PENNSYLVANIAN STRATIGRAPHY OF TEXAS 19 



Previous work. — The Pennsylvanian area of Texas was first 

 explored by Roemer^ in 1846 and later by Shumard,^ Ashburner,^ 

 and others. The most important contributions to the stratigraphy 

 of the north Texas country, however, are contained in the writings 

 of Tarr,"* Cummins,^ and Drake,^ who made investigations of the 

 coal fields of the Colorado and Brazos river valleys in the late 

 eighties and early nineties for the first Texas Geological Survey. 



Cummins'' recognized six divisions in the rocks of the Texas 

 Pennsylvanian, (i) Bend, including the black shale and limestone 

 typically exposed in San Saba County; (2) Millsap, comprising 

 shale, limestone, and sandstone exposed in the Brazos River Valley; 

 (3) Strawn, including the strata, chiefly shale and sandstone, 

 between the first coal and the base of the massive limestones of the 

 succeeding division; (4) Canyon, the dominantly limestone division 

 in the middle or upper part of the Pennsylvanian section; (5) 

 Cisco, composed of shale, sandstone, and thin limestones above the 

 Canyon limestones and below the Red Beds; and (6) Albany, 

 consisting of thick limestones and shales above the Cisco, at first 

 thought to belong to the Coal Measures, but later referred to the 

 Permian. Cummins did not attempt to subdivide these large 

 units, but the broad groups which he recognized and the names 

 which he applied are those in use at the present time. In the 

 main they appear to be very well chosen and the contributions of 

 this pioneer worker based on work done under great difficulties are 

 most important. 



Drake^ was first to make a detailed study of any portion of the 

 Pennsylvanian in Texas. In mapping the coal field of the Colorado 

 River Valley, he differentiated the large groups of Cummins into 

 many smaller units which he described and named. He fijced the 



^ F. Roemer, Die Kreidebildungen von Texas (Bonn, 1852). 



2 B. F. Shumard, Trans. St. Louis Acad. Sci., Vol. I (i860), pp. 686-87. 



3 C. A. Ashburner, Trans. Amer. Inst. Min. Engrs., Vol. IX (1881), pp. 495-506. 



* R. S. Tarr, Texas Geol. Surv., First Ann. Kept. (1889), pp. 201-16. 



5 W. F. Cummins, Texas Geol. Surv., First Ann. Kept. (1889), pp. 145-82; Second 

 Ann. Kept. (1890), pp. 359-94. 



^ N. F. Drake, Texas Geol. Surv., Fourth Ann. Kept. (1892), pp. 357-481. 

 ' W. F. Cummins, Texas Geol. Surv., Second Ann. Rept. (1890), p. 375. 



* N. F. Drake, loc. cit. 



