Comparison of the modern stratigraphical scheme for the Ordovician and Silurian with the stratigraphical usage of Murchison, Sedgwick and Lapworth.

The global standard stratigraphy and a graptolite biostratigraphical zonation, calibrated against two recent chronometric scales derived from radiometric age determinations.

a) Representative lithostratigraphical columns from the main palaeogeographical areas of Silurian Britain: Midland Valley from Bull and Loydell (1995) and Robertson (1989), Southern Uplands from Rushton et al. (1996). b) Representative lithostratigraphical columns from the main palaeogeographical areas of Silurian Britain: Lake District from Kneller et al. (1994), central Wales from British Geological Survey (1993), Welsh Borderland from Cocks et al. (1993).

A global sea-level curve for Silurian time (after Johnson et al., 1991).

Backstripped, water-loaded subsidence curves for the Silurian of (a) the Midland Platform and central Welsh Basin (From Woodcock et al., 1996), and (b) the Lake District (from King, 1994). The time scale is that of Tucker and McKerrow (1995).

The stratigraphical columns of successive tectonic slices across the south-west end of the Southern Uplands of Scotland (after Rushton et al., 1996). Inset shows the geometry of an accreting sedimentary prism.

Palaeocontinental map at the time of the Ordovician–Silurian boundary (~440 Ma). (After Pickering and Smith, 1995.)

Palaeogeographical elements of Silurian Britain.

Palaeogeographical maps of Britain for three intervals of Silurian time: (a) early to mid-Llandovery, (b) late Llandovery to early Ludlow, (c) late Ludlow and PÍídolí.

GCR sites arranged by palaeogeographical setting and stratigraphical age. Bold typeface denotes a basal boundary stratotype for the global standard stratigraphy.

Maps of the distribution of Geological Conservation Review sites from each Silurian series. For detail and site names see Figures 3.1 (Llandovery), 4.1 (Wenlock), 5.1 (Ludlow) and 6.1 (PÍídolí).

The undivided Lower Palaeozoic strata in the Welsh part of William Smith’s 1817 cross-section from London to Snowdon, redrawn from Fitton, W.H.F. 1832, ‘Notes on the History of English Geology’, Philosophical Magazine 1, Plate 2, fig. 4.

North Welsh part of Murchison’s 1854 map and section of the Silurian Rocks of England and Wales, which accompanied his first edition of Siluria. The Lower Palaeozoic is divided into Upper and Lower Silurian with Sedgwick’s Cambrian subsumed into the basal part of the Lower Silurian (Longmynd or Bottom Rocks).

One of the first depictions of the history of life, engraved by John Emslie and published by James Reynolds (1849), shows life originating (at the bottom of the figure) within the period of the Silurian System.

Successive classifications and subdivision of the Lower Palaeozoic rocks of Britain from 1855 to 1879, when Lapworth introduced the Ordovician between the Silurian and Cambrian periods.

An example of taphonomic processes of fossil burial, showing the various modes of preservation of Silurian myodocope ostracods (from Siveter et al., 1991).

An acritarch biozonal scheme for the Silurian proposed by Martin (1989).

The stratigraphical ranges of selected chitinozoans, compared with the graptolite biozones of the Silurian (after Paris, 1989).

Sporomorph biozones and plant megafossil events from the late Ordovician to earliest Devonian, compared with the graptolite biozones (after Richardson and Edwards, 1989).

Spore: Synorisprites tripapillatus, Cliffords Mesne Sandstone Formation, Gorsley, Herefordshire; × 2000. (Photo: John Richardson.)

Astropherid radiolarian, Wenlock Series, Herefordshire. Left: complete specimen, × 130. Right: detail of test, × 520. (Photos: David Siveter; from Briggs et al., 1996.)

Foraminifera: (a) Hyperammina harrisi; (b) Ammodiscus exsertus; (c) Lituotuba? sp.; (d) Hemisphaerammina thola. All from the uppermost Purple Shales or lowermost Buildwas Formation, Llandovery–Wenlock boundary beds, Wenlock Edge, Shropshire, × 70. (Photos: from Mabillard and Aldridge, 1982.)

Corals: Left: Ketophyllum sp., × 1. Right: Heliolites interstinctus, × 2. Both from Much Wenlock Limestone Formation, Dudley, West Midlands. (Photos: from Siveter et al., 1989.)

Bivalves. Left: Cardiola interrupta, Ludfordian Stage, Ludlow Series, Usk, Gwent: × 1. Right: Fuchsella amygdalina, Whitcliffe Group, Ludlow Series, Malvern Hills, Herefordshire; × 2. (Photos: from Siveter et al., 1989.)

The relative abundance (number of genera per stratigraphical interval) of various bivalve groups through the Silurian (from KÍíñ, 1984).

Gastropod: Poleumita discors, Much Wenlock Limestone Formation, Wenlock Edge, Shropshire, × 0.5. (Photo: from Siveter et al., 1989.)

The nautiloid Polygrammoceras bullatum, Oxford University Museum C.94., Lower Bringewood Formation, Ludlow Series, Ledbury, Herefordshire; longitudinal section, × 1. (Photo: C.H. Holland.)

A reconstruction of Telychian marine life with swimming squid-like nautiloids, shrimp-like phyllocarids and seabed crawling ostracods, snails and bivalves. Also shown is the selective recruitment of their hardparts to the sediment as potential fossil remains (from Siveter et al., 1991).

The shift in habitats of myodocopid ostracods from benthic to pelagic through the Silurian, as reconstructed from analysis of their fossil remains in strata from Laurentia (Scotland) to Avalonia (Wales) and Gondwana (Australia and China), (from Siveter et al., 1991).

