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Geology of the country around Epping. Memoir for 1:50 000 geological sheet 240 (England and Wales)

By D. Millward, R. A. Ellison, R. D. Lake and B. S. P. Moorlock

Bibliographical reference Millward, D., Ellison, R. A., Lake, R. D., and Moorlock, B. S. P. 1987. Geology of the country around Epping. Memoir, British Geological Survey, Sheet 240 (England and Wales), 80pp

• Authors
• D. Millward, R. A. Ellison, R. D. Lake and B. S. P. Moorlock
• Contributors
• Stratigraphy
• C. R. Bristow
• Palaeontology C. J. Wood M. J. Hughes
• Economic geology R. J. Marks
• R. A. Monkhouse

British Geological Survey, Natural Environment Research Council

London: Her Majesty's Stationery Office 1987. © Crown copyright 1987 First published 1987. ISBN 0 11 884400 8. Printed in the United Kingdom for Her Majesty's Stationery Office Dd.238933/6.87/C20/12521

• Authors
• R. A. Ellison, BSc, R. D. Lake, MA and B. S. P. Moorlock, BSc, PhD British Geological Survey Keyworth, Nottingham NG12 5GG
• D. Millward, BSc, PhD British Geological Survey Windsor Court, Windsor Terrace Newcastle upon Tyne NE2 4HB
• Contributors
• C. R. Bristow, BSc, PhD British Geological Survey St Just, 30 Pennsylvania Road Exeter EX4 6BX
• C. J. Wood, BSc, M. J. Hughes, MSc and R. J. Marks, BSc British Geological Survey, Keyworth,
• R. A. Monkhouse, BSc, MA British Geological Survey Maclean Building, Crowmarsh Gifford, Wallingford, Oxfordshire OX10 8BB

(Front cover)

(Rear cover)

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

Books

• British Regional Geology
• London and the Thames Valley (3rd Edition)
• Memoirs
• Geology of the country around Braintree, Sheet 223
• Geology of the country around Chelmsford, Sheet 241
• Well Catalogue
• Epping (240), Chelmsford (241) and Brightlingsea (242) sheets

Maps

• 1:625 000
• Solid geology (south sheet)
• Quaternary geology (south sheet)
• 1:50 000 and 1:63 360 (Solid and Drift)
• Sheet 223 Braintree
• Sheet 239 Hertford
• Sheet 240 Epping
• Sheet 241 Chelmsford
• Sheet 256 North London
• Sheet 257 Romford
• Sheet 258/259 Southend and Foulness

Preface

The Epping district was included in the Old Series one inch geological maps 1 and 47, published as separate solid and drift editions during the period 1868 to 1884 and described in the memoirs of 1872 (Whitaker) and 1878 (Whitaker, Penning, Dalton and Bennett). Six-inch mapping of the eastern part of the district was begun during 1969 by Mr R. D. Lake and Dr C. R. Bristow under Mr S. C. A. Holmes, District Geologist. The main part of the sheet was mapped in 1975–77 by Messrs R. A. Ellison, R. D. Lake, M. J. Heath and Drs B. S. P. Moorlock and D. Millward under the direction of Dr W. A. Read, District Geologist. The account of the sand and gravel resource survey was prepared by Mr R. J. Marks and that of the hydrogeology by Mr R. A. Monkhouse.

The memoir contains contributions on the palaeontology of the Cretaceous and of the London Clay by Mr C. J. Wood and Mr M. J. Hughes.

The work of Mr G. R. Ward of the Passmore Edwards Museum, London on the fauna of the London Clay is greatly appreciated. The photographs were taken by Mr C. J. Jeffery. Thanks are due to the landowners and to the Harlow Development Corporation for much helpful cooperation. The memoir has been compiled by Dr D. Millward, and edited by Mr R. D. Lake, Mr W. B. Evans and Dr B. N. Fletcher.

G. Innes Lumsden, FRSE Director,  British Geological Survey Keyworth,  Nottingham NG12 5GG,  2 June 1987.

List of six-inch maps

The following is a list of six-inch geological maps included wholly or in part, in the area of 1:50 000 Epping (240) Geological Sheet, with the initials of the surveyors and the date of the survey for each six-inch map; the surveyors were C. R. Bristow, R. A. Ellison, M. J. Heath, R. D. Lake, D. Millward and B. S. P. Moorlock.

Notes

• The word 'district' used in this memoir means the area included in the 1:50 000 Geological Sheet 240 (Epping).
• National Grid references are given in square brackets throughout the memoir. All lie within the 100 km square TL.
• The authorship of fossil species is given in the Index of fossils.

Geology of the country around Epping—summary

This memoir describes parts of west Essex and of Hertfordshire extending from the west of Harlow and Epping to the outskirts of Chelmsford. Much of the ground in the north of the district forms part of the extensive boulder clay plateau of southern East Anglia. To the south the higher ground, which includes part of Epping Forest, displays more diverse landforms and geology; the heathland is underlain by sands of Tertiary age and varied drift deposits. Locally, complex sequences of drifts are present, particularly in the Stort valley near Sawbridgeworth and at the site of a former glacial lake at Fyfield. The results of the geological survey together with drilling and trenching programmes are described herein, with accounts of the economic geology and water supply.

(Geological succession) Geological sequence in the Epping district.

Geological sequence in the Epping district

Chapter 1 Introduction

This memoir describes the district covered by the 1:50 000 Epping (240) Geological Sheet which lies within the counties of south-west Essex and east Hertfordshire. The centre, north and east of the district forms part of the monotonous East Anglian plateau; in contrast the higher ground to the west and south with its moderate degree of dissection has given rise to pleasantly undulating countryside. The plateau falls progressively southward from about 100 m above sea level in the north to 76 m south of Fyfield and southeastwards to 65 m in the Chignalls. Extensive high ground is also present in the south around Epping and to the northwest of Ingatestone. The former is part of the extensive north-easterly trending Epping Forest ridge which rises to 117 m OD near the Ambersbury Banks, and extends northward from Epping to near Harlow. High ground rising to 103 m OD continues eastward from Epping to Toot Hill. The Roding valley separates this from the Stondon Massey and Mill Green areas at 80 to 100 m OD.

The drainage falls into three major systems: the tributaries of the Lea, including the Ash and the Stort in the north-west of the region and Cobbin's Brook in the south-west; the Roding and its tributaries; and the tributaries of the Chelmer including the Can and Wid. The first two systems drain to the Thames at London and the latter eastward to the Blackwater estuary. Near Hadham Cross and Widford the Ash falls from about 56 m OD at Hadham Cross to below 46 m west of Widford; in its lower reaches the valley is deeply incised. The Stort meanders across a valley floor 1 km in width at Eastwick and falls from about 53 m OD at Spellbrook to 31 m at Roydon. The Ash, Stort and Pincey Brook flow southward in their upper reaches before changing sharply to a west-south-west direction. Cobbin's Brook has a similar west-south-west direction through the Epping Upland area and, although the present stream is small, the valley is some 50 m deep.

The economy of the south-western part of Essex is dominantly agricultural; the slow draining but fertile clay soils derived from the extensive boulder clay of the plateau area form good arable land and are cropped mainly for cereals. On undulating areas in the south, which are underlain by the Tertiary formations, the soils are generally much heavier and are best suited to grazing, although cereal crops are grown on the better drained land to give a balanced farming economy. Agriculture has been accompanied by deforestation leaving the two major natural woodlands of Epping Forest and the area east of Blackmore.

Outline of geology

Most of the district is covered by drift deposits, with wide tracts of boulder clay capping the plateau area in the central and northern parts. Dissection by the rivers has exposed both the drift and solid sequences in the valleys. The glacial succession is best exposed in the main valleys and tributaries of the Ash, Stort, Roding, and Can. Solid formations of Upper Cretaceous and Tertiary age are recorded, the latter occurring especially in the southern part of the area around Epping and Ingatestone (Figure 1). The oldest exposed beds are of Upper Chalk, cropping out near Widford [TL 420 158] and Sawbridgeworth [TL 481 150]; boreholes prove the Middle and Lower Chalk. Although the Palaeocene beds are entirely drift-covered the succession is known from boreholes and from records of old sections penetrating the drift cover.

Little is known of the strata beneath the Chalk but boreholes in neighbouring regions at Ware [TL 3531 1398] and Canvey Island [TL 8215 8330] proved the Palaeozoic basement at relatively shallow depths. These and other boreholes show that the early history of this area was dominated by the formation of the London Platform (Figure 2). In the above boreholes, Triassic and Jurassic rocks were absent, although boreholes elsewhere in the London area to the south have shown that Jurassic sediments are present on the flanks of the London Platform which at this time formed a massif extending eastwards into Belgium. By Albian (Gault) times the London Platform had become inundated, and Gault and Upper Greensand sequences have been recorded from the Ware, Loughton [TL 4247 9567] and Canvey Island boreholes. Marine conditions continued with the deposition of the Chalk in shallow warm seas in which the supply of argillaceous material decreased with time. Throughout the Upper Cretaceous minor vertical movements of the London Platform caused minor breaks in sedimentation, recognised by non-sequences, phosphatic nodule beds and hardgrounds. Movements of a greater magnitude at the end of the Cretaceous resulted in erosion of part of the Upper Chalk prior to the deposition of Palaeocene sediments.

Marine conditions prevailed during the lower part of the Palaeocene. The thinning of the Thanet Beds within the district probably reflects a shore-line positioned to the northwest of the district; some erosion of the Thanet Beds may have preceded deposition of the Woolwich and Reading Beds. The palaeogeography of the area was more complicated during Woolwich and Reading Beds times; the glauconitic sands in the lower part of the sequence were deposited in a shallow marine sea, a wider extension of that existing during the earlier part of the Palaeocene. Later, estuarine conditions became established, probably in association with a very broad delta in which arenaceous deposits filled numerous channels. Swampy subaerial conditions occurred intermittently, producing mottled clays in the northern and central areas, whilst brackish water and marine conditions were established in the south.

A further period of erosion preceded a widespread return to marine conditions and the deposition of the London Clay. Marine conditions continued throughout the Eocene in this area; after an initial influx of sandy material, large amounts of fine material were carried into the sea from mud-laden streams. A study of the abundant plant remains suggests that the vegetation of the surrounding land was probably tropical rain forest. The Claygate Beds represent a transition zone adumbrating the sandy Bagshot Beds. The fauna of the more sandy Claygate Beds indicates deposition in a zone of fluctuating slack water and turbulent water in depths of 20 to 40 m, whereas the clayey deposits were laid down in deeper water similar to that of the London Clay.

There is no sedimentary record of events during the latter part of the Tertiary and the early part of the Quaternary which were characterised by uplift, minor folding and erosion. These processes were probably initiated during the culmination of the Miocene earth movements of Europe. A deterioration of the climate to subarctic and arctic conditions was interspersed with warmer periods during the latter part of the Quaternary. Prior to the Anglian ice advance, the Kesgrave Sands and Gravels were deposited from high energy streams bringing materials from areas outside Essex. Periglacial action resulted in the formation of ice-wedges, cryoturbation, and the development of an arctic soil. Thawing of the upper layers produced solifluction lobes, now preserved as the Older Head. During the Anglian glaciation, a thick ice-sheet covered the area, with its southern margin close to the southern edge of the district. This has left a heterogenous assemblage of deposits and structures. Sub-glacial melt-water under high hydrostatic pressure eroded tunnel valleys along the Stort and immediately to the east of the district at Chelmsford. Subsequent infilling of these during the melting of the ice has re-suited in a complex sequence of till and outwash gravels. In the waning phase of the ice-advance the mass of ice in the central part of the area was probably largely stagnant. It gave rise to thick sequences of till with shallow lake deposits. Further outwash streams followed the line of the Roding. Later, several fluctuations in climate resulted in lacustrine peats and silts and deposits of Head. Landslipping of oversteepened London Clay valley sides was probably initiated in glacial times.

History of research

Geological research in the London Basin has developed in several stages, the most significant landmark being the publication of the Geological Survey Old Series maps at one inch to one mile scale between 1868 and 1898. The basic structure and stratigraphy of the region had been deciphered in the years prior to the Survey's work, and only detail and interpretation has changed much since that time. The systematic descriptive work of the early years has been followed by more detailed investigations of the drift and solid geology, especially in the context of the regional palaeogeography of the London Basin. The more important general accounts are mentioned below; other more specific works are given in the references.

One of the earliest papers on the geological structure and stratigraphy of the area to the north-east of London is William Smith's 'Geological View and Section in Essex and Hertfordshire' (1819). A year later Smith published the first geological map of the region. Accounts of the Eocene deposits of the London Basin were produced by Prestwich (1847, 1850, 1852 and 1854), describing the major rock types, locations and palaeontology of the constituent divisions.

Even at this early stage the significance of much of the drift sequence was recognised, although Wood (1867) referred to the boulder clay as 'subaqueous glacial clay'. He did, however, comment on two important factors; firstly the similarity of the boulder clay from Essex to Lincolnshire, a feature that has since been substantiated by mechanical and petrological investigation (Perrin, Davies and Fysh, 1973), and secondly the localisation of the glacial sand and gravel (his 'middle glacial beds'). He regarded the latter as having been deposited in an area of submerged valley systems.

A systematic geological survey of the northern part of the Thames basin was carried out by the Geological Survey during the latter half of the nineteenth century. The southern part of the Epping district was covered by the Old Series One-inch Sheet 1 for the London area, published in 1868 (solid edition) and 1871 (drift). The northern part was included in Sheet 47, of which separate solid and drift editions were published in 1881 and 1884 respectively. Much of this pioneering work was carried out by W. Whitaker, W. H. Penning, W. H. Dalton, F. J. Bennett, H. W. Bristow and W. B. Dawkins.

The first comprehensive description of the central part of the London Basin was contained in the memoir (Whitaker, 1872) for the London Basin. Whitaker described in detail the exposed formations of the Upper Cretaceous and Tertiary. He established the general sequence of 'Lower Eocene' deposits in the Essex area to include Thanet Beds, Woolwich and Reading Beds and the London Clay. Logs of water-wells and borings in the area were appended to the memoir. The explanatory memoir for Sheet 47 was produced in 1878 (Whitaker, Penning, Dalton and Bennett). The complex nature of the drift sequence in part of the Epping district (e.g. Harlow) was noted in that publication. These early memoirs remain invaluable for their records of geological exposures, many of which have long since been obscured. The borehole records were updated by a Water Supply Memoir for Essex (Whitaker and Thresh, 1916) and by a more comprehensive catalogue for Sheet 240 by Davies and Standon-Batt (1965).

Previous geological surveying at a scale of six inches to one mile in the Epping district was restricted to overlaps from adjoining New Series sheets 239 (Hertford) and 257 (Romford) which were completed during the first half of the century. The survey of the eastern side of the Lea valley was carried out by Sherlock between 1914 and 1922; solifluction deposits and landslips have since been added to his observations. The southern overlap was mapped by Dines and Edmunds prior to 1924.

After Whitaker's (1872) account of the solid geology of the London Basin, little work was published on the Tertiary deposits until Boswell's (1916) description of the stratigraphy and petrology of the Lower Eocene deposits of northern Essex. Stamp (1921) further developed the comparison of the English Tertiary deposits with those of the Paris Basin. The minor structural features of the London Basin, particularly the en echelon folds parallel to the strike in the Epping and Chelmsford areas, were discussed by Wooldridge (1923), and later (1926) he outlined the structural control on the sedimentation of those beds. More recent regional strati-graphical and palaeogeographical studies relating to the Tertiary deposits have been published by Davis and Elliott (1957), Hester (1965), Curry (1965) and King (1981).

Investigation of the details of the glacial sequence began with the early work of Prestwich (1847) who first clearly distinguished hill and valley gravels, and noted the presence of 'Pebble Gravel' or 'Pebbly Clay Drift' on hills in the southern part of Hertfordshire and Essex that are collectively described in this memoir as Older Head. These deposits have been regarded as pre-glacial in age, although their depositional environment has been interpreted variously from fully marine (e.g. Whitaker, 1889) to fluviatile (e.g. Woodward, 1909, Wooldridge, 1927) and glacial (e.g. Sherlock, 1924, Thomasson, 1961). Problems of interpretation of the glacial sequence in Essex have been under discussion during the last 30 years. The state of knowledge has been reviewed several times by, for example, West and Donner (1956) and Baker (1971). DM

Chapter 2 Pre-Tertiary rocks

The solid rocks at outcrop and immediately beneath drift in the Epping district range from the Upper Chalk to the Bagshot Beds. No borehole has penetrated below the Chalk, and older formations can be inferred only from neighbouring districts, and in particular from three holes drilled within 5 km of the western and southern boundaries–Ware [TL 352 138], Turnford [TL 3600 0444], and Loughton [TQ 4247 9567]. These borehole' s prove that Upper Greensand and Gault rest directly on Palaeozoic rocks.

Palaeozoic rocks

The surface of the Palaeozoic basement falls from 209 m below sea level near Ware to 398 m below sea level at Canvey Island. Inferred depths to this surface in the Epping district (Figure 2) range from 200 m below OD to the north of Harlow to more than 300 m below OD south-west of Chelmsford. A summary of the logs of some of the wells that have reached it is contained in the memoir for the adjacent Chelmsford district (Bristow, 1985) and mention is made below of only the nearer boreholes. Beneath the Gault in Ware Borehole, 10.7 m of grey, slightly calcareous sandstones and mudstones with shell beds and grey shelly limestones were recovered. A Wenlock age was assigned to these fossiliferous rocks. Farther south, Turnford Borehole proved 9.0 m of purple calcareous shale of Late Devonian age (Mortimer and Chaloner, 1972), and it is likely that rocks of Silurian or Devonian age everywhere underlie the Epping district.

Mesozoic

Lower Cretaceous

Rocks of Triassic and Jurassic age are unlikely to be present beneath the district and the lower part of the Cretaceous is also thought to be absent. The Upper Gault rests unconformably on the basement rocks throughout this district.

The combined thicknesses of the Gault and Upper Green-sand in the Ware, Turnford and Loughton boreholes were 62.9 m, 59.9 m and 63.7 m respectively. Thinning of these deposits towards the north-east was established by a deep borehole at Harwich where the combined thickness was 18.6 m. The Gault consists of dark grey clays, silty and calcareous in places, which are underlain by glauconitic sands in Ware Borehole. The Loughton Borehole terminated in a clay containing phosphatic nodules, similar to material found at the base of the Gault at outcrop in the south of England. Fine-grained grey calcareous sandstones and siltstones comprise the 12 m of Upper Greensand recorded from these boreholes. In parts the deposits become micaceous and glauconitic.

Upper Cretaceous

The Chalk is the oldest group to crop out in the Epping district, occurring in the valleys of the Nimney Bourne and Ash. In addition its presence beneath drift has been proved from boreholes in the Stort valley and in large parts of the area north-west of this river.

The rare roadside, railway and stream sections in the Chalk show extremely soft, putty-like chalk usually beneath drift deposits. The surface of the Chalk is locally very irregular, and an increasing number of small, angular, firm to hard, chalk blocks occurs with depth in the marly matrix beneath the drift. The soft nature of the uppermost chalk is probably due to intense weathering in both periglacial and glacial climates, and some of the putty-like chalk may not be in situ, having been transported by periglacial mass-flows. Two examples of such deposits are recorded. At Nobland Green, in the valley of Nimney Bourne [TL 4017 1732], up to 4 m of very weathered chalk were seen beneath chalky gravel. A trial pit [TL 4296 1886] excavated through terrace deposits near Hadham Cross was completed in the Chalk which was very weathered and of a putty-like consistency. With increasing depth small angular blocks of chalk occurred within a soft chalk matrix.

The quality of the drillers' logs for wells into the Chalk are generally poor and give little indication of any stratigraphy.

A few boreholes, however, record some detail: for example, in a well [TL 4235 0867] west-south-west of Katherines in Great Parndon, 42.7 m of 'Hard grey chalk' were recorded beneath 70.7 m of 'Chalk and flints', forming the uppermost Chalk beneath the Tertiary deposits. Similarly, west of Nazeing the record of a hole includes the following beneath 28.7 m of Tertiary deposits: 'Chalk and Flints' for 75.9 m; 'Hard chalk and flints' 4.3 m; 'Hard rock Chalk' 1.8 m; and 'Hard chalk' 3.7 m. Another well nearby [TL 4039 0440] records 'grey chalk' at shallower levels beneath 35.1 m of London Clay and Lower London Tertiaries: the sequence in descending order was 'Chalk and flints' 59.4 m; 'Grey chalk' 2.4 m; 'Chalk and flints' 12.2 m; and 'Grey chalk' 12.8 m. Without a detailed sequence for the Chalk of the district, it is not possible to interpret these logs.

The total thickness of the Chalk in the district is not known, but the thickest sequence drilled was 153.3 m at a pumping station at Widford [TL 419 166]. Subdivision of the Chalk in this region can usually be made into Lower, Middle and Upper, the base of the Middle Chalk being marked by the Melbourn Rock and that of the Upper by the Chalk Rock. These marker bands can be identified in boreholes by electrical logging, and in the above hole this indicated thicknesses of 60.0 m for the Upper Chalk, 86.9 m for the Middle Chalk and 6.4 m (unbottomed) for the Lower Chalk. The thickness for the Upper Chalk is presumably a minimum for that area, since the borehole began in drift.

Estimates of the total thickness of Chalk in the district can be made by extrapolation from boreholes in the surrounding areas. These show that the Chalk thickens north-eastwards from London, a feature which was first noted by Prestwich (1852). The thinnest sequence (175.3 m) was encountered in Park Royal (London) Borehole, whereas 206.3 m were recorded at Canvey Island and 271.2 m at Harwich. A short distance to the west of the Epping district, Turnford Borehole proved 208 m of Chalk, and on this evidence it is likely that upwards of 200 m of Chalk underlie the district. In Ware and Turnford boreholes the Chalk has been subdivided. The presence of soft greyish marly chalk resembling the Plenus Marls, and its confirmation by electrical logging in Ware Borehole, give thicknesses of 49.7 m for the Lower Chalk and 69.2 and 55.8 m for the middle and upper divisions respectively. Slightly higher figures (56.0, 72.2 and 79.4 m) were obtained for Turnford Borehole. These figures contrast with those for Widford Borehole, suggesting that the broad overall trend may be a simplification that conceals significant local variations.

The varying thicknesses of the Upper Chalk have been attributed to both depositional thinning and to the erosion that has resulted in the occurrence of different zones directly below the Tertiary deposits. A map of the subcrop of the zones in the London and Hampshire basins was compiled by Curry (1965), and indicates that the Chalk immediately underlying the Epping district is of the coranguinum Zone. DM

Preliminary observations on the 6.1-m of Upper Chalk penetrated at the base of Cobbin's Brook No. 1 Borehole [TL 4160 0238] were published by Hildreth (1972) who gave a short fossil list and noted an Orbirhynchia-rich band in the lowest 0.46 m. The revised faunal list comprises the following additions: Labyrinthidoma dumptonensis, Porosphaera globularis, Kingena lima, Orbirhynchia cf. pisiformis, Chlamys cretosa, Cladoceramus undulatoplicatus, Cordiceramus cordiformis [juv.], Limea granulata, 'Ostrea' incurva, Plicatula barroisi, Pseudoperna sp.[adnate on inoceramid shells], Pycnodonte sp., Sphenoceramus ex gr. cardissoides/pachti, Bourgueticrinus columnals, minute crinoid brachials (probably Bourgueticrinus), Stereocidaris sceptrifera and ostracods. The occurrence of pink thin-shelled inoceramid fragments is strongly suggestive of the base of the Santonian, and this is confirmed by the association of Cladoceramus undulatoplicatus with Sphenoceramus ex gr. cardissoideslpachti indicating an horizon at or about the equivalent of the Bedwell's Columnar Flint Band of Thanet. A microsample from the same level examined by Dr H. W. Bailey (Paleoservices) pointed to an horizon low in the Stensioeina granulata polonica foraminiferal Biozone (Bailey and others, 1983), supporting the evidence from the inoceramids. The large lituolacean foraminifer Labyrinthidoma dumptonensis, which ranges through the greater part of the Santonian portion of the coranguinum Zone of the Thanet coast (Adams, Knight and Hodgkinson, 1973, fig.1), has not previously been reported outside that area. CJW

Chapter 3 Tertiary rocks (Palaeocene and Eocene)

Nomenclature

The Tertiary deposits, consisting mainly of clays and sands, rest unconformably on the Chalk. No angular discordance is seen but the unconformable relationship is shown over a wide area by the differing Chalk zones lying immediately below the Palaeocene deposits (Curry, 1965, fig. 2). The lithostratigraphical divisions of the Tertiary formations present in this district, and their generally accepted chronostratigraphy are given in (Table 1). The position of the upper boundary of the Palaeocene, defined as the base of the Ypresian stage, within the lithological sequence has caused much discussion. On stratigraphical and palaeontological grounds, Curry (1958) placed the junction at the bottom of the Oldhaven Beds, which occur below the London Clay in North Kent but are not recognisable in the Epping district. Later, he (1966) and Cooper (1976) placed it at the top of that sequence, and subsequently Curry and others (1978) stated that the base of the Eocene should be taken at the base of the London Clay. The problem is still by no means completely resolved because the microfaunal assemblages within the sequences indicate that there is a non-sequence at the base of the London Clay (Knox and Ellison, 1979; Knox and Harland, 1979; Knox, Harland and King, 1983). However, it is apparent that in East Anglia the chronological divisions are broadly coincident with the lithologies, and the base of the London Clay may thus be regarded as approximately coincident with the base of the Eocene.

In other parts of southern England attempts have been made recently to determine radiometric ages for these boundaries (Odin, Curry and Hunziker, 1978; Fitch, Hooker, Miller and Brereton, 1978) using K-Ar determinations on glauconites. The latter authors place the Palaeocene–Eocene boundary at the base of the Ypresian stage at 54.3 Ma, whereas the former place the Series boundary at the base of the Sparnacian at 52 Ma.

The initial two-fold division in this area was made by Prestwich (1852, p.236) when he referred to all the beds below the London Clay as 'Lower London Tertiaries'. These consisted of the Thanet Beds and the Woolwich and Reading Beds (see (Table 1)). The Thanet Beds were first recorded as 'Thanet Sand' by Prestwich (1852), and described as a sequence of yellow to grey sands, with some glauconite and unabraded green-coated flints at the base. The base of the Thanet Beds was recorded in the neighbourhood of Grays in Essex, and referred to as the Bull's-head Bed (now Bullhead Bed) by Morris (1876). The mottled clays and sandy beds between the Thanet Beds and the London Clay were named the Woolwich and Reading Series by Prestwich (1854), and later the Woolwich and Reading Beds by Whitaker (Hull and Whitaker, 1861). Prestwich also recognised the variable nature and penecontemporaneity of sands with shelly clays, mottled clays, and a glauconitic, locally fossiliferous, pebbly sand, which together comprise the Woolwich and Reading Beds. Later, Hester (1965) classified these divisions of the Woolwich and Reading Beds as the Woolwich (estuarine) facies, the Reading (fluviatile) facies, and the Bottom Bed (marine) facies respectively.

The silts and sands lying between the Woolwich and Reading Beds and the clays of the London Clay have been assigned to different formations by various authors. Prestwich (1850) regarded these deposits as the basement bed of the London Clay (since renamed London Clay Basement Bed by various authors). Later, Whitaker (1866) defined the lowest sands with rounded flint pebbles in the type section at Oldhaven Gap near Herne Bay in Kent as the Oldhaven Beds. The classification of Whitaker was widely used even as recently as 1970 when King regarded the Oldhaven Beds as distinct from the London Clay (including the Basement Bed) on faunal evidence. However, Cooper (1976) placed the lower part of Whitaker's London Clay Basement Bed in the Oldhaven Formation, and considered the upper part to be the true basal beds of the London Clay. In the Epping district only limited data are available, and it is not possible to distinguish the Oldhaven Beds with confidence. The sands which occur at the base of the London Clay are here described as the Basement Bed of that formation.

The Lower London Tertiary deposits of the Epping district are entirely covered by younger solid deposits or by drift. A subdrift crop is present on either side of the Stort and Lea valleys and between Widford and Hunsdon (Figure 3) and (Figure 4), but evidence of its presence is restricted to a few ditch and pit sections penetrating the drift and to well and borehole records. The generally poor drillers' logs place constraints on the recognition and classification of these deposits. The descriptions 'mottled sandy clay' and 'Thanet Sand' have been commonly used in the logs for the Woolwich and Reading Beds and the Thanet Beds respectively. Even in the most carefully described logs (see Appendix 1, also Hildreth, 1972), it has not been possible to distinguish between sands that can be equated with the type Oldhaven Beds and the sands of the London Clay Basement Bed. Hence only the Thanet Beds and Woolwich and Reading Beds are recognisable divisions in this district. The top of the Woolwich and Reading Beds is taken below the glauconitic basal sand or pebble bed of the London Clay (the Basement Bed). In the south of the Epping district the mottled clays are absent and their position taken by grey very shelly clays, termed the 'Woolwich Shell Beds'. In this area the base of the London Clay has been taken at the top of these shelly clays.

Beds above the Lower London Tertiaries include London Clay, Claygate Beds, and Bagshot Beds. The London Clay, as originally defined by Prestwich (1854) was, on the basis of exposures in the London area, divided by Wrigley (1924, 1940) into five faunal units. Other palaeontological subdivisions of these predominantly clayey sediments have been made by King (1970; 1981) and Cooper (1976). BGS boreholes at Hadleigh [TQ 8220 8655] and Stock [TL 7054 0045] in the adjacent Southend (258) and Chelmsford (241) districts recorded sequences which were subdivided on the basis of lithology and palaeontology. They are discussed in detail in the memoirs accompanying these sheets (Lake, Ellison, Henson and Conway, 1986; Bristow, 1985). No detailed sequence through the London Clay was available for the Epping district and no subdivisions have been made.

At the top of the London Clay the dominantly clay sediments are succeeded conformably by interbedded fine-grained sands, silts and clays, similar to those classified as Claygate Beds in the Claygate area of Surrey (Dewey, 1912). These so-called 'Passage Beds' (Wooldridge and others, 1924) mark a transition between the London Clay and the sands of the Bagshot Beds, and were first mapped in 1922 in Essex by Dines and Edmunds in the Romford (257) district. More recent work by Bristow, Ellison and Wood (1980) discusses in detail the occurrence, lithology and palaeontology of the Claygate Beds in Essex.

Prestwich (1847) also recognised the Bagshot 'sands' in Essex, and the term Bagshot Beds of this account follows work by Wooldridge and others (1924) and Dines and Edmunds (1925). The Bagshot Beds in Stock Borehole have been divided by Bristow (1985) into a lower sand division, corresponding to the Bagshot sands of Prestwich and other early workers, a middle clay and silt division, and the Bagshot Pebble Bed. In the Epping district, the lower sand division is widely recognised on high ground in the south but the middle division has not been recognised. The Bagshot Pebble Bed is present only in the extreme south-east of the district, and further discussion of that occurrence is presented on p. 20. DM, RAE, RDL

Thanet Beds

The Thanet Beds consist of homogeneous grey to greenish grey fine-grained sands with a basal pebble bed (Bullhead Bed). In drillers' logs this formation is described either as 'Thanet Sand', grey sands, or 'running sand'. In addition the basal bed of 'flints' or 'green-coated flints', forming the Bullhead Bed, is often recorded. The Bullhead Bed is thought to be present over most of the district to the south and east of the Stort valley, and maintains a constant thickness of 0.3 m. The bed consists of angular to sub-rounded and nodular flints, up to 40 cm across, mostly with a green glauconite coating. It was the globular type of flint that gave the original name of Bull's-head Bed to this unit. In addition, some logs record reworked well-rounded, black, green and blue-coated flint pebbles at this horizon.

In the Cobbin's Brook boreholes [TL 4160 0238]; [TL 4200 0257]; [TL 4243 0273] Hildreth (1972) divided the Thanet Beds into a lower unit of homogenous pale to dark grey silts and clayey silts, which are in parts glauconitic, and an upper, homogeneous, pale greenish grey, fine-grained, glauconitic, clayey sand. The upper sandy beds are mainly poorly compacted, and some beds of loose sand were recorded by Hildreth.

The basal part of the Lower London Tertiaries to the north-west of the Stort valley, as recorded in Gilston Borehole [TL 4417 1349], consist of strongly bioturbated clayey sands which are glauconitic at the base. In contrast the succeeding Woolwich and Reading Beds are distinctly micaceous, and contain stringers of well-rounded black flints and some clay laminae.

The Thanet Beds vary in thickness from less than 5 m in the north-west to 20 m in the south-east (Figure 4). The broad pattern of the north-westward thinning of the Thanet Beds is matched by a similar pattern in the Lower London Tertiaries as a whole.

Although no fauna has been recorded from the Thanet Beds in the Epping district, they are regarded as marine shallow-water deposits on the evidence of the presence of glauconite and the fauna collected from contiguous areas.

Details

The typical grey fine-grained sands have not been recognised in boreholes to the north-west of the Stort valley, and no information was available from the northern part of the district east of this area from Hatfield Heath [TL 520 150] to Pleshey [TL 665 145].

In the west of the district between Harlow [TL 45 10] and Cobbin's Brook, borehole records show the Thanet Beds to be 5 to 10 m thick. In many the strata are described as 'Thanet Sand'; for example a borehole [TL 4696 1373] in the Stort valley, north of Harlow, contained 8.2 m of 'Thanet Sand'. In several of the logs the basal flint layer (Bullhead Bed) was separately described as 'green flints'; for example in boreholes 1 km west of Nazeing Church [TL 4005 0670] and in Roydon Hamlet [TL 4174 0768]. The Thanet Beds in the Cobbin's Brook boreholes, [TL 4160 0238]; [TL 4200 0257]; [TL 4243 0273], attained thicknesses of between 6.2 and 7.9 m. Summaries of the complete logs are contained in the Appendix 1 (p. 72).

The Thanet Beds thicken eastwards from the Lea valley and Harlow areas, as indicated by a borehole at Tilegate Green near High Laver, where 17.4 m of 'grey sand and basal, green coated flints' were recorded [TL 5129 0877]. In Epping, 13.1 m of 'wet sand and basal black flints and pebbles' were proved [TL 4618 0145], while the thickest sequence of Thanet Beds was at Skreens Park [TL 6261 0809], west of Roxwell, where there were 20.7 m of grey sand with a basal flint bed (Figure 5). DM

Woolwich and Reading Beds

The Woolwich and Reading Beds are a complex sequence of sands, clayey sands and clays, which show some lateral variation in this district (Ellison, 1983). In the literature, numerous names have been given to the individual parts of the Woolwich and Reading Beds in the London and Hampshire Basins. These names have not been found useful in this account but are mentioned below for comparison with other districts. The glauconitic sands are referred to as the 'Bottom Bed'; the micaceous brownish fine sands as the 'Woolwich Beds'; the mottled clays as the 'Reading Beds'. The term facies has also been applied to each of these formations. The thin shelly clays have been named the 'Woolwich Shell Bed'.

