Content and licensingview original scan buy a printed copy

Geology of the country around Ramsgate and Dover. Memoir for 1:50 000 geological sheets 274 and 290 (England and Wales)

By E R Shephard-Thorn

Bibliographical reference: Shephard-Thorn, E R. 1988. Geology of the country around Ramsgate and Dover. Memoir of the British Geological Survey, Sheets 274 and 279 (England and Wales).

• Author
• E R Shephard-Thorn
• Contributors
• Stratigraphy G Bisson P E Harding S Warren
• Biostratigraphy M J Hughes M Mitchell C J Wood
• Sedimentology J Dangerfield G E Strong C W Wheatley
• Geophysics Mrs E A Howells

British Geological Survey

London: Her Majesty's Stationery Office 1988. © Crown copyright 1988 First published 1988. ISBN 0 11 884461 X B. Printed in the United Kingdom for Her Majesty's Stationery Office Dd 240434 C20 1/89 398 12521

• Author
• E R Shephard-Thorn, PhD British Geological Survey, Keyworth
• Contributors
• G Bisson, ARSM, BSc., Rev P E Harding, MA, M Mitchell, BSc., C J Wood, BSc. Mrs E A Howells, BSc formerly of British Geological Survey
• M J Hughes, MSc., G E Strong, BSc., C W Wheatley, BSc British Geological Survey, Keyworth
• J Dangerfield, BSc British Geological Survey, Gray's Inn Road, London
• S Warren, BSc British Coal, Dover

(Front cover)

(Rear cover)

Other publications of the Survey dealing with this district and adjoining districts

Books

• British Regional Geology
• The Wealden District (4th Edition)
• Sheet memoirs
• Geology of the country around Faversham (Sheet 273)
• Geology of the country around Canterbury and Folkestone (Sheets 289, 305 and 306)
• Well catalogues
• Faversham (273) and Ramsgate (274) sheets, 1964
• Dover (290) Sheet, 1964

Maps

• 1:625 000
• Solid Geology (South Sheet)
• Quaternary Geology (South Sheet) Aeromagnetic map (South Sheet)
• 1:250 000
• Thames Estuary: Bouguer gravity anomaly (1982)
• Thames Estuary: Aeromagnetic anomaly (1982)
• Thames Estuary: Solid geology (In press)
• 1:126 720
• Hydrogeological Map of the Chalk and Lower Greensand of Kent (1970)
• 1:50 000
• Sheet 273 Faversham (1974)
• Sheet 289 Canterbury (1982)
• Sheets 305/6 Folkestone and Dover (1974)

Note

All National Grid references sited in the following text lie within the 100 km square TR.

Preface

The original geological survey of the Ramsgate and Dover area at the 'one-inch' (1:63 360) scale was published in 1868 as part of the 'Old Series' Sheet 3. This was recast in the 'New Series' format and published as Sheets 274 and 290 in 1928, incorporating minor additions by F H Edmunds. A joint memoir for the two sheets by H J Osborne White appeared in 1928.

Surveys at the 'six-inch' (1:10 560) scale were carried out in 1960–62 chiefly by E R Shephard-Thorn, G Bisson and P E Harding; small areas of overlap from adjacent sheets had been surveyed by S C A Holmes and S Buchan, in 1938, and J G O Smart, in 1953. The new Sheets 274 and 290 were published at the 'one-inch' scale in 1967 and 1966 respectively and were reissued at the 1:50 000 scale in 1980 and 1977. The author has compiled this short memoir from the notes of the other surveyors and has drawn on manuscripts by the following: Mr G Bisson on the Coal Measures; Mr M Mitchell on the Carboniferous Limestone; Mr C J Wood on the stratigraphical palaeontology of the Chalk; Mrs E A Howell on geophysics; Mr M J Hughes on Tertiary micropalaeontology; Messrs G E Strong and C W Wheatley on the petrology and clay mineralogy of the Thanet Beds; and Mr J Dangerfield on the petrology of the Head Brickearth. The correlation diagram for the Coal Measures has been prepared by Mr S Warren of British Coal, Dover, and is published with their kind permission. The memoir has been edited by Dr A Brandon.

Various individuals and concerns, too numerous to mention here, have assisted with information and access to property, and our grateful thanks are due to them.

F G Larminie, OBE, Director, British Geological Survey, Keyworth, Nottinghamshire. 17 October 1988

Geology of the country around Ramsgate and Dover—summary

Lying in easternmost Kent, the Ramsgate and Dover district is the part of England closest to mainland Europe. Thus there are strong cross-Channel links in both geology and culture. The Chalk dip-slope of the North Downs extends to the sea at the South Foreland, forming part of the famous 'White Cliffs of Dover'. On clear days their counterparts at Cap Blanc-Nez are clearly visible across the 33 km of the Strait of Dover. North of Deal, the Chalk dips beneath Palaeocene strata preserved in the Richborough Syncline, to emerge once more in the broad 'whaleback' anticline of the Isle of Thanet. The Richborough Syncline forms a flat, low-lying area of reclaimed coastal marshland through which the River Stour flows to the sea in Sandwich Bay.

The Middle and Upper Chalk and the Thanet Beds dominate the surface outcrops of the district and are well exposed in the surrounding sea cliffs; they are described generally in this short memoir. The numerous deep boreholes drilled in the Kent Coalfield, which underlies the district, have provided much data on the stratigraphy and structure of the Carboniferous Limestone, Coal Measures, Jurassic and Lower Cretaceous strata, which underlie the Chalk; brief accounts of these concealed formations are given.

The Quaternary period has left a marked imprint on the area notably in the form of periglacial deposits and weathering phenomena and in the coastal deposits laid down in pace with rising sea levels over the past 10 000 years.

Geological sequence in the Ramsgate and Dover district

Within the combined area of the Ramsgate and Dover sheets the following superficial drift deposits (Quaternary) and solid formations (Tertiary and Cretaceous) are present at surface outcrop. The concealed formations include rocks of Upper Palaeozoic and Mesozoic age which are known from boreholes and shafts in the Kent Coalfield.

(Geological succession)

Chapter 1 Introduction

Geology and landscape

The eastern portion of the county of Kent represented on the Ramsgate (274) and Dover (290) geological sheets is the closest part of England to the European mainland. On clear days, the chalk cliffs of Cap Blanc-Nez are easily visible across the 33 km of the Strait of Dover. Because of this proximity there are strong cross-Channel similarities in the geology.

It has long been recognised that the Boulonnais anticline in Northern France is the eastern end of the major Wealden anticlinorium of south-east England. The Chalk escarpment of the North Downs, which forms the northern limb of the Wealden structure, meets the sea between Folkestone and Kingsdown giving rise to the 'White Cliffs of Dover' (Plate 2). The cliffs on the French side continue this structural pattern. Recent borings and geophysical surveys for the Channel Tunnel project have proved the continuity of the Chalk across the Strait of Dover.

The Chalk is the thickest and most widespread formation at outcrop and has been the dominant element in the development of the physiography and hydrology of the district (Figure 1) and (Figure 2). Most of the southern area of the Dover sheet lies on the dip-slope of the North Downs escarpment. At the foot of the dip-slope, in the north of the sheet, and continuing onto the Ramsgate sheet, Paleocene and Eocene strata are preserved in the Richborough (or Want-sum) Syncline. The Chalk reappears northward in the Isle of Thanet, where it is brought up by the Thanet Anticline. The Richborough Syncline forms a topographical low in which the River Stour flows seaward across a wide alluvial plain formed by the silting up and reclamation of the Wantsum Channel, which formerly isolated the Isle of Thanet. Similar coastal alluvium has accumulated in the Lydden Valley area, north of Deal, which has the protection of a barrier of shingle beach ridges and sand dunes. Offshore, the Goodwin Sands lie within the area of the combined geological sheets; their hydrography and origin has been discussed by Cloet (1954) and Carter (1953).

Previous workers (Coleman and Lukehurst 1967; McRae and Burnham 1973) have noted the close relationship. between geology, scenery and land use in this part of Kent. They have outlined a number of land-use or physiographical regions which are illustrated in

The chief towns are Dover, Deal, Sandwich, Ramsgate, Broadstairs and Margate. Dover, Deal and Sandwich were members of the Cinque Ports, but only Dover now has any real claim to prominence as a port, with its busy cross-channel trade. The Thanet towns are chiefly holiday resorts, although Ramsgate harbour still handles some trade and hovercraft ply from Pegwell Bay. There are few sizeable settlements inland, although many of the villages have churches of some antiquity. An unexpected feature of the rural landscape is the pit-head of Betteshanger Colliery, which exploits the concealed Coal Measures north and west of Deal.

Outline of previous research

The excellent cliff sections in Chalk and Tertiary strata, which virtually surround the present district, have attracted the attention of numerous researchers over the years. Some of the major contributions are briefly mentioned below, but fuller discussions of research will be found in the appropriate chapters which follow.

In the field of Chalk stratigraphy, Phillips (1821) was the first to attempt a lithostratigraphical subdivision of the Chalk of east Kent. Subsequently the French geologists Hebert (1874) and Barrois (1876) introduced biostratigraphical concepts of zonation, which they had developed in their own country. Further refinement was provided by Rowe (1900), whose detailed studies of the evolution of Micraster and other echinoderms gave a stronger basis for zonation. Jukes-Browne's memoirs on the Chalk of Great Britain (1903, 1904) include discussions of sections within the area. More recently, boreholes drilled for the proposed Channel Tunnel have provided valuable lithological and microfaunal data for the Lower Chalk (Destombes and Shephard-Thorn, 1971, 1972; Carter and Destombes 1972; Carter and Hart, 1977). The stratigraphy of the Chalk of the North Downs has recently been revised by Robinson (1986a).

The Thanet Beds are well exposed in the low cliffs of Pegwell Bay, near Ramsgate, and were first described by Prestwich (1852) and subsequently by Whitaker (1872) and Gardner (1883). The foraminiferal faunas of this type-section were originally studied by Burrows and Holland (1897) and more recently by Haynes (1954, 1956, 1957, 1958a, 19586, 1958c). The succeeding Woolwich Beds were also described by Prestwich (1854) and Whitaker (1872). A modern review of their occurrence has been provided by Hester (1965). In recent years, papers by members of the Tertiary Research Group have added to our knowledge of these formations and their faunas.

The presence of concealed Coal Measures beneath east Kent was predicted by Godwin Austen in 1856, but was not proved until 1890 when the opportunity was taken to sink a deep borehole on the site of the abortive Channel Tunnel works at the foot of Shakespeare Cliff, west of Dover (Sheet 306). Approximately 40 deep boreholes were subsequently sunk by various commercial undertakings to aid the exploration and development of the Kent coalfield. The story of these early years has been recorded by Ritchie (1920). The separate development of different parts of the coalfield delayed the establishment of a unified correlation system. An early account of the stratigraphy and faunal sequence in the coalfield was given by Bolton (1915), but Dines (1933, 1945) was the first to attempt a comprehensive correlation. Later developments in the study of the stratigraphy of the coalfield were reported by Stubblefield and Trueman (1946), Bisson, Lamb and Calver (1967) and Calver (1969). The last-named established the presence of Westphalian A, B, C and D substages in Kent.

The borings for coal penetrated the Chalk, Gault and Lower Greensand and proved the presence of an attenuated series of Jurassic formations overlapping onto the eroded surface of the Coal Measures, which here form part of the Palaeozoic London–Brabant massif. The Jurassic sequences in these boreholes have been described by Lamplugh and Kitchin (1911), Lamplugh, Kitchin and Pringle (1923) and Bisson, Lamb and Calver (1967).

A variety of drift deposits, including Clay-with-flints, Head, Head Gravel, Head Brickearth and Dry Valley and Nailbourne deposits, occur on the Chalk and Tertiary outcrops of the district. In some instances their distribution shows a strong relationship to topography. Head Brickearth is important agriculturally because of the good fruit-growing properties of the soils developed on it. It generally has a large wind-blown silt content, and may be classified in part as a loess, as was first demonstrated in exposures at Pegwell Bay by Pitcher, Shearman and Pugh (1954).

The development of the coastline in historical times has been studied mainly by historians and physical geographers. Interest has centred on the silting up of the former Wantsum Channel, which once isolated the Isle of Thanet from main land Kent (Hardman and Stebbing, 1940, 1941, 1942), the coastal evolution of Sandwich Bay and the origin of Goodwin Sands (Robinson and Cloet, 1953; Carter, 1953; Cloet, 1954).

Chapter 2 Concealed formations

From the results of the numerous boreholes put down to prove and develop the eastern part of the Kent Coalfield, we know that the following Mesozoic and Palaeozoic formations are represented beneath the Chalk and Tertiary strata.

Devonian rocks have not been proved by boreholes sited within the district, but their presence has been established by drilling in the areas of the adjacent Faversham (273) and Canterbury (289) Sheets (Holmes, 1981, Smart and others, 1966). The characteristic Old Red Sandstone lithologies of red and green mottled sandstones were noted. On this evidence and that of geophysics (Shephard-Thorn and others, 1972) it is considered probable that Devonian rocks underlie the Mesozoic rocks of northern Thanet and extend southwards beneath the Carboniferous rocks of the Kent Coalfield.

Carboniferous

Carboniferous Limestone

Limestones of Dinantian age underlie the earliest Coa Measure rocks and have been proved in fourteen borehole in the present district (Figure 4). Their age has been reviewed by Mitchell (1981) and his work indicates that all the provings within the district are of Viséan (Upper Dinantian; age. In each case, where direct faunal evidence is available. the rocks have been assigned to the Holkerian Stage (Georg( and others, 1976) approximately equivalent to the Seminula Zone (S2) of the coral-brachiopod zonation of Vaughar (1905). Older Dinantian rocks have been penetrated in the Trapham and Harmansole boreholes near the western margin of the coalfield (on Sheet 289).

There is no complete drilled section of the Carboniferous Limestone in the Kent Coalfield and no indication of its total thickness, as for the most part, boring did not extend far beneath the Coal Measures. The maximum thickness penetrated in the present district is 70.1 m, in the Ebbsfleet Borehole. To the west, 135 m of Dinantian rocks, assigned to the Holkerian and Ivorian stages, were proved in the Trapham Borehole. It is probable that the Dinantian rocks are up to 300 m thick beneath the coalfield. The geophysical evidence suggests a slight eastward thickening. The available evidence from the boreholes within the district is summarised in (Table 1).

The lithologies represented in borehole cores of the Dinantian rocks include calcite-mudstones, oolitic limestones and bioclastic limestones; thin interbeds of mudstone, siltstone or sandstone have been noted in some instances. The above carbonate lithologies may occur as thick, relatively homogenous units, mixed banded units or as mixed lithologies. Colours range from pale creamy grey to bluish grey and brownish black. Traces of possible dolomitisation have been noticed and some of the darker limestones are carbonaceous. The calcite-mudstones commonly show banding which in some cases are of a definite stromatolitic or algal origin; structures comparable to the stromatactis' of reef limestones have also been noted. Other limestones have small drusy cavities lined by sparry calcite, with apparently oily inclusions. Stylolitic sutures are commonly developed in the limestones, as are calcite veins on joints and tension gashes. The stylolites appear to predate the Westphalian, suggesting that diagenesis of the Dinantian limestones was well advanced by that time. The lithologies suggest that deposition of the Dinantian limestones took place in relatively shallow, quiet waters with little input of terrigenous sediment.

