AGE OF THE GOLD. ۱ 279 
epoch when the powerful and general denudations took place which destroyed the large extinct 
mammalia.!’’ Although, as before observed, the relations of the auriferous drift to the older or 
Tertiary strata at the base of the Sierra Nevada are not yet clearly shown, it is believed that 
these marine strata containing Miocene fossils are free from gold. Gold is found under hori- 
zontal strata of great thickness and extent, but it will probably be found that these deposits 
are comparatively modern; more recent than the period of the Mammoth and Mastodon. 
It is also the opinion of the distinguished geologist, whose name has been mentioned, that it 
is probable that the impregnation of the Urals with gold took place when the highest peaks of 
the chain were thrown up and its present watershed established, and when the syenitic granites 
and other comparatively recent igneous rocks were erupted along its eastern slopes.? It is 
probable that the impregnation of the rocks of the Sierra Nevada was similarly produced. We 
find great lines of erupted syenitic granite and dykes of greenstone and serpentine traversing 
the auriferous districts. It seems most probable that the appearance of the gold was nearly 
coincident with that mighty convulsion which resulted in the elevation of a great part of the 
Coast Mountains and the drainage of the whole western base of the Sierra Nevada, until that 
time covered by the waves of a Post-Tertiary sea. 
At such a time denudation by floods would be most active; and, until the newly risen conti- 
nent had attained its permanent elevation, the streams and rivers must have been constantly 
changing their channels; lakes must have been formed, and then drained, and a series of effects 
produced corresponding to those we now witness over the whole region. 
There is no doubt of the Post-Tertiary, or at least the Post-Pliocene, age of the Coast Moun- 
tains. We find them composed in great part of Tertiary strata, thrown into great wave-like 
flexures, with here and there a granitic axis of limited extent, but with serpentine abundant. 
In the auriferous regions a similar serpentine abounds, and has in all cases the aspect of an 
intrusive rock. The movements which attended the uplift and plication of the Coast Mountains 
must have affected the whole western slope of the Sierra Nevada. Iam thus led to the conclu- 
sion that the impregnation of the rocks with gold and the formation of the Coast Mountains 
were nearly synchronous. 
1 Siluria. . 
2 Russia in Europe and the Urals. 
