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Geology of the Fareham and Portsmouth district — brief explanation of the geological map sheet 316 Fareham and part of sheet 331 Portsmouth

P M Hopson

Bibliographic reference: Hopson, P M. 2000. Geology of the Fareham and Portsmouth district — a brief explanation of the geological map. Sheet Explanation of the British Geological Survey. 1:50 000 Sheet 316 Fareham and part of Sheet 331 Portsmouth (England and Wales).

Keyworth, Nottingham, British Geological Survey

© NERC 2006. All rights reserved.

Copyright in materials derived from the British Geological Survey's work is owned by the Natural Environment Research Council (NERC) and/or the authority that commissioned the work. You may not copy or adapt this publication without first obtaining permission. Contact the BGS Intellectual Property Rights Section, British Geological Survey, Keyworth, e-mail ipr@bgs.ac.uk. You may quote extracts of a reasonable length without prior permission, provided a full acknowledgement is given of the source of the extract.

The grid, where it is used on figures, is the National Grid taken from Ordnance Survey mapping. © Crown copyright reserved Ordnance Survey licence no. GD272191/2000.

(Front cover) HMS Victory, the flagship of the Royal Navy. A view looking east from the harbour. The juxtaposition of the natural, safe harbour created by the drowning of the lower reaches of streams and a hinterland of formerly extensive oak, yew and beech forests growing on the Palaeogene strata of the Bere Forest and the chalk of the Downs encouraged the growth of Portsmouth as a ship building centre and the home of the navy (GS475). (Photographer: P M Hopson.)

(Rear cover)

(Geological succession) Geological succession of the Fareham and Portsmouth district

Notes

The word 'district' refers to the area of Sheet 316 Fareham and 331 Portsmouth. National grid references are given in square brackets; unless otherwise stated all lie within the 100 km square SU. Borehole records referred to in the text are prefixed by the code of the National Grid 25 km2area upon which the site falls, for example (SU31SE/227). Symbols in brackets for example (LeCk) refer to symbols used on the 1:50 000 map. Numbers at the end of photograph descriptions refer to the official collection of the British Geological Survey.

Acknowledgements

This Sheet Explanation was compiled and written by P M Hopson from data held in the open file Technical Reports for this district. S Holloway is thanked for his comments on the structure, concealed geology and hydrocarbon sections, and M A Woods for his review of the biostratigraphy. The manuscript was edited by A A Jackson and R D Lake.

We acknowledge the Department of the Environment (DoE: now DETR) for their support of the field mapping of the southern portion of the Fareham sheet and the mainland portion of the Portsmouth sheet between 1978 and 1984. Landowners, tenants and quarry companies are thanked for permitting access to their lands.

The National Grid and other Ordnance Survey data are used with the permission of the Controller of Her Majesty's Stationary Office.

Geology of the Fareham and Portsmouth district (summary from (Rear cover))

The primary chalk scarp of the South Downs and the Portsdown anticline dominate the landscape of the Fareham and Portsmouth district. Travelling northward from the low, flat-lying coastal plain with its extensive natural harbours, the prominent chalk feature of Ports Down is encountered. From the crest of that feature, there is a wide northward vista over the Bere Forest Syncline and onwards towards the main chalk scarp, which is dominated by the communication mast at Butser Hill. Looking from Butser Hill towards the north and north-east, the characteristic ridge and vale country at the western end of the Weald can be appreciated.

The coastal plain is underlain by a thin Quaternary sequence masking Palaeogene strata, and the Bere Forest is characterised by sandy heath and heavy clay pastureland directly overlying Palaeogene sediments. Long, gentle dip slopes of the Upper Chalk form much of the open downland in the north of the district, whereas the face of the primary scarp and the ridge and vale country in the extreme north-east are formed by the Middle and Lower Chalk and alternating sands and clays of the Lower Cretaceous, respectively.

The landscape seen today is the culmination of a long geological history which stretches back to the Early Jurassic and beyond. The rocks at surface and those beneath the district provide valuable information for the understanding of such major events as the opening of the Atlantic and the Channel Basin, the inundation of most of Europe during the Cretaceous Period, the Alpine earth movements and the wide climatic variations of the most recent past.

These events also created the conditions for the development of oil and gas and their entrapment in the rocks at depth, a feature which manifests itself in the 'nodding donkeys' pumping oil to the surface at places such as Horndean. On the human side, the extensive natural harbours created during the youngest phase of geological history have led to the development of Portsmouth and its surrounding area to support the naval and ferry port and the great boom in leisure boating industry.

Chapter 1 Introduction

This Sheet Explanation describes the geology of the south-east Hampshire coastal plain and its extension into West Sussex, together with the downland and primary scarp of the South Downs in the north (Figure 1).

Structurally, the district lies within the Wessex Basin (Figure 2) which extended over much of southern England, to the south of the London Platform and Mendip Hills during Permian to Mesozoic times. At greater depth, lie Palaeozoic strata which were strongly deformed during the Variscan Orogeny, a period of tectonic compression and mountain building that culminated at the end of the Carboniferous. The rocks of the 'Variscan Basement' are only weakly metamorphosed; they consist of Old Red Sandstone of probable Devonian age. Several major southward-dipping thrust zones and north-west-oriented wrench faults have been tentatively identified in the basement, principally from seismic reflection data. The Variscan Orogeny was followed by a long period of erosion, and a major unconformity marks the base of the Permo-Triassic sequence.

In Permian times, subsidence associated with periods of tectonic extension began to affect southern England initiating the development of a number of fault-bounded, smaller basins within the Wessex Basin but the earliest rocks deposited within this district are red beds probably of Triassic age. Crustal extension was accommodated by reactivation of existing faults in the Variscan basement which show evidence of syn-depositional downthrow to the south during Permian and Mesozoic times. The largest of these faults divide the region into a series of structural provinces (Chadwick, 1986) such as the Weald and Channel Basins, separated by the Hampshire–Dieppe High (also known as the Cranborne–Fordingbridge High).

This district straddles the northern margin of the Hampshire–Dieppe High and part of the Weald Basin; the boundary between these two structural provinces lies along the Portsdown-Middleton Faults, which underlie the northern margin of the Portsdown and Littlehampton anticlines. Syndepositional movement of the major faults caused thicker sequences of sediments to be laid down on their downthrown (hanging wall) sides. Changes in the thickness of the strata across the Portsdown-Middleton faults indicate major periods of active faulting during both Early and Late Jurassic times as well as during deposition of the Wealden Group of the Lower Cretaceous. During periods of tectonic quiescence, rates of sedimentation increased evenly towards the centre of the Weald Basin.

The sea began to flood the Wessex Basin in Rhaetian (Late Triassic) times, and the Penarth Group was deposited. The area of deposition increased gradually throughout the Jurassic although minor periods of erosion occurred, mainly at the basin margins. By Upper Oxfordian to Kimmeridgian times, the London Platform was probably entirely submerged. Towards the end of the Kimmeridgian, the London Platform began to re-emerge, probably as a result of global sea-level fall and a reduction in the rate of tectonic subsidence. This resulted in erosion on the margins of the Wessex Basin and the development of the Late-Cimmerian unconformity. This marine regression continued into Cretaceous times, while the environment of deposition changed from offshore marine (Kimmeridge Clay Formation), to shallow marine (Portland Group), brackish water and evaporitic (Purbeck Group), to fluviatile (Wealden Group). The final period of extensional fault movement, marked by normal faulting, resulted in the accumulation of thick sequences of Wealden Group sediments in the main fault-bounded troughs in the eastern Wessex Basin, whereas the intervening exposed highs suffered severe erosion.

A period of regional subsidence followed and combined with eustatic sea-level rise, led to a renewed marine transgression of the Wessex Basin. The ensuing deposition of the Lower Greensand, Gault, Upper Greensand, and eventually the Chalk, probably extended over all the surrounding high areas including the London Platform.

A global sea-level fall at the end of the Cretaceous resulted in erosion of parts of the Upper Chalk and the development of a pre-Cainozoic unconformity. Later, deposition in Eocene to Oligocene times was followed by the onset of a compressive tectonic regime during mid-Tertiary 'Alpine' earth movements. These movements effectively reversed the sense of movement on the major bounding faults of the Wessex and Channel Basins and caused inversion of the basins and highs. Uplift is estimated at about 1500 m (Simpson et al., 1989) for both the former Weald and Channel depocentres. Subsequently, erosion has unroofed these inverted basins giving rise to the present-day landscape.

Cross-sections showing the main structures are presented on both sheets 316 (Fareham) and 331 (Portsmouth). The major listric growth faults bounding the Hampshire–Dieppe High are shown beneath Ports Down (Sheet 316, Section 1 and 2) to the north, and beneath the Arreton Down (Sheet 331, Section 1), on the Isle of Wight, where the high is bounded by the Portland–Wight Fault. Both faults are associated with monoclinal inversions at a higher structural level. Asymmetric fold structures, such as the Portsdown Anticline, the Bere Forest Syncline, and the Warnford Dome and East Meon anticlines (Plate 1), affect both the Cretaceous and Tertiary strata.

The northward thickening of the Jurassic and the Wealden strata into the Weald Basin, away from the Hampshire–Dieppe High, is clearly shown on the Sheet 316 Fareham sections. Erosion associated with the Cimmerian unconformity is demonstrated on Section 1 of Sheet 331 (Portsmouth) where strata down to the Oxford Clay are cut out beneath the thin upper part of the Lower Greensand (the Carstone) and the Gault.

Chapter 2 Geological description

The stratigraphy of the rocks buried beneath the district is known from boreholes sunk primarily for the hydrocarbon industry. Those at Lomer (SU52SE/18) [SU 5959 2356], Hinton Manor (SU61SE/83) [SU 6795 1489], Horndean (SU71SW/59a) [SU 7154 1260], Portsdown (SU60NW/76) [SU 6380 0652] and Potwell (SU60NW/83) [SU 6399 0774] form the basis of this account.

