10 BULLETIN 42, UNITED STATES NATIONAL MUSEUM. 



frequently found, especially volcauic products. ]!^early all of this gravel 

 is kuowu to contain gold, yet much of it can not be worked from vari- 

 ous causes, the most important being the lack of water, and the fact 

 that the material is overlaid by a more or less heavy cap of lava. Re 

 cently operations have been stopped by the courts on account of the 

 damage done to farmers along the streams by the large amounts of tail- 

 ings that were discharged into the river. 



A single workable deposit will sometimes cover hundreds of acres in 

 extent, and be from 100 to 300 or even 400 feet in depth. The gold is 

 generally more or less concentrated in certain strata, but it is only 

 occasionally that these strata can be removed without moving the whole 

 mass. The rich stratum or "pay" is sometimes found near the top, 

 and also at various other levels, but it is generally confined to the re- 

 gion of the bottom or bed rock of the deposit. The average amount of 

 gold that it is necessary that a deposit should carry in order to consti- 

 tute a workable deposit varies greatly with circumstances, but, under 

 moderately fair conditions, as small an amount as 4 cents worth of 

 gold to a cubic yard of gravel will yield a reasonable profit. 



The means used for breaking down the gravel and separating the gold 

 from the worthless material is water, hence the name "hydraulic pro 

 cess." For this purpose it is necessary to construct immense reservoirs 

 for the storage of water. These reservoirs are constructed high up in 

 the mountains, frequently 50 or more miles away from the gravel de- 

 ppsit, and are very expensive. Several reservoirs hold more than 

 1,000,000,000 cubic ieet of water each. 



The water is brought from these reservoirs by means of ditches, 

 flumes, and iron pipes, according to the character of country traversed, 

 as near as possible, to the gravel deposit; it is then dropped down in 

 nearly a straight and vertical pipe to the level of the bed-rock, where, 

 by means of suitable pipes and nozzles, it is directed against the face 

 of the gravel deposit. The pressure at which the water leaves the 

 nozzle is very great, being seldom less than 50 feet, and sometimes being 

 four to five hundred feet. When such a stream of water is properly 

 directed against the gravel it disintegrates the deposit very rapidly and 

 effectually. After the material is broken down it is carrie<l along by 

 the stream of water over the bed-rock, and then through a channel cut 

 in the bed-rock to a series of sluices. A general view of the operation 

 of this process is shown in PL. ii. 



A suitable amount of mercury is placed in the sluices which amalga- 

 mates with the gold, on coming in contact with it, and this amalgam, 

 being very heavy, settles to the bottom of the sluices, and is held there 

 by the riffles provided for that purpose. 



At certain suitable intervals the stream of water is much reduced, so 

 that no fresh material is washed down, and a " clean-up " is made. The 

 gold that occurs in nuggets of any size is generally retained in the 

 crevices and depressions on the bed rock, and the sizes of the particles 

 decrease with the distance from the working face. In the clean-up men 



