164 



M INERALO GICAL ACCOUNT 



The rocks of this island appear to be the follow- 

 ing : Sandstone, Slate-clay, Amygdaloid, Green- 

 stone, Breccia, Compact-felspar, Porphyritic-slaty- 

 felspar, and Claystone. I shall, therefore, proceed 

 to give an account of the appearances accompa- 

 nying each of these rocks, beginning with the 



SANDSTONE. 



The rocks of sandstone chiefly occur at House- 

 avoe and the Kirk-sand. The beds are usually 

 thin. It is often of a brown and also of a green- 

 ish-grey colour. It is fine-grained in some in- 

 stances. It frequently contains rounded nodules of 

 quartz, and is much mixed with quartz. When it 

 contains much mica, it splits into plates. The sur- 

 face of the beds is sometimes elegantly undulated, 

 similar to the impressions made on the sand of the 

 sea shore by the retiring waves. This appearance 

 on the surface of the beds of sandstone has in all 

 probability been occasioned by the action of the 

 same cause. 



The different seams of the sandstone are ge- 

 nerally separated from each other by thin beds of 

 clay, and also by beds of breccia. On the north 

 side of Houseavoe, the sandstone covers a bed of 

 amygdaloid, and at the Kirk-sand it alternates 

 with beds of amygdaloid and greenstone. At a 

 place called Little-Peatie's-gio *, the sandstone is 

 covered with a bed of breccia, upon which it also 

 rests, and both these beds of sandstone and breccia 



Pronounced gio or geau* 



