Last Interglacial deposits at Folkestone, Kent

D. R. Bridgland*, D. H. Keen t , C. P. Green", D. Q. Bowentand G. A. Sykes§

BRIDGLAND, D. R., KEEN, D. H., GREEN, C. P., BOWEN, D. Q. & SYKES, G. A. 1995. LastInterglacial deposits at Folkestone, Kent. Proceedings of the Geologists' Association, 106, 183-193.Pleistocene temperate-climate deposits at Folkestone Battery, Kent are described and attributed to a smallstream draining from the nearby Chalk escarpment. Their contained molluscan fauna is indicative ofconditions similar to those at the present in southeast England. The occurrence of a mammal fauna withHippopotamus amphibius (Linne) and of D : L amino-acid ratios from molluscan shell with a mean of0.124 combine to suggest an age in the Last Interglacial (Oxygen Isotope Substage 5e).

* Department ofGeography, University of Durham, Science Laboratories, South Road, DurhamDH13LE.t Division of Geography, School ofNatural and Environmental Sciences, Coventry University,Priory Street, Coventry CV1 5FB.t Centre for Quaternary Research, Department of Geography, Royal Holloway, University ofLondon,Egham Hill, Egham, Surrey TW20 OEX.§ Department of Geology, University ofCardiff, Box 914, Cardiff CFl 3YE.

1. INTRODUCTION

2. STRATIGRAPHY

The section excavated was at [TR 23I 359] in the groundsof the Battery. The surface height, levelled from a temp­orary benchmark tied to the Ordnance Survey benchmarkon Folkestone Church, was at 29.85 mOD.

The section measured was as follows:

FolkeSloneOute r Harbour

150mo

Fig. 1. Location map of the Battery, Folkestone.

0.66-1.12 m(3) Made ground. Variable thickness

of soil and rubble.(2) Sandy marl. Pale cream to yellow

sandy marl with banded and patchyiron staining and pellets of Chalk.Shells present throughout, with

The occurrence of Pleistocene deposits, containing bonesand shells, and overlying the Lower Greensand of the WestCliff at Folkestone, Kent, was ftrst noted by Mackie (1851).The bone content of the deposits was further described byFalconer (1868), and a consolidated mammalian fossil listwas published in the Folkestone Geological Survey Memoir(Smart, Bisson & Worssam, 1966). A short list of molluscanspecies recovered from the deposits was published byKennard & Woodward (1901). Despite occasional morerecent ftnds of bone in temporary sections in the area ofoutcrop of Mackie's 'bone-bed' (Fig. I), including those ofHippopotamus in 1991, no modem description of thedeposit has been attempted. An excavation was thereforeopened in June 1992 at the Battery (Fig. 1) with the aim ofexposing the 'bone-bed' and collecting material foranalysis.

Proceedings ofthe Geologists' Association, 106, 183-193. 0016-7878/95 $07·00 © 1995 Geologists' Association

184 D . R. BRIDGLAND ET AL.

C C~ "mud "'~someunrt and m..~l$

~saM.. andmote petJbty 00¥wnw3 f(l

b GrltVfl - Il. PlT'lAI,ng."., and CGaf'$(! t beds

e ! Ct w1k pvl 'et lay" ... lfl

Il"lIAcIC~

c2 s..U''oljlens

b 1 none l ragnent

FG1·2 Sa~tot CfaSlIllhoIogc.l1ana.,...

I

-...........

2965mO D

m III

,J

posinon can be seen on Fig. 2. The 16-32 mm and11.2-16 mm fractions were analysed by DRB & CPG,respectively. Lithological analyses of both fractionswere undertaken; additionally, the angularitylroundnesscharacteristics of flint clasts in the 16-32 mm fraction weredetermined.

Fig. 2. Section of Pleistocene deposits at the Battery.

Lithologies

The lithological analyses revealed the dominant comp­onents of the gravel to be flint (20-40%) and Chalk(25-75%). The relative proportions of flint and Chalk arereversed between the two samples, with the lower sample(FG2) being the richer in flint. The Chalk component of thegravel is made up of pale grey and grey-brown fine-grainedlimestone, of the type that characterizes the Lower Chalk ofthe North Downs escarpment, together with homogeneouswhite chalk, presumably from the higher divisions of theChalk. It is possible that some clasts of pale grey or grey­brown limestone have been derived from harder bands inthe Gault , which would be difficult to distinguish fromdiscoloured chalk in clast analyses . Such harder calcareousmudstones were noted by Smart et al. (1966) in the Gault ofthe Folkestone area.

Calcareous fragments that are clearly neither Chalk norclastic rocks are counted as 'other limestones'. Theseinclude concretionary limestone, 'vein' (crystalline) calciteand very occasional sandy limestones, which probably

1.12-1.69 m

some conspicuous shelly lenses .Unit becomes more pebbly towardsthe base and passes into gravel atc. 1.69 m.

