202 Dr. Mac Culloch on Mineral Veins. 



been constructed, may easily pursue further what it is here 

 unnecessary to detail more minutely. 



In examining now the metallic minerals, so as to determine 

 which of them may have been formed from aqueous solutions, 

 we may first have recourse, partly to direct experiments in our 

 laboratories, and partly to analogies drawn from these. The 

 ready means which chemistry affords for producing many of 

 these substances, render these artificial proofs, if they may be 

 so called, much more complete than in the case of the earthy 

 minerals. 



The other kind of proof which may be considered natural is, 

 as in the former case, drawn from their association with those 

 earthy minerals which are already proved to be of aqueous 

 origin. That association is in some cases very accurate, because 

 the metallic is imbedded in the earthy mineral ; and thus the 

 proof from nature is complete. It is twofold, however ; the 

 metallic mineral being either crystallized within an earthy 

 crystallized one, as rutilc is in quartz, or else disposed in strata 

 of aqueous origin, such as shale and secondary limestone, that 

 have not undergone the action of fire. 



The natural proofs are not quite incontrovertible, when the 

 metallic minerals are merely associated in the cavities of veins 

 with those earthy ones which are of aqueous origin. Yet they 

 are, perhaps, sufficiently strong ; particularly when it is seen 

 that many of these are, in reality, substances which, in other 

 cases, carry much more decided proofs with them, either from 

 other natural associations, or from chemical experiments and 

 analogies. As the present remarks are not offered as including 

 a series of positive facts on which a theory is to be erected, but 

 merely as hints towards one, or as indicating the road that 

 ought to be followed in attempting to explain the origin of 

 mineral veins, any inaccuracies or doubtful particulars can be 

 of no moment. The observations will answer all that is 

 intended, if they turn the attention of mineralogists to a subject 

 which ought to hava been examined by those who have pro- 

 posed or adopted theories of this nature ; and who, in this 

 case, seem to have proceeded by inverting the rules of phi- 



