Narrative of the surveying voyages of His Majesty's Ships Adventure and Beagle, Vol. 3 [of 3] · Charles Darwin
STRAIT OF MAGELLAN.
A chain of mountains, which we will call the Cordillera, running north and south through the Alps (but having an altitude much inferior to the latter), would connect them with the central part of Denmark. Along this whole line nearly every deep sound would end in “bold and astonishing glaciers.” In the Alps themselves (with their altitude reduced by about half) we should find proofs of recent elevations, and occasionally terrible earthquakes would cause such masses of ice to be precipitated into the sea, that waves tearing all before them, would heap together enormous fragments, and pile them up in the corners of the valleys. At other times, icebergs, “charged with no inconsiderable blocks of granite,”[35] would be floated from the flanks of Mont Blanc, and then stranded on the outlying islands of the Jura. Who then will deny the possibility of these things having actually taken place in Europe during a former period, and under circumstances known to be different from the present, when on merely looking to the other hemisphere, we see they are among the daily order of events? To the northward of our new Cape Horn, we should only have certain knowledge of a few island groups, situated in the latitude of the south part of Norway, and others in that of Ferroe. These, in the middle of summer, would be buried under snow, and surrounded by walls of ice; so that scarcely a living thing of any kind would be supported on the land. If some bold navigator attempted to penetrate beyond these islands towards the pole, he would run a thousand dangers, and only meet an ocean strewed with mountain-masses of ice.
At the Ferroe islands (or we may say a little to the southward of the Wiljui, where Pallas found (in lat. 64° N.) the frozen rhinoceros), a body buried under the surface of the soil would undergo so little decomposition, that years afterwards (as in the instance mentioned at South Shetland, 62°-63° S.), every feature might be recognised perfect and unchanged. I particularly allude to this circumstance, because the case of the Siberian animals preserved with their flesh in the ice, offers the same apparent difficulty with the glaciers; namely, the union in the same hemisphere of a climate in some senses severe, with one allowing of the life of those forms which _at present_, although abounding _without_ the tropics, do not approach the frozen zones.
The perfect preservation of the Siberian animals, perhaps presented, till within a few years, one of the most difficult problems which geology ever attempted to solve. On the one hand it was granted, that the carcasses had not been drifted from any great distance by any tumultuous deluge, and on the other it was assumed as certain, that when the animals lived, the climate must have been so totally different, that the presence of ice in the vicinity was as incredible, as would be the freezing of the Ganges. Mr. Lyell in his “Principles of Geology”[36] has thrown the greatest light on this subject, by indicating the northerly course of the existing rivers with the probability that they formerly carried carcasses in the same direction; by showing (from Humboldt) how far the inhabitants of the hottest countries sometimes wander; by insisting on the caution necessary in judging of habits between animals of the same genius, when the species are not identical; and especially by bringing forward in the clearest manner the probable change from an insular to an extreme climate, as the consequence of the elevation of the land, of which proofs have lately been brought to light.[37]
In a former part of this volume, I have endeavoured to prove, that as far as regards the _quantity_ of food, there is no difficulty in supposing that these large quadrupeds inhabited sterile regions, producing but a scanty vegetation. With respect to temperature, the woolly covering both of the elephant and the rhinoceros seems at once to render it at least probable (although it has been argued that some animals living in the hottest regions are thickly clothed) that they were fitted for a cold climate. I suppose no reason can be assigned why, during a former epoch, when the pachydermata abounded over the greater part of the world, some species should not have been fitted for the northern regions, precisely as now happens with deer and several other animals.[38] If, then, we believe that the climate of Siberia, anteriorly to the physical changes above alluded to, had some resemblance with that of the southern hemisphere at the present day--a circumstance which harmonizes well with other facts,[39] as I think has been shown by the imaginary case, when we transported existing phenomena from one to the other hemisphere,--the following conclusions may be deduced as probable: First, that the degree of cold formerly was not excessive; secondly, that snow did not for a long time together cover the ground (such not being the case at the extreme parts 55°-56° of S. America); thirdly, that the vegetation partook of a more tropical character than it now does in the same latitudes; and lastly, that at but a short distance to the northward of the country thus circumstanced (even not so far as where Pallas found the entire rhinoceros), the soil might be perpetually congealed: so that if the carcass of any animal should once be buried a few feet beneath the surface, it would be preserved for centuries.