(I) Gravel composed mainly of Chalkand flint. Crudely stratified andwith sandy lenses 1.69-2.65 m

At 2.65 m weathered top of the Lower Greensand

3, COMPOSITION, PROVENANCE ANDDEPOSITIONAL ENVIRONMENT OF THE GRAVEL

Analyses were carried out on two separate size fractions ofclast s from the two gravel samples (FG I & FG2) whose

This stratigraphy is similar to that described by Mackie(1851 : 260) from foundation trenches dug for 'MrCraxford's House ', and by Smart et al. (1966) amending

a section recorded by De Rance (1868). Mackie notedthat the 'bone-bed' (gravel, unit I) was from 'I to 5 ft'(0.30-1.50 m) in thickness. This is succeeded by a marl 3 ft(1.0 m) thick, and by 'black earth containing bones of Canislupus and Sus scrofa with fragments of ancient pottery andiron arms ' up to 6 ft (1.8 m). Similar sections , although withslightly varying thicknesses for the units, were noted bySmart et al. (1966). The latter authors recorded their 'whiteloam with shells' (unit 2 of the present account) as being6 ft 4 in. (1.9 m) thick, overlying a gravel of 'angular flintwith mammal bones ' (unit 1 of the present account) onlyI ft 6 in. (0.45 m) thick.

The gravel of unit 1 is intermittently cemented with ironand is composed of rounded Chalk clasts up to 2 cm in longaxis , and flint, mainly angular, and of similar size, butwith a few larger flint clasts (up to 5 cm). The marl unit isgenerally sandy, with the sand comprising medium-gradequartz and subsidiary quantities of glauconite, probablyfrom the Lower Greensand. Both gravel and sand containsilicified fossil debris from Cretaceous sources. Mostnumerous are small rhynchonellid brachiopods, but solitarycorals (predominantly Trochocyathus harveyanus Edwards& Hairne , an Albian species), foraminifera (largelyFrondicularia cordai Reuss) , echinoderm debris and piecesof ammonite phragmocone are also present. In the marlthese fossils form a significant part of the coarse content ofthe deposit. It is possible that the poorly consolidated LowerGreensand in this area contributes no gravel-sized clasts tolater formations, and that these fossils represent the onlyrecognizable material from the Lower Greensand in thePleistocene sediments at the Battery.

Mackie (1851) provided a general section (fig. 2, p. 259)showing that the succession of marl and bone-bed can betraced for 175 ft (53.5 m) to the east of the Battery. Thesections are no longer visible because of vegetation and cliffstabilization works , but small pockets of marl, gravelly attheir base, can be seen intermittently along the cliff top eastof the 1992 section, demonstrating that Mackie's generalobservations are reliable.

LAST INTERGLACIAL DEPOSITS AT FOLKESTONE. KENT 185

* IA & 2A: Palaeogene pebbles from samples) & 2 respect ively, shown as

% total non-Palaeogene.

Table 1. Clast lithological analysis at the Battery, Folkestone ­16--32 nun (11.2-16.0 nun in italics)

(a) Angularity/roundness of flint (excluding whole nodulesand Palaeogene pebbles)

capping the highest parts of the North Downs in theFolkestone area (e.g. Prestwich, 1858; Wooldridge, 1927),and these may represent the source of the less well­developed beach pebbles in the gravel at the Battery.Palaeogene beach flints were also distinguished from theremainder of the flint in the 11.2-16 mm fraction.'

In addition to individual clasts, occasional fragments oftufa and iron-cemented gravel also occur, both probablyderived from earlier Pleistocene sources. The iron­cemented gravel contains fragments of shell, mostly

28.3]

6 10

2 2

3.5 5.80.7 2.5

IA* 2A*

0.8

238 531

1.7 0.24.2 1l.7

11.8 9.61.30.4

24.8 46.0

5.9 6.61.3

10.538.3

55.9 32.6

4.0

Sample 2

wellroundedrounded 2.1 2.5sub-rounded 4.2 4.1sub-angular 9.1 9.9angular 30.8 28.1very angular 53.9 55.4

Total count 143 121

(b) Lithologies of clasts

Sample 1

Flint, Palaeogene 3.1 3.0Flint, post-PalaeogeneFlint, nodular 8.7Flint, weatheredlbroken 21.6

Total flint 33.3 23.4

Chalk(may include 60.4 71.8

some cementstone)Otherlimestone 2.2Phosphatic nodules 1.3 1.4Sandstones (var. cement) 2.0 1.8Clay ironstone 0.2 0.1Hassocklwea. ragstone?Chert(not L. Gsd type) 0.6Tufafragments 0.4Bone fragments 0.6

