We had yet to scale the steepest part of the mountain, the Piton, which forms the summit. The slope of this small cone, covered with volcanic ashes, and fragments of pumice-stone, is so steep, that it would have been almost impossible to reach the top, had we not ascended by an old current of lava, the debris of which have resisted the ravages of time. These debris form a wall of scorious rock, which stretches into the midst of the loose ashes. We ascended the Piton by grasping these half-decomposed scoriae, which often broke in our hands. We employed nearly half an hour to scale a hill, the perpendicular height of which is scarcely ninety toises. Vesuvius, three times lower than the peak of Teneriffe, is terminated by a cone of ashes almost three times higher, but with a more accessible and easy slope. Of all the volcanoes which I have visited, that of Jorullo, in Mexico, is the only one that is more difficult to climb than the Peak, because the whole mountain is covered with loose ashes.
When the Sugar-loaf (el Piton) is covered with snow, as it is in the beginning of winter, the steepness of its declivity may be very dangerous to the traveller. M. Le Gros showed us the place where captain Baudin was nearly killed when he visited the Peak of Teneriffe. That officer had the courage to undertake, in company with the naturalists Advenier, Mauger, and Riedle, an excursion to the top of the volcano about the end of December, 1797. Having reached half the height of the cone, he fell, and rolled down as far as the small plain of Rambleta; happily a heap of lava, covered with snow, hindered him from rolling farther with accelerated velocity. I have been told, that in Switzerland a traveller was suffocated by rolling down the declivity of the Col de Balme, over the compact turf of the Alps.
When we gained the summit of the Piton, we were surprised to find scarcely room enough to seat ourselves conveniently. We were stopped by a small circular wall of porphyritic lava, with a base of pitchstone, which concealed from us the view of the crater.* (*
Called La Caldera, or the caldron of the peak, a denomination which recalls to mind the Oules of the Pyrenees.) The west wind blew with such violence that we could scarcely stand. It was eight in the morning, and we suffered severely from the cold, though the thermometer kept a little above freezing point. For a long time we had been accustomed to a very high temperature, and the dry wind increased the feeling of cold, because it carried off every moment the small atmosphere of warm and humid air, which was formed around us from the effect of cutaneous perspiration.
The brink of the crater of the peak bears no resemblance to those of most of the other volcanoes which I have visited: for instance, the craters of Vesuvius, Jorullo, and Pichincha. In these the Piton preserves its conic figure to the very summit: the whole of their declivity is inclined the same number of degrees, and uniformly covered with a layer of pumice-stone very minutely divided; when we reach the top of these volcanoes, nothing obstructs the view of the bottom of the crater. The peaks of Teneriffe and Cotopaxi, on the contrary, are of very different construction. At their summit a circular wall surrounds the crater; which wall, at a distance, has the appearance of a small cylinder placed on a truncated cone. On Cotopaxi this peculiar construction is visible to the naked eye at more than 2000 toises distance; and no person has ever reached the crater of that volcano. On the peak of Teneriffe, the wall, which surrounds the crater like a parapet, is so high, that it would be impossible to reach the Caldera, if, on the eastern side, there was not a breach, which seems to have been the effect of a flowing of very old lava. We descended through this breach toward the bottom of the funnel, the figure of which is elliptic. Its greater axis has a direction from north-west to south-east, nearly north 35 degrees west. The greatest breadth of the mouth appeared to us to be 300 feet, the smallest 200 feet, which numbers agree very nearly with the measurement of MM. Verguin, Varela, and Borda.
It is easy to conceive, that the size of a crater does not depend solely on the height and ma.s.s of the mountain, of which it forms the princ.i.p.al air-vent. This opening is indeed seldom in direct ratio with the intensity of the volcanic fire, or with the activity of the volcano. At Vesuvius, which is but a hill compared with the Peak of Teneriffe, the diameter of the crater is five times greater. When we reflect, that very lofty volcanoes throw out less matter from their summits than from lateral openings, we should be led to think, that the lower the volcanoes, their force and activity being the same, the more considerable ought to be their craters. In fact, there are immense volcanoes in the Andes, which have but very small openings; and we might establish as a geological principle, that the most colossal mountains have craters of little extent at the summits, if the Cordilleras did not present many instances to the contrary.* (* The great volcanoes of Cotopaxi and Rucupichincha have craters, the diameters of which, according to my measurements, exceed 400 and 700 toises.) I shall have occasion, in the progress of this work, to cite a number of facts, which will throw some light on what may be called the external structure of volcanoes. This structure is as varied as the volcanic phenomena themselves; and in order to raise ourselves to geological conceptions worthy of the greatness of nature, we must set aside the idea that all volcanoes are formed after the model of Vesuvius, Stromboli, and Etna.
The external edges of the Caldera are almost perpendicular. Their appearance is somewhat like the Somma, seen from the Atrio dei Cavalli. We descended to the bottom of the crater on a train of broken lava, from the eastern breach of the enclosure. The heat was perceptible only in a few crevices, which gave vent to aqueous vapours with a peculiar buzzing noise. Some of these funnels or crevices are on the outside of the enclosure, on the external brink of the parapet that surrounds the crater. We plunged the thermometer into them, and saw it rise rapidly to 68 and 75 degrees. It no doubt indicated a higher temperature, but we could not observe the instrument till we had drawn it up, lest we should burn our hands. M. Cordier found several crevices, the heat of which was that of boiling water. It might be thought that these vapours, which are emitted in gusts, contain muriatic or sulphurous acid; but when condensed, they have no particular taste; and experiments, which have been made with re-agents, prove that the chimneys of the peak exhale only pure water. This phenomenon, a.n.a.logous to that which I observed in the crater of Jorullo, deserves the more attention, as muriatic acid abounds in the greater part of volcanoes, and as M. Vauquelin has discovered it even in the porphyritic lavas of Sarcouy in Auvergne.
