Narrative of the surveying voyages of His Majesty's Ships Adventure and Beagle, Vol. 3 [of 3] · Charles Darwin
PASSAGE OF CORDILLERA.
MARCH 7TH, 1835.--We staid only three days at Concepcion, and then sailed for Valparaiso. The wind being northerly, we only reached the mouth of the harbour of Concepcion before it was dark. Being very near the land, and a fog coming on, the anchor was dropped. Presently a large American whaler appeared close alongside of us; and we heard the Yankee swearing at his men, to make them keep quiet, whilst he listened where the breakers were. Captain FitzRoy hailed him in a loud clear voice, to anchor where he then was. The poor man must have thought the voice came from the shore: such a Babel of cries issued at once from the ship--every one hallooing out, “Let go the anchor! veer cable! shorten sail!” It was the most laughable thing I ever heard. If the ship’s crew had been all captains, and no men, there could not have been a greater uproar of orders. We afterwards found that the mate stuttered. I suppose all hands were assisting him in giving his orders. On the 11th we anchored at Valparaiso; and two days afterwards I set out on an excursion to cross the Cordillera. I proceeded to Santiago, where Mr. Caldcleugh most kindly assisted me in every possible way, in making the little preparations which were necessary. In this immediate part of Chile there are two passes across the Andes to Mendoza, and the plains on the opposite side. The one most commonly used, namely, that of Aconcagua, or Uspallata, is situated some way to the northward of the capital: the other, called the Portillo, is to the southward, and less distant. The latter is, however, rather more lofty, and from the double chain, more dangerous during a snow-storm. For these reasons it is but little used, especially late in the season.
MARCH 18TH.--We set out for the Portillo pass. Leaving Santiago we crossed the wide burnt-up plain on which that city stands, and in the afternoon arrived at the Maypo, one of the principal rivers in Chile. The valley, at the point where it enters the first Cordillera, is bounded on each side by lofty barren mountains; and although not broad, it is very fertile. Numerous cottages were surrounded by vines, and by orchards of apple, nectarine, and peach trees; the boughs of the latter breaking with the weight of the beautiful ripe fruit. In the evening we passed the custom-house, where our luggage was examined. The frontier of Chile is better guarded by the Cordillera, than by the waters of the sea. There are very few valleys which lead to the central ranges, and, except by these, the mountains are far too steep and lofty for any beast of burden to pass over them. The custom-house officers were very civil; which was perhaps partly owing to the passport which the President of the republic had given me; but I must also express my admiration at the natural politeness of almost every Chileno. In this instance the contrast with the same class of men in most other countries was strongly marked. I may mention an anecdote with which I was much pleased at the time. We met near Mendoza a little and very fat negress, riding astride on a mule. She had a _goître_ so enormous, that it was scarcely possible to avoid gazing at her for a moment; but my two companions almost instantly, by way of apology, made the common salute of the country, by taking off their hats. Where would one of the lower classes in Europe have shown such feeling politeness to a poor and miserable object of a degraded race?
At night we slept at a cottage. Our manner of travelling was delightfully independent. In the inhabited parts we bought a little firewood, hired pasture for the animals, and bivouacked in the corner of the same field with them. Carrying an iron pot, we cooked and ate our supper under the cloudless sky, and knew no trouble. My companions were Mariano Gonzales, who had formerly accompanied me, and an “arriero,” with his ten mules and a “madrina.” The madrina (or godmother) is a most important personage. She is an old steady mare, with a little bell round her neck; and wheresoever she goes, the mules, like good children, follow her. If several large troops are turned into one field to graze, in the morning the muleteer has only to lead the madrinas a little apart, and tinkle their bells; and, although there may be two or three hundred mules together, each immediately knows its own bell, and separates itself from the rest. The affection of these animals for their madrinas saves infinite trouble. It is nearly impossible to lose an old mule; for if detained for several hours by force, she will, by the power of smell, like a dog, track out her companions, or rather the madrina; for, according to the muleteer, she is the chief object of affection. The feeling, however, is not of an individual nature; for I believe I am right in saying, that any animal with a bell will serve as madrina. In a troop each animal carries, on a level road, a cargo weighing 416 pounds (more than twenty-nine stone); but in a mountainous country a hundred pounds less.[1] Yet with what delicate slim limbs, without any proportional bulk of muscle, these animals support so great a burden! The mule always appears to me a most surprising animal. That a hybrid should possess more reason, memory, obstinacy, social affection, and powers of muscular endurance, than either of its parents, seems to indicate that art has here out-mastered nature. Of our ten animals, six were intended for riding and four for carrying cargoes, each taking turn about. We carried a good deal of food, in case we should be snowed up, as the season was rather late for passing the Portillo.
