74 GLACIERS OF THE CANADIAN ROCKIES AND SELKIRKS. 



The surface is soiled with wind-blown dirt but it carries little' debris. At an 

 earlier stage it brought down from above the left lateral niorainic material for the 

 Yoho, and its ice extends still well under this ancient moraine. The axis of the 

 glacier is curved as it is forced around the rock embossment, which it hugs closely 

 and is still engaged in fluting and polishing (plate xxvii, figure i). The upper 

 crest of the rock embossment has an elevation of 6,960 feet, while that of the 

 nose is 6,320 feet, or 650 feet above that of the main glacial stream. The average 

 slope would be at the rate of about i ,300 feet to the mile. It is evidently in retreat 

 although no data are available for determining the rate. In the upper portion 

 of its course, it appears to descend over a steep step in its bed and is much 

 crevassed. These crevasses completely heal, however, or are destroyed to their 

 bases by melting, leaving the lower half exceptionally smooth. Over this portion 

 of the small glacier there are developed three very pretty drainage systems, two 

 of them marginal and the third central. The central drainage, which is collected 

 into a trunk stream (plate xxvii, figure i) from a network of small tributaries, 

 has cut a longitudinal channel in the ice, and continues to a point just east of the 

 nose. Habel's map of the Yoho Glacier shows this tongue of ice continuous 

 around the rock embossment, forming of it a rock island, or so-called "nunatak." 

 Such a position it originally held, but not less than 200 years ago, so far as we 

 may judge from the size of trees growing in the valley. At a still earlier stage 

 of glaciation the entire embossment was oveiTidden by the ice, much of it being 

 disrupted, wherever the ice could get a satisfactory grip upon the strata. The 

 resistant portions were planed down, rounded, and fluted. 



4. Moraines. 



Because of the lack of overtowering clift's, above noted, the general surface of 

 the Yoho is practically free from coarse rock d6bris, in striking contrast with the 

 Victoria and Wenkchemna. For the same reason also the lateral moraines 

 are poorly developed and almost absent in the lower half mile. Upon the western 

 margin, just before reaching a broad glaciated valley, originally carrying a 

 tributary, the right lateral moraine begins to make its appearance and develops 

 across the mouth of the valley into a well defined ridge of stony till, or ground- 

 morainic matter. This ridge is continuous up the slope to the line of junction 

 of the main Yoho with the glacier from the eastern slopes of Mt. Collie, wheie 

 the latter is seen to be delivering this material from its under side to the surface 

 of the Yoho. This ground moraine has been produced between the Collie 

 Glacier and its bed, frozen into the ice, and urged down the slope. 



The left lateral moraine begins along the southern side of the rock emboss- 

 ment, down in the valley, as a double ridge from which the ice has been withdrawn. 

 It extends around the embossment, on the west side, for a distance of some 

 4,500 feet, developing into a prominent, high, sharp-crested ridge at the head 

 and curving across to the eastward. This consists, also, almost entirely of ground- 

 morainic matter, which must have been derived from the basal layers of the ice, 

 which became stranded at the head and about the west side of the rock emboss- 



