Various - "Washington Square Plays"

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Percy Bysshe Shelley - "The Witch of Atlas"

The Voyage Of The Beagle

C >> Charles Darwin >> The Voyage Of The Beagle




One day, two of the officers and myself rode to Ribeira Grande, a
village a few miles eastward of Porto Praya. Until we reached the
valley of St. Martin, the country presented its usual dull brown
appearance; but here, a very small rill of water produces a most
refreshing margin of luxuriant vegetation. In the course of an
hour we arrived at Ribeira Grande, and were surprised at the
sight of a large ruined fort and cathedral. This little town,
before its harbour was filled up, was the principal place in the
island: it now presents a melancholy, but very picturesque
appearance. Having procured a black Padre for a guide, and a
Spaniard who had served in the Peninsular war as an interpreter,
we visited a collection of buildings, of which an ancient church
formed the principal part. It is here the governors and
captain-generals of the islands have been buried. Some of the
tombstones recorded dates of the sixteenth century. (1/2. The
Cape de Verd Islands were discovered in 1449. There was a
tombstone of a bishop with the date of 1571; and a crest of a
hand and dagger, dated 1497.) The heraldic ornaments were the
only things in this retired place that reminded us of Europe. The
church or chapel formed one side of a quadrangle, in the middle
of which a large clump of bananas were growing. On another side
was a hospital, containing about a dozen miserable-looking
inmates.

We returned to the Vênda to eat our dinners. A considerable
number of men, women, and children, all as black as jet,
collected to watch us. Our companions were extremely merry; and
everything we said or did was followed by their hearty laughter.
Before leaving the town we visited the cathedral. It does not
appear so rich as the smaller church, but boasts of a little
organ, which sent forth singularly inharmonious cries. We
presented the black priest with a few shillings, and the
Spaniard, patting him on the head, said, with much candour, he
thought his colour made no great difference. We then returned, as
fast as the ponies would go, to Porto Praya.

Another day we rode to the village of St. Domingo, situated near
the centre of the island. On a small plain which we crossed, a
few stunted acacias were growing; their tops had been bent by the
steady trade-wind, in a singular manner--some of them even at
right angles to their trunks. The direction of the branches was
exactly north-east by north, and south-west by south, and these
natural vanes must indicate the prevailing direction of the force
of the trade-wind. The travelling had made so little impression
on the barren soil, that we here missed our track, and took that
to Fuentes. This we did not find out till we arrived there; and
we were afterwards glad of our mistake. Fuentes is a pretty
village, with a small stream; and everything appeared to prosper
well, excepting, indeed, that which ought to do so most--its
inhabitants. The black children, completely naked, and looking
very wretched, were carrying bundles of firewood half as big as
their own bodies.

Near Fuentes we saw a large flock of guinea-fowl--probably fifty
or sixty in number. They were extremely wary, and could not be
approached. They avoided us, like partridges on a rainy day in
September, running with their heads cocked up; and if pursued,
they readily took to the wing.

The scenery of St. Domingo possesses a beauty totally unexpected,
from the prevalent gloomy character of the rest of the island.
The village is situated at the bottom of a valley, bounded by
lofty and jagged walls of stratified lava. The black rocks afford
a most striking contrast with the bright green vegetation, which
follows the banks of a little stream of clear water. It happened
to be a grand feast-day, and the village was full of people. On
our return we overtook a party of about twenty young black girls,
dressed in excellent taste; their black skins and snow-white
linen being set off by coloured turbans and large shawls. As soon
as we approached near, they suddenly all turned round, and
covering the path with their shawls, sung with great energy a
wild song, beating time with their hands upon their legs. We
threw them some vintéms, which were received with screams of
laughter, and we left them redoubling the noise of their song.

One morning the view was singularly clear; the distant mountains
being projected with the sharpest outline, on a heavy bank of
dark blue clouds. Judging from the appearance, and from similar
cases in England, I supposed that the air was saturated with
moisture. The fact, however, turned out quite the contrary. The
hygrometer gave a difference of 29.6 degrees, between the
temperature of the air, and the point at which dew was
precipitated. This difference was nearly double that which I had
observed on the previous mornings. This unusual degree of
atmospheric dryness was accompanied by continual flashes of
lightning. Is it not an uncommon case, thus to find a remarkable
degree of aerial transparency with such a state of weather?

