470 GEOLOGY AND MINING INDCSTRT OF LEADVILLE. 



The foot-wall of the dike is here not very distinct, but the hanging or 

 northern wall has a smooth, well-defined face, standing at an angle of 70°. 

 The porphyry of the dike is often very much iron-stained in this ground, for 

 which reason on the foot-wall it is sometimes almost impossible to distinguish 

 between vein material and dike. On the hanging wall, however, there is 

 generally a sort of clay selvage, with polished surfaces. The outline of 

 the dike is very irregular, as shown by the fact that the hanging wall in this 

 ground varies in angle from 75° to 45°, though the steeper dip is the pre- 

 vailing one. 



In the northern body the rich ore comes directly up to contact with 

 the dike. It consists mainly of hard carbonate. Near the No. 4 shaft it 

 is very thick, averaging about thirty feet, and in one part reaching 45 feet. 

 It is practically continuous eastward to the No. 3^ shaft, where it is again 

 30 feet thick, and beyond that into the Amie ground. To the northward, 

 however, the rich ore bodies are very irregularly distributed in the ore 

 horizon, and the ore horizon itself is apparently rather irregular. It has a 

 general steep dip to the northward, and in the eastern part of the mine a 

 tendency to dip also to the northwest. The boundaries between the rich ore 

 bodies and the black iron or chert are very abrupt also, and often con- 

 founded with those of the formation. As the drifts were mostly run with 

 no other system than to follow these rich ore bodies, it was very difficult, 

 in the absence of any systematic mapping of the underground workings, to 

 form a clear conception of the ore horizon and all its dips and strike. 



As an instance of the confusion brought about in the minds of those 

 working the mines by this want of system, it may be mentioned that a 

 drift was run back southward from near No. 4 shaft into the porphyry dike 

 for 30 feet, and then a raise was put up in search of the ore bed, which 

 was abandoned, after being driven up 35 feet, on account of the danger of 

 caving as they approached the Wash. The manner in which explorations 

 were carried on from No. 5 shaft, to the north of No. 3, further illustrated 

 this. The bottom of the shaft was in chert, which here forms the upper 

 part of the ore horizon. A drift run north passed out of this chert in a 



'The number of this shaft has been omitted on the map. It can readily be distinguished, how- 

 ever, by its position near the eastern boundary line and a short distance north of the dike. 



