Geology Site Account

Temporary exposures in the 19th century revealing unusual geological features. Further excavations in the vicinity could yield further information.

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Site description

In 1898 a 'remarkable section of contorted gravels' was exposed in a pit about a furlong north-west of Wanstead Park. The contorted gravel was overlain by a layer of undisturbed gravel which was recognised to be of more recent age. The pit is described in a paper by Martin Hinton published in the Essex Naturalist in 1900. Hinton said that the seams of sand and gravel were so twisted up as to resemble loose knots.

Hinton attributed the disturbances to the grounding of river ice but they are now known to have had a different origin. Contortions such as these are called involutions and geologists know how they were formed because the same processes are going on in the Arctic today. In southern Britain, during the coldest periods of the Ice Age, the ground was permanently frozen (permafrost) with only the top metre or so thawing during each brief summer and freezing again in the autumn. Constant freezing and thawing over thousands of years created remarkable contortions in layers of gravel close to the surface.

The geological map shows this area to be situated on the high terrace, known as the Boyn Hill/Orsett Heath Terrace. The gravel of this terrace is thought to have been originally laid down by the river about 400,000 years ago following the diversion of the Thames by the Anglian Ice Sheet (Marine Isotope Stages12¬10). The lower gravel in this pit is therefore of this great age and was contorted during a subsequent glacial stage. The undisturbed layer of gravel above was laid down thereafter.

The exact location of the pit is not known but the most likely candidate is the pit that formerly existed on land now occupied by Addison Road and Dangan Road (approx. TQ 402 881) and clearly shown on the 1868 six inch Ordnance Survey map.