GLACIERS OF THE CANADIAN ROCKIES AND SELKIRKS. 



II 



necessitated the erection of numerous snow-sheds over the tracks of the Canadian 

 Pacific Railway, to guard against the frightful avalanches which come crashing 

 down the mountain slopes. 



Although Donald is located but a few miles east of Glacier House, it is upon 

 the lee slope of the Selkirks and in the Columbia Valley some 1,500 feet lower. 

 The precipitation here drops to 25.39 inches. The still higher Rockies im- 

 mediately follow, but the Selkirks have proven greedy and there is relatively 

 little left in the way of moisture. Full precipitation data in the region of the 

 crest ranges of the system are wanting. The snowfall at Field, however, 

 averages about 27 feet, at practically the same elevation as that of Glacier 

 House. If we assume that the same ratio holds here, between snow and rain, 

 as at the latter place the precipitation at Field, lying just west of the main 

 crest, would be about 42 inches. Passing the continental crest the currents 

 are drawn to lower levels, they become warmed by their descent, and their 

 capacity for retaining moisture increases. At Banff the precipitation for the 

 13 complete years available averages 20.14 inches, of which 39 per cent, falls 

 as snow. Beyond the foot-hills, at Calgary, the precipitation is reduced to 16.64 

 inches, of which 28 per cent, is snow. The following table furnishes a summary 

 of the climatic data of special interest in connection with this report. 



TABLE I. 



Climatic Data, from Records of the Canadian Meteorological Service. 



Quite in contrast with the still higher mountains of this same system to 

 the south in the United States, the following factors conspire to yield the neces- 

 sary meteorological conditions for extensive perennial snowfields and glaciers; — 