I sketched on the spot a view of the interior edge of the crater, as it presented itself in the descent by the eastern break. Nothing is more striking than the manner in which these strata of lava are piled on one another, exhibiting the sinuosities of the calcareous rock of the higher Alps. These enormous ledges, sometimes horizontal, sometimes inclined and undulating, are indicative of the ancient fluidity of the whole ma.s.s, and of the combination of several deranging causes, which have determined the direction of each flow. The top of the circular wall exhibits those curious ramifications which we find in c.o.ke. The northern edge is most elevated. Towards the south-west the enclosure is considerably sunk and an enormous ma.s.s of scorious lava seems glued to the extremity of the brink. On the west the rock is perforated; and a large opening gives a view of the horizon of the sea. The force of the elastic vapours perhaps formed this natural aperture, at the time of some inundation of lava thrown out from the crater.
The inside of this funnel indicates a volcano, which for thousands of years has vomited no fire but from its sides. This conclusion is not founded on the absence of great openings, which might be expected in the bottom of the Caldera. Those whose experience is founded on personal observation, know that several volcanoes, in the intervals of an eruption, appear filled up, and almost extinguished; but that in these same mountains, the crater of the volcano exhibits layers of scoriae, rough, sonorous, and shining.
We observe hillocks and intumescences caused by the action of the elastic vapours, cones of broken scoriae and ashes which cover the funnels. None of these phenomena characterise the crater of the peak of Teneriffe; its bottom is not in the state which ensues at the close of an eruption. From the lapse of time, and the action of the vapours, the inside walls are detached, and have covered the basin with great blocks of lithoid lavas.
The bottom of the Caldera is reached without danger. In a volcano, the activity of which is princ.i.p.ally directed towards the summit, such as Vesuvius, the depth of the crater varies before and after each eruption; but at the peak of Teneriffe the depth appears to have remained unchanged for a long time. Eden, in 1715, estimated it at 115 feet; Cordier, in 1803, at 110 feet. Judging by mere inspection, I should have thought the funnel of still less depth.
Its present state is that of a solfatara; and it is rather an object of curious investigation, than of imposing aspect. The majesty of the site consists in its elevation above the level of the sea, in the profound solitude of these lofty regions, and in the immense s.p.a.ce over which the eye ranges from the summit of the mountain.
The wall of compact lava, forming the enclosure of the Caldera, is snow-white at its surface. The same colour prevails in the inside of the Solfatara of Puzzuoli. When we break these lavas, which might be taken at some distance for calcareous stone, we find in them a blackish brown nucleus. Porphyry, with basis of pitch-stone, is whitened externally by the slow action of the vapours of sulphurous acid gas. These vapours rise in abundance; and what is rather remarkable, through crevices which seem to have no communication with the apertures that emit aqueous vapours. We may be convinced of the presence of the sulphurous acid, by examining the fine crystals of sulphur, which are everywhere found in the crevices of the lava. This acid, combined with the water with which the soil is impregnated, is transformed into sulphuric acid by contact with the oxygen of the atmosphere. In general, the humidity in the crater of the peak is more to be feared than the heat; and they who seat themselves for a while on the ground find their clothes corroded. The porphyritic lavas are affected by the action of the sulphuric acid: the alumine, magnesia, soda, and metallic oxides gradually disappear; and often nothing remains but the silex, which unites in mammillary plates, like opal. These siliceous concretions,* (* Opalartiger kieselsinter. The siliceous gurh of the volcanoes of the Isle of France contains, according to Klaproth, 0.72 silex, and 0.21 water; and thus comes near to opal, which Karsten considers as a hydrated silex.) which M. Cordier first made known, are similar to those found in the isle of Ischia, in the extinguished volcanoes of Santa Fiora, and in the Solfatara of Puzzuoli. It is not easy to form an idea of the origin of these incrustations. The aqueous vapours, discharged through great spiracles, do not contain alkali in solution, like the waters of the Geyser, in Iceland. Perhaps the soda contained in the lavas of the peak acts an important part in the formation of these deposits of silex. There may exist in the crater small crevices, the vapours of which are not of the same nature as those on which travellers, whose attention has been directed simultaneously to a great number of objects, have made experiments.
