GEOLOGY OF THE SIERRA NEVADA. 
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known to the writer, no positive statement has ever been made public bear- 
ing upon this subject, except by members of the Geological Survey Corps; 
and that no information has, since the close or last suspension of that work 
in 1874, been added to that previously obtained. 
The first statement of the Secondary age of the auriferous rocks of the 
Sierra was made by the writer, in a synopsis of the results of the operations 
of the California Survey, under his direction, in the American Journal of 
Science, in the number for September, 1864. It is in these words: “ While we 
are fully justified in saying that a large portion of the auriferous rocks of Cali- 
forma consists of metamorphic Triassic and Jurassic strata, we have not a par- 
ticle of evidence to uphold the theory that has been so often maintained, 
that all, or even a portion, of the auriferous slates are older than the Car- 
boniferous ; not a trace of a Devonian or Silurian fossil having been dis- 
covered in California, or indeed anywhere to the west of the 116th meridian.” 
This statement still remains true so far as the non-existence of Silurian and 
Devonian fossils in the Sierra Nevada is concerned. Nothing older than 
Carboniferous has been found in the gold-bearing region proper of California, 
while quite a number of new localities and isolated specimens of Secondary 
fossils have been obtained from various points in the heart of the mining 
region along the western slope of the Sierra Nevada. The evidence afforded 
by fossils thus far collected by the Survey, with reference to the age of the 
gold-bearing rocks, will now be briefly set forth. 
Calling to mind, again, the fact that, up to the commencement of our 
work in 1860, not a single fragment of a fossil from the auriferous rocks of 
California had ever been described or noticed in print, so that it seemed 
almost hopeless to expect to find any evidence bearing on the extremely in- 
teresting question of the geological age of this formation, we will mention in 
their historical order the principal occurrences which came to our notice. 
The first ray of light on this obscure subject was shed by a specimen ob- 
tained from Hon. John Conness, in 1861, and which was stated by him to 
have been found in the slates near Georgetown, El Dorado County. It was 
stoutly adheres to his favorite theory of the Silurian age of all the auriferous rocks of the world, perhaps 
may have found the desired confirmation of his views in a communication made to the Geological Society 
of France, by Elie de Beaumont, in behalf of Mr. L. Simonin (Comptes Rendus, Tome 50, page 391), in 
which the latter claims to have recognized Trilobites in the auriferous slates of the Sierra Nevada, with- 
out giving any further information on the subject, or mentioning even the name of the locality where he 
made this fortunate discovery. To Mr. Simonin’s value as an authority we shall have occasion to refer 
again in a future chapter. 