The base of the sequence is commonly marked by a thin bed of black, well-rounded flint pebbles resting on a burrowed surface. The succeeding sands are fine-grained, glauconitic, green, mauve and yellow mottled, with stringers and lenses of black flints, white patinated flints and some quartz pebbles. These sands pass upwards into silty fine-grained, micaceous sands which are dominantly brown with red and grey-green mottling. Scattered quartz and flint pebbles are present. In the northern part of the district, there are intercalations of waxy clays towards the top of these sands. In places the silt and sand contents of the clays become high, but the important characteristic is the polychromatic colour variation, with grey, red, green, brown and blue mottling. Some small calcareous nodules (race) are present locally near the surface.

The mottled clays become thinner and less numerous to the south of the district, and south of an east–west line from Cobbin's Brook to Writtle (Figure 3) they are replaced by grey very fossiliferous silts and clays. In the Cobbin's Brook boreholes (see Appendix 1), these consist of 0.6 to 1.0 m of dark grey and grey-green, finely laminated, pyritic, silty clays and mudstones containing abundant shell debris and shell beds. These three closely spaced boreholes lie apparently on the northern margin of the shelly clays because both mottled clays and grey fossiliferous clays are present within the sequence (Figure 5). Here the glauconitic sands of the bottom part of the Woolwich and Reading Beds pass upwards into pinkish to reddish brown, fine-grained sands, and clayey sands with scattered flint pebbles. Within these sands are thin intercalations of stiff, waxy, mottled grey, red and orange-brown silty and sandy clay.

In the borehole and well logs it is not always possible to recognise the constituents of the Woolwich and Reading Beds; for example, in many cases the glauconitic sands and the micaceous sands are commonly not distinguished although the polychromatic clays are generally recorded where present.

Although the thickness of the Woolwich and Reading Beds is variable throughout the district, there is no discernable simple pattern. Many of the boreholes in the north-west encounter these strata immediately beneath drift, and hence the number of boreholes in that area giving the complete thickness for the Woolwich and Reading Beds are few. Gilston Borehole, however, proved a full succession of 10.0 m. Farther south in the Cobbin's Brook and Epping areas, these beds attain thicknesses of between 10 and 14.5 m; 5 to 10 m have been recorded from the east of the district in the Magdalen Laver, Willingdale and Roxwell areas. The glauconitic sands in the Cobbin's Brook boreholes are 6.5 to 9.0 m thick. In the north-west of the district the sandy beds at the base vary in thickness from 3 to 11 m. In contrast to the neighbouring Chelmsford district where the combined thickness of the Woolwich and Reading Beds and Thanet Beds is fairly constant (Bristow, 1985, fig. 6), there is a north-westward thinning in the Epping district from 28 m at Writtle to 15 m north-west of the Stort valley (beyond the present district).

Little is known about the fauna of the Woolwich and Reading Beds of the district. The uppermost parts of the se-sequence in the north-west have yielded abundant oyster debris and operculae of small gastropods. The operculae are 1.0 to 3.0 mm across, and the growth-rings show a marked amount of rotation during ontogeny. The shelly mudstones of the Cobbin's Brook boreholes contained an abundant fauna (Hildreth, 1972). In the lower part of the sequence the brackish-water fossils Brotia melanioides and Corbicula sp.were present. A shell bed above this contained fragments of Ostrea sp.and Corbicula cordata. Shelly clays at the top of the sequence included C. cordata, C. sp.and Scrobicularia condamini, the gastropod Stenothyra parkinsoni and and insect wing.

The environment of deposition of the Woolwich and Reading Beds is complex. The pebble bed at the base of the sequence represents an erosion interval prior to the deposition of the glauconitic sands in a marine environment. Elsewhere in the London Basin, Hester (1965) has claimed that there is a futher erosion surface at the top of the glauconitic sands, but the transitional nature of this junction in the Cobbin's Brook and Gilston boreholes is more indicative of a gradual facies change to a non-marine environment. The polychromatic and, in particular, the reddened clays and sandy clays indicate periods of lowered water-table, and the presence of the operculae in beds around the Gilston area indicate the presence of ephemeral pools and water courses. In the southern part of the district periods of emergence were probably short-lived, with deposition continuing in an estuarine environment of constantly changing water courses. Towards the top of the sequence a transition to brackish water and marine conditions took place with the deposition of the shelly clays. The pattern of sedimentation recognised in the Woolwich and Reading Beds of this district has also been demonstrated in the neighbouring Chelmsford district (Bristow, 1985). DM

Details

The Woolwich and Reading Beds crop beneath drift in the area to the north-west of, and in, the Stort valley. Several exposures have been recorded in ditches and trial pits, but these outcrops are too small to show on the 1:50 000 map. Information is also available from well and borehole records. In 1976, a deepened ditch [TL 4304 1775] about 1 km south-east of Hadham Cross showed grey and red mottled sands. Exposures in the Hadham Mill area [TL 425 170] were recorded by Whitaker and others (1878): beneath drift they noted 0.3 m of pale brown clay with race, overlying 0.9 m of green fine-grained sand, somewhat clayey at the base, and with green-coated flints, in a pit approximately 0.4 km east of Hadham Mill. Mottled clays and sands were also seen in the section along the western side of the road east of Hadham Mill, but no details were given. A trial pit [TL 4310 1746] in the base of the gravel workings at Hadham Mill showed 0.35 m of stiff mottled red and blue-grey clay overlain by sands of the basal London Clay. West of Widford a gas-line trench [TL 4111 1578] was bottomed in grey and red mottled sands. As Chalk crops out at slightly lower levels in the Ash valley, these sands probably represent lower parts of the Woolwich and Reading Beds. About 200 m north- east of the trench is an area of landslip and, although Lower London Tertiaries were not proved there, it is probable that water from the sandy beds was responsible for the slope failure. Whitaker and others (1878) also recorded approximately 0.9 m of fine-grained, light green sand, clayey in part and with green-coated flints, in a road-cutting south of Widford Railway Station [TL 417 164]. BSPM

Thickening of the Woolwich and Reading Beds south-east of Widford to the Stort valley can be demonstrated from several borehole records along a line running north-west to south-east. At the village of Widford [TL 4208 1605], mottled clays overlying 5.6 m of green loamy sand and green sand, were recorded beneath brown and blue clay (?London Clay) and above the Chalk, whereas the BGS borehole at Gilston [TL 4417 1349] contained 10.0 m of Woolwich and Reading Beds, of which the upper unit, 6.5 m thick, consisted dominantly of mottled silty clays. The lower sandy unit was variably clayey, micaceous and generally brown, but with some red and green mottling. A concentration of well rounded black flints occurred at the base. The log of Gilston Borehole is summarised in Appendix 1 (p. 74).

In the northern part of the district, shelly beds within the Woolwich and Reading Beds were noted from only one borehole [TL 4486 1157], approximately 0.5 km NNE of the railway station at Harlow, where the following sequence was recorded:

Numerous boreholes in the Nazeing area [TL 41 06] showed the thickness of Woolwich and Reading Beds to vary from 8 to 12 m. The logs of most boreholes distinguish the mottled clays from the sands, but only in some can the glauconitic nature of the lower part of the sequence be inferred from the records of 'green sandy loam'.

Eastwards from this area to Chelmsford, the Woolwich and Reading Beds appear to be less than 10 m thick, with 4.9 m as the thinnest record from a borehole [TL 5129 0877] at Tilegate Green. Farther east, 9.3 and 5.8 m were recognised in boreholes at Torrell's Hall [TL 6009 0832], north of Willingale, and at Skreens Park [TL 6261 0809], 1.5 km west of Roxwell (Figure 5).

The southern limit of the mottled clays has been demonstrated by sequences encountered in the boreholes at Cobbin's Brook. Red mottled clays were present only in No. 2 Borehole; they are absent at Epping [TL 4618 0145] and at Ingatestone [TL 6445 0000]. The thicknesses of the Woolwich and Reading Beds were 14.1, 14.0 and 10.1 m in Cobbin's Brook Nos. 1 to 3 respectively ((Figure 5) and Appendix 1), 11.6m at Epping, and 9.8m at Ingatestone; shelly material was recovered from the upper part of the Woolwich and Reading Beds in each borehole. A further record of 4.3 m of 'blue clayey sand and occasional shells' comes from the borehole at Epping, and 1 m of 'clay and shells' was recorded from the borehole at Ingatestone. DM

London Clay

Lithology

The London Clay crops out over large areas in the southwest of the district and has the largest subdrift area of the solid formations. The most extensive areas of outcrop are at Epping Long Green, Nazeing, Cobbin's Brook, Bobbingworth and Theydon Garnon. At subcrop, it is present in outliers beneath glacial deposits in the Hunsdon and Gilston areas north-west of the Stort. Over much of the central and eastern part of the district it is directly overlain by glacial deposits, but small outcrops are present in the valleys of the Chelmer, Cripsey Brook, Roding and Roxwell Brook (Figure 6) . In the south it is succeeded and overlain by Claygate Beds in the Rye Hill, Epping, North Weald, Norton Heath, Stondon Massey and Ingatestone areas.

At the base of the formation, the Basement Bed comprises dominantly sandy and silty lithologies between 1.5 and 7 m thick. In drillers' logs these are commonly described as 'sand with pebbles' or 'with shells'. In the south-east near Ingatestone an anomalously high figure of 10 m was recorded for this unit, but may be unreliable. In the Cobbin's Brook boreholes (Hildreth, 1972; see also Appendix 1) the junction between the Woolwich and Reading Beds and the London Clay was marked by a thin bed of well-rounded, black flint pebbles (see also p. 15). Above this the Basement Bed consisted of brown to grey silts and clayey sands, containing shell and carbonaceous debris, and interbedded thin cement-stones and hard calcareous sandstones. The top of this bed in Cobbin's Brook Nos. 1 and 3 boreholes was marked by a shell layer.

At surface the remainder of the London Clay is a soft to stiff, chocolate-brown to reddish brown clay or silty clay, commonly micaceous, and with race nodules where it is in proximity to calcareous materials such as boulder clay. Selenite is also present in places. Towards the base, in Gilston Borehole [TL 4417 1349], an increasing amount of glauconitic fine-grained sand was recorded. In unweathered sequences the colour is blue to blue-grey, and the clay is hard and fissured, commonly laminated, pyritic, and with shell detritus.

The depth of weathering, as marked by the brown colouration, is very variable; where London Clay occurs at the surface, the weathering may be to depths of 8 m as in the Cobbin's Brook area, indicating extensive periods of penetrative weathering possibly under periglacial conditions. In places the depth of weathering beneath drift deposits varies inversely with the thickness of the overlying drift, a feature difficult to explain from the available data. Elsewhere, however, weathering to depths of 12 m below the base of thick drift has been noted in boreholes for the M11 motorway between Harlow and North Weald. In borehole logs the London Clay is variously recorded as 'blue clay' and 'brown clay'. The records of 'stones' or 'clay stones' probably refer to the presence of calcareous mudstones (septarian nodules).

The degree of firmness of the weathered zone in exposed areas is commonly related to the form of the slope, with the softest material present in valley bottoms and on concave slopes and the firmest material on steep and convex slopes.

Very soft, destructured London Clay in the valley bottoms at Nazeingwood Common and in Cobbin's Brook may be partly due to deep weathering and to solifluction. The junction between the very soft material and the stiff fresh material below is indeterminable and no Head has been shown in this situation on the 1:50 000 map. The oversteepening of the London Clay slopes in the Nazeing and Galley Hill areas in the west of the district has resulted in the formation of landslips.

No complete detailed sequences are available in this district, but Bristow (1985) has provided a detailed subdivision of the sequence at Stock Borehole a few kilometres to the south-east of the district. Farther afield, Wrigley (1924) has subdivided the formation into five on the basis of faunal and lithological variations and, although strictly applicable only to the London area, these divisions have been loosely extended to other parts of the London Basin. A more simplified lithological subdivision into upper, middle and lower divisions was made by Burnett and Fookes (1974) in a review of the regional variation of the engineering properties of the London Clay. Subsequently King (1981) has subdivided the London Clay and Claygate Beds into five biofacies units (A to E in ascending order), of which division E embraces the highest beds of the London Clay and the Claygate Beds.

The thickness of the London Clay in this district can only be given approximately because few boreholes in the southern area penetrate its full thickness; and because it is difficult to identify the base of the overlying Claygate Beds with precision and consistency (see p. 17). The estimates appear to show a consistent thinning westwards. The cored Stock Borehole [TL 7054 0045] in the south-west of the Chelmsford district showed a thickness of 126.3 m. A borehole [TL 6692 0168] at Margaretting, sited on the lower part of the Claygate Beds and approximately 4 km northwest of Stock, proved 126.5 m of London Clay below an unlogged dug well; the well was excavated in the Claygate Beds, and therefore, a complete sequence of the London Clay was thus recorded. At Epping 96.0 m of London Clay were recorded in a well [TL 4618 0145], giving a calculated total thickness of 117 m extrapolated from the position of the nearby Claygate Beds outcrop; at Hunter's Hall Farm [TL 4310 0445] another gives a calculated thickness of 102 m.

An anomalously large thickness for the London Clay has been recorded from a borehole [TL 6445 0000] at Fryerning, only 5 km from the boreholes at Margaretting and Stock. It is either 144.8 or 164.0 m, depending on where the base of the Claygate Beds is taken. However, the lower figure gives a minimum thickness of 27.4 m for the Claygate Beds which is too high for this area (see p. 17). The base of the Claygate Beds in the Ingatestone area falls southward possibly indicating a high local dip, and it is possible that the hole intersected a fault. DM, RAE

Palaeontology

The basal sands in Gilston Borehole yielded an incomplete pyritised bivalve with some decomposed shell still attached; it is probably Arctica cf. morrisi. Although no other macro-fauna has been recorded from this stratigraphical level in the district, an abundant microfauna was present in samples from three boreholes in the north-west [TL 4319 1751]; [TL 4917 1505]; [TL 4417 1349]. The microfaunal assemblage, included the following foraminifera: Epistominella sp.aff. E. vitrea, Glandulina sp.1, Glandulina sp. 2., Globulina inaequalis, Guttulina austriaca, G. communis, Haplophragmoides sp., Nonion laeve, Nonionella sp.aff. N. cretacea, Pararotalia spinigera, Protelphidium sp.3 of Murray and Wright (1974), Spirillina sp.aff. S. perforata. The marine ostracods were Clithrocytheridea sp.1, Clithrocytheridea sp. 2, Cytheretta aff. scrobiculoplicata, Cytheridea unispinae, Cytheropteron wetherelli, Loxoconcha sp., Schuleridea perforata. Some of these species have also been reported from the Oldhaven Beds in Stock Borehole (Bristow, 1985, p.21).

New sections along the route of the M11 during its construction between 1973 and 1976 provided several sections in both the London Clay and Claygate Beds. Collections by Ward (1978 and pers. comm.) from these sections provide important palaeontological data for these beds in the southern part of the district. The individual sections and faunas are listed below; most of the records, and collections are from the Passmore Edwards Museum, London.

Boreholes for bridge piles at Little Hallingbury [TL 512 174] encountered very silty clay containing Arctica sp., Spiratella mercinensis and ostracods. Lithologically this sequence is characteristic of the lower part of the London Clay. Further bridge piles [TL 491 104], sunk to 30 m near Feltimores, yielded Graphularia wetherelli, Euspira glaucinoides, Hemipleurotoma prestwichi, Pseudoneptunea curta, and Nuculana amygdaloides.

Cutting sections and drainage trenches [TL 483 087] 500 m WNW of Foster Street contained the following: Graphularia wetherelli and Laevidentalium nitens common, Euspira glaucinoides, Fusiturris prestwichi, Pseudoneptunea curta and Nuculana amygdaloides frequent, with Fusinus unicarinatus, F. wetherelli, Galeodea gallica, Mathilda sororcula, Murex argillaceus, and Cuspidaria inflata, together with foraminifera, ostracods, fish teeth, otoliths and fruits including Nipa burtini. The brachiopod Terebratulina wardenensis was common at one horizon. Two kilometres to the south of this section the sequence at the interchange with the Harlow road [TL 476 067] yielded the following: Rotularia bognoriensis, Euspira glaucinoides, Daphnobela juncea, Tibia lucida, ?Abra splendens, Teredina sp., Glyphithyreus wetherelli, Cylindracanthus rectus, Eugomphodus (E.) hopei, E. (Striatolamia) macrotus, Physodon tertius, Scyliorhinus biauriculatus, 'S. ' minutissimus, a teleost tooth (?Cybium sp.), bones, and indeterminate fruit and fragments of wood. The lithology and the location of the section in relation to the base and top of the formation indicate that the sequence is within the upper part of the London Clay.

Two sections from M11 cuttings south-east of Epping gave faunas from the uppermost part of the London Clay. The following were recorded from the bottom of the cutting 600 m south-west of Gaynes Park [TL 479 015]: Rotularia bognoriensis, Athleta nodosus, Tibia lucida and Calpitaria sulcataria; 'Striarca' wrigleyi was found in drainage trenches and bridge foundations. To the south [TL 473 004] at Theydon Garnon, the following were recorded from the west face of the cutting: Laevidentalium nitens abundant, Graphularia wetherelli, Euspira glaucinoides, Hemipleurotoma spp., Pseudoneptunea curta, Tibia sublucida/lucida and Nucula consors common, together with Bullinella sp., Fusinus unicarinatus, F. wetherelli, Mathilda sororcula, Orthochetus elongatus, Scaphander parisiensis, Sinum clathratum, Stellaxis pulcher, Turricula sp., Nucula consors, Nuculana amygdaloides, foraminifera, fish teeth, otoliths and the fruit Nipa burtina. Terebratulina wardenensis was common at one horizon, and Xenophora agglutinans was found in a septarian layer near the top of the section. This sequence is immediately overlain by the Claygate Beds (cf. fauna p. 17).

At Coopersale Lane [TL 466 989] a cutting yielded Rotularia bognoriensis, Athleta nodosus, Tibia lucida and Calpitaria sulcataria common, with Xenophora agglutinans, Abra splendens, otoliths including Pristigenys bella and sporadic fish teeth. Venericardia trinobantium was common in a bed of dark green silty sand near the bottom of the cutting and 'Striarca' wrigleyi occurred commonly, in many places as clusters, in the underlying clay. These beds are thought to lie in the highest London Clay although the Claygate Beds may also be thinly represented (King, 1981, p.45; Ward, 1978, p.20).

Apart from the motorway sections little is known about the fauna from other localities except for important sections near Epping. In a former brickyard (exact site uncertain) near the railway station in Epping, specimens of Teredo borings in calcified wood have been found, along with septaria containing numerous shells of 'Striarca' wrigleyi.

The fullest faunal list has been recorded by Cooper (1974) from a pit near Hallsford Bridge at Ongar [TL 562 024]. The revised list is given in full below.

Annelida

Ditrupa Plana, Rotularia bognoriensis, ?Sclerostyla sp.and scolecodonts.

Bryozoa

Batopora clithridiata Protozoa 'Ammodiscus', 'Globigerina', Lenticulina', 'Marginulina', 'Nodosaria', 'Quinqueloculina' and 'Textularia'.

Coelenterata

Graphularia wetherelli, Paracyathus caryophyllus. Brachiopoda Terebratulina wardenensis Scaphopoda Laevidentalium nitens Gastropoda Ancistrosyrinx sp., Bathytoma sp., Bonellitia ?laeviuscula, Bullinella cf. consors, B. sp., Conospira concznna, Epitonium undosum, Eratotrivia sp., Euspira glaucinoides, Euthriofusus transversarius, Ficopsis multiformis, Fusinus wetherelli, Galeodea gallica, Litiopa sulculosa Edwards MS, Murex subcristatus, Odostomia sp., Orthochetus elongatus, Phalium (Galeodosconsia) striatum, Pollia londini, Scaphander parisiensis, Scaphella wetherelli, Solariaxis pincher, Sphaerocypraea alata, Streptolathyrus cymatodis, S. trilineatus, Surculites errans, S. velatus, Tibia lucida, T. sublucida, Trochotugurium extensum, Turricula teretrium.

Bivalvia

Abra splendens, Astarte filigera, Calpitaria sulcataria, Corbula globosa, Cuspidaria inflata, C. triradiata, Modiolus tubicola, Nucula cornpressa, Nuculana amygdaloides, Ostrea sp., Pholadomya cf. margaritacea, Pinna affinis, Pterelectroma media, Thracia sp. (?oblata), Teredina personata, teredinid tubes.

Cephalopoda

Cimomia imperialis, nautiloid fragments, Eutrephoceras regalis, E. aff. regalis.

Arthropoda

Ctenocheles sp. nov., Dromilites lamarcki, Hoploparia gammaroides, Linuparus sp., Portunites incerta, Zanthopsis leachi and various ostracods and barnacles.

Echinodermata

Coelopleurus wetherelli, Democrinus londinensis, Ophioglypha wetherelli.

Pisces (bony fishes and sharks)

Albula oweni, 'Ardicolus marriotti', Halecopsis sp.(?insignis), ?Megalops sp.[scale], Trichiurides orpiensis, Eugomphodus (E.) hopei, E. (Striatolamia) macrotus, Galeorhinus lefevrei, G. minor, Isistius trituratus, Isurolamna affinis, Jaekelotodus trigonalis, 'Lamna' lerichei, Notorynchus serratissimus, Odontaspis winkleri, Physodon tertius, Scyliorhinus gilberti, 'S.' biauriculatus, Squalus minor, Squatina prima.

Pisces (teleost otoliths–nomenclature revised in some cases)

Ampheristus toliapicus, Apogon glaber, Argentina extenuata, Brosmophycis sagittalis, Brotula arcuata, Centroberyx crenulatus, C. lemoinei, Cepola densa, Citharinus circularis, Dentex pentagonalis, Dermatopsis argutus, Ditrema sheppeyensis, Glaucosoma pentagonalis, Holocentrus sheppeyensis, Hoplostethus densus, Hypomesus pennatus, Leuresthes distans, Microgadus subnotus, ?Molva dubia, ?Muraenesox cymbium, Myripristis sinuatus, Nemopteryx serratus, Neobythites obtusus, Paralabrax tenuicauda, Paratrachichthys angulatus, Peristedion semiglobosum, Pristigenys bella, Pterothrissus angulatus, Raniceps papillosus, Sebastodes bognoriensis, Synodus davisi, Uranoscopus rotundatus, Uroconger validus.

Aves

'Proherodus' sp.(Tarsometatarsal)

Reptilia

Fragments of turtle shell

Ichnofossils

burrow infills, callianassid burrows, faecal pellets and various other trace fossils.

Plantae

Anonaspermum commune, Dunstania multilocularis, Icacinicarya amygdaloidea, Magnolia lobata, Nipa burtini, Wetherellia variabilis.

The fauna is indicative of the upper middle part of the London Clay, i.e. divisions C and D of King (1981, p.48).

The London Clay was deposited in a marine environment in which mud derived from a nearby river estuary was the dominant sediment. It has been suggested that the surrounding land was relatively low lying and abundantly forested, thus supplying the abundant plant remains (Sherlock, 1960). Chandler (1961) concluded that the climate of the time was one of high temperature and rainfall that favoured tropical rainforests. Sea-bottom conditions were variable: the sequence of homogeneous clays was extensively burrowed and sifted by the indigenous fauna, whereas the presence of finely laminated clays and silty clays suggests the absence of a contemporaneous bottom-feeding fauna. In general the London Clay sea was probably shallow and relatively near to land though Curry (1965, p.159–162) maintained that the sea was greater than 180 m deep. Most of the indigenous fauna listed above are, however, shallow water dwellers. DM, MJH, CJW

Details

London Clay Basement Bed

For ease of comparison the London Clay Basement Bed is described separately from the remainder of the formation. These basal beds have been recorded in several boreholes to the north-west of the Stort. At the north end of the gravel pit at Hadham Mill a borehole [TL 4319 1751] showed the Shelly nature of some of the beds:

Nearby, a trial pit [TL 4310 1746] excavated in the base of the large gravel pit east of Hadham Cross proved the following:

Farther south at Hunsdon, [TL 4174 1353] the basal beds are 3.5 m thick and consist of grey sandy clays and fine-grained, water-bearing sands. Gilston Borehole [TL 4417 1349], also proved the London Clay Basement Bed (see Appendix 1).

At Roydon a trial pit [TL 4047 1016] yielded the following details of the London Clay:

No evidence for the thickness of the basal beds is available in the northern part of the district east of the Stort valley. Farther south, however, where the Lower London Tertiaries are covered by thick sequences of drift and younger solid rocks, there are a few records of the Basement Bed in boreholes. In the Lea valley immediately west of Nazeing, several boreholes show the presence of sand at the base of the London Clay.

Farther east at Tilegate Green, High Laver, a borehole [TL 5129 0877] showed 6.6 m of grey sand containing shells and pebbles between thick blue clay interpreted as London Clay and the mottled clay of the uppermost Woolwich and Reading Beds. The thinnest records of the basal beds were in boreholes west of Potter Street at Latton Priory [TL 4669 0945] and at Abbess Roding [TL 5726 1147]. In the former a 1.5 m unit of 'sand and shells' is recorded, and in the latter 0.6 m of 'clay with shell fragments' is taken to represent the London Clay Basement Bed.

In the Cobbin's Brook boreholes, lithological descriptions were made by Hildreth in 1972 (see Appendix 1). The boreholes proved similar sequences, but thin beds of glauconitic fine-grained sand were observed in boreholes 1 and 2.

In the east of the district at Skreens Park, 2 km west of Roxwell, 5.5 m of 'sand, green sand, and clay with shells' from a borehole [TL 6261 0809] have been interpreted as the London Clay Basement Bed (Figure 5). A similar sequence and thickness was recorded at Great Oxney Green [TL 6689 0612] west of Writtle.

An anomalous thickness of 10.1 m for the basal beds was recorded from a borehole in the extreme south-east of the district [TL 6445 00001. The sequence was:

An exceptionally thick sequence of London Clay is recorded in the log, and this may be in error. DM, BSPM

Remainder of London Clay

The main part of the London Clay is described below under geographical sub-headings.

Widford to the River Stort

North-west of the Stort valley, London Clay is present on the higher ground beneath drift, and some small outcrops were observed in areas where the drift cover is thin. Several exposures were present in the bottom of Fiddler's Brook just west of Golden Grove [TL 4455 1414]. Water borings prove only a small thickness of London Clay. In Gilston Borehole [TL 4417 1349], 5.8 m of clay were present beneath Head (see Appendix 1). North of Harlow, a borehole [TL 4654 1308] north-east of Redericks Farm proved 9.6 m of London Clay beneath drift. BSPM

Hatfield Heath and Harlow

The area bounded by the rivers Stort and Roding, and extending south to Cobbin's and Cripsey brooks, shows a varying degree of exposure of London Clay . In the Hatfield Heath and the Rodings area, the London Clay is generally obscured by drift but is recorded at depth from boreholes. South-westwards the drift cover is less extensive, revealing large tracts of the formation. Two wells in the north of this area proved London Clay beneath drift. Opposite the church at Abbess Roding a well boring [TL 5726 1147] encountered 37.5 m of London Clay, and 58.8 m were proved in a well [TL 5332 1100] at Matching Green. BSPM

Extensive outcrops of London Clay occur on the slopes of the east side of the Lea valley from the Downhall Farm area [TL 401 089] southwards to Bumble's Green [TL 408 051] and eastwards into the tributary valley of the Lea at Nazeingwood Common [TL 425 058]. The formation also crops out to the north-east of Epping Long

Green from Nazeingwood to near Harlow Common [TL 480 087] and to Potter Street [TL 475 094]. The slopes of the Lea valley and Nazeingwood Common are steep, in some cases up to 15°, and in places landslips have resulted from slope-failure (Chapter 6). Whereas the London Clay in the valley bottom south of Downhall Farm and Stoneshot Common [TL 40 07] is covered with Head, much of the wide, undulating valley bottom at Nazeingwood Common and Nazeing Gate [TL 412 052] is underlain by very soft reddish brown clay and silty clay. The London Clay is weathered to a depth of at least 3 m. The maximum depth of weathering in this area is conjectural but a well [TL 4014 0695] south of Stoneshot Common showed a thickness of 5.5 m of soft clay.

Although the base of the formation is not exposed, the lowest beds of the London Clay are present on the east side of the Lea valley, as indicated by a well [TL 4084 0704] north-east of Clay Hill where 12.2 m were penetrated. Similar figures were recorded from several wells south of Stoneshot Common; for example in a well [TL 4039 0640] east of Greenleaves where 12.5 m of 'clay and sand' were recorded beneath 2 m of Head. The thickness of London Clay preserved becomes greater eastwards with 61 m recorded beneath boulder clay in a well at Latton Priory [TL 4669 0645].

South of Harlow, where drift cover is extensive, the depth of weathering can be determined from site investigation boreholes made for the M11 motorway. The weathered, oxidised, brown clays varied in thickness from 0 to 12 m, overlying fresh blue and blue-grey material. Blue clay was recorded from a borehole [TL 4918 0900] in the Foster Street area immediately beneath 10.1 m of drift; 12.8 m of weathered brown material were recorded beneath 10.7 m of drift in a borehole [TL 4951 0966] 1 km north of Foster Street. The London Clay in this area typically consisted of silty clays with thin partings of silt. The 'blue' London Clay is commonly laminated and, in places, Shelly; for example a borehole [TL 4768 0705] sunk at the interchange of the M11 with the All south of Harlow showed 'stiff fissured, blue silty clay, partly laminated, and with shells' below 14.3 m.

Between Hastingwood [TL 490 075] and Magdalen Laver [TL 515 075] small outcrops of London Clay are present both in the valleys of Shonks Brook [TL 490 076] and in the stream [TL 517 076] north-east of Weald Lodge. Other small outcrops occur on the boulder clay plateau.

Between Harlow and Moreton, 62 m of 'brown and blue clay' beneath drift occur in a well at Tilegate Farm [TL 5129 0877], Tilegate Green. Extrapolation of the base of the London Clay southward for 3 km to the Claygate Beds outcrop gives a total thickness for the London Clay of approximately 125 m, assuming a dip of 1°. DM

Extensive outcrops of London Clay are present between Epping Long Green and Cobbin's Brook. Small calcareous (race) nodules were observed within the clay to depths of at least 1 m, particularly immediately downslope from the edge of the boulder clay, for example, near Nazeing Long Green [TL 4066 0459], Copy Wood [TL 4210 0499], and on Epping Upland [TL 4401 0379].

The prominent knoll some 600 m north of Breach Barns Farm [TL 4079 0226] is not capped by boulder clay as are other similar features in the district; brown silty clay was found consistently across it.

In areas of lower elevation and gentle slopes, for instance around Aimes Green [TL 40[TL 404 029], a very soft brown silty clay was commonly augered. Although this is undoubtedly highly weathered and probably affected by solifluction, it has been mapped as London Clay.

A well at Hunter's Hall Farm [TL 4130 0445] commenced at about 94.5 m OD and was drilled 'through the London Clay' (Prestwich, 1854, p.403) to the Lower London Tertiaries at about 12.2 m below OD. During the present survey, the base of the Claygate Beds near this borehole was mapped at about 90 m OD. In the nineteenth century the Claygate Beds had not been recognised, but it is now clear that about 4.5 m of the formation were penetrated and that the full thickness of London Clay amounts to about 102 m.

No other wells in the area penetrate the full thickness of London Clay although well records show that its base rises southwards from about 12 m below OD to 2 m OD near Cobbin's Brook, probably due to a local flexure (see p. 22).

A well at Woodyers Farm, south-east of Deerpark Wood [TL 410 035], indicates the depth of weathering, for 6.1 m of soil and brown clay were penetrated above unweathered London Clay. RAE

Upshire, Epping and Toot Hill

Extensive Tertiary deposits crop out between Cobbin's Brook, Cripsey Brook and the southern margin of the district. Drift deposits become more extensive eastwards, but in the north near Tyler's Green [TL 510 050], Bovinger [TL 522 053] and Bobbingworth [TL 534 055] the London Clay at surface consists of stiff reddish brown clays and silty clays that are commonly micaceous. These occur in the upper part of the London Clay because extensive outcrops of Claygate Beds were mapped on high ground south of Tyler's Green.

Between Thornwood Common, Epping and Upshire, the London Clay crops out extensively; thin Head occurs in the major valleys, and drift and Claygate Beds cap the higher ridges at Copthall Green [TL 421 010] and at Copped Hall [TL 431 014]. Characteristic of the area are rounded knolls between 100 and 300 m across. The best examples are 200 m south of Obelisk Farm [TL 4172 0133], 500 m east of Upshire Hall [TL 4138 0012], and 550 m south-west of New Farm [TL 4418 0119]. They have oversteepened slopes which have failed in places, particularly near Obelisk Farm where small degraded mudslides are visible. Knolls with lower relief and correspondingly lower slope-angles are also present [TL 4081 0184]; [TL 4095 0128]; [TL 4240 0104]; [TL 4387 0165].

Site investigation boreholes at Waltham Holy Cross [TL 400 007] showed unweathered London Clay between 6 and 8.2 m below the surface; there is a thin (less than 1.5 m) cover of stony drift in places. The London Clay on concave slopes is generally a soft brown clay in contrast to the firm to stiff clay on the steeper and convex slopes. In Cobbin's Brook the basal 30 m of London Clay were recorded in detail by Hildreth (1972) (see Appendix 1). Above the Basement Bed, he divided the London Clay into three units. A summary of these units, in ascending order, is: silty clays with subordinate silt beds and a high content of carbonaceous material, 11.9 to 13.7 m thick; finely bedded silts, 7.8 to 8.3 m thick; clay with silt horizons.

It is in practice difficult to define the junction between the London Clay and the Claygate Beds (see p. 17). In the Upshire, Epping and Toot Hill area, sandy and silty bands occur in the uppermost 15 to 25 m of the London Clay as mapped. For instance a borehole [TL 4141 0010], drilled on the knoll east of Upshire Hall, records 9 m of sandy clay, (down to 65.1 m OD) in an area where the base of the Claygate Beds is mapped at about 91 m. Further records of sandy beds are noted in borings along the M25 motorway between Copped Hall [TL 431 014] and Bell Common [TL 444 008], where the top of the London Clay lies at 90 to 93 m OD. A borehole [TL 4350 0093] proved 'stiff grey fissured silty clay, sandy at some levels' at depths of between 4.4 and 10.0 m (82.8 to 77.2 m OD). Similar sequences, with sand layers occurring down to a similar level, are recorded from other boreholes [TL 4361 0099]; [TL 4393 0101]; [TL 4401 0116]. South and east of Epping Forest, fine-grained sandy beds occur in the top 15 m of the London Clay, down to about 80 m OD between Great Gregories Farm [TL 452 006] and Ivy Chimneys [TL 454 011]. A borehole in that area [TL 4536 0089] penetrated a sandy clay lying between 80.6 and 81.9 m OD. A water well [TL 4618 0145] near Epping station commenced in London Clay at 80.5 m OD and entered Lower London Tertiaries at a depth of 106.9 m. The base of the Claygate Beds in the vicinity is at 90 m OD; the full thickness of London Clay thus amounts to about 117 m.

