Geology Site Account

Historical information only In 1981, during construction of the M25 motorway, a deep cutting was excavated in the London Clay and the overlying Claygate Beds just south of the point where Nags Head Lane crosses the motorway. Over a kilometre in length, the cutting exposed brown weathered clay overlying blue-grey clay containing a wealth of marine fossils such as bivalves and gastropods. Also present was the pearly nautilus “ a clear indication that the seas some 50 million years ago were subtropical. More fossils were probably collected from here than from any other temporary London Clay exposure in Britain. A large collection of the fossils from this site went to the former Passmore Edwards Museum in Stratford. Due to the need to maintain a stable slope in unstable London Clay, the shallow angle of the banks required one of the largest motorway cuttings in the country but this had the advantage of exposing a considerable area of clay for collecting. On completion of the motorway the exposure was covered with topsoil and grass but the cutting is still an impressive sight.

The giant Nags Head Lane motorway cutting today. The cutting produced thousands of fossils from the London Clay when it was excavated in 1981. Photo: G. Lucy