DOMAIN I. SIDEROUS. 



MODE XIV. SIDEROMAGNESIAN ROCKS. 



These rocks are far from being uncommon 

 /among primitive mountains, being chiefly com- 

 posed of magnesia and oxyd of iron. In the 

 Chlorite and substance called chlorite by Werner, from its 

 green colour, the iron often exceeds forty parts 

 in the hundred ; and it is even used as an ore of 

 that metal. Of actinote*, by some called acty- 

 nolite, some kinds contain as much iron as is 

 found in siderite ; and it is in general considered 

 as only a different structure of that rock. Saus- 

 sure indeed regarded chlorite as only a kind of 

 earthy siderite; but as it contains a far greater 

 portion of magnesia than siderite, in which that 

 substance is scarcely recognisable, it seems more 

 proper to allot to these rocks an article apart : 

 and the chemical mode of combination is at least 

 very different. 



To this Mode may also be added another 

 Some mixture of iron and magnesia, those serpentines 



serpentines. <- 



which contain so great a portion of iron as to 

 affect the magnet. Most of the siderous rocks 

 consist of iron and clay. The eisenkesel, that is 



* From the Greek anriVOT'o;, radiated, so that the y is foreign to 

 the orthography. 



