Scottish Journal of Geology

Tree trunks of Pitus primaeva in Mississippian (Courceyan) rocks at Montford, near Rothesay, Isle of Bute, Scotland

Howard J. Falcon-Lang, Elsa Henderson and Jean Galtier

Scottish Journal of Geology 2010; v. 46; p. 59-65 doi: 10.1144/0036-9276/01-404

Email alerting click here to receive free e-mail alerts when new articles cite this article service Permission click here to seek permission to re-use all or part of this article request Subscribe click here to subscribe to Scottish Journal of Geology or the Lyell Collection

Notes

Downloaded by on May 13, 2010

1,2,* 3 4 HOWARD J. FALCON-LANG ,ELSA HENDERSON &JEAN GALTIER 1Department of Earth Sciences, University of Bristol, Bristol BS8 1RJ, UK 2Present address: Department of Earth Sciences, Royal Holloway, University of London, Egham, Surrey TW20 0EX, UK 3Rosemount, Ascog, Isle of Bute PA20 9ET, UK 4UMR Botanique et Bioinformatique CIRAD, TA40/PS2, 34398 Montpellier, France *Corresponding author (e-mail: [email protected])

Synopsis Silicified tree trunks are described for the first time from Montford, near Rothesay, Isle of Bute, Scotland. The fossils occur in a fault-bounded succession, which is probably part of the Mississippian (Courceyan) Kinnesswood Formation. Quantitative anatomical analysis indi- cates that the tree trunks belong to the arborescent pteridosperm, Pitus primaeva Witham. Growth interruptions preserved in branches imply that these trees experienced aperiodic water stress, perhaps reflecting monsoonal seasonality in this part of palaeoequatorial Laurasia.

Introduction 6448) and extend 170 m south along the coast towards Ascog within the conﬁnes of a small unnamed bay (Grid Anatomically preserved fossil plants are extremely Reference NS 1067 6431). According to the 1: 63000 common in Mississippian rocks in Scotland’s Midland British Geological Survey map (Scotland Sheet 29, Valley and surrounding areas (Scott et al. 1984a). Most Rothesay, 1971) this area lies within a small NE–SW- spectacular of all are the large fossilized tree trunks trending fault-bounded basin containing Mississippian belonging to the genus Pitus, ﬁrst discovered, in 1826, at rocks, close to the NW basin margin (Fig. 1). Craigleith Quarry, Edinburgh (Witham 1831, 1833), and The precise age of the fossil-bearing strata is uncer- subsequently recognized at many other sites across the tain. A British Geological Survey borehole (NS 06 SE/8) region (Gordon 1935; Long 1979; Galtier & Meyer- Berthaud 2006). For many years, the systematic position drilled at Ascog (Grid Reference NS 0986 6302), 1.1 km of Pitus was enigmatic (Scott 1900). However, anatomical SW of the site, proves the existence of a 296 m thick studies have since provided support for the hypothesis that Mississippian succession within the basin (Amstrong it was a large arborescent pteridosperm (Long 1963). 1978). From base to top, the stratigraphic succession Where found in growth position at Kingwater, Cumbria, comprises the Tournaisian Kinnesswood, Ballagan, and tree stumps of Pitus primaeva are up to 2.5 m in diameter Clyde Sandstone formations (Paterson & Hall 1986), (Long 1979). Based on these dimensions, biomechanical and the early Visean Clyde Plateau Volcanic Formation inferences suggest these trees were more than 40 m high (Waters et al. 2007). Cementstones of the Ballagan (Mossbrugger 1990), making them the largest trees on Formation occur downdip of our fossil site, 200 m to the Earth at that time. Evidently, Pitus, together with other south, at Mill Hole (Grid Reference NS 1067 6411) on gymnosperms and ferns, formed a prominent component of the downthrow of a fault (Hill 1979). This structural the seasonally dry tropical forests that covered southeast relationship implies that beds at our site are older than Laurasia in Mississippian times (Falcon-Lang 1999a, 2000). the Ballagan Formation. Following Hill (1979), we Here we report a new site containing tree trunks of Pitus therefore assign these rocks, with uncertainty, to the primaeva Witham 1833 from the Isle of Bute, Scotland. Kinnesswood Formation, which is of early Courceyan age (c. 350–359 Ma; Waters et al. 2007). Between April 2007 and June 2008, one of us (EH) Geological setting collected about 350 fossil wood fragments from the The fossil tree trunks, which form the focus of this inter-tidal zone at the Montford site (Fig. 2). Almost of paper, were found at Montford, 1.5 km SE of Rothesay, all of these specimens occurred as water-worn pebbles on the east coast of the Isle of Bute. The fossils occur in and cobbles, 0.04–0.21 m in diameter, having earlier very poorly exposed, barnacle-encrusted, intertidal out- eroded out of the underlying rocks. However, a few crops that begin immediately adjacent to the entrance of specimens were observed in situ demonstrating that the Ardencraig Road, Montford (Grid Reference NS 1068 rest of the material had originated in the immediate

