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Thus are we indebted to the gradual progress of vegetation for some imposing, and many graceful varieties in nature. A bare and rugged rock may, in some situations, produce a grand, but never a beautiful effect; tinged with mosses and lichens, its sterile aspect disappears, and it becomes an object of interest to the painter and botanist; when its rugged sides are mantled with flowers and foliage, it acquires a considerable degree of beauty; but when clothed with a deep and ancient wood, it becomes, especially if reflected by a sheet of water, one of the sublimest objects connected with natural scenery.
In the mountainous regions of the globe, this gradation of vegetable life assumes a decided character, and varies in grandeur and luxuriance according to circumstances and situation, a gradation which is particularly observable in many parts of Switzerland and Norway. In the former, the vallies and lower parts of the mountains are beautifully enriched with corn-fields, vineyards, and meadows. To these succeed forests of larch and pine; next, short grass, with several species of herbs adapted to the pasturage of cattle; then, mosses and lichens; and lastly, bare, rugged, and frowning rocks, covered with eternal snow. M. Esmark, member of the Norwegian Council of Mines, has in a tour in Norway, made many interesting experiments in order to determine the boundary line of vegetation towards the regions of perpetual ice. For this purpose he ascended Schnechuttun. It was shrouded with snow, and at one point where a partial thaw had taken place, discovered twenty-five layers, each of them separated by a rind of ice. The surface of the snow resembled waves, and the hollows were of an amethyst colour, an appearance which is often remarked on the Alps. The boundary line of vegetation differed considerably on the sides of the mountain, as likewise the kind of trees and shrubs, according as they were capable of bearing a greater or less degree of cold. Fruit trees throve and became productive, at the height of one thousand feet; barley and oats, in sheltered situations, from fifteen to eighteen hundred above the level of the sea. To these succeeded forests of pine, fir, and birch-trees, in regular gradations; higher up the mountain a few stunted birches, willows, and juniper trees were alone discoverable, and towards the frozen regions vegetation entirely disappeared.
Cryptogamous plants, in the northern parts of the temperate zone, are the first that cover the stony surface of the globe; these humble plants peep forth from beneath the snowy mantle which envelopes them, and are succeeded by other vegetable productions. On the borders of the torrid zone, and in the countries between the tropics, or approximating to them, the order of vegetation considerably varies, there, as in the Canary islands, Guinea, and on the rocky coasts of Peru, the pioneers of Flora's kingdom are the succulent plants, the pores of which, provided with an infinite number of orifices and cutaneous vessels, deprive the ambient air of the water which it holds in solution. Fixed in the crevices of volcanic rocks, they form the first layer of vegetable mould with which the currents of lava are encrusted, but when these lavas are scorified and retain a shining surface, as in the basaltic moulds of the north of Lanzarotta, the unfolding of vegetation is extremely slow, and ages roll away before shrubs and trees are enabled to take root. When, on the contrary, volcanic islands are covered with ashes and scoria, they lose the appearance of desolation which mark their origin, and robe themselves with a rich and brilliant covering.
The island of Teneriff exhibits five zones of plants, those of vines, laurels, pines, shrubs, and grasses. These zones are arranged in stages one above the other, and occupy, on the steep declivity of the Peak, a perpendicular height of one thousand seven hundred and fifty toises, while fifteen degrees farther north, on the Pyrenees, the snows already descend to thirteen or fourteen hundred toises of absolute elevation. If the plants of Teneriff do not reach the summit of the volcano, it is not because the perpetual snows, and the cold of the surrounding atmosphere, lay down limits which they cannot pass; it is the scorified lava of the Malpays, the powdered and barren pumice stone of the Piton, which offer insurmountable barriers to the vegetable tribes, and imperiously forbid their further migration towards the brink of the crater.