I2O GLACIERS OF THE CANADIAN ROCKIES AND SELKIRKS. 



by Russell upon the Malaspina for the lakelets and boulder mounds, but it 

 applies also to the other features as well. Dust wells may persist through a 

 season, or a series of seasons presumably, the dirt patches to which they owe 

 their existence being continuously retained in the miniature wells. Although 

 very shallow at any one time, their total depth might measure many feet. From 

 wind action and small trickles of water more dust is being added slowly and in 

 time there may be enough to protect the bottom, instead of causing its melting. 

 The dirt now appears at the surface and the ice beneath melts less rapidly than 

 the unprotected adjacent ice, giving rise to a miniature cone, marking the original 

 site of the well. Such cones are found of various sizes and covered with dirt, 

 sand, or gravel. By lateral melting the slopes eventually become so steep that 

 the veneering slides off, or it may be washed down by heavy rains and distributed 

 about the base of the ice cone. The bare ice is now attacked by the sun and a 

 hollow is produced where the cone stood, about the rim of which stands more or 

 less of the material by which it was covered. This material rolls and slides back 

 into the depression as the sides are widened and steepened by melting. When 

 enough has been concentrated at the bottom and about the sides to prevent 

 further melting, the adjacent ice which has lost its protective cover, just in 

 proportion as the depression has gained, now melts away to a level with the 

 bottom and then still lower, causing the material collected in the basin to again 

 assume the form of the cone. The miniature examples of this action might pass 

 through these stages several times in the course of the season, while the boulder 

 mounds and lakelets would require many seasons for the completion of a single 

 cycle. In the case of a medial moraine, or a lateral resting upon ice of sufficient 

 thickness, the same stages may be passed through, except that when the material 

 is shed it assumes the form of a double ridge, between which the elongated 

 trough is developed and into which the de"bris may slide to produce a single 

 ridge again. In this way the superficial debris of a glacier may be subjected 

 to much tossing and bruising before it comes to rest in the frontal or ground 

 moraine. In the case of a debris-covered ice surface all that is necessary to start 

 the process is to have the material unevenly distributed, a little thinner or a 

 little thicker patch of foreign matter. 



7. ICE STRUCTURE 



a. Stratification. From a comparison of the thickness of the strata in the 

 Asulkan with the available records of snowfall it seems probable that the strata in 

 this glacier, as well as in the Illecillewaet and Yoho glaciers, represent the 

 annual accumulation of snow in the region. The fall snows are combined with 

 those of the following winter and spring, compacted by the summer's melting 

 and rainfall into a white, porous stratum of granular ice. At any given place 

 upon the ne"ve" by means of wind action a stratum may have gained, or lost in 

 thickness. Owing to the deposition of the snow in successive layers and the 

 periodic distribution of wind-blown rock debris, each stratum acquires a more 

 or less distinct lamination; conformable with the stratum itself. During the 



