MINING. 251 



sluices, there is a considerable savin o; in nsinsf the former. 

 The block riffle-bars are onlv two or three feet lonsf. 



In some small sluices the riffle-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, 

 but 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 zi2fza«" 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 zis^zag: 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 grettino; 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 device is, to fill the pores of such riffle-bars with 

 quicksilver. This is done by drivnng an iron cylinder with 

 a sharp edge into the surface of the bar, then putting mercury 



