SALMON — ON THE FORMATION OF ORE- VEINS, 



395 



almost universally received as an establislied fact, altliongli it seems 

 to be objected to in some Englisli mining- districts by " practical" 

 men. There can be no question as to its truth, which is demonstrated 

 in numberless cases beyond all doubt ; but, with respect to it, we 

 must guard ourselves against supposing that all veins or "lodes" 

 have such an origin. Of course I here use the woTdiVein in its proper 

 sense, and not as a necessary synonym of a re-filled fissure, as it is 

 in some cases employed. Used in this sense, I shall in the next 

 paragraph refer to a class of veins originating otherwise. The ob- 

 jections referred to above originated from an imperfect acquaintance 

 with the general principles of physical geology, without a knowledge 

 of which it is useless to attempt to deal with the subject of mineral- 

 veins, which, as Prof. Cotta remarks, are not " to be regarded as an 

 isolated phenomenon." If we consider, for one moment, the great 

 revolutions of upheaval and subsidence that every portion of the 

 sm'face has undergone during ascertained geological periods, all of 

 which, whether occuring by gradual or spadmodic movements, must 

 have caused rents, we have no reason to be sui^rised at the existence 

 of fissures. 



Y. But all metalliferous-veins ivere not fissures. — There are some 

 metalliferous veins, " lodes," or channels that we meet with which 

 cannot be regarded as re-filled fissures. Considerable confusion has 

 existed on this point ; for it has been held, but rather rashly, that a 

 metalliferous deposit must be either a re-filled vein-fissure, or a 

 strictly stratified deposit thrown down contemporaneously with the 

 embedding strata itself, like beds of coal, or rock-salt. The difficulties 

 and improbabihties connected with the latter hypothesis, have led to 

 the acceptance of the supposed alternative of a " fissm^e" theory, which 

 would not have been otherwise suggested by the individual facts. 

 But more recent investigations in this direction now tend undoubtedly 

 to show that such deposits may have arisen, without any original 

 fissure, by a slow metamorphic action gradually replacing the original 

 rock- constituent by the now-found metallic-ore. That under certain 

 circumstances such changes have taken place, and are even at present 

 slowly taking place by aqueous agency, seems now to be demon- 

 strated, although of course the difficulty as to the source whence the 

 metal is derived still remains. 



