GEOLOGIC HISTORY 447 



Wasatch to the Black hills there was, however, a relatively small amount 

 of deposition in the aggregate from Cambrian to the Devonian, inclusive. 

 It was a period in which no marked earth movements developed. The 

 land areas were of considerable extent, but of low altitude, and the shore- 

 lines were extended or receded slowly, and no extensive series of sedi- 

 ments were laid down as compared with those of the Great Basin region. 

 With the beginning of the Carboniferous, however, there was a marked 

 change. The Mississippian sea transgressed as far as central and south- 

 ern Nevada, and in the -eastern Cordilleran region comparatively uniform 

 conditions of sedimentation prevailed to the close of the Trias. In the 

 Uinta region the Mississippian and overlying limestones, the Weber 

 quartzite or sandstones, the Permo-Carboniferous standstones and shales, 

 the Triassic sandstones, and the Jurassic limestones and shales were de- 

 posited. With the beginning of the Cretaceous the sea receded to the 

 Wasatch. To the- west of this range no later marine sedimentary record 

 is known. In the Wasatch and Uinta region a considerable thickness of 

 Cretaceous sediments was laid down. In post-Cretaceous time the great 

 orogenic movements were inaugurated which resulted in elevations giving 

 rise to the Uinta range and others to the east. Upon the flanks of these 

 ranges and in the depressions a great thickness of Tertiary sediments 

 was subsequently deposited. 



