56 THE AURIFEROUS GRAVELS OF THE SIERRA NEVADA. 
Butte and Plumas, partly because the rocks begin to be more and more cov- 
ered with volcanic materials, and partly because of other conditions, to be 
hereafter explained. 
It is true, in a general way, that the region of auriferous gravels is also 
that of quartz veins. For in the Sierra Nevada, as almost everywhere 
else in the world, there seems to be an intimate and not easily explained 
connection between the metal gold and the mineral quartz. It cannot be 
said that quartz is the exclusive “ gangue” or accompanying vein-stone of 
gold; but this metal is found, with comparatively small exceptions, in the 
veins of quartz which intersect metamorphic rocks, and also, to some extent, 
in the slates which lie adjacent to such veins. A large portion of the gold 
actually obtained, however, throughout the world comes from the débris of 
such veins and rocks, formed by the operation of those eroding and disinte- 
grating agencies which are and have been at work ever since rocks began to 
be formed. There are regions of the earth where gold has been procured in 
large quantities from “ washings,” —that is, from the working of detrital 
materials, especially of gravels and sands, and where no mining in the solid 
rock has ever been attempted, or indeed any veins of quartz discovered ; but 
it is, perhaps, not unreasonable to say, that, im any region where this metal 
is found in the superficial detritus in even a moderate amount, there or 
somewhere in the vicinity metamorphic rocks would be discovered, after some 
search, and that these would be found to be intersected with veins or masses 
of quartz. Further investigations would prove, in the great majority of 
cases, that the gold in the detritus came from those quartz veins, or from the 
rocks immediately adjacent to them. Every great gold-producing district in 
the world furnishes a portion of the metal from washings, and another part 
from mining in the solid rock. There have been facts observed in California, 
however, which would seem to indicate a different origin for a portion of the 
gold there obtained, as will be mentioned farther on. 
It is a remarkable fact that the veins which are productive of gold, the 
world over, are in a very great majority of cases, much simpler in their mode 
of occurrence than those which are productive of the ores of the other metals. 
Auriferous quartz veins are made up of quartz alone, with little or no admix- 
ture of other earthy minerals, such as calcite, brown-spar, heavy-spar, and fluor- 
spar, which, im ordinary veins, are of frequent occurrence, often making up a 
large part of the gangue. The writer has never seen, among the many quartz 
veins examined in the Sierra Nevada, a trace even of fluor-spar, or anything 
