Physiography Topics

Quick Tour of the Provinces

Click on label to find read the details.

• Coastal Plain

• Extends from New York to the Gulf of Mexico.

• Contains flat topography with the highest elevations on the west (500 feet) to sea level. The gradient is only a few feet per mile, making it appear flat to the human eye in most places.

• It is composed of sedimentary rocks that are relatively young (Cretacepis to recent). The sediments are arranged in near-horizontal layers that are composed mostly of sand, silt, and mud . The layers record many rises and falls of sea level. During times of highest sea level, the beach extended west to at least Richmond.

• During times of high sea level, the sediments were mostly deposited in shallow water that indicates beach (sand or near shore) or continental shelf (mud), and during times of low sea level, the Coastal Plain and parts of the continental shelf were exposed to land.

• The Coastal Plain formed when the Atlantic Ocean opened as Pangaea split at the same time that the Ancient Appalachian mountains were eroding. This provided a huge area of eroding rocks that supplied the sediment that formed the continental shelf on the edge of the Atlantic Ocean.

• The rocks contain many fossil layers, all late Mesozoic to Cenozoic age, composed of clams, snails, sharks teeth, whale bones, and more that are consistent with shallow water ocean environments.

• The Fall Line

• The Fall Line is the distinctive boundary between the Coastal Plain and the Piedmont.

• Interstate 95, which connects the cities of Washington D.C., Fredericksburg, Richmond, and Petersburg, roughly follows the Fall Line in Virginia.

• On the Coastal Plain side, the land is flat, and the rivers are easily navigable. The rocks are sedimentary and are Mesozoic to Cenozoic in age.

• On the Piedmont side, the land is hilly, the rivers have rapids, and the rocks are igneous and metamorphic and are Precambrian to Paleozoic in age.

• In river valley walls and quarries along the Fall Line, geologists can see that the Coastal Plain sediments lie on top of Piedmont rocks, making the Piedmont the "basement" and the Coastal Plain the "cover" sediments. Geologists know from drill borings that Piedmont type rocks extend eastward underneath nearly all of the Coastal Plain rocks.

• The Appalachian Mountains

• The Piedmont, Blue Ridge, and Valley and Ridge provinces were part of the ancestral Appalachians. There is abundant evidence of deformation in the three provinces, and igneous activity and metamorphism in the Piedmont and Blue Ridge.

• The differences between the provinces are indicated by the type and age of rocks, and how they have been eroded.

• The ancestral Appalachian Mountains were at their height during the Permian period. The modern Appalachians that we see now are the result of the deep erosion of the ancestral mountains.

• The ridges of the modern Appalachians are composed of harder, more resistant rock. The lowlands or valleys are composed of softer easily eroded rock.

• Piedmont

• The Piedmont is famous for its low, rolling landscape.

• The geology is complex and is composed of regions of differing rocks called terranes, with each terrane containing its own set of rocks with its own geologic history and ages.

• The ages of the rocks vary from Precambrian to Mississippian. The rocks vary from metamorphic to igneous intrusions to belts of ancient volcanoes, depending on which terrane you are in.

• The belts of ancient volcanoes contain deposits of copper and gold that were important to Virginia's history.

• Thick layers of soil now cover much of the Piedmont, making study of the rocks a challenge to geologists.

• Blue Ridge

• The Blue Ridge contains the oldest rocks in Virginia as well as the highest elevations in the state and with rugged slopes.

• The rocks are range from Precambrian (1.1 billion years) to Cambrian, making them generally older than Piedmont rocks. They are a combination of metamorphic, igneous intrusive, and ancient volcanic rocks.

• North of Roanoke, the geomorphic Blue Ridge is a narrow ridge that is followed by Skyline Drive and the Blue Ridge Parkway, providing spectacular view both to the east and west.

• South of Roanoke, the Blue Ridge has a distinctive escarpment on its east site, with a highland of rolling hills on the west side. The Blue Ridge Parkway follows the top of the escarpment.

• Valley and Ridge

• The Valley and Ridge is composed of folded and faulted sedimentary rocks of Paleozoic age. The tilted rock layers cause the edges of the sedimentary layers to be exposed on the ground. Long ridges are found where the edges of resistant rock layers such as sandstone are exposed. Valleys form where soft shale or soluble carbonate layers are found.

• The sediments were deposited mostly in a shallow sea bed. Since Coastal Plain rocks were also deposited in shallow water, one can find similar rocks such as beach sandstones and offshore shales.

• However, the Valley and Ridge rocks have some important differences with the Coastal Plain:

° They are much older than the Coastal Plain and contain fossils of animal groups that are rare today or extinct such as trilobites, brachiopods and crinoids.

° The sedimentary layers are tilted, folded, and faulted, indicating they were deposited before the Ancestral Appalachians existed and they were deformed during the building of the mountains.

° There were times of warm, tropical climates during the deposition of the rocks as evidenced by thick carbonate (limestone and dolostone) rocks. The carbonate rocks form in broad belts of easily eroded soluble rocks to form wide valleys such as the Shenandoah Valley and the New River Valley. Interstate 81 follows this belt from Winchester to Bristol, Va.

° Caves and karst topography are features found in the carbonate valleys.

• Appalachian Plateaus

• The Appalachian Plateau province forms the western-most of the geologic provinces and are only found in the far southwestern counties, primarily Buchanan, Dickenson, and Wise Counties.

• The rocks are similar in age and type to Valley and Ridge rocks. However, unlike the Valley and Ridge, these rocks are not deformed and they are found in horizontal layers. The sediments range in age from Cambrian to Pennsylvanian forming a stack of layers with the oldest rocks on the bottorm, but only the younger layers at the top, primarily Mississippian and Pennsylvanian are exposed on the ground.

• The fact that that they were never deformed during the building of the ancestral Appalachians indicates that they were not actually in the ancient mountains, and were positioned just to the west of the edge of the mountains in the bordering lowlands.

• The area today is quite mountainous, but the landscape is caused by modern river and stream erosion cutting deep valleys into the bedrock.

• The sandstones, shales, siltstones, and coal indicate shallow water, coastal environments with rivers and swamps during Mississippian and Pennsylvanian time. The coal is a major source of industry and energy for southwest Virginia.

• Each of Virginia’s five physiographic provinces has distinct geologic features that are different from the geologic features of other provinces.

Geologic cross section of Virginia. Each province has distinct geology.