Region studied.—During the past field season I have made studies of the structure of a part of the high Sierra with a view to elucidating the orogenic forces involved. My observations were made chiefly from the south fork of the Stanislaus river to the Truckee, a distance of about 80 miles, and covered a belt of some 30 miles in width immediately west of the eastern scarp of the range. The results are in some respects incomplete even for this limited area, but they appear to be of sufficient interest to justify a preliminary paper. During the field-work I did not find myself able to frame any hypothesis to account for the phenomena, although these were in some of their features singularly regular. This was in one respect advantageous, for it left me free from all bias in the collection of facts. On the other hand, . . .