Geology Site Account

Temporary exposure of fossiliferous deposits. Further excavations in the vicinity could yield further fossils.

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Site description

Excavations at the junction of the A406 North Circular Road and the A104 in 1969 produced many fossils from the London Clay which provided a snapshot of life in the subtropical sea that covered the London area about 50 million years ago. The work involved a new roundabout and approach road, and a new reservoir for the Metropolitan Water Board, all of which required excavations in the clay up to 7 metres (25 feet) deep. There were also two 17 metre (55 feet) deep shafts connected by a tunnel which was constructed in connection with the new reservoir.

The London Clay exposed at the surface in the road cuttings and for the reservoir was deeply weathered and decalcified which meant that all fossil shells had long ago been dissolved by the weathering process. Most of the fossils that were found, such as the shells of molluscs and brachiopods, therefore came from the deep, unweathered clay that was excavated from the tunnel. The fossils were collected by examining freshly tipped clay as it was brought to the surface and also by searching the tip heaps as they weathered down over a period of several months. A bulk sample of 137 kg (over 300 lb) of clay that was taken away for sieving produced most of the smaller fossils that could not have been found by surface picking.

The fossils at Waterworks Corner indicate that the London Clay here falls within Division C which is in the middle of the full thickness of London Clay represented beneath London and Essex. It contained typical knobbly and tubular nodules of pyrite (fools gold) and phosphatic nodules which sometimes contained the carapaces of crabs or lobsters. Also typical of the London Clay were bands of flat, spherical septarian nodules up to 35 centimetres (one foot) in diameter, the surfaces of which displayed intricate patterns which represented the infilled burrows of marine creatures such as crustaceans. This indicates that the London Clay, which was originally mud on the sea floor, is intensely burrowed throughout but evidence of this is only visible on the nodules.

Although fossils were certainly not common, the meticulous collecting by amateur and professional geologists produced hundreds of specimens which included molluscs (37 species), sharks teeth (7 species), crabs, lobsters, nautilus and over 300 individual bones of fish from the bulk sample. Many fossilised seeds and fruits were also found which represented some of the plants and trees that were growing in the rainforest on the shores of the London Clay Sea.

A surprising aspect of the geology at this site was the sharp, irregular folds in the London Clay near the surface which was in complete contrast to the almost horizontal bedding of the clay below. This must be due to the intense cold of the most recent glacial period, some 50,000 years ago, when the ground was frozen to a considerable depth (permafrost) with the topmost layer constantly freezing and thawing during thousands of years of brief summers and long winters.