Coal Measures

The Kent Coalfield lies in an elongated WNW–ESE synclinal basin whose limits are poorly defined, and possibly faulted in part. The eastern portion of the coalfield underlies the whole area of the Dover sheet and the southern part of the Ramsgate sheet (Figure 5). Recent deep boreholes suggest that the coalfield basin may comprise two subsidiary troughs separated by an anticlinal structure to the south-west of Snowdown and Tilmanstone collieries. In the northern trough, the deepest part lies in the area between Waldershare and St Margaret's-at-Cliffe, where the St Margaret's Bay Borehole penetrated 860 m of Coal Measures, terminating an estimated 20 m above their base (at about 1160 m below OD). The form of the southerly trough is less well known, but its axis may lie south-west of Dover. The maximum known thickness of Coal Measures within it was proved in the Swanton Court Borehole [TR 2386 4431] on Sheet 289, where up to 968 m were deduced to be present (by extrapolation to the inferred position of the base of the Coal Measures).

The Kent Coal Measures sequence (Figure 6) differs in lithology and fauna from most other British coalfields, but correlation has proved possible with the aid of several marine bands and diagnostic non-marine bivalve assemblages. Calver (1969) has shown the equivalents of Westphalian A, B, C and D to be present in the Kent sequence, though there appear to be gaps at some levels. The correlation of Westphalian A, B and C strata in some selected borehole and colliery sections is shown in (Figure 7), which has been prepared by Mr S Warren of British Coal, Dover.

The nature of the Carboniferous Limestone floor beneath the Coal Measures has been discussed by Bolton (1915) and Dines (1933). The contours on this surface are broadly parallel to those on the Kent No. 6 seam (Rumsby, 1972, (Figure 1) and (Figure 4)). From this and the almost ubiquitous presence of Holkerian strata beneath the unconformity, it would appear that Westphalian A sedimentation commenced on a fairly flat and structurally simple erosion surface. As seen in borehole cores the surface of unconformity is sharp, and there is little sign of deep weathering of the underlying limestones despite the complete absence of Namurian rocks. In a few cores the limestone surface has been shown to be fissured, with infills of arenaceous and pyritous Westphalian A sediments extending for several metres below the unconformity.

The Coal Measures are unconformably overstepped by Mesozoic rocks (p.10). The sub-Mesozoic erosion surface undulates slightly, being shallower than 260 m below OD south of Deal and in general declining to the north-west and south-west to levels beneath 335 m below OD. The variation in depth of this surface is probably partly due to faulting; folding and pre-Mesozoic erosion have also played a part.

The Coal Measures comprise a suite of mudstones, silty mudstones, siltstones and sandstones, with seatearths and coal seams, which were laid down in a series of cyclothems (i.e. cycles of deposition). In each cyclothem, lithological variations reflect changes in depositional environment consequent on climate, relief of the source areas and rate of subsidence in the basin. The so-called 'marine bands' are usually black shaly mudstones with a shelly marine fauna, and represent wide-ranging marine transgressions over the coal swamps. Certain of these marine horizons are traceable throughout the coalfields of northern Europe, and are an invaluable basis of correlation.

Dines (1933) recognised two broad lithostratigraphical subdivisions in the Kent Coal Measures, namely, a lower 'Shale Division', about 215 m thick, and an upper 'Sandstone Division', up to 670 m thick (Figure 6). The Shale Division includes the Lower and Middle Coal Measures with eight main coal seams and four marine horizons. The Sandstone Division, equivalent to the Upper Coal Measures, has six main coal seams.

The broad framework of seam correlation in the Kent Coalfield (Dines, 1933, 1945), recognised the occurrence of fourteen generally persistent seams, numbered from 1 to 14 in descending order, characterised by their coal properties and associated lithologies and fauna. This correlation superseded the previous notation based on individual collieries. It was slightly modified by Bisson and others (1967) who took the sequence in the Ripple Borehole [TR 3432 4997] (see (Figure 7)) as the standard for the coalfield. Further modifications by Mr S Warren, of British Coal, with biostratigraphical assistance from Drs M A Calver and N J Riley of BGS, were necessitated in the light of recent boreholes. Westphalian A, B and C are now termed the Langsettian, Duckmantian and Bolsovian stages respectively. The faunal zones referred to in the following text are chronozones i.e. time-zones.

Lower Coal Measures (Westphalian A)

The rocks immediately overlying the eroded surface of the Carboniferous Limestone are described in borehole records as pyritous sandstone or sandy 'bind' (sandy mudstone) with black shale or 'bind'. The Dinantian–Westphalian unconformity is not marked by a conspicuous basal conglomerate.

In a few cases, these basal sands fill karstic fissures several metres deep in the surface of the underlying limestone. Bioturbated mudstones with Planolites opthalmoides, bivalves and ostracods have been noted close above the surface of the Carboniferous Limestone in several boreholes and appear to mark a weak marine episode. In the absence of diagnostic fossils, the zonal age of these rocks cannot be determined.

The strata above, up to the Kent No. 14 seam, are dominantly mudstones, with some minor sandstones; thin dark limestone bands have been also noted in one or two sections. Fossils from these rocks include fish, trace fossils and bivalves, indicative of a horizon close to the base of Westphalian A.

Black silty mudstones, above the Kent No. 14 seam, have yielded foraminifera and fish scales indicative of marine influences. The strata up to and including this marine horizon have been assigned to the Anthraconaia lenisulcata Zone.

The measures above include the Kent No. 13 and No. 12 seams, with seatearths and some sandstone, in a dominantly mudstone sequence. Bivalve faunas include species characteristic of the Carbonicola communis Zone.

Middle Coal Measures (Westphalian B and C (lower part))

The Ripple Marine Band, occurring immediately above the Kent No. 12 seam, is a unit of dark grey, sandy mudstones with a rich marine shelly fauna (individual shells tend to be very small) containing the goniatite Donetzoceras vanderbeckei. This discovery has enabled it to be firmly correlated with the marine horizon marking the base of the Middle Coal Measures throughout the British and North European coalfields (Stubblefield and Trotter, 1957). The marine strata generally occur as a single bed, up to 8.8 m thick (in the Kingsdown Borehole [TR 3717 4922]), but in underground boreholes north and west of Betteshanger Colliery shafts they split into two or three parts separated by seatearths, with some minor coals, so that the marine fauna ranges through as much as 20.7 m of strata.

Mudstones with some sandstones above the Ripple Marine Band, contain fossil plants locally. The sedimentary rhythm below the Kent No. 11 seam has yielded non-marine bivalves suggestive of the late part of the Anthracosia modiolaris Zone. Shells above the Kent No. 11 seam indicate the earliest Lower Anthracosia similis–Anthraconaia pulchra Zone, the base of this zone being taken for convenience at the base of the Kent No. 11 seam (Bisson and others, 1967, p 160). Two faunal bands between the Kent No. 10 and No. 9 seams are also referred to the Lower similis-pulchra Zone.

Considerable variations in thickness and difficulties in correlation affect the Kent No. 9 and No. 8 seams and associated strata. The seams are often close together and of workable thickness (about 1 metre). Mudstones and silty mudstones predominate between the Kent No. 8 and No. 7 seams and have yielded Lower similis-pulchra zone bivalve faunas. The Kent No. 7 seam has previously been worked in Betteshanger Colliery and the abandoned Chislet Colliery, where it averaged slightly over a metre in thickness. Above this seam there is commonly a group of three or four thin coal seams, constituting the 'G' group of Betteshanger and interspersed with mudstones, thin sandstones and seatearths. They are excluded from Dines' scheme and are conventionally labelled G1 to G4 in descending order. Associated bivalve faunas suggest an horizon in the late part of the Lower similis-pulchra Zone. In the mudstones above the top coal of the 'G' group, the Snowdown Marine Band, with Lingula, Hollinella and the faecal pellets known as Tomaculum, correlates with the Haughton Marine Band of the Pennine coalfields.

Several seatearths, sometimes with thin coals above, occur in the strata between the Snowdown and Lower Tilmanstone marine bands. The latter is believed to correlate with the Cefn Coed–Mansfield (A. aegiranum) marine horizon of other British coalfields and marks the base of Westphalian C. It contains a varied marine fauna, notably "rich in brachiopods. The marine band is up to 13.7 m thick in the Ringwould Borehole [TR 3529 4812] and 21.6 m in the St Margaret's Bay Borehole [TR 3665 4533]. Records of a supposed Upper Tilmanstone Marine Band, between the Lower Tilmanstone Marine Band and the Kent No. 6 seam, in the Ripple and Tilmanstone No. 3 Shaft boreholes have not been confirmed in subsequent boreholes.

About 8 m above the Lower Tilmanstone Marine Band, a non-marine bivalve fauna suggests the presence of the Upper similis-pulchra Zone. Available evidence in the Kent Coalfield indicates that the latest part of the similis-pulchra Zone and the A. phillipsii Zone may be absent or attenuated in thickness. Furthermore, in the absence of a marine band equivalent to the Anthracoceras cambriense horizon of other coalfields, the boundary between the Middle and Upper Coal Measures is arbitrarily taken at the junction of the Shale and Sandstone divisions, i.e. at the base of the major sandstone about 20 m above the Lower Tilmanstone Marine Band. This marine band is absent in the Snowdown No. 5 Underground Borehole, apparently cut out by an erosional channel or 'washout', filled with sandstone. This lends some support for an erosional break at this level.

Upper Coal Measures (Westphalian C (upper part) and D)

The Upper Coal Measures coincide with the Sandstone Division and are dominated by thick sandstone units reminiscent of the Pennant sandstones of South Wales. Of the six numbered coal seams present, only the Kent No. 1 and No. 6 seams have been worked. There are no known marine bands and non-marine faunal beds are thinly scattered through the 670 m of strata.

The medium- to coarse-grained sandstones below the Kent No. 6 seam are up to 30 m in thickness, and are often conglomeratic and highly indurated. The Kent No. 6 seam has been widely exploited in Betteshanger, Snowdown and Tilmanstone collieries, where it varies from 0.9 to 1.2 m thick. Non-marine bivalves associated with Euestheria in the measures immediately above the seam have been referred to the Anthraconauta tenuis Zone. In the apparent absence of the A. phillipsii Zone, the Westphalian C/D boundary is taken at this level. Faunas of similar character occur below the Kent No. 5 seam. A minor but fairly persistent coal has been noted 9 to 36 m above the Kent No. 5 seam in a number of boreholes, where faunas in the roof and 5 to 15 m higher indicate the A. tenuis Zone.

Faunal bands are generally less common and less well known in the higher measures associated with the Kent No. 4 to Kent No. 1 seams. They are all been referred to the A. tenuis Zone (Calver 1969). The Kent No. 1 seam was formerly worked at Snowdown and Tilmanstone collieries.

Jurassic

Boreholes drilled to prove and develop the Kent Coalfield, have demonstrated that beneath Cretaceous rocks, a wedge of Jurassic strata tapers northward over the eroded surface of the London–Brabant massif. The massif, composed of Coal Measures and older Palaeozoic formations, formed a land mass or positive area through much of the Jurassic period and had an important effect on sedimentary patterns.

Many coal borings were cored through the Jurassic rocks to provide information on their lithology and hydrogeology with regard to shaft-sinking and mining operations. The Geological Survey has issued reports on a number of these cored Jurassic sequences (Lamplugh and Kitchin, 1911; Lamplugh, Kitchin and Pringle, 1923; Bisson, Lamb and Calver, 1967).

The proximity of the London–Brabant massif and syndepositional earth movements have led to complicated facies and thickness variations in the Jurassic sequence of east Kent. Important overlaps and unconformities are developed at some horizons. Generally the formations are much thinner than their counterparts to the west, in the centre of the Wealden Basin, but in some instances they retain something of the characteristic lithologies of the Cotswolds and Dorset outcrops, as for example the Great Oolite strata. Because of the paucity of index fossils in the available core materials and the fragmentary nature of the east Kent record, it is difficult to correlate in detail with the rocks at outcrop (Cope and others, 1980a; Cope and others, 1980b). In practice, the broad lithostratigraphic groupings adopted by Lamplugh and others, (1923) remain the most useful for correlation in east Kent and are used here. (Figure 8) illustrates the sub-Cretaceous geology of the district deduced from the coal borings and shafts.

Lower Jurassic

Lias

Liassic strata have been proved in the Chilton and Waldershare boreholes, where they are 6.7 and 1.5 m thick respectively, and 3 m are inferred in the Stonehall Borehole. Lamplugh and others (1923 pp.75 and 81–83) distinguished thin developments of the Lower, Middle and Upper Lias divisions in the 6.7 m of strata penetrated in the Chilton Borehole. The Lower Lias includes 0.6 m of shelly limestones, interbedded with soft oyster-bed partings and with a thin coral-bearing limestone at the base, overlain by 0.6 m of grey clay with rhynchonellid brachiopods. A conglomeratic bed 0.3 m thick marks the base of the Middle Lias and is overlain by 4.0 m of sandy and silty shales with belemnites and shells, interbedded with hard sandy limestone. The Upper Lias is represented by 1.2 m of dark grey, semi-nodular limestones with shells.

The Lias is unconformably overlain and overstepped north-eastward by rocks of the Great Oolite Series because the Inferior Oolite Series (although proved up to 8.2 m in the Dover Colliery shaft to the south) is apparently absent within the district. The approximate northern limit of the Lias is indicated on (Figure 8).

Middle Jurassic

Great Oolite Series

The Great Oolite is the lowest Middle Jurassic formation in the district, and comprises above a locally pebbly base, up to 30 m of chiefly oolitic and sandy limestones, with subordinate clays and marls. From its maximum proved thicknesses, in the Chilton and Stonehall boreholes, it thins northeastwards and eastwards, overstepping the Lias by up to 8 km to rest on the eroded surface of the Coal Measures. As stratigraphically significant fossils are rare in the cores, these beds have been broadly correlated with the Great Oolite Limestone of the Cotswolds on lithological grounds. There is some suggestion within the formation, of a northerly overlap of the higher beds over the lower.

Forest Marble

This thin and variable formation is fairly widely represented in the deep boreholes in the district. It comprises blackish and greenish grey calcareous mudstones with hard nodular and oolitic limestones, and ranges from 1 to 6 m in thickness.

Cornbrash

The Cornbrash is up to 7.7 m thick in the Tilmanstone Colliery Shaft and comprises variable, rubbly to compact, oolitic and shelly limestones with a rich shelly fauna, usually overlain by a thin dark manly clay. There appears to be a stratigraphical break at the base of the formation. Fossil evidence indicates that only the Lower Cornbrash is represented in the boreholes.

Upper Jurassic

Kellaways Beds

Up to 15.6 m of this formation have been proved in the present district. It is variable in lithology, but representatives of both the Kellaways Rock and the underlying Kellaways Clay (1 to 2 m thick) have been recognised. The Kellaways Rock comprises chiefly sandstones and sandy clays, more or less ferruginous and including, in the Chilton and Maydensole boreholes, one or more beds rich in polished brown limoniteooliths, comparable to the 'millet seed' iron ore of the east Kent Corallian. Typical shelly faunas have been obtained from the borehole cores.

Oxford Clay

This formation shows typical and consistent lithological development in the east Kent borings although the thickness is reduced; a maximum of 40 m has been proved in the Guilford Colliery Shaft. Three subdivisions were recognised by Lamplugh and others (1923): at the base, the 'Ornatus Beds' comprise brown and greenish brown manly clays containing bivalves and species of Kosmoceras; these are overlain by the so-called 'Renggeri Beds' which are smooth bluish grey clays with Quenstedtoceras; the topmost division, the 'Mariae Beds' consist of pale, bluish grey clays with Quenstedtoceras mariae and perisphinctid ammonites. The available material has not allowed detailed correlations to be made with the Lower, Middle and Upper Oxford Clay of the outcrop area, but probably most of the zones are represented.

