GENESIS OF TONOPAH ORES. 261 



Professor Suess, in the essay referred to," thus describes the funiarolic activity 

 at Vesuvius: 



"Turning now to the gases accompan3 r ing the eruptions. After steam, chlorine 

 and gases containing sulphur are the most important, and carbonic acid gas comes 

 next. Their occurrence follows a definite law. So far as it has been possible to 

 approach them, all fumaroles actually within vents contain steam; but the hottest 

 fumaroles (over 500 C.) on the surface of cooling lava streams, where approach is 

 easier, are dry. In the emanations from these high-temperature fumaroles are found 

 chlorine compounds, and along with them fluorine, boron, and phosphorus sub- 

 stances which are the first to disappear as the temperature of the f umarole sinks. 

 Sulphur persists longer, often combined with arsenic. Carbonic acid' is given off 

 freely till a much later stage, sometimes till the fumarole is comparatively cool, 

 notwithstanding that it is observed in the hottest dry fumaroles. Fumaroles in 

 different 'phases of emanation' may occur quite near one another. The steam of the 

 volcano can not be derived from vadous infiltration, for if it is, whence the carbonic 

 acid ? Both must come from the deeper regions of the earth. They are the outward 

 sign of the process of giving off gases which began when the earth first solidified, 

 and which to-day, although restricted to certain points and lines, has not yet come to 

 a final end." 



MINERALS DEPOSITED AROUND FUMAROLES. 



Around the orifices of the steam jets (fumaroles) at Vesuvius sulphides of arsenic 

 and mercury and chlorides of copper and lead have been deposited, showing the 

 efficacy of such gases in separating, dissolving, and precipitating these relatively 

 rare substances. Dana* quotes Mallet as authorit\ r for the statement that native 

 silver ore occurs rarely in volcanic ashes. 



CONCLUSIONS AS TO GENESIS OF TONOPAH ORES. 



The considerations above pointed out appear to the writer to indicate 

 strongly the following conclusions: 



The Tonopah district was, during most of Tertiary time, a region of active 

 volcanism, and probably after each eruption, certainly after some of them, 

 solfataric action and fumarolic action, succeeded by hot springs, thoroughly 

 altered the rocks in many parts of the district. At the surface, during those 

 periods, the phenomena of fumarolic and solfataric action and of hot springs 

 were similar to those to-day witnessed in volcanic regions; but the rocks now 

 exposed were at that time below the surface. The veins fill conduits which were 

 formed by the fractures due to the heavings of the surging volcanic forces 

 below and along which the gases, steam, and finally hot waters, growing gradually 



aSuess, E., Geog. Jour., vol. 20. p. 520. & System of Mineralogy, 6th ed., p. 20. 



