DOMAIN II. SILICEOUS. 145 



Joined with iron, argil, and magnesia, it 

 constitutes the primitive and most import- 

 ant rocks, rising to the regions of perpetual 

 snow, and thus supplying unfailing aliment 

 to the great rivers that fertilise the earth. 

 When considered in these mountains, in 

 sand, and in clay, it may be pronounced 

 the most abundant of all the earths : and 

 if iron form the nucleus, the shell of this 

 planet may be said to consist chiefly of 

 silex. It is suspected that it is coeval 

 and intimately connected with iron ; as the 

 aerolites or meteoric stones, and the large 

 masses of native iron, discovered in Siberia 

 and South America, contain abundance of 

 silex mixed with some magnesia*. 



Siliceous substances generally strike fire 

 with steel ; and flint or quartz yields a pe- 

 culiar odour, supposed by some to arise 

 from a subtile substance which chemistry 

 has not been able to discover. A strong- 

 phosphorescence is also produced by col- 



* Chrysolite, a mixture of silex and magnesia, is always found in 

 native iron. The exclamation of Henkel is well known : 



O silex! silex! quae te raatercula gessit? 

 VOL. I. L 



