8 GLACIERS OF THE CANADIAN ROCKIES AND SELKIRKS. 



three, or four, and especially numerous near the summits of the mountain 

 passes. These lakes show no regularity in fonn, or location, are usually shallow, 

 and frequently have neither inlet nor outlet. 



Second — Lakes dammed by terminal moraines. In the same class may be 

 included those dammed by alluvial cones, or deltas formed in preexisting lakes. 

 Third — Lakes lying in rock basins, excavated by former glacial action. 

 Fourth — A special type of lake, of which Lake Louise is an example, formed 

 just within the mouth of a tributary valley. These lakes are leaf-shaped and 

 from three to ten times longer than they are wide. They owe their existence 

 to the presence of a ridge of ground-morainic material, thrown across the mouth 

 of the tributary valley from the up-stream side and curving gently out into the 

 trunk valley. These ridges have apparently been formed beneath the ice_ 

 when the valleys caiTied glaciers, by the joint action of the tributary and titmk 

 glaciers. The lakes may be shallow and so filled with silt that they are reduced 

 to swamps, or, where the ice was especially active, as in the case of Lake Louise, 

 the depth may still be surprisingly great. As recognized by Wilcox, these 

 lakes may present a combination of the rock-basin and morainic-dam types. 



d. Alterations in drainage. In a region of the character above described, 

 exposed for countless ages to the effects of weather, water, and ice, marked 

 alterations in the drainage would be expected, such as reversals, stream capture, 

 and the migration of divides. A study of the Columbia-Kootenay Valley has 

 shown that the upper 200 miles of the Columbia flowed at one time to the south, 

 instead of encircling the Selkirks to the north as at present. This must neces- 

 sarily have been the case so long as that portion of the valley known as the 

 "Big Bend" was in possession of the ice. The withdrawal of the glaciers into 

 the tributary valleys would permit the present northward flow from the Columbia 

 Lakes while the Kootenay, flowing in the opposite direction in the valley to 

 the east, enters the main valley, approaches within one and one-half miles of 

 the head- waters of the Columbia, but completely skirts the Selkirks to the south 

 before joining it. Upon the opposite side of the Rockies attention has been 

 called by Dawson, McConnell, and Ogilvie to changes in the Bow and its tribu- 

 taries. The long, slender Lake Minnewanka Valley, near Banff, was evidently 

 the course of a prepleistocene valley that was occupied and modified by an ice 

 stream during the maximum period of glaciation of the region. Dawson con- 

 sidered this to mark the former course of the Bow, which was deflected to the 

 southeastward, along the strike of the soft Cretaceous shales, when the lake 

 valley was occupied by ice.' From barometric observations made by Dawson, 

 his assistant McConnell noted that the Ghost River opposite the Devil's Gap, 

 the mouth of the Lake Minnewanka Valley, is considerably higher than the valley 

 floor and concluded that the Ghost River turned and entered the mountains 

 through this vaUey, joining thus the Cascade and with it forming a tributary 



^Annual Report of Canadian Geological Survey for 1885, "Preliminary Report on the Physical and 

 Geological Features of that Portion of the Rocky Mountains between latitudes 49° and 51° 30'," 1886, 

 p. 141B. 



