MODIFIED by COMPRESSION. 73 



elude its fuppofed agency 3 fince experiment mews, that, in 

 our fires, they are totally changed or deflroyed. 



Under fuch circumftances, the advocates of either element 

 were enabled, very fuccefsfully, to refute the opinions of their 

 adverfaries, though they could but feebly defend their own : 

 and, owing perhaps to this mutual power of attack, and for 

 want of any alternative to which the opinions of men could 

 lean, both fyflems maintained a certain degree of credit ; and 

 writers on geology indulged themfelves, with a fort of im- 

 punity, in a ftyle of unphilofophical reafoning, which would 

 not have been tolerated in other fciences. 



Of all mineral fubftances, the Carbonate of Lime is unque* 

 ftionably the raoft important in a general view. As limeftone 

 or marble, it conftitutes a very conliderable part of the folid 

 mafs of many countries ', and, in the form of veins and no- 

 dules of fpar, pervades every fpecies of Hone. Its hiftory is 

 thus interwoven in fuch a manner with that of the mineral 

 kingdom at large, that the fate of any geological theory mull 

 very much depend upon its fuccefsfui application to the va- 

 rious conditions of this fubftance. But, till Dr Black, by his 

 difcovery of Carbonic Acid, explained the chemical nature of 

 the carbonate, no rational theory could be formed, of the che- 

 mical revolutions which it has undoubtedly undergone. 



This difcovery was, in the firil inftance, hoflile to the fup- 

 pofed action of fire ; for the decompofition of limeftone by fire 

 in every common kiln being thus proved, it feemed abfurd to 

 afcribe to that fame agent the formation of limeftone, or of 

 any mafs containing it. 



The contemplation of this difficulty led Dr Hutton to view 

 the action of fire in a manner peculiar to himfelf, and thus to 

 form a geological theory, by which, in my opinion, he has fur- 

 nifhed the world with the true folution of one of the moil inte- 



Vol. VI.— P. I. K refling 



