Dr Daubeny on the Columnar Structure Trap-Rochs'. 67 
to the rock has in all cases been so concealed as to require to 
be developed by mechanical causes 
As in the case of a simple mhieral, the crystalline structure 
probably always exists, although more commonly it may be ob- 
served by the subsequent deposition of other matter ; so may 
we suppose that the materials of which basalt is composed al- 
ways affect a peculiar structure, notwithstanding the amorphous 
character which it so often presents ; and, on the other hand, it 
would be as absurd to suppose that this structure was uniformly 
concealed, until made apparent by the denuding action of water, 
as to contend that there was no such thing as a crystal of quartz 
or felspar, until the angles of the originally shapeless mass were 
exposed by the operation of some extraneous cause. 
Yet that, in many instances in which the columnar structure 
ivas concealed in the manner above described, it may since have 
been developed by the agency of water, appears to me probable 
a priori, from considering that the amorphous portions of a 
rock are generally of an hardness inferior to those in which a 
regular arrangement is visible, and that it is therefore natural 
that the former should be first affected by mechanical abrasion ; 
in confirmation of which idea, I may mention the following 
facts, observed by myself during my excursion in Auvergne. 
The rock, at the foot of which the town of Muret, depart- 
ment of Contal, is situated, exhibits, on the side which over- 
looks the houses, some remarkably regular basaltic columns, 
which, towards the summit, are vertical, but, as they descend. 
* Some curious experiments have been published by Mr Daniel in the Journal 
of the Royal Institution, on the manner in which the crystalline structure of mine- 
rals may be developed even in amorphous masses by the action of acids, water, 
and other substances, which possess a chemical affinity for them. 
Such experiments seem to afford considerable confirmation to the views I have 
here offered, in proving that a crystalline structure exists in more mineral sub- 
stances, although frequently concealed by an upfiUing of other matter, and that 
when this is the case, the latter, being of a looser texture, \s first acted upon, thus 
causing the crystalline arrangement underneath to be gradually developed. It 
will not then be considered improbable, that this process of dissection (if I may 
so express myself), which, in the cases mentioned by Mr Daniel, appears to have 
been carried on in our laboratories, should sometimes take place on a grander scale 
in nature. 