MARCH 19TH.--We rode during this day to the last, and therefore most elevated house in the valley. The number of inhabitants became scanty; but wherever water could be brought on the land, it was very fertile. All the valleys in the Cordillera agree in the same kind of structure. An irregularly-stratified mass of well-rounded shingle, together with a little mud and sand, fills up the bottom to the depth of some hundred feet. This deposit follows the course of the valley, sloping upwards with a most gradual and gentle inclination. The rivers have removed a large part in the centre; thus leaving a terrace of equal height, but varying width, on each side. This narrow space between the cliffs bordering the bed of the river, and the foot of the mountains, is the only part fit for cultivation, and on it likewise the road is carried. The rivers, such as the Maypo, which flow in these valleys, should rather be called mountain torrents. Their inclination is very great, and their water the colour of mud. The roar which the Maypo made, as it rushed over the great rounded fragments, was like that of the sea. Amidst the din of rushing waters, the noise from the stones, as they rattled one over another, was most distinctly audible even at a distance. This rattling noise, night and day, may be heard along the whole course of the torrent. The sound spoke eloquently to the geologist: the thousands and thousands of stones, which, striking against each other, make the one dull uniform sound, are all hurrying in one direction. It is like thinking of time, where the minute that now glides past is irrecoverable. So is it with these stones; the ocean is their eternity, and each note of that wild music tells of one other step towards their destiny.
It is not possible for the mind to comprehend, except by a slow process, any effect which is produced by a cause repeated so often, that the multiplier itself ceases to convey any more definite idea, than the savage receives when he points to the hairs of his head. As often as I have seen beds of mud, sand, and shingle, accumulated to the thickness of many thousand feet, I have felt inclined to exclaim that causes, such as the present rivers and the present beaches, could never have ground down such masses. But, on the other hand, when listening to the rattling noise of these torrents, and calling to mind that whole races of animals have passed away from the surface of the globe, during the period throughout which, night and day, these stones have gone rattling onwards in their course, I have thought to myself, can any mountains, any continent, withstand such waste? In this part of the valley, the mountains on each side are from about three to six or eight thousand feet high: their outline is rounded, but with steep and bare flanks. The general colour of the rock is a dullish purple, and the stratification very distinct. If the scenery is not beautiful, it is remarkable and grand. We met during the day several herds of cattle, which men were driving down from the higher valleys in the Cordillera. This sign of the approaching winter hurried our steps, more than was convenient for geological purposes. The house where we slept was situated at the foot of a mountain, on the summit of which are the mines of S. Pedro de Nolasko.
Sir F. Head wonders how mines have been discovered in situations so extraordinary, as the bleak summit of the mountain of S. Pedro de Nolasko. In the first place, metallic veins in this country are generally harder than the surrounding strata: hence, during the gradual degradation of the hills, they project above the surface of the ground. Secondly, almost every labourer, especially in the northern parts of Chile, understands something about the appearance of ores. In the great mining provinces of Coquimbo and Copiapó, firewood is very scarce, and men are employed in searching for it over every hill and dale; and by this means nearly all the richest mines have there been discovered. Chanuncillo, from which silver, to the value of many hundred thousand pounds has been raised in the course of a few years, was thus discovered: a man having thrown a stone at his loaded donkey, afterwards thought that it was very heavy, and picking it up again, he found it was full of pure silver. The vein occurred at no great distance, standing up like a wedge of silver. The miners also, on Sundays, taking a crowbar with them, often set out on such discoveries. In the south part of Chile, the men who drive cattle into the Cordillera, and who frequent every ravine where there is a little pasture, are the usual agents.