Both Humboldt[40] and Lyell have remarked, that at the present day, the bodies of any animals, wandering beyond the line of perpetual congelation which extends as far south as 62°, if once embedded by any accident a few feet beneath the surface, would be preserved for an indefinite length of time: the same would happen with carcasses drifted by the rivers; and by such means the extinct mammalia may have been entombed. There is only one small step wanting, as it appears to me, and the whole problem would be solved with a degree of simplicity very striking, compared with the several theories first invented. From the account given by Mr. Lyell of the Siberian plains, with their innumerable fossil bones, the relics of many successive generations, there can be little doubt that the beds were accumulated either in a shallow sea, or in an estuary. From the description given in Beechey’s voyage of Eschscholtz Bay, the same remark is applicable to the north-west coast of America: the formation there appears identical with the common littoral deposits[41] recently elevated, which I have seen on the shores of the southern part of the same continent. It seems also well established, that the Siberian remains are only exposed where the rivers intersect the plain. With this fact, and the proofs of recent elevation, the whole case appears to be precisely similar to that of the Pampas: namely, that the carcasses were formerly floated into the sea, and the remains covered up in the deposits which were then accumulating. These beds have since been elevated; and as the rivers excavate their channels the entombed skeletons are exposed.
Here then, is the difficulty: how were the carcasses preserved at the bottom of the sea? I do not think it has been sufficiently noticed; that the preservation of the animal with its flesh was an occasional event, and not directly consequent on its position far northward. Cuvier[42] refers to the voyage of Billing as showing that the _bones_ of the elephant, buffalo, and rhinoceros, are nowhere so abundant as on the islands between the mouths of the Lena and Indigirska. It is even said that excepting some hills of rock, the whole is composed of sand, ice, and bones. These islands lie to the northward of the place where Adams found the mammoth with its flesh preserved, and even ten degrees north of the Wiljui, where the rhinoceros was discovered in a like condition. In the case of the _bones_ we may suppose that the carcasses were drifted into a deeper sea, and there remaining at the bottom, the flesh decomposed.[43] But in the second and more extraordinary case, where putrefaction seems to have been arrested, the body probably was soon covered up by deposits which were then accumulating. It may be asked, whether the mud a few feet deep, at the bottom of a shallow sea which is annually frozen, has a temperature higher than 32°? It must be remembered how intense a degree of cold is required to freeze salt water; and that the mud at some depth below the surface, would have a low mean temperature, precisely in the same manner as the subsoil on the land is frozen in countries which enjoy a short but hot summer. If this be possible,[44] the entombment of these extinct quadrupeds is rendered very simple; and with regard to the conditions of their former existence, the principal difficulties have, I think, already been removed.
I have already mentioned the sombre and dull character of the forests,[46] in which two or three species of trees grow, to the exclusion of all others. Above the forest land, there are many dwarf alpine plants, which all spring from the mass of peat, and help to compose it. The central part of Tierra del Fuego, where the clay-slate formation occurs, is most favourable to the growth of trees; on the outer coast the poorer granitic soil, and a situation more exposed to the violent winds, do not allow of their attaining any great size. Near Port Famine I have seen more large trees than any where else: I measured a winter’s bark which was four feet six inches in girth, and several of the beech were thirteen feet. Captain King also mentions one of the latter which was seven feet in diameter, seventeen feet above the roots. The zoology of Tierra del Fuego, as might have been expected from the nature of its climate and vegetation, is very poor. Of mammalia, besides Cetacea and Phocæ, there is one bat, a mouse with grooved front teeth (_Reithrodon_ of Waterhouse), and two other species, the tucutuco (the greater number of these rodents are confined to the eastern and dry part), a fox, sea-otter, guanaco, and one deer. The latter animal is rare, and is not, I believe, to be found south of the Strait of Magellan, as happens with the others.
