must have stood, as it now does, above the level of the sea. This
conclusion accords with the highly scoriaceous condition of all the rock on
it, appearing to be of subaerial formation: and this is important, as there
are some beds of calcareous matter near its summit, which might, at a hasty
glance, have been mistaken for a submarine deposit. These beds consist of
white, earthy, carbonate of lime, extremely friable so as to be crushed
with the least pressure; the most compact specimens not resisting the
strength of the fingers. Some of the masses are as white as quicklime, and
appear absolutely pure; but on examining them with a lens, minute particles
of scoriae can always be seen, and I could find none which, when dissolved
in acids, did not leave a residue of this nature. It is, moreover,
difficult to find a particle of the lime which does not change colour under
the blowpipe, most of them even becoming glazed. The scoriaceous fragments
and the calcareous matter are associated in the most irregular manner,
sometimes in obscure beds, but more generally as a confused breccia, the
lime in some parts and the scoriae in others being most abundant. Sir H. De
la Beche has been so kind as to have some of the purest specimens analysed,
with a view to discover, considering their volcanic origin, whether they
contained much magnesia; but only a small portion was found, such as is
present in most limestones.

Fragments of the scoriae embedded in the calcareous mass, when broken,
exhibit many of their cells lined and partly filled with a white, delicate,
excessively fragile, moss-like, or rather conferva-like, reticulation of
carbonate of lime. These fibres, examined under a lens of one-tenth of an
inch focal distance, appear cylindrical; they are rather above one-
thousandth of an inch in diameter; they are either simply branched, or more
commonly united into an irregular mass of network, with the meshes of very
unequal sizes and of unequal numbers of sides. Some of the fibres are
thickly covered with extremely minute spicula, occasionally aggregated into