75 



TAB. CXL. 



Of the indurated Bitumens, one of the first we met with 

 was included in coarse, somewhat earthy, elastic Bitumen, 

 and much represented in form a gun flint, with fractures 

 not unlike those in common flints. It proved extremely 

 pure, of a dark olive green, and was closely surrounded by 

 the other bitumen, as if it had been the fragment of a 

 larger piece preceding in formation the earthy sort. We 

 have since found a larger specimen of a similar nature, 

 with a black outside — see the bottom. figure, and also a small 

 stalactite or lengthened drop. The smaller fractures in 

 these show transmitted lights or illinitions of a warm 

 yellow colour. 



Thus it should appear that an accumulation of this 

 yellow light, mixed with the black, gives the greenish hue to 

 the substance. We suspect that these colours are more or 

 less caused by the different degrees of oxygenizement of 

 Iron. v 



Dull greens are seldom happily imitated by illuminators ; 

 thus, our figures may in this instance be rather too gay. 

 According to the best chemists, Bitumen is formed prin- 

 cipally of Hydrogen* with more or less Oxide of Carbon, 

 Oxide of Iron, and other incidental substances. 



* Combined with but a small portion of Calor. 



