The Tunbridge Wells Sand Formation is a geological unit which forms part of the

Wealden Group The Wealden Group, occasionally also referred to as the Wealden Supergroup, is a group (a sequence of rock strata) in the lithostratigraphy of southern England. The Wealden group consists of paralic to continental (freshwater) facies sedimentary ...

and the uppermost and youngest part of the unofficial

Hastings Beds The Wealden Group, occasionally also referred to as the Wealden Supergroup, is a group (a sequence of rock strata) in the lithostratigraphy of southern England. The Wealden group consists of paralic to continental (freshwater) facies sedimentary ...

. These geological units make up the core of the

geology Geology () is a branch of natural science concerned with Earth and other astronomical objects, the features or rocks of which it is composed, and the processes by which they change over time. Modern geology significantly overlaps all other Ear ...

of the

Weald The Weald () is an area of South East England between the parallel chalk escarpments of the North and the South Downs. It crosses the counties of Hampshire, Surrey, Sussex and Kent. It has three separate parts: the sandstone "High Weald" in the ...

in the English counties of

West Sussex West Sussex is a county in South East England on the English Channel coast. The ceremonial county comprises the shire districts of Adur, Arun, Chichester, Horsham, and Mid Sussex, and the boroughs of Crawley and Worthing. Covering an ar ...

East Sussex East Sussex is a ceremonial and non-metropolitan county in South East England on the English Channel coast. It is bordered by Kent to the north and east, West Sussex to the west, and Surrey to the north-west. The largest settlement in East Su ...

and

Kent Kent is a county in South East England and one of the home counties. It borders Greater London to the north-west, Surrey to the west and East Sussex to the south-west, and Essex to the north across the estuary of the River Thames; it faces ...

. The other component formations of the

are the underlying

Wadhurst Clay Formation The Wadhurst Clay Formation is a geological unit which forms part of the Wealden Group and the middle part of the now unofficial Hastings Beds. These geological units make up the core of the geology of the High Weald in the English counties of We ...

and the

Ashdown Formation The Ashdown Formation is a geological unit, which forms part of the Wealden Group and the lowermost and oldest part of the now unofficial Hastings Beds. These geological units make up the core of the Weald in the English counties of East Sussex an ...

. The

in turn form part of the

which underlies much of southeast

England England is a country that is part of the United Kingdom. It shares land borders with Wales to its west and Scotland to its north. The Irish Sea lies northwest and the Celtic Sea to the southwest. It is separated from continental Europe b ...

. The sediments of the

, including the Tunbridge Wells Sand Formation, were deposited during the

Early Cretaceous The Early Cretaceous ( geochronological name) or the Lower Cretaceous (chronostratigraphic name), is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 145 Ma to 100.5 Ma. Geology Pro ...

Period, which lasted for approximately 40 million years from 140 to 100 million years ago. The Tunbridge Wells Sands are of Late

Valanginian In the geologic timescale, the Valanginian is an age or stage of the Early or Lower Cretaceous. It spans between 139.8 ± 3.0 Ma and 132.9 ± 2.0 Ma (million years ago). The Valanginian Stage succeeds the Berriasian Stage of the Lower Cretaceou ...

age.Hopson, P.M., Wilkinson, I.P. and Woods, M.A. (2010) ''A stratigraphical framework for the Lower Cretaceous of England''. Research Report RR/08/03. British Geological Survey, Keyworth. The Formation takes its name from the spa town of

Tunbridge Wells Royal Tunbridge Wells is a town in Kent, England, southeast of central London. It lies close to the border with East Sussex on the northern edge of the Weald, High Weald, whose sandstone geology is exemplified by the rock formation High Roc ...

Lithology

The Tunbridge Wells Sand Formation comprises complex cyclic sequences of siltstones with sandstones and clays, typically fining upwards, and is lithologically similar to the older

.Codd, J.W. (2007) ''Analysis of the distribution and characteristics of landslips in the Weald of East Sussex''. MSc dissertation, University of Brighton. It has a total thickness typically in the region of about 75 m. However, near

Haywards Heath Haywards Heath is a town in West Sussex, England, south of London, north of Brighton, south of Gatwick Airport and northeast of the county town, Chichester. Nearby towns include Burgess Hill to the southwest, Horsham to the northwest, Crawl ...

borehole data has proven the formation to be up to 150m thick.Young, B. & Lake, R.D. (1988) ''Geology of the country around Brighton and Worthing: Memoir for 1:50,000 geological sheets 318 and 333''. British Geological Survey, London. In the western parts of the High

the Tunbridge Wells Sands can be divided into four separate divisions; the Lower Tunbridge Wells Sand, the Ardingly Sandstone Member, the Grinstead Clay Member, and the Upper Tunbridge Wells Sand.

Lower Tunbridge Wells Sand

The Lower Tunbridge Wells Sand shows the best cyclic fining up sequences in the formation. The division comprises mainly interbedded siltstones and silty sandstones and occurs up to 27m thick.Lake, R.D. & Shepard-Thorn, E.R. (1987) ''Geology of the country around Hastings and Dungeness: Memoir for 1:50,000 geological sheets 320 and 321''. British Geological Survey, London.

Ardingly Sandstone Member

A massive thick cross bedded fine to medium grained quartz sandstone separates the Tunbridge Wells Sands from the overlying Grinstead Clay. This horizon is known as the Ardingly Sandstone and occurs in thicknesses of up to 18m. It is particularly well exposed throughout the region between

East Grinstead East Grinstead is a town in West Sussex, England, near the East Sussex, Surrey, and Kent borders, south of London, northeast of Brighton, and northeast of the county town of Chichester. Situated in the extreme northeast of the county, the civ ...

