For many centuries[84] the Tin Mines in Cornwall have given to the country a very important place in the œconomical history of nations, and furnished a perpetual source of employment to a very large population, which exclusive of the artisans, tradesmen, and merchants, cannot be estimated at less than sixty thousand persons.
All the transactions connected with the Tin Mines are under the controul of the Stannary Laws. Courts are held every month, and they decide by juries of six persons, with a progressive appeal to the Lord Warden, and Lords of the Duke of Cornwall's council; no custom, however, or ancient law, prevails as to the working of Copper or Lead in the Stannaries, and therefore all agreements are made upon such terms as are decided on by the contracting parties.
At present the greatest metallic product of the county is Copper,[85] although this metal is, comparatively of modern discovery, and has not 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 Mineralogia 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 in Cornwall have been much deeper. Trevenen Mine was 150,—Hewas Downs 140,—Poldice 120, and Huel Vor is now upwards of 130 fathoms in depth.
Upon the first discovery of Copper ore, the miner to whom its nature was entirely unknown, gave it the name of Poder; and it will hardly be 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."[86] 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; he accordingly entered into a contract to purchase as much of it as could be supplied. The scheme succeeded, and Coster long continued to profit by Cornish ignorance.
The mines in the county of Cornwall consist chiefly of Tin and Copper, besides which there are some which yield Lead[87], Cobalt,[88] and Silver.[89] The ores are in veins which are provincially termed Lodes, the most important of which run in an east and west direction; during their course they vary considerably in width, from that of a barley-corn to 36 feet;[90] the average may be stated at from one to four feet. It is, however, by no means regular, the same lode will vary in size from six inches to two feet, in the space of a few fathoms. No instance has yet occurred of lodes having been cut out in depth; the deepest mine now at work is Dolcoath, which is about 235 fathoms from the surface to the lowest part.[91] Crenver and Oatfield have lately been stopped; they were 240 fathoms deep. The rocks through which the lodes descend are of different kinds, thus are Copper and Tin found in granite, as well as in slate.[92] The Tin in these veins[93] generally occurs in the state of an oxide; the only Copper ore of any consequence is Copper Pyrites, or Sulphuret of Copper; the arseniates, carbonates, &c. being too small in quantity to be of any importance in a mining point of view. Iron and Arsenical Pyrites are also very common attendants, and are both confounded under the name of Mundic. Besides the metalliferous veins which run easterly and westerly, we have already stated that there are others, not generally containing ore, which maintain a direction from North to South, and on that account are called cross courses, and often prove to the miner a great source of trouble and vexation; for they not only cut through the other veins, but frequently alter their position, or heave them, as it is termed; and it is a very curious fact that most of the Tin and Copper lodes, thus heaved, are shifted in such a manner, as to be generally found by turning to the right hand; left handed heaves being comparatively rare. In Huel Peever this vexatious phenomenon occurred, and it was not until after a search of forty years that the lode was recovered.[94] The discovery of metalliferous veins is effected by various methods, the most usual one is by sinking pits to the solid rock, and then driving a trench north and south, so as to meet with every vein in the tract through which it passes; the process is a very ancient one, and is termed Costeening.[95] The operation, however, of opening a new mine from the surface, or from Grass,[96] as it is called, is not one of frequent occurrence.[97] The reworking of mines which have been formerly abandoned, on account of the produce being insufficient to pay the costs, from the fall of the standard price of ore, is quite sufficient to absorb all the speculative spirit of the country.
But by whatever accident or method a lode may be discovered, the leave of the proprietor of the soil must be obtained before any operations can be commenced, except in such cases of Tin Mines as are anciently embounded according to the provisions of the Stannary Laws. The owner of the land is technically called the Lord, whose share (which is termed his Dish) is generally one-sixth, or one-eighth of the profits; the parties who engage to work the mine are called Adventurers, their shares depending upon their original contributions and agreements.
