56 



the pyramidal faces : — there is some indication of it in 

 some of the Crystals of tab. 319. 



The position and angles of these Crystals caught in the 

 fracture of the Petuntse give the curious appearance. The 

 Petuntse has rather an amorphous appearance in general, 

 but is all crystallized; and when the large primitive sides 

 are reflected to the eye, they show its beautiful and peculiar 

 lustre. It sometimes shows the terminations. The Quartz 

 varies in colour from transparent to gray brown and nearly 

 black — the Feldspar, from white to reddish and brown. 

 Mica is found in moderate-sized specimens. Two of the in- 

 gredients would constitute it a Granitel; three, a Granitine 

 of Kirwan: but these distinctions are not really of conse- 

 quence ; and I am afraid the term Sienite is not much 

 better, unless perhaps as an original term used by Pliny. 

 It is understood cbiefly to consist of Feldspar inclining to 

 red, and Hornblende, and sometimes are added Quartz and 

 Mica, as I and others have it from Egypt ; myself by fa- 

 four of Mr. W. Morel, being detached from one of the 

 pillars at the entrance of the temple of Isis in the ancient 

 Canopus near the fort of Aboukir. Its structure is that of 

 Granite with the addition of Hornblende in a small propor- 

 tion. 



