Richardson — Stratigraphy of the upper Carboniferous. 325 



Art. XXYI. — Stratigraphy of the upper Carboniferous 

 in West Texas and Southeast New Mexico / by Gr. B. 

 Richardson.* 



Introduction. 



In the trans-Pecos portion of Texas and New Mexico, every- 

 where that basal strata of upper Carboniferous age have been 

 observed they lie unconformably on older Paleozoic strata or 

 on pre-Cambrian rocks. This unconformity marks one of the 

 important time breaks in the geological history of the south- 

 west. The upper Carboniferous rocks consist of limestone, 

 shale, sandstone, and variegated red beds. Limestone, with 

 locally a basal conglomerate, usually forms the lower part of 

 the section, and the uppermost strata are red beds which are 

 unconformably overlain by deposits of Triassic age. The 

 sequence, however, is extremely varied. The lowest rocks 

 are Pennsylvanian and the uppermost are Permian, but where 

 to draw the dividing line between Pennsylvanian and Permian 

 in this region is an open paleontological question. These rocks 

 comprise a maximum of more than 15,000 feet and thus con- 

 stitute one of the thickest upper Carboniferous sections known. 



In connection with work in the Van Horn quadrangle in 

 west Texas, it became desirable to examine the northward con- 

 tinuation of the rocks there exposed, and last summer (1909) I 

 had the opportunity to make a short trip to the Guadalupe 

 and Sacramento mountains and adjacent portions of New 

 Mexico. The result enables a comparison of several upper 

 Carboniferous sections in the little-known area between the 

 Rio Grande and Pecos River. In the following descriptive 

 sections I have summarized the results of my own work of the 

 past several seasons, and for comparison I have referred to the 

 work of J. A. Udden in the Chinati Mountains and of C. H. 

 Gordon and "Willis T. Lee in Rio Grande Valley. I grate- 

 fully acknowledge my obligations to Dr. Girty, who has accom- 

 panied me on several trips into the field and has examined all 

 of my collections of fossils. 



Section in Chinati Mountains, Texas (No. 1, figs. 1 and 2). — 

 J. A. Uddenf in 1904 reported the presence of some 6,000 feet 

 of upper Carboniferous rocks in the Chinati Mountains, about 

 175 miles southeast of El Paso. These consist of conglomer- 

 ate, sandstone, shale, and limestone, which he separated into 



* Published by permission of the Director of the U. S. Geological Survey, 

 f Udden, J. A., The Geology of the Shafter Silver Mine District: Bull. 

 University of Texas Mineral Survey No. 8, 1904, pp. 11-25. 



Am. Jour. Sci.— Fourth Series, Vol. XXIX, No. 172.— April, 1910. 

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