When it has been determined to work a mine, three material points are to be considered; viz. the discharge of the water,—the removal of the barren rock and rubbish (deads),—and the raising of the ore. One of the first objects, therefore, is to cut an Adit,[98] as it is called, which in an inclined underground passage, about six feet high, and 2½ wide, and is generally commenced at the bottom of a neighbouring valley, and is driven up to the vein, for the purpose of draining it of water above their point of contact; these Adits are sometimes continued to a very considerable distance, and although the expense of forming them is necessarily very considerable, yet they are found to afford the most œconomical method of getting rid of the water, in as much as it saves the labour of the steam-engine in raising it to (Grass) the surface. As soon as the vertical aperture, or Shaft, is sunk to some depth, a machine called a Whim is erected, to bring up the deads, and ore. It consists of a perpendicular axis on which a large hollow cylinder of timber, termed the Cage, revolves; and around this a rope, directed down the Shaft by a pulley, winds horizontally. In the axis a transverse beam is fixed, at the ends of which two horses are fastened, and going their rounds haul up a basket (or Kibbul) full of ore, or deads, whilst an empty one is descending.[99] As the lode never runs down perpendicularly it is necessary to cut galleries, called Levels, horizontally on the vein, one above another. These levels are, in the first instance, about two feet wide, and six feet high, but varying according to circumstances, and being frequently extended much beyond their original dimensions. They are driven one above the other at intervals of from 10 to 20, or 30 fathoms. When extended to a certain distance from the original vertical Shaft, it is necessary, for the sake of ventilation, as well as for other reasons, to form a second which is made to traverse all the levels in the same manner as the first. A communication is frequently only made between two galleries by a partial shaft (called a Wins) in the interval between the two great shafts. When there are more than one lode worked in the same mine, as frequently happens, Levels often run parallel to each other at the same depth. In this case they communicate by intermediate Levels driven through the rock (or Country as it is called) which are denominated Cross-cuts. A mine thus consists of a series of horizontal galleries, generally one above the other, but sometimes running parallel, traversed at irregular intervals by vertical shafts, and all, either directly or indirectly, communicating with each other.[100] The subterranean excavations are effected by breaking down the looser parts by the pickaxe, and by blasting the more solid rock by gunpowder.[101] In accomplishing this latter operation the most melancholy accidents have occurred, in consequence of the iron rammer coming in contact with some siliceous substance, and thus striking fire. The recurrence of this evil it is hoped has been prevented by the laudable efforts of the Geological Society as above related (see page [30]), and that the "Iron Age" has taken its final departure.
If the traveller is inclined to descend into a mine he is to be first accoutred in a flannel jacket and trowsers, a close cap, an old broad-brimmed hat, and a thick pair of shoes; a lighted candle is put into one hand, and a spare one suspended to a button of his jacket. The flannel dress is worn close to the skin, in order to absorb the perspiration, and every part of the ordinary dress is laid aside; thus equipped, if he possess sufficient strength of nerve, he may descend the vertical ladders with the most perfect ease and security;—but will a view of the mine repay all this trouble and fatigue?—let us hear what Dr. Forbes has said upon this occasion.[102] "A person unacquainted with the details of mining, on being informed of many hundreds of men being employed in a single mine, might naturally imagine that a visit to their deep recesses would afford a picturesque and imposing spectacle of gregarious labour and bustle, tremendous noise, and much artificial brilliancy to cheer the gloom. Nothing, however, is further from the truth, as far as regards the mines of Cornwall; for, like their fellow labourers the moles, the miners are solitary in their operations. Seldom do we find more than three or four men in one level, or gallery, at a time, where they are seen pursuing the common operations of digging or boring the rock, by the feeble glimmering of a small candle, stuck close by them, with very little noise or much latitude for bodily movement; besides whom there are generally one or two boys employed in wheeling the broken ore, &c. to the shaft. Each of these boys has also a candle affixed to his wheelbarrow, by the universal subterranean candlestick, a piece of clay. A certain band of men, who, however numerous, are always called "a Pair," generally undertake the working of a particular Level. These subdivide themselves into smaller bodies, which, by relieving each other at the end of every six or eight hours, keep up the work uninterruptedly, except on Sunday. By means of this subdivision of the Pairs, there is in general not more than one-third of the underground labourers below at any one time. Very seldom are the miners within the sound of each other's operations, except occasionally when they hear the dull report of the explosions. In the vicinity of the main shaft, indeed, the incessant action of the huge chain of pumps, produces a constant, but not very loud noise, while the occasional rattling of the metallic buckets against the walls of the shaft, as they ascend and descend, relieves the monotony both of the silence and the sound. Still every thing is dreary, dull, and cheerless; and you can be with difficulty persuaded, even when in the richest and most populous mines, that you are in the centre of such extensive and important operations." For keeping the workings from being inundated, each mine is furnished with a chain of pumps, extending from the bottom to the adit-level, worked by a single pump-rod; each pump receiving the water brought up by the one immediately below it. All the water of the deepest level finds its way into the bottom of the mine, technically called the Sump, whence it is finally elevated to the adit, through which it flows by a gentle descent to the surface.[103]
We have yet to notice a fact connected with the natural history of these subterranean recesses, which has lately excited a very considerable share of interest in the members of the Cornish Geological Society,—that the natural temperature of the earth in these mines is considerably above that of the mean of the climate, and increases with the depth, at the rate of about one degree for every 50 or 60 feet.[104] Does there exist then a permanent source of heat in the interior of the earth?