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Show COMPARISON OF OROGRAPHIC FORMS. 53 Kaibabs, suffered but little from erosion. In neither district can we look for the same causation of faults and flextures as we might at first feel inclined to employ to explain those of Colorado and the Uintas. In the first chapter I have alluded to the possible effects attending the removal of great loads of strata from one locality of considerable area and the deposition of the same materials in adjoining areas; and while we may rationally suppose this transfer of loads to have important consequences in respect to vertical movements, we seem compelled to postulate additional forces, which for want of any definite conception as to their real nature we call Plutonic forces. The necessity for such a postulate seems perfectly obvious in the plateaus, and a little consideration will, I think, make its necessity apparent in the mountains of Colorado and the Uintas. It is not impossible that the differences existing between the structural profiles of the Plateaus on the one hand and those of the Parks and Basin Ranges on the other may be largely, or even wholly, due to the fact that in the latter regions the debris has been deposited at the bases of the mountains, while in the Plateau country it is carried away through the canons to another part of the world. Hence in the Plateaus we have the result of the uplifting forces, almost pure and simple, while elsewhere it is complicated, and generally reinforced, by the effects of the transfer of great loads from the mountain platforms to the plains and. valleys around their bases, followed by a readjustment of the plastic earth to a statical equilibrium of its profiles. In comparing the plateaus with the Basin Ranges we have to deal with the fact that the displacements of the latter are in the main older than those of the former, though younger than those of the Eastern Rocky Ranges. Erosion has operated powerfully upon all of the Basin Ranges, and the aggregate displacements are greater than in the plateaus. The strata ordinarily incline at larger angles and exhibit a greater amount of subordinate fracturing and dislocation. There is, however, some similarity between the plateau and basin uplifts. Both present a succession of inclined platforms, sloping in the same direction, with greater dislocations upon the uplifted sides. In the Basin Ranges, the uplifting being greater, the inclination is correspondingly greater, so much so, that we pass from the notion of a plateau or platform to that of a mountain slope. The inclination of the |