MINE, in natural history, a place un der ground, where metals, minerals, or even precious stones, are dug.
As, therefore, the matter dug out of mines is various, the mines themselves acquire various denominations, as gold mines, silver-mines, copper-mines, iron mines, diamond-mines, salt-mines, mines of antimony, of alum, &c.
Mines, then, in general, are veins or cavities within the earth, whose sides re ceding from, or approaching nearer to each other, male them of unequal breadths in different places, sometimes forming larger spaces, which are called holes : they are filled with substances, which; whether metallic or of any other nature, are called the loads : when the substances forming these loads are redu cible to metal, the loads are by the miners said to be alive; otherwise they are called dead loads. In Cornwall and Devon, the Malls always hold their course from east ward to westward; though in other parts of England they frequently run from north to south. The miners report, that the sides of the load never bear in a per pendicular, but constantly underlay, ei ther to the north or to the south. The load is frequently intercepted by the crossing of a vein of earth or stone, or some different metallic substance ; in which case it generally happens, that one part of the load is moved a considerable distance to the one side. This transient load is by the miners called Hooking: and the part of the load which is to be moved is said to be heaved. According to Dr. Nichols's observations upon mines, they seem to be, or to have been, the chan nels through which the waters pass with in the earth, and, like rivers, have their small branches opening into them, in all directions. Most mines have streams of water running through them; and when they are found dry, it seems to be owing to the waters having changed their course, as being obliged to it, either because the load has stopped up the ancient passages, or that some new and more easy ones are made. Mines, says Dr. Shaw, are liable to many contingencies; being sometimes poor, sometimes soon exhaustible, some times subject to be drowned, especially when deep, and sometimes hard totrace ; yet there are many instances of mines proving highly advantageous for hun dreds of years : the mines of Potosi are to this day worked with nearly the same success as at first ; the gold-mines of Cremnitz have been worked almost these thousand years.; and our Cornish tin. mines are extremely ancient. The neat profit of the silver alone, dug in the Mis nian silver-mines in Saxony, is still, in the space of eight years, computed at a thou sand six hundred and forty-four millions, besides seventy-three tons of gold. Many mines have been discovered by accident: a torrent first laid open a rich vei of the silver-mine at Friberg in Germany ; some times a violent wind, by blowing up trees, or overturning the parts of rocks, has discovered a mine ; the same has happen ed by violent showers, earthquakes, der, the firing of woods, or even the stroke of a plough-share, or horse's hoof.
But the art of mining clues not wait for these favourable accidents, but directly goes upon the search and discovery of such mineral veins, ores, or sands, as may be worth the working for metal. The principal investigation and discovery of mines depend upon a particular sagacity, or acquired habit of judging from particu lar signs, that metallic matters are con tained in certain parts of the earth, not far below its surface. The principal signs of a latent metallic vein seem reducible to general heads, such as, 1. The discovery of certain mineral waters. 2. The disco loration of the trees orof a place. 3. The finding of pieces of ore on the sur face of the ground. 4. The rise of warm exhalations. 5. The finding of metallic sands, and the like. All which are so ma ny encouragements for making a stricter search near the places where any thing of this kind appears; whence rules of practice might be formed for reducing this art to a greater certainty. But when no evident mark of a mine appears, the skilful mineralogist usually bores into the earth, in such places as from some analogy of knowledge, gained by experience, or by observing the situation, course or na ture of other mines, he judges may con tain metal : this method of boring we have already given under the article BORING.
After the mine is found the next thing to be considered is whether it may be dug to advantage. In order to determine this, we are duly to weigh the nature of the place and its situation, as to wood, water, carriage, healthiness, and the like, and compare the result with the richness of the ore, the charge of digging, stamping, washing, and smelting.
Particularly the form and situation of the spot should be well considered. A mine must either happen, 1. In a moun tain. 2. In a hill. 3. In a valley. Or, 4. in a flat. But mountains and hills are dug with much greater ease and convenience, chiefly because the drains and burrows, that is, the edits or avenues, may be here readily cut, both to drain the water and to form gangways for bringing out the lead, &c. In all the four cases we are to look out for the veins, which the rains, or other accidental thing, may have laid bare; and if such a vein be found, it may often be proper to open the mine at that place, especially if the vein move bly large and rich : otherwise the most commodious place for situation is to be chosen for the purpose, viz. neither on a flat, nor on the tops of mountains, but on the sides. The best situation for a mine, is a mountainous, woody, wholesome spot, of a safe easy ascent, and bordering on a navigable river. The places abounding with mines are generally healthy, as stand ing high, and every where exposed to the air ; yet some places where mines are found, prove poisonous, and can, upon no account, be dug, though ever so rich : the way of examining& suspected place of this kind is, to make experiments upon brutes, by exposing them to the effluvia or exhalations, to find the effects.