DOI 10.1144/0036-9276/01-404 Scottish Journal of Geology 46, (1), 59–65, 2010 60 H. J. FALCON-LANG ET AL.

F. 1. Geological map of Rothesay area, east side of Isle of Bute, Scotland, showing the main geological units and the location of the fossil site at Montford (after British Geological Survey, Scotland Sheet 29, Rothesay, 1971). vicinity. The largest of these in situ specimens was a trunk, 0.72 m in diameter and <1.84 m long, its full F. 2. Photographs of the field area. (A) The intertidal extent being obscured by overlying rocks and beach outcrop belt at Montford, Isle of Bute (looking south from Ardencraig Road), showing Cenozoic dyke (d), gravel. Many of the water-worn specimens of fossil basaltic tuffs (t) and sandstone beds (s), and (B) a silicified wood share very close petrographic similarities and fossil tree trunk embedded in sandstone in the southern probably represent fragments of a relatively small collection area (arrowed). Note rucksack for scale. number of large tree trunks, which have disintegrated in the intertidal zone over the past few decades. This the lake by drainage channels (sandstone and siltstone process can be seen in action, as small fragments have facies). The concentration of abundant fossils adjacent broken off the large in situ trunk in the course of our to the basin margin may suggest that the tree-trunks own observations. were growing on Devonian rocks to the NW. Poor Fossil wood occurs in one of two modes at Montford. exposure limits further interpretation. The first type, dark calcified wood, is confined to the north of our collection area. Where rarely seen in situ it ff occurs in successions of carbonate-cemented basalt tu s Fossil tree trunks and vesicular agglomerates showing undulatory lamination. The second type, pale- to dark-coloured silicified Most of the c. 350 fossil wood specimens were trans- wood, is found in a few barnacle-encrusted outcrops in versely sectioned, polished, and examined with a hand the southern part of our collection area. Specimens lens to assess the quality of preservation of plant occur in medium- to coarse-grained, poorly sorted sand- anatomy and to undertake preliminary identification. stone and siltstone beds showing undulatory lamination, On the basis of these observations all specimens ripple cross-lamination, symmetrical ripples, and draped comprise a gymnospermous structure with prominent mounds. multicellular rays, and probably represent a single These very limited observations imply that the fossil- morphotype. Specimens range from compressed or bearing succession was deposited in a shallow, standing recrystallized material with poor anatomical preserva- body of water (probably a small lake) near a basaltic tion to those showing excellent cellular detail. Generally, volcanic centre. The fossil assemblages probably repre- silicified material shows far better anatomical preserva- sent tree trunks that were either stripped from the tion than calcified material. adjacent shoreline following a volcanic eruption (water- Seven of the best-preserved silicified specimens were lain basaltic tuffs and agglomerate facies) or carried to selected for thin sectioning. For each, three standard COURCEYAN PITUS PRIMAEVA TREE TRUNKS 61

