MINES, METALS, AND GEMS [See Plates, No. 38, 39, 40, 41.] Through dark retreats pursue the winding ore, How metals first were framed, and whence they spring: When yet unpoised the world's great fabric hung: YALDEN. THOSE excavations in which metals, minerals, and precious stones are dug, are called MINES, and receive, from the substances they yield, various denominations. The richest and most celebrated gold and silver mines are those of Mexico and Peru, in South America. Iron mines are more abundant in Europe than elsewhere. Copper mines are chiefly found in England, Sweden, and Denmark; and lead and tin mines in England: the latter, more particularly in the county of Cornwall. Quicksilver mines abound principally in Hungary, Spain, Friuli, in the Venitian territory, and Peru; diamond mines, in the East Indies, and in the Brazils; and salt mines in Poland. To explain the structure of mines, it should be observed that the internal parts of the earth, as far as they have yet been investigated, do not consist of one uniform substance, but of various strata, or beds, of substances, extremely different in their appearances, specific gravities, and chemical qualities, from one another. Neither are these strata similar to each other, either in their nature or appearance, in different countries; insomuch that, even in the short extent of half a mile, the strata will be found quite different from what they are in another place. As little are they the same either in depth or solidity. Innumerable cracks and fissures are found in all of them; but these are so entirely different in size and shape, that it is impossible to form any inference from what may have been met with, velative to that which remains to be explored. In these fissures the metallic ore is contained. In Cornwall, the most common opinion entertained by the miners is, that crude immature minerals nourish and feed the ores with which they are intermixed in the mines; and that the minerals themselves will, in process of time, be converted into ores productive of those metals to which they have the nearest affinity, and with which they have the greatest intercourse. In his mineralogy of Cornwall, Mr. Price thinks it most reasonable to conclude, that metals were made and planted in veins, at, or very soon after, the creation of the world: but that, in common with all other matter, they are subject to a degree of fluctuation, approaching to, or receding from, their ultimate degree of perfection, either quicker or slower, as they are of greater or less solid and durable frame and constitution. He supposes in every metal a peculiar magnetism, and an approximation of particles of the same specific nature, by which its component principles are drawn and united together; more particularly the matters left by the decomposition of the waters passing through the contiguous earths or strata, and deposited in their proper nidus or receptacle, until, by the accretion of more or less of its homogeneous particles, the metallic vein may be denominated either rich or barren. DIAMOND MINES. THE high value attached to diamonds does not depend so much on their beauty and hardness, as on their great scarcity, and the labour and expense necessary in procu ring them. Hitherto they have been observed in the torrid zone alone; and Brazil is the only part of the Americas in which they have been found. The historical account of their discovery in that country is as follows. Near the capital of the territory of Serro do Frio flows the river Milho Verde, where it was the custom to dig for gold, or rather to extract it from the alluvial soil. The miners, during their search for gold, found several diamonds, which they were induced to lay aside in consequence of their particular shape and great beauty, although they were ignorant of their intrinsic value. The diamond works on the river Jigitonhonha are described by Mr. Mawe as the most important in the Brazilian territory. The river, in depth from three to nine feet, is intersected by a canal, beneath the head of which it is stopped by an embankment of several thousand bogs of sand, its deeper parts being laid dry by chain-pumps. The mud is now washed away, and the cascalhao, or earth which contains the diamonds, dug up, and removed to a convenient place for washing. The process is as follows. A shed, consisting of upright posts, which support a thatched roof, is erected in the form of a paralelogram, in length about ninety feet, and in width forty-five. Down the middle of its area a current of water is conveyed through a canal covered with strong planks, on which the earth is laid to the thickness of two or three feet. On the other side of the area is a flooring of planks, from twelve to fifteen feet in length, imbedded in clay, extending the whole length of the shed, and having a gentle slope from the canal. This flooring is divided into about twenty compartments, or troughs, each about three feet wide, by means of planks placed on their edges; and the upper end of these troughs communicate with the canal, being so formed that water is admitted into them between two planks about an inch separate from each other. 