Seated on the northern brink of the crater, I dug a hole of some inches in depth; and the thermometer placed in this hole rose rapidly to 42 degrees. Hence we may conclude what must be the heat in this solfatara at the depth of thirty or forty fathoms. The sulphur reduced into vapour is condensed into fine crystals, which however are not equal in size to those M. Dolomieu brought from Sicily. They are semi-diaphanous octahedrons, very brilliant on the surface, and of a conchoidal fracture. These ma.s.ses, which will one day perhaps be objects of commerce, are constantly bedewed with sulphurous acid. I had the imprudence to wrap up a few, in order to preserve them, but I soon discovered that the acid had consumed not only the paper which contained them, but a part also of my mineralogical journal. The heat of the vapours, which issue from the crevices of the caldera, is not sufficiently great to combine the sulphur while in a state of minute division, with the oxygen of the atmospheric air; and after the experiment I have just cited on the temperature of the soil, we may presume that the sulphurous acid is formed at a certain depth,* in cavities to which the external air has free access. (* An observer, in general very accurate, M. Breislack, a.s.serts that the muriatic acid always predominates in the vapours of Vesuvius. This a.s.sertion is contrary to what M. Gay-Lussac and myself observed, before the great eruption of 1805, and while the lava was issuing from the crater.
The smell of the sulphurous acid, so easy to distinguish, was perceptible at a great distance; and when the volcano threw out scoriae, the smell was mingled with that of petroleum.)
The vapours of heated water, which act on the fragments of lava scattered about on the caldera, reduce certain parts of it to a state of paste. On examining, after I had reached America, those earthy and friable ma.s.ses, I found crystals of sulphate of alumine.
MM. Davy and Gay-Lussac have already made the ingenious remark, that two bodies highly inflammable, the metals of soda and potash, have probably an important part in the action of a volcano; now the potash necessary to the formation of alum is found not only in feldspar, mica, pumice-stone, and augite, but also in obsidian.
This last substance is very common at Teneriffe, where it forms the basis of the tephrinic lava. These a.n.a.logies between the peak of Teneriffe and the Solfatara of Puzzuoli, might no doubt be shown to be more numerous, if the former were more accessible, and had been frequently visited by naturalists.
An expedition to the summit of the volcano of Teneriffe is interesting, not solely on account of the great number of phenomena which are the objects of scientific research; it has still greater attractions from the picturesque beauties which it lays open to those who are feelingly alive to the majesty of nature. It is a difficult task to describe the sensations, which are the more forcible, inasmuch as they have something undefined, produced by the immensity of the s.p.a.ce as well as by the vastness, the novelty, and the mult.i.tude of the objects, amidst which we find ourselves transported. When a traveller attempts to describe the loftiest summits of the globe, the cataracts of the great rivers, the tortuous valleys of the Andes, he incurs the danger of fatiguing his readers by the monotonous expression of his admiration. It appears to me more conformable to the plan I have proposed to myself in this narrative, to indicate the peculiar character that distinguishes each zone: we exhibit with more clearness the physiognomy of the landscape, in proportion as we endeavour to sketch its individual features, to compare them with each other, and to discover by this kind of a.n.a.lysis the sources of the enjoyments, furnished by the great picture of nature.
Travellers have learned by experience, that views from the summits of very lofty mountains are neither so beautiful, picturesque, nor so varied, as those from heights which do not exceed that of Vesuvius, Righi, and the Puy-de-Dome. Colossal mountains, such as Chimborazo, Antisana, or Mount Rosa, compose so large a ma.s.s, that the plains covered with rich vegetation are seen only in the immensity of distance, and a blue and vapoury tint is uniformly spread over the landscape. The peak of Teneriffe, from its slender form and local position, unites the advantages of less lofty summits with those peculiar to very great heights. We not only discern from its top a vast expanse of sea, but we perceive also the forests of Teneriffe, and the inhabited parts of the coasts, in a proximity calculated to produce the most beautiful contrasts of form and colour. We might say, that the volcano overwhelms with its ma.s.s the little island which serves as its base, and it shoots up from the bosom of the waters to a height three times loftier than the region where the clouds float in summer. If its crater, half extinguished for ages past, shot forth flakes of fire like that of Stromboli in the Aeolian Islands, the peak of Teneriffe, like a lighthouse, would serve to guide the mariner in a circuit of more than 260 leagues.
When we were seated on the external edge of the crater, we turned our eyes towards the north-west, where the coasts are studded with villages and hamlets. At our feet, ma.s.ses of vapour, constantly drifted by the winds, afforded us the most variable spectacle. A uniform stratum of clouds, similar to that already described, and which separated us from the lower regions of the island, had been pierced in several places by the effect of the small currents of air, which the earth, heated by the sun, began to send towards us.
The port of Orotava, its vessels at anchor, the gardens and the vineyards encircling the town, shewed themselves through an opening which seemed to enlarge every instant. From the summit of these solitary regions our eyes wandered over an inhabited world; we enjoyed the striking contrast between the bare sides of the peak, its steep declivities covered with scoriae, its elevated plains dest.i.tute of vegetation, and the smiling aspect of the cultured country beneath. We beheld the plants divided by zones, as the temperature of the atmosphere diminished with the elevation of the site. Below the Piton, lichens begin to cover the scorious and l.u.s.trous lava: a violet,* (* Viola cheiranthifolia.) akin to the Viola dec.u.mbens, rises on the slope of the volcano at 1740 toises of height; it takes the lead not only of the other herbaceous plants, but even of the gramina, which, in the Alps and on the ridge of the Cordilleras, form close neighbourhood with the plants of the family of the cryptogamia. Tufts of retama, loaded with flowers, adorn the valleys hollowed out by the torrents, and enc.u.mbered with the effects of the lateral eruptions. Below the retama, lies the region of ferns, bordered by the tract of the arborescent heaths. Forests of laurel, rhamnus, and arbutus, divide the ericas from the rising grounds planted with vines and fruit trees. A rich carpet of verdure extends from the plain of spartium, and the zone of the alpine plants even to the groups of the date tree and the musa, at the feet of which the ocean appears to roll.
