195 

 PRIMARY CLASS. 



GRANITE. 



THIS rock necessarily contains two or more of 

 the following minerals, quartz, felspar, mica, and 

 hornblende, but does not exclude others. These 

 are aggregated by a confused crystallization ; 

 and, by the marks of mutual interference thence 

 resulting, this rock is to be distinguished from 

 coarse sandstones, or conglomerates, composed 

 of similar ingredients ; some indications of pre- 

 vious attrition and mechanical agglutination 

 being visible in these. 



Some varieties of granite may be confounded 

 with other substances in the secondary family of 

 overlying rocks ; and, in such a case, the geolo- 

 gical position must be resorted to ; the rocks ap- 

 pertaining to granite being inferior to every rock 

 which they accompany, (when in the mass,) and 

 the others being superior, if not precisely at the 

 point examined, yet in some part of their position 



SERPENTINE. 



It is seldom difficult to recognize this rock. 



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