Rivers and Watersheds - The Geology of Virginia
T H E   J A M E S


Bullpasture Gorge,
Highland County

T

he James River flows across four of Virginia’s physiographic provinces draining approximate one fourth of the Commonwealth. The James rises in the high country along the Allegheny Mountains of western Virginia. An array of small streams tumble off the flanks of Monterey Mountain, Jack Mountain, and Bullpasture Mountain converging to form to southwest-flowing rivers such as the Jackson, Bullpasture, and Cowpasture. These streams occupy valleys underlain by less resistant layers such as Devonian shales, shaley limestones, and limestone. The upper James River basin is characterized by a trellised drainage pattern typical of the Valley & Ridge province. Major streams flow down strike valleys and are joined by short tributaries that cascade off northeast-southwest trending ridges. Gorges, such as the Bullpasture, occur where rivers cut through mountains and pass from one valley to another. At Iron Gate, the Jackson and Cowpasture meet and the James River takes its name. In the Valley & Ridge the James is 30 to 50 meters wide with a gradient of ~1 meter per kilometer. At Eagle Rock the James cuts a dramatic gap in Rathole Hole Mountain and Crawford Mountain.

James River Gorge, SE of Glasgow
James River Gorge,
southeast of Glasgow

The James reaches the Great Valley at Buchanan and meanders to the northeast along the edge of the Blue Ridge province. At Glasgow the Maury River joins the James: here the river turns to the east and enters the Blue Ridge. The James cuts a 15 kilometer, 700 meter deep gorge through the Blue Ridge exposing siliclastic rocks of the Chilhowee Group and the underlying Proterozoic basement gneisses. In the James River gorge the gradient steepens to 8 meters per kilometer and significant rapids (such as Balcony Falls) occur. At Big Island the James River emerges from the Blue Ridge Mountains and flows to the southeast across basement rocks of the Blue Ridge anticlinorium. Although the James drops 50 meters in the 30 kilometers from Big Island to Lynchburg much of that drop is consumed behind five dams that block the river over this section.

The James turning NE near Lynchburg
The James turning NE along
the less resistant Evington Group.
Lynchburg is in the SW corner.

A few kilometers east of Lynchburg the river turns to the northeast and flows for over 100 kilometers along this course. Between Lynchburg and Howardsville the James River flows over phyllites and schists of the Paleozoic Evington Group. The Evington Group forms a weak belt of rock in the western Piedmont and the James may take advantage of these weaknesses. Over this stretch the James River has a modest gradient of 0.5-1.0 meters per kilometer with a few riffles breaking long stretches of flat water. The Tye and Rockfish Rivers are significant tributaries that join the James River from the northwest. Between Howardsville and Scottsville the James River crosses a Mesozoic basin with coarse-grained conglomerates and arkosic sandstones.

The Falls of the James at Richmond
Falls of the James at
the Fall Zone, Richmond

The river turns to the east at Scottsville and crosses the remainder of the Piedmont. Along this stretch the river is approximately two hundred meters wide and gently meanders with a grade of 0.2-0.5 meters per kilometer. Over the 100 kilometers from Scottsville to western Richmond the James crosses multiple geologic terranes and several major fault zones, but these features are subtle and not well expressed in the river. At Richmond the James begins its final descent to the Coastal Plain in the Fall Zone. In 20 kilometers the river drops 30 meters and major rapids occur. The late Paleozoic Petersburg granite crops out along the Fall Zone in Richmond. Tremendous potholes have been scoured in the bedrock channel and are well exposed in the river channel on the south side of Belle Island.

James River scarp face
Pleistocene sediment scarp,
Surry County

On the eastern side of Richmond the James reaches sea level and becomes a tidal river. Still 100 kilometers from the sea, the James is primarily a freshwater river. The river flows south from Richmond to Hopewell. Cretaceous sedimentary rocks are exposed along some of the James River bluffs and record high stands of the Atlantic Ocean. At Hopewell the Appomattox River joins the James. From Hopewell the river flows east and dramatically widens becoming a broad 1-3 km wide estuary. The flat-lying country along the river is underlain primarily by Pleistocene sediments deposited by the ancient James River during higher stands of sea level. At Hampton Roads the James meets the Chesapeake Bay.




(1/5/2000)