Narrative of the surveying voyages of His Majesty's Ships Adventure and Beagle, Vol. 3 [of 3] · Charles Darwin
STRAIT OF MAGELLAN.
In the end of May, 1834, we entered for the second time the eastern mouth of the Strait of Magellan. Having beat our way against wind and wave we anchored at Gregory Bay, and had an interview with the so-called gigantic Patagonians; of whom Captain FitzRoy has given so good an account. The country on both sides of the strait, in this part, consists of level plains, like those of the rest of Patagonia. Cape Negro, a little past the second narrow, may be considered as the point where the land begins to assume the marked features of Tierra del Fuego. On the east coast, south of the Strait, broken park-like scenery in a like manner connects these two countries, which are opposed to each other in almost every point. It is truly surprising to find in a space of twenty miles such a change in the landscape. If we take rather a greater distance, as between Port Famine and Gregory Bay, that is about sixty miles, the difference is still more wonderful. At the former place we have rounded mountains concealed by impervious forests, which are drenched with the rain, brought by an endless succession of gales; while at Cape Gregory there is a clear and bright blue sky over the dry and sterile plains. The atmospheric currents,[1] although rapid, turbulent, and unconfined by any apparent limits, yet seem to follow, like a river in its bed, a regularly determined course.
JUNE 1ST.--We anchored in the fine bay of Port Famine. It was now the beginning of winter, and I never saw a more cheerless prospect; the dusky woods piebald with snow, could be only indistinctly seen through a drizzling hazy atmosphere. We were, however, lucky in getting two fine days. On one of these. Mount Sarmiento, a distant mountain 6800 feet high, presented a very noble spectacle. I was frequently surprised, in the scenery of Tierra del Fuego, at the little apparent elevation of mountains really lofty. I suspect it is owing to a cause, which would not at first be imagined, namely, that the whole mass, from the summit to the water’s edge, is generally in full view. I remember having seen a mountain, first from the Beagle channel, where the whole sweep from the summit to the base was full in view, and then from Ponsonby Sound across several successive ridges; and it was curious to observe in the latter case, as each fresh step afforded means of judging of the distance, how the mountain appeared to rise in height.
The Fuegians twice came and plagued us. As there were many instruments, clothes, and men on shore, it was thought necessary to frighten them away. The first time, a few great guns were fired, when they were far distant. It was most ludicrous to watch through a glass the Indians, as often as the shot struck the water, take up stones, and as a bold defiance, throw them towards the ship, though about a mile and a half distant! A boat was then sent with orders to fire a few musket-shot wide of them. The Fuegians hid themselves behind the trees; and for every discharge of the musket they fired their arrows: all, however, fell short of the boat, and the officer as he pointed at them laughed. This made the Fuegians frantic with passion, and they shook their mantles in vain rage. At last seeing the balls cut and strike the trees, they ran away; and we were left in peace and quietness.
On a former occasion, when the Beagle was here in the month of February, I started one morning at four o’clock to ascend Mount Tarn, which is 2600 feet high, and is the most elevated point in this immediate neighbourhood. We went in a boat to the foot of the mountain (but not to the best part), and then began our ascent. The forest commences at the line of high-water mark, and during the two first hours I gave over all hopes of reaching the summit. So thick was the wood, that it was necessary to have constant recourse to the compass; for every landmark, though in a mountainous country, was completely shut out. In the deep ravines, the death-like scene of desolation exceeded all description; outside it was blowing a gale, but in these hollows, not even a breath of wind stirred the leaves of the tallest trees. So gloomy, cold, and wet was every part, that not even the fungi, mosses, or ferns, could flourish. In the valleys it was scarcely possible to crawl along, they were so completely barricaded by the great mouldering trunks, which had fallen down in every direction. When passing over these natural bridges, one’s course was often arrested by sinking knee deep into the rotten wood; at other times, when attempting to lean against a firm tree, one was startled by finding a mass of decayed matter ready to fall at the slightest touch. We at last found ourselves among the stunted trees, and then soon reached the bare ridge, which conducted us to the summit. Here was a view characteristic of Tierra del Fuego;--irregular chains of hills, mottled with patches of snow, deep yellowish-green valleys, and arms of the sea intersecting the land in many directions. The strong wind was piercingly cold, and the atmosphere rather hazy, so that we did not stay long on the top of the mountain. Our descent was not quite so laborious as our ascent; for the weight of the body forced a passage, and all the slips and falls were in the right direction.
