...Water levels were much lower then; scientists have found, for example, ancient sites like stone walls and hunting blinds that are now 100 feet underwater.
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The see was 100 feet lower before the series of meltwater pulses following the end of the last Ice Age. 10,000 years ago these was no North Sea. England was attached to Europe in a single landmass.
Yes, so much water locked up in glaciers then.