608 OVERLYING ROCKS. 



is granitic, and varies exceedingly, according to 

 the magnitude of the parts and their relative 

 proportions. Thus it sometimes resembles large 

 grained granite, at others, ordinary greenstones. 

 It also contains, in some cases, additional imbed- 

 ded crystals of felspar, resembling thus the por- 

 phyritic granite. Occasionally it is so fine as to 

 approach in appearance to basalt. It varies fur- 

 ther according to the colours of the felspar, which 

 is greenish grey, or white, or smoke grey, or 

 dark purple grey. It seems, at times, to contain 

 hornblende, as well as hypersthene, but not so 

 conspicuously as to render it necessary to adopt a 

 separate variety. 



. jfc 



Pyrites, mispickel, garnets, and octoedral 

 oxidulous iron, occur in hypersthene rock ; and 

 the latter in such abundance as to modify its cha- 

 racter and aspect. 



SECOND SUBDIVISION. 



Compounded of two substances ; one of which 

 is more or less distinctly crystallized and imbed- 

 ded in a simple base of another. Includes some 

 of the porphyries. 



