Sir Charles Lyell, a noted British geologist, visited South Carolina in 1842 and named the bedrock limestone underlying this area the Santee Limestone. He estimated that the Santee Limestone dated from the Eocene epoch, more than 40 million years ago. Many kinds of fossil marine animals are embedded in it, and in solution the limestone forms sinks and subsurface caves. Eutaw Springs, now flooded by Lake Marion, flowed from such channels. An impure limestone-based clay known as Cooper Marl overlies the Santee Limestone throughout the lowcountry, and both are primary raw materials in portland cement produced nearby.