The economic geology of the Weald

The economic geology of the Weald D. E. HIGHLEY HIGHLEY. D. E. 1975. The economic aeolozv of the Weald. Proc. Geol. Ass .. 86 (4). 559--569. The major proportion of the minerals of economic importance in the Weald IS consumed by the construction industry. These minerals include sand and gravel for aggregate. clay for brick manufacture, chalk for cement, limestone (ragstone) for roadstone, and gypsum for plaster, plasterboard and cement manufacture. In addition the Weald is a major source of silica sand. used in glass-making and for foundry purposes, and also of fuller's earth. The geological distribution of these minerals is described, together with an account of their quality, present exploitation and industrial usage.

Mineral Resources Division. Institute of Geological Sciences. Exhibition Road. London SW7 2D£.

CONTENTS I. 2. 3. 4. 5. 6. 7. 8. 9. 10.

page 559 560 561 562 564 565 566 567 568 568 569 569

INTRODUCTION SAND AND GRAVEL CLAY CHALK SILICA SAND GYPSUM LIMESTONE AND SANDSTONE FULLER'S EARTH HYDROCARBONS CONCLUSIONS ACKNOWLEDGMENTS REFERENCES

l. INTRODUCTION In 1875, at the time of the publication of Topley's Geology of the Weald. mineral extraction in the area was largely confined to the production of building stone and roadstone, most of the harder formations of the Weald being worked for this purpose, and to the exploitation of the numerous clay formations for the manufacture of bricks and tiles. The Wealden iron industry was by then defunct, the last furnace having been closed down in 1828, but the area was already a major source of fuller's earth, which was produced between Redhill and Nutfield, and glass (silica) sand was also being extracted near Reigate in Surrey and near Aylesford, Bearsted and Hollingbourne in Kent. The ironstone deposits of the Weald have no economic importance today, but production of fuller's earth and silica sand has continued to expand. Phosphatic nodules were formerly extracted from the Gault and Upper Greensand near Farnham and Cheriton, and the last mine in the Upper Greensand producing 'hearthstone', a calcareous sandstone used for whitening hearths and stone floors, closed at Reigate in 1960. Horsham Stone, a thinly bedded, calcareous sandstone in the lower part of the Weald Clay, was formerly extensively exploited around Horsham for use as paving-stones and roofing-tiles. 559

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Today the construction industry is still by far the largest consumer of the mineral output of the Weald. Most of the formations which were formerly exploited for building stone and roadmaking are too soft to meet the stringent modern specifications for concrete aggregate and roadstone. Building stone is now also little in demand. The Weald has a shortage of good quality aggregate, both of flint gravel and hard rock suitable for crushing, and large quantities have to be imported. The area, however, contains large resources of other raw materials for construction. The Lower Greensand is an important source of building and asphalting sand. Various clays, in particular the Weald Clay, are used in the production of bricks. The Chalk is exploited for cement manufacture, and gypsum, which was discovered in the sinking of the Sub-Wealden borehole in 1872, is also mined on a large scale near Robertsbridge for use by the building industry. A major proportion of the region's water requirements are met from underground sources: the Chalk, Lower Greensand and, to a lesser extent, the sandstone horizons of the Hastings Beds are important aquifers. 2. SAND AND GRAVEL The Weald is largely composed of clays and soft sandstones, which do not produce hard, durable pebbles, and the area is, therefore, deficient in gravel suitable for aggregate. Where gravels do occur, however, in the lower reaches of some of the rivers, they consist largely of flints derived from the Chalk and some chert from the Lower Greensand. Although there are important beach and soliflucted coombe deposits in the Chichester area, large alluvial and river terrace gravels similar to those associated with the Thames and its tributaries are absent. Flint gravels are used mainly in concrete. They are not usually suitable for road construction, other than for the sub-base, as bonding between the bituminous binder and the flint surface is poor. In contrast to the general gravel deficiency of the area, the Folkestone Beds of the Lower Greensand are extensively quarried throughout their outcrop and are one of the most important sources of sand in southeast England, meeting a wide range of industrial specifications. The only extensive gravel deposits in the area are the old beach shingles of Dungeness, Rye and the Crumbles near Eastbourne, which consist almost entirely of flint pebbles with only a low proportion of sand (Beaver, 1968). These deposits are extensively exploited near Lydd, Rye and Eastbourne. Flint pebbles suitable for pottery, decorative and grinding purposes are also produced by hand-picking the oversize material. Flints for use in pottery manufacture must be clean, free of iron and generally over about 50 mm in diameter. The extensive spreads of soliflucted coombe rock which occur at the junction of the Chalk Downs and the coastal plain of West Sussex are also an important source of gravel. The deposits extend in a belt from Fareham to Brighton, although they are only exploited between Arundel and Havant, and reach their maximum extent in the Chichester area. The deposit consists of coarse, angular flint gravel with a low proportion of sand, and contains chalk and clay as impurities. The deposits probably extend southward under the brickearths of the area (Ministry of Town and Country Planning, 1950). Underlying Pleistocene sands and gravels of probable marine origin are worked in conjunction with the coombe deposits. River gravels and concreting sand are extracted from beneath the alluvium of the River Medway, near New Hythe and Leybourne, and the River Darent around Riverhead, near Sevenoaks. The Medway river terraces are also worked at Aylesford and near Yalding, south of Maidstone, the latter deposits containing a large proportion of Wealden sandstone pebbles (Worssam, 1963). The sand and gravel deposits of the Arun, Adur, Ouse and Cuckmere contain flint in their lower sections but there is an increase in the proportion of deleterious sandstone in their upper reaches. Similarly the river gravels of the Weyand Mole in Surrey and the Stour in Kent contain,