F. 3. Anatomical features seen in trunk wood of Pitus primaeva at Montford, Isle of Bute. All images from BRSUG28884. (A) Tracheids showing 2–3-seriate, alternate bordered pitting, scale: 75 µm, RLS; (B) tracheids showing 1–2-seriate, alternate bordered pitting, scale: 75 µm, RLS; (C) tapered ends of tracheids showing terminal curvature, probably around a ray, scale: 100 µm, RLS; (D) ray showing elongate parenchyma with oblique end-walls, scale: 100 µm, RLS; (E) cross-field pitting, scale: 25 µm, RLS; (F) 2–4-seriate rays, scale: 300 µm, TLS; (G) rays, up to 12-seriate, scale: 150 µm, TLS; (H) files of tracheids, separated by rays, scale: 350 µm, TS; (I) profusely pitted ray parenchyma, scale: 25 µm, TS. petrographic sections were prepared along Radial Lon- (BRSUG28880–28883), organic material was entirely gitudinal (RLS), Tangential Longitudinal (TLS) and lacking, such that there was no colour contrast between Transverse (TS) sections. This material, and associated the silicified cell walls and the crystals filling the lumen. thin sections, is stored in the Bristol University Geology This made detailed anatomical observation very difficult. Museum (accession numbers: BRSUG 28880–28886). The following anatomical description is based on the Although well preserved, in four of these specimens remaining three mature trunk specimens (BRSUG28884– 62 H. J. FALCON-LANG ET AL.

F. 4. Anatomical features seen in branch wood of Pitus primaeva at Montford, Isle of Bute. All images from BRSUG28886. (A) Pith and surrounding xylem, scale: 2 mm, TS; (B) Transition from parenchymatous pith (bottom) to periderm (top). Note the presence of growth interruptions in the xylem. Arrows highlight bifurcating leaf trace in xylem, scale: 2 mm, TS; (C) Transition from xylem (bottom) to parenchymatous pith (top), scale: 400 µm, TS; (D) pith showing opaque secretary cells, and thick-walled and thin walled parenchyma, scale: 250 µm, TS; (E) Mesarch xylem bundle (arrowed) embedded in parenchyma near edge of pith, scale: 50 µm, TS; (F) Xylem, phloem, and periderm, scale: 1 mm, TS.

28886), which to varying degrees retain organic material in terminate at the same height in the trunk (probably their cell walls. A lateral branch, 14 mm in diameter, is around rays). Ray parenchyma cells are elongate (245– embedded in one of these trunks (BRSUG28886) and this 307 µm long) with oblique end-walls (Fig. 3D) and show juvenile material is described separately from the mature 3–7 (mean 5.62, n=100) circular to oval pits (4 µm wood seen elsewhere. Following the standard quantitative diameter) in each cross-field (Fig. 3E). Cross-field pits approach to wood anatomy (Falcon-Lang & Cantrill 2000; are of taxodioid or araucarioid type. Falcon-Lang 2005; Oakley & Falcon-Lang 2009), 100 In TLS, rays are typically 1–6-seriate or rarely up to measurements were taken for each character, and the mean 12-seriate (mean 4.41, n=100) and 1–29 cells high, or and range are given. very rarely up to 55 cells high (mean 11.71 cells, n=100; Fig. 3F, G). Measured with a graticule, rays comprise Trunk wood 30–42% of the tangential area of the wood (mean: 34%, Mature secondary xylem is best preserved in n=15), the remainder made up of tracheids; this equates BRSUG28884, a 0.11 m diameter specimen, represent- to 7.3 complete rays per tangential mm2 (n=10). Ray ing a fragment of a much larger trunk. It shows the parenchyma cells are 20–32 µm high (median 26 µm) following characters: In RLS, tracheid bordered pitting and 18–30 µm wide (median 24 µm), and locally filled is 1-seriate (19%), 2-seriate (63%), 3-seriate (16%) or with opaque material; cells are commonly circular in 4-seriate (2%), with pits always being alternately TLS and leave small intercellular spaces between adja- arranged and contiguous (Fig. 3A, B). Tracheid pits are cent cells. Rare bordered pits occur on tangential trac- circular to hexagonal (10.4 µm diameter) with circular or heid walls as uniseriate, contiguous rows, comprising up oval, obliquely orientated apertures (4.8 µm diameter). to 3–4 pits. Tracheids are commonly short (1.2–1.8 mm high), show In TS, tracheids are rectangular to square with a a terminal taper and curvature near their tip (Fig. 3C). radial diameter of 37–74 µm (mean 61 µm, n=100) and Clusters of 3 or 4 adjacent curved tracheids may locally a tangential diameter of 35–68 µm (mean 59 µm, COURCEYAN PITUS PRIMAEVA TREE TRUNKS 63

