![Pine woods, Oxshott Heath - geograph](https://upload.wikimedia.org/wikipedia/commons/3/38/Pine_woods%2C_Oxshott_Heath_-_geograph.org.uk_-_2806331.jpg)
The London Clay Formation is a
marine geological formation
A geological formation, or simply formation, is a body of rock having a consistent set of physical characteristics ( lithology) that distinguishes it from adjacent bodies of rock, and which occupies a particular position in the layers of rock exp ...
of
Ypresian
In the geologic timescale the Ypresian is the oldest age (geology), age or lowest stage (stratigraphy), stratigraphic stage of the Eocene. It spans the time between , is preceded by the Thanetian Age (part of the Paleocene) and is followed by th ...
(early
Eocene
The Eocene ( ) Epoch is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene' ...
Epoch, c. 56–49 million years ago) age which
crops out in the southeast of
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 London Clay is well known for its
fossil
A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...
content. The fossils from the
lower Eocene
In the geologic timescale the Ypresian is the oldest age or lowest stratigraphic stage of the Eocene. It spans the time between , is preceded by the Thanetian Age (part of the Paleocene) and is followed by the Eocene Lutetian Age. The Ypresian ...
rocks indicate a moderately warm climate, the
tropical
The tropics are the regions of Earth surrounding the Equator. They are defined in latitude by the Tropic of Cancer in the Northern Hemisphere at N and the Tropic of Capricorn in
the Southern Hemisphere at S. The tropics are also referred to ...
or
subtropical
The subtropical zones or subtropics are geographical zone, geographical and Köppen climate classification, climate zones to the Northern Hemisphere, north and Southern Hemisphere, south of the tropics. Geographically part of the Geographical z ...
flora. Though
sea level
Mean sea level (MSL, often shortened to sea level) is an average surface level of one or more among Earth's coastal bodies of water from which heights such as elevation may be measured. The global MSL is a type of vertical datuma standardised g ...
s changed during the deposition of the clay, the
habitat
In ecology, the term habitat summarises the array of resources, physical and biotic factors that are present in an area, such as to support the survival and reproduction of a particular species. A species habitat can be seen as the physical ...
was generally a lush forest – perhaps like in
Indonesia
Indonesia, officially the Republic of Indonesia, is a country in Southeast Asia and Oceania between the Indian and Pacific oceans. It consists of over 17,000 islands, including Sumatra, Java, Sulawesi, and parts of Borneo and New Guine ...
or
East Africa
East Africa, Eastern Africa, or East of Africa, is the eastern subregion of the African continent. In the United Nations Statistics Division scheme of geographic regions, 10-11-(16*) territories make up Eastern Africa:
Due to the historical ...
today – bordering a warm, shallow ocean.
The London Clay is a stiff bluish
clay
Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4).
Clays develop plasticity when wet, due to a molecular film of water surrounding the clay par ...
which becomes brown when weathered and oxidized. Nodular lumps of
pyrite
The mineral pyrite (), or iron pyrite, also known as fool's gold, is an iron sulfide with the chemical formula Iron, FeSulfur, S2 (iron (II) disulfide). Pyrite is the most abundant sulfide mineral.
Pyrite's metallic Luster (mineralogy), lust ...
are frequently found in the clay layers. Pyrite was produced by microbial activity (
sulfate reducing bacteria
Sulfate-reducing microorganisms (SRM) or sulfate-reducing prokaryotes (SRP) are a group composed of sulfate-reducing bacteria (SRB) and sulfate-reducing archaea (SRA), both of which can perform anaerobic respiration utilizing sulfate () as termina ...
) during clay sedimentation. Once clay is exposed to atmospheric oxygen, framboidal pyrite with a great
specific surface
Specific surface area (SSA) is a property of solids defined as the total surface area of a material per unit of mass, (with units of m2/kg or m2/g) or solid or bulk volume (units of m2/m3 or m−1).
It is a physical value that can be used to dete ...
is rapidly oxidized.
Pyrite oxidation produces insoluble brown
iron oxyhydroxide (
FeOOH
Iron(III) oxide-hydroxide or ferric oxyhydroxideA. L. Mackay (1960): "β-Ferric Oxyhydroxide". ''Mineralogical Magazine'' (''Journal of the Mineralogical Society''), volume 32, issue 250, pages 545-557. is the chemical compound of iron, oxygen, ...
) and
sulfuric acid
Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid ( Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen and hydrogen, with the molecular formu ...
leading to the formation of relatively soluble
gypsum
Gypsum is a soft sulfate mineral composed of calcium sulfate dihydrate, with the chemical formula . It is widely mined and is used as a fertilizer and as the main constituent in many forms of plaster, blackboard or sidewalk chalk, and drywall. ...