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south of the North Downs escarpment, detritus derived from the Lower Greensand and Hastings Beds, and are, therefore, generally unsuitable for concrete aggregate. The Folkestone Beds are an important source of building sand, commonly called 'soft' sand, which is generally finer than concreting or 'sharp' sand. Building sand is extensively quarried from the Folkestone Beds, particularly on their northern outcrop, around Farnham, between Redhill and Maidstone, and near Ashford, and on the southern outcrop between Storrington and Washington, and Petersfield and Midhurst. In this latter area the Folkestone Beds also yield concreting sand (Ministry of Town and Country Planning, 1950). In addition to their use as a general-purpose building sand and, to a smaller extent, concreting sand, the sands of the Folkestone Beds are also used in the production of concrete roofing-tiles, wall-blocks and pavingstones, and in the manufacture of calcium silicate bricks. The Folkestone Beds are also an important source of fine sand for use as the fine aggregate in hot-rolled asphalt. 'Carstone', or veins and doggers of ferruginous sandstone, occurs in the Folkestone Beds and is screened out at many quarrying operations. However, because of its attractive coloration, it is sometimes sold as a decorative stone for rockeries. In 1973 production of gravel within the Wealden area was estimated to be about 4 million tonnes, and that of sand , including building, concreting and asphalting sand, 3·5 million tonnes.

3. CLAY The clay formations of the Weald are, in ascending stratigraphical order, clays within the Ashdown Sand, the Wadhurst Clay. clays within the Tunbridge Wells Sand, the Weald Clay, the Atherfield Clay and the Gault. All of these formations are believed to have been used in brick manufacture in the past. Historically and at present, however, the Weald Clay continues to be by far the most important, accounting for approximately 80 per cent of an estimated total brick production of 325 million for the Wealden area. There has been a considerable contraction in the industry in recent years; the present distribution of brick clay operations in the Weald is shown in Fig. I. The majority of the quarries working the Weald Clay are situated in its more extensive western outcrop; a few scattered operations situated on the Hastings Beds and Gault remain. Sedimentary clays consist essentially of clay minerals, quartz and mica, although many other minerals may occur in accessory quantities and considerably affect the suitability of the clay for brick manufacture. In general, the clay mineral content of brick clays varies from 30 to 50 per cent, although material with as little as 20 per cent clay may be sufficiently plastic to mould and retain its shape (Keeling, 1963). Sufficient fluxing material should be present for the clay to vitrify at a temperature of 950°-1100° c., and also an adequate quantity of a non-plastic constituent, usually quartz, to prevent excessive shrinkage and deformation during drying and firing (Grimshaw, 1971). Most brick clays contain disordered kaolinite or illite, or a mixture of the two, as the main clay mineral. Disordered kaolinite occurs in deposits laid down under fairly fresh to brackish water conditions, whilst illite is generally found in a marine environment. The Weald Clay consists of a mixture of illite and disordered kaolinite, although illite is generally dominant in the Gault (Keeling, 1963). The clays of the Hastings Beds generally contain disordered kaolinite, illite and a chloritic mineral (Butterworth & Honeyborne, 1952). Many other minerals may occur as impurities; in the Weald Clay, for example, the main impurities are calcite, siderite, iron sulphides and gypsum. Limestone beds and ostracod-bearing clays are avoided during quarrying because of the problems they can cause during firing. The Weald Clay is used mainly in the manufacture of facing and engineering bricks. There is also a relatively small output of floor-blocks, field-drains, and clay roofing and wall-cladding tiles. Within the Hastings Beds bricks are produced from a mixture of Wadhurst Clay and Lower Tunbridge Wells Sand near Tonbridge (Dines, Buchan, Holmes & Bristow , 1969) and silts and

