The western plains and the Rocky Mountain region of Canada undoubtedly constitute one of the most important fields of investigation in connection with the glacial period in North America. The area there characterized by glacial deposits is an enormous one, but the facts derived from it have so far been accorded comparatively little weight in the construction of hypotheses for the continent. Of these hypotheses those in best standing have grown up chiefly during the detailed study of the southern portion of the glaciated region of the east. Distance, and a general unfamiliarity with the somewhat complex physical features of this western region, have undoubtedly prevented a ready appreciation of its phenomena, but these also must in the end be fully reckoned with before satisfactory conclusions of a general kind can be definitely reached. In former papers* the writer has endeavored to combine the observations made by himself and . . .