London Clay

London Clay Formation Stratigraphic range: Ypresian
London Clay at Reculver
Type	Formation
Underlies	Bagshot Formation (London Basin), Wittering Formation and Poole Formation (Hampshire Basin and English Channel)
Overlies	Harwich Formation
Location
Region	southern England
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 consists of a stiff, bluish coloured clay which becomes brown when weathered. Nodular lumps of pyrite and crystals of selenite (sometimes called "waterstones") frequently occur within the clay, and large septarian concretions are also common. These have been used in the past for the manufacturing of cement. They were once dug for this purpose at Sheppey, near Sittingbourne, and at Harwich, and also dredged off the Hampshire coast. The clay itself has been used commercially for making bricks, tiles, and coarse pottery. It is infertile for gardens and crops.

Distribution

The London Clay is well developed in the London Basin, where it thins westwards from around 150 metres (490 ft) in Essex and north Kent to around 4.6 metres (15 ft) in Wiltshire.^[1] 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. 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 km of foreshore at Bognor Regis, West Sussex.^[2]

Formation

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.^[1]

Tunnels in London Clay

The London Clay is an ideal medium for driving tunnels, which is why the London tube railway network expanded so quickly North of the Thames, but South of the Thames the London Clay is much deeper, and the stratum is water-bearing sand and gravel (not good for tunnelling) at tube level, 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 ground-water 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. Sometimes the London Clay is prettily coloured, and is called shepherd's plaid, but generally the colours disappear when the clay is fired.

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.^[1] 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.^[3]

Fossil fauna and flora

Notable coastal exposures from which fossils can be collected are on the Isle of Sheppey in Kent and Walton-on-the-Naze, Essex in the London Basin, and Bognor Regis in the Hampshire Basin.

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.

Plant fossils, including seeds and fruits, may also be found in abundance. The flora demonstrates the much hotter climate of that time, with plants such as Nypa (Nipah palms) being frequently encountered. Plant fossils 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 varied for fossil seeds and fruits.^[4]

The following species list follows Clouter (2007).^[5]

Vertebrates

Mammals

• Argillotherium
• Coryphodon eocaenus – a pantodont
• Hyracotherium^{[Note 1]} – the famous horse ancestor
• Oxyaena – a creodont

Birds

• 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

Reptiles

Crocodilians

• Diplocynodon – an alligator
• Crocodilus spenceri – a crocodile

Snakes

• 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

Bony fish

• 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 lancetfish relative
• Aulopopsis depressifrons, A. egertoni and Labrophagus esocinus – aulopuses
• Beerichthys ingens and B. sp. – Two species of luvar or luvar-like fish^[6]
• 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

Cartilaginous fish

• 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]} Jackelotodus 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

Crustaceans

Exuvia of Hoploparia

• Lobsters and shrimp
  • Archiocarabus bowerbanki
  • Callianassa sp.
  • Homarus morrisi ^[7]
  • Hoploparia gammaroides
  • Linuparus eocenicus & L. scyllariformis
  • Scyllarides tuberculatus
  • Scyllaridia koenigi
  • Thenops scyllariformis
• Barnacles
  • Arcoscapellum quadratum
  • Scalpellum minutum and S. quadratum
• Crabs
  • Campylostoma mutatiforme
  • Cyclocorystes pulchellus^{[Note 10]}
  • Dromilites bucklandi & D. lamarki
  • Glyphthyreus wetherelli
  • Goniochela angulata
  • Mithracia libinioides
  • Oediosoma ambigua
  • Portunites incerta & P. stintoni
  • Xanthilites bowerbanki
  • Zanthopsis bispinosa, Z. dufori, Z. leachei, Z. nodosa and Z. unispinosa
• Mantis shrimp
  • Squilla wetherelli

Molluscs

Cephalopods

• 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

Bivalves

• 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

Gastropods

• 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

Tusk shells

• Antalis anceps and A. nitens

Echinoderms

Ophiura wetherelli from the London Clay of Bognor Regis

• 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

Cnidarians

• Paracyathus brevis and P. caryophyllus – corals
• Graphularia wetherelli – hydrozoan

Other invertebrates

• 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

Ichnofossils

• Ditrupa plana, Rotularia bognorensis and Serpula trilineata – polychaete worm tubes?
• Scolithos

Engineering

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.

