|London Clay Formation
Stratigraphic range: Ypresian
London Clay at Reculver
|Unit of||Thames Group|
|Underlies||Bagshot Formation (London Basin), Wittering Formation and Poole Formation (Hampshire Basin and English Channel)|
|Thickness||up to 150 m|
Geological map of the London Basin; the London Clay is marked in dark brown.
The London Clay Formation is a marine geological formation of Ypresian (Lower Eocene Epoch, c. 56-49 Ma) age which crops out in the southeast of England. The London Clay is well known for the fossils it contains. The fossils from the Lower Eocene indicate a moderately warm climate, the flora being tropical or subtropical. Though sea levels changed during the deposition of the Clay, the habitat was generally a lush forest - perhaps like in Indonesia or East Africa today - bordering a warm, shallow ocean.
The London Clay is a stiff bluish clay which becomes brown when weathered. There are nodular lumps of pyrite and crystals of selenite (sometimes called "waterstones") frequently in the clay, and large septarian concretions are also common. These have been used in the past for making cement. They were once dug for this purpose at Sheppey, near Sittingbourne, and at Harwich, and also dredged off the Hampshire coast. The clay is still used commercially for making bricks, tiles, and coarse pottery in places such as Michelmersh in Hampshire. It is infertile for gardens and crops.
- 1 Distribution and geology
- 2 Fossil flora and fauna
- 2.1 Plants
- 2.2 Animals
- 3 Engineering
- 4 Agriculture
- 5 See also
- 6 Notes
- 7 References
Distribution and geology
The London Clay is well developed in the London Basin, where it thins westwards from around 150 metres (492 feet) in Essex and north Kent to around 4.6 metres (15 feet) in Wiltshire. though it is not frequently exposed as it is to a great extent covered by more recent Neogene sediments and Pleistocene gravel deposits. One location of particular interest is Oxshott Heath, where the overlying sand and the London Clay layers are exposed as a sand escarpment, rising approximately 25 metres (82 feet). This supported a thriving brick industry in the area until the 1960s. The London Clay is also well developed in the Hampshire Basin, where an exposure 91 metres (299 ft) thick occurs at Whitecliff Bay on the Isle of Wight and around 101 metres (331 ft) is spread along 6 kilometres (4 miles) of foreshore at Bognor Regis, West Sussex.
The clay was deposited in a sea up to 200 metres (660 ft) 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 pebbles), followed by clay which becomes increasingly sandy. The final cycle ends with the 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 above. This is shown separately on many geological maps, and often caps hills. It is up to 15 metres (49 ft) thick at Claygate, Surrey. It is now believed to be diachronous, with the formation at Claygate for example being the same age as the end of the fourth cycle of deposition further east.
Fossil flora and fauna
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 Nypa (Nipah palms) and other palms being frequently encountered. The following plants list is incomplete and is based on Chandler.
- Acrostichum - mangrove fern
- Salviniaceae - water ferns
- Araucariaceae - monkey puzzle, bunya pine, and Norfolk pine
- †Araucarites spp.
- Pinus spp.
- ?Taxaceae indet.
- Cephalotaxus bowerbanki
- †Cupressinites spp.
- Podocarpus argillaelondinensis?
- Arecaceae - palms
- Oncosperma anglica
- †Caryotispermum cantiense
- Sabal spp.
- Livistona minima
- †Palmospermum spp.
- Nypa burtini (syn. Nipa burtini)
- Betulaceae - birch, alder and hornbeams
- Alnus richardsoni (syn. Petrophiloides richardsoni) - an alder
- Magnolia spp.
- Lauraceae - avocado and cinnamon family
- Beilschmiedia spp.
- Cinnamomum spp.
- †Crowella globosa
- Endiandra spp.
- †Laurocalyx spp.
- †Laurocarpum spp.
- Litsea spp.
- †Protoaltingia europaea
- †Protoravensara sheppeyensis
- Moraceae - mulberry and fig family
- ?Morus sp.
- Menispermaceae - moon seed family
- †Anonaspermum spp.
- †Bowerbankella tiliacoroidea
- †Davisicarpum gibbosum
- †Eohypserpa parsonsi
- †Microtinomiscium foveolatum
- †Tinomiscoidea scaphiformis
- Tinospora excavata
- †Wardenia davisi
- Nymphaeaceae - water lilies
- †Protobarclaya eocenica
- Erythropalum spp.
