No. 3125: July 1, 1931 THE GEOLOGY OF GRAYSON COUNTY, TEXAS By FRED M. BULLARD Bureau of Economic Geology J. A. Udden, Director E. H. Sellards, Associate Director PUBLISHED BY THE UNIVERSITY OF TEXAS AUSTIN Publications of The University of Texas Publications Committees: GENERAL: • FREDERIC DUNCALF MRS. C. M. PERRY J. F. DOBIE C.H. SLOVER J. L. HENDERSON G. W. STUMBERG H.J. MULLER A. P. WINSTON OFFICIAL: E. J. MATHEWS KILLIS CAMPBELL C. F. ARROWOOD C. D. SIMMONS E. C. H. BANTEL BRYANT SMITH The University publishes bulletins four times a month, so numbered that the first two digits of the number show the year of issue and the last two the position in the yearly series. (For example, No. 3101 is the first bulletin of the year 1931.) These bulletins comprise the official publica­tions of the University, publications on humanistic and scientific subjects, and bulletins issued from time to time by various divisions of the University. The following bureaus and divisions distribute bulletins issued by them; communications concerning bulletins in these fields should be addressed to The University of Texas, Austin, Texas, care of the bureau or division isguing the bulletin: Bureau of Business Research, Bureau of Economic Geology, Bureau of Engineering Research, Interscholastic League Bureau, and Division of Extension. Communications concerning all other publications of the University should be addressed to University Publications, The University of Texas, Austin. Additional copies of this publication may be procured from the Bureau of Economic Geology, The University of Texas, Austin, Texas THE UNIVERSITY OF TEXAS PRESS ~ THE UNIVERSITY OF TEXAS BULLETIN No. 3125: Jal,. 1, 1931 THE GEOLOGY OF GRAYSON COUNTY, TEXAS By FRED M. BULLARD Bureau of Economic Geology ..J. A. Udden, Director E. H. Sellards, Associate Director PUBLISHED BY THB UNIVERSITY FOUR TIMBS A MONTH, AND ENTERED AS SECOND-CLASS MATTER A.TTHB POSTOFFICBAT AUSTIN, TEXA.S, UNDER THB ACT OF AUGUST 24, 1912 The benefits of education and of useful knowledge, generally diffuaed through a community, are eaaential to the preservation of a free govern­ment. Sam Houston Cultivated mind is the guardian genius of Democracy, and while guided and controlled by virtue, the noblest attribute of man. It is the only dictator that freemen acknowledge, and the only security which freemen desire. Mirabeau B. Lamar CONTENTS Page Introdue------­---­---------­-----------­---­--­---­----------------------­- 0 1 8 0 TotaL__ _______ _________ _ __ _ __ ________ _____________ _ ___________ _ _________ 6 2 Trinity Sand: Gray, white, and blue pack sands, containing many mar­casite nodules. Section of Goodland Limestone and Walnut Shaly Member in Creek About Five Hundred Feet West of Jackson's Elberta Peach Farm, Two Miles West of Preston, Grayson County, Texas Goodland Limestone Ft. In. Hard massive white limestone which scales off in thin plates at right angles to the bedding plane on weath­ering -----------------------------------------------------------------------------15 0 Walnut Shaly Member Mottled blue and yellow sandy shale, with a thin layer of fine loose sand of half-inch thickness at the top______ 0 6 Soft yellow ferruginous pack sand occurring in layers two inches in thickness and separated by thin partings of clay__________ _____ __ _ ___________________ ________________ 1 0 Blue clay which locally contains indurated lenses car­rying abundant fossils_______ __ _ _______ _______________________ 1 6 Water level of creek. The thickness of the Goodland limestone is fairly con­stant throughout Grayson County, but is rather variable over larger areas. In Cooke County the average thickness of the Goodland is about 25 feet along the northern border, but it gradually thickens to the southward. Along the southern border of Cooke County it has a thickness in excess of 30 feet and contains several clay horizons near the top. The Goodland limestone is regarded as the time equivalent of the Walnut clay, the Comanche Peak and Edwards limestone of Central Texas, which have a thick­ness of 300 feet or more at Austin. The Goodland usually outcrops in a narrow, sinuous band, frequently forming the cap rock of a bluff overlooking an expanse of Trinity sand. In Grayson County the Goodland is found in the Preston Bend area and in the extreme north­western corner of the county near Orlena. Attention is called to the small inlier of Goodland on Shawnee Creek, just below the city reservoir, northwest of Denison. This outcrop represents approximately the crest of the Preston anticline. WASHITA GROUP Overlying the Fredericksburg with apparent conformity is the Washita, the highest group of the Comanche series. The term Washita was applied to this group by Hill28 from the old Fort Washita, Bryan County, Oklahoma, which has become famous in the history of Cretaceous stratigraphy through the observations made there by Marcou and Shumard. The Washita group is composed of marine shaly clays, marls, and subordinate limestones, having a total thickness of approximately 400 feet in Northern Texas. Toward the top there is a sandy formation, the Pawpaw, which is the only marked exception to the non-sandy character of this division. The limestones, although subordinate to the clays in thickness, form several definite horizons that con­tain characteristic fossils and are readily traceable through­out the area, and for this reason are of the utmost impor­tance in determining the stratigraphic sequence and structure of the region. The Washita group has been subdivided by Hill24 and also by Taff.25 The classification used in this report is essen­tially that given by Hill, except that several of the appar­ently unnecessary group terms have been omitted and the members under these groups described as formations. The Washita represents the beginning of the withdrawal of the Comanchean sea which reached its maximum expanse either during the preceding epoch or at the beginning of Washita time. This shallowing of the sea during Washita time is recorded in the increase of clay and shale toward 23Hill, R. T., Annotated check list of the Cretaceous invertebrate fossils of Texas; Geo!. Survey of Texas Bull. 4, 1889. "Hill, R. T., U. S. Geo!. Survey 21st Ann. Rept., pt. 7, pp. 240-292, 1901. 25Taff, J. A., U.S. Geo!. Survey Geo!. Atlas, Atoka folio (No. 79), 1902. the top of the group, and finally in the deposition of sand. The numerous sand layers throughout the Washita group bear evidence of shallow water deposition in the form of ripple marks and cross-bedding. Finally, at the end of Washita time, it is believed that the sea retreated entirely from the area, and a short erosional interval, indicated by a slight disconformity, intervened between the Comanche series and the Gulf series. The following subdivisions of the Washita group have been mapped in Grayson County: Grayson marl Main Street limestone Pawpawsand Weno clay Denton clay Fort Worth limestone Duck Creek formation Kiamichi clay KIAMICHI CLAY The Kiamichi clay was named for the Kiamichi River of Southeastern Oklahoma. It was in the valley of this river that Dr. Pitcher collected the now famous Gryphea pitcheri of Morton in 1827, the first fossil of the Comanche series to be described. The Kiamichi clay, which includes all the sediments between the Goodland limestone and the Duck Creek formation, is easily recognized due to its position between two relatively hard, resistant, limestone forma­tions. It is composed of about thirty-five feet of dark yellow to olive-green to black shaly clay with thin platy lenses of a yellow siliceous limestone in the basal portion; at the top the formation is marked by two or three ledges of a hard yellowish shell breccia made up of Gryphea navia Hall and Gryphe·a corrugata Say. This Gryphea conglomerate is always present at the top of the Kiamichi, the individual beds ranging from a few inches up to three feet in thick­ness. It is confined entirely to this one horizon and is probably the most characteristic horizon in the entire Comanche series. The erosion of the soft clay underlying the hard oyster-shell breccia (Gryphea conglomerate) causes it to slump and break off in large slabs which fre­quently cover the outcrop of the Kiamichi clay. Some of the slabs may finally come to rest standing on edge or making various angles from horizontal to vertical. They are commonly referred to as "edge rock" by the layman. The contact between the Goodland limestone and the Kiamichi clay is usually marked by a rather persistent bench or terrace, due to the erosion of the soft clay over­lying the hard limestone. The contact between these two formations is not a gradation, but rather a sharp break from the pure limestone to the typical greenish-brown clay of the Kiamichi. Usually a few inches of a thinly laminated, brown, siliceous limestone occurs at the base of the Kia­michi, representing the transition from the Goodland lime­stone to the Kiamichi clay. It has been suggested that there is an unconformity between these two formations. The writer did not find any evidence to support this sug­gestion except the fact that a very sudden change occurs in the type of sediments. The Kiamichi usually outcrops on the slopes above the Goodland escarpment or on the sides of hills capped by the lower Duck Creek limestone. Since the Kiamichi lies between two relatively hard escarpment-forming lime­stones, its outcrop is narrow and tortuous. Its occurrence in Grayson County is about the same as the Goodland lime­stone, being limited to the northwestern portion of the county along the Red River. The following section is typical of the formation: Se --------------------------------------------20 Clay, greenish-gray calcareous from which weather nu­merous specimens of Plicatula cf., P. incongrua Conrad, and small rusty ammonites, probably young of Pachy­discus and Schloenbachia, also a few specimens of Gryphea washitaensis Hill_____________ _ ______ __ _ ______ ______ _____ __ 15 Limestone, ledges with interbedded layers of gray shaly clay, poorly exposed; the limestone, especially one layer near top, contains numerous keeled and non-keeled am­monites, many of which are of large size (maximum 2 feet in diameter) --------------------------------------------------------------------20 Limestone and gray shaly clay, in alternate beds, ammonite bearing, well exposed in bluff along creek_______________ ____________ 20 Kiamichi Clay Total____ ____________________________________ ___________ __ _ _____________________ 105 The lower part of the Duck Creek formation contains an abundance of well-preserved fossils. The large ammonite (Desmoceras brazoense Shumard) occurs at the top of the series of alternating limestone and shaly clay layers in the lower part of the Duck Creek formation. About thirty feet above the Gryphea breccia, at the top of the Kiamichi clay, there is a massive white limestone bed averaging two feet in thickness. This limestone ledge is a very persistent bed and one of the most prominent layers in the lower Duck Creek formation. In its unweathered appearance it resem­bles the Goodland limestone. The large ammonites, above referred to, occur in this limestone bed and in the shaly clay directly above and below it. They are limited to a vertical range of not more than eight or ten feet, and for this reason are valuable as a key bed in structural work. Below the "large ammonite" horizon there is an abundance of fossils, the most prominent of which are as follows: Inoceramus comancheanus Cragin, Hamites fremonti Mar­cou, Hem'iaster whitei Clark, Pervinquieria trinodosa (Bose). The upper part of the Duck Creek formation, composed principally of shaly clay, contains very few fossils. The Duck Creek outcrops in a belt along Red River, where it has been brought to the surface by the Preston anticlinal uplift. FORT WORTH FORMATION Overlying the Duck Creek formation is the Fort Worth limestone, named from the city of Fort Worth, Texas, where it is typically exposed along the streets. The Fort Worth limestone is readily separated into three members. The lower member consists of from 10 to 15 feet of yellowish­white limestone and grayish to blue shaly clay. The middle member is chiefly shale and also ranges from 10 to 15 feet in thickness. The upper member is predominately lime­stone, separated by thin layers of shaly clay. The limestone is a hard, cream-colored limestone, very similar to the more massive beds of the lower Duck Creek. The resemblance in lithologic character between the Duck Creek and Fort Worth makes it difficult to distinguish between the two for­mations except on the basis of the fossils. Each formation contains an abundance of easily recognized and charac­teristic fossils, and a few minutes' search is usually sufficient to establish the identity of the formation on the basis of the fossils. The most outstanding fossils used in identifying the Fort Worth are as follows: H olaster sim­plex Shumard, H emiaster elegans Shumard, Pervinquieria leonensis (Conrad), and a large oyster, Exogyra americana Marcou. The thickness of the Fort Worth averages between forty­five and fifty feet in Grayson County. Following is Hill's32 description of the Fort Worth at the type locality: The Fort Worth formation, as exposed in the railway cuts north of the Union Station at Fort Worth, and underlying all the business portion of that city, 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. "Hill, R. T., U. S. Geol. Survey 21st Ann. Rept., pt. 7, p. 259, 1901. 