0(^8 ^N VOLCANIC SUBSTANCES. 



IX. 



Extract from a Letter to J. C. Delametherie, on Vokanit 

 Substances, by Lewis Cordier, Mine Engineer*. 



Work on vol- JL Have again visited the mountains of Auvergne, and have 

 ^""^romted"' ^"ished certain observations and experiments, which will 

 enable me to present the public with a work on different 

 volcanic productions. The following are some of their re- 

 sults. 

 Titanium in *< All the ferruginous sands of volcanoes capable of be- 



■volcanic san s -^^^ attracted by the magnet are composed of oxide of iron, 



and oxide of titaniumf. 

 and most lavas. « The major part of lavas contain a perceptible portion 



of oxide of titanium. 

 Granitoid *' The porous or massive granitoid lavas of the extinct 



lavas. volcanoes in the exterior of France are composed of feld- 



spar, pyroxene, and titanized iron." On comparing them 

 Summit of with the green granitello which is found on the summit of 

 Meisner. Meisner in Germany, and which Werner places in the first 



rank of those rocks that he calls secondary greenstone, they 

 appear to be perfectly similar. It is no doubt difficult to 

 conceive, how all the avithors who have written on the grani- 

 tello of Meisner could deceive themselves respecting its 

 composition : and such a mistake is so much the more sur- 

 prising as this rock has given rise to various commentaries. 

 It is certain however, that it is not formed of feldspar and 

 amphibole, as has hitherto been supposed, but of feldspar, 

 pyroxene, and titanized iron, which are very different. This 

 discovery adds fresh weight to the opinion advanced by Mr. 

 Voigt and several German mineralogists respecting the 

 IPiobabTy vol- Meisner. It is extremely probable, that the summit of this 

 ^^^^' mounlain is in reality a fragment of volcanic strata, 



* Journal de Physique, vol. LXIII, p. 235. 



f We must except those sands however, the base of which is specular 

 iron ore -, but these are exuemelj' rare. 



