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 mass, 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 coke. The northern edge is most elevated. Towards the south-west the enclosure is considerably sunk and an enormous mass 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 principally 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 space 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 masses, 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, asserts that the muriatic acid always predominates in the vapours of Vesuvius. This assertion 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 masses, 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 analogies 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 space as well as by the vastness, the novelty, and the multitude 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 analysis 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 mass, 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 mass 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, masses 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 destitute 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 lustrous lava: a violet,* (* Viola cheiranthifolia.) akin to the Viola decumbens, 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 encumbered 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 pass slightly over the principal 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 passing 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 passage. When from the shores 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 surpasses 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 mass 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.