MODE I. S1DERITE. 



utterly unknown, it is sufficient to say, that the 

 rocks which the acute Werner, and his disciples, 

 have classed under HORNBLENDE, here appear 

 under SIDERITE, and some of their TRAPS under 

 BASALT; while the trap of the Swedes, with a 

 fine grain, is here called BASALTIN. The dif- 

 ference indeed is rather in the transition ; the 

 chemical analysis of siderite and basalt being 

 nearly the same. 



SIDERITE. BASALT. 



Silex 37 Silex 50 



Argil 22 Argil 15 



Magnesia 16 Magnesia 2 



Lime 2 Lime 8 



Oxyd of iron ... 23 Iron 25 



100 100 



It scarcely needs to be observed, that in all 

 substances the proportion of ingredients varies 

 according to circumstances. 



In general therefore where the substance has 

 a crystallised and silky appearance, it must be 

 classed among the siderites ; but when it wears 

 a dull or earthy aspect, it belongs to the basalts, 

 though in the latter shining crystals of siderite 

 may be interspersed. 



When mica alone is found in a substance, it 

 cannot alter the denomination, for, as Mr. Kir- 

 wan has observed, there is scarcely a mineral in 



