Looking north and west there is no high ground between us and the Wash. If we could sweep out the soft superficial deposits and abolish the sea banks the tide would still ebb and flow over the whole area.
If we look north and east we see the high ground stretching from Downham Market to Stoke Ferry and sweeping round to the south by Methwold and Feltwell and the islands of Hilgay and Southery, thus enclosing a great bay into which the Wissey on the north and the Brandon River on the south deliver the waters collected on the eastern chalk uplands.
The island known as Shippea Hill marks the trend of an ancient barrier blocking the northward course of the river Lark. (Fig. 6, p. 29.)
Here, then, it seems probable that we might find evidence of a local change from the conditions we now see in the Wash and those which have resulted in the formation of the Fens.
Buttery Clay.
In deep trenching in the Fen between Littleport and Shippea Hill in order to obtain clay for laying on the peaty surface a very fine unctuous deposit was found at a depth of four or five feet. The overlying Fen Beds were chiefly peat with lenticular beds of white marl and grey clay, obviously laid down from time to time in small depressions in the surface of the peat. This marl was often largely made up of, or was at any rate full of, freshwater shells but sometimes showed evidence of having been gathered on the stems of Chara which on perishing have left small cylindrical hollows penetrating the partly consolidated marl. Under these beds of peat and marl there was the unctuous clay, which is sometimes referred to as the Buttery Clay. It is an estuarine deposit like that mentioned above as occurring in the Wash off Heacham, for instance. It contains shells of Cardium edule, Tellina (Tacoma) balthica, Scrobicularia piperata, and other estuarine shells, some of which had the valves adherent or rather adjoining, for the ligament had perished. Mrs Luddington has in her collection the bones of the Urus, Wild Boar and Beaver, obtained from the peat above this Buttery Clay.
On the other or south-western side of Shippea Hill, which is an island of Kimmeridge Clay, we get further into the embayed and isolated portions of the Fen and we find more peat in proportion to the other deposits although it is very thin. There are still small lenticular beds of white marl similar to that nearer Littleport and the peat rests upon Buttery Clay of unknown thickness. In this part, however, no shells have yet been noticed. Near Shippea Hill the peat has recently been trenched with a view to obtaining clay with which to dress the surface of the peat and it was here, at a depth of four feet from the surface and four inches above the Buttery Clay, that the human bones described below (pp. 27-35) were found.
The Age of the Fen Beds.
Now we may enquire what are the limits within which we may speculate as to the age of the Fen Beds.
These Turbiferous deposits all belong to one stage, though it may be one of long duration. They are sharply separated from the Areniferous deposits, i.e. the sands and gravels of the terraces and spurs which always pass under and, in fairly large sections, can always be clearly distinguished from the resorted layers at the base of the Fen Beds.