DEPARTMENT OF THE INTERIOR 

Hubert Work. Secretary 

U. S. GEOLOGICAL SURVEY 

George Otis Smith. Director 

Professional Paper 146 

MISSISSIPPIAN FORMATIONS OF SAN SABA COUNT'Y, 

TEXAS 

BY 

P. V. ROUNDY, GEORGE H. GIRTY, 

AND MARCUS I. GOLDMAN 

WASHINGTON 

GOVERNMENT PRINTING OFFICE 

1926 
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OF THIS PUBLICATION MAY BE PROCURED FROM 

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. WASHINGTON, D. C. 

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CONTENTS 

Page 

introduction, by P. V. Roundy_____ _ _ _ __ __ _ _ __ _ _ ____ _ _ ______ ____ __ ______ _______ ___ __ _ _____ ____ ______ __ __ ___ ____ 1 

Part I. Geologic age and correlation, by G. H. Girty _____________________________________________________________ 3 

Part II. The micro-fauna, by P. V. Roundy_____________________________________________________________________ 5 

Foraminif era ________________________________________________________________________________ . _ _ _ _ _ _ _ _ _ _ _ _ _ 5 

Ostracoda _____________________________________________________________________________ ~ ________ ~________ 5 

Conodonts ___________________________________________________________________ ~___________________________ 8 

Fish remnins ____________________________________________________________________________ . ______________ :.. _ _ 17 

Register of localities _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 17 

Part III. The macro-fauna of t.he limestone of Boone age, by G. H. Girty ___________________________________________ 24 

Coelenterata ______ . ________ .:. ___________________________________________________________ ._ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 24 

Brachiopoda_____________________________________________________________________________________________ 24 

Pelecypoda______________________________________________________________________________________________ 36 

Gastropoda______________________________________________________________________________________________ 36 

Pteropoda_______________________________________________________________________________________________ 38 

Cephalopoda_____________________________________________________________________________________________ 38 Trilob~a ______________________ ~ __________________________________________________________________ ~------ 39 

Part IV. Petrology of the contact of the Ordovician Ellenburger limestone and the Mississippian limestone of Boone age, by M. I. Goldlnan_' _________________________________________________________________________________ r _ _ _ _ _ _ _ 44 

Introduction ____________________________________________________________________________________________ 44 

Source of ~he specimens _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 44 

Specimen G 105: Contact of the Ellenburger limestone and the limestone of Boone age _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 44 

General description and interpretation _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 44 

The Ellenburger of specimen G 105 ___ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 45 

Generalfeatures__________________________________________________________________________________ 45 

Origin of the pellets ______________________________________ . _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 45 

Matrix of the pellet layers _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 47 

Silicification in the Ellenburger limestone___________________________________________________________ 47 

Stylolites in the Ellenburger limestone ___________________________ ·___________________________________ 48 

The basal Mississippian; an "echinoderm breccia" __________________________ ~____________________________ 48 

General description and interpretation _______________________ ._ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 48 

Cause of th.e fragmentation of the skeletal remains and growth of secondary calcite _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 48 

Rate of accumulation - - - - _ - - - _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 49 

Silicification in the basal Mississippian_____ __ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __ _ _ _ _ _ _ _ _ _ _ _ _ __ _ _ _ _ __ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __ _ _ _ 50 

Character of the Ellenburger directly underlying the contact with the Mississippian_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 50 

Specimen G 114: A fold at the contact of the Ellenburger and Mississippian _____________________________________ 50 

f\.nalysis of the fold_ - - - - - - - - - - - - - - - - - _ - - - - - _ - _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 50 

Method of study - - - - --- - --___ _ ___ _ _ _ ___ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __ ___ _ __ _ _________ _ _ __ __ _ _ _ _ _ _ __ _ _ _ 50 

Characteristics of the Ellenburger and the limestone of Boone age used in working out the structure of 

specimen G 114________________________________________________________________________________ 50 

Review of the thin sections of specimen G 114 I, and conclusions ____________ ~_________________________ 51 

Interpretation of the origin of the fold_ _ _ __ _ __ _ __ _ ___ __ _ _ ___ _ __ __ _ _ _ _ ___ _ _ _ _ _ __ _ _ _ _ __ _ _ _ _ _ _ _ _ _ _ _ _ ___ 52 

Age of the fold and load under which folding took place_______________________________________________ 54 

Orientation of calcite fragments in the folded rock_ - __ - ___ ..!._ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 55 

Features of the limestone of Boone age, especially of its basal contact in specimen G 114 ______________________ 55 

Pockets of material of Boone age in the Ellenburger limestone_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 55 

Sulphide along the contact_ -- - - - - - - - ~ - - - _ - _ - _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 55 

En vel opes around calcite fragments_ - - - - - _ - _ - _ - _ - _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 56 

Staining of the Ellenburger limestone by the Mississippian_____________________________________________ 56 

General observatiolls on silicificatioll_ - - - - - - - - - - - - - - - - - - - - - - - - - ~ _ - _____________________________________ ._ _ _ _ _ _ 56 

Three types of silicificatioll_ - - - ---- - -- ---.. ----- - ----- - _ - ______ :... _ __ __ __ ___ _ ____ _____________ _ _ _ _ _ _ _ _ _ _ _ _ 56 

Method of silicification:._______________________________________________________________________________ 58 

Sullunary________________________________________________________________________________________________ 58 Index _______________ . _________________________ ~ __________________ .__________________________________________ 63 

m 
ILLUSTRATIONS 

PLATES I-IV. Micro-fauna of the Mississippian formations of San Saba County, Tex _____________________________ _ 

V-VI. Macro-fauna of the limestone of Boone age in San Saba County, Tex ______________________________ _ 

VII. Specimen G 105: Ellenburger limestone and limestone of Boone age in contact ______________________ _ 

VIII. A, Detail of i, Plate VII, showing internal cast of a fossil in direct contact with surrounding pellets of 

Ellenburger limestone; B, Thin section of the upper part of the Ellenburger limestone, corresponding about to the position of B, Plate VIL _______________________________________________________ _ 

IX. A, Detail of y, Plate VIII, B, showing pellets partly embedded in the underlying solid layer; B, Detail of 

thin section corresponding about to area C, Plate VII, showing partial disintegration of Ellenburger pellets _______________________________________________________ ~ ___________________________ _ 

X. A, Detail of b, Plate VII, showing an angular fragment of Ellenburger limestone inclosed in a later 

layer of the Ellenburger; B, Detail of k, and l, Plate VII, showing rounded pebble composed of Ellenburger pellets inclosed in a later layer of the Ellenburger, and fissure containing granular yellow car- bonate ___________________________________________________________________________________ _ 

XI. A, Thin secti,on of Ellenburger limestone corresponding to position F, Plate VII, showing especially 

the distribution of yellow granular calcite and partly silicified fragments of Ellenburger; B, Thin 

section of typical limestone of Boone age, full of large fossil fragments ___________________________ _ 

XII. Detail of Plate XI, A, showing a partly silicified fragment in the Ellenburger limestone: A, Plain light; B, Between crossed nicols __________________________________________________________________ _ 

XIII. A, Detail around r, Plate VII, showing appreciable movement along stylolite S-S; B, Detail along 

stylolite S'-S', Plate VII, showing little movement along the stylolite ____________________________ _ 

XIV. General view of thin section G 105-D, showing contact of Ellenburger material and basal material of Boone age ________________________________________________________________________________ _ 

XV. Detail of irregular calcite fragments ill Plate XIV _______________________________________________ _ 

xvi. Enlargement of echinoderm fragment from Plate XI, B ___________________________________________ _ 

XVII. A, Detail of Plates VIII, B, and IX, A, showing secondary growth of calcite around a fossil fragment in 

the Ellenburger; B, Detail of Plate XI, B, showing secondary growth of calcite around fossil fragments in the limestone of Boone age ________________________________________________________ _ 

XVIII. Detail of Plate XIV, showing a silicified fossil fragment from the limestone of Boone age: A, Plain light; B, Between crossed nicols ___________________________________ ~ ______________________________ _ 

XIX. Polished face of specimen G 114-1, showing folded and silicified Ellenburger limestone and limestone of 

Boone age, with generalized diagram of the distribution of types of rock in area 8 and adjacent parts 

of the polished f ace ________________________________________________________________________ _ 

XX. Specimen G 114-II, showing. a polished surface about 2~ centimeters below that of Plate XIX ______ _ 

XXI. Diagrammatic illustration of flow lines and of the distribution of the five different types of rock in speci- men G 114-11, shown in Plate XX ____________________________________________________ .. _____ ,. 

XXII. General view of thin section G 114-1, showing silicified Ellenburger limestone ______________________ _ 

XXIII. General view of thin section G 114-5, showing limestone of Boone age not much dist~rbed, resting on silicified and probably fault-fractured Ellenburger limestone ______________________________ .:..:: ____ _ 

XXIV. General view of thin section G 114-4, showing unsilicified Ellenburger limestone somewhat subjected to 

flowage and to fracture ______________________ :. __________ :. __________________________________ _ 

XXV. General view of thin section G'114-2, showing the limestone of Boone age partly silicified and perhaps affected byfiowage ______________________________________________________________ :. __________ _ 

XXVI. General view of thin section G 114-3, showing a mixture of Ellenburger limestone and limestone of 

Boone age partly silicified __________ :. _______________________________________________________ _ 

XXVII. General view of thin section G 114-6, showing Ellenburger limestone and limestone of Boone age 

mixed and shattered by flowage and partly silicified ___________________________________________ _ 

XXVIII. General view of thin section G 114-8, showing Ellenburger limestone and limestone of Boone age 

mixed and shattered by flowage against the fault line X-X, Plate XIX __________________________ _ 

XXIX. General view of the glauconitic and phosphatic sand of thin section G 114-8, with some of the wall rock 

of silicified Ellenburger limestone: A, Plain light; B, Between crossed nicols _____________ .:. _______ _ 

XXX. A, Detail of Plate XXIII, showing calcite crystal with cloudy granular rim and very irregular clear 

center, plain light; B, Same a§! A, between crossed nicols; C, Similar to A, but with a more regular clear 

nucleus, plain light; D, Same as C, between crossed nicols ______________________________________ _ 

XXXI. A, Detail of Plate XXIII similar to Plat~ XXX, but showing three grains in contact, plain light; B, Same 

as A, between crossed nicols; C, Enlargement of a, Plate XXVII, showing an organic fragment partly 

silicified, plain light; D, Same as C, between crossed nicols _____________________________________ _ 

XXXII. A, Detail of a, Plate XXII, showing pellets in silicified Ellenburger limestone of fine grain and the margins 

of a calcite crystal of organic origin replaced by coarse-grained silica; B, Detail around d! Plate XXII, 

showing coarse calcite crystals of organic origin in the midst of silicified Ellenburger limestone of fine 

grain, the large calcite crystals replaced by fine and coarse grained silica ______ - ____ - - - - - __ - - - - - - - - -

XXXIII. A, Detail of e, Plate XXII, showing a large calcite crystal in the midst of silicified Ellenburger limestone of fine grain replaced by coarse and fine grained silica, plain light; B, $arne as A, between crossed 

nicols; C, Detail of thin section G 114-1, showing meshwork of veins in silicified Ellenburger limestone; 

D, Detail of thin section G 114-1, showing intersecting group of straight veins in silicified Ellenburger limestone _______________ - -' ____ - ___ - - - - - - _ - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

'.FIGURE 1. Diagrams showing the supposed development of the fold in specimen G 114_ - ____ - ____ - - - - - --- - - ---- --- - ---

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53 
MISSISSIPPIAN FORMATIONS OF SAN SABA COUNTY, rrEXAS 

INTRODUCTION 

By P. V. ROUNDY 

Deep drilling, for oil is now in progress in many 

fields, in spite of its great cost-a cost so great that 

the operators can no longer ignore the importance of 

using science to its fullest degree to reduce the cost 

of drilling and the risk of failure. Both in wildcat 

operations and in work in proved fields the identification of the formations penetrated by the drill is 

essential to intelligent development. Many wells have 

probably been drilled more than a thousand feet below tb~ ~owest point at which there is a chance of 

obtaining oil, and many other wells have been abandoned before they had reached the oil-bearing beds of 

near-by producing fields. Several methods of studying and correlating the strata penetrated by the drill 

are now used by the more progressive oil producers. 

Among these methods are (1) the plotting and comparison of the drillers' logs; (2) the preparation and 

study of accurate logs by inspection of drill cuttings; 

(3) the study of the heavy minerals in drill cuttings 

from different formations; and (4) the study of fossils found in drill cuttings and the comparison of 

such fossils with those found in known formations at 

their surface exposures. The first of these methods is 

probably more widely used and less accurate than 

any of the others. The next two are of great use in 

fields where a know:ledge of the stratigraphy is well, 

established, but the fourth method is of most service 

in fields where the subsurface beds lack distinctive 

lithologic characteristics and in exploratory work. 

This paper is the first of a projected series that 

will describe several micro-faunas (associations of 

microscopic fossils known to occur in a single formation or in s~lected groups of formations) from different parts of the Mid-Continent field, in order 

to furnish other students of such organisms a basis 

for comparison and identification. Where diamond 

core drills are used it is comparatively easy and 

not uncommon to obtain many specimens of the larger 

fossil invertebrates that have been studied in this 

country for, over half a century. In cuttings from 

u. well drilled with cable tools it is very unusual to 

obtain the large fossils in ot1;ler than a: fragmentary, 

unidrntifiable condition. The very small fossils, however, are usually present unbroken in some of the 

cuttings from deep wells that penetrate m,arine 

strata, such as prevail in much of the Mid-Continent 

region. Although most of them are visible to the 

naked eye when separated from the rock fragments, 

a microscope is required to study them successfully. 

For this reason they are called micro-fossils. 

In the Carboniferous rocks, micro-fossils con,sist 

of representatives' 'of the Protozoa, Coelenterata, 

Vermes, Mollusca, Crustacea, plants, and conodonts. 

Below is briefly set forth t,he value of these groups 

for correlation and identification of horizons. 

Of chief importance under the phylum Protozoa 

are the Foraminifera, which are very abundant in 

some of the Pennsylvanian and Permian formations 

and not uncommon in some of the Mississippian f?rmations. From our present know ledge of these 

forms, the species of some genera appear to be valuable horizon markers, but those of other genera are 

so variable that they appear to be worthless for this 

purpose. 

In the phylum Coelenterata only the sponges need 

be considered. In certain beds, such as the Marble 

Falls limestone, sponge spicules are exceedingly abundant. Very little has been done with these forms, 

but it appears that they may be of great regional importance as auxiliary evidence in stratigraphic work. 

Although several kinds of worm tubes have been 

found they either represent long-range species or else, 

if in reality they belong to many species, they do not 

preserve well-defined specific characters. Consequently they appear to be of comparatively minor importance in correlation. Annelid worm jaws may 

prove to be of stratigraphic significance, but they are 

su rare in Carboniferous rocks that they need not be 

considered here. Conodonts, according to some authorities, should be classed under the phylum Vermes, 

but until more is definitely known of their zoologic 

position I prefer to consider them an independent 

, group. 

In the phylum Mollusca some of the gastropods, 

though very minute, are yet apparently mature, and 

I believe that when more carefully studieCl, they will 

1 
2 MISSISSIPPIAN FORMATIONS OF SAN SABA COUNTY, TEXAS 

prove to be of considerable aid in determining horizons. Although minute specimens representing other 

classes of this phylum are often found, they ,appear 

to be immature or else so lacking in character that 

they might well represent the young of anyone of 

several larger species. The last statement applies also 

to most of the brachiopods, which, however, belong to 

the phylum Molluscoidea. 

In the class Crustacea, which is a part of the phylum Arthropoda, the ostracodes are, decidedly the 

most important in correlation. They were abundant 

throughout the Carboniferous period. 

Of the fossil plants, seeds and spore cases nlay 

prove to be of great importance. Naturally, they Inay 

be found in strata that do not contain marine forms. 

The conodonts, small, jawlike fossils whose zoologic 

position is still a matter of conjecture, occur in both 

the Pennsylvanian and the Mississippian rocks. 

These forms I believe will prove to be of considerable importance in stratigraphic work when they 

have been more fully studied. 

In the identification and correlation of horizons, 

especially over considerable geographic distances, the 

use of faunas (associations of species) is more to be 

relied upon than the' use of individual species. 

In the two faunas described in this paper, the ostracodes and conodonts include most of the micro-fossils. 

A mmodiscus is the only foraminifer present. These 

micro-fossils are described in Part II. A few minute 

Mollusca are present, but they appear to be the young 

of larger forms and therefore are not described. The 

larger forms obtained from the lower formation are 

described by George H., Girty in Part III. These 

fossils are much smaller than the usual macro-fossils, 

and therefore might sometimes be obtained In an 

identifiable condition from ,veIl cuttings. 

The Mississippian rocks of San Saba County, Tex., 

consist of two distinct formations-a limestone of 

Boone age and the Barnett shale. The lower formation is a gray, medium-hard, somewhat crinoidallimestone exposed, so far as I am a ware, only along the 

road to Chappel about 3 miles southeast of the courthouse at San Saba. This limestone,' which is only 

about a foot thick, at first glance appeared to be the 

top part of the Ellenburger limestone, as it is not conspicuously separated from the top of the true Ellenburger and gave evidence of unconformity with the 

Barnett shale. Numerous fossils collected by K. C. 

Heald and me from this limestone show .it to be of 

Boone age. The line of' contact between the two 

lImestones is hard to determine, as there appears to 

be a transition from the light-colored Ellenburger 

(Cambrian and Ordovician) limestone into the darker 

:l\1ississippian limestone. This interesting contact is 

discussed by Marcus I. Goldman in Part IV. 

The upper formation of the ~1ississippian in this 

area consists of black shale with some limestone beds 

in its upper part. Plummer and ]\100reiri 1921 gave 

the name Barnett shale to the "shale and limestone 

strata between the massive beds of the Marble Falls 

limestone above and the Ellenburger (Ordovician) 

limestone. " 

In Part I of this paper George H. Girty discusses 

the age and correlation of these formations. The 

evidence furnished by the micro-fossils, described in 

Part II, strongly confirms the reference of these beds 

to the Mississippian, despite the fact that most of the 

forms are new. 
Part I. GEOLOGIC AGE 'AND CORRELATION 

By GEORGE 1I. GmTY 

The Mississippian rocks of San Saba County, Tex., 

consist of two formations. The upper is the Barnett 

shale, which has always been included in the" Bend 

series," and the lower is an undescribed limestone 

which has always been excluded from the "Bend 

series" and, if observed at all, considered to be a part 

of the Ellenburger limestone, of Ordovician and 

Cambrian age. . 

The fauna of the lower limestone is wholly unknown and is in many respects peculiar. On th:.s 

account I have, in Part III, described it in detail, 

both because such treatment seemed essential as ('.l, 

warrant for the conclusions as to geologic age who'5B 

ucceptance is asked and because the fauna may prove 

of economic importance as well as of scientific interest, for all the species are small, almost minute, 

and thus expectable of preservation in drillings from 

,Yells, so that the information thus supplied may 

prove useful to the oil producer. 

The other formation referred to the Mississippian 

is the Barnett shale. The Barnett shale as originally 

defined by Professor Moore 1 is not exactly the same 

as his" lower Bend shale" but includes at the top 

some calcareous beds that were formerly inclucle;l 

in the Marble Falls limestone of this region. Stratigraphically the change is immaterial; paleontologically it is highly important, as it turns both formations into units, faunally considered, and makes the 

content of the Marble Falls limestone her~ the same, 

so far as we can tell, as in the typical section at 

~1arble Falls. 

The geologic age of the Barnett shale has been considerably debated. It. contains abundant fossils, but 

its fauna is not especially varied and is not comparable with any of the typical faunas of the American 

Carboniferous section. If it were more closely allied 

to our typical Mississippian faunas such difference of 

opinion could not well exist, and, I might add., it 

would likewise in large measure melt away if all the 

evidence at present unpublished were generally 

known. To present this evidence for the consideration of anyone who is interested in it is impossible at 

this time; I can do no more than outline its' general 

character. 

1 Plummer, F. B., find Moore, R. C., Stratigraphy of the Penllsylvnnian formntlons of north-centrnl Texfis: Texas Unlv. Bull. 2132, 

p. 24, 1922. 

The most striking elements of the Barnett fauna. 

are Leiorhynchus in great abundance, goniatites 

closely allied to the European species G. C'f'enistria 

and G. striatus, and Posidonia-like shells that I 

have referred to the genus Oaneyella. There are other 

types that in a less cursory treatment would be important, but these are the salient ones. This fauna 

at once recalls that found in the lower part of the 

Carney ~hale, 2 and one can hardly doubt that both 

are of the same geologic age. Thus far there is very. 

little to indicate whether this age is Mississippian or 

Pennsylvanian, unless we transfer our consideration 

to certain faunas of Europe, for, as just noted, the 

Barnett and lower Caney faunas contain very little 

that would aid in establishing their place .in the 

American Carboniferous section. They are, however, 

strikingly similar to the Moorefield fauna in northern 

Arkansas and the "Mayes fauna" (or part of it) in 

northeastern Oklahoma, and the Mississippian age 

of the Moorefield and "Mayes" formations is beyond 

possibility of question; the Moorefield is overlain by 

rocks that contain a whole series of faunas which, 

although they present a number of peculiar features, 

are universally recognized as of Chester age. 

These are by no means isolated facts. FauJias of 

this general type are widely distributed on the North 

American continent; they occur in the Appalachian 

region, in lJtah, in Nevada, and in Alaska, and everywhere they are of Mississippian age. This does not 

mean, as it might, merely that I have classified them 

in the same way; it means that in most instances 

more or less conclusive Mississippian evidence, and 

in no instance any Pennsylvanian evidence exists, 

for the age of these faunas. It should be borne well 

in mind that I am using the term fauna in a broad 

way, for as no two collections, even though they are 

made at the same place, bring to light exactly the 

same series of species, still less do two collections from 0 

beds at the same horizon at different places. Thus 

M oorejieldella eurekensis is not known in either the 

Barnett shale or the Caney shale, but it is abundant in 

northern Arkansas, in north~astern Oklahoma, in the 

Appalachian region, and in Nevada; and so with other 

forms, such as Productella hirsutiform.ds. As nearly 

as the facts are known to me this type of fauna is apt 

2 Girty, 'G. H., The fauna of the Caney shale of Oklahoma' 11 S 

Goo1., Survey BUll. 377. 1909.' . . • 

3 
4 MISSISSIPPIAN FORMATIONS OF S.AN SABA COUNTY, TEXAS 

to have lived where black shales or black shaly limestones were forming; it varies from place to place but 

is always restricted to Mississippian time. In other 

words, of the numerous faunas coming under my observation all that seem related to the Barnett (or the 

lower Caney) fauna, or that secondarily are related to 

one of those so related·, are of Mississippian age, whereas of the faunas determined as Pennsylvanian none seem 

related to the Barnett (or the lower Caney) fauna. 

Detailed study of the collections when they ~re brought 

together and compared may show that these statements 

are too sweeping, but the preponderance of evidence 

in th,is sort is at present practically overwhelming. 

On the opposite side, I know of very few facts or 

arguments deserving comment. I shall mention but 

not in this place discuss the fact that the Jackfork 

sandstone, which underlies the Caney shale, and the 

Stanley shale, which underlies the Jackfork, have by 

some writers been referred to Pennsylvanian time. 

The paleontologic evidence from the Stanley is hardly 

wo~th considering. The fauna on which the Jackfork 

ha's been assigned to Pennsylvanian time is probably 

Pottsville, as claimed, but it also' probably does not 

come from the Jackfork but from another sandstone, 

which is locally superimposed on the Jackfork and 

whi~h, by a more than doubtful usage, has been included under the same formation name. 

'Returning to the Barnett shale from a wide digression, I find its fauna to be related to faunas of Mississippian age and only to faunas of Mississippian age 

so far as known. From the overlying Marble Falls 

fauna it is separated by an abrupt and profound 

change at a horizon marked in San Saba County by 

an obscure unconformity, the evidence for which is 

presented by Mr. Goldman.1 Though the unconformity is far from obvious in this region it is more 

manifest at Marble Falls, where the Barnett shale 

is apparently absent, so that the Marble Falls limestone, which is of Pennsylvanian age, seems to rest 

direCtly on the Ellenburger limestone. One might 

feel justified in believing this to be the widespread 

unconfornilty that is so' generally found between 

Mississippian and Pennsylvanian rocks in eastern 

N o~th America. 

:I. U. S. Geol. Survey, Prof. Pa~ 129, pp. 1-22, 1922. 

Although the close relationship between the Barnett and certain Mississippian faunas can not be disputed, the suggestion has sometimes been made that' 

in this region faunas of the Barnett type survived 

into Pennsylvanian time. One would be rash to deny 

that such 'a survival could take place, while wondering on what grounds it is supposed to have taken 

place in San Saba County. Certainly such a hypothesis should not be adopted in any case without weighty 

evidence and almost as a last resort, but the facts 

here point very much the other way. Evidence for 

or against this hypothesis might perhaps best be 

looked for in northeastern Oklahoma and in adjacent parts of Arkansas, where exposures are numerous, where fossils are abundant, and where the boundary between Mississippian and Pennsylvanian is 

well recognized. This region is known in considerable detail both stratigraphically and paleontologically, but in no instance has a fauna even remotely 

res~mbling the fauna of the Moorefield, Caney, and 

Barnett formations been found above the top of the 

~1ississippian. In other words, out of many hundred 

collections none having a l\rIoorefield facies has been 

found stratigraphically above one having a Morrow 

or any other Pennsylvanian facies. 

The fauna of the Barnett shale would tend to link 

that formation with the lower part of the Caney 

shale, and on similar grounds the lower part of the 

Caney shale would be linked with the Moorefield 

shale. I have hesitated to restrict the correlation of 

the lower Caney to the Moorefield alone, however, because, although the prevailing fossils of the Fayetteville shale, fossils which determine its age quite definitely as Chester, do not occur in the Caney, certain 

of the characteristic Caney forms do occur in the 

Fayetteville. Caneyellas and goniatites like those of 

the Caney shale are found near Fayetteville, and 

Leiorhynchus occurs in abundance near Marshall. It 

seems possible, therefore, that the lower Caney may 

represent the whole Moorefield-Fayetteville interval 

'of the Arkansas sect~on. The 'upper Caney, or beds 

that have been included in the upper part of the 

Caney, are without much doubt of Pennsylvanian 

( Pottsville) age. 
Part II. THE MICRO-FAUNA 

By P. V. ROUNDY 

FORAMINIFERA 

Family LITUOLIDAE 1 

Genus AMMODISCUS Reuss 

Ammodiscus sp. 

The only Forall.linifera found in the collections 

from the Barnett shale are. a few poorly preserved 

specimens of Am1nodiscus. They . are minute flat , disldike forms. The central part of the disk is undeterminable, bllt the outer part shows on the best 

specimens from four to six coils. The tube appears 

to be without constrictions and to be very gentle in 

its tapering. Although clearly belonging to the genus 

A17~'l1wdiscus, these specimens do not warrant thc 

establishment of a specific name. They range from 

{).25 to 0.35 millimeters in diameter. 

I-Iorizon and locality: Barnett shale, San Saba. 

-County, Tex., (stations 7011A and 7687). 

OSTRACODA 

Ostracodes belong to the same class as the trilobites. 

They are small indistinctly segmented Crustacea with 

not over seven pairs of appendages; inclosed in a 

horny or calcareous bivalved shell. The Carboniferous ostracodes are usually less than 2 millimeters in 

length. These forms have been studied extensivelv 

in Europe, T. Rupert Jones,' of England, having published from 1855 to 1895 over 50 papers, most of 

which deal with Paleozoic o·stracodes. Other authors 

ha ve added to the literature of the.se interesting forms 

until there is now a vast amount of mow ledge a ,Yail· 

able. Occasionally smne American material has been 

described by some of these workers, but on the whole 

the American ostracodes frOl11 Carboniferous strata 

are mainly still undescribed. The greatest amount 'of 

work on these forms has been done by G. R. Girty, 

E. O. Ulrich, and R. S. Bassler. Ulrich and Bassler 

have also written papers on many of the pre-Carboniferous species and probably the best text on the Paleozoic ostracodes. 2 

1 'l'be genus Ammodiscus is placed in the family Lituolidae by Fred-

·ericl{ Chapman (Tbe Foraminifera, an introduction to the study of 

the Protozoa, 1902). Joseph A. Cushman places this genus in the 

fllmUy Astrorhizidae (U. S. Nat. Mus. BUll. 100, vol.· 4, 1921). 

1I Paleozoic Ostracoda; their morphology, classification, and occur-

,'(\IlCC: Maryland Geol. Survey, Silurian, pp. 271-322, 1923. 

n1448-26--2 

In the Barnett shale ostracodes are cOlnparatively 

rare. In the subjacent limestone of Boone age, however, ostracodes are abundant. As many of these ostracodes are new I have described some about which 

my present conclusions seem rather definite. Other 

forms that probably represent several genera and 

species, mairily new, I feel are inadequate to serve 

as types and therefore I am passing them with this 

brief mention. 

In the erection of two new genera in this' paper~ 

I have described two .species of ostracodes from the 

Pennsylvanian so that I might have better and more 

typical genotypes. 

Family APARCHITIDAE Ulrich 

Genus SANSABELLA Roundy, n. gen. 

Carapace small, less than 2 millimeters in length; 

outline varying somewhat from a parallelogram; 

greatest thickness in anterior half. Left valve larger 

than right, overlapping on ends and ventral margin. 

Hinge line straight, equal in both valves and, in part, 

slightly lower than the dorsal margins of the two 

valves, giving an excavated or channeled appearance 

in the dorsal view of a bivalved specimen. The hinge 

structure consists of a longitudinal groove and tongue 

on each valve. On the left valve the upper or dorsal 

margin of the groove is slightly larger and forms the 

tongue; on the right valve the lower margin of the 

groove is considerably stronger and forms the tongue. 

Genotype, SansabeZZa ampZectans. 

All the specimens of the two species of Sansabella 

described in this paper are bivalved specimens, which 

do not show the hinge structure. However, in a collection from the Caney shale there are some single 

valves which show the character of the hinge structure clearly. 

This genus is evidently related to J onesina in relative size of valves. In the figure of the type species of 

that genus, JO'Msina fastigiata, the left valve is shown 

as overlapping on the dorsal as well as on the end and 

ventral margins. This would seem to indicate that 

the genotype of that genus could not have possessed 

~ cardinal V groove such as is characteristic of Sansabella. In Sansabell~ ampZectans the valves are 

l? 
6 MISSISSIPPIAN FORMATIONS OF SAN SABA COUNTY, TEXAS 

without sulcus or node; in S. sulcata a simple sulcus 

and deep central pit are present. 

Of the species now placed under J onesina, J. bolZiiformis, originally described as Beyrichiella bolliiformis, should probably be placed under SansabeZla 

on account of its exca vated or channeled dorsum. 

This transfer should certainly be made if the relative 

size and manner of joining of the two valves are of 

more importance than the sculpture of the sides, especially as the sculpture of the species now placed under 

J onesina are so far from uniform. 

Sansabella ampleetans Roundy, n. sp. 

Plate I; Figures 3a-5 

Shell small, outline resembling a parallelogram. 

Hinge. line straight, slightly exca vated. Posterior 

end somewhat rounded. Anterior end slightly more 

rounded. Backward swing pronounced. Left valve 

larger than right, broadly overlap.ping it on the·.anterior, posterior, and ventral margins. A portion of 

the dorsal margin of each valve projects slightly 

above the hinge line and then is sharply reflexed so 

that the two meet evenly at the hinge line, giving the 

excavated appearance to the dorsal aspect of the species .. Greatest thickness just in front of and slightly 

above the middle of the shell. The left valve is 

slightly depressed a short distance back from the anterior end, producing, in dorsal view, symmetry with 

the overlapped anterior end of the right valve. Surface smooth. About one-tenth of the specimens 

faintly suggest a median pit. All specimens are 

. nearly uniform in size, the average dimensions being, 

length, 0.88 millimeter; height, 0.55 millimeter; 

greatest thickness; 0.40 millimeter. 

Horizon and locality: Marble Falls limestone; San 

Saba County, Tex. (station 2690). 

Sansabella sulcata Roundy, n. sp. 

Plate I, Figures 6a-7 

Shell small, outline resembling a parallelogram, 

ends somewhat rounded. Hinge line straight and 

about two-thirds as long as greatest length of carapace. Left valve larger than right, overlapping 

broadly on ventral margin and moderately on anteriOl~ 

and posterior margins. Valves reflexed on dorsal 

edge so as to form a V channel along the hinge line, 

which lies in the bottom of channel, the two valves 

meeting equally at the hinge line. A deep distinct pit 

occurs on each valve slightly above and behind the 

center of the carapace. A shallow but distinct sulcus 

extends from the pit part way toward the dorsal edge. 

Greatest thickness of the shell near middle of the anterior half. Average dimension~ of most specimens: 

Length, 1.28 millimeters; height, 0.76 millimeter; 

greatest thickness, 0.60 millimeter. A few specimens, 

evidently young, are much smaller but they also show 

the pit and sulcus. 

This species is distinguished from S. arnplecta;ns by 

the deep pit and shallow sulcus, by its large size, 

and by its more elongated appearance due in part to 

its straighter ventral edge. 

Horizon and locality: Barnett shale, San Saba 

County, Tex. (station 2618). 

Genus AURIGERITES Roundy, n. gen. 

Shell small, sub ovate, left valve overlapping the 

right on the ends and ventral margin. In the ventroposterior quarter of each valve is a· simple loop ridge 

with the two ends pointing anteriorly. As only one 

species is known, the complete generic characters 

probably have not been determined. 

Genotype, .A urigerites texanus. 

Aurigerites texanus Roundy, n. sp. 

Plate I, Figures 8-10· 

Shell small, subovate. Hinge line straight and 

short, being slightly over half the greatest length of 

the shell. Dorso-anterior angle gently rounded; 

dorso-posterior angle slightly more angular. Ends 

of shell and ventral angles smoothly rounded; middle 

of ventral margin nearly straight. Posterior end of 

shell both "thicker and higher than anterior end. Left 

valve larger and overlapping the right valve on all 

margins except along hinge line, where the two meet 

evenly. In the ventro-posterior quarter of each valve 

is an elevated horseshoe-like ridge, highest at its 

middle, which projects nearly as far back as the shell 

margin. The ridge diminishes gradually in strength 

from the center and the ends become obsolete about 

h'alf-way to the middle of the shell. The shell surface 

inclosed by the loop is flat. This loop ridge causes 

the shell to appear as if it had an ear on each valvl3. 

Surface of shell smooth. The specimens of this spe~ 

cies vary but little in size, the average dimensions 

being, length, 0.84 millimeter; height, 0:51 millimeter; 

thickness, 0.39 millimeter. 

Horizon and locality: Limestone df Boone age UIlderlying the Barnett shale, San Saba County, Tex. 

(station 2623). 

Genus PARAPARCHITES Ulrich 

Paraparchites sp. 

Three poorly preserved specimens probably belong 

to this genus, but they do not appear to conform 

with any of the described species and their imperfect 

condition does not warrant a detailed description. 

Horizon and locality: Limestone of Boone age underlying the Barnett shale, San Saba County, Tex. 

(station 2623). 
THE MICRO-FAUNA 7 

Family XIRXBYIDAE 

Genus XIRKBYA Jones 

Kirkbya lindahli Ulrich? 

1891. [\.il'l.;blJ((. li1Mlahli Ulrich, Cincinnati Soc. Nat. Hist., 

Jour., yol. 13, p. 207, pI. 18, figs. Ga-6c. St. Louis 

group: Columbin, Ill. 

Two separate right valves appear to be much nearer 

to this species than to any described form. In shap~ 

and convexity they are nearly identical with the 

type as figured. They are smaller, howe.ver, being 

approximately half the size. The specimens are 

poorly preserved, apparently etched by weathering, 

so that it is not possible to determine if the surface 

was originally smooth or reticulate .. A marginal rim 

is definitely pr~sent. 

Horizon and locality: Barnett shale, San Saba 

County, Tex., (station 2613D). 

Kirkbya lindahli var. arkansana Girty 

Plate I, l!'igures 14a-16 

1910. Kh·l.;blla U,1ul(t1l,U yar. a1·l.;(tnsa.na Girty, New York Acad. 

Sci. Annals, vol. 20, p. 234, Basal Fayetteville shale, 

Fayetteville quadrangle, Ark. 

