GLACIERS OF THE CANADIAN ROCKIES AND SELKIRKS. 121 



summer melting the fine dirt is concentrated at the surface, forming a soiled 

 streak which contrasts strongly with the fresh snowfall of the fall. The water 

 resulting from the surface melting and rainfall sinks into the stratum and con- 

 tributes to the growth of the n6v6 granules, forming a crust of different texture 

 and color, by which the strata may be distinguished when no dust is present. In 

 the case of a regenerated glacier, such as the Lefroy, the stratification results 

 from periodic avalanching of snow and ice during the late spring, summer, and 

 early fall. The strata may vary much in thickness and have no immediate con- 

 nection with the amount of precipitation. They may become charged through- 

 out with ground-morainic material and give rise to very distinct zoning. When 

 a glacier is fed in part by neVe snow, and in part by avalanches from hanging 

 glaciers the stratification may appear very irregular, as in the case of the Victoria. 

 In passing an ice cascade the stratification and lamination may be completely 

 destroyed, or the uppermost strata may be destroyed and the lower more or 

 less perfectly preserved, as pointed out by Reid. It is not supposable that the 

 stratification could be thus destroyed and the more delicate lamination preserved. 

 In the case of the regenerated Lefroy the stratification is restored, after having 

 been lost, but it is not possible to restore the lamination completely, or regularly, 

 in the case of such a glacier. It should be noted in this connection that under 

 exceptional conditions shearing planes may be developed in the body of the 

 glacier which do not coincide with the limiting planes of the depositional strata. 

 In this way there may be acquired another type of secondary stratification 

 having no relation whatever to that which originates in the neVe". 



b. Shearing. Observations upon the oblique front of the Victoria in 1904 

 indicated that the upper strata were moving bodily over those upon which they 

 rested. The upper strata projected more and more daily, when there was not 

 enough additional debris in the lower to account for the phenomenon by differ- 

 ential melting. A small amount of sand and fine gravel, washed down from 

 above, collected in the lee of the upper projecting layers. Some days this was 

 in small enough quantity to accelerate the melting of a narrow strip of ice upon 

 which it rested, but quite as often melting was retarded by the material. At 

 one place where the shearing action seemed pronounced three heavy spikes were 

 driven into the base of the upper stratum and three corresponding ones in the 

 face of the subjacent layer. These spikes were six inches in length and were 

 driven horizontally into the ice until their heads were flush with the surface, 

 about eighteen inches apart. The average surface slope of the ice was 46 and 

 the vertical height of the ice 50 to 52 feet. The upper stratum had a thickness 

 of about three feet, the lower two feet, and each contained, apparently, about 

 the same amount of foreign matter, and this small in amount. At the beginning 

 of the observations the upper stratum projected 19.7 inches beyond the lower 

 (July 21), and by August 3, 25.6 inches, showing a gain in the 13 days of about 

 six inches of the upper beyond the lower. The spikes were visited daily and 

 reset and showed that while the upper stratum was advancing with reference 

 to the lower it was also melting back more rapidly, because of its more exposed 



