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Geology of the country around Horsham. Memoir for 1:50 000 geological sheet 302 (England and Wales)

By R W Gallois and B C Worssam

Bibliographical reference: Gallois, R W, and Worssam, B C. 1993. Geology of the country around Horsham. Memoir of the British Geological Survey, Sheet 302 (England and Wales).

• Authors
• R W Gallois B C Worssam
• Contributors
• Stratigraphy and Structure R G Thurrell I E Penn
• Palaeontology F W Anderson
• Hydrogeology R A Monkhouse

London: HMSO 1993. NERC copyright 1993 First published 1993. ISBN 0 11 884480 6. Printed in the UK for HMSO. Dd 291139 C8 10/93 531/3 12521

• Authors
• R W Gallois, BSc, DIC, PhD, CGeol, CEng, FIMM British Geological Survey Exeter
• B C Worssam, BSc formerly British Geological Survey Keyworth
• Contributors
• R G Thurrell, BSc, PhD I E Penn, BSc, PhD British Geological Survey Keyworth
• F W Anderson, BSc, PhD, DSc, F Inst Biol, FRSE formerly British Geological Survey London
• R A Monkhouse, BSc British Geological Survey Wallingford

(Front cover) Cover photograph Stone Farm Rocks [TQ 3814 3477], near East Grinstead. Ardingly Sandstone, Great-upon-Little [TQ 349 321], Chiddingly Wood, West Hoathly. This block has been detached from the adjacent Ardingly Sandstone crags by cambering. Its undercutting is partly due to wind action, caused by sand blasting in a periglacial climate; it has subsequently been accentuated by water seepage along a more silty, less permeable horizon. The upper part of the block, massive sandstone with disturbed bedding, is formed by the 'earthquake bed'. (A10218)

(Rear cover)

Othr publications of the Survey dealing with this and adjoining districts

Books

• British Regional Geology
• The Wealden District (4th edition), 1965
• Regional Offshore Reports
• The geology of the English Channel, 1992
• Memoir
• Geology of the country around Haslemere, Sheet 301, 1968
• Geology of the country around Tunbridge Wells, Sheet 303, 1972
• Geology of the country around Brighton, Sheets 318/333, 1987
• Geology of the country around Lewes, Sheet 319, 1987

Maps

• 1:625 000
• Solid geology of Great Britain (South) Quaternary geology of Great Britain (South) Sheet 2 Aeromagnetic
• 1:126 720
• Hydrogeological map of the Chalk and Lower Greensand of Kent, 1970
• 1:50 000 and 1:63 360 (Solid and Drift)
• Sheet 285 (Aldershot), 1976
• Sheet 286 (Reigate), 1978
• Sheet 287 (Sevenoaks), 1971
• Sheet 301 (Haslemere), 1981
• Sheet 303 (Tunbridge Wells), 1971
• Sheet 318/333 (Brighton and Worthing), 1984
• Sheet 319 (Lewes), 1979
• 1:25 000
• Cuckfield–West Hoathly, 1975

Preface

This memoir is the first comprehensive account of the geology of an area which, although within easy reach of the Greater London conurbation, remains essentially agricultural and scenically unspoiled. It includes some of the highest relief areas in south-east England, and some of the most geologically complicated ground. Although the solid rocks that crop out in the district, the Hastings Beds and Weald Clay, were deposited during a relatively short period of time in the early to mid-Cretaceous, their sedimentology and structure were influenced by tectonic events that can be traced back some 400 million years to the Devonian.

It has long been known the Cretaceous Hastings Beds and Weald Clay were deposited in a variety of fluviatile and lacustrine environments, but it was not until the systematic surveys of the 1950s and 1960s that progress was made in the development of detailed models for these past environments. The link, described here for the first time, between the sedimentology of the Hastings Beds and penecontemporaneous reactivation of major faults with a long history of intermittent movement, provides a glimpse of the complexity of the sedimentary history.

The Horsham district lay south of the last two great ice sheets that extended down into southern England, but there is ample evidence in the district of the periglacial climates that accompanied the advance of the ice. The outcrops of the Hastings Beds show some of the best-preserved periglacial landforms in southern England. These include tor-like sandstone crags shaped by frost and wind erosion in a cold desert. The clays of both the Hastings Beds and Weald Clay contain fine examples of features initiated by permafrost, including valley bulging and associated cambering.

The district is still predominantly agricultural, although its proximity to London has caused the main urban areas at Crawley (including Gatwick Airport), East Grinstead, Haywards Heath and Horsham to grow rapidly and to increase the pressure on land use. The area was once important for its ironstone deposits, but today the only minerals being worked are brick clays and some sandstones in the Hastings Beds and Weald Clay. There are few other workable deposits in the area, and the search for hydrocarbons has not, to date, led to any development. The geological maps and this memoir will therefore find their greatest practical use in land-use planning and the development of the best balance between urban, agricultural and leisure uses within the district.

Peter J Cook, DSc Director, British Geological Survey, Keyworth, Nottingham NG12 5GG, 12 April 1992

Notes

• The word 'district' is used in this memoir to mean the area represented by the 1:50 000 Geological Sheet 302 (Horsham).
• National Grid references are given in square brackets throughout this memoir. They all lie within the 100 km square TQ (or 51) except where otherwise indicated.
• Numbers preceded by A refer to photographs in the Survey's collection.
• Numbers preceded by E refer to thin sections in the BGS sliced rock collection (England and Wales).

Acknowledgements

This memoir has been written mainly by Dr R W Gallois and Mr B C Worssam, and incorporates information from Dr R G Thurrell and Dr C R Bristow. Dr I E Penn has contributed to the account of the geological structure and has jointly written the description of the concealed formations. The Appendix on Wealden ostracod faunas is by the late Dr F W Anderson. The section on hydrogeology and water supply was written by Mr R A Monkhouse. It includes hydrogeological information provided by the Southern and Thames water authorities. Geological Survey photographs, a list of which is given in Appendix 3, were taken by Mr J M Pulsford.

The thanks of the British Geological Survey are due to Messrs Redland Bricks Limited, to the London Brick Company Limited, to the Crawley Borough Engineer for details of trial boreholes, and to the Esso Petroleum Company for logs and specimens from the Bolney and Collendean Farm boreholes. Sketch maps showing the subsurface structure of the district are published by permission of the Department of Energy.

The geologists involved in the mapping programme would like to acknowledge the many fruitful discussions on the geology of the Horsham district that they held in the field with Professor P Allen, Professor J E Prentice and Mr J D S MacDougall. They are also grateful to the many quarry and brickpit owners, and the landowners and tenants of the district for their ready co-operation in facilitating access to their properties. The memoir has been compiled by Dr Gallois and edited by Dr Thurrell.

Geology of the country around Horsham–summary

The Horsham district is one of the most scenically attractive and geologically complex areas of south-east England. Its scenery consists of a central High Weald tract of wooded ridges and deeply incised valleys on the Hastings Beds outcrop, which is bordered by lower-lying, more pastoral Low Weald country on the Weald Clay. Although close to London, it remains essentially unspoiled and is devoted mainly to agriculture. The district has growing importance as a residential area and has rapidly developing centres of high-technology industry, notably around Horsham and in the vicinity of Crawley and Gatwick Airport. This memoir is the first comprehensive account of the geology of the district. It describes in detail the lithologies and structure of the rocks that crop out, and reviews their sedimentary history and relates it to the deep geological structure that has been revealed by exploration for hydrocarbons.

Its present-day landscape attained much of its form during the Quaternary ice ages when meltwater torrents and wind action were important agents of erosion and transport, and permafrost caused weathering of the surface layers. A study of the superficial deposits explains the evolution of the present-day river system. However, to understand the scenery as a whole one needs to examine the geological history of the district back to Carboniferous times, more than 300 million years ago. Mountain-building episodes at that time imprinted a fabric of mostly east–west fractures on the Devonian and Carboniferous strata which deeply underlie much of the Weald. These fractures were subsequently reactivated and today they markedly affect the distribution of the Cretaceous sediments in the district. The headwaters of both the Rivers Medway and Ouse rise within faulted ground which overlies the two major basement fractures in the district.

Brick-making is an important local industry and quarrying for building stone, important in the past, is still carried out at West Hoathly. In the 16th and 17th centuries the Wealden iron industry was the most important in Britain and many traces of mining, smelting and forging activities are still visible.

Geological succession in the Horsham district

(Geological succession) Geological succession in the Horsham district.

The formations shown on the Horsham 1 to 50 000 map are summarised below. Details of the concealed Devonian to early Cretaceous strata proved in the Bolney Borehole and of the Jurassic and early Cretaceous strata proved in the Collendean Farm Borehole are given in Chapter Two.

(Front cover) Cover photograph Stone Farm Rocks [TQ 3814 3477], near East Grinstead. The Ardingly Sandstone forms picturesque tor-like crags throughout the north-western part of the Weald. They were probably developed in a periglacial climate in the late Pleistocene, and many show evidence of wind erosion, such as undercutting by sand blasting. At Stone Farm the crags are capped by a massive bed containing traces of deformed bedding (the 'earthquake bed'), which overlies thin units of trough cross-bedded sandstone. The crags face south across Weir Wood Reservoir. (A10012)

Chapter 1 Introduction

Location and settlement

The Horsham district is situated within the western part of the Weald. It includes the western end of the High Weald on the Hasting Beds outcrop and part of the surrounding Low Weald, on the Weald Clay outcrop. The district is mostly in Sussex, but its northernmost fringe is in Surrey (Figure 1).

The natural vegetation of the district in early postglacial times, like that of the rest of the central Weald, was dominated by oak forest. The tiny 'microlithic' flint implements of Mesolithic hunters have been found in large numbers locally, on higher ground on both the Hastings Beds and the Weald Clay outcrops. The forests seem to have deterred large-scale Neolithic, Bronze Age or Iron Age (including Romano-British) settlement. Stane Street, the Roman road between London and Chichester, crossed the north-western corner of the district, running through Ockley and west of Slinfold, and is still followed in part by the modern A29. The London–Brighton way of the Romans, taking a more easterly course than its modern equivalent, passed through Felbridge and Ardingly and to the west of Haywards Heath. Both roads were in places made of slag from Wealden ironworks (Straker and Margary, 1938). Extensive Romano-British ironworks were established near Crawley (Gibson-Hill, 1975; 1976).

The present-day counties of Surrey and Sussex were established in early Saxon times (5th to 6th century AD), but like the rest of the central Weald, the Horsham district appears to have been settled only gradually as the forest was cleared during Saxon and medieval times.

Iron smelting grew in importance during the Middle Ages and, with the introduction of blast furnaces, became an important industry in the sixteenth and seventeenth centuries. At the present day, most of the area is given over to farming and forestry. Industries based on local resources are quarrying for sandstone, near West Hoathly, and brickmaking.

Horsham was the principal town of the district from Norman times until the 1950s, but since then it has been overtaken in size by Crawley, which was established as a New Town in 1949. The development of Gatwick Airport has contributed to the growth of Crawley. The third main urban centre is Haywards Heath, a mainly residential town owing its initial growth to its position on the London Brighton railway line.

Relief and drainage

The highest ground in the district is on the outcrop of the Hastings Beds close to the main axis of the Wealden Anticline (Plate 1), exceeding 180 m above OD in a small area at Selsfield Common [TQ 350 344] and in another [TQ 362 330] at West Hoathly. Westwards from West Hoathly a broad dissected ridge, much of which is more than 120 m above OD, extends through the St Leonard's Forest area to Horsham. Structurally, this ridge is an anticline. Bounding it to the south is a faulted syncline that forms the upper valley of the River Ouse, and south of that again is a lesser east–west ridge, barely attaining 120 m above OD, followed by the Warninglid [TQ 250 261] to Cuckfield road. South of this lesser ridge the ground falls southwards to the Weald Clay outcrop, beyond the southern margin of the district. North of the St Leonard's Forest ridge is an east–west valley along the southern limb of the Faygate Syncline, and a parallel ridge to the north along the axis of the syncline.

Most of the Weald Clay outcrop is less than 75 m above OD; its relief is largely determined by outcrops of sandstone and limestone beds. A prominent escarpment, with its crest more than 90 m above OD, is formed by the Small-'Paludina' Limestone (Charlwood Stone) outcrop between Charlwood and Rusper. Another well-marked physical feature is the Horsham Stone escarpment, which extends in an arc westwards from Warnham to Slinfold and thence south-eastwards to Denne Park, south of Horsham. The parallel outcrops of sandstone and Large-'Paludina' limestone beds in the south-west corner of the district give a WNW–ESE structural 'grain' to the country there, though the relief is not great. In the north-western part of the district, gently folded sandstone beds within the Weald Clay give country of moderate relief, though with no predominant topographical trend.

The district is drained partly southwards to the English Channel, by the rivers Arun, Adur and Ouse, and partly northwards to the Thames, by the Wey, Mole and Medway (Figure 1). The rivers draining to the channel have shorter courses to the sea than those flowing into the Thames, and their basins are therefore more deeply dissected and show more diversity of scenery than do those of the rivers draining northwards. The River Arun drains the central part of the district and most of its north-western quarter, and the Adur and the Ouse share between them the drainage in the south. The lowest points in the district are on its southern margin, where tributaries of the Adur descend less than 15 m above OD.

In this account the names given on Ordnance Survey large-scale maps are used as far as possible, but some quite long streams appear to be without names. Certain names have therefore been introduced for descriptive purposes. A tributary of the North River that rises on the lower slopes of Leith Hill is here called the Sheep Green Stream. The name Bramley Wey has been used in previous geological descriptions (e.g. Thurrell et al., 1968) for the branch of the River Wey that rises south of the Lower Greensand escarpment. The westerly tributary of the Adur above Henfield is here named the Shipley Stream.

Outline of geological history

Within the confines of the Horsham district many of the structural and stratigraphical features of the Weald as a whole are represented. The earliest rocks recorded are the Devonian mudstones, sandstones and limestones proved in the Bolney No. 1 Borehole [TQ 2801 2427]. These sediments were probably deposited, some 400 to 350 Ma ago, in a shelf sea on the southern border of a continent, at the core of which were the Caledonide mountain chains of the Lake District, the Southern Uplands and the Scottish Highlands. Sedimentation continued into the early Carboniferous (Dinantian), acout 340 Ma ago, but the Carboniferous limestones of the Weald, though in continuity with those of the Mendips, were separated from those of northern England by an upland belt, the Mercian Highlands, that stretched east–west across Wales and the Midlands. This Mercian landmass may have extended southwards into the Wealden area during the Namurian (320 Ma) but, in Silesian times (300 Ma), sedimentation probably resumed in the Horsham district, giving Coal Measures similar to those of east Kent. The Weald was strongly affected by the Variscan earth movements, which complexly folded the Devonian and Carboniferous rocks. Late Carboniferous and Permian uplift and subsequent Permian and Triassic erosion (290 to 200 Ma) resulted in the removal of any middle to late Carboniferous, Permian and early Triassic strata that were deposited in the district.

Throughout much of the Mesozoic, southern England was a depositional area. The western parts of the Wessex Basin began to subside in the Permian, but in the Weald subsidence started in the late Triassic (200 Ma). The Horsham district lies in the central part of the Wealden Basin. For the next 60 million years the Weald was affected by the gentle subsidence movements that allowed the development of the Jurassic shelf seas across southern England and the Midlands. Subsidence in the Weald was almost continuous from earliest Jurassic to late Cretaceous times. The latest Jurassic and earliest Cretaceous deposits (Purbeck Group) were deposited in an enclosed gulf-like area, at first hyper-saline, but later brackish to freshwater. In the early Cretaceous, the Midlands and parts of East Anglia were uplifted and subjected to erosion. Subsidence of the Weald continued, however, and the sands, silts and muds that make up the Wealden Group were deposited over a 20 Ma period (135 to 115 Ma) in a humid, subtropical climate which produced swamp-like environments.

The Wealden beds are the youngest 'solid' strata preserved in the district (Figure 2). Evidence from the adjacent districts suggests that, after almost continuous marine deposition during the middle and late Cretaceous, subsidence in the Weald was replaced by intermittent compressive movements. It is probable that the Lower Green-sand, Gault and Chalk originally covered the entire Weald, but uplift and the formation of the Wealden anticline soon after the end of the Cretaceous led to their removal by erosion. Folding culminated in the Alpine earth movements in the Miocene, about 15 Ma ago.

The Weald lay beyond the southern limits of Quaternary ice sheets. The drift deposits of the Horsham district are inferred to date mostly from the later part of the Quaternary (0.3 Ma BP onwards). Their relation to landforms shows how the landscape has evolved by interaction between geological structure and fluviatile and periglacial processes of erosion and deposition.

Previous research

The earliest references to the geology and physical geography of the Horsham district occur in descriptions of the agricultural economy and the iron industry which date from the 17th century onwards. Fairey's geological section across the Weald (1806), and William Smith's map of England (1815) and his geological maps of the counties of Surrey (1819) and Sussex (1819) provide the first systematic record of the distribution of the rocks of the district. The published description in 1822 by Gideon Mantell, a doctor in practice in Lewes, of newly discovered teeth of the giant herbivorous dinosaur Iguanodon at Cuckfield attracted numerous other workers to the district in the first half of the 19th century.

The Geological Survey commenced work in the Weald in 1855. The Horsham district was surveyed on the scale of one inch to one mile (1:63 360) by F C Bishopp, H W Bristow, F Drew, J Hay and W Topley. It was published partly on Old Series one-inch Sheet 8 in 1862 and partly on sheets 5, 6 and 9 in 1864. The geology was described in the memoir Geology of the Weald by Topley in 1875. Several of the Geological Survey 'Water Supply' memoirs have dealt in part with the district, including the Water Supply of Sussex (Whitaker and Reid, 1899) and its Supplement (Whitaker, 1911), the Water Supply of Kent (Whitaker, 1908), the Water Supply of Surrey (Whitaker, 1912) and Wartime Pamphlet No. 10, part VII (Buchan et al., 1940). A systematic geological survey on the six-inch (1:10 560) scale was carried out by Dr R W Gallois, Dr R G Thurrell and Mr B C Worssam in 1960 to 1964, and a small tract was surveyed by Dr C RBristow in 1962, under the supervision of Mr S C A Holmes as District Geologist. Sheet 302 was published on the one-inch scale in 1972; future editions will be at the 1:50 000 scale.

Although there has been little other systematic work within the district, numerous workers have contributed to the better understanding of particular aspects of the sedimentology and stratigraphy of the Wealden. Prominent among these is Professor P Allen who has been instrumental in elucidating the depositional environments (1941–1989).

The stratigraphical contributions include Hughes' (1958–1976) study of the plant microfossils, Anderson's accounts (1940–1985) of the ostracods, Kermack et al.'s (1965) description of the mammalian teeth and Jarzembowski's (1981–1991a) descriptions of the insects. The structure of the Weald was reviewed by Lake (1976) and the history of the development of the Wealden Basin was detailed in Whittaker (1985).

The results of these works, and those of more local interest, are discussed in the main text.

Chapter 2 Concealed formations

The Horsham district occupies a central position in the Wealden sedimentary basin, in which up to 2500 m of Jurassic and early Cretaceous rocks were deposited on a 'basement' of folded and thrust-faulted Devonian and Carboniferous rocks (Figure 3). Only one borehole, drilled for hydrocarbon exploration at Bolney [TQ 2801 4429], has reached the basement rocks, but the Collendean Farm Borehole [TQ 2480 4429], 2.5 km north of the district boundary, penetrated almost to the base of the Jurassic sequence (Table 1). The basement rocks have been proved in deep boreholes in the adjacent districts at Brightling [TQ 6725 2182] (Butler, 1981) and Westham [TQ 6097 0535] (Lake et al., 1987).

The search for hydrocarbons in the region has generated much seismic-reflection data and these have been calibrated against geophysical log and core data obtained from the corresponding drilling programmes to produce a regional synthesis of the tectonic and sedimentary evolution of the Weald in the Mesozoic and Cainozoic eras (Whittaker, 1985). The thickness ranges for the Triassic and Jurassic strata beneath the Horsham district, shown in (Table 1) are based in part on that study.

Devonian

Complexly folded and faulted Devonian strata probably underlie the whole of the Horsham district. The Devonian sequence proved between 1945.5 and 2440.2 m in the Bolney Borehole is almost wholly argillaceous and consists of indurated mudstones with much shearing. Only six cores were taken; they, the rock cuttings and the geophysical logs show that the sequence is composed dominantly of dull greyish brown, reddish brown and brownish grey, thinly bedded, hard, compact mudstones with rare lenses of greenish grey mudstone and sporadic wisps of shell detritus. The mudstones contain a few thin beds of greenish grey, slightly calcareous siltstone and very fine-grained sandstone in the lower 420 m. Dark brown to pale yellowish brown, fine-grained limestones, recrystallised in part and locally dolomitic, also occur. A prominent limestone bed at 2054 to 2058 m contains poorly sorted, medium to large, ovoid to round ooids in a poorly dolomitised micritic matrix.

The upper 70 m of beds are an alternating sequence of limestones and mudstones in the lower part and of sandstones and mudstones in the upper part. The mudstones are locally Shelly and are variously dark reddish brown, brownish grey, pale grey, dark grey and, less commonly, olive or greenish grey. The limestones are micritic, sporadically crinoidal and cryptocrystalline, and are in shades of buff, cream, yellowish grey, red and green. The sandstones are white, coarse- to fine-grained grading to siltstone, and comprise subangular quartz grains in a siliceous matrix. The lowest sandstone is notably calcareous. A core at 1950.7 to 1953.8 m, from close below the junction with the Carboniferous succession, consists of friable reddish brown mudstone with some greenish grey mottling and with small calcareous caliche concretions and no obvious bedding, the last two features being indicative of subaerial weathering.

The mudstone-dominated sequence below c.2020 m gives rise to a mildly serrated gamma-ray curve of high average values, and a corresponding sonic trace of medium to high velocity, with high velocity peaks diagnostic of thin limestones (Figure 4). Much more strongly serrated (' spikey') curves reflect the presence of the prominent high velocity limestones and sandstones above 2020 m. These beds, particularly the quartzitic sandstones, yield low gamma-ray values. A feature of the hard, possibly diagenetically altered, mudstones immediately beneath the unconformable Carboniferous Limestone, is a high sonic velocity and complementary moderate to high gamma-ray values.

Dips in the Devonian sequence, in the cores and as indicated by dip-meter logs, are mostly between 30° and 50° down to about 2300 m. Below that depth dips mostly exceed 60°; the deepest core, at 2437.2 to 2440.2 m contained small tight folds with dips varying from 70° to 70° inverted. All the mudstone cores exhibit slickensided bedding planes and high-angle fractures, and they contain thin veins of calcite. The cores are largely unfossiliferous and yielded little identifiable material. Chaloner (in House et al., 1977, p.30) noted the presence of fragmentary bryozoa, foraminifera, possible ostracods, crinoid stems, brachiopod moulds and other shells. Middle Devonian (?Givetian) miospores were obtained at 2321.36 m (Mortimer and Chaloner, 1972), and an Upper Devonian Frasnian fauna, including Buchiola palmata (Goldfuss) and tentaculoideans, was obtained at 2028 to 2031 m (Butler, 1981).

Because of the complexity of the structure, it is impossible to estimate the true thickness of the Devonian rocks in the borehole. Overall, their faunal and sedimentary features suggest deposition on a muddy open marine shelf which periodically received influxes of clastic siliceous and calcareous debris from more nearshore areas. The correlatives of the Bolney sequence are likely to lie in the marine Devonian of south Devon and the Boulonnais of France where the Fammenian to Frasnian sequence (e.g. Wallace, 1968) resembles the succession at Bolney.

Carboniferous

Carboniferous Limestone

Carboniferous rocks have extensive subcrops beneath the eastern and northern margins of the Weald, but beneath the central Weald (where they have been more strongly affected by the Variscan earth movements) they are rare and their stratigraphy is poorly known. In the Bolney Borehole massively bedded limestones with thin mudstone interbeds were proven between 1898.9 and 1945.5 m. The limestones are mostly micritic and shell-fragmental, olive-grey and pinkish white with some red mottling; they are crinoidal at some levels. They contain veins of coarsely crystalline hematite and calcite. They give rise to a very mildly serrated geophysical log signature characterised by low gamma-ray values and high sonic velocity. Dipmeter measurements indicate dips of 17° to 24° in a northerly direction.

There is no direct palaeontological evidence for the age of these beds, but their lithology, geophysical-log character (Whittaker et al., 1985) and stratigraphical position suggest that they are Carboniferous Limestone. Comparison with sequences elsewhere in the Weald indicates that they are likely to be Tournaisian in age. The nature of the junction with the Devonian strata is not known, but it is likely to be unconformable: this is supported by the presence of probable subaerial weathering features in the highest Devonian strata.

Triassic

Penarth Group (formerly Rhaetic)

The Carboniferous Limestone in the Bolney Borehole is overlain with angular unconformity by gently dipping, olive-grey and dark grey mudstones interbedded with fine-grained grey limestones and muddy limestones. Comparison of the geophysical log signatures with those of other boreholes in the Wessex Basin (Whittaker et al., 1985) suggests that representatives of the Westbury Formation (dark grey mudstones) and the Cotham and Langport members (limestones and muddy limestones) of the Lilstock Formation are present between 1888.5 and 1898.9 m.

Jurassic

The Jurassic lithological sequence is constant over large areas of the Wessex Basin, despite considerable regional variations in thickness (in the Weald the thicknesses range from less than 500 m beneath parts of the North and South Downs to over 2000 m beneath parts of the western Weald) and rapid local variations close to major growth faults. The full thickness of the Jurassic was penetrated in the Bolney Borehole (1555 m thick) and in numerous other boreholes in the Weald and Wessex. As a result, the sparsely sampled borehole sequences can now be correlated in detail with the well exposed Dorset and Somerset coastal outcrops by means of geophysical logs (Whittaker et al., 1985). The Collendean Farm Borehole penetrated 1222 m of Jurassic strata: the sequence is complete down to a level in the Upper Lias and similar in thickness to that of the comparable beds at Bolney (Table 2).

Lower Lias

The Lower Lias sequence at Bolney (274.5 m thick, from 1614.0 to 1888.5 m) can be geophysically divided into the five units recognised in the Dorset type sections. The Blue Lias (1727.9 to 1888.5 m) comprises grey to yellowish grey, argillaceous, micritic limestones thinly interbedded with pale to dark grey, more or less calcareous mudstones, some of which are silty and micaceous or contain organic material. The limestones in the basal 50 m are sandy and contain abundant, very fine- to medium-grained, subangular to subrounded quartz grains set in a calcite cement. Slightly sandy limestones recur near the top of this division. The rapid alterations between limestone and mudstone give rise to spikey gamma-ray and sonic log traces which are characteristic of the Blue Lias. A core of dark grey, shelly, highly calcareous mudstone at 1753.3 to 1756.3 m yielded a poorly preserved fauna, determined by Dr H C Ivimey-Cook, in which bivalves and brachiopods are predominant. The presence of Arnioceras miserabile? (Quenstedt) together with Calcirhynchia calcaria S S Buckman and Piarorhynchia sp. is indicative of the Arnioceras semicostatum Zone. Other forms include Spiriferina walcotti (J Sowerby), Lobothyris? , Camptonectes mundus Melville, Chlamys textoria (Schlotheim), Gryphaea arcuata Lamarck, G. sp. arcuata trans to macculochii J de C Sowerby and Palaeoneilo cf. oviformis Troedffon.

The Shales with Beef at Bolney (1700.5 to 1727.9 m) consist of interbedded dark grey, brownish grey and olive-grey, slightly pyritic, argillaceous limestones and calcareous mudstones with gradational contacts. The overlying Black Ven Marls (1700.5 to 1660.0 m) comprise dark grey, brownish grey and olive-grey slightly pyritic mudstones which are sporadically calcareous and silty. The geophysical log profile of the Shales with Beef is characteristically mildly serrated with moderate to low gamma-ray values and sonic velocity in contrast to the more serrated profiles of the more thickly bedded Black Ven Marls which yield higher gamma-ray and lower velocity values.

The Belemnite Marls (1660.0 to 1628.7 m) are grey to yellowish grey, micaceous, shelly, silty mudstones which are sporadically calcareous. The geophysical logs show a subdued character, indicating a somewhat monotonous lithology with a hard calcareous bed at the top of the sequence marked by a minor high velocity peak.

The Green Ammonite Beds (1614.0 to 1628.7 m) are similar in lithology to the Belemnite Marls and show a similar, relatively subdued log signature. This shows a gradual upward increase in sonic velocity and decrease in gamma-ray values, indicative of an upward increase in lime content which culminates in the presence of thin limestone ribs towards the top of the sequence.

Middle Lias

The Middle Lias in the Bolney Borehole (95.0 m thick, from 1519.0 to 1614.0 m) consists of interbedded brown to greyish brown mudstones and muddy siltstones. More silty material predominates in the higher beds which are overlain by interbedded pale grey to yellow calcareous siltstones and silty limestones with subordinate grey to dark green silty mudstones. The limestones are white and green mottled, fine- to medium-grained, pelloidal and 'chamositic' (berthierinitic). Similar sequences proved in boreholes elsewhere in southern England have been grouped under the name Middle Lias Silts, the higher beds being the equivalent of the Marlstone Rock Bed. Gamma-ray values decrease and sonic velocities increase upwards, reflecting the upwards increase in silt content of the Middle Lias Silts. The Marlstone Rock Bed equivalent marks the culmination of this trend, but yields a signature of alternating higher and lower values of both gamma-ray and sonic velocity, reflecting interbedded siltstones and limestones.

Upper Lias

The Upper Lias at Bolney (111.0 m thick, from 1408.0 to 1519.0 m) comprises, in its lower part, dark grey to olive and brown, micaceous, calcareous, silty mudstones with scattered organic fragments. A thin, shelly, micritic limestone, thought to be the correlative of the uppermost part of the Junction Bed, occurs about 4 m above the base. Higher in the sequence, the mudstones become more silty and are interbedded with medium to dark grey, calcareous, glauconitic siltstones which grade up into silty sandstones. Towards the top of the sequence, dark grey to white, argillaceous siltstones and mottled sandstones predominate. The latter are locally calcareous and in their highest part become hematitic and 'chamositic'. The upwards increase in silt and sand content is reflected in decreasing gamma-ray values and a corresponding increase in sonic velocity. Individual silty and sandy beds are delineated by discrete levels of low gamma-ray values and high sonic velocity. Some of the sandy beds, however, yield low sonic velocity, indicating that they may be poorly consolidated.

The upper part of the Upper Lias, consisting largely of siltstones and silty sandstones as at Bolney, was proved at 1726.7 to 1755.6 m in the Collendean Farm Borehole.

Inferior Oolite

As elsewhere in southern England, the Inferior Oolite at Bolney (141.0 m thick, from 1267.0 to 1408.0 m) and Collendean Farm (169.2 m thick, from 1557.5 to 1726.7 m) is characterised by massive, shelly oolitic limestones with common calcite veins. These are readily distinguished in rock cuttings and by their geophysical log signatures from the underlying and overlying muddy formations. A three-fold division into Lower, Middle and Upper Inferior Oolite can be recognised in both boreholes; some of their features correspond to those of the Cotswold sequence.

The lowest 15 m of the Lower Inferior Oolite at Bolney consists of buff to pale grey, oolitic and micritic limestones, hematitic at some levels, interbedded with shelly, oolitic limestones containing silt and sand. These beds are overlain by over 30 m of cream to buff, medium- to coarse-oolitic, friable and porous limestone with a white, chalky matrix. A systematic decrease in sonic velocity occurs in the overlying oolites, reflecting their porous nature. The water-filled oolites are also well marked by the low resistivity values, while the prominent negative deflection of the SP curve indicates some permeability. A similar sequence, except with prominent interbeds of dark grey to brown fissile, silty, pyritic shales in the lower part, was recorded at Collendean Farm. Both sequences are similar to that described by Cave (1977) for the Lower Inferior Oolite of the mid-Cotswolds. The occurrence of the dinoflagellate cyst Nannoceratopsis gracilis Alberti (determined by Dr J B Riding) in association with a Middle Jurassic miospore assemblage at 1405.2 m at Bolney indicates this horizon to belong to the Lower to Middle Bajocian substages; the lithologies at this level suggest the former.

The Middle Inferior Oolite at Bolney and Collendean Farm consists of medium grey, buff and white, recrystallised, medium- to coarse-oolitic limestones which locally contain micritic material and shell and carbonate detritus. Stylolitic surfaces and thin calcite veins occur at many levels. Sandy limestones and friable oolitic limestones with a chalky matrix also occur. High gamma-ray values and high sonic velocities near the base of the sequence may relate to previously undetected phosphatised horizons, but otherwise the log character resembles that of the underlying strata. The presence of sandy beds is a distinguishing feature similar to that of the Middle Inferior Oolite of the Cotswolds (Cave and Penn, 1972).

The lower 27 m of the Upper Inferior Oolite at Bolney comprises grey, brown and white, shelly, oolitic, micritic limestones, some of which are dolomitic. These are overlain by grey, brown and white, fine-grained, argillaceous limestones which may be phosphatised near their base. A similar sequence was proved at Collendean Farm. The geophysical log character of both boreholes is similar. The gamma-ray and sonic log signatures of the lower oolites resemble those of underlying strata at Bolney. A gamma-ray peak and high sonic velocity at the base may again indicate the presence of some phosphatised material. The principal feature of the geophysical log signature, however, is the decline in sonic velocity to the top of the sequence and the marked rise in gamma-ray values, reflecting the presence of the argillaceous limestones. The presence of such relatively oolite-free limestones overlying shelly oolites is known elsewhere in the Upper Inferior Oolite.

Great Oolite Group

All the constituent formations of the Great Oolite Group recorded at outcrop in Dorset and the Cotswolds can be recognised in the Bolney (95.3 m thick, from 1171.7 m to 1267.0 m) and Collendean Farm (85.3 m thick, from 1472.2 to 1557.5 m) boreholes in their typical facies, although the boundary between the Great Oolite and the Forest Marble is unclear in the boreholes.

Fuller's Earth

The Lower Fuller's Earth at Bolney and Collendean Farm consists of about 11 m of grey to pale grey silty and calcareous mudstones interbedded with thin argillaceous limestones. High gamma-ray values and low sonic velocity characterises the mudstones, while the limestones give rise to opposing values, which give the log signature a characteristically deeply serrated appearance. The thickness and lithologies are similar to the Lower Fuller's Earth of the Bath area (Penn and Wyatt, 1979, p.29). The overlying Fuller's Earth Rock consists of alternating limestones and shelly calcareous siltstones. Near the base, the limestones are white to greyish brown, massive and detrital, with a chalky matrix. Towards the top, they are pale, yellowish brown, thinner bedded, argillaceous and micritic. The upward decrease in bed thickness and the increasingly argillaceous nature of the succession is similar to that recorded in the Wessex Basin (Penn, 1982, pp.61–62). In both boreholes the geophysical log signature is marked by a decrease in gamma-ray values and increase in sonic velocity compared with contiguous strata. A prominent sonic spike denotes the uppermost limestone. A typical Fuller's Earth Rock fauna was found in the corresponding beds in the Ashdown No.1 Borehole [TQ 5006 3035] (Bristow and Bazley, 1972).

The Upper Fuller's Earth at Bolney consists of pale brown to olive-grey, calcareous mudstones, silty in part, which pass up into grey silty mudstones and siltstones which become sandy and glauconitic in their upper part. These, in turn, pass up into grey and white mottled, detrital, argillaceous, silty and sandy limestones. The upward passage from mudstone to silty and sandy limestones is reflected in the upward decrease in gamma-ray values and interval transit time shown by the geophysical logs of both Bolney and Caen-dean Farm, and is similar to that which occurs in some of the Wessex and Cotswold outcrops where the limestones give rise to local names, for example the Tresham Rock. Foraminifera from 1240.5 to 1243.6 m, determined by Dr I P Wilkinson, include rare Lenticulina cf. dictyodes (Decke) at Bolney; the correlative strata in the type area yield the same form (Penn et al., 1979, fig. 4).

Great Oolite Formation and Forest Marble Formation

The Great Oolite and Forest Marble formations at Bolney and Collendean Farm comprise massive, white, buff and grey oolitic limestones with variable proportions of shell debris, detrital carbonate and micritic material. Argillaceous partings and cross-bedding are present in cores of shell-fragmental oolitic limestone at 1183.2 to 1184.5 m at Bolney. Neither the rock cuttings nor the geophysical log signatures are sufficiently distinctive for the two formations to be separated. The massive limestones give rise to uniformly low gamm-ray values and high sonic velocity. In both boreholes well-marked levels display reduced sonic velocity, indicating porosity, while corresponding SP deflections show that they are also permeable.

Cornbrash

The Cornbrash at Bolney (2.3 m thick) has been identified only by its characteristic geophysical log signature which shows a well-marked high velocity sonic 'spike' . As at outcrop, the Lower Cornbrash is less argillaceous than the Upper Cornbrash and the corresponding gamma-ray values show an upwards increase at Bolney. The succession is probably the same at Collendean Farm where the gamma-ray curve is similar but the distinctive sonic 'spike' is missing. The base of the Cornbrash there is not obvious and so its thickness is unknown.

Kellaways Beds

The Kellaways Beds at Bolney (13.9 m thick, from 1157.8 to 1171.7 m) and Collendean Farm (13.1 m thick, from 1459.1 to 1472.2 m) consist of pale yellowish brown, silty and sandy mudstones at the base, which pass up into siltstones and brownish grey to white, burrowed, argillaceous, silty, fine-grained sandstones. At the top the sandstones are buff, fine grained and well sorted, with subrounded quartz grains in a calcite cement, and they are locally porous. The Kellaways Rock, consisting of sandy limestones, is well developed at the top of the Collendean Farm sequence, but less obviously so at Bolney. Cores in siltstone and very fine-grained sandstone at Bolney (1168.0 to 11.71.3 m) and Collendean Farm (1465.2 to 1468.5 m) consist of complexly burrowed mixtures of pale grey fine-grained sand and pale grey silt with some darker grey mud. They are calcareous throughout, partially cemented at some levels, and contain numerous bivalves and trace fossils. In both boreholes, the geophysical logs show the typical combination of a gradual upwards decrease in gamma-ray values and an intermittent upwards increase in sonic velocity as the argillaceous Kellaways Clay passes upwards into the Kellaways Sand and Kellaways Rock.

Oxford Clay

The Oxford Clay at Bolney (104.3 m thick, from 1053.5 to 1157.8 m) and Collendean Farm (117.7 m thick, from 1341.4 to 1459.1 m) can be divided into three parts which correspond to the Lower, Middle and Upper Oxford Clay of the East Midlands. The Lower Oxford Clay is characterised by the presence of thin beds of brown bituminous (organic-rich) mudstone in a sequence of grey slightly silty and silty, more or less calcareous shelly mudstones. A thin bed of siltstone, which may be the equivalent of the Comptoni Bed of the Midlands, occurs a few metres below the top of the sequence.

The Middle and Upper Oxford Clay in both boreholes consists largely of pale and medium grey, slightly silty and silty calcareous mudstones with some thin beds of siltstone, the silt content increasing upwards in the sequence. The junction between the two units is marked by a bed of silty limestone, the equivalent of the Lamberti Limestone of the type area.

The subdued, serrated gamma-ray signature shows high values at the base of the Oxford Clay, but these decrease upwards as the beds become more calcareous and silty towards the top of the Middle Oxford Clay where a distinct low corresponds to the siltstone of the presumed Comptoni Bed. The sonic log signature is similarly serrated and shows a complementary upwards increase in velocity. A minor peak at 1140 m occurs at a similar stratigraphical level to that which marks the level of the Comptoni Bed throughout southern England (Whittaker et al., 1985). The Lower/ Middle Oxford Clay boundary at Bolney may, therefore, be located at the top of the succeeding less calcareous beds. Although there is a sharp increase in gamma-ray values above the top of the Middle Oxford Clay, this is part of an initial trend towards increasing gamma-ray values which characterises the lower part of the Upper Oxford Clay. This is reversed about 25 m above the base, where an upwards decrease accompanied by a slightly more serrated log character occurs. The sonic log signature is again complementary. The upwards change in log character reflects the increasing predominance of the silty and more calcareous levels towards the top of the formation.

Corallian Beds

The Corallian Beds of southern England are made up of variable sequences of argillaceous, arenaceous and calcareous strata which have given rise to a large number of local names at outcrop. Although the full sequence has been penetrated in a large number of boreholes in the Weald and its lateral variation is well known, there are few core samples and its internal correlation with other areas is uncertain. The sequences at Bolney (67.5 m thick, from 986.0 to 1053.5 m) and Collendean Farm (163.4 m thick, from 1178.0 to 1341.0 m) are markedly different in thickness and it seems likely that much of the lower part of the Corallian Beds is cut out by a fault at Bolney.

The sequence at Collendean Farm can be broadly divided into four parts. A basal unit of pale grey, oolitic limestone overlain by medium to dark grey, calcareous siltstones rests with marked lithological contrast on the Oxford Clay. This is overlain by a thick unit of grey calcareous mudstone and silty mudstone which passes up into the third unit, composed of fine-grained limestones with thin interbeds of mudstone. The highest unit is lithologically complex: a thick bed of calcareous silty mudstone overlain by thinly interbedded, fine- to medium-grained carbonate-sandstones, shelly fine-grained limestones and oolitic limestones which pass up into heavily burrowed calcareous silty sandstones, siltstones and muddy siltstones. A core in these siltstones at 990.6 to 994.0 m at Bolney consists of a bioturbated mixture of pale grey silt and dark grey muddy silt, calcareously cemented in part, with numerous subhorizontal wispy bedding streaks which may indicate penecontemporaneous flow in the sediment.

Although differing in detail, the Bolney sequence is not dissimilar from that of the middle and upper parts of the Collendean Farm sequence, some 40 m to 105 m (but probably nearer the lower value) of the basal unit being cut out by a fault at Bolney.

The lowest limestone of the Corallian Beds registers a prominent gamma-ray low and a sonic log peak. Above this the silty mudstones give rise to mildly serrated curves in which gamma-ray values increase and sonic velocity decreases upwards.

The limestones and mudstones of the third unit give rise to a more strongly serrated signature of moderate to low gamma-ray value and moderate to high sonic velocity. High gamma-ray values and low sonic velocity form a well-defined peak and trough corresponding to the basal mudstones of the fourth unit. The calcareous sandstones of the latter give rise to a poorly serrated 'cylindrical' gamma-ray signature and corresponding sonic curve whose moderate velocity values indicate the presence of some porosity. Geophysical log correlation with the Ashdown boreholes (Bristow and Bazley, 1972, pp.20–21) and with the Brightling Borehole (Lake et al., 1987) show the lower units to belong to the lower to middle parts of the Oxfordian Stage. Similar comparison with the more argillaceous sequence in the same boreholes and the Penshurst Borehole (Dines et al., 1969) shows the uppermost unit within the district apparently to lie within the lowest Kimmeridgian zones, although direct evidence of this has not been found at Collendean Farm and Bolney. By the same reasoning, the third Corallian Beds subdivision is assumed to lie within the middle to upper part of the Oxfordian Stage.

Kimmeridge Clay

The Kimmeridge Clay of the Wessex Basin consists almost wholly of dark and medium grey mudstones and pale grey calcareous mudstones with thin beds of oil shale (organic-rich mudstone) common at several levels; a few thin tabular and concretionary bands of muddy limestone (cementstone) and rare thin siltstone horizons also occur. The highest part of the formation, the Pavlovia zones, is commonly silty or sandy and forms an upward transition into the overlying Portland Beds.

The beds assigned to the Kimmeridge Clay in the Bolney (521.0 m thick, from 465.0 to 986.0 m) and Collendean Farm (506.0 m thick, from 672.0 to 1178.0 m) boreholes are lithologically as described above, and are presumed to include representatives of the full sequence exposed in the Dorset type section. In the upper part the mudstones become silty and pass into calcareous siltstones which may be glauconitic, and are interbedded with fine-grained, argillaceous sandstones. Cores at 898.6 to 900.7 m at Bolney and 1152.4 to 1155.5 m at Collendean Farm consist of pale grey and dark, faintly brownish grey smooth textured mudstones with bivalve and ammonite fragments preserved mostly as brown ferruginous films. The ammonites include Aulacostephanus eulepidus (Schneid): the lithology and fauna is similar to that of Bed KC 16 of Gallois and Cox (1976) of the Mutabilis Zone. Cores at 648.6 to 651.7 m at Bolney and 798.0 to 801.0 m at Collendean Farm are both in dark grey mudstones with thin oil shale (organic rich) seams, in which Lingula is the only common fossil. Both cores are probably in the Pavlovia zones.

At Bolney, a subdued, serrated gamma-ray profile and a more strongly serrated sonic log signature reflect the inter-bedding of the mudstones. The more calcareous lithologies give rise to lower gamma-ray values and higher sonic velocities; the silty and argillaceous sandstones give rise to intermediate values. Large-scale variation in log values enables the Kimmeridgian zones to be identified (Whittaker et al., 1985). This shows the basal part of the Kimmeridge Clay to lie within the Mutabilis Zone and well-developed calcareous levels (at 670 680 m and 630 to 600 m) to lie within the Wheatleyensis and Hudlestoni zones. Siltstones and sandstones are well developed within the Rotunda Zone at 490 to 510 m. A core at 708.0 to 717.2 m at Collendean Farm consists of greyish green, fine- and medium-grained sandstones with some calcareous cementation, in which cross-bedding is picked out by grains of glauconite and dark grey plant debris. These lithologies are similar to parts of the Portland Sand of the Dorset outcrops. However, there is geophysical evidence to suggest that at Collendean Farm they form part of a sand body within the highest part of the Kimmeridge Clay.

The highest part of the Kimmeridge Clay throughout the Wessex Basin passes up without major sedimentary break into the Portland Beds, the junction being taken at a rapid upward increase in sand content in a sequence of sandy mudstones, siltstones and muddy sandstones.

Portland Beds

The Portland Beds in the Bolney Borehole (51.5 m thick, from 413.5 to 465.0 m) consist of interbedded medium to dark grey, variably silty, calcareous mudstones with disseminated organic matter, and argillaceous siltstones with thin beds of glauconitic sandstone in their lowest part. More-or-less serrated sonic and gamma-ray signatures reflect this interbedding but lower average gamma-ray values and higher sonic velocity distinguish the more silty Portland Beds from the underlying Kimmeridge Clay.

In contrast, much of the Collendean Farm sequence (54 m thick, from 618.0 to 672.0 m) consists of glauconitic, fine- to coarse-grained sandstones, calcareous in part, with thin beds of siltstone and, in the highest part, fine-grained muddy, sandy limestone. These lithologies give rise in the gamma-ray and sonic curves to a marked overall upwards decrease in gamma-ray values and interval transit time.

Comparison with the sequences proved at Warlingham (Worssam and Ivimey-Cook, 1971), Ashdown (Bristow and Bazley, 1972) and Fairlight [TQ 8592 1173] (Lake and Shephard-Thorn, 1987) suggests that the Bolney and Collendean Farm sequences may include the correlatives of both the Portland Sand and Portland Stone of the Dorset type area.

Purbeck Group

The basal Purbeck Beds at Bolney and Collendean Farm, as elsewhere in the Weald, contain thick beds of anhydrite which are readily identifiable in rock cuttings and by their geophysical log character. The overlying sequences, 147.8 m thick (from 265.7 to 413.5 m) and 152.0 m thick (from 466.0 to 618.0 m) respectively, are similar to that described from a fully cored borehole [TQ 6195 2214] at Broadoak, Sussex (Lake and Holliday, 1978), and comparison of the geophysical logs enables the principal members of Morter (1984) to be recognised in the Bolney and Collendean Farm boreholes. The Purbeck Group has been divided into two formations, the boundary between them being marked by a brackish marine transgression which gave rise to widespread oyster shell beds, including the Cinder Bed of Dorset. It has been suggested that this incursion marks the Jurassic–Cretaceous boundary (see p.15) in the Wessex Basin (Casey, 1963). For convenience, both Purbeck formations are discussed in this chapter.

Lulworth Formation

The basal Gypsiferous Beds comprise thick beds of gypsum-anhydrite with thin interbeds of dark grey, brown and white, micritic, shelly and pelletal limestones (sandy in part), and pale to medium grey, red or pink mudstones. The gypsiferous layers give rise to highly distinctive low gamma-ray, high sonic velocity geophysical log signatures. The overlying Broadoak Calcareous Member consists of interbedded, dark grey, greenish grey and brownish grey, calcareous mud-stones, very pale grey and yellowish brown, highly calcareous mudstones, and thin beds of pale buff, shelly, micritic limestone. Traces of gypsum occur at several levels. The Plant and Bone Beds are represented by brownish grey to dark greyish brown mudstones with much coalified plant debris. The geophysical log signatures of the Broadoak Calcareous Member are markedly spikey, reflecting the alternating thin-bedded lithology, but they show higher gamma-ray values and lower sonic velocity than the underlying beds. The gamma-ray signature of the Plant and Bone Beds is distinctive in that it shows, on average, higher values than beds immediately above or below, but contains a prominent medium to low value trough and a corresponding subdued sonic peak.

Durlston Formation

The Cinder Bed in the Bolney and Collendean Farm boreholes consists of interbedded shelly mudstones and grey to olive-grey, argillaceous shelly limestone, as elsewhere in boreholes in the Weald.

The overlying Arenaceous Beds consist in both boreholes of medium to dark grey and olive, shelly mudstones interbedded with grey to olive-grey, shelly limestones; the sandstones characteristic of this member at outcrop in Sussex were not recorded. The Greys Limestones comprise pale olive-grey and pale grey mudstones which are locally gypsiferous, calcareous or silty, thinly interbedded with greenish grey, pale grey and yellowish grey, micritic, shell-fragmental limestones which are locally dolomitic and hematitic. Cores at 495.6 to 499.0 m and 509.0 to 521.5 m at Collendean Farm and at 301.8 to 306.3 m and 316.7 to 319.1 m at Bolney are in mudstones, very shelly mudstones and shell- limestones in which the bivalve 'Cyrena' is abundant and the only common fossil.

The geophysical log signatures are characteristically highly serrated (the sonic log deeply so); low gamma-ray values and corresponding sonic spikes correspond to the thin limestones whereas the converse is true of mudstones. The signatures show an upwards increase in gamma-ray values and decrease in sonic velocity as the limestones become impure. This makes the Cinder Bed, at the base, easily recognisable by its low gamma-ray value and high sonic velocity.

The junction with the Ashdown Beds has been taken at an upward change from mudstones to silty and sandy mud-stones with thin sandstone interbeds. This change is well marked on the geophysical logs in both boreholes, particularly by an increase in gamma-ray values.

Chapter 3 Cretaceous: Hastings Beds

In the late Jurassic, earth movements related to the opening of the Atlantic brought to an end the long period of tectonic stability which had given rise to the almost continuous shallow-marine sedimentation of the Jurassic of southern Britain. The Portland Beds sea was replaced by a fresh to brackish-water lake which extended over the Weald and Hampshire and across to the Boulonnais in northern France. Within this lake the deposits of the Purbeck Group were succeeded first by the predominantly arenaceous Hastings Beds and then by the mainly argillaceous Weald Clay. Much of the sediment for the Wealden deposits probably came from Palaeozoic rocks which cropped out on land areas lying to the north (London–Ardennes massif) beneath what is now the North Downs, London and East Anglia, and to the west (Cornubian massif), now parts of Devon and Cornwall. To the north of the London Platform, notably in Bedfordshire, Norfolk, Lincolnshire and North Yorkshire, shallow-water marine sedimentation continued throughout the early Cretaceous. The sequences there are much thinner than the contemporaneous Wealden strata, for although the central Weald was subjected to variable and at times rapid subsidence along the lines of major faults (see Chapter Five), sedimentation kept pace with the subsidence. As a result, the shallow northern sea never encroached upon the Weald, although its influence, as evidenced by thin but widespread brackish-water horizons, was felt from time to time.

For this reason, it has not yet proved possible to make correlations between the Wealden sequence and the ammonite-bearing Lower Cretaceous sequences farther north. The age of the Wealden beds is, therefore, still not known in detail. The junction between the Jurassic and Cretaceous in southern England was for many years taken for convenience at the marked lithological change from argillaceous to arenaceous beds which occurs at the junction of the Purbeck Group and Hastings Beds. Casey (1963) suggested, from a study of the ammonite sequences in northern England and Russia, that the base of the Cretaceous was marked everywhere in Europe by a marine transgression. He concluded that in the predominantly nonmarine, late Jurassic/early Cretaceous sequence in southern England this transgression was represented by the brackish-marine incursion of the Cinder Bed in the middle part of the Purbeck Group. Subsequent work has failed either to confirm or disprove this suggestion, probably because too little is yet known about the complex sequences of subsidence events and sea-level changes that affected the region at that time. In the stable marine-shelf area of northern Britain, relatively small rises in sea level are readily apparent as transgressive horizons. Similar events in the Wealden depositional area may have been masked by subsidence events and by climatic and denudational changes in the sediment source areas. Thus, a transgressive event in the marine depositional area might have had a transgressive correlative in the Weald, but it might also, at a time of slow subsidence and rapid sedimentation, have been marked by no event or a regressive event.

In Surrey and Kent, the Weald Clay is overlain with minor unconformity by the marine Atherfield Clay, which contains early Aptian ammonites. The Wealden beds therefore provide a sedimentary record of much of the early to mid-Cretaceous, and probably span the Ryazanian to Barremian stages. The change from predominantly arenaceous to argillaceous sedimentation which marks the Hastings Beds/Weald Clay boundary has generally been correlated with a transgression which marks the base of the Hauterivian Dersingham Beds in the marine Norfolk sequence. In the Weald, movements along the growth faults which had dominated much of the Jurassic and early Cretaceous sedimentation ceased in the Hauterivian or Barremian. The change to more argillaceous sedimentation, which did not involve any great change in water depth in the Wealden lake, may therefore simply adumbrate the increasing maturity of the land areas.

