THE TRIASS1C PERIOD. 



25 



Throughout most of this area, the Triassic beds are red, and in the 

 absence of fossils, and of structural unconformity, are not readily differ- 

 entiated from the Permian below. 1 



In Texas the beds generally regarded as Triassic underlie the 

 'Staked plains" of the western part of the State, and outcrop along 



Fig. 335. — Triassic sandstone five miles south of Lander, Wyo., showing characteristic 



cross-bedding. (Branson.) 



their eastern base. The deposits of this locality show that the water 

 in which they were laid down was shallow and fresh, and the belief 

 is that the sediments entered it from the east. 2 



In the Black Hills of South Dakota 3 unfossiliferous, gypsiferous 

 beds (Spearfish) which are believed to be Triassic overlie the Permian 

 conformably, 4 and underlie the Jurassic unconformably. The rela- 

 tions of the Triassic to the Permian and Carboniferous indicate that 

 though the interruption of sedimentation at the close of the Paleozoic 

 era was by no means complete in this part of the continent, the marine 

 sedimentation of the earlier era gave place to salt-lake sedimentation 

 in the later. 



A series of nearly unfossiliferous strata, among which are many 

 " Red beds " occupying the stratigraphies! position of the Triassic 

 system, outcrop interruptedly along the eastern base of the Rockies 

 from British America to New Mexico. These beds are thin, and nearly 

 everywhere contain more or less gypsum and sometimes salt. Occa- 



1 The Red Beds of Kansas, formerly thought to be Triassic in part, are probably 

 all Permian (Williston). The opposite view is advocated by Prosser, University of 

 Kansas Geol. Surv., Vol. II. 



2 Geol. Surv. of Texas, 1896, pp. 227-234. 



3 Newton, Geol. of the Black Hills, U. S. Geol. Surv. 



*Darton, 21st Ann. Rept. U. S. Geol. Surv. Also Oelrichs and Edgemont, 

 S. D.-Neb., New Castle, Wyo.-S. D., and Hartville, Wyo., folios, U. S. Geol. Surv. 