The M25 boreholes south and west of Coopersale Hall [TL 465 004] proved the London Clay to be weathered to a depth of between 4 and 10 m beneath the surface of a thin cover of Head. Generally the thinnest weathered zone is found where drift is thicker than 2 m. Selenite was common in the brown weathered clay.

Reddish brown clays and silty clays are present extensively on the valley sides between Wansfell [TL 452 995] and Coleman's Farm [TL 495 997]. The wide valley floor between Garnish Hall and Hill Hall [TL 4899 995] is undulating, and reddish brown silty clays occur on small knolls and ridges, surrounded by Head. Examples occur east of Garnish Hall [TL 473 998]; [TL 478 998] where steep slopes with landslips involve the London Clay to the west of Hill Hall.

The head of the valley near Coleman's Farm [TL 495 997] has steep slopes on the north and east which are affected by landslips. The reddish brown silty clay in the valley floor is extremely soft to a depth of at least 2 m. Reddish brown silty clays belonging to the uppermost part of the London Clay crop out in the narrow valley near Howfields [TL 509 998]. DM

There are further outcrops to the east of Epping in the tributary valleys of Cripsey Brook and Roding. One such example is at Greensted Green [TL 527 030] where orange-brown silty clay with beds of orange and pale grey fine-grained sandy clay were seen in footings 200 m south-west of Greensted House [TL 5237 0342]. These beds probably lie within the uppermost 5 m of London Clay.

Only 0.5 and 1.8 m of brown London Clay above blue London Clay was penetrated beneath alluvial deposits in boreholes at Langford Bridge [TL 5590 0143]. These relatively thin weathering profiles suggest that the groundwater in the suballuvial gravel has had little oxidising effect. RAE

Leaden Roding, Writtle, Stondon Massey and Ingatestone

The London Clay is obscured completely by drift in the High Roding, Leaden Roding and Willingale areas, but outcrops are present on the valley sides of the Roding near Little Forest Hall, 2 km south of Fyfield in Roxwell Brook, near Patience Bridge [TL 633 071] and at Hoestreet [TL 655 077]. More extensive outcrops are present in the Roding valley south of High Ongar and in the valleys south of High Woods and Blackmore.

London Clay is dug from a large pit [TL 562 023] north of Hallsford Bridge at Ongar. This pit has for a number of years provided the largest London Clay exposure in mid-Essex, and has yielded a fauna and flora which has been described by Cooper (1974) (see p. 13; King, 1981, p.48). Because of degradation of the steep faces of the pit and the drag-line method of extraction, the following thicknesses are approximate:

From a lithological comparison with the standard sequences in Stock (Bristow, 1985, p.14) and Hadleigh (Lake, Ellison, Henson and Conway, 1986) boreholes the sequence is thought to fall within Unit LD and Unit LE of these authors; the top of the sequence lies approximately 30 m below the top of the formation, a figure that is verified by the occurrence of Claygate Beds 500 m to the south-east of Little Myles [TL 568 016].

In BGS boreholes, drilled to investigate the drift north-east of Blackmore, the London Clay was weathered to a depth of less than 1 m, and generally less than 10 cm. RAE

High Easter and Pleshey

The area north and east of the River Can is mainly drift-covered. Small outcrops of London Clay are present in the valley of the Can with more extensive outcrops in the Chelmer valley.

Boreholes which penetrated London Clay (see Marks, 1980) show that the London Clay beneath the drift is weathered to a brown colour for a maximum thickness of 20 cm, below which is unweathered olive-grey silty clay with pyritised burrows. One hole [TL 6201 1225] penetrated fresh olive-grey London Clay immediately beneath 16.7 m of drift. RAE

Claygate Beds

The Claygate Beds crop out extensively in the southern part of the district. The main areas of exposure are on the high ground of Epping Forest, north and eastward to Toot Hill, and on the east side of the Roding valley between Great Oxney Green, Stondon Massey and Ingatestone. In addition, outliers have been proved at Epping Long Green and Rye Hill. Although the Claygate Beds have extensive surface outcrops, there is also a substantial cover of drift, and in the extreme south of the district they are overlain by Bagshot Beds.

The Claygate Beds are transitional between the dominantly clay deposits of the London Clay and the sandy Bagshot Beds. Consequently their base is difficult to define precisely. In this district it has been taken below the lowest recognisable sand beds. In areas of moderate slope these sands may give rise to a weak spring-line and a related feature; the latter has been taken as the best approximation to the boundary. However, using this criterion, it is possible that unrecognised, but locally extensive, sands may have been included with the uppermost beds of London Clay. The presence of sand bodies at this level has been responsible for local slope instability and a number of landslips occur along steep slopes at the base of the Claygate Beds.

The dominant lithologies within the Claygate Beds are silt and silty clay, with subordinate sandy clay and fine-grained sand beds, the latter particularly in the lower part. Locally, stiff brown clay is present, lithologically identical to the London Clay. In contrast to the reddish or chocolate-brown colour of the weathered London Clay, these deposits characteristically weather to a brownish grey colour, with orange and lilac mottling. In the unweathered state the Claygate Beds are grey, laminated, micaceous, Shelly, and contain some pyritic lenses. There is no clear relationship between the depth of weathering of the Claygate Beds and the thickness of the overlying drift. In the absence of drift, the weathered zone is between 4 and 6 m deep, whereas 1.6 to 6.8 m of weathered Claygate Beds have been recorded beneath the Older Head in boreholes. The overall permeability, both of the Claygate Beds and its overburden, is probably the important factor governing the depth of weathering.

Because of the imprecise nature of the base of the Claygate Beds in the field and the lack of cored boreholes, the thickness can only be estimated. Mention has already been made in the earlier description of the London Clay of one anomalously thick sequence for that formation and also for the Claygate Beds; the borehole in question [TL 6445 0000] showed a minimum thickness of 27.4 m, a figure which is high when compared with the 19.4 m at Stock, just 5 km to the ESE. In this eastern part of the district, mapping suggests a thickness of approximately 18m. Farther west, around Kelvedon Hatch, the estimated thickness is 14 m, whereas in Epping Forest, west of Theydon Bois, an apparently undulating base gives rise to a range of thicknesses from 15 to 24m.

The Claygate Beds, as defined here, fall within division E of King's (1981) subdivision of the London Clay and Claygate Beds (p. 12), contrary to the correlation put forward by Bristow and others (1980, fig. 2). King has demonstrated that the base of the Bagshot Beds (his Virginia Water Formation) is diachronous between Essex and Kent (1984, fig. 12) and has argued (1982) that the term Claygate Beds should be restricted to strata having the finely-laminated character of the type area. Nevertheless, in this account the term is retained on the grounds of general practicability; further, the generally persistent thickness of the Claygate Beds in the Epping district suggests that the much attenuated sequence at Beredens Lane [TL 577 898], south-west of Brentwood and 9 km south of this district (King,1984, fig. 12), may be a very localised feature.

A cutting on the route of the M11 motorway provides the only palaeontological information for the Claygate Beds in this area. This cutting at Gaynes Park [TL 480 018] exposed almost 10 m of Claygate Beds (as defined here). It should be noted, however, that Mr C. King (personal communication) considers that, from regional correlations, this section is equivalent to the highest London Clay of adjacent districts. In the lower part of the cutting some 5 m of clays and sandy clays with three bands of septarian nodules were overlain by a sand bed 0.6 m thick. A loose nodule, probably from the lowest band of septaria, contained abundant 'Striarca' wrigleyi: the clays above this band were characterised by common Calpitaria sulcataria. The middle band yielded seven specimens of the nautiloid Cimomia imperialis, and one nodule contained a concentration of Cultellus affinis. A fragment of Venericardia trinobantium was collected at or about the horizon of the top band of septaria, while the nodules themselves were characterised by large specimens of Athleta nodosus. Additional fossils listed by Ward (1978) from this section include Rotularia bognoriensis, Ancilla atrebatum, Calyptraea aperta, Epitonium sp. 7 Euspira glaucinoides, Hemipleurotoma spp., Stellaxis pulcher, Syrnola sp., Tibia lucida, Xenophora agglutinans and Corbula globosa.

The fauna of the Claygate Beds includes mostly shallow water forms and, when considered together with the lithological alternations, indicates deposition in an area affected by tidal currents, probably at depths of less than 30 m. (Bristow, Ellison and Wood, 1980). DM, RAE

Details

Epping Long Green

The Claygate Beds crop out on the NW-facing slopes of the Epping Long Green ridge, and in small 'windows' within the drift cover on Rye Hill [TL 46 06]. The base of the Claygate Beds is marked by a spring-line which coincides with a break of slope near Little Canons Farm [TL 4365 0638], north-west of Rivetts Farm [TL 4600 0615], and north of Horseshoes Farm [TL 4700 0628]. The weak springs at the base of the Boulder Clay and at the base of the Claygate Beds were probably responsible for the removal of drift producing the 'windows' . DM

Near Hunter's Hall Farm [TL 431 044] much of the Claygate Beds is concealed by drift; 200 m west of the farm the base of the formation lies above 90 m OD, but it falls eastwards to around 85 m OD south of Chambers Manor Farm [TL 438 043]. At this latter locality there is a particularly strong spring-line on the south-facing slopes. RAE

Epping and Toot Hill

The ridge of high ground from Epping Forest to Epping, North Weald and Toot Hill is capped by Claygate Beds which are overlain for the most part by Older Head. In Epping Forest the base of the Claygate Beds occurs at about 90 m OD. The London Clay on the steep north-facing slope of The Warren [TL 436 007] is dissected by numerous small streams emanating from a spring-line within the Claygate Beds; to the south of Ambersbury Banks earthworks [TL 438 003], the south-facing side of the ridge has been similarly dissected.

The problem of delineating the base of the Claygate Beds can be demonstrated in the westernmost outcrop [TL 4187 0004] of Claygate Beds. To the west of Woodredon Farm the base occurs at about 77 m OD. A borehole 500 m north-west of the farm, sited on the junction between Claygate Beds and London Clay, penetrated 5.0 m of weathered sandy silty clay overlying grey silty clay which was noted to be 'very sandy at some levels'. The borehole indicates lithologies similar to those of the Claygate Beds in the top of the London Clay below 70 m OD. In contrast, a borehole [TL 4163 0040] drilled only 170 m to the east penetrated a bed of very silty, sandy clay from 84.4 to 82.4 m OD, below 'grey, silty clay' of London Clay type. South of the ruined Copped Hall [TL 4302 0147] the mapped base of the Claygate Beds lies around 94 m OD, but borehole [TL 4298 0102]; [TL 4300 0098] show that sandy beds occur down to about 84 m OD although brown silty clay (mapped as London Clay) was augered at this elevation. No sandy beds were recorded in a borehole [TL 4139 0100] drilled 500 m south-east of Copped Hall and starting at 81.2 m OD. A thick bed (1.5 to 2 m) of orange fine-grained sand was exposed in a ditch on the north side of The Warren [TL 4350 0082], and this was taken as the basal sand of the Claygate Beds.

Between Epping and North Weald, on the northern side of the ridge, the Claygate Beds–London Clay junction is covered by drift deposits, and appears only in the more deeply dissected tributary valleys. The level of the contact can be ascertained from a borehole [TL 4594 0290] which proved 4.6 m of silty and sandy clay overlying London Clay (which was 'silty at some levels') at about 90 m OD.

Motorway trial boreholes [TL 4827 0374]; [TL 4844 0374] near Woodside penetrated a clayey silt band at between 88 and 89 m OD. This is considered to represent the base of the Claygate Beds.

About 35 boreholes have penetrated the Claygate Beds, mostly beneath drift along alternative proposed routes of the M11, between Woodside and Gaynes Park [TL 484 016]. Levels of the lowest recorded sandy or very silty bands were between 91.5 and 97.5 m OD.

The upper Claygate Beds are commonly more distinctive and more readily recognised in borehole logs; in a borehole [TL 4808 0304] near Woodlands the sequence was:

In other borings nearby, the upper parts of the Claygate Beds are variously described as firm, mottled orange-brown, clayey silt; mottled brown and grey, silty clay with layers of silt; soft, laminated layers of brown clay and fine-grained sand; blue (unweathered) silt; and blue silty clay with pockets (or partings) of soft silt.

The southern flank of the Epping Forest ridge is much steeper than the northern one. Claygate Beds crop out above about 90 m OD although several boreholes sited on or near the London Clay–Claygate Beds boundary between Ivy Chimneys [TL 454 010] and Great Gregories Farm [TL 4515 0600] proved sandy beds extending down to at least 82 m OD. The Claygate Beds occur at about this level less than 1 km westwards in the tributary valleys southeast of Ambersbury Banks.

The base of the Claygate Beds lies between 84 and 91 m OD from Ivy Chimneys to a point 650 m north-west of Gaynes Park. From here it falls to below 70 m OD at its lowest level in the M11 motorway cutting south-west of Gaynes Park (see below). Orange-brown, clayey, fine-grained sand is present at the base of the Claygate Beds at 76 m OD in a ditch [TL 482 022] along the western side of the motorway. On the eastern side of the motorway, but at the same elevation, brown silty clay was augered below a spring in the tributary valley down which the motorway runs.

During motorway construction in 1974–5 the cutting 600 m south-west of Gaynes Park provided good sections in the Claygate Beds and the uppermost London Clay (p. 13). The base of the Claygate Beds occurs at 69 m OD. A trial pit [TL 4791 0148] proved 'loose, green and brown mottled, slightly sandy, very clayey silt' grading down into brown, fissured, sandy, very silty clay at a depth of about 1.7 m.

Small outliers of Claygate Beds are present on high ground west of Garnish Hall and at Hill Hall [TL 489 995]. The former occurs beneath boulder clay and was exposed only in the motorway cutting [TL 4665 9900].

In the North Weald Bassett area, and in particular to the east of the radio-station north-west of Ongar Park Hall [TL 505 040], the base of the Claygate Beds is poorly defined and no springs are present. On the western slope of the high ground c.[TL 5085 0420] a weak spring-line lies at the base between 84 and 90 m OD. Here the surficial Claygate Beds consist of orange-brown, very silty clay with some beds of fine-grained sandy clay.

A prominent silty fine-grained sand bed within the upper part of the Claygate Beds forms a feature on several spurs near Toot Hill [TL 5057 0327] to [TL 5163 0316]. A trial pit [TL 5162 0303] dug 5 m downslope from the sand at 90 m OD proved Claygate Beds as follows:

At around 82 m OD, there is a break of slope associated with a spring-line which has been followed by field drainworks.

Near Blake Hall station the base of the Claygate Beds lies at about 73 m OD, and seepages were seen about 10 m above the base on the north-facing slope of the knoll, 400 m WNW of Greensted Green.

On the south-facing slopes of the ridge from Ongar Park Wood to Toot Hill, the Claygate Beds consist mainly of orange-brown fine-grained sandy clay with some soft, orange, very silty clay. These give rise to characteristic loamy soils. Springs lie at the head of several short valleys [TL 5044 0266]; [TL 5096 0277] at the junction with the London Clay, which lies at about 93 m OD and falls eastwards to 86 m OD on Toot Hill. RAE

Stondon Massey, Blackmore, High Woods and Ingatestone

Extensive Head thinly covers the Claygate Beds above about 86 m OD around Norton Heath. Silty and clayey fine-grained sand was augered beneath Head south of Readings [TL 6050 0395], and a trial pit behind the public house opposite Readings [TL 6049 0420] proved 1.6 m of Head overlying Claygate Beds:

About 20 m of Claygate Beds are present in the Writtle Park area. The nature of the topmost beds is known from a trial pit sited on Bagshot Beds east of Writtle Park Farm [TL 6520 0380]:

Claygate Beds occur at about 60 to 65 m OD in the Kelvedon Hatch and Stondon Massey area. The base is not well defined because the contact with the London Clay appears gradational. Locally, however, a fine-grained sandy clay or clayey silt was augered near the base of the Claygate Beds.

One small temporary exposure [TL 5685 0162] was observed southeast of Little Myles in the bottom of a tributary valley, where excavations for a small reservoir revealed 1.5 m of fine- to coarse-grained sand with scattered angular to rounded gravel in a clay matrix (Head) overlying 2 m of brown silty clay and clayey fine-grained sand.

Orange-brown, clayey fine-grained sand and silty fine-grained sand were augered in the deeply incised stream [TL 5817 0041] upstream from the Stondon Massey to Ongar Road. RAE

Around Germains Farm [TL 557 996] the base of the Claygate Beds is marked by a break of slope. Locally the basal sand was proved by augering [TL 5512 9960]; [TL 5620 9961].

In the valley to the east of Hook End, the base of the Claygate Beds is generally poorly defined; sandy clays are apparently present in the uppermost beds of the London Clay. RDL

Except for a thin capping of Bagshot Beds at Tip's Cross it is thought that Claygate Beds underlie all the drift lying above about 80 m OD between Tip's Cross [TL 5882 0007] and Paslow Wood Common [TL 588 018]. Since the thickness of the drift cover is unknown, the extent of the Claygate Beds is conjectural.

The topmost 5 m of these beds in the vicinity of Nine Ashes [TL 593 027] are predominantly silty or clayey fine-grained sands. These lithologies were augered on the north flank of the rise at Nine Ashes [TL 5956 0312]. About 2 m of fine-grained sand were exposed in a ditch north-east of Nine Ashes Stud Farm [TL 5900 0266]; downslope in the ditch, a spring issues from a sandy bed, which in turn overlies a brown, glauconitic, fine-grained sandy clay at about 87 m OD [TL 5887 0271].

A trial pit [TL 5874 0228], north of Paslow Wood Common, and at 90 m OD, showed:

The Claygate Beds were penetrated beneath drift in boreholes [TL 5933 0070]; [TL 5958 0094] north-east of Tip's Cross. The latter hole terminated in 0.9 m of unweathered, slightly clayey, glauconitic, fine-grained sand at 72.4 m OD; it is considered that this sand is the basal bed of the Claygate Beds.

A temporary trench section 250 m north of Stubbers Farm [TL 612 002] showed 2 m of Claygate Beds:

Water seeped from the lowest sand, which is about 5 m above the base of the Claygate Beds at this locality. In a further section in the degraded face of an old brickworks [TL 6098 0053], up to 2 m of laminated, grey-brown, lilac and orange-brown silty clay with pockets of fine-grained sand were recorded.

The upper part of the Claygate Beds, that is that part lying above 90 m OD in the Birch Spring area [TL 627 022], consists mainly of fine-grained sand [TL 6248 0256]; [TL 6292 0198]. A number of springs emanate from the base of these arenaceous beds in Birch Spring at about 88 m OD.

Degraded pits formerly dug for brick clay [TL 6325 0140]; [TL 6286 0073] lie in the valley which drains south between Mill Green Park [TL 6361 0118] and St Leonards [TL 6260 0070], and on the west side of the road north of Moore's Ditch [TL 641 016] near the Viper public house.

The base of the Claygate Beds to the north and east of Mill Green lies at between 69 and 76 m OD. RAE

The section at the former brickworks [TL 6455 9940] at Ingatestone was described by Edmunds in 1923 (in MS) as showing 'buff sandy loam with alternate marly and clay layers each about 2 inches [5 cm] wide'.

Around Margaretting the base of the Claygate Beds is well delineated by a weak spring-line and an associated break of slope on south-facing slopes. Elsewhere this boundary is less sharp. Near The Hyde [TL 6515 0065] silts are commonly present, and sand beds within and at the base of the formation were augered at two localities [TL 6502 0073]; [TL 6500 0095]. Brickclays were formerly worked near Edney Common. RDL

On the south side of the River Wid the base of the Claygate Beds, which is marked by a weak feature, occurs at about 53 m OD. In general, the Claygate Beds at the surface in this vicinity consist of yellowish brown silty clay and no basal sand was found.

Sections noted in a trench [TL 6847 9921]–[TL 6852 9976]–[TL 6880 9987], which traversed approximately the upper three-quarters of the Claygate Beds, did not reveal any interbedded sands. However, at two points [TL 6823 9965]; [TL 6818 9918] in the nearby fields, fine-grained sands were augered in the middle to upper part of the Claygate Beds. The dominant lithology was found to be silt and silty clay, although stiff brown clay was noted at several points [TL 6870 9983]; [TL 6880 9988]. CRB

Bagshot Beds

Numerous outliers of Bagshot Beds are present on high ground in the extreme south of the district. The main outcrops are at Epping Forest to the south of the Ambersbury Banks, Kelvedon Hatch and Tip's Cross, and Ingatestone.

The base of the Bagshot Beds is moderately well-defined because of the associated marked lithological change from silty clay and silt to fine-grained sand. The boundary is commonly marked by a spring-line, particularly on the steeper slopes. Some difficulty is, however, encountered on south-facing slopes which in some cases appear to be dip-slopes.

Throughout the Epping district the Bagshot Beds consist mainly of fine-grained sands which are pale yellow to ochreous brown and orange in colour. In Stock Borehole, in the adjoining Chelmsford district, Bristow (1985) recorded three divisions of the Bagshot Beds; the Bagshot Sands (13.2 m thick), the Stock Clay (10.1 m), and the Bagshot Pebble Bed (4.2 m). The Stock Clay has not been recognised in the Epping district, but the Bagshot Pebble Bed has been mapped in the extreme south-east. This deposit consists of gravels and sandy clays similar to those described as Older Head. The gravel does, however, contain a significant proportion of black flints. It is not certain whether such a deposit is the Bagshot Pebble Bed in situ or is a drift deposit derived from this bed by solifluction.

The recorded thicknesses of the incomplete sequence preserved in this district include 5.9 m in a borehole [TL 4312 9946] 1 km south-west of the Ambersbury Banks in Epping Forest, approximately 7 m in the Kelvedon Hatch area, and 10 to 14 m in the Ingatestone area. The total thickness of the tripartite Bagshot Beds in Stock Borehole was 27.5 m, a maximum for the Chelmsford district (Bristow, 1985). DM, RAE

Details

In the Edney Common area of High Woods, a trial pit [TL 6520 0380] to the east of Writtle Park Farm proved 1 m of silt and fine-grained sands overlying Claygate Beds (see also p. 29).

An outlier of Bagshot Beds which is largely obscured by the Older Head occurs north of Mill Green [TL 628 016]. The base is poorly defined, but is probably marked by a spring [TL 6409 0136] on the eastern side of the outcrop. Shallow diggings in fine-grained sand occur uphill from this spring. A trial pit [TL 6391 0138] on the Older Head, north of the water tower, revealed Bagshot Beds at 2.0 m depth; they comprised finely laminated, pale greyish yellow, silty fine-grained sands, and contained scattered rounded black flints, less than 1 cm in diameter. An adjoining pit [TL 6394 0137] showed the following:

The gravel with coarse-grained sand may possibly be drift because no comparable lithology has been recognised in the Bagshot Beds elsewhere in this district or indeed in the London Basin.

Orange-brown fine-grained sand was seen in a trench dug from Tip's Cross along the Blackmore Road [TL 5882 0007] to [TL 5889 0018]. RAE

South of Stondon Massey the base of the Bagshot Beds is marked by a well-defined spring-line. In a former pit [TL 5690 9952] to the east of the A128, fine-grained sand was recorded beneath 1 m of the Older Head. Similar fine-grained sands were formerly dug from a pit [TL 5955 9990] near Hook End.

In the outlier to the west of Ingatestone, sandy clays and clayey sands were locally proved by augering. Edmunds (in MS) recorded 4.3 m of sand to be (?reputedly) present in a field [TL 6365 9940] near Dodd's Farm.

In the Edney Common area, the base of the Bagshot Beds is marked by a weak spring-line. Strong springs are present near Coptfold Hall Farm [TL 665 029]. RDL

An outlier of Bagshot Beds, partially obscured by the Head, is present on the east side of Ingatestone [TL 655 995]. The base is marked by a spring-line [TL 6577 9941] to [TL 6580 9964] on the east side of the outcrop. Brown fine-grained sands or yellow-brown silty sands were proved in auger-holes. At the south-western end of the railway cutting [TL 6524 9937], some 1.8 m of yellow fine-grained sands were noted above the Claygate Beds. At the north-western end over 2.4 m of sand were proved in a bank [TL 6572 9983].

The Bagshot Pebble Bed is present east of Tye Green [TL 688 994]. In Swan Lane, 1 m of mottled orange and grey pebbly clay was seen. A borehole [TL 6916 9909] just beyond the district boundary proved 4.7 m of 'Bagshot Pebble Bed' above 9.6 m of Bagshot Sands. The Bagshot Sands consist of yellow fine-grained sands and silts. They were seen to exceed 1.5 m in thickness in sections exposed by pipe-line trenches [TL 6845 9914] to [TL 6847 9921]; [TL 6851 9940] to [TL 6855 9959] which crossed the edge of the outlier.

Springs mark the base of the Bagshot Beds at several localities in the extreme south-east c.[TL 6865 9929]; [TL 6863 9919]; [TL 6835 9916]. The springs at these localities have given rise to small sheets of head which obscure the boundary. At one point [TL 6830 9915] a small landslip is associated with the spring-line. CRS

Chapter 4 Structure

Three formational boundaries in the district contribute towards an assessment of the structure; the base of the Lower London Tertiaries, the base of the London Clay, and the base of the Claygate Beds. The lowest boundary is the most valuable because of its extent and its ease of recognition in water-wells.

Although numerous boreholes in the western half of the district reach the Chalk, few do so elsewhere. Hence an accurate structure contour map for the whole district cannot be produced. The limited information broadly indicates that the strike of the base of the Tertiary deposits lies between NE and ENE, with an apparently fairly consistent dip of about 1 in 120 in the Nazeing area and 1 in 200 in the east. No minor structures have been recognised. In the Cobbin's Brook area, Hildreth (1972) indicated that there was a slight doming of the Chalk, but it is uncertain that this is a tectonic effect because the upper contact is an erosional surface. The bases of the London Clay or Claygate Beds provide little additional information. In the case of the latter, the boundary may indeed be influenced more by sedimentological variation than by structure.

The overall synclinal disposition of the Tertiary deposits in the London Basin is well known, and minor structures in this district were described by Whitaker (1872) and Wooldridge (1923). Wooldridge recognised two SW-trending synclines, one with an axis through the Epping Forest ridge and the other with an axis through Mill Green in the east. The presence of fold-axes was interpreted from the Bagshot Beds outliers on high ground in the south of the district. Wood (1882) had suggested earlier that the asymmetrical form of the Lea valley was due to faulting along its eastern side, but Wooldridge concluded that this feature was caused by a monoclinal structure. The available evidence from the recent survey sheds no further light on these matters. DM

Chapter 5 Quaternary deposits–pre-Anglian and Anglian

The widespread deposits of Quaternary age in this district are all regarded as drift. The sediments consist essentially of clays, sands and gravels and can be broadly grouped into those related to one main glacial episode and those of a post-glacial origin. The former are described in this chapter.

The base of the Quaternary in Europe has been defined, from a type sequence in Italy, as the base of the Calabrian stage, where there is a substantial change to a cold marine fauna (Blanc and others, 1953). In Britain fourteen stages of the Quaternary have been proposed to coincide with warm and cold oscillations in climate (Mitchell and others, 1973). Correlation of the more recent British glacial and interglacial events with those of the continent has reached some general agreement, but still remains uncertain (Mitchell and others, 1973). Shotton (1975, 1977) has summarised the major methods employed in the absolute dating, and it is now generally agreed that the base of the Quaternary is at 1.8 Ma.

In the Epping district there is a large unconformity between the youngest solid formation (Bagshot Beds) and the oldest drift deposits which are regarded as Middle Pleistocene in age.

The deposits described in this chapter include the Older Head, Kesgrave Sands and Gravels, Boulder Clay, Glacial Sand and Gravel, Head Gravel and Glacial Lake Deposits. Contours on the base of these drift deposits are shown in (Figure 6); the contours are coincident with the rock-head in the areas covered by the above deposits. To the north-west of the Stort valley, rock-head is generally consistently between 50 and 60 m OD; this area is separated from the main drift-covered area of Hatfield Broad Oak, the Rodings and Chignalls by the deep drift-filled buried channel of the Stort valley which descends to a known minimum of 11 m below OD and is one of the major glacial erosional features of north-west Essex. A wide shallow valley, referred to as the 'mid-Essex depression' by Wooldridge and Henderson (1955), trends ESE from just south of Hatfield Broad Oak through the Chignalls to the Chelmsford area. To the east of the district it leads to a buried channel in the valleys of the Can and Chelmer. To the south of these features is an irregular dissected ridge, which is particularly notable in the Epping Long Green area where it rises to 100 m OD. It is broken near Ongar by a depression coinciding more or less with the present southward-flowing River Roding. In the Highwood area the ridge, up to 90 m OD, is dissected by a northward-flowing tributary to the 'mid-Essex depression'.

Nomenclature and previous research

The term 'drift' was first introduced by Murchison (1839), and shortly afterwards became common usage in referring to deposits of a glacial origin ('Glacial drift'). It is now used in this district for those deposits of Quaternary age that postdate the earliest evidence of glaciation; these include boulder clay, outwash sands and gravels, river terraces and Head.

The first subdivision of the glacial deposits in East Anglia was made by Wood (1867) into 'Lower', 'Middle', and 'Upper Glacial'. In describing the area of the Old Series One-inch Geological Sheet 47, which included the northern part of the Epping district, Whitaker and others (1878) commented that the deposits there were confined to Wood's Middle and Upper divisions.

The oldest superficial or drift deposits in the district are clayey gravels and pebbly clays capping the higher ground in the south at levels generally above 90 m OD. Although these deposits had been recognised earlier, their distribution was first depicted on Old Series One-inch Geological Sheet 1 NW for south Essex and Hertfordshire. The age and origin of these deposits have been the subject of much conjecture. Wood (1867) ascribed the deposits to his 'Middle Glacial', and Whitaker (1880) referred to these as Pebble Gravel. A regional compilation was presented by Prestwich (1890) who, in his correlation of sands and gravels in southern East Anglia and London, grouped the Pebble Gravel with the Westleton Beds, though the evidence for such a correlation, on his own admission, was tenuous. Subsequently the term Pebble Gravel was adopted in the Epping, Romford and Hertford areas by, for example, Wells and Wooldridge (1923), Warren (1910, 1942), Dines and Edmunds (1925) and Sherlock and Pocock (1924).

Whereas the earlier workers had noted the essentially gravelly nature of these deposits, Whitaker (1889) and Monckton (1890) recorded clayey beds within the deposits and regarded them as weathered boulder clay. Later, Thomasson (1961) recognised an upper clayey deposit in the Hertford area which he named Pebbly Clay Drift, but disagreed with the original authors as to its origin. Cuttings and bore-holes for the M11 motorway in the Epping Forest area [TL 48 02] were examined by Baker (1971), who concluded that although some of the clayey deposits could be weathered boulder clay, others had diagnostically different lithological and engineering characteristics, and were referred informally by him to 'head'. These clayey 'head' deposits have been shown by the present mapping to be widespread in the southern part of the district (p. 25). Temporary sections indicated that they were overlain by boulder clay, and extensively cryoturbated and reworked together with the underlying bedrock. The term Older Head is used throughout this account for such deposits.

The presence of two chalky boulder clays in southern East Anglia has been suggested by many authors (for example, Bennett, 1884; Harmer, 1928; Boswell, 1931; Baden-Powell, 1948). In Suffolk the upper unit became known as the Gipping Boulder Clay or Till and the lower the Lowestoft Boulder Clay or Till. However, Baden-Powell found difficulty in confirming the stratigraphical relationships of the two since they were seldom seen in direct superposition. In the south the two tills were referred to as the Springfield and Maldon Tills respectively by Clayton (1957), in descriptions of the glacial deposits of the Chelmsford and Harlow areas. The gravels which separate the two boulder clays in the latter area were equated by him with the Chelmsford Gravels of the former area: the gravel beneath the lower boulder clay at Harlow was not, according to Clayton, represented in the Chelmsford district. To the south of Harlow the boulder clay capping the Epping Long Green area was referred to by Clayton as the Hanningfield Till, the product of an earlier glaciation. On the pebble content and mineralogy, Solomon (in discussion, Clayton, 1957) disagreed with some of these conclusions, and was of the opinion that within the Essex area there were two types of gravel; one was related to the boulder clay in stone content while another characteristically contained much quartz and quartzite. He concluded that the latter could not have been derived from the same source as the overlying boulder clay.

The existence of chalky boulder clay of different ages has since been doubted by Ranson (1968). Turner (1970) concluded that fossiliferous silts of Hoxnian age at Marks Tey near Colchester post-dated the Lowestoft Till in that area; he could not confirm the existence of a Gipping Till above it, though a return to colder climatic conditions towards the end of the Hoxnian was shown from the pollen content. Bristow and Cox (1973) discussed the glacial sequence of parts of East Anglia, and on the basis of extensive regional mapping concluded that the main sheet of chalky boulder clay formed in a single glacial period, and that the Lowestoft and Gipping Tills could not be distinguished lithologically. They also stated that in the Chelmsford district the Hanningfield Till had been misidentified by previous workers and was partly Head and partly Springfield Till. The Maldon Till was strictly local, but was attributable to the same glacial period as the Springfield Till.

The age of the boulder clay in comparison with the glacial periods recognised on the continent has been much discussed. Bristow and Cox (1973) concluded that it was dependant on the equivalence of the Hoxnian with the continental Holsteinian. With the introduction of Quaternary stages in Britain, the Chalky Boulder Clay is assigned to the Anglian Stage (Mitchell and others, 1973). From oxygen isotope results on shells from ocean- floor sediments, the base of the Hoxnian is placed at 250 000 years BP (Shackleton and Opdyke, 1973).

Both glacial and non-glacial origins have been proposed for the widespread gravels occurring beneath the Chalky Boulder Clay. Prestwich (1890) included quartz-rich flint gravels within his Westleton Beds, which he regarded as marine. Later, Wooldridge and Henderson (1955) and Wooldridge (1960) suggested that the Thames once had an eastward course through central Essex, following the 'Stort depression' near Harlow and the 'Mid-Essex trough'. This idea has recently been developed further by Rose, Allen and Hey (1976), who have recognised throughout much of Essex and south Suffolk a two-fold division of sand and gravel beneath the Chalky Boulder Clay; in places the subdivisions are separated by a palaeosol. The lower elastic unit consists of a thick sequence of sands and quartz/quartzite-rich rounded flint gravel, termed by them the Kesgrave Sands and Gravels and regarded as the product of an early proto-Thames. Above the palaeosol, irregularly distributed, thin and clayey, angular gravels and sands form the Barham Sands and Gravels, and contain clasts linking the deposit genetically with the overlying till. The clay-enriched, reddened and involuted horizon commonly separating these two units was described in detail from southern Suffolk by Rose and Allen (1977) who regarded it as a rubified sol lessivé with a superimposed arctic soil structure. They concluded that the palaeosol originally formed in a humid warm temperate climate, and then was subjected to arctic conditions before the onset of the Anglian glaciation. Their proposed chronostratigraphy is shown in (Table 2).

