GLACIERS OF THE CANADIAN ROCKIES AND SELKIRKS. 



6l 



filling of the lake bed here with glacial sediment and debris from the Mt. Fair- 

 view slide, to the extent, at least, of 50 to 60 feet. 



c. Lake Louise delta. After the ancient Victoria peiTnanently retreated from 

 the head of the lake, there began the fonnation, at the head of Lake Louise, of 

 a gravel, sand, and silt delta, which is a minimum measure of the amount of 

 glacial erosion that has since been taking place in the upper part of the valley. 

 This delta extends into the lake 400 feet, with an average breadth of about 300 

 feet, as shown upon the map, plate xx, that was prepared with a plane-table in 

 July, 1904. A shelf of fine sediment borders that portion above water and 

 then drops off rapidly, forming a layer of unknown thickness over the bottom 

 of the lake. Much of the delta is elevated but 10 to 12 inches above the 

 lake level and is under water during high water stages of the lake. Portions 

 of it are flooded during midsummer after periods of excessive melting. In this 

 way the delta is gradually growing in height. Low, broad levees line the 

 main stream. This comparatively small portion, which projects into the lake, 

 is simply part of a very much more extensive deposit of glacial silt, sand, and 

 gravel, which reaches up the valley for a distance oi \ to \ oi a. mile and has a 

 breadth of 500 to 600 feet. Over this very gradual slope the glacial drainage 

 courses in three rapid, turbid streams, which unite into a single channel, 40 to 

 50 feet broad and one to two feet deep. Grasses and moss cover the lower, 

 fiat portion of the deposit, close set willow and spruce the central part, and 

 isolated willows the upper gravelly region. The rock-slide from Mt. Fairview 

 has encroached upon the lake as well as the morainic dam at the foot of the 

 lake, upon which stands the chalet. Between this dam and the range of moun- 

 tains in the background lies the Bow River Valley, which supported a great trunk- 

 glacier, leading eastward from the mountains (plate xiv, figure 2). 



d. Lake Louise Valley. When the mountains were in process of making it 

 is very probable that this valle>' began as a sti-uctural feature either as a trough 

 between mountain folds, or from the opening of a joint in the rock strata. 

 Before the coming of the glaciers it is probable that ages of stream action, aided 

 by atmospheric weathering, deepened and broadened the original feature into a 

 V-shaped valley. With the advent of the perennial snowfields a new geological 

 agent entered, deepening the bed and broadening out the base so that the cross- 

 section of the valley, particularly the lower half, assumed the characteristic 

 U-shape of glacially excavated, or glacially modified valleys. An inspection of 

 the general views of the valley, such as plate i, shows a lower portion with steeply 

 inclined, nearly vertical walls, while the upper portion has more flaring walls, 

 the arms of a truncated v. This upper portion was glaciated to a height of about 

 9,000 feet above sea level, or some 3 ,000 feet above the valley floor, the walls being 

 smoothed and fluted and the spurs evenly truncated ; see the shoulder of Mt. 

 Fairview at the right in plate xix, figure 2. It is not improbable that these 

 more gentle, higher slopes represent portions of the original pre-glacial valley, 

 produced mainly by the action of weather and running water, and not very 

 materially modified by the ice. These slopes produced until they intersect may 



