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Happisburgh, home to about 1,100 people, is so susceptible to erosion because the cliffs are made from boulder clay which slumps when wet.

Great deposits of till and boulder clay that lay beneath the glaciers were abandoned in situ, and remain as an unsorted mixture of large boulders, pebbles and mingled fragments, embedded in clay or sand.

Glacial boulder clay lies over much of the lower ground, and ridges of gravel and sand flank the hills and form extensive sheets.

Most of the county is covered by a superficial deposit of glacial drifts, sands, gravel and in places boulder clay, as at Epping, Dunmow and Hornchurch where the drift lies beneath the Thames gravel.

The largest transported mass occurs at Linksfield, where a succession of limestones and shales rests on boulder clay and is covered by it, which from the fossils may be of Rhaetic or Lower Lias age.