The limestone is composed of calcite and fossils of marine creatures. It is so dark in appearance that it was marketed in the 18th and 19th century as "black marble" and was used for the construction of the U.S. Capitol building and the National Gallery of Art. Structures made of the stone still visible on the island are the Isle La Motte Public Library, the Isle La Motte Methodist Church, Isle La Motte Historical Society (formerly the South Stone School House), ruins of the Fisk House at Fisk Farm, and the original Fisk House (once owned by Lieutenant Governor Nelson Fisk).