DOMAIN XII. VOLCANIC. 



countries, that I feel myself necessitated 

 to detect them ; a liberty which, I am per- 

 suaded, his candour and love of truth will 

 readily induce him to excuse. 



" All real lavas, except those of the vi- 

 treous kind, affect the magnetic needle, 

 unless the iron they contain be much oxy- 

 genated, as it often is in those of a red 

 colour ; but even these are frequently mag- 

 netic, by reason of the schorls embodied 

 in them. 



" The component ingredients of lavas 

 are various, according to the nature of the 

 original stones, and the accidents they 

 meet with in the liquified state. M. Do- 

 lomieu found them to contain from 40 to 

 60 per cent, of silex, from 16 to 3 of mag- 

 nesia, from 5 to 1 of lime, and from 6 to 

 25 of iron. Ponces, 184."* 



These reflections are certainly cogent, 

 and worthy of the sagacious author, who 

 has rendered great services to the science : 



* Kinvan, Min. i. 404. 

 VOL. II, U 