At depth, a thin Permo-Triassic sequence of limestone, siltstone, sandstone and breccia overlies beds of siltstone and orthoquartzite tentatively assigned to the Devonian 'basement'. The structural contours and subcrops of the sub-Permian surface for the southern half of the United Kingdom (Smith, 1985) show a broad band of Devonian rocks stretching from south of the Mendips south-eastwards into the eastern part of the English Channel. A similar map (Sellwood and Scott, 1986) of the sub-Mesozoic floor beneath southern England incorporates a thin and patchy Triassic cover with the older 'basement'.

Devonian to Triassic

The Devonian (D–C) rocks proved beneath the district are predominantly cleaved reddish brown and purplish grey calcareous siltstone and claystone with subordinate siliceous sandstone. The mica, chlorite and epidote content indicates that they have been subjected to low-grade metamorphism. The thickest proved sequence within the district is in the Horndean Borehole where 85.95 m of strata, dipping 26° north-north-westwards, were encountered beneath a marked angular unconformity. Similar rocks from boreholes elsewhere provide further information about these sedimentary rocks. The Marchwood Borehole (SU31SE/227) [SU 3991 1118] to the north-west of the district, penetrated 890 m of sandstones with subordinate siltstones and mudstones. This sequence contains fining-upwards cycles of fluviatile origin similar to the Old Red Sandstone elsewhere in the UK (Whittaker, 1985). In a comparable succession in the Arreton Borehole (SZ58NW/1) [SZ 5320 8580] on the Isle of Wight, 40Ar/39Ar dating indicated deposition between 380 and 390 Ma, and a low grade metamorphism at approximately 340 Ma. These Early Devonian continental sequences were deposited on the Brabant Massif to the north of the Cornwall Basin (Ziegler, 1982), a part of the Variscan Foredeep Basin; both basins derived much of their sediment from the continent of Laurasia to the north.

A thick sequence of Permian and Triassic (P–T) strata is preserved to the west of this district in the Portland–Wight Basin (Hamblin et al., 1992) but hereabouts only a thin sequence of doubtful age is known. Permo-Triassic red beds and marine Rhaetian (Penarth Group) sedimentary rocks have been tentatively identified in some boreholes locally. The Lomer and Horndean boreholes proved 35.4 and 13.4 m respectively of limestone, dolomitic limestone and breccia. These lithologies may be the equivalent of the much thicker sequence seen to the west or, more likely, they represent a basal conglomerate of the Mercia Mudstone Group, analogous to the Dolomitic Conglomerate of the Mendips. Whatever their age, they were probably preserved against bounding faults of the Hampshire–Dieppe High. There is some evidence to suggest an angular discordance between these basal beds and the overlying strata.

Above the basal beds, the Mercia Mudstone Group and Penarth Group have a maximum proved thickness of 31.7 m in this district. The Mercia Mudstone Group consists of mottled reddish brown and greyish green calcareous siltstone and mudstone ('marl') with some thin sandstone. The overlying Penarth Group comprises fissile, dark grey mudstone and white to pale brown limestone.

Jurassic

The whole of the Jurassic System is represented in rocks at depth below the district (Figure 3). They are mainly marine in origin and were deposited within the subsiding Wessex Basin. They rest conformably on the Penarth Group, and reflect predominantly shallow marine deposition. The relatively uniform, cyclical sequences of the Jurassic provide evidence for an eastward shift of the area of maximum subsidence in the Wessex Basin when the faults bounding the Hampshire–Dieppe High became active. The Weald and Channel basin depocentres developed at this time. In general, the beds thicken northwards against major faults and into the Weald Basin.

Cretaceous

The Cretaceous period opened with a short-lived marine transgression which produced the characteristic Cinder Bed of the Durlston Formation (Purbeck Group). Despite renewed subsidence at this time, clastic deposition in the Weald Basin was maintained in a nonmarine facies by an abundant sediment supply derived from the uprising London–Brabant Ridge to the north, Armorica to the south, and other landmasses to the west and south-west. These early Lower Cretaceous sedimentary rocks are informally called the Wealden 'Group' here and include the Hastings Group and Weald Clay Formation. This section will not describe the Lower Cretaceous sequence exposed on the Isle of Wight which was deposited south of the Portland–Wight Fault.

Wealden 'Group'

These beds were deposited in predominantly freshwater conditions, in a large shallow lake or lagoon that occupied much of the present area of Hampshire and the Weald. Some indications of periodic erosion and shallow-water brackish conditions suggest minor flood events from the 'East Anglian Sea' to the east (Allen, 1975). Alluvial and lagoonal mud plains were periodically invaded by braided rivers carrying coarser material. Some of the major siltstone-sandstone bodies are thought to have formed by lateral accretion from migrating channels, but the thickest sand units are attributed to accretion of sediment transported into the basin from a rejuvenated block-faulted source area. At this time, the Channel and Weald basins are thought to have been separated by the 'Portsdown Swell' (the successor to the Hampshire- Dieppe High), and the Wealden 'Group' is known to thicken northwards away from this structure.

Lower Greensand Group

Rising sea level in Aptian times flooded the Wessex Basin and eventually led to the re-establishment of a marine connection with the North Sea Basin around the western end of the London–Brabant Ridge. The boundary between the lower, nonmarine sequence, the Wealden 'Group', and the upper, marine Lower Greensand Group, is marked by the Late-Cimmerian Unconformity. The unconformity represents a gap in the sequence that is greatest at the margins of the Weald Basin, where much of the Lower Cretaceous is missing, and reduces progressively towards the centre of the basin. In the central Weald, the unconformity is represented by a number of closely spaced minor erosion surfaces, close to the boundary between the Wealden 'Group' and the Lower Greensand Group (Chadwick, 1986; Ruffell, 1992).

Tidally influenced, shallow-marine and shoreline sands and clays form the Lower Greensand succession. Thicker sequences were deposited in the Wessex Basin which subsided faster than the London–Brabant Ridge. Deepening of the basin continued into Albian times when the Gault, a sequence of deeper water marine clays, was deposited. By late Albian times, the London–Brabant Ridge had been completely overstepped by the Gault. The Upper Greensand is, in part, the lateral equivalent of the Gault (Upper Gault in this district) and reflects a shallow-water nearshore environment. It increasingly replaces the Gault towards the western part of the Wessex Basin. The lowest exposed subdivision of the Lower Cretaceous in this district is the Sandgate Formation (in the Lower Greensand Group) which crops out in the north-east. The concealed Lower Cretaceous strata are summarised on (Figure 4).

Bristow (1991) gave a detailed description and subdivision of the Sandgate Formation around Petersfield to the north. However, due to the paucity of information, it is not clear if his subdivisions persist southwards, at depth in this district, where overstep may have occurred on to the Portsdown Structure. The Lower and Upper Marehill Clay members (LMhC, UMhC) are separated by the Pulborough Sandrock Member (UPSk). The clay members comprise dark grey to purplish grey, silty, locally glauconitic clay. They are sparsely fossiliferous, containing only undiagnostic foraminifera. The upper and lower members are respectively 4 and 8 m thick.

The Pulborough Sandrock comprises 8 to 12 m of grey sandstone which weathers yellowish brown. It is friable, uniformly fine grained, glauconitic and rarely cross-bedded. Locally, the beds are richly fossiliferous: the fauna includes Parahoplites cunningtoni, the subzonal index fossil at the top of the Parahoplites nutfieldensis Zone.

Folkestone Formation (F)

This comprises about 10 to 54 m of cross-bedded, fine to coarse-grained, sands and sandstones. The upper part of the succession contains common white, grey or lilac clay partings. Much of the succession is exposed in the West Heath sand pit [SU 785 228] where it consists of 25 m of cross-bedded, yellow to yellow-brown, medium- to coarse-grained sand, showing an overall southerly dip of about 4°. The sands characteristically occur in large-scale cross-beds, in units up to 3 m thick, but the upper part of the succession consists of 6 m of tabular, friable sandstones each about 0.1 m thick and separated by thin (10 mm) grey clays.

At the top of the Folkestone Beds, a thin, brightly coloured, sandy ironstone, the Iron Grit (up to 0.1 m thick), is well developed in the Chichester district to the east. The most westerly exposure noted in the Weald was near Petersfield (around [SU 725 236] (White, 1910)) but it may be present in the north-east part of this district.

Gault Formation (G)

The Gault consists mainly of pale to dark grey, fissured, soft, silty clay with scattered phosphatic nodules up to 15 mm across. It is 80 to 95 m thick in this district. The weathered profile of natural exposures shows a gradation up into very soft, pale yellow-brown, plastic clay beneath the active soil layer.

Upper Greensand Formation (UGS)

This formation consists of pale yellow-brown, pale grey and greenish grey bioturbated siltstone and silty, very fine- grained sandstone with variable amounts of mica and glauconite. The beds show a characteristically wispy-bedded structure due to small lenses of clay and sand. In this district, there occur apparently lenticular masses of uniform siltstone that are very hard, grey to bluish grey, calcareous with a porcellanous texture, and weather to a buff or white colour. These siltstones were worked for building stone, particularly around South Harting, where they are colloquially known as the 'bluestone' or 'malmstone'. The latter term has also been applied to the local facies of the Upper Greensand as a whole. The Upper Greensand forms a distinct scarp along its crop from Ramsdean to East Harting. It is between 20 to 35 m thick in this district, but thickens rapidly north-westward.

Chalk Group

Upper Cretaceous chalks underlie much of the district, up to about 500 m thick. They form the scarp of the South Downs in the north-east, the extensive dip slopes to the south and west, and the anticlinal inlier of Ports Down in the south. The stratigraphical nomenclature used in this district is based on that of Mortimore (1986a) and of Bristow et al. (1995, 1997). The Chalk Group is divided informally into Lower, Middle and Upper Chalk formations, whose stratotypes have not yet been designated; ten members form the basis of lithological mapping (Bristow et al., 1997) (Figure 5).

In Cenomanian times, emergent land masses were present in south-west England, Wales, Scotland and Northern Ireland, and further afield in Brittany and elsewhere. Southern Britain lay approximately 10Þ of latitude farther south than at present. Chalk accumulated on the outer shelf of an epicontinental subtropical sea of normal salinity and with little terrigenous input.

Lower Chalk

This unit comprises three members, namely the Glauconitic Marl, the West Melbury Marly Chalk and the Zig Zag Chalk. Together they are approximately 90 m thick.