Shell small, subrhomboidal, narrowing slightly 

toward the front, and with a distinct backward swing. 

Hinge line straight. Anterior end well rounded and 

narrow, posterior end broad and rounded on lower 

two-thirds, nearly straight on upper third. Greatest 

height posterior to the middle of the shell. The faint 

surface sculpture is preserved only on specimens from 

station 2623; the' other specimens, b~ing somewhat 

weathered, appear to be smooth. A slight depression, 

probably the remains of a central pit, is faintly discernible. Length, 1.5 millimeters; height, 0.8 millimeter. 

As the original description of this variety appeared 

without illustrations I am also giving figures of the 

type specimen here. 

I-Iol'izon and locality: Barnett shale and the underlying limestone of Boone age, San Saba County, Tex. 

(stations 2613D, 2618, 2623). 

Genus AMPHISSITES Girty 

1910. Am,ph'issites Girty, New York Acad. Sci. Annals, vol. 20, 

No.3, pt. 2, p. 235. 

This genus has as its type Amphissites rugosus 

Girty, described in the same paper with the generic 

definition, but not illustrated. For. that reason I am 

giving figures of the genotype (PI. I, figs. la-c). 

The original definition of the genus is as follows: 

A number of ostracode shells in the fauna of. the basal 

)fayetteville shale belong to types which have been loosely 

referred to the genus Ki1'kbya, but they really appear to represent three generic or subgeneric groups. Kirkbya itself 

b described as having the right valve larger than the left 

and overlapping it. This is the condition of K. Zindahli val'. 

a1·kansana. The shell described below as Amphissite.s. ntg08us has the two valves equal, meeting each other along a 

line, neither one overlapping the other. It is furthermo're 

distinguished by having the surface marked by a number of 

tubercles in addition to the fine reticulations. On both these 

nccounts it seems that this form can readily and advantageously be distinguished from Ki1·1.;bya proper. The third 

type is represented by Glyptopleura inopinata, which has the 

left valve overlappjng the right. Conjoined with this difference in configuration is one of sculpture, the sides being without knobs or plications but ornamented with oblique, inosculating costae instead of the fine reticulations and flanges 

of the other types. 

This genus is rather common in the Carboniferous 

rocks of America, from which I have several undescribed species. Besides the genotype, two described 

species, If irkbya cent1'onatus Ulrich and Bassler and 

Kirkbya tricollina Jones and Kirkby, belong under 

this genus. 

Amphissites chappelensis Roundy, n. sp. 

Plate I, Figure 2 

Shell small, subquadrate. Hinge line straight, posterior angle rather sharp, anterior angle more rounded. 

Ends and ventral margin gently curved; nliddle of 

ventral margin nearly straight and parallel to hinge 

line. A smooth narrow flange extends along the ends 

and ventral margin, completely concealing the valve 

margin in side view. However, there is a narrow 

. area of the shell between. this flange and the edge of 

the shell, perpendicular to the plane of the valve 

juncture. The flange is slightly reflexed near the 

ventro-anterior margin, a feature probably due' to 

accident to the shell before fossilization. Within this 

flange occurs a secon~, slightly heavier though not 

wider smooth flange. It is nearly parallel to the 

first except near the posterior cardinal angle, where 

it approaches the angle with diminishing' size and 

becomes obsolete before touching the outer flange, 

and near the anterior cardinal angle it merges with 

the outer flange. A central low, well-rounded broad 

tubercle is slightly posterior to the center of the 

valve. At its front edge is a very slight depression' 

corresponding to the usual central pit of this genus. 

However, it is not of the. definite character usually 

noted in other species of this genus. Midway between 

this tubercle and the anterior end of the valve but 

nearer the dorsal margin is a gentle elevation or 

swelling of the shell surface surmounted by a low, 

short, smooth, slightly curved ridge, nearly parallel 

to the corresponding portion of the second flange. 

A similar ridge occurs on the central part· of .the 

posterior half of the valve, but it is about twice as 

long as the· anterior- one, and without ·the· special' 

swelling of the shell surface beneath it. Surface of 
8 . __ ~:('-: .. ",. MISSISSIPPIAN FORMAT,IONS OF SAN SABA COUNTY, TEXAS 

,the valve finely reticulate. Length, 0.80 millimeter; 

height, 0.46 millimeter. 

This species is based on a single well-preserved 

right valve. The species it nearest resembles is A. 

'centr-onatus. In A. centronatus the central node is 

directly above the central pit, much nearer the dorsal 

margin, 'and more central as regards the ends. The 

s.hort ridges anterior and posterior to the central 

tubercle are of nearly equal length and strength, and 

there appears to be no special swelling of the shell 

surface under either of them. 

Horizon and locality: Barnett shale, San Saba 

County, Tex. (station 7011A). 

Family BAIRDIlDAE ~ 

Genus HEALDIA Roundy, n. gen. 

Shell usually small. Dorsal margin curved, almost 

angular in the middle, 'the posterior slope in most 

species straight as if the dorso-posterior corner' were 

removed by truncation. The anterior dorsal slope 

gently curved and rounding off into the broadly 

curved anterior end. Posterior margin more sharply 

rounded. Slightly in front of that end is a swollen 

area on each valve, not well differentiated from the 

shell contour in front but more conspicuous at its 

rear end. The vf,mtral margin is nea'rly straight in 

its middle portion, rounding off into the ends. Left 

valve larger than the right, conspicuously overlapping it on all sides except on the dor~o-posterior slope, 

where the overlap is usually slight. Separate left 

valves show a distinct groove fo'r the reception of the 

right val-ve. Surface of the valves smooth; most 

species have on the posterior swollen area of each 

valve two backward-pointing spines, and one species 

has a small punctate area in front of the two spines. 

Jones and Kirkby 3 described under the name Bytho cypris ? cornigera a species that, probably belongs to this genus. This form, however, is clearly 

distinct from the typical Bythocypris, as originally 

proposed by Brady. 

Genotype H ealdia 8implex. 

Healdia simplex Roundy, n. sp. 

Plate I, Figures lla-He 

Shell very small. Dorsa,l margin gently curved in 

the anterior half, nearly straight in the posterior 

half, and subangular near the middle point. Ventral 

lnargin nearly straight but curving gradually into 

the rounded ends. The carapace viewed from above, 

is wedgelike, the anterior end being thin and sharp. 

The thickened or swollen posterior end and the rather 

peculiar dorso":posterior slope are characteristic of 

the genus. In this species the dorso-posterior portion 

8 Annals and Mag. Nat. Hist., 5th ser., vol. 18, p. 2!'il. pI. 6, figs. 

8-9, 1886. 

appears as if it were flattened by a hammer. On the 

outward posterior portion of the swollen area no 

spines are developed, although in most of the species 

of this common Carboniferous genus spines in this 

region are a normal part of the shells. Left valve 

larger, overlapping the right on all sides. On the 

flattened dorso-posterior margin, howe'ver, the overlap is almost negligible in its exterior expression. Although there is a slight variation in the greatest 

dimensions of the individuals, all are fairly close to 

the average; which is, length, 0.67 miilimeter; height, 

0.42 millimeter; thickness, 0.29 millimeter. 

Horizon and locality: Grahanl formation (Cisco 

group), Stephens County, Tex. This species ~lso oceurs in other Pennsylvanian formations. 

Healdia am pIa Roundy, n. sp. 

Plate I, Figures '12a-13 

This species differs from H. sirnplex by having its 

dorso-posterior slope less conspicuously flattened, by 

its much largel~ size, and by its more pointed posterior 

end. In addition it has the stumps of two rather 

large spines on the outward posterior part of the 

swollen portion of each valve. These spines are 

broken on all the specimens from San Saba County, 

but specimens from other localities show them to be 

large and conspicuous. Length, 1.51 millimeters; 

height, 0.84 millimeter; thickness, 0.63 millimeter. 

Horizon and locality: Limestone of Boone age, underlying the Barnett shale, San Saba County, Tex. 

(station 2623). 

Family CYTHERIDAE 

Genus XESTOLEBERIS Sars 

Xestoleberis? subcorbuloides Jones and Kirkby? 

1886. Xestoleberis' s1tboorb'ltloides Jones and Kirkby, Annals 

and Mag. Nat. Hist., 5th ser., vol. 18, p. 264, pI. 0, figs. 

8 a-b. 

A single specimen in my collections appears to be 

nearly identical with the English form in outline and 

contour. Its great tumidness' and flattened dorsal and 

:ventral margins with rounded ends distinguish it at 

once from the other species in the San Saba collections. The overlap is much less pronounced in my 

specimen than in Jones and' I{irkby's figure. My 

specimen is 0.84 millimeter long; theirs is 0.75 lnillimeter. 

Horizon and locality: Limestone of Boone age, underlying the Barnett shale, San Saba County, Tex. 

(station 2623). 

CONODONTS 

The name conodont was given by Pander 4 to certa.in minute toothlike fossils, of which he described 

4. Pander, C. H., Monographie der fossilen Flsche des silischen Sys· 

tems der rnsslsch-baltischen Gonvernements, St. Petersburg. 1856. 
THE MICRO-FAUNA 9 

13 genera and many species. The zoologic relationship of conodonts has been a subject of much contr.oversy, and they ha ve been regarded by various 

a,uthors as parts of gastropods, fishes, annelid worms, 

nnd crustaceans. Until more is known about these 

organisms their zoologic position must remain unproved. 

I-linde IS described several conodonts and grouped 

together under one 'name, Polygnath'l.{'s dubius, many 

diverse forms. FIis reason for considering that these 

various forms bclonged to one species was that he 

found crushed together in a small ball~like mass many 

teeth and plates. (See his description quoted under 

Poly.qnathus, p. 13.) 

Probably the grouping of this great variety of 

forms under a single species by Hinde and later by 

Clarke G has tended to discourage a systematic study 

of the conodonts and to retard the development of a 

detailed classification of these forms. As the character of the organisms bearing these teeth is not 

]mown, a classification of them must at best be very 

artificial. Yet such a classification must be establi.shed in order to study and determine the value, of 

these forms as horizon markers. Therefore, I believe 

that many of the genera already recorded in the 

literature should be more or less redefined and restricted. 

Conodonts are classed as simple or compound.. The 

s.imple conodont consists of a single Illinute tusklike, 

usually more or less conical tooth, the lower or larger 

cnd of which is the base. No simple conodonts are 

described in this paper. The compound conodont 

consists of two or nlore teeth attached to a straight, 

bent, or irregularly shaped bar, rod, or plate which 

is lOlOwn as the base. The teeth may be like short or 

long, slender or robust spines, like sawteeth, like 

knobs, or like wedges. The teeth on a single speci·. 

men Inay be of similar or various types and sizes. 

The base usually bears on its lmde·r side an excavation 

or depression, which is called by some authors a pulp 

cavity, although in reality its function may have 

been far from that of the pulp cavity in the true 

teeth of the higher vertebrates. The San Saba County 

conodonts are mostly more or less translucent,' some 

being almost transparent, and are mainly of a light 

amber color. Chemically they appear to be a phosphatic carbonate of lime. 

Accurate and concise description of 'animal remains 

of complicated structure or contour requires some 

system of orientation. In dealing with remains such 

as the conodonts, whose zoologic rehitionship is un·· 

proved, any system of orientation must of necessity 

be purely artificial. For the purpose of more exactly 

I Hinde, G. J., Geo1. Soc. London Quart. iour.,, vol. 35, p,p. 351-369, 

1879. 

o Clnri{c, J. M., New Yorl, State Geologist Sixth Ann. Rept., pp. 

:30-33, 1887. 

and concisely depicting the characters of these fossils, I am considering that each conodont occurred 

in the side of an imaginary lower jaw with the sharp 

ends of the teeth or of the largest tooth pointing upward, inward, or backward, and with the base, when 

like a rod or bar, parallel with the side or front or 

the jaw. Consequently the descriptive terms I have 

u~ed are without anatomic or zoologic significance. 

Although conodonts occur in several, of the Car-' 

boniferous formations of Texas they a.ppear to be 

abundant only in the Barnett shale, where from 

comparatively few collections I have obtained many 

hundred individuals. From the Strawn formation, 

Marble Falls limestone, and Canyon and Cisco 

groups, with lllany times the nunlber of collections, 

I have obtained but a comparatively small number 

of individuals. Therefore, a well cutting or shale 

sample from north-central Texas that contains sev-

. €iral conodonts at once suggests but not necessarily 

proves the age to be Barnett. However, I believe that 

when the conodonts from the higher horizons arc 

more perfectly known, very few of the species described here will be found to occur in the higher 

rocks. 

A bibliography of conodont literature i~ given below. It includes everything except textbooks on paleontology, which in general give but a brief mention 

and reproduce a fe,v previously published figures. 

1856. Pander, O. H., Monographie del' fossilen Fische des 

silurischen Systems del: russisch-baltischen GO,uvernements, St. Petersburg, 91 pp., 9 pIs. (Original definition of conodonts. Many species and genera described.) 

1861. Harley, J., London GeoI. Soc. Quart. Jour., vol. 17, pp. 

543-552, pI. 17. (Discusses zoologic position. Probably seyeral specimens that be described are not conodonts.) 

1861. Owen, Richard, Paleontology, 2d ed., Edinburgh, p. 117. 

(Brief discussion of systematic position.) 

1863. Von Eichwald, O. E., Soc. imp. nat. Moscou Bull., vol. 

36, p. 375. (Brief discussion of systematic position.) 

,1870. Moore, Oharles, British Assoc. Adv. Sci. Rept. 39th 

Meeting, 1869, pp. 375-377. (Oonodonts discussed 

but no speCific descriptions or figures.) 

, 1875. Newberi:y,J. S., Ohio Geol. Survey Rept., vol. 2, pt. 2, 

Paleontology, pp. 41~4, pI. 57. (Discusses zoologic 

position and illustrates several specimens without 

, generic or specific names.) 

1878. Ulrich, E. 0., Oincinnati Soc. Nat. Hist. Jour., vol. 1. 

pp; 87-91, pI. 4. (Describes some true annelids and 

briefly discusses conodonts.) 

1879. Hinde, G. J., GeoI. Soc. London Quart. Jour." vol. 35, 

pp. 351-369, pIs. 15-17. (Gives a general review of 

conodonts. Discusses zoologic relations and describes. 

many new forms.) 

1880~ Young, John, Glasgow Nat. Hist. Soc. Proc., vol. 4~ 

pp. 5, 74. (Abstract of paper read recording the 

discovery of conodonts in Carboniferous of Scotland 

and discussing zoologic position. Notice of occurrence of conodonts in Silurian and Devonian strata 

in England,) 
• <.) 

10 MISSISSIPPIAN FORMATIONS OF SAN ~ABA COUNTY, TEXAS 

1881. ¥asori, Robert, Glasgow Nat. Hist. Soc. Proc., vol. 4, . 

p. 190. (Notes the finding of conodonts at a new 

locality in Scotland.) 

'1882. Rolle, :H'r., Handworterbuch del' Mineralogie, Geologie 

und Palaeontologie, Band 1, p. 408. (Short discusSion.) 

1884. James, U. P., Cincinnati Soc. Nat. Hist. Jour., vol. 7, 

pp. 143-149, pI. 7. (Describes two conodonts and 

two annelid jaws, all new.) 

1886. Rohon, J. V., and Zittel, V., K.-k. Akad. Wiss. Mlinchen, 

Math.~phys. Classe, Sitzungsber., Band 16, pp. 108-

136, pIs. 1-2. (Mainly a discussion of the zoologic 

position of the conodonts from a chemical and physical standpoint.) 

1887. Clarke, J. M., New Yorl\: State Geologist Sixth Ann. 

Rept., for 1886, pp. 30-33, pI. A 1. (Good plate of 

figures. Description very general and short.) 

1898 Girty, G. H., Am. Jour. ScL; 4th ser., vol. 6, pp. 393, 395. 

(Describes· and figures a conodont from Devonian 

shale of Kentucky.) 

1899. Grabau, A. W., Buffalo Soc. Nat.o Sci. Bull., vol. 6, pp. 

150-158. (Rather poor reproductions of Hinde's figures, reduced in size, with condensed descriptions.) ~ 

1900. Smith, John, Glasgow Nat. Hist. Soc. Trans., new ser., 

vol. 5, pp. 336-338. (Discusses occurrence of conodonts in Carboniferous limestone of Scotland.) 

1900. Hinde, G. J., Glasgow Nat. Hist. Soc. Trans., new ser., 

vol. ·5, pp. 338-346, pIs. 9-10. (Describes and figures 

13 species of Scotch Carboniferous conodonts.) 

1907. Smith~ John, Glasgow Nat. Hist. Soc. Trans., new ser., 

vol. 7, pt. 3, pp. 235-252, pIs. 5-9. (Long discussion 

of occurrence of conodonts in Silurian rocks of Scotland and short descriptions of about 40 species, 

mostly new. Four new genera' introduced.) 

1~12. Girty, G. H., New York Acad. Sci. Annals, vol. 22, p. 

304. (Notes the occurrence of conodonts in Bedford shale of Ohio.) .. 

1913. Hadding, Assar, Lunds Universitets Arsskrift, N. F., 

Afd. 2, Band 9, Nr. 15; Kongl. fysiografiska Siillskapets Handlingar, N. F., Band 24, Nr. 15, pp. 30-32, 

pI. 1. (Describes several new species from the Ordovician of Sweden.) 

1921. Thomas, A. 0., Bull. GeoI. Soc. Amer., vol. 32, p. 131. 

(Notes the occurrence of conodonts in Devonian of 

Iowa.) 

1921. Bryant, W. L., Buffalo Soc. Nat. Sci. Bull., vol. 13, No. 

2, pp. 1-58, pIs. 1-16. (Reviews the literature on 

conodonts and discusses zoological pOSition. Describes and figures' over 30 species,' part of which. 

are new.) 

1923. Parks, A. W., Ontario Dept. l\:IinesThirty-first Ann. 

Rept., pt. 9, pp;' 35-37, pI. 6. (Reprod uces Hinde's' 

descriptions and figures of five species.)-

1925. Roundy, P. V., Bibliography of Conodont and Paleozoic 

annelid jaw literature, 4 pp. (mimeographed; distributed by the Division of Geology and GeograpilY, 

National Research Council, 'Washington, D. C.) 

Genus PRIONIODUS Pander 

1856. Ptioniodus Pander, Monographie der fossilen Fische des 

silurischen Systems del' russisch-baltischen Gouvel'nements, p. 29. 

, A free translation of the original description is 

:given below: 

We unite under this designation all those teeth or jaws in 

which a very large tooth juts forth, with a row of smaller 

ones arranged against it on one or both sides. The excavated 

base extends the entire length under these teeth to a certain 

height. 

First species, Prioniodus elegans. 

Pander placed five species under this genus, and 

other authors have adde'd 26 more species until now 

t.he genus contains several distinct types of conodonts. 

In order to simplify the classification frOln a purely 

. paleontologic point of view it would seem advisable 

to restrict the genus to types close to P. elegans and 

establish new genera for those markedly different 

from that species. 

. Pander's figures of the genotype are here reproduced (PI. IV, figs. 3a-4). 

Prioniodus healdi Roundy, n. sp. 

Plate IV, Figures 5a-5b 

~1ain tooth slender, elongate, arid slightly curved 

in two directions (backward ~ and inward ~) . Tooth 

has a slight yet distinct longitudinal carina on its two 

more acute margins. The oase of this tooth expands 

very rapidly, forming a large, in part thin -'walled 

pulp cavity. The expansion is mainly inward ( ~) 

and to the two sides (backward ~ and forward ~) On 

each side of the main tooth a smaller slender elongate 

tooth arises. Originally the base may have been prolonged further and bore more Qf the smaller teeth. 

This conodont is of a clear, almost transparent amber 

color. 

Horizon and locality: Barnett shale, San Saba 

County, Tex. (stations 2688, 2613E?). 

Prioniodus peracutus Hinde 

Plate IV, Figures 6-8 

1900. Prioniod,lts per(l.cutu.~ Hinde, Glasgow Nat. Hist. Soc. 

Trans., new ser., vol. 5, pt. 3, p. 343, pI. 10, figs. 21-2:3. 

Upper, Middle, and Lower limestones, Carboniferous, 

Scotland. 

Hinde's description is given below: 

A single straight or slightly curved compressed main tooth, 

which extends below a small horizontal base to an obtuse 

point; the outer margin and both margins below the horizental process are acute. There are a few minute, closely set 

denticles on the horizontal base. This form differs from 

P. spicat1tS in its larger size, the sharp edges of the main 

tooth, and in the very short horizontal base. * '" 1(1 Specimens measure from 0.8 to 1.5 millimeters in length. 

The description and my spec;imens agree best with 

Hinde's Figure 22 (reproduced here, PI. IV, fig. 6). 

The other figures appear to represent what I would 

consider distinct species, or at least varieties, so I 

anl designating Hinde's Figure 22 as representing the 

type specime~. The description of my specimen is as 

follows: 

A broad, rather flat elongate tooth with· a nearly 

straight, sharp lmifelike front edge and wit~ the back 

edge rounded in section, nearly straight in its upper 
THE MICRO-FAUNA 11 

half, and rapidly curving in its lower third, forms 

the main part of this conodont. These two margins 

meet above and below in sharp points. Somewhat 

below the middle of the tooth a small, rather thin, 

slender base extends backward, bearing several small, 

upright, rounded, sharp-pointed teeth. A small pulp 

cavity lies partly in' the bottom of this base and partly 

in the adjacent portion of the large tooth. The entire conodont is thin, and the lateral aspects are 

slightly different in the convexity. ~1y specimens 

are all incomplete. 

I-Iorizon and locality: Barnett shale, San Saba 

County, Tex. (stations 2609, 2613 E, 2613 G). 

PrionioduB sp. A . 

Plate IV, Figure 9 

This form, represented by a single specinlen, consists of a long, almost strai ght, slender, slightly flattened main tooth. The pulp cavity, which lies directly under this tooth, is relatively small and without fla.ring walls. From one side of the main tooth a 

slender base projects outward and downward, bearing the lower parts of five small teeth. Its lower end 

is incomplete. On the other side of the nlain tooth 

there is a short part of a broken base bearing the stubs 

of two teeth. This'base may have been similar to the 

opposite one. 

I-Iorizon and locality: Barnett shale, San Saba 

County, Tex., (s.tation 2609). 

Prioniodus sp. B 

Plate IV, Figure 10 

Like P. pe'raC'l.tt~t8, described above, this conodont 

consists chiefly of a rather flat elongate main tooth. 

This tooth, however, is subtriangular in outline. The 

front margin is sharp and practically straight. The 

back margin is slightly rounded, and the first tooth 

on the small base that juts from it in part coalesces 

with the main tooth. The apex of the main tooth is 

missing in all my specimens. The bottom of this 

large tooth, instead of being a point formed by the 

union of the ba~k edge extending downward from 

the edge·of the pulp cavity for some distance and then 

uniting with the front edge, as in P. peraC~tt~t8, is' 

formed by the direct union of the front margin of 

the pulp cavity with th~ bottom of the front margin. 

The pulp cavity itself is much larger than in P. pm'-

acut'l.t8, both in length and width. The small base 

evidently bore several small teeth, of which my speci- . 

mens show only the one adj acent to the large tooth 

and (in my best specimen) the lower parts of fi ve 

others. These lower parts, although completely embedded in the base, are yet distinct, owing to their 

slightly whiter color and less transparent condition. 

I-Iorizon and locality: Barnett shale~ San Saba 

Connty, Tex. (stations 2609, 2688). 

Prioniodus sp. C 

~late IV, Figure 11 

Of a still different character is the single incomplete specimen I am describing under this heading. 

It consists of a long tooth with rounded lateral sides 

meeting in two distinct blunted knifelike edges or 

carinae. The apex is broken, and the bottom is occupied by the central portion of the pulp cavity. From 

each side of this tooth, in line with the carinae, bases 

jut outward and slightly downward. On one side 

there is a long, slender, sharp-pointed, slightly curved 

tooth, partly coalesced with the main tooth. The base 

is broken at this point, so whether it originally bore 

more teeth is impossible to determine. On the other 

side of the main tooth the base has parts of four teeth, 

three broken off close to the base and the fourth (adjacent to the main tooth) broken at some distance 

from the base. This base terminates also in a broken 

end. 

Horizon and locality: Barnett shale, San Saba 

County, Tex. (station 2609). 

Prioniodus sp. D 

Plate IV, Figures 12-13b 

~1ain tooth elongate, with two edges (front and 

back ~) rather sharp. One side of the tooth ( outside ~) is very gently convex, both transversely and 

longitudinally. The other side (inside n is rather 

concave longitudinally-that is, the tooth curves inward. Transversely this side is very convex. The 

pulp cavity, which is large, occupies the area below 

the main tooth. From the lower part of' the main 

tooth bases jut both forward (~) and backward (~) 

and bear very small teeth: 

Under this species I have placed about 20 specimens which although varying in minor characters 

could not in their present imperfect condition be satisfactorily classed as distinct species or varieties. 

Horizon 'and :locality: Barnett shale, San Saiba 

County, Tex .. (stations 2609, 2613E, 2613G, 2613H, 

7011A~, 7687). 

I have described these specimens of Prioniod~t8 

somewhat at length because I believe that they can 

be recognized and used in stratigraphic work despite 

their imperfect condition. 

Prioniodus sp. 

Under this heading I am including about 60 incomplete specimens which .do not appeal: to warrant detailed descriptions in the present paper. These specimens undoubtedly represent a large number of species, but without better reference nlaterial than is 

now' available it is not possible even to definitely establish the generic relations of several of them. Sev-
12 MISSISSIPPIAN FORMATIONS OF SAN SABA COUNTY, TEXAS 

eral large tusklike teeth may belong either to Prioniodus or to Drapanodus if the part broken away was 

originally either a side base bearing small teeth or 

merely a piece of the pulp-cavity side wall. Likewise in some other specimens a restoration of the 

-missing portion might show a relationship to Prion,zodus, Lonclwdus, or some other genus. 

Horizon and locality: Barnett shale, San Saba 

County, Tex. (stations 2609, 2610B, 2610C, 2613D, 

2613E, 2613G, 2613H, 2618,2688). 

Genus GNATHODUS -Fander 

1856. Gnathod1/,8 Pander, Monographie der fossilen Fische des 

silurschen Systems der russisch-baltischen Gouvernements, p~ 33. 

The following is a translation of Pander's description: 

In the marls of the lowest shales of the Mountain limestone in Tula and the higher Governments of Mosca wellpreserved jawlike fossils are found, which by their configuration and by their base are distinguished from those as 

yet described, but which are closely joined to them by their 

microscopic structure. }j~rom a high, narrow, compressed 

base, constructed of double walls, arise in a row minute teeth, 

givhlg it the appearance of being bordered with a denticulate 

margin. Below, these walls at one end diverge strongly 

from one another and build a cavity, while at the opposite 

end they remain close together. This cavity, which represents the pulp cavity, lengthens out laterally and, as would 

b<; expected, -affords for each denticle an ascending continuation. 

Only one species, G. mGsquensis, is given, ~nd Pander evidently considered that his generic description 

was sufficient for -the species, as under the species 

name he- -gives only the locality and horizon with 

plate references. His figures are reproduced here 

(PI. II, figs. 6a-d). 

Gnatlwdus seems to be essentially a Carboniferous 

genus. Only one species, G. americanus, a Genesee 

shale form, has been described from pre-Carboni ferems rocks. Specimens of this genus are perhaps 

among the most common conodonts in the Barnett 

_ shale, one shale sample furnishing 99- specimens of a 

single species. 

The most striking characters of this genus appear _ 

to be the very thin, high bases and the character of 

the teeth on the higher end, which seem, under low 

magnification, to be merely the crenulated edge of 

the base. Under high magnification, however, the 

minute structure lines shown by Pander are visible. 

Gnathodus tex~nus Roundy,n. sp. 

Plate II, Figures 7a-8b 

Seen from -above, this species consists of a long, 

nea~ly straight row of thin, -short, sharp-edged teethwhich resemble somewhat saw teeth without any set. 

Near the center the wide-spreading upper -surface of 

the pulp chamber is conspicuous, and fronl its -top, a 

little to one side of the row of teeth, there arises a 

single tusk or tooth, whose top usually but not in all 

specimens is slightly depressed in the middle, giving 

it the appearance of having two small nodes. 

Seen in side view, the bottom is rather straight, and 

the top, starting nearly straight at the wide end~ 

gradually bends downward on the sharper or thinner 

front (n -end. _Th~ teeth are largest on theback or 

higher end and show a gradual though not constant 

reduction in size until at the front end they are not 

much more than mere points on some specimens. 

Seen from below, this species shows the higher or 

posterior (~) end to consist of a narrow projection 

with a very fine line in the center. Under strong 

magnification this line is shown in fractured specimens 

to be the lower contact of two thin plates actually in 

contact but not fused until in the vicinity of the base 

of the individual teeth. About the middle of the base 

these plates rapidly separate to form the pulp cavity. 

At the front end the bottoms of the two plates again 

unite but only at the point. 

This species is very delicate and easily broken, the 

base and walls of the pulp cavity being very thin. 

The only massive structure of this conodont is the 

large tusk or tooth arising from the top of the pulp 

cavity at one -side of the elongate crenulated base. 

O. temanus is the nlost common species in the Barnett 

shale, six collections furnishing over 200 specimens. 

This species is strikingly like the illustrations of G. 

mosquensis, differing mainly in having the side tusk 

or tooth mentioned above. Length of a large incomplete specimen, 1.30 millimeters; greates-t height of 

posterior end, 0.50 millimeter; thiclmess of this end at 

the same point, 0.13 millimeter. 

Horizon and locality: Barnett shale, San Saba 

County, Tex. (stations 2609, 2613D, 2613G,_ 2613E, 

2688, 2613H). 

Gnathodus texanus yare bieuspidus Roundy, n. var. 

Plate II, Figures 9a-~b 

One broken specimen of Gnathodus is very similar 

to G. temanus except that it has a tusk or tooth arising 

from the top of the pulp cavity, on each side of the 

main row of denticles, instead of on only one side, as 

in that species. '.rhis additional tooth is more nearly 

circular in cross section, pointed, and not quite as high 

as the opposite tusk. 

This form may prove to be a distinct species, but 

until more evidence is obtained I feel that it should 

rank as a variety. 

Horizon and locality: Barnett shale, San Sa ba 

County, Tex. (station 2613E). 
THE .I\llCIW-!I'A UNA 13 

Genus POLYGNATHUS Hinde, emended by Bryant 

1879. PoZ1JunatlMt8 Hinde, Geol. Soc. London Quart. Jour., 

vol. 35, p. 361. 

1921. Pol1Juncithtt8, emended under description of Centrocl1ts 

invalicl1t8 Bryant, Buffalo Soc. Nat. Sci. Bull., Y01. 

13, No.2, p. 22. 

Hinde's original description is quoted here in full: 

I propose this genus for an animal possessing numerous 

minute and variously formed conodont teeth and similarly 

minute tuberculated plates grouped together, but of which 

the natural arrangement is not at present known. 

'l'his meager definition is aU that is afforded by the single 

example of tlle genus met with, in whi<;h about 24 entire 

and fragmentary teeth and 6 plates have beeri crushed together in a small patch of about one-fourth of an inch in 

diameter, in blnck sllale. The specimen was discovered in 

splitting open a slab of the rock, the division taking plaee 

in the center of the specimen. No indication can be seen of 

the natural position of the teeth and plates; but it can 

hardly be doubted that they all belonged to one individual, 

as it' would be beyond all reasonable probability that so 

many diversely formed teeth, of such delicate structure, could 

have been thus brought together into so small a space by 

mechanical means, 1110re particularly when it is a very 

rare circumstance to fil}d, in the same rock, even two detached 

teeth at all close together; and in only one other instance 

have I found two conodonts partially connected together, and 

these are forms which aro present in this compound example. 

If, however, these various teeth and plates were attached to 

their natural positions by soft tissues merely, by the decay 

of these they would be liable to be crushed together into a 

shapeless mass like that presented by the specimen. 

The following js Bryant's emendation: 

In the present uncertainty, even as to the class of animals 

which bore these teeth, it seems to me advh:mble to retain 

Pander's generic names for forms described by him and to 

restrict Hinde's genus PoZ1Junat1l,tt8 to those crested crushing 

or tritoral plates so characteristic of his type specimen. 

Although I have not seen the material described by 

IIinde, I agree with Bryant 7 that this" small patch," 

in which many teeth and plates, some fragmentary, 

nre crushed together, is very probably the ejecta of 

SOlne fish. IIowever, if this assemblage of various 

teeth and plates had proved to belong to a single individual, then the generic name Polygnathus would 

have become a synonym of Lonchodus, as it contained 

teeth which were identical with some previously described by Pallder under that genus. 

As Polygnathus is now restricted to the crested 

crushing or tritoral plates and many of the various 

teeth described and figured under the type species, 

P. dubius; have been referred to previously described 

genera, it is necessary to select the genotype. Of the 

forms figured by IIinde as P. dubius but three (PI. 

]6, figs. 16, 17, and 18) could now remain under the 

genus. Bryant, however, says that figure 17 is only a 

differently oriented vjew of the form described by 

7 Brynnt, W. L., Buffnlo Soc. Nat. Rlst. Bull., vol. 13, No.2, pp. 9, 

21, 23, 1921. 

Hinde as Polygnathus lJennatus, and that figures 16 

and 18 show different aspects of the form described 

as P. cristatus. I therefore propose that the genotype Polygnathus dubius lIinde be restricted to the 

specimen shown on his Plate 16 as fig~re 17; Rence 

Polygnathus pennatus Hinde becomes a synonym of 

P. dubius. Hinde's figure is reproduced on Plate III 

as Figure 9. 

Polygnathus bilineatus Roundy, n. sp. 

Plate III, Figures 10a-lOc 

Seen from aboV"e, the nearly parallel ridges surmounted by small teeth or denticles converge slightly 

on the forward end of this form. The anterior end is 

broken, but these ridges probably met in a sharp point, 

as shown by other fragments. One of these ridges projects backward considerably beyond the main part of 

the conodont, where it also is broken. The portion of 

the base between these ridges forms a more or less 

shallow V-shaped valley. At one side of the longer 

ridge and somewhat forward of the center of the conodont a portion of the pul p cavity is seen standing out 

as a prominent platform with srpall rounded denticles 

on its upper surface, forming what may be considered 

a tritoral plate. Where this platform joins the side 

of the long ridge a line of denticles is visible on the 

forward portion. Some of my fragmentary specimens suggest that either in a variation or a variety of 

this species a third denticle-surmounted ridge is developed on the anterior part of the form. 

Seen from below, the pulp cavity occupies nlost of . 

the base, and the backward-projecting portion of the 

longer ridge is composed of two closely folded plates. 

These are fused in the upper or denticle-bearing portion. Length, 1.0 millimeter; width, 0.46 millimeter. 

Horizon and locality: Barnett shale, San Saba 

County, Tex. (stations 2609, 2688, 2613E). 

Polygnatlius taffi Roundy, n. sp. 

Plate III, Figures lla-llb 

Seen from above, this form consists of an elongate 

plate with the two lateral edges bent. upward, slightly 

more in the middle than at the ends of the sides. The 

edges are very slightly scalloped. The plate is smooth 

and nearly transparent. A median ridge has denticles or small teeth' on its upper edge and extends backward beyond the end of the plate a short distance, 

beyond which it is broken. Evidently, as in the typical specimens of th~ genus, this ridge originally extended as f~r again as in this imperfect specimen, the 

only one found in the Barnett sha1p .' 

Seen in side view, the top appears as a nearly 

straight line wit~ the bent-up edges of the plate con-
14 MISSISSIPPIAN FO~MATIONS OF SAN SABA COUNTY, TEXAS 

cealing all. but the teeth on the top of the forward. 

portion of the median ridge. This ridge extends backward and its base swings downward,. so that the 

he.ight increases rather -rapidly. 

Seen· from below, a somewhat spindle-shaped pulp 

cavity occurs in the middle portion of the end of the 

plate. The backward-projecting end of the median 

rjdge evidently is a double plate, as in the genus 

Gnathodus. Length, 0.62 n1illimeter; width of plate, 

0.26 millimeter. 

