Narrative of the surveying voyages of His Majesty's Ships Adventure and Beagle, Vol. 3 [of 3] · Charles Darwin
MAURITIUS TO ENGLAND.
The history of the changes, which the elevated plains of Longwood and Deadwood have undergone, as given in General Beatson’s account of the island, is extremely curious. It is said the plain in former times was covered with wood, and was therefore called the Great Wood. So late as the year 1716 there were many trees upon it, but in 1724 the old trees had mostly fallen; and as goats and hogs were at that time suffered to range about, all the young trees had been devoured. It appears also from the official records, that the trees were unexpectedly, some years afterwards, succeeded by indigenous wire grass, which now spreads over its whole extent.[3] He then adds, “These are curious facts, since they trace the changes which this remarkable spot of land has undergone, for now this formerly naked plain (after the trees had fallen) is covered with fine sward, and is become the finest piece of pasture on the island.” The extent of surface, which was probably covered by wood at a former period is estimated at no less than two thousand acres; at the present day scarcely a tree can be found there. It is said, that in 1709 there were quantities of dead wood in Sandy Bay: this place is now so utterly desert, that nothing but so well-attested an account could make me believe that trees had ever existed there. The fact, that the goats and hogs destroyed all the young trees as they sprung up, and that in the course of time the old ones, which were safe from their attacks, perished from age, seems clearly made out. Goats were introduced in the year 1502; eighty-six years afterwards, in the time of Cavendish, it is known they were exceedingly numerous. More than a century afterwards, in 1731, when the evil was completed and found irretrievable, an order was issued that all stray animals should be destroyed.
When at Valparaiso, I heard it positively affirmed, that the Sandal-wood tree had been found on the island of Juan Fernandez in considerable numbers, but that all without exception were standing dead. At the time, I thought it was some mysterious case of the natural death of a species; but when it is remembered, that goats for very many years have abounded on that island, it seems most probable that the young trees were prevented growing, and that the old ones perished from age. It is a very interesting fact, to observe that the arrival of animals at St. Helena in 1501 did not change the whole aspect of the island, until a period of two hundred and twenty years had elapsed: for they were introduced in 1502, and in 1724 it is said “the old trees had mostly fallen.” There can be no doubt, this change affected not only the Bulimus and probably some other land-shells (of which I obtained specimens from the same bed), but likewise a multitude of insects. St. Helena, situated so remote from any continent, in the midst of a great ocean, and possessing a unique Flora,--this little world within itself,--excites our curiosity. Birds and insects,[4] as might have been expected, are very few in number; indeed I believe all the birds have been introduced within late years. Partridges and pheasants are tolerably abundant: the island is much too English, not to be subject to strict game-laws. I was told of a more unjust sacrifice to such ordinances, than I ever heard of even in England. The poor people formerly used to burn a plant, which grows on the coast-rocks, and export soda; but a peremptory order came out prohibiting this practice, and giving as a reason, that the partridges would have nowhere to build!
In my walks, I passed more than once over the grassy plain, bounded by deep valleys, on which Longwood stands. Viewed from a short distance, it appears like a respectable gentleman’s country-seat. In front there are a few cultivated fields, and beyond them, the hill of coloured rocks called the Flagstaff, and the square black mass of the Barn. On the whole the view is rather bleak and uninteresting. The scrupulous degree to which the coast must formerly have been guarded, is quite extraordinary: there are alarm houses, alarm guns, and alarm stations on every peak. I was much struck with the number of forts and picket houses, on the line leading down to Prosperous Bay. One would have supposed that this at least was an easy descent: I found it however a mere goat-path, and in one spot the use of ropes, which were fixed into rings in the cliff, were almost indispensable. At the present day two artillery-men are kept there; for what use it is not easy to conjecture. Prosperous Bay, although with so flourishing a name, has nothing more attractive than a wild sea-beach, and black utterly barren rocks. The only inconvenience I suffered in my walks, was from the impetuous winds. One day I noticed a curious circumstance: standing on the edge of a plain, terminated by a great cliff of about a thousand feet in depth, I saw at the distance of a few yards right to windward, some tern, struggling against a very strong breeze, whilst, where I stood, the air was quite calm. Approaching close to the brink, I stretched out my arm, which immediately felt the full force of the wind: an invisible barrier of two yards wide, separated a strongly agitated from a perfectly calm air. The current meeting the bold face of the cliff, must have been reflected upwards at a certain angle, within which plane there necessarily would be either an eddy or a calm.