I here pa.s.s slightly over the princ.i.p.al features of this botanical chart, as I shall enter hereafter into some farther details respecting the geography of the plants of the island of Teneriffe.*
(* See below.)
The seeming proximity, in which, from the summit of the peak, we behold the hamlets, the vineyards, and the gardens on the coast, is increased by the prodigious transparency of the atmosphere.
Notwithstanding the great distance, we could distinguish not only the houses, the sails of the vessels, and the trunks of the trees, but we could discern the vivid colouring of the vegetation of the plains. These phenomena are owing not only to the height of the site, but to the peculiar modifications of the air in warm climates. In every zone, an object placed on a level with the sea, and viewed in a horizontal direction, appears less luminous, than when seen from the top of a mountain, where vapours arrive after pa.s.sing through strata of air of decreasing density. Differences equally striking are produced by the influence of climate. The surface of a lake or large river is less resplendent, when we see it at an equal distance, from the top of the higher Alps of Switzerland, than when we view it from the summit of the Cordilleras of Peru or of Mexico. In proportion as the air is pure and serene, the solution of the vapours becomes more complete, and the light loses less in its pa.s.sage. When from the sh.o.r.es of the Pacific we ascend the elevated plain of Quito, or that of Antisana, we are struck for some days by the nearness at which we imagine we see objects which are actually seven or eight leagues distant. The peak of Teyde has not the advantage of being situated in the equinoctial region; but the dryness of the columns of air which rise perpetually above the neighbouring plains of Africa, and which the eastern winds convey with rapidity, gives to the atmosphere of the Canary Islands a transparency which not only surpa.s.ses that of the air of Naples and Sicily, but perhaps exceeds the purity of the sky of Quito and Peru. This transparency may be regarded as one of the chief causes of the beauty of landscape scenery in the torrid zone; it heightens the splendour of the vegetable colouring, and contributes to the magical effect of its harmonies and contrasts.
If the ma.s.s of light, which circulates about objects, fatigues the external senses during a part of the day, the inhabitant of the southern climates has his compensation in moral enjoyment. A lucid clearness in the conceptions, and a serenity of mind, correspond with the transparency of the surrounding atmosphere. We feel these impressions without going beyond the boundaries of Europe. I appeal to travellers who have visited countries rendered famous by the great creations of the imagination and of art,--the favoured climes of Italy and Greece.
We prolonged in vain our stay on the summit of the Peak, awaiting the moment when we might enjoy the view of the whole of the archipelago of the Fortunate Islands:* we, however, descried Palma, Gomera, and the Great Canary, at our feet. (* Of all the small islands of the Canaries, the Rock of the East is the only one which cannot be seen, even in fine weather, from the top of the Peak. Its distance is 3 degrees 5 minutes, while that of the Salvage is only 2 degrees 1 minute. The island of Madeira, distant 4 degrees 29 minutes, would be visible, if its mountains were more than 3000 toises high.) The mountains of Lancerota, free from vapours at sunrise, were soon enveloped in thick clouds. Supposing only an ordinary refraction, the eye takes in, in calm weather, from the summit of the volcano, a surface of the globe of 5700 square leagues, equal to a fourth of the superficies of Spain. The question has often been agitated, whether it be possible to perceive the coast of Africa from the top of this colossal pyramid; but the nearest parts of that coast are still farther from Teneriffe than 2 degrees 49 minutes, or 56 leagues. The visual ray of the horizon from the Peak being 1 degree 57 minutes, cape Bojador can be seen only on the supposition of its height being 200 toises above the level of the ocean. We are ignorant of the height of the Black Mountains near cape Bojador, as well as of that peak, called by navigators the Penon Grande, farther to the south of this promontory. If the summit of the volcano of Teneriffe were more accessible, we should observe without doubt, in certain states of the wind, the effects of an extraordinary refraction. On perusing what Spanish and Portuguese authors relate respecting the existence of the fabulous isle of San Borondon, or Antilia, we find that it is particularly the humid wind from west-south-west, which produces in these lat.i.tudes the phenomena of the mirage. We shall not however admit with M. Vieyra, "that the play of the terrestrial refractions may render visible to the inhabitants of the Canaries the islands of Cape Verd, and even the Apalachian mountains of America."* (* The American fruits, frequently thrown by the sea on the coasts of the islands of Ferro and Gomera, were formerly supposed to emanate from the plants of the island of San Borondon.
This island, said to be governed by an archbishop and six bishops, and which Father Feijoa believed to be the image of the island of Ferro, reflected on a fog-bank, was ceded in the 16th century, by the King of Portugal, to Lewis Perdigon, at the time the latter was preparing to take possession of it by conquest.)
