198 STRUCTURAL GEOLOGY. 







region down so that an axial ridge was not produced. If elevation was 

 intermittent it might have been fast for a time, and then ceased until the 

 region was planed down to a general level now represented only by the 

 summits of the highest peaks, and then a new upheaval carried it to its 

 present elevation. But the rate of this last uplift must have been slow or 

 the axial ridge would have been more pronounced, and hence we may infer 

 that the elevation was either slow by continuous motion, or what would be 

 its equivalent, slow through intermission of movement, with the last epoch 

 of elevation slow. Further light will be thrown on this subject when we 

 consider sedimentation. It is manifest that if elevation was slow so that 

 degradation progressed nearly as fast as displacement, then degradation was 

 slow. Again consider the amount of degradation. From this portion of 

 the Uinta range a block three and one-half miles in thickness has been 

 carried away, all since the close of Mesozoic Age ; and for this degradation 

 the declivity was small so that its progress was slow, and we have some 

 conception of the amount of time which has elapsed since the beginning of 

 the Uinta upheaval. 



SCHOLIUM. 



Let us now turn aside for a moment from the main argument to consider 

 a statement which I have elsewhere made concerning the Basin Ranges. These 

 are monoclinal ridges of displacement, of narrow base and steep declivities 

 where conditions for rapid degradation obtain, but the amount of degrada- 

 tion of any Basin Range is exceedingly small as compared with the Uinta 

 Range, and we are forced to conclude that the epoch of its upheaval is much 

 later than that of the inception of the Uinta uplift, but may be of about 

 the same date as the last throw of the Uinta displacement. 



SEDIMENTATION. 



Soon after the inception of this upheaval, sedimentation began on either 

 flank and continued during the progress of the uplift until on the north 

 side more than 6,000 feet of sandstones and shales had been deposited, and 

 where the Brown's Park beds overlap Bridger beds about 8,000 feet. On 

 the south side also there was a great accumulation, the extent and charac- 