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thin clay seams in the middle of the Ashdown Sand are similarly worked at Jarvis Brook, near Crowborough (Bristow & Bazley, 1972). Bricks are also produced from clays and silts in the Tunbridge Wells Sand near Bexhill, from the Wadhurst Clay near West Hoathly and from clays and silts within the Upper Tunbridge Wells Sand near Danehill. The only sizeable brickworks situated on the Gault is at Sevenoaks. The Gault Clay is, however, also quarried near Halling and Snodland in the Medway Valley, at Beddingham, near Lewes and at Horton, near Upper Beeding (Fig. I), for cement manufacture, the clay supplying the necessary silica, alumina and iron oxide for the production of cement clinker. South of Cranleigh in Surrey, Weald Clay is worked for use as a carrier for seed dressings, and silty clays at the top of the Ashdown Sand are quarried at Reading Street, near Tenterden, for use as a binder in animal feedstuffs. 4. CHALK The Chalk escarpment, extending from eastern Kent through Surrey, Hampshire and into southern Sussex, forms an incomplete ring around the Weald proper. Stratigraphically, the formation may be divided into three units-the Upper, Middle and Lower Chalk. Much of the Chalk downland surrounding the Weald is underlain by the Upper Chalk, whilst the Middle and Lower Chalk crop out in the scarp faces and some valleys. The Chalk consists principally of the minute remains of calcareous organisms called coccoliths and represents a high purity limestone often containing in excess of 95 per cent calcium carbonate. Although of fairly uniform appearance the Chalk does, however, vary significantly in composition vertically, although there is little lateral variation. The Lower Chalk and the basal portion ofthe Middle Chalk contain sufficient argillaceous material to be classified as a marl at many horizons. The Upper Chalk is purer but is everywhere characterised by the presence of flints. In the United Kingdom the cement industry is the largest consumer of chalk and the Wealden

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area is no exception, with productive capacity for cement totalling some 1.2 million tonnes a year, requiring about 2 million tonnes of chalk. In the manufacture of Portland cement a carefully controlled , uniform mixture of chalk (or any other source of lime) and clay, shale or marl is calcined at about 14500 - 1 6 0 0 0 C, and to the resultant clinker between 4 and 8 per cent gypsum is added to control the setting time. The clinker, with gypsum added, is then finely ground to produce Portland cement. Chalk and clay are usually mixed in the proportion three to one, although this depends on the composition of the raw materials used. Howe ver, the Lower Chalk , part icula rly near its base, contains sufficient argillaceous material to suppl y, in addition to lime, the necessary silica, alum ina, ferri c oxide and other minor components required for the production of cement clinker. It may be used, therefore, as is the case at Southerham , near Lewes, as a natural cement mix. Elsewhere, clay, usually the Gault, has to be specially quarried, slurried and piped to the cement works where it is mixed, in the required proportions, with a chalk slurry. Most of the cement works in the Weald utilise the Lower and Middle Chalk, but where material is quarried from the Upper Chalk, as at Upper Beeding, near Shoreham, flints will inevitably be present. These act as a grinding medium in the raw slurry mill, but the larger flints, after washing and screening , are sent to the pottery industry for use in the manufacture of a variety of pottery bodies, whilst the smaller flints are used for construction purposes. 500

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Numerous other chalk qua rrying operations. mainly situated on the scarp faces in the Lower and Middle Chalk, are scattered throughout the area, and the ir distribution, together with those used for cement manufacture, a re shown in Fig. 2. Chalk has a wide variety of other applications, prob ably the largest tonnage, after cement manufacture, being utilised as fill for civil engineering work and strengthening river banks. Other uses include chalk for agricultural purposes, for the manufacture of lime and for the production of chalk whiting . The latter term is applied to a high purit y chalk with a calcium carbonate content of between 96 and 99 per cent , which has been

