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Dallas

Paleontological

Society

P.O. Box 223846

Dallas, Texas 75222-

3846

Surface Geology of Dallas and

Ta rra nt Cou nties, Texas

by Phil Scoggins

TABLE OF CONTENTS

1. INTRODUCTION

2. TOPOGRAPHY AND FORMATION EXPOSURES 3. FORMATION DESCRIPTIONS and INFORMATION 4. REFERENCES

INTRODUCTION

Rocks, minerals, and fossils found on the surface of Dallas and Tarrant Counties were

deposited in the Mesozoic Era and Cenozoic Era. (See Time Chart) The resulting

formations are .either of cretaceous Age, 66 to 144 million years ago (ma) or

Quaternary Age, present day to 10,000 years ago (Dates are approximations.) In

Dallas County, the Cretaceous ranges from about 75 ma to 90 ma. In Tarrant County,

the Cretaceous ranges from 90 ma to 115 ma. In other parts of Texas more of the

Cretaceous Era is represented. For instance, the Cretaceous/Tertiary (K/T) boundary.

Cretaceous deposits in North Texas are mostly marine in origin. The Western Interior

Seaway at its greatest extent spanned the the North American continent from the

Artic Circle to the present day Gulf of Mexico. Although this was the Age of the

Dinosaur, their habitats were sparse in Tarrant County and non-existent in Dallas

County. The most abundant habitat was marine. The depth of the ocean rose and fell

many times. In doing so, the sediments deposited varied from generally sandy

shorelines and deltaic complexes to low energy, deeper water.

Quaternary sediments were deposited in areas adjacent to the Trinity River and its

tributaries. As the Trinity winnowed over time, it would leave terraces covered with

sand and gravel. These river deposits range in age from 1.8 ma. to recent.

Mammoth and bison bones are sometimes found along the Trinity and its tributaries.

The Sedimentary Record

To understand the sedimentary rock record there are three fundamental ideas to

grasp: Time units, Rock units, and Time-rock units.

Time units are names given to intervals of time: The designation forTime units is in

years before the present. Designations are abbreviated, often as mya (millions of

years ago) or ma (mega-annum or millions ago). Time units define the chronological

sequence of the events in rocks. Their ranking from longest to shortest is Eon, period,
Epoch, then Age. Age dating by radiometric and/or the fossil record are two methods

to define the timing of events.

Rock units are the initial stratigraphic ranking of rocks, Ranking from largest to

finest the order is Group, Formation, Member, bed.

The most common use of the rock unit classification is the Formation. A formation is

a layer of rock that is uniform in its makeup, corresponds to other layers deposited

during that period, and can be defined (by recognition, fossil correlation or other

means) over an area large enough to be traced and mapped. Geologists call this

lithographic and stratigraphic homogeneity. Members subdivide a formatlon when

there are distinctive changes in some of the mlnor component. These changes can be

an increase or decrease in the number of shale, llmestone or sandstone beds in a

relatlvely short vertical section of the formation.

Formation nomenclature is colloquial in nature. Formation names commonly come

from their general make-up, the location where it was first described, or the person

whom first discovered the layer. This can lead to some confusing names until you

learn your way around - for instance, we have the "Austin Chalk" in Dallas County!

Recognizing formations will assist in finding fossils, identifying them, and recording

them for study. Constructlon of most geologic maps is at the formation level. In

addition to maps, observations of the rock types, the fossils, and even the vegetation

can help identify the formation. For example, the cedar trees around Cedar Hill prefer

limy soil; Post Oak trees prefer sandy soil. More detailed information on the

formations comes later in this document,

Time-rock units , System, Series and stage, provide the concept of a sequence in

time. Time-rock units do not equate with a specific time interval. Instead, they define

the duration of a geologic event in a geographic region.

Here is an example of Rock units, Time-rock units and Time units.

Arlington, Texas was once the setting for a delta on the eastern shore of

the Western Interior seaway. Sands, and clays are the individual öeds

that comprise the three Members , Rush Creek, Dexter, Lewisville and

Arlington of the Woodbine Formation . They are in the Woodbine Group.

These are the rock units. Time-rock units and Time units can be confusing

because the same name often applies to both.

The Time-rock units of the Woodbine Formation place it in the

Cenomanian Stage. The stage tells you the Woodbine is in the lower part

of the Gulf Series in the Cretaceous System. These are all relative times

because they differ according to geographic location. Deposition of the

Woodbine did not occur at the same time in all the same places. It took

millions of years for the delta to advance out into the sea way.