The depositional environments of the Wealden lithologies are now broadly understood from their sedimentology and palaeontology, but much of the detail remains unresolved because of the paucity of exposure. The thicker sandy parts of the sequence, notably much of the Ashdown Beds and the Tunbridge Wells Sand, were deposited on broad alluvial flats cut by meandering distributary channels. The argillaceous parts of the sequence, the Wadhurst Clay, Grinstead Clay and much of the Weald Clay, were deposited in shallow lakes which were at times locally traversed by distributary channels bordered by sandy levees. At a few localities it has been possible to examine sections in three dimensions and thus make a fuller sedimentological appraisal. For example, by recording changes in working quarry faces over a period of many years, Allen (1989) has been able to establish detailed models for local environments.

Fossils are locally abundant in the Wealden beds, but are restricted almost entirely to species of the bivalves Neomiodon and Unio, the gastropod Viviparus and the ostracod Cypridea. Fish teeth and rare mammal teeth, and bones and teeth of large dinosaurs including Iguanodon occur in some of the sandstones, in thin pebble beds in the sandstones and at the bases of the major clay formations. Dinosaur footprints show that parts of the lake and the stream levees far distant from the upland areas were accessible to these animals.

The flora, reviewed by Seward (1913), is dominated by ferns, cycads and conifers, most of which were swept into the depositional area. However, at several horizons within the clay formations there are widespread occurrences of the horsetail Equisetites growing in situ, presumably in very shallow water. Elsewhere, the tree-fern Tempskya has been found and it is likely that at times the Wealden swamp was heavily vegetated. Research on the macroflora, the clay mineralogy and the plant spores (Sladen and Batten, 1984), and on the insects (Jarzembowski, 1984–1991a), indicates a subtropical climate with a moderately high rainfall. Batten (1974) and Harris (1981) have suggested that the rainfall was seasonal and that much of the carbonised plant debris preserved in the Wealden beds was derived from dry-season forest fires.

The sandstone formations which are so prominent a feature of the Hastings Beds have been interpreted (Allen, 1976; Sladen and Batten, 1984) as resulting from uplift of the London–Ardennes massif. The consequent increase in river gradients and river flow caused sandplains to be built out from the uplands. During deposition of clays, notably the Wadhurst Clay, the relief of the bordering uplands was less. From a study of the pebbles in the thin, but very widespread pebble beds at the bases of the Wadhurst Clay, Lower Grinstead Clay and Upper Grinstead Clay (Table 2), Allen (1967, 1989) has recorded progressive changes in the outcrop geology of the two main source areas, Cornubia and the London–Ardennes massif.

In Weald Clay times, deposition of muds predominated. There was a tendency to higher salinity and probably deeper-water depositional conditions during the earlier part of this time interval, and to freshwater conditions during the later part. None of the environmental changes were so pronounced as to give rise to lithostratigraphical units recognisable throughout the Weald.

Allen (1976) has documented a change in source areas that occurred soon after the onset of Weald Clay deposition. While the Hastings Beds sediments came predominantly from the London–Ardennes landmass (the Londinia of Allen, 1989), those of the Horsham Stone and other thin sandstones in the Weald Clay show a significant input from

Cornubian sources. At times a northern sea may have introduced brackish-marine faunas into the north-western Weald (Worssam and Ivimey-Cook, 1971). Allen (1976, p.421) has recorded heavy minerals of presumed East Anglian origin in some of the Weald Clay pebble beds.

Stratigraphical subdivision

The term Hastings Sands (now Hastings Beds) was introduced by Fitton (1824) to describe the predominantly arenaceous sediments between the Purbeck Beds and the Weald Clay. Mantell (1827) divided the Hastings Beds of the western High Weald, between Cuckfield and Horsham, into the Tilgate Beds, Worth Sandstone and Horsted Sand. However, these formations were never satisfactorily defined or mapped and it was not until 1861, when the first results of the systematic Geological Survey mapping of the northern High Weald had been completed, that Drew proposed the modern subdivisions of Ashdown Sand, Wadhurst Clay and Tunbridge Wells Sand (Figure 5). The names Grinstead Clay, for a persistent bed of clay which separates the Lower and Upper Tunbridge Wells Sand in the East Grinstead area, and Cuckfield Clay, for a clay bed within the Upper Tunbridge Wells Sand at Cuckfield, were introduced during the same survey (Topley, 1875). Two new names, Ardingly Sandstone and Cuckfield Stone, have been introduced during the present survey to describe distinctive sandstone members within the Tunbridge Wells Sand. The names Cuckfield Clay, Middle Tunbridge Wells Sand (Milner, 1923; Reeves, 1949), Balcombe Clay (Reeves, 1949), Lingfield Beds (Edmunds, 1935) and Lower Tunbridge Wells Clay (Michaelis, 1969) have all been shown to be unnecessary (Gallois et al., in Bristow and Bazley, 1972, pp.28–37).

The broad tripartite subdivision of the Hastings Beds into the Ashdown Beds, Wadhurst Clay and Tunbridge Wells Sand can be recognised throughout the whole of the Hastings Beds outcrop. The thinner units, the Ardingly Sandstone, Grinstead Clay and Cuckfield Stone are known only from the western and northern High Weald. Similarly, there are thin sandstone horizons in the eastern High Weald, for example the Hawkhill Sand of Allen (1947), which are not represented in the present district.

The boundaries of the Hastings Beds formations and members have been mapped in the present district on the evidence of topographical features, soil brash, subsoil type proved by augering, and spring lines. Even in heavily wooded, poorly exposed ground there is enough evidence for the boundaries to be plotted with confidence. In the steep-sided ghylls in the High Weald, the formation boundaries are commonly obscured by downwash and/or are displaced by cambering or landslip. In such areas, the features and spring lines provide the best evidence of the positions of boundaries. The thin, but laterally persistent pebble beds at the junctions of the Ashdown Beds and Wadhurst Clay, Ardingly Sandstone and Lower Grinstead Clay, and the Cuckfield Stone and Upper Grinstead Clay give rise to durable and distinctive rock fragments in the soil which aid the mapping of these boundaries.

The full thickness of the Hastings Beds can only be estimated from partial sequences proved in boreholes within and close to the district (Figure 6). The beds thicken from an estimated 300 m in the southern part of the district near Bolney to over 400 m in the northern part beneath the Worth Forest. Within the Weald, the group fills an elongated east–west-trending basin: consequently, it thins both southwards and northwards from the Horsham district, this thinning becoming pronounced as the edge of the London Platform is approached beneath the North Downs in Surrey and Kent. Eastwards, beneath the highest parts of the High Weald, over 400 m of Hastings Beds were probably deposited in the area now occupied by the Crowborough Anticline. Westwards, where they are overlain by the Weald Clay, there is no reliable record of the thickness of the Hastings Beds.

Ashdown Beds

The lowest formation of the Hastings Beds, the predominantly arenaceous Ashdown Beds, crops out over an area of less than ten km² in the eastern part of the district. Within that area, on the western edge of the Ashdown Forest, the highest 60 m of the formation is brought to the surface by the Crowborough Anticline (Bristow and Bazley, 1972). Borehole evidence shows that the full thickness of the formation around the Ashdown Forest outcrop is about 210 to 230 m. Boreholes within and immediately adjacent to the district at Worth Forest (225.6 m) and East Grinstead (207.61 m) show comparable thicknesses. In the Bolney Borehole [TQ 2801 2427], the sequence is incomplete due to faulting. Beyond the Hastings Beds outcrop the full thickness of the Ashdown Beds has been proved only in deep hydrocarbon boreholes. It appears to thin markedly in both northerly and southerly directions (Figure 6), the full thickness being about 177 m at Collendean Farm [TQ 2480 4429] near Holley, and about 148 m at Henfield [TQ 1799 1457] (Young and Lake, 1988), 3.2 km north and 6.4 km south of the sheet boundaries respectively. There is no evidence as to the thickness and nature of the Ashdown Beds west of a line from Three Bridges to Bolney.

Continuous core samples of Ashdown Beds have been taken from only two boreholes within the district, Worth Forest [TQ 2891 3500] and Cuckfield No.1 [TQ 2961 2731]. The remainder of the borehole descriptions are based, in the case of the hydrocarbon-exploration boreholes, on a combination of rock cuttings and geophysical logging methods and, in the case of the water boreholes, on drillers' descriptions of debris collected from the flushing water. In these accounts it is difficult to place the precise junction of the argillaceous lower part of the Ashdown Beds and the underlying Purbeck Beds, and in some cases the junction chosen may be in error by as much as 30 m.

The Ashdown Beds that crop out in the district consist of silty fine-grained sandstones and siltstones, with subordinate amounts of silty clay. Four coarsening-upwards, predominantly sandy and silty rhythms (Figure 7), each terminating in a prominent sandstone 12 to 15 m thick, can be recognised. Their outcrops are shown on the 1:10 560-scale geological maps, and the highest three are shown on the 1 to 25 000 scale Cuckfield–West Hoathly map (Gallois, 1975).

The borehole evidence both here (e.g. Worth Forest Borehole) and in adjacent districts (e.g. Frant boreholes: Bristow and Bazley, 1972, pp.133–143) suggests that these rhythms become more argillaceous with depth and are underlain by predominantly silty rhythms, and by silty clay rhythms in the middle and lower parts of the formation respectively.

The geophysical logs for the Ashdown Beds sequence in the Collendean Farm Borehole [TQ 2480 4429] show the upper 120 m (288.6 to about 408 m) to consist of predominantly arenaceous rhythms as at outcrop. Below about 408 m the sequence becomes progressively more argillaceous until it passes down into the Purbeck Beds at 466.0 m. A similar sequence is present in the Bolney Borehole [TQ 2801 2427] from 120.1 m down to about 190 m where it is faulted against the more argillaceous basal beds.

The Ashdown Beds are poorly exposed and can be seen only in a few degraded quarries where they have been worked for either roadstone, building sand or building stone, and in rare natural sections. The more argillaceous parts of the rhythms are well exposed only in those quarries where the underlying sandstone has been worked from beneath a protective clay capping. The individual rhythms are readily mapped, however, because each is marked by a good feature in which the silty or clayey lower part of the rhythm occurs at the foot of a steep sandstone slope. Superficial deposits are rare on the Ashdown Beds outcrop; thus argillaceous and pebble-bed debris commonly occur in ploughed fields and in temporary sections. Such evidence, combined with augering and feature mapping, has enabled each rhythm to be traced with some degree of confidence. In the detailed account, the four rhythms are referred to as the first to fourth in descending order.

The first rhythm is capped by the Top Ashdown Pebble Bed (Allen, 1949a) which marks the junction of the Ashdown Beds and the overlying Wadhurst Clay (see p.22). Although the base of the pebble bed theoretically marks the junction, the pebble bed being the basal transgressive bed of the Wadhurst Clay, it is so thin and patchily developed in the present district that it is more convenient to describe it as part of the sandstone sequence. The pebble bed and the top few centimetres of sandstone are commonly cemented by secondary iron minerals (deposited by groundwater movement along the clay–sandstone junction) and are durable as soil fragments.

Elsewhere in the Weald, the sandstone that forms the upper part of the first rhythm has been called the Top Ashdown Sandstone (Allen, 1949a, p.267). In the present district this bed is probably less massive than in the eastern Weald and although it gives rise to a strong feature it is no more prominent than the sandstones of the second and third rhythms. The lower beds of the first rhythm and the junction rhythms. The lower beds of the first rhythm and the junction with the second rhythm are exposed in several sections in the district. In each case, the contact is marked by a single layer of ripple-marked coarse-grained sandstone, locally with included tiny quartz pebbles. The first rhythm appears to be consistently about 15 m thick and can readily be identified because of its proximity to the Wadhurst Clay outcrop. Around Horsted Keynes, between the Great Oddynes and Danehill faults, the recognition of this and the lower rhythms depends on the assumption that they are overlain by two small outliers of Wadhurst Clay.

The second rhythm appears to be lithologically more complex and laterally more variable than the first. At several localities a single strong feature is present, apparently formed by about 15 m of predominantly sandy strata. This feature passes laterally into two distinct features which can be shown to be formed by beds of two separate rhythms, each of which contain laterally impersistent pebble beds and clay seams. The beds of the third rhythm form a strong continuous feature comparable to that of the first; they are poorly exposed and occur only in the deep valley north of Horsted Keynes and around Mayes [TQ 384 337]. The beds of the fourth rhythm, although poorly exposed, seem to vary laterally in a fashion similar to those of the second.

The Ashdown Beds contain a limited, but locally abundant fauna and flora which includes bivalves, gastropods, ostracods and plant fragments such as ferns, cycads and conifers. Well-preserved plants are restricted to the silty and clayey lithologies: the fauna, mostly poorly preserved moulds, is present only in the finer-grained sediments in the lower parts of the rhythms. In the quartzose sands, only coalified plant fragments are common.

Details

First Rhythm

An old quarry [TQ 3669 3416] 520 m east-north-east of Gravetye Manor, which was probably worked for sharp sand, showed the following section at the junction of the first and second rhythms. No pebble bed was seen at the junction of the quartzose sandstone and the overlying mudstone.

The beds dip 10° to the south, probably because of proximity to the Neyland Farm Fault.

Exposures of ripple-marked, flaggy sandstone within the rhythm occur in the courses of the streams [TQ 3600 3377]; [TQ 3629 3371] that run from Giffard's Wood to Gravetye Manor lakes, and in the northern part [TQ 3752 3415] of the railway cutting near Birch Farm. Silty beds near the base of the rhythm are exposed farther south [TQ 3747 3379] in the same cutting.

A road cutting [TQ 3794 3428] north-north-west of Neyland Farm exposed the following section at the junction of the first and second rhythms which, in detail, contrasts with that described above:

The following temporary section [TQ 3822 3442] south-south-west of Stone Farm, which was exposed during regrading of the bank of the River Medway, lies within the Charlwood fault belt (see p.92) and is separated by faulting from the main Ashdown Beds outcrop. Its precise stratigraphical position is uncertain, but it showed the junction of two rhythms, probably either the first/second or the second/third. Fragmentary plant remains, poorly preserved bivalves and trace fossils were noted throughout.

A stream section [TQ 3703 3346] north-north-west of Old Coombe showed basal Wadhurst Clay silts overlying 1.1 m of hard, brown, flaggy, silty, fine-grained sandstone which passed down into about 3 m of thickly bedded sandstones with thin intercalations of grey silt.

The junction with the Wadhurst Clay was exposed in a farm road [TQ 3782 3156] at Deanlands Farm, where a poorly developed Top Ashdown Pebble Bed, consisting of a parting of rippled coarse sand containing tiny quartz pebbles, rested on 0.5 m of ripple-marked, silty, fine-grained sandstone.

The topmost Ashdown Beds also crop out in three small inliers exposed in the stream beds near Northwood [TQ 3717 3166] to [TQ 3739 3182]; [TQ 3678 3120] to [TQ 3687 3130] and Horsted House [TQ 3711 3059]. In the first of these sections about 1.4 m of hard, white, ripple-marked, thickly bedded, fine-grained sandstone was overlain with a sharp contact, but apparently without a pebble bed, by basal Wadhurst .Clay siltstones. The second section west of Northwood showed similar beds. The last section showed an apparently transitional junction with 0.8 m of flaggy, ripple-marked silty sandstone (Ashdown Beds) overlain by mottled yellow and red silts, thinly interbedded with silty sandstones in their lowest 30 to 6 cm (Wadhurst Clay).

Through Grubbero Wood [TQ 377 306], much of the first rhythm is exposed in the stream bed as flaggy sandstones interbedded with silts and siltstones. Exposures in the basal part of the rhythm at Long Plantation [TQ 3767 3086] show interbedded flaggy sandstone and grey silt with plant fragments.

An old sandstone quarry [TQ 3871 3100], north-north-west of Restlands, showed the following section in the upper part of the first rhythm:

Loose fragments of fine-grained pebble bed, consisting of ripples of coarse sand containing tiny quartz pebbles, occur in the soil debris at the base of the Wadhurst Clay east of Restlands [TQ 3878 3078] and north of Broadhurst Manor [TQ 3876 3018].

A water borehole at Horsted Keynes Station [TQ 3706 2914], sited on about the middle of the Wadhurst Clay, proved 34.8 m of Wadhurst Clay overlying 89.4 m of Ashdown Beds (Whitaker and Reid, 1899, p.55). Several sandstone beds in the top 60 m of the Ashdown Beds exceed 6 m in thickness and these may represent the arenaceous parts of four rhythms ranging from 12.8 to 16.2 m in thickness. These rhythms roughly correspond with those described at outcrop. Below 97.0 m the sandstone beds are generally much thinner. Beds of 'lignite', recorded at 80.16 and 115.2 m in association with 'brown marl-rock', are probably purplish brown, carbonaceous siltstones containing lignitic plant fragments, similar to those seen at outcrop.

A temporary exposure [TQ 3886 2854] north-east of Horsted Keynes showed flaggy sandstone overlain by a thin, ferruginous, fine-grained pebble bed which, in turn, was overlain by grey silt. The silt is thought to be basal Wadhurst Clay but it may lie at the base of one of the lower rhythms within the Ashdown Beds.

Silty beds at the base of the first rhythm produce a spring line and are marked by a good feature which can be traced from a spring in The Warren [TQ 3912 2882], via Horsted Keynes church and Ludwell [TQ 380 282] to terminate against the Danehill Fault near Parson's Wood [TQ 3757 2778]. The following section [TQ 3839 2837] within the silts, recorded in the lane leading to the church, lies close to the junction of the first and second rhythms:

A water borehole [TQ 3865 2872] north-east of Horsted Keynes church, sited near the top of the Ashdown Beds, proved these beds to 61.0 m (Buchan et al., 1940, p.17). The driller recorded 9.1 m of sandstone that passed down into 'hard clay and mottled clay' to 13.7 m. (probably silty and clayey beds at the base of the first rhythm). Below this, rhythmic alternations of sandstone and sandy clay were recorded.

Second Rhythm

The second rhythm is the most difficult to follow of those mapped. It can be traced from Neylands Wood [TQ 376 340], near Birch Farm, via New Coombe to Miry Copse [TQ 378 327], north-west of Tyes Cross, as a single feature, but from there northwards to Mayes and south eastwards to the crossing of the Crowborough anticlinal axis [TQ 391 324] two distinct features are present. In the steep-sided ghylls south of the axis, a single strong feature is again present. It is difficult to determine whether this splitting of the features represents the division of a single rhythm, or whether two rhythms are present throughout the district and the differences in their topographical expression are due to weathering. In the areas where two rhythms are known to be present they are referred to below as the lower and upper second rhythms. A lenticular bed of silty clay, up to 2 m thick, at the base of the lower second rhythm forms a small outcrop near Mayes. It passes laterally into grey silt.

A strong spring [TQ 3839 3273], north-north-east of Tyes Cross, is thrown out by the silts at the base of the upper second rhythm. The following section [TQ 3843 3275], recorded in the stream below the springs, shows the junction of these silts with the underlying lower second rhythm:

The pebble bed was traced for about 90 m north of this point, and for about 550 m to Blackdog Wood [TQ 3886 3265] to the east, becoming finer grained in both directions.

Exposures in the upper sandy part of the rhythm in the deep ghylls north-west and north-east of Wickenden Farm [TQ 3811 3195]; [TQ 3867 3172] showed 2.7 m and 2.4 m respectively of thickly and flaggy bedded sandstone. Three metres of similar beds were seen in an old quarry [TQ 3749 2877] east-north-east of Great Oddynes, adjacent to the Great Oddynes Fault.

Third Rhythm

The third rhythm crops out in a small area around Mayes, in the deep valleys on either side of that area, and in the valley north of Horsted Keynes where it is upthrown by the Great Oddynes Fault. Small exposures of thickly cross-bedded sandstone and interbedded sandstone and silts, near the bottom of the rhythm, occur in the stream bed [TQ 3770 3371] north-north-east of New Coombe.

Fourth Rhythm

The fourth rhythm crops out only in the lowest part of the valley north of Horsted Keynes and in the valley at Plaw Wood, east of Mayes. A stream section [TQ 3882 3376], 385 m east of Mayes, showed the following section, which may be at the junction of the third and fourth rhythms:

Thickly bedded sandstones exposed in the lane cutting [TQ 3911 3401], east-north-east of Mayes, are probably the lowest Ashdown Beds exposed within the present district.

Boreholes

The Ashdown Beds have been proved in a number of boreholes away from the outcrop but, with the exception of the Worth Forest [TQ 2891 3500] (see Appendix 1) and Cuckfield No.1 [TQ 2961 2731] (Lake and Thurrell, 1974) boreholes, the logs contain only poor lithological descriptions. The Worth Forest Borehole proved about 226 m of Ashdown Beds consisting of predominantly sandy and silty rhythms in the upper part, and silty and clayey rhythms in the lower part.

The topmost 41.69 m of the Ashdown Beds were penetrated in the Cuckfield No.1 Borehole, where the sequence was as follows:

The higher part of the sequence can be divided into an upper rhythm (14.4 m thick) and a lower rhythm (12.2 m thick) which may correspond with the first and second rhythms respectively of the outcrop area. Lake and Thurrell (1974) regarded these two rhythms as part of one 'cycle' which showed an upward progression through structurally mottled beds and striped beds to a pebbly sandstone unit.

Wadhurst Clay

The main outcrop of the Wadhurst Clay, 1 to 2 km wide, runs from East Grinstead via Sharpthorne to Horsted Keynes in the eastern part of the district. Inliers, some partially fault-bounded, occur at Turners Hill, in the deep valleys on either side of the Balcombe ridge, in the Ouse valley near Lindfield and at Cuckfield, in the Cockhaise Brook valley south of Horsted Keynes, and in the steep-sided valleys south of Cuckfield and Haywards Heath.

The Wadhurst Clay consists of dark grey mudstones and silty mudstones which weather to greenish grey and yellowish brown clays. Thin beds of shelly limestone and clay-ironstone, some thicker developments of siltstone, and lenticular bodies of calcareous sandstone also occur. The detailed sequence is shown in (Figure 8). Both in lithology and in thickness the Wadhurst Clay is the most laterally uniform formation in the Hastings Beds. It is probably present at depth throughout the district. Because of its obvious unsuitability as an aquifer, relatively few boreholes have been put down on the Wadhurst Clay outcrop, except near the junction with the Ashdown Beds. However, a number of boreholes that have been started on the Tunbridge Wells

Sand and which have obtained insufficient yields from that formation, have continued through the full thickness of the Wadhurst Clay to obtain additional supplies from the Ashdown Beds. The complete Wadhurst Clay sequence has been penetrated at Balcombe (about 70 m), Cuckfield (about 69.2 m), Kingscote (about 76.5 m, but possibly thickened by faulting), Worth (about 78.3 m) and, just outside the present district, at Dormans Park (about 73.2 m) and East Grinstead (71.63 m). The most completely described Wadhurst Clay sequence in the district, 64.1 m thick, is that in the BGS Cuckfield No.1 Borehole (Lake and Thurrell, 1974). Northward thinning (Figure 6) is indicated by a thickness of 34.1 m in the Collendean Farm Borehole [TQ 2480 4429], just beyond the district.

The base of the formation is taken at the base of the Top Ashdown Pebble Bed, produced by winnowing of sands at the commencement of the transgression that led to the deposition of the Wadhurst Clay. The basal 2 to 3 m of the Wadhurst Clay in the present district are siltstones, which locally form a transitional junction with the Ashdown Beds. At outcrop, the highest 5 to 6 m weather to a stiff red clay and this provides a useful aid to geological mapping. The formation is poorly exposed and can be seen only in working brickpits, and in valley-bulged stream sections where rapid downcutting removes the weathered materials.

The Cuckfield No.1 Borehole [TQ 2961 2731] proved a complete, 64.1 m-thick unweathered Wadhurst Clay sequence (Lake and Thurrell, 1974, pp.44–54) which consists almost entirely of mudstones and shales with sporadic inter-laminated siltstones. Siltstone is dominant only in a 1.2 m interval in the middle part of the formation. Clay-ironstone bands occur throughout, but are more numerous in the lowest part. At outcrop this concentration of seams has been extensively worked in open pits and minepits (known also as bell-pits) around Sharpthorne and near Horsted Keynes, shown collectively as a single band on the geological map; the seams are referred to here as the basal ironstones. Sphaerosiderite, a major source of the red colouration at outcrop in the clay, is prominent in the topmost beds and supports the interpretation that penecontemporaneous emergence and oxidation of the swamp muds occurred. At the top and in the lower two-thirds of the formation, there are bivalve shell beds consisting of disarticulated Neomiodon valves; limestones of similar content are common in the lower part of the formation. Beds with the gastropod Viviparus were noted at three levels in the lower part. Rootlet beds are numerous, and five Equisetites 'soil beds' (Allen, 1947) were noted in the borehole. At outcrop, siltstone casts of the rhizomes and rootlets of the horsetail Equisetites lyelli (Mantell) occur in growth position at more than one horizon in the upper part of the Wadhurst Clay in the district. Although individual beds have been given local names, for example High Brooms Soil Bed and Balcombe Soil Bed, they cannot by themselves be regarded as marker horizons.

Details

Turners Hill and East Grinstead area

Boreholes at East Grinstead, in the adjacent Tunbridge Wells district, indicate a thickness of about 72 m for the Wadhurst Clay (Bristow and Bazley, 1972, p.65). Of this, a maximum of about 30 m crops out in the inliers in the fault complex between Turners Hill, East Grinstead and Gravetye Manor [TQ 360 339].

Red clays at the top of the formation crop out in the long fault-bounded inlier from Fen Place to South Hill. Minepits in Target Shaw [TQ 3550 357] may have been dug for ironstone in the lowest part of the Wadhurst Clay: the stream bed [TQ 3469 3549] north east of Rashes Farm exposed an ironstone which may be at a similar stratigraphical level.

The old pits on the south side of Turners Hill are at various stratigraphical levels and were probably dug largely for marl, but a line of seven pits south of the church [TQ 338 352] are all at about the same stratigraphical level and may also have been dug for ironstone. Disturbed grey shales, faulted against Upper Tunbridge Wells Sand, crop out in Threepoint Ghyll [TQ 3354 3482].

Old pits [TQ 354 353] north-east of Great Wildgoose Wood are in red clays which appear to have been thrust over the Lower Tunbridge Wells Sand. Red shales, overlain by sandstones and silts of the Lower Tunbridge Wells Sand crop out in Rookery Wood [TQ 3524 3545]. The junction with the Lower Tunbridge Wells Sand, consisting of red clays overlain by flaggy silty sandstones, is also exposed in a nearby lane cutting [TQ 3489 3500].

In Minepit Wood [TQ 363 350], there are numerous minepits and former shallow open workings for clay-ironstone. The strati-graphical position of the ironstone there is uncertain because the outcrop is bounded by faults. It seems likely, however, that it is one of several closely spaced bands, the 'basal ironstones', that occur in the lowest part of the Wadhurst Clay. The full thickness for the Wadhurst Clay was proved to be about 76.5 m in a borehole at Kingscote [TQ 3679 3596], close to a fault.

Around Coombe Hall, Imberley Lodge, Sunshine House and in Hollybush Wood [TQ 390 353], south of Standen, the outcrop is extensively pitted. A stream bed [TQ 3825 3641] showed valley-bulged grey shales with a 0.6 m-thick bed of silty sandstone, estimated to be about 9 m below the top of the formation.

A large old pit [TQ 373 352], 320 m north of Mill Place, has worked Wadhurst Clay beneath Lower Tunbridge Wells Sand. Red clays at the top of the formation crop out in the adjacent fields and in nearby Hen Robin [TQ 377 356] and Cock Robin [TQ 381 355] woods. The 3 to 4 m-thick bed of sand within the Wadhurst Clay near Mill Place referred to by Topley (1875, p.82) is probably Cuckfield Stone.

Gravetye Manor and Horsted Keynes area

Over most of the main outcrop of the Wadhurst Clay from Gravetye Manor [TQ 360 339] to Horsted Keynes the upper part of the formation occupies slopes below the Lower Tunbridge Wells Sand escarpment and is largely obscured by downwash, solifluction and landslip material (Plate 1). The formation is well exposed in the stream sections in the deep ghylls south and west of West Hoathly, but valley bulging there makes it impossible to deduce any stratigraphy. The outcrop of the basal ironstone can be followed by means of former minepits and open workings from Birds Eye Wood [TQ 357 338], via Stockards Wood [TQ 361 337] and Tile Barn Shaw [TQ 364 337], to Giffard's Wood [TQ 369 339].

A stream section [TQ 3703 3346] north-north-west of Old Coombe showed grey shales weathering to grey and yellow clay (0.9 m), resting on the basal silty beds, which consist of flaggy pale grey siltstones with clay partings (about 1.5 m) on Ashdown Beds sandstones (see p.20).

In 1961 the Sharpthorne Brickworks pit [TQ 374 329] exposed some 8 m of beds in the lower Wadhurst Clay, including the basal siltstones. In 1983, when further notes on the section were made by Mr Worssam, the main (south and east) faces of the pit had been worked back some 100 m from their 1961 positions, and exposed up to 20 m of strata. The floor in 1983 was a near-flat surface, presumably a bedding plane, dipping south-south-west at about 1° to 2° and the high southern face was being worked in three stages, its middle part being set back about 3 m from the bottom face, and the top face about 10 m back from the middle.

The sections measured in 1961 and 1983 appear below. No correlation is implied by the numbering of the beds. At the later date no Neomiodon-rich bed or plant-rich horizon corresponding to those recorded in 1961 in the lowest part of the Wadhurst Clay were noted and, in the absence of such marker bands, matching of the two sections can only be attempted with some uncertainty (Figure 9), on the basis of ironstone seams.

Composite section recorded in 1983

Section recorded in 1961

Fine-grained sandstone (Ashdown Beds) was exposed in a ditch close below the pit floor. The brick pits sections show a gradual passage upwards, with some alternation, from silty mudstone with plant detritus and ironstone bands to less silty and non-silty clays with Neomiodon shell layers, suggesting a waning terrestrial influence on sedimentation. The soft powdery condition of Neomiodon shells in the upper part of the succession may result from a reversion to calcite from an originally aragonitic preservation.

The working faces of the pit have at times intersected old ironstone workings, both open pits and minepits, in Grinstead Wood and the adjacent field. Sections through minepits, 3 to 4 m wide and up to about 12 m deep, were conspicuous on the south face in 1983 (Figure 9). Their absence from the middle part of the top stage of this face appeared to be due to the face being beyond the southern limit of the worked area. The minepits were described by Worssam and Swift (1987), who recorded 12th and 13th century timber (radiocarbon dates) in one of the pits, which makes them the earliest dated minepits in the Weald.

Old pits in Mare Pit Wood [TQ 375 326], adjacent to Grinstead Wood, and at Courtlands [TQ 378 323] were probably dug for the basal ironstones.

The basal ironstones were extensively worked by means of shallow open pits and minepits in Sloe Garden Wood [TQ 3710 3177] to [TQ 3753 3214]. At the northern end of the wood [TQ 3755 3219] a stream section showed valley-bulged grey shales thinly interbedded with siltstone and containing a thin Neomiodon limestone.

In a farm road at Deanlands Farm [TQ 3782 3156], 1.7 m of flaggybedded siltstone with clay partings were seen to rest on the Top Ashdown Pebble Bed (see p.20). A stream section [TQ 3711 3059] near Horsted House showed 0.6 m of deeply weathered stiff yellow clay containing siltstone fragments, resting on 3 m of mottled yellow and red silt interbedded, at the base, with thin beds of silty sandstone, resting on ripple-marked silty sandstones (Ashdown Beds). The apparently transitional boundary and unusual colouring seen here were not recorded elsewhere in the district. The following section was recorded along a tributary brook [TQ 3692 3018]; the beds dip westwards at about 50 to 70° and are affected by minor crumpling and overturning:

A stream section [TQ 3767 3004] to [TQ 3782 3011] near Ravenswood showed valley-bulged grey shales overlying siltstones which, in turn, rested on sandstones of the Ashdown Beds. The outcrop of the basal ironstones from Ravenswood, through Restlands and Broadhurst Manor, to the Great Oddynes Fault is marked by many former pits.

Red, purple and brown clays crop out around the small outlier of Lower Tunbridge Wells Sand near Cinder Hill and on top of the ridge at Cinder Hill itself. Minepits in Leamland Wood [TQ 374 293], on the south side of the outlier, appear to have been dug for ironstone near the top of the formation.

A water borehole [TQ 3706 2914] at Horsted Keynes Station began with a dug well for 13.72 m and then penetrated 21.03 m of Wadhurst Clay to 34.75 m (see also p.23). The Wadhurst Clay contained ironstone nodules at 24.7 to 25.9 m and at 33.8 to 34.7 m and bands of shelly limestone between 25.9 and 33.8 m.

Almost continuous exposures in valley-bulged shales and mudstones are exposed in the stream course in Ludwell Ghyll and Hook Ghyll, on the west side of Highbrook, between Hammingden Wood [TQ 359 302] and Ashurst Wood [TQ 363 317]. Clay-ironstone nodules and thin beds of Neomiodon limestone are present in the shales at several places in Hook Ghyll e.g. [TQ 3622 3107]; [TQ 3620 3157].

Inliers between Handcross and Balcombe

The junction with the Lower Tunbridge Wells Sand is marked by a strong spring line in the valley near Oldhouse [TQ 277 293]. Two small inliers, largely obscured by sandy Head and by landslip, occur in the valley floors in Northland Wood [TQ 289 297] and in Seyron Wood [TQ 295 292], north-west and south-east of Northland Farm respectively.

An almost complete Wadhurst Clay sequence was proved in a shaft and boreholes at Balcombe Pumping Station [TQ 290 313] (Whitaker, 1911, pp.155–156). The records indicate a probable thickness for the Wadhurst Clay of about 73.7 m, referred to as "blue marl", "shelly beds" and "hard rock" (probably the basal siltstones). The full Wadhurst Clay thickness proved in the Worth Forest Borehole, about 1.6 km to the north, is 78.33 m.

Approximately the top 24 m of Wadhurst Clay is exposed in the inlier in the valley of the stream which runs from Balcombe Station southwards to the River Ouse. A strong spring line at the junction with the Lower Tunbridge Wells Sand has contributed to the sandy wash and numerous small landslips which obscure the upper part of the Wadhurst Clay. Olive and brown clays have been worked in old clay pits in the top 7.5 to 9 m of the formation, possibly in part for ironstone. Extensive exposures of valley-bulged shales and mudstones occur in the stream bed between Pilstye Wood [TQ 3094 2910] and Balcombe Station. In places e.g. [TQ 3068 2973], the shales are rich in ostracods and bivalves, and contain thin beds of Neomiodon limestone.

Allen (1947, p.311 and 1959, p.306, fig.13) first recorded his 'Balcombe Equisetites lyelli Soil-Bed' in a road cutting [TQ 3108 2900] north-east of Pilstye Farm, at an horizon shown on the Old Series geological map as high in the Grinstead Clay. He later (1960a, p.25) interpreted the bed as being high in the Wadhurst Clay (i.e. at a stratigraphical level similar to that of the High Brooms Soil Bed); this was confirmed by the present survey. The soil-bed is about 7 m below the top of the Wadhurst Clay.

On the western side of the Paddockhurst Park Fault, in the stream valley [TQ 317 330] east of Monks, 6 to 7.5 m of the topmost Wadhurst Clay, consisting of red and grey shales and mudstones, are faulted against grey shales and mudstones of the Grinstead Clay. Numerous sections occur in the stream bed but all are intensely disturbed by valley bulging and by the fault, making the precise junction of the two formations difficult to place (see p.92). A stream-bed section [TQ 3167 3306], at the northern end of the inlier, shows the contact of the Wadhurst Clay with the Lower Tunbridge Wells Sand to be affected by a small fault: disturbed grey shales are juxtaposed with hard flaggy sandstones and pale grey silts. Elsewhere in the inlier this boundary is undisturbed and is marked by red clays.

Inliers between Shell Brook and Ardingly Brook

Between Balcombe Mill [TQ 3180 3043] and the confluence with the Ardingly Brook [TQ 3309 2914] the Wadhurst Clay crops out in the lower part of the steep-sided valley of the Shell Brook but is largely obscured by landslip. Up to 27 m of beds are present.

In the valley of the Ardingly Brook, the outcrop is also largely obscured by landslip and downwash. The boundary with the Lower Tunbridge Wells Sand is marked by a prominent feature and a spring line. A section in Long Wood [TQ 3376 3223] showed up to 2.4 m of sandy Head resting unevenly on 12 m of valley-bulged, red- and greenish yellow-mottled clays and grey shales. The shales contain thin beds of calcareous siltstone and nodules of clay-ironstone.

Brook Street and Paxhill Park area

Two small inliers of Wadhurst Clay adjacent to the Borde Hill Fault at Brook Street [TQ 305 266]; [TQ 311 266] expose red, grey and yellow clays near the top of the formation.

North west of Brook Street, the following complete Wadhurst Clay sequence was proved in the Cuckfield No.1 Borehole [TQ 2961 2731] (Lake and Thurrell, 1974, pp.44–54):

Between Borde Hill [TQ 324 266] and Paxhill Park, up to 24 m of the upper Wadhurst Clay crops out between the Borde Hill and Lind-field faults, largely covered by downwash from the Lower Tunbridge Wells Sand. Between the railway line [TQ 3275 2672] and the entrance to the deep cutting on the long-abandoned Lindfield to Uckfield railway [TQ 3358 2686], the top of the formation is marked by a strong spring line and a good feature. There is no clear evidence here of the precise position of the Borde Hill Fault, which throws Wadhurst Clay against Weald Clay. A low feature, the crest of which runs along Copyhold Lane from west of the railway [TQ 3306 2688] to the eastern end of the lane [TQ 3385 2704], is probably formed by a thin calcareous sandstone in one of these formations.

The section in the deep cutting on the Lindfield to Uckfield railway, figured by Topley (1875, fig.15, p.87), is now largely obscured. The section was incorrectly classified by Topley as Upper Tunbridge Wells Sand and Grinstead Clay: it shows the Lower Tunbridge Wells Sand (thickly bedded sandstones and silts) overlying Wadhurst Clay (red clays).

South of Sugworth Farm [TQ 327 262], the Wadhurst Clay consists mainly of red clays near the top of the formation; it was formerly dug for brick-making [TQ 3265 2597].

Cockhaise Brook

About 18 to 21 m of Wadhurst Clay crops out in the valley of the Cockhaise Brook and its tributary between Holywell Halt [TQ 370 277] and Cockhaise Mill Farm. Red clays have been worked in a number of old pits in Goddenwick Wood [TQ 365 276]. The reddening appears to affect an unusual thickness of beds (12 to 15 m) below the top of the Wadhurst Clay, but the complexity of the faulting here makes any stratigraphical conclusion uncertain. Some of the red clay in the lower part of the wood [TQ 3665 2770] may be interpreted as Upper Grinstead Clay faulted against Wadhurst Clay.

The most important section in the upper part of the Wadhurst Clay within the Horsham district is exposed in the lower workings of Freshfield Lane Brickworks, on the north side of a tributary valley [TQ 3815 2656]. This pit shows a remarkable section through part of a valley bulge in which the dip of the beds steadily increases to vertical towards the valley axis (Figure 27) and (Figure 28). The vertical, stratigraphically lowest part of the sequence contains minor crumples and disturbances, and the thicknesses below Bed 10 in the following composite section are estimated.

Drewitts and Cuckfield area

The most westerly inliers of Wadhurst Clay occur in three steep-sided valleys between Drewitts [TQ 240 250] and Wykehurst Park. The boundary with the Lower Tunbridge Wells Sand was traced in each by means of a good feature and a spring line. In the inlier 365 m east of Drewitts, valley-bulged grey shales containing a bed of pale grey, fine- to medium-grained sandstone, 0.9 m thick (dip 4° NNW), were seen in the stream bed in Port Wood [TQ 2429 2469]. A section in a landslip [TQ 2535 2457] showed 1.8 m of silty wash overlying 1.2 m of disturbed khaki and grey clay close to the boundary with the Lower Tunbridge Wells Sand.

Between Wykehurst Park and Cuckfield Park, the topmost 18 to 20 m of the Wadhurst Clay is exposed in a large inlier, bounded on its southern side by a fault complex. The boundary between the Lower Tunbridge Wells Sand and the Wadhurst Clay is marked by a strong spring line and is commonly obscured by downwash and small landslips.

Viviparus limestone, in slabs up to 8 cm thick, crops out in the stream bed [TQ 2777 2437] west of Broxmead Lane, in valley-bulged grey shales. Farther upstream [TQ 2750 2453], stratigraphically higher, disturbed shales contain a 0.30 m-thick bed of calcareous, fine-grained sandstone. Exposures of valley-bulged shales and siltstones with Neomiodon are almost continuous from there to Seven Acre Hanger [TQ 2725 2500].

Two shelly beds were dug from a trench along Broxmead Lane, one of Neomiodon limestone at [TQ 2803 2443] and the other of Viviparus limestone, some 55 m to the south.

A temporary exposure [TQ 2872 2512] near The Wyllies showed the following section through the topmost beds of the formation:

The position of the soil bed suggests that it is at a similar stratigraphical level to the High Brooms Soil Bed and those at Freshfield Lane Brickworks (Beds 20 and 21).

The Cuckfield Hospital (Workhouse) Well [TQ 3082 2565] proved Wadhurst Clay below 36.27 m (Whitaker and Reid, 1899, p.22). The top of the Ashdown Beds is difficult to place and may fall within the interval 95.40 to 105.46 m, thus giving a thickness for the Wadhurst Clay of between 59.13 m and 69.19 m. In the Cuckfield No.1 Borehole [TQ 2961 2731], approximately 1.6 km to the north, 64 m of Wadhurst Clay were proved.

The small inlier [TQ 305 230] against the Henfield Wood Fault probably exposes the top 12 to 15 m of the formation. A stream section [TQ 3035 2998] showed the Wadhurst Clay faulted against the Upper Tunbridge Wells Sand; in the former, about 6 m of disturbed grey shales contain two beds of Neomiodon limestone.

A small inlier [TQ 323 224] against the Sandrocks Fault exposes valley-bulged grey shales containing an E. lyelli soil bed. The mode of preservation of this bed exposed at [TQ 3225 2238] and its stratigraphical position, estimated to be 6 to 7.5 m below the top of the formation, resemble that of the soil bed near The Wyllies.

Two small, fault-bounded inliers occur in the valleys running through Penland Wood [TQ 324 250] and Harlands Wood [TQ 324 246].

Lower Tunbridge Wells Sand

Throughout the district, the Lower Tunbridge Wells Sand can be divided into two parts. A lower unit of thinly interbedded silty, fine-grained sandstones and subordinate (but appreciable) amounts of siltstone, and rare beds of clay and silty clay; and an upper unit (the Ardingly Sandstone) composed largely of massive and thickly bedded, fine- and medium-grained sandstones (Figure 10). Throughout much of the district the Ardingly Sandstone is composed largely of 'sandrock', a clean white or greyish white, soft, quartzose sandstone.

The formation crops out in an arcuate tract between East Grinstead and Ardingly where it occurs, for the most part, in steep valley sides between ridges capped by Grinstead Clay. It is best seen in the wooded ghylls between Handcross and West Hoathly, where the 'sandrock' facies of the Ardingly Sandstone gives rise to impressive lines of crags. In the southern part of the district the Lower Tunbridge Wells Sand outcrop is much broken by faulting and, particularly south-east of Haywards Heath where the sandrock' facies is rare, it is less well exposed.

The boundary with the underlying Wadhurst Clay is commonly obscured by landslip or downwash, but it is thought, from soil and auger-hole data, to be everywhere marked by a sharp lithological change from red-stained mudstones below to interbedded siltstones and silty sandstones. The base of the Ardingly Sandstone is also rarely exposed, but where seen it is sharp and possibly erosional (Plate 2). The contact with the overlying Grinstead Clay is well exposed in old stone quarries and is taken at the base of the Top Lower Tunbridge Wells Pebble Bed (see p.17). This distinctive marker is well developed in the eastern part of the district, but in the west it is represented only by a single line of ripples of coarse-grained sand.

The Ardingly Sandstone undergoes broad lithological changes within the district, becoming gradually finer grained overall when traced southwards along its outcrop. In the East Grinstead area, stringers of small quartz and quartzite pebbles are common at many levels in the sandstone, but these are rare south and west of the River Medway. The pebbles become larger and more common when the Ardingly Sandstone is traced eastward to Tunbridge Wells. Between the River Medway and the River Ouse, the Ardingly Sandstone is mostly made up of the same range of sandstone lithologies, and this is reflected in its bedding features. At many of the natural sandrock outcrops, almost parallel bedded units are overlain by shallowly trough cross-bedded sandstones, which are capped by an apparently massive bed which contains wisps of contorted bedding. This last weathers to produce the bulges and overhangs which add greatly to the scenic nature of the crags, and which makes them so attractive to rock climbers. It appears to be a widespread feature and to be everywhere at a similar stratigraphical level throughout the area, from Balcombe to East Grinstead and beyond. Its disturbed bedding may therefore have resulted from seismic activity, and it has here informally been termed the 'earthquake bed'.

Locally, as in the Turners Hill area, much of the upper part of the Ardingly Sandstone, including the stratigraphical equivalents of the sandrock crags, consists of distinctively trough cross-bedded (festoon-bedded) sandstone which may occupy a large channel. In the West Hoathly area Allen (1962) has recorded large, shallow, trough cross-bedded structures ('scoops') in the highest part of the Ardingly Sandstone, but it is not known how common or widespread such structures are because the highest 3 to 5 m of the member, the beds between the sandrock crags and the base of the Grinstead Clay, are rarely exposed.

South of the River Ouse, the Ardingly Sandstone is finer grained and has a higher silt content: it is mostly thickly or flaggy bedded and has few natural outcrops. This lithological change seems to occur over a short distance in the complexly faulted area between Lindfield and Cuckfield, and may be related to penecontemporaneous faulting. The beds attributed to the Ardingly Sandstone in the Cuckfield No.1 Borehole [TQ 2961 2731] (Lake and Thurrell, 1974) within this fault belt consist of fine-grained sandstones and siltstones with disturbed bedding structures throughout (Plate 3). They contrast markedly with the Ardingly Sandstone outcrops close to the north.

The Lower Tunbridge Wells Sand is between 25 and 33 m thick over much of the outcrop, thinning to 18 to 24 m southeast of Haywards Heath. A few boreholes downdip from the outcrop have penetrated part or all of the formation, but the records of these, with the exception of that of the continuously cored Cuckfield No.1 Borehole, are based on drillers' logs and cannot be interpreted in detail. The Crawley Pumping Station Borehole [TQ 265 359] penetrated the full thickness of the formation, but the record is not sufficiently informative for it to be clearly defined. Red and grey sandstones at 234 to 266 m depth may represent the Ardingly Sandstone, but this and the overlying Grinstead Clay and Upper Tunbridge Wells Sand appear to be abnormally thick (Edmunds, 1928, pp. 78–79).

The full thickness of the formation was also penetrated in boreholes at Worth Forest [TQ 2891 3500] (27.8 m), Bolney [TQ 2801 2427] (23.9 m) and Cuckfield [TQ 2962 2729] (26.5 m). A site-investigation borehole at Bridleshaw Wood [TQ 332 286], near Ardingly, proved a thickness of 27 m.

Details

East Grinstead area

The Lower Tunbridge Wells Sand is about 33 m thick in this area, of which the upper 15 to 18 m is Ardingly Sandstone. Boreholes in the adjacent Tunbridge Wells district, at Dormans Park [TQ 397 405] and at Placelands, East Grinstead [TQ 3932 3841], penetrated 32.6 and 32.3 m of Lower Tunbridge Wells Sand respectively. A water borehole [TQ 3895 3870] at London Road, East Grinstead, proved 17.4 m of Lower Tunbridge Wells Sand, described as 'red sand-rock' (Whitaker and Reid, 1899, p.28); a second borehole at the same site (Edmunds 1928, p.88) encountered 13.6 m of 'hard rocky sand'. These beds are overlain by Grinstead Clay and are clearly the Ardingly Sandstone.

Exposures in the lower part of the formation are rare in the district, but the Ardingly Sandstone is well exposed in road and rail cuttings and in old quarries. Ardingly Sandstone has been worked from beneath a capping of Grinstead Clay in a number of old pits, all now completely degraded, between the Kennels and Baldwins Hill. A pit [TQ 3879 3984] north-east of Baldwins showed 2.4 m of flaggy and thickly bedded, brown, ferruginous sandstone overlying 1.8 m of massive, grey-white, fine-grained sandstone. When in work, both pits were presumably entirely in massive sandstone and the flaggy sandstones now visible are probably only a weathering feature.

A line of degraded stone pits runs from near East Grinstead station [TQ 3864 3814] through Garden Wood and Coles Wood to High Grove. Streams in Garden Wood [TQ 383 380] have cut small gorges in sandrock and thickly bedded sandstone. Exposures of thickly and flaggy-bedded silty sandstone interbedded with siltstones in the stream bed [TQ 3789 3773] to [TQ 3798 3778] in Coles Wood are in the lower part of the formation, close to the boundary with the Wadhurst Clay. The highest part of the Ardingly Sandstone has been worked in a number of pits at High Grove, where the following section [TQ 3789 3736] was recorded:

Sections in the sunken road [TQ 3834 3740] to [TQ 3843 3746], adjacent to Brook House, showed cambered sandstones with valleyward dips of up to 40° (see Chapter Six); these are from the upper part of the Ardingly Sandstone in a position stratigraphically higher than their present outcrop position suggests. The following composite section was measured along the north side of the cutting:

The highest 2.4 m of this section were exposed in a degraded quarry [TQ 3845 3751] at the northern end of the cutting. A carbonaceous horizon with ferruginous rootlets below it, described at this locality by Allen (1947, p.310–311) as the East Grinstead Soil Bed, is no longer visible.

Small crags of sandrock crop out on the steep Ardingly Sandstone feature between Imberley Lodge [TQ 3821 3662] and Fonthill [TQ 3824 3611]. About 5 m of massive, trough cross-bedded sandstone, showing large intersecting troughs 0.3 to 0.6 m deep, were exposed in the sunken road [TQ 3882 3622] near Sunshine House. The beds there and in an adjacent farm track [TQ 3898 3614] have camber dips up to 7°. An old quarry [TQ 3883 3569] at Standen, at about the same stratigraphical level, exposed 6 m of massive, grey-white and brown, trough cross-bedded, fine-grained sandstone. A small exposure in a farm road at Standen [TQ 3907 3563] showed 1.2 m of cambered flaggy sandstone close to the boundary with the Wadhurst Clay. Flaggy and thickly bedded sandstones at a slightly higher stratigraphical level, but still within the lower part of the formation, were noted in the roadside [TQ 3864 3531] nearby.

An old quarry at Saint Hill 3836 [TQ 3595] showed 4.5 m of grey-white and brown, massive but fissile-weathering, cross-bedded, fine-grained sandstone with large shallow troughs in 0.2 to 0.6 m units. Long vertical carbonaceous traces, probably roots, occur in the upper part of the section.

A line of sandrock crags up to 6 m high extends from near Ridge Hill Manor [TQ 3708 3580] to east of Kingscote House [TQ 3738 3625]. An old quarry at Hazleden [TQ 3748 3666] exposed the following section near the top of the Ardingly Sandstone:

Ardingly Sandstone has been worked for building stone in a number of large pits, now all degraded, from beneath a capping of Grinstead Clay, between Saint Hill and Ridge Hill Manor and between Ridge Hill Manor and Hazleden Cross. Similar old workings occur between Kingscote House and Tilkhurst. The following section, recorded in an old pit [TQ 3708 3642] near Kingscote House, showed an unusual contact between the Grinstead Clay and the Ardingly Sandstone:

The pellet bed, which contains angular, flattened and deformed clasts of mudstone, siltstone and soft sandstone, is probably a local development. The typical lithology of the Top Lower Tunbridge Wells Pebble Bed appears to be absent over only a very small area around this locality. The pebble bed is well developed between there and Hazleden Cross, at High Grove, between Hazleden Cross and Ridge Hill (fine-grained), and between Ridge Hill and Saint Hill (fine-grained) where it can be traced in the soil by means of augering and soil fragments. It was not recorded between Kingscote House and Tilkhurst, but north of Tilkhurst it is again present.

The following section was recorded in an old stone quarry at Tilkhurst [TQ 3691 3722]:

Former sandstone quarries at Hurley Farm [TQ 3658 3635] and 500 m from the farm [TQ 3693 3603] showed 3.7 and 3.0 m respectively of massive, cross-bedded sandstone near the base of the Ardingly Sandstone.

The Top Lower Tunbridge Wells Pebble Bed is well developed northwards from Fen Place Mill to the Three Bridges railway where the underlying sandstone has been worked in several pits. The following section [TQ 3647 3613] was recorded at Furze Field, south of the mill:

Sandrock crags, up to 4.5 m high, crop out in the Holms [TQ 3629 3549], south-west of Kingscote Station. Small exposures of thickly bedded sandstone, disturbed by faulting, crop out in Holstein Wood [TQ 3593 3524], west of The Holms. A borehole at Tickeridge Farm [TQ 3615 3520], Kingscote, was sited on steeply dipping (up to 50°) Lower Tunbridge Wells Sand close to a fault and, although 35 m deep, probably penetrated only about 24 m of beds within the formation. The strata encountered were described as sandstones and clay with lesser amounts of ironstone and sandy clay (Buchan et al., 1940, p.12).

A line of natural sandrock crags extending from south of Standen [TQ 3902 3515] westwards towards Mill Place culminates in the impressive Stone Farm Rocks [TQ 3800 3477] to [TQ 3814 3477]. These rocks, up to 7.5 m high (Front Cover), show the threefold division of bedding features typical of many of the sandrock outcrops in the Horsham and Tunbridge Wells districts. A basal unit of almost parallel-bedded sandstones is overlain by trough cross-bedded sandstones in which the individual troughs are shallow (typically 0.2 to 0.4 m) but very broad (several metres across). This unit is capped by a thick, apparently massive sandstone, which contains wisps of distorted bedding (the 'earthquake' bed) and which weathers to produce the bulges and overhangs. The beds hereabouts dip 10° northward due to faulting. The highest bed visible probably lies about 4.5 m below the base of the Grinstead Clay.