TABLE 1 Quantitative comparison of our specimens with the four known morphospecies of Pitus, based on description of type material Morphospecies Ontogeny Tracheid diameter (µm) Rays (no. of cells) Ray cells (µm) Ray density Radial Tangential High Wide High Wide (rays/mm2) P. antiqua KID 674 HM Mature 64–85 (72) 79 3–146 (29) 1–8 (4.4) 35 29 3 KID 598 HM Juvenile 47–73 (58) 43 2–80 (18) 1–4 (2) 32 21.5 9 P. dayi GOR 1478 NHM Juvenile 30–61 (44) n.d. 2–43 (14) 1–6 (3) 23.5 18 13.8 P. primaeva KID 210/211 HM Mature 61–75 (69) 68 2–63 (16.4) 1–8 (3.5) 37 31 5 GOR 1386 NHM Mature 54–60 (58) 49 2–58 (14.4) 2–10 (3.4) 47 34 8.2 P. withamii KID 485 HM Mature 68–88 (79) 69 2–78 (14) 1–3 (1.6) 29 22 10 SCO 9319 NHM Mature 50–70 (58) 56 2–53 (14) 1–4 (1.7) n.d. n.d. 10.2 This paper BRSUG28884 Mature 37–74 (61) 35–68 (59) 1–55 (11.7) 1–12 (4.4) 26 24 7.3 BRSUG28886 Juvenile 15–59 (42) – 1–53 (12.3) 1–3 (2.3) 31 28 16 KID, Robert Kidston Collection; SCO, D.H. Scott Collection; GOR, William T. Gordon Collecton; HM, Hunterian Museum and Art Gallery, Glasgow; BMNH, Natural History Museum, London. n=100; Fig. 3H). Rays are typically 1.5–2.4 mm long Very poorly preserved tissue, interpreted as periderm, (mid-value: 1.95 mm) and separated by 2–9 (mean lies outside the phloem layer (Fig. 4F). 4.13, n=100) rows of tracheids. Ray parenchyma cells locally show profuse circular pits on transverse walls (Fig. 3I). Growth rings, or subtle growth interruptions, Systematics are entirely absent. Secondary xylem is generally classified as either manoxylic, as in calamopityans, lyginopteridaleans, and Branch wood medullosan pteridosperms (tracheids >150 µm diameter Branch wood is only seen in BRSUG28886, where a and multiseriate rays >200 cells high), or pycnoxylic lateral branch, 14 mm in diameter, is embedded within a (tracheids <50 µm diameter and short, uniseriate rays) 0.14 m diameter specimen of trunk wood (the original as seen in conifers (Galtier 1992). In this system, our diameter of the trunk is estimated to have been woods would be considered transitional showing both c. 0.19 m). The branch comprises pith, xylem and pycnoxylic and manoxylic characteristics. Fossil trunks phloem (Fig. 4A, B). The pith, 7 mm in diameter, is showing secondary xylem similar to our material include exclusively parenchymatous. Pith parenchyma cells are several Mississippian pteridosperms such as Archaeopi- equidimensional, 58–106 µm diameter, and include three tys, Cauloxylon, Eristophyton, Faironia, Megaloxylon, types: thin walled cells with empty lumen, thick-walled Pitus and Pycnoxylon (Galtier et al. 1998; Galtier & cells with empty lumen, and secretory cells filled with Meyer-Berthaud 2006; Decombeix et al. 2006, 2008). opaque material (Fig. 4A, C–D). However, the occurrence of primary xylem bundles In one thin section, two, possibly three, mesarch embedded within the pith (as seen in our specimens) is a primary xylem bundles are embedded in the pith, feature only present in Archaeopitys and Pitus. Of these c. 1 mm from its edge (Fig. 4E). Primary xylem trac- morphogenera, Pitus shows the closest match in terms of heids, 11–20 µm diameter (mean: 14.2 µm), show secondary xylem. scalariform-thickening. Secondary xylem is similar to Four morphospecies of Pitus are known: P. antiqua that seen in mature trunk wood, differing in having Witham, P. dayi Gordon, P. primaeva Witham and P. smaller tracheids, 15–59 µm radial diameter (mean: 42.2 withamii Lindley and Hutton (Arnold). A quantitative µm), and narrower rays, 1–3-seriate (mean: 2.3), of description of type material of these morphospecies was greater density (16 mm2, n=1). One notable feature of made by one of us (JG) and summarized in Table 1. For the secondary xylem in TS