Page:Canadian Alpine Journal I, 2.djvu/124

260 of sub-glacial streams patches of stratified sand and gravel may occur locally, the clay being carried away by the drainage. On account of the relatively slight grinding action of the present Canadian glaciers and lack of opportunity for lodgment, no extensive deposits of this ground-moraine or till are now forming. In connection with the great continental ice-sheets, however, deposits were formed several hundreds of feet in thickness.

During the process of retreat all the material carried in or upon the ice must be deposited as fast as complete melting proceeds. The rock débris of the lateral and medial moraines will be set down in corresponding lines or ridges, but of surprisingly insignificant proportions when contrasted with the original moraines. Rock fragments distributed over the general surface of the glacier will be somewhat evenly distributed over the bed as it is uncovered, so long as the retreat is fairly uniform. In case the melting at the lower extremity, however, just equals the forward movement, the end of the glacier comes to a halt and its load is dumped in a ridge, forming a terminal moraine, providing we have a glacier of the alpine type, which alone can be considered to have an end. In the case of the three other types of glaciers such moraines, testifying to the stages of halt of the front, but not of the ice itself, are known as frontal moraines. A good example is seen in connection with the Wenkchemna, previously referred to.

A noteworthy type of ancient moraine is found in connection with the five most accessible glaciers along the Canadian Pacific Railway, viz., the Victoria, Horseshoe, Wenkchemna. Illecillewaet and Asulkan Glaciers. In each case its double character can be made out, either through its disposition in separate ridges, or differences in age where heaped together. The moraines consist of massive blocks of quartzite and sandstone heaped tumultuously together without the usual filling