398 ON MINERAL VEINS. 



experiments, and to analogies drawn from these. The 

 ready means which chemistry affords for producing 

 many of these substances, render these artificial 

 proofs much more complete than in the case of the 

 earthy minerals. The proof from nature is, as in 

 the former case, drawn from their association with 

 the earthy minerals already proved to be of aqueous 

 origin. That association, and the consequent proof, 

 is often very accurate, because the metallic is im- 

 bedded in the earthy mineral ; crystallized within an 

 earthy crystallized one, as Rutile is in quartz, or else 

 disposed in strata of aqueous origin, such as shale 

 and secondary limestone, which 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, as 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 ana- 

 logies. As the present remarks are not offered as in- 

 cluding a series of positive facts on which a theory is 

 to be erected, but merely as indicating the road to be 

 followed in attempting to explain the origin of mi- 

 neral veins, any 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 have been examined by 

 those who have proposed theories of this nature ; and 

 who, in this case, seem to have proceeded by invert- 

 ing the rules of philosophy. It will hereafter be seen 

 that some minerals, both earthy and metallic, have a 

 double origin, or are formed both from fusion and 



