Geologic Time. — Walcott. 35* 
I lind abundant evidence of the presence of spicule of sponges and 
•what appear to be worn fragments of some small fossils. There is ab- 
solutely nothing to indicate more rapid denudation and corresponding 
deposition in this early pre-Cambrian series than we find in the Paleo- 
zoic, Mesozoic or Cenozoic formations. 
Paleozoic Sediments of the Cordill,era>' 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 connected 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 availa- 
ble the width of this sea varies 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 
northward in Alberta and British Columbia. Roughly computed, it cov- 
ered, south of the 5oth parallel, 400,000 square miles, exclusive of any 
extension westward into northern-central California and southwestern 
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 Al- 
berta and British Columbia area the width of the zone of Paleozoic 
rocks has probably been reduced one-half by the folding and faulting, 
•or from 200 to 100 miles.* The area assumed for the Cordilleran sea is 
on this account probably one-half less than it was before the Appalach- 
ian revolution. 
The Wasatch section, on the eastern side of the area under consider- 
ation, has 30,000 feet of strata, of which 10,400 feet are limestone.t 
Further to the west, 250 miles W. S. W., at Eureka, Nevada, there are 
30,000 feet of strata in the entire section, and of this amount 19,000 
feet are referred to limestone.j In the.Pahranagat range and vicinity, 
200 miles south of the Eureka section,^ the limestones of the Paleozoic 
measure over 13,000 feet in a section of 15,500 feet. This section in- 
cludes only 350 feet of the upper beds of the lower quartzite series, 
which is upwards of 11,000 feet in thickness in the Schell Creek range 
of eastern Nevada. ' 
On the eastern side of the area, in Montana, 300 miles north of the 
Wasatch section of Utah, the deposit of Paleozoic sediment is less in 
volume. Dr. A. C. Peale's section gives 3,800 feet of limestone in 5,000 
feet of strata.** This does not include the 6,000 feet or more of sedi- 
ments that occur below the fossiliferous Cambrian. I believe that the 
Paleozoic section will be found to be considerably thicker to the west- 
*Bull. Geol. 8oc. Am., vol 2, 1891, p. 176. 
tGeoL Expl. Fortieth Parallel, vol. 1, 1878, pp. 155-136. 
iMon. V. S. Geo]. Surv.y, vol. 20, IMC, p. 17s 
SLoc. cit.,i>p. 1-15-200. 
< ted. and Geog. Survey* west of lOoth Merid., vol. 8; Geologj , 1875, p. 167. 
"Author's manuscript. 