Captain King has given a sketch of the geology of Tierra del Fuego, to which I have little to add. A great formation of clay-slate, rarely containing organic remains, but sometimes presenting casts of a kind of ammonite, is fronted on the east side by plains belonging probably to two tertiary epochs. On the west coast, a prolongation of the grand crevice of the Andes, from which so much heat has escaped from the interior of the globe, has metamorphosed the slate. There is, however, a double line, the structure of which I do not quite comprehend. The interior one consists of granite and mica slate; the exterior one (perhaps more modern), of greenstone, porphyritic and other curious trappean rocks. Almost every one at first thinks that this country owes its grand name of “the Land of Fire,” to the number of its volcanoes. Such, however, is not the case: I did not see even a pebble of any volcanic rock, except in Wollaston Island, where some rounded masses of scoriæ were embedded in a conglomerate of no modern date. In a geological point of view this circumstance allows us to consider the grand linear train of ancient and modern volcanoes, which fall on parallel fissures in the Andes, as extending from lat. 55° 40′ south to 60° north, a distance little less than seven thousand geographical miles.
Perhaps the most curious feature in the geology of this country, is the extent to which the land is intersected by arms of the sea. These channels, as Captain King remarks, are irregular and dotted with islands, where the granitic and trappean rocks occur, but in the clay-slate formation are so straight, that in one instance “a parallel ruler placed on the map upon the projecting points of the south shore, extended across, also touched the headlands of the opposite coast.” I have heard Captain FitzRoy remark, that on entering any of these channels from the outer coast, it is always necessary to look out directly for anchorage; for further inland the depth soon becomes extremely great. Captain Cook, in entering Christmas Sound, had first 37 fathom, then 40, 60, and, immediately afterwards, no soundings with 170. This structure of the bottom, I presume, must arise from the sediment deposited near the mouths of the channels, by the opposed tides and swell; and likewise from the enormous degradation of the coast-rocks, caused by an ocean harassed by endless gales.
The Strait of Magellan is extremely deep in most parts, even close to the shore. About mid-channel eastward of Cape Froward, Captain King found no bottom with 1536 feet: if, therefore, the water should be drained off, Tierra del Fuego would present a far more lofty range of mountains than it does at present. I will not here enter on any speculations regarding the causes which have produced this remarkable structure, in a district in which the latter movements at least have been those of elevation. I may, however, observe, that pebbles, and great boulders of various and peculiar crystalline rocks, which have undoubtedly travelled from the south-west coast, lie scattered over the whole of the eastern part of Tierra del Fuego. One enormous block of syenite near St. Sebastian Bay was barn-shaped, and had a girth of 47 feet; it projected five feet above the sand, and appeared to be deeply buried. The very nearest point to which we can look for the parent rock, is about ninety miles distant. On the shores of the Strait of Magellan, near Port Famine, numerous semi-rounded fragments of various granites and hornblendic rocks are strewed on the beach, and on the sides of the mountain, to an elevation of thirty or forty feet. Now to this point the high road from the Southern and Western shores passes directly over the great abyss of more than 1500 feet deep. Whatever may have been the means of transport, it has not been one of indiscriminate violence: for the two places, St. Sebastian Bay and Shoal Harbour, where the great fragments are most numerous, certainly existed previously to the last and smallest change of level, as channels connecting the Strait of Magellan, in the one case with the open sea, and in the other with Otway Water.
