Geological Field Trip to South Street Caves, Dorking
Several Southern Testing staff attended the South East Regional Group of the Geological Society field trip South Street Caves, Dorking, in Surrey at the end of July.
The North Downs defines the northern flank of the up-fold (anticline) of sedimentary strata of the Weald Basin, and the southern limb of the large down-fold (syncline) of the London Basin. The strata involved in these folds are all of Cretaceous age (deposited approximately 140-70 million years ago).
The North Downs are composed of Chalk and lying immediately below is a thin bed of stone known as the Upper Greensand which rises to the surface. At the foot of the North Downs an east-west aligned valley, has been eroded into the impermeable Gault Clay, across which the River Mole flows towards Dorking. Beneath the Gault Clay is the Lower Greensand. This forms the line of the Surrey Hills.
The Dorking ‘caves’ are, technically speaking, tunnels, being entirely manmade. They have been excavated into the Folkestone Sand at the top of the Lower Greensand and may have been used originally to mine building sand and stone. It is believed that the main parts of the caves were excavated in the late 17th century.
The present entrance to the caves is located beside the War Memorial in South Street in the centre of Dorking. The guides started the tour by explaining how historically South Street was once a narrow lane like West Street. Prior to the widening of South Street, the entrance to the caves was through a door in the back garden of a cottage that fronted onto South Street. Prior to this the original entrance to the caves is believed to have been in the grounds of a larger house. There is evidence of a number of original entrances to the caves, with many of the shops and houses of Dorking having had extensive cellars and inter-connecting galleries. These were probably used initially for storage, but have had a variety of uses. All with the exception of the South Street entrance are now believed to have been sealed.
The upper level of the Dorking caves is laid out as a wine cellar and was last used for this purpose in the 19th century. In the centre of the upper level is a set of steps leading down to a landing, from which leads a further set of steps to a lower passage. At the far end of this passage is a circular room with a bench cut out of the rock locally referred to as the “Mystery Chamber”.
We would like to thank Richard Selley (Emeritus Professor of Imperial College), Jim Harvey and Graham Speed of Dorking Museum for what was a very informative and interesting tour.