17 



subject of a nomenclature although that ques- 

 tion is more fully examined in its proper place at 

 the end of this inquiry. 



If it be admitted that such an arrangement 

 could even be perfected, and that a complete se- 

 ries of rocks could be formed, classed according 

 to their natural affinities of structure and compo- 

 sition, or classed under a convenient artificial 

 system on such a basis, it is plain that it would 

 require a numerous, as well as an appropriate set 

 of terms, which, as far as it has been executed, 

 it actually does. 



As also there is no necessary or constant re- 

 lation between one species of composition in 

 rocks, and their affinities or positions in the 

 order of nature, while many varieties of compo- 

 sition also occur in the same mass of rock, it 

 would frequently happen that many terms would 

 be required in describing one fact or one set of 

 geological connexions, and that such connexions 

 would often appear to be implied where they did 

 not exist, in consequence of the similarity of the 

 names by which rocks corresponding in compo- 