Brachiopods. Left: Eospirifer radiatus, Coalbrookdale Formation, Wenlock Series, Walsall , West Midlands; × 2. Centre: Meristina obtusa, Coalbrookdale Formation, Wenlock Series, Walsall, West Midlands; × 1.25. Right: Shalleria ornatella, Leintwardine Group, Ludlow Series, Usk district, Gwent; ×2.5. (Photos: from Siveter et al., 1989.)

A chronologically arranged selection (1–34) of British Silurian graptolites (broken bar 10 mm, solid bar 1 mm, open bar 0.20 mm). 1. Glyptograptus persculptus; 2. Parakidograptus acuminatus; 3. Akidograptus ascensus; 4. Atavograptus atavus; 5. Lagarograptus acinaces; 6. Coronograptus cyphus; 7. Monograptus triangulatus; 8. Diplograptus magnus; 9. Monograptus argenteus; 10. Pribylograptus leptotheca; 11. Coronograptus gregarius; 12. Monograptus convolutus; 13. M. sedgwickii; 14. M. turriculatus; 15. Rastrites maximus; 16. Monograptus crispus; 17. Monoclimacis griestoniensis; 18. Monoclimacis crenulata; 19. Cyrtograptus centrifugus; 20. C. murchisoni; 21. Monograptus riccartonensis; 22. Cyrtograptus rigidus; 23. Monograptus flexilis; 24. Cyrtograptus ellesae; 25. C. lundgreni; 26. Gothograptus nassa; 27. Monograptus ludensis; 28. Neodiversograptus nilssoni; 29. Lobograptus progenitor; 30. L. scanicus; 31. Pristiograptus tumescens; 32. Saetograptus incipiens; 33. S. leintwardinensis; 34. Bohemograptus bohemicus (after Rickards, 1989a).

Phylogenetic relationships amongst Silurian graptolites as analysed from their morphological characteristics (from an original drawn by R.B. Rickards, unpublished).

The graptolite biozonation of the British Silurian with the ranges of the biozonal species (compiled by R.B. Rickards, unpublished).

The stratigraphical ranges of some important Silurian conodont taxa; solid bars represent British occurrences and broken bars are based on data from elsewhere (after Aldridge and Schönlaub, 1989).

The distribution of the major vertebrate fish groups through time, showing significant radiation during the Silurian leading to the earliest occurrence of the tetrapods in the Upper Devonian (modified from Janvier, 1996).

A modern view of phylogenetic relationships in the early vertebrates arranged against geological time. The diagram emphasises the Ordovician–Silurian radiation of the agnathan fish and their possible relationships to earlier vertebrates such as the conodont animal and the newly discovered early Cambrian vertebrates (with permission from Donoghue et al., 2000).

Conodont and vertebrate biozonation for the Silurian with the base of each biozone defined by the appearance of the index taxon; the vertebrates are largely microvertebrate scales of thelodonts and acanthodians (modified from Aldridge and Schönlaub, 1989 and Dineley and Metcalf, 1999).

The distribution in space and time of some Silurian vertebrates (from Märss, 1989) relative to the Silurian palaeogeography of Scotese et al. (1979). Solid circles = vertebrate distribution areas: 1. East Baltic and Poland; 2. Scandinavia; 3. Southern Britain; 4. Scotland; 5. Novaya Zemlya and Vaigach; 6. Timan-Pechora Region; 7. Central Urals; 8. Severnaya Zemlya. Stippled areas were probably land. Biozonation and characteristic scales of vertebrates, largely based on the fossil record of the Baltic region, with numbers under the index species in the left hand column referring to the areas shown on the map above. A. Logania taiti; B1. L. martinssoni; B2. Thelodus laevis; B3. Tremataspis schmidti; B4 and 5 Birkeniida sp; C1. Phlebolepis elegans; C2. Thelodus carinatus; C3. Tremataspis mammillata; D1. Andreolepis hedei; D2. Archegonaspis schmidti; D3. Birkeniida sp.; E1. Thelodus sculptilis; E2. T. admirabilis; E3. Poracanthodes porosus; F1. Nostolepis gracilis; F2. N. striata; F3. Gomphoncus sandelensis; G1. Poracanthodes punctatus; G2. Gomphoncus hoppei; G3. Tylodus deltoides; G4. Strosipherus indentatus; G5. Lophosteus superbus; H1. Katoporus timanicus; H2. Logania kummerowi; H3. Goniporus alatus.

The role of the Silurian in both the actual known and putative radiation of the Palaeozoic land plants is shown in this simplified phylogeny. The stratigraphical ranges of selected groups of land plants (thick bars) and their minimum ranges, as implied by their interrelationships, are shown (thin bars). Also illustrated are minimum age estimates for the appearance (from the bottom) of spore tetrads, cuticles, single trilete spores, megafossils and stomates (after Kenrick and Crane, 1997).

Selected reconstructions of Silurian brachiopod dominated seabed associations from relatively shallow (Lingula) to deeper (Stricklandia) shelf seas (from McKerrow, 1978, with permission).

Global distribution of Wenlock reefs related to the palaeogeography of the time (after Copper and Brunton, 1991).

Reconstruction of a coral-dominated Silurian reef assemblage (from McKerrow, 1978, with permission).

Worm: Wenlock Series, Herefordshire; ×7.5. (Photo: Derek J. Siveter; from Briggs et al., 1996).

Distribution of the Geological Conservation Review sites for the Llandovery Series, set against the palaeogeographical elements of Silurian Britain.