, and

, at localities such as; Stone Farm south of

; Chiddinglye Rocks near

West Hoathly West Hoathly is a village and civil parish in the Mid Sussex District, Mid Sussex District of West Sussex, England, located south west of East Grinstead. In the 2001 census 2,121 people, of whom 1,150 were economically active, lived in 813 ho ...

; Toad Rock, Bull's Hollow and Happy Valley west of

; and

Harrisons Rocks Harrison's Rocks is a series of sandstone crags approximately south of the village of Groombridge in the county of East Sussex. The site is a notable example of a periglacial tor landform developed in rocks of the Ardingly Sandstone Member of t ...

Bowles Rocks Bowles Rocks is a sandstone crag in the county of East Sussex, on the border with Kent, approximately south of the town of Royal Tunbridge Wells. It is popular with rock climbers due to the excellent, south-facing, quick-drying rock, the range ...

and

High Rocks High Rocks is a geological Site of Special Scientific Interest west of Tunbridge Wells in East Sussex and Kent. It is a Geological Conservation Review site. Prehistory The location was formed when a melting ice sheet at the end of the last ic ...

near

. At all of these places the Ardingly Sandstone forms a weathering-resistant layer, relative to the rest of the formation, which has become very popular with

rock climbers Rock climbing is a sport in which participants climb up, across, or down natural rock formations. The goal is to reach the summit of a formation or the endpoint of a usually pre-defined route without falling. Rock climbing is a physically and ...

and is known locally as

Southern Sandstone Southern Sandstone is a local name for the Ardingly Sandstone of southeast England, a soft sandstone of Cretaceous age separating the Tunbridge Wells Sands from the overlying Grinstead Clay. The outcrops in the Weald of Kent are the rock climbi ...

. These are the closest

rock climbing Rock climbing is a sport in which participants climb up, across, or down natural rock formations. The goal is to reach the summit of a formation or the endpoint of a usually pre-defined route without falling. Rock climbing is a physically and ...

crags to

London London is the capital and largest city of England and the United Kingdom, with a population of just under 9 million. It stands on the River Thames in south-east England at the head of a estuary down to the North Sea, and has been a majo ...

and as a result are the most heavily used in the country.

Grinstead Clay Member

The Grinstead Clay comprises mudstones and silty mudstones with siltstone, ironstone and shelly limestone. This member is lithologically similar to the older

Wadhurst Clay The Wadhurst Clay Formation is a geological unit which forms part of the Wealden Group and the middle part of the now unofficial Hastings Beds. These geological units make up the core of the geology of the High Weald in the English counties of West ...

and also has weathered red mottled clays at its top. The formation is up to 20m thick but is only present around the border of

and

. It can be further subdivided into the Lower Grinstead Clay and Upper Grinstead Clay. These divisions are separated by a lenticular calcareous sandstone known as the Cuckfield Stone. This is probably best known as the strata in which

Gideon Mantell Gideon Algernon Mantell MRCS FRS (3 February 1790 – 10 November 1852) was a British obstetrician, geologist and palaeontologist. His attempts to reconstruct the structure and life of ''Iguanodon'' began the scientific study of dinosaurs: in ...

discovered

Iguanodon ''Iguanodon'' ( ; meaning 'iguana-tooth'), named in 1825, is a genus of iguanodontian dinosaur. While many species have been classified in the genus ''Iguanodon'', dating from the late Jurassic Period to the early Cretaceous Period of Asia, Eu ...

in the early 19th century.

Upper Tunbridge Wells Sand

The Upper Tunbridge Wells Sand is similar to the Lower Tunbridge Wells Sand. It comprises soft red and grey mottled silts and clays in its lower part, and alternating silts and silty clays with thin beds of sandstones. The base of the Tunbridge Wells Sand is marked by a distinct change from the predominantly argillaceous sediments of the

to siltstones and silty sands. This boundary is often indicated on maps by spring lines and seepages, where groundwater percolating through the permeable Tunbridge Wells Sand is forced to surface at the junction with the

. The top of the Tunbridge Wells Sand Formation is well defined in the southwest of

but is gradational elsewhere. In the area north of

Brighton Brighton () is a seaside resort and one of the two main areas of the City of Brighton and Hove in the county of East Sussex, England. It is located south of London. Archaeological evidence of settlement in the area dates back to the Bronze A ...

and west of

Lewes Lewes () is the county town of East Sussex, England. It is the police and judicial centre for all of Sussex and is home to Sussex Police, East Sussex Fire & Rescue Service, Lewes Crown Court and HMP Lewes. The civil parish is the centre of ...

the boundary is marked by a massive sandstone, though this is not seen anywhere else.

Engineering Geology

Landslips often occur at or close to the lower boundary of the Tunbridge Wells Sands, between it and the underlying

. This is partly caused by the steep sided hill, valley and ravine topography of the

High Weald High may refer to: Science and technology * Height * High (atmospheric), a high-pressure area * High (computability), a quality of a Turing degree, in computability theory * High (tectonics), in geology an area where relative tectonic uplift t ...

and partly by the lithological variation between the formations and the presence of spring lines and seepages. When percolating groundwater in the permeable sandstones of the Tunbridge Wells Sands comes into contact with the upper impermeable clay beds of the

, it is forced to find alternative migration pathways to the surface. This results in the saturation and weakening of the upper portion of the Wadhurst Clay, increasing the chances of failure.

Paleobiota

Pterosaurs

Crocodyliformes

Dinosaurs

Mammals

References

{{Reflist

External links

British Geological Survey lexicon
Geologic formations of England Lower Cretaceous Series of Europe Cretaceous England Valanginian Stage Sandstone formations