MOLLUSCAN BIOSTRATIGRAPHY OF FLANDRIAN SLOPE DEPOSITS
IN EAST SUSSEX.
By
CAROLINE SARAH ELLIS B.Sc.
A thesis submitted for the degree of Doctor of Philosophy of the University of London and for the Diploma of membership
of the Imperial College.
1985 Department of Geology,
Royal School of Mines,
Imperial College of Science
and Technology,
LONDON SW7 2BP. ABSTRACT
Until recently Quaternary Scientists have concentrated almost exclusively upon the botanical evidence, especially pollen, for both palaeoenvironmental and chronological interpretation. However, highly oxidized calcareous sediments such as chalk slope deposits do not preserve pollen well, but do contain abundant fossil
Mollusca. Since the pioneering work of Sparks (1961, 1964), Kerney
(1963) and Kerney et al (1964) molluscs have been increasingly used as valuable environmental indicators. More recently, a series of molluscan biozones spanning the Late-glacial and Postglacial
(Flandrian) periods has been established from work in Kent (Kerney
1977; Kerney et al 1980), and these have allowed sites to be correlated biostratigraphically.
The molluscan biostratigraphy of sixteen sequences of mainly
Flandrian slope deposits from six sites in East Sussex has been studied, and these are described in detail. The results are presented in the form of percentage frequency histograms allowing easy comparison between sequences and sites.
The slope deposits consist of a tripartite sequence of sediments. Poorly stratified Late-glacial chalk silts and rubbles are overlain by a forest soil which in turn has been buried by several metres of colluvium. The Late-glacial deposits are interpreted as having formed by a combination of fluvial and mass movement processes, and between them and the earliest Postglacial deposits there is a hiatus of several thousand years. The in situ
soil formed under stable woodland which covered the valley sides
and floors and represents the earliest Postglacial sediment found
in the valleys. Lastly woodland clearance by man for agriculture
and settlement caused an acceleration of soil erosion, creating
colluvium.
Analysis of these slope deposits has shown that the molluscan
biozones can be recognised on the South Downs and so can be used to
correlate sites both within Sussex and elsewhere in southern
England. These studies have elucidated the anthropogenic biozones e
and f, especially the order of arrival into the area of the
accidentally introduced molluscan species (Monacha cartusiana,
Helix aspersa, Cernuella virgata, Candidula gigaxii, Candidula
intersecta and Monacha cantiana). A general molluscan succession
has also been established for the eastern end of the South Downs,
relating the changes in the molluscan assemblages to alterations in
vegetation and land use. Radiocarbon dates from the buried soils and basal colluvium have been obtained from four sites, indicating
that forest clearance began in some areas in the Neolithic period and in others as late as the Iron Age. These dates have added
significantly to existing information about the onset and duration of the molluscan biozones. Ii
ACKNOWLEDGEMENTS
Firstly I should like to thank my supervisor Dr. Michael
Kerney for his support, encouragement and helpful discussion throughout this project for without him this work could never have been undertaken.
I am also grateful to all the many friends and colleagues who have helped me with fieldwork and by making helpful comments during writing up. These include my mother, Mr. M. Wingman, Mr. S. Salmon and Dr. M. Bell. I would especially like to thank Mr. D. Gordon for his helpful advice and to also acknowledge the joint work described in Chapter 16. Also I would like to thank Dr. R. B. G. Williams for arranging and helping with the excavations at the Devil's Dyke and for organising the transportation of the samples.
Specialist opinions were sought from the following sources:—
Dr. J. Boardman, Earth Sciences, Brighton Polytechnic (Palaeosols);
Mr. A. Currant, British Museum Natural History (Bones); Miss R.
Gale, Royal Botanical Gardens, Kew (Charcoal); Mr. D. Gordon,
Geography Department, Bristol (S.E.M.); Dr. D. Holyoak, Geography
Department, Nottingham (Seeds); Mr. I. Kinnes, British Museum
(Pottery); Dr. H. Rendell, Geography Department, Sussex
(Thermoluminescence); Dr. C. Turner, Botany School, Cambridge
(Pollen).
Advice and technical assistance was kindly given by Mr. N.
Morton, Photography Department, Imperial College and from Mr. I. i v
Watts, Cartography Department, Sussex.
The radiocarbon assays were kindly provided by Mr. R.
Burleigh at the British Museum Research Laboratory.
Thanks must also be given to the people and Institutions that gave permission for access to the sites. To Brighton Corporation for allowing excavations in the floor of the Devil's Dyke and to
Mr. Lee for giving access across his fields. Also to Blue Circle
Cement Company who allowed excavations at Asham and to Mr. Newby and Mr. Gascoigne for access at South Heighton and Exceat respectively.
Finally I should like to thank the Geology Department at
Imperial College for the use of facilities and to N.E.R.C. for providing a research studentship. I would also like to acknowledge the money provided by the Fourth International Flint Symposium for the excavations at the Devil's Dyke. CONTENTS
Page No.
ABSTRACT
ACKNOWLEDGEMENTS
Contents
List of Figures ix
List of Tables
CHAPTER 1: INTRODUCTION 1
CHAPTER 2: ENVIRONMENTAL HISTORY OF THE SOUTH DOWNS 7
i) Geology and Geomorphology 7
ii) Soils 11
iii) Palaeobotany 15
iv) Fossil Molluscan Work 22
v) Archaeology of Sussex 30
vi) Present day Conditions 33
CHAPTER 3: GEOMORPHOLOGICAL PROCESSES RESPONSIBLE FOR
SLOPE PROCESSES 36
i) Introduction 36
ii) Late—glacial Deposits 37
iii) Postglacial Deposits 40
v i
Page. No.
CHAPTER 4: METHODS 48
i) Fieldwork 48
ii) Laboratory Work 50
iii) Data Presentation 57
CHAPTER 5: INTERPRETATION OF THE FOSSIL ASSEMBLAGES 61
i) Introduction 61
ii) History of the Technique 61
iii) Recent Advances 66
iv) Biozones 68
v) Taphonomy 72
CHAPTER 6: NOTES ON CERTAIN MOLLUSCAN SPECIES 78
i) Biozones y and z 78
ii) Early Postglacial Biozones a-c 78
iii) Biozone d 79
iv) Biozones e and f 81
CHAPTER 7: DEVIL'S DYKE 85
i) Introduction 85
ii) Pit 1 89
iii) Pit 2 94
iv) Pit 3 95
v) Pit 4 97
vi) Pit 5 100
vii) Other Remains 104
viii) Dating 104
vi i
Page No.
ix) Discussion and Conclusions 106
CHAPTER 8: ASHAM QUARRY 109
i) Introduction 109
ii) South Section 111
iii) North Section 120
iv) Discussion and Conclusions 131
CHAPTER 9: SOUTH HEIGHTON 135
i) Introduction 135
ii) Stratigraphy 135
iii) Mollusca 137
iv) Interpretation 140
v) Other Remains 140
vi) Dating 140
vii) Discussion and Conclusions 141
CHAPTER 10: HOPE GAP 143
i) Introduction 143
ii) Stratigraphy 143 .
iii) Mollusca 144
iv) Discussion and Conclusions 147
CHAPTER 11: EXCEAT 149
i) Introduction 149
ii) Formation of Strip Lynchets 149
iii) Exceat 1 150 viii
Page No.
iv) Exceat 2 156
v) Discussion and Conclusions 159
CHAPTER 12: COW GAP 162
i) Introduction 162
ii) Central Infill Section 165
iii) Interfluve Deposits. 175
iv) Discussion and Conclusions 178
CHAPTER 13: ARION GRANULES 182
CHAPTER 14: DATING OF THE DEPOSITS 186
CHAPTER 15: NOTES ON POMATIAS ELEGANS 194
CHAPTER 16: OPTIMUM SAMPLE SIZE 202
CHAPTER 17: DISCUSSION AND GENERAL CONCLUSIONS 213
REFERENCES 224
APPENDIX 259 ix
LIST OF FIGURES
Fig. No. Page No.
