 Sonar and lake sediment probing of a few of these structures, which are now submerged beneath Dalhousie Lake, revealed the presence of crater-like features, which underlie these floors and are inferred to be buried by lake sediment and peat.Petrographic analysis of bedrock samples collected near the eastern rim crests of the North Group identified features that are suggestive of shock metamorphism.These features include kink-bands in feldspar and biotite and planar microstructures in quartz and feldspar.