In geological terms, ‘‘orogeny’’ refers to the process of mountain building. The Appalachian Orogeny, previously called the Appalachian Revolution, describes the collective geological events that produced the belt of folded, faulted, and metamorphosed rock that stretches from Newfoundland to northern Alabama. All of West Virginia is included within this belt. It was produced during the ancient collision of the North American, European, and African continents.
The current Appalachian Mountains are an erosional remnant of mountains formed millions of years ago during the Appalachian Orogeny. These ancestral mountains were much more extensive and probably appeared something like today’s Himalayas or Canadian Rockies. They were eroded nearly flat, then split in two during the opening of the Atlantic Ocean, so that rocks and structures of similar age can be found on both sides of the ocean, in North America, Europe, and Africa. In North America, these remnant structures were uplifted and eroded again to form the present Appalachians. They are pale by comparison to their rugged ancestors.
The Appalachian Orogeny is generally separated into three periods, referred to as the Taconic, Acadian, and Alleghenian orogenies. In West Virginia, the evidence for these three events is limited to the thick sedimentary rock units that were deposited in the basin that formed to the west of the mountains.
The Taconic Orogeny is named after the Taconic Mountains of New York. The Taconic Orogeny is thought to be the result of the collision of a volcanic arc with the east coast of North America. Extensive folding and metamorphism from New England to southeastern Pennsylvania is attributed to this event. In West Virginia, the evidence is limited to a great wedge of Ordovician and Silurian sedimentary rocks, including the Tuscarora Sandstone and the underlying red mudstones of the Juniata Formation, both of which are exposed on North Fork Mountain along U.S. 33 in Pendleton County. Seneca Rocks is a spectacular Tuscarora formation.
The Acadian Orogeny is named for Acadia, a historical term for the Canadian Maritime provinces, and resulted from deformed and metamorphosed sedimentary rocks. Extensive metamorphism and deformation in the Late Silurian and Devonian eras produced deposits of sedimentary rock often referred to as the Catskill Delta. In West Virginia, these sediments are exposed on U.S. 33 east of Elkins.
The Allegheny Orogeny is named after the high ridges of the Allegheny Mountains in Pennsylvania and West Virginia. The evidence for this event is two-fold. The thick Pennsylvanian Era sediments of West Virginia, including most of the commercial coal beds, were deposited along the ancient coastal plain that flanked the highlands to the east. These sediments consist of alternating terrestrial and marine deposits and are found throughout West Virginia west of the Allegheny Front. The other evidence can be seen in the Ridge and Valley physiographic province, which displays sedimentary rock deposited during the previous two orogenic events that were folded and faulted during the Alleghenian event.
Written by David Matchen
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Hatcher, R. D. Jr., W. A. Thomas & G. W. Viele, eds. The Appalachian-Ouachita Orogen in the United States. Boulder: Geological Society of America, 1989.
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