I so much enjoyed my rambles among the rocks and mountains of St. Helena, that I felt almost sorry on the morning of the 14th to descend to the town. Before noon I was on board, and the Beagle made sail for Ascension. We reached the anchorage of the latter place on the evening of the 19th (July). Those who have beheld a volcanic island, situated within an arid climate, will be able at once to picture to themselves the aspect of Ascension. They will imagine smooth conical hills of a bright red colour, with their summits generally truncated, rising distinct out of a level surface of black rugged lava. A principal mound in the centre of the island, seems the father of the lesser cones. It is called Green Hill; its name is taken from the faintest tinge of that colour, which at this time of the year was barely perceptible from the anchorage. To complete this desolate scene, the black rocks on the coast are lashed by a wild and turbulent sea. The settlement is near the beach; it consists of several houses and barracks placed irregularly, but well built of white freestone. The only inhabitants are marines, and some negroes liberated from slave-ships, who are paid and victualled by government. There is not a private person on the island. Many of the marines appeared well contented with their situation; they think it better to serve their one-and-twenty years on shore, let it be what it may, than in a ship: in which choice, if I were a marine, I would most heartily agree.
The next morning I ascended Green Hill, 2840 feet high, and thence walked across the island to the windward point. A good cart-road leads from the coast settlement to the houses, gardens, and fields, placed near the summit of the central mountain. On the road-side there are milestones, and likewise cisterns, where each thirsty passer-by, can drink some good water. Similar care is displayed in each part of the establishment, and especially in the management of the springs, so that a single drop of water shall not be lost: indeed the whole island may be compared to a huge ship kept in first-rate order. I could not help, when admiring the active industry which had created such effects out of such means, at the same time regretting that it was wasted on so poor and trifling an end. M. Lesson has remarked with justice, that the English nation alone would have thought of making the island of Ascension a productive spot; any other people would have held it without any further views, as a mere fortress in the ocean.
Near the coast nothing grows; a little inland an occasional green castor-oil plant, and a few grasshoppers (true friends of the desert), may be met with. Some grass is scattered over the surface of the central elevated region, and the whole much resembles the worse parts of the Welsh mountains. But scanty as the pasture appears, about six hundred sheep, many goats, a few cows and horses, all thrive well on it. Of native animals, rats and land-crabs swarm in numbers: of native birds, there are none; but the guinea-fowl, imported from the Cape de Verd Islands, is abundant, and the common fowl has likewise run wild. Some cats, which were originally turned out to destroy the rats and mice, have increased so as to become a great plague. The island is entirely destitute of trees, in which, and in every other respect, it is very far inferior to St. Helena. Mr. Dring tells me, that the witty people of the latter place say, “we know we live on a rock, but the poor people of Ascension live on a cinder:” the distinction in truth is very just.
On the succeeding days, I took long walks and examined some rather curious points in the mineralogical composition of some of the volcanic rocks, to which I was guided by the kindness of Lieut. Evans. On the basaltic masses, which are daily washed by the tide, most curious calcareous incrustations have been deposited. They resemble in form certain cryptogamic plants, especially the Marchantiæ; their surface is perfectly smooth and glossy, and their colour black, which seems owing to animal matter. I have shown these incrustations to several geologists, and not one guessed their true origin. Any one would suppose that they had been the product of fire, rather than of a deposition of calcareous matter, now constantly undergoing a round of decay and renovation from the action of the breakers. Near the settlement where these incrustations occur, there is a large beach of calcareous sand, entirely composed of comminuted and rounded fragments of shells and corals. The lower part of this, from the percolation of water containing calcareous matter in solution, soon becomes consolidated, and is used as a building stone; but some of the layers are too hard for freestone, and when struck by the hammer ring like flint.
The main line of beach is directed N.E. and S.W.; Lieutenant Evans informs me, that during the six months included between the 1st of April and the 1st of October, the sand accumulates towards the N.E. extremity, and during the other six it travels back again towards the S.W. end. This periodical movement is due to a change in the direction of the swell, which is influenced by the general direction of the trade-wind, during the two periods of the year. Lieutenant Evans also informs me that during the six years he has resided on this island, he has always observed, that in the months of October and November, when the sand commences travelling towards the S.W., the rocks which are situated at that end of the long beach, become coated by a white, thick, and very hard calcareous layer. I saw portions of this remarkable deposit, which had been protected by an accumulation of sand. In the year 1831 it was much thicker than during any other period. It would appear that the water, charged with calcareous matter by the disturbance of a vast mass of calcareous particles, only partially cemented together, deposits this substance on the first rocks against which it impinges. But the most singular circumstance is, that in the course of a couple of months this layer is either abraded or redissolved, so that after that period, it entirely disappears. It is curious thus to trace the origin of a periodical incrustation on certain isolated rocks, to the motion of the earth with relation to the sun; for this determines the atmospheric currents, which give the direction to the swell of the ocean, and this acts on the arrangement of the sea-beach, and this again on the quantity of calcareous matter held in solution by the waters of the neighbouring sea.