In 1940, workings in the Kent No. 1 seam at Tilmanstone Colliery intersected a NW–SE fault and entered beds high in the Oxford Clay (Bullerwell, 1954; Plumptre, 1959). This led to the recognition of a graben, containing Jurassic rocks, let down into the Coal Measures and unconformably overlapped by Cretaceous rocks. The faulting was thus post-Oxford Clay and pre-Cretaceous in age.

Corallian

These are the youngest Jurassic rocks .proved within the present district. They reduce in thickness from a possible 45.7 m recorded in the Stonehall section, to of 33.8 m in the Chilton Borehole, to 17.4 m in the Bere Farm Borehole and to only 13.1 m in the Guilford Colliery shaft. The details of this thinning are not clear, but in part it is due to pre-Cretaceous erosion. Lamplugh and others (1923) recognised three subdivisions in east Kent, namely Lower Corallian, Corallian Limestone and Upper Corallian. The Lower and Upper divisions are lithologically similar, comprising clays and marls, marlstones and rubbly oolites with minor beds of impure limestone. These divisions commonly contain brown polished limonite grains, locally sufficiently abundant for the rock to constitute 'millet seed' iron ore. The middle division comprises pale coralline limestones.

Within the present district, there is no direct evidence of Upper Corallian strata but typical Corallian Limestone was penetrated in the Chilton and Stonehall boreholes. To the south-west the Upper Corallian passes up into Kimmeridge Clay; although this has not been proved within the district its presence is inferred in the south-west corner (Figure 8).

Cretaceous

Wealden

Reactivation of older faults in late Jurassic times gave rise to a block-faulted terrain in east Kent. This relief was considerably eroded prior to the deposition of the earliest Wealden rocks (Figure 8). Like their counterparts in the Weald, the concealed Wealden rocks beneath the area were laid down in dominantly freshwater environments.

Up to about 18 m of Wealden rocks comprising both the Hastings Beds and Weald Clay, have been proved in the district. The Hastings Beds, 0 to 10.7 m thick, are developed in a coarse, commonly pebbly, sand facies, with minor siltstones and mottled clays, and have yielded lignite and identifiable plant fossils. The Weald Clay, up to 17.7 m thick, comprises pale bluish grey, commonly finely laminated, silty mudstones and muddy siltstones, with freshwater bivalves, ostracods and fish.

The Hastings Beds appear to be thickest in the south-west of the district and to thin generally to the east and north-east, infilling two valleys or embayments eroded in the underlying surface of Jurassic and older rocks (Allen, 1967, fig. 2, p.30). The most northerly provings are in the Fleet and Ebbsfleet boreholes, where the Hastings Beds rest on the Coal Measures.

The Weald Clay is more widespread and uniform than the Hastings Beds, but appears to have suffered some erosion prior to the deposition of the Lower Greensand.

Lower Greensand

Lower Greensand rocks probably underlie the entire district: They represent a widespread marine transgression of Aptian age and extend into the Lower Albian Stage. The component formations of the coastal area between Hythe and Folkestone, thin and rapidly change character as they are traced down dip beneath the younger Cretaceous rocks of the district. The maximum thickness of the Lower Greensand proved below the district is about 26 m, compared with up to 115 m in the Folkestone area.

The lithological changes and indifferent borehole descriptions make subdivision of the Lowei Greensand into the formations seen at outcrop difficult. At the base, characteristic chocolate-coloured mudstones in borehole sections indicate the widespread occurrence of the Atherfield Clay beneath the area of the Dover sheet. It is overlain by rocks of 'Sandgate Beds' type, including muddy and 'loamy' glauconitic sands and clays. At the top of the sequence a thin bed of coarser, cleaner glauconitic sand of 'Folkestone Beds' aspect occurs; the upper part of this bed is usually indurated into a concretionary band of hard calcareous glauconitic grit. Lithologies comparable to those of the Hythe Beds have not been noted. Evidence of an eroded top to the Atherfield Clay may explain this apparent absence.

The only borehole in the Isle of Thanet area to enter the Lower Greensand was a trial for water at Dane Pumping Station, Margate [TR 3656 7017] in 1899 (Whitaker, 1908, p.169). It passed through Gault into 22.6 m of Lower Green-sand without proving the base. Only about 11 m of Lower Greensand were proved in the Fleet and Ebbsfleet boreholes south of the Isle of Thanet.

Gault

The Gault extends at depth across the area and is from 17.4 to 48.0 m thick. It comprises bluish grey mudstones and silty mudstones, with bands of phosphatic nodules and thin glauconitic layers. Fossils are generally abundant including ammonites, bivalves, gastropods and belemnites as well as rarer echinoids and crustaceans. The type section of the Gault is at Copt Point, Folkestone (Sheet 305), where a refined zonal ammonoid scheme has been established (Smart and others, 1966 and Owen, 1975). Numerous widespread layers of phosphatic nodules, marking periods of non-deposition or erosion, are useful markers which, in conjunction with fossils, allow firm correlations over considerable distances. Lower and Upper subdivisions of the Gault are recognised, the boundary being taken at the 'Junction Bed', a prominent double band of phosphatic nodules. These subdivisions coincide with the Lower, Middle and Upper parts of the Albian Stage respectively. The Lower Albian includes the upper part of the Folkestone Beds and the 'mammilmillatum' Bed. Detailed studies (e.g. Owen, 1971a, 1971b, 1975) have shown that the Upper Gault oversteps the Lower Gault extensively in southern England. Variations in Gault thickness are partly due to erosion during a pre-Lower Chalk interval.

At Copt Point, 10.4 m of Lower Gault and 29.8 m of Upper Gault have been recorded. In Dover Harbour, Channel Tunnel Borehole P000 [TR 3342 4137] penetrated 11.6 and 26.8 m of these divisions respectively. Elsewhere the quality of borehole records precludes the subdivision of the Gault, and locally the junction with the Lower Chalk is not firmly fixed. Generally, however, the Gault thins to the north and east with a minimum record of 17.4 m in the Dane Pumping Station Borehole at Margate.

Chalk

The Chalk 'White Cliffs of Dover' (Plate 2) are a world-famous landmark. In this district they are formed by the upper part of the Middle Chalk and the Upper Chalk (see Chapter 3). Between Folkestone and Dover (Sheet 305/306), the Lower Chalk and the lower part of the Middle Chalk are seen in the cliffs, but are carried down below sea level at the foot of Shakespeare Cliff by the gentle north-north-easterly dip and so do not outcrop within the present district.

The Folkestone–Dover cliff sections, although affected by a major landslip at Folkestone Warren, have formed the basis of much previous work on Lower and Middle Chalk stratigraphy (e.g. Jukes-Browne and Hill, 1903, Smart and others, 1966, Kennedy, 1969). Investigations carried out for the Channel Tunnel project have also added to our knowledge of Lower Chalk stratigraphy (Destombes and Shephard-Thorn, 1971, Carter and Destombes, 1972, Carter and Hart 1977).

The Chalk is believed to have been deposited in a shelf sea, up to 300 m deep, which extended over much of northern Europe in late Cretaceous times. This was a period of world-wide rising sea level, when the supply of clastic sedi ments from the land areas was becoming progressively reduced. Thus, in the Lower Chalk, the clay content falls from over 30 per cent to under 10 per cent (Destombes and Shephard-Thorn, 1971). The pure white chalks of the Middle and Upper Chalk, made up largely of innumerable microscopic calcite platelets of the marine algae known as 'coccoliths' (coccolithophorids), are virtually free of terrigenous material. Hardgrounds and nodular chalks represent periods of relative shallowing and increased current activity in the Chalk sea, possibly associated with local tectonic uplifts.

Over twenty boreholes and shafts within the district penetrate the base of the Chalk, but in many cases the records are not sufficiently descriptive to facilitate subdivision. The interval from the base of the Lower Chalk to the top of the Marsupites testudinarius Zone (as measured or estimated where removed by recent erosion) has been used to compare overall Chalk thicknesses. Although reliable isopachytes cannot be drawn, the scattered data show the greatest thicknesses (over 275 m) are concentrated in a 4 km-wide, approximately WNW–ESE belt, including the Stonehall, Waldershare, Bere Farm and St Margaret's Bay boreholes. A slight reduction in thickness to the SSW is noted, but down-dip to the NNE, a marked decrease occurs, with a minimum estimate of 237 m at Dane Pumping Station, Margate. It is not possible to apportion the reduction in thickness to the subdivisions of the Chalk with any confidence, but it seems most likely that the observed northward thinning chiefly involves the Lower and Middle Chalk.

Lower Chalk

The Lower Chalk is broadly equivalent to the Cenomanian Stage, although in Britain some controversy still attends the precise placing of the upper limit of the stage. Near Dover, the formation comprises 80 m of variably argillaceous chalk with its base defined by the Glauconitic Marl and its top by the Plenus Marl (Figure 9). The clay content is considerably higher than in the Middle or Upper Chalk, but it decreases upward from over 30 per cent of the rock to less than 10 per cent. Small-scale sedimentary cycles, 0.3 to 1.3 m thick, are also characterised by an upward decrease in clay content. The more clayey and darker base of each cycle grades upward in paler more calcareous chalk, topped by a burrowed erosion surface. Robinson (1986b) has suggested that the cycles may reflect variations in the strength of tidal currents linked to the Earth's orbital cycles. The typical sequence in the Lower Chalk in one of the Channel Tunnel boreholes (P000 [TR 3341 4146]) is summarised in (Figure 9).

Jukes-Browne and Hill (1903) described the Lower Chalk sequence between Folkestone and Dover, in terms of nine numbered beds and grouped these into three broad lithological units. At the base, resting on the eroded surface of the Upper Gault, the dark greenish grey Glauconitic Marl forms Bed 1. This passes up into the 'Chalk Marl' or Beds 2 to 5, a group of highly argillaceous, bluish grey manly chalks with thin spongiferous limestone beds at the tops of the sedimentary cycles. Beds 1 to 5 were assigned to the Zone of Schloenbachia varians. The 'Grey Chalk', or Beds 6 and 7, comprises less clayey and paler manly Chalk with well marked sedimentary cycles. Bed 7 is composed of coarse gritty chalk with abundant shell debris and conveniently marks the top of the 'Grey Chalk'. The 'White Bed', or Bed 8, is paler and less clayey than the Grey Chalk, and has less distinct sedimentary cycles. The Plenus Marl (Bed 9), named from the belemnite Actinocamax plenus, is a thin but widespread unit of greenish grey marls and limestones (Jefferies, 1963) which completes the Lower Chalk sequence. Beds 6 to 9 were placed in the Zone of Holaster subglobosus.

Kennedy's (1969) review of Lower Chalk stratigraphy in south-east England considerably modified Jukes-Browne's work. He described 14 'bands' of strata (excluding the Plenus Marl) and erected three new faunal zones to replace the earlier varians and subglobosus Zones; these were the Mantelliceras mantelli, Acanthoceras rhotomagense and Calycoceras naviculare (now C. guerangeri) zones in ascending order. Kennedy recognised three faunal assemblages for each of his two lower zones. His Band 9, the Orbirhynchia mantelliana Band forms a useful marker just below the boundary between the Chalk Marl and Grey Chalk, characterised by the abundance of the small rhynchonellid brachiopod O. mantelliana.

Robinson (1986a) has recently proposed a series of new Chalk formations based on with type-sections in east Kent. Within the Lower Chalk, he recognised the following formations in ascending order: East Wear Bay Chalk Formation (including the Glauconitic Marl Member, the 'Chalk Marl' and the 'Grey Chalk' up to base of Jukes-Browne's Bed 7); Abbots Cliff Chalk Formation (including Bed 7 and the 'White Bed') and the Plenus Marl Formation (equivalent to Bed 9).

Site investigations for the Channel Tunnel have led to further stratigraphical refinement. A zonal scheme based on foraminifera was proposed by Carter (in Bruckshaw and others, 1961), which was later developed in conjunction with planktonic/benthonic ratio and calcimetry studies to facilitate detailed correlation between the many boreholes drilled in 1964–65 (Carter and Destombes, 1972, Carter and Hart, 1977). The later work demonstrated a widespread mid-Cenomanian non-sequence in Carter's Zone 11, just above the Orbirhynchia mantelliana Band. A corresponding break in the borehole calcimetry curves (percentage CaCO₃) was taken to define the top of the 'Chalk Marl', the rock selected, because of its ideal engineering properties, as the preferred ground for a bored Channel Tunnel (Destombes and Shephard-Thorn 1971).

Variations in the magnitude of the mid-Cenomanian break mainly account for the changes in the total thickness of the Lower Chalk. Significant variations in lithology and thickness also occur in the lower part of the 'Chalk Marl' division.

Chapter 3 Middle and Upper Chalk

The Middle and Upper Chalk crop out over most of the district, where not concealed by Tertiary and drift deposits. The Middle Chalk is exposed inland only in the Dour valley and tributary dry-valleys, but its higher part is well seen in cliff sections from east of Dover to the South Foreland (Figure 10) and (Plate 1).

The Middle and Upper Chalk, on the geological maps of the district, make up the 'White Chalk' (Rowe, 1900). In contrast to the grey and marly Lower Chalk, they comprise pure white chalks, composed mainly of coccoliths and Inoceramus shell debris with many layers of nodular and tabular flint. The 'White Chalk' is lithologically very variable and contains bands of hard lumpy or nodular chalk (which are in part indurated hardgrounds), thin greyish green marl seams, beds with trace fossils (e.g. Zoophycos) and pyrite nodules (Hancock, 1976, Mortimore, 1986, Robinson 1986a).

Bioturbation is an ubiquitous feature of the Middle and Upper Chalk, although it is seldom conspicuous because of the lack of colour contrast. Most of the nodular flints, which occur in regular bands, are infills of crustacean burrows (Bromley, 1967). Individual flint bands, marl seams and hardgrounds may show great lateral persistence and form valuable markers for local and regional correlation.

Rich Shelly faunas, including sponges, brachiopods, gastropods, bivalves, belemnites, ammonites and echinoderms, occur throughout the sequence and form the basis of the old-established faunal zones listed below:

The labiatus Zone is seen in the cliff sections south-west of Dover, but does not crop out within the district.

The traditional system of faunal zones listed above was employed during the resurvey of the district in the early 1960's, when careful collecting of fossils and measurement of critical sections were carried out to reassess and up-date the work of Rowe (1900), amongst others. The result enabled a zonal map (Figure 11) and cliff sections (Figure 10) and (Figure 12) to be drawn which have helped to elucidate the structure of the Chalk and its unconformity with the Thanet Beds.

More recent work had led to refinements in the bio- and lithostratigraphical correlations of the Upper and Middle Chalk (e.g. Bailey and others, 1983, 1984), requiring minor modifications to some zonal boundaries.

Recently, new lithostratigraphical classifications of the Chalk of the North Downs of Kent and Surrey (Robinson, 1986a), and Sussex (Mortimore, 1986) have unfortunately used separate nomenclatures which can only be correlated by common marker bands (Mortimore, 1987). Neither scheme will be fully expounded here, but Robinson's detailed sections are referred to. A useful comparison of the Cretaceous sequence in Kent with that in the Boulonnais, across the Strait of Dover, has been given by Robaszynski and Amedro (1986).

The local, simplified Middle and Upper Chalk sequence is shown in (Figure 13) and is described here by zone in ascending order.

Zone of Mytiloides [Inoceramus] labiatus (c.18 m)

The base of the Middle Chalk, and of the labiatus Zone, is taken at the top of the Plenus Marl, which approximately marks the position of the Cenomanian–Turonian stage boundary. The Melbourn Rock at the base of the labiatus Zone, is about 10 m thick, and comprises a complex of hard, yellowish white, nodular chalk with irregular subhorizontal streaks and partings of greenish grey marl. It contains abundant shell debris, and was once, consequently, called the 'Grit Bed' (Price, 1877). As it is resistant, it forms a prominent feature on the scarp-face of the North Downs in the adjacent Canterbury and Folkestone district, and is conspicuous in the cliffs between Folkestone and Dover. The rock is accessible in the Aker's Steps cliff path section [TR 297 394] (Smart and others, 1966, p.136; Robinson, 1986a, (Figure 9)). From Aker's Steps, the Melbourn Rock descends steadily to beach level east of Shakespeare Cliff [TR 308 398]. It is known only from boreholes in the present district, notably Channel Tunnel Borehole P000 in Dover Harbour (Figure 9).

