XVIII GEOLOGY AND MINING INDUSTRY OF LEADVJLLE. 



. 

 Older eruptives Continued. 



Diorite ................................................................................... 333 



Quartz-mica-diorite Hornbleude-diorite ............................................. 333 



Augite-bearing diorite ................................................................ 334 



Porphyrite ............................................................................... 334 



Principal group ............... . ...................................................... 335 



Sacramento Porphyrite ............................................................... 341 



Silverheels Porphyrite ................................................................ 342 



Miscellaneous porphyrites ............................................................. 343 



YOUNGER ERUPTIVES ......................................................................... 345 



Rhyolite ................................................................................. 345 



Chalk Mountain Nevadite ............................................................ 345 



Black Hill Rhyolite .................................................................. 349 



McXulty gulch Rhyolite ............................. , ................................ 350 



Empire gulch Rhyolite ....................................................... ........ 351 



Other rhyolites ....................................................................... 352 



Rhyolitic tufa Dike in Ten-Mile amphitheater Breccia .......................... 352 



Qnartziferous trachyte ................................................................ 352 



Audesite ................................................................................. 353 



Pyroxene-bearing hornblende-audesite ................................................. 353 



Hypprsthene-andesite Tufaceons andesites ........................................... 354 



RESUME ..................................................................................... 354 



Rock structures observed Individual rock types .......................................... 355 



Mutual relations of rock types Rock constituents Their decomposition .................. 356 



Negative observations Chemical composition ---- ........................................ 357 



NOTES UPON TUB HENRY MOUNTAIN ROCKS ................................................... 35U 



Hornblendic rocks ..................................... .................................. 359 



Augitic rocks ............................................................................ 361 



Re'snme' .................................................................................. 362 



PART II. 

 MINING INDUSTRY. 



CHAPTER I. 



ORE DEPOSITS ................................................................................ 367 



Classification of ore deposits in general ................................................... 307 



Leadville deposits ............................................. - ................ ......... 375 



Manner of occurrence ................................................................ 375 



Composition ......................................................................... 376 



Distribution ......................................................................... 377 



Secondary alteration Mode of formation ............................................. 378 



Age of deposits Origin of the metallic contents ...................................... 379 



CHAPTER II. 



IRON HILL GROUP OP MINES ................................................................. 360 



Iron Hill ................................................................................. 380 



General description ......................................................... - ........ 380 



Geological structure .. ............................................................ 3^1 



Later intrusive sheets ............................................................ 382 



White Porphyry .................................................................. ''-'' 



Blue Limestone Silurian Cambrian Iron fault ................................ ; '~l 



California fault ................................................................. 385 



Dome fault Emmet fault Dome Hill ........................................... 386 



Ore deposits ...................................................................... 388 



