534 GEOLOGY AND MINING INDUSTRY or LEADVILLE. 



is also very much iron stained, and it seems probable that this is'merely a 

 secondary deposition, resembling the gangue matter of some of the Lead- 

 ville mines. The ore is galena and hard carbonates, with a little copper, 

 generally in the form of carbonate. 



WESTERN SLOPES OF MOSQUITO RANGE. 



On the west side of the range, outside the limits ot the Leadville map, 

 are many prospect holes, both at the contact of the Blue Limestone and 

 White Porphyry and in the underlying and overlying rocks indiscrimi- 

 nately. The former have generally developed a little ore, even as far south 

 as Weston Pass, but the developments are extremely superficial and unsys- 

 tematic. Here, as elsewhere, miners seem particularly attracted by the black 

 layers which are common in the Weber Grits, and considerable labor has 

 been fruitlessly expended in exploring the bed of black shales on Empire 

 Hill, which contains fossils whose casts have been replaced by iron pyrites. 

 In the region north of Leadville, on the west side of the range, owing to 

 the fact that the surface is principally occupied by the Weber formation, 

 the by no means inconsiderable labor expended by prospectors has been 

 comparatively fruitless. Slight traces of ore are frequently found in con- 

 tact with the numerous bodies of porphyry which traverse this formation, 

 but as yet none worthy of any extended development. The teachings of 

 this examination are that remunerative ore bodies are far more likely to be 

 found in the calcareous than in the silicious beds, and for this reason pros- 

 pectors would be wise to direct their labors principally to prospecting the 

 outcrops of limestone strata. The actual ore contact between Blue Lime- 

 stone and overlying porphyry occurs on the wooded slopes bordering Ten- 

 nessee Park, and is so much obscured by surface accumulations that it is 

 practically unprospected. 



EI capitan mine. This mine is situated just west of the extreme north- 

 west corner of the Mosquito map, the location of its shaft being given in 

 the margin. Greater importance attaches to it than the economical value 

 of the ore bodies would otherwise warrant, because it is the first discovery 

 of rich ore in Blue Limestone north of the Leadville district. No indica- 

 tions of ore were found upon the surface in this region, and it was simply 



