Plateaus are situated either between two lofty mountain chains, which
form their margins, or descend by successive terraces to the nearest
seas; or they pass, by gradations, from the base of high mountains to
the low plains in the interior of the continents.
The Great American Basin, between the Rocky and Sierra Nevada Mountains,
and the plateau of Tibet, between the Himalaya and Kuenlun mountains,
are examples of the first position; and the table-land of Mexico, of the
second. The third is seen in the high plains at the eastern foot of the
Rocky Mountains, which descend from an altitude of five thousand or six
thousand feet, at the foot of the mountains, to the low plains of the
Mississippi basin.
The plateaus most remarkable for their elevation are, Tibet, from ten
thousand to eighteen thousand feet above the sea; and the elongated
valley-like highlands, from ten thousand to thirteen thousand feet high,
between the two chains of the Andes, in South America. East Turkestan
and Mongolia, in central Asia; the plateau of Iran, in western Asia;
Abyssinia, and the vast plateau which occupies all the southern part of
Africa; and the broad table-land which fills the western half of North
America with a continuous mass of high land, range in height from four
thousand to eight thousand feet.
The great peninsulas of Deccan, Arabia, Asia-Minor and Spain, the
central plateau of France, and those of Switzerland, Bavaria, and
Transylvania, vary from one thousand to four thousand feet in elevation.