No. 6.] DOUGLAS — LAKE SUPERIOR COPPER MINES. 33l 



which may be accounted for by the fact that in the Calumet 

 there is a well-defined selvage, whereas in the Quincy the drifts 

 are run through solid rock, and grooves must be scooped out 

 beneath the face of this advancing drift, — an operation not easily 

 performed with a cumbrous drill. 



The ore is broken in two ore-houses, each of which is provided 

 with a pile driver to shatter the large masses — a Blake's crusher 

 with 18 by 24 inch opening, and six smaller Blakes, with 8 by 

 15 inch openings, but no attempt is made at selecting b}' hand, 

 but all the ore raised passes to the mill. 



From the crushers the ore falls into huge hoppers, whence it 

 is discharged as called for into the railway cars. All the appli- 

 ances, in fact, are on a scale such as we are in the habit of as- 

 sociating with iron mining. A five-mile railroad unites the 

 concentrating works on Torch Lake with the mine, and over it 

 two hundred car-loads of 4-ton capacity each are carried daily. 



The mills present no feature of special interest. Tu one are 

 three of Ball's stamps, and in the other four. Six of these 

 powerful machmes are running regularly, and crush up the whole 

 yield of the mines. To each stamp there are assigned 20 jigs. 



The stamps are steam-hammers. The slide valve is worked 

 by eccentric gearing, and the piston rod is inserted into the head 

 of the shaft, which is 9 inches in diameter.. The stamp-head is 

 22 by 14 inches, and weighs 6 cwts. Its upper surface is pro- 

 vided with a bevelled ridge, which slides into a slot in the bottom 

 of the shaft, and is then keyed home. When working on the 

 amygdaloidal trap. Ball's stamp heads, made with white iron 

 and a small percentage of Franklinite and tough pig, last a 

 month. At the Calumet Mills they are worn out in six daj's, 

 but the renewal involves a stopping of a stamp of only 50 

 minutes. Each stamp works in a separate stamp-box, which is 

 five-sided, and discharges from three sides through steel plates, 

 perforated with 3-16th inch holes. Each stamp can crush daily 

 120 tons of this exceedingly hard rock, and is said to consume 

 25 horse-power; 3000 gallons of water a minute are pumped to 

 the two mills. The great advantages of using the stamp are 

 that so much work can be done with so little machinery and in 

 so contracted a space, and that so little time is occupied in re- 

 pairs. The Calumet Mills never stop. The Quincy mill is idle 

 for about one month out of twelve. 



