydrogen sulphide is a weak acid and its salts are decomposed by a stronger acid. Sulphuric and other mineral acids should certainly react upon sulphides liberating H 2 S. Carbonic acid when abundant reacts upon alkali sulphides to produce hydrogen sulphide. It is true that the alkali sulphides are normally not abundant in the crust of the earth. Stokes has shown, however, that the reaction of sodium carbonate within the earth upon pyrite or marcasite produces sodium sulphide. The reaction given by him is as follows: 8FeS 2 + 15Na 2 C0 3 =4Fe 2 0 3 +14Na 2 S+Na 2 S 2 0 3 +15C0 2 . # It is a well known fact that the carbon dioxide which unites with water to form carbonic acid is abundant in the deep waters, especially in the limestone formations, the pressure ex- isting at considerable depth enabling the water to hold great quantities of carbonic acid. The series of reactions given by Stokes accounts for the presence of alkali sulphides , in solution in the deep waters. It may be added that all sulphides are soluble to some extent in water, and in that condition may be acted upon by carbonic acid.t The partial oxidation of sulphides is, according to Van Hise, a possible additional method of the formation of hydrogen sul- phide, the reaction being as follows 4 3FeS 2 +4H 2 0+40=Fe 3 0 4 +4H 2 S +2S0 2 The oxidizing processes are the most rapid. near the surface, especially above the underground water level, and H 2 S derived from this source probably supplies relatively shallow, rather than deep waters. Since iron sulphide (pyrite) is known to be present in the *From Van Hise, loc. cit., p. 1107. flnorganic Chemistry. International Library of Technology. Sec. 12, p. 11. $ Inorganic Chemistry. International Library of Technology. Sec. 12, p. 1113. 108 University of Texas Bulletin water-bearing formations it seems probable that the hydrogen sulphide of the deeper formations in Bexar County is very largely from this source. CEMENT The one cement plant in operation in this county at the present time is that of the San Antonio Portland Cement Com- pany, located on the International and Great Northern Railway two miles north of the north city limits of San Antonio, at the north side of the range of Austin Hills already referred to as originating at San Antonio and extending northeast (Fig. 2). The location appears to be near the contact of the Austin and Taylor formations. The materials from which the cement is made accordingly include the uppermost strata of the Austin formation together with more clayey material overlying this rock, which may represent the Taylor formation. The rock of the Austin formation is here of a light yellow color and of medium hardness. Upon partial disintegration, it breaks by exfoliation and upon further exposure crumbles to small frag- ments. The rock as seen in the face of the quarry is much broken by jointing, including small faulting. The dividing line between this rock and the more clayey material above is distinct and well marked. Overlying the clay and rock is a surface accumulation of gravel and pebble deposits. The gravel overburden is removed and the underlying clay and rock after being loosened by blast- ing is loaded into tram cars by steam shovel and in the case of the harder rocks, by hand. The thickness of the clay stratum overlying the rock probably increases as the quarry is worked back into the hill. In practice, however, it is found necessary to use only a limited amount of clay mixture with the rock of this locality. The product of the quarry is marketed under the name of the Alamo Portland Cement. An analysis of the limestone and clay utilized in this plant was made some years ago by the Bureau of Economic Geology under the direction of Dr. W. B. Phillips, and is recorded on Geology and Mineral Resources of Bexar County 109 page 65 of Bulletin 365 of the University of Texas. analyses are as follows: Limestone Shale (clay) per cent per cent Silica 7.80 55.30 Alumina 3.45 13.56 Oxide of iron *1.35 4.50 Lime 46.64 9.48 Magnesia None Carbonic acid 36.65 7.45 Loss on ignition 3.35 8.85 99.24 99.14 Formerly, the limestone of the Austin formation exposed in what is now Brackenridge Park at the north city limits of San Antonio was utilized in cement manufacture. Remnants of the old plant are still to be seen, and the sunken garden of Bracken- ridge Park marks the location of the pit from which was re- moved material for cement manufacture and to some extent for other purposes, such as road material and ballast. The firm operating at this locality, the Alamo Portland Cement Company, was the predecessor of the present San Antonio Portland Cement Company. UNDEVELOPED PORTLAND CEMENT RESOURCES In addition to the plant now operating in Bexar County, it is probable that other localities are found within the county capa- ble of development for Portland cement manufacture. In select- ing such localities, however, it is important to give careful attention both to transportation and to raw materials. The location should be easily within reach of rail transportation and should, of course, be favorably located with regard to raw materials. Since in the manufacture of Portland cement there are re- quired both limestone and clay, it is essential that a location for a plant be selected where these ingredients are both readily available. Approximately three times as much limestone is used as clay; or more, if the limestone contains clayey impurities as it often does. Favorable localities, therefore, are those in which clays and limestones may be. obtained from the same pit, such as are to be found on the contact line between limestone and 110 University of Texas Bulletin clay formations. One such contact is that between the Austin and Taylor formations on which, as already stated, the plant of the San Antonio Portland Cement Company is located. By reference to the map showing surface outcroppings of the for- mations, the approximate line of separation between these formations may be located in the county, thus Aiding in the search for such favorable localities. Another geologic horizon worthy of attention in this con- nection is that of the Del Rio clay together with the underlying Georgetown-Edwards limestones and the overlying Buda lime- stone. The Del Rio clay in this county has an awerage thick- ness of from 65 to 70 feet. The Buda limestone, which lies above this clay, is a very close-grained, quite pure limestone, having a thickness when fully developed of about 60 or 65 feet. The Georgetown-Edwards series of limestone below the Del Rio clay has a thickness of several hundred feet. The Del Rio clay, as noted in the description of that forma- tion, contains in places considerable pyrite and gypsum. In considering this clay for cement manufacture it will be neces- sary to make sure that these ingredients are not present at the locality selected. Nodules of calcium carbonate such as are sometimes present in this clay are, according to Eckel*, also to be avoided. The Buda limestone is a dense and usually very pure limestone rock, having a thickness of from 60 to 65 feet. Following is an analysis of the limestone of this formation as developed in the Chisos Mountains of Trans-Pecos Texas. The formation as developed in Bexar County probably differs to some extent from that used in this analysis, but the test is nevertheless illustrative of the chemical composition of the rock of this formation. Analysis of Buda limestone from the Chisos Mountains. From the Buda Horizon, one mile east of Boquillas.f * Cement Materials and Industry of the United States. U. S. Geol. Surv. Bull. 243, p. 38, 1905. fA Sketch of the Geology of the Chisos Country, Brewster County, Texas. By J. A. Udden, Bull. 93, University of Texas, p. 28, 1907. Per cent Silica . Alumina 2.35 .21 Geology and Mineral Resources of Bexar County 111 Per cent Ferric oxide 2 4 Lime 53.90 Magnesia 15 Carbonic acid 42.23 Water (hygroscopic) 18 Water (combined) 33 Sulphur • Trace 99.59 The Georgetown-Edwards’ series of limestones lying beneath the Del Rio clays has a combined thickness of several hundred feet. The Edwards limestone contains at some horizons large masses and layers of flint such as would render it undesirable for cement making. The upper part of this limestone series, however, probably chiefly in that part of the section represent- ing the equivalent of the Georgetown formation, contains relatively little flint. Hence there is an opportunity of finding limestones suitable for cement-making underlying, as well as overlying, the Del Rio clays. By referring to the map it will be seen that the San Antonio and Aransas Pass Railway crosses the formation referred to in the northern part of the county. Another formation that should receive consideration in a search for cement materials is the Eagleford. This forma- tion, which consists of calcareous shales with interbedded thin limestones, lies between the Buda and Austin formations. In Bexar County the Eagleford formation as already stated is but little developed, having a thickness of about 30 or 35 feet only. Its distribution is such that surface exposures /are numerous in which this formation is found lying upon the Buda Limestone, or underlying the hard limestones at the base of the Austin formation. No chemical analyses of the Eagle- ford shales of Bexar County are at hand, and so far as the writer is aware, no attempts have been made to utilize this formation in this county in cement manufacture. In Dallas County, the shales of this formation are combined with the 112 University of Texas Bulletin limestones of the overlying Austin formation in the manu- facture of cement.* CLAY The clays of Bexar County are found chiefly in the Del Rio, Taylor, Navarro, Midway and Wilcox formations. The clays of the Del Rio formation are referred to under the discussion of cement materials. The clays of the Midway and Wilcox formations are utilized in the manufacture of building bricks. The clays of the other formations are undeveloped in this county. BUILDING BRICK Three plants in this county are producing building brick. These are : the Bern Brick Company, San Antonio ; the Star Clay Products Company, Elmendorf; the San Antonio Sewer Pipe Works, Saspamco. In the plant of the Bern Brick Company the clay used is that of the Midway formation. According to unpublished notes of C. L. Baker, the clay of this pit is a dark blue-gray, easily slaking clay, carrying much fibrous and platy selenite, and weathering light yellowish and drab, containing large brown cone-in-cone concretions and small nodules of limonite. The fossils recognized were Turrit ella mortoni, Venericardia, Volutilithes, and Dentalium. The clay of this pit is very sim- ilar to that exposed in the cut of the Missouri, Kansas and Texas Railway nearby. The bricks made from this clay burn to a light red color. Up-draft kilns are used, with mesquite wood as fuel. The bricks burn to a light red. The. clay used by the Star Clay Products Company is from the Wilcox formation. The manufacturing plant is at Elmen- dorf, but the clay pits are on the south side of the San Antonio River, about four miles from Elmendorf, the clay being trans- ported from the pit to the plant by aerial tram. The following description of these clays is from notes made by Mr. Baker. *The Geology of Dallas County. By Ellis W. Shuler, llniv. of Tex. Bull. No. 1818, p. 35, 1918. Geology and Mineral Resources of Bexar County 113 In the clay pit the dip (perhaps not greatest) is 8° in the direction south 20° west. The Wilcox here consists of coarsely-laminated clayey sands. The sand is medium-grained and contains flakes of muscovite, some layers being more clayey, while others are lami- nated with thin seams of limonite. The clay is taken just as it occurs without sorting. The clay contains many leaf impressions. Layers of bluish white clay six to eight inches thick occur in the upper half of a fifteen foot section. These clay layers, if thicker, would probably make pottery clay. The overburden at the pit consists of alluvial material amounting to from four to fifteen feet. This covering is often cemented with iron oxide indicating a near approach to the Mt. Selman formation. After removing the overburden the clay is plowed and dumped into tramway cars and hauled a couple of hundred feet by mule, and then attached to aerial tramway. Mexican labor is used. This company formerly made jars, crocks, jugs, and flower pots, both glazed and unglazed, out of picked blue clay. At the present time this firm is making hollow tile and some brick. The tile and brick are wet-molded, then dried in kilns. Crude oil is used for firing the kilns, lignite being used for the boilers. One of the pits of the San Antonio Sewer Pipe Works is in Bexar County near the south boundary, while the manufactur- ing plant and other pits are just across the line in Wilson County. The clay used is from near the top of the Wilcox formation. The following description of this plant is from the notes taken by Mr. Baker : The overburden ati the pit in Bexar County is a cross-bedded sand from 10 to 12 feet thick. The upper six to eight inches are light gray, below which is found four feet of light brick red sands, while the remainder beneath is a light brownish red. The sands are often mottled with red, the mottling! being sometimes bordered with limonite or other cement. This overburden is removed by steam shovel. The dip in this pit as indicated at the contact between these sands and the underlying clay is one degree to the south. The total thickness of the clay worked at this pit is about 18 feet. The clay is blue-drab in color and slakes on long exposure to the weather. It weathers in bedding planes and joint cracks with a rusty to brick red coating of limonite. It contains small nodules of limonite and stains of yellow alum. It contains also many well preserved fossil plant impressions, especially leaves of dicotyledon- ous plants. At the manufacturing plant the clay from this pit is mixed with sandy clay from another pit. This company, which has been in 8-Bex. 114 University of Texas Bulletin operation for twenty-two years, originally made stoneware, but is now making sewer pipe, drain tile, and wall copings. The beehive type of kiln is used. The clay burns dark brown. FULLER’ S EARTH The fuller’s earth deposits of Bexar County are being ex- ploited at the present time by but one firm, the Medina Fullers Earth Company. The deposit that is being mined is located near the headwaters of a small stream north of the Castroville Road and west of the Cagnon cross road about 16 miles from San Antonio. The plant at which the earth is dried, ground, and prepared for market is located in San Antpnio, the crude earth being hauled from the pit by trucks. In the pit at the present time there is seen an exposure of as much as 35 feet of workable fuller’s earth. The overburden is moderate con- sisting of a few feet of soil and gravel. The fuller’s earth' is of a light gray or drab color, becoming lighter colored upon drying. Upon fresh fracture, the clay breaks in a very characteristic manner which suggests at once the resemblance to the divisions of shells of ammonoids. The clay is seemingly entirely free from sand, and contains little if any calcareous material. When placed in water, or upon long exposure, the clay slakes into very finely-divided material. The soils derived from it are sticky, and with the inclusion of organic matter become dark in color. The fuller’s earth beds themselves contain no fossils, so far as observed. Their relation to the overlying fossil-bearing beds indicates, however, that they are either of the Navarro or Taylor formations of the Upper Cretaceous. From the record of the well drilled at the pit the place of the fuller’s earth bed appears to be about 600 feet above the base of the Upper Cretaceous. Of this interval, the Eagleford and Austin forma- tions occupy between 335 and 400 feet. While the records are less exact than could be desired, the fuller’s earth bed of this pit is placed provisionally with the Taylor formation probably near its top. In the cut at the entrance to the plant a short distance northeast of the pit and also on the hills near the pit, are found exposures of the yellow clay containing an Geology and Mineral Resources of Bexar County 115 abundance of the oyster Exogyra costata. These exposures lying at a slightly higher level probably indicate the Navarro formation. The fuller ’s earth produced by this company is crushed into pieces of moderate size, not exceeding two or three inches in diameter and is then passed through a rotating drying cylinder to remove the excess of moisture. The clay is then ground and sacked for market. It is said to be chiefly used in clarifying vegetable oils including cottonseed oil, for which purpose the present practice is to grind the earth to pass a 200-mesh sieve. It is used also in clarifying lard. Aside from the finely ground earth, a part of the product is ground to a mesh of 16-32-60, the earth of this grade being used for mineral oils. BENTONITE In addition to the fuller’s earth there is found in this county also in the Upper Cretaceous formations the material known as bentonite. The bentonite deposits of this county have been described in a circular previously issued by the Bureau of Economic Geology, which for convenience of reference is here reprinted. The circular was based on the work of Mr. C. L. Baker. In the course of work in Bexar County, the Bureau of Economic Geology and Technology of the University of Texas has discovered a bed of the peculiar clay called bentonite, heretofore known only from Wyoming. Bentonite has the property of absorbing large quantities of various liquid substances. When freshly exposed, it is generally light yellowish-green or creamy white in color and has the appearance of wax. It often appears as a joint clay, breaking with a conchoidal fracture into roughly rectangular blocks. On surfaces exposed to the weather the outcrop looks much like that of ordinary clay, so it is necessary to dig in and expose the fresh material in order to be certain that bentonite really occurs. Ben- tonite has a soft, soapy feel, has very little or no grit, and is brittle. Mixed with the proper amount of water, it becomes very plastic; it differs from all ordinary clays or kaolins in being easily fusible at moderate heat. When placed in water it rapidly swells up and slacks, like quicklime. It completely absorbs over three times its weight or seven times its volume of water, and twice as much gly- cerin as diatomaceous earth will absorb. 