104 ENVIRONMENT OF VERTEBRATE LIFE, ETC. 



Descriptions are given by Udden^ of the beds of certain deposits of 

 Permo-Carboniferous age in Trans-Pecos Texas: 



"The Shafter Region, Presidio County, 

 "the cibolo beds. 



"The rocks which represent the Permian have been called by Udden the 

 Cibolo beds, and they have been subdivided by the same author from below to 

 above in: Transition beds. Lower Brecciated Zone, Zone of Sponge Spicules, 

 Thin-bedded Zone, and Yellow Limestone. 



" Transitioti Beds. — Gray marly shale with lenticular ledges of organic and 

 siliceous sand. Their thickness is about lOO feet. 



"Lower Brecciated Zone. — Grayish-white limestone in heavy ledges often 

 thoroughly brecciated. The thickness is about 133 feet. 



"Zone of Sponge Spicules. — In the lower part, this consists of thinner-bedded 

 limestone. Above it becomes siliceous and changes into pure sandstone. The 

 thickness of this bed is 85 feet. 



" Thin-bedded Zone. — Dark, evenly bedded and compact limestone, including 

 some sandy strata. The limestone contains cherty material which weathers 

 out in rusty edges of plates of irregular shape, or porous spherical shells and 

 nodules. Much of the rock is bedded in uniformly thin ledges; occasionally the 

 ledges thicken lenticularly. Thickness, about 470 feet. 



" Yellow Limestone. — Hard, yellow, siliceous, and dolomitic limestone, showing 

 bedding planes only in the lower part, while higher up the stratification becomes 

 indistinct. Thickness, about 650 feet. 



"This series has been observed on Cibolo Creek near the Chinati Mountains 



west of Shafter. 



"The Marathon Region. 



"The Permian is very well developed in the Glass Mountains. It has been 

 subdivided by Udden in four formations, which are, from below to above, the 

 Leonard, Word, Vidrio, and Gilliam. The lower formations are found in the 

 southern and southeastern hills, while the upper ones — the Vidrio and Gilliam 

 formations — occupy the center and the whole northern slope. Towards the 

 southwest the continuation of this Permian is found in the Altuda Mountain 

 and south of it, in the Ord Mountain Range. Toward the north we find an 

 isolated outlier in the Sierra Madre. The highest parts of the Permian are 

 covered unconformably by the Comanchean Cretaceous. * * *. 



" WORD FORMATION 



"In the upper part this is composed of thin- and thick-bedded gray and 

 yellow to reddish limestone, in part dolomitic, containing chert concretions with 

 some interbedded strata of sandstone (about 380 feet) ; below this we find some 

 120 feet of yellow sandstone, in part laminated. The lowest part of this formation 

 consists of 120 feet of heavy-bedded gray limestone, with chert concretions. 

 The entire thickness of this formation is approximately 600 feet. 



"VIDRIO FORMATION. 



"This series is composed of a very uniform, dark to light gray, dolomitic 

 limestone, or dolomite, with very few layers of pure limestone. The dolomite 



^ Udden, J. A., Review of the Geology of Texas, Bull. University of Texas No. 44, p. 50, 1916. 



