102 S. Powers — Gastropod Trails in Sandstones. 



Permian Cibolo limestone. 



f Transition beds. 



Lower Pennsylvania!! J £}£ «jg tone - 



I^Cieneguita beds. 

 (Intrusive contact) 



The correlation of the Pennsylvanian section is with 

 the Tesnus, Dimple, Haymond, and Gaptank formations 

 of the Marathon uplift, with the Strawn formation (?) 

 of Northern-central Texas, and with part of the Hneco 

 limestone of western Texas. The Cibolo limestone is 

 correlated with the Capitan limestone on the New Mexico 

 line. 2 



Exposures of Pennsylvanian rocks are limited to six 

 localities, but further investigation will doubtless reveal 

 others. Two of these have not been verified. The prin- 

 cipal exposures are north of Shaffer, one "east and 

 southeast of the Ojo Bonito and the Cieneguita ranches," 

 and one along Sierra Alta creek east of Cibolo ranch. An 

 exposure only a few hundred feet long is found on the 

 southernmost Morita creek one mile southwest of the 

 Morita road, and a short distance northeast of a mine 

 tunnel. Two exposures are reported below the box 

 canyon south of the junction of Cibolo and Morita creeks, 

 one above the site of the Spunk ranch, and above the site 

 of the Dutchover ranch. Another exposure is mapped 

 by B. F. Hill on the western side of the Chinati Moun- 

 tains. Pennsylvanian rocks also outcrop southeast of 

 Shafter in the Solitario dome and in Mexico where they 

 have been found by Dr. Udden. 



Northeast of the present Cieneguita ranch and east 

 of the volcanics there is an area of black shales and 

 quartz-pebble conglomerates striking north-south and cut 

 off on the northeast by fine-grained, porphyritic, gray 

 granite, the femic constituents of which are pyroxene 

 and biotite. There is little metamorphism at the contact, 

 but the igneous rock has invaded the shales in the form 

 of tongues and fragments of the shale are included in the 

 granite. The granite at the contact is of moderate grain 

 with pink feldspar and colorless quartz crystals of equal 



2 J. A. Udden et al., Eeview of the geology of Texas, Univ. of Texas, Bull. 

 44, p. 43, 1916. • • 



