236 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. 



sometimes accompanied by a slight deposit of galena, as, for instance, in the 

 Printer Girl, Lalla Rookh, and Lillle tunnel. Thus far no valuable deposits 

 of ore have been found in this bod}^, nor, except on its northern edge, has 

 its thickness been determined. On its southern and western borders it is 

 found to be underlaid by White Porphj-ry, and on the northeastern edge 

 the main sheet of Gray Porphyry intervenes between the two. As already 

 explained, it is evidently cutting- up across the formations in California 

 gulch, and on White's Hill it rests directly on the lower sheet of White Por- 

 phvry, probably cutting up across Blue Limestone and upper White Por- 

 phyry to the north, as shown in the north and south sections, K and L, 

 Atlas Sheet XXI. The numerous prospect shafts which have been sunk 

 in this body were mostly deserted at the time of this visit, so that definite 

 data as to their depth could not always be obtained The Com.stock (L-17) 

 and Tribune (L-11) shafts had reached a depth of 300 feet and were 

 still in it. Tlie Cumberland shaft, at a depth of 450 feet, had struck the 

 underlying Gray Porphyry, into which it had penetrated 25 feet. The 

 Lady Jane shaft, a little to the west, had also reached the Gray Porphyry, 

 but its depth was not ascertained. At the northwestern corner of the body, 

 the Ishpeming shaft (L-42) and the Kent shaft (L-43) had also pene- 

 trated the Pyritiferous Porplnry, the former to a depth of 90, the latter of 

 100 feet, and reached the underlying White Porphyry, showing that the 

 Pyritiferous Porphyry rapidh' thins out in this direction. 



Breece lauit. — The northern limits of the body are sharply defined by 

 the Breece cross-fault. This fault, which has porphyry on either side and 

 at its western end identically the same rock, cannot be traced on the sur- 

 face. It has a nearly east and west direction, extending across Adelaide 

 Park, through the Silver Cloud (K-59) and Eureka shafts, north of the 

 Kent, south of the Breece Iron, north again of the Glasgow and Comstock 

 shafts, which are in the Pyritiferous Porphyry, and south of the Pennsyl- 

 vania shaft (K-19), Avhich is in the Gray Porphyry. The porphyry in the 

 Silver Cloud shaft shows the same evidence of pressure as that already de- 

 scribed in the Mike, while the Eureka shaft shows a breccia material made 

 up of small fragments of what would appear, under the microscope, to be 

 volcanic rock of the rhyolitic type. No satisfactory explanation of this 



