106 DOMAIN I. SIDEROUS. 



and French mineralogists, being by all ranked as 

 a primitive rock. As it has been found to con- 

 tain from 14 to 20 of iron, it strictly belongs to 

 this domain, the clay being a very inferior con- 

 sideration. It has also a metallic appearance 

 and sound, very different from schistose clay or 

 clay-slate, strictly to be so denominated. The 

 simple term SLATE, besides the advantage of 

 being in general use, has been thought sufficient 

 to discriminate it by way of eminence. It ge- 

 nerally contains a portion of magnesia; and 

 when this is abundant, as appears to be indi- 

 cated in those kinds which have a very silky or 

 satiny appearance, it may be ranked among 

 the magnesian rocks. It often presents pyrites, 

 either in a cubic or dundritic form, sometimes 

 schorl, and even garnet and siderite. Actinote 

 also appears ; and a recent discovery chiastolite, 

 or hollow spar. Scales of mica often occur, as 

 in many other substances; nay it sometimes 

 passes into mica-slate : and Daubuisson has de- 

 monstrated, by an operose chemical analysis, 

 that they may be regarded as different modes of 

 the same ingredients. 



It often forms entire mountains, but com- 

 monly only a part, alternating with gneiss and 

 mica-slate : nay, according to Kirwan and Pal- 

 las, both granite and gneiss often rest upon slate. 



