continent: Geology and Topography of the Continents

Geologically and topographically the continents are exceedingly complex and variable in detail, yet certain large-scale structural and topographic features appear to be common to all. The continents are composed mainly of granitic rocks and measure an average of 25 mi (40 km) thick. Underlying the ocean are denser basaltic rocks measuring about 4 mi (7 km) thick. Basaltic rocks may also form the lower portions of the continental crust in many regions. The upper and lower crust zones deform by different mechanisms; the upper crust is brittle and deforms by faulting (see fault) while the lower crust is ductile and capable of flow. The crust and the solid upper mantle form the lithosphere.

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

The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2024, Columbia University Press. All rights reserved.

See more Encyclopedia articles on: Geology and Oceanography