MINING is a general term for the underground operations by which the valious metals and other minerals are procured. It has been practiced to some extent from the remotest times, as is proved by the reference to it in the 28th chapter of the bo,.:k of Job. In its proper sense, the art was certainly known to the ancient Phenicians and Egyp tians, and also to the Greeks and Romans. Mining operations were carried on in Britain by the latter at the time of the Roman conquest. After the Norman conquest, Jews, and, at a later time, Germans were largely employed in our mines. The introduction of gunpowder as a blasting umterial in 1620, led the way to many improvements in min ing; so also did the introduction of powerful engines for pumping water, about the beginning of the 18th century.
There are two principal methods of mining: one of which is adopted vvhere the mine ral occurs in veins or lodes, as copper and lead ore; and the other where the mineral occurs in more or less parallel beds, as coal. Mining in alluvial deposits is a third method, largely practiced in the gold regions of California and Australia, and includes the novel process of " hydraulic mining." In mines like those of Cornwall and Devonshire, where most of the copper and tin of Great Britain, and also some of the lead, are obtained, the ores occur in veins filling cracks or fissures in the rocks. Such veins are termed lodes, to disting,iiish them from vein.s of quartz and other non-metallic mineralo. Lodes are very irregular in size, and in the directions they take, though they usually follow one general line.
A lode consists of a main or " champion " lode and branches, called feeders, shoots, and strings. Mineral veins sometimes extend for several miles through a country; but they expand and contract so much, and split up into so many branches, that it is per haps uncertain whether the same lode has ever been traced for rnore than a mile. Veins seldom deviate more than 45 degrees from a perpendicular line, and descend to unknown depths. They penetrate alike stratified and unstratitied rocks. Those veins which run e. and w. have been observed to be the most productive.
Fig.. 1 shows a section of a Cornish mine across the lodes /, /, /, 1; a is the engine shaft, in which are the pumps and the ladders for ascent and descent; b, b are whim shafts for raising the ore, which is done by means of buckets. The
adit, or day-level, is a long passage to which the water of the mine is pumped up and conveyed away. Some adits are made to traverse several mines. The great adit which drains the mines of Glennap and Redruth, in Cornwall, is 30 m. long. At c, c, c, are cross cuts, by which the workings on the differ ent lodes are connected.
A horizontal section in the rection of a lode would show the horizontal galleries, termed levels, which are driven upon the lode, and small upright shafts, called winces. Levels are generally about ten fathoms (60 ft.) apart. They are rarely perpendicular above each other, as they follow the clination of the vein. In the tion, the richer portions of the lode, termed " bunches," are shown shaded; and where these have been removed, and their place filled with rubbish, angular fragments are sented. This is necessary to prevent the sides of workings from falling in. The bottom of the engine-shaft is the lowest portion of the mine. It is called the sump, and is the place where the water from the various levels and workings collects, in order to be pumped up to the adit. The galleries and shafts in an extensive mine are very numerous, making it altogether a very complicated affair. The shafts, however, have all distinct names, and the levels are known by their depth in fathoms, so that particular places are as easily found as streets in a town. The ground workings of the Consolidated mines, which are the largest in Cornwall, being a conjunction of four mines, are 55,000 fathoms, or 63 m., in extent. In working out the lode between one level and another, the miner usually goes upwards, it being easier to throw down the ore than to raise it up. He works with the light of a candle, stuck with clay to the side of the mine. His tools are few—namely, a pick, a hammer, and some wedges where the vein is soft and friable; but it is generally hard enough to require blasting, in which case he uses a borer or jumper, and some smaller tools for cleaning and stemming the hole which is made. The ore is filled into wagons, and then drawn along the gallery to the shaft, to be raised to the surface in kibbles.