One of my excursions took me towards the S.W. extremity of the island. The day was clear and hot, and I saw the island, not smiling with beauty, but staring with naked hideousness. The lava streams are covered with hummocks, and are rugged to a degree, which, geologically speaking, is not of easy explanation. The intervening spaces are concealed with layers of pumice, ashes, and volcanic tuft. In some parts rounded volcanic bombs, which must have assumed this form, when projected red-hot from the crater, lie strewed on the surface. Whilst passing at sea this end of the island, I could not imagine what was the nature of the white patches, with which the whole plain was mottled; I now found they were seafowl, which were sleeping in such full confidence, that even in midday a man could walk up to, and seize hold of them. These birds were the only living creatures I saw during the day. On the beach a great surf, although the breeze was light, was tumbling over the broken lava rocks. Upon leaving Ascension the ship’s head was directed towards the coast of South America, and on August 1st, we anchored at Bahia or San Salvador. We staid here four days, in which time I took several long walks. I was glad to find my enjoyment of tropical scenery had not decreased even in the slightest degree, from the want of novelty. The elements of the scenery are so simple, that they are worth mentioning, as a proof on what trifling circumstances exquisite natural beauty depends.
The country may be described as a level plain of about three hundred feet in elevation, which in every part has been worn into flat-bottomed valleys. This structure is remarkable in a granitic land, but is nearly universal in all those softer formations, of which plains usually are composed. The whole surface is covered by various kinds of stately trees, interspersed with patches of cultivated ground, out of which houses, convents, and chapels arise. It must be remembered that within the tropics, the wild luxuriance of nature is not lost even in the vicinity of large cities; for the natural vegetation of the hedges and hill-sides, overpowers in picturesque effect the artificial labour of man. Hence, there are only a few spots where the bright red soil affords a strong contrast with the universal clothing of green. From the edges of the plain there are distant glimpses either of the ocean, or of the great bay bordered by low wooded shores, and on the surface of which numerous boats and canoes show their white sails. Excepting from these points, the range of vision is very limited: following the level pathways, on each hand alternate peeps into the wooded valleys below can alone be obtained. Finally, I may add that the houses, and especially the sacred edifices, are built in a peculiar and rather fantastic style of architecture. They are all whitewashed; so that when illuminated by the brilliant sun of midday, and as seen against the pale blue sky of the horizon, they stand out more like shadows than substantial buildings.
Such are the elements of the scenery, but to paint the effect is a hopeless endeavour. Learned naturalists describe these scenes of the tropics by naming a multitude of objects, and mentioning some characteristic feature of each. To a learned traveller, this possibly may communicate some definite ideas: but who else from seeing a plant in an herbarium can imagine its appearance when growing in its native soil? Who from seeing choice plants in a hothouse can magnify some into the dimensions of forest-trees, and crowd others into an entangled jungle? Who when examining in the cabinet of the entomologist the gay exotic butterflies, and singular cicadas, will associate with these objects, the ceaseless harsh music of the latter, and the lazy flight of the former,--the sure accompaniments of the still, glowing, noonday of the tropics. It is, when the sun has attained its greatest height, that such views should be beheld: then the dense splendid foliage of the mango hides the ground with its darkest shade, whilst the upper branches are rendered from the profusion of light of the most brilliant green. In the temperate zones, as it appears to me, the case is different, the vegetation there is not so dark or so rich, and hence the rays of the declining sun, tinged of a red, purple, or yellow colour, add most to the beauties of the scenery of those climes.
When quietly walking along the shady pathways, and admiring each successive view, one wishes to find language to express one’s ideas. Epithet after epithet is found too weak to convey to those, who have not visited the intertropical regions, the sensation of delight which the mind experiences. I have said the plants in a hothouse fail to communicate a just idea of the vegetation, yet I must recur to it. The land is one great wild, untidy, luxuriant hothouse, which nature made for her managerie, but man has taken possession of it, and has studded it with gay houses and formal gardens. How great would be the desire in every admirer of nature to behold, if such were possible, another planet; yet to every one in Europe, it may be truly said, that at the distance of a few degrees from his native soil, the glories of another world are open to him. In my last walk, I stopped again and again to gaze on these beauties, and endeavoured to fix for ever in my mind an impression, which at the time I knew, sooner or later must fail. The form of the orange-tree, the cocoa-nut, the palm, the mango, the tree-fern, the banana, will remain clear and separate; but the thousand beauties which unite these into one perfect scene must fade away; yet they will leave, like a tale heard in childhood, a picture full of indistinct, but most beautiful figures.
