240 TH E R T of the EAR ? H. 



ON the one hand, we know by experiment, that oily and 

 bituminous fubftances can be melted and partly changed into 

 vapour by heat, and that they become harder and denfer, in 

 proportion as the more volatile parts have evaporated from, 

 them. On the other hand, coaly fubftances are deftitute of fu- 

 fibility and volatility, in proportion as they have been expofed 

 to greater degrees of heat, and to other circumftances -favour- 

 able to the diffipation of their more volatile and fluid parts. 



IF, therefore, in mineral bodies, we find the two extreme 

 ftates of this combuflible fubftance, and alfo the intermediate 

 ftates, we muft either conclude, that this particular operation 

 of heat has been thus actually employed in nature, or we muft 

 explain thofe appearances by fome other means, in as fatisfaclo- 

 ry a manner, and fo as fhall be confident with other appear- 

 ances. 



IN this cafe, it will avail nothing to have recourfe to the falfe 

 analogy of water diflolving and cryftallizing falts, which has 

 been fo much employed for the explanation of other mineral 

 appearances. The operation here in queftion is of a different 

 nature, and neceflarily requires both the powers of heat and 

 proper conditions for evaporation. 



THEREFORE, in order to decide the point, with regard to 

 what is the power in nature by which mineral bodies have be- 

 come folid, we have but to find bituminous fubftance in the 

 inoft complete ftate of coal, intimately connected with fome 

 other fubftance, which is more generally found confolidating 

 the ftrata, and affifting in the concretion of mineral fubftances. 

 But I have in my pofTeflion the moft undoubted proof of this 

 kind. It is a mineral vein, or cavity, in which are blended to- 

 gether coal of the moft fixed kind, quartz and marmor metalli- 

 cum. Nor is this all ; for the fpecimen now referred to is con- 

 tained in a rock of this kind, which every naturalift now-a-days 

 will allow to have congealed from a fluid ftate of fufion. I 

 have alfo fimilar fpecimens from the fame place, in which the 



coal 