Graptolite biozonation in the Llandovery Series of Britain, after Rickards (1976, 1989b), Loydell (1991, 1993), Loydell and Cave (1993, 1996) and Zalasiewicz (1994).

Sedimentary log of representative open marine sandstones in the main face at Hope Quarry (after Bridges, 1975).

Geological map of the area to the south-east of the Long Mynd, Shropshire, showing the sites at Hillend Farm and Wistanstow (modified after Siveter et al., 1989).

Mudstones of the Pentamerus Beds at the road cutting near Hillend Farm; a thin limestone lens rich in Pentamerus shells is exposed above the hammer head (arrowed). (Photo: R.J. Aldridge.)

Representative sedimentary log through the mudstones and thin limestones of the Pentamerus Beds at Hillend Farm (after Bridges, 1975).

Reconstruction of the Pentamerus benthic community, based on a collection from the Pentamerus Beds of Shropshire (after Ziegler et al., 1968a). The fossils represented are: (1) Pentamerus oblongus; (2) a bryozoan; (3) Eocoelia hemisphaerica; (4) Atrypa reticularis; (5) a rugose coral; (6) Halysites sp..

The unconformity between Onny Shales of Caradoc age and the Hughley Shales of Llandovery age in the bank of the River Onny at Wistanstow; the Hughley Shales are exposed in the upper third of the river cliff, dipping at a lower angle than the Onny Shales. (Photo: R. J. Aldridge.)

Outline geological map of the southern Malvern Hills, showing the location of Gullet Quarry (after Aldridge and Smith, 1985).

The unconformable contact between the Malvernian metamorphosed igneous rocks (right) and the Telychian Wyche Formation at Gullet Quarry. (Photo: Derek J. Siveter.)

The Wyche Formation at Gullet Quarry (Photo: Derek J. Siveter).

Reconstruction of the Costistricklandia benthic community, based on a collection from Gullet Quarry (after Ziegler et al., 1968a). The fossils represented are: (1) Costistricklandia lirata alpha; (2) Pholidostrophia salopiensis; (3) Eospirifer radiatus; (4) Atrypa reticularis; (5) Clorinda globosa; (6) Protathyris sp.

Representative conodont elements from Gullet Quarry. (a–c) Apsidognathus tuberculatus, platform, lenticular and lyriform elments, × 40; (d) Pterospathodus celloni, Pa element, × 40; (e) Icriodella inconstans, Pa element, × 50; (f) Ozarkodina gulletensis, Pa element, × 40. (Photos: from Aldridge, 1975.)

Geological map of the Tortworth Inlier (after Curtis, 1972).

Reconstruction of the Eocoelia benthic community, based on a collection from the Damery Formation 30 m south of Damery Bridge (after Ziegler et al., 1968a). The fossils represented are: (1) Eocoelia curtisi; (2) Ferganella aff. decemplicata; (3) Dalejina sp.; (4) a leptostrophiid brachiopod.

Geological sketch-map and lithostratigraphy for Buttington Brickworks (modified after Loydell and Cave, 1993).

The south-eastern part of the main (north-east) face at Buttington Brickworks, showing the upper part of the Buttington Mudstone Formation (to the left) and the lower part of the Trewern Brook Mudstone Formation. (Photo: Derek J. Siveter.)

The geology of southern Pembrokeshire, showing the major structural blocks, the important faults, and the network localities at Gasworks Lane (Haverfordwest) and Marloes Sands; modified after Sanzen-Baker (1972).

Geological map of Marloes Sands (after Walmsley and Bassett, 1976).

The base of the Lower Marloes Basalt (to the right), within the Skomer Vocanic Group, Marloes Sands. (Photo: R. J. Aldridge.)

Marloes Sands, with the Skomer Volcanic Group, including the Three Chimneys, to the left and the Coralliferous Group, dipping at a lower angle, to the right. (Photo: R. J. Aldridge.)

Reconstruction of the depositional environment of interbedded sediments and volcanic rocks in the lower part of the Skomer Volcanic Group, Marloes (after Bridges, 1976).

Geological map of the northern part of the type Llandovery area (after Cocks et al., 1984).

Geological map of the southern part of the type Llandovery area (after Cocks et al., 1984).

Exposures along and around the Trefawr Track, including the stratotype section for the base of the Aeronian Stage (modified after Cocks et al., 1984).

Range chart of brachiopod and graptolite taxa across the Rhuddanian–Aeronian boundary in the Trefawr Track section (after Cocks et al., 1984).

Exposures along and around the Fron Road, showing the stratotype locality for the base of the Telychian Stage (modified after Cocks et al., 1984).

Stratotype section for the base of the Telychian Stage; the position of the Aeronian–Telychian boundary is within the bed with its base marked by the broken line. The section youngs to the left (south). (Photo: P.D. Lane.)

Distribution of selected brachiopod and acritarch species across the Aeronian–Telychian boundary in the Fron Road section (after Cocks et al., 1984).

Geological map of the Garth Bank area, Powys, showing the location of Cwm Clyd Quarry (after Williams and Wright, 1981).

Geological sketch-map of the area around Caban Côch quarry (after Waters et al., 1993).

Turbiditic sandstones and conglomeratic submarine channel fills, Caban Côch quarry. (Photo: R.J. Aldridge.)

Detail of the conglomeratic infill of a submarine channel, Caban Côch quarry; the lower part of the conglomerate unit shows reverse grading. (Photo: R.J. Aldridge.)

Depositional model for the development of nested channels and lobes in the Caban Côch area during the Llandovery Epoch (after Davies and Waters, 1995; Davies et al., 1997).

