In the northwest corner of the area represented by the stereogram are a few faults belonging to a system which occupies a large area in that direction. The system of faults and the system of flexures are independent, the latter having originated at the close of the Cretaceous period, and the former after the formation of the Tertiary rocks of the region, which are referred by Professor Powell to the Bitter Creek epoch. Over a large district the Tertiary strata were covered by a deep mantle of lava, which has protected them from erosion to such an extent that the structure of the district is portrayed in its topography. The district is its own stereogram, each uplifted block constituting a mountain and each depressed block flooring a valley. Not all the displacements of the later system are by faulting, but by far the greater number. Of the earlier system of displacements none are simple faults, but a few are combinations of fault and flexure. [Illustration: FIG. 2.—Cross-section of the Waterpocket Flexure, opposite the Masuk Plateau. Scale, one inch = 3,500 feet. 1, Masuk Sandstone. 2, Masuk Shale. 3, Blue Gate Sandstone. 4, Blue Gate Shale. 5, Tununk Sandstone. 6, Tununk Shale. a, Gryphea Sandstone. 7, Henry’s Fork Conglomerate. 8, Flaming Gorge Shale. 9, Fossiliferous Limestone. 10, Gray Cliff Sandstone. 11, Vermilion Cliff Sandstone. 12, Upper Shinarump Shale. 13, Shinarump Conglomerate. 14, Lower Shinarump Shale. 15, Aubrey Sandstone. ] [Illustration: FIG. 3.—View of the Waterpocket Cañon and the Waterpocket Flexure. The cliff at the left is capped by the Henry’s Fork Conglomerate. The arched rocks at the right are the Gray and Vermilion Cliff Sandstones. ] [Illustration: FIG. 4.—Waterpocket Flexure, as seen from the south end of Mount Ellen. ]