Richmond’s Diatom Deposits

Few people know that this city lies atop one of the most diverse diatom deposits in the world. Diatoms are single-cellular aquatic plants that have been fossilized—quite beautifully—within their silica walls. The diatoms pictured are leftover from the era 5 million years ago, when Richmond lay under a shallow sea.

Our diatom deposits first gained attention through the efforts of the Richmond Microscopical Society, founded in 1880 by local microscope hobbyists. They had been aware of diatoms in the soil here, although it was not until the C&O Railroad attempted to dig a tunnel downtown in the 1890s that the sheer diversity of Richmond’s diatoms became clear.

Thomas Christian, one of the founding members of the society, lived near the project dig beneath 8th Street. He and his daughter would venture into the construction zone every evening to take samples of the day’s excavated earth.  He spent much of his time arranging different species of diatoms into beautiful and elaborate slides, such as the one pictured above.

Soon, his findings attracted the attention of the Smithsonian and the world.  The futile digging of the 8th Street tunnel soon became a national joke, as the slippery earth repeatedly caved in. Diatomaceous earth—earth rich in diatoms—is very unstable. Eventually, the railroad had to abandon the project, though the lessons of Richmond’s diatom-rich soil were quickly forgotten, with tragic results. When C&O attempted to repair the Church Hill Tunnel in 1925, the famous cave-in that entombed a work engine and at least three workers was due to the diatom-rich clay.