Personal Narrative Of Travels To The Equinoctial Regions Of America During The Years 1799-1804 - Volume 3 - By Alexander Von Humboldt And Aime Bonpland.
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Many
Solitary Cultivated Spots Already Exist In The Midst Of The Pastures
Where Running Water And Tufts Of The Mauritia Palm Have Been Found.
These Farms, Sown With Maize, And Planted With Cassava, Will Multiply
Considerably If Trees And Shrubs Be Augmented.
The aridity and excessive heat of the mesas do not depend solely on
the nature of their surface and the local reverberation of the soil;
their climate is modified by the adjacent regions; by the whole of the
Llano of which they form a part.
In the deserts of Africa or Arabia,
in the Llanos of South America, in the vast heaths extending from the
extremity of Jutland to the mouth of the Scheldt, the stability of the
limits of the desert, the savannahs, and the downs, depends chiefly on
their immense extent and the nakedness these plains have acquired from
some revolution destructive of the ancient vegetation of our planet.
By their extent, their continuity, and their mass they oppose the
inroads of cultivation and preserve, like inland gulfs, the stability
of their boundaries. I will not enter upon the great question, whether
in the Sahara, that Mediterranean of moving sands, the germs of
organic life are increased in our days. In proportion as our
geographical knowledge has extended we have discovered in the eastern
part of the desert islets of verdure; oases covered with date-trees
crowd together in more numerous archipelagos, and open their ports to
the caravans; but we are ignorant whether the form of the oases have
not remained constantly the same since the time of Herodotus. Our
annals are too incomplete to enable us to follow Nature in her slow
and gradual progress. From these spaces entirely bare whence some
violent catastrophe has swept away the vegetable covering and the
mould; from those deserts of Syria and Africa which, by their
petrified wood, attest the changes they have undergone; let us turn to
the grass-covered Llanos and to the consideration of phenomena that
come nearer the circle of our daily observations. Respecting the
possibility of a more general cultivation of the steppes of America,
the colonists settled there, concur in the opinions I have deduced
from the climatic action of these steppes considered as surfaces, or
continuous masses. They have observed that downs enclosed within
cultivated and wooded land sooner yield to the labours of the
husbandman than soils alike circumscribed, but forming part of a vast
surface of the same nature. This observation is extremely just whether
in reference to soil covered with heath, as in the north of Europe;
with cistuses, mastic-trees, or palmettos, as in Spain; or with
cactuses, argemones, or brathys, as in equinoctial America. The more
space the association occupies the more resistance do the social
plants oppose to the labourer. With this general cause others are
combined in the Llanos of Venezuela; namely the action of the small
grasses which impoverish the soil; the total absence of trees and
brushwood; the sandy winds, the heat of which is increased by contact
with a surface absorbing the rays of the sun during twelve hours, and
unshaded except by the stalks of the aristides, chanchuses, and
paspalums.
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