Atherfield Clay Research Articles

A marine microvertebrate fauna from a temporary exposure of the Atherfield Clay Formation, Reigate, Surrey

A temporary exposure of the nearshore marine Atherfield Clay (Lower Greensand Formation, Aptian, Early Cretaceous) in the Reigate area (Wonham Mill) of Surrey was sampled for microvertebrate remains in Autumn 2013. Samples amounting to 858 kg of sediment were washed, dried, and sieved to 0.325 mm and the residue searched for all fossil content. This is the first definitive study of the Atherfield Clay chondrichthyan fauna of Surrey. The samples yielded teeth of hybodont sharks (Planohybodus ensis, Lonchidion breve), neoselachian sharks (Heterodontus sulcatus, Cretascyllium hassei, Protospinax sp., Protolamna sokolovi, Lamnid indet., Scyliorhinus muelleri, Scyliorhinus gen. et sp. indet., Protoscyliorhinus sp.) and batoids (Belemnobatis picteti, Squatirhina sp.). The neoselachian sharks and rays all constitute the first confident records for the various genera in the Atherfield Clay of the United Kingdom. Dermal denticles and bony fish teeth are also present in the samples, which also yielded small numbers of invertebrates (ammonite and crustacean), microcoprolites (Tomaculopsis tomaculopsis) and plant remains (fern indusia). The state of preservation of the chondrichthyan material suggests that none of the specimens are derived from older strata; the fauna is indigenous. The Surrey Atherfield Clay fauna is distinct from that recorded from the Atherfield Bone Bed on the Isle of Wight and the roughly coeval boreal fauna of the Speeton Clay.

A new neoselachian shark from the marine Early Cretaceous of Southern England

Rare, isolated teeth of Corysodon multicristatus sp. nov. are described from two levels in the Atherfield Clay Formation (Early Aptian, Early Cretaceous) of Atherfield Point on the Isle of Wight, UK. Ten teeth of the new species were recovered from 1095 kg of washed and graded sediment residues. The teeth themselves are very small (around 0.5 mm high) and possess a distinctive crown bearing a tiered series of transverse crests adapted for rasping. Details of the dental architecture of the Atherfield Clay Formation specimens clearly indicate that the Cretaceous material differs significantly from the teeth of the type species for the genus, Corysodon cirinensis, recorded from the Kimmeridgian of northern France and Switzerland. C. multicristatus is the first substantiated record of the genus from the Early Cretaceous, thereby extending the stratigraphic range of the genus from the latest Jurassic, and the geographical range from continental Europe to the UK.

Preparing detailed morphological features of fossil brittle stars (Ophiuroidea, Echinodermata) for scanning electron microscopy using a combination of mechanical preparation techniques

The comprehensive taxonomic study of fossil brittle stars (Echinodermata: Ophiuroidea) requires the plates of the disk and arms to be cleared of matrix as fully as possible to reveal significant characters, such as spine articulations, ornament and clear plate boundaries. However, this needs to be done delicately, as the plate surfaces and boundaries are fragile and easily obliterated when only using air abrasive techniques. Ophiuroid fossils are frequently over-prepared, which becomes apparent particularly when examined by scanning electron microscopy (SEM), hampering taxonomic studies. Preparation may be further complicated by the entanglement of the arms of multiple individuals. In order to facilitate detailed SEM analysis of recently available, undescribed fossil ophiuroid material from the Aptian, Lower Cretaceous, Atherfield Clay Formation of the Isle of Wight, Hampshire, UK a combination of careful mechanical preparation techniques was employed to great effect. Specimens were initially exposed using standard air abrasive techniques, but the final few millimetres of matrix were removed using pins. To get individual arm pieces exceptionally clear of matrix, they were removed from the blocks using a mini pedestalling technique and then further cleaned using an ultrasonic pen. This combination of techniques fully exposed all the elements required for full taxonomic study without causing severe damage to the plate surfaces and greatly improved the overall aesthetic of the specimens. These techniques could be more widely applied in fossil preparation.

A guide to the fossil Decapoda (Crustacea: Axiidea, Anomura, Brachyura) of the British Isles

Ranging from the Jurassic to the Pleistocene, the fossil record of decapod crustaceans in the British Isles is extensive, comprised of 159 species (including those in open nomenclature) assigned to 101 genera. Preservation is variable, but most taxa are based upon carapace material; the study of disarticulated limb elements has added surprisingly little to the known diversity. No new taxa are erected herein, but some species have been reassigned to more appropriate genera and/or families. The stratigraphic distribution of these crustaceans is such that most, if not all, species are known from the Mesozoic and Cenozoic successions of southern and eastern England. Some areas and horizons are particularly rich in decapod species, including the Aptian Atherfield Clay Formation, Isle of Wight; the Albian Gault Clay Formation; the Cenomanian Beer Head Limestone Formation, Wilmington Sands Member; the Lower Eocene London Clay Formation; the Paleogene of the Isle of Wight; and the various crag formations of East Anglia.

