FACTS IN AMEBIC AN MINING. 79 



The gold-dredging machine has perhaps never been heard of 

 except in California ; but it is an actual fact that such a machine 

 was constructed, and used on the Yuba River, the bottom of which 

 was very rocky and rugged, and the machine proved a failure. 



The arrastra is too well known to need any remark, except that 

 material that would not yield gold to the value of £15 per ton 

 could not be treated by this apparatus at a profit. 



The torn, rocker, the sluice, and hydraulic mining have been 

 made the subject of instructive comparative experiments as to 

 their capabilities ; and it has been shown, after careful investigation, 

 that with the torn one man might wash 1 cubic yard of earth per 

 day ; with the rocker one man might wash 2 cubic yards of earth 

 per day ; with the sluice one man might wash 4 cubic yards of 

 earth per day ; with the sluice and hydraulic one man might wash 

 50 to 100 cubic yards of earth per day. 



It is not unusual to use two tons of powder at a blast in some 

 of the large hydraulic claims. 



Flumes of great magnitude have been erected in different parts 

 of the States — ODe to drain the Feather Eiver, at Oroville, cost 

 £35,000, and yielded a profit of £15,000 the first year, but sub- 

 sequently proved an unprofitable undertaking. 



The Frieberg German Barrel and Mexican yard, or Patio pro- 

 cesses (which will require no description here) were the principal 

 processes employed for the extraction of silver from its ores ; but 

 these are gradually being supplanted by the iron pan. 



The Sutro Tunnel. — Among the most remarkable works of 

 magnitude in mining being carried out in the State, one of the 

 foremost is the Sutro tunnel. It is to extend a distance of three 

 and three-fifths miles, and draw the Comstock lodes to a depth of 

 2,000 feet, and will cost, when completed, one million sterling. 

 The Companies on this great lode have agreed to pay a certain 

 sum on every ton of ore raised from the mines on completion of 

 the work. On the 1st November 1874 the tunnel had been driven 

 7,792 feet. During three weeks- in October the tunnel was driven 

 80 to 83 feet per week ; the last week in October, 116 feet. The 

 size of the tunnel is 10 X 14, and in one month 360 feet had been 

 driven by the Burleigh drill, being the heaviest work of this kind 

 on record. Comparing this work with some of our Australian 

 mining, we will take, by way of example, the adit driven into the 

 Belmore Mine, on the Great Western Company's property, near 

 Icely. The size of their adit is 6 x 4|, and in eighteen months 

 they have driven 480 feet. This gives 631 lineal, or 170 cubic 

 feet per week ,while the Sutro tunnel, 116 x 10 X 14, gives 16,040 

 cubic feet, or nearly ten times the work in a given time. In the 

 Hoosac tunnel the average progress under the old system was 49 

 feet per month. The work performed with the drills was at the 

 rate of 150 feet per month, at a greatly reduced cost, effecting a 



