As the Peak rises amid a system of basalts and old lava, and as the whole part which is visible above the surface of the waters exhibits burnt substances, it has been supposed that this immense pyramid is the effect of a progressive accumulation of lavas; or that it contains in its centre a nucleus of primitive rocks. Both of these suppositions appear to me ill-founded. I think there is as little probability that mountains of granite, gneiss, or primitive calcareous stone have existed where we now see the tops of the Peak, of Vesuvius, and of Etna, as in the plains where almost in our own time has been formed the volcano of Jorullo, which is more than a third of the height of Vesuvius. On examining the circumstances which accompanied the formation of the new island, called Sabrina, in the archipelago of the Azores;* (* At Sabrina island, near St. Michael's, the crater opened at the foot of a solid rock, of almost a cubical form. This rock, surmounted by a small elevated plain perfectly level, is more than two hundred toises in breadth. Its formation was anterior to that of the crater, into which, a few days after its opening, the sea made an irruption. At Kameni, the smoke was not even visible till twenty-six days after the appearance of the upheaved rocks. Philosophical Transactions volume 26 pages 69 and 200, volume 27 page 353. All these phenomena, on which Mr. Hawkins collected very valuable observations during his abode at Santorino, are unfavourable to the idea commonly entertained of the origin of volcanic mountains. They are usually ascribed to a progressive accumulation of liquified matter, and the diffusion of lavas issuing from a central mouth.) on carefully reading the minute and simple narrative, given by the Jesuit Bourguignon of the slow appearance of the islet of the little Kameni, near Santorino; we find that these extraordinary eruptions are generally preceded by a swelling of the softened crust of the globe. Rocks appear above the waters before the flames force their way, or lavas issue from the crater: we must distinguish between the nucleus raised up, and the mass of lavas and scoriae, which successively increases its dimensions.
It is true that from all existing records of revolutions of this kind, the perpendicular height of the stony nucleus appears never to have exceeded one hundred and fifty or two hundred toises; even taking into the account the depth of the sea, the bottom of which had been lifted up: but when considering the great effects of nature, and the intensity of its forces, the bulk of the masses must not deter the geologist in his speculations. Every thing indicates that the physical changes of which tradition has preserved the remembrance, exhibit but a feeble image of those gigantic catastrophes which have given mountains their present form, changed the positions of the rocky strata, and buried sea-shells on the summits of the higher Alps. Doubtless, in those remote times which preceded the existence of the human race, the raised crust of the globe produced those domes of trappean porphyry, those hills of isolated basalt on vast elevated plains, those solid nuclei which are clothed in the modern lavas of the Peak, of Etna, and of Cotopaxi. The volcanic revolutions have succeeded each other after long intervals, and at very different periods: of this we see the vestiges in the transition mountains, in the secondary strata, and in those of alluvium. Volcanoes of earlier date than the sandstone and calcareous rocks have been for ages extinguished; those which are yet in activity are in general surrounded only with breccias and modern tufas; but nothing hinders us from admitting, that the archipelago of the Canaries may exhibit some real rocks of secondary formation, if we recollect that subterranean fires have been there rekindled in the midst of a system of basalts and very ancient lavas.
We seek in vain in the Periplus of Hanno or of Scylax for the first written notions on the eruptions of the Peak of Teneriffe. Those navigators sailed timidly along the coast, anchoring every evening in some bay, and had no knowledge of a volcano distant fifty-six leagues from the coast of Africa. Hanno nevertheless relates, that he saw torrents of light, which seemed to fall on the sea; that every night the coast was covered with fire; and that the great mountain, called the Car of the Gods, appeared to throw up sheets of flame, which rose even to the clouds. But this mountain, situated northward of the island of the Gorilli, formed the western extremity of the Atlas chain; and it is also very uncertain whether the flames seen by Hanno were the effect of some volcanic eruption, or whether they must be attributed to the custom, common to many nations, of setting fire to the forests and dry grass of the savannahs. In our own days similar doubts were entertained by the naturalists, who, in the voyage of d'Entrecasteaux, saw the island of Amsterdam covered with a thick smoke. On the coast of the Caracas, trains of reddish fire, fed by the burning grass, appeared to me, for several nights, under the delusive semblance of a current of lava, descending from the mountains, and dividing itself into several branches.
Though the narratives of Hanno and Scylax, in the state in which they have reached us, contain no passage which we can reasonably apply to the Canary Islands, it is very probable that the Carthaginians, and even the Phoenicians, had some knowledge of the Peak of Teneriffe. In the time of Plato and Aristotle, vague notions of it had reached the Greeks, who considered the whole of the coast of Africa, beyond the Pillars of Hercules, as thrown into disorder by the fire of volcanoes. The Abode of the Blessed, which was sought first in the north, beyond the Riphaean mountains, among the Hyperboreans, and next to the south of Cyrenaica, was supposed to be situated in regions that were considered to be westward, being the direction in which the world known to the ancients terminated. The name of Fortunate Islands was long in as vague signification, as that of El Dorado among the conquerors of America. Happiness was thought to reside at the end of the earth, as we seek for the most exquisite enjoyments of the mind in an ideal world beyond the limits of reality.* (* The idea of the happiness, the great civilization, and the riches of the inhabitants of the north, was common to the Greeks, to the people of India, and to the Mexicans.)
