Blue Lias

Blue Lias Formation
Stratigraphic range: Rhaetian-Lower Sinemurian Planorbis-Semicostatum ~201–198 Ma
Lower Lias Nash Point Glamorgan.JPG
Lower Lias sequence exposed at Nash Point, Glamorgan, Wales
TypeGeological formation
Unit ofLias Group
Sub-unitsWilmcote Limestone Member, Saltford Shale Member, Rugby Limestone Member
UnderliesCharmouth Mudstone Formation
OverliesLilstock Formation
Thicknessup to 120 metres (390 ft)
CountryUnited Kingdom
ExtentSouth West England,
Type section
LocationSaltford railway cutting

The Blue Lias is a geological formation in southern, eastern and western England and parts of South Wales, part of the Lias Group. The Blue Lias consists of a sequence of limestone and shale layers, laid down in latest Triassic and early Jurassic times, between 195 and 200 million years ago. The Blue Lias is famous for its fossils, especially ammonites.

Its age corresponds to the Rhaetian to lower Sinemurian stages of the geological timescale, thus fully including the Hettangian stage. It is the lowest of the three divisions of the Lower Jurassic period and, as such, is also given the name Lower Lias. Stratigraphically it can be subdivided into three members: the Wilmcote Limestone, Saltford Shale and Rugby Limestone.[1]

Lithology and facies

The Blue Lias comprises decimetre scale alternations of argillaceous limestone and mudstone. These alternations are caused by short-term climatic variations during the Early Jurassic attributed to orbital forcing (Milankovitch cycles). These limestone-mudstone alternations pass up into a clay member formerly known as the Lower Lias Clay now the Charmouth Mudstone. This lithology consists of monotonous mudstones weathering to clay at the surface. Sparse thin limestone and nodule bands are seen where the rocks are exposed. The deposition of a clay-rich mudstone member normally indicates deposition in a deeper marine environment. The lowest beds of the formation are referred to as the "Pre-planorbis beds" in reference them being deposited before the first appearance of the ammonite Psiloceras planorbis.

Wilmcote Limestone

In certain restricted parts of Britain, the lowermost member of the Blue Lias is the Wilmcote Limestone. It lies above the Cotham Member of the Lilstock Formation and beneath the Saltford Shale Member.[2] The Wilmcote Limestone of central England was formerly quarried close to Stratford-upon-Avon, for example at Wilmcote, Temple Grafton and Binton. It is roughly 200 million years old, dating back to the dawn of the Jurassic Period.

Much of the Wilmcote Limestone is very fine-grained, blue-grey when fresh, and very finely layered. Fossils are quite rare, except in the lowest beds. It was formerly used for a variety of purposes, including walling, building, paving, gravestones, cement-making and as a source of agricultural lime. It is no longer quarried, and most of the old quarries are either infilled or overgrown.

Geologists think that the Wilmcote Limestone originated as layers of fine-grained mud on the floor of a sheltered, shallow muddy sea or lagoon that covered parts of central England at the dawn of the Jurassic Period. Very little life could tolerate the stagnant conditions on the seabed. As a consequence the mud was seldom disturbed, which is why the fine, paper-like layering is preserved.

Above the sea bed, the shallower waters supported ammonites, fish, and marine reptiles (ichthyosaurs and plesiosaurs). Their remains were discovered in the Wilmcote Limestone quarries during the nineteenth century. The Warwickshire Museum[3] houses a collection of these fossils and some are on display at the Market Hall Museum in Warwick.[4][5]


The Blue Lias is a prevalent feature of the cliffs around Lyme Regis and Charmouth, on the Jurassic Coast in Dorset, where it exists in layers of limestone interspersed with softer clay. It is also notable for its presence in Somerset, particularly around the Polden Hills, Keinton Mandeville and Glastonbury area, and it forms a broad plain across the East Midlands. It also appears near Whitby in Yorkshire and Southam in Warwickshire where a pub is named after it. There are outcrops along the coast of South Wales, notably that of the Vale of Glamorgan.[6] The type section of the Blue Lias is at Saltford near Bath.

Use in construction

Lytes Cary, Somerset, built of Blue Lias with Ham stone dressings around the windows

Blue Lias is useful as a building stone, and as a source of lime for making lime mortar. Because it is argillaceous, the lime is hydraulic. Since the mid-nineteenth century, it has been used as a raw material for cement, in South Wales, Somerset, Warwickshire, and Leicestershire. The cement plant quarry at Rugby, Warwickshire is probably the best exposure of the formation: more than 100 layers can be seen.