The cold we felt on the top of the Peak, was very considerable for the season. The centigrade thermometer, at a distance from the ground, and from the apertures that emitted the hot vapours, fell in the shade to 2.7 degrees. The wind was west, and consequently opposite to that which brings to Teneriffe, during a great part of the year, the warm air that floats above the burning desert of Africa. As the temperature of the atmosphere, observed at the port of Orotava by M. Savagi, was 22.8 degrees, the decrement of caloric was one degree every 94 toises. This result perfectly corresponds with those obtained by Lamanon and Saussure on the summits of the Peak and Etna, though in very different seasons. The tall slender form of these mountains facilitates the means of comparing the temperature of two strata of the atmosphere, which are nearly in the same perpendicular plane; and in this point of view the observations made in an excursion to the volcano of Teneriffe resemble those of an ascent in a balloon. We must nevertheless remark, that the ocean, on account of its transparency and evaporation, reflects less caloric than the plains, into the upper regions of the air; and also that summits which are surrounded by the sea are colder in summer, than mountains which rise from a continent; but this circ.u.mstance has very little influence on the decrement of atmospherical heat; the temperature of the low regions being equally diminished by the proximity of the ocean.
It is not the same with respect to the influence exercised by the direction of the wind, and the rapidity of the ascending current; the latter sometimes increases in an astonishing manner the temperature of the loftiest mountains. I have seen the thermometer rise, on the slope of the volcano of Antisana, in the kingdom of Quito, to 19 degrees, when we were 2837 toises high. M.
Labillardiere has seen it, on the edge of the crater of the peak of Teneriffe, at 18.7 degrees, though he had used every possible precaution to avoid the effect of accidental causes.
On the summit of the Peak, we beheld with admiration the azure colour of the sky. Its intensity at the zenith appeared to correspond to 41 degrees of the cyanometer. We know, by Saussure"s experiment, that this intensity increases with the rarity of the air, and that the same instrument marked at the same period 39 degrees at the priory of Chamouni, and 40 degrees at the top of Mont Blanc. This last mountain is 540 toises higher than the volcano of Teneriffe; and if, notwithstanding this difference, the sky is observed there to be of a less deep blue, we must attribute this phenomenon to the dryness of the African air, and the proximity of the torrid zone.
We collected on the brink of the crater, some air which we meant to a.n.a.lyse on our voyage to America. The phial remained so well corked, that on opening it ten days after, the water rushed in with impetuosity. Several experiments, made by means of nitrous gas in the narrow tube of Fontana"s eudiometer, seemed to prove that the air of the crater contained 0.09 degrees less oxygen than the air of the sea; but I have little confidence in this result obtained by means which we now consider as very inexact. The crater of the Peak has so little depth, and the air is renewed with so much facility, that it is scarcely probable the quant.i.ty of azote is greater there than on the coasts. We know also, from the experiments of MM.
Gay-Lussac and Theodore de Saussure, that in the highest as well as in the lowest regions of the atmosphere, the air equally contains 0.21 of oxygen.* (* During the stay of M. Gay-Lussac and myself at the hospice of Mont Cenis, in March 1805, we collected air in the midst of a cloud loaded with electricity. This air, a.n.a.lysed in Volta"s eudiometer, contained no hydrogen, and its purity did not differ 0.002 of oxygen from the air of Paris, which we had carried with us in phials hermetically sealed.)
We saw on the summit of the Peak no trace of psora, lecidea, or other cryptogamous plants; no insect fluttered in the air. We found however a few hymenoptera adhering to ma.s.ses of sulphur moistened with sulphurous acid, and lining the mouths of the funnels. These are bees, which appear to have been attracted by the flowers of the Spartium nubigenum, and which oblique currents of air had carried up to these high regions, like the b.u.t.terflies found by M. Ramond at the top of Mont Perdu. The b.u.t.terflies perished from cold, while the bees on the Peak were scorched on imprudently approaching the crevices where they came in search of warmth.
Notwithstanding the heat we felt in our feet on the edge of the crater, the cone of ashes remains covered with snow during several months in winter. It is probable, that under the cap of snow considerable hollows are found, like those existing under the glaciers of Switzerland, the temperature of which is constantly less elevated than that of the soil on which they repose. The cold and violent wind, which blew from the time of sunrise, induced us to seek shelter at the foot of the Piton. Our hands and faces were nearly frozen, while our boots were burnt by the soil on which we walked. We descended in the s.p.a.ce of a few minutes the Sugar-loaf which we had scaled with so much toil; and this rapidity was in part involuntary, for we often rolled down on the ashes. It was with regret that we quitted this solitude, this domain where Nature reigns in all her majesty. We consoled ourselves with the hope of once again visiting the Canary Islands, but this, like many other plans we then formed, has never been executed.
We traversed the Malpays but slowly; for the foot finds no sure foundation on the loose blocks of lava. Nearer the station of the rocks, the descent becomes extremely difficult; the compact short-swarded turf is so slippery, that we were obliged to incline our bodies continually backward, in order to avoid falling. In the sandy plain of Retama, the thermometer rose to 22.5 degrees; and this heat seemed to us suffocating in comparison with the cold, which we had suffered from the air on the summit of the volcano. We were absolutely without water; our guides, not satisfied with drinking clandestinely the little supply of malmsey wine, for which we were indebted to Don Cologan"s kindness, had broken our water jars. Happily the bottle which contained the air of the crater escaped unhurt.
