HUTTONIAN THEORY. 



523 



explains all the phenomena with which we are 

 at prefent acquainted, will be found to explain 

 all thofe that remain to be difcovered. 



456. The time indeed was, and we are not yet 

 far removed from it, when one of the moll im- 

 portant principles involved in Dr Hutton's theo- 



r 



ry was not only unknown, but could not be dif- 

 covered. This was before the caufticity produ- 

 ced in limeftone by expofure to fire was under- 



ftood. and when it was not kn 



th 



it arofe 



from the expulfion of a certain aerial fluid, which 

 before was a component part of the flone. It 

 could not then be perceived, that this aerial part 

 might be retained by preffure, even in fpite of 

 the udion of fire, and that in a region where 

 great compreffion exifted, the abfence of caufti- 

 city was no proof that 



g 



heat had not been 



applied. The difcoveries of Dr Black, therefore, 

 mark an era, before which men were not qualified 

 to judge of the nature of the powers that had 

 aded in the confolidation of mineral fubflances. 

 Thofe difcoveries were, indeed, deftined to pro- 

 duce a memorable change in chemiftry, and in 

 all the branches of knowledge allied to it ; and 

 have been the foundation of that brilliant pro- 

 grefs, by which a colledion of pradical rules, 

 and of infulated fads, has in a few years rifen 

 to the rank of a very perfed fcience. But even 



before they had explained the nature of carbo- 



Kl 



r» 



