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The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.
(or effusive rocks), igneous rocks which, like modern lavas, poured out onto the surface of the earth through volcanic vents or cracks in the earth’s crust and solidified in the form of flows, sheets, and domes.
The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.