76 GLACIERS OF THE CANADIAN ROCKIES AND SELKIRKS. 



of its bed. In making this rapid descent the ice is crevassed both transversely 

 and longitudinally. The irregular blocks of ice formed melt into sharp points, 

 or steeples, to which the term "seracs" is applied. The transverse crevasses 

 have been noted which open just behind the archway at the nose, allowing the 

 arch to collapse toward the close of the melting season. The absence of pressure 

 in front allows the arch to drop forward, faster than the ice can yield to the ten- 

 sional strain, and the crevasse is the result. Along both margins, for nearly the 

 entire three miles, the normal lateral crevasses, described for the Victoria, occur. 

 They extend inwards and upwards for varying distances, are irregularly spaced 

 and become less numerous toward the n^v^, where some of them are snow-filled 

 and snow-covered. In passing the ice cascade the ice is too much shattered to 

 permit the formation and preservation of the dirt bands described upon page 

 5 2 of this report. However, at the crest of one of the minor slopes the phenome- 

 non may be seen, as shown in plate xxix, figure i, where the depressions for 

 three bands are plainly marked out. These mark the sites of former crevasses, 

 and, if rightly interpreted, the distances between them show the approximate 

 annual motion at this portion of the glacier. 



6. Ice Structure. 



In both the main glacier and the distributary the stratification of the ice 

 is poorly preserved, possibly because of its destruction in passing the cascade. 

 General views, as well as detailed ones, give almost no trace of the strata. In plate 

 xxvii, figure 4, one stratum, relatively much charged with debris, forms the base 

 of the arch, but does not appear upon the opposite side. This basal stratum 

 where seen is 2 to 5 feet in thickness. Its upper surface may represent a shearing- 

 plane, the body of the stratum being held more rigidly by its content of d6bris 

 while the superincumbent ice is forced over it.' In places where the strata are 

 still preserved, the dividing planes show poorly, and it is to be noted that this 

 may arise because of the paucity of foreign material concentrated at the upper 

 surfaces of the strata. In the case of this particular glacier the size of the nev^ 

 field precludes any but the finest dust from reaching the general surface, and 

 with so few peaks uncovered in the region the supply of dust must be meager. 

 No opportunity was afforded for observing the structure of the nevd itself. As 

 pointed out by Reid, in the paper cited upon page 43, the basal layers of a 

 glacier may be able to pass a cascade without suffering destruction, while the 

 upper strata may be destroyed and in large part melted away. This may be the 

 cause of the poor development of strata in the case of the Yoho, and the absence 

 of the dirt zones, which should show especially well over the smooth lower half 

 of the distributary. 



In spite of the almost complete obliteration of the strata in the upper part, 

 the blue bands are shown in great perfection where the ice presses against the 

 west valley wall. The edges run parallel with the margin and the bands dip 



1 " The Influence of Debris on the Flow of Glaciers," I. C. Russell, Journal of Geology, vol. iii, p. 823, 

 1895. 