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. The gradation from hard marly lime bands to firm limestone is apparently sharp, but on close examination it is found to be very gradual so that well-defined lines cannot always be clearly drawn between them. Upon weathering in vertical bluffs the hard ledges become projecting shelves and the marls form recessions between them. Before exposure the rocks are dull blue, but when weathered they are glaring white, sometimes with a slightly yellowish tinge. Following is a typical section of the formation: Section of the Fort Worth Limestone on Branch of Duck Creek One Mile North of Denison, Texas. Base of Sec­tion Just Below Tank on Tobin's Stock Farm Denton Clay Fort Worth Limestone: Ft. In. Alternating layers of massive white limestone and thin beds of clay. The limestone layers are much thicker than those lower in the section, and contain iron stains. There are numerous fossils including Gryphea washitaensis Hill, Pervinquieria leonensis (Conrad), Holaster si1nplex Shumard, Hemiaster elegans Shu­mard, Exogyra americana Marcou, and some Spheno­discus-like forms. At the top there is a thin bed of fossiliferous marl which grades into the Denton.......... 19 0 Thick beds of clay shale with thin alternating beds of impure limestone containing the following fossils: Pervinquieria leonensis (Conrad), Holaster simplex Shumard, Gryphea washitaensis Hill, and Pecten sp. 19 O White limestone containing Pervinquieria sp. and Hemi­aster sp. ----------------------------------------------------------------------0 6 Light gray shaly clay containing iron stains; also some small specimens of Gryphea washitaensis Hill.____________ 3 9 Impure yellowish limestone containing fucoids._______________ 1 O Clay shale, blue·----·-------------·--------------------------------------------------2 6 Light blue shaly limestone___________ ______________________________________ O 5 Blue clay shale·--·---------------·--------·-----------------·-·--------------------1 2 Impure chalky limestone_ _____________________________ ____________________ O 9 Blue clay shale·--------------------·---------·---·---------------------------------O 10 Hard blue impure limestone containing traces of fer­ ruginous material which gives the ledge a rusty color. The bed contains many large fucoids on its under surface --------------------------------------------------------1 O Fort Worth Limestone: Ft. In. Blue clay shale with several thin ferruginous bands; contains several specimens of a small Gryphea washi­taensis Hill______________________________________________________________ __________ 1 4 White, impure, chalky limestone, slightly arenaceous______ 1 2 Duck Creek Formation Total______________________________________________________________________ ____________ 52 5 The top of the Fort Worth is usually characterized by a marked abundance of Gryphea washitaensis Hill. This is the lowest horizon where this particular Gryphea has been noted in abundance, although it ranges throughout the Washita division. Exogyra americana Marcou is easily identified due to its size and is a valuable marker for the top of the Fort Worth. The two echinoids, Holaster sim­plex Shumard and Hemiaster elegans Shumard, begin in the upper part of the Duck Creek, but their zone of abun­ dance is in the Fort Worth, usually near the middle of the formation. The Fort Worth limestone, like the other Comanchean formations, outcrops in northern Grayson County in a belt .along Red River, on the south flank of the Preston anticline. DENISON FORMATION The Fort Worth limestone passes upward into a group of sediments of various aspects laid down in shallower water .and characterized by certain well marked paleontologic zones. They are for the most part near shore, littoral deposits, some of which have no traceable representative farther south than North-Central Texas, and arenaceous .and argillaceous formations in Grayson County grade into marls and limestones in Central Texas. The effect of this gradation may be seen by comparing the thickness of the Washita division in Grayson County and Central Texas. In Northern Texas the Washita division, as previously stated, is composed chiefly of shaly clays, marls, and subordinate amounts of thin limestones, with an average thickness of about 400 feet, while in the vicinity of Austin, Texas, it is represented by three formations, the Georgetown limestone, the Del Rio clay, and the Buda limestone, having a total combined thickness of approximately 160 feet.ss Hill's description of the beds which make up the Denison formation in the Denison area, which he states may be con­sidered the type locality for North Texas and Indian Ter­ritory, is as follows :84 In this region it consists of laminated ferruginous clays, sandy clays, impure limestones (littoral breccias), and sand. These beds are all characterized by the strong ferruginous colors peculiar to near shore deposits, which appear only faintly, if at all, in the lower lying Comanche series, or the extension of the Denison beds south of the Brazos, while the white chalky element is entirely absent. In the Denison section the Denison beds consist of about 300 feet of ferruginous dark-colored clays and sands, free from the lighter-colored calcareous (chalky) element of the underlying beds, with occasional conspicuous indurated layers of impure limestone, ferruginous sandstone, iron ore, and clays, which lie between the top of the Fort Worth limestone and the Grayson marl. Hill applied the term Denison beds to a portion of this series and then divided it into a number of members. In this regard he says :85 In a general manner the Denison beds may be subdivided into three conspicuous subgroups; the lower, middle, and upper. The lower subgroup of the Denison beds, including all that por­tion below the top of the 0. carinata horizon, will be generally alluded to as the Denton beds. The medial or Weno subgroup of the Denison beds, including all that portion above the 0. carinata horizon and beneath the Main Street limestone, for convenience may be divided into the Weno and Pawpaw formations. For the upper subgroup con­sisting of the Main Street limestone and Grayson marl, the term Pottsboro may be used. Stephenson36 in his work accepted Hill's subdivision of the beds, but simplified his nomenclature somewhat by dis­ 13Hill, R. T., and Vaughan, T. W., U. S. Geol. Survey Geo!. Atlas, Austin folio (No. 76), 1902. 84Hill, R. T., U. S. Geol. Survey Twenty-first Ann. Rept., pt. 7, p. 266, 1901. "Hill, R. T., Idem., p. HT. •Stephenson, L. W., U. S. Geo!. Survey Prof. Paper 120, 1918. carding all the subgroup names, calling the whole series the Denison formation, with the following members: Grayson marl member Main Street limestone member Pawpaw sandy member W eno clay member Denton clay member Taff37 grouped all the beds in Southern Oklahoma lying below the Main Street limestone (which he called Benning­ton) and above the Fort Worth limestone under the name Bokchito formation. In recent reports38 the Bokchito has been separated into the three subdivisions recognized in Texas; namely, the Denton, Weno, and Pawpaw members, respectively. The Main Street and Grayson are described as separate formations. In order to further simplify the already complicated nomenclature of these beds, all unneces­sary terms have been dropped and the following formations described: Grayson marl Main Street limestone Pawpawsand Weno clay Denton clay While it is recognized that these beds have a certain unity or similarity both in lithologic and paleontologic char­acteristics, it is believed that the dropping of all unessential terms is justified. DENTON CLAY The Denton clay immediately overlies the Fort Worth limestone. In Grayson County the Denton consists of from thirty to forty feet of brownish-yellow clay with numerous sandstone beds and lenses ranging throughout the forma­tion. The top of the Denton is marked by a brownish­yellow arenaceous shell limestone, made up frequently of countless numbers of Gryphea washitaensis Hill and Ostrea, 31Tatf, J. A .. U.S. Geo!. Survey Geo!. Atlas, Atoka folio (No. 79), 1902; Tisho­mingo folio (No. 98), 1903. 18Bullard. Fred M., Geology of Marshall County, Oklahoma: Oklahoma Geo!. Survey Bull. 39, 1926. carinata Lamarck. This zone rarely exceeds one or two feet in thickness. Hill39 makes the following statement in regard to the Denton: The lower part of the Denton subgroup consists of beds of blue marly clays, terminating above by conspicuous indurations of oyster breccia made up largely of Gryphea washitaensis accom­panied by Ostrea carinata. The lower five to ten feet of the Denton is decidedly a calcareous clay. The first horizon that stands out promi­nently in the Denton is a sandstone bed, ranging from one to two feet in thickness. This sandstone is thinly lami­nated, a yellowish-brown on weathered surfaces, and frequently contains well preserved "ripple marks." This ripple-marked sandstone lies, as a rule, near the middle of the Denton, varying from twenty to thirty feet above the base. However, the Denton is somewhat variable, and fre­quently the sandstone is much nearer the top than the middle of the formation. This sandstone is usually the only indurated layer in the Denton, and for this reason is very useful in mapping, since it is very easy to locate, as large slabs frequently cover the slope of a small escarpment or bench which it forms. The top of the Denton, as previ­ously stated, is marked by an impure, fossiliferous limestone, the Ostrea cari1'1Jl,ta horizon of Hill. Section of the Denton Clay on the Riverside Park Road About Two Miles Northeast of Denison, Grayson County, Texas Denton Clay : Ft. In. Shell breccia ---------------------------------------··-----------------------------------5 5 Thinly laminated, brown sandstone.