Plain,

Plain, a geographical term which hardly admits of precise definition. It is generally applied to extensive tracts of approximately level or undulating country, which occur at less than 1000 feet above the sea. Broad areas of similar character at higher elevations are usually termed Tablelands (q.v.) or Plateaus. This is the general rule, but when the surface of a plain slopes gradually upwards to heights of several thousand feet, the whole tract is still called a plain. As an example may be cited the great plains east of the Rocky Mountains, which fall imperceptibly away towards the east from an elevation of 6000 feet or so. Among the most characteristic plains are the wide alluvial lands of the greater rivers. But the term is extended to such low-lying regions as central Ireland, the Midlands of England, middle Europe, &c.—regions which have no great elevation and present a gently undulating surface, interrupted now and again by isolated hills, and lines of cliffs and escarpments. From the same point of view the whole interior of North America lying between the Rocky Mountains in the west and the Alleghany and White Mountains in the east, and extending from the Gulf of Mexico to the shores of the Arctic Ocean, may be called a plain. So likewise more than half of Europe is a plain that is continued into Asia and extends northward over vast regions of that continent. Plains necessarily differ much in appearance according to the nature of soil and climate, from the dreary, sandy wastes of north Africa to the luxuriant fertility of the South American silvas. Wide regions of comparatively level ground in each of the great continents have acquired various names, such as the Steppes and Tundras of eastern Europe and Asia, the Deserts of Arabia and Africa, the Savannas and Prairies of North America, and the Llanos, Pampas, and Silvas of South America. See DESERT.