Geologists today may be divided into two schools regarding the origin of regions of comparatively smooth surface from which a large volume of overlying rocks have been removed. These regions occur under two conditions: First, as buried “oldlands” on which an unconformable cover of later formations has been deposited, the oldlands being how more or less locally revealed by the dissection or stripping of the cover; second, as uplands or plateaus whose once even surface is now more or less roughened by the erosion of valleys.

The older school, now represented chiefly by English geologists, follows the theory of Ramsay, and regards these even oldlands as plains of marine denudation. The newer school, represented chiefly by American geologists, but also by a number of continental European geologists, may be said to follow Powell, who first emphatically called attention to the possibility of producing plains by long continued subaerial depudation. . . .

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