312 DOMAIN XII. VOLCANIC. 



If the observations on this curious 

 topic, which has so long occupied scien- 

 tific men, should in this and other parts of 

 the work sometimes appear contradictory, 

 let it be regarded as a proof of the author's 

 candour, and not of his inattention to a 

 subject far from being ascertained. 



The account of the volcanic substances 

 will extend to considerable length, and 

 some degree of prolixity may be found in 

 the minuteness of the details, which was 

 necessary for the sake of accuracy ; espe- 

 cially as these substances have been objects 

 of repeated disputes and contestations 

 among the mineralogists and geologists. 



