The basement rock of Jamesland, exposed in much of the Blue Ridge and inner Piedmont, is well over a billion years old. This rock was transformed by intense heat and pressure during the Grenville orogeny (mountain-building event), when the continents piled up to create the supercontinent Rodinia. The lava flows of the Blue Ridge’s Catoctin formation testify to the giant rifts that opened as that supercontinent began to split apart in the late Proterozoic, birthing a new ocean called the Iapetus. Around this time came the “Snowball Earth” period, when our region and much of the planet may have been covered in ice.
A period of quiet followed as much of the continent was covered by the warm, shallow Sauk Sea. Marine life, including the earliest animals, thrived, and their shells helped form vast deposits of limestone—like those in our Great Valley—during the Cambrian and Ordovician. But another series of violent collisions was on its way, beginning with the Taconic and Acadian orogenies, during which island arcs and continental fragments were welded to our east coast to assemble the outer Piedmont. These events thrust up a mountain range that shed massive blankets of sediment to the west, which are now exposed as the shales and sandstones of the Ridge and Valley region.
The crowning blow came during the Carboniferous period, as the Alleghanian orogeny sutured North America to Africa as part of the new supercontinent of Pangea. The granite boulders at the Falls of the James, made from magma churning far below the crashing continents, bear witness to this cataclysmic event that rearranged all of our region’s existing rocks. The Blue Ridge and Piedmont were shoved as far as 100 miles westward to where they sit today, while the Ridge and Valley was tipped on its side, so that layers of harder sandstone now stick out as vertical ridges from the softer, eroded limestone and shale.
Once again Jamesland was now covered by towering mountains, at the dry heart of an enormous landmass. These mountains slowly eroded into other, distant regions, leaving few records here of the era. That began to change in the Triassic, when Pangea started to come apart at the seams. The Richmond Basin is one of many areas in the resulting rift valley where swampy conditions helped to accumulate vertebrate fossils—as well as coal from the lush vegetation, later to be mined at Midlothian. When the infant Atlantic opened up around 200 million years ago, a precursor to today’s James River was finally able to take shape. Dinosaurs roamed the shores of the new ocean as the river helped to wear away the mighty proto-Appalachians.
By the time of the dinosaurs’ extinction, that job was mostly done and our region was a relatively flat plain. During the Cenozoic the region enjoyed a burst of uplift, producing the mountains we know today, and the river kept pace by cutting through the rising rock.
Although the last fifty million years here have been quiet as far as tectonic drama, they have been punctuated by major events nonetheless. During the Eocene a giant meteor, the biggest ever to hit the United States, crashed into the Atlantic just offshore from Jamesland. This impact may have sent a tsunami surging all the way to the Blue Ridge, and its crater shaped what became the Chesapeake Bay.
Meanwhile, swings in the climate caused sea levels to see-saw, culminating in the ice ages of the Pleistocene when glaciers advanced as far south as Pennsylvania. Spruce forests and parklands like those of modern Canada covered much of our region, and large animals like mastodons and ground sloths abounded. These provided good hunting for Jamesland’s first humans, who arrived sometime around 18,000 years ago (as attested by the finds at the nearby Cactus Hill site)—either by way of the Bering land bridge, or by way of boats across the Pacific.
Scroll to the bottom of the page to see a map of Jamesland’s major geological formations (click the map to access the full-size version). Or visit our interactive map to explore this data in more detail.