Glauconitic Marl (GM)

This member comprises between 1 and 3 m of partly indurated, fine- to medium-grained, calcareous sand with black phosphatic nodules, 2 to 20 mm in diameter (Plate 2). It is bright olive-green, highly glauconitic and bioturbated. This friable rock weathers to loose, dark green clayey sand.

West Melbury Marly Chalk Member (WMCk)

This member is dominated by cycles of soft, pale to medium grey, marly chalks with thin, grey to brown limestones. The base of the succession is marked by a grey marl with a variable glauconite content, which rests on an eroded surface of the Glauconitic Marl and Upper Greensand. The top of the succession is taken at the Tenuis Limestone. The thickness, estimated from the outcrop, ranges from approximately 10 to 35 m. The basal marl with conspicuous glauconite is only a metre or so in thickness but sparse glauconite ranges up to 2 to 3 m into the overlying strata. A hard spongiferous limestone, or closely spaced series of such limestones occurs 1 to 2 m above the basal bed and these may also contain sporadic glauconite grains.

A characteristic, pale greyish brown, rough textured, thin (10 to 30 cm) limestone packed with Schloenbachia marks the middle of the West Melbury succession. Woods (1994) tentatively equated this bed with the 'M3 limestone' at Folkestone (Gale, 1989).

Above and below this limestone, a number of thin, grey, poorly fossiliferous limestones occur. In general those below the distinctive limestone contain sponges. These various limestones vary in hardness. Some appear locally as 'cemented lenses' and all are laterally impersistent, so that individual beds cannot be identified reliably by 'counting up' (or down) the sequence.

The Tenuis Limestone at the top of the sequence is similar in appearance to the 'M³ limestone'. It is a pale greyish brown, rough textured, calcarenitic limestone with Schloenbachia and is distinguished by the presence of the inoceramid bivalve I. tenuis and by its uneven hackly fracture (particularly after frost action).

Zig Zag Chalk Member (ZCk)

This chalk is composed typically of medium hard, greyish white, blocky chalk. The lower part is more marly and contains some thin limestones. In this district the Zig Zag Chalk is estimated to be between 40 and 60 m thick. The base of this member is taken at the Cast Bed (Bristow et al., 1997), a very fossiliferous silty chalk immediately above the Tenuis Limestone. Some 3 to 4 m higher, a pale grey, hard, splintery limestone with conspicuous Sciponoceras is the only other marker identified during the resurvey. Higher in the succession the member becomes less marly and is pale cream or white in colour. This colour change is thought to occur at the level of 'Jukes-Browne Bed 7' (a calcarenite bed with phosphatic nodules). The top of the member is taken at the top of the Plenus Marls, a series of closely spaced, brightly coloured marl beds; these are rarely exposed but can be identified in field brash at a number of localities.

Middle Chalk

This includes the beds from the base of the Melbourn Rock to the base of the first, hard, nodular chalks that marks the base of the Lewes Chalk. Of the two members present in this district, the lower and thinner Holywell Nodular Chalk includes the Melbourn Rock at its base. The upper, thicker member, is the New Pit Chalk. The combined thickness of these is about 90 m.

Holywell Nodular Chalk Member (HCk)

This member is composed of medium hard to very hard, nodular chalks, with flaser marls throughout. It is commonly shelly and has a gritty texture. The Melbourn Rock at its base is a very hard nodular chalk but generally lacks significant shell debris. Including the Melbourn Rock (which is about 5 m thick), this member is between 15 and 35 m thick, based on field estimates.

New Pit Chalk Member (NPCk)

The New Pit Chalk comprises medium-hard, massive-bedded, pure white chalk with regularly spaced pairs or groups of marls, each up to 15 cm thick. It is sparsely fossiliferous with brachiopods dominant. In this district, flints are confined to the upper half of the succession although, elsewhere in Sussex, they are known to occur sparsely down to within a few metres of the base of the member. This member is between 25 and 35 m thick in this district.

Upper Chalk

The base of the Upper Chalk is taken at the base of the Lewes Chalk, which approximately coincides with the incoming of hard nodular chalks at the top of the New Pit Chalk. In general, the Upper Chalk is characterised by white chalk with numerous flint seams. In Sussex and Hampshire, the Upper Chalk is divided into six members and all are mapped in this district. The formation is approximately 320 m thick, nearly twice as thick as the combined Lower and Middle Chalk.

Lewes Nodular Chalk Member (LeCk)

The Lewes Chalk comprises interbedded, hard to very hard, nodular chalks, with soft to medium-hard chalks and marls. The first persistent seams of flint appear near the base. The flints are typically black or bluish black with a thick white cortex. The member is generally between 50 and 55 m thick over much of its crop, but it may be as little as 35 m on the southern side of the Warnford Dome and up to 75 m in the east around Beacon Hill [SU 807 184]. The Lewes Chalk is divided into two units by the paired Lewes Marls and Lewes Flints, comprising a ramifying system of black cylindrical burrow-form flints. The lower unit consists of medium- to high-density chalk and conspicuous, iron-stained, hard, nodular chalks. The upper unit is mainly of low- to medium-density chalks with evenly spaced thin nodular beds.

Seaford Chalk Member (SCk)

The Seaford Chalk is composed mainly of soft white chalk with seams of large nodular and semi-tabular flint. Near the base (described below), thin harder nodular chalks also occur, associated with seams of carious flints, giving this member a similar appearance to the upper part of the Lewes Chalk. Hence the boundary is not clear-cut in mapping terms. Higher in the sequence, the flints are black and bluish black, mottled grey, with a thin white cortex, and they commonly contain shell fragments. Typical brash from the lower part of the Seaford Chalk contains an abundance of fragments of the bivalves Volviceramus and Platyceramus; brash from the upper part contains Cladoceramus and Platyceramus (Mortimore, 1986a). In the absence of these bivalves, the flaggy bedded nature and pure whiteness of the soft chalk serve to distinguish it from the Lewes Chalk below. In this district the Seaford Chalk is 55 to 80 m thick.

Newhaven Chalk Member (NCk)

This member is composed of soft to medium- hard, smooth white chalks with numerous marl seams and flint bands (Plate 3). Typically, the marls vary between 20 and 70 mm thick. They are much attenuated or absent locally, over positive synsedimentary features, where the distinction between the Seaford and Newhaven members is difficult. Channels with hardgrounds and phosphatic chalks have been recorded elsewhere within the member (Hopson, 1994; Mortimore, 1986b), but only one locality, east of Nore Down [SU 773 130], has been identified hereabouts during this resurvey. In this district the Newhaven Chalk is estimated to be 50 to 75 m thick.

The brash is composed of smooth, angular, flaggy fragments of white chalk very similar in appearance to that of the Seaford Chalk. The incoming of abundant flints with Zoophycos (a spiral trace fossil) near the base of the member serves as a useful marker for mapping the lower boundary. Individual thecal plates of the zonal index, Marsupites testudinarius, occur in numerous small pits and track-side exposures, but otherwise macrofossils are rare.

Tarrant Chalk Member (TCk)

The Tarrant Chalk, up to 40 m thick, comprises soft white chalk without significant marl seams, but with some very strongly developed nodular and semi-tabular flints.

Spetisbury Chalk Member (SpCk)

This member consists of firm, white chalk with large flints, including tabular, paramoudra and potstone forms, and with Gonioteuthis and distinctive forms of Echinocorys (Plate 4). It is estimated to be about 40 m thick at its maximum. North of the Palaeogene outcrop, the Spetisbury Chalk only occurs as a small outlier around Racton Monument [SU 776 094]. The main crop is on Ports Down where the member forms much of the crest.

Portsdown Chalk Member (PCk)

The Portsdown Chalk consists of relatively soft white chalk with common marl seams and some flints; in its lower part there are several horizons rich in inoceramid shell debris. The base is taken at the Portsdown Marl at Farlington Redoubt [SU 687 065] east of Fort Purbrook on Ports Down. This member only crops out on the northern and south-western flanks of Ports Down. An estimated maximum of 20 m of strata is preserved.

Well defined, strike-orientated, near-vertical, narrow fracture zones are a feature of the chalk members exposed on Ports Down (Plate 5). Some of the best examples occur in the Paulsgrove [SU 635 067] and Warren Farm [SU 604 068] pits but these structures have also been noted in exposures at Farlington Redoubt [SU 686 066] and the George Inn [SU 666 065]. The zones are narrow, usually between 0.5 and 1 m wide, with parallel, commonly slickensided faces. The chalk is highly fractured but the origin of the fractures is not known; the chalk was probably deformed both in a plastic and in a brittle state, during and immediately after deposition.

Palaeogene

The Palaeogene strata are preserved in the asymmetrical Bere Forest Syncline, and in the 'Solent Syncline' (Figure 1). The sequence consists predominantly of clay, silt and sand. Much of the early and late Palaeocene is not represented by strata in this district because at that time the region formed part of a land area separating the Paris and North Sea basins.

In latest Thanetian times, deposition was in a warm, swampy lowland traversed by braided rivers that deposited sands. After a short hiatus, a marine transgression spread from the north and the district then lay within a broad embayment which included the London, Hampshire, Belgium and Paris basins. The presence of nummulitids attests to a marine connection to the west into the Tethyan Province at this time. The London Clay and the Wittering formations were deposited in this broad sea.

A hiatus separates the late Ypresian Wittering Formation from the overlying formations of the Bracklesham Group of Lutetian age, reflecting a eustatic sea-level lowstand. Subsequent deposits are confined to a narrow marine embayment (approximating to the present-day Solent) off the Channel Basin. Conditions within this embayment were slightly hyposaline due to freshwater runoff. The Barton Clay indicates a return to a more normal marine environment.

Lambeth Group

Reading Formation (Rea)

These beds, part of the Lambeth Group, consist of mottled bright red and grey clays and silty clays. Lenticular bodies of well-sorted, fine- to medium-grained sand occur locally at various levels, particularly at the top and base. Only the most laterally persistent of these sand bodies are shown on the map. South of Ports Down, White (1915) recorded some lignites. The formation rests unconformably on the eroded surface of the Chalk, and is between 30 and 35 m thick. Glauconitic sand or interbedded sand and clay constitute a basal bed, analogous to the 'Bottom Bed' of the London Basin. This basal bed is up to 4 or 5 m thick in places.