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ground so that at least 90 per cent passes a 325 B.S. mesh sieve (Cummings & Bichan, 1970). Whiting has many applications and is used principally as a filler in the rubber and plastics, putty, paint, paper and linoleum industries. Chalk whiting is produced at one locality near Newhaven. 5. SILICA SAND The Lower Greensand is the most important source of high-grade silica sand in the United Kingdom, and in the Weald the Folkestone Beds are extensively exploited between Buckland and Oxted in Surrey and near Borough Green, West Mailing and Aylesford in Kent (Fig. 2). Production of silica sand in the area is estimated to be of the order of one million tonnes a year, accounting for about 18 per cent of total United Kingdom output in 1973. The Folkestone Beds consist predominantly of poorly consolidated quartzose sands which are generally brown or yellow in colour due to iron-staining. However, high purity white sands, generally containing between 96 and 99 per cent Si0 2 , also occur as discontinuous beds and lenses of varying size. Impurities include small amounts of clay minerals and limonite coating the surface of the sand grains, discrete heavy minerals, such as ilmenite, hematite, magnetite and siderite, and some muscovite and feldspar (Segrove & Stanyon, 1970). These high-grade silica sands are used principally as synthetic foundry moulding sands, which require the addition of a bonding agent such as bentonite (unlike naturally occurring bonded moulding sands), and for glass-making, although they also have numerous other applications, for example, in ceramics and in the manufacture of sodium silicate. Glass sands, containing about 99 per cent Si02 and having very low iron and chromium contents, are produced in the Buckland-Redhill area. The minimum silica contents specified for the three different grades of glass sand used for colourless glass manufacture are between 98·5 and 99·5 per cent; maximum Fei03 content between 0·030 and 0·008 per cent, and maximum Cri03 content between 0·0006 and 0·0002 per cent (British Standard 2975 : 1958). The Folkestone Beds only meet the lowest quality of these three grades. Alumina, about O· 1-0·2 per cent, is derived from the micas and feldspar, and is desirable as it acts as a fluxing agent. As with many other industrial minerals consistency of quality is very important. Glass sands should have a narrow size distribution, the presence of oversize and undersize material in the sand tending to lead to inhomogeneity in the glass melt, and generally particle sizes lie between 100 and 500 microns. Despite their relative purity, however, the Folkestone Beds are not suitable for use in colourless glass manufacture until they have been beneficiated by sophisticated processing techniques, which include washing and attrition scrubbing to remove clay minerals, leaching with hydrofluoric acid and sodium hydrosulphite to remove the iron oxide coating the quartz grains, and finally flotation to remove heavy minerals and any remaining clay (Segrove & Stanyon, 1970). The ease with which impurities, in particular iron oxides, can be removed from a sand is an important factor in determining its potential value as a glass sand. A higher iron content (0· 25 per cent Fe 203 ) is required, however, for coloured glass manufacture, and Folkestone Beds are worked for this purpose at Aylesford in Kent without further treatment. Synthetic moulding sands, particularly for steel castings, should be pure, containing at least 96 per cent Si0 2 , as the presence of impurities generally reduces their refractoriness. The particle size distribution of a moulding sand is also of fundamental importance in determining its usefulness as a foundry sand, and normally a well-graded sand with a major proportion of the grains falling on three or four adjacent sieves is required. Rounded to sub-angular grains are preferred to angular particles because they give more uniform compaction, flow easily around the pattern, impart greater strength to the mould and require less binder. The Folkestone Beds are the only productive source of silica sand in the Weald at present, although a number of other formations have been worked in the past, including sandstone beds

