The Dungeon is a small wooded ravine quarter of a mile to the north west of Heswall which shows a natural stream section through the Tarporly Siltstone Formation of the Mercia Mudstone Group, of Triassic age.
At the south west end of the section the faulted contact with the older Wilmslow Sandstone Formation is seen
The Tarporley Siltstone section is similar to that in other parts of the Cheshire basin, being made up of red fine sandstones and siltstones, with parallel and rippled bedding, and salt pseudomorphs. Current ripple crests indicate that sediment transport was towards the north west.
Sediment and sedimentary structures in these rocks make it possible to infer that they were deposited in a marine intertidal environment.
Site Name: The Dungeon S.S.S.I.
Site Code: S7
Date of Notification: 1977
Date of Revision: 1987
Grid Reference: SJ 251831