Thames Group

London Clay Formation (LC)

This formation, within the Thames Group, consists mainly of grey, pyritic, bioturbated, silty and fine-grained sandy clay with interbedded seams of calcareous cementstone and rounded flint pebble beds; a glauconitic sandy bed occurs at the base ('Basement Bed'). The sequence contains sheet-like and lenticular bodies of fine-grained sand which generally mark the top of coarsening-upward sedimentary rhythms (King, 1981). Each rhythm, when complete, has a basal pebble bed or richly glauconitic horizon that passes up into silty clay, which becomes progressively more silty and sandy upwards. The rhythm is completed by cross-bedded sand or interbedded channel-fills. Some of these sands may be very shelly such as the informally named 'Lingula Sands' (Meyer, 1871). The lithological changes in each rhythm reflect an early marine transgression, followed by low-energy marine sedimentation and a final progradation of coarse sediment from the margins of the depositional basin. The thickness of the formation varies between 77 and 120 m, with the greatest thickness beneath Gosport and Portsmouth. This thickening may be due to the presence of thicker sand bodies within the London Clay in that area, or to a general basinward thickening to the south-east.

Four members are identified within the formation as well as the informal 'Lingula Sands'. King (1981) formalised the rhythms associated with four of these sand bodies as units A to D of the London Clay. Five rhythmic units, A to E, have been identified in the western London Basin (King, 1981) and are correlated with the Hampshire Basin. Divisions A to C and the lowest part of D are equivalent to the London Clay of the Hampshire Basin; the upper part of D (above the 'Modiola-bed') and all of E are equivalent to part of the Wittering Formation of the Bracklesham Group (Figure 6).

The top of the rhythmic units, A to D, are marked by the Bognor Sand (BoS), 'Lingula Sands', Portsmouth (Po) and Whitecliff (Whi) members. The Whitecliff Member includes a separate facet named the Durley Member (Du). Each member is generally 4 to 6 m thick, but is impersistent. The well developed Bognor, Portsmouth and Whitecliff members may reach 10 m at their maximum.

Bracklesham Group (BRB)

This group contains a varied succession of interbedded clay, silty and sandy clay, silt and sand. Shell, lignite and pebble-bed horizons throughout the succession reflect deposition in transgressive/ regressive sedimentary cycles. The greater part of these beds was probably deposited in an offshore marine environment, but the presence of brackish water molluscs and abundant lignite suggests that a more restricted coastal marsh environment was established from time to time. The group is divided into four formations. The group is estimated to be about 87 to 137 m thick. The (lowest) Wittering Formation makes up about half of this thickness, and the other formations are of comparable overall thickness.

Wittering Formation (Wtt)

The lower part of this formation comprises bluish grey clay and sandy clayey silt with two prominent flint pebble beds ('Allbrook Formation' of King and Kemp, 1982). The middle part consists of sand and silty sand with lignite and pyritised bivalves ('Knowle Hill Formation'). The upper part comprises a sequence of shelly clay, silt and sand overlain by a complex series of lignitic silts and sands with pebble beds. The base of this upper part contains a vertebrate fauna ('Cakeham Formation'). Overall the formation varies between 25 and 65 m in thickness.

Earnley Sand Formation (Ea)

This formation consists of clayey, silty, bioturbated glauconitic sand with a rich molluscan fauna, some of which give their names to marker beds. Near the top, sands containing abundant Nummulites laevigatus form a valuable marker horizon. The formation is 16 to 25 m thick.

Marsh Farm Formation (MrF)

This formation is composed predominantly of thinly bedded, shelly, clayey silt and silty sand. Marine molluscs occur in the lower part but towards the top there are brackish forms. Channel-form clean sands are common in the sequence around Gosport and these contain much plant debris. This formation is up to 22 m thick.

Selsey Sand Formation (Slsy)

This formation comprises about 25 m of interbedded shelly sandy clay and clayey silt with a thin basal glauconitic sand bed.

Barton Group

Barton Clay Formation (BaC)

The beds are typically of sandy clay with a thin basal glauconitic sand. Kemp et al. (1979) recorded a foreshore section including their 'Coral Bed' some 7 m from the base of the deposit. This formation is the lowest division of the Barton Group; only the lowest 9 m or so are preserved in the district.

Quaternary

About 60 Ma is estimated to have elapsed between the deposition of the youngest preserved Palaeogene and the oldest Quaternary deposits in this district. During this time younger Palaeogene and Neogene strata were deposited across much of southern Britain, and subsequently removed following uplift along the Wealden axis (as part of the general inversion of the Wessex Basin). During the Quaternary, a further significant break in deposition occurred after the accumulation of the clay-with-flints and before the deposition of the younger Pleistocene drift (Figure 7).

During the Pleistocene, sea level rose and fell according to the quantity of water locked up in ice caps. At times of glacial maxima, a periglacial environment was established in this district. There was enhanced erosion both by solifluction and by an extensive river system flowing to much lower base levels. Three such glacial maxima affected southern England: the most severe was of Anglian age.

During the intervening warm stages, marine transgressions caused drowning of the lower courses of the river systems, principally the Solent River and its tributaries, and the breaching of the Straits of Dover. Beach and near-shore sediments were deposited along the margin of the English Channel. Two degraded clifflines related to those marine transgressions are preserved on the Sussex coastal plain, part of which lies in the south-east of this district. The southern flank of Ports Down forms the westward extension of those cliffs.

The following descriptions of the deposits are grouped on the basis of their origin. Mass movement deposits are described first, followed by fluviatile, aeolian and marine deposits. Their order does not imply relative age.

Clay-with-flints

Clay-with-flints is composed typically of orange-brown or reddish brown clays and sandy clays containing abundant flint nodules and rounded pebbles. At the base of the deposit the matrix is stiff, waxy and fissured (slickensided), and dark brown in colour. Relatively fresh nodular flints are stained black and/or dark green possibly by manganese compounds and/or glauconite. The deposit gives rise to a stiff, red-brown, silty clay soil strewn with flints. This is primarily remanié deposit resulting from the modification of the original Palaeogene cover and dissolution of the underlying chalk. The thickness of the clay-with-flints is about 5 to 6 m as a general maximum but this may rise to over 10 m in limited areas, usually where dissolution of chalk is most pronounced.

The margin of the clay-with-flints is sharply defined on the scarp edge but the boundary is diffuse on the chalk dip slope. This down-slope feather edge is obscured by a lateral passage into the late-stage solifluction deposit or head gravel, distinguished with the prefix G on the map. These deposits have a more sandy matrix and a surfce brash composed principally of gravel-sized broken angular flints.

Older Head

A single outctop of grey, flinty, locally chalky clay is shown on the map [SU 733 227]. It is thought to have originated as solifluction lobes at the foot of the Upper Greensand scarp.

Head Gravel

These broad sheet-like deposits are composed mainly of angular flint gravel set in a stiff, sandy clay matrix. In some exposures the matrix contains chalk but elsewhere this has been lost by decalcification. On the coastal plain, where it is largely obscured by aeolian deposits, the head gravel is thickest and coarsest near the older cliff line, at the north of its outcrop. Here it is generally between 5 and 7 m thick, becoming thinner and finer grained southwards. Although mapped as a single deposit, interbedded fine-grained sediments , which are perhaps aeolian in origin, indicate that it was formed in more than one Pleistocene episode. The head gravel is generally regarded as the result of soliflucation of Chalk, Palaeogene deposits and clay-with-flints down the dip slope of the South Downs during cold phases of the Quaternary.

Head

In general, head comprises yellow-brown, silty, sandy clay with variable proportions of coarser granular material, but all deposits have an earthy texture. Clast composition varies depending on source materials; those deposits derived mainly from the chalk were formerly mapped as 'dry valley deposits' or 'coombe deposits'. These heterogeneous deposits accumualted by solifluction, hillwash and hillcreep and are generally only a few metres deep.

River Terrace Deposits

In the south, flanking the rivers draining into the Solent, these deposits consist of gravels and sandy gravels, commonly clayey in the higher terraces. In the north, associated with the River Rother, the deposits are more sandy and many are graded as pebbly sands. In places, clayey and sandy sily and silty clay overlie the aggregate, perhaps indicating preservation of overbank or aeolian deposits at the top of each fluvial cycle. In the south, the gravel component is predominantly flint with subordinate quartz and rare 'exotic' clasts. In terrace deposits of the Rother, flint again predominates, together with chert, polished fine quartz and larger fragments of pebbly 'carstone' (sandstones with ferruginous cement) derived from the Folkestone Beds. In general the terrace deposits are up to 6 m thick.

Terrace formation, related to the 'Solent River', occurred over a considerable time span during the Pleistocene. The sixth terrace is thought to equate with the pre-Anglian raised beach at Portsdown (ApSimon et al., 1977), which in turn may be equivalent to the older raised beach at Boxgrove in the Chichester district to the east. There is little direct evidence of the age of the younger terraces, but most aggradations were probably periglacial in origin. The third and higher terrace deposits all show cryoturbation structures indicating that they have suffered at least one periglacial event, and thus suggesting they are all pre-Devensian. Palaeolithic stone implements are common in the fourth and lower terraces: the Acheulian tool industry affinities of some of these suggest an Ipswichian age.

Alluvium

The alluvium comprises soft, organic, mottled, silty and sandy clay which generally overlies a basal lag gravel. Thin stringers of gravel may occur within the sequence, indicating channel migration or periodic increases in the flow regime of the river. In general the deposit is thin, commonly between 1 and 3 m thick in the upper reaches of rivers, but at major confluences and in the lower reaches of the rivers up to 8 m have been proved. A common characteristic of streams flowing over chalk bedrock is the presence of calcareous tufa associated with peat accumulations at springs. No occurrences weresufficiently large to be mapped in the district, but thin concretionary carbonate deposits coating stream bed gravels were noted in places in the River Meon south of Warnford.

Alluvial Fan Deposits

A single narrow outcrop of these deposits was mapped in the east of the district, south of Funtington [SU 808 054]. By analogy with more extensive deposits in the Chichester district, the deposits are a late-stage, possibly postglacial (about 6000 years BP), chalk-rich, fluvial outwash gravel, entrenched into the head gravel and raised beach deposits of the Sussex coastal plain.

