22 



from the former so as to give them their due 

 value, 



It affords, upon the whole, equal facility for 

 reference as a mineralogical arrangement; ad- 

 ding, moreover, to the discriminating characters 

 of rocks, the history of their order in nature. 

 Thus it frequently may remove doubts respecting 

 the nature of a rock, in those cases of frequent 

 occurrence where words are insufficient to render 

 intelligible the differences in aspect and compo- 

 sitiqn that may exist between two compounds. 



Although the mode of arranging a cabinet on 

 this system is different, it is neither less easy nor 

 less convenient than one derived from characters 

 merely mineralogical. 



The imperfections of such a system are how- 

 ever very considerable ; and it is only by com- 

 paring these with the advantages, that we can be 

 guided in our choice. 



The following objections have been made 

 against it by the authors who are advocates for a 

 mineralogical arrangement ; but most of these 



