MODE III. BASALTMN. 57 



furnaces; therefore it is not surprising that ba- 

 salts may be changed by an artificial fusion; and 

 it is no reason for believing that they have not 

 before undergone the action of volcanic fires. 



" 5. Even supposing that volcanic fire pos- 

 sesses a great heat, it is known, by the beautiful 

 experiments, made in England by sir James Hall, 

 comparatively on the whinstone*, and on the 

 lavas of Vesuvius, that a contexture and aspect 

 may be given to a rocky mass, melted and cooled, 

 which shall have the characters of glass or stone, 

 according as the cooling is quicker or slower. 

 These experiments having been repeated on 

 several kinds of whinstone,*there has always been 

 obtained by a gentle cooling, a stony mass, com- 

 pact, dull, exactly similar to the whinstone em- 

 ployed ; and on the contrary, a vitreous mass 

 was obtained by a rapid cooling. The same 

 essays made on the substance of bottle glass, 

 gave the same results. 



" We see then that the absence of scoriae and 

 vitrifications is not a reason for denying the vol- 

 canic origin of basalt; besides, it is a known 

 fact that burning volcanoes have produced it. 



" * The whinstone of the English is generally a secondary trap ; 

 but among several specimens that 1 have seen given under that 

 4iame, some resembled basalt, others grunstein ; others in fine had 

 4he structure of amygdalite." 



