PENNSYLVANIAN STRATIGRAPHY OF TEXAS 21 



Acknowledgments. — Cordial acknowledgment is made of the 

 assistance of Dr. W. A. Van Waterschoot Van der Gracht, president 

 of the Roxana Petroleum Corporation, and of Mr. Richard Conk- 

 ling, head geologist, through whose courtesy the results of the 

 stratigraphic studies of the Texas Pennsylvanian are presented. 

 Among the geologists who have contributed importantly to the 

 progress of the study are Messrs. John Burtt, Paul Applin, James 

 Armstrong, Sam Wells, Chester Hammill, Angus McLeod, Grady 

 Kirby, E. G. Allen, and Miss Linda Green. 



GENEEAL DESCRIPTION OF THE NORTH CENTRAL 

 TEXAS PENNSYLVANIAN 



Location. — The Pennsylvanian area of north central Texas may 

 be described as two great inliers of Carboniferous rocks which 

 protrude through the Cretaceous strata on the east and dip beneath 

 Permian rocks on the west and north. The two areas are separated 

 by a narrow tongue of Cretaceous (Trinity) sand, and the southern 

 outcrop rests against Ordovician rocks for a short distance along 

 the Llano uplift, so that the southern portion does not possess the 

 relations of a true inlier. 



The total area covered by the Pennsylvanian is about 7,000 

 square miles. It includes the west part of Montague, the south- 

 east part of Clay, the greater portion of Jack, Young, Stephens, 

 Palo Pinto, Eastland, Brown, the east half of Coleman, the north 

 part of San Saba, and the northeast of McCulloch counties. The 

 shape and location of the Pennsylvanian area are shown on the 

 index map, Figure i. 



Lithologic character. — 'The lower portion of the Pennsylvanian 

 rocks consists of massive blue, gray, or black limestone, and greenish- 

 gray to black argillaceous and bituminous shale. As observed at 

 the outcrop, these are not interbedded, but a division consisting 

 almost wholly of limestone, 400 to 500 feet in thickness, Hes between 

 two shale formations. This portion of the Pennsylvanian, the 

 Bend, contrasts in Hthologic character with the remaining rocks of 

 the system. It is the chief petroHferous horizon in north Texas. 



The Millsap and Strawn divisions are dominantly clastic, the 

 latter, especially, being composed of very massive, more or less 



