Personal Narrative Of Travels To The Equinoctial Regions Of America During The Years 1799-1804 - Volume 1 - By Alexander Von Humboldt And Aime Bonpland.
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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.
On surveying the different zones of the vegetation of Teneriffe, we
perceive that the whole island may be considered as a forest of
laurels, arbutus, and pines, containing in its centre a naked and
rocky soil, unfit either for pasturage or cultivation. M.
Broussonnet observes, that the archipelago of the Canaries may be
divided into two groups of islands; the first comprising Lancerota
and Forteventura, the second Teneriffe, Canary, Gomera, Ferro, and
Palma.
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