- Olax depressa
- Platanaceae - sycamore or plane tree
- †Plataninium decipiens
- Trochodendron pauciseminum
- †Urticicarpum scutellum
Animal fossils include bivalves, gastropods, nautilus, worm tubes, brittle stars and starfish, crabs, lobsters, fish (including shark and ray teeth), reptiles (particularly turtles), and a large diversity of birds. A few mammal remains have also been recorded. Preservation varies; articulated skeletons are generally rare. Of fish, isolated teeth are very frequent. Bird bones are not infrequently encountered compared to other lagerstätten, but usually occur as single bones and are often broken.
The following fauna species list follows Clouter (2007).
- Coryphodon eocaenus – a pantodont
- Hyracotherium[Note 1] – the famous horse ancestor
- Oxyaena – a creodont
- Anatalavis oxfordi – a waterbird possibly related to the Magpie-goose of Australia
- Argillipes – perhaps a landfowl
- Dasornis, Odontopteryx and Pseudodontornis – pseudo-tooth birds
- Eocolius – a coliiform
- Eostrix – an owl
- Halcyornis – a parrot or roller relative
- Lithornis and Promusophaga – paleognaths
- Parvigyps – perhaps a diurnal raptor
- Pediorallus – a paleognath or landfowl
- Percolinus – perhaps another landfowl
- "Precursor" – apparently a chimera of Charadriiformes and Psittaciformes (and possibly other) bones
- Primapus – a swift-like bird
- Primodroma – a tubenose, possibly a storm-petrel
- Prophaeton – a tropicbirds relative
- Proherodius – another waterbird
- Proplegardis – a stork or ibis
- Pulchrapollia – a parrot relative[Note 2]
- Stintonornis – probably a hawk relative
- Palaeophis toliapicus and P. typhaeus
Turtles and tortoises
- Allaeochelys – a pig-nosed turtle
- Argillochelys, Eochelone, Puppigerus and "Thalassochelys" sp. – true sea-turtles
- Chrysemys bicarinata and C. testudiniformis – pond turtles
- Eosphargis – a leatherback sea-turtle
- Homopus comptoni – a tortoise
- Lytoloma crassicostatum and L. planimentum – prehistoric sea-turtles
- Palaeaspis – an African sideneck turtle
- Podocnemis bowerbanki – an American sideneck turtle
- Trionyx pustulatus and T. sp. – softshell turtles
- Dacochelys and Pseudotrionyx – incertae sedis
- Acestrus elongatus, A. ornatus, Aglyptorhynchus sulcatus, A. venablasi, Xiphiorhynchus parvus and X priscus – swordfish relatives
- Acipenser toliapicus – a true sturgeon
- Albula oweni – a bonefish
- Ampheristus toliapicus – a scorpionfish
- Ardiodus marriotti – incertae sedis
- Argillichthys toombsi – a lizardfish relative
- Aulopopsis depressifrons, A. egertoni and Labrophagus esocinus – flagfins
- Beerichthys ingens and B. sp. – Two species of luvar or luvar-like fish
- Bramoides brieni and Goniocranion arambourgi – pomfrets
- Brychaetus muelleri – an arowana
- Bucklandium diluvii – a naked catfish
- Cylindracanthus rectus and Hemirhabdorhynchus elliotti – Blochiidae
- Cymbium proosti, Eocoelopoma colei, E. curvatum, E. gigas, E. hopwoodi, Eothynnus salmoneus, Scombramphodon crassidens, S. sheppeyensis, Scombrinus macropomus, S. nuchalis, Sphyraenodus priscus, Tamesichthys decipiens, Wetherellus brevior, W. cristatus, W. longior and Woodwardella patellifrons – mackerel and tuna relatives
- Diodon sp. – a porcupinefish
- Egertonia isodonta and Phyllodus toliapicus – Phyllodontidae
- Elops sp., Esocelops cavifrons, Megalops oblongus, M. priscus, Promegalops sheppeyensis and P. signeuxae – ladyfish
- Enniskillenus radiatus – acanthomorph
- Eutrichurides winkleri – a cutlassfish
- Halecopsis insignis – Halecopsidae
- Laparon alticeps and Whitephippus tamesis – spadefish
- Lehmanamia sheppeyensis – a bowfin
- Myripristis toliapicus, Naupygus bucklandi and Paraberyx bowerbanki – soldierfish
- Percostoma angustum, Plesioserranus cf. wemmeliensi and Serranopsis londinensis – groupers
- Podocephalus curryi, P. nitidus, Sciaenuropsis turneri and Sciaenurus bowerbanki – porgies
- Progempylus edwardsi – a snake mackerel
- Pseudosphaerodon antiquus and P. navicularis – wrasses?
