330 THE CANADIAN NATURALIST. [Vol. vii. 



by the South Pewabic Mine on Portage Lake, but there its rich- 

 ness is deceptive, for the copper forms in this shell only around 

 an earthy nucleus. 



The long levels of the Calumet and Hecla run through three 

 rich chimnies of conglomerate, the longest about 1300 feet. 

 They dip to the north, and* are widening out rather than other- 

 wise in its lower levels. Between these rich streaks, large tracts 

 of which will yield a 20 per cent ore, are others of poorer ground, 

 and others still almost barren, which are left standing. The 

 average width of the productive portions is 13 feet. 



There are broken, raised, and concentrated 740 tons of rock a 

 day. To handle such a large quantity, work has necessarily to 

 be thoroughly systematised both below and above ground, and 

 machinery utilised to the utmost. 



Each mine possesses six shafts, — or twelve in all, — eight only 

 of which are connected by levels, and four only used as hauling 

 shafts. The shafts are sunk at 400 feet apart, and levels are 

 driven every 90 feet. Between each two shafts two winzes are 

 sunk, and three stopes 30 feet high are opened on each side of 

 each winze, so that eighteen stopes are worked between each two 

 shafts. Six feet of ground are left standing on each side the 

 shafts, and a heavy arch below each level supports the roof, and 

 gives firm foundation to the road-way. A wall of heavy stulls 

 provided with gates at every 10 feet protect the road-ways, and 

 allow large accumulations to be made in the stopes. Timbering 

 in a heavy item of expense, as the trap which composes the roof 

 is very liable to fall out in pyramidal blocks. The mine-work 

 is done by contract, — stoping by the fathom, drifting and sink- 

 ing by the foot. The contractor must deliver his rock at the 

 nearest hauling-shaft. The traps are 4 feet apart in the levels, 

 and 4 feet 4 inches in the shafts, as the cars have to be large to 

 receive the heavy blocks which break away in the stopes. The 

 miners are allowed to send to the surface blocks not over 1 ton 

 weight, but the cars are constructed to hold 2 tons. 



Drifting is done with great economy, by machine-drilling. 

 Seven Burleigh drills of large size, with 2-inch bits, are steadily 

 at work in each mine, and it is found that with them a drift 10 

 feet wide can be driven at 8*00 dols. less per foot than a 6-foot 

 drift by hand-labour. This calculation leaves out, however, the 

 cost of the motor power. In the Quincy Mine, the same drills 

 are being thrown aside as uneconomical, — a discrepancy in result 