Peat

Accumulations of peat and peaty material are associated with alluvium, river terrace deposits and the tidal river deposits but are generally too small in extent to map. An outcrop of dark, silty peat, apparently still forming today, was noted west of Ryefield [SU 772 226] in the extreme north-east of the district. Peat also occurs in the valley of the River Alver in Gosport. Three small areas of peat are identified in Southsea [SZ 647 987] associated with estuarine alluvium in the area known as the 'Great Morass'. This peaty fen is isolated from the sea by a shingle bar and is now largely built over after being covered by fill in the 19th century.

Aeolian Deposits ('Brickearth')

These deposits consist of fairly homogeneous, structureless, yellow-brown, mainly non- calcareous silt or clayey silt. They are commonly stoneless, but locally contain a few flint fragments, particularly near the base. Chalk detritus is common where the deposits rest on Chalk bedrock. Thicknesses are typically from 2 to 4 m, but some boreholes have proved up to 6 m. They variously overlie head gravel, terrace and raised beach deposits.

Blown Sand

East of West Heath there is a tract of hummocky ground [SU 794 224] composed of coarse-grained sand, irregularly mantling the Folkestone Beds, Marehill Clay and Pulborough Sandrock. Here it is thought to be only a few metres thick. Blown sand is also associated with the storm gravel beach deposits along the present-day coastline. This occurrence forms a series of relatively stable dunes of well-sorted, medium- grained sands with a small proportion of shell debris.

Marine Deposits, undifferentiated

This group of nearshore and intertidal deposits includes tidal flat and beach depo- sits below high water level. They comprise organic mud, channel sand, gravel and sand shoals, together with shell banks within the inlets of the coastal plain.

Tidal River Deposits (Estuarine Alluvium)

These deposits comprise brown and grey mottled, soft, silty clay and silt with a sparse shell fauna. They are thin except where they occupy former drainage channels. The main tracts of tidal river deposits occur above mean high water at the margins of the natural harbours and their elevation distinguishes them from the marine deposits of the tidal flats.

Raised Marine Deposits

This term is used to distinguish the marine muds and sands protected by sea walls at the margins of the inlets.

Raised Beach Deposits (Older)

These thin deposits are not exposed, but are thought to be present on an older raised beach plat- form beneath head gravel in the east around Funtington [SU 800 085] and at a similar height (about 35 m above OD) beneath younger deposits at the western end of Ports Down (ApSimon et al., 1977).

The sediments of the older raised beach are best seen to the east at Boxgrove [SU 906 074] where fine-grained sands are associated with a varied vertebrate fauna, Palaeolithic artifacts and hominid remains (Boxgrove Man). The association indicates a pre-Anglian (probably Cromerian) age for this deposit.

Raised Storm Beach Deposits

These deposits comprise fine- to coarse- grained, well rounded flint gravel in a sparse, silty sand matrix. In this district, they are little more than a metre thick but are up to 7 m thick to the east. The outcrop north of Westbourne [SU 755 088], at about 40 m above OD, is the only occurrence of this deposit in the district. It represents the westernmost end of a more extensive tract of storm beach deposits stretching across the Chichester district. To the east, the geomorphological context becomes appar- ent where a low ridge of these deposits is clearly associated with the older raised beach platform and is truncated to the south by the younger raised beach cliffline. The deposits forming the ridge are considered to be the remnants an offshore shingle bar.

Raised Beach Deposits (Younger)

In the east of the district these deposits comprise a complex sequence of sand, pebbly sand, and rarely sandy gravel and clean, well rounded shingle. The greater part of the deposit is of thinly bedded, calcareous, silty, fine- to medium-grained, sand containing a few fine flint and/or chalk pebbles. Generally, a thin basal gravel is present with scattered large exotic boulders. The deposit is commonly yellow-brown, oxidised and noncalcareous at the surface. Unoxidised material is pale yellow or greyish white depending on the amount of chalk detritus. The thickness of the deposit may vary considerably over short distances. In general, the deposit ranges up to 3 or 4 m in thickness but over the Chalk it may be thin or absent. The underlying wave-cut platform shelves gently to the south from the degraded lower cliffline. The surface lies at about 10 m above OD in the north and is just below present sea level at Portsea Island. The beds RaI re poorly exposed and largely mantled by younger drift.

These deposits are correlated with the high sea level of the Ipswichian interglacial but this stage is known to span three temperate intervals separated by two short cold phases. It is likely that the history of the beach may be more complex than a single transgressive–regressive event. There is some evidence for an intermediate platform between those of the older and younger raised beaches.

Towards the west, the younger raised beach deposits grade into fine- to coarse-grained gravel which also rests on a platform at about 10 m above OD; this gravel has been mapped as the second terrace of the 'Solent River'.

Storm Gravel Beach Deposits

During postglacial times the eastern margins of The Solent locally became accretionary shorelines. Longshore drift, generally from east to west (to the west of Chicester Harbour), actively builds up, above mean high tide level, wide bars of fine- to medium-grained gravel with some interstitial sand and shell debris. Recurved spits of gravel flank the entrances to Langstone and Chichester harbours. Historical relict shingle ridges are evident on Sinah Common [SU 695 995] where the storm beach has advanced by about 200 m to its present position since the last century. Ablation of these shingle ridges contributes to the blown sand deposits.

Landslips

These are a ubiquitous feature of the Upper Greensand/Gault contact along much of the crop. They result from a combination of spring-head erosion and the physical properties of pore pressures and high moisture content. The resultant landforms are quite striking; for the most part they are composites of successional rotational slips and slab slides, with fault-like backscarps up to 30 m high, ponds trapped by slip slices, and hummocky ground commonly with a prominent toe separating the slips from the undisturbed Gault surface. The age of the slips is uncertain. Almost certainly they were initiated under periglacial conditions, but the land1forSms are still remarkably fresh, suggesting recent movement. Elsewhere in the district, landslips are uncommon. Two small sites near Blendworth Common [SU 705 107] and Shirrell Heath [SU 580 144] occur on the London Clay or sand bodies within that formation.

Made ground

Extensive areas of made ground are shown around Gosport, Portsmouth Harbour and Langstone Harbour and associated with major routeways. Much of this material is related to the development of the naval facilities of the port in historical times and to the recent building of the major road network. The nature of the fill is not known in detail, but the reclaimed land around the naval port must include the Quaternary and Palaeogene materials extracted during the excavation of the deep dockyard basins in the late 19th and early 20th centuries.

Worked ground

Only major areas of worked ground, generally associated with mineral extraction, are shown on the published maps. Smaller areas of worked and made ground are not shown on the 1: 50 000 scale maps but are depicted on the larger scale geological maps held in BGS archives.

Chapter 3 Applied geology

Hydrogeology

The Chalk is the major aquifer in the district and has the largest storage capacity and catchment area. Water is also obtained in the north from the Upper Greensand, which is in hydraulic continuity with the chalk, and from the Lower Greensand. The latter is a separate aquifer beneath the aquiclude of the Gault. Water is also obtained in small quantities from the Palaeogene and to a lesser extent from the drift, but supplies are variable in both quantity and quality. Supplies from the sand bodies within the Reading and London Clay formations are small and there may be problems associated with high concentrations of sulphate and iron. In the Gosport area, supplies of up to 6 l/s (litres per second) have been recorded from the Bracklesham Group but yields are much lower to the east and north. Small supplies have been obtained from the terrace deposits. However, in the coastal area they are vulnerable to sea-water invasion and pollution from surface sources and, in consequence, are now little exploited.

Yields from the Chalk Group of the Fareham district (Hargreaves, 1982) vary between the three formations with values of the order of 100 l/s in the Upper Chalk and values of 35 l/s and 5 l/s in the Middle and Lower Chalk, respectively. The highest yields, up to 270 l/s, are obtained from large diameter shafts, boreholes and headings in the Upper Chalk. The Upper and Lower Greensand typically show maximum yields of 0.44 l/s and 0.43 l/s respectively (Hargreaves and Parker, 1980).

The chalk is microporous with low intrinsic permeability and derives much of its yield from interconnected fissures. The Upper and Lower Greensand and the Palaeogene sands are porous, essentially non-fissured aquifers, although the Upper Greensand is loosely indurated with some fissuring. Wells in the chalk are generally unlined, while those in the sands require screening.

Perennial springs occur near the base of the Chalk, commonly at the top of the West Melbury Marly Chalk. Along this part of the South Downs, these springs typically yield up to 3.79 l/s, but yields of up to 151.6 l/s have been recorded from examples in the Chichester district. The aquifer also contributes to the baseflow of the rivers draining southwards across the district.

With the exception of the Hamble, Ems and Meon rivers and the lowest reaches of minor streams in the district, valleys on Chalk bedrock are normally devoid of surface water. However, during the extreme weather conditions of the early spring of 1994, when torrential rain fell on a number of consecutive days, surface flow was noted in a number of these 'dry' valleys and the local water table was measured at over 20 m higher than previously recorded averages (for example in the public supply well near Brickkiln Farm ((SU81SW/4)[SU 835 125] in the Chichester district). Villages such as Hambledon and Stoughton were flooded for the first time in living memory.

Bulk minerals

Sand and gravel

Sand and gravel has been won from the Folkestone Beds, sand units in the Palaeogene, terrace deposits of the former 'Solent River' and present-day rivers, raised beach deposits and head gravel.

Fine- to medium-grained sands are extracted from the Folkestone Beds at West Heath [SU 785 228]. Similarly, graded deposits have been taken from a large sand body in the Reading Formation at Bishop's Waltham, and from the Whitecliff Member of the London Clay at North Boarhunt [SU 605 103].

Sand and gravel has been extensively worked from the second terrace east of Lee-on-Solent and from the first terrace of the Meon at Mislingford [SU 587 143]. Elsewhere, a number of small degraded pits have been noted in terrace deposits. Flint gravel has been extracted from the head gravel in the east of the district around Hambrook [SU 785 080] and Southleigh Park [SU 738 085].

