260 Messrs. Jackson and Alger on the 
anomalous and grotesque forms occasionally assumed by them. 
They refer us to the striking analogies subsisting between sec- 
ondary trap rocks, and the more recent volcanic lavas, as exhib- 
ited in their columnar configuration and arrangement, their 
cellularity and texture; and, by these analogies, clearly deduce 
their origin from similar, though, it may be, very remote causes. 
It is obvious therefore, that the occasional incurvated appearance 
of the trap referred to, is explained as easily as the same thing 
when shown in the columns of lava, and is, in both cases, probably 
the mere effect of some lateral motion given to the mass at the 
time it was beginning to develope its columnar structure from its 
previous state of igneous fluidity. In mineralogy too, we meet 
with similar appearances, though on a smaller scale, as, for exam- 
ple, in the curved or bent up crystals of scapolite, sillimanite, 
sappare, and some others, which are not only curved, but are 
bent nearly double, and are sometimes even broken off at their 
centres, as if, in hardening, they had become too brittle too yield 
any further without separating at those points. 
It is among the hexagonal masses of the trap composing this 
island, that we meet with those possessing the greatest symmetry 
of form. Some of them, indeed, have almost the symmetry of 
erystals; but they are not so smooth as the regular blocks of 
trap brought from Ireland, and, internally, they are of a coarser 
texture, resembling more nearly some of the masses brought 
from the Western Islands of Scotland. In their simple mechan- 
ical texture, they vary considerably, as might well be expected 
in reasoning from their origin; but this is a character which has 
little or no weight, from the very circumstance of its being so 
variable. The island presents many crystallized mineral sub- 
stances that cannot fail to interest and enrich the traveller. But 
