SULPHUR BANK MINE. 263 



There is no trace of substitution of ore for the rock in .iny part of the 

 mine. It is true that ore is souietimes found in the crevices of concentric 

 layers of decomposed basalt, but it is evident that these crevices have first 

 formed through decomposition and that the cavities have subsecj^uently been 

 partially filled with ore, as any other openings would have bean. In true 

 substitution, the solution of the snbstance of the rock is a condition of the 

 deposition of ore and the interchange takes place molecule by molecule. 



It appears from the above that no absolute evidence of the deposition 

 of ore at the present time has been reached, but that the precipitation of 

 cinnabar, under some pressure, in the lower portion of the ore-bearing 

 ground, is not improbably still in progress.' Professors Le Conte and Rising 

 have also expressed the opinion that ore deposition has not ceased. 



The mine—The surfacc mine at Sulphur Bank is a labyrinth of excavations 

 in and below the decomposed layer of basalt. In a few spots the workings 

 have passed through the basalt, and lake beds, carrying cinnabar in greater 

 or less quantity, were found below it. Between tlie Hermann shaft and the air 

 shaft shown on the map an important ore body was followed down for several 

 hundred feet. This body had l)een worked out before my examination and 

 only the lowest portion of it was accessible. The small amount of ore re- 

 maining consisted, as has already been stated, of partially metamorphosed 

 sandstones and shales of tlie Knoxville grou-p, carrying small stringers of 

 cinnabar, quartz, and pyrite. The top of the ore body is said to have been 

 in lake beds similar to exposures made near by during my visit, but I was 

 not able to get satisfactory information as to the dei)th from the surface of 

 the contact between the pebble-bearing lake deposits and the brecciated, 

 metamoi-phic sandstones and .shales. This, however, is not a matter of great 

 consequence. 



I'iie underground mine consists of a shaft 417 feet deep, with seven 

 short levels. The rock is everywhere of the Knoxville group and sand.stone 

 predominates; it is much disturbed and is full of slickensides, l)ut the prev- 

 alent dip is to the southeast. No second ore body of importance has been 

 discovered, though traces of cinnabar are common. 



Excepting for the solfataric springs the underground mine at Sulphur 

 Bank resembles the other principal quicksilver mines of California. The 



'For a confirmation of tins deduction, see the addendum to this chapter (p. _2C9). 