Total count 450 719

[cemented gravel, oftenshelly. Not included intotal. Shown as %totalcountI [ 0.4

represent the ragstone facies of the Lower Greensand.Definite ragstone clasts are very rare in the gravel. how­ever, as is other Lower Greensand material. No Greensandchert was encountered, perhaps reflecting the paucity ofsuch material in the Lower Greensand of east Kent. Fourchert clasts from the 11.2- 16 mm fraction of sample FG Iare not of Greensand type ; these are probably pre­Cretaceous cherts reworked from pebble beds with theLower Greensand or other local strata. The sandstonecategory includes calcareous and ferruginously cementedrocks with rounded grains. characteristics that suggest aLower Greensand origin. although other possible sourcesexist, such as the poorly exposed Pliocene beds that cap theNorth Downs escarpment to the north of Folkestone.

Phosphatic nodules form an important minor componen tof the gravel, more common in the lower than the uppersample (Table I). These are probably derived from theGault, a supposition that is supported by the fact thatoccasional examples are fragmentary casts of ammonites.Some of the larger sandstone clasts also have a phosphaticmatrix , suggesting a similar source.

At the 16-32 mm size it was possible to adopt a morerefined classification of flint clasts than at the 11.2-16 mmsize. In the larger fraction, flint clasts were divided into anumber of categories, on the basis of provenance infor­mation provided by their surface characteri stics. Thusexamples retaining nodular cortex were class ified as'nodular flint' . Similarly, well-rounded pebbles (some sub­sequently broken) of the type that characterizes the 'LowerLondon Tertiaries' were counted as 'Palaeogene flint'.Clasts in which all surfaces were of breakage origin, orin which the only non-broken surfaces were weatheredor patinated beyond recognition, were classified as'weatheredlbroken flint' .

Rounded and sub-rounded beach pebbles were alsoencountered, particularly in sample FG2. These areseparable from the characteristic Palaeogene flints in thatthey have less well-developed chatter-marked pebblesurfaces. The form of these pebbles is suggestive of a post­Palaeogene marine origin. Most are rather weathered,precluding examination of surface details, and were thuscounted in the weathered category, but the best examples,all in sample FG2, were counted as post-Palaeogenebeach clasts. Studies of various Pleistocene marine depositshave revealed that flints in most Middle and UpperPleistocene beach gravels are relatively angular, oftenapproaching the generally angular and sub-angular charac­teristics found in the gravels of the larger rivers (see Fisher& Bridgland, 1986; Bridgland, in Preece, Scourse,Houghton , Knudsen & Penny, 1990). This may be areflection of the short-lived nature of beaches during thePleistocene, as a result of the frequent sea-level changesbrought about by climatic fluctuation . Sea-level was morestable, because climatic fluctuation was less marked, duringthe Pliocene and early Pleistocene, when more rounded flintgravels were formed (on presumably longer-lived beaches),such as the Westleton Beds of East Anglia. Pliocene(Lenham Beds) marine deposits have been recognized

186 D. R. BRIDGLAND ET AL.

Table 2. Comparison of Angularity/roundness data from Folkestone with those from other marine and fluviatile deposits

(a) All flints as % total flint (excluding unmodified nodules)

Locality Well rounded Rounded Sub-rounded Sub-angular Angular Very angular Total

Samples from FolkestoneFolkestone I 3.4 2.7 4.8 8.7 29.5 51.7 149Folkestone 2 5.3 4.6 3.8 9.2 26.2 5\.2 131

Samples from Pleistocene beach gravelsBembridge' 1 9.6 2\.0 30.5 24.6 11.4 2.9 509Bembridge" 2 4.6 11.7 30.0 35.9 13.6 4.3 582Brooks Farm'' 1 2.6 2.5 8.1 37.6 23.6 25.6 774Brooks Farm'' 2 1.7 5.9 18.7 45.3 2\.9 6.6 547Aldingboume 1 2.4 6.0 14.0 45.4 19.1 13.1 335

Parkb

Boxgrove" 1 \.9 5.8 23.0 29.9 21.0 18.0 618Boxgrove? 2 1.4 7.4 38.5 28.8 19.1 4.8 351Southwold'' 1 37.7 27.1 16.9 10.7 3.2 4.4 591

