In commencing the mining operations, the usual system is, to dig down from the surface •ntil the vein or bed is reached. A spot is selected as the site of a shaft, which is fre quently sunk in an inclined direction upon the course of the vein, or if intended to be per pendicular, it is commenced upon that side towards which the vein inclines or underlies, and at such a distance from its 'back' or out crop, as to come down upon it at a given depth, say 10, 20, or 30 fathoms, On cutting the vein, the shaft is for a time suspended, and two horizontal passages, often termed galleries,' but by the miner 'levels,' are excavated or driven' upon the vein in both directions. These passages are usually about six feet in height and three or four in breadth, and rather smaller above than below. They are the principal means of exploring the contents of veins. If the shaft is deep, cross cuts' and other levels are made at different heights, so as to explore the vein at different parts. After cutting the vein, there are two modes of proceeding —continuing the shaft perpendicularly through the vein, or obliquely upon the vein ; the choice between these two plans depends on a number of practical cir cumstances. Supposing the shaft to proceed perpendicularly after cutting the vein, on reaching the depth of ten fathoms or there abouts below the point of intersection another crosscut will be driven to it. In this manner the shaft proceeds indefinitely, cross-cuts being driven at every ten fathoms or whatever distance is most convenient, and levels extended from each upon the course of the vein, the nature and value of which are thus thoroughly explored.
The mining operations are soon affected by the impurity of the air. It is chiefly in the ends of the levels that the evil of imperfect ventilation begins to be felt, the air here gradually becoming close and unfit for respira tion, as the levels advance further from the shaft, especially when from the hardness of the ground frequent blasting is necessary. As soon as this is found to be the case, a remedy of a very simple nature is applied, which consists in sinking a small pit, termed a winze,' upon the vein, from the upper levtl to the extremity of the one below it. This communication having been effected, the two levels became perfectly ventilated, each having a double communication with the atmosphere by which both an ascending and descending current is produced. The winzes are generally made at intervals of 20 or 30 fathoms apart, and from each level to those above and below it : they serve not only for ventilating the galleries, but also assist the exploring and working of the vein.
The various operations may proceed indefi nitely, according to the richness of the vein The shaft will continue to be sunk, cross cuts driven to the vein at every ten fathoms or thereabouts, levels extended in both directions from them, and the ground between them subdivided by winzes. The excavations will now have assumed a regular form, and become what is properly termed a mine. In mining operations, where the vein is not very hard, the ore may be broken down with the pick' only, but it is generally necessary to blast it with powder, by which process large quantities are detached from the vein by every shot. The ore having been detached is carried in tram-waggons to the shaft, and thence raised to the surface. When the levels have been
extended to a considerable distance from the shaft, the ventilation will again become defec tive, notwithstanding their communication by winzes. The expense of the transport of ore and masses of rock and rubbish to the shaft also becomes considerable ; and if the pros pects of the mine continue such as to warrant the expense, a new shaft must now be sunk on one or both sides of the former. This new shaft will be so placed as to intersect the vein much deeper than the former, and this point will be so arranged as to correspond either with one of the deepest levels, or some proposed level deeper still. By accurate measurements, mining engineers are able to work a second shaft from many different depths at one time. At the Consolidated Mines in Cornwall, a perpendicular shaft, 204 fathoms in depth; was worked from fifteen different points at once. Mining shafts are generally about eight feet by six in area.
As veins are generally found to run nearly parallel, and often at no great distance from each other, and as the neighbourhood of a productive vein is a favourable indication of the contents of others in its vicinity, transverse levels or cross-cuts' are frequently driven from mines at various depths, with a view to discover side-veins or to make trial of branches which diverge from the main lode. Metal liferous veins are often traversed by other veins crossing them at nearly right angles, which seldom contain ore, except perhaps near the points of intersection: they are termed cross-courses,' or cross-veins.' Where a vein has been worked by driving a level towards it from a valley or other conve nient point on the surface, the drainage to the point of intersection is, of course complete ; and hence in mountainous countries, where deep ravines occur, levels may be made for draining at a much smaller expense than where engines are required to pump the water up from a great depth.
The tools and processes employed by the miner in the excavation of the rock or the vein are simple. As his work is chiefly of two kinds, simly excavating the ground when soft, and blasting it when hard, his tools are suited to each process, the pick' and gad' being used for the former ; the ' borer' or 'jumper,' and the hammer used to propel it, for the latter, with several minor accessories for firing the shots, when the hole has been completed to its proper depth. The pick resembles a common pickaxe, but is smaller and more convenient, the iron head being sharp and pointed at one end, and very short and hammer-shaped at the other. The wedge or gad' is sometimes used in conjunction with the pick ; it is made of wrought iron, and often with curved sides. The borer' or jumper' is an iron rod or circular bar, usually about two feet in length, steeled, and formed into a flat sharp edge at the end ; it is driven into the rock by one man with a heavy hammer, while the other continually turns it round so as to expose the cutting edge to fresh surfaces of' the rock. The pulverised matter is drawn out from time to time by a tool called a ' scraper; ' and in the hole so formed are placed the powder and fuse for blasting.