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UNITED STATES DEPARTMENT OF THE INTERIOR 

Harold L. Ickes, Secretary

GEOLOGICAL SURVEY 

W. C. Mendenhall, Director

Professional Paper 186—G

STRATIGRAPHIG RELATIONS

OF THE AUSTIN, TAYLOR, AND EQUIVALENT

FORMATIONS IN TEXAS

BY

LLOYD WILLIAM STEPHENSON

Shorter contributions to general geology, 1936

(Pages 133-146)

UNITED STATES

GOVERNMENT PRINTING OFFICE 

WASHINGTON : 1937

For sale by the Superintendent of Documents, Washington, D. C. ------- Price 10 cents
CONTENTS

	Page 

Abstract_________________.__________.____________________._________-____-__-___.. 133

Introduction.___-_-_-_______________________-_____________________________-_-__-_________-____-----------___ 133

Section in Travis County_____________________-__________.____________________________________________________ 133

Sections along belt of outcrop to the south and to the north of Travis County-_________________________________________ 136

Vicinity of New Braunfels_______--____--______-______-_________-------------------_--------_-_--------__- 136

North and west of San Antonio__________________________________________________________________________ 136

Hondo and Seco Creeks, Medina County___-____-______________-------------__----_-___---_-----_-------___ 136

Travis County to Falls County_-_----_-------_______-_-___._____-_____________________-_ 137

Waco and vicinity.______________________________________________________________________________________ 137

McLennan County to Dallas County___________________________________________________________________ 138

Dallas and vicinity____________________________________________L_.____________________________________ 138

Collin County_________________________________________________________________ 139

Grayson, Fannin, and Lamar Counties__________.______________________________________________________ 139

Chalks and marls in Red River County_______________________________________________________—— 141

Stratigraphic relations in Red River and Lamar Counties.-------------------------------------------------------- 141

Section in Red River County compared with that in southwestern Arkansas_______________________________________ 143

Texas and Alabama sections compared_________________________________________________________________________ 144

Summary and conclusions__________________________________________________________________________________ 145

ILLUSTRATIONS

Page 

PLATE 44. Reconnaissance geologic map of parts of Lamar and Red River Counties, Tex_____________________________ 138

FIGXJBE 7. Correlation of the exposed sediments of Austin and lower Taylor age in the Gulf Coastal Plain—_______________ 135

II
EXPLANATION OF FIGURE 7, PAGE 135, PROFESSIONAL PAPER 186-G

Numbers designate faunal zones as follows:

7. Diploschiza cretacea minor zone (=Diploschisa cretacea zone in Alabama).

6. Ostrea elegantula zone.

5. Ostrea travisana zone.

4. Ostrea centerensis zone.

3. Exogyra tigrina zone.

2. Gryphaea wratheri zone.

1. Inoceramus undulato-plicatus zone.

ERRATUM

On page 133, first column (abstract), line 18 from bottom of page, southeastern Arkansas should read southwestern Arkansas.

135230—37

U. S. GOVERNMENT PRINTING OFFICE: 193?
STRATIGRAPHIG RELATIONS OF THE AUSTIN, TAYLOR, AND EQUIVALENT

FORMATIONS IN TEXAS

By LLOYD WILLIAM STEPHENSON

ABSTRACT

The relation of faunal zones in the upper part of the Austin 

chalk to the top of the chalk indicates the presence of an unconformity of regional extent separating the Austin and beds of 

Austin age from the overlying Taylor marl and beds of Taylor 

age. The time value of this unconformity varies greatly from 

place to place along the strike, owing in part to unequal erosion 

at the top of the Austin and in part to differential warping in 

early Taylor time.

The maximum erosion at the top of the Austin is found in 

the vicinity of Waco, where the Taylor rests directly on the 

Inoceramus undulato-plicatus zone, and the minimum erosion is 

found in Fannin and Lamar Counties, where the top of the Gober 

tongue of the Austin chalk is estimated to be on the order of 400 

feet above the same zone.

Differential warping caused the deposition of the Taylor sediments to begin earlier in the Waco area than elsewhere; there the 

thickness of lower Taylor sediments below the Pecan Gap chalk 

member is 900 feet; the minimum thickness or complete absence 

of lower Taylor sediments beneath beds of Pecan Gap age is 

between New Braunfels and San Antonio.

The Austin-Taylor unconformity is marked at most places by 

a thin phosphatic bed that forms the base of the Taylor marl. 

In northeastern Texas this bed is traceable from Lamar County, 

where it immediately overlies the Gober tongue of the Austin 

chalk, eastward to eastern Red River County, where it forms the 

basal bed of the Annona chalk immediately overlying the 

Brownstown marl.

The field relations of the traceable beds in Red River and Lamar 

Counties indicate that the Annona chalk as a whole is the time 

equivalent of the lower part of the Taylor marl, the Wolfe City 

sand member, and the typical Pecan Gap chalk.

The macrofauna in the Annona chalk and in the underlying 

Ozan formation in southeastern Arkansas and the unconformity 

at the base of the Ozan suggest that these two formations together 

are the time equivalents of the Annona chalk of Red River 

County, Tex. The Brownstown marl of Arkansas appears to 

be correctly correlated with the marl to which the same name 

has been applied in Texas.

A zone of concretions near the top of the Blossom sand in Red 

River County, Tex., which carries many shells of Ostrea elegantula 

White, is correlated with a marine sand carrying the same 

species, near Hatchechubbee, Russell County, Ala.; this sand is a 

facies corresponding in age to the lower part of the Selma chalk 

farther west in Alabama.

As both the Annona chalk and the Anacacho limestone include 

several hundred feet of beds older than the typical Pecan Gap 

chalk, and as these older beds are of the age of the Taylor marl 

(lower), which underlies the typical Pecan Gap chalk, the supplanting of the names "Annona" and "Anacacho" by "Pecan 

Gap" is not justified.

INTRODUCTION

In early accounts of the Upper Cretaceous formations 

of Texas, by Hill,1 Vaughan,2 and other pioneer geologists, the Taylor marl is interpreted as resting conformably on the Austin chalk, the implication being that the 

top of the Austin and the base of the Taylor are of about 

the same age throughout their geographic extent.

In 1929 the writer 3 presented evidence that an unconformity separates the Austin and Taylor, at least from 

Travis County to the northern part of Ellis County. 

Evidence collected since 1929, particularly during the 

autumn of 1935, indicates that the two formations are 

separated by an unconformity of regional extent, that 

both the top of the Austin and the base of the Taylor 

differ in their stratigraphic positions from place to 

place, and that the maximum interval, measured in 

thickness of strata, approximates 900 feet.

The data given on the following pages are selected 

from a large amount of detailed information, as having a 

critical bearing on the stratigraphic relations of the 

Austin and Taylor sediments.

SECTION IN TRAVIS COUNTY

In its type area in Travis County the Austin chalk 

has an estimated thickness of 420 feet. The formation 

consists of interbedded layers of hard chalk, softer 

chalk, and chalky marl; some of the marly layers are 

rather strongly argillaceous, as in the upper part that 

Adkins 4 has called the Burditt marl, though this part 

of the formation is no more marly than other lower 

parts of the formation elsewhere in Texas.

The formation is capable of subdivision into faunal 

zones, and several zones recognized in its upper onefourth in Travis County have been traced for considerable distances away from that area both toward the 

north and toward the south. These zones in ascending 

order are the Inoceramus undulato-plicatus zone,

i Hill, R. T., Geography and geology of the Black and Grand Prairies, Tex.: U. S. 

Geol. Survey 21st Ann. Kept., pt. 7, p. 330,1901.

i Hill, R. T., and Vaughan, T. W., U. S. Geol. Survey Geol. Atlas, Austin folio 

(no. 76), p. 5,1902.

3 Stephenson, L. W., Unconformities in Upper Cretaceous series of Texas: Am. 

Assoc. Petroleum Geologists Bull., vol. 13, pp. 1328-1330, pi. 13,1929.

* Adkins, W. S., Texas Univ. Bull. 3232, pp. 449-451,1932.

133
134 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1936

Gryphaea wratheri zone, Exogyra tigrina zone, Ostrea 

centerensis zone, and Ostrea travisana zone.

The lowest and most persistent of the zones has been 

designated the "Inoceramus undulato-plicatus zone", 

because of the occurrence of great numbers of this large 

and easily recognized bivalve in the zone. This species 

was first described by Roemer,5 who found it at the 

classic exposure of the Austin chalk on the Guadalupe 

River, called by him the "Wasserfalle der Guadalupe", 

about 2 miles below the highway bridge at New Braunfels, in Guadalupe County. In Travis County the 

species is contained in a hard, massive facies of the 

chalk exposed in the bed and banks of Little Walnut 

Creek upstream for 1,000 feet or more from a fault 

that crosses the creek 300 feet above the iron Sprinkle 

road bridge, now abandoned. Because of the faulting 

it is not possible to determine the exact position of the 

undulato-plicatus zone with respect to the Austin-Taylor 

contact, but the zone is obviously 100 feet or more 

stratigraphically below the contact; the observed thickness of the massive chalk above the bed of the creek at 

this locality is 15 or 20 feetj

A few shells of the species Gryphaea wratheri Stephenson were observed in the upper part of the massive chalk 

at the locality just described, indicating that the G. 

wratheri zone 6 closely overlies the Inoceramus undulatoplicatus zone; this is the normal relation of these two 

zones, as shown by other sections in Texas that will be 

described on subsequent pages.

The fault above mentioned crosses the creek obliquely, striking approximately north and dipping 

70°-75° E.; the beds are downthrown on the downstream 

side, and although the amount of the throw is unknown 

the massive chalk that appears on the upthrown side 

is dropped from sight below the stream bed. The section exposed in the bluffs and upper slopes of the creek 

in the immediate vicinity of the old bridge and for 1,000 

feet or so downstream therefrom comprises about 70 

feet of chalk and chalky marl as described below.

Section on left bank of Little Walnut Creek, in the vicinity of the 

old Sprinkle road bridge (abandoned), Travis County

Feet

Taylor marl: Marly clay, poorly exposed in upper slope. _ 10 

Unconformity (not clearly exposed here). 

Austin chalk:

Alternating layers of massive marly chalk and harder 

chalk; contains Ostrea travisana Stephenson about 

10 feet below top, Exogyra ponderosa var. erraticostata Stephenson, and toward the base Gryphaea 

aucella Roemer and Exogyra aff. E. laeviuscula 

Roemer_________________________________ 20 ±

Grainy chalk, irregularly indurated _______________ 3

Chalky marl, slightly shaly______________________ 5

Chalky marl containing many shells of Ostrea center, 

ensis Stephenson____.________________________ 1

' Roemer, Ferdinand, Die Kreidebildungen von Texas, p. 12, Bonn, 1852. 

6 Stephenson, L. W., New Upper Cretaceous Ostreidae from the Gulf region: U. S. 

Oeol. Survey Prof. Paper 186-A, pp. 1-12,1936.

Austin chalk—Continued. p-eet

Chalky marl, slightly shaly, glauconitic in lower 2 or 

3 feet; J. A. Cushman identified characteristic 

Austin Foraminifera in a sample taken 5 feet above 

base ________________________________________ 8^

Rather hard, grainy chalk, containing incompletely 

phosphatized internal molds of Cucullaea and other 

mollusks and many shells of Exogyra tigrina 

Stephenson (type locality)_-__-_----___--___-_- 1

Hard chalk containing many shells of a small smooth 

Exogyra related to E. laeviuscula Roemer and other 

larger Exogyras which have not been described; 

this resistant layer forms a bench along the bluff. _ 3

Hard, massive chalk with thinner intervening layers of 

relatively softer chalk; contains widely scattered 

shells of Exogyra ponderosa Roemer_____________ 23

. Hard chalk containing vast numbers of Gryphaea 

aucella Roemer and a few shells of Exogyra laeviuscula Roemer and Exogyra ponderosa; to water's 

edge._______________________________________ 7

79/2

The 7-foot bed of chalk at the base of this section is 

conspicuous for the great number of the small shells of 

Gryphaea aucella Roemer that it contains. This species 

is not confined in its range to this bed but has been 

observed rarely at lower levels in the Austin chalk and 

is common at higher levels, particularly in a thin bed 

15 or 20 feet below the top of the chalk in this section.

The hard chalk 23 to 26 feet above the Gryphaea 

aucella layer, which contains great numbers of a small, 

smooth Exogyra related to E. laeviuscula RoeiQer and 

other medium to large shells of Exogyra, probably 

belonging to two or more species, is resistant enough to 

produce a distinct bench along the bluff. The 1-foot 

layer of glauconitic chalk immediately above the hard 

bed is designated the l 'Exogyra tigrina zone" 7 because of 

the abundance of the shells of this Exogyra, which is 

notable for the preservation of its color markings. 