116 University of Texas Bulletin Bentonite has been put to various uses. It is used for the man- ufacture of hoof-packing, a dressing for the inflamed hoofs of horses; and also in the manufacture of the medical dressing, anti- phlogistine. Its chief use is to give body and weight to paper. It is also used as soap filler, in the manufacture of high grades of soap; to dilute powerful drugs in powdered form; and as an adulterant in candy. It is a good retarder for use with the hard cement plasters and would probably make a better absorbent of glycerin in the manufacture of dynamite than the diatomaceous earth now used for that purpose. Owing to its peculiar properties, it is likely to find more extensive and varied use in the future. Bentonite has so far been found in commercial quantities in two widely distant localities in Bexar County. Probably further work will show up a number of Qther localities or perhaps a continuous bed outcropping across the country in an east-west direction. G'ne of the known localities is in a long white bluff on the east side of Lucas Creek about % mile northeast of the oil derrick on the B. F. Masterson ranch, north of the Castroville road in the western part of the county. The other locality is on Salitrillo Creek on the F. Siebold land, in the eastern part of the county. The bentonite has been found in a low north bank, a short distance downstream from the old road crossing the Salitrillo Creek. CONCRETE The concrete materials of Bexar County are obtained from the hard limestones, flints, cherts, and from the pebble and boulder deposits of the stream beds and valleys. The lime- stones best adapted for crushing for concrete are of the follow- ing formations : the Georgetown-Edwards limestone series ; the Buda limestone ; the basal strata of the Austin Formation ; and the heavy limestone concretions of the Midway and Wilcox formations. In addition there are certain hard limestone ledges in the Glenrose and in the Eagleford and probably in some other formations that will serve this purpose. By reference to the map the general distribution of the surface outcroppings of these formations may be located. The flint and cherts that may be used for concrete are chiefly those of the Edwards formation The 'gravel and boulder deposits of the stream beds include material derived from the other formations, especially from the heavy Coman- chean limestones. The stream deposits contain as a rule a mixed accumulation of flint and limestone pebbles and Geology and Mineral Resources of Bexar County 117 boulders. The deposits of this kind are best developed in the Recent and Pleistocene stream beds for several miles south of the Balcones Escarpment. In all the central and northern parts of the county concrete materials may be obtained locally or at least by transportation for no more than a few miles GREENSAND The Navarro formation as developed in Bexar County is characterized by beds of greensand, the distinguishing feature of which is the presence of the green-colored mineral, glauconite ; a mineral containing a small amount of potassium. Numerous exposures of the greensand strata of this formation are found in the county. Of these perhaps the best known is an exposure at the south bank of Leon Creek between the Castroville and Pearsall road crossings. An analysis of this greensand has been given by Dr. Wm. B. Phillips in Bulletin 365 of the University of Texas, Page 69, 1914. The account of this phosphatic greensand deposit given by Dr. Phillips is as follows : On Leon Creek, about 7 miles west of San Antonio, on the Castro- ville Road, there is a heavy deposit of phosphatic greensand of the following composition: Per cent Silica 35.18 Alumina 5.30 Lime .*16.00 Oxide of iron 17.25 Magnesia Trace Soda 1.39 Potash 1.69 Carbonic acid 8.00 Loss on ignition 10.10 Phosphoric acid 3.30 98.21 118 University of Texas Bulletin This deposit contains rounded phosphatic pebbles, from 1/8-inch to ^-inch in diameter, of the following composition: f Per cent Silica 7.50 Alumina 31.03 Oxide of iron 4.58 Lime 18.08 Carbonic acid 4.60 Phosphoric acid 18.19 Loss on ignition 12.60 98.34 The larger pebbles are not abundant. For the most part, the pebbles are very small, less than 1-20 inch in diameter. An examination of 10 feet of this phosphatic green sand foot by foot gave the following results, from above downward: Phosphoric acid Per cent First foot 3.09 Second foot 2.38 Third foot 3.22 Fourth foot 3.07 Fifth foot 4.00 Sixth foot 2.73 Seventh foot 4.32 Eighth foot 2.60 Ninth foot 3.70 Tenth foot 3.97 Average 3.30 The total thickness of the deposit is about 20 feet, and it sets in at from 4 to 6 feet below the surface. Taking the deposit as a whole, it carries enough lime, potash and phosphoric acid to make it a good fertilizing agent. The rock is soft and easily pulverized. It could be finely ground and used with distinct advantage on many farm lands in south Texas, especially those in the vicinity of San Antonio. With the exception of some “stray” phosphate in Fayette County, the exact locality of which is somewhat uncertain, the phosphatic pebbles from Leon Creek carry considerably more phosphoric acid than any other known deposit in the State. LIGNITE Lignite is found in commercial quantities in Bexar County- in the Wilcox formation of the Tertiary system. The areal Geology and Mineral Resources of Bexar County 119 distribution of the surface outcropping of this formation is indicated in a general way on the accompanying map. In the well logs, lignite is frequently reported in this formation . These strata lie at varying depths below the surface and are of varying thickness from one to several feet. The individual lignite beds are doubtless of relatively local development, but the frequency with which they are reported indicates the possibility of beds of commercial value at places in the part of the county occupied by the Wilcox formation. At the present time, a lignite mine is being opened up about 1 y 2 miles west of Somerset. The company operating here is the Brackenridge Coal Company. The test pits indicate a lignite bed having a thickness of from 5 to 9 feet, lying about 44 feet below the surface, and including a sufficient areal extent to justify development. A branch line is now being built to the mine from the Artesian Belt Railway. LIMESTONE The limestone resources of this county are extensive. The Comanchean system in particular contains a great succession of thick limestones, particularly those of the Glenrose, Ed- wards, Georgetown and Buda formations. In the Upper Cretaceous the Austin formation is the chief limestone member. The distribution of these formations is indicated on the geo- logic map. The limestone formations are crossed by several of the railroads, particularly by the San Antonio and Aransas Pass Railway north of San Antonio. The limestones suitable for cement and lime manufacture, and for building stone and road materials are separately dis- cussed. Another possible use for the limestones is to grind and apply to acid soils. As is well known many of the soils of *It is necessary to distinguish in well logs between the term “lig- nite” as used by drillers operating in the central part of the county, and the same term as used by drillers in the southern part of the county. The latter refer to the true lignite of the Wilcox forma- tion, while the former refer to the dark carbonaceous shales of the Eagleford formation. 120 University of Texas Bulletin the Gulf Coastal Plains are acid in reaction and are benefited for some crops by the application of ground limestone. For this purpose a pure limestone is desirable, thus reducing the amount of inert matter that it is necessary to transport Analyses of the limestones of the Austin and Buda formations have already been given. The following test of a sampie of the limestone of the Edwards formation has previously been published in University of Texas Bulletin 365, p. 66, 1914: Analysis of limestone from San Antonio Lime Company. Per cent Silica 0.70 Alumina 0.28 Oxide of iron 0.72 Lime 55.05 Carbonic acid 41.9.0 Loss on ignition 2.10 100.00 Physical qualities: Crushed at pounds per square inch 6,66 6 Weight of cubic foot 167.60 * Per cent of cells by volume . . 0.20 Volume of cells in a hundred parts by weight. . . . 0.07 Pounds of water absorbed per cu. ft 0.11 LIME The limestones suitable for the manufacture of lime in Bexar county are extensive. The Edwards formation is a very pure . calcium carbonate and several quarries have been opened in this formation for the manufacture of lime. Owing to un- favorable labor conditions no one of these quarries was in actual operation during 1918, although it is expected that this industry will be resumed as soon as conditions will permit. The San Antonio Lime Company located on the San Antonio and Aransas Pass Railway 14 miles from San Antonio us^ rock from this formation. The analysis of the limestone rock used by this company has already been given. With large quantities of limestone rock available for lime manufacture the success of a plant of this kind will be de- Geology and Mineral Resources of Bexar County 121 termined by the location with respect to markets, convenience and cost of transportation. BUILDING STONE The limestones of the Comanchean system offer very at- tractive stone for building, and are of service especially where conditions are such that they can be used without being transported and great distance. The Glenrose, Edwards, Georgetown and Buda formations are all capable of furnishing desirable building-stone. In the Upper Cretaceous the in- durated ledges of the Eagleford formation have been used locally for building. These hard layers have the advantage of uniform thickness The basal members of the Austin formation likewise include ledges of hard limestone available locally for building purposes. PETROLEUM AND NATURAL GAS Petroleum in Bexar County was probably first produced in commercial quantities from the Dulnig wells about eight miles east of San Antonio. Subsequently oil and gas have been discovered at other localities, and at the present time there are perhaps between 60 and 70 producing wells in the county. The oil has been obtained chiefly in the southern part of the county, south and southwest of San Antonio. Although somewhat scattered, the producing wells, all of which are small in production, may be grouped as the wells are now known into four or five more or less well defined fields or areas. The location of these areas is indicated on the key map to the resources of Bexar County (Fig. 6). They are as follows: Alta Vista, Mission, South Medina, Gas Ridge, Somerset, and some oil wells southeast and southwest of the Somerset field. The Alta Vista field lies about eight miles due south of San Antonio on the west side of the Pleasanton Road. The Mission field lies about three miles west of the Alta Vista field, or about twelve miles slightly west of south of San Antonio. The Somer- set field is near the Bexar-Atascosa county line miles south- west of San Antonio. A gas and oil field lies between Leon 122 University of Texas Bulletin and Media Creeks from eight to twelve miles southwest of San Antoni 3 . To this field no name seems to have been applied although it is referred to locally as the “Gas Ridge”. South of the Medina River, three or four miles south of the Mission field, several wells have been brought in recently, located on the Kimbley-Brown lease chiefly on the Swearingen property. A few additional wells are found in the county not included within any one of the areas mentioned. At the present time (1918) five wells are producing in the Alta Vista field, of which one flows and four are pumped. In and near the old Mission field there are about seven wells producing. In and near the old Somerset field within Bexar County, about fifty small wells are now producing. All of the wells at present producing in these three fields are small, mak- ing from two or three to five or six barrels per day. In the Atascosa County extension of the Somerset field, better wells are obtained some of which are reported to make fifteen barrels or more per day. All of the wells thus far obtained in this county obtain oil from the Upper Cretaceous formations; in the Alta Vista and Mission fields, from the Austin formation; and in the other fields chiefly from the Taylor and Navarro formations. The oil from the Austin formation is a heavy oil, reported to be about 14 or 15 degrees Baume, while that of the Taylor and Navarro formations is much lighter, averaging about 36 degrees Baume. Some of the oil from the Somerset wells may come from the Midway formation. THE ALTA VISTA FIELD The first showing of oil in the Alta Vista field is said to have been in a well drilled for water. This led subsequently to other wells being drilled, and in September, 1915, the Mars % Discovery well was brought in, the initial production of which was reported at the time to be as much as 125 barrels per day. The impetus given to drilling by this and by subsequent suc- cessful wells led to very active development in this field for a short time. Subsequently the wells rapidly dropped off in production. Geology and Mineral Resources of Bexar County 123 THE MISSION FIELD The Mission oil field may be regarded as essentially the southwestward extension of the Alta Vista field. The first well indicating oil drilled in what subsequently became known as the Mission oil field is said to have been drilled for water in June, 1901. This well showed oil at the depth of 275 feet. Following the discovery of this showing of oil, drilling was undertaken in this field by Nash and Fitzgerald who finally completed, in 1907, a 2900 foot well on the Linn farm. This deep well, a record of which is given under the section on well records, yielded a flow of sulphur water and was non-pro- ductive of oil. In this field after passing through showings of light oil, heavy oil similar to that of the Alta Vista field is obtained at the depth of about 1000 feet. Sulphur water is encountered below the heavy oil as in the Alta Vista field. GAS RIDGE OIL AND GAS FIELD The Gas Ridge oil and gas field lies west of L'eon Creek and north of the Pearsall (Frio) road, and is located chiefly on what is known as the Hamilton-Sw^ain and Cohen lands. Two wells were drilled in this field some years previous to 1916. Additional wells yielding gas and some oil were drilled during 1916 and at the time of the preparation of this report several additional wells were being drilled. This field was visited in 1916 by Mr. E. L. Porch, Jr., and the following extract is from the report made to the Bureau of Economic Geology by him at that time on the new wells then being drilled or recently com- pleted. These wells are all within a few hundred feet of two gas wells which were drilled here several years ago. The gas from one of these wells is 'used as fuel for the present work, the other well being connected up so that it can be used if needed. There is a third well, about a half mile south of these two gas wells, which is said to have also been a gas well Sarber well No. 1, in ‘which oil was first struck, is located on the Hamilton-Swain tract, while Sarber No. 2 is located on the Abe Cohen tract, and is about 500 feet east of No. 1. Well No. 1 was 124 University of Texas Bulletin drilled with a standard rig, and is 492 feet deep. No. 2 was drilled with a rotary rig, to a depth of 1035 feet. At the time of my first visit on Friday, a packer was being placed in No. 1, and I could hear the gas bubbling in it. No. 2 was down about 1000 feet and was showing some oil and gas. I took a sample of the oil said to have come from No. 1, and samples of all of the cuttings from known depths. There was a barrel of the oil near the derrick, and it had been standing some eighteen hours, but notwithstanding this fact, it smelled something like gasoline, and had a specific gravity of 29.1° Baume. The oil sand in No. 1 is said to be 22 feet thick. On the afternoon of the next day (Saturday) oil was struck in No. 2 at a depth of 1035 feet, it being estimated that the drill pene- trated the “oil ,sand” less than a foot. On Sunday afternoon I made my second trip, but could not obtain a sample of the “oil sand,” and all the oil I could secure was some skimmings from the slush pit. This oil has a specific gravity of 12.8° Baume, and ap- pears very similar to the oil obtained in the Alta Vista field, which is about 8 miles southeast of this field. These gas wells were said to have had an initial pressure of 350 lbs. per square inch, and they still have sufficient pressure (judging from observations of the one I saw tried) to shoot a flame out about forty feet from the mouth of a four inch pipe, with a roar that could probably have been heard over a mile away. . . . The logs of the wells in this field indicate a succession of clay shale and gumbo. Chalky rock is noted in some of the deeper wells. There is little or no water in the higher forma- tions although water is doubtless to be expected in wells drilled somewhat deeper. The wells start, aside from the surface materials, in the Navarro formation. The shallow oil and gas with little doubt comes from the Taylor formation. The deeper oil, which is much heavier than the shallow oil, may come from the Austin formation. The gas is probably from the Taylor formation at the depth of about 800 feet. THE SOMERSET OIL FIELD As in the case of the Alta Vista and Mission fields, the Somerset field was discovered as the result of drilling for water. About 1913, Mr. C. Kurz while drilling for artesian water on his property two miles east of Somerset encountered oil which led to other wells being drilled by himself and others. Geology and Mineral Resources of Bexar County 125 The field in Bexar County now has about 50 small wells. In this field the oil immediately east of Somerset is reported as being obtained from hard shale at from 850 to 900 feet. South and southwest of Somerset, however, the wells are deeper, reaching in this county a maximum of about 1250 feet. In the extension of the field into Atascosa County, somewhat deeper wells are required to reach the producing horizon. On the Kurz property boulders are reported as being en- countered occasionally to the depth of about 300 feet. Below this level is chiefly shale and gumbo. On the Witherspoon lease adjoining the Kurz property similar conditions are en- countered. The generalized log of the wells on this property is given by Mr. Kurz as follows: Alternating beds of sand and rock from the surface to the depth of 270 feet. Water in the formation at intervals to about 300 feet. Below about 270 or 300 feet is alternating shale and gumbo strata with little or no water. The wells on the Harrison property, Slimp and Davidson lease, south of Somerset, reach the producing sand at about 800 feet. The wells of the Crosby lease, on the other hand, near the county line, reach a producing horizon at the depth of about 1250 feet. THE SOUTH MEDINA OIL FIELD Several oil wells were brought in south of the Medina River during 1918 by Kimbley and Brown. These wells reach the producing horizon here at the depth of from 1250 to 1350 feet. The materials passed through are indicated by the logs of the wells kindly supplied by Mr. Brown, and published in the chapter on well records. The wells start in the Tertiary formations and probably terminate in either the Navarro or Taylor formation. In the Park Oil and Gas Co. test well, Apple- white No. 1, located less than one mile southeast of Kimbley and Brown, Swearingen No. 4, the Austin formation appears to have been reached at 1896 feet from the surface. RELATION OF THE BEXAR COUNTY OIL FIELDS TO STRUCTURE In the Alta Vista field the producing horizon lies more than 100 feet nearer the surface at the north side of the field than 126 University of Texas Bulletin at the south side. A part and perhaps the greater part of this difference in elevation is accounted for by the small lault or abrupt monoclinal fold which passes through this field to which reference has already been made. The following data on the depth to the producing horizon in this field were secured chiefly from Messrs. Ross, Mull and Raborn, operators and drillers in this field. Wells of Alta Vista field arranged approximately in order from north to south. Depth to Actual level Name of well Elev. Prod. Prod. Horizon Horizon Ingram well 615 102 0 405 Fuchs No. 2 615 1020 405 Aiken 605 1020 415 Mars Discovery 600 1070 450 National Oil Co 585 1120 585 Busby Well 555 1150 595 The most striking feature of these records is the apparent change in level of more than a hundred feet between the last two wells and those which precede. This change in the level of the producing horizon appears to be essentially in the line of