624 



GEOLOGY. 



arated Permian between. In northern Arizona, however, and in south- 

 western Colorado, 1 and perhaps at other points, there is an uncon- 

 formity at the base of the Trias. 



If the beds tentatively referrred to the Permian be really such, 

 they show that the relatively continuous and clear seas of the Pennsyl- 



Fig. 288. — A butte composed largely of Permian rock, Northern Arizona (Dutton, 



U. S. Geol. Surv. 



vanian period in this region had given place to much shallower and 

 less continuous bodies of water, often of more than normal salinity, 

 and that at many points there were interruptions of sedimentation 

 at the close of the Pennsyl vanian. 



Red Beds, generally classed as Triassic, occur even north of the 

 United States. 2 Their thickness is not great, and they perhaps belong 

 with the Red Beds farther south, most of which are now usually classed 

 as Permian. 3 



The Permian deposits of the far west, as well as some of those of 



1 Cross, unpublished evidence. 



2 Dawson, Bull. Geol. Soc. Am., Vol. XII, p. 74. 



3 Some of the upper Red Beds of central Wyoming are thought to be Triassic 

 (Williston) on the basis of fossils collected by Knight and Branson. The horizon 

 of the Triassic fossils is 550 feet above the base of the Red Beds, and 250 feet below 

 the top. 



