162 



CHAP. X. 



REMARKS ON THE COMPOSITION OF ROCKS, 

 WITH A CATALOGUE OF THE SIMPLE MINE- 

 RALS OF WHICH THEY ARK COMPOSED. 



IT has already been remarked, that the know* 

 ledge of minerals in their simple state, is an in- 

 dispensible requisite in the investigation of rocks. 

 It is also necessary that this knowledge should 

 not be limited to mere experience respecting the 

 aspect of such minerals in their most simple 

 and perfect forms. The student must be able 

 to recognize them by their essential characters, 

 even when under their most irregular modifica- 

 tions ; often, when very minute, or when inter- 

 mixed and confounded with others, or when 

 obscured by unexperienced variations of colour. 

 It is true that the number of minerals enter- 

 ing into the composition of rocks, is so small, 

 that a very limited acquaintance with the cata- 



