﻿SHKRZER] GLACIAL STUDIES IN CANADIAN ROCKIES 457 



period 3.6 inches daily ;md for the entire period (July 9 to 29) 

 2~^ inches, which latter figure may be taken as the average daily 

 summer motion for this part of the glacier. If we assume a mini- 

 mum winter motion of one-fourth this amount we shall gel as the 

 probable yearly motion here about 5-' ft. Further up where the in- 

 clination is greater there is reason for thinking that the rate of move- 

 ment is much greater. 



4. Ablation. — Accurate elevations upon the steel plates used in 

 the above work were taken with a spirit level for the purpose of con- 

 structing a cross-section of the glacier here and also for the purpose 

 ot determining the amount of surface melting tor a definite period. 

 It was thus found that the surface of the ice was being lowered 

 most rapidly in the neighborhood of the plate which showed the 

 maximum forward movement and from July 9 to August 4 amounted 

 to 3.794 ft., or a daily average of 1.75 inches. This effect is produced 

 mainly by the sun, which in the rarified atmosphere of these high 

 altitudes, strikes with surprising force, transforming the water from 

 its solid to its liquid condition, without changing its temperature. 

 Other agencies are the atmosphere, generally above the freezing tem- 

 perature during' the summer months, and the rain, I.506 inches of 

 which fell during the above period of observation. Subglacial erosion 

 and melting may assist also in lowering the surface of the glacier 

 at any given point, as may also the longitudinal stretching, or lateral 

 spreading of the ice. but for limited periods these effects may be 

 disregarded. From the above data it would appear that the surface 

 melting over the lower third of the Victoria for July and August 

 should be about 9 ft. Independent observations upon the lower 

 Lefrov showed that the ice surrounding certain morainic heaps had 

 been lowered during the season by about this same amount. Xo 

 glacial tables of this height are to be found, owing to the under- 

 cutting effect of the sun's rays and their consequent destruction of 

 their pedestals. The broad medial depression lying to the west of 

 the medial moraine (pi. lx) has been produced by the relatively 

 greater melting here and this is permitted by the thinner covering 

 of rock debris, the ice o\ this portion of the glacier coming from 

 the Lefroy side of the valley. This depression continues down the 

 valley for 2.200 feet, where it thins out. apparently by surface melt- 

 ing. If the estimated forward movement is approximately correct 

 and continuous for this region it wou'd require about 42 years for 

 the ice to pass from the line of plates to the lower edge, during 

 which time, at the rate of <) ft. a year, about 378 ft. of ice could be 

 melted, and this shovld represent the approximate thickness of the 



