[ --4 I 



y" As Sir James hus negleded giving a complete accounf 

 of the external charadcrs of the natural whins, which were the 

 fubjed of his experiments, as alfo of the regenerated or arti- 

 ficial whins derived from them, and as I have not myfelf feen 

 them, it is difficult .for me to compare them with each other, 

 and would indeed be im[iofiible if fome account of them had 

 not been given by Mr. Pidlet in his valuable Journal Britannique, 

 copied into the 5th Vol. of the new Rozier's Journal, p 313. 

 It is the refult of the examination b^th of the natural and 

 artificial whins by the Society of Natural Hiftory at Geneva. 



As to the natural grunftein, No. i. they remark that it be- 

 trays not the leaft mark, of an igneous origin, but that the 

 whins which Sir James produced from it had every diftindtive 

 charader of a lova^ and even of a porous lava,- 



The bafalt (or rather trapp) on which the caftle of Edinburgh 

 ftands is of a compad flrudure ; the artificial produced from it, 

 Sir James tells us, fo greatly refembles it both in colour and 

 texture that it would be difficult or perhaps impoffible to diftin- 

 guifli them, but for a feiv minute air bubbles^ dijlinguijhable in 

 the artificial. Neptunifts will however confider this as a leading 

 charader of diftindion. The mineralogifts of Geneva add, that 

 the colour of the artificial is deeper, and its hardnefs greater 

 thaa that of the natural. If the fpecific gravity and other 



charaders 