Observing the general correspondence of the cliffs of soft sandstone, mud, and shingle, on the opposite sides of the Strait, together with those on some intervening islands, one is strongly tempted to believe that the land was once joined, and thus allowed animals so delicate and helpless as the tucutuco, and Reithrodon, to pass over. The correspondence of the cliffs is far from proving any junction; because such cliffs generally are formed by the intersection of sloping deposits, which, before the elevation of the land, had been accumulated near the then existing shores. It is, however, a remarkable coincidence, that in the two large islands cut off by the Beagle channel from the rest of Tierra del Fuego, one has cliffs composed of matter that may be called stratified alluvium, which front similar ones on the opposite side of the channel,--while the other is exclusively bordered by the older rocks: in the former, called Navarin Island, both foxes and guanacoes occur; but in the latter, Hoste Island, although similar in every respect, and only separated by a channel a little more than half a mile wide, I have the word of Jemmy Button for saying that neither of these animals are found. I must confess to an exception to the rule, in the presence of a small mouse, of a species occurring likewise in Patagonia.
The gloomy woods are inhabited by few birds: occasionally the plaintive note of a white-tufted tyrant-flycatcher may be heard, concealed near the summit of the most lofty trees; and more rarely the loud strange cry of a black woodpecker, with a fine scarlet crest on its head. A little, dusky-coloured wren (_Scytalopus fuscus_) hops in a skulking manner among the entangled mass of the fallen and decaying trunks. But the creeper (_Synallaxis Tupinieri_) is the commonest bird in the country. Throughout the beech forests, high up and low down, in the most gloomy, wet, and impenetrable ravines, it may be met with. This little bird no doubt appears more numerous than it really is, from its habit of following, with seeming curiosity, any person who enters these silent woods: continually uttering a harsh twitter, it flutters from tree to tree, within a few feet of the intruder’s face. It is far from wishing for the modest concealment of the true creeper (_Certhia familiaris_), nor does it, like that bird, run up and down the trunks of trees; but industriously, after the manner of a willow wren, hops about, and searches for insects on every twig and branch. In the more open parts three or four species of finches, a thrush, a starling (or _Icterus_), two furnarii, and several hawks and owls occur.
The absence of any species whatever in the whole class of Reptiles is a marked feature in the zoology of this country, as well as in that of the Falkland Islands. I do not ground this statement merely on my own observation, but I heard it from the Spanish inhabitants of the latter place, and from Jemmy Button with regard to Tierra del Fuego. On the banks of the St. Cruz in 50° south, I saw a frog; and it is not improbable that these animals, as well as lizards, may be found as far south as the Strait of Magellan, where the country retains the character of Patagonia; but within the damp and cold limit not one occurs. That the climate would not have suited some of the orders, such as lizards, might have been foreseen; but with respect to frogs, this was not so obvious.
Coleopterous insects occur in very small numbers. Until I had endeavoured by every means to find them, I could not believe, that a country as large as Scotland, covered with vegetable productions, and with a variety of stations, would ever have been so unproductive. The greater part of my small collection consists of alpine insects (_Harpalidæ_ and _Heteromera_) found beneath stones, above the limit of the forest. Lower down, with the exception of some few Curculiones scarcely any could be found. The Chrysomelidæ, which are so pre-eminently characteristic of the Tropics, are here almost entirely absent.[47] This must depend on the climate; for the quantity of vegetable matter is superfluously great. In the hottest part of the summer the mean of the maxima for thirty-seven successive days was 55°, and the thermometer on some of the days rose to 60°; yet there were no orthoptera, very few diptera, lepidoptera, or hymenoptera. In the pools of water I found but few aquatic beetles, and not any fresh-water shells. Succinea at first appears an exception; but here it must be called a terrestrial species, for it lives on the damp herbage far from water. Land-shells could only be procured in the same situations with the alpine beetles. I have already contrasted the climate, as well as the general appearance of Tierra del Fuego with that of Patagonia; and the difference is strongly exemplified in the entomology. I do not believe they have a species in common; certainly the general character of the insects is widely different.
