54 



could be carried on upon the new deposits. The rubbish left 

 in old workings becomes often cemented by mineral salts, which 

 sometimes crystallize in the crevices, so as to render it worth 

 working over again in the course of a very few years. In the 

 mines of Hanover a leather thong suspended from the roof of a 

 mine was found coated with silver ore, and also native silver and 

 vitreous ore coating the wooden supports of a mine which had 

 been under water for several years. 



These chemical actions, governed by the subterranean polar 

 currents, continue to fill every fissure or vacuity with crystals, 

 the growth of which swells open the cracks, and thus causes new 

 fractures and dislocations, according to the variable nature of 

 the containing rocks, and the amount of resistance. This gra- 

 dual opening of the veins with the growth of the crystals from the 

 sides accounts for the isolated masses of the bounding rocks found 

 in veins (Plate XIIL), which could not possibly occur had they 

 been open fractures. Indeed the hypotheses supposing mineral 

 veins to have been filled by solution from above, or that of the 

 injection of igneous matter into an open fissure from below, are 

 so crude and irreconcilable with the nature of their contents 

 that they do not deserve our attention : the facts brought for- 

 ward fully justify the conclusion that all veins, whether they be 

 mineral or not, have been formed and filled on the same prin- 

 ciple of polar action as above described. In the east and west, 

 or transverse fissures, the crystals are formed from side to side, 

 and in the splits, longitudinally, in parallel plates, as shown in 

 Plate X. The bunches of mineral in the splits are in diagonal 

 and longitudinal shoots. (Plate XV.) 



Roots and Branches of Mineral Veins. 



The meeting of a number of small veins either in depth or in 

 a horizontal direction is favourable for the accumulation of mi- 

 nerals. Plate XVIII. represents a plan of a split vein in New 

 Grenada containing silver ores ; the feeders or roots, and the 

 northern branches, are laid down according to the manner in 

 which the mineral concentrated and dispersed northward. Many 

 are called feeders by miners which in reality have had the con- 

 trary effect. 



The feeders of the east and west veins, like those of the splits, 



