continent: Plateaus, Shields, and Mountains

Generally, the continents contain vast interior plains or plateaus, underlain by a basement complex of igneous and metamorphic rocks of Precambrian age. In some places, the basement complex is exposed at the surface, where it is often called the shield, or craton. The interior of shield areas contain some of the oldest rocks known on the earth's surface. The Canadian Shield area of E Canada is the exposed basement complex of North America. Portions of shield areas are covered with veneers of flat-lying sedimentary rocks of younger age. The interior plains of the continents are frequently bounded on one or more sides by ranges of mountains. These mountains have been intricately folded and faulted. They also display abundant evidence of volcanic activity, large-scale igneous intrusions, and deformation structures associated with convergent plate movement. In the United States the folded Appalachian Mts. lie to the east of the interior plains and were caused mainly by the collision of two continents. The Rocky Mts. are to the west, formed by huge igneous masses that pushed upward through overlying sedimentary rocks, which were then eroded away.

Sections in this article:

• Introduction
• Theories of Continental Formation
• Floating Continents and Isostasy
• Plateaus, Shields, and Mountains
• Geology and Topography of the Continents
• Geographic Distribution of the Continents

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