At Other Times They Darted Tail First, With The Rapidity
Of An Arrow, From One Side Of The Pool To The Other, At The
Same Instant Discolouring The Water With A Dark Chestnut-Brown
Ink.
These animals also escape detection by a very
extraordinary, chameleon-like power of changing their colour.
They appear to vary their tints according to the nature
of the ground over which they pass:
When in deep water,
their general shade was brownish purple, but when placed on
the land, or in shallow water, this dark tint changed into one
of a yellowish green. The colour, examined more carefully,
was a French grey, with numerous minute spots of bright
yellow: the former of these varied in intensity; the latter
entirely disappeared and appeared again by turns. These
changes were effected in such a manner, that clouds, varying
in tint between a hyacinth red and a chestnut-brown, [4] were
continually passing over the body. Any part, being subjected
to a slight shock of galvanism, became almost black: a similar
effect, but in a less degree, was produced by scratching
the skin with a needle. These clouds, or blushes as they may
be called, are said to be produced by the alternate expansion
and contraction of minute vesicles containing variously
coloured fluids. [5]
This cuttle-fish displayed its chameleon-like power both
during the act of swimming and whilst remaining stationary
at the bottom. I was much amused by the various arts to
escape detection used by one individual, which seemed fully
aware that I was watching it. Remaining for a time motionless,
it would then stealthily advance an inch or two, like a
cat after a mouse; sometimes changing its colour: it thus
proceeded, till having gained a deeper part, it darted away,
leaving a dusky train of ink to hide the hole into which it
had crawled.
While looking for marine animals, with my head about
two feet above the rocky shore, I was more than once saluted
by a jet of water, accompanied by a slight grating noise. At
first I could not think what it was, but afterwards I found
out that it was this cuttle-fish, which, though concealed in a
hole, thus often led me to its discovery. That it possesses
the power of ejecting water there is no doubt, and it appeared
to me that it could certainly take good aim by directing the
tube or siphon on the under side of its body. From the
difficulty which these animals have in carrying their heads,
they cannot crawl with ease when placed on the ground. I
observed that one which I kept in the cabin was slightly
phosphorescent in the dark.
ST. PAUL'S ROCKS. - In crossing the Atlantic we hove-to
during the morning of February 16th, close to the island of
St. Paul's. This cluster of rocks is situated in 0 degs. 58'
north latitude, and 29 degs. 15' west longitude. It is 540
miles distant from the coast of America, and 350 from the island
of Fernando Noronha. The highest point is only fifty feet above
the level of the sea, and the entire circumference is under
three-quarters of a mile. This small point rises abruptly out
of the depths of the ocean. Its mineralogical constitution
is not simple; in some parts the rock is of a cherty, in others
of a felspathic nature, including thin veins of serpentine. It
is a remarkable fact, that all the many small islands, lying
far from any continent, in the Pacific, Indian, and Atlantic
Oceans, with the exception of the Seychelles and this little
point of rock, are, I believe, composed either of coral or of
erupted matter. The volcanic nature of these oceanic islands
is evidently an extension of that law, and the effect of those
same causes, whether chemical or mechanical, from which it
results that a vast majority of the volcanoes now in action
stand either near sea-coasts or as islands in the midst of the
sea.
The rocks of St. Paul appear from a distance of a brilliantly
white colour. This is partly owing to the dung of a
vast multitude of seafowl, and partly to a coating of a hard
glossy substance with a pearly lustre, which is intimately
united to the surface of the rocks. This, when examined
with a lens, is found to consist of numerous exceedingly
thin layers, its total thickness being about the tenth of an
inch. It contains much animal matter, and its origin, no
doubt, is due to the action of the rain or spray on the birds'
dung. Below some small masses of guano at Ascension, and
on the Abrolhos Islets, I found certain stalactitic branching
bodies, formed apparently in the same manner as the thin
white coating on these rocks. The branching bodies so closely
resembled in general appearance certain nulliporae (a family
of hard calcareous sea-plants), that in lately looking hastily
over my collection I did not perceive the difference. The
globular extremities of the branches are of a pearly texture,
like the enamel of teeth, but so hard as just to scratch plate-
glass. I may here mention, that on a part of the coast of
Ascension, where there is a vast accumulation of shelly sand,
an incrustation is deposited on the tidal rocks by the 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.
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