Although Adkins did not designate this bed as the 

lower limit of his Burditt marl, it is at the base of the 

marly portion of the section and should probably be so 

regarded. The 1-foot bed of chalky marl 8% feet above 

the Exogyra tigrina zone is appropriately called the 

"Ostrea centerensis zone." 8 The holotype and one 

paratype of Ostrea travisana Stephenson 9 were found 

in a chalk layer about 15 feet above the 0. centerensis 

zone and about 10 feet below the top of the Austin 

chalk. Although 0. travisana does not seem to form a 

continuous zone with a uniform distribution of individual shells, the species has been found at several 

more or less widely separated localities near the top 

of the Austin chalk, and for the purposes of this paper 

it is convenient to refer to this part of the section as 

the Ostrea travisana zone.

i Stephenson, L. W., U. S. Nat. Mus. Proc., vol. 76, art. 18, pp. 4, 5, pi. 3, 1929. 

s Idem, pp. 2-4, pis. 1, 2.

s Stephenson, L. W., New Upper Cretaceous Ostreidae from the Gulf region: U. S. 

Geol. Survey Prof. Paper 186-A, pp. 4-5,193C.
STRATIGRAPHIC RELATIONS OF AUSTIN, TAYLOR, AND EQUIVALENT FORMATIONS 135

In a bluff on the right side of Little Walnut Creek, 

three-quarters of a mile downstream from the old 

Sprinkle road crossing, a sample of marly chalk taken 

22 feet above the Ostrea centerensis zone yielded 

characteristic Austin Foraminifera (determined by 

Cushman).

The zones indicated above are important in determining the stratigraphic relation of the Austin chalk 

to the Taylor marl in central Texas, for in places some 

of the zones have been cut out by the erosion recorded 

in the unconformity that separates the two formations, 

allowing the marl to rest on successively lower beds 

of the chalk at least down to the top of the Inoceramus 

undulato-plicatus zone.

As shown beyond, the base of the Taylor marl is 

marked at most places by a bed of strongly phosphatic 

chalk or marl, which at some localities has the characteristics of a thin basal conglomerate and is interpreted 

to indicate an unconformity. The Austin-Taylor 

contact is not clearly exposed in the section on Little 

Walnut Creek at the old Sprinkle road bridge, but 

good exposures are afforded by the banks and bluffs of 

the same creek both above and below the crossing of 

the Austin-Manor road (State Highway 20). The 

section given below is made up from outcrops extending from the bridge downstream for a quarter of a mile. 

The beds dip downstream, so that the lowest beds in 

the section appear under the bridge, and the AustinTaylor contact passes beneath the stream bed about 

0.2 mile below the bridge. The beds are broken here 

and there by minor faults.

Section on Little Walnut Creek from the crossing of the Manor 

road downstream for a quarter of a mile

Feet 

Pleistocene alluvium: Mainly calcareous loam________ 9

Unconformity. 

Taylor marl:

Gray, slightly shaly, relatively soft calcareous clay 

or marl; contains imprints of large Inoceramus and 

Taylor Foraminifera (identified by Cushman) _ _ _ _ 23

Gray argillaceous chalk, slightly nodular, showing 

traces of filled borings and containing scattered 

phosphatic nodules and internal molds of mollusks; this rock is rather tough and much harder 

than the marl above and is not so brittle as typical 

chalk..____________________________________ 1

Unconformity (contact irregular in minor detail). 

Austin chalk: Interbedded layers of medium- to thickbedded hard chalk and thinner, softer marly chalk; an 

upper massive 2-foot layer of chalk is perforated with 

borings filled with material like the matrix of the 

phosphatic bed at the base of the overlying Taylor 

marl.___________________________________________ 14

47

From the Manor road crossing upstream to the old 

Sprinkle road bridge, an air-line distance of 1.8 miles, 

the outcrops along Little Walnut Creek reveal either 

the upper beds of the Austin chalk or the lower beds 

of the Taylor marl, or both. There is a general but

i ''

|\|V

£ -2 S Ti

gentle dip of the beds downstream, but the regularity 

of this monoclinal structure is interrupted by faults, 

mostly of minor displacement, which lo- < 

cally drop the AustinTaylor contact below i 

the level of the creek; 

at a big bend about < 

three-quarters of a 

mile upstream from 

the Manor road < 

bridge, 40 or 50 feet 

of the gray marl of « 

the Taylor appears ; 

above water level in , 

the left bank. At a , 

point about 2,300 feet 

from the Manor road 

bridge the AustinTaylor contact is well g 

exposed a few feet % 

above the creek bed 0| 

on the up thrown side 

of a fault; it is essentially like the contact 

in the section below , 

the bridge.

An exposure in the 

right bank 1,100 feet 

upstream from the 

Manor road bridge on 

the upthrown side of a 

normal fault reveals 

20 feet of massivebedded chalk with 

subordinate interbedded layers ofjfsofter 

marly chalk; this section shows that at 

least the upper 20 feet 

of the Burditt marl of 

Adkins is chalk comparable in all respects 

with the more typical 

chalk of the Austin.

East of Austin the 

width of the belt of 

outcrop of that part 

of the Taylor marl 

which lies between 

the top of the Austin 

chalk and the base of 

the Pecan Gap member is only 2 or 3 miles, 

and its thickness is 

probably less than 300 

feet. In comparison
136 SHOETEE CONTEIBUTIONS TO GENEEAL GEOLOGY, 1936

the width of the belt of outcrop of the lower Taylor, 

including the Wolfe City sand member, east of Waco, 

in McLennan County, exceeds 15 miles, and well logs 

show that its thickness below the Pecan Gap member 

is over 900 feet; the lower Taylor is therefore thinner 

by 600 feet or more in Travis County than it is in 

McLennan County. The thinning of this part of the 

Taylor section was recorded in 1934 in a valuable contribution by Ellisor and Teagle,10 who found that the 

zone carrying a Pecan Gap microfauna progressively 

approaches the top of the Austin chalk from north to 

south and southwest.

SECTIONS ALONG BELT OF OUTCROP TO THE SOUTH 

AND TO THE NORTH OF TRAVIS COUNTY

Vicinity of New Braunfels.—The lower part of the 

Taylor becomes still thinner toward the southwest 

than in Travis County, for at New Braunfels 50 or 

60 feet of chalky marl that was correlated by Ellisor 

and Teagle n with the Pecan Gap chalk is separated 

from the Austin chalk below by 50 feet or less of 

marl.

Before the power dam was constructed on the Guadalupe River just east of New Braunfels, the right bank 

of the river about 400 feet upstream from the International-Great Northern Railroad bridge afforded a 

clean-cut exposure of the Austin-Taylor contact, which 

is now concealed by the impounded water; this is the 

classic "Furt der Guadalupe" of Roemer. The section 

here, as observed in 1911, is described below:

Section on right bank of Guadalupe River 400 feet upstream from 

International-Great Northern Railroad bridge, New Braunfels

Pleistocene terrace deposit: Feet 

Brown pebbly loam___________________________ 10

Irregularly bedded sand and gravel.______________ 6-15

Unconformity. 

Taylor marl:

Dark clay marl______________________________ 0-10

Sandy limestone containing phosphatic nodules___ 0-0. 6 

Unconformity.

Austin chalk: Hard chalky limestone containing Gryphaea 

aucella Roemer (very abundant in layer 4 or 5 feet below top), Exogyra ponderosa Roemer, and other fossils._ 0-13

The beds of the Austin and Taylor in this section 

dip perceptibly to the northwest; they are involved in 

block faulting that has tilted the Upper Cretaceous 

formations in the vicinity of New Braunfels toward a 

major fault of the Balcones fault zone, the scarp of 

which passes in a northeasterly direction just north of 

New Braunfels.

North and west of San Antonio.—Between New 

Braunfels and San Antonio the lower marl of the 

Taylor seems to pinch out entirely, for in the vicinity

i" Ellisor, A. C., and Teagle, John, Correlation of the Pecan Gap chalk in Texas: 

Am. Assoc. Petroleum Geologists Bull., vol. 18, pp. 1506-1536,1934. 

« Idem, pp. 1522-1523.

of San Antonio the Austin chalk is immediately overlain by soft marly chalk which, on the basis of its 

contained Foraminifera, was classed by Ellisor and 

Teagle 12 as Pecan Gap chalk; in the opinion of the 

present writer this chalk, although approximately of 

Pecan Gap age, should be regarded as an eastwardthinning wedge of the Anacacho limestone. A section 

observed in 1933 in the main pit of the cement plant at 

Cementville, 4.7 miles north of the Alamo at San 

Antonio, is described below:

Section in pit of cement plant at Cementville, north of San Antonio

Feet

Anacacho limestone: White brittle marly chalk, glauconitic in the lower 6 inches, with a phdsphatic conglomerate 2 to 3 inches thick at the base; the phosphate 

is in the form of irregular nodules an inch or more in 

maximum length; the chalk contains the imprints of 

Inoceramus, Scaphites, Baculites, Placenticeras?, Parapachydiscus?, Hamites, and other fossils———_________ 45 +

Unconformity (contact sharp and gently undulating). 

Austin chalk: Hard, tough, massive chalk with layers 

containing many shells of Gryphaea aucella Roemer and 

a few of Exogyra laeviuscula Roemer; one 2-foot layer 

full of G. aucella lies 3 feet below the top.___________ 50

The 95 feet of strata described are not seen in one 

continuous vertical section; as observed in 1933, the 

Austin-Anacacho contact was 50 feet above the floor 

of the pit toward the north end of the excavation, where 

the face of the pit was 60 feet high; near the middle of 

the pit the contact was dropped to a level within 15 feet 

of the floor by a normal fault, thus revealing about 45 

feet of Anacacho above the contact; and at the south 

end another normal fault carried the contact below 

the floor.

The Anacacho limestone in the vicinity of San 

Antonio is estimated by A. N. Sayre 13 to be 200 or 250 

feet thick. As indicated in the section at the cement 

plant, the Anacacho rests unconformably on the 

Austin chalk, the unconformity representing a large 

part of the lower Taylor beds. From San Antonio 

westward the Anacacho thickens rapidly in its lower 

part, and the marl becomes interbedded with the more 

typical impure limestones of the formation. The place 

nearest to San Antonio at which the impure limestone 

of the Anacacho was observed is in the bed and banks 

of Leon Creek from about 1.6 to 4 miles upstream from 

the Castroville road crossing.

Hondo and Seco Creeks, Medina County.—In Medina 

County impure limestone becomes the dominant rock 

of the Anacacho, though its full thickness cannot be 

determined from surface outcrops, owing to fault 

displacements. Some good exposures are afforded by 

the bed and banks of Hondo Creek, 2% to 4 miles north 

by west of Hondo. The well-known section at King's

» Ellisor, &.. C., and Teagle, John, op. cit., pp. 1533-1536. 

" Oral col raunication.
STRATIGRAPHIC RELATIONS OP AUSTIN, TAYLOR, AND EQUIVALENT FORMATIONS 137

Water Hole, which Liddle u incorrectly referred to 

the Escondido formation, is a typical example of Anacacho limestone.

The Anacacho in the longitude of D'Hanis is estimated by A. N. Sayre 13 to be 400 feet thick above the 

Austin chalk.

A fine section several hundred yards long in a northward-facing bluff on Seco Creek on the Rothe ranch, 

about 3 miles north of D'Hanis, exposes the upper 

part of the Anacacho and reveals its relation to the 

overlying Escondido formation.

Section on Seco Creek about 3 miles north of D'Hanis, Medina

County

Escondido formation (marl facies): feet

Cream-colored glauconitic sandy marl, irregularly indurated and weathering to a roughened surface but 

showing fairly definite stratification lines________ 30

Light-gray laminated clay and sand with thin interbedded layers of ocherlike clay _________________ 4

Unconformity (sharp contact). 

Anacacho limestone:

Soft to medium-hard sandy marl; contains great 

numbers of Terebratulina cf. T. filosa Conrad, a few 

Diploschiza cretacea minor Stephenson, 15 and a 

few other shells. _____________________________ 1

Relatively hard cream-colored sandy, rather tough 

limestone, which is, however, easily cut with a 

sharp tool; contains scattered tests of the large 

echinoid Echinocorys texana (Cragin) and a few 

shells of Gryphaea mutabilis Morton; to creek bed. 5

Upstream from the place where the preceding section 

was examined a normal fault, with downthrow to the 

north, drops the Anacacho limestone below the stream 

bed; here the beds are in gentle reverse dip upstream. 

Near the fault the lower 25 or 30 feet of the section is 

sandy marl of the Escondido formation, like that in the 

uppermost division in the preceding section, and the 

marl is conformably overlain by 20 feet or more of 

shaly clay, sandy clay, and interbedded hard calcareous 

platy sandstone, typical of the Escondido formation. 

