Although copper is now the greatest metallic product of the county of Corn wall, it is comparatively, to the other metals, of modern discovery, not having been worked longer than a century. The reason assigned for its having so long remained concealed, is the assumed fact, that copper generally occurs at a much greater depth than tin ; and that, consequently, the ancients, for want of proper machinery to drain off the water, were compelled to relinquish the metallic vein before they reached the copper. It is stated by Pryce in his Mbeeralogia Cornubiensis, as a general rule, that tin seldom continued rich and worth working lower than 50 fathoms ; but of late years the richest tin mines of Cornwall have been much deeper. Trevenen mine was 150 ; Hewes Downs, 140 ; Poldice, 120 ; and Herd Vor is now upwards of 130 fathoms in depth. the first discovery of copper ore, the miner, to whom its nature was entirely unknown, gave it the name of poder; and it will be hardly credited in these times, when it is stated that he regarded it not only as useless, but upon its appearance was actually induced to abandon the mine: the common expression upon such an occasion was, " that the ore came in and spoilt the tin." About the year 1735, Mr. Coster, a mineralogist of Bristol, observed this said poder among the heaps of rubbish ; and seeing that the miners were wholly unacquainted with its value, he formed the design of converting it to his own advantage, and accordingly entered into a contract to purchase as much of it as could be sup plied. The scheme suceeeded. and Coster long continued to profit by Ccrnieh ignorance. Beaides tin and copper, some of the Cornish mines yield cobalt, lead, and silver. The ores are in veins or lodes, the moat important of which run in an east and west direction : during their course they vary considerable in width from that of a barley-corn to thirty-six feet ; but the average may be stated at from one to four feet. The number of mines usually at work in Cornwall, is estimated at about 130.
The mines of Cornwall and Devon are generally worked by a company of proprietors, called adventurers, who agree with the owner of the land, or the lord of the soil, as he is usually denominated, to work the mine for a certain number of years, paying him, by way of rent, a proportion of the ores raised, or an equivalent in money. The grant thus made to the adventurers is called a set, and the lord's rent, if paid in ore, is said to be the lord's dial, ; if paid in money, his dues. The adventurers divide their undertaking into shares of -dif ferent magnitude, the smallest usually held being one sixty-fourth part. Any part of the concern held by one person is called a dole, and its value is known by its being denominated an eighth-dole, a sixteenth-dole, &c. The bounds or limits of a mine are marked on the surface by masses of stone pitched at equal distances ; but the property of the soil above is entirely distinct from that part of the mine beneath it ; the miner, however, has the privilege of making open ings or shafts at stated intervals, for the purpose of raising the ore, and admitting air to the works. In opening a new mane, considerable knowledge of the country, and of the most likely situation of the metallic veins, is of course necessary to avoid the chance of useless labour. The spot for commencing
operations having been selected, a perpendicular pit or shaft is sunk, and at the depth of about sixty feet a horizontal gallery or level is cut in the lode by two seta of miners, working in opposite directions, the ore and materials being raised in the first instance by a common windlass. As soon as the two sets of miners have cut or driven the level about 100 yards, they find it impossible to proceed for want of air ; this being anticipated, two other sets of men have been sinking from the surface two other perpendicular shafts to meet them ; from these the ores and materials may also be raised. By thus sinking perpendicular shafts, a hundred yards from each other, the first level or gallery may be carried to any extent. While this horizontal work is going on, the original, or as it is termed, the engine shaft, is sunk deeper ; and at a second depth of 60 feet, a second horizontal gallery or level is driven in the same direction as the first, and the perpendicular shafts are all successively sunk down to meet it ; in this manner galleries continue to be formed at different depths, as long as the state of the lode renders the labour profitable. The engine shaft in the mean time is always continued to a greater depth than the lowest level, for the purpose of keeping the working shafts free from water. The object of these perpendicular shafts is not so much to get at the ores, which are directly procured from them, as to put the lode into a state capable of being worked by a number of men ; in short, to make what is termed a mine. It is evident that the shafts and galleries divide the rock into solid right-angled masses, each 300 feet in length, and 60 in depth. These masses are again subdivided by small perpendicular shafts into three parts ; and by this arrangement the rock is finally divided into masses called pitches, each 60 feet in height, and about 100 feet in length.
In the Cornish mines, the sinking the shafts, and driving the levels, is paid for by what is termed tut-work, or task-work, that is, so much per fathom ; iu addition to this the miners receive a small per ventage on the ores, in order to induce them to keep the valuable portions as separate as possible from the deads, or rocky parts of the mass.
In addition to these horizontal and perpendicular shafts, another description of gallery is formed, called an the use of this shaft is to drain the water from the lower parts of the mine. Where the mine is formed in an exposed rock, as in the Botallick mine, in Cornwall, the adit can carry off the water without the aid of machinery, as long as the lowest shaft is above the level of the sea; but when the shafts are sunk below that level, or that of the adit itself, recourse must be had to the assistance of steam-engines to pump up the drainage to a sufficient height. The great Cornish adit, which commences in a valley near Carnon, receives branches from fifty different mines in the parish of Guennap, forming altogether an excavation nearly thirty miles in length. The longest continued branch, is from Cardrew mine, five and a half miles in length ; this stupendous mine empties itself into Falmouth harbour.