the fault already referred to. In the Somerset field the data .on structure are unfortunately very limited. In that part of the producing area lying from y 2 to 1% miles southeast of Somerset, the dip in the strata is pretty definitely shown to be to the southeast. On the Kurz property near the Artesian Belt Railway about 1% miles from Somerset, the dip was found from well records to amount to 40 feet in about one-third of a mile. In addition to a southeast dip the structures in the vicinity of Somerset plunge to the southwest as is indicated by the increased depth of well in passing from Bexar to Atascosa County. On the Swearingen property south of the Medina River the dip in the producing horizon in a direction slightly east of south, as shown by the wells of the Kimbley-Brown lease, is as much as 115 feet in a little more than a mile in a direction slightly east of south. It is thus seen that the producing wells in the fields on which Geology and Mineral Resources of Bexar County 127 •definite data are available are located on the southeast slope of the structures. On other data already presented it is shown that these structures are asymmetrical, having a long south- east slope and a more abrupt northwest slope or limb ; some of the structures possibly being at the northwest side by abrupt dips or by dips and faults. In extending explorations it ap- pears reasonable, therefore, to anticipate the possibility of similar structures with, in general, a northeast-southwest trend farther to the southeast from those already known. QUALITY OP THE BEXAR COUNTY OIL As has already been stated the oil obtained from the Austin formation is much heavier than that from the overlying Taylor or Navarro formations. The following gravity tests of the Bexar County oils have been made at various times in the testing laboratory of the Bureau of Economic Geology. The first three oils are probably from the Taylor or Navarro formations ; the others are probably from the Austin formation. The gravity was taken at 60° F. No. 1. Crude petroleum from near Somerset, 18 miles south of San Antonio; gravity, 35.8 ° B. No. 2. Prom a well at Somerset, Bexar County; gravity, 30.7 ° B. No. 3. Said to have come from Sarber well No. 1, Hamilton Swain Tract, about 9 V 2 miles southwest of San Antonio, at a depth of 492 feet; gravity 29.1 ° B. No. 4. Collected from scum of pit on H. Cohen Tract, Sarber No. 2 well, about 500 feet east from Sarber No. 1, at a depth of 1035 feet; gravity, 12.1 ° B. No. 5. Prom National Oil Company No. 1, 1115 feet below sur- face, in Alta Vista field, Bexar County; gravity, 14 ° B. No. 6. From Marr’s No 1 well, Bexar County; gravity, 14 ° B. No. 7. Crude oil from Kelso well No. 1, 8 miles south of San Antonio; gravity, 14 ° B. GENERAL CONSIDERATIONS The oil fields of Bexar County are located on structures which lie within and are a part of the disturbed area of the Baleones fault-zone, the structure approximately paralleling 128 University of Texas Bulletin the Bale ones Escarpment. The location of this county near the turn of this fault zone from the northeast-southwest to an east-west direction accounts possibly for the very heavy faulting as well as for the southwest plunge of the structures. The structurally high areas appear to be limited at either side in part by faults and in part by abrupt dips, the longest slopes being to the southeast. It is probable that the producing wells are located chiefly on the southeast slope of the structures. This is true at least for the Alta Vista, South Medina, and Som- ersat fields, the data on the Mission and Gas Ridge fields being at present less definite. Production in this county is from the Upper Cretaceous, the Lower Cretaceous not having been found to be producing. Wells drilled to test formations below the Cretaceous, if located in the central or southern part of the county, must expect to drill through 3500 feet or more of sediments before reaching formations older than the Cretaceous. Near the Balcones Escarpment the formations next beneath the Cretaceous have been found to be schists. Whether or not the Pennsylvanian or other formations come into the section farther to the south, between the Cretaceous and the schists, has not been determined. If wells are drilled in search of production below the Cretaceous, the more promising locations are on structures as far removed, the required drilling depth being considered, as practicable from the Balcones Escarpment. In the further development in the Upper Cretaceous and Terti- ary formations it is suggested that structures already known may be followed in their southwest trend, and that other similar structures may be looked for to the south or south- east of those already known. ROAD MATERIALS The road materials in Bexar County include gravel, limestone rock and sandy clays. Of these materials the gravels are the most generally utilized, and are found in the stream beds and in the flood plain deposits of the Leona and Uvalde forma- tions. The distribution of the limestones and clays has already been indicated. Geology and Mineral Resources of Bexar County i29 WELL RECORDS In this section will be found records of the wells that have been utilized in making the contour map showing structure and in describing the water supply conditions in the county. Since in the structural map the key horizon used is the Del Rio formation, the actual level of the top of this formation is given for all wells as nearly as this can be determined or estimated from the well logs. The wells are numbered for convenience of reference and are entered according to the formations in which they terminate, those reaching the oldest formations be- ing first listed. WELLS ENTERING THE PRE-CRETACEOUS FORMATIONS As has already been stated, two wells in this area enter the pre-Cretaceous formations. The description of the cuttings of these wells will subsequently be published by Dr. J. A. Udden in connection with the destription of samples from other wells in the State. The two wells are as follows : 1. Well on Leon Springs Military Reservation, about 2 miles northeast of Leon Springs Station; elevation about 1156 ft. above sea level; log made from the driller’s records and submitted to the Bureau of Economic Geology by Alexander Deussen. Depth in feet Quaternary: Black soil 0- 4 Gravel 4- 15 Glenrose: Yellow limestone 15- 25 Blue limestone, a little water 25- 44 15" casing set at 44 s Blue clay 44- 50 Blue limestone 50- 5 8 Blue clay 58- 70 Blue clay and yellow lime mixed 70- 95 Yellow limestone 95- 125 Blue limestone 125- 140 Blue clay 140- 155 Gray limestone 155- 160 Yellow limestone 160- 180 9 -Bex. 130 University of Texas Bulletin Glenrose: Depth in feet Yellow limestone honey-combed 180- 109 Blue clay 199 _ 210 Gray limestone 210- 2 47 When 600' was reached, water dropped to 300' of surface. Water struck at 230' appeared to be a strong vein; rose 50' Blue clay 247- 254 Gray limestone . ... 254- 309 Crystallized limestone 309- 315 Blue limestone •. 315- 366 Gray limestone 366- 375 Hard white crust limestone 375- 382 Gray limestone clay in seams 382- 400 Yellow limestone 400- 433 Blue clay 433- 487 Gray limestone 487- 535 Travis Peak formation: Dark gray sandstone °535- 570 Blue clay 570- 620 Blue sandstone 620- 690 10" casing set at about 635' Brown stone 690- 708 Blue stone 708- 775 Blue clay 775- 790 Red clay 790- 7 92 Brown stone 792- 800 Light blue clay 800- 842 Red clay 842- 847 Blue clay 847- 855 Green and red clay mixed 855- 865 Gray stone 865- 875 Red clay 875- 950 Red clay 950- 975 Red sandstone 975- 985 Gray sandstone 985-1010 Conglomerate rock, small vein of water struck 1010-1015 Pre-Cretaceous: Brown clay 1015-1045 Slate 1045-1077 Slate 1077-1184 Slate seamed with quartz 1184-1244 Slate mixed with quartz 1244-1305 Geology and Mineral Resources of Bexar County 131 Pre-Cretaceous: Depth in feet Slate and oil 1305-1344 Vein opened in cleaning out well. Water rose to 280' of surface Slate mixed with quartz 1344-1645 At 1645', casing reduced from 8" to 6". Slate mixed with quartz *. 1645-203 5 At 1728', 8" casing from surface Slate 2035-2500 No water. 6" casing 2. Well on Camp Bullis Reservation, east of S. A. P. Ry., about 14 miles northwest of San Antonio. Benkendorfer, driller. Eleva- tion, about 1050 feet. Record based on examination of samples by Dr. J. A. Udden and V. V. Waite. The surface exposure at the well shows remnants of the Buda limestone underlaid by the Del Rio clay which is recognized as ex- tending to a depth of 53 feet. Beneath the Del Rio is found the thick series of Comanchean limestone including presumably the Georgetown, Edwards, Comanche Peak, Walnut clays, Glenrose, Travis Peak and Basement sands. The Glepros^,ins^LD^bj4«44na was recognized in samples from 584 feet and deeper, indicating that the Georgetown, Edwards, and Comanche Peak formations are included in the interval from 53 to 594 feet, or less, from the surface. Orbi- tulina continues to the depth of 1036 feet. From about 1270 to 1770 the cuttings show numerous layers of blue clay and shale alternating with limestones and marls together with red calcareous clays and shales and some quartz sand this part of the section presumably being within the Travis Peak formation. At 1799 feet and below to the bottom of the well, 1905 feet, the cuttings indicate shists similar to those of the deep well on the Leon Springs Reservation. The formations encountered in this well may be tentatively given as fol- lows: Buda, 0-14 feet; Del Rio, 14-53 feet; Georgetown, from about 53 to about 95 feet; Edwards, (including Comanche Peak and Walnut clays if present) from about 95 to 580 feet; Glenrose and Travis Peak (not inclusive of basement sands) 580 to about 1710 feet. Basement sands 1710 to 1790 feet. Below 179*0 feet to the depth of the well (1910 feet) is pre-Cambrian schist. With regard to schists Dr. Udden states: The two dark schists seen in the lowest one hundred feet of this boring were carefully tested by J. H. Stullken and found to contain four per cent of fixed carbon, but practically no combined carbon. This fixed carbon is graphite. Tests for manganese were negative. The formation represented is probably the Pack Saddle schist. This well is of especial interest as giving practically the full sec- tion of the Comanchean, and also as indicating the presence of schists beneath the Comanchean immediately south of the Balcones Escarpment. Of the Comanchean formations there is wanting at 132 University of Texas Bulletin this well only the upper part of the Buda. The actual thick- ness of Comanchean drilled through is 1770 feet. To this should be added about 50 feet to account for the full thickness of the Buda limestone. Thus the Comanchean at this locality is about 1820 feet thick. Log of well at Camp Bullis Reservation, San Antonio, Bexar County, Texas, August, 1919. Furnished by F. G. Chamberlain, Constr. Q-M., Camp, Travis. Buff colored limestone 0- 7 Buff colored limestone, lighter than above 7- 14 Buff colored marl 14- 38 Yellow marl 38- 50 Yellow clay 50- 53 Straw colored limestone 53- 65 Yellow limestone, fine texture 65- 68 White limestone 68- 7 2 Yellow limestone 72- 78 White limestone 78- 89 Cream colored limestone 89- 93 White limestone x 93- 113 Cream and light gray limestone 113- 118 Light gray limestone with gray flint 118- 124 Cream and light gray limestone 124- 129 Compact gray limestone 129- 14 6 Cream colored limestone, some flint 146- 158 Cream colored and light gray limestone 15 8- 170 Compact cream colored limestone 170- 186 Cream and light gray limestone 186- 194 Cream colored and some yellow limestone 194- 197 Grayish white limestone 197- 207* Compact cream colored limestone 207- 221 Light cream colored limestone 221- 230 Yellow foraminiferal limestone 230- 232 Yellow limestone red blotches 232- 237 Yellow and gray limestone, red streaks 237- 244 Blue limestone 244- 246 Bluish gray limestone 246- 255 Yellow limestone 255- 260 Yellow and gray limestone 260- 277 Yellow limestone 277- 288 Yellow limestone and light gray sandstone 288- 292 Light gray dolomite 292- 302 Gray limestone 302- 315 Gray dolomite 315- 325 Gray limestone 325- 331 Dolomitic gray limestone 331- 348 Geology and Mineral Resources of Bexar Comity 133 Oolitic foraminiferal gray limestone 34 8- 352 Gray marly limestone 3 52- 360 Gray impure limestone 360- 387 Gray fine grained limestone . . 387- 392 Light blue gray limestone 392- 397 Fine-grained gray limestone 397- 415 Gray soft marly limestone ...» 415- 456 Gray oolitic foraminiferal limestone 456- 472 Gray marly limestone . . . . 4 72- 493 Gray soft organic limestone 493- 515 Gray dolomite, limestone, . some shale 515- 520 Gray foraminiferal limestone 520- 530 Gray dolomite, limestone, some quartz sand 530- 535 Gray organic fragmental limestone 535- 608 White foraminiferal limestone 60 8- 612 White fine-grained limestone 612- 617 White porous organic fragmental limestone 617- 626 White limestone, some quartz sand 62 6- 630 Light gray foraminiferal and organic fragmental limestone 636- 641 Gray limestone, some bluish gray marly shale 641- 64 6 Gray limestone 64 6- 655 Fragment of stalactite 65 5- 6 60 Gray foraminiferal and organic fragmental limestone. . 660- 6 79 Gray marly limestone and bluish gray marly shale. ... 679- 683 Light gray foraminiferal and organic fragmental limestone 683- 707 Bluish gray marl 707- 737 Light gray marly limestone 737- 743 Light gray limestone 74 3-10 90 Gray limestone 1090-1100 Dark gray limestone 1100-1112 Dark gray limestone and gray marl . ; 1112-1119 Gray limestone and white marl 1119-1120 Gray limestone and gray marl 1120-1125 Gray limestone, organic fragmental 1125-1144 Gray limestone, some gray marl 1144-1150 Dark gray marl and .some dark gray limestone 1150-1161 Gray marl 1161-1167 Gray limestone, white limestone, blue marl 1167-1173 White and dark gray marl, some yellow limestone. . . .1173-1179 Light gray limestone 1179-1186 Light gray marly limestone 1186-1209 Blue and white marly limestone 1209-1219 Light gray marly limestone 1219-1232 Gray and cream colored limestone 1232-1240 134 University of Texas Bulletin Greenish gray marl, some fine gray sandstone 1240-12 47 Light gray and marly limestone 1247-1253. Light blue marly clay 1253-1255 Fragment of echinoid spine, cytherea 1255-1258 Gray limestone 1258-1259 Light buff colored limestone, some marl, pyrite and sand 1259-1262 Gray marl 1262-1269 Buff colored limestone, gray limestone, gray marl, some calcite, sandstone, and chert 1269-1270 Blue and white marl 1270-1279 Light blue shale, some white marl 1279-1284 Blue marly clay 1284-1303 Dark gray organic fragmental limestone 1303-1310 Blue marly shale, some white marl and fine buff colored limestone 1310-1316 Blue marl with gray limestone 1316-1322 Blue marly shale 1322-1334 Dark gfay organic fragmental limestone 1334-1345 Gray organic limestone 1345-1475 Blue marly shale, some quartz and sand 1475-1479 Blue marly shale and some gray limestone 1479-1484 Blue marly shale and some sand 148 4-1501 Soft blue marl 1501-1528 Dark olive green and some light gray marl. 1528-1533 Bluish green marl and some light gray marl 1533-1539 Bluish gray marl, some marly shale, and quartz 1539-1549 Blue marly shale 1549-1623 Soft blue calcareous shale 1623-1625 Light red marly shale 1625-1647 Soft light green marl . . . 1647-1654 Bluish gray marl 1654-1657 Brownish gray marl 1657-1660 Light gray marl 1660-16 66 Light greenish gray marl 1666-1673 Light brownish colored marl, much sand 1673-1675 Light brownish colored marl and less sand : . . .1675-1689 Light colored marl , 1689-1703 Light buff colored siliceous limestone 1703-1711 Light buff colored calcareous sand 1711-1766 Light buff colored limestone with fine and coarse sand . 1766-1770 Dull yellowish gray schistose shale * 1770-1779 Yellowish gray schist, part purple 1799-1802 Dirty brownish gray and bluish gray schist 180 2-1808 Dark and light brownish gray schist .1808-1816 Slightly micaceous schist, white and gray quartz 1816-1822 Geology and Mineral Resources of Bexar County 135 Dark gray schist, some quartz 1822-1830 Dark gray, dull red and purplish schist, some quartz. .1830-1835 Dark gray schist, some greenish and reddish 1835-1847 Dark with- little pinkish gray schist 1847-1850 Dark gray schist with reddish and light greenish gray . 1850-1869 Very dark almost black graphitic schist 1869-1875 Schist, dark gray, reddish, and greenish gray 1875-1895 Like preceding but more green 1895-1900 Blackish gray graphitic schist, some quartz 1900-1910 WELLS TERMINATING IN THE COMANCHEAN The term “non-flowing” is used for wells in which the water rises in the boring but does not reach the surface. “Flowing” wells are those in which the water overflows at the surface. The head of the water above or below the surface is given for some of the wells; however, the head varies considerably, as already stated, wdth the season, and the record for any well is likely to vary according to the season in which the measure- ment was made. In the well records, the following data are given in order, so far as available: Name of owner; location of well ; depth ; elevation at the well ; water, whether flowing or non-flowing; elevation of the top surface of the Del Rio< formation above or below sea level. These data are followed by the log of the well if available. The approximate location of most of the wells is indicated on the contour map by the entry showing the level of the top surface of the Del Rio formation. With the elevation of the top of the Del Rio recorded, the level of the other Comanchean and Cretaceous formations can be approximately determined. The top of the Comanchean (base of the Upper Cretaceous) lies about 65 or 70 feet higher than the Del Rio; the Georgetown-Edwards series of lime- stones, the principal water reservoirs of this county, lie im- mediately below the Del Rio or about 70 feet lower than the elevation given. The Upper Cretaceous formations are 1200 or 1300 feet thick. An asterisk placed after the number of the well in the table indicates that a log or other data are given following the tabulated record. WELLS TERMINATING 1JS TJH£ COMANCHEAN (.LUVVEK CKETACEUUS; FORMATIONS. i :*6 University of Texas Bulletin 0^0 ? °S £§■$ 3 H Q E £ > > 05 t» ffi « s « r s : O ^ K £ < < O S o 3 8.5 0.0 00>l0030^-^ll0000c0 co ok 4 5 S tS o o 03 CO O CJ o o X 2 j I bfl T 0 bfl 6 fl £ g o o o o o o 2 ; fc « S M r-< 05 5 o &o So, 5|1 6 a -a a o a •3 o CS '-/2 o 9 o bfl c3 E £ 1-1 o a> g S S3 •3 a 3 >♦ a 1 a a < <4 I 3 s « « « « « m CO b- So 03 O Geology and Mineral Resources of Bexar County J 37 6 03 O & o TS w o o cS c3 h H es ^ ,x > >> >> ca tz Eh Eh Eh Eh Eh h fc Eh Eh „ „ C3 >> P*> 03 !Z i T i i s a H < E- lO m t- S IS w N ii li ol li § & S 8 §8 i S 1 I U*3 H* ob 1 1 1 • 1 i i i i i « i i i i ! i 1 l 1 1 1 1 I 1 1 i i i u c3 l 1 1 1 l 1 1 1 1 1 i i i i i i i i i i i i i i i eo 1 1 1 1 i t> i i i i • i i i i i 1 1 i i i 1 l 1 l i i fl 1 1 1 1 7 1 i i i i 7 1 1 04 1 l i i i 1 s 1 bo bo i i i i be 1 1 a + i i i i 6fl 1 1 1 1 1 60 1 bfl i i i i i bfl c< 4 j i i i i 1 60 bfl 1 60 i bo + 1 60 1 bo h P a i a i a a a a i C G P fl a c o o S Fh a c o o £ !z s 3 © 1 1 Qj 1 1 O 1 i : o t 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 • 1 'S ! ! o i ! 4-> 1 t 0Q 1 1 -o 5 !. C3 « E-i H i* to^ SBfl •3 ft 1 r* 03 , P G ft O S£ So • «o «5 - 03 ^ m a a PS P3 W n o a >> js 5 ,C j_ G N oT ® * '« s | s !5 ■ - € 03 03 03 !G O ffi h a s a 25 Hornenberger 9 miles nortbwestt 570 Non-flowing 400- 470± 470 Austin to Comanchean. 64 | Hubble, L. Menchaca Streetf 490 670 Geology and Mineral Resources of Bexar Comity 139 WELLS TERMINATING IN THE COMANCHEAN (LOWER CRETACEOUS) FORMATIONS— Continued. 