30,000 to 15,000 years ago, during the last glacial maximum, much of New England lay under the massive Laurentide Ice Sheet. At its maximum, it was several kilometers thick. All of New England north of the Pennsylvania turnpike was under permanent ice, but this ice sheet extended as further south from time to time. The ice sheet denuded all the ancient soils, exposed and the eroded the underlying bedrock, and then retreated. A remnant of the Laurentide Ice Sheet remains to this day - the Barnes Ice Cap on Baffin Island. As it retreated, it left behind a giant pile of rubble including the clay and silt which would eventually become the backbone of the colonial economy, and the cobbles and boulders that would eventually become the stone walls all across New England.
Although northern Virginia was never under ice (except or Mount Rogers) it commonly froze, fracturing and breaking apart bedrock and receiving sediment from the glacial outwash.