142 Effects of Heat modified hy Compression. 



dom, seem, by their presence, to preclude its supposed 

 agency ; since experiment shows, that, in our fires, they are 

 totally changed or destroyed. 



Under such circumstances the advocates of either element 

 were enabled, very successi'ully, to refute the opinions of 

 their adversaries, though they could but feebly defend their 

 own : and owing perhaps to this mutual power of attack, 

 and for want of any allernative to which the opinions of 

 men could lean, both systems maintained a certain degree of 

 credit ; and writers on geology indulged themselves, with a 

 sort of impunity, in a style of unphilosophical reasoning 

 which would not have been tolerated in other sciences. 



Of all mineral substances the carbonate of lime is un- 

 questionably the most important in a general view. As 

 limestone or marble it constitutes a very considerable part of 

 the solid mass of many countries, and in the form of veins 

 and nodules of spar pervades every species of stone. Its 

 history is thus interwoven in such a manner with that of the 

 mineral kingdom at large, that the fate of any geological 

 theory must very much depend upon its successful applica- 

 tion to the various conditions of this substance. But till 

 Dr. Black, by his discovery of carbonic acid, explained the 

 chemical nature of the carbonate, no rational theory could 

 be formed of the chemical revolutions which it has undoubt- 

 edly undergone. 



This discovery was in the first instance hostile to the sup- 

 posed action of fire; for the decon)positiou of limestone by 

 fire in every common kiln being thus proved, it seemed ab- 

 surd to ascribe to that same agent the formation of lime* 

 stone, or of any mass containing it. 



The contemplation of this difficulty led Dr. Tlutton to 

 view the action of fire in a manner peculiar to himself, and 

 thus to form a geological theory, by which, in my opinion, 

 he h^s furnished the world with the true solution of one o*' 

 the most interesting problems that has ever engaged the 

 attention of men of science. 



He supposed, 



I. 'That heat has acted, at some remote period,, on all 

 rock s . 



II. That 