Geological sketch map of the Banwy River section (after Loydell and Cave, 1996). The letters represent marker horizons from which measurements in metres are taken to graptolitic levels.

Measured section through the Tarannon Shales Formation and the lower Nant-ysgollon Shales Formation in the Banwy River (after Loydell and Cave, 1996), showing the extent of identified graptolite biozones. The letters represent marker horizons from which measurements in metres are taken to graptolitic levels.

Geological sketch-map of central western Wales, showing the extent of the Aberystwyth Grits Group and the GCR network sites at Aberarth and Craigyfulfran (Aberystwyth) (after Siveter et al., 1989).

Deformed bedding in the Aberystwyth Grits Group (Subzone 4b) at Aberarth. (Photo: M.R. Dobson.)

Representative measured section in the turbidite sequence, Aberystwyth Grits Group, between Aberarth and Morfa, with environmental interpretations (after Dobson et al., 1995a).

Idealized graphic log of the full Tabcde Bouma turbidite cycle (modified from Selley, 1978, after Bouma, 1962).

Sketch map of the area from Craigyfulfran to the north end of the Aberystwyth promenade (after Bates, 1982a).

Turbidite units of the Aberystwyth Grits Group at the northern end of Aberystwyth promenade. (Photo: R.J. Aldridge.)

Convolute lamination in a sandstone bed, Aberystwyth Grits Group, northern end of Aberystwyth promenade. (Photo: R.J. Aldridge.)

Flute marks giving a palaeocurrent direction from the SSW, on the base of a 15 cm-thick sandstone unit, Aberystwyth Grits Group, northern end of Aberystwyth promenade. (Photo: R.J. Aldridge.)

Trace fossils on the base of a sandstone unit, Aberystwyth Grits Group, northern end of Aberystwyth promenade. Width of frame, approximately 1 m. (Photo: R.J. Aldridge.)

Representative sedimentary log of the turbidite Tcde rhythms measured at the headland at the north end of Aberystwyth promenade (after Dobson et al., 1995a).

Geological map of the Rheidol Gorge (left) and detailed map of the area around the contact between the Cwmere and Derwenlas formations (right), showing the positions of graptolitic horizons (after Siveter et al., 1989).

View of the Rheidol Gorge (Photo: Derek J. Siveter.)

Outline geological map of the Lake District and Howgill Fells (modified after Rickards, 1989a).

Geological sketch-map of Yewdale Beck showing the distribution of graptolite biozones (after Hutt, 1974).

Measured sedimentary succession through the Skelgill Formation in Yewdale Beck, showing the graptolite biozonation (modified after Hutt, 1974).

Reconstucted west–east sections across the Lake District, showing the development of the depositional environment during the early Llandovery (after Rickards, 1978).

Geological map of the area around Skelghyll Lower Bridge, showing the main graptolitic horizons within the Skelgill Formation (after Hutt, 1974).

Sedimentary log of the succession of the Skelgill Formation at Skelghyll Lower Bridge, showing the graptolite biozonation and the positions of the main graptolitic horizons (after Hutt, 1974).

The Lower Bridge section, Skelghyll Beck. (Photo: R.B. Rickards.)

The ‘green streak’ within the argenteus Biozone, Lower Bridge section, Skelghyll Beck. (Photo: R.B. Rickards.)

Stratigraphical log and geological plan of the Browgill Formation in Stockdale Beck, showing the main graptolitic horizons (after Hutt, 1974).

Plan of the Spengill section, showing the outcrops of the graptolite biozones represented in the Skelgill and Browgill formations (after Rickards, 1970a).

Measured section through the Skelgill and Browgill formations in the Spengill section, showing the graptolite biozonation (modified after Rickards, 1970a).

Spengill Member, Ordovician–Silurian boundary, Spengill, Howgill Fells. (Photo: R.J. Aldridge.)

Exposure of the Browgill Formation in Spengill, Howgill Fells, showing strata of the turriculatus Biozone. (Photo: R.J. Aldridge.)

Simplified geological map of Dob’s Linn, with a stratigraphical section; inset shows location relative to the A708 (after Williams, 1980).

Section on the Main Cliff at Dob’s Linn, showing the Upper Hartfell Shale Formation and the Birkhill Shale Formation. The two geologists are standing approximately at the position of the Ordovician–Silurian boundary. (Photo: David J. Siveter.)

Strata incorporating the internationally recognized base of the Silurian System, northern side of the Linn Branch gorge, Dob’s Linn. For scale see sketch opposite (Figure 3.65). The section youngs to the left and the Ordovician–Silurian boundary is arrowed between beds 1 and 2. (Photo: S.H. Williams.)

Sketch of the geology of the northern side of Linn Branch gorge (after Williams, 1988).

Section through the Birkhill Shale Formation at Dob’s Linn, showing the graptolite biozonation (after Toghill, 1968). The base of the Silurian System is at the base of the P. acuminatus Biozone.

Some biostratigraphically important graptolite taxa from the Birkhill Shale Formation of Dob’s Linn (after Webb et al., 1993). (a) Glyptograptus persculptus; (b) Parakidograptus acuminatus; (c) Cystograptus vesiculosus; (d) Atavograptus atavus; (e) Coronograptus cyphus cyphus; (f) Coronograptus gregarius; (g) Monograptus triangulatus triangulatus; (h) Monograptus triangulatus fimbriatus; (i) Diplograptus magnus; (j) Pribylograptus leptotheca; (k) Monograptus argenteus; (l) Rhaphidograptus toernquisti; (m) Monograptus convolutus; (n) Monograptus sedgwickii; (o) Rastrites maximus. Figure (c) × 1.3, all other figures approximately × 2.