- Pycnodus bowerbanki and P. toliapicus – Pychnodontidae
- Rhinocephalus planiceps and Trichurides sagittidens – hakes
- Rhynchorhinus branchialis and R. major – Eccelidae
- Tetratichthys antiquitatis – a jack mackerel
- Abdounia beaugi, Carcharhinus sp.[Note 3] and Physogaleus secundus[Note 4] – requiem sharks
- Aetobatis irregularis, Burnhamia daviesi,[Note 5] Myliobatis dixoni, M. latidens, M. raouxi and M. toliapicus – eagle rays
- Anomotodon sheppeyensis – a goblin shark
- Carcharias hopei,[Note 6] Jaekelotodus trigonalis, Odontaspis winkleri, Palaeohypotodus rutoti and Striatolamia macrota[Note 7] – sand sharks
- Edaphodon bucklandi and Elasmodus hunteri – chimaeras
- Dasyatis davisi and D. wochadunensis – stingrays
- Galeorhinus lefevrei, G. minor, G. recticonus, G. ypresiensis, Mustelus whitei and Triakis wardi – hound sharks
- Heterodontus vincenti, H. wardenensis and H. woodwardi – bullhead sharks
- Hexanchus agassizi, H. collinsonae, H. hookeri, Notorhynchus serratissimus and Weltonia burnhamensis – cow sharks
- Isisteus trituratus and Squalus minor[Note 8] – dogfish sharks
- Isurolamna affinis, Isurus nova, I. praecursor, Lamna inflata, L. lerichei, Otodus obliquus and Xiphodolamia eocaena[Note 9] – white sharks
- Megascyliorhinus cooperi, Scyliorhinus casieri, S. gilberti, S. pattersoni and S. woodwardi – catsharks
- Pararhincodon sp? – an indeterminate shark
- Raja sp.? – an indeterminate ray
- Squatina prima – an angel shark
- Lobsters and shrimp
- Campylostoma mutatiforme
- Cyclocorystes pulchellus[Note 10]
- Dromilites bucklandi & D. lamarki
- Glyphthyreus wetherelli
- Goniochela angulata
- Harpactoxanthopsis cf. quadrilo
- Mithracia libinioides
- Oediosoma ambigua
- Portunites incerta & P. stintoni
- Xanthilites bowerbanki
- Zanthopsis bispinosa, Z. dufori, Z. leachei, Z. nodosa and Z. unispinosa
- Mantis shrimp
- Aturia ziczac, Cimomia imperialis, Deltoidonautilus sowerbyi, Euciphoceras regale, Eutrephoceras urbanum, Hercoglossa cassiniana and Simplicioceras centrale[Note 11] – nautiluses
- Belopterina levesquei, Belosepia blainvillei and B. sepioidea – cuttlefish
- Abra splendens – Semelidae
- Amygdalum depressum[Note 12] and Modiolus tubicola – Mytilidae
- Anomia scabrosa – a jingle shell
- Arca nitens, A. tumescens and Glycymeris wrigleyi[Note 13] – ark clams
- Arctica planata[Note 14] – Arcticidae
- Astarte davisi, A. filigera and A. rugata[Note 15] – Astartidae
- Calpitaria sulcataria[Note 16] – a venus clam
- Corbula globosa – Corbulidae
- Cuspidaria inflata and C. lamallosa[verification needed] – Cuspidariidae
- Nuculana amygdaloides[Note 17] and N. prisca – Nuculanidae
- Lentipecten corneus[Note 18] and Pecten sp. – scallops
- Nemocardium nitens[Note 19] and N. semigranulatum – Cardiidae
- Nucula consors – Nuculidae
- Ostrea sp. – a true oysters
- Pinna affinis – a pen shell
- Pleurolectroma media[verification needed][Note 20] and Pteria papyracea – pearl oysters
- Pycnodonte gryphovicina[Note 21] – Pycnodontidae
- Teredina personata and Teredo sp. – shipworms
- Thyasira goodhali – Thyasiridae
- Venericardia trinobantium – Carditidae
- Verticordia sulcata – Verticordiidae
- Acrilla cymaea, Foratiscala perforata, Litoriniscala scalaroides and Undiscala primaeva[Note 22] – wentletraps
- Aporrhais sowerbii[Note 23] and Eotibia lucida[Note 24] – true conchs
- Bathytoma granata, B. turbida, Clavatula conica,[Note 25] Cochlespira gyrata, Conolithus concinnus,[Note 26] Endiatoma cerithiformis, Fusiturris selysi,[Note 27] F. simillima, F. wetherelli,[Note 28] Gemmula koninckii,[Note 29] Hemipleurotoma fasciolata, H. prestwichi, Pseudotoma topleyi, Surculites errans,[Note 30] S. velatus, Turricula crassa, T. helix, T. latimarginata,[Note 31] T. nanodis,[Note 32] T. symmetrica and T. teretrium – Conoidea