If we turn from the land to the sea, we shall find the latter as abundantly stocked with living creatures as the former is poorly so. In all parts of the world a rocky and partially protected shore perhaps supports, in a given space, a greater number of individual animals than any other kind of station. Here, under every stone, numerous crawling creatures swarmed, and especially crustacea of the family of _Cymothoades_. The number of Sphæroma was truly wonderful: as these animals, when coiled up, have some resemblance to Trilobites, they were an interesting sight to a geologist. On the tidal rocks patelliform shells of large size were very abundant. Even at the depth of forty or fifty fathoms, the bottom of the sea was far from sterile, as was shown by the abundance of small strong corallines.
There is one marine production, which from its importance is worthy of a particular history. It is the kelp or _Fucus giganteus_ of Solander. This plant grows on every rock from low-water mark to a great depth, both on the outer coast and within the channels. I believe, during the voyages of the Adventure and Beagle, not one rock near the surface was discovered, which was not buoyed by this floating weed. The good service it thus affords to vessels navigating near this stormy land is evident; and it certainly has saved many a one from being wrecked. I know few things more surprising than to see this plant growing and flourishing amidst those great breakers of the western ocean, which no mass of rock, let it be ever so hard, can long resist. The stem is round, slimy, and smooth, and seldom has a diameter of so much as an inch. A few taken together are sufficiently strong to support the weight of the large loose stones to which in the inland channels they grow attached; and some of these stones are so heavy, that when drawn to the surface they can scarcely be lifted into a boat by one person.
Captain Cook, in his second voyage, says, that at Kerguelen Land “some of this weed is of a most enormous length, though the stem is not much thicker than a man’s thumb. I have mentioned, that on some of the shoals upon which it grows, we did not strike ground with a line of twenty-four fathoms. The depth of water, therefore, must have been greater. And as this weed does not grow in a perpendicular direction, but makes a very acute angle with the bottom, and much of it afterwards spreads many fathoms on the surface of the sea, I am well warranted to say that some of it grows to the length of sixty fathoms and upwards.” Certainly at the Falkland Islands, and about Tierra del Fuego, extensive beds frequently spring up from ten and fifteen fathom water. I do not suppose the stem of any other plant attains so great a length as 360 feet, as stated by Captain Cook. Its geographical range is very considerable; it is found from the extreme southern islets near Cape Horn, as far north, on the eastern coast (according to information given me by Mr. Stokes), as lat. 43°,--and on the western it was tolerably abundant, but far from luxuriant, at Chiloe, in lat. 42°. It may possibly extend a little further northward, but is soon succeeded by a different species. We thus have a range of fifteen degrees in latitude; and as Cook, who must have been well acquainted with the species, found it at Kerguelen Land, no less than 140° in longitude.
The number of living creatures of all orders, whose existence intimately depends on the kelp, is wonderful. A great volume might be written, describing the inhabitants of one of these beds of sea-weed. Almost every leaf, excepting those that float on the surface, is so thickly incrusted with corallines, as to be of a white colour. We find exquisitely-delicate structures, some inhabited by simple hydra-like polypi, others by more organized kinds, and beautiful compound Ascidiæ.[48] On the flat surfaces of the leaves various patelliform shells, Trochi, uncovered molluscs, and some bivalves are attached. Innumerable crustacea frequent every part of the plant. On shaking the great entangled roots, a pile of small fish, shells, cuttle-fish, crabs of all orders, sea-eggs, starfish, beautiful Holuthuriæ (some taking the external form of the nudibranch molluscs), Planariæ, and crawling nereidous animals of a multitude of forms, all fall out together. Often as I recurred to a branch of the kelp, I never failed to discover animals of new and curious structures. In Chiloe, where, as I have said, the kelp did not thrive very well, the numerous shells, corallines, and Crustacea were absent; but there yet remained a few of the flustraceæ, and some compound Ascidiæ; the latter, however, were of different species from those in Tierra del Fuego. We here see the fucus possessing a wider range than the animals which use it as an abode.