140 University of Texas Bulletin © 3 .2 a > oa > c3 3 as « < O «. 2 « s|§ * 5 ^ fl .2 a +j ~ <3 02 © O o ■ a 2 co 5 s q a w o | S & a a £ ^ s i * >. s O ft ■S& 2 CQ o o a a §■ c? « 8 5 OJ .X .a7 O •Si? CO 8 8^8 -13 =8 & A 5s Is a <_• C3 < < g* G 0 ZD ZD ZD ZD * OS 001 o s h 657? | 153? Geology and Mineral Resources of Bexar County 41 a & o 3 o tn 5 o W co tn »»» 3 3 03 03 03 3 03 03 c-H S w ® 'C 03 £ 'O w o o- o 03 03 £ O O O O >1 s>, fc A & os — .5 > ts t: a Q> g> £ H E- 'I I ^ ^ i eo t- O <4 4 O 0-1 i ^ ^ i o oo on o> CO 03 c£> t» 8 £ s s s s 124*1 Terrell Hot Wells— 5.2 miles southf. WELLS TERMINATING IN THE COMANCHEAN (LOWER CRETACEOUS) FORMATIONS— Continued. 142 University of Texas Bulletin as . 3 ^ 0 1 I o -5 o k Eh Eh <1 > , d o V 8 £ I I s§ s 0 3 o 3 . 2=2 01 O V Q =3 oh & i 4 <4 <4 i 19 4 + 5 f i 7 f£ £ bfl bj) £ 0 o a a o 1 f ||” o o 2, o Z< £ ^ Ph 25 O ^ XI a a o o £ £ i£ 3 f£ 2 o 3 3 8 8 S A £ 0 3 o C3 O . «-) a x s O) a> a; H Eh Eh Eh H ■= W O 58 £ £ £ £ £ 3 3 b b Log or other additional record given helow under the heading “Supplementary Data.’ (Location indicated on contour map. Geology and Mineral Resources of Bexar County 143 SUPPLEMENTARY DATA ON WELLS’ TERMINATING IN THE COMANCHEAN The following data including logs is supplementary to that given in the preceeding tabulated records. 3. H. J. Ackerman, 6 miles east of San Antonio, east side of tlie W. W. White Road, % mile south of St. Hedwig Road. This well is near the limits of the area of surface flow from the Georgetown- Edwards limestones. When first drilled, the well is said to have flowed slightly over the pipe but to have subsequently ceased to flow. The well is also near the south limits of non-sulphur water in these limestones. 5. Alamo Water Works, Alamo Heights. Lorenz Bros., drillers. Log by drillers from memory. Yellow clay (Austin?) 0- 140 Yellow rock (Austin) 140- 350 (First) mud hole (Eagleford) 350- 380 .White rock (Buda) 380- 430 Dark blue mud, caves (Del Rio) 430- 500 Yellow sand rock (limestone?) 500- 540 6. D. J. Allen, in Kelly Field south of Pearsall (Frio) Road, 1 mile S. W. of city limits. T. H. Little, driller, 1910. Gravel and yellow clay (Pleistocene) 0- 60 Shale (Taylor and Navarro) 60- 600 White limestone (Austin) 600- 900 Lignite of shale (Eagleford) 900- 940 Hard rock (Buda) 940-1000 Mud hole (Del Rio) 1000-1054 Brown and white limestone v 1054-1254 White and gray limestones 1254-1595 The gravel deposits of this well are those of the Pleistocene. Aside from these flood-plain deposits the materials to the depth of 600 feet represent the Taylor and a part of the Navarro. The Austin formation is recorded as “white limestone,” 600 to 900 feet. The Eagleford, “lignite” is given as 40 feet; the Buda, “white rock,” 60 feet; and the Rel Rio “mud hole” as 54 feet. The top of the Comanchean was reached at 940 feet. The water-bearing limestones were here reached at 1054 feet and were penetrated to 540 feet, thereby securing a very large flow of water, the well being re- ported to yield 3000 gals, per minute by pumping. Mr. Allen has several other similar wells on this property. 12. Ed E. Basse, west side S. A. & A. P. Ry., south side Olmus 144 University of Texas Bulletin Creek, 5 miles north of San Antonio. Alex Lorenz, driller, l.og by driller from memory. Surface materials 0- 30 Blue mud, thickness not recorded 30- 425 Lignite (Eagleford) 425- 450 Not recorded (Buda) 450- 500 Clay (Del Rio) 500- 555 Limestone (Georgetown) 555- 590 14. Mrs. Kate Benke, north side of Culebra Road near the west county line. A. E. Goforth, driller. Log by driller from memoiy. Yellow clay and rock (Taylor) 0- 300 White magnesian limestone and blue medium hard limestone (Austin) 300- 785 Lignite (Eagleford) 785- 820 Buda limestone 820- 880 Clay (Del Rio) 880- 940 Limestone (Georgetown-Edwards) 940-1000 Although located within a mile or so of the Balcones Escarpment, the first 300 feet of this well with little doubt pass through the Taylor formation. This is followed by 485 feet most or all of which is to be referred to the Austin, representing the thickest recorded section of that formation. The Eagleford is assigned the usual thickness of 35 feet; the Buda, 60 feet; and the Del Rio 60 feet. The top of the Comanchean formations lies at the depth of 820 feet from the surface. The magnitude of faulting in this area is indi- cated by the fact that within two miles west from this well the Glenrose formation is seen lying at the surface at elevations of from 1200 to 1400 feet above sea level, while in this well the top of the Glenrose, probably lies 300 feet or more below sea level. 16. H. T. Biering, west side Bandera Road, 15.6 miles from San Antonio. Record from owner. This well is located in the Del Rio plain a mile or so from the Balcones Escarpment. The surface materials at the well are heavy stream washed gravel, although the Del Rio nearby lies at about' the same level. The well starting at the Del Rio level terminates in the Edwards limestone. 18. J. T. Blank, south side Castroville Road, 6 miles west of San Antonio. Surface materials, blue clay and rock 0- 928 Not recorded 928-1163 “Mud hole” (Del Rio) 1163-1228 Limestone 1228-1483 The principal water supply is reported to come from only 4 feet Geology and Mineral Resources of Bexar County 145 below the surface of the Georgetown-Edwards limestones. Above this level are the formations of the Upper Cretaceous, the Eagle- ford, Austin, Taylor, and probably a part of the Navarro. The sur- face materials here are the gravel flood plain deposits. 19. Blue wing Club, west side of San Antonio River, 12 miles south of San Antonio. Drilled by cable. Jacob Wolf, driller. Show- ings of oil at 900 feet, and continuing more or less to 1200 feet. Sand 1- 5 Clay, yellow 5- 85 Sand, white, with water 85- 90 Rock, hard, blue 90- 92 Clay, soft, blue 92- 112 Rock, hard, blue 112- 115 Clay, soft, blue 115- 133 Rock, hard, blue ' 133- 135 Clay, soft, blue 135- 150 Rock, hard, gray . 150- 153 Clay, soft, blue 153- 170 Rock, hard, gray 170-- 174 Clay, soft, blue 174- 191 Rock, hard, blue 191- 193 Clay, soft, blue 193- 211 Rock, hard, blue 211- 215 Clay, soft, dark blue 215- 231 Rock, hard, dark blue 231- 234 Clay, soft, blue . 234- 250 Rock, hard, gray 250- 252 Clay, soft, blue 252- 270 Rock, hard, gray 270- 273 Clay, soft, dark blue 273- 289 Rock, hard, blue 289- 293 Clay, soft, blue 293- 311 Rock, hard, blue 311- 313 Clay, soft, blue 313- 320 Rock, hard, blue 320- 322 Clay, soft, blue 322- 334 Not recorded 334- 337 Rock, hard, blue 337- 357 Clay, soft, blue . . 357- 3 60 Rock, hard, blue . 360- 383 Clay, soft, blue 3 83- 387 Rock, hard, gray 387- 405 Clay, soft, blue 405- 407 Rock, hard, blue 407- 425 Rock, hard, gray 425- 428 10-Bex. 146 University of Texas Bulletin Clay, soft, dark blue 42 8- 445 Rock, hard, gray 445- 4 47 Clay, soft, light blue 447- 4 60 Rock, hard, gray 460- 464 Shale, soft, blue 464- 468 Rock, hard gray 468- 470 Shale, soft, dark 470- 472 Rock, hard, white 472- 478 Shale, soft, dark blue 478- 567 Rock, hard, blue 567- 569 Shale, soft, blue 569- 728 Shale and boulders, soft, blue 728- 755 Shale, soft blue 755- 905 Sand rock, soft, gray 905- 925 Shale, soft, blue 925- 960 Shale, soft and hard, blue 960- 996 Rock, soft, blue 996-1006 Clay, soft, blue 1006-1050 Shale, hard, blue 1050-1072 Shale, hard, blue 1072-1092 Shale, hard blue 1092-1106 Sand rock, hard, blue 1106-1115 Shale, hard, blue 1115-1145 Rock, hard, gray 1145-1149 Shale, hard, blue 1149-1184 Rock, hard, blue 1184-1191 Shale, soft, blue 1191-1212 Clay, soft, light blue 1212-1300 Rock, hard, blue 1300-1306 Shale, soft, blue 1306-1356 Shale, hard, blue 1356-1387 Rock, hard, gray 1387-1390 Clay, soft, blue 1390-1409 Rock, hard, light blue 1409-1446 Gumbo, hard, dark 1446-1746 Rock, soft, white 1746-1850 Rock, soft, blue 1850-1910 Rock, hard, white 1910-1987 Rock, hard, blue 1987-2015 Rock, hard, gray 2015-2054 Rock, hard, light blue 2054-2080 Rock, hard, gray 2080-2140 Rock, soft, dark blue 2140-2152 Rock, hard, white 2152-2189 Rock, hard and soft, yellow; water 2189-2269 Rock, hard, white; no water • 2269-2304 Geology and Mineral Resources of Befrar County 147 Rock, soft, yellow; water 2304-2374 Rock, soft, yellow, and hard; water 2374-2433 Rock, hard, flint; no water 2433-2 437 Rock, hard, dark blue; no water 2437-2444 The log of this well is difficult to interpret. The driller states that he was unable to recognize either the Eagleford “lignite” or the Del Rio “mud hole.” The water obtained from the well is re- ported to have had a temperature of 117° and to have had a head of about 75 feet above the surface. The water which was first ob- tained at the depth of 2189 feet, or at the actual level of about 1700 feet below sea, is derived with little doubt from the Georgetown- Edwards limestones. The Del Rio formation is placed provisionally in this well at 2140 feet from the surface or at the actual level of about 1685 feet below sea. This interpretation is permissible from the log. 21. D. Boerman, south side of Bandera Road, 11 miles north- west of San Antonio. Record from owner. Chiefly limestone and shale (Austin-Eagleford) 0- 280 Hard limestone (Buda) 280- 320 Mud hole (Del Rio) 320- 385 Limestones (Georgetown) 385- 403 24. H. Brendle, 527 Bandera St., about one mile north of west of San Pedro Springs, San Antonio. Log published in 18th Ann. Rpt., U. S. G. S., p. 293. Blue marl and clay described as sea mud in this well from 493- 583 feet, is interpreted as the Del Rio formation, which accordingly lies at the level of from 227 to 317 feet above sea. 27. ^ C. C. Clamp, south of the Castroville Road, east of Leon Creek, 6 miles west of San Antonio. Log by Mr. Fred Lewis. Clays, mostly blue in color (Navarro-Taylor) 0- 662 White shale (Austin?) 662- 825 White lime rock (Austin) 825-1023 Lignite (Eagleford) 1023-1054 White limestone (Buda) 1054-1110 Mud hole (Del Rio) 1110-1162 Limestone 1162-1195 Water sand 1195-1196 Limestone 1196-1220 Crevice, water 1220-1221 Sandy limestone rock ... * 1221-1275 Crevice, water 1275-1277 Limestone 1277-1292 “Sand” 1292-1308 148 University of Texas Bulletin Not recorded 1308-1395 Limestone rock 1395-1452 Aside from the surface materials the first 662 feet in this well probably represent the Taylor and a part of the Navario forma- tions. The 361 feet recorded as white shale and white lime rock probably represent the Austin formation. The Eagleford lignite is assigned a thickness of 31 feet; the Buda, 56 feet; and the Del Rio, 52 feet. The water-bearing limestones lie at the depth of 1162 feet. As hearing on structural conditions it is of interest to note that the Comanchean formations here lie at a lower level than at the Allen well in Kelly Field, about 2 Y 2 miles farther south, the Allen well being nearer the axis of the San Antonio structure, al- ready described. 28. Collins Manufacturing Company, 900 yds. northeast by north of Courthouse, San Antonio. Record from U. S. G. S. 18th Ann. Rpt., p. 293. At this well blue clays were passed through from about 720 to 800 feet which with little doubt represent the Del Rio formation. The Del Rio here lies at about 60 feet below sea level. 30. Collins Gardens, near I. & G. N. Ry. track below Union Stockyards, used for irrigation. Jacob Wolf, driller. Yellow clay and gravel (Pleistocene) 0- 40 Blue clay, mostly soft and caving (Navarro-Taylor) . . .40- 525 Limestone (Austin) ,, 5 25- 855 Lignite (Eagleford) 855- 890 Hard limestone (Buda) 890- 930 Mud hole (Del Rio) 930-1000 Limestone The blue clays of this well from 40 to 525 feet represent the Taylor and probably a part of the Navarro formations. The lime- stones which may be assigned to the Austin formation have a thick- ness of 330 feet. The Buda limestone, the first of the Coman- chean formations, is reported at 890 feet. In this well good water is reported to have been obtained while in the limestones of the Austin formation, at the depth of 638 feet. 33. Dickenson well, north side of Culebra Road, 8 miles north- west of San Antonio. Alex Lorenz, driller. Elevation of Del Rio, 353 feet. Surface materials, blue clay and limestone (Taylor- Austin) 0- 420 Lignite (Eagleford) 420- 447 Hard rock (Buda) 447- 497 Mud hole (Del Rio) 497-567 Limestone rock (Georgetown-Ed wards) 567- 602 Geology and Mineral Resources of Bexar County 149 The surface materials at this well include remnants of the grav- els of the Uvalde formation. A part of the clays represent the lower part of the Taylor formation as indicated by exposures nearby. The limestones under the clays to the depth of 420 feet are of the Austin formation. The Comanchean is entered at 447 feet and the water-bearing Comanchean limestones are reached at 567 feet. 42. Geunther Milling Company, 902 Morales St., east side of I. & G. N. Ry., San Antonio. Yellow clay and gravel (Pleistocene) 0- 50 Blue clay (Taylor) 50- 250 Soft gray rock (Austin) 250- 350 White limestone, water (Austin) 350- 550 Bluish black shale, lignite (Eagleford) 550- 600 Hard white limestone (Buda) 600- 650 Sea mud (Del Rio) 650- 700 Blue limestone 700- 750 “Sand” and black flint strata, water 750- 800 Hard sandstone 800- 850 Flint, gray (and limestone) 850- 875 The log of this well as preserved is evidently a somewhat gen- eralized record. However, it serves to place approximately the top surface of the water-bearing limestones at 700 feet. Some part of the Taylor formation here lies above the Austin and Eagleford, although concealed at the surface by flood-plain deposits. ^ 43. A. E. Goforth, north side Culebra Road, 18 miles northwest of San Antonio. Goforth, driller. Surface materials and limestone rock, the lower part hard and blue in color (Austin formation) 0- 349 Lignite (Eagleford)* 34 9- 384 Hard limestone (Buda) 384- 444 Del Rio clay (mud) 444- 504 Limestone rock (Georgetown-Edwards) 504- 564 44. Government well, at Aviation Post, on Austin Road, about 6 miles from San Antonio, Benkendorfer, driller. Soil 0^ 2 Yellow clay 2- 55 Blue clay (small vein good water at 190, rose within 100 ft. of surface) 55- 190 Magnesian limestone, soft, light blue 190-210 Soft shale 210- 220 Light gray hard limestones 220- 240 Blue gray very hard limestone 24 0- 2 60 Hard white limestone 260- 280 150 University of Texas Bulletin Soft white limestone 280- 300 Blue and white hard limestone 300- 320 Not recorded 320- 330 Hard white and blue limestones 330- 340 (8" casing rested at 340 ft) Very hard white limestone 340- 353 Lignite, black and soft (Eagleford) . . 353- 380 Gray shaly rock 380- 400 White hard limestone 400- 418 Del Rio “mud,” soft, blue-gray 418- 494 (6" casing rested at 494 ft) Limestone, slightly yellow, hard 494- 557 Limestone, light in color . . . 557- 575 Porous limestone 575- 580 Hard brown limestone 580- 590 Soft limestone 590- 625 Hard brown limestones 625- 655 Flinty limestone 655- 657 Soft limestone 657- 671 White hard limestone 671- 680 Soft brown limestone 680- 690 Hard limestone 690- 748 Black flint 748- 750 Hard yellow limestone 750- 795 Very hard limestone 795- 835 Light brown soft sandstone 835- 855 Light brown limestone 855- 874 The formation penetrated in this well to the depth of 353 feet is chiefly the Austin including possibly some of the Taylor at the surface. The combined thickness of the Eagleford “lignite” and Buda “shaly rock and white limestone” is recorded as 65 feet. This is unusually thin for these formations unless a part of the Eagle- ford has been included with the limestones referred to the Austin. All wells bejtween the east city limits of San Antonio and Salado Creek record a reduced thickness of the Eagleford, Buda, and Del Rio formations. 45. Government well, Fort Sam Houston, near west limits of Government Reservation between Pine Street and River Avenue, San Antonio. Judson, driller; 1903; depth 729 ft.; casing 10-in. to 630 ft. Elevation, 689. Non-flowing, although stood in well when completed within a few feet of the surface. Elevation Del Rio, 69. Blue loam and flint boulders 0- 3 Yellow clay 3- 41 Blue clay 41- 258 Magnesian limestone. Small streak of good water at Geology and Mineral Resources of Bexar County 151 350 ft 258- 354 Gray limestone, sulphur water 354- 392 Gray limestone, hard 392- 429 Yellow limestone 429- 468 Gray limestone 4 68- 535 “Lignite” (Del Rio) 535- 566 Gray limestone (Buda) 566- 620 Blue clay with shells (Del Rio).. 620- 673 Blue limestone 673- 688 Hard yellow limestone 688- 706 Calcareous limestone 706- 708 Struck water at 705 ft. Open cavity 708- 713 Hard limestone with fissures filled with clay 713-729 This well may be compared with the new city well drilled at the north city limits in 1918. Although only about 1 mile farther north, the Del Rio at the city well is found at the level 497, or . more than 400 feet higher than in this well, the two wells being separated by a large fault. 46. F. Grote, south side of Bulverde Road, OV 2 miles from San Antonio. Alex Lorenz, driller. Soft “adobe” lime 0- 17 Hard limestone (Austin) 17- 187 Lignite (Eagleford) 187- 222 Hard limestone (Buda) 222- 272 Clay (Del Rio) 272- 332 Hard limestones (Georgetown) 332- 339 This well starts in the Austin formation surface exposures of which are seen nearby. The Comanchean formations are entered at the depth of 222 feet. The water-bearing limestones were reached at 332 feet and were drilled into only 7 feet. The well is located on the structurally high area elsewhere described as the San Antonio structure. 49. Jud Harrison, west side Blanco Road south of Coker cross road, 8 V 2 miles north San Antonio. Alex Lorenz, driller. Not recorded (Austin) 0- 185 Lignite (Eagleford) 185- 190 Hard limestone (Buda) 190- 245 Clay (Del Rio) 245- 300 Limestone (Georgetown) 300- 328 56. Herff well, formerly the Werner property, north of Castro- ville Road, between Stephenson Road and West 34th St. Benken- dorfer, driller. Record from driller’s notebook. Del Rio mud 152 University of Texas Bulletin recorded at from 1000 to 1060 feet, the water-bearing Coman- chean limestones thus lying at the level 350 below sea. Surface clay and gravel (Pleistocene) 0- 31 Yellow clay (Navarro) 31- 81 Blue clay (Navarro-Taylor) 81- 621 Magnesian limestone (Austin) 621- 781 Blue limestone (Austin) 781- 811 White limestone (Austin) 811- 951 Lignite (Eagleford) 951- 969 Gray limestone (Buda) 969-1050 Clay (Del Rio) . 1050-1110 Brown limestone 1110-1140 Porous limestone, water rock 1140-1286 The surface clay and gravel at this locality includes that of the flood-plain deposits. Aside from these surface materials the Upper Cretaceous is here recorded as having a thickness of over 900 feet, •the Comanchean limestones (Buda formation) having been reached at 969 feet. Judging from the thickness of the Upper Cretaceous there are probably present here the Eagleford, Austin, Taylor, and lower part of the Navarro formations. 57. Hill and Roby, east side Pleasanton Road, 7 X A miles south of San Antonio. Jacob Wolff, driller. 1910. Depth, 1890. Elevation about 625. Flowing warm sulphur water. In this well the Del Rio clay is said to have been passed through at from 1695 to 1750 feet, or at the actual level of from 1060 to 1125 below sea. The formation thus lies more than 300 feet lower than its estimated level in the Alta Vista oil field, a few miles farther southwest, and but little less than 200 feet lower than in the Ripps well a short distance southeast. 59. R. H. Hofheintz on Pearsall (Frio) Road between public road and railway, just north of Kelly Field, four miles from San Antonio. Benkendorfer, driller. In this well the Comanchean formations were entered at 950 feet. The overlying Cretaceous includes probably the Eagleford, Austin, Taylor and the lower part of the Navarro formations, as well as the surface flood-plain deposits. The Del Rio formation was entered at 1000 feet, or at the level of 315 feet below sea. The water-bearing Comanchean limestones lie at the depth of 1054 feet and were drilled into to- the total depth of 1453 feet. A log? of this well is given in Bull. 298, U. S. G. S., p. 268. 