Diapirs, sensu stricto, are bodies of sedimentary ma terial which have pierced (or appear to have pierced) overlying material as a result of their mobility at comparatively low temperatures. They are composed of evaporites, shales, mud, etc. and range in size literally from molehills to mountains and in age from Precambrian to Recent. They occur associated with marine as well as continental sedimentary sequences and in areas which have been subject to intense tectonic deformation, virtually no deformation other than basin subsidence or to all amounts of deformation in between. As a result of the numerous possible combinations of these different attributes, diapirs of many types occur dispersed over much of the earth. Among those structures which are considered to be forms of diapirs, some of the best known are the diapiric folds of Roumania; the piercement salt domes of the Middle East, the Gulf Coast of Mexico, the United States, and Russia; the salt diapirs of Australia, Europe, and South America; the salt stocks and salt walls of Germany; some of the salt anticlines of the Canadian Maritime Provinces and the western United States; the gypsum diapirs of the Canadian

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Arctic Islands; the clay diapirs of Borneo, Italy, and the Black Sea area; the mud volcanoes of Colombia and Trinidad; and the intrusive shale domes of the Gulf Coast of the United States.

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