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within the Weald Clay which supplied the medieval Wealden glass industry (Thurrell, Worssam & Edmonds, 1968). The Ashdown Sand and Tunbridge Wells Sand also contain largely unexploited resources of silica sand at various horizons. White, quartzose sandstones occur within the Ashdown Sand in the Hastings district, and Boswell (1918) records a high silica content (99·47) per cent Si0 2) for a sand at Fairlight which was formerly quarried for glass manufacture (Hunt, 1860). As recently as the late 1950s the deposit was worked as a source of glass sand, although it suffered from a high chrome content. Good quality silica sand is also reported to occur in the Ashdown Sand at Brede, Crowhurst, Battle and Burwash in East Sussex (Sweeting, 1950), and a very fine silica sand occurring at the top of the Ashdown Sand at Reading Street, near Tenterden, has been used for foundry purposes. A high silica content (98 .77 per cent) is also recorded by Boswell (1918) for the Ardingly Sandstone horizon within the Tunbridge Wells Sand at Ashurstwood, near East Grinstead. A problem common to the silica sand deposits of the central and southern Weald is their distance from the major markets, and whilst adequate resources exist elsewhere the high cost of transport will probably discourage their development. 6. GYPSUM The only commercially exploited gypsum deposit s of Jurassic age in the United Kingdom occur in the Purbeck Beds of the Weald, where they approach the surface in three major inliers exposed along the crest of the Wealden anticline between Heathfield and Battle, to the north-west of Hastings. The Purbeck Beds consist largely of shales and thin limestones , but four main gypsum seams, varying from 2 m to 4 m in thickness, are present in some 15 m of strata at the base of the succession, immediately above the Portland Sandstone (Howitt, 1964; Anderson & Bazley, 1971) (Fig. 3). Three of these seams have been worked in the past but only the lowest (No.4 seam) is worked at the Mountfield mine, which opened in 1876. The highest (No. I seam) and No .4 seams are worked at the nearby Brightling mine, which came into production in 1963 and now accounts for a major proportion of the output. The gypsum is worked by conventional pillar and stall mining techniques, with extraction rates of 75 per cent, and it is estimated that some 25 per cent of the Sa nd

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total United Kingdom gypsum output in 1973 of 3,849,000 tonnes was derived from these mines (Notholt & Highley, 1975). Gypsum from the Mountfield mine is used principa1ly by the cement industry as a retarder in Portland cement, but material from the Brightling mine is used in the manufacture of plaster and plasterboard. On average the gypsum seams contain about 80 per cent gypsum. The main impurities, forming about 20 per cent of the mined rock , are shale , dolomite and anhydrite, and these are removed by heavy media separation from the Brightling production. These rejects can be further treated by heavy media separation to yield a dolomite by-product, for use as coated roadstone. An interesting feature of the Mountfield mine is that after the No.4 gypsum seam has been removed , the top 1·5 m of the underlying Portland Sandstone is extracted and sold as crushed , screened and coated aggregate for roadstone, and provides one of the few indigenous sources of hard rock suitable for aggregate in south-east England. From the limited amount of borehole information available, evaporites at the base of the Purbeck Beds are known to occur over a large part of southern England, corresponding to the Dorset-Weald Jurassic basin (Holliday & Shephard-Thorn, 1974). However, commercia1ly exploitable deposits of gypsum are usually formed by the hydration of anhydrite where the latter approaches the surface through uplift or erosion, or at depth where anhydrite is in contact with water-bearing strata. Commercial deposits of gypsum rarely occur at great depth , and in the Weald anhydrite is thought to be dominant below about 250 m. Potentially workable reserves of gypsum in the Weald are confined, therefore, to the vicinity of the major inliers, with anhydrite becoming increasingly more abundant with depth . 7. LIMESTONE AND SANDSTONE Hard, sandy limestones, known as Kentish Rag (or ragstone), form part of the Hythe Beds of the Lower Greensand of Kent and extend from Seven oaks to Hythe. The ragstone beds, usually between 0 ·15 m and I m or so thick, are interbedded with a loosely cemented calcareous, argillaceous sandstone known as 'hassock'. The thickness of the Hythe Beds varies considerably along the outcrop in Kent from an average of 30 m in the Ightham-Maidstone area to 10 m in eastern Kent, with ragstone comprising a variable proportion of the total, ranging from about 50 per cent at Ditton to 20-25 per cent at Borough Green (Anon, 1967). Northward, towards the Downs, the rags tone thins out. Kentish Rag has been an important building stone in the past and was widely used in Roman and medieval times and again during the nineteenth century. During the twent ieth century, however, ragstone has become an important local source of roadstone and concrete aggregate and provides, with the exception of the roadstone mined at Mountfield, the only source of hard rock suitable for crushing in south-east England in close proximity to the London market. The limestone has a variable, but sufficiently high crushing strength for it to be used as coated roadstone, but it is not resistant to polishing and is rarely used in the wearing course. Large-scale quarrying is carried out between Borough Green and Maidstone (Fig. I), but in eastern Kent , quarrying has now largely been abandoned. Production of ragstone in 1969, when there were nine operating quarries, was approximately 600,000 tonnes (Somerset County Council, 1971). However , only four ragstone quarries are being worked at present and production must now be considerably less than this figure . Workable reserves of ragstone have been estimated at about 14 million tonnes of which less than 8 million tonnes has planning consent (Somerset County Council, 1971). The cost of extraction is high, however, owing to the presence of large amounts of hassock, which have to be separated from the limestone either by heavy media separation, as at the Borough Green Quarry (Anon, 1967), or selective mining. The sandy beds are usually treated as waste although some is sold as concreting sand, industrial filler, hardcore and fi1l. The 'rag and

