At certain times of year the tides are high and low enough to change the whole appearance of the beach at Seaton Carew. The submerged forest starts to emerge for short periods.
It's the remains of fens and a birch and alder forest in a peat bed from 8000 years ago when there was still a land bridge from England to Europe.
These posts, however, are the remnants of the supports of some drainage pipework from the 20th Century rather than anything foresty from the Mesolithic. Does make me think of Flag Fen, though.