Horizon and locality: Barnett shale, Lampasas 

County, Tex. (station 7016), 

Polygnathus texanus Roundy, n. sp. 

form, if embedded in matrix, might easily be classed 

as another genus, being an elongate form with various sized close-set teeth. A delicate threadlike cavity 

a.ppears to extend from the ba;se nearly to the apex 

of the teeth. On the under side the central part has 

a slight longitudinal groove and is slightly depressed. 

This description is based on a single specimen ; and 

were it not for the broken ends I would give it a new 

name, as it appears' to be distinct from any forn1 previously described. Greatest length, 1.01 millimeters; 

width, 0.51 millimeter. 

Horizon and locality: Barnett shale, San Saba 

County, Tex. (station 2609). 

Plate HI, Figures 13a-13b. Polygnathus? claviger Roundy, n. sp. 

Upper aspect unsymmetrical, with a long medj an Plate IV, lI'igures la-2b 

keel whose fractured end projects a slight distance Seen from~bove, base massive, elongate, pointed at 

backward beyond the plate. The forward end of one end, broad and blunted at the other. Base 

the keel joins the pointed end of the plate. This smooth, with a row of large elongate teeth. Each 

keel has minute rounded tubercles. On one side of t.ooth has about equally convex sides, which lneet in a 

the keel (the right in the figure) is a broad area sharp edge or carina on the front and rear. Forpnrwith the upper surface covered with small irregular poses of description the sharp end of the base is congrinding ridges, some with papilli-like nodes on the sidered the front. Individuals vary as to the relative 

crest. The downward-sloping edges are smooth. On size of the teeth and the space between them. Some 

the other side of the keel the grinding ridges are are in contact in their lower third, some only at their 

more irregular, and the area is longer but not as wide base, and occasionally two adjacent teeth have a pera.s the right. When viewed from the broad-area side: , ceptible distance between their bases. There is also 

of the ·plate the outer grinding ridge conceals tIDe a variation in the length of the teeth, the shorter ones 

other grinding ridges of this area. The entire top usually being nearly straight and the longer ones 

of the median keel is visible, as is a portion of the curved slightly backward. This backward curve is 

outer part of the far area. A view of the under stde the main reason for my considering the pointed end 

shows that the pulp cavity spreads out under· the of the base as the anterior. In position, the row of 

entire plate. Greatest length, 1.05 millimeters; great- teeth is in the center of the base at the front end, then 

est width, 0.61 millimeter. gradually swings to one side of the base toward the 

This species, based on a single individual, is dis- broad end, where a solitary tooth occurs on the other 

tinct from any species previously described. edge opposite the last tooth of the row. These teeth 

Horizon and locality: Barnett shale, San Saba so resemble in miniature the old-style farmer's spike 

County, Tex., (station 2618). drag that I have given them the name P. clavige1' 

Polygnathus sp. A 

Plate III, Figures 12a-12b· 

Seen from above, the plate is elongate, unsymmetrical, with front and back ends broken. A little 

to one side of the middle of the plate is a sinuate 

ridge surmounted by bluntly pointed rounded teeth. 

The central tooth is the largest, and there is a .very 

small one on each side. The smaller teeth gradually 

increase in size from the very small one adjacent to 

the big central one to the .forward (~) end. To the 

left (~) of this row of teeth is a shorter ridge culminating in an elevated point, about the height of 

the intermediate-sized teeth. The remaining upper 

part of the plate is slightly roughened .... by microscopic irr·egular reticulate lines. In side view this 

(clavus, spike; gero, I bear). Adjacent to the abovementioned solitary teeth a small portion of the base is 

broken, so that it is possible that another tooth might 

, originally have been present. 

In side· view the base seems to be about equal in 

thickness except at the extreme ends .. 

Seen from below, a pulp cavity wider than long, 

subrectangular in outline, is located near the posterior 

end, and a narro·w groove extends in the center of the 

base nearly to the extreme front end. . 

This description is based on several inGomplete indi viduals, and consequently a misconception of the 

species may have arisen. Therefore, I designate the 

best specimen of the rear or broad end of the base as 

the type. This species probably represents a new 

genus, but my specimens do not warrant the erection 
• THE MICRO-FAUNA 15 

of a new genus, so I am placing it under Polygnathus? 

Greatest width of type specimen, 0.63 millimeter; 

length, 1.2 millimeters, which I believe would be 

about half the length of a complete individual. 

I-Iorizon and locality: Barnett shale, San Saba 

County, Tex. (stations 2609, 2618, 2613E, 2613G?, 

2613D, 2610C). 

Genus LONCHODUS Pander 

1856. Cen,h'oU'llS Pander, l\[onographie del' fossilen Fische des 

sllurischen Systems del' russisch-baltischen Gouverne- I 

ments, p. 31. 

1856. Lonchod'lts Pander, idem, p. 80. 

A trnnslation of Pander's description is as follows: 

On Plate 2a, ]j'igures 2-9, are represented several apparently different forms of similar internal structure, wh~ch 

could nevertheless be separated from one another. In Figures 

2, 3, 5, and 6 (C. simlJZea;) we see very slender teeth standing vertically or obliquely and bending more or less, turned 

in one or two different directions, and situated upon a hori-' 

zontal base. Between these in Figures 7 and 8 (0. dUl)licat'lt8) and especially in Figure 9 (C. lineatus) arise smaller 

teeth. If we compare the larger teeth with those represented 

in :H'igure 4 (0. convc{lJtts) , the agreement is certainly very 

stTiking, although they here rest upon a convex base. If 

we then establish the character of the genus in this general 

way, that it includes large, slender, po\nted, lamellose teeth, 

quite alone or alternating with smaller ones of various size 

aud number, attached to a horizontal or convex base, we can 

very well unite all together and at any rate make specific 

sepllwtions that hnve perhnps more paleontologic thnn zoologic YnIue. 

On page 80 of Pander's report he states that the 

Ilame Oentrodus had previously been used and names 

this genus. Lonclwdu8. This note appears to have 

been overlooked by both Hinde and Bryant, for both 

have used the name Oentrodus without comment. 

First species, Lonchodus 8'i1nlJlew. 

It is not uncommon to find many fragments of 

conodonts, consisting of several teeth on a base, which 

. n~ found could with propriety b~ placed only under 

the genus Lonchodus. Yet some of these specimens 

may well be parts of conodonts which if complete 

would be placed under other genera. However, as a 

means of aiding in the classification and range determinntion of the conodonts for stratigraphic· purposes I believe it desirable to describe more of these 

fragmentary specimens than would be desirable so 

far as their mere zoologic aspect is concerned. 

Lonchodus simplex Pander 

Plnte III, Figures 1-5 

1856. Cerl-t1'od'lls si'mplea; Pander, Monographie del' fossilen 

Fische des siluriscllen Systems del' russ:sch-baltischen 

Gouvernements, p. 31, pI. 2A, figs. 2, 3, 5, 6. (Changed 

to. Lonchod'lts on p. 80). Mountain limestone, Tula, 

Russia. 

.1870. Polyynath1ts d1.tbius (part) Hinde, Geol. Soc. London 

Quart. Jour., vol. 35, p. 362, pI. 16, figs. 10, 11. Genesee shale, Nortll Evans, N. Y. 

A translation of Pander's original description is as 

follows: , Long, sharp-pointed, straight, oblique, or bent teeth projecting vertically from a generally llorizontal base. 

My collections include many specimens which correspond with this species as figured and described by 

Pander. All have both ends of the comparatively 

slender horizontal bases broken, and they bear from 

two to five sharp-pointed straight or oblique teeth. 

The relative size and length of teeth of these specimens vary considerably. Although my forms may 

represent several species, in their present condition I 

can hardly do other than tentatively refer these specimens to this species. 

Horizon and locality: Ba.rnett shale, San Saba 

County, Tex. (stations 2609, 2613E, 2688, 2613G, 

2613D ?, 2610C, 2613H?). 

Lonchodus? lineatus Pander 

Plate III, Jj-'igures 6-8 

1856. Oentrodus lineat1ls Pander, Monographie del' fossilen 

Jj-'ische des silurischen Systems der russisch-baltischen 

Gouvernements, p. 31', pI. 2A, fig. 9 (Loncl"odus, p. 

80). Mountain limestone, Russia. 

11875. Conodont. Newberry, Ohio Geol. Survey Rept., vol. 

2, pt. 2, Paleontology, pI. 57, fig. 8. Cleveland shale, 

Bedford, Ohio. 

?1879. Polyynath'l£s d'ltb-ius (part) Hinde, GeoI. Soc. London 

Quart. Jour., vol. 35, p. 3!32, pI. 16, fig. 14 (fig. 13?). 

Genesee shale, North Evans, N. Y. 

1900. Oentrod'lts Zineatus Hinde, Nat. Hist. Soc. Glasgow 

Trans., new ser., vol. 5, pt. 3, p. 341, pI. 9, figs. 13, 14. 

Carboniferous limestone, western Scotland. 

Long, slender, straight base with several large, 

slightly oblique, round, slender teeth. These large 

teeth are separated by two to five similar-shaped but 

much smaller teeth. Some specimens show nearly the 

complete variation in number, but most specimens 

show only three or four small teeth between the larger 

ones. The base in cross section (excl.uding the teeth) 

is oval, being in one specimen, which is but slightly 

below the average size, 0.05 millimeter thick and 0.08 

millimeter high. All my specimens, like Pander's' 

type, have both ends missing, so that the character of 

the extremities is not known. No pulp cavity has been 

noted. On the bottom of the base some specimens 

faintly show a very shallow groove. 

'Vith these spec.imens I have tentatively placed some 

. ,other specimens, which uniformly have a much higher 

though thinner base. These are perhaps a variety 

and in shape of the base might be considered intermediate between this form and the form below described as Otenognathu8 sp. A. However, they have 

the. larger teeth separated by three or four smaller 
16 MISSISSIPPIAN FORMATIONS OF SA-N SABA @OUNTY, TEXAS 

ones, as in this species. Also ·theY lack the cellulal! 

structure so clearly shown by tran~mitted light in the 

tt'eth of specimens of Otenogriathus. 

One of the individual specimens included in Hinde's 

species Polygnathus dubius seems to be an example of 

this species. One end app~ars to be complete and exhibits two teeth, which are much larger than the ordinary large teeth that separate the smaller ones on the 

main portion of the base. I am not yet ready, however, to place Hinde's specimen definitely in the 

synonymy of this species. 

Of the specimens from the Carboniferous of Scotland figured by Hinde I can form only a very gen-

·eral opinion, because of the generalized description 

and rather indefinite character of the figures. I see 

no objection to including these in the synonymy of 

this species. 

Newberry's specimen is figured but not named, 

though briefly described. Hinde considers it to be 

the same as his species. I think, however, that it is 

distinct from Pander's and the Scotch forms. 

Horizon and locality: Barnett shale, San Saba 

County, Tex. (stations 2609, 2613D, 2613E, 2613H, 

'r016) . 

Genus CTENOGNATHUS Pander 

1856. Gtenognath~~8 Pander, Monographie der fossilen Fische 

des silurischen Systems der russifoCh-baltischen Gonvernements, p. 32. 

A tran~lation of the original description follows: 

Small teeth, pressed cl9sely together in a row, solidly 

lUounted on a horizontal or convex hollow base and continuing to the end without change, in their for the most part 

cellular structure. Not found in the. Lower Silurian 

shale. ... '" .... Not rare in the Mountain limestone of 

Tula. '" .,. '" Closely related to the foregoing genus; we 

distinguish it chiefly on account of the character of the internal structure,' which in all, without exception, appears to 

stand at a higher stage of development. In Otenognathu8 

the cellular structure rules. 

The "foregoing genus" referred to above is Lonchodus (Oentrodus). The first species described is 

Ctenognathus murchisoni. The description is very 

short, .being as follows: "Small pointed teeth of 

yaried size rise from their hollow base and form a 

connected row." I am reproducing one of Pander's 

figures of the type (Pl. II, fig. 2). 

Ctenognathus sp~ A 

Plate II, Figure 3 

Base thin, high, elongate and nearly straight. 

Near one end there is what appears to be the base of 

a large', very flat, wide tooth. In front of this surely 

one small tooth and perhaps two or more were present. Back of this supposed main tooth there are, in 

one specimen, over 30 small, slender rounded teeth, 

all broken and most of them broken off close to the 

top of the base. They are all at an angle of about 

50° with the base. Viewed by reflected light under 

high magnification with a black background, the teeth 

appear like light-colored round teeth set well into the 

very faintly amber-colored transparent base. Viewed 

by transmitted light, however, the teeth appear to be 

made up of distinct cells, which appear as black spots, 

while the base substance remains structureless except 

for very fine, rather indistinct lines. The aspect under this magnification is strikingly like that shown 

by Pander in a greatly enlarged view of O. verneuilli. 

However, the shape of the base and the relative proportions of the teeth in my specimens show it to be 

distinct from that species. The teeth are embedded in 

the base about half the height of the base. The base· 

is solid and has on its under side a very shallow 

rounded groove, which could hardly be classed as a. 

pulp cavity. As both ends of all my specimens are-

-broken away, a pulp cavity may have been present. 

. without my specimens showing it. 

Although I can find no trace of a hollow base such 

as Pander's descriptions show to be present in his. 

form, I feel quite confident that this form belongs in 

his genus. I am reproducing one of Pander's figures. 

of O. verneuiUi (PI. II, fig. 1). 

Dimensions of my best specimen: Length, 1.8 lnilli-· 

meters; height of base near center, 0.60 millimeter; 

thiclmess at same place, 0.08 millimeter. 

Horizon and locality: Barnett shale, San Saba. 

County, Tex. (stations 2609, 2610C, 2613D, 2613E" 

2613G, 2618). 

Ctenognathus sp. B 

Plate II, Figures 4-5 

Base thin but high, elongate, the lower margin 

slightly convex. In the central part of the base is a 

small well-developed elongate pulp cavity, which in 

width does not exceed the average thickness of the' 

base. Directly above this cavity is the main tooth 

or denticle. On 'each side of this tooth there are 

several somewhat smaller teeth. All are flattened an d 

crowded together, and many are broken, but the few 

complete teeth are rather sharply pointed. 

This form is comparatively rare, being represented 

by three specimens, all of which show the characteristic tooth structure of this genus. 

This species resembles O. verneuilli as figured by 

Pander 8 but differs decidedly in having the cellular 

structure of the teeth penetrating only a short distance into the. base. It also resembles the form described and figured by Hinde 0 as Polygnathus radiatus. Bryant also figures several specimens which he 

8 Pander, C. H., op. cit., pI. 2 A, figs. 16 and 17. 

o Hinde, G. J., op. cit. (187D), pI. 16, fig. ~O. 
THE MICRO-FAUNA 17 

says ,are the same as Hinde's, and on account of the 

lack of the Otenognathu8 structure he refers the forrn 

to Prioniodu8. Under the name Polygnathu8 dubiu8 

I-linde 10 figures two specimens which may be true examples of OtenognaJ.thus and which appear to be close 

to the species here describ~d. 

Horizon and, locality: Barnett shale, San Saba 

County, Tex. (stations 2609, 2613). 

FISH REMAINS 

One cqllection that contained many conodonts included also a few rather small fish teeth, but no fish 

scales. ' The specimens are too fragmentary to warrant 

desci'i ption at the present time. 

Horizon and locality: Barnett, shale, San Saba 

County, Tex. (station 2609). 

REGISTER OF LOCALITIES 

2609. South side of road to Bend post office about 6 miles 

from San Saba. Lower part of Barnett shale. 

2610B, 26100. Across the road from locality 2609, about 30 

to 40 feet below the top of the Barnett shale. 

]0 Idem, pI. 16, fig. 8; op. cit. (1900), pI. 9, fig. 1. 

2613D-2613H. On southwest side of road to Ohappel, about 

3 miles southeast of San Saba courthouse, at first sharp turn 

well up hill. Several collections made in one shale cut, from 

9 inches to 14 feet above the limestone of Boone age, '''hich 

here lies in contact with the Ellenburger limestone. 

2618. About 1,000 feet east of locality 2613D. Barnett shale 

from 5 to 10 feet above the limestone of Boone age. 

2618A. Same locality as 2618. Limestone of Boone age. 

2623. Very near locality 2613D. Thin limestone of Boone 

age between the Ellenburger limestone and the Barnett shale. 

2688. 4.9 miles east and 0.9 mile south from the courthouse 

at Sap Saba. Upper part of Barnett shale. 

2690. In cut just above bridge over small stream 1.3 miles 

west of the courthouse at San Saba, along road to Richland 

Springs. Marble Falls limestone. 

70llA. 4 miles southwest of Ohappel on road to Oherokee, 

San Saba Oounty. From 25 to 30 feet above base of Barnett 

shale. 

7016. 5* miles west of Lampasas on Sulphur Oreek rono 

to Llano. Barnett shale. 

7687. Probably the same locality as 70lla but collection made 

several years later by another collector. 

Locality 7016 is in Lampasas Oounty; the others are all in 

San Saba County, Tex. The collections were made during 

a period of about 17 years by George H. Girty, E. O. Ulrich, 

J. W. Beede, K. C. Heald, and P. V. Roundy. 
_ . : i:~~~,. -, : 
-- - -- -- --- ---- --======================================================= 

PLATES I-IV 

--- --~~--::-: 

19 
PLATE 1 

FIGURES 1a-1c. Amphissites rugosus Girty (p. 7). The genotype; the first time figured. la, Right valve; 1b, ventral vic ,v; 1c, 

dorsal yiew. From Fayetteville quadrangle, Ark.; basal Fayetteville shale. 

FIGURE 2. Amphissites chappelensis Roundy, n. sp. (p. 7). The only specimen; right valve. From station 7011A; Barnett shale. 

FIGURES 3a-5. Sansabella amplectans Roundy, n. gen. and sp. (p. 6). 

3a-3b. Bivalve specimen, genotype. 3a, Right valve; 3b, dorsal view. 

4. Bivalved specimen, genotype; left valve. 

5. One of the few specimens showing a faintly suggested median pit, specimen somewhat crushed, left valve. 

All three specimens from station 2609; Marble Falls limestone. 

FIGURES 6a-7. SCinsabella sulcata Roundy, n. sp. (p. 6). 

6a-6b. Bivalve specimen, cotype. 6a, Right valve; 6b, dorsal view. 

7. Bivalved specimen, cotype; left valve. 

Both specimens from station 2618, Barnett shale. 

FIGURES 8-10. Aurigerites texanus. Roundy, n. gen. and sp. (p. 6). 

8. Bivalve specimen, cotype; left valve. 

9a-9b. Bivalve specimen, cotype. 9a, Right valve; 9b, dorsal view. 

10. The thinnest specimen; shows the nearest approach to having the dorsal and ventral edges parallel; right valve. 

All three specimens from station 2623; limestone of Boone age underlying the Barnett shale. 

FIGURES 11a-11c. Healdiasimplex Roundy, n. gen. and sp. (p. 8). Bivalve specimen, the genotype. lla, Right valve; 11b, 

left valve; 11c, dorsal view. From station 2915; Graham formation (Cisco group). 

FIGURES 12a-13. Healdia ampla Roundy, n. sp. (p. 8). 

12a-12b. Slightly imperfect bivalve specimen, type. 12a, Left valve; 12b, dorsal view in outline. 

13. Fragmentary specimen showing part of spine bases; right valve. 

. Both specimens from station 2623; limestone of Boone age underlying the Barnett shale. 

FIGURES 14a-16. Kirkbya lindahli var. arkansana Girty (p. 7). 

14a-14c. The type specimen. 14a, Left valve; 14b, right valve; 14c, dorsal view. From Fayetteville quadrangle, Ark.; 

basal Fayetteville shale. 

15. A single valve somewhat weathered; right valve. From station 2618; Barnett shale. 

16. An imperfect valve sho~ing faint surface sculpture; right valve. From station 2623; lime~tone o,f Boone age underlying 

the Barnett shale. 

20 
U. S. GEOLOGICAL SURVEY PROFESSION AT, PAPE1~ 146 PLATE I 

2 X 25 

3a 

la 

Ib Ie 

4 

6a 3b 

7 

5 

8 

9b 

6b 9a 

12a 

lla 13 

12b 

15 

llb 

lle 16 14e 14b 

MICRO-FAU A OF THE MISSISSIPPIAN FORMATIONS OF SAN SABA COUNTY, TEX. 
U S. GEOLOGI CAL SURVEY PHOFESSIONAL PAPEH 146 l'T,A'["g II 

2 

3 X40 4 X 3 5 5 X 38 

6a 

6d 

6b 6c 

X 30 

7a 9a 

X 30 

7b 8a X 30 

X 30 

8b 9b X 30 

MICRO-FAUNA OF T HE MISSISSI PPIAN FORMATIONS OF SAN SABA COUNTY, TEX. 
PLA'rE II 

FIGURE 1. Ctenognathus verneuilli Pander (p. 16). Reproduction of Pander's figure, illustrating the cellular structure characteristic of this genus. Magnificati"on not known. 

FIGURE 2. Ctenognathus murchisoni Pander (p. 16). Reproduction of one of Pander's figures uf the genotype. Magnification 

not known. 

FIGURE 3. Ctenognathus sp. A (p. 16). Seen from the side. From station 2609; Barnett shale. 

FIGUUES 4-5. Ctenognathus sp. B (p. 16). 

4. Seen f~om the side. From station 2609; Barnett shale. 

5. Seen from the side. From station 2613E; Barnett shale. 

FIGmmS 6a-6d. Gnathodus mosquensis Pander (p. 12). Reproduction of Pander's figures of the genotype. 6a and 6b, seen from 

the side; 6c, base seen from below; 6d, fragment seen from side with greater enlargement. Magnification not known. 

FIGUUES 7a-8b. Gnathodus texanus Roundy, n. sp. (p. 12). ' 

7. Specimen with part of large end and part of pulp cavity broken. 7a, Seen from side with large tusk; 7b, seen from below. 

From station 2609; Barnett shale. . 

8. Nearly complete specimen, the type. 80., Seen from side with tusk; 8b, seen from above (looking down on points of teeth). 

From station 2688; Barnett shale. 

Figures 7 and 8 represent conodonts from opposite sides of the mouth. 

FIGURES 9a-9b. Gnathodus texanus var. bicuspid"us Roundy, n. sp. (p. 12). The type and only specimen. 9a, Seen from above; 

9b, seen from the side. From station 2613E; Barnett shale. 

21 
PLATE III 

FIGURES 1-5. Lonchodus simplex Pander (p. 15). 

1-4. Reproduction of Pander's figures of the genotype. Magnification not known. 

5. An incomplete specimen seen from the side. From station 2609; Barnett shale. 

FIGURES 6-S. Lonchodus'l lineatus Pander (p. 15). 

6. Reproduction of Pander's figure, seen from the side. Magnification not known. 

7. An incomplete specimen seen from the side. From station 2609; Barnett shale. 

S. Another incomplete specimen seen from the side. From station 26l3E; Barnett shale. 

FIGURE 9. Polygnathus dubius Hinde (p. 13). Reproduction of Hinde's figure 17 of his Plate 16, which I am taking as the genotype; seen from the side. 

FIGURES lOa-lOco Polygnathus bilineatus Roundy, n. sp. (p. 13). The type specimen. lOa, Seen from the side, which is the 

right side shown in figure lOb; lOb, seen from above; 10c, seen from below, a small amount of matrix conceals the 

bottom of the center part of the pulp cavity. From station 2609; Barnett shale. 

FIGURES lla-:llb. Polygnathus taffi Roundy, n. sp. (p. 13). The type specimen. lla, Seen from above; llb, seen from the side 

(left side shown in fig. lla). From station 7016; Barnett shale. 

FIGURES 12a-12b. Polygnathus sp. A (p. 14). The only specimen (incomplete). 12a, Seen from above; 12b,·seen from the side 

(right side sho'wn in fig. 12a). From station 2609; Barnett shale. 

FIGURES 13a-13b. Polygnathus texanus Roundy, n. sp. (p. 14). Type specimen. 13a, Seen from below; 13b, seen from above 

FroID: station 261S; Barnett shale. 

22 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 146 PLATE III 

3 

1 

4 

5 X 4 0 

2 

"' . 8 X 50 

6 

9 X 20 

X 50 

7 

X 4 0 

lOe 

lIb X 50 

X 4 0 

lOa lOb 

12b 

lla l2a 13a 13b 

MICHO-FAUNA OF THE MISSISSIPPIAN FORMATIONS OF SAN SABA COUNTY. TEX. 
U. S. GEOLOGICAL SVRVEY PROFESSIONAL PAPER 146 PLATE IV 

2a X 30 

X 30 

2b 

1a Ib 

X44 

5a 

X24 

5b 

7 

8 X 40 

.' 

13a X42 

X 32 X43 

9 12 11 13b X 42 

MICRO-FAUNA OF THE MISSISSIPPIAN FORMATIONS OF SAN SARA COUNTY. TEX. 
PLATE IV 

FIGUlUJS la-2b. Polygnathus? claviger Roundy, n. sp. (p. 14). 

la-Ie. The type specimen (incomplete). la, Seen from above; lb, seen from uelow; lc, seen from the side (the left side of 

. figure la). From station 2609; Barnett shale. 

2a-2b. Specimen which I believe represents the front end or" this species; 2a, seen from the side; 2b, seen from above. From 

station 26l3E; Barnett shale. 

FIGUIUJS 3a-4. Prioniodus elegans Pander (p. 10). Reproduction of Pander's figures of the genotype. 3a, 3b, Views of opposite 

sides; 4, side view of another specimen. Magnification not known. 

FIGumns 5a-5b. Prioniodus healdi Roundy, n. sp. (p. 10). The type. 5a, Seen from the side; 5b, the top of the specimen as 

shown in 5a is tipped backward 90° giving the view seen from below. From station' 2688; Barnett shale. 

FIGUHES 6-8. Prioniodus perac1ttus Hinde (p. 10). 

6. Reproduction of one of Hinde's three figures which I am designating the type specimen. 

7. An incomplete specimen seen from the side. From station 26l3G; Barnett shale. 

S. Seen from the side. From station 2609; Barnett shale. 

Ii'IGUHloJ 9. Prioniod1ls sp.A (p. 11). The only specimen, seen from the side. From station 2609; Barnett shale. 

FIGUHE 10. P'rioniodus sp. B (p. 11). An incomplete specimen, seen from the side.' From station 2609; Barnett shale. 

FIGUHE 11. P'rioniodus sp. C (p. 11). The only specimen, seen from the side. From station 2609; Barnett shale. 

li"IGUHES l2-l3b. Prioniodus sp. D (p. 11). 

12. An incomplete specimen seen from the side. From station 2613E; Barnett shale. 

13n.-13b. An incomplete specimen. l3a, Seen from the side; l3b, top of specimen as shown in l3a tilted backward 90°, giving 

a view seen from below. From station 2609; Barnett shale. 

23 
Part III. THE MACRO-FAUNA OF THE LIMESTONE OF BOONE AGE 

By GEORGE H. GIRTY 

COELENTERATA 

Family A ULOPORIDAE 

Genus CLADOCHONUS McCoy 

Cladochonus? sp. 

In general appearance the few specimens cited in 

this way resemble those referred to Oyathamorvia 

1ninor.?, but so far as observed (though this is not 

very conclusive) they lack septa on the inside and 

longitudinal striae on the outside and indeed even 

the transverse growth lines and corrugations of the 

rugose coral. Furthermore, one of them has a stolonlike projection which might be, though it probably is 

Ilot, an extraordinary irregularity due to attachment 

to some foreign. object. 

Locality: San Saba, Tex. (station 2623 1) . 

Family CYATHAXONIIDAE 

Genus CYATHAXONIA Michelin 

Cyathaxonia minor Weller? 

Two specimens are referred here. The more perfect one has a length of 6 millimeters and a diameter 

of about 3 millimeters; the other must have had 

originally 'about the same proportions. The' shape 

is, 'as usual, that of an elongated cone, distinctly 

though not strongly curved. The specimens are 

rather conspicuously marked by fine, more or less 

regular incremental striae, which are intensified here 

and there in varying degrees, the strongest forming 

distinct constrictions. The surface is also marked 

by regular faint longitu.dinal striae corresponding to 

the'septa. As shown by the imperfect specimen, the 

sf:pta are relatively numero,us, slender, and persistent 

to the center, where they appear to unite with a styliform columella, though this is far from assured. 

The septa themselves can not well be counted, but as 

determined by the longitudinal corrugations that correspond to them on the outside they number 24. 

In all the observed characters this form approaches 

nearest to 0·. minor, though my specimens have not 

attained the extreme elongation of some specimens of 

that species. The septa also are less numerous by 

1 For a close description of this locality and other localities cited 

by number, see the register of localities on p. 17 .. 

24 

2 to 5. Furthermorl~, it is not certain that the present 

form belongs to the same genus, though all the indications point that way. 

Locality: San Saba" Tex. (station 2623). 

Family EUPSAMMIIDAE 

GenusPALEACIS Milne-Edwards and Halme 

Paleacis? sp. 

This name is used for a single specimen whose 

real nature and relations are problematic but whose 

characters, so far as determined, sugge!?t a coral of 

the genus Paleacis. The specimen is small, having 

about 5 millimeters for the longest diameter, and its 

original: shape is uncertain. It has a porous or 

spongy structure very silnilar to that of Paleacis, and 

this character, in default of any that would help to 

place it more definitely, is the reason for the reference 

adopted. 

Locality: San Saba, Tex. (station 2623). 

"- BRACRIOPODA 

Family DISCINIDAE 

Genus LINGULIDISCINA Whitfield 

Lingulidiscina aff. L. minuta Mather 

The single specimen referred here is an upper 

or brachial valve characterized by its very small size, 

(less than 2.5 millimeters in diameter), by its rather 

depressed shape, and by its distinctly though not 

strongly eccentric apex, which is small and relatively 

inconspicuous. The surface shows fine obscure concentric markings. 

This specimen does not have the ,phosphatic look 

nor the sharply lirate surface of the common Carboniferous discinoid, although it has the general expression of "Orbiculoidea." On the other hand, it 

does not show the punctate structure nor the characteristic expression of OrGinia. Being without doubt 

one or the other, it probably belongs in the group 

commonly cited as "Orbiculoidea." As regards the 

generic name, it can be shown that without making a 

change in our rules of nomenclature or else without 

making an exception of this particular name, Orbiculoidea can not properly be applied to the" Orbicu-
MACRO-FAUNA OF THE LIMESTONE OF BOONE AGE 25 

loidea ".group. It is now equally clear that the name 

Lingulidiscina also properly belongs to a different 

group of shells, but as I have for some time been 

employing it for this one and am at present unable 

to turn to a better term, or at least to give my reasons for such a change, I am continuing the use of 

Lin,qulidismna provisionally in the same' sense. 

In its specific relations the form in hand is quite 

sinlilar to that which Mather called O. 1ninuta. That 

species, of which I have many specimens, seems, however, to have the brachial valve as a rule more elevated 

and its apex more eccentric, so that an identification 

can not really be made. Few other species are comparable to this in minute size. O. limaJta and O. 

parvaJ, both of Rowley, are the ·only ones' that meet 

this specification, and to neither, apparently, does my 

form belong. 

Locality: San Saba, Tex. (station 2623). . 

Family CRANIIDAE 

Genus CRANIA Retzius 

Crania pertenuis Girty, n. sp. 

Plate V, Figures la-3b 

It is difficult to describe this form without to some 

extent describing individual specimens, for each of 

the six individuals in my collections is more or less 

peculiar. To this method, then, I shall have recourse. 

All the specimens are upper valves .. 

One rather striking individual has an outline conspicuously quadrate though with rounded angles. Th9 

posterior end is considerably narrower than the anterior end, and the width, which may be a little 

greater than the length, is 4 millimeters. The general 

shape is therefore depressed pyramidal, the apex of 

the pyramid being conspicuously posterior. A narrow longitudinal groove divides the posterior side of 

the specimen, which is an internal mold, while broad 

undefined deflections occur on the three other snrfaces. 

Another smaller specinlen has the same general 

~haracters but is more irregular. The posterior side, 

which is relatively narrow, bears a median groove, 

and the three other sides also are more or less im· 

proosed, especially the anterior side. The apex, which 

is pointed, is strongly' posterior and appears to be 

directed backward, so that the outline on the posterior 

side is gently concave while that on the anterior side 

is gently convex. 

A third specimen, which is testiferous, agrees in 

a general way with those just considered. 

A fourth specimen, mostly testiferous, is conical 

rather than pyramidal, only the posterior side being 

distinguished as a broad oblique plane which is not 

Inodified by a median groove. The height of this 

specimen is esp.ecially low, and the apex is especially 

posterior in position. 

A fifth specimen is rather similar to the foregoing 

except that it is a little more elevated and a little 

more inflated, so that the outlines from the apex to 

the front and to the sides are distinctly convex. 

A sixth specimen is generally conical, but its elevation is especially low. Its apex appears to be central 

or even anterior (if the shell is not broken at the 

anterior margin); the anterior side is slightly convex, while the posterior side is gently concave. 

The surface of all these specimens where not exfoliated is marked by fine, rather irregular lines of 

growth of varied intensity. 

The shell is thin and apparently punctate, but this 

character is far from certain. 

Several features of this species bring its reference 

to the genu~ 01'ania somewhat in doubt. It can not, 

of course, be a 01'ania if the shell structure is impunctate. The tb,inness of the shell and the absence of 

muscle scars, which in Orania are usually large and 

ret>resented by prominent nodes, are also adverse to 

this reference. 

If not a Orania, I should consider this form a gastropod of the general relationship (in form, at least) 

of Patella or Acmaea. If the shell structure is really 

punctate, however, it would debar this relationship 

and almost conclusively corroborate that with Orania. 

This Orania, if such is its character, is quite distinct from any of the described species. It clearly 

belongs to the group of smooth forms and by this 

fact is immediately distinguished from O. blairi and 

others like it. The smallness of its size suggests such 0 

species as O. delicata and O.? lemoni, but in other 

respects it is notably different. 

" Locality: San Saba, Tex. (station 2623). 

Family ORTHIDAE 

Gen us RHIPIDOMELLA Oehlert 

Rhipidomella perminuta Girty, n. sp. 

Plate V, Figures 4a-6 

Shell very small, the largest specimens being only 

5 or 6 millimeters in length~ Length and width about 

equal. Shape broadly ovate or ,subcircular. 

Pedicle valve rather gibbous, in the umbonal region, 

depressed toward the cardinal angles and toward the 

front. Cardinal line short, one-third to one-fourth of 

the greatest width. Cardinal area moderately high 

and more or less coincident with the plane of the shell. 

margin. Beak small, pointed, strongly incurved, ahd 

projecting beyond the beak of the brachial valve. 

Brachial valve more nearly circular than the pedicle 

and less convex; somewhat inflated in the umbonal 

region, with a small, distinct, strongly incurved beak. 
26 MISSISSIPPIAN FORMATIONS OF SAN. SABA COUNTY, TEXAS 

A median sinus begins in the ulnbonal region as a 

narrow depression and widens rather strongly to the 

front, where !t is a conspicuous feature. 

Surface marked by the usual radiating lirae, which 

are sharply defined, though low, and are rather coarse 

for the size of the shell. About four occur in 1 millimeter. The shell is relativ'ely thick, and when it is 

exfoliated the liration appears finer than when it is 

well preserved. 

A pedicle valve from station 2618A shows the large 

flabelliform muscle scars characteristic of Rhipido-

'lnella. They extend about halfway to the front margIn. 

These shells are so small that one might at first be 

led to regard them as merely immature. N everthekss, I have about 100 specimens, the largest of which 

Hrc only 5 or 6 millimeters long. This fact and certain others, such as the thick test and the well-developed sinus of the brachial valve, indicate that the 

specimens, in spite of their small size, are fully grown. 

It is quite possible, of course, to have a species represented by a large aggregation of young shells without 

any mature ones, but it must be borne in mind that 

all the specinlens of all the species of the present 

fauna are minute. That there should be an entire 

fauna of young shells without any mature ones of any 

species is a possibility too remote to contemplate, and 

the more likely hypothesis is that we have here a 

fauna of generally mature shells all of which are very 

small. It may be that these specimens represent a 

species of RhipidO'lnella that elsewhere reached a 

large size but here was dwarfed by some unfavorable 

o condition in the environment. If so, I am unable to 

trace this form to its normal one. It is distinguished 

by its small size, its short hinge line, and its gibbous 

Yalves, at least in the umbonal region. . 

Locality: San Saba, Tex. (station 2623). 

