THE CENOZOIC GROUPS. 161 



implication, and are usually considered to be metamorphosed sandstones, the 

 metamorphisin due to deep seated agencies ; but this quartzite is of very late 

 Cretaceous Age or may even belong to higher unconformable Tertiaries. 

 In either case the same strata on every hand are soft, comparatively friable, 

 granular sandstones ; they are immediately underlaid by great thicknesses of 

 sandstones of like characteristics. They have not been implicated or even 

 plicated. No extravasated material is found in the immediate vicinity to 

 which reference can be made as the origin of crystallization, and these beds 

 on Black Butte are more than 200 feet in thickness, and metamorphism from 

 contact with eruptive rocks, so far as my studies extend in this western coun- 

 try, is exceedingly slight, and indeed such slight change is rarely shown. 

 There is nothing in the surroundings to suggest metamorphism. 



Is it possible that conditions obtained here favorable to the deposition 

 of silica by chemical precipitation? This question has been often suggested 

 by facts observed at many other places in the Plateau Province. In my 

 remarks on the Uinta Group I mentioned that some of the sandstones were 

 quasi quartzites, and where such beds of quartzite are found the quartzite 

 structure is invariably local. The same beds traced laterally are typical 

 sandstones ; and above and below, soft sandstones and excessively friable 

 shales are found, and there is no local disturbance of these beds. They 

 have simply been displaced in the grand upheaval in common with the sand- 

 stones and shales; and if this lithologic characteristic is due to conditions of 

 deposition and have not been imposed by the agencies of metamorphism, at 

 what place in the table of sedimentary groups shall we begin to consider 

 quartzites to be products of metamorphism? At Black Butte the quartzite 

 is as high at least as the very summit of the Cretaceous; in the Uinta Mount- 

 ains the quartzites are low down in the Paleozoic series and these are sepa- 

 rated by nearly 30,000 feet of sedimentary accumulations. May we go one 

 foot farther down in the rocks, but across the great gap of unconformity, and 

 say that the Red Creek quartzites were such from original constitution? 



THE CENOZOIC GROUPS. 



This description of the geographic distribution of the Cenozoic Groups 

 will be confined to the region north of the Uinta Mountains, except in the 

 11 P G 