The climate of the southern part of South America presents many phenomena of the highest interest. It has long been observed that there exists some essential difference between it, and that of the countries in the northern hemisphere. I have already remarked on the surprising contrast between the rank vegetation of the broken west coast, consequent on the humid climate, as compared with the dry and sterile plains of Patagonia. The clouded and boisterous state of the atmosphere is necessarily accompanied by a decrease in extreme temperature; hence we find that fruits which ripen well, and are very abundant, such as the grape and fig, in lat. 41° on the east coast, succeed very poorly in a lower latitude on the opposite side of the continent.[2] The result is more strongly marked, if we take Europe as the standard of comparison. In Chiloe, lat. 42°, corresponding to the northern parts of Spain, peaches require the greatest care, and seldom produce fruit; but strawberries and apples succeed to admiration. At Valdivia, lat. 40°, or that of Madrid, standard peaches bear abundantly; grapes and figs ripen, but are far from common; olives seldom even partially ripen, and oranges not at all; yet in Europe this is the parallel most productive of these fruits. Even at Concepcion, lat. 36°, oranges are not abundant, though the other named fruits succeed perfectly. At the Falklands, in the same latitude as the south of England, wheat very seldom comes to maturity; but we ought to feel little surprise at this, when we hear that in Chiloe (lat. 42°) the inhabitants are frequently compelled to cut their corn before it is ready, and bring it into their houses to dry.
With respect to the climate of Tierra del Fuego during the colder parts of the year, Captain King has published some most interesting tables in the Geographical Journal.[3] The Beagle during this voyage, was employed in the extreme southern parts of the country, from December 18th to February 20th. From the appearance of the vegetation during the first part, and from the weather we experienced at the Falkland Islands, subsequent to the last date, I feel little doubt that these sixty-five days included the best part of the summer. Perhaps if another fortnight had been added, the mean would have been a little higher. The first eighteen of these days were spent partly at sea, near Cape Horn, and we were drifted for a short time by bad weather to nearly ninety miles to the southward. The mean temperature, from observations made every two hours by the officers on board the Beagle, was 45°. During the succeeding thirty-seven days[4] the Beagle was at anchor in different harbours a few leagues north of Cape Horn, and then the mean from observations at 6 A.M., noon, and 6 P.M., was 50°. The mean, therefore, between these two periods, which include the hottest part of the year, is only 47°.5.
It will be seen by this that the temperature at Port Famine is very considerably lower, both during summer and winter, than at Dublin, and that at the former the difference between the seasons is not so great, or that the climate is there more equable. It seems the general opinion of those who have visited this country, that the frosts are not so severe or so long as in England. The sealers say that throughout the year they wear the same quantity of clothing. Nevertheless Captain King states, that during the winter of 1828 the temperature was once as low as[7] 12°.6. I have drawn up these rough and approximate statements merely for the sake of illustrating some of the following remarks. The kind of climate here described appears to be common to the _southern_ parts of the whole of the southern hemisphere. Although so inhospitable to our feelings, and to most of the plants from the warmer parts of Europe, yet it is most favourable to the native vegetation. The forests, which cover the entire country between the latitudes of 38° and 45°, rival in luxuriance those of the glowing intertropical regions. Whilst in Chiloe (lat. 42°) I could almost have fancied myself in Brazil. Stately trees of many kinds, with smooth and highly coloured barks, are loaded by parasitical plants of the monocotyledonous structure; large and elegant ferns are numerous; and arborescent grasses intwine the trees into one entangled mass, to the height of thirty or forty feet above the ground. Palm-trees grow in lat. 37°; an arborescent grass very like a bamboo in 40°; and another closely-allied kind, of great length but not erect, even as far south as 45°.
In another part of this same hemisphere, which has so uniform a character owing to its large proportional area of sea, Forster found parasitical orchideous plants living south of lat. 45° in New Zealand. Tree-ferns thrive luxuriantly near Hobart Town, in Van Diemen’s Land. I measured one there which was exactly six feet in circumference; and its height from the ground to the base of the fronds appeared to be very little under twenty. Mr. Brown says[8] “an arborescent species of the same genus (_Dicksonia_) was found by Forster, in New Zealand, at Dusky Bay, in nearly 46° S., the highest latitude in which tree-ferns have yet been observed. It is remarkable that, although they have so considerable a range in the southern hemisphere, no tree-fern has been found beyond the northern tropic: a distribution in the two hemispheres somewhat similar to this has been already noticed respecting the Orchideæ that are parasitical on trees.” Even in Tierra del Fuego, Captain King describes the “vegetation thriving most luxuriantly, and large woody stemmed trees of Fuchsia and Veronica, in England considered and treated as tender plants, in full flower, within a very short distance of the base of a mountain covered for two-thirds down with snow, and with the temperature at 36°.” He states, also, that humming-birds were seen sipping the sweets of the flowers, “after two or three days of constant rain, snow, and sleet, during which time the thermometer had been at the freezing point.” I myself have seen parrots feeding on the seeds of the winter’s bark, south of latitude 55°.