Although Rose, Allen and Hey (1976) pointed out the widespread distribution of the Kesgrave Sands and Gravels, the name was not extended by them to the very similar deposits in Essex which had in the past been referred to as the Essex White Ballast (Mitchell and others, 1973). However, it is clear from regional mapping throughout Essex and south Suffolk that the deposit represents an almost continuous sheet (Bristow, 1985; Ellison and Lake, 1986; Rose, Sturdy, Allen and Whiteman, 1978). In this account, therefore, the quartz- and quartzite-rich flint gravels are described as the Kesgrave Sands and Gravels (Table 3). Although the Barham Sands and Gravels have been recognised locally in the Epping district as a thin deposit (Rose and others, 1976, fig. 1), there are also more widespread glaciofluvial sands and gravels which have not been formally named, and which are referred to as Glacial Sand and Gravel on the 1:50 000 sheet. DM

Older Head

The Older Head is restricted entirely to the south of the district at elevations generally above 90 m OD; its relationship to the Kesgrave Sand and Gravel thus cannot be determined, but locally it is overlain by isolated patches of boulder clay. In the south-west, Epping Forest is situated on the largest outcrop which continues north-eastwards to Epping, Mount Wood [TL 493 023] and Ongar Park Wood [TL 507 029]. Much of this country is above 107 m OD and rises to 117 m near Ambersbury Banks [TL 438 003], the highest point in the district. The northern part of an extensive outcrop in the adjacent Romford district to the south is present near Pole's Wood [TL 570 996] and Tip's Cross [TL 588 001]. Elsewhere, there are only isolated outcrops of the Older Head, invariably capping Bagshot Beds or Claygate Beds; those of importance are between Parsons Spring [TL 625 025], Mill Green [TL 64 00] and Edney Common [TL 655 040]. In Fryerning Wood [TL 655 011] and College Wood [TL 625 018] the Older Head lies beneath a widespread cover of thin younger Head.

The Older Head gives rise to clayey soils containing abundant rounded flint pebbles and minor amounts of small white vein-quartz pebbles. The matrix consists of orange-brown and pale grey mottled sandy clay or clayey sand. Locally a bright red mottled colouration has been recorded. Vertical and lateral variations within the deposit are common. The grading characteristics of samples taken by the former IGS Industrial Minerals Assessment Unit in the eastern part of the district indicate that fines (less than 116 mm diameter) constitute between 12 and 25 per cent by weight, whereas the gravel fraction (greater than 4 mm) varies from nil to 40 per cent, and more rarely to 67 per cent (Hopson, 1981).

The local reddening of the clayey matrix is concentrated around pebbles, in laminations near the base, and as mottling within the whole deposit. The sandy clay matrix is generally soft to firm, and the sand grains are fine to coarse and subangular. In a few localities thin lenses or pockets up to 0.5 m thick, of ochreous, brown, structureless, silty, medium-grained sand have been recorded. Locally irregular seams of reworked Claygate Beds also occur.

The pebble content of the Older Head has been recorded and interpreted by various authors; in particular the small number of Lower Greensand chert pebbles has aroused much interest. The pebble counts from two BGS boreholes are given in (Table 4). The well-rounded flint pebbles consist mainly of white patinated or black Tertiary-derived flints, having a maximum diameter of 15 cm but generally less than 5 cm; others are brittle and frost-shattered, brown and red coloured, or completely patinated. The subangular flints are patinated, white or brown, and together with locally recorded nodular flints are derived from the overlying Boulder Clay.

At Bell Common [TL 442 007], Epping [TL 467 026] and Ongar Park Wood [TL 507 029] the nearby till has provided numerous erratic pebbles as well as angular flints in the upper parts of the deposit. For this reason some confusion has surrounded the original pebble content of the deposits (Monckton and Herries, 1889; Warren, 1942), both in this and adjacent districts. The problem is illustrated by the Head mapped in the Fryerning Wood–College Wood area where the soils contain appreciable amounts of angular as well as rounded flint gravel. Although there is no evidence of the Chalky Boulder Clay thereabouts, it is probable that soliflucted and decalcified boulder clay has mixed with the Older Head to produce a thin veneer of later Head.

The outcrops at Parsons Spring [TL 625 025] and College Wood [TL 625 018] are characterised by .rather different pebble assemblages compared to occurrences elsewhere in the district. The soil is generally rather more sandy and contains a greater proportion of angular flints. Thomasson (1961) attributed similar sandy soils on the Pebbly Clay Drift of Hertfordshire to eluviation of the surface layers and redistribution of clay into the underlying gravelly beds. The results of systematic pebble counts from the College Wood area and from Writtle Deer Park are shown in (Table 4), and compared with the results of Prestwich (1890) on Coopersale Common [TL 483 026], and of Warren (1910) in Monk Wood [TL 42 99] immediately south of the district.

The Older Head is commonly cryoturbated, and involutions up to 1 m across are lined with pebbles that are oriented sub-vertically or vertically. These structures have been previously recorded by Wells and Wooldridge (1923), Dines and Edmunds (1925), Warren (1942) and Thomasson (1961), but none appreciated their cause. McKenny-Hughes (1868) described the involutions as 'channels of clay cutting through the gravel', and Wells and Wooldridge (1923) observed weathered boulder clay filling the involution troughs. Although the base of the deposit is sharp, these local irregularities caused by cryoturbation pose difficulties in the estimation of the total thickness of the Older Head. The thickest known deposits occur around Coopersale Common, where 10.4 m were penetrated, and at Parsons Spring, where 7.2 m were recorded. Elsewhere the thicknesses range from 2 to 5 m.

The presence of a dominantly gravel facies within the Older Head has been proved by borings near Coopersale Common where up to 6 m have been proved beneath 3 to 4 m of clayey Older Head. Baker (1971, p.320) assigned the gravels to the Pebble Gravel of Dines and Edmunds (1925, p.22). No exposure of these gravel deposits was recorded during the present survey; they are described in this account as part of the Older Head.

Various modes of deposition have been postulated for the Older Head. It has been claimed to be the product of a marine Pliocene transgression (McKenny-Hughes, 1868; Prestwich, 1890; Barrow, 1919), or the result of mudflows and fluviatile action accompanied by mixing of Bagshot Beds and glacial material (Monckton and Herries, 1889). The theory put forward by Prestwich (1890) that the Older Head and the Kesgrave Sands and Gravels had a similar origin is not now regarded as tenable.

Of the two lithological facies here included within the Older Head, the sand and gravel unit is the older. It was deposited in a braided river system. The presence within these deposits of clasts other than flints led Wooldridge and Linton (1955) to suggest a source river that brought Lower Greensand chert pebbles into the district from the west; the Tertiary Barton Beds have also been regarded as having supplied some of the clasts (Dines and Edmunds, 1925); it is also probable that the later Eocene deposits provided a source of material which could be easily mobilised, particularly under periglacial conditions. The age of the sand and gravel is difficult to determine; its lithology and distribution indicate contemporaneity with the Pebble Clay Drift and the Pebble Gravel of the adjacent Hertford and Romford districts. Rather similar high level gravels have been described from the Vale of St Albans at heights ranging from 60 to 115 m OD (Green and McGregor, 1978). The presence of far-travelled erratics in both may indicate an ultimate glacial derivation from a pre-Anglian ice-sheet, but no direct correlation can, however, be made between these deposits and the Older Head gravels. These latter are clearly older than the Chalky Boulder Clay, lying below that till. By virtue of their higher elevation, they presumably predate the Kesgrave Sands and Gravels though nowhere are the two superposed.

The clayey upper layer may be appreciably younger than the gravels, but is still older than the Chalky Boulder Clay. It is here regarded tentatively as of Anglian age, formed by periglacial solifluction of the Claygate Beds and Bagshot Beds in advance of the Anglian ice-sheet. Red coloured involutions have been recorded at several different levels within the deposit. They are particularly pronounced at the top of the deposit. While these involutions are similar to those at the top of the Kesgrave Sands and Gravels, they may be earlier in age.

Details

Cobbin's Brook to the River Roding

Shallow gravel workings commonly occur on the Epping Forest ridge near Ambersbury Banks [TL 436 003] where rounded flint pebbles in a smooth, slightly sandy, orange-brown, red, and grey mottled clay characterise the deposits. The base of the Older Head lies at 105 to 112 m OD, although local solifluction lobes extend downhill below 105 m OD. Variable thicknesses of the deposit have been recorded from the Epping Forest area; for example, a borehole [TL 430 997] near the southern limit of the district south of the Ambersbury Banks proved 4.9 m of grey-brown mottled sandy clay with 'stones and layers of sand' overlying probable Bagshot Beds at 107 m OD. Adjacent boreholes [TL 430 996]; [TL 430 994] penetrated only 1.2 and 1.7 m of the Older Head respectively, resting on Bagshot Beds at 111.8 and 110.3 m OD. Involutions caused by cryoturbation are common in ditches, and examples have been recorded by Warren (1942). Festoons, 2 m deep, containing either gravel or boulder clay, were observed in ditches east of Woodredon Farm near the Wake Arms [TL 4270 9943].

A trial pit on Bell Common [TL 4419 0067] north-east of Ambersbury Banks, proved the following sequence in the Older Head:

At St Margaret's Hospital, Epping, a trial borehole [TL 4681 0268] penetrated 2.4 m of boulder clay, and 2.1 m of 'soft brown and grey sandy clay with some small rounded stones' overlying Claygate Beds. The stony clay almost certainly represents the Older Head. A small exposure [TL 4737 0258] south-east of the hospital showed about 1 m of cryoturbated rounded flint gravel in an orange and grey, silty clay matrix with bright red veining, overlying orange, very silty clay (Claygate Beds); the red staining is quite typical of the Older Head. A trial Dit [TL 4737 02571 near this site showed:

Small degraded gravel workings up to 2 m deep were recorded in the vicinity of Woodlands [TL 4815 0307]; a borehole there [TL 4808 0304] proved 6.1 m of the Older Head, comprising 4.3 m of gravel in mottled grey-brown sandy clay overlying 1.8 m of 'Sand and gravel'. Mottled orange and grey sandy clay containing rounded flint pebbles forms the soil. A further boring [TL 4826 0272] penetrated 3.3 m of the Older Head, consisting of 2.7 m of mottled clay on 0.6 m of gravelly clay.

A trial pit [TL 4878 0218] near Birching Coppice proved:

There are shallow disused gravel workings up to 3 m deep in Gravel Pit Wood, east-south-east of Gaynes Park [TL 458 018]; rounded flint gravel is common in the spoil from these excavations.

The Older Head near Ongar radio station, west of Ongar Park Hall [TL 513 039], contains relatively small quantities of gravel, and the deposit is mainly orange-brown and grey mottled sandy clay. In places, rounded flints lie near the base of the deposit [TL 5045 0426]; [TL 5063 0418]. In the nearby railway cutting [TL 5060 0367] 2 m of orange clayey coarse-grained sand overlie Claygate Beds.

On the edge of Ongar Park Wood [TL 5055 0298] a trial pit sited on a small outlier of the Boulder Clay, and adjacent to an old marl pit, proved degraded boulder clay in cryoturbated contact with the underlying Older Head deposits:

A further trial pit some 630 m along the track to the east [TL 5117 0287] showed a similar sequence resting on Claygate Beds at about 99 m OD.

River Roding to Margaretting

An outlier of the Older Head at Nine Ashes [TL 592 027] lies between 91 and 98 m OD. Subrounded flint gravel is common in the soil. One degraded shallow gravel pit was recorded [TL 5910 0279]. In a ditch section near the edge of the Older Head outcrop, the gravel fraction contained 60 to 80 per cent of rounded flints; in addition subangular flints, rounded white vein-quartz and rounded quartzite pebbles were present in the orange sandy clay matrix. The long axes of the pebbles were vertically oriented indicating cryoturbation.

The Older Head is found at elevations above 91 m OD in the area around Tip's Cross [TL 5882 0007], and a temporary trench along the road running north-east from Tip's Cross proved red mottled sandy clay with rounded flints overlying Bagshot Beds; solifluction has probably transported the deposit downslope, probably from an original elevation of about 96 m OD.

Shallow gravel workings up to 2 m deep occur at Norton Heath [TL 602 043]. On early geological maps the outcrop was referred to as Bagshot Pebble Beds, but Monckton and Herries (1889) disputed this and suggested that the gravels were a complex of deposits of different ages. A borehole [TL 6014 0452] in this area proved 3.3 m of the Older Head.

Numerous shallow gravel pits are present at Parsons Spring [TL 623 028], and a trial pit there [TL 6229 0280] proved the following:

Further disused gravel pits lie in College Wood [TL 623 015]. A small borrow-pit north-west of Fryerning House [TL 6237 0168] exposed 2.5 m of red, orange-brown and grey mottled cryoturbated and poorly sorted sand and gravel. About 50 per cent of the gravel is composed of well rounded flints, the remaining gravel including angular flints, rounded vein-quartz, rounded quartzite and rare small Lower Greensand pebbles; the long axes of pebbles were vertical, and there were local remnants of clay laminae. A borehole in this area [TL 6222 0149] proved 4.8 m of the Older Head overlying Claygate Beds; pebble counts recorded only 27 per cent of rounded flints.

The Older Head was proved beneath Head in a trial pit [TL 6179 0106] in Fryerning Wood:

At Mill Green the presence of the Older Head was only ascertained from trial pits. The complex nature of the drift deposits and the reworking of the underlying Bagshot Beds is illustrated in the two pits described below. The first of these [TL 6394 0137] west of Harding's Farm, proved:

The uppermost bed of clay is regarded as locally derived Head from clayey Bagshot Beds. Although the beds between about 1.0 and 2.4 m depth are lithologically identical to the Bagshot Beds the inclusion of nodular flints in the underlying pebble bed indicates reworking of the deposits.

The second pit [TL 6391 0138] showed:

Thickness m

A patch of the Older Head in Fryerning lies above 91 m OD. Abundant rounded flint pebbles, generally less than 5 cm in diameter and set in a coarse sandy clay matrix, were noted in the spoil from a reservoir [TL 6386 0046] north-east of Dodd's Farm. Borings at the site proved 4.1 m of rounded fine and coarse flint gravel in a brown and pale grey sandy clay matrix; pebble counts indicate that 92 per cent of the pebbles are well rounded flints. The Older Head thins to less than 1.0 m NW of the reservoir, where a ditch section [TL 6377 0058] exposed 0.8 m of cryoturbated rounded pebbly loam with ice-wedge casts that extended about 1 m into the Claygate Beds. A trial pit [TL 6394 0039] nearby showed:

The basal bed of the Older Head was probably derived in part from the locally micaceous Claygate Beds. RAE

In the Kelvedon Hatch area, coarse-grained sands and pebbly sands were augered within the Older Head deposits. The pebbly clays were formerly worked for gravels e.g. [TL 5725 9927] (Edmunds in MS).

There are many small former workings for gravel in the wooded area of Writtle Park. Whitaker (1889, p.227) noted that 'at Writtle Park Wood ?[TL 6565 0300] there were about 9 feet (2.7 m) of pebbles and sand'. One fragment of quartzite was noted but otherwise the pebbles were all of flint. RDL

Kesgrave Sands and Gravels

Well sorted rounded flint, quartz and quartzite gravels and associated sands occur beneath the Chalky Boulder Clay and crop out in narrow strips in Cripsey Brook and its tributary in the Moreton area [TL 53 07], in the Chelmer valley [TL 68 17] and in Roxwell Brook [TL 63 07]. However, the small outcrop pattern gives an incomplete impression of the extent of the deposit. Boreholes drilled as part of the Industrial Mineral Assessment Unit's resource survey give a better appreciation of the distribution (Figure 7). It is apparent that these Kesgrave Sands and Gravels are absent in the southernmost part of the district and north-west of the River Stort where, however, the glacial gravels may contain recycled Kesgrave material. Irregular lenses of this material have been recorded from boreholes north-west of Hatfield Heath, and between Great Canfield [TL 59 18] and Pleshey [TL 66 14]. There are also similar areas at Matching Green [TL 54 11], between Moreton [TL 53 07] and Beauchamp Roding [TL 58 10], and from Roxwell [TL 64 08] to Chignall St James [TL 67 10] (Figure 7). The deposit may also underlie the intervening area of Matching Tye,

White Roding and High Easter, but data are insufficient to establish this, because most boreholes terminated in Chalky Boulder Clay. However, only a few proved bedrock beneath boulder clay and it is unlikely that the deposit is very thick in these areas.

These sediments are characteristically pebbly sands, sandy gravels and gravels; locally sands dominate. At the surface the deposits are generally ochreous or orange-brown, medium- to coarse-grained quartzose sands with abundant rounded pebbles. At depth the colour is commonly pale olive-grey or whitish grey.

The gravel fraction essentially comprises well-rounded (with subordinate angular) coarse to fine flint gravel with a significant proportion of rounded to subrounded white vein-quartz and quartzite pebbles; cobbles occur in small numbers in some beds. Quartzose pebbles commonly account for about 30 per cent of the clasts and this is a characteristic feature of these deposits. In addition, small percentages of more exotic erratics have been recorded, including pebbles of volcanic origin, cherts, and various sandstones. Although estimates of the proportions of the pebble types in the gravel have been made during the recent survey detailed counts were not carried out. The sands and gravels in the pit at Moreton were, however, examined by Hey and Brenchley (1977); of 372 pebbles in the 16 to 32 mm sieve fraction 73.5 per cent were flint, 12.1 per cent quartz, 10.5 per cent quartzite, 3.0 per cent chert and 0.8 per cent of volcanic origin. The last were generally fresh, fine-grained acid igneous rocks and vitric tuffs, with microscopic quartzo-feldspathic mosaics and with a few secondary minerals indicative of a provenance in low-grade metamorphic terrains. (Smaller volcanic pebbles were discarded since they had been extensively altered, possibly during transport.) Small green volcanic pebbles were also recorded.

The sand fraction consists of medium- to coarse-grained, angular to subrounded quartz with a small percentage of angular flint shards. Generally the silt and clay fraction is less than 10 per cent.

The sequence is generally well-bedded, and there is no apparent trend of grain-size variation or sorting. For example, the sequence in the pit at Newney Green consisted of a lower part with well-bedded alternating sands and sandy gravels, and an upper 2 to 3 m of coarse, poorly sorted gravel with discrete beds of well-sorted sand up to 0.5 m thick. Thin discontinuous lenses of fine-grained sand and silt are locally present, as are laminae of pale greenish grey, clayey, coarse-grained sand. At Moreton, a sharply defined bed of olive-brown pebbly clay, 2 m thick, was faintly colour-banded in parts, and probably represents part of a mass-flow deposit.

The gravels are commonly planar-bedded, but they also show channel structures and cross-bedding, the thicker sequences commonly showing low angle cross-bedding. The sands show a variety of cross-bedding structures including ripple-drift cross-lamination. Examination of the sedimentary structures in the pit at Moreton (Hey and Brenchley, 1977) indicated their origin in braided streams having a south-eastwards flow, and an eastwards flow seems likely at Newney Green (Rose, Sturdy, Allen and Whiteman, 1978). The significance of the palaeocurrent directions is discussed later (p. 32).

The base of the Kesgrave Sands and Gravels is generally planar, well defined and readily distinguished from the underlying bedrock. Similarly, the upper junction is sharp and markedly erosional (Plate 1). Bedding structures (and the rubified sol lessivé where present, see below) are commonly truncated by the overlying till.

The Kesgrave Sands and Gravels vary in thickness up to a maximum of approximately 13 m (Figure 7). In the Matching Green, Moreton and Fyfield area up to 8 m have been recorded in boreholes at Matching Green and Beauchamp Roding and in the gravel pit at Moreton. The deposits thin rapidly northwards, but details of the form of the body in the Fyfield area are not known. In the northern part of the district, between Great Canfield [TL 59 18] and the River Chelmer, thicknesses vary between 2 and 10.9 m; between Pleshey [TL 66 14] and Ford End [TL 68 17] the thickness ranges from 5.7 m to greater than 9.8 m, but boreholes indicate there is a very rapid thinning towards the limit of the deposit. The thickest sequence recorded in the district is from the Roxwell area where it attains 12.8 m; within this area major extraction has taken place at Great Waltham, Chignall St James and Newney Green.

Thin pale grey clayey silts up to 0.08 m thick have been recorded from the pit at Chignall St James. Miss D.Gregory of the BGS Biostratigraphy Research Group examined the microfauna present and reported that in addition to many Jurassic species the following Quaternary foraminifera were present: Elphidium clavatum, Quinqueloculina cliarensis, Ammonia batavus, Protelphidium anglicum, Bulimina elongata, Lagena sp.and cf. Haplophragmoides sp.These specimens were not significantly abraded. The sediments lie at an elevation of 40 m above OD which is far above the likely contemporaneous sea-level; their origin is uncertain. DM, RDL

Above the Kesgrave Sands and Gravels, there is a distinctive pebbly clayey sand in pits at Newney Green, Moreton and Great Waltham. This bed, which is cut out laterally by the overlying boulder clay, is up to 2 m thick and is generally orange-brown with grey and red mottling with hues up to 5YR and 1OR (Geol. Soc. America, 1975). Reddish brown clay coatings to the pebbles are common (cutans of Rose and Allen, 1977). The grey mottled parts are richer in clay than the remainder of the deposit (Rose and others, 1978). A further important feature is the moderately regular involution pattern in the upper part, with involutions 20 to 70 cm across. These are commonly filled with a fine- to medium-grained, very well-sorted, yellow-brown sand with rare, round, well polished quartz pebbles. This material has been referred to as cover sand by Rose and others (1978, p.93) who found that the involutions formed a regular polygonal pattern in plan. The 'rubified' horizon has been likened to the illuvial horizon of a sol lessivéby Rose and others (1978). It has not been mapped separately because of its thin and impersistent nature. It is possible that the more clayey lithologies have been locally included within the Boulder Clay on the published map.

Disturbances of the primary structures within, rather than above, the Kesgrave Sands and Gravels have been noted at a number of localities and are generally caused by glacitectonics, injection of the bedrock, or periglacial conditions. Glacitectonic structures are apparently uncommon in Essex, and particularly so in the Epping district; the rarity is probably related to the mechanics of movement of the ice-sheet and the nature of the bedrock rather than to lack of evidence. Structures produced by ice-movement within this area are confined to the pit at Chignall St James where fold structures in the higher contorted sands and gravels are truncated at the base of the overlying Chalky Boulder Clay (Figure 8). A number of small subcircular outcrops of London Clay have been mapped in the Roxwell area at heights greater than the regional bedrock level; they have been interpreted as 'intrusive' bodies or diapirs related to periglacial loading. Further evidence of injection of London Clay into the drift sequence comes from small but widespread features in several of the large gravel pits. Bosses of London Clay have been observed in the floor of the pit at Chignall St James, and at Great Waltham a pattern of low ridges was noted. At Great Waltham there is also a dyke-like intrusion of London Clay in the lower part of an ice-wedge structure (Figure 8); at the margins of the intrusion the pebbles were aligned with long-axes parallel to the margins of the 'dyke' and the outer parts of the latter was sheared approximately in the same orientation. These ridges and 'dykes' probably acted as feeders to the irregular, discontinuous lenses of London Clay observed in the pit at Chignall St James. These injections cut across the structures in the gravels at levels up to the boulder clay contact. The injected London Clay was brecciated and sheared, but in one structure an undeformed subspherical cementstone nodule was present within it. The highest injection feature was in one instance truncated by the base of the overlying Chalky Boulder Clay. Near the uppermost parts of some 'cliapirs' small pieces of the clay have been incorporated along the bedding planes of the surrounding sediments. These examples suggest that the intrusion of the London Clay took place during deposition of the sands and gravels. The mechanism of injection is not fully understood, but it is probable that remobilised London Clay was injected through the relatively unconsolidated sands and gravels during the freezing and thawing cycles of a periglacial climate. This process would have been enhanced by the contrasting permeabilities which would also have led to the trapping of abundant water at the base of the sands and gravels during melting periods.

The periglacial structures recognised in the Epping district include ice-wedges and involutions. At Great Waltham the entire sand and gravel sequence was seen to be cut by an ice-wedge up to 2 m wide which incorporated London Clay in its central basal part (Figure 8). The margins of the ice-wedge were sharply defined by vertical to subvertical alignment of the long-axes of the rounded flint pebbles. The bedding in the gravels outside the structure was undisturbed, but slight downward flexuring was noted in the sand beds. Discrete vertical to subvertical lenses of clean, medium- to coarse-grained sand occurred within the wedge, some of which were interconnected with the sand outside the structure. In the Braintree district to the north-east, intraformational ice-wedges have also been recorded within the Kesgrave Sands and Gravels (Ellison and Lake, 1986).

In Norfolk and Suffolk the Westleton Beds and the overlying quartz and quartzite-rich flint gravels (similar to the Kesgrave Sands and Gravels of Essex) were regarded by Prestwich (1890) as marine. It was clearly established by Solomon (1935) that the distinctive lithology and heavy mineral assemblages of these deposits precluded linking them with the Chalky Boulder Clay; because they underlie the latter, they are much older. However, Clayton (1957) maintained that the sands and gravels of the Harlow and Chelmsford areas were all of glacial origin, as did Bristow and Cox (1973). Solomon, in discussion of Clayton (1957) maintained his position, and Rose and others (1976) and Rose and Allen (1977) accepted his view, including the Kesgrave Sands and Gravels in the Beestonian because of their similarity to the deposits overlying the Westleton Beds in Norfolk.

The lithology, cross-bedding structures and grading characteristics of the Kesgrave Sands and Gravels indicate that they were deposited in a fluvial environment, probably in braided river channels. Palaeocurrent directions indicate a south-eastward flow in the Moreton area (Hey and Brenchley, 1977) and an eastwards one at Newney Green (Rose and others, 1978). Rose and others (1976) concluded that these sediments formed as a suite of terraces of a proto-Thames, but this cannot be substantiated since the present upper surface of the Kesgrave Sands and Gravels is clearly erosional, particularly in the Moreton and Chignalls area where bedding structures in the gravels are truncated by the overlying till.

The provenance of the abundant rounded quartz and quartzite pebbles in the Quaternary deposits of East Anglia has been discussed by Hey (1976), who concluded that most of those examined were probably derived from the Bunter of the Midlands. The rare volcanic pebbles may have come from North Wales or may have been recycled from Triassic conglomerates (Hey and Brenchley, 1977). Although no glacial striae have been recorded from the pebbles, some of the sand grains from Alphamstone in north Essex have surface textures indicative of glacial activity (Hey and Brenchley, 1977); it is conceivable, therefore, that these deposits may be a far-travelled glacial outwash of a pre-Anglian glaciation.

Rose and Allen (1977) also interpreted the involuted, clay-enriched and reddened horizon at the top of the sequence as a palaeosol, though this is not universally accepted. The horizon has been claimed by them to represent a temperate sol lessive overprinted by an arctic soil structure. The arctic structures have not been observed where the reddened, clay-and iron-enriched horizon is absent, though they might perhaps be expected to be present in such situations. It may be that both the alleged palaeosols formed under periglacial conditions, a conclusion implied by Lake and others (1977), particularly since similar features are present in parts of the clayey Older Head (p. 25), for red ahumisols have been described from Enderby Land, Antarctica (MacNamara, 1969) where they have formed solely by chemical weathering. If the lower palaeosol is indeed a temperate one, then it presumably formed in the Cromerian, and the underlying deposits presumably in the Beestonian: if it formed by chemical weathering in an arctic climate then the entire sequence could be Anglian. DM, RDL

Details

Matching Green and Moreton

A lensoidal sheet of Kesgrave Sands and Gravels is present in the Matching and Moreton area, but is largely concealed by the overlying boulder clay. Numerous boreholes prove thick Kesgrave Sands and Gravels beneath Chalky Boulder Clay near Matching Green and Abbess Roding. For example, at Matching Greeen [TL 5350 1115], up to 8.3 m of gravel and sandy gravel with rounded to subangular flint, quartzite and vein-quartz were recorded overlying London Clay at 57.1 m OD. Some 800 m to the west, only 2.8 m were recorded [TL 5267 1116], and here the top of the London Clay was at 61.3 m OD. South of this borehole, boulder clay rests directly on London Clay [TL 5235 1031] at 59.1 m OD, north-east of Faggotters Farm. South-east of Abbess Roding, thick Kesgrave Sands and Gravels were also encountered; for example, 7.9 m of gravel and sandy gravel were recorded in a borehole [TL 5824 1048] east of Longbarns, above London Clay at 49.2 m OD.

Immediately north of these boreholes around Matching Green and Abbess Roding, boreholes [TL 5293 1207]; [TL 5764 1213]; [TL 5868 1219] failed to reach the base of the till, although they reached levels comparable with the level of the base of the Kesgrave Sands and Gravels described above. It is thought, therefore, that the Kesgrave Sands and Gravels are thin or absent here.

Kesgrave Sands and Gravels crop out in the southward flowing tributary of Cripsey Brook and in the brook itself between Little Laver [TL 536 098] and just north-west of Wood Farm [TL 545 060]. West and south of these streams the deposit is absent, as shown by the widespread outcrops of London Clay occurring immediately beneath the till in Magdalen Laver [TL 51 07] and Bovinger [TL 52 05]; it was also absent in a well at Tilegate Farm [TL 5129 0875], Tilegate Green. There is no evidence for the extent and thickness of gravels east of the brook. At surface the deposit consists of pale brown, medium- to coarse-grained sands and rounded flint gravel, reaching a maximum known thickness of 9 m in the Moreton gravel pit.

The northernmost outcrop in this area [TL 535 096] is on the west side of the valley east of Robins Acre. The deposit was probably worked for local use in a small pit. This is now ploughed over, but sand and gravel was proved in 1977 by a nearby temporary excavation [TL 5348 0953], in which well bedded, yellow-brown, coarse-grained sand and round gravel 1.9 m thick lay beneath 0.9 m of loamy sandy clay. The clasts in the gravel were mainly flint, but there were subordinate amounts of vein-quartz, quartzite and green volcanic rocks. A layer of weakly laminated, mottled grey-green and ochreous brown, very sandy clay, 0.2 m thick, was present within the sands and gravels. This bed had a local dip of 5° east, and is interpreted as a mudflow deposit. To the south, at High Laver, the sand and gravel is said to have been approximately 3.7 m thick in a water-hole [TL 5300 0873]. Spoil heaps were composed of rounded flint gravel and reddish brown London Clay.

The thickest known occurrence of Kesgrave Sands and Gravels in this valley was recorded in the northern face of a working gravel pit [TL 536 074] at Moreton. The boulder clay overburden varied from 2.5 m thick at the western limit of the pit to 9 m at the eastern part. The composite sequence (with the thickness variation given from west to east) was as follows:

The clayey sand bed with involutions wedges out eastwards beneath the overlying boulder clay. It has the characteristics of the rubified 'sol lessivé' described by Rose and Allen (1977).

South of Moreton, the Kesgrave Sands and Gravels consist dominantly of sand. They are exposed in sections [TL 5353 0658]; [TL 5353 0644] in a pit on the north side of the road south-east of Moreton. The sequence consists of thinly bedded, ochreous yellow, brown, well-sorted, medium-grained sand, apparently without flint clasts. This old pit approaches the southern limit of sand and gravel in the area, for only 300 m to the south Chalky Boulder Clay rests directly on bedrock. DM

River Roding to River Can

The Kesgrave Sands and Gravels are not widespread at outcrop in this area but have been proved beneath boulder clay cover. Thin sequences are present on the east side of the Roding valley and in Roxwell Brook and several important working gravel pits are present in the latter area. DM

(Figure 7) shows a lens of Kesgrave Sands and Gravels that extends south of Newland Brook [TL 64 10] to Cooksmill Green [TL 63 06]. The deposit has been worked in two pits, [TL 660 100]; [TL 647 065]. The maximum recorded thickness is 12.8 m in a borehole at Roxwell [TL 6501 0814].

At the former pit at Chignall St James a typical section [TL 6580 1008] (Plate 1) in 1976 showed:

Prominent diapirs of London Clay were noted in 1977 see (Figure 8). In the pit-floor, bosses of bedrock were observed in vertical contact with the gravels. In the faces, distended injection structures of London Clay, which have been subsequently deformed by ?cryoturbation and faulting, were noted. Shears were present in the injection features. The presence of complete septarian nodules suggests that the London Clay was intruded in a cohesive state and not in a remobilised form.

A more recent section [TL 6628 069] on the east side of the River Can showed a diapiric structure affecting the sands and a tapering lens of pebbly sands within the Chalky Boulder Clay. The underlying gravels are 9.5 m thick, and contain four thin beds of clayey silts, which have yielded microfossils (p. 30).

On the east side of the Roding valley the gravels are thin or absent at outcrop. In the tributary valley near Warden's Hall [TL 5935 0695] thin gravels were formerly dug in small pits.

Near Newland Hall, sandy deposits were proved locally in the bank of the Newland Brook [TL 6351 0949]. At Newland Hall [TL 635 096] Woodward (in Whitaker, 1889, p.318) noted 'a small inlier of gravel, which contains pebbles of chalk'. This gravel, possibly of glacial origin, was not found during the recent survey, but it may have been dug from the now degraded pits in the immediate vicinity of the Hall.

On the upper valley slopes to the west of Roxwell Brook, isolated outcrops of Kesgrave Sands and Gravels are present, and have been worked in the past. Variations in their thickness may be related to the presence of diapiric structures. In two examples near Pooty Pools and Tye Hall [TL 624 066]; [TL 630 077], thicker gravels have been worked in the west of the outcrops whereas thin gravels overlie London Clay to the east. One trial pit [TL 6318 0776] near Tye Hall showed the London Clay to be brecciated.

Whitaker (1889, p.319) figured a section, about 3.7 m high, at Hoestreet [TL 654 076]; this showed surface wash resting on reddish sand and gravel, with a channelled base overlying loamy sands with a contorted and distended black peaty clay bed. Greyish sand and gravel underlay these beds. The peaty clay is no longer accessible.

The Newney Green gravel pit [TL 647 065] exposed some 5 m of sandy gravels. The southern limit of gravel extraction at this site was controlled by a marked increase in the height of the London Clay surface. Current directions in the gravels are from the southwest and appear to conform with the bedrock surface. In the northern face [TL 6480 0654] the succession was:

In the northern face the involuted beds are cut by ice-wedge casts, which are filled with clean fine- to medium-grained sand (cover sand). A complex network of these was exposed during the early excavation of the pit (Dr J. Rose, pers. comm.)

Gravels were formerly worked from pits near Moor Hall and Blackwall Bridge [TL 657 064]; [TL 656 086]; [TL 664 080], but no detailed descriptions are available. RDL

North-east of the River Can

The only outcrops of Kesgrave Sands and Gravels in this area are in the Chelmer valley where thicknesses vary considerably. Boreholes indicate that quartzose sands and gravels are probably present beneath boulder clay in the northern and eastern part of the area. They are up to 10 m thick near Pleshey, but are thin or absent immediately to the north around Ford End.

