The study of the Sierra Nevada-Cascade region has not progressed far enough to warrant a decision, but the fact referred to above strongly suggests that the two ranges, as we now term them, are essentially a single uplift, a large portion of which, extending from Lassen Peak, in California, northward across Oregon and into Washington as far as the Northern Pacific Railroad, is buried beneath a great blanket, so to speak, of lava-flows. The tract of elevated and rugged country in northern Washington embraced in the Cascade Mountains, as has been observed by the writer, passes into Canada without a marked change in either its geology or geography, and there is no occasion for a change of name when the international boundary is crossed. The Cascade Mountains in Oregon and southern Washington, where the surface rocks are mainly and perhaps wholly of volcanic origin, are rugged for two principal reasons: First, volcanic energy has built up great individual peaks; and second, erosion has carved deep valleys and numerous ravines and gorges. The volcanoes are now extinct, or have long been dormant, and their cold summits are in several instances crowned with perennial snow and small glaciers. The forms given to the more prominent elevations by the eruptions which built them have to a great extent been defaced by erosion. As they stand to-day they furnish an instructive series of more or less deeply dissected volcanic mountains. [Illustration: FIG. 21.--Crater Lake in the summit of Mount Mazama, Oregon.]