24 GLACIERS OF THE CANADIAN ROCKIES AND SELKIRKS. 



exposures of the outcropping edges of the strata, to be noted later. These 

 depressions furnish confirmatory evidence that the general movement of the 

 superficial layers is across and not parallel with the valley. The position of the 

 left lateral moraine from the debris cone, above noted, to the Victoria, shows, 

 however, that along the base of the Lefroy cliff the movement is normal and 

 due to the Mitre, although the strata belong to the Lefroy. In consequence 

 of this a relatively small amount of morainic material is captured from the 

 Lefroy and delivered to the medial moraine of the Victoria at the nose of Mt. 

 Lefroy. This double tributary joins the Victoria at an elevation of about 

 6,670 feet, having an average surface slope of 1,360 feet to the mile, and is at 

 once compressed to about 600 feet, as compared with 3,200, or as 5^- is to i. 

 There being no corresponding increase in the height of the ice, the inference 

 is that the tributary delivers relatively little ice to the Victoria and that its 

 movement is correspondingly slow. 



4. DRAINAGE. 



a. Surface ablation. The drainage supply of the glacier originates from 

 the rainfall over the glacier and adjacent mountain slopes, from the melting of 

 the snow and ice in the region of the hanging glaciers, and from the general 

 melting of the glacier itself and its tributaries. No definite data are available 

 concerning the rainfall over the glacier and adjacent slopes. Owing to its greater 

 altitude it would be much less than at Field and Banff and would practically 

 all fall during June, July, August, and September. After heavy showers the 

 streams from the mountain slopes are in many cases highly charged with 

 sediment, those originating from the melting of snow being generally clear. 



The temperature of the ice during the summer was found to be either 

 just at the freezing point, or so near it that any addition of heat was 

 sufficient to start the process of melting. In the abandoned drainage tunnel, 

 to which reference will be made later, holes were bored into the ice wall, 140 

 feet back from the entrance, and a standard minimum thermometer inserted 

 its full length. Owing to the course of the tunnel the point of observation 

 was estimated to be 70 feet from the foot of the oblique ice wall and about 17 

 feet from the actual ice face (plate vin, figure 4). During the week from 

 July 31 to August 7, 1904, the readings were 31.8 F., 31.6, 31.8, 31.9, 31.7, 

 and 32. The maximum temperature of the air in the tunnel during the week 

 ranged from 31.4 to 33.0 F. Owing to the warmth of the body and that of 

 the candle used, it was found impracticable to get the temperature of the air 

 at the same time that the temperature of the ice was taken. 



In the rarified atmosphere at these high altitudes the midsummer sun 

 strikes with surprising force and the surface ice, so near its melting point, is at 

 once converted into water without changing its temperature. In the case of 

 scores of observations made upon the surface streams of the series of glaciers 

 the temperature was almost uniformly 32 F. In rare cases it was found to be 

 a small fraction of a degree above. In order to secure some data for an estimate 



