Geology Site Account

Summary

Hangman's Wood is a scheduled ancient monument. It is also a biological SSSI because the deneholes are the most important underground hibernation site for bats in Essex, three species have been recorded. At the present time it is thought that only two shafts are open but these are securely gated and underground access is prohibited. The Deneholes are also of geological interest.

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Site description

Hangmans Wood contains the most extensive and best preserved set of deneholes in existence. Deneholes are thought to be medieval chalk mines and consist of vertical shafts through the Thanet Sand and end in branching chambers cut into the underlying chalk. The Hangmans Wood deneholes are particularly deep, the shafts being over 20 metres deep before the Chalk is reached.

The Essex Field Club carried out the first extensive investigation into the nature and origin of these deneholes and published a comprehensive report in 1887. At that time 51 shafts were known at Hangmans Wood but all except 5 were blocked and could only be identified by depressions on the surface. The club entered and examined 15 shafts and associated chambers, mainly by cutting tunnels through from one set of chambers to the next. The Field Club carried out further investigation of the site in the 1950s and early 1960s. It is thought that there may be as many as 72 shafts, or deneholes, on this site.

Although a 20 metre vertical ladder descent is needed to appreciate it, from a geological perspective there is a remarkable section here from the Thames terrace gravels through the Thanet Sand, into the Chalk with its bands of flint which are visible in the chamber walls.

Deneholes have been discovered elsewhere in Thurrock, frequently encountered (and subsequently destroyed) by chalk quarrying. Accounts of several of these discoveries have been recorded in the Essex Naturalist.

A section and plan of a typical denehole. Illustration © British Geological Survey.