Time units give us a specific measurement in millions of years. The

Cenomanian Age (91 to 97.5 ma) is in the Late Epoch (66.4 to 97,5 ma)

of the Cretaceous Period (66.4 to 144 ma).

TOPOGRAPHY AND FORMATION EXPOSURES

During the Cretaceous Period, the seas rose and fell leaving multiple

layers of deposits with various çpmpositions. These formations represent

several deposltlon environments: shallow marine, deltaic, and coastal.

Ancient land deposits to deeper-water sediments provlde a rich varlety of

fossils: vertebrate specimens lnclude marine reptiles, sharks, turtles,

flshes and rarely dinosaurs. There are also plenty of invertebrate fossils:

sea urchins, shells of clams, snails, and ammonltes (related to the

Nautilus).
After the cretaceous Period the area tilted slightly resulting in a L/2

degree dip due east. This slight dip across the thin deposits causes many

formations to outcrop on the surface - much like slicing an onion. The

exposures form bands that run generally north-south. since the various

rock units are deposited one on top of another, the oldest is on the

bottom and youngest on top. The tilting exposes the oldest rocks in the

western part of the area and the youngest in the east.

During the Quaternary Period, the Trinity River carved out terraces

through the Cretaceous deposits. The river left behind clays, sands, and

gravel that are of economic value. Today, the Trinity River headwaters

form in western Tarrant county, fed by the many creeks flowing from

Parker, Jack and Denton counties. The river causes a dendritic drainage

pattern across most of western Tarrant country. Fossil mammoth, bison

and other mammal bones can be found along the Trinity River.

Dallas county has six formations represented on the surface. Tarrant

county has fifteen formations on the surface. The list below is from most

recent to oldest.

PERIOD FORMATION

Quaternary: Alluvium and terrace deposits

Cretaceous: Ozan (Lower Taylor Marl)

Austin Chalk (often referred to as a

Group)

Eagle Ford (often referred to as a

Group)

Woodbine (often referred to as a

Group)

Grayson Marl

Main Street Limestone

Par¡¿-Paw Formation

Weno Limestone

Denton Clay

Fort Worth Limestone

Duck Creek Limestone

Kiamichi Formation

Goodland Limestone

Walnut Clay

Paluxy Formation

COUNTIES

Dallas and

Tarrant

Dallas

Dallas

Dallas and

Tarrant

Dallas and

Tarrant

Tarrant

Tarrant

Tarrant

Tarrant

Tarrant

Tarrant

Tarrant

Tarrant

Tarrant

Tarrant

Tarrant

FORMATION DESCRIPTIONS and INFoRMATION

Quaternary alluvium and terrace deposits - Dallas and Tarrant

Counties

The Quaternary period has two subdivisions. The Holocene Epoch ranging

the present to about 12,000 years ago and the pleistocene from 12,000

to about 1.8 ma. Although the Pleistocene is referred to as the Ice Age,
none of the ice sheets extended as far south as Fort Worth or Dallas. The

maximum extent, 18 to 20 thousand years ago, of the Laurentide ice

Sheet was barely touching northeast Kansas, The ecology of DFW area

was somewhere in the transition zone with respect to vegetation. A

broadleaf forest (included: chestnut, Paw Paw or "Prairie Banana", Osage

Orange) was present in eastern North Texas (Is that why they call it the

Eastern Cross Timbers?) which gave way to open woodlands (include:

juniper and mesquite) to the west. The boundary is likely close to where

it is today because, in part, the soils becomes more rocky to west and the

climate is dryer.

Alluvial deposits of clay, sand, and gravel are found in the flood-plain

areas. They are the youngest deposits in the area. Some deposits are

present day as the result of storms moving large volumes of water

requires high energy. Subsequently there is enough energy to erode and

move sediments as large as gravel and boulders. Gravel bars are a good

place to look for fossils.

Terrace deposits outcrop adjacent to and outside of the immediate

channels the Trinity River and its tributaries. Their composition is that of

alluvium. Terraces were formed when the river changed course,

abandoning the previous flood-plain, and the new channel cuts deeper

into the earth.

anttguus), camel, horse and other mammal bones are can be found in

these Quaternary deposits.

Quaternary deposits unconformably overlie the Ozan formation. The

hiatus lasted about 70 million years.

