THE THREE PROVINCES DURING CENOZOIC TIME. 33 



and Eozoic rocks, are, as mountains, of very late upheaval. For some pur- 

 poses, and in broad generalization, erosion furnishes a valuable measure of 

 geological times. A mountain, as a mountain, is comparatively ephemeral. 

 The evidence of this is found on every hand as we study the Rocky Mount- 

 ain region. There can be no conclusion reached from reasoning on 

 geological data more certain than that the Uinta upheaval began at the close 

 of Mesozoic time, and has continued intermittently near to the present, and 

 during that time this- upheaval has suffered a degradation in areas of maxi- 

 mum erosion of no less than 30,000 feet; and there is evidence also which 

 leads to the conclusion that the conditions for great erosion were not per- 

 sistently maintained during this time. I have already stated that the Basin 

 Ranges occupy the area of maximum upheaval, and they are monoclinal 

 ridges. Had these ridges been upheaved greatly beyond their present 

 altitudes it is manifest that erosion would have carried them far back from 

 the lines of faults, a condition not found to obtain. 



In the erosion of these ridges, as an independent subject of study, the 

 geologist is impressed with the magnitude of the work which has been per- 

 formed by atmospheric agencies. It appears that each ridge is but a small 

 residuary fragment of the great inclined block, and the interrange spaces are 

 filled with clays, sands and gravels, the waste of these blocks, in such a 

 manner as to bury the underlying rocks over broad areas ; and whether we 

 consider the amount which has been lost from the blocks or the amount 

 which has been accumulated in the valleys, the loss here or the gain there, 

 this transferred material is very great. It is worthy of remark that over 

 much of the area, the deposit of this transferred material in the valleys was 

 subaerial, but in the northwestern portion of the province it was lacustrine. 



But when we compare the erosion which these inclined blocks have 

 suffered with that of many of the great blocks in the Plateau Province of 

 the Kaibab structure, or with that of the Uinta uplift, or with the great 

 uplifts in the Park Province, the erosion of the Basin Range ridges sinks 

 into insignificance. And when we consider, further, that the erosion in the 

 Plateau and Park Provinces which we are able to study has all been per- 

 formed during Cenozoic time, and that the conditions of maximum erosion 



were but- intermittent during that time, we are forced to the conclusion that 

 3 P G 