Samples from Pleistocene river gravels (river identified)Little Hayes I 9.6 4.9 1.7 22.5 29.3 3 \.9 (Crouch) 648Little Hayes 2 10.7 5.1 2.5 24.9 33.5 23.3 (Crouch) 570Barling" 1 6.1 2.5 1.2 38.4 26.1 25.7 (Thames-Medway) 245Barling" 2A 11.4 5.1 \.8 17.2 13.6 50.9 (Thames-Medway) 273Barling" 2B 10.7 6.5 2.1 3\.2 22.5 27.0 (Thames-Medway) 666Barling? 3 13.4 5.7 1.7 27.0 21.7 30.4 (Thames-Medway) 470Dammer Wick" 1 12.7 5.2 0.4 24.0 15.3 42.4 (Thames-Medway) 229Barvills Farm" 1 24.8 7.2 3.1 24.1 2\.2 19.6 (Thames) 638Tollesbury lA 13.0 3.3 2.2 39.4 26.3 15.8 (Blackwater) 670Shakespeare 2A 24.1 6.9 1.3 18.5 22.3 26.8 (Medway) 622Holland Havens lA 4.1 2.5 0.9 25.6 26.2 40.8 (Thames-Medway) 321Holland Havens IB 9.7 1.4 1.4 33.8 16.7 37.0 (Thames-Medway) 216Holland Havens 2 3.9 1.8 0.7 22.4 26.5 44.7 (Thames-Medway) 434Cooks Greens lA 3.1 \.5 1.9 44.7 29.6 19.2 (Thames-Medway) 521Cooks Greens IB 4.8 3.2 1.7 41.9 29.8 18.6 (Thames-Medway) 413Cooks Greens 2 I\.6 3.1 \.2 41.3 28.4 14.4 (Thames-Medway) 327

Samples from soliflucted gravelsGt Fanton Hallh 1 21.3 9.2 2.3 23.8 23.3 20.2 798Skinners Wick 1 12.8 6.2 5.1 15.3 60.6 274

unidentified, but those which could be determined were ofspecies, such as Trichia hispida (Linne), represented in themolluscan assemblage recovered from the deposits at theBattery and thus are conceivably of similar age.

Pebble angularity/roundness, 16-32 mm fraction

It was hoped that an analysis of angularity/roundness of theflint in the 16-32 mm size range would provide informationabout the environment of deposition of the gravel. Asubstantial database of comparable analyses of Pleistocenegravels, of this same size fraction, is now in existence, aselection of which is provided in Table 2. The analysis isbased on that (for sand grains) proposed by Powers (1953)

and modified by Schneiderhohn (1954; in Prior, 1971), butadapted for flint clasts in the 16-32 mm size range. The sizecategories recognized by Schneiderhohn have beenredefined for application to flint clasts (Fisher & Bridgland,1986; Table 3) and a type collection has been assembled toprovide a standard for comparison. For the interpretation ofthe results of these analyses it has been found that somecategories are more meaningful than others. The 'veryangular' category, comprising freshly fractured flint, is ofextremely variable frequency. Post-depositional frostshattering has sometimes produced considerable amounts ofvery angular flint, particularly in the upper levels ofdeposits, within what would have been the permafrostactive-layer during periods of periglaciation. For this reasonit is often advantageous to disregard the very angular class

LAST INTERGLACIAL DEPOSITS AT FOLKESTONE, KENT 187

Table 2. Continued

(b) Angularity/roundness of flint (as % fresh & broken reworked, very angular excluded; reworked unbroken beach pebbles, whereseparable, are shown in the right-hand part of the table, as % of total broken)

Fresh & broken reworked Unbroken reworked

Well Sub- Sub- Well Sub- Sub-Locality rounded Rounded rounded angular Angular rounded Rounded rounded angular Nodular

Samples from FolkestoneFolkestone I 4.6 9.1 19.7 66.7 7.6 1.5 1.5Folkestone 2 5.6 9.3 22.2 63.0 13.0 5.6 3.7

Samples from Pleistocene beach gravelsBembridge' I 9.6 21.0 30.4 24.5 11.4 0.2Bembridge' 2 4.6 11.7 30.0 35.9 13.6Brooks Farm" 1 3.9 3.7 12.3 56.8 35.7 0.2Brooks Farmb 2 2.1 7.5 23.9 57.6 28.1 0.2Aldingbourne 1 3.3 8.1 19.2 62.0 26.1 0.4

Parkb

Boxgrove'' 1 1.9 5.8 23.1 30.0 21.1 0.3Boxgrove- 2 1.4 7.4 38.5 28.8 19.1 1.7Southwold, 1 39.5 28.3 17.7 11.2 3.4

