The scheme succeeded, and Coster long continued to profit by Cornish ignorance. Besides tin and copper, some of the Cornish mines yield cobalt, lead, and silver. The ores are in veins or lodes, the most 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 dish; if paid in money, his dues. The adventurers divide their undertaking into shares of different 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, etc. 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 openings or shafts at stated intervals, for the purpose of raising the ore, and admitting air to the works. In opening a new mine, 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 sets 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; m addition to this the miners receive a small per centage 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 adit; 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.
The lode, when divided as above described, is open to the inspection of all the neighbouring miners in the country, and each mass or compartment is let by public competition for two months, to two or four miners, who may work it as they choose. These men undertake to break the ores, and raise them to the surface, or as it is termed to grass, and pay for the whole process of dressing the ores, that is, preparing them for market. The men by whom the mines are worked in this manner are called tributers, and their share of the value of the ore, which varies according to its richness in metal, is named tribute. This tribute is paid over to them every week, the mineral being disposed of at a ticketing, or weekly sale. In addition to the working miners, a set of men, whose experience entitle them to the office, are engaged at a stated salary, to act as overlookers, and direct the labours of the rest; those whose business lies in the mines, are called under-ground captains, and those employed above ground grass captains. The weekly produce of the mine being made up by the tributers into heaps of about one hundred tons each, samples, or little bags from each heap, are sent to the agents for the different copper companies.