Upstream from this locality the beds continue for some 

distance in reverse dip, beyond which they first flatten 

out and then bend up again to their normal southward 

dip. The Anacacho reappears from beneath the Escondido half a mile or so upstream from the fault and 

is the country rock in a belt 3 miles wide north of the 

Rothe ranch locality; this belt is paralleled on the 

north by the outcrop of the Austin chalk.

Trams County to Falls County.—The faunal zones 

recognized in the upper part of the Austin chalk in 

Travis County (gee pp. 133—136) are all present in the 

section from this county northward as far as Bell 

County, although one or more of them may be locally 

concealed by normal faults, downthrown to the east, 

which have dropped them below the surface. The

13 Oral communication.

" Liddle, R. A., The geology and mineral resources of Medina County: Texas 

Univ. Bull. 1860, pp. 64-C5, 1918.

15 Stephenson, L. W., The genus Diploschiza from the Upper Cretaceous of Alabama and Texas: Jour. Paleontology, vol. 8, pp. 279-280, 1934.

Ostrea travisana zone, the highest of the zones, has not 

been observed farther north than southern Bell County. 

The Ostrea centerensis zone has been observed as far 

north as a point on a small branch 5 miles south of 

Temple. The Ostrea tigrina zone has been traced to 

Little Elm Creek 2.7 miles north-northeast of Temple; 

Foraminifera obtained in this zone at the Little Elm 

Creek locality were identified by J. A. Cushman as 

Austin species.

On a branch of Deer Creek 2 miles southeast of 

Eddy, Falls County, a phosphatic bed (see p. 135), 

believed to be the one at the base of the Taylor marl, 

lies only 5). feet above a hard bed of chalk containing 

many shells of Gryphaea aucella, and this in turn is only 

a few feet above the top of the Gryphaea wratheri zone. 

The phosphate bed is overlain by chalky marl of undetermined thickness, presumably a facies of the Taylor 

marl; this appears to indicate that the phosphate bed, 

which from Travis County to Bell County lies above the 

Ostrea travisana zone, has here descended to a stratigraphic position a little above the Gryphaea wratheri zone.

The phosphate bed was again seen in the right bank 

of a small branch west of the Mooresville road 1.6 

miles east-southeast of Eddy. Here a bed of hard 

Austin chalk containing Gryphaea aucella Roemer 

forms the bed of the branch and is overlain by 8 feet 

of marly thin-bedded chalk having the conglomeratic 

phosphate bed, 1 to 4 inches thick, at its base. An 

absence of Austin species was noted by Cushman in a 

sample taken 2% feet above the base of the phosphate 

bed, and the marly chalk is believed to be basal Taylor 

marl.

Waco and vicinity.—The relation between the Austin 

chalk and overlying chalky marl believed to be the 

base of the Taylor marl in this area is revealed by 

exposures in the banks and valley slopes of several of 

the southeastward-flowing creeks between the southern 

boundary of MeLennan County and Waco. In a 

steep northeastward-facing slope of South Cow Bayou 

Valley, in a road leading to the northeast, 1.4 miles 

northeast of Bruceville, 60 feet of Austin chalk is 

exposed in the road ditches. Near the top of the 

section is a layer containing Gryphaea aucella Roemer, 

and Gryphaea wratheri occurs in considerable numbers 

15 to 30 feet below the G. aucella layer. The lower 

30 feet of the section was not very well exposed at the 

time it was examined.

In going down South Cow Bayou from the crossing 

of the road just mentioned many exposures of Austin 

chalk were observed, and the imprints of Inoceramus 

undulato-plicatus Roemer were noted here and there in 

the chalk; several good imprints of this species were 

seen in the right bank at the mouth of Prather Creek, 

0.2 mile below the bridge. A bluff along the left bank 

about 0.85 mile below the bridge revealed 12 feet of massive chalk containing many shells of Gryphaea wratheri, 

and associated with this species were several large
138 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1936

imprints of Inoceramus undulato-plicatus Koemer. The 

last place at which the Austin chalk was seen was a low 

exposure in the right bank about 1.2 miles below the 

bridge. Here the top of the chalk slopes downstream 

from 3 feet above water level at the upper end of a 

100-foot stretch to water level at its lower end; the 

chalk is overlain by chalky marl, which is concealed by 

vegetation except at its lower end, where 6 inches of 

the marl is sharply separated from the chalk and has 

at its base a thin phosphatic conglomerate. A short 

distance farther downstream characteristic chalky 

marl rises 10 feet above water level in a steep bluff.

The phosphatic bed at the base of the chalky marl, 

resting unconformably upon the much harder Austin 

chalk, was observed at several places in the bed and 

low banks of North Cow Bayou 1.3 to 1.7 miles below 

the crossing of the old U. S. Highway 81. Here the 

chalk is broken by numerous minor faults.

On Bullhide Creek about 0.6 mile below the crossing 

of a public road leading to the northeast, 2% miles 

northeast of Lorena, the following section was examined near the east edge of a fault block tilted to the 

west:

Section on Bullhide Creek 2/i l miles northeast of Lorena, McLennan

County

Feet

Pleistocene terrace deposit: Silty loam with a gravel 

bed at base._____________________________________ 8

Unconformity. 

Taylor marl:

Gray chalky marl, weathering into angular, irregular

fragments._ _________________________________ 10

Conglomerate composed of many phosphatic nodules 

and internal molds of mollusks and containing a 

few shells of Gryphaea wratheri mechanically included from the underlying chalk_______________ %-%

Unconformity (contact sharp).

Austin chalk: Hard massive-bedded chalk containing

shells of Gryphaea wratheri- ________________________ 1-5

On account of the westward dip the Austin-Taylor 

contact rises downstream, and within a few hundred 

feet 10 feet of chalk is exposed above water level; 

imprints of Inoceramus undulato-plicatus Koemer were 

seen in the lower part of the chalk exposure. A short 

distance still farther downstream, at the eastern edge 

of the fault block, the chalky marl has been brought 

down against the Austin chalk. About 0.4 mile upstream from the place where the preceding section was 

observed the west edge of the fault block is marked 

by a major fault, which brings the chalky marl down 

against the Austin chalk.

Adkins 16 has suggested that the chalky marl just 

described may represent his Burditt marl; opposed to 

this suggestion is the fact that none of the characteristic macrofossils of his Burditt have been found in the 

marl, although the conditions appear to have been 

favorable for their existence, and the field relations

16 Adkins, W. S., The geology of Texas, pt. 2, The Mesozoic systems in Texas: 

Texas Univ. Bull. 3232, pp. 449-451, 1933.

suggest that the phosphate bed is the northward continuation of the one at the base of the Tayior on Little 

Walnut Creek, in Travis County. Confirmatory evidence is afforded by Foraminifera obtained near the 

base of the chalky marl 1}_ miles southwest of Lorena, 

which were identified by J. A. Cushman as of Taylor 

age. Cushman also identified Taylor Foraminifera 

from a sample taken in the upper part of the chalky 

marl in a road ditch on the northward-facing slope of 

Bullhide Creek, 5% miles east by south of Lorena.

On North Flat Creek 5 miles south of Waco the 

phosphate bed has descended still lower and rests 

directly upon the Inoceramus undulato-plicatus zone 

with an abundance of the imprints of this characteristic 

species. The best exposure noted was in a low bank 

of the creek, 1,500 feet upstream from the crossing of 

the new U. S. Highway 81. Cushman noted an 

absence of characteristic Austin species in a sample of 

chalky marl taken 2 feet above the phosphate bed, and 

Austin species were wanting in a similar sample of 

chalky marl taken 350 feet downstream from the highway bridge.

McLennan County to Dallas County.—Northwest of 

Elm Mott, in McLennan County, the Austin chalk is 

completely cut out by a major normal fault, trending 

north-northeast, that drops the Taylor marl against 

the Eagle Ford shale; toward the north the throw of 

this fault decreases, and the chalk reappears on the 

upthrown side of the displacement. The first place 

north of McLennan County at which the AustinTaylor contact was observed is on a small branch, 2}_ 

miles east-southeast of Bynum, Hill County; here the 

two formations are separated by an obvious unconformity marked by a thin phosphatic layer at the base, 

but the zonal position of the top of the chalk was not 

determined. Good exposures of a conglomeratic phosphate bed were observed at the base of the Taylor 

at several localities between Bynum and the northern 

part of Ellis County; the one farthest north is on 

Bear Creek, 6}_ miles east-northeast of Sterrett. Inasmuch as the Gryphaea wratheri zone is exposed to its 

maximum observed thickness of 35 feet at a point 1 

mile north of Sterrett, 5.7 miles west by south of the 

Bear Creek locality, it appears that the phosphatic 

bed rises stratigraphically toward the north.

Dallas and vicinity.—In Dallas County the' Inoceramus undulato-plicatus zone of the Austin chalk is well 

exposed just below the dam of White Rock Lake, at the 

northeastern outskirts of Dallas, and the overlying 

Cfryphaea wratheri zone may be seen in a cut on Gaston 

Avenue near the intersection of West Shore Drive, less 

than a mile west of the dam. From 40 to 50 feet of 

shaly chalk with several interbedded harder, more 

chalky layers is exposed in gullies in the northwardfacing slope and in the banks of a small branch draining into White Rock Lake 1.6 miles northeast of the 

dam; the section is stratigraphically somewhat higher
STRATIGKAPHIC RELATIONS OP AUSTIN, TAYLOR, AND EQUIVALENT FORMATIONS 139

than the Inoceramus undulato-plicatus zone at the dam. 

The presence of the Qryphaea wratheri zone is indicated 

by a few shells of that species in the banks of the branch 

low in the section, and Qryphaea aucella occurs in 

abundance in a 1-foot layer 20 or 25 feet higher in the section, about 20 feet below the level of U. S. Highway 67.

The Austin-Taylor contact is fully 4 miles east of 

the Gaston Avenue locality and must be at a considerably higher stratigraphic position than the Gryphaea 

wratheri zone—perhaps as much as 200 or 250 feet. 

The upper 50 or 60 feet of the Austin in Dallas County 

consists of interbedded layers of chalk, marly chalk, 

and chalky marl.

No phosphatic material was observed at the AustinTaylor contact in Dallas County, but the contact is 

marked by a bed of limestone ranging in thickness 

from less than 1 inch to 6 inches, which lies at the base 

of the Taylor; this limestone is granular in texture and 

contains scattered shells of Diploschiza n. sp. and fragments of the shells of Inoceramus and ostreids. Although at most places this limestone is nearly parallel 

to. the bedding of the underlying chalk, at one locality 

on Prairie Creek, 1,000 feet upstream from an eastwest road, IK miles northeast of Pleasant Grove, a 

marked angular discordance was observed between 

the limestone and the chalk; in a horizontal distance of 

100 feet the limestone bed rises from a stratigraphic 

position 2 feet above a traceable layer of chalk to 9 feet 

above it, thus apparently indicating an unconformity. 

Localities in Dallas County, in addition to the one on 

Prairie Creek, at which this limestone with its characteristic Diploschiza shells have been observed are in a gully 

on the bank of Cottonwood Creek, 200 feet east of the 

Southern Pacific Kailroad bridge north of Wilmer; on a 

branch of Prairie Creek just above a public-road bridge 

1.15 miles east of Pleasant Grove; and at the heads of 

gullies in the northward-facing slope of a small branch 

of Kowlett Creek, south of U. S. Highway 67, 1.3 miles 

east of the public square at Garland.

The sediments immediately above the thin limestone 

consist of soft gray marl weathering yellow, typical oi 

the Taylor and lacking chalky layers. The limestone 

is interpreted to be the basal bed of the Taylor marl, 

resting with unconformable relations upon the Austin 

chalk, and this conclusion is supported by the microfaunal evidence; on the authority of J. A. Cushman, a 

sample taken 1 foot below the limestone contained 

Austin Foraminifera, and one taken 1 foot above the 

limestone yielded Taylor Foraminifera.

Collin County.—North of Dallas County the first 

place at which the exact contact between the Austin 

chalk and Taylor marl was seen was in a crooked eastwest second-class road 0.85 mile east of Lucas and 6.2 

miles east by south of Alien, Collin County. The 

ditch at the side of the road exposed about 1 foot of the 

chalk, overlain by 2 or 3 feet of soft yellowish marl;

78739—37——2

the contact is sharp, and a few phosphatic nodules are 

present along the base of the marl. In a chalk quarry 

just south of State Highway 24, 3 miles east of McKinney, Collin County, shells of Gryphaea aucella Roemer 

occur in abundance in a layer 10 feet above the bed of 

the quarry; as the Austin-Taylor contact, though not 

well exposed, is 2 miles east of this quarry, the regional 

eastward dip of the beds would indicate that the shell 

bed is stratigraphically considerably below the top of 

the chalk—perhaps as much as 100 or 150 feet.

