60 MINING IOT)USTRT. 



interesting where it shows the Bullion and the Chollar syenite horses, and the 

 remarkable manner in which the interior structure-lines of the North Savage 

 mine conform to the sudden change of direction of the west wall. The reader 

 will find in the three transverse clays which mark the west wall, the termina- 

 tion of the ore-bearing quartz, and the immense seam which bounds the 

 Potosi strike, most interesting examples of the power of a rigid wall over less 

 coherent materials. 



Fig. 2 of Atlas-Plate 12 shows the aspect of the chamber on the present 

 lowest levels. In the Chollar-Potosi the vein is entirely wanting, the walls of 

 propylite and syenite being simply parted by an almost imperceptible sheet of 

 clay. The quartz-body which begins in the North Chollar, and extends for 

 200 feet into the Hale and Norcross, along the west wall, is of white crushed 

 rock, mixed with clay and porphyry, and barren of all silver. 



The three bonanzas described in the Chollar-Potosi, see Atlas-Plate 7, 

 are the uppermost limits of the fan-like expansion of the whole silver system 

 of the chamber. The Hale and Norcross bonanza is about equally divided 

 between the Norcross and Savage mines. Its upper level was 355 feet below 

 the surface, and it extended to the 850-foot level, terminating in barren quartz. 

 The average thickness was about 15 feet; its greatest width of 50 feet was on 

 the 535-foot level. Next below, a little further east, lies the second Hale and 

 Norcross bonanza, the present lowest ore in this group. The Savage bonanza 

 rises toward the north, filling the same sheet of quartz from the 868-foot level 

 to the 486, inclined constantly to the north, and reproduced still further toward 

 the surface by the great Gould and Curry bonanzas. These two bodies have a 

 combined length on their greater, or inclined, axes of 800 feet, and an average 

 horizontal length of 300 feet, while their width across the vein increases from 

 20 feet in the lower Savage bonanzas to 100 feet in the upper levels of the 

 Gould and Curry. 



Chemical decomposition has progressed somewhat further than in Gold 

 Hill; the lithological structure of the propylite is rather more obliterated, the 

 whole mass tending more into clay. 



As was remarked of the Gold Hill workings, this clay matter possesses 

 wonderful expansive power. The timbering and galleries have been crushed 

 with an almost incalculable force, in several instances requiring greater expen- 

 diture to keep the drifts open than for the original cost of construction. Where 



