ADVANCE AND RETREAT OF CANADIAN GLACIERS 733 



may acquire steep sides as well as steep ends by this breaking off 

 process. When the rock sides are higher than the f^oor beneath the 

 ice, the sides of the cliff glaciers are buried' in snow, and so, either 

 actually or apparently, are not steep.' In the valley glaciers the steep 

 end has some other cause which appears to result from a combination 

 of shape and manner of melting. 



These glaciers of the central and eastern 

 Rockies remain approximately constant in thick- 

 ness, melting on the surface at their upper ends, -^^^^ ^■ 

 and beneath the surface at their fronts. The regions of accumu- 

 lation and of maximum surface melting are similar. Fig. 8 shows 

 diagrammatically the front of one of these glaciers. The upper 

 layers are protected from melting, hence remain intact at the front, 

 while the melting of the lower layers leads to the formation of a cliff 

 and of an angle between surface and front. Glaciers of the ordinary 

 alpine type push forward, at a high gradient, from a region of per- 

 petual snow, melting at the surface and thinning toward their lower 

 ends. Fig. 9 represents the front of one of these glaciers. The end 

 slope may be as steep in the second case as in the first, but there is 

 invariably the difference that among these glaciers there is a gradual 

 curve from surface to end, while among those of the first group there 

 is a sharp angle between a nearly horizontal 

 surface and a nearly vertical front. The slope 

 of the front of the second type of glaciers is 

 determined in part by the gradient of their 

 beds, in part by the rapidity of surface melt- 

 ^^' ^' ing at the front. Among glaciers of the first 

 type, slope and surface melting are both at a minimum, and the angle 

 of the front is determined by rate of sub-surface melting. 



Steep sides as well as steep ends are characteristic of high-latitude 



I Cliff glaciers were defined by Salisbury in this Journal, 1895, p. 888. The 

 cliff glaciers -in Alberta are of a shghtly different type from those described from 

 Greenland. They form in essentially the same way, but the ends of the Canadian 

 cliff glaciers usually push over the ends of precipices and break off, leaving several 

 hundred feet of vertical ice which forms an ice-cliff above the rock cliff. Those figured 

 by Salisbury appear to end like steep alpine glaciers. Another point of difference is 

 that these Canadian chff glaciers lie on the general slope of the mountain and are 

 much broader than they are long, while those in Greenland lie in steep gullies. 



