walcott.J UTAH AND NEVADA. 157 



A reconnaissance of the northwestern portion of the Wasatch Moun- 

 tains in Utah was made by Prof. P. H. Bradley in 1872. He found that 

 the crest and eastern slopes are composed of quartzite and limestone. 



The former, a white and ferruginous quartzite, 1,500 feet in thick- 

 ness, was referred to the Potsdam, and a band of superjacent gray 

 calcareous shale, 1,000 to 1,200 feet thick, to the Lower Silurian. The 

 section as arranged by Prof. Bradley is as follows : 1 



3. Blue and gray ruagnesian limestones, partly pebbly, \ Upper ? and 



1,900 to 2,000 feet > Lower 



4. Gray calcareous shales, 1,000 to 1,200 feet ; Silurian. 



5. White and ferruginous quartzite, base pebbly, 1,500 \ 



feet * ^Potsdam. 



Under the title of " Paleozoic subdivisions of the fortieth paral- 

 lel" Mr. Clarence King describes the strata referred to the Cambrian 

 system. This includes 12,000 feet of quart zites and argillites in the 

 Big Cottonwood Canon section of Utah, superjacent to which is a shaly 

 zone some 75 feet in thickness, carrying well defined Primordial fossils. 

 He says : 



Comparing the quartzites and argillites with those of the Cambrian section in 

 Wales, the likeness is too great to pass unnoticed, and in view of the enormous de- 

 velopments of these low-lying" rocks, as compared with the Silurian lying above the 

 Primordial horizon, I have determined to draw a line at the upper limit of the Pri- 

 mordial period to include the uppermost members of the Potsdam epoch and to con- 

 sider the whole underlying conformable series as Cambrian down to the point of 

 their nonconformity with the Archean. In the extreme east of our work, in the re- 

 gion of the Rocky Mountains, the Cambrian formation is of variable thickness and 

 nowhere reaches an exposure of over 100 feet. Iu middle Nevada the uppermost zone 

 of the Cambrian, equivalent to the calcareous and argillaceous shales of the 

 Wahsatch, is an immense body of dark limestones at least 3,000 feet in thickness 

 carrying Primordial fossils throughout; the downward continuation of the series 

 being there entirely hidden by the overlying Quaternary desert. 2 



This general definition of the Cambrian is accompanied by a list of 

 the fossils described by Messrs. Hall and Whitfield. 



The Cambrian section of Big Cottonwood Canon referred to by Mr. 

 King is described by Mr. S.F. Emmons with more detail. 3 On the 

 west side of Box Elder Peak, near the little village of Call's Fort, in 

 a body of dark blue argillaceous slates in the lower portion of the Ute 

 limestone body, Mr. Emmons states that the following fossils of the 

 Quebec group were found: Dikelocephalus icasatchensis, D. gothicits, 

 Crepiccphalus (Loganellus) quadram, and Lingulepls ella.* In the sec- 

 tion on Muddy Canon, within 25 feet of the base of the series, occurs a 

 body of calcareous shales, interstratified with narrow beds of a dark, 



Explorations of 1872 ; United States Geological Survey of the Territories, under Dr. F. V. Havdcn ; 

 Snake River division. Am. Jour. Sci., 3d ser., vol. 6, 1873, p. 194. 



2 King, Clarence: Paleozoic subdivisions on the 40th parallel. Am. Jour. Sci., 3d ser., vol. 11, 1876, p. 

 476. 



3 Hague, Arnold, and S. F. Emmons : Descriptive Geology. U. S. Geol. Expl. of the Fortieth Par. j 

 vol. 2, 1877, pp. 366, 367. 



*Op.cit.,p.405. 