Gamma-ray log correlation and interpretation of Fitton’s and Casey’s stratigraphy with offshore borehole 99/16-1

The Chale Bay type section of the Lower Greensand Group (LGS) Atherfield Clay, Ferruginous Sands and Sandrock formations is characterised by members, bounded by hiatuses, formerly recognised (if not named as such) by Fitton as his ‘groups’ and Casey in defining ammonite zone and sub-zone boundaries. Subsequent work has shown that some of the formations of the LGS are recognised elsewhere on the Isle of Wight, in southern England and in northern France. Likewise, some members of the Atherfield Clay and Ferruginous Sands formations can be recognised beyond the Chale Bay type section. In this work, we have measured outcrop gamma-ray emission from the type section: gamma-ray peaks recognised on all datasets are used to attempt a correlation of the Lower Greensand Group between the Isle of Wight and an offshore borehole (99/16-1). This is partially successful, showing that Fitton and Casey’s stratigraphy maybe recognised basin-wide.

A new ammonite fauna from the Walpenites horizon of the upper Aptian (Lower Cretaceous), Isle of Wight, southern England

The Lower Greensand Group on the Isle of Wight in southern England forms the basis for the Aptian ammonite biostratigraphy in western Europe mainly established by the work of Raymond Casey between 1960 and 1980. It thus became a world reference succession, due to many ammonite finds from excellent outcrops along the coastline of the Island exposing the fossiliferous Atherfield Clay and Ferruginous Sands formations. Nevertheless, some of the members of these formations only rarely contain ammonites: an example is the horizon containing Walpenites (Group X according to the classical nomenclature of Fitton), in the upper Aptian Epicheloniceras martinioides Zone. Hitherto, this horizon has yielded only very rare Walpenites, a cryptic micromorphic ammonite only known from the type specimen. We report additional specimens of this rare ammonite, unequivocally demonstrating that Walpenites is a heteromorphic ammonite with only a part of the early whorls coiled in a planispiral with whorls attached to each other. Furthermore, the new material allows us to regard Luppovia as a junior subjective synonym of Walpenites, a genus based on material from Kazakhstan and Turkmenistan. Additionally, a new fauna of small ammonites from the Walpenites horizon is described; it contains Epicheloniceras martinioides, E. subnodosocostatum, E. tschernyschewi and the heteromorph cf. Toxoceratoides. This has improved the biostratigraphical dating and correlation of the stratigraphical level herein called the Walpenites horizon and, in contrast to earlier ideas, it contains ammonites that are distributed almost globally in all major faunal realms.

Bivalves on mecochirid lobsters from the Aptian of the Isle of Wight: Snapshot on an Early Cretaceous palaeosymbiosis

Fossil symbioses (Bary 1879) that are not recognized in modern assemblages are rare. This holds true especially because fossil remains of interspecific association are sporadic and difficult to document. Thus, fossil associations illustrated on a large number of specimens are of particular interest. Numerous specimens of mecochirid lobsters (Glypheidea, Decapoda, Crustacea) from the Lower Cretaceous of the Atherfield Clay Formation (Isle of Wight, UK) seer small epibiotic bivalves on their exoskeleton. We propose to identify the post-mortem or syn-vivo nature of this association. To this end, we test and revise the systematic assignment of both crustacean and molluscan partners. A new genus name is proposed for the crustacean Meyeria magna M'Coy, 1849, as well as the new combination Atherfieldastacus magnus (M'Coy, 1849). To understand the nature of the association, a qualitative and quantitative study of the association is conducted on newly examined material (161 lobsters) looking at prevalence, density and abundance of the infestation (per anatomical region of the lobsters). Angularities and flat surface of exoskeletons were also evaluated. The distribution of the bivalves on both sides of the crustaceans (60% of the colonized lobsters), their preservation and their downward growth orientation suggests no post-mortem attachment of the mollusks. Hence, the association may be ascribed to a true palaeosymbiosis between these organisms. The non-homogeneous distribution of bivalves, that is to say an important colonization of the angular ridges of the carapace, is interpreted as selected sites by the mollusks for larval fixation, and may indicate possible half-burrowing posture of lobsters. This palaeosymbiosis has no modern equivalent, as cemented bivalve shells have never been reported on any population of decapod crustaceans. This fossil association may be ascribed to a local Aptian palaeoenvironment comprising swarming spats of anomiid bivalves.

