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- 

 elusions in regard to the formations in question, although correctly 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 



S 



terra. 



* 



Dr. Hector, a geologist attached to the Government Exploring Expedition 

 under the command of Captain J. Pallisor (1857 - CO), 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.f 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 



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, arc of the same age as those from which fossils were ob- 



tamed 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 had attained 

 Its permanent elevation, the streams and rivers must have been constantly changing their channels ; lakes 

 ftuist have been formed, and then drained, and a series of effects produced corresponding to those Ave now 

 Witness over the whole region." — W. P. Blake, in lie port of a Geological Reconnaissance in California. 

 18; ^. 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 vvaterworn coast of the same material at the present day The evidence we 



