344 SCIENTIFIC RECORD lOR 1882. 



and like it serving as a channel through which rise waters having a tem- 

 perature of 160° r., holding carbonates and sulphids of sodium and 

 ammonium with borates and sulphureted hydrogen ; free carbonic 

 acid bubbling up abundantly. The interstices of this breccia are lined 

 with cinnabar, "pyrites, and silica, the first predominating, and some- 

 times alternating with the silica, which is gelatinous, caseous, and occa- 

 sionally chalcedonic in character. This irregular metalliferous deposit, 

 now in i^rocess of formation, is in large part in the brecciated stratum, 

 but is not confined thereto, sometimes disappearing, to reappear in 

 another stratum, with barren rock between, and at other times diffused 

 through the shattered sandstone on one side or the other of the brec- 

 cia. The authors conceive this to have been originally a stratum of 

 breccia, which, beiug less coherent than the adjacent beds, presented a 

 l^lane of weakness, and was more shattered by the movements of the 

 strata than they. Where the inclination was less steep, however, the 

 disruption, and consequently the ore-bearing fissures, extended to the 

 adjacent beds. These deposits, which are wrought for cinnabar, con- 

 tain no sulphur, except near the surface, where its separation is due to 

 the action of atmospheric oxygen. The agency of the alkaline sulphids 

 in transporting and depositing the cinnabar seems clear. Details of 

 the condition of the sulphids and the silica are wanting, but this locality 

 yields beautifully crystallized cinnabar enclosed in opaline silica. J. A. 

 Phillips moreover has shown that the silica deposited from certain 

 thermal waters in California, and from the Steamboat Springs in Washoe 

 County, Nevada, is of the nature of crystalline quartz. 



The authors insist upon the twofold character of the action going on 

 in connection with these solfataras. The oxidation of sulphureted 

 hydrogen under certain conditions gives rise, as is well known, to sul- 

 phuric acid, which, carried downward by atmospheric waters, exerts a 

 solvent action on the decaying rocks and by neutralizing the ascending 

 alkaline waters, helps to diminish their solvent power, to which result, 

 however, diminished temperature and pressure contribute. These 

 studies are important as throwing light on the formation of veins and 

 other posterior deposits of minerals in rock-masses. When we recall, 

 in this connection, the effects of thermal waters, as seen in the masonry 

 of ancient Roman baths, where various crystalline silicates and other 

 mineral species have been developed in historic times, we are able to 

 understand many cases of so-called local metamorphism, not only in 

 visible proximity to igneous masses, but elsewhere in sediments far 

 removed from such, where faults or i)ermeable strata have served as 

 channels to heated waters from below. Matters dissolved in these 

 waters, and others present in the sediments, contribute alike under 

 these conditions to the genesis of crystalline minerals. 



Hunt has described the reactions going on independent of solfataric 

 or thermal waters in the auriferous gravel of California. This consists 

 in large part of the ruins of feldspathic and hornblendic rocks, holding 