We at length enjoyed the refreshing breeze in the beautiful region of the arborescent erica and fern; and we were enveloped in a thick bed of clouds stationary at six hundred toises above the plain. The clouds having dispersed, we remarked a phenomenon which afterwards became familiar to us on the declivities of the Cordilleras. Small currents of air chased trains of cloud with unequal velocity, and in opposite directions: they bore the appearance of streamlets of water in rapid motion and flowing in all directions, amidst a great ma.s.s of stagnant water. The causes of this partial motion of the clouds are probably very various; we may suppose them to arise from some impulsion at a great distance; from the slight inequalities of the soil, which reflects in a greater or less degree the radiant heat; from a difference of temperature kept up by some chemical action; or perhaps from a strong electric charge of the vesicular vapours.
As we approached the town of Orotava, we met great flocks of canaries.* (* Fringilla Canaria. La Caille relates, in the narrative of his voyage to the Cape, that on Salvage Island these canaries are so abundant, that you cannot walk there in a certain season without breaking their eggs.) These birds, well known in Europe, were in general uniformly green. Some, however, had a yellow tinge on their backs; their note was the same as that of the tame canary. It is nevertheless remarked, that those which have been taken in the island of the Great Canary, and in the islet of Monte Clara, near Lancerota, have a louder and at the same time a more harmonious song. In every zone, among birds of the same species, each flock has its peculiar note. The yellow canaries are a variety, which has taken birth in Europe; and those we saw in cages at Orotava and Santa Cruz had been bought at Cadiz, and in other ports of Spain. But of all the birds of the Canary Islands, that which has the most heart-soothing song is unknown in Europe.
It is the capirote, which no effort has succeeded in taming, so sacred to his soul is liberty. I have stood listening in admiration of his soft and melodious warbling, in a garden at Orotava; but I have never seen him sufficiently near to ascertain to what family he belongs. As to the parrots, which were supposed to have been seen at the period of captain Cook"s abode at Teneriffe, they never existed but in the narratives of a few travellers, who have copied from each other. Neither parrots nor monkeys inhabit the Canary Islands; and though in the New Continent the former migrate as far as North Carolina, I doubt whether in the Old they have ever been met with beyond the 28th degree of north lat.i.tude.
Toward the close of day we reached the port of Orotava, where we received the unexpected intelligence that the Pizarro would not set sail till the 24th or 25th. If we could have calculated on this delay, we should either have lengthened our stay on the Peak,* or have made an excursion to the volcano of Chahorra. (* As a great number of travellers who land at Santa Cruz, do not undertake the excursion to the Peak, because they are ignorant of the time it occupies, it may be useful to lay down the following data: In making use of mules as far as the Estancia de los Ingleses, it takes twenty-one hours from Orotava to arrive at the summit of the Peak, and return to the port; namely, from Orotava to the Pino del Dornajito three hours; from the Pino to the Station of the Rocks six hours; and from this station to the Caldera three hours and a half. I reckon nine hours for the descent. In this calculation I count only the time employed in walking, without reckoning that which is necessary for examining the productions of the Peak, or for taking rest. Half a day is sufficient for going from Santa Cruz to Orotava.) We pa.s.sed the following day in visiting the environs of Orotava, and enjoying the agreeable company we found at Don Cologan"s. We perceived that Teneriffe had attractions not only to those who devote themselves to the study of nature: we found at Orotava several persons possessing a taste for literature and music, and who have transplanted into these distant climes the amenity of European society. In these respects the Canary Islands have no great resemblance to the other Spanish colonies, excepting the Havannah.
We were present on the eve of St. John at a pastoral fete in the garden of Mr. Little. This gentleman, who rendered great service to the Canarians during the last famine, has cultivated a hill covered with volcanic substances. He has formed in this delicious site an English garden, whence there is a magnificent view of the Peak, of the villages along the coast, and the isle of Palma, which is bounded by the vast expanse of the Atlantic. I cannot compare this prospect with any, except the views of the bays of Genoa and Naples; but Orotava is greatly superior to both in the magnitude of the ma.s.ses and in the richness of vegetation. In the beginning of the evening the slope of the volcano exhibited on a sudden a most extraordinary spectacle. The shepherds, in conformity to a custom, no doubt introduced by the Spaniards, though it dates from the highest antiquity, had lighted the fires of St. John. The scattered ma.s.ses of fire and the columns of smoke driven by the wind, formed a fine contrast with the deep verdure of the forests which covered the sides of the Peak. Shouts of joy resounding from afar were the only sounds that broke the silence of nature in these solitary regions.
Don Cologan"s family has a country-house nearer the coast than that I have just mentioned. This house, called La Paz, is connected with a circ.u.mstance that rendered it peculiarly interesting to us. M. de Borda, whose death we deplored, was its inmate during his last visit to the Canary Islands. It was in a neighbouring plain that he measured the base, by which he determined the height of the Peak.
In this geometrical operation the great dracaena of Orotava served as a mark. Should any well-informed traveller at some future day undertake a new measurement of the volcano with more exactness, and by the help of astronomical repeating circles, he ought to measure the base, not near Orotava, but near Los Silos, at a place called Bante. According to M. Broussonnet there is no plain near the Peak of greater extent. In herborizing near La Paz we found a great quant.i.ty of Lichen roccella on the basaltic rocks bathed by the waters of the sea. The archil of the Canaries is a very ancient branch of commerce; this lichen is however found in less abundance in the island of Teneriffe than in the desert islands of Salvage, La Graciosa, and Alegranza, or even in Canary and Hierro. We left the port of Orotava on the 24th of June.
