DOMAIN XII. VOLCANIC. 



are all more or less vitrified ; but many of the 

 third show no signs of vitrification, are extremely 

 friable, and of a pale red colour. 



" This pumice, though destitute of any fibrous 

 texture, is specifically lighter than water. To 

 obtain it, large pieces of white pumice, of the 

 first species, in which it is enveloped, must be 

 removed ; and it commonly lies in long tracts, 

 in the direction of which its vesicles are some- 

 times lengthened, which may induce us to sus- 

 pect that this likewise, when it was liquid, 

 formed small currents. It contains no extra- 

 neons bodies. 



" In the furnace it condenses into an obscure 

 mass of glass, almost opake, but little porous, 

 and sufficiently hard to give sparks with steel. 



" These are the three kinds of pumice which 

 the people of Lipari dig for sale. The first is 

 employed in polishing different substances ; and 

 the other two are used in the construction of 

 arched vaults, and the corners of buildings/' 



From these descriptions the following arrange- 

 ment naturally arises. 



HYPONOME J. POROUS PUMICE. 



From Lipari. It sometimes presents small 

 crystals of felspar. 



Porous pumice, from Hecla. 



