Triassic Water
An aerial view along the River Thames at sunset, with Tower Bridge in the middle distance and the towers of the City of London beyond.

Was London underwater?

The rock database this site uses stops at the Channel. Ask it what lies under London and it answers, politely and emptily, that it has nothing — not because Britain's rock is a mystery, but because that database was built to cover North America. The British Geological Survey's own map answers perfectly well, and you can read it further down this page. Meanwhile the fossils tell the loudest story of anywhere we looked: 1,088 of them dug up around this city, 856 from the sea and 232 from land — more than Denver, Kansas or Los Angeles, and including dinosaurs you will have heard of. Every one of those fossils came out of the ground a good distance from Trafalgar Square.

Real photograph · Sven Hansche/Shutterstock.com · Shutterstock Standard License

The answer, age by age

Five ages in the past of this place, each one a window rather than a day. Each says which witness spoke — and where our evidence cannot answer yet, it says that too.

  1. 250MaOur evidence has no witness here
  2. 200MaOnly the fossils speak
  3. 150MaOnly the fossils speak
  4. 100MaOnly the fossils speak
  5. 66MaOnly the fossils speak

“Ma” means millions of years ago. The dashed mark means our sources have nothing for that age — which is a finding, not a fault.

The database that ends, the map that still answers, the record that overflows

The database that ends

Asked about the rock under London, the database we use for regional geology returns an empty answer — successfully. In its own record:

geologic_units/map returned 3 unit(s) across 3 of 4 scales; columns returned 0; units returned 0 (macrostrat api/v2 2.3.9, queried 2026-08-27). columns and units returned an empty success (HTTP 200, data: []) — Macrostrat does not cover this point on those routes, so those facts are absent, not omitted.

The map that still answers

Britain’s rock is not a mystery — it is one of the most carefully mapped places on Earth. The geological map of this exact point returns the Thames Group, and it is the British Geological Survey’s own work:

British Geological Survey. DiGMapGB-625. British Geological Survey ©NERC.

The record that overflows

113 fossils dug up near London have an age range covering 100 million years ago: 111 from the sea, 2 from land. The closest of them was found about 12 km away — near the city, never under it.

Databases grow outward from wherever their builders started, and this one started in North America. That is worth knowing before you ever read an empty answer as an absence in the world rather than an edge of a dataset. The honest version is the one on this page: this database does not reach here, another one does, and a third holds more fossils for London than for any American city we checked.

Travel back in time

London is the one page where the model can place the ground at every single age. Watch the disagreement between models grow as you go back, though — by the oldest row it is the largest anywhere on this site.

250
million years agojump to the evidence250 million years ago, the plate model puts this ground about 13° north of the equator. This is one of the ages the models argue about most: published reconstructions put it as much as 6.4° of latitude apart, which is several hundred kilometres. Treat it as one model's answer, not a photograph.
200
million years agojump to the evidence200 million years ago, the plate model puts this ground about 18° north of the equator. Published models disagree by about 4.4° of latitude here — a few hundred kilometres — so it is one model's answer, not a photograph.
150
million years agojump to the evidence150 million years ago, the plate model puts this ground about 23° north of the equator. Published models disagree by about 4.3° of latitude here — a few hundred kilometres — so it is one model's answer, not a photograph.
100
million years agojump to the evidence100 million years ago, the plate model puts this ground about 33° north of the equator. This is one of the ages the models argue about most: published reconstructions put it as much as 5.4° of latitude apart, which is several hundred kilometres. Treat it as one model's answer, not a photograph.
66
million years agojump to the evidence66 million years ago, the plate model puts this ground about 44° north of the equator. Published models disagree by about 3.8° of latitude here — a few hundred kilometres — so it is one model's answer, not a photograph.

What was the water doing?

Five ages, oldest first. Each one has two kinds of witness — the rock of the wider region, and the fossils dug up near the city — and they are kept apart on purpose, because they are answers to different questions.

Each age here is a marker on the timeline, not a single day. The evidence that belongs to it comes with an age range of its own that overlaps the marker — so it can tell you what this stretch of time was like, and never what was happening on one exact date.

