MODIFIED ty COMPRESSION. 73 
clude its fuppofed agency ; fince experiment fhews, that, in 
our fires, they are totally changed or deftroyed. 
Unper 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 fyftems 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. 
Or all mineral fubflances, the Carbonate of Lime is unque-— 
ftionably the moft important in a general view. As limeftone 
or marble, it conftitutes a very confiderable part of the folid 
mafs of many countries ; and, in the form of veins and no- 
dules of fpar, pervades every fpecies of ftone. Its hiftory is 
thus interwoven in fuch a manner with that of the mineral 
kingdom at large, that the fate of any geological theory muft 
very much depend upon its fuccefsful, application to the va- 
rious conditions of this fubftance.. But, till Dr Biack, 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. 
Tuis difcovery was, in the firft inftance, hoftile 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. 
‘Tue contemplation of this difficulty led Dr Hutton to view 
the aétion 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 moft i inte- 
Vor. VI—P.I. K refting 