In areas where Blue Lias is quarried it has been used in buildings and churches as well as tombstones in cemeteries. An example of a Blue Lias town is Street, near Glastonbury. Other examples of Blue Lias buildings can be found in the nearby towns of Somerton and Ilchester.

It remains popular in more modern-day surroundings where it is used in the construction of new housing developments and extensions for existing buildings in conservation areas. Blue Lias is mainly used in flooring, walling and paving slabs – both coursed and layered. It is also used in the making of flagstones and cobbles.

There are only four quarries in Somerset quarrying Blue Lias at present. AR Purnell at Ashen Cross Quarry in Somerton have been mining blue lias stone since 1996. Hadspen Quarry Ltd. Hadspen Quarry operate one in Keinton Mandeville. Ham & Doulting Stone Co Ltd. operate one of these, Tout Quarry near Somerton.[7]


The rock is rich in fossil remains from the Jurassic period. The blue-grey colour is provided by its iron content, enclosed to a large extent in pyrites.[8]


Dinosaurs of the Blue Lias
GenusSpeciesLocationStratigraphic positionMaterialNotesImages
DracoraptorD. haniganiLavernock PointPre-planorbis Beds, lowermost HettangianNMW 2015.5G.1–2015.5G.11 "a disarticulated, but associated partial skeleton"A coelophysoid theropod
SarcosaurusS. woodiWilmcoteangulata zone, late Hettangian (NHMUK PV R3542) Rugby Limestone Member liasicus to semicosatum zones, lowermost Sinemurian (WARMS G667–690)Paratype specimens: NHMUK PV R3542, complete right tibia WARMS G667–690, partial skeletonBasal neotheropod, holotype specimen is known from the Scunthorpe Mudstone


Pterosaurs of the Blue Lias
GenusSpeciesLocationStratigraphic positionMaterialNotesImages
DimorphodonD. macronyxAust Cliff, Lyme RegisNHMUK PV R 1034, NHMUK PV OR 41212, NHMUK PV R 1035A basal pterosaur
Dimorphodon macronyx.jpg


Ichthyosaurs of the Blue Lias
GenusSpeciesLocationStratigraphic positionMaterialNotesImages
IchthyosaurusI. larkini[9]SomersetUnknown, possibly Pre-planorbis bedsHolotype: BRSUG 25300, referred: AGC 11, CAMSM J5957, NHMUK PV OR5595
I. somersetensis[9]Holotype: ANSP 15766 referred: BRSMG Cb4997, NHMUK PV OR2013AGC 16, ROM 26029
LeptonectesL. tenuirostrisSoutham Cement Works, WarwickshireWilmcote Limestone MemberWARMS G15647, a partial skeleton[10]
ProtoichthyosaurusP. prostaxalis[11]SomersetUnknown, probably Pre-planorbis bedsHolotype: BRLSI M3553, "a partial skull, pectoral girdle and both forefins, preserved in ventral view"
WahlisaurusW. massarae[12]Sutton Hill (Stowey) Quarry, Bishop SuttonPre-planorbis bedsBRSMG Cg240, "a practically complete right coracoid"
?ShastasauridaeIndeterminatePenarthPsiloceras planorbis BiozoneNMW95.61G.1, radius[13]Estimated length of 12-15 metres


Plesiosaurs of the Blue Lias
GenusSpeciesLocationStratigraphic positionMaterialNotesImages
AtychodraconA. megacephalus[14]Street-on-the-FosseLowermost Blue LiasHolotype:BRSMG Cb 2335Rhomaleosaurid
Plesiosaur skeleton, New Walk Museum.JPG
AvalonnectesA. arturi[15]Street, Somerset (referred specimen)NHMUK 14550, "the posterior portion of the skull, and a partial postcranial skeleton" uncatalogued partial specimenRhomaleosaurid
Holotype of Avalonnectes arturi NHMUK 14550.png
EurycleidusE. arcuatusStreetBMNH 2030 (lectotype), 2027-2029, 2047, 2061, R1317-1319 (paralectotypes, probably belonging to the same individual)Rhomaleosaurid
EoplesiosaurusE. antiquior[15]Watchet, SomersetTTNCM 8348, postcranial skeletonBasal Plesiosauroid
Holotype of Eoplesiosaurus antiquior.png
StratesaurusS. taylori[15]Street, Somersetlowermost HettangianOUMNH J.10337, "a skull and partial postcranial skeleton including anterior cervical and pectoral vertebrae, a partial hindlimb and ilium"Rhomaleosaurid
Holotype of Stratesaurus taylori OUMNH J.10337.png
ThalassiodraconT. hawkinsiiStreetPre-planorbis BedsBMNH 2018 "almost complete skeleton missing distal parts of limbs" CAMSM J.35181, partial skeletonPliosaurid affinities[16]
Thalassiodracon NHM.jpg