Sandrock forms small crags at Mill Place and has been quarried near the railway [TQ 3719 3462]. This and slightly higher beds were seen in the adjacent railway cutting [TQ 3727 3465] where 5.5 m of massive, trough cross-bedded, fine-grained sandstone were exposed. The top 1.2 m contained lenses and stringers (12 to 25 mm thick) of tiny quartz pebbles (about 2 mm across) and two impersistent plant-rich clay seams, up to 25 mm thick. This is the most southerly locality within the district at which pebbles have been recorded in the Ardingly Sandstone in such abundance.

Pebbly, thickly bedded sandstones crop out in the stream bed [TQ 3645 3489] in Mill Place Wood. An old quarry [TQ 3687 3473] in the same wood showed 1.6 m of grey and brown sandrock, which included a 25 mm-thick bed of fissile, carbonaceous, plant-rich sandstone.

Ardingly Sandstone has been quarried in old pits near Rashes Farm [TQ 3474 3526]; [TQ 3527 3547], the first in fissile (probably weathered), festoon-bedded sandstones near the top of the formation, the other in thickly bedded sandstones near the base.

Turners Hill area

The full thickness of the Lower Tunbridge Wells Sand cannot be directly measured in this area because of faulting. It is estimated to be about 30 m, of which about 18 m is the Ardingly Sandstone.

The festoon-bedded facies of the Ardingly Sandstone, apparently restricted to the upper part of the member in the East Grinstead area, is much thicker in the Turners Hill area and appears to have partly or wholly replaced the underlying sandrock facies. Indeed, there is no natural sandrock crag or quarry in sandrock around Turners Hill, and possibly this facies is absent, so that the festoon-bedded sandstones rest directly on the thickly bedded sandstones of the lowest part of the member.

Festoon-bedded sandstones are exposed in a number of quarries and road sections along the crest of the Turners Hill ridge. One old quarry [TQ 3330 3511] showed festoon-bedded, fine-grained sandstone (1.8 m) passing up into thinly bedded sandstone (3 m), while another [TQ 3384 3541], close to Turners Hill Church, and roadside exposures [TQ 3368 3532] 90 m south-west of the church, showed up to 2.5 m of festoon-bedded sandstone; the last-mentioned locality is figured by Allen (1962, fig.4, p.241). Similar roadside sections were noted in Turners Hill village [TQ 3406 3550]; [TQ 3416 3567] and in a small quarry [TQ 3449 3579] on the east side of the village at Burleigh Farm. At this last locality, 0.75 m of brown festooned sandstone, similar to that in the village, rested on the rippled top of 0.75 m of grey and white sandstones with more gentle, open festoon-bedding.

A section in a farm road [TQ 3475 3615], 550 m west-north-west of Fen Place, showed interbedded flaggy silty sandstones and grey silts near the base of the Lower Tunbridge Wells Sand. The top of the Ardingly Sandstone, consisting of ripple-marked, thickly bedded sandstone, is exposed in the stream bed [TQ 3446 3651] south of The Grange, where it is faulted against Wadhurst Clay. The junction with the Grinstead Clay there is obscured by slipped material.

Ardingly Sandstone has been worked from beneath a Grinstead Clay capping in a number of small pits [TQ 3265 3485] to [TQ 3293 3527] near The Grove, and sandstones at a slightly lower level have been extensively worked in nearby Quarry Wood [TQ 329 355]. A small exposure [TQ 3285 3543] near the top of one of these latter workings, showed 0.9 m of thinly bedded micaceous sandstone with plant fragments. The extensive nature of the workings suggests that this friable material overlies a more massive sandstone which was worked for building purposes.

Almost continuous sections of the upper Ardingly Sandstone, consisting of flaggy and thickly bedded, ripple-marked sandstones, were seen in the stream bed downstream from Tulleys Farm as far as Yewtree Cottage [TQ 3297 3586] to [TQ 3266 3619].

The topmost Ardingly Sandstone is well exposed in a stream section on the north side of Standinghall Farm [TQ 3194 3561] to [TQ 3146 3557]. The following composite section was measured at the western end:

The following section in the bed of the adjacent stream [TQ 3143 3551], north-west of the farm, serves to illustrate the variable nature of these beds over a short distance:

Samples of the pellet bed from this locality were figured and their petrology described by Taylor (1963, pp.16–17 and 23–24). In addition to the clasts noted above, he recorded pellets of calcite mudstone, irregular spastolithic bodies of 'chamositic' (berthierinitic) clay and flattened and undistorted 'chamosite' ooliths.

Inliers between Handcross and Balcombe

The full sequence of the Lower Tunbridge Wells Sand, there about 30 m thick, crops out in the two large inliers near Ditton Place and Northland Farm but, as elsewhere, only the Ardingly Sandstone is well exposed. The upper part of the Ardingly Sandstone is exposed in small inliers near White House and near Cooper's Corner Farm.

The best section showing the base of the Ardingly Sandstone within the Horsham district is that exposed in a stream gorge [TQ 2823 2974] west of Ditton Place (Plate 2), where the following composite section was measured:

Crags of cambered sandrock, up to 6 m high, occur in Jack Reedings Wood [TQ 2752 2966] to [TQ 2766 2993] and in Pookchurch Wood [TQ 2694 2957] to [TQ 2730 2952], 450 m east-north-east of Nymans.

Several pits have been dug through the lower part of the Grinstead Clay to win the Ardingly Sandstone between near Nymans [TQ 2723 2941] and Dencombe Farm [TQ 2936 3016]. An old quarry [TQ 2825 2922] showed 3 m of massive, grey-white sandrock dipping at 7° to the south-south-east; another, at Woodlands [TQ 2725 2983], exposed 2.5 m of sandstone with thick, trough cross-bedded units. The Top Pebble Bed was not recognised in this area. If it is present here, it is likely to be represented as a pellet rock or as ripples of coarse sand.

Natural crags of cross-bedded sandrock have been extended by quarrying in the small inlier [TQ 299 290] north-east of The White House. About 4.6 m of cross-bedded, brown and grey sandrock are visible. Similar small crags have been worked in the inlier in Seyron Wood [TQ 295 291], on the north-west side of The White House. Sand-rock crops out and has also been quarried in the sides of a small dry valley [TQ 292 297] at Northland Farm.

The top of the Ardingly Sandstone, comprising ripple-marked flags, was seen in the stream bed [TQ 2970 3072] 260 m south of Great Cooper's Corner Farm, and downstream as far as Casteye Wood [TQ 3016 3078]. They are overlain by cambered grey shales and clays of the Grinstead Clay, which obscure the precise junction of the two formations. A pellet breccia from this inlier (Michaelis in Allen, 1959, p.304) has been interpreted by Allen (1959, fig.12) as a lateral equivalent of the Top Lower Tunbridge Wells Pebble Bed.

Balcombe area

The Lower Tunbridge Wells Sand is about 30 m thick around Balcombe, and the Ardingly Sandstone, well exposed both as picturesque crags and in old quarries on the flanks of the Balcombe ridge, comprises the upper 18 m of the formation. The top of the Ardingly Sandstone has been worked from beneath a capping of Grinstead Clay in a large number of pits in the Balcombe district, all of which are now completely degraded. Such pits occur between Balcombe Lake and West Hill [TQ 3184 3112] to [TQ 3286 3015], near Balcombe Place [TQ 3242 2938], between Bridleshaw Wood and Coney Gill [TQ 3323 2870] to [TQ 3193 2835], between Stone Hall and Bowder's Cottages [TQ 3198 2866] to [TQ 3146 2920], between Pilstye Wood and the entrance to Pilstye Farm [TQ 3068 2892] to [TQ 3108 2853] at Upper Pilstye [TQ 3039 2864], near Northland Farm [TQ 2949 2970] and near Great Coopers Corner Farm [TQ 2990 3079].

The best section in the Ardingly Sandstone in this area is exposed on the eastern side of the railway cutting at Balcombe Station [TQ 3068 3018] to [TQ 3074 2984] where the following composite section was measured:

The general dip is gently northward, but many cambered sandstone blocks have dips of about 12° and are separated by widened joints which have vertical displacements of up to 0.9 m.

Another section in the railway cutting [TQ 3054 3046], 365 m north of the station, showed:

Much of Balcombe village is built on alternations of sandstone, siltstone and silty clay that crop out in the fault-bounded block between the Balcombe House and Paddockhurst Park faults. The beds in this area are poorly exposed, except for a stream section [TQ 3132 3066] east-south-east of Balcombe House, where flaggy and massive, fine-grained sandstones alternate with thick beds of fawn and brown mottled silts and clayey silts. Exposures of similar silts have been noted in temporary sections in the village. The lithology of these beds is in such marked contrast to that of the Ardingly Sandstone of the nearby station and Balcombe Mill exposures, and so similar to that of the Upper Tunbridge Wells Sand of the nearby Balcombe Forest, that their stratigraphical position might seem beyond dispute. Such an interpretation would, however, require this block to be enclosed within a trapezium of self-cancelling faults, all with downthrows in excess of 60 m. These strata have therefore been tentatively mapped as Ardingly Sandstone and are presumed to infill a channel or other large sedimentary structure which has locally removed the sandstone facies.

A borehole at Oldland Nurseries [TQ 3099 2998], close to the Balcombe House Fault, was probably correctly classified by Buchan et al. (1940, p.16) as penetrating Lower Tunbridge Wells Sand, described as 'sandstone and sandy clay', to 23 m. Boreholes at Balcombe Waterworks [TQ 290 313] proved a complete sequence of Lower Tunbridge Wells Sand about 30 m thick (Whitaker and Reid, 1899, p.9; Edmunds, 1928, p.49). The nearby Worth Forest Borehole [TQ 2891 3500] probably proved 27.8 m of Lower Tunbridge Wells Sand, from 66.1 to 93.9 m depth, described as 'marls and sand'.

A line of small crags in Rowhill Wood [TQ 3029 2941] to [TQ 3040 2912] shows about 6 m of cross-bedded, greyish white sandrock with thin cross-bedded units, overlain by a massive unit with traces of disturbed bedding. The same beds crop out in the sunken lane [TQ 3032 2972] at the north end of the wood, and up to 10 m of cross-bedded sandstones were seen in old quarries nearby [TQ 3040 3001]; [TQ 3052 2904]. Another quarry [TQ 3022 2972] showed the following section:

The top of the siltstone was obscured, but no fragment of pellet bed or pebble bed was seen.

The contact between the Ardingly Sandstone and the Grinstead Clay was also seen in old quarries at the entrance to Pilstye Farm [TQ 3114 2855] and in Coney Gill [TQ 3171 2822]. The first of these sections was described in detail by Allen (1959, p.304–305, fig.13). The Top Lower Tunbridge Wells Pebble Bed is represented by a thin seam of coarse sand which separates the basal Grinstead Clay siltstones from massive siltstones and silty sandstones of the Ardingly Sandstone. The second section is separated from the surrounding outcrops by faults and its stratigraphical position is uncertain. However, it is interpreted as showing the same junction as that described above:

Interbedded siltstones and sandstones of the lower part of the formation were seen in the stream bed [TQ 3148 3327] to [TQ 3166 3307] south of Worth Priory. The lowest of these exposures is close to the base of the formation and shows thinly and flaggy-bedded silty sandstones resting on cream siltstones, which are faulted against the Wadhurst Clay. Similar sections, all disturbed by the Paddockhurst Park Fault, occur along the stream bed in Balcombe Rough [TQ 3193 3357] to [TQ 3188 3342] and in The Warren [TQ 3165 3246] to [TQ 3171 3210].

The following section in the upper part of the Ardingly Sandstone was recorded in a stream section [TQ 3122 3249] to [TQ 3137 3246] 550 m south-south-east of Monks:

Crags of sandrock, disturbed by cambering and landslip, occur in Tilgate Wood [TQ 3301 3048] to [TQ 3302 3138] and in the valley of the Sheel Brook near Balcombe Mill [TQ 3174 3021] to [TQ 3176 3056]. At Balcombe Mill [TQ 3174 3049] natural outcrops have been extended by quarrying and about 11 m of thinly and thickly trough cross-bedded, greyish white sandrock is visible. As elsewhere, the sandrock is poorly sorted at some levels and contains lenticular beds with coarser sand, plant debris and mica flakes. An old quarry [TQ 3178 3064] north of the mill shows a similar section with 2 m of interbedded sandstone and silty sandstone overlying 3.2 m of white cross-bedded sandrock.

Ardingly area

The Ardingly Sandstone takes its name from the fine natural outcrops of sandstone which occur along the valley sides in the parish of Ardingly and neighbouring areas. The records of boreholes at Pearcelands [TQ 345 327] and Ardingly College [TQ 339 285] indicate that the Lower Tunbridge Wells Sand is about 30 m thick in this area; only the 'sandrock' facies (in the valley sides) and the upper part of the Ardingly Sandstone (in numerous old pits on the Grinstead Clay capped ridge) are well exposed.

The top of the Ardingly Sandstone has been quarried beneath a capping of Grinstead Clay in several pits around Newhouse Farm [TQ 3335 3200]; [TQ 3335 3242]; [TQ 3344 3302] and north of Great Strudgate Farm [TQ 3382 3370]; [TQ 3387 3390]; [TQ 3405 3365]; [TQ 3415 3392]. No pebble bed material was recorded on this ridge and the Top Lower Tunbridge Wells Pebble Bed appears to be represented by a thin bed of coarse ferruginous sand.

A stream section [TQ 3394 3409], 730 m north of Great Strudgate Farm, showed an unusual section near the top of the Ardingly Sandstone:

The interbedded sandstones and silts continue upwards for about 2 m to the base of the Grinstead Clay.

A large disused quarry [TQ 330 324], near Little Strudgate Farm, exposed the following composite section:

The Ardingly Sandstone has been worked in pits at and south of Little Strudgate Farm [TQ 3288 3218]; [TQ 3297 3177] and in Paddockhurst Park [TQ 3278 3342]; [TQ 3310 3378]. At the last-named locality, 0.6 m of clay with silt lenses rested on 0.8 m of flaggy bedded, micaceous, fine-grained, brown silty sandstones without an intervening pebble bed junction. A stream section in Threepoint Wood [TQ 3338 3442] showed the following section at the same stratigraphical level:

An old quarry [TQ 3440 3384], 410 m north of Old House, showed 3.35 m of alternating thickly and thinly cross-bedded sandstones, overlying 4.5 m of massive, thickly cross-bedded sandstone. Small crags of sandrock up to 3 m high occur on the western side of the valley between this quarry and Bloomer's Valley. An old quarry [TQ 3406 3292], west of Pearcelands, showed 8 m of sandstone similar to that described above.

Crags of sandrock up to 4.5 m high crop out for over 1 km in Bloomer's Valley from [TQ 3340 3140] almost to Old House [TQ 3437 3342]. Brown and white cross-bedded sandrock crags up to 5.5 m high crop out in West Wood [TQ 336 312]. Up to 11 m of sandstone of similar lithology, disturbed by cambering and landslip, were seen in old quarry workings [TQ 3355 2978] west of Ardingly Church.

Ardingly Sandstone was worked from beneath a capping of Grinstead Clay in many pits on the ridge in and around Ardingly village and near Pearcelands, Wakehurst Place, Old House and Tillinghurst Farm. Allen (1959, p.304) recorded the Top Lower Tunbridge Wells Pebble Bed in some of these, and fine-grained pebble bed debris occurs in the area.

An old roadside quarry [TQ 3446 3215], 710 m south of Pearcelands, exposed:

A trench section [TQ 3446 3210], 45 m south of this quarry, provided fragments of ferruginous pebble bed containing pebbles up to 1 cm across. An old quarry [TQ 3582 2892], west of Lower Sherriff Farm, showed 4.9 m of thickly and flaggy bedded silty sandstone at the top of the Ardingly Sandstone, disturbed by cambering. Massive sand-rock, at a lower stratigraphical level, crops out in the valley side 45 m north of the quarry.

West Hoathly area

The Lower Tunbridge Wells Sand is about 30 m thick at West Hoathly, the upper 18 m of which is the Ardingly Sandstone. As elsewhere, the lower part of the formation is poorly exposed, but the Ardingly Sandstone, consisting here almost entirely of sandrock, forms numerous impressive natural crags and has been extensively worked for building stone.

A large quarry at Selsfield House [TQ 3479 3411] showed faces up to 4.9 m high in trough cross-bedded, fine-grained sandstone in the upper part of the Ardingly Sandstone. A quarry [TQ 3453 3439], 320 m north-west of Selsfield House, exposed 4.6 m of fissile, thinly bedded sandstone, overlying 6 m of massive, cross-bedded sand-rock. A small exposure nearby [TQ 3447 3427], at a slightly lower stratigraphical level, showed sandrock with thin lenses and stringers of tiny quartz pebbles.

The most impressive and extensive natural crags of sandrock in this district occur in the upper part of tie valley of the Cob Brook in Chiddingly Wood [TQ 349 321] (Frontispiece), Walls Wood [TQ 349 325] and around Stonehurst [TQ 324 316]. In Chiddingly Wood, trough cross-bedded sandrock forms crags up to 11 m high. The cambered outcrop is broken by narrow vertical chasms which have opened along major joints, and large detached joint-bounded blocks occur up to 70 m downhill from the main outcrop e.g. at [TQ 3475 3203]. Along much of the outcrop the rock wall has been undercut, probably initially by periglacial wind action but latterly by water seepage and frost action. The rock at this level is a thinly bedded, silty sandstone about 0.75 m thick, in which trough cross-bedding is present in units 0.3 to 0.45 m thick. Above this, in the main face, trough cross-bedded units are generally 0.9 to 1.2 m thick and pass up into the massive, wispy-contorted bedded sandstones of the 'earthquake' bed. Thus, as at Stone Farm and elsewhere in the district, the sand-rock shows a tripartite division. The crags are continuous from north of Philpots [TQ 352 320] to Walls Wood [TQ 3493 3258]. A minor crag [TQ 3488 3286] to [TQ 3493 3306], south-west of Stonelands, shows up to 3.7 m of massive sandrock with scattered pebbly horizons.

An old quarry [TQ 3496 3325] at Stonelands exposed:

A continuous line of crags, up to 9 m high, extends northwards from Stonehurst [TQ 3439 3153] to [TQ 3452 3235]. The following composite section was measured at Stonehurst [TQ 3441 3158] to [TQ 3442 3165]:

The highest beds seen here and at Chiddingly Wood (see above) are estimated to lie about 4.5 m below the base of the Grinstead Clay.

Between Vinols Cross [TQ 366 325] and Duckyls [TQ 353 340] there are a number of natural crags and old quarries at approximately the same stratigraphical level as the sandrock described above.

A laneside exposure [TQ 3647 3328] showed the following section close to the base of the Tunbridge Wells Sand:

Crags of sandrock, up to 4.5 m high, crop out on the north side of the Turners Hill road [TQ 3594 3318] to [TQ 3572 3317]. North-westwards from here [TQ 3533 3351] to [TQ 3524 3371] there are roadside exposures in the upper part of the sandstone. The following composite section was measured:

The shale bed is at a similar level to that recorded at Philpots Quarry (see below).

A quarry section [TQ 3646 3258], 130 m east of West Hoathly Church, showed the junction of the Ardingly Sandstone with the underlying beds:

The top of the Ardingly Sandstone has been worked from beneath a capping of Grinstead Clay in many pits in the Grinstead Clay outliers at West Hoathly and Hook Farm. Two quarries, at Philpots and at Hook Farm, have been the subject of detailed sedimentological studies over many years by Professor P Allen who has built up a composite three-dimensional picture of the complex sedimentary structures present in the top sandstone.

At Philpots Quarry [TQ 3545 3225] (Plate 4), Allen recorded a series of 'scoops' (large-scale troughs) separated by partings of clay, in some places sun-cracked and with molluscan trails and shell casts on top (1962, fig.2, p.232 and pp.236–240; 1975, fig.4 and pp.400–401; 1981, fig.5 and p.385). The following composite section was measured in 1989; it contains additional observations taken from Allen (personal communication and 1989), where the sequence is described and summarised graphically (fig.2).

Allen (fig.2, 1989) has recorded logs of Lycopodites more than 2.6 m long, together with pterosaur, crocodile and possible Iguanodon remains in the Bottommost Lift. Taylor (1991) has shown the phosphatic concretions in the pebble bed at the top of the Bottommost Lift to be composed of francolite (hydroxy-carbonate apatite), and has suggested that they have been reworked. In contrast, the berthierine pseudo-ooids and pisoids in the conglomerate beneath the Bottommost Lift are believed to have been formed by in situ transformation of transported iron oxyhydroxide ooids and pisoids that had formed in soils in the Weald Basin.

The succession at Hook Quarry [TQ 3555 3135] is broadly similar to that at Philpots (Allen, 1962, fig.1, pp.232–235). The Top Lower Tunbridge Wells Pebble Bed was first recorded at Hook Farm by Topley (1875, p.84) in the now disused quarry [TQ 356 312] on the opposite side of the road from the present day working quarry. A detailed analysis of the pebble content of the pebble bed, based on a 6.1 tonne sample taken from the working quarry, was given by Allen (1960b, with an appendix by W J Arkell on the derived Jurassic ammonite fragments, pp.165–168; 1961; 1967).

The pebble bed crops out over a large area on the flat-topped ridge running north and south from Hook Farm and exposures of it occur in the roadside up to 275 m away from the base of the clay e.g. at [TQ 3592 3187] and [TQ 3546 3107]. In addition to the working pit, there are four old workings for sandstone at Hook Farm. Similar workings occur on the south side of West Hoathly [TQ 360 323], in the village itself [TQ 363 328], at Stonelands [TQ 354 331] and at Chiddlinglye (formerly Rockhurst) [TQ 352 329].

The following section was recorded in the Stonelands Quarry [TQ 354 331]:

Southward from the church to Pickeridge Farm there are a number of small exposures and old quarries [TQ 3618 3215]; [TQ 3562 3078]; [TQ 3542 3057] on the steep feature made by the lower part of the Ardingly Sandstone, all in massive, cross-bedded sandstones, and most with false dips due to cambering.

Highbrook area

A natural tor-like crag of brown and white cross-bedded sandrock [TQ 3628 3068] at Whitestone has been quarried for building stone to form a face 6.4 m high.

An old quarry near Upper Sheriff Farm [TQ 3619 2916] has widened joints with vertical displacements up to 1.4 m due to cambering; brecciated material fills the larger joints. The following section, at about the same stratigraphical level as that at Whitestone, was measured:

Paxhill Park and Wyatts area

An old pit [TQ 3563 2819] at Lywood Common showed:

Topley (1875, p.84) noted that the "conglomerate which occurs at the top of the sand" (Top Lower Tunbridge Wells Pebble Bed) was well developed in two quarries in the Paxhill Park area. The first, in Quarry Wood [TQ 3642 2673] "east of Paxhill", formerly showed:

At the time of the present survey only the top part of this section was visible, as follows:

The distribution of the pebble bed is patchy and the grain size variable in this area, and Topley's section may have been up to 90 m north of the modern section, in a now obscured part of the workings. The site of Topley's second section, in which he found a Jurassic ammonite fragment in the conglomerate, is less certain.

The direction "about a mile north-east of that place [Lindfield] by the east side of the road" could be taken to refer to an old and now completely degraded pit [TQ 3611 2688], but it is more likely that Allen's (1960b, p.157) suggestion that the locality is near Buxshalls [TQ 3560 2725] (see below), about 1.5 km east-north-east of Lindfield, is correct.

The distribution of the pebble bed is patchy in the Quarry Wood area. Fragments of coarse pebble bed occur on the north-east side of the quarry [TQ 3655 2698], but southwards from there as far as [TQ 3643 2658] the pebble bed is thin and fine grained. By contrast, a section in the lane side [TQ 3606 2692] on the north side of Paxhill Park showed up to 0.3 m of coarse pebble bed. The following section was recorded in the quarry adjacent to the north side of this lane:

A coarse pebble bed was traced from there, via Buxshalls, as far as the Danehill Fault. Exposures in Target Pit [TQ 3574 2709] showed very large ripples, up to 8 cm high, of medium to coarse pebble bed resting on 0.6 m of massive fine-grained sandstone. The pebbly material was confined to the linear ripple crests, which strike north-north-east.

A similar section, with a coarser pebble bed, was seen in the old quarry [TQ 3560 2725] 400 m east of Buxshalls, from which Allen (1960b, p.157) collected a 150 kg pebble-bed sample (referred to as being from Paxhill). His analysis of the concentrations of the main pebble types and their suggested origins is summarised in (Table 2). Many of the more durable pebbles have themselves been derived from pebbly sediments such as the Old Red Sandstone and the Bunter Pebble Beds. Arkell (in Allen, 1960b) identified many of the phosphorite pebbles as phosphatised fragments of Pavlovia spp, derived from late Kimmeridgian sediments. An old pit [TQ 3502 2753], 140 m south-east of Hillhouse Farm, showed large ripples, up to 8 cm high, of coarse pebble bed resting on 1.8 m of massive silty fine-grained sandstone.

Sandstones at a lower stratigraphical level within the Ardingly Sandstone have been quarried [TQ 3637 2729] 360 m north-west of Woodsland Farm. Sections there and in the adjacent lane cutting showed about 0.6 m of brown, iron-stained, flaggy, silty sandstone overlying up to 2.4 m of grey-white, massive, trough cross-bedded sandstone.

A stream section [TQ 3829 2738], 360 m south-south-west of Wyatts, showed the following section at the top of the Ardingly Sandstone:

In a nearby pit [TQ 3832 2724], Ardingly Sandstone has been worked beneath a capping of Cuckfield Stone and thin Lower Grinstead Clay (see p.48). Up to 0.2 m of moderately coarse Top Lower Tunbridge Wells Pebble Bed is exposed at this locality.

The following section was recorded in the access road [TQ 3829 2647] at Freshfield Lane Brickworks:

Drewitts to Cuckfield area

The Lower Tunbridge Wells Sand is 24 to 27 m thick in this area, and the Ardingly Sandstone is well developed in the faulted inlier near Drewitts [TQ 239 248]. Eastwards from there, however, the sandstones become more silty and thickly and flaggy bedded, and in the area south and east of Cuckfield massive sandstones and the 'sandrock' facies appear to be absent.

Crags of Ardingly Sandstone on the east side of The Glen [TQ 2447 2512] to [TQ 2438 2491] show up to 6 m of sandrock with cambering and joint-widening. The junction with the underlying beds, marked by a spring, was exposed in a slipped block (dip 20 to 30°) on the same side of the valley [TQ 2438 2458]:

Old sandstone pits on the west side of The Glen [TQ 2426 2467] exposed deeply weathered, fine-grained sandrock, flaggy at the top but becoming massive and cross-bedded below.The pit at Hillhouse Farm [TQ 262 248] exposed Lower Grinstead Clay (see p.49) resting on 0.9 m of massive, buff, fine-grained Ardingly Sandstone, calcareous in part, weathering flaggy.

A waterfall section [TQ 2729 2547] showed 1.4 m of fine-grained sandstone overlying 2.8 m of soft, grey, friable sandstone with ripple marks and sooty plant traces. Further downstream a section which may expose the base of the Ardingly Sandstone showed:

Close by, downstream, ferruginous seepages break out of silty sandstones, silts, clayey silts and silty clays. The clayey silts have a conchoidal fracture and contain pale buff clay-ironstone nodules.

A waterfall section [TQ 2829 2525] in the Ardingly Sandstone, 640 m north-east of Broxmead, exposed:

Two old quarries [TQ 2838 2621]; [TQ 2846 2628] at Slough Green were dug in the middle part of the Ardingly Sandstone. The western one exposed about 2.4 m of pale buff to white, loose, fine- to medium-grained sand containing sporadic harder coherent seams, 2.5' to 15 cm thick, of orange-brown sandstone and thin seams, up to 5 cm, of pale grey silt. This overlies about 2.4 m of massive, medium-grained sandstone, with few vertical joints.

An old pit [TQ 2884 2567] at Henmead Hall showed:

The Top Lower Tunbridge Wells Pebble Bed, comprising a coarse sand containing tiny pebbles or a coarse ferruginous sand without pebbles, appears to have a patchy distribution on the Cuckfield ridge. Small exposures of Ardingly Sandstone, consisting generally of thickly or flaggy bedded sandstones, were noted in a number of ditch and stream sections on either side of the Cuckfield ridge, for example near Whitemans Green [TQ 3007 2595] and near Woodcroft [TQ 3016 2517]. An old quarry [TQ 3039 2596] at Whitemans Green was worked for thickly bedded sandstones near the top of the Ardingly Sandstone.

The water borehole at Cuckfield Hospital (Workhouse) [TQ 3082 2565] proved 27.1 m of Lower Tunbridge Wells Sand (Whitaker and Reid, 1899, p.22).

Numerous exposures of Ardingly Sandstone occur in the gorge at High Bridge [TQ 2915 2415] to [TQ 2980 2362], 730 m north-east of Ansty. An exposure in the north face [TQ 2929 2417] shows up to 15 m of thickly and flaggy bedded, silty, fine-grained sandstone disturbed by a small fault and having dips ranging from 5° to 60°. A section 110 m upstream exposes 0.9 m of fissile and rubbly weathered sandstone resting on 2.1 m of greyish white, massive, silty, fine-grained sandstone. An exposure on the south side of the valley [TQ 2924 2408] shows:

These exposures indicate that the Ardingly Sandstone here consists mostly of flaggy and thickly bedded sandstones with a few thin beds of the more typical grey-white massive sandstone. A silicified fragment of the tree fern Tempskya, probably derived from the Ardingly Sandstone, was found in a field [TQ 2950 2426] on the north side of the gorge.

A pit [TQ 3142 2534], 320 m south-east of Horsgate, exposed:

The following sequence was proved in the Cuckfield No.1 Borehole:

Haywards Heath area

The Lower Tunbridge Wells Sand, particularly the Ardingly Sandstone, is well exposed in the fault-bounded outlier running from Brook Street [TQ 305 266] to the golf course, where the typical sandrock facies is developed. It is much less well exposed in the faulted inliers south and south-east of Haywards Heath where the Ardingly Sandstone consists mainly of thickly and flaggy bedded sandstones. To the north of the town the formation is about 27 m thick; to the south and south-east it is probably only 18 to 24 m thick, thinning to the south-east.

Haywards Heath Golf Course [TQ 336 264] is situated on slightly cambered Ardingly Sandstone comprising massive and thickly bedded, grey-white, fine-grained sandstone and silty sandstone.

The following section was recorded in the deep railway cutting [TQ 3283 2644] near Sugworth Farm:

A quarry [TQ 3248 2630], 260 m west of Sugworth Farm, which formerly worked the upper part of the Ardingly Sandstone, showed 3.4 m of brown and grey, thickly flat-bedded, fine-grained sandstone. The following section was recorded at Spring Copse [TQ 3216 2583] nearby:

A trench [TQ 3239 2495] at Harlands Estate, Haywards Heath, 570 m south of Penland Farm, showed the following composite section:

The Ardingly Sandstone is weakly developed south and east of Haywards Heath, where the typical sandrock lithologies are thin or absent. Up to 1.5 m of massive greyish white sandstone at the top of the Ardingly Sandstone was recorded in two old quarries [TQ 3582 2303]; [TQ 3615 2309] south of Awbrook. Small crags of similar lithology occur in a nearby valley side [TQ 3820 2282]. The Lower Tunbridge Wells Sand is poorly exposed in the inliers near the Henfield Wood and Sandrocks faults.

Grinstead Clay

The main outcrop of the Grinstead Clay runs southwestwards from East Grinstead to Handcross, and thence eastward for 2 km or so to the western end of the Pilstye Farm Fault [TQ 283 288]. The formation is concealed beneath the Upper Tunbridge Wells Sand on the southern, downthrow side along most of this fault but re-emerges near the eastern end of the fault at Ardingly Station, whence its outcrop, much displaced by faulting, extends eastwards, south of Horsted Keynes, on the southern flank of the main Wealden anticlinal axis. Some large outliers cap high ground within the East Grinstead–Handcross–Horsted Keynes area. Numerous inliers, with a complicated outcrop pattern produced by faulting, occur south of the Borde Hill Fault in an east–west belt between Drewitts [TQ 240 250] and Haywards Heath, along the axis and on the north flank of an anticlinal fold. Other, smaller, fault-bounded inliers on the southern flank of this fold occur eastwards from West Riddens [TQ 293 228] to the south-eastern corner of the district.

The Grinstead Clay resembles the Wadhurst Clay in lithology, consisting largely of grey to greenish grey mudstones and silty mudstones with thin beds of shelly limestone and nodular clay-ironstone, rootlet horizons and Equisetites-rich beds. Its base is taken at the base of a pebble bed, the Top Lower Tunbridge Wells Pebble Bed (Allen, 1967). The upper part of the formation is characterised by red clays. Throughout much of the outcrop, a lenticular body of fine-grained sandstone, the Cuckfield Stone (Plate 5), divides the Grinstead Clay into Lower and Upper members (Figure 11). The last-named has a basal pebble bed, the Cuckfield Pebble Bed (Gallois, 1964; Allen, 1967b), throughout much of the crop.

The greatest proved thickness of Grinstead Clay in the district is 26.9 m, in the Cuckfield No.1 Borehole [TQ 2962 2729]. This is made up of Lower Grinstead Clay 6.4 m, Cuckfield Stone 8.3 m and Upper Grinstead Clay 12.2 m. A full thickness of 21.2 m was proved in a borehole at Balcombe Waterworks [TQ 290 313]; in the Bolney Borehole it was apparently 25.5 m (see p.7). Estimates of the total Grinstead Clay thickness, based on quarry measurements and mapping, indicate 20.0 to 21.5 m around Cuckfield, thinning westwards to 13.5 m near Drewitts, northwards to 15 to 18 m at East Grinstead and eastwards to 15 to 17 m south of Horsted Keynes. The Cuckfield Stone is about 4.5 m thick at Cuckfield and thins to 1.5 m around Drewitts and to 1.5 to 3 m at Ardingly. It dies out to the north-west of an arc extending from Handcross to Turners Hill and to the south of East Grinstead (Figure 11). In some places beyond this north-western limit, the Grinstead Clay is thin, attaining just 9 m between Worth Priory and the Balcombe House Fault (where it is mostly red clay) and near Standinghall Farm [TQ 306 353] and north-west of Baldwins Hill [TQ 386 397]. In the Collendean Farm Borehole [TQ 2480 4429], where the Cuckfield Stone is absent, the thickness of the Grinstead Clay is 18.6 m. East of Paxhill Park [TQ 363 268], the Cuckfield Stone thickens at the expense of the underlying Lower Grinstead Clay, a trend continued to the south-east corner of the district near Scaynes Hill, where the Lower Grinstead Clay is cut out altogether and the Cuckfield Stone rests on the Ardingly Sandstone (Figure 11).

The presumed depositional environments which gave rise to these marked local facies variations are summarised in (Figure 12).

Details

East Grinstead area

The Grinstead Clay is generally about 15 to 18 m thick near East Grinstead, and the Cuckfield Stone is absent.

A complex of well shafts and connecting galleries at London Road, East Grinstead [TQ 390 387], proved up to 19.2 m of Grinstead Clay consisting of 'blue clay, shaly clay and rock'. One of these shafts encountered 2.3 m of 'rocky sand' in the middle of this clay sequence at about the level of the Cuckfield Stone of other areas. However, the Cuckfield Stone is absent at outcrop in the East Grinstead area and this sand bed was not recorded in an adjacent shaft (Whitaker and Reid, 1899, p.28).

The Grinstead Clay appears to be no more than 9 m thick northeast of Baldwins Hill, but thickens to 15 to 18 m a few hundred metres to the south-east. Where thin, the clay is almost entirely red, a feature normally associated elsewhere only with the Upper Grinstead Clay. The thinning may be a tectonic feature associated with the adjacent fault, or it may be due to a sand-filled channel cutting out the lower part of the formation (as at Freshfield Lane Brickworks, see p.48). Exposure is poor and such a channel could have been mistakenly mapped as part of the Ardingly Sandstone.

To the south-east, red clays near the top of the formation have been worked for briclu^-naking in a number of shallow pits [TQ 390 390].

A disturbed section [TQ 3881 3829], adjacent to the low-level station at East Grinstead, showed grey shales with a nodular clay-ironstone bed and a calcareous and ferruginous cemented bed which appeared to fill scour hollows and which contained detrital bone and plant material, together with many Unio shells. A bed of similar lithology occurs at the same stratigraphical level, about 2.4 m above the base of the formation, at Philpots Quarry (see p.48). A section in the more easterly railway cutting [TQ 3891 3852] showed about 3 m of khaki- and purple-mottled shales weathering to red clay at the top of the formation. The more westerly cutting [TQ 3880 3873] exposed:

Between High Grove, Kingscote House and Tilkhurst, a prominent feature about 7.5 m above the base of the formation, accompanied by rare soil fragments of fissile calcareous sandstone, marks the outcrop of the attenuated Cuckfield Stone.

A railway cutting [TQ 3770 3815] near Imberhorne Manor showed 5.8 m of disturbed grey shales and silty mudstone containing several thin beds of 'Cyrena' limestone and nodular clay-ironstone. An horizon packed with crushed, probably rafted, carbonaceous Equisetites rhizomes was seen 2.4 m above the track-bed at a similar stratigraphical level to that of the Hackenden Soil Bed (Gallois in Bristow and Bazley, 1972) at East Grinstead. However, the Imberhorne specimens are rafted materials and not part of an in-situ soil bed.

Orange-brown flaggy sandstone (weathered Cuckfield Stone) caps the ridge [TQ 378 363] north-west of Saint Hill, and is overlain by red clays of the Upper Grinstead Clay adjacent to the Fonthill Fault.

North of Stone Farm the Cuckfield Stone forms an impressive dip slope littered with flaggy sandstone fragments. A ditch section [TQ 3783 3513] showed about 1.5 m of Cuckfield Stone consisting of ferruginous fine-grained sandstones, weathering to fissile flags and containing numerous casts of bivalves.

The stratigraphy of the strata mapped as a fault-bounded outlier of Grinstead Clay and Lower Tunbridge Wells Sand, 800 m [TQ 359 362] west of Mill Place, is uncertain. The presence of a well-defined pebble bed overlying pebbly sandrock at the boundary of the two formations favours the interpretation shown on the published map. However, at one locality [TQ 3665 3508] in Mill Place Wood, mine pits have been dug for ironstone close to the base of the clay. Such pits are unknown elsewhere on the Grinstead Clay outcrop, and the possibility remains that this fault block is more complicated than depicted on the published map and encloses Wadhurst Clay on Ashdown Beds.

Turners Hill area

Between Burleigh House and Tulleys Farm, the Grinstead Clay outcrop is pocked by numerous water-filled pits which were presumably dug for marl. Those in the upper half of the formation are almost all in red clay, those in the lower in grey or buff clay. Valley-bulged grey and red shales crop out in the stream bed [TQ 3260 3629] to [TQ 3266 3660] north-north-west of Tulleys Farm, and are overlain by slipped red and grey clays.

A small patch of sandstone and silty sandstone caps a spur [TQ 316 338] south-south-west of Worth Priory and separates red clays of the Upper Grinstead Clay from yellow and grey clays of the Lower Grinstead Clay. Grey shales with thin beds of silt and Neomiodon limestone crop out in the beds of small streams west and north-west of this outlier [TQ 3143 3366]; [TQ 3137 3405]. Between Worth Priory and the Balcombe House Fault and north of Standinghall Farm [TQ 315 353], the Grinstead Clay appears to be locally no more than 9 m thick and to consist almost entirely of red clays, in a manner reminiscent of the Baldwins Hill area (p.45). Here too, contemporaneous channelling may be the cause.

Handcross and Balcombe area

The following section, disturbed by valley bulging, was recorded in the stream bed [TQ 2824 2873] 660 m west of Rocks Farm:

The Cuckfield Stone is only a few centimetres thick on the ridge immediately west of Ditton Place, but thickens rapidly towards the Pilstye Farm Fault. An old quarry [TQ 2991 2865] near The White House exposed 2.9 m of festoon-bedded Cuckfield Stone on grey Lower Grinstead Cmay. A pit [TQ 3136 2820] north of Great Bentley showed:

An old quarry [TQ 3171 2822] in Coney Gill, on the opposite side of the valley, exposed an apparently thick Cuckfield Stone infilling a channel cut into the Lower Grinstead Clay:

This section was figured by Taylor (1963, pl.IIE, p.25).

A well at Balcombe Waterworks [TQ 290 313] proved a complete sequence of Grinstead Clay, 21.2 m thick and consisting of red-mottled marl, shale and rock below 43.4 m depth (Edmunds, 1928, p.49).

Sections in valley-bulged grey shales with clay-ironstone nodules crop out in the stream bed [TQ 2989 3147] to [TQ 3014 3119] adjacent to the railway line north-west of Balcombe. Red and grey clays were seen in numerous small slips along this valley and in the railway cutting approaching the southern portal of the tunnel. Large amounts of Grinstead Clay spoil occur around the tunnel air shafts. The section at the northern portal [TQ 291 326], described by Topley (1875, p.86), now shows only weathered red and grey clay.

Valley-bulged grey shales with thin beds of hard bluish grey silty sandstone crop out in a stream bed [TQ 3075 3174] 365 m west of Yewtree Farm.

The Cuckfield Stone thins north-westwards towards the Paddockhurst Park Fault. On the north-west side of the fault, thin flaggy calcareous sandstone is overlain by red clays in Balcombe village [TQ 3076 3025]. The stone forms an extensive plateau south and east of Balcombe. A quarry [TQ 3171 2934] 685 m west-north-west of Balcombe Place showed:

The Lower Grinstead Clay of the southern part of the Balcombe ridge contains thin lenses, locally numerous, of fine-grained sandstone, some of which probably fill scour hollows and others of which are probably trains of ripples. At one locality [TQ 3277 2893] to [TQ 3313 2879], 640 m east-south-east of Balcombe Place, these sandstones are so abundant that they appear to occupy a broad channel in the Lower Grinstead Clay. It is tempting to link this channel with that at Coney Gill (see above), but the two features appear to be separated west and south of Stone Hall by an unbroken Lower Grinstead Clay outcrop.

The Cuckfield Stone forms an extensive flat around West Hill and thins northwards towards Woodward's Farm. Roadside exposures [TQ 3269 3038] at West Hill, showed up to 1.2 m of flaggy fine-grained sandstone. The stone has been worked in several pits from beneath a clay capping between West Hill and Bramblehill Farm, but these are all now degraded. They include the pit at Paddockhurst Park [TQ 3250 2341] from which Taylor (1963, p.23) obtained mammalian bones.

Stream sections in Grove Wood [TQ 330 344] and Threepoint Wood [TQ 334 344], 800 m west of Bramblehill Farm, exposed valley-bulged grey shales (Lower Grinstead Clay) and red- and purple-mottled shales (Upper Grinstead Clay) respectively. A section in Threepoint Wood showing the base of the Grinstead Clay is described on p.36. An old pit dug for Ardingly Sandstone [TQ 3388 3451], 365 m west of Bramblehill Farm, revealed about 1.2 m of grey shales with ostracods and bivalves, and containing a thin bed of 'Cyrena' limestone.

Ardingly area

Extensive outliers of Grinstead Clay cap the ridges at Great Strudgate Farm [TQ 339 333] and Ardingly. The full thickness of the formation there is about 18 to 21 m, comprising of 6 to 7.5 m of Lower Grinstead Clay, 1.5 to 3 m of Cuckfield Stone and 7.5 to 9 m of Upper Grinstead Clay. Where within about 2 m of ground level, the junction of the Lower Grinstead Clay and the Cuckfield Stone has been much disturbed by periglacial cryoturbation and is very irregular.

The Cuckfield Stone was seen only as large amounts of sandstone rubble capping the Great Strudgate ridge. A loose block of pale and dark brown (apparently decalcified), silty, fine-grained sandstone packed with casts of Unio, apparently in life position, was found at the southern end of the ridge [TQ 343 322].

A roadside section [TQ 3431 3150] 365 m east of Wakehurst Place showed 0.6 m of orange, silty, fine-grained sandstone (Cuckfield Stone) with ostracods. About 1.2 m of the same sandstone was seen in a nearby laneside section [TQ 3410 3047]. Orange-brown silty sandstones were seen to overlie about 1.5 m of slipped grey shales (Lower Grinstead Clay) in the top of an old pit [TQ 345 297] in Ardingly. A section in a farm track [TQ 3394 2935] 450 m south of the church showed 1.1 m of flaggy and thickly bedded silty Cuckfield Stone resting on yellow clays (Lower Grinstead Clay).

Red clays have been worked at the old brickworks [TQ 3487 2865] 900 m east of Ardingly College. Similar red clays crop out in the nearby railway cutting [TQ 3545 2845] at the western entrance to Lyewood tunnel. A complex of old quarries [TQ 356 282] 275 m south of the tunnel has worked both Ardingly Sandstone and Cuckfield Stone beneath cappings of clay. The following section was estimated from scrapings; only the contact above the Ardingly Sandstone (see p.36) was exposed:

The small fault-bounded inlier of Cuckfield Stone and Upper Grinstead Clay mapped around Ardingly Station is poorly exposed. Grey and red clays were augered in the floor of the railway cutting [TQ 3410 2768], at the station and in the fields around Avins Farm.

A temporary excavation [TQ 3402 2749] to [TQ 3405 2733] alongside the Haywards Heath road at Ardingly showed the following composite section:

It is possible, however, that the beds assigned to the Grinstead Clay within this inlier are a local clayey development within the Upper Tunbridge Wells Sand. Such an occurrence of red clay overlying massive sandstone suitable for building purposes and mimicking the Cuckfield Stone–Upper Grinstead Clay sequence, has been noted at Haywards Heath (see p.65).

The stratigraphical evidence from the adjacent fault-bounded block, around Hillhouse Farm, is more convincing. A deep pit [TQ 3450 2755], showed:

West Hoathly area

Only the Lower Grinstead Clay and the lower part of the Cuckfield Stone are present in the outliers at West Hoathly and Hook Farm. Ardingly Sandstone has been extensively worked from beneath the clay in both areas. The sections in Grinstead Clay at Philpots (Plate 4) and Hook Farm quarries are the best in the area. The former [TQ 3545 3225] showed:

The Hook Farm quarry [TQ 3555 3135] exposed similar beds of Lower Grinstead Clay above Ardingly Sandstone.

Slough Green to Horsted Keynes

Between Slough Green [TQ 280 260] and Borde Hill [TQ 324 266] the Grinstead Clay forms a series of dip slopes on the north side of the Cuckfield ridge, where it dips into the Borde Hill Fault. A ditch section [TQ 3068 2627] in the Cuckfield Stone at Brook Street showed 8 cm of decalcified, very ferruginous, dark brown, fine-grained sandstone, containing casts of small Viviparus, resting on 0.3 m of thickly bedded, silty, fine-grained sandstone.

Ferruginous Cuckfield Stone with rare casts of Viviparus crops out on the dip slopes south-east of Lullings Farm. Stiff red and chocolate-brown clays of the Upper Grinstead Clay crop out in the fields south and west of Horsgate and in the Old Fish Pond [TQ 3100 2565], formerly a Cuckfield Stone pit. The Lower Grinstead Clay appears to have been cut out by a thickening of the Cuckfield Stone in a small area near Cuckfield Hospital [TQ 3047 2586] to [TQ 3073 2575]; this is reminiscent of the channels at Balcombe (p.46).

Small exposures of shales occur in several of the old Ardingly Sandstone pits in the outlier north of Paxhill Park (see p.40).

The following section was measured in the railway cutting [TQ 3283 2644] at Sugworth Farm:

The following section was measured in a small quarry [TQ 3627 2688] on the north side of Paxhill Park:

The same sandstone bed, or possibly an ironstone at the base of the Upper Grinstead Clay, appears to have been worked in minepits [TQ 3619 2704] 180 m north-north-west of this quarry. The full Grinstead Clay sequence on this ridge appears to be Lower Grinstead Clay about 7 m, Cuckfield Stone 2.4 to 3 m and Upper Grinstead Clay 6 to 7.5 m.

Between the outlier at Paxhill Park and that at Wyatts, and between Plummerden Farm and Freshfield Lane Brickworks, the Cuckfield Stone cuts out almost all the Lower Grinstead Clay. An old quarry [TQ 3832 2724], south-west of Wyatts, showed thin Lower Grinstead Clay:

A stream section [TQ 3848 2745] nearby exposed:

A small quarry [TQ 3862 2738], at the same level, showed 1.4 m of festoon-bedded, very fissile sandstone resting on 1.5 m of thickly and trough cross-bedded sandstone, the former probably being the weathering product of the latter.

The Grinstead Clay at the western end [TQ 364 262] of the outcrop at Plummerden Farm appears to comprise Lower Grinstead Clay 1.5 to 3 m, Cuckfield Stone about 3 m and Upper Grinstead Clay 6 to 7.5 m. Eastwards, the Cuckfield Stone thickens within a few hundred metres to about 6 m, at the expense of the underlying clay. The top of the Cuckfield Stone is marked by the Cuckfield Pebble Bed. An old quarry in Cuckfield Stone [TQ 3745 2618], 460 m north-north-west of Cockhaise Mill, showed 3.7 m of dark brown, iron-stained, festoon-bedded, fine-grained sandstone, weathering to very fissile fragments.

The following complete Grinstead Clay section is exposed from time to time in the access road at Freshfield Lane Brickworks [TQ 383 265].

The beds are disturbed by small faults and probably by frost heaving. Gulls in the top of the Ardingly Sandstone are filled by shale debris from above. The Upper Grinstead Clay may have been attenuated by these disturbances.

Drewitts and Cuckfield area

Old quarries [TQ 2417 2467] in Cuckfield Stone, south-east of Drewitts, exposed yellow-buff, compact, fine-grained sandstone, finely cross- bedded in part. The beds were flaggy in the upper part but more massive below and broken by vertical joints.

The sequence in the outlier at Rout Farm [TQ 251 250] is estimated as Lower Grinstead Clay about 6 m, Cuckfield Stone 1.5 m and Upper Grinstead Clay 6 m. The faulted inliers around Wykehurst Park showed a few sections in Cuckfield Stone. A stream section [TQ 2569 2382], 550 m south of Wykehurst Park House, exposed 1.4 m of pale greyish blue, very fine-grained sandstone, calcareous in part, in 5 to 8 cm beds, weathering fissile and brown. Some 32 m downstream more massively bedded, noncalcareous, buff-orange, fine-grained sandstone was noted. An old quarry [TQ 2616 2456] in the Cuckfield Stone exposed:

An old pit at Hillhouse Farm [TQ 262 248] exposed:

An old quarry [TQ 2631 2485] in Cuckfield Stone, 140 m north-east, showed 1.8 m of fine-grained sandstone, festoon cross-bedded in its upper part, more massive and jointed below.

A complete Grinstead Clay sequence is present around Great Thorndean Farm, the thicknesses of the three members being comparable to those in the Rout Farm area. A stream section in Cuckfield Stone [TQ 2746 2564], 360 m east-south-east of the farm, showed:

The lower bed possibly rests on a hard, greenish grey, calcareous sandstone. Brown and red clays of the Upper Grinstead Clay crop out around the farm and between there and Slough Green. A deep pit [TQ 2795 2490] at Broxmead showed the following weathered section:

Cuckfield Stone debris litters the gently sloping dip slope immediately north of this pit. A stream section [TQ 2793 2534] at the northern edge of this dip slope exposed about 2.4 m of yellowish brown, flaggy sandstone.

The Grinstead Clay outcrop along the steep valley side [TQ 274 242] to [TQ 288 242] north of Hoadsherf Farm is affected by cambering, landslipping and faulting.

Cuckfield Stone crops out as flaggy sandstone rubble around Hoadsherf Farm. An old pit [TQ 2843 2380] 230 m north-north-west of the farm showed 4.5 m of deeply weathered khaki-grey clay, and was probably worked for Cuckfield Stone. Similar pits occur adjacent to the farm [TQ 2858 2355] and eastwards along the Upper Grinstead Clay outcrop [TQ 2899 2398]; [TQ 2908 2374]; [TQ 2963 2354] as far as the Lucas Grange Fault. A small quarry [TQ 2897 2404] in Cuckfield Stone yielded several blocks of Cuckfield Pebble Bed spoil in which Allen (1967, table 2) found a pebble suite similar to that in samples from Cuckfield village.

The divisions of the Grinstead Clay are most clearly seen around Cuckfield, where beds dipping gently southwards form long dip slopes through the village and where almost horizontal beds cap the Whitemans Green ridge. The full thickness of the formation in this area is about 20 to 21.5 m, comprising Lower Grinstead Clay about 6 to 7.5 m, Cuckfield Stone about 4.5 m and Upper Grinstead Clay about 9 m. A few pits exposed the basal part of the Grinstead Clay and the Top Lower Tunbridge Wells Pebble Bed (see p.41).

The Cuckfield Stone has been worked both at outcrop and from beneath a capping of Upper Grinstead Clay (Figure 13). The extensive pits at Whitemans Green, famous as the site of many of Mantell's dinosaur finds, cover a large area bounded by [TQ 2985 2545], [TQ 3017 2537], [TQ 3017 2554] and [TQ 2989 2557]; most have been backfilled, reclaimed and landscaped, and it is no longer possible to determine whether the whole area was worked out or whether only parts of it were worked in separate pits. Working appears to have progressed from east to west and only the latest of the quarries, that in the south-west corner [TQ 2988 2550] contained any exposure at the time of the survey. This showed about 2.4 m of fine-grained sandstone, in part calcareously cemented and blue-hearted, elsewhere orange-brown to dark brown where decalcified.

