Plains occupy nearly one-half of the surface of the continents. They are
most extensive and unbroken on the Arctic slopes of the Old World, and
in the interior of the two Americas.
Treeless plains, whose vegetation consists of grasses and other
herbaceous plants, or stunted shrubs, occur in every continent, and are
designated by a variety of terms. Wherever treeless plains are subject
to periodical rains, they lose their verdure in the season of drought,
and assume the aspect of a desert; but they resume their freshness on
the return of the rain, and many are adorned with a great variety of
beautiful flowers.
PLAINS OF THE OLD WORLD. The great Siberian plain extends from the
northeastern extremity of Asia to the Ural Mountains and Caspian Sea;
and the European plain stretches from the Ural westward, through Russia
and North Germany, to the lowlands of Holland.
The plains of the Caspian Sea and western Siberia are dreary steppes,
covered with coarse grasses, often growing in tufts, alternating with
patches of heather, furze, dwarf birch, and other stunted shrubs; or
old sea bottom, covered with salt efflorescence. Immense reaches of flat
country, near the Arctic shores of Asia and Europe, consist of frozen
marshes, called tundras, where mosses and lichens are almost the only
vegetation. Those of eastern Europe and Asia are denominated steppes;
while more limited treeless regions in western Europe are called landes
and heaths.
On the alluvial plains of the Old World, civilization began and
developed; and their inexhaustible fertility supplied the wants of the
most populous nations of antiquity. The great centers of ancient
civilization in Egypt, China, India and Babylonia, all had their growth
in alluvial plains, built up and fertilized by the mighty rivers which
traverse those countries.
PLAINS OF THE NEW WORLD. In North America the great _Central Plain_
extends, with but slight interruptions, from the Arctic shores to the
Gulf of Mexico. The fertile, treeless plains are termed “prairies”
(meadows), while the sterile ones, east of the Rocky Mountains, are
known as “the plains.” There are vast cane fields and forests in the
lower Mississippi Valley.
In South America the plains of the Orinoco basin, the _Selvas_ of the
Amazon, and the _Pampas_ of the La Plata, form an uninterrupted series
of lowlands which, continued by the plains of Patagonia to the southern
extremity of the continent, extend over a distance of three thousand
five hundred miles from north to south. The Spanish term “llano”
(plain), and the Peruvian “pampa,” designate the treeless plains of the
Orinoco and La Plata basins. The Llanos of the Orinoco, during one-half
of the year are covered by the richest pasturage, bright with flowers,
but during the other half are a parched waste. The Selvas of the Amazon,
a luxuriant forest, cover more than a million square miles; and the
treeless Pampas, with their tall grasses and thickets of clover and
thistles, illustrate the endless richness and variety of nature.
Alluvial and marine plains generally have but a slight altitude, while
the undulating plains are sometimes considerably elevated. The
Mississippi Valley, at St. Louis, one thousand miles from the ocean, is
hardly four hundred feet above the sea-level; and the Amazon, at an
equal distance from the sea, does not reach two hundred and fifty feet.
The marine plains adjacent to the Caspian and Aral seas are still lower,
the larger portion being below the sea-level.