FORMER VIEWS OF GEOLOGISTS IN REGARD TO THEM. 69 
important localities from Tuolumne to Nevada County. At that time the 
hydraulic system of mining was already extensively used, and the miners 
were beginning to have some idea of the real nature of the high gravel 
deposits. Mr. Blake, however, did not arrive at any very satisfactory con- 
clusions in regard to the formations in question, although correctl y describ- 
ing some of their peculiar features. He considered them to be partly of 
fresh-water, and partly of marine origin, and that these deposits once covered 
the whole region, and were brought into their present form and condition by 
erosion and denudation, which took place during the elevation of the 
Sierra.* 
Dr. Hector, a geologist attached to the Government Exploring Expedition 
under the command of Captain J. Palliser (1857-60), on his return from 
British Columbia, visited the mining region of the Sierra Nevada, and briefly 
describes what he saw, in an article published in the Quarterly Journal of the 
Geological Society of London.t He speaks of the gravel as being of marine 
* “These formations — the erupted and metamorphic rocks — form the floor or bed-rock upon which 
a very different series of formations is deposited. These formations consist of the auriferous drift in its 
various forms, and of a more uniform and extended series of nearly horizontal strata of clays, sand, and 
gravel. ‘The last are of marine origin, and probably Miocene or Pliocene Tertiary. In many parts of the 
region they are entirely swept away, and scarcely a vestige remains ; but at other points they are found 
in extensive plateaux, or gently-sloping table-lands bordering the rivers, which have cut their way down- 
wards through the strata and exposed them to view. The table-like hills or mountains seen from Knight’s 
Ferry, on the Stanislaus, and between the Mammoth Grove and the Great Cave, are examples of these 
deposits. In many places they are overlaid by a stratum of basaltic lava, like that at Fort Miller, on the 
San Joaquin. It is most probable that the principal deposits of this great series of nearly horizontal strata, 
flanking the Sierra Nevada in the Gold Region, are of the same age as those from which fossils were ob- 
tained farther south along the Tulare Valley... . . Great changes have been produced in all these 
deposits by denudation and erosion during and since the elevation of the region to its present level..... 
It seems most probable that the appearance of the gold was nearly coincident with that mighty con- 
vulsion 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 continent ha’ 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.” — W. P. Buaks, in Report of a Geological Reconnaissance in California. 
1858. pp. 276, 278. 
t “Before leaving these shingle-deposits, which are so largely distributed throughout the mountain 
valleys of British North America, I may mention that in California I found these terraces ranging on the 
western slope of the Sierra Nevada, at least to the height of 3,000 feet... .. At Nevada City, where 
the coating of shingle-deposit has thus been cleared from the surface of the coarse-grained and soft granite 
which underlies it, gigantic masses were exposed on what had once been the rugged shore of an inlet, just 
as may be seen on a waterworn coast of the same material at the present day... . . The evidence we 