(CaSO
4·2H
2O,
calcium sulfate
Calcium sulfate (or calcium sulphate) is the inorganic compound with the formula CaSO4 and related hydrates. In the form of γ-anhydrite (the anhydrous form), it is used as a desiccant. One particular hydrate is better known as plaster of Pari ...
dihydrate). This latter is more soluble and mobile than
iron oxide
Iron oxides are chemical compounds composed of iron and oxygen. Several iron oxides are recognized. All are black magnetic solids. Often they are non-stoichiometric. Oxyhydroxides are a related class of compounds, perhaps the best known of whic ...
s and can further recrystallize to form larger crystals sometimes called
selenite
Selenite may refer to:
Substances containing selenium
*A selenium-containing anion or ionic compound with the SeO32− anion:
**Selenite (ion), anion is a selenium oxoanion with the chemical formula SeO32−
***Selenous acid, the conjugate acid, w ...
(coming from the
moon
The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...
, but not related to
selenium
Selenium is a chemical element with the symbol Se and atomic number 34. It is a nonmetal (more rarely considered a metalloid) with properties that are intermediate between the elements above and below in the periodic table, sulfur and tellurium, ...
, although the
etymology
Etymology ()The New Oxford Dictionary of English (1998) – p. 633 "Etymology /ˌɛtɪˈmɒlədʒi/ the study of the class in words and the way their meanings have changed throughout time". is the study of the history of the Phonological chan ...
is the same), or "waterstones".
Large
septarian concretions, produced by microbial activity (oxidation of
organic matter
Organic matter, organic material, or natural organic matter refers to the large source of carbon-based compounds found within natural and engineered, terrestrial, and aquatic environments. It is matter composed of organic compounds that have c ...
) in the ancient seafloor during clay early
diagenesis
Diagenesis () is the process that describes physical and chemical changes in sediments first caused by water-rock interactions, microbial activity, and compaction after their deposition. Increased pressure and temperature only start to play a ...
, are also common. These have been used in the past for making cement. They were once dug for this purpose at Sheppey, near
Sittingbourne
Sittingbourne is an industrial town in Kent, south-east England, from Canterbury and from London, beside the Roman Watling Street, an ancient British trackway used by the Romans and the Anglo-Saxons and next to the Swale, a strip of sea separa ...
, and at
Harwich
Harwich is a town in Essex, England, and one of the Haven ports on the North Sea coast. It is in the Tendring district. Nearby places include Felixstowe to the north-east, Ipswich to the north-west, Colchester to the south-west and Clacton-on- ...
, and also dredged, off the
Hampshire
Hampshire (, ; abbreviated to Hants) is a ceremonial county, ceremonial and non-metropolitan county, non-metropolitan counties of England, county in western South East England on the coast of the English Channel. Home to two major English citi ...
coast. The clay is still used commercially for making
brick
A brick is a type of block used to build walls, pavements and other elements in masonry construction. Properly, the term ''brick'' denotes a block composed of dried clay, but is now also used informally to denote other chemically cured cons ...
s, tiles, and coarse pottery in places such as
Michelmersh
Michelmersh is a small, scattered village in Hampshire, England some three miles () north of Romsey.
It forms a civil parish with Timsbury, Hampshire, Timsbury that forms part of the Test Valley district.
The Monarch's Way long-distance footpath ...
in Hampshire.
Distribution and geology
The London Clay is well developed in the
London Basin
The London Basin is an elongated, roughly triangular sedimentary basin approximately long which underlies London and a large area of south east England, south eastern East Anglia and the adjacent North Sea. The basin formed as a result of compre ...
, where it thins westwards from around in Essex and north Kent to around in
Wiltshire
Wiltshire (; abbreviated Wilts) is a historic and ceremonial county in South West England with an area of . It is landlocked and borders the counties of Dorset to the southwest, Somerset to the west, Hampshire to the southeast, Gloucestershire ...
.
It is not frequently exposed as it is to a great extent covered by more recent
Neogene
The Neogene ( ), informally Upper Tertiary or Late Tertiary, is a geologic period and system that spans 20.45 million years from the end of the Paleogene Period million years ago ( Mya) to the beginning of the present Quaternary Period Mya. ...
sediments and
Pleistocene
The Pleistocene ( , often referred to as the ''Ice age'') is the geological Epoch (geology), epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fina ...
gravel deposits. One location of particular interest is
Oxshott Heath
Oxshott Heath and Woods is an area of woods and heathland in Oxshott, Surrey, England covering approximately , as an area of common land. It is owned by a local authority, however historic rights of access and gathering dead wood where necessary ...
