418 Dr. Mac Culloch on the Geology of 



It is bounded on the north-west by perpendicular cliffs, 200 or 

 300 feet in height, but on the other sides it declines by a rapid 

 grassy slope to the sea, intermixed however with rocky faces, and 

 covered with heaps of fragments, which are perpetually falling from 

 the bare rock. The square ruined tower which remains at about a 

 third part of its elevation, offers nothing interesting to the antiquary, 

 but the botanist will be delighted with the profusion of lychnis 

 dioica and silene amaena which covers it with a dense coat of 

 flowers ; to the exclusion of even the grass. It contains springs at 

 about 200 feet below its summit, which unite in a small marshy 

 plain, covered with enormous plants of hydrocotyle vulgaris. 



The rock which forms this insular mountain is in general amor- 

 phous, and breaks into large irregular masses, sometimes approach- 

 ing to a rectangular shape, sometimes without that tendency, and 

 resembling the fragments of quartz rock. In many places it ap- 

 proaches to an obscure columnar structure, and this occasionally 

 acquires great regularity. It is on the north-west side that the 

 columns are most perfect. They are here well defined in their 

 angles, yet adhere together, so as to appear to form one continuous 

 mass, their true structure being only detected by the occasional 

 falling of the huge fragments which strew the narrow beach on this 

 quarter of the island. They vary in the number of their sides, but 

 like basaltic columns, the most general forms are the pentagonal and 

 hexagonal. I could not any where perceive that they v>^ere jointed, 

 but they break at right angles to their axes, forming those flat sum- 

 mits which are tenanted by clouds of gannets. Their dimensions 

 are universally large, as they are from six to eight feet in diameter, 

 and extend in height as far as the eye can judge, to a continuous 

 altitude of 100 feet and upwards. Nothing can exceed the magni- 

 ficence of the columnar wall on this side of the rock ; even the 