- Bonellitia clathratum and B. laeviuscula – nutmeg shells
- Bullinella sp., Crenilabium elongatum, ?Roxiana sp., Scaphander ?parisiensis and Tornatellaea simulata – opisthobranchs
- Camptoceratops prisca, Spiratella mercinensis, S. taylori and S. tutelina – sea-butterflies
- Cassis striata and Mambrina gallica[Note 33] – tun shells
- Cepatia cepacea, Daphnobela juncea, Litiopa sulculosa, Orthochetus elongatus[Note 34] and Stellaxis pulcher[Note 35] – incertae sedis
- Eocypraea oviformis – a cowrie
- Euspira glaucinoides[Note 36] and Sinum clathratum – moon snails
- Falsifusus londini,[Note 37] Fusinus coniferus, F. wetherelli, Pseudoneptunea curta,[Note 38] Siphonalia highgatensis, Streptolathyrus triliniatus, S. zonulatus, Wrigleya complanata[Note 39] and W. transversaria[Note 40] – true whelks
- Ficopsis multiformis[Note 41] – a fig shell
- Lacunella sp. – a periwinkle
- Mathilda sororcula - Mathildidae
- Murex subcristatus and Paziella argillacea[Note 42] – murex snails
- Pachysyrnola sp. and Turbonilla subterranea[Note 43] – pyramid shells
- Patella sp. – Patellidae
- Ptychatractus aff. interuptus, Scaphella wetherelli[Note 44] and Volutospina nodosa – volutes
- Rilla cf. tenuistriata – Streptaxidae
- Ringicula turgida – Ringiculidae
- Sassia morrisi – a triton shell
- Sigapatella sp.[Note 45] – Calyptraeidae
- Tornus sp.[Note 46] and Turboella cf. misera – Rissoidae
- Xenophora extensum[Note 47] – a carrier shell
- Antalis anceps and A. nitens
- Asteropecten crispatus, Coulonia colei, Hemiaster bowerbanki, Hippasteria tuberculata, Ophioglypha wetherelli and Teichaster stokesii[Note 48] – starfish
- Coelopleurus wetherelli and Schizaster sp. – sea urchins
- Democrinus londinensis[Note 49] – crinoid
- ?Ophiacantha sp., Ophioglypha wetherelli, Ophiomusium sp. and Ophiura wetherelli – brittlestars
- Adenellopsis wetherelli, Aimulosia sp., Batopora clithridiata, Beisselina sp., Cribrilina sp., Didymosella sp., Dittosaria wetherelli, Entalophora sp., Idmonia sp., Lunulites sp., Nellia sp., Pachythecella incisa, Vibracellina sp. and Websteria crissioides – bryozoans
- Hemiptera gen. et sp. indet. – true bug
- Lingula tenuis, Terebratulina striatula and T. wardenensis – lampshells
- Stelleta sp. – sponge
The presence of a thick layer of London Clay underneath London itself, providing a soft yet stable environment for tunnelling, was instrumental in the early development of the London Underground, although this is also the reason why London has no true skyscraper buildings, at least to the same degree as many other cities throughout the world. Erecting tall buildings in London requires very deep, large and costly piled foundations.
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 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.
Tunnels in London Clay
The London Clay is an ideal medium for driving tunnels, which is why the London Tube railway network expanded quickly north of the Thames, but south of the Thames the stratum at tube level is water-bearing sand and gravel (not good for tunnelling) with London Clay below, which is why there are few tube tunnels there. London Clay has a stand-up time long enough to enable support to be installed without urgency. It is also almost waterproof, resulting in virtually no seepage of groundwater into the tunnel. It is over-consolidated, which means that it is under pressure, and expands upon excavation, thus gradually loading the support, i.e. it is not necessary to stress the support against the ground.
