2 B, Silliman on the Deep Placers of 
well known to the Spanish missionaries from an early period, — 
long anterior to the date commonly mentioned (1849) for the — 
first discovery of gold in California. Prudential considerations 
led these ecclesiastics to prevent as far as possible the spread of 
any knowledge respecting the existence of gold on or near ~ 
their mission lands. 
rom this statement it will be observed that the gold in © 
California is probably of two distinct geological ages, that of 
the Sierra Nevada being Jurassic or Triassic, that of the Coast _ 
range Cretaceous or Tertiary. 7 
' Sources to which the Gold in California is referable.—The original — 
is undoubtedly the veins of gold-bearing quartz which occur so 
abundantly in all the slates and metamorphic rocks of the west- 
ern slope of the Sierras within the areas known as the gold re- 
gions. But this original or great source of the precious metal is 
historically secondary to the shallow and deep diggings or placers, 
in the former of which the gold was first discovered, and which ~ 
during the early years of California history furnished nearly the 
whole of the metal sent into commerce. That the placers were 
derived from the degradation or breaking up of the auriferous — 
veins and the distribution of the detritus thus formed by the ~ 
agency of running water and ice does not admit of a question. 
It appears also to be pretty conclusively proved that the gold- 
bearing gravel is of two distinct epochs, both geologically very 
modern, but the later period distinctly separated in time from — 
the earlier, and its materials derived chiefly from the breaking up 
and redistribution of the older or deep placers. These appear — 
to be distinctly referable to a river system different from that — 
which now exists, flowing at a higher level, or over a less eleva- 
ted continental mass, and with more power, but generally in the — 
direction of the main valleys of the present system. The reasons 
for this opinion will be hereafter stated more at length. : 
The sources to which the gold in California is referable are 
therefore 
Ist. The distribution of placer gold by the present River Sys- _ 
tem, giving the ‘Shallow diggings.’ | 
2d. The distribution of placer gold by an ancient River Sys- — 
tem, known as ‘ Deep liggings. 
of the Sie Ne quartz veins in the metamorphic rocks 
‘This is also the order in which the development of the coun- _ 
try by human industry has brought the gold to light: the com- _ 
paratively small number of exceptions to this generalization from _ 
the early workings of quartz mines forming in fact a confirma- — 
tion of its general accuracy. , 
The first rush of adventurers was to the shallow placers, 