To avoid disconnecting the narrative of the excursion to the top of the Peak, I have said nothing of the geological observations I made on the structure of this colossal mountain, and on the nature of the volcanic rocks of which it is composed. Before we quit the archipelago of the Canaries, I shall linger for a moment, and bring into one point of view some facts relating to the physical aspect of those countries.
Mineralogists who think that the end of the geology of volcanoes is the cla.s.sification of lavas, the examination of the crystals they contain, and their description according to their external characters, are generally very well satisfied when they come back from the mouth of a burning volcano. They return loaded with those numerous collections, which are the princ.i.p.al objects of their research. This is not the feeling of those who, without confounding descriptive mineralogy (oryctognosy) with geognosy, endeavour to raise themselves to ideas generally interesting, and seek, in the study of nature, for answers to the following questions:--
Is the conical mountain of a volcano entirely formed of liquified matter heaped together by successive eruptions, or does it contain in its centre a nucleus of primitive rocks covered with lava, which are these same rocks altered by fire? What are the affinities which unite the productions of modern volcanoes with the basalts, the phonolites, and those porphyries with bases of feldspar, which are without quartz, and which cover the Cordilleras of Peru and Mexico, as well as the small groups of the Monts Dores, of Cantal, and of Mezen in France? Has the central nucleus of volcanoes been heated in its primitive position, and raised up, in a softened state, by the force of the elastic vapours, before these fluids communicated, by means of a crater, with the external air? What is the substance, which, for thousands of years, keeps up this combustion, sometimes so slow, and at other times so active? Does this unknown cause act at an immense depth; or does this chemical action take place in secondary rocks lying on granite?
The farther we are from finding a solution of these problems in the numerous works. .h.i.therto published on Etna and Vesuvius, the greater is the desire of the traveller to see with his own eyes. He hopes to be more fortunate than those who have preceded him; he wishes to form a precise idea of the geological relations which the volcano and the neighbouring mountains bear to each other: but how often is he disappointed, when, on the limits of the primitive soil, enormous banks of tufa and puzzolana render every observation on the position and stratification impossible! We reach the inside of the crater with less difficulty than we at first expect; we examine the cone from its summit to its base; we are struck with the difference in the produce of each eruption, and with the a.n.a.logy which still exists between the lavas of the same volcano; but, notwithstanding the care with which we interrogate nature, and the number of partial observations which present themselves at every step, we return from the summit of a burning volcano less satisfied than when we were preparing to visit it. It is after we have studied them on the spot, that the volcanic phenomena appear still more isolated, more variable, more obscure, than we imagine them when consulting the narratives of travellers.
These reflections occurred to me on descending from the summit of the peak of Teneriffe, the first unextinct volcano I had yet visited. They returned anew whenever, in South America, or in Mexico, I had occasion to examine volcanic mountains. When we reflect how little the labours of mineralogists, and the discoveries in chemistry, have promoted the knowledge of the physical geology of mountains, we cannot help being affected with a painful sentiment; and this is felt still more strongly by those, who, studying nature in different climates, are more occupied by the problems they have not been able to solve, than with the few results they have obtained.
The peak of Ayadyrma, or of Echeyde,* (* The word Echeyde, which signifies h.e.l.l in the language of the Guanches, has been corrupted by the Europeans into Teyde.) is a conic and isolated mountain, which rises in an islet of very small circ.u.mference. Those who do not take into consideration the whole surface of the globe, believe, that these three circ.u.mstances are common to the greater part of volcanoes. They cite, in support of their opinion, Etna, the peak of the Azores, the Solfatara of Guadaloupe, the Trois-Salazes of the isle of Bourbon, and the cl.u.s.ters of volcanoes in the Indian Sea and in the Atlantic. In Europe and in Asia, as far as the interior of the latter continent is known, no burning volcano is situated in the chains of mountains; all being at a greater or less distance from those chains. In the New World, on the contrary, (and this fact deserves the greatest attention,) the volcanoes the most stupendous for their ma.s.ses form a part of the Cordilleras themselves. The mountains of mica-slate and gneiss in Peru and New Grenada immediately touch the volcanic porphyries of the provinces of Quito and Pasto. To the south and north of these countries, in Chile and in the kingdom of Guatimala, the active volcanoes are grouped in rows. They are the continuation, as we may say, of the chains of primitive rocks, and if the volcanic fire has broken forth in some plain remote from the Cordilleras, as in mount Sangay and Jorullo,* (* Two volcanoes of the Provinces of Quixos and Mechoacan, the one in the southern, and the other in the northern hemisphere.) we must consider this phenomenon as an exception to the law, which nature seems to have imposed on these regions. I may here repeat these geological facts, because this presumed isolated situation of every volcano has been cited in opposition to the idea that the peak of Teneriffe, and the other volcanic summits of the Canary Islands, are the remains of a submerged chain of mountains. The observations which have been made on the grouping of volcanoes in America, prove that the ancient state of things represented in the conjectural map of the Atlantic by M. Bory de St. Vincent* (* Whether the traditions of the ancients respecting the Atlantis are founded on historical facts, is a matter totally distinct from the question whether the archipelago of the Canaries and the adjacent islands are the vestiges of a chain of mountains, rent and sunk in the sea during one of the great convulsions of our globe. I do not pretend to form any opinion in favour of the existence of the Atlantis; but I endeavour to prove, that the Canaries have no more been created by volcanoes, than the whole body of the smaller Antilles has been formed by madrepores.) is by no means contradictory to the acknowledged laws of nature; and that nothing opposes the supposition that the summits of Porto Santo, Madeira, and the Fortunate Islands, may heretofore have formed, either a distinct range of primitive mountains, or the western extremity of the chain of the Atlas.
