Because longshore transport on the Georgia coast is towards the south, islands are eroded at the northern ends and develop spits at the south. However, the northern end of Jekyll Island consists of a wedge-shaped area of Holocene beach ridges indicating local accretion. Vibracoring reveals a retrogradational sequence beneath these ridges with dune and beach sands resting on lagoonal muds that infill an old inlet. It is inferred that these lagoonal deposits formed in the lee of spits that developed seaward of their present position, retreated landwards and were then accreted to the island. Orientation of the old inlet-fill suggests that St. Simons Sound (between Jekyll & St. Simons Islands) was originally controlled by flow from Mackay River rather than by the modern Brunswick River. Mackay River is a former distributary of the Altamaha River that currently empties north of St. Simons Island. The absence of a spit on the north side of St Simons Sound suggests that Brunswick River has been captured only recently.