506 OVERLYING ROCKS. 



b. In a state of minute intermixture, and 



the parts nearly, or altogether, invi- 

 sible. 



This rock occurs of different colours, namely, 

 pale or dark greenish grey, or greenish black, or 

 black. Tt has the fracture and general appear- 

 ance of the basalts, with which the darkest varie- 

 ties have been confounded. Its nature, as yet, 

 can only be ascertained by tracing its intermix- 

 ture with, and gradation from the preceding 

 variety ; as there appears to be at present no 

 method of distinguishing augit from hornblende 

 when in this minute state of division and mixture. 



c. The felspar in excess, and both the 



minerals distinct. 



This rock resembles the analogous variety of 

 syenite into which hornblende enters. It occurs 

 in Rum, and may possibly be found elsewhere, 

 when mineralogists shall turn their attention to 

 these hitherto neglected compounds. Like the 

 common syenites, it presents considerable diver- 

 sity of aspect. 



G. Augit with glassy felspar. 



This beautiful rock occurs in Rum. 



It is probable that there are also compounds 



