MINING. 253 



very tightly l»y the sand collected between them. In large 

 sluices, wooden riffle-bars are worn away very rapidly — the 

 expense amounting sometimes, in very large and long sluices, 

 to twenty or thirty dollars a day ; and in this point tliere is an 

 important saving by using the stone bottoms. They are used 

 only in large sluices, and they generally have a grade of twelve 

 or fourteen inches to tlie box of twelve feet. 



§ 185. Hydraulic Mining. — After the board-sluice, with its 

 various adjuncts of rifflc?-b:irs, stone bottoms, co})per plates, 

 and so forth, the next instrument of importance in the gold- 

 mining of California is the hydraulic hose, used to let water 

 down from a considerable height, and throw it under the press- 

 ure of its own weight against the pay-dirt, which is thus torn 

 dowoi, broken up, dissolved, and carried into the sluice below. 

 The sluice is a necessary part of hydraulic mining. The hose 

 is used, not to wash the dirt, but to save digging with shovels, 

 and to carry it to the sluice. 



The hydraulic process is applied only in claims where the 

 dirt is deep and where the water is abundant. If the dirt 

 were shallow in the claim and its vicinity, the necessary head 

 of water could not be obtained. Hydraulic claims are usually 

 in hills. The water is led along on the hill at a height varying 

 from fifty to two hundred feet above the bed-rock, to the claim 

 at the end or side of the hill, where the water, playing against 

 the dirt, soon cuts a large hole, with perpendicular or at least 

 steep banks. At the top of the bank is a little reservoir, con- 

 taining perhaps not more than a hundred gallons, into which 

 the water runs constantly, and from which the hose extends 

 down to the bottom of the claim. The hose is of heavy duck, 

 sometimes double, sewn by machine. This hose when full is 

 from four to ten inches in diameter, and will bear a perpendic- 

 ular column of water fifty feet high ; but a greater height will 

 burst it. Xow, as the force of the stream increases with the 

 height of the water, it is a matter of great importance to have 

 the hose as strong as possible ; and for this purpose, in some 

 claims, it is surrounded by iron bands, which are about two 



