6 



ILLtrSTRATlONS OF 



only remaining objedion that could be 

 againft the igneous origin of whinftone. 



irged 

 This 



objedlion is founded on the common obferva- 

 tion, that when a piece of whinftone or bafaltes 



is adually melted 



ble 



on 



ooling, it 



becomes glafs, and lofes its original charader 



tirely 



and from thence it was concluded, that 



th 



charadler had not been 



ginally produ 



ced by fufion. The experiments ab 



men 



tioned, however, have fh 



in the moft fa 



\ 



tisfadory manner, that melted whin, by re^ii, 



lated or by flow cooling, is prevented from alTu- 



ming the appearance of glafs, and becomes a fto^ 



ny fubftance, hardly to be diftinguifhed from 

 whinftone or lava. 



The experiments of another ingenious che- 

 mift, Dr Kennedy, have ftiewn, that whinftone 

 contains mineral alkali, by which, of courfe, its 

 fufion muft have been affifted *. Dr Hutton ufed 

 to afcribe its fufibility, in a great meafure at 

 leaft, to the quantity of iron contained in it : 

 both thefe caufes have no doubt united to ren- 

 der it more eafily melted than the ordinary ma- 

 terials of the ftrata. 



76. In a word, therefore, to conceive aright the 

 origin of that clafs of unftratified rocks, diftin- 

 guiftied by the name of whinftone, we muft fup- 



pofe, 



/ 



/ 



^* Tranf, R, S. Edin. vol. v. p. 85. 



(. 



