Evidence has for long been accumulating to show that the shores of the Thames estuary now lie at least 15 ft. lower in relation to the sea than in early Romano-British times (summarized, e.g. Wheeler, 1928; Francis, 1932). Francis has suggested that this submergence began early in the 2nd century A.D., its effects being widely felt by the end of the century. Similar evidence has been noted both from the east and south coasts of England though, in the East Anglian ‘Great Estuary’ (Yare-Bure-Waveney) behind Yarmouth, it had formerly been assessed as about 2 ft. only.
Most writers, however, have been content to assume without confirmatory evidence that these changes took place in a simple progression, so that a graph of them from Roman times to the present day might be represented by a roughly straight line. Godwin, indeed, had sounded a warning note in his analysis of the Fenland deposits at Wiggenhall St German (Godwin and Edmunds, 1933; Godwin, 1940), Jennings had pointed to a ‘standstill’ or slight regression after the Romano-British transgression of the Broadland valleys (1952, 50) and a short note by Swinnerton (1955) discussing pottery found below marine clays at Chapel St Leonards, Lincs, came to confirm them. But now substantial evidence from the Yarmouth district has been adduced to show that, after the Iron Age—Romano-British marine transgression, represented by the Broadland ‘Upper Clay’, land emergence took place during the Saxon period to culminate about the time of the Norman Conquest or soon after, the ‘Saxo-Norman Marine Regression’ as it has been named (Green and Hutchinson, 1960). Under the South Denes at Yarmouth, a beach with its low water mark now at - 17.5 ft. O.D. has been dated by pottery finds to the 13th century, with a silt covering-layer also containing pottery, inferred to have been deposited by the great flood of A.D. 1287. Supported by a variety of other evidence, they have shown that, at that date, the coast here still stood some 13 ft. higher in relation to the sea than it does today. Thereafter a rapid submergence began which, by Tudor-Stuart times, was much retarded and which today has been reduced to the very low rate of some 1.6 mm. per annum.