A good exposure of the Austin-Taylor contact is 

afforded by a small quarry just south of an east-west 

road 2.9 miles north by west of Blue Ridge, Collin 

County. The contact is marked by a well-developed 

phosphatic layer, with many of the usual nodules and 

internal molds of mollusks, among which Baculites is 

conspicuous. The stratigraphic position of the top of 

the chalk in the quarry could not be directly determined, but the field relations suggest a high position 

with respect to the faunal zones of the upper part of 

the Austin.

Grayson, Fannin, and Lamar Counties.—The next 

place at which the chalk and the overlying Taylor marl 

were seen in a good exposure was in a small wash in 

the westward-facing slope of a creek valley 0.55 mile 

south of State Highway 78 and 5.8 miles west by south 

of Leonard, Fannin County. Here the contact is sharp 

and lies 20 feet above the creek bed; it is marked by a 

thin line of phosphatic nodules and internal molds of 

mollusks.

A section having a significant bearing on the relation 

of the Gober tongue of the Austin chalk to the main 

body of the Austin is exposed in a low bluff on the 

right side of an eastward-flowing headwater branch of 

Bois d'Arc Creek, 150 feet upstream from the crossing 

of U. S. Highway 69 and 0.7 mile northwest of the 

business center of Whitewright, in eastern Grayson 

County. The section is as follows:

Section 0.7 mile northwest of Whitewright, Grayson County

Austin chalk: Feet 

Marly chalk, breaking in irregular fragments; contains

Foraminifera of Austin age (identified by J. A.

Cushman) ________________________— ___ —— __ 10

Bentonite containing a sprinkling of fine biotite ruica_ 3 

Hard, massive, brittle chalk containing a few large

imprints of Inoceramus undulato-plicatus Roemer

and Foraminifera of Austin age (identified by J. A.

Cushman)______-___-___-____---______--______ 1-2

15

This locality is 11 miles north by west of the place 

west of Leonard, described above, at which the contact 

of the chalk with the overlying Taylor marl was seen. 

The area between the Whitewright and Leonard localities appears to be continuously underlain by chalk, as 

shown by many outcrops along roads and in stream
140 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1936

banks. The chalk in this area may be regarded as the 

root of the Gober tongue. If the southward dip of the 

strata amounts to as much as 50 feet to the mile, the 

thickness of the chalk in the interval of 11 miles would 

be 500 feet or more. If the conservative figure of 40 

feet to the mile is assumed, the thickness would be at 

least 400 feet. The evidence therefore appears to 

indicate that the Austin-Taylor contact rises stratigraphically from a position immediately above the 

Inoceramus undulato-plicatus zone in McLennan 

County, south of Waco, to a position at least 400 feet 

above that zone in Fannin County, west of Leonard.

North and northeast of Whitewright the lower beds 

of the Austin chalk merge eastward along the strike 

into the facies unit to which the name "Bonham clay" 

has been given. In east-central Fannin County the 

upper part of the Bonham merges eastward into the 

Blossom sand and perhaps also into the lower part of 

the overlying Brownstown marl; however, the stratigraphic relations of the formations in this area have 

not been determined in detail.

From the Whitewright-Leonard area the belt of 

outcrop of the Gober tongue of the Austin chalk extends 

first northeastward and then eastward through Fannin 

and Lamar Counties; the tongue becomes progressively 

thinner in that direction and finally pinches out, as 

such, a little less than 4 miles northeast of Pattonville, 

before reaching the Red River County line. As the 

upper part of the Gober, which consists of 10 feet or 

less of cream-colored tough, .soft chalk or limestone, 

suitable for building stone, has been traced continuously from the vicinity of Bailey, in Fannin County, 

to the eastern terminus of this tongue, it appears that 

the top of the tongue is at one stratigraphic position 

throughout this distance; the tongue thins therefore 

at the expense of its lower portion, successively higher 

beds of which probably merge toward the east into the 

Brownstown marl facies.

A foraminiferal sample taken in an eastward-facing 

slope in a public road just east of its junction with 

U. S. Highway 69, 1 mile east of Trenton, Fannin 

County, was determined by J. A Cushman to contain 

an Austin fauna; this locality is estimated to be approximately in the middle of the Gober tongue as it is 

developed in this area. Another sample of chalk 

taken near the top of the Gober tongue in a small 

branch about a quarter of a mile southeast of Bailey, 

Fannin County, yielded Foraminifera which Cushman 

referred to the Austin.

The top of the Gober tongue crops out on State 

Highway 24, 4.3 miles south of the Texas & Pacific 

Railway at Paris, and the width of the belt of outcrop 

of tnis tongue along the highway is only about 1J£ 

miles. Between this belt and the railroad at Pa.ris 

the country is underlain by Brownstown marl. In a 

small creek at the southwest edge of Paris shells of 

Ostrea travisana are present in a phosphatic, glauconitic

marl that forms the base of the Brownstown. At a 

southward dip of 50 feet to the mile, the thickness 

of the strata between the base of the Brownstown 

marl and the top of the Gober tongue more than 4 

miles to the south would be at least 200 feet. If 

Ostrea travisana is a reliable index fossil marking the 

upper part of the Austin chalk in central Texas, as 

it is believed to be, its presence in the base of the 

Brownstown marl near Paris indicates that the containing bed there corresponds to the uppermost part 

of the Austin chalk in Travis County. It follows, 

therefore, that in Fannin and Lamar Counties the 

top of the Gober tongue lies stratigraphically 200 feet 

or more higher than the top of the typical Austin 

chalk in Travis County. The Gober tongue at its thick 

end in southwestern Fannin County would necessarily include representatives of the Burditt marl of 

Adkins.

To return to consideration of the contact between 

the Austin chalk (Gober tongue) and the Taylor marl, 

examination of a large quarry in the building-stone 

facies at the northwestern edge of the village of Gober 

showed that this rock is overlain by several feet of 

typical Taylor marl, and the sharp contact between the 

Gober and the Taylor is marked by a thin line of 

phosphatic nodules and internal molds of mollusks. 

No attempt was made to determine the presence or 

absence of phosphate at the top of the Gober tongue 

between Gober and eastern Lamar County, but at a 

small quarry a quarter of a mile west of a north-south 

road 3 miles north of Pattonville (pi. 44), phosphatic 

material of the usual type was observed in great 

abundance at the top of the Gober tongue. This 

locality is near the eastern tip of the Gober tongue, 

for within the next 3 or 4 miles to the east the chalk 

disappears as such and is replaced by marl.

The phosphatic bed seen at the locality last mentioned does not come to an end with the pinching out 

of the chalk but continues eastward and was seen well 

developed in fields on each side of a north-south road 

about 4 miles northeast of Pattonville and 1% miles 

west of the Red River County line. The phosphate 

bed crops out in shallow gullies about 25 feet below 

the crest of the hill. It is only a few inches thick but 

contains many of the typical nodules and internal 

molds of mollusks in a matrix of slightly glauconitic 

marl; these weather out in the soil in great numbers. 

Here the bed is not underlain by chalk but by clay 

marl, which is interpreted to be the upper part of the 

Brownstown marl. The phosphate bed is immediately 

overlain by several feet of slightly sandy marl containing numerous thin flakes of fine sandy limestone of 

varying sizes, one-eighth to one-fourth inch thick and 

having a maximum length of about 3 inches; as shown 

below, these flakes are useful markers in identifying 

this phosphate bed at other localities farther to the 

east in Red River County.
STRATIGRAPHIC RELATIONS OF AUSTIN, TAYLOR, AND EQUIVALENT FORMATIONS 141

Chalks and marls in Red River County.—About 11 

miles east of the locality just described the continuation of the phosphatic bed was observed intersecting 

U. S. Highway 82, 1.8 miles south-southeast of Bagwell, Red River County. The bed is poorly exposed 

in the road ditch, is only a few inches thick, and has a 

matrix of glauconitic marl; it can be traced along the 

slopes in the adjoining fields by the great abundance of 

phosphatic nodules and molds of mollusks, which 

weather out in the soil and are scattered down the 

slope from the outcrop. Here, as at the locality last 

described, the marl within a few feet above the phosphate bed contains thin laminae of sandy limestone, 

the flaky fragments of which weather out in the soil 

in profusion. About 20 feet of gray marl (Brownstown) is exposed in the gullies below the phosphate 

bed; a sample of marl taken 20 feet below the phosphate bed yielded Foraminifera of Austin age, as 

determined by Cushman. Above the phosphate bed 

30 feet of Taylor marl, poorly exposed, makes up the 

slope to the crest of the hill. Exposures of chalky 

marl are afforded by ditches along the highway 2% to 

3 miles south-southeast of Bagwell; Cushman determined a sample of this marl, taken 2.8 miles from 

Bagwell, to be of lower Taylor age.

The next observed exposure of the phosphate bed to 

the east is near the crest of a northward-facing slope 

on the road leading north by east from Clarksville, 

at a point 1 mile south of Vandalia. The phosphate 

bed is at the base of the chalky marl that weathers 

white, about 10 feet lower than the crest of the hill. 

The phosphatic materials occur in a matrix of glauconitic marl, and here again flakes of a sandy limestone 

occur in the chalky marl immediately above the phosphatic layer. .

The phosphatic bed intersects the road to Reed's 

store IK miles north of White Rock, 0.8 mile north 

of a small cemetery, and about 8% miles northeast of 

Clarksville; the bed may also be seen poorly exposed 

in the northward-facing slopes within half a mile east 

of the road. Here the phosphatic nodules and molds 

are abundant and characteristic. Particular interest 

attaches to this locality because here the phosphatic 

bed lies at the base of the thick body of chalk that 

forms numerous bald spots in the White Rock neighborhood, whereas at all the other localities examined 

west of White Rock in Red River and Lamar Counties 

the material overlying the phosphate bed is either 

chalky marl or marl. As confirmatory evidence that 

this is the eastward continuation of the phosphate 

bed observed at the other localities described above, 

one rather poor exposure about 1,000 feet east of tl^e 

road to Reed's store revealed the presence of the telltale flakes of sandy limestone in the chalk within a 

few feet above the phosphate bed.

As the phosphate bed that lies at the base of the 

chalk north of White Rock continues westward through

Red River County into Lamar County, where it lies 

at the base of the Taylor marl, resting upon the Gober 

chalk, it follows that the chalk at White Rock corresponds in age to the lower part of the Taylor marl, 

which, in Lamar and Fannin Counties, overlies the 

Gober tongue; in other words, the chalk may be looked 

upon as a facies that merges westward through marly 

chalk and chalky marl into the nonchalky Taylor 

marl. This conclusion is not in harmony with the 

interpretation of Ellisor and Teagle 17 that the Annona 

chalk in Red River County, including the chalk at 

White Rock, should be classed as Pecan Gap chalk, 

which at its type locality, in northwestern Delta County, 

is only 40 or 50 feet thick and lies stratigraphically some 

400 or 500 feet higher than the top of the Gober chalk.

STRATIGRAPHIC RELATIONS IN RED RIVER AND 

LAMAR COUNTIES

The correlations presented in this paper seem to 

accord with the known facts as expressed in the accompanying geologic map (pi. 44). Hill 18 as early as 1901 

recognized the fact that the Annona chalk in Red 

River County is younger than the Austin chalk, and 

he correctly correlated the Annona with the chalk 

at White Cliffs on the Little River, in southwestern 

Arkansas.

The Pecan Gap chalk member of the Taylor marl 

at its type locality, in Delta County, is 50 feet or less 

in thickness. The chalk enters Lamar County from 

Delta County in the valley of the South Fork of the 

Sulphur River, 12 miles south of Paris, where, at the 

crossing of State Highway 24, its belt of outcrop is so 

narrow that it is completely concealed by the alluvium 

of the river; its width can scarcely be more than half 

a mile. The chalk continues as a thin, sharply defined 

unit in a general east-northeasterly direction through 

Lamar County past Deport and into Red River County 

in the direction of Clarksville; it maintains a narrow 

width of outcrop, less than half a mile to perhaps a 

mile, at least as far as McCoy Creek, 5 miles westsouthwest of Clarksville; between McCoy Creek and 

Clarksville the Pecan Gap chalk passes into and forms 

the upper part of the Annona chalk. (See pi. 44.)

The Wolfe City sand member of the Taylor marl, 

which at its type locality, in Hunt County, is 100 feet 

or less in thickness, underlies the Pecan Gap chalk and 

extends eastward beneath the chalk into southeastern 

Lamar County, where it appears to merge into marl. 

