Narrative of the surveying voyages of His Majesty's Ships Adventure and Beagle, Vol. 3 [of 3] · Charles Darwin
BAHIA BLANCA.
The Beagle arrived on the 24th of August, and a week afterwards sailed for the Plata. With Captain FitzRoy’s consent I was left behind, to travel by land to Buenos Ayres. I will here add some observations, which were made during this visit, and on a previous occasion, when the Beagle was employed in surveying the harbour. Not much can be made out respecting the geology. At the distance of some miles inland, an escarpment of a great argillaceo-calcareous formation of rock extends. The space near the coast consists of plains of hardened mud, and broad bands of sand-dunes, which present appearances, that can easily be accounted for by a rise of the land; and of this phenomenon,[1] although to a trifling amount, we have other proofs.
At Punta Alta, a low cliff, about twenty feet high, exposes a mass of partly consolidated shingle, irregularly interstratified with a reddish muddy clay, and containing numerous recent shells. We may believe a similar accumulation would now take place, on any point, where tides and waves were opposed. In the gravel a considerable number of bones were embedded. Mr. Owen, who has undertaken the description of these remains, has not yet examined them with care; but the following list may give some idea of their nature: 1st, a tolerably perfect head of a megatherium, and a fragment and teeth of two others; 2d, an animal of the order Edentata, as large as a pony, and with great scratching claws; 3d and 4th, two great Edentata related to the megatherium, and both fully as large as an ox or horse; 5th, another equally large animal, closely allied or perhaps identical with the Toxodon (hereafter to be described), which had very flat grinding teeth, somewhat resembling those of a rodent; 6th, a large piece of the tesselated covering like that of the armadillo, but of gigantic size; 7th, a tusk which in its prismatic form, and in the disposition of the enamel, closely resembles that of the African boar; it is probable that it belonged to the same animal with the singular flat grinders. Lastly, a tooth in the same state of decay with the others: its broken condition does not allow Mr. Owen, without further comparison, to come to any definite conclusion; but the part that is perfect, resembles in every respect the tooth of the common horse.[2] All these remains were found embedded in a beach which is covered at spring tides; and the space in which they were collected could not have exceeded one hundred and fifty yards square. It is a remarkable circumstance that so many different species should be found together; and it proves how numerous in kind the ancient inhabitants of this country must have been.
At the distance of about thirty miles, in another cliff of red earth, I found several fragments of bones. Among them were the teeth of a rodent, much narrower, but even larger than those of the _Hydrochœrus capybara_; the animal which has been mentioned as exceeding in dimensions every existing member of its order. There was also part of the head of a Ctenomys; the species being different from the Tucutuco, but with a close general resemblance. The remains at Punta Alta were associated, as before remarked, with shells of existing species. These have not as yet been examined with scrupulous care, but it may be safely asserted, that they are most closely similar to the species now living in the same bay: it is also very remarkable, that not only the species, but the proportional numbers of each kind, are nearly the same with those now cast up on the pebble beaches. There are eleven marine species (some in an imperfect state), and one terrestrial. If I had not collected living specimens from the same bay, some of the fossils would have been thought extinct; for Mr. Sowerby, who was kind enough to look at my collection, had not previously seen them. We may feel certain that the bones have not been washed out of an older formation, and embedded in a more recent one, because the remains of one of the Edentata were lying in their proper relative position (and partly so in a second case); which could not have happened, without the carcass had been washed to the spot where the skeleton is now entombed.
We here have a strong confirmation of the remarkable law so often insisted on by Mr. Lyell, namely, that the “longevity of the species in the mammalia, is upon the whole inferior to that of the testacea.”[3] When we proceed to the southern part of Patagonia, I shall have occasion to describe the case of an extinct camel, from which the same result may be deduced. From the shells being littoral species (including one terrestrial), and from the character of the deposit, we may feel absolutely certain that the remains were embedded in a shallow sea, not far from the coast. From the position of the skeleton being undisturbed, and likewise from the fact that full-grown serpulæ were attached to some of the bones, we know that the mass could not have been accumulated on the beach itself. At the present time, part of the bed is daily washed by the tide, while another part has been raised a few feet above the level of the sea. Hence we may infer, that the elevation has here been trifling, since the period when the mammalia, now extinct, were living. This conclusion is in harmony with several other considerations (such as the recent character of the beds underlying the Pampas deposit), but which I have not space in this work to enter on.
