ALLEGHENIAN OROGENY

a mountain-building event that affected the Appalachian Geosyncline in late Paleozoic (Permian) time, from about 300 million to 250 million years ago. The term Appalachian Revolution formerly was applied to this event. The Alleghenian orogeny is most pronounced in the central and southern Appalachians and produced the compressional folding and faulting of the Ridge and Valley Province, the westward thrusting of the Blue Ridge over Valley and Ridge rocks, and folding and minor metamorphism and igneous intrusion in the Piedmont Province. Evidence of the Alleghenian orogeny is less prominent in the northern Appalachians, but late Paleozoic folding and igneous intrusions are present along the east coast of New England and parts of the eastern Maritime Provinces of Canada. The Alleghenian orogeny may have resulted from the collision of the central and southern Appalachian continental margin with that of North Africa in late Paleozoic time.