The Wolfe City sand at its type locality is underlain 

by an estimated thickness of 400 feet or more of 

Taylor marl, which in turn rests upon the Gober 

tongue of the Austin chalk. This marl section thins 

somewhat as it passes eastward through Lamar County

" Ellisor, A. C., and Teagle, John, Correlation of the Pecan Gap chalk in Texas: 

Am. Assoc. Petroleum Geologists Bull., vol. 18, pp. 1506-1536, 1934.

"Hill, R. T., Geography and geology of the Black and Grand Prairies, Tex.: 

U. S. Geol. Survey 21st Ann. Eept., pt. 7, p. 340,1901.
142 SHOETEE CONTRIBUTIONS TO GENEEAL GEOLOGY, 1936

into Red River County, where it merges into the 

Annona chalk.

The width of the belt of outcrop of the Annona chalk 

east of Clarksville in the longitude of White Rock is 4 

miles. The thickness of this chalk has not been accurately determined but is estimated to be 300 or 400 

feet. The facts given in the foregoing text and the 

field relations as expressed in plate 44 indicate that the 

Annona as a whole in the longitude of White Rock is 

the age equivalent of the combined Taylor marl (lower), 

Wolfe City sand member, and Pecan Gap chalk member in Lamar, Delta, and Fannin Counties.

A phosphatic bed at the base of the Pecan Gap chalk 

at Pecan Gap is interpreted by Ellisor and Teagle as 

marking an unconformity of considerable importance. 

This bed is present at the base of the chalk through 

southeastern Lamar County into Red River County, 

and they assume that it continues to the northeast past 

Clarksville and is continuous with the phosphate bed 

at the base of the Annona chalk north of White Rock. 

A necessary corollary of this interpretation is that the 

unconformity cuts out the lower beds of the Taylor 

marl and the Wolfe City sand member, which, in the 

longitude of western Delta County, intervene between 

the Gober tongue and the Pecan Gap chalk. As shown 

on preceding pages, the phosphate bed at the base of 

the Annona is not continuous with the one at the base 

of the Pecan Gap but extends with a more nearly westward strike across Red River County into Lamar 

County, where it is continuous with a phosphate bed 

at the base of the Taylor marl, resting on the Gober 

chalk; in Lamar County this phosphate bed is 400 or 500 

feet stratigraphically lower than the one at the base of 

the Pecan Gap chalk.

Ellisor and Teagle divide the Annona chalk (their 

Pecan Gap chalk) of northeastern Texas into three 

faunal zones—in ascending order, the Flabellamina 

compressa zone, the Diploschiza cretacea zone, and the 

Bolivina incrassata zone. Foraminifera identified from 

these zones are tabulated on pages 1529-1532 of their 

paper. They recognize all three of the zones in the 

Annona chalk of eastern Red River County. They 

also recognize the three zones at different places within 

the limits of the narrow belt of chalk (true Pecan Gap 

chalk of the present writer) that extends from Pecan 

Gap, Delta County, to McCoy Creek, 5 miles west of 

Clarksville, in Red River County (pi. 44). The species 

listed in the table total 106; of these, 64 range through 

all three zones, 26 range through the Flabellamina compressa and Diploschiza cretacea zones, and 6 range 

through the Diploschiza cretacea and Bolivina incrassata 

zones. One species is restricted to the Flabellamina 

compressa zone, 6 species are restricted to the Diploschiza cretacea zone, and 2 species are restricted to the 

Bolivina incrassata zone. Flabellamina compressa 

ranges through all three zones. Bolivina incrassata is 

restricted to the zone that bears its name and is said to

occur in abundance in that zone. No information is 

given as to the range of the species in the sediments 

older and younger than the three zones.

The foregoing analysis does not disclose wholly convincing evidence of the distinctiveness of the three 

faunal zones recognized. Such faunal differences as 

may appear among samples from different localities in 

any series of closely related sediments may perhaps be 

accounted for by facies differences in the sediments, or 

by other environmental differences, rather than by 

differences in the time of sedimentation. Conversely, 

the recurrence of similar faunal assemblages in beds of 

different ages, as shown by the field relations, may perhaps reasonably be ascribed to the recurrence of similar favorable environmental conditions in the later 

beds.

The individual beds of chalk and chalky marl that 

compose the Annona chalk east, northeast, and north 

of Clarksville are not readily traceable across the 

county, but the phosphate bed at the base of the Annona can be easily recognized, not only in good exposures but in the intervening fields, where the resistant 

phosphatic nodules and internal molds of mollusks 

weather out in the soil in great numbers. The distribution of this bed across Red River County north of 

the latitude of Clarksville, as shqwn in plate 44, determines the general strike of the beds to be 7° or 8° 

north of east. If it were true that this bed is continuous with the similar bed at the base of the Pecan 

Gap chalk, the strike of the beds above the phosphatic 

layer should be at least 25° north of east. The map 

accompanying the paper by Ellisor and Teagle (their 

fig. 1, p. 1516) is on too small a scale and is too much 

generalized to indicate the direction of strike accurately.

Confirmation of the strike of the Cretaceous beds in 

Red River County north of the latitude of Clarksville, 

as determined by the trace of the phosphate bed at 

the base of the Annona chalk, is afforded by two other 

easily traceable beds stratigraphically lower than the 

Annona. Another phosphatic bed, at the base of the 

Brownstown marl, has an east-west zone of outcrop 

across both Red River and Lamar Counties, and a few 

feet below it, in the Blossom sand, a bed marked by 

hard glauconitic, calcareous concretions is known to 

extend nearly across Red River County; the latter bed 

is here designated the Ostrea elegantula zone 19 on 

account of the abundance of the shells of this oyster 

in the concretions. Localities where one or both of 

these beds have been examined are described below.

On the road to Reed's store 1.5 to 1.9 miles north 

of the store at White Rock the Brownstown marl is 

poorly exposed below the Annona chalk in the northward-facing slope of Pecan Bayou Valley. Near the 

foot of the slope 2 miles north of the store 10 feet of 

glauconitic sand formmg the upper part of the Blossom

i« Stephenson, L. W., New Upper Cretaceous Ostreidae from the Gulf region: 

U. S. Oeol. Survey Prof. Paper 186-A, pp. 2, 6-8,1936.
STRATIGRAPHIC RELATIONS OF AUSTIN, TAYLOR, AND EQUIVALENT FORMATIONS 143

sand is well exposed in a cut and ditch on the east side 

of the road; the Blossom-Brownstown contact is not 

exposed, but it is estimated to be about 75 feet vertically lower than the phosphate bed at the base of the 

Annona. In the sand are hard, concretionary sandstones containing many shells of Ostrea elegantula 

White, a few individuals of Placenticeras sp., and a few 

other fossils. The oyster is known in northeastern 

Texas only at this and the few other localities described 

below and is believed to be restricted in its vertical 

range to a very narrow zone.

In a small draw in a field west of the ClarksvilleVandalia road 0.4 mile south of Vandalia fossiliferous 

concretions like those at the locality just described 

weather out in the soil. They contain many shells of 

Ostrea elegantula and a few shells of Inoceramus sp., 

Aphrodina sp. (large), and other fossils. About 0.15 

mile south of this point a few phosphatic internal 

molds of mollusks were found weathered out in the 

soil in the road ditch; these came from the phosphatic 

bed marking, the base of the Brownstown marl.

Imprints of Ostrea elegantula were obtained from 

weathered ferruginous, glauconitic sandstone in a 

small earthen tank east of the Dimple road, toward 

the foot of the northward-facing slope of a branch valley 

of Tanyard Bayou 4.2 miles north by west of the public 

square at Clarksville. The phosphatic bed at the 

base of the Brownstown marl was observed poorly 

exposed in a small headwater branch about threequarters of a mile southwest of the tank locality.

The base of the Brownstown marl with its characteristic phosphatic materials is poorly exposed in a publicroad ditch half a mile west of the Cherry settlement, 

about 5 miles northwest of Clarksville.

Glauconitic, phosphatic marl marking the base of the 

Brownstown marl is exposed in the ditch of the old 

Clarksville road 2.2 miles east-southeast of Detroit. 

A few specimens of Ostrea elegantula were obtained 

from an indurated layer in the Blossom sand about 

3 feet below the phosphatic bed.

An exposure of the Blossom-Brownstown contact is 

afforded by a ravine just east of the old Clarksville 

road 1.4 miles southeast of Detroit. The section 

consists of about 15 feet of glauconitic sand overlain 

by 10 feet of marl; the sand-marl contact is marked by 

a thin bed of phosphatic nodules and molds of the usual 

character. A concretionary sandstone about 3 feet 

below the contact contains shells of Exogyra ponderosa 

Roemer and internal molds of a very large nautiloid 

of the genus Eutrephoceras. One shell of Ostrea 

elegantula was found in the sand about 6 feet below 

the contact, and several loose pieces of concretionary 

sandstone in the ravine at the base of the section, 

which had fallen from above, contained great numbers of 

this small oyster in a fairly good state of preservation.

Phosphatic materials weathered from the base of 

the Brownstown marl immediately above the Blossom

sand were observed along the old Paris-Clarksville 

road south of the Texas & Pacific Railway at three 

places within a stretch 1% to 3% miles west by south 

of Blossom, Lamar County.

Glauconitic, phosphatic marl at the base of the 

Brownstown marl is poorly exposed beneath an alluvial 

covering at several places along a small creek in the 

southwestern outskirts of Paris, about a quarter of a 

mile southeast of the crossing of the Texas & Pacific 

Railway and Texas & New Orleans Railroad. This 

bed is believed to correspond approximately in stratigraphic position to the top of the Austin chalk in 

Travis County, as indicated by the presence of shells 

of Ostrea travisana. (See p. 138.) In this connection 

it is worthy of note that the shells of Oryphaea aucella 

Roemer are present in marl exposed along U. S. Highway 271 at two places, 4% and 7 miles north of the 

public square at Paris; each of these localities also 

yielded Foraminifera determined by Cushman to be 

of Austin age. The paleontologic evidence indicates 

that the beds cropping out in an east-west belt 7 or 

8 miles wide, having its southern boundary just south 

of Paris, correspond in age to the upper part of the 

typical Austin chalk in Travis County. From north 

to south this belt includes the upper part of the 

Bonham clay, consisting in part of marl and in 

part of clay and sandy clay; the Blossom sand, which 

forms a sandy belt about 2 miles wide in the vicinity 

of Paris; and the lowermost part of the Brownstown 

marl.

SECTION IN RED RIVER COUNTY COMPARED WITH 

THAT IN SOUTHWESTERN ARKANSAS

From Red River County, Tex., the Annona chalk is 

traceable eastward through Bowie County into Arkansas, past Rocky Comfort, Little River County, to 

White Cliffs, Sevier County. According to Ellisor 

and Teagle,20 the massive white chalk that forms the 

upper 60 feet of the section at White Cliffs comprises 

the upper one of the three faunal zones into which 

they divide the Pecan Gap chalk; they consider that 

near Clarksville, Tex., this upper zone is completely 

cut out by the unconformity which there separates the 

Annona chalk from the overlying Taylor marl (upper). 

Although a phosphatic conglomerate containing also a 

few water-worn novaculite pebbles is present at the 

base of this marl near Clarksville and is believed to 

mark an unconformity, it remains to be established 

that the upper 60 feet of the White Cliffs section is 

completely unrepresented in the Clarksville area; the 

occurrence of the large echinoid Echinocorys texana 

(Cragin) both in the upper part of the chalk near 

Clarksville and in the upper 60 feet of massive chalk 

at White Cliffs suggests approximate age equivalency 

of the containing beds, for this species is supposedly

2° Ellisor, A. C., and Teagle, John, Correlation of the Pecan Gap chalk in Texas: 

Am. Assoc. Petroleum Geologists Bull., vol. 18, pp. 1609-33,1934.
144 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1936

restricted to a narrow vertical range. Dane 21 refers 

the lower 50 feet of the section at White Cliffs to the 

upper part of his Ozan formation, and it appears that 

the Ozan as a whole is a sandy facies corresponding 

to the middle and lower parts of the Annona in Red 

River County. The correlation of the unconformity 

that Dane 22 recognized at the base of the Ozan formation with the unconformity marked by the phosphatic 

bed at the base of the Annona chalk in Red River 

County is probably correct.

The ostreid species Gryphaea vesicularis Lamarck 

(var.) is frequently mentioned by Ellisor and Teagle 

as present in the Diploschiza cretacea zone (the middle 

one of their three Pecan Gap zones). Most of the 

shells of this genus in this zone should more properly 

be referred to Gryphaea convexa (Say); examples of 

the species are illustrated in Dane's Arkansas report 23 

under the name ''Gryphaea sp." Although this species 

is common at about the horizon of the Diploschiza 

cretacea zone, it is known to have considerable vertical 

range in beds of lower Taylor age and is hardly a safe 

index fossil in close correlation; its abundance at any 

given locality may be due to favorable local environmental conditions.

