228 GEOLOGY OF THE HIGH PLATEAUS. 



alluvial conglomerate derived from their degradation. Only at the north- 

 ern and southern ends are the sedimentaries clearly seen in mass lying 

 beneath the old lavas. At a few intermediate points, however, and espe- 

 cially in East Fork Canon, some metamorphosed beds of peculiarly inter- 

 esting character are exposed, and these will receive special attention in the 

 latter part of this chapter. 



The eruptions which compose the plateau mass belong to several well- 

 separated periods, which for the most part had their locations at the same 

 centers or axes. Of these centers or axes there are in the Sevier Plateau 

 three — one at the loftiest part of the table at the summit of its northern 

 slope, the second about 2 miles farther south, the third in the southern 

 section of the plateau, right abreast of Panquitch Canon and about 30 

 miles south of the second. They may be distinguished as the northern, 

 central, and southern eruptive centers respectively. Of these the largest 

 and most voluminous is the northern one ; in truth it is apparently the 

 most important one of the entire district. 



Immediately opposite the Mormon town Monroe the great wall of the 

 plateau rises more than a mile above the valley plain, presenting the edges 

 of the volcanic beds, which appear to be very nearly horizontal and more 

 than 4,000 feet in thickness. How much more is impossible to say, for the 

 lowest sheets are concealed. Upon the summit of the wall a transverse 

 ridge runs across the table to the eastern side and ends in a high knob 

 overlooking Grass Valley and named the Blue Mountain. It was in the 

 vicinity of this ridge that the grander eruptions had their origin. 



The great amphitheater near Monroe has laid open the table to its 

 foundation, but the promise of information conveyed by such a section is 

 not fulfilled. It has revealed a bewildering maze of earlier rocks lying in 

 all possible positions and having but few intelligible relations to each other. 

 Upon them rest later floods in rather regular bedding, which succeed each 

 other to the summit. I have revisited this locality repeatedly, but have 

 generally found at each visit more questions than answers. The confusion 

 among the lower rocks is indescribable, and the exposures of any given 

 bed so fragmentary that I have been compelled to abandon the effort to 

 unravel the knot, and can give an account of only the most general rela- 