Around Ford End and Hartford End, where the Kesgrave Sands and Gravels are generally thin and impersistent, small pits were worked in the past for domestic supplies of gravel. The boundary between Chalky Boulder Clay and London Clay is typically marked by pebbly soil and by weak springs. RDL

Gravelly soil containing many rounded flints near Pentlowend [TL 618 162] suggests the presence of Kesgrave Sands and Gravels. A nearby borehole [TL 6130 1611] penetrated 3.0 m of Kesgrave Sands and Gravels, comprising mostly sand with a clayey matrix. RAE

In the Walthambury Brook valley, gravels were noted locally beneath the Head. A borehole [TL 6836 1446] proved 6.3 m of gravelly sands beneath boulder clay.

The Great Waltham gravel pit [TL 683 118] exposed the following succession in 1969:

Again diapiric structures affect the London Clay at this pit (Figure 8). They varied in shape from low ridges to distended 'flame-structures'. It is reported that the latter locally pierce the base of the boulder clay. One example showed evidence of syndepositional injection; the clay was apparently redeposited in the surrounding gravelly sands. The diapirs have no preferred orientation. An ice-wedge cast lay within the gravels above a dyke-like diapir.

A gas-pipeline excavation near Woodhali Farm [TL 683 109] showed evidence of another diapir and wedges of Chalky Boulder Clay (2 m wide) and London Clay (0.3 m) occur within the gravels c.[TL 6803 1057]. RDL

Boulder Clay

Boulder clay is the most extensive surface deposit and covers about 75 per cent of the district. In the north, centre and east of the district it forms a plateau falling in height from approximately 90 m OD in the north to 50 m OD in the east. It is covered only by Head and Alluvium in the valleys and by Head Gravel around Hatfield Heath and Matching. Towards the south-west and south, erosion has cut through the boulder clay sheet; patches of boulder clay remain on the high ground of Epping Forest, and boulder clay is apparently banked against solid ridges south of Stondon Massey, being generally absent from the highest parts of this area.

Generally the Boulder Clay forms a single unit, though north-west of the Stort valley and in Harlow, there are inter-fingering lenses of gravel (p. 42). Its base is generally sharp and easily recognised. Where the deposit directly overlies impervious bedrock such as London Clay, small seepages are present, usually accompanied by a physical feature or change in slope. In the west of the district around Nazeing the valley slopes have been oversteepened by erosion; this has resulted in landslips (see Chapter 6). The level of the base varies throughout the district from less than 30 m OD to approximately 100 m OD (Figure 9). In the north-west of the district and in Harlow, the height of the base has been determined (Figure 9) by using the lowest occurrence of the deposit: here heights vary from 50 to 70 m. In the Stort valley between Sawbridgeworth and Old Harlow, boulder clay also occurs within the buried channel. Between Hatfield Broad Oak and the Chignalls, the contours indicate a wide, shallow depression trending west–east to Good Easter, and from there a depression deepening south-east, approximately coincident with the Can valley. This feature was first recognised by Wooldridge and Henderson (1955) as the 'mid-Essex depression'. Southwards, the base rises to a maximum in Epping Long Green, against the Epping Forest ridge and at Norton Heath. The contin'iity of the ridge is broken by several linear depressions, such as those running southward along the Cripsey Brook, the lower part of the Roding valleys, and north-eastwards from Blackmore [TL 60 02] to Cooksmill Green [TL 63 06].

Several pits and sections in the Epping district show boulder clay to rest discordantly upon the Kesgrave Sands and Gravels. For example, in the pit at Chignall St James [TL 663 099] the bedding in the gravels is contorted and, in places, truncated by the overlying boulder clay. At Moreton [TL 534 074] near Ongar the reddened clay-enriched horizon with involutions at the top of the Kesgrave Sands and Gravels is cut out eastwards along the north face of the pit.

Near the surface the boulder clay is a remarkably uniform stiff, brown, yellow and grey mottled sandy clay with chalk pellets and scattered angular flints. The sand grains are typically angular, and the upper 1.5 m of the deposit are commonly affected by decalcification. The weathered zone, which is regarded as extending to the depth at which a homogeneous blue-grey colour is encountered, is extremely variable in thickness. In some deep ditches it is less than 2 m thick, but in some boreholes yellow or brown mottling continues to depths of up to 6 m. In sections and borehole cores, fissures within the boulder clay are associated with pale grey streaks and with some iron-staining along the fractures. At Hadham Mill [TL 430 170] (Plate 2) decalcification has taken place along pipe-like bodies to leave a reddish brown sandy flinty clay. No apparent volume change has occurred in the decalcification zones. Although brown, grey and white patinated flints, both angular and nodular, form the bulk of the stone content of the boulder clay, the erratics also include other rocks of varying durability. The more durable include rounded vein-quartz and quartzite pebbles similar to those encountered in the Kesgrave Sands and Gravels; others include large chalk pebbles, rotted quartzite, chert, Jurassic shelly limestone, Carboniferous limestone, pink siltstone (probably Triassic) and black shale (probably Kimmeridge Clay). The rare igneous and metamorphic rocks include rotted granite, rhomb porphyry, basalt and mica-schist. Fossil fragments derived from Jurassic and Cretaceous strata are also quite common, including fragments of Gryphaea, belemnites, echinoids and sponges.

Few mechanical analyses of the Chalky Boulder Clay have been made within the district, and estimates of the quantity of chalk present range from zero in the weathered and decalcified zone to 30 per cent. In general this only accounts for the observable pellets; in addition there is much chalk flour in the matrix of the clay. Analyses of the total chalk content in the Harlow area were carried out by the Harlow Development Corporation, and the range of calcium carbonate varied from zero to approximately 50 per cent. The chalk content in boreholes appears to increase with depth, but there are many exceptions; where visible chalk is present the content is usually greater than 25 per cent of the whole deposit.

Although for the most part the Chalky Boulder Clay appears to be uniform, one of the most noticeable variations is in its colour. In some instances the typical pale blue-grey of the unweathered material passes down into olive-grey or olive-black. This change does not appear to be related to weathering; commonly it occurs at or near the base and, although the colour boundaries are gradational, the olive lithologies are up to 3 m thick and, at the base, are locally underlain by brownish grey pebbly sandy clay. In one case the olive-black boulder clay lay immediately beneath alluvium. It has been suggested (Rose and others, 1978) that the brown pebbly material may include a large quantity of London Clay and locally derived gravel.

In some boreholes up to 3 m of mottled orange-brown or pale blue-grey to olive-grey very clayey pebbly sand has been recorded at the base of the sequence; the upper boundary is gradational over a few centimetres, and most of the clasts consist of subangular to subrounded flint and rounded vein-quartz and quartzite pebbles. It is probable that this material is comparable to the banded and pebbly material seen in some pits (see below), where it has been interpreted as a basal flow-till.

There are lenses and beds of water-bearing sandy gravel and laminated silts within the Chalky Boulder Clay; more rarely small rafts of reconstituted and mobilised London Clay occur. The sandy gravel lenses are commonly ochreous brown and clayey. The laminated silts and fine sands, typically chalky, are not common, and range in thickness from about 1 m to thicker deposits of mappable extent (p. 52). Weakly laminated and colour banded boulder clays have been observed in the pit at Chignall St James [TL 660 100], where 10.5 m of Chalky Boulder Clay also shows local, shallow, channel-like structures suggesting a subaqueous depositional environment. The nearby occurrence of laminated silts and a buried channel in the Can valley east of the present district lends support to such an interpretation. There is, however, a fine dividing line between aqueous deposition and mudflows and it is possible that these structures may have formed in a very mobile flow-till.

The base of the Chalky Boulder Clay is exposed in pits at Hadham Mill [TL 430 170], at Great Waltham [TL 683 118] and at Moreton [TL 536 074]. Here a thin (up to 4 cm) discontinuous calcrete layer is common. The basal metre of boulder clay is colour banded with pale brown and grey streaks, stringers of silt and calcareous material, and scattered round pebbles of quartz, quartzite and flints with long axes aligned horizontally. Some of the laminations mark small but distinct variations in grain size. The unit proved unmappable, but probably represents a flow-till.

The present thicknesses of boulder clay are less than the amount deposited because of subsequent erosion. The boulder clay appears to be thickest on the plateau between Hatfield Heath and the Easters, where many boreholes indicate that more than 18 m are present, with a few indicating a thickness of up to 26 m. The Boulder Clay thins southward to 10 to 15 m at most around Foster Street [TL 490 090] and North Weald airfield [TL 490 045]. In the Epping and Upshire areas the thickness is less than 10 m, and less than 5 m locally. Thick boulder clay is present in the Willingale area, thinning south and east to a maximum of 14 m in the Blackmore area and less than 10 m in the Great Oxney Green area. Where the boulder clay contains a bed of sand and gravel, as in the Hunsdon and Harlow areas, the thicknesses of the lower and upper boulder clays vary up to 10 m and 21 m respectively.

To the south of Harlow this two-fold boulder clay succession is complicated by the steep rock-head slopes which have resulted in an overlapping sequence, the wedge of sand and gravel and the lower boulder clay both thinning southwards against the rising ground (Figure 10). This has led to some erroneous interpretations of the local sequence. Irving and Irving (1913) recognised a 'lower till' in the Harlow area, and described it as 'a compact silt, devoid of chalk detritus'. More recently, however, Clayton (1957) referred to the lower till as being more chalky than the upper till, and suggested that the two were of different ages. Although there may be considerable differences in the detailed lithologies, perhaps due to decalcification within the lower till, the present survey suggests that the two boulder clays are indistinguishable, and are part of the main sheet of Chalky Boulder Clay.

It is difficult to delineate precisely the extreme limit of the Anglian ice-sheet. Most workers have taken the present extent of the Chalky Boulder Clay to be a rough indication of this limit. Contours on the base of the boulder clay (Figure 9) indicate that the ice encountered progressively rising topography south of the mid-Essex depression, and was mainly funnelled into broad depressions, one of which followed the present Roding valley. The presence of the Older Head on the high ground nearby confirms that the ice hereabouts had little erosive power and must have been near its limit, though there is no extensive outwash along the postulated ice-margin. DM, RDL

Details

North-west of the River Stort

Chalky Boulder Clay covers most of the area north-west of the River Stort with the exception of the Ash valley, where the junction with the underlying Glacial Sand and Gravel is seen along the valley sides. At the surface the boulder clay is typically a stiff brown clay with flints. Chalk pellets are abundant except near the surface where leaching has usually removed most of them. The clay changes colour to grey with depth, except at the base of the deposit which is commonly brown, especially where it rests on Glacial Sand and Gravel. Locally the Boulder Clay rests directly on bedrock e.g. [TL 4320 1888]. On the higher parts of the interfluves, the thickness of the boulder clay sheet has been proved in several boreholes to be in excess of 18.6 m.

The relationship between the Chalky Boulder Clay and the Glacial Sand and Gravel is complex around Hadham Mill [TL 4245 1695]. Several excellent sections were seen in an abandoned gravel pit [TL 430 170] east of Hadham Mill. This pit was being backfilled during the survey (1974–77), and the sections changed considerably over this period. Along much of the eastern face [TL 4320 1729] to [TL 4317 1703], a thin boulder clay occurred at the top of the section, overlying Glacial Sand and Gravel. This boulder clay, about a metre thick, was more sandy and silty than that generally mapped at the surface in the neighbourhood. It was also poorly banded, with variations in colour and in silt and sand content. A calcrete, 3 to 5 m thick, was commonly present at its base. Over much of the section the upper part of the boulder clay has been decalcified. Locally this process has affected the entire thickness and, in places, has penetrated into the Glacial Sand and Gravel below. It is difficult to separate the decalcified boulder clay from the decalcified sand and gravel, both deposits consisting of dark red-brown clayey gravel. In the southern end of the eastern section, the boulder clay overlies a 'lower' boulder clay, the junction between the two being marked by a string of well spaced flint pebbles. The 'lower' bed is banded locally, although this is less obvious with increasing depth. In one part of the exposure a channel, filled with red-brown clayey decalcified gravel, separated the two boulder clays. A trial pit [TL 4317 1724] excavated in the bottom of the gravel workings adjacent to the eastern face revealed 0.9 m of a chalky 'lower' boulder clay beneath Glacial Sand and Gravel. This boulder clay, which was not bottomed, was grey, chalky and sandy in its upper part, but passed down into a grey boulder clay with only sparse chalk pellets. It contained a higher proportion than usual of sandstone, and shale fragments and septarian nodules. An excavation [TL 4319 1727] into the lower part of the eastern face revealed an interdigitation of boulder clay with sand and gravel. The fingers of boulder clay were colour banded like the 'upper' boulder clay. In the extreme north of the pit, an excavation [TL 4310 1746] revealed boulder clay resting directly on London Clay. This contact was topographically lower than any boulder clay seen elsewhere in the pit and, because of the interfingering of deposits, may not be equivalent to the 'lower' boulder clay. The complexity of this area has not been depicted on the 1:50 000 sheet.

One small area of boulder clay low down in the Ash valley [TL 4230 1698] just west of Hadham Mill is separated from the extensive Chalky Boulder Clay of the plateau by an outcrop of Glacial Sand and Gravel, and is probably stratigraphically lower. Several boreholes between Hadham Mill, Perry Green and South-end [TL 4319 1751]; [TL 4440 1775]; [TL 4465 1670]) encountered two beds of boulder clay separated by Glacial Sand and Gravel.

This rather complex sequence extends southwards from Hadham Mill, through the Hunsdon area to the Stort valley just north of Roydon. Two boulder clays separated by Glacial Sand and Gravel occur in several boreholes [TL 4385 1240]; [TL 4077 1450]; [TL 4178 1165]. Three boulder clays separated by Glacial Sand and Gravel have been recorded in some boreholes [TL 4076 1372]; [TL 4172 1289]; [TL 4037 1288]. BSPM

Hatfield Heath and White Roding

Chalky Boulder Clay, crops out over almost the entire area between the Stort valley and the Roding valley, except where it is locally covered by deposits such as the Head Gravel. Although generally absent in the lower sides of the Stort valley, the till thickens rapidly eastwards, attaining a thickness of more than 25.9 m about 1.5 km south-east of Sawbridgeworth.

Exposures are limited to the numerous ditch sections throughout the area, and to a small isolated patch [TL 4940 1632] in a gravel pit at Gaston Green (Figure 11) near Sawbridgeworth where, however, the relationship of the boulder clay to other drift deposits seen in the pit could not be fully determined; it may be the uppermost part of the fill of a buried channel in the Stort valley (p. 47). BSPM

Roydon, Halls Green and Harlow

Two boulder clays have been recorded in many boreholes around Harlow. The upper boulder clay caps much of the high ground of the New Town [TL 449 102]. The lower boulder clay crops out along the sides of the Canons Brook valley and along the southern side of the Stort valley from Canons Brook in the west to the Eastern Industrial Estate [TL 470 118] in the east. BSPM

Farther west and south, a boulder clay was mapped beneath sand and gravel in the Roydon area [TL 410 098] and north-west of Hare Street in Todd Brook [TL 435 098]. A borehole [TL 4305 0975] in the Pinnacles district of Harlow gave the following sequence:

Farther east, at The High, another borehole [TL 4467 0955] proved 1.8 m of 'hard, dry, light brown chalky clay' beneath 3.7 m of clayey sand and gravel.

In the Netteswell [TL 450 095], Latton [TL 466 095] and Tye Green [TL 455 085] districts of east Harlow, the till is thin; Glacial Sand and Gravel crops out in the shallow Todd Brook valley, and bedrock crops out less than 1 km to the south. For example 2.0 m of brown clay with chalk pellets and small flints were recorded above sand from a borehole [TL 4539 0936] in Netteswell, and 3.7 m of boulder clay were recorded above London Clay in a borehole [TL 4669 0945] at Latton Priory. Immediately south of Todd Brook the thickest boulder clay (9.1 m) was in a borehole [TL 4710 0929] at Half Hide Nursery.

The glacial deposits thin southwards from Roydon to Nazeing as shown by the following water well records. In Halls Green a borehole [TL 4228 0858] proved 9.75 m of an upper boulder clay separated by 4.27 m of sand from 8.23 m of a lower boulder clay. Farther south at Roydon Hamlet, 21 m of boulder clay were recorded in a well [TL 4174 0768]. At Tylers Cross Nursery, Roydon Hamlet, the boulder clay was 9.1 m thick [TL 4215 0741]. South of Todd Brook in Great Parndon and Passmores [TL 44 08], the sand and gravel thins out rapidly.

From Nazeingwood Common [TL 425 058] to Potter Street [TL 475 093] the base of the Chalky Boulder Clay generally crops out below 76 m OD and directly overlies London Clay except where a few small outcrops of intervening gravel occur. The till appears to be banked up against the Epping Long Green ridge. DM

Epping Long Green, Hastingwood and the Lavers

Chalky Boulder Clay occurs on the northern interfluve of Cobbin's Brook and has been extensively dissected by small south-flowing tributaries. In the western part of the area, the surface material is an orange-brown and grey mottled chalky sandy clay; to the east a yellowish brown chalky clay is more typical. Decalcification appears to be variable both in depth and extent; even in small outliers, for example near Galleyhill Green [TL 4030 0430]; [TL 4044 0440]; [TL 4066 0450], chalky clay was augered within 1.3 m of the surface. Small temporary excavations and ditch sections indicate that, in general, decalcification has affected only the uppermost 0.5 to 1.3 m. The total thickness of boulder clay in this area is not known, although in the more extensively dissected tracts, where old marl pits are common, it is probably less than 4 m. The height of the base of the Chalky Boulder Clay falls progressively into the Cobbin's Brook valley, from above 90 m OD on the ridge running through Harold's Park Farm [TL 4125 0445] to around 50 m OD west of Maynards Farm [TL 4178 0279]. In contrast the base is above 91 m OD along the Epping Long Green ridge north-west from Harold's Park Farm [TL 4125 0445]. RAE

Between Hastingwood and the Lavers, the boulder clay plateau is at 76 to 91 m OD, and is dissected by shallow, wide valleys. Boulder clay is ubiquitous at surface, except in Shonks Brook [TL 490 078] and Cripsey Brook and its main tributary [TL 53 07]. The surface material consists of a brown to greyish brown, silty clay with a small amount of angular sand grains, chalk pellets up to 5 mm diameter and angular flints. At the bottom of deep ditches (c.2 m) a pale to medium blue-grey colour is common, decalcification being generally confined to plough depth.

Between Latton Park [TL 47 07], Thornwood Common [TL 47 05] and Magdalen Laver [TL 51 07], boulder clay rests directly on bedrock, which crops out south-east of Latton Priory [TL 466 065] and in Shonks Brook [TL 486 080]. The only record of sand and gravel beneath boulder clay is a record of 1.2 m of gravel in a borehole [TL 4768 0704] for the M11 motorway. At Sewalds Hall [TL 4959 0746] the junction between the Chalky Boulder Clay and London Clay was marked by 0.3 m of round flint pebbles in a chalky sandy clay matrix.

Boreholes drilled along the M11 illustrate the variable thickness of the till. Between Rundells [TL 474 068] and Foster Street [TL 49[TL 49 09] it is less than 10 m thick; in a borehole [TL 4955 0995] north-west of Roffey Hall 12.5 m were recorded; north-east of Hastingwood, 18.3 m of boulder clay overlying London Clay were proved in a well [TL 5129 0875]. The thickness east of the valley between Little Laver and Moreton is not known. South of Moreton the plateau is more dissected, and the London Clay has an extensive outcrop around Bobbingworth [TL 530 055]. DM

Epping, Bobbingworth and Stanford Rivers

Much of this area lies to the south of the main boulder clay plateau, and only outliers of till are present south-east of Epping.

Two outliers of Chalky Boulder Clay in the vicinity of Copthall Green [TL 421 011] occupy a narrow ridge which falls from around 99 m OD near Wood Green [TL 419 003] to 75 m OD east of Obelisk Farm [TL 4177 0153]. Boreholes on the highest part of the ridge, show the deposits to be 'brown clay with grey veins and calcareous nodules', 'brown silty clay with veins of sand and grey clay' and 'brown clay with stones and chalk'. Less than 3 m of the lithologically variable material are present. A small outlier of yellowish brown sandy clay containing chalk lies at Spratts Hedgerow Wood [TL 4303 0279] in the Cobbin's Brook valley at a height of 60 m OD.

An extensive tract of boulder clay extends below 95 m OD on the north side of the ridge near Epping from New Farm [TL 4440 0165] to the vicinity of North Weald airfield [TL 495 043] and is dissected by three tributaries of Cobbin's Brook. There is a general fall in the level of the base of the boulder clay towards Cobbin's Brook; a borehole [TL 4831 0392] on North Weald airfield penetrated 6.8 m of boulder clay overlying London Clay at 88.3 m OD, and another [TL 4803 0491] proved 12.2 m of boulder clay overlying London Clay at 70 m OD. Over the whole area the Chalky Boulder Clay consists at surface of pale yellowish brown chalky and sandy clay. Boreholes drilled along the M11 motorway show that this weathered zone extends to between 3.4 and 6 m below the surface.

A trial pit [TL 4419 0067] dug on Bell Common, Epping, proved:

Percolating groundwater was probably responsible for the precipitation of the secondary calcareous material and cryoturbation, involving the underlying Older Head, has introduced more sandy material into the boulder clay than is typical.Old marl pits near St Margaret's Hospital, Epping [TL 4685 0252], have been dug in an outlier of Chalky Boulder Clay whose base lies at approximately 107 m OD. A nearby borehole [TL 4681 0268] proved 2.5 m of brown and grey mottled clay with 'some large amounts of small dark fragments', overlying the Older Head.

Near Mount Wood, Colliers Hatch, a trial pit [TL 4945 0148] illustrated the composition of the boulder clay.

A second pit, [TL 4983 0230] proved Claygate Beds below 2.5 m of chalky boulder clay containing many subangular and nodular flints in sandy clay.

Between Stanford Rivers [TL 510 010] and Cripsey Brook, patches of boulder clay cap interfluves at heights ranging from 100 m OD south-west of Colliers Hatch [TL 495 016] down to around 50 m OD in the Roding valley near Marden Ash [TL 557 022], Great Colemans [TL 5485 0152] and Little End [TL 5394 0039]. Over much of this area their thickness is not known, although in the numerous small outliers, for instance, those immediately west and south of Toot Hill

[TL 516 024], it is probably less than 4 m. In the more extensive tracts a greater thickness is likely, as shown by the record of a well at Stanford Rivers [TL 534 010] which proved about 12.2 m of 'Pleistocene Drift' overlying London Clay; any Glacial Sand and Gravel in the area is likely to be less than 4 m thick. RAE

Boulder clay caps a hill south-east of Garnish Hall [TL 4700 9970]. Its base is irregular and it overlies London Clay between 46 and 65 m OD; the deposit varies from brown chalky sandy clay at the higher points to orange-brown sandy clay with abundant angular flints in the lower sections, and decalcification to depths of 1.5 m is common. The thickest boulder clay recorded was 5.6 m in a borehole [TL 4597 9885] adjacent to the district, 1 km south-west of Garnish Hall.

At Hill Hall [TL 489 995] ochreous brown chalky sandy clay with abundant flint clasts overlies London Clay at between 62 and 75 m OD. Weak springs at the junction have lubricated landslips involving both boulder clay and bedrock west of Hill Hall. Small outcrops of gravel are present beneath boulder clay south-south-west of Coleman's Farm [TL 4939 9937].

A wider tract of boulder clay was mapped between Coleman's Farm and the River Roding. The deposit is typically a fawn to pale grey, sandy clay with small chalk pellets and scattered angular flints; decalcification rarely extends to greater than plough depth. In this area the deposit rests partly on bedrock as in the valley. [TL 508 998] west of Howfields, and partly on Glacial Sand and Gravel, as in the valley [TL 520 998] near Murrells Farm. DM

The Rodings to the Can valley

This area is one of contrast because the Chalky Boulder Clay forms a nearly complete cover between High Roding [TL 605 170] and Highwood [TL 630 050], whereas to the south the plateau becomes more dissected with bedrock cropping out. The boulder clay consists of pale brown and grey chalky sandy clay with flints and rare erratics. The depth of decalcification is generally less than about 1.5 m. North of Roxwell, [TL 650 850] the deposit is generally greater than 18 m thick; for example two boreholes [TL 6027 1110]; [TL 6311 1053] were terminated after proving 18.3 and 18.1 m of boulder clay respectively. Some boreholes near High Roding e.g. [TL 6031 1653] proved intercalations of clayey sand, up to 1 m thick.

The gravel pit [TL 660 100] at Chignall St James showed the following typical section in 1976:

On the plateau to the west of the Roxwell Brook, a well [TL 6009 0837] at Torrell's Hall indicates a rare occurrence of boulder clay beneath Glacial Sand and Gravel:

A well [TL 6257 0710], farther west at Butt Hatch Farm, proved a rather different succession:

Two boreholes near Tye Hall and Roxwell [TL 6303 0742]; [TL 6501 0814] proved similar intercalations of clayey gravel about 1 m thick within boulder clay.

A trial pit to the east of Roxwell Brook [TL 6417 0741] showed:

In the gravel pit [TL 648 065] at Newney Green the sequence formerly exposed in the western face [TL 6452 0641] was:

The flow-till in the western face is believed to thicken and to crop out to the north-west. A trial-pit [TL 6415 0685] near Benedict Otes showed:

In the Ongar area, boulder clay was well exposed in clay pits, 1 km east of Marsden Ash [TL 553 022]. A disused pit [TL 5630 0258] showed 1 m of grey-brown sandy clay with scattered angular flints, chalk pebbles and race, overlying 3 m of orange and pale grey mottled sandy clay containing rounded flints and quartzite pebbles and broken Gryphaea fragments; the basal part of the sequence was crudely bedded and rested with a sharp contact on Glacial Sand and Gravel. In a working pit close to the south-east, up to 5.7 m of boulder clay were exposed: at the top there were 3 m of pale orange-brown to yellow-brown chalky sandy clay containing mostly subangular flints and with a thin calcrete or pockets of marl at the base; the underlying 2.7 m were of grey sandy clay with only scattered small chalk pellets but scattered rounded flint, quartzite, vein-quartz and other erratics including jaspers, sandstones, black shales (Kimmeridge Clay) and derived Jurassic shell fragments. The base of the Chalky Boulder Clay in this area lies at about 56 m OD, and in the pit was sharp and planar.

Grey-brown sandy clay containing only scattered small chalk pellets was augered in the tributary valley south-west of Norton Mandeville [TL 580 046]. The clay is probably equivalent to the lower bed of the pit described above. Other exposures between High Ongar and Highwood are rare. Surface decalcification may be generally less than the 1.5 m noted in a small excavation at Nash Hall [TL 5694 0360].

Outliers, at between 50 and 60 m OD occur in the Roding valley and its tributaries. A trial pit [TL 5700 0184] north-west of Stondon Massey House proved thin boulder clay, lithologically complex and probably including a flow-till at its base:

Between Norton Heath [TL 602 043] and Parsons Spring [TL 623 028] a spread of boulder clay occupies a shallow depression between outcrops of bedrock. Continuous-flight auger boreholes in this depression showed that the boulder clay rests directly on London Clay, with only a thin impersistent intervening gravel bed as in boreholes [TL 6058 0253]; [TL 6020 0225] near Red Rose Farm.

Adjacent to the road running towards Blackmore from Nine Ashes [TL 593 026] the base of the Chalky Boulder Clay lies at 91 m OD. Some 60 m downhill, however, a borehole [TL 5956 0256] has penetrated 7.3 m of boulder clay resting on London Clay at 82 m OD. Another borehole to the south-east [TL 5976 0241]) proved 8.5 m of boulder clay on London Clay at 77.2 m OD. A similar appreciable rock-head gradient exists near Parsons Spring [TL 623 028]. In the Blackmore area, the boulder clay typically shows a fairly constant lithological pattern with depth, a pattern which is distorted only where lenses of gravel or silt are present. A typical profile is illustrated by a borehole [TL 6049 0220] near Red Rose Farm, which proved:

The base of the Chalky Boulder Clay between Hook End [TL 590 998] and Ingatestone [TL 655 998] is marked by sandy clays with rounded pebbles that are locally red and ochreous brown mottled.

Trial boreholes for the Margaretting by-pass proved at least 3 m of Chalky Boulder Clay in the outcrop near Margaretting Hall.

Sand and gravel is thin or absent in this area. However, an excavation [TL 6594 0066] near Little Hyde proved:

Small outliers on either side of the River Wid in the Ingatestone area have clearly defined bases which fall towards the valley from 70 m to about 55 m OD. Although for the most part the boulder clay is chalky at the surface, chalk fragments are absent locally, giving rise to a surface deposit of mottled orange and grey sandy clay.

Old marl pits are characteristic on the boulder clay surface. Nearly half of one small outlier [TL 673 992] has been dug over. CRB

North-east of the Can valley

Chalky Boulder Clay, pale brown and grey mottled and decalcified in the top 1 m, is the dominant surface deposit. Exceptions occur around Pentlowend [TL 618 162] and in the Chelmer valley near Ford End [TL 675 170], where London Clay crops out. Boulder clay underlies the Head and Alluvium in the valleys of the River Can and its tributaries; and underlies the Head Gravel near Garnetts Wood [TL 634 181]. In the north of the area, particularly around Hounslow Green, the till is locally non-calcareous, and contains a high proportion of rounded pebbles particularly towards its base.

Fresh dark grey or olive-grey chalky till has been proved at depths ranging from about 3 m north of High Easter [TL 6031 1653] to 7.8 m at Yewtree [TL 6408 1623]. In the latter borehole a thin sandy and gravelly bed lay between 4.4 and 5.3 m below the surface; the small gravel fraction included rounded to angular flints, rounded quartz, rounded quartzite, sandstone, black shale (probably Kimmeridge Clay), red siltstone, oolitic limestone, ironstone, and Jurassic shell fragments. The basal part of the boulder clay is commonly recorded as 'black boulder clay' in drillers' logs, probably because of a relatively high Kimmeridge Clay content in the matrix. In some borings e.g. [TL 6432 1755], up to 0.5 m of paler coloured olive-grey or yellowish brown sandy clay with rounded pebbles is recorded at the base of the till.

A trial bore [TL 6338 1783] near Bishop's Green proved 2 m of silty laminated beds within boulder clay below 5.7 m. A borehole [TL 6634 1608] near Oldpark Farm, north of Pleshey proved:

The Chalky Boulder Clay is generally in excess of 18 m thick around the Easters and towards Chignall Smealy. The maximum proved thickness is 25 m in a well near Bedfords [TL 640 132]. A thick sequence in the River Can valley is suggested by a borehole [TL 6385 1126] west of Great Newarks, which proved 19.4 m without reaching the base of the boulder clay. Around Pentlowend [TL 6130 1611], however, only 5.1 m overlie Glacial Sand and Gravel.

The base of the till falls from 70 m OD north of High Roding [TL 604 177] to below 25 m OD in the River Can valley (see (Figure 9)).

North of Chignall St James, gas-pipeline excavations revealed irregular inclusions of buff silts up to 1.5 m across in the boulder clay [TL 6685 1058]; [TL 6733 1055]; [TL 6742 1053]. A little farther east [TL 6761 1052], near Gray's Farm, loam was interbedded with boulder clay.

A passage from chalky till to cream and grey silts up to 1.5 m thick occurred nearby [TL 6779 1053].

Woodward (in Whitaker, 1889, p.326) described a pit 'between Breton Hall [Brittons Hall] and Beaumont Oats [Otes]' as follows:

The Great Waltham gravel pit [TL 683 118] has exposed up to 17 m of boulder clay in recent years. In 1969, when 12 m of boulder clay were present in the face, the upper 6 m was noted to be buff coloured, whereas the lower part was dark bluish grey. The basal metre or so was typically brown and without chalk (decalcified) but with pebbles incorporated from the beds below. RAE, RDL

Glacial Sand and Gravel

Poorly sorted flint gravels, sands and thin interbedded silts occur above, within and beneath the Chalky Boulder Clay. They crop out extensively in the Ash and the Stort valleys and their tributaries, particularly in the Harlow area (Figure 7), (Figure 10). To the north-west of the Stort valley and in Harlow, the drift sequence is comparatively complex. Boreholes at Harlow New Town, together with field mapping, show that over much of this area a two-fold sequence of gravels is present, separated by and overlain by boulder clay (Figure 10). The lower division crops out in the Stort valley, but does not extend for more than 1.5 km southwards before it is overlapped by boulder clay which rests on London Clay. The upper division is much more widespread throughout Harlow, particularly in the tributary valley at Hare Street and Netteswell [TL 44 09]. Although the extent of this unit is greater than that of the lower, it is itself overlapped by boulder clay between Roydon Hamlet [TL 420 075] and Potter Street [TL 475 095]. North-west of the River Stort at least two gravel units have been recorded locally in a linear belt between Hadham Cross [TL 43 18], Hunsdon, and Eastwick [TL 43 12]. A single gravel unit is present beneath boulder clay over much of the remainder of this north-western area although thin lenses have been recorded within the boulder clay.

The gravels consist of poorly sorted, fine- to coarse-grained flints, in a yellowish brown sand matrix that shows some pale grey mottling and locally has an appreciable clay content; the flints are mostly angular to subangular and nodular, and there are small proportions of exotics including subrounded to rounded quartz and quartzite pebbles, rounded brown sandstones, rounded grey limestones and some fossil debris. A few well-rounded black flints of Tertiary origin are locally present. Most of the medium and coarse grade flints are relatively fresh and grey with a thin white marginal patina, whereas the fine gravel consists mainly of completely patinated flints. Chalk debris is also an important feature of the deposit, particularly in gravel lenses within boulder clay. Larger masses of soft white chalk have been recovered from the deposits in boreholes close to the buried channel beneath the Stort valley.

In sections such as that at Hadham Mill gravel pit [TL 430 170] the sands and gravels are bedded, although commonly crudely and irregularly so; many of the coarser units are internally unstratified, structureless and extremely poorly sorted. In general the finer material is well-bedded, and forms lenses or thicker beds within the coarse gravels. The finer sediments locally show graded bedding, and cross-bedding with channels, small scale slumps, and syndepositional microfaults. Laminated chalky silts and fine-grained sands occur as lenses and continuous beds up to several metres in thickness. In some cases these finer deposits are confined to the upper part of the unit, but in others silt and fine-grained sand occur as lenses within gravel. The pit at Hadham Mill shows thin stringers and lenses of chalky till, possibly flow-tills, within the silts.

Vertical or subvertical pipes and lenses of gravel within the sequence at Hadham Mill were noted to be decalcified; where this has occurred, the bedding in the gravel appears undisturbed despite the loss of the chalk component and the material is now a dark orange-brown clayey gravel. The lack of disturbance within the bedding suggests that some of the decalcification may have taken place during deposition or that additional clay material was introduced during the process.

