174 



CHAP. XL 



ENUMERATION OF THE SEVERAL ROCKS, AR- 

 RANGED UNDER THE DIFFERENT MINERALS 

 WHICH ENTER INTO THEIR COMPOSITION. 



IN this chapter, the several minerals enumerated 

 in the preceding, as essential to the composition 

 of rocks, are introduced, for the purpose of ar- 

 ranging under them all the rocks in which such 

 minerals are severally found. 



This enumeration will assist the student in 

 discovering the place of any rock of which the 

 name is unknown to him. It being already pre- 

 sumed that he is able to distinguish the com- 

 ponent minerals, his researches among the fami- 

 lies of rocks will thus be limited within certain 

 bounds ; as, the presence of any one simple sub- 

 stance in a specimen, will direct him to those in 

 which alone it exists. 



