Continuous seismic profiler surveys have defined the limits of the Paleozoic outlier in Ungava Bay, and indicate that similar rocks occur to the north beneath Hudson Strait. These surveys have shown also that the strata underlying Hudson Strait are down-warped to form a synclinal structure with its axis parallel to the bathymetric trend of the Strait. Extrapolations based upon the dips and thicknesses indicated on the seismic profiler records and on physiographic evidence, suggest that the southwestern side of Hudson Strait has been down-faulted relative to the block of Paleozoic strata in Ungava Bay. These relationships postulated on the basis of seismic profiler results are supported by aeromagnetic, sea-magnetometer, and sea-gravimeter data from that region. A seismic and magnetic profile from Frobisher Bay indicates that a Paleozoic outlier occurs there as well. Although the submarine physiography of this region is primarily controlled by structure and secondarily modified by sub-aerial erosion, glacial erosion may account for local detail.