SAI.JIOX— ON TItl? FOIJMATION OK OUU-VEINS. 
395 
almost universally I'eceived as an established fact, although it seems 
to be objected to in some English 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 oui-selves against supposing that all veins or " lodes" 
have such an orig-in. Of course I here use the word vein in its proper 
sense, and not as a necessary synonym of a re-filled fissure, as it is 
in some cases emjiloyed. Used in this sense, I shall in the next 
paragTaph refer to a class of veins originating other^vise. 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 iipheaval and subsidence that every portion of the 
surface has undergone dm'ing ascertained geological periods, all of 
which, whether occuring by gradual or spadmodic movements, must 
have caused rents, we have no reason to be surprised at the existence 
of fissures. 
"V. But all metaUifenms-veins were 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-fiUed vein-fissm^e, or a 
strictly stratified deposit thrown down contemporaneously with the 
embedding strata itself, like beds of coal, or rock-salt. The difficulties 
and improbabilities connected Avith the latter hypothesis, have led to 
the acceptance of the supposed alternative of a " fissure" 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 
fissui'e, 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, althougli of course the difficulty as to the source whence the 
metal is derived still remains. 
