THE BUILDING OF THE TDSHAU. 183 



Whether the somewhat abrupt western boundary is due to the faulting 

 suggested above or to the termination of the old couUes it is not possible to 

 say with confidence, but the former view seems to furnish the easiest 

 explanation. 



At the western base of the Tushar, near the town of Beaver, is seen a 

 very recent basaltic crater in a very perfect state of preservation. Farther 

 northward are others, some of them so recent that we may easily suppose 

 that their eruptive activity has ceased within a few hundred years. Many 

 of the basaltic craters throughout the Plateau Country seem to be equally 

 recent, though many others have considerable antiquity. On the whole, 

 however, the true basalts are the most recent of all eruptions. They are 

 seldom found in the heart of the older eruptions — indeed, I am able to 

 recall but few such instances — but they occur around the outskirts of 

 older volcanic districts, and often at a considerable distance from them. In 

 respect to magnitude of eruptive mass, the basalts are here decidedly 

 inferior to every other class of rocks. 



THE BUILDING OP THE TUSHAR. 



To go back to the commencement of the series of events and pro- 

 cesses which ha,ve combined to rear this majestic range to its present alti- 

 tude and proportions and give it its present details is no easy task. But 

 while there is much room for conjecture, there are many facts which appear, 

 after careful analysis, and which are sufficient, when properly arranged, to 

 give a connected history, even though it be but a faint outline. 



It is necessary to find, in the first place, some initial epoch marking 

 the beginning of the train of events which have been directly concerned 

 in the construction of the range, and this is the same epoch which forms 

 the starting-point probably of the processes which have built all of the 

 High Plateaus. This is the close of the Upper Green River epoch. The 

 direct evidence that the Tushar had its birth-throes at this period is not so 

 clear as in the others, but the cumulative indirect evidence is very strong 

 and will become apparent as the discussion proceeds. It may be sufficient 

 to remark just here that this view harmonizes with all known facts and aU 

 observations, and is in conflict with none. 



