322 GEOLOGIC TIME. 



bia. Eoughly computed, it covered, tsoutli of the fifty-fifth parallel, 

 400,000 square miles, exclusive of any extension westward into north- 

 ern-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 contrac- 

 tion 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 Paleozoic rocks has probably been rednced 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 close of the Appalachian 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.! 

 Further to the west, 250 miles west-southwest, at Eureka, ISTev., there 

 are 30,000 feet of strata in the entire section, and of this amount 10,000 

 feet are referred to limestone.f In tlie Pahranagat range and vicinity, 

 200 miles south of the Eureka section, § the limestones of the Paleo- 

 zoic measure over 13,000 feet in a section of lo,500 feet. This section 

 includes 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, f] This does not include the 0,000 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- 

 ward, in Idaho. Continuing to the north 450 miles, the sections meas- 

 ured by Mr. E. G. McConnell give 29,000 feet of Paleozoic strata, 

 including 14,000 feet of limestones.** In a " Note on the Geological 

 Structure of the Selkirk Eange," Dr. (ieo. M. Dawson describes a sec- 

 tion containing upwards of 40,000 feet of mechanical sediments, which 

 he refers largely to the Cambrian.tt 



The Paleozoic limestones extend to the north, on the line of the east- 

 ern Eocky Mountains, to the Arctic Ocean. In latitude oo° to CO^ 

 north, the Devonian limestones are over 2,500 feet in thickness, and 

 there are other still lower Paleozoic rocks that have not yet been 

 studied in detail. The Devonian limestones extend 700 miles in the 

 valley of the Mackenzie, from Great Slave Lake to below Fort Ciood 



""Bnll. Geol. Soc. Am., 1891, vol. ii, p. 176. 



iGeoL Expl. Fortieth Parallel, 1878, vol. i, pp. 15.>-156. 



\Mon. U. S. Geol. Survey, 1892, vol. xx, p. 178. 



^Loc. 0(7., pp. 186-200. 



II Geol. and Geog. Surveys west of 100th Merid., vol. iii; 1875, Geology, p. 167. 



^ Author's manuscript. 



"* Geol. and Nat. Ewt. Sur., Can.; Ann. Rep., 186C.. pp. 17D-30D. 



\\Bull, Geol, Soc, Am., 1891, vol, n, p. 168, 



