336 GEOLOGY. 



In Utah, the greatest glaciers were in the Uinta mountains, where within 

 an area about 80 miles long by 35 miles wide, there was an aggregate area of 

 about 1000 square miles of glacier ice. 1 Near the crest of the range, only nar- 

 row divides with steep slopes escaped glaeiation. Every considerable valley 

 of the range whose head had an elevation of 10,000 feet, contained a glacier. 

 In a few cases, the glaciers descended below the mountains into the open valleys 

 of the plateau below. The lowest altitude reached by any glacier in the range 

 was about 6500 feet, and the ice descended on the average about 1000 feet lower 

 on the south side than on the north, primarily because the catchment basins 

 on the south slope were larger. Individual glaciers attained a thickness of some 

 2500 feet. Glaeiation was less extensive in the Wasatch mountains, though 

 the number of glaciers there exceeded 50. The ice was still more limited in the 

 Bear River mountains of Idaho, just north of the Wasatch range. 



Glaeiation was of slight extent in the basin ranges of Nevada, though there 

 were several centers of glaeiation among the higher ranges. 



There were extensive glaciers in the Sierras. Under favorable conditions, 

 they descended to an altitude of 4500 feet, and at a few points even lower. 2 

 In few other places in the west were conditions so favorable either for heavy snow- 

 fall or for ready descent of the ice to low altitudes. 



These isolated areas of glaeiation are instructive as indicating the extension 

 of the requisite conditions beyond the limits of the great continental ice-sheets. 

 If, however, the plains have been elevated since, as the distribution of the Kee- 

 watin ice and some other facts suggest, the altitude both of the eastern moun- 

 tains of the Cordilleran system, such as the Bighorns, and of the limits of 

 glaeiation, were probably lower than now at the time of glaeiation. 



In Wyoming, Colorado, Utah, California, and Washington, the only places 

 where the glacial history of the western mountains has been studied in detail 

 the drift is referable to two or more glacial epochs, somewhat widely separated 

 in time. 



Island glaeiation. — The Island of Newfoundland seems to have 

 been a separate area of glaeiation. The same was probably true of 

 Nova Scotia, and evidence is presented by Canadian geologists that 

 the elevated peninsula between the Bay of Fundy and the lower St. 

 Lawrence shed ice northward and eastward as well as southward. 3 

 Greenland was glaciated somewhat more extensively than now, but 

 its glaciers appear never to have extended to the continent, as was 

 formerly conjectured. A little clriftless region in the Inglefield Gulf 



1 Atwood, unpublished data; also King, Geol. Surv. of 40th Parallel, Vol. I. 



2 California folios, U. S. Geol. Surv. 



3 Dawson, J. W. The Canadian Ice Age; Chalmers, Can. Rec. of Sci., 1899, and 

 Rept. Geol. Surv. of Can., 1885; Murray, Geology of Newfoundland. 