AUGUST 6TH.--In the afternoon we stood out to sea, with the intention of making a direct course to the Cape de Verd Islands. Unfavourable winds, however, having delayed us, on the 12th we ran into Pernambuco,--a large city on the coast of Brazil in latitude 8° south. We anchored outside the reef; but in a short time a pilot came on board, and took us into the inner harbour, where we lay close to the town. Pernambuco is built on some narrow and low sand-banks, which are separated from each other by shoal channels of salt water. The three parts of the town are connected together by two long bridges built on wooden piles. The town is in all parts disgusting, the streets being narrow, ill-paved, and filthy; the houses are very tall and gloomy. The number of white people, which during the morning may be met with in the streets, bears about the proportion of foreigners in any other nation; all the rest are black or of a dusky colour. The latter, as well as the Brazilians, are far from prepossessing in their appearance. The poor negroes, wherever they may be, are cheerful, talkative, and boisterous. There was nothing in the sight, smell, or sounds within this large town, which conveyed to my mind any pleasing impressions. The season of heavy rains had hardly come to an end, and hence the surrounding country, which is scarcely elevated above the level of the sea, was flooded with water. I failed in all my attempts to take any long walks. I was, however, enabled to observe that many of the country-houses in the outskirts, had like those of Bahia a gay appearance, which harmonized well with the luxuriant character of the vegetation.
The flat swampy land on which Pernambuco stands, is surrounded at the distance of a few miles, by a semicircle of low hills, or rather by the edge of a country elevated perhaps two hundred feet above the sea. The old city of Olinda stands on one extremity of this range. One day I took a canoe, and proceeded up one of the channels to visit it; I found the old town from its situation both sweeter and cleaner than that of Pernambuco. I must here commemorate what happened for the first time during the four-and-a-half years we have been wandering about, namely, having met with a want of politeness amongst any class of people: I was refused in a sullen manner at two different houses, and obtained with difficulty from a third, permission to pass through their gardens, to an uncultivated hill, for the purpose of taking a view of the country. I feel quite glad that this happened in the land of the “Brava Gente,” for I bear them no good will--a land also of slavery, and therefore of moral debasement. A Spaniard would have been ashamed at the thought of refusing such a request, or of behaving to a stranger with rudeness. The channel by which we went to, and returned from Olinda, was bordered on each side by mangroves, which sprang like a miniature forest out of the greasy mud-banks. The bright green colour of these bushes always reminded me of the rank grass in a churchyard: both are nourished by putrid exhalations; the one speaks of death past, and the other too often of death to come.
The most curious thing which I saw in this neighbourhood, was the reef that forms the harbour. It runs for a length of several miles in a perfectly straight line, parallel to, and not far distant from, the shore. It varies in width from thirty to sixty yards; it is dry at low water, has a level smooth surface, and is composed of obscurely-stratified hard sandstone. Hence, at first sight, it is difficult to credit that it is the work of nature, and not of art. Its utility is great; close within the inner wall there is a good depth of water, and ships lie moored to old guns, which are fixed in holes on its summit. A lighthouse stands on one extremity, and around it the sea breaks heavily. In entering the harbour, a ship passes within thirty yards of this point, and amidst the foam of the breakers; close by, on the other hand, are other breakers, which thus form a narrow gateway. It is almost fearful to behold a ship running, as it appears, headlong into such dangers.
With respect to the origin of the reef, I believe a bar composed of sand and pebbles formerly existed beneath the water (a circumstance no ways improbable) when the low land, on which the town now stands, was occupied by a large bay; and that this bar was first consolidated, and then elevated. These two processes are of such frequent occurrence in South America, that there can be no objection to using them in accounting for any remarkable structure in the land. There is another and slightly different explanation which possesses equal probability, namely, that a long spit of sand, like some that now run parallel to parts of the neighbouring coast, had its central part consolidated, and then by a slight change in the set of currents, the loose matter removed, so that the hard nucleus alone was left. Although the swell of the open ocean breaks heavily on the outside of this narrow and insignificant line of reef, yet there is no record of its decay. This durability is much the most curious circumstance in its history. Its protection appears due to a layer of calcareous matter, formed by the successive growth of several kinds of organic bodies, chiefly serpulæ, balani, nulliporæ, but no true corals. It is a process strictly analogous to the formation of peat; and like that substance, its effects are to preserve from degradation the matter on which it rests. In true coral reefs, when the upper extremities of the living mass are killed by the rays of the sun, they become enveloped and protected by a nearly similar process. It is probable, that if a breakwater, such as that at Plymouth, was built in these tropical seas, it would be imperishable; that is, as imperishable as any part of the solid land, all of which must some day suffer decay and renovation.
Text from Project Gutenberg, public domain in the United States.