60. Holtz well, on left bank of Leon Creek below the Somerset Road crossing, nine miles southwest of San Antonio. This well was drilled by rotary by Holtz to a depth of 1200 feet where hard rock Geology and Mineral Resources of Bexar County 153 was readied and where the 6" casing was rested. From this depth the well was drilled with cable tools by Benkendorfer. Temperature of water said to be 106.5 F. 7 63. Hot Wells Hotel, on San Juan Boulevard, 1*4 miles south of the south city limits of San Antonio, east side of San Antonio river. Robert Newton, driller. Soil 0- 5 Yellow clay 5- 15 Black sand 15- 20 Sand and gravel, water 20- 30 Yellow clay 30- 52 Blue shale 52- 90 Streaks of lignite 90- 95 Gumbo and blue clay 95- 125 Sandy shale 125- 175 Gumbo 175- 323 Sand rock 323- 325 Gumbo 325- 337 Sand rock 337- 340 Gumbo 340- 351 Rock 351- 353 Sandy shale m . 353- 412 Gumbo 412- 506 Sandy shale 506- 577 Sand rock, oil show 577- 587 Gumbo 587- 597 Sandy shale 597- 710 Hard gumbo 710- 990 Lime rock, casing 8" set 990-1003 Lime rock 1003-1445? Gumbo and hard shale 1445-1454 Lime rock 1454-1740 Hard shale 1740-1748 Hard lime rock, pink 1748-1865 Sand lime, some water 1865-1875 Porous rock, sulphur water 1875-1878 This well having been drilled by rotary does not afford as defi- nite information as the wells drilled by cable tools. The log is given as made out by the driller. While the interpretation of the log is in doubt, it is probable that aside from surface materials, the first 990 feet represents chiefly Navarro and Taylor formations; while from 990 to about 1445 represents the limestones of the Austin, Eagleford, and Buda formations. On this interpretation the Del Rio lies here at about 1445 feet from the surface or about 870 feet below sea level. 154 University of Texas Bulletin >/ 67. Kearney Oil and Pipe Line Company, No. 3, west side of Palo Alto Road about one mile south of Leon Creek crossing. Yellow clay 0 - 42 Blue clay 42- 125 Black sand, gas show 125- 161 Blue clay 161- 226 Sand rock 226- 234 Gumbo 234- 261 Sand rock 261- 262 Gumbo 262- 268 Soft rock 268- 269 Gumbo 269- 273 Soft rock 273- 275 Gumbo and soft rock 275- 392 Shale 392- 433 Hard rock 433- 449 Gumbo 449- 486 Gumbo and shale, oil show 486- 527 Gumbo 527- 569 Gumbo and shale, oil show 569- 621 Soft rock, oil show 621- 636 Gumbo 636- 703 Shale 703- 724 Gumbo 724- 745 Not recorded 745- 837 Rock (limestone) 837- 869 Gumbo 869- 872 Soft rock 872- 886 Gumbo 886 <- 890 Soft rock 890- 892 Gumbo 892- 957 Hard rock (limestone) 957-1063 Yellow rock (limestone) 1063-1151 Sand, heavy oil, about 2 bbls. per day 1151-1161 White limestone and water 1161-1211 Yellow limestone and water (sulphur) 1211-1221 White limestone 1221-1321 Lignite, kind of mud (Eagleford) 1321-1357 Black limestone (Buda) 1357-1451 Mud hole, sea shells (Del Rio) 1451-1491 Hard black limestone 1491-1591 Warm sulphur water 1591-1861 White rock, salty water 1861-1881 Cold water, brackish 1881-1991 Not recorded 1991-2355 This well, log of which has been given by Mr. Kearney, affords a very important and reliable record of the depth of the formations Geology and Mineral Resources of Bexar County 155 at this locality. The well is located within the belt of Tertiary exposures, provisionally mapped as Midway. The interval from the surface to 957 is assigned to the Midway, Navarro and Taylor for- mations. The Austin formation apparently is represented by the interval from 957 to 1321 feet, 364 feet, consisting chiefly of lime- stones, with some slight production of heavy oil at 1151 feet. The record of the Eagleford “lignite”, Buda limestone, and Del Rio clay is unmistakable. To the Eagleford is assigned a thickness of 36 feet, to the Buda, 94 feet; and to the Del Rio, 40 feet. The Georgetown-Edwards limestones were entered at 1491 feet. Warm sulphur water was obtained in these limestones. The drill hole was continued below the top of these limesones 964 feet, probably terminating in the Glenrose formation. Mr. Kearney believes that the water obtained below 1881 feet was neither so warm nor so salty as that from a somewhat higher level. Mr. Jacob Wolff believes that the cool non-sulphur water lies below 1900 feet from the surface. The interval between the oil sands in the Austin and the top of the Del Rio formation in this well is about 300 feet. The whole thickness of the upper .Cretaceous as indicaed by this well is about, or a little more than, 1200 feet. The stratigraphic in- terval from the greensand horizon near the top of the Navarro to the top of the Del Rio is 1326 feet. The actual level of the Del Rio at this locality is 841 feet below sea level. 73. Well in Lakeview Addition, near 24th Street, west part of San Antonio, north of Elmendorf Lake. Black soil . . . 0- 4 Yellow clay 4- 31 Soft blue clay 31- 43 Not recorded 43- 187 Hard streaks at 187 Not recorded 187- 190 Sand rock, six inches at 190 Not recorded 1 190- 206 Hard lime rock.... 206- 281 Black lignite (Eagleford) 283- 291 Streaks black lignite at 349 Not fully recorded • 291- 441 Blue mud (Del Rio) 441- 494 Soft dark sandrock 494- 522 “Granite” 522- 586 Sand rock with water 586- 591 This log is very unusual and is difficult to interpret. If the blue clay at 441 feet represents the Del Rio, the formation lies here at about the actual level of 239 feet above the sea. 156 University of Texas Bulletin 74. W. F. Legler, on north side Castroville Road, 5 miles west of San Antonio. Alex Lorenz, driller. Soil 0- 5 Clay and gravel (Pleistocene) 5- 18 Yellow clay (Navarro) 18- 52 Blue clay (Navarro-Taylor) 52- 670 White shale (Austin) 670- 910 Limestone (Austin) 910-1080 Lignite (Eagleford) 1080-1108 Hard rock (Buda) 1108-1167 Clay (Del Rio) 1167-1220 Limestones, water bearing at successive horizons 1220-1555 The top of the Comanchean formation in this well is reached at 1108 feet below the surface, the upper Cretaceous formations present being probaly the Eagleford, 28 feet; Austin, 310 feet; Taylor and loweri part of the Navarro, 618 feet; and the Pleistocene flood-plain deposits amounting to about 18 feet. 75. J. Locke, west side of Blanco Road, 5 miles north of San Antonio. Alex Lorenz, driller. Yellow calcareous marl (Austin) 0- 50 Blue limestone rock (Austin) 50- 250 Lignite (Eagleford) 250- 265 Hard white rock (Buda) 265- 310 Sea mud (Del Rio) 310- 370 Limestone (Georgetown) 370- 385 77. Alex Lorenz, north side Bulverde Road, about 6 miles north of San Antonio. “Adobe” 0- 25 Blue “mud” rock (Austin) 25- 150 White limestone rock (Austin) 150- 270 Lignite (Eagleford) 270- 295 Hard limestone (Buda) 295- 345 Clay (Del Rio) 345- 400 Limestone rock (Georgetown) 400- 420 80. B. F. Masterson, about 1 mile north of the Castroville Road, 18 miles west of San Antonio. Test well for oil. Record from Geo. B. Mechem Co. In this well, according to a summary of the log supplied by the owners, the Del Rio formation is believed to have been entered at the depth of 734 feet from the surface, and to be 83 feet thick. The Georgetown-Edwards limestones were reached at 817 feet, and the drill hole was continued to 1620 feet probably terminating in the Glenrose formation. Geology and Mineral Resources of Bexar Comity 57 81. Chas. Matyear, near 24th Street, in Lakeview Addition, San Antonio. Alex. Lorenz, driller. Elevation, 678. Elevation of Del Rio, 186. Black earth 0- 4 Yellow clay 4- 31 Soft blue clay 31- 43 Not recorded 43- 187 Hard streaks 187 Black sand rock 190 Hard lime rock 206- 281 Like black lignite (Eagleford) . . . . 283- 291 Streak black lignite.... 349 Blue mud (Del Rio) ! 441- 494 Soft dark sandrock 519- 522 “Granite” . . 584- 586 Sand rock, water 591 82. Medina Fuller’s Earth Company, about one mile north of Castroville Road, and west of Cagnon Cross Road, 16 miles west of San Antonio. Alex. Lorenz, driller. From the stratigraphic inter- val from the surface to the Del Rio formation it appears that this well starts in the Taylor formation. Blue marl 0- 400 White soft rock 400- 600 Eagleford 600- 635 Buda 635- 685 Del Rio 685- 750 Georgetown 750- 778 Actual level, Del Rio 100 -t- * 83. Medina Oil Company, south of Leon Creek, west of Apple- white Road. Jacob Wolff, driller. 4-inch casing set at 1530 feet; first flow of sulphur water at 1540 feet; second flow, 1800 feet; depth of well 1833 feet. Yellow clay 1_ 15 Gravel 15_ 25 Black sand 25- 50 Blue clay 50- 100 Blue rock 100- 104 Blue clay 104- 124 Blue rock, showing oil . 124- 129 Blue clay 129- 145 Blue rock 145- 153 Light blue clay 153- 165 Blue rock 165- 169 Blue clay . 16 9- 176 Blue rock 176- 186 158 University of Texas Bulletin Blue clay 186- 200 Blue rock 200- 206 Blue clay 206- 217 Gray rock 217- 255 Clay and sand, gas 255- 296 Gray rock 296- 302 Blue clay 302- 348 Gray rock 348- 355 Light blue clay 355- 408 Blue rock 408- 416 Blue gumbo 416- 436 Dark blue clay 436- 496 Dark gray rock 496- 500 Hard blue clay 500- 548 Dark gray rock . 548- 552 Dark gray shale, gas and oil 552- 564 Dark gray rock 564- 567 Dark clay and sand, gas and oil 567- 630 Gray rock 630- 633 Dark hard clay 633- 665 Hard gray rock 665- 671 Hard blue clay 671- 728 Gray rock 728- 736 Blue clay 736- 783 Black rock 783- 791 Dark clay 791- 806 Dark rock 806- 836 Gray shale with oil 836- 858 Hard dark rock 858- 912 Hard light blue rock 912- 922 Hard dark gray rock 922- 943 Hard white rock 943- 950 Hard light blue rock 950- 953 Yellow shale with oil 953- 957 White rock 957- 960 . Light blue rock 960- 964 Yellow shale with oil 964- 982 Light blue rock 982- 986 White soft rock 986- 990 Light blue hard rock 990- 994 Yellow shale with oil 994-1012 White rock 1012-1014 Blue rock 1014-1015 In this well, the Del Rio formation is reported at 1450 feet from the surface, or at about 920 feet below sea level. At 25 feet there is reported a black sand which very possibly is the glauconitic Geology and Mineral Resources of Bexar County 159 sand horizon of the Navarro formation. If so, the thickness of the Upper Cretaceous as recorded in this well is 142 5 feet, which is somewhat greater than farther northwest as indicated by the Kear- ney, Vogt, and Ridder wells. 93. A. J. Ridder, east side of Medina River, 13 miles southwest of San Antonio, north of Pearsall Road. Several wells on this property. L. N. Knight, driller. In all of these wells the glau- conitic greensand is noted, and the wells are of interest as indi- cating a south or southeast dip. They are as follows: Deep well, north side Southern Pacific track; depth, 2911 feet; elevation 628; flowing artesian water. In this well no water was found until below 1502 feet, the forma- tions being entirely dry to that depth. Successive water horizons between 1557 and 1980 feet were found. A glauconitic greensand horizon was recognized at 165 feet from the surface, the greensand being 50 or 60 feet thick. The Del Rio formation was recognized at 1444 feet and continued to 1497 feet. The limestones below the Del Rio were drilled into 1413 feet. From this record it appears probable that the well terminated either near the base of the Glen- rose or in the Travis Peak formation. In this connection it is of interest to note that the driller reports having drilled into fossil wood not petrified, but more or less lignitized, near the bottom of this well. This deep well affords a record of practically the full thickness of the Upper Cretaceous. While the Buda is not recorded, its uni- form thickness of 65 or 70 feet overlying the Del Rio makes it pos- sible to place the top of the Comanchean at about 1374 feet from the surface. The greensands reached at 165 feet are with little doubt those of the Navarro formation as exposed on Leon Creek. The Upper Cretaceous is therefore 1200 feet thick at this well, possibly a little more. This agrees closely with the thickness of these formations as determined from the Kearney well, about 6 miles farther southeast, where the Upper Cretaceous formations appear to have a thickness of about 1232 feet. Another measurement obtained from this well and from the Kear- ney well, used in estimating the place of the Del Rio in some wells, is the stratigraphic interval between the glauconitic greensand and the top of the Del Rio formation. In this well this interval is 1279 feet; in the Kearney well, the same interval was found to be 1326 feet, or 47 feet greater. Ridder well, near west line of property. Elevation 617. Green- sand at 200 feet from surface, or at level of 417 feet above sea. Ridder well, on north side of Pearsall Road, about % mile from Medina River. Elevation 617. Greensand at 235 feet from the sur- face, or at level 382 feet above sea. Ridder well, on east side of Medina River. Elevation 595. Some 160 University of Texas Bulletin water obtained at 1056 feet; additional water at 1410 feet. Green- sand at 285 feet from the surface, or at level 310 feet above sea. The dip in the formations from the deep well north of the railway to this well on the river, a distance of about one mile, according to these records is 150 feet. That this dip continues to the south is indicated b,y the Vogt well, subsequently recorded. 97. St. Louis College, between Culebra and Bandera roads, about 5.4 miles west of San Antonio. Elevation, 760. Flint Adobe Yellow clay Blue clay Magnesian lime rock Hard blue lime Hard yellow rock . . . Hard gray rock Lignite (Eagleford) . Limestone (Buda) . . . Blue clay (Del Rio) . Dark blue limestone . Yellow limestone . . . Crystallized limestone Water rock 0- 3 3- 5 5- 65 65- 215 215- 288 288- 392 392- 402 402- 455 455- 485 485- 542 542- 590 590- 600 600- 636 636- 680 680- 702 The Del Rio in this well lies at 547 feet from the surface. An- other well on this property located 375 feet west of the one re- ported reached the Del Rio at 590 feet or 43 feet lower than in the first well. Aside from this difference in level, the formations are much the same in the two wells. By reference to the struc- tural map it will be seen that these wells are located but a short distance north of the large fault which passes between the wells and the Castroville Road. 98. Salado Water Supply Company, % mile south of Austin Road, about 5 miles northeast of San Antonio, on Salado Creek. Jacob Wolff, driller. 6000 gallons water per minute. Surface 0- 8 Dark blue clay 8- 108 Light blue clay 108- 215 White rock, soft 215- 330 Yellow rock, sulphur water 330- 350 White chalk, hard 350- 445 Lignite (Eagleford) 445- 470 White rock, hard 470- 510 White pearl rock 510- 520 Blue hard rock 520- 540 Geology and Mineral Resources of Bexar County 161 Sand hole 540- 585 White rock, hard 585- 610 Red sand rock, gas flow 610- 617 Hard white rock 617- 642 Brown flint 642- 647 Yellow water rock, white streaks 647- 702 99. San Antonio and Aransas Pass Railway, at “roundhouse” on railway near the intersection of Proban and Simpson streets, west of the San Antonio River, near intersection of S. P. Ry. and S. A. & A. P. Ry. south of San Antonio. Allen Burman, driller. Sulphur water was obtained from the Austin at 620 feet, from the surface; good water was obtained at 1065 and at 1090 feet. The water is reported to rise 50 feet above the ground level. The Del Rio clay in this well lies at 270 feet below sea level. Casing, 7 V 2 " to 550 feet. The Del Rio is cased off by 70 feet of 6^" casing. Soil 0- 6 Soft white clay 6- 22 Sticky yellow clay 22- 80 Hard blue clay 30- 100 Soft blue clay 100- 250 Hard gray clay 250- 300 Soft white soapstone 300- 350 Hard blue clay 350- 400 Soft white clay 400- 500 Hard white rock 500- 550 Hard white rock 550- 600 Soft gray rock, sulphur water at 620' 600- 700 Hard gray rock 700- 750 Hard white rock 750- 850 Hard brown rock 850- 900 Hard blue sea mud (Del Rio) 900- 950 Hard white limestone 950-1103 101. San Antonio City Water Supply, about 400 yards west of Concepcion Mission, south San Antonio. A second well drilled about 200 .feet north of this one records only about 7 feet of Del Rio, entered at 1270 feet. The reduced thickness of the Del Rio to- gether with the abrupt dip probably indicates faulting at this locality with the downthrow to the south. Surface elevation of this well about 605 feet. Water in completed well rises 72 feet above. floor of derrick, or to elevation of 680 feet. Surface materials 0- 54 Blue clay 54- 7 80 “Magnesian” limestone 780- 900 10" pipe rested at 800 11 -Bex. 162 University of Texas Bulletin Gray limestone 905-1197 Water at 1130. Lignite (Eagleford) 1197-1223 Limestone with crevices and water flowing at surface 3000 gals, per min 1223-1280 Mud (Del Rio) 1287-1328 Limestone with crevices and water 1323-1440 102. San Antonio City Water Supply, Market Street. Surface elevation about 660 feet. Actual level top of Del Rio, 725. Surface materials 0- 35 Blue clay •.'... 35- 220 Hard rock 220- 375 “Magnesian” rock 375- 500 Sulphur water at 505 Lignite (Eagleford) 600 Buda not given “Mud” (Del Rio) 725- 775 Limestone rock 775- 887 Water mostly at 860- 88 5 103. San Antonio City Well, north city limits on San Antonio River. Benkendorfer, driller. This well starts in the Austin al- though as the record indicates, within about 100 feet of the base of this formation. The Eagleford is thin, apparently only about 15 feet thick. By reference to the map it will be seen that this well is located very close to a large fault. Mud and soil 0- 12 Rock 12- 21 Yellow rock 21- 65 Blue rock 65- 73 Yellow rock 73- 82 Brown rock 82- 87 Blue rock 87- 96 Yellow rock 96- 101 Brown lignite (Eagleford) 101- 116 Yellow hard rock 116- 144 White hard rock 144- 149 Gray hard rock 149- 17 3 Blue mud (Del Rio) 173- 234 Yellow water rock, very hard; some flint to bottom of well 234- 702 Principal water supply at 650-670 feet; water rises just to top of pipe. Does not flow over. 104. San Antonio Portland Cement Company, on I. & G. N. Ry., 5 Geology and Mineral Resources of Bexar County 1 63 miles northeast of San Antonio. Log from memory; depth of formations approximate: Yellow clay 0- 60 Blue hard rock . 60- 250 White and yellow limestones 250- 400 Hor.ey-combed hard limestones 400- 450 Lignite (Eagleford) 450- 462 Hard yellow limestone 462- 572 Black rock 572- 587 Sea mud (Del Rio) 587- 657 Hard limestones 657- 667 This record given to the writer by the driller from memory can be used only as an approximate statement of depths to the forma- tions. Another record of a well at this locality, from notes con- tributed by Mr. Deussen, differs somewhat, placing the Del Rio probably nearer the surface. The uppermost 60 feet in this well is probably the Taylor formation. The next 390 feet is to be re- ferred to the Austin formation. The materials recorded as lignite, hard yellow limestone, and as black rock presumably include the Eagleford and Buda formations, giving them a combined thick- ness of 122 feet. The Del Rio, “Sea mud,” is recorded as having its usual thickness of 70 feet. The well is here recorded as entering the Georgetown at 657 feet, this formation having been drilled into only about 10 feet. 107. George Sauer, Bulverde Road, near Haags’ store, 6% miles from San Antonio. Alex Lorenz, driller. Limestone (Austin) 0- 170 Shales. (Eagleford) 170- 210 Limestone (Buda) 210- 2 60 Clay (Del Rio) 260- 330 Limestones (Georgetown) 330- 370 108. Henry Shumeier, 1 mile south of Wetmore, west side Bulverde Road. Lorenz, driller. Elevation 760; non-flowing ar- tesian water. Adobe and hard rock (Austin) 0- 250 Lignite (Eagleford) 250- 275 Hard rock (Buda) 275- 325 Mud (Del Rio) 325- 375 Limestone rock 375- 420 109. Shattuck well, on 19th i Street, about 1 mile south of El- mendorf Lake, and near the west city limits of San Antonio. L. N. Knight, driller. Chiefly yellow and blue clay 0- 335 Limestone ! 