1. Dry Valley System in Sussex. 8
2. Fossil Mollusc and Pollen Sites in Sussex. 17
3. S.E.M. Photographs of the Helicellids. 55
4. Idealised Diagram of the Molluscan Biozones. 70
5. Taphonomic Processes. 74
6. Long Profile of the Devil's Dyke.
7. Sketch Diagram of Pit 1. 90
8. Molluscan Histogram of Pit 1. 92
9. Sketch Diagram and Molluscan Histogram of Pit 3. 96
10. Sketch Diagram and Molluscan Histogram of Pit 4. 99
11. Sketch Diagram of Pit 5. 101
12. Molluscan Histogram of Pit 5. 103 Fig. No Page No.
13. Molluscan Histogram Redrawn from Williams 1971. 110
14. Sketch Diagram of Asham, South Section. 112
15. Molluscan Histogram South Section, Column A. 116
16. Molluscan Histogram South Section, Column B. 119
17. Sketch Diagram of Asham, North Section. 121
18. Molluscan Histogram North Section, Column C. 124
19. Molluscan Histogram North Section, Column D. 128
20. Sketch Diagram of South Heighton. 136
21. Molluscan Histogram of South Heighton. 138
22. Sketch Diagram and Molluscan Histogram of Hope
Gap. 145
23. Section Through a Lynchet. 151
24. Sketch Diagram of Exceat 1. 153
25. Molluscan Histogram of Exceat 1. 155 xi
Fig. No. Page No.
26. Sketch Diagram of Exceat 2. 157
27. Molluscan Histogram of Exceat 2. 160
28. Molluscan Histogram of Cow Gap taken from Kerney. 163
29. Sketch Diagram of Cow Gap, Central Infill Section. 169
30. Location of Pottery from Bell 1981a. 170
31. Molluscan Histogram of Cow Gap, Central Inf ill
Section. 171
32. Stratigraphy and Molluscan Histogram of Cow Gap,
Interfluve Section. 177
33. Histogram of Shells and Anon Granules from Cow
Gap, Central Infill Section. 184
34. Distribution of Pomatias elegans in the British
Isles taken from Kerney 1976a. 196
35. Distribution of the Sizes of Pomatias elegans
at Asham. 199
36. Distribution of the Sizes of Pomatias elegans at
Cow Gap. 200 xii
Fig. No. Page No.
37. Number of shells vs. sample weight 204.
38. Number of species vs. sample weight. 205
39. Cumulative number of species vs. sample weight. 207
40. Sample weight vs. percent error. 209
41. Molluscan histogram of the different sample
weights. 212
42. Succession on the Chalk on the South Downs. 221 LIST OF TABLES
A. Characteristics of valley inf ill deposits.
APPENDIX I
1. Devil's Dyke, Pit 1
2. Devil's Dyke, Pit 2
3. Devil's Dyke, Pit 3
4. Devil's Dyke, Pit 4
5. Devil's Dyke, Pit 5
6. Asham, Column A
7. Asham, Column B
8. Asham, Column C
9. Asham, Column D
10. South Heighton
11. Hope Gap
12. Exceat 1
13. Exceat 2
14. Cow Gap, Central Inf ill Section, Column C
15. Cow Gap, Central Inf ill Section, Column B
16. Cow Gap, Central Infill Section, Column A
17. Cow Gap, Interfluve Section
APPENDIX II
18. Shell and Anon Granules from Cow Gap
19. Radiocarbon Dates from Sussex x i v
20. Measurements of Mature Pomatias elegans from Asham, Column D
21. Measurements of Mature Pomatias elegans from Cow Gap
22. Summary of the Morphometric Data Available from Pomatias
elegans
23. Optimum Sample Size Results from Asham, Column A I. INTRODUCTION
The term Flandrian has been used for the most recent stage of the Quaternary Era, the 10,000 years since the end of the Devensian glacial stage. The stratotype of the Flandrian is in the plain of
Flanders (northern Belgium), where thick deposits representing the eustatic marine transgression are preserved. Our knowledge of the climatic and environmental changes of this period is based mainly on biostratigraphical investigations of terrestrial deposits. Work on Flandrian peat bogs and lake sediments began at least as early as 1841, when Steenstrup described four periods in the Postglacial
(aspen, pine, oak and alder). Later Blytt introduced the terms boreal, atlantic, sub-boreal and sub-atlantic to explain the origins of various elements of the Scandinavian flora. Sernander went further, and used the same terms in a chronological sense, the well-known Blytt-Sernander scheme.
In Britain similar work on plant macrofossils was carried out in Scotland by Geikie in the late nineteenth century. He described the remains of trees preserved in a peat bog. Two layers of trees were present which he called the Lower and Upper Forestian, consisting of remains of silver birch and Scots pine respectively.
These were separated by peat composed of Sphagnum and Eriophorum and were in turn overlain by another layer of Sphagnum peat. These layers were termed the Lower and Upper Turbarian. Later Lewis and
Samuelsson were able to correlate Geikie's work with the
Blytt-Sernander scheme, the Lower Forestian being of late boreal age, the Lower Turbarian Atlantic, and the Upper Forestian 2
Sub-Boreal and Sub-Atlantic.
In terms of understanding the environmental changes during the Flandrian the greatest advance was made with the advent of pollen analysis, developed by Von Post and others (Mitchell 1984).
This technique enabled a regional pattern of vegetational changes to be established in contrast with the fairly local ones constructed from macroscopic plant evidence. From these early palynological studies it was evident that the Flandrian could be split into three main periods:- a period of increasing warmth, a period of maximum warmth, and a period of decreasing warmth. For these periods Von Post coined the terms protocratic, mediocratic and terminocratic, based on the appearance of warmth loving trees, their dominance and subsequent decline. These ideas of climatic and vegetational change were extended by Iversen to interglacial cycles generally, based on vegetational, climatic and edaphic changes.
More recently Turner and West (1968) made a four fold division of interglacial vegetation sequences (zones I-IV) and attempts have been made to apply these zones to Flandrian pollen diagrams
(Hibbert et al 1971; Hibbert and Switzur 1976). All these schemes for Flandrian zonation have recognised a thermal optimum around
5000 B.P. when the mean annual temperature in Britain was 2-3°C higher than today. The evidence is mainly biological and is based on the presence of animals and plants whose northern limits of distribution are today found south of Britain. An example is the
European pond tortoise, Emys orbicularis (Scharff 1907; Stuart
1979).
It has long been recognised that a much finer subdivision of 3
the Flandrian could be made using pollen zones (Godwin 1956). Eight zones were formulated for England, zones I to III covering the
Late-glacial and IV to VIII the Postglacial. The Postglacial zones are approximately equivalent to zones I to III of the interglacial sequence of Turner and West (1968).
Pollen zones are assemblages of particular pollen types that reflect broad regional changes, and are best recognised in diagrams where local effects are minimised, for example from a core from the centre of a large lake basin where local pollen will have been filtered out. A fine zonation of the Flandrian has allowed the effect of man on the vegetation to be included, in addition to the vegetational changes in response to climatic and edaphic alterations - for example, the widespread deforestation begining at the Atlantic/Sub-Boreal transition (zones VIIa/VIIb), local afforestation in zone VIII, and the introduction of alien tree species.
Today the use of pollen in a chronological role (except in interglacials) has been largely superseded by radiocarbon dating, which allows correlation between deposits independent of biostratigraphy. There has also been a trend towards redefining the
Blytt-Sernander periods in absolute radiocarbon years, that is as formal chronozones (Mangerud et al 1974). West (1970) is of the opinion that absolute time zones based on radiocarbon dates will eventually replace the biostratigraphical pollen assemblage zones for the Flandrian.
Other biological remains have also been used in addition to 4
pollen to reconstruct the environmental history of the Flandrian,
as, for example, insects, plant macrofossils, ostracods,
vertebrates and molluscs. Not all of these are found in the same
sediments, acidic waterlogged conditions favouring macroscopic
plant remains, insects and pollen, whereas calcareous environments
preserve molluscs, ostracods, phytoliths and vertebrates. For
various reasons it is not always easy to reconcile the information
from different sources, as has been shown by Dimbleby and Evans
(1974) in their work on pollen and molluscs from calcareous
sediments.
