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Show 14 INTEODUCTOEY. But if we are to admit that the strata sank as rapidly as they accumulated we cannot shake off some ulterior questions. By virtue of what condition of the underlying magmas was such a subsidence possible? If they sank, they must have displaced matter beneath them, and what became of the displaced matter? If we look around the borders of the area and partially within it, we shall find a problem of an inverse order. The Uintas, the Wasatch, the Great Basin have suffered an amount of degradation by erosion, which is perhaps one of the most impressive facts which the physical geologist has yet been brought to contemplate. From the Uintas more than 30,000 feet of strata have been removed since their emergence. From the Wasatch the removal has been much more; from the Great Basin the degradation has been many, we know not how many, thousand feet. We are not prepared to believe that the Uintas ever stood 8 miles high, nor the Wasatch 12 miles high, but we know that their altitudes are merely the difference between elevation and erosion. It was from these ranges that the heaviest masses of the Cretaceous-Eocene sediments were derived. As fast as, or even faster than, the mountains were devastated to supply mass for the new strata, they continued to rise. But if they rose, fresh matter must have been thrust under their foundations, replacing the rising strata. Whence came the replacing matter? It may be premature as yet to say that the elevation of the mountains and subsidence of the strata are correlated in the way which these inquiries suggest, but the juxtaposition of the facts must be regarded as significant. POST-EOCENE HISTOEY----EROSION. With the desiccation of the Eocene lake began a new order of events in the history of the Plateau Country; in truth, its most instructive and impressive chapter. The lessons which may be learned from this region are many, but the grandest lesson which it teaches is Erosion. It is one which is taught, indeed, by every land on earth, but nowhere so clearly as here. If we could but find the evidence, we might be able in other regions to point to erosions of much greater amount. We may suspect that in the Appalachians a denudation has occurred compared with which the denudation of the Plateaus is small; and such an inference has no intrinsic |