Clay

In the past, the Gault, Reading Formation, London Clay, Wittering Formation and the 'brickearth' were used in the manufacture of bricks and tiles. The Reading Formation was worked at Padnell and Rowlands Castle, the London Clay at Padnell, Cowplain and Swanwick, and the Wittering Formation at Lower Swanwick. Outline geotechnical data on these deposits are given in Lake et al. (1985).

Chalk There are many pits in the district attesting to the great historical use of chalk for the liming of fields. Most are abandoned and degraded but agricultural lime is still produced from Butser Hill Quarry [SU 726 205] and periodically from a pit east-south-east of Chalton [SU 748 156]. Chalk was worked intensively on Ports Down for cement, agricultural lime, burnt lime and fill, but only small quantities are still worked at Warren Farm Pit near Fort Nelson.

Building stone

Building stone is not produced commercially in this district but in the past locally derived materials have been used in construction. Only the Upper Greensand 'malmstone' or 'bluestone' was extensively worked. The best quality building stone comes from indurated calcareous siltstones ('bluestone') found as discrete beds within the malmstone. Excellent examples of houses built of this stone can be seen in all of the villages along the foot of the escarpment (Plate 6a).

Limited use has been made of the harder beds within the Chalk sequence (Melbourn Rock, nodular beds within the Lewes Chalk). The phosphatic chalks used in the construction of Boxgrove Priory were obtained from within the Newhaven Chalk near Stoke Clump [SU 835 097] (Lavant Stone) in the Chichester district. A similar phosphatic chalk, also quarried historically, occurs to the east of Nore Down [SU 774 130]. Flint nodules were extensively worked for building, both as dressed squared-flint and single-faced trimmed nodules, particularly in churches and larger houses (Plate 6b). Flint, as a 'waste' product of chalk extraction and from 'field picking', has also been used to maintain farm tracks on the chalk dip slope.

Hydrocarbons

The district was first explored in the 1930s and, more successfully, in the 1970s with the discovery of the Horndean Oilfield. The reservoir rocks are in the Great Oolite Formation of the Jurassic. The processes of hydrocarbon formation, migration and entrapment were controlled by east-west, pre-Albian extensional faults. In the basins to the south of the major faults, and particularly in the centre of the Weald Basin, the Lias source rocks, and possibly the Kimmeridge Clay were buried sufficiently deep to generate hydrocarbons. The hydrocarbons migrated south from the centre of the basin into the Great Oolite rocks of the palaeohighs, where antithetic faults provided traps. Migration probably began in Early Cretaceous times and may have continued until uplift in mid-Cainozoic times (Penn, et al., 1987). Although Cainozoic compression caused inversion of the Weald Basin, it did not destroy all the traps. Many anticlines in the Wessex Basin, for example the Portsdown and Littlehampton anticlines, do not contain oil and gas, suggesting that primary oil migration ceased before they were formed.

Geotechnical considerations

In addition to the incidence of flooding mentioned in the hydrogeology section there are four potential hazards inherent in the strata of this district. The following statements should be taken only as a guide to likely or possible problems and should not replace site-specific studies.

The relatively loose sands of the Folkestone Formation and some sand units within the Palaeogene strata provide unreliable foundations on steep slopes. The Gault and parts of the Palaeogene (mainly the London Clay Formation) contain highly shrinkable clays with a high smectite content. Consequently they may crack and move during extreme drought conditions. Suitable precautions should be taken during construction. Peat and other alluvial and marine deposits that contain thin beds of peat may be liable to compression and differential compaction when the ground is subject to loading.

Landslip and foundering of strata along the spring line between the Upper Greensand and the Gault is a known hazard along stretches of the crop. Elsewhere only minor landslipping has been noted in the London Clay sequence. Most other natural slopes are thought to be stable in the district but slope stability can be strongly influenced by human activity, particularly where oversteepened slopes are created during construction work. The chalk may be affected by solution phenomena which result in small surface depressions (dolines) that range in size up to 50 m across and up to 6 m deep. As a consequence of this dissolution, fractures naturally occurring in the chalk are enlarged. The resultant pipes, that may be filled with clay-with-flints, continue to provide sumps for excess surface water, and may be liable to further subsidence. Solution features are more common on the crops of the higher members of the Upper Chalk, particularly where a thin cover of clay-with-flints or Palaeogene deposits occurs nearby. Chalk has a high natural water content and this may lead to slurrying if over compacted. The stability of excavations in chalk is largely controlled by the frequency and direction of natural cavities and joints.

In addition to the naturally occurring hazards, man has had considerable influence on the landscape. Large parts of the ground adjacent to the natural harbours have been reclaimed, usually by filling and the construction of sea walls. In many cases the nature of the fill, and hence its geotechnical properties are unknown. In some cases the fill was the product of the excavation and expansion of the dockyard in the 19th century, when both thin Quaternary and Palaeogene (principally London Clay) materials were extracted. Large amounts of fill were also derived from the site clearance of parts of Portsmouth and Gosport, follow ing bomb damage in the Second World War. Many of the abandoned sand and gravel, chalk and clay pits in the area have been used as landfill sites particularly adjacent to the urban areas. Records are held by the local authorities but old areas of fill are often poorly documented. Outline information accrued from local authorities is given in the BGS Open File Reports for Fareham and Havant.

Information sources

Further geological information held by the British Geological Survey relevant to the Fareham and Portsmouth district is listed below. Enquiries concerning geological data for the district should be addressed to the Manager, National Geological Records Centre, BGS, Keyworth. Geological advice for this area should be sought from the Regional Geologist, Southern and Eastern England, BGS, Keyworth.

A Geoscience Index system is available for consultation in BGS libraries. This is a developing computer-based system which searches indexes to the collections. It has a backdrop based on the 1:250 000 scale maps. Available indexes include:

• Index of boreholes
• Outlines of BGS maps at 1:50 000 and 1:10 000 scale and 1:10 560 scale County Series
• Chronostratigraphical boundaries and areas from British Geological Survey 1:250 000 maps
• Geochemical sample locations on land
• Aeromagnetic and gravity data recording stations
• Land survey records

Books

• British Regional Geology
• The Hampshire Basin and adjoining areas, 4th edition, 1982
• The Wealden district, 4th edition, (1965) 4th impression 1992
• Memoirs
• Geology of the country around Winchester and Stockbridge (Sheet 299) 1912†
• Geology of the country around Alresford (Sheet 300) 1910†
• Geology of the country around Haslemere (Sheet 301) 1968
• Geology of the country around Southampton (Sheet 315) 1987
• Geology of the country around Fareham (Sheet 316) 1913†
• Geology of the country around Chichester (Sheet 317) 1903†
• Geology of the country around Lymington and Portsmouth (Sheet 330/331) 1915†
• Geology of the country around Bognor (Sheet 332) 1897†
• † out of print

Technical Reports

Technical Reports relevant to the district are described below. Most are not widely available but may be purchased from BGS or consulted at BGS and other libraries.

Geology

Reference numbers for the technical reports covering the geology of individual or combined 1:10 000 scale geological sheets are given with the list of 1:10 000 Series maps.

Biostratigraphy

There are 43 biostratigraphical reports (one is cited in the text*) covering the Fareham and Portsmouth district. These are held as internal open file reports by the Biostratigraphy Group of BGS under the prefixes WH and PDL. Readers are recommended to contact The Group Manager, Biostratigraphy and Basin Analysis Group at BGS, Keyworth for access to these reports and to the Palaeontological collections.

* Woods, M a. 1994. Macrofaunas from the Gault, Upper Greensand and Chalk of the Fareham Sheet (316) and Chichester Sheet (317). British Geological Survey Technical Report, WH/94/55R.

Maps

• Geology
• 1:1 500 000
• Tectonic map of Britain, Ireland and adjacent areas, 1996
• 1:1 000 000
• Pre-Permian geology of the United Kingdom, 1985
• 1:625 000
• Solid geology of the United Kingdom (south sheet), 1979
• Quaternary map of the United Kingdom (south sheet), 1977
• 1:250 000
• Sheet 51N 02W Chilterns, Solid geology, 1991 Sheet 50N 02W Wight, Solid geology, 1995
• 1:50 000
• Solid and Drift
• Sheet 299 Winchester (1976)*
• Sheet 300 Alresford (in press)*
• Sheet 301 Haslemere (1981)
• Sheet 315 Southampton (1987)
• Sheet 316 Fareham (1997)
• Sheet 317/332 Chichester and Bognor (1996)
• Sheet 330 Lymington (1997F)
• Sheet 331 Portsmouth (1994)
• * remapping recently completed or in progress
• F 1:50 000 facsimile of earlier 1:63 360 scale map
• 1:10 000/1:10 560
• Details of the original geological surveys are listed on editions of the 1: 50 000 geological sheets. Copies of the fair-drawn maps of the earlier surveys may be consulted at the BGS Library, Keyworth.
• The maps covering the 1: 50 000 Series Sheet 316 Fareham and the mainland portion of Sheet 331 Portsmouth are listed below together with the surveyors' initials and the date of survey. The surveyors were D T Aldiss, G Berridge, F G Berry, C R Bristow, E C Freshney, P M Hopson, R D Lake, S J Mathers,A Pedley, R C Scrivener, E R Shephard-Thorn, R K Westhead, R J Wyatt, and J A Zalasiewicz.
• The maps are not published but are available for public reference in the libraries of the British Geological Survey at Keyworth and Edinburgh and the BGS London Information Office in the Natural History Museum, South Kensington, London. Uncoloured dyeline sheets or photographic copies are available for purchase from the BGS Sales Desk.