The precise site of the quarry from which Mantell obtained the first remains of the large herbivorous dinosaur Iguanodon has been the subject of much speculation. Mantell (1825) described how his wife had found the first Iguanodon tooth embedded in a block of sandstone in a pile of roadstone at Cuckfield in 1822. This led him to the nearby quarry where he found bones and more than 250 Iguanodon teeth in situ, and where he subsequently found the remains of other large dinosaurs including Hylaeosaurus and Pelorosaurus. The working quarry was figured and described by Mantell at several stages during its development. In 1851 (fig.45) he figured the quarry as it had been in 1820, close to the time of the first dinosaur discovery; from the position of Cuckfield Church and Ditchling Beacon in the drawing it can be deduced that the site was in the south-east corner of the worked-out area shown in (Figure 13). The dip of the strata and the apparent presence of cambering in the sandstones further suggest that the site was close to the edge of the small valley that runs through Cuckfield Park. He noted (1851, p.202) that this particular quarry had long since been filled up and that the area was now "covered by pasturage and gardens".

Mantell's descriptions of the sections, together with that of a later section by Topley (1875, p.91), suggest that the sequence was laterally persistent overall, but variable in detail. The following composite section is based on several (1822; 1833; 1851) of Mantell's descriptions; the geological classification is based on the present survey:

No two sections described are precisely the same, although all agree as to the nature of the Lower Grinstead Clay and the overall sequence in the Cuckfield Stone. The distinction between the lower, more calcareous sequence and the softer, upper sequence in the Cuckfield Stone may reflect the depth of weathering, although the presence of a thin pebble bed at the junction of the two units in some sections suggests that the upper sequence may be a channel fill. It is reminiscent of the sequence in the highest Ardingly Sandstone at Philpots Quarry (see p.39). Topley (p.92, 1875) also described a pebble bed at this stratigraphical level, separating 2.4 m of ripple-marked sandstone from an underlying 2.4 m of sandstone with Tilgate Stone. A second channel-lag gravel appears to be present at the base of the Cuckfield Stone in some of Mantell's sections.

The thicknesses recorded for the Cuckfield Pebble Bed and the overlying soil and subsoil are difficult to explain. The pebble bed is mostly less than 10 cm thick in the area, and Topley (p.92, 1875) recorded it as up to 2.4 cm (one inch) thick in his Whitemans Green section. One can, therefore, only presume that the 'diluvial aggregate' was a mixture of disaggregated pebble bed and weathered Cuckfield Stone sand, possibly mixted by cryoturbation. A similar situation occurs around Hook Quarry, West Hoathly (see p.47) where a dip slope capped by the Top Lower Tunbridge Wells Pebble Bed occurs in cryoturbation pockets over a large area. The great thickness of 'loam' at the top of the section is also puzzling. In the northern part of the worked-out area shown in (Figure 13) this would have included the lowest beds of the Upper Grinstead Clay, but there is no evidence for an outlier of the clay in the area of the Iguanodon quarry. Topley (p.92, 1875) recorded the highest bed in his section as "Weald Clay"; this suggests that the section was cut into the Upper Grinstead Clay outcrop and was in the workings shown at about 150 m north-west of the site of the former windmill on the 19th century Ordnance Survey map.

The fossils collected by Mantell, mostly preserved in the British Museum and Geological Survey collections, fall broadly into two preservational types. Those preserved in a pebbly grit matrix are mostly small (less than 2.5 cm), partially abraded teeth and bone fragments preserved in yellow to brown opaque phosphate. They are clearly from the Cuckfield Pebble Bed or one of the underlying channel-lag deposits. The bulk of the material is preserved in a calcareous fine-grained sandstone matrix (Mantell's Tilgate Stone) and is mostly derived from the lower half of the Cuckfield Stone. It includes large teeth preserved in shiny black phosphate with beautifully preserved ornaments, small and large bones including dinosaur remains, turtle shells and well-preserved plants.

A temporary section [TQ 2977 2577] at Whitemans Green showed:

Westwards from there, the basal bed of the Upper Grinstead Clay passes into a pellet rock with coarse sand, then into a fine-grained pebble bed. On the south side of the outlier, a fine-grained pebble bed passes westwards into a coarse pebble bed in the extensive old workings mentioned above.

A road cutting [TQ 3044 2584] at Whitemans Green formerly showed:

A section in High Street [TQ 3040 2462], Cuckfield, showed grey clays of the Upper Grinstead Clay resting on fissile calcareous sandstone (Cuckfield Stone); the intervening Cuckfield Pebble Bed was present as a layer of large ripples of pebbly sand. Samples of the pebble bed were analysed by Professor Allen (1967, table II): the results are summarised in (Table 2).

The stream bank [TQ 3047 2387] 230 m south-east of Laines Farm exposed:

A lime-rich spring issues from the top of the clay and forms a tufaceous deposit. Cuckfield Stone has been worked at outcrop [TQ 305 238], in pits second only in extent to those at Whiteman's Green, on the spur immediately south of this exposure.

The Cuckfield Stone thins rapidly eastwards from a metre or two to a few centimetres on the ridge [TQ 315 246] 550 m east of Warden Court, and then thickens to a metre or two east of Blunts Wood [TQ 320 247].

A borehole [TQ 3355 2500] at Gordons Road, Haywards Heath, penetrated the full sequence of Grinstead Clay, probably 20.1 m thick, described as red-mottled and blue clay below 65.2 m (Edmunds, 1928, p.119).

The following sequence was proved in the Cuckfield No.1 Borehole:

Inliers south of Haywards Heath

Red clays (Upper Grinstead Clay) crop out in the valley sides, and brown flaggy sandstones (Cuckfield Stone) in the stream bed in the small inlier [TQ 317 235] south of Chownes Mead.

Flaggy calcareous Cuckfield Stone was seen at the top of a pit [TQ 3021 2277] east of West Riddens. Eastwards, the Cuckfield Stone thickens at the expense of the Lower Grinstead Clay, the latter being reduced from about 6 m at Hanger Wood, south of Copyhold Farm, to about 1.2 m at Bolnore Wood, south of Bolnore. Over much of this distance, the Lower Grinstead Clay is typically grey, weathering yellow and buff, but west of Bolnore Wood [TQ 3170 2313] it is stained red and contains nodules of brick-red clay-ironstone.

Festoon-bedded Cuckfield Stone is exposed in Rookery Lane [TQ 3247 2231] to [TQ 3236 2213] (Plate 5). The railway cutting at High Bridge [TQ 3255 2237] nearby showed:

Festoon-bedded Cuckfield Stone crops out at the entrance [TQ 3293 2251] to Sandrocks.

The following composite section was recorded in the railway cutting [TQ 3295 2415] 360 m south of Haywards Heath Station, where Grinstead Clay is brought up by a small fault:

A full Grinstead Clay sequence is present in the fault-bounded inlier north-east of Abbots Leigh. A deep stone pit in Eastland Wood [TQ 3614 2309], adjacent to the Scayne's Hill Fault, showed the following composite section:

Another quarry [TQ 3582 2303], 275 m to the west, showed a slightly different section comprising Cuckfield Stone (about 4.5 m) and Lower Grinstead Clay (about 3 m) resting on Ardingly Sandstone (1.5 m). The true thickness of the Cuckfield Stone was difficult to estimate because the outcrop had been transformed into a rockery.

The full thickness of the Upper Grinstead Clay in the north-west corner of the inlier is estimated to be about 7.5 m. The inlier 550 m south-east of Abbots Leigh contains a number of pits for Cuckfield Stone which there appears to be about 3 to 3.7 m thick.

A full Grinstead Clay sequence crops out between Anchor Wood and Lindfield Farm, south-east of Scayne's Hill; the Lower Grinstead Clay is generally reduced in thickness here and the Cuckfield Stone expanded. The following composite section, based on ditch sections near [TQ 3815 2295] and features near Hammond's Farm, is probably typical of this inlier:

Cuckfield Stone crops out as a line of small crags in Rock Wood [TQ 372 228]; at the eastern end [TQ 3744 2286] these crags appear to be overlain by 1 to 2 m of pale grey and red mottled clay, which lies within the Cuckfield Stone.

A large quarry [TQ 3696 2279] at Ince's Farm reputedly supplied much of the stone for the chapel at Lancing College. Massive, greyish white, fine-grained sandstone has been worked in a series of steps in a fashion similar to the method used for the Ardingly Sandstone at Selsfield House (see p.37).

The top of the Cuckfield Stone between Ince's Farm and Hammond's Farm is sharp and marked by a thin fine-grained Cuckfield Pebble Bed. An old quarry [TQ 3759 2275] on the Cuckfield Stone outcrop showed 2.75 m of orange-brown, flaggy and thickly cross-bedded, fine-grained sandstone weathering to very fissile, festoon-bedded sandstone with open gulls.

The Lower Grinstead Clay consists of only a metre or two of silty clay in the inlier around Pegden Farm and Senates Farm. An old quarry [TQ 3733 2336] exposed about 3.7 m of white, massive, fine-grained sandstone with shallow trough cross-bedding, similar to that in the quarry at Ince's Farm. Small crags of the same material occur in the adjacent fields and at Yewtree Farm [TQ 381 237]. At the latter locality the Cuckfield Stone is overlain by a fine-grained pebble bed and by yellow and red Upper Grinstead Clay. About 2.4 m of brown and 'white, thickly bedded and massive Cuckfield Stone crops out in Ham Shaw [TQ 3824 2411]. It is possible that the faulting in this area is more complex than that shown on the published map and that the Grinstead Clay inlier around Pegden Farm is separated by faulting along the Ouse valley from the small outcrop on the north side of the valley.

Small crags of dark brown, massive, iron-stained Cuckfield Stone occur alongside the lake [TQ 384 227] west of Lindfield Farm. Between there and the farm, the Lower Grinstead Clay consists of only 0.3 to 0.6 m of red and grey mottled silty clay. An old quarry at the farm [TQ 3909 2280] showed about 4.5 m of white and brown massive sandstone, festoon-bedded in part which, although lithologically similar to the Ardingly Sandstone of other areas, is thought to be bleached Cuckfield Stone.

A pit [TQ 3866 2331] south of Masset's Place exposed 2.1 m of dark and pale brown, fissile, festoon-bedded sandstone. The Lower Grinstead Clay was traced in the adjacent fields as a thin bed of red silty clay. Another quarry [TQ 3883 2329], 275 m south-west of Senates Farm, showed the best section through the Cuckfield Stone in this area:

Upper Tunbridge Wells Sand

From the vicinity of Felbridge, in the north-east corner of the district, the outcrop of the Upper Tunbridge Wells Sand forms a tract of high ground about 5 km in width and extending west-south-westwards to Horsham. Along much of this tract, there is a slight north-north-westerly dip, changing through westerly (at Horsham) to south-westerly in the vicinity of Mannings Heath [TQ 205 285], south-east of Horsham, as a consequence of the east-west Colgate Anticline. Between Mannings Heath and the south-eastern corner of the district, on the southern flank of the main Wealden up-fold, the outcrop is fragmented by faults and folds of predominantly east–west trend. The larger outcrops occur eastwards of Slaugham, between the Pilstye Farm and Sidnye Farm faults, almost as far as Ardingly Station, near Lower Beeding, and between Bolney and Haywards Heath, on the southern flank of the east–west anticline through Cuckfield.

The Cuckfield No.1 Borehole proved a total thickness of 100.6 m of Upper Tunbridge Wells Sand. In St Leonard's Forest a thickness of 75 m is estimated for the beds at outcrop, but the highest part of the formation is absent. The total original thickness in the vicinity of the Whitesbridge Pumping Station [TQ 1874 2913], near Horsham, may be near 90 m. In Crawley, one interpretation of the log of a borehole [TQ 265 359] suggests a thickness of between 113 and 128 m. North of the district, at Collendean Farm [TQ 2480 4429], the thickness is about 64 m.

Lake and Thurrell (1974) described the formation in the Cuckfield No.1 Borehole as consisting of a complex sequence of thinly interbedded deposits, with both fining-upwards and coarsening-upwards cycles. The borehole showed that silt is the dominant component, but grey and greenish grey silty mudstones, some showing red mottling, tend to predominate in the lower part of the formation, whereas beds of pale grey to yellowish grey sandstone mostly occur in the upper part. Channel and slump structures, and ripple-drift and other cross-bedding structures occur in the sandstones and, less commonly, in the siltstones. Bioturbation is common in the siltstones, less so in the silty mudstones; the latter typically contain thin silt laminae. The same silty mudstone, siltstone and sandstone lithologies, also thinly bedded but at many levels laterally persistent over long distances, occur in varying proportions throughout the outcrop.

Exposures are numerous, but are mostly of the harder siltstone and sandstone beds. Typically, the sandstones at outcrop are fine grained and quartzose, with small amounts of mica and interstitial clay, and they weather to a pale yellowish grey to yellowish brown colour. In many beds the quartz grains are about 0.06 mm in diameter, a grain size on the borderline between that of fine sand and silt.

Over much of the outcrop, sandstone beds form prominent scarp and dip-slope features. Where possible, the sandstone beds have been mapped separately and their outcrops are distinguished on the published map by pale blue stippling over the yellow colour used for undivided Upper Tunbridge Wells Sand. Mapping of sandstones proved particularly effective in the tract between Horsham and Crawley, where the dip is slight and there is strong relief owing to dissection of the high ground of St Leonard's Forest by headstreams of the Arun and Mole rivers (Plate 6). In this tract there is also a strong contrast between the light sandy soils on sandstone outcrops and clayey soils on intervening units of silt and silty mudstone. Three lithologically similar sandstone units in the St Leonard's Forest area are persistent enough to merit separate names. In ascending order these are the Shelley Plain Sandstone, the Colgate Sandstone and the Roffey Park Sandstone. Their outcrops are indicated on the 1:10 560 geological sheets.

In the southern part of St Leonard's Forest, the sequence of alternating sandstone and clayey units develops increasing lenticularity in a south-westerly direction. Around Lower Beeding, the Upper Tunbridge Wells Sand can only locally be subdivided into sandstone and clay members owing to the faulted nature of the outcrop, while east and south of Warninglid [TQ 250 261] mapping of sandstone beds generally proved impracticable owing to the prevalence of steep dips and faulting. A persistent bed of red- and pale grey-mottled silty clay about 12 to 15 m above the base of the formation has been identified around Haywards Heath (p.66).

Clay-ironstone is exposed in some stream sections; its widespread occurrence is attested by belts of minepits, which occur particularly in the Horsham–Crawley area (Worssam, 1972) but rarely to the east of Crawley. Much of the ironstone dug for ore may have been siderite-impregnated siltstone, which forms layers around 15 cm thick, though flat ovoid siderite mudstone nodules also occur within mud-stones. The clay-ironstones west of the longitude of Mick Mills Race, a long north–south ride [TQ 217 319] to [TQ 217 300], both in the northern part of the forest (Worssam, 1972, p.43) and in the southern part (details below), are below the Colgate Sandstone; those to the east are above it. This distribution suggests an easterly shift with time of the belt of ironstone deposition. Ironstone was noted at only two levels in the Cuckfield No.1 Borehole, in the upper part of the formation.

Both in the borehole and at outcrop the base of the formation is fairly sharp; near Scayne's Hill [TQ 369 233] it is marked by a massive, 2 m-thick fine-grained sandstone bed. The upper contact with the Weald Clay is shown by the resistance log of the borehole (Lake and Thurrell, 1974, fig.3) to be gradational over an interval of about 4 to 5 m. At outcrop, north of Crawley, the boundary is also essentially transitional; silty and clayey sediments with rare thin sandstone beds pass up into silty and clayey sediments without sandstones. The boundary was therefore placed at the top of the highest sandstone bed, a level which also marks a change in topography to the more subdued landscape of the Weald Clay outcrop. West of Crawley, the base of the Weald Clay is largely faulted out or obscured by hillwash, but in the south of the district, between Hilders Farm [TQ 285 224] and the Burgess Hill Fault, and in the adjoining part of the Brighton district, the top of the Upper Tunbridge Wells Sand is marked by a thick bed of massive sandstone, locally capped by very ferruginous, ripple-marked sandstone or by clay-ironstone.

Details

Crawley to East Grinstead area

The Upper Tunbridge Wells Sand has an extensive unfaulted outcrop in the country between Crawley and East Grinstead in which the sandstone and harder siltstone beds cap long gentle dip slopes. Although more than 60 m of strata are estimated to crop out in this area, only a few metres of this total are exposed. The sequence is made up largely of coarsening-upward rhythms, most of which are probably between 2 and 5 m thick, in which silty red mottled clays pass up into pale grey silts which are capped by a silty fine-grained sandstone up to 1 m thick. At three horizons the basal clay is sufficiently thick for it to be mapped. Each of these horizons gives rise to a spring line and heavy clay soils, and their outcrops are in places pitted for brickclay and an attendant clay-ironstone ore. Fining-upward rhythms of siltstone and silty mudstone also occur, notably near the top of the formation.

The lowest clay horizon, 12 to 15 m above the base of the Upper Tunbridge Wells Sand, has been continuously traced from East Grinstead via Felbridge and Crawley Down to Worth Forest and Balcombe. The best exposure in recent years has been that at the spasmodically worked brick-pit [TQ 331 364] at Hundred Acres Wood, Rowfant, where up to 2.5 m of red- and grey-mottled silty mudstone have been worked from beneath a capping of up to 3.5 m of thinly interbedded siltstones and sandstones (Plate 7). A similar bed occurs at much the same stratigraphical level in the Ardingly, Cuckfield and Haywards Heath areas (see p.66).

The middle horizon can be traced from the district boundary at Mill Wood [TQ 362 414] via Domewood and Copthorne to Three Bridges. The highest horizon, close below the junction with the Weald Clay, has a broad outcrop that extends from West Park [TQ 345 413] via Shipleybridge and Tinsley Green to Crawley.

A borehole at the Brighton Road Pumping Station, Crawley [TQ 265 359] proved Weald Clay and Hastings Beds to 281 m (Edmunds, 1928, pp.78 and 79; Buchan et al., 1940, p.9). The top of the Upper Tunbridge Wells Sand may lie at 84.4 m, at the first record of sand below the Weald Clay. Below this depth the drilling log is too vague to be interpreted in detail. An apparently sharp clay–sandstone contact at 230.1 m may indicate the Grinstead Clay–Lower Tunbridge Wells Sand junction. If so, the Upper Tunbridge Wells Sand–Grinstead Clay junction may lie within an undescribed group of beds between 197.5 and 211.8 m, indicating a thickness of between 113.1 and 127.4 m for the Upper Tunbridge Wells Sand.

Yellow-brown, flaggy siltstone, locally with specks of plant debris, was dug in temporary excavations [TQ 2626 3658]; [TQ 2662 3671] west of Crawley High Street, and similar material was seen in other excavations on a dip slope trending north-north-east, east of the High Street. Along the crest of the slope and on its low east-southeast-facing scarp, red- and grey-mottled clay overlies grey to fawn silty clay. The latter forms most of the wide clay outcrop in the eastern part of Crawley. Pale grey- and yellow-brown-mottled silty clay and some thinly bedded soft siltstone were excavated from foundations for the Town Hall [TQ 2715 3685]. East of the clay outcrop shown on the map, in the built-up area between Crawley and Three Bridges, auger holes and temporary exposures showed red- and grey-mottled clay, grey to fawn silty clay, and grey to yellow-brown silt and siltstone. A seam of clay-ironstone was proved in 1963 in excavations for Crawley swimming pool [TQ 2772 3645] and was exposed in a stream section [TQ 2778 3740]. Possibly this rock gives rise to the scarp-like ridge which, declining in altitude northwards, trends north-north-east for about 1 km from the swimming pool site.

The following composite section, showing three fining-upward rhythms that are typical of much of the Upper Tunbridge Wells Sand of that area, was exposed [TQ 2831 3836] in Crawley Industrial Estate:

Between Tinsley Green and the district boundary at West Park, the junction of the Upper Tunbridge Wells Sand and the Weald Clay is essentially transitional, in that predominantly silty and clayey sediments with rare thin sandstone beds (UTW) pass up into silty and clayey sediments without sandstone beds (WC). The junction has therefore been placed at the top of the highest sandstone bed seen, a level which coincides with a major topographical change from the higher relief Upper Tunbridge Wells Sand outcrop to the much more subdued relief of the Weald Clay. No major topographical feature occurs between the base of the Weald Clay at Burstow and the striking ' Small-Paludina limestone' escarpment near Smallfield, several kilometres to the north.

Small temporary exposures of the topmost sandstone, showing 0.3 to 0.6 m of flaggy silty sandstone, were seen on the same estate [TQ 2768 3792]; [TQ 2850 3893]. This sandstone is exposed in the stream bed [TQ 2914 3983] at Tinsley Green, where the following composite section was measured:

A stream section [TQ 3104 4078], 550 m south-south-west of Burstow Church showed:

Another stream section [TQ 3235 4108] showed 0.45 m of fine- and medium-grained (topmost) sandstone overlain by fissile khaki silts and underlain by interbedded silty mudstones and siltstones.

Small exposures showed the seam of clay mapped out on the north side of Copthorne village to consist of mottled pale grey and red silty clays, which include a seam of clay-ironstone. Minepits and small brick-pits occur at this level locally for example [TQ 3005 3885]; [TQ 3138 3979] and westwards to the River Mole for example [TQ 292 384], [TQ 293 379].

A stream section [TQ 3115 3868] to [TQ 3115 3815] at Pot Common showed small exposures of plant-rich silty sandstones, generally 0.4 to 0.6 m thick, interbedded with grey siltstones. A ferruginous pellet bed, 0.15 m thick, in one of the sandstones contains angular clasts of sandstone and probably floors a small erosional channel.

Silty sandstones were noted in drainage trenches [TQ 3217 3879]; [TQ 3227 3897] on Copthorne Golf Course. A sewer trench [TQ 3276 3883] to [TQ 3273 3800], which ran down the sandstone dip slope through Coombers Wood, proved a metre or two of flaggy, orange-brown, silty sandstone underlain by pale grey, plant-rich siltstones and overlain in two small areas by red-mottled silty clays.

A pit [TQ 3438 3994] on the southern edge of Domewood exposed 2.4 m of flaggy, pale grey siltstones with plant fragments including Weichselia reticulata (Stokes & Webb) and, at the top, sand lenses and shallow channels up to 1.5 m wide and 0.3 m deep (Plate 8). These latter were largely infilled with similar siltstones, but included balled-up silty sandstones which had slumped from the channel sides (Figure 14). The purpose of the pit is unknown.

A water borehole at Felbridge [TQ 3606 3914] probably proved Upper Tunbridge Wells Sand to about 21 m, consisting of 'sand-rock and clay' (Edmunds, 1928, p.89).

Horsham area

A water borehole at Wickhurst Lane, Broadbridge Heath [TQ 1514 3120], surface level 42.7 m above OD, proved Weald Clay to 43.9 m on Upper Tunbridge Wells Sand, described as alternations of clay, rock and sand, to 74.7 m (Buchan et al., 1940, p.18).

A well at Christ's Hospital [TQ 1491 2902], surface level 50.3 m above OD, probably proved Upper Tunbridge Wells Sand from about 76.2 to 139.3 m but the record (Buchan et al., 1940, p.5) is far from clear. The top of the Upper Tunbridge Wells Sand has been taken at the first appearance of layers of 'sandy rock', which alternate with clay and shale to the final depth. Thin layers of 'coal' were recorded at 123.1 m.

A water borehole at Southwater Brickworks [TQ 1573 2594] proved the top of the Upper Tunbridge Wells Sand at 115.8 m (Edmunds 1928, pp.131–133); the driller's log records mostly 'sandstone' to the final depth of 131.4 m. Another borehole, at Field House [TQ 1870 2811] near Sedgewick Home Farm, surface level 74.1 m above OD, probably proved Weald Clay to about 18 to 23 m and Upper Tunbridge Wells Sand to 50.9 m (Buchan et al., 1940, p.16). The drilling record describes the strata assigned to the Upper Tunbridge Wells Sand as blue clay, 'clay shingle' and sandstone.

Topley (1875, p.40) recorded that the railway cutting [TQ 174 330] south-west of Park Farm exposed a faulted junction of Weald Clay and Tunbridge Wells Sand, the fault throwing down to the north. Slickensides were inclined at 60° from the vertical towards the west. Massive courses of buff, flaggy, cross-bedded sandstone with an easterly dip are still exposed on the east side of the cutting.

The Upper Tunbridge Wells Sand in the north-west, west and south of Horsham, between the Holmbursh Fault in the north and the Sedgewick Fault in the south, is not divisible into separate sandstone and clay units. To the south of Warnham Mill Pond, some of these beds, and others mapped as an underlying sandstone unit, were exposed in the overflow channel of the pond, for some 800 m downsteam from Warnham Mill Bridge (Plate 9). A section [TQ 1677 3221] 70 m downstream from the bridge showed the following beds of the sandstone unit:

Southwards, these beds dip below the bed of the channel, and harder siltstones with some well-defined sandstone beds were exposed. A typical section [TQ 1646 3197] showed:

A temporary section [TQ 1630 3079] near the west end of The Bishopric, Horsham, exposed 2 m of buff siltstone and clayey silt. South-eastwards, on the belt of undivided Upper Tunbridge Wells Sand mapped past the parish church [TQ 171 303] to New Town, scattered small exposures showed thinly bedded silty sandstone. The central part of Horsham, around the Carfax [TQ 172 306], is on a sandstone outcrop, although beds of silty clay occur near the surface in places in this area.

East of the Park Farm Fault, a brick-field [TQ 1670 3152] formerly existed on a small clay outcrop. Sandstone overlying this clay has an extensive outcrop between The Common and North Heath Farm. Excavations near the south-western end of Pondtail Road [TQ 1725 3105] proved pale orange and buff clayey silt and flaggy fine-grained sandstone to 2 m depth. Below the sandstone, grey to buff clay and pale grey and red mottled clay were dug at a housing site [TQ 1735 3245] east of Warnham Mill Pond. Clay at the same stratigraphical level has an irregularly shaped outcrop extending north-east from Horsham Park [TQ 173 311]. The clay was proved to 6.1 m depth in trial boreholes sunk in 1968, 100 m north of Horsham Station.

Two water boreholes at King and Barnes' Brewery, Horsham [TQ 169 308], surface level 42.4 m above OD, proved Upper Tunbridge Wells Sand to 54.6 m and 85.3 m respectively, described as alternations of clay, sandy shale, sand and stone (Edmunds, 1928, p.130; Richardson et al., 1968, p.48).

A well at Ciba Laboratories Ltd, Parsonage Road [TQ 1778 3176], surface level 61 m above OD, proved Upper Tunbridge Wells Sand to 76.3 m (Buchan et al., 1940, p.21). The borehole records describe alternations of mottled clay, marl, rock and sandstone with traces of lignite, and two thick beds of shale and marl. These latter were interpreted as 'Cuckfield Clay' and Grinstead Clay but are probably only minor clay beds within the Upper Tunbridge Wells Sand.

A water borehole at Horsham Station [TQ 1805 3134], surface level 55.8 m above OD, is sited near the top of the Upper Tunbridge Wells Sand and proved alternations of sandstone and 'marl rock' to 101.0 m (Whitaker and Reid, 1899, pp.53–54). This borehole may be entirely in Upper Tunbridge Wells Sand or it may have reached the Grinstead Clay, possibly at 91.1 m depth.

East of the site of Harwood House [TQ 184 312], an extensive area, now built over, has been excavated to a depth of 4 to 5 m for brick clay. An argillaceous unit in the Upper Tunbridge Wells Sand appears to have been overlain here by a relatively thin sandstone (Roffey Park Sandstone), about 1 m thick. The clay–sandstone boundary shown on the published map follows the edge of the old workings. In 1961, part of the former pit face at [TQ 1870 3124] behind a factory in Blatchford Road showed:

Ferguson (1926) recorded the following section at the 'Depot Brick Field' [TQ 186 311]:

He noted an 'almost imperceptible' dip towards the south-west, and some minor faulting and folding.

The Oakhill district of Horsham is named after a small sandstone-capped rise of ground [TQ 1850 3055]. Clay crops out east and south of this rise. On higher ground around [TQ 183 300] south of Oakhill and east of New Town both sandstone and clay are present but their outcrops are poorly defined.

A group of boreholes and shafts at Whitesbridge Pumping Station [TQ 1874 2913] is sited close to the base of the Weald Clay. If the 'blue shale with red patches' proved at 78.3 to 80.8 m is correctly interpreted as Grinstead Clay and is not a minor clay seam within the Upper Tunbridge Wells Sand, then the full thickness of the formation at this locality is about 90 m.

Roffey, Colgate and Pease Pottage area

This is the type area for the Shelley Plain Sandstone, the Colgate Sandstone and the Roffey Park Sandstone. The 'plains' of St Leonard's Forest are areas of flat ground, some, like Shelley Plain [TQ 248 316], fairly extensive, but others, like Stonelodge Plain [TQ 213 323], quite small, that are underlain by sandstone beds. These areas are mostly farmland, whereas most of the present woodland of the forest is on the ill-drained clay outcrops.

The Shelley Plain Sandstone is estimated to be about 3.0 to 4.5 m thick and is overlain by grey clay and sandy clay, in parts red mottled. These clays form outliers on the plain and also crop out on rising ground to the east, near Woodhurst [TQ 259 321].

The Colgate Sandstone makes a prominent shelf-like feature [TQ 232 329] where its outcrop is crossed by the road through Colgate village. The thickness of the unit is estimated to be about 3.0 m at Colgate. At and to the west of Colgate it is separated by an argillaceous unit from the underlying Shelley Plain Sandstone. Grey clay, silt and silty clay, with an extensive outcrop, occur above the Colgate Sandstone at Colgate and are succeeded by the Roffey Park Sandstone which, in Roffey Park [TQ 213 330], is about 3 m thick and forms a dip slope inclined north-westwards. This sandstone is the highest bed in the St Leonard's Forest area; the thickness of the stratigraphical interval between this and the base of the Weald Clay is uncertain.

The Colgate Sandstone forms well-marked dip slopes near Roffey Church [TQ 196 322] and around St Leonards [TQ 201 311]. Hard, dark brown, fine-grained sandstone from a trench 90 m north-east of the latter shows, in thin section (E32442), angular to subangular quartz grains (0.06 mm) together with a few flakes of muscovite mica, in a matrix of limonite–goethite. The rock may be a weathered sideritic sandstone similar to bed 2 of the Hook's Copse quarry, described below (Worssam, 1972, p.39).

In temporary exposures in a building site [TQ 191 312] on the west side of the Hornbrook valley, and in a section [TQ 213 310] in a forest ride 550 m south of St Leonard's Forest Grange School, the Colgate Sandstone was seen to comprise two sandstone beds each about 1 to 1.5 m thick, the lower flaggy, very ferruginous and fine-grained and the upper fairly coarse, separated by about 1.5 m of grey clay.

Below the lower bed at the building site, grey clay was proved for at least 4.5 m to the valley bottom. Above the upper bed, a band of grey clay of the order of 6 m thick was traced northwards from the building site to Roffey where, apparently increased in thickness, it extends as a tongue over high ground. Three outcrops of sandstone on this tongue appear to be outliers. To the north-west, the ground slopes in the same direction as the dip, though more steeply, and the consequent expansion of the outcrops enabled a clay seam within the Colgate Sandstone to be mapped from a point [TQ 1940 3285] 690 m north-north-west of the church south-westwards for 800 m to the line of a north–south-trending fault.

Red clay occurs below the Colgate Sandstone near Lily Beds at [TQ 211 309] (Worssam and Thurrell, 1967, p.269). In the wooded valley north of St Leonards, a stream section [TQ 1973 3130] exposed a 15 cm bed of weathered, silty, limonitic ironstone, including box-stones 1.3 cm thick and 5 cm across. This may be similar to the ore dug from minepits farther upstream, in and south-west of Owlbeech Wood (Worssam, 1972, fig.3).

Both east of Roffey Hurst and at St Leonard's Forest Grange School, grey clay crops out between the Colgate Sandstone and the Roffey Park Sandstone. Springs issue at the base of the latter to the south of the school. The Roffey Park Sandstone hereabouts is highly ferruginous, occurring in the soil as small, hard, platy fragments and as boxstones. Temporary excavations [TQ 214 328] indicated layers of grey silty clay interbedeed with the sandstone.

Minepits on the clay outcrop between the Roffey Park Sandstone and a lower sandstone, presumed to be the Colgate Sandstone, occur in wooded valleys between Roffey Park and Holmbush. A third, still lower sandstone, which may be the Shelley Plain Sandstone, includes in its outcrop an overgrown pit at Sand Plat [TQ 2220 3293] where Ferguson (1926, p.405) measured a 2 m section, noting the dip as 14° NW.

A shelf-like feature (Stonelodge Plain) [TQ 214 323] near the bottom of the valley between Roffey Park and St Leonard's Forest Grange School is formed by the Shelley Plain Sandstone, on the axis of the Colgate Anticline. Blocks of grey-white fine-grained sandstone up to 15 cm thick and 0.6 m across were dug in excavations here. At the head of this valley, there is a wide outcrop of clay, some of it red mottled, between the Colgate Sandstone and the Roffey Park Sandstone. Minepits are numerous here; some in an enclosure known as The Minepits [TQ 221 324] are 6 m in diameter and 3 m deep (Straker, 1931, pp.106–107).

The Roffey Park Sandstone is exposed in the Hook's Copse Quarry [TQ 220 338], mentioned by Ferguson (1926, p.406). In 1963 the north face exposed, above talus, 0.6 m of sandstone showing small-scale cross-bedding, overlain by 1.6 m of friable weathered sandstone and sandy wash. The south face showed:

A thin section of sandstone (E32280) from this quarry, of the type occurring in bed 4, shows subangular quartz grains averaging 0.06 m in diameter, a small amount of muscovite mica and clay mineral laths, and some interstitial clay mineral and limonitic cement. Dr R Dearnley (in Worssam, 1972, p.39) reported that a thin section of sandstone from bed 2 (E32281) shows unweathered, fine-grained (0.01 mm) siderite making up about half the bulk of the rock. This forms a matrix to the angular quartz grains (0.09 mm) which constitute the remainder of the sandstone, except for very minor amounts of muscovite.

Exposures of Colgate Sandstone and Shelley Plain Sandstone were seen in the banks of newly cut rides on the north-west slope of the deep valley (Coombe Bottom) north of Springfield Farm (Worssam and Thurrell, 1967). One section [TQ 2235 3225] showed yellow-brown, fine-grained sandstone with plant debris, in blocks up to 12.5 cm thick, assigned to the Colgate Sandstone. Downslope [TQ 2245 3215], below a clayey interval 6 to 9 m thick, the Shelley Plain Sandstone forms a double feature, as if comprising two sandstone bands. The lower band is marked by large blocks of soft, micaceous, coarse-grained sandrock.

The Colgate Sandstone is draped, as if cambered, over the crest of the spur between the Coombe Bottom valley and Pyefall Gill, to the south. The Shelley Plain Sandstone makes a well-developed feature on the lower slopes on both sides of this gill. Above it are mainly grey clays and silty clays. Red and grey mottled clay was seen immediately below it in a ditch section [TQ 223 312] to the south of Springfield Farm, though grey clay appeared at a similar horizon in places on the south side of the valley.

At Combe Wood, Colgate, a borehole [TQ 2280 3260] penetrated 71 m of shale, marl, clay and stone, with a vein of 'coal' (Buchan et al., 1940, p.21). Clay beds in this borehole previously interpreted as 'Cuckfield Clay' and Grinstead Clay may be thicker clayey beds within the Upper Tunbridge Wells Sand.

In 1963, a now backfilled brickpit [TQ 241 333], 550 m north-east of Colgate Church, showed faces up to 3 m high in grey silty clay and red and grey mottled clay. The lowest part of this clay, together with the underlying Shelley Plain Sandstone, was exposed as follows in an old quarry [TQ 2340 3378] 870 m east of Holmbush, the dip being 2° NNE:

Black Hill [TQ 241 330] is capped by an outlier of sandstone, and a lower sandstone crops out on its slopes. The clay beneath this lower sandstone on an east-north-easterly spur of the hill rests on an extensive surface of the Shelley Plain Sandstone where it straddles the Colgate Anticline. North of the anticlinal axis, the surface slopes fairly steeply northwards at Buchan Hill and in Pease Pottage Forest, dissected by north-flowing valleys in each of which is an inlier of the underlying clay. South of the anticlinal axis the sandstone, dipping south-east, caps flat-topped interfluves between valleys draining south-west.

On Shelley Plain an outlier of grey clay and sandy clay, some of it red-mottled, forms a low rise [TQ 247 315] some 3 m high. Similar clay outliers with indefinite boundaries, some showing indications of a sandstone capping, occur 550 m south-east of Shelley Farm, south of Tilgate Forest Lodge, and in Highbeeches Forest, north of Brantridge Forest Farm.

In the deep valley west of Shelley Plain, a stream section [TQ 2447 3194] showed 1.5 m of yellow-brown sandstone in layers up to 15 cm thick; 135 m downstream, 1.5 m of thinly bedded, orange-brown sandstone with siltstone and clay seams were seen. This sandstone, 9 m or so below the Shelley Plain Sandstone, makes a feature on the south-east side of the valley and springs issue from it. Below it, in the stream bed 120 m downstream from the last-mentioned exposure, 1 m of grey-white and red-mottled clay was seen.

About 550 m north-east of Shelley Farm, grey clay, silt and silty clay overlying the Shelley Plain Sandstone form a well-marked south-west-facing slope capped by sandstone, the latter having a wide outcrop around Pease Pottage, where it forms the crest of the Colgate Anticline. Sandstone on the top of Benson's Hill [TQ 268 325] appears to be an outlier of that at Pease Pottage. Grey clay with some red mottling, between this and the Shelley Plain Sandstone, makes a marked slope around the hill.

The Shelley Plain Sandstone dip slope in Pease Pottage Forest declines northwards to the foot of a range of hills comprising Silver Hill [TQ 235 341], Spruce Hill [TQ 241 342], Target Hill [TQ 248 343] and Broadfield Forest [TQ 258 345]. The three more westerly hills each have a steep northerly dip slope of Roffey Park Sandstone, cut off sharply to the north along the line of the Holmbush Fault, and an equally steep scarp face on which minor features are formed by the Colgate Sandstone and an unnamed sandstone in clay between that and the Shelley Plain Sandstone. In Broadfield Forest the ridge crest is formed by the Colgate Sandstone. Correlation of the sandstones was aided by the presence of a continuous belt of iron-ore minepits in the clay slack below the highest sandstone (Worssam, 1972, fig.3).

Red and grey mottled silty clay overlying the Shelley Plain Sandstone was ploughed up 360 m north of Buchan Hill; on the slope above [TQ 250 340], grey silty clay and soft flaky siltstone were exposed in a trench. Plant remains in loose fragments of soft yellow sandstone on a boundary bank [TQ 2565 3435] have been identified by Professor W G Chaloner as Weichselia reticulata (Stokes & Webb) and Equisetites sp. In 1972, a trench [TQ 2598 3443] 420 m west-south-west of Broadfield showed:

The beds dip at about 6° NW. The sandstone at the base of the section is probably the Colgate Sandstone, which crops out 60 m to the south. The clay-ironstone bed near the top of the section appears to be a siderite-impregnated, fine-grained sandstone, and to have been worked in minepits (Worssam and Gibson-Hill, 1976).

Highbeeches Forest, Tilgate Forest, and Worth Forest area

In a gully [TQ 2830 3243] on the north side of the Stanford Brook valley, red clay of the Grinstead Clay was seen immediately below a sandstone bed taken as the base of the Upper Tunbridge Wells Sand. The north-flowing stream in Brantridge Forest crosses this bed at a waterfall [TQ 2835 3225], exposing 1.5 to 2 m of sandstone. The top of the sandstone was seen in a ditch section [TQ 2825 3245] on the north slope of the valley. This was succeeded by weathered, grey and yellow clay and by red and grey mottled clay overlain by a sandstone bed, estimated to be 0.6 m thick where exposed in the ditch [TQ 2800 3244].

Northwards, the upper slopes of the valleys, as shown by sections in the banks of a trackway [TQ 2825 3370], are much cambered and characterised by sandstone debris.

The hill range north of Pease Pottage Forest, described above, continues east of the Brighton road as far as Tilgate [TQ 276 344], where the Roffey Park Sandstone forms a distinct dip slope. East of Tilgate, however, this sandstone is not traceable. Sections in the banks of a stream channel [TQ 2806 3485] and in an old quarry [TQ 2817 3465] showed 1 to 1.5 m of grey to buff silty shale and laminated argillaceous siltstone, a thin section of the latter (E32279) showing closely packed quartz grains (0.010 mm in diameter) with interstitial clay. South of the quarry, a low ridge showed evidence of sandstone on its crest. About 360 m south of the ridge is an isolated group of minepits [TQ 2820 3415] aligned north-eastwards, in the same direction as the ridge, and covering an area 135 m by 25 m.

The Worth Forest Borehole [TQ 2891 3500], sited on the Upper Tunbridge Wells Sand, probably proved the formation to about 44 m depth.

Balcombe area

The complex of shafts and connecting galleries at Balcombe Waterworks [TQ 290 313] is sited on the Upper Tunbridge Wells Sand and proved this formation, which consists of alternations of 'sandstone, sand, clay, rock and ironstone', to 43.4 m (Edmunds, 1928, p.49).

Mannings Heath and Handcross area

In the southern part of St Leonard's Forest, alternating sandstone and clay units, dipping gently south-westwards and developing increasing lenticularity in the same direction, are dissected by the deep valleys of small streams draining south-westwards to the River Arun. An outlier of the Roffey Park Sandstone caps a ridge along the crest of which [TQ 217 319] to [TQ 217 300] runs the long, straight, north- south ride known as Mick Mill's Race (Worssam and Thurrell, 1967, p.269). Some old diggings up to 1.5 m deep in orange-brown flaggy sandstone were noted [TQ 2176 3063] near the southern end of the outlier. Other outliers of the sandstone occur at spot height 323 ft (98.45 m) [TQ 215 298] and near St Leonard's at [TQ 205 309].

The Colgate Sandstone has a narrow outcrop on the steep eastern slope of the Mick Mill's Race ridge, but its outcrop widens at the southern end at [TQ 215 296] and [TQ 210 297] and on the western side of the ridge [TQ 213 305]. The same sandstone forms a wide dip slope around [TQ 205 305] south of St Leonard's. A lens of clay occurs within the sandstone on both sides of the Hornbrook valley from near Hampers Lane [TQ 194 301] southwards to Doomsday Green [TQ 193 291]. Minepits occur on the clay below the lower layer of sandstone on the east side of the valley in Highland Copse [TQ 1955 3025]. A stream section [TQ 1882 2988] in the Colgate Sandstone exposed:

South of the River Arun, between Amiesmill Farm [TQ 184 291] and Mannings Heath, are sandstones and siltstones with interbedded clays, approximately at the horizon of the Colgate and Roffey Park sandstones, though exact correlation with the beds north of the river is not possible. A section in a plunge-pool on the south side of the main road at Birchen Bridge [TQ 1936 2913] showed:

Beds at about the same horizon as those at the top of this section were seen as follows in an old quarry [TQ 1946 2910] on the north side of the road 100 m south east of Birchen Bridge:

The same sandstone, 1.5 m thick, occurs in a waterfall [TQ 2025 2906] in Gaggle Wood, about 0.8 km to the east. Slightly higher beds crop out in a stream section [TQ 1965 2879] 450 m south east of Birchen Bridge:

These beds are involved in a small anticlinal valley-bulge structure.

A water borehole at Waterpit Lane, Mannings Heath [TQ 2128 2881], surface level 80.8 m above OD, proved Upper Tunbridge Wells Sand to 41.5 m (Buchan et al., 1940, p.4). A bed of 'blue clay' from 34.7 to 41.4 m, assigned by earlier authors to the Grinstead Clay, is probably a clay within the Upper Tunbridge Wells Sand.

In the deep valley (Sheepwash Gill) north of The Goldings, up to 3 m of massive, medium- to coarse-grained sandstone, in layers 15 to 45 cm thick, and possibly at the horizon of the Shelley Plain Sandstone, are exposed in two waterfalls [TQ 2082 2990]; [TQ 2078 3007] and in a stream section [TQ 2075 2993]. Sandstone at about the same horizon, overlying siltstone and silty mudstone, the latter including a 7.5 cm bed of hard blue-grey shelly limestone or ironstone, was noted 250 m south-east of The Goldings, along a stream [TQ 2120 2946] to [TQ 2116 2930] on Mannings Heath Golf Course.

A hilltop outlier of Colgate Sandstone, capped by clay, occurs in Barnsnap Wood. A partly overgrown quarry [TQ 2270 3103] showed 1.2 m of massively bedded, buff and yellow-orange, fine-grained sandstone in courses up to 0.6 m thick, overlain by up to 1.5 m of interbedded flaggy, silty sandstone and clayey silt. The Colgate Sandstone also caps the parallel ridge top to the south-east [TQ 233 310]. Near the southern end of this ridge a lenticular outcrop of clay lies above the sandstone. Minepits were noted in a small area [TQ 223 297] on the west side of the road along the ridge crest (Plate 6). Other small patches of mine-pitted ground were noted in Lily Beds [TQ 2115 3080] and elsewhere on the slopes of Sheepwash Gill [TQ 2092 3100]; [TQ 2092 3067]; [TQ 2105 3045]; [TQ 2130 3003]; [TQ 2050 2990]; [TQ 2090 2975], and to the north of Hawkins Pond [TQ 2185 3025].

A section [TQ 2194 2891] at the outfall of Hammer Pond, south of the road, showed:

At a slightly lower stratigraphical level and 200 m to the west, a stream section [TQ 2176 2887] showed 2 m of pale grey, silty mudstone overlying 1 m of massive, blocky, blue-grey siltstone in 10 cm bands.

Between The Hyde [TQ 246 302] and Nashland Farm there is a broad dip slope formed by sandstone at much the same altitude and stratigraphical level as the Shelley Plain Sandstone to the north. South of Handcross Park [TQ 265 307], mainly silts overlie this horizon. They are exposed in a cutting [TQ 2612 2968] on the Hand-cross bypass road, and have a narrow outcrop that in Handcross village is capped by a higher sandstone. This latter sandstone, which is in a stratigraphical position equivalent to that capping Benson's Hill, to the north, forms two outliers, one on each side of the Brighton road. Old pits [TQ 2640 3025] at 'Gravelpit Corner' near the northern end of the outlier, to the east, showed up to 2 m of rubbly, fine-grained sandstone. Near the southern end of the western outlier, a 3 m-deep road cutting [TQ 2520 2865] showed flaggy, friable sandstone with a southerly dip.

Ashfold Crossways, Slaugham and Staplefield area

In this area, north of the Sidnye Farm Fault, the regional dip is southwards. An outlier of sandstone caps a flat-topped rise of ground [TQ 246 289] at Ashfold. Two boreholes at Ashfold Farm [TQ 249 291], surface level 122.8 m above OD, proved Tunbridge Wells Sand to 79.2 and 88.4 m respectively (Edmunds, 1928, pp.112 and 188). The deeper of these boreholes is tentatively classified as Upper Tunbridge Wells Sand to 42.7 m, Grinstead Clay to 62.6 m and Lower Tunbridge Wells Sand to the final depth. The Upper Tunbridge Wells Sand was described predominantly as sandstone with thinner beds of clay and sandy clay.

Sections [TQ 2451 2750] 50 m north of the Sidnye Farm Fault showed 2 m of pale grey to yellow-brown clayey silt and fine clayey sand containing seams of compact silty sandstone, on 0.45 m of laminated clayey silt with partings of grey clay. At about the same stratigraphical level, minepits occur in the southern part of a small wood (Holes Wood) [TQ 255 277]. In the outfall [TQ 2580 2775] of Slaugham Mill Pond, between 3 and 4.5 m of buff, pale grey and yellowish brown siltstone, well-bedded in courses up to 7.5 cm thick, is exposed below a cascade. The rock shows cross and ripple-drift bedding and load-casting, and carbonaceous detritus occurs on most major bedding planes. To the south is Mill Hill, an escarpment formed by southward-dipping sandstone.

At Stone Court, Staplefield [TQ 2791 2800], a borehole proved Upper Tunbridge Wells Sand (alternations of clay and sandstone) to 31.7 m on Grinstead Clay (Richardson et al., 1968, p.58).

Nuthurst, Lower Beeding, Crabtree, Warninglid and Cuckfield area

South of the Nuthurst Fault and the Borde Hill Fault, the Upper Tunbridge Wells Sand can only locally be divided into clay and sandstone units. Between Nuthurst [TQ 192 262], where an unfaulted contact with the Weald Clay is present, and Lower Beeding a maximum of about 46 m of Upper Tunbridge Wells Sand are present.

A borehole at Maplehurst Cottage, Nuthurst [TQ 1889 2432], surface level 36.6 m above OD, is sited on Weald Clay close to the Maplehurst Fault. The drilling record is poor but the field evidence suggests that the borehole may have passed through a faulted Weald Clay–Upper Tunbridge Wells Sand contact at about 20.7 m; Upper Tunbridge Wells Sand, described as shale, marl, 'rock' and sandstone, was encountered to 42.2 m (Buchan et al., 1940, p.18).

A section in a stream bed [TQ 1864 2637] close to the junction with the Weald Clay exposed:

A section 75 m downstream showed 0.3 m of khaki-grey, shaly siltstone containing plant debris; a 15 cm band of clay-ironstone nodules set in grey clayey siltstone occurs a further 75 m downstream. A stream section [TQ 1917 2625] 75 m north-west of Nuthurst Church, and a roadside exposure [TQ 1944 2677] 600 m north-north-east of the church exposed massive and flaggy medium-grained sandstones.

Almost continuous exposures occur in the stream bed in Cook's Copse [TQ 1951 2680] to [TQ 2026 2695]. The more westerly show mainly orange, buff and khaki, flaggy and friable, fine- to medium-grained sandstones and silty sandstones, pale brown siltstones, and orange, brown and yellow clays including a seam of nodular clay-ironstone, all disturbed by valley bulging. A stream bank [TQ 1975 2695] showed:

A 0.6 m bed of flaggy sandstone containing a thin seam of clay-ironstone forms a ripple-marked pavement in the stream bed 55 m downstream from the above section. Exposures at a confluence [TQ 1989 2702] showed:

In the tributary stream, 45 m to the north, sandstone was seen to be overlain by 0.3 m of grey clay with laths of lignite, capped by 0.3 m of soft yellow coarse sandstone.

A waterfall in Nine Acre Gill [TQ 2024 2696] exposed:

Fine-grained, silty sandstones, including an 8 cm bed of clay-ironstone, crop out a further 235 m downstream.

At Plummers Plain, sandstone beds in the Upper Tunbridge Wells Sand form a succession of gently sloping dip slopes. A stream section [TQ 2237 2842] adjacent to the Nuthurst Fault showed:

Numerous springs issue from sandstone seams in a silt and silty clay sequence in the wooded valley immediately south of Newells. Small exposures showing bedded clay-ironstone and ripple-marked, fine-grained sandstone occur in the stream bed between here and Job's Castle [TQ 2124 2625] to [TQ 2121 2530].

Sandstones have been extensively dug in a large number of pits at Cooper's Hill [TQ 225 272] to [TQ 228 270], south-east of Lower Beeding. Small exposures along a stream [TQ 2260 2704] to [TQ 2270 2723] nearby showed up to 1.8 m of sandstone, locally with plant debris, silty clays and clay-ironstone.

A thick bed of sandstone forms a long, gentle dip slope between Beedinglee and Crabtree village. This sandstone is locally cambered over the underlying more clayey beds, particularly along the western edge of the dip slope. Ironstone, probably lying beneath this sandstone bed, has been extensively worked in and around Minepits Wood [TQ 225 253], on the east side of the village. Minepits nearby at Eastland Hill [TQ 2281 2648], 680 m west of Copyhold, appear to have been dug for a clay-ironstone within a more clayey part of the Upper Tunbridge Wells Sand.

Between Leonardslee [TQ 222 259] and Warninglid [TQ 250 262], the Upper Tunbridge Wells Sand outcrop, comprising alternations of clayey silt and silty clay with more sandy beds, is dissected by steep-sided valleys in which numerous small springs issue where sandstone beds are in contact with less permeable strata. Exposures in stream beds commonly show only the more resistant sandstone and siltstone beds.

A stream section [TQ 2371 2649], 550 m west-south-west of Eastland Farm, exposed:

A waterfall [TQ 2385 2605] in Bishop's Wood showed:

A section 165 m downstream, in East Hanger Wood showed:

Small crags of sandstone occur in the sides of the steep-sided valley between Bishop's Wood and Iron Gill. A waterfall section in Iron Gill [TQ 2446 2626] shows 1.8 m of orange, planty, well-jointed, fine- to medium-grained sandstone overlying 7.3 m of pale grey-buff compact silt and silty fine-grained sandstones which have been mapped as clay in the Upper Tunbridge Wells Sand.

A degraded pit in Dudwick Wood [TQ 2384 2573] exposed 3.7 m of purplish pink and buff grey silt and siltstone, containing several levels of more clayey silt with plant debris.

The park at Lydhurst and much of the village of Warninglid are built on the dip slope of a more prominent sandstone bed within the Upper Tunbridge Wells Sand.

Many small exposures of sandstone, siltstone and silty mudstone occur in the stream bed in Rout Gill in the outlier of Upper Tunbridge Wells Sand between the Lydhurst and Freechase faults. The best section [TQ 2472 2534], with dips up to 45°, probably due to the proximity of the Freechase Fault, showed:

A section 320 m upstream showed an 8 cm seam of clay-ironstone resting on fine- to medium-grained sandstone.

A temporary section along the London to Brighton road [TQ 2669 2600], 385 m north of Old Haslings, showed alternations, in 7.5 to 15 cm units, of orange-buff, fine-grained sandstone, silty clay and red clay for 0.9 m.

The following sequence was proved in the Cuckfield No.1 Borehole:

The driller's log of a well at Brook Street [TQ 306 275] (exact site uncertain) has been the subject of some controversy but now, by comparison with the nearby Cuckfield No.1 Borehole, may be classified as Upper Tunbridge Wells Sand from 87.6 m to the final depth of 122 m.