Mollusca are useful tools for environmental reconstruction as
they are usually present in sediments where pollen is absent. They have been recorded from a wide range of deposits including
fluviatile deposits (Preece and Robinson 1982; Holyoak and Seddon
1984), lacustrine sediments (Sparks 1962), silted kettle holes
(Keen et al 1984), tufa (Preece 1978), cave deposits (Evans and
Jones 1973; Kerney 1976a; Ellis 1983b), loess (Kerney 1963, 1971), blown sand (Kennard and Warren 1903; Spencer 1975), slope-washes
(Kerney et al 1964; Lozek 1977; Bell 1981a) and soils (Evans 1972).
Flandrian palaeoecology is simplified as almost all the species are living today, so that detailed knowledge of their ecology is often available (Boycott 1934, 1936; Kerney and Cameron
1979). Mollusca are particularly valuable palaeoenvironmental indicators as -
1. They are common in calcareous sediments.
2. The extraction technique is fairly easy and small shell fragments are usually identifiable to the species level. 5
3. There is a manageable number of species.
4. Their ecological requirements and distribution are sufficiently well known to allow reliable interpretation of fossil communities.
5. They are valuable indicators of local environments and regional climates.
The Flandrian slope deposits of East Sussex are well suited for molluscan biostratigraphy because of the availability of suitable sections and the richness of the molluscan faunas preserved. This area of the South Downs was densely settled by man during the Flandrian making a detailed study of the environment especially interesting, tracing man's increasing influence and ability to initiate changes. The area has not been glaciated, or covered by sandy drift or extensive clay with flints. The soils are therefore mostly calcareous, unlike those, for example, on the dip slope of the Chilterns or in the East Anglian Breckland.
Furthermore sediments rich in Mollusca were known to occur in the area (Kennard unpub. M.S.; Williams 1971; Bell 1981a). Finally the area provided an opportunity to test the applicability of the molluscan biozones established in Kent (Kerney 1977; Kerney et al
1980) and elsewhere in southern England.
Dry valleys and lynchet deposits were selected as the most suitable type of slope deposits as they have long been recognised as a potentially important source of palaeoenvironmental information because they contained stratified biological materials recording the environmental history of the landscape. The sediments can also be dated independently either by stratified artifacts or by radiocarbon as sufficient charcoal fragments usually occur 6
within the buried soils and basal colluvium. The sites were chosen to cover as wide a range of local environments as possible, including scarp and dip slope valleys, coastal and inland sites, and sites of varying aspect. This was to try and identify the purely local factors in the molluscan successions and to establish an overall regional pattern. 7
2. ENVIRONMENTAL HISTORY OF THE SOUTH DOWNS
j. Geology and geomorphology
The chalk outcrop of the South Downs stretches for 93km from the Hampshire border to Beachy Head, Sussex, where it reaches its maximum height of 165 metres. The Downs form an escarpment with a steep north facing slope and a more gentle dip slope grading into the coastal plain in the west and culminating in chalk cliffs to the east. From Brighton westwards there is a discontinuous secondary escarpment capped by Gonioteuthis zone chalk, in contrast with Micraster zone chalk that caps the main escarpment. The escarpment is breached in four places only by the Rivers Adur,
Arun, Ouse , and Cuckmere, which drain the weald to the north. They have excavated through several hundred metres of chalk and have been described literally as 'water gaps' to the sea (Jones 1981).
This discordant drainage pattern has long been a source of controversy. The standard explanation was put forward by Wooldridge and Linton (1939, 1955) as superimposition but more recently Jones
(1974) has proposed an antecedent drainage hypothesis.
The most notable landforms of the South Downs are the morphologically variable dry valley systems that dissect the scarp and dip slopes (see Figure 1). They are extremely variable in form, ranging from shallow, linear valleys to branching flat-bottomed systems, and from corrie-like hollows to incised ravines.
The origin of these chalk dry valleys is somewhat
9
problematical. The variety in form suggests that they have been produced by several or a combination of processes. There are two main schools of thought concerning their formation:—
1. That they developed during periglacial conditions as a result of solifluxion and fluvial erosion.
2. That they formed by fluvial processes alone during temperate periods — by spring sapping and overland flow when the water table was higher.
Clement Reid (1887) was the first to propose a periglacial origin for the chalkland dry valleys, suggesting that when the chalk substrate was frozen and hence impermeable overland flow resulted during the summer rains. Cold conditions have also been used to explain the corrie—like hollows that characterise the dip slope of the Downs in the Eastbourne area (Bull 1940). Bull suggested that these were nivation features resulting from snow patch cover whereas French (1976) interpreted them as forming from meltwater erosion from beneath snowdrifts.
It is now well established that periglacial processes substantially reshaped the South Downs landscape by large scale erosion. The amount of erosion involved has been estimated by
Kerney et al (1964) at the Devil's Kneading trough a scarp face dry valley on the North Downs in Kent, where at least 30% of the volume of the valley was removed by solifluxion during pollen zone III
(less than 500 years). The date and minimum amount of erosion was calculable as the material was redeposited by fluvial processes as a debris fan overlaying a zone II soil. This valley therefore appears to have been eroded late in the Devensian, but studies of 10
dry valley deposits elsewhere eg. at Folkestone, the Medway valley and at Cow Gap, Sussex (Kerney 1963) and at Pitstone,
Buckinghamshire (Evans 1966a), have shown that much of the erosion occurred earlier as the valleys contain long sequences of older deposits.
The second school of thought about dry valley formation is that the valleys were formed by fluvial processes during temperate periods by the processes of spring sapping and erosion by flowing water. This point of view has been advocated by Sparks and Lewis
(1957), Small (1962) and others. It is based on the hypothesis that in the past the water table was higher and water flowed in the valleys. Springs were more numerous and valleys were cut by sapping back along a joint in the bedrock or a similar line of weakness.
Evidence to support a temperate origin is that the valleys form a dendritic pattern that is a natural extension of the present day drainage system. Also at times ephemeral streams do flow in the lower parts of some of the dry valleys.
Both hypotheses can be used to explain diferences in valley form. Scarp face valleys tend to be steep—sided with a small valley bottom and often contain a spring in their lower parts. These are probably of a more recent origin than the dip slope valleys which are more shallow with less steep sides and in some cases contain longer sedimentary sequences.
The evidence from dry valleys substantiates neither one hypothesis nor the other and there is no reason why these two hypothesis should be mutually exclusive. Certainly periglacial 11
processes played a large part in the development of the valleys to
their present form but there may well have been re-excavation of
valleys already initiated in the earlier Quaternary or possibly
superimposed on Tertiary valleys. There is no evidence that the
valleys originated in the Postglacial since they almost invariably
contain Devensian periglacial sediments. Most dry valleys show a
complete lack of fluvial deposits or water molluscs with the
exception of some of the lower lying valleys which have been shown
to contain a central strip of water sorted gravel (Catt and Hodgson
1976). Many dry valleys do have periodic flow as a result of freak,
heavy rainstorms as for example the Lewes Winterbourne in Sussex.
It is possible that these low frequency- high magnitude events were more common in the past because the water table of the chalk has
been lowered substantially by pumping but it is inconceivable that
the flow was ever sufficient to cut a valley.
Soils
The soils of this area of Britain have recently been remapped
by McKae and Burnham (1975) using the soil classification of Avery
(1973). The soils found in the study are rendzinas on the steep and middle slopes, and calcareous brown earths on the lower slopes and
footslopes. In addition, on very small areas on the plateau,
palaeo-argillic brown earths have developed on clay-with-flints,
and podsols on areas of loess.
Rendzinas
These are shallow (not exceeding 40cm deep), highly 12
calcareous soils developed on calcareous parent materials on steep slopes.
Brown calcareous earths
These are deeper soils, often very stoney, with a high silt content that is usually loessic in origin. They develop from parent materials that have been removed from hillsides by periglacial solifluxion (head) and more recently by Postglacial hillwash
(colluvium). They are found on the lower slopes and footslopes.
Palaeo—argillic brown earths
These soils have been mapped on the South Downs by Hodgson et al (1967) and develop from clay—with—flints.