A new small-bodied azhdarchoid pterosaur from the lower cretaceous of England and its implications for pterosaur anatomy, diversity and phylogeny.

BackgroundPterosaurs have been known from the Cretaceous sediments of the Isle of Wight (southern England, United Kingdom) since 1870. We describe the three-dimensional pelvic girdle and associated vertebrae of a small near-adult pterodactyloid from the Atherfield Clay Formation (lower Aptian, Lower Cretaceous). Despite acknowledged variation in the pterosaur pelvis, previous studies have not adequately sampled or incorporated pelvic characters into phylogenetic analyses.Methodology/Principal FindingsThe new specimen represents the new taxon Vectidraco daisymorrisae gen. et sp. nov., diagnosed by the presence of a concavity posterodorsal to the acetabulum and the form of its postacetabular process on the ilium. Several characters suggest that Vectidraco belongs to Azhdarchoidea. We constructed a pelvis-only phylogenetic analysis to test whether the pterosaur pelvis carries a useful phylogenetic signal. Resolution in recovered trees was poor, but they approximately matched trees recovered from analyses of total evidence. We also added Vectidraco and our pelvic characters to an existing total-evidence matrix for pterosaurs. Both analyses recovered Vectidraco within Azhdarchoidea.Conclusions/SignificanceThe Lower Cretaceous strata of western Europe have yielded members of several pterosaur lineages, but Aptian pterosaurs from western Europe are rare. With a pelvis length of 40 mm, the new animal would have had a total length of c. 350 mm, and a wingspan of c. 750 mm. Barremian and Aptian pterodactyloids from western Europe show that small-bodied azhdarchoids lived alongside ornithocheirids and istiodactylids. This assemblage is similar in terms of which lineages are represented to the coeval beds of Liaoning, China; however, the number of species and specimens present at Liaoning is much higher. While the general phylogenetic composition of western European and Chinese communities appear to have been approximately similar, the differences may be due to different palaeoenvironmental and depositional settings. The western Europe pterodactyloid record may therefore be artificially low in diversity due to preservational factors.

Ostracoda during the Early Aptian (Early Cretaceous) greenhouse period on the Isle of Wight, England

The earliest Aptian marine transgression of the Lower Cretaceous across southern England resulted in the collapse of the generally freshwater Barremian environment and the initiation of marine mileux. Salinities passed from fresh-oligohaline to meso- and pliohaline, reaching fully marine conditions during the obsoletum Subzone ( P. fissicostus Zone). Newly formed environmental niches were rapidly occupied by ostracod associations. In the Isle of Wight, freshwater Cypridea-rich assemblages in the lower Shepherd's Chine Member (Vectis Formation) were gradually replaced by faunas dominated by Sternbergella cornigera, Mantelliana mantelli and Theriosynoecum fittoni. Marine taxa recorded from the Atherfield Clay Formation migrated predominantly from the Paris Basin and include Asciocythere albae, Schuleridea derooi, Neocythere gottisi, N. bordeti, Cythereis geometrica, Cytheropteron stchepinskyi and Protocythere croutesensis.

Behavior of a Stiff Clay behind Embedded Integral Abutments

Integral bridges can significantly reduce maintenance and repair costs compared with conventional bridges. However, uncertainties have arisen in the design as the soil experiences temperature-induced cyclic loading behind the abutments. This paper presents the results from an experimental program on the behavior of Atherfield clay, a stiff clay from the United Kingdom, behind embedded integral abutments. Specimens were subjected to the stress paths and levels of cyclic straining that a typical embedded integral abutment might impose on its retained soil. The results show that daily and annual temperature changes can cause significant horizontal stress variations behind such abutments. However, no buildup in lateral earth pressure with successive cycles was observed for this typical stiff clay, and the stress–strain behavior and stiffness behavior were not influenced by continued cycling. The implications of the results for integral abutment design are discussed.