Generally the atmosphere is hazy; and this is caused by the
falling of impalpably fine dust, which was found to have slightly
injured the astronomical instruments. The morning before we
anchored at Porto Praya, I collected a little packet of this
brown-coloured fine dust, which appeared to have been filtered
from the wind by the gauze of the vane at the masthead. Mr. Lyell
has also given me four packets of dust which fell on a vessel a
few hundred miles northward of these islands. Professor Ehrenberg
finds that this dust consists in great part of infusoria with
siliceous shields, and of the siliceous tissue of plants. (1/3. I
must take this opportunity of acknowledging the great kindness
with which this illustrious naturalist has examined many of my
specimens. I have sent (June 1845) a full account of the falling
of this dust to the Geological Society.) In five little packets
which I sent him, he has ascertained no less than sixty-seven
different organic forms! The infusoria, with the exception of two
marine species, are all inhabitants of fresh-water. I have found
no less than fifteen different accounts of dust having fallen on
vessels when far out in the Atlantic. From the direction of the
wind whenever it has fallen, and from its having always fallen
during those months when the harmattan is known to raise clouds
of dust high into the atmosphere, we may feel sure that it all
comes from Africa. It is, however, a very singular fact, that,
although Professor Ehrenberg knows many species of infusoria
peculiar to Africa, he finds none of these in the dust which I
sent him. On the other hand, he finds in it two species which
hitherto he knows as living only in South America. The dust falls
in such quantities as to dirty everything on board, and to hurt
people's eyes; vessels even have run on shore owing to the
obscurity of the atmosphere. It has often fallen on ships when
several hundred, and even more than a thousand miles from the
coast of Africa, and at points sixteen hundred miles distant in a
north and south direction. In some dust which was collected on a
vessel three hundred miles from the land, I was much surprised to
find particles of stone above the thousandth of an inch square,
mixed with finer matter. After this fact one need not be
surprised at the diffusion of the far lighter and smaller
sporules of cryptogamic plants.

The geology of this island is the most interesting part of its
natural history. On entering the harbour, a perfectly horizontal
white band in the face of the sea cliff, may be seen running for
some miles along the coast, and at the height of about forty-five
feet above the water. Upon examination, this white stratum is
found to consist of calcareous matter, with numerous shells
embedded, most or all of which now exist on the neighbouring
coast. It rests on ancient volcanic rocks, and has been covered
by a stream of basalt, which must have entered the sea when the
white shelly bed was lying at the bottom. It is interesting to
trace the changes, produced by the heat of the overlying lava, on
the friable mass, which in parts has been converted into a
crystalline limestone, and in other parts into a compact spotted
stone. Where the lime has been caught up by the scoriaceous
fragments of the lower surface of the stream, it is converted
into groups of beautifully radiated fibres resembling arragonite.
The beds of lava rise in successive gently-sloping plains,
towards the interior, whence the deluges of melted stone have
originally proceeded. Within historical times no signs of
volcanic activity have, I believe, been manifested in any part of
St. Jago. Even the form of a crater can but rarely be discovered
on the summits of the many red cindery hills; yet the more recent
streams can be distinguished on the coast, forming lines of
cliffs of less height, but stretching out in advance of those
belonging to an older series: the height of the cliffs thus
affording a rude measure of the age of the streams.

During our stay, I observed the habits of some marine animals. A
large Aplysia is very common. This sea-slug is about five inches
long; and is of a dirty yellowish colour, veined with purple. On
each side of the lower surface, or foot, there is a broad
membrane, which appears sometimes to act as a ventilator, in
causing a current of water to flow over the dorsal branchiae or
lungs. It feeds on the delicate seaweeds which grow among the
stones in muddy and shallow water; and I found in its stomach
several small pebbles, as in the gizzard of a bird. This slug,
when disturbed, emits a very fine purplish-red fluid, which
stains the water for the space of a foot around. Besides this
means of defence, an acrid secretion, which is spread over its
body, causes a sharp, stinging sensation, similar to that
produced by the Physalia, or Portuguese man-of-war.

