CONTENTS. 



InLroduction <^1" 



Classification of Mosquito Range cruptives 322 



Older eruptives 323 



Qnartz-Porphyry 323 



Mount Zion Porphyry 323 



AVhite or Leadville Porphyry 324 



Pyritiferous Porphyry 326 



Mosquito Porjihyry 327 



Lincoln Porphyry 328 



Gray Porphyry 330 



Diorite 333 



Quartz-mica-diorito 333 



Hornhlende-dionte 333 



Augite-hearing diorite 334 



Porphyrite 334 



Principal group 335 



Sacramento Porphyrite 341 



Silverheels Porphyrite 342 



Miscellaneous porphyrites 343 



Younger eruptives. 



345 



Ehyolite 345 



Chalk Mountain Nevadite 345 



Black Hill rhyolito 349 



McNiilty gulch rhyolite 350 



Empire gulch rhyolite 351 



Other rhyolites 352 



Ehyolitic tufa in South Park 352 



Dike in Ten-Mile amphitheater 352 



Breccia in the Eureka shaft 352 



Quartziferous trachyte 352 



Andesite - - 353 



Pyroxene-hearing hornblendeandesite 353 



Hypersthene-audesite 354 



Tufaceous andesites 354 



E^sumg 354 



The rock structures observed ■^•^■^ 



Individual rock types 355 



Mutual relations of rock types 35<3 



Rock constituents 3o0 



317 



