﻿GLACIAL STUDIES IX CANADIAN ROCKIES 



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its component granules, the surfaces oi which are seen to be covered 

 with a system of fine ridges and rows of points, about 1 mm. apart 

 and resembling, more than anything else, the markings upon the 

 ball of one's thumb. Internal melting of the granule gives rise to 

 the " Tyndall melting figures," originally figured by Agassiz and 

 described by him as flattened air bubbles. 



8. Extensive Plucking. — A peak, as yet unnamed, lying between 

 the nose of the glacier and Mt. Balfour, is made up of a succession 

 of curved, concentric strata, the upper <>\ which are a dark lime- 

 stone, dipping to the southwest at an angle of about 30 . This peak 



p IG , 88. — A " plucked " mountain peak, head of Yoho valley. 



was overridden by ice moving from the north, which ripped off 

 bodily the strata, leaving the more resistant portions, overlapping 

 and projecting (fig. 88). Upon the upper surfaces and upon either 

 side of these remnants the disrupted blocks were completely removed, 

 but in their lee they accumulated as shown in the figure. Evidently 

 the entire mountain peak has been reduced in height to a consider- 

 able, but unknown amount, by the process of "plucking." 



9. Block Moraines. — Not realizing at the time the significance of 

 this type of moraine, no special study was made of them in the \ oho 

 valley. Two massive ridges are crossed but they are soil covered 

 and forested and their real nature was not investigated for lack of 

 time. They may be mountain spurs or rock slides, but are more 

 probable moraines; rather too old, apparently to be correlated with 

 the block moraines previously described. If they are not really 



