Sonic subbottom profiles reveal that glacial deposits off the Kennebec River, all shallower than 65 m, show an erosional topography with a relief of up to 30 m. At greater depths, in the area between Cape Small and Damariscove Island, these deposits are flat surfaced. A possible berm is present at the transition from dissected to undissected deposits, and the entire area is covered by a veneer of recent sediments. The erosional topography is thought to have formed subaerially during a postglacial period of emergence. A curve has been constructed for the isostatic change of the Gulf of Maine area during the past 13,000 yr. Crustal rebound commenced at a rate of 19 cm per yr, exceeding the rate of eustatic sea-level rise, so that by 12,300 yr B.P. the sea had retreated to the present coastline. Maximal emergence was reached about 8,500 yr B.P. when the crustal subsidence commenced; this settling is still continuing.