Our evidence has no witness here

Around 250 million years ago

250 million years ago, the plate model puts this ground about 13° north of the equator. This is one of the ages the models argue about most: published reconstructions put it as much as 6.4° of latitude apart, which is several hundred kilometres. Treat it as one model's answer, not a photograph.

An open question

Neither of the evidence sources we use can answer this one: the regional rock database does not cover this place at all, so it has nothing to say about 250 million years ago, and no fossil dug up nearby covers that age either. That is a real gap in the evidence, not a gap in the past — and saying so is more useful than guessing.

Only the fossils speak

Around 200 million years ago

200 million years ago, the plate model puts this ground about 18° north of the equator. Published models disagree by about 4.4° of latitude here — a few hundred kilometres — so it is one model's answer, not a photograph.

The rock of the region

The regional rock record does not cover this place at all, so there is no regional answer for 200 million years ago.

The fossils dug up nearby

16 fossils dug up near London have an age range covering 200 million years ago: 16 from the sea, 0 from land. The closest of them was found about 30 km away — near the city, never under it.

Only the fossils speak

Around 150 million years ago

150 million years ago, the plate model puts this ground about 23° north of the equator. Published models disagree by about 4.3° of latitude here — a few hundred kilometres — so it is one model's answer, not a photograph.

The rock of the region

The regional rock record does not cover this place at all, so there is no regional answer for 150 million years ago.

The fossils dug up nearby

16 fossils dug up near London have an age range covering 150 million years ago: 16 from the sea, 0 from land. The closest of them was found about 30 km away — near the city, never under it.

Only the fossils speak

Around 100 million years ago

100 million years ago, the plate model puts this ground about 33° north of the equator. This is one of the ages the models argue about most: published reconstructions put it as much as 5.4° of latitude apart, which is several hundred kilometres. Treat it as one model's answer, not a photograph.

The rock of the region

The regional rock record does not cover this place at all, so there is no regional answer for 100 million years ago.

The fossils dug up nearby

113 fossils dug up near London have an age range covering 100 million years ago: 111 from the sea, 2 from land. The closest of them was found about 12 km away — near the city, never under it.

Only the fossils speak

Around 66 million years ago

66 million years ago, the plate model puts this ground about 44° north of the equator. Published models disagree by about 3.8° of latitude here — a few hundred kilometres — so it is one model's answer, not a photograph.

The rock of the region

The regional rock record does not cover this place at all, so there is no regional answer for 66 million years ago.

The fossils dug up nearby

16 fossils dug up near London have an age range covering 66 million years ago: 16 from the sea, 0 from land. The closest of them was found about 12 km away — near the city, never under it.

What was dug up nearby?

Every fossil below was dug up somewhere around London, never underneath it, so each carries the distance to where it was actually found. One group is missing on purpose: the sixteen fossils whose age range covers 66 million years ago are counted in the 100 million year group instead, because each fossil belongs to exactly one group — and the page would rather show you that than count anything twice.

Around 100 million years ago

  • An Iguanodon — its group, Ornithischia, is the bird-hipped dinosaurs, mostly plant-eaters, including Iguanodon — from around this time (its own age range is 113.2–119.57 million years) was dug up about 43 km from here, in the Sandgate (Bargate Sandstone), Surrey.
  • A Baryonyx walkeri — its group, Reptilia, is reptiles and their extinct relatives; this broad group includes animals such as lizards, snakes, turtles, crocodilians and many prehistoric reptiles — from around this time (its own age range is 121.4–125.77 million years) was dug up about 44 km from here, in the Weald Clay (Upper), Surrey.
  • A Mantellisaurus atherfieldensis — its group, Ornithischia, is the bird-hipped dinosaurs, mostly plant-eaters, including Iguanodon — from around this time (its own age range is 121.4–125.77 million years) was dug up about 44 km from here, in the Weald Clay (Upper), Surrey.
  • A Dercetis elongatus — its group, Osteichthyes, is bony fishes and their relatives — most of the familiar fish a child could name belong here — from around this time (its own age range is 85.7–89.8 million years) was dug up about 11 km from here, in the Seaford, Greater London.
  • An Elasmostoma scitulum — its group, Calcarea, is the calcareous sponges, whose supporting spicules are made of calcium carbonate — the same material as chalk — from 100 million years ago was dug up about 12 km from here, in Greater London.
  • A Pharetrospongia strahani — its group, Demospongiae, is most of the sponges, soft animals that sit still and filter their food from the water — from 100 million years ago was dug up about 12 km from here, in Greater London.