335- 703 164 University of Texas Bulletin Eagleford 703- 735 Buda 735- 798 Del Rio 798- 850 Limestones 856 111. Southern Ice Company, Durango and Frio streets, east of I. & G. N. Ry., and south of Commerce Street, San Antonio. Soft pebbles 0- 5 Hard pebbles 5- 8 Yellow clay 8- 4 8 Brown clay 48- 160 Brown clay, light 160- 260 Magnesian rock 260- 385 Lime rock 385- 520 Sulphur water at 428 White limestone 557 Not recorded 557- 566 White clay 566 Not recorded 566- 585 “Coal” (Eagleford) 585-600? “White lime (Buda) 600- 650 “Mud” (Del Rio) 650- 711 Limestone (Georgetown-Edwards) 711- 911 113. Southwest Land Corporation, abodt 300 yards south of Commerce Street and 1 mile west of Lady of the Lake College, San Antonio. T. H. Little, driller. Sulphur water at 410 feet. Elevation, 708. Good water at 715 and 850 feet. Gravel and yellow clay (Navarro-Taylor) 0- 60 Shale (Navarro-Taylor) 60- 390 Soft white lime (Austin) : 390- 528 Lignite (or shale) (Eagleford) 528- 560 Hard white lime (Buda) 560- 620 Mud hole (Del Rio) 620- 672 Light brown lime (Georgetown-Edwards) 672- 700 White to gray lime (Georgetown-Edwards) 700-1000 118. Steves Irrigated Gardens, San Antonio. First water came to top at 1065-1070 feet. Drilled into water rock at 1185 feet when drilling had to be abandoned, on account of flow of water. Surface materials, water 0- 2 8 Blue clay 59- 604 White clay or rock 604- 728 Gray rock 728- 780 Yellow rock 780- 805 Gray rock 805- 894 Geology and Mineral Resources of Bexar County 165 Sulphur water 850 Lignite (Eagleford) 894- 922 Gray rock (Buda) 922- 983 Mud hole (Del Rio) 983-1041 Gray rock 1041-1060 Water at 1065 Brown rock 1060-1100 Brown hard flint 1100-1140 Gray hard flint? 1140-1160 Yellow hard flint? 1160-1185 119. Steves well, 509 King William St., San Antonio. Surface elevation about '650 feet. First sulphur water at 449; big flow at 742 feet. Surface 0- 2 Hard pan 8 - 19 Gravel 19 _ 34 Yellow clay 34 _ 42 Blue clay 42- 250 Austin chalk . 250- 442 White limestone 442- 472 Yellow limestone 472- 489 Gray limestone 489- 580 Lignite (Eagleford) 580- 613 Gray limestone 61 3 _ 682 Crystallized lime 682- 734 Total depth 758 120. Steves well, south of Chavanaux Road, west of S. A. & A. P. Ry. Benkendorfer, driller. Flowing warm sulphur water. The Del Rio clay in this well although not very definitely placed is reported to lie 1790 feet from the surface, or at the level 1130 feet below sea. This record places the formation nearly 400 feet lower than in the Alta Vista oil field. Scarcely more than a mile to the east-southeast. Y/123. Superior Oil Company, Linn farm, east of Palo Alto Road, 12 miles south of San Antonio. Fitzgerald, driller. Test well for oil. Oil showings as noted. Also warm flowing sulphur water from the Comanchean formations. Black, soil and clay 1 _ 14 Yellow clay 14 _ ig Yellow clay 1 8 _ 50 Yellow and l}lue clay 50 - 80 Blue and red shale 80- 125 shal e 125- 145 166 University of Texas Bulletin Greensand (set 178' 8" pipe) 145- 168 Tough shale 168- 187 Shale and slate 187- 263 Gas rock 263- 275 Soft lime rock 275- 279 Gas sand, hard 279- 282 Shale 282- 320 Lime rock 320- 328 Fine sand 328- 335 Shale with occasional boulders 335- 420 Soft shale and white slate 420- 500 Shale and soft slate 500- 750 Soft white lime 750- 753 Gypsum and shale 753- 758 Soft gray lime . . . . 758- 761 Shale 761- 783 Lime and shale 783- 796 Lime rock and pyrite of iron 796- 800 Gypsum and shale 800- 830 Lime rock 830- 834 Shale 834- 840 Lime, rock 840- 853 Shale 853- 855 Slate 855- 873 Shale ' 873- 904 Slate 904- 909 Shale .1 909- 922 Slate / ... 922- 925 Rock, gray limes 925- 926 Blue mud 926- 950 Pyrites of iron 950- 953 Rock, lime 953- 980 Oil-bearing sand 980- 985 Set 989 feet of 6" pipe Soft shale and mud 985-1020 White shale, strong gas 1020-1060 Oil-bearing shale 1060-1088 Rock, gray lime 1088-1125 Shale and slate 1125-1200 Lime, soft 1200-1235 Sand, showing little oil .1235-1241 Slate and shale 1241-1300 Soft shale, caving 1300-1420 Slate 1420-1430 Soft lime 1430-1439 Shale and sand, soft, caving 1439-1500 Geology and Mineral Resources of Bexar County 167 Slate and shale 1500-1520 Soft blue shale, caving 1520-1557 Set 4" pipe Lime rock 1557-1600 Blue slate 1600-1635 Hard white lime 1635-1740 Honey-combed, soft lime, hot sulphur water 1740-1800 Hard and soft lime 1800-2 600 Oil sand, small showing of oil .2600-2606 Hard blue lime 2606-2 900 Little sand and fresh water 2900 In this well a greensand horizon is reported at 145 feet from the surface. The Del Rio clay appears from the log to lie at about 1500 feet from the surface, the interval between the green sand and the top of the Del Rio here being 1375 ft. while in the Kearney well nearby this interval appears to be 1326 feet. When reduced to actual elevations, the greensand horizon in the two wells is found to be about 20 feet higher in the Kearney than in this well. The well was drilled approximately 1500 feet into the Comanchean formations and hence probably terminates in the Travis Peak formation. Although not so stated in the log, one of the drillers on this well reports that near the bottom of the well was found little altered wood resembling cedar, similar to that found in the Ridder well. 124. Terrell Plot Wells, west of the Pleasanton Road, 5 y 2 miles south of San Antonio. Record published, in U. S. G. S., 18th Ann. Rpt., Pt. 2, p. 294. Flowing warm sulphur water, temperature reported to be 106° F. From the record of this well it appears that the Del Rio clay was passed through here at from 1380 to 1425 feet or at the actual level of 750 feet below sea. From these data the top of the Comanchean formations would be expected at about 1320 feet from the surface. Accordingly the whole of the Upper Cretaceous and possibly some of the Tertiary is penetrated by this well. At the depth of 600 feet from the surface were fossils identified by Dr. Hill as Gryphea vesicularis, indicating the Navarro formation. Brown coal, or lignite, is reported in this well at 140, 240, and 280 feet from the surface. The lignite suggests that the Wilcox may be present, extending into this structurally low area possibly from the southwest. 125. J. H. Terrell, at west city limits, V 2 mile north of south limits of San Antonio. Sulphur water from the Austin at 765 feet; good water at 1134 to 1140 feet. Gravel and yellow clay 0- 60 Shale 60- 550 Soft white rock 550- 903 Lignite (or shale) (Eagleford 903- 938 Hard white lime (Buda) 938- 998 168 University of Texas Bulletin Mud hole (Del Rio) 998-1058 Brown and white lime 1058-1140 127. Louis Tezel, one mile north Culebra Road, 13 miles north- west of San Antonio. Goforth, driller. Actual level of Del Rio, 715 feet. Rock, not hard (Austin) 0- 55 Lignite (Eagleford) 55- 90 Buda 90- 150 Del Rio 150- 210 Rock (Georgetown-Edwards) 210- 245 132. Townsite well, Somerset. This well was drilled to the depth of 2002 feet many years ago, and of this part of the well no log has been found. Showings of oil were reported at 800-1100 and 1400 feet. During the summer of 1919 the well was deepened to 2320 feet by Dr. F. L. Thompson. From 2002 to 2030 feet no record has been made altho the drilling is said to have been in rock (Buda?). Below 2030 the samples indicate 70 feet of light blue clay. Altho no fossils were found this clay in general ap- pearance resembles the Del Rio formation. Below the clay from 2100 to 2320 the cuttings indicate limestones varying in texture and apparently representing the Georgetown-Edwards formations. The well terminated in strata containing a great deal of pyrite. While the data on this well are not as complete as desired it ap- pears probable that the Del Rio formation at this place lies from about 2030 to 2100 feet from the surface. The elevation at the depot at Somerset as shown by the profile of the Artesian Belt Railway is 650 feet above sea. The elevation at the well altho not accurately determined does not vary greatly from that at the depot. Accordingly the Del Rio is placed provisionally at this locality as lying about 1380 feet bslow sea level. 135. Union Meat Company, south Laredo street, between Ralph and Brazos. Sulphur water at 491 feet; good water at 1150 feet. Gravel and yellow clay 0- 60 Blue shale . . 60" 340 White limestone 340- 656 Lignite (or shale) (Eagleford) 656- 686 Hard white limestone (Buda) 686- 751 Mud hole (Del Rio) * 751- 820 Light brown limestone 820-1150 White and gray limestone 1150-1400 No water below 1250 137. Wm. Yogt, 1 V 2 miles west of the Medina River and 1/2 Geology and Mineral Resources of Bexar County 169 mile north the Quintana Road. Flowing warm sulphur water from the Conianchean formations. In this well the greensand was reached at 297 feet from the surface, or at the level 308 feet above sea. The Del Rio formation was reached at about 1485 feet and was found to be 52 feet thick. Water was obtained from the limestones at 1560 feet and succes- sively thereafter to the bottom of the well, 1850 feet. This well was drilled into the limestones below the Del Rio 313 feet and hence teiminates probably in the Edwards formation. The strati- graphic interval from the glauconitic greensand to the top of the Del Rio is here given as about 1188 feet, or 91 feet less than in the Ridder well. The record of the Ridder well is probably the more reliable. 138. Mrs. A. Voight, on the north side> of Culebra Creek, 14 miles from San Antonio on the Culebra Road. This well is lo- cated near the axis of the large structure described as the Culebra anticline. Surface materials and rather soft rock (Austin) 0- 35 Lignite (Eagleford) 35- 65 Buda 65- 120 Mud hole (Del Rio) 120- 180 Rock (Georgetown-Edwards) 180- 216 Actual level top of Del Rio 730 139. Waiing well, on south side Bandera Road, about miles northwest of San Antonio. D. Benkendorfer, driller. Non- flowing artesian water probably from the Travis Peak formation. Soil 0- 3 Gravel 3- 13 Adobe, lime and boulders 13- 70 Blue clay 70- 215 Yellow limestone 215- 23 0 Crevice 230- 232 White limestone 232- 265 Blue clay 265- 275 White limestone 275- 295 Blue slate 295- 325 Adobe limestone 325- 335 White limestone 335- 370 Lignite (Eagleford) 370- 400 White limestone (Buda) 400- 460 “Mud hole” (Del Rio) 460- 510 White limestone 510- 530 Crevice with water 530- 532 Yellow limestone 532- 550 Crevice with water 7 550- 555 170 University of Texas Bulletin White limestone 555- 600 White limestone 600- 615 Sand, brown limestone and water 615- 745 White limestone 745- 7 85 Brown limestone 785- 795 White limestone 795- 815 Brown limestone, water 815- 830 White limestone 830- 865 Brown limestone, water 865- 870 White limestone . 870- 920 Brown limestone 920- 925 White limestone 925- 950 Crevice, brown limestone 950- 955 White limestone 955-1035 Brown limestone 1035-1080 Blue limestone 1080-1190 White limestone 1190-1230 Blue limestone 1230-1260 Blue slate 1260-1262 White limestone 1262-1455 Hard brown crystallized limestone 1455-1478 Blue limestone 1478-1505 Hard brown crystallized limestone 1505-1510 White limestone 1510-1530 Hard blue limestone . . . 1530-1565 Blue limestone 1565-1580 Brown limestone 1580-1595 White limestone 1595-1635 Hard blue limestone 1635-1655 Brown limestone, white hard streaks 1655-1700 Hard blue limestone 1700-1715 Brown limestone 1715-1735 White limestone 1735-1795 Hard brown limestone 1795-1860 Soft gray rock 1860-1870 Hard blue ,mndy rock 1870-1915 No description 1915-1935 Mud 1935-1953 White limestone 1953-1985 Mud 1985-1987 White limestone 1987-1997 Mud at 2000 One foot of mud at 2008 Hard limestone, shells aild mud to 204 0 Soft white limestone 2040-2070 Very hard sandy limestone 2070-2100 Geology and Mineral Resources of Bexar County 171 White limestone . -. 2100-2115 Mud 2115-2140 Limestone ..2140-2100 Blue mud 2190-2483 Hard limestone, streaks of mud 2483-2600 White sand 2600-2645 White limestone ...2645-2675 Dark limestone and sand 2675-2699 Trinity white sand, water 2699-2705 Very hard cap rock 2705-2711 Sand and hard streaks 2711-2784 Sondstone, very hard, filled with red mud 2784-2810 Crevice 281 0-2 813 Sandstone shale 2813-2853 This well is of interest as affording apparently the maximum thickness thus far recorded for the Comanchean formations in this county. The Buda limestone was entered at 400 feet from the surface, and while no cuttings were preserved, it would appear from the log that the Cretaceous extends to 2705 feet, if not to the full depth of the well. Assuming the base of the Cretaceous to lie at 2705 feet there is indicated a thickness of the Cretaceous of not less than 2300 feet. The age of the materials from 2705 feet to the bottom of the well. 2853, is in doubt. Dirt taken from the dump around the well when washed and examined failed to show the presence of schists such as were found below the Cretaceous farther to the north, altho this test can not be -assumed to be con- clusive as to the presence or absence of schists. WELLS TERMINATING IN THE UPPER CRETACEOUS Among wells terminating in the Upper Cretaceous the fol- lowing are listed as indicative of conditions met with in drill- ing into these formations. The wells entering the Comanchean as already noted, are chiefly water wells, while those of the Upper Cretaceous are chiefly either oil-producing wells or wells drilled in testing for oil or gas. 145. Cohen & Roby, north of and near to the jog in the Dwyer cross road in the Gas Ridge oil and gas field. Depth, 1035 feet, Elevation about 750 feet. Showings of gas between 170 and 249 feet, large gas production 865-990; showings of oil at 480, 492, 550, 615, 780, 815, and 1000-1035. Gravel 0- 10 Yellow clay 10- 9 0 Black shale 90- 100 172 University of Texas Bulletin Blue shale 100- 120 Light blue shale 120- 100 Dark blue shale 160- 170 Shelly rock, gas 170- 240 Blue shale 240- 400 Small shell rock, first oil 400- 444 Sand 6 inches 444- 450 Blue shale. 450- 460 Shell of rock, oil sand 460- 475 Oil sand 475- 498 Blue shale .* 498- 500 Shell of rock, oil sand 500- 550 Blue shale 6 inches . ^ 550- 570 Small shell rock, oil sand 6 inches 57 0- 615 Shell rock : . 615- 650 Blue shale 650- 700 Shell rock, more oil sand 700- 780 Blue shale 780- 800 Small shell rock, more showing of oil 800- 815 Shell rock and gas 815- 840 Blue shale 840- 850 Large shell rock, large gas 850- 865 Gas rock 865- 890 Gas rock 890- 990 Blue shale 990-1000 Oil sand 1000-1035 This well starts in the Navarro formation and probably ter- minates in the Austin formations. The large gas supply at about 850 feet is probably in the Taylor formation. The heavy oil from this well at the depth of 1035 feet, analysis of which has been given, is probably from the Austin formation. 14 6. Crosby well No. 4, in Bexar County, north of Somerset. Soil 1- 16 Rock 16- 20 Black gumbo 20- 60 Rock 60- 62 Shale 62- 92 Water sand 92- 107 Gumbo 107- 132 Shale 132- 262 Rock 262- 265 Gumbo 265- 275 Water sand 275- 293 Gumbo 293- 343 Rock 343- 34 7 Gumbo 347- 382 Geology and Mineral Resources of Bexar County 173 Shale 382- 482 Gumbo 482- 552 Soft shale 552- 602 Gumbo - 602- 682 Soft sandy shale 682- 742 Hard sandy shale, shell of rocks 742-10 20 Very hard rock 1020-1022 Sand shale 1022-1048 Rock 1048-1051 Shale and gumbo 1051-1116 Shale 1116-1126 Gumbo 1126-1141 Shale 1141-1181 Gumbo 1181-1191 Shale 1191-1217 Rock 1217-1231 Shale and oil sand 1231-1251 Gumbo 1251-1254 As in the case of other wells in the Somerset field, in Bexar County, this well starts in the Wilcox formation. The formation in which it terminates and from which oil is obtained is not definitely determined but is assumed to be either the Navarro or the Taylor. 14 7. Ingram well in the Alta Vista Field, drilled 1905, Jacob Wolff, driller. Depth, 1120 feet; 6" casing set at 960 feet. Greensand stratum recognized at 260 feet 30 ft. thick This stratum according to Wolff made a barrel of oil per day, gravity 32 (some other tests reported the gravity 38). Second stratum greensand at 700 or 740 feet, about. .70 ft. thick Contained a good deal of gas and some oil. Made 2 y 2 to 3 bar- rels per day. Austin chalk rock recognized at 1000 ft. Heavy Alta Vista oil found at 1060 to 1080 ft. This heavy oil from a 5 or 6 foot crevice in the rock containing asphalt like material. Although not a procjucing well, this well is of interest as the first well drilled within the Alta Vista field in which a pronounced showing of oil was obtained. The well was drilled for water. The first producing oil well in this field was drilled about ten years later. 14 8. Wells of the Kimbly and Brown lease on the Swearingen property, south of the Medina River. The producing horizon is reported in the wells on this property at the following depths: Swearingen No. 1, located at north side of the property, producing sand at from 1210 to 1235 ft; Swear- ingen No. 2, producing sand at from 1216 to 1245 ft; Swearingen No. 3, producing sand at from 1248 to 1280 ft; Gale No. 1, produc- 174 University of Texas Bulletin ing sand at from 1360 to 1400 ft; Swearingen No. 4, producing sand at from 1425 to 1485 ft. The wells are listed in the order of their location from north to south or east of south. The dip of the formations is thus seen to amount to as much as 115 feet between wells No. 1 and No. 4. The distance between these wells is a little more than a mile. These wells start in the Tertiary. The formation in which they terminate is undetermined but may be either the Navarro or Taylor, The following log is of the Nimbly and Brown Swearingen No. 4. This is the southernmost and deepest of the five wells drilled in this field to the close of 1918. Log furnished by Mr. Brown. Soil 0- 3 Red clay 3- 27 Yellow clay 27- 50 Sand 50- 80 Lignite 80- 81 Sand 81- 140 Streaks of lignite 140- 146 Sand 146- 200 Rock 200- 208 Sand 208- 317 Rock • 317- 323 Brown gumbo 323- 386 Rock 386- 394 Shale, thin rocks 394- 490 Gumbo 496- 575 Rockj 575- 581 Shale 58 1“ 750 Rock 750- 752 Gumbo ' 752- 880 Black sand, gas 880_ 900 Gumbo 900-1395 Soft rock shows some lime 1395-1425 Oil sand 1425-1458 Gumbo 1458-1462 14 9. Well of J. K. Lamb, drilled by Park Oil and Gas Co., west of Corpus Christi Road, about 2 miles south of the Medina River. Test well for oil. Surface sand 2 Red sandy clay 2- 20 Water sand and boulders 29_ Loose gumbo and boulders 112- 150 Gumbo 150- 160 Sand rock 160- 165 Gumbo 165- 172 Geology and Mineral Resources of Bexar County 175 Sand rock Sandy gumbo Sand rock Gumbo (Set 8" pipe at 265 ft.) Hard sand rock Gumbo Sandy gumbo Sandy gumbo Sand rock Water sand Sand rock Sandy gumbo and boulders . . . . Shale and gumbo Hard rock and gumbo Sand rock Shale and boulders Sand rock Shale Hard rock Shale Sand and lime rock Shale Sand rock Shale Sand rock . Shale Sand rock Shale Sand rock Hard shale Sand rock Shale Sand rock Shale and rock Gumbo Sand rock . Shale and gumbo Sand rock Shale and boulders Gumbo . Sand rock Shale Gumbo (Set 6" pipe at 1118 ft) Coarse shale Fine shale Shale (slight showing of oil) . 172- 174 . 174- 222 . 222- 227 . 227- 342 . 342- 362 . 362- 388 . 388- 392 . 392- 450 . 450- 453 . 453- 460 . 460- 465 . 465- 505 . 505- 565 . 565- 582 . 582- 587 . 587- 701 . 701- 704 , 704- 708 . 708- 711 , 711- 720 , 720- 723 , 723- 747 . 747- 751 , 751- 790 . 790- 793 793- 800 . 800- 803 . 803- 811 , 811- 815 , 815- 850 , 850- 853 853- 860 860- 863 863- 940 940-* 980 980- 983 983- 987 987-1000 1000-1030 1030-1046 1046-1048 1048-1095 1095-1110 1110-1160 1160-1190 1190-1309 176 University of Texas Bulletin w R o ck 1309-1313 Shale 1313-1375 Gumbo 1375-1385 Shale 1385-1450 Rock 1450-1453 Shale 1453-1510 Gumbo 1510-1535 Rock 1535-1538 Shale (Set 4" pipe at 1555 ft) 1538-1600 White lime 1600-1620 Shale 1620-1638 Rock 1638-1641 Shale . 