is the presence of irregular, each morphospecies, both juvenile wood, being tissue closely spaced growth interruptions (sensu Falcon-Lang within a few millimetres of the pith, and mature wood, 2003). These are defined by narrow zones (2–3 cells) of being tissue more than a few centimetres from the pith, smaller than average tracheids (15–20 µm diameter; Fig. were studied, the exception being P. dayi for which only 4B) and typically spaced 0.25–0.46 mm apart (mean juvenile wood is known (Gordon 1935). Based on sec- 0.34 mm, n=8). Where seen departing through the secondary xylem alone, only ray width and height allow ondary xylem, leaf traces bifurcate a short distance from discrimination between morphospecies (Gordon 1935) the pith (Fig. 4B). and these characters are highly dependent on ontogeny The secondary phloem is locally present, up to 1 mm (Falcon-Lang 2005). P. primaeva bears closest resem- wide, shows poor preservation, and comprises a complex blance to our material, having rays up to 63 cells high structure of parenchyma, rays, fibres and sieve cells. (up to 55 cells high in our material) and up to 10 cells 64 H. J. FALCON-LANG ET AL. wide (up to 12 cells in our material). In mature speci- of Montagne Noire, France. Review of Palaeobotany and mens of P. antiqua, rays are of greater height and lower Palynology, 142, 79–92. density, and in P. withami are substantially narrower DECOMBEIX, A.L., MEYER-BERTHAUD, B. & GALTIER, J. 2008. Diversity of Mississippian arborescent (Table 1). Several qualitative characters of uncertain lignophytes: A new species o. Eristophyton from the Middle systematic value support assignment to P. primaeva Tournaisian of France. International Journal of Plant Sci- including the occurrence of pith parenchyma of three ences, 169, 1116–1127. types, and the terminal curvature of tracheids. FALCON-LANG, H.J. 1999a. The Early Carboniferous (Courceyan–Arundian) monsoonal climate of the British Isles: evidence from growth rings in fossil woods. Geological Magazine, 136, 177–187. Palaeoecology FALCON-LANG, H.J. 1999b. The Early Carboniferous One of the most notable features of the branch of (Asbian–Brignatian) seasonal tropical climate of northern Britain. Palaios, 14, 116–126. Pitus primaeva from Montford is the occurrence of FALCON-LANG, H.J. 2000. Fire ecology of the Carbonifer- growth interruptions. Similar growth interruptions have ous tropical zone. Palaeogeography, Palaeoclimatology, Pal- been previously observed in Mississippian gymnosperms aeoecology, 164, 339–355. from the Midland Valley of Scotland and surrounding FALCON-LANG, H.J. 2003. Growth interruptions in conifer areas (Falcon-Lang 1999a, b). These occur in certain woods from the Upper Cretaceous (Late Campanian) Two Medicine Formation, Montana, USA: implications for specimens of Pitus primaeva (Gordon 1935), P. withamii paleoclimate and dinosaur ecology. Palaeogeography, Pal- (Galtier & Scott 1994), P. antiqua (Galtier et al. 1994) as aeoclimatology, Palaeoecology, 199, 299–314. well as in Bilignea, Endoxylon, Eristophyton, Stanwoodia FALCON-LANG, H.J. 2005. Intra-tree variability in wood and Stenomyelon (Scott et al. 1994b; Falcon-Lang anatomy, and its implications for fossil wood systematics 1999a, b). Growth interruptions are only found in small and palaeoclimatic studies. Palaeontology, 48, 171–183. FALCON-LANG, H.J. & CANTRILL, D.J. 2000. Cretaceous diameter axes suggestive of branches or a position close (Late Albian) Coniferales of Alexander Island, Antarctica. to the stem apex. This is most clearly shown by our Part 1: Wood taxonomy, a quantitative approach. Review of material where growth interruptions are absent in Palaeobotany and Palynology, 111, 1–17. ontogenetically mature wood in