Two models accounting for the structural and stratigraphical development seen in the Southern Uplands (from McAdam et al., 1992). (a) accretionary prism model of Leggett et al. (1979a); (b) back-arc basin model of Stone et al. (1987).

The Gala Group in Grieston Quarry, Innerliethen. (Photo: TS1455, reproduced by kind permission of the Director, British Geological Survey, © NERC.)

Fissile thin greywackes and shales of the Gala Group, Grieston Quarry, Innerliethen. (Photo: TS1457, reproduced by kind permission of the Director, British Geological Survey, © NERC.)

The ichnospecies Dictyodora scotica from Thornylee Quarry (after Benton and Trewin, 1980). (a) irregular meanders; (b) plan view of basal burrow (stipple) and top wall (solid line); (c) regular meanders; (d) reconstruction of three-dimensional morphology showing basal burrow and wall; (e) block diagram to illustrate different preservational aspects of burrows in plan and in section. Arrows indicate direction of travel of burrowing animal.

Geological map of the area around Siccar Point and Old Cambus Quarry (after Craig, 1986).

Sketch-map of the geology at Woodland Point (after Cocks and Toghill, 1973).

Geological map of the Craighead Inlier, showing the location of Roughneck Quarry (after Cocks and Toghill, 1973).

Geological map of the Penwhapple Burn area, Main Outrcrop, Girvan (after Cocks and Toghill, 1973).

Sedimentary log through the Lower Camregan Grits, Wood Burn Formation and Maxwellston Mudstones in Penwhapple Burn (after Cocks and Toghill, 1973).

Purple mudstones of the Penkill Formation, Penwhapple Burn. (Photo: TS1493, reproduced by kind permission of the Director, British Geological Survey, © NERC.)

Correlation of the Llandovery successions within the various outcrops in the Girvan area (modified after Cocks and Toghill, 1973).

Geological map of the Blair–Knockgardner district, Girvan area (after Cocks and Toghill, 1973).

Gutterford Burn, North Esk Inlier, showing patchy exposures of the Reservoir Formation. (Photo: E.N.K. Clarkson.)

Measured section of the Reservoir Formation in Gutterford Burn (after Robertson, 1989). G = Gutterford Burn Limestone, E = Eurypterid Bed, S = Starfish beds.

Location of the main Silurian inliers of the Midland Valley of Scotland (after Wellman and Richardson, 1993).

???Wrong in the published book???

Reconstruction of the agnathan Jamoytius kerwoodi White by Ritchie, 1968, showing terminal round mouth, elongate body scales, paired lateral fin lobes, single anal and dorsal fins and asymmetrical tail.

The body profile of the agnathan thelodont Loganellia scotica (Traquair) and areas with scales of different morphology. Abbreviations: cp, cephalo-pectoral; l, lateral; o, orbital; p, pinnal; pc, precaudal; pp, postpectoral. Magnification × 1 (from Märss and Ritchie, 1998).

Ainiktozoon loganense Scourfield. (a) interpreted as a possible chordate by Ritchie, 1985. (b) inverted and reinterpreted as a thylacocephalan arthropod by Brugghen et al. 1997 (drawing D. Palmer after Brugghen et al.).

Distribution of the Geological Conservation Review sites for the Wenlock Series, set against the palaeogeographical elements of Silurian Britain.

The ‘Barr Trilobite’, Bumastus barriensis Murchison, 1839, from the Barr Limestone Member, Coalbrookdale Formation, Wenlock Series, Hay Head Quarries, Walsall area, West Midlands. Lectotype, British Geological Survey specimen (GSM 54421); dorsal view, × 0.8; figured by Jukes (1829), Salter (1849, 1867) and Lane and Thomas in Thomas (1978). (Photo: P.D. Lane.)

Daw End Railway Cutting, Walsall area, West Midlands. Section on north side of the track, immediately east of Rushall Canal bridge, showing three small bioherms (in the distance and the centre of the photo) in the Basement Beds of the Much Wenlock Limestone Formation, beneath which is the uppermost part of the Coalbrookdale Formation. (Photo: Derek J. Siveter.)

A lecture by Sir Roderick Murchison in the ‘Dudley Cavern’, West Midlands. From The Illustrated London News, September 22nd, 1849.

The ‘Dudley Bug’: Calymene blumenbachii Brongniart, 1817, Much Wenlock Limestone Formation, Wenlock Series, Dudley, West Midlands. Sedgwick Museum Cambridge specimen (SM A3225); dorsal view, × 1; figured Shirley (1936) and Siveter (1996). (Photo: Derek J. Siveter.)

Geology of Wren’s Nest Hill, Dudley, West Midlands (after Cutler et al., 1990).

Wren’s Nest Hill, Dudley, West Midlands. East–west cross section taken at about 400 m south of the college buildings (after Hamblin et al., 1978 and Cutler et al., 1990).

Wren’s Nest Hill, Dudley, West Midlands. Steeply dipping bedding planes of upper part of the Nodular Member, Much Wenlock Limestone Formation, west side of inlier. (Photo: Derek J. Siveter.)

Wren’s Nest Hill, Dudley, West Midlands. Succession in the 1977 NCC cutting and adjacent exposures (after Hamblin et al., 1978 and Cutler et al., 1990).

Location of Scutterdine Quarry and Little Hill quarries, and geology of the Woolhope Inlier, southern Welsh Borderland (after Squirrell and Tucker, 1960; and Earp and Hains, 1971).

Location of Linton Quarry and geology of the Gorsley area, southern Welsh Borderland (after Lawson, 1954).

