Basement relief has been mapped by continuous seismic profiling beneath southern New England's inner shelf. A southward-trending, dendritic drainage pattern is well defined with the parts of the valleys landward of the coastal plain cuesta distinctly narrower and deeper than the segments underlying the coastal plain strata. Glaciation has deepened but has not rearranged the preglacial inner lowland or fall zone fluvial valleys. Ancient pre-Upper Cretaceous channels were reoccupied by preglacial streams where coastal plain deposits had been stripped away. The basement's lithologic and structural grain is probably north-south if the general drainage pattern is controlled by lithology and structure as implied by mainland relations.