155 



Vakonic Productions are chiefly pum- 

 ice-stones, lava and basaltes. 



Pumice-stone is real glass, in the form 

 of small greyish, white, and exceeding- 

 ly brilliant filaments. These filaments 

 always leave vacuities of greater or less 

 size between them, which occasions great 

 variations in its specific gravity. In 

 general it is lighter than water. 



Lava is that burning matter which runs 

 down, in such prodigious quantities, from 

 volcanoes, when in a state of eruption., 

 and often extends to a great distance. 

 This matter is a semi-vitrified substance, 

 which appears blackish, on account of 

 its density. 



Basaltes is blackish and opaque. By 

 the action of heat it may be converted 

 into glass, of a very beautiful black co- 

 lour. It often crystallizes in prisms, 

 of three, four, five, six, or seven planes- 

 Of some kinds, such as that known un- 

 der the name of touchstone, the grain is 

 exceedingly fine. 



II. Of Salts. The alkalies, the acids, 

 and the combinations in which they enter 

 insufficient quantities, are called salts , 



