MINING 



297 



acting from within the earth ; and that the foreign matter, having been in a fluid 

 state, has afterwards slowly crystallised. Accurate observation shows that in the large 

 majority of cases the metalliferous deposits are of aqueous, and not of igneous origin. 



In the lodes, the principal matters which fill them are to be distinguished from the 

 accessory substances ; the latter being distributed irregularly, amidst the mass of the 

 first, in crystals, nodules, grains, seams, &c. The non-metalliferous portion, which is 

 often the largest, is called gangue, from the German Gang, vein. The position of a 

 vein is denoted, like that of the stratum, by the angle of inclination, and the point of 

 the horizon towards which it dips, whence the direction is deduced. In popular lan- 

 guage a lode may be described to be a crack or fissure, such as is formed in the drying 

 of a pasty mass, extending over a considerable extent of country, and penetrating to a 

 great depth into the earth. 



A metalliferous substance is said to be disseminated when it is dispersed in crystals, 

 spangles, scales, globules, &c., through a large mineral mass. Tin is not unfrequently 

 thus disseminated through granite and clay-slate rocks. 



Certain ores which contain the metals most indispensable to tyuman necessities, 

 have been treasured up by the Creator in very bountiful deposits ; constituting 

 either great masses in rocks of different kinds, or distributed in lodes, veins, nests, 

 concretions, or beds with stony and earthy admixtures ; the whole of which become 

 the objects of mineral exploration. These stores occur in different stages of the 

 geological formations ; but their main portion, after having existed abundantly in 

 the several orders of the older strata, cease to be found towards the middle of 

 the secondary rocks. Iron ores are, with a few exceptional cases, the only ones 

 which continue among the more modern deposits, even so high as the beds imme- 

 diately beneath the chalk, when they exist almost entirely as colouring-matters of 

 the tertiary beds. 



Granite, gneiss, mica, and clay-slate, constitute in Europe the grand metallic 

 domain. There is hardly any kind of ore which does not occur in these in sufficient 

 abundance to become the object of mining operations, and many are found in no 



1446 



A general view of mining operations as given in Tille-Fosse's ' Sur la Riches.se Minfrale.' 



other rocks. The transition rocks, and the lower part of the secondary ones, are 

 not so rich, neither do they contain the same variety of ores. But this order of 

 things, which is presented by Great Britain, Germany, France, Sweden, and Norway, 

 is far from forming a general law ; since in equinoctial America the gneiss is but 

 little metalliferous ; while the superior strata, such as the clay-schists, the syenitic por- 

 phyries, the limestones, which complete the transition series, as also several secondary 



