Holocene peat and piddocks

Found on the beach: Holocene peat and piddocks. After winter storms, Brighton Beach occasionally reveals dark, rounded lumps scattered among the flint shingle. At first glance they resemble stone, but they break easily in the hand and crumble rather than fracture. They are not rock. They are fragments of Holocene peat, washed ashore from submerged deposits offshore.

These pieces are part of a prehistoric landscape that once lay above sea level. Between about 6,000 and 8,000 years ago, rising post-glacial sea levels flooded low-lying woodland and peat bogs across what is now the English Channel. Waterlogged, oxygen-poor conditions preserved the compressed remains of trees, roots and plant matter. Those peat beds still lie buried beneath sand and gravel offshore.

Strong seas periodically erode these deposits and release fragments, which are rolled smooth by waves before appearing on the beach. When dry, the peat is light and brittle; when wet, it is dense, dark brown to almost black, and easily mistaken for stone.

This fragment found on Brighton Beach shows a second stage in its history. One face is densely perforated by rounded holes of varying sizes. These are piddock borings, made by marine bivalves such as Pholas and Barnea. Piddocks rasp into soft substrates - chalk, clay and peat - to create permanent shelter. They cannot bore into flint or hard rock, which is why such holes appear only in the peat and not in the surrounding shingle.

The presence of these borings shows that the peat fragment lay exposed on the seabed for a prolonged period before being torn free and washed ashore. Most peat fragments lose this evidence through abrasion; only a few retain a clearly bored surface.

Together, the peat and the piddock holes record two deep timescales at once: the slow drowning of prehistoric land as sea levels rose, and the later colonisation of that drowned landscape by marine life. What reaches the beach is not just debris, but a small, durable remnant of Brighton’s submerged past.