Ozan Formation - Dallas County

The Ozan is also referred to as the Lower Taylor Marl. The Ozan

unconformably overlies the Austin Chalk. Descriptions of color and

composition vary widely because often the descriptions are either state

wide summaries or of particular localities. The Geology of Texas Volume

1, Stratigraphy by Sellards, Adkins, and Plummer describe the Ozan as a

dark gray marl. The marl can be sandy, chalky or glauconitic and can be

mostly sand. Its generally a calcareous micaceous clay that coarsens

upward though the section with increasing proportions of calcareous silt

and sand. Occasionally present are glauconite, hematite and pyrite in

nolular form, and phosphate pellets. When weathered, it is a brownish

gray color. The clay in this formation contains the clay mineral

montmorillonite that expands when wet. Montmorillonite is descused in

more detail in the section on the Eagle Ford. The Ozan was deposited in a

deep marine, low energy, environment.

The bivalve Inoceramus is much smaller than those found in the Austin

Chalk. Other fossils include shark's teeth and microfossils. Trace fossils

being burrows of Ophiomorpha (shrimp), Thalassinoides (arthropod) and

Planolittes (worm) can be found while vertebrate fossils are close to

nonexistent. Although not in Dallas or Tarrant Counties, probably the best

exposure and fossil collecting is in the North Sulphur River. The Society's

Occasional Papers Volume 4, Fossil Collector's Guidebook to the North

Sulphur River, by Mark McKinzie, Ron Morn and Ed Swiatovy,2001 is an

excellent resource.

Austin Chalk - Dallas County

The Austin Chalk is considered by many to be a group of formations. The
Austin chalk has five members. From bottom to top is the Atco Member,

the Austin chalk, Blossom sand, Brownstown Marl and Gober chalk. In

Dallas county, the Geologic Atlas of Texas, Dallas sheet has not

differentiated mapped area. specifically, the condensed section at the

base of the Atco Member and known as the Fish Bed conglomerate is

present where the Austin chalk-Eagle Ford Group contact outcrops. The

Fish Bed conglomerate is a light greenish sandy calcareous clay.

Phosphate nodules are abundant. However, the reason for the name is

the extreme abundance of small to microscopic fish teeth. The easiest

way to collect from the Fish Bed conglomerate is to submerse large

chunks of material in a weak acid bath like vinegar for a few days thèn

wash the material through a fine sieve to catch the teeth. The acid bath

and wash may have to be repeated several time. the There used to be a

great exposure along FM 1382 west of clark Road in cedar Hill, Texas.

unfortunately, a retaining was was erected prevent erosion and rock falls

along the sharp and tall roadcut,

The western extent of the Austin chalk is sometimes referred to as the white Rock Escarpment. The contrast between the chalk and the

underlying Eagle Ford is striking. Looking east from locations in Grand

Prairie and Irving, the Austin chalk raises out of the plains and appears

white overlying the dark gray or black Eagle Ford. composition of the

chalk is primarily coccolithophores from foraminifera. Coccoliths are

calcareous plates found on the suface of some flagellate microorganisms.

Austin chalk covers one-third to one-half of the surface of Dallas county.

Cedars prefer limy soil and are prolific.

The chalk dips at a rate between 15 and 40 feet per mile to the east or

southeast. has many normal faults and fractures, all inactive so don't

worry. This is the same formation that made horizontal drilling famous.

oil companies use the faults and fractures to their advantage, especially

in Brazos and Burleson counties, Texas, oil companies bore vertically to

the target depth then bore horizontally through the chalk. A horizontal

boring encounters more oil filled faults and fractures a vertical boring. So, the horizontal well produces much more oil or gas. several quarries

located near Midlothian, Texas mine the chalk for use in cement. The

quarries occasionally grant permission for members of this society to

enter the quarries and collect fossils. Fosslls are generally sparce in the

Austin chalk. A shark and a few mosasaur skeletons have been found.

Eagle Ford Formation or Eagle Ford Group - Dallas and Tarrant

Counties

The gently rolling hiils are referred to as the "Black prairie" and the

residual soil as "black gumbo." The Eagle Ford contains bentonite, an

impure clay that is a product of weathered volcanic ash. Bentonite

consists mainly of the clay mineral montmorillonite. Differential

swell/contraction of montmorillonite as it absorbs or looses water can be

as much as seven inches causing problems for foundations and roads,

Bentonite occurs in the Eagle Ford in layers up to ten inches thick. The good news is that the bentonite layers are good sources of samples for

radiometric age dating.

The Eagle Ford is a bituminous shale with calcareous concretions and

large septaria; sandstone and sandy limestone in the upper parts; and

bentonitic in the lower part. The laminated bedding structure and dark

color makes the Eagle Ford easy to identify.

