( 5* ) 



pearances in them are, elTentlally, the fame. 

 The red colour in the internal parts infenfi- 

 bly vanifhes ; the grey by degrees fucceeds 

 the white, which, ftill deeper, acquires a 

 luftre, the lava at the fame time becoming 

 harder, and at length diftindly exhibiting 

 all the chara^ers of the petrofilex. 



One of thefe lavas, ftreaked with white 

 and a clear red like that of the peach- 

 flower, is fpotted on the furface with points 

 almoft pulverulent* Thefe are decompofed 

 feltfpars, though they ftill retain a refidue 

 of cryftallization. This lava has been more 

 changed by the acids than the others, being 

 ibfter, and even pulverable ;. though at the 

 depth of two feet it is hard, heavy, of a 

 bkck-grey colour, evidently has a petrofili- 

 eeous bafe, and contains feltfpars which are 

 perfedly entire. 



In deicribing the varioufly decompol^d- 

 lavas of Solfatara, we have feen that felt- 

 fpars are a kind of ftones which ftrongly 

 refift the adtion of acids. It frequently 

 7 happensy 