a trunk but present in GALTIER, J. 1992. On the earliest arborescent gymnosperms. the juvenile wood of an attached branch. Courier Forschungsinstitut Senckenberg, 147, 119–125. The factors that give rise to growth interruptions GALTIER, J. & MEYER-BERTHAUD, B. 2006. The diver- sification of early arborescent seed ferns. Journal of the include temporary disturbances to growth such as fires, Torrey Botanical Society, 133, 7–19. frosts, floods, droughts, wind damage, insect defoliation GALTIER, J. & SCOTT, A.C. 1994. Arborescent gymno- and leaf flushes (Falcon-Lang 2003). Twigs and branches sperms from the Viséan of East Kirkton, West Lothian. tend to preferentially develop growth interruptions (as Transactions of the Royal Society of Edinburgh: Earth Sci- seen in our material) because their peripheral position ences, 84, 261–266. GALTIER, J., BROWN, R.E., SCOTT, A.C., REX, G.M. & means they are more sensitive to subtle environmental ROWE, N.P. 1994. A late Dinantian flora from Weaklaw, changes (Falcon-Lang 2005). The British Isles lay close to East Lothian, Scotland. In Scott, A.C. & Collinson, M. (eds) the equator on the SE coast of Laurasia during Missis- Studies in palaeobotany and palynology in honour of Professor sippian times. Growth interruptions in the Montford W. G. Chaloner. Special Papers in Palaeontology, 49, 57–74. fossil trees and those found elsewhere most likely reflect GALTIER, J., SCHNEIDER, J-L. & GRAUVOGEL- monsoonal seasonality with occasional droughts leading STAMM, L. 1998. Arborescent gymnosperms and the occurrence of Protopitys from the Lower Carboniferous of to aperiodic water stress. This is consistent with the the Vosges, France. Review of Palaeobotany and Palynology, occurrence of vertic and calcrete paleosols (Wright 1990; 99, 203–215. Wright et al. 1991; Andrews & Nabi 1998), and schizo- GORDON, W.T. 1935. The genu. Pitys, Witham, emend. haline lagoonal deposits (Leeder 1974), all of which point Transactions of the Royal Society of Edinburgh, 58, 279–308. to pronounced seasonality in tropical rainfall. HILL, J. 1979. Reading the Landscape of Bute through its Geology. Buteshire Natural History Society Publication, Rothesay. Acknowledgements LEEDER, M.R. 1974. Lower Border Group (Tournaisian) fluviodeltaic sedimentation and palaeogeography of the HFL gratefully acknowledges receipt of a Leverhulme Early Northumberland basin. Proceedings of the Yorkshire Geo- Career Fellowship at the University of Bristol. logical Society, 40, 129–180. LONG, A.G. 1963. Some specimens o. Lyginorachis papilio Kidston associated with stems of Pitys. Transactions of the References Royal Society of Edinburgh: Earth Sciences, 65, 211–224. LONG, A.G. 1979. Observations on the Lower Carboniferous AMSTRONG, M. 1978. IGS Ascog Borehole core description genu. Pitus Witham. Transactions of the Royal Society of (NS 06 SE/8). British Geological Survey report (unpub- Edinburgh: Earth Sciences, 70, 111–127. lished). OAKLEY, D. & FALCON-LANG, H.J. 2009. Morphometric ANDREWS, J.E. & NABI, G. 1998. Palaeoclimatic signifi- analysis of Cretaceous (Cenomanian) angiosperm woods cance of calcretes in the Dinantian of the Cockburnspath from the Czech Republic. Review of Palaeobotany and Outlier (East Lothian, North Berwickshire). Scottish Journal Palynology, 153, 375–385. of Geology, 34, 153–164. MOSSBRUGGER, V. 1990. The tree habit in land plants. DECOMBEIX, A.L., GALTIER, J. & MEYER- Lecture Notes, Earth Sciences, 28, 1–161, Berlin, Springer. BERTHAUD, B. 2006. Faironia difasciculata, a new gym- PATERSON, I.B. & HALL, I.H.S. 1986. Lithostratigraphy of nosperm from the Early Carboniferous (Mississippian) the late Devonian and early Carboniferous rocks in the COURCEYAN PITUS PRIMAEVA TREE TRUNKS 65