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hassock' facies of the Hythe Beds also occurs in West Sussex, east of the Arun, but is not commercially exploited as aggregate. Thin beds of shelly limestone, 'Paludina' limestone, within the Weald Clay were formerly exploited as an ornamental building stone and known locally as 'Sussex Marble'. A variety of sandstones within the Hastings Beds, Lower Greensand and Upper Greensand have been worked for building stone in the past, but the rocks are usually porous and have low crushing strengths and are unsuitable for use as good quality aggregate. The Hythe Beds near Fittleworth are quarried for hardcore and fill, with minor amounts for building and walling, and Bargate Stone, a calcareous sandstone, is quarried at Churt in Surrey for similar purposes. MInor quantities of Bargate Stone are produced near Midhurst mainly to repair bridges , and at West Hoathly in West Sussex there is a small building stone industry based on the Ardingly Sandstone (Lower Tunbridge Wells Sand) . Production of sandstone in Sussex and Surrey amounted to 167,000 tonnes in 1972. As previously mentioned, calcareous sandstone is mined from beneath the No.4 gypsum seam at the Mountfield Mine, near Robertsbridge. 8. FULLER'S EARTH Since ancient times many clays and some silts have been referred to as 'fuller's earth' because they had the ability to absorb oil, grease and colouring matter, and were therefore used for cleansing or 'fulling' woollen cloth. This has lead to some confusion in terminology, but in the United Kingdom the term 'fuller's earth' is now restricted to a clay consisting essentially of the clay mineral montmorillonite, in which calcium is the main exchangeable cation present. Fuller's earth was produced in the Weald near Redhill as early as Roman times and this area is still the main centre of production in the United Kingdom today. The structure of the clay mineral montmorillonite is such that exchangeable cations, usually calcium and sodium, are loosely held on the surface of the mineral to balance negative charges within the crystal lattice. These exchangeable cations are easily removed so that calcium may readily be replaced by sodium. Sodium montmorillonite does not occur naturally in Britain, but because it has physical properties of considerable industrial importance it is produced from fuller's earth simply by the addition of small quantities of sodium carbonate. A major proportion of the fuller's earth produced in Britain today is converted to sodium montmorillonite or commercial bentonite. Bentonite is used principally as a bonding agent in foundry moulding sands, and as a suspension agent in oil-well drilling muds and for various civil engineering applications. Natural fuller's earth is used as an absorbent and carrier, and acid-activated fuller's earth, produced by treating the clay with either sulphuric or hydrochloric acid, is used mainly for glyceride oil refining and as a catalyst (Highley, 1972). Lenticular beds of fuller's earth occur intercalated with calcareous sandstones in the Sandgate Beds of the Lower Greensand between Redhill and Godstone. The beds vary considerably in thickness, quality and extent and only the lowest, thickest bed, averaging 2 m to 3 m and attaining a maximum of 5 ·5 m, is worked between Redhill and the village of Nutfield, where the Sandgate Beds attain their maximum thickness of 21 m (Dines & Edmunds, 1933). The beds dip northwards at between 5° and /00 and the fuller's earth thins out northwards beneath increasing overburden. Up to 25 m of overburden is now being removed to work some 2 m of fuller's earth, and some of this overburden, consisting of loosely consolidated, clean sands of the Folkestone Beds, is sold as building and asphalting sand. The fuller's earth beds were originally thought to thin out at Bletchingley (Dines & Edmunds, 1933), but recent drilling has shown fuller's earth to be present in this area (S . E. Coomber, personal communication, 1975). Moreover, beds of fuller's earth up to 1· 2 m thick are exposed in the overburden of a sand-pit working the Hythe Beds south-east of