Samples from Pleistocene river gravelsLittle Hayes 1 0.9 43.1 56.1 18.3 9.4 2.4 0.3Little Hayes 2 0.9 42.6 57.4 18.3 8.7 3.3Barling" I 1.3 58.8 40.0 9.4 3.8 0.6Barling" 2A 2.3 54.7 43.0 36.1 16.3 3.5 1.2Barling" 2B 0.3 2.7 56.4 40.7 19.2 11.4 1.1 1.1Barling" 3 2.1 54.3 43.6 26.9 11.5 1.3Dammer Wick" 1 1.1 60.4 38.5 14.3 13.2Barvills Farm' 1 4.3 51.0 44.7 52.3 15.2 2.3 1.3Tollesbury lA 2.0 58.8 39.2 19.4 4.9 1.3 0.7Shakespeare 2A 1.2 44.8 54.1 58.4 16.7 2.0 2.0Holland Havens lA 0.6 49.1 50.3 7.8 4.8 1.2Holland Haveng lA 1.8 65.8 32.4 18.9 2.7 0.9Holland Havens 2 45.8 54.3 8.0 3.8 1.4 1.9Cooks Greens lA 1.5 59.3 39.2 4.1 2.0 1.0 0.3Cooks Greens IB 0.3 2.0 57.1 40.6 6.6 4.0 0.3 0.3Cooks Greens 2 0.9 58.5 40.6 16.6 4.4 0.9 0.4

Samples from solitlucted gravelsGt Fanton Hallh 1 0.8 50.1 49.1 44.9 19.3 4.0Skinners Wick 1 25.0 75.0 62.5 30.4

a Bembridge Raised Beach(Preeceet al.• 1990)b Aldingbourne Raised Beach,WestSussexC Boxgrove RaisedBeach(Roberts, 1986)d Westleton Beds(Lower Pleistocene)e Post-diversion Thames-Medwayf Post-diversion Thames (LowerThames)g Pre-diversion Thames-Medway

and recalculate the remainder of the data with this excluded of angularity/roundness classes. This is typically the case in(Table 2b). fluvial gravels in southeast England, since these contain,

In some analyses two populations of flint clasts can be in addition to fresh flint that has been shaped by riverrecognized, indicated by a bimodal frequency distribution transport, abundant reworked rounded pebbles from marine

188 D . R. BRIDGLAND ET AL.

Table 3. Verbal descriptions of roundness/angularity classes,modified from Schneiderhiihn (1954 , in Prior, 1971), redefinedby Fisher & Bridgland (1986)

Class

l. Well rounded

2. Rounded

3. Sub-rounded

4. Sub-angular

5. Angular

6. Very angular

Definition

No flat faces, comers or re-entrantsdiscernible; a uniform convex clastoutline.

flat faces nearly absent, with comers allgently rounded . Small re-entrantsabsent and large re-entranls onlysuggested.

Poorly developed flat faces with comerswell rounded . Few small and gentlyrounded re-entrants ; large re-entrantswealcly defined .

Strongly developed flat faces withincipient rounding of comers. Smallre-entrants only suggested.

Strongly developed faces with sharpcomers. Sharply defined, largere-entrants with numerous smallre-entrants.

As 5, but comers and edges very sharp,with no discernible blunting . [Thisclass was added to the visual chartsby Powers (1953), although only forsand grains . For pebbles it may bereserved for frost-fractured and otherfreshly broken clasts.]

acteristic and are often rather weathered, it has not beenpossible to separate these from the remainder of the gravel ;thus the rounded and sub-rounded classes shown in Table2b include these presumably reworked pebbles.

Over 50% of the flint in both Folkesrone samples is veryangular; i.e. it is freshly broken and retains edges sharpenough to cut and scrape materials such as wood . Suchhigh proportions of freshly broken flint have only beenencountered previously in fluviatile gravels from near­surface situations (Barling 2A [from the top of the gravel ofa ThameslMedway terrace, near Southend, Essex(Bridgland, 1983)]; Table 13) or in solifluction gravels(sample from Skinners Wick, in the Crouch valley; Table2a). A solifluction origin for this very angular flint atFolkestone is certainly likely, but sorting in a small streamis perfectly possible, especially as there are significantnumbers of angular, in addition to very angular, clasts . Datafrom fluvial gravels show that sub-angular flint dominatesthe gravels of large rivers, especially in those parts of theircatchments downstream from the main sources of flint(Fisher & Bridgland, 1986), whereas the flint in the depositsof smaller rivers is more angular (compare the analy ses ofgravel s of the Thames and other smaller rivers in Tables 2a& b). The considerable dominance of angular flint in theFolkestone gravel s, as shown in Table 2b (very angularexcluded), is therefore suggestive of a small stream, aninterpretation that conforms with the palaeontologicalevidence.