Periglacial effects such as cryoturbation are confined to those parts near to the surface. Examples were recorded at Gaston Green (Figure 11), but the age of the cryoturbation cannot be determined.

Thin seams of clayey gravel have been recorded within boulder clay in boreholes in the Rodings and Easter area. The lateral extent of these occurrences is unknown, but their thickness, generally less than 2 m, suggests that they are lensoid in form and very local. Outcrops of sandy and gravelly material in the tributary of the Roding, 1 km south-west of Great Canfield [TL 58 16], may be analogous, both on lithological grounds and on their position relative to the thick boulder clay proved in this area. These deposits consist mostly of orange-brown, poorly sorted, coarse, angular, flint gravel in a very clayey sandy matrix. Small chalk fragments and pellets are common, and a few well rounded quartz and quartzite pebbles have also been recorded. Thin streaks of compact, chalky, sandy clay lie within them. Many of these thin gravel lenses are close to the base of the Chalky Boulder Clay.

The Glacial Sand and Gravel varies in thickness up to about 10 m (Figure 7). In the Hunsdon and Widford area, north-west of the River Stort, the persistent lower unit of sand and gravel is generally between 3 and 10 m thick, whereas the impersistent upper unit varies between 1 and 4 m. A similar maximum has been recorded for the lower sand and gravel lens in the Harlow area, but the upper division in that area locally reaches about 10 m in thickness. The thin seams of gravel within the till east of the motorway are generally less than 2 m thick, whereas in the lower parts of the Roding valley south of Chipping Ongar the deposit is generally less than 5 m thick.

The similarity in lithology and the geological relationship between this material and the Chalky Boulder Clay is indicative of a close link in origin and source. The material within the gravels is derived from the various underlying formations of the district and those that the ice-sheet passed over to the north-west and north. The material incorporated includes earlier drift deposits, particularly the Kesgrave Sands and Gravels. The Glacial Sand and Gravel is regarded as the glaciofluvial product of the melting of the ice-sheet at or near its margins. The association of the deposits with the Stort valley buried channel is also of importance in the glacial history of the area (p. 46). DM

Details

North-west of the Stort valley

In the north-west, outcrops of Glacial Sand and Gravel are confined to the valleys and tributaries of the Ash and Stort. Extensive outcrops are present in the Ash valley, except in the Hadham Cross area where they are concealed by the Head.

A stream section [TL 4026 1752] in Nimney Bourne showed up to 2 m of gravel resting on Chalk. The gravel was generally poorly sorted with nodular, round and subangular flints, and contained some chalk fragments. The upper surface of the Chalk was extremely irregular, with isolated pinnacles protruding into the gravel.

In the Ash valley, a trial pit [TL 4254 1855] at Hadham Cross proved:

To the north-east of Hadham Mill a large disused gravel pit showed extremely variable deposits. In 1976 the following sequence was exposed in the northern face [TL 4305 1748] of the pit:

The silts and fine-grained sands showed small-scale cross-stratification. In places thin (less than 5 cm) stringers of chalky and sandy till occurred within the silts. They extended laterally for up to 20 m, and appeared to be thin flow-tills. Small-scale sedimentary structures included microfaults, slumps and channels.

A trial pit [TL 4310 1746], about 100 m to the east of the above section and at about the same height as its base proved:

A section [TL 4320 1745] about 50 m east of this pit showed:

Over much of the length of the eastern face of the pit chalky till rested on sand and gravel. Locally both deposits were decalcified along pipes and channels. The lamination in the flow-tills and the bedding in the gravels passed with only very minor distortion through the decalcified zones.

A trial pit [TL 4317 1724] in the floor of the gravel pit adjacent to the eastern face proved:

A third trial pit [TL 4295 1722] in the west of the gravel pit proved  3.4 m of Glacial Sand and Gravel on Woolwich and Reading Beds.  To the north of the gravel pit a borehole [TL 4319 1751] proved:

A well north-west of Hadham Mill [TL 4210 1721] proved:

Near the floor of the Ash valley to the south-east of this borehole, chalky till occurs at a lower height than the subjacent Glacial Sand and Gravel; the relationship of the deposits is unclear.

Glacial Sand and Gravel rests on Upper Chalk in the western part of the Ash valley. West of Widford, a disused railway cutting [TL 4063 1581], showed:

However, a temporary section [TL 4112 1577], close to the east and only a few metres above the previous exposure, proved 1 m of sand and gravel on Woolwich and Reading Beds.

Numerous boreholes between the Ash and Stort valleys prove a simple sequence of Chalky Boulder Clay above Glacial Sand and Gravel overlying bedrock. The thickness of the Glacial Sand and Gravel is between 4 and 9 m. For example, a borehole [TL 4465 1670] west of Allen's Green proved 4.1 m of sandy gravel beneath boulder clay, and in Gilston, 8.5 m of clayey sandy gravel were recorded beneath boulder clay in another borehole [TL 4388 1437]. Only in a few boreholes has more than one unit of Glacial Sand and Gravel been recorded. One such example is at Jeffs, near High Wych [TL 4543 1464] where the sequence was:

Boreholes drilled to the north and south of High Wych proved thick boulder clay to a depth of more than 18 m, but encountered no Glacial Sand and Gravel.

In the Stort valley, the Glacial Sand and Gravel crops out beneath the Chalky Boulder Clay on the valley sides but is generally obscured by the Head. There is a buried channel beneath the valley (p. 47).

In an old pit [TL 4797 1498] west of Sawbridgeworth, chalky till rested on laminated cream silts in the eastern part of the workings; in the western side gravel was recorded. The relationship between the gravel and the silts was not clear, but both are probably of similar age, and the silts may represent penecontemporaneous local ponding during the deposition of the gravel. A small sand-pit [TL 4721 1446] south-west of Sawbridgeworth showed 1 m of chalky fine-grained sand and laminated silts.

Contours on the base of the Chalky Boulder Clay suggest that an outcrop of Glacial Sand and Gravel [TL 4750 1430] mapped about 1 km south-west of Sawbridgeworth occurs within, rather than beneath, the till. This may also be true of the sand and gravel in the previous two pits.

'A gravel pit north-east of Gilston Church' was mentioned by Whitaker and others (1878); it showed 0.9 m of boulder clay resting on gravel, with flint, quartz and other pebbles, seen to 3.6 m. This pit appears to have been subsequently backfilled and cannot now be located with certainty, but was probably associated with shallow workings [TL 4420 1375] near Overhall Farm, Gilston. There is a narrow outcrop of sand and gravel, partially obscured by Head along this tributary of the Stort. London Clay was seen in the bed of the brook, and so the sand and gravel may only be a few metres thick. A borehole [TL 4464 1404] south of Great Pennys Farm, on the edge of the boulder clay outcrop, proved:

The outcrop of Glacial Sand and Gravel around Rowneybury [TL 4735 1325] consists mainly of sand and pebbly sand, with some silt. Farther west at Pole Hole Farm, Whitaker and others (1878) described a gravel pit ?[TL 455 127], and recorded:

They also described a gravel pit north-east of Pole Hole Farm [?455 127] which, like the previous pit, is now backfilled, recording 6.1 m of gravel.

Glacial Sand and Gravel crops out extensively along the unnamed tributary running south from Hunsdon to Roydon. The outcrop is difficult to delimit at its northern extent where it adjoins an area of Head Gravel. The lithology varies from gravel to clean sand. At Hunsdon, in an old gravel pit [TL 4160 1366] now containing several houses, a residual face showed 2 m of rounded flint gravel. An adjacent borehole [TL 4175 1353] showed:

Rivers Stort to Roding and Cobbin's to Cripsey brooks

The drift of the area bounded by these streams has a complex stratigraphy see (Figure 7) and (Figure 9). Glacial Sand and Gravel was mapped along the eastern side of the Stort valley and extends northeast to Little Hallingbury. A well [TL 4915 1792] at Wallbury Camp just east of the River Stort, proved 15.2 m of sand and gravel, the bottom of which was not reached. Such a thickness of Glacial Sand and Gravel is unusual, and the deposit may be part of the filling of a buried channel. Just to the north of the district, a borehole [TL 4920 1867], in a similar position in relation to the buried channel, proved 18.6 m of sand and gravel resting directly on Upper Chalk.

A trial pit [TL 4964 1820] near Little Hallingbury proved 2.3 m of made ground, resting on 1 m of soliflucted clayey gravels, in turn overlying Glacial Sand and Gravel. The Glacial Sand and Gravel was seen for 0.7 m, and consisted of chalky sand with gravel bands. The fine- to medium-grained gravel comprised mainly angular flints with some rounded chalk and quartzite.

A gravel pit south of Gaston Green showed a complex sequence along its southern face [TL 4940 1628] (Figure 11). One unusual feature of this section was a bed of involuted silty clays and clayey silts which occurred beneath the boulder clay in places. In the base of the pit, small trial pits encountered a gravel composed of rounded black flints in a sand matrix; the flints may have been derived from the Basement Bed of the London Clay.

A borehole [TL 5264 1704] north of Hatfield Heath proved 7.5 m of sandy gravel and gravel beneath 15.6 m of boulder clay. South and east of this area the presence of gravel beneath boulder clay is not proven, though one borehole [TL 5343 1481], just east of Hatfield Heath reached bedrock below 10.5 m of alluvial deposits and boulder clay. The valley of the upper part of the Roding is a shallow feature cut into the boulder clay plateau. Contours on the base of the boulder clay suggest that small patches of sand and gravel [TL 5815 1481]; [TL 5800 1690]; [TL 5780 1672] west of Great Canfield occur within, rather than beneath, the Chalky Boulder Clay.

A trial pit [TL 5834 1244] at Hales Farm, Leaden Roding, proved:

In the Harlow area, there are typically two alternations of Chalky Boulder Clay and Glacial Sand and Gravel. The field evidence suggests that the two units of sand and gravel are lenses which pinch out southward against the Epping Long Green ridge and northeastwards near the buried channel in the Old Harlow area. The latter feature is indicated by the outcrop of London Clay directly beneath boulder clay at Feltimores [TL 490 107], east of Old Harlow. An interpretation of the relationships is shown in (Figure 10). The lower of the Glacial Sand and Gravel units crops out along the lower flank of the Stort valley from north of Little Parndon to Harlow Town station.

A sketch of the railway cutting section east of Harlow station was given by Whitaker and others (1878, p.49, fig. 13). The section (now overgrown) of the southern side of the cutting showed:

Between Roydon and Halls Green [TL 415 083] Glacial Sand and Gravel was mapped in a tributary valley; immediately to the north of Lightfoots [TL 408 097] it was underlain by boulder clay, and in the side of a track [TL 4098 0980] at Roydon, coarse-grained brown sand lay above chalky till. The Glacial Sand and Gravel thins rapidly to the west and south of this area. To the west and south-west bedrock crops out on the steep slopes of the Lea valley, from its confluence with the Stort west of Roydon to Roydon Hamlet [TL 410 076]. Although the valley has been subjected to landslipping, it is apparent that boulder clay rests directly on bedrock.

In the Pinnacles, Hare Street and Great Parndon areas of southwest Harlow both the Chalky Boulder Clay and the Glacial Sand and Gravel have lensoidal forms. An interpretation of borehole evidence west to east from the Pinnacles [TL 42 09] to Hare Street [TL 44 09] districts of Harlow is given in (Figure 10). In one borehole [TL 4270 0948] in the Pinnacles district the following sequence was recorded:

A temporary excavation [TL 4298 0942] on a building site in west Harlow showed:

In Hare Street, north and east of the tributary of the Stort (Todd Brook) flowing through Harlow, a two-fold sequence is again probably developed. At about 52 m OD on the east bank of Todd Brook, a borehole [TL 4362 0958] showed the following sequence; the boulder clay representing the lower of the two units:

Farther east, a borehole [TL 4403 0975] started in the upper boulder clay unit:

In a borehole [TL 4400 0919] near Todd Brook Farm the upper unit of Glacial Sand and Gravel rested directly upon London Clay. The material was mostly sandy gravel, reddish brown in colour, and clayey in places.

At outcrop, gravels that are in contact with London Clay are strongly cryoturbated. In the stream bank at Netteswell, for example, 0.4 m of bedded and cryoturbated gravels was exposed [TL 4485 0942] beneath 1.4 m of Head; small flame-structures of London Clay protruded up into the gravels.

Gravels crop out in Todd Brook as far eastwards as the Al1 road where they thin, for London Clay lies directly beneath boulder clay south-west and east of Barnsley Cottage [TL 476 099]. The gravels appear to be the lateral equivalents of the upper gravel unit of the west Harlow area and commonly have a clayey sandy matrix. Boreholes east of the church [TL 4561 0935] at Netteswell proved less than 2 m of coarse gravel with a sandy clay matrix. Cryoturbated gravel, 2.2 m thick, and with an ochreous brown to dark reddish brown fine- to coarse-grained sand matrix, was exposed in a disused gravel pit [TL 4618 0968] north of the A1025. One borehole [TL 4597 0921] just south of the A1025 proved the following unusual sequence:

The southward thinning of the Glacial Sand and Gravel can be demonstrated in the Halls Green and Roydon Hamlet area where a well [TL 4228 0858] at Fouracres Nursery, Halls Green proved:

About 1 km farther south at Merryweather Nursery [TL 4174 0768] the sand bed had thinned to 0.3 m, and the lower gravel to 0.9 m. In a borehole at Tylers Cross Nursery [TL 4215 0741] the lower unit was represented by 0.9 m of sand.

South of Todd Brook, in Great Parndon [TL 436 087] an extensive outcrop of gravel represents part of the upper gravel unit and is underlain by boulder clay at depths of 1 to 1.6 m. DM

Epping, Bobbingworth and Stanford Rivers

Glacial Sand and Gravel crops out in the valleys of Cripsey Brook, the Roding, and their tributaries, from Greensted [TL 54 03] to Stapleford Tawney [TL 51 95]. There are old gravel workings up to 3 m deep north-west of Greensted Hall [TL 5390 0305]. Other small areas of Glacial Sand and Gravel in the vicinity are probably thin at outcrop, although they may be continuous and thicker beneath the Chalky Boulder Clay.

An old gravel pit near Marden Ash [TL 5563 0231] was dug through about 3 m of Glacial Sand and Gravel to expose London Clay at about 46 m OD. A nearby ditch [TL 5570 0214] showed the gravel to comprise angular and rounded flint gravel, with some rounded quartz and nodular flint, and medium- to coarse-grained brown sand.

Rounded flint gravel with some rounded quartz pebbles characterise the soil on the small outliers of Glacial Sand and Gravel in the tributary valley which runs by Stewarts Farm [TL 5208 0152] to the River Roding. The deposit is probably nowhere thicker than 5 m, and locally may be represented only by a few rounded pebbles in a sandy clay matrix sandwiched between the Chalky Boulder Clay and London Clay e.g. [TL 5228 0106]; [TL 5346 0103]. RAE

There is no sand and gravel between Theydon Bois [TL 45 99] and Hill Hall [TL 499 995]. Eastwards towards the Roding, small patches of sandy gravel occur beneath boulder clay, and crop out in the south and SE-flowing tributary valleys and on the main valley sides. These gravels do not exceed 4 m in thickness. An exposure in a ditch section [TL 5172 9920], just outside the district, showed 1.5 m of coarse, rounded, flint gravel in a brown sandy clay matrix. DM

Rivers Roding to Can

In the northern part of this area there are no outcrops of Glacial Sand and Gravel, but thicknesses of between 1 and 5 m were recorded in boreholes around High Roding. One hole [TL 6083 1767] south-west of Barnston House, High Roding, showed 3.2 m of greyish orange sandy gravel and gravel, consisting mainly of subangular to subrounded flints, beneath 14.7 m of boulder clay. South of High Roding, only 0.9 m of clayey sand was recorded [TL 6031 1653]. DM

The Glacial Sand and Gravel that crops out along the eastern side of the Roding valley south of High Ongar [TL 565 038] comprises mostly yellow to orange-brown, fine- to medium-grained sand, with only subordinate amounts of gravel. A disused pit [TL 5630 0252] exposed the following sequence above London Clay:

In the working clay pit near Hallsford Bridge [TL 5612 0219] the Glacial Sand and Gravel is removed as overburden. During the survey, between 1.5 and 5 m were exposed, resting on a gently undulating London Clay surface; a strong spring issued from the bottom part of the deposit, which comprised yellow, cross-bedded, micaceous, fine- to coarse-grained sand. The sand included lenses of gravel, mostly of subangular to rounded flints, with some quartz and quartzite pebbles. The gravel content increased along the face towards the north-east, while the whole deposit thinned eastwards.

Gravelly material of possibly ice-marginal origin was formerly extensively worked in Pole's Wood [TL 571 999], north of Kelvedon Hatch. In 1929 Edmunds (BGS MS) saw a worked face, 8.5 m high, which exposed up to 3.7 m of gravel in a dominantly sandy sequence. At the base of the face, washed sand with small chalk pebbles was noted. Large boulders of London Clay (3 m x 1.5 m x 1.5 m) were common, and occurred along an east-west line in the northern part of the pit. These masses obstructed the excavations and were left to form pinnacles along the side of the pit. Edmunds noted that the material excavated was of an inferior quality 'being midway between a boulder clay and a glacial gravel'. Only one exposure was noted in 1977 in this pit-complex [TL 5706 9996]. It showed up to 2 m of brown sandy clay with rounded flint and quartz pebbles. The long axes of the pebbles were observed to be horizontally aligned, suggesting that the deposit may be a flow-till. The extensive waste piles present make the former limits of the deposits difficult to determine.

In an area [TL 682 025] near Webb's Farm, to the north-east of Margaretting, boreholes have proved the glacial deposits to have an undulating base which falls towards the valley. This irregularity is apparently due to the presence of channels filled with gravelly material. For example, two adjacent boreholes [TL 6844 0257]; [TL 6837 0258] near the railway proved 4.75 and 2.10 m of Glacial Sand and Gravel beneath boulder clay.

In the valley floor between Margaretting and Hylands Park glacial deposits may be generally absent, though there are a few impersistent pockets of gravel: a well [TL 6707 0145] at Peacocks, Margaretting proved 5.8 m of sand and gravel beneath Head. RDL

South of Margaretting only one small patch of Glacial Sand and Gravel has been recognised. It was formerly worked for sand and gravel [TL 6695 9914]. Edmunds saw 0.9 m of gravel in this pit in 1923, and described its composition as 50 per cent stone and 50 per cent sandy loam (BGS MS). The pebbles included many large nodular flints up to 10 cm in diameter, Bunter sandstones, and vein-quartz pebbles up to 35 mm, set in a matrix of a quartz and angular flint grit. CRB

Buried channels

Anomalously thick sequences of drift have been known from boreholes in East Anglia and adjacent counties for many years. In this district Irving (1898) summarised numerous such records in the Stort valley, and in particular near Sawbridgeworth, where the base of what would now be interpreted as glacial deposits occurs at a minimum level of 51.8 m (170 ft) below the surface. The widespread nature and occurrence of such deposits in channels in East Anglia were discussed by Woodland (1970) who compared the channels with the tunnel valleys of Denmark. In north Essex and south Suffolk deep drift-filled depressions occur in two sets, generally beneath present-day valleys: i) aligned approximately radially to the presumed ice-front, e.g. the Stort and Gipping systems; ii) aligned approximately parallel to the ice-front, both within the glaciated tract, as between Clare and Cavendish in the Stour valley, and along the ice-front, as in the Chelmer and Blackwater. The radial channels are filled with both till and outwash; some are composite, containing two channels with different fills. Those of the other set are apparently filled almost exclusively with till and glacial (?sub-glacial) silts. Glacial Sand and Gravel is present, at least locally, adjacent to all the channels, and interdigitates with boulder clay on their flanks.

The till-filled channels are steep-sided, and apparently have undulating thalwegs, though borehole data are rarely conclusive on this point; there are even less data on the gravel-filled channels. In general the channels lie beneath the modern alluvium, and modern erosion has locally modified the original form of the underlying bed-rock surface. To the north, however, in the Cam–Stort system, it can be demonstrated that the latter falls towards the centre of the channel in a number of steps.

The mode of origin of the channels is incompletely understood. Woodland (1970) ascribed their steep sides to sub-glacial erosion, probably by gravel-laden melt-water under hydrostatic pressure. It is possible, however, that local overdeepening along the centre-lines of the channels was enhanced by rupture of the underlying permafrost layer by sub-glacial erosion, thus initiating upwelling of groundwater from the Chalk. This hypothesis may help to explain why there are two distinct types of channels, the deep ones described above and other much shallower ones, without deep central sections. All the large examples are believed to cut down at least locally into the Chalk, and the undulating long-profiles may be related to differing degrees of fissuring in the bed-rock.

The best documented channel in the district underlies the present course of the River Stort between Spellbrook in the north and Old Harlow; a deep drift-filled channel extends northwards along the valley into the adjacent Bishop's Stortford area. The infilling deposits are mostly glacial, although their uppermost parts are post-glacial river deposits. The base of the drift to the west and east of the channel is at between 40 and 50 m OD; to the south, the bedrock surface rises markedly to the south and east of Harlow forming the southern limit of the channel (Figure 6). Although the presence of the channel is confirmed, few details are available; locally, however, closely-spaced boreholes indicate that the sides are relatively steep. RDL, DM

Details

At Sawbridgeworth, drift extends in one borehole [TL 4875 1476] to a depth of 54.9 m ( −7 m OD). The sequence is as follows:

A nearby borehole [TL 4917 1505] reached London Clay at a depth of only 2.3 m, illustrating the steep sides of this channel.

Just south of Sawbridgeworth, boreholes provide further information about the deposits (Figure 12). A section through them shows the channel to be filled largely with grey silts, although boulder clay was recorded beneath the silts in one borehole [TL 4894 1396]. The boreholes confirm the steepness of the channel sides.

Farther south, north of Harlowbury, a borehole [TL 4790 1302] proved:

At about this point the Stort valley turns sharply westwards but the borehole evidence suggests that the buried channel, or at least one branch of it, continues southwards. A borehole [TL 4804 1134] at New Hall Farm, east of Harlow, proved 62.5 m of drift on Upper Chalk (rock-head at −11 m OD). The drift deposits consisted mainly of silty and loamy clays with flints and chalk pellets, but with beds of gravel from 42.7 to 47.1 m, and again from 51.8 to 62.5 m. This borehole penetrated the channel near its southern extremity because London Clay crops out at between 60 and 80 m OD in the Potter Street area 2 km to the south. There is no borehole information to the west of the proven channel to indicate whether there is a westward extension beneath the River Stort. DM

Head Gravel

In the western part of the district tracts of clayey gravels overlie the Chalky Boulder Clay. A short linear group of outcrops is present in the Widford and Hunsdon area [TL 41 14], and there are other outcrops around Little Hallingbury [TL 50 18] and between Foster Street and Feltimores [TL 48 11]. Although isolated outcrops are also present in the Roding valley near Leaden Roding and Beauchamp Roding and at Garnetts Wood, north-east of High Roding, by far the most extensive occurrence is a sinuous tract of outcrops between Hatfield Heath [TL 520 150] and Chipping Ongar [TL 554 031] (Figure 13).

A significant feature of these deposits is the progressive southward fall in their surface elevation along the trains of outcrops. In the Widford and Hunsdon area the height falls from approximately 80 m OD in the north to 63 m OD in the south. In the longer train, there is a marked fall from 82 m OD at Hatfield Heath to 67 m OD at Bobbingworth and 57 m OD at Chipping Ongar; the approximate gradient southward is 1 in 500. Although in the southern part of the train the outcrops follow the present course of Cripsey Brook, those to the north lie on the plateau and cross the course of Pincey Brook.

Everywhere the base of these deposits is sharp and associated with water seepages; in places the base is channelled, with concentrations of gravel at the base of the sequence. Where the deposits are thin the gravel is cryoturbated into the underlying boulder clay, but in all observed cases the latter appears unweathered.

At the surface these high-level gravels consist of mostly angular and rounded brown flints in roughly equal proportions, with an orange-brown sandy clay matrix. Other clasts include vein-quartz, quartzite, several different sandstones including pale pink marly Triassic and iron-cemented Jurassic ones, and rare boulders of saccharoidal granite. The heterogeneous character of the deposits was clear in trial pits. In most of these the surficial gravelly sandy clay was cryoturbated with some vertically oriented pebbles. The internally structureless nature may indicate that solifluction has played some role either in the deposition or in the subsequent redistribution of the deposit. That this is so is suggested by the downward warp of the outcrop pattern into the valleys, notably in the Cripsey Brook area. In the thinner patches, particularly in the Foster Street area, this gravel probably represents but a remnant of the original deposit.

In the thicker examples the surface gravelly material passes down into heterogeneous, structureless, orange-brown, pebbly sandy clays and clayey sands. There are also discrete thin seams of ochreous brown to grey-green mottled and laminated silt, lenses of sandy clay (interpreted as till) containing angular and nodular flints with some chalk pebbles, and lenses of ochreous brown, pale grey or greenish grey sandy clay. The lenses of till in some cases are similar to the underlying boulder clay. Although the polychromatic sandy clay contains flints and pods of coarse-grained sand it may represent reconstituted and reworked Lower London Tertiary deposits. The boundaries of these additional materials are sharp but irregular; some lithologies may represent rafts transported by the ice-sheet.

Traces of crude bedding within the overall deposit were locally recorded, particularly at Ongar in the most southern outcrop. Here the gravel is cleaner and thicker than farther north, suggesting that progressive sorting and washing may have taken place.

The thickness of the deposit varies considerably within each outcrop and between neighbouring ones: the maximum recorded thickness is 7.3 m in the Little Hallingbury area, and the variation is illustrated in (Figure 13). The most striking differences were noted at Little Hallingbury and Hatfield Heath. In the former area a borehole proved 7.3 m, whereas some 300 m north, but still well within the bounds of the deposit, only 0.9 m was recorded. At Hatfield Heath the difference ranged from 1.5 to 6.6 m.

Compared to the Glacial Sand and Gravel, the deposits that have been classified as Head Gravel are markedly more clayey and heterogeneous. However, the clast content and the relationship of the deposits to the underlying till indicate that they are closely linked to the glaciation, although in many cases the sediments have been affected by subsequent solifluction and erosion. The upper part of the boulder clay beneath the Head Gravel is unweathered, lending further support to a closely related time of deposition. The sinuous and linear form of these trains, particularly that between Hatfield Heath and Chipping Ongar, are strongly suggestive of deposition within fluvial channels, possibly on the ice or within ice-walled channels. The sorting of the material within the deposit improves to the south indicating that the direction of flow of the streams was southwards. DM, BSPM

Details

The description of the deposits which form the Head Gravel can be presented according to the linear trains which their outcrops form (Figure 13). Isolated outcrops to the east of these trains are also described.

Widford and Hunsdon

In the Widford and Hunsdon area, the Head Gravel occurs in a SSW-trending train capping the Chalky Boulder Clay between the Ash and Stort valleys. The gravels are confined to the plateau, but much of the highest ground is free from gravel. The thickness of the deposits is extremely variable; because of this and their low quality they have been worked only on a small scale. Numerous small hollows mark old workings for 'hoggin', and it is usually possible to auger chalky till in these, which are up to 1.5 m deep. A trench [TL 4185 1510] south of Widford showed the following succession in 1975:

Farther south a trial pit [TL 4114 1413] near Hunsdon proved:

Stort valley

In the Little Hallingbury area, the Head Gravel occurs between the River Stort to the west and the boulder clay plateau to the east. One of the few exposures in the Head Gravel was in a ditch [TL 4980 1878] just to the north of the district near Latchmore Bank. Here about 1.5 m of clayey flint gravel overlay ochreous brown flinty boulder clay. A borehole [TL 4977 1813] in Little Hallingbury proved:

A trial pit [TL 4985 1852] in the same outcrop of Head Gravel showed:

Another trial pit [TL 4807 1419] dug in an isolated patch of Head Gravel in the north of Pishiobury Park, south of Sawbridgeworth, proved:

A borehole [TL 4798 1409] only 100 m SW of the above pit showed:

A possible extension of this train of gravels lies south of the Stort to the east and south of Old Harlow. Recent workings [TL 4886 1170] for 'hoggin' showed up to 2 m of clayey gravel resting on boulder clay. The gravel consisted mainly of angular flints with subordinate subrounded and rounded flints and a few quartzites. BSPM

Abundant angular and rounded flint pebbles are present in the soil [TL 484 095] between Barnsley Cottage and the M11 motorway, and form the southernmost outcrop of this train. DM

Hatfield Heath to Ongar

Between Hatfield Heath and Ongar there is a sinuous train of Head Gravel. Ditch sections [TL 5300 1514]; [TL 5287 1510] north-east of Hatfield Heath showed 2.5 m of gravel, resting on chalky till. Several boreholes were sunk through these deposits and the maximum thickness was proved at Hatfield Heath [TL 5258 1499]:

A further seven boreholes proved similar clayey gravels resting on boulder clay. The sites of these, their surface levels and the thicknesses in metres of the Head Gravel proved are as follows: [TL 5180 1529], 80.8, 1.5; [TL 5263 1401], 75.6, 3.6; [TL 5233 1305], 78.5, 4.1; [TL 5232 1217], 75.6, 1.3; [TL 5293 1207], 78.3, 3.8; [TL 5350 1115], 78.9, 2.8; [TL 5385 1052], 76.5, 2.2. BSPM

In the High Laver and Moreton [TL 53 08] areas, Head Gravel crops out on the plateau edge as an almost continuous linear feature on the western side of the southward flowing tributary of Cripsey Brook. The deposits thicken southward to a maximum near the confluence of the tributary with Cripsey Brook. South of this the deposits thin and become discontinuous; small outcrops of gravels, no greater than 1.5 m thick, occur south of Bovinger Lodge [TL 526 061], west of Wood Farm [TL 540 060] and north-east of Blake Hall [TL 541 055]. At surface, angular and rounded brown flint pebbles in approximate equal proportions are set in an orange-brown sandy clay matrix. The gravel was exposed to a depth of 1.6 m in a ditch [TL 5298 0927] at High Laver Grange where, in addition to the preponderant flints, a few white vein-quartz pebbles were present. The gravel rested with an irregular, sharp base on the underlying boulder clay, which was decalcified in the upper 0.2 m.

Five trial pits were excavated in 1977 in the thicker parts of the Head Gravel. All but one proved the deposits to overlie boulder clay. One pit [TL 5294 0909] (Figure 13) inset south of High Laver Grange, showed:

A lens of degraded till was recorded from another pit [TL 5278 0838], but the bedded sands and silts were absent. In addition to the sequence of mass-flow and waterlain deposits recorded from the above excavations, a third pit [TL 5279 0776] contained two lenses, 1.2 and 0.2 m thick, of reworked and reconstituted Lower London Tertiary material. The sequence was:

Some 600 m SSE of Bushes, the Head Gravel was more than 4.1 m thick [TL 5285 0742].

South of Cripsey Brook, the Head Gravel thins to 1.6 m in a pit [TL 5393 0590] west of Wood Farm, Bobbingworth. The sequence there consisted of structureless sandy clays with a varying gravel content, overlying boulder clay. The top 0.4 m of till contained some well rounded flint pebbles but no chalk. DM

A gravelly soil containing brown-stained, angular to rounded and nodular flint gravel, is present around the Motte and Bailey [TL 5545 0310] at Chipping Ongar on the interfluve between the River Roding and Cripsey Brook. It is probably the southernmost remnant of the gravel train. The base of the deposit at Chipping Ongar lies at about 61 m OD on the crest of the ridge, and falls to around 50 m OD in the Cripsey Brook valley, and to below 45 m OD near the confluence of Cripsey Brook and the River Roding. Old gravel pits [TL 5570 0260] near the confluence were probably dug into Head Gravel.

An exposure in a petrol station forecourt [TL 5522 0340] showed 1.0 to 1.5 m of Head Gravel, consisting mostly of subangular flints in a reddish brown clayey sand matrix, with a sharp, gently sloping base overlying boulder clay. The upper part of the gravel was cryoturbated, and the pebbles in the top 0.6 to 1.0 m were oriented with their long axes vertical or sub-vertical. A trial pit [TL 5557 0310], dug near the Motte and Bailey proved the following:

High Easter area

The outcrop of Head Gravel which occurs at above 85 m OD near Garnetts Wood [TL 634 181] is characterised by a very gravelly soil that contains mainly angular to subrounded flint pebbles; shallow hollows mark old gravel diggings [TL 6343 1772]; [TL 6355 1785]. A trial pit dug beside the track [TL 6331 1788] proved:

A nearby borehole [TL 6338 1783] proved 2.7 m of Head Gravel, comprising mottled orange to pale grey sandy clay with some angular flints and scattered rounded flints, becoming yellowish brown and less sandy with depth. RAE

Glacial lake deposits

There are only three thick deposits of bedded silts and sands of possible lacustrine origin in the district (see p. 2). One is demonstrably of glacial lake origin; by analogy the other two have been classified similarly. In addition silts also form a major constituent of the infilling of the Stort valley buried channel (p. 47). The three extensive occurrences of silts are: north of Writtle [TL 680 085]; in the Roding valley south of Fyfield [TL 567 060]; and on the plateau north-east of Blackmore [TL 610 030]. In the Chelmer valley, Bristow (1985)has recorded Glacial Lake Deposits along the flanks of the buried channel: the deposit of silt at Writtle is possibly related to this channel (p. 53) and may have been laid down in a lake that formed in a depression when the ice melted. Varying thicknesses of silt and sand have also been recorded in boreholes in the northern part of the district, but these are interbedded within thick boulder clay.

At surface in the Fyfield area, the only place that seems certain to be an old lake, the Glacial Lake Deposits comprise cream or pale grey clays, silts and fine-grained sands. Thin seams of sand and gravel occur at the margins of the outcrop  (Figure 14) and probably represent marginal lake deposits. Sections through the lake deposits show a complex sequence of grey and brown, unfossiliferous, laminated clays, silts and fine- to medium-grained sands; the laminae are typically about 2 to 3 mm thick. The coarser materials are commonly cross-bedded and contain abundant small chalk pellets. The deposits, which are unconsolidated and commonly water-saturated, occupy approximately 1 km² and have been investigated in some detail with trial pits and boreholes; they fill a hollow in the boulder clay surface, and at one point cut through it to rest directly on London Clay (Figure 14). Structures observed within them include cross-bedding and a distinct dip to the laminations: in the north there is a slight dip to the north-west; at Herons Farm the beds dip southeast; and south of Boarded Barns Farm, they dip to the west. On topographic evidence the western margin of the lake probably lay not far west of the Chipping Ongar–Fyfield road; the northern margin is loosely marked by the marginal sand and gravel, though small outcrops of silt north of these may have been laid down in small ponds; to the south the deposits are covered by Head, but trial pits suggest that they continue across much of the interfluve between Cripsey Brook and the Roding; the eastern margin does not seem to have extended beyond the present valley.

