GEOLOGIC TIME. 66 1 



the limestones of the Paleozoic measure over 13,000 feet in a 

 section of 13,500 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. 1 



On the eastern side of the area, in Montana, 300 miles north 

 of the Wasatch section of Utah, the deposit of Paleozoic sedi- 

 ment is less in volume. Dr. A. C. Peale's section gives 3,800 

 feet of limestone in 5,000 feet of strata. 2 This does not include 

 the 6,000 feet or more of sediments that occur below the fossilif- 

 erous Cambrian. I believe that the Paleozoic section will be 

 found to be considerably thicker to the westward in Idaho. 

 Continuing to the north 450 miles, the sections measured by Mr. 

 R. G. McConnell, give 29,000 feet of Paleozoic strata, including 

 14,000 feet of limestone 3 . In a " Note on the Geological Structure 

 of the Selkirk Range," Dr. Geo. M. Dawson describes a section 

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

 he refers largely to the Cambrian 4 . 



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

 the eastern Rocky Mountains, to the Arctic ocean. In latitude 

 55 to 60° N. the Devonian limestones are over 2,500 feet in 

 thickness, and there 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 Good Hope. 5 No Carboniferous limestones 

 have been described from this region. 



Tabulating the sections south from the 55th parallel and 

 allowing for a great thinning out of the sediments in Idaho and 

 Montana, we obtain an approximate general average of 21,000 

 feet of strata, of which 6,000 feet are limestone over an area 

 estimated to include 400,000 square miles. Each square mile 



I Geol. and Geog. Surveys West of 100th Merid., Vol. 3; Geology, 1875, P- l ^>7- 



2 Author's manuscript. 



3 Geol. and Nat. Hist. Sur. Canada ; Am. Rep., 1866, pp. 17, D-30 D. 

 "Bull. Geo. Soc. Am. Vol. 2, 1891, p. 168. 



5 Rept. Expl. Yukon and Mackenzie Rivers Basins, N. W. Terr. Geolo. & Nat. 

 Hist. Sur. Canada, Vol. 4 (i888-'89), 1890, pp. 13 D-18 D. 