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Bletchingley and are removed as a by-product of this operation. Beds of fuller's earth 0·6 m to 0·7 m thick are present south of Godstone, but farther east, towards Tandridge, the Sandgate Beds are poorly exposed and fuller's earth is not recorded by Dines & Edmunds (1933). Fuller's earth also occurs within the Sandgate Beds at Maidstone. This was an important centre of the fuller's earth industry in the seventeenth century, and although production declined subsequently, it was resumed during the mid-1950s and still continues. Fuller's earth occurs mostly as a single seam some 1·8 m thick at the top of the Sandgate Beds and appears to be almost continuous between Maidstone and Bearsted, but only traces are present east of Leeds (Worssam, 1963). West of Maidstone the fuller's earth gradually thins out and crops out intermittently between Leybourne and Ditton, where it is only 0·3 m thick. Numerous outliers of Sandgate Beds occur south of Leybourne and on Barming Heath, and overgrown pits suggest that fuller's earth was formerly worked in this area (Worssam, 1963). Recent production has been at Bearsted and Grove Green, and quarrying still continues at the latter locality. The fuller's earth bed dips to the north-east and appears to thicken in this direction as 3 m was discovered at a depth of 70 m in a borehole at Thurnham (Worssam, 1963). However, it is extremely unlikely that this material could ever be worked. Elsewhere within the Lower Greensand of the Weald 'fuller's earth' has been recorded at a number of localities. Thin beds of montmorillonitic clays 0·23 m to 0·6 m thick are known in Kent at the top of the Sandgate Beds north of Saltwood and west of Sandgate and near the base of the Folkestone Beds at Willesborough Lees, near Ashford (Smart, Bisson & Worssam, 1966). Material described as 'fuller's earth', 1·2 m thick, was found in a well at Henfield in Sussex (Whitaker & Reid, 1899), and 'fuller's earth' is also reported to have been extracted from the Hythe Beds near Tillington, west of Petworth (Topley, 1875; Hunt, 1860). Fuller's earth is also believed to have been produced near Headley in Hampshire. 9. HYDROCARBONS The Jurassic and to some extent the Lower Cretaceous rocks of the Weald have been known for many years to contain traces of oil and gas. Small surface seepages of oil have been recorded, mainly from the Tunbridge Wells Sand (Reeves, 1948), and wells put down for water in the vicinity of Heathfield, East Sussex, in 1894-6 encountered natural gas, probably in the Purbeck Beds. The gas was used to light the railway station at Heathfie1d until it closed in 1964(Bristow & Bazley, 1972). The Brightling gypsum mine was also declared a 'safety light mine' in 1965 following an emission of methane gas from No. I seam. Exploration has generally been aimed at favourable anticlinal structures in potential reservoir rocks such as the Inferior Oolite, Great Oolite, Corallian Beds, Portland Beds and Ashdown Beds (Bristow & Bazley, 1972). Results have been disappointing, however, and only small quantities of oil and gas have been discovered (Falcon & Kent, 1960), although undisclosed amounts of gas were encountered in a borehole drilled in the early 1960s at South Godstone in Surrey (Padgham, 1967). Two mining licences are held for this area although no production has taken place to date. 10. CONCLUSIONS The Weald has a wide variety of mineral resources, particularly those of importance to the building industry, and a major proportion of the mineral output of the area is consumed in one form or another, in the production of concrete, mortar, roadstone, building bricks, cement, plaster and plasterboard. Reserves of gravel, and particularly limestone, are limited, but the Weald possesses very large and extensive reserves of chalk, clay and sand. Fuller's earth, although of limited extent, is of considerable economic importance because of its many industrial