Wallhurst Manor and Bolney area

Between the Frithknowle–Drewitts Fault and Ansty [TQ 291 233], the Upper Tunbridge Wells Sand appears to dip regularly southwards and to be little affected by major faulting. However, large faults displace the Weald Clay-Upper Tunbridge Wells Sand junction nearby and others displace the Grinstead Clay outcrop. They cannot be traced through the poorly exposed Upper Tunbridge Wells Sand outcrop, but it seems likely that these faults, mostly strike faults, continue through the Upper Tunbridge Wells Sand and locally cut out large parts of the sequence. Borehole evidence suggests that the full thickness of the formation in this area exceeds 90 m.

Old sandstone quarries in Wallhurst Copse [TQ 2295 2416]; [TQ 2296 2400], roadside crags and small old quarries e.g. [TQ 2372 2428], 410 m east of Longhouse Farm, probably lie at a similar stratigraphical level. Another old pit [TQ 2383 2428] nearby showed:

Small crags of sandstone probably at the same level occur on a promiment escarpment through Colwood.

An old quarry [TQ 2506 2368] 370 m north of Old Mill House, exposed:

Small exposures of sandstones were also noted [TQ 2574 2360]; [TQ 2618 2389]; [TQ 2685 2410] in the Bolney Common area.

Between Bolney village [TQ 261 228] and Merryfields [TQ 273 241], sandstone beds within the Upper Tunbridge Wells Sand form a series of long dissected dip slopes; more silty and clayey beds crop out in the valley sides. The long outcrop of Upper Tunbridge Wells Sand brought up by the Bolney Fault forms a narrow sandstone and silt-capped ridge. At Bolney village, ferruginous sandstone is locally common close to the contact with the Weald Clay.

The outcrop of the Upper Tunbridge Wells Sand is unusually narrow between Pickwell Farm and Hilders Farm due to a combination of steep dips and strike faulting. The faulting in this area is probably more complicated than that depicted on the published map but the field evidence is too poor for faults to be detected. The Henfield Wood Fault is most probably connected to the Garston's Farm Fault (in the Brighton district) by a cross fault. Similarly, it seems likely that the Lucas Grange Fault continues west of Ansty.

The Bolney No.1 Borehole in Broxmead Lane [TQ 2801 2427] penetrated 31.6 m of Upper Tunbridge Wells Sand, but no sample was preserved other than washings of clay, silt and fine-grained sand.

Haywards Heath, Lindfield and Freshfield area

Throughout this area there occurs a persistent sequence of red and pale grey-mottled silty clays and clayey silts about 12 to 15 m above the base of the Upper Tunbridge Wells Sand. This unit, about 12 m thick, is divided into two roughly equal parts by a bed of silty sandstone, 0.9 to 1.5 m thick, which is locally dark brown and iron-stained. The topmost clay is mostly uniformly red, and locally the underlying sandstone has been worked from beneath a capping of clay in the same way that the Cuckfield Stone has been worked beneath Upper Grinstead Clay. In places, the dark ferruginous staining of the sandstone suggests that it may, like the Cuckfield Stone, be calcareous in the unweathered state. The whole sequence can be readily mistaken for the Grinstead Clay where the latter is divided by the Cuckfield Stone.

The following section at the base of the Upper Tunbridge Wells Sand was measured above the north portal of the Haywards Heath railway tunnel:

Small disturbed sections showing siltstones and sandstones, similar to those described above, occur in the cutting [TQ 3295 2423] to [TQ 3299 2440] between a fault and the station.

A temporary section [TQ 3291 2448] at the telephone exchange showed, beneath 0.75 m of grey- and reddish brown-mottled silty clay wash (Head), 2.44 m of orange-grey, flaggy, interbedded siltstones and silty sandstones; thin lenses of khaki and red-mottled silty mudstone were seen towards the base, probably near to the junction with the Grinstead Clay.

A trench in Lucastes Road [TQ 3232 2427] to [TQ 3235 2449], 460 m north-east of Butlersgreen House, showed the following composite section:

Red and grey mottled silty clays, at a stratigraphically higher level than those described above, were formerly worked for bricks at Haywards Heath (Topley, 1875, p.94), but the workings at South Road [TQ 3325 2370] and Ashenground Road [TQ 333 233]; [TQ 330 230] have now been built on.

A line of pits within this clay runs from Chownes Mead to Butlersgreen House. One of them [TQ 3128 2364] is in the lower clay, but the remainder are all in the upper. Those at Chownes Mead [TQ 3165 2371]; [TQ 3179 2370] are sited on the upper clay but may have worked the sandstone. Other pits at Butlersgreen House [TQ 3200 2388] and at Bolnore [TQ 3202 2364] appear to be entirely within the upper clay. On the north side of the Cuckfield- Haywards Heath ridge these clays crop out in the valley on the north side of Butlersgreen House, and are probably equivalent in part to the thick, red-mottled, clayey siltstone bed recorded in a temporary section at Lucastes Road (see below). The same clay unit, again divided by a thin ferruginous sandstone, forms a series of prominent features and is well exposed in the soil debris between Pink's Wood [TQ 287 226], Harvesthill [TQ 297 225] and Upper Ridges [TQ 307 226], and between Hookhouse Wood [TQ 308 219] and Folly Farm [TQ 327 219].

A water borehole at Gordons Road, Haywards Heath [TQ 3355 2500] proved 'loamy sand, clay and rock' to 65.2 m, which may all be Upper Tunbridge Wells Sand (Edmunds, 1928, p.119). This borehole is sited on the Upper Tunbridge Wells Sand in an area complicated by faulting, and the stratigraphy at depth is unknown. Some of the beds below 65.2 m (to 98.4 m), which have tentatively been assigned to the Grinstead Clay (p.52) and the Lower Tunbridge Wells Sand, may belong to the Upper Tunbridge Wells Sand. A well at Sunte House [TQ 3341 2548] proved 30.5 m of strata described as alternations of 'sandstone, clay and rock' (Buchan et al., 1940, p.20), probably all in Upper Tunbridge Wells Sand.

Sections in predominantly sandy and silty Upper Tunbridge Wells Sand were seen in the steep-sided valleys near Lodge Farm [TQ 3030 2339] to [TQ 3068 2364] and Copyhold Farm [TQ 3077 2313] to [TQ 3139 2340]. A section [TQ 3044 2344] 200 m west of Lodge Farm showed 2.1 m of flaggy and thickly bedded, fine-grained, silty sandstone, cross-laminated and with scour features. Similar sandstones, disturbed by a fault, crop out nearby in the main stream [TQ 3026 2351].

A waterfall [TQ 3033 2300] 320 m south-west of Copyhold Farm exposed 3.6 m of thickly bedded and massive silty sandstone disturbed by a major fault. In the lower part of the valley, near Copyhold Farm, the stream is floored by flaggy and thickly bedded silty sandstones and by grey siltstones. Red- and grey-mottled silty clays are more common in the middle and upper part of the valley where they give rise to landslips. A disturbed section at the upper end of the valley [TQ 3135 2338] 780 m east-north-east of the farm, showed:

Several thin beds of ferruginous sandstone crop out near Ansty. The most prominent forms a distinctive feature and can be traced from Butler's Farm [TQ 2865 2300] to an area [TQ 2965 2309] east of Mount Noddy, on the south side of the crossroads.

Between Leigh Manor and the Burgess Hill Fault, and between there and the Lunce's Common Fault, the junction with the Weald Clay has been taken at the top of a prominent thick bed of sandstone which is locally capped by very ferruginous sandstone or clay ironstone.

A section in the road cutting [TQ 2963 2231] 180 m south of Harvesthill exposed part of the top sandstone:

A trench [TQ 3041 2238] 780 m east of this road showed 0.15 m of clay-ironstone resting on flaggy, silty sandstone equivalent to the top bed of the previous section. Between these two sections the strong dip slope feature of the top sandstone is littered with fragments of very ferruginous sandstone.

A prominent bed of ironstone was traced from near the laundry [TQ 349 248] via Cripland Court [TQ 349 243] to south of Walstead Place Farm [TQ 357 242]. A roadside section at Cripland Court showed:

The ironstone has been worked in shallow open pits [TQ 350 244] and minepits [TQ 350 245] near Cripland Court Farm, and eastwards from there [TQ 3558 2427] in steeply dipping beds close to Walstead Place Farm.

The following composite section was measured in an access shaft [TQ 3617 2465] to a sewerage-pipe tunnel:

An old pit [TQ 3613 2429] 685 m south-west of Great Walstead showed 0.25 m of massive, silty, fine-grained sandstone beneath red and grey mottled silty clay.

Over 45 m of Upper Tunbridge Wells Sand, folded into a gentle syncline, crops out in Wapsbourne Wood, north of Massets Place [TQ 388 236]. At least four good features, each formed by a thin sandstone, were mapped, but exposure was poor: locally, red- and grey-mottled silty clays form spring lines.

Small quarries on either side of the road at Freshfield Place [TQ 3852 2399] exposed up to 2.1 m of massive, orange and greyish white, fine-grained sandstone at the base of the Upper Tunbridge Wells Sand. This bed is of local extent, in contrast to the more typical basal beds of silt and silty clay; it appears to rest directly on Upper Grinstead Clay.

Scaynes Hill area

The Upper Tunbridge Wells Sand is very poorly exposed around Pegden Common, Henfield Wood, Bedales and Scaynes Hill. There are numerous shallow workings in the area and many of these expose up to 2 m of silt or silty sandstone. Some of these pits appear to have been dug for sandstone for roadmaking, but others may have worked ironstone or possibly even siltstone for its fulling properties. All these workings are very small and widely spaced and none follow a persistent geological horizon. Such pits occur in Hen-field Wood [TQ 3672 2425], at Henfield Barn [TQ 3693 2375], near Scaynes Hill Church [TQ 3662 2329] and [TQ 3686 2309], Scaynes Hill Common [TQ 3714 2361] and Nash Farm [TQ 3737 2361].

The sandstone which rests directly on Grinstead Clay at Freshfield Place (see above) extends into the Scaynes Hill area and has been worked in pits in Costell's Wood [TQ 3629 2374] and [TQ 3658 2361], 800 m north-west of Scaynes Hill Church, and in Henfield Wood [TQ 3731 2426]. This last locality shows 0.9 m of mottled grey and orange silts overlying 1.8 m of thickly bedded, fine-grained sandstone.

A temporary section at Hammond Farm [TQ 3806 2300] showed the following composite section at this same level, illustrating the variable nature of the junction with the Grinstead Clay:

The prominent bed of red- and pale grey-mottled, silty clay in the lower part of the Upper Tunbridge Wells Sand at Haywards Heath can be traced via Abbots Leigh to the district boundary at Pellingbridge. It has been worked for brickclays at Scaynes Hill [TQ 3657 2298]; [TQ 3687 2294].

Chapter 4 Cretaceous: Weald Clay

The Weald Clay is present throughout much of the western part of the district where it has a broad outcrop on mostly low-lying ground (Plate 10). The dip is north-westerly in the north, changing through westerly to southerly in the south as the formation crosses the axial region of the Wealden anticline. In addition there is an elongate outlier in the upper Ouse valley, downfaulted between the Sidnye Farm and Borde Hill faults.

The formation consists predominantly of clay and silty clay but also includes thin beds of sandstone, shelly limestone and clay-ironstone which, being more resistant to erosion, form low escarpments and diversify the otherwise low relief. On the published geological map and in (Figure 15), (Figure 16) and (Figure 17), numbers are given to sandstone and limestone beds, following the system used in the Haslemere district (Thurrell et al., 1968, p.23). These broadly follow the succession of seven subordinate Weald Clay 'beds' recognised by the first geological survey (Topley, 1875). Names have been applied to many of these beds by Allen (1976, p.429).

The Weald Clay near the ground surface is typically pale grey or pale greenish grey, variably mottled with yellowish grey or yellowish brown due to weathering. There is generally a sharp base to the weathered zone, at about 4 to 6 m depth. Unweathered clays, as seen in borehole cores, are mostly greenish grey, but medium to dark grey and olive-grey clays also occur. Many of the clay beds contain laminae of quartz silt.

Red clays (including red and grey mottled 'catsbrain' clays) are generally associated with sandstone beds, although no evidence has been found for the continuity of red clay seams over long distances as suggested by Reeves (1949, 1958, 1969). Most red clays are probably primary red-beds, produced by penecontemporaneous emergence of newly deposited sediments, followed by lowering of the water table so as to bring them within the zone of oxidation. Some red mottling may result from present-day weathering processes, as indicated by some temporary exposures at Broadfield (p.76).

Sandstone beds in the Weald Clay rarely exceed 3 m in thickness and are generally fine-grained, quartzose, soft, and grey to greenish grey, weathering yellowish brown. Lamination and small-scale cross-bedding are seen in places. A crystalline calcite cement is present in some beds, giving lustre-mottling. Some of the sandstones contain glauconite. The most prominent and laterally persistent sandstone in the Weald Clay of the western Weald is the Horsham Stone, which was formerly extensively worked for building purposes in pits in the prominent escarpment that the sandstone caps on the south and west sides of Horsham. It can be traced as a single seam from Crawley to Horsham, and south-east from there as two seams until it passes into the Brighton district.

The grain size of the sandstones is commonly around 0.06 mm, at the lower size limit of fine sandstone, but some Weald Clay 'sandstones', on a grain-size basis alone, should strictly be classed as siltstones. In their field relationships, however, the sandstones of this district form a group distinct from Weald Clay siltstones. The latter commonly occur in small (0.1 to 1.0 m diameter) lenses that do not form mappable units. A thin-section (E32287) of typical siltstone, from a stream section [TQ 154 370] 350 m south-south-west from Oakdale Farm, shows subangular quartz grains up to 0.03 mm in diameter in a crystalline calcite matrix, the ratio of quartz to calcite being about 60:40.

'Pebble beds' in the Weald Clay comprise thin layers of gritty to pebbly calcareous sandstone, usually about 3 cm but locally up to 15 cm thick. They may also occur as lenticles, 30 to 50 cm in width, forming the 'trails of pebbly flute and gutter casts' of Allen (1976, p.412). The pebbles, mainly of quartz and chert, are commonly only 2 to 4 mm in diameter, but some attain 10 mm. The beds commonly have ripple-marked tops like the Hastings Beds pebble beds (Allen, 1959). A particularly persistent pebble bed, or group of individually impersistent lenses, at what for practical purposes is one horizon, has been mapped as the Gossops Green Pebble Bed.

The limestone beds are of three types: 'Cyrena' limestone, Small-'Paludina' limestone and Large-'Paludina' limestone (the obsolete fossil names are retained for the sake of continuity in lithostratigraphical usage). 'Cyrena' limestone occurs in layers up to 5 cm thick, that consist of closely packed shells of the brackish-water bivalve Filosina gregaria Casey (see Casey, 1955) in a bluish grey crystalline matrix. Small-'Paludina' limestone, also generally a hard, blue, crystalline rock, occurs in thicker layers, commonly between 2 and 15 cm thick, containing closely packed shell detritus of the gastropod Viviparus infracretacicus Huckriede (Morter, 1978). This stone has its thickest development in the vicinity of Charlwood, in the north of the district, and is known locally as Charlwood Stone. Large-'Paludina' limestone forms beds from 10 to 30 cm thick, composed largely of gastropods of the globose species Viviparus fluviorum (J Sowerby non de Montfort), in a fine-grained matrix that commonly contains ostracods and which may also be manly. Local names for Large-'Paludina' limestones are Sussex Marble, Petworth Marble and 'winklestone'. In places, as at the Warnham Brickworks, beds of 'Paludina' limestone are found to pass laterally into mere scatterings of Viviparus shells on bedding planes.

Clay-ironstone, or siderite mudstone, occurs as closely spaced nodules or as thin bands in the lower part of the Weald Clay in this district. Some of these ironstones are sphaerosideritic (Worssam, 1972), and 'chamosite' mud-stone (Thurrell et al., 1970) occurs rarely.

The Weald Clay as originally deposited may have attained 400 m in thickness in the northern part of the Horsham district, thinning to some 300 m in the south. Above the highest beds at outcrop, in the north-west, there are in adjacent districts some 75 m of strata up to the base of the Lower Greensand. The Collendean Farm Borehole [TQ 2480 4429] started just above the highest horizon of Small-'Paludina' limestone (Bed 2b) and entered the Upper Tunbridge Wells Sand at about 148 m depth.

Cyclic sedimentation

Throughout the Weald Clay there appears to be a rhythmic alternation between beds of silty clay, 0.3 to 1.5 m thick, with closely spaced silt laminae, and slightly thinner beds of nonsilty or only slightly silty clay (MacDougall and Prentice, 1964, p.258; Prentice, 1969; Worssam and Ivimey-Cook, 1971). Bioturbation has commonly disrupted the laminated silty clays, though fossils tend to be scarce in these rocks. In contrast, the nonsilty clays commonly contain ostracods (scattered in profusion on some bedding planes) and fish remains. This rhythmic deposition, which may have resulted from oscillation between deeper-water conditions, in which the less silty clays were deposited, and relatively shallower-water conditions with increased influx of silt, was interrupted from time to time, either by intervals of restricted terrigenous sedimentation, in which shell-limestones accumulated, or by periods of marked shallowing in which sand bodies were built out into the basin of deposition. The clay-ironstones appear to have formed most commonly at the periphery of sand bodies (Worssam, 1972).

Two large-scale cyclic units can be discerned within the Weald Clay. The first began with deposition of predominantly silty clays, followed in the western part of the Weald by that of the Horsham Stone, in shallower-water conditions. The cycle culminated with deeper-water conditions in which were formed, successively, 'Cyrena' limestone, Small 'Paludina' limestone and up to three brackish-marine bands. These latter bands are of the order of 1 m thick and consist of clay with abundant shells of Filosina or of the ornamented gastropod Cassiope. Thin pebble beds occur close below and above these bands.

The second cyclic unit commenced with the deposition of sands and red clays. It is characterised by the occurrence, as isolated lenticles or beds, of Large-'Paludina' limestone. Above the highest limestone occurs red clay and sandstone, overlain by grey clays and silty clays that form the top 30 to 75 m of the Weald Clay. Deeper water conditions are indicated by brackish-marine intercalations near the top of the formation (Chatwin in Dines and Edmunds, 1933, p.115; Thurrell et al., 1968, p.20; Lake and Young, 1978), not preserved within this district.

The cycle concept helps to explain many features of the Weald Clay succession. For example, Topley's (1875) seven subordinate 'beds' can be interpreted in terms of the two cycles, the first comprising Bed 1 (Horsham Stone) and Bed 3 (Small-'Paludina' limestone), and the second consisting of Bed 4 (Large-'Paludina' limestone), Bed 5 (sandstone), Bed 6 (Large-'Paludina' limestone) and Bed 7 (sandstone). The existence of Bed 2 (sandstone) has not been confirmed. Basin casts are common in the upper part of the first cycle (Prentice, 1962; 1969), where high sea-level phases during the ap proach and recession of brackish-marine incursions may have led to crevassing, as indicated by the sharply erosional bases of these structures. In the second cycle, a predominantly freshwater influence on sedimentation, except at the extreme top of the Weald Clay, is suggested not only by the common occurrence of sandstones and red clays but also by the association, in some Large-'Paludina' limestones, of Viviparus fluviorum with species of the bivalve Unio.

Sequence of minor beds

Weald Clay below the Horsham Stone

The Cuckfield No.1 Borehole (Lake and Thurrell, 1974) proved about 65 m of mudstones and silty mudstones between the base of the Weald Clay and the Horsham Stone. Lenticular developments of sphaerosideritic clay-ironstone occur an estimated 44 m below the Horsham Stone between Horsham and Crawley, south of the Crawley Fault (Worssam, 1972). Similar ironstone at about the same horizon extends northwards from the Crawley Fault past County Oak [TQ 270 390], while a lower bed of ironstone has been mapped from near Rowley Farm [TQ 280 396] northeastwards through Burstow [TQ 312 413]. In the highest beds, ironstone bands closely underlie the Horsham Stone throughout the district and persist north of the Crawley Fault where the Horsham Stone is absent.

Bed 1 (Horsham Stone)

Over much of the area south-east of Christ's Hospital, the Horsham Stone consists of two units (beds la and lb) separated by grey clays. Shallow-water deposition is suggested by the presence of an Equisetites soil bed at Slinfold (Allen, 1959), but there were also short-lived brackish-marine incursions, as indicated by Cassiope in a borehole at Barns Green (p.82) and by Ophiomorpha burrows at Southwater and Sedgewick Park (Kennedy and MacDougall, 1969). The 'chamosite' (berthierine) in the underlying ironstone at Horsham also probably indicates brackish water nearby.

Bed 2

In the north of the district, Bed 2a consists of 'Cyrena' limestone with a Small-'Paludina' limestone about 2.5 m above it, together mapped as one unit, and Bed 2b of Small-'Paludina'limestone, some 20 m higher in the succession. The outcrop of Bed 2a has been traced in the area between Charlwood and a point [TQ 116 334] 1 km south-west of Rowhook.

Bed 2b forms a bold escarpment from near Rusper [TQ 195 378] to Charlwood. The bed has also been mapped in the valley south-east of Bury St Austens [TQ 108 348] and for a short distance into the Haslemere district. In the Faygate Syncline, between Warnham Brickworks and Crawley, Small-'Paludina' limestone at the horizon of Bed 2b of Charlwood was not continuously traceable, but a scarp-like feature is formed by pebbly sandstone, the Gossops Green Pebble Bed, which appears to lie within 1 m or so of the limestone horizon. This sandstone is therefore shown on the map as Bed 2b, within the syncline.

The Warnham Brickworks and Clock House Brickworks pits have provided excellent sections of the beds between 2a and 3a (see (Figure 18)). Scattered temporary exposures have indicated that a Cassiope-rich band at the horizon of that in the lowest part of the Clock House section is widespread in the northern part of the district.

In the south, 'Cyrena' and Small -'Paludina' limestones have been noted south of Slinfold and as far east as Gaveston Hall School [TQ 186 250], but the limestones could be mapped only at the Southwater Brickworks [TQ 158 257] and 2 km south-west of there. At these places on the published map, 'Cyrena' limestone is shown as Bed 2a and Small-'Paludina' limestone as Bed 2b. 'Cyrena' and Small-'Paludina' limestones were recorded in the Cuckfield No.2 Borehole and their outcrop has been mapped, as one unit, in its vicinity. A Small-'Paludina'limestone bed south of the Maplehurst Fault around [TQ 150 232] is shown as Bed 2.

Bed 3

Mapping has shown that the Clock House Sand, which is exposed in the Clock House pit, is lower than Bed 3a of the Haslemere district. It is therefore simply numbered Bed 3 in this district. In the Faygate Syncline, even allowing for the steepness of the dip, the Gossops Green Pebble Bed and this sand are separated by an estimated 10 m or less of clays as against some 21 m at the Clock House Brickworks. This southward thinning, together with a strong development of the pebble bed along the Faygate Syncline, suggests that the syncline may have been an area of restricted deposition in early Weald Clay times.

Beds 3a and 3c (the Okehurst Sand and the Billingshurst Sand) have been traced as continuous units through the adjacent Haslemere district and in the south-western and north-western parts of this district. A marine influence is indicated by the presence of Ophiomorpha at this horizon in the north-west of this district.

Bed 4

This Large-'Paludina' limestone was found only in the southwestern corner of this district. It extends westwards for 2 km or so into the adjoining Haslemere district.

Bed 5

Three lenticular sandstones, beds 5a, 5b and 5c (the Alfold Sand), with some intervening red clay, make up Bed 5 in the south-western corner of this district. Bed 5c and a higher bed (5e) occur in the north. Iguanodon has been found at Smokejacks Brickworks, Ockley, in a sandstone of Bed 5.

Bed 6

This Large-'Paludina' limestone extends southwards from the south-west corner of this district into the Brighton district and is well developed in the central part of the Haslemere district.

Bed 7

The sandstone has not been recognised in this district but it has been mapped in the Brighton and Haslemere districts (Figure 16); it is the most prominent sandstone in the Haslemere district but dies out eastwards in the north crop of the Weald Clay.

BEDS 8 TO 11

These beds comprise alternating Large-'Paludina' limestone and sandstone beds on the north crop of the Weald Clay in the Haslemere and Horsham districts. Bed 11 is the highest Weald Clay sandstone.

Summary of stratigraphy

The minor beds at outcrop in the south-west and north-west corners of the district are linked by outcrops in the Haslemere district, to the west (Figure 16). (Figure 17), derived from (Figure 16), shows the relative extents of minor beds in the Weald Clay of geological sheets 301 and 302 in horizontal section, with the base of the Atherfield Clay taken as a datum.

In the lower part of the Weald Clay, a southward weakening of brackish-marine influences is indicated by the southward dwindling of 'Cyrena' and Small-'Paludina' limestones. In the northern part of the section, this influence is reflected in beds as high as the Bed 3 sandstone, which contains Ophiomorpha borings and which at Clock House underlies a brackish-marine band with Filosina and (as proved by a borehole) Cassiope (see (Figure 18)). In the upper part of the Weald Clay, on the northern edge of the section shown in (Figure 17), the southern limit of a brackish-marine influence occurs above Bed 9b at Newdigate Brickworks (see p.70).

(Figure 17) suggests that the greater part of the thickening of the Weald Clay in the central Weald is due to expansion of the clays with Large-'Paludina' limestone. The disposition of Large-'Paludina'limestone lenses (beds 4 to 10) suggests a gradual northward migration of centres of limestone deposition. The relationship of the sandstones of Bed 7 of the Haslemere district to the Large-'Paludina' limestones and sands numbered 8 to 11 was discussed by Worssam (1978, p.9). Eastward thickening of the strata between beds 9c and 11b, noted in the north eastern part of the Haslemere district (Worssam in Thurrell et al., 1968, pp.14, 27), is not evident in the Horsham district, and may result from locally intensified subsidence.

Details

The following details are provided in sub-areas in the order: northern crop, western crop, southern crop. The descriptions within each section follow approximately stratigraphically ascending order.

Kingsfold, Warnham Brickworks, Graylands and The Misers area

Heavy grey clays crop out on the ridge between Mayes [TQ 158 351] and Kingsfold. The summit is gently rounded, without a sharp contrast between dip slope and scarp, and possibly owes its resistance to erosion to lenticular beds of laminated calcareous siltstone.

The banks of a stream [TQ 156 365] 800 m west of Tickfold Farm exposed dark grey, shaly clay with lenticles of massive siltstone up to 0.6 m across and 15 cm thick, and thinly bedded and laminated siltstone in slabs up to 10 cm thick and 1 m across, some showing ripple marks. In a field [TQ 159 366] east of the stream are irregular shallow depressions, probably former pits dug for this fissile stone. The drive leading to Tickfold Farm from Kingsfold is made up of fragments of siltstone and Small-'Paludina' limestone, both said to have come from these diggings. Fragments of Small- 'Paludina'limestone, perhaps not far from source, were seen in stream banks [TQ 166 369] north of the farmhouse.

An outcrop of Small-'Paludina' limestone (Bed 2b) at the general horizon of that near Tickfold Farm has been mapped eastwards from a point [TQ 179 379] south of Upper Gages Farm; some fragments of pebbly sandstone in the soil here indicate the Gossops Green Pebble Bed. Clay with Small-'Paludina' limestone, lenticular siltstone and pebbly sandstone was excavated from a trench [TQ 181 383] beside the road to Capel. About 40 m to the east along the same trench, and a metre or two stratigraphically higher, occurred clay with abundant Cassiope. Taylor's Gill [TQ 184 385] exposes Small-'Paludina' limestone and a pebble bed at the Gossops Green Pebble Bed horizon (Worssam and Thurrell, 1967). Eastwards from Taylor's Gill, the limestone outcrop forms a slight feature on a valley-slope south of Lyne House [TQ 191 385]. Slabs of Small-'Paludina' limestone and pebbly sandstone were dug 200 m southeast and 550 m east-south-east of the house.

Slabs of 'Cyrendlimestone, 2.5 cm thick and 15 cm across, were seen in a ditch [TQ 165 344] on the side of a steep valley (Andrew's Gill) 800 m north-east of Warnham; Small-'Paludina' limestone was noted in a stream section farther west, where the gill is crossed by the Horsham–Dorking road. Northwards from here, 'Cyrena' limestone was seen in a ploughed field [TQ 167 358], and also in a stream section [TQ 179 374] 400 m south-west of Ridge Farm; Small-'Paludina' limestone was exposed in another stream section nearby [TQ 175 368]. In the deep valley (Gages Gill) [TQ 185 380] north-east of Lower Gages Farm much 'Cyrena' limestone was seen, some of it in situ, with some small loose fragments of Small-'Paludina' limestone. Southwards thence, on the east side of the Boldings Brook valley, there are few exposures, but outcrops of a bed of 'Cyrena' limestone up to 9 cm thick, with a bed of Small-'Paludina' limestone about 3 m above, were seen at valley-heads [TQ 199 376]; [TQ 203 373]. Valley-bulged grey shales with siltstone bands in the deep valley bottom south of Newbarn Farm showed dips of 65° to 80° in various directions, and minor anticlines.

The section exposed at the Warnham Brickworks pit [TQ 175 350] from 1962 to 1966 (Figure 15) was given in detail by Worssam (1978, p.17). Ferguson (1926) recorded an 11.5 m section of clay and shale at this pit including, near the middle, two limestone bands 1.8 m apart, each 25 to 40 mm thick, the upper composed of Viviparus shells, the lower of 'Cyrena'shells. Most probably, these were beds 15 and 11 of the present-day section. Shale below the'Cyrena' limestone contained fragmentary gastropods identified by L R Cox as Viviparus cf. infracretacicus [elongatus]Huckriede. Away from the pit, beds 15 and 11 are not separable for mapping purposes, and the limestone outcrop 2a of the published map includes both of them. Within the area of the quarry, beds 5 and 15 are not everywhere developed as limestones. In 1971 Mr J D S MacDougall noted that in the northern part of the quarry near [TQ 174 350], Bed 5, there in limestone facies, included sparse Cassiope cf. lujani (Verneuil & Collomb) (Morter, 1978, p1.1).

Small-'Paludina' limestone layers higher in the sequence (beds 30 and 35 of the pit) have not been mapped in the vicinity of Warnham Brickworks. A correlation of trial boreholes to the north and east of the quarry shows U D S MacDougall, personal communication) that limestones in this part of the sequence persist for only short distances before passing into clays with Viviparus. Above these clays with impersistent limestone bands, there is a thin pebbly sandstone shown on the map as Bed 2b and correlated with the Gossops Green Pebble Bed. Pebbly sandstone was dug within 1 m of the ground surface at the site of the Graylands Borehole [TQ 1770 3463], 100 m west of Graylands, and may represent one of the pebbly sandstone layers (possibly bed 18 or 21) of the lower part of the succession at the Clock House Brickworks (p.00). The borehole sequence (Worssam and Thurrell, 1967, p.267; Worssam, 1978, p.17) is summarised in (Figure 18).

Basin casts and other sedimentary structures described by Prentice (1962) from Bed 29 were well exposed in 1960 at the north end of the Warnham pit. Basin casts also occur in the Clock House pit, in stream sections at the same general horizon (between beds 2b and 3 of the general succession) north-east of there, and at the Newdigate Brickworks pit (Worssam and Thurrell, 1967). The conditions responsible for their formation seem to have been associated with the gradual approach and recession of brackish-marine incursions; Prentice (1962, p.184) suggested they might be the deposits of crevasse tongues.

The structure around Brookhurst Farm [TQ 180 350] appears to represent the downfaulted western termination of the Faygate Syncline. A fault trending east-north-east and with a northerly downthrow of 18 to 27 m about 180 m north of the brickworks pit, may be interpolated from logs of trial boreholes, and provides an explanation of the presence of fragments of pebbly sandstone and Small-'Paludina' limestone in the bed of the stream in the valley between Brookhurst Farm and Langhurst. Clay from a temporary excavation [TQ 174 354] included limestone with mainly fragmental small Viviparus and ripple-marked sandstone with pebbles.

The ridge between Langhurst [TQ 178 357] and Great Benhams is inferred to be an escarpment formed by the Gossops Green Pebble Bed or by associated Small-'Paludina' limestone layers. No exposures of either rock were seen, though a temporary excavation [TQ 182 361] 200 m south-south-west of Great Benhams showed grey to fawn clay with small Viviparus. The outcrop of limestone (Bed 2a) shown on the map as low down on the northern slope of the ridge is largely conjectural; evidence for it was provided by Small-' Paludina' limestone fragments along a short stretch of the stream bed [TQ 185 365] 275 m north-east of Great Benhams.

The Park Farm Fault, trending north-north-east has a westerly downthrow estimated as 60 m near Graylands. On its upthrow side some roadside excavations [TQ 185 346] exposed 'Cyrena' limestone and Small-'Paludina' limestone at above 91 m OD, i.e. 45 m above their level in the Graylands Borehole. In the angle between this fault and a shorter east-south-east-trending fault, 685 m north-north-east of Graylands, sandstone, in beds 15 to 30 cm thick in a stream section [TQ 182 352], has been tentatively correlated with Bed 3. Boreholes indicate that the shorter fault has a southerly downthrow of about 45 m. To the north of it, fragments of 'Cyrena' limestone and Small-'Paludina' limestone are abundant in the beds of streams [TQ 182 354].

Dr Bristow noted a clay-ironstone that forms a low escarpment east and west of Benson's Farm [TQ 205 340]; weathered fragments of the stone were abundant on the floor of a disused brick-pit 180 m south of Faygate Station. The Horsham Stone makes a low shelflike feature to the north of here. Near Wimland Farm [TQ 209 349], scattered pieces of 'Cyrena' and Small-'Paludina' limestone occur in the soil on a narrow dip slope.

A stream flows east by north from The Misers [TQ 194 354] along the axis of the Faygate Syncline. The northern dip slope of the valley appears to be less steep than that to the south. Fragments of gritty to pebbly sandstone of the Gossops Green Pebble Bed (Bed 2b) were ploughed up on the northern scarp crest at [TQ 203 357], 250 m south of Baldhorns Park, and along the southern scarp crest in a field [TQ 196 350] south-east of The Misers. A sandstone forming a ring-shaped outcrop around The Misers has been correlated with Bed 3; a section [TQ 197 355] in Furzefield Coppice showed up to 1.5 m of clay, including 30 cm of hard, grey, flaggy sandstone with borings. In Upper Rapelands Wood [TQ 189 354] are old minepits on and just above the sandstone outcrop; the clay-ironstone was shown to persist for only a short distance underground (Worssam, 1972). In the centre of the syncline, a sandstone at [TQ 191 355] is probably an outlier of Bed 3a; the clay beneath it is greenish grey with a dull purplish red mottling, characteristic of the clay beneath Bed 3 near Oakwoodhill.

Faygate and Lambs Green area

Dr Bristow recorded 2 to 3 m of grey silty clay and siltstone in the disused pit [TQ 234 344] of a brick, tile and pottery works, 1 km northwest of Holmbush, was partially filled in 1962, but showed 2 to 3 m of grey silty clay and siltstone. Similar material was exposed in an excavation 3 m deep, [TQ 237 345] in a wood east of the pit. To the north of Faygate Station, the outcrop of the Horsham Stone is marked by a poorly defined break of slope at the foot of a ridge, of which the crest is formed by a limestone (Bed 2a). On the Horsham Stone outcrop, minepits occur in the small woods known as Durrants Copse [TQ 216 346], Fullers Shaw [TQ 222 348] and Pondtail Shaw [TQ 230 352] (Worssam, 1972, fig.3). Signs of old diggings were also noted on the line of the outcrop in the fields between Fullers Shaw and Pondtail Shaw. On the ridge crest, 'Cyrena' and Small-'Paludina' limestone fragments were noted in a ploughed field [TQ 215 352] 450 m west-north-west of Carylls Lea, and 'Cyrena' limestone fragments in fields with signs of old diggings 300 m north-northwest and 300 m north-east of Carylls Lea.

In the core of the Faygate Syncline there is a small sandstone outlier [TQ 226 362], probably Bed 3. To the north, between Axmas Farm and Whitehall Grange, a well-marked sandstone outcrop forms a distinct ridge. This sandstone is regarded by Dr Bristow as Bed 2b, though thicker and finer-grained than usual, and with no evidence of pebbly sandstone. The corresponding outcrop on the southern flank of the syncline generally shows only siltstone debris, though pebbly sandstone was noted at [TQ 218 358] 400 m north-east of Carylls.

The presence of the Crawley Fault between Rusper Court and Hyde Hill is inferred from the lack of a Small-'Paludina' limestone outcrop here. At Lambs Green, the clay-pit of the old brickworks [TQ 221 368] showed small exposures of grey clay and scattered fragments of siltstone and clay-ironstone. Minepits in a small wood, The Grove, [TQ 2325 3723] were probably dug for ironstone at a level equivalent to that of the Horsham Stone.

Ifield, Crawley and Ifieldwood area

Four lenticular outcrops of clay-ironstone, all an estimated 40 to 45 m below the Horsham Stone, form low ridges between Bewbush Manor [TQ 241 348] and Furnace Farm [TQ 284 356]. Much of this ironstone is sphaerosideritic. In 1971 a sewer trench [TQ 262 349], up to 5 m deep and crossing the outcrop 400 m north-west of Broadfield showed that the beds mapped as an ironstone unit comprise silty mudstone, dipping 11° to the north, with ironstone, mostly in lenses, at many levels:

The section revealed that the feature taken for mapping purposes as the ironstone outcrop is caused by at least five layers of ironstone (beds 12, 14, 16, 18 and 23). Very slight breaks of slope were formed by beds 2 and 4. From about bed 6 upwards, the mudstone beds appear to form rhythmic units that are silty in their lower parts, becoming less silty and more finely laminated upwards. The average thickness of the units is 1.2 m. Ironstone lenses are present at the bases of the units. In beds 22 and 24, the pale reddish brown mottling of the weathered clays appeared to be caused by iron-staining along joints rather than to primary red coloration. Three zones of relative weathering were apparent. In the topmost 1 m there was weathered, iron-stained clay, with bedding mostly destroyed. In the next 3 m, the mudstones were weathered pale grey or greenish grey with patchy iron-staining, mainly on joints. Within this zone, the ironstone above 2 m depth appeared to be weathered to goethite. In the third zone, below 4 m depth, dark grey unweathered clay was present.

Ironstone from a temporary excavation [TQ 249 350] 850 m east-north-east of Bewbush Manor is a spherulitic siderite mudstone (E32284) with interstitial clay minerals, probably mainly kaolinite; the proportion of siderite to clay minerals is about 60:40.

In 1963 a sewer trench [TQ 282 354] on the ironstone outcrop near Furnace Farm showed 3 m of interbedded grey-brown shale, thinly bedded silty mudstone and argillaceous siltstone, including a 15 cm shale band with ostracods, overlain by a 12.5 cm bed of grey sphaerosideritic ironstone, partly weathered to goethite (E32444)–(E32445) and splitting into layers 1 to 2.5 cm thick.

Red and grey mottled clay, approximately at the ironstone horizon, was augered 500 m east-north-east of Bewbush Manor, while to the north of Bewbush Manor, a similar bed was located about midway between the sphaerosideritic ironstone and the Horsham Stone. It is uncertain whether these are true red clay horizons, or red-weathered clays similar to those in beds 14 and 16 of the Broadfield section, above.

A few sandstone fragments along a low ridge extending for about 1 km eastward from a point [TQ 2415 3545] 650 m north of Bewbush Manor were taken to represent the Horsham Stone, though the stone here may be very thin (15 cm or less) and impersistent. Clay-ironstone is probably continuous in this tract, and much of the Horsham Stone outcrop, which is scarred by minepits, was formerly woodland (Worssam, 1972, fig.3). In excavations for new houses [TQ 257 354] in 1970, south-east of the Horsham road, minepits but no sandstone were seen.

The Horsham Stone and associated ironstone give rise to a steep escarpment 1 km south-east of Crawley church. Minepits abound in a copse (The Hawth) [TQ 277 360] on the dip slope, considered by Straker (1931, p.465) to have been dug to supply Tilgate Furnace [TQ 284 355]. An ironstone (E32448) fragment from the dug ground is a homogeneous aggregate of siderite grains (about 0.002 mm diameter) with sporadic angular to subangular quartz grains (0.02 mm diameter). A temporary excavation [TQ 278 359] at the scarp crest exposed hard, greenish grey sandstone (Horsham Stone) consisting (E32447) of angular to subangular quartz grains (0.10 mm diameter) and scattered muscovite flakes, with interstitial siderite grains and rhombs (up to 0.01 mm diameter).

In 1966, deep trenches on a building site east of The Hawth exposed brown and grey silty clay, with some red mottling near the top, 6 to 10 m thick [TQ 2825 3608]; overlain by a bed of yellow fine-grained sandstone (not mapped) about 0.5 m thick [TQ 2817 3608] to [TQ 2830 3617]; overlain by laminated siltstone and buff-weathered silty clay; followed in turn by red- and grey-mottled clay with clay-ironstone nodules [TQ 2815 3625]; [TQ 2816 3637]; and by ferruginous, slabby Horsham Stone [TQ 2808 3628] to [TQ 2811 3633].

'Cyrena' limestone and Small-'Paludina' limestone were exposed at a building site [TQ 2552 3594] south-west of Ifield Station and in a roadside trench [TQ 2605 3595] south of Goff's Park. Above the limestones at the former site there were grey to dark brown shales with laminated calcareous siltstone, mostly in thin lenses (up to 2.5 cm thick). The largest lens seen was a shallow basin cast, 1.0 x 0.5 m across and up to 10 cm thick. At the crest of an escarpment above the site [TQ 2540 3608], several fragments of pebbly sandstone were noted in a clay soil. A Small-'Paiudina' limestone 5 cm thick at a similar stratigraphical level (not mapped) was exposed in a cutting [TQ 2565 3610] on the east side of the bypass road.

A former building site 400 m east-south-east of Ifield Station is the locality after which the Gossops Green Pebble Bed (Bed 2b) was named (Worssam, 1965). On the lowest ground, north of the Crawley Fault, pale grey silty clays with discontinuous courses of clay-ironstone were noted, dipping north-west. Immediately south of the fault [TQ 2529 3652], Small-'Paludina' limestone (Bed 2a), 7.5 cm thick, was exposed for a distance of 15 m, dipping 8° to the south. Trenches near the hill crest [TQ 2534 3645]; [TQ 2540 3642] showed spoil of the pebble bed at about 9 m higher in the succession. Some fragments were of siltstone with pebbles, 5 mm in diameter, in groove casts at its base, others of ripple-marked sandstone up to 7.5 cm thick. Many pieces of Small-'Paludina' limestone, mostly about 1 cm thick, also occurred among the debris from these trenches. Evidently the pebble bed and limestone occurred within about 1 m of beds. They are thought to be about 3 m below a band of clay, rich in shells of Cassiope, which was exposed about 30 m to the south at [TQ 2534 3643].

Temporary excavations during building operations in 1969 showed that an isolated hill at Southgate, Crawley, is an escarpment formed by 'Cyrena' limestone and Small-'Paludina' limestone (Bed 2a). To the east, the old Brighton road crosses the hill in a cutting [TQ 2660 3555] in which William Smith's map of 1815 showed an outcrop of limestone, assigned by him to the Purbeck Beds. Topley (1875, p.104) recorded sand with a little calcareous grit (which he believed to be Horsham Stone) on this hill ('Hog Hill') but this bed (?2b) was not relocated.

The Brighton Road Pumping Station Borehole [TQ 2652 3595] of 1897, surface level 81.7 m above OD, started below Bed 2a but above the Horsham Stone horizon. The log (Whitaker and Reid, 1899, p.20; Edmunds, 1928, p.78) indicates a lithological change at 84.4 m depth from clays to underlying sands, taken as the base of the Weald Clay.

In the cemetery [TQ 256 368] much clay-ironstone in slabs up to 2.5 cm thick and 25 cm across was noted. Farther north, the ironstone makes a low escarpment; sphaerosideritic ironstone (E32446) was found near its crest [TQ 266 375]. Foundation trenches [TQ 271 386] showed at 2 m depth, 1 m of greenish grey, thinly bedded mudstone with numerous nodules of argillaceous, pseudospherulitic siderite mudstone (E32283).

To the north-west of the River Mole, another ironstone extends northwards from Ifield Court, at a stratigraphical level about 45 m below the 'Cyrena' limestone (Bed 2a) of Russ Hill. An ironstone fragment (E32450) found in a field [TQ 245 392] is a homogeneous siderite rock of approximately 0.005 mm grain size. Minepits occur in places at the foot of the dip slope. To the east, ironstone from about 10 to 12 m lower in the Weald Clay forms scarp-like ridges, one at Old Bonnetts and the other 1 km west of Charlwood Park. Ironstone nodules from a field [TQ 256 414] west of Charlwood Park are of a siderite rock of siltstone grade (0.05 mm grain size) with small patches of clay mineral (E32285).

Between Ifieldwood and Charlwood, grey to fawn clays and silty clays crop out between the ironstone and 'Cyrena' limestone horizons, with red-mottled clay in places about midway between the two. A prominent flat-topped spur extends east-north-east for about 1 km beyond the 'Cyrena' limestone outcrop at Langhurst [TQ 223 381], and may be formed by a hard siltstone bed in the Weald Clay. There is a similar flat-topped spur at the same horizon 2.5 km to the north [TQ 236 405].

Lowfield Heath and Burstow area

The lowest part of the Weald Clay is very silty between Tinsley Green and Burstow. The higher parts of the sequence are more clayey, and contain impersistent nodular clay-ironstones at several levels. A number of these cap prominent features and have been mapped.

Almost continuous sections of frost-heaved mudstones, silty mudstones and siltstones are exposed in the tributary of the River Mole where it flows past Rowley Farm [TQ 2758 3973] to [TQ 2802 3868]. The following composite section was measured in the stream bed in Rowley Wood [TQ 2785 3918]:

Similar sections, all intensely disturbed by frost heaving, occur in intervals downstream and most show an 8 cm layer of well-bedded clay-ironstone. All of these sections lie within 9 to 15 m of the base of the Weald Clay and are below the lowest mapped ironstone seam.

A temporary section [TQ 2768 3873] at Crawley Factory Estate showed the following section at the level of the lowest mapped ironstone:

Red clays are commonly associated with the ironstone seams and red-mottled clays crop out around Rowley Farm, which is built on the crest of the feature formed by the second ironstone.

Continuous exposures of frost-heaved and weathered shales, mudstones and silty mudstones were seen in the perimeter drains at Gatwick Airport. The following section was measured in one of the deeper parts of a drain [TQ 2803 4128] on the north side of the airport:

A section 140 m north-east of the above showed a 2.5 to 5 cm bed of nodular clay-ironstone passing laterally into iron-stained shales at the base of the previous section. Red- and brown-mottled shales containing a 2.5 to 5 cm clay-ironstone bed were noted in the bed of the River Mole [TQ 2834 4167].

Dark grey, olive and grey-green mudstones and silty mudstones with some thin siltstone beds and striped beds were formerly worked for brick clays in Horleyland Wood [TQ 2910 4065]. Fragments of bedded clay-ironstone, up to 6 cm thick, occur in the tip and are probably from the second mapped ironstone.

Small, shallow pits at Old Rolls Farm [TQ 2927 4038] may have worked the second ironstone, which crops out as a tabular bed 8 cm thick in the stream bed [TQ 2870 4042] 500 m west of the farm. The following composite section [TQ 2881 4023] was measured 230 m upstream from this locality.

The two ironstones form strong continuous features between Burstow and Dowlands Farm [TQ 329 418] (in the Reigate district) but neither was exposed.

Rusper and Charlwood area

The well-defined dip slope of the Small-'Paludina' limestone (Bed 2b) north of Highams Farm [TQ 203 379] passes westwards into a spur with a gently rounded top near Newbarn Farm, whereas the main outcrop continues as a narrow band on the north side of the valley south of Lyne House. Small-'Paludina' limestone in large slabs up to 6 cm thick occurs at old diggings in a wood [TQ 194 381].

Between Rusper and Charlwood, Bed 2a crops out on the lower slopes of an escarpment formed by Bed 2b. The two beds are separated by an estimated 21 m of grey clays. 'Cyrena' limestones 2.5 to 5 cm thick were seen in stream sections [TQ 207 377]; [TQ 217 386], apparently 1.5 m apart stratigraphically at the latter site. Small-'Paludina' limestone fragments and an outcrop of 'Cyrend limestone were noted in a stream bed [TQ 221 390] 570 m east-north-east of Orltons, and fragments of both rock types occurred in ditch sections [TQ 230 400] on Russ Hill. On the evidence of stream sections in the deep valley (Welland Gill) 1.2 km west-north-west of Charlwood church, 'Cyrena' limestone and at least three layers of Small-'Paludina' limestone, 10 to 15 cm thick, in overlying clays, were mapped as one unit (Bed 2a).

Topley (1875, p.105) recorded Small-'Paludind limestone between Jordans and Chaffolds (formerly Evershed) Farm, and there are signs of old diggings on the dip slope between these places. Northwards from Jordans, limestone was seen locally, notably in the banks of the road [TQ 225 400] up Russ Hill. There are numerous old pits for limestone in woods [TQ 234 415] on the hill-crest west-north-west of Charlwood. In one pit, F H Edmunds (in MS) noted massive blue Small-'Paiudina' limestone, 0.6 m thick, overlain by 0.6 m of clay.

The clays between Bed 2b and Bed 3 (sandstone), which are about 27 m thick at the Clock House Brickworks [TQ 175 385], appear to expand in thickness up to 36 m where their outcrop widens northeast of Lyne House. Heavy grey to buff clays with siltstone, some showing ripple marks, were seen in small exposures. Loose fragments of gritty to pebbly sandstone were noted [TQ 201 387]; [TQ 209 385]; [TQ 231 416] just above Bed 2b. Mantell (1833, p.230) reported finding ostracods and a shell resembling 'Melania' [Cassiope] at Norwood Hill, about 2.5 km north of Charlwood (in the adjacent Reigate district). It is likely that these shells were from an horizon not far above Bed 2. A stream section [TQ 209 388] 440 m east-northeast of Chaffolds Farm showed about 1 m of thinly bedded mudstone with Viviparus and ostracods; another [TQ 197 395] showed shaly clay with ostracods and a siltstone basin cast of about 1.5 m diameter.

Clock House, Temple Elfande and Tanhouse Farm area

The Clock House Brickworks pit [TQ 175 385] has provided a wealth of stratigraphical detail for the middle part of the Weald Clay. The section was referred to by Worssam and Ivimey-Cook (1971, p.29), and details of the succession as seen between 1962 and 1965 were given by Worssam (1978, p.17) and are summarised in (Figure 18), which includes other information from a nearby borehole (Clock House No.4/68) [TQ 1781 3922].

The brackish-marine band represented by beds 4 to 10 is 2.42 m thick. Kilenyi and Allen (1968, fig.8) assigned a thickness of 1.83 m to this band and described it as consisting, both in the Clock House pit and in boreholes near Warnham Brickworks, of two beds with Cassiope separated by 0.6 m of clay with few ostracods and much lignite.

Pebbly sandstone or siltstone in beds 1, 18 and 21 is of similar lithology to the Gossops Green Pebble Bed. Beds 33 to 40 correspond to beds 1 to 12 of Kirkaldy and Bull (1948). Bed 34 (Bed 2 of Kirkaldy and Bull, 1948) comprises 0.9 m of silty clay with layers of sandstone up to 20 cm thick, with abundant Ophiomorpha (Kennedy and MacDougall, 1969, p.466). Kirkaldy and Bull recorded small pebbles and concentrations of fish remains which were noted locally in the troughs of ripples on the upper surface of Bed 38, on a 0.25 m-thick sandstone, also studied by Allen (1948, 1972, 1976).

Widely spaced basin casts occur in siltstone beds in the lower part of the succession and in Bed 34. On the floor of the lower part of the quarry were found loose blocks of fine-grained stone crowded with Corbula sp. nov. (Morter in Worssam, 1978, p1.1, figs 14, 15), probably from a level between beds 20 and 34. Kirkaldy and Bull (1948) obtained from workmen a piece of an Oxford Clay ammonite, said to have come from the pit; from its smoothed character and large size (90 x 75 x 37 mm), they considered it to have been a gastrolith of an Iguanodon. Jarzembowski (1981 and 1991a) has described a termite, Valditermes brenanae Jarzembowski, the earliest social insect yet described, and (1991b) damselflies from this locality.

Bed 34 was traced eastwards from the pit through Taylor's Farm, where it forms a bold escarpment between Lyne House and Temple Elfande. Bed 38 is of variable lithology within the pit and has not been recognised elsewhere in section, although possibly it may have been included with beds 34 or 41. Bed 41, the highest sandstone in the section, caps a knoll at the north-east corner of the working. Its main outcrop lies 275 m to the north and has been shown to be part of Bed 3a (the Okehurst Sand).

West of Clock House, old sand pits, 1.5 to 3 m deep, in a wood [TQ 172 385] on the west side of the Horsham–Dorking road, are at about the level of Bed 34 of the pit. Bounding the wood on the south-west is a railway cutting which Topley (1875, p.106) described as east of Lyewood Farm (now Osbrooks) and as showing sandstone and grits dipping north, and 4.5 or 6 m thick, with a thin wedge-shaped bed of clay. Near Newhouse Farm, the escarpment formed by Bed 3 is lower than south of Temple Elfande, and there is a clay soil on the dip slope. Cross-bedded micaceous sandstone in rough slabs 1 cm thick was seen 45 m north of the farm, and traces of old pits for sandstone were noted in fields 275 to 730 m north-north-east of the farm.

Blocks of hard grey calcareous sandstone with inclined burrows, probably Ophiomorpha, were dug from a ditch [TQ 175 389] at Clock House. The sandstone is evidently at a higher level than the sandstone with Ophiomorpha (bed 34) of the brickworks pit and is assigned to Bed 3a. A ditch section [TQ 183 392] showed grey calcareous sandstone in rough flags up to 6 cm thick, and a stream bed [TQ 186 397] exposed hard, grey, cross-bedded and ripple-marked sandstone penetrated by burrows of Ophiomorpha type, 6 to 18 mm in diameter, both in Bed 3a. Beyond the north-eastern termination of sandstone 3a, grey to brown clay, with two beds of red clay cropping out 75 m apart, was indicated by spoil from a roadside trench extending for 275 m south from the bridge at Tanhouse Farm [TQ 199 408].

