Page:Canadian Alpine Journal I, 2.djvu/122

258 very heads and excavate often a semi-circular amphitheatre, or cirque, which may eat its way into the heart of a mountain and assist the atmospheric agencies in its destruction. A good example of such work is seen in the elevated Lake Agnes Valley, the glacier having nearly or quite disappeared from the region.

(b) Transportation. The loose material which a glacier finds in its path, along with that which it is able to pluck from its bed, is urged forward by sliding and rolling, or it may be incorporated into the base of the ice and transported bodily. Aside from the wind-blown dust which may be more or less evenly distributed throughout the body of the ice, the bulk of the material transported by the local ice-caps and continental ice-sheets lies in the basal layers. In the case of alpine and piedmont glaciers, however, from overtowering cliffs the active atmospheric agents may detach rock fragments which find their way to the surface of the glacier. If they reach the neve they may be incorporated into the body of the glacier, to appear later either at the surface of the dissipator or its extremity. Material carried thus either upon or within the ice suffers little abrasion compared with that at the base, but by means of crevasses and moulins it may work its way down to the lower zone. The transporting power of a glacier differs very markedly from that of a river since it is in no wise dependant upon its velocity. Rocks as large as a city block may be handled quite as easily as a grain of sand.

Owing to its relation to the steep cliffs of the Ten Peaks the Wenkchemna receives rock fragments along its entire breadth. In the case of the Victoria the upper valley is sufficiently narrow so that avalanches from Lefroy and Victoria may reach entirely across the neve, thus distributing rocky debris throughout the glacier there in process of formation. When brought below the snow-line by the forward movement there is a concen-