The peak of Teyde forms a pyramidal ma.s.s like Etna, Tungurahua, and Popocatepetl. This physiognomic character is very far from being common to all volcanoes. We have seen some in the southern hemisphere, which, instead of having the form of a cone or a bell, are lengthened in one direction, having the ridge sometimes smooth, and at others bristled with small pointed rocks. This structure is peculiar to Antisana and Pichincha, two burning mountains of the province of Quito; and the absence of the conic form ought never to be considered as a reason excluding the idea of a volcanic origin.
I shall develop, in the progress of this work, some of the a.n.a.logies, which I think I have perceived between the physiognomy of volcanoes and the antiquity of their rocks. It is sufficient to state, generally speaking, that the summits, which are still subject to eruptions of the greatest violence, and at the nearest periods to each other, are SLENDER PEAKS of a conic form; that the mountains with LENGTHENED SUMMITS, and rugged with small stony ma.s.ses, are very old volcanoes, and near being extinguished; and that rounded tops, in the form of domes, or bells, indicate those problematic porphyries, which are supposed to have been heated in their primitive position, penetrated by vapours, and forced up in a mollified state, without having ever flowed as real lithoidal lavas. To the first cla.s.s belong Cotopaxi, the peak of Teneriffe, and the peak of Orizava in Mexico. In the second may be placed Cargueirazo and Pichincha, in the province of Quito; the volcano of Puracey, near Popayan; and perhaps also Hecla, in Iceland. In the third and last we may rank the majestic figure of Chimborazo, and, (if it be allowable to place by the side of that colossus a hill of Europe,) the Great Sarcouy in Auvergne.
In order to form a more exact idea of the external structure of volcanoes, it is important to compare their perpendicular height with their circ.u.mference. This, however, cannot be done with any exactness, unless the mountains are isolated, and rising on a plain nearly on a level with the sea. In calculating the circ.u.mference of the peak of Teneriffe in a curve pa.s.sing through the port of Orotava, Garachico, Adexe, and Guimar, and setting aside the prolongations of its base towards the forest of Laguna, and the north-east cape of the island, we find that this extent is more than 54,000 toises. The height of the Peak is consequently one twenty-eighth of the circ.u.mference of its basis. M. von Buch found a thirty-third for Vesuvius; and, which perhaps is less certain, a thirty-fourth for Etna.* (* Gilbert, Annalen der Physik B. 5 page 455. Vesuvius is 133,000 palmas, or eighteen nautical miles in circ.u.mference. The horizontal distance from Resina to the crater is 3700 toises. Italian mineralogists have estimated the circ.u.mference of Etna at 840,000 palmas, or 119 miles. With these data, the ratio of the height to the circ.u.mference would be only a seventy-second; but I find on tracing a curve through Catania, Palermo, Bronte, and Piemonte, only 62 miles in circ.u.mference, according to the best maps. This increases the ratio to a fifty-fourth. Does the basis fall on the outside of the curve that I a.s.sume?) If the slope of these three volcanoes were uniform from the summit to the base, the peak of Teyde would have an inclination of 12 degrees 29 minutes, Vesuvius 12 degrees 41 minutes, and Etna 10 degrees 13 minutes, a result which must astonish those who do not reflect on what const.i.tutes an average slope. In a very long ascent, slopes of three or four degrees alternate with others which are inclined from 25 to 30 degrees; and the latter only strike our imagination, because we think all the slopes of mountains more steep than they really are.
I may cite in support of this consideration the example of the ascent from the port of Vera Cruz to the elevated plain of Mexico.
On the eastern slope of the Cordillera a road has been traced, which for ages has not been frequented except on foot, or on the backs of mules. From Encero to the small Indian village of Las Vigas, there are 7500 toises of horizontal distance; and Encero being, according to my barometric measurement, 746 toises lower than Las Vigas, the result, for the mean slope, is only an angle of 5 degrees 40 minutes.
In the following note will be seen the results of some experiments I have made on the difficulties arising from the declivities in mountainous countries.*
(* In places where there were at the same time slopes covered with tufted gra.s.s and loose sands, I took the following measures:--
5 degrees, slope of a very marked inclination. In France the high roads must not exceed 4 degrees 46 minutes by law; 15 degrees, slope extremely steep, and which we cannot descend in a carriage; 37 degrees, slope almost inaccessible on foot, if the ground be naked rock, or turf too thick to form steps. The body falls backwards when the tibia makes a smaller angle than 53 degrees with the sole of the foot; 42 degrees, the steepest slope that can be climbed on foot in a ground that is sandy, or covered with volcanic ashes.
When the slope is 44 degrees, it is almost impossible to scale it, though the ground permits the forming of steps by thrusting in the foot. The cones of volcanoes have a medium slope from 33 to 40 degrees. The steepest parts of these cones, either of Vesuvius, the Peak of Teneriffe, the volcano of Pichincha, or Jorullo, are from 40 to 42 degrees. A slope of 55 degrees is quite inaccessible. If seen from above it would be estimated at 75 degrees.)