The beds in northeastern Texas to which the name 

"Brownstown marl" has been applied appear to be 

correctly correlated with the typical Brownstown marl 

of southwestern Arkansas. Israelsky 24 has correlated 

the latter with the Bonham clay of Texas, but he does 

not state where he obtained his sample or samples of 

Bonham clay. As shown in figure 7, the Blossom 

sand appears to merge westward in Fannin County 

into less sandy or nonsandy clay or marl; the body of 

clay in the vicinity of Bonham, to which the name 

"Bonham" has been given, probably includes representatives of the Blossom and perhaps also the Brownstown marl. A sample collected a mile or two south of 

Bonham might very well yield a Brownstown microfauna, whereas a sample collected in the beds mapped 

as Bonham north of Paris, Lamar County, would be 

stratigraphically lower than the typical Brownstown 

and presumably would be of Tokio age. As interpreted in the present paper the main body of the 

Brownstown marl merges westward into the Gober 

tongue of the Austin chalk (fig. 7), the upper part of 

"which is younger than the youngest beds of the typical 

Austin chalk in Travis County.

TEXAS AND ALABAMA SECTIONS COMPARED

The down-warped Mississippi embayment, which 

dates from early Upper Cretaceous time, has produced 

a wide geographic gap between the outcrops of the

21 Dane, C. H., Upper Cretaceous formations of southwest Arkansas: Arkansas 

Geol. Survey Bull. 1, pp. 58-79,1929.

22 Idem, p. 76 and fig. 3, p. 81.

23 Idem, pi. 11, fig. 2, and pi. 12, figs. 3, 4.

24 Israelsky, M. C., Correlation of the Brownstown (restricted) formation of 

Arkansas: Am. Assoc. Petroleum Geologists Bull., vol. 13, pp. 683-684, 1929. See 

also Stephenson, L. W., idem, pp. 1073-1074.

Upper Cretaceous sediments of Texas and Arkansas 

on the one hand and those of Mississippi and Alabama 

on the other. The differences in the successions of 

sediments making up the sections in the two areas 

and the paucity of fossils of sufficiently restricted 

vertical range to serve as index markers have rendered 

the exact correlation of the sections somewhat difficult.

Fossil floras from the Woodbine sand of Texas and 

from the Tuscaloosa formation of Alabama, studied 

by Berry,25 have been correlated with each other, 

with the Raritan formation of Maryland and New 

Jersey, and with the Cenomanian of Europe. The 

Eagle Ford shale (Turonian) of Texas, which is last 

seen in Lamar County, in the northeastern part of 

the State, has not been recognized at the surface east 

of the Mississippi River and is believed to be represented in an unconformity that is now known to 

separate the Tuscaloosa from the Eutaw formation 

entirely across Alabama. There is a paucity of fossils 

in the lower and middle parts of the Eutaw formation, 

but the few that have been found suggest an age 

younger than that of the Eagle Ford shale.

The Tombigbee sand member, which forms the 

upper part of the Eutaw formation (see fig. 7), is fossiliferous in its upper part. Some of the fossils are 

not known outside of the eastern Gulf region; some 

have not been critically studied, and their meaning 

in long-distance correlation is not well known; a few 

have value as time markers, but it happens that 

these few are more useful in correlating the containing 

beds with sections in distant areas than with the 

Texas section. For example, the free-floating crinokl 

Marsupites americanus Springer, found in the Tombigbee sand at Plymouth Bluff, on the Tombigbee 

River in Mississippi, has a close analog in M. testudinarius Schlotheim, in the upper Santonian of Europe, 

and Marsupites sp. is present in the Telegraph Creek 

formation of Montana, which immediately overlies 

beds of Niobrara age. The ammonite genus Texanites (Mortoniceras of authors) is represented in the 

Tombigbee sand by species related to Texanites delawarense (Morton) from the Merchantville clay of New 

Jersey. Ammonites of this group have a considerable 

range in Texas from beds of uppermost Austin age 

up into about the lower one-fourth of the Taylor 

marl and beds of lower Taylor age, and the group is 

represented in the Eagle sandstone of Montana, which 

immediately overlies the Telegraph Creek formation. 

This group of ammonites, although indicating approximate correspondence in the age of the containing beds 

in different areas, has a considerable stratigraphic 

range and in our present state of knowledge does not 

afford a basis for the exact correlation of narrowly 

restricted zones; a better knowledge of the species of 

the group may later afford such a basis. Gryphaea

25 Berry, W. E., Upper Cretaceous floras of the eastern Gulf region: U. S. Geol 

Survey Prof. Paper 112, pp. 39-41,1919.
STRATIGRAPHIC RELATIONS OF AUSTIN, TAYLOR, AND EQUIVALENT FORMATIONS 145

wratheri Stephenson 26 is common to the upper part of 

the Tombigbee sand and to the Gryphaea wratheri 

zone, which lies in the upper part of the type Austin 

chalk, 100 feet or more below its top in Travis County, 

Tex.; this fossil is believed to indicate only approximate synchroneity.

The nearest approach to an exact correlation of a 

narrowly restricted zone west and east of the Mississippi embayment is that afforded by the small oyster 

Ostrea elegantula White,27 which has recently been 

identified from the two areas. As indicated on previous 

pages, this species has been collected from five localities 

in a very narrow zone within a few feet of the top of the 

Blossom sand, extending nearly across Ked Kiver and 

Lamar Counties, Tex. The species has also been collected in a narrow zone in marine sand of basal Selma 

age, overlying the Tombigbee sand, at two localities 

near Hatchechubbee, in Kussell County, Ala. If 

Ostrea elegantula characterizes a narrowly limited zone 

throughout the Gulf region, as seems likely, it affords 

a basis for correlating the marine sand near Hatchechubbee with the upper part of the Blossom sand. As 

the Blossom sand has been shown to be of upper type 

Austin age, it follows that the Eutaw formation, including the Tombigbee sand member, which underlies the 

sand at Hatchechubbee, is of Austin age.

The next zone stratigraphically above the Ostrea 

elegantula zone that affords a fairly exact tie between 

the eastern and western Gulf regions is the Diploschiza 

cretacea zone.28 In Alabama this zone lies within the 

Selma chalk a little above its middle; in Texas it forms 

the upper part of the Annona chalk in Ked Kiver 

County, is traceable in the Pecan Gap chalk in the 

central part of the State, and forms the upper part of 

the Anacacho limestone in Medina County.

SUMMARY AND CONCLUSIONS

The data presented on foregoing pages and the conclusions drawn therefrom may be summarized as 

follows:

1. At least five well-characterized and easily traceable faunal zones are differentiated in the upper onefourth of the typical Austin chalk in Travis County. 

These zones, in ascending order, are (a) the Inoceramus 

undulato-plicatus zone, 100 feet or more below the top 

of the chalk; (6) the Gryphaea wratheri zone, closely 

above the preceding zone; (c) the Exogyra tigrina zone, 

about 40 feet below the top of the chalk, probably the 

basal bed of the Burditt marl of Adkins; (d) the Ostrea 

centerensis zone, about 30 feet below the top of the 

chalk; (e) the Ostrea travisana zone, about 10 feet below

» Stephenson, L. W., New Upper Cretaceous Ostreidea from the Gulf region: 

U. S. Geol. Survey Prof. Paper 186-A, pp. 1, 2-4, 1936.

« Idem, pp. 2, 6-8.

28 Stephenson, L. W., The genus Diploschiza from the Upper Cretaceous of Alabama and Texas: Jour. Paleontology, vol. 8, no. 3, pp. 273-280, pi. 38,1934; Further 

notes on the Cretaceous pelecypod genus Diploschiza: Jour. Paleontology, vol. 9, 

no. 7, pp. 588-591, pi. 70, figs. 1-12,1935.

the top of the chalk. The relation of these zones to the 

top of the chalk from place to place along the strike of 

the formation and the presence of a thin phosphatic 

bed at the base of the overlying Taylor marl throughout 

central Texas, except in Dallas County, indicate the 

presence of an erosional unconformity at the top of the 

chalk.

2. The Burditt marl of Adkins, if recognized as a 

separate lithologic unit, should be treated as an upper 

marly member of the Austin chalk; it consists essentially of chalk, marly chalk, and chalky marl; typical 

chalk is an important part of the unit, as shown by 

exposures on Little Walnut Creek upstream and downstream from the Manor road crossing, where hard, 

brittle chalk makes up at least the upper 20 feet of the 

section immediately below the basal phosphatic bed of 

the Taylor marl. Foraminifera collected between the 

Ostrea tigrina and 0. centerensis zones were studied by 

"J. A. Cushman, who regards them as constituting an 

Austin fauna.

3. The five zones present in the Austin chalk beneath the phosphatic bed in Travis County continue 

along the strike at least as far north as Bell County, 

except where cut out by faulting. In the vicinity of 

Waco the phosphatic bed rests directly upon the 

Inoceramus undulato-plicatus zone, the lowest of the 

five zones, the other zones having been cut out by 

erosion between Bell County and Waco. In Dallas 

County the top of the chalk has risen again until it is 

stratigraphically 200 or 250 feet above the Inoceramus 

undulato-plicatus zone. In Fannin County the top of 

the Gober tongue of the Austin chalk is estimated to be 

at least 400 feet above the Inoceramus undulatoplicatus zone, which is exposed just northwest of Whitewright; a thin phosphatic bed is present at the base of 

the Taylor marl, which immediately overlies the Gober 

tongue in Fannin County. In Laniar County the top 

of the Gober tongue is estimated to be 200 feet above 

the Ostrea travisana zone, which is exposed at the 

southwestern outskirts of Paris, indicating that the 

top of the Gober is stratigraphically about 200 feet 

higher than the top of the Austin in Travis County.

4. The hiatus between the Taylor marl and the 

Austin chalk differs in time value from place to place, 

owing in part to the erosional unconformity at the top 

of the Austin and in part to differences in the stratigraphic position of the base of the Taylor. At Waco 

the phosphatic bed is fully 900 feet below the Pecan 

Gap chalk; in Travis• County the phosphatic bed is 

estimated to be only about 300 feet below the Pecan 

Gap; in Comal County near New Braunfels it is probably less than 50 feet below beds of Pecan Gap age; 

and in northeastern Texas the phosphatic bed is 400 or 

500 feet below the Pecan Gap chalk.

5. The evidence indicates that in Fannin and Lamar 

Counties the top of the Gober tongue of the Austin 

chalk is of the order of 200 feet stratigraphically
146 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1936

higher than the top of the type Austin in Travis County. 

This relation was recognized by the writer in former 

papers, but owing to failure to recognize a regional 

unconformity between the Austin and Taylor, the upper 

part of the Gober tongue was correlated with the lower 

part of the Taylor marl; it is now believed that the 

uppermost beds of the Gober are older than the Taylor 

and are assignable in time to the hiatus separating the 

Austin and Taylor; it follows also that the Brownstown marl is older than the Taylor. A foraminiferal 

fauna collected near the top of the Gober tongue near 

Bailey, Fannin County, was assigned by J. A. Cushman 

to the Austin.

6. The evidence of the Foraminifera, as interpreted 

by Cushman, tends strongly to confirm the conclusion 

here expressed, that the Austin chalk and Taylor marl 

in outcrop are separated by a pronounced erosional 

unconformity.

7. The Annona chalk, which in eastern Red River 

County is estimated to be 300 or 400 feet thick, is the 

time equivalent of the combined lower part of the 

Taylor marl, Wolfe City sand member, and Pecan Gap 

member of Lamar, Delta, and Fannin Counties. The 

phosphatic bed that forms the base of the Annona 

chalk north of White Rock, in Red River County, has 

been traced westward and found to be continuous with 

a phosphatic bed at the base of the Taylor marl just 

above the Gober tongue of the Austin chalk in Lamar 

County. The tracing of the phosphatic bed is facilitated by the presence of thin flakes of characteristic 

sandy limestone in the material immediately above it; 

in eastern Red River County these limestone flakes 

are in the base of the Annona chalk, whereas farther 

west in the same county and in eastern Lamar County 

they are in the base of the Taylor marl.

8. The Pecan Gap chalk is traceable from its type 

locality near Pecan Gap east-northeast in a narrow 

belt through Delta County, southeastern Lamar 

County, and western Red River County; it passes into 

and forms the upper part of the Annona chalk in 

central and eastern Red River County.

9. The interpretation of the stratigraphy in Red 

River County, as expressed above, is supported by the 

strike of the beds through the northern parts of Red 

River and Lamar Counties; the phosphatic bed at the 

base of the Annona chalk (strike, 7° or 8° north of east 

and its westward continuation at the base of the Taylor 

marl are approximately paralleled by a similar phosphatic bed at the base of the stratigraphically lower

Brownstown marl and by a narrow zone of fossiliferous 

concretions within a few feet of the top of the still 

lower Blossom sand; the concretions are characterized 

by the presence in great numbers of the small oyster 

species Ostrea elegantula White.

