470 



" fuccefs, to explain liic moll rayfterious phajnomma of the miaeral 

 '* kingdom." 



Sect. 15. " The tendency of an increafed prefl'ure on the bodies 

 " to which heat is applied, is to reilrala the volatility of thofe pans 

 " which, othervvife, would make their efcape, and to force them to 

 " endure a more intenfe aftion of heat. At a certain depth under 

 " the furface of the fea, the power even of a very intenfe heat might 

 " therefore be unable to drive off" the oily or bituminous parts from 

 " the inflamable matter there depofited." And again, (fefllon 29) 

 " The weight incumbent on the ftrata of coal, when they were ex- 

 " pofed to the intenfe heat of the mineral regions, may have been 

 *' fufScient to retain the oily and bituminous parts, as well as the 

 " fulphureous." 



Coal, indeed, he feems to feleft, as a favourite fubftance for fufmg 

 without burning; he fays, (feftion 28,) " This argument for the ig- 

 " neous origin of the ftrata, is applicable to them all, but efpecially 

 " to thofe of coal." 



It appears that calcareous fubftances are as eafily melted as the 

 combuftible, in Mr. Play/air's laboratory, (feftion 17,) " Somebodies, 

 " fuch as the calcareous, are able to reCft the force of heat on the 

 " furface of the earth, yet it is perfectly agreeable to analogy to 

 *' fuppofe, that under great prefl'ure, the carbonic {late being pre- 

 " ferved, the pureft limeftone or marble may be foftened or even fu- 

 " fed :" and Seftion 25, " calcareous earth, under great compreflion, 

 " may have its fixed air retained in it, notwithftanding the aftion of 

 t' intenfe heat, and may by that means be reduced into fufion." 



Such is the mode by which Mr. Playfair endeavours to eftablifli 

 his Angular pofitions ; and that his friend Dr. Hutton, has alfo fuc- 

 " ceeded, he feems perfe£lly fatisfied : for he tells us, (fe£tion 25,) 

 " In all this, I do not think he has departed from the ftrift rules of 

 *' philofophical inveftigation." 



Yet 



