_Dry Digging._--Dry digging is that mining where the miner, after using the shovel to strip off the barren dirt, scrapes the pay-dirt over with a knife, picking out the particles of gold as he comes to them, and throwing away the earthy matter. This is a slow process, but in rich placers may be profitable. The miner is, of course, particular to examine all the crevices in the bed-rock; and if the material be slate, he digs up part of it, to see whether the gold has not found its way into cracks scarcely perceptible on the surface. "Dry digging," as a mode of mining, must not be confounded with "dry diggings," a kind of mining ground which has been described near the beginning of this chapter. Knife-mining differs a little from dry digging. In the latter, a shovel is used to strip off the barren dirt; whereas the knife-mining is practised in those places where the gold is deposited in crevices in rocks along the banks of streams, without any covering of barren dirt, so that the knife alone is used in scraping out the dirt; and afterward the dirt, being placed in a pan, may be washed in water, which is never used in dry digging. _Puddling-Box._--The puddling-box is a rough wooden box, about a foot deep and six feet square, and is used for dissolving very tough clay. The clay is thrown into the box, with water, and a miner stirs the stuff with a hoe until the clay is all thoroughly dissolved, when he takes a plug from an auger-hole about four inches from the bottom, and lets the thin solution of the clay run off, while the heavier material, including the gold, remains at the bottom. He then puts in the plug again, fills up the box with water, throws in more clay, and repeats the process again and again until night, when he cleans up with a cradle or pan. The puddling-box is used only in small mining operations, and never with the sluice, or in hydraulic claims. _Quicksilver-Machine._--The quicksilver-machine, or Burke rocker, is a cradle about seven feet long, two feet wide, and two feet high. In the bottom are a number of compartments, all containing quicksilver. One man rocks the machine without cessation. A constant stream of water pours into the machine at its head. The riddle extends the whole length of the machine; and the stones, after being washed clean, fall off the riddle at the lower end. One man is employed constantly working with a shovel to keep the dirt on the riddle under the stream of water, and in throwing off the big stones. If the pay-dirt is very convenient, two men can shovel enough to keep the machine in operation. The Burke rocker was extensively used in California eight and ten years ago, but now it is a great rarity.