10. In southwestern Arkansas the Annona chalk and 

the underlying Ozan formation are together the approximate time equivalent of the Annona chalk in Red 

River County, Tex.; however, in Red River County 

an undetermined though probably small thickness of 

chalk has been removed from the top of the Annona 

by erosion, as shown by an unconformity separating 

the Annona from the overlying Taylor (upper). The 

phosphatic bed at the base of the Ozan formation is 

believed to be the eastward continuation of the phosphatic bed at the base of the Annona chalk in Red 

River County.

11. The species Ostrea elegantula White occurs in a 

narrow zone in marine sand of basal Selma age near 

Hatchechubbee, Russell County, Ala., and is believed 

to indicate the time equivalence of the containing bed 

there with the upper part of the Blossom sand (of 

upper Austin age) of northeastern Texas, which also 

carries this species in a narrow zone of concretions.

12. The Tombigbee sand member of the Eutaw 

formation of Alabama and Mississippi underlies the 

Selma chalk; the Tombigbee carries a fauna which 

relates it in age to the upper one-fourth or less of the 

typical Austin chalk in Travis County, and this fauna 

and the meager fauna of the more typical part of the 

Eutaw formation below are definitely younger than the 

fauna of the Eagle Ford clay of Texas. The Eutaw is 

separated from the still lower Tuscaloosa formation 

(Cenomanian) by an unconformity that is believed to 

be the time representative in the eastern Gulf region 

of the Eagle Ford clay (Turonian).

13. The name "Pecan Gap chalk" is used by Ellisor 

and Teagle essentially in the sense of a faunal zone, 

rather than a lithologic unit. It is made to supplant 

the formational names "Annona chalk" and "Anacacho 

limestone", both of which have many years' priority; 

each of these units embraces a thicker section (several 

hundred feet) and a much longer time period than the 

typical Pecan Gap chalk (thickness less than 60 feet). 

There is no justification, either in priority or in the 

actual relations of beds, for extending the application 

of the name "Pecan Gap chalk" to include these two 

formations, and to attempt to do so tends to obscure 

and confuse the true stratigraphic relations.

o
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UNITED STATES DEPARTMENT OF THE INTERIOR 

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GEOLOGICAL SURVEY 

W. C. Mendenhall, Director

Professional Paper 186—L

THE CORRELATION OF THE UPPER CAMBRIAN SECTIONS

OF MISSOURI AND TEXAS WITH THE SECTION

IN THE UPPER MISSISSIPPI VALLEY

BY

JOSIAH BRIDGE

Shorter contributions to general geology, 1936

(Pages 233-237)

UNITED STATES

GOVERNMENT PRINTING OFFICE 

WASHINGTON : 1937

For sale by the Superintendent of Documents, Washington, D. C. Price 5 cents

THE CORRELATION OF THE UPPER CAMBRIAN SECTIONS OF MISSOURI AND TEXAS 

WITH THE SECTION IN THE UPPER MISSISSIPPI VALLEY'

By JOSIAH BRIDGE

The Upper Cambrian section in the upper Mississippi 

Valley has long been accepted as the standard for North 

America, largely because it was the first to be studied 

in detail, because it contains a large number of distinct 

faunas, and because it is still the best-known and the 

most complete Upper Cambrian section in the Middle 

West. Various classifications have been proposed 

from £ime to time, but the latest and most detailed is 

that used by the ninth annual field conference of the 

Kansas Geological Society in the summer of 1935.2

It is not the purpose of this paper to discuss the 

merits and demerits of the Kansas Geological Society's 

classification, which is frankly a compromise that will 

require further elaboration, refinement, modification, 

and the elimination of certain names and their replacement by others before it can be generally accepted. 

Reference to it in this paper does not imply that it has 

been accepted either by the writer or by the United 

States Geological Survey. The proposed reduction of 

formations to three or four is certainly a step forward, 

for the Conference seems to have kept the definition of 

a formation—that is, a cartographic unit—firmly in 

mind and has drawn the boundaries on that basis. 

Whether some of the units now classed as members 

should be regarded as formations or not is beyond the 

scope of this paper. The proposed column is noteworthy in that it presents the most complete sequence 

of faunas published to date, and in then* proper order, 

thereby facilitating the correlation with other sections.

Table 1 of this paper presents a tentative correlation 

of the Upper Cambrian of three different areas—the 

upper Mississippi Valley, Missouri, and central Texas. 

The sequence of faunas as worked out in the upper 

Mississippi Valley is shown in the first column, and 

the presence of these faunas in the various stratigraphic 

units is indicated by a dot, or, if doubtful, by an interrogation point.

The determination of the succession of faunas is 

largely the work of Ulrich and Resser, Edwards, and 

Raasch; and although they are not in complete agreement concerning details of the stratigraphy, they and 

all other students of the Upper Cambrian of the Pacific 

province of North America agree very closely as to the 

details of the faunal succession.

1 Presented before the Paleontological Society, Dec. 27,1935.

2 Kansas Geol. Soc., Guidebook, Ninth Annual Field Conference, upper Mississippi Valley, p. 18, fig. 1 and elsewhere, 1935.

79233—37

The upper Mississippi Valley section is dominantly 

clastic, whereas the sections in Missouri and Texas 

are in the main calcareous. Therefore, lithologic 

correlations have been of very little value. Many of 

the faunas and especially certain elements of them are 

distinctly facies faunas, and this, together with the 

lack of study of the Missouri and Texas sections and 

certain miscorrelations in the upper Mississippi Valley 

section which have only recently been corrected, has 

greatly retarded correlations among these three areas.

Recent work in Texas by Miss Christina Lochman 

and the writer has shown that the section in the Central 

Mineral Region is nearly as complete as the upper 

Mississippi Valley section and that most of the faunal 

zones of the latter are present there. As now classified 

by the United States Geological Survey for the forthcoming geologic map of Texas, the Upper Cambrian of 

Texas comprises three formations and part of a fourth. 

These formations were all established on the basis of 

lithology and without direct reference to the newly 

proposed upper Mississippi Valley classification. There 

is, however, a striking similarity between the two 

classifications.

The Hickory sandstone, which forms the base of the 

Texas Cambrian section, appears to grade upward into 

the limestones of the Cap Mountain formation, and 

together these formations make a unit which is roughly 

the equivalent of the Dresbach formation of the 

Conference classification.

As the Hickory thickens the Cap Mountain thins, 

the combined thickness of the two formations remaining 

about constant. A further proof of the gradational 

character of the two formations is the presence of the 

Cedaria zone in both formations. This relationship will 

be more fully described in a forthcoming paper by Miss 

Lochman. The Crepicephalus zone is present, although 

Crepicephatus itself is not a common form. The dominant genera of this zone are Tricrepicephalus, which 

extends downward into the Cedaria zone, and Coosia. 

The Aphelaspis zone, characterized by Aphelaspis 

depressa (Shumard), is well developed and is probably 

the most widespread of all the Cap Mountain faunal 

zones. It occurs in the highest limestone beds of the 

formation immediately beneath a thick bed of glauconitic sandstone which Paige 3 included in the Cap

3 Paige, Sidney, U. S. Geol. Survey Geol. Atlas, Llano-Burnet folio (no. 183) 

p. 45 (field ed.), p. 6 (library ed.), 1912.

233
234 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1936

TABLE 1. — Tentative correlation of Upper Cambrian of upper Mississippi Valley, Missouri, and central Texas

Faunas

Gasconadia. 

Burenoceras.

Plethopeltis.

Acheilops.

Eurekia-Euptychaspis.

Dikelocephalus minnesotensis.

Scaevogyra. 

Lower Dikelocephalus.

Briscoia. 

Prosaukia. 

Ptychaspis. 

Billingsella. 

Eoorthis.

Camaraspis.

Hypseloconus, a local shore 

phase of the Camaraspis 

fauna.

Aphelaspis. 

Crepicephalus. 

Cedaria.

73

t-t

o

Cambrian Upper 

Upper Mississippi Valley 

(Kansas Geological Society Conference classification, 1935)

Oneota dolomite •

Not represented

Trempealeau formation

Franconia formation

Dresbach formation

Madison [sandstone] member •

Jordan sandstone of 

Ulrich

Jordan [sandstone] 

member • 

Norwalk sandstone 

of Ulrich •

Lodi [shale and siltstone] member •

St. Lawrence dolomite [member] •

Mazomania formation of

Ulrich

Franconia 

formation UJrich of 

Bad Axe [sandstone] member •

• 

Hudson [sandstone] member •

•

• 

Goodenough [sandstone] member

•

• 

Ironton [sandstone] member

•

Galesville [sandstone] member

• 

Eau Claire [sandstone] member •

•

Mount Simon [sandstone] member

Missouri 

(U. S. Geological Survey, 1936)

Gasconade dolomite •

Van Buren formation •

• 

Eminence dolomite •

?

Potosi dolomite •

Elvins group

Doe Run dolomite 

?

Derby dolomite

• 

• 

Davis formation

• 

•

Bonneterre dolomite 

• •

Lamotte sandstone

Texas 

(II. S. Geological Survey, 

1936)

• 

? 

?

Ellenburger limestone 

(lower part) •

• 

t

?

• 

•

Wilberns formation ?