Rhipidomella perminuta var. 

Plate V, Figures 7-9 

The shells referred to R hipidomella per'J1~inuta 

show considerable variation in shape, especially with 

regard to fullness of outline in the region of the 

cardinal angles. In some specimens the outline. narrows so gradually at the posterior end that the shap~ 

suggests a triangle rather more than a circle. Such 

specimens might be referred to the dubia group of 

R hipidomella. In other specimens the outline at the 

posterior end is ;more full or rounded and the shap~ 

is more oval. 

A few specimens are especially ample in the region 

of the cardinal angles and have a more nearly cir'-

cular outline. The valves are less gibbous than in 

the typical variety, and there are perhaps other differences. It is difficult to tell from the material at hand 

whether these more circular shells represent a distinct 

species or an unimportant modification of the other 

form. 

As just intimated, there seems to be a gradual 

transition from shells of one shape to those of another, and only a few and only the most conspicuous examples of the rounded shape. have been set 

aside to represent this variety. A nicer discrimination might have increased this number by specimens 

that, if less fully rounded than those selected, weri~ 

yet too round for the other form. 

Locality: San Saba County, Tex. (stations 2618A, 

2623). . 

Family STROPHOMENIDAE 

Genus SCHUCHERTELLA Girty 

Schl1chertella morsei Foerste? 

This is one of the rarer species, and the few specimens that have been examined do. not show enough 

to sustain a definite identification. 

The size is small, a width of 7 millimeters not being 

exceeded by t~e specimens seen. The pedicle valve 

is low and not quite regular in growth. The brachial 

valve is almost flat. The surface markings are of the 

usual type and are quite comparable to those of 

S. lens and other species. One pedicle valve seelns 

to show that there is present neither a median. septum 

nor dental plates. . 

The generic reference of this form to Schuchertella 

seems fairly safe if I have correctly determined the 

structure of the pedicle valve, while the very small 

size and the general appearance indicate a close specific relationship to S. 'lno1'sei. On the other hand, 

except for its small size, it might with equal reason 

find place with S. lens. It probably is not identical 

with either species, though distinctive characters 

would be hard to find in the present material. 

Locality: San Saba, Tex. (station 2623). 

Schl1chertella? sp. 

Two specimens, in a large way similar to those 

placed under Scnuchertella morseif, are distinguished 

by having the radii paired. . In other words, the 

grooves separating two radii of the same pair are 

narrower and shallower than those separating adjacent pairs. If this feature is persistent, one can 

hardly doubt that it marks an as yet undescribed 

species. As to this vital point, my evidence is unsatisfactory, and in any event the material is too imperfect for descriptive purposes. 

Locality: San Saba, Tex. (station 2623). 
MACRO-FAUNA OF THE LIMESTONE OF BOONE AGE 27 

Family PRODUCTIDAE 

Genus CHONETES Fischer-de-Waldheim 

Chonetina subcarinata Girty, n. sp. 

Plate V, Figures lOa-16 

Shell small, rarely more than 6 millimeters in width, 

deeply semicircular, the length in some specimens being nearly if not quite equal to the greatest width, 

which occurs ~t or near the hinge line. The cardinal 

angles are quadrate or slightly acute; the outline contracts below and is strongly rounded across the front. 

'1.'he pedicle valve is inflated, especially the median 

half, and the auricles, which comprise about onefourth of the shell on either side, are large and much 

depressed. In conformity with the inflated mesial 

region, the umbo is unusually prominent. The strong 

convexity from front to back, the prominent umbonal 

parts, the large depressed auricles, and the remarkable length of the shell, which is nearly as great as 

the width, gives this form an expression unusual for 

Ohonetes and one recalling in many respects the kindred genus Productus. The cardinal spines are large 

and suberect. Two, or rarely three, are to be counted 

on each side. 

The brachial valve fo~lows in configuration the 

pedicle valve, but it is much less strongly arched in 

the umbonal region. l\fore specifically, the median 

half of the shell is conca va both in a transverse and 

1nore strongly in a longitudinal direc.tion, and about 

one-fourth on each side is reflexed into a somewhat 

]':'Lrge auricle, itself gently concave. 

The surface of both valves appears to be nearly or 

quite without radial costae and to be marked only by 

fine inci'emental lines, a few of which are somewhat 

stronger than the rest and faintly lamellose. A more 

or less distinct cleft c,an sometimes be seen on the 

pedicle valve along the median line in the umbonal 

l'egi9n, and, corresponding to this, the slight convexity that in many species of 0 honetes marks the umbo 

of the otherwise' concave brachial valve tends in this 

one to take on an elongated or linear shape, appearing as a short evanescent ridge. 

On the inner surface the pedicle valve shows the 

small spines or prickles that are characteristic of 

o lwnetes. A median septum, especially stout in the 

umbona.l region, is also regularly present. In the 

brachial valve these internal spinules are developed 

to an exaggerated degree and become connected into 

strong continuous radial ridges having a definite and 

constant arrangement. They are restricted to about 

t he median half (or to the strongly arched portion) 

of the shell, but a strip down the middle is plain or 

traversed by only one or two fine obscure ridgeS. 

The other ridges begin abruptly. They are developed 

to the number of five to seven on each side and are 

succeeded laterally, on the auricles, by large spinules 

radially arranged. The ridges and rows of spinules 

tend to graduate into one another, the antel'ior parts 

of the mo~e lateral ridges being replaced by spinules 

similar to those on the auricles. 

The inner surface of the brachial valve. presents a 

peculiar and striking appearance, and evidently the 

soft parts by which it was secreted could not have 

had quite the same structure as in the ordinary 

o honetes. This fact and the configuration of the 

valves, which is likewise out of the ordinary, indicate that the present species, t~ugh related to 0 honetes, is not a true Ohonete8 at all. It seems, indeed, 

t.o possess many of the distinctive characters of Ohonetina. 0 hone tina is known to me only through Hall 

and Clarke's description, and they in turn consulted 

Oehlert instead of Krotow, the origin~l author. My 

form agrees with 0 honetina in that the pedicle valve 

is very convex, although it does not possess a "profound sinus." The most significant point of agreelnent, however, is found in the brachial valve, of' 

which the inner surface in 0 hone tina is said to be 

covered with tubercles" arranged in radiating series 

which unite to form high, compact lam~llae, extending from the beak to the anterior margin; two of 

these,more prominent than the rest, limit the surface occupied by the sinus of the larger valve." In 

my form this arrangement of the lamellae is somewhat modified, probably because the pedicle valve is 

without a sinus, but even in the arrangement of these 

ridges or lamellae a certain agreement can be 

traced. 

The foregoing description is based upon specimens 

from the dark silicious shales of western Tennessee. 

In the fauna under consideration this is one of the 

rarer brachiopo'ds. Only 12 specimens have come to 

hand, and each leaves something to be desired in the 

way of preservation. My description, .then, must 

needs be more than usually composite, picked up in 

part from one specimen and in part from another. 

All the specimens are small; the largest may have 

been 6 millimeters in width, but most are smaller. 

The length for a shell of this genus is uncommonly 

great, being nearly equal to the width, though. probably always less. The outline of a brachial valve is 

somewhat four-sided, or it is like a triangle truncated 

at the apex, being widest near the hinge line and 

narrow across the front and having sides that contract strongly forward. The entire outline is of course 

made up of curves, except the long straight hinge 

line. The cardinal angles are abruptly rounded. The 

pedicle valve would have a similar outline except for 
28 MISSISSIPPIAN FORMATIONS OF SAN SABA COUNTY, TEXAS 

the projection of the umbonal parts, which would 

be relatively though not actually great. 

The pedicle valve is strongly convex, especially 

,along the median line and in the umbonal region. As 

a result the beak is unusually prominent and incurved, 

while in a transverse direction the surface tends to 

have a steep descent from the median part to large 

depressed alar regions on either side. A faint sulcus 

sometimes traverses the median line for a short distance near the' beak. 

The configuration of the brachial valve follows in 

,general that of the pedicle valve except that its con-

,cave curvature is much less strong than the convex 

curvature of the other, especially in the umbonal 

region. Indeed, the umbonal region is rather conspicuously flattened and bears a short ridgelike elevation corresponding to the sulcus of the other valve. 

The surface appears to be smooth except possibly for 

very faint incremental lines. Suggestions of radiating 

-costae can sometimes be seen, though not on the best 

specimens, and this appearance, where present, seems 

to be due to minute spinules on the inner surface of: 

the shell, which are arranged in radiating rows and 

are made partly visible by exfoliation. 

This form is inconspicuous by reason of its small 

size and the small number of specimens that represent 

it, but it is of exceptional interest. It appears to be 

a species which I have described in manuscript, under 

the name 0 honetina subcarinata. The agreement 

amounts almost to identity in all essential characters. 

and the species itself is so peculiar that I can scarcely 

attribute the present form to a different species, even 

if a kindred one. O. suboarinata occurs in the Boone 

formation at more than one horizon. It is very abundant in the fauria having a Moorefield facies which 

Snider includes in his Mayes formation, and it is also 

present in the blackish siliceous shales of early Mississippian age in western Tennessee. It is by no 

means an undiscovered species, but if cited at all it 

has commonly been cited as Amboooelia, a genus for 

which, owing to its peculiar configuration, it is readily 

mistaken if the specimens do not happen to show the 

characters that really determine its generic position. 

Locality: San Saba, Tex., (stations 2618A, 2623). 

Genus PUSTULA Thomas 

Pustula inconspicua Girty, n. sp. 

Plate V, Figures 17-21b 

Shell very small. Width about 5 millimeters or in 

the largest specimens somewhat more, but in most 

specimens somewhat less. Length decidedly less than 

the width. Outline semicircular with quadrate cardinal angles. 

Pedicle valve gently convex, more or less inflated 

in the umbonal region. Auricles large, depressed, and 

poorly differentiated. 

Surface marked by fine incremental lines and at 

more or 'less irregular and remote intervals by concentric grooves or striae, which, ·though moderately 

strong for the size of the shell, are actually rather 

inconspicuous. Costae none. Spines very small and 

apparently scarce. They are so difficult to observe 

that I was for some time uncertain whether they were 

present at all, and they may be more numerous than 

my observations would indicate. . 

The brachial valve in general follows the curvature of the pedicle valve, though in diminished 

strength, while a variable area in the umbonal region 

is planate or even slightly convex instead of concave. 

External molds, therefore, are gently convex except 

for the umbonal region, which is flattened or somewhat concave. 

The surface is marked by fine growth lines and by 

small angular concentric ridges, which appear to have 

been lamellose. The ridges occur at rather regular 

intervals, but they are farther apart on some specimens than on others and also less distinct. The 

banded effect which they produce is more pronounced on this valve than on the other, while the 

bands are not only somewhat more distinct but somewhat narrower. No evidence whatever of -radial 

costae has been observed nor any evidence of spines. 

Spines may actually be present, however; all the 

conditions are unfavorable to their being observed. 

The uncommonly minute size of these specimens 

and their general character suggest that they are 

young shells belonging to some species that. at maturity would have quite a different appearance. They 

constitute, however, the most abundant species in the 

entire fauna, and of the 200 specimens (more or less) 

that I have examined all are nearly uniform in size. 

If these shells are considered as representing a species 

in a mature stage, then there are few other species with 

which they can profitably be compared, while if they 

are considered as a dwarfed species, their relations are 

speculative. Pustula inconspicua may be compared to 

Productella hirsutifor.mis in miniature, but that species is relatively more depressed and lacks the concentric corrugations in any corresponding degree.' 

The same character would also distinguish it from 

l'roductella conoentrica, young specimens of which it 

resembles in many ways. The species to which it 

scems more nearly related than to any at present 

known is one that occurs in the Ridgetop shale of 

the Waynesboro quadrangle in Tennessee. That species; which I have described in manuscript as Pustula planiconvexa, though resembling this in many 
• 

MACRO-FAUNA OF THE LIMESTONE OF BOONE AGE 29 

ways, and especially in being marked only by concentric corrugations without any evidence of radial 

costae, is considerably larger and has a nearly planate 

brachial valve. 

Locali ty : San Saba, T{'x. (station 2623). 

Pustula mool'efieldana val'. pusilla Girty? 

A small P~(,stula occurs in the collection from sta"-

tion 2618A which differs from P. incons]Jicua and 

appears to be more nearly relat~d to the species named 

above. The material consists of an imperfect pedicle 

yuh1'C and three brachial valves. 

Of the pedicle valve only the surface markings can 

be described. These consist of fine incremental lines 

and of coarser striae which are neither v~ry prollOunced nor equul nor regular and which consequent~y 

produce corrugations that are, if quite distinct, more 

01' less faint and sporadic. Spine scars are rather 

large and numerous, and as they occur upon the 

ruised zones bebveen the striae, they form themselves, 

though imperfe"ctly, along concentric lines across the 

shell. l'he shell appears to be slightly elevated 

around the bases of the spines, which are therefore 

conspicuous. 

brachial valve of P. incon8]J'icua, in keeping with the 

small obscure spines of the pedicle valve of that 

speCIes. 

Locality: San Saba, Tex. (station 2618A). 

Pustula aff. P. indianensis Hall 

Of this form but a single specimen has come to 

hand. It is a pedicle valve, very small and highly 

arched. In length it measures but 2.5 millimeters, 

Hnd though but half as large, "It simulates very 

closely in other respects the specimens of P. india!nensis figured by 'VelIeI'. It is a rather elongate shell 

with small depressed auricles, the outlines at the 

sides being nearly parallel and the cardinal angles 

subquadrate, so far as one can make out. The surface 

is entirely without longitudinal costae. It is marked 

transversely by increnlental lines and striae, a few of 

". hich . are strong enough to make conspicuous constrictions. Spine bases are rather sparse and extremely small, and they tend to form transverse rows, 

although fe·w rows contain many bases. 

, Locality: San Saba, Tex. (station 2623). 

Family PENTAMERIDAE 

Gen us CAMAROPHORIA King 

Camarophoria? aff. C. bisinuata Rowley 

The best of the three brachial valves has a subquadrate shape, sommvhat wider than long. The convexity is llloderate and rather regular, the umbqnal 

region being depressed and the greatest convexity 

OccLuTing about the mid-length. "The surface is Among the numerous indeterminata in the collecmarked by fine striae of growth and by coarser ones hon this one is especially striking and deserving of 

of varying strength. In the more marginal parts mention. It is an imperfect pedicle valve, about 6 

there are also a few angular ridges that appeal' to be millimeters in length and the sanle in width. Its 

lumelliferous. In addition to these structures, there shape is broadly o.vate., its convexity low, the beak 

are scattered nodes (as seen on extern,al molds) corr~- ,~11ber8ct, and the s1nus. bro.ad, shall?w,. and abrupt~y 

sponding to spines on the pedicle valve and not a few" : mflected. The surface IS WIthout phcahons, except In 

small spines proper to this valve its~lf. The othel' .: the sinus, where a rib is indicated, or possibly two, 

brachial valves agree in a general '''lay with this one; this part of the shellbeing broken and the characters 

although they do not agree c9m"pletely. One of them not clear." 

'is less convex and has all its markings more subdued. The internal structures are imperfectly known, but 

This form is obviously closely similar to P. moore:' "at least the presence of a median septum can be 

fieldana val'. 1:yu8illa. It is or appears to be consid- vouched for, though whether this septum supported a 

erably smaller-only about half as large, in fact. spondylium is not known. The presence of the sepThe spines on the pedicle valve have "small spine bun, however, and the general resemblance superficibases, but the bases are not elongated as they coin- ally to O. bisin'lwta lend much probability to the 

monly are in the :Moorefield form. In the brachial generic reference and a possibility at least to the' 

valve t he nodes are fainter and less numerous than specific relation indicated. 

they are in the typi cal specimen represented by Fig- "Locality: San Sa~a, Tex. (station 2623). 

llL'eS 7 and ",a. 

From P. inconspicua the differences are more pro1I0U1H.:od. In the pedicle valve the spine scars are 

larger and far more numerous. The brachial valve 

is l{'ss wide in proportion to its length; it has spines 

of its own, and it has distinct nodes scattered over 

the sllrface. As the nodes correspond to spines on 

tit£' pedicle vn1\'o, nodes are obscure or lacking in the 

!J144H-26--3 

Family TEREBRATULIDAE 

Genus DIELASMA King 

Diclasma? sp. 

That the form under consideration is a terebratuloid is evidenced by its punctate shell; that it belongs 

in the genus Diela817ta is much more' doubtful-in-
30 MISSISSIPPIAN FORMATIONS OF SAN SABA COUNTY) TEXAS 

deed, somewhat unlikely. The specimen taken, as it 

were, for the type of this group is a brachial valve, 

and one of the largest shells in the collection. It is 

about 7.5 millimeters in length and essentially the 

same in width, having a broadly ovate shape and ft 

low convexity. ' No internal characters are shown. 

With this specimen I am including some smaller 

shells having a similar broad shape. One of these 

which retains both valves deserves special mention. 

It has a length of less than 5 millimeters in the pedicle 

valve. It is lenticular, the convexity of both valves 

being low. The pedicle valve, which is the more 

convex, has a small, suberect beak pierced apparently 

by a triangular foramen. The small beak, its erect 

shape, and the characters of its foraminal opening 

are more suggestive of some other group than the 

terebratuloids, yet the shell is punctate, even if obscurely so, and the characters just recited, though 

out of keeping with a mature condition, would not 

be out of keeping with a youthful one. 

It lnight be questioned whether the form described 

as Selenella subcircularis does not consist merely of 

young specimens of this species. Such a relation is 

quite possible. Yet those smaller, more slender shells 

are very abundant; the larger ones very rare.' It 

would perhaps seem more probable that there are two 

species present, but that some of the young shells of 

the large form have in my grouping b,een included 

with the smaller Selenella? subcircularis. There exists no c~iterion for distinguishing the two species in 

their younger stages so far as" I :;tm a ware except 

their proportions, and this criterion, which at be~t 

is not conspicuous, probably would not serve in all 

cases. 

Locality: San Saba County, Tex. (station 2?23). 

Family CENTRONELLIDAE 

Genus SELENELLA Hall and, Clarke 

Selenella? subcircularis Girty, n. sp. 

Shell small, 5 millimeters or less in length. Proportions variable; width distinctly less than the lengtl) 

01' nearly equal to it. The greatest width is about. 

midway or a little bel;ow; consequen~ly tp.e qutline is 

broadly ovate. The convexity is rather low and about 

equal in the two valves. A faint sinus.is commonly 

developed in the brachial valve arid so"metimes in the 

p~dicle valve as well. The beak of the pedicle valve 

is small, moderately incurved, and truncated by a 

round foramen. The pedicle valve bears the usual 

dental plates, but the internal structure of the brachial 

valve is not shown. The shell is finely punctate. 

The position of this little species among the terebratuloids is beyond question, as IS, attested by the 

punctate shell and the'configuration of the'beak of the 

pedicle valve. Some of the specimens covered under 

this title, however, do not satisfactorily show the shell 

st.ructure, which at best is finely and obscurely punc- 0 

tate, "and these might really belong to unrelated genera: 

for the configuration of the beak of the pedicle valve, 

even if it is shown at all, is not sufficiently distinctive 

to locate the specimen in this group, or, on the other 

hand, debar it from some others. 

Though most of the specimens can confidently be 

identified as terebratuloids, it could with much better 

reason be claimed that-they are not mature shells, but 

young ones of some larger species. Their diminutive 

size, low convexity, and small and sub erect or at least 

not strongly incurved beak all suggest this inference. 

Opposing it are the facts that these shells are numerous, that they are essentially uniform in size, and 

that although a larger terebratuloid is known in the 

fauna it is very rare. No characters are shown which 

would lead to the assignment of this form to one 

genus among the terebratuloids more than to another 

and it is cited under Selenella only because of its 

resemblance-purely external, too-to S. pediculus,' 

whose position under Selenella is none too secure. It 

seems to be on the average somewhat broader than 

S. pediculus and to have the widest part somewhat 

farther forward. 

In this connection a comment may be permitted 

upon one or two other species included by Weller 

among the terebratuloids, though they are not similar to the present form. The species that I have in 

mind are Oentronella louisianensis and Trigeria? CU1'-

'1'ieri. Chance rather than purpose has made me familiar wi th immature shell forms in several brachiopod genera, and I am almost sure fronl \Veller~s excellent figures that the species mentioned are not 

,terebratuloids but young rhynchonelloids. In their 

very young stages rhynchonelloids have a spat:ul,ate 

, 8hape, and the relative convexity of the valves is just 

the' reverse of what it is at maturity. As is well" 

known, in these shells the brachial valve is characterr istically convex and has the median part raised into 

I a. fold, while the pedicle valve has the median part 

depressed into a sinus, these features being more pronounced, perhaps, than in any .other type of Paleozoic 

~rachiopod .. Somewhat paradoxically, very young 

rhynchonelloids have' the pedicle valve convexly 

arched from side to side and the brachial valve depressed into a' concave curve. Plications appear 

earlier in some species than in others, so that the 

t\,;o forms from the Louisl'ana limestone would apparently belong to different spe::ies. The. posterior 

region alone of Trigeria? cU1"'rieri is without plications; on the other hanel, incipient plications appear' 

to be shown by ""Veller's figure of Oentr01ieUa' louisir;7wns-is close. to the margin. Other characters of' 

young rhynchonelloids' are the p'ointed and erect beak' 

of the pedicle valve and the triangular pediCle open-
MACRO-FAUNA OF THE LIMESTONE OF BOONE AGE 31 

ina both of which are ch"aracteristically shown in b' 

Figuro 29, representing Oentronella louisianensis. I 

doubt if terebrakuloids even at this young stage would 

11a ve such a configuration. Furthermore 'VelIeI' notes 

that in neither species was he able to detect punctate 

shell structure, a circumstance which is not, perhaps, 

very conclusive in either direction; though even. if 

punctate structure were eventually to be found, the 

fact would not militate against the rhynchonelloid 

relationship of these shells, because the rhynchonelloid 

genus Rll,ynclwpo1'a has this as a distinguishing character. 

Locality: San Saba, Tex. (station 2623). 

Family SPIRIFERIDAE 

Genus AMBOCOELIA Hall 

Ambocoelia laevicula Rowley? 

It is a noteworthy fact that the genus A17~bocoelia, 

somewhat like the genus Olwnetes, is abundant in 

rocks of lower Mississippian age and again in rocks 

·of Pennsylvanian age, but is, according to the records, 

almost absent from the intermediate faunas. This 

statement must, however, be qualified in two particulars. In the eady Mississippian strata these shells are 

not perhaps so abundant as they are highly differentiated, whereas in the Pennsylvanian they are highly 

.abundant but are practically all of one species, though 

in the Permian again greater diversity appears. 

From the faunas of the lower Burlington and Kinderhook no less than five species have been described; 

in strong contrast with these appears the single Pennsylvanin.n species, A. planiconvexa, which exhibits a 

much longer range and a wider distribution. 'Vhether 

the facts are as they appear to be or whether the 

species recognized in the Mississippian are too many 

and those in the Pennsylvanian too few are questions 

open to discussion. 

The other qualification that might be made to my 

opening statement is that in the upper :Mississippian 

rocks of the Southwest (in l\1issouri, Arkansas, and 

Oklahoma) A.mbocoelia is by no means a rare genus, 

and Olwnetes also in certain places and horizons is 

Itlmost incredibly abundant. 

These shells are abundant also in the fauna under 

consideration, being scarcely if at all second to P'ttStula inconspioua in numbers. They belong with little 

doubt to A1nbocoelia, yet as a matter of speculation 

yery young Spirifers and especially very young specimens of Brachythyris would present much the same 

appearance externally, while of the internal characters 

not enough is known to place the generic reference in 

an unassailable position. The small and essentially 

uniform maximum size of the specimens suggests that 

they represent a mature condition an¢! makes the 

natural reference to A mbocoelia avery probable one. 

The form under consideration possesses a number 

of distinctive cha!,acters, which, however, are subject 

to material variation in different specimens so as to 

raise the question (especially if we consider the small 

differences by which some of the early Mississippian 

species are distinguished) whether the specimens· 

would not better be referred to several specific groups 

than to one. As compared with species of the plani-· 

convexa type, the pedicle valve has a rather low elevation and the bra::hial valve a rather high, though, 

of course, the elevation of the one greatly exceeds that 

of the other. The umbonai parts of the pedicle valve 

are rather tumid than attenuated, but they do not 

project far beyond the hinge line. The shape is 01'-

clinHrily transverse, but some specimens are, for the 

genus, uncommonly long in proportion to their width. 

The cardinal angles are rather conspicuously rounded. 

As a rule a median sinus, narrow but not deep and 

commonly sharply depressed along the median line, 

indents the pedicle valve and the brachial valve as 

well, producing a distinct emargination in the anterior outline. These structures may be, however, 

though somewhat rarely, all but obsolete. 

Most of the specimens seem to have more characters 

in common with A.. laevicula than with any of the 

four other lower Mississippian species, and to have' 

kast of all in common with A. minuta, being larger, 

more nearly equivalve, and more distinctly marked 

by a median sinus on either valve. The relative convexity of the valves and the projection of the umbo 

of the pedicle valve beyond the hinge line seem to be 

more as in A. laevicula, though these shells are on the 

average more elongate and have apparently deeper 

sinuses, especially the sinus in the brachial valve. A. 

unionensis is a much larger species, and the typespecimens at least have larger, blunter umbonal parts in 

the pedicle valve. The umbonal parts of A.. parva, 

on the other hand, are more prominent and more 

pointed, at least in one of the specimens figured, and 

the brachial valve of that species is unknown. In the 

size and shape as well as in the pronounce~ sinuses 

in both valves, the present shell suggests A. nor-woodi, 

but the beak of the pedicle valve is more erect and less 

ptominent than in the side view given by Foerste, 

which, be it noted, does not seem to agree very well 

with the other figure of the same specimen. Differences of this chara.cter shown in corresponding 

v1evfs by comparisons with figures are, however~ 

not altogether conclusive, because of the difficulty of 

posing two' specimens in the same way and the very 

appreciable differences in the -apparent' bulk 'arid 

prominence of the umbonal parts made by slight in--

equalities in the pose. If the factor of size were relegated to the unimportant position where it probably 

belongs, the present form, in view of the variation 

shown by different specimens and also in view 'Of the 
32 MISSISSIPPIAN FORMATIONS OF SAN SABA COUNTY, TEXAS 

variation shown by the figures of typical specimens, 

might be almost equally well referred to any of the 

five species of early Mississippian age, except .A. 

'1ninuta. Some specimens agree rather closely with 

one, others with another, though perhaps no specimen 

completely with any. 

As to the Pennsylvanian .A. plamiconvexa and the 

upper Mississippian form which I described as a variety of that species (fayettevilien8is) , a few words 

'will suffice. Both those types differ in being relatively 

broader, in having a flatter brachial valve, and in 

having the umbonal part of the pedicle valve narrower 

and more pointed. 

Locality: San Saba, Tex. (station 2623). 

Genus'SPIRIFER Martin 

Spirifer sp. 

rhe . shells included here are for the most part 

pedicle valves, and they. are ij.ot only.small but imp~rfect.. In configuration they much resemble some 

of our speGies of Brachythyris, so that I at first included them under that genus. More careful examination, how~ve.r, h,as shown that they possess well-devel.oped dent~l lam~llae; thu~, they are at once excluded' fi'om Brachy.thyri8: Other differences, though 

of Jess In~)Irient,' qa:p. also b.~ pointed out, for these 

sh~lls ha ~e 'no pllcations ip. the ~ery distinct sinus, 

sti~h'-as are found in many, though ,not all species 0 £ 

Bra..Qhythy'lis, ~nd in add~tionQ~e specimen see,,?s to 

show supe):,ficial markings of exceedingly fin~ radial 

stdae.. ' 

, 'tt would be hard to,.say.that these were not oldel' 

shells of the same speci~s, of which those desc,ribed as 

Brachythyris? simulans are young ones. B .. r; simulans is smaller;· it has apparently a lower pedicle va~ve, 

with a less prominent umbo; and,' so far as known, 

it is without dental plates, a very important differ.-

ence if it really exists. So,me of the differences, howeyer, are s~lCli. as might characterize young stages 

and' old st,ages of the same specie~. Comparisons 

oased oIi the brachial valve can not be made between 

this f01'~l and ·B. si1nulans; as the brachial valves coll~cted' are few and poor and as none of them occurs 

Httached to a pedicle valve, a fact precluding a c6mpa\~isonbetw:een the two ~orms on equal terms: 

. In general appearance this for~is :very similar to 

Bracl?ythy"ris peculiarris. , ' 

T0 specify their main characters, the~e pedicle valves 

'h~ye a .rather strong simple median sinus, and each 

-of the l~teral areas thus separated from one another' 

',bears, in the larger specjmens, at least, six lateral 

.costae, graqually decreasing in size and distinction, I 

'to,ward the sides. The b,eak -is poin,ted but prominent 

;and upstanding, and the configuration is. strikingly I 

:spiriferoid. 

The brachial valves that would appear to belong 

with these pedicle valves have a low convexity, and 

the mesial fold is defined more by having grooves on 

either side that are stronger than those elsewhere 

on the surface, than by being elevated above the general contour. Indeed, in some specimens the fold is 

slightly depressed, so that the configurljttion, like that 

of Brachythyris.f? simula-ns, might be described as a 

broad, shallow sinus nearly occupied by a low mesial 

fold. The fold in some specimens has the appearance 

of being divided by an obscure sulcus down the median 

line. 

A single specimen of this type (a pedicle valve) 

has been found in lot 2618A and has been provisionally included with these others. It agrees with them, 

indeed, quite closely in a superficial way but seems 

to show almost conclusively that dental plates are 

not present. Though small doubt seems possible on 

this head, the evidence does not show that dental 

plates were not present at one time. They might 

concei vably have been broken from a single specimen, 

though scarcely from a series of them, and as I haVe 

only this one, it seelI!s better to .adopt this explanation for an otherwise anomalous situation. 

Locality: San Saba, Tex. (station 2623). 

Spirifer sp. var. 

A few specimens (also pedicle valves) reselnble 

those cited as Spirifer sp. but seem to differ in having 

somewhat larger and less ·numerous lateral plications. 

J-t is not possible to state the degree of this difference 

01' even- that it actually exists, the specimeRs .being 

so srnall and. imperfect, but the distinction here sug-' 

gested may prove to be a valid one. 

Locality: San Saba, Tex. (station 2623). 

Genus RETICULARIA McCoy 

ReticuIaria sp. 

This type is repre~ented by a single specimen, a; 

pedicle Yalve, which has little to distinguish it except 

its slna.ll size.. It measures about 6 millimeters in 

width a~d somewhat less in length. In its specific relations it might belong, so far as one can tell, to 

almost any .of op.r ~1issis~ippian species, and for this 

reason, though to me it re:::alls an early Mississippian 

species like RetiC'l.6laria coope'l'e'11~'is, I have refrained 

from suggesting a ~pecifi~ identification, which might 

carry definite stratigrap4ic implic~tions. 

. 'l\> the generic assignment a fe,w words may be 

spared. The speciIl1:en shows a low but distinct median septum, but I have been unable to ascertain the 

presence of dental plates. These ,internal structures 

(especially the dent~l plates) are likely to be fee~ly 

developed in the early Mississippian Reticularias, and 

consequently one of those species is espe.:ially sug-
MACRO-FAUNA OF THE LIMESTONE OF BOONE AGE 33 

gested by my specimen. T~e feeble development, 

however, might be ascribed to immaturity, and in the 

case of a single specimen the significance of this fact 

is slight. The specimen could hardly be taken out of 

Reticulm'ia and assigned to Squam,ulmria, but even 

were that possible it is obviously a different species 

from our common S. pe'rplema. 

Locality: San Saba, Tex. (station 2618A). 

Genus BRACHYTHYRIS McCoy 

Brachythyris? simulans Girty, n. sp. 

Plate VI, Figures lOn-lOe 

Somewhat paradoxically certain characters found 

in th.is species suggest a relationship to Hustedia? 

1,(JJI'vicostata, although others indicate an altogether 

different generic reference. This shell is relatively 

broader than Ii.? pa'l'vicostata and has a distinct and 

rather long hinge line, which is, however, shorter 

than the width below. It is even more inequivalve 

than II .. '? pa1'vicostata, the brachial valve in fact being ulmost flat. The pedicle valve, however, is ,veIl 

arched, especially in the umbonal region, and the 

beak is prominent "topographicnlly ," nlthough it 

d.oes not project far beyond the hinge and is not 

prominent in the outline. Consequently the cnrdinal 

area in this form hus n direction almost at right 

nnc.rles to that in the other. bein!! here more or less b , ~ 

perpendicular to the plane of the shell margin, there 

more or less parallel to that plane. The pedicle valve 

is. divided in the nliddle by a rather broad, shallow 

~jmple sinus, and each of the lateral areas bears five 

or six rather slender, rather ill-defined costae. The 

hrachial valve has a corresponding shape. The broad 

.simple fold is lnuch larger than the lateral plications, 

but (and in this it is especially reminiscent of H.? 

pa:}'vicostata) it lies in a gentle depression instead of 

being elevated as the brachiopod fold normally is. 

The lntel·ttl plications number five or six and are 

rather small and feebly developed. 

It is impossible to sny anything positive about the 

structure of the pedicle valve in the umbonal region, 

but the configuration is strongly spiriferoid, whereas 

that of H .. 9 PQl}"vicostata is apparently quite otherwise. 

Looality: San Saba, Tex. (station 2623). 

Family RKYNCHOSPIRIDAE 

Genus HUSTEDIA Hall and Clarke ¥ 

The ·small shelis referred under this genus present n 

problem in their general relationship which I have 

found it impossible to solve in H, satisfactory manner. 

Here, as in most other unsolved problems, the obstacle consists in the difficulty of ascertaining facts. 

Flustedia? tewana is fairly abundant, and consequently 

its chnracters are more fully and more definitely 

knmyn than those of the rarer species here referred 

to the same genus. Its general relations are fairly 

clear. It apparently belongs to a group of retzioid 

shells that occur in our early Mississippian faunas 

with some persistence and resemble Hustedia rather 

than EumA3tria in their coarser plications and possibly 

in other characters. Weller has in fact referred these 

shells tentatively to IIustedi{J), but we still lack substantial evidence as to their exact generic relations. 

Although the general relations of Hustedia? temana 

are fairly clear, the same may not be said of the less 

known and less characteristic H .. '! proole1TWJtica, H .. '! 

suoaequalis, and Fl.? parvicostata. It is to these, 

then, that the following discussion relates. 

Slight metamorphism of the shell substance has obscured the structure in all the specimens of whatever 

species, so that it was only after careful examination~ 

several times repeated, that I was able to satisfy myself of the punctate structure of the form described 

as HustediaJ! temama. Several times I have thought 

that I found evidence of punctate shell structure in 

specimens of some of the othei' species, but examination under higher magnifications seemed rather to discredit than to corroborate the first impression. It is 

true that a few specimens which seeln to belong with 

Ii.? inaequalis show punotate structure that can not 

be doubted, but their specific identity is not beyond 

question. If we may conclude that they belong at 

le.ast to the same group and that all of these forms 

nre related to one another, I can not doubt that all 

possessed this same character of a punctate shell. 

The configuration of the beak and of the pedicle 

opening would have an important bearing upon the 

generic affinities of these shells, but they occur in a 

rather hard limestone, and when recovered, as they 

must be, by being broken out of the rock, they are 

exfoliated. The shells themselves are so small and 

the rostral part 'so small a portion of the whole that if 

the beak still remains concealed by rock it can scarcely 

bE' uncovered by manipulation, or if it happens to 

have come free, the beak, even if not broken off entirely, has been disfigured by exfoliation so that its 

original characters can not be determined. My observations suggest that the beak of the pedicle valve was 

suberect and pierced by a round foralnen, but this 

character also can not be definitely asserted, as it was 

definitely ascertained for only one of the specimens. 

The scarcity of material, which is by no means 

abundant, has prevented the determination of any 

internal characters, an attempt to do which would be 

discouraged in ad vance by the small size of all the 

specimens seen. 

The small size of the specimens, which has thwarted 

the determination of several essential characters, has 

also complicated the interpretation of the characters 

that can be determined. The general expression of 

brachiopod shells is often sufficient to indicate their 
34 MISSISSIPPIAN FORMATIONS OF SAN SABA COUNTY, TEXAS 

gener:ic relations, even if actual generic· characters 

can not 1 be made out. This is true, however, only of 

shells that have reached their mature form, and one 

might .. go' far. astray in using such evidence if the 

specimens ,were thought to be mature when they were 

really very immature. 

