88 GLACIERS OF THE CANADIAN ROCKIES AND SELKIRKS. 



The two readings were 32.oFand 31.9, indicating that this portion of the glacier 

 was very near to its melting temperature. Before liquefication, however, can 

 occur a large amount of heat must be rendered latent, when water is produced with 

 the same temperature as that possessed by the ice just before melting. The 

 heat necessary for this conversion is supplied in the main directly from the sun 

 but in part by that of the atmosphere, rain, friction and pressure of the ice 

 against the valley floor and sides, and whatever heat may be reflected, radiated, 

 or conducted, from the same source. Almost without exception the surface 

 drainage was found to have a temperature of 32, varying but a very small 

 fraction of a degree from this. The surface ablation is rapid during the summer, 

 owing to the exposure of the ice to the sun and the absence of protective debris. 



As would be expected from the greatly crevassed condition of the ice, no 

 surface streams of any size can develop, either over the general surface or along 

 the margins. Small streams flow directly to the ice margins and cut channels, 

 in a few cases, to the depth of a foot. This water may be absorbed at once by 

 the loose materials covering this portion of the bed, or it may collect and give 

 rise to scant marginal or subglacial drainage streams. These flows soon cease 

 when the sun drops behind Glacier Crest and throws the glacier into shadow. 

 In 1904, for a distance of some 500 feet, a small drainage stream was found 

 between the left lateral and the adjoining ice slope. Since the ice of the glacier 

 is here continuous with the morainic ice core, this stream was a surface rather 

 than a marginal one. From the lower end of this moraine there occurred also 

 two small flows of water, apparently coming from englacial channels in the 

 moraine. After a six hours' rain, September 8, 1904, during which 0.58 of an 

 inch of rain fell, the water of these streams was rendered muddy, while the 

 turbidity of the main glacial flow was not perceptibly affected. 



b. Terminal drainage. Upon the eastern side of the glacier, drainage 

 streams leave the ice margin in the neighborhood of the elevated distributary 

 noses, as shown upon the map. The ice here rests upon bedrock and the streams 

 have sought the lowest depression, there being three such which are draining this 

 portion of the glacier. The westernmost of these breaks into a network of streams 

 upon emerging from the ice, and cascading over the rocky ledges again enters 

 the side of the glacier, to reappear at the nose. The two other streams have 

 cut gorges 50 to 60 feet deep across the hard strata, showing that they must 

 have been at work for considerable periods, probably as subglacial streams. 

 However, the high velocity of the water and the sharp glacial sediment enable 

 it to work very effectively, even upon quartzite. These two cascade over the 

 ledges and unite some 1,600 feet down into a single stream, which receives 

 tributaries from the slopes of Sir Donald. Just outside of the right lateral 

 moraine the stream divides into numerous branches, which reunite upon the 

 gentle gravelly slope and form what is known as a "braided stream." East- 

 ward of the upper, right lateral moraine, between it and Perley Rock, there is a de- 

 serted gorge, similar to those now being formed, partially filled with gravel and 

 morainic matter. The drainage has been deflected westward to a lower level. 



