The Plain is that low land which usually has a height above 160 meters; but many plains above 400 meters exist in many places. Some plains like that of Netherlands are below sea level. The Jordan's valley plains are below sea level by more than fifty meters.
Classification of Plains. Plains have been classified in many ways but the following classifications have found acceptability:
(A) Structural Plains
These plains were formed by the play of endogenetic forces. These forces affect land and sea areas and, therefore, the plain so produced have been further sub-divided.
(i) Plains of Horizontal Layers - These plains consist of horizontal layers. At places, the layers of these plains are little disturbed or warped. For example, Russian Platform, the Central West plains of North America are some such plains.
(ii) Plains or Emergence - These are the plains which have emerged out as a result of the uplift of seacoast. Before emergence, these areas received deposition of sediments. Such plains are leveled areas. Examples-The eastern and gulf coast of the U.S.A., the western coast of India, etc.
(B) Erosional Plains
Plains are formed by erosional activities. The running water, glaciers, winds and sea waves mainly take part in erosional activities. Hence, the erosional plains have been subdivided on the basis of erosional agents.
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