PENNSYLVANIAN STRATIGRAPHY OF TEXAS 7,7, 



above the Thurber coal. It is very well exposed in the vicinity of 

 Mineral Wells and along Brazos River, its outcrop extending in a 

 belt 10 to 15 miles wide from Erath to Jack and Wise counties. 

 Four prominent sandstone members produce prominent escarp- 

 ments which are the chief topographic features of the region. The 

 shales are sandy and are at least in part very fossiliferous. 



Fossils from the Strawn collected by the writers are chiefly from 

 the Millsap and the middle portion of the Mineral Wells formation 

 in the Brazos Valley. The fauna of the Millsap, so far as known, is 

 not very large, nor does it contain strongly diagnostic elements, but 

 it appears to be more closely related to that of the Bend than the 

 Mineral Wells. A large and varied fauna is found in the Mineral 

 Wells formation, more than 90 per cent of which is common to the 

 Wewoka fauna of southern Oklahoma which has been studied in 

 detail by Girty.^ Without doubt these faunas are very closely 

 related, but since this fauna with some minor changes occurs in the 

 Canyon group and in the Graham formation of the Cisco, and since 

 in southern Oklahoma it is found as low as the Hartshorn sand- 

 stone,^ many hundreds of feet below the Wewoka formation, it is 

 believed that the stratigraphic equivalent of the upper Strawn in 

 southern Oklahoma is below the horizon of the Wewoka. From 

 evidence at hand the Strawn of Texas may be correlated with 

 beds below the Calvin sandstone of the section northeast of the 

 Arbuckle Mountains, with the Vinita and Winslow formations of 

 the region farther north, and probably in part the Cherokee shale 

 of Kansas and Missouri. It is evidently of Allegheny age. 



CANYON GROUP 



The Canyon group includes the beds formed after the deposition 

 of the coarse sandstones, conglomerates, shales, and coal of Strawn 

 time, when the land to the east had been worn low, the accumulating 

 sediments forming a series of thick limestones and fine calcareous 

 clays, with only a few lenses of sandstone. As here defined, the 

 Canyon group includes the strata assigned to it by Cummins^ in his 



1 G. H. Girty, U.S. Geol. Surv., Bull. 544 (1915). 



2 G. H. Girty, U.S. Geol. Surv., Nineteenth Ann. Rept. (1898), Part III, p. 541. 



3 W. F. Cummins, Texas Geol. Surv., Second Ann. Rept. (1890), p. 374. 



