36 



GLACIERS OF THE CANADIAN ROCKIES AND SELKIRKS. 



forward, but they did not seem to penetrate the ice any by such action. But 

 even if such an effect was produced to an appreciable extent, it would have 

 been more pronounced upon the upper row of spikes, which received more sun's 

 heat owing to their more exposed position, and the actual melting upon the upper 

 layer would have been still greater than is indicated in the table. Although 

 the purpose of the experiment was to ascertain the differential melting, rather 



TABLE VI. 



Shearing Observations, Victoria Ice Front. 



than the actual, it is interesting to compare the maximum average daily effect 

 here observed with the maximum melting observed upon the surface of the 

 glacier, where least protected by debris. See table v, column 6, plate 13, page 31. 

 d. Crevasses. The general forward movement of the ice, and its inability to 

 adjust itself to inequalities in its bed, give rise to systems of cracks, or crevasses. 

 These show that the limit of tensional strain, without rupture, has been exceeded 

 in this part of the ice. They occur in all parts of the glacier from the bergschiamd 

 to the very nose, and when insecurely covered with snow, they form the greatest 

 menace to glacial exploration. The inexperienced cannot be too strongly 

 cautioned against the danger arising from these concealed traps, against which the 

 judgment of best trained Swiss guides is sometimes pitted in vain. In passing 

 from one portion of its bed to a sufficiently steeper slope, as that opposite the nose 

 of Mt. Lefroy, v-shaped cracks in the ice occur, extending directly across the 

 glacier. They penetrate to considerable depths into the ice, as measured in 

 feet, but their depth, compared with the total thickness of the ice, is probably 

 small, unless the change in the inclination of the bed is very abrupt, when they 

 may reach the bed of the glacier. When these transverse crevasses have an east- 

 west trend, the sun's rays strike the northern lip of the crevasse more strongly 

 than the southern and, in the course of the season, it becomes more rounded. 

 In passing down the slope the crevasse walls come together and the crevasse is 

 healed, except for the slight depression caused by the greater melting upon the 



