14 *V CONTENTS. 



Page. 



CHAPTER VIII. INCREASE OF TEMPERATURE WITH DEPTH 263 



Method of. measurement 263 



Temperatures in the Mizpah Extension and the Ohio Tonopah 263 



Temperatures in the Montana Tonopah 264 



Temperatures in Mizpah Hill workings 264 



Thermal surveys on the Comstock 265 



Comparison of Comstock and Tonopah data 265 



CHAPTER IX. COMPARISON WITH SIMILAR ORE DEPOSITS ELSEWHERE 267 



Veins of Pachuca and Real del Monte, in Mexico 267 



Other similar mineral districts in Mexico 269 



The Comstock lode 270 



Silver City and De Lamar districts, Idaho 271 



Relation of the described districts to Tonopah 273 



The petrographic province of the Great Basin 274 



Extension of the Great Basin petrographic province into Mexico 274 



Probable still further extension of the Great Basin-Mexico petrographic province 275 



A metallographic province coextensive with the petrographic province 276 



Origin of shoots or bonanzas in the veins of this nietallographic province 276 



Existence of a major Pacific Tertiary petro-metallographic zone 278 



