52 GEOLOGY OF THE HIGH PLATEAUS. 



ever the mind recurs to it. Many thousands — nay, even tens of thou- 

 sands — of feet of strata have been strijjped off from their summits and 

 scattered far and wide. As fast as they were denuded they arose, maintain- 

 ing, 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 platfoiTQS on one side and the 

 sinking of the newer deposits on the other. In the plateaus the action of 

 erosion has been strikingly difi'erent. The tables have been afi'ected only 

 in comparatively shght 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 plat- 

 forms 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 differen- 

 tial elevations of the Plateau Province has not peraiitted 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 suffi- 

 cient 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 



