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Show 52 GEOLOGY OF THE HIGH PLATEAUS. ever the mind recurs to it. Many thousandsâ€"nay, even tens of thousandsâ€"of feet of strata have been stripped off from their summits and scattered far and wide. As fast as they were denuded they arose, maintaining, and probably even increasing, their altitudes in spite of the waste. Much of the denuded material has been redistributed in strata around their flanks upon the old lake-bottoms of Tertiary time, where there has been, relatively at least, a gradual subsidence as sedimentation progressed. The great faults and monoclinal flexures where the strata are now hog-backed against the flanks of the ranges are the apparent results of the shearing motion set up by the rise of the mountain platforms on one side and the sinking of the newer deposits on the other. In the plateaus the action of erosion has been strikingly different. The tables have been affected only in comparatively slight degree more than the adjoining lowlands. Indeed, erosion has wrought almost equally upon high and upon low levels. In some portions the denudation has been stupendous, but the denuded material has not been carried down and redistributed in the plains below, but has found its way into the deep canons which cut below its lowest platforms and has been swept through the Colorado to the ocean. Now, it is unquestionably a true law of nature that the denuding agencies operate more vigorously against highlands than against lowlands, and it is quite as true in the Plateau Country as elsewhere. But the recency of the differential elevations of the Plateau Province has not permitted any very great difference to show itself as yet, though it is easy to see that a difference really exists, and is even conspicuous. Furthermore, the peculiar fact that the deeply sunken drainage channels of the province do not allow of great accumulation and restratification at the bases of the loftier masses is a sufficient reason why lower levels should be eroded as well as higher ones, though to a less extent. We cannot, therefore, attribute the faulting and monoclinal flexing of the plateaus to erosion of the uplifts and the deposition of the debris at their flanks, for no such (relatively greater) amount of erosion is found upon the uplifts, and no such depositions take place upon their flanks. The Kaibabs have been enormously denuded, but not much more upon the highest than upon the lowest portions. The High Plateaus have, compared with the |