The Eagle Ford has four members: the basal unit is Tarrant Beds or six

Flags Limestone, Britton shale, the Kamp Ranch Limestone and the

Arcadia Park shale, top member, The Tarrant Beds is dark gray shale that
weathers to brownish or bluish-gray. It also includes small lenses of

either calcareous sandstone or fossiliferous limestone covering a few feet

laterally and approximately two inches thick. Overlying the basal unit is

the Britton Formation consisting of dark gray, silty shale that grades

laterally into gray and tan shale. A thin limestone, flaggy,layer above the Britton is named the Kamp Ranch Limestone. Depositional

environment of the Kamp Ranch was in shallow water with moderate to

high energy. The abundance of shell fragments aid in the determination

of the energy level. Overlying the Kamp Ranch is the Arcadia Park shale.

The Arcadia Park and the Britton are very similar in appearance and were

deposited in low energy waters with depths between 120 and 600 feet

which is part of the controversy as whether the Eagle Ford is a single

formation or a group.

The Eagle Ford produces quality specimens: ammonites with shells

composed of the original mother of pearl; shark teeth of Leptostyrax and

Ptychodus, fish and other marine vertebrate skeletons. Dallas

Paleontological Society member Arlene Pike was honored for her fossil

crab find which was named Homolopsis pikeae. Society members Van

Turner was also honored for his find Dallasaurus turneri, and Mark Cohen

for Russelosaurus Coheni, D. turneri and R. Coheni are the two the oldest

known specimens of mosasaur-like marine reptiles in North America.

Woodbine Formation or group - Dallas and Tarrant Counties

As a group, the Woodbine consists of the Rush Creek Member, Dexter

member, Lewisville Member and the Arlington Member The Woodbine was

a fluvial deltaic system consisting of both marine and non-marine

facies. The Woodbine Formation consists of mostly fine grained sandstone

with clay and shale. The basal unit, Rush Creek Member, is composed of

marine prodelta clays, silts and sands. The overlying Dexter Member is

predominately sandstone with clay and sandy or carbonaceous shales

interbedded. Features include large scale cross-bedding, ripple marks,

and large discoid concretions. The Dexter Member is interpreted to be

deposited from both marine and non-marine sediments. The Lewisville

Member is a marine shale with various quantities of sand, silt and

carbonaceous clays. The Arlington Member is composed of sandstone

and calcareous sand lenses interbedded with sandy shales, Beds of

ironstone and ironstone conglomerate also occur in the lower part.

Sandstones are occasionally conglomeritic and contain occasional to

abundant oyster shells. The Woodbine unconformably overlies the

Grayson Marl.

The Woodbine provides soil for a wooded region called the Eastern Cross

Timbers where Post Oaks are common. The Woodbine is a sandy soil, rich

with iron. Iron nodules litter the ground. Iron nodules form when

solutions deposit around a "seed" or nucleus of sand or organic material,

These concretion nodules look like iron meteorites but are distinguishable

because they do no have the magnetic propefties. Iron mineral mostly

limonite and hematite give the Woodbine a characteristically reddishbrown any yellow hues.

The Woodbine Formation, a secondary aquifer in Nofth Texas. To the

east, the Woodbine produces hard-water as a result of the iron. Many

water wells produce from the Woodbine aquifer. Pesticides, herbicides

and petrochemicals on spilt onto surface exposures have the potential to

seep down into this aquifer and pollute water wells down dip (to the

east.) Tan colored clays are interbedded in the Woodbine, and used by

companies in Denton County to make brick. In east Texas, the Woodbine

is the largest oil and gas producing reservoir rock in the state.
Fossils from the woodbine include the ammonite Acanthoceras, the oyster

Gryphea, dinosaurs include an unnamed nodosaurid, an unnamed

nodosaurid and an unnamed hadrosaur and vadous mollusks. society

member Bill Lowe was honored by having a trace fossil footprint of a

theropod dinosaur named after him, Magnoavipes lowei. Also, member

Gary Bird was honored with his discovery, protohadros byrdii.

Grayson Formation - Tarrant County

The Grayson Formation is a chalky, yellow-white to gray marl with gray

shale beds. The transition from Grayson to overlying woodbine

represents a withdrawal or regression of Cretaceous seas.

Fossils include ammonites : scaphites subevolutus, Turrilites bosquensis,

T. brazoensis, Adkinsia sp.; pelecypods, Exogyra arientina (also known as

"rams horn") and E.plexa. Trace fossils include Thalassinoides (arthropod)

and Serpula (worm tubes).