MARCH 20TH.--As we ascended the valley, the vegetation, with the exception of a few pretty alpine flowers, became exceedingly scanty; and of birds, animals, or insects, scarcely one could be seen. The lofty mountains, their summits marked with a few patches of snow, stood well separated from each other; the valleys being filled up with an immense thickness of stratified alluvium. I may here briefly remark, without detailing the reasons on which the opinion is grounded, that in all probability this matter was accumulated at the bottoms of deep arms of the sea, which running from the inland basins, penetrated to the axis of the Cordillera,--in a similar manner to what now happens in the southern part of this same great range. This fact, in itself most curious, as preserving a record of a very ancient state of things, possesses a high theoretical interest, when considered in relation to the kind of elevation by which the present great altitude of these mountains has been attained. The features in the scenery of the Andes which struck me most, as contrasted with the few other mountain chains with which I am acquainted, were,--the flat fringes sometimes expanding into narrow plains on each side the valleys,--the bright colours, chiefly red and purple, of the utterly bare and precipitous hills,--the grand and continuous wall-like dikes,--the strongly-marked strata which, when nearly vertical, form the most picturesque and wild pinnacles, but where less inclined, great massive mountains; the latter occupying the outskirts of the range, and the former the more lofty and central parts,--lastly, the smooth conical piles of fine and brightly-coloured detritus, which slope at a high angle from the flanks of the mountains to their bases, some of the piles having a height of more than two thousand feet.
I frequently observed both in Tierra del Fuego, and within the Andes, that where the rock was covered during the greater part of the year with snow, it was shivered in a very extraordinary manner into small angular fragments. Scoresby[2] has observed the same fact in Spitzbergen: he says, “The invariably broken state of the rocks appeared to have been the effect of frost. On calcareous rocks, some of which are not impervious to moisture, the effect is such as might have been expected; but how frost can operate in this way on quartz is not so easily understood.” The whole phenomenon appears to me rather obscure: for that part of the mountain which is covered during many months by a mantle of snow, must be less subject to repeated and great changes of temperature than any other, yet it is the most affected. I have sometimes thought, that the earth and fragments of stone lying on the surface, were perhaps less effectually removed by means of slowly percolating snow-water,[3] than by the agency of rain, and therefore that the appearance of a quicker decay of the solid rock may be deceptive. Whatever the cause may be, the quantity of crumbling stone on the Cordillera is very great. Occasionally in the spring, masses of such matter slide down the mountains, and cover the snow-drifts in the valleys; thus forming natural ice-houses. We rode over one, the elevation of which was far below the limit of perpetual congelation.
As the evening drew to a close, we reached the Valle del Yeso. This is a very singular basin, which must have once been a very deep and large lake: the barrier is formed by a huge mountain of alluvium, on one side of which the river has cut a gorge. The plain is covered by a little dry pasture, and amidst the surrounding rocky deserts we had the pleasant sight of a herd of cattle. The valley takes its name of Yeso from a great bed, I should think at least two thousand feet thick, of white, and in some parts quite pure, gypsum. We slept with a party of men, who were employed in loading mules with this substance, which is used in the manufacture of wine. MARCH 21ST.--We set out early in the morning, and continued to follow the course of the river, which by this time had become small, till we arrived at the foot of the ridge that separates the waters flowing into the Pacific and Atlantic oceans. The road, which as yet had been good, with a steady but very gradual ascent, now changed into a steep zigzag track. The Cordillera in this part consists of two principal ranges; the passes across which attain respectively an elevation of 13,210 and 14,365 feet.[4] The first great line (consisting of course of many subordinate ones) is called Peuquenes. It divides the waters, and therefore likewise the republics of Chile and Mendoza. To the eastward, a mountainous and elevated region separates it from the second range (called the Portillo) overlooking the Pampas. The streams from the intermediate tract find a passage a little way to the southward through this second line.