In the disused Auclaye Brickworks pit [TQ 170 388], 500 m west of Clock House (Kirkaldy and Bull, 1948, p.82), clays in the upper part of the interval between beds 3a and 3c were worked. The upper part of the pit, to the north, seems to have worked weathered clays to a depth of about 3 m, but it was overgrown in 1962. Sections in the lower part of the pit exposed 6 to 9 m of grey shaly clay with some layers of soft laminated siltstone, the whole weathered buff or pale brown within about 4.5 m of the ground surface. In a 150 mm band of laminated silt near the top of the section, there were two lenses of clay-ironstone, 4.5 m apart, each up to 10 cm thick and about 0.45 m wide. Some bedding planes in the ironstone were covered with the carapaces of a conchostrachan (clam shrimp) (Jarzembowski, 1991b). A 'hawker' dragonfly Valdaeshna surreyensis Jarzembowski, complete with body colour markings, was discovered in a phosphatic nodule in this pit (Jarzembowski, 1988), together with numerous other insects (Jarzembowski, 1991b).

Grey clays, with red mottling in places, predominate in the interval between beds 3a and 3c east of the Auclaye pit. Bed 3c forms a well-defined escarpment east of the brickworks, through Clark's Green and Pleystowe Farm, with sandy soils on the dip slope. The same feature continues through Aldhurst Farm, where the sandstone appears to be interbedded with layers of grey clay, and the soils on the dip slope are clayey in places. Sandstone slabs 2.5 cm thick with ripple marks of 2.5 cm wavelength, together with weathered clay, were dug 140 m south-east of the farm. North of Tanhouse Farm the sandstone makes only a low ridge; slates of calcareous sandstone were dug [TQ 198 414] 600 m north of the farm.

Bury St Austen's, Rowhook Manor, Denne and Sands Farm area

Slabs of 'Cyrena' limestone were seen loose in a stream bed [TQ 108 341] 640 m south of Bury St Austen's, indicating a nearby outcrop. Some 10 to 15 m higher, Small-'Paludina' limestone from a field [TQ 106 342] has been assigned to Bed 2b. In thin section (E32286) this limestone showed a crystalline calcite matrix with closely packed fragments of Viviparus shells in roughly parallel alignment, together with scattered, mostly fragmented ostracod shells. Fragments of Small-'Paludina' limestone were seen in a stream bed [TQ 112 349] near the head of the valley 400 m east of Bury St Austen's. A little way upstream, fragments of a ripple-marked pebbly sandstone (Gossops Green Pebble Bed) were noted. An exposure [TQ 116 341] at a knickpoint in a tributary valley showed Small-'Paludina' limestone, 3.5 cm thick. Numerous slabs, 1 cm thick, of Small-'Paludina limestone at the same horizon were seen at [TQ 110 340] in the debris from a trench through Roman Woods. Farther east between [TQ 115 339] and [TQ 119 340], the same trench proved, at a slightly higher horizon, grey clay with sparse debris of Small-'Paludina' limestone and dark grey clay with Cassiope. Small-'Paludina'and 'Cyrena' limestones (Bed 2a) were revealed by the trench at [TQ 123 335] south of Rowhook. An outcrop of 'Cyrena' limestone was noted in a stream section [TQ 1183 3370] in Roman Woods, and Small-'Paludina' limestone fragments, 10 mm thick, were seen 20 m upstream from there.

A stream bank [TQ 128 344] 650 m north-east of Rowhook showed dark blue, crystalline Small-'Paludina' limestone in slabs up to 2.5 cm thick, some apparently in situ. Pieces of'Cyrena' limestone were seen 275 m north-north-east of here, and also in shaly clays excavated from a pond [TQ 133 350]. Between the two places a slight break of slope is believed to mark the outcrop of the bed. Fragments of Small-'Paludina' limestone were seen in a stream bed [TQ 145 342] 500 m south-west of Warnham Lodge. Thence northward, for about 1.5 km, no exposures were seen on the east side of the North River valley. A ditch [TQ 143 359] 180 m north of Northlands showed stiff buff clay with 'Cyrena' limestone up to 2.5 cm thick at one point; 37 m away, and an estimated 1.5 to 3 m above, Small-'Paludina' limestone, 2.5 cm thick, was exposed.

Fragments of Small-'Paludina' limestone were seen in a stream bed [TQ 146 365] 180 m south of Denne. An excavation [TQ 152 369] produced greenish grey clay with Viviparus and Cassiope. This horizon, above the highest Small-'Paludina' limestone but below the next sandstone in the sequence (Bed 3a), is approximately that of the Cassiope beds of the Clock House Brickworks pit.

Up to 0.5 m of cross-bedded sandstone in 15 cm layers was seen near the bottom of a 4.5 m-deep pit, 180 m north of Sands Farm [TQ 151 345]. The sand, which thins markedly northwards, may be an outlier of Bed 3a. Red clay commonly occurs just below Bed 3a.

Walliswood, Oakwoodhill and Ockley area

Sandstone (Bed 3a) caps a prominent spur at Bury St Austen's [TQ 108 348], and although only red clay was seen at this level for 750 m to the west, the sandstone was traced eastward for about 1.5 km. Excavations for a pond [TQ 1296 3512] revealed a layer of micaceous calcareous sandstone, 5 to 7.5 cm thick, breaking into slabs 0.5 to 1 m across. The sandstone blocks, pale grey and lustre-mottled at the centre but with a decalcified rind, showed burrows of 12 mm diameter, probably Ophiomorpha. A thin section (E32289) showed ill-sorted subangular quartz grains of about 0.05 to 0.10 mm diameter in a crystalline calcite matrix. North-eastwards, this sandstone appears impersistent, and near Farm Place the thickness of the clays between it and the Small-'Paludina' limestone, an estimated 23 m, is less than near Rowhook. North of a point 400 m east of Farm Place, however, the sandstone was traced continuously around the Walliswood Anticline, where it overlies dark red clay or clay of a distinctive purple-brown colour.

Around Eversheds Farm, in the core of the Walliswood Anticline, there are heavy grey clays with laminated calcareous siltstones, seen notably in the bed of a small stream in Wallis Gill [TQ 151 382]. Small-'Paludina' limestone may possibly occur in the deeper valleys around the farm, but no exposure was seen. The thickness of the clays between the sandstone (Bed 3a) and the Small-'Paludina' limestone is likely to be greater than the 23 m southward of Farm Place.

The next sandstone above Bed 3a in this area is Bed 3c, which persists westwards into the Haslemere district. Between the two sandstones, grey clays with beds of red or red- and grey-mottled clay occur, but their distribution varies from place to place. The sandstone forms the prominent rise on which Ridge Farm is situated. An isolated sandstone outcrop [TQ 111 357] north of the ridge is possibly an upfaulted part of the same bed.

At Honeywood House [TQ 122 357], two shallow wells sunk in 1899 and earlier are believed to have reached Bed 3c, downfaulted from its outcrop on the ridge. Much red clay occurs in Oakwood Wood [TQ 126 360] and the position of the sandstone outcrop there is conjectural. However, sand was seen by Monk's Farm, near Stane Street, and thence eastward and northward the!sandstone outcrop around the Oakwoodhill Syncline and Walliswood Anticline was clearly recognised. About 1.5 to 3 m of flaggy sandstone were exposed in a ditch [TQ 135 365] on the county boundary, and another outcrop was seen in a stream bed [TQ 137 369] 400 m to the north. A stream section [TQ 124 381] 460 m west-north-west of Oakwood Chapel showed 0.45 m of massive sandstone overlain by 0.6 to 0.9 m of flaggy sandstone; another stream section [TQ 132 394] revealed 1.5 to 3 m of thinly bedded calcareous sandstone, some of it ripple marked. For about 800 m eastward from the last-mentioned exposure the sandstone forms an escarpment. Topley (1875, p.106) recorded that the railway cutting [TQ 167 390] north-east of Knoll Farm showed 6 m or more of sand and sandstone, dipping north.

Two sandstone beds, 5c and 5e, an estimated 9 to 12 m apart vertically, produce a complicated outcrop pattern in the core of the Oakwoodhill Syncline and on the western part of the Walliswood Anticline. The clays between Bed 3c, described above, and Bed 5c are estimated to total about 21 m in thickness. Generally they are grey to fawn in the lower part, and beds of red clay characterise the upper part, but this order of succession is not invariable. The main outcrop of Bed 5c enters the Horsham district 400 m south of Hillhouse Farm, whence it runs northwards through Somersbury Wood. It is cut out by a north-south fault west of Walliswood Farm, reappears 550 m north of the farm, and has a sinuous outcrop traceable thence to the north-north-east for about 1 km, dying out north of Mayes Green. The bed was exposed in the Ewhurst Brickworks pit [TQ 108 379], 900 m west-south-west of Walliswood Farm, where the section in 1963 was:

The calcareous sandstone from unit 6 (E32290) shows pellets of finely granular calcite, up to 2.5 mm diameter, in a sandstone matrix consisting of subangular quartz grains of 0.1 mm diameter, with scattered mica flakes.

The Smokejacks Brickworks pit [TQ 114 372], 640 m west of Smokejack Farm, showed about 1.5 m of grey clay, overlain by 1.2 m of sandstone (Bed 5c), overlain by up to 3.5 m of red clay. The sandstone varied from place to place in the pit. In the north face, its lower 0.75 m included two or three prominent but impersistent 15 to 23 cm-thick beds, each thinning out within 6 to 9 m, to be replaced by another at a slightly different level. This was overlain by 0.3 m of buff and dark red shaly clay, in parts sandy, in turn overlain by 15 cm of soft yellow-brown sandstone. The eastern part of the south face was capped for a distance of 140 m by friable soft sandstone, 0.23 m thick, overlain by flaggy sandstone, 0.23 m thick, with up to 0.75 m of grey sandy clay overlying it; these beds together showed sharp little upfolds caused by frost heaving. At the western end of the face, the sandstone, 0.3 m thick, extended beneath an outlier of red clay where, protected from frost action, it was massive, crystalline, calcareous, and unfolded.

Between 1945 and 1951, Rivett (1953, 1956) found numerous dinosaur bones of a Titanosaurus-like herbivore and of Iguanodon, including a vertebra of I. bernissartensis type, together with pebbles up to 7.5 cm in diameter which are probably gastroliths. The bones, some broken and waterworn, mostly rested on or were embedded in sandstone beds. They are now in the British Museum (Natural History). In the then north face, Rivett (1953) measured 1.2 m of blue clay overlain in turn by silty clay and sandstones, 2.1 m; sandstone with iron-staining and green particles, 2.1 m; and red clay, 0.9 m. The bones were found in the southern part of the pit where 'very hard sandstone' occurred. Mantell (1833, p.230) noted that, 'at Oakwood Hill', several vertebrae and a carpal bone of an enormous reptile were discovered in 1828. At Oakwoodhill [TQ 130 374], sandstone of Bed 5c forms a wide, southward-facing dip slope.

Red clay is common between beds 5c and 5e in the Oakwoodhill Syncline but grey clays also occur. South of Bullcroft Farm [TQ 125 399] and west of Fishfold Farm red clay is present beyond, but in line with the northern termination of Bed 5c. Around Lowerhouse Farm [TQ 113 392], Bed 5c is overlain by grey clays, in places silty. In the woods for 800 m to the south-west of the farm, these include lenticular beds of silty sand.

Outliers of Bed 5e, comprising fine-grained sand with some clay, occur on high ground, mostly capped by patches of river gravel, in Somersbury Wood, near Hillhouse Farm, and between Broadstone Farm and Oakwoodhill. The main outcrop of Bed 5e terminates 400 m to the west of this district.

Grey to fawn clays were seen in a belt about 800 m wide between Lower Breache Farm [TQ 107 396] and Ockley church. The banks of an overflow channel [TQ 143 403] from a pond (Middle Pond) in Jayes Park showed 1 m of grey shaly clay with two seams of clay-ironstone, 5 to 7.5 cm thick. The lower of the seams was traced for about 9 m laterally. Just below it, at one place, was a lens of laminated fine-grained sandstone up to 15 cm thick and 30 cm wide, probably a basin cast, containing moulds of small bivalves (cf. Filosina membranacea J de C Sowerby).

Lower Breache Farm, Forest Green, Ockley Station and Capel area

A bold escarpment is formed by Large-'Paludina' limestone (Bed 8b) north of Lower Breache Farm [TQ 107 396]; much limestone is ploughed up in the heavy clay soils on the dip slope. Sand (Bed 9a) occurs immediately above these clays with limestone and forms a slight ridge at the foot of the dip slope and an outlier [TQ 105 400] on the slope. The escarpment is less prominent east of Lyefield Farm and limestone was not seen farther east than a temporary exposure [TQ 120 407] 805 m east-north-east of the farm, which showed shale with ostracods and limestone containing large Viviparus.

Dark red clay, up to 1.5 m thick, was seen at an old brickworks pit, [TQ 125 406] 400 m south of Forest Green. About 90 m to the east and stratigraphically slightly higher, a sandstone was traced eastwards nearly to Capel, apparently at the horizon of the sand (Bed 9a) at Lyefield Farm. In a stream section [TQ 156 415] 800 m north of Ockley church the bed, seen for 0.6 m, includes doggers of calcareous sandstone up to 0.23 cm thick. A thin section (E32291) showed subangular to subrounded quartz grains of 0.06 to 0.10 mm diameter in a fine-grained calcite matrix. Some mica flakes, a few tourmaline grains and some greenish grains, possibly of glauconite, were also noted. A section in a confluent stream 90 m to the east showed sandstone, probably not more than 3 m thick, underlain by grey silty clay and overlain by brownish grey, fine-sandy mudstone, seen for some 1.5 m. Another stream section [TQ 162 413] exposed 0.5 m of red and grey clay beneath sand and soft sandstone, seen for 1.2 m. The bed appears to terminate 550 m north-east of Young's Farm. Along much of its outcrop red- and grey-mottled clays underlie the sandstone. They occur on the face of the low escarp ment which the sandstone forms in Jayes Park, where they include a thin bed of fine sand traceable for about 700 m. Lenticular sands possibly at the same horizon as the latter were traced on the spur [TQ 153 407] 400 m west of Ockley church and, more extensively, between a point 270 m west of Ockley church and Capel. The latter bed was worked together with overlying red clay at an old brick-pit [TQ 166 405] immediately east of Ockley Station. Topley (1875, p.106) recorded 'perhaps 30 feet' (9 m) of sand at the station, the dip being northerly, 2 or 3 degrees. A hill to the north of Clark's Green is capped with an outlier of the sandstone.

A sand bed numbered 9b, though not necessarily at the same horizon as Bed 9b of the Haslemere district, forms dip slopes on either side of the deeply cut valley (Holmswood Gill) west of Young's Farm. It was seen to 0.6 m, overlain by Head, in a stream section 460 m north of the farm. East of the fault at Ockley Station, loamy to clayey fine-grained sand forms a low escarpment [TQ 171 416] which is believed to be the same bed. A continuous sand outcrop was traced for about 2.5 km east of this escarpment, mainly in the Reigate district, though within the Horsham district at [TQ 183 416] and forming a hilltop outlier [TQ 192 413] north-west of Green's Farm. This bed was not mapped east of Newdigate (in the Reigate district) where its outcrop trends in the direction of the Newdigate Brickworks clay-pit, 800 m to the east-north-east; the bed may be at the same general horizon as the pebbly sandstone reported from the pit (Worssam and Thurrell, 1967).

Red clay, including a thin lenticular bed of sand with a sinuous outcrop, occurs around North Breache Manor. Limestone slabs 5 cm thick, with large Viviparus, were dug at a gatepost 250 m southwest of Coophurst Farm (Bed 10a). East of the farm the limestone outcrop is thought to follow a slight break of slope, as far as a mill pond 400 m north-west of Forest Green. A second limestone bed (Bed 10b), an estimated 6 m higher and cropping out about 140 m to the north of Bed 10a, was recognised 400 m west of the mill pond, and its outcrop was traced thence eastwards, partly in the Reigate district, past Etherley Farm [TQ 129 416]. Fitton (1836, p.160) recorded three contiguous courses of greenish micaceous grit at 'Atherley', with 'Paludina' and 'Unio', resting on sand. Massive, ferruginous sandstone with scattered moulds of bivalves and large Viviparus, was collected in 1962 from a stream bank exposure [TQ 126 419] 460 m north-west of Etherley Farm in the adjoining district. This sandstone is a few metres stratigraphically above the Large-'Paludina' limestone. Near Coophurst Farm, grey and fawn clays succeed the Large-Paludina' limestone, forming a belt 180 to 270 m wide, with a sharp boundary to the north against pale grey and red mottled clay and silty clay. Within the latter are two beds of fine-grained sandstone, the upper of which (Bed 11c), just falling within the north-west corner of this district, is the highest sandstone in the Weald Clay. Its outcrop was traced eastwards for some 5 km in the Reigate district on the lower slopes of Leith Hill, as far as Broome Hall [TQ 150 425].

Slinfold and Warnham area

Theale Copse [TQ 125 318] and Birch Copse [TQ 127 319] have been completely dug over for Horsham Stone. There were also extensive diggings in a field to the east, known as Quarry Field, where a section [TQ 1269 3183] in 1960 showed 1.2 m of hard, partly calcareous, fine-grained sandstone, in two or three layers separated by 5 mm seams of pale grey clay. The sandstone was overlain in turn by 0.45 m of pale brown silty clay and 0.9 m of grey and buff, shaly clay. An Equisetites soil bed was recorded in stream exposures west of here at [TQ 1237 3162] (Allen, 1959, p.313). Slabs of Horsham Stone, 7.5 cm thick, were seen in the south bank of the River Arun, 400 m east of Hill House.

Old Horsham Stone diggings abound on the wide dip slope between Rapkins and Brookhurst, east of the North River. Nowhurst Quarry [TQ 135 325] was described by Ferguson (1926, p.408, p1.28).

No evidence was found of the inlier of Horsham Stone thought by Ferguson (1926) to occur in the small valley 400 m north of Townhouse Farm about [TQ 124 331]; fragments of Horsham Stone found hereabouts are probably not in situ.

A sandy clay soil occurs on the dip slope between Ends Place and Warnham Court. Horsham Stone diggings, mostly small, are scattered over this slope. Exposures of soft sandstone were seen on the banks of a stream at the foot of the slope [TQ 150 335]; and hard pale grey fissile calcareous sandstone, 1 m thick, and dipping 3°N, was seen in a road section [TQ 151 333]. At the crest of the slope, pits in a small wood (Horsham Corner Wood) [TQ 148 330] and in a copse to the east, known as The Pits, appear to have been dug for ironstone below the Horsham Stone. In Wasp Pit [TQ 142 323], another copse, a 3.5 m-deep excavation was probably also made for ironstone. Other pits, probably for ironstone, occur south of Weston's Place around [TQ 164 337] and east and west of Graylands Farm [TQ 173 341]; [TQ 177 339]. In a copse aligned east–west between Graylands Farm and Warn-ham Station there are distinct minepits (Worssam and Thurrell, 1967, p.267; Worssam, 1972).

A former brick-pit lies south-east of Slinfold Station. Its southern face [TQ 1144 3079] exposed 3.5 m of yellow-buff shaly clay.

A borehole at Rowfold Farm, Slinfold [TQ 1214 3190], surface level 45.7 m OD, starting from the bottom of an old well 18 m deep, proved clay, rock and 'marl', probably all Weald Clay, to 39 m depth. A borehole, surface level 48.8 m OD, at Rapkins House [TQ 1355 3199] starting in Horsham Stone, proved clay and 'rock', probably all Weald Clay, to 49.7 m. Another borehole at Wickhurst Lane, Broadbridge Heath [TQ 1514 3120], proved the Weald Clay–Upper Tunbridge Wells Sand junction at 1.2 m below OD (p.00). The base of the Horsham Stone at this site is more than 60 m, possibly near 75 m, above OD.

Christ's Hospital and Nuthurst area

An outlier of Horsham Stone was mapped on the evidence of loose fragments of sandstone in High Wood [TQ 147 300]. Numerous pits, probably dug for clay-ironstone, estimated to be 3 to 4.5 m below the Horsham Stone, occur hereabouts. Stone pits occur on the outlier of Horsham Stone in the abandoned meander core [TQ 143 297] of the River Arun and on a lobate projection of the Horsham Stone escarpment, 300 m to the north. Topley (1875, p.102) noted that the railway cuttings north and north-east of Itchingfield exposed mainly clay and shale with some thin beds of sandstone. Near Christ's Hospital Station and south-eastwards, the Horsham Stone is split by an intervening buff and grey clay into lower and upper sandstone units (beds la and 1b).

Lyell (in Mantell, 1829, p.133) recorded the following section at 'Stammerham Quarry'; the names in brackets are those then used for particular layers of stone:

Mantell (1833, p.244), quoted by Lyell (1865, p.348), reported that traces of the plant 'Sphenopteris', apparently in position of growth, were seen in a Horsham Stone quarry at Stammerham. The exact site of Stammerham Quarry is uncertain. Topley (1875) thought it might lie 'within the triangle formed by the three lines of railway' at Christ's Hospital i.e. at [TQ 146 291].

Ferguson (1926) recorded 3.12 m of interbedded clay and sandstone in a roadside quarry [TQ 1535 2870] east-north-east of Christ's Hospital school, and illustrated ripple marking on the Horsham Stone.

Old diggings for Horsham Stone in Sparrow Copse [TQ 151 294] were extended deeper as minepits for the extraction of clay-ironstone. The adjacent Horsham Bypass road cutting exposed a lens of remarkably pure 'chamosite mudstone', up to 20 cm thick and seen to extend for 45 m laterally, approximately 4.5 m below the base of Bed la (Thurrell et al., 1970). The east side of the cutting [TQ 1535 2923] exposed: flaggy sandstone and sand with sandy loam, disturbed by frost-heaving, 0.75 m; on slightly silty clay, pale grey streaked greenish brown, 0.6 m; on compact sandstone and calcareous sandstone with thin clay seams, 1.7 m; on grey shaly and silty clay, 3.8 m.

Diggings for Horsham Stone abound on the dip slope of Bed la south of Tower Hill and in Denne Park. Some large open pits at and just below the scarp-crest e.g. at [TQ 1720 2933] were dug partly or wholly for clay-ironstone. Stream sections in siltstone with seams of clay-ironstone, just below the base of the Horsham Stone, were seen to the east of Denne Park at [TQ 1721 2850]; [TQ 1740 2802].

Numerous old stone diggings occur on the dip slope of Bed lb, between 500 m and 1 km south of Christ's Hospital. Fragments of flaggy sandstone litter the stream bed in Two Mile Ash Gill [TQ 149 271], 300 m south-east of Watlings Farm. An exposure some 350 m farther south revealed: brown clayey silt with flaggy medium-grained sandstone, 0.3 m; on hard calcareous sandstone, 0.2 m; on pale silty clay with 5 cm seams of sandstone, 0.6 m.

A ditch section [TQ 1608 2821] about 1 km east of Christ's Hospital showed 3 m of khaki-brown laminated siltstone included with Bed lb. About 1 km south-south-west of here, a temporary exposure [TQ 1570 2740] showed the following strata, all in Bed lb: buff sandy clay loam, 0.15 m; on grey-brown clay, 0.3 m; on dark brown and yellow mottled, fine- to medium-grained sandstone, 0.15 m; on pale grey and brown clay and sandy clay, 0.75 m; on nodular, calcareous, pale bluish grey, fine- to medium-grained sandstone, 0.15 m; on grey to buff clay and silty clay, 0.6 m; on nodular and blocky, pale brown and grey, highly micaceous sandstone, 0.6 m. The long, fault-bounded tongue of Weald Clay extending for 3 km east of Swallowfield [TQ 205 282] consists of grey silty clays.

Large open pits, probably dug for ironstone, occur just below the crest of the escarpment formed by Bed la between Jones's Wood [TQ 198 278] and Knights Wood [TQ 190 270]. The dip slope of Bed la north-east of Kites Copse [TQ 182 272] has been extensively dug for stone. Stream sections in Kites Copse showed ripple-marked calcareous sandstone, disturbed by valley bulging.

The upper division of the Horsham Stone is well exposed in stream sections near Sedgewick Castle. One section in The Gill [TQ 1773 2600] showed a 0.6 cm bed of medium-grained sandstone dipping 5°S, overlying grey to buff clayey silt and fine sand, 1 m thick. A section 18 m to the south showed flaggy sandstone, 7.5 cm thick, on yellowish brown laminated siltstone and fine-grained sandstone with plant debris, 0.45 m; on massive, hard sandstone, 0.45 m.

Beds 1a and 1b form parallel outcrops, trending east–west between Long Wood and the Maplehurst Fault. A stream section in Long Wood [TQ 1800 2571] exposed part of Bed la dipping 5°S: 2 m of sand, with 7.5 cm layers of sandstone, overlying 0.6 m of massive calcareous sandstone, in two or three courses. Old pits possibly dug for ironstone were noted along the crest of the Bed la escarpment between Harriot's Hill, 400 m south of Nuthurst church, and Prings Farm. A stream section [TQ 1876 2550] in Bed lb showed 1 m of alternating hard and soft, flaggy sandstone beds, each about 7.5 cm thick, folded into a gentle anticline.

Slinfold Manor, Barns Green and Marlpost Wood area

Much debris of 'Cyrena' limestone and Small-'Paludina' limestone was noted in a field [TQ 1115 2900] 400 m south of Slinfold Manor. A section in a stream bank [TQ 1085 2840], 650 m to the south-southwest, showed 1 m of buff, steeply dipping shale with a seam of Small-'Paludina' limestone, 5 cm thick. Fragments of 'Paludina' limestone are common in the bed of the Shipley Stream near the southern corner of Dirtydale Wood [TQ 105 273]. A little upstream from here, a section [TQ 1056 2742] showed 1.5 m of acutely folded grey and greyish brown shale, containing a bed of brown shale crowded with ostracods and bivalves. Dark grey shale, 1 m thick, including a 1 cm layer of Small-'Paludina' limestone, was exposed in the stream bank [TQ 1027 2637] 600 m west-south-west of Lower Woodhouse.

Beds between the 'Cyrena' limestone and the Horsham Stone were proved in three boreholes drilled in 1964 by the Sussex and Dorking United Brick Company, about 1 km south of Barns Green. The cores were described by Mr J D S Macdougall, whose abridged log of the deepest hole (BNG/A) [TQ 1245 2594], surface level 28.7 m above OD, reads:

This borehole was not deep enough to prove whether the sandstone represents the whole of the Horsham Stone or only its upper division, Bed 1b.

The second borehole (BNG/B) [TQ 1270 2600] started at 34.6 m above OD and proved 22.86 m of greenish grey to medium grey clays and silty clays, with ostracods in places.

The third borehole (BNG/C) [TQ 1289 2577] started at 51.5 m above OD and proved: clays and silty clays with ostracods in places, and with Viviparus at 10.24 m, to 12.75 m; on 'Cyrena' limestone, 5 cm thick; on greenish grey clays and silty clays with ostracods in a few layers, to 32 m depth.

West of Marlpost Wood, slabs of 'Cyrena' limestone up to 5 cm thick were exposed in a ditch [TQ 1370 2572]. Some 250 m south-east of this section, 'Cyrena' limestone was exposed in a shallow excavation made for a forest ride. In Marlpost Wood, 'Cyrena' limestone and Small-'Paludina' limestone were mapped for a short distance. 'Cyrena' limestone, 5 cm thick, was revealed in shallow cuttings in a forest ride [TQ 1455 2540]; [TQ 1461 2549]. The Small-'Paludina' limestone, at a higher level, was exposed in a plunge-pool [TQ 1442 2507] in a side valley and forms dip slopes of small extent on both sides of the main valley through the wood.

At the Southwater Brickworks, the following section was measured on the southern face of the main clay-pit [TQ 1570 2570]:

Sharp folds in the central part of the pit [TQ 158 258], probably resulting from valley bulging (p.106), are illustrated in (Plate 12).

A water borehole [TQ 1573 2594] sunk in 1910 at Southwater Brickworks (Edmunds, 1928, pp.131–133), surface level 55.5 m above OD, appears to have entered the Upper Tunbridge Wells Sand at 115.8 m depth. At 43.9 m there was an 0.76 m bed of 'hard blue limestone' which Edmunds thought might be the Horsham Stone.

A slab of 'Cyrena' limestone and fragments of Small-'Paludina' limestone were noted in a stream bed [TQ 1840 2516] 180 m north-west of Gaveston Hall School.

Palmer's Farm and Dragons Green area

All sites at which red clay was seen at surface or was proved by augering in this area are shown in (Figure 19).

Red clay occurs between beds 3a and 3c between Palmer's Farm [TQ 108 249] and Dragons Green. Beds 3a and 3e, and each of the beds making up 3c, form distinct ridges along their outcrops. At Palmer's Farm, on Bed 3e, an excavation for a swimming pool showed red clay overlain successively by buff-yellow silty clay, and buff-brown clayey silt with thin hard ferruginous sandstones. A stream section [TQ 1460 2458] in Bed 3a revealed 1 m of buff and yellow, compact, iron-stained, fine-grained sandstone, in 10 cm layers, dipping 5°S. Red clay occurs beneath Bed 3a at and east of Trawler's Farm; it is particularly well developed south of Copsale, where the sandstone is locally absent. Hard, calcareous, flaggy sandstone was formerly dug from Bed 3a in a copse known as The Delph [TQ 155 246], and from Bed 3c in another copse [TQ 142 241].

In the railway cutting east of Tuckmans Farm, the sandstone of Bed 3a is 1 m thick. Exposures in the northern part of the cutting [TQ 1759 2416] showed the bed dipping north-west, on the south-east limb of a syncline. South of here a fault is thought to intersect the cutting at a point [TQ 1761 2411] where the cutting, 8.5 m deep, is entirely in clay, shale and siltstone. South of the fault the sandstone, forms an anticline. The sandstone, where unweathered, is pale bluish grey, hard, calcareous and massive, but tends to be flaggy or laminated when weathered. It is evenly graded, with few dark grains or mica flakes, and sporadic clay pellets; ripple marks and cross-bedding were noted.

A small stream-section [TQ 1590 2380] in Bed 3c showed the following beds in downward succession: red clay loam, lm; buff to brown, flaggy, calcareous, fine-grained sandstone, 0.8 m; red clay and silty clay, 0.6 m; blocky green-grey and khaki silty shale and siltstone, 0.3 m. South of here, a well-defined sandstone outcrop, dipping south, forms a distinct ridge trending east-north-east. At the eastern end of this outcrop, in 1962, the sandstone was exposed in a cutting on the Worthing road [TQ 1652 2365]. This sandstone may be a part of Bed 3, isolated from the main outcrop of beds 3a to 3c to the north by faulting; alternatively, but less likely, it could be Horsham Stone. Correlation with Bed 3 is supported by the local presence of red clay (unknown at the Horsham Stone horizon) above the sandstone (Figure 19), and by the outcrop of a single bed rather than of the two beds characteristic of the Horsham Stone in this vicinity. Temporary sections along the Worthing road, south of the exposure of sandstone, showed southward dipping grey and brown clays for a distance of about 250 m, and then at [TQ 1662 2340] Small-'Paludina' limestone overlain by some 5 m of grey to brown shale, silt and clayey silt. It is anomalous to find Small-'Paludina' limestone stratigraphically above Bed 3 and it is probable that the beds in question are separated by a branch of the Maplehurst Fault.

Above Bed 3e, buff-weathered grey clay crops out on the slope rising south from the Shipley Stream to Court Farm [TQ 108 243], where there are signs of old diggings for Large-'Paludina' limestone in copses 100 m south-west and 250 m west of the farm buildings. At Court Farm (formerly known as Slaughters), in the early 19th century, four layers of 'Sussex marble', totalling about 0.45 m (Martin 1828; quoted by Topley, 1875, p.105), were recorded. Some 300 to 400 m south-east of the farm, slabs of the stone, 10 cm thick and 0.45 m square, were ploughed up. A ditch section [TQ 1157 2384] exposed clay with shells of large Viviparus and ironstone with ostracods. East of the Shipley Stream, another outcrop of limestone, at about the same horizon, occurs in Hoe's Wood [TQ 132 235], where fragments of Large-'Paludina' limestone and signs of small diggings were seen.

Sandstone (Bed 5a) occurs as a lens terminating westward of Coolham House, with red clay near its western extremity (Figure 19). Pale grey and buff clay occurs south of Coolham House, between sandstone of beds 5a and 5b. Red clay forms a lens in Bed 5b, and also occurs between beds 5b and 5c, north of Oldhouse Farm. Khaki-brown clay was noted between the outcrops of Bed 5c and Large-'Paludina' limestone (Bed 6), which forms a dip slope at Oldhouse Farm. Small exposures of limestone were seen near the farm, and Viviparus shells were noted in a roadside ditch [TQ 1068 2252].

Coolham, Green Street and West Grinstead area

Bristow (in Topley, 1875, p.103) recorded that Horsham Stone was quarried a little north of Conies Farm [TQ 191 238], where it was about 1.5 m thick, although in that particular area the stone is generally not more than 0.6 m thick.

Small-'Paludina' limestone was exposed west of Lodge Farm in a water-main trench [TQ 1536 2281] to [TQ 1546 2287]; the stone may have been formerly dug in old pits in woods [TQ 147 232] 700 m farther west-north-west. Sandstone (Bed 3a), with dull red clay beneath in places, forms an outlier [TQ 190 230] east of Smallham Farm.

At Green Street [TQ 143 228], Bed 3a comprises two separate sandstones. Immediately overlying the lower layer (Bed 3a₁) is red clay with an outcrop 50 to 100 m wide, above which there is pale grey to buff clay. Above Bed 3a₂ occurs grey to buff clay, east and west of Butterstocks Farm. The next higher sandstone, Bed 3c₁, was not well exposed but was traced by augering. A still higher lens of sandstone, Bed 3c₂, includes much red clay near the southern border of the district around [TQ 131 225]. Between Hoe's Farm and the north–south fault through Coolham crossroads, sandstone beds are poorly defined. A belt of red clay appears to link a lens at Batley's Farm [TQ 1210 2315] with Bed 3c₂.

Maplehurst, Warninglid and Cowfold area

Two stone seams (beds 1a and 1b) separated by grey clays were traced by means of a low double escarpment feature and an abundance of calcareous sandstone soil fragments from Haven Farm [TQ 175 237], via Joles Farm, to the Woldringfold–Crabtree Fault. At Conies Farm, a pit [TQ 1917 2397] exposed 1.2 m of flaggy, buff, blue-hearted, calcareous sandstone (Bed 1a) overlain by about 5 m of yellow-buff to grey clay and silty clay. An old sand pit [TQ 2038 2447] in the lower seam, adjacent to Woldringfold Park, showed:

Small pits along the crest of the escarpment of the lower stone between here and Joles Farm were probably dug for ironstone.

Two seams are similarly present between the Woldringfold–Crabtree Fault and the Frithknowle–Drewitts Fault, but only the lower is present in the faulted area at Longhouse Farm. The stone there has been dug in a number of small pits e.g. [TQ 2340 2425], some with small exposures of flaggy calcareous sandstone.

The Weald Clay in the fault-bounded outlier [TQ 245 255] south of Warninglid village is poorly exposed. The lower seam of the Horsham Stone forms a prominent escarpment adjacent to the Lydhurst Fault.

Between Cowfold and the Bolney Fault at Bolney, the Horsham Stone was traced along a double ridge as two seams of stone separated by grey clays.

Between Westlands and Cowfold village a line of old pits, which have been dug to a constant horizon about 4.5 m below the lower stone, probably for the clay-ironstone, was traced from Browning's Farm to the Bolney Fault. The following section in the lower stone seam was seen in the stream bed [TQ 2023 2247], 410 m south-southwest of Browning's Farm:

Seams of calcareous, flaggy, ripple-marked sandstone of Bed 1b were noted in the stream bank about 140 m downstream.

Near Cooper's Farm [TQ 228 231], both stone seams are much reduced in thickness over a distance of about 370 m, and the upper stone bed is absent near the Bolney Fault.

The outlier in the Ouse valley

The following composite section is based on the Cuckfield boreholes (Lake and Thurrell, 1974) and field evidence:

Within this faulted outlier, the lower seam of the Horsham Stone forms a number of low east–west escarpments, disrupted by faulting. Approximately the same suite of beds crop out on each of the ridges, in some cases dipping southwards, in others northwards. The low ground between the ridges is obscured by sandy and silty wash.

The beds cropping out on the small ridge south-east of Sidnye Farm [TQ 298 275] to [TQ 304 274] dip southwards at about 5 to 10°. Large old pits [TQ 2992 2752]; [TQ 3030 2743] were probably dug for marl and for ironstone below the Horsham Stone, but may also have worked small amounts of sandstone. Exposures of up to 0.75 m of fissile, flaggy, calcareous sandstone were seen on the southern edges of both pits; these showed anomalous northerly dips due to collapse of the sides of the old workings. Smaller pits [TQ 3007 2749]; [TQ 3021 2747] were probably dug solely for ironstone. The clays immediately below the ironstone are generally red or red and brown mottled.

Between Bigges Farm and the eastern end of the ridge south of Sidnye Farm [TQ 2880 2716] to [TQ 2986 2729], the beds dip southwards at about 10°. Large pits occur on the crest of the ridge [TQ 2850 2715]; [TQ 2930 2725]; [TQ 2970 2728]. Topley (1875, p.102) recorded that 'grit and sandstone' were dug at the most westerly of these pits; Jones (quoted in Topley, 1875) described ripple-marks and trace fossils from a slab of sandstone from the same quarry. This section is now completely degraded, but calcareous sandstones were seen in the most easterly of the pits. Each of these pits is too deep to have worked the sandstone alone and probably exploited the underlying ironstone as well. Smaller pits, which worked only the ironstone, also occur on the same ridge [TQ 2912 2723]; [TQ 2956 2730]. West of Bigges Farm the ridge is crossed by a fault, west of which the beds dip northwards.

The ironstone beneath the Horsham Stone has been worked on the ridge north-west of Mizbrook's Farm in shallow open pits [TQ 2857 2689]; [TQ 2870 2689] and in minepits [TQ 2900 2687]; [TQ 2853 2690]. The beds here dip gently northwards.

The Cuckfield No.2 Borehole [TQ 3013 2683] proved clays with thin beds of Small-'Paludina limestone from 14.17 to 22.68 m. The thickest limestone, from 16.64 to 16.84 m depth, consisted of two beds separated by 6.4 cm of very clayey limestone. The base of the lower limestone rested on a thin calcareous sandstone. Thin beds of 'Cyrena' limestone were recorded at a number of levels below 22.68 m (Lake and Thurrell, 1974). Fragments of Small-'Paludina' limestone and of thin calcareous sandstone were seen in old pits [TQ 3006 2708]; [TQ 2988 2692] nearby, which may have been dug for limestone. The limestone shown on the map is probably that proved at 16.64 m in the borehole. Other pits at the same level occur at Brook Street [TQ 3066 2699]; [TQ 3071 2734].

A borehole at Brook Street [TQ 306 275, precise site uncertain] has been the subject of conflicting interpretations. Edmunds (1928, p.82) and Reeves (1948, p.255) interpreted the log as showing different amounts of Weald Clay on Tunbridge Wells Sand, whereas Michaelis (1969, p.528) thought it showed Lower Tunbridge Wells Sand, on Wadhurst Clay and Ashdown Beds. It is now evident that the borehole is sited at a level between the Horsham Stone and the Small-'Paludina' limestone. The beds down to 87.63 m, described mainly as clays and marls (Edmunds, 1928), are attributed to the Weald Clay, and the beds below to the Tunbridge Wells Sand (see p.65). A sandstone at 16.61 m is probably the lower seam of the Horsham Stone, giving a thickness of 71.0 m for the Weald Clay below the Horsham Stone, a figure similar to that deduced from the Cuckfield No.1 Borehole. A second sandstone bed, at 63 to 64 m depth, does not crop out in the outlier. As elsewhere in the Horsham district, the lowest part of the Weald Clay is predominantly silty.

A trench [TQ 3182 2661] to [TQ 3217 2739] which crossed the outlier east of Wetlands Wood exposed sections in dark grey and reddish brown shales and silty mudstones, weathering to yellow and red silty clays. Thin siltstone beds, nodules of clay-ironstone and thin slabs of calcareous siltstone and silty, fine-grained sandstone with ripple marks and abundant trace fossils were also present.

Another temporary section [TQ 3249 2712] showed similar weathered silty clays, disturbed by frost heaving and containing slabs of calcareous, fissile, silty, fine-grained sandstone, only a few centimetres thick but lithologically similar to the Horsham Stone south of Sidnye Farm. Many of these slabs were seen to be ripple marked and to have a variety of sole markings on their lower surfaces. Others carried a variety of trace fossils, trails, grazing tracks and footprints, together with desiccation cracks and possible sun cracks.

Chapter 5 Structure

The Horsham district straddles the main axis of the Wealden Anticline, which runs roughly east–west across the district from the Ashdown Forest to Slinfold. This broad, gentle anticline, in which dips are mostly less than 2° and rarely exceed 5°, was superimposed in Miocene times on a series of older and much more complex structures. These older structures dominate the outcrop of the Hastings Beds and the lower part of the Weald Clay, where their surface expressions are belts of faulting, mostly east–west in trend, in which blocks of strata dip at up to 25° and the bounding faults of which commonly have vertical displacements of more than 100 m.

In the northern part of the district, a discontinuous fault belt between Weir Wood Reservoir and Turners Hill, and between Three Bridges and Warnham separates a large central tract of gently dipping, largely unfaulted strata from a major complex fault belt which runs from Horsted Keynes to Nuthurst. Both fault belts, which delineate minor graben structures at shallow depths, have numerous minor attendant faults, and both can be traced eastwards into the Tunbridge Wells (Sheet 303) district where they form part of a laterally very persistent set of east–west-trending fault belts ((Figure 20)C).

In the Weald Clay outcrop in the present district, all the major faults and almost all the lesser faults which cut the Hastings Beds outcrop die out westwards. For many years the apparent absence of major faults in the Weald Clay outcrop throughout the Weald was interpreted as being due either to a mechanism by which fault displacements are dissipated in mudstones as numerous tiny movements along bedding planes, or to lack of detection in the absence of a detailed Weald Clay stratigraphy. Both interpretations are now known to be incorrect. Throughout Jurassic and early Cretaceous time the major faults in the central Weald were intermittently reactivated and they locally affected both the type and pattern of sedimentation. These syndepositional ('growth-fault') movements ceased in the Barremian, mostly in the early Barremian, and as a result all the faults affect the Hastings Beds and many affect the lower part of the Weald Clay, but few displace the middle and upper Weald Clay strata.

Structurally, the Wealden Anticline is a good example of 'basin inversion', a present-day periclinal structure sited over a Mesozoic sedimentary basin in which the axes of subsidence and tectonic uplift are roughly coincident. From late Triassic to mid-Cretaceous times the Wealden sedimentary basin, like the larger Wessex Basin of which it forms an easterly embayment, subsided intermittently as a result of rifting along east–west-aligned normal faults. To the north of the Horsham district, now concealed beneath the Cretaceous and Tertiary rocks of the North Downs, a major fault belt separated the London Platform from the Wealden basin. To the south, the Hampshire–Dieppe High, now concealed beneath the South Downs and the English Channel, formed the southern boundary of the sedimentary basin (Figure 3). Within the Wealden Basin, subsidiary eastwest-trending faults formed grabens and half grabens which controlled the local rates of subsidence.

The recent availability of seismic data from the Weald and adjacent areas has enabled correlations to be made between surface structures and those at depth. Throughout the Wessex–Weald region, major fault belts traceable at the surface can be shown to pass down into steeply dipping fractures in the underlying Permo-Triassic and Jurassic rocks which, in turn, are aligned over major Variscan thrusts in the Carboniferous and older rocks (Chadwick et al., 1983). In the late Carboniferous and early Permian, rapid erosion of the Variscan mountains occurred throughout much of England south of a line from the Thames to the Bristol Channel, and resulted in local disequilibrium in the lower crust. This reactivated the major Variscan lines of weakness, mainly east–west-trending thrusts, as tensional faults in the younger rocks. This crustal stretching continued intermittently from the Permian until mid- to late Barremian times in the Weald. During each extensional phase, normal faulting developed to form local asymmetrical grabens, mostly along the lines of earlier faulting. Two major Variscan thrusts, the Ashdown Thrust and the Brightling–Bolney Thrust, have been recognised beneath the present district; these gave rise to grabens in the Jurassic and complex graben-like fault belts in the early Cretaceous (Figure 20). The subcrop of the Ashdown Thrust is overlain by complex of faults which includes the Charlwood faults and Stone Farm Fault, and the graben bounded by the Holmbush and Crawley faults. The Bolney–Brightling Thrust is overlain by the complex east–west belt of faults that runs from Danehill to Maplehurst and which includes the Danehill and Great Oddynes faults, the bounding faults of the Ouse Valley graben (Figure 21), and the Sedgewick, Nuthurst and Maplehurst faults.

Although the more important faults in the Horsham district have general east–west trends for most of their lengths, many have a local NE–SW trend and there are numerous minor faults which trend between NNE–SSW and ENE–WSW. Prominent among the latter are the faults at the western end of the Faygate Syncline, those between Turners Hill and Balcombe which separate the Crow-borough Anticline and the Colgate Anticline, and those in the complexly faulted ground between Lindfield and Cowfold. The persistence of this secondary fault trend throughout the High Weald might suggest the presence of a second set of major faults, possibly wrench faults, in the Variscan basement.

The seismic data show that during the Jurassic extensional phases, when the faults were active, differential rates of subsidence occurred between the graben and intergraben areas. The same must also have been true adjacent to and between the individual growth faults which were active during the deposition of the Hastings Beds and lower Weald Clay. However, there is little direct evidence to prove the presence of either thickness or facies variations in the Wealden rocks because of the scarcity of exposure and borehole data. There are, however, some indications of this in Wealden stratigraphy; thus local thickness and facies changes in the Weald Clay on either side of the Crawley Fault (see page 92) indicate the presence of active growth faults, and the widespread 'earthquake bed' in the Ardingly Sandstone of the Horsham and Tunbridge Wells districts (see p.32) probably indicates strong local contemporaneous seismic activity.

The best exarnple of the sedimentary effects of growth faulting in the present district is provided by the continuous cores of the Cuckfield No.1 Borehole, drilled close to the deepest part of the Weald-Clay-filled graben which runs from south of Ardingly to Lower Beeding. Although it was possible in the borehole to identify the full range of Hastings Beds formations and members recognised in the mapping of adjacent areas (Lake and Thurrell, 1974), the beds at several stratigraphical levels are markedly more argillaceous than their equivalents at outcrop (Plate 3). Furthermore, deformation structures caused by contemporaneous flow, triggered either by rapid sedimentation, seismic activity or a combination of the two, occur at many stratigraphical levels even though such structures are rarely observed at outcrop in the district.

The coarser Hastings Beds lithologies, the more massive sandstones in the Ashdown Beds and Ardingly Sandstone, are represented predominantly by siltstones and very silty fine-grained sandstones in the Cuckfield No.1 Borehole. The argillaceous formations, the Wadhurst Clay, Grinstead Clay including the Cuckfield Stone, and the lower part of the Weald Clay have similar lithologies in the borehole to those at outcrop. Similarly anomalous sequences have been recorded adjacent to major faults in the Hastings Beds in the Tunbridge Wells district where boreholes in the Ashdown Beds in the Frant graben[TQ 588 345] and in the Tunbridge Wells Sand in faulted ground at Bartley Mill 1631 356] proved both formations to be more argillaceous than the equivalent beds in unfaulted outcrops nearby (Gallois in Bristow and Bazley, 1972, pp.133–146).

The compressive movements which formed the Wealden Anticline in the Alpine Orogeny do not appear to have reactivated any of the major faults in the Weald. However, the evidence is poor at outcrop and some steepening of dips and minor movement is likely to have occurred within the tilted blocks of strata in the major fault belts. The main effect of the compression was to produce gentle folds between the fault belts, including, in the present district, the Crowborough and Colgate anticlines which form part of the sinuous axial trace of the main Wealden fold. Minor folds such as the Oakwood Hill Syncline, Walliswood Anticline and Faygate Syncline in the Weald Clay also have sinuous axes which roughly parallel that of the main Wealden Anticline (Figure 22).

The presence of late Pliocene and early Pleistocene marine beach deposits at heights of up to 200 m on the North Downs indicate that the Weald has undergone uplift throughout the Quaternary. Worssam (1973) has suggested, on geomorphological grounds, that more than 180 m of uplift occurred in the central Weald during the Quaternary, a factor that may explain the high relief of the Hastings Beds outcrop.

The detailed structure of the district is summarised in the structural contour map (Figure 22). In the Hastings Beds outcrop, the contoured surface is the base of the Lower Tunbridge Wells Sand; the use of the same surface on structural contour maps of the Tunbridge Wells (Sheet 303) and Tenterden (Sheet 304) districts (Bristow and Bazley, 1972, Shephard-Thorn et al. , 1966, pl.II respectively) enables direct comparison to be made throughout the High Weald.

In the St Leonard's Forest area, the depth of the base of the Tunbridge Wells Sand has been calculated by extrapolation from the known levels of named sandstone beds in the Upper Tunbridge Wells Sand. The base of the Tunbridge Wells Sand has been taken as 84 m below the Shelley Plain Sandstone, 114 m below the Colgate Sandstone and 122 m below the Roffey Park Sandstone.

The base of the Weald Clay has been contoured where practicable, but the junction with the Tunbridge Wells Sand boundary at the crop is mostly faulted in the present district. The structure of the lower part of the Weald Clay is indicated by contours on the base of the Horsham Stone. Contours on Bed 2a 'Cyrena' limestone and Small-'Paludina' limestone) in the vicinity of Warnham Brickworks are in part based on an interpretation by Mr J D S MacDougall of information from trial boreholes drilled by Messrs. Redland Bricks Ltd. Beds 3a, 3c and 5c of the Weald Clay were chosen for contouring to provide continuity with the structural contour map of the Haslemere (Sheet 301) district (Thurrell et al., 1968, pl.II). In the north crop of the Weald Clay, Bed 3c seems to be everywhere 23 m above Bed 3a. Contours on the latter bed only are therefore shown in this northern part of the district. Bed 5c dies out about 3 km east of the boundary with the Haslemere district, on both the north and south crops of the Weald Clay.

Details

In the following notes on faults, the grid reference given in the caption refers to the locality after which the fault has been named.

Three Bridges to Warnham

Crawley Fault [TQ 267 363]

The throw of this fault is about 60 m to the south in its eastern part, diminishing gradually from Lambs Green [TQ 220 368] westwards to about 6 m near The Nunnery [TQ 190 364]. Its effect on the topography in Crawley is marked. The features on its south side are aligned east–west, parallel to the axis of the Faygate Syncline: those on its north side, where the beds have a steady north-westerly dip, are aligned SW–NE.

Holmbush Fault [TQ 225 337]

Along the line of the Holmbush Fault there is a sharp boundary between hilly forested country on Upper Tunbridge Wells Sand to the south and low-lying, mainly pastoral, Weald Clay land to the north. The amount of throw is uncertain, but it is probably about 30 m along most of the fault.

Park Farm Fault [TQ 178 334]

The plane of this fault was seen in a railway cutting [TQ 175 331] by Topley (1875, p.80). An element of wrench movement is indicated by his observation that slickensides were inclined 60° from the vertical towards the west, such that Weald Clay beds seemed to have moved laterally down to the west. The trial boreholes drilled by Messrs Redland Bricks Ltd indicated a WSW–ENE fault through Brookhurst Farm, with a northward downthrow of about 60 m in the west [TQ 1722 3516] and about 90 m in the east [TQ 1780 3530].

Weir Wood Reservoir to Balcombe

Paddockhurst Park Fault [TQ 320 337]

This fault links the two complex fault belts which bound the otherwise unfaulted block of country between Balcombe and West Hoathly. Between Worth Priory and Kingscote it brings Wadhurst Clay into contact with Upper Tunbridge Wells Sand and the downthrow probably exceeds 120 m. The fault was seen in the bed [TQ 3475 3551] of a small tributary of the Medway where vertical flaggy sandstones are in contact with grey clays. The sandstones were traced southwards in almost continuous section to a point 165 m south of the fault, where the dip is only 25°.

The fault was also seen in Threepoint Gill [TQ 3354 3482], where it brings disturbed grey shales of the Wadhurst Clay into contact with thickly bedded sandstones of the Upper Tunbridge Wells Sand. A subsidiary fault in the stream bed 140 m to the south throws disturbed, thinly bedded sandstones and siltstones of the Upper Tunbridge Wells Sand against purple and grey shales of the Upper Grinstead Clay. Another subsidiary fault in Great Wildgoose Wood appears to thrust red and grey clays of the upper part of the Wadhurst Clay over the Lower Tunbridge Wells Sand.

Between Worth Priory and Balcombe Lake the fault has a throw ranging from 30 to about 45 m. For most of this section the line of the fault is repeatedly crossed by a small stream. Flaggy sandstones [TQ 3191 3352] in the lower part of the Lower Tunbridge Wells Sand, 820 m south of the Priory, showed progressively steeper dips as the fault plane was approached, there running a few metres east of the stream.

Between Balcombe Lake and a small cross-fault, near Kemp's House, the throw and nature of the fault are difficult to determine. Together with the Balcombe House Fault, which roughly parallels the Paddockhurst Park Fault and which terminates against the small cross-fault, it bounds a block of strata of uncertain age (see p.35). Between Kemp's House and Pilstye Farm the small displacements on the Paddockhurst Park Fault are only 6 to 9 m.

Turners Hill Fault [TQ 340 353]

This fault is roughly parallel to the Paddockhurst Park Fault: it has a uniform displacement of about 30 m. Much of the fault is clearly defined between a line of old sandstone pits in the Ardingly Sandstone and a line of old marl pits in the Wadhurst Clay. The Wadhurst Clay between this and the Paddockhurst Park Fault has been preferentially eroded to form a narrow col on the Medway–Ouse watershed.