Due to its impermeability especially when exposed by ploughing, London clay does not make good agricultural soil. In Middlesex it has historically been called "ploughing up poison."
- Geology of Hampshire
- Geology of Hertfordshire
- Geology of London
- Geology of the United Kingdom
- List of fossil sites
- Often called Eohippus
- Includes "Primobucco" olsoni
- Sometimes placed in Aprionodon
- Sometimes placed in Physodon
- Sometimes placed in Rhinoptera
- Sometimes called Hypotodus robustus
- Sometimes called Eugomphodus macrotus
- Sometimes placed in Acanthius
- Sometimes placed in Xendolamia
- Sometimes called Necrozius bowerbanki
- Sometimes placed in Eutrephoceras
- Sometimes called Modiolus depressus
- Sometimes placed in Striarca
- Sometimes placed in Cyprina
- Sometimes called A. rugatus
- Sometimes called Pitaria tenuistriata
- Sometimes placed in Ledina
- Sometimes called Amussium corneum
- Sometimes placed in Protocardium
- Sometimes placed in Pteria
- Sometimes placed in Ostrea
- Sometimes considered a variety of Scala undosa
- Sometimes called A. sowerbyii
- Sometimes placed in Tibia
- Sometimes in Hemipleurotoma
- Sometimes placed in Conospirus
- Sometimes in Hemipleurotoma
- Sometimes in Hemipleurotoma
- Sometimes in Hemipleurotoma
- Sometimes S. bifaci or S. bifacsi
- Sometimes included in T. teretrium
- Sometimes included in T. teretrium
- Sometimes placed in Galeodea
- Sometimes called Newtoniella charlsworthi
- Sometimes called Solarium pulchrum
- Sometimes placed in Natica
- Sometimes called Fusinus unicarinatus
- Sometimes placed in Bartonia
- Sometimes called Euthriofusus complanatus
- Sometimes called Euthriofusus transversarius
- Sometimes placed in Ficus
- Sometimes called Murex argillaceus
- Sometimes called T. tenuiplica[verification needed]
- Sometimes placed in Aurinia
- Sometimes placed in Calyptraea
- Sometimes placed in Adeorbis
- Sometimes called Onutusus extensa
- Sometimes placed in Asteropecten
- Sometimes placed in Rhizochrinus
- "Michelmersh Brick and Tile Company". Retrieved 2013-05-19.
- Sumbler, M. G. (1996). London and the Thames Valley. British Regional Geology series (4th ed.). British Geological Survey. ISBN 0-11-884522-5.
- Melville, R. V. & E. C. Freshney (1992). The Hampshire Basin and adjoining areas. British Regional Geology series (4th ed.). British Geological Survey. ISBN 0-11-884203-X.
- Ellison, R. A. et al. (2004). Geology of London: Special Memoir for 1:50,000 Geological sheets 256 (North London), 257 (Romford), 270 (South London) and 271 (Dartford) (England and Wales). British Geological Survey. ISBN 0-85272-478-0.
- Chandler, M.E.J. 1961. The lower Tertiary floras of southern England I. Palaeocene floras, London Clay flora. London: British Museum (Natural History).
- Collinson, M. (1983). Fossil plants of the London Clay. The Palaeontological Association.
- Poole, I., K.L. Davies and H.P. Wilkinson 2002. A review of the platanaceous woods from the Eocene paratropical rainforest of south-east England. Botanical Journal of the Linnean Society, 139: 181–191.
- Clouter, Fred (June 29, 2007). "London Clay Species List". Retrieved June 16, 2008.
- Alexandre F. Bannikov & James C. Tyler (1995). "Phylogenetic revision of the fish families Luvaridae and †Kushlukiidae (Acanthuroidei), with a new genus and two new species of Eocene luvarids" (PDF). Smithsonian Contributions to Paleobiology 81: 1–45. doi:10.5479/si.00810266.81.1.
- W. J Quayle (1987). "English Eocene Crustacea (lobsters and stomatopod)" (PDF). Palaeontology 30 (3): 581–612.
- Buildings on Clay The effects of geology, climate and vegetation on heave and settlement, Derek Clarke and Joel Smethurst
- View of the Agriculture of Middlesex: With Observations on the Means of Its Improvement, and Several Essays on Agriculture in General. By Board of Agriculture (Great Britain), John Middleton. Published by G. and W. Nicol, second edition, 1807. Page 20.