All these specimens are very small, a fact which suggests that they represent an immature stage. On the 

other hand~ all the ·specimens of all the species in this 

collection are. equally small, a fact' which would tend 

to suggest that we are considering a whole fauna of 

small species rather than a whole fauna of immature 

specimens. The latter alternative would furthermore 

be discredited by the fact that many of the specimens 

possess characters which usually indicate a mature 

condition, such as convexity, inflection of the beak 

or the pedicle valve, and development of the fold and 

SInus. On these criteria some of the shells in the 

present group also represent a mature or at least a 

not very immature condition. 

lations of the Texas forms appear .to be with the 

Rhynchospiridae, or··at . least rather with the Rhynehospiridae than with the Atrypidae. The peculiarity of the depressed" fold" appears in the Carboniferous rhynchospirid genera Ptychospira and H ustedia, but it is absent in Eumetria or at least is confined 

to so early a stage of development that it appears to 

be absent altogether. It is shown conspicuously by 

the species associated with these which I have described as Hustedia.9 texana. 

The three species under consideration show little of 

generic value by which one could. determine whether 

they belong under Ptyehospira, Hustedia, or some 

other genus, possibly one not yet described. It may 

be that on the basis of configuration alone diverse 

relations are suggested. H ustedia.f! proble'l'lWtica, 

with its few strong plications and even its lamellose 

concentric striae, suggests Ptychospi1'a, for concentric 

striae are strongly developed in Ptychospira and conspicuously absent from the common types of Hustedia; 

in this H ustedia agrees with Eumetl'ia. On the othei' 

hand, Hustedia? subequalis and possibly H.? parvicostata are more semblable to H ustedia than to Ptychospira. 

Hustedia? texana Girty, n. sp. 

. Plate VI, Figures 1-4d 

Shell small, about 5 millimeters in length, elongate, 

ovate, the anterior outline more or less straightened or 

indented 'across the middle. 

Pedicle valve narrowing gradually backward and 

somewhat acuminate at the posterior end. Cardinal 

One of the peculiar features found in all three species under discussion concerns the fold and sinus. 

The·sinus is not sharply distinguished from the other 

plicati~ns of the· pedicle valve; it is merely a little 

larger and a little deeper and is situated on the median 

line.· The corr~sponding elevation on the brachial 

valve, which would consequently be the fold, is, in ' 

contrast to. the normal brachiopod fold, not elevated 

but depressed.· This peculiarity is shared by several 

widely different groups of brachiopods and points to 

as many different relationships, all of which must 

naturally be false except one. It is shared by the 

associated shell described as Brae hy thY1'iS .9 sirn;ulans; 

but it is, for Braehythyris or for types related to it, so 

anomalous that its possession by the form just mentioned tends less to translate these three species to 

Braehythyris than '. to translate Brachythyris? sirnulans from Brachythyris,-to ,this group of shells. The 

configuration of the pedicle. valve of Brack"ythy1-is? 

8imulans appears to be very different from that of 

these shells anci·, characteristically spiriferoid, and I 

believe that jJ.rac1~ythyris? simulans and the three 

species under consideration are fundamentally unlike. 

· line short, less than half the width of the shell. Convexity strong, somewhat inflated posteriorly, bnt much 

Some of the Atrypidae share in the peculiarity to 

'which I have referred, the subordination of the lnedian rib or ribs of the brachial valve, and furthermore their sculpture is characterized by the development of lamellose concentric striae to which the 

sculpture of H .. CR proble'l'lWtiea is in a measure comparable.' If the present group possesses a punctate 

8hell structure, as on the whole seems probable, the 

Atrypidae need no further consideration. 

The same peculiarity occurs also in the Rhynchospiridae and' is perhaps more characteristic of them 

than of the Atrypidae, and furthermore the Rhynchospiridae construct punctate shells. Thus the true re-

· diminished toward the front. The median part is· 

, commonly depr'essed into a narrow sinus, which is 

never strong and may be obsolete. 

Brachial valve in general like the pedicle valve, except that it is truncated by the cardinal line and that 

its beak is much smaller and less prominent. . The 

nmbonal region is rather conspicuously inflated, and 

the convexity is generally about equal to that of the 

· other valve. This valve also bears a median si'nlls; 

~rhich, though narrow, is persistently Pl'csc!lt and 

may be rather strong. 

The costae are sleI).der, and sharply raised . fron1 

dividing striae of about the same width .. They are 

broadly rounded on top, as are the striae at bottom. 

They gradually decrease in size toward the sides, the 

final ones being very small. The exact nmnber is difficll1t to ascertain because of this fact, and it is difficult 

to state in general terms, because it varies with the 

size of the shell. Ten or eleven costae are commonly 

to be found on mature specimens on each side of the 

sinus, and one or more somewhat smaller costae arc 

also developed in the sinus itself. On some sperimens 
MACRO-FAUNA OF THE LIMESTONE OF BOONE AGE . 35 

as many as fourteen occur on each side, making the 

total number as many as thirty. Individual variation, 

exfoliation by which some of the costae are obscured, 

and the degree of magnification (according as one 

Hses a hand lens or a binocular) would cause considerable variation in the total count. Some specimens 

are more finely costate than others-apparently the 

narrower ones. 

The shell structure i§l finely punctate. This feature is not easily observed, but it has been determined 

with certainty on a number of specimens. The process 

by' which the specimens have been obtained, small as 

they are, by breaking them from solid roc-k, has caused 

imperfections in the umbonal parts of the pedicle 

valve, so that the original configuration of the beak is 

shown by very few specimens. So much is manifest, 

however, that the beak was incurved and truncated 

by a round foramen in the way common among the 

retzioids. 

The generic position of this little shell can not be 

exactly determined, but one can scarcely doubt that it 

belongs with a limited group of species that have been 

variously referred under Retzia or H ustedia, to 

neither of which it may actually belong. It differs 

from Hustedia pygmaea and H .. triangulOJris in having more numerous costae and especially in having a 

pronounced sinus in the brachial valve. By the latter character, as well as by its smaller size, it is also 

distinguished from H. 'lnulticostata. The fine striation and the large number of costae suggest a generic 

reference to EU'lrwtria, but the strength of the costae, 

with their' wide interspaces, as well as the median 

sinus that is developed on both valves but especially 

on the brachial valve, are more or less alien to 

Eumetria, and distinguish the present species, if not 

from the genus itself, at least from any American 

speeies referred to it. 

Locality: San Saba, Tex. (station 2623). 

Hustedia? problematica Girty, n. sp. 

Plate VI, Figures 6a-7c 

Shell small, elongate, subpentagonal to subovate. 

The type specimen is somewhat less than 5 millimeters 

in length, but in this measurement is included a certain restoration at the posterior end. Though oval in 

genernl shape, the outline is straightened across the 

front and also nt the sides in the umbonal region, so 

that a somewhat pentagonal effect is produced. The 

convexity is rather strong, that of the pedicle valve 

being greater than that of the brachial valve. The 

beak of the pedicle valve (as shown by a second specimen) is but slightly incurved, and for this reason, 

though small and pointed, it is prominent in the 

outline. . The beak is apparently not truncated by a 

round :foramen such as is characteristic of genera like 

Hustedia, EU'l7U3tria, and others similarly shaped, and; 

on the other hand, it is apparently not provided with 

a distinct cardinal area like that of SpinIer, though 

this is far from certain. The beak of the brachial 

valve is small and not at all prominent. The hinge 

Ijne is short. 

The shell is nlarked by a. few large, strong, radial 

plications. One of these on the pedicle valve, as it 

occupies the median part, may be. considered the sinus, 

though it is not especially distinguished from the 

other plications, which are graduated in size and 

strength. A strong rib bounds the sinus on either 

side, wit~ a fairly strong r.ib beyond and a faint .one 

beyond that, making six in all, three on each of the 

lateral areas. The grooves or sulci number five (including the median sinus) , or seven if the final rib can 

be said to have a boundary on the outer side. Corresponding to this arrangement there are on the brachi~l 

valve five ribs and six sulci, but there the lnedian rib 

(or fold) is subordinate to those on either side of it, 

being smaller and less prominent and not continued 

backward quite to the beak. The configuration. of this 

valve, considered in another way, might be described 

as comprising a large, strong sinus which has a plication in the middle of it, for the "fold" is distinctly 

depressed below the adjacent parts. . 

The surface characters are not shown by the type 

specimen, which is exfoliated, but other specimens 

have the surface concentrically marked by i'egularly 

arranged, relatively strong, sublamellose strife. 

The internal structures a~e not known. In the type' 

specimen the broken beak of the pedicle valve affords 

no evidence of dental plates. The shell structure may 

be punctate. It has so appeared to me at times, but 

examination under higher powers has failed to corroborate this appearance; It would hardly be safe, 

however, to conclude that the shell was impunctate. 

Locality: San Saba, Tex. (station 2623). 

Hustedia? subaequali~ Girty, n. sp. 

Plate VI, Figures 8-9c 

Shell 3ubovate, varying' in proportions, but as a 

rule rather broad. 

Pedicle valve having a small round foramen in a 

small, suberect, and pointed beak. Surface marked by 

rounded plications separated by grooves of the same 

size and shape, except that the median line is occupied by a groove larger than the others and that all 

the plications gradually diminish in size and inte~sity 

toward the side. The typical specimen has five 

. rounded plications on each side of the median groove. 

In a second specimen referred here the median 

groove is more conspicuously stronger than the other~. 

The median plication answering to it in the brachial 

~alve is, however, weaker than the adjacent ones, 
36 MISSISSIPPIAN FORMATIONS OF SAN SABA COUNTY, TEXAS 

being depressed below them and, as it were~ rising 

from a gentle sinus. 

The shell structure of the typical pedicle val ve is of 

doubtful character. I can not say that it is punctate, 

much less that it is not. One of the associated specimens gives evidence of being finely punctate; another 

specimen is distinctly punctate, though it may not be 

of the same species. 

Locality: San Saba, Tex. (station 2623). 

Hustedia? parvicostata Girty, n. sp. 

Plate VI, Figures 5a-5c 

This species may possibly graduate into H .. ~ problematica, although the differences are pronounced as 

between typical specimens. The outline is relatively 

broader and more nearly circular, tending to oval. 

The plications are smaller,. feebler, and more nunlerous~ 

As in H.? p1'oble'l7UJ;tica, the pedicle valve has a 

sman, pointed, suberect beak. The convexity is moderate. The" sinus" is rather broad. Each of the 

lateral areas supports four or five feeble costae, 

which are separated by sulci much smaller than the 

nledian one, or sinus. The brachial valve is somewhat depressed, distinctly lower. than the pedicle 

valve. The median part is depressed into a broad 

sinus, most of which is occupied by a median plication or fold somewhat larger than the lateral plications, of which there are four on each side. The 

evidence as to the shell structure is not clear, and the 

character of the pedicle opening is also uncertain. 

The suberect and pointed beak almost .precludes a 

structure comparable to that of the retzioids. 

Locality: San Saba, Tex. (station 2623). 

Family ATHYRIDAE 

Genus CLIOTHYRIDINA Buckman 

Cliothyridina? sp. 

The group of little shells included under this title 

is probably composite, for even much care could hardly 

eliminate the possibility that imperfect specimens of 

several other species, especially specimens of Selenella? 

8ubcircularis that failed to show the punctate structure, 

might have found their way here. The shells that I 

Ita ve especially in mind and that are especia~ly beyond 

suspicion, however, are none of these, but something 

distinct. They are broadly ovate and about 4 millimeters in length. The convexity is fairly strong, and 

the beak of the pedicle valve is rather small and not 

much incurved. The surface in its present exfoliated 

condition appears to be smooth or nearly so, and the 

shell substance rather fibrous than lamellose and punctate. 

The generic position of these shells, if they may be 

treated as of one genus, is doubtful. They suggest, 

as the most probably related, the genus OO'Tl1P 0 sita , 

or better, because of the small beak of the pedicle 

valve, the allied genus Oliothyridina. The absence 

of distinct fold and sinus would also harmonize with 

Oliothyridina., though not incompatible with the interpretation that the shells are young Compositas. 

Another genus that is suggested by the general configuration is Nucleo8pira, and only a more accurate 

know ledge of the internal and other structures would 

lead to a satisfactory conclusion as to where thi8 

form really belongs. 

Locali ty: San Saba, !ex.' (station 2623). 

PELECYPODA 

Family PLEUROPHORIDAE 

Gen us CYPRICARDINIA Hall 

Cypricardinia? aft.' C. subcuneata Weller 

The two specimens included here are small, 5 millimeters or less in width, and they are not sufficiently 

perfect to permit a satisfactory generic reference eveh 

on the criteria of shape and general expression. A 

reference to the genus Sphenotu8' would, perhaps, 

ha ve as much to recommend it. Among the species 

referred under Oypricardinia none is so similar as 

Cypricardinia 8ubcuneata; though only about half as 

large, my spe'ciinens resemble Weller's figures of that 

species quite closely. 

Locality: San Saba, Tex. (station 2623). 

GASTROPODA 

Family PLEUROTOMARIIDAE 

Genus BEMBEXIA Oehlert 

Bernbexia aft. B. lativittata Girty 

If we except the few forms that are extremely 

abundant, the present species may be called fairly 

common in the fauna under consideration. Yet of the 

five or six specimens at my command, none is sufficiently complete to be available as a type specimen, 

although enough (an be determined to indicate that 

the species is probably new. 

This is a small shell, about 3 millimeters in height 

and not far from 3 millimeters in diameter. The 

general shape is ovate or conical, but the whorls are 

sufficiently distinct to make it somewhat turreted. 

The yolutions are more or less inflated and have a 

broad, prominent carina about midway on the outer 

side, the surface above being somewhat flatter than 

the surface below. The carina, which is the site of 

the slit band, is defined on both sides by raised lines 
MACRO-FAUNA OF THE LIMESTONE OF BOONE AGE 37 

and is accentuated by a slight sulcus adjacent to its 

lower boundary. The volutions overlap to the carina 

or to a line just below it, and this gives the shell its 

slightly turreted shape already mentioned. 

The w horIs are marked by' regular transverse lirae, 

which nre lineal' and sharply elevated from the 

broader intcrspnces. These markings ate cilistinctly 

('oarser on the upper surface (above the carina) than 

on the lowct·. In shape they are gently convex on the 

llpper sUl':fnce, strongly concave on the slit band, and 

gently convex on the lower surface, the strongest part 

of the curve occurring immediately below the sulcus, 

which in turn is immediately below the carina. The 

~eneral direction of the lirae (and of the aperture) 

is gently backward fr0111 the suture. 

1\. pronounced difference in the fineness of the transverse lirae is shown by different specimens, a circumstance that suggests the possible presence of more 

than one species, or, if only one, of a rather variable 

species. 

This fOl'ln is clearly distinct from B. nodi'l11a1'ginata, 

having a less conical (or more turreted) shape and 

finer sculpture, less distinctly or indeed not at all 

fasciculate near the suture. It seems to show a closet· 

agreement, in fact, with the form ,from the Fayette. 

ville shale that I described as B. lativitta;ta. On the 

other hand, the Boone cherts contain a species that is 

possibly identical with this and is equally variabl~. 

Shells of this general type are, in fact, rather characteristic of the ~1ississippian faunas of Arkansas 

and Oklahoma. They show great variation, especially 

in the strength and fineness of the sculpture, and, as 

inost of the specjmens are imperfect, it is difficult to 

judge whether they should be classed as several species 

or as only one. If the entire series including B. 

nodi'lna1'gvnata is held in mind, one can hardly doubt 

that several species are really present, though one 

gains the impression that they intergrade. Q 

Locnlity: San Saba, Tex. (station 2623). 

Genus PLEUROTOMARIA: Sowerby 

Pleurotomaria several sp. 

Sculptured gastropod shells of-several different types 

ure represented in the collection, but though they retain characters by which this fact is shown, they do 

not retain enough for an intelligent consideration of 

the specific relations of these types or even of their 

superficial resemblances. The sculptured surface and 

its general characters suggest that all the specimens, 

ir they could be completely described, would find 

place am01ig 'the Pleurotom'arias, 11ut beyond tl1at it, 

would not be profitable to go. 

Locality: San Saba, Tex. (station 2623). 

51448-26--4 

Family CAPULIDAE 

Genus PLATYCERAS Conrad 

Platyceras aff. P. nasutum Miller 

The single specimen referred here is less complete 

than those cited under Platyceras aff. P. glenparlcense 

and may differ in other characters than the one upon 

which it has been provisionally distinguished from 

them. It is more compressed and is somewhat angular down the anterior side instead of broadly rounded. 

This gives it a certain resemblance to P. nasutu'ln 

and, somewhat less, to OapUl1tS occidens. 

Locality: San Saba, Tex. (station 2623). 

Platyceras atf. P. ,glenparkense Weller 

Very few .of the Platyceras group of shells are 

small enough to be coml)ared with the p'resent species on at all equal terms, for my specimens measure 

but Iii tIe more than 5 millimeters in length. There 

nre several, however, which it resembles in miniature. 

The shell exp~nds rapidly and is strongly curved, 

but even the apical pint probably does not make n 

closed coil. Transversely the shell is broadly arched 

over the anterior side, and the width and length of 

the aperture do not differ greatly. The surface is 

crossed by growth lines which are rather strong, if 

the small size of the shell is considered, and which 

, have a sinuous COl~rse. Whether the size and distribution 'of the lobes indicated by the growth lines is 

a constant feature has not been determined. The surface also shows a few minute scarlike impressions, 

which may have been the bases of small spines., Both 

specimens bear these tiny nicks, but they can hardly 

be interpreted as being more than a possible indicatipn of spines. That a few of the Platycerata bore 

spines is well known, but the present for!ll is not 

identical with any of these spinose species. 

The sha.pe in a general way is like that of P. e'l'ectoides, but the apical parts are less inrolle~ and less 

t.urned to one side, while the anterior parts are somew hat fuller and less detached. My form is similar to 

,~r eller's figures of P. glenp(Jfflcense, but Weller says 

that the apical part of that species is closely coiled 

for one to one and a half volutions, which I believe 

is not the condition of my specimens. His figures of 

P.· paralius are also similar, though, of course, far 

larger. IIis figures of P. p{Jfralius resemble those of 

Capulus capax, which consequently my own specimens resemble. 1\fy form is likewise similar to 0 apulus nasutus, though it is .less conlpressed and more 

broadly rounded across the anterior side. These resemblances do not take into account great. difference 

in size; and, to, repeat, if the present form really did 
38 MISSISSIPPIAN FORMATIONS OF SAN SABA COUNTY, TEXAS 

bear spines (w hich is open to question), the resem - I 

blances are accidental an:l do not indicate real relations. 

Locality: San Saba, Tex. (station 2623). 

PTEROPODA 

Family· HYOLITHIDAE 

Genus HYOLITHES Eichwald 

Hyolithes parvulus Girty, n. sp. 

Plate VI, Figures 18a-19d 

This species is represented by two specimens, both 

of them somewhat incomplete and one preserved as an 

internal lnold. 

The shell is straight and much elongated. The 

original length must have been about 8 millimeters 

and the "ridth at the anterior end 3 millimeters. 

Thus the outline tapers very gradually. The cross . 

section is somewhat triangular, one side being much 

more strongly arched than the· other. It may be 

thought of as formed either by two surfaces of 

which one is much more convex than the other or 

by three surfaces two of which (the two narrower) 

meet indefinitely in a curve. The cross section may 

be compared to a triangle having a broad base and 

two short equal sides. If the shell is thought of as 

composed of two surfaces, the less convex surface is 

gently and regularly curved fron1 side to side; the 

other has the locus of greatest curvature along the . 

median line, which, however, is arched, not angular. 

The two surfaces meet at the sides abruptly, almost in 

an angle. Both sides, especially the more convex one, 

may be slightly compressed close to the lateral margin. This description, which is drawn from the testiferous specimen, applies also to the decorticated 

specimen, except that on the latter a groove is developed close to the margin of the gibbous side, causing the edge of the shell to appear (in side view) as 

if formed by a sort of ridge. 

The decorticated specimen is complete at the anterior end, at least so far as the flat side is concerned. 

This side extends well beyond the other, and its margin is boldly arched, the outline retreating strongly 

on each side. The anterior outline of the gibbous side, 

on the other hand, is a gentle curve, as will shortly 

appear. 

The testiferous specimen shows the surface markings with reasonable distinctness. The flatter side is 

essentially smooth, though it may have been marked 

oy delicate incremental lines not now visible. The 

gibbous side is crossed by 'sharp transverse striae, the 

incised markings being narrower than the raised ones 

which they separate. Of the raised lines, about six 

come within the space of 1 millimeter. These markings, which are very sharp across lnost of the suriace, subside son1ewhat abruptly as they near the lateral margins, along which apparently a narrow strip 

is nearly or quite sn100th. These striations do not pass 

directly across the shell in a straight line, but are perceptibly arched (the convex side toward the aperture) , with a flattening of the· arch or perhaps a slight 

reversal of direction near the lateral margins. 

This species appears to be a veritable representativ(l: 

of the genus Hyolithes, a type ,vhich is extremely 

rare in the Carboniferous faunas of this continent. 

At present only two. species can be referred to it, 

Ii. ca1'bona'J"ills 'Valcott, from the Eureka district of 

Nevada, and H. aculeatus, from the" Goniatite limestone" of Rockford, Ind. The present form is clearly 

not H. carbonmoills, so much is certain; Hall's description of H. aculeatus, on the other hand, gives so 

little that is definite and is so difficult to cOlnprehenu 

in what it does give that his species can not be dealt 

with until more is known about it. The present form 

might prove to be the same as H. aculeat1.lS, but on the 

other hand, it lnight prove to be widely different, 

depending upon characters not specifically giyen by 

Ha II or not given at all. 

Locality: San ~aba, Tex. (station 2623). 

CEPHALOPODA 

Family ORTHOCERATIDAE 

Genus ORTHOCERAS Breyn 

Orthoceras sp. 

Only one of. the objects included here is certainly 

an 01,tlwceras, the others, being without septa, lnight. 

represent either the living chamber of an 01,tlwcer .. 1s 

or one of the Dentalia. The chambered shell, which, 

as usnal, is only a fragment, is perhaps 5 n1illimetel:s 

long and 3 millimetets in diameter. The chambers 

are rathel~ long (about 1.5 millimeters), and the rather 

·large siphuncle is conspicuously eccentric, thougoh by 

no means marginal. 

Locality: San Saba, Tex. (station 2623). 

Family GLYPHIOCERATIDAE 

Genus GONIATITES de Haan 

Goniatites? sp. 

Of this fonn the collection contains but a single 

specimen, which is so small and fragmentary as 

scarcely to deserve even this brief mention. Its chief 

character and the one that suggests the forn1 of cita-

. tion employed is ~ constriction so like the constrjctions 

that are periodically developed by the Goniatites as 

vividly to recall that group. 

Locality: San Saba, Tex. (station 2623). 
MACHO-FAUNA OF THE JJIM}<~STONE OF BOONE AGE 39 

TRILOBITA 

Family PROETIDAE 

Genus PROETUS Steininger 

Proetus roundyi Girty, n. sp. 

Plato VI, li'igul'cs lla-12b 

As all the trilobites in the collection are represented 

by separated parts whose relation to each other can 

at present only be surmised, it seems necessary to base 

the present species upon one specified member~ and 

for the purpose of typification I am using the pygidinm. 

PYf/id'iu?JI-.- -The pygidium is small and generally 

semieircnlar. The width of the largest specimen is 

about G Inillimeters and the length considerably less. 

The surface is divided longitudinally into five welldefined parts--an axial lobe in the middle with a 

pleural lobe nnd a broad border on each side of it. 

The axial lobe rises high above the pleural lobes, to 

which it descends steeply nt the sides and from which 

it is defined by a sharp groove. The pleural lobes 

also descend steeply at the outer side and are distinctly 

defined from the border both by a groove, more or less 

faint, and by the segmentntion, which is distinct on 

the one and absent on the other. The border is narrow 

aliteriorly and broadest where it passes around the 

t'nd of the pygidium. The pleural and axial lobes, on 

the other hnnd, contract posteriorly. This is especially true of the pleural lobes, which at the same 

time become nlore and more oblique toward the posterior end, where they unite with the abruptly terminated pygidium into a relatively long and steep descent to the border. 

The axial and pleurnl lobes are segmented, but the 

segnlents are low and fiat, distinctly defined, but not 

much elevated. This .is especially true of the pleural 

lobes. The segments decrease in size and definition 

toward the posterior end, and the final ones are so 

obscure that a personal factor is introduced in counting them. About eleven ('an be counted on the axial 

lobe and about seven on each of the pleural lobes, the 

seventh segment being lnore or less obsolete and the 

sixth but faint. The segmentation of the axial and 

pleural lobes does not correspond. The pleural lobes 

are defined by grooves that pass inward fronl the 

border but die down before reaching the axial furrow. 

On the other hanel, the geooves that separa~ the axial 

segnH'lli"s cross the axial furrow and pass out on the 

median line of the In,teral lobes but die down before 

reaching the border. This process affects only the 

first three or fOlll' of the pleural segments, which accordingly appeal' ,to be double 01' to be subdivided. 

The more posterior pleural segments are more discrepant with the axial ones and are subdivided by 

t,he axial grooves little, if at all. The definition of 

the lobes and of the segments composing them varies 

considerably, part of the variation being apparently 

due to difference in .age. As the pygidiunl grew 

older, it apparently became lower and nlore spreading 

and correspondingly lost definition in all its parts. 

The superficial markings are highly inconspicuous. 

The surface is roughened by minute punctae or granules, it is diflicult to tell which. The axia,l segments 

are marked hy coarser granules along the posterior 

margin, the granules becoming coarser and more 

numerous on each segnlent, so that while the lnore 

anterior segments are mostly smooth the nlore posterior segments are wholly granulate. The granules 

there also tend to become confluent, so that the final 

part of the axis may appear to b~ marked by irregular inosculating longitudin,al striae. The pleural 

lobes lack any special surface characters except that 

where the pleural segments are subdivided by prolongations of the grooves that separate the axial segments, the granulation that occurs just in front of 

those grooves in the one is faintly continued onto the 

other. 

P. 1'oundyi'is nearest in its characters to P. ellipticuB of the American species referred to P1'oetUg. 

It is even smaller than P. ellipticus, itself a smail 

species, and differs in other ways. P. roundyi has :l 

broad and well-defined border; P. ellipticus one that 

is narrow' and ill-defined: In P. ellipticus the axial 

lobe is said to be about as broad as the pleural lobes, 

whereas in P. 1'oundyi, if we include the narrowed 

border with the lateral lobe, the axial lobe is considerably narrower. Of the other species at present 

included in P1'oetus, P. 1nissouriensis and P. s'Wallo'Wi 

alone resemble this closely in the number of segments on the pygidium. P. rnrissoul"iensis with its 

much larger size and strongly granulated surface is 

clearly distinct. P. swallowi, also much larger, appears ,to be without a smooth border surrounding 

the pygidium, the grooves tha:t define the segments 

being continued to the margin. 

As the generic arrangement of our Carboniferous 

trilobites is still mol.·e or less tentative, the present 

species, though referred to P1'oet1IJS, needs to be comrared also'with species of PhillilJsia and Gritfithides. 

In general the species referred to P hillilJlsia have mQre 

numerous segnlents on the pygidium than P. 1'01IJndyij 

few have less than ten pleural segments. The Pennsylvanian species P. cliftonensis has but seven pleural 

segments, but it has thirteen or fourteen axial segments. P. Sa1nlJSoni has but six pleural segJnents; its 

axial segments, on the other hand, number only seven, 

80 that if all the other characters are disregarded the . 

lJresent species shows marked differences in this one. 

The species of Gritfithides are more cOlnparable in 

the segmentation of the pygidium than those of P hillipsta, espe:'ially G. 01'nat1IJS (which has seven pleul~al 
40 MISSISSIPPIAN FORMATIONS OF SAN SABA COUNTY, TEXAS 

and eleven axial segments), G. parvulus (which has 

seven pleural and twelve axial segments), and G. 

scitUlus (which has six pleural and eleven or twelve 

axial segments). The ornamentation of G. ornatus 

a~ once distinguishes it from P. roundyi. G. parvulus 

and G. scitulu.s (which may be the same species) are 

cljstinguished by the ornamentation, the abrupt flexure 

of the pleural lobes, and the absence upon them of 

any grooves such as in this species subdivide many of 

the pleural segments and connect "\vith the stro'nger 

grooves that separate the axial segments. 

01'anidiu1fL-The glabella is rather convex, about 

half as wide as it is long, and almost parallel-sided. 

In most specimens an oblique curved furrow faintly 

defines on each side a basal lobe. This structure is 

ordinarily unmistakable but at the same time by no 

Iileans conspicuous. The observer's eye, however, may 

follmv this furrow so that the glabella appears to narrow posteriorly. I have been unable to make out any 

indication of lateral furrows. A rather broad border passes around the front of the glabella, strongly 

upturned at the anterior margin, where a thickened 

ridge is formed which is striated in the characteristic 

manner. The border consequently makes a troughlike depression between its own ,upraised margin and 

the steeply descending front of the glabella. In some 

specimens the border is more narrow, and in others 

ItsS upturned. The fixed cheeks are fairly large and 

somewhat oblique. The occipital furrow is moderately strong and narrow, sharply defining the neck 

rIng. 

The surface of the glabella is finely granulated, 

more distinctly on the anterior and posterior parts 

than on the intermediate ones'. I have distinguished 

as u separate variety a few cranidia that are rather 

strongly and coarsely granulated, the granules being 

elongated transversely so that the glabella has the 

appearance of being finely marked by irregular cross 

st.riae. These markings may cover the entire glabella 

and luay extend also onto the free cheeks. It seems 

rather doubtful whether this difference in sculpture 

(which is the only one observed, though others may 

have escaped observation owing to the imperfection 

of my specimens) really marks a distinguishable type, 

but if so, no means have been found for assigning the 

two types of cranidia respectively to the different va-

, rieties that I have distinguished among the pygidia. 

It can hardly be, however, that among the cranidia 

here grouped together and cioted under Proet1ts.9 

roundyi some do not also represent the varieties depressus and alternatus. 

. Free. cheeks.-As representing the free cheeks [ 

have only three specimens, two of' which"are fragmentary and one very small. In the latter the only 

character that seems deserving of mention is the pre$-

ence of a long, slender genal spine. This structure 

may have been present in the larger specimens as well, 

though they are too imperfect to show it. 

a ypostoma.-This structure is poorly and in some 

instances doubtfully represented. It has the usual 

elongated pear-shaped outline, but further than thi.s 

my specimens do not warrant me in going. 

Locality: San Saba, Tex. (station 2623). 

Proetus roundyi var. depressus Girty, n. var. 

PIa te YI, E'igures 16n-17b 

This form is distinguished from the principal one 

,in a general way and in some respects by its lower 

"topography," or diminished superficial differentiation. The axial lobe is, indeed, high and sharply defined, but the pleural lobes are low and spreading. 

They are practically continuous with the border, 

which in typical P. roundyi is broad and well defined 

but which here is scarcely distinguished either by a 

bounding groove or by the abruptly terminated segments. Indeed, the segments die out gradually, and 

the more anterior ones may be continued well-nigh 

to the nlargin. The segments themselV1es are depressed, though distinct. They are not subdivided ex~ 

cept in the outer part, where they have a bifurcated 

appearance. Many of them, however, are thus subdi vided. The pleural lobes are not deflected in passing around the end of the pygidium, so that the 

prominent termination of the axial lobe is situateu 

far from the posterior outline-much farther in appearance than in typical P. roundyi, in which these 

parts are steeply inclined. 

Locality: San Saba, Tex. (station 2623). 

, Proetus roundyi var. alternatus Girty, n. var. 

Plate VI, Figures 13a-15b 

This variety is based on pygidia and is apparently 

a derivative from typical P. 1'oundyi. It is primarily 

distinguished by being more strongly segmented and 

in addition, or as a consequence, by having all or 

nearly all the pleural segments subdivided and so arranged that every alternate semisegment is slightly 

depressed.' At first appearance, then, the pygidium 

seems to 'be very numerously segmented. 

The strong grooves that separate the axial segments 

are continued laterally onto the pleural segments, which 

they subdivide, the pleural segments themselves being 

defined by grooves leading up from the border to the 

axial furrows. If the pleural segments are regarded 

as defined in this manner, of each pair of semisegments the posterior one is depressed and the anterior 

one elevated. It might be.,added that in some lights 

the depressed 'semisegmerit appears to run out into the 

groove that separates the axial segnlents, but this is 

not the real arrangement. 

Locality: San Saba, Tex. (station 2623). 
PLATES V-VI 

41 

c 
PLATE V 

FIGURES la-3b. Crania pertenuis Girty, n. sp. (p. 25). 

la-lb. A brachial valve in large measure retaining the shell. la, Seen from above; lb, side view in outline. 

2a-2b. A brachial valve in large measure an internal mold. 2a, Seen from above; 2b, side view in outline. 

3a-3b. A brachial valve in large measure an internal mold. 3a, Seen from'above; 3b, side view in outline. 

FIGURES 4a-6. Rhipidomella permin1tta Girty, n. sp. (p. 25). 

4a-4c. An average specimen. 4a, Ventral side; 4b, dorsal side; 4c, same in outline, natural size. 

5a-5c. An unusually ovate specimen. 5a, Ventral side; 5b, dorsal side; 5c, same in outline, natural size. 

6. A pedicle valve of the gibbous type; there are many such. Seen from above. 

FIGURES 7-9. Rhipidomella perminuta var. (p. 26). 

7. A brachial valve that probably belongs with this variety; it may belong with R. perminuta itself, however. Seen from above 

Sa-Sd. A specimen representing a round form that may be a species distinct from R. perminuia. Sa, Dorsal side; Sb, same in 

outline, natural size; Sc, side view in outline; Sd, vpnt.rRl "irl(" 

9. A brachial valve referred to this variety, seen from above. 

FIGURES 10a-16. Chonetina subcarinata Girty, n. sp. (p. 27). 

lOa-lOco A characteristic pedicle valve. lOa, Seen from above; lOb, posterior view; 10cj side view. 

lIa-lIc. Another characteristic pedicle valve. lIa, Seen from above; lIb, side view in outline; lIc, posterior view in outline. 

l2a-12b. A pedicle valve having a different configuration. l2a, Seen from above; l2b, side view in outline. 

l3a-13c. A pedicle valve representing a broad variety which is abundant in the Moorefield fauna of Oklahoma. l3a, Seen 

from above; l3b, same in outline, natural size; l3c, anterior view in outline. 

14. A brachial valve reduced almost to the condition of an external mold, seen from above. 

15. A small pedicle valve, seen from above. 

16. A larger pedicle valve, seen from above. 

FIGURES l7-2lb. Pustula inconspiwa Girty, n. sp. (p. 2S). 

17. Mold of a strongly corrugated braqhial valve, seen from above. 

l8~ "Exterior of a brachial valve, showing the corrugated and lamellose surface, seen from above. 

19a-19b. A pedicle valve. 19a, Seen from above; 19b, side view in outline, natural size. 

20. A feebly striated brachial valve, preserved as an external inold, seen from above. 

2la-2lb. A pedicle valve. The umbo is truncated, apparently not by fracture but as the result of fixation. A fragmentary 

crinoid segment has just the size and shape and position to have fitted into the indented umbo. 2la, Seen from 

above; 2lb, same in outline, natural size. 

FIGURES 22a-24b. Selenella? subcircularis Girty, n. sp. (p. 30). 

22a-22b. A specimen whose greatest width is somewhat above the middle. 22a, Dorsal side; 22b, side view in outline. 

23a-23c. A specimen of somewhat different shape. 23a, Dorsal siele; 23b, same in outline, natural size; 23c, side view in 

o outline. 

24a-24b. Another specimen. 24a, Dorsal side; 24b, side view in outline. 