The thickness of the deposits within the district is variable. In the Fyfield area the thicknesses proved in boreholes range from 5.2 m in the west, where boulder clay overlies the deposits, to a proved maximum of 12.8 m (Figure 14) though projection of the 'upper' boulder clay across the axis of the basin gives an estimated maximum original thickness of about 20 m. The thickness of the deposits north of Writtle is unknown; a trial pit showed that it exceeds 3 m.

To the north of Blackmore the silts are 10.7 m thick, and overlie boulder clay. Isolated occurrences of silt within the boulder clay are typically less than 5 m thick, except near the Stort buried channel where up to 15 m have been recorded. Possibly some of the silts are subglacial or have been deposited in a lake that was over-ridden by a further advance of the ice. DM

Details

It is difficult to assess which of the silt deposits are lacustrine in origin. Discrete bodies of silt and fine-grained sand associated with the Chalky Boulder Clay or Glacial Sand and Gravel are relatively uncommon in the district. There are some within the drift-filled channel of the Stort (p. 47) and other isolated occurrences have been recorded in boreholes in the Hatfield Heath to the Rodings area.

The only occurrence of silts to the north-west of the River Stort is in a borehole [TL 4627 1552] north of High Wych where thin beds of soft grey laminated clayey silts were encountered within boulder clay. In the Rodings, there are several further records of silts within boulder clay in boreholes. Near Great Canfield [TL 5865 1739], 5.3 m of laminated, ochreous, brown and buff, clayey silts and fine-grained sands lay within boulder clay, 1.5 m below the surface. In the Roding valley at New Hall, 1.1 m of grey laminated silts and fine-grained chalky sands was encountered in one borehole [TL 5812 1639]. Similarly, 2.7 m of laminated greyish orange to yellow-brown silt and fine-grained sand with some grey laminae 2 to 3 m thick were recorded from a borehole [TL 6634 1608] at High Easter.

In the Harlow to Matching area, records of silt lenses within the boulder clay are few. South-east of Harlowbury a borehole [TL 4862 1220] penetrated 3.9 m of fine-grained chalky sand, and a hole [TL 4906 0804] for the M11 motorway just south of Foster Street proved 1.5 m of 'firm yellow-brown sandy silt' beneath 1.8 m of weathered boulder clay. DM

Writtle area

Between the Can and one of its tributaries in the Roxwell area [TL 676 084], there is a large outcrop of silt though its full extent is masked by Head. In the tributary valley to the north-east of Warren Farm, cream silts and silty clays with calcareous race were augered. Although much of the outcrop is surrounded by Head, a sharp boundary with till was proved north-west of Warren Farm. Details of the sequence were provided by a trial pit [TL 6812 0791] north- north-east of Warren Farm:

At a slightly lower elevation, fine-grained sands were augered [TL 6819 0800]; [TL 6820 0813] and may relate to the above sequence. A former brickyard [TL 689 072] at Beach's Drive worked silty loams which were probably reworked lacustrine silts. Up to 3 m of brickearth were recorded (J. S. Turner in MS) in one excavation [TL 6895 0738] (see also Bristow, 1985). RDL

Fyfield to Chipping Ongar

In the Fyfield area of the Roding valley there are a number of silt outcrops (Figure 14). The sediments, which comprise pale grey silts and clays, form small outcrops [TL 571 083]; [TL 573 076] north of Fyfield, and one large outcrop south of the village. The brickyard [TL 5725 0764] at the second location was described by Woodward (in Whitaker, 1889, p.314) as: boulder clay, 0.9 to 1.2 m; sand, with seams of gravel (chiefly composed of angular flints and quartz), 1.5 to 1.8 m; loamy clay (?London Clay).

In the same account, Dawkins recorded up to 2.4 m of 'brickearth' overlying boulder clay above sandy gravel. The brickyard has been disused for many years and the brickearth appears to have been worked out. The present western face is in boulder clay, whereas in the degraded north face (2 m high) pale grey silty clay ('brickearth') can be augered above medium- grained sand, which in turn rests on flinty clay. The floor of the pit is composed of sand, which may not be in situ.

In the large outcrop south of Fyfield, a ditch section [TL 5667 0628] showed cream silty clay on ochreous sand on chalky sandy clay. Similar sequences were proved by augering near Clatterford End, Herons Farm, and east of Shelley [TL 5667 0660]; [TL 5645 0593]; [TL 5594 0508] to [TL 5622 0505]. To the south of Herons Farm, augering in a ditch [TL 5642 0554] suggested that there was a vertical junction between chalky silts and sands and a pale grey clay. In places the Chalky Boulder Clay forms slightly elevated ground above the general level of the Glacial Lake Deposits, but a line of boreholes east of Shelley showed the silts to interdigitate with boulder clay.

A trial pit [TL 5650 0637] at Clatterford End proved:

The sediments showed a slight dip to the north-west. Another trial pit [TL 5667 0581] at Herons Farm showed:

The clay laminae dipped south-eastwards at a low angle. RDL

The southern extension of the Glacial Lake Deposits to Chipping Ongar has been demonstrated by trial pits dug through the surficial Head. One [TL 5601 0454], near the top of the valley slope south of Boarded Barns Farm, showed:

A general dip to the west was noted. Some 80 m downslope the deposit becomes chalky. The succession in a second pit [TL 5609 0453] was:

Blackmore area

A small tract of Glacial Lake Deposits lies near Saybridge Lodge, Blackmore [TL 610 030], where orange-brown micaceous silt was augered. A borehole sited on the outcrop [TL 6099 0291] proved 10.7 m of silty fine-grained sand with some small chalk pellets overlying boulder clay; the deposit was pale brown above 6 m, and dark grey below. A nearby borehole [TL 6135 0319] penetrated 5.7 m of soft, dark yellowish brown silt to fine-grained sand beneath 10.1 m of boulder clay. A further borehole south-east of Ashling's Farm [TL 5933 0070] proved 4.87 m of silt and fine-grained sand beneath 4.27 m of boulder clay and resting on Claygate Beds at 78.3 m OD. RAE

Glacial diversions of drainage

It has been long accepted that the Thames followed a more northerly route in pre-Anglian times than it does now. Wooldridge (1938, 1960) believed that its initial route lay along the Vale of St Albans, and thence from Ware eastwards along the line of the mid-Essex depression towards the Blackwater estuary (Figure 15).

He postulated two southward diversions of the river, induced by successive advances of the Chalky Boulder Clay ice. Clayton refined this model by visualising the blocking of the proto-Thames near Harlow to impound Glacial-lake Hertford (Clayton and Brown, 1958), followed by a further advance of the ice-sheet. Both Wooldridge and Clayton seem to have considered that the development of the lower Lea valley postdated the diversion of the Thames which was initiated considerably farther upstream.

With modern advances in Quaternary stratigraphy, attempts have been made to fit these drainage changes into a more exact time framework. It is now generally accepted that Rose, Allen and Hey (1976) were correct in considering that the Kesgrave Sands and Gravels were deposited by the proto-Thames prior to its diversion. If their suggested Cromerian dating of the capping palaeosol is correct (see p. 32), then the Kesgrave Sands and Gravels are probably Beestonian in age. The river had cut into these deposits and migrated southwards in a down-dip direction by Cromerian times, and the palaeosol developed on flanking terraces, though it probably still lay to the north of a continuous ridge stretching from Hampstead to Epping. More recently, Baker and Jones (1980) have claimed, though on scanty evidence, that the lowest deposits in the floor of the mid-Essex depression at Harlow demonstrate the continuous eastward passage of the proto-Thames. However, they consider that later deposits are absent in eastern Essex, due to an early deflection of the proto-Thames along the low Lea valley, itself probably formed as a result of the melting of penetrative lobes of the Anglian ice: this leaves unanswered the problem of the course of the pre-Anglian proto-Thames. Clearly much work remains to be done before the details of the development of the lower Thames drainage can be established and dated with certainty. RDL

Chapter 6 Quaternary deposits: Hoxnian to Flandrian

The post-Anglian (Hoxnian to Flandrian) deposits in the district include silts, clays and gravels. These may be broadly grouped as Interglacial Lacustrine Deposits, Head, River Terrace Deposits, and Alluvium; all except Head are of quite limited distribution. The deposits provide a scanty record of this time interval, partly because much erosion has occurred since their deposition. Interglacial deposits, of both Hoxnian and Ipswichian ages, occur sporadically throughout Essex and East Anglia, and Turner (in Mitchell and others, 1973) commented that the later deposits are typically associated with the river terraces. The examples recorded in the Epping district overlie boulder clay and have not previously been reported. Those products of solifluction and sheet-wash that have accumulated mainly in the valleys have been classified as Head, while erosion in the south-west of the district has produced unstable valley slopes in both drift and solid formations, thus resulting in landslips.

Interglacial lacustrine deposits

The presence of fossiliferous silts overlying the Chalky Boulder Clay has been known for some time (West and Donner, 1956) and deposits of this type have been described at Marks Tey in north-east Essex (Turner, 1970; Ellison and Lake, 1986). In the Epping district comparable shelly silts have been identified at two localities, only one of which is shown on the 1:50 000 map; near Spellbrook [TL 484 168] and in a borehole through the Head [TL 6835 0759] near Writtle.

At Spellbrook the surface deposits consist of brown silts with scattered angular flints, but several trial pits revealed the shelly nature at depth. The sequence in one pit [TL 4846 1681] was:

Adjacent to this section two further pits showed the total thickness of the deposit to be between 2.05 and 2.15 m; the silts were distinctly tufaceous. In one excavation [TL 4844 1682] the basal 0.35 m consisted of shelly tufas with silt and organic partings. Both of these pits showed the silts to overlie boulder clay.

The borehole near Writtle showed the following sequence:

The extent of the above deposit and its relationship to the surrounding deposits, particularly the Glacial Lake Deposits to the north on higher ground, is unknown. The presence of peat and shells distinguish it in lithology and age from the Glacial Lake Deposits, and it occurs at a lower level than them and rests directly on boulder clay. The shelly peats appear to have accumulated in a depression or channel on the surface of the glacial deposits.

An interglacial age is probable for both these deposits, but as yet no age determinations have been made and the environment of deposition has not been determined. It seems likely, however, that the silts and peats are associated closely with the buried channels which probably persisted as topographic depressions when the ice melted. DM, RAE, RDL

Head

These deposits comprise a variety of sediments, including pebbly silts and clays, which occur extensively in many of the low-lying areas and valleys of the district. They are essentially the products of solifluction, although other processes such as spring-sapping and sheet-wash have contributed to them.

The outcrops are generally narrow where the Head mantles the valley floors, although they are significantly wider in places at the confluence of streams. There is an extensive outcrop in the low-lying area of the Lea valley at Stoneshot Common [TL 40 07] where there is an embayment in the valley fed by several tributaries. In the Pincey Brook, north of Hatfield Heath, and in the Roding valley north of Fyfield, the Head is mainly present on the western slopes. Extensive sheets floor the gentle slopes between the Roxwell Brook and Writtle and to the south in the Wid valley and its tributaries.

The deposits are extremely variable in composition and reflect the parent bedrock or drift from which they were derived. The material derived from boulder clay is generally a stiff mottled orange and grey-brown sandy clay with scattered angular flints, whereas that derived from London Clay consists of soft brown and greenish buff silty clay, locally with some fine-grained sand. The deposits have an open or blocky structure, and scattered flints are commonly oriented with their long axes horizontal. An irregular thin layer of closely packed, angular flints with a sandy clay matrix occurs at the base of the deposit in many places. Cryoturbation has disturbed many of the sediments: involutions and lobes may also affect the underlying sediments, and the gravel-sized particles are concentrated in the involutions.

Where the basal gravel layer is present, the base of the deposit is readily discernable, but elsewhere, particularly in the tracts of boulder clay and London Clay, the base can be difficult to recognise. In areas of boulder clay, for example, deeply weathered decalcified till in situ can be identical in lithology to the Head derived from it.

In the extreme south-west of the district, in the Cobbin's Brook and Upshire areas [TL 40 01], some of the low-lying land is covered by very soft reddish brown clay similar in all respects except firmness to London Clay. In temporary sections this material passes down into the firm to stiff solid clays. Much of the soft superficial material may have been transported by solifluction and is, therefore, strictly Head, but it cannot be mapped because of the difficulty in distinguishing it from in situ London Clay.

The thickness of the Head deposits varies considerably, partly because of the effects of cryoturbation. The maximum recorded is about 5 m, but 2 to 3.5 m is more common. In both the Ash and Stort valleys the Head is less than 3.5 m thick, while the thickest deposits are in the Writtle area and in the Wid valley. DM

Details

The Ash valley

Head floors the valleys of Nimney Bourne and the River Ash, and consists mainly of silty and sandy loams. At Hadham Cross a trial pit [TL 4254 1855] exposed 1.6 m of silty angular gravel resting on Glacial Sand and Gravel, below 0.25 m of soil.

A further pit [TL 4049 1257] at Hunsdon showed the following:

The Stort valley and tributaries

Head occurs on the flanks of the wide alluvial plain of the Stort, and floors the tributary valleys of Pincey Brook and Todd Brook in Harlow. A wide expanse of Head covers the Old Harlow area [TL 47 12].

At Newhouse in Lower Sheering, gravelly Head was recorded in a trial pit [TL 4891 1416] downslope from boulder clay. The section exposed was:

In some areas it is difficult to differentiate between Head and decalcified boulder clay; for example, a trial pit [TL 4812 1240] near Harlowbury proved:

A trial pit [TL 4047 1016] at Roydon was sited between the first and second terraces on sloping ground which had been mapped as Head. The excavation showed an upper unit that may be partly hill-wash, and a lower unit derived largely from the underlying London Clay. The sequence was:

Narrow outcrops of grey-brown sandy clays and clayey sands characterise the small valleys in the Roydon area [TL 401 099]; [TL 414 096]. Much of this material was derived from the Glacial Sand and Gravel. At the confluence of two streams [TL 4144 0976] 1 km east of Lightfoots, Roydon, a small area (c.3500 m²) is underlain by soft peaty sands to a depth of over 3.5 m.

Clayey sandy loams with a varying gravel content are present in the bottom of the Todd Brook valley and its tributaries draining Harlow. Glacial Sand and Gravel and London Clay are the dominant materials underlying the Head deposits in the main valley, and the character of the Head reflects these sources. Between Netteswell [TL 450 094] and Potter Street [TL 473 096] the deposits are dominantly sandy clays containing scattered angular flints and pockets of gravel. In a section [TL 4485 0942] in Todd Brook in Netteswell, 1.6 to 1.8 m of dark brown and pale brown mottled sandy clay with scattered flints was exposed. DM

Stoneshot Common and Bumble's Green, Nazeing

Large expanses of Head occupy the undulating valley floor of the Lea valley between Downhall Farm [TL 4007 0880] and the road westward from Roydon Hamlet, and from Stoneshot Common [TL 402 073] to the road [TL 402 065] westward from Nazeing. The deposits are brown silty clay loams, locally sandy, and with some angular flint pebbles. The thickness of Head in the valleys is unknown, since well records do not distinguish Head from the underlying London Clay.

In addition to the silty clays, patches of thin gravel were noted at six localities in the Bumble's Green area [TL 4008 0606]; [TL 4075 0613]; [TL 4097 0594]; [TL 4062 0556]; [TL 4100 0517]; [TL 4188 0528]. In each case the deposit occurred on a bench 5 to 15 m above the valley bottom, and consisted of 0.5 to 2.0 m of rounded flint gravel, with clasts ranging up to 4 cm in diameter in a dark brown coarse-grained sandy clay matrix. Except in the two examples [TL 4075 0613] and [TL 4097 0594] 1 km west of Nazeing Park, these deposits have no consistent surface level. DM

Cobbin's Brook

A heterogeneous deposit, comprising coarse sand grains and generally subangular flints in a clay matrix derived from London Clay, fills the Cobbin's Brook tributary valleys. Its thickness is not proved although it probably does not exceed 2 m. In the Cobbin's Brook valley, the deposit is a more homogeneous, orange-brown clayey silt and very silty clay. Within the main valley the Head is thicker than in the tributaries, but it is unlikely to exceed 6 m. RAE

Theydon Garnon

Head deposits floor the valleys south-east of Epping in the Theydon Garnon area [TL 470 005]. A small stream-bank section [TL 4551 0040], south-east of Great Gregories Farm, is in 1.8 m of Head resting with an uneven cryoturbated base on London Clay. The Head is a pale brown silt with pockets of angular to well-rounded flint gravel, particularly at the base. Similar Head deposits have been recorded in numerous borings between the above locality and Theydon Garnon. A maximum thickness of 3.2 m of brown clay with sand pockets has been proved in a borehole [TL 4632 0091] east of Ivy Chimneys. Many other borings prove 'brown silty clay with stones', and gravel-grade material is common near the base of the deposits.

A borehole [TL 4757 0163] south-east of Coopersale House penetrated 4.9 m of Head, recorded as firm mottled brown sandy clay containing 'large gravel' to a depth of 2.4 m and with 'occasional stones (and chalk)' to 4.9 m. The presence of chalk suggests that the deposit may be weathered boulder clay, but the only boulder clay hereabouts is confined to the higher ridges. RAE

Head has accumulated in the southward flowing tributary valleys of the Theydon Bois [TL 452 995] to Stapleford Tawney [TL 525 995] area. For the most part it overlies London Clay, and between Theydon Bois and Hill Hall [TL 489 995] the contributary sources are Chalky Boulder Clay and London Clay. The wide valley [TL 459 995] between the London Transport railway line and the motorway east of Theydon Bois is floored by ochreous and reddish brown sandy clay with small, but varying, amounts of angular flints. The gentle slopes of the valley between Garnish Hall [TL 4700 9970] and Hill Hall [TL 4890 9950] are largely covered by brown sandy clay with some pockets of flints. A ditch section [TL 4814 9965] south-west of Peakes Farm showed pockets of angular gravel in an ochreous brown sandy matrix, cryoturbated into soft London Clay below.

From Hill Hall towards the Roding valley, pockets of Glacial Sand and Gravel provided additional sandy material to the Head. In the valley bottom around Coleman's Farm [TL 495 997], brown sandy clay loam contains numerous patches of round and angular flints. DM

Roding valley and tributaries

Head deposits are preferentially preserved on the west side of the valley southward from Aythorpe Roding [TL 58 16]. The predominant lithology is a brown silty loam with scattered angular flints. Flinty sandy clays are present near Fyfield. In the floor of the tributary valley west of the Willingales [TL 59 07], a loamy wash covers much of the London Clay outcrop. RDL

Between Hallsford Bridge [TL 5613 0225] and Langford Bridge on both banks of the Roding, orange-brown clayey silt probably overlies terrace deposits. RAE

Cripsey Brook

Head is present along the valley of the Cripsey Brook and its tributaries, including the main stream flowing southward through Little Laver [TL 53 09] to Moreton [TL 53 07]. Its composition is dependant on the contributary solid and superficial deposits, and these vary from clays and loams to silty angular gravels.

In the northern part of the main tributary valley west of Little Laver [TL 535 094], the Head deposits are brown silty and sandy clays with a few angular flint pebbles, and have been derived from boulder clay. Southwards along the valley between the church at High Laver [TL 531 087] and Moreton an increase in the gravel and sand content in the Head was noted. This is attributed to the proximity of outcrops of Head Gravel and Kesgrave Sands and Gravels. The thickness of Head in this valley is unknown, but stream bank sections indicate a minimum of 1.5 m.

In fields [TL 5345 0690] east of the post office at Moreton, 1.5 m of gravelly sandy clay is present on London Clay, and probably formed as a result of spring action at the junction of the Kesgrave Sands and Gravels with London Clay which lies upslope.

For 1 km west of Weald Bridge [TL 511 064] 1.5 to 3.0 m of Head overlie London Clay in the banks of Cripsey Brook, and consist of 1.0 to 2.0 m of brown silty clay loam resting on an irregular basal bed of angular and subordinate rounded flint gravel.

In the Cripsey Brook valley south-east from Moreton towards Ongar, the Head is derived mainly from bedrock and gravels. North-west of Wood Farm, shallow slopes [TL 539 062] are covered by a wide expanse of ochreous brown and grey silty clayey loam containing only scattered angular flints; south of Wood Farm and west of the road to Ongar the Head is very gravelly in part. A ditch section nearby [TL 5439 0542] to [TL 5460 0545] showed ochreous brown clayey sands with irregular patches of angular flint gravel at the top of the section, passing into brown silty clays near the Moreton–Ongar road. DM

Stanford Rivers

The Head in the small valleys draining towards Stanford Rivers [TL 534 009] is mostly silt or clayey silt, with variable amounts of gravel. Thicknesses probably do not exceed 3 m. RAE

The London Clay on gentle valley slopes south-west of Murrells Farm [TL 525 996] is masked by brown sandy clay and patches of flint pebbles. In ditch sections the maximum recorded thickness was 2 m. DM

Stondon Massey and Norton Heath

An irregular patch of Head just south of Stondon Massey House [TL 574 012], comprising orange-brown sandy clay with some rounded gravel, probably represents decalcified boulder clay which is partially cryoturbated as is the underlying Claygate Beds. The area lies close to the inferred margin of the ice, behind which Chalky Boulder Clay was deposited around Stondon Place [TL 577 015].

Around Norton Heath [TL 602 043] the Head is a solifluction deposit derived from the Older Head and Claygate Beds. It is generally thin and probably does not exceed 2 to 3 m. A pit [TL 6049 0420] dug behind the White Horse public house opposite Readings proved 1.6 m of top soil and Head (see p. 19).

Extensive areas of Head between Fryerning Wood and College Wood and smaller tracts around Moore's Ditch and north-west of Handley Barns [TL 6485 0147] are soliflucted Older Head, having increased amounts of clay compared to the parent material; orange and pale grey mottled sandy clay is the dominant lithology. Generally the small gravel pits characteristic of the Older Head outcrop are absent, probably because there are less stones in the Head. Head also overlies Older Head in trial pits in Fryerning Wood [TL 6179 0106] and at Mill Green [TL 6394 0137] (see p. 28). RAE

Wid valley and tributaries

In the Ingatestone area, cryoturbated pockets of clayey rounded gravels are common on the Claygate Beds outcrop. At one site [TL 6440 9935], the wedge-shaped occurrences were reported to be over 3 m deep. Reddish clays with rounded pebbles were noted in the soil [TL 639 992]; [TL 643 996] to the west of the by-pass.

Between Margaretting Hall and Writtle, the Head consists of brown and ochreous flinty clays; silty loams are present on the lower slopes. Cryoturbated pockets of clayey gravels occur locally and gravels have been dug in places, for example near Peacocks [TL 671 015] and Stapel's Farm [TL 678 017], Margaretting, though it is not clear whether glacial gravels were also worked. RDL

East of Ingatestone, Head mantles the lower valley sides, and caps some of the higher ground. In an area [TL 680 000] to the north of Ramsey Tyrrells, brown clayey sand and mottled orange and grey sandy clay locally overlies the Chalky Boulder Clay. A more extensive spread occurs on the east side of Ingatestone. Over much of the surface the deposit consists of mottled orange and grey sandy clays which are locally pebbly [TL 653 995]; [TL 6513 9935]; [TL 6525 9925].

The most extensive spread of Head mantles the valley slopes on the west side of the River Wid. At surface the deposit generally consists of mottled orange and grey or brown silts, clayey sands and silty loams, locally pebbly [TL 661 994]; [TL 6619 9983]; [TL 6640 9992]; [TL 6677 9993]. These may in part have their origin in springs at the base of the Bagshot Beds.

Head is confined to the lower slopes of the valleys on the east side of the River Wid, where it consists of mottled orange and grey sandy clays and yellowish brown clayey silts. CRB

Can valley and tributaries

In the Newland Brook valley near Boyton Cross, the Head comprises silty loams with angular flints; tufaceous debris was noted locally. In the valley of the Roxwell Brook sandy clays with angular flints are generally present and have been derived mainly from boulder clay. In the Can valley south of Chignall Hall and in the tributary valley to the east, silty loams mantle the western slopes. These loams are apparently underlain by patinated angular flint gravels because the latter crop out locally upslope. In the tributary valley, glacial lacustrine deposits have contributed to the silty material (see p. 53).

A shallow depression near Beaumont Otes [TL 686 096] is floored by solifluction deposits. Up to 2 m of silty loam with a basal bed of clayey gravels occur throughout much of the area. These deposits overlie thin Kesgrave Sands and Gravels and London Clay.

Thick solifluction deposits are present in the Hoestreet and Writtle area. Silty loams are present on the lower slopes, whereas clayey gravels are locally extensive on the higher ground. Much of these deposits was apparently mobilised and moved down the north-facing slope of the ridge by solifluction. A ditch section [TL 6559 0773] near Hoestreet showed up to 1.2 m of clayey gravels, resting with an irregular festooned base on the Chalky Boulder Clay; silty loam between 0 and 1.2 m thick overlay the gravels with an even base. Red and brown mottled sandy clays with rounded flint pebbles were noted in road sections [TL 6685 0765]; [TL 677 076] near Warren Bridge. A former pit [TL 6718 0695] at the Institute of Agriculture exposed 3 m of rounded gravels in a brown clayey sand matrix; the clasts showed a preferred vertical orientation due to cryoturbation. In an excavation [TL 6825 0657] for the sewage works 1.5 m of loam was reported to overlie 1.5 m of clayey gravel, which in turn rested on weathered London Clay. The clayey gravels and underlying Kesgrave Sands and Gravels (where present) have been worked in small pits to a depth of 4 m in the Writtle area. Near Writtle Mill [TL 686 062] a section formerly thought to be decalcified boulder clay (Whitaker, 1889, p.326) was described as follows:

The Chelmer valley

Around Ford End and Hartford End, the Head comprises dominantly silty loams which are typically present below the springline near the base of the boulder clay. RDL

River Terrace Deposits

Small areas of River Terrace Deposits occur in the Ash and Stort valleys and in the lower part of the Roding valley south of Chipping Ongar. In the Ash valley two levels have been recognised at about 1 to 2.5 m and at 3.5 m above the alluvium. Similarly in the Stort valley there are two levels at 1 to 1.5 m and 5 to 8 m above the alluvium. Both rivers flow into the Lea, and the terrace levels recognised within the Epping district may be of only local utility. Two levels have also been mapped in the Roding valley although these are degraded in places; the numbering system here is also provisional.

The deposits comprise mainly flint gravels with subordinate sandy gravels and pebbly sands. In addition to the abundant subangular flints there are subrounded and rounded pebbles of flint, quartz, quartzite, chalk and sandstone. The sand fraction consists of subrounded to rounded quartz grains, with a small amount of coarse-grained angular flint and chalk. The uppermost 0.5 to 1 m is commonly slightly clayey.

The thicknesses of the deposits are not known in detail, but up to 5 m have been recorded in the Ash and Stort valleys. Similar thicknesses are probably present in the Roding valley: one borehole in this area recorded 4.5 m. DM

Details

River Ash

Small patches of Terrace Deposits occur along the Ash valley. Terrace 1 occurs about 1 to 2.5 m above alluvium level. North of Widford it was worked for sand and gravel [TL 4180 1650]; [TL 4233 1673]. A borehole in the terrace encountered:

Terrace 2 Deposits, about 3 to 5 m above the Alluvium, have been preserved near Hadham Cross. A trial pit [TL 4296 1886] proved:

A small mound [TL 4293 1810] of loamy material restricts the width of the Alluvium in the Ash valley just south of Hadham Cross. It may be a degraded terrace, and has been shown as such on the published geological sheet. BSPM

River Stort

Two terraces have been recognised in the Stort valley. Terrace 1 Deposits are most widespread between Thorley [TL 4900 1880] and Harlowbury [TL 480 120], although they occur also in the extreme west. The terrace, about 1 to 1.5 m above the Alluvium, is composed of gravels, sandy gravels, and sand.

The eastern industrial estate [TL 46 12] of Harlow, although built mainly on made ground, may locally overlie deposits of Terrace 1. Old Ordnance Survey maps show areas of higher ground within the alluvial tract of the Stort: a Roman temple was built on one such area [TL 4680 1230].

Terrace 2 Deposits occur discontinuously about 5 to 8 m above the present Alluvium along much of the Stort valley. They have been worked locally [TL 4860 1365] for sand and gravel south of Sawbridgeworth. These workings are now largely overgrown, but reveal rounded and angular flint gravel in a sandy silt matrix. Old workings [TL 4010 1000] were also seen in a sandy gravel just west of Roydon. BSPM

River Roding

River Terrace Deposits are present in the Roding valley south of the confluence with the Cripsey Brook at Chipping Ongar. Gravel was extracted between 1937 and 1939 from deposits exposed on the north-west of the Roding. The flooded pits [TL 556 015] lie north-west of Langford Bridge, and a degraded working face on the north side of the largest lake [TL 5564 0152] showed 2 m of angular and rounded, mostly flint gravel, in a silty and medium- to coarse-grained sandy matrix. The extent of the terrace upslope beneath Head, is indicated by shallow degraded diggings [TL 5570 0165]. This ground rises to about 43 m OD, some 5 m above alluvium-level. The full thickness of the terrace deposits was recorded in only one borehole at Littlebury Mill [TL 5518 0121] which is reported to have penetrated 4.5 m of sand and gravel on London Clay.

On the south-eastern bank of the river, there were 3.5 m of sand and gravel near the back of the terrace in a borehole south-west of Langford Bridge Farm [TL 5575 0095]. Gravel has been extracted from the terrace near Langford Bridge [TL 559 012], where diggings 2 to 3 m deep are still visible, and from the front of the terrace [TL 548 006] east of Bridge Farm. RAE

Alluvium

Silty clay and clay floor the floodplains of many of the mature rivers and streams. Marked breaks of slope separate the Alluvium from the deposits forming the valley slopes. The widest expanse of Alluvium occurs in the Stort valley, with a maximum width to the north of Harlow of approximately 700 m; a narrow strip occupies its main tributary of Pincey Brook. In the Temple Fields area of Harlow [TL 46 11], part of the Alluvium has been covered with up to 3 m of made ground in order to provide stable foundations for the industrial complex. Extraction of gravel from beneath the surface clays is widespread to the west of Roydon [TL 40 10]. In this district extensive tracts of Alluvium occur along the entire length of the Roding and its tributary Cripsey Brook as far as Weald Bridge [TL 511 065]; the maximum width of 250 m in the Roding is towards the southern boundary of the district. In the eastern part towards Chelmsford, narrow alluvial belts margin most of the main streams including the Chelmer, where the Alluvium is up to 200 m wide, the Can, the Newland and Roxwell Brooks, and the Wid.

These river deposits comprise two distinct units, an upper clayey part and a lower (or sub-alluvial) gravelly part. The clays and silts are soft, open-textured and dark brown. Locally they are sandy, with thin beds and stringers of rounded pebbles, including chalk, particularly in the northwest of the district where Chalk bedrock and chalk-bearing glacial gravels crop out. The organic content of the silts and clays is high and thin lenses of peat also occur. The lower gravel is generally present beneath most of the alluvial tracts, although in places the silts and clays rest directly on older drifts or bedrock. The gravels are generally moderately well sorted and bedded, fine- to coarse-grained, with angular to rounded flints, vein-quartz and quartzite; locally chalk is present. In most areas the lower gravel is readily distinguished from the underlying deposits, but in parts of the Ash and Stort valleys clayey alluvium rests on relatively thick sands and gravels, and it is not everywhere possible to separate the alluvial gravel from the underlying Glacial Sand and Gravel.

The thickness of Alluvium varies throughout the district. In the Ash valley the maximum recorded is 3.6 m, of which the uppermost 2.9 m are clays and silts. In the Stort valley the alluvial gravels comprise a large part of the thickness; for example 5.1 m of a total thickness of 6.0 m, and 2.3 m of a total of 4.2 m. In the upper reaches of the Roding valley near Hatfield Heath, the total thickness is about 2 m, though alluvial gravels are commonly thin or absent. However, in the Ongar area at least 1 m of gravel was recorded in most places. In the east of the district much of the Alluvium is apparently silty clay with less than 0.5 m of gravel. DM

Details

River Ash

A narrow belt of Alluvium between 50 and 200 m wide is present in the Ash valley. The deposit consists of a soft brown silt or clayey silt, with a variable organic content. A borehole [TL 4029 1573] south-west of Blakesware proved:  Thickness m

River Stort

A belt of Alluvium occupies the floor of the Stort valley. It varies in width from about 150 m in the north to over 700 m north of Harlow, and consists generally of organic silty clay overlying 3 to 5 m of sandy gravel.

Just south of Sawbridgeworth a borehole [TL 4874 1459] sited on Alluvium encountered:

Less than 1 km farther south, near Pishiobury Park, a second borehole [TL 4877 1392] proved:

Farther south, a third borehole [TL 4570 1227], south-east of Pole Hole Farm iust north of Harlow, recorded the following:

In all the borehole logs examined, gravel is recorded beneath the surficial silts and clays. BSPM

River Roding

The valley of the Roding has a floor of alluvial material extending along all the valley that lies within the district. Of its main tributaries, only Cripsey Brook has a similar deposit.

A narrow band of Alluvium, generally between 50 and 150 m wide, extends along the Roding valley between Great Canfield and Beauchamp Roding [TL 595 180] to [TL 589 100]. At Hatfield Broad Oak a borehole [TL 5368 1379] sited on Alluvium proved 1 m of soil and silty subsoil resting sequentially on 1 m of mottled brown silt with organic remains and boulder clay. Approximately 1 km farther south, a borehole [TL 5343 1481] encountered 1.4 m of brown, slightly sandy, silty clay, on 0.4 m of very sandy silty clay containing abundant round and angular flint pebbles. This gravelly clay rests directly on boulder clay. BSPM

Because of the artificial straightening of the river in the Ongar area, exposures in the banks of the Roding are rare. The flood-plain has a brown and grey mottled silty soil. Where the river valley widens, particularly below Hallsford Bridge [TL 5613 0225], a soft dark grey and brown clayey silt to silty clay was augered to more than 1.4 m. A borehole [TL 5604 0189] south-south-west of Hallsford Bridge proved:

The gravel bed at the base of the Alluvium may thicken downstream, as illustrated in a borehole at Langford Bridge [TL 5587 0145] which penetrated:

Gravel is, however, not everywhere present beneath the Alluvium; near Langford Bridge a borehole [TL 5590 0141], only some 40 m to the south-east of the previous borehole, proved 3.5 m of top soil and Alluvium, with only 0.6 m of gravel at its base, resting directly on London Clay. The limited evidence available suggests that the alluvial gravel occupies shallow depressions in the London Clay surface. RAE

A thin strip of Alluvium is present in the Cripsey Brook valley, and extends upstream as far as Weald Bridge [TL 511 065]. Bank sections at localities between Weald Bridge and Wood Farm [TL 5180 0660]; [TL 5344 0679]; [TL 5431 0607] show between 1.5 and 2.0 m of brown silty clay loam, that overlies approximately 0.5 m of coarse angular to subrounded flint gravel, resting on brecciated brown and grey London Clay. DM

Up to 2 m of brown silt are exposed in the banks of the Cripsey Brook where sharp meanders have been cut between Wood Farm and the confluence with the River Roding at Chipping Ongar. Angular flint gravel seams occur in places within the lower part of the bank, usually almost at river level, for instance north-east of Greensted Hall [TL 5435 0371].

