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GLACIAL STUDIES IN CANADIAN ROCKIES 



469 



of relatively clean ice (fig. 73). The dirt is entirel) superficial a! 

 though one might think otherwise from the manner in which these 

 bands run down into the crevasses (fig. 74) and cover the marginal 



Fu 



Dirt stripes " and laminae, Lefroy glacier, cutting strata at 

 high angle. 



slopes. They may be so fine as to average but one-tenth of an inch 

 in breadth, but are generally considerably coarser. This feature is 

 dependent upon the laminated structure of glacial ice and is of im- 

 portance in that it enables one to judge of the size, number and 

 arrangement of the laminae, directly from the surface. The out- 

 cropping edges of the "blue hands" of solid ice resist the action 

 of the sun somewhat better than the white, vesicular layers by which 

 they are separated. As a result there is produced a series of fine 

 troughs, or furrows, separated by corresponding ridges, into the 

 former of which fine dirt accumulates, reproducing in miniature the 

 dirt bands of Forbes. It is suggested that the term "dirt stripes" 

 he used for this phenomenon. 



10. Ice Dykes. — A phenomenon not known to have been noted 

 elsewhere, seen frequently upon the lower Lefroy in midsummer 