42 

All the specimens figured on this plate were collected from the limestone of Boone age in San Saba County, Tex., 

except the originals of Figures 10, 11, and 12, which came from the Ridgetop shale, in the Waynesboro quadrangle, Tenn., and the original of Figures 13, which came from the" Mayes" formation, in the Muskogee quadrangle, 

Okla. 
U. S. GEOLOGICAL SURVEY PROFESSIONAJ, PAPER H6 PLATE V 

X4 Ib X4 X4 2b 

la 2a 3b 3a X4 

o o 

4e 5e X4 

4a 4b 5a 5b 

0 

. 8b 

7 X 4 8a 8d 9 8e 

lOb X3 0, X3 

lOa 10e 

~ l2a 

X3 lla llb 

lle 

0 ,,0 13b 

~ 12b 

l 3a 15 16 

13c X3 14 

0 0 

19b 2lb X3 X 3 X3 20 17 18 19a 21a 

W" (D, 0 X3 

23b W, 22 a 22b 23a 23c 24b 24ax 3 

MACRO-FAUNA OF TilE LIM&<;TONE OF BOONE AGE IN SAN SABA COUNTY, TEX. 
U. S . GEOLOGICAL SURVEY PROFESSIONAL PAPER 146 PLATE VI 

X3 

1 2a 2b 3a 3b 4a 

~ X3 

U 

4d 

6a 6b 5c 5b 5a 4b 

X3 '--- X3 

@ 

6c 7a "i/ x 3 7c 7b 8 

~t 9b 

~" ~, lOc lOb lOa 9c 

llb lla 

. , 

l2a 13a l3b 

..' X4 

14a ~" 14b 12b 

' 4 ~X 4 tJ S 

~ X4 

16b 16a .5b 15a 

7b 17a 

~~ t1 

18b x 8 19b 

0 X4 X4 Q4 

I8a 18c 18d 18e 19d 19c 19a 

MACRO-FAUNA OF THE UMESTONE OF BOONE AGE IN SAN SABA COUNTY, TEX. 
FIOUUES 1-:-4d.' Hustedia texan a Girty, n. sp. (p. 34). 

1. A ,small specimen, dorsal side. 

PLATE VI 

...... . .... ~ 

?a-:2b. A larger specimen. 20., Dorsal side; 2b, si,de view in outline. 

3a-3b. A specimen which shows the circular foramen. 3a, Dorsal side; 3b, ventral side. 

4a-:'4d. A rather large specimen conspicuously indented along the median line of the qrachial valve. 4a, Yentral side.; 4b, 

side view in outline; 4c, dorsal side; 4d, same in outline, natural size. . 

FIQURI~S 5a-5c. Fhtstedia? parvicostata Girty, n. sp. (p. 36). The typical specimen. 5a, Dorsal side; 5b, side view in outline; 

5c, ventral side. 

li'IOUHES 6lt-7c. ll'ustedia'l problematica Girty, n. sp. (p. 35). 

6a-6c. The typical specimen. 6a, Dorsals'ide; 6b, side view in outline; 6c, ventral side. 

7a-7c. Another specimen.' 7a, Ventral side; 70, side view in outline; 7c, dorslli side. 

li'IOuuES S-9c: 111tstedia s1tbaequalis Girty, n. sp. (p, 35). 

8. The typi"cal specimen, a pedicle valve, seen from above. 

9a-9c. Another specimen. ,9a, Ventral side; 9b, side view in outline; 9c, dorsal side. 

FIOUHES lOa-lOco Bmchythyris simulans Girty, n. sp. (p. 33). The typical specimen, which surprisingly resembles the form 

described as H'ustedia'l parv.icostata. lOa, Dorsal side; lOb, side view in outline; 10c, ventral side. 

li'Ioum~s lla-12b. Proet1ts roundyi Girty, n. sp. (p. 39). 

lla-Ub. A characteristic pygidium. Ua, Seen from above; Ub, side view in outline. 

12a-12b. Another broader pygidium. l2a, Seen from above; 12b, side view in outline. 

li'IOUJUJS 13a-·15b. Proetus r01tndyi var. altematus Girty, n. var. (p. 40). 

13a-13b. A typical pygidium. 13a, Seen from above; 13 b, side view in outline. 

14a-14b. Another pygidium similar to the last. 14a, Seen from above; 14b, side view in outline. 

15a-15b. A.small but nearly perfect pygidium. 15a, Seen from above; 15b, side view in outline. 

FIOUHES 16a-17b. Proet'us ro1tndyi var. depress1ts Gfrty, n. var. (p. 40). 

, '16a-16b. A pygidium which may be taken as the type. 16a, Seen from above; 16b, side view' in outline. 

17n.-17b. A pygidium of somewhat different character referred to the same species. l7a, Seen from above; 17b, side, view in 

outline. 

li'IGUIlI~S 18a-19d. Hyolithes parlml1ts Girty, n. sp. (p. 3S). 

18a-iSe. A specimen preserved as a mold. 18a, Convex side; 1Sb, more or less schematic figure showing the course of the 

very fine transverse striae on the convex side; 1Sc, cross section in outline; lSd, flattened or depressed side; 1Se, 

side view. . 

19a-19d. A specimen retaining the shell in part. 19a, Convex side, which is subangular down the middle; 19b, same in 

outline, natural size; 19c, cross section in outline; 19d, side view in outline. 

All the specimens figured on this plate came from the limestone of Boone age, San Sa?,a County, Tex. 

43 

.; 
Part IV. PETROLOGY OF THE CONTACT OF THE ORDOVICIAN ELLENBURGEH 

LIMESTONE AND THE MISSISSIPPIAN LIMESTONE 'OF BOONE AGE IN 

SAN SABA COUNTY, TEX.AS 

By l\fARCUS I. GOLDl\1·AN 

INTRODUCTION 

The contact of the Ellenburger limestone with the 

limestone of Boone age, whose fauna is described 

above, is represented in the collections of the Geological Survey by two specimens (PIs. V~I, XIX, and 

XX). As the complexity of the problem presented 

by the$e specimens was not realized at the time they 

'were collected, the problem did not receive the field 

study it requires. The following discussion, therefore, based purely on laboratory study, can not do it 

justice, and is offered, with accompanying illustrations, mainly to put on record the many interesting 

and peculiar features of the contact, the problems, 

they raise, and some of the interpretations they 

suggest. 

SOURCE OF THE SPECIMENS 

The specimens were obtained from a locality in San 

Saba County, Tex., about 3 miles south of the town 

of San Saba, on the south side of a fault that brings 

the bottom of the Smithwick shale on the north side 

several hundred feet below the bottom of the Mississippian on the south side.1 Specimen G 105, illusb'ated in Plate VII, was in place probably not more 

than 200 to 300 feet south of the fault; and specim'en 

G 114, illustrated in Plates XIX and XX, was probably only a few feet south of the fault. 

SPECIMEN G 105: CONTACT OF THE ELLENBURGER 

LIMESTONE AND THE LIMESTONE OF BOONE AGE 

GENERAL DESCRIPTION AND INTERPRETATION 

Specimen G 105 will be considered first, because it 

shows the ,more normal re1ations of the two formations at their contact. As it is illustrated in Plate 

VII, the dark-gray rock full of undulating, parallel 

white markings in the upper part of the specimen 

above the line Y -Y is undoubted l\1ississippian. The 

1 Plummer, F. B., and Moore, R. C., Stratigraphy of the Pennsylvanian formations of north-central Texas: Texas Univ. Bull. 2132, 

map pI. 8, p. 52, 1921. On this map the fault Is shown running 

southwest from Barnett Spring, crossing the road that goes southeast 

from San Saba to Chapel at a sharp bend in the road. It is just west 

of the road and south of the fault at this point that the specimens 

here discussed were collecte(]. 

44 

lighter-colored rock below the line ~Y-X is undoubted Ellenburger. The question that initiated this 

il:vestigation was whether the intervening layer belonO"s to the Mississippian or the Ellenburge;l', or b 

whether it includes a transition from one to the other. 

The fact that this layer is made up of pebbly limestone sum:rests that it is basal and therefore belongs bb 

te· the l\1ississippian, and its apparent transition to 

the l\1ississippian fits this interpretation. On the 

other hand, it closely resembles, especially in its lower 

part, 'pebbly layers in the Ellenburger in the lower 

part of the specimen. The presence of these pebbles 

below unquestioned Mississippian may therefore be 

due merely to the chance that before the Mississippian 

was deposited the Ellenburger was eroded down to 

one of these pebble layers instead of to a more homogeneous layer in the Ellenburger. 

Another possible interpretation suggested by the 

. peculiarities of the pebble layers in the Ellenburger 

and of their relations to the more homogeneous layer8 

and by the evident tectonic disturbance of the Ellenburger near by, as illustrated by specimen G 114 

(PIs. XIX and XX), is that the pebble layers and 

some features of the contact may be' due to tectonic 

crushing with shearing approximately parallel to the. 

contact. 

My conclusion is that the contact is a normal contact of the limestone of Boone age on a pebbly layec 

in 'the Ellenburger. On' Close examination with a 

hand lens the boundary as represented by the line 

Y -Y is found to be much sharper than it appear~.; 

at first glance. I do not believe it lies more than 1 

or 2 millimeters on either side of the line Y - Y. A 

principal cause of the apparent vagueness of the contact is the dark-gray color of the Ellenburger in the 

upper part: of the zone between the line ~Y-LY and 

the line Y-Y. Undoubtedly this color is due to 

penetration of the coloring matter of the overlying 

'Mississippian, a coloring matter which is presumably 

of organic origin. 

A satisfactory interpretation of the contact requires 

an interpretation of the origin of the characteristic 

features of both formations near their contact. The 

I 'features of the Ellenburger will be considered first. 
CONTACT OF THE ELLENBUR.GER AND BOONE LIMESTONES 45 

THE ELLENBURGER OF SPECIMEN G 105 

In general appearance in hand specimen the Ellenburger of specimen G 105 is a very fine grained light 

yellow-gray calcareous rock. It consists of an irregular a.lternation of more or less solid and continuOllS layers with layers niade up of pellets or pebbles 

and nngulnr fragments of material similar to the 

sol iel layers. Cross sections of thin shells or fragments of shells of mollusks, trilobites (t, PI. VII), 

nnd perhaps brachiopods are characteristics of the 

so] id layers. Some also occur in the pellet layers, 

ns at f and .r;, Plat.e VI~. Most of the shells are 

represented by clear calcite, and some have cavities 

f"illed with it. As this material absorbs much light. it 

appears dark on the polished face against th~'1i~legrained opaque matrix of the solid layers. This contrast is emphasized by the photograph. The pellets 

are in a matrix that consists partly of clear, rather 

<.'olu:sely cl·ysta.lline calcite and very largely of a 

light yellow granular calcite, which, on account of its 

('olor, appears vel'y dark in the photograph. For this 

)'f'ason the general characteristics of the r?ck stand out 

mnch morc clearly .in the photograph than in the 

specimen itself. 

Microscopic details of the Ellenburger are represented in Plates VIII, B, and IX, which illush'ate parts 

of thin sections from about the areas marked. Band 0 

on Plate VII, but from a layer that was about 1 centimeter above the surface of the specimen shown in 

Plate VII. 

It seems improbable that the pebbly portions of the 

Ellenburger and the rough and irregular boundaries 

of the homogeneous layers originated by crushing and 

shearing after consolidation. The boundaries of 

jlOmogeneous layers are too irregul~r to have been 

sheared; the pebbles are too rounded and are oriented 

too nluch at random, without indications of a direction of flowage; the matrix of the pebbles, which is 

essentially ru.ther coarse clear calcite, is too clear and 

free fr01n rock meal such as would be expected to 

result fr01n crushing and grinding of ~h~ rock 

Another mode of origin that suggests itself is subJnarine flow or solifluxion of the beds at the time of 

deposition, but most of the objections against tectonic 

origin hold against this origin also. Especially it 

seems thnt flowage of -relatively soft beds could not 

produce the irregular sharp boundaries of the large 

homogeneous portions. 1\10reover, the approxiniate 

horizontnlity and parallelism of these portions seem 

to confol'Jn better with primary sedimentation.· Probnbly in the field these bands, in spite of the irregulnrity of their boundaries and the variations in their 

composition, which in places in the hand specimen 

make them almost pinch out, would be found to be 

essentially continuous over so great a horizontal extent as to. eliminate the possibility of origin by submarine flowage. 

By what process, then, did these lnaterials originate? The material of the homogeneous layers and 

of the pebbles is the same very fine grained calcareous 

matt.er (presumably of the type called drewite by 

·Field and Kindle) 2 that makes up the homogeneous 

layers, so that the rock is presumably what IGndle 3 

calls vaughanite and the British geologists call calcite-mudstone.4 It diverges from the definition of 

both names, however, in containing many fossils, of 

which the sections show plainly in the homogeneous 

rock as illustrated in Plate VII. Some can also be 

seen ~mong the pebbles. At e and i, Plate VII, there 

are the internal casts of two, and at 9 another. At 9 

some of the original shell is represented. At f part 

of the cross section of a shell with the matrix adhering 

to it can be seen. A number can also be seen among 

the pellets in the thin section {PI. VIII, B)-for instance, at a, b, c, and d. At 9 anct h, Plate VIII, B, 

are groups of pellets as seen in cross section that 

plainly represent the internal casts of fossils (presumably gastropods) but appear to lack re~nants of 

the shell in which they formed; and others, such as 

those at e and f, by their shape and their size clenrly 

suggest the same origin. These evidences of the 

origin as shell casts of many of the pellets has led me 

to the conclusion that most of them originated in this 

way. Some others are perhaps the excrement of animals that passed the calcareous mud on which they 

lived through their intestines, and some are probably 

mechanically fragmented portions of the calcareous 

mud rock. 

If this explanat~on of the origin of the pellets is 

accepted, the question still remains whether the absence of shells and of the fine-grained calcareous mud 

matrix is due to processes that were contemporaneous 

. "'ith the formation of the rock or to waters that cireulated subsequently through the rock. The weight 

of evidence seems clearly in favor of the syngenetic 

origin of the essential features of the rock, though 

there are some features that can perhaps be better· 

explained as the result of waters circulating in the 

rock after its formation and some that appear puzzling on either hypothesis. The interpretation proposed involves the assumption that thIS part of the 

Ellenburger ,vas deposited at or near marine base2 Field, R. 1\:1., Investigations regarding calcium carbonate oozes at 

'J'ortugas and the beach rocks at Loggerhead Key: Carnegie Inst. 

Washington Yearbook, 18, pp. 197-198, 1920 .. Kindle, E. 1\1., Nomenclature and genetic relations of. certain calcareous rocks: Pan·Am. 

Geologist, vol. 39, pp. 368-369, 1923. 

30p. cit., p. 370. 

'Dixon, E. E. L., Carboniferous succession in Gower: Geol. Soc. 

London Quart .• lour., yol. 67, pp. 516-517, 1911. 
46 MISSISSIPPIAN FORMATIONS OF SAN SABA COUNTY, T'EXAS 

level, where slight changes in co.nditio.ns· co.uld cause 

a change fro.m depo.sition to. ero.sio.n and the reverse, 

so. that these changes o.ccurred frequently .. The result 

w,as to. ero.deand rewo.i·k previo.usly depo.sited calcareo.us mud, which o.n different o.ceasio.ns and in different lo.calities was in different stages o.f so.lidificatio.n, 

fro.m so.ft " and inco.herent mud to. material hard 

eno.ugh to. fo.rlll angular fragments. .. When the· matrix was so.ft eno.ugh, which it was usually, the inclo.sed'shells, lllany o.f them filled with the sanle mud, . 

were freed. A. chemical change in the co.nditio.n o.f 

the surro.unding water by which it disso.lved instead 

o.f . precipitating calcium carbo.nate caused the so.lutio.n of mo.st o.f the shells, which were pro.bably mo.re 

so.luble than the calcium carbo.nate o.f the luud that 

filled them. On acco.unt o.f the 'time required fo.r 

so.lutio.n o.f the shells, and perhaps also. as a result o.f 

organic matter in them, the mud filling them was 

so.metimes hardened by the time it was freed, and 

thus under favo.rable circumstances the internal cast 

'was preserved' to. fo.rn1 a pellet. It is no.t to. be understo.o.d that each pellet layer 0.1' accumulatio.n o.f pel:-

lets represents a single interval o.f ero.sio.nand so.lutio.n. The 'accumulatio.n o.f many perio.ds may be represented in o.ne layer o.f pellets-so.me perio.ds having 

left no. tr.ace" because the mud was no.t hard eno.ugh, 

and so.me having furnished angular fragments. o.f the 

hardened mud matrix like that 'at f, Plate IX, B, o.r 

the angular fragment at f, Plate VII, in ,vhich the 

inclusio.n o.f part o.f a shell wo.uld seem to. imply that 

hardening had go.ne so. far that fracturing to.o.k place 

thro.ugh matrix and shell alike instead o.f bet"'een 

, matrix and shell. 

Po.ints in favo.r o.f such an o.rigin may be briefly 

summarized as fo.llo.ws: 

1. The sharpness and fo.rm o.f. the bo.tto.m co.ntact. 

of ':;the. pellet layers. Surfaces like, tho.se· sho.wn in 

Plate· VII might be expected to. result by. subaqueo.us 

ero.sion o.f a partly to.ughened luud co.ntaining. shells, 

but no.t by shearing o.f the ro.ck after induratio.n, no.r 

by so.lifluxio.n dtuing depo.sitio.n.., . 

,2. The appro.ximate ho.rizo.ntality o.f this bo.undary, 

\yhich co.rrespo.nds to. bedding. 

3. The partial inclusio.n o.f so.me pellets, as at a, 

Plate IX, A, in the underlying co.ntinuo.us layer. 

This seems hard to. explain except, o.n the assumptio.n 

that the underlying layer :was so.ft and that the pellets 

were relatively hard at. the tim.e, the pellets were in.· 

clo.sed by the mud. These pellets, frOlu their fo.rm 

and 'size,' might -Well be the excrement o.f small 'animals, and their gre'ater hardness ,oat the time they 

were buried in the mud might have been, clue to. ,mechanical and chemical effects o.f their mo.de of o.rigin. 

4. The ii:regular and transitiQnai. ch~racter '0'£ the, 

upper bo.undary as it appears especially in the .top 

I)f zo.ne M -M, Plate VII, indicating burial o.f the 

upper part o.f the pellet layer in subsequently precipitated calcareo.us mud. 

.5. The direct asso.ciatio.n with a predo.minance of, 

ro.unded pellets o.f such angular pellets as that at f, 

Plate IX, B, and o.ne still co.ntaining a remnant of a 

fo.ssil "like that atf, Plate VII, which seems explicable 

o.nly by the, assumptio.n.of syngenetic fragmentatio.n. 

,6. The clo.se cro.wdi~g o.f shelless internal castE? o.f ' 

fo.ssils, as at i, Plate VII" sho.wn enlarged o.n Plate 

VIII, A. If the shell had been disso.lved after the 

fo.rmatio.n o.f the ro.ck the surro.unding pellets sho.uld 

no.t be in direct co..ntact with the cast, as so.me o.f them 

are. Ho.wever, it is pro.bable that so.me shells that SUl'-

vived so.lutio.n befo.re inclusio.n in the clear calcite 

IT,latrix ,were replaced a'fter inclusio.n in that matrix. 

Thus between the po.rtio.ns o.f a gastro.po.d shell fill, 

ing ;een in cro.ss sectio.n at g, Plate VIII" B, there ;js 

no.t shell structure but granular crystalline, calcite like 

the clear calcite matrix. It seems impro.ba ble that 

witho.ut the shell this internal cast wo.uld have survived entire the rewo.rking which it is assumed acco.mpanied the accmuulatio.n o.f the pellets fro.m their 

matrix o.f calcite mud, so. that the shell layer between 

the who.rls o.~ this gastro.po.d was pro.bably recrystallized or replaced after the cast was embedded in the 

dear calcite matrix. ' 

7. Perhaps the ·lno.st co.nclusive evidence o.f co.ntempo.raneo.us o.rigin is furnished by ,fragments such d 

, as tho.seat b, and lc, Plate VII (sho.wn enlarged at b, 

PI. ·X, A, and k, PI. X, B), which themselves co.ntain 

pellets in ·a clearer matrix. These fragments are particularly significant because they sho.w that no.t only 

the pellets' had been formed befo.re the succeeding 

layer o.f co.ntinuQus calcite mud ro.ck which, inclo.ses 

them was depo.sited, but that the clearer co.arser calcite matrix had also. been fo.rmed aro.und then). In 

fact, at a, Plate X, B, o.ne o.f the co.ntained pellets can 

be plainly seen cut o.ff by the margin o.f the fragment, 

indicating' abrasio.n 0.1' so.lutio.n o.f the fragment as. 

a who.le befo.re its inclusio.n in its present matrix. 

The pebble marked b, Plate X, .A, is ,also. significant 

because it appears to. sho.w in co.njunctio.n a bo.dy of 

pellets and a .bo.dy o.f the co.ntinuo.us calcareo.us luud 

ro.ck, indicating that they had' been hardened into. a 

single bo.dy befo.re: fragment b was fo.rmed. 

·That mechanical wear may have taken so.me part 

in ro.unding 0.1' o.therwise modifying the fo.l'lu· o.f 

so.me o.f the pellets is indicated by k, Plate 'X, B. But 

th~' very, elo.ngated and irregular fo.rm o.f, many o.f 

them and ·~heir prevailing lack o.f so.rting makes it 

seem pro.bable that· it":'was no.t an important- facto.r in 

their o.rigin ... ', It appears, rather, 'as '·might be expected 

under co.nditio.ns· o.f delicate· balance between ero.sio.n 

an.fl, sedimentation,' that. wave"o.r ·>CUl1r'ent action .,was 

intermittent and lo.cal. On the o.ther hand, it seems 

.likely, if the pellets o.riginated as assumed, that syn-
CON~rACT OJ!' THE ELLENBURGER AND nOONE LIMESTONES 47 

genetic solution has somewhat modified their form, 

though no evidence on·this point has been found. 

It is worth noting that pellets of this type are an 

iUlportant constituent of many oolite rocks. Of some 

. rocks called oolites they are the essential constituent, 

but they occur also in rocks of which the principal 

constituent is true concentrically banded oolites. The 

deduction that they are related to true oolites in 

Qrigin is supported by the similarity of some of tlv~ 

processes indicated by this specimen to those under 

which, according to Cayeux 5 and others, some oolites 

appear to have originated, and by the similarity of 

many constituents of this rock to constituents described by him as occurring in oolitic rocks. 

}\f ATIUX O}~ TIU] l"l~LJ ... I~T r ... A YEnS 

The matrix of the pellet layers is of two kinds. One 

is n, rather coarsely crystalline clear calcite, as illustt'ated in Plates VIII, B, and IX. Evidence has been 

adduced from th~ :inclusions at band 7e, Plates VII 

and X, to show that this material .is syngenetic. The 

other is a finely granular, impure yellow carbonate material. This appears from the polished face to constitute a large pnrt of the matrix in zone ]If-ill, Plate 

VII. Its yellow color gives the strong contrast in the' 

photograph between matrix and pellets in that banel. 

This material can be seen in thin section at 9, 

Plate IX, B, and at points nlarked a in Plate XI, A, 

whieh illustrates part of thin section G 105-F. From 

these two illust~'ations 'it is clear that matrix of this 

type occurs charllcter,istieally not directly enveloping 

the pellets but rather in the midst of the coarse calcite mntrix that does dir'ectly envelop them. This 

mode of occurrence, its association \vith a 'fissure at l 

·and below fi;, Plates VII and X, B, and the fact that 

i[ cuts into the spheroidal boundary of the rounded 

fragment at k jndicate that it is later than the clear 

('alcite matrix nnd probably formed after the compacting of the rock. This material is limited to the 

Ellenburger in the specimen of Plate VIr (G 10,)) 

,nnd does not occur aboye the line 1'-1' shown in that 

plate. 

There is evidence thnt in places the deal' crystalline 

mal'rix has grown at the expense of the material of 

t.he pellets and of the solid layers. This evidence 

may be found throughout the thin sections of Plates 

'VIII, B, and IX, B; but it is particularly well illus-

·tL'ated at d, e, and f, Plate IX; IJ. Here· thetntaterial 

.of rounded pellets and of an nngular fl'agmertt'seelHs' 

t.o be partly penetrHted and replaced by the coul'sely 

,cl'ystalline matrix, as if it had been dissolving in the 

'matrix. Sit'ililar reiations can perhaps ,be' s'een in .the 

vague basal boundHl')' at lc, Plate VIII; '/:/.' -... '.,.-"" . 

ij Cnycux, L., Les Illinel'ais de fer oolithique de Fmnce: Soc. ge,ol. 

. FrHnce Bull., 4th 8er., yol. 24, No.5, pp. 2G3-277, 1924. 

The association of the partly replaced pellets illusb'ated on Plate IX, B, with the fracturing of the 

calcite mud matrix at a, b, and c, Plate IX, B, '\vhich 

apparently l)receded the formation of the coarsely 

crystalline matrix at these points, suggests that the 

penetration of the coarse cal.cite into the pellets at 'd, 

e, and f was also the result of syngenetic fracture of 

these pellets. But such a condition would be difficult 

to explain. For the fragments seen in cross sectiol) 

at ai, b, and c may well have been supported some· 

where along their length, in their displaced position. 

But that is not likely to have been the case with the 

pellets at d, e, and f, which were presnmably approximately equidimensional. The disintegration of the 

pebbles at d, e, and f could have been syngenetic only 

if the coarsely crystalline matrix had been ·formed 

by some process of instantaneous precipitation from 

solution and if the disintegration ·of· the pellets had 

coincided with this precipitation and perhal)S been 

the result of it. In the absence of more conclusive 

evidence such a process can not reasonably be assumed, though the assumption of epigenetic origin 

of the penetration of the pellets by the coarser-grained 

calcite leaves the localization of this penetration in 

relati vely few of the pellets unexplained. Perhaps 

.they were less firmly indurated 01' 'contained some 

constituent like shell fragments which facilitated pei1'-

etration by the coarser-grained calcite. 

Sudden precii)itation of the coarsely' crystalline cal-

, cite ma'trix in the midst of pellets kept in suspension' 

by agitated water might also explain the wide' spacing 

of many of the pellets. But the great range in size 

, 'of the pellets is opposed to the assumption that they 

were kept in susp~ri'sion i~ agitated water, as snch' 

suspension would pre'sumably result in better, sorting, 

and the wide spacing can be satisfactorily accounted 

for by growth of calcite in the mat'i·ix. 

SILICIFTCA'.rION IN THI-J EI.LENBDRfmn LIl\n~STON}] 

The Ellenburger limestone of specj~en G 105 COll~ 

tains silicified fragme11ts. .J llst below' tp~ contaCt ii~e 

r -Y, Plate VII, they are' fairly numerous, but below 

the line X-X only three, identified by their ~lujshwhite color, could be foul?d in the polished face. 

These three are shown at 0; p, and q,.plate VII. They 

are not more than 1 millimeter in diameter. Two are 

also inciudec1 in thin sectio~ G 105-F, and nre illus~ 

trate'd in .Plate XI, A" at c and d~ and the one at d 

enlarged ,around d, Plate XII. There are also two 

occurrences illustrated at v, in the upper left corner <:>f 

~late VIII, B . . As ,can be, seen from the photomicrog'raphs, tl~ese fragments are not detrital fragm~~ts of 

chert 'but are silicified el~ments·of th~ limestone. The 

significance of silicification in these i'orks is discussed 

on pages 56-58 . 
48 MISSISSIPPIAN FORMATIONS OF SAN SABA COUNTY, TEXAS 

STYJ.OLITES IN THE ELLENBURGER LIMESTONE I is strongly supported by material from a highly £os-

.giliferous layer of this same limestone from about 1 

The stylolites in specimen G 105 (PI. VII, S-S and' I foot above the base but not directly 01rerlyinO' the spot 

S' -S') clearly illustrate solution along stylolite sur- I from which specim~n G 105 was collected. :It is illusfa~es.6 In Plate XIJI,A, whic~ is a detail of the stret.ch trated in Plate XI~ B. Most of the larger fl:agments in 

adJacent to 1', Plate VII, a. fos~Il at a and a l~rge calcIte this thin section are single calcite crystals. I~ is well 

mud pebble at b show truncatIOn by a st.ylolIte surface known that in the echinoderms each element of the 

directly underlain by a mass of ·s.mal~ pellets .. On the skeleton is a single calcite crystal with a characterisether hand, Plate XIII, B, WhICh IS a detaIl along tic mesh structure in three dimensions and that cal·· 

S' -S', Plate VII, from' a surface that was about 1 cite which secondarily fills these mesh~s assumes the 

centimeter above the face of specimen G 105, shows C'rysta.llographic orientation of the original framealmost no solution along the suture, fragments on op- work. 7 At a, Plate XI, B,. shown enlarged in Plate 

positG sides, as at a. and u, apparently having con- XVI, there is a fragment which shows this mesh structinuous boundaries. This, together with the absence ture in its inner part, passing outward into a granular 

of pronounced columns and of any appre~'iable film of specked structure which seems characteristically to 

solution residue, indicates that these stylolites are take the place of the mesh structure as it alters with 

young, though the extent to which these last two time. As. this granularity and the crystallographic 

features are developed must evidently depend in great continuity are exhibited by the larger fragments 

part on' the original character of the rock involved. shown in Plates XIV and XV the conclusion is inAn interesting effect of a stylolite can be seen at b, dicated that these fragments also are echinodermal in 

Plate X, B, where a piece of a shell has been displaced ori (Tin I> The rock then may be reO'arded as an echino- . c . " b 

with respect to the rest of the shell on Loth sides of it. derm limestone-by analogy with other rocks of the 

kind probably a crinoidallimestone or crinoid breccia, 

tHE BASAL MISSISSIPPIAN, AN ". ECHINODERM BRECCIA" a common type of basal bed. 

GI~NERAL DESCRIPTION AND INTERPRETATION 

The general features of the basal Mississippian, the 

limestone of Boone age, whose fauna is described on 

preceding pages by' Messrs. Roundy and Girty, are 

weU shown on Plate VII. It; is necessary to add only 

that this rock is dark blackish gray, in contrast with the 

light yellow-gray of the underlying Ellenburger. Its 

more detailed characteristics are well illustrated by 

thin section G 105-D, Plate XIV, which shows typical 

Ellenburger .pellet rock in the lower part. In distinction to the fine calcite mud of the Ellenburger the material of this 'basal part of the limestone of Boone age 

is a distinctly granular calcite containing (as at a, b, 

c, and d, PI. XIV) many coarser fragments, each of 

wh ieh is a single crystal of ealcite:· In the finergrained portion which forms the greater part of the 

rock in ,this basal inch or, two and which may therefore 'be spoken of as a matrix, each grain, no matter 

how fine, appears distinct, surrounded by a thin dark 

film that is probably of organic origin. The grains 

are pool~ly sorted, passing by all gradations into the 

very coarse fragments. These characteristics are ,veIl 

illustrated by Plates XIV and XV. In most of the 

coarser fragments a nucleus of a cloudy granular nature can be more o.r less sharply distinguished from a 

very irregular envelope of clearer calcite, the wh,ole 

grain formipg a single crystal. These large grains at 

onc~ suggest fo.s~il fragments, a~d this interpretation 

6 Cf, Stockdale, P. B., Stylolites; their nature and origin: Indiana 

Uulv .. Studies, vol. 9, No. 55, 97 pp., 1922. 

CAUSE OJ<' THE FRAG1\IENTATIOX OF THE SKELETAL RE-

-:\lA1)\S AND GROWTH OF SECJ~DARY CALCITE 

The principal problem regarding the origin of this 

basal portion of the rock is the cause of the fragmentation which apparently produced most o£ both the 

coarser fragments and the finer matrix from crinoidal 

and other skeletal material. The fragmented condition 

of this basal material compared with the material a foot 

or so higher, as shown in Plate XI, B, accords with the 

idea that the characteristics of the Ellenburger and 

Mississippian at their contact here Inight be due to. 

shearing along that contact. From the study of the 

basal Mississ,ippian of this specimen alone, in the 

absence of flJrther field observation of this contact, 

I am not prepared to. refute that interpretation. I 

reject it, mainly because the chaTacter of the top of 

the underlying Ellenburger, as brought out above, 

does not accord with it, and because the features 

of the basal Mississippian can be explained in other 

ways. The very jagged indented outlines of the 

coarse calcite fragments might seem to be opposed 

to the idea of origin by shearing, but these outlines, 

as will be shown, offer difficulties to the other interpretations offered. For instance, mere mechanical 

wear at the time of deposition would produce rounded 

fragments of the original 'skeletal elements; it would 

not produce' angular fragments except of very delicate and fragile shells. 

7 Cf. Cayeux, I"., Introduction a. l'etude ~trogl'aphjque des roches 

s~dimentaires;' p. 435, Paris, 1916; and Deecke;' W., . Die Fossilization, 

(). 63, Berlin, 1928. 

8 Cf. Cayeux, L., op. cit., pp. 436-437. 
• 

CONTACT OF THE ELLENBURGER AND BOONE LIMESTONES 49 

The very irregular outline' of fragments like those 

at a and 0, Plates XIV and XV, however, is probably 

not in the main due to the agents which originally 

fragmented them, but apparently to the addition of 

secondary calcite to the original organic fragments. 

That is to say, it is very probable that mlWh if not 

all of the clear calcite that surrounds the granular 

nucleus of these fragments is calcite added in continuous crystallographic orientation with the nucleus. That such addition of calcite has taken place 

il1 the limestone of Boone age is proved by Plate 

XVIII, B, which shows between crossed nicols an 

area in thin section G lO,'5-E (PI. XI, B), ° and 0 in 

one plate corresponding to ° and 0 in the other. 'Here 

the eontacts between grains, which are all close and 

many of them very straight, prove secondary development of material around the original nucleus. The 

fragment 0, of which the nucleus and added calcite 

can be differentiated in Plate XI, B, is sho'wn at extinction in Plate XVII, B, to bring out the continuity of nucleus and envelo1>e, and 0' in both plates 

marks the large areas of clear calcite that· between 

crossed nicols, though not in Plate XVII, B, are seen 

to belong crystallographicaJly to the part of the nucleus immediately adjacent to o. In this grain the 

organic nucleus appears to be compound, and only 

the part immediately adjacent to 0 extinguishe3 simultaneously with the envelope 0'. The same secondary growth of calcite around organic fragments has 

occurred in the Ellenburger, as shown at i, Plates 

VIII, B, IX, 11, and XVII, 11, where the nucleus is 

Hlso distinctly an echinoderm fragment. There i~ no 

reason for supposing that this secondary caJc~te was 

l1dded, while the fragments of the limestone of BOOIie 

age lay on the bottom exposed to the fragmenting 

agents; therefo;'e, if the clear calcite of irregular 

grains like those nt a, 0, 0, and d, Plate XIV, and ((, 

and 0, Plate XV, is secondary, it could not show the 

effect of these agents. .. 

The irregular form of these grains is undoubtedly 

due mainly to the growth of the secondary calcite in 

the unhomogeneous medium that their matrix affords. 

This interpretation is made very probable by the 

fragment marked le, Plates XIV and XV. In Plate 

XV, Ie is the nucleus and le' added secondary calcite. 

The angular, nearly rectilinear outline of the upper 

part, 1.;', of this grain is evidently an attempt of the 

added calcite to develop its crystal form, and it is 

hard to escape the conclusion that the calcite has 

worked toward the same end at the left side but haR 

been prevented by the unhomogeneity of the matrix 

there. Some irregularity in outline may be due to 

the original form of the fragment, as it is in fragments g and h, Plate XIV, which apparently have 

no added calcite. 

'Vhat may have been the original outline 'of grains 

to which secondary calcite 'has been added is uncer· 

tain, as it may be obscured by blurring of the boundary between nucleus and added calcite, as in a and b, 

Plate XV, probably because recrystallization of the 

nucleus has destroyed its granular structure. This 

might and according to Cayeux 1) does happen by continuation of the process that converted the original 

mesh structure of echinoderm fragments into the granular structure. There is some evidence, in fragment;:; 

which show a well-defined echinodermal nucleus, that 

that nucleus was not well rounded, but regardless of 

, the original form of the nuclei the fact to be accounted for is the much greater comminution of skeletal fragments in this basal part compared with fragments of similar origin as they are found a foot or 

so above the base (as illustrated in PI. XI, B), and 

according to Cayeux,10 as they are found in most of 

their occurrences. It seems likely to me that fragmentation by shell-crushing animals, as described by 

'iV alther, 11 has produced this material. He finds that 

under moderI?- conditions fishes with broad teeth, and 

crabs, are the main agents causing this fragmentation. 