___________________________________ O 9 Brown claY---------------··--------··-------------------------------------------------------25 O Total_ ______________________________________________________________________________________ 31 2 390p. Cit. , p. 268. Section of the Denton-Weno Contact in Cut of St. Louis and San Francisco Railroad, Just West of the River­ side Park Road, About One and One-Half Miles Northeast of Denison, at the 633.1+ Mile Post Ft. In. (a) Denton-Weno contact: alternating layers of breccia and brown clay marl. Contains Gryphea washi­ taensis Hill, Ostrea, carinata Lamarck, and Leioci­ daris plates and spines_ ______________________ ________________ ______ 3 8 (b) Hard, brown sandstone occurs approximately three feet below base of shell breccia. A thin clay parting occurs in the middle of the sandstone bed -------------------0 10 (c) Dark bituminous stratum, 8 inches below sandstone, which alternates with a yellow, ferruginous shale. Many small shells were observed throughout the dark-colored clay_____________________________ _ _________ _ _______________ 1 13 The thickness of the Denton is quite variable. In Cooke County the average thickness is approximately sixty feet, while in Grayson County it ranges under forty feet. How­ever, the nature of the material indicates deposition in a shallow, littoral zone, which would be favorable to marked variations of thickness in short distances. For comparison, a section of the Denton clay in Cooke County, Texas, is here given: Section of the Denton Clay on Hampton Hollow About Two Miles Down Stream From the Toll Bridge on Red River, North of Gainesville, Cooke County, Texas Denton Clay: Ft. In. Yellowish-brown clay marl with scattered individuals of Gryphea washitaensis Hill ___ _________ ________ _______________________ 35 4 Yellowish-brown, thinly laminated, ripple marked sand­stone --------------------------------------------------------------------------------------1 6 Brown to yellow marly clay with a few iron nodules______ 30 2 TotaL____ _________________ _________________________________________________ _______ 67 0 It is notable that practically all the variations in thick­ness of the Denton occur above the sandstone bed, as its position with respect to the Fort Worth limestone is fairly constant over the entire region. Excellent exposures of the Denton may be seen in Munson Park, one mile north of Denison, and, as above stated, along the road to Riverside Park, northeast of Denison. WENO CLAY The Denton clay is overlain by a dark gray to yellow shaly clay with subordinate thin partings, lenses, and layers of fine gray to yellow sand, some of which are indurated and form ledges of sandstone. To this material Hill gave the name W eno, from the small village of W eno, on Red River five miles northeast of Denison. The postoffice of W eno has been abandoned for many years and does not appear on recent maps. Following is Hill's40 description of this formation: This subgroup attains its maximum development in the Deni­son section, where it includes all the beds between the top of the G. waskitaensis agglomerate and the top of the Quarry limestone. It is well developed in the Red River region, where its several beds are important stratigraphic units, but these lose individ­ uality southward across the State. The Weno formation is characterized by a littoral fauna of many small species occurring in great quantities in certain hori­zons, notably 0. quadriplicata and certain ammonitic forms of the Engonoceras type, which are now being studied by paleon­tologists. Character of beds at Denison.-In the Denison section these beds embrace several well-defined members consisting of very ferruginous brownish marls, with occasional presistent harder beds, such as large lens-shaped segregations, beds of ferruginous sandstone, impure limestone, etc., all of which are locally per­sistent and some very conspicuous. The indurated beds of the Denison section are interesting. One of these indurated layers, 80 feet below the summit, is especially noticeable, in as much as it consists of large lenticular indurations of a clay ironstone which are thinly laminated and break into sheets along the line of lami­nae. These concretions are blue interiorly and brown exteriorly, and are often 4 or 5 feet in diameter. About 22 feet below the in­durations, or 104 feet below the Quarry limestone, there is another indurated bed consisting of sandstone, as exposed near the ceme­tery gate north of Denison. Below this, extending down to the '°Op. Cit.• p . 274. 0. carinata beds, there are brown clay marls to a depth of about 22 feet. In the Denison section the strata of the Weno subgroup are clearly defined and easily recognizable. Southward toward Fort Worth they lose their individuality, after the disappearance of the Quarry limestone in Denton County, which to the north­ward separates the Weno from the Pawpaw formation. . . . Fur­thermore, the limestone element increases proportionately until the lithologic character so changes that along the banks of the Trinity the beds somewhat resemble the underlying Fort Worth beds. The Weno is very similar to the Denton in lithologic char­acter, the principal differences being that the Weno contains more thin, soft sandy layers and also contains many clay ironstone concretions. The thickness of the Weno is somewhat variable, although it is fairly constant for Grayson County. The average thickness in Grayson County is from 85 to 95 feet. To the west of Grayson County, in Cooke County, the Weno is usually about 100 feet in thickness. To the north of Gray­.son County, in Marshall County, Oklahoma, sections of the Weno have been measured which total 135 feet. A marked variation in the thickness of the Weno is noted on opposite sides of the Preston anticline, the thicker sections being on the north side of the anticline, or the shoreward side. No clear explanation of this fact is offered, but it is thought that underlying the Preston anticline is a pre-Cretaceous ridge, which probably influenced sedimentation in this area. A more detailed discussion of this phase of the subject will be found under the heading of "Structure." Section of the Weno Clay One Mile North of the City of Denison. Base of Section in Bed of Ditch One-third Mile N. 12° E. of City Stand Pipe. Section Measured Approximately N. 70° E. W eno Clay: Ft. In. 12. Loose yellowish-brown arenaceous clay...................... 7 0 11. Clay ironstone bed filled with Turritella sp., numer­ous gastropods, pelecypods, and other fossils........ 0 4 10. Yellowish-brown arenaceous clay containing iron concretions. Layer of soft yellow sand 7 feet from base.................. ------------··········-·······-···-···········-9 5 Weno Clay: Ft. In. 9. Fine, soft, yellow sandstone________ _ _______________________________ 0 8 8. Series of soft yellow sandstone ledges, 1 to 2 inches in thickness, containing iron concretions, sepa­rated by yellowish-brown clay 1 to 4 inches in thickness ---------------------------------------------------------------------15 8 7. Thinly laminated soft yellowish-brown sandstone____ 0 8 6. Argillaceous sand, cream-colored with slight yel­ lowish tinge filled with clay ironstone concre­tions. Also contains some selenite_ _____________ _________ 16 8 5. Yellowish-brown compact sandstone, apparently concretionary, 4 inches in thickness, and a layer of clay, ironstone, and sandstone concretions interstratified with yellowish-brown arenaceous clay --------------------------------------------------------------------------------1 2 4. Blue clay, lenticular________________________________ _ ____________________ 6 0 3. Covered by stream fill_______________________________ __________________ 10 2 2. Fine yellowish-brown arenaceous clay with bed of Ostrea quadriplicata Shumard two feet above top of underlying shell breccia. Lenses of blue clay 10 inches above 0. quadriplicata horizon fol­lowed by one foot of yellowish-brown clay____________ 5 1 1. Shell breccia composed of Gryphea washitaensis Hill and Ostrea carinata Lamarck cemented in an argillaceous limestone__ ______________________ ___________ ____ 2 11 Total measured thickness __________ ________ ___________________ _ 75 9 Correction for measuring down a dip of 1° 30' for a distance of 760 feet from base of section to station four ------------------------------------------------------------------17 3 Total thickness__ _______________________________ ________________________ 93 feet The above section stops at the base of the "Quarry limestone," remnants of which may be seen on top of the hill. Section of the Weno C"lay on Armstrong Avenue Road One­ half Mile North of Stand Pipe, Denison, Grayson County, Texas Weno Clay: Ft. In. Light yellow clay alternating with thin layers of fer­ ruginous sandstone___________________________________________________________ _ 24 9 Light chocolate-colored pack sand________________ _ _________________ O 10 Clay, dark brown________ _______________ _ ________ __ _______________________ O 7 Weno Clay: Ft. In. Light, chocolate-colored pack sand, containing large sand concretions, which are thinly laminated and break in large round slabs, resembling table tops______ 8 9 Pack sand, light brown, ferruginous, cross bedded__________ 0 10 Light brown clay containing calcareous nodules and thin layers of ferruginous sand in the clay______________ __ _ 3 8 Red, sandy, ferruginous clay________________________________________________ 14 7 Chocolate-brown clay containing calcareous concretions 6 4 Hard, yellow, slightly calcareous clay containg clay ironstone concretions______________________ ___________________________________ 0 10 Arenaceous clay with fucoid-like calcareous concre­tions --------------------------------------------------------------------------------------1 0 Alternating layers of thin brown shale and shell breccia composed principally of Gryphea washitaensis Hill and Ostrea carinata Lamarck_________________________________________ 5 2 TotaL------------------------------------------------------------------------------------67 4 A good section of the Weno clay is exposed about one mile northeast of the city of Denison, just north of the Denison­Carpenters' Bluff Road. The thickness of the Weno, meas­ured at this point, is ninety-five feet. The Weno can usually be recognized by the large amount of clay ironstone concretions which it contains. This will ordinarily help to distinguish it from the Denton. The top of the Weno is marked by the so-called "Quarry limestone." The name limestone is somewhat of a misnomer, for the typical Quarry is more of a sandstone than a limestone. The bed was called Quarry by Hill because it was commonly quarried for local use as a building stone. The type area of the Quarry is about a mile east of Denison, where rather extensive local quarries were formerly operated. Hill's41 description of the "Quarry limestone" is as follows: Quarry lim.estone.-This is a persistent band of siliceous lime­stone, which is notable in the series of otherwise unconsolidated beds and is the chief building stone in the country underlain by the Denison beds. Its interior portion is steel-blue in color, but it is oxidized for a depth of 2 or 3 inches from the surface into a chrome yellow. Its thickness at Denison is about 1.7 feet. This is an especially conspicuous formation within the relatively lim­ited area of its occurrence, although at no place over 2 or 3 feet 41Qp. Cit., p. 275. in thickness. It is very arenaceous and might as well be con­sidered a sandstone as a limestone. It is accompanied above by great quantities of the peculiar Ostrea quadriplicata. Much confusion has resulted as to the thickness of the Weno, due to the fact that in the lower portion of the Pawpaw there are several beds which resemble the Quarry, and it is sometimes very difficult to be sure the bed in ques­tion is the Quarry and not one of the other horizons. At Carpenters' Bluff, on the eastern edge of Grayson County, good exposures of the Quarry may be seen near the water's edge. Fossil pelecypods and gastropods in a good state of pres­ervation are numerous in the ferruginous lenses and con­cretions in the upper part of the Weno. Stephenson42 noted the following: Nucula sp., Ostrea quadriplicata Shumard, Protocardia texana (Conrad), Cyprimeria sp., Corbula (three species), Cymbophora sp., Turritella sp., Anchura, mudgeana White, Engonoceras serpentinum (Cragin). A point which seems worthy of note is that the ferru­ginous layers in the upper Weno are to a very large extent made up of Turritella sp., while similar beds in the Pawpaw are composed principally of small pelecypods. The Weno clay weathers very readily and as a rule is poorly exposed on the upland and valley slopes. For this reason sections which will permit of detailed study are exceedingly rare. The W eno is best exposed in the area to the north and east of Denison, but is present, like the other formations, in a narrow belt bordering Red River across the entire north side of Grayson County. PAWPAW SAND The Weno clay is overlain by about fifty feet of irregu­larly bedded sandy clays and sands extending from the Quarry limestone at the base to the Main Street limestone at the top. The Pawpaw is here restricted to those sedi­ments lying between the two limestones above named. Stephenson included the Quarry limestone with the Paw­ "'U. S. Geo!. Survey Prof. Paper 120, 1918. paw, but in this paper Hill's original usage-that is, con­sidering the Quarry as the top of the Weno-is followed. Following is Hill's description of these beds in the Deni­son area :is Pa,wpaw beds.