174 | Copper Mines of Lake Superior. [April, q 
completely filled with copper, in others a small nucleus of © 
copper is enveloped in calc spar or epidote, while a coating 
of red ferruginous-looking earth lines the cell. A trap, — 
similar in appearance, is worked by the South Pewabic 
Mine on Portage Lake, but there its richness 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 otherwise in its lower levels. Between these 
rich streaks, large tra¢ts 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 go 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 pro- 
vided with gates at every 10 feet protect the road-ways, and 
allow large accumulations to be made in the stopes. 
Timbering is 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 contra¢t,—stoping by 
the fathom, drifting and sinking 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 r 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’oo dols. less per 
foot than a 6-foot drift by hand-labour. This calculation 