, where the overlying sand and the London Clay layers are exposed as a sand escarpment, rising approximately . This supported a thriving brick industry in the area until the 1960s. The London Clay is also well developed in the
Hampshire Basin
The Hampshire Basin is a geological basin of Palaeogene age in southern England, underlying parts of Hampshire, the Isle of Wight, Dorset, and Sussex. Like the London Basin to the northeast, it is filled with sands and clays of Paleocene and y ...
, where an exposure thick occurs at
Whitecliff Bay
Whitecliff Bay is a sandy bay near Foreland which is the easternmost point of the Isle of Wight, England, about two miles south-west of Bembridge and just to the north of Culver Down. The bay has a shoreline of around and has a popular sandy ...
on the
Isle of Wight
The Isle of Wight ( ) is a county in the English Channel, off the coast of Hampshire, from which it is separated by the Solent. It is the largest and second-most populous island of England. Referred to as 'The Island' by residents, the Isle of ...
and around is spread along of foreshore at
Bognor Regis
Bognor Regis (), sometimes simply known as Bognor (), is a town and seaside resort in West Sussex on the south coast of England, south-west of London, west of Brighton, south-east of Chichester and east of Portsmouth. Other nearby towns ...
,
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 ...
.
The clay was deposited in a sea up to deep at the eastern end. Up to five cycles of deposition (representing
transgression followed by shallowing of the sea) have been found, most markedly at the shallower, western end. Each cycle begins with coarser material (sometimes including rounded
flint
Flint, occasionally flintstone, is a sedimentary cryptocrystalline form of the mineral quartz, categorized as the variety of chert that occurs in chalk or marly limestone. Flint was widely used historically to make stone tools and start fir ...
pebbles), followed by clay which becomes increasingly sandy. The final cycle ends with the Claygate Beds.
[
]
Claygate Beds
The youngest part of the London Clay, known as the ''Claygate Beds'' or ''Claygate Member'' forms a transition between the clay and the sandier Bagshot Beds
In geology, the Bagshot Beds are a series of sands and clays of shallow-water origin, some being fresh-water, some marine. They belong to the upper Eocene formation of the London and Hampshire basins, in England and derive their name from Bags ...
above. This is shown separately on many geological maps, and often caps hills. It is up to thick at Claygate
Claygate is an affluent suburban village in Surrey, England, southwest of central London. It is the only civil parish in the borough of Elmbridge. Surrounded by green belt, it lies inside the Greater London Built-up Area.
Claygate was once in t ...
, Surrey.[ It is now believed to be ]diachronous
In geology, a diachronism (Greek ''dia'', "through" + ''chronos'', "time" + ''-ism''), or diachronous deposit, is a sedimentary rock formation in which the material, although of a similar nature, varies in age with the place where it was deposited. ...
, with the formation at Claygate for example being the same age as the end of the fourth cycle of deposition further east.
Engineering
The presence of a thick layer of London Clay underneath 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 ...
itself, providing a soft yet stable environment for tunnel
A tunnel is an underground passageway, dug through surrounding soil, earth or rock, and enclosed except for the entrance and exit, commonly at each end. A pipeline is not a tunnel, though some recent tunnels have used immersed tube cons ...
ling, was instrumental in the early development of the London Underground
The London Underground (also known simply as the Underground or by its nickname the Tube) is a rapid transit system serving Greater London and some parts of the adjacent ceremonial counties of England, counties of Buckinghamshire, Essex and He ...
, although this is also the reason why London had no true skyscraper
A skyscraper is a tall continuously habitable building having multiple floors. Modern sources currently define skyscrapers as being at least or in height, though there is no universally accepted definition. Skyscrapers are very tall high-ris ...
buildings, at least to the same degree as many other cities throughout the world. Erecting tall buildings in London required very deep, large and costly piled foundations. This has changed in recent decades due to the development of 'plunge piles'. London's skyscrapers float on rafts embedded in the clay.