-These include the strata between the "Quarry" and the Main Street limestones. In the Denison section these are very impure laminated sandy clays and sands, dark blue and bituminous in places, oxidizing surficially into brown ferruginous colors, very much like the Woodbine (Dakota) formation. They are very sandy in the upper 5 feet at the crossing of Pawpaw Creek and the Texas Central Railway. This aspect is local, however. There are also small fragments of lignite in the sands and the character of the sediments appears to be favorable to the preservation of leaf impressions, but careful search up to date has failed to discover these. The Pawpaw is the most impure of all the Denison beds, and was apparently laid down near the shore, being accompanied by beds of ferruginous sand, which are not elsewhere found in the Washita division. The total thickness at Denison is 45 feet. At the base of the Pawpaw, just above the Quarry limestone, are lead-colored clay shales with sandy alternations containing innumerable well-preserved nacreous shells, which in some places are replaced by pseudomorphs of iron ore. One band, just above the Quarry limestone, consists of one foot or more of impure, friable ferruginous material, containing beautifully preserved fossils. These fossils are especially abundant in the lower 12 feet and consist of littoral Mollusca of many species. In certain clay layers the nacreous shells are preserved with all their pearly luster. In sandy layers where ferruginous per­colation has taken place the shell substance is dissolved and they are preserved as casts and moulds in an arenaceous matrix of limonitic ironstone. While the Pawpaw is called a sand, it should be noted that it contains, especially in the lower part, many clay beds which may be easily confused with the Weno. The upper part of the Pawpaw is usually dominantly sand, highly f erruginous, and cross-bedded. The iron usually occurs as a thin sheet between the bedding planes, or filling fissures which cut the sand at every angle. This portion of the Pawpaw is very similar to the Woodbine, with which it is frequently confused . ..U. S. Geo!. Survey, 21st Ann. Rept., pt. 7, p. 276, 1901. Section of the Pawpaw Sand on Pawpaw Creek in the East­ ern Edge of the City of Denison, Between the Bridge on East Main Street and the Outcrop of Main Street Limestone to the South Main Street Limestone : Ft. In. Pawpaw Sand: Covered by soil and fragments of Main Street limestone 21 0 Light yellowish-br-0wn pack sand________________________________________ 24 0 Alternating layers of blue shale and pack sand in beds varying from 6 to 18 inches______________________________________________ 2 10 Blue shale containing a thin layer of ferruginous lime­stone about 2 inches thick 8 feet from base_________________ 13 2 Total______________________________________ __________________________________________________ 61 0 The above section may be in excess of the actual thick­ness of the Pawpaw, as the upper contact, the Main Street­Pawpaw contact, is not clear cut and could not be definitely located, due to debris which covered the outcrop. The following section gives in detail the upper portion of the Pawpaw sand: Section of Pawpaw Sand (in part) on the Bank of Little Mineral Creek About 500 Feet South of the Bridge on the Locust Road, One Mile South of Fink, Grayson County, Texas Ft. In. Main Street Limestone (detailed section on page 44) _______ 13 9 Pawpaw Sand: Blue to brown, loose, argillaceous sand containing iron n-0dules ------------------------------------------------------------------------------3 O Coarse brown sandstone, highly colored by iron____________ O 6 Light blue pack sand__________________________________________________________ 1 O Coarse, brown sandstone highly colored by iron____ _________ O 8 Massive, gray to yellow sandstone which breaks off in large blocks on weathering______________________________________________ 1 4 Alternating beds of fine yellow sand and blue shale________ 0 8 Massive, gray to yellow sandstone which breaks off in large blocks on weathering. Contained in this bed are two thin layers of reddish-brown ironstone__ _______________ 2 10 Brown sandy shale containing an abundance of small fossils ------------------------------------------------------------------------------------O 4 Blue shale stained on surface to brown by iron________________ 1 10 Level of water in creek Total --------------------------------------------------------------------------------25 11 The upper part of the Pawpaw is highly ferruginous and also very cross-bedded. A good example of the cross­bedding may be seen near the subway south of the Missouri, Kansas, and Texas Railway Station at Denison, Texas. At this outcrop the Main Street forms the top of the cut and, underneath, the thinly laminated sands and clay of the upper Pawpaw make high angles with the true bedding planes. The ferruginous layers in the Pawpaw frequently con­tain well preserved fossils similar to those found in the Weno. Stephenson44 lists the following fossils from the thin lenses of ferruginous, oxidized, soft sandstone: Nucula sp., Protocardia texana (Conrad), Cymbophora sp., Cor­bula sp., Anchura mudgeana White, and Engonoceras SP pentium (Cragin). It will be noted that the above list is practically identical with the one given for the Weno, except that Turritellas are absent. The Pawpaw is more likely to be confused with the Woodbine than any of the other formations of the Cre­taceous. It is very similar to the Woodbine, both in type of topography produced and in the soil and vegetation that it supports. Excellent exposures of the Pawpaw are found at many places in Grayson County. The Pawpaw outcrops in the northern part of the city of Denison, and it is also well exposed along Pawpaw Creek in the eastern part of the city. In general it forms a belt extending along the north­ern boundary of Grayson County, adjacent to Red River. MAIN STREET LIMESTONE The Main Street limestone, so named by Hill because it outcrops on the main street of the city of Denison, Texas, immediately overlies the Pawpaw sand. It consists of from ten to twenty feet of massive, hard, brown, semi-crystalline limestone, with thin subordinate layers of calcareous clay or marl. As a rule the limestone beds are more massive near the base and become thinner toward the top, with the marly layers becoming more prominent. The Main Street "Op. Cit., p. 143. is the only limestone of any consequence in a thick series of clay and sand, and for this reason is a very important marker for stratigraphic and structural work. It differs from the other limestones of the Washita division in that it contains more ferruginous material which gives it a dis­tinctly brownish color. Taff45 applied the name Bennington to this limestone in Southern Oklahoma. Following is Hill's46 description of the Main Street lime­stone in the Denison area : Main Street limestone.-In the Red River section the Main Street limestone constitutes a very conspicuous formation, not only on account of the hardness of the strata, but because of its effect as a topographic factor. It consists of a coarsely crystal­line, bedded, brecciated, white limestone, which, on oxidation, turns a deep yellow, showing much more ferruginous coloring than any of the other limestones of the Comanche series. It occurs in strata of various thicknesses. Usually there are more massive beds at the base and thinner strata at the top, with occa­sional sandy marl layers. The formation nowhere aggregates more than 25 feet. Taff notes a thickness of 23 feet at Rock Creek, Grayson County. At Denison 15 feet have been noted. The Main Street is characterized by two easily recognized fossils, Exogyra arietina Roemer, which occurs throughout the formation but is more abundant in the upper part, and Kingena wacoensis Roemer, the only brachiopod of common occurrence in the Comanche series, which is found more abundantly in the lower portion. The following sections give in detail the character of this formation: Section of Main Street Limestone on Rock Creek North­ ' western Grayson County, Texas (from Hill) 47 Grayson Marl: Ft. In. Marl light yellow with bands of limestone and great numbers of Gryphea mucronata Gabb, the upper por­tion concealed_____ ________________________________________________________ 15 O :u. S. Geo!. Survey Geo!. Atlas, Atoka folio (No. 79) , 1902. "UU. S. Geo!. Survey, 21st Ann. Rept., pt. 7, p. 280, 1901. · S. Geo!. Survey 21st Ann. Rept., pt. 7, p. 281, 1901. Main Street Limestone: Ft. In. Limestone, beginning at the base with compact yellow shell and grading upward into friable marl. Kingena wacoensis occurs in the upper portion, while Exogyra arietina ranges throughout__________________________ __ __________ _ _____ 18 0 Arenaceous shell limestone, with Ostrea quadriplicata and 0. subovata at the base, and Exogyra arietina and Kingena wacoensis succeeding_ ____ __________________________ 5 0 38 feet Section of Main Street Limestone in Railroad Cut on Potts­ boro Cut-Off of Missouri, Kansas, and Texas Rail­ road, About Four Miles West of Denison, Grayson County, Texas Woodbine Sand Grayson Marl Main Street Limestone: Ft. In. Marl, containing nodules of lime________________________________________ 2 9 Limestone, somewhat arenaceous, containing many fos­sils, including Exogyra arietina Roemer, Exogyra plexa Cragin, Kingena wacoensis Roemer_____________________ 0 8 Marl, containing Kingena wacoensis Roemer___________________ 0 7 Limestone, turns yellow on exposure, contains Kingena wacoensis Roemer---------------------------------------------------------------1 6 Marl, yellowish-white, containing Kingena wacoensis Roemer, Exogyra plexa Cragin_____________________ _______________ __ 0 3 Limestone, ferruginous, arenaceous, white, coarse grained, turns yellow on weathered surface. Con­ tains : Exogyra plexa Cragin, Exogyra arietina Roe- mer, Ostrea quadriplic.ata Shumard, and Pecten sp._ 0 9 Marl, containing fossils similar to limestone above________ 0 2 Limestone, similar to above______________________________________________ __ 0 8 Marl, sandy, ferruginous, contains Exogyra plexa Cragin ---------------------------------------------------------------------------------1 0 Limestone, ferruginous, coarse grained, white, yellow on weathered surface. Contains: Kingena wacoensis Roemer, Exogyra arietina Roemer, Exogyra plexa Cragin ----------------------------------------------------------------------------------1 4 Marl, containing Exogyra plexa Cragin and Exogyra arietina Roemer··------------------------------------------------------------------0 6 Limestone, impure bluish semi-crystalline, containing irregular veins of calcite___________________________________________ _____ 1 1 Pawpaw Sand Total·--------------------------------------------------------------------------------------11 3 Section of Main Street Limestone and Grayson Marl at Bridge on Choctaw Creek, Near Denison, on Denison and Bonham Road (by Hill) 48 Grayson Marl: Ft. Yellow marl and limestone in alternating strata, con­ taining Turrilites brazoensis (?) , Gryphea mucro­ nata, 0. subovata, Cyprimeria sp. ( ?) , echinoids, Cardium hillanum, Ostrea sp. ( ?) , and Nautilus sp. (?) ---------------------------------------------------------------------------------5 Main Street Limestone: Limestone with Exogyra arietina, which grades up­ward into white limestone and marL______________________________ 12 Limestone with Terebratula wacoensis________________________________ 4 or 5 Pawpaw Beds Section of the Main Street on Little Mineral Creek, 500 Feet South of the Bridge on the Locust Road, One Mile South of Fink, Grayson County, Texas Main Street Limestone: Ft. In. Alternating beds of hard, massive, yellowish limestone, 4 to 6 inches thick, and brownish shaly limestone, 3 to 8 inches thick, containing E. ametina and E. plexa and Pectens --------------------··--····-·--··--··-···-4 5 Hard, blue, slightly argillaceous limestone approach­ing a shell breccia and containing E. arietina and E. plexa ·-------------------------------------------------------------------------1 6 Massive, yellow limestone containing an abundance of K. wacoensis___________________________________ ____________________________ __________ 2 2 Limestone, yellow, argillaceous, containing fucoids, K. wacoensis, E. plexa, E. arietina, and Pee.tens_______ _ ____ 0 6 Limestone, blue, massive.