MINIXG. 257 



sluices have paid large profits to their owners. Tail-sluices 

 are always large, long, and paved with stones ; and sometimes 

 they are double, so that one side may be cleaned up while the 

 other continues washing. In a branch of the Yuba there is, 

 or was not lonsr since, a tail-sluice twentv feet wide. 



§ IS 8. Tunnel- Sluice. — A tunnel-sluice is a sluice in a tun- 

 nel. It sometimes happens that a considerable body of water 

 runs out throusfh a tunnel : and in such case, a sluice at the 

 bottom of the tunnel offers the easiest method of getting out 

 and washing the dirt. The tunnels are never cut level, but 

 with a slightly-ascending grade, so that the water will always 

 run out. The grade is so low, that transverse riffle-bars must 

 be used ; for with lonoritudinal riffle-bars or stones, there would 

 be too much dansfer of chokinsr. These tunnel-sluices, because 

 of their low grades, require much more attention than any 

 other kind of sluices. 



§ 189. Ground- Sluice. —X\\ the sluices hitherto mentioned 

 and described have wooden boxes, but the ground-sluice has no 

 box : the water runs on the ground. The place selected for the 

 ground-sluice is some spot where there is a considerable supply 

 of water, a steep descent for it, and much poor dirt. The stream 

 is turned through a httle ditch, which the miners labor to deepen 

 and enlarge, and when it is deep they prize off the high banks 

 so that the dirt may fall down into the ditch. This is a very 

 cheap and expeditious way of washing, but it is not applied 

 extensivelv. It is used to the most advantage for washing 

 where the water is abundant for only a few weeks after heavy 

 rains, and where it would not pay to erect large sluices. A 

 few cobble-stones should be left or thrown at intervals in the 

 bed of the ground-sluice to arrest the gold, for if the bed were 

 smooth clay, the j>recious metal might all be carried off. 

 Quicksilver is not used in the ground-sluice. After the dirt 

 has all been put through the ground-sluice, it is cleaned up in a 

 short board-sluice, or a tom. 



190. Long Tom. — The tom or long torn, an instrument ex- 

 tensively used in the Caiifornian mines in 1851 and 1852, but 



