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which case it has been confounded with pitch- 

 stones ; at others^ it is dull and earthy. It is 

 commonly very brittle, and scarcely less hard than 

 quartz. The fracture is generally flat, or con- 

 choidal, where the lustre is considerable : more 

 or less granular, or splintery, when dull. It is a 

 simple rock. 



SILICEOUS SCHIST* 



This rock varies materially in aspect and in 

 hardness, as might be expected from its origin. 

 When least hard, it is scarcely distinguishable by 

 the eye from the schists whence it is derived ; 

 even in this case, however, the power of resisting 

 the knife is a sufficient test. The structure is 

 simple and uniform, the fracture more or less 

 perfectly conchoidal, and also splintery. The 

 lustre sometimes approaches to that of pitch; 

 but, at the other extreme r the aspect is earthy. 

 The colours vary considerably; as it is found of a 

 reddish brown, dark purple, yellowish brown, 

 and greenish, but the tints of grey, and black, 

 are the most frequent. It is often striped with 

 different colours. ; 



p 2 



