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Show 228 GEOLOGY OF THE HIGH PLATEAUS. alluvial conglomerate derived from their degradation. Only at the northern and southern ends are the sedimentaries clearly seen in mass lying beneath the old lavas. At a few intermediate points, however, and especially in East Fork Canon, some metamorphosed beds of peculiarly interesting character are exposed, and these will receive special attention in the latter part of this chapter. The eruptions which compose the plateau mass belong to several well-separated periods, which for the most part had their locations at the same centers or axes. Of these centers or axes there are in the Sevier Plateau threeâ€"one at the loftiest part of the table at the summit of its northern slope, the second about 2 0 miles farther south, the third in the southern section of the plateau, right abreast of Pan quitch Canon and about 30 miles south of the second. They may be distinguished as the northern, central, and southern eruptive centers respectively. Of these the largest and most voluminous is the northern one; in truth it is apparently the most important one of the entire district. Immediately opposite the Mormon town Monroe the great wall of the plateau rises more than a mile above the valley plain, presenting the edges of the volcanic beds, which appear to be very nearly horizontal and more than 4,000 feet in thickness. How much more is impossible to say, for the lowest sheets are concealed. Upon the summit of the wall a transverse ridge runs across the table to the eastern side and ends in a high'knob overlooking Grass Valley and named the Blue Mountain. It was in the vicinity of this ridge that the grander eruptions had their origin. The great amphitheater near Monroe has laid open the table to its foundation, but the promise of information conveyed by such a section is not fulfilled. It has revealed a bewildering maze of earlier rocks lying in all possible positions and having but few intelligible relations to each other. Upon them rest later floods in rather regular bedding, which succeed each other to the summit. I have revisited this locality repeatedly, but have generally found at each visit more questions than answers. The confusion among the lower rocks is indescribable, and the exposures of any given bed so fragmentary that I have been compelled to abandon the effort to unravel the knot, and can give an account of only the most general rela- |