water of the sea, resembling, as represented in the woodcut, certain
cryptogamic plants (Marchantiae) often seen on damp walls. The surface
of the fronds is beautifully glossy; and those parts formed where fully
exposed to the light are of a jet black colour, but those shaded under
ledges are only grey. I have shown specimens of this incrustation to
several geologists, and they all thought that they were of volcanic or
igneous origin! In its hardness and translucency--in its polish, equal
to that of the finest oliva-shell--in the bad smell given out, and loss
of colour under the blowpipe--it shows a close similarity with living
sea-shells. Moreover, in sea-shells, it is known that the parts
habitually covered and shaded by the mantle of the animal, are of a
paler colour than those fully exposed to the light, just as is the case
with this incrustation. When we remember that lime, either as a
phosphate or carbonate, enters into the composition of the hard parts,
such as bones and shells, of all living animals, it is an interesting
physiological fact [6] to find substances harder than the enamel of
teeth, and coloured surfaces as well polished as those of a fresh
shell, reformed through inorganic means from dead organic
matter--mocking, also, in shape, some of the lower vegetable
productions.
We found on St. Paul's only two kinds of birds--the booby and the
noddy. The former is a species of gannet, and the latter a tern. Both
are of a tame and stupid disposition, and are so unaccustomed to
visitors, that I could have killed any number of them with my
geological hammer. The booby lays her eggs on the bare rock; but the
tern makes a very simple nest with sea-weed. By the side of many of
these nests a small flying-fish was placed; which I suppose, had been
brought by the male bird for its partner. It was amusing to watch how
quickly a large and active crab (Graspus), which inhabits the crevices
of the rock, stole the fish from the side of the nest, as soon as we
had disturbed the parent birds. Sir W. Symonds, one of the few persons
who have landed here, informs me that he saw the crabs dragging even
the young birds out of their nests, and devouring them. Not a single
plant, not even a lichen, grows on this islet; yet it is inhabited by
several insects and spiders. The following list completes, I believe,
the terrestrial fauna: a fly (Olfersia) living on the booby, and a tick
which must have come here as a parasite on the birds; a small brown
moth, belonging to a genus that feeds on feathers; a beetle (Quedius)
and a woodlouse from beneath the dung; and lastly, numerous spiders,
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