The Sandersville Limestone is a micritic limestone with diverse molluscan, echinoderm and vertebrate fauna at its type locality near Sandersville, Georgia. The age for this unit has been determined to be middle Jacksonian stage of the Eocene Series by bryozoa, foraminifera, and various echinoderm fossils. The echinoid species Periarchus quinquefarius is the established index fossil for this unit. New exposures of the Sandersville member east and west of the type locality have now been correlated based on this index fossil and an abundant bryozoa assemblage. West of the type locality what has been called the “Cooper marl,” a micritic limestone, is correlated to the Sandersville Limestone member based on the index fossils.

In the new exposures east of Sandersville, the micritic cement is replaced by silica and the lithology ranges from a micrite with chert nodules to a very competent ferruginous chert . Petrographic and transmission electron microscopy analysis of the chert reveals the silica precipitated epitaxial to well preserved filamentous microfossils. Carbonate dissolution and iron-silica replacement appears to be a localized pedogenic alteration produced within the weathering profile when silica was leached from the overlying Tobacco Road Sandstone. A middle Jacksonian shallow marine depositional environment is interpreted for the Sandersville Limestone member of the Tobacco Road Sandstone on the Coastal Plain of Georgia.