70 SEDIMENTARY GROUPS OF THE PLATEAU PROVINCE 



UINTA GKOUP. 



The Uinta Sandstone rests unconformably upon the Red Creek Quartz- 

 ite; ten thousand feet of its upper members are deposited unconformably 

 against that metamorphic group. It is evident, also, that the metamorphism 

 was anterior to the deposition of the Uinta Group, for the beds of the latter, 

 especially near the junction, are chiefly made up of fragments of the former; 

 hence the unconformity is very great. 



The period of erosion separating the sandstones from the Carboniferous 

 beds above was sufficient to carry away at least 3,000 feet of the Uinta 

 Sandstone in some places. How much more was carried away we cannot 

 say. To my mind this suggests that the Uinta Sandstone may be considered 

 Devonian an opinion which I would yield upon the slightest paleontologic 

 evidence to the contrary. 



GRAND CANON GROUP. 



The Grand Canon Group rests uncomformably upon the crystalline 

 schists. The evidence of this is complete, for the lower sandstones and 

 conglomerates first filled the valleys and then buried the hills of schistic 

 rocks, and these conglomerates at the base of the group are composed of 

 materials derived from the metamorphic hills about ; and hence metamor- 

 phism was antecedent to the deposition of the conglomerates. 



The plane of demarkation separating this group from the Tonto Group 

 is very great. At least 10,000 feet of beds were flexed and eroded in such 

 a manner as to leave but fragments in the synclinals. Then followed a 

 period of erosion during which beds of extravasated material were poured 

 .over the fragments, and these igneous beds also were eroded into valleys 

 prior to the deposition of the Tonto Group. 



Fossils have been found at the base of the Grand Canon series, but 

 they are not well preserved and little can be made of them. . Still, on geo- 

 logical evidence, I am of the opinion that these beds should be considered 

 Silurian. 



RED CREEK QUARTZITE AND GRAND CANON SCHISTS. 



These are believed to be Eozoic. 



