California, and they often indicate the place where the stream ran in some very remote age. Bars are low collections of sand and gravel at the side of a river and above its surface at low water. River-bed claims are those beneath the surface of the river at low water, and access is obtained to them only by removing the water from the bed by flumes or ditches. Ancient river-bed claims are those of which the gold was deposited by streams in places where no streams now exist. Gulch claims are those in gullies which have no water, save during a small part of the year. A "claim" is the mining land owned or held by one man or a company.

The placer mines are again classified according to the manner in which, or the instruments with which they are wrought. There are sluice claims, hydraulic claims, tunnel claims, dry washing, dry digging, and knife claims. In 1849 and 1850, the main classification of the placers was into wet diggings and dry diggings, the former meaning mines in the bars and beds of rivers, and dry diggings were those in gullies and flats where water could be obtained only part of the year or not at all. That classification was made while nearly all the mining was done near the surface, before the great deposits of pay-dirt in the hills had been discovered, and before ditches, sluices, and the hydraulic process had been introduced. The class of mines then known as the "dry diggings," and which for several years furnished nearly half of the gold yield of the state, are now, with a few unimportant exceptions, exhausted, or left to the attention of the Chinamen.

The purpose of all placer miners is not to catch all the gold in the dirt which they wash, but to catch the greatest possible quantity within a given time. It is not supposed that any process used in gold mining catches all the metal. Part of it is lost; in some processes a considerable proportion. The general estimate in California is, that one-twentieth of the gold in the dirt which is washed is lost. Many of the particles are so very small as to be invisible to the naked eye, and so light that their specific gravity does not avail to prevent them from being carried away by the water like sand. The larger pieces will sink to the bottom and resist the force of the water; the smaller the particles, the greater the danger that it will be borne away. Many devices have been tried to catch all the gold, but none have succeeded perfectly, and some which have caught a portion of what escaped from the ordinary modes of mining, have been found to cost more than their yield. The miner does not grieve about that which he cannot catch. He is not careful to catch all that he could. His purpose is to draw the largest possible revenue per day from his claim. He does not intend to spend many years in mining, or if he does, he has become thriftless and improvident. In either case, he wishes to derive the utmost immediate profit from his mine. If his claim contain a dollar to the ton, and he can save five dollars by slowly washing only six tons in a day, while he might make ten dollars by rapidly washing fifteen tons in a day, he will prefer the latter result, though he will loose twice as much of the precious metal by the fast as by the slow mode of working. The object of the miner is the practical dispatch of work, and his success will depend to a great extent upon the amount of dirt which he can wash within a given space of time. He regrets that any of the gold should be wasted, but his regret is because it escapes from his sluice and his pocket, rather than because it is lost to industry and commerce.

The Sluice.—The board-sluice is a long wooden trough, through which a constant stream of water runs, and into which the auriferous dirt is thrown. The water carries away the clay, sand, gravel and stones, and leaves the gold in the bottom of the sluice, where it is caught by its gravity and by quicksilver. The board-sluice is the great washing machine, and the most important instrument used in the placer mining of California. It washes nearly all the dirt and catches nearly all the placer gold of the country. It was invented here, although it had previously been used elsewhere; it has been more extensively employed here than in any other country, and it can be used here to more advantage than elsewhere. It is not less than fifty feet long, nor less than a foot wide, made of boards. The width is usually sixteen or eighteen inches; and never exceeds five feet. The length is ordinarily several hundred and sometimes several thousand feet. It is made in sections or "boxes" twelve or fourteen feet long. The boards are an inch and a half thick, and are sawn for that special purpose, the bottom boards being four inches wider at one end than the other. The narrow end of one box therefore fits in the wide end of another, and in that way the sluice is put together, a long succession of boxes, the lower end of each resting in the upper end of another, and not fastened together otherwise. These boxes stand upon trestles, with a descent varying from eight to eighteen inches in twelve feet. It is therefore an easy matter to put up or take down a sluice after the boxes are made, and it is not uncommon for the miners to haul their boxes from one claim to another. The descent of a sluice is usually the same throughout its length, and is called its "grade." If there be a fall of eight inches in twelve feet, the sluice has an "eight-inch grade," and if the fall be twice as great, it is a "sixteen-inch grade." The grade depends upon the character of the pay-dirt, the length of the sluice, and its position. The steeper the descent, the more rapidly the dirt is dissolved, but the greater the danger also that the fine particles of gold will be carried away by the water. The tougher the dirt, that is, the greater its resistance to the dissolving power of the water, the steeper, other things being equal, should be the sluice. A slow current does not dissolve tough clay, and that is the greater part of the pay-dirt, so rapidly as a swift one. The shorter the sluice, other things being equal, the smaller the grade should be. There is more danger that the fine particles of gold will be lost by a short sluice than by a longer one, and to diminish this danger, the rapidity of the current must be reduced by a small grade. The greater the amount of dirt to be washed, other things being equal, the steeper should be the grade; for a swift current will wash more dirt than a slow one. In many claims the pay-dirt is full of large stones and boulders, weighing from one hundred to five hundred pounds each, all of which must be carried away through the sluice. Some are sent down whole, and others are broken into pieces with sledge hammers before they are thrown into the box. These require a swift current and a large body of water. The larger the supply of water, the steeper the sluice is made, other things being equal. Of course economy and convenience of working require that the sluice should be near the level of the ground, and as that may be steep or level below the claim, the grade of the sluice must to some extent conform to it. There are thus a multitude of points to be taken into consideration in fixing the grade of a sluice; but a fall of less than eight or more than twenty inches, in a box of twelve feet, would be considered as unsuitable for the board-sluice. Sometimes the upper part of the sluice is made steeper so as to dissolve the dirt, and the lower part has a small grade to catch the gold. The clayey matter of ordinary pay-dirt is fully dissolved in a sluice two hundred feet long with a low grade, so the use of the boxes beyond that length is merely to catch the gold. There are claims however in which the clay is so extremely tough that it will roll in large balls more than a quarter of a mile through a steep sluice with a large head of water, and come out at the lower end scarcely diminished in size.

The gold is caught in the sluice-boxes by false bottoms of various kinds. It would not do to leave the smooth boards, for the water would sweep