14 JJill—I'alcoidolo(jij of the Trlnltij Dlcli^luii. 



Mulluseau and other iuvortol)rate remains a[)pear coincident 

 with tlie calcareous beds, accoin})anied in some instances by 

 pkmt and vertebrate remains, as at the phmt beds three miles 

 west of Glen Eose, Somervell county, Texas. 



Aggregations of Species in Great Beds. — In various parts of the 

 Glen Rose beds there arc strata composed of shells of one pre- 

 dominant species, while in other cases there is an agglutination 

 of shell fragments of many species in masses similar to the 

 recent formation on the coast of Florida known as Coquina. 



Coqidna Beds. — These usually aj^pear at the base of the Glen 

 Rose beds or at the first appearance of marine mollusks in the 

 series. In Arkansas, owing to greater alteration through cal- 

 cification, they consist of much more indurated limestone mate- 

 rial than in T(!xas. The massive beds are com[)osed almost ex- 

 clusively of small shells of many species, and usually have a 

 dark-yelUnv color upon weathering. They outcrop at many 

 places along the old military road Ijctween Antoine and Ultima 

 Thule. Shell beds are especially well develoj)ed near Travis 

 Peak i)Ost-ofiice, near the Colorado river, where the Coquina 

 beds are pure white in color and the shell fragments more sili- 

 ceous and comminuted than in Arkansas. 



The Ogder jigglouierate. — Near the base of tlie Ti'avis Peak sec- 

 tion is a stratum some four feet in thickness, composed exclu- 

 sively of a fossil Ostrea, so poorly preserved that the specific 

 nature cannot be ascertained, 'but which resembles 0. franJdini 

 Coquand. A similar bed of Ostrea franklini occurs in the west 

 bluff of the Little Missouri, three miles west of Murfreesboro, 

 Arkansas. 



The Vicarya Beds. — At Post Mountain, west of the town of 

 Burnet, there is the remnant of a vast bed of agglomerate, com- 

 posed entirely of the shells herein described as Vicarya lujani 

 de Verneuil, cemented by a hydrocarbon matrix ,'i3robably,gra- 

 hamite. This bed is some ten feet in thickness, and is evidently 

 near the base of the Glen Rose beds. 



Tlie Orhitidites Chalk.— ^car the base of the Pluffs of the Col- 

 orado, about the middle of the Glen Rose l)eds (Upper sul)divis- 

 ion) is a stratum of ten feet or more in thickness, comi)osed 

 entirely of a massive white chalk, studded with the minute shells 

 of the foraminifera P(dellhia. (Orljitiditcs) texana Roemer. This 

 chalk extends southward into Hays, Comal, and adjacent coun- 

 ties. 