1641-1661 Rock 1661-1662 Shale 1662-1740 Rock 1740-1742 Shale 1742-1900 Black shale 1900-1940 Sand and shale 1940-1980 This well starts in the Wilcox formation. The Austin forma- tion would seem, so far as can be judged from the log, to have been entered at about 1600 feet from the surface. Allowing for the Taylor and Navarro formations their usual combined thickness of about 900 feet, there is indicated at least 700 feet of Tertiary at this locality. The Austin formation apparently is 300 feet thick, the Eagleford “black shales” having been entered at 1900 feet. Cuttings from this well were examined at the time the well was drilled, by Dr. J. A. Udden, who identified the Austin formation as extending from about 1600 to 1900 feet and the Eagleford below 1900 feet. If this well terminates in the Eagleford at 1280, as seems probable from both the log and the cuttings, there is here the maximum thickness, 80 feet, recorded for this formation in Bexar County. Assuming that the well terminates at or near the base of the Eagleford, the estimated level of the top of the Del Rio at this place is somewhat more than 2000 feet from the surface, or near 1500 below sea level. 150. Mars Discovery well, Alta Vista oil field. Elevation, 600 feet. Drilled in 1915, on Kelso tract, 8 miles south of San Antonio. Surface 0- 2 Gravel 2- 4 Red clay 4- 16 Joint clay 16- 40 Rock lime 40- 46 Yellow sand 4 6- 54 Blue shale 5 4- 70 Geology and Mineral Resources of Bexar County 177 Sand rock, red 70- 72 Blue shale 72- 110 Sand rock, rough 110- 113 Blue gumbo 113- 133 Sand, showed oil 133- 160 Blue gumbo 160- 180 Lime shale, hard 180- 325 Rock, lime shell 32 5- 326 Blue gumbo v 326- 340 Blue shale 340- 380 Rock, showed pyrites 380- 400 Hard blue shale 400- 436 Blue gumbo 436- 450 Hard blue shale 450- 470 Sand, hard and black 4 70- 482 Hard blue shale 482- 550 Blue gumbo 550- 590 Hard blue shale 590- 655 Blue gumbo 655- 691 Hard blue shale 691- 715 Blue gumbo 715- 763 Soft sand, showed oil 7 63- 780 Soft blue shale . . : 780- 808 Sand, showed oil 808- 818 Blue gumbo 818- 840 Hard blue sand 840- 851 Blue shale 851- 875 Blue gumbo 875- 890 Lime rock 890- 891 Soft blue shale 891- 90 8 Soft sand rock 908- 911 Sand, showed oil 911 - 915 Blue hard shale 915- 9 40 Blue lime rock 94 0- 941 Gray, hard sand 941- 946 Hard blue shale 946- 995 Blue gumbo 995-1010 Sand, showed oil 1010-1014 Soft blue shale 1014-1030 Hard, gray sand 1030-1033 Blue gumbo 1033-1050 Hard gray sand 1050-1058 Hard blue shale 1058-1070 Oil sand, hard .1070-1090 (Did not drill to bottom of oil sand) 12-Bex. 178 University of Texas Bulletin 151. Mathey No. 1 of the Bexar Petroleum Company, located on the J. H. Mathey property about one mile west of Losoya. Eleva- tion 515 feet. Depth 29 2 5. Notes on this well supplied by Hamilton and Walker have been included in connection with a discussion of the thickness of the Midway and Wilcox formations, which appear to extend to the depth of between 1340 and 1402 feet. The driller believes that the Austin formation was reached at the depth of 189 2 feet and con- tinued to the bottom of the well, 2025. I£ the top of the Austin be placed at 1892 feet, and from the drillers log apparently it can not be nlaced at any higher level, the Del Rio formation is to be expected in this well at a depth approximating 2342 feet, or near the actual level of 182 7 feet below sea. The seemingly great thick- ness of the Tertiary in this well and in the Sarah Smith well, log of which is given later, indicates that a part of the interval assigned to the Upper Cretaceous in the Ridder, Kearney, and Superior Oil Co. wells may possibly also be Tteriary. LOG OF J. H. MATHEY WELL NO. 1 Bexar Petroleum Company, near Losoya, Bexar County, Texas. Elevation 515 feet. Commenced drilling Nov. 18th., 1919. 0- 68 feet, red clay and small gravel. 68- 7 4 feet, blue-gray sand rock. 74- 78 feet, black gumbo. 78- 80 feet, blue-gray sand rock. 80- 100 feet, red clay and small gravel. 100- 102 feet, blue-gray sand rock. 102- 130 feet, red clay and sand. 130- 135 feet, black gumbo. 135- 180 feet, red gumbo and hard sand (water). 180- 190 feet, black gumbo. 190- 201 feet, black shale. 201- 208 feet, black gumbo. 208- 222 feet, dry brown sandy shale. 222- 224 feet, brown sand rock. 22 4- 240 feet, black gumbo. 24 0- 260 feet, dry brown sandy shale. 2 60- 263 feet, shell. 263- 290 feet, dry brown sandy shale. 290- 293 feet, brown sand rock. 293- 330 feet, brown sandy shale (dry and hard). 330- 336 feet, black gumbo. 336- 350 feet, brown sandy shale (dry and hard). 350- 358 feet, black gumbo. 358- 359 feet, gray sand rock. Geology and Mineral Resources of Bexar County 359- 365 feet, black sandy gumbo. 365- 367 feet, gray sand rock. 367- 385 feet, black shale with lignite. 385- 409 feet, black sandy gumbo. 409- 445 feet, gray sand rock (water) (used roller bit) 445- 465 feet, black gumbo. 465- 466 feet, gray sand rock. 466- 471 feet, black sandy gumbo. 4 71- 472 feet, gray sand rock. 472- 505 feet, black sandy gumbo and boulders. 505- 515 feet, black shale. 515- 519 feet, gray sand rock. 519- 557 feet, black sandy gumbo and small boulders. 557- 570 feet, black shale and lignite. 570- 574 feet, gray sand and lime rock. 574- 590 feet, black shale and lignite. 590- 640 feet, black gummy shale. 640- 645 feet, black gummy shale and boulders. 645- 730 feet, black hard gummy shale. 730- 740 feet, black soft shale. 740- 770 feet, black hard gummy shale. (Some fossils). 770- 815 feet, black hard gummy shale. 815- 819 feet, black soft coarse shale, with green marl. 819- 841 feet, black hard gummy shale. 841- 850 feet, black soft coarse shale. 850-1084 feet, black hard gummy shale. 921-928. Core No. 1 1084- 1085 feet, gray hard sand. 1085- 1090 feet, black hard gummy shale. 1090-1097 feet, black hard gummy shale. 1097-1117 feet, black hard gummy shale. 1117-1124 feet, black hard sandy shale. 1124-1127 feet, black hard gummy shale. 1127-1129 feet, gray sand rock. 1129-1165 feet, black hard gummy shale. 1165-1170 feet, brown hard sandy shale. 1170-1200 feet, black hard gummy shale. 1200-1202 feet, gray sand rock. 1202-1214 feet, black hard gummy shale. 1214- 1215 feet, gray sand rock with pyrites. 1215- 1360 feet, black hard gummy shale (Core 1320-1322) No. 2. 1360-1372 feet, black hard sandy shale. 1372-1407 feet, black hard gummy shale (Core 1402-1406) No. 3. 1407-1417 feet, black soft shale. 1417-1472 feet, black hard gummy shale (Core 1457-1459) No. 4. 1472-1490 feet, gray shale with lime. (Lime only thin layers). 1490-1548 feet, gray hard gumbo. 180 University of Texas Bulletin 1548-1556 feet, gray hard shale. 1556-1570 feet, gray hard gumbo. 1570-1582 feet, gray hard shale. 1582-1600 feet, gray hard gumbo. 1600-1622 feet, gray soft shale. 1622-1632 feet, gray hard gumbo. 1632-1670 feet, gray soft shale. (Gas and little oil showing). 1670-1710 feet, gray hard gumbo. 1710-1720 feet, black soft gummy shale. 1720-1740 feet, gray hard gumbo. 1740-1763 feet, black hard gummy shale. (Core 1760-1763) No. 5. 1763-1820 feet, black hard gummy shale. 1820-1825 feet, black soft gummy shale. 1825-1840 feet, black hard gummy shale. 1840-1845 feet, black soft shale. 1845-1861 feet, gray hard sandy gumbo. 1861-1862 feet, gray lime rock. 1 862-1870 feet, gray hard sandy gumbo. 1870-1885 feet, gray soft shale. 1885-1892 feet, gray hard sandy shale. (Set 6-inch easing at 1892), 1892-1938 feet, blue-gray chalk. (Showing little gas and oil). 1938-2007 feet, blue-gray chalk. 152. National Oil Co., Alta Vista oil field: Depth, 1132; eleva- tion, 585. Producing horizon, Austin formation, 1120; sulphur water encountered at 1132. Actual level, top of producing sand, 635 feet below sea level. Estimated position top of Del Rio clay, 835 feet below sea level. 153. Oliver well, 9^ miles southwest of San Antonio. Depth 1030 feet. Oil showing at 200 and at 600 feet. Strong gas flow at 800 feet. Gas flow reported to have been 350,000 cu. ft. per day at time well was drilled, subsequently probably reduced in flow. This well probably reached to the Austin formation; however, the showing of oil and the gas with little doubt is from the Taylor and Navarro formations. 154. Openheimer well No. 1. Alta Vista field, about 1400 feet northeast of Fuchs, No. 1. Smith, driller. Depth 1295 feet; eleva- tion 620. About 500 feet east of the Pleasanton Road. Producing horizon at 1150 feet. Sulphur water at 1295 fe«t. Actual level producing sand, 530 feet below sea. Estimated place of the Del Rio 830 feet below sea. 155. Park Oil and Gas Co. Applewhite No. 1 well. North side of Rockport Cross-road, 1 V 2 miles east of Applewhite Road, 16 Geology and Mineral Resources of Bexar County 181 miles south of San Antonio on south side of T. C. Applewhite prop- erty. Thompson, driller. Depth, 1952 feet. Elevation 500 feet, more or less. Test well for oil. Clay 0- 50 Rock 50- 51 Sand 51- 60 Rock 60- 62 Sand and boulders 62- 80 Rock 80- 82 Sand : 82- 90 Rock 90- 98 Sand and boulders 98- 120 Rock 120- 122 Sand and boulders 122- 150 Rock 150- 152 Hard sand 152- 200 Rock 200- 202 Sand and boulders 202- 240 Shale 240- 275 Packed sand 275- 280 Shale and boulders 280- 340 Packed sand and gravel 340- 370 Packed sand 370- 400 Rock 400- 405 Shale 405- 420 Rock 420- 421 Rock (water sand) 421- 542 Sand rock 542- 630 Shale 630- 675 Rock 675- 685 Gumbo 685- 706 Rock 706- 715 Gumbo 715- 740 Shale and boulders 740- 825 Gumbo 825- 885 Shale, boulders, oil and gas sand 885- 940 Gumbo 940- 972 Hard shale 972- 995 Gumbo 995-1011 Shale .1011-1020 Gumbo ........ 1020-1030 Hard shale 1030-1036 Gumbo and boulders . . . .* 1036-1048 Shale 1048-1050 Shale and boulders, showing oil 1050-1080 Gumbo 1080-1110 Gumbo 11 IQ-1127 • 182 University of Texas Bulletin Rock 1127-1133 Gumbo 1133-1148 Rock (red sand and iron) 1148-1155 Shale and oil sand, showing oil 1155-1175 Gumbo 1175-1185 Rock 1185-1187 Hard shale 1187-1258 Gumbo 1258-1262 (Set 1261 ft. 6" line pipe in cement) Gumbo 1262-1268 Hard shale 1268-1290 Soft shale 1290-1380 Gumbo 1380-1390 Shale and boulders 1390-1425 Gumbo 1425^1435 Shale and boulders 1435-147 2 Hard sand 1472-1491 Gumbo 1491-1512 Hard rock 1512-1514 Shale showing oil 1514-1524 Gumbo 1524^1530 Rock 1530-1532 Chalk rock 1532-1572 Gumbo 1572-1598 Shale and oil sand (showing oil and gas 1598-1645 Gumbo 1645-1655 Shale 1655-1688 Gumbo 1688-1710 Hard shale 1710-1715 Gumbo, white 1715-1720 Shale showing oil 1720-1730 Gumbo (Set 3" lines) 1730-1732 Shale (Oil show) 1732-1796 Shale 1796-1809 Dark brown sand and shale (Oil show) 1809-1816 Shale 1816-1827 Sand 1827-1830 Gumbo 1830-1842 Soft shale 1842-1847 Gumbo 1847-1852 Soft shale 1852-1857 Gumbo 1857-1862 Shale and hard sand 1862-1867 Gumbo 1867-1874 Shale 1874-1877 Gumbo 1877-1886 Soft rock 1886-1889 Geology and Mineral Resources of Bexar County 183 Soft shale 1889-1896 Chalk rock 1896-1915 Chalk rock 1915-1934 Oil sand 1934-1952 The well starts probably in the Wilcox formation and to the depth of 1050 feet or more may be Tertiary, although one cannot be sure of this. The reference is chiefly because of the reported presence of boulders to that dpth. From 1050 to 1896 feet, so far as can be judged from the log, the Navarro and Taylor formations may very well be represented, their combined thickness being early 900 feet. The Austin formation appears to lie at about 1896 feet. If this is true the Del Rio may be expected at about 2350, or something like the actual level of 1850 feet below sea. 15 6. Perrinot well, about 2 miles southwest of Martinez, east of the Foster Cross-road on J. F. Schlather’s property. Test well for oil. Soil 0- 2 Yellow clay 2- 22 Shale 22- 63 Rock 63- 64 Shale and boulders 64- 87 Shale 87- 150 Gumbo 150- 236 Shale 236- 249 Gumbo 249- 269 Rock i. 269- 270 Shale 270- 297 Gumbo 297- 307 Shale and boulders 307- 359 Gumbo 359- 371 Shale 371- 391 Gumbo 391- 401 Shale 401- 438 Gumbo 438- 446 Shale 446- 451 Rock 451- 453 Shale 453- 478 Gumbo 478- 483 Rock 483- 492 Shale 492- 501 Gumbo 501- 522 184 University of Texas Bulletin Rock 522- 523 Shale, oil showing 523- 534 Gumbo 534- 547 Rock 547- 549 Gumbo 549- 559 Rock 559- 565 Blue clay 565- 570 Gumbo 570- 583 Rock 583- 585 Gumbo 585- 602 Sand and shale 602- 607 Gumbo 607- 661 Rock 661- 663 Shale, oil showing 663- 669 Gumbo 669- 684 Shale and boulders 684- 709 Shale and gumbo 709- 730 Gumbo, very tough 730- 7 61 Shale 761- 774 Gumbo 774- 779 Shale and boulders 77 9- 789 Soft rock % 789- 806 Shale 806- 816 Rock 816- 827 Gumbo 827- 837 Rock 837- 848 Shale 848- 860 Black sand and shale, showing oil and gas 860- 868 Gumbo 868- 873 Black sand and shale 873- 900 Rock 900- 902 Not recorded 902- 953 Gumbo 953- 984 Shale 984- 986 Gumbo . . 986-10 64 Chalk 1064-1080 Shale 1080-1107 Gumbo 1107-1118 Shale 1118-1129 Gumbo 1129-1134 Shale 1134-1150 Rock and shale .1150-1162 Shale 1162-1167 Gumbo 1167-1178 Shale 1178-1188 Gumbo 1188-1193 Shale 1193-1208 Geology and Mineral Resources of Bexar County 185 Rock 1208-1212 Shale, show gas and oil . . .1212-1239 Chalk rock 1239-1375 This well starts in the Tertiary, probably in the Midway forma- tion, and extends into but not through the Austin formation. The dividing line between the Tertiary and Cretaceous can scarcely be determined from the log, although the Midway may provisionally be regarded as extending to 360 feet, as this is the last record of boulders suggestive of those of the Tertiary formations. From 360 to something more than 1200 feet is apparently referable to the Navarro and Taylor formations. Below about 1239 feet, the drilling record indicates the Austin formation in which the well terminates. Assuming that the top of the Austin formation lies at about 1250 feet, the Del Rio at this locality is to be expected at about 1700 feet below the surface or at about the actual level of 1000 feet below sea. 157. Porch well, east of the Pleasanton Road between ; Mit- chell’s Lake and the Medina River on Arroyo Hondo. Depth, 1505 feet; elevation about 530 feet. Test well for oil; showings of oil at about 1000 feet, and from about 1292 to 1493 feet. No water except small amounts between 60 and 70 feet, and a little salt water at the bottom of the hole. Record submitted to Bureau of Eco- nomic Geology by E. L. Porch. Soil and clay 0- 30 Hard pan 30- 5 0 Soft sand rock 50- 6 0 Gravel, loose; water 60- 66 Very hard rock 66- 69 Sand fine, black 69- 72 Clay, 10" casing set at 81' 72- 87 Lignite 87- 90 Sand rock 90- 13 5 Very hard sand rock, gray 135- 137 Sand rock 137- 164 High grade lignite or coal 164- 172 Sand rock 172- 182 Hard rock 182-184 Shale 184- 193 Hard sand rock, blue 193- 203 Shale 203- 213 Gumbo 213- 286 Shale and boulder 286- 297 Rock, hard 297- 299 Gumbo, very stiff 29 9- 309 Rock, very hard 309- 312 Gumbo 312- 333 186 University of Texas Bulletin Sand rock, soft 333- 353 Hard blue rock 35 3- 35.5 , Gumbo 355- 3 62 Hard rock 362- 364 Gumibo 36 4^ 379 Boulder, flint 379- 381 Gumbo 381- 3-87 Rock, hard 387- 389 Gumbo, tough 389- 409 Rock 409- 410 Gumbo 410- 417 Rock 417- 420 Gumbo ' 420- 454 Hard rock 454- 456 Gumbo 456- 473 Rock 473- 474 Gumbo, very stiff 474- 492 Boulder . 492- 494 Gumbo 494- 518 Gumbo and shell 518- 523 Very hard rock 523- 526 Gumbo 526- 544 Shale and boulder 544- 565 Gumbo with boulder 565- 595 Gumbo and shell (Cretaceous) 595- 609 Shale with boulders 609- 627 Rock 627- 629 Gumbo 629- 637 Shale 637- 647 Gumbo and boulder 647- 671 Shale and boulder 671- 689 Gumbo 689- 705 Rock 705- 706 Shale and shell 706- 719 Gumbo 719- 775 Shale and shell 775- 791 Gumbo 791- 865 Shale *. 865- 872 Rock 872- 874 Shale, blue 874- 881 Gumbo 881- 888 Shale 888- 892 Gumbo, light colored 892- 894 Shale, coarse, blue 894- 897 Rock, soft 897- 898 Shale and boulder 898- 904 Gumbo 904- 966 Geology and Mineral Resources of Bexar County 187 Shale, some soft 9 66- 9 85 Shale and sand 985-1003 Gumbo 1003-1056 Shell and rock 1056-1058 Gumbo 1058-1129 Shale and sand, compact 1129-1133 Shale 1133-1138 Shale, with large proportion of green sand 1138-1148 Shale and darker sand 1148-1157 Gumbo, dark sand, very fine 1157-1171 Boulder 1171-1172 Shale 1172-1175 Gumbo 1175-1180 Boulder 1180-1181 Gumbo 1181-1192 Boulder or rock 1192-1193 Gumbo 1193-1208 Very fine shale 1208-1213 Gumbo with pyrites 1213-1233 Gumbo, tough blue 1233-1292 Shale, gas and oil showing 1292-1296 Soft shale and sand, gas 1296-1329 Shale or gumbo and sand 1329-1394 Gumbo, blue, no sand 1394-1430 Shale and sand, gas and oil 1430-1464 Oil sand, little shale 1464-1483 Very dark shale, sand 1483-1493 Dark blue gumbo and sand, very hard 1493-1505 Supplementary data from owners of well: “From 1296 to 1394 the shale or gumbo was in alternate layers of about six inches, sand between; drilling was hard, while in the shale or gumbo and would go quickly through the sand. From each sand layeT fine showings of gas and some oil were noticed. Five joints of Layne & Bowler screen were set to catch this, but was too coarse. A fine black sand came through and formed a bridge and would form as fast as was washed out. The oil sand from 1464 to 1483 would undoubt- edly have made a well if same had been properly cased and washed. Live oil of light gravity and parafine base came out continually while going through with heavy gas pressure pieces of parafine as large as end of thumb came up with cuttings. In this well there was no evidence of Austin chalk which was struck in other wells 3 miles to the northwest at 1100 to 1200 feet; other sections show shallow oil ahd gas, none noticed in this well until about 1000 feet down; no water encountered except between 60 and 70 feet, although a little salt water showed up from the bottom of the hole.” 188 University of Texas Bulletin 158. Log of Oil Prospecting Well of W. C. Steubing, 2 miles southeast of Somerset, Bexar County, Texas. Sarah Smith No. 1. (Prepared by L. W. Stephenson from samples furnished by the owner; fossils identified by C. W. Cooks). Thickness Depth feet feet 1. Reddish brown, slightly ferruginous, fine sand. . 4 4 2. Light gray, very fine argillaceous, micaceous sand blotched with yellow 16 20 3. Fine gray sand like No. 2 but more completely blotched with sulphur yellow and some pur- plish tint 20 40 4. Dark gray finely sandy, micaceous, carbona- ceous clay with fragments of fine reddish to yellowish ferruginous sandstone 20 60 5. Gray fine slightly calcareous sand with some mica and numerous reddish, yellowish and brownish grains; water bearing 20 80 6. Gray sand like the preceding, but contains numerous small, white flaky grains that are probably rotten shell fragments, as they effervesce freely in acid; water bearing 20 100 7. Fine gray clean sand with pinkish and yellow- ish grains, and some mica; water bearing. ... 20 120 8. Dark gray fine micaceous sand with numerous fragments of gray shaly clay 20 140 9. Fint gray calcareous sand with some mica and numerous dark grains; water bearing 20 160 10. Gray sand like No. 9; water bearing 20 180 11. Fine gray clean sand, with some mica and numerous dark grains; water bearing 20 200 12. Gray sand like No. 11, but contains small fragments of gray shaly clay and small" frag- ments of vein calcite; water bearing 20 220 13. Fine clean sand like No. 11, with a few frag- ments of shaly clay; water bearing 35 255 14. Ground-up gray hard slightly calcareous sand- stone 4 259 15. Fine gray clean sand with some mica and nu- merous dark grains 20 279 16. Gray sand like No. 15 12 291 17. Ground-up light gray medium grained sand- stone 21 312 18. Sandstone like No. 17 10 322 ?9. Fine gray sand with some mica, numerous dark grains, numerous fragments of gray Geology and Mineral Resources of Bexar County 189 Thickness Depth feet feet shaly clay, and small particles of black lignite 22 344 20. Light gray clean sand with numerous dark grains and small fragments of black lignite. . 