It has been made eminently clear by Suess1 in his great synthesis of the structure and form of the planet that between those mountain systems which come into contact with one another there are very different types of structural connection. Suess' interpretations of various examples, now famous, are so well known that no repetition is here necessary, Moreover, his brilliant work has invested the subject with a surpassing interest which has led many others to give it their attention. Already the structures of the junctions between many of the world's mountain systems are understood. But the connection between two of the great mountain systems of western North America, the Coast Range of British Columbia and the Cascade Range of Washington, has been largely neglected by geologists, or misinterpreted, if not indeed completely misunderstood. Even Suess' interpretation is open to objections: it fails to separate the two ranges, and to correlate the structures of the Cascades in any way with those of the Interior Plateaux or the Rocky Mountain System.