MINING. 251 
sluices, there is a considerable saving in using the former. 
The block riffle-bars are only two or three feet long. 
In some small sluices the riffie-bars are not placed in the 
boxes longitudinally, nor in sets; but one bar near the head 
runs downward at an angle of forty-five degrees to the course 
of the box, not touching its lower end to the side of the box, 
jut leaving an open space of an inch there. Just below this 
open space another bar starts from the side of the box and 
runs downward at right angles to the course of the first bar, 
and an open space is again left at the end of this bar; and so 
on down to near the lower end of the sluice, where there are 
longitudinal riffle-bars in sets as described in the preceding 
paragraphs. The consequence of using this kind of riffle-bar 
is, that though much of the water and light dirt runs straight 
over the bars, the heavier material runs down from side to side 
in a zigzag course. Near the head of the sluice is a vessel, 
from which quicksilver falls by drops into the box; and it fol- 
lows the course of riffle-bars, overtaking the gold which takes 
the same route. These zigzag riffle-bars are nailed down. In 
all sluices, men must keep watch to see that the boxes do not 
choke; that is, that the dirt and stones do not collect in one 
place, so as to make a dam, and cause the water to run over 
the sides, and thus waste the gold. 
There are small sluices, from which all stones as large as a* * 
doubled fist are thrown out. For this purpose the miner uses 
a sluice-fork, which is like a large manure-fork or garden-fork, 
but has tines which are blunt and of equal width all the way 
down; the bluntness being intended to prevent the tines from 
catching in the wood, and the equality of width to prevent the 
stones from getting fast in the fork. 
In some sluices, the “block riffle-bars”—that is, bars cut 
across the grain of the tree—are set transversely in the boxes, 
and about two inches apart. 
Another deyice is, to fill the pores of such riffle-bars with 
quicksilver. This is done by driving an iron cylinder with 
a sharp edge into the surface of the bar, then putting mercury 
