CONTENTS. 13 



CHAPTER VI. ROCK ALTERATION CONNECTED WITH MINERALIZATION Continued. Page. 

 Alteration of the earlier andesite Continued. 



Changes in rarer constituents during alteration of earlier andesite 233 



Resume of effects of mineralizing waters 234 



Changes in waters as a consequence of rock alteration 235 



Propylitic alteration of earlier andesite 236 



Final composition of mineralizing waters 237 



Alteration of the later andesite 238 



Study of typical specimens 238 



Nearly fresh later andesite from Mizpah Extension shaft 238 



Nearly fresh later andesite from Halifax shaft 239 



Entirely altered later andesite from North Star shaft 239 



Entirely altered later andesite from Montana Tonopah shaft 240 



Analyses of described types of later andesite 241 



Differences of composition expressed by diagrams 242 



Comparison of later andesite with Washoe and Kureka rocks 244 



Degree of alteration of freshest Tonopah later andesite 244 



Principles of studying alteration of later andesite 245 



Alteration of later andesite from North Star shaft 246 



Alteration of later andesite from Montana Tonopah shaft 247 



Siderite as an alteration product -48 



Scarcity of epidote as an alteration product 250 



Composition of altering waters 250 



Period of alteration of later andesite 250 



Alteration mainly antecedent to faulting 250 



Relation of alteration to vein formation 251 



Exudation veinlets in later andesite 251 



Metalliferous veins in later andesite 251 



Conclusion 251 



Alteration of the Oddie rhyolite 252 



CHAPTER VII. ORIGIN OF MINERAL VEINS 253 



Origin of the mineralizing and altering waters 253 



Antithesis between waters and associated rock 253 



Theory of atmospheric origin of hot springs 254 



Theory of magmatic origin of hot springs 254 



Characteristics of Nevada hot springs 256 



Coupling of hot and cold springs 256 



The Devil's Punchbowl 257 



Amount of present and recent hot-spring action . 257 



Origin of extinct hot springs at Tonopah 258 



Connection with volcanic eruptions 258 



Consequences of antithesis between rocks and waters 258 



Meaning of nature of metals in veins 258 



Nature of solfataric action 260 



Minerals deposited around fumaroles 261 



Conclusions as to genesis of Tonopah ores 261 