4. PALAEONTOLOGY

Note: When confronted with clasts which show evidence of a poly.genetic morphological history, the most angular aspects, reflecting themost recent influence, should determine classification. A beach pebblewith unabraded frost-pitting should therefore be c1asssified as 'Veryangular' ,

Palaeogene beds. The presence of this reworked materialmarkedly affects the angularity/roundness data. Tominimize this effect, clasts are always categorized forroundness/angularity analysis according to the most recentdamage they have sustained; thus a small angular frost pit ina well-rounded reworked pebble results in its classificationas angular. This means that the results of the analyses reflectthe immediate origin of the gravel being examined, but notnecessarily the general appearance of the clasts. Reworkedrounded pebbles that are unbroken and have therefore notbeen modified during Pleistocene reworking are excludedfrom the analyses ; so too are whole, unbroken nodules offresh flint. The shape of these clasts owes nothing to thePleistocene depositional environment and would thusdistort the analysis if included (this point can be illustratedby a comparison of the data in Tables 2a and b). As wasdiscussed above , the gravel at Folkestone appears to containreworked beach pebbles of post-Palaeogene origin as wellas the well-rounded Palaeogene flints . As they are less char-

Samples were taken from the 1992 excavation formolluscan analysis. Below the level of the soil , six samplesrepresenting 0.20 m thicknesses of sediment and weighingc. 2-4 kg were taken . At depths below 1.25 rn, largersamples representing 0.25-0.35 m and weighing 6-8 kgwere taken. The final sample at 2.65 m represented thelowermost 0.10 m of the succession. The samples wereoven dried and washed through sieves to 500 urn apertureand sorted under a 1Q..-{iOx Kyowa binocular microscope.

Mollusca

All ten samples examined produced Mollusca. The faunarecovered is shown in Table 4 and Fig. 3. The bulk of thefauna is from open ground terrestrial and marsh habitats.The most numerous species represented is T. hispida(Linne), an inhabitat of open, poorly vegetated ground.Other species well represented are indicative of grassland[Cochlicopa lubrica (MUller), Vallonia spp. and Vertigopygmaea (Draparnaud)], and marsh [Lymnaea truncatula(MUller), Carychium minimum MUlier, Succinea putris(Linne), Oxyloma pfeifferi (Rossmassler), Vertigo angustiorJeffreys and Zonitoides nitidus (Mullerj], Shade-demandingspecies are few in number, although the ocurrence ofCarychium tridentatum (Risso), Discus rotundatus (MUller)and Clausiliidae, all elements of Kerney et al.'s (1980)'Terrestrial B' class, shows the presence of scrub or wood-

LAST INTERGLACIAL DEPOSITS AT FOLKESTONE, KENT 189

Table 4. Molluscan fauna at Folkestone Battery (1994)

Sample No. 2 3 4 5 6 7 8 9 10

Valvata piscinalis (MUller) 1Bithynia tentaculata (Linne) 1Lymnaea truncatula (MUller) 2 18 27 21 2 54 2Anisus leucostoma (MUller) 2Planorbidae undet. 2Sphaerium lacustre (MUller)Pisidium casertanum (Poli) 2Pisidium henslowanum(Sheppard) 2Pisidium sp. 2Carychiumminimum MUller 3 2 2Carychium tridentatum (Risso) 3 1Carychium sp. 1 3Succineaputris (Linne) 4 11 6Oxylomapfeifferi (Rossmassler) 5 10 2 1Succinidae undet. 14Azeca goodalli (Ferussac)Cochlicopa lubrica (MUller) 3 41 14 2 12 2Cochlicopa lubricella (Porro) 1Cochlicopa sp. 12 4 29 2Columella sp.Truncatellina sp. 1Venigo antivertigo (Drapamaud) 1 1Vertigo pygmaea (Drapamaud) 4 4 10 6vertigo alpestris Alder 1vertigo angustior Jeffreys 1 3 1Venigo sp. 1 4 6 6 2Pupilla muscorum (Linne) 3 2 4 7 11 1Vallonia costata (MUller) 1 4 2 1 3Vallonia pulchella (MUller) 6 5 25 5 2 17 3Vallonia enniensis (Gredler) 3 8 1 5Vallonia excentrica Sterki 1 6 6 5 2Vallonia sp. 2 10 40 21 12 3 45 8Acanthinula aculeata (MUller) 1Punctum pygmaeum (Drapamaud) 8 13 10 2 4 18 5Discus rotundatus (MUller) 1 1 4 2 1 11 3Vitrina pellucida (MUller) 3 1 6 1 5 1Vitrea crystallina (MUller) 3Vitrea contracta (Westerlund) 1Vitrea sp. 1Nesovitrea hammonis (Strom) 4 3Aegopinellapura (Alder)Aegopinella sp. 5Zonitoides nitidus (MUller) 4 54 97 25Milax sp. 1 4 3 3 5 5 1Limax sp. 5 1 5 10 2 8 20 10 3Euconulusfulvus (MUller) 1 2 1 1 1Clausilia sp. 2Cemuella virgata (da Costa) 21 31 49 5Helicella itala (Linne) 9 1 15 1 1Trichiahispida (Linne) 55 347 1040 608 87 41 872 129 43Cepaea sp. 1 2 1 9 2 1 8 3

Total 86 430 1325 776 145 72 1313 265 64 6

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D,H. Keen. 1993

Fig. 3. Percentage molluscan diagram (ecological classes 'Terrestrial A and Terrestrial B' after Kerney, Preece & Turner (1980).

