68 



THE AUBIFEROUS 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 



e " followed the course of a stream, filling its bed and 



banks. 



■}"> 



He found both shells and leaves in the clavs under the volcanic 



capping, which fossils he, however, considers as identical with those now liv- 



Dr. Trask perceived that this lava stream must have 



■ 

 ■ 



ing in the region. $ 

 crossed the Stanislaus River where the canon is some 1,G00 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 pecnEari ties which characterize this formation, and which distinguishes it from all. others in 

 the State, are the following : the bonlders 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, ,, etc. — J. B„ 

 Trask, 1. c. 62, 63. 



t " 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. Trask, 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 tin; streams and in the deep ravines 

 adjoining." — J. B. Trask, Report on the Geology of Northern and Southern California, etc., Doc. 14, Session 

 of 1850. p. 21. 







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