I was much interested, on several occasions, by watching the
habits of an Octopus, or cuttle-fish. Although common in the
pools of water left by the retiring tide, these animals were not
easily caught. By means of their long arms and suckers, they
could drag their bodies into very narrow crevices; and when thus
fixed, it required great force to remove them. 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, were continually passing over
the body. (1/4. So named according to Patrick Symes's
nomenclature.) 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. (1/5. See "Encyclopedia of
Anatomy and Physiology" article "Cephalopoda.")

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, 1832, close to the island of St. Paul's. This
cluster of rocks is situated in 0 degrees 58' north latitude, and
29 degrees 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 feldspathic 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.

(PLATE 4. INCRUSTATION OF SHELLY SAND.)

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 Plate 4, 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 to find
substances harder than the enamel of teeth, and coloured surfaces
as well polished as those of a fresh shell, re-formed through
inorganic means from dead organic matter--mocking, also, in
shape, some of the lower vegetable productions. (1/6. Mr. Horner
and Sir David Brewster have described ("Philosophical
Transactions" 1836 page 65) a singular "artificial substance
resembling shell." It is deposited in fine, transparent, highly
polished, brown-coloured laminae, possessing peculiar optical
properties, on the inside of a vessel, in which cloth, first
prepared with glue and then with lime, is made to revolve rapidly
in water. It is much softer, more transparent, and contains more
animal matter, than the natural incrustation at Ascension; but we
here again see the strong tendency which carbonate of lime and
animal matter evince to form a solid substance allied to shell.)

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 seaweed. 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, which I suppose
prey on these small attendants and scavengers of the waterfowl.
The often-repeated description of the stately palm and other
noble tropical plants, then birds, and lastly man, taking
possession of the coral islets as soon as formed, in the Pacific,
is probably not quite correct; I fear it destroys the poetry of
this story, that feather and dirt-feeding and parasitic insects
and spiders should be the first inhabitants of newly formed
oceanic land.

The smallest rock in the tropical seas, by giving a foundation
for the growth of innumerable kinds of seaweed and compound
animals, supports likewise a large number of fish. The sharks and
the seamen in the boats maintained a constant struggle which
should secure the greater share of the prey caught by the
fishing-lines. I have heard that a rock near the Bermudas, lying
many miles out at sea, and at a considerable depth, was first
discovered by the circumstance of fish having been observed in
the neighbourhood.

FERNANDO NORONHA, FEBRUARY 20, 1832.

As far as I was enabled to observe, during the few hours we
stayed at this place, the constitution of the island is volcanic,
but probably not of a recent date. The most remarkable feature is
a conical hill, about one thousand feet high, the upper part of
which is exceedingly steep, and on one side overhangs its base.
The rock is phonolite, and is divided into irregular columns. On
viewing one of these isolated masses, at first one is inclined to
believe that it has been suddenly pushed up in a semi-fluid
state. At St. Helena, however, I ascertained that some pinnacles,
of a nearly similar figure and constitution, had been formed by
the injection of melted rock into yielding strata, which thus had
formed the moulds for these gigantic obelisks. The whole island
is covered with wood; but from the dryness of the climate there
is no appearance of luxuriance. Half-way up the mountain some
great masses of the columnar rock, shaded by laurel-like trees,
and ornamented by others covered with fine pink flowers but
without a single leaf, gave a pleasing effect to the nearer parts
of the scenery.

BAHIA, OR SAN SALVADOR. BRAZIL, FEBRUARY 29, 1832.

