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GLACIAL STUDIES IN CANADIAN ROCKIES 



489 



detailed map, or general description, of the entire glacier has yet 

 been prepared. In the size of its collecting area, freedom from 

 debris, and crevassed condition il is similar to the Wapta, and like 

 it has been in steady retreat for a number of years (fig. 89). 



j. /(•(• Retreat. — For some years previous to 1887 the tllecillewaet 

 was stationary and engaged in building a small frontal moraine. In 

 1887 the front was photographed by the Vaux Bros, and its position 



Fig. 90. — Roche moutonnee, Illecillewaet glacier. 



with reference to a massive block definitely determined. ( )ne year 

 later it was photographed by Notman and Son, as well as others, 

 as it was starting to withdraw from the moraine (pi. lxx). Since 

 this retreat began numerous reference blocks have been established 

 and the rate determined from time to time and published. The rate 

 of retreat has thus been found to vary according to the season. In 

 the entire 17 years the ice front has receded 603.5 ft., measured 

 horizontally, or at an average rate of 35.5 ft. a year ; the recession 

 for the past year being but 11 ft. when measured to the nose which 

 has shifted to the west (pi. lxxi). The ground moraine thus ex- 

 posed constitutes a " boulder pavement," the boulders at the last 

 having been so lightly ridden by the ice that the}' were slightly 

 striated, without being disturbed. Beneath the margin of the ice 

 the boulders are seen to produce rlutings upon its underside, some 

 of these extending 70 to 80 ft. beyond the boulder by which they 



