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REVIEW AND GENERAL DISCUSSION. 



507 





The relative height of these grander spurs above the adjacent regions may, indeed, have been far 

 less originally than it now is, for the tremendous denudation which has since taken place would 

 naturally be felt in its greatest power in the lower regions, while the more elevated ridges, being free 

 from the devastating floods and currents, would wear away more slowly, and thus the difference of 

 altitude between adjacent higher and lower regions would be, in many localities at least, increased 

 instead of diminished by time. But I think that the relief of the range in its earliest history was 

 sufficient and of such a character as to mark out, even then, a drainage system for its western 

 slope, which, so far as the outlines of its greater basins at least are concerned, has remained Essen- 

 tially unchanged from that day to the present time. 



At all events, the evidence that such was the case with the basin of the American Eiver, not 

 simply as a whole, but even with the separate basins of its North, its Middle, and its Southern 



Forks, is very strong. 



I know of no proof that any portion of the western slope of the Sierra which I have seen has 

 been beneath the sea at any time subsequent to the Jurassic Period. Nor do I know of any evi- 

 dence that the range has been greatly disturbed in altitude since the Cretaceous, while the 

 evidence seems to me conclusive that it has not been subject to any considerable change in this 

 respect since the earliest of the ancient auriferous gravels began to accumulate on its western 



slope. 



What vast periods of time may have elapsed between the original upheaval of the range in the 

 Jurassic (if then it was) and the time when the auriferous gravels now underlying the volcanic 

 matter began to accumulate, as also what changes may have taken place within those periods in 

 the surface sculpturing of the range, I do not know. But I think it was within this period that 

 the auriferous quartz veins themselves were formed. They were certainly formed before the gravel 

 period began ; while it also seems eminently probable, if not altogether certain, that the date of 

 their formation was entirely subsequent to that of the great upheaval of the rocks. 



But, if asked my opinion as to whence came the gold contained in the quartz veins, I should 

 say from the enclosing and surrounding rocks themselves. There are abundant facts to prove 

 beyond all doubt that gold is distributed in minute quantities far and wide throughout the great 

 mass of the metamorphic rocks themselves, entirely independent of all the quartz veins. Indeed, 

 it may well be questioned whether there is so much as a single ton of metamorphic rock of the 

 auriferous series above the level of the sea in the Sierra Nevada in which a sufficiently delicate 

 chemical analysis might not detect a trace of gold ; and it can hardly admit of a doubt that the 

 aggregate quantity of the gold which is thus distributed through the mass of the rock is incom- 

 parably greater than that which exists in the quartz itself. There is thus no lack of resource from 

 which the gold in the quartz may have easily been derived ; while, on the other hand, the general 

 character of the quartz veins themselves appears to me to furnish strong evidence in favor of the 

 view that the gold in them has been thus derived. They are not often what are technically called 

 lissure veins. They are generally intercalated between the planes of stratification of the slates, 

 and irregular bunches and lenticular masses of limited extent are common among them. Further- 

 more, the rocks in many localities are penetrated in every direction by little irregular quartz 

 veinules and stringers, which often carry gold, and are sometimes in spots extremely rich, even 

 when less than an inch in thickness. 



As examples of many of the facts just stated above, we need only glance at such localities as 

 Spanish Dry Diggings, Georgia Slide, Greenwood, and the country between Johntown and George- 

 town in El Dorado County, Quail Hill in Calaveras County, Whiskey Hill (the locality of the 

 Harpending mine) in Placer County, etc. 



Since the whole theory of the ancient gravel streams of the Sierra is so intimately connected with 

 the topography of the range during and immediately preceding the gravel period, it may be well 

 before going further to notice some of the theories previously held upon this subject, together with 

 some of the more prominent objections against them. 



It has been believed by some that the ancient gravel banks are the work of an ocean or inland 



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