ON MINERAL VEINS. 399 



solution ; so that, perhaps, some of these, such for 

 example as those which are included in carbonat of 

 lime, may possibly be exclusively of igneous origin. 

 In examining the chemical evidence, it will be con- 

 venient to class the metallic minerals according- to 

 their leading relations of this nature ; as I do not in- 

 tend to investigate every complicated species or variety 

 which mineralogists have described. The following 

 classification will answer the present purpose. 



METALS ; including the alloys. 



OXYDES j whether simple or complicated. 



SALTS j comprising Carbonats, Sulphats, Muriats, Phosphats, 

 Arseuiats, Molybdats, Tungstats, Chromats and Silicats : 

 or combinations of more than one of these. 



SULPHURETS ; simple or complicated. 



PHOSPHUKETS. 



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. Possibly this may hap- 

 pen to many others ; from deoxydating processes in 

 nature which we either have not examined, or which 

 may be unattainable in our own 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 arti- 

 ficial chemistry has not yet contrived to obtain these 

 in a crystallized form, it must be recollected that we 

 cannot, like Nature, command the element of Time. 

 Yet perhaps the case of oxydulous iron, which may 

 be procured from the mnriat by dissipating the acid, 

 may be esteemed an instance in point; though the 

 application of heat is necessary for this purpose. 



