Well. There you go then.
Ancient geography lesson.
It's a fascinating subject, made even more so by the fact that it existed not that long ago reminding us that sea levels can and do change, altering the landscape dramatically.
Random fact: Fishermen who fish the Dogger Bank in the North Sea sometimes come into contact with a creature called a sea chervil, which causes a form of dermatitis - known to them as "Dogger Bank Itch".