Main Street Formation - Tarrant County

The Main street formation overlaying the paw paw is a resistant

limestone formed from supersaturated lime mud. The contact between

the two formations represents a transgression of the cretaceous oceans,

The Main street weathers to a white or grayish white color. was a deeper

water environment than the Paw Paw.

Paw Paw Formation, Denton Clay, Weno Limestone, Fort Worth

Limestone and the Duck Creek Formation - Tarrant County

In Tarrant County, these formations are mapped undivided on the

Geologic Atlas of Texas.

The Paw Paw's type locality is Paw Paw creek which begins in Dennison

and flows generally northeast to the Red River. The clay is dark gray or

blackish and somewhat lustrous when fresh and weathers red-brown to

yellowish. shales and clays with some sandstone ledges comprise the

formation. Particularly in northern Tarrant county, concretions and iron

nodules are abundant. The Paw Paw is a ferruginous clay of shallow

marine origin. Rocks here represent the transgression of cretaceous seas.

Fossils include a unique miniature fauna such as ammonites less than one

inch in diameter; frequently pyritized with intricate detail. other genera

also exhibit dwarlism but the reasons for the dwarfism are unknown.

Shark's teeth are common fossil in the paw paw.

The area north of Loop 820 and North Beach street and the community of

Fossil creek was productive until development covered the site. Typical

fossils include shark teeth and vertebrae and cartilage, crab claws and

carapaces fragments, and dwarf ammonites, and the pelecypod, ostrea

quadriplicafa. This area has also produced some unusual finds for a

marine depositional environment. A nodosaur, Nodosauridae indet, was

found by then L2-year old Johnny Maurice the son of society member.

John Maurice. unfortunately, it was not named in his honor. Another

nodosaur, Pawpawsaurus campbelli was found by then 19-year old

cameron campbell. society afFiliation unknown. Member Robert Reed

found a (unnamed) turtle associated with nodosaur bones.

weno Limestone has three units. The upper unit is chiefly limestone, It

varies from hard and massive to soft and chalky. when fresh it is light

gray to yellowish gray and weathers gray to yellowish brown. Hard
limestone will form topographic benches. The middle unit is generally a

calcareous clay with occasional lenses of sand-sized shell fragments.

Color varies from olive brown to olive gray. The lower unit is

predominantly limestone with some sand. This fossiliferous formation is

light gray, except where it is sandy it is medium gray. The lower unit

weathers to a yellowish brown. Echinoids Macraster obesus,

Tetragramma; worm tubes S_etWla; gastropods Gyrodes Conrad,

Leptomarìa austinensis can be found.

Denton Clay has alternating layers of calcareous clay with marl and

limestone weathers dusky brown. At the time of the Denton Clay, deeper

water covered the area. The calcium carbonate deposits hardened into a

micritic limestone. Clay units have abundant shell debris and some

burrowing is evident. Marl beds vary from argillaceous limestone to

calcareous clay. Limestone units are dark gray when fresh and can have

thin (<0.6 ft.) Gryphea beds. Fossils include pelecypods: Anomia, Pectin,

Gryphea and Alectryonia; echinoids: Heteraster and Macraster;

a m mon ite : Pervi n quieria

The Fort Worth Limestone and the Duck Creek Limestone are both

grayish to yellow-gray or yellow-brown. Both formations are limestone

and difficult to differentiate. Fort Worth Limestone is a limestone with

alternating thin layers of marly clay. The upper 40 feet are creamcolored. The lower 10 to 15 feet has alternating layers of grayish-blue

clay/marl with yellowish-white limestone. Pecten are more abundant in

the Fort Worth Limestone while Gryphea are more abundant in the Duck

Creek Fm. They are generally prairie land. Fossils include echinoids:

Holaster simplex, Macraster; ammonites: Pervinquieria, Mortoniceras;

pelecypods: Exogyra, Gryphea and Alectryonia; brachiopod: Kingena

wacoensis, and na uti loids

Goodland Limestone Formation - Tarrant County

The Goodland is a white, fossiliferous, micritic, coarsely nodular,

limestone. Bedding is massive with some thin clay beds, The upper 5 feet is a fossiliferous, massive, limestone with oolites. Depositional

environment is interpreted as shallow, warm water, marine (not

necessarily near shore), and within the forces and actions of waves.

