These Plains Would Serve As Natural Boundaries Like The Seas Or The Virgin Forests Of The Tropics, Were It Not That Armies Can Cross Them With Greater Facility, As Their Innumerable Troops Of Horses And Mules And Herds Of Oxen Furnish Every Means Of Conveyance And Subsistence.

What we have seen of the power of man struggling against the force of nature in Gaul, in Germany and recently (but still beyond the tropics) in the United States, scarcely affords any just measure of what we may expect from the progress of civilization in the torrid zone.

Forests disappear but very slowly by fire and the axe when the trunks of trees are from eight to ten feet in diameter; when in falling they rest one upon another, and the wood, moistened by almost continual rains, is excessively hard. The planters who inhabit the Llanos or Pampas do not generally admit the possibility of subjecting the soil to cultivation; it is a problem not yet solved. Most of the savannahs of Venezuela have not the same advantage as those of North America. The latter are traversed longitudinally by three great rivers, the Missouri, the Arkansas, and the Red River of Nachitoches; the savannahs of Araura, Calabozo, and Pao are crossed in a transverse direction only by the tributary streams of the Orinoco, the most westerly of which (the Cari, the Pao, the Acaru, and the Manapire) have very little water in the season of drought. These streams scarcely flow at all toward the north; so that in the centre of the Llanos there remain vast tracts of land called bancos and mesas* frightfully parched. (* The Spanish words banco and mesa signify literally bench and table. In the Llanos of South America little elevations rising slightly above the general elevation of the plain are called bancos and mesas from their supposed resemblance to benches and tables.) The eastern parts, fertilized by the Portuguesa, the Masparro, and the Orivante, and by the tributary streams of those three rivers, are most susceptible of cultivation. The soil is sand mixed with clay, covering a bed of quartz pebbles. The vegetable mould, the principal source of the nutrition of plants, is everywhere extremely thin. It is scarcely augmented by the fall of the leaves, which, in the forests of the torrid zone, is less periodically regular than in temperate climates. During thousands of years the Llanos have been destitute of trees and brushwood; a few scattered palms in the savannah add little to that hydruret of carbon, that extractive matter, which, according to the experiments of Saussure, Davy, and Braconnot, gives fertility to the soil. The social plants which almost exclusively predominate in the steppes, are monocotyledons; and it is known how much grasses impoverish the soil into which their fibrous roots penetrate. This action of the killingias, paspalums and cenchri, which form the turf, is everywhere the same; but where the rock is ready to pierce the earth this varies according as it rests on red sandstone, or on compact limestone and gypsum; it varies according as periodical inundations accumulate mud on the lower grounds or as the shock of the waters carries away from the small elevations the little soil that has covered them.

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