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applications and high value. The Weald also possesses important reserves of silica sand and gypsum, the output of both minerals accounting for a significant proportion of the respective United Kingdom totals. ACKNOWLEDGMENTS The author would like to thank his colleagues at the Institute of Geological Sciences for their comments and helpful advice and, in particular, Dr. R. N. Crockett for his assistance. Thanh are also due to the numerous mineral operators in the Weald who supplied information on their products. This paper is published by permission of the Director, Institute of Geological Sciences. REFERENCES ANON, 1967. Borough Green ragstone quarry. Quarry Mgrs' J,. 51, (II), 433-6. ANDERSON, F, W, & R. A. B. BAZLEY. 1971. The Purbeck Beds of the Weald (England). Bull, geo/. Surv. Gt Br.. 34, 173 pp. BEAVER, S. H. 1968, The Geology ofSand and Gravel, Sand and Gravel Association of Great Britain, London. 66 pp. BOSWELL, P. G. H. 1918. A Memoir on British Resources ofSands and Rocks used in Glass-making. 2nd edn. Longmans, Green & Co., London, 183 pp. BRISTOW, C. R. & R, A. BAZLEY. 1972.Geology ofthe country around Royal Tunbridge Wells. Mem, geol. Surv. UK. 161 pp. BRITISH STANDARD 2975: 1958. Sand for Making Colourless Glasses, British Standards Institution, London. BUTTERWORTH, B, & D. B. HONEYBORNE. 1952. Bricks and clays of the Hastings Beds. Trans. Br. Ceram, Soc., 51 (4), 211-59. CUMMINGS, R. H. & H. R. BICHAN. 1970. Economic geological appraisal of British carbonate deposits. Proc. 9th Commonw, Min. metall. Congr., 2, 431-74.The Institution of Mining and Metallurgy, London, DINES, H. G, & F. H. EDMUNDS. 1933. The geology of the country around Reigate and Dorking. Mem. geo/. Sur v, U,K. 204 pp. DINES, H. G., S. BUCHAN, S. C. A. HOLMES & C, R. BRISTOW. 1969. Geology of the country around Sevenoaks and Tonbridge. Mem. geol. Surv. UK. 183 pp, FALCON, N. L. & P. E. KENT. 1960. Geological results of petroleum exploration in Britain 1945-1957. Mem. geol. Surv. Lond., 2, I-56. GRIMSHAW, R. W. 1971. The Chemistry and Physics of Clays and Allied Ceramic Materials, 4th edn, Ernest Benn, London. 1024 pp. HIGHLEY, D. E. 1972. Fuller's Earth. Mineral Dossier, Miner. Resour. consult, Comm. NO.3, H,M, Stationery Office, London. 26 pp, HOlLiDA Y, D. W, & E. R. SHEPHARD-THORN. 1974. Basal Purbeck evaporites of the Fairlight Borehole, Sussex, Rep. Inst. geol. Sci., No. 74/4, 14 pp. HOWITT, F. 1964. Stratigraphy and structure of the Purbeck inliers of Sussex (England). Q. Jl geo/. Soc, Lond.. 120, 77-108.

HUNT, R. 1860. Mineral stanstics of the United Kingdom of Great Britain and Ireland. Part II for 1858. Mem. geol. Surv. U.K. 379 pp. KEELING, P. S. 1963, The Geology and Mineralogy of Brick Clays. Brick Development Association, london. 83 pp. KEELING, P. S. 1970. Nature and appraisal of clay deposits. Proc. 9th Commonw. Min. metall. Congr., 2,475-93. The Institution of Mining and Metallurgy, london. MINISTRY OF TOWN AND COUNTRY PLANNING. 1950. Report of the Advisory Committee on Sand and Gravel. Part 5: Wessex. 43 pp. NOTHOLT, A. J. G, & D. E. HIGHLEY. 1975. Gypsum and anhydrite. Mineral Dossier. Miner. Resour. consult. Comm. No, 13. H.M. Stationery Office, London. 38 pp. PADGHAM, R. C. 1967. Industry and Wealden geology. Geol. Jl Queen Mary Coli.. 15,31-52. REEVES, J. W. 1948. Surface problems in the search for oil in Sussex. Proc. Geol. Ass" 59, 234-69. SEGROVE, H. D. & R. W. STANYON. 1970. Processing of British sand for glass-making. Proc. 9th Commonw. Min, metall. Congr., 3, 583-601. The Institution of Mining and Metallurgy, London. SMART, J. G. 0., G. BISSON & B. C. WORSSAM. 1966. Geology of the country around Canterbury and Folkestone. Mem. geol. Surv. UK. 337 pp. SOMERSET COUNTY COUNCIL. 1971. Quarrying in Somerset. 349 pp. SWEETING, G. S. 1950. The mineral resources of the Weald. S East s«, 55, 31-9, THURRELL, R. G., B. C. WORSSAM & E. A. EDMONDS. 1968. Geology of the country around Haslemere. Mem. geol. Surv. U,K. 169 pp. TOPlEY, W. 1875. The geology of the Weald. Mem. geol. Surv. UK. 503 pp. WHITAKER, W, & C. REID. 1899. The water supply of Sussex from underground sources. Mem, geol. Surv. U.K. WORSSAM, B. C. 1963. Geology of the country around Maidstone. Mem. geol. Surv. UK. 152 pp.

Received 3 May 1975 Revised version received 22 October 1975