298 MINING 



deposits, include the greater portion of the immense mineral wealth of that region of 

 the globe. 



All the substances of which the ordinary metals form the basis, are not equally 

 abundant in nature ; a great proportion of the numerous mineral species which figure 

 in our classifications arc mere varieties scattered \ip and down in the cavities of the 

 great masses or lodes. The workable ores are few in number, being mostly sulphides, 

 oxides, and carbonates. These occasionally form of themselves very large masses, 

 but more frequently they are blended with lumps of quartz, felspar, and carbonate of 

 lime, which form the main body of the deposit. The ores in that case are arranged 

 in small layers parallel to the strata, or in small veins which traverse the rock in all 

 directions, or in nests or concretions stationed irregularly, or finally disseminated in 

 hardly-visible particles. These deposits sometimes contain only one species of ore, 

 sometimes several, which must be mined together, as they seem to be of contempora- 

 neous formation; whilst in other cases they are separable, having been probably 

 formed at different epochs. 



In mining, as in architecture, the best method of imparting instruction is to display 

 the master-pieces of the respective arts. It is not so easy, however, to represent at 

 once the general effect of a mine as it is of an edifice ; because there is no point of 

 sight from which the former can be sketched at once, like the latter. The subterra- 

 nean explorations certainly afford some of the finest examples of the useful labours of 

 man ; but, however curious and grand in themselves, they cannot become objects of a 

 panoramic view. It is only by the lights of geometry and geology that mines can be 

 contemplated and surveyed, either as a whole or in their details ; and, therefore, 

 these marvellous subterranean regions, in which roads are cut which, with their 

 sinuosities, extend at different levels over many hundred miles, are altogether un- 

 known or disregarded by men of the world. Should any of them, perchance, from 

 curiosity or interest, descend into these dark recesses of the earth, they are prepared 

 to discover only a few insulated objects, which they may think strange or possibly 

 hideous; but they cannot recognise either the symmetrical disposition of mineral 

 bodies, or the laws which govern geological phenomena, and serve as sure guides to 

 the skilful miner in his adventurous search. It is only by exact plans and sections of 

 subterraneous workings, that a knowledge of the nature, extent, and distribution of 

 mineral wealth can be acquired. 



General Obsei-vations on the Localities of Ores, and on the Indications of 

 Metallic Mines. 



1. Tin exists in the primary rocks, appearing either in interlaced veins, in beds, 

 as a constituent part of the rock itself, or in distinct veins. Tin ore is found in allu- 

 vial land, filling up low situations between lofty mountains ; but this tin (stream-tin) 

 has been derived from the older rocks of the neighbourhood. See TIN. 



2. Gold occurs either in beds, or in veins, frequently in primary rocks ; though in 

 other formations, and particularly in alluvial deposits, it is also found. When this 

 metal exists in the bosom of primitive rocks it is particularly in schists ; it is not 

 found in serpentine, but it is met with in greywacke in Transylvania. The gold of 

 alluvial districts, called stream-gold or placer-gold, occurs, as well as alluvial tin, 

 among the debris of the more ancient rocks. See GOLD. 



3. Silver is found, particularly in veins and beds, in primitive and transition 

 formations ; though some veins of this metal occur in secondary strata. The 

 rocks richest in it are gneiss, mica-slate, clay-slate, greywacke, and old alpine lime- 

 stone. Localities of silver ore itself are not numerous, at least in Europe, among 

 secondary formations ; but silver occurs in combination with the ores of copper or 

 of lead. See SILVER. 



4. Copper exists in the three mineral epochs : 1, in primary rocks, principally in 

 the state of copper pyrites, in lodes or veins ; 2, in transition districts, sometimes in 

 masses, usually in veins of copper pyrites ; 3, in secondary strata, especially in beds of 

 cupreous schist. The Kupferschirfcr is, however, of palaeozoic age, but copper ores are 

 also found in true secondary strata, as at Alderley Edge. See COPPER. 



5. Lead occurs, also, in each of the three mineral epochs ; abounding particularly 

 in primary and transition grounds, where it usually constitutes lodes, and occasion- 

 ally bods of sulphide of lead (galena). The same ore is found in strata or in veins 

 among secondary rocks, associated now and then with ochreous iron-oxide and cala- 

 mine (carbonate of zinc) ; and it is sometimes disseminated in grains through more 

 recent strata. See LEAD. 



6. Iron is met with in four different mineral eras, but in different ores. Among 

 primary rocks magnetic iron ore and specular iron ore occur chiefly in beds, sometimes 

 of enormous size ; the ores of red or browu oxide of iron (haematite) are found 