The Chalk of the remainder of the labiatus Zone is less nodular than the Melbourn Rock; the nodules being more widely dispersed and not aggregated to form rock bands. The top of the zone is taken at a conspicuous marl seam (Round Down Marl of Robinson, 1986a) about 8 m above the Melbourn Rock. The gentle dip carries the highest beds of the zone below beach level near the south-western end of Dover Harbour (White 1928), just outside the present district.

Zone of Terebratulina lata (c. 54 m)

Middle Chalk of the lata Zone is exposed in the Dour Valley and its tributaries near Dover, and in the cliff sections from the Eastern Arm of Dover Harbour to the South Foreland. The entire thickness of the zone occurs at outcrop, but the lower beds are generally obscured in sections in the old cliffs behind Dover Harbour.

The zone consists for the most part of fairly massive soft white chalk with several persistent marl seams. The faintly nodular or lumpy character of the upper labiatus Zone chalk is maintained through the lower 10 m or so of the lata Zone, up to a pair of marl seams separated by 3.5 m of uniform chalk. Similar uniform chalk continues upward for a further 8 m to another pair of marls, 2.5 m apart. Flint appears for the first time in the sequence as a band of small scattered nodules, 3 m above the highest pair of marls: a stronger band of nodular flint, occurs 1.5 m above, at Lydden Spout [TR 283 388] and Aker's Steps [TR 297 394] south-west of Dover (Robinson, 1986a, (Figure 9)). Some 12 m above the Lydden Spout flint band, a group of four marl seams occurs within 1.2 m of chalk; and was referred to as the 'four-foot' band by Rowe (1900). It forms a marker in the base of the cliffs east of Dover Harbour to Langdon Bay. Several bands of weakly nodular chalk with scattered layers of flint nodules occur in the 5 m of chalk below the 'four-foot' band.

Another prominent marl seam, the Crab Bay Marl of Robinson, 1986a, occurs 8 m above the 'four foot' band; the lower part of this interval contains bands of weakly nodular chalk, and the upper part has several layers of scattered small flint nodules. Above the marl, the chalk is nodular for about 4 m to the base of a conspicuous 1.2 m band of nodular chalk, with many large flints scattered throughout, which is regarded by the Geological Survey as the base of the Sternotaxis planus Zone and Upper Chalk. The precise location of this boundary has been controversial for many years.

Fossils collected from the upper part of the lata Zone exposed in the cliffs east of Dover include Micraster corbovis, M. michelini, Sternotaxis planus, Gauthieria radiata, Isocrinus ? granosus, Gibbithyris sp., Orbirhynchia dispansa, Terebratulina lata, Inoceramus lamarcki, Guettardiscyphia sp. and Spondylus spinosus.

Zone of Sternotaxis planus (15 m)

The complex of hard nodular chalks, marl seams and large flint nodules at the base of the planus Zone is clearly seen in the air-weathered cliff faces below Castle Hill, Dover, but is more conveniently examined in the East Cliff cutting [TR 335 420] and at the bottom of the Langdon Stairs cliff-path [TR 345 425] ((Figure 10)a and (Plate 3)) where it is about 4.0 m thick.

The lowest part of the 'basal complex' is a 1.2 m unit of nodular lumpy chalk with bands of large flints (up to 0.15 X 0.07 m) at its top and base, with scattered smaller flints between. Lumpy chalk, with very few small flints, occurs for 1.0 m above to a strong marl seam 0.05 m thick, the Fan Bay Marl 1 of Robinson, 1986a. A further marl seam, the Fan Bay Marl 2 of Robinson, 1986a, 0.06 m thick, occurs 1.2 m above. This marl has a pair of strong flint bands, 0.36 m below and 0.38 m above it, each with nodules up to 0.06 X 0.18 m. This distinctive Upper Chalk basal assemblage is widespread throughout south-east England.

Above the 'basal complex' there are 3.5 m of softer white chalk with three or more bands of indurated nodular chalk which have yielded the 'reussianum' fauna, comprising various molluscan species, including the ammonite Hyphantoceras reussianum, preserved as hollow moulds. The association of nodular chalks and the reussianum fauna links the lower part of the planus Zone with the Chalk Rock of the Chilterns outcrops, even though the typical massive 'rock' facies is not developed in Kent. The 'basal complex', however, gives rise to a mappable feature marking the base of the Upper Chalk on the flanks of the Dour Valley, near Dover. The upper part of the planus Zone comprises 7.2 m of chalk with bands of flint nodules, with one or more bands of nodular chalk near the base and, at the top, a strongly developed, 0.6 m thick, yellowish nodular chalk (with an upper hardground surface), the 'Top Rock'. The trace fossil Zoophycos is abundant for about 1 m below the 'Top Rock'. Bailey and others (1984) have recommended that the top of the Turonian Stage be taken immediately below the 'Top Rock'.

The planus Zone is richly fossiliferous around Dover and the range of species and faunal assemblages are well known and accurately defined. Some species show apparent ecological preferences: for example, Micraster is abundant above the several hardgrounds low in the Zone.

In the lower part of the zone, the 'reussianum' fauna noted above includes many molluscan species which originally had shells of aragonite rather than calcite; some of the more common forms are: Calliostoma schlueteri, Lewesiceras cf. mantelli, Scaphites cf. geinitzi, Subprionocyclus sp., Hyphantoceras reussianum.

Elsewhere in the zone echinoids are fairly common and include the zonal index Sternotaxis planus with Sternotaxis placenta, Echincorys cf. gravesi, Micraster praecursor, M. leskei, M. corbovis, Cardiotaxis cotteaui and Gauthieria radiata. Plicatula barroisi is a common bivalve and brachiopods are represented by species of Cretirhynchia, Terebratulina and Gibbithyris.

Zone of Micraster cortestudinarium (c.20 m)

This zone occupies the lower part of the Coniacian Stage. It comprises fairly coarse off-white shelly chalk with courses of flint nodules at regular intervals; bands of nodular chalk with occasional hardground surfaces occur in the lower part of the zone. The thickness of the zone is variable in the coast sections north-east of Dover, being about 24 m at East Cliff and about 20 m at Langdon Stairs (Plate 4); this probably reflects the differing amounts of erosion represented by the hard-grounds.

At the base of the zone, a thin marl seam lies immediately above the 'Top Rock' at East Cliff and Langdon Stairs. A half metre-thick, strongly nodular chalk band with fossil sponges and traces of phosphatisation, extends for up to 2 m above the Top Rock. A thinner nodular band, capped by a hardground, lies about 3 m higher, and is followed by a thin tabular flint seam. A band of large flints (the Strood Flint of Robinson, 1986a) occurs about 1.5 m above the tabular flint at Langdon Stairs and is overlain by a further nodular chalk band capped by a hardground. A conspicuous nodular chalk band with hardground (0.8 m thick) has its top 2.4 m above the latter. Finally, another thin nodular band capped by a hardground occurs 0.9 m above and is the highest strongly nodular level in the Upper Chalk, about 10 m above the base of the zone.

The remainder of the zone is in fairly uniform white chalk with regularly spaced flint bands, the top being taken at the higher of two marl seams (East Cliff Marls). A discontinuous tabular flint, about 3 m below the top, was taken by Rowe (1900) to mark the base of the zone (Plate 5). However, detailed work during the survey demonstrated that Rowe had taken the same tabular flint at St Margaret's Bay to mark the base of the overlying coranguinum Zone. Rowe's miscorrelations of the three tabular flint levels exposed along the coast from East Cliff to St Margaret's Bay caused problems in assessing changes in zonal thickness and faunal ranges, which are now resolved.

The cortestudinarium Zone chalk is generally fossiliferous, with many species continuing through from the planus Zone, for example Micraster praecursor, Echinocorys cf. gravesi and Sternotaxis placenta. More globose Micraster, attributable to M. cortestudinarium, appear 5 to 6 m above the zonal base and continue to the top. Other echinoids include Salenia sp. and Tylocidaris clavigera. The brachiopod fauna is characterised by Cretirhynchia subplicata (in the basal 5 metres) with other rhynchonellids and terebratulids above.

Zone of Micraster coranguinum (c.65 m)

This, the thickest zone in the Upper Chalk of east Kent, is completely exposed in the cliff sections north of Langdon Stairs to Kingsdown (Figure 10). In the low cliffs of the Isle of Thanet, only the higher part of the zone is visible (Figure 12). Blocky white chalk, with evenly spaced bands of nodular flint at intervals of a metre or so, give the zone a characteristic aspect in cliff faces. There are rare occurrences of faintly nodular chalk bands, thin marl seams and tabular flints. Several flint bands are distinctive in appearance and have proved to be useful markers over considerable distances (Robinson, 1986a). Tabular flint bands, however, are not always persistent and can change levels in the cliff sections.

Above the marl seam, taken as the top of the cortestudinarium Zone, the lowest 17 m of the coranguinum Zone comprises white chalk, faintly yellowish and nodular at a few levels, with regularly spaced bands of flint nodules and a number of very thin and often indistinct marl seams. At Langdon Stairs, a tabular flint 6.8 m above the base was taken by Rowe (1900) to mark the base of the zone; it occurs within a group of thin marls, the Hope Point Marls of Robinson, 1986a) below which is a 0.5 m band of chalk with grey marly streaks. Another thin marl occurs about 10 m above the base of the zone. A strong almost continuous layer of nodular flint, called the East Cliff Semitabular by Gale and Smith, 1982, and the Oldstairs Bay Flint by Robinson, 1986a, concludes the lower 17 m of the zone.

The zone continues upward for approximately 35 m in chalk with many bands of nodular flint. Two prominent marker flints occur in this interval. Bedwell's 'Columnar' Band is a 0.3 m-thick, double band of nodules with distinctive upward-pointing, vertical protuberances, 22 m above the East Cliff Semitabular. Whitaker's '3-inch' Band is a relatively thick almost continuous band of nodules 13 m higher. Both of these are visible in the cliffs of the South Foreland and of the Isle of Thanet (Figure 12). The chalk above Whitaker's '3-inch' Band has fewer flints for some 6.5 m, and then follows the Barrois Sponge Bed, a thin layer of chalk with many yellowish ferruginous fossil sponges. Above the sponge bed the echinoid Conulus albogalerus is abundant enough to form the so-called Conulus Band. At the time of the resurvey the Barrois Sponge Bed–Conulus Band horizon was taken as the base of the overlying Uintacrinus socialis Zone. This boundary is now taken at the weaker Peake's Sponge Bed, 6 m above, where the zonal index first appears (Peake, 1958, Bailey and others, 1983). Flints are small, scattered and fail to form regular layers in this upper part of the coranguinum Zone; rusty nodules of pyrite are also common.

Macrofossils are generally common in the coranguinum Zone, though they tend to be concentrated at certain levels. The groups represented include sponges, brachiopods, inoceramid and other bivalves, echinoids, crinoids, asteroids, bryozoans and small corals. The evolution of the Micraster lineage has traditionally been the basis of biostratigraphical zonation, but more recent studies show Inoceramus and related genera of bivalve molluscs to be more useful for interregional correlation.

At the base of the zone, Micraster of cortestudinarium type are replaced by coranguinum forms and the rhynchonellid and terebratulid brachiopods of the underlying zone disappear. Inoceramids are perhaps the most abundant fossils throughout the zone, and include species of the genera Inoceramus, Volviceramus, Platyceramus, Cladoceramus and Cordiceramus. Other echinoids present are Conulus and species of Echinocorys which, because they undergo changes in shape, are useful stratigraphically in the upper part of the zone (Peake, 1958).

The Coniacian–Santonian stage boundary occurs within the upper part of the coranguinum Zone. Bailey and others (1984) proposed that it should be taken at a shelly layer with Cladoceramus, which first appears about 5 m below Bedwell's 'Columnar' Band.

Zone of Uintacrinus socialis (7m)

Soft white blocky chalk with few flints make up this zone; calcitic body plates of the free-swimming crinoid Uintacrinus socialis become common at the level of Peake's Sponge Bed and continue through the zone. Another rusty nodular sponge bed, marks the top of the zone. Immediately above it Echinocorys elevata occurs in some abundance, forming the elevata Band; a band of scattered flints (the Bedwell Line) is present about 0.6 m above the elevata Band.

The cliffs of the Isle of Thanet provide excellent continuous sections in the chalk of this zone. It also caps the cliffs around the South Foreland and north of St Margaret's Bay. Inland, it crops out extensively, although partly obscured by Clay-with-flints, on the narrow dip-slope interfluves north of the Dour Valley, where the zonal index has been recorded from many old chalk-pits.

Apart from the zonal index, macrofossils are not notably abundant. Of interest are the rust-stained casts of the large ammonite Parapuzosia leptophylla, first recorded by Bedwell (1874), that occur at intervals through the zone and indeed down to the Barrois Sponge Bed. The more common fossils include the calcareous sponge Porosphaera globularis, the small crinoid Bourgueticrinus papilliformis , the brachiopods Terebratulina rowei , T. striatula, Kingena lima, and Orbirhynchia sp., the echinoids Phymosoma koenigi, Stereocidaris sceptifera small forms of Micraster coranguinum, species of Echinocorys and Conulus. Belemnites are found at some levels and include common Actinocamax verus and rare Gonioteuthis granulata.

Zone of Marsupites testudinarius (15 m)

This zone is exposed in the cliffs of the north coast of the Isle of Thanet from Grenham Bay to Kingsgate Bay. The greatest thickness is seen at Foreness Point [TR 384 716] where the elevata Band drops to beach level (Figure 12). At Pegwell Bay, west of the fault, the zone is present beneath the unconformity at the base of the Thanet Beds. To the south of the Tertiary outcrops of the Richborough Syncline testudinarius Zone chalk caps the dip-slope interfluves between Staple and Eastry and as far south as Tilmanstone (Figure 11).

The lithology of the zone is very similar to that of the socialis zone, with a somewhat larger number of flints, arranged in scattered courses. The zonal index Marsupites is a larger free-swimming crinoid than Uintacrinus. Marsupites body plates from the lower few metres of the zone are smooth, but become progressively more ornamented higher in the sequence, providing a useful guide to horizon. Another species Uintacrinus, U. anglicus which occurs in the top 2 to 3 m of the zone, was discovered during the survey in chalk dug from graves in St Peter's churchyard [TR 3779 6862], near Broadstairs, and was recorded from the top of the cliff at Foreness Point by Rasmussen (1961). Other fossils generally continue through from the socialis Zone. The band of chalk with U. anglicus has been given the status of a Zone by Bailey and others (1983).

Zone of Offaster pilula (up to 6 m)

This is the highest zone of the Chalk preserved in east Kent. Although previous workers had suggested its presence in the Isle of Thanet (White, 1928, p.44; Peake, 1958), this was only confirmed during the survey by the finding of the zonal index, Offaster pilula in disused lime pit [TR 3843 6863] 400 m north-east of St Peter's Church, Broadstairs. Here, up to 3 m of chalk was visible beneath the base of the Thanet Beds. The lower part of the pit, in which Marsupites and Echinocorys had been recorded by White (1928), was backfilled at the time of the survey. The zone forms a small outlier preserved in a synclinal flexure on the northern flank of the Thanet Anticline, between Broadstairs and Foreness Point (Figure 11). The chalk of the zone is poorly known, but flints appear to be uncommon; up to 6 m are believed to be present.