The predominance of thin rendzinas and calcareous brown earths is probably a reflection of interference by man on the vegetation cover. It is thought that if left undisturbed soils would have been much deeper, especially on the hillslopes which have now been stripped to bedrock by erosion.
There has been much debate over the effect of man on soil development and the nature of "undisturbed" soils. Iversen (1958) proposed a glacial/interglacial cycle defining periods of edaphic and vegetational development based not only on climatic change but also on the passage of time. He suggested that with time soil deterioration and acidification would occur and this has been used to explain the late immigration of acid tolerant species of trees 13
during the second half of interglacials. One might therefore expect
to find that buried soils that formed under forests of mid
Postglacial age would be podsolic, even on calcareous substrates.
This hypothesis has been supported by Valentine (1973) who showed
that in south Lincolnshire a podsol developed under mixed oak
forest during the Atlantic period and was subsequently buried by
the encroachment of fen peat. On the other hand Dimbleby's work at
the Mesolithic site at Iping Common (Keef et al 1965) and the
Neolithic site at Rackham (Holden and Bradley 1975; Dimbleby and
Bradley 1975), both on Greensand, has shown that in the early
Postglacial the soils that developed under forest were brown earths and that podsolisation occurred only after forest clearance. The
pollen diagrams from these sites show that prior to clearance the vegetation was dominated by a mixed oak forest assemblage but that after clearance a Calluna Heath (acid) vegetation developed. -
It seems that on the chalk in the South Downs local patches
of acidification were present in the earlier Postglacial.
Palaeoecological work at Itford Bottom (Bell 1983) and at the Vale of Brooks (Thorley 1981) has shown that pine grew locally on the chalk, and at Cow Gap the calcifuge mollusc Zonitoides excavatus
(extinct on the South Downs) occurred as part of a fossil woodland assemblage. Local patches of acidification still occur on the chalk
today, mainly to the east of the River Ouse. It has been suggested
that these small patches of chalk heath vegetation develop where
there is a thick cover of loess, obscuring the chalk bedrock. The
soil that develops from the chalk bedrock is sufficiently decalcified to support this type of vegetation. 14
Catt (1978) postulated that a cover of between one and four metres of loess was deposited in the early part of the Late
Devensian. Along the chalk cliffs in Sussex, as for example at Hope
Gap, sections of four to five metres of loess can be seen capping the interfluves. Some of this loess has become incorporated into the Postglacial soils. This has a highly ameliorating effect on the soils, creating a silty texture and hence a high porosity, making them well aerated and easy to work. In addition the incorporation of fresh bedrock containing easily weathered minerals into the soil greatly increases its fertility. But a high loess component in a soil also makes it highly susceptible to erosion as its structure is maintained by clay bridges and if completely waterlogged the structure is destoyed and it collapses. It is because of this property of loess that there is a complete lack of it over large areas of the Weald, as it would have been deposited on an impermeable clay substrate, resulting in saturation of the overlying loess and subsequent erosion.
Limbrey (1978) has suggested that soils with a high loessic component such as on the chalk slopes might have been preferentially selected for cultivation because of high fertility.
Clearance of the primary woodland for cultivation would have been done by the burning of small patches of woodland to create room for settlement and agriculture. Burning has a profound effect on soils as it removes the protective vegetation cover which increases the erodibility of the soil. This is further increased by the loss of the soil organic matter by burning which destroys the structure and the cohesion of the peds. Finally the new plant shoots attract animals, which trample and cause compaction, further reducing the 15
soil's infiltration capacity and increasing the amount of overland flow. Adams (1975) has obtained values of 190 mm/hr for infiltration rates of water into soil beneath ungrazed woodland, in contrast to 1 mm/hr beneath grazed oak woodland.
Palaeobotany
Vegetation type is related to the nature of the soil which in turn is dependent on the parent material. Throughout this study area the parent material is chalk, either as bedrock or modified by periglacial slope processes, but occasionally acidic chalk heaths have developed in areas where a residual covering of loess has removed the influence of the underlying chalk bedrock. Examples of acidic chalk heaths occur at Lullington Heath, Manor Farm Down,
Cocking and Bow Hill (Tansley 1939; Perrin 1956).
As a result of this dominance of basic soils, pollen is rarely preserved in this area, making palaeobotanical reconstruction of the South Downs difficult. This has led to dependence on-
1. Charcoal and seeds either from archaeological sites (for example
Bell 1977; Drewett 1982) or from organic-rich layers as for example those found during the present study (Ellis 1983a).
2. Pollen analysis from the valley peat bogs (Thorley 1971a, 1971b,
1981).
3. Pollen analysis from peripheral sites on the Greensand to the north (Keef et al 1965; Dimbleby and Bradley 1975; Keatinge 1983).
4. The evidence from fossil Mollusca (Bell 1981a, 1983; Thomas
1982; Ellis 1983a). 16
Charcoal has its limitations as it can usually only be identified to genus and is unquantifiable. Dimbleby and Evans
(1974) have shown that analyses of pollen and associated molluscs from basic soils at nine sites in southern England do not produce identical results. They suggest that the discrepancy arises because the pollen extracted from buried soils will represent only the last floral assemblage to grow on the surface (pollen is quickly oxidized in sediments of this type), whereas molluscs accumulate more slowly and survive for a much longer period.
The location of the palaeobotanical sites discussed in this section is shown in Figure 2.
Late—glacial vegetation
Work by Seagrief (1959) at Nursling, Hampshire and Seagrief and Godwin (1960), and Carpenter and Woodcock (1981) at Elstead,
Surrey has shown on the basis of pollen and macrofossil evidence that during pollen zone III the landscape was open, with herbaceous vegetation and scattered clumps of pine and birch. Scaife (1982) has argued that the way these diagrams were calculated has resulted in a serious over—estimation of the tree taxa. In his work on the
Isle of Wight Scaife (1982) has therefore calculated each species as a percentage of the total pollen sum. His work suggests that the vegetation of zone III was very much more open than previously thought and that the bulk of the pine and birch pollen results from long distance transport. The openness of this zone III vegetation suggests a very harsh climate, possibly cold enough to have FOSSIL MOLLUSCAN SITES
•Ecisi.griristecia.,
Horsham
iirujell I I Dyke .Lerzsi x sh-Ci-61 I x South Height() •Chichester Littlehampton •Brighton Exceat f• Eastbourne Hope G Xtow Gap X slope deposits studied / scarp slope
FOSSIL MOLLUSCAN SITES
.E0st.prinstead_
•Horsham
.Harting Beacon Borkhaleo .Offham Hill Bury Hill o x Harrow Hill Ashccrnbei --1.44,1 Trundleo x BlackPatch x xCissbury BottomL Beddingham i x Stoke Down Church Hill •Ittonl Bottom's/ o Combe Hill Whitehawk X flint mine •Chichester Altriston 4- / Littlehampton Bishopstone-. •Kiln Combe o Neolithic enclosure L4pw Gap + burial monument ircn Age hill fort L Late glacial deposits • dry valley deposits • lynchet
POLLEN SITES
• Ecst Gr.nstead
N,
!ping Common xPockham xKmbeHey Wild Arundel. Brooxs—"L
.Chichester cton •Eastbourne • pciier sites
C 5 IC 20km
Figure 2. Fossil Mollusc and Pollen Sites in Sussex. 18
destroyed the birch that occurred during pollen zone II.
Postglacial vegetation
Local work has been carried out by Thorley (1971a, 1971b,
1981) at the Vale of Brooks, Lewes (TO 416088) and at Amberley Wild
Brooks (TO 037145), and by Brooks (in Robinson and Williams 1983)
at Wellingham, Lewes (TO 428137). These sites are isolated valley
peats and alluvial sequences resulting from the Flandrian rise in
sea level. The peat at the Vale of Brooks developed from the
Mesolithic to the mid Bronze Age, whereas at Pevensey Level (Barnes
1974) it formed only during the Medieval period.
Sites further afield include the Wareham Basin, Dorset
(Haskins 1978), the Isle of Wight (Scaife 1980, 1982), Winchester,
Hampshire, and Okers and Rimsmoor, Dorset (Waton 1982). All these
studies have added information to the earlier works by Erdtman
(1928), Godwin (1940, 1962), Godwin and Godwin (1940), Seagrief
(1959, 1960) and Seagrief and Godwin (1960) on south-east England.