Fonthill Fault [TQ 381 362]

The maximum throw of this fault is probably at the southern end, where it is about 12 to 15 m; the throw decreases northwards to about 7.5 m at High Grove.

Stone Farm Fault [TQ 383 345]

The throw of the fault probably exceeds 60 m south of Stone Farm, but decreases steadily to less than 30 m at Gravetye Manor [TQ 361 340]. West of there the fault causes only a small displacement, about 6 m, of the base of the Tunbridge Wells Sand outcrop.

Charlwood Faults [TQ 393 342], Tunbridge Wells district

Two major faults, the North and South Charlwood faults, bound a complex graben on the south side of Weir Wood Reservoir and bring Wadhurst Clay and Tunbridge Wells Sand into contact with Ashdown Beds. The northern and southern boundary faults have throws of about 65 and 105 m respectively, but subparallel faults within the graben add to an overall downthrow which may locally exceed 200 m.

The North Charlwood Fault, together with one of the subsidiary faults, was exposed in a road cutting [TQ 3871 3446], where a section from north to south showed:

The two faults are about 4.5 m apart in this section. The highly sinuous nature of the South Charlwood Fault suggests that it dips northward at a relatively low angle, and is antithetic to the more northerly faults in the complex.

Horsted Keynes to Nuthurst

Danehill Fault [TQ 402 276]

The Danehill Fault is part of the major line of fracturing which runs from the south side of the Ashdown Forest to Nuthurst via the Ouse Valley Weald Clay outlier. It downthrows southwards, juxtaposing Upper Tunbridge Wells Sand and Ashdown Beds, and has a maximum throw of about 140 m near Wyatts [TQ 388 279].

Great Oddynes Fault [TQ 373 286]

The line of the fault is clearly marked between the Ouse valley [TQ 3661 2836] and Oddynes Holt [TQ 3787 2895], where it brings Wadhurst Clay into contact with Ashdown Beds. The throw is everywhere down to the north, with an estimated maximum of 107 m at the River Ouse, where high Wadhurst Clay abuts against Ashdown Beds.

Lindfield Fault [TQ 345 255]

The fault has a southerly downthrow, apparently decreasing steadily from west to east. At Penland Farm [TQ 321 258], the fault splits into a complex of lesser faults which pass westwards through Lullings Farm to Slough Place and form an important subsidiary part of the fault complex of the Weald Clay outlier. At Finches [TQ 343 260], Lindfield, a number of deep marl pits in red Wadhurst Clay were dug almost up to the fault plane. Elsewhere, the fault brings beds of similar lithologies into contact with one another, and its precise position can only be fixed sporadically. The maximum throw is probably near Sunte House [TQ 333 256] where it exceeds 90 m and may be as much as 120 m, the uncertainty being due to the lack of detailed knowledge of the Upper Tunbridge Wells Sand stratigraphy. Between Lullings Farm and Slough Place [TQ 287 261] a branch of the Lindfield Fault separates an almost horizontal sequence in Lower Tunbridge Wells Sand and Grinstead Clay to the south from beds at much the same horizon on the north, but which dip northwards at 5 to 10° into the Borde Hill Fault.

Pilstye Farm Fault [TQ 307 282]

This fault is probably a continuation of the Danehill Fault. The maximum throw is probably near the London–Brighton railway line [TQ 322 280], where it may exceed 140 m to the south. Westwards from there the displacement decreases steadily until the fault terminates against a small subsidiary fault near Rock Farm.

Borde Hill Fault, Sidnye Farm Fault and associated faults

A continuous belt of faulting has been traced for about 45 km from Southwater [TQ 160 260], via the Weald Clay outlier and Danehill, to Mayfield in the Tunbridge Wells district. The most intensely disturbed part of this zone of fracturing is between Lower Beeding and Ardingly where the Weald Clay outlier is brought into contact with beds ranging from Wadhurst Clay to Upper Tunbridge Wells Sand. The outlier is bounded by two major faults, the Sidnye Farm and Borde Hill faults. At Sidnye Farm [TQ 296 277], a thickly bedded sandstone in the upper part of the Upper Tunbridge Wells Sand, possibly the equivalent of the top sandstone of the Harvesthill area (see p.63), forms a dip slope which falls southwards at 15 to 20° into the Sidnye Farm Fault. The throw of the fault may be as little as 30 m at this point.

Within the outlier, between Old Park and Brook Street, there are numerous minor cross-faults. Dips within the fault-bounded blocks vary, some to the north others to the south, mostly at 5 to 10°. Topley (1875, p.102, and Old Series Sheet 9) recorded a section in a pit at Bigges Farm [TQ 2894 2712] with a dip of 25°S. In the Cuckfield No.1 Borehole [TQ 2961 2731], dips of about 15° were observed near the surface, but these decreased with depth. Shear surfaces were present at several levels in the cores.

The southern boundary fault of the outlier, the Borde Hill Fault, has a maximum proved throw of about 290 m at Brook Street village where it brings Weald Clay above the Horsham Stone against Wadhurst Clay. This is the largest proven throw at surface of any fault yet recorded in the Weald.

At the western end of the Weald Clay outlier near Lower Beeding, the Sidnye Farm and Borde Hill faults come to an abrupt termination in which they appear to cancel one another out. They are linked by a minor fault to the Sedgewick [TQ 181 273] and Nuthurst [TQ 186 265] faults, which continue the graben westwards, but with rapidly decreasing throws. Both faults displace the Horsham Stone outcrops but die out in the middle part of the Weald Clay.

Scaynes Hill to Maplehurst

Henfield Wood Fault [TQ 370 242]

This fault is probably a continuation of, or is linked to, the major fault which displaces the base of the Weald Clay south of Bolney. The Henfield Wood Fault was seen in both banks of a stream [TQ 3035 2298] 320 m south-west of Copyhold Farm, where shales in the Wadhurst Clay, vertical at the fault, are brought into contact with thickly bedded, very broken, steeply dipping sandstones of the Upper Tunbridge Wells Sand. The plane of the reverse fault dips southwards at about 75° here. A second small fault, entirely within the Wadhurst Clay, crosses the stream 90 m to the south. In both instances the fold axes in the Wadhurst Clay are transverse to the valley, unlike disturbances produced by valley bulging. Between Lyoth Common [TQ 353 239] and the Ouse valley the fault separates areas of markedly different dips. To the north, around Walstead Place Farm, dips of up to 20° are shown by an ironstone bed within the Upper Tunbridge Wells Sand. To the south, around Awbrook, long dip slopes fall gently southwards. The maximum proven throw on the fault, where it is exposed near Copyhold Farm, exceeds 90 m.

Burgess Hill Fault [TQ 320 190]

Much of this fault lies in the Brighton district where it causes a dextral displacement of almost 600 m in the outcrop of the base of the Weald Clay, which there dips south at about 8 to 10°. This corresponds to a downthrow of between 85 and 105 m to the east. Northwards, the fault intersects a major strike fault which runs east–west just north of Harvesthill. The width of the Upper Tunbridge Wells Sand outcrop between this latter fault and the unfaulted junction with the Weald Clay, which lies 360 m to the south, suggests that much of the Upper Tunbridge Wells Sand is cut out. The unnamed fault was seen in a stream section [TQ 3064 2265], where red clays of the Upper Grinstead Clay are thrown against sandstones in the Upper Tunbridge Wells Sand.

Lucas Grange Fault [TQ 326 245]

Between Ansty and Haywards Heath this fault brings Upper Tunbridge Wells Sand into contact with strata ranging from Wadhurst Clay to Upper Tunbridge Wells Sand. It has a similar effect to that of the Lindfield Fault, to which it is connected by a cross-fault running through Penland Farm. At its eastern end it probably continues across the Upper Tunbridge Wells Sand outcrop, where there is very little stratigraphical control, to join the Lindfield Fault. The fault plane was exposed in a stream bed [TQ 3026 2351], where it cuts thickly bedded sandstone with dips up to 40°, those to the south being in the Upper and those to the north in the Lower Tunbridge Wells Sand. The maximum observed throw of the fault, near Lucas Grange, exceeds 75 m.

Sandrocks Fault [TQ 330 224]

Between its termination against the Burgess Hill Fault (in the Brighton district) and Sandrocks, the fault repeats the sequence brought up by the Henfield Wood Fault some 800 m to the north. The maximum throw, where it brings Wadhurst Clay into contact with Upper Tunbridge Wells Sand siltstones and sandstones, is in excess of 90 m.

Abbots Leigh Fault [TQ 352 227]

This fault acts in the same way as the Henfield Wood and Sandrocks faults, to which it is joined, forming on its south side inliers of Grinstead Clay within the Upper Tunbridge Wells Sand outcrop. Its maximum displacement probably occurs near its junction with the Sandrocks Fault, and may be as little as 30 m. Between Anchor Wood and Hammond's Farm the displacement is very small and appears to be reversed, with the downthrow to the south.

Scaynes Hill Fault [TQ 369 232]

Near Scaynes Hill at [TQ 372 233] and south of Awbrook [TQ 362 231], outcrops of Grinstead Clay are abruptly terminated by the fault. The throw of the fault, at least 30 m, is probably greatest where it joins the Abbots Leigh Fault; it decreases steadily eastwards. North of Hammond's Farm [TQ 382 235], a subsidiary fault produces small displacements and a change of dip in the Cuckfield Stone outcrop.

Bolney Fault [TQ 259 229], Frithknowle–Drewitts Fault [TQ 220 240] to [TQ 239 248] and Maplehurst Fault [TQ 189 245]

These are subparallel to and similar in effect to the Burgess Hill Fault, all having downthrows on their north-western side which cause lenticular outcrops of Weald Clay to penetrate the Tunbridge Wells Sand outcrop. The Frithknowle–Drewitts and Woldringfold–Crabtree [TQ 210 246] to [TQ 220 253] faults form part of a fault complex which trends roughly NE–SW and is linked by the Lydhurst [TQ 246 260] and Freechase [TQ 239 253] faults to form two small grabens infilled with Weald Clay.

These are in turn linked, by minor faulting at their north eastern end, to the Ouse Valley Weald Clay outlier. Throws on the bounding faults of the small grabens, which bring Horsham Stone in contact with beds low in the Upper Tunbridge Wells Sand, locally exceed 100 m. The Frithknowle–Drewitts and Woldringfold–Crabtree faults meet [TQ 195 231] near Westlands where their displacements largely cancel one another out. The latter fault continues southwestwards to displace the Horsham Stone outcrop, but dies out in the overlying mudstones.

The Maplehurst Fault has a long, sinuous outcrop which trends between NE–SW and east–west. Its maximum throw exceeds 150 m near Tuckmans [TQ 178 240], where it brings Upper Tunbridge Wells Sand in contact with sandstones of Bed 3 of the Weald Clay. The throw declines rapidly north-eastwards to less than 50 m near Prings Farm [TQ 207 255], where it displaces the Horsham Stone outcrop, and the fault dies out nearby in the Upper Tunbridge Wells Sand. To the south-west, where the fault displaces successive beds in the Weald Clay up to and including Bed 6, the Large-'Paludina' Limestone, the throw again steadily decreases.

Chapter 6 Quaternary

Large climatic variations characterised the Quaternary period throughout Britain, and at times a continental ice sheet reached as far south as the River Thames. Small, semipermanent snowfields probably capped the higher parts of the Hastings Beds outcrop from time to time, but there is no evidence that ice ever reached the district. However, some of the landforms and most of the drift deposits in the district were formed in a periglacial climate. Freeze-thaw processes associated with permafrost are indicated, most commonly in the areas of higher relief, by cambering and valley bulging, and by the deposition of Head; wind erosion in a cold arid climate is shown by the undercut nature of many of the sandstone outcrops in the Hastings Beds; and deposition from torrents of meltwater is indicated by many of the River Terrace Deposits in the district.

Drift deposits, mostly locally derived Head, are widespread in the district, but only the thicker deposits and those thin deposits which obscure the underlying geology are shown on the published map. River Terrace Deposits, mostly along the rivers Adur, Arun and Mole, are the second most extensive drift deposit. Narrow strips of alluvial deposits, including small patches of peat, occur along the floodplains of the major rivers.

The present-day distribution of Quaternary deposits in the Weald is patchy and provides only a fragmentary record of the history of the period. The oldest drift deposits in the district are probably the older Head of the Bramley Wey and Mole valleys and the Second Terrace of the Bramley Wey, all of which are cold-climate deposits which may be pre-Devensian (using the British Standard Pleistocene Stages of Mitchell et al., 1973) in age. The younger Head and all the remaining terrace deposits are Devensian in age, and much of the landslipping, cambering, valley bulging and cryoturbation took place in the latter part of this stage. The

Alluvium and Peat, and reactivation of some of the superficial structures, are Flandrian (postglacial) in age.

Head

Head deposits characteristically consist of poorly sorted, locally derived materials which have accumulated by in-situ weathering, solifluction, hillcreep and similar processes in which water acts as a lubricant rather than as a primary agent of transport. All gradations occur between the most poorly sorted Head and well-sorted river deposits, and in some areas it is difficult to draw a line between the two. The Head deposits of the present district occur in two distinct areas: on the Weald Clay in the north-west, where they are primarily derived from the Lower Greensand; and in the more steep-sided valleys on the Hastings Beds outcrop, where they are derived from nearby outcrops. Most of the Head deposits now preserved in the district are presumed to have formed in the late Pleistocene during periods of periglacial climate, when repeated freeze-thaw action caused large amounts of pedological soil and subsoil to become mobilised. Small amounts of Head continue to be formed at the present day, as hillwash and soil creep, on those steeper slopes which have not been stabilised by vegetation.

The Head deposits in the north-west can mostly be divided into an older and a younger Head on the basis of their topographical occurrence. Some isolated patches are difficult to assign to either group, and the two are not therefore distinguished on the published geological map. The older Head deposits occur mostly as residual patches on hilltops and are graded to the second terrace of the River Wey (Figure 23). The younger Head deposits occur as fan-shaped spreads in the upper parts of the present-day valleys of the North River around Forest Green [TQ 125 410], its Sheep Green tributary to the west of Jayes Park, and the Kit Brook [TQ 167 416] north of Ockley. The Head at the first two localities grades downstream into the fourth terrace of the River Arun, and that of the Kit Brook valley to the second terrace of the River Mole.

These Head deposits are mostly gravelly but, unlike the river terraces, they have a marked downstream slope (Figure 23). The slope of the upper part of the Sheep Green spread, for example, is 2.5° and is readily apparent in the field.

On the Weald Clay outcrop, the distribution of Head deposits is strongly influenced by the outcrop of sandstone and limestone beds, which form topographical features that set barriers to the downstream prolongation of fans of Head. Alluvial conditions, probably flash floods caused by meltwater run-off, may have dominated the deposition of some of the more extensive spreads of Head on the Weald Clay.

By contrast, almost all the Head mapped out on the Hastings Beds outcrop accumulated as slope deposits. Around East Grinstead, in the deep ghylls between West Hoathly and Balcombe, and in the Ouse and Cob Brook valleys between Horsted Keynes and Lindfield, the Wadhurst Clay outcrop in the valley floors and sides is commonly overlain by up to several metres of silty and sandy Head derived from nearby outcrops of Lower Tunbridge Wells Sand. Similarly, extensive spreads of silty and sandy Head, derived from the Upper Tunbridge Wells Sand, overlie the Grinstead Clay in the valleys on the north side of Balcombe. Similar Head derived largely from the Upper Tunbridge Wells Sand overlies much of the Weald Clay outcrop in the low ground adjacent to the Ouse Valley near Sydnye Farm [TQ 296 277], and large patches of locally derived silty and sandy wash occur in the floors of some of the valleys in the Upper Tunbridge Wells Sand outcrop between Three Bridges and Felbridge.

Head deposits of the same type are widespread in the valley sides and floors of the steeper valleys throughout the remainder of the Hastings Beds outcrop, but they have not been mapped on the outcrops of the silty and sandy formations because of the difficulty of differentiating in-situ weathering (regolith) from materials of the same lithology which have moved only a short distance.

Piper (1972) described the Head deposits that mantle the valley sides and floors in the Balcombe area as Pleistocene mass-flow deposits. Some are associated with boulder deposits at the foot of Ardingly Sandstone cliffs. He noted that sand grains from one locality [TQ 3181 2833] showed surface textures indicative of wind action.

Details

Forest Green to Jayes Park

Between Forest Green and Jayes Park [TQ 144 405], Head deposits spread out like fans in strike vales between sandstone and limestone ridges. The oldest and highest deposit is on the interfluve between present-day valleys near Forest Green. It is represented by gravel at 107 m above OD on Etherley Hill and, possibly, by sandy clay with cherts near 120 m above OD on the limestone ridge at Etherley Farm [TQ 129 417]. Its altitude suggests that it grades to the Bramley Wey Second Terrace (Figure 23) and it is therefore likely to be of the same age as the Older Head of the Haslemere district.

Three younger stages of Head deposition at Forest Green are probably of local significance only, equivalent in age to the Fourth and possibly in part to the Third Terrace of the River Arun. The oldest is represented by small patches of Head at 90.5 m OD. near the Parrot Inn [TQ 124 413] and at 75 m above OD [TQ 1225 4045] west of Ives Farm; the next stage by more extensive spreads at a lower level, at 80 m above OD around the church [TQ 1202 4121] and at 76 m OD around Waterland Farm [TQ 118 419] and Goster Wood [TQ 1255 4140]. An outlying patch [TQ 108 416] north of Coophurst Farm may belong to this stage. The lowest stage is represented by small patches of Head near stream level at Forest Green [TQ 119 411] and [TQ 121 407] and by more extensive spreads south of Bridgeham Farm [TQ 120 402] and around Bullcroft Farm [TQ 125 399]. The deposits in all the spreads consist of clayey sand with chert fragments. Much iron-cemented gravel (locally known as 'ragstone'or shrave') was met in mole-draining a field [TQ 1240 3995] north-west of Bullcroft Farm, and a ploughed-up block of 'ragstone' measuring 0.6 x 0.4 m was noted in a hedge bank 450 m east-north-east of the farm.

The Head south-west of Lower Breache Farm [TQ 107 396] has the form of a fan, laid down below the confined valley through the ridge made by Large-'Paludina' limestone (beds 8a and 8b) (Thurrell et al., 1968, p.119). Up to 1 m of sandy clay, overlying gravel which is probably not more than 0.5 m thick, was augered in this tract.

Around Sheep Green [TQ 140 412], small exposures show 1 to 2 m of clay overlying a metre or more of gravel. The clay was probably derived from Weald Clay and Atherfield Clay which form the lower slopes of Leith Hill, and the gravel, of chert and cherty sandstone fragments, from Hythe Beds that form the upper slopes. One temporary excavation [TQ 137 413] showed that smaller fragments in the gravel (1.5 to 5 cm diameter) are well rounded, and larger ones (up to 15 cm) angular. The rounding is more pronounced farther downstream, which suggests that the deposit may have been mainly waterlain; but the presence of large angular blocks of chert, considered together with the coarseness of the gravel and the great bulk of material emplaced in a valley drained presently by a small stream, suggests that the deposit was laid down under wetter, probably colder climatic conditions than those of the present, in a regime lacking vegetation to stabilise slopes.

The Head between Sheep Green [TQ 140 412] and Fishfold Farm [TQ 132 398] (Figure 23) has been less dissected than that at Forest Green. It occupies the gently sloping floor of the valley of a stream shown as the Sheep Green Stream in (Figure 23). In height and probably in age it corresponds broadly to the three younger stages at Forest Green, and declines to the same level (61 m above OD) as the lowest of those stages near Gatton Manor [TQ 128 389]. A ditch section [TQ 139 414] showed 1 m of grey-brown clay on 1.3 m of roughly bedded chert gravel. Clay with scattered cherts, more than 3 m thick, was exposed in another ditch section [TQ 1465 4160].

Ockley to Capel

Spreads of sandy clay with cherts on the west side of the valley (Figure 23), upstream from Ockley Church [TQ 157 406], have valleyward-sloping surfaces. These and some smaller patches on the same side of the valley downstream from the church grade into the Fourth Terrace of the River Arun below the point where the stream breaches the escarpment of sandstone Bed 3a.

The Head deposit on the northern margin of the district, north of Ockley Station, is important because it indicates how the Kit Brook became diverted from the Mole drainage basin into that of the Arun (p.00). A drainage ditch on the southernmost lobe of the deposit [TQ 164 414] showed 2 m of alluvial clay on 0.2 to 0.5 m of chert gravel, on Weald Clay. Farther north the gravel is thicker; a stream bank [TQ 1660 4185] (in the Reigate district) showed 1.2 m of alluvial clay sand an on chert gravel, seen for 1.5 m. Patches of Head along the Misbrook valley (Figure 23) are probably not more than 2 m thick. Small exposures indicated a thin basal gravelly layer (including rounded cherts) overlain by 1 m or so of sandy clay.

River terrace deposits

Each river basin in the Horsham district has its own set of terraces. The deposits that form the terraces are of local derivation, and probably nowhere exceed 3 m in thickness. They are composed predominantly of Wealden siltstone and soft sandstone pebbles and consequently have limited economic value as gravel aggregate. The terraces represent former floodplains, and the deposits of low terraces, in particular, resemble those of the present floodplains in comprising a basal gravel overlain by silt, clay or sandy clay. The upper beds are generally oxidised by weathering to a yellowish brown colour and may be loosely described as loam or sandy loam. On the higher terraces, the capping of loam has commonly been eroded away. The gravel, however, resists denudation, and spreads that may be only 0.5 m thick protect the underlying Weald Clay from erosion to give rise to quite prominent hills. Some residual patches of gravel are shown on the map because of their importance in indicating former river courses.

In the soil-forming process, where drainage is impeded, iron oxides are deposited in the interstices of gravel of river terraces, or of gravelly patches in terrace loam, so forming masses, up to 2 m or more in diameter, of a hard concretionary conglomerate known as 'ragstone' or 'shrave'. This stone is commonly brought to the surface by ploughing.

Chert fragments, more or less rounded, occur in gravels derived from Lower Greensand outcrops. Elsden (1887, pp.637–638) reported flint fragments in Arun gravels in a gravel pit near Amiesmill Bridge, south of Horsham, but these were probably artefacts.

In (Figure 23) and (Figure 24), profiles of parts of the rivers Bramley Arun, Wey, Mole and Adur have been drawn along lines following approximately the middle of present-day floodplains. The lines representing terrace and Head deposits give a reasonably correct impression of the thickness of the deposits, but are primarily meant to show the surface heights of terraces, relative to the floodplain level. Also shown are intersections of hard beds in the Weald Clay with the stream profiles, and the approximate courses of outcrops of these beds on the valley sides. Some knickpoints, like that near the outcrop of Bed 2a in the North River, occur where hard beds cross the river; others are difficult to detect. Hard beds in the Weald Clay have influenced terrace formation in that the wider spreads of gravel have developed on belts of soft clay between successive sandstone and limestone escarpments.

The river gravels in the Bramley Wey valley belong to the Second Terrace of that river, those in the Arun to the Third and Fourth Arun terraces, as established in the Haslemere district (Thurrell et al., 1968). The evidence from the present district reaffirms that the Second Terrace of the Bramley Wey, which is contemporaneous with the Older Head, and the Fourth Terrace of the Arun, contemporaneous with the Younger Head, are climatic terraces. The profile of the North River, which is the main tributary of the Arun (Figure 23), shows that the Third Terrace can be traced upstream only as far as the point where the outcrop of the Small-'Paludina' limestone (Bed 2a) crosses the river. This terrace, which is of low gradient and only slightly lower altitude than the Fourth Terrace, may also be a climatic terrace, formed during a stillstand of sea level slightly lower than that of Fourth Terrace times.

In the part of the River Mole basin that lies in the Horsham district, two terraces can be distinguished, the Second Terrace being about 2 m above the First. There can be little doubt from their relation to the topography (Figure 24) that these are of Devensian age, and possibly equivalent to the Fourth and Third terraces of the Arun. Deposits within the Mole catchment, south of Crawley, occur in fan-like spreads with a slight but distinct slope. However, since they consist of well-rounded Wealden siltstone and sandstone fragments, they are lithologically indistinguishable from gravels with a more typical terrace-like form farther downstream and have accordingly been mapped as river gravels rather than as Head.

In the Reigate district, Dines and Edmunds (1933) distinguished two terraces of the River Mole on the Weald Clay. The lower, extensive around Horley, appears to correspond to the Second Terrace of the present district (Figure 24). Their higher terrace does not extend into the Horsham district, but some patches of it in the Reigate district, indicated on (Figure 24), appear to be related in level to the Older Head, and may be the same age as the Second Terrace of the Bramley Wey.

In the Adur basin all gravels are assigned to the Second Terrace. The terrace development along a western branch of the Adur, named for the purposes of this account the Shipley Stream, is illustrated in (Figure 25). The profile of the stream, as Kirkaldy and Bull (1940, p.126) found, appears to be a smooth curve, with no obvious knickpoints. In contrast with the Arun, Wey and Mole, gravels are absent from the higher reaches of this branch of the Adur, presumably because its source is located on Weald Clay. The highest extensive gravel spreads occur along the foot of the dip slope of Bed 3c. Between Fewhurst and Coolham the terrace deposits were largely derived from sandstone outcrops which run nearly parallel to the stream. Downstream from Shipley, in the Brighton district, much material appears to have been brought from the Lower Greensand escarpment to the south. Thus to the south of Knepp Castle, in a valley draining northwards into the Shipley Stream, there are Head deposits that decline in level northwards. One patch of Head is indicated in (Figure 25), with adjoining river gravels that decline in a short distance to the level of those in the main valley. The patch of gravel shown at Shipley, at a slightly higher level than much of the Second Terrace, is at the northern end of a spread that originates in another tributary valley.

Only the upper reaches of the Medway and the Ouse are present in the district and, as a consequence of the youthful nature of both their valleys, only small patches of the youngest terrace of each are present. Small patches of the First Terrace of the Medway occur adjacent to the present floodplain at heights of up to 1.5 m above it between Weir

Wood Reservoir and near Ridge Manor [TQ 368 355]. Similar small patches of First Terrace occur adjacent to the Ouse floodplain near Buxshalls [TQ 347 270], at East Mascalls [TQ 370 252] and near Pegden [TQ 380 244].

Details

River Bramley Wey

Second Terrace

The northernmost patch of this terrace caps a hill 300 m east of Lowerhouse Farm. Abundant worn chert fragments, mostly of 5 to 7.5 cm diameter, occur in the soil on the hilltop [TQ 117 392]. A block of cherty sandstone, probably from the Hythe Beds, 0.3 x 0.15 m across and 0.15 m thick, derived from the gravel, was noted here. Near Walliswood Farm [TQ 116 384] much 'ragstone' in blocks up to 0.3 x 0.15 m across was found at 0.25 m depth in temporary excavations. Small patches of this terrace, containing chert pebbles mostly of 2.5 to 5 cm diameter, occur around Smokejack Farm [TQ 120 372], in Somersbury Wood [TQ 1040 3775] and east of Hillhouse Farm [TQ 103 369]; they are hill-top relics of what once was probably an extensive gravel sheet.

River Arun

Fourth Terrace

In the North River valley, around Oakwood Mill Farm [TQ 137 383], gravel of the Fourth Terrace forms a fan over a clay area bounded by low sandstone escarpments. Auger holes proved brown gravel of soft Wealden siltstone pebbles at least 1 m thick in the spreads west of Oakwood Mill Farm and around Halehouse Farm [TQ 1365 3782]; chert fragments were noted on the ground surface in places. Small roadside depressions 50 to 200 m north-east and 320 m east-north-east of Halehouse Farm are probably old gravel pits.

In the Boldings Brook valley, deposits of the Fourth Terrace south of Blackfriars Bridge [TQ 176 363] are siltstone gravels, probably little more than 1 m thick. Gravels in the Channells Brook valley downstream from Owlscastle [TQ 200 336] are also thin; they include sandstone fragments from the Upper Tunbridge Wells Sand.

In fields on either side of the lane (Kerves Lane) between Horsham and Amiesmill Bridge, there are signs of old gravel diggings around [TQ 181 293]. There, probably, was sited the section recorded by Elsden (1887, p.638) as showing about 2.4 m of stratified gravel consisting of water-worn Wealden fragments with intercalated beds of sand and a few flint flakes (p.97). In 1961, road cuttings 100 m north and 50 m south of Amiesmill Bridge showed 1.2 to 1.5 m of loam, sand and gravel on Upper Tunbridge Wells Sand. Iron-cemented river gravel up to 1 m thick was seen in the banks of a ditch [TQ 1768 2948] at Chesworth Farm.

The widest spreads of Fourth Terrace deposits in the Boldings Brook valley occur between the Horsham Stone and Upper Tunbridge Wells Sand outcrops, east of Great Daux [TQ 166 335], where auger holes proved 1 m or so of buff sand or loam overlying ferruginous sandy gravel. Terrace deposits, gravelly at the base, at and northwards of Hills Farm [TQ 156 303] are probably about 1.2 m thick.

The gravel on top of the hill [TQ 135 313] 600 m east-south-east of Theale Farm is less than 1 m thick. Wealden sandstone debris was noted in the soil here. In the Townhouse Farm [TQ 124 327] spread, the terrace deposits include chert fragments, brought down by the North River. The spread on Stane Street, and another 400 m southwest of Dedisham, form flat-topped hills. In the latter spread, 0.75 m of gravelly loam overlies the Weald Clay.

Third And Fourth Terrace, undifferentiated

Two spreads of gravel, together about 1 km long, and some smaller patches in the North River valley between Northland [TQ 143 358] and Rowhook Manor [TQ 133 342] are believed to include representatives of both the Third and the Fourth Terrace. These deposits occur where the valley widens out between the Small-'Paludina' limestone and Horsham Stone escarpments. Well-rounded cherty sandstone pebbles, mostly of 2 to 5 cm diameter, were noted in a 0.6 m ditch section [TQ 1370 3482].

Another spread occurs at the Boldings Brook–Arun confluence. The terrace surface is 2 m above the level of the alluvium at the north end of the spread; at the south end it slopes very slightly towards the river. A ditch section [TQ 1545 2983] showed 1.8 m of yellow-brown gravelly sand on Weald Clay.

Third Terrace

Between Broadbridge Farm [TQ 146 303] and Theale Farm, Slinfold, the Third Terrace floors a flat-bottomed valley, which represents a former loop of the River Arun; another strip of gravel belonging to the terrace fringes the present-day alluvial tract 500 m or so east of Theale Farm. Temporary excavations [TQ 1360 3075] showed 0.9 m of gravel composed of sandstone debris, on Weald Clay. About 100 m south of here, some rounded Horsham Stone fragments, up to 5 cm in diameter, were noted in iron-stained gravel.

At Power's Barn [TQ 1350 3370], auger holes proved 1.35 m of ferruginous sandy loam on cherty gravel; 250 m west-south-west of Townhouse Farm, chert gravel was seen in post holes. About 300 m west-south-west of Dedisham at [TQ 108 327], yellowish brown sandy gravel was proved for 1.35 m; clay occurs at shallow depth 100 m south of here along the border with the Fourth Terrace.

River Mole

Deposits of the 'Higher Terrace'

Two patches of gravel in the upper part of the Beam Brook valley in the Reigate district , at 79 m [TQ 206 420] and 73 m above OD [TQ 211 420], grade upstream (Figure 24) to the probable Older Head of Hillhouse Copse. They are therefore likely to be equivalent in age to the Second Terrace of the Bramley Wey. Downstream they grade to a small patch of gravel at 71.5 m above OD [TQ 225 438], mapped by Dines and Edmunds (1933, pp.160–163) and assigned by them to their Higher Terrace.

Second Terrace

Near Bewbush Manor [TQ 241 348], Second Terrace gravel on the Weald Clay outcrop occurs in patches, probably not more than 2 m thick, that are remnants of larger spreads laid down by River Mole headstreams on emerging onto low-lying ground from narrow valleys incised in the Upper Tunbridge Wells Sand (Figure 24). North of Ifield Mill, an elongate tract of Second Terrace gravel extends northwards through Ifield to Lowfield Heath; the gravel consists of siltstone and fine sandstone pebbles and probably averages not more than 2 m in thickness. A deep ditch [TQ 2650 4053] through an outlying patch at Gatwick Airport showed gravel in pockets from 0.5 to 2 m deep, in Weald Clay. Downstream from Gatwick Airport this terrace appears to grade to the 'Low Terrace' of the Reigate district, which is extensive around Horley. Some small patches of gravel in the Beam Brook valley are assigned to the Second Terrace (Figure 24). In a patch at 67 m above OD [TQ 207 415], gravel from a 1 m deep excavation consisted of subrounded pebbles of 5 to 75 mm diameter, some of chert (mostly in the larger sizes) and others of Wealden siltstone, sandstone and, in the smallest sizes, weathered clay-ironstone.

In Charlwood village there is a small patch of clayey gravel, in effect an alluvial fan issuing from the deep valley in Glover's Wood. Auger holes at [TQ 2432 4104] proved 0.45 m of loamy clay, on 0.7 m of clayey siltstone gravel, on Weald Clay.

First Terrace

A wide spread of gravel in the Tilgate neighbourhood of Crawley New Town, with the form of three coalesced fans, is at the level of the floodplain of the streams that drain it, east of the Stanford Brook and west to The Brook via Ifield Mill. Gravel was proved in trial boreholes, most of which did not penetrate it, at 2.4 m depth. Boreholes that proved the full thickness of gravel are: [TQ 2732 3504], gravel 1.5 m on clay 0.9 m; [TQ 2786 3555], gravel 2.4 m on clay 0.6 m. Other patches of First Terrace gravel adjoin the floodplain in the region of Lowfield Heath and Gatwick Airport. A deep ditch [TQ 2614 4046] showed gravel disturbed by frost action, though less so than in a slightly higher patch 300 m to the east which is assigned to the Second Terrace. These gravels appear to be lower than those of the Low Terrace of the Reigate district.

River Adur

Second Terrace, Shipley Stream

On the small spread of gravel [TQ 104 259] upstream from the escarpment of sandstone Bed 3a, many locally derived siltstone and sandstone pebbles occur in the soil. Between Fewhurst [TQ 103 249] and the river there is flat ground with a sandy loam soil. Dark brown, coarse, sandy gravel was proved by augering, in places its base being less than 1 m in depth. South of the stream and to the north of Court Farm near [TQ 112 244], siltstone and fine-grained sandstone fragments occur in the soil. The drift in this spread and in small patches along the north of the stream appears to average about 1 m in thickness. Terrace deposits in a spread farther downstream centred on [TQ 119 242] consist of 0.6 to 1.5 m of sandy loam, on Weald Clay.

In the spread west of Purveyor's Farm, siltstone and sandstone fragments up to 5 cm diameter occur in the soil. These deposits, and those of two spreads east of Purveyor's Farm, appear to have been laid down in part by tributaries of the Shipley Stream coming from the north.

Terrace deposits downstream from Slaughterbridge Farm [TQ 122 237] produce loamy soils; auger holes proved about 1 m of sandy loam on gravel or gravelly sand. Cherty gravel noted at one place [TQ 119 225], about 300 m south-south-west of Coolham crossroads, indicates derivation from the Lower Greensand to the south. West of West Grinstead station, some patches of Second Terrace deposits along a tributary of the Shipley Stream that rises near Southwater, consist of dark brown, ferruginous, sandy gravel about 1 m thick. A little over 1 km east of Cowfold, on the southern border of the district, there are two patches of gravel laid down by another southward-flowing tributary of the River Adur. In the more westerly patch [TQ 224 225], the base of the terrace is 3 to 3.5 m above the modern floodplain. The easterly patch consists of a veneer of gravel on Weald Clay.

Rivers Medway and Ouse

Small flat-topped patches of sand and silt adjacent to the floodplains of the Rivers Medway and Ouse, each about 1.5 m above the floodplains, have been interpreted as First Terrace deposits. In the Ouse valley, the patch near Pegden [TQ 380 244] includes pockets of ferruginous sandstone gravel. An excavation [TQ 3793 2443] showed this to be underlain by silt and sand which rested at about 1.5 m depth on sandy wash (Head). The other presumed terrace deposits in the Ouse Valley, near East Mascalls [TQ 370 352] and near Buxshalls [TQ 347 270], are lithologically indistinguishable from both the adjacent sandy/silty Head and Alluvium. The same is true of the two small patches of First Terrace in the Medway valley [TQ 368 355] and [TQ 375 347].

Alluvium and peat

The tracts shown on the map as underlain by Alluvium are the floodplains of rivers. Because the catchment areas of the rivers Arun and Adur are largely on the Weald Clay, heavy rain causes these rivers to rise rapidly and, if it is sufficiently prolonged, to overflow their banks. The largest tract of alluvium is that at Gatwick Airport. Typically these deposits comprise soft silty clays with a thin basal lag gravel. Peat floors part of a tributary valley of the Medway [TQ 388 337] near Mayes: it is unlikely to exceed 1 m in thickness.

The Alluvium of the River Ouse is composed largely of clayey silt, silt and fine-grained sand. Burrin (1981) concluded that, owing to their high silt content, the alluvial deposits of the Ouse at Sheffield Park [TQ 406 235] and Sharpsbridge [TQ 443 208], downstream from the present district, could not have been derived from the Hastings Beds and must therefore be largely loess–wind-blown material derived from some distant source. However, given that more than 80 per cent by volume of the Hastings Beds consists of mud- and silt-grade materials, the silt in the alluvium could equally well have been derived from local rocks and the presence of loess from more distant sources has yet to be proved (Gallois, 1982).

River development

As long ago as 1864 Ramsay suggested that the present-day radial drainage system of the Weald was initiated on a plain of marine denudation that truncated the Wealden anticline. Wooldridge and Linton (1955) broadly accepted this hypothesis, but suggested that the river system of the central Weald developed during a Miocene–Pliocene cycle of erosion, the area having formed an island that escaped submergence during the Pliocene to early Pleistocene marine incursion. Jones (1980) and Small (1980) have both suggested that this is an oversimplified hypothesis, and that periods of uplift and marine erosion dating back to the Eocene can be recognised in relict drainage features in parts of the Weald and the adjacent areas.

There is, however, no published geological evidence to indicate the presence of such features in the present district, where the topography is mostly freshly dissected and the stream courses are largely controlled by the exposed geological structure, on both large and small scales. This is especially true on the Hastings Beds outcrop where there are numerous examples of stream diversion and river capture that can be directly related to changes in the exposed structure and lithologies revealed by progressive downcutting. The headwaters of the Rivers Medway and Ouse are good examples. Both rivers have upper reaches that follow east–west trending, heavily faulted ground which overlies the two major basement fractures in the region, the Ashdown Thrust and the Bolney–Brightling Thrust respectively (Figure 20), and both have undergone small-scale modifications related to local lithological and structural features.

River Bramley Wey

The Bramley Wey rises in a shallow clay-floored valley at about [TQ 110 387], but its Second Terrace deposits extend farther to the north (Figure 23) and their level grades to that of Older Head deposits upstream from the Large-'Paludina' limestone (Bed 8b) escarpment. Thus, there is little doubt that the Bramley Wey originally rose on the Hythe Beds escarpment but lost its headwaters to the North River at the Older Head stage. Too much erosion has taken place since that stage for the point of diversion to be located precisely, but the process was likely to have been one of overflow from the Wey into the Arun drainage basin, as in the more recent case of the diversion of the Kit Brook into the Arun north of Capel (see below).

River Arun

In the Horsham district, as in the Haslemere district (Thurrell et al., 1968), the Fourth Terrace of the Arun grades upstream into younger Head which, from the freshness of its topography, is likely to be of Devensian age. In the Haslemere district a well-developed suite of three terraces occurs below the Fourth Terrace. This suggests adjustment of the river profile to a falling Devensian sea level. A lengthy time is likely to have been required for the formation of these lower terraces, and the Fourth Terrace–younger Head phase may therefore date from early in the Devensian. The Fourth Terrace is about 18 m above OD on the southern margin of the Haslemere district and may have been graded to the Brighton Raised Beach sea level (but see below). The maximum height of the top of this beach is 14.3 m above OD, and the date of the beach is likely to be Ipswichian to early Devensian (Hodgson, 1964).

The Arun terraces are numbered upwards from the First Terrace, this being the lowest one developed in the Haslemere district, at about 6 m above OD above on the southern margin. In the Horsham district (Figure 23) the lowest Arun terrace is the Third Terrace. This has a low gradient and is slightly lower than the Fourth Terrace, and may have resulted from redistribution, during a stillstand in sea level, of material brought downstream in Fourth Terrace time.

Kirkaldy and Bull (1940, p.134) suggested that a tributary of the Horsham Arun (the Channell's Brook) is 'rapidly' pushing eastwards towards Faygate and is 'filching' from the Mole the streams draining down the northern side of St Leonard's Forest. Two small headstreams of the Arun, east and west of Middle Hill [TQ 216 335], do in fact show a northeasterly trend just before they leave the forest, which may indicate that they were once directed towards the Ifield Mill gap [TQ 245 364]. Second and First Terrace deposits of the Mole east of Faygate, which are probably of younger Head age (p.00) are, however, all in the present Mole drainage basin, and the Arun–Mole watershed at Faygate may therefore have moved eastward only slightly during the Devensian.

Diversion of the Kit Brook into the Arun

Green (1936, p.14) observed that the Kit Brook flows from Leith Hill directly towards a Mole headstream (the Misbrook of (Figure 26)), only to turn sharply a quarter of a mile from one of the sources of the latter to join the Arun system. Geological mapping has now confirmed his suggestion that, until quite recently, the Kit Brook formed part of the Mole system, and has also illuminated the process by which it was diverted. The 'elbow of capture' lies on a broad fan of younger Head deposits laid down by the Kit Brook in a strike-vale between a 'Paludina' limestone ridge to the north and a lower ridge to the south, formed by Weald Clay sandstone (Beds 9a, 9b). In its early stages of deposition, Head passed eastwards along the Misbrook valley as far as the next lower sandstone (Bed 3c) escarpment (Figure 26).

The sheet of Head deposits, however, is also prolonged south-westwards towards the Arun, and the diversion of drainage therefore took place before deposition of Head finished. At one stage during the accumulation of Head it seems likely that floodwater spilled over the sandstone feature formed by Beds 9a and 9b, at a point where the feature was low due to the presence of a fault (Figure 26), and established a new channel into a headstream of the North River.

River Ouse

The upper reaches of the River Ouse between Slaugham and Lindfield follow an irregular west to east course that roughly parallels, but lies to the north of the complexly faulted Weald Clay outlier. Between Lower Beeding and its junction with the Ouse valley [TQ 345 266], south of Ardingly Station, the Weald Clay outcrop occupies low ground with extensive sheets of Head. On the south side of Sidnye Farm [TQ 284 274] to [TQ 306 274] and near Rivers Farm [TQ 326 274] to [TQ 339 272], broad outcrops of Head occupy what appears to be a former valley of the River Ouse, prior to its capture at Great Bentley [TQ 313 278] and Little Ashford [TQ 275 273] by tributaries of dipslope streams on the Hastings Beds. A suggested sequence of events is summarised in (Figure 27); this is inevitably oversimplified in that the outcrop patterns for the early stages of development can only be crudely deduced.

River Adur

Wooldridge and Linton (1938, fig.6, p.52) indicated that some tributaries of the River Arun west of Horsham may originally have been headwaters of the River Adur. Kirkaldy and Bull (1940, p.118) found this unacceptable, but the suggestion was later elaborated by Wooldridge and Linton (1955, pp.82–84). In this later work they pointed to the North River as the presumed former head of the Adur. This, they supposed to have flowed south-eastwards from Slinfold to Christ's Hospital Station along what is now the course of the Horsham Arun, and to have been joined by the Boldings Brook at the latter place, whence the combined river flowed through a broad gap, at about 54 m above OD south of Christ's Hospital, into the present head of the Adur. However, geological mapping provides no support for this hypothesis. Wooldridge and Linton seem from their account (1955, p.83) to have regarded the North River, previous to capture by the Arun, as having risen on the northern escarpment of the Lower Greensand, the Adur having 'pushed back' its headwaters that far. From considerations of altitude (see (Figure 25)), it seems likely that a river at about 54 m above OD near Christ's Hospital would have been at about 75 to 90 m above OD near Forest Green. At that level, the Lower Greensand escarpment at Leith Hill was being drained by the River Wey, as its Second Terrace gravels show. Previous to the Wey headwaters being diverted into the North River the latter was probably only a short stream rising on the Weald Clay, like the present Boldings Brook. The most likely explanation of the relationship of the Adur to the Arun, therefore, seems to be that the Horsham Stone outcrop has formed the divide between their basins for much of Pleistocene time, as it does at present.

River Mole

Reasons for regarding the Low Terrace of the River Mole near Horley (equivalent to the First and Second Terraces of the Mole in the Horsham district) as being Devensian in age rather than of much earlier Boyn Hill Terrace age, as suggested by Green (in Bull, 1933,) have been put forward elsewhere (Worssam, 1973).

Superficial structures

Landslips, cambering, valley bulges and cryoturbation

Landslips

Large rotational landslips occur in all the deep valleys floored by Wadhurst Clay between Sharpthorne and Hand-cross. They are all fed by springs which issue from the junction with the Lower Tunbridge Wells Sand, and several have cut back as far as the Ardingly Sandstone. Smaller rotational landslips and mudflows occur at and below the junction of the Wadhurst Clay and the Lower Tunbridge Wells Sand on the higher valley slopes in the same area, and in the Grinstead Clay (fed by springs at the base of the Cuckfield Stone) in the valleys at Hillhouse [TQ 345 278], near Ardingly, and near Ansty [TQ 286 242]; [TQ 290 241]; [TQ 300 236]. The toes of all the landslips which extend down to stream level are being eroded and the slips are clearly still active. All the other slips are likely to be active during periods of high runoff.

In addition to the rotational slips shown on the map, the steeper slopes on all the clay formations in the district commonly show tension cracks and gentle undulations indicative of creep or flow of the near-surface layers. These and the landslip movements were probably initiated during the periglacial climates of the late Pleistocene, and although many are now inactive they are underlain by former failure surfaces. In many areas Medieval deforestation has increased the moisture contents in the surface layers and made them potentially unstable.

Details

Landslips occur in the highest beds of the Wadhurst Clay, all fed by springs at the base of the Tunbridge Wells Sands, on the north side of the ridge [TQ 367 328] at West Hoathly, and along the valley of Ludwell Ghyl between West Hoathly and the confluence with the Cockhaise Brook. The larger landslips occur at West Hoathly [TQ 365 323], near Whitestone [TQ 363 310], and at Hammingden Wood [TQ 358 302]. Landslips between Brookhouse Wood [TQ 354 297] and Lower Sheriff Farm [TQ 360 290] in part incorporate head deposits and in part are overlain by them. An extensive landslip occupies the west bank of the Cockhaise Brook opposite these last-named localities, and extends as high as the base of the Ardingly Sandstone.

Small landslips [TQ 331 307] and [TQ 331 312] on the west bank of the Ardingly Brook at Tilgate Wood are largely in the lower part of the Lower Tunbridge Wells Sand, fed by springs at the base of the Ardingly Sandstone. Extensive landslips occur on both sides [TQ 319 299] and [TQ 320 303] of the valley downstream from Balcombe Mill; they are largely in the highest part of the Wadhurst Clay and the lower part of the Lower Tunbridge Wells Sand, but have cut back into the Ardingly Sandstone over most of their lengths.

Small landslips [TQ 346 278] and [TQ 349 278] occur in the Grinstead Clay near Stone Barn Cottages, Ardingly, and in the sides [TQ 286 231]; [TQ 291 231] and [TQ 300 236] of the small valley adjacent to Cuckfield Park.

Cambering

Cambering, the downslope movement of massive beds of sandstone where they crop out on steep ground, is also thought to be a periglacial feature in the Weald, and occurs in most of the valleys on the Hastings Beds outcrop which show valley bulging. Cambering is best developed where gently dipping massive beds overlie less competent strata, and is especially well seen in many of the Ardingly Sandstone outcrops in the district (e.g. Frontispiece), including Stone Farm Rocks, Chiddingly Wood and Balcombe Station. In each case, blocks of sandstone have become detached from the outcrop along major joints and have moved downhill for distances ranging from a few centimetres to tens of metres. In the more extreme cases, valleyward tilting of the blocks gives rise to dip-and-fault structure (Plate 11). From the overall geometry of the beds in such cases, it is clear that material must have been removed from beneath the sandstones. In the case of the Ardingly Sandstone, this material is largely Wadhurst Clay, but probably includes some Lower Tunbridge Wells Sand, lost by erosion from valley bulges (Figure 28).

Valley bulges

Abnormally steep dips which result from valley bulging (Plate 12) and (Plate 13) are common in stream-sections in the clay formations in the district. Valley-bulging may result from more than one process. Kellaway and Taylor (1953) suggested that ground-ice (permafrost) was essential for the development of large bulges in the Lias of the East Midlands, where many of the bulged valleys have low relief. Simmons (1966), however, described similar structures in alternating Ordovician limestones and shales, in areas of high relief in Kentucky, USA, as 'stream anticlines' which are forming under present-day conditions. He referred to a late-19th century eyewitness account of an anticline rising up as a low ridge in the bed of a stream and advancing upstream "at the rate of a slow walk".

Steep dips, tight folds and dislocation surfaces caused by valley bulging occur in the mudstones and in some of the muddy siltstones in the floors of all the steeper-sided valleys on the Hastings Beds outcrop, and in some of the valleys on the Weald Clay. Where well exposed, the average strike of the disturbed beds can be seen to be roughly parallel to the valley axis, the strike turning to follow bends in the valley and changing direction to follow tributary valleys. The best example of a valley bulge in the district, exposed from time to time when the pit is dewatered, is that in the Wadhurst Clay at Freshfield Lane Brickworks [TQ 3815 2656]. There, dips in the Wadhurst Clay steadily increase towards the valley axis until a central zone of tightly folded, near vertical beds with numerous shear surfaces is reached (Plate 13) and (Figure 28) and (Figure 29). Within this zone erosion continues to be active, and the long-term mechanism of formation is clearly one of diapiric upwelling of the mudstones as their confining load is removed by erosion along the valley floor.

In some of the steep-sided ghylls between West Hoathly and Handcross, iron oxide-cemented gravels in the stream beds can be seen to be contorted by heaving in the underlying Wadhurst Clay. It is not clear, however, to what extent these modern movements are due to continuing valley bulging or rotational landslip.

Because large-scale valley bulging can be observed in many areas of present-day low relief in England, including the Weald Clay outcrop, it is generally presumed that the bulk of the movements took place in the late Pleistocene under periglacial conditions, at times when the strengths of the clays were much reduced by alternate freezing and thawing of the permafrost layer.

Details of the valley bulges which affect the argillaceous beds in the Hastings Beds are given in Chapter Three. They are indicated by steep dips on the geological map. Some examples in the Weald Clay are described below.

Details

The increasing steepness of dip in the Weald Clay with depth of incision of the valley headwaters of the Boldings Brook between Friday Street [TQ 184 368] and Rusper Church [TQ 205 374] suggests that bulging there may have resulted from progressive unloading of clays in the valley floor while the valley was deepened. Any ridge formed in this situation would have been quickly planed off by stream erosion. Because the valley is incised below the level of the Arun Fourth Terrace, the structure must be Devensian or later in age. The freshly incised appearance of the valley suggests that downcutting and development of the bulges may have continued into recent times, but there is no direct evidence for this. In the lower part of the valley, near Friday Street, steeply dipping Weald Clay is overlain by undisturbed alluvium.

A 'fossil' valley bulge of possible Wolstonian date (Worssam in Skempton and Weeks, 1976, p.526) is indicated by sharp folds in Weald Clay overlain by thin cherty gravel of the 'Higher Terrace' of the River Mole at the Newdigate Brickworks pit [TQ 206 426] in the Reigate district. The present topography near the pit is quite low (Worssam and Thurrell, 1967, p.266).

Steeply dipping beds occur in the valley north of Graylands at [TQ 177 355], south of Lyne House around [TQ 190 380], near Temple Elfande around [TQ 198 396], east of Rusper near [TQ 210 377] and west of Charlwood near [TQ 230 413]. The deeply cut valleys at each of these places are on or close to outcrops of Small-'Paludina' limestone beds, which are resistant to erosion and tend to form ground of high relief. Hence bulging in these valleys was probably enhanced by the effects of unloading.

Spectacular anticlinal folds were formerly exposed in a central part of the Southwater Brickworks pit [TQ 158 258] (Plate 12). There is little in the present topography of the area around the pit to indicate why such folds should be developed there. They may have formed in a former valley bottom, affected by valley bulging at some period during the Pleistocene too remote for evidence of the topography of that time to have been preserved.

Cryoturbation

Cryoturbation or frost heave is a periglacial phenomenon which resulted from seasonal freezing and thawing of water in the near-surface deposits. In the present district it is especially well developed where permeable strata, such as gravels or well-bedded and jointed sandstones, overlie clays within 1 to 3 m of the ground surface. Successive freezing and thawing of the clays, fed by water from the permeable beds, caused them to become progressively more mechanically weathered until, at times of rapid thawing, they became 'quick' and formed diapiric structures by upward flow. Good examples of cryoturbation structures occur where the river terrace gravels of the Mole rest on the Weald Clay (Plate 14) in the Gatwick area, and where a thin layer of Cuckfield Stone rests on the Lower Grinstead Clay, for example at Ardingly [TQ 345 290]. Less obvious cryoturbation structures occur throughout the district wherever there is a permeability contrast in the surface layers; they can also occur in relatively uniform lithologies which are sufficiently permeable to allow ice masses to grow within them.

