COMPARISON OP OROGRAPHIC FORMS. 53 



Kaibabs, suffered but little from erosion. In neither district can we look 

 for the same causation of feults and flextures as we might at first feel in- 

 clined 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 sup- 

 pose this transfer of loads to have important consequences in respect to ver- 

 tical 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 ordi- 

 narily 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 