Zonal map of the Chalk

The zonal map reproduced here as (Figure 11) has been based on fossils collected from over 150 localities (which are indicated on the map) and the cliff sections. The supporting evidence for this is preserved in BGS archives.

Chapter 4 Tertiary

Up to 50 m of Paleocene to Eocene strata are preserved in the Richborough Syncline and as residual outliers on the flanking Chalk outcrops to the north and south. The Bullhead Bed, at the base of the Thanet Beds, rests unconformably on Upper Chalk, ranging from the socialis to the pilula Zone (Figure 11). This represents up to 25 m of differential erosion of the Chalk, with some flexuring, prior to the deposition of the earliest Paleocene rocks.

The Tertiary rocks were laid down in marine to marginal-marine environments in a sedimentary basin including what is now south-east England, the Paris Basin and part of Belgium. Deposition was cyclic, each formation commencing with a marine transgression, often overlapping or overstepping its predecessors (Stamp, 1921). In a marginal situation such as east Kent, sequences are thinner and more frequently interrupted than those in the North Sea known from hydrocarbon exploration. It is thus difficult to relate the formations in east Kent to the zonal and stage classifications based on the fuller sequences. In particular, the Paleocene–Eocene boundary in east Kent cannot be placed with any confidence. For this account, the traditional 'Lower London Tertiaries' formations, the Thanet Beds, Woolwich Beds and Oldhaven Beds, are taken as Paleocene, and the London Clay as Eocene.

Thanet Beds (c.30 m)

In the present district the Thanet Beds comprise a varied sequence of clays, marls, silts and fine sands, reaching a maximum thickness of about 30 m in the centre of the Rich-borough Syncline. The type-locality is at Pegwell Bay [TR 354 643], near Ramsgate, where most of the sequence is exposed for 1 km in a low cliff section (Figure 14). It was first described by Prestwich (1852) as the 'Thanet Sands'. However, Whitaker (1866, 1872) considered the term 'Thanet Beds' more fitting in view of the mixed lithologies making up the formation. Other early accounts were given by Gardner (1833) and Burrows and Holland (1897), and summarised by White (1928).

In his studies of the Lower Tertiary foraminifera from Pegwell Bay and other Kentish sections, Haynes, (1956–58) adapted Whitaker's (1872) division of the Thanet Beds into sedimentary units, which are, in upward sequence: The Bullhead Flint Conglomerate, The Stourmouth Clays, the Pegwell Marls and the Reculver Silts. The 'Kentish Sands' replace the last two divisions in west Kent.

Since Prestwich's early studies, the section at Pegwell (Plate 6) has been partially obscured by natural talus and by the construction of the hoverport. Ward (1977) described the sections visible after the hoverport had been built and gave faunal lists for the several subdivisions used by Whitaker (1872) and Haynes (1956–58).

It is difficult to estimate the formational thickness at Pegwell Bay (Figure 14) because of gaps in the sequence and slight flexuring especially when the junction with the overlying Woolwich Beds is not seen. Ward (1977) gave a total of about 24 m, although much of the Pegwell Marls was obscured. Boreholes indicate that up to 30 m are present in the centre of the Richborough Syncline.

The Pegwell Bay section

At Redcliff Point [TR 3536 6438] ((Figure 14) and (Plate 7)) the unconformable contact of the Thanet Beds with Upper Chalk of the testudinarius Zone, dips south at 8°. At the contact, but beneath the Bullhead Bed, a thin layer of tabular flint, 50 mm thick, is of late secondary origin and appears to postdate the Bullhead Bed, into which it is partly incorporated locally. The distinctive Bullhead Bed (Plate 8) comprises 0.15 m of dark green glauconitic sandy marl packed with green-coated, rounded flints. It passes up into about 0.75 m of compact very fine-grained glauconitic sandy marl, the glauconite content being highest in the lowermost 0.25 m, which includes rare flint pebbles. Ward (1977) named this higher bed the 'Cliffsend Greensand Bed', which with the Bullhead Bed constitutes his 'Base-bed Member'.

The 4.5 m-thick Stourmouth Clays above, have a banded aspect in the cliff face due to the alternation of clays with silty clays at approximately 0.15 m intervals. Their overall colour is greenish grey with ochreous staining due to weathered pyrite. Fossils are rare or absent, but ferruginous burrow fills are fairly common.

The Pegwell Marls, about 13 m thick, are not well exposed in the cliffs at present. As seen, they comprise rather uniform dark greenish grey marls or silty marls, with some mica and glauconite. They show faint banding in the lower part and become more silty near the top. Burrows and Holland (1896) described the basal 0.9 m as the 'Black Band', made up of bioturbated glauconitic sandy marl with the foraminifer Astacolus crepidula. The Pegwell Marls in the cliffs develop a conchoidal fracture and weather whitish. Foraminifera occur in some abundance throughout (Haynes 1956–58), but macrofossils are less common. Bivalves such as Arctica morrisi, Thracia oblata and Eutylus cuneatus (Morris) occur near the top.

The highest Thanet Beds, the Reculver Silts are exposed for up to 5 m beneath the capping of Head Brickearth (Plate 10). They are yellowish grey, very fine silty sands speckled with fine glauconite and mica flakes. Drifted bivalve shells are fairly common, forming a persistent 0.15 m band at the base. They also occur in some abundance through up to 0.7 m at the top of the section, where the maximum thickness is preserved [TR 3495 6415], though this is now partly obstructed by the hoverport. Species present include Arctica morrisi and Corbula regulbiensis . A feature of the Reculver Silts at Pegwell is the occurrence of large calcareous doggers, about 0.4 m thick and 1.5 m across, in bands parallel to the bedding. The basal shell bed is locally cemented in this way and two bands occur in the silts about 1.25 and 2.5 m above the base.

The mineralogy of the Thanet Beds at Pegwell has been described by Weir and Catt (1969). The fine sand and coarse silt fractions of the rocks studied are composed mainly of quartz, flint, glauconite and alkali feldspars. The clay fractions are dominated by montmorillonite (65–95%) and mica (5–25%). These results are broadly confirmed by X-ray diffractometry studies by Mr C W Wheatley of BGS, who reports 45 to 65% of smectite (Ca-montmorillonite) and 35 to 55% illite (mica) from the clay fractions of the basal Thanet Beds. Small amounts of the zeolite clinoptilolite occur in the lowest part of the Thanet Beds (Brown, Weir and Catt, 1969) and were taken to be authigenic crystals in the absence, at the time they wrote, of any known igneous activity in the Paleocene. Knox (1979) has shown, subsequently, that the clinoptilolite in the basal Thanet Beds at Pegwell Bay is associated with contemporary ash-fall material, comparable in age with examples from North Sea borehole sections.

The Hammill Brickworks section

Interesting exposures of the lower 7 m of the Thanet Beds were recorded in 1961 in the brickpit [TR 299 562] then being worked:

The complex Bullhead Bed here is unusual; there was no trace of the tabular flint noted in the Pegwell Bay exposure at this level. In some parts of the pit the Bullhead Bed has sagged into solution hollows in the underlying Chalk. The displacement of the base was up to 2 m over a horizontal distance of 4 m, with steep dips near the centre of the depressions. Mr M J Hughes reports that the microfauna from bed d above, is equivalent to that of the Black Band (or crepidula Band) at Pegwell recorded by Haynes (1956–58). The Stourmouth Clay division at Hammill is, therefore, only 1.5 m thick compared with 4.5 m at Pegwell. This might imply a depositional overlap onto the southern margin of the Richborough Syncline, which would thus seem to have been in existence in Paleocene times. The presence of chalk granules and flint chips in the Bullhead Bed supports the concept of penecontemporaneous local erosion of the Chalk on the basin margin. The clay fraction of the Thanet Beds at Hammill is made up of 30–70% smectite and 30–70% illite according to X-ray determinations by Mr. C W Wheatley.

Woolwich Beds

Within the present area the Woolwich Beds, up to 9 m thick, crop out in a series of small outliers around East Stour-mouth, Nash, Ash and Richborough Castle, but are partly concealed by Head Brickearth and other drift deposits. Exposures are now rare and most of those described in the past (Whitaker, 1872; White, 1928) are overgrown or backfilled. From published descriptions and the limited exposures noted during the survey, the formation mostly comprises fine- to medium-grained glauconitic sands with a speckled 'pepper and salt' appearance. Fossils are rarely seen, but the sands are heavily bioturbated, with burrows commonly highlighted by iron-staining. In the apparent absence of a 'Bottom Bed' of flint pebbles, the junction with the Thanet Beds is transitional and hard to define. The Woolwich Beds are generally notably coarser than the Reculver Silts at the top of the Thanet Beds. They are locally reduced in thickness because of the unconformable relationship with the Oldhaven Beds above.

Former sections in old sandpits and in the railway cutting near Richborough Castle [TR 3245 6010], described by Whitaker (1872) and White (1928), are now overgrown. Whitaker described about 5.2 m of sands of variable grain size and glauconite and clay content, including a bed of Corbula a metre above the base. Near Herne Bay, a bed of silicified Corbula regulbiensis has been taken as the base of the Woolwich Beds by some authors (e.g. Ward 1978). In the sand pit near Richborough Castle, White (1928, p.54) recorded about 6 m of 'evenly stratified, fine-grained, greyish, glauconitic sand'.

Oldhaven Beds

The Oldhaven Beds rest with marked erosional unconformity on the Woolwich Beds. They are very poorly exposed in the present district, but appear to consist mainly of up to 6 m of fine-grained buff and grey sands with a thin basal pebble bed of small, black, rounded flint pebbles. These pebbles are commonly conspicuous in the soil and have been taken as indicators of small residual outliers around Nash. Whitaker (1872) alluded to the possible presence of a residual sub-drift outlier capping Richborough Castle hill and this has been confirmed during the survey. Fuller descriptions of the formation in adjacent districts are given in the appropriate memoirs (Smart and others, 1966; Holmes, 1981).

London Clay (c.4.6 m)

This dominantly mudstone formation is not seen at outcrop within the present district. The presence of up to 4.6 m of the lowest beds, beneath Head Brickearth, is inferred from mapping on the adjacent Faversham (273) Sheet (Holmes, 1981).

Chapter 5 Structure

The surface structures in the Chalk and Tertiary formations (Figure 15) are controlled to a large degree by those in the Palaeozoic basement. This is demonstrated by evidence from boreholes and mining operations in the Kent Coalfield, boreholes and geophysical traverses for the Channel Tunnel project and regional geophysical surveys (Shephard-Thorn and others, 1972).

An unpublished review of the available geophysical evidence for east Kent, was carried out in BGS by Mrs E A Howell (nee Atitullah).By a 'gravity stripping' exercise (to remove the effects of the Mesozoic and Tertiary formations from the regional Bouguer anomaly map and clarify the density distribution and gradients due to the Palaeozoic basement rocks), she inferred Lower Palaeozoic rocks (of density 2.8) at a depth of about 300 m below OD beneath north Thanet and a down-faulted mass of lighter Devonian rocks (density 2.6) beneath the southern monoclinal limb of the Thanet Anticline. The Kent Coalfield basin with a northwest to south-east axial trend appears to have a subsidiary ridge or anticlinal structure between Dover and Folkestone, which is supported by borehole evidence.

Structures in the Kent Coalfield are fairly well known from the colliery workings (Figure 5). The pattern of faulting was summarised by Rumsby (in Shephard-Thorn and others, 1972). In Snowdown and Tilmanstone collieries the dominant fault trends lie between W10°N -E10°S and N30°W–S30°E; a small proportion of north-south faults occur at Snowdown. The Betteshanger Colliery take has comparatively few faults, but these have the same general trend. The faults are commonly normal with comparatively small vertical displacements of 2 -15 m; they are generally steeply inclined with hades below 20° to the vertical. The Stodmarsh Faults, between the former Chislet Colliery and the Betteshanger and Tilmanstone collieries, have somewhat greater displacements.

The western margin of the coalfield is not clearly defined by the existing boreholes. It appears to be steep and a strong 'ridge' on the Bouguer gravity anomaly map suggests that it might be faulted against Lower Palaeozoic rocks on a north–south alignment. A parallel dislocation has been proposed in the Strait of Dover, by Shephard-Thorn and others (1972), who suggest that the dominant faults in the coalfield may be regarded as second order wrench-faults between these two north-south dislocations. In Snowdown Colliery (now closed), horizontal slickensides in borehole cores indicate some lateral movement.

In north-west Europe, the Hercynian orogeny was responsible for the thrusting of folded Lower Palaeozoic, Devonian and Carboniferous rocks over relatively undeformed rocks of similar age which make up the London–Brabant massif. The northward limit of thrusting is known as the Hercynian (or Variscan) Front and is represented in northern France by the Grande Faille du Midi (Bouroz, 1960) which crosses the French coast just south of Cap Gris-Nez. Its continuation into southern England across the Channel has been speculated on by many previous workers. Shephard-Thorn and others (1972) suggest, on the evidence of a steep gravity gradient feature, that it crosses the English coast near Dymchurch, having been displaced northward a few kilometres by the north-south mid-Channel dislocation referred to above. On this basis, the Palaeozoic rocks which underlie the present area may be regarded as part of the relatively undeformed 'foreland' north of the Hercynian Front, and are unlikely to be affected by thrusts.

Evidence for late movement on the main north-west to south-east set of faults was provided by workings in the Kent No. 1 seam at Tilmanstone Colliery in 1940 which passed through broken ground, associated with a fault plane, into Oxford Clay strata (Bullerwell, 1954). This disturbance is believed to represent the southern edge of a graben between Tilmanstone and Betteshanger collieries, in which up to 100 m of Jurassic rocks are preserved. Movement on these faults postdates the Oxford Clay and appears from lack of surface expression to predate the Lower Cretaceous. Geophysical and borehole evidence suggests that the Carboniferous Limestone surface has been displaced during post-Westphalian episodes of faulting and folding.

On the Dover Sheet the Chalk outcrop forms part of the dip-slope of the North Downs of Kent. The dip is 1° or less to the north-north-east. A number of minor faults in the cliff sections between Dover and Kingsdown [TR 380 483] trend dominantly about north-west to south-east with downthrows of 0.3 to 3 m to the north-east and hades of 10° to 40° to the vertical. The joint pattern in the Chalk along this stretch has been studied by Middlemiss (1983) in relation to cliff stability. The major joint direction (300°N) coincides with the trend of the minor faults noted above, and also with the faults in the concealed Coal Measures. This is probably due to basement control, where the faults in the Mesozoic and Tertiary cover are successive reactivations along old basement fractures.

Further probable examples of basement control are provided by two strike valleys on the Chalk dip-slope, which have been eroded along fracture zones related to late movements on Hercynian faults in the Coal Measures. The most obvious of these is the Dour Valley which has the same trend as the dominant north-west to south-east faults of the coalfield and has been traced out to mid-Channel as a zone of deeply weathered Chalk in the Channel Tunnel investigations (Shephard-Thorn and others, 1972). The Dour Valley fracture zone is not associated with any appreciable vertical displacement of the Chalk and it is possible that late movements here were of a strike-slip nature. West of Deal, between Great Mongeham [TR 345 515] and Felderland [TR 330 560], a minor valley of north-east to south-east trend is developed at the foot of the .dip-slope. Its origin may be analogous to that of the Dour Valley, but there are no coincident major faults in the Betteshanger Colliery workings.

