IRON MINE WORKINGS. 395 



The Iron Hill map shows the principal underground drifts in this area, 

 taken from the actual working maps of the mine, the level of different 

 points in these drifts l)eing given by figures which denote their respective 

 elevations above the 10,000-foot curve. The outlines of the ore bodies are 

 given in generalized form, as deduced from the same maps and from personal 

 observations. As in the case of all the mine maps, both drifts and ore 

 bodies are indicated in projection, that is, as if the ground over them were 

 transparent, and in this respect they differ from and are independent of the 

 geological colors, which indicate the formations constituting the rock surface. 



The mine is opened by three principal inclines, the North, Main, and 

 South, the last of which is no longer in use. The bulk of the ore is ex- 

 tracted through the middle or Main incline, which is carried down at an 

 angle of 12 to 13 C in approximate conformity with the surface of the lime- 

 stone; it is provided with powerful hoisting engines and has a double track. 

 In Atlas Sheet XXIV a section is given through each of these inclines, desig- 

 nated A, B, C, respectively, the line of the last running partly through the 

 North incline of the Bull's Eye claim, which adjoins the line of tlie Iron claim. 



In this area the contact has been and is productive over an unusually 

 large surface, the main ore body extending diagonally through the claims 

 in a northeast direction from the croppings, with an average width of 200 

 feet. This productive zone is separated from the zone of the adjoining 

 Silver Cord Combination by comparatively barren ground ; that is, barren as 

 far as present explorations have gone, although it is not absolutely certain 

 that ore may not still exist in the body of the limestone. The irregularity 

 with which the replacement action of the ore currents has acted upon the 

 limestone is well shown in the Main incline. Here, after the ore had been 

 extracted along the actual contact from the first to the fifth level and it was 

 supposed that pay ore in this area was quite exhausted, it was found in one 

 place to extend considerably below what was supposed to be the floor of 

 the ore body, often simply a layer of black chert, and a lower drift was run 

 back from the fourth station in the direction of the fault, disclosing a very 

 large body of vein material and rich ore, extending nearly to the fault plane, 1 



1 Later de\ elopineutu have shown that this ore body extends actually to the fault plane. Several 

 thousand tous of ore have been extracted from it through the new McKeon shaft, at about fifty feet 

 below the contact. 