Insect compression fossils are known from the localities of Binton in Warwickshire and Copt Heath near Birmingham.[17]

See also

  • White Lias
  • List of dinosaur-bearing rock formations


  1. ^ Ambrose, K.; 2001: The lithostratigraphy of the Blue Lias Formation (Late Rhaetian–Early Sinemurian) in the southern part of the English Midlands Archived 7 March 2006 at the Wayback Machine, Proceedings of the Geologists' Association 112(2), pp. 97-110.
  2. ^ "Wilmcote Limestone Member". The BGS Lexicon of Named Rock Units. British Geological Survey. Retrieved 20 April 2014.
  3. ^
  4. ^ Ambrose, K., 2001. The lithostratigraphy of the Blue Lias Formation (Late Rhaetian - Early Sinemurian) in the southern part of the English Midlands. Proceedings of the Geologists' Association vol. 112, 97-110.
  5. ^ Williams, B.J. & Whittaker, A., 1974. Geology of the Country around Stratford-upon-Avon and Evesham. Memoirs of the Geological Survey of Great Britain. HMSO, London.
  6. ^ Wilson et al., 1990 Geology of the South Wales Coalfield, Part VI, the country around Bridgend Mem Br Geol Surv sheet 261 & 262 (England and Wales)
  7. ^ "Strategic Stone Study: A Building Stone Atlas of Somerset and Exmoor" (PDF). English Heritage. p. 11. Retrieved 11 October 2011.
  8. ^ Weishampel, David B; et al. (2004). "Dinosaur distribution (Early Jurassic, Europe)." In: Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.): The Dinosauria, 2nd, Berkeley: University of California Press. Pp. 532–534.ISBN 0-520-24209-2.
  9. ^ a b Lomax, Dean R.; Massare, Judy A. (February 2017). Benson, Roger (ed.). "Two new species of Ichthyosaurus from the lowermost Jurassic (Hettangian) of Somerset, England". Papers in Palaeontology. 3 (1): 1–20. doi:10.1002/spp2.1065.
  10. ^ Smith, A. S.; Radley, J. D. (November 2007). "A marine reptile fauna from the Early Jurassic Saltford Shale (Blue Lias Formation) of central England". Proceedings of the Yorkshire Geological Society. 56 (4): 253–260. doi:10.1144/pygs.56.4.253. ISSN 0044-0604.
  11. ^ Lomax, Dean R.; Massare, Judy A.; Mistry, Rashmiben T. (3 September 2017). "The taxonomic utility of forefin morphology in Lower Jurassic ichthyosaurs: Protoichthyosaurus and Ichthyosaurus". Journal of Vertebrate Paleontology. 37 (5): e1361433. doi:10.1080/02724634.2017.1361433. ISSN 0272-4634. S2CID 90238537.
  12. ^ Lomax, Dean R.; Evans, Mark; Carpenter, Simon (January 2019). Somerville, Id (ed.). "An ichthyosaur from the UK Triassic-Jurassic boundary: A second specimen of the leptonectid ichthyosaur Wahlisaurus massarae Lomax 2016". Geological Journal. 54 (1): 83–90. doi:10.1002/gj.3155.
  13. ^ Martin, Jeremy; Vincent, Peggy; Suan, Guillaume; Sharpe, Tom; Hodges, Peter; Williams, Matt; Howells, Cindy; Fischer, Valentin (2014). "A mysterious giant ichthyosaur from the lowermost Jurassic of Wales". Acta Palaeontologica Polonica. doi:10.4202/app.00062.2014.
  14. ^ Smith, As (2015). "Reassessment of 'Plesiosaurus' megacephalus (Sauropterygia: Plesiosauria) from the Triassic-Jurassic boundary, UK". Palaeontologia Electronica. 18 (1): 1–20. doi:10.26879/504. ISSN 1094-8074.
  15. ^ a b c Benson, Roger B. J.; Evans, Mark; Druckenmiller, Patrick S. (16 March 2012). Lalueza-Fox, Carles (ed.). "High Diversity, Low Disparity and Small Body Size in Plesiosaurs (Reptilia, Sauropterygia) from the Triassic–Jurassic Boundary". PLOS ONE. 7 (3): e31838. Bibcode:2012PLoSO...731838B. doi:10.1371/journal.pone.0031838. ISSN 1932-6203. PMC 3306369. PMID 22438869.
  16. ^ Benson, Roger B. J.; Bates, Karl T.; Johnson, Mark R.; Withers, Philip J. (May 2011). "Cranial anatomy of Thalassiodracon hawkinsii (Reptilia, Plesiosauria) from the Early Jurassic of Somerset, United Kingdom". Journal of Vertebrate Paleontology. 31 (3): 562–574. doi:10.1080/02724634.2011.572937. ISSN 0272-4634. S2CID 39844147.
  17. ^ Kelly, Richard S.; Ross, Andrew J.; Coram, Robert A. (2018). "A Review of Necrotauliids from the Triassic/Jurassic of England (Trichoptera: Necrotauliidae)". Psyche: A Journal of Entomology. 2018: 1–12. doi:10.1155/2018/6706120. ISSN 0033-2615.

