Geological Survey of California. 263 
The vast Tertiary formations on the flanks of the Sierra Nevada, so im- 
portant as being the locality of the hydraulie mining operations, are not 
of marine origin, as has been s Poceses asserted, 
deposits, their position, age, and other characters, are exceedingly inter- 
esting ; ‘but it is impossible, in this inistieeting: to do more than hint at 
There is perhaps no subject cars ge with v8 geology of the Pacific 
coast, in regard to which ther so many misapprehensions, as there 
are in what has been published be cstesieaial on ahs nature and distribu- 
tion of the detrital deposits which are so extensively voile by the 
methods known as hydraulic and tunnel mining. It has been assumed 
that these deposits are of marine origin, and that they originally ex- 
tended over the whole western slope of the Sierra Nevada, a condition of 
things which, were it true, it would be of vast importance 1 California 
to “i but the real facts of the case are entirely differe 
In the first place, these deposits are uot of marine ee as is proved 
by the Biot that, although frequently found to contain impressions of leaves, 
masses of wood and imperfect coal, and even whole buried forests, as well 
as the remains of land — and occasionally those of fresh water, 
not 3 trace of any marine production has ever been found in them. 
Again, these detrital depts: are distributed over the flanks of the 
Sierra j in any such ae as they wo ave been if _? were the result 
of the action of the sea. On shinee contrary, there is every reason to be- 
lieve that they consist of materials which have been brought down from 
the mountain-heights above and deposited in predzinting valleys : some- 
imes in v. ry narrow accumulations, simple beds of ancient rivers, 
at other times in wide lake-like expansions of — water-courses; and 
this under the a action of causes similar to those now existing, but proba- 
of itu: 
The e deposition of this auriferous detritus was succeeded, throughout 
the whole extent of the Sierra Nevada, by a ‘tremendous outbreak of vol- 
They effect of abe oe which has taken place _—s these streams 
= stops flowed down the mountains, has been most extraordinary. For 
Ow, these de epoeita eo gravel a overlying voleanic materials, ins — of 
is 
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