LAST INTERGLACIAL DEPOSITS AT FOLKESTONE, KENT 191

land near the site of deposition. Aquatic elements are attheir most numerous in the lowest sample (8) with a signifi­cant mollu scan count, although small numbers of bivalvesoccur at all levels in the succession suggesting the presenceof small pool s or seepages of water. Sample 8 contains fouraquatic taxa indicative of water bodies larger than smallponds. Valvata piscinalis (MUller), Bithynia tentaculata(Linne) and Pisidium henslowanum (Sheppard) in particularare normally inhabitats of streams or at least large ponds. Itis unlikel y that the Battery was the site of such a large waterbody, but the existence of Hippopotamus (see below) nearthe site, suggests at least a moderate-sized stream in the nearvicinity. The aquatic molluscs could have been washed tothe site of the Battery excavation from this larger channel.The occurrence of B. tentaculata is also noted by Kennard& Woodward (1901) from the Battery, suggesting that otherparts of the sediment body may have represented wetterconditions than those indicated for the site described here.

All the species of Mollusca identified currently inhabitthe British Isles , except Vallonia enniensis (Gredler) whichis found in scattered localities from south Sweden toGermany (Kemey & Cameron, 1979) . Several taxa in theBattery sequence, however, have restricted distributions inBrita in at present. Venigo alpestris Alder is restricted toNorthern England and two sites in Wales, Venigo angustiorJeffreys to only a very few sites in east Anglia and inIreland. The two British species of Truncatellina have theirstronghold on the south coast from the Isle of Wight toTorbay [Truncatellina callicratis (Sccachi)], and at ascattering of sites, mostly in the east of Britain north to theMidland Valley in Scotland [Truncatellina cylindrica(Ferussacj ], All three of these species however, occurred inEast Kent in the Holocene (Kerney, 1976), and both speciesof Venigo were recorded at Folkestone in Holocene levelsby Kerney et al. (1980).

The single shell apex of a clausiliid gastropod insample 6 may represent a second non-British species. Theidentification of Clausiliidae in the absence of the shellaperture is very difficult, and the specimen in Sample 6lacks the aperture and the lowest two whorls. However, theremaining part of the shell is wider than that of the commonBritish clau silid Clausilia bidentata (Strom) and also has amore pronounced sculpture. It is possible that this shell is afragment of Macrogastra sp., most of the species of whichare restricted to Central Europe at present, or of Clausiliapumila Pfeiffer, which has a distribution in easternGermany, Sweden and Poland today. Alternatively the shellapex could belong to the rare British species Macrogastrarolphii (Turton) which still occurs in Kent .

There is little change in the fauna through the deposit,with the same mix of species present throughout. althoughthis suggests little in the way of environmental changethrough time , the changing proportions of the various taxamay point towards some decrease in shaded habitats and anincrease in grassland. The slight decrease in D. rotundatusand in aquatic taxa above the basal samples may indicate adecrease in woodland cover or a diminution of water flowacros s the site. Increasing numbers of grassland taxa like

Pupilla muscorum (Linne), Vallonia pulchella (MUlier), andVallonia excentrica Sterki in the topmost samples may alsoindicate an opening out of the vegetation by the end of theperiod of deposition.

The number of species in the fauna (43), together with theoccurrence of certain indicator taxa, suggest fully temperateconditions for the deposition of the Battery sediments. Thetotal number of molluscan species is similar to those forsites in southern England described by Preece (1979, 1980)and dated to the Holocene before and around the ClimaticOptimum. The smaller numbers of shade-dwelling speciesat Folkestone may suggest a more open local habitat thanthose described by Preece. Individual species in the Batteryassemblage are distinctly southern in their current ranges.Several species (c. tridentatum, C. minimum, T. hispida) arerestricted in their distribution in Scandanavia, only reachingcentral Sweden today (Kerney & Cameron, 1979). Othertaxa such as Venigo antivertigo (Draparnaud), Yertigoangustior Jeffreys, Acanthinula aculeata (MUller) andD. rotundatus only occur as far north as southernScandanavia. There is little hint of continentality in theevidence from the Mollusca, with only V. ennien sis havingthe major part of its range in eastern Europe at present. Asnoted above almost all the species recorded live in Britainnow and there is no exotic element suggesting a particularage for the fauna.

