The present-day salt-marsh estuaries of Georgia are shallow-water bodies having expanses of intertidal realms as the result of a relatively large tidal range of 2 m. Three characteristic macro-invertebrate assemblages are distinguished in the intertidal realms: ( 1) an assemblage of vagrant benthos including numerous different clams and snails lives in and upon the sediments of the lower intertidal to shallow subtidal zone; ( 2) the oyster biocoenosis consists chiefly of sessile benthos associated with colonies of Crassostrea virginica in the lower intertidal zone; ( 3) the tidal-marsh assemblage is confined to grassy marshes of the higher intertidal zone; molluscs are represented by Littorina irrorata and Modiolus demissus. Processes of sedimentation dominate over erosional processes in the estuaries. Detrital sand, silt and clay, together with organic debris and skeletal carbonates, contribute to the accumulations. Destruction of shell remains is promoted by marine borers, particularly Cliona, and by chemical leaching. Especially in tidal-marsh soils shells are subject to dissolution unless they are buried rapidly. In a marsh sediment calcitic concretions were found, which formed around severely leached shell remains. Where shells within a reduced sediment are leached, the local rise in pH often promotes precipitation of iron monosulfide, which eventually is converted into pyrite. Once included in fine-grained sediments, however, shells have a good chance of becoming preserved, especially if they are thick and consist of calcite rather than aragonite. Oyster shells are thus particularly durable. Because of their local abundance, oysters yield sizable shell deposits, including reefs, reworked deposits, and cheniers. Reworked accumulations of considerable extent occur in intertidal and shallow subtidal realms, usually in the vicinity of major tidal inlets. The accumulations, which form lenticular bodies of varying lateral extent, are interbedded with detrital sediments. The matrix of the shell concentrates is generally muddy, but can also be sandy or conglomeratic. Oyster beds of Late Pleistocene and mid-Tertiary ages in Georgia are similar to the recent ones.