330 Richardson — Stratigraphy of the upper Carboniferous 



which is at least 1,800 feet thick. The stratigraphic position 

 of these formations is not determinable in Texas, but their 

 position in the upper Carboniferous section is shown in the 

 northern part of the Guadalupe Mountains in New Mexico 

 and will presently be referred to. On the eastern flanks of 

 the Delaware Mountains, which constitute virtually a dip slope, 

 the Capitan limestone is missing — presumably either because 

 of non-deposition or erosion — and the Delaware Mountain 

 formation is directly overlain by a mass of bedded gypsum. 

 This deposit, named the Castile gypsum, is approximately 300 

 feet thick and covers an area of several hundred square miles. 

 The gypsum is overlain by magnesian limestone and associated 

 lenses of sandstone, in all about 200 feet thick, which have 

 been named the Rustler formation. The section is here inter- 

 rupted by Quaternary deposits in Pecos Valley, but occasional 

 outcrops of red beds, which overlie the Rustler formation, are 

 locally exposed and it is evident that both the Castile gypsum 

 and the Rustler formation are members of the red bed com- 

 plex that underlies the valley of Pecos River. 



Red Beds of Pecos Valley. 



The red beds of Pecos Valley were examined in 1891 by 

 W. F. Cummins,* and they have been studied in the vicinity 

 of Roswell by C. A. Fisher, f but thick deposits of unconsoli- 

 dated Quaternary debris conceal complete exposures and com- 

 paratively little is known of them. They consist of a group 

 of vari-colored sandstone and shale, red predominating, inter- 

 stratified with beds of magnesian limestone and gypsum. In 

 detailed study it is desirable to divide these rocks into a num- 

 ber of formations of comparatively limited extent similar to 

 the Castile gypsum and the Rustler formation, which when 

 traced for a number of miles beyond the area in which they 

 were named, lose their individual character and become diffi- 

 cult to recognize as such. The formations of the red bed 

 group are lenticular in character but the group as a whole is a 

 distinct unit. 



Measurements of thickness are practically impossible to 

 obtain short of drilling, and as yet no hole has been sunk 

 through the entire group. Minimum figures, however, are 

 afforded by two deep wells ; one, sunk by Capt. John Pope in 

 1855-57, about ten miles east of where Delaware Creek enters 

 Pecos River in ISTew Mexico near the Texas boundary, was 

 1,050 feet deep and appears to have been in red beds all the 



* Cummins, W. F., Notes on the Geology West of the Plains : Third Ann. 

 Rept. Geol. Survey of Texas, 1892, pp. 201-218. 



f Fisher, C. A, Geology and Underground Waters of the Eoswell Artesian 

 Area, New Mexico : Water Supply Paper TJ. S. Geol. Survey, No. 158, 1906. 



