ADVANCE AND RETREAT OF CANADIAN GLACIERS 739 



less regularity. The station is nearly 3,000 feet lower than the Ille- 

 cillewaet neve. The amount of precipitation received by the glacier 

 is therefore probably greater than that of the valley. An average 

 of seven years' observations gives an annual snowfall of 36 feet and 

 5 inches. 



No records are kept in the immediate vicinity of the Rocky Moun- 

 tain glaciers. Records here would be of less signiiicance, for pre- 

 cipitation is exceedingly local in character. Moreover, owing to the 

 occasional occurrence of Chinook winds, there is far greater evapora- 

 tion than in the Selkirks. It is safe to say that here, as elsewhere in 

 the Rockies, there is far less precipitation than among the mountains 

 to the west, and that there is more evaporation. 



The prevailing winds coming from the west and from the sea, the 

 moisture is first precipitated on the westernmost mountains. As 

 they progress eastward, the prevaihng winds have less moisture. 

 Ha\ing less moisture, the daily range in temperature becomes greater, 

 and the difference in temperature and in precipitation between valley 

 and mountain slopes, greater. In the Bow Valley, near the glaciers 

 of the first group, the maximum depth of snow in winter is said to be 

 2 or 3 feet; on the slopes near the glaciers of the same region, 10 or 

 15 feet. The depth of snow on the ground in the Selkirks, near the 

 Glacier House, is 20 feet or more. 



Load carried. — It has been shown by I. C. Russell,^ and also by 

 Messrs. Chamberlin and Salisbury,^ that glaciers heavily loaded 

 with debris move more slowly than those which have no load. This 

 is due in part to the lessening of the viscosity of the ice by the 

 introduction of rigid material, and in part to the formation of debris- 

 charged ice-dams at the ends, which hold back the advancing ice. 

 So far as could be observed, the amount of englacial material is 

 small in both types of Canadian glaciers, and there is probably little 

 difference in viscosity from this cause. But it is common for the 

 glaciers of the first type to end in a mass of ice thickly charged with 

 debris and forming a sort of ice conglomerate. This was the case 

 also with the three debris-charged glaciers of Laughing Fall Valley; 



1 Journal of Geology, Vol. Ill (1895), pp. 823-32. 



2 Ibid., 1894-95. 