From the general structure of the coast of this part of South America, we are compelled to believe, that the changes of level have all (at least of late) been in one direction, and that they have been very gradual. If, then, we look back to the period when these quadrupeds lived, the land probably stood at a level, less elevated only by a few fathoms than at present. Therefore, its general configuration since that epoch cannot have been greatly modified; a conclusion which certainly would be drawn from the close similarity in every respect, between the shells now living in the bay (as well as in the case of the one terrestrial species) with those which formerly lived there. The surrounding country, as may have been gathered from this journal, is of a very desert character. Trees nowhere occur, and only a few bushes, which are chiefly confined to depressions among the sand-hillocks, or to the borders of the saline marshes. Here, then, is an apparent difficulty: we have the strongest evidence that there has occurred no great physical change to modify the features of the country, yet in former days, numerous large animals were supported on the plains now covered by a thin and scanty vegetation.
That large animals require a luxuriant vegetation, has been a general assumption, which has passed from one work to another. I do not hesitate, however, to say that it is completely false; and that it has vitiated the reasoning of geologists, on some points of great interest in the ancient history of the world. The prejudice has probably been derived from India, and the Indian islands, where troops of elephants, noble forests, and impenetrable jungles, are associated together in every account. If, on the other hand, we refer to any work of travels through the southern parts of Africa, we shall find allusions in almost every page either to the desert character of the country, or to the numbers of large animals inhabiting it. The same thing is rendered evident by the many sketches which have been published of various parts of the interior. When the Beagle was at Cape Town, I rode a few leagues into the country, which at least was sufficient to render that which I had read more fully intelligible.
Dr. Andrew Smith, who, at the head of his adventurous party, has so lately succeeded in passing the Tropic of Capricorn, informs me that, taking into consideration the whole of the southern part of Africa, there can be no doubt of its being sterile country. On the southern and south-eastern coasts there are some fine forests, but with these exceptions, the traveller may pass, for days together, through open plains, covered by a poor and scanty vegetation. It is difficult to convey any accurate idea of degrees of comparative fertility; but it may be safely said, that the amount of vegetation supported at any one time[4] by Great Britain, exceeds, perhaps even tenfold, the quantity on an equal area, in the interior parts of Southern Africa. The fact that bullock-waggons can travel in any direction, excepting near the coast, without more than occasionally half an hour’s delay, gives, perhaps, a more definite notion of its scantiness. Now if we look to the animals inhabiting these wide plains, we shall find their numbers extraordinarily great, and their bulk immense.
We must enumerate the elephant, three species of rhinoceros, and as Dr. Smith is convinced two others also, the hippopotamus, giraffe, the bos caffer--as large as a full-grown bull, and the elan--but little less, two zebras, and the quaccha, two gnus, and several antelopes even larger than these latter animals. It may be supposed that although the species are numerous, the individuals of each kind are few. By the kindness of Dr. Smith, I am enabled to show that the case is very different. He informs me, that in lat. 24°, in one day’s march with the bullock-waggons, he saw, without wandering to any great distance on either side, between one hundred and one hundred and fifty rhinoceroses, which belonged to three species. That the same day he saw several herds of giraffes, amounting together to nearly a hundred; and that, although no elephant was observed, yet they are found in this district. At the distance of a little more than one hour’s march from their place of encampment on the previous night, his party actually killed at one spot eight hippopotamoses, and saw many more. In this same river there were likewise crocodiles. Of course it was a case quite extraordinary, to see so many great animals crowded together, but it evidently proves that they must exist in great numbers. Dr. Smith describes the country passed through that day, as “being thinly covered with grass, and bushes about four feet high, and still more thinly with mimosa-trees.” The waggons were not prevented travelling in a nearly direct line.
Besides these large animals, every one the least acquainted with the natural history of the Cape, has read of the herds of antelopes, which can be compared only to flocks of migratory birds. The numbers indeed of the lion,[5] panther, and hyæna, and the multitude of birds of prey, plainly tell of the abundance of the smaller quadrupeds. As Dr. Smith remarked to me, the carnage each day in Southern Africa must indeed be terrific! I confess it is truly surprising, how such a number of animals can find support in a country producing so little food. The larger quadrupeds no doubt roam over wide extents in search of it; and their food chiefly consists of underwood, which probably contains much nutriment in a small bulk. Dr. Smith also informs me that the vegetation has a rapid growth; no sooner is a part consumed, than its place is supplied by a fresh stock. I apprehend, however, that our ideas respecting the quantity necessary for the support of large quadrupeds are exaggerated. It should have been remembered that the camel, an animal of no mean bulk, has always been considered as the emblem of the desert.
The belief that where large quadrupeds exist, the vegetation must necessarily be luxuriant, is the more remarkable, because the converse is far from true. Mr. Burchell observed to me that when entering Brazil, nothing struck him more forcibly than the splendour of the South American vegetation, contrasted with that of South Africa, together with the absence of all large quadrupeds. In his Travels,[6] he has suggested that the comparison of the respective weights (if there were sufficient data) of an equal number of the largest herbivorous quadrupeds of each country would be extremely curious. If we take on the one side the elephant,[7] hippopotamus, giraffe, bos caffer, elan, certainly three species of rhinoceros, and probably five; and on the other side, two tapirs, the guanaco, three deer, the vicuna, peccari, capybara (after which we must choose from the monkeys to complete the number), and then place these two groups alongside each other, it is not easy to conceive ranks more disproportionate. After the above facts, we are compelled to conclude, against anterior probability,[8] that among the mammalia there exists no close relation between the _bulk_ of the species, and the _quantity_ of the vegetation, in the countries they inhabit.
