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METALLIC VEINS. 



Other counties, which have been described as veins, are in reality 

 beds ; the distinction between beds and veins not being well under- 

 stood, they are both called veins by working miners. The manga- 

 nese mines at Doddiscombe Leigh, in Devonshire, are irregular beds 

 of oxide of manganese, in red sandstone. The iron mine at Danne- 

 mora in Sweden is an enormous bed, which has swelled out to the 

 thickness of one hundred and eighty feet, of nearly compact ore. 

 Copper pyrites sometimes occurs in beds ; mercury has also been 

 found, disseminated in beds of clay and sandstone. Black oxide of 

 cobalt is found in beds, at Alderly Edge in Cheshire. 



Metallic Veins. — Perhaps the reader may obtain a clearer notion 

 of a metallic vein, by first imagining a crack or fissure in the earth, 

 a foot or more in width, and extending east and west on the surface, 

 many hundred yards. Suppose the crack or fissure to descend to an 

 unknown depth, not in a perpendicular direction, but sloping a little 

 to the north or south. Now, let us again suppose each side of the 

 fissure to become coated with mineral matter, of a different kind 

 from the rocks in which the fissure is made, and then the whole fis- 

 sure to be filled by successive layers of various metallic and mineral 

 substances ; we shall thus have a type of a metallic vein. Its course 

 from east to west is called its direction, and the dip from the perpen- 

 dicular line of descent is called in miners' language the hading of 

 the vein. Thus, it is said to hade or dip to the south or north, &ic. 

 Now it is obvious, that if the direction of the vein were changed, or 

 its width increased or diminished, and the hade or dip were increased 

 or diminished also, we should still have all the essential conditions of 

 a metallic vein remaining. Let us now proceed to describe existing 

 metallic veins. They appear to have been, originally, fissures cutting 

 through different beds of rock, that have been subsequently filled 

 with metallic ores, intermixed with other mineral matter, of a differ- 

 ent nature from that of the rock which is intersected. Metallic veins 

 are, therefore, considered to be of posterior formation to the rocks 

 in which they are found : and where a vein cuts through different 

 rocks, it is evident that its formation must have been more recent 

 than that of the rocks which it intersects ; but, where a vein is found 

 only in one bed of rock, the fissure may have been formed and filled 

 at the period when the rock was consolidated. Metallic veins are 

 found principally in primary and transition rocks, or in the very low- 

 est of the secondary strata : they are often separated from the rocks 

 they intersect, by a thin wall or lining of mineral substances distinct 

 from the rock, and sometimes also by a layer of clay on each side of 

 the vein. The same substance which forms the outer coat of the 

 vein, is also frequently, intermixed with the ore, or forms layers al- 

 ternating with it : this is called the matrix, gangue, or veinstone. It 

 appears as if the ore and the veinstone had at different times, been 

 formed over each other, on the sides of the vein, till they met and 

 filled up the fissure. 



