170 QUICKSILVER DEPOSITS OF THE PAOIFIO SLOPE. 



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 of primitive rocks came to a complete close. The last exposed primitive 



rocks must have subsided and liave been buried under sediments formed 

 from pre-existing strata, and this subsidence must have exceeded in amount 

 tlie sum of all the upheavals to which they have since been subjected- 

 This seems to me a very artificial hypothesis, quite out of harmony with 

 those theories which have been found to accord best with other geological 

 facts. It is seldom that we find in nature abruptly arrested processes, sucli 

 as this is supposed to be, excepting where these are reversible, which tliis 

 is not. It is more natural to suppose that the area of primitive rocks 

 diminished progressively without ever being completely or irrevocably 

 buried. Thus, in the second million of years after oceans came into ex- 

 istence, one may imagine half as much fresh detritus to have formed as in 

 the first million years; in the third such period half as much as in tlie 

 second, and so on to the present day. Had this been the actual case, the 

 total amount of sediment at the end of an infinite time would differ infi- 

 nitely little from twice the quantity of sedimentary material at the end 

 of the first million years, and infinitesimal areas of primeval rocks would 

 still remain exposed even after the process had continued for an infinite 

 time. In using this numerical illustration I do not of course intend to imply 

 that the particular numbers selected are in themselves probable. The 

 length of the successive periods, in eacli of which the total quantity of 

 fresh detritus derived from the primeval massive rocks was half that sim- 

 ilarly produced in the preceding period, may have varied regularly or 

 irregularly. But I do maintain that neither theory nor observation afi'ords 

 any ground for the hypothesis that, during some one period in the eartli's 

 history, the entire area of primeval rocks was obliterated, never to reappear 

 If I am right in doing so, it is improbable that the primeval rocks have 

 been or ever will be entirely concealed froiu view at all points on the earth's 

 surface during any considerable time. In other words, contemplation of 

 the process of erosion leads to the same result as was reached by consid- 

 ering the mechanism of upheaval. 



Relations of granite — The obscrvatious wliich are usually cited in support of 

 tlie sedimentary origin of lavas depend upon the relation of granites to other 

 rocks. That granites are sometimes so connected with crystalline schists 