Performance of push-in pressure cells in overconsolidated clay

Low-profile push-in pressure cells (spade cells) are commonly used to measure total horizontal stresses in both normally and overconsolidated clays. It is known that spade cells over-read the in situ stress in such deposits as a result of the complex localised stresses created during installation. Previous investigations into the magnitude of over-read are limited in number and have produced scattered results. During construction of the Channel Tunnel Rail Link at Ashford, Kent, a spade cell was installed horizontally in an overconsolidated clay, aligned to measure initial vertical stress, and the change in vertical stress due to excavation of material above the cell. The results of this experiment are presented and interpreted with reference to a finite element analysis and a comparison of spade cell and self-boring pressuremeter test data of horizontal stresses at the same site, to assess the performance of this type of spade cell in the Atherfield Clay.

Clay mineralogy of the Cretaceous strata of the British Isles

AbstractThe clay mineralogy of the Cretaceous strata of the British Isles is described and discussed within its lithostratigraphical and biostratigraphical framework using published and unpublished sources as well as 1400 new clay mineral analyses. The regional clay mineral variation is described systematically for the following strata:(1)Southern England — Purbeck Limestone Group (Berriasian/Ryazanian; Lulworth and Durlston formations), Wealden Group (Valanginian—Barremian/Aptian; Ashdown, Wadhurst Clay, Tunbridge Wells Sands, Grinstead Clay Member, Wealden Clay, Wessex and Vectis formations), Lower Greensand (Aptian—Lower Albian; Atherfield Clay, Hythe, Sandgate, Folkestone Sands, Ferruginous Sands, Woburn Sands and Faringdon Sponge Gravels formations), Selborne Group (Middle—Upper Albian; Gault Clay and Upper Greensand formations) and the Chalk Group (Cenomanian—Lower Maastrichtian).(2)Eastern England — Cromer Knoll Group (Ryazanian—Upper Albian; Speeton Clay, Spilsby Sandstone, Sandringham Sands, Claxby Ironstone, Tealby, Roach Ironstone, Dersingham, Carstone and Red Chalk (or Hunstanton Red Limestone) formations).(3)Scotland — Inner Hebrides Group (Cenomanian—Campanian; Morvern Greensand, Gribun Chalk, Coire Riabhach Phosphatic Hibernian Greensands formations).(4)Northern Ireland — Hibernian Greensands (Cenomanian—Santonian) and Ulster White Limestone formations (Santonian—Lower Maastrichtian).The stratigraphical patterns of clay mineral variation divide naturally into two types; firstly, the more complex pattern of the Lower Cretaceous strata and secondly, the simple pattern of the Upper Cretaceous. Clay mineral variations in the non-marine and marine Lower Cretaceous strata of England are best explained by the interplay of two main clay mineral assemblages between which all gradations occur. The assemblage which dominates the main clay formations consists of mica, kaolin and poorly defined mixed-layer smectite-mica-vermiculite minerals, and sometimes includes vermiculite and traces of chlorite. It is dominantly of detrital origin and detailed evidence indicates it is derived largely from the reworking of Mesozoic sediments although ultimately from weathered Palaeozoic sediments and metasediments. Although mainly of detrital origin, this assemblage contains a persistent component that formed coevally with the approximate depositional age of its host sediment. Whether this component is of soil origin or was neoformed in the sediment shortly after deposition is unclear. There is little firm evidence indicating the sources of this clay mineral detritus. However, in the strata of the Wealden Group of southern England, mineral trends suggest three sources; one of these was to the west (Cornubian Massif), another must have been the Anglo- Brabant landmass. In the Selborne Group (Middle—Upper Albian) and in the overlying Lower Chalk (Cenomanian) where this assemblage makes its last appearance in the Cretaceous of England, there is good evidence of easterly and south-easterly sources.The second main assemblage tends to be largely monominerallic, and usually dominated by smectite with or without small amounts of mica; less frequently, kaolin, berthierine or glauconite sensu lato is the sole or dominant component. It is considered to be of volcanogenic origin, derived from the argillization of volcanic ash under different conditions of deposition and diagenesis. The source of the ash in Berriasian—Aptian times seems to have been an extensive volcanic field in the southern part of the North Sea and in the Netherlands, whereas in the Albian (and extending into the Cenomanian) a westerly source dominated. The current controversy about the role of climate or pattern of volcanic activity controlling the clay mineral stratigraphy of the Lower Cretaceous is reviewed.In the lower part of the Upper Cretaceous strata of England, Scotland and Ireland, sand-grade glauconite is particularly abundant. Much of it represents the glauconitization of pene- contemporanous volcanic ash, possibly of basaltic origin, associated with continental breakup and the opening up of the Atlantic Ocean and the earliest stages in the development of the Hebridean Tertiary Igneous Province. The Upper Cretaceous Chalk facies of England and Ireland is dominated by a smectite-rich clay assemblage containing mica, and the various hypotheses for its origin (detrital, neoformation, volcanogenic) are reviewed in the light of available mineralogical, chemical and geological data.

