368 On Metallic Minerals. 



on charcoal, it becomes magnetic ; to borax it communi* 

 cates a lively greenish yellow colour. 



GRAPHIC SLATE. 



Associated with the above, and forming a sort of incrust- 

 ation upon it, is a mineral which has been confounded with 

 it. It agrees very closely, in all its characters but one, 

 with graphic slate. This excepted character is the peculiar 

 phenomenon which it exhibits when exposed to a candle or 

 the blow-pipe, and which has not been mentioned by 

 mineralogists as belonging to graphic slate. The moment it 

 is exposed to red heat, it expands, exfoliates, curls up, and 

 rapidly falls into powder. It has been mistaken for graphite, 

 but the streak it communicates to paper, is very different 

 to the shining metallic trace which the latter affords. On 

 the contrary, it is quite dull black, like that of black chalk, 

 of which species it appears to be unque?tionably a variety. 

 When first collected, it marks paper very freely, but after 

 keeping it in a dry room, it does not do so as readily. Its 

 specific gravity is 2-6. It is not in the least magnetic after 

 roasting on charcoal, but to borax it communicates a 

 yellowish colour, showing the presence of a small portion 

 of iron. 



These ores appear to hold the following relative position, 

 — the argillaceous oxide forms the walls of the vein ; the 

 red and yellow ochre, with sparry ore, form the lining next 

 the walls ; and the specular ore is found in the middle, not 

 however, in continuous masses, but rather in fragments. 



Chlorite, scaly talc, and quartz, sometimes form veins 

 in the sienite, which holds these ores imbedded. 



SECOND ORE BED. 



The next deposit of ore I have to describe is on the right 