The Tertiary formations are mostly confined to the shallow east–west Richborough Syncline, whose axis lies about 2 km north of Richborough Castle. The syncline is asymmetrical, with low dips on its southern limb closely matching the magnitude and direction of those in the Chalk and steeper dips on the north, coinciding with the monoclinal southern limb of the Thanet Anticline. It has been suggested above, on geophysical evidence, that the monocline is related to a fault bounding a graben of possible Devonian rocks. There is no surface evidence of this relationship, with the possible exception of an anomalous thickness of about 28 m of Thanet Beds in a well at Minster [TR 3090 6485] close to the Chalk outcrop. However, the record is possibly unreliable.

The Thanet Anticline is parallel to the Richborough Syncline (Figure 15). Its northern limb dips gently with minor flexuring. Many faults, mostly too small to show on the geological map, cut the Chalk of the Thanet coast (Figure 12). Those which are shown [c.395 664] appear to be tensional faults related to the formation of the Thanet Anticline.

The structural evolution of east Kent, from the Lower Palaeozoic to the present day, is shown to be quite complex. A unifying theme is the way in which basement structures, predominantly imprinted by the Hercynian orogeny, have influenced subsequent tectonics and sedimentation. The main features of the structural evolution are summarised below:

1. The Lower Palaeozoic rocks were tectonised during the Caledonian and possibly earlier orogenies to give rise to the London–Brabant massif, on which the Devonian and Carboniferous cover was laid down.
2. Intra-Carboniferous uplift and erosion probably accounts for the absence of Namurian strata in the Kent Coalfield–a feature also noted in the Forest of Dean Coalfield.
3. The post-Carboniferous Hercynian orogeny resulted from a major plate collision, and gave rise to extensive thrusting of Lower Palaeozoic, Devonian and Carboniferous rocks over the London–Brabant massif. Wrench-faulting on north–south and north-west to south-east lines occurred in the foreland rocks. In the Kent Coalfield, wrench and normal-faulting preceded the deposition of the earliest Jurassic rocks. The inferred graben of Devonian rocks underlying the southern limb of the Thanet Anticline is likely to be a Hercynian structure.
4. Late Jurassic movements on the north-west to southeast faults produced the graben of Oxford Clay near Tilmanstone.
5. In the Lower Cretaceous Wealden period, fluvial sediments were derived from the London–Brabant massif by the repeated rejuvenation of fault-scarps (Allen 1981).
6. Cretaceous sedimentation shows a number of sedimentary breaks, such as the mid-Cenomanian hiatus, which may be linked to syndepositional tectonic activity.
7. Gentle flexuring and erosion following the deposition of the Chalk, produced angular unconformity, so that Paleocene rocks rest on different zones of the Upper Chalk.
8. The present structural arrangement was mainly created during the mid-Miocene Alpine orogeny, with the inversion of the Wealden basin. Basement-control is probably responsible for the steep southern limb of the Thanet Anticline and the Dour valley fracture zone.

Chapter 6 Quaternary

Drift deposits of Pleistocene and Flandrian (Recent) age cover a considerable proportion of the land area; their distribution shows a strong relationship to the present topography. With the exception of the Clay-with-flints, the drift deposits are believed to have formed during the Devensian (Last Glacial) and Flandrian stages in periglacial and coastal environments.

Head Gravel

Head Gravel is associated with possible remnants of pebbly Oldhaven Beds, overlying sandy Woolwich Beds near Paramour Street [TR 289 612]. It comprises brown sandy silty loam with numerous small black rounded flint pebbles, and may be up to 2 m thick.

Clay-with-flints

The Clay-with-flints occurs as a residual deposit on the Upper and Middle Chalk outcrops and is believed to result from the degradation of pre-existing Tertiary deposits, with some solution of the Chalk, during the Pliocene and Quaternary. It is mostly a stiff reddish brown clay with many flints, some of which retain their original white cortices and appear to have been directly derived from the Chalk, whereas others have been derived from the local Tertiary formations. Locally, silty and sandy facies occur within the main spreads of Clay-with-flints; some have been mapped separately as Head Brickearth. In the adjacent areas relicts of marine Pliocene deposits have been preserved within solution hollows in the Chalk beneath the Clay-with-flints. Solution pipes of cylindrical or irregular form are a common feature of the interface with the Chalk and may extend vertically downward for 10 m or more. The base of the Clay-with-flints is broadly planar and has been held to represent a 'sub-Tertiary erosion surface' or bench representing the unconformity between the Chalk and the formerly more extensive Tertiary deposits, from which it is presumed to have been formed by weathering and periglacial action.

In the country south of the Dour Valley and on the Coldred–Whitfield–South Foreland ridge to the north, the Clay-with-flints is extensive and about 6 m thick overall; its base lies between 113 and 121 m above OD dropping gently to the north-east. Smaller isolated patches cap the dip-slope interfluves, for example, at Sutton Hill [TR 334 502], where the base of the deposit lies at about 60 m above OD.

At the contact with the Chalk, the clay is smooth for up to 0.3 m and varies in colour from tints of pale to dark grey, to reddish brown, chocolate brown and black. In solution pipes, the clay next to the Chalk commonly contains flints resembling those of the Bullhead Bed.

There is no way of dating the Clay-with-flints, though it is presumably post–Pliocene where it overlies Pliocene remnants. Its formation has probably continued through the Quaternary with successive temperate and cold episodes playing their part in the degeneration of the presumed Tertiary parent material.

Head (undifferentiated)

This slope deposit has been formed by the solifluxion of Clay-with-flints, Head Brickearth and Chalk under periglacial conditions. It occurs on the valley sides of the River Dour and the dry valleys of the Chalk dip-slope, where it is preferentially sited on the south-eastward-facing slopes. The composition of the Head varies locally, depending on the parent materials, but it is typically a mid-brown sandy clayey loam with scattered flints. In some places its basal layers include clasts of chalk from the underlying bedrock arranged in streaks parallel to the slope. It tends to increase in thickness downslope to 2 or 3 m.

In the steep-sided Dour Valley, the Head is commonly a fossil scree of chalk and flint rubble, formed by frost action and hill wash. Deposits of calcareous tufa have been noted at fifteen sites in the Dour Valley between Buckland and Dover. They appear to be located close to the base of the Head deposits, just above the flood-plain Alluvium and were probably formed by springs emerging at this level. Up to 2 m of calcareous deposits, incorporating chalk clasts and flints, have been recorded from temporary sections. Spherical concretions from fist to football size were noted in an excavation at Buckland School [TR 305 428]. Similar tufa deposits elsewhere in south-east England have been attributed to the temperate Atlantic episode of the Flandrian (c.6000 years BP).

At Pegwell Bay, a complex infilled channel is visible in the cliff [TR 355 644] south of Little Cliffsend Tunnel (Shephard-Thorn in Shephard-Thorn and Wymer, 1977). It shows (Figure 16) several early to mid-Devensian phases of Head formation, frost heaving and erosion and is overlain by Head Brickearth. A small channel-fill in the Thanet Beds was noted in 1961 at the former Hammill Brickworks pit [TR 299 553]; it was cut to a depth of 3 m and width of 9 m, with sides sloping at approximately 45°. The fill was apparently structureless pale grey silt, with clasts of Thanet Beds, derived Tertiary flint pebbles and unsorted broken flints. The clasts were most common in the lowest 1 m and close to the channel margins. Its origin is not clear, though it could possibly represent a periglacial mud-flow.

Head Brickearth

This is the most widespread drift deposit and occurs on the Isle of Thanet and on the lower dip-slope of the Chalk, south of the Stour. It falls into two groups: an older brickearth resting on plateau surfaces and associated with outcrops of the Thanet Beds and a younger brickearth chiefly located on south-east and north-east-facing slopes of the Chalk dip-slope. As its name implies, the material is suitable for the manufacture of bricks and was formerly exploited for this purpose at a number of sites within the area. In natural and man-made sections it is a yellowish brown silty loam, from 1 to 4 m thick, overlying bedrock or older drifts as a fairly uniform mantle. It consists predominantly of silt-grade quartz grains, with a proportion of clay minerals and sometimes a calcareous cement.

Early consideration of the origin of the brickearth suggested that it might have resulted from widespread 'sheet-flooding' of the surrounding areas where Tertiary rocks are a convenient source of silt-grade sediment (e.g. White, 1928). More recently a loessic (wind-blown) origin has been demonstrated for the Head Brickearth exposed in the Peg-well Bay cliff section by Pitcher and others (1954). They used the following distinctive criteria (Russell, 1944): grain-size distribution (over 50 per cent silt), yellowish brown colour, strong vertical 'prismatic' jointing combined with the ability to stand well in vertical faces, a general calcareous nature with a well marked upper leached zone of darker colour and the presence of tiny calcareous root-tubes and nodules.

Studies of the Pegwell brickearth and of related deposits from other localities (Dangerfield 1973) have confirmed the loessic character of the former, but suggest that some of the others may have been reworked and mixed with other material under periglacial conditions. Thus it would be unwise to attribute a purely loessic origin to Head Brickearth without supporting data. Many occurrences may be primary loesses which have been moved downslope by hillwash and solifluxion, incorporating bedrock material. The older brickearth of the Isle of Thanet may have been derived from the degradation of outliers of silty Thanet Beds in a similar manner to the Clay-with-flints.

The marked preferred location of Head Brickearth on north-east and south-east facing slopes in the dry valleys of the Chalk dip-slope is readily apparent from the geological map. Two possible explanations for this phenomenon may be considered. The first calls on the differential insolation of south-east and north-west-facing slopes in a periglacial regime; summer thaw and solifluxion would be most effective on south-east-facing slopes and almost negligible on north-west facing slopes, which would be subject to frost action. This agrees with the observed asymmetry of the dry valleys, where drift deposits occur on the gentler south-east-facing slopes and the north-west-facing slopes are steep, drift free and have frost-shattered Chalk at or near the surface (Plate 9). An alternative explanation (Hjulstrom, 1955) suggests that the anticyclonic winds from the north-east, carrying the loess, as a dust cloud, are progressively deflected to the west with increasing height above the valley bottoms. It may well be that both of these mechanisms have operated in east Kent.

The Pegwell Bay section

Loessic Head Brickearth is well exposed above the Thanet Beds in the Pegwell Bay cliff section ((Figure 14) and (Plate 10)), where it was formerly dug for brick-making. It is up to 4 m thick and displays the characteristic features of loess identified by Pitcher and others (1954). Below ground level the brickearth is decalcified for a metre or so by leaching and is darker reddish brown, in contrast to the yellowish brown calcareous material below. In the basal 0.3 m small black flint pebbles of Tertiary derivation are commonly vertically orientated due to former frost action. At the northern end of the Pegwell section the brickearth rests on Upper Chalk on which a well-marked cryoturbated frost-soil with brodelb8den (flask-shaped involutions) is developed. The brickearth post-dates the frost-soil, which represents the seasonal thaw layer above permafrost. Locally a fossil soil is developed on the brickearth and is overlain by hillwash of Neolithic and later date. Organic material from this soil has yielded a radiocarbon date of 6120 ± 250 years BP (Weir, Catt and Madgett, 1971), which provides a minimum age for the end of loess deposition in the area. Thermo-luminescence dating of the loess and the fossil soil (Wintle, 1981, Wintle and Catt, 1985) indicate a possible age of 14 800 years for the loess, while those for the soil profile developed on it show anomalies due to optical bleaching. Post-glacial deposits overlying the loess at North Cliff,

Broadstairs [TR 400 685] were studied by Kerney (1965). He inferred a comparable minimum age and assigned the main period of loess deposition in east Kent to the Pleniglacial Stadial B of the Weichselian ( = Devensian) which ranges from 14 000 to 30 000 years BP.

True loesses and related silt-grade deposits may become metastable when their moisture content reaches the critical level, when particle-to-particle bonding is destroyed; this has been studied at Pegwell Bay and other localities in Kent by Fookes and Best (1969).

Dry valley and Nailbourne deposits

The Chalk dip-slope of the Dover Sheet area is traversed by a close grid of north-easterly-directed dry valleys, some of which may occasionally have 'bourne' flows when the water table rises to the level of their floors in unusually wet winters. At present, however, the valleys are to all intents and purposes fossil features in which surface water is rarely seen.

The valleys are asymmetric and have narrow flat floors due to an infill of Dry Valley and Nailbourne deposits. The composition of these deposits tends to reflect that of the material on the adjacent valley sides, though they are commonly more-or-less decalcified. They may be up to 3 or 4 m in thickness at the centre of the valleys. The basal portion of these deposits is usually made up of a coarse flint rubble with some chalk clasts and derived Tertiary pebbles locally. Their upper portion is fine-grained and is commonly a brown silty clayey loam with scattered flint clasts.

Alluvium

Freshwater Alluvium is present only in the floodplain of the River Dour between Dover and Temple Ewell and in its south-west tributary to Ewell Minnis. It is almost entirely built over, but a few well records indicate that up to 7 m of flinty gravel overlain by up to 1 m of dark organic soil are present. The occurrence of calcareous tufa in the Dour Valley has been discussed under Head.

Storm gravel beach deposits

Flint shingle, derived from the Chalk cliffs, has been transported around the South Foreland by longshore drift, under the prevailing regime of wind and tides, to form a complex of spits across Sandwich Bay. The name implies that the gravels have been thrown up above high water mark by occasional storm waves to form semi-permanent upstanding features of the coastal landscape.

The gravels first appear at the foot of the Chalk cliffs near Hope Point [TR 379 464] as a narrow strip. At Kingsdown, 2 km to the north, they have broadened out to a 200 m-wide spread with its surface about 6 m above OD. Trial boreholes have shown the presence of over 7 m of gravels hereabouts. The old town of Deal was established on the continuation of this shingle barrier. A trial borehole near Walmer Castle [TR 378 502] shows these deposits to overlap Head Brickearth, which in turn rests on the Chalk. Beyond Sandown Castle, extensive dunes of Blown Sand obscure the coastal shingle barrier, which fans out into a number of discrete ridges where it reappears about 1 km north of the Sandwich Bay Estate. Northward, beyond Deal, there is a progressive reduction in the size of the pebbles making up the shingle ridges, Sand becomes increasingly important in the make-up of the ridges beyond the Sandwich Bay Estate, so that the distal ends of the ridges at the mouth of the River Stour (Shell Ness) comprise shelly beach sand with a small proportion of fine shingle.

The Stonar shingle ridge, within the southerly loop of the River Stour, north of Sandwich, has largely been removed by gravel working. It appears to have originated by the landward migration of an offshore bank comparable to the present Brake Bank in Sandwich Bay (Robinson and Cloet, 1953, Cloet, 1961). Boreholes drilled to evaluate the deposit, show that it rests in a buried channel of the Stour extending to depths of 16 m below OD. It contains a proportion of igneous erratic pebbles of northern origin (Hardman and Stebbing, 1940–42), which could not have been supplied from the south by the present regime of longshore drift.

The evolution of the Sandwich Bay coastline and reclaimed marshlands will be discussed briefly in a following section.

Marine and estuarine alluvium

This includes deposits of silty clay, with interbedded peats, and fine sands formed in salt marsh and intertidal environments during the Flandrian. They occupy part of the former Wantsum Channel, which once separated the Isle of Thanet from mainland Kent, and the Lydden Valley. The northerly growth of the shingle barrier across Sandwich Bay provided a sheltered location for the accumulation of salt marsh deposits, but also caused the demise of Sandwich as a major port. The history of the reclamation of these marshlands by the construction of sea-walls, and the conflicting interests of the new land owners and maritime operators, is a fascinating tale, but one which cannot be developed further here.

A peat bed penetrated in a trial borehole for the Sandwich By Pass [TR 323 592] rested on Thanet Beds at a depth of 4.3 m below OD and yielded a radiocarbon date of 5315 ± 1000 BP. The overlying silty clays have been deposited with rising sea level up to the present.

