The Encyclopedia Americana (1920)/Cliff

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CLIFF. Nearly vertical rock walls are formed in a variety of ways by natural means. In the development of a drainage system in any high-lying tract of country, ravines, gorges, and canyons are formed by the down-cutting streams, as Watkins Glen, N. Y., the gorge of the Niagara River and the Grand Canyon of the Colorado. After long erosion the softer rocks may be removed, leaving the harder with steep faces standing above the surrounding country, as at the Delaware Water Gap, in the Catskills and many places in the Appalachian Mountains. In high mountains glaciers dig out deep channels. Cliffs formed in these ways may be called cliffs of erosion. Where a high coast borders any large body of water the waves eating into the land form cliffs, as on the northern shores of Scotland, southern England, the coast of Maine and elsewhere. Such cliffs may be called sea cliffs. Cliffs may also be formed by the rock fractures known as “faults,” where the rocks on one side of a fracture rise faster than they are worn down by weathering. Such cliffs are not uncommon; they are found in many parts of the West, being especially prominent in arid regions like the Colorado plateau, where weathering is slow. Such cliffs may be called “fault cliffs.”