350 QUICKSlLVEll DEPOSITS OF TUE PACIFIC SLOPE. 



triuled furnish a shorter road back to the surfiice.' The water nmst he well 

 tihored on its course, since there is no evidence that organic matter is cai'- 

 ried to the source of heat. 



The cinnabar deposit. — Tlic quantity of uicrcuric sulphide in the deposits 

 from the active springs is very minute, and there is in this district nothing 

 wliicli could be called quicksilver ore in a connuercial sense, excepting near 

 the mine workings and furnace on the northern central portion of the area 

 mapped. Cinnabar is deposited in considerable abundance only in the de- 

 composed granite, though a few paints and seams have penetrated into the 

 basalt at the southern end of the basin-like depression. By no means all 

 of the decomposed granite, however, even in this area, shows an}- ore, the 

 cinnabar occurring only as impregnations in the decomposed area, appar- 

 entlv along the courses of half-obliterated tissures in the soft material. 

 The underground workings are now almost wholly inaccessible, and some 

 prospecting would bo necessary to ascertain anything definite with regard 

 to the amount of ore available. The mode of occurrence of cinnabar indi- 

 cates that the deposition did not proceed pari passu with the decomposition 

 of the granite, but fallowed it. Had it been otherwise, cinnabar would be 

 found generally over the decomposed area and the impregnated granite 

 would be tolerablv iirm, instead of forming a gravel-like, incoherent mass. 

 It is verv probable that at depths of a hundred feet, more or less, the char- 

 acter of the deposit would be found to differ markedly from that at the sur- 

 face, for the phenomena here, as at Sulidiur Bank, are complicated by the 

 action of sulphui'ic acid due to the oxidation of sulphureted hydrogen. 



Metals in the granite. — Tlio prcscut spHugs arc ccrtaiuly decomposing granite 

 to some extent, and decomposition of this rock on a large scale has occurred 

 within no long period. It seemed probable that at least a portion of the 

 heavv metals found in the deposits were derived from the granite and pos- 

 sible that all of them had this origin. Kock from the area east of the rail- 

 road was selected because it was fre.sh and well removed from springs, act- 

 ive or extinct. Large quantities of granite, in one case 15.5 pounds, were 

 finely pulverized and decomposed either by aqua regia, which does not 



' Compare my suggestion as to the source of the water enteriug the miueo on the Comstock (Gteol- 

 ogy of the Comstock Lode, p. 243). 