London Clay is highly susceptible to volumetric changes depending upon its moisture content. During exceptionally dry periods or where the moisture is extracted by tree root activity, the clay can become desiccated and shrink in volume, and conversely swell again when the moisture content is restored. This can lead to many problems near the ground surface, including structural movement and fracturing of buildings, fractured sewers and service pipes/ducts and uneven and damaged road surfaces and pavings. Such damage is recognised to be covered by the interpretation of subsidence
Subsidence is a general term for downward vertical movement of the Earth's surface, which can be caused by both natural processes and human activities. Subsidence involves little or no horizontal movement, which distinguishes it from slope move ...
in buildings insurance policies, and the periods of dry weather in 1976/77 and 1988/92, in particular, led to a host of insurance claims. As a result, many insurance companies have now increased the cost of premiums for buildings located in the most susceptible areas where damage occurred, where the clay is close to the surface.
London Clay is also used to line exhausted quarries. This is because old quarry holes are generally refilled with waste material and by lining it with London Clay (which is virtually impermeable) it prevents waste and hazardous substances from entering the groundwater.
Tunnels in London Clay
London Clay is an ideal medium for boring tunnels, which is one reason why the London Underground
The London Underground (also known simply as the Underground or by its nickname the Tube) is a rapid transit system serving Greater London and some parts of the adjacent ceremonial counties of England, counties of Buckinghamshire, Essex and He ...
railway network expanded very quickly north of the River Thames
The River Thames ( ), known alternatively in parts as the The Isis, River Isis, is a river that flows through southern England including London. At , it is the longest river entirely in England and the Longest rivers of the United Kingdom, se ...
. However, south of the Thames, the stratum at tube level is composed of water-bearing sand and gravel (not good for tunnelling) with London Clay below, which partly explains why there are very few tube tunnels south of the Thames. London Clay has a stand-up time long enough to enable support to be installed without urgency. It is also almost waterproof
Waterproofing is the process of making an object or structure waterproof or water-resistant so that it remains relatively unaffected by water or resisting the ingress of water under specified conditions. Such items may be used in wet environme ...
, resulting in virtually no seepage of groundwater
Groundwater is the water present beneath Earth's surface in rock and soil pore spaces and in the fractures of rock formations. About 30 percent of all readily available freshwater in the world is groundwater. A unit of rock or an unconsolidate ...
into the tunnel. It is over-consolidated, which means that it was once subject to an overburden pressure higher than it is subjected to today, and expands upon excavation, thus gradually loading the support, i.e. it is not necessary to stress the support against the ground.
Uses
Due to its impermeability especially when exposed by ploughing, London Clay does not make good agricultural soil. In Middlesex
Middlesex (; abbreviation: Middx) is a Historic counties of England, historic county in South East England, southeast England. Its area is almost entirely within the wider urbanised area of London and mostly within the Ceremonial counties of ...
, ploughing London Clay land so deep that it brings up clay has historically been called "ploughing up poison".
It was also disliked for building houses on, though inevitably most of Greater London
Greater may refer to:
*Greatness, the state of being great
*Greater than, in inequality (mathematics), inequality
*Greater (film), ''Greater'' (film), a 2016 American film
*Greater (flamingo), the oldest flamingo on record
*Greater (song), "Greate ...
is built on it. Jane Ellen Panton
Jane Ellen Panton or Jane Ellen Frith Panton; Jane Ellen Frith (18 October 1847 – 13 May 1923) was an English writer.
Life
Panton was born as Jane Ellen Frith in Regent's Park in 1847. Her father, William Powell Frith was a successful painter ...
in her ''Suburban Residences and How To Circumvent Them'' (1896), remarks: "I do not believe clay is or even can be fit for anyone to reside upon ... though roses flourished magnificently children didn't, and coughs and colds asted_through_autumn_and_winter,_this_at_asted_through_autumn_and_winter,_this_at_Shortlands">Shortlands.html"_;"title="asted_through_autumn_and_winter,_this_at_Shortlands">asted_through_autumn_and_winter,_this_at_Shortlands.
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_Fossil_flora_and_fauna
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Many London buildings have ultimately been constructed with London Clay. When compressed and burnt, London Clay can be fashioned into brick known as London stock brick">London stock
London stock brick is the type of handmade brick which was used for the majority of building work in London and South East England until the growth in the use of Flettons and other machine-made bricks in the early 20th century. Its distinctive y ...
, identifiable by its yellowish brown hue.
Plant fossils, especially seeds and fruits, are found in abundance and have been collected from the London Clay for almost 300 years.
Some 350 named species of plant have been found, making the London Clay flora one of the world's most diverse for fossil seeds and fruits.
The flora includes plant types found today in tropical forests of Asia and demonstrates the much warmer climate of the Eocene epoch, with plants such as ''
'' (Nipah palms) and other Arecaceae, palms being frequently encountered.
Notable coastal exposures from which fossils can be collected are on the
in the Hampshire Basin.