m 



West Texas and Southeast New Mexico. 329 



nent and finally disappears and the top of the Manzano group 

 is marked by an erosional unconformity above which are strata 

 of unknown age. Numerous fossils, which are described by 

 Dr. G-irty in the bulletin above referred to, have been found 

 in the Manzano group, those occurring in the several forma- 

 tions being not radically different. They are referred to the 

 Pennsylvanian and the Manzano group is correlated with part 

 of the Hueco formation. 



Section in west Texas north of the Texas and Pacific Rail- 

 way (No. 2, figs. 1 and 2). — One of the thickest sections of the 

 upper Carboniferous in the area considered in this paper is 

 exposed in Texas between the western escarpment of the Staked 

 Plains and the Rio Grande. Although this section is not com- 

 plete, being interrupted by faults and by a local unconformity, 

 it is more than 10,000 feet thick. 



The lower part of the section consists of the Hueco forma- 

 tion, which underlies an area of several hundred square miles 

 and outcrops in the Hueco. Franklin, Finlay, Cornudas and 

 Sacramento mountains and in the Sierra Diablo. It is in many 

 areas mainly limestone but in other areas consists also of shale 

 and sandstone, including red beds, and in places a basal con- 

 glomerate is well developed. A well recently sunk in the 

 Hueco formation in the drift-covered area between the Sierra 

 Diablo and the Cornudas mountains, about 40 miles north of 

 Sierra Blanca, is reported to have encountered a thin deposit 

 of red beds intercalated in the prevailing limestone. This is of 

 interest in the correlations discussed below (p. 335). Exact 

 measurements are difficult to obtain, but in Texas the Hueco 

 formation is approximately 5,000 feet thick. Wherever 

 exposed, the base of the Hueco lies unconformably on rocks 

 ranging in age from pre-Cambrian to Silurian. Over wide 

 areas the top of the formation has been eroded ; locally the 

 Hueco is overlain by Lower Cretaceous strata and relations 

 to higher rocks in the Carboniferous section are completely con- 

 cealed in Texas by the bolson plain known as Salt Flat. 



The Hueco formation bears a rich Pennsylvanian fauna 

 which Dr. Girty states is widely distributed over the Western 

 States and which he provisionally correlates with the fauna of 

 the Aubrey group in Arizona, etc. 



The upper Carboniferous section is continued east of the 

 Salt Flat bolson, in the Delaware and Guadalupe Mountains, by 

 4,000 feet of strata which contain Girty's* Guadalupian fauna. 

 These rocks have been separated into the Delaware Mountain 

 formation, consisting of 2,200 feet of variable beds of sand- 

 stone and limestone, and the overlying Capitan limestone, 



* Girty, George H., The Guadalupian Fauna: Prof. Paper U. S. Geol. 

 Surrey, No. 58, 1908. 



