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22 They belong, however, to another and more ancient chapter of the geological record than that with which we are now dealing. I do not say a less interesting one, for they are of the greatest importance when we study the times when Palaeolithic man flourished; but at present we have as much as we can do to understand the later deposits and to realize the great changes to which they point. We must not turn aside for everything of interest that we come across in this study; these earlier strata are worthy of a book to themselves.

As we travel northward along the coast, again and again we meet with evidence of a submerged nearly level platform, "basal plane," or ancient "plane of marine denudation," lying about 50 feet below the sea. We find it at Langer Fort, which lies opposite to Harwich on a spit of sand and shingle stretching across Harwich Harbour. Here the floor of London Clay was met with in a boring at 54 feet below the surface.

The Suffolk coast north of Southwold yields yet another complication, for between Southwold and Sherringham in Norfolk there appears at the sea-level a land-surface considerably more ancient than anything we have yet been dealing with. This is the so-called "Cromer Forest-bed," which consists of alternating freshwater and estuarine beds, with ancient land-surfaces and masses of peat. It contains