MINING 303 



wall, and the occurrence of elvan courses is shown at the different levels. By studying 

 the plan, with the horizontal and transverse section, the operations of metalliferous 

 mining will be understood. 



1452 



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OF MlXIXG IX PABTICULAB. 



The mode of working mines is two-fold ; by open excavations, and subterranean ex- 

 ploitation. 



Workings in the open air present few difficulties, and occasion little expense, unless 

 when pushed to a great depth. They are always preferred for working deposits little 

 distant from the surface ; where, in fact, other methods cannot be resorted to, if the 

 substance to be raised be covered with incoherent matters. The only rules to be 

 observed are, to arrange the workings in terraces, so as to facilitate the cutting down 

 of the earth ; to transport the ores and the rubbish to their destination at the least 

 possible expense : and to guard against the crumbling down of the sides. With the 

 latter view, they ought to have a suitable slope, or to be propped by timbers whenever 

 they are not quite solid. 



Open workings are employed for valuable clays, sands, as also for the alluvial soils 

 of diamonds, gold, and oxide of tin, iron ores, &c., limestones, gypsums, building 

 stones, roofing slates, masses of rock salt in some situations, and certain deposits of 

 ores, particularly the specular iron of the island of Elba ; the masses of stanniferous 

 granite of Geyer, Altenberg, and Seyffen, in the Erzgebirge, a chain of mountains 

 between Saxony and Bohemia ; the thick veins or masses of magnetic oxide of iron 

 of Norclmarch, Dannemora, &c., in Sweden ; the mass of cupreous pyrites of Bseraas, 

 near Drontheim, in Norway; several mines of iron, copper, and gold in the Ural 

 mountains. Some of the iron mines near Whitehaven, and Carclase tin mine in 

 Cornwall, may also be quoted. 



Subterranean workings may be conveniently divided into five classes, viz. : 



1. Veins, or beds, much inclined to the horizon, varying much in thickness. 



2. Beds of slight inclination, or nearly horizontal, the power or thickness of which 

 does not exceed two yards. 



3. Beds of great thickness, but slightly inclined. 



4. Veins, or beds highly inclined, of great thickness. 



5. Masses of considerable magnitude in all their dimensions. 



Subterranean mining requires two very distinct classes of workings : the preparatory, 

 and those for extraction. 



The preparatory consist in galleries, or in pits (shafts) and levels destined to conduct 

 the miner to the point most proper for attacking the deposit of ore, for tracing it from 

 this point, for preparing chambers of excavation, and for concerting measures with a 

 view to the circulation of air, the discharge of waters, and the transport of the ex- 

 tracted minerals. 



If the vein or bed in question bo placed in a mountain, and if its direction forms 

 a very obtuse angle with the line of the slope, the miner begins by opening in its 

 side, at the lowest possible level, a gallery (level) of elongation, which serves at once 

 to give issue to the waters, to explore the deposit through a considerable extent, 

 and then to follow it in another direction ; but to commence the real mining 

 operations, he pierces either shafts or galleries, according to the slope of the deposit, 

 across the first gallery. 



For a stratum but little inclined to the horizon, placed beneath a plain, the first thing 

 is to pierce two vertical shafts, which are usually made to arrive at two points in the 

 same line of slope, and a gallery is driven to xinito them. It is, in the first place, for 

 the sake of circulation of air that these two pits are sunk ; one of them, which is also 

 destined for the drainage of the waters, should reach the lowest point of the intended 



