482 



On Mineral and Metallic Veins. 



important veins, and it can lead to no injurious consequences, if, 

 with the exception of a few cases of contraction and consequent 

 separation of masses, we admit this origin. It would not be 

 equally safe, if, considering veins to be ancient fissures, we were 

 to come, with some geologists, to the conclusion, that all those 

 containing metallic matter, have been filled by injection from 

 below, when the fissures were produced. This would be to im- 

 pede the progress of knowledge, since we can suppose other 

 modes by which metallic substances can be produced in veins. 

 If all veins had their origin from below, miners might form cal- 

 culations upon penetrating to depths, the which, if they could 

 be reached, would perhaps be delusive, whilst the effort would 

 be ruinous. That many metallic deposits have come from be- 

 low, is perhaps demonstrable ; whilst it is equally demonstrable, 

 that metals are formed by other processes, analogous to those 

 upon which the formation of saline crystals depends. Mines 

 which have been closed, on account of inundation, for two cen- 

 turies, have, on re-opening, exhibited the curious spectacle of 

 native silver coating the wooden supports which had been left 

 there. If metals, then, grow, as it were, under our own eyes, we 

 cannot limit the extent to which nature may be productive, when 

 we reflect that the periods of time which preceded human know- 

 ledge are immeasurable, and during which, her processes were 

 always in action. It is perhaps, then, more reasonable to sup- 

 pose, that the mineral and metallic contents of veins and cavi- 

 ties have been brought into their places by the agency of more 

 than one cause. 



Veins may have either mineral or metallic matter, or both, in 

 them. They are found vertical, inclined, horizontal ; often run- 

 ning in parallel courses, as if they had a cotemporaneous origin, 

 and intersecting each other in such various ways, as to leave no 

 doubt, that many of the intersected ones have been formed prior 

 to those by which they are intersected. It is upon this last fact 

 an opinion has been founded, that metals are of different ages. 

 The principal veins in the English mines run nearly east and 

 west. This is especially the case with the tin veins, or lodes, 

 in Cornwall, as well as the lodes containing copper. The veins 

 which run nearly north and south, are not as metalliferous as 

 the others, which are intersected by them. Many of these, 

 called Jlucan in Cornwall, are filled with clay. Clay is some- 



