I might terminate these geological sketches by enquiring into the nature of the combustible which has fed for so many thousands of years the fire of the peak of Teneriffe;—I might examine whether it be sodium or potassium, the metallic basis of some earth, carburet of hydrogen, or pure sulphur combined with iron, that burns in the volcano;—but wishing to limit myself to what may be the object of direct observation, I shall not take upon me to solve a problem for which we have not yet sufficient data. We know not whether we may conclude, from the enormous quantity of sulphur contained in the crater of the Peak, that it is this substance which keeps up the heat of the volcano; or whether the fire, fed by some combustible of an unknown nature, effects merely the sublimation of the sulphur. What we learn from observation is, that in craters which are still burning, sulphur is very rare; while all the ancient volcanoes end in becoming sulphur-pits. We might presume that, in the former, the sulphur is combined with oxygen, while, in the latter, it is merely sublimated; for nothing hitherto authorises us to admit that it is formed in the interior of volcanoes, like ammonia and the neutral salts. When we were yet unacquainted with sulphur, except as disseminated in the muriatiferous gypsum and in the Alpine limestone, we were almost forced to the belief, that in every part of the globe the volcanic fire acted on rocks of secondary formation; but recent observations have proved that sulphur exists in great abundance in those primitive rocks which so many phenomena indicate as the centre of the volcanic action. Near Alausi, at the back of the Andes of Quito, I found an immense quantity in a bed of quartz, which formed a layer of mica-slate. This fact is the more important, as it is in strict conformity with the conclusions deduced from the observation of those fragments of ancient rocks which are thrown out intact by volcanoes.
We have just considered the island of Teneriffe merely in a geological point of view; we have seen the Peak towering amid fractured strata of basalt and mandelstein; let us examine how these fused masses have been gradually adorned with vegetable clothing, what is the distribution of plants on the steep declivity of the volcano, and what is the aspect or physiognomy of vegetation in the Canary Islands.
In the northern part of the temperate zone, the cryptogamous plants are the first that cover the stony crust of the globe. The lichens and mosses, that develop their foliage beneath the snows, are succeeded by grumina and other phanerogamous plants. This order of vegetation differs on the borders of the torrid zone, and in the countries between the tropics. We there find, it is true, whatever some travellers may have asserted, not only on the mountains, but also in humid and shady places, almost on a level with the sea, Funaria, Dicranum, and Bryum; and these genera, among their numerous species, exhibit several which are common to Lapland, to the Peak of Teneriffe, and to the Blue Mountains of Jamaica. (This extraordinary fact was first observed by M. Swarz. It was confirmed by M. Willdenouw when he carefully examined our herbals, especially the collection of cryptogamous plants, which we gathered on the tops of the Andes, in a region of the world where organic life is totally different from that of the old world.) Nevertheless, in general, it is not by mosses and lichens that vegetation in the countries near the tropics begins. In the Canary Islands, as well as in Guinea, and on the rocky coasts of Peru, the first vegetation which prepares the soil are the succulent plants; the leaves of which, provided with an infinite number of orifices* (* The pores corticaux of M. Decandolle, discovered by Gleichen, and figured by Hedwig.) and cutaneous vessels, deprive the ambient air of the water it holds in solution. Fixed in the crevices of volcanic rocks, they form, as it were, that first layer of vegetable earth with which the currents of lithoid lava are clothed. Wherever these lavas are scorified, and where they have a shining surface, as in the basaltic mounds to the north of Lancerota, the development of vegetation is extremely slow, and many ages may pass away before shrubs can take root. It is only when lavas are covered with tufa and ashes, that the volcanic islands, losing that appearance of nudity which marks their origin, bedeck themselves in rich and brilliant vegetation.
In its present state, the island of Teneriffe, the Chinerfe* (* Of Chinerfe the Europeans have formed, by corruption, Tchineriffe and Teneriffe.) of the Guanches, exhibits five zones of plants, which we may distinguish by the names—region of vines, region of laurels, region of pines, region of the retama, and region of grasses. These zones are ranged in stages, one above another, and occupy, on the steep declivity of the Peak, a perpendicular height of 1750 toises; while fifteen degrees farther north, on the Pyrenees, snow descends to thirteen or fourteen hundred toises of absolute elevation. If the plants of Teneriffe do not reach the summit of the volcano, it is not because the perpetual snow and the cold of the surrounding atmosphere mark limits which they cannot pass; it is the scorified lava of the Malpays, the powdered and barren pumice-stone of the Piton, which impede the migration of plants towards the brink of the crater.
The first zone, that of the vines, extends from the sea-shore to two or three hundred toises of height; it is that which is most inhabited, and the only part carefully cultivated. In the low regions, at the port of Orotava, and wherever the winds have free access, the centigrade thermometer stands in winter, in the months of January and February, at noon, between fifteen and seventeen degrees; and the greatest heats of summer do not exceed twenty-five or twenty-six degrees. The mean temperature of the coasts of Teneriffe appears at least to rise to twenty-one degrees (16.8 degrees Reaumur); and the climate in those parts keeps at the medium between the climate of Naples and that of the torrid zone.