Peat is present near the surface in the Ham Brooks [TR 330 555] area and some parts may be described as fen. An area [TR 355 535] to the south of Betteshanger Colliery tip is flooded due to impeded drainage. Areas of sand with fine shingle, east of Sandwich appear to be the remnants of sand spits which grew across the mouth of the former Lydden Valley haven.

Marine beach deposits and tidal flats

This group includes all the deposits exposed between high and low water marks. In Sandwich Bay, the tidal flats are usually made up of fine sand which passes seaward into sand with dark clay laminae. To the north at Pegwell Bay an extensive area of saltings, with typical salt marsh vegetation, is developed near the mouth of the Stour and in the tidal reach of the river to Sandwich. Sandy beaches have accumulated in sheltered bays around the Thanet coast.

Blown Sand

Dunes of Blown Sand rising to heights of over 8 m above OD are a feature of the Sandwich Bay coastline where they have been developed as a series of notable golf links. The dunes are constructed of fine beach sand blown up from the intertidal zone at low water.

Coastal evolution

In 1927, the late F H Edmunds sketched (Figure 17) a section in the railway cutting [TR 349 536] to Betteshanger Colliery tip, showing a low fossil cliff with 'coombe deposits' banked against it and brickearth overlapping onto the Chalk. He did not record any beach deposits as such in the 'notch' at the foot of the cliff, which is at about 4 to 5 m above OD. This fossil cliff probably extends for some distance north-west to south-east between Worth and Deal and may represent an Ipswichian (last interglacial) raised beach equivalent in altitude and age to those at Black Rock, Brighton, and at Sangatte, near Calais, in northern France. The Strait of Dover may have first been breached during this period of high sea level.

After the high sea level associated with the Ipswichian interglacial, expansion of the polar ice-caps during the last (Devensian) glacial stage resulted in a world-wide fall of sea-level to 100 m or more below that of the present day. The Isle of Thanet would then have been connected to mainland Kent. As climate ameliorated in post-glacial times the polar ice-caps retreated and sea-level began to rise. In the early Flandrian, from 10 000 to 5000 years BP, the rise of sea-level was relatively rapid, with one or two minor oscillations due to climatic variations. The Strait of Dover was flooded once more by this early Flandrian rise in sea level. By 5000 BP the sea stood close to its present level, and there have been only minor oscillations since. It is probable that the Stonar shingle ridge was emplaced at about this time, if the hypothesis of Robinson and Cloet (1953) that it migrated onshore from a position in Sandwich Bay is accepted. The channel of the Stour, which had been reduced to at least 16 m below OD (and extended eastwards beneath the present Goodwin Sands), was blocked by the Stonar shingle and the river entered the sea west of Thanet as the Richborough Syncline was flooded to form the Wantsum channel. The Romans established settlements at Richborough and Stonar, which served as bridgeheads for their invasion of Britain.

The northward growth of the Sandwich Bay spit complex probably commenced soon after 5000 BP, as there is archaeological evidence of Mesolithic and Neolithic occupation of the Lydden Valley area and Roman remains are recorded from below the sand dunes north of Deal. As the spit complex grew northward it enclosed an estuarine lagoon in which salt marsh would have been established fairly rapidly, assisting the silting-up process. Sandwich grew to importance as one of the Cinque Ports; it had a sheltered haven in the lee of the Sandwich Bay coastal barrier corresponding to the northern part of the Lydden Valley. Further growth of the coastal barrier diverted the mouth of the Stour northward progressively and led to the decline of Sandwich as a port and the silting-up of the Wantsum Channel. Reclamations of the marshlands, chiefly by monastic orders, proceeded during the Middle Ages.

The Goodwin Sands, an extensive area of sandy shoals, appear to have evolved as the result of tidal interplay between the North Sea and the English Channel, via the Strait of Dover (Carter, 1953, Cloet, 1954). As sea-level rose during the Flandrian, sea bed sediments were accumulated to form the present banks, covering the continuation of the buried channel of the Stour. An early Trinity House borehole (1849) proved about 24 m of sediment overlying Chalk bedrock.

Chapter 7 Economic geology

At present, coal mining and water supply are the only significant aspects of the economic geology of the area. Chalk was formerly exploited (presumably for lime manufacture) in numerous small- to medium-sized pits scattered around the area; latterly it has been dug near Guston to provide fill for the expansion of terminal facilities at Dover Harbour. Head Brickearth was formerly worked for brick manufacture near Deal and Ramsgate; more recently bricks were made from Thanet Beds at Hammill [TR 299 562]. The gravel workings at Stonar, north of Sandwich, are now exhausted.

Coal mining has been carried on in Kent during this century at four collieries. Three of these, Snowdown, Betteshanger and Tilmanstone are sited within the present area, though Snowdown and Tilmanstone collieries have been closed recently. The workings have been largely concentrated in three seams: The Kent No. 1 (Beresford) Seam, The Kent No. 6 (Millyard) Seam and the Kent No. 7 Seam. The No. 1 Seam was formerly worked at Snowdown and Tilmanstone collieries. Latterly the No. 6 Seam has been worked at all three collieries. The No. 7 Seam was formerly worked at Betteshanger.

Because of the friable nature of Kent coals and mechanical cutting, most reaches the pit-head as small coal. The coals are of fairly high rank and high calorific value, with low sulphur and ash contents. They meet the specifications for coking coal for steel making, but demand for this purpose has fallen in recent years; they are valuable for general industrial use and most of the present output is sold for electricity generation and paper making in north Kent. Before the coal strike of 1984–85 annual output averaged about 700 000 tonnes.

The water supply of east Kent is derived almost entirely from deep wells in the Chalk. They yield water of potable but hard or very hard quality. A number of wells are sited on the Isle of Thanet, where the influx of summer holidaymakers provokes a seasonal peak in demand. Saline intrusion has affected the coastal area of Thanet, where chloride concentrations (as chlorine) of over 500 mg/l are recorded. The Chalk aquifer is also relatively saline under Tertiary cover in the Richborough Syncline where chloride values of 100 to 500 mg/l occur.

A number of wells for public supply are situated in the Dour Valley and in the dry valleys of the Chalk dip-slope where chloride values are generally acceptably low.

However, discharge of mine waters from Tilmanstone Colliery formerly created an 'island' of high salinity, with chloride values of over 1000 mg/l, which necessitated the construction of a pipeline to discharge these waters to the sea.

The hydrogeology of the area is illustrated by a 'half-inch (1:126 720) map of the Chalk and Lower Greensand aquifers of Kent, published by BGS in 1970. The water supply of Kent was reported on by Whitaker (1908). Catalogues of wells in the Faversham/Ramsgate (Sheets 273/274) and Dover (Sheet 290) district have also been published (Cooling and others, 1964, Harvey and others, 1964). The underground waters of the Kent Coalfield have been discussed by Forster-Brown (1923) and Plumptre (1959).

The Channel Tunnel project is once again topical. Investigations (Destombes and Shephard-Thorn, 1971) have concentrated on proving a route as much as possible in the Chalk Marl, whose physical properties provide ideal tunnelling ground. Particular attention is being paid to areas of high permeability linked to fissuring and the presence of drift-filled hollows in the sea bed near the tunnel line. The presently approved route crosses the English coast at the foot of Shakespeare Cliff and hardly impinges on the present area.

Appendix 1 List of Geological Survey photographs

Copies of these photographs are available for reference in the British Geological Survey Library, Keyworth, Nottingham NG12 5GG. They may be ordered as black and white or colour prints, or as colour transparencies at standard tariffs. The photographs were taken by Mr M Pulsford. All numbers belong to Series A.

Appendix 2 List of boreholes and shaft sections

The following boreholes and colliery shafts were sunk to prove or develop the concealed Coal Measures of the Kent Coalfield. Descriptive logs of the Cretaceous, Jurassic and Carboniferous strata penetrated in these holes are held in the National Geosciences Data Centre, British Geological Survey, Keyworth, Nottingham NG12 5GG, and may be inspected by arrangement (a standard charge may be levied). The records are backed up by extensive collections of fossils and lithological samples from most of the boreholes and shafts. Published references to these sections may be found in the following works (see References):

1. Dines, 1933.
2. Lamplugh, Kitchin and Pringle, 1823.
3. Bisson, Lamb and Calver, 1967.
4. Mitchell, 1981.

The bold numbers are quoted in the list below to indicate where further information on these boreholes may be sought. The records and samples of boreholes drilled by British Coal (National Coal Board) in 1976 and thereafter are held on a confidential basis; written permission of the Board must be obtained to view such materials. In addition to the material listed below, material is also held relating to underground boreholes drilled for development purposes at Betteshanger, Tilmanstone and Snowdown collieries. Abbreviations used in the list are as follows: NCB: National Coal Board; SL: surface level; TD: total depth.

References

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. Conclusions. Proc. Geol. Assoc., Vol. 78, 241–276.

BAILEY, K W, GALE, A S, MORTIMORE, R N, SWIECICKI, A and WOOD, C J. 1983. The Coniacian-Maastrichtian Stages of the United Kingdom with particular reference to southern England. Newsl. Stratigr., Vol. 12, 29–42.

BAILEY, K W, GALE, A S, MORTIMORE, R N, SWIECICKI, A and WOOD, C J. 1984. Biostratigraphical criteria for the recognition of the Coniacian to Maastrichtian Stage boundaries in the Chalk of North West Europe, with particular reference to southern England. Bull. Geol. Soc. Denmark, Vol. 33, 31–39.

BARROIS, C. 1876. Recherches sur le terrain cretace superieur de l'Angleterre et de l'Irlande. Mem. Geol. Soc. Nord., Lille.

BEDWELL, F A. 1874. The Isle of Thanet. The ammonite zone, the depth of the Chalk in section, and the continuity of its flint floorings. Geol. Mag. Second Series, Vol. 1, 16–22.

BISSON, G, LAMB, R K, and CALVER, M A. 1967. Boreholes in the concealed Kent Coalfield between 1948 and 1959. Bull. Geol. Surv. G.B., No. 26, 99 -166.

BOLTON, N. 1915. The fauna and stratigraphy of the Kent Coalfield. Trans. Instn. Min. Eng., Vol. 49, 643–702.

BOUROZ, A. 1960. La structure du paleozoique du Nord de la France, au sud de la Grande Faille du Midi. Ann. Soc. Geol. Nord, Vol. 80, 101–112.

BROMLEY, R G. 1967. Some observations of burrows of thalassinidean Crustacea in Chalk hardgrounds. Q. J. Geol. Soc. London,Vol. 123, 157–182.

BROWN, G, CATT, J A, and WEIR, A M. 1969. Zeolites of the clinoptilolite-heulandite type in sediments of south-east England. Min. Mag., Vol. 37, 480–488.

BRUCKSHAW, J M, GOGUEL, J, HARDING, H J B, and MALCOR, R. 1961. The work of the Channel Tunnel Study Group 1958–1960. Proc. Inst. Civ. Eng., Vol. 18 (for 1961), 149–178.

BULLERWELL, W. 1954. A gravimeter survey over the Tilmanstone Fault, Kent Coalfield. Bull. Geol. Surv. G.B., No. 6, 13–20.

BURROWS, H W, and HOLLAND, R. 1896. The foraminifera of the Thanet Beds of Pegwell Bay. Proc. Geol. Assoc., Vol. 15, 19–52.

CALVER, M A. 1969. Westphalian of Britain. 6e Congr. Int. Stratigr. Geol. Carbonif., Sheffield 1967, Vol. I, 233–254.

CARTER, D J, and DESTOMBES, J-P. 1972. Stratigraphie du Cenomanien du Detroit du Pas-de-Calais. Mem. Bur. Rech. Geol. Min., No. 79, 118–121.

CARTER, D J, and HART, M B. 1977 Aspects of mid-Cretaceous stratigraphical micropalaeontology. Bull. Br. Mus. Nat. Hist. (Geol.), Vol. 29, No. 1, 1–135.

CARTER, G G. 1953. The Goodwin Sands. London. 148 pp.

CLOET, R L. 1954. A hydrographic analysis of the Goodwin Sands. Geogr. J., Vol. 120, 203–215.

CLOET, R L. 1961. Development of the Brake Bank. Geogr. J., Vol. 127, 335–339.

COLEMAN, A M, and LUKEHURST, C T. 1967. British landscapes through maps, 10, East Kent. 30 pp. Geographical Association, Sheffield.

COOLING, C M, and OTHERS. 1964. Records of wells in the area of the New Series one-inch (Geological) Faversham (273) and Ramsgate (274) sheets. Wat. Supply Pap. Geol. Surv. G.B., Well Cat. Ser.

COPE, J C W, GETTY, T A, HOWARTH, M K, MORTON, N, and TORRENS, H S. 1980. A correlation of the Jurassic rocks in the British Isles, Part One: Introduction and Lower Jurassic. Spec. Rep. Geol. Soc. London, No. 14.

COPE, J C W,  DUFF, K I, PARSON, C F, TURRENS, M S, WIMBLEDON, W A, and WRIGHT, J K. 1980. A correlation of the Jurassic rocks in the British Isles Part Two: Middle and Upper Jurassic. Spec. Rep. Geol. Soc. London, No. 15.

DANGERFIELD, J. 1973. Sedimentary analysis of brickearths and associated sediments from Kent. I.G.S. Sedimentary Analysis Laboratory Internal Report No. 47.

DESTOMBES, J-P, and SHEPHARD-THORN, E R. 1971. Geological results of the Channel Tunnel site investigation 1964–65. Rep. Inst. Geol. Sci., No. 71/11.

DESTOMBES, J-P, and SHEPHARD-THORN, E R. 1972. Resultats geologiques des recherches pour l'implantation d'un tunnel sos la Manche (1964–65). Mem. Bur. Rech. Geol. Min., Vol. 79, 101–115.

DINES, H G. 1933. Contributions to the geology of the Kent Coalfield. Summ. Prog. Geol. Surv. G.B. for 1932, Pt. 2, 15–43

DINES, H G.1945. Report of the Geological Survey in Kent Coalfield Regional Survey Report, Ministry of Fuel and Power, 7–25.

FOOKES, P G, and BEST, R. 1969. Consolidation characteristics of some late Pleistocene periglacial metastable soils of East Kent. Q. J. Eng. Geol., Vol. 2, 103–128.

FORSTER BROWN, E 0. 1923. Underground waters in the Kent Coalfield and their incidence in mining development. Proc. Inst. Civ. Eng., Vol. 215, 27–114.

GALE, A S, and SMITH, A B. 1982. The palaeobiology of the irregular echinoids Infulaster and Hagenowia. Palaeontology, Vol. 25, 11–42.

GARDNER, J S. 1883. On the Lower Eocene section between Reculvers and Herne Bay, and on some modifications in the classification of the Lower London Tertiaries. Q. J. Geol. Soc. London, Vol. 39, 197–210.

GEORGE, T N, JOHNSTON, G A L, MITCHELL, M, PRENTICE, J E, RAMSBOTTOM, W H C, SEVASTOPULO, G D, and WILSON, R B. 1976. A correlation of Dinantian rocks in the British Isles. Spec. Rep. Geol. Soc. London, No. 7.

GODWIN-AUSTEN, R. 1856. On the possible extension of the Coal Measures beneath the south-eastern part of England. Q. J. Geol. Soc. London, Vol. 12, 38–73.

HANCOCK, J M. 1976. The petrology of the Chalk. Proc. Geol. Assoc., Vol. 86, 499–535.

HARDMAN, F W, and STEBBING, W P D. 1940–42. Stonar and the Wantsum Channel. Pt. 1 Arch. Cant. Vol. 53, 62–80. Pt. 2 Arch. Cant. Vol. 54, 41–55. Pt.3 Arch. Cant. Vol. 55, 37–52.

