CHOCTAW AND liRAYSON TERRANES OF THE ARIETINA. 41 



River,* who correlated the upper ineuiber with the Shoal 

 creek (Yola) limestone. 



THE CHOCTAW LIMESTONE. 



The lower of these two members, the Choctaw liniestone, 

 is the limestone that, in Cooke and Grayson counties, rests 

 upon the Pawpaw clays (and sands) of Hill, and a typical 

 locality of which is at the quarry owned by Mr. J. T. Munson 

 et al., on the summit of the Pawpaw creek bluifs, southeast 

 of the Union depot of Denison. Thence it extends aloni,^ 

 the brow of the creek-blutf to the northeastward, to a point 

 north of the Denison-Bouham road. It also outcrops exten- 

 sively on Choctaw creek, from which it is named, and thence 

 westward on most of the tributai'ies of Red river, and on the 

 bluffs of the river itself to Gainesville, just west of the Cross 

 Timbers, where it takes a southerly course. It is well devel- 

 oped in Denton county also, on Denton creek, near Roanoke. 

 Though softer and less durable than the so-called "quarry- 

 limestone" of Denison (at base of the Pawpaw clays), it is a 

 true quarry-limestone, and has been quarried for building 

 purposes not only at the quarry above named, but also at 

 many other localities. It is the same limestone that is called 

 by Taff. '" the Exogyra limestone," in the report above cited 

 (pp. 281, 282, 283," etc.) 



The thickness of the Choctaw limestone in Grayson county 

 is ordinarily about five feet, though locally it becomes a few 

 feet greater. In Cooke county the same limestone attains a 

 maximum thickness of ten or fifteen feet. 



The paleontologic aspect of this terrane may be seen in 

 the following list, which includes most, if not all, of the 

 fossils that have been obtained from it: 



FAUNA OF THE CHOCTAW LIMESTONE. 

 Hemipedina charltoni, Cragin. Cuculhea recedens, Crag.:j: 

 Holectypus charltoni, Crag.t Cardutmsp. (distinct from texanum) 



Enallaster texanus, Roenier. Card ium{Protocard.)texanuvi,Con. 



* Pages 27r)-2S3. 



t 111 till! small peristome and posteriorly placed periproet, this species is closely 

 related to Holectijpus casiilloi, Cottoau, from which it differs chiefly lu the form of 

 the periproet. 



t This species is apparently distinct from C. terminnlM, Conrad, of the Glen Rose 

 beds ; but the question can perhaps hardly be settled till specimens of terminulis can 

 be found showing the details of the iiiiige. 



