logical investigation, and only demand* a previ- 

 ous knowledge of minerals. 



It involves no hypothetical views. 



* 

 To each of these advantages may be opposed 



corresponding disadvantages ; independently of 

 some general objections to the system. It will be 

 convenient to consider these first ; adding to them 

 such remarks as appear requisite for the more 

 perfect illustration of the subject. 



We must, in the first place, avoid being misled 

 in favour of a mineralogical arrangement of rocks 

 by the very obvious analogy of classifications of 

 minerals. The study of minerals is distinct from 

 that of the structure of the earth, however inti- 

 mately allied these two subjects may be : and, in 

 as far as that alone is concerned, they must be con- 

 sidered as independent natural productions, pos- 

 sessing^external characters more or less definite, 

 and subject to certain laws, whether of chemi- 

 cal composition or geometrical arrangement, by 

 which they are, or may be, arranged in some na- 

 tural or artificial method. Their connection with 



