526 PECULIARITIES OF THE VOLCANIC DEPOSITS. 
to furnish strong additional evidence as to the source of the ancient streams and the general direc- 
tion of their flow. It is also worthy of note that universally, so far as I have yet seen, wherever 
there is much volcanic matter on the western slope of the Sierra Nevada, its quantity increases as 
we ascend, and the farther and the higher we go toward the summit of the range, the heavier does 
its mass become. 
I have seen but little of the actual summit of the range at any portion of its course northwest 
of the Sonora Pass, under such circumstances as enabled me to recognize the materials of which it 
is formed. But from the little that I have seen, I should be inclined to infer that the comparative 
scarcity even here of compact solid lavas, and the great prevalence of enormous quantities of brec- 
cia and other fragmentary materials, often stratified in nearly horizontal beds, was a curious fact, 
and not altogether an easy one to satisfactorily explain. I do not know, indeed, that it is the 
general fact. But, if it be so, it is one from which much might possibly be learned by careful 
study of the summit. 
The greatest hindrance at present to mining operations, wherever I have travelled in the gravel 
region, is the scarcity and uncertainty of water for hydraulic purposes, and the high prices which 
the miners are obliged to pay for what they do get of it. If water were plenty, reliable, and some- 
what cheaper, the extent of mining operations here would be rapidly and greatly increased, and in 
many localities with profit to all. 
I do not know that I have used in these notes any popular terms or expressions which require 
any further explanation than has already been given, unless it be the single word ‘ cement.” 
Under this designation is included, in different parts of the country, almost everything which 
occurs in the gravel region except the solid bed-rock ; and its meaning varies in different localities. 
But throughout the southern part of Placer and the northern part of El Dorado County it is used to 
designate anything and everything which overlies the auriferous gravel, and which does not contain 
any appreciable amount of gold. Here therefore it corresponds, of course, in general, to volcanic 
matter of every kind. But by far the commonest form of volcanic matter in the region examined 
by me is the variety which I have elsewhere called a “‘ coarse conglomerate ” ; this consists essen- 
tially of a mass of fine earthy material, more or less thickly filled from bottom to top with volcanic 
pebbles and roughly rounded boulders of every size, from the smallest to the greatest, which exhibit 
much variety of texture, and also, among darker colors, a large variety of shades. 
I am thoroughly satisfied that a very large proportion of the shallow-placer gold, that is, the 
gold which made the beds of the modern streams so rich in the early days of California history, 
was derived from the ancient gravel which those streams have washed away; though another 
portion, and undoubtedly a large one too, came directly from the quartz and the bed-rock which 
have been cut away in the excavation of the modern caiions. Furthermore, I greatly suspect that 
the aggregate quantity of gold which, in the process of excavating these cafions, has been ground 
to almost impalpable dust, and scattered by the water, as finest flour-gold, all over and throughout 
the mass of the whole Sacramento Valley, may be incomparably greater than all that the early 
miners found remaining in the gulches and the caiions. 