Observations on the lithostratigraphy and ammonite succession of the Aptian (Lower Cretaceous) Lower Greensand of Chale Bay, Isle of Wight, UK

A revised lithostratigraphy is given for parts of the Atherfield Clay and Ferruginous Sands Formations (Lower-Upper Aptian) of the Lower Greensand Group of the standard section in Chale Bay, Isle of Wight, retaining in essence the classic nomenclature of Fitton. Changes in zonal and subzonal boundaries are proposed on the basis of new collections of ammonites obtainedin situ. The Upper Lobster Beds Member of the Atherfield Clay is detached from the Subzone ofDeshayesites callidiscusand placed in a separate Subzone ofDeshayesites annelidusat the top of the Zone ofD. forbesi. The influx ofMegatyloceras, Cheloniceras, PseudosaynellaandSinzoviaat this level has palaeogeographic implications, pointing to the opening of a marine link with the Paris Basin and confirming the Upper Lobster Beds as a transgressive horizon. The upper part of the Scaphites Beds Member of the Ferruginous Sands, previously included in thedeshayseiZone, is transferred to the Subzone ofDufrenoyia transitoria, at the base of the Zone ofTropaeum(T.)bowerbanki, on the strength of the occurrence therein of species ofTropaeumandDufrenoyia.Tropaeumis not present below thebowerbankiZone as now defined; its primitive ancyloceratoid (hooked) forms such asT. (T.)hillsiihave limited biochronological value, persisting alongside the criocone (spiral) species of thebowerbankiZone and giving rise to a local horizon ofT. (T.)pseudophillsiat the bottom of the Upper Crioceras Beds (basal Upper Aptian). A more precise delimitation of the Walpen Clay & Sands from the Upper Crioceras Beds is made and the junction of these two members of the Ferruginous Sands is reaffirmed as the Lower/Upper Aptian boundary, coinciding with the junction of the Zones ofT. (T.)bowerbankiandEpicheloniceras martiniodes. Bed-by-bed collecting across the boundary shows thatEpichelonicerascan no longer be taken as the prime biostratigraphical marker for the base of the Upper Aptian; greater significance is given to the extinction ofDufrenoyia. The sources of the genusVectisitesand some species ofAmmonitocerasandCaspianites, hitherto fixed only vaguely in the column, are pinpointed in themartinioidesZone. The horizon ofTropaeum(T.)drewiis confirmed as high in thebowerbankiZone (meyendorffiSubzone) and the validity of a ‘drewiZone’ at the base of the German Upper Aptian (=base of Middle Aptian, Kemper, 1995) is questioned. In a review of the Lower/Upper Aptian boundary, it is suggested that the German stratum be called the Horizon ofCicatrites?tenuinodosusand placed tentatively at the top of the Lower Aptian. These and other changes in ammonite nomenclature are explained in the systematic notes.

Tectonic controls on the variation in thickness and mineralogy of pebble-beds in the Lower Greensand Group (Aptian-Albian) of the Isle of Wight, southern England

Pebble-rich horizons occur throughout the Aptian-Albian Lower Greensand Group of the Isle of Wight. The four distinctive pebble-beds selected for detailed analysis in this study occur above transgressive and/or erosive surfaces and have previously been used as stratigraphie markers. The Perna Member in the Atherfield Clay Formation marks the first Aptian transgression across the area. Pebble-beds at the bases of Members XI/XII and XIII, in the Ferruginous Sands Formation are associated with the regional martiniodes regression and the subsequent nutfieldiensis transgression. The topmost pebble-beds in the Lower Greensand Group occur in the Carstone Formation which transgresses and oversteps across the Isle of Wight-Portsdown High to the north of the Channel Basin. The pebble-beds show different mineralogical contents, thickness distributions and palaeocurrent patterns to the surrounding sediments. The pebble-beds comprise far-travelled clasts derived from the distant Welsh Massif to the north and locally derived detritus eroded from Jurassic strata exposed on the Isle of Wight-Portsdown High. Most Lower Greensand Group formations thicken from north to south across the island, whereas the pebble-beds are typically thickest in the north and thin southwards. The pebble-beds are also associated with increases in kaolinite abundance relative to other parts of the Lower Greensand Group. The introduction of locally derived detritus together with evidence of local variations in the thickness, palaeocurrents and clay content of pebble-beds provides a clear indication of rejuvenation of topographic highs in the area and shedding of locally derived detritus into the adjacent basins. These changes resulted principally from contemporaneous movement along the Isle of Wight fault, uplift and erosion of the footwall and subsidence and deposition in the hangingwall basin.