I will here give a very brief sketch of the geological structure of these mountains: first, of the Peuquenes, or western line; for the constitution of the two ranges is totally different. The lowest stratified rock is a dull red or purple claystone porphyry, of many varieties, alternating with conglomerates, and breccia composed of a similar substance: this formation attains a thickness of more than a mile. Above it there is a grand mass of gypsum, which alternates, passes into, and is replaced by, red sandstone, conglomerates, and black calcareous clay-slate. I hardly dare venture to guess the thickness of this second division; but I have already said some of the beds of gypsum alone attain a thickness of at least two thousand feet. Even at the very crest of the Peuquenes, at the height of 13,210 feet, and above it, the black clay-slate contained numerous marine remains, amongst which a gryphæa is the most abundant, likewise shells, resembling turritellæ, terebratulæ, and an ammonite. It is an old story, but not the less wonderful, to hear of shells, which formerly were crawling about at the bottom of the sea, being now elevated nearly fourteen thousand feet above its level. The formation probably is of the age of the central parts of the secondary series of Europe. These great piles of strata have been penetrated, upheaved, and overturned, in the most extraordinary manner, by masses of injected rock, equalling mountains in size. On the bare sides of the hills, complicated dikes, and wedges of variously-coloured porphyries and other stones, are seen traversing the strata in every possible form and direction; proving also by their intersections, successive periods of violence. The rock which composes the axis of these great lines of dislocation, at a distance very closely resembles granite, but on examination, it is found rarely to contain any quartz; and instead of ordinary felspar, albite.
The metamorphic action has been very great, as might have been expected from the close proximity of such grand masses of rock, which were injected when in a liquefied state from heat. When it is known, first, that the stratified porphyries have flowed as streams of submarine lava under an enormous pressure, and that the mechanical beds separating them owe their origin to explosions from the same submarine craters; secondly, that the whole mass in the lower part has generally been so completely fused into one solid rock by metamorphic action, that the lines of division can only be traced with much difficulty; and thirdly, that masses of porphyry, undistinguishable by their mineralogical characters from the two first kinds, have been subsequently injected;--the extreme complication of the whole will readily be believed.
We now come to the second range, which is of even greater altitude than the first. Its nucleus in the section seen in crossing the Portillo pass, consists of magnificent pinnacles of coarsely-crystallized red granite. On the eastern flank, a few patches of mica slate still adhere to the unstratified mass; and at the foot a stream of basaltic lava has burst forth at some remote period,--perhaps when the sea covered the wide surface of the Pampas. On the western side of the axis, between the two ranges, laminated fine sandstone has been penetrated by immense granitic dikes proceeding from the central mass, and has thus been converted into granular quartz rock. The sandstone is covered by other sedimentary deposits, and these again by a coarse conglomerate, the vast thickness of which I will not attempt even to estimate. All these coarse mechanical beds dip from the red granite directly towards the Peuquenes range, as if they passed beneath it; though such is not the case. On examining the pebbles composing this conglomerate (which, to my surprise, betrayed no signs of metamorphic action), I was astonished to find perfectly rounded masses of the black calcareous clay-slate with organic remains,--the same rock which I had just crossed _in situ_ on the Peuquenes. These phenomena compel us to arrive at the following conclusion:--that the Peuquenes existed as dry land for a long period anterior to the formation of the second range, and that, during this period, immense quantities of shingle were accumulated at its submarine flank. The action of a disturbing force then commenced: these more modern deposits were injected by dikes, altered by heat, and tilted towards the line whence, in the form of sediment and pebbles, they had originally proceeded,--thus making the offspring at first appear older than its parent. This second, grand, and subsequent line of elevation is parallel to the first and more ancient one.