A general picture can be built up of the Postglacial
vegetation sucession on the South Downs. At the end of the
Late-glacial, the climate improved allowing the spread of temperate
plant species northwards into southern England. At that time there was no physical barrier as the Channel and the southern part of the
North Sea were still dry. One of the first temperate woody shrubs
to become established was juniper (Juniper communis) (Seagrief and
Godwin 1960). This was quickly superseded by birch (Betula
pubescens and B. pendula) and pine (Pious sylvestris). These were 19
joined at about 9000 B.P. by oak (Quercus robur and Q.petraea) and elm (Ulmus glabra) which gradually become the dominant flora but with local patches of pine persisting (Thorley 1971a). Later arrivals into the area were lime (Tilia cordata and T.platyphyllos)
(Moore 1977) and alder (Alnus glutinosa) which had become well established by the Postglacial thermal maximum at approximately
7000-7500 B.P. At this time the mean annual temperature was about
2.5°C higher than today (Godwin 1975) and the rainfall increased as a result of the marine transgression in the southern part of the
North Sea basin. This re-established the English Channel and prevented further immigration of species from the continental mainland.
The mid Postglacial woodland on the South Downs was a mixed oak forest of oak, elm, lime and alder. This is the climax community of the South Downs (a climax community is one that has reached stability under a particular set of environmental conditions (Ricklefs 1973)). The only possible refuges for the shade-intolerant species were sea cliffs, screes and riverbanks.
Rose (1973) has identified five areas in southern Britain as possible refuges, including the stretch of chalk cliffs from Beachy
Head to the Ouse in East Sussex and around the Arun Gap in West
Sussex. These are areas where the soils were unstable, hence favouring the persistance of the open-country species characteristic of the area prior to the Boreal period. Many of these relic species have reinvaded the chalk downlands after forest
clearance, as for example the box trees at Box Hill, Surrey (Pigott and Walters 1953), but others have been lost due to competition
from many of the weeds that have been introduced into Britain since 20
the Neolithic.
The mixed oak forest cover of the South Downs appears to have
persisted with little alteration until its removal by man for
settlement and agriculture. At the Vale of Brooks (Thorley 1981)
and at Iping Common (Keef et al 1965) small temporary clearances
were made as early as the Mesolithic. The evidence from Iping and
West Heath, both on the Greensand suggests that fire was used to
clear the woodland, restricting further forest growth and favouring
the gradual development of hazel and gorse thickets (Tebbut 1975).
The palaeobotanical study most relevant to this area is by
Thorley '(1971b, 1981) on the peat and alluvial sequences in the
Vale of Brooks. The site is almost entirely surrounded by chalk
downland and it can be assumed that the pollen spectra reflect
fairly accurately the local vegetation, with much - of the long
distance pollen filtered out by the surrounding hills. Peat
deposition began here in the Mesolithic, and with a slight
interuption continued on until the end of the Bronze Age. From a
dated layer of Mesolithic age (6290 T 167 b.p.; Birm -168) the
pollen indicates woodland with small patches of clearance, the
major clearance not occurring until the middle Bronze Age (3190 +
125 b.p. 1-4454).
Thorley (1971b) has also studied a peat bog near to Amberley
Wild Brooks which is slightly to the west of this study area. The
basal horizons of this peat have been dated to 2620 T-. 100 b.p.
Q-690, (Godwin and Willis 1964) and contained high arboreal pollen
counts. Above these layers occurred a dramatic expansion of grasses 21
and ruderals, followed by the return of birch. An interesting feature is that beech (Fagus sylvatica), a species typical of secondary woodland on the chalk today, is rare until very late in the pollen sequence, confirming that this tree was not an important element of the chalk vegetation until the Iron Age or later
(Pennington 1974).
Additional local work has been carried out by Brooks (In
Robinson and Williams 1983) at Wellingham peat bog, Lewes. His diagram shows a marked decline of elm and lime with a corresponding increase in ash. The dramatic rise in grass pollen suggests that the area was first utilised as pasture, but then this rise is quickly followed by an increase in pollen from arable weeds such as
Rumex and Artemesia spp.
All the palaeobotanical work suggests that the Downs had a mixed oak forest cover which was gradually removed by man.
Clearance probably began locally in the Mesolithic, becoming more widespread by the end of the Neolithic and the beginning of the
Bronze Age. It is unlikely that any primeval woodland has survived on the downs; many of the oldest woodland areas contain remnants of
"Celtic" field systems (Bell 1981a).
Most of the Downs appear to have been cleared of their woodland cover by the late Bronze Age and early Iron Age. Clearance was accompanied by the spread of beech which today is the dominant tree in secondary or man—modified woodland. Cultivation and ploughing occurred throughout the Iron Age and for much of the
Roman period until the middle and upper slopes were abandoned 22
during the Roman or Anglo-Saxon periods. Throughout this era of cultivation the pollen spectra were dominated by species of broken ground until the land was returned to turf during the Anglo-Saxon period, and cultivation restricted to the valley bottoms and the areas of Greensand to the north. This turf cover was maintained primarily by sheep grazing, and later with the help of rabbits, until the Second World War when much of the land was ploughed up for cereal cultivation. This change of land use together with the myxomatosis epidemic of 1954 has caused the widespread destruction of the chalk grassland swards. The Nature Conservancy Council has estimated that between 1966 and 1980 about 902 ha of old chalk grassland has been lost on the South Downs, which is about 25% of the total. In addition to the extension of cereal cultivation, about half this loss is due to the relaxation of grazing pressure and the consequent encroachment of scrub.
iv. Fossil molluscan work
The calcareous nature of the soils and sediments on the South
Downs is ideal for the preservation of non-marine mollusc shells.
Despite this, little systematic work has been carried out on them.
A.S.Kennard (1871-1948) studied fossil Mollusca from more than 30 sites in Sussex of interglacial, glacial and Postglacial age, but the majority remain unpublished. Faunal and sometimes stratigraphical details can be found in his notebooks which are kept in the Department of Palaeontology, British Museum (Natural
History). More recently archaeologists in Sussex (O'Connor 1976;
Thomas 1982) have examined molluscs from soils buried beneath monuments. Bell (1981b, 1983) has studied dry valley infill 23
deposits on the Downs and has linked sedimentary and molluscan change to alterations in the land use. Most of the recent fossil molluscan work in this area has been related to archaeological sites, the only exceptions being the work by Kerney (1963) and
Evans and Williams (Williams 1971) on Late-glacial deposits at Cow
Gap and Beddingham (Asham) respectively. The most important fossil molluscan studies carried out on the chalk in Sussex are as follows. Their location is shown in Figure 2.
Alfriston TQ 508035 (O'Connor 1976)
Burial monument of middle Bronze Age. Samples from the barrow contained open-country species including Vallonia costata,
V.excentrica and Helicella itala.
Arundel TQ 0108 (Kennard unpub. M.S.)
Postglacial slope deposit containing Romano-british pottery sherds and molluscs including Monacha cartusiana, Cernuella virRata and Candidula Rigaxii.
Ashcombe bottom TQ 385093 (Williams 1971)
Late-glacial deposits consisting of two bands of fine chalk silt within coarse rubble. Bands contained Pupilla muscorum and
Vitrina pellucida.
Barkhale SU 976126 (Thomas 1982)
Neolithic enclosure of a single ditch. The ditch infill contained both woodland and catholic species. 24
Beddingham TQ 440061 (Kennard in White 1926; Williams 1971;
Ellis 1983a)
Hillwash from a ditch infill exposed in a road section
analysed by Kennard contained an open country fauna, including
Helix aspersa.
Late glacial deposits have also been described from this grid
reference by Williams (1971). They contained a typical Late-glacial
fauna including P.muscorum, Abida secale, Punctum pygmaeum and
Trichia hispida. Additional work has now been carried out on the
Late-glacial and Postglacial deposits at this site (see section on
Asham).
