The Disappearing River Mole
Swallows in the banks of the River Mole, near Burford Bridge.
The River Mole between Dorking and Leatherhead flows both on the surface and in a system of underground passages in the Chalk bedrock. The water enters the underground system via a number of swallow holes – not normally seen when the river level is high. At times of drought the river bed can be exposed and the swallow holes become visible. The subterranean flow can periodically be seen emerging at Fetcham Mill Pond. These features have long been recognised and were first illustrated in Brayley’s Topographical History of Surrey in 1850, from which this illustration is taken.
Map of Mole Valley between Mickleham and Leatherhead.
The river bed of the Mole between the Mickleham Bridge and the Thorncroft Bridge has been exposed in parts during the dry spell of July 2022. MVGS member Tod Wilson has photographed the situation at various points along the river – shown as the following seven photographs. Also shown is the Ham Bank locality where the river bed and swallow holes were exposed in the drought of 1949. [Image © GoogleEarth].
River Mole at the Stepping Stones near Burford Bridge in July 2022.
Reduced surface flow of the River Mole at the Stepping Stones, downstream to left (NGR TQ 1723 5130).
Exposed river bed at Norbury Park in July 2022.
View looking north, Young Street road bridge in distance (TQ 1639 5513).
Mole river bed at Young Street, Leatherhead in July 2022.
Low water level in River Mole at Young Street Bridge (A246 road) looking north, downstream (NGR TQ 1637 5517).
Ham Bank near Mickleham in 1949
The drought in 1949 exposed the Mole river bed at Ham Bank, near Mickleham (c. TQ 161 527) and the event was recorded in several photographs taken by J. Rhodes - this and following two images. View of exposed swallow hole looking north. [Image © British Geological Survey, Geoscenic Collection, no. P208320].
Ham Bank near Mickleham in 1949
View of exposed swallow hole looking south. [Image © British Geological Survey, Geoscenic Collection no. P208321].
Geological Sites and Sights in the Mole Valley
Denbies Wine Estate
Field Excursion to the Lizard Peninsula: A Journey to the Centre of the Earth
The objective of the trip was to examine exhumed mantle and oceanic crust and the overlying deepwater facies of Devonian age (c.400 Ma) exposed around the Lizard Peninsula.
Overlying deepwater facies: Pendower Formation mudstones overlain by Pleistocene raised beach, Pendower Beach.
Mantle to crust transition at Coverack Cove. Mantle peridotites (left foreground), and crustal gabbros (far right distance). Troctolites (centre, and under the bay) mark the position of the Mohorovicic Discontinuity.
Detail of gabbro: dark grey plagioclase (altered to white prehnite), green augite, green olivine, black ilmenite.
Hornblende schists (amphibolites) at Cadgwith Cove. A shear zone runs through the centre of the outcrop.
An Excursion to the Dorking Caves
Field Excursion to Philpott's Quarry, West Hoathly, Sussex
Briefing for the group at the start of the trip. The quarry has exposures of the Lower Cretaceous Tunbridge Wells Sandstone below an overburden of Grinstead Clay.
Sedimentary features in the Tunbridge Wells Sandstone: cross-bedding, younging to the left, with iron liesegang.
Some Other Member Activities
Visit to Ibstock Quarry and Brickworks, Beare Green. The bricks are made from the Lower Cretaceous Weald Clay.