Crabs are not known to have existed in Mississippian 

time, but among the fishes that existed then there arc 

some ,vith platy teet.h that might have been used to 

crush shells. 

nATE OF ACCUMULATION 

vVhatever the cause of the fragmentation of the 

skeletal material that makes up this basal Mississippian deposit, it seems clear that the material must' 

1m ve lain for some time on the bottom in order to 

have attained this state. That is to say, slow accillnulation of this lower part of the limestone of Boone 

age is indicated. 11ere, as at so many basal contacts, 

submergence was apparently at first slow, so that the 

bottom remained for some time near base-level, exposed to frequent alternations of erosion and deposjtion; hence accumulation was slow, and time was 

a vailable for agencies of destruction, alteration, or 

chemical precipitation to act on the accumulating deposit. As submergence progressed it probably became more rapid, hence organic fragments could 

accumulate faster, and because of this more rapid 

accumulation and because the depth in which they 

~ccumulated was beyond the influence of the agencies. 

cf extensive fragmentation that produced the lower 

part of the deposit, the more complete material of 

Plate' XI, B, was accumulated. 

o Cayeux, J •. , Introduction it l'etude p~trogl-a.phiqllc des I'oches 

sMimentuil'es, pp. 436-4:37, Paris, 1916. 

10 Idem, PP. 319, 438. 

11 Walthel', Johannes, Die Sedimente del' Taubenbank im Golfe von 

Neapel : K. (>reuss. Akad. Wiss. Abh., Anhang 1910, ()p. 39-40, nt't·lIn. 

1910. 
50 MISSISSIPPIAN FORMATIONS OJ!' SAN SABA COUNTY, TEXAS 

SILICIFICA'l'ION IN THE BASAL MISSISSIPPIAN 

The silicified material in the Mississippian of specimen G 105 ha~ the same general character as that in 

the Ellenburger of this specimen. In thin section 

G 105-D three fragments, marked e and f on Plate 

XIV and w on Plate XV, were found. The one 

marked eo is shown more in detail in Plate XVIII. 

The silicified fragments appear to average slightly 

larger than those iI\ the Ellenburger, are very much 

more numerous, and in the hand specimen,. under a 

hand lens, appear to be more completely silicified. 

CHARACTER. OF THE ELLENBURGER DIRECTLY UNDER-· 

LYING THE CONTACT WITH THE MISSISSIPPIAN 

The pellets in the Ellenburger directly underlying 

t.he Mississippian as they appear in thin section 

(;. 105-D, plate XIV, are of much coarser grain than 

most of those in the deeper part of the rock as they 

appear in Plates VIII, B, and IX. This gives them 

the more transparent, less sharply defined character 

that can be recognized in the lower left-hand part of 

Plate XIV. This character may be dU'e to recrystallization during exposure of the upper part of the 

Ellenburger before and during the deposition of the, 

lilnestone of Boone age, to more ready circulation of 

underground water along the contact of the tVi'O beds 

~dter the deposition of the limestone, or to reworking 

of these pellets from the top of the Ellenburger into 

the limestone of Boone age. 

As noted on page 47, there has also apparently 

been more silicification in this upper part of the Ellenburger, which, as set forth in the general discussion 

of silification on pages 58, lends s.ome support to 

the last interpretation. 

SPECIMEN G 114: A FOLD AT THE CONTACT OF THE 

ELLENBURGER AND MISSISSIPPIAN 

ANALYSIS OF THE FOLD 

METHOD OF STUDY 

Specimen G 111:, which shows a fol~l at the contact 

of the two, formations, is illustrated in Plates XIX 

und XX. The two polished ~aces illustrated ar~ sawed 

parallel faces of the same original, specimen. The 

surface illustrated in Plate XIX (G 114-1) lay about 

2.5 centilneters above that illustrated in Plate XX 

(G 114-11). The numbered areas on Plate XIX rep-

~'esent areas taken for thin sections. With the l\nowledge of the more detailed structure of the roc)\: ,thftt 

these sections afforded a careful study ~as made, wIth 

a hand lens, of the distribution of the Ellenburger 

and the limestone of Boone age on the polished. surface of specimen G 114-11. The results are shown 

in Plate XXI. 

I 

I 

It would not be possible to illustrate every detail of 

the evidence on which . Illy interpretation is based. 

That evidence can be obtained only from a close examination of the polished face. Even stich an examination leaves very lnuch to personal judgment. 

Probably no two individuals, or even the same individual making two independent examinations, would 

delimit the areas of the different types of rock in just 

the same way; and on the mere basis of observation 

of the hand specimen, some nlight even question the 

entire interpretation offered. But the evidence of the 

thin sections, even as J,eproduced in the accompanying 

Plates XXII to XXVIII, seems very convincing. 

That the results obtained from the study of the 

polished face probably agree pretty closely with the 

nlore trusbvol'thy results that would be obtained by 

the study of thin sections is indicated by a cOlllparison 

of the insert on Plate XIX with Plate XXVIII. The 

insert on Plate XIX shows diagrammatically the distribution of rock types as worked out from the polished area from which -thin section G 114-8, illustrated i.n Plate XXVIII, was made. The relations 

worked out in the insert of Plate XIX agree well 

with those that can be recognized in Plate XXVIII 

and thus indicate the general trustworthiness of the 

results obtained from the study of the polished face. 

CHARACTERISTICS OF THE ELLENBURGEH AND THE LIl\UJSTONE OF BOONE AGE USED IN WORKING OUT THE 

STRUCTUHE OF SPECIMEN G 114 

l\10st of the characteristic features on which the 

differentiation of the. Ellenburger and the Mississippian is based are set forth above. For the sake of. 

definiteness they are briefly summarized here. 

The Ellenburger is fine grained and contains pellets 

of similar fine-grained material, andD the fossils in it 

are predominantly shells which show as thin curved 

lines in cross section. In its original condition it is 

ligh .. yellowish gray. On silicification it turns white. 

. On Plates XIX and XX the areas lettered 0 and E 

are predominantly unsilicified Ellen.burger, the areas 

Band F predominantly silicified Ellenburger. 

The basal l\1ississi ppian limestone of Boone age 

characteristically shows llluch coarser grained calcite 

and large calcite crystals, most of which are probably 

echinodermal in origin. Similar large calcite crystals 

with the characters of echinodermal fragments occur 

,also in the Ellenburger, as shown, for instance, at i, l~ 

IJn, n, 0, p (where several ate associated), q, 8, t, and u, 

Plate VIII, ,!B j and it' contains some coarse calcite 

c.rystals in small veins or pockets or filling the shells 

of organisms, 11l0St of theIll not lnore than a few milli-

!lleters across, as shown in the lower part of Plate IX, 

B. But grains of this kind· form in the Ellenburger 

D. small and .inconspicuous proportion of the rock. 

• 
CONTAOT 'OF THE ELLENBURGER AND BOONE LIMESTONES 51 

The li.llll'stone of Boone :tg~ is of a dark neutral 

gray ('0101' in .its original ('ondition and a somewhat lighter gl'U,y aftel.' partial silicification. Under 

the Inicroscope this dark color appears to be due to H. 

film, pl.'obably of organic origin, between the calcite 

grams. On Plates XIX and XX area A is limestone 

of Boone age, somewhat siJicifi.ecl adjacent to the silicified EII.(\nlnn:gcl.' on the left. The letter J) is placed 

neal' the bottom of an area eonsisting predominantly 

of Ii lIH'stone of Boone age, which is not much silicified 

in t.he darker portion adjacent to J) but considerably 

si liei fi(\cl in the lipper, light(\r gray portion (cf. PInte 

XXI). 

In general there seems to be a difference in the 

chal'nctel' of silicification of the t,,:o types of rock, 

which corresponds to their original difference in 

grain. In so far as the two rocks could be differentiated after silicification, silicification in the Ellenburger is more cOlnplete and the silica is finer grained. 

In the limestone of Boone age the original coarser 

calcite grains are intimately mixed with most of the 

silica. 

l{BVl];;W O}' 'l'Hl~ THIN Sl~CTIONS O}' Sl'.l<;CIMEN G 114-1 

AND CONCI ... USIONS 

o From its general appearance and relations (PI. 

XIX) the area of thin section G 114.--1 would be 

taken to be typical and pretty fine Ellenburger, silicified. The thin section (PI. XXII) entirely confirms 

this interpretation. The apparently. structureless 

gl'oundmass is chert, and the darker and granular 

portions nre calcite. A number of cross sections of 

thin shells cnn rendily be recognized, as at f. The 

coarsc-looking material at c appears to be the granuluI' yellow cnrbonate Inaterial described above, mixed 

with coarser, purer calcite. At b this band runs into 

u single large calcite crystal with veinlike branches. 

Arollncl a, especinlly as shown in Plate XXXII, A, . 

Ellen bnrger pellet structure can be recognized, and 

1 mdcl' the microReope it can be found in other parts 

of thiR thin section. 

The area of thin section G 114.--:'), Plate XIX,· evidently shows the contact between normal limestone 

of Boone age and silicified Ellenburger limestone, 

and the thin section (PI. XXIII) confirms this 

assumption. 

The aren of thin section G 114.--4, Plate XIX, would 

appeal' to be representative unsilicified Ellenburger 

material, though even in the plate, and still more 

dendy in the hand specimen itself, thin curving 

bands of material of slightly different texture, suggesting flownge, can be recognized. These curving 

bands can be still more clearly recognized in the corresponding area on Plate XX. Thin section G 114.--4 

(PI. X.XIV) shows typical del)Se, fine-grained Ellenburger limestone with many thin cross sections of 

fossils, but many of these fossils appear to be broken. 

At the points marked c, in Plate XXIV, for instance, 

shells appeal' clearly to have been broken after inclusion in the rock. Some pellets of Ellenburger type 

can be seen at points Inarked d and elsewhere. At a 

and b are alternate curved bands such as could be 

Sten on the polished face of this area. The lighter 

bands (b) consist of clearer, slightly coarse calcite intergrown with the dense fine-grained Ellenburger. 

This is, then, the first thin section in which evidences 

of flowage and fracturing can be seen. The cOlnpact 

condition of the rock, as indicated by the absence of 

scattered pellets in a clear calcite Inatrix, Inay be due 

to these processes. 

The area of thin section G 114.--2, Plate XIX, appears to be entirely dark-gray limestone of Boone 

age, but the upper part is lighter colored than the 

lower and suggests silicification. On account of a 

slight defect in illumination this contrast does not 

show as well on the photograph as in the specinlen 

itself. It shows very clearly, however, in the thin 

section (PI. XXV), in which the lower paTt is typical 

fresh-looking limestone of Boone age, but some of the 

larger fragments in the upper part (the areas 111arked 

b in PI. XXV) aTe cloudy and poorly defined as a result of silicification. The whole slide, however, has 

distinctly the characters of the limestone of Boone 

age. The rock appears to be flow banded, but this 

appearance may be due mainly to bedding.12 

The area of thin section G 114.--3, Plate XIX, appears 

to be a contact between white silicified Ellenburger 

limestone and gray silicified limestone of Boone age, 

with fragmentation and m.ixing of the two types of 

rocks, fragments of the white silicified Ellenburger 

showing particularly ,clearly in the gray Mississippian. 

Although the relations here are evidently so complex 

that;it would be impossible to determine from which of 

the two formations each integral part of the thin section 

is derived, still the general area occupied prevailingly 

by each formation is r~adily recognized in Plate 

XXVI. As right and left and hence the slopes of 

boundaries are reversed in the photomicrographs (see 

footnote 12), the right-hand part of the crack that 

formed in the thin section is seen to corre~pond about 

with the boundary between the bvo formations. 

Below the crack is fine-grained, largely silicified Ellenburger limestone; above it are coarse calcite fragments with some coarser matrix. Along nlost of the 

bottom of Plate XXVI the cross section of a single 

large gastropod or a group of mollusk shells can be 

1!1 It must he noted that the section is made with the polished face 

mounted on the object glass so that when bottom and top are seen 

in their correct relations undel· the microscope, tlll'ough the covel' 

glass, right and left are reversed. Hence the slope of the boundary 

between the unsllictfied and mOl'e silicified bands, which in the polished 

face rises from left to right, is re'vel'sed in the photograph. 
52 MISSISSIPPIAN FORMATIONS OF SAN SABA COUNTY, TEXAS· 

'seen in the Ellenburger. At the left of Plate XXVI, 

which corresponds to the right-hand side of the area 

seen in Plate XIX, silicified cloudy Ellenburger material can be seen extending more or less in patches 

across the crack into an area consisting more dominantly of material of Boone age; and below the crack 

to the left there is some more coarsely granular calcite 

that looks like Mississippian in the midst of prevailing 

Ellenburger. The coarser yellow carbonate of Ellenburger type occurs in patches all through the rock, 

as at a, and, with the coarse calcite crystals of the 

type of the limestone of Boone age, brings out the I 

intimate mingling that has taken place. 

General appearances suggest that the area of thin 

section G 114-6, Plate XIX, covers merely a contact 

between silicified and unsilicified Ellenburger Inaterial, but there are two facts that might cast doubt on 

this supposition. One is the absence of any trace of a 

sharp contact between dark-gray limestone of Boone 

age and light yellow-gray Ellenburger limestone at 

the left-hand end of specimens G 114-1 and G 114-11, 

Plates XIX and XX, below the are.a D. But for 

that it might be assumed that the Ellenburger had 

been merely thrust over the top of this body of limestone of Boone age and the limestone of Boone age 

slightly folded into it at its upper right-hand corner. 

The other suggestive and puzzling fact is that the 

dark neutral-gray color of the Mississippian extends 

as a vague but recognizable band all along the upper 

part of the unsilicified Ellenburger just below ,the 

silicified part-that is, between areas Band 0 and 

even across the line X-X between the areas E and F, 

Plates XIX and XX. 

Thin section G 114-6, Plate XXVII, is the crucial 

section in the entire problem of the relations in specimen G 114. It can leave no doubt, I think, that much 

shattered material of Boone age occurs here between 

and mingled' with silicified and unsilicified Ellenburger material. Coarse calcite fossil fragmeJ.lts are' 

abundant in the middle part of the area; below, especially to the left, fine-grained Ellenburger and Ellenburge,t· pellets can· be recognized; to the lower right 

fragments of thin Ellenburger shells; and in the upper part to the left probably silicified Ellenburger 

and more t<;> the right an irregular b~nd of what looks 

like dark coarse-grained material of Boone age running up from the large circular fossil fragment a, 

which is distinctly of the type of the limestone of 

Boone age. 

With the information obtained from these thin sections as a basis the distribution of rock types and the 

flowage· lines· in the polished iace--of G 114-11 were 

worked out bit by bit and without any conscious 

interpretation in mind, with the results shown in a 

generalized way in Plate XXI. As a final check on 

these surprising results, and especially on the peculiar 

spreading of the fold against the line .LY-.LY, thin 

section G 114-8 was made Before the thin section 

was cut a diagram was Inade of the distribution of 

rock types and of flow lines as they appeared in the 

polished face of the rock fr0111 which it was to be 

prepared. This diagram is shown in the insert on 

Plate XIX; Plate XXVIII is a photomicrograph of 

the thin section taken through the back of the object glass in order, to show the parts in the sam-: 

relations as in the polished surface. The photomicrograph leaves no doubt that Mississippian material 

represented by coarse calcite fragments like those at 

1n, Plate XXVIII, is abundant along a roughly I11edian strip, and the sharp upward flowage above the 

median line near X~X is clearly seen. In general 

the agreement with the insert on Plate XIX is very 

good, though the area of silicified limestone of Boone 

age may be a little too wide. Abundant Ellenburger 

material marked e on Plate XXVIII crowds l\1ississippian material closely in the upper left part of the 

plate and seems to predominate in all the more or 

less silicified area back of the distinctly flowed bands, 

but even in the thin section it would be difficult to 

decide to just which rock to assign certain areas. The 

intimate mixture of the two rock types in this thin 

section and the consequent difficulty of assigning some 

areas, even in thin section, to one or the other of 

them, makes it evident how great the difficulty must 

be of working out their distribution in the polished 

face. In doubtful areas identification may depend on 

a single coarse calcite crystal fragment or a single 

thin shell fragment that happens to be recognizable, 

and as such fragments may occur in either rock, 

isolated streaks and patches of one or the other 

might be wrongly identified. Thus there may be 

some doubt about the little streaks of Ellenburger 

material indicated in patch D of Mississippian at the 

left of Plate XXI. Otherwise, I believe the general 

features of Plate XXI are trustworthy. The streaks 

of Mississippian at the top center of Plate XXI are 

indicated both by the gray color, which can be recognized in Plate XX, and by the still darker and more 

characteristic extension of area A to the back of this 

part of the specimen about 2 centimeters back of 

the polished face. 

INTERPRETATION O}<' THE ORIGIN O}<' THE FOLD 

The assUl11ed steps in the origin of the fold are 

shown qualitatively in the successive diagrams of 

Figure 1. 

Two possible origins of the line X-X, which apparently remained practically unaffected by the- folding, have been considered. One is that it is a pre-Mississippian fault plane, the other that it is the wall 

of a pocket in the Ellenburger formed while the 
CONTACT OF THE ELLENBURGER AND BOONE LIMESTONES 53 

Ellenburger was exposed on the surface of the earth 

tl fter its formation. Against this second assumption 

iR the fact that the Imver pa.rt especially is filled 

mainly with normal Ellenburger pellets. If it were 

n pocket formed under the conditions assumed it 

should presumably contain angular fragments of the 

rock as a whole, even more mixed in size than those 

in the npper s~l:icified part. On the other hand, if it 

/ 

Limestone 

-

of Boone age 

0] 

Ellenbureer limestone 

11'IOURlO l.-·Dlngrams showing the supposed development of the fold 

in specimen G 114 

were n fault, the material in area E should be more 

a.ngnlar n,nd look more fl'ac.tured. That the boundary between silicified area F and unsilicified area E 

agrces so nearly with the boundary between a po~·tion 

F consisting largely of angular fragments and a portion E consisting almost only of pellets is under any 

interpretation puzzling. :However, the fact, recognizable on Plate XX, that the boundary does not quite 

agree-that the silicification boundary falls a little 

Lelow the top 'of the more obvious pellet boundaryleads Ine to assume that the coincidence is accidental. 

J\1y assumption is that the line X-X is a fault. The 

difference between the upper angular material and the 

lower pellet layer is assumed to be due to a primary 

difference. The angular upper part is assumed to 

have been one of the solid Ellenburger layers and to 

have been shattered somewhat when the faulting took' 

place; the lower pellet part is assumed to have been 

originally a pellet layer, which was able to adjust 

itself to the faulting nlOvement without appreciable 

shattering. The movement along the fault was in 

any case probably not great. 

That the folding was nearly perpendicular to the 

plane of this fault which is roughly perpendicular to 

the polished face is confirmed by the evidence of the 

orientation of large calcite crysta.ls in the folded rock, 

as brought out below. As this fault plane is practically undisturbed by the folding it must be assumed 

that the folding was due to an underthrust from the 

left. 

As specimen G 114 was collected within a few feet 

of a fault which drops the bottom of the Smithwick 

shale (see stratigraphic table) several hundred feet 

below the top of the Ellenburger/3 while specimen 

G 105, which is considered not to have been influenced 

by structural disturbances, was collected only 200 or 

300 feet away from the fault, the fold is probably 

connected with the faulting. The plane X-X probably resulted from an earlier movement parallel to 

the post-Smithwick fault. 

Stratigraphic section of formations from the Ellenburger limestone 

to the Strawn formation in San Saba County, Tex. 

Age Formation I Approxi· 

mate thick- ness (feet) 

~---------

Strawn formation. 

~~~ .. ,,, ..... .......,.... ............ ,- ... I'" .......... , ....... -~- ....................... ""'--..... ,.....,...,. ............................... -----

Pennsylvanian Smithwick shale. 1_. ___ ~75 

Marble Falls limestone. 440 

v~~"'v .... ",....".""'''''''..., ....... ''''..,.,..,......-...... ...,." ...... ...".., __ ...... ..,.'.,. 

Q) Limestone. 20 

~ 

..c 

rf) 

+" Shale. 90 +" 

Mississippian Q) 

I-< 

s:l ---- ~ 

~ Glauconitic, pho~phatic sand. 0.5 

..... ~-..-~--...... --""'.~~~ --- -- ----

Limestone of Boone age. 0-2 

~~~-.....-..... ...... ...,. ..... """, ............... , ........... ~----

Ordovician Ellenburger limestone. 

13 See footnote 1. 

\ 
54 MISSISSIPPIAN FORMATIONS OF SAN SABA COUNTY, TEXAS 

AGE OF THE FOLD AND LOAD UNDER WHICH FOLDING TOOK 

PLACE 

The faulting that is assumed to have produced 

the fold. may have occurred at any time after the 

deposition of the limestone of Boone age.· In connection with the problem of its age the fissure 

fillings of glauconiti~ sand shown oli Plate XXI, 

some of which are marked a in Plate XX, must be 

considered. Under the. microscope (thin ·section 

G 114-10, Pl. XXIX) the filling of one of the largest 

of these fissures is found to consist mainly of coarse 

angular calcite grains, with round and angular quartz. 

grains (b, PI. XXIX), brown isotropic phosphate 

pellets (c), phosphatic or phosphatized fossil fragments (d), and ~hert fragments (e). Around f part 

of the rock itself has been partly chertified in place. 

In the polished face of specimen G 114-11 green 

grains, undoubtedly· glauconite, can be recognized. 

There is every reason for assuming that this Inaterial 

is derived from the directly overlying glauconite bed 

at the base of the Barnett shale (see stratigraphie 

table) and that it worked down into these cracks, 

·which must have formed after the folding of the 

rock. . The interpretation of this relation depends 

on whether the glauconite sand could have been present only a -foot or two above the base of the limestone 

of Boone age, at the time that limestone was folded, 

without itself being involved. It does not seem probable, and yet on account of the slight coherence of the 

sand and the localization of the folding it must be regarded as possible; 

If the glauconitic sand was present at the time of 

folding, a great but very indeterminate thickness 

of overlying beds may have overlain the Ellenburger here. H. D. Miser 14 says that as the source 

of the Pennsylvanian sediments prob~bly lay to the 

east or northeast 15 it· is quite possible that they 

formerly covered this region. As the latest uplift of 

the Llano region was post-Cretaceous, it is also quite 

possible that Comanche and Upper Cretaceous deposits 

once covered it. On the other hand, as the geologic 

map of Texas 16 plainly shows, the Comanche overlaps 

the Pennsylvanian and Permian with. great unconformity, so that it may hardly be assumed that both 

Pennsylvanian and Comanche were fully represented. 

How the thicknesses of the different formations of 

these series would be related to their thicknesses at 

their nearest occurrences is all the more difficult to 

estimate in view of the uncertainties already enumerated. In general the Llano region was a positive 

U Oral communication. 

15 Miser, ·R. D., Llanoria, the Paleozoic land area in Louisiana and 

eastern Texas: Am. Jour. SCi., 5th ser., vol. 2, pp. 74-75, 1921. 

10 Udden, J. A.,. Baker, C. L., and Bose, Emil, Review of the geology 

of Texas, 3d ed. : Texas Univ. Bull. 44, Aug. 5, 1916. 

geologic: element 17 during Paleozoic, Triassic, and 

Jurassic times, so that there were probably during 

Pennsylvanian, Permian, and Mesozoic times many 

more intervals of nondeposition and erosion in that 

region than in the surrounding areas where the formations of these periods are now preserved, and the sediments deposited there were probably of a shallowerwater facies. But many coarse near-shore sediments 

are thicker than their deeper-water equivalents, ·so 

that this factor tends to counterbalance the possible 

nondeposition or erosion. The best that can be done 

under the circumstances is to take rough figures for 

the nearest areas in which sediments of the periods 

involved are now present. Figures for the Pennsylvanian furnished by Mr. Roundy as derived from the 

areas to the north for the Permian from un published 

records of the United States Geological Survey and 

for the Cretaceous and lower Tertiary from the 

Austin folio· give the following thicknesses: 

Feet 

Lower Tertiary_________________________ 500 

Upper Cretaceous _______________________ 1,500 

Cornanche ______________________________ 1,500 

Perrnian ________________________________ 6,000 

Pennsylvanian __________________________ 6,000 

Barnett shale (Mississippian) ___________ 100 

15,600 

This total is probably much more than was ever present but probably may be safely taken as a maximum 

possible amount. 

If the glauconitic sand of the Barnett shale was not 

present, how~ver, then the greatest stratigraphic interval represented could not' have been more than the 

larger part of Boone time and perhaps most or all 

of St. Louis time. The lower part of the Barnett 

shale, as explained in the preceding text, is believed 

. by Messrs. Girty and Roundy to be correlatable with 

the Moorefield shale of Arkansas, which is very tentatively assigned by them 18 to St. Louis time, and may 

be as young as the later part of that epoch. The deposits overlying the Ellenburger could not haverepresented all of this interval, however, for the later part 

of it would have been taken up with the erosion of 

what was present before the glauconitic sand at the 

base of the Barnett shale was deposited. The thickness of such a column is also difficult to estimate, as 

no beds representing it occur in the neighborhood; but 

using figures from the nearest regions in which they 

are present Mr. Girty has roughly estimated a thickness of about 500 feet: 

It is generally assumed that flowage of rock can 

take· place only under great pressure, but as a matter 

17 Miser, H. D., op .. cit. 

18 Oral communication. 
OONTAOT OF THE ELLENBURGER AND BOONE LIMESTONES ~5 

Qf fnct little seems to be known about the conditions 

·of this kind o:f flowage, without fusion, in nature. 

In the field, too, most studies have been concerned 

with the n~ore extreme types of flowage in regional 

metnmorphism. Here, on the other hand, there has 

:been flowage which has not even ground the flowed 

Inateria.l very fine. 10 The preservation of large fossil 

'cross sections in most of specimen G 114 is one of its 

striking features. Geophysicists of the Geophysical 

IAaboratory of the Carnegie Institution 20 believe that 

folding such as occurred here could not occur under a 

,column as short as the 500 feet or so that n~ight have 

been present if the Barnett shale had not yet been 

deposited when folding took place. But no quantitative data appear to be available, and they. recognize 

that other factors, especially the amount of water 

present in the rock, might have a big modifying influ-

-ence. Moreover, the apparent extreme localization of 

the folding, directly adjacent to the faults, must be 

borne in mind. 

ORIENTATION OF CALCITE FRAGMENTS IN THE FOLDED 

ROCK 

A feature worth mentioning-is the large proportion 

of large calcite fragments in specimen G 114, oriented 

with their bases nearly parallel to the plane of the 

section-that is, with their optic axes nearly at right 

angles to it. They stand out clearly between crossed 

nicols on account of their relatively low birefringence 

colors, bright green, red, blue, yellow, or even gray 

predominating in each crystal. Thin sections G 114-5 

(PI. XXIII) and G 114-7 show the phenomenon 

especially well. It is more conspicuous in the limestone of Boone age, because large calcite fragments 

are particularly abundant there; but it is also common 

in the Ellenburger limestone of thin section G 114-5, 

in large grains of calcite that fill fissures and are therefore clearly not of organic origin. This orientation 

i:3 therefore apparently a result of flowage of the rock. 

The fact that 'the optic figures of all the calcite grain~ 

observed in specimen G 114 are slightly biaxial, indicating strain, would lead naturally to the conclusion 

that that condition is due to the unusual stresses to 

.which the material of this specimen has been subjected. But the facts that a slightly biaxial figure 

was found also in a fossil crin.,9id stem from the Pennsylvanian Graham formation of Youngs County, Tex., 

\",here so far as known it has been involved in only the 

mildest folding, and that a recent crinoid stem and 

sea-urchin spine show normal uniaxial figures, indicate that the mere weight of overlying material or 

the slightest folding is able to produce enough stress 

10 Cnyeux has noted the stdklng absence of fragmentation of fossil 

fragments in many beds which have been subjected to considerable 

tectonic disttll'bance. (Introduction il. l'Hude petrogmphlque des 

roches ~dimentail'es, p. 319, Paris, 1916.) 

:.'Q Orlll comlUunlcation. 

to make the optic figure of these echinoderm fragments slightly biaxial. 

FEATURES OF THE LIMESTONE OF BOONE AGE, ESPECIALLY O~ ITS B,ASAL CONTACT, IN SPECIMEN G 114 , 

POCKETS OF MATERIAL OF BOONE AGE IN '£HE ELLENBURGER LIMESTONE 

Some features of the Mississippian in specimen G 

114 that were not found in specimen G 105 deserve 

brief description. One is the presence of granular calcareous material, like the Mississippian, in pockets 

and fissures several millimeters below the contact in 

the underlying Ellenburger. Some of these pockets 

are indicated by b on Plate XXIII. 

SULPHIDE ALON G THE CONTAC'£ 

-Another peculiar feature of the contact here is the 

seam of yellQw ocher along it. Because it photographs black it does not appear clearly in Plate XIX, 

but. it stands out well in the thin section as the opaque 

matter at e in Plate XXIII. The inherent probability that this material was originally iron sulphide is 

supported by the groups of small more or less cubical 

grains (aro'und 0.03 to 0.04 millimeter), which 'by 

reflected light can be distinguished in the thin section 

at some points. The transparent portions of this mass 

(a, PI. XXIII) are silicified, and they are a mU:ch 

larger part of the mass than appears from the illustration. 

Small accumulations of ocherous material of this 

same kind are not uncommon in the basal part of the 

limestone of Boone age of specimen G 105. Some of 

them, are indicated a.t v, Plate VII. They are very 

common in the mass of skeletal fragments which 

makes up thin section G 105-E (PI. XI B), which 

comes from the limestone o~ Boone age about 1 foot 

above ,the contact, and in this most of them are intimately associated with the skeletal fragments. In 

the Ellenburger of specimen G 105 they are very 

scarce, and most though not all of those that occur 

are associated with the few silicified portions or with 

the n10re coarsely granular ocherous calcite, which~ 

as explained above (p. 47), is believed to be epigenetic. 

In the silicified Ellenburger material of specimen G 

114, as for instance in thin section G 114-1, they appear to be slightly more common than in the Ellenburger of specimen G 105. In thin section G 114:-5 

some of the ocherous matter occurs in the ve'ry top 

of the Ellenburger, as along the line f-f, Plate 

XXIII. There is therefore some reason .for thinking 

that the large amount of this material along the contact in thin section G 114-5 is epigenetic, especially 

as the association of epigenetic silica and sulphide is 

common. 
56 MISSISSIPPIAN FORMATIONS OF SAN SABA COUNTY, TEXAS 

I am nevertheless inclined to believe that the mass 

of original sulphide along this contact was syngenetic. 

The circulation of underground water might be more 

active along such a contact, and therefore, if the sull,hide was epigenetic, it might be more abundant 

there, but it is hard t.o conceive of a factor that would 

lead to the formation by such a process of a single 

large mass such as the main mass at e, Plate XXIII. 

l\t[oreover, masses that are not much smaller occur in 

the Mississippian of specimen G 105, where there has 

been no silicification, and concentrations of syngenetic 

sulphides at basal contacts are a partic'ularly characteristic mode of occurrence of that type of mineral. 21 

They are probably due to abundance of organic matter. The presence of the sulphides in the top of the 

underlying Ellenburger along line f-f, Plate XXIII, 

may well be due to a secondary redistribution of sulphide syngenetically formed at the base of the 

l\Jississi ppian. 

ENVELOPES AROUND CALCITE FRAGMENTS 

Another peculiar feature of thin section G 114-5 

is the presence around many of the coarse calcite fragments in the limestone of Boone age of an irregular 

cloudy 6'Tanular. envelope in continuous crystallographic orientation with the crystal it surrounds. 

. Some of the crystals which show it best in the photograph are marked g, h, i, k, l, on Plate XXIII, and in 

Plate XXX, A, B, 0, D, and Plate XXXI, A and B, 

different types are shown enlarged. The way in which 

the~e '~nvelopes merge with the granular matrix and 

inclOSL lragments of it independently oriented, as 

brought out between crossed nicols, indicates that the 

envelopes are the result of absorption and molecular 

rearrangement of the surrounding matrix by the large 

calcite crystal. This indication receives some support 

from a comparison of the boundaries of the inner part 

and of the cloudy envelope. In a, Plate XXX, A and 

lJ, which was chosen on account of the extreme irregularity of the outline of its inner clear part, that outline resembles the outline of the grains prevailing 

in this same limestone in its more normal condition, 

as illustrated in Plates XIV and XV. Plate XXX, 

(! and D, illustrates at a a grain with less irregularly 

bounded inner clear part, but in both these grains 

the tendency of the outer envelope to assume a spherical form is plainly indicated between crossed nicols. 

This is opposed to the idea that the envelope is the 

result of marginal alteration of the original calcite 

and shows 'also that the conditions which produced it 

were different from those which produced the clear 

envelopes in the less disturbed limestone of Boone age 

of specimen G 105. Some doubt, however, is raised 

by Plates XXXI, .A. and B, in which three grains 

:n Goldman, M. I., Basal g:auconite and pbospbate beds: SCience, 

new sel' .. vol. 56, pp. 171-173, 1922. 

(a, b, and c) with cloudy borders are shown not only 

in contact but two of them (b and c) extinguishing 

together and the third (a) almost with these two. 

They have sharp contacts, as shown by the contact of 

band c at w, Plate XXXI, A. The common orientation of these grains suggests some original relationship between them. If they were in contact before 

the border was formed, then the border must be due 

not to absorption of the matrix but to alteration of 

original clear calcite from the outside inward. However, the evidence from the other grains, discussed 

above, the· lack of perfect common orientation between 

a and b, and the deep penetration of the matrix between band c,' as brought out in Plate XXXI, B, 

lead me to believe that the common orientation is 

merely a coincidence and that these grains have come 

into contact by taking into their crystal structure the 

calcite of their matrix. 

As these envelopes are peculiar to the limestone of 

Boone age in this specimen of strongly folded rock 

they are probably the result of pressure, perhaps with 

accompanying waters, acting on the rock. 

STAINING OF THE ELLENBURGER LU[ESTONE BY THE 

l\fISSIRSIPPIAN 

N ow that the folding in specimen G 114 has been 

explained, a word of comment should be offered on 

the gray stain between. the silicified and unsilicified 

Ellenburger, . referred to . ..above (p. 52) .To the left 

of the line X-X, Plates XIX and XX, this stain is 

evidently due to actual inclusion of material of Boone 

age. To the right of that line, however, it nlust be 

due to spreading of the coloring matter, probably of 

organic origin, from the left side of the fault into the 

unsilicified Ellenburger limestone to the right of the 

fault. A similar spreading of the coloring matter of 

the Mississippian into the Ellenburger, as pointed out 

above (p. 44), occurs at their contact in specimen 

G 105, where it had the effect of obscuring the contact. 

GENF1RAL OBSERVAT'ION8 ON SILICIFICATION 

THREE TYPES OF SILICIFICATION 

The silicified portions of the Ellenburger limestone' 

and the limestone of Boone age in the specimens under 

consideration are of three kinds-one very fine 

grained and the other two in coarse crystals but with 

different manners of occurrence, as will be explained. 

The fine-grained variety is in these specimens un4 

doubtedly epigenetic. There is some evidence in 

favor of the belief that one of the coarsely crystalline 

varieties is syngenetic and that the other is probably 

not. Of the two coarsely crystalline varieties only 

one was found in specimen G 105. It is illustrated 

at e and f, Plate XIV, and at a, Plate XVIII, which 

shows e of Plate XIV, enlarged. These are in the 
CONTACT OF THE ELLENBURGER AND BOONE LIMESTONES 57 

linlestone of Boone age. ·Plate XII, 11 nnd 1), which 

are enlargements of d, Plate XI, 11, illustrate an 

occurrence of this type in the Ellenburger lllaterial 

of specimen G 105. For convenience of reference this 

will be called coarse type A. 

The other coarse-grained type was found only in 

specimen G 114. It is illustrated by a, Plate XXII, 

a, Plate XXXII, A" and by b, Plate XXXIII, 11 and 

B. For convenience of reference this will be called 

conrse type B. 