Bishopstone TQ 470010 (O'Connor in Bell 1977; Thomas in Bell
1977)
A site occupied from the Neolithic to the Anglo-Saxon period.
The Neolithic pit contained woodland species including Balea
perversa and Ena obscura. Radiocarbon date obtained from top of pit was 4460 2: 70 b.p. (Har-1662). The Iron Age pit contained
open-country species including some introduced helicellids which
are interpreted by Thomas as contamination. Radiocarbon date from
pit was 2220 ± 80 b.p. (Har-1086). The Romano-british deposits
contained very few shells but Anglo-Saxon samples contained open-country species dominated by P.muscorum suggesting a reversion
from ploughed land to lush pasture. At the Rookery Hill Lynchet,
the pre-lynchet ditch contained woodland species whereas the body
of the lynchet contained an open-country, highly xerophile fauna including Truncatellina cylindrica and Vertigo pygmaea. The modern topsoil contained H.aspersa and introduced helicellids. 25
Blackpatch flint mines TQ 096095 (Kennard and Woodward unpub.;
Pull 1932; Kerney 1957; Evans and Jones in Mercer 1981)
Mollusca from this Neolithic site were originally examined by
Kennard and Woodward and were subsequently discussed by Pull
(132). Recently the shells have been re-examined by Kerney (1957) who identified one of the specimens of Laura cylindrica as
L.sempronii, a species now extinct in Britain. The fauna was almost entirely of woodland species including Heliciodonta obvoluta.
Brighton (Johnson 1900; Kennard unpub. M.S.)
Johnson described three feet of chalky rainwash overlying rubble drift containing Neolithic flakes and shells of P.muscorum,
Cepaea nemoralis and H.itala. The site was described by Kennard in his notebooks.
Bury Hill TQ 005124 (Thomas 1981, 1982)
Neolithic enclosure of one circular ditch. Woodland species in base of ditch replaced at higher levels by open-country forms.
Radiocarbon dates from base of ditch were 4570 ± 80 b.p. (Har-3593) on antler and 4680 ± 80 b.p. (Har-3596) on bone. Molluscs suggest that enclosure was constructed in newly cleared woodland.
Church Hill flint mines TQ 115082 (Kennard unpub. M.S.; Davis unpub.; Evans and Jones in Mercer 1981)
Neolithic shaft fills contained woodland fauna including
H.obvoluta and Helicigona lapicida. The upper fill and topsoil contained open-country genera. Evidence suggests that the Downs 26
were heavily wooded when the mines were dug and were cleared after the mines had been abandoned.
Cissbury flint mines TQ 140080 (Willett 1872; Rolleston 1875;
Lane Fox 1876; Pull unpub.; Kennard unpub.; Evans and Jones in
Mercer 1981)
Shaft inf ills contained woodland species including
H.obvoluta, H.lapicida and Acicula fusca in contrast to the upper fill and surface soil which contained an open-country fauna.
Combe Hill TQ 574021 (Jackson 1950; Thomas 1982)
Neolithic enclosure of two concentric bank and ditch systems.
Originally excavated by Musson (1950) and the molluscs identified by Jackson. More recent work has produced a radiocarbon date of
4590 110 b.p. (1-11, 613) from the ditch (Drewett and Bedwin
1981) and is associated with a woodland assemblage of molluscs.
Court Hill SU 899138 (Thomas in Bedwin 1984)
Neolithic enclosure of a ditch and bank system. Radiocarbon date from base of ditch was 5420 ± 180 b.p. (1-12,893). Molluscs suggest that enclosure was constructed either in newly cleared woodland or in an open-country environment.
Cow Gap TV 595957 (Davis unpub.; Kerney 1963)
Davis records in his notebooks an open-country fauna including C.virgata and M.cartusiana from the terraced landslips.
The Late-glacial deposits have been examined in detail by Kerney
(1963) and will be discussed in the section on Cow Gap. 27
Harrow Hill flint mines TQ 082099 (Curwen et al 1927; Kennard
unpub. M.S.; Holleyman 1937; Kerney 1983)
A sample from the recent excavations in 1982 has been
analysed for molluscs by Kerney (1983). It contained a pure
woodland fauna including the rare L.sempronii. A radiocarbon date
of 4670 t 60 b.p. (BM 2071) was obtained from the sample.
Harting Beacon SU 762188 (Davis unpub.)
Samples from the Iron Age hill fort yielded a woodland fauna
including H.obvoluta.
Itford Bottom TQ 440048 (Bell 1981a, 1983)
Site is _down slope from the mid Bronze Age settlement Itford
Hill (Burstow and Holleyman 1957; Holden 1972). Base of a subsoil
hollow was radiocarbon dated on charcoal (Fraxinus and Pinus) as
8770 t 85 b.p. (BM 1544) and is associated with woodland species
including Oxychilus cellarius, A.fusca, Discus rotundatus and
Pomatias elegans. This fauna is not contemporary with the
radiocarbon date as all these species have arrived in Britain since
the mid Postglacial. The buried soil contained a few woodland
species but mainly open-country forms, and has been radiocarbon
dated to 3770 ± 120 b.p. (BM 1545). The upper colluvium contained
Monacha spp, C.virgata, C.intersecta, H.aspersa and Cochlicella acuta.
Kiln Combe TQ 570960 (Bell 1981a, 1983)
This dry valley is at Bullock Down, an area extensively excavated by Drewett (1982). A decalcified buried soil has been
radiocarbon dated to 3630 ± 90 b.p. (Har-5469) but contained no 28
shells. The overlying colluvium contained open-country species including H.aspersa, C.virgata and C.intersecta in the upper levels. Samples from a subsoil hollow contained only woodland species.
Littlehampton (Lang 1932)
Sea cliff of brickearth overlain by Postglacial silts containing shells of open-country species including M.cartusiana,
H.aspersa and H.pomatia. Also some water snails (Lymnaea peregra and L.truncatula) derived from the old river bed that passes through the section.
Offham Hill TQ 399118 (Thomas 1977, 1982)
Neolithic enclosure of two concentric bank and ditch systems.
Radiocarbon dates obtained from the inner ditch were 4925 ± 80 b.p.
(BM 1414) from the primary silts and 4740 60 b.p. (BM 2790) from the layer stratigraphically above (Drewett and Bedwin 1981).
Molluscan species from the ditch inf ill were all woodland and catholic.
Peacehaven TQ 4200 (Kennard unpub. M.S.)
Five feet of hill wash from the cliff tops at Peacehaven contained open-country species including C.virgata, C.gigaxii and
H.aspersa.
Portfield (Prestwich 1892; Kennard and Woodward in Palmer and
Cooke 1923)
This site was first described by Prestwich. His samples and additional ones collected by Lt-Col Cooke were reanalysed by 29
Kennard and Woodward. Three barns contained a Late-glacial fauna including A.secale, Columella columella and Succinea oblonga.
Seaford TV 495978 (Kennard unpub. M.S.)
Hillwash at cliff top contained an open-country fauna including M.cartusiana, M.cantiana, H.aspersa, C.intersecta,
C.gigaxii and C.virgata.
Stoke Down SU 825096 (Wade 1923)
Siltings from Shaft 3 of these Neolithic flint mines were examined by Wade. A woodland fauna was preserved, and included
H.obvoluta and Balea perversa.
Trundle SU 877110 (Kennard and Woodward 1929; Thomas 1982)
The Neolithic enclosure is almost entirely contained within the remains of an Iron Age earthwork. Excavations were carried out by Curwen (1929, 1931) and the molluscs analysed by Kennard and
Woodward. A rescue dig by Bedwin (1980) has produced radiocarbon dates from the ditches of 5240 t 140 b.p. (I-11,615) and 4860 ± 100 b.p. (1-11,612) (Drewett and Bedwin 1981) and provided samples for molluscan analysis. These contained a predominantly woodland fauna.
Whitehawk TQ 330048 (Kennard 1934, 1936, Kennard and Woodward
1930; Thomas 1982)
Neolithic enclosure of four rings of banks and ditches. First excavated by Williamson (1930) and later by Curwen (1934, 1936).