I will only make one other geological observation: the Portillo chain in the neighbourhood of the pass is rather more elevated than the Peuquenes, yet the waters of the intermediate district have burst a passage through it. On the supposition of a subsequent and gradual elevation of the second line, this can be understood; for a chain of islets would at first appear, and as these were lifted up, the tides would always be working out deeper and broader channels between them. At the present day, even in the most retired sounds on the southern coast, the currents in the transverse breaks which connect the longitudinal channels, is so strong, that I have heard of one instance where a small vessel under sail was whirled round and round. Mr. Pentland,[5] when describing an hydrographical phenomenon of a nearly similar kind, but on an infinitely grander scale, which occurs in Bolivia, says, “This very curious fact, of rivers escaping through such an immense mountain-mass as the Bolivian Cordillera, is perhaps one of the most important points connected with the physical geography of this portion of the Andes, and deserves to be noticed at greater length.” It would be extremely rash to affirm that the eastern chain in Bolivia, like that of central Chile, must be of subsequent origin to the western one, or that nearer to the Pacific: but excepting through the explanation above offered, the circumstance that rivers flowing from a less elevated chain, should penetrate one far more lofty, appears to me quite inexplicable.
About noon we began the tedious ascent of the Peuquenes, and then for the first time experienced some little difficulty in our respiration. The mules would halt every fifty yards, and then the poor willing animals after a few seconds started of their own accord again. The short breathing from the rarefied atmosphere is called by the Chilenos “puna;” they have most ridiculous notions concerning its origin. Some say, “all the waters here have puna;” others that “where there is snow there is puna;”--and this no doubt is true. It is considered a kind of disease, and I was shown the crosses over the graves of some who had died “punado.” Excepting perhaps in the case of a person suffering from some organic disease of the heart or chest, I should think this must be an erroneous conclusion. A person near death, would probably at this elevation experience a more unusual difficulty in breathing than others; and hence the effect might be assumed as the cause. The only sensation I felt was a slight tightness over the head and chest; a feeling which may be experienced by leaving a warm room and running violently on a frosty day. There was much fancy even in this; for upon finding fossil shells on the highest ridge, I entirely forgot the puna in my delight. Certainly the exertion of walking was extreme, and the respiration became deep and laborious. It is incomprehensible to me, how Humboldt and others were able to ascend to the elevation of 19,000 feet. No doubt a residence of some months in the lofty region of Quito would prepare the constitution for such an exertion; yet I am told that in Potosi (about 13,000 feet), strangers do not become quite accustomed to the atmosphere for an entire year. The inhabitants all recommend onions for the puna; as this vegetable has sometimes been given in Europe for pectoral complaints, it may possibly be of real service:--for my part, I found nothing so good as the fossil shells!
When about halfway up we met a large party with seventy loaded mules. It was interesting to hear the wild cries of the muleteers, and to watch the long string descending; they appeared so diminutive, there being nothing but the bleak mountains with which they could be compared. When near the summit, the wind, as generally happens there, was impetuous and extremely cold. On each side of the ridge we had to pass over broad bands of snow, which perpetually lie there, and were now soon to be covered by a fresh layer. When we reached the crest and looked backwards, a glorious view was presented. The atmosphere resplendently clear; the sky an intense blue; the profound valleys; the wild broken forms; the heaps of ruins, piled up during the lapse of ages; the bright-coloured rocks, contrasted with the quiet mountains of snow; all these together produced a scene I never could have figured to my imagination. Neither plant nor bird, excepting a few condors wheeling around the higher pinnacles, distracted the attention from the inanimate mass. I felt glad I was alone: it was like watching a thunderstorm, or hearing a chorus of the Messiah in full orchestra.
Text from Project Gutenberg, public domain in the United States.