466 GEOLOGY AND MlJSfl^^G INDUSTRY OF LEADVILLE. 



sunk through the underlying White Porphyry and reached the Silurian 

 tormation at a depth of 198 feet, finding 2 feet of iron^ at the top and 

 penetrating it 16 feet. No. 5 shaft, due south of this, after passing through 

 63 feet of Wash, struck the underlying White Porphyry, and reached the 

 Silurian formation at a depth of 159 feet. The ore bodies reached from 

 No. 1 shaft are at an elevation of about 10,400 feet, and lie directly beneath 

 the Wash. Those opened by No. 7 shaft are about fifty feet lower, and are 

 covered by White Porphyry and by a thin sheet of Gray Porphyry which is 

 seen in a drift leading from No. 2 shaft. The ore body in this portion of the 

 workings was nearly horizontal and from one to two and a half sets of timber 

 in thickness (8 to 20 feet). North of No. 2 shaft, however, the formation 

 dips rapidly to the northward, and on the line of Section J a considerable 

 body of unreplaced Blue Limestone, occupjang almost the whole thickness 

 of the ore horizon and underlaid by Parting Quartzite, is developed by an 

 up-raise from the 320-foot level ; a little south of this up-raise iron is found 

 to rest directly on the Parting Quartzite, thus affording a direct proof that 

 it replaces the limestone. A drift runs east and west 150 feet, at the level 

 of the bottom of the up-raise, in this body of unreplaced limestone. This 

 body of limestone differs from the smaller masses of lime-sand hitherto 

 observed, in that the ore deposition has gone on above rather than below it. 

 Gray Porphyry dike. — The dike Hos immediately north of this body of un- 

 replaced limestone. So far as observed it nowhere reaches the rock surface 

 Avithin this claim, but ends at the top in a rounded end, as shown in Section 

 J. Shaft No. 3, near the Carboniferous line, is sunk through Wash into 

 ore, and at its bottom is directly in the dike. By the outlines of the dike, 

 shown on the sides of this shaft, it is seen that it here stands nearly vertical, 

 dipping at a steep angle to the north. Drifts to the north and east from 

 the bottom of the shaft pass out of the Gray Porphyry directly into the 

 ore body, and cross-cuts south from the main eastern drift strike it again, in 

 some cases stopping at the dike, in others passing through or over it to connect 

 with the south workings. The ground along the Carboniferous-Little Chief 

 line on the line of the dike was, at the time of visit, a mass of crushed 



'The term "iron," as used in these descriptions, is the miner's abbreviation for vein material 

 carrving more or less iron oxide. 