Molluscs were examined by Kennard and Woodward and were all woodland and catholic species. 30
The majority of these sites are those studied by Kennard, and the molluscan analyses consist of the large-shelled species picked out by eye from the section face. The rest are samples from archaeological contexts to provide information about the local palaeoenvironments. Until now no Postglacial molluscan biostratigraphy has been carried out in this area of Sussex.
v. Archaeology of Sussex
The different topographical regions of Sussex have been exploited by man during the different cultural periods. The chalk was occupied from early prehistory until the Romano-British period, when settlements moved off the chalk onto the coastal plain and into the Weald and river valleys. General works on Sussex include
Curwen (1937, 1954), Brandon (1974) and Drewett (1978).
Palaeolithic period
General accounts of this period have been given by Grinsell
(1929), Curwen (1954), Roe and Holden (1968) and Woodcock (1978). A large number of Palaeolithic artifacts of all ages have been found in Sussex, concentrated mainly along the top of the Downs and in the raised beaches. Most finds have been casual, not from controlled excavations.
The only excavated Upper Palaeolithic site in East Sussex is at Newhaven (Bell 1976) where flint artifacts were found in an ice-wedge cast in coombe deposits. This is interpreted as having formed between 16000 and 30000 B.P. 31
Mesolithic period
Evidence of occupation during this period in Sussex comes mainly from the Greensand where large numbers of microliths have been found. Excavated sites include Iping Common (Keef et al 1965) and at West Heath (Drewett 1976).
Neolithic period
Evidence of settlement on the Downs during this period is scarce but the large numbers of flint mines, causewayed enclosures and long barrows indicate that the Downs were extensively used.
Thorley (1981), Thomas (1982) and Bell (1983) have shown that most of the Downland was still wooded in the Neolithic but with small, local patches of clearance. The most studied archaeological features are the causewayed enclosures which are thought to have been used as communal meeting places (Smith 1965). The long barrows in Sussex have been listed by Grinsell (1934) and the oval barrow at Alfriston, excavated by Drewett (1975), is thought to have been built towards the end of the long barrow tradition. The eleven known flint mines are all located in West Sussex, as erosion of the
Chalk sea cliffs in the east would have provided an adequate supply of flints without mining.
Bronze Age period
There is little evidence of Bronze Age settlement on the
Chalk. The only extensively excavated settlement of this period is 32
at Itford Hill (Burstow and Holleyman 1957; Holden 1972) and from the remains it was possible to deduce that mixed farming took place.
Iron Age period
During this period there was a marked increase in the population, reflected in the large number of monuments. On the chalk there are at least twenty hill forts which vary in size and shape, the largest being Belle Tout and the smallest Harrow Hill.
They have been classified into early hill forts and developed hill forts by Cunliffe (1976). The early hill forts include Harrow Hill,
Belle Tout and Hollingbury, and were probably used mainly as stock corrals. It is not known if these forts were permanently inhabited, but the excavations at Hollingbury revealed the remains of several round huts. The developed hill forts are all found to the west of the River Adur and were surrounded by strong defences. The evidence from these suggests that they were permanently occupied. To the east of the Adur there are no comparable forts although it seems that many of the,earlier hill forts were occupied towards the end of the Iron Age, for example at Devil's Dyke, Mount Caburn and at
Castle Hill.
During these periods people were attracted to the chalk because of the lighter, fertile soils and the ease with which they could be cultivated. They were aware of the necessity to keep the soil fertile, as is demonstrated by the Roman marling pits found at
Bullock Down (Drewett 1982) and the probable use of seaweeds as fertilizers (Bell 1981c). 33
Romano—British period
During this period, settlement and land use moved away from the chalk for the first time and most remains are found in the coastal plain around Chichester and Selsey. Consequently much of the downland reverted fron cultivated to grazing land.
Anglo—Saxon period
Knowledge of this period comes from both documentary and field evidence. The areas settled by the Anglo—Saxons tended to be those that were not occupied by the Romans, that is mainly between the lower Ouse and the Cuckmere. Evidence from investigated sites now suggests that animal husbandry was practised, supplemented by marine molluscs as a food source. Many of these Anglo—Saxon settlements were occupied throughout the Medieval period and remain today as villages or towns, as for example Bishopstone, Eastbourne and Friston.
vi. Present day_ conditions
There is a distinct contrast between the Eastern and Western parts of the Sussex Downs. In the East (the area covered by this study) much of the downland is affected by urban sprawl. This is most noticeable along the coastal stretch between Brighton and the
River Ouse which is covered by the Brighton — Rottingdean —
Peacehaven — Seaford conurbation. The rest of this area is a mixture of grassland, cultivated fields and forestry plantations. 34
Old chalk grassland is biologically one of the richest habitats in Great Britain and results from the intensive grazing of a thin infertile calcareous rendzina soil for many years. This floral community may be termed a disclimax ecosystem, that is a stable community which is not the climatic or edaphic climax for the given site but is maintained by man or by his domestic animals
(Odum 1971).
The chalk grassland community is mostly composed of species with continental or southern distributions, and many are calcicoles. There is a rich invertebrate fauna, including several rare species of butterfly (e.g., the small blue, Cupido minimus) and grasshoppers (e.g., Stenobothrus lineatus). Molluscs are also common and this area of southern Britain provides a habitat for several rarities such as Monacha cartusiana, a southern European species still fairly common on the South Downs but almost totally absent or extinct in the rest of the country (Kerney 1970). It is unfortunate that this chalk grassland is disappearing fast. This is due to several factors:-
1. A decline in sheep grazing;
2. A decline in the rabbit population due to the outbreak of myxomatosis in 1954;
3. An increase in ploughing and other agricultural activities;
4. The use of fertilizers and selective weedkillers, causing a decrease in species diversity and the development of a monoculture;
5. Forestry plantations;
6. Urban sprawl and road construction. 35
Once disturbed by man, or if the grazing pressure is removed, the chalk grassland is quickly invaded by scrub species, notably hawthorn (Crataegus monogyna), dogwood (Thelycrania sanguinea) and the wayfaring tree (Viburnum lantana). The scrub develops eventually into the true climax vegetation of the Downs, which is a mixed deciduous forest.
The western part of the Downs is less affected by urbanisation which is concentrated on the coastal plain. Much more of the Downs in this area has been replanted with trees, for example the scarp slope between Arun and Petersfield is almost totally wooded and supports the continental snail Heliciodonta obvoluta. This species is unknown elsewhere in the British Isles as it at the extreme north—west limit of its European range. It is considered to be a good indicator of undisturbed, though not primary, woodland (Cameron 1972). The presence of this species together with the evidence of the soils and the flora suggests that these woodlands predate the Restoration plantings (Streeter 1983). 36
3. GEOMORPHOLOGICAL PROCESSES RESPONSIBLE FOR SLOPE DEPOSITS
1. Introduction
The deposits at all the sites studied are described in detail later in this thesis. The processes responsible for their formation are analysed briefly below.
In the sections through the slope deposits on the South Downs no deposits earlier in age than the Late-glacial (Devensian) were found, with the possible exception of the basal periglacial deposits at the Devil's Dyke and at Cow Gap which were unfossiliferous and could therefore not be dated.
Postglacial and Late-glacial deposits can usually be easily differentiated in the field. The Late-glacial slope deposits are composed of angular, chalk fragments interbedded with fine chalky silts giving an overall very pale appearance whereas the
Postglacial slope deposits are usually light brown in colour and contain reworked soil, abundant small subangular chalk pellets, weathered minerals, humic compounds, charcoal fragments and abundant mollusc shells. The contrast between the deposits is most noticable with the flints. In the Late-glacial deposits the flints are fewer in number and are fresh looking and angular in appearance as if they had only recently been shattered by frost action whereas in the Postglacial slope deposits the flints are worn and well rounded and often patinated. It must be noted that many of the
flints in the Late-glacial and Postglacial deposits are reworked 37
from more ancient sediments such as the clay-with-flints capping
the escarpment.
Despite the differences in appearance of the deposits, the
processes responsible for their formation show certain features in
common.