Agriculture

"London clay is not hospitable to most plants... ploughing it up where it lies so near the surface as to be accessible to the plough is injurious to the surface soil and future crops. In Middlesex it is called 'ploughing up poison'"^[8]

See also

• Geology of London
• Geology of the United Kingdom
• Geology of Hertfordshire
• Geology of Hampshire
• List of fossil sites

Notes

1. ^ Often called Eohippus
2. ^ Includes "Primobucco" olsoni
3. ^ Sometimes placed in Aprionodon
4. ^ Sometimes placed in Physodon
5. ^ Sometimes placed in Rhinoptera
6. ^ Sometimes called Hypotodus robustus
7. ^ Sometimes called Eugomphodus macrotus
8. ^ Sometimes placed in Acanthius
9. ^ Sometimes placed in Xendolamia
10. ^ Sometimes called Necrozius bowerbanki
11. ^ Sometimes placed in Eutrephoceras
12. ^ Sometimes called Modiolus depressus
13. ^ Sometimes placed in Striarca
14. ^ Sometimes placed in Cyprina
15. ^ Sometimes called A. rugatus
16. ^ Sometimes called Pitaria tenuistriata
17. ^ Sometimes placed in Ledina
18. ^ Sometimes called Amussium corneum
19. ^ Sometimes placed in Protocardium
20. ^ Sometimes placed in Pteria
21. ^ Sometimes placed in Ostrea
22. ^ Sometimes considered a variety of Scala undosa
23. ^ Sometimes called A. sowerbyii
24. ^ Sometimes placed in Tibia
25. ^ Sometimes in Hemipleurotoma
26. ^ Sometimes placed in Conospirus
27. ^ Sometimes in Hemipleurotoma
28. ^ Sometimes in Hemipleurotoma
29. ^ Sometimes in Hemipleurotoma
30. ^ Sometimes S. bifaci or S. bifacsi
31. ^ Sometimes included in T. teretrium
32. ^ Sometimes included in T. teretrium
33. ^ Sometimes placed in Galeodea
34. ^ Sometimes called Newtoniella charlsworthi
35. ^ Sometimes called Solarium pulchrum
36. ^ Sometimes placed in Natica
37. ^ Sometimes called Fusinus unicarinatus
38. ^ Sometimes placed in Bartonia
39. ^ Sometimes called Euthriofusus complanatus
40. ^ Sometimes called Euthriofusus transversarius
41. ^ Sometimes placed in Ficus
42. ^ Sometimes called Murex argillaceus
43. ^ Sometimes called T. tenuiplica^{[verification needed]}
44. ^ Sometimes placed in Aurinia
45. ^ Sometimes placed in Calyptraea
46. ^ Sometimes placed in Adeorbis
47. ^ Sometimes called Onutusus extensa
48. ^ Sometimes placed in Asteropecten
49. ^ Sometimes placed in Rhizochrinus

References

1. ^ ^{a b c} Sumbler, M. G. (1996). London and the Thames Valley. British Regional Geology series (4th ed.). British Geological Survey. ISBN 0-11-884522-5. 
2. ^ 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. 
3. ^ 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 0-85272478-0. 
4. ^ Collinson, M. (1983). Fossil plants of the London Clay. The Palaeontological Association. 
5. ^ Clouter, Fred (June 29, 2007). "London Clay Species List". http://www.sheppeyfossils.com/pages/london_clay_species_list.htm. Retrieved June 16, 2008. 
6. ^ 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. http://www.sil.si.edu/SmithsonianContributions/Paleobiology/pdf_lo/SCtP-0081.pdf. 
7. ^ W. J Quayle (1987). "English Eocene Crustacea (lobsters and stomatopod)" (PDF). Palaeontology 30 (3): 581–612. http://palaeontology.palass-pubs.org/pdf/Vol%2030/Pages%20581-612.pdf. 
8. ^ 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, accompanied with remarks of several respectable gentlemen and farmers. Published by G. and W. Nicol, second edition, 1807. Page 20.