{ 5' ) 



happens, that their hafe is completely 

 decompofed, while they are fcarcely in 

 the leaft changed. As, therefore, ia th^ 

 prefent lava, the fekfpars are decompofed 

 equally with their bafe, we muft be con- 

 vinced that the ftrength of thefe acids muft 

 have been very great* In general, thefe 

 lavas at their furface are foft, like doughy 

 and almoft faponaceous; characters th^- 

 ufually accompany thefe decompofitionsh -'^ * 



We muft not omit toWQtke'a lava oif the 

 breccia kind, the bafe df whichis likewife 

 petrofilex, and in which the action of the- 

 acids has extended only tO' the depth of a 

 few inches. This bafe, even near the fur- 

 face, has not entirely loft its natural colour, 

 refembling that of iron, and in it are incor- 

 porated irregular fmall mafles of whitened 

 and pulverulent lava. Thefe, therefore, 

 have yielded more to the decompofition 

 than the bafe that contains them. -At a 

 -greater depth we find them unaltered 3 -and 

 they are then only fragments of^kva bf ^ 

 horn-ftone bafe. ' <'^iJjI:,i bnh ^o-iun^^ 

 E 3 Though 