Linton Quarry, Gorsley area, southern Wales Borderland. Dr Jim Lawson indicating the Wenlock–Ludlow series boundary: the Gorsley Limestone of Wenlock age lies below the hammer head and the Lower Siltstones of Ludlow age above it. The middle part of the quarry face comprises a much condensed Ludlow sequence, with the PÍídolí age Clifford Mesne Sandstone forming the top. (Photo: Derek J. Siveter.)

Sleia procincta Siveter, 1980, a beyrichiacean ostracod from the Much Wenlock Limestone Formation, Hobbs Ridge, May Hill Inlier, southern Welsh Borderland. Holotype, British Museum of Natural History specimen (BM OS6413); female, left valve, lateral view, × 45; figured Siveter (1980). (Photo: David J. Siveter.)

Location of Cwm-Ton area and Cilwrgi Quarry, and geology of the central and southern parts of the Usk Inlier, southern Wales (after Walmsley, 1959).

Location of Brinkmarsh Quarry and Buckover Road Cutting, and geology of this southern part of the Tortworth Inlier (after Curtis, 1972).

Buckover Road Cutting, Tortworth Inlier. General geology (after Curtis and Cave, 1964).

Lithological log of the Brinkmarsh Formation at Buckover Road Cutting, Tortworth Inlier (after Curtis and Cave, 1964).

Buckover Road Cutting, Tortworth Inlier. Geological section. Beds 1–18 belong to the Brinkmarsh Formation, Wenlock Series; beds 19–52, above the unconformity, belong to the Upper Old Red Sandstone (Devonian). (After Curtis and Cave, 1964.)

Diagrammatic cross-section across the East Mendips (Silurian) Inlier, running southwards from Stoke Lane (after Hancock, 1982).

Stratigraphy of the East Mendips Inlier (after Hancock, 1982).

Location of Penylan Quarry, Rumney Quarry and Rumney River section, and geology of the Cardiff district (after the British Geological Survey, 1986).

Silurian stratigraphy of the Cardiff district (fom Waters and Lawrence, 1987).

Silurian stratigraphy of the Rumney Borehole, Cardiff District (after Waters and Lawrence, 1987).

Rumney Quarry, Cardiff district. Showing the Rhymney Grit and overlying strata. (Photo: Derek J. Siveter.)

The geology of Pembrokeshire, showing the main structural blocks (after Walmsley and Bassett, 1976). The letters A–H refer to the successions in Figure 4.24.

Correlation of Silurian sections in Pembrokeshire (after Walmsley and Bassett, 1976). Sections A–H are located on Figure 4.23.

Marloes Sands, Pembrokeshire. View looking south-east and including exposures of the Skomer Volcanic, Coralliferous and Grey Sandstone groups. (Photo: Derek J. Siveter.)

Geology of the Freshwater East area, Pembrokeshire (after Walmsley and Bassett, 1976).

Geology of the Wenlock Edge–Benthall Edge area between Eaton and Ironbridge, Shropshire (after Bassett et al., 1975).

Hughley Brook, Shropshire. Location and summary section for the stratotype base of the Wenlock Series, Sheinwoodian Stage and the Buildwas Formation, with the ranges of some important microfossil species used in correlation (after Bassett, 1989a).

Whitwell Coppice, Ape Dale, Shropshire. Location of the standard section for the base of the Homerian Stage, coincident with the base of the Whitwell Chronozone, together with the graptolites recorded from strata above and below this base (after Bassett, 1989a).

Eaton Track, Wenlock Edge, Shropshire. Location of the standard section for the base of the Gleedon Chronozone, Homerian Stage, together with the graptolites recorded either side the boundary (after Bassett, 1989a).

Farley Road Cutting, between Much Wenlock and Ironbridge, Shropshire. Farley Member, Coalbrookdale Formation, Homerian Stage. (Photo: Derek J. Siveter.)

Farley Road Cutting, between Much Wenlock and Ironbridge, Shropshire. Alternations of thin shaley mudstones and nodular limestones, Farley Member, Coalbrookdale Formation, Homerian Stage. (Photo: Derek J. Siveter.)

Easthope–Harley Hill, Wenlock Edge, Shropshire. Lithofacies distribution in the Much Wenlock Limestone and Lower Elton formations of the reef area between Easthope and Much Wenlock (after Shergold and Bassett, 1970).

Bioherm, about 6 m wide by 4 m thick, within bedded limestones, Much Wenlock Limestone Formation, Coates Quarry, Easthope–Harley Hill site, Wenlock Edge, Shropshire. (Photo: Derek J. Siveter.)

Lower Elton Formation overlying Much Wenlock Limestone Formation, Stretton Westwood Quarry, Easthope–Harley Hill site, Wenlock Edge, Shropshire. (Photo: Derek J. Siveter.)

Longville–Stanway Road Section. Lithofacies distribution in the Much Wenlock Limestone and lower Elton formations of the non-reef area between Marked Ash and Easthope, Wenlock Edge, Shropshire. (after Shergold and Bassett, 1970).

Lincoln Hill area, Ironbridge, Shropshire. Steeply dipping face of Much Wenlock limestone Formation. (Photo: Derek J. Siveter.)

Lincoln Hill, Ironbridge, Shropshire. Reproduction of the wood-cut from The Silurian System (Murchison, 1839), showing sites (dark-shaded hollows) of extraction of the ‘concretions’ or ‘ballstones’ from the (Much) ‘Wenlock Limestone’ (Formation), with the ‘coal grits’ (Carboniferous) forming the small scarp in the distance (upper right).