__________ ___________________________________________ 0 8 Limestone, bluish-brown, argillaceous, containing E. arietina, E. plexa, O. quadriplicata._______________________________ 0 3 Alternating beds of laminated yellow limy shale and yellow limestone, containing E. plexa, E. arietina, O. quadriplicata·-----------------------------------------------------------------1 10 Limestone, highly fossiliferous, approaching a shell breccia, containing fossils similar to ones listed above, poorly preserved_________________________________________ ________________________ 0 9 Marl, soft, bluish-yellow, fossiliferous______ _______________________ O 5 Limestone, massive, yellow, containing iron stains, breaks in plates perpendicular to the bedding on weathering --------------------------------------------------------------------------1 3 Total__________ _________ ____________________ ______________________________________________ 13 9 "'Op. Cit., p. 281. Section of the Main Street Limestone on a Tributary of Little Mineral Creek, About One Mile South of Fink on Public Highway Grayson Marl Main Street Limestone: Ft. In. Massive limestone, containing iron stains__ ______________ 0 11 Marl, yellow___________________________________ ___________________ _____________________ 0 4 Limestone --------------------------------------------------------------------------------0 5 Marl, yellow______________________________________________ __ _ ___ ________ ___________ 0 5 Limestone, light brown_____________ _______________ _ _ ____ ________________ 0 11 Limestone, hard, brown, coarse grained, surface honey­combed by weathering. Contains E. plexa, E. arie­tina, well preserved_________ __ ________ ____________________________________ 0 8 Marl, brown, highly fossiliferous, containing same fos­sils as limestone bed below_____________ ________________ ------------------0 4 Limestone, containing red, ferruginous stains on top, highly fossiliferous, containing E. arietina and O. quadriplicata ----------------------------------------------------------------------­0 10 White limestone ---------------------------------------------------------------------1 4 Covered by water in creek___________ _____ _ ________ _______________________ 1 6 Total_ _____________ _ _________ _______________________ ______ _________________________ 7 10 The above sections show the variation in thickness of the Main Street, even in comparatively short distances. A very interesting section of the Main Street occurs on the public road just to the east of Cedar Mills, on the west bank of Sandy Creek, a tributary to Mineral Creek. At this loca­ tion the Main Street does not exceed five feet in thickness and is overlain directly by the Woodbine sand. This will be further discussed in connection with the Grayson marl. Excellent exposures of the Main Street may be seen in the western edge of the city of Denison; on the bluff on the east bank of Pawpaw Creek, one mile east of Denison; and for several miles along the public highway west of Fink, where the road follows the outcrop. The Main Street forms a well-defined band, easily traced, trending in a general northwesterly direction across the northern side of Grayson County. It is an excellent horizon for structural work. GRAYSON MARL The Grayson marl is the uppermost formation of the Comanche series in this region. The type exposure of the Grayson is in an abandoned cut of an old unused railroad grade in the southeastern portion of Denison, Texas, dis­covered by Cragin, who named the formation. The Grayson marl consists of light-colored fossiliferous clays or marls with many small lumps and thin bands of lime and limestone nodules, having a total thickness of approxi­mately twenty-five feet. The Grayson rests immediately upon the Main Street, and in fact its contact with the Main Street is sometimes rather difficult to establish definitely, as the contact is rather a gradation from the limestone into a marl. The upper contact of the Grayson, or the Grayson-Woodbine contact, is usually covered by ferruginous sandstone and other debris from the overlying Woodbine sand. Indeed, in very few places can a clear-cut Grayson-Woodbine sand contact be seen, and for this reason the question of the con­formity of the Grayson and Woodbine has long been a matter of dispute. In many places the outcrop of the Grayson is entirely covered by debris from the Woodbine. The lower part of the Grayson contains an abundance of Exogyra arietina Roemer. Other fossils characteristic of the Grayson and found in abundance are: Gryphea mucronata Gabb and Turrilites brazoensis Roemer. The contact of the Grayson-Woodbine is exceptionally well shown in the following complete section of the Gray­son marl as exposed on Pawpaw Creek in the northwestern portion of Grayson County. This is the best exposure of Grayson known to the writer in the county. Section of the Grayson Marl and Basal Woodbine Sand on Pawpaw Branch, Three Miles East of Stillhouse Ferry, Northwestern Grayson County, Texas Woodbine Sand: Ft. In. Soil ----------·-----------·---------·-----------------··-----··-------·--·-----------------­ Sandstone, reddish-yellow______________________ _____________________________ 3 O Sandstone, yellowish-------------·-·-·-·---·------·---··------·---------·-·-------· 3 0 Woodbine Sand : Ft. In. Sand, pack, fine grayish-white__________________ _ ________________ _____ 2 0 Clay, bluish-gray arenaceous_____________________________________________ 11 3 Sand, fine white pack_________ _________________________________________________ 7 10 Blue-gray marly clay, grading into black bituminous clay, then into yellow sandy clay (this zone repre­ sents a gradation from Grayson into Woodbine) ________ 8 5 Grayson Marl: Limestone, white, soft_______________________ _______ _ ______ _ _______________ 0 4 Clay, marly, bluish-gray___________ ___________________________________ _ 6 8 Limestone, nodular-------------------------------------------------------------0 10 Marl, bluish-gray___________________________________________________________ 3 10 Limestone, nodular_____________________________________________ 0 8 Marl, bluish-gray, limy, nodular_____ ________________ __________________ 7 8 Two beds of marly clay separated by a bed of bluish clay --------------------------------------------------------------------------------------3 10 Blue to gray clay marl filled with limestone nodules containing two rather prominent six-inch beds of impure nodular limestone containing Turrilites sp., Sphenodiscus sp., Holecty'[>Us sp., Nautilus sp.__________ 3 0 Total Woodbine__________________ _______________ _ _________________________ 35 6 Total Grayson·-----------------------------------------------------------------26 10 In the above section there seems to be rather perfect gradation from the typical Grayson marl into the Wood­bine sand. Evidence of a sudden break or change is, how­ever, contained in the rather abrupt change from limestone to a bituminous clay and the gradation of this clay into typical Woodbine sand, all in a very few feet. The ques­tion of the relation of the Comanche series and Gulf series has long been discussed. Most writers have agreed that the relation is probably one of unconformity, but the word unconformity is usually written with a question-mark fol­lowing. The contact between the Grayson marl and the Woodbine sand is, of course, the contact in question. Pos­sibly a reason for uncertainty on this point is the absence of clear-cut contacts between these formations, due to the debris from the Woodbine covering the contact zone. A very interesting area which throws some light on this problem is in the vicinity of Cedar Mills. Sandy Creek, a small tributary to Mineral Creek, flows just to the north and east of Cedar Mills, and is crossed by the public high­way a short distance north and also a short distance east of Cedar Mills. At the point to the north of Cedar Mills where the highway crosses the creek there is a good exposure of Main Street limestone, and immediately over­lying is the Woodbine sand, with the Grayson marl entirely m1ssmg. Furthermore, the Main Street limestone is less than seven feet in thickness. At the crossing of the same creek on the public highway east of Cedar Mills another outcrop of Main Street, followed by the Woodbine with the Grayson missing, was noted. At this latter place several feet of coarse conglomeratic ferruginous sand and sandy clay occur at the base of the Woodbine. About one-half mile upstream from Cedar Mills on Sandy Creek excellent exposures of the Grayson are found, and here it appears to have its normal thickness. However, the upper contact of the Grayson is somewhat irregular, and its contact with the Woodbine, instead of being a straight sharp line, is a wavy surface. There is without doubt excellent evidence in favor of a nonconformity between the Grayson and Woodbine at the Cedar Mills locality. However, at the Pawpaw Creek locality, section of which is given above, there is no evi­dence, which, however, does not preclude the possibility of a break between these formations. It is believed that a widespread nonconformity separates the Grayson and Woodbine, or the Comanche series and the Gulf series. Abundant evidence supporting this view is found in the general region to the east of Grayson County, as illustrated by the condition in Southwestern Arkansas, where the Gulf series rests on the basal portion of the Comanche series or on the Trinity sand. It is believed that a nonconformity separates the Grayson marl and the Woodbine sand in Grayson County, but the area was not distinctly above sea level, or for only short periods, and the break is not clearly recorded. Section of the Grayson Marl and Basal Woodbine Sand on the Public Highway at the Crossing of a Tributary of Little Mineral Creek About One Mile South of Fink, Grayson County, Texas Woodbine Sand Ft. In. Sandstone, massive fine grained, light gray at base grading into yellow sand at the top__ __ __ ________ ________________ 11 3 Clay, sandy, light gray grading upward into a purple clay --------­--------­------------­-----­--­----­---------­---­------------­---­-----­-----­1 Sandstone, fine grained, white.