In the southeastern United States, kaolinite is the dominant clay mineral and hornblende the dominant heavy mineral in the Piedmont Province. Montmorillonite is the major clay mineral in the Coastal Plain. Only minor amounts of hornblende are found in this latter province. Illite is the dominant clay mineral in the Continental Shelf sediments off the coast of this area. Rivers draining the two continental source areas carry diagnostic suites of sediments. In the rivers and estuaries, the ratio kaolinite/montmorillonite serves to identify the relative proportion of clay size sediment derived from the two source areas. Hornblende can be used to follow the dispersal of sand-size materials. Illite can be used to determine the off-shore contribution to the estuaries. Much of the sediments in Port Royal Sound, fed only by small Coastal Plain rivers, is carried in from the Continental Shelf by flood tides. The distribution of the various minerals suggests that Coriolis force is a major factor in determining the dispersal pattern in this estuary and in Charleston Harbor. Both bottom and suspended sediments from Charleston Harbor and vicinity were studied. This information was used in conjunction with salinity and velocity data to determine the source of the sediment and the circulation and depositional pattern inside and outside the harbor. This study shows the effects of partially diverting a major Piedmont River (Santee) into a harbor which was formerly entirely within a Coastal Plain drainage basin. A study of Brunswick Harbor, which is situated within a Coastal Plain drainage basin, showed that it obtains much of its sediment from a Piedmont River (Altamaha) via a salt marsh stream running parallel to the coast.