BED OF THE RIVER LAID DRY BY AN AQUEDUCT TO CONNECT THE ALLUVIAL SOIL IN ORDER TO WASH IT FOR DIAMONDS, GOLD, &c.
The deeper parts of the channel of the river are laid dry by means of large caissons or chain-pumps, worked by a water-wheel. The mud is then carried off, and the cascalho is dug up and removed to a convenient place for washing. This labor was, until lately, performed by the negroes, who carried the cascalho in gamellas on their heads, but Dr. Camara has formed two inclined planes about one hundred yards in length, along which carts are drawn by a large water-wheel, divided into two parts, the ladles or buckets of which are so constructed that the rotatory motion may be altered by changing the current of water from one side to the other; this wheel, by means of a rope made of untanned hides, works two carts, one of which descends empty on one inclined plane, while the other, loaded with cascalho, is drawn to the top of the other inclined plane, where it falls into a cradle, empties itself, and descends in its turn. At a work, called Cangica, formerly of great importance, about a mile up the river on the opposite side, there are three cylindrical engines (wims) for drawing the cascalho, like those used in the mining country of Derbyshire, and also rail-ways over some uneven ground. This was the first and only machinery of consequence which I saw in the Diamond District, and there appear many obstacles to the general introduction of it. Timber, when wanted of large size, has to be fetched a distance of one hundred miles at a very heavy expense; there are few persons competent to the construction of machines, and the workmen dislike to make them, fearing that this is only part of a general plan for superseding manual labor.
The stratum of cascalho consists of the same materials with that in the gold district. On many parts, by the edge of the river, are large conglomerated masses of rounded pebbles cemented by oxide of iron, which sometimes envelop gold and diamonds. They calculate on getting as much cascalho in the dry season as will occupy all their hands during the months which are more subject to rain. When carried from the bed of the river whence it is dug, it is laid in heaps containing apparently from five to fifteen tons each.
Water is conveyed from a distance, and is distributed to the various parts of the works by means of aqueducts, constructed with great ingenuity and skill. The method of washing for diamonds at this place is as follows:—A shed is erected in the form of a parallelogram, twenty-five or thirty yards long, and about fifteen wide, consisting of upright posts which support a roof thatched with long grass. Down the middle of the area of this shed a current of water is conveyed through a canal covered with strong planks, on which the cascalho is laid two or three feet thick. On the other side of the area is a flooring of planks, from four to five yards long, embedded in clay, extending the whole length of the shed, and having a slope from the canal, of three or four inches to a yard. This flooring is divided into about twenty compartments or troughs, each about three feet wide, by means of planks placed on their edge. The upper ends of all these troughs (here called canoes) communicate with the canal, and are so formed that water is admitted into them between two planks that are about an inch separate. Through this opening the current falls about six inches into the trough, and may be directed to any part of it, or stopped at pleasure by means of a small quantity of clay. For instance, sometimes water is required only from one corner of the aperture, then the remaining part is stopped; sometimes it is wanted from the centre, then the extremes are stopped; and sometimes only a gentle rill is wanted, then the clay is applied accordingly. Along the lower ends of the troughs a small channel is dug to carry off the water.
NEGROES WASHING FOR DIAMONDS, &c.
On the heap of cascalho, at equal distances, are placed three high chairs[45] for the officers or overseers. After they are seated, the negroes[46] enter the troughs, each provided with a rake of a peculiar form and short handle, with which he rakes into the trough about fifty or eighty pounds weight of cascalho. The water being then let in upon it, the cascalho is spread abroad and continually raked up to the head of the trough, so as to be kept in constant motion. This operation is performed for the space of a quarter of an hour; the water then begins to run clearer, having washed the earthy particles away, the gravel-like matter is raked up to the end of the trough; after the current flows away quite clear, the largest stones are thrown out, and afterwards those of inferior size, then the whole is examined with great care for diamonds[47]. When a negro finds one, he immediately stands upright and claps his hands, then extends them, holding the gem between his forefinger and thumb; an overseer receives it from him, and deposits it in a gamella or bowl, suspended from the centre of the structure, half full of water. In this vessel all the diamonds found in the course of the day are placed, and at the close of the work are taken out and delivered to the principal officer, who, after they have been weighed, registers the particulars in a book kept for that purpose.