In the broad sector included between the continental divide in Montana and the crest of the Cascades in northern Washington, the glacial drift offers a number of important problems, some of which are clearly set forth in the existing literature on this region. The purpose of the present discussion is to review the significant data, to trace the drift border through a part of this sector, and to offer an interpretation of the age of the drift, as a result of three seasons of field study in eastern Washington.
Northeastern Washington (Pls. 2, 5) consists of two very different regions. The more northerly region is a highland marked by northward-trending ranges lying between pronounced parallel valleys, and underlain by rocks predominantly crystalline, among which are abundant granitic and metamorphic rocks, including much argillite. The range crests descend from extreme elevations of more than 7000 feet near the International . . .