______ ____ ______________________________ _ 2 6 7 Clay, yellowish-brown grading into a sandy clay____________ 4 6 Sandy clay, hard, fine grained white__________________________________ 3 10 Yellow sandy clay containing beds of alternating red and yellow sandstone about 2 inches in thickness. The lower of these beds is made up principally of steel- gray limonite·---­-------­----­---------­----­--------­----­---------­-----­--------­4 1 Grayson Marl: Marl, light gray, grading into thinly laminated beds of gray clay and thin veins of red and yellow iron oxide. Very few fossils__ _____ _ ______________________________ ___________________ _______ 8 2 Clay marl, blue-gray, containing thin beds of nodular limestone and an abundance of Gryph.ea mucronata Gabb ------------------------------------­-------­----­-----­-7 0 Marl, containing thin beds of nodular limestone____ _________ 5 5 Limestone, chalky, shaly, nodular, containing Turrilites brazoensis Roemer, Pee-Un sp._______________ __________________________ 1 0 Clay marl, gray_______ _______________ __ ________________ ______________________________ 4 1 Clay marl grading into shaly limestone at the top__________ 2 2 Clay marl, light yellow to white, containing Turrilites brazoensis and E xogyra arietina .__ __ _________ _ __ ___ ___ ________ 1 3 Total Woodbine ·-----------------------------------------------------------------27 9 Total Grayson·-------------------------------------------------------------------29 1 A section of the Grayson was measured at the railroad cut on the Missouri, Kansas, and Texas Railroad freight cut-off about two miles east of Pottsboro and a thickness of a little over eighteen feet noted. The Grayson is easily recognized by the lime nodules and characteristic fossils which it contains in abundance. GULF SERIES As has been stated in the Introduction, the Cretaceous :rocks are divided into two great divisions, the Comanche series forming the lower part and the Gulf series the upper part of the system. The relation of these major divisions has been discussed in connection with the Grayson marl and it was shown that the Gulf series overlies the Comanche series disconformably. The disconformity is only slightly developed in Grayson county, but becomes more marked to the eastward. The Gulf series in North Texas is divided into the follow­ing formations: Navarro formation Taylor marl Gulf series Austin chalk Eagle Ford shale { Woodbine sand Only the three basal formations listed above are present in Grayson County. Following is a brief description of the formations exposed in Grayson County: WOODBINE SAND The Woodbine sand, named from the village of Wood­bine, in eastern Cooke County, Texas, is the basal forma­tion of the Gulf series in North Texas. It is a highly variable formation consisting of strongly cross-bedded, more or less ferruginous sands, and laminated shaly clays, with some interbedded layers of lignite and bituminous clay. On account of the highly cross-bedded nature of the formation, it is extremely difficult to estimate the thickness from surface outcrops, but according to Stephenson49 "it is reasonably certain that in Grayson County the thickness is not less than 300 to 400 feet and may be as great as 500 feet." Hill recognized two subdivisions of the Woodbine-a lower member called by him the Dexter sands, consisting "of brown and yellow ferruginous sandstone heavily laden with siliceous ironstone" with an estimated thickness of 160 feet, and an upper member, called by him the Lewisville beds, consisting of 150 feet or more of "laminated, lignitic sands and sandy clays, interstratified with brown sands, ••u. S. Geo!. Survey, Prof. Paper 120, p. 145, 1918. ferruginous reddish-brown sandstone, shell sandstone, and argillaceous shelly sandstone which contains large lens-like calcareous concretions and laminated argillaceous sand­stone at the top." Hill's50 description of the Woodbine sand is as follows : The rocks of the Woodbine formation are largely made up of ferruginous, argillaceous sands, characterized by intense brown­ish discoloration in places, which are accompanied by bituminous laminated clays. These sands, like those of the Trinity division (Western Cross Timbers), are unconsolidated in places, but differ from them by containing a greater proportion of iron and other mineral salts, which materially influence the character of the waters derived from them. The sands, which in the unoxidized substructure are usually white and friable, contain particles of iron occurring as glauconite and pyrite. These minerals oxidize toward the superfacies, and their solutions consolidate the more porus beds of sand into dark brown siliceous iron ore, occurring in immense quantities in certain localities. Other beds of sand break down into deep, loose soils. These support a vigorous timber growth and are especially adapted to fruit culture. The clays are usually sandy and sometime bituminous, although in some places, as near Denton, of sufficient purity for making stone­ware. They occur either as extensive beds or as laminae and thin strata interbedded in the sands. The presence of fossil vegetation, such as leaf impressions and lignite, distinguishes the beds of this division from the other formations of the upper Cretaceous and attests its shallow-water littoral origin. Sand seemi:; to predominate throughout the Woodbine, and it weathers in a typical sand-hill type of topography which is well illustrated in the area adjacent to Denison. However, locally it appears that clay predominates, and on weathering it produces a rolling prairie topography as illustrated in the vicinity of Pottsboro. The iron veins and segregations mentioned as occurring especially in the lower half of the Woodbine concentrate on the hill tops, due to the removal of the soft friable sand. Many of the hills are protected by a capping of this siliceous iron material. Due to the variable character of the Woodbine, it would be impossible to give a section which would apply to a very 00U. S. Geo). Survey 21st Ann. Rept., pt. 7, p. 294, 1901. large area. The following section, however, will give a good idea as to the character of the individual beds in the lower part of the Woodbine. Due to the extreme cross­bedding at the locality where the following section was taken, there is danger that the thicknesses are slightly in error. However, it is the most complete section available, and for that reason is given. Section of the Lower Portion of the Woodbine Sand in Rail­ road Cut of Missouri, Kansas, and Texas Freight Cut-Off Near Pottsboro, About Four Miles West of Denison, Grayson County, Texas Woodbine Sand: Ft. In. Yellowish-brown, mottled arenaceous clay____ __________________ 10 0 Yellowish-blue-gray sandy clay somewhat more arenace­ous than the lower bed, grading upward into a soft yellowish-brown sandstone above which is a fine, soft, yellowish sand containing numerous iron concretions _ 41 7 Yellowish-blue-gray sandy clay containing masses and concretions of lim-0nite which form several well defined layers near the top. The t-Op of the bed is marked by a ferruginous shell bed 4 inches in thick­ness containing numerous pelecypods and gastropods_ 62 3 Sandy clay containing beds of soft ferruginous sand­ stones ranging in thickness from 2 to 4 inches._______ ___ 12 6 Soft red to brown sandstone_ _______________________________________________ 2 O Series of alternating beds of red sandstone ranging from 2 inches to 18 inches in thickness separated by thin beds of sandy gray shale averaging about 2 inches in thickness. The sandstone beds are promi­nent in the lower part, while in the upper part the shale beds become thicker. Contains throughout veins and masses of impure limonite______________________________________ 22 8 Sandstone, cross-bedded, lenticular, white to red, con­taining thin veins, bands, and segregations of impure limonite -------------------------------------------------------------------------------8 5 Sandy clay, light buff alternating with a gray sandy clay ----------------------------------------------------------------------------------------7 10 Sandstone, cross-bedded, massive, yellowish-brown at base grading into a light yellow at top. Contains thin beds of ferruginous sand in the basal portion______ 14 5 Massive grayish-white sandstone with more or less irregular contact on upper surface________________________ _______ 3 4 Woodbine Sand: Ft. In. Clay, yellowish-brown at base grading upward into a light yellow -------------------------------------------------------------------------13 10 Clay, yellow at base grading upward through blue to a somewhat impure mottled reddish-brown at top__________ 15 1 Massive gray sandstone, irregularly bedded containing at the base a thin bed of ferruginous sandy clay______ ___ 11 6 Sandy clay, ferruginous, with thin layers of dark black to blue impure limonite with metallic luster__________________ 1 3 Lead-colored clay containing bands of light yellow and red clay grading upward into a series of alternating beds of brown and light gray sandy clay___ ____________________ 5 5 Yellow to brown clay grading upward into thinly lami­nated blue to gray clay shale containing bands of black carbonaceous material and red iron oxide.__________ 10 11 Grayson Marl TotaL_ _____ ___________________________· --------------------------------------------------243 0 No definite horizons have been recognized in the Wood­bine, but as a general rule the base contains a bed of black bituminous clay or shale ranging from a few inches to several feet in thickness. However, this is not always pres­ent, as several sections have been noted where the basal Woodbine consists of massive pack sand. It has also been noted that as a general rule the zone which contains the segregations of iron in greatest abundance, and which is the one usually recognized, occurs approximately 140 feet above the base of the Woodbine. This cannot be checked at all localities, but was noted at several places to be approximately correct. The relation of the Woodbine to the underlying Comanche series has been discussed in connection with the Grayson marl. The Woodbine apparently rests unconformably on the underlying Grayson marl. In this connection Stephen­son51 says: The nature of the contact separating the Gulf series from the underlying Comanche series has not been satisfactorily deter­mined in northeastern Texas. Probably it is that of uncon­formity, the basal member of the upper series, the Woodbine sand, having been deposited in shallow waters of the trans- SJ.Op. Cit., p. 144. gressing sea, in the deeper waters of which the succeeding truly marine sediments of the series were laid down. Fossil leaves were obtained from the lower portion of the Woodbine on the public highway, about five miles south of Denison, near Iron Ore Creek. A rather extensive col­lection of plants has been made from Arthur's Bluff, on Red River fifteen miles north of Paris, Lamar County, Texas, which has been described by Berry.52 The upper por­tion of the Woodbine yields a peculiar shallow-water marine fauna best known from exposures on Timber Creek, near Lewisville, Denton County, Texas. This fossiliferous hori­zon can be recognized in Grayson County, but is very poorly developed as compared with the exposures near Lewisville. The Woodbine outcrop covers a much more extensive area in Grayson County than any of the formations of the Comanche series. Its outcrop forms a broad belt ranging from two to five miles in width extending along the northern side of Grayson County, and then as it nears the western border swinging southward and forming a belt from four to five miles in width along the western boundary of the county. The big bend in the outcrop is caused by a broad shallow syncline, the Sherman syncline, which is described under Structure. Several beds of a very impure and poor grade of lignite outcrop in the vicinity of Redbranch, in the western part of Grayson County. The lignite at these outcrops is of such an inferior quality as to be of no value as a fuel supply. EAGLE FORD SHALE The Woodbine sand is overlain by the Eagle Ford shale named by Hill from Eagle Ford, a small village six miles west of Dallas. The writer has not studied