Oolites are formed around a nucleus where aragonite crystals grow in

layered rings as a result of the back and forth action of the waves. Since

aragonite is a polymorph of and is less stable than calcite, over, geologic,

time will convert to calcite. The fragmentation of the shells indicates an

erosional energy source (waves) and the intraclasts also indicate waves

as an erosional agent. The formation is medium to dark gray when fresh

and weathers to a yellowish brown. This unit has a low clay content

making it a good support for buildings.

Fossils include the ammonite Oxytropidoceras acutocarinatum,

pelecypods Protocardia, Pinna and Lima wacoensis, heaft-shaped urchins

in abundance, and miscellaneous gastropods.

Kiamichi Formation - Tarrant County

The Kiamichi has alternating layer of clay and limestone with units

generally not exceeding 5 feet in thickness. Sandstone is a minor

component. olive brown flaky shale that weathers to tan. Unconformities

bound the Paluxy above and below. A transgressing sea deposited clays

to form the Walnut Clay formation. Oyster reefs of Gryphea mucronata

create resistant, cliff forming benches over the underlying Walnut Clay.

Walnut Clay Format¡on - Tarrant County
calcareous clay and limestone interspersed with Gryphea beds. some of the beds form topographic benches. clay units are fossiliferous.

Limestone units when fresh, the color is dark gray and weathers to a

yellowish brown. clay units are olive brown and weathers to a yellowish

brown.

Paluxy Formation - Tarrant County

characteristically, the Paluxy Formation is a reddish sandstone and shale

unit that supports Post oaks. The environments of deposition were

coastal streams and beach environments. Ancient beach deposits form

localized dunes of white, well rounded, friable sand. some iron stains are

present in these dunes. These clean beach sands are unmistakable -

miles away from the present day ocean. Although not from Tarrant

county, dinosaurs like the Tenontosaur at the Dallas Museum of Natural

History are found in the Paluxy Formation in parker and Jack counties.

REFERENCES (not referenced by hyperlinks)

Caldwell, 8., and Brogdon, L., 1995, Leaders, Field Trip, Fotl Worth

Geological Society Geology of Tarrant County. (publisher not listed.)

Dawson, W.C., McNulty, C. L., Reaser, D. F., Leaders, L979, Fieldtrip

Guidebook for stratigraphy and structure of selected lJpper cretaceous

Rocks in No¡theast Texas. (Texas Academy of Science 82nd Annual

Meeting, Arlington, Texas.)

Fisher, W. L., Director, t972, "Geologic Atlas of Texas, Dallas Sheet":

Bureau of Economic Geology, (The universiÇ of Texas at Austin, Austin,

Texas.)

Graham, A. 1999, Late Cretaceous and Cenozoic history of North

American vegetation north of Mexico. (Oxford Univ. press, New york.)

Hagland, J., McKinzie, M.G. and Wilson, M.,2OOL, Field Guide to the

stratigraphy of the Dallas Fort wotth Area. (self published by the Dallas

Paleontological Society. )

Mason, 8., Berry, L. G., 1968, Elements of Mineralogy (Freeman and

Company, San Francisco, CA.)

Matthews, R, K., L974, Dynamic Stratigraphy. (prentice-Hall, Inc.,

Englewood Cliffs, New Jersy,)

Mckinzie, M., Morin, R., Swiatovy,8.,2001-,

the North Sulphur River. (Dallas Paleontological Society.)

Sellards, E. H., Adkins, W. S., and F. B. plummer, The Geotogy of Texas

(UniversiÇ of Texas Bulletin 3232, t932).

Surles, M,A. Jr., L984, "Nature and significance of Austin-Taylor

unconformity on western margin of east Texas basin.,' (American

Association of Petroleum Geologists, Bull. ; Vol/Issue:68:4; AAPG

annual convention; 2O May 1984; San Antonio, il, USA.)

þiþtþ.j sp?osti_!d=652290 S

"Texas Dinosaurs, Systematics" http tm
Welton, B. J., PHD, Farish, R. F., 1993, The Collector's Guide to Fossil

Sharks and Rays from the Cretaceous of Texas. (Before Time, Lewisville,

TX.)

Winkler, D. A., Murry, P. 4., Jacobs, L. L., Editors, 1989, Field Guide To

The Vertebrate Paleontology Of The Trinity Group, Lower Cretaceous Of

Central Texas. (Institute for the Study of Earth and Man, Southern

Methodist University, Dallas, Texas.)

Winton, W. M., Adkins, W. S. 1919, The Geology of Tarrant County,

(University of Texas Bulletin No. 1931.)

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