Midland Valley of Scotland. British Geological Survey boniferous successions of Great Britain (onshore). British Report, 18, No. 3. Geological Survey, Research Report RR/0701. SCOTT, D.H. 1900. Studies in Fossil Botany. Black, London. WITHAM, H.T.M. 1831. Fossil Vegetables: Representation of SCOTT, A.C. 1990. Preservation, evolution and extinction of Their Internal Structure as seen through the Microscope. plants in Lower Carboniferous volcanic sequences in Blackwood and Cadell, Edinburgh and London. Scotland. In Lockley, M.G. & Rice, A. (eds) Volcanism and WITHAM, H.T.M. 1833. The Internal Structure of Fossil Fossil Biotas. Geological Society of America, Special Paper Vegetables found in the Carboniferous and Oolitic deposits of 244, Boulder, Colorado, 25–38. Great Britain. Black, Edinburgh. SCOTT, A.C., GALTIER, J. & CLAYTON, G. 1984a. The WRIGHT, V.P. 1990. Equatorial aridity and climatic oscilla- distribution of Lower Carboniferous anatomically preserved tions during the Mississippian, southern Britain. Journal of ﬂoras in Western Europe. Transactions of the Royal Society the Geological Society, London, 147, 359–363. of Edinburgh: Earth Sciences, 75, 311–340. WRIGHT, V.P., VANSTONE, S.D. & ROBINSON, D. 1991. SCOTT, A.C., BROWN, R., GALTIER, J. & MEYER- Ferrolysis in Arundian alluvial paleosols: evidence of a ERTHAUD, B. 1994b. Fossil plants from the Viséan of East shift in the Mississippian monsoonal system. Journal of the Kirkton, West Lothian, Scotland. Transactions of the Royal Geological Society, London, 148, 9–12. Society of Edinburgh: Earth Sciences, 84, 249–260. WATERS, C.N., BROWNE, M.A.E., DEAN, M.T. & POWELL, J.H. 2007. Lithostratigraphic framework for Car-

MS. accepted for publication 14 July 2009