Geology of the Burrington area, Ludlow Anticline (after Lawson and White, 1989).

Geology of the Dolyhir area, Radnorshire (after Garwood and Goodyear, 1919, Woodcock, 1988, and Siveter et al., 1989).

Dolyhir Quarries, Radnorshire. Dolyhir and Nash Scar Limestone Formation (Wenlock Series) overlying Strinds Formation (Precambrian), with evidence of faulting, Strinds Quarry. (Photo: Derek J. Siveter.)

Geology of the Trecoed–Castle Crab area, Builth district (after Bassett, 1993 and Siveter et al., 1989).

River Irfon, Builth Wells. Wenlock– Ludlow boundary section (after Siveter et al., 1989 and Bassett, 1993).

River Irfon, Builth Wells. Right bank, looking south, about 180 m south of the bridge over the A483 road, showing lundgreni Biozone (foreground) and ludensis Biozone (river bluff, background) strata, Homerian stage, Wenlock Series. (Photo: Derek J. Siveter.)

Geology of the Sawdde Gorge, Llandeilo–Llandovery area (after Bassett, 1982b and Siveter et al., 1989).

Geology of south-central Wales and location (rectangle, see Figure 4.47) of Wernbongam (after Squirrell and White, 1978).

Geology of the area in the vicinity of Wernbongam Quarry, Llandeilo area (after Squirrell and White, 1978).

Schematic section depicting relationships between the basal Old Red Sandstone, Silurian and Ordovician rocks of the Cennen valley and adjacent areas (after Squirrell and White, 1978).

Buttington Brickworks, Long Mountain area. Log through the upper Llandovery (Telychian) and lower Wenlock (Sheinwoodian) strata (after Loydell and Cave, 1993).

Buttington Brickworks, Long Mountain area. Fissile, graptolite-rich calcareous rocks of the Trewern Brook Mudstone Formation, Wenlock Series. (Photo: Derek J. Siveter.)

Range chart of graptolite species from the Banwy River section, Meifod area, Powys, from the spiralis Biozone (Telychian) to the riccartonensis Biozone (Sheinwoodian). The gap in the section indicates the position of a slide (within the insectus Biozone) (after Loydell and Cave, 1996).

Penstrowed Quarry, Newtown, Powys. Flute casts on the base of a sandstone bed within a turbidite sequence. (Photo: Derek J. Siveter.)

Map of Wales showing outcrop of Wenlock and Ludlow rocks, selected palaeogeographical features and depth-related faunal communities for rigidus Biozone time. Facies boundaries are conjectural away from outcrop control (after Dimberline et al., 1990).

Reconstruction of the Wenlock turbidite system in relation to the contemporary tectonic setting of the Welsh Basin (after Dimberline and Woodcock, 1987).

Stratigraphical section of Wenlock and Ludlow strata, Denbigh Region, north Wales (after Warren et al., 1984).

Location of Arcow Quarry, near Horton-in-Ribblesdale, and geology of the Craven inliers (after Arthurton et al., 1988).

Arcow Quarry, near Horton-in-Ribblesdale. Sandstone beds of the Austwick Formation. (Photo: David J. Siveter.)

River Rawthey, Howgill Fells. Basal strata of the Wenlock Series at the junction of Wandale Beck and the River Rawthey. (Photo: Derek J. Siveter.)

Lithostratigraphical map of the Windermere Supergroup around Coniston Water, south-west Cumbria (after Kneller et al., 1994).

Torver–Ashgill. Logs of the best exposed Wenlock sections across the Lake District, with tie-lines indicating the correlation of graptolite biozones (after Rickards, 1969, 1989a, with revision of lithostratigraphy after Kneller et al., 1994).

Geology of the original type areas of the Brathay and the Coldwell formations, the Lake District (after Rickards, 1989a, with revision of lithostratigraphy after Kneller et al., 1994).

Geology of the Balmae coast area, south of Kirkcudbright, Southern Uplands (modified from Clarkson et al., 1975, with minor revision of lithostatigraphical terminology after White et al., 1992).

Stratigraphical schemes for Silurian strata occurring in the Balmae coast area, south-east of Kirkcudbright, Southern Uplands (after quoted published sources).

Balmae Coast. Turbidites of the Ross Formation, Riccarton Group, Wenlock Series, south-east of Torrs Point, Kirkcudbright Bay, Southern Uplands. (Photo: Derek J. Siveter.)

Geology of the Meikle Ross (Borgue coast) area, SSW of Kirkcudbright, Southern Uplands (modified from Clarkson et al., 1975, with minor revision of lithostatigraphical terminology after White et al., 1992).

Geology of the area between Knockgardner and Blair Farm, Girvan District (after Clarkson et al., 1998, and Cocks and Toghill, 1973).

Sedimentary log through the Knockgardner Formation, Knockgardner Quarry, 350 m east of Knockgardner Farmhouse, Girvan district (after Clarkson et al., 1998).

Schematic block diagram illustrating depositional environments within the middle and upper part of the Straiton Group (latest Llandovery to early Wenlock in age), Knockgardner area, Girvan district. (A), Deep water graptolitic shales of the Blair Formation. Tectonic excision along the contact with the overlying Knockgardner Formation may have removed the more proximal mid to outer shelf facies to juxtapose deep-water sediments with shallow water facies at the junction between the two formations. (B), (C), and (D), in upward sequence, through the Knockgardner Formation, shallow-water prodelta facies (B), overlain by intertidal deposits subject to storm surges (C), and then shallow-water delta front sediments (D). (E) and (F), coarse grained back barrier facies (E) and lagoonal facies (F) of the Straiton Formation (after Clarkson et al., 1998).

