304 



ILLUSTRATIONS OF THE 



inllance cf it at the mouth of the river Ayr 

 where there is a v/hinilone dike *. I had the 

 fatisfadion of vifiting it along with him. It 

 was in the bed of the river, below the high-wa, 

 ter mark ; the fpecimens had the exad appear- 

 ance of a cinder. 



In 



highe 



the ba 



f the fam 



fome 



p, he found a piece of 



belonging 



regular ftratum, involved in whinftone, and 



remely 



1 



mbuftible 



It 



onfumed very 



llowly in the fire, and deflagrated with nitre like 



plumbago 



Th 



he 



fidered as th 



4\ 



fame 



H ft ' 



K 



foffil which has been defcfibed under the name 

 Q? plombagine. Near it, and connedled with 

 the fame vein of whinllone, w^s a real and un- 

 doubted plunibago. 



From thefe circumftances he alfo conclu- 

 ded, that plumbago is the extreme of a gra- 

 dation, of which foflil-coal is the beginning, and 

 is nothing elfe than this lafl reduced to per- 

 fedl charcoal. This agrees with the chemical 



■ - ^ 



analyfis, which fhows plumbago to be compofed 

 of carbon, combined with iron. 



In confirmation of this theory, he men- 

 tions a fpecimen, in his pofieflion, of fteati- 

 tical whinftone, from CumberJand, containing 



r 



nodules of a very perfed and beautiful plum- 

 bago ; and he alfo takes notice of a mine of this 



laft, 



% 



Theory of the Earth, vohi, p. 611. 



i 



m 



w 



