xc GENERAL SUMMARY OF SCIENTIFIC AND 



of quartzites, conglomerates, and slates ; attaining in the Wahsatch 

 12,000 feet in thickness, and, so far as known, destitute of fossils, 

 with the exception of about seventy-five feet of impure limestones 

 and shales at the top, which contain a ftiuna designated as Potsdam. 

 In Middle Nevada, however, this thin fossiliferous layer is expanded' 

 to at least 3000 feet of dark-colored limestones, carrying throughout 

 a Lower Cambrian fauna ; while in the Rocky Mountains, to the ex- 

 treme east, these strata thin out, and never exceed 100 feet. 



THE UTE LIMESTONE. 



Immediately overlying these Cambrian shales is what is named the 



Ute limestone which, from 1000 feet to the southward, attains 2000 



feet in the Wahsatch ; while in Western Nevada, where the calcareous 



strata of the Potsdam are greatly thickened, we have 4000 or 5000 



feet of limestone. In the Wahsatch the middle part alone of this 



limestone has yielded fossils, which are of Quebec (that is, of Levis 



or Tremadoc) age, while the great calcareous mass farther west has 



more than one half its volume of so-called Primordial or Potsdam 



age, and a portion of Levis ; a large part contains forms of Niagara, 



followed by Lower Helderberg, the precise limits of these not being 



yet defined. 



THE WAHSATCH LIMESTONE. 



Succeeding this is the Wahsatch limestone, having a thickness of 

 7000 to 8000 feet, and containing faunas of Devonian (Upper Helder- 

 berg and Chemung) age. This is separated from the Ute limestone 

 by the Ogden quartzite, a green or white sandstone sometimes 

 schistose and at other times conglomerate which in dificrent local- 

 ities varies from IGOO to 700 feet in thickness, and in some parts is 

 wanting, or represented only by silicious impurities in the limestone. 

 It is regarded as the representative of the Schoharie and Cauda-galli 

 grits of New York. The base of the Wahsatch limestone presents in 

 some localities an intermingling of Lower with Upper Helderberg 

 forms making as yet somewhat uncertain the horizon between 

 Silurian and Devonian. Black slates, which in one locality overlie 

 the Chemung limestone, are supposed to be equivalent to the Genesee 

 group, above which are beds holding a Waverley or Upper Devonian 

 fauna. Still higher in the Wahsatch limestones occur Lower Car- 

 boniferous, followed by true Coal-measure forms. This vast body of 

 limestone above the Ogden quartzite thus contains from 1000 to 1400 

 feet of Devonian, from 1000 to 1200 of sub-Carboniferous and Waver- 

 ley, and from 4000 to 4500 of true Carboniferous. 



THE WEBER QUARTZITE. 



To this succeeds the Weber quartzite, which in the Wahsatch has 

 a thickness of 6000 feet, increasing to 9000 or 10,000 feet in the 

 Oquirrh, and probably to even a greater volume in Western Nevada. 



