l8S 4 -i "Hydraulic Mining ” in California. 449 
dsXX.lThi* ‘ff 6 ^ 0 . 6 of the g*' avel t0 be washed, exer- 
cisin^ inci edible effedtivity. 
woT/^tn hl U l? e ° f i VatSr empl °y ed varies of course with the 
streams ^ ^ 1S n0t uncommon to see four such 
ve W f ^ g slmultane r ousl y on the same bank, each con- 
y ng from 100 to 600 inches of water per hour 
1000 miners inches being equal to 106,600 cubic feet* of 
of on h ° Ur ’ con , stantl y verting its force under a pressure 
height of th°e P cXmn. t0 ^ “•*’ ^8 with the 
J?" der ff 6 continuous adt ion of this enormons force, aided 
y he softening power of the water, large sections of the 
7 m H S i ai 'r dlslodged ’ and faI1 with great violence, the 
dehns speedily disintegrating and disappearing under the 
lesistless force of the water, and is hurried forward in the 
s uice S to the mouth of the shaft, down which it is precipi- 
tated with the whole volume of turbid water. Boulders of 
ioo to 200 lbs. in weight are dislodged and shot forward by 
tbe impetuous stream, accompanied by masses of the harder 
cement w ich meet in the fall, and by the concussion from 
e gieat boulders the crushing and pulverising agency 
required is found to disintegrate it. The heavy banks, of 
bo feet and upwards, are usually worked in two benches 
the upper never being so rich as the lower, and also less firm! 
ancl therefore worked away with greater rapidity. 
Ihe lower section is much the most compact, as this 
stratum on the bed rock being strongly cemented resists 
great pressure, and even sometimes the full force of the 
stieams of water, until it has been loosened by gunpowder 
or other explosives. For this purpose adits are driven in 
on its foundation-point of from 40 to 70 feet and more from 
the face of the bank, and drifts are extended at right angles 
therefrom to a short distance on each side of the adit, and 
in these drifts a large quantity of gunpowder is placed (from 
1 to 3 tons), and fired at one blast, having been previously 
built in with masonry. And in this manner the compact con- 
glomeiate is bioken up, and then the water easily completes 
its w 01 k. . Sometimes in the soft upper strata the system of 
tunnels is extended, as in a coal-mine, by cross alleys 
leaving blocks which are afterwards washed away, and then 
the whole mass settles, and is disintegrated under the in- 
fluence of water. The wooden sluices in the tunnels already 
described are often made double for the convenience" of 
“ cleaning up ” one of them, whilst the other remains in 
adtion. The process of cleaning up is performed according 
to the quantity and richness of the material worked upon* 
