5i()0 DOMAIN XII. VOLCANIC* 



stance*." That even the hardest metals and 

 other substances have pores of extreme minute- 

 ness, undiscernable by the best microscopes, is a 

 well known fact in natural history ; and gases may 

 penetrate where the purest water may be excluded. 

 " Calcareous spars, or crystalised carbonate of 

 lime, is the most abundant substance in these an- 

 cient lavas. It is sometimes confusedly crystal- 

 ised like stalactites, and like them also with con- 

 centric layers, which indicate the successive de- 

 positions ; but often in solid globules, which per- 

 fectly fill the cavity, as is generally the case with 

 all the lavas of southern Sicily. I found some 

 with those globules six lines in diameter, on the 

 mountain of Carlintini ; and behind Lentini, near 

 Ferla, there are masses of lava in fragments, in 

 Sites. which these calcareous globules are so numerous, 

 that they may be said to be conglomerated by a 

 little argillaceous cement. These masses are very 

 friable, and the diameter of the globules varies 

 with the size of the vesicles in which they were 

 formed. I have also found them abundant in the 

 lavas near Pedagaggi, Palagonia, and other 

 places. Many of these globules, but chiefly the 

 larger, have a radiated structure, and may be ob- 

 served to be formed by the union of several py^ 



* Ferr. 184. 