31 375 21. Dark gray argillaceous sand with some mica and some fragments of gray shaly clay 22 397 22. Dark gray to blackish, finely sandy carbona- ceous clay, containing some marcasite 16 413 23. Dark gray carbonaceous clay mixed with fine gray sand 24 437 24. Mottled mixture of fine white and light gray partly indurated sand, the cementing sub- stance apparently being white and gray clay; some fragments of gray shaly clay 21 458 25. Mixture of fragments of dark gray shaly clay, and white sandy clay (?) 20 478 26. Mixture of dark gray calcareous sand, frag- ments of dark gray shaly clay, and black lignite 20 498 27. Mixture like No. 26 21 519 28. Mostly fragments of gray shaly clay, with some loose fine gray sand, and a few shell fragments 19 538 29. Mixture of fine gray calcareous sand and frag- ments of gray shaly clay 19 557 30. Mixture like No. 29; some shell fragments.... 21 578 31. Mixture like No. 30 22 600 32. Mixture like No. 30; some lignite and shell fragments 21 621 33. Mixture like No. 30; recognized the fossil shell Toinostoma? sp — 17 638 34. Mixture like No. 30; some shell fragments and some marcasite 21 659 35. Mostly gray shaly clay with a few shell frag- ments; recognized the fossil shell Ringicula dalli Clark? 21 680 36. Shaly clay like No. 35; recognized the fossil shells Cyclichna sp., Corbula sp., and Tur- ritella sp 20 700 37. Dark gray clay (gumbo of the driller) with a few shell fragments; recognized the fossil shell Fuses sp. cf F Meleri Aldrich 21 721 38. Gray shaly clay 19 740 39. Gray shaly clay, with some shell fragments recognized Turritella sp 21 761 190 University of Texas Bulletin Thickness Depth feet feet 40. Gray shaly clay; recognized the fossil shells, Olivella mediavia Harris, Natica sp. Turri- tella sp 21 782 41. Gray shaly clay, larger fragments; recognized the fossil shell Pleions rugata (Hilprin) ? ? . . 19 801 42. Dark gray clay (from bit?) 21 822 43. Gray finely shaly clay 21 843 44. Gray shaly clay; recognized the fossil shells Venericardia, sp and Natica sp 22 865 45. Gray shaly clay; larger fragments 20 885 46. Gray (finely shaly clay with a mixture of dark glauconitic sand; recognized the fossil shells Venericardia sp., and Turritella sp 21 906 47. Gray shaly clay and glauconitic sand, like No. 4 6 . 20 926 48. Gray shaly clay and glauconitic sand like No. 46 21 947 49. Gray finely shaly clay 21 968 50. Gray finely shaly clay with some dark glau- conitic grains and some shell fragments. . . . 21 989 51. Gray shaly clay, slight showing of oil and gas. . 23 1012 52. Gray shaly clay with some glauconite grains; recognized the fossil shell Venericardia plan- icosta Lamark. Some showing of oil and gas. . 21 1033 53. Shaly clay like No. 52, slight showing of oil and gas 22 1055 54. Shaly clay like No. 52, gas and oil showing increase 4 1059 According to Dr. Cooke, the fossils enumerated in the log indi- cate the Midway Age of the containing beds. Continuation of Log of Oil Prospecting Well .of W. C. Steubing (Sarah Smith No. 1) 2 miles southeast of Somerset, Bexar County, Texas. (Prepared by L. W. Stephenson from samples furnished by the owner). 55. Light gray to whitish, highly calcareous clay or argillaceous limestone ground to fine mud, with fragments of platy impure limestone. . 56. Gray, calcareous somewhat shaly clay with some admixture of material like No. 55 57. Gray, calcareous, shaly clay 58. Gray, shaly clay like No. 57; observed 2 speci- mens of Foraminifera 59. Gray, shaly clay, like the preceding, with a few shell fragments 16 1075 20 1095 20 1115 21 1136 21 1157 Geology and Mineral Resources of Bexar County 191 Thickness Depth 60. Gray shaly clay like the preceding, with a few feet feet shell fragments, recognized Venericardia? and a small smooth gastropod 20 1177 61. Gray finely shaly, calcareous clay 20 1197 62. Gray calcareous clay like No. 61 21 1218 62. Gray calcareous clay like No. 61 21 1239 63. Gray calcareous clay like No. 61 21 1239 64. Gray calcareous clay like No. 61 20 1259 65. Gray calcareous clay like No. 61 20 1279 66. Gray calcareous clay like No. 61 20 1299 67. Grav calcareous clay like No. 61 20 1319 68. Gray calcareous clay like No. 61 20 1339 Not represented by sample 11 1350 69. Gray shaly calcareous clay 50 1400 70. Gray shaly calcareous clay 20 1420 71. Gray shaly calcareous clay 14 1434 72. Gray shaly calcareous clay 6 1440 73. Gray shaly calcareous clay with a little fine sand 4 14 4 4 74. Gray shaly clay like No. 73 11 1455 75. Gray shaly clay like No. 7 3 5 1460 76. Gray shaly clay like No. 73 20 1480 77. Gray shaly clay like No. 73 4 1484 78. Gray shaly clay like No. 73 5 1489 Not represented by sample 5 1494 79. Gray shaly clay like No. 73 5 1499 80. Gray shaly clay like No. 73; contains a small gastropod 4 1503 81. Gray shaly clay like No. 73 21 1524 82. Gray shaly calcareous clay and very fine sand . . 20 1544 83. Gray shaly calcareous clay with some fine sand; one or two shell fragments 21 1565 84. Gray shaly clay and some sand; like No. 83. . . 21 1586 85. Gray shaly calcareous clay and very fine sand. . 19 1605 86. Gray shaly calcareous clay and very fine sand . . 21 1626 87. Gray shaly calcareous clay and very fine sand. . 20 1646 88. Gray shaly calcareous clay and very fine sand. . 21 1667 This set of samples (Nos. 55-88) is very much alike throughout. A fragment of a Venericardia? from sample No. 60 (depth 1157- 1177 ft.) seems to indicate that the shalv clay at that depth be- longs to the Midway group of the Eocene. Nothing was found below that depth to indicate that the well had passed from the Eocene into the underlying Cretaceous. If it is all Eocene the strata of this age are thicker at this place than we had supposed. 192 University of Texas Bulletin w ' o xi © £ d ^ tO O © - © j® ^ -S - m^d ^ -4-> *-< O c /2 $ J gi*;? SS-^ d d bee© o-^.S° CO fc © m 00 0 ) O+j j a o 2 § m gtjfi.d 2 13 .S •§ s ^dfldp oQ .<*£ 8 “I|o £ £ d -S .• 'G'g W)’ 0 ^ “2 ■*.§-* d CO >> 2 ^ 2 *2 ^ T3 © d O ©^ o kJ cd to^ ^ d > K © > .2 „ . CO £h rT> •S S 05 <® ^ tH 1 (p = °c« ^4§ N •§ § -d - © o-S a^S ^ > o o tc P- © o (D ‘2 7-1 «M CD > Si ©^ CO 33 CO 6 fto gd^H co be ce o a® © £ ^8S8f 8l‘Sff Sl'j8SgaaS5!KiS3«5ffig2 82Sfe HHHHHNIMWlNW (MMCOC003W^'3'M<'i»l^lftlOi2s 0 ^g§ 8888 § 888888 £SS£ 3 £fe££$££: r-li-Hi-li^ riWNNN NNCOMM B « Tt" ^ ^ Tf Tf 1 O OOOO OOOOO oO-OuO OiSuOO-OOOOOOOOO WKJWWajGIDODtatBCQQQ'W'OQMGOCQMWOQDQOQDOODODODCOCQODOQ © ^ ^ I jj 4 i +s 1 1+1 •d©°' 2 d.c.c*g£,c 3 r'flflflfliJknbri 8 "' 1 "'’-' ® a) e 3 w - 44 1 i +J 4J 43 44 j-i+ioJjjJoJjjjj! 1 I I 44 1 1 1 * o44.flrimn.ii n n i- < f i f!^Tjj-s44 l i,S^T 3 n 33 ^T 3 ^' 0 't 34 !'a' 04 ! fliscscsciciciciflaaafloflfl^ I I cc O « 1 »-l^ii-l £/ 5 KKt»COt»OOtB»ajCCOOMCO Shale 1 Dark | Soft Geology and Mineral Resources of Bexar County 193 I . O I T3 44 ! a S S i £ 5 23 o3 «23.=i23 »-H O 1-° ® o | T3 T3 ^ 4 " > 5 !gaa®3' i® ® ® : « « « > os .a 2323 ®xj !02gogg GO • a i ' ° a Si -M 0 ® : is? ! a M 3 cq'h cj ta ,S° fl 2 i^sa§ 1 2 2 . 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(M W ^ 1C < 88 8 8 8 13-Bex. 194 University of Texas Bulletin o o xn w $0 ~ ft U <0 £S3 O rH • M !S§ foS^S „ boS n I M © C ° *H CD 1-35^ « i o q g o o a> 3 a .O a? 3 is 33 o 0} ■O 3 g l 0-0 £ a cs a o ° m 43 « 03 23 a> 3 a O’ .2-S 6dS5 S +j-OmO g ’S ‘53 ■ H ■« 00 a a w 44 •" 'S o ri O •— bfl bfl XI ft fl 5 .s.s +jH 1 * • “OONB 2-cx: 5 a=3 §S OOft - x: ^ o ft **• " 60 a o co ,2} 33 03 -g O 03 .2 •« cs d O aj ® go gs.sl .So d ^>2 bo‘~ O s firt •Sb'iS n o y CO 33 o . «d fcuo s, S £ d 60 S -S* boD 2 w d -w .2 > Jt I g § °Og .'-5 £ O'O § rg * g «d5 0 33 ^ |> ; ws & bo -3 co o bfl £ •1 bfl 03 O o fc * S3 a t-i > S 2 o r*i »*-* r-t a OS .33 „ bo Trt eC ftn o5^« 02 02 O OJ co £ 03 CO gj bO ft Sort's *j°d S„ 03 Sh 33 mfl O O & 4J «*H O 3 O *H £ _ • P — < io«»? o'Sll '81 +^0+^0 0^- O OO I O 03 a 3 ® > 3 w .S bo H « o rC ■4-^ 02 GQ cS'S CO s «* O 03 -ss " fi ! I s g 03 O tjj § a xi o 33 X3 >80S ■3< 33 r-t 33 03 a w ' bp cd g d -e S’* S d os M to o O M rH ■*» 03 *H 44 9 O o O tH 03 M 33 srS Is* +* ft-, d o3 O *; io « 33 i-t t> Cl « §3 IE3S3 g C3 03 g' 1 °: 05 N CD a m to ,g *H 3 Ocq X3 «x pd iH Q , >> ,03 33 . cd m P- ft 02 1 1 1 >> 1 1 44 >» t>> co Cd g cd cd bo bio ho bo bio 44 44 44 44 44 cd 3 cd 3 cd ft ft ft ft ft 33 33 *H S-l CS 03 X3,d a a 3 3 33 33 M (H 03 03 X! X3 CO ^H ° ^ > 8 oo d :|g! 03 .. K02 02 bo bfl to ^ ^4 44 03 03 03 OOP ft ft ft ft ft ft a® o ® 03 03 ass o o o co co co 33 33 d d 03 cd CO CO 03 03 a a o o 8s: half Geology and Mineral Resources of Bexar County 195 > 03 _0Q ! 'S -3 TJ I V 03 'O o a o s O W bfl ££ 03 q; o3 £ >X! E bo 9.9 a £ ^ o 00 ® ’■§ r-t J5 c3 3?“ a- si a ^ a § t-H g 05 O 05 g- 6 * 83 02 ■e. a O 05 fcS 60 CO _g,2 o,h lO +5> 1—1 a o g a to S 05 t-i tf> o Ss° O I 53 a o o 2 = S a« g •9S^| "g,.as ^<2 s' 0 O 'f 03 ,, « 5 3 +j5C g H X >> bo-C 5 “si ; a ® ° .2 JgS’Se* b a «*— S' 3 .a > 'a .5 •> ? oS - S3 •- O C bfi p a-S§ t; £ S ® o ° a . . - . ® -m •g 05 9 « to bfl rt ' w ■2 .9 60 993^ iiSs ri S D«bO 8 S 03 ,5 to © _e> .a a ° “ H Pi bjOC 3 io a o Sj S £cfc: X! ^1 ’ -M O , bp’SS*, 03 ^ags 5 a “2 m 2 ° A w ad xi «« ® © W S 2 M 5-0 k:c.32 Q O p 60 c3 w >> tuo g 05 tH p a >h >:s a I 2 1® . 5* b®£ p -a+e x'HEg ® .03 a -a 83 X3 c a ■0 .£? >.a o Ifl s “ o w £ x: £ p K 1524 1544 1565 1586 i«a5 1726 1646 1668 1514 1524 1544 1565 infifi - 1605 1626 1646 1.1 -Bex. 196 University of Texas Bulletin 159. Walsch Oil Company, well No. 1 on south, side of Leon Creek in Mission Oil Field, near the Applewhite Road crossing. This well starts probably in the Navarro formation, as indicated by the greensand horizon near the surface. They probably termi- nate in the Austin formation and illustrate the character of drilling in the Mission oil field. Gravel 0- 18 Greensand and soapstone L8- 40 Clay, blue 40- 60 Clay and gumbo 60- 80 Shale and rock, soft; a little gas 80- 97 Shale, a little oil . 97- 180 Rock 130- 132 Shale 132- 134 Rock 134- 135 Shale 135- 140 Rock and sand 140- 155 Shale 155- 167 Rock 167- 181 Mud and small boulders 181- 192 Shale 192- 250 Shale and mud 250- 350 Rock 350- 352 Gumbo 352- 360 Rock 360- 364 Gumbo and shale 364- 430 Rock 430- 432 Shale 432- 441 Rock, hard and soft 441- 445 Shale and mud 445- 523 Rock 523- 530 Shale 530- 637 Rock 637- 657 Shale 657- 661 Rock 661- 665 Shale 665- 670 Gypsum 670- 698 Rock 698- 702 Shale 702- 765 Rock 765- 786 Shale 786- 791 Rock 791- 801 Shale 801- 814 Iron pyrite 814- 815 Shale 815- 821 Boulders 821- 824 Geology and Mineral Resources of Bexar County 197 Shale 824- 835 Rock 835- 853 Shale 853- 861 Rock 861- 869 Rock 869- 876 Shale and pyrite 876- 893 Pyrites, hard 893- 902 Shale . . . . 902- 925 Rock 925- 937 Rock and shale 937- 957 Shale 957- 982 Rock, hard 982- 988 Rock and shale . 988-1002 Brown rock 1002-1024 Shale and some iron pyrite . 1024-1067 160. Wolfe and Elder, Alta Vista Oil Field, depth 1286, Eleva- tion 600. Test well for oil. Samples from this well from 965 feet to the bottom were sub- mitted by E. L. Porch and described by Dr. J. A. Udden (Mns). According to Dr. Udden’s interpretation of the samples the well entered the Buda limestone at 1270 feet and terminated in this formation at 1286 feet. From this record it would seem that the Del Rio formation is to be expected at this locality at between 1300 and 1400 feet, or at an actual elevation of between 700 and 800 feet below sea level. INDEX Page Ackermaft, H. J., well of.... 143 Alamo 8 Alamo Heights 42 Alamo Portland cement. .... .108 Alamo Waterworks well 143 Alectryonia larva 50 Allen, D. J., well of 143 Alluvial deposits 72 Alta Vista oil field 121, 122 Alta Vista structure 85 Area of artesian flow 101 Artesian water 97 Artesian wells 98 Austin chalk, analysis of 109 Austin formation 108, 116 oil from 122, 124 water of 104 Austin Hills 16 Aviation Post, well at 37 Avicula 43 Babcock Road 96 Baculites 43 Baker, C. L. 8, 43, ,52, 55, 58, 112, 115 Balcones escarpment ..11, 13, 77 Bandera Road 95 Barbattia sp 43 Basement sands 21 Basse, Ed. E., well of 143 Beckman 26 Bern Brick Co 112 Bend formation 19 Benke, Kate, well of ......... 144 Bentonite 115 Berry, E. W 10 Bexar County, area of 7 drainage 12 literature on 10 settlements in 7 topography 12 Biering, H. T., w'ell of 144 Blanco Road 90 Blank, J. T., well of 144 Bluewing Club, well of 145 Boerman, D., well of 147 Bose, Emil 10, 40 Brackenridge Coal Company.. 119 Brackenridge Park ..42, 81, 109 Brendle, H., well of 147 Brooks Field 8 Buda formation ....31, 110, 116 water of 103 Buda limestone, analysis of... 110 Page Building brick 112 Building stone 121 Bulimulus 73, 74 Bulverde Road 91 Calcareous concretions 75 Caliche 75 Camp Bullis Reservation .... 19 log of well on .131 Camp John Wise 8 Camp Stanley 8 Carbon dioxide in under- ground water 107 Carrizo formation 63 Carrizo sand hills 18 Castroville Road 114, 117 Cave deposits 73 Cement 108 Cenozoic 54 Clamp, C. C., well of 147 Clay 112 Climate 13 Cohen and Roby, well of ....171 Collins’ Gardens, well at ....148 Collins Mfg. Co., well of 148 Columnar section 20 Comanchean 21 Comanche Peak formation ... 24 Conception Mission 7 Concrete 116 Concretions 58 Cooke, C. W 190 Cretaceous 21 Crosby lease, wells on 125 Crosby well No. 4 172 Culebra Road 95 Culebra structure 83 Cyprina mediale 24 Del Rio clay 110 Del Rio formation 28, 86, 87, 112 water of 103 Del Rio Plain 16 Dentalium 112 Deussen, Alexander 9, 22, 75, 129 Dickinson well 148 Dips 43, 51, 58, 85, 113 Dumble, E. T 10 Eagleford formation 34, 111, 116 water of 104 Earle 62 Economic Geology 97 Edwards flint hills 15 Edwards formation.. 25, 110, 116, 120 200 University "of Texas Bulletin Page water of 101 Edwards limestone, analysis of 120 Elephas ^ . 73 Elevations 12 Eocene 54 Exogyra arietina 28, 29 costata 50, 94, 115 laeviuscula 40, 43 ponderosa 40, 41, 45, 47, 48 texana 25 Faulting 29 Faults 77 Flood-plain deposits 64 Flowing artesian wells 102 Fort Sam Houston 8 well at 22, 81 Fredericksburg Road 96 Friesenhahn, A., cav^of. ... 73 Frio Road 93 Fuller’s earth 114 Gartner, T. A 22 Gas . . . . 121 Gas Ridge field 7. .’.7.7.7 .122,’ 123 Geological map 86 Georgetown formation 27, 110, 116 water of 101 Geunther Milling Co., well of. 149 Glauconite 49, 52, 117 Glenrose formation 23, 116 water of 100 Glenrose Hills 14 Goforth, A. E., well of 38, 149 Government well at Aviation Post 149 at Ft. Sam Houston 150 Green marl 49 Greensand, analysis of, 117 Grote, F., well of .’ 151 Gryphea aucella 40 micronata 29 vesicularis 50 Gulf Coastal Plains 10 Hamilton, H. L 54 Harrison, Judd, well of 151 Harrison property, wells on.. 125 Hayes, C. W 75 Herff well 151 Hickory formation 19 Hill 25 Hill & Roby, well of 132 Hill, R. T 10, 21, 50, 77 Hoffman Ranch, exposures on. 33 Hofheintz, R. H., well of 152 Holtz well 152 Hot Well Hotel, well at 153 Hydrogen sulphide in under- ground waters 106 Index to map entries 87 Ingram well 173 Kearney Oil & Pipe Line Co., Kelly Field 8 Kelly Field Plain 70 Kimbly-Brown wells 173 Kurz, C., wells of 125 Lakeview addition, well in... 155 Lamb, J. K., well of 49, 174 Legler, W. F., well of 156 Leona formation 69 Leon Creek, exposures on. 51, 117 Leon Springs, Military Reservation 8 log of well on 129 wells on 19 Lignite H8 Lime 120 Limestone 119 Liopsitha elegantula 43 Locke, J., well of 156 Lorenz, Alex, well of 156 Lunatia pedernalis 24 Madison, R. M 9 Map 86 Mars Discovery well 176 Masterson, B. F., well of 156 Mathey well 45, 54, 178 Maty ear, Chas., well of 157 Medina Fuller’s Earth Co 114 well of 157 Medina Oil Co., well of 157 Medina River, alluvial de- posits of 72 exposures on 58, 62 Mercke, R., well of 21 Mesozoic 21 Midway formation 54, 116 Midway-Wilcox Hills 18 Mission Oil Field 121, 123 Missions 7 Monopleura 27 Mt. Selman formation 64 Nacogdoches Road 91 National Oil Co., well of 180 Navarro formation ..49, 112, 114, 117 oil from 122 water of 104 Non-flowing artesian wells.... 102 Oil 121 Oliver well 180 Geology and Mineral Resources of Bexar County 201 Page Openheimer well 180 Packsaddle schists 21 Pancoast, A. C 9 Park Oil & Gas Co., well of ..180 Pearsall Road 93, 117 Pecten 43 Perrinot well > 183 Petroleum 121 Phillips, W. B. ...10, 108, 117 Phosphate 49 Phosphatic pebbles, analysis of 118 Physiography 14 Placenticeras sp 43 Pleasanton Road 92 Pleistocene 64 Porch, E. L. : 123 Porch well 185 Potash 49 Potassium 117 Potranca Road 94 Pre-Cretaceous 19 Pyrite, source of hydrogen sulphide 108 Radiolites 27 Rainfall 13 Recent 74 Red Lands 16, 25 Requienia 27 Ridder, A. J., well of . .22, 49, 139 Road materials 128 Sabre-toothed tiger 74 Saint Denis 7 Saint Hedwig Road 92 Saint Louis College, well at ..160 Salado Creek 32, 96 Salado Creek, section on .... 46 Salado River, springs of 105 Salado Waterworks, well at . . 160 San Antonio and Aransas Pass Ry., well of 161 San Antonio City Water Supply, well of 161, 162 San Antonio city well 162 San Antonio de Valero, mission of 7 San Antonio Lime Co 27, 120 San Antonio Portland Cement Co 108 well of 162 San Antonio River 76 springs of 105 San Antonio Sewer Pipe Works 112 San Antonio structure 84 San Pedro Park 40, 42, 105 Saunders Creek, exposures ... 58 Sauer, George, well of 163 Page Scaphites sp 43 Schists 19 Shattuck well 163 Shumard, Geo. C 10 Shiwneier, Henry, well of ....163 Smith, Sarah, well of ....55, 187 Somerset oil field 121, 124 Somerset Road 92 Southern Ice Co., well of 164 South Medina Oil field 125 Southwest Land Corporation well of 164 Source of hydrogen sulphide. .106 Springs 104 Star Clay Products Co 112 Stephenson, L. W. 9, 43, 45, i .56, 62, 188 Steubing, W. C., well of . . 187 Steve’s Irrigated Gardens, well at 164 Steve’s well . . . .* 165 Stratigraphic geology 19 Stream Terrace Plains 18 Structural geology 77 Sulphides, oxidation of 107 Sulphur water 105 Superior Oil Co., well of 165 Table of geologic formations.. 20 Tabulated data on wells 136 Tapetate 75 Taylor formation 44, 108, 112, 114 oil and gas from ....122, 124 water of 104 Taylor-Navarro Plain 17 Taylor, T. N 10, 105 Terrell, J. H., well of 167 Terrell Hot Wells 167 Tertiary, water of 104 Tezel, Louis, well of 168 Topography 12 Townsite well 168 Travis, W. B 8 Travis Peak formation 21 water of 100 Trinity 21 Turritella 112 Tylostoma 24 Udden, J. A. 9, 19, 22, 45, 49, 57, 110, 129 Underground water 97 Union Meat Co., well of 168 U. S. Geological Survey 9 Uvalde formation 65 Vaughan, T. W. ..21, 25, 28, 50, 69, 77 Venericardia 21, 25, 28 Villa de Bexar, mission of 7 202 University of Texas Bulletin Pago Vogt, Win., well of 168 Voight, A., well of 169 Volutilithes 112 Van Ormy 58 Walsch Oil Co., well of 196 Warm sulphur water ; .105 Waring Estate, well on 22, 38, 100, 169 Well records 129 Page Wells entering the Pre- Cretaceous formations 129 Wells terminating in the Comanchean formations ...135 in the Upper Cretaceous ...171 Wilcox formation .... 57, 112, 116 lignite of 118, 167 Wolfe and Elder, well of 197 / /?~) cJU^3> - /;3 *rs s T3J p C Pi ?trtU .Avondale Keller ^Hicks' Saginav Kdivp WO R TR }*’ORT\V()RTH V Tambieton ! Ken ire dale feWobb ELLIS GEOLOGICAL MAP OF TARRANT COUNTY GEOLOGY BY W. M. WINTON AND W. S. ADKINS TEXAS DRAWN BY H. T. WINTON DD Kagleford 1--*?* i Woodbine n*n LEGEND Main Street l>enton.Weno- Fort Worth Duck Creek 1 "g 1 Ml Goodland- Paluxy Comanche Peak- 1^1 SAXBT BO YTieflBVIMU ( i / ua ' UNIVERSITY OF TEXAS BUREAU OF ECONOMIC GEOLOGY AND- TECHNOLOGY J. A. UDDEN, DIRECTOR BULLETIN 1932. GEOLOGICAL MAP OF BEXAR COUNTY, TEXAS BY E. H. SELLAKDS ! S§ ILhl il S j, iff ! SS l| S II It l! 11