CONTENTS. 



Pnge 



Introduction 319 



Classification of Mosquito Range eruptives 322 



Older eruptives 323 



Quartz-Porphyry 



Mount Zioii Porphyry 323 



White or Leadville Porphyry . - 324 



Pyritiferous Porphyry 326 



Mosquito Porphyry 327 



Lincoln Porphyry 328 



Gray Porphyry 330 



Diorite ' 333 



Quartz-mica-diorite 333 



Hornblende-diorite 333 



Augite-hearing diorite 334 



Porphyrite 334 



Principal group 335 



Sacramento Porphyrite _,. 341 



Silverheels Porphyrite 342 



Miscellaneous porphyrites 343 



Younger ernptives - 345 



Rhyolite 345 



Chalk Mountain Nevadite 345 



Black Hill rhyolite 349 



McNulty gulch rhyolite 350 



Empire gulch rhyolite 351 



Other rhyolites 352 



Rhyolitic tufa in South Park 352 



Dike in Ten-Mile amphitheater 352 



Breccia in the Eureka shaft 352 



Quartziferous trachyte 352 



Andes! te 353 



Pyroxene-bearing hornblende-andesite 353 



Hyperstheue-andesite 354 



Tufaceous audesites 354 



R&junie" 354 



The rock structures observed 355 



Individual rock types 355 



Mutual relations of rock types 356 



Rock constituents 350 



317 



