Dr. Mac Culloch on Mineral Veins, 203 



losophy. It will hereafter be seen that some minerals, both 

 earthy and metallic, have a double origin, or are formed both 

 from fusion and solution ; so that perhaps in some of the 

 cases here enumerated, some of these, such for example as 

 those which are concluded to be aqueous from their association 

 with carbonat of lime, may possibly be exclusively of igneous 

 origin. 



In examining the chemical evidence, it will be convenient to 

 class the metallic minerals according to their leading relations 

 of this nature, as it is not proposed to investigate every com- 

 plicated species or variety which mineralogists have described. 

 The following classification will answer the present purpose : 



Metals ; including the alloys. 



Oxydes ; whether simple or complicated. 



Salts ; comprising carbonats, sulphats, muriats, phosphats, 

 arseniats, molybdats, tungstats, chromats and silicats ; or 

 combinations of more than one of these. 



Sulphurets ; simple or complicated. 



Phosphurets. 



"We do not yet know how many metals can be separated 

 from their solutions in a metallic state ; but gold, silver, copper, 

 and lead, can be procured in this manner with great facility. 

 These may, therefore, be metals of an aqueous origin. Pos- 

 sibly this may happen to many others, from deoxydating pro- 

 cesses in nature which we either have not examined, or which 

 may be unattainable in our experiments. 



All the metallic oxydes which involve a large number of 

 these minerals, can be procured in the same manner ; at least 

 in a powdery state. If artificial chemistry has not yet con- 

 trived to obtain these in a crystallized form, it must be recol- 

 lected that we cannot, like Nature, command the elements of 

 time. Yet, perhaps, the case of oxydulous iron, which may be 

 procured from the muriat by dissipating the acid, may be 

 esteemed an instance in point ; although the application of 

 heat is necessary for this purpose. The oxyde appears here to 

 crystallize at the moment of its separation from the acid, 