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. Along the lower ends of the troughs a small channel is dug, to carry off the water. On the heap of earth, at equal distances, three high chairs are placed for the overseers, who are no sooner seated than the negroes enter the troughs, each provided with a rake of a peculiar form, and having a short handle, with which he rakes into the trough from fifty to eighty pounds weight of the earth. The water being then allowed to pass in by degrees, the earth is spread abroad, and continually raked up to the head of the trough, so as to be kept in constant motion. This operation is continued for a quarter of an hour, when the water begins to run clearer: and, the earthy particles having been washed away, the gravel-like matter is raked up to the end of the trough. At length the current flowing quite clear, the largest stones are thrown out, and afterwards those of an inferior size: the whole is then examined with great care for diamonds. When a negro finds one, he immediately stands upright, and claps his hands: he then extends them, holding the gem between the fore finger and the thumb. An overseer receives it from him, and deposits it in a bowl, suspended from the centre of the structure, and half-filled with water. In this vessel all the diamonds found in the course of the day are deposited, and at the close of the work are taken out and delivered to the principal overseer, who, after they have been weighed, registers the particulars in a book kept for that purpose. When a negro is so fortunate as to find a diamond of the weight of seventeen carats and a half, the following ceremony takes place: he is crowned with a wreath of flowers, and carried in procession to the administrator, who gives him his freedom by paying his owner for it. He also receives a present of new clothes, and is permitted to work on his own account. For small stones proportionate premiums are given; while many precautions are taken to prevent the negroes from stealing the diamonds, with which view they are frequently changed by the overseers, lest these precious gems should be concealed in the corners of the troughs. When a negro is suspected of swallowing a diamond, he is confined in a solitary apartment, and means taken to bring the gem to light. In the EAST INDIES, THE KINGDOM OF GOLCONDA, extending two hundred and sixty miles along the bay of Bengal, and having a breadth of two hundred miles from east to west, abounds in DIAMOND MINES. They are chiefly in the vicinity of the rocky hills and mountains which intersect the country, and in the whole of which diamonds are supposed to be contained. In several of the mines they are found scattered in the earth, within two or three fathoms of the surface, and in others are met with in a mineral substance in the body of the rocks, forty or fifty fathoms deep. The labourers having dug five or six feet into the rock, soften the stone by fire, and proceed till they find the vein, which often runs two or three furlongs under the rock. The earth being brought out, and carefully searched, affords stones of various shapes, and of a good water. This earth is of a yellowish, and sometimes of a reddish colour, frequently adhering to the diamond with so strong a crust that the separation becomes difficult. To find the diamonds, the workmen form a cistern of a kind of clay, with a small vent on one side, a little above the bottom; in this vent they place a plug, and throwing into the cistern the earth they have dug, pour in water to dissolve it. They then break the clods, and stir the wet earth in the cistern, allowing the lighter part to be carried off in the form of mud, when the vent hole is opened to let out the water. They thus continue washing until what remains in the cistern is pretty clean; and then, in the middle of the day, when the sun shines bright, carefully look over all the sand, at which practice they are so expert, that the smallest stone cannot escape them. The brightness of the sun being reflected by the diamonds, aids them in their research, which would be foiled if a cloud were to intervene. The specific gravity of the diamond is to that of water in the proportion of somewhat more than three and a half to one. It is the hardest of all precious stones, and can only be cut and ground by itself and its own substance. To bring it to the perfection by which its price is so greatly augmented, the lapidary begins by rubbing several of these stones against each other, while rough, having first glued them to the ends of two wooden blocks, thick enough to be held in the hand. The powder thus rubbed off the stones and received in a small box for the purpose, serves to grind and polish them. The greatest known diamond was found in Brazil, and belongs to the King of Portugal. It weighs 1680 carats ; and, although uncut, is estimated by Rome de l'Isle at the enormous sum of two hundred and twenty-four millions sterling, which gives an estimate of nearly eighty pounds sterling for each carat, the multiplicand of the square of its whole weight being taken. The one next in magnitude and value is that purchased in 1772 by the late Empress of Russia: it weighs seven hundred and seventy-nine carats, and has been estimated at nearly five millions sterling. It ought, however, to be observed, that these estimates, founded on the magnitude and brilliancy of the gems, are |