OVERLYING HOCKS. 505 



D. Common felspar and quartz. 



This also occurs among the syenites and ana- 

 logous rocks, but apparently as an incidental 

 variation only. 



E. Hornblende with glassy felspar. 



This variety is rare, and appears to occupy 

 but small spaces where it occurs. 



F. Augit with compact felspar. 



a. The augit in superior or equal propor- 

 tion to the felspar; distinctly inter- 

 mixed. Augit rock. 



I have distinguished this by the name of augit 

 rock. It is in every respect analogous to the 

 similar compounds of hornblende and compact fel- 

 spar, with which it has been hitherto confounded. 

 It varies materially in appearance, according to 

 the colours of the augit, which are either black 

 or dark green, and according to \he magnitude, 

 relative proportions, and intermixture of the 

 parts. It is occasionally laminar, and also colum- 

 nar, and is found both in veins and in extensive 

 masses. It abounds in Scotland, chiefly in the 

 Western Islands, as in Rum and Sky. 



