Two physiographic provinces meet under this metro, and the wheel can tell
Richmond sits on the fall line, Piedmont material west and Coastal Plain material east. No primary source for that boundary was retrievable; the evidence here is three USDA-NRCS series descriptions.
West, the benchmark is Cecil: residuum weathered from felsic igneous and high-grade metamorphic rocks, with a subsoil of 35 to 70 percent clay and saprolite from around 50 inches. Wet, that subsoil smears instead of cutting, spoil comes out as heavy clay-and-wood paste not free chip, and the hole holds water, though saprolite rather than rock lies beneath, so nothing refuses the wheel.
East, Bourne formed in stratified marine and fluvial deposits: bedded sand and gravel that cuts fast and dulls teeth faster, over a brittle fragipan commonly 18 to 35 inches down, which is why a finished hole out east can pond.
Along the James, State-series alluvium on stream terraces is listed in both the Southern Piedmont and Southern Coastal Plain land resource areas, and terrace ground is where rounded gravel turns up in a loamy matrix: soft cutting, then a cobble.