this formation in as much detail as the preceding formations, but in order to make this report as complete as possible a summary of the work of Stephenson and Hill is given, supplemented by '"'Berry, E. W., U. S. Geo!. Survey Prof. Paper 129, pp. 153-181, 1922. the data obtained by the writer. The following informa­tion is taken chiefly from Stephenson's58 work. The Eagle Ford consists chiefly of dark bluish-gray to nearly black shaly clay, which is as a rule gypsiferous and more or less bituminous; in places crystals of selenite weather from the clay in great numbers. In Grayson County the formation has an estimated thickness of 300 to 400 feet. Thin platy layers of sandstone and sandy lime­stone, some bearing the imprints of small costate and keeled ammonites, occur in the formation, particularly in the cen­tral portion. Flattish calcareous nodules occur in the lower part of the formation, and oval to spherical hard limestone septaria are characteristic of the upper part. In the upper twenty to twenty-five feet of the formation in the vicinity of Sherman the dark clays are interstratified with beds of sand, one of which, fifteen to twenty feet below the base of the Austin chalk, carries vast numbers of a small fluted oyster, Ostrea lugubris Conrad. Ten feet below the base of the Austin chalk, in Grayson County, is a conglomeratic layer of gray sandstone, carrying numerous more or less rounded phosphatic pebbles, shells of Ostrea alifera Cragin, and fish teeth, of which shark teeth are common. This is the "fish-bed conglomerate" of Taff, which, according to Stephenson, should be regarded as the base of the Austin chalk, rather than part of the Eagle Ford shale. Section of the Upper Part of Eagle Ford Shale Between the Base of "Fish-Bed Conglomerate" and Base of Austin Chalk on the West Sherman-Denison Highway About Five Miles North of Sherman Austin Chalk-Exposed on top of hill Ft. Eagle Ford Shale: Light blue to yellow clay with thin veins of ferruginous clay, grading into light yellow marl containing veins of chalk in upper 5 feet_______ ________ ______________________________________ 18 In. 3 Sand, dark, ferruginous and argillaceous, containing concretions of calcite with small pebbles forming the nucleus of the concretions. Weathers to a dark green­ ish color --------------­---­---------------------------------------­-------------­--­ 3 3 "U. S. Geo!. Survey Prof. Paper 120, 1918. Eagle Ford Shale: Ft. In. Shell breccia, arenaceous, and cemented with calcium carbonate, containing fucoids throughout and Ostrea lugubris, Ostrea sp. ------------------------------------------------------------1 0 Sand, soft, argillaceous and ferruginous, interstratified with thin layers of ferruginous clay. The color of this bed ranges from light yellow to brown, and on weathering assumes a dark greenish color-------------------2 6 Shell breccia, slightly arenaceous, cemented with cal­cium carbonate, containing Ostrea lugubris and Ostrea SP·------------------------------------------------------------------------------2 0 TotaL___ _ ______________ _ ______ ______________________________________________ __________ 27 0 Hill54 gives the following section of the upper part of the Eagle Ford shale : Section at Sherman, Grayson County, Te·xas, Two Miles West of Binkley House Austin Chalk Eagle Ford Shale: Ft. In. Sandy clay shales with 0. lugubris -------------------------------­10 0 Thin slabs of brown sandstone with small rounded conglomerate of jasper pebbles, 0. lugubris, and fish teeth -------------------------------------------------------------------------------------5 0 Blue laminated clay weathering into limonitic colors______ 10 0 Massive agglomerate of 0. lugubris_________ --------------------------2 0 Sandy clay shale in thin alternations of clay and sand; clay efflorescent and drab colored on drying----------------40 0 Blue clays with gigantic septaria Total___ ___ __ __ _____________________________________ _____ ------------------------------67 O Hill's55 general description of the Eagle Ford in this area is as follows : In the counties of Dallas, Collin, and Grayson, where the beds have their greatest development, near Sherman, they show the following sequence: The lower portion is made up of very thin laminations of deep blue or black clays with occasional laminae of sand, passing upward into purer clays locally containing irregular bands of thin calcareous matter and ferruginous clay nodules. This clay is usually highly indurated and of a laminated "Op. Cit., p . 326. "Op. Cit., p. 324-325. character. It is generally largely intermixed with selenite which is disseminated through it in the form of minute lenticular crys­tals. Sometimes the gypsum is so abundant as to constitute a fourth or fifth of its bulk, and consequently the water flowing through this formation is generally bitter and disagreeable. In a few instances thin seams of selenite have been detected travers­ing the clay horizontally, and in others the clay appears reticu­lated with the selenite. Small septaria composed of hard, com­ pact, blue argillaceous limestone are also sometimes met with in the lower bed. The only limestone element of the lower part of the formation occurs in the nodules or segregations em­bedded in the clay. These are generally flattened, from 1 to 2 inches thick, and vary in width from a few inches to 1 to 2 feet. They are unusually hard, compact, and of an earthy texture. Externally they are of an iron rust color, but when broken exhibit various shades of blue and brown. These nodules usually occur in the clay in the form of distinct bands or layers, which are nearly horizontal. Sometimes several of these bands are seen in the same section. In the central portion of the formation are a few persistent flaggy layers of a laminated arenaceous-argillaceous limestone, seldom over an inch in thickness and aggregating 10 feet, which weather into buff colors. Although in themselves not very durable, these are of sufficient relative hardness to produce a dis­ tinct escarpment and dip plain, which makes a conspicuous topographic feature, as seen west of Dallas, between that city and Eagle Ford. These layers are also exposed in Grayson County, near the source of Mustang Creek,. in northern Denton County, and west of Hillsboro in Hill County, and are appar­ ently the base of the beds which in the southward extension con­ stitute the prevalent material of the Eagle Ford formation. Succeeding these medial arenaceous layers are considerable thick­ nesses of the blue-black clays in which are numerous spherical septaria, some of which attain a diameter of three feet. These are composed interiorly of a dense blue limestone and are cracked in numerous directions by cross fissures which are filled with crystals of calcite and selenite. This portion of the section con­ tains beautifully preserved fossils with a nacreous coating, including many ammonites, such as Buchiceras swallovi, Placen­ ticeras, etc. In the upper portions of these clays and about 50 feet below the summit of the formation in the Dallas-Sherman sections there are other calcareous and flaggy sheets containing numerous remains of fish teeth, Inoceramus sp., and Ostrea lugubris Conrad. These flaggy, arenaceous layers increase in general thickness and in percentage of sand in their northward extension, having a thickness of 10 or 15 feet in Grayson County, as seen in the western portion of the city of Sherman. Above this there are 10 or 20 feet more of the blue laminated shale. According to Stephenson, the fossils most useful in the identification of the Eagle Ford are: Ostrea lugubris Con­rad, 0. alifera Cragin, fish teeth belonging to the species Ptychodus whipplei Marcou, Jnoceramus labiatus Schlot­heim, /. fragilis Hall and Meek, and small-keeled ammonites belonging to Prionotropis or Prionocyclus, or to both. Of these the first three occur only in the upper forty or fifty feet of the formation. Excellent outcrops of the Eagle Ford occur in the vicinity of Bells, eastern Grayson County. Near Cook Springs, between Denison and Sherman, the lower part is particu­larly well exposed and was formerly used in the manufac­ture of brick at that place. The upper part of the Eagle Ford is well exposed in the western edge of the city of Sherman along the banks of Sand Creek. The outcrop of the Eagle Ford shale forms a rolling prairie, and only locally, as near Bells, do the sandy layers become prominent enough to produce a sand-hill topogra­phy. The Eagle Ford weathers very readily, forming a black waxy soil. AUSTIN CHALK With the exception of recent stream deposits, the Austin chalk represents the youngest formation exposed in Gray­son County. It immediately overlies the Eagle Ford shale and according to Stephenson reaches a thickness of approxi­mately 1,000 feet in this region. The type area of the Austin chalk is at Austin, Travis County, Texas, where, according to Hill, it has a thickness of 410 feet. It con­sists of white chalky limestone in beds of varying thick­ness, with interbedded marly layers especially in the upper part. However, in Grayson County the Austin chalk, while possessing many of the characteristics of the Austin chalk of Travis County, has in many respects assumed new fea­tures. It is much thicker and contains, in addition to the typical chalky limestone, interbedded layers of marl and argillaceous clay. Some of the fossils commonly found and characteristic of the Austin chalk are : Inoceramus undulato-plicatus Roemer Ostrea aff. diluviana Lamarck (uppermost part) Gryphea aucella Roemer Exogyra ponderosa Roemer (upper half) Radiolites austinensis Roemer Mortoniceras texanus Roemer The Austin chalk usually outcrops in a bluff or escarp­ment overlooking a broad plain or prairie formed by the Eagle Ford shale. The outcrop of the Austin chalk was referred to by Hill as the "white rock escarpment." The Austin chalk weathers readily, forming a black sticky soil very similar to that formed by the Eagle Ford shale. The outcrop of the Austin chalk is confined to the southeastern portion of Grayson County. STRUCTURE The Cretaceous formations of Grayson County were deposited on the eroded surface of Paleozoic rocks, 56 with depositional slope or initial dip of from thirty to eighty feet per mile to the south and east. The general monoclinal dip of the Cretaceous strata is interrupted in Grayson County by two rather prominent folds, the Preston anticline and the Sherman syncline. THE PRESTON ANTICLINE This large anticlinal fold is one of the most important structural features of North Texas. A structural contour map of the Preston anticline was published57 in 1922. The fold begins in northern Marshall County, Oklahoma, and extends in a southeasterly direction, passing near Preston and just to the north of Denison. As outlined on Figure 4, it is a broad plunging arch representing an upthrust of '"Pre-Cretaceous Rocks Found in Wells in the Part of the Gulf Coastal Plain South of the Ouachita Mountains by Hugh D. Miser and E. H . Sellards. Bull. Amer. Assoc. Petr. Geo!. (in press). °'Hopkins, O. B., Powers, Sidney, Robinson, H. M., Structure of the Madill­Denison area, Okla. and Texas, with notes on Oil and Gas development: U. S. Geo!. Sur. Bull. 736, pp. 1-34, 1922. some 700 or 800 feet, the crest of the fold being located in southern Marshall County, Oklahoma, about eight miles northwest of Fink. From the crest the anticline plunges rather rapidly to the southeast until it finally disappears in the vicinity of Gober, Fannin County, Texas. The Pres­ton anticline has a total length of approximately forty miles and an average width of about ten miles. The axis of the Preston anticline enters Grayson County from the northwest, crossing Preston Bend, passing near Rock Bluff, continues on to the southeast, past the city waterworks plant on Shawnee Creek, and then becomes rather indistinct a few miles to the east of Denison. In the Preston Bend area the axis of the fold is marked