The trachyte injections are not confined to the fault planes, nor is their area so restricted as the fault area. Dikes and sheets abound from the crest of the dome down to what might be called its springing line—the line of maximum dip. At the center, dikes are more numerous; near the limit, sheets. The central area is crowded so full of dikes, and the weathering brings them so conspicuously to the surface, that the softer sedimentaries are half concealed, and from some points of view the trachyte appears to make the entire mass. The accompanying plan (Figure 12) shows the arrangement of the dikes in one of the outer amphitheaters of the mountain, where they are less complicated than in the central region. The trends of two spurs (_a b_ and _c d_) are indicated by the hatchings. They join the main crest of the mountain at _e_, and inclose between them a deep amphitheater which opens to the west. Upon the steep walls of the amphitheater the dikes outcrop in lines of crags, dividing rough slopes of yellow and purple and brown sandstone. The profile of one of the walls of the amphitheater (from _a_ to _b_, Figure 12) is drawn in Figure 13 for the sake of exhibiting the relation of the dikes to faulted blocks of sandstone. It will be seen that the throw of the faults is not constantly in one direction. [Illustration: FIG. 14.—Profile of the Northern Spur of Mount Ellsworth. 1, 2, 3, 4, and 5 are Trachyte Dikes. _A_, Aubrey Sandstone. _S_, Shinarump Shale. _V_, Vermilion Cliff Sandstone. _G_, Gray Cliff Sandstone. ] The zone of sheets is just inside the line of maximum dip. Usually only one or two sheets are laid bare by the erosion, but at one point (see Figure 14) four can be counted. Toward the center of the uplift all of these are limited by the erosion and exhibit their broken edges. Downward, or toward the periphery, they dip out of sight. Laterally they can be traced along the mountain side for varying distances, but they soon wedge out and are replaced by others _en echelon_. In thickness the sheets rarely exceed 50 feet, and never 100. They are always thin as compared to the rock masses which separate them, but, by reason of their superior ability to resist erosion, monopolize a large share of the surface, and mask a still greater amount with their _débris_. [Illustration: FIG. 12.—Ground plan of Trachyte Dikes on the western flank of Mount Ellsworth. ] [Illustration: FIG. 13.—Profile of a western spur of Mount Ellsworth, showing the arrangement of Dikes and Faults. The dotted bed is the purple band at the top of the Vermilion Cliff Sandstone. The dikes of trachyte are indicated by letters. ]