The region of the vines exhibits, among its vegetable productions, eight kinds of arborescent Euphorbia; Mesembrianthema, which are multiplied from the Cape of Good Hope to the Peloponnesus; the Cacalia Kleinia, the Dracaena, and other plants, which in their naked and tortuous trunks, in their succulent leaves, and their tint of bluish green, exhibit distinctive marks of the vegetation of Africa. It is in this zone that the date-tree, the plantain, the sugar-cane, the Indian fig, the Arum Colocasia, the root of which furnishes a nutritive fecula, the olive-tree, the fruit trees of Europe, the vine, and corn are cultivated. Corn is reaped from the end of March to the beginning of May: and the culture of the bread-fruit tree of Otaheite, that of the cinnamon tree of the Moluccas, the coffee-tree of Arabia, and the cacao-tree of America, have been tried with success. On several points of the coast the country assumes the character of a tropical landscape; and we perceive that the region of the palms extends beyond the limits of the torrid zone. The chamaerops and the date-tree flourish in the fertile plains of Murviedro, on the coasts of Genoa, and in Provence, near Antibes, between the thirty-ninth and forty-fourth degrees of latitude; a few trees of the latter species, planted within the walls of the city of Rome, resist even the cold of 2.5 degrees below freezing point. But if the south of Europe as yet only partially shares the gifts lavished by nature on the zone of palms, the island of Teneriffe, situated on the parallel of Egypt, southern Persia, and Florida, is adorned with the greater part of the vegetable forms which add to the majesty of the landscape in the regions near the equator.
On reviewing the different tribes of indigenous plants, we regret not finding trees with small pinnated leaves, and arborescent gramina. No species of the numerous family of the sensitive-plants has migrated as far as the archipelago of the Canary Islands, while on both continents they have been seen in the thirty-eighth and fortieth degrees of latitude. On a more careful examination of the plants of the islands of Lancerota and Forteventura, which are nearest the coast of Morocco, we may perhaps find a few mimosas among many other plants of the African flora.
The second zone, that of the laurels, comprises the woody part of Teneriffe: this is the region of the springs, which gush forth amidst turf always verdant, and never parched with drought. Lofty forests crown the hills leading to the volcano, and in them are found four species of laurel,* (* Laurus indica, L. foetens, L. nobilis, and L. Til. With these trees are mingled the Ardisia excelsa, Rhamnus glandulosus, Erica arborea and E. texo.) an oak nearly resembling the Quercus Turneri* (* Quercus canariensis, Broussonnet.) of the mountains of Tibet, the Visnea mocanera, the Myrica Faya of the Azores, a native olive (Olea excelsa), which is the largest tree of this zone, two species of Sideroxylon, the leaves of which are extremely beautiful, the Arbutus callicarpa, and other evergreen trees of the family of myrtles. Bindweeds, and an ivy very different from that of Europe (Hedera canariensis) entwine the trunks of the laurels; at their feet vegetate a numberless quantity of ferns,* (* Woodwardia radicans, Asplenium palmatum, A. canariensis, A. latifolium, Nothalaena subcordata, Trichomanes canariensis, T. speciosum, and Davallia canariensis.) of which three species* (* Two Acrostichums and the Ophyoglossum lusitanicum.) alone descend as low as the region of the vines. The soil, covered with mosses and tender grass, is enriched with the flowers of the Campanula aurea, the Chrysanthemum pinnatifidum, the Mentha canariensis, and several bushy species of Hypericum.* (* Hypericum canariense, H. floribundum, and H. glandulosum.) Plantations of wild and grafted chestnut-trees form a broad border round the region of the springs, which is the greenest and most agreeable of the whole.
In the third zone (beginning at nine hundred toises of absolute height), the last groups of Arbutus, of Myrica Faya, and of that beautiful heath known to the natives by the name of Texo, appear. This zone, four hundred toises in breadth, is entirely filled by a vast forest of pines, among which mingles the Juniperus cedro of Broussonnet. The leaves of these pines are very long and stiff, and they sprout sometimes by pairs, but oftener by threes in one sheath. Having had no opportunity of examining the fructification, we cannot say whether this species, which has the appearance of the Scotch fir, is really different from the eighteen species of pines with which we are already acquainted in Europe. M. Decandolle is of opinion that the pine of Teneriffe is equally distinct from the Pinus atlantica of the neighbouring mountains of Mogador, and from the pine of Aleppo,* (* Pinus halepensis. M. Decandolle observes, that this species, which is not found in Portugal, but grows on the Mediterranean shores of France, Spain, and Italy, in Asia Minor, and in Barbary, would be better named Pinus mediterranea. It composes the principal part of the pine-forests of the south-east of France, where Gouan and Gerard have confounded it with the Pinus sylvestris. It comprehends the Pinus halepensis, Mill., Lamb., and Desfont., and the Pinus maritima, Lamb.) which belongs to the basin of the Mediterranean, and does not appear to have passed the Pillars of Hercules. We met with these last pines on the slope of the Peak, near twelve hundred toises above the level of the sea. In the Cordilleras of New Spain, under the torrid zone, the Mexican pines extend to the height of two thousand toises. Notwithstanding the similarity of structure existing between the different species of the same genus of plants, each of them requires a certain degree of temperature and rarity in the ambient air to attain its due growth. If in temperate climates, and wherever snow falls, the uniform heat of the soil be somewhat above the mean heat of the atmosphere, it is probable that at the height of Portillo the roots of the pines draw their nourishment from a soil, in which, at a certain depth, the thermometer rises at most to nine or ten degrees.
The fourth and fifth zones, the regions of the retama and the gramina, occupy heights equal to the most inaccessible summits of the Pyrenees. It is the sterile part of the island where heaps of pumice-stone, obsidian, and broken lava, form impediments to vegetation. We have already spoken of those flowery tufts of alpine broom (Spartium nubigenum), which form oases amidst a vast desert of ashes. Two herbaceous plants, the Scrophularia glabrata and the Viola cheiranthifolia, advance even to the Malpays. Above a turf scorched by the heat of an African sun, an arid soil is overspread by the Cladonia paschalis. Towards the summit of the Peak the Urceolarea and other plants of the family of the lichens, help to work the decomposition of the scorified matter. By this unceasing action of organic force the empire of Flora is extended over islands ravaged by volcanoes.