In the Ongar area boreholes drilled for a proposed relief road penetrated Alluvium; for example a borehole west of the Motte and Bailey at Chipping Ongar [TL 5506 0311] penetrated 2.9 m of brown mottled clay, with scattered pebbles and traces of peat, overlying London Clay. Farther downstream in another borehole c.[TL 5505 0273], the alluvial gravel is 1.25 m thick, beneath 2.55 m of 'firm brown mottled clay', and overlies London Clay. RAE

River Can

A thin tract of Alluvium, consisting mainly of soft organic silty clays, lies in the Can valley upstream to Good Easter [TL 615 122]. Numerous tributaries, including part of Roxwell and Newland Brook, are similarly floored with these deposits. RDL

River Wid

The Alluvium of the River Wid has a poorly defined western boundary. The surface deposits consist of dark grey clay, up to at least 1.2 m thick [TL 6685 9971]. Dredging in the bed of the river has established that gravels underlie the clay, and in 1923 Mr F. H. Edmunds noted 0.6 m of clay overlying 0.9 m of gravel in the stream bed [TL 6898 9978]. Where lenses of gravel lie near the surface, a hummocky profile is developed by differential weathering. RDL, CRB

Landslips

Extensive landslips occur in the south-west of the district, on the steep eastern slopes of the Lea valley and its tributaries from Roydon to Waltham Abbey, and on the steep flanks of the Epping Forest ridge. The distribution is closely related to particular rock types (Figure 16).

To the east of the Lea valley the main tributary valley of the Cobbin's Brook and numerous other short streams have relatively deeply-incised valleys. In the Stoneshot Common area [TL 40 07] and at Nazeingwood Common [TL 42 05] there are low, steep-sided knolls and narrow dissected ridges, with landslips on the steeper parts. Other steep slopes in the area are apparently stable, for example the steep slopes of Epping Long Green, south of Nazeingwood Common, though there may be slips that have been masked by recent cultivation. Several landslips lie on the south-facing slopes between Coopersale Street [TL 47 01] and Gaynes Park [TL 48 01] and at Mount End [TL 48 00], but they are smaller than those near the Lea valley. On the north side of the ridge, there are others at Bell Common [TL 44 01] and south of Upshire [TL 41 00].

In the Lea valley and its tributaries the failed slopes essentially involve the London Clay, notably the silty clays in the lower part of the formation, though there seem to be no beds of fine-grained sand in the sequence. In some cases only London Clay is involved, for example at Galleyhill Wood [TL 39 03], west of Galley Hill, but in most cases the upper slopes are capped by boulder clay. The landslips of the Epping Forest area are also generally confined to the solid formations, but involve the uppermost London Clay and the overlying Claygate Beds. In comparison to the firm surface material of stable London Clay slopes, the clays in the failed areas are very soft and plastic.

Recent landslips are characterised by hummocky, uneven and irregular slopes of about 8° or more. Recognition of movement in wooded areas and hedgerows is assisted by tilted trees and by very wet ground even during dry periods. Commonly, longitudinal ridges, individually up to 300 m or more in length, occur on failed slopes. They parallel the contours and are attributed to rotational slipping. Smaller features consist of irregular arcuate ridges commonly less than 80 m across. Several phases of movement can be recognised in the latter examples by the presence of small cross-cutting mudslides, less than 10 m across, which give rise to generally very soft and waterlogged ground. Large toes to the slips are common at the base of the slopes, but other features have been largely destroyed by cultivation. Some of the smaller landslips occur on waste ground, however, and here the characteristic features of sliding and tension cracks can be seen on the upper slopes.

The causes of the landslipping are twofold. Firstly, in the examples at the junction of the London Clay and Claygate Beds, water seepages through permeable strata have provided an essential lubricant. To a limited extent similar, but smaller, seepages at the junction between the Chalky Boulder Clay and London Clay have caused instability. Secondly, and more significantly, oversteepening has led to failure: many of the slopes have inclinations of between 10 and 15°, considerably greater than 8°, the ultimate angle of stability for London Clay (Hutchinson, 1967). Rapid erosion after the recession of the Anglian ice-sheet was responsible for the oversteepening, though exact dating is not possible. The small mudslides which cut the arcuate failures are relatively modern, and some may still be active. Because many of the slopes are greater than 8° it is probable that further landslipping will occur. Hutchinson and Gostelow (1976) regarded climatic conditions, particularly climatic change, as extremely important in the initiation of landslips; at Hadleigh Cliff in south-east Essex, for example, movement has occurred episodically between the late Devensian and the present. DM

Details

Lea valley–Nazeingwood Common

Extensive tracts of the steep eastern side of the Lea valley south from its confluence with the Stort have been involved in landslipping. The steep slopes from The Grove [TL 398 092], to Roydon Hamlet [TL 410 077], show a number of rounded ridges running parallel to the contours. The slope failures in this area are probably old; though the features have been modified considerably by ploughing, identification of slips has been supported by trees tilted at 5 to 8° from the vertical. Sharp breaks of slope occur near the toes of the slips. Both London Clay and Chalky Boulder Clay are involved in the slips. The thickness of the strata affected is not known in detail, but several boreholes in the southern part of this area, north of the minor road running westward from Roydon Hamlet through Stoneshot Common, indicate the thickness of the weathered London Clay. One such borehole [TL 4084 0796], near to the top of the landslip, recorded soft pale brown clay to plastic greyish brown clay to a depth of 11.9 m. Near to the base of the slip, a borehole [TL 4077 0774] proved 10.8 m of uniform soft brown clay with selenite crystals.

Small areas of more recent slipping lie on the north-western and northern slopes of Clay Hill [TL 401 078] and to the north of the church at Nazeing [TL 415 071]. Permanent pasture and waste ground both have hummocky surface features. It is evident that several phases of slipping have occurred; for example, on the north side of Clay Hill [TL 4107 0780] one arcuate-shaped failure, 40 m across, is cut through by a small, more recent mudslide. Clay Hill is entirely underlain by London Clay, whereas north of Nazeing church, boulder clay overlies London Clay.

The steep-sided, almost U-shaped, tributary valley of the Lea at Nazeingwood Common [TL 425 056] has been oversteepened. The resultant landslips occur on the northern, and part of the southern, sides of the valley. Springs have assisted in the formation of the landslips. DM

The London Clay slopes rising southwards from Nazeing Long Green [TL 403 047] to Galleyhill Green [TL 403 040] are extensively land-slipped, and the ground is uneven and hummocky as a result of mudslides on the oversteepened slopes. Low, rounded London Clay knolls, some 100 to 150 m across, near the bottom of this slope [TL 4005 0445] may be the degraded remnants of a large rotationally landslipped block of London Clay, though this possible landslip has not been shown on the 1:50 000 geological map. A less extensive area of hummocky landslipped ground occurs on the north-facing slope [TL 4130 0473], north of Harold's Park Farm.

Along the south-facing slope below Galley Hill [TL 406 034], a similarly oversteepened London Clay slope is extensively land-slipped. The affected area extends upslope to boulder clay capping the hill. Soft orange-brown silty clay, probably destructured London Clay, is present at the surface across the unstable area. Many small mudslides appear to be active, and are marked by low linear scarps about 1 to 1.5 m in height with only a scanty vegetation cover. RAE

Epping Forest and Stapleford Tawney

On the flanks of the ridge (composed of London Clay, Claygate Beds and Older Head), landslips are almost invariably associated with the steeper slopes developed on the Claygate Beds outcrop. Along the northern flank of the ridge, uneven ground suggests the presence of landslips at two localities in small tributary valleys [TL 4175 0050]; [TL 443 013]. Landslips of London Clay lie on the northern side of a knoll [TL 4140 0017] near Wood Green, and also [TL 4418 0186] north-west of New Farm.

There are numerous other steep slopes which are potentially unstable, but no evidence of landslipping has been detected. Much of the Claygate Beds outcrop as far east as New Farm falls into this category, along with the slopes of many of the London Clay knolls [TL 4175 0132]; [TL 4254 0096]; [TL 4418 0119].

Small areas of landslip, characterised by uneven hummocky ground, have been recognised in the following localities: south-west of St Margaret's Hospital, Epping [TL 4651 0216]; [TL 4662 0205]; on the southern side of the railway south of the hospital, where there are mudslides [TL 4700 0230]; [TL 4716 0237]; on the west-facing slope of a small valley north-east of Coopersale House [TL 480 023]; and northwest of Coleman's Farm, where some 700 m of west-facing slopes are unstable [TL 498 001]. In all these examples failure has occurred at the base of, or within the basal part of, the Claygate Beds. The only landslip noted within London Clay is on the western side of the ridge around Coopersale Hall [TL 4625 0030]. RAE

A small slip [TL 454 999] is associated with springs at the London Clay–Claygate Beds boundary to the north of Theydon Bois. A larger area of landslip occupies the steep west-facing slope [TL 487 995] immediately west of Hill Hall. The slips extend for 1.4 km [TL 4895 9998] to [TL 4809 9895], and are recognisable by a large number of hummocky ridges parallel, to the contours, with trees tilted at least 5° from the vertical [TL 489 998]. The slips are associated with springs issuing from the base of the Chalky Boulder Clay and from the  London Clay–Claygate beds junction DM

Roding valley

East of Aspen Wood, two small slips of London Clay lie below the  junction with the Claygate Beds [TL 5481 9941]; [TL 5487 9925]: the slips measure 150 by 60 m and 80 by 80 m respectively. DM

Margaretting

Only one small slip [TL 6830 9915] has been noted. It measures 90 by 80 m, and is associated with springs issuing from the base of the Bagshot Beds. CRB

Chapter 7 Economic geology

Building materials

The Tertiary deposits of the London area have in the past been extensively used for brickmaking, an important building material in an area lacking natural constructional stone. The Woolwich and Reading Beds were commonly exploited in the Hertford and Bishop's Stortford districts, and small London Clay brickyards in the Epping district were recorded by Whitaker and others (1878) and Whitaker (1889). Important examples were in the Stort valley downstream from Roydon, just north of the station in Epping [TL 46 01], and north of Theydon Mount.

In more recent years the production of artificial building materials has been introduced into this area. A pilot-plant at Rye House, Hoddesdon, to the west of Roydon, produced bricks in the mid-1950s, using pulverised fuel-ash from the power-station mixed with about 15 per cent of locally derived London Clay as the binder. The London Clay in the Stoneshot Common [TL 40 07] area was examined with the purpose of opening a clay-pit to supply the plant with binder material.

The only currently working pit is near Ongar, where lightweight clay aggregate is produced for use in building blocks and precast concrete at Mill Lane, near Hallsford Bridge [TL 562 023]. After extraction the London Clay is broken down into a plastic state and then rolled into a pancake, before being passed into a rotary kiln in particle sizes ranging from 6 to 44 mm and subjected to a temperature of 1200°C. The expanded product is a stable ceramic aggregate which, when used as a building material, has good fire resistance, poor thermal conductivity and good acoustic properties, but its structural use is confined to situations involving limited compression. DM, RAE

Sand and gravel

This account outlines the results of drilling and sampling surveys undertaken by the former IGS Industrial Minerals Assessment Unit between 1975 and 1978, which form the basis of reports by Hopson (1979; 1981) and Marks (1980) on the sand and gravel resources of the northern and eastern parts of the Epping district.

The criteria used to define sand and gravel resource deposits are:

1. the deposit should average at least one metre in Thickness
2. the ratio of overburden to sand and gravel should be no more than 3:1
3. the proportion of fines should not exceed 40 per cent; the fines, clay and silt, are the sizes less than 0.063 mm. The deposits are as classified in (Figure 17).
4. the deposit should lie within 25 m of the surface.

The major resources of sand and gravel in the Epping district are the extensive spreads of Kesgrave Sands and Gravels and Glacial Sand and Gravel; Older Head, Head Gravel and River Terrace Deposits, are of minor importance.

There are six sand and gravel pits in the district: at Hadham [TL 43 17], Gaston Green [TL 495 163], Moreton [TL 535 072], Great Waltham [TL 687 122], Chignall St James [TL 664 106] and Newney Green [TL 648 065]. All except those at Hadham and Gaston Green exploit Kesgrave Sands and Gravels, and are situated in valleys where there is generally less than 8 m of overburden. Hadham and Gaston Green worked Glacial Sand and Gravel and are now disused. The other pits meet local demand. Summarising the results of the three published sand and gravel resource surveys, which cover 60 per cent of the Epping district, it is estimated that total resources in the areas assessed amount to approximately 532 million m3; of these about 92 per cent are from the Kesgrave Sands and Gravels and Glacial Sand and Gravel. Reservations concerning this global figure are contained in the published reports.

Older Head

This deposit covers large tracts in the southern part of the Epping district, but it has been assessed only in the east (Figure 18). The overburden is less than 1.0 m, and the mineral ranges up to 4.7 m in thickness. The deposit varies from very clayey sandy gravel to clayey gravel. The mean grading is gravel 46 per cent, sand 39 per cent, and fines 15 per cent. Locally more than 40 per cent silt and clay is present; in such cases the deposit is regarded as non-mineral.

Kesgrave Sands and Gravels, and Glacial Sand and Gravel

These represent the main resources of the district. To the south of the area assessed, the resources diminish. Although the lenses of Kesgrave Sands and Gravels are extensive, a thick and economically prohibitive overburden of boulder clay is present in much of the northern part of the district (Figure 18). Potentially workable Glacial Sand and Gravel is present within the valleys of the Ash and Stort, and Kesgrave Sands and Gravels occur in those of the Roding and Chelmer. Thin overburden is present in the Matching Green [TL 53 11] and Abbess Roding area and around Roxwell [TL 464 085]. The mineral occurrences vary in thickness from 1.2 to greater than 10.5 m. The Kesgrave Sands and Gravels are generally gravels, although sandy gravel is also present, particularly south of Roxwell (Figure 18). The Glacial Sand and Gravel varies from a gravel to a sandy gravel, and in places is a pebbly sand. It becomes markedly clayey to the south of Hunsdon and in the Sawbridgeworth area.

Head Gravel

Overburden is generally thin, less than 1.0 m. The Head Gravel is heterogeneous, and several sampled sequences proved non-mineral throughout because of a content of silt and clay greater than 40 per cent. Resources of Head Gravel range in thickness from 1.2 to 6.3 m. At Matching Green resources of Head Gravel are separated from underlying mineral-bearing Kesgrave Sands and Gravels by 10.6 m of boulder clay (Figure 18). Overall the deposit is a 'clayey' gravel with a mean grading of fines 18 per cent, sand 41 per cent, and gravel 41 per cent.

River deposits

First and second Terrace Deposits are potential resources of gravel in the valleys of the Ash and Stort. They are typically gravelly and have a high chalk content; the uppermost metre is commonly clayey and silty. In parts of the Ash, Stort, Roding and Wid valleys, Alluvium overlies potential resources of alluvial gravels. In the lower part of the Roding, south of Chipping Ongar, river gravels are extensive and may be potential resources. They were worked for aggregate between 1937 and 1939. The overburden of the alluvial gravels varies up to about 3 m, and the thickness of the gravels from 1.0 to 5.9 m. The gravels have a mean grading of fines 8 per cent, sand 36 per cent and gravel 56 per cent. RJM

Hydrogeology and water supply

The district lies within Hydrometric areas 37 and 38. The western and central parts (including the Roding catchment) are administered by the Thames Water Authority., the eastern part by the Anglian Water Authority. The district lies within units 5 to 8 of the Thames Water Authority and resource units 46 and 48 of the Anglian Water Authority (Monkhouse and Richards, 1982).

The west of the district is drained by the rivers Ash and Stort and by the Pincey and Cobbin's brooks, all of which are tributaries of the River Lea. The central area is drained by the River Roding. The east is drained by streams flowing to the River Can whose main course lies beyond the sheet margin. Due to the extensive, and largely impermeable, drift cover, the surface streams tend to be flashy with peak flows 50 to 70 times the daily means and with only small contributions from groundwater flow.

The mean annual rainfall varies from about 550 mm in the extreme east to nearly 650 mm in the west. The mean annual evaporation is of the order of 440 to 460 mm.

The hydrogeology of the Chalk aquifer has been considered in some detail by the Water Resouces Board (Anon, 1972), and a catalogue of wells was published by the Geological Survey of Great Britain (Davies and others, 1965). The north-west corner of the district appears on the Hydrogeological Map of the area between Cambridge and Maidenhead published by the British Geological Survey (1984) on a scale of 1:100 000. Earlier works containing references to the district include Whitaker and Thresh (1916) and Woodland (1945).

Much of the water used for public supply is provided from sources outside the district. Three sources take groundwater from the Chalk in the north-west, at Hadham Mill [TL 420 166], Roydon [TL 410 101] and Sawbridgeworth [TL 465 130], which are together licensed for 9.1 million cubic metres per annum (m³/a). About 650 million m³/a are licensed from superficial deposits, mostly for gravel washing, and there are a few small agricultural, industrial and domestic abstractions from the Chalk. About 1000 million m³/a are licensed from streams and rivers for irrigation and for gravel washing, but there are no surface intakes for public supply (the stream flows do contribute to such intakes downstream and outside the district).

Most of the district is covered by superficial deposits. Of these, the most widespread is Boulder Clay which is a very poor source of water and generally yields only a few cubic metres per day (m³/d) by seepage to shallow wells. The Glacial Sand and Gravel can yield quantities of water to shallow wells, up to 300 m³/d where they are well developed, and mainly in the south and south-east of the district. The groundwater often contains a high concentration of iron which may impart an unpleasant taste, and the aquifer is vulnerable to pollution from surface sources. River Terrace Deposits generally drain rapidly to the adjacent streams amd are rarely able to support continuous demands.

The outcrop of the Bagshot Beds in the district is very limited, and these strata are hydrogeologically of little importance. The Claygate Beds contain small quantities of groundwater in the sandy horizons, but the amounts are small and suitable only for small, occasional domestic requirements. The groundwater is often rich in iron.

The London Clay is not an aquifer, but small supplies of groundwater can sometimes be obtained from the basement beds, or from the weathered zone close to the ground surface where the drift cover is thin or absent. The water tends to be extremely hard with sulphate concentrations (as SO₄) often exceeding 2000 milligrammes per litre (mg/1).

The Woolwich and Reading Beds of the Lower London Tertiaries can yield small supplies from the sandier horizons, but the groundwater is generally hard with high concentrations of calcium, magnesium and sulphate. Yields from the Thanet Beds are difficult to assess because overlying sandy horizons (in the Woolwich and Reading Beds) are seldom lined out and most wells reaching this formation are continued into the Chalk. A borehole of 150 to 300 mm diameter penetrating 10 m of saturated Thanet Beds might yield as much as 500 m³/d, but carefully designed and developed filter packs and sand screens are needed to prevent silting. The Thanet Beds are usually in hydraulic continuity with the underlying Chalk, and the two formations contain groundwater with broadly similar qualities.

The Chalk is the major aquifer within, and underlies the whole of, the district. The matrix of this formation is permeable only to a very limited degree, and groundwater yielded to boreholes flows through, and is stored in, fissure systems. The width of the fissures is small, usually less than 1 mm, and the density of fissuring varies areally with a consequent variation in borehole yield.

From the viewpoint of borehole yield, the district is in two parts. The first encompasses the Chalk outcrops in the north and north-west, together with the Chalk that is confined beneath the Lower London Tertiaries and the London Clay up to a distance of about 2 km from the edge of the outcrop of the latter. A statistical study of borehole performance in this area indicates that a borehole of 300 mm diameter penetrating a thickness of 50 m of saturated chalk would have a mean yield of about 750 m³/d for a drawdown of 15 m. An excavated, large-diameter shaft with headings may yield considerably more, and yields of more than 6000 m³/d have been recorded.

Elsewhere in the district, the Chalk is confined beneath substantial Tertiary cover and yields water much less readily. A borehole of 300 mm diameter and penetrating a thickness of 50 m of saturated chalk would have a mean yield of about 150 m3/d for a drawdown of 15 m or more. Due to the depth to the top of the Chalk, excavated shafts are uncommon, and only a limited number of boreholes have been constructed.

When boreholes are constructed into chalk, the drilling action causes the formation of a slurry of chalk particles mixed with water. This slurry forms a 'wall-cake' which tends to block the fissures intersected by the borehole. It is normal practice to treat the borehole on completion with hydrochloric acid to clean off wall-cake and develop the full potential yield.

The quality of groundwater in and adjacent to the Chalk outcrop is usually good. The total hardness, mostly carbonate (temporary) hardness, is generally in the range 300 to 400 mg/1, while the chloride ion concentration is usually less than 30 mg/l. Concentrations of iron are usually low, less than 0.2 mg/1. In the Chalk beneath thick Tertiary cover, the total hardness tends to decrease to the east while the chloride ion concentration increases. At a site at Felsted [TL 688 175], Chalk groundwater had a total hardness of about 240 mg/1 and a chloride ion concentration of more than 150 mg/l.

Superficial aquifers are commonly vulnerable to pollution; the water-table is close to the ground surface and the time taken for pollutants to reach the saturated zone is short. In the sands and gravels, permeabilities tend to be high, and lateral groundwater flow to be rapid, carrying contaminants quickly towards pumping wells.

Over most of the Epping district, the Chalk is covered by Tertiary strata or by Boulder Clay, both of which provide a good protective cover. In this situation, the danger of pollution from surface drainage varies from slight to nil. In the river valleys of the north and north-west, where the Chalk may be overlain only by alluvium, Head or river gravels and where the water-table is close to the ground surface, it is possible for pollutants (for example, leachate from landfill waste disposal sites) to reach the saturated zone very rapidly. RAM

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Appendix 1 Abstracts of borehole logs

Cobbin's Brook No. 1 Borehole

(TL40SW/1) NGR [TL 4160 0238] Drilled in 1967. Logged by P. N. Hildreth. Surface level + 36.27 m.

Cobbin's Brook No. 2 Borehole

(TL40SW/2) NGR [TL 4200 0257] Drilled in 1967. Logged by P. N. Hildreth. Surface level + 39.62 m.

Cobbin's Brook No. 3 Borehole

(TL40SW/3) NGR [TL 4243 0273] Drilled in 1967. Logged by P. N. Hildreth. Surface level + 39.84 m.

Gilston Borehole

(TL41SW/35) NGR [TL 4417 1349] Drilled in 1976. Logged by P. M. Hopson Surface level + 49.8 m

Appendix 2. List of Geological Survey photographs

Copies of these photographs are deposited in the Libraries of the Geological Museum, South Kensington, London SW7 2DE, and of the British Geological Survey, Keyworth, Nottingham NG12 5GG. Prints and slides can be supplied at a standard tariff. All numbers belong to Series A.

Index of fossils

• Abra splendens (J. de C. Sowerby)
• Albula oweni (Owen)
• 'Ammodiscus' sp.
• Ammonia batavus (Hofker)
• Ampheristus toliapicus Konig
• Ancilla atrebatum Wrigley
• Ancistrosyrinx sp.
• Anonaspermum commune Reid & Chandler
• Apogon glaber Stinton
• Arctica sp.
• Arctica cf. morrisi (J. de C. Sowerby)
• 'Ardicolus marriotti' White
• Argentina extenuata Stinton
• Astarte filigera S. V. Wood
• Athleta (Volutospina) nodosus (J. de C. Sowerby)
• Bathytoma sp.
• Batopora clithridiata (Gregory)
• Bonellitia ?laeviuscula (J. Sowerby)
• Bourgueticrinus sp.
• Brosmophycis sagittalis (Frost)
• Brotia sp.
• Brotia melanioides (J. Sowerby)
• Brotula arcuata Stinton
• Bulimina elongata d'Orbigny
• Bullinella sp.
• Bullinella cf. consors (Deshayes)
• Calpitaria sulcataria (Deshayes)
• Calyptraea aperta (Solander)
• Centroberyx crenulatus Stinton
• Centroberyx lemoinei (Priem)
• Cepola densa Stinton
• Chlamys cretosa (Defrance)
• Cimomia imperialis (J. Sowerby)
• Cladoceramus undulatoplicatus (Roemer)
• Clithrocytheridea sp.1
• Clithrocytheridea sp.2
• Coelopleurus wetherelli Forbes
• Conospira concinna (J. Sowerby)
• Corbicula sp.
• Corbicula cordata (Morris)
• Corbula globosa J. Sowerby
• Cordiceramus cordiformis (J. de C. Sowerby)
• Ctenocheles sp. nov.
• Cultellus affinis U. Sowerby)
• Cuspidaria inflata (J. Sowerby)
• C. triradiata Wrigley
• ?Cybium sp.
• Cylindracanthus rectus (Dixon)
• Cyrena cordata Morris
• Cytheretta aff. scrobiculoplicata (Jones)
• Cytheridea unispinae Eagar
• Cytheropteron wetherelli (Jones)
• Daphnobela juncea (Solander)
• Democrinus londinensis Forbes
• Dentex pentagonalis Stinton
• Dermatopsis argutus (Stinton)
• Ditrema sheppeyensis Frost
• Ditrupa Plana (J. Sowerby)
• Dromilites lamarcki (Desmarest)
• Dunstania multilocularis Reid & Chandler
• Elphidium clavatum Cushman
• Epistominella sp.aff.
• Epistominella vitrea Parker
• Epitonium sp.
• Epitonium undosum J. de C. Sowerby
• Eratotrivia sp.
• Eugomphodus (Eugomphodus) hopei (Agassiz)
• Eugomphodus (Striatolamia) macrotus (Agassiz)
• Euspira glaucinoides (J. Sowerby)
• Euthriofusus transversarius Wrigley
• Eutrephoceras regalis (J. Sowerby)
• Ficopsis multiformis (Wrigley)
• Fusinus unicarinatus (Deshayes)
• Fusinus wetherelli Wrigley
• Fusiturris prestwichi (Edwards)
• Galeodea gallica Wrigley
• Galeorhinus lefevrei (Daimeries)
• Galeorhinus minor (Agassiz)
• Glandulispina sp.1
• Glandulispina sp.2
• Glaucosoma pentagonalis (Stinton)
• Globigerina sp.
• Globulina inaequalis Reuss
• Glyphithyreus wetherelli (Bell)
• Graphularia wetherelli Milne-Edwards
• Gryphaea sp.
• Guttulina austriaca d'Orbigny
• Guttulina communis d'Orbigny
• Halicopsis sp.
• Haplophragmoides sp.
• Hemipleurotoma sp.
• Hemipleurotoma prestwichi (Edwards)
• Holocentrus sheppeyensis (Frost)
• Hoplopari a gammaroides M'Coy
• Hoplostethesus densus Stinton
• Hypomesus pennatus Stinton
• Icacinicarys amygdaloides Chandler
• Isistius trituratus Winkler
• Isurolamna affinis (Casier)
• Jaekelotodus trigonalis (Jaekel)
• Kingena lima (Defrance)
• Labyrinthidoma dumptonensis Adams, Knight & Hodgkinson
• Laevidentalium nitens (J. Sowerby)
• Lagena sp.
• 'Lamna' lerichei Casier
• Lenticulina sp.
• Leuresthes distans Stinton
• Limea granulata (Nilsson)
• Linuparus sp.
• Litiopa sulculosa Edwards MS
• Loxoconcha sp.
• Magnolia lobata (Bowerbank)
• Marginulina sp.
• Mathilda sororcula Wrigley
• ?Megalops sp.
• Microgadus subnotus (Frost)
• Modiolus tubicola (S. V. Wood)
• ?Molva dubia Stinton
• ?Muraenesox cymbium Stinton
• Murex argillaceus Wrigley
• Murex subcristatus d'Orbigny
• Myripristis sinuatus Stinton
• Nemopteryx serratus (Stinton)
• Neobythites obtusus (Frost)
• Nipa burtini (Brongniart)
• Nodosaria sp.
• Nonion laeve (d'Orbigny)
• Nonionella sp.aff.
• Nonionella cretacea Cushman
• Notorhynchus serratissimus (Agassiz)
• Nucula compressa J. de C. Sowerby
• Nucula consors S. V. Wood
• Nuculana amygdaloides (J. de C. Sowerby)
• Odontaspis winkleri Leriche
• Odostomia sp.
• Ophioglypha wetherelli (Forbes)
• Orbirhynchia sp.
• Orbirhynchia cf. pisiformis Pettitt
• Orthochetus elongatus Wrigley
• Ostrea sp.
• 'Ostrea' incurva Nilsson
• Paracyathus caryophyllus (Lamarck)
• Paralabrax tenuicauda Stinton
• Pararotalia spinigera (Le Calvez)
• Paratrachichthys angulatus Stinton
• Peristedion semiglobosum Stinton
• Phalium (Galeodosconsia) striatum (J. Sowerby)
• Pholadomya cf. margaritacea (J. Sowerby)
• Physodon tertius (Winkler)
• Pinna affinis J. Sowerby
• Plicatula barroisi Peron
• Pollia londini Wrigley
• Porosphaera globularis (Phillips)
• Portunites incerta Bell
• Pristigenys bella Stinton
• 'Proherodus' sp.
• Protelphidium sp.
• Protelphidium anglicum Murray
• Pseudoneptunea curta (J. de C. Sowerby)
• Pseudoperna sp.
• Pterelectroma media (J. Sowerby)
• Pterothrissus angulatus Stinton
• Pycnodonte sp.
• Quinqueloculina sp.
• Quinqueloculina cliarensis Heron-Allen & Earland
• Raniceps papillosus Stinton
• Rotularia bognorensis (Mantell)
• Scaphander parisiensis d'Orbigny
• Scaphella wetherelli (J. de C. Sowerby)
• Schuleridea perforata (Roemer)
• ?Sclerostyla sp.
• Scrobicularia condamini (Morris)
• Scyliorhinus biauriculatus Casier
• 'Scyliorhinus' gilberti Casier
• 'Scyliorhinus' minutissimus Winkler
• Sebastodes bognoriensis (Stinton)
• Sinum clathratum (Gmelin)
• Solariaxis pulcher (J. de C. Sowerby)
• Sphaerocypraea alata (Edwards)
• Sphenoceramus ex. gr. cardissoides/pachti (Goldfuss)/(Arkhangelsky)
• Spiratella mercinensis (Watelet & Lefevre)
• Spirillina sp.aff. S. perforata (Schultze)
• Squalus minor Leriche
• Squatina prima (Winkler)
• Stellaxis pulcher (J. de C. Sowerby)
• Stenothyra parkinsoni (Morris)
• Stereocidaris sceptrifera (Mantell)
• Streptolathyrus cymatodis (Edwards)
• Streptolathyrus trilineatus (J. Sowerby)
• 'Striarca' wrigleyi (Curry)
• Surculites errans (Solander)
• Surculites velatus Wrigley
• Synodus davisi (Frost)
• Syrnola sp.
• Terebratulina wardenensis (Elliott)
• Teredina sp.
• Teredina personata (Lamarck)
• Teredo sp.
• Textularia sp.
• Thracia sp.
• Tibia lucida (J. Sowerby)
• Tibia sublucida (Edwards)
• Trichiurides orpiensis (Leriche)
• Trochotugurium extensum (J. Sowerby)
• Turricula sp.
• Turricula teretrium (Edwards)
• Uranoscopus rotundatus Stinton
• Uroconger validus Stinton
• Venericardia trinobantium Wrigley
• Wetherellia variabilis Bowerbank
• Xenophora agglutinans (Lamarck)
• Zanthopsis leachi (Desmarest)

Figures, plates and tables

Figures

(Figure 1) Solid geology of the Epping district.

(Figure 2) Structure contours on the top of the Palaeozoic basement. The borehole sites and proved depths to Palaeozoic rocks are shown.

(Figure 3) Isopachytes of the Lower London Tertiaries. Where known the thickness of the immediately overlying basal sands of the London Clay is also shown.

(Figure 4) Isopachytes of the Thanet Beds.

(Figure 5) Simplified graphic sections of selected boreholes through the base of the London Clay and the Lower London Tertiaries.

(Figure 6) Contours on rock-head beneath drift. Isopachytes are omitted in the Harlow area.

(Figure 7) Isopachytes of the combined Kesgrave Sands and Gravels and the contiguous Glacial Sand and Gravel.

(Figure 8) Field sketches of the Kesgrave Sands and Gravels at Chignall St James and Great Waltham.

(Figure 9) Contours on the base of the Boulder Clay.

(Figure 10) Sketch cross-sections through the glacial deposits at Harlow.

(Figure 11) Southern face of Gaston Green Gravel Pit 7. Head; clayey gravel, brown; up to 2m thick. 6. Chalky boulder clay; degraded, weathered at top grading into Head. 5. Buff and grey silty clays and clayey silts, scattered angular and rounded pebbles; involutions throughout; maximum 1 m thick. 4. Laminated ochreous pale grey silts and clayey sands; up to 0.3m thick. 3. Sandy gravel, angular flints; up to 0.3m thick. 2. Silty clay and clayey sand, laminated; up to 0.5m thick. 1. Coarse flint gravel with angular flints in ochreous brown clayey sand matrix.

(Figure 12) Cross-section of the Stort buried channel south of Sawbridgeworth.

(Figure 13) Distribution and thickness of Head Gravel in the Sawbridgeworth, Harlow and Moreton areas. Inset shows a sketch of one temporary section.

(Figure 14) Map and cross-section of the Glacial Lake Deposits near Fyfield.

(Figure 15) Stages in the diversion of the River Thames (mainly after Wooldridge, 1938 and Gibbard, 1979) showing the lines of drainage in pre-Anglian (1), post-Anglian (2) and present times (3).

(Figure 16) Distribution of landslips in the south-western part of the district.

Figure 17 Categories used in the mineral assessment resource survey.

Figure 18 Areas of mineral and their classification. The area assessed is shown. Potential deposits outside this area are also indicated.

Plates

(Front cover)

(Rear cover)

(Geological succession) Geological sequence in the Epping district.

(Plate 1) Boulder Clay, pale and talus-covered in the upper part rests with a sharp erosional base on Kesgrave Sands and Gravels, Chignall St James (A12984).

(Plate 2) Weakly laminated boulder clay with pebbly partings shows a decalcification 'pipe' structure to the right of centre, Hadham Mill (A12974).

Tables

(Table 1) Classification of the Tertiary strata.

(Table 2) Nomenclature of Pleistocene succession employed within the district.

(Table 3) Summary of the glacial and post-glacial deposits of the Epping district.

(Table 4) Comparative pebble count compositions for the Older Head.

Tables

(Table 1) Classification of the Tertiary strata

(Table 2) Nomenclature of Pleistocene succession employed within the district

(Table 3) Summary of the glacial and post-glacial deposits of the Epping district

(Table 4) Comparative pebble count compositions for the Older Head

The samples of Hopson (1981) are recorded as weight percentages but the methods of Prestwich and Warren are unknown