210 QUIOKSlLVEll DEPOSITS OF THE TACIFIC SLOPE. 



posing at least a partial separation of these areas daring the Carboniterous. 

 This snpposition is in entire accord not only with the structural anal- 

 ogies of the region, but with the detailed observations of Mr. Clarence 

 Kino-i j^i^^l l,i^ colleagues, who were led to infer the existence of a conti- 

 nental area daring the Paleozoic west of longitude 117° 30', in latitude 40°. 

 Such a range as the Sierra, though partaking in the general compression 

 and movement of the whole country, must offer a tremendous resistance, 

 and, at any one of the active periods during which the physical conditions 

 permitted contortion of strata along the western flank of the Sierra, these 

 must have been driven against the barrier until they could yield no more. 

 Thus if a pile of cloths were compressed from their edges (as in Hall's 

 famous experiment) with enormous energy, they Avould be forced into 

 plications so sharp that the dip at any point would be neai-ly vertical It 

 seems to follow that at different upheavals (some of them perhaps as yet 

 untraced) strata to the west of the great Sierra may have been driven into 

 the nearly vertical position of the gold slates, their original stratigraphical 

 relations thus becoming completely obscured. I do not consider it certain, 

 therefore, or even probable, that the Carboniferous slates near Pence's 

 ranch first assumed their present position subsequently to the Knoxville 

 period. It may be that they have stood nearly as now^ ever since the Car- 

 boniferous of Utah was raised above water, while the slates of Horsetown, 

 of the ao-e of which nothing is know'n, may possibly owe their vertical dip 

 to still earlier convulsions. 



The Carboniferous slates of Pence's ranch are serpeutinoid, and, 

 thouo-h distinctions between them and the metamorphosed Knoxville beds 

 mifht perhaps be drawn, the rocks are very similar. But, just as it seems 

 to me that successive upheavals may have produced similar effects upon the 

 arrano-ement of strata, I think the association of a certain uplift with a par- 

 ticular series of chemical changes tends to show that analogous dynamical 

 conditions might lead to molecular changes of the same kind. It seems 

 therefore not at all impossible that both upheaval and metamorphism at 

 Pence's ranch were in the main earlier phenomena than those traced in the 

 Coast Rano-es. If so, their effect must have been felt throughout a great por- 



1 U. S. Gcol. Expl. 40tb Parallel, vol. 1, Systematic Geology, p. 534. 



