SYNOPSISGeological and geophysical investigations in the southern part of the Sound of Jura reveal numerous deep and narrow closed channels in a sequence of thick post-glacial muds. It is proposed that the channels were formed subsequent to the deposition of the sediments by the erosive action of the strong tides observed in the Sound. Several problems related to this mode of origin are considered, but more data are required to provide greater insight into the post-glacial history of the Sound.