MODE Hi. BASALTS. 



Lustre dull, except when mixed with siderite. 

 Opake. 



Colour greyish black, greenish, rarely brown 

 Or reddish. 



This is the basalt, or fine-grained trap, of the 

 moderns. Karsten has supposed that even the 

 finest basalt is a mixture of impalpable grains of 

 siderite and felspar, or quartz; which would in- 

 deed appear to be confirmed by the identity of 

 the chemical constituents. Faujas also argues 

 in favour of his volcanic theory of basalt, that 

 trap, which he allows not to be of a volcanic 

 nature, is merely a granite of a very fine grain. 

 This idea partly rose from the confused and lax 

 manner in which the term granite has been hi- 

 therto used ; and partly from his theory that 

 real basalt is always a lava. But in this way alf 

 the mixed rocks might be classed under granites $ 

 for there is scarcely a mixture which has not 

 been arranged under that head by some mi- 

 neralogist, as the reader may perceive from the 

 edition of Linnaeus by Gmelin. It is true that 

 a mixture of siderite felspar and quartz would 

 form a genuine granite, and that some of the 

 ; basalts of the ancients might be classed, as Wad 

 has observed, among the granitels : but where 

 the siderite so preponderates as to give a great 

 prevalence to its colour; and especially where 



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