660 THE JOURNAL OF GEOLOGY. 



ence of spicule of sponges, and what appear to be worn frag- 

 ments of some small fossils. There is absolutely nothing to indi- 

 cate more rapid denudation and corresponding- deposition in this 

 early pre-Cambrian series than we find in the Paleozoic, Mesozoic 

 or Cenozoic formations. 



PALEOZOIC SEDIMENTS OF THE CORDILLERAN SEA. 



The great sections of sedimentary rocks in Arizona, Nevada, 

 Utah, Montana, and in Alberta, B. A., all bear evidence that the 

 sediments of which they are built up were deposited in a con- 

 nected and continuous sea that extended from the vicinity of the 

 34th parallel, on the south, to the Arctic ocean on the north. 

 Judging from the data now available, the width of this sea varied 

 from 300 miles in Nevada to 500 miles on the line of the 40th 

 parallel, and, with interruptions by mountain ridges, to 250 miles 

 on the 49th parallel. It appears to have narrowed to the north 

 in Alberta, British Columbia. Roughly computed, it covered 

 south of the 55th parallel 400,000 square miles exclusive of any 

 extension westward into northern-central California and south- 

 western Oregon and to the eastward over the area subsequently 

 covered by the great interior Cretaceous sea. There is also an 

 addition that might be made to allow for the contraction of the 

 area by the later north-and-south faults and thrusts. Dr. G. M. 

 Dawson estimates that in the Alberta and British Columbia area 

 the width of the zone of the Paleozoic rocks has probably been 

 reduced one-half by the folding and faulting, or from 200 to 100 

 miles. J This area assumed for the Cordilleran sea is on this account 

 probably one-half less than it was before the Appalachian revolution. 

 The Wasatch section, on the eastern side of the area under 

 consideration, has 30,000 feet of strata, of which 10,400 feet are 

 limestone. 2 Further to the west, 250 miles W.S.W., at Eureka, 

 Nevada, there 30,000 feet of strata in the entire section, and of 

 this amount 19,000 feet are referred to limestone. 3 In the Pahran- 

 agat range and vicinity, 200 miles south of the Eureka section, 4 



''Bull. Geol. Soc. Am., Vol. 2, 1891, p. 176. 



2 Geol. Expl. Fortieth Parallel, Vol. 1, 1878, pp. 155-156. 



3Mon. U. S. Geol. Survey, Vol. 20, 1892, p. 178. 



4 Loc. cit. pp. 186-200. 



