We have now carried our examination of the Fen Beds up to the sea, but
to understand this interesting area we must cross the sea bank and see
what is happening in the Wash. There is no peat being formed there, nor
is there any quantity of drifted vegetable matter such as might form
peat. There are marginal forest beds near Hunstanton and Holme, for
instance, and it is not clear whether they point to submergence or to
the former existence of sand dunes or shingle beaches sufficient to
keep out the sea and allow the growth of trees below high water level
behind the barrier, such as may be seen at Braunton Burrows, near
Westward Ho, or at the mouth of the Somme. What is the most conspicuous
character of the Wash is that the upland waters, now controlled as to
their outlet, keep open the troughs and deeps while tidal action throws
up a number of shifting banks of mud, sand and gravel, many of which
are left dry at low water. Along the quieter marginal portions fine
sediment is laid down, and relaid when storms have disturbed the
surface. On these cockles and other estuarine molluscs thrive. Before
the sea banks were constructed these tidal flats extended much further
inland.