Metalliferous Veins. 39 



converted into pulverulent substances, or, partly while retain- 

 ing their peculiar form, into varieties of a different species ; 

 and, lastly, minerals are met with, regarding which, from the 

 circumstances under which they occui - , we must assume that 

 they have been produced by the destruction of others. All 

 these are proofs of the changes which have taken place in veins, 

 and, in so far as regards the destruction, especially in the up- 

 per portions. The outgoings, and even considerable portions 

 of the upper regions of veins, are thus frequently so altered, 

 that we are scarcely able to recognise them ; inasmuch as the 

 outgoings, and not unfrequently the upper parts of veins, proba- 

 bly originally of considerable breadth, being pi'essed together, 

 and deprived more especially of their metallic contents, often ap- 

 pear as mere small, barren fissures, containing clay, or entirely 

 empty. But, at the same time, the neighbouring rock has ge- 

 nerally suffered considerable alterations, which often extend 

 from the sides of the veins for considerable distances into 

 the hanging and lying sides, and clearly distinguish such a rock 

 from the fresh one. These alterations of the rock are deno- 

 minated weathering or decomposition, and are always regarded 

 as a sign which betokens the approach to ore. These ap- 

 pearances are particularly important in the search for vein-like 

 repositories ; and, therefore, places in mountain-masses, which, 

 without any particular cause, occur in a state of decomposi- 

 tion, just so much the more deserve attention and minute in- 

 vestigation ; because a mere barren, empty, or sterile fissure 

 may be the outgoing of a vein, which may prove very rich, only 

 when it reaches a certain, frequently a considerable depth. 

 Hence it is necessary, in districts in which veins are already 

 known, and have been mined, to investigate expressly their 

 outgoings, and to study them well, in order that, with their 

 assistance, we may be able to recognise other veins when they 

 occur. We must not depend too much on the coloured and 

 peculiar looking Sclmeife ; for few veins are of such a nature 

 that they appear with those Schweife at the surface of the rock. 

 In bed- like repositories, these appearances occur less frequently, 

 although even they are not entirely without examples of this 

 kind. Their position, the mode of arrangement of their mine- 

 rals, and even the nature of the«e minerals, may be the cause 