A note on the Weald–Atherfield Clay junction at Brook, Surrey

The junction of the Weald and Atherfield Clays has been recorded throughout the Weald many times in the past 100 years. The only present day exposure of this important horizon, outside the Isle of Wight and Purbeck, is described here in terms of its lithological sequence, palaeontology, and possible correlation.

The stratigraphy and palaeontology of the Lower Greensand of the Hoes Farm Borehole, near Petworth, Sussex

The Hoes Farm Borehole provides a cored sequence through the Atherfield Clay, Hythe Beds and the lowest part (Fittleworth Beds) of the Sandgate Beds. Macrofaunas and ostracods have been collected from many levels and, for the first time, the Ostracoda from the English Aptian have been examined over an extended sequence with good macropalaeontological control. A 0.7 m seam of fuller's earth, recorded near the base of the Hythe Beds, yielded an ostracod fauna of bowerbanki Zone age. A new stratal unit, the Hoes Farm Member, mainly of deshayesi Zone age, has been defined at the base of the Hythe Beds.

The stratigraphy of the Atherfield Clay Formation (Lower Aptian, Lower Cretaceous) at the type and other localities in southern England

A description of the lithostratigraphy of the Atherfield Clay Formation at the type locality (Atherfield, Isle of Wight) is presented, and a comparison made with the ammonite zonal scheme of Casey (1961). The members of the formation are defined and the stratigraphical nomenclature is revised; the ‘Atherfield Clay’ of Fitton (1847), comprising only that part of the Atherfield succession which represents the Deshayesites fittoni Subzone, is here renamed the Chale Clay Member. The macrofauna of the entire formation at Atherfield is recorded; it includes a newly discovered assemblage of decapod crustaceans which contains Meyeria ornata (Phillips), a species previously known only from the Boreal Lower Cretaceous. A correlation is made between the sequence at Atherfield and those of Compton Bay and Redcliff (Isle of Wight) and the Dorset Coast. A review is also made of the succession in the Weald.

Gross morphology and the mode of life of two species of lobster from the Lower Cretaceous of England:Meyeria ornata(Phillips) andMeyerella magna(M'Coy)

ABSTRACTMacrurous decapod crustaceans are generally uncommon and are often incompletely preserved. However, at certain horizons in the Speeton Clay (Ryazanian–Albian) and Atherfield Clay (Lower Aptian) of Yorkshire and the Isle of Wight respectively, macrurans form the dominant element of the fauna. Two species in particular,Meyeria ornata(Phillips) andMeyerella magna(M'Coy), are not only very common in these formations, but are also very well preserved. Recent collections have yielded a large number of specimens of both species. This material is examined with the aid of SEM techniques, gross morphology is discussed, and the details of the exoskeletons are compared. In the case ofM. magna, examples are figured which show traces of a colour pattern and the effects of regeneration on the first pereiopods. A discussion is included of the possible function of the appendages inM. magnaandM. ornata, and of their other, unique features. Finally, the mode of life of both species is inferred from a consideration of their morphology, and of the evidence from their preservation, distribution and relationships with associated faunas.

Field Meeting: A traverse of the Weald, 6 June 1982

During the meeting members were able to study the lithologies, and some faunas, of nearly all the formations and their members from the Atherfield Clay to the Gault in the area between Fittleworth and Storrington, Sussex.

The stratigraphy of the Lower Greensand of the South-West Weald

The stratigraphy of the Lower Greensand of rather more than 100 square miles of the south-west Weald is described. While the major sub-divisions can be recognised, there is considerable lateral and vertical variation in lithology. The Atherfield Clay is poorly exposed and is not described in detail. The Hythe Beds are calcareous east of the River Arun. Westwards they pass into an arenaceous and cherty facies and finally become loamy round Petersfield. The Sandgate Beds are subdivided into five units, the highest of which, the Marehill Clay, is traceable throughout the area. The Pulborough Sandrock is of intermittent development as are the Selham Ironshot Sands, which pass laterally into loams. The lowest member of the Sandgate Beds, the Bargate Beds, is best developed in the west and dies out eastwards. The coarse, current-bedded Folkestone Sands are present throughout the area but towards the west the upper part becomes finer grained and contains numerous pipeclay seams.