14 Hill Paleontology of the Trinity Division. 



Molluscan and other invertebrate remains appear coincident 

 with the calcareous beds, accompanied in some instances by 

 plant and vertebrate remains, as at the plant beds three miles 

 west of Glen Rose, Somervell county, Texas. 



Aggregations of Species in Great Bed*. In various parts of the 

 Glen Rose beds there are 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. 



Coquina Beds. These usually appear 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 Texas. The massive beds are composed almost ex- 

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

 dark-yellow color upon weathering. They outcrop at many 

 places along the old military road between Antoine and Ultima 

 Thule. Shell beds are especially well developed near Travis 

 Peak post-office, 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 Oyster Agglomerate. Near the base of the Travis 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. franldud 

 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 

 cle Verneuil, cemented by a hydrocarbon matrix, probably gra- 

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

 near the base of the Glen Rose beds. 



The Orbittditcs Chalk. Near the base of the Bluffs of the Col- 

 orado, about the middle of the Glen Rose beds (Upper subdivis- 

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

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

 of the forarninifera Patettina (Orbit (dues') texana Roemer. This 

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

 ties. 