Mammalia

The occurrence of the bones of large mammals in Mackie's'bone-bed' first drew the attention of geologists to theBattery area in the last century. In the current investigationfragments of bone were most numerous in the lowest threesamples (equating to Mackie's 'bone-bed') but consistedlargely of rolled indeterminate pieces. One larger piece is afragment of skull , perhaps of a bovid , and a single bovidtooth was also recovered. Mackie (1851 ), Falconer (1868)and Smart et al . (1966) listed the following species from theBattery:

[Current nomenclature in brackets where names havechanged]

Ursus sp.Hyaena spelaea [?Crocuta crocuta Erxleben]Elephas primigenius [Mammuthus primigenius

(Blumenbach)]Elephas antiquus [Palaeoloxodon antiquus (Falconer &

Cautley)]Equus sp.Rhinoceros tichorhinus [Coelodonta antiquitatis

(Blumenbach)]Rhinoceros hemitoechus [Dicerorhinus hemitoechus

(Falconer)]Bos primigenius BojanusBison priscus BojanusRangifer tarandus (Linne)Cervus elaphus (Linne)

192 D. R. BRIDGLAND ET AL.

5. DATING

Thirteen specimens of T. hispida were submitted to theAmino-acid Geochronology Laboratory, University College

Table 5. D:L amino acid ratios(ABER-1204 Folkestone marlTrichia hispida)

Megaceros hibernicus [Megaloceros giganteusBlumenbach]

Sus sp.Hippopotamus major [Hippopotamus amphibius Linne]

Most of this material is now lost, although FolkestoneMuseum possess a number of Hippopotamus bones andteeth, Bos hom cores and other bones, and antler fragmentsof both C. elaphus and M. giganteus. The fauna listed aboveis somewhat mixed ecologically. Species characteristicof cold stages, such as R. tarandus, C. antiquitatis andM. primigenius, are at odds climatically with temperate­climate taxa such as Hippopotamus, D. hemitoechus andP. antiquus. In view of the amount of material ofHippopotamus in the catalogue of Folkestone Museum,which includes a ramus and femur as well as teeth, it seemsprobable that in situ mammalian material relating to atemperate climate is present at the Battery. A temperate­climate mammal fauna is also consistent with the climaticindications of the molluscan fauna. The cold- climate faunalremains may represent either derivation from earlierdeposits, or the presence on the West Cliff of later cold­climate sediments.

of Wales, Aberystwyth for analysis (Table 5). The meanratio of 0.124 fits very well with the ratio to be expected forthe Last Interglacial, Oxygen Isotope Substage 5e, (Bowen,Hughes, Sykes & Miller, 1989). The occurrence ofHippopotamus in the Folkestone deposits also indicates a 5eage as this species is particularly characteristic of depositsassociated with this temperate episode (Stuart, 1976).

ACKNOWLEDGEMENTS

6. DISCUSSION

The deposits at Folkestone Battery were laid down undertemperate climatic conditions during the Last Interglacial.The composition and (flint) clast shapes of the gravel at theBattery indicates deposition by a small stream flowing fromthe North Downs escarpment to the north, possibly rising insprings at the Gault/Chalk junction in scarp-face hollowssuch as Holywell Coombe (Kerney et al. 1980; Preece,1991,1992). Most of the gravel has probably come, perhapsoriginally through solifluction, from the escarpment (Chalkand flint), from the underlying Gault and, possibly, fromthe overlying Neogene sediments. The Lower Greensandhas supplied a surprisingly small proportion of the gravel,considering that it forms the bedrock at the Battery. Therare clasts of tufa probably come from occurrences ofinterglacial tufa that may have formed in scarp-facecoombes. These would have been comparable to theHolocene tufas of Holywell Coombe described by Kerneyet al. (1980) and Preece (1991, 1992).

The molluscan fauna is indicative of temperateconditions, although the slight reduction in shade­demanding molluscs and increase in open-ground speciesmay indicate that the bulk of deposition was accomplishedduring the latter part of the interglacial. Although themammalian fauna includes material from cold-climatedeposits, the majority of the most intact bones and teeth areof temperate mammals, thus indicating deposition undertemperate conditions.

The 0 : L amino-acid ratios and the ocurrence of num­erous fossils of Hippopotamus leave little doubt that theFolkestone deposits were laid down in Oxygen IsotopeSubstage 5e.

The authors are grateful to Mr and Mrs P. Fox of the Battery,Folkestone for permission to excavate on their land. Theexcavations on the site were assisted by Mr E. Green. Thefigures were drawn by Ms R. A. Gaskell (CoventryUniversity). Fieldwork at Folkestone by D. R. Bridglandwas supported by a grant from the G. W. Young Fund ofthe Geologists' Association. Comments by the referees, DrR. C. Preece and Dr J. E. Robinson, improved the final draftof the typescript.

Ratio

0.1440.1150.1100.1330.1190.1180.1220.1230.1380.1060.1210.1380.131

0.1240.012

13

Sample No.

AHBHCHDHEHGHHHIHJHKHLHMHNH

MeanSD

N

LAST INTERGLACIAL DEPOSITS AT FOLKESTONE, KENT

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Received 10 May 1994; revised typescript accepted 28 June 1994