The day has past delightfully. Delight itself, however, is a weak
term to express the feelings of a naturalist who, for the first
time, has wandered by himself in a Brazilian forest. The elegance
of the grasses, the novelty of the parasitical plants, the beauty
of the flowers, the glossy green of the foliage, but above all
the general luxuriance of the vegetation, filled me with
admiration. A most paradoxical mixture of sound and silence
pervades the shady parts of the wood. The noise from the insects
is so loud, that it may be heard even in a vessel anchored
several hundred yards from the shore; yet within the recesses of
the forest a universal silence appears to reign. To a person fond
of natural history, such a day as this brings with it a deeper
pleasure than he can ever hope to experience again. After
wandering about for some hours, I returned to the landing-place;
but, before reaching it, I was overtaken by a tropical storm. I
tried to find shelter under a tree, which was so thick that it
would never have been penetrated by common English rain; but
here, in a couple of minutes, a little torrent flowed down the
trunk. It is to this violence of the rain that we must attribute
the verdure at the bottom of the thickest woods: if the showers
were like those of a colder clime, the greater part would be
absorbed or evaporated before it reached the ground. I will not
at present attempt to describe the gaudy scenery of this noble
bay, because, in our homeward voyage, we called here a second
time, and I shall then have occasion to remark on it.

Along the whole coast of Brazil, for a length of at least 2000
miles, and certainly for a considerable space inland, wherever
solid rock occurs, it belongs to a granitic formation. The
circumstance of this enormous area being constituted of materials
which most geologists believe to have been crystallised when
heated under pressure, gives rise to many curious reflections.
Was this effect produced beneath the depths of a profound ocean?
or did a covering of strata formerly extend over it, which has
since been removed? Can we believe that any power, acting for a
time short of infinity, could have denuded the granite over so
many thousand square leagues?

On a point not far from the city, where a rivulet entered the
sea, I observed a fact connected with a subject discussed by
Humboldt. (1/7. "Personal Narrative" volume 5 part 1 page 18.) At
the cataracts of the great rivers Orinoco, Nile, and Congo, the
syenitic rocks are coated by a black substance, appearing as if
they had been polished with plumbago. The layer is of extreme
thinness; and on analysis by Berzelius it was found to consist of
the oxides of manganese and iron. In the Orinoco it occurs on the
rocks periodically washed by the floods, and in those parts alone
where the stream is rapid; or, as the Indians say, "the rocks are
black where the waters are white." Here the coating is of a rich
brown instead of a black colour, and seems to be composed of
ferruginous matter alone. Hand specimens fail to give a just idea
of these brown burnished stones which glitter in the sun's rays.
They occur only within the limits of the tidal waves; and as the
rivulet slowly trickles down, the surf must supply the polishing
power of the cataracts in the great rivers. In like manner, the
rise and fall of the tide probably answer to the periodical
inundations; and thus the same effects are produced under
apparently different but really similar circumstances. The
origin, however, of these coatings of metallic oxides, which seem
as if cemented to the rocks, is not understood; and no reason, I
believe, can be assigned for their thickness remaining the same.

(PLATE 5. DIODON MACULATUS (DISTENDED AND CONTRACTED).)

One day I was amused by watching the habits of the Diodon
antennatus, which was caught swimming near the shore. This fish,
with its flabby skin, is well known to possess the singular power
of distending itself into a nearly spherical form. After having
been taken out of water for a short time, and then again immersed
in it, a considerable quantity both of water and air is absorbed
by the mouth, and perhaps likewise by the branchial orifices.
This process is effected by two methods: the air is swallowed,
and is then forced into the cavity of the body, its return being
prevented by a muscular contraction which is externally visible:
but the water enters in a gentle stream through the mouth, which
is kept wide open and motionless; this latter action must,
therefore, depend on suction. The skin about the abdomen is much
looser than that on the back; hence, during the inflation, the
lower surface becomes far more distended than the upper; and the
fish, in consequence, floats with its back downwards. Cuvier
doubts whether the Diodon in this position is able to swim; but
not only can it thus move forward in a straight line, but it can
turn round to either side. This latter movement is effected
solely by the aid of the pectoral fins; the tail being collapsed
and not used. From the body being buoyed up with so much air, the
branchial openings are out of water, but a stream drawn in by the
mouth constantly flows through them.

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