Geology of the Ree Burn–Glenbuck Loch area, Hagshaw Hills (after Rolfe, 1962a, 1992).

Some arthropods and fish from the Ree Burn (a) and Fish bed Formations (b–e), Glenbuck Group, Wenlock Series, Hagshaw Hills. (a) Ceratiocaris papilio, a phyllocarid crustacean; (b) Lanarkia horrida, a thelodont fish; (c) Lasanius problematicus and (d) Birkenia elegans, anaspid fish; (e) Ateleaspis tessellata, a cephalaspid fish; (f) Lanarkopterus dolichoschelus, a eurypterid (modified from Rolfe, 1992, and Märss and Ritchie, 1998).

Glenbuck Loch, Hagshaw Hills. Dovestone Redbeds, Glenbuck Group, Wenlock Series. (locality 8 of Rolfe, 1992). (Photo: Derek J. Siveter.)

Geology of the North Esk Inlier and location of Lyne Water and Lynslie Burn (after Robertson, 1986, and the British Geological Survey, 1977).

Measured section of the Henshaw Formation, Wenlock series, Baddingsgill Reservoir to Lyne Water, North Esk Inlier (after Robertson, 1989).

Distribution of the Geological Conservation Review sites for the Ludlow Series, set against the palaeogeographical elements of Silurian Britain.

Geological cross-sections drawn by Sir Roderick Murchison for a lecture given in 1852 to the Ludlow Natural History Society and now housed in Ludlow Museum. The upper section runs from east to west, from the Cambrian of Wales, through Murchison’s ‘Lower Silurian’ (now Ordovician) of the Stiperstones area of Shropshire and beyond to Ludlow Castle, to the Old Red Sandstone and, ultimately, the Carboniferous of the Clee Hills to the north-east of Ludlow. The lower section runs north–south, from Bromfield just north of Ludlow, across the Ludlow Anticline and into Herefordshire.

Location of Pitch Coppice, Wigmore Road, near Ludlow Quarry, Shropshire (after Lawson and White, 1989).

The boundary stratotype section for the base of the Ludlow Series and the base of the Gorstian Stage at Pitch Coppice, Wigmore Road, near Ludlow (Holland et al., 1963; diagram after Lawson and White, 1989; both papers describe lithological divisions A–F).

The boundary stratotype section for the base of the Ludlow Series and the base of the Gorstian Stage at Pitch Coppice, Wigmore Road, near Ludlow, Shropshire (for lithologies see Figure 5.4). (Photo: Jane Washington-Evans.)

Map of the geology south-west of Ludlow, showing GCR sites along the Wigmore Road and elsewhere in the eastern part of the Ludlow Anticline (after Holland et al., 1963; Lawson, 1977; Lawson and White, 1989).

Geology of the section along the Goggin Road, Mortimer Forest, near Ludlow, Shropshire (after White and Lawson, 1978, with modifications from Siveter et al., 1989 and Sutherland, 1994).

Middle Elton Formation at White and Lawson’s (1978) locality 16–18 along the Goggin Road, Mortimer Forest, near Ludlow, Shropshire: mudstones containing bentonites (whitish horizons). (Photo: Derek J. Siveter.)

The acritarch Multiplicisphaeridium variable (Lister, 1970) Dorning, 1981 (left, × 1050) and the chitinozoan Ancyrochitina gogginensis Sutherland, 1994 (right, × 320), from the Lower Elton Formation, Goggin Road, Mortimer Forest, near Ludlow. (Photos: G. Mullins.)

Geology of Sunnyhill Quarry and contiguous trackside section, Mary Knoll Valley, Mortimer Forest, near Ludlow, Shropshire (after White and Lawson, 1978, with modifications from Siveter et al., 1989; localities 14 and 31 are repositioned after Lawson and White, 1989, p. 90, fig. 58).

Log through the boundary stratotype section for the base of the Ludfordian Stage at Sunnyhill Quarry, Mary Knoll Valley, Mortimer Forest, near Ludlow, Shropshire (after Holland et al., 1963, A–I = lithological divisions; and Lawson and White, 1989, C5–14 = combined locality and collection numbers).

The boundary stratotype section for the base of the Ludfordian Stage at Sunnyhill Quarry, Mary Knoll Valley, Mortimer Forest, near Ludlow, Shropshire. The recessed horizon is ‘C12’ of Figure 5.11. (Photo: David J. Siveter.)

Flaggy, calcareous siltstones; Lower Leintwardine Formation, east part of Sunnyhill Quarry, Mary Knoll Valley, Mortimer Forest, near Ludlow, Shropshire. (Photo: David J. Siveter.)

Geology of the section along the Deer Park Road, Mortimer Forest, near Ludlow, Shropshire (after White and Lawson, 1978 with modifications from Siveter et al., 1989).

Location and general stratigraphical position of localities at GCR sites The Whitcliffe and Ludford Lane and Corner, Ludlow, Shropshire (after Holland et al., 1963; modified from Siveter et al., 1989).

Geology of an area adjacent to the riverside path on the Whitcliffe, Ludlow, Shropshire, which shows the basal boundary stratotypes and body stratotypes for the Upper Leintwardine and Lower Whitcliffe formations (after Holland et al., 1963; modified from Siveter et al., 1989); see also Figures 5.17–5.19.

The boundary stratotype section for the base of the Upper Leintwardine Formation (see Figures 5.16 and 5.18), adjacent to the riverside path on the Whitcliffe, Ludlow, Shropshire (after Holland et al., 1963; modified from Siveter et al., 1989).