• Geochemical maps
• 1:625 000
• Methane, carbon dioxide and oil suceptibility, Great Britain — south sheet, 1995.
• Radon potential based on solid geology, Great Britain — south sheet, 1995.
• Distribution of areas with above national average background concentrations of potentially harmful elements (As, Cd, Cu, Pb and Zn), Great Britain — south sheet, 1995.
• Geophysical maps
• 1:1 500 000
• Colour shaded relief gravity anomaly map of Britain, Ireland and adjacent areas, 1997.
• Colour shaded relief magnetic anomaly map of Britain, Ireland and adjacent areas, 1998.
• Sheet 51N 02W, Chilterns, 1980, aeromagnetic anomaly
• Sheet 50N 02W, Wight, 1978, Bouguer gravity anomaly
• Sheet 51N 02W, Chilterns, 1983, Bouguer gravity anomaly
• 1:50 000
• A geophysical information map (GIM) at a scale of 1:50 000 is available for this district. This shows information held in BGS digital databases, including Bouguer gravity and aeromagnetic anomalies and locations of data points, selected boreholes and detailed geophysical surveys.
• Hydrogeological maps
• 1:625 000
• Sheet 1 (England and Wales), 1977
• 1:100 000
• South Downs and part of the Weald, 1978
• Hampshire and Isle of Wight, 1979
• Groundwater vulnerabilty of north west Hampshire, Sheet 44, 1994
• Groundwater vulnerabilty of West Sussex and Surrey, Sheet 45, 1995
• Groundwater vulnerabilty of south Hampshire and Isle of Wight, Sheet 52, 1996
• Minerals maps
• 1:1 000 000
• Industrial minerals resources map of Britain, 1996
• 1:25 000
• The sand and gravel resources of the country around Chichester and north of Bognor Regis, Sussex, Mineral Assessment Report 138

Documentary collections

Boreholes

Borehole data for the district are catalogued in the BGS archives (National Geological Records Centre) at Keyworth on individual 1:10 000 scale sheets. For further information contact: The Manager, National Geological Records Centre, BGS, Keyworth.

BGS Lexicon of named rock unit definitions

Definitions of the named rock units shown on BGS maps, including those shown on the 1:50 000 Series 316/321 Fareham and Portsmouth Sheets are held in the Lexicon database. This is available on Web

Site http://www. bgs. ac.uk. Further information on the database can be obtained from the Lexicon Manager at BGS, Keyworth.

Material collections

Palaeontological collections

Macrofossil and micropalaeontological samples collected from the district are held at BGS Keyworth. Enquiries concerning all the fossil material should be directed to the Curator, Biostratigraphy Collections, BGS, Keyworth.

Petrological collections

Hand specimens and thin sections of rocks from the district are held in the England and Wales Sliced Rocks collection at BGS, Keyworth. A collection database is maintained by the Mineralogy and Petrology Group at BGS, Keyworth. The Group Manager should be contacted for further information, including methods of assessing the database. Charges and conditions of access to the collection are available on request from BGS, Keyworth.

Bore core collection

Samples and entire core from a small number of boreholes in the Fareham and Portsmouth district are held by the National Geosciences Records Centre, BGS, Keyworth.

BGS photographs

Copies of these photographs are deposited for reference in the BGS Library, Keyworth. Colour or black and white prints and transparencies can be supplied at a fixed tariff.

Other relevant collections

Groundwater licensed abstactions, Catchment Management Plans and landfill site

Information on licensed water abstraction sites, for groundwater, springs and reservoirs, Catchment Management Plans with surface water quality maps, details of aquifer protection policy and extent of Washlands and licensed landfill sites are held by the Environment Agency.

Earth science conservation sites

Information on the Sites of Special Scientific Interest present within the Fareham and Portsmouth districts is held by English Nature, Headquarters and Eastern Region, Northminster House, Peterborough.

Selected bibliography

Most of the references listed below are held in the Library of the British Geological Survey at Keyworth, Nottingham. Copies of the references can be purchased subject to the current copyright legislation. BGS Library catalogue can be searched online at: http://geolib.bgs.ac.uk

Allen, D J, Brewerton, L J, Coleby, L M, Gibbs, B R, Lewis, M A, MacDonald, A M, Wagstaff, S J, and Williams, A T. 1997. The physical properties of major aquifers in England and Wales. British Geological Survey Technical Report, WD/97/34. Environment Agency R&D Publication, No. 8.

Allen, J R L. 1961. The highest Lower Old Red Sandstone of Brown Clee Hill, Shropshire. Proceedings of the Geologists' Association, Vol. 72, 205–219.

Allen, J R L. 1977. Wales and the Welsh Borders. 40–54 in A correlation of Devonian rocks of the British Isles. House, M R, Richardson, J B, Chaloner, W G, Allen, J R L, Holland, C H and Westoll, T S (editors). Special Report of the Geological Society of London, No. 8.

Ball, W H. 1951. The Silurian and Devonian rocks of Turner's Hill and Gornal, South Staffordshire. Proceedings of the Geologists' Association, Vol. 62, 225–236

Ball, W H, and Dineley, D L. 1952. Notes on the Old Red Sandstone of the Clee Hills. Proceedings of the Geologists' Association, Vol. 63, 207–214.

Ball, W H, and Dineley, D L. 1961. The Old Red Sandstone of Brown Clee Hill and the adjacent area. Bulletin of the British Museum, Natural History, Vol. A5, 177–242.

Barclay, W J. 2004. Devil's Hole, Shropshire. 228–9 in The Old Red Sandstone rocks of Great Britain. Barclay, W J, Browne, M A E, McMillan, A A, Pickett, E A, Stone, P, and Wilby, P R (editors). Geological Conservation Review Series, No. 31. (Peterborough: Joint Nature Conservation Committee.)

Bassett, M G. 1974. Review of the stratigraphy of the Wenlock Series in the Welsh Borderland and South Wales. Palaeontology, Vol. 17, 745–777.

Bassett, M G. 1989. The Wenlock Series in the Wenlock area. 51–73 in A global standard for the Silurian system. Holland, C H, and Bassett, M G (editors). National Museum of Wales Geological Series, Vol. 9.

Besly, B M. 1988a. Late Carboniferous sedimentation in northwest Europe: an introduction. 1–7 in Sedimentation in a synorogenic basin complex: the Upper Carboniferous of Northwest Europe. Besly, B M, and Kelling, G (editors). (Glasgow and London: Blackie.)

Besly, B M. 1988b. Palaeogeographical implications of late Westphalian to early Permian red-beds, central England. 200–221 in Sediment-ation in a synorogenic basin complex: The Upper Carboniferous of Northwest Europe. Besly, B M, and Kelling, G (editors). (Glasgow and London: Blackie.)

Besly, B M, and Cleal, C J. 1997. Upper Carboniferous stratigraphy of the West Midlands (U K) revised in the light of borehole geophysical logs and detrital compositional suites. Geological Journal, Vol. 32, 85–118.

Boulton, W S. 1917. Mammalian Remains in the Glacial Gravels at Stourbridge. Proceedings of the Birmingham Natural History and Philosophical Society, Vol. 4, 107.

B R E, 1999. Radon: guidance on protective measures for new buildings. C RC Ltd.

Cleal, C J, and Thomas, B A. 1996. British Upper Carboniferous Stratigraphy. Geological Conservation Review Series, No. 11 (London: Chapman and Hall.)

Cocks, L R M, Holland, C H, and Rickards, R B. 1992. A revised correlation of Silurian rocks in the British Isles. Special Report of the Geological Society of London, No. 21.

Cutler, A, Oliver, P G, and Reid, C G R. 1990. Wren's Nest National Nature Reserve. Geological Handbook and Field Guide. (Dudley Leisure Services Department.)

Dawson, M R. 1985. Environmental reconstructions of a late Devensian terrace sequence: some preliminary findings. Earth Surface Processes and Landforms, Vol. 10, 237–246.

Dawson, M R. 1989. Chelmarsh. 80–85 in West Midlands: Field Guide. Keen, D H (editor). (Hampshire: Quaternary Research Association.)

Dineley, D L. 1999. Devil's Hole. 119–125 in The fossil fishes of Great Britain. Dineley, D L, and Metcalfe, S J (editors). Geological Conservation Review Series, No. 16. (Peterborough: Joint Nature Conservation Committee.)

Eastwood, T, Whitehead, T H, and Robertson, T. 1925. The geology of the country around Birmingham. Memoirs of the Geological Survey of Great Britain, Sheet 168 (England and Wales).

Galtier, J, Scott, A C, Powell, J H, Glover, B W, and Waters, C N. 1992. Anatomically preserved conifer-like stems from the Upper Carboniferous. Proceedings of the Royal Society of London, Vol. 247, 211–214.

Glover, B W. 1991. Geology of the Wombourne District. British Geological Survey Technical Report, WA/90/74.

Glover, B W, and Powell, J H. 1996. Interaction of climate and tectonics upon alluvial architecture: Late Carboniferous–Early Permian sequences at the southern margin of the Pennine Basin, U K. Palaeogeography, Palaeoclimatology, Palaeoecology, Vol. 121, 13–34.

Glover, B W, Powell, J H, and Waters, C N. 1993. Etruria Formation (Westphalian C) palaeoenvironments and volcanicity on the southern margins of the Pennine Basin, South Staffordshire, England. Journal of the Geological Society of London, Vol. 150, 737–750.

Goodwin, M, Maddy, D, and Lewis, S G. 1997. Pleistocene Deposits at Gibbet Hill (Stewponey Pit), Stourbridge, Staffordshire. 91–94 in The Quaternary of the South Midlands and the Welsh Marches: Field Guide. Lewis, S G, and Maddy, D (editors). (Hampshire: Quaternary Research Association.)

Greig, D C, Wright, J E, Hains, B A, and Mitchell, G H. 1968. Geology of the country around Church Stretton, Craven Arms, Wenlock Edge and Brown Clee. Memoir of the Geological Survey, Sheet 166 (England and Wales).

Geomorphological Services L TD. 1987. National review of research into landsliding in Great Britain. Report to the Department of the Environment.

Guion, P D, and Fielding, C R. 1988. Westphalian A and B sedimentation in the Pennine Basin, U K. 153–177 in Sedimentation in a synorogenic basin complex: the Upper Carboniferous of Northwest Europe. Besly, B M, and Kelling, G (editors). (Glasgow and London: Blackie.)

Hamblin, R J O, and Coppack, B C. 1995. Geology of Telford and the Coalbrookdale Coalfield. Memoir of the British Geological Survey, parts of sheets 152 and 153 (England and Wales).

Horton, A. 1989. Quinton. 69–76 in The Pleistocene of the West Midlands: Field Guide. Keen, D H (editor). (Cambridge: Quaternary Research Association.)