Although the limit of an almost tropical vegetation extends thus far southward, yet the dearth of living things, both vegetable and animal, on the islands situated even far without the antarctic circle, is surprising, compared with the corresponding parallels in the northern hemisphere. In South Shetland in lat. 62° to 63° (same as Ferroe, or southern part of Norway) Weddell[9] states, “None of the islands afford any vegetation save a short straggling grass, which is found in very small patches in places where there happens to be a little soil. This, together with a moss similar to that which is found in Iceland, appears in the middle of January, at which time the islands are partially clear of snow.” In Deception Island, one of the same group, Lieutenant Kendall, says,[10] “There was nothing in the shape of vegetation except a small kind of lichen.” The island itself is partly composed of ice and volcanic ashes interstratified. Another curious proof of the rigour of the climate is mentioned: “Having observed a mound on the hill immediately above this cove, I opened it, and found a rude coffin, the rotten state of which bespoke its having been long consigned to the earth; but the body had undergone scarcely any decomposition. The legs were doubled up, and it was dressed in the jacket and cap of a sailor, but neither they nor the countenance were similar to those of an Englishman.”
Sandwich Land, which is nearly three degrees further from the pole, is thus described, by Captain Cook (February 1st, hottest time in the year, and in same latitude as north of Scotland): “Every part was blocked or filled up with ice, and the whole country, from the summits of the mountains down to the very brink of the cliffs which terminate the coast, covered many fathoms thick with everlasting snow. The cliffs alone were all which was to be seen like land.” Again he adds, talking of two islets, “These only were clear of snow, and seemed covered with a green turf.” In Georgia, lat. 54° to 55°, the bays are terminated by ice-cliffs of considerable height, and, according to Cook, the country “in the very height of summer, is in a manner wholly covered many fathoms deep with frozen snow, but more especially on the south-west coast.” The only vegetable is “a strong-bladed grass growing in tufts, wild burnet, and a plant-like moss.” Although 96 miles long and about ten broad, it possesses not a single quadruped, and only one land-bird, namely a small titlark (an Anthus), a specimen of which I procured in the Falklands.
This bird, if undescribed, certainly well deserves the name of _antarcticus_, for although not living within that circle, it inhabits a more inhospitable region than any other terrestrial animal. Anderson, in Cook’s Voyage, says, even in Kerguelen Land (an island 120 miles long by 60 broad, and situated in lat. 50°, corresponding to the extreme southern point of England), “The whole catalogue of plants does not exceed sixteen or seventeen, including some sorts of moss, and a beautiful species of lichen which grows upon the rocks higher up than the rest of the vegetable productions. Nor is there even the least appearance of a shrub in the whole country.” It is doubtful whether there is a single land-bird; and then he adds, “The hills are of a moderate height; yet many of their tops were covered with snow[11] at this time, though answering to our June.” These statements forcibly prove the intemperance of the climate even far without the frozen limits of the antarctic circle.
There are no direct observations, by which to judge of the mean temperature of the year in these southern islands. But after reading the above accounts, it will readily be granted that it must be very low. Even in Georgia, in lat. 54°-55°, it is not improbable that the soil is perpetually frozen at a few feet beneath the surface. At Deception Island in lat. 62°-63° from the preservation of the dead body alluded to, and the interstratification of ice with the volcanic ashes, we may feel almost sure that such must be the case. In the northern hemisphere, it is only on the great continents that so low a mean temperature is found in corresponding latitudes. In North America, according to Richardson,[12] north of lat. 56°, the thaw does not penetrate to a greater depth than three feet. In the Steppes of Siberia, Humboldt[13] states that to the northward of 62°, the ground between twelve and fifteen feet below the surface is always frozen. In the space, however, between these two great northern continents, the line of perpetual congelation rises considerably towards the north.
