BEAK VALLEY. 191 



about 1,400 feet. It cannot be regarded as a part of the Markdgunt, but 

 occupies an intermediate position between that plateau and the Tushar. It 

 is interesting chiefly as being the locality from which emanated a large 

 portion of the lavas of the trachytic eruptive epoch. Probably it was the 

 scene of eruptions of the first epoch also, though the lavas which it may 

 have there poured forth are deeply buried beneath the great extravasated 

 masses of the second period, and are revealed only in the fragments of 

 andesite which are seen in the older conglomerates and by the lower beds 

 at the base of the Tushar, which are brought up to daylight by the fault at 

 its base. 



Crossing the southern rim of Dog Valley we descend into another 

 valley of a little lower altitude, called Bear Valley. The divide between 

 the two consists of a low range of hills, which are the degraded remnants 

 of old volcanic piles which were once, no doubt, of imposing magnitude, 

 giving vent to the huge sheets of lava which diverge from them, but are 

 now reduced to mere hills and discrete masses of dolerite and basalt. 

 Reaching the bottom of Bear Valley, we find a smooth, park-like inclosure 

 of ample dimensions, with high hills of trachyte on the east and the bril- 

 liant rosy red of the Eocene (Bitter Creek) on the west. It has already 

 been stated that the Markagunt has a fringe or border of sedimentary rocks 

 upon its western and southern sides, and this border is from 2 to 6 

 miles in width. In other words, the volcanic beds which cover its central 

 and eastern portions do not extend to the western and southern margins of 

 the uplift. Bear Valley lies at the foot of a broken crest which is formed 

 by the sudden termination of these eruptive masses. This boundary is a 

 very irregular one, having westward projections and eastward recesses. 

 But it is necessary to keep in mind one important relation. The vents stood 

 near this western margin. The main flow of the erupted materials was 

 towards the east, in which direction they extended probably as far as the 

 Sevier Plateau, or until they are lost beneath more recent sub-aerial accu- 

 mulations. Towards the west their progress was arrested by the rising 

 slope of the country, and they do not appear to have extended more than a 

 very few miles in that direction. Then, as now, the face of the country 

 sloped downward from west to east, though the gradient was considerably 



