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Show 236 GEOLOGY OF THE HIGH PLATEAUS. degree of consolidation is always considerable and is quite sufficient to enable the edges to stand in great mural fronts many hundreds of feet in height. In this respect it is as consistent as any of the calcareous sandstones of the region. It is, however, more easily attacked by the rains and frost than the volcanics or even than the more massive kinds of sandstone. The included fragments exhibit all degrees of roundness by attrition; are often quite sharp and angular; most frequently a little worn by current-action; sometimes greatly so. Where the fragments are least worn they are most abundant In many places the amount of cement is much less than others, while in some places the fragments are relatively few. In size, the fragments var}^ from a mere granule to two or three tons. The conglomerates are seen upon the slopes of Sevier Valley at the foot of the western front of the plateau usually flexed upward a little and then cut off by the great fault,. On the east side of the plateau they slope down towards Grass Valley (which is in great part a valley of erosion), and are cut off in some places and dip beneath its floor in others, but reappear in the western front of the Awapa Plateau. Whether these beds which are seen in the Awapa are continuations of those in the Sevier Plateau is not absolutely certain, but I think they are. About midway between the middle and southern eruptive centers the Sevier Plateau is cut completely in twain by a mighty gorge called the East Fork Canon. It is the old storyâ€"erosion. The plateau rose athwart the course of the stream and was sawed in two. It is not a narrow chasm, but a valley walled by ledge upon ledge. The dissevered beds above stand a couple of miles or more apart facing each other across the depths; below, the walls are from 1,000 to 2,000 feet assunder. The total depth varies in different parts from 1,400 to 3,700 feet. The structure of the plateau is thus clearly revealed. The upper rocks are volcanic conglomerate of immense thickness, with intercalary sheets of coarse trachyte, the former well stratified. The lower rocks are of a highly exceptional character, and will be treated of at length in the latter part of this chapter. The third eruptive focus of the Sevier Plateau stands east of the head of Panquitch Canon. It bears a strong resemblance in its features and the character of its emanations to the northern vent (Blue Mountain). It is |