King, W W. 1921a. The plexography of South Staffordshire in Avonian times. Transactions of the Institute of Mining Engineering, Vol. 61, 155–168.

King, W W. 1921b. The geology of Trimpley. Transactions of the Worcestershire Naturalists' Club, Vol. 7, 319–322.

King, W W. 1925. Notes on the 'Old Red Sandstone' of Shropshire. Proceedings of the Geologists' Association, Vol. 36, 383–389.

King, W W. 1934. The Downtonian and Dittonian strata of Great Britain and north-western Europe. Quarterly Journal of the Geological Society of London, Vol. 90, 526–567.

Karpeta, W P. 1990. The morphology of Permian Palaeodunes — a reinterpretation of the Bridgnorth Sandstone around Bridgnorth, England, in the light of modern dune studies. Sedimentary Geology, Vol. 69, 59–75.

Kirton, S R. 1984. Carboniferous volcanicity in England, with special reference to the Westphalian of the East Midlands. Journal of the Geological Society of London, Vol. 141, 161–170.

Lawson, J D, and White, D E. 1989. The Ludlow Series in the Ludlow area. 73–90 in A global standard for the Silurian system. Holland, C H, and Bassett, M G (editors). National Museum of Wales Geological Series, Vol. 9.

Maddy, D, Green, C P, Lewis, S G, and Bowen, D Q. 1995. Pleistocene Geology of the Lower Severn Valley, U K. Quaternary Science Reviews, Vol. 14, 209–222.

Maddy, D. 1997. Midlands Drainage Development. 7–18 in The Quaternary of the South Midlands and the Welsh Marches: Field Guide. Lewis, S G, and Maddy, D (editors). (Hampshire: Quaternary Research Association.)

Marshall, C. 1942. Field relations of certain of the basic igneous rocks associated with the Carboniferous strata of the Midland counties. Quarterly Journal of the Geological Society, London, Vol. 98, 1–25.

Marshall, C. 1946. The Barrow Hill Intrusion, South Staffordshire. Quarterly Journal of the Geological Society of London, Vol. 101, 177–205.

Morgan, A V. 1973. The Pleistocene geology of the area north and west of Wolverhampton, Staffordshire, England. Philosophical Transactions of the Royal Society of London, B265, 233–297.

Morgan, A V, and West, R G. 1988. A pollen diagram from an interglacial deposit at Trysull, Staffordshire, England. New Phytologist, Vol. 109, 393–397.

Owens, B. 1990. Palynological report on a coal sample from Little London Brook, Alveley, Shropshire. British Geological Survey Technical Report, WH/90/254.

Poole, E G. 1966. Trial boreholes on the site of a reservoir at Eymore Farm, near Bewdley, Worcestershire. Bulletin of the Geological Survey of Great Britain, Vol. 24, 131–156.

Poole, E G. 1970. Trial boreholes in Coal Measures at Dudley, Worcestershire. Bulletin of the Geological Survey of Great Britain, Vol. 33, 1–41.

Powell, J H, Glover, B W, and Waters, C N. 1992. A geological background to planning and development in the Black Country. British Geological Survey Technical Report, WA/92/33.

Powell, J H, Glover, B W, and Waters, C N. 2000. Geology of the Birmingham area. Memoir of the British Geological Survey, Sheet 168 (England and Wales).

Ramsbottom, W H C, Calver, M A, Eagar, R M C, Hodson, F, Holliday, D W, Stubblefield, C J, and Wilson, R B. 1978. A correlation of Silesian rocks in the British Isles. Special Report of the Geological Society of London, Vol. 10.

Siveter, D J. 2000. Wren's Nest (S O 937 920). 191–198 in British Silurian Stratigraphy. Palmer, D, Siveter, D J, Lane, P, Woodcock, N, and Aldridge, R (editors). Geological Conservation Review Series, No. 19. (Peterborough: Joint Nature Conservation Committee.)

Siveter, D J, and Lane, P D. 2000. Brewin's Canal. 438–440 in British Silurian Stratigraphy. Palmer, D, Siveter, D J, Lane, P, Woodcock, N, and Aldridge, R (editors). Geological Conservation Review Series, No. 19. (Peterborough: Joint Nature Conservation Committee.)

Smith, N J P, Kirby, G A, and Pharaoh, T C. 2005. Structure and evolution of the south-west Pennine Basin and adjacent areas. Subsurface memoir of the British Geological Survey.

Warrington, G, Audley-Charles, M G, Elliott, R E, Evans, W B, Ivimey-Cook, H C, Kent, P E, Robinson, P L, Shotton, F W, and Taylor F M. 1980. A correlation of the Triassic rocks in the British Isles. Special Report of the Geological Society of London, No. 13.

Waters, C N. 1991. Geology of the Rowley Regis District (S O98N E). British Geological Survey Technical Report, WA/91/55.

Waters, C N. 2003. Carboniferous and Permian igneous rocks of central England and the Welsh Borderland. 279–316 in Carboniferous and Permian Igneous Rocks of Great Britain North of the Variscan Front. Stephenson, D, Loughlin, S C, Millward, D, Waters, C N and Williamson, I T (editors). Geological Conservation Review Series, No. 27. (Peterborough: Joint Nature Conservation Committee.)

Waters, C N, Glover, B W, and Powell, J H. 1994. Structural synthesis of S Staffordshire, U K: implications for the Variscan evolution of the Pennine Basin. Journal of the Geological Society of London, Vol. 151, 697–713.

Waters, C N, Glover, B W, and Powell, J H. 1995. Discussion on structural synthesis of south Staffordshire, U K: implications for the Variscan evolution of the Pennine Basin. Journal of the Geological Society of London, Vol. 152, 197–200.

White, D E, and Lawson, J D. 1989. The Přídolí Series in the Welsh Borderland and south-central Wales. 73–90 in A global standard for the Silurian system. Holland, C H, and Bassett, M G (editors). National Museum of Wales Geological Series, Vol. 9.

Whitehead, T H, and Eastwood, T. 1927. The geology of the southern part of the South Staffordshire Coalfield. Memoir of the Geological Survey of Great Britain.

Whitehead, T H, and Pocock, R W. 1947. Dudley and Bridgnorth. Memoir of the Geological Survey of Great Britain, Sheet 167 (England and Wales).

Wilson, D, and Waters, C N. 1991. Geological notes and local details for 1:10 000 Sheet S O98N W (Brierley Hill). British Geological Survey Technical Report, WA/91/62.

Wills, L J. 1938. The Pleistocene Development of the Severn from Bridgnorth to the Sea. Quarterly Journal of the Geological Society of London. Vol. 94, 161.

Index to the 1:50 000 Series maps of the British Geological Survey

The map below shows the sheet boundaries and numbers of the 1:50 000 Series geological maps. The maps are numbered in three sequences, covering England and Wales, Northern Ireland, and Scotland.The west and east halves of most Scottish 1:50 000 maps are published separately. Almost all BGS maps are available flat or folded and cased.

(Index map)

The area described in this sheet explanation is indicated by a solid block.

British geological maps can be obtained from sales desks in the Survey's principal offices, through the BGS London Information Office at the Natural History Museum Earth Galleries, and from BGS-approved stockists and agents.

Figures and plates

Figures

(Figure 1) Main geomorphological elements of the landscape of the district.

(Figure 2) Structure of the Wessex Basin. 1. The principal elements of the Wessex Basin; 2. Cross section along the line A–B; 3. Depth to the pre-Permian basement.

(Figure 3) Major subdivisions of the concealed Jurassic strata.

(Figure 4) The concealed Lower Cretaceous strata.

(Figure 5) Sequence of Upper Cretaceous rocks in the district and their correlation with biozonal and earlier chalk nomenclature schemes

(Figure 6) Lithological logs and correlation of the Palaeogene Beds in the district.

(Figure 7) A generalised summary of the principal deposits and events of the Quaternary of the district.

Plates

(Plate 1) The East Meon valley looking east from Old Winchester Hill towards Butser Hill and the closure of the Weald. The valley is founded on chalk folded into a pericline with the steeper limb to the north (left in this view) (GS474).

(Plate 2) The Upper Greensand and Glauconitic Marl contact along Greenway Lane, East Meon. Hammer 30 cm (GS471).

(Plate 3) Part of the face at Paulsgrove demonstrating the upward change from massive chalks with marl seams, characteristic of the Newhaven Chalk, to bedded chalks with regular large flint seams characteristic of the highest Newhaven and basal Tarrant Chalk. Face 30 m high. (GS370).

(Plate 4) The western face in the Warren Farm Pit showing the regularly spaced flint seams in blocky chalk of the topmost Spetisbury and lower Portsdown Chalks. The prominent flint pair, which are 0.8 m apart, (marked) are about 5 m above the position of the Portsdown Marl in this exposure (GS334).

(Plate 5) Paulsgrove upper bench. One of the best examples of the high-angle fracture zones common on Portsdown. Scale: yellow board is 0.5 m high (GS386).

(Plate 6a) Examples of the use of locally derived building stones in the district. a. The Upper Greensand 'Malmstone' or 'Bluestone' here used in a barn at Church Farm, South Harting. The dark fragments pressed into the mortar for decoration are ironstone fragments from the Iron Grit at the top of the Folkestone Beds (GS472).

(Plate 6b) Examples of the use of locally derived building stones in the district.b. Dressed flint nodules used in the Church Cottages, Compton. Flint shards created during the dressing are pressed into the wet mortar for decoration a process known as 'galletting'. Hammer 25 cm (GS473).

(Front cover) HMS Victory, the flagship of the Royal Navy. A view looking east from the harbour. The juxtaposition of the natural, safe harbour created by the drowning of the lower reaches of streams and a hinterland of formerly extensive oak, yew and beech forests growing on the Palaeogene strata of the Bere Forest and the chalk of the Downs encouraged the growth of Portsmouth as a ship building centre and the home of the navy (GS475). (Photographer: P M Hopson.)

(Rear cover)

(Geological succession) Geological succession of the Fareham and Portsmouth district

(Index map) Index to the 1:50 000 Series maps of the British Geological Survey.

Figures

Figure 3 Major subdivisions of the concealed Jurassic strata.

Figure 4 The concealed Lower Cretaceous strata