Around 150 million years ago

  • An Iguanodon — its group, Ornithischia, is the bird-hipped dinosaurs, mostly plant-eaters, including Iguanodon — from around this time (its own age range is 121.4–132.6 million years) was dug up about 44 km from here, in the Weald Clay (Lower).
  • A Megalosaurus — its group, Reptilia, is reptiles and their extinct relatives; this broad group includes animals such as lizards, snakes, turtles, crocodilians and many prehistoric reptiles — from around this time (its own age range is 119.57–139.1 million years) was dug up about 48 km from here, in Kent.
  • A Tarsophlebia eximia — its group, Insecta, is the insects — a group already ancient by the time the first dinosaurs appeared — from around this time (its own age range is 154.8–161.5 million years) was dug up about 33 km from here, in the Ampthill Clay, Hertfordshire.
  • A Planohybodus — its group, Chondrichthyes, is the sharks, rays and their relatives, whose skeletons are made of cartilage rather than bone — from 150 million years ago was dug up about 30 km from here, in Surrey.
  • A Lonchidion heterodon — its group, Chondrichthyes, is the sharks, rays and their relatives, whose skeletons are made of cartilage rather than bone — from 150 million years ago was dug up about 30 km from here, in Surrey.
  • A Hylaeobatis problematica — its group, Chondrichthyes, is the sharks, rays and their relatives, whose skeletons are made of cartilage rather than bone — from 150 million years ago was dug up about 30 km from here, in Surrey.

Around 200 million years ago

  • A Tetrarhynchia (Tetrarhynchia) tetrahedra — its group, Rhynchonellata, is the lamp shells, sea animals with two shells that look like clams but are not — from around this time (its own age range is 184.2–192.9 million years) was dug up about 56 km from here.
  • A Tetrarhynchia subconcinna — its group, Rhynchonellata, is the lamp shells, sea animals with two shells that look like clams but are not — from around this time (its own age range is 184.2–192.9 million years) was dug up about 56 km from here.
  • A Quadratirhynchia quadrata — its group, Rhynchonellata, is the lamp shells, sea animals with two shells that look like clams but are not — from around this time (its own age range is 184.2–192.9 million years) was dug up about 56 km from here.

We show these places to the nearest few kilometres rather than pinning them exactly. The scientists who recorded them know the spot far better than that — the full record is one click away in the Paleobiology Database, and it is free for anyone to read. We round them here because a map made for children is not a map for digging things up, not because anything is being hidden.

What changed?

The model can place this ground at every one of the five ages — the only page on this site where the journey has no gap in it. It carries London from about 13° north of the equator to about 44° north, which is most of the way from the tropics to where it sits today.

But look at what the geological map returns at this exact point: every unit is younger than every age on this page — none older than 66 million years. The rock that would remember these five moments is not what you would hit first if you dug here, which is a large part of why the fossils and the model are doing the answering.

How the ground here rose, sank or folded is not something our datasets answer — so this page does not say.

Try it yourself

Iguanodon and Megalosaurus were dug up in the clay forty-odd kilometres from here, and they drank from rivers. That water is still going round — some of it is in the tap in your kitchen. Work out how much of your next glass has been through a dinosaur.

Do the dinosaur water maths

For school

  • One database returned nothing at all for the rock under London, and a different one held 1,088 fossils dug up around it — the most of any place on this site. Both answers are correct, about different questions.
  • The same sixteen shark fossils are the whole answer at two different ages, because their own age range is wide enough to cover both — but each fossil is counted in one group only.
  • Every rock the map shows at this exact spot is younger than every age on this page.

One database had nothing for London’s rock. Another drew the map of the ground under it. A third held a thousand fossils. Why might a database cover one country better than another — and what would you check before ever saying “there is no data”?

How sure are we?

