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Show 20 LNTTKODUCTOBY. There are five of these concentric lines of cliffs. In the centre there is an elliptical area about 40 miles long and 12 to 20 broad, its major axis lying north and south, and as completely girt about by rocky walls as the valley of Rasselas. It has received the name of the San Rafael Swell. Its floor is covered with the lowest Triassic strata, and probably in some portions of it the Carboniferous is laid bare, though it has not yet been seen. But, at all events, we know that the Carboniferous is very thinly covered, even if it be not exposed. Thus, as we pass from the summit of the Wasatch Plateau to the floor of the Red Amphitheatre, we cross the outcrops of nearly 10,000 feet of strata. The Tertiary is found only at a distance of 40 miles from it. Yet if we look back to Eocene time we shall find that the whole stratigraphic series from the base of the Mesozoic to the summit of the Eocene covered this amphitheatre. One. after another, in orderly succession, the vast stratigraphic members have been stripped off, and the edges of the remaining portions are seen in the successive cliffs which bound the encircling terraces. Still more vast has been the erosion which took place in the vicinity of the Grand Canon of the Colorado. Here the Carboniferous now forms the floor of the country, though a few patches of Trias still remain in the vicinity of the river. But the main body of Triassic rocks now stands 50 miles north of the river, and beyond them, in a series of terraces, rise the Jura, the Cretaceous, and the Tertiary, the latter usually capped by great masses of volcanic rock. We may note here another question which presents itself in connection with the differential movements among the various parts of the province. Those areas which have been uplifted most have suffered the greatest amount of denudation. Is it not possible in some cases and under certain restrictions to invert this statement and say that those regions which have been most denuded have been most uplifted, thereby assuming the removal of the strata as a cause and the uplifting as the effect? May not the removal of such a mighty load as 6,(00 to 10,000 feet of strata from an area of 10,000 square miles have disturbed the earth's equilibrium of figure, and |