It is a remarkable meteorological fact, that in the northern and southern hemispheres, a low mean temperature, in latitudes without the frigid zone, is the result of a directly opposite condition of things. In the northern hemisphere the atmosphere is rendered extremely cold, from the radiation of a large extent of country during a long winter; nor is it moderated by the warmer currents of any neighbouring sea: hence the extreme cold of the winter more than counterbalances the heat of summer. In the southern hemisphere, on the other hand, although the winter is moderate, the summer is cold; for a sky constantly clouded rarely permits the rays of the sun to warm the surface (itself a bad absorbent) of the great ocean: hence, the mean temperature of the year falls below the freezing point. It will at once be evident, that a kind of vegetation which requires an equable temperature, will approach much nearer the line of perpetual congelation in a climate such as this of the southern hemisphere, than in the opposite one subject to extremes. The height of the plane of perpetual snow in any country, seems chiefly to be determined by the extreme heat of summer, rather than by the mean of the year. As the summer in Tierra del Fuego is so very wretched, we ought not to feel surprised at the fact stated by Capt. King,--that in the Strait of Magellan, the line descends to about 3500 or 4000 feet. In the northern hemisphere, we must travel about fourteen degrees nearer the pole to meet with so low a limit, namely, between lat. 67° and 70° on the mountains of Norway.
In the Cordillera of South America, between latitudes 41° and 43° 30′, the culminant peaks have altitudes pretty nearly equal. Several were measured by the officers of the Beagle with considerable care, by angles of elevation, the positions of the mountains being accurately known. Osorno is 7550 feet; mountain south of Osorno 5609; Minchinmadiva 7046; northern end of same range 6862; Corcovado 7510; Yntales 6725. Not only these points, but a great part of the range[14] was thickly clothed with snow, in the beginning of February (answering to our August), which descended some way down the mountains, and presented to a distant beholder a perfectly horizontal line. We were assured that the snow, which it appeared must inevitably be the case, remained throughout the year. On January 26th, after a week of uncommonly fine weather, Mr. King measured with a pocket sextant, the angle of this line with the summit of the Corcovado; and subtracting the result from the total height, the snow-line was found to descend to 4480 feet. It is possible that there may have existed some unknown cause of error; but as the average height of the few _highest peaks_ in the _snow-clad range_ is under 7000 feet, it is evident that the height of the snow-line cannot at most much exceed 6000 feet.
As this is a point of interest, I shall mention a few other circumstances, by which I think we may come to a nearly definite conclusion. On February 2d (1835) I obtained the last view of the Cordillera; on that day the lower line of the snow descended some way (so as to form a considerable angle with the summit, when viewed from a distance of 61 miles) on the mountain south of Osorno (lat. 41° 20′), which stands by itself, and has a height of 5607 feet. Since arriving in England I have received a letter from Mr. Douglas in Chiloe, who, describing some volcanic phenomena, accidentally mentions the snow-line. He says, on February 20th (same year), on the volcano of Minchinmadiva (lat. 42° 48′), which has an elevation of 7046 feet, lava was ejected from a crater “just above the verge of the snow.” Again, on February 27th, he alludes to the summit of the Corcovado (7510 feet) being covered with snow, as was Yntales[15] (6725 feet) in lat. 43° 30′. Again Mr. Douglas, speaking of the Corcovado, says, “On the 16th of March the snow appeared to cover one-fifth of its (_visible_) perpendicular height.” By this date the snow-line must have attained its greatest height (if, indeed, fresh snow had not fallen); and, as the Corcovado rises in an unbroken slope close to the sea, the proportion covered by snow might be judged of, with _some_ degree of accuracy. The height of the Corcovado (7510 feet) was obtained by three angular measurements, made by the officers on the survey, and the mean nearly agreed with the three separate results. Reflecting on all these circumstances, we may conclude with perfect safety, that the limit of perpetual snow, between the latitudes 41° and 43°, cannot much, if at all, exceed 6000 feet.
Text from Project Gutenberg, public domain in the United States.