176 THE IGE AGE IN NORTH AMERICA. 



In the chapter upon " Terminal Moraines " we will speak 

 of the extension of the Missouri coteau into British America, 

 as determined by Dr. George M. Dawson. But, while this 

 coteau is the limit of the heavier accumulations of Laurentian 

 drift, it is evidently not the limit of the extent of glacial ice, 

 for over an indefinite border to the west of it there is, accord- 

 ing to Dr. Dawson, a large percentage of Laurentian mate- 

 rial, amounting to nearly fifty per cent of the surface accumu- 

 lations, mingled with about the same proportion of quartzite 

 drift brought down from the Rocky Mountains by the numer- 

 ous streams originating in them. Dr. Dawson says that these 

 Laurentian and eastern limestone bowlders continue to occur 

 to within twenty-five miles of the base of the Rocky Mount- 

 ains, and up to a height of 4,200 feet above tide. The dis- 

 tance of these traveled blocks from the nearest part of the 

 Laurentian region is about 700 miles. Beyond this point, to 

 the west, eastern and northern rocks are not found. The 

 elevation of this marginal drift is about 2,000 feet above the 

 present height of the Laurentian plateau from which it came.* 



"To the westward, in the valleys of Flathead, Pend 

 D'Oreille, and Osoyoos Lakes, and of Puget Sound, are 

 massive deposits of drift, partly of northern and partly of 

 local mountainous derivation. The Pend D'Oreille and 

 Puget Sound deposits appear unquestionably to be tongues 

 of the drift of British Columbia, which, if not constituting 

 a continuous mantle, at least passes beyond the character of 

 simple local mountain drift." f 



In the Rocky Mountain region and to the westward there 

 were formerly extensive glaciers in Montana, Wyoming, 

 Colorado, Utah, Nevada, and California, where now they are 

 almost entirely absent. But the glaciation of this region was 

 never general. According to "Whitney, there are no signs 

 of ancient glaciers in western Nevada, though some of the 

 mountains rise to a height of 10,000 feet. In the east Hum- 



* See the " Quarterly Journal of the Geological Society," vol. xxxi, lS^S. 

 •f See Chamberlin, as above. 