With regard to the number of large quadrupeds, there certainly exists no quarter of the globe which will bear comparison with Southern Africa. After the different statements which have been given, the extremely desert character of that region will not be disputed. In the European division of the world, we must look back to the tertiary epochs, to find a condition of things among the mammalia resembling that which is now found at the Cape of Good Hope. That tertiary epoch, which we are apt to consider as abounding to an astonishing degree with large animals, because we find the remains of many ages accumulated at certain spots, could boast of but few more of the large quadrupeds, than Southern Africa does at present. If we speculate on the condition of the vegetation during that epoch, we are at least bound so far to consider existing analogies, as not to urge as absolutely necessary a luxuriant vegetation, when we see a state of things so totally different in the region to which we refer.
We know[9] that the extreme regions of North America, many degrees beyond the limit where the ground at the depth of a few feet remains perpetually congealed, are covered by forests of large and tall trees. In a like manner, in Siberia, we have woods of birch, fir, aspen, and larch, growing in a latitude[10] (64°), where the mean temperature of the air falls below the freezing point, and where the earth is so completely frozen, that the carcass of an animal embedded in it is perfectly preserved. With these facts we must grant, as far as _quantity alone_ of vegetation is concerned, that the great quadrupeds of the later tertiary epochs might, in most parts of Northern Europe and Asia, have lived on the spots where their remains are now found. I do not here speak of the _kind_ of vegetation necessary for their support; because, as there is evidence of physical changes, and as the animals have become extinct, so may we suppose that the species of plants have likewise been changed.
These remarks directly bear on the case of the Siberian animals preserved in ice. The firm conviction of the necessity of a vegetation, possessing a character of tropical luxuriance, to support such large animals, and the impossibility of reconciling this with the proximity of perpetual congelation, was one chief cause of the several theories of sudden revolutions of climate, and of overwhelming catastrophes, which were invented to account for their entombment. I am far from supposing that the climate has not changed since the period when those animals lived, which now lie buried in the ice. At present I only wish to show, that as far as _quantity_ of food _alone_ is concerned, the ancient rhinoceroses might have roamed over the _steppes_ of central Siberia (the northern parts probably being under water) even in their present condition, as well as the living rhinoceroses and elephants over the _Karros_ of Southern Africa.
After our long digression, if we return to the case of the fossil animals at Bahia Blanca, there is a difficulty from our not knowing on what food the great Edentata probably lived. If on insects and larvæ, like their nearest representatives the armadilloes and anteaters, there is an end to all conjecture. But as vegetation is the first source of life in every part of the world, I think we may safely conclude that the country around Bahia Blanca, with a very little increase of fertility, would support large animals. The plains of the Rio Negro, thickly scattered over with thorny bushes, I do not doubt would supply sufficient food equally well with the _Karros_ of Africa. As there is evidence of a physical change to a small amount, so may we allow it to be probable that the productiveness of the soil has decreased in an equally small degree. With this concession I apprehend every difficulty is removed. On the other hand, if we imagine a luxuriant vegetation to be necessary for the support of these animals, we become involved in a series of contradictions and improbabilities.
As the notices of the remains of several quadrupeds, which I discovered in South America, are scattered in different parts of this volume, I will here give a catalogue of them. After having enlarged on the diminutive size of the present races, it may be of interest to see that formerly a very different order of things prevailed. First, the megatherium, and the four or five other large edentata, already alluded to; 6th, an immense mastodon, which must have abounded over the whole country; 7th; the horse (I do not now refer to the broken tooth at Bahia Blanca, but to more certain evidence); 8th, the toxodon, an extraordinary animal as large as a hippopotamus; 9th, a fragment of the head of an animal larger than a horse, and of a very singular character; 10th, 11th, and 12th, parts of rodents--one of considerable size; lastly, a llama or _guanaco_, fully as large as the camel. All these animals coexisted during an epoch which, geologically speaking is so recent, that it may be considered as only just gone by. These remains have been presented to the College of Surgeons, where they are now in the hands of those best qualified to appreciate whatever value they may possess.
