at Sulphur Bank, California. 27 



changed by oxidizing agents carried down from above. But 

 when we go still deeper — beyond the influence of atmospheric 

 agencies, though still within the limits of the lava-cap — an 

 entirely different appearance and reaction is observed. The 

 decomposition is now no longer universal, but only in streaks 

 along water-ways; the res 

 chalky silica, but tough 

 earthy residuum is no longer acid from down-going acid waters. 

 but alkaline from up-coming alkaline or solfataric waters. In 

 this region and extending a little way above it, irregular cracks 

 and fissures running in all directions are filled with a hydrous 

 silica (opal) in a soft cheesy condition which might easily be 

 mistaken for ozocerite. This half-consolidated gelatinous silica, 

 evidently very recently deposited from the alkaline water, 

 when cut or broken is nearly always found to be streaked and 

 clouded with cinnabar. Here then undoubtedly we have still 

 forming under our eyes, mineral veins with quartz vein-stuff 

 -and metallic ore. "The work of nature has been interrupted 

 by the work of the miner." But of this more anon. 



Beneath the lava-cap. — Thus far we have confined ourselves 

 within the limits of the lava-cap. The observations of all 

 previous writers have been thus confined, and most of the facts 

 thus far mentioned have been noticed also by others. The 

 facts now about to be mentioned, however, have not been 

 previouslv described. 



At the time of our earlier visits, viz : from 1877 to 1880 in- 

 clusive, the underlying country rock was reached and examined 

 only in one place, viz: in the excavation called "the wagon- 

 spring cut."* This, at that time the deepest opening, is situated 

 near the margin of the lava-flow, where the lava is thin, and 

 therefore the stratified country rock is quickly reached and is 

 penetrated thirty or forty feet The stratified bed-rock consists 

 here of sandstones and "shales standing nearly on edge. The 

 opening has followed a soft breceiated stratum, several feet 

 thick, composed of a mere rubble of angular fragments of 

 sandstone and shale with mud of bluish clay between. On 

 either side of this rubble-mud stratum is firmer rock; on one 

 sale sandstone and on the other shale. The mud is hot and at 

 the bottom of the cut, hot alkaline waters highly charged with 

 sulplmlnc. carbonic and boraeic acids, are seen to- bubble up 

 freely. The rubble-mud stratum is evidently a water-way for 

 the up-coming of hot water containing alkaline sulphides with 

 excessof sulphydric and carbonic acids (solfataric waters). This 

 rubble-mud stratum is rich in cinnabar, though in invisible 



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