Fossils. 1 5 ' : 



petro si lex, agate, calcedony, cornelian, 

 3arcknyx,\\\zjade, and iheprasium. 



Common flint posesses very little 

 transparency. All the different kinds of 

 it have a dark dull colour, and are con- 

 cave, or convex, on the fracture. They 

 do not fuse in the fire, but are calcined 

 and become white. 



The distinguishing character of petro 

 silex is its semi-transparency, similar to 

 that of wax. It becomes white in the 

 fire, like the common flint, but it is more 

 fusible, as it runs without any addition. 



Agate has a smooth shining fracture, 

 and will take a very high polish ; it is 

 much variegated. When exposed to 

 heat, it loses its colour, and becomes o~ 

 paque, but without fusing. 



The calcedony has a milky semi-trans- 

 parency. Every kind of it takes a fine 

 polish. These stones are white, inter- 

 mixed sometimes with tints of red, yel- 

 low, and blue. 



The cornelians are all either entirely^ 

 or in part, of a beautiful red colour, but 

 they lose their colour in the fire, and be- 

 come opaque. They are all susceptible 

 of a fine polish. 



