pukington.] HYDRAULIC MINING. 99 
In the Fairbanks district it has not yet been found necessary to 
timber the underground workings to any great extent. The main 
runway, if it is to be used for the whole season or for a period exceed- 
ing a month, should be timbered for safety. Six-foot sets of posts and 
caps only, with lagging over the roof, are generally sufficient. Pole 
lagging is cheaper and more advisable than split lagging. The caving 
system, working always toward the shaft, allows the faces to be carried 
forward without timbering of the stopes. The elaborate timbering 
methods necessary in the Klondike benches and in many parts of Cali- 
fornia in drifting operations are happily not needed in this portion of 
Alaska, and are not likely to be required in any extension of the 
Tanana area. No case has been seen in the operations, as thus far 
developed, where false sets were carried in taking out the gravel. 
When the operations at Fairbanks become more extensive, however, 
and drifting is carried on more systematically with wide faces, it is 
very likely that the workings will require timbering. At present it 
is not possible to give the cost of this work, as the figures were not 
obtainable. 
HYDRAULIC MINING. 
GENERAL REMARKS. 
The hydraulic method of working gold gravel deposits is the most 
economical method from the standpoints of power, capacity, and labor. 
It is, on the other hand, exceedingly wasteful of water, and the topo- 
graphic conditions under which it may be successfully and profitably 
onductedarenot of common occurrence, even in mountainous districts.' 
The hydraulic method of mining was invented by Edward E. Matte- 
on, a native of Sterling, Conn., and applied by him to the auriferous 
ravels in California in 1852. b One or more jets of water under 
respire are thrown from a pipe or pipes with great velocity against 
he face of a gravel bank, and the gravel is loosened by the stream so 
hat it falls or "caves." The gravel is struck with sufficient force to 
>e disintegrated and broken up so that it can be carried by the current 
nto the sluice if the bed rock has a sufficient grade. For assistance in 
aoving and washing the gravel after it leaves the bank, additional 
« The amount of water used in hydraulicking is shown by the following illustration: Three hun- 
red million gallons of water a day are used at present for the supply of Greater New York City, or 
5,666 miner's inches, of twenty-four-hour service. Taking the duty of an inch at 2 cubic yards, and 
tenor of 15 cents in gold per cubic yard, the above amount would supply only 13 hydraulic mines, 
tch using 2,000 miner's inches under head. The total amount of gravel washed would be 52,000 
ibie yards per day, and the product $7,800; or (with a season of one hundred and twenty days) 
inually, 6,210,000 cubic yards, and a product of $936,000, an amount not startlingly large, consider 
g the magnitude of the operations involved. 
lit is to be expected that persons with a limited knowledge of hydraulic mining will object to the 
w capacity and short season assumed in the above, bul operators of long experience will realize 
at the conditions and results are assumed, if anything, more favorable than is found in average 
lactice. 
■p Whitney, J. D., The auriferous gravels of the Sierra Nevada of California: Mem. Mus. Comp. 
Lol. Harvard Coll., vol. 6, 1SS0. 
