105 



scribed by Mr. Cordier, which contains sulphur 

 in it's cavities ; the alumiferous rocks of Parad 

 and Beregh in Hungary, which belong also to 

 trachytic and pumice conglomerates ; are no 

 doubt ovving to the penetrating of sulphurous 

 acid vapours*. They are the products of a 

 feeble and prolonged volcanic action, as may be 

 easily ascertained in the solfaterras of Puzzuoli 

 and the Peak of TenerifFe. The alumite of Tolfa, 

 which, since my return to Europe, I examined 

 conjointly with Gay-Lussac on the spot, has, by 

 it's oryctognostic characters and it's chemical 

 composition, a considerable affinity to compact 

 feldspar which constitutes the basis of so 

 many trachytes and transition porphyries. It is 

 a siliciferous subsulphat of alumin and potash, 

 a compact feldspar, with the ^addition of sul- 

 phuric acid completely formed in it. The waters 

 circulating in these alumiferous rocks of volcanic 



* Gay-Lussac, in the Annates de Chimie (old series), 

 Tom. 55, p. 266. Descotils in the Annales des Mines, 1816, 

 p. 374. Cordier, in the Annales de Chimie et de Physique, 

 Tom. 9, p. 71 — 88. Beudant, Voyage en Hongrie, torn. 3, 

 p. 446-471. 



+ This feldspar contains, according to Klaproth, more 

 silica than the alumite of Tolfa. The quantity of potash is the 

 same, but three times less than in common (lamellar) and 

 vitreous feldspars. We see however, on comparing the analyses 

 of Klaproth and Vauquelin, that the relative proportions of 

 silica and alumin vary much in different specimens obtained 

 from the mine of Tolfa. 