by a belt of Trinity sand between outcrops of the Goodland lime­stone. At the city waterworks plant of the city of Denison, on Shawnee Creek, an inlier of Goodland limestone, just below the bridge on the public highway, marks the crest of the anticline at that place. The dip of the formations away from the axis of the Preston anticline varies from a few feet per mile to more than 300 feet per mile. In general, the south limb of the fold is steeper than the north limb. The steepest part of the fold is on the south limb just to the northeast of Potts­boro. The steep dip is first noticed in the railroad cut of the Missouri, Kansas, and Texas freight cut-off near Potts­boro. Here the beds, particularly the Main Street lime­stone, are dipping at an angle of approximately 14 degrees. Traced northwestward from this point, the Main Street forms a well-defined ridge, or a semi-hogback, extending for a distance of approximately two miles, the dip becoming much less in the vicinity of Fink. The pronounced narrow­ing of the width of the outcrop of the Woodbine sand in this area, due to the steep dip, is perhaps the basis for the so-called Cook Springs fault postulated by Taff and Lev­erett, and also by Hill. The south limb of the Preston anticline is not a smooth regular dip to the southeast, but, on the contrary, it con­ tains many irregularities, such as flattening, terraces, FIG. 2. Structure section across the Preston Anticline from a point on Red River, one mile northeast of Preston, southward through Pottsboro. O':> C>:l noses, and on the whole, is most irregular. No attempt has been made to include these small irregularities on the structural contour map, but in detailing this structure it was noted that many such features are present. One of the most prominent of these variations is found northeast of Pottsboro, where a rather distinct nose occurs. A detailed map of this nose shows a small amount of closure. It is on this structure that the Pottsboro gas field, the only oil and gas-producing area in Grayson County, is located. Traced northwestward into Oklahoma, the axis of the Preston anticline is observed to coincide with that of the Criner Hills. It is believed that the Criner Hills represent a portion of the Preston anticline in which the Cretaceous covering has been removed by erosion, exposing the core of ancient Paleozoic rocks. The Preston anticline has brought to the surface the Comanche series of formations, which normally would be buried beneath the overlapping Gulf series. However, the uplift of approximately 800 feet has caused erosion to remove not only the Gulf series but the underlying Coman­che series from a considerable area along the axis of the uplift. The outcrop of the formations of the Comanche series parallel the sides of the anticline and wrap about its eastward plunging nose in a typical fashion. The strike of all the Comanchean formations in Grayson County has been deflected considerably to the southeast, due to this broad uplift. The axis of the Preston anticline conforms in direction to that of the Criner Hills and the Arbuckle Mountains, and it is very probable that the folding of the Cretaceous beds was merely incident to later movement along this previous line of folding. THE SHERMAN SYNCLINE To the south of the Preston anticline, and with its gen­eral trend parallel to it, is the Sherman syncline, a broad shallow trough with a steep slope on the north side and a very broad open slope on the south. This asymmetrical syncline was named the Sherman syncline because the ~ ] 0 t ~ ! (; . i c f !fi ~ ~ 3 f ·SOO -•oo O{ FIG. 3. Structure section across Grayson County on a line through Denison and Ethel. trough of the syncline passes through the city of Sherman. It is believed that the Sherman syncline is continuous with the Marietta syncline in Love County, Oklahoma. It would be expected that other anticlines and synclines would be present to the south of the Sherman syncline, but the character of the surface rocks makes their detection very difficult. The surface is covered by the outcrop of the Austin chalk and the difficulty in locating horizons in this formation makes detailed structural work very diffir­cult. To the north of the Preston anticline, in Marshall County, Oklahoma, there is a series of anticlines and syn­clines which are located on the general structural map (Fig. 4). No faulting of any magnitude was observed in Grayson County. Some small faults having a throw of six inches to one foot were observed in the Eagle Ford shale north of Gordonville, but these were probably due to a settling of the sediments. THE POTTSBORO GAS FIELD This field is located about six miles west of Denison and about two miles northeast of Pottsboro, and, as previously stated, is on a structural nose on the south limb of the Preston anticline.58 The gas-producing horizon occurs at depths ranging from 880 to 900 feet and is at or near the base of the Trinity sand, which makes an unconformable contact with the underlying Paleozoic rocks. At the pres­ent time (January, 1931) there are two wells producing oil in this field; namely, the Sherman Oil Company Nos. 1 and 2 R. C. Dalton, on the James Ingram Survey. The production is obtained from a depth of 921 to 933 feet and the oil has a gravity of 25 degrees Baume. The producing horizon is highly elastic, erratic, and lenticular, and is believed to represent approximately the unconformable contact at the base of the Trinity sand. "'The writer is indebted to Mr. J. B. Lovejoy, of the Gui{ Production Company,for the information on the Pottsboro field and the statement in regard to the test near Tioga. OE.NTON !IlillIIll PENNSYLVANIAN D CRETACEOUS PRE.-PENNSYLVANIAN H SCA.L E : 0 I "2. 4 6 8 10 \"l. MILES A Fd &a E3 Fm. 4. Map showing axes of principal folds in Grayson County and adjacent areas. The following table shows the several wells in the field, the depth, amount of production, and other information: Company Farm Depth Initial Prod Pay Survey Sherman Oil No. 1 R. C. Dalton........ 892' 9 MCFG 882-92' Jas. Ingram DD-924 %' 27 bbls. oil 921-24%' 2 " ........ 899' 3 MCFG 897-99' " DD-933' 33 bbls. oil 931-33' Simpson-Fell 1 H. Guilloud, Sr... 900' 11,200,000 CFG 887-900' " (305# RP) Murchison Oil 1 G. W. Wall.......... 903' 6-1/ 5 MCFG 880-903' " (305# RP) 891-97' G. R. Greeves 3 " ----------897' 2 MCFG (est) Simpson-Fell 1 G. W. WalL........ 2515' 2MCFG 849-50' " PB-1294' 887-88' 919-21' 1160-62' 1191-94' 3 " .......... 881' 4,207,000 CFG 870-81' " The subsurface conditions in the Pottsboro field are not well known. Most of the wells have not been drilled deep enough to give satisfactory control on the older formations. Between two wells drilled by Simpson and Fell, Nos. 1 and 2 G. C. Wall, located due east and west of each other and 500 feet apart, a west dip of 470 feet is noted. Whether this is due to faulting or to sharp folding is not known. It is interesting to compare the gravity of the oil found at Pottsboro with that of the Madill pool in Marshall County, Oklahoma. The Madill pool is approximately thirty miles north of the Pottsboro field and produces from approximately the same stratigraphic horizon. The gravity of the Madill oil is 47.5 degrees Baume while that at Potts­boro is 25.3 degrees Baume. It seems likely that the oil of the Pottsboro field, as well as that of the Madill pool, is not indigenous to the Cretaceous, but has migrated from some of the underlying formations. No attempt is made to list the various tests which have been drilled in Grayson County. However, a test drilled by the Texas Company, No. 1 G. W. Cannon, S. A. & M. G. Survey, A-1142, near Tioga, southwestern Grayson County, encountered a slight showing of oil near the base of the Cretaceous at a depth of 1,100 feet. Several showings of oil were reported at the following depths in the Paleozoic: 2,556-2,601 feet, 2,602-06 feet, 2,666-73 feet, and 2,793­2,800 feet. No surface folds are in evidence in this area and the subsurface control is too limited for definite mapping. INDEX Page "!:ft~~~s:r. "f:._!_::::::::~~:::::::=:=:::::::::::-~ 2~ Ammonites acutocarinatus Shumard___ 25 Anchura mudgeana White ____ 40, 43 Antlers sand ---------------------------------19 Arbuckle Mountains _________________ 64 Ardmore, Oklahoma ---------------16 Arick, M. B. ---------------------------------7 Arkansas, southwestern --------------50 Arthur's Bluff -------------------------56 Atlantic Ocean ----------------------------11 Atoka folio ---------------------·--------19 Austin formation ____________ 12, 52, 60 ff., 66 Austin, Texas ___________15, 18, 19, 21, 31, 60 Balcones fault----------------------8 Basement sands ·-------------------------------18 Bells, Grayson County -----------------------60 Bennington limestone --------------------33, 44 Binkley House --------------------------58 Black Prairie --------------------·-------------12 Blake, W. P. -------·----------------------------9 Bokchito formation -------------------------------33 Brown, Robert -----------------------------------7 Buchiceras swallovi ----------------------69 Buda limestone ---------------------------------32 Caddo limestone -------------------------------27 Cardium hillanum ---------------------------46 Carpenters' Bluff -------------------------------40 Ced:.r Mills --------'--------------------47, 49, 50 Choctaw Creek -----------------------·--12, 46 Christner, J. B. -----------------7 Collin County ----------------------------------58 Comanche Peak limestone__________ ___l9, 21 Comanchean sea ----------------_____________ 16, 22 Comanche series ___10, 14 ff., 44, 49, 51, 64 Cooke County -----------------------·---------21 Cook Springs --·-·--------·--------------·-··-------_ 60 Corbula -------------------------------------40, 43 Cragin, F. W. ---------------·-···-----------48 Crawford, F. B. --------------------------7 Cretaceous ----···-------------------------------·----15 Cretaceous, lower ------------------·-----9, 14 Cretaceous stratigraphy ----------_____ ______7, 22 Cretaceous rock series of Texas_________ 10 Cretaceous, upper -------------------------------9. 12 Criner Hine -------------------------------------· ___ 64 Cross Timbers, lower ------..----------------··. _ 15 Cross Timbers, eastern ------------------12, 13 Cross Timbers, western ___________ 12, 13, 53 Cymbophora sp. ------------------------------40, 43 40 ~~H~mc~:nti·___=:::::::::::::::::::::::::::::-• t: Dallas, Texas _____ ....____ _ __ 19, li9 Dalton, R. C., Well Nos. 1 and 3.._66, 68 Davis. Jefferson -------------·-··--····---··----9 Del Rio clav ·----------------------------·-·-. 32 Denison beds _ _____ ----___ _______ -----------32 Denison-Carpenters' Bluff road -----------39 Den'son formation -----···-------------____ 31 ff. Denison sheet ____ -·-_____ _ _____________ -----· _ 6 Denison,Texas 7, 9, 22, 26, 43, 47, 48,56, 61 Denton clay ·-----------------------------------·-·· 33 "'· Denton County ·---------------·----·-·------------59 Denton, Texas ____ ---·-··-----------·--·----·-<3 Denton-Weno contact -----·-·--·----------------35 Dexter sands ___.. ---------------·----------------52 Doherty, Raymond -------------·-·----·-· _ __ 7 Duck Creek formation -------------·----7, 26 ff. Duck Creek limestone ____________________13, 24 Eagle Ford formation _________ _ _____ __ 12 Eagle Ford shale -------·-·--.52, 56 ff., 66 Eagle Ford, Texas _ _________________________ 56, 59 Edwards limestone -----·-------------------21 Page El Paso, Texas -----·-------------------------9, 26 Engonoceras ------------··----------------36 Engonoceras serpentinum (Cragin) ________________ ____40, 43 Exogryra americana Marcou --------·29, 31 Exogyra arietina Roemer 44, 45, 46, 47, 48 Exogyra plexa Cragin ________45, 46, 47 Exogyra ponderosa Roemer --------------·-61 Exogyra texana Roemer _________19, 26 Fink, Texas -------------------42, 46, 47, 51, 62 Florida ·-------------·-----·-·--------·----------·-------11 Fort Belkn.&Co. IJ.:tlti>110)re,}.td. /