402 GEOLOGY AND MINING INDUSTRY OF LEADVlLLE. 



The most striking peculiarity of the structure is the cutting across of 

 the Blue Limestone formation by the White Porphyry, this region being 

 on the line already mentioned as extending from Fryer Hill to West 

 Sheridan, where this cutting down of the White Porphyry sheet occurs. 

 Its effect is graphically shown on Atlas Sheet XXVII, Section B. It will 

 be observed that whereas at the south end of the section the White Por- 

 phyry occurs, as it generally does, above and parallel with the Blue Lime- 

 stone, at the northern end, where exposed by the workings of the Argentine 

 mine, it crosses the basset edges of the Blue Limestone, and at the outcrop 

 it probably comes in contact with the underlying Parting Quartzite. As 

 the remainder of the Blue Limestone, above the cross-cutting of the White 

 Porphyry, has been removed by erosion, it is not possible to determine 

 whether it was mineral-bearing or not. As far as determined by the present 

 workings the deposition of the richer ore has gone on, not as is ordinarily 

 the case at the contact of the White Porphyry with the Blue Limestone, 

 but at its contact with the Parting Quartzite. 



iron fault. In this area the Iron fault is struck in the Iron Hat shaft, 

 and on the Codfish Balls claim by a shaft and tunnel. Beyond this claim 

 to the northward its location is only approximate, though beyond the limits 

 of the map it is determined very closely by adjoining shafts on either side. 

 Its movement is the same as it was at the south, namely, an upthrow on 

 the east, but the amount of that throw is constantly decreasing as one 

 goes north. 



Adelaide fault. The location of this fault is also approximate, owing to 

 the infrequency of shafts in its neighborhood, and also to the fact that it 

 often has porphyry on either side. Its movement is a slight upthrow on 

 the northeast. ' Its location is determined by the discrepancy of the forma- 

 tions disclosed by the Laura Lynn, Park, and adjoining shafts in Adelaide 

 Park, and by the Double Decker group of shafts opposite the Argentine 

 tunnel, on the one side, and by the workings of the Adelaide and Argentine 

 mines on the other. 



Rock formations. The sedimentary formations disclosed in this area are 

 the same succession of Paleozoic beds, from the Lower Quartzite up to the 

 Blue Limestone, that outcrop on the southern end of Iron Hill. The por- 



