GLACIERS OF THE CANADIAN ROCKIES AND SELKIRKS. 83 



flows westward between the Asulkan and Dawson ranges. The collecting 

 basins for the Illecillewaet and Yoho glaciers are almost equal in size, but the 

 estimated precipitation over the former is 41 per cent, greater than over the lat- 

 ter, giving a correspondingly greater volume of ice to be disposed of. This ena- 

 bles the Illecillewaet to attain a much lower altitude, as previously pointed out. 

 The mean elevation of the surface of the neVe" lies between 8,000 and 8,500 

 feet above sea level; ranging from 7,500 to 9,500 feet, not essentially different 

 from the Yoho neve. In the central portion the nevd is much crevassed, from 

 which one may infer that the thickness of the snow and ice is not great in the ba- 

 sin. The surface is covered with parallel ridges and furrows, probably result- 

 ing from the rippling action of the wind while the snow was being deposited. 

 These ridges when frozen render the walking somewhat difficult and treacherous. 



3. MORAINES. 



a. Surface debris. Because of the wide extent of the neVe" field and the 

 absence of precipitous cliffs about the margins, there is very little opportunity for 

 the ne"ve" to acquire any rock debris. There is no evidence that any considerable 

 quantity is gathered from the bed and carried subglacially, or englacially. It 

 may be that the basal layers in the neVe" region are sluggish, or even stagnant, 

 and that only the upper layers are being pressed out over the rim of the basin. 

 The result of this lack of debris in the neVe" is that the general surface of the 

 glacier, as in the case of the Yoho, is unblemished with rock fragments, but is 

 somewhat soiled from wind-blown dust concentrated over its surface by melting. 

 Some dust wells occur sparingly and a few poor examples of glacial tables. 



b. Left lateral moraine. Along the western margin of the glacier fed by 

 the ordinary atmospheric agencies of rock decay operating upon the cliffs of 

 Glacial Crest and Mt. Lookout, there has been built up a high, sharp- 

 crested, left lateral moraine. The angular rock fragments are supplied 

 mainly by two prominent debris cones, which have formed upon the eastern 

 face of Glacier Crest and which rest with their bases upon the margin of the ice, 

 the forward movement of which has distorted the cones down stream, plate xxxn. 

 In the summer rocks may be seen coming down these slopes, one block starting 

 others and these still others, until a regular cannonading is in progress. As one 

 rock collides against another with terrific force, small clouds of dust arise and 

 we have simulated not only the roar but the smoke of 'battle. John Muir has 

 given us a graphic description of the streaks of fire to be seen when these ava- 

 lanches occur at night. In the way previously described for the Victoria (page 

 47) this material arranges itself in the form of a sharp-crested ridge perhaps 

 100 feet above the margin of the ice and 150 feet above the valley floor. The 

 melting of the ice core upon the inner slope makes it steep and unsteady, while 

 the outer has settled into a condition of more stable equilibrium and is being 

 slowly covered with vegetation. Upon the inner slope occasional slides of the 

 rock veneering occur, by which the ice core is temporarily exposed. The materials 

 from the upper part and sides of the scar produced roll and slide down, collecting 



