DENVER CITY MINE. 487 



below the cross-cutting White Porphyry, since the Parting Quartzite, which 

 defines the base of the Blue Limestone horizon, has not yet been reached. 

 As it is a question of considerable economical importance for owner.s of 

 property in this vicinity to know whether a second ore horizon is likely to 

 be found beneath the second White Porphyry body, the evidence on which 

 it has been indicated on Section C as probably not occurring beneath the 

 Denver City shaft will be given in some detail. 



The Denver City shaft is situated in strike between the Lee mine on 

 the north and the Agassiz on the south, as may be seen by reference to the 

 larger map of Leadville and vicinity. In the former and in the Surprise 

 workings the whole IMue Limestone horizon is above the second White 

 Porphyry, as evidenced by the occurrence of the Parting Quartzite at its 

 base The Agassiz mine, on the other liand, is near the south point of the 

 wedge of Blue Limestone, while the greater part of this formation must be 

 below the second White Porphyry, forming a continuous sheet, except 

 when crossed by later intrusions of Gray Porphyry, from the outcrop on 

 the west face of Carbonate Hill. This lower portion of Blue Limestone 

 or ore horizon, on the other hand, must wedge out to the north and east, 

 as the upper one does to the south and west, and the questioji to be decided 

 is whether it has wedged out before the line of the Denver City shaft is 

 reached or not. It is proved on Stray Horse Ridge, to the west of the Denver 

 City and below the lower White Porphyry, by the Moyamensing, Joe Bates, 

 Vanderbilt, Pierson, and other shafts, and in the valley of Little Stray 

 Horse gulch by the Stonewall Jackson shaft. With regard to the latter, 

 it is only known that a body of vein material has been found beneath the 

 Wash. In the Pittsburgh shaft next north of this, however, White Lime- 

 stone is found directly beneath the lower White Porphyry, showing tliat 

 the wedging-out occurs between these two shafts and approximately as indi- 

 cated on the map. The extension of the line of wedging-out to the south- 

 east, which is the general direction of the cross-cutting porphyry, would 

 pass to the west of the Denver City shaft, but in all probability not veiy 

 far from it, so that there is a probability that no second ore horizon occurs 

 there. On the other hand, as the porphyry sheets are necessarily some- 

 what irregular in shape, it cannot be said to be impossible that a thin sheet 



