68 THE: AURIFEROUS GRAVELS OF THE SIERRA NEVADA, 
mass, and distinguishing this deposit from all others in the State.* In his 
Report of the next year, 1854, Dr. Trask seems to have been led by more 
extended observations to abandon the idea of a river channel, and he divides 
the “placer mines” (including under this designation all the gravel wash- 
ings of the Sierra, whether high or low) into three “ranges,” the Upper or 
Eastern Range, the Middle Placers, and the Valley Mines.f The rationale of 
this division is not apparent from the description given; it seems, in view of 
the facts as at present developed, to be entirely artificial. In his last Report 
(1855), this author confines himself to the quartz mining interest, so far as 
the Sierra Nevada is concerned, except that he describes at some length the 
lava flow known as the Sonora, or Tuolumne County, Table Mountain, which 
he recognizes as having “ followed the course of a stream, filling its bed and 
banks.” He found both shells and leaves in the clays under the volcanic 
capping, which fossils he, however, considers as identical with those now liy- 
ing in the region. Dr. Trask perceived that this lava stream must have 
crossed the Stanislaus River where the caiion is some 1,600 feet deep, and 
concludes that it took possession of a former bed of this river, displacing the 
latter and filling up the space between its banks. Nothing further is added 
in this, his last Report, in regard to the phenomena of the gravel deposits. 
In 1854, Mr. W. P. Blake, one of the geologists attached to the Pacific 
Railroad Survey, made a tour through the gold mining districts of the Sierra 
Nevada, in the course of which he visited a considerable number of the most 
* “The peculiarities which characterize this formation, and which distinguishes it from all others in 
the State, are the following: the boulders found throughout its entire extent are very uniform in their 
characters, and are composed of quartz exclusively (or nearly so) this has a bluish-watery color in the 
mass, highly translucent and vitreous when fractured, constituting ninety-seven per cent. of all the stones 
found in the deeper diggings, they are invested by a dull but deep blue earthy material highly charged 
with pyrites..... The blue color of the drift in this range has been found to pervade all parts of this 
peculiar deposit wherever it occurs, its boulders maintain their character and percentage,” ete. — J. B. 
TRASK, l. c. 62, 63. 
+ “In order to convey a better idea of the mining districts, they will be divided into three distinct ranges, 
denominated the Upper or Eastern Range, the Middle Placers, and the Valley Mines. This has now be- 
come necessary from the fact that the characteristics of these districts are as distinctly marked as are the 
northern, middle, and southern portions of the State. It separates also three evidently distinct periods 
of the geological history of this part of the continent, in which marked changes are apparent upon the sur- 
faces that had emerged above the ocean during that epoch.” — J. B. Trasx, Report on the Geology of the 
Coast Mountains, etc., Doc. No. 14, Session of 1855. p. 72. 
+ “The fine clays contain an abundance of leaves of present existing genera and species, most of them 
may be found in the adjacent country distributed along the banks of the streams and in the deep ravines 
adjoining.” — J. B. TRasK, Report on the Geology of Northern and Southern California, etc., Doc. 14, Session 
of 1856. p- 21. 
