THE PLAINS PROVINCE 103 



Apache Mountains, the lower part of the Guadalupe Mountains, and part of 

 the Wylie Mountains. It extends into New Mexico. 



"Capitan Limestone. 



"This formation is composed of a massive white limestone remarkably homo- 

 geneous in appearance. The entire thickness can not be determined, but it is 

 at least 1,700 feet. It is known only in the Guadalupe Mountains and extends 

 far into New Mexico. 



"Castile Gypsum. 



"This formation is in great part composed of a massive, white, granular 

 gypsum, but interbedded with it are thin beds of gray and yellow limestone and 

 dolomite, as well as thicker beds of the same rock and considerable masses of 

 gray, red, and green shales and marls. The thickness of this formation is not 

 exactly known, but two deep wells near Rustler Springs show that it can not be 

 less than 1,000 feet. The Castile gypsum forms a band about 15 miles broad, 

 west of the hills composed of the Rustler limestone ; toward the north the Castile 

 gypsum is found also east of the Rustler Hills, so that the breadth of the zone 

 increases to about 30 miles near the boundary of New Mexico. Some isolated 

 exposures are found on the west side of the Delaware Mountains. As far as 

 known, the Castile gypsum rests everywhere unconformably on the Delaware 

 formation. Some shale in this formation is sulphur-bearing in Culberson County. 



"Rustler Formation. 



"Compact, fine-textured, gray doldmitic limestone and dolomite, generally 

 quite heavy-bedded, compose this formation. At the base there is in most 

 places a considerable mass of light pink or yellowish brecciated limestone. In 

 the northern part of the region some yellow sandstone alternating with limestone 

 is developed below the brecciated limestone. The thickness of the Rustler forma- 

 tion has not been determined, but it must be at least several hundred feet. The 

 Rustler formation appears in a series of low hills extending from a point about 

 12 miles north of Kent to the boundary of New Mexico." 



It has been shown by Case^ that the red beds of upper Permian age in 

 western Texas do not extend across eastern New Mexico in the latitude of 

 Tucumcari and Las Vegas, and he has pointed out that the beds of Texas 

 and New Mexico that far north are parts of distinct provinces, a fact borne 

 out by his discovery of vertebrates similar to those occurring in Rio Arriba 

 County, New Mexico, near Socorro. It would, then, appear that the beds of 

 western Oklahoma (Whitehorse) are in reality above the Capitan limestone. 

 The difference in stratigraphic position, however, need not be alarming, as 

 in such beds the rate of accumulation might be at times exceedingly rapid. 



The suggestion of Beede that the elevation and erosion of the Delaware 

 and Capitan limestones was an occurrence quite similar to that occurring 

 in eastern central and eastern North America In the same general time 

 interval is very pertinent here. 



1 Case, E. C, The Red Beds Between Wichita Falls, Texas, and Las Vegas, New Mexico, 

 in Relation to Their Vertebrate Fauna, Jour. Geol., vol. xxii, p. 243, 1914; Carnegie 

 Inst. Wash. Pub. 207, p. 61, 191 5. 