I can only compare these great aquatic forests of the southern hemisphere with the terrestrial ones in the intertropical regions. Yet if the latter should be destroyed in any country, I do not believe nearly so many species of animals would perish, as, under similar circumstances, would happen with the kelp. Amidst the leaves of this plant numerous species of fish live, which nowhere else would find food or shelter; with their destruction the many cormorants, divers, and other fishing birds, the otters, seals, and porpoises, would soon perish also; and lastly, the Fuegian savage, the miserable lord of this miserable land, would redouble his cannibal feast, decrease in numbers, and perhaps cease to exist. JUNE 8TH.--We weighed anchor early in the morning, and left Port Famine. Captain FitzRoy determined to leave the Strait of Magellan by the Magdalen channel, which had not long been discovered. Our course lay due south, down that gloomy passage which I have before alluded to, as appearing to lead to another and worse world. The wind was fair, but the atmosphere was very thick; so that we missed much curious scenery. The dark ragged clouds were rapidly driven over the mountains, from their summits nearly to their bases. The glimpses which we caught through the dusky mass were highly interesting: jagged points, cones of snow, blue glaciers, strong outlines marked on a lurid sky, were seen at different distances and heights. In the midst of such scenery we anchored at Cape Turn, close to Mount Sarmiento, which was then hidden in the clouds. At the base of the lofty and almost perpendicular sides of our little cove, there was one deserted wigwam, and it alone reminded us that man sometimes wandered in these desolate regions. But it would be difficult to imagine a scene where he seemed to have less claims, or less authority. The inanimate works of nature--rock, ice, snow, wind, and water--all warring with each other, yet combined against man--here reigned in absolute sovereignty.
JUNE 9TH.--In the morning we were delighted by seeing the veil of mist gradually rise from Sarmiento, and display it to our view. This mountain, which is one of the highest in Tierra del Fuego, has an elevation of 6800 feet. Its base, for about an eighth of its total height, is clothed by dusky woods, and above this a field of snow extends to the summit. These vast piles of snow, which never melt, and seem destined to last as long as the world holds together, present a noble and even sublime spectacle. The outline of the mountain was admirably clear and defined. Owing to the abundance of light reflected from the white and glittering surface, no shadows are cast on any part; and those lines which intersect the sky can alone be distinguished: hence the mass stood out in the boldest relief. Several glaciers descended in a winding course, from the snow to the sea-coast: they may be likened to great frozen Niagaras; and perhaps these cataracts of blue ice are to the full as beautiful as the moving ones of water. By night we reached the western part of the channel; but the water was so deep that no anchorage could be found. We were in consequence obliged to stand off and on, in this narrow arm of the sea, during a pitch-dark night of fourteen hours long.
JUNE 10TH.--In the morning we made the best of our way into the open Pacific. The Western coast generally consists of low, rounded, quite barren, hills of granite and greenstone. Sir John Narborough called one part South Desolation, because it is “so desolate a land to behold;” and well indeed might he say so. Outside the main islands there are numberless scattered rocks, on which the long swell of the open ocean incessantly rages. We passed out between the East and West Furies, and a little further northward there are so many breakers that the sea is called the Milky Way. One sight of such a coast is enough to make a landsman dream for a week about shipwreck, peril, and death; and with this sight, we bade farewell for ever to Tierra del Fuego.
Text from Project Gutenberg, public domain in the United States.