External links

Media files used on this page

Holotype of Eoplesiosaurus antiquior.png
Author/Creator: Roger B. J. Benson, Mark Evans and Patrick S. Druckenmiller, Licence: CC BY 2.5
Holotype of Eoplesiosaurus antiquior (TTNCM 8348) in right lateral view. Image in A is a composite made from four photographs (divisions are indicated by black and white lines), with enlargement of anterior cervical vertebrae (B; magnified portion is enlarged x2.0 times). Gastralia are not shown in line drawing (C). Abbreviations: ca, caudal vertebra; ce, cervical vertebra [number following indicates order in preserved series]; chv, chevron; l., left [followed by name of element]; pro, lateral projection; prz, prezygapophysis; r., right [followed by name of element]; trp, transverse process. Scale bars equal 200 mm (A, C) and 50 mm (B).
Thalassiodracon NHM.jpg
Author/Creator: the paleobear, Licence: CC BY 2.0
Thalassiodracon NHM
Holotype of Stratesaurus taylori OUMNH J.10337.png
Author/Creator: Roger B. J. Benson, Mark Evans and Patrick S. Druckenmiller, Licence: CC BY 2.5
A–B, skull in dorsal view, C–E, anterior cervical vertebrae in left lateral (C), ventral (D) and anterior (E) views, F, H–I, left ilium in dorsal (F), lateral (H) and posterior (I) views, G, ‘pectoral’ vertebra; in left lateral view. In line drawing (B), grey tone indicates damage. Abbreviations: bs, basisphenoid; exof, exoccipital facet of basioccipital; jug, jugal; fr, frontal; hy, hyoid; lpmx, left premaxilla; mx, maxilla; occ, occipital condyle; pal, palatine; par, parietal; po, postorbital; popr, posterolateral process of prezygapophysis; prz, prezygapophysis; pt, pterygoid; qua, quadrate; rmx, right maxilla; rpmx, right premaxilla; scler, sclerotic ring; sq, squamosal. Scale bars equal 50 mm (A–B, F, H–I) and 20 mm (C–E, G).
Author/Creator: David M. Martill, Steven U. Vidovic, Cindy Howells, John R. Nudds, Licence: CC BY 2.5

Skeleton outline of Dracoraptor hanigani.

Bones highlighted green for present, orange for external moulds and blue for tentatively identified bones. Many unidentified or uncertain elements have been omitted.
Holotype of Avalonnectes arturi NHMUK 14550.png
Author/Creator: Roger B. J. Benson, Mark Evans and Patrick S. Druckenmiller, Licence: CC BY 2.5
A–B, skull in dorsal view; C–E, postcranial skeleton; in left dorsolateral (C) and left lateral (D–E) views. In line drawings (B, E) dark grey tone indicates damage and light grey tone indicates the palate. Abbreviations: ca, caudal vertebra [number following indicates order in preserved series]; ce, cervical vertebra; d, dorsal vertebra; depr, depression; ecto, ectopterygoid; epip, epipterygoid; exp, expanded neural spine apex; fr, frontal; jug, jugal; l., left [followed by name of element]; mx, maxilla; p, ‘pectoral’ vertebra; par, parietal; pmx, premaxilla; po, postorbital; pofr, postfrontal; prfr, prefrontal; qua, quadrate; r., right [followed by name of element]; s, sacral vertebra; sq, squamosal; unexp, unexpanded neural spine apex. Scale bars equal 50 mm (A–B), 20 mm (C), and 200 mm (D–E).
Plesiosaur skeleton, New Walk Museum.JPG
Author/Creator: Poliphilo, Licence: CC0
Atychodracon megacephalus (formerly Rhomaleosaurus, specimen LEICS G221.1851) skeleton, New Walk Museum, excavated at Barrow-upon-Soar, popularly known as the "Barrow Kipper"
Lower Lias Nash Point Glamorgan.JPG
Author/Creator: Wilson44691, Licence: CC0
Lower Lias sequence exposed at Nash Point, Glamorgan, Wales.
Dimorphodon macronyx.jpg

Dimorphodon macronyx skeleton from Dragons of the Air

1901 United States