The sea in the Fens
The Fens have been inundated by the sea on various occasions as shown by the marine silts and clays that can be found over large areas, even in the southern fenland of Cambridgeshire. The complex history of freshwater marshes changing to salt marshes and back again, for example in the Late Neolithic/Early Bronze Age and in Romano-British times, has left interwoven peat and silt/clay layers that reveal the timing and extent of the ‘flooding’ in each local area. See the Fen Edge Trail website for more information.
A lidar image of the island of Thorney shows the remnants of tidal creeks (roddons) in the surrounding fields (often visible by the change in height and colour of the soil).