The most recent improvements which have been introduced into mining are those which regard the mechanical treatment of the ores after they have been extracted from the mine, and previous to their being fit for the furnace. The processes used for this purpose are technically termed "washing" and " dressing," by means of which the ore is freed from many of its earthy impurities, and thus rendered much richer for metal, in an equal bulk. In affecting this object several kinds of apparatus are employed, chiefly the stamping-mill, the crushing-mill, and the jigging-machine, the use of which has been known from time immemorial; but more attention has latterly been paid to their application, and it has also become far more general, to the great benefit of all mines, especially those in which a Large pro portion of the poorer ores are obtained. The competition with foreign mines, in which labour can be obtained more cheaply than in this country, has done much to promote this class of improvements, which, though less striking than some others, have, within the last few years, been productive of extremely beneficial effects, and may still be considered as in progress.
The history of coal-mining is in great measure distinct from that branch of the art which we have been treeing, and which chiefly relates to the extraction of the metals. The introduction of gunpowder, the invention of the steam-engine, and the improved manufacture of iron, have formed however epochs of common importance to both, having greatly contributed to the present extended scale upon which our coal mines are worked. The great objects to which improvement has within the present century been directed are the ventilation of the works and the invention of lamps which should not be liable to explosion on contact with the fire-damp. The system of ventilation in our collieries has been greatly improved of late years by Mr. Huddle and others; and the beautiful and well-known invention of the safety-lamp, in 1815, by Sir Humphry Davy, has afforded the miner a valuable though not in all cases an effectual preservative against explosion. [LAMP, SAFETY.] One of the most important events in the recent history of mining in this country is the establishment of suitable means of instruction for the mining engineer. This desideratum wag first supplied by the university of Durham, which opened a class for instruction in civil and mining engineering, in January, 1838. In the latter part of the same year a similar department was opened in King's College, London ; and a similar institution was organised by Sir Charles Lemon at Truro, in Cornwall, but, unfortunately, it did not meet with the support it so justly merited, and has since been discontinued. The local positions of the Durham
University and of the Truro institution were highly favourable to the joint acquisition of theoretical and practical instruction—an advantage in which neither King's College nor the Government School of Mines in Jermyn Street 'can participate, although both must afford valuable preliminary instruction to the mining engineer. These various insti tutions can hardly fail, in time, to produce an important effect on the mining industry of this country.
Mineral Deposits.—In proceeding to treat of the practice of mining, some preliminary details will be useful ; for as mining operations are of course in great measure regulated by the nature of the mineral or metalliferous deposits to which they are directed, and by which are determined the form and construction of the mine, and much of its internal economy, it will be necessary briefly to glance at this subject, and to point out some of the most important modes in which mineral masses are presented by nature to our research. Of the various classes into which mineral deposits may be divided, it will be sufficient for our present purpose to notice four only,—reins, beds, masses, and frag mentary deposits,—each of which is the repository of vast mineral treasures, but more especially the first two.
Veins have originally been, in most eases, long, narrow, and irregular fissures, traversing the rocky crust of the globe, which they penetrate to an unknown depth, and often at a high angle of inclination. They are for the most part filled with sparry and stony substances, called the " vcinstone," or the "gangue" of the vein, but contain here and there irregular masses or " buncies" of the metallic) ores, often of iinineneo sire and value, and which it is the principal business of the miner to discover and extract. Most of the metals are of common occurrence in veins, as, in this country, copper, tin, load, and zinc, to which, in other parte of the world, may be added gold and silver.
Beds are layers of mineral substances interposed between the strata , of solid reek, which, except in their containing valuable matter, they very much resemble. The layers of flint, which may be often seen imbedded in chalk wherever a section of this rock is made, will convey a good idea of a mineral-bed. Several of the metals, especially lead, are occasionally found in beds; coal, cla-ironstone and rock-salt exclu sively so ; but the last-mentioned mineral is far less regular and continuous than the former.