l>LAiS'T BEDS OF OROVILLE, CALIFORNIA 389 



There can be no question that the plant beds at Oroville contain impor- 

 tant ore deposits, which may be correlated with those found elsewhere in 

 the Gold belt along the western slope of the Sierra Nevada. 



DISTRIBVTIO}} 



The known area occupied by the Monte de Oro beds is small, not over 

 2,000 feet in width, and about 2 miles in length, extending from the slope 

 of Monte de Oro, the end of Table mountain almost directly south, to 

 Feather river, where an excellent section is exposed. To the northward 

 they pass beneath the lava cap and Neocene deposits of Table mountain ; 

 to the southward their extent beyond Feather river is unknown, but is not 

 believed to be great — perhaps a mile — for on both sides the beds are lim- 

 ited by volcanic rocks which cover a large area east and southeast of Oro- 

 ville. " 



STRUCTURE A^D THICKyESS 



The strike of the rocks in the vicinity of the Banner mine is north 20 to 

 55 degrees west, with a dip of not less than 54 degrees to the northeast. 

 Some places the beds are vertical, but generally they dip from 62 to 70 

 degrees to the northeast. Along the river, which affords a continuous sec- 

 tion across the belt, the beds strike north and south and dip 52 to 85 de- 

 grees to the east, giving an estimated thickness for the monoclinal mass of 

 approximately 900 feet. The fact that the conglomerates and sandstones 

 are mainly along the borders, with slates prevailing in the middle of the 

 area, suggests that the mass may be an apprest synclinal. If so, the 

 thickness exposed is about 450 feet. 



RELATION TO ADJACENT VOLCANICS 



The fragmental character of the adjacent igneous rocks upon both 

 sides of the plant beds shows that they are tuffs and am3'gdaloids, and 

 consequently of volcanic origin. The tuffs are rarely bedded, but their 

 contact above and below the plant beds dips to the eastward approxi- 

 mately parallel to the stratification, so that the plant beds, as first shown 

 by Mr Turner (Journal of Geolog}', volume iii, page 394), appear to be 

 interstratified with the tuffs. This view is favored by the fact that the 

 conglomerates of the plant beds contain many pebbles like those of the 

 tuffs. Furthermore, there are in the same region, at a different horizon, 

 other masses of fossiliferous tuffaceous sandstone interbedded with the 

 regular tuffs. j\Ir Storrs recently discovered a small one on the north 

 bank of Feather river, one-fourth of a mile west of the mouth of IMorris 

 ravine, and the fossil shells it contains are the same as those of the Ban- 



