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68 glaciation seems to have been a few feet higher than that of the present day, for glacially transported erratics are found strewn over the flat coastal plain of Sussex. One erratic block, probably derived from the Channel Islands, was discovered under the loess as far east as Sangatte cliff, close to Calais. The icy English Channel must therefore have met the icy North Sea some time during the Glacial Epoch.

Some time after the cold had passed away there came in the period with which this book deals—when the lowest submerged forest flourished, on land now 50 or 60 feet below the sea. This elevation of the land, as already shown, converted a great part of the North Sea into a wide alluvial plain. At the same time it raised above the sea-level and obliterated the newly-formed strait, leaving it in all probability as a shallow valley sloping both ways and filled up with alluvium. The Strait of Dover was again a watershed, or perhaps its position was occupied by a small stream, which may have flowed in either direction.

Thus the work done during the Glacial Epoch was almost cancelled and had to be done again; but now there was merely a low narrow divide of chalk and a strip of marsh between the two basins, and the chalk ridge was steadily being attacked by the waves of the sea from the west.

When subsidence again set in the strip of alluvium was soon submerged and the two seas again met; but