The nmorphous to fine-grained cryptocrystalline 

type is that which is characteristic of areas Band F 

and parts of J) and A, plates XIX and XX. It is 

ill ustrated by Plate XXII, by Plate XXXII, 11 and 

JJ, which show it between crossed nicols, and by Plat.e 

XXXIII. That this type is epigenetic is obvious from 

the fact that it cuts at random across the boundaries 

of formations and across structural features formed 

long after the deposition of the rocks. The association of this fine-grained type with the coarse type B, 

the shnrp boundaries between them, and the contrast 

between them is well brought out at a in Plate 

XXXII, il, where the granular inner part is a single 

cnlcite crystal, the coarse-grained rim is silica, and the 

matrix is the fine-grained silicified Ellenburger. The 

contrast between the three parts also shows well at a 

in Plate XXII. The large calcite crystal is undoubtedlya fossil fragment. It might be assumed that the 

difference in gl'ain of silicn between the matrix and 

the included calcite crystal is due to their original 

difference in grain-that is, that fine-grained calcite· 

gives pI nee to fine-grained silica, and coarse-grained 

culcite to coarse-grained silica. But Plate XXXII, 

Ii, which is a detail of an area around d, Plate XXII, 

shows at a a number of similar coarse calcite crystals 

whose edges are very irregularly corroded as a result 

of replacement by fine-grained silica. However, further search reveals the fact that in a great many ot4er 

.Large calcite crystals in thin section G 114--1, which 

are replaced, especially around their margins," .by 

coarse-grained' silica, the border of the coarse silica 

against the fine-grained silica of the matrix is much 

more vague and irregular than in a, Plate XXXII, A, 

and' parts of the same specimen are replaced by fine-. 

grained silica. One of these is illustrated in plain light 

1I.nd between crossed nicols at a in Plate XXXIII, ft, B. 

(which is an enlargement of e, PI. XXII), and another a,t b in Plate XXXII, B. In Plate XXXIII, 11, 

the area of coarse silica (b) can be clearly recognized, 

and its grain appears somewhat in Plate XXXIII, 13 .. 

But at c, in Plate XXXIII, 11, the fine-grained cloudy 

sil iceous matrix can be seen directly in contact with 

the large calcite grain a, and in Plate XXXIII, B, 

this contact can be seen to have the same corroded 

charl).cter as in the grains a of Plate XXXII, B. 

1-1ere, then, the same grain has been silicified in both 

'vays. 

Equally significant is grain b, Plate XXXII, B, 

for it shows remnants of coarse cat~ite and complete 

transition from relatively clear and coarse silica to the 

very fine grained silica. The central darker part, b, 

is the fine-grained silica, d marks the coarser-grained 

silica, and c marks patches of relatively coarse calcite 

grains. This evidence, together with the scarcity of 

coarse silicified fragments in the' Ellenburger of 

specimen G 105, as compared with their abundance in 

the silicified Ellenburger of Plate XXII, indicates 

th at the coarse-grained secondary silica of type B is 

epigenetic and is connected with the silicification of 

the body of the rock. 

The evidence from the silicified fragments in specimen G 105, which are all of type A, is different. 

These silicified areas in cross section are not bounded. 

by the irregular outlines of the quartz crystals as in 

a, Plate XXXII, A, but by a scalloped line which in 

three dimensions would presumably have the botryoidal form characteristic o~ many concretionary 

growths. The individual grains of this type differ 

from those of type B in having serrate' interlocking 

borders as compared with the much more regular, 

straighter .borders of type B, and in showing pronounced wavy, extinction, due probably to divergent 

fibrous structure and to overlapping of grains. They 

also do not attain as great size as those o-f type B. 

rhe mineralqgy of the two types has not been ·determined. Most if not all of these silicifie'd portions of 

type A occur entirely within the fo~sil' fragments that 

contain them. In Plate XVIII, 11, the chert areas, 

most of which are marked ([" all seem to lie within 

t11e granular nuclei, which, as shown above, un· 

doubteqly represent remains of organisms. There is 

no doubt that the ma~n body at d, Plate XII, is 

withi,n such a gr,anular nucleus but a l,ittle doubt 

about the e~tension to the right. In (/ and D, Plate 

XXXI, two enlargenlents of a, thin section G 114--6, 

Plate' XXVII, the chert areas, most of which are 

marked b, are clearly all within the organic fragment. If ,silicified rock of this type had been formed 

epigenetically by circulating waters it seems much 

more likely that the silica would spread inward from 

the outside, as in type B. Of the three examples 

shown that of Plate XXXI, 0 and D, is the only one 

that occurs in a partly silicified matrix, but there the 

silicification in the immediate neighborhood is slight, 

and the silicified rock does not come into direct contact with fragment a. If, as was indicated above, tht! 

calcite cement of the pellet layers in the Ellenburger 

is syngenetic, it is particularly difficult to conceive of 

silicifying waters reaching individual elements without affecting the surrounding rock. It seems prnh. 
58 MISSISSIPPIAN FORMATIONS OF SAN SABA COUNTY, TEXAS 

able, therefore, that coarse silicification of type A 

took place at the time of deposition. It is significant 

that all the fragments in which silicification of this 

type has been noted except c, Plate XI, A, have the 

characteristics of echinoderm fragments. It seeIns 

probable that to the open-mesh structure of this material is due the development of syngenetic silica in it. 

Within this meshwork conditions would be more stagnant than in the water surrounding the fragments, 

and decaying organic matter may have been present 

and been a factor in the precipitation of the silica. 

The circular outline of c, Plate XI, A, suggests that 

it fills a canal in some organism, where conditions 

would have been similar to those within the echinoderm fragments. 22 

It has been suggested above (p. 49) that the lower, 

more fragmented part of the limestone of Boone age, 

as illustrated in Plate XIV, may have been depo~ited 

more slowly and therefore been exposed longer to 

conditions on the ocean bottom than the fragments 

in the higher part as illustrated in Plate XI, B. 

This may account for the relative frequency of silicification of type A in the lower part and its absence, 

as far as I could find,. in thin section G 105-E, Plate 

XI,B. 

If this interpretation of the coarse silica of type A 

is accepted it has an important bearing on the history 

of the zone of material between X-X and Y -Y, Plate 

VII. I have concluded that this material is all of 

Ellenburger age, not Ellenburger reworked into the 

base of the Mississippian. As pointed' out on pages 47 

and 50, however, more or lesschertified fragments are 

much more common in the upper part of this layer, 

above the stylolite 8-8, than in the underlying part 

of the Ellenburger. This feature allies it with the 

overlying Mississippian. But if the chert of the overlying Mississippian is syngenetic thig underlying layer 

of Ellenburger material would also have to be of 

Boone age to share that character. Perhaps, then, 

the pellets of the topmost part of the Ellenl?urger 

material of specimen G 105 were reworked into the 

basal part of the Mississippian. Perhaps there wa~ 

even a recognizable boundary, which has been oblit.p.l· 

ated by the stylolite 8-8. 

METHOD OF SILICIFICATION 

Plate XXXIII, 0, a view taken by reflected light 

and showing an enlarged area of thin section G 114-1 

around hand i, Plate XXII, illustrates fairly well a 

meshwork of lines of clearer silica in the. midst of 

finely granular silica. This meshwork is believed to 

represent channels along which the "silicifying waters 

2l Cayeux states that silicification is rare in echinoderm fragments, 

but finds t.his sUl'prising in view of the presumably favorable conditions tlUl,t. I .have just enumerated. Caycux, L., IntroducUon a l'etud0 

pHt'ogi'aphique des roches sMimentalres, p. 438, Parls, 1916. 

penetrated the rock of specimen G 114. It is intersected in places by long straight lines, like those at 

a-a and b-b, Plate XXXIII, 0, some of which can 

be traced it length of 6 millimeters. Plate XXXIII~ 

D, which is a detail of thin section G 114-1. around 

g', Plate XXII, illustrates these straight lines particularly well but shows little of the meshwork. In plain 

light the straight lines and the meshwork of lines can 

be seen as clear vein lets between slightly granular 

cloudy-looking areas. The straight lines are probably 

joint planes, and the surrounding meshwork lateral 

channels along whi:..h the silicifying solution penetrated the rock. This penetration by a multitude of 

minute channels accounts for' the even front of. the 

silicified area as a whole in specimen G 114, Plates 

XIX and XX. In fine-grained material these channels are probably more closely crowded than in 

coarser-grained Inaterial; hence the apparently more 

complete and finer-grained silicification of the Ellenburger than of the limestone of Boone age in spe:::imen 

G 114. 

SUMMARY 

This paper falls into three distinct parts. The 

first deals with the petrographic characteristics of the 

Ellenburger and the ~1ississippian as they bear on the 

origin of the contact of the bvo formations. The conclusion is reached that the contact is a normal sedimentary contact. Evidence is brought out to shov.r 

that· the Ellenburger is a fine calcareous mud rock, of 

the "vaughnite" type but full of fossils, and that it 

was formed near marine base-level under conditions 

of frequent alternation of accumulation and erosion, 

precipitation and solution, which resulted in alternation of solid layers full of shells and of accumulations 

of pellets and fragments of the rock. The formation 

of the coarser .calcite matrix of the pellets was contemporaneous with the formation of the rock. 

T.he limestone of Boone age is shown to be an 

.; echinoderm breccia" or "crinoidal limestone." The 

material of the basal part is much more fragmented 

than t hat a foot or two above the bottom. This condition also is attributed to accumulation near marine 

base level, where the material was exposed for some 

time on the bottom and fragmented probably by she11-

crushing fishes.' After burial of tl,le echinoderm and 

other fragments secondary calcite in continuous crystallographic orientation with the fragments of echinoderm skeletons developed very irregularly aro'und the 

. individual fragments. Silicification of individual 

fragments, believed to be syngenetic, is much more 

common in th~ base of the limestone of Boone age 

than in the higher parts or than in most of the Ellenburger. But abundance of silicified fragments in the 

topmost part of the rock of Ellenburger type .'may 
OONTAOT OF THE ELLENBURGER AND BOONE LIMESTONES 59 

indicnte reworking of some of the pellets of that rock 

into the limestone of Boone age. 

The second pnrt of the pnper deals with the det1lils 

jf folding, in n hand specimen, of the two types of 

rock nt their contact. A complicated underthrust 

fold, which resulted in mixing of the two rocks in 

places but not in grent shattering, is worked out by 

the study of polished fnces and of thin sections. The 

fold is ascribed to a fault to which it is directly adjacent. On the basis of the presence of a sandstone 

of probnble Barnett age in fissures in the folded rock 

the qnestion of the age of the fold and the load under 

which it formed is discussed. Orientation of calcite 

crystals as a result of folding is pointed out. Special 

features of the limestone of Boone age in the folded 

rock are described. 

In the third part of the paper three types of silicification are described and interpreted. A pervading 

fine-grained silicification which followed folding in 

specimen G 114 and a coarser-grained type invading 

the borders of large calcite crystals are considered 

epigenetic. A coarse-grained botryoidal type affecting the inside of organic fragments is .considered 

probably syngenetic. 

PLATES VII-XXXIII 

51448-20--5 61 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 146 PLATE VII 

SPEClMEN G 105: ELLENBURGEl1 LIMESTONE AND LIMESTONE O~' BOONE AGE IN CONTACT 

Y- Y. Approximate base of Mississippian material. A. B. C. D. and F indicate approximatfl position of thin sectioflll 
U. S. GEOLOGICAL SURVIDY PROFESSIONAL PAPER 146 PLATE VIII 

A. DETAIL OF i. PLATE VII. s nowI G INTERNAL CAST OF A FOSSIL IN DIRECT CONTACT WITH SURROUNDING PELLETS OF 

ELLENBURGER LIMESTONE 

OF T ilE ELLENBURGER LTMESTO E CORRESPONDING ABOUT TO THE POSITIO O~· 

B. PLATE VII 

Shows a pellet layer and a solid layer 
U . S. GEOLOGICAL SURVEY 

A . DETAIL OF y, PLATE VIII, B. SHOWING PELLETS PARTLY EMBEDDED IN THE 

UNDERLYING SOLID LAYER 

PROFESSION AL PAPER 146 PLAT!': IX 

B. DETAIJ. OF THIN SECTION CORHESPONDING ABOUT TO AREA C, PLATE VII. SHOWING 

PARTIAL DISINTEGRATION OF ELLENBURGER PELLETS 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 146 PLATE X 

A. DETAIL OF b, PLATE VII, SHOWING AN ANGULAR FRAGMENT OF ELLENBURGER LIMESTONE 

INCLOSED IN A LATER LAYER OF THE ELLENBUHGER 

B. DETAIL OF k AND I, PLATE VIT, SllOWING ROU DED PEBBLE COl\IPOSED OF ELLE~BURGER 

PELLETS I CLOSED IN A LATER LAYER OF THE ELLE nURGER AND FISSURE CONTAI ING 

GRANULAR YELLOW CARBONATE 
·U. S. GEOLOGICAL SURVEY PHOFESSIONAL PAPEH 14G PLATE XI 

A. THIN SECTION OF ELLENBURGER LIMESTONE COHRESPONDING TO POSITION F, PLATE VII, 

SHOWING ESPECIALLY THE DISTRIBUTION OF YELLOW GRANULAR CALCITE AND PARTLY 

SILICIFIED FRAGMENTS OF ELLENnURGER 

B . THIN SECTION OF TYPICAL LIMESTONE OF BOONE AGE, FULL OF LARGE FOSSIL FRAGMENTS 

Specimen taken about 1 Coot above the base 
U. S. GEOLOGICAL SURVEY PROFESSIONAl, PAPER 146 PLATE XII 

A B 

DETAIL OF PLATE XI. A,SHOWING APARTLY SILICIFIED FRAGMENT IN THE ELLENBURGER LIMESTONE 

A, Plain light; B, hetween crossed nicol. 
U. S. GEOLOGICAL SUHVEY PHOFESSIONAL PAPEH 146 PLATE XIII 

A. DETAIL AROUND r , PLATE VII, SHOWING APPRECIABLE MOVEMENT ALONG STYLOLITE S-S 

B. DETAIL ALONG STYLOLITE S'-S ', PLATE VII. SHOWING LITTLE MOVEMENT ALONG TilE STYLOLITE 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 146 PLATE XIV 

GENERAL VIEW OF TlIIN SECTION G 105- D, SHOWING CONTACT OF EI.LE BURGER MATERIAL AND 

RASAL MATElllAL OF BOONE AGE 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 146 PLATE XV 

DETAIL OF IRREGULAR CALCITE FRAGMENTS IN Pl.ATE XIV 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 146 PLATE XVI 

ENLARGEMENT OF ECHINODEHM FRAGMENT FROM l'LATE XI, B 
• 

O. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 146 PLATE XVII 

A. DETAIL OF PLATES VIII, B, AND IX, A, SHOWING SECONDARY GROWTH OF CALCITE AROUND 

A FOSSIl. FRAGMENT IN TIlE ELLENBURGER 

B . DETAIL OF PLATE XI, B, SHOWING SECONDARY GROWTH OF CALCITE AROUND FOSSIL FHAGMENTS 

IN THE LIMESTONE OF BOONE AGE 
U. S. GEOLOGICAL SUHVEY PROFESSIONAL PAPEH 146 PLATE XVIII 

• 

A B 

DETAIL OF PLATE XIV, SHOWING A SILICIFIED FOSSIL FRAGMENT FROM TIlE LIMESTONE OF BOONE AGE 

At Plain light; B. between crossed nicols 
U. S. GEOLOGICAL SURYEY PROFESSJON~L PAPER 146 PLATE XIX 

:·::·:·:·:·P}~(.:..':\ " r 

POLISHED FACE OF SPECIMEN G 114-1, SHOWING FOLDED AND SILICIFIED ELLENBURGEH LIMESTONE AND LIMESTONE OF 1I00NE AGE, WITH 

GENERALIZED DIAGRAM OF T HE D ISTRI BUTION OF TYPES OF ROCK IN AREA 8 AND ADJACENT PARTS OF THE POLISHED FACE 

For explanation see P late XXI 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 146 PLATE XX 

SPECIMEN G II'HI, SH()WIl\'G A POLISHED SURFACE A130UT 2.5 CENTIMETERS BELOW TIlAT OF PLATE XIX 
OJ, 

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.... 

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I 

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U. S. GEOLO GI CAL SURVEY 

--

~ 

Ellenburger 

~ lim estone, 

unsilicified 

r,--'--1 

/~ 

D 

Ell enburge r limestone, si I icified 

Li mest one of Boone age, unsi licified 

PROFESSION AL PAPER 146 PLATE XXI 

:', .. : .: 

: .:.'~ .. ,. :,,:. :;::'~'~ .:": .'.-::.:'. :. ': . :,-:. :'. 

~: ':.:."": ~':''': . '. ~'.'.~:: .. ~ ... : 

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D 

Li mestone of Boone age, si licifi ed 

[ZJ 

Glaucontic sand 

DIAGRAMMATIC ILLUSTHATION OF FLOW LINES AND OF THE DISTRIBUTION OF THE FIVE DIFFEHENT KINDS OF ROCK IN SPECIM EN 

G 114-II, SHOWN IN PLATE XX 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 146 PLATE XXIT 

GENERAL VIEW OF THIN SECTION G 114-1, SHOWING SILICIFIED ELLENBURGER LIMESTONE 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 146 PLATE XXIII 

GENERAL VIEW OF THIN SECTION G 114-5, SHOWING LIMESTONE OF BOONE AGE NOT MUCH DISTURBED, RESTING 

ON SILICIFIED AND PROBABLY FAULT-FRACTURED ELLENllURGER LIMESTONE 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 146 PLATE XXIV 

GENERAL VIEW OF THIN SECTION G 114-4, SHOWING UNSILICIFIED ELLENBURGER LIMESTONE SOMEWHAT SUBJECTED TO FLOWAGE 

AND TO FRACTURE 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 146 PLATE XXV 

GENERAL VIEW OF THJN SECTION G 114-2, SHOWING THE LIMESTONE OF BOONE AGE PARTLY SILICIFIEQ 

AND PERHAPS AFFECTED BY FLOWAGE 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 146 PLATE XXVI 

GENELlAL VIEW OF THIN SECTION G 114-3, SHOWING A MIXTURE OF ELLENBURGER LIMESTONE AND LIMESTONE 

01" BOONE AGE PAHTLY SILICIFIED 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 146 PLATE XXVII 

GENERAL VIEW 01'" THIN SECTION (; Ll4- 6. SHOW ING ELLENBURGER LIM ESTO E AND LlMESTO E OF BOONE 

AGE M IXED AND SII ATTEBED BY LOWAGE A · 0 PAHTLY SILICIFIED 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 146 PLATE XXVIlI 

GENERAL VIEW OF THIN SECTION G 114- 8, SHOWING ELLENBURGER LIMESTONE AND LIMESTONE OF BOONE 

AGE MIXED AND SHATTERED BY FLOWAGE AGAINST THE FAULT LINE X -X, PLATE XIX 
U. S. GEOLOGICAL SURVEY iROFESSION AL PAPER 146 PLATE XXIX 

A B 

GENERAL VIEW OF THE GLAUCON ITIC AND PHOSPHATIC SAND OF THI N SECTION G 114-10, WITH SOME OF TIlE WALL ROCK OF SILI CIFI ED ELLENllURGER LIMESTONE 

A. Plain ligh l; B, bclween crossed nicol. 
G. S. GEOLOGICAL SUIWEY PROFESSIONAL PAPElI 146 PLATE XXX 

A B 

DETAIL OF PLATE XX IIJ, SHOW I ' G CALCITE CRYSTAL WITH CLOUDY GRANULAH RIM AND VEHY IRREGULAR CLEAR 

CENTER 

A, Plain light.; B, bet.ween crossed nicols, showing t.he inclusion of t,he calcite matrix in t.he envelope of granular cloudy calci te 

c D 

DETAIL SIMILAR TO A BUT WITH A MOHE HEGULAH CLEAR NUCLEUS 

C, Plain light; D. between crossed llicols 
U. S. GEOLOGICA l. SU IWEY PROFESSIONAL PAPER 14G PLATE XXXI 

A 1J 

DETA IL OF PLATE XXIII , Sl lVlILAII TO PLATE XXX BUT SHOWING 'l'IlIU;[<; GIIA INS IN COl\TACT 

At Plaiu light; B. between crossed nicols 

c D 

ENLA GE~ ENT OF a, PLATE XX VII, SIlOWl G AN ORGAN IC FnAG~[ENT PAHTLY SILICIFIED 

C, P lalu light; D. between crossed nicols, showing the coarse grain of the silica 

• 
• 

U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 146 PLATE XXXII 

A. DETAIL OF a, PLATE XXII. SHOWING PELLETS I SILIC H' IEO ELLENBURGER LIMESTONE O~' FINE GIlAIN A ' D THE 

MAHGINS OF A CALCITE CRYSTAL OF ORGANIC ORIGIN HEPLACED BY COAHSE-GHAINED SILICA 

Detween crossed. njcols 

B. DETAIL AHO[JND d, PLATE XXII. SHOWING COARSE CALCITE CHYSTALS OF OHGANIC OHIGIN IN THE MIDST OF 

SILICIFIED ELLENBUHGEH LIMESTONE OF n E GHAI • THE LAHGE CALCITE CRYSTALS PAHTLY HEPLACED 

BY FINE AND COAHSE GHAI ED SILICA 

Be t.ween crossed nicols 
U. S. GEOLOGICAL SU1Wm-y PROFESSIONAL PAPER 14G PLATE XXXJtI 

A E 

DETAIL OF e, PJ.>\TE XXII, SHOW ING A LARGE CALCITE CRYSTAL IN THE MIDST OF SILICIFIED ELLENBURGER LIMESTONE OF FINE GRAIN 

REPLACED AROU D THE BORDER BY COARSE A 0 FINE GRAINED SILICA 

A, Plain lighL; E, bet.ween crossed nicol. 

c. DETAIL NEAR i, PLATE XXII, SHOWI G MESHWORK OF VEINS IN 

SILICIFIED ELLENBURGER LIMESTONE 

D. DETAIL AROUND g, PLATE XX II, SHOWIN G INTERSECTING GROUP OF STRAIGHT VEINS IN SILICIFIED 

ELLENBURGER LIMESTONE 
INDEX 

Page A mbocoolia laevicula Howley? _____________________________________ ~ _______ 31- 2 

A 111 lI10discIIs Sp _____________________________________________________________ _ 

A mphissites Oil'l.y ____________________ • ____ .. _____ .________________ _ ____ _ ____ 7 

chllppelellsi~ HOlllldy, II. sll ___________________ ,. ___ , __________________ i-S, 1'1. 1 

I'lIgoslIs 0 ilty _______________________ ., _________________________________ 7, PI: I 

AlIl'igoriles HOlilldy, 11. gOIl ______________________________________________ . ___ O· 

tOXlllIIIS HOlllldy, II.Sl;' ________________________________________________ 0,1'1. [ 

Barnott shllle, dofillition IIl1d age or._________________________________________ 3~l 

BOlli boxill nil'. H. lntivittllta 0 il'ty ___________ '.. _____________________________ 30-37 

Bmohylhyl'is'( silllulans Oil'ty, n. sp ____________________________________ 33, PI. VI 

13I'Yllllt, W. L., oitod _____________________________________________________ .. __ 13 

Cllloil.o, crystllls of, ropillcod by silion, plntes showing_~ _____________________ . 01 

ol'ysl.lIls of, with clolldy grnlllllnr rilll nlld very irreglliar clcnr center, plntes 

showillg_________________________________________________________ iiI 

frnglll()lll;s of, ()Ilvelopes llrolllld ________________________________________ ·__ .'iii 

orielltatioll of.._ __ _________ ____ __ ____ _ ___ _ _ __ __ _ _ ____ ____ _ __ _ __ _ _ __ _ _ !i5 

plate showillg_ _ ________________________________________ _________ ____ fit 

sooolldlll'y growth of, nrolllld fossil fl'aglllellts, plnte showillg ___________ -___ fil 

ClllllnrophOl'ia'( nil'. C. hisillllnta Howley____________________________________ 29 Celltrolius____ _ _ __ __ ___ __ __ _ __ __ _ ___ _ _ __ ____ _ __ __ __ _ ___ _ __ __ _ _ _ __ __ _ _ _ __ __ ___ 15 

llllontus ___________________________ . _ _ _ _ _ __ __ ____ _ _ _ _ _ _ __ __ _ __ __ _ _ ____ _ __ 15 

SilJ.lplox-_-_-_---_ _ ___ _______ _ ___ _ _ _ __ _ _ ___ _ __ __ _ __ ___ _ __ __ _ _ _ _ _ _ _ _ _ __ __ _ _ 15 

ChOllol;ina subcllrilllll;1I Oirl.y, n. sp __________________________________ 27-28, PI. V 

Cladochonus'l sp____________ _ _ __ __ ____ _ _ _ _ ____ ___ ___ __ _ _ __ __ _ _ _ _ _ _ _ _ _____ __ __ 24 

Cliothyridillll'l sp_____ ___ _ ___ ___ _ ___ _ ____ __ _ _ ____ _ ___ __ __ __ __ __ __ _ __ ___ ___ _ __ 36 

COllodonl;s, bibliogrnphy or. _______________________ "_____________ ____________ 9-10 

nlltul'O of. _ ____________ ______ ___ _ _ __ _____ _ __ _ _ _ __ __ __ __ _ _ _ _ ___ ___ ____ __ __ 8-9 

COlltllCt of tho Ellenburgor and Hoollo lilllestones ____________________________ 44-59 

thin sootion on, piato showillg___________________________________________ 01 

Cmnia pertenllis Oirty, n. sp ____________________________________________ 25, PI. V 

Ctouognntlllls Pnnder ___________________ '. _ ___ __ _ __ ____ _ _ __ ____ _ _ __ __________ W 

nHirchisoni PalJdel' _________________________________________________ W, PI. II . 

vel'llouilli Pllllde!" __________________________________________ c ________ W, PI. II 

sp. A._ ••• _ •• _. ____ • __ ._. ___ • __ • _____________________________________ 10, PI. II 

sp. B .•.••• ___ ._._._. __ • __________________________________________ 10-17, PI. II 

Cyuthaxonitllllinor Wollor'l __ .--------------- .______________________________ 24 

Cypriclll'dillini' ntY. C. sllbcul1entll Weller ___ .• _______________________________ 36 

Diolasnlll'l sp •••••• _ ••• __ • __ •• _. -.- -7 _____ • ______________ .----- _______________ 29-30 

I~chillodel'ln frngllleut, plnte showing ____ • _____________________________ ._.___ 01 

Ellonburger limestone, shattered by tlownge, plntes showing________________ 01 sllicifiod, plates showillg ____ • ____________________ ~__________________ ____ 01 

thill soctions of, plntes showing ______________________________________ .___ (jl 

IIlIsilic:iflod, somewhnt subjeoted to tlownge nnd t.o fracture, plnte showing_ 01 

Fish romuius._ ••••••••• _. _ •• _ •• __ ._ •• ___ ._ __ __ ___ ___ __ ___ _ __ __ __ ___ ____ _ ___ _ 17 

Flow llnos, pInto showing _____ •• _. _________________________________________ , 01 

Fold at contact of Ellellburger nnd IVUssissippian, age ot. _________ : _________ 54-55 

lond under whieh it wns formed_. _______________________________________ 54-55 

1II0thod of studying_.______________ __ __ _ _ _ __ ___ _ __ ____ _ __ ___ __ _____ _ ____ _ 50 

origiu ot •••••• _ •• _ •• _________ • __________________________________________ 52-53 

Fossil ill oontnot with Eilellbul'gel' lil11estollo, pIn I.e sho~\'ing_ ________________ 01 

o uathodus Pandor._ ••• _. ___________ • ____ • _____________ .__ __ _ __ __ __ _ _ _ __ _ ____ l2 

Illosqllonsis pulldo:'. __ ._. _____ • ___ • ____ • _____ • ______________________ 12, PI. II 

texanlls Houndy, n. sp. ____ ._. ______________________________________ 12, PI. II 

vnr. bicllspidlls HOlllldy, II. var _________________________________ 12, PI. II 

OOllinUtes'1 sP_. __ • __ • ___ ._ ~ __ _ _ __ _ __ __ __ __ _ ____ __ _ __ _ _ _ _ _ __ _ _ __ ___ ____ _ _ ____ 38 

Hcnldill Houlldy, II. gen _______________ ._____________________________________ 8 

ampln Houndy, n. sp _____________________________ ~ ____________________ 8, PI. I 

simplex HOllndy, II. sp_. ______________________________________________ 8, PI. I 

Hinde, O. J., cited _ • ___ ._ •• ____________ • ____________________________________ 10,13 

Hustedin HIIII Hilt! CIllrke'!.. ________________________________________________ 33-34 

Hllstodini' pnrvicosl;lll;a Oirty, II. sp ____________________________________ 30, PI. VI 

problomutiea Oirty, II. sp __________________________________________ 35, PI. VI 

subnequalis Oirty, II. sp _________________________________________ 35-30, PI. VI 

tOXlIlI1\ Oirty. II. sp __ •• _________ ._.________________ . ___________ 34-35, PI. VI 

lIyolithos parvullls Oirty, II. sp. ___________ • __________ ~ ________________ 38, PI. VI 

Jackfork snlldstone, nge of _____________ ~ ___ • ________________________________ _ 

KirkbYIl lilldllhli Ulrich'! ___ • _______________ .________________________________ 7 

lindnhli Vlll'. arkanslllla Oirty ________________________________________ ' __ i, PI. I 

Limestone of Boone age, features ot. _______ • _______________________ · _____ • __ _ 

1I0t muoh disturbed, resting on silicified anci probably fnult·frnctured 

Ellonburger' Iimestono, pInte showing._. ___ • ________________ .___ 61 

partly silicified, plates showing._ •• _.____________________________________ 01 

shattored by f1ownge, pI utes showing •• _. ________________________ " _ _ _ _ _ _ _ (il 

thin soetions of, plates showing_. ___ • ___ .________________________________ 01 

o 

Page 

Lingllliciiscina nfl'. L. minuta :Mather ________________________________________ 24-25 

Locnlities where fossils were collected________________________________________ 17 

LO,nchocius Pander ___________________________________________________ . _. ____ I:. 

simplex Pan·de!'. _______________________ ' _____________________________ Iii, PI. III 

Lonchodlls? Iinentus Pallder____ __ __ _ __ __ __ _ __ ___ __ _ __ _ _ _ _ _ _ _ __ _ _ _ _ _ _ I.5-J(j, PI. I I [ 

Micro-fossils, value of, for correlation________________________________________ 1-2 

Orthocera sp ___________ "_ _ ___ _ ___ ___ ____ _ _ _ ___ ____ __ __ __ _ ___ ____ __ _ _ ___ ___ __ . 38 

Ostrncoda __________________________________________________________________ _ 

Paleacis? sp_ _ ______ _ _ _____ ____ _ _ __ _____ _______ __ _ __ __ _ __ _ ___ _ _ _ __ _ _ _ _ _ _ _ _ __ _ 2·1 

Pander, C. H., cited ___________________________________________________ 10,12,15,16 

Paraparchites sp_ __ _ ____ _ __ ___ ____ __ ____ _ _ __ _ _ _ ___ ___ __ ___ _ _ _ _ __ __ _ __ _ _ _ __ _ _ 6 

Platyceras afl'. P. glenparkense Welle!'. ______________________________________ 37-38 

, nfl'. P. nnsutllm IV[iIIel'._________________________________________________ 37 

Plellrotomnria, several spceies___ ___ ___ __ __ __ _ _ _ _ __ __ __ _ ___ ____ _______ _ ____ __ 37 

Poiygnathus Hinde_ _ ___ __ ____ _ _ _ ___ _ _ __ _ _ _ _ _ _ _ _ __ _ __ ___ __ _ _ _______ _ _ __ _ __ __ 13 

bilinentlls Houndy, n. sp ___________________________________________ la, PI. ILL 

dubius, Hinde _______________________ .. ____________________________ 13, PI. 111 

tam Houndy, n. sp ___ ~ __________ . _______________________________ 13-14, PI. III 

texan us Houndy, n. sp _____________________________________________ 14, PI. III 

sp. A ______ , _________________________________________________ .-------- 14, PI. III 

Polygnathus'! claviger Houndy, II. sP _______________________________ 14-15, PI.IV 

Prioniodlls Pander _ _ _ __ ___ __ _ _ _ _ _ __ _ __ _ _ _ _ _ __ _ _ _ __ _ _ __ _ _ __ __ _ __ _ __ _ _____ ___ _ 10 

elegans Pander ________ ~ ___________________________________________ 10, PI. IV 

henldi Houndy, n. sp _______________________________________________ 10, PI. IV 

peracutus Hinde ______________________ ~ __________________________ 10-11, PI. IV sp _______________________________________________________________________ 11-12 

sp. A, 13, C, and D _________________________________________________ II, PI. IV 

Proetus roundyi Oirty, n. sp ________________________________________ : :)9-40, PI. VI 

roundyi val'. alternntus Oirty, II. var. _______________________________ 40, PI.VI 

var. deprosSlls Oirty, n. vm· _____________________________________ 40, PI. VI 

Pllstula inconspicua Oirty, n. sp ______________________________________ 28-29, PI. V 

moorefieldana var. pusilia Oilty '! _ _ _____________________________________ 29 

afl'. P. indianensis 11all. _______________________ ·__________________________ 29 

Heticularia sp _______________________________________________________________ 32-33 

Hhipidomella perminllta Oirty, n. sp _________________________________ 25-26, PI. V 

perminuta var _______________________________________________________ 20, PI. V 

Sand, glauconitie and phosphatic, plate showing ____________________________ • 61 

Sansabella Roundy, n. gon ___________________________________ .______________ 5-0 

amplectans Rounely, n. sp _____________________________________________ 0, PI. 1 

sulcata Houndy, n. sp _________________________________________________ 0, PI. I 

Schllehortolla morsei Foerste ?_______________________________________________ 26 

Schuchertella? sp _____________ .. __________________________________ ; __ ___ _ __ _ __ 20 

Solonella? subcircularis Oirty, n. sr;--- _______________________________________ 30-31 

Silicification, method oL ______ .. _ _____ __ ___ __ __ ______ ___ _____ ________ __ ___ _ __ 58 

three types or.___________ _ ____ __ . ______________________________________ 56-58 

Specimen 0 105, Ellenburger Iiu.cstone ill, charneter of, directly under the- contact _____________ ~_ _ __ _____ ___ __ ___________ _______ __ ____ ___ __ _ 50 

Ellenburger limestone in, general features or.____________________________ 45 

matrix of the pellet layers or.________________________________________ 47 

origin of the pellets i11.. ______________________________________________ 45-47 

silicificntion in _______ " ____ _ __ __ ___ ____ ___ __ ___ _____ ___ __ _____ ___ _ __ __ 47 

stylolites in ________________ , _ __ __ _ _ _ _ _ _ __ _ __ ___ ___ _ _____ ___ ______ __ _ _ 4S 

genernl features and interpretation of. ____ _ __ _ _ __ _ _ _ _ __ __ ___ __ _ __ _ __ ___ __ 44 

limestone of Boone age, in accul11ulatioll or._____________________________ 4() 

fragmentation of skeletal remains in _________________________________ 48-49 

general fentures and interpretation or._______________________________ 48 

silicification in ______________________________________ :___ __ _ __ _ __ ___ _ _ 50 

plates showing_______ ________ ________ ____ ___________ _____ _ _______ ______ __ fil 

source or. ______________________________________________________ • _________ . 44 

Specimen 0 114, Ellenburger limestone in, charncteristic features ot. __________ 50-51 

Ellenburger limestone in, staining oL.__________________________________ 50 

limest.one of Boone age in, charncteristic features 9£..-------------- __ 50-51,55-50 

method ofstlldying_________ ___ __ ____ _ _________ ___ _ __ ________ ______ ______ 50 

polished faces of, platesshowing__________________________________________ 01 

thin sections of, relations shown by _________________________ ~ _____ • ______ ,5L-52 

Spirifer sp ____________________ , __________________ :______ ______ __________ ___ ___ 32 

vnr _______________________ • _ _ _ ___ _ _ __ _ _ _ _ __ _ _ _ _ _ _ _ _ _ _ _ _ __ _ _ __ _ _ _ _ _ _ _ _ _ _ _ _ 32 

Stylolite, movement along, plates showing ___________________ ._._____________ 01 

Sulphide along tho contact of the Ellenburger and the Mississippinn •• __ • ____ 55-50 

Well drilling, guidance of geology needed for __________________________ -- ____ _ 

Xestoleberis? sllbcorbuloides Jones and Kirby?______________________________ 8 

'G3