396 LITHOLOGICAL OBSERVATIONS 



The N. W. shoulder exhibits quartzy-mica- 

 slate, tending to gneiss, which probably occurs at 

 no great distance in this direction. This species 

 of mica-slate, is unusually undulated, and its 

 structure affects a greater variety of singular and 

 fantastic appearances, than any I have met with. 

 It is also remarkable how much the layers of the 

 stone are affected by the intermixture of pure 

 quartz. 



Examining the base, which is thickly covered 

 with brush- v\^ood and debris, to the north of Row 

 Ardennan, I found two beds of felspar-porphyry ; 

 but the existence of many more is ascertained, 

 from numerous blocks and fragments of that sub- 

 stance, scattered at certain distances along the 

 shore. The mass of this rock is much pene- 

 trated with hornblende, chlorite, and crystals of 

 pistacite, generally crossing one another in pairs, 

 like the shape of an X. These last are very nu- 

 merous even in the smallest detached specimens, 

 and produce an uncommon effect to the eye. 

 There are also vast strata of porphyritic mica- 

 slate, thickly studded with crystals of quartz, par- 

 ticularly one, which may be observed near a cot- 

 tage on the side of the Loch, about miles 

 N. E, from Row Ardennan. Its structure seems 

 precisely the same with that of an extremely hard 

 and indestructible kind, formerly described^, at 



f W^rnerian Memoirs, vol. i. p. 287. 