HARVEY, B I, and OTHERS. 1964. Records in wells in the area of New Series one-inch (Geological) Dover (290) sheet. Wat. Supply Pap. Geol. Surv. G.B., Well Cat. Ser.

HAYNES, J. 1955. Pelagic foraminifera in the Thanet Beds, and the use of Thanetian as a stage name. Micropalaeontology, Vol. 1, 189 -?

HAYNES, J. 1956–58. Certain smaller British Palaeocene foraminifera, Parts I-V. Contr. Cushman Fdn., Vol. 7, Pt. 3, 79–101; Vol. 8, Pt. 2, 45–53; Vol. 9, Pt. 1, 4–16, Vol. 9, Pts. 3, 58–77; Vol. 9, Pt. 4, 83–92.

HÉBERT, E. 1874. Comparaison de la Craie des cotes d'Angleterre avec celle de France. Bull. Soc. Geol. Fr. (3), Vol. 2, 416–428.

HESTER, S W. 1965. Stratigraphy and palaeogeography of the Woolwich and Reading Beds. Bull. Geol. Surv. G.B., No. 23, 117–137.

HJULSTRÖM, F. 1955. The problem of the geographic location of wind-blown silt. An attempt of explanation. Geografiska Annaler, Vol. 37, 86–93.

HOLMES, S C A. 1981. Geology of the country around Faversham. Mem. Geol. Surv. G.B., Sheet 273 (England and Wales).

JUKES-BROWNE, A J, and HILL, W. 1903. The Cretaceous rocks of Britain. II. The Lower and Middle Chalk of England. Mem. Geol. Surv. G.B.

JUKES-BROWNE, A J, and HILL, W. 1904. The Cretaceous rocks of Britain. III. The Upper Chalk of England. Mem. Geol. Surv. G.B.

KENNEDY, W J. 1969. The correlation of the Lower Chalk of south-east England. Proc. Geol. Assoc., Vol. 77, 459–560.

KERNEY, M P. 1965. Weichselian deposits in the Isle of Thanet, East Kent. Proc. Geol. Assoc., Vol. 76, 269–274.

KNOX, R W O'B. 1979. Igneous grains associated with zeolites in the Thanet Beds of Pegwell Bay, north-east Kent. Proc. Geol. Assoc., Vol. 90, 55–60.

LAMPLUGH, G W, and KITCHIN, F L. 1911. On the Mesozoic rocks in some of the coal explorations in Kent. Mem. Geol. Surv. G. B.

LAMPI.UGH, G W, and KITCHIN, F L. and PRINGLE, J. 1923. The concealed Mesozoic rocks in Kent. Mem. Geol. Surv. G.B.

McRAE, S G, and BURNHAM, C P. 1973. The rural landscape of Kent. 214 pp. (Ashford, Kent: Wye College.)

MIDDI.EMISS, F A. 1983. Instability of Chalk cliffs between the South Foreland and Kingsdown, Kent, in relation to geological structure. Proc. Geol. Assoc., Vol. 94, 115–122.

MITCHELL, M. 1981. The age of the Dinantian (Lower Carboniferous) rocks proved beneath the Kent Coalfield. Geol. Mag., Vol. 118, 703–711.

MORTIMORE, R N. 1986. Stratigraphy of the Upper Cretaceous White Chalk of Sussex. Proc. Geol. Assoc., Vol. 97, 97–139.

MORTIMORE, R N. 1987. Upper Cretaceous Chalk in the North and South Downs, England: a correlation. Proc. Geol. Assoc., Vol. 98, 77–86.

OWEN, H G. 1971a. Middle Albian stratigraphy in the Anglo-Paris Basin. Bull. Br. Mus. (Nat. Hist.), London, Geol., Suppl. No. 8, 1–166.

OWEN, H G. 1971b. The stratigraphy of the Gault in the Thames estuary and its bearing on the Mesozoic tectonic history of the area. Proc. Geol. Assoc., Vol. 82, 187–207.

OWEN, H G. 1976. The stratigraphy of the Gault and Upper Greensand of the Weald. Proc. Geol. Assoc., Vol. 86, 475–498.

PEAKE, N B. 1958. The coastal Chalk of north-east Thanet. Itinerary VI. In Geologists' Association Guide No. 30. The London Region. (First edition). PITCHER, W S, PEAKE, N B, CARRECK, J N, KIRKALDY, J F, HESTER, S W, and HANCOCK, J M.

PHILLIPS, W. 1821. Remarks on the Chalk cliffs in the neighbourhood of Dover. Trans. Geol. Soc. London, Vol. 5, 16–51.

PITCHER, W S, SHEARMAN, D J, and PUGH, D C. 1954. The loess of Pegwell Bay, Kent, and its associated frost soils. Geol. Mag., Vol. 91, 308–314.

PLUMPTRE, J H. 1959. Underground waters of the Kent Coalfield. Trans. Inst. Min. Eng., Vol. 119, 155–169.

PRESTWICH, J. 1852. On the structure of the strata between the London Clay and the Chalk in London and Hampshire Tertiary systems. Part III Thanet Sands. Q. J. Geol. Soc. London, Vol. 8, 235–268

PRICE, F G H. 1877. On the beds between the Gault and Upper Chalk near Folkestone. Q. J. Geol. Soc. London, Vol. 33, 431–448.

RASMUSSEN, K W. 1961. A monograph on the Cretaceous Crinoidea. Biologiske skrifter udviget of det kongelige Danske Videnskabernes Selskab, Bd 12, No. 1.

RITCHIE, A E. 1920. The Kent Coalfield, its evolution and development. London.

ROBASZYNSKI, F, and AMEDRO, F. 1986a. The Cretaceous of the Boulonnais (France) and a comparison with the Cretaceous of Kent (United Kingdom). Proc. Geol. Assoc., Vol. 97, 171–208.

ROBASZYNSKI, F, 1986b. Report of a field meeting to the Cretaceous of the Boulonnais, Northern France, 28–30 September 1984. Proc. Geol. Assoc., Vol. 97, 209–212.

ROBINSON, A H W, and CLOET, R L. 1953. Coastal evolution in Sandwich Bay. Proc. Geol. Assoc., Vol. 64, 69–82.

ROBINSON, N D. 1986a. Lithostratigraphy of the Chalk Group of the North Downs, southeast England. Proc. Geol. Assoc., Vol. 97, 141–170.

ROBINSON, N D. 1986b. Fining-upwards microrhythms with basal scours in the Chalk of Kent and Surrey, England, and their stratigraphical importance. Newsl. Stratigr. 7 Vol. 17, 21–28.

ROWE, A. 1900. The zones of the White Chalk of the English coast. 1. Kent and Sussex. Proc. Geol. Assoc., Vol. 16, 289–368.

RUSSELL, R J. 1944. Lower Mississippi Valley loess. Bull. Geol. Soc. Am., Vol. 55, 1–40.

SHEPHARD-THORN, E R, LAKE, R D, and ATITULLAH, E A. 1972. Basement control of structures in the Mesozoic rocks in the Strait of Dover region, and its reflexion in certain features of the present land and submarine topography. Philos. Trans. R. Soc. London, Vol. A272, 99–113.

SHEPHARD-THORN, E R, and WYMER, J J. 1977. Guidebook for Excursion A5: South East England and the Thames Valley. 10th International Quaternary Association Congress, 1977.

SMART, J G O, BISSON, G, and WORSSAM, B C. 1966. Geology of the country around Canterbury and Folkestone. Mem. Geol. Surv. G.B.

STAMP, L D. 1921. On the cycles of sedimentation in the Eocene strata of the Anglo-Franco-Belgian Basin. Geol. Mag. Vol. 58, 108–114, 146–157, 194–200.

STUBBI.EFIELD, C J, and TROTTER, F M. 1957. Divisions of the Coal Measures on Geological Survey maps of England and Wales. Bull. Geol. Surv. G.B., No. 13, 1–5.

STUBBLEFIELD, C J,  and TRUEMAN, A E. 1946. The faunal sequence in the Kent Coalfield. Geol. Mag., Vol. 83, 266–279.

VAUGHAN, A. 1905. The palaeontological sequence in the Carboniferous Limestone of the Bristol area. Q. J. Geol. Soc., Vol. 61, 181–305.

WARD, D J. 1977. The Thanet Beds exposure at Pegwell Bay, Kent. Tertiary Res., Vol. 1, 69–76.

WARD, D J. 1978. The Lower London Tertiary (Palaeocene) succession of Herne Bay, Kent. Rep. Inst. Geol. Sci., No. 78/10.

WEIR, A H, and CATT, J A. 1969. The mineralogy of Palaeogene sediments in northeast Kent (Great Britain). Sediment. Geol, Vol. 3, 17–33.

WEIR, A H, and CATT, J A. and MADGETT, P A. 1971. Post-glacial soil formation the loess of Pegwell Bay, Kent. Geoderma, Vol. 5, 131–149.

WHITE, H J O. 1928. Geology of the country near Ramsgate and Dover. Mem. Geol. Surv. G.B., Sheets 274 and 290.

WINTLE, A G. 1981. Thermoluminescence dating of late Devensian loesses in southern England. Nature, London, Vol. 289, 479–480.

WINTLE, A G. and CATT, J A. 1985. Thermoluminescence dating of soils developed in late Devensian loess at Pegwell Bay, Kent. J. Soil. Sci., Vol. 36, 293–298.

WHITAKER, W. 1866. On the Lower London Tertiaries of Kent. Q. J. Geol. Soc., London, Vol. 22, 404–435.

WHITAKER, W. 1872. The geology of the London Basin. Mem. Geol. Surv. G. B.

WHITAKER, W. 1908. The water supply of Kent. Mem. Geol. Surv. G.B.

Figures, plates and tables

Figures

(Figure 1) Relief and drainage.

(Figure 2) Simplified solid geology.

(Figure 3) Physiographic regions. These are briefly as follows: A The upper dip-slope of the North Downs (including the Dour valley), largely given over to pasture and woodland (on steeper slopes). B The lower dip-slope of the North Downs. This is bevelled by the so-called sub-Paleocene surface (marking the Cretaceous–Tertiary unconformity) which has been exhumed by erosion. The surface is trenched by numerous narrow dry valleys. Arable farming for grain and market gardening is important here. C The Isle of Thanet forms a broad Chalk 'whaleback' with radial dry valleys. It is well favoured climatically and is famous for grain crops and market gardening. D The fruit belt includes the Tertiary outcrops of the lower dip-slope and the southern flank of Thanet. Much brickearth is present, so that both soils and climate are well suited to fruit growing. E The coastal marshlands of the Wantsum and Lydden valleys are areas of Estuarine and Marine Alluvium that have been reclaimed within histoiical times. They are largely given over to pasture and arable farming, depending to some degree on the quality of drainage. F Coastal sand and shingle with dunes of blown sand form a protective barrier extending along Sandwich Bay. Some famous golf links are sited along this strip, which is otherwise used only for rough pasture.

(Figure 4) Structural contours on the top of the Carboniferous Limestone.

(Figure 5) Simplified structural geology of the Kent Coalfield. B: Betteshanger, C: Chislet, S: Showdown, T: Tilmanstone.

(Figure 6) Generalised sequence in the Coal Measures of east Kent.

(Figure 7) Correlation diagram of Westphalian A, B and C strata in selected boreholes.

(Figure 8) Sub-Gault geology.

(Figure 9) Simplified sequence in the Lower Chalk in Channel Tunnel Borehole P000.

(Figure 10) Sketch sections of the cliffs between Dover and Walmer showing the Middle and Upper Chalk zones. a. Diagrammatic section of Upper Chalk exposed in Langdon Stairs Cliff path.

(Figure 11) Zonal map of the Chalk outcrops.

(Figure 12) Sketch sections of the Upper Chalk exposed in the cliffs of the Isle of Thanet.

(Figure 13) Zonal sequence of the Middle and Upper Chalk.

(Figure 14) Chalk, Tertiary and Quaternary deposits in the Pegwell Bay cliff section.

(Figure 15) Structures in the Chalk and Tertiary strata present.

(Figure 16) Quaternary infilled channel at Pegwell Bay: a, frost-shattered chalk; b, chalky-flinty solifluxion deposits; c, flinty gravel; d, silty loam channel-fill; e, solifluxion gravel; f, loess (brickearth); g, fossil soil.

(Figure 17) Fossil cliff beneath cover of Head Brickearth and Coombe Deposits in railway cutting near Betteshanger Colliery.

Plates

(Front cover)

(Rear cover)

(Geological succession) Geological sequence in the Ramsgate and Dover district

(Plate 1) Cliffs in Upper Chalk of the planus, cortestudinarium and coranguinum zones at Bantam Hole [TR 358 431], near the South Foreland. (ERST).

(Plate 2) The 'White Cliffs' of Dover cut in Middle and Upper Chalk [TR 320 410]. Storm beach gravel deposits in the foreground. (A9699).

(Plate 3) The 'basal complex' of the planus Zone exposed at the foot of Langdon Stairs [TR 345 425]. See also text and (Figure 10)a. (ERST).

(Plate 4) Langdon Bay [TR 345 425]; the cliffs, up to 100 m in height expose Middle and Upper Chalk strata including the upper beds of the lata Zone and the whole of the planus, cortestudinarium and coranguinum zones. The Langdon Stairs cliff path occurs in the vegetated cliff in the middle distance (see also (Figure 10). (A10056).

(Plate 5) Upper Chalk in cliffs near the South Foreland [TR 358 430]. This section, about 75 m high, includes the planus, cortestudinarium and coranguinum zones. The prominent tabular flint band midway up the section is Rowe's 'cortestudinarium' tabular. (ERST).

(Plate 6) General view of cliff sections near Little Cliffsend, Pegwell Bay [TR 351 642]. In the middle distance Head Brickearth rests on the lower part of the Thanet Beds. In the distance the cliffs, up to 18 m high, are cut in Upper Chalk of the socialis and coranguinum zones. (A9965).

(Plate 7) Unconformable junction of the Thanet Beds and the Upper Chalk at Redcliff Point [TR 353 643], Pegwell Bay. Chalk of the testudinarius Zone, at the foot of the cliff, is overlain by the basal Bullhead Bed (0.15 m) of the Thanet Beds (see also (Plate 8)). This is succeeded by the Cliffsend Greensand Bed (0.75 m), Stourmouth Clays (4.5 m) and the lower beds of the Pegwell Marls (up to 4 m). At the cliff top deposits of Head Brickearth, with underlying solifluction gravel, total up to 3 m in thickness. (A9968).

(Plate 8) Close-up view of the Thanet Beds–Upper Chalk unconformity at Redcliff Point [TR 353 643], Pegwell Bay. Closely fractured chalk of the testudinarius Zone is overlain by the Bullhead Bed (0.15 m). A sheet of tabular flint (50 mm), at the contact, is believed to be of late, secondary origin. Above glauconitic sandy marl with green-coated, rounded flints (100 m) complete the Bullhead Bed. The Cliffsend Greensand Bed is seen above. (A9969).

(Plate 9) The Lynch, an asymmetrical dry valley on the Chalk dip-slope near Ringwould [TR 363 479]. The gentle ESE-facing slope in the foreground is mantled with Head Brickearth, across the valley the steep WNW-facing slope (in rough pasture with bushes) is cut in frost-shattered Chalk, which is exposed in the sides of a track on the left of the photograph. (A9705).

(Plate 10) Head Brickearth overlying Thanet Beds, Pegwell Bay [TR 350 642]. At the top of the cliff, 2.4 m of loessic brickearth showing characteristic 'prismatic' jointing is well seen. Scattered flint pebbles occur in its basal layer above the contact with the Relculver Silts division of the Thanet Beds. (A9973).

Tables

(Table 1) Summary of information on the Carboniferous Limestone.

Tables

(Table 1) Summary of information on the Carboniferous Limestone