We must not be surprised that, previous to the time of Aristotle, we find no accurate notion respecting the Canary Islands and the volcanoes they contain, among the Greek geographers. The only nation whose navigations extended toward the west and the north, the Carthaginians, were interested in throwing a veil of mystery over those distant regions. While the senate of Carthage was averse to any partial emigration, it pointed out those islands as a place of refuge in times of trouble and public misfortune; they were to the Carthaginians what the free soil of America has become to Europeans amidst their religious and civil dissensions.
The Canaries were not better known to the Romans till eighty-four years before the reign of Augustus. A private individual was desirous of executing the project, which wise foresight had dictated to the senate of Carthage. Sertorius, conquered by Sylla, and weary of the din of war, looked out for a safe and peaceable retreat. He chose the Fortunate Islands, of which a delightful picture had been drawn for him on the shores of Baetica. He carefully combined the notions he acquired from travellers; but in the little that has been transmitted to us of those notions, and in the more minute descriptions of Sebosus and Juba, there is no mention of volcanoes or volcanic eruptions. Scarcely can we recognise the isle of Teneriffe, and the snows with which the summit of the Peak is covered in winter, in the name of Nivaria, given to one of the Fortunate Islands. Hence we might conclude, that the volcano at that time threw out no flames, if it were allowable so to interpret the silence of a few authors, whom we know only by short fragments or dry nomenclatures. The naturalist vainly seeks in history for documents of the first eruptions of the Peak; he nowhere finds any but in the language of the Guanches, in which the word Echeyde denotes, at the same time, hell and the volcano of Teneriffe.
Of all the written testimonies, the oldest I have found in relation to the activity of this volcano dates from the beginning of the sixteenth century. It is contained in the narrative of the voyage of Aloysio Cadamusto, who landed at the Canaries in 1505. This traveller was witness of no eruptions, but he positively affirms that, like Etna, this mountain burns without interruption, and that the fire has been seen by christians held in slavery by the Guanches of Teneriffe. The Peak, therefore, was not at that time in the state of repose in which we find it at present; for it is certain that no navigator or inhabitant of Teneriffe has seen issue from the mouth of the Peak, I will not say flames, but even any smoke visible at a distance. It would be well, perhaps, were the funnel of the Caldera to open anew; the lateral eruptions would thereby be rendered less violent, and the whole group of islands would be less endangered by earthquakes.
The eruptions of the Peak have been very rare for two centuries past, and these long intervals appear to characterize volcanoes highly elevated. The smallest one of all, Stromboli, is almost always burning. At Vesuvius, the eruptions are rarer than formerly, though still more frequent than those of Etna and the Peak of Teneriffe. The colossal summits of the Andes, Cotopaxi and Tungurahua, scarcely have an eruption once in a century. We may say, that in active volcanoes the frequency of the eruptions is in the inverse ratio of the height and the mass. The Peak also had seemed extinguished during ninety-two years, when, in 1798, it made its last eruption by a lateral opening formed in the mountain of Chahorra. In this interval Vesuvius had sixteen eruptions.
The whole of the mountainous part of the kingdom of Quito may be considered as an immense volcano, occupying more than seven hundred square leagues of surface, and throwing out flames by different cones, known under the particular denominations of Cotopaxi, Tungurahua, and Pichincha. The group of the Canary Islands is situated on the same sort of submarine volcano. The fire makes its way sometimes by one and sometimes by another of these islands. Teneriffe alone contains in its centre an immense pyramid terminating in a crater, and throwing out, from one century to another, lava by its flanks. In the other islands, the different eruptions have taken place in various parts; and we nowhere find those isolated mountains to which the volcanic effects are confined. The basaltic crust, formed by ancient volcanoes, seems everywhere undermined; and the currents of lava, seen at Lancerota and Palma, remind us, by every geological affinity, of the eruption which took place in 1301 at the island of Ischia, amid the tufas of Epomeo.
The exclusively lateral action of the peak of Teneriffe is a geological phenomenon, the more remarkable as it contributes to make the mountains which are backed by the principal volcano appear isolated. It is true, that in Etna and Vesuvius the great flowings of lava do not proceed from the crater itself, and that the abundance of melted matter is generally in the inverse ratio of the height of the opening whence the lava is ejected. But at Vesuvius and Etna a lateral eruption constantly terminates by flashes of flame and by ashes issuing from the crater, that is, from the summit of the mountain. At the Peak this phenomenon has not been witnessed for ages: and yet recently, in the eruption of 1798, the crater remained quite inactive. Its bottom did not sink in; while at Vesuvius, as M. von Buch has observed, the greater or less depth of the crater is an infallible indication of the proximity of a new eruption.