I will now give an account of the habits of some of the more interesting birds, which are common on these wild plains; and first of the _Struthio Rhea_, or South American ostrich. This bird is well known to abound over the plains of Northern Patagonia; and the united provinces of La Plata. It has not crossed the Cordillera; but I have seen it within the first range of mountains on the Uspallata plain, elevated between six and seven thousand feet. The ordinary habits of the ostrich are familiar to every one. They feed on vegetable matter; such as roots and grass; but at Bahia Blanca, I have repeatedly seen three or four come down at low water to the extensive mud-banks which are then dry, for the sake, as the Gauchos say, of catching small fish. Although the ostrich in its habits is so shy, wary, and solitary, and although so fleet in its pace, it falls a prey, without much difficulty, to the Indian or Gaucho armed with the bolas. When several horsemen appear in a semicircle, it becomes confounded, and does not know which way to escape. They generally prefer running against the wind; yet at the first start they expand their wings, and like a vessel make all sail.
On one fine hot day I saw several ostriches enter a bed of tall rushes, where they squatted concealed, till quite closely approached. It is not generally known that ostriches readily take to the water. Mr. King informs me that at the Bay of San Blas, and at Port Valdes in Patagonia, he saw these birds swimming several times from island to island. They ran into the water both when driven down to a point, and likewise of their own accord when not frightened: the distance crossed was about 200 yards. When swimming, very little of their bodies appear above water, and their necks are extended a little forward: their progress is slow. On two occasions, I saw some ostriches swimming across the Santa Cruz river, where its course was about four hundred yards wide, and the stream rapid. Captain Sturt, when descending the Murrumbidgee, in Australia, saw two emus in the act of swimming.
The inhabitants who live in the country readily distinguish, even at a distance, the cock bird from the hen. The former is larger and darker-coloured,[11] and has a bigger head. The ostrich, I believe the cock, emits a singular deep-toned, hissing note. When first I heard it, standing in the midst of some sand-hillocks, I thought it was made by some wild beast, for it is a sound that one cannot tell whence it comes, or from how far distant. When we were at Bahia Blanca in the months of September and October, the eggs, in extraordinary numbers, were found all over the country. They either lie scattered single, in which case they are never hatched, and are called by the Spaniards, huachos; or they are collected together into a shallow excavation, which forms the nest. Out of the four nests which I saw, three contained twenty-two eggs each, and the fourth twenty-seven. In one day’s hunting on horseback sixty-four eggs were found; forty-four of these were in two nests, and the remaining twenty scattered huachos. The Gauchos unanimously affirm, and there is no reason to doubt their statement, that the male bird alone hatches the eggs, and for some time afterwards accompanies the young. The cock when on the nest lies very close; I have myself almost ridden over one. It is asserted that at such times they are occasionally fierce, and even dangerous, and that they have been known to attack a man on horseback, trying to kick and leap on him. My informer pointed out to me an old man, whom he had seen much terrified by one chasing him. I observe in Burchell’s travels in South Africa, that he remarks, “having killed a male ostrich, and the feathers being dirty, it was said by the Hottentots to be a nest bird.” I understand that the male emu, in the Zoological Garden, takes charge of the nest: this habit, therefore, is common to the family.
The Gauchos unanimously affirm that several females lay in one nest. I have been positively told, that four or five hen birds have been seen to go, in the middle of the day, one after the other, to the same nest. I may add, also, that it is believed in Africa, that two females lay in one nest.[12] Although this habit at first appears very strange, I think the cause may be explained in a simple manner. The number of eggs in the nest varies from twenty to forty, and even to fifty; and according to Azara to seventy or eighty. Now although it is most probable, from the number of eggs found in one district being so extraordinarily great, in proportion to that of the parent birds, and likewise from the state of the ovarium of the hen, that she may in the course of the season lay a large number, yet the time required must be very long. Azara states,[13] that a female in a state of domestication laid seventeen eggs, each at the interval of three days one from another.
If the hen were obliged to hatch her own eggs, before the last was laid the first probably would be addled; but if each laid a few eggs at successive periods, in different nests, and several hens, as is stated to be the case, combined together, then the eggs in one collection would be nearly of the same age. If the number of eggs in one of these nests is, as I believe, not greater on an average than the number laid by one female in the season, then there must be as many nests as females, and each cock bird will have its fair share of the labour of incubation; and that during a period when the females could not sit, on account of not having finished laying. I have before mentioned the great numbers of huachos, or scattered eggs; so that in one day’s hunting the third part were found in this state. It appears odd that so many should be wasted. Does it not arise from the difficulty of several females associating together, and persuading an old cock to undertake the office of incubation? It is evident that there must at first be some degree of association, between at least two females; otherwise the eggs would remain scattered over the wide plains, at distances far too great to allow of the male collecting them into one nest. Some have believed that the scattered eggs were deposited for the young birds to feed on. This can hardly be the case in America, because the huachos, although oftentimes found addled and putrid, are generally whole.
Text from Project Gutenberg, public domain in the United States.