452 MINING INDUSTEY. 



beds of quartzite and rough grit. A more minute subdivision of this group 

 is carefully discussed in the earlier volumes. Overlying these limestones is the 

 Triassic series, composed through the lov^^er tw^o-thirds of quartzite, passing 

 upward into fine siliceous limestones, and finally into heavy beds of dolomitic 

 limestones 1,800 feet thick. Above this and closing the Triassic series are 

 further developments of siliceous lime-beds, capped by very typical red sand- 

 stone, which forms an excellent datum-point in a description and study of the 

 whole region. Overlying this again are alternate limestones and quartzose 

 beds, which are here and there replaced by argillaceous and calcareous 

 strata, forming a group in which lime, clay, and sand mingle themselves in 

 extremely varied proportions. With these the conformable group ceases, and 

 here the rock of the old Wahsatch Range may be said to end. To the west 

 no others are superimposed upon their bases, but upon the eastern side a 

 series of Cretaceous and Tertiary deposits are laid down unconformably. 



From the Wahsatch to the Sierra Nevada there is no evidence of marine 

 rocks subsequent to the Jurassic. Indeed, the whole great basin is a system 

 of folds of the infra-Jurassic rocks, whose accidental depressions and whose 

 broad, continuous synclinals are more or less filled with the fresh wafer Ter- 

 tiary deposits, which indicate a former system of fresh-water lakes. No- 

 where along the west side of the Wahsatch has any trace of Cretaceous forma- 

 tions been found. The only beds more recent than the Cordillera group are 

 certain calcareous and sandy strata, in which are found large quantities of 

 fresh water fossils, both of mollusks and vertebrate life. The mammalian re- 

 mains indicate a fauna similar to, if not identical with, that which has been 

 so thoroughly described in the papers of Meek, Hayden, and Leidy on the 

 Niobrara and White River formations. Besides these are a few stratified, 

 volcanic deposits, chiefly tufas of the Rhyolite and Trachyte periods. Subse- 

 quently to those nothing is found, except the Quaternary deposits, which, over 

 the whole west, mark the post-glacial erosion. 



The Wahsatch, then, is the dividing line between the Central and the At- 

 lantic geological systems. It was the westward barrier to the Atlantic Creta- 

 ceous formation. The ocean, during the Cretaceous, so far as v^^e know, never 

 penetrated that region which is called the Great Basin. The rocks of that 

 period are made up of about 9,000 feet of cream-colored and buff sandstones 



