SKY. P1TCHSTONE. 401 



I must yet add to this account, the description of 

 a vein for which there is no other place in the arrange- 

 ment. This consists of a reddish brown compact felspar 

 with a splintery fracture, the fragments being translucent, 

 and it is in some parts slightly porphyritic. The vein 

 is vertical and of considerable thickness, occurring among 

 the sandstone near the Kyle rich. 



Among the rocks, for which 9, place could not be found 

 in the geological description without disturbing its order, 

 pitchstone requires to be noticed. Although not found 

 in situ it offers, as a mineral specimen, some appearances 

 which are interesting, and which I shall therefore describe.* 

 The specimens in question were found on the hill of 

 Glamich, and it is probable that they had been detached 

 from veins which I was unable to trace. There are two 

 varieties, one of which is black and very little differing 

 from that of Rum, except that it contains a few dispersed 

 crystals of glassy felspar ; the other is olive green, and as 

 it offers some apparently important peculiarities hitherto 

 unobserved, it must be described more fully. 



This variety presents a granular, combined with a small 

 conchoidal fracture, and is generally disposed in distinct 

 concretions, which are either of the flat or curved lamellar 

 form. It is remarkable for containing irregular rounded 

 cavities similar to those of the amygdaloids, filled with 

 compact grains of a greyish hue. The structure of these 

 is so singular as to be deserving of notice. On breaking 

 the smaller nodules they are discovered to consist of a 

 greyish white enamel similar to that which is formed 

 by the fusion of felspar. But in the larger, the centre 

 is composed of glassy felspar, the crystalline transparency 

 and platy fracture of which are perfect, while the surface to 



* Loose specimens of pitchstone are also scattered at the foot of Ben 

 na Caillich, and I have just been informed by Professor Jameson that 

 he has this year found the vein in a stream descending from that 

 mountain, \vhere we had both formerly sought for it in vain. 1818. 

 VOL. I. D D 



