G6 CLASSIFICATION OF ROCKS. 



It has indeed been one of the toils of Natural His- 

 tory, universally, to invent or adopt some arrangement 

 of its objects for the purpose of facilitating their study; 

 while if this minor purpose has often been answered 

 by an artificial classification, the philosopher of another 

 ambition has attempted to discover the proceedings of 

 Nature herself, and thus to combine science with uti- 

 lity. Geologists may assume this praise, if they feel 

 entitled to it : but the minuter details of this science 

 are such, and the great relations and analogies so ob- 

 vious, that without much claim to philosophy, they 

 have followed the right road, though not hitherto with 

 any peculiar success. It is my duty to commence by 

 showing what they have done; since I shall thus, at 

 least, point out what is wanted, though I should leave 

 things little better than I have found them. 



Under infinite varieties of aspect, the real and defi- 

 nable differences of rocks are very limited; and hence 

 but few names are required for distinguishing them. 

 In a single mass, also, of one rock, bearing a fixed 

 relation to its associates in nature, the mineralogical 

 characters are subject to variations ; whence a still nar- 

 rower limitation of those names which a superficial 

 consideration might have applied, has been found ex- 

 pedient; by geologists at least of philosophical views. 

 Thus the varieties of granite, of gneiss,, and so forth, 

 have been united into mineralogical families, distin- 

 guished by a general title. If the terms, genus, and 

 species, have been alternately applied to these, we may 

 neglect this parade of an inapplicable logic, by persons 

 jnore familiar with words than with their purposes and 

 limitations. But on such a basis may be formed a 

 Mineralogical Classification of Rocks ; and arrange- 

 ments of this nature have been accordingly attempted. 



