174 GEOLOGY OF THE HIGH PLATEAUS. 



of craters, but mere remnants of the uppermost sheets, which have been 

 almost wholly removed by erosion. From their bases radiate profound 

 gorges separated by huge buttresses, which extend to the lowest valleys 

 and plains, while beyond them rough crags and shattered domes rear their 

 bald summits to the clouds. But all this grand detail of mountain form 

 has been carved out of the vast block of the tabular mass by the ordinary 

 process of erosion. The lavas accumulated sheet upon sheet, the subter- 

 ranean forces uplifted the block and tilted it, and the rains and torrents have 

 done the rest. 



The eastern front of the Tushar is far more rugged and mountainous 

 than the western, and the explanation is obvious. The western slope is along 

 the dip of the strata, which, though considerable near the crest, is slight as 

 we recede from it westward. The eastern slope is across the upturned 

 edges, and from the nature of the case is very abrupt. The power of water 

 to corrade and carve rapidly increases with the slope, and the resultant 

 sculptural forms are correspondingly bold and craggy. 



The loftiest, boldest, and most diversified portion of the Tushar fronts 

 the Sevier Valley in the vicinity of a little hamlet called Marysvale, situ- 

 ated about 27 miles south of Richfield. The great mountain wall leaps at 

 once from the narrow platform of the valley to nearly its greatest altitude. 

 Immense ravines, rivaling those of the Wasatch in depth, but narrower and 

 with steeper sides, have deeply cleft the great tabular mass, and subdivided it 

 into huge pediments, which from below appear like individual mountains. 

 The finest gorge is named Bullion Canon, in the jaws of which the little 

 village of Marysvale is situated. Ascending it, we may gain some informa- 

 tion concerning the structure of this portion of the Tushar mass. The 

 lowest beds forming the base courses of the uplift are quartzites resulting 

 from the metamorphism of sedimentary strata, which are believed to be of 

 Jurassic age. They are considerably disturbed, yet not excessively so. 

 The prevailing dip is to the west, though it is by no means uniform. The 

 main fault, which has thrown down the platform of the Sevier Valley, 

 runs north and south along the base of the mountains, but the whole dis- 

 placement is probabl} 7 by a series of parallel repetitive faults. I have seen 

 but one of the faults west of the principal displacement, but have inferred 



