GLACIERS OF THE CANADIAN ROCKIES AND SELKIRKS. 55 



glacier, by means of the capillaries developed between the granules, leaving 

 the well free from water, but with its ice cover. Where pebbles, or small 

 dirt patches, are abundant, as shown in the last figure, the ice between the 

 adjoining wells is melted more rapidly by the sun than it would ordinarily be, 

 forms minute pinnacles and appears whitish and spongy. In this way the lower- 

 ing of the general surface of the glacier by ablation is accelerated. By keeping 

 itself thus at the bottom of a small well the dirt of these small patches is pre- 

 vented from being blown away, or washed away, and thus it is possible that the 

 same well may persist through, not only a season, but a succession of seasons. 

 Should the well, however, collect additional dirt, beyond a certain limit, this 

 excess would then protect the bottom of the well from further melting, the 

 adjoining ice would soon be lowered below the bottom of the well and the well 

 would be literally turned wrong-side-out. Where one has a few days to spare 

 about the same glacier an interesting experiment would be to sift dirt into a 

 group of typical wells, filling them to varying depths, and observing the result. 

 Such an experiment may easily be performed upon a snow bank of sufficient 

 depth, when it is being strongly acted upon by the spring sun. It would prepare 

 the way for a clear understanding of the next three surface features to be 

 described. 



h. Debris cones. When the amount of dirt, sand, gravel, or rock debris, 

 is sufficient to protect the surface of the ice from melting, or to even partially 

 protect it, over a limited area, the surrounding ice surface will be lowered 

 more rapidly than that beneath the protecting material and the debris will 

 begin to be elevated, with reference to the neighboring surface. The loose 

 debris will slide, or roll down about the side, exposing the edges and corners to 

 the melting action of the sun, allowing still more sliding of the debris and still 

 further melting. The ice core will finally assume the form of a ridge, cone, or 

 mound, with its thin veneering of foreign matter, as in the case of the lateral and 

 medial moraines already described. The companion figures 3 and 4, plate xvn, 

 show the structure of a small gravel cone, only 15 to 16 inches in height; figure 3, 

 as it was found upon the ice, figure 4, after the gravel upon one side had been 

 washed off to show the ice core. It is seen what a thin covering will suffice to 

 bring about the result. Depending upon the nature of the covering they are 

 known as dirt, sand and gravel cones, and boulder mounds, and they may vary 

 in height from a few inches to many feet. In plate xix, figure i is shown 

 a mound upon the Wenkchemna Glacier, estimated to be 80 feet high. This 

 pile of rock rubbish was either dumped in a heap by an avalanche, or collected 

 in the bottom of a lakelet, as described by Russell for the Malaspina in Alaska. 1 

 Cones of all types, varying in height, from a few inches to 12 or 15 feet are 

 to be found upon the Victoria in the region of maximum melting. They may 

 persist from one season to another, but there is a limit to the height to which 

 any particular cone may attain. As the height of the cone grows the lateral 

 surface is increased, over which the debris must be spread in order to suffi- 



1 Glaciers of North America, p. 115. 



