DOMAIN I. SIDEROUS. 



radical a part in the constitution of our 

 planet, that it deserves to be viewed under 

 various aspects, not only as a metal, but 

 as an earth, strongly impregnating most 

 of the others, and often exerting a pre- 

 dominating influence. For as, since the 

 recent discoveries, many earths have been 

 known to assume the form of metals, so 

 there can be no impropriety in considering 

 this universal metal under the form of an 

 earth. 



When a substance contains more than 

 twenty-five parts in the hundred, or, in 

 other words, one quarter, of iron, it may 

 be worked as a metallic ore, and arranged 

 under that denomination. But in a smaller 

 quantity it will fall under the present divi- 

 sion, especially when intimately combined 

 with the other earths. It was by metallo- 

 gists considered as a calx, or latterly called 

 an oxyd. Mr. Kirwan*, who has rightly 

 added calces of iron to his description of 

 the earths, says, that they are formed of 

 that metal, combined with different pro- 



* * Min.i. 17. 



