AILSA. GENERAL DESCRIPTION. 493 



each producing a small marshy plain covered with plants 

 of Hydrocotyle vulgaris, attaining, like all the plants 

 found on this spot, an enormous size. 



The perpendicular part of the rock extends from the 

 south, round by the west, towards the north side, the 

 greater portion being of a columnar form. Where it first 

 commences, at the southern end, it is thirty or forty 

 feet high, with a slight tendency to the columnar fracture. 

 Further on, as the altitude of the cliffs increases, the 

 columnar forms become more perfect, until a single face 

 presents itself, attaining in a perpendicular position to 

 a great height, and so divided as to exhibit, on a general 

 view, an aspect of ^regularity equal to that of the well 

 known columnar basalts of Scotland. The broken summits 

 of the columns, huge fragments of which encumber the 

 beach below, serve to give a variety that increases the 

 general picturesque effect. These are the habitations 

 and nests of the gannets, of which innumerable flocks 

 annually breed here ; forming, with the various tribes 

 of gulls, puffins, auks, and other sea fowl, a feathered 

 population scarcely exceeded by that of St. Kilda, or 

 the Flannan isles. As the alarm occasioned by the 

 arrival of a boat spreads itself, the whole of this noisy 

 multitude takes wing, forming a cloud in the atmo- 

 sphere which bears a striking resemblance to a fall of 

 snow, or to the scattering of autumna^ leaves in a storm. 

 To prevent interference in their courses, each cloud of 

 birds occupies a distinct stratum in the air, circulating in 

 one direction and in a perpetual wheeling flight. 



There are no ready means of measuring the length 

 of the columns, but it may be estimated by comparing 

 them from a sufficient distance with the total altitude 

 of the island. By this estimate I should judge them 

 to be upwards of 400 feet in height, an elevation before 

 which the columns of Staffa, not reaching to sixty 

 feet, sink into comparative insignificance. Although 

 the total effect of this range is columnar, the pillars 