•

• 

•

Lion Mountain sandstone member

Cap Mountain for- • 

~~~~~~ — -~__mation •

• ~""~"~^—- -~~ ;

Hickory sandstone

Mountain formation. This sandstone, which is perhaps the best horizon marker in the Central Mineral 

Region, is here designated the "Lion Mountain sandstone member of the Cap Mountain formation." The 

name is taken from Lion Mountain, in the northwestern 

part of the Burnet quadrangle. The section of the Cap 

Mountain formation exposed along State Highway 29 

on the southwest side of Lion Mountain is much thicker 

and far superior to the type section on Cap Mountain. 

The presence of the three faunas in both the upper 

Mississippi Valley and Texas definitely establishes the 

equivalence of this part of the section. Whether the 

Lion Mountain sandstone member is to be considered 

the full equivalent of the Galesville member of the 

Conference classification is, of course, purely conjectural.

In Missouri the lower portion of the Upper Cambrian 

section is composed of the Lamotte sandstone and the 

Bonneterre dolomite. The contact between the two 

formations is believed to be gradational, although St. 

Clair 4 has postulated an unconformity between them. 

The Cedaria fauna has been found in the lower 50 feet of 

the Bonneterre dolomite along the Farmington anticline east of the St. Francois Mountains, where the 

basal beds are predominantly limestone, and this 

occurrence serves to tie this portion of the section with 

the uppermost Hickory and basal Cap Mountain of 

Texas and with the lower part of the Eau Claire member 

of the Conference classification for the upper Mississippi 

Valley. The Crepicephalus and Aphelaspis faunas

4 St. Olair, Stuart, Geology of Ste. Genevieve County, Mo.: Missouri Bur. Geology 

and Mines, vol. 22, pp. 37, 44, 1928.
CORRELATION OF UPPER CAMBRIAN SECTIONS OF MISSOURI AND TEXAS 235

have not been found in Missouri, but one or both of 

them might well occur in the upper portion of the 

Bonneterre dolomite, which thus far has yielded no 

fossils.

Overlying the Cap Mountain formation in Texas is 

the Wilberns formation, which comprises all the strata 

between the top of the Lion Mountain sandstone member and the base of the Ellenburger limestone. It is 

almost exactly the equivalent of the Franconia of 

the Conference classification, or of the Franconia 

and Mazomanie of Ulrich's classification.5 The base 

of the Wilberns is marked by the widespread Camaraspis fauna, which serves to correlate it with the 

Ironton sandstone member of the Franconia. The 

other important trilobite genera in this asemblage are 

Elvinia, Burnetia, Housia, IrvingeUa, and Pterocephalia. 

Overlying the Camaraspis zone are the Eoorthis and 

BUlingsdla or Taenwephalus faunules, which together 

make up the Conaspis zone and serve to correlate this 

portion of the Wilberns with the Goodenough member 

of the Conference classification. The upper zones of 

the Wilberns are not as definitely known, but the 

Ptychaspis, Prosaukia, and Briscoia faunas are known 

to be present, and there are indications of the lower 

Dikelocephalus zone. These are contained in the socalled "post-Wilberns beds—Fort Sill and Signal 

Mountain faunal equivalents" of Dake and Bridge,6 

but until these formations are better known it seems 

wise to restrict the names "Fort Sill" and "Signal 

Mountain" to rocks in the type areas (Wichita and 

Arbuckle Mountains, Okla.). Beds carrying these 

faunas were locally included in the Wilberns formation 

by Paige, although at places he assigned beds at the 

same horizons to the Ellenburger limestone. The 

Wilberns as now defined includes these beds.

In Missouri the Camaraspis, Eoorthis, and Taenicephalus faunas occur in the Davis formation and serve to 

correlate it with the lower portion of the Wilberns and 

with the lower part of the Franconia (Ironton and 

Goodenough members of the Conference classification). A further tie between Missouri and the upper 

Mississippi Valley is found in the peculiar assemblage 

of gastropods known as the Hypseloconus fauna. This 

is distinctly a facies fauna characteristic of shallowwater conditions along a rocky coast and at present is 

known from only three localities—one at the base of 

the Franconia at Taylors Falls, Minn., the other two 

at the base of the Davis in Missouri.

* Ulrich, E. 0., Notes on new names in table of formations and on physical evidence of breaks between Paleozoic systems in Wisconsin: Wisconsin Acad. Arts, 

Sci., and Letters Trans., vol. 21, pp. 72-94, 1924.

6 Dake, C. L., and Bridge, Josiah, Faunal correlation of the Ellenburger limestone 

Of Texas: Qeol, Spc. America Bull., vol. 43, pp. 725-741, 1932,

The presence of the Camaraspis fauna in the base of 

the Davis is another reason for assuming that the nonfossiliferous portion of the Bonneterre may represent 

the Crepicephalus and Aphelaspis zones.

Overlying the Davis are two thin dolomitic formations—the Derby and Doe Run dolomites—which have 

yielded practically no fossils. Their position in the 

upper Mississippi Valley and Texas sections is therefore doubtful, but they are believed to represent the 

upper half of the Wilberns formation and the upper 

half of the Franconia, either wholly or in part. There 

is one tie with the Texas section which of itself is of 

no great value but which when taken with the general 

sequence of faunas is at least significant. Near the 

base of the upper half of the Wilberns formation, in 

what was called the "Fort Sill faunal equivalent," 

there are several layers of limestone filled with small 

spherical bodies which show traces of structure and 

have been provisionally identified as Girvanella sp.7 

These bodies occur above the Billingsella zone and 

beneath the Prosaukia zone. In Missouri small spherical bodies of approximately the same size are found 

at a definite horizon in the Derby dolomite, but dolomitization has destroyed all traces of structure. These 

bodies occur above the Taenicephalus zone, but as 

previously stated the Prosaukia zone has not been 

recognized in Missouri.

A further reason for correlating the Derby and Doe 

Run formations with the upper part of the Franconia 

(Hudson and Bad Axe members of the Conference 

classification) and with the upper half of the Wilberns 

is found in the presence of the Scaevogyra fauna in the 

overlying formation in all three areas. This fauna is 

characterized by various species of the gastropod 

Scaevogyra and the trilobites Plethometopus and Platycolpus. It occurs in the St. Lawrence dolomite member 

of the Trempealeau formation of the Conference 

classification, in the Potosi dolomite of Missouri, and 

in the basal portion of the Ellenburger limestone in 

sections along the Colorado River, Tex., thus serving 

to correlate the beds in these three areas. This same 

fauna has been found about 500 feet beneath the top 

of the Copper Ridge dolomite in eastern Tennessee.

The Trempealeau of the Conference classification 

is the youngest of the three formations recognized in 

that classification. It contains several lithologic units, 

many of which have been accorded formational rank 

by others. Most of these units contain distinctive 

faunas. The various classifications in current use are 

indicated in table 2.

' See The geology of Texas, vol. 1: Texas Univ. Bur. Econ. Geology Bull. 3232, 

1932,

79233—37-
236 SHOKTEK CONTRIBUTIONS TO GENERAL GEOLOGY, 1936

TABLE 2.—Various classifications of the late Upper Cambrian strata in the upper Mississippi Valley

Kansas Qeol. Soc. Conference, 1935 

(K. G. S. Guidebook, fig. 2)

a

0'•§ 

1

o3

r2'oS 

0>1o> S

Madison sandstone 

member

Jordan sandstone 

member

Lodi shale member

St. Lawrence dolomite 

member

Franconia formation 

Bad axe sandstone member

Ulrich, 1935 (personal communication)

Madison sandstone

Jordan sandstone

Trempealeau 

formation

Norwalk sandstone

Lodi shale

St. Lawrence dolomite

Mazomanie formation

U. S. Geol. Survey (present classification)

Madison sandstone

Jordan sandstone

St. Lawrence formation

Sandstone

Norwalk sandstone member

Lodi shale member

Mendota dolomite member

Shale

Minnesota, 1935 

(K. G. S. Guidebook, fig. 2)

Jordan sandstone

St. Lawrence formation 

(includes at base shales 

and sandstones placed in 

underlying formations in 

other classifications).

Overlying the St. Lawrence dolomite member of the 

Conference classification is the Lodi shale member, 

which carries the Dikelocephalus fauna, "universally 

(but with little justification) held to be the type fossil 

for the Upper Cambrian of the Pacific province." 8 

Beds carrying this fauna are not known in Missouri 

and Texas. Some ascribe this absence to nondeposition 

of a Lodi equivalent, or to deposition and subsequent 

erosion, although neither region shows conclusive 

evidence of a hiatus between the beds carrying the 

pre- and post-Dikelocephalus faunas. An alternative 

interpretation is that the Dikelocephalus fauna is made 

up of forms that lived in the mud and are restricted 

to areas in which the deposits are shales. This explanation receives additional support from the upper 

Mississippi Valley, where at some places, according 

to Raasch,9 the shales and siltstones of the Lodi shale 

member grade laterally into coarser clastic deposits, 

which have been called "Norwalk" by Ulrich, and 

"Jordan" by the Conference; and where this occurs 

the characteristic Dikelocephalus fauna is replaced by 

other forms. There are no shales in this part of the 

section in either Missouri or Texas, and this would 

explain the absence or scarcity of this fauna.

The Norwalk or lower Jordan faunas are still imperfectly known, and more detailed studies must be 

made before exact correlations are possible. However, 

Raasch 9 claims that all the genera described from the 

Eminence dolomite of Missouri 10 occur in the Jordan 

and Madison of Wisconsin. Characteristic genera 

among the trilobites are Euptychaspis, Triarthropsis, 

Calvinella, Stenochilina, and StenopUus. The gastropod 

Sinuopea is sparingly represented in the Eminence 

and is abundant at one horizon in the Jordan; these 

two occurrences mark the first appearance of that 

genus in these two regions. Near the top of the

• Baasch, G. O., Paleozoic strata of the Baraboo area: Kansas Geol. Soc. Guidebook, Ninth Annual Field Conference, p. 407, 1935. 

' Raasch, G. O., personal communication. 

10 See Missouri Geol. Survey, vol. 24, ch. 6,1930.

Eminence is a zone characterized by several large 

species of Plethopeltis and Calvinella, which may 

correspond to the Madison. Raasch records the 

unique trilobite Entomaspis from the Madison, and 

the same genus occurs in both the Eminence and 

Proctor dolomites of Missouri. The Proctor is a unit 

which some consider to be a distinct formation but 

which the writer considers to be the upper part of the 

Eminence formation in certain areas.

The correlation of the Eminence with a zone in the 

Ellenburger limestone lying above the Scaevogyra 

zone has been established by the presence of several 

Eminence species in the Elleoburger, among them 

Euptychaspis typicalis Ulrich and various species ,of 

StenopUus and Plethopeltis. 11

In Wisconsin the Madison sandstone is overlain 

by the Oneota dolomite, of Lower Ordovician age. 

This formation carries a large molluscan fauna which 

can be divided into several faunules. It is a widespread fauna and has been recognized in practically 

every important area of early Ordovician rocks in 

North America. By means of this fauna the equivalence of the Oneota dolomite with the Gasconade 

dolomite of Missouri and with beds at a horizon near 

the middle of the Ellenburger of Texas (the so-called 

Gasconade faunal equivalent) has been definitely 

established. All stratigraphers familiar with, this 

portion of the section agree with this correlation.

Among the characteristic gastropods that occur in the 

three areas under consideration are Gasconadia putilla 

(Sardeson), Helicotoma uniangulata (Hall), Pelagiella 

paucivolvata (Calvin), and many species of Ophileta. 

The cephalopods are represented by several genera, 

among them Clarkeoceras and Cameroceras, and many 

species are common to all three areas.

Beneath the Gasconade in Missouri is another formation of Lower Ordovician age, the Van Buren, which

11 Dake, C. L., and Bridge, Josiah, Faunal correlation of the Ellenburger limestone 

of Texas: Geol. Soc. America Bull., vol. 43, pp. 730-732, 1932.
CORRELATION OF TIPPER CAMBRIAN SECTIONS OF MISSOURI AND TEXAS 237

carries a fauna related to but different from that of the 

overlying formation. It is composed primarily of 

gastropods and cephalopods. Among the gastropods 

are numerous species of Sinuopea and Schizopea. 12 

Among the cephalopods which appear in this formation 

in great abundance, various species of Burenoceras and 

Dakeoceras are especially characteristic. For this 

reason it is termed the "Burenoceras zone." Strata 

carrying this fauna are unknown in the upper Mississippi Valley and at present are only doubtfully known 

from Texas, though there now seems to be reason for 

believing that this fauna occurs in the Ellenburger 

limestone in strata lying between beds carrying the 

Eminence and Gasconade faunas. It is known to 

occur in the Arbuckle limestone beneath beds carrying 

the Gasconade fauna. The strata carrying this fauna 

were probably the initial deposits of the advancing 

early Ordovician submergence, which did not reach 

the upper Mississippi Valley.

The correlation of these early Ordovician zones is 

well established, and the chief innovation of the 

present correlation is the placing of the Eminence and 

Potosi of Missouri and their Ellenburger equivalents 

as correlatives of the Trempealeau formation of the 

Conference classification.

It has been claimed that correlations based on similar 

associations of genera are of little or no value, and that 

the only correlations that can be trusted are those 

founded on a comparison of finely discriminated species. 

It is also assumed by some that a fauna, once developed, 

becomes practically universal in the sea in which it lives, 

and that it should be present in all the strata deposited 

in this sea during the time this particular fauna was 

living. However, there are many examples on record 

in which strata carrying faunas far more strikingly 

dissimilar than the ones that are considered to be 

homotaxial in this paper are correlated with one 

another because of their stratigraphic position between 

strata carrying cosmopolitan faunas. Also it is well 

known that the sea bottom today is not uniformly and 

universally populated, but that it contains areas which

'2 Butts, Charles, Geology of Alabama: Alabama Geol. Survey Special Eept. 14, 

p. 88, pi. 14, figs. 23, 24,1926. The name Schizopea Ulrich, 1926, takes precedence 

over Rhachopea Ulrich and Bridge (Missouri Bur. Geology and Mines, vol. 24, pp. 

190-193, 1930), and S1 . washburim Butts must be regarded as the genotype.

are crowded with living forms and other areas which 

are practically barren of life. It is just as logical to 

assume that two faunas which are for the most part 

specifically and even generically dissimilar can exist 

a few hundred miles apart in the same epeiric sea under 

slightly different environmental conditions as it is to 

invoke crustal warpings and erosion or nondeposition 

in order to make two very similar faunas occur in one 

area at one time and recur in another area at a later 

time. It is difficult to imagine a sea invading the 

continent from the southwest, as the Upper Cambrian 

seas are believed to have done, which would leave a 

series of deposits such as the Trempealeau formation 

(Conference classification) in the upper Mississippi 

Valley and at the same time fail to leave any record of 

its presence in any of the Cambrian areas to the south 

of it. It is also equally difficult to imagine how a 

second sea could come in from the same quarter (it 

must have done so, because it contains so many identical 

genera) and leave a second set of deposits in all the 

areas from which the first set were either eroded or 

never deposited and at the same time fail to leave a 

well-defined record in the one area where these earlier 

deposits remain. Yet these are the assumptions that 

must be made if the Potosi and Eminence formations 

of Missouri and the beds of pre-Gasconade age in the 

Ellenburger of Texas are to be considered as being 

younger than the Jordan sandstone of the upper 

Mississippi Valley. No one today questions the 

practical equivalence of the Cedaria, Crepicephalus, 

Aphelaspis, Camaraspis, Eoorthis, Taenicephalus, Ptychaspis, Prosaukia, lower Dikelocephalus, and Gasconadia 

faunas in the three areas under consideration. In view 

of this striking parallelism it seems more logical to the 

writer to regard the four known occurrences of the 

Scaevogyra fauna as a single zone instead of making the 

occurrence in the St. Lawrence of the Conference 

classification older than the other three. Similarly it 

seems best for the present to consider the occurrence of 

similar forms in the Jordan and Madison of the upper 

Mississippi Valley, in the Eminence of Missouri, and 

hi the lower'part of the Ellenburger of Texas as representing a single horizon instead of placing the upper 

Mississippi Valley forms in an earlier zone and the 

others in a later one.

o