  • Column facts describe an area of thousands to tens of thousands of km², centred tens of kilometres from the town coordinate. They are claims about a region, never about the rock beneath the town.
  • Fossil facts are a bounding-box sample around the town, each with its own distance from it; a fossil is never "here". The absence of fossils is not evidence of the absence of life — only of the absence of a recorded, published dig in this box.
  • Positions are model outputs, not observations. Independent plate models disagree by hundreds of kilometres at these ages, and that spread is the honest size of the uncertainty.
  • The land/sea question is answered only by the regional rock and the local fossils, separately, and never by the reconstruction — which says where this ground was and cannot say whether it was wet. There is deliberately no single field holding a one-word answer, because answering in one word would require merging a regional claim with a local one (CLAUDE.md rule 5). The nearby fossils are reported as a census of what has been found — which kinds are present, and how many of each — and never counted into a verdict: occurrence records are not statistically equivalent observations, so a plurality of them cannot establish an environment (science review, 2026-08-30).
  • Fossils are binned to their nearest slice age by age-range midpoint, with boundaries at the inter-slice midpoints 83, 125, 175 and 225 Ma. Those boundaries are an editorial choice, not a published stratigraphic scheme; a reviewer may prefer stage boundaries. Every occurrence keeps its own age range so the choice can be re-examined.

Sources

  • Macrostrat — the rock of the regionRead from version 2.3.9 of its data service on 27 August 2026.Peters, S.E. et al. Macrostrat: a platform for geological data integration and deep-time research. https://macrostrat.org, accessed on (date)Palaeogeography: Wright, N., Zahirovic, S., Müller, R. D., and Seton, M. Towards community-driven paleogeographic reconstructions: integrating open-access paleogeographic and paleobiology data with plate tectonics. Biogeosciences 10:1529-1541
  • The Paleobiology Database — the fossils dug up nearbyPBDB publishes no dataset version string; the data-service path (data1.2) and the datainfo access_time bound this claim.Fossil occurrence data from the Paleobiology Database (https://paleobiodb.org), released under CC0 1.0.Palaeo-coordinate cross-check (Paleobiology Database `pgm=gplates`): Wright et. al., 2013; Towards community-driven paleogeographic reconstructions.Palaeo-coordinate cross-check (Paleobiology Database `pgm=scotese`): Scotese, C.R., 2021. An Atlas of Paleogeographic Maps: The Seas Come In and the Seas Go Out, Annual Reviews of Earth and Planetary Sciences, v. 49, p. 669-718.Palaeo-coordinate cross-check (Paleobiology Database `pgm=seton`): Seton et. al., 2012; Global continental and ocean basin reconstructions since 200 Ma.
  • The EarthByte plate model — where this ground used to beMULLER2019 version 3.0, run with pyGPlates 1.0.0, licensed CC BY 4.0.GPlates: Müller, R. D., Cannon, J., Qin, X., Watson, R. J., Gurnis, M., Williams, S., Pfaffelmoser, T., Seton, M., Russell, S. H. J., Zahirovic S. (2018). GPlates: Building a virtual Earth through deep time. Geochemistry, Geophysics, Geosystems, 19, 2243-2261. https://doi.org/10.1029/2018GC007584Reconstructions computed with the GPlates Web Service (EarthByte Group, The University of Sydney).Plate model: Müller, R. D., Zahirovic, S., Williams, S. E., Cannon, J., Seton, M., Bower, D. J., Tetley, M. G., Heine, C., Le Breton, E., Liu, S., Russell, S. H. J., Yang, T., Leonard, J., and Gurnis, M. (2019), A global plate model including lithospheric deformation along major rifts and orogens since the Triassic. Tectonics, vol. 38, https://doi.org/10.1029/2018TC005462. Licensed CC BY 4.0.Plate model: Zahirovic, S., Eleish, A., Doss, S., Pall, J., Cannon, J., Pistone, M., Tetley, M. G., Young, A., & Fox, P. (2022). Subduction kinematics and carbonate platform interactions. Geoscience Data Journal, 9(2), p.371-383. Licensed CC BY 4.0.Coastline and static-polygon data by the EarthByte Group, licensed CC BY 3.0 Unported.

This record was assembled on from the datasets above. The ancient positions are reconstructions from a published plate model, not observations.

Where to next

Back to the start