522 GEOLOGY A^"D MIMJJG IXDUSTRY OF LEADYILLE. 



cipally galena, with some sulphates and carbonates of copper, associated 

 with a gangue material of sulphate of baryta. The deposit, where found 

 at the contact, averages about three feet in thickness, and frequently opens 

 out into large irregular chambers extending down into the mass of the lime- 

 stone. Some of these chambers are 25 feet liigh, the general average being 

 about ten to fifteen feet. In working the mine a thin streak of mineral, 

 carrying gypsum associated with galena or barite, was followed until it 

 opened out into a chamber or pocket. The ore appears to be richer as it 

 approaches the summit of the peak. About seventy-five feet from the en- 

 trance to the tunnel, a slide or fault was found, pitching 45°, with a down- 

 throw to the east. Very little mineral was found on this faulted surface, 

 but following it up from where it was struck in the tunnel it led to a great 

 ore body 45 feet above. 



On the extreme of the northeast spur of Lincoln, overlooking the town 

 of Montgomery, are a number of abandoned openings in the Blue Lime- 

 stone, showing a similar character of irregular deposits of galena, associated 

 with barite, which have been worked principally by open cuts. 



MOUNT BROSS. 



Moose mine. — The principal mine on Mount Bross is the Moose mine, which 

 was discovered in July, 1871, though the Dwight, which is supposed to be 

 an extension of the same deposit, was first found in 1869. As the mine was 

 closed to visitors at the time of examination, the data with regard to its work- 

 ings have been obtained from former sujDerintendents. It is situated on the 

 northeast slope of Mount Bross, near the summit of the wall overlooking 

 the Cameron amphitheater. Its ore is galena and copjier pyrites, with their 

 various oxidation products, carbonates and sulphates, and the gangue largely 

 barite or heavy spar. It is found in the Blue Limestone, at or near the con- 

 tact with the overlying Lincoln Porphyry. The ore has been very rich, 

 yielding from two hundred to three hundred ounces of silver per ton. The 

 formation here dips to the southeast. Besides the overlying Lincoln Por- 

 ph}'ry, a dike of White Porphyr}' was observed, crossing the formation a little 

 west of the mine, and doubtless an examination of the underground workings 

 might have disclosed other bodies of porphyry. The tongue of Blue Lime- 



