FIG. 49.—The East Flank of Mount Ellen, showing the Scrope, Peale, and Jukes Laccolites, and the Maze and Crescent Arches. ] Little is known of the form of the _Peale laccolite_. One edge is lost in the obscurity of the alpine sculpture, and the other has been removed along with the crest of the Maze arch, on which it rested. But by this removal a section has been opened across the laccolite, revealing its internal structure from top to bottom. It is shown to be composite, attaining its height of 850 feet by the compilation of three distinct beds of trachyte, separated by partings and wedges of shale. The lowest bed is thin and of small extent. Next is the main bed, six hundred feet thick and a mile or more broad; and on top is a bed two hundred feet thick and proportionately narrow. Each of the beds is lenticular in section, and the piling of the less upon the greater produces a quasi-pyramidal form. The interleaved shale bands are metamorphosed to the condition of slate. Under the laccolite are one or two hundred feet of shale, apparently unaltered except at the contact. Then come the Henry’s Fork conglomerate, 350 feet thick, and the Flaming Gorge shale, several times thicker. Within the upper shale is a restricted trachyte sheet and near the top of the lower shale is a broader one. The latter is double throughout, its two layers having been intruded at different times. The top of the escarpment is at the top of the laccolite, and only a short distance back from the brow are shale and sandstone resting upon the trachyte and conforming to its uneven surface. _The Scrope laccolite_ resembles the Jukes in everything except that its erosion has progressed so far as to obliterate every trace of the original upper surface. Its position in the strata is about the same, and the erosion of its matrix has left it a conspicuous crag. It rests on the flank of the Maze arch, just as the Jukes laccolite rests on the Dana arch. The remnant of trachyte is less than one thousand feet high, and has been carved into a subconical form in which no hint of the original size and proportions of the trachyte body is conveyed.