Page:Canadian Alpine Journal I, 2.djvu/123

Rh tration of this material over the entire surface of these two glaciers, forming a thin veneering by which further melting is much retarded. Ordinarily the rock fragments accumulate in a relatively narrow zone along the margin of the glacier where they are moved very slowly forward, protecting from melting the ice upon which they rest until there is produced a sharp-crested ridge upon either side of the glacier—the lateral moraines. When such a moraine towers above the nose of the glacier more than a hundred feet, as is the case with the Illecillewaet, it is difficult for the ordinary observer to believe that it is essentially an ice-ridge with scarcely a foot of rock veneering. For the last few years the left lateral of the Asulkan has been shedding its cover near the lower end and this ice-core is well exposed and is being slowly destroyed.

When a glacier has a tributary, as in the case of the Victoria, the adjacent lateral moraines of the trunk and tributary streams unite and form a medial moraine, which has much the same appearance as the laterals. Under ideal conditions there will be one such medial for each tributary stream. Owing to the more rapid movement of the ice upon which they rest there is not the opportunity for the development found in the laterals. The material which rests upon the surface of the glacier has suffered but little abrasion and is thus readily distinguished from that which has occupied a basal position. Whenever a glacier is nourished, however, by a hanging glacier, as is the Lefroy, Victoria and Yoho, there occurs a mixture of the two types of material in the lateral moraine.

(c) Deposition. While the glacier is still in possession of a region there is being deposited in certain protected places beneath the ice the clay, sand and glaciated boulders, firmly pressed together and typically unassorted. Bluish-gray in color, until it is oxidized, this constitutes the ground-moraine. Owing to the action