Chapter 7 Economic geology

Agriculture and soils

The Horsham district is predominantly agricultural, with the lower parts of the Hastings Beds and Weald Clay outcrops being largely mixed arable, and much of the higher part of the Hastings Beds outcrop being afforested. The soils, as in the Weald in general, are determined largely by the nature of the underlying geology and are dominated, by two soil associations. The first, mixed stagnogleys and brown earths, is developed on the Ashdown Beds, Cuckfield Stone and Tunbridge Wells Sand; the second, stagnogleys, on the Wadhurst Clay, Grinstead Clay and Weald Clay. These soils, and their farming potential, are described in broad terms by McRae and Burnham (1976).

Owing to the predominance of silt in the Hastings Beds, impeded drainage is as characteristic of the 'sandy' areas of the Hastings Beds outcrop as it is of the clays; hence the predominance of stagnogleys throughout the district. These are soils which show mottling of grey colours produced by microbiological reduction and localised mobilisation of iron during the winter when the soil is waterlogged, and ochreous mottles and concretions from reoxidation during the summer months when the soil dries out and air can penetrate it. Brown earths are better drained, loamy to fine-sandy soils, developed to a lesser extent on the Hasting Beds, particularly on the lower slopes, where silty or loamy drift accumulates. Some areas of seminatural woodland on the Hastings Beds carry soils of the podzolic group.

The soils developed on the sandstone outcrops of the Hastings Beds were described by McRae and Burnham (1976, p.601) as having only a slightly better agricultural value than the heavier soils on the clays. The textural inadequacy of the sandstone soils is not counterbalanced by increased fertility and the Hastings Beds outcrop is deficient overall in calcium and potassium as well as in most heavier metallic elements (Applied Geochemical Research Group, 1978).

Weald Clay soils are typical stagnogleys, waterlogged in winter and early spring when the precipitation fails to percolate through the stiff subsoil, and hard on drying out in summer. The heaviest and most intractable clay soils are those between the outcrop of the Horsham Stone and that of the mid-Weald Clay sandstone (Bed 3 or 3a), including those on Small-'Paludina' limestone outcrops. The sandstones in the north-west of the district and in its south-west corner produce significantly lighter and more workable soils.

McRae and Burnham (1876, p.606) described the soil association typical of Weald Clay as giving land of below average agricultural quality, best suited to pasture or cereals, particularly wheat. The wetness of the land makes heavy machinery essential for cultivation, which needs to be carefully times and carried out when the soil is sufficiently dry.

Patches of Head tend to have heavy, wet soils despite their stone content. In contrast, soils on river terrace gravels are lighter, although impeded drainage (as evidenced by ironoxide-cemented concretions known locally as 'shrave' or 'chevick') is common because the gravels are generally thin and full of water, which is held up by an underlying clay.

Brick clays

Brickmaking has been a major industry in the district in the past and continues to be important at a few locations. Current workings utilise lower Wadhurst Clay at Sharpthorne Brickworks [TQ 374 329], a mixture of upper Wadhurst Clay and Upper Tunbridge Wells Sand at Freshfield Lane Brickworks [TQ 382 266] and Weald Clay at Warnham [TQ 175 350], Clock House [TQ 175 385] and Ockley or Smokejacks [TQ 114 372] brickworks. A large works at Southwater, using clays from the same Weald Clay horizon as that at Warnham, has recently closed. Other disused brickpits are widely scattered. Extensive shallow quarries in the eastern part of Horsham, the Crossways Brick Field and Depot Brick Field, now built over, were dug for a clay in the Upper Tunbridge Wells Sand.

Highley (1976, p.560) noted that the clay-mineral content of brick clays generally varies from 30 to 50 per cent, that sufficient fluxing material should be present for the clay to vitrify at a temperature of 950° to 1100°C, and that there should be an adequate content of a non-plastic constituent, usually quartz, to prevent excessive shrinkage and deformation during firing. In the Weald Clay at Warnham, quartz silt fulfills this last-mentioned function, the intimate mixture of silt and clay, resulting from bioturbation at the time of deposition, making the clay particularly suitable for engineering bricks known as 'Southwater Bricks' (Prentice, 1967).

Most brick clays (Highley, 1976) contain kaolinite or illite, or a mixture of the two, as the main clay mineral. The Weald Clay contains a mixture of these minerals; clays of the Hastings Beds have been described as containing kaolinite, illite and a chlorite mineral. In the Weald Clay, the limestone beds and ostracod-bearing clays are avoided when winning the clay because they can cause problems during firing. Gypsum (calcium sulphate), which results from weathering of calcium carbonate and sulphides in ostracod and shell-bearing clays, occurs between about 2 and 6 m below ground surface; excessive sulphate causes an unsightly white efflorescence on the surface of brickwork and such clays are therefore avoided.

The products of the industry vary from time to time in response to customer requirements. In recent years the bricks from Wealden brickworks, which have a rich, variegated colouring, have been much in demand.

Building stone

Quarrying for building and roofing stones was formerly widespread in the district, and the attractive appearance of many of the older buildings in the region owes much to the use of locally quarried stone. The Ardingly Sandstone was the most extensively worked, and is the only horizon worked at the present day. The Cuckfield Stone, Horsham Stone and the 'Paludina' limestones in the Weald Clay were formerly of local importance. Small amounts of stone have also been worked from the Ashdown Beds and Upper Tunbridge Wells Sand in the district. Details of the individual quarries are given in the text.

There are several hundred old workings in the Ardingly Sandstone, mostly on the ridges around East Grinstead, West Hoathly, Ardingly, Balcombe and Cuckfield, where unweathered stone has been worked from beneath a protective capping of Grinstead Clay. Beneath this capping, the stone was largely won by driving wedges into appropriate vertical joints to produce suitably sized blocks for handling and sawing. Where worked at outcrop, the stone was gener ally softer because of the loss of traces of ferruginous cement by leaching; in quarries, therefore, the stone was sawn in situ. In both types of working the cut stone was left to harden on exposure, during which iron minerals within the body of the rock are transported by leaching and evaporation to form a ferruginously cemented skin of an attractive honey colour with some more yellow or more orange mottling. The working quarries at Philpots [TQ 3545 3225] and Hook [TQ 3555 3135] both work the highest bed of the Ardingly Sandstone from beneath a Grinstead Clay capping (Plate 4). The stone is used as building ashlar, for internal features such as fire places and ornamental work, and as roughly dressed stone for walling, chimney stacks and rockeries.

Calcite-cemented sandstone ('Tilgate Stone') was formerly worked in the Cuckfield Stone, mostly around Cuckfield (Figure 13), for roadstone, flooring slabs and, where at its most fissile, for roofing. As with the Ardingly Sandstone, the top part of the stone has been extensively worked from beneath a protective capping of clay on the ridges at Ardingly, Balcombe and Cuckfield, and in the inliers between Haywards Heath and Scaynes Hill where the stone is thicker and more massive than in more northerly and westerly areas.

Some of the thicker sandstone beds in the Upper Tunbridge Wells Sand have been worked for building stone and roadstone, but nowhere on a major scale.

The principal stone in the Weald Clay was the Horsham Stone, which was used for roadstone, paving and roofing (Plate 15). Ripple-marked slabs provided useful nonslip paving for stable yards. As a result, all the Horsham Stone outcrops in the district, including those in the Ouse Valley inlier, contain old stone quarries, the most extensive being south of Horsham between Christ's Hospital and Southwater.

Small-'Paludina' limestone was formerly quarried near Charlwood under the name Charlwood Stone, and was used for paving. The ornamental Large-'Paludina' limestone or 'Sussex Marble' has also been exploited in the district.

Iron ore

Iron smelting began on the Hastings Beds outcrop in pre-Roman times, and during the 16th and 17th centuries, when at its peak, it was a major industry. The product of furnaces in the latter period was cast iron, some of which was made directly into cannon, for which the Weald was renowned, or into fire-backs, pots and pans, while some was cast in the form of pig iron. The pig iron was refined into wrought iron in forges, known locally as 'hammers', which were separate works from the furnaces. The furnaces utilised locally dug clay ironstone and were fired by charcoal obtained from managed woodlands on the Hastings Beds and Weald Clay outcrops. The bellows of furnaces and the hammers of forges were driven by water power and the works were sited in valleys which could be suitably dammed to provide reservoirs known as 'hammer ponds'. Good examples of ponds occur in the steep-sided valleys adjacent to Horsted Keynes, Wakehurst Place, Balcombe, Crabtree (Furnace Pond) and Slau gh am .

The sites of furnaces and forges are scattered throughout the district. Straker's (1931) classic account of the iron industry has been updated (Cleere and Crossley, 1985) and the new work gives all known iron-working sites. These include both bloomery furnaces from the early (pre-16th century) period of the industry, and blast furnaces and forges from the later period, which lasted in the Horsham district probably until the late 17th century.

Clay ironstone was obtained from the Ashdown Beds, the Wadhurst Clay, probably from the Grinstead Clay, and from the Upper Tunbridge Wells Sand and Weald Clay. Some bloomeries may have used concretionary iron-pan from river-terrace gravels, but this material was probably too sporadic in its distribution and too variable in quality to be suitable for the blast furnaces, which needed large and dependable supplies of ore (Worssam, 1965, 1972).

The ore from the Upper Tunbridge Wells Sand and the Weald Clay was obtained from minepits (Plate 16), which were shafts up to about 12 m deep that were backfilled after the extraction of the ore. Many minepits also occur on the Wadhurst Clay, close to the outcrop of the basal ironstones (for example (Figure 9)), but much of the ore from the forma- tion was probably a by-product of open 'marl' pits. Clay-ironstone nodules were probably also collected from the Lower Grinstead Clay from the many pits dug to work the underlying Ardingly Sandstone.

Details of the workings recorded during the present survey are given, formation by formation, in the stratigraphical part of this memoir and on the large-scale (1:10 560) geological maps.

Water supply

The district lies mainly within Hydrometric Areas 41 and 42, administered by the Southern Region of the National Rivers Authority (NRA). A small area in the north lies within Hydrometric Area 39, managed by the Thames Region of the NRA.

There is no major river crossing the district; it is drained mainly by the headwaters of the rivers Arun, Adur and Ouse which discharge to the sea on the south coast at Littlehampton, Shoreham and Newhaven respectively. The remainder of the district is drained by the headwaters of the Medway and the Mole which discharge to the Thames and its estuary.

The mean annual rainfall is about 800 mm, ranging from about 750 mm in the north of the district to 850 mm in the south. The annual evaporation amounts to between 420 and 450 mm.

Surface water provides the greater part of the resources taken in the district. The licensed abstraction is currently about 19 million cubic metres per annum (m³/a), about 16 million m³/a being taken from the River Ouse at Ardingly [TQ 333 283]. The great bulk of the surface water taken is for public supply; the remainder is used for agriculture and irrigation. A direct-supply reservoir at Weir Wood [TQ 390 345] which straddles the eastern border of the district has an estimated daily yield of 5600 million m³/a, and meets the demands of this and the adjacent districts.

Abstraction of groundwater is small and the licensed annual take is less than 2 million m³/a. Of this, 80 per cent is pumped for public supply, about 9 per cent for private supplies and 10 per cent for industrial use; agricultural usage amounts to less than one per cent.

Earlier references to water supply are to be found in Whitaker and Reid (1899) and in Edmunds (1928). A well catalogue (Richardson et al., 1968) gives details of all the wells known to that date. Reports under Section 14 of the Water Resources Act 1963 were published by the Sussex River Authority (1970), the Kent River Authority (1970 and the Thames Conservancy (1969). The southern half of the district is included in a 1:100 000-scale hydrogeology map (Institute of Geological Sciences, 1978).

The Ashdown Beds, despite their small area of outcrop, support about 80 per cent of the public supply abstraction in the Horsham district, mostly from beneath a cover of Wadhurst Clay. A trial borehole at the Balcombe pumping station [TQ 290 313] penetrated over 40 m into this aquifer; unfortunately, there is no information as to the resultant yield. Well supplies are very variable, ranging from nil to 1000 m³/d. Most boreholes penetrating 30 m of confined Ashdown Beds probably have a mean yield of less than 400 m³/d for 10 m drawdown. The quality of groundwater from the Ashdown Beds is usually good, with a total hardness of 50 to 200 milligrams per litre (mg/l), and a chloride ion concentration of less than 30 mg/l. However, the concentration of iron is often high, and has been recorded up to 13 mg/l in this aquifer.

The Wadhurst Clay forms an aquiclude which separates the Ashdown Beds from the Tunbridge Wells Sand. Some groundwater can be locally taken from thin shelly or silty layers in the clay; the natural replenishment to these layers is, however, very slow and initial yields reduce rapidly as the storage is depleted.

The most extensive aquifers in the district are the Lower and Upper Tunbridge Wells Sand. In general, larger yields are obtained from the Lower Tunbridge Wells Sand, especially from the Ardingly Sandstone. However, few wells draw water solely from this member; most penetrate the Upper Tunbridge Wells Sand and reach the Lower Tunbridge Wells Sand. No useful supplies have been obtained from the intervening Grinstead Clay, although the Cuckfield Stone is a potential aquifer.

Springs at the bases of the Lower Tunbridge Wells Sand and the Ardingly Sandstone have sometimes been used for domestic or agricultural supply. The base of the Upper Tunbridge Wells Sand also provides spring flows of up to 1000 m³/d.

Groundwater flow within the Tunbridge Wells Sand is both intergranular and through joints, and well yields tend to be variable. A shaft at Ardingly [TQ 339 285] yielded up to 870 m³/d from the Lower Tunbridge Wells Sand and one at Crawley [TQ 288 370] yielded 650 m³/d from the Upper Tunbridge Wells Sand. Because of variable yields and siltation with usage, it has often proved necessary to excavate adits to obtain and maintain useful yields. Borehole supplies are equally variable, with yields varying from 20 to more than 2000 m³/d. The mean yield for a 300 mm diameter borehole penetrating 30 m of saturated Tunbridge Wells Sand in the Wealden district has been calculated to be 750 m³/d for a 10 m drawdown. The same analysis suggests that there would be a 20 per cent probability that the yield would be less than 300 m³/d for the same drawdown.

Siltation is a serious problem in both shafts and boreholes in the Tunbridge Wells Sand. A shaft of 24 m depth at Worth Park pumping station [TQ 296 373] had headings at the base which silted up. Subsequently, the shaft was deepened to 61 m and then provided a yield of 600 m³/d. In the ensuing 20 years, siltation reduced the yield to less than half, and the station was taken out of service. While it is difficult to prevent this problem, boreholes can be constructed with filter packs which greatly reduce or prevent silting. Nonetheless, if a borehole has been so constructed, and then developed to a particular yield, a subsequent increase in pumping rate over that achieved in development can lead to an onset of either silting within the borehole or clogging of the filter pack or sand screen; the consequent reduction in yield cannot in general be remedied.

Groundwater in the Tunbridge Wells Sand is usually soft, with a total hardness in the range of 30 to 100 mg/l. Exceptionally, hardnesses of more than 200 mg/l have been recorded. The chloride and sulphate ion concentrations are generally low, less than 30 mg/l. The iron content is usually low, less than 0.3 mg/l, but local concentrations may be as high as 7.0 mg/l, particularly where the water table is close to the ground surface.

Groundwater in the Weald Clay has been obtained from intercalated beds of sand, sandstone, limestone and iron- stone, the Horsham Stone being probably the most productive. It is difficult to predict the success of a borehole at any given site because of lateral variations in thickness and permeability of these horizons. Most boreholes have been constructed to a depth of 30 m or less, and yields are generally less than 50 m³/d. The greatest recorded is from a 30 m-deep shaft at Ifield [TQ 232 384] where 82 m³/d was pumped; a 60 m-deep borehole at Capel [TQ 173 385] was tested to 76 m³/d. The Horsham Stone was intersected at both sites. At Shipley [TQ 135 231], a 70 m-deep well yielded no water.

Replenishment to the water-bearing horizons in the Weald Clay is limited and initial yields tend to reduce as the storage is depleted. Groundwater derived from the limestone horizons is generally very hard, while that from the sandy layers can be very soft. At Rusper [TQ 209 371], groundwater from a limestone had a total hardness of 1200 mg/l, whereas a sandstone, intersected at a greater depth in the borehole, had a total hardness of only 86 mg/l. High concentrations of iron and sulphate are commonly encountered in water from the Weald Clay.

Superficial deposits are of limited occurrence in this district and have little hydrogeological significance. Where sands and gravels overlie the Tunbridge Wells Sand, they may cause locally high concentrations of iron in shallow wells constructed in the latter aquifer.

References

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.

A comprehensive chronological list of references to the geology of The Weald, covering the period 1596 to 1874, is given in Topley, 1875, 446–480. Many of these refer directly to the present district: only those referred to in the text are repeated below.

ALLEN, P. 1941. A Wealden soil bed with Equisetites lyelli (Mantell). Proceedings of the Geologists'Association, Vol. 52, 362–372.

ALLEN, P. 1947. Notes on Wealden fossil soil-beds. Proceedings of the Geologists' Association, Vol. 57, 303–314.

ALLEN, P. 1948. Petrology of a Wealden sandstone at Clock House, Capel, Surrey. Geological Magazine, Vol. 85, 235–241.

ALLEN, P. 1949a. Wealden petrology: The Top Ashdown Pebble Bed of the Top Ashdown Sandstone. Quarterly Journal of the Geological Society of London, Vol. 104, 257–321.

ALLEN, P. 1949b. Notes on Wealden bone-beds. Proceedings of the Geologists' Association, Vol. 60, 275–283.

ALLEN, P. 1959. The Wealden environment: Anglo-Paris Basin. Philosophical Transactions of the Royal Society, London, No. B242, 283–346.

ALLEN, P. 1960a. Geology of the Central Weald: a study of the Hastings Beds. Geologists' Association Centenary Guide No. 24.

ALLEN, P. 1960b. Strand-line pebbles in the mid-Hastings Beds and the geology of the London Uplands. General features. Jurassic pebbles. Proceedings of the Geologists'Association, Vol. 71, 156 -168.

ALLEN, P. 1961. Strand-line pebbles. Proceedings of the Geologists' Association, Vol. 72, 271–286.

ALLEN, P. 1962. The Hastings Beds deltas: recent progress and Easter field meeting report. Proceedings of the Geologists' Association, Vol. 73, 219–243.

ALLEN, P. 1967. Strand-line pebbles in the mid-Hastings Beds and the geology of the London Uplands. Old Red Sandstone, New Red Sandstone and other pebbles. Conclusion. Proceedings of the Geologists' Association, Vol. 78, 241–276.

ALLEN, P. 1972. Wealden detrital tourmaline: implications for northwestern Europe. Journal of the Geological Society, London, Vol. 128, 273–294.

ALLEN, P. 1976. Wealden of the Weald: a new model. Proceedings of the Geologists' Association, Vol. 86 (for 1975), 389–437.

ALLEN, P. 1981. Pursuit of Wealden models. Journals of the Geological Society of London, Vol. 138, 375–405.

ALLEN, P. 1989. Wealden research-ways ahead. Proceedings of the Geologists' Association, Vol. 100, 529–564.

ANDERSON, F W. 1940. Ostracod zones of the Wealden and Purbeck. Advancement of Science, Vol. 1, 259.

ANDERSON, F W. 1967. Ostracods from the Weald Clay of England. Bulletin of Geological Survey of Great Britain, No. 27, 237–269.

ANDERSON, F W. 1971. The sequence of ostracod faunas in the Wealden and Purbeck of the Warlingham Borehole. Appendix B in The stratigraphy of the Geological Survey borehole at Warlingham, Surrey. WORSSAM, B C, and IVIMEY-COOK, H C. Bulletin of the Geological Survey of Great Britain, No. 36.

ANDERSON, F W. 1985. Ostracod faunas in the Purbeck and Wealden of England. Micropalaeontology, Vol. 4, 1–68.

ANDERSON, F W. BAZLEY, R A, and SHEPHARD-THORN, E R. 1967. The sedimentary and faunal sequence of the Wadhurst Clay (Wealden) in boreholes at Wadhurst Park, Sussex. Bulletin of the Geological Survey of Great Britain, No. 27, 171–235.

APPLIED GEOCHEMICAL RESEARCH GROUP, IMPERIAL COLLEGE OF SCIENCE AND TECHNOLOGY. 1978. The Wolfson geochemi cal atlas of England and Wales. (Oxford: Clarendon Press.)

BATTEN, D J. 1974. Wealden palaeoecology from the distribution of plant fossils. Proceedings of the Geologists'Association, Vol. 85, 433–458.

BRISTOW, C R, and BAZLEY, R A. 1972. Geology of the country around Royal Tunbridge Wells. Memoirs of the Geological Survey of Great Britain, Sheet 303.

BUCHAN, S, ROBBIE, J A, HOLMES, S C A, EARP, J R, BUNT, E F, and MORRIS, L S O. 1940. Water supply of south-east England from underground sources. Geological Survey Wartime Pamphlet, No. 10, Part VII.

BULL, A J. 1933. Field meeting in the Mole Gap. Proceedings of the Geologists' Association, Vol. 44, 312–313.

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Appendix 1 Selected borehole logs

Summary logs are given below for the five best-documented boreholes in the district, and for the Collendean Farm Borehole close to the district boundary. Detailed lithological logs, geophysical logs and representative specimens are held in the BGS archive at Keyworth, Nottingham, where they may be examined by appointment.

Bolney No.1 Borehole

BGS Ref. (TQ22SE/17); Grid. ref. [TQ 2801 2427] Surface level 70.8 m above OD; total depth 2440.2 m Drilled for Esso Petroleum Co. Ltd in 1963. See Chapter 2 for summary and detailed descriptions. The following geophysical logs were made:

Collendean Farm Borehole

BGS Ref. (TQ24SW/1); Grid. ref. [TQ 2480 4429] Surface level 80.3 m above OD; total depth 1755.6 m Drilled for Esso Petroleum Co. Ltd in 1964 See Chapter 2 for summary and detailed descriptions The following geophysical logs were made:

Cuckfield No.1 Borehole

BGS Ref. (TQ22NE/2); Grid. ref. [TQ 2962 2729]; [TQ 2961 2731]. This borehole was re-drilled twice due to difficulties encountered in the Wadhurst Clay. Surface level c.91 m above OD; total depth 325.22 m. Drilled for BGS in 1966 Cuckfield No.2 Borehole

Cuckfield No.2 Borehole

BGS Ref. (TQ32NW/1); Grid. ref. [TQ 3013 2683] Surface level c.68.6 m above OD; total depth 32.61 m Drilled for BGS in 1966

Warninglid Borehole

BGS Ref. (TQ22NW/1); Grid. ref. [TQ 2488 2701] Surface level c.91 m above OD; total depth 77.42 m Drilled for BGS in 1966

Worth Forest Borehole

BGS Ref. (TQ23NE/34); Grid. ref. [TQ 2891 3500] Surface level 83.8 m above OD; total depth 572.4 m Drilled for NMD Syndicate Ltd in 1932 to 1934

Appendix 2 Wealden ostracod faunas

The sequence of ostracod faunas in the Wealden of the Horsham district compares well with that recorded elsewhere in the Weald. It consists of assemblages dominated by species of Cypridea (C-phase faunas) which alternate with those dominated by genera which are presumed to represent more saline conditions (S-phase faunas), as described by Anderson (1967, 1971, 1985). Each couplet of an S-phase and succeeding C-phase comprises a faunicycle which can be used for correlation. The ostracod zones and the faunicycles within them are shown in (Table 3). The zones of the Wealden sequence at outcrop in the district can be summarised as follows:

Cypridea brevirostrata Zone

The faunas of the Ashdown Beds are a continuation of those of the highest Purbeck strata. The uppermost part of the Purbeck Beds, Cypridea setina Zone, contains an ostracod fauna in which Cypridea setina Anderson and its subspecies are the dominant forms. These and other characteristic Upper Purbeck species including C. aemulans Anderson, C. alta formosa Wolburg, C. brevirostrata Martin, C. dolabrata Anderson, C. penshurstensis Anderson, C. propunctata Sylvester-Bradley, C. tuberculata adjuncta Jones, C. ventrosa Jones and C. wicheri Wolburg continue into the Ashdown Beds, although they are sparsely represented there. Cypridea melvillei Anderson, C. menevensis Anderson and C. paulsgrovensis Anderson make their first appearance in the Ashdown Beds.

Cypridea paulsgrovensis Zone

The sequence of ostracod faunas in the Wadhurst Clay has been described in detail by Anderson et al. (1967). In the lower half of the formation Cypridea paulsgrovensis is the dominant species together with C. menevensis and C. tuberculata. Cypridea laevigata (Dunker) and C. lasius Anderson are typical species; C. aculeata Jones, C. bispinosa Jones, C. frithwaldi Anderson, C. helenae Anderson, C. recta Wolburg and C. valdensis de C Sowerby) are also present.

Cypridea aculeata Zone

In the upper half of the Wadhurst Clay, C. aculeata, C. arenosa Anderson, C. bispinosa and their subspecies dominate the fauna; C. melvillei is locally abundant. Cypridea asseri Anderson, C. pendae Anderson and C. vericae Anderson appear to be confined to this zone. This fauna continues upwards to the base of the Weald Clay. In the Grinstead Clay; C. recta tillsdenensis Anderson is the common form accompanied by C. bispinosa, C. melvillei, C. tuberculata, and C. valdensis, C. verrucosa.

Cypridea dorsispinata Zone

There is a marked faunal change at the base of the Weald Clay. The only species of Cypridea to survive from the Hastings Beds are C. tuberculata and rare examples of C. valdensis. Cypridea clavata Anderson and C. pumila Anderson first appear in this zone. In the lowest Weald Clay the fauna is dominated by C. dorsispinata Anderson and its subspecies almost to the exclusion of all other forms.

Cypridea tuberculata Zone

Cypridea dorsispinata dies out a little above the Horsham Stone, and several new species appear in this zone. This produces a distinctive assemblage in which C. brendae Anderson, C. marina Anderson, C. pumila Anderson and C. tuberculata are the dominant species. Cypridea clavata and C. valdensis are also present.

Cypridea marina Zone

Cypridea marina replaces C. pumila as the dominant C-phase species in the middle of this zone: C. hispida Anderson is locally abundant, for example at Clock House Brickworks.

Cypridea clavata Zone

Although C. clavata and C. valdensis are generally the more common species, C. bogdenensis Anderson commonly occurs in abundance and is apparently restricted to this zone. Incoming species include C. fasciata, C. pseudomarina Anderson, C. rotundata Anderson, C. spinigera (J de C Sowerby), and C. tenuis Anderson.

Cypridea valdensis Zone

The highest beds of the Weald Clay contain a distinctive fauna characterised by the incoming of C. caudata Anderson, C. comptonensis Anderson, C. cuckmerensis Anderson, C. hamata Anderson, C. vectae Anderson and C. warlinghamensis Anderson. Of the earlier species, C. fasciata, C. pseudomarina, C. spinigera, C. tenuis and C. valdensis, and rare C. rotundata continues to be part of the assemblage.

Details of the S-phase faunas are given below in the descriptions of the zonal occurrences.

Details

Cypridea paulsgrovensis and Cypridea aculeata zones

The most extensive Wadhurst Clay section in the Horsham district is that exposed in Freshfield Lane brickpit [TQ 3815 2650] where the highest 21 m of the formation have been exposed from time to time (see p.28). The C. paulsgrovensis and C. aculeata zones (Fairlight to Fletching faunicycles) have been recognised.

The lowest 1.5 m of strata seen contain poorly preserved C. bispinosa and C. laevigata, indicative of the upper part of the Fairlight Faunicycle.

The S-phase of the overlying Lindfield Faunicycle (6.5 m thick) contains 61 per cent of S-phase species, mainly Darwinula leguminella (Forbes) with Theriosynoecum alleni (Pinto and Sanguinetti). In the C-phase, Cypridea bispinosa (subspecies birini Anderson, bispinosa Jones and suthrigensis Anderson) is the dominant species, accompanied by C. aculeata antiqua Anderson, C. arenosa, C. pendae and C. recta recta Wolburg.

In the Wadhurst Faunicycle (2.4 m) the S-phase is well represented by Damonella buchaniana Anderson, Darwinula leguminella (Forbes) and Mantelliana phillipsiana (Jones), and Darwinula leguminella (Forbes) which locally account for 70 per cent of the fauna. The C-phase fauna, as in the type section at Wadhurst, is poor. At both localities C. recta s.l.is the dominant form and is accompanied by C. aculeata and C. laevigata.

The S-phase of the Crowhurst Faunicycle (6.4 m) contains a fauna dominated by Rhinocypris jurassica (Martin) (80 per cent). The C-phase fauna is rich and varied and, as at Wadhurst, is dominated by C. recta (mainly the subspecies tillsdenensis Anderson) (40 per cent) and with C. melvillei (37 per cent). Cypridea aculeata (subspecies eppili Anderson), C. asseri, C. bispinosa (subspecies birini , bispinosa and suthrigensis), C. frithwaldi, C. laevigata, and C. pendae are also present.

The S-phase of the Hawkhurst Faunicycle (3.9 m) contains a fauna dominated by Darwinula leguminella and Rhinocypris jurassica. In the C-phase, C. melvillei is the dominant species (42 per cent), as at Wadhurst Park, accompanied by C. aculeata s.l., C. bispinosa s.l., C. frithwaldi and C. recta s.l.

Only the lower 1.2 m of the Fletching Faunicycle was recorded. The S-phase is dominated by Rhinocypris jurassica, and the C-phase by C. melvillei (66 per cent). C. aculeata (subspecies aculeata and eppilz), Cypridea bispinosa, C. frithwaldi and C. vericae were also recorded in the C-phase.

The Chilcombe, Grinstead, Philpotts, Copyhold and Highbridge faunicycles of the Cypridea aculeata Zone were recorded in the Grinstead Clay in the Cuckfield No.1 Borehole [TQ 2962 2729] between 166.04 m and 192.94 m.

In Chilcombe Faunicycle, at 188.1 to 192.9 m, ostracods are abundant and generally well preserved. The C-phase fauna includes C. recta (42 per cent) (subspecies recta and tillsdenensis), C. bispinosa (23 per cent) (subspecies bispinosa), C. tuberculata, C. aculeata (late form and subspecies eppilz), C. laevigata, C. valdensis (subspecies valdensis and claudii Anderson), C. verrucosa and C. elvillei.

Between 186.06 m and 188.1 m, in the highest Lower Grinstead Clay, the Grinstead Faunicycle yielded the C-phase species C. recta (59 per cent) (recta is the common subspecies), C. valdensis (37 per cent) (subspecies claudii, clareae Anderson and valdensis) and C. aculeata (late form). In the S-phase, between 187.8 and 188.1 m, S-phase species, mainly darwinulids, represented 63 per cent of the fauna.

The Philpotts Faunicycle was indicated by S-phase species (75 to 80 per cent) at 185.17 to 186.06 m.

A C-phase fauna, consisting of C. recta (86 per cent: almost all C. recta tillsdenensis), C. aculeata (late form), C. laevigata and C. valderzsis, was recorded between 175 m and the base of the Upper Grinstead Clay at 178.27 m. Intercalations of silty mudstone in the underlying Cuckfield Stone contained a similar fauna, but with C. valdensis more abundant.

The S-phase of the Highbridge Faunicycle, at about 175 m, contained 58 per cent of S-phase species, but these were too badly preserved for specific identification. The C-phase fauna occurred between 168.6 m and 175 m where it consisted of C. recta (mostly the subspecies tillsdenensis but with some recta and a few edithae Anderson) (77 per cent), C. valdensis (subspecies valdensis and claudit) (15 per cent), and a possible late form of C. aculeata.

Representatives of the Chilcombe, Grinstead and Philpotts faunicycles were also recognised in the Lower Grinstead Clay at Philpots Quarry [TQ 3545 3225], West Hoathly (see p.47). Between 1.0 and 1.5 m above the Ardingly Sandstone the shales yielded crushed ostracods, the majority of which (69 per cent) belong with the S-phase of the Chilcombe cycle. They are Darwinula oblonga, Mantelliana phillipsiana, Rhinocypris jurassica and Theriosynoecum alleni (dominant). The C-phase of the cycle, 1.3 m thick, contains a rich and varied fauna including Cypridea recta (36 per cent) (mostly the subspecies tillsdenensis), C. bispinosa (31 per cent) (mostly the subspecies suthrigensis), C. tuberculata (19 per cent) (mostly the subspecies indigens), C. laevigata philpottsi (10 per cent), C. valdensis claudii 2 per cent, C. verrucosa (1 per cent) and C. melvillei (1 per cent). The composition of this assemblage is almost exactly the same as that seen in this cycle in the Cuckfield No.1 Borehole.

The S-phase of the Grinstead Cycle, about 3 m above the Ardingly Sandstone, yielded Mantelliana phillipsiana and Darwinula leguminella, which accounted for 50 per cent of the species present. The C-phase, about 1 m thick, contained Cypridea bispinosa bispinosa (55 per cent), C. tuberculata indigens (17 per cent), C. verrucosa (15 per cent), C. recta (7 per cent) (subspecies inflata and tillsdenensis), C. laevigata (3 per cent), C. valdensis (2 per cent) (subspecies valdensis and claudiz). Cypridea bispinosa was the commonest form in the lower part of the cycle and C. verrucosa at the top.

The S-phase of the Philpotts Cycle, its base about 4 m above the Ardingly Sandstone, yielded dominantly Darwinula leguminella, Mantelliana phillipsiana, and Rhinocypris jurassica (45 per cent of the fauna). In the C-phase, Cypridea recta tillsdenensis was the dominant form (49 per cent), accompanied by C. laevigata (27 per cent), C. tuberculata indigens (15 per cent) and C. recta recta and C. ?valdensis.

The S-phase of the Chilcombe Faunicycle, dominated by Theriosyoecum alleni with Darwinula oblonga and Mantelliana phillipsiana, and the C-phase, dominated by Cypridea bispinosa suthrigensis (84 per cent) accompanied by C. recta tillsdenensis, C. tuberculata indigens and C. melvillei, were recorded in the Lower Grinstead Clay at High Bridge railway cutting [TQ 320 224].

Cypridea dorsispinata to Cypridea valdensis zones

Few fossiliferous sections have been recorded in the C. dorsispinata Zone in the district. The Hackhurst Faunicycle, the lowest above the Horsham Stone, was recorded at Warnham where 1.4 m of blue shaly clay contained Darwinula leguminella, D. oblonga, Fabanella boloniensis (Jones) (punctate variety), Mantelliana mantelli (Jones) Miocytheridea henfieldensis Anderson, Theriosynoecum fittoni (Mantell) and foraminifera accompanied by the C-phase species Cypridea clavata, C. dorsispinata and C. tuberculata indigens (thin-spined variety). In the 0.3 m of clay immediately above, the assemblage was dominated by C. dorsispinata roemeri (Anderson) (84 per cent). In the former Southwater Brickworks [TQ 158 257] an ostracod fauna was collected from the floor of a deep pit in shaly clay, which appeared to represent an horizon in the Hackhurst Faunicycle. The dominant species was C. tuberculata indigens (thin-spined variety).

At Warnham Brickworks [TQ 175 257], the lowest ostracod-bearing beds seen in the main pit yielded an S-phase fauna with Miocytheridea henfieldensis (53 per cent), Theriosynoecum fittoni, Darwinula oblonga and D. leguminella. This horizon probably represents the Langhurst S-phase. The S-phase of the overlying Henfield Faunicycle was 3 m or more thick.

At Southwater, the S-phase fauna of the Rolvenden Faunicycle (2.4 m thick) was dominated by Miocytheridea henfieldensis, and accompanied by Darwinula leguminella, D. oblonga and Theriosynoecum fittoni. A similar assemblage was recorded at Warnham. At both pits the C-phase of the Rolvenden Faunicycle was dominated by C. tuberculata in the lower part and C. marina in the upper part. The Edenbridge Faunicycle at both localities was represented by up to 1.8 m of shales with C. dorsispinata roemeri.

At Southwater the S-phase of the Sandhurst Faunicycle consisted of about 1.1 m of silty shale with Miocytheridea henfieldensis dominant in the lower 0.3 m and Damonella pygmaea (Anderson) in the upper 0.75 m. Other species present were Darwinula leguminella, D. oblonga and Cypridea valdensis. The S-phase assemblage at Warnham was similar, with M. henfieldensis as the dominant species in the lower part and Damonella pygmaea in the upper part. Cypridea dorsispinata roemeri and C. valdensis were also found. At Southwater and Warnham the C-phase of the Sandhurst Faunicycle was poorly represented in silts; ostracods were found only in the lower 0.6 m with C. valdensis the commonest species, accompanied by C. marina. The Sandhurst Faunicycle is represented in the Cuckfield No.2 Borehole [TQ 3013 2683] between 31.4 m and the final depth of 32.6 m. There, a shaly mudstone contained C. tuberculata as the dominant form with C. dorsispinata gemella Anderson, C. dorsispinata roemeri, C. clavata and C. valdensis.

An 0.6 m-thick horizon low in the Crawley Faunicycle at Warn ham, contained predominantly Cypridea marina and C. tuberculata tuberculata, with C. clavata, C. valdensis and up to 46 per cent of S-phase species, mostly Miocytheridea henfieldensis. This faunicycle was well developed in the Cuckfield No.2 Borehole: at the base (31.1 to 31.4 m) the S-phase was represented by a fauna of which 90 per cent consisted of indeterminable, but non-Cypridea, forms. Cypridea tuberculata tuberculata dominated the fauna (50 to 89 per cent in ten samples) between 24.4 and 30.8 m, accompanied by C. brendae Anderson, C. clavata and C. marina. Between 23.2 to 23.8 m, C. clavata was the dominant species, with C. valdensis also present.

At Warnham the silty clays of the S-phase of the Fernhurst Faunicycle contained a fauna consisting mainly of Cypridea tuberculata tuberculata with a few examples of C. brendae, C. clavata and C. marina. The beds above contained only fragmentary ostracods. In the Cuckfield No.2 Borehole, although the percentage of S-phase species was variable, in general they dominated the faunas between 18.6 and 22.9 m. The highest beds at Warnham contained a predominantly S-phase fauna of the Plumpton Faunicycle, of which only Darwinula jonesi and Miocytheridea henfieldensis were identifiable.

The Plumpton Faunicycle was poorly represented in the Cuckfield No.2 Borehole, but the complete S-phase of the succeeding Buxted Faunicycle was recorded between 16.2 and 16.8 m. It consisted of silty mudstones with Miocytheridea henfieldensis as the dominant species. In the C-phase above, at 14.0 to 15.8 m, only the lowest 0.6 m contained ostracods including C. marina and C. tuberculata indigens. The most complete section of the S-phase of the Buxted Faunicycle was seen in the lowest beds at Clock House Brickworks [TQ 175 385] where 3.5 m of shaly clay yielded a rich macrofossil fauna including Cassiope, Paraglauconia, the cirripede Zeugomatolepas and the foraminifer Ammobaculites, indicative of a brackish environment. The ostracods include Miocytheridea henfieldensis (dominant), Damonella pygmaea, Darwinula leguminella, D. oblonga, Fabanella boloniensis, Hutsonia capelensis Kilenyi & Allen, Mantelliana mantelli, Rhinocypris jurassica, Schuleridea wealdensis Kilenyi & Allen and Sternbergella wolburgi Kilenyi and Allen. In 1.5 m of blue shelly clays 0.6 m above the highest S-phase fauna, the assemblage consisted of up to 100 per cent of Cypridea pumila.

In the Cuckfield No.2 Borehole the succeeding Ockley, Horley and Slinfold faunicycles were poorly represented; between 11.7 and 13.7 m depth, Miocytheridea henfieldensis was the dominant species with Mantelliana mantelli, Darwinula leguminella and D. oblonga except between 12.2 and 12.5 m where 77 per cent of the fauna consisted of Cypridea tuberculata indigens (long-spined form). At Clock House brickpit, 1.2 m of clays at the level of the S-phase of the Ockley Faunicycle contained Miocytheridea henfieldensis (up to 83 per cent), Mantelliana mantelli, Darwinula leguminella and a few examples of Cypridea marina. The C-phase was represented by at least 0.9 m of shelly, blue-grey clay with C. marina. The S-phase of the Holley Faunicycle was about 1.2 m thick and the fauna was dominated by Miocytheridea henfieldensis. Throughout the C-phase at Clock House Cypridea marina, the dominant species (up to 95 per cent), was found together with the thin-spined variety of C. tuberculata indigens.

The S-phase of the Slinfold Faunicycle was poorly represented at Clock House, but Miocytheridea henfieldensis, Damonella pygmaea and Darwinula leguminella constituted from 50 to 78 per cent of the assemblage. Part of this phase, with M. henfieldensis, was seen in the Cuckfield No.2 Borehole. In the C-phase at Clock House, Cypridea marina was the dominant form accompanied by a few specimens of C. tuberculata tuberculata and C. valdensis.

The S-phase of the Newdigate Faunicycle was a brief episode which was represented at Clock House by 0.3 m of clay in which the fauna consisted of about 90 per cent of small S-phase species. The C-phase was recognised in about 1.2 m of clay in which C. marina was the dominant species (91 to 98 per cent).

At Clock House brickpit the S-phase of the Romney Faunicycle extended through at least 3 m of sediment in which Miocytheridea henfieldensis was the dominant species together with Schuleridea wealdensis, Mantelliana mantelli, Darwinula leguminella and D. oblonga. Some C-phase forms were present in varying proportions, namely Cypridea tuberculata indigens and C. clavata talaria Anderson. The C-phase occurs in about 4.6 m of clay which yielded ten ostracodbearing samples in which C. clavata talaria was the dominant form, accompanied by C. tuberculata indigens and C. valdensis.

A grey shale with small turreted gastropods may represent the S-phase of the Ewhurst Faunicycle at Clock House. The only ostracods seen were crushed and indeterminable, but all appeared to be S-phase genera. This bed was followed by a gap in the section of 2.4 m. The Capel Faunicycle S-phase, dominated by Miocytheridea henfieldensi s accompanied by Mantelliana mantelli, occurs in a silty clay about 0.5 m below the top of the pit together with examples of Cypridea clavata gordana Anderson and a form resembling C. tenuis. The C-phase here is thought to lie in the overlying sandstones.

Appendix 3 Geological Survey photographs

Copies of these photographs are deposited for reference in the British Geological Survey library, Keyworth, Nottingham NG12 5GG. Black and white prints and slides can be supplied at a fixed tariff, and in addition colour prints and transparencies are available for all the photographs. All numbers belong to Series A.

Topography

Wealden (listed in stratigraphical order)

Superficial structures

Industrial archaeology

Appendix 4 Six-inch maps

The following is a list of the six-inch geological maps included in the area of one-inch map Sheet 302 with the initials of the surveyors and the dates of survey; the surveyors were: C R Bristow, R W Gallois, R G Thurrell and B C Worssam.

Manuscript copies of the maps are deposited for public reference in the library of the British Geological Survey, Keyworth. Uncoloured dyeline copies of the complete sheets are available for purchase.

Figures, plates and tables

Figures

(Figure 1) Topographical setting of the Horsham district.

(Figure 2) Geological sketch map of the Horsham district.

(Figure 3) Estimated depositional thicknesses for the Lias to Wealden strata (inclusive) of the Weald (after Chadwick, 1986).

(Figure 4) Total-gamma-ray and sonic velocity logs of the Bolney Borehole.

(Figure 5) Formations and members in the Hastings Beds of the district.

(Figure 6) Hastings Beds sequences proved in deep boreholes in and adjacent to the district.

(Figure 7) Idealised Ashdown Beds rhythm.

(Figure 8) Generalised vertical section for the Wadhurst Clay.

(Figure 9) Wadhurst Clay sequence at Sharpthorne Brickworks.

(Figure 10) Generalised vertical section for the Lower Tunbridge Wells Sand.

(Figure 11) Lithological variations in the Grinstead Clay.

(Figure 12) Hypothetical depositional environments of the Grinstead Clay.

(Figure 13) Former sandstone quarries in the Ardingly Sandstone and Cuckfield Stone in the Cuckfield area.

(Figure 14) Sedimentary channel in the Upper Tunbridge Wells Sand, Domewood.

(Figure 15) Generalised vertical section for the Weald Clay of the district.

(Figure 16) Sketch map showing the distribution of minor beds in the Weald Clay of the western Weald.

(Figure 17) A schematic cross-section through the Weald Clay of the western Weald.

(Figure 18) Sections in the Weald Clay at Clock House and Warnham brickworks.

(Figure 19) Occurrences of red clay in the Weald Clay of the Dragons Green area.

(Figure 20) Evolution of fault patterns in the district. A Major faults in the Devonian rocks B Major faults in the Cornbrash (Middle Jurassic) C Outcrops of major faults

(Figure 21) Section across the Ouse Valley graben.

(Figure 22) Structure contour map of the formations at outcrop in the Horsham district.

(Figure 23) Distribution of head and river terrace deposits in the upper Arun valley.

(Figure 24) River terraces and their relation to head deposits in the upper reaches of the Mole and Arun valleys.

(Figure 25) River terraces of the upper Adur valley.

(Figure 26) 'Capture' of the Kit Brook.

(Figure 27) River capture and development in the upper Ouse valley.

(Figure 28) Valley bulging and cambering at Freshfield Lane Brickworks.

(Figure 29) Detail of valley-bulged Wadhurst Clay at Freshfield Lane Brickworks.

Plates

(Front cover) Cover photograph Stone Farm Rocks [TQ 3814 3477], near East Grinstead.

(Frontispiece) Ardingly Sandstone, Great-upon-Little [TQ 349 321], Chiddingly Wood, West Hoathly. This block has been detached from the adjacent Ardingly Sandstone crags by cambering. Its undercutting is partly due to wind action, caused by sand blasting in a periglacial climate; it has subsequently been accentuated by water seepage along a more silty, less permeable horizon. The upper part of the block, massive sandstone with disturbed bedding, is formed by the 'earthquake bed'. (A10218)

(Rear cover)

(Geological succession) Geological succession in the Horsham district.

(Plate 1) Hastings Beds scenery, Hook Ghyll, West Hoathly [TQ 365 325]. From this viewpoint near the main Wealden anticlinal axis, dips are almost exclusively southwards to the South Downs (far distance) and beyond. Hook Ghyll is a youthful, steep-sided valley cut by a stream which is fed by springs issuing at the base of the Lower Tunbridge Wells Sand: the sands cap the adjacent ridges. The valley sides are mostly in Wadhurst Clay, much obscured by sandy Head and slipped clays. This and similar valleys are mostly thickly wooded, only the ridges and upper valley slopes being suitable for agriculture and building. (A10234).

(Plate 2) Junction of Ardingly Sandstone and underlying silty sandstones and siltstones, stream gorge [TQ 2823 2974], Ditton Place, Handcross. Thickly cross-bedded sandstones at the base of the Ardingly Sandstone rest with a sharp junction, just below the lip of the waterfall, on thinly interbedded fine-grained silty sandstones and siltstones which make up the lower (undifferentiated and un-named) part of the Lower Tunbridge Wells Sand. (A10183).

(Plate 3) Sedimentary structures in the Hastings Beds in the Cuckfield No. 1 Borehole [TQ 2961 2731]. A Sandy siltstone deformed by penecontemporaneous flow: Ardingly Sandstone: Bz 2824: 198.7 m depth: x ¾ . B Interlaminated silty sandstone (pale) and silty mudstone (dark) with penecontemporaneous deformation caused by loading and/or flow: Ashdown Beds: Bz 3396: 320.4 m depth: x ¾ . C.Interlaminated silty mudstone (dark) and siltstone (pale) showing rhythmic alternations and with much bedding disturbance caused by plant roots and bivalve burrows: Lower Grinstead Clay: Bz 2801: 191.7 m: x ¾ . D Pebble bed with mostly angular clasts of sandy siltstone (pale) and ironstone (dark) in a fine-grained sand matrix; probable channel lag deposit: overlain by sandy siltstone in which wispy bedding is picked out by abundant carbonised plant fragments: Upper Tunbridge Wells Sand: Bz 2655: 156.7m: x ¾. E Siltstone in which lamination, picked out by dark mudstone, is broken by bioturbation, probably mostly plant rootlets: Upper Tunbridge Wells Sand: Bz 2460: 101.4 m: x ¾ .

(Plate 4) Ardingly Sandstone and Grinstead Clay, Philpots Quarry, West Hoathly [TQ 354 322]. The top 3 to 4 m of the Ardingly Sandstone is worked here for building purposes from beneath an overburden of about 7 m of Lower Grinstead Clay mudstones and up to 2 m of flaggy Cuckfield Stone sandstone (arrowed). Well-developed near-vertical joints in the sandstone, many of them partially opened by cambering, facilitate its working. (A10014).

(Plate 5) Cuckfield Stone, Rookery Lane, Haywards Heath [TQ 324 223]. In the area between Danehill and Haywards Heath, the Cuckfield Stone occupies a channel which cuts out much of the Lower Grinstead Clay. Within this channel the sandstones are commonly distinctively trough cross-bedded ('festoon-bedded'). As elsewhere in the Cuckfield Stone, the sandstones characteristically weather to attractive dark to honey browns, an indication that they were in part originally calcareous. (A10224).

(Plate 6) Upper Tunbridge Wells Sand scenery, St Leonard's Forest, Mannings Heath [TQ 223 297]. This view northwards shows the heathland and thin woodland with scattered clearings for agriculture that is typical of much of the Upper Tunbridge Wells Sand outcrop. The bracken on the slope in the foreground conceals old minepits for clay ironstone. (A10189).

(Plate 7) Upper Tunbridge Wells Sand lithologies, Hundred Acres Wood [TQ 331 364], Rowfant. The Upper Tunbridge Wells Sand consists of silts with interbedded sandstones and silty clays. Distinctive horizons are commonly impersistent and are difficult to trace laterally. At this locality a red and grey mottled alluvial silty clay (lowest 2.5 m of section) is worked for brickmaking. In the upper part of the face, a thin sandstone bed within a predominantly siltstone succession passes from thickly bedded (right) to flaggy with silt partings (centre). (A10209).

(Plate 8) Siltstones in the Upper Tunbridge Wells Sand, Domewood [TQ 3438 3994], near East Grinstead. Thick beds of pale grey thinly bedded siltstone are one of the most common lithologies in the Upper Tunbridge Wells Sand, where they give rise to extensive heath and woodland areas on thin, poorly drained soils. A small channel at the top of the middle part of the face is shown in ((Figure 14)). The purpose of the quarry is unknown. The siltstones are too soft for construction uses; they may have been mixed with clay for brickmaking, or have been used as a poor substitute for fuller's earth. (A10221).

(Plate 9) Rhythms in Upper Tunbridge Wells Sand, Warnham Mill Pond outfall, Horsham [TQ 164 318] Well-bedded, fine-grained sandstone and silty sandstone form coarsening-upward rhythms in the highest part of the Upper Tunbridge Wells Sand, within 6 m of the base of the Weald Clay. (A10015).

(Plate 10) View northwards across Horsham from the crest of the Horsham Stone escarpment of Denne Hill [TQ 171 294]. The hill slope and meadows in the foreground are on the lower part of the Weald Clay. The town, partly concealed among trees, is on Upper Tunbridge Wells Sand on the westward-plunging nose of the Colgate Anticline. The wooded ridge in the middle distance, left of the church spire, is formed of Weald Clay capped by Horsham Stone, dipping away from the observer. In the far distance is the Lower Greensand escarpment of Leith Hill, near Dorking. (A10200).

(Plate 11) Cambering in Ardingly Sandstone, Brook House, East Grinstead [TQ 385 375] Well-jointed Ardingly Sandstone is cambered downslope, to the right, and shows characteristic dip-and-fault structure. Four tilted blocks are present, each block having rotated along a major joint, which now dip into the valley. (A10215).

(Plate 12) Folds in Weald Clay, Southwater Brickpit [TQ 158 259]. These folds in Weald Clay are of the type associated with valley-bulging. However, this section is far from any modern valley and it may be a 'fossil' example related to a landscape now largely removed by erosion. Boreholes in the floor of the pit suggest that the disturbance dies out rapidly downwards. (A5368).

(Plate 13) Vertical Wadhurst Clay in the core of a valley bulge, Freshfield Lane Brickworks [TQ 382 265], Danehill. In the most intensely deformed part of the bulge, the shales have undergone plastic flow, and thin hard beds of limestone and clay ironstone have been stretched out to produce a boudinage-like effect. Small, tight folds (right centre) are present and some of the hard beds in the left of the picture may even be repeated by large isoclinal folds. Oxidation (brown colouration) has penetrated the more permeable beds to differing extents. (A10250).

(Plate 14) Cryoturbation structures, in bank of a tributary of the River Mole, Rowley Farm [TQ 277 395]. Periglacial cryoturbation structures, which affect both the Weald Clay and overlying gravel, are overlain by an undisturbed gravel layer and modern Alluvium. The upper gravel, cutting off the folds in the clay and lower gravel, is seen in the right half of the picture. Below the hammer is a lens of clay ironstone in the Weald Clay. The pale streaks result from leaching by plant roots. (A10211).

(Plate 15) Horsham Stone in a 17th-century house in The Causeway, Horsham [TQ 171 303]. It shows Horsham Stone, a thinly splitting calcareous sandstone from the lower part of the Weald Clay, used as a roofing material. (A10042).

(Plate 16) Minepits for clay ironstone, Budd's Copse, Faygate [TQ 210 345] the presence of filled-in minepits for clay ironstone is revealed by circular patches of blackened leaves on the woodland floor. Slight settlement of their filling gives hollows that are waterlogged in the winter months. (A10040).

Tables

(Table 1) Summary of thicknesses of strata penetrated in the Bolney and Collendean Farm boreholes and their estimated range for the Horsham district.

(Table 2) Comparison of pebble ( > 0.25 in) types and concentrations (%) in the three most prominent pebble beds in the Hastings Beds (based on Allen, 1960b, table 1 and Allen, 1976, table 2).

(Table 3) Wealden ostracod zones and faunicycles.

Tables

(Table 1) Summary of thicknesses of strata penetrated in the Bolney and Collendean Farm boreholes and their estimated range for the Horsham district

(Table 2) Comparison of pebble ( > 0.25 in) types and concentrations (%) in the three most prominent pebble beds in the Hastings Beds (based on Allen, 1960b, table 1 and Allen, 1976, table 2)

(Table 3) Wealden ostracod zones and faunicycles