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.

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.

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