Late-glacial Deposits
A. MASS MOVEMENT PROCESSES
Solifluxion (periglacial soil flow)
A term literally meaning "soil flow" but most usually
- restricted to cold climate deposits formed by mass movements. This
process 'includes :-
a. The flow of saturated materials downslope under the influence of
gravity (mudflow solifluxion).
b. Frost creep (regelation solifluxion)
In a periglacial environment freeze-thaw cycles rapidly
disintegrate chalk, producing large amounts of angular,
unconsolidated, unstable slope debris. In permafrost areas the
upper layer of the ground thaw in spring, saturating the debris
which is poorly drained due to the underlying frozen, impermeable
ground. This causes the sediments to flow under gravity into the
valley bottoms, a process which may occur on slopes as shallow as
1-20 . Gentler slopes are prone to solifluxion as saturation occurs
readily because of poor drainage. 38
Frost creep is the downslope movement of materials caused by gravity acting upon the debris which is being progressively restructured by alternate freezing and thawing. This process is thought not to have been as widespread as solifluxion in southern
Britain during the Late—glacial.
The term Coombe rock (Coombe deposit) is often applied to chalk solifluxion deposits. These deposits are characteristically unsorted, but may grade laterally into stratified sediments formed by fluvial processes (see below).
B. FLUVIAL PROCESSES
In periglacial environments on the chalk these are thought to have been the most important processes that moved the solifluxion materials from the valley sides into the valley bottoms and out onto the plains.
Slopewash
This process occurs in both temperate and glacial environments and is dependent upon the infiltration capacity of the soil or sediment being exceeded due to a high input (rain, snow or meltwater) or a low infiltration capacity (frozen, impermeable or compacted ground). The water flow can occur either as sheet wash or channelled into rills or gullies. In periglacial environments slopewash deposits are poorly sorted and crudely stratified, occurring in valley bottoms and as fans at the valley mouths. 39
In addition to surface flow, flow through the subsurface
layers also occurs. The erosion and transportation of small soil
particles through the soil interstices occurs together with
minerals dissolved and transported in solution. This subsurface
flow is not very important in periglacial environments.
Niveofluvial processes
These occur where there are snow patches, as would be
expected on the escarpment. Transport by meltwater and subsequent
redeposition of the sediments is responsible for the coarse
well-sorted pebbly horizons seen in some sections.
C. AEOLIAN PROCESSES •
Deflation
The main product of aeolian processes is loess. The source
area of southern Britain was mainly the dry bed of the North Sea,
'where glacial outwash deposits were present. The finer sediments,
usually quartz grains, were deflated and redeposited over much of
southern Britain. A dry, windy climate is needed, such as occurred
in the earlier part of the Late Devensian (c. 28000-14000 B.P.;
Catt 1977). Thick deposits of loess of pre-Late-glacial age have
been recorded from many coastal sections, such as at Pegwell Bay,
Kent (Pitcher et al 1954; Weir et al 1971), and thinner sequences
have been noted overlying pellety chalk muds of pollen zone II age
in Kent and Sussex (Kerney 1963, 1965). Loess is characteristically 40
buff in colour with distinct vertical jointing. It is mainly silt sized ranging between 6-60 pm.
Niveoaeolian
This process is responsible for the many small pebble strings that can be traced for many metres in some sections. They are thought to be formed by the wind entraining snow with small adhering pebbles and redepositing them as a thin cover over valleys and interfluves.
Postglacial Deposits
Clear parallels can be drawn between the Late-glacial environment and the Postglacial landscape after forest clearance.
Both environments were open and sparsely vegetated, and slopewash and creep were the main geomorphological processes.
A. MASS MOVEMENT PROCESSES
Creep
This is a mass movement process, usually much slower than mudflow solifluxion. Creep has been defined by Sharpe (1938) as resulting from three different forces:-
- gravity (continuous creep),
- climatic (seasonal creep)
- biotic (random creep).
Continuous creep was further defined by Terzaghi (1950) as the 41
slow, steady movement of soil downhill in response to gravity.
Seasonal creep is the net downslope displacement of the soil by heaving and settling of particles resulting from freezing and thawing cycles (frost creep) and from changes caused by insolation and variations in soil moisture content. The effectiveness of these processes is related to soil type; for example, moisture changes produce their greatest effect if the soil contains swelling clay minerals. Random creep results from the activities of soil organisms (plants and animals) causing a net downslope displacement of soil particles. This process includes the collapsing of root channels and animal burrows, the accidental displacement of soil material by large animals and the transport by worms of fine soil particles to the surface which are then more easily moved downslope. Darwin (1881) showed that worm casts flowed a little way downhill when moistened by rain. This occurred on slopes as shallow as 1 0 . When dry the casts were inclined to roll downhill if disturbed.
Creep produces poorly stratified deposits usually containing large numbers of small subangular chalk pellets.
B. FLUVIAL PROCESSES
The importance of these processes is dependent upon the frequency and amount of overland flow, which in turn is dependent upon how often the infiltration capacity of the soil is exceeded.
Water can flow as a continuous sheet or in channels (rills and gullies). Together these processes make up wash transport. 42
Rainsplash erosion
This results from the impact of raindrops on the soil surface. They have the effect of dislodging the smaller soil particles and flinging them into the air. The larger particles are gradually undermined by the impact of the raindrops and the rebounding of smaller soil particles. On slopes a net downslope movement results. In addition the compaction caused by raindrops and the rebounding soil particles makes the ground more susceptible to runoff because the infiltration capacity is reduced.
Overland Flow
The flow is most likely to be concentrated into channels, the position of which will alter from storm to storm but are usually related to irregularities such as hollows, boulders or even trees.
Flowing water has the ability to entrain particles both as bedload and suspended load and its capacity to do so increases with velocity. The efficiency of the process is dependent upon factors such as soil cohesion, particle size and, most important, the type of vegetation and the percentage of the surface which it covers.
The erodibility of the soil is greatly reduced by vegetation as the network of roots binds the soil particles together and the foliage and leaf litter insulates it from the impact of flowing water and raindrops. Finally vegetation produces a good soil structure which increases the infiltration capacity of the soil.
These overland flows would be 16w frequency / high magnitude events that is occurring only during exceptionally heavy rainstorms or where the ground was unprotected due to the lack of a vegetation 43
cover. Evidence of these events in the past can be seen in colluvial deposits in dry valleys. These flows are indicated by bands of large rounded pebbles in the colluvium that have been brought down the valley sides by overland flow and redeposited as a sheet covering the valley floor. Similar deposits that have formed recently can be seen on the Downs in areas where large fields have been ploughed ready for crop plantation and heavy rainfall occurred prior to vegetation growth. Stammers and Boardman (1984) have shown that the most vulnerable areas are fields ploughed for the cultivation of autumn and winter cereals.
Subsurface flow
The factors that reduce runoff and overland flow favour an increase in the loss of sediment by subsurface flow through the most permeable soil horizons (usually the boundary between the A and B horizons). This sediment loss is either by the entrainment of small soil particles into suspension or the dissolving of minerals into solution. The erodibility of the soil by subsurface flow is dependent upon several factors. The size of the soil particles that are able to be removed depends upon the size of the soil pores and voids and the velocity of the flow. The least erosion will occur in a well sorted sediment. The slower the subsurface flow the more that can be taken into solution. If the flow is slow enough it becomes in chemical equilibrium with the soil solution around the peds.
Very little work has been carried out on the amount and the impact of subsurface flow and solution on soils and topography. 44
Atkinson (1957) has documented the effects of these processes over
archaeological time by comparing the level of the chalk bedrock
protected by prehistoric monuments with unprotected surfaces. He
estimated a loss of 50cm of subsoil during the last 4000 years. The main effect of this erosion is the loss of the silt and clay sized
particles from the upper portions of the valley and the enrichment
of soils in the valley floor with these particles and carbonates.
Additional features found in association with slope deposits
are subsoil hollows. These are surprisingly common in chalk areas and have been studied by Evans (1972) at sites including Pitstone,
Buckinghamshire, and at Ascott-under-Wychwood, Oxfordshire, and
also by Bell (1981a) at Itford Bottom and at Kilne Coombe in
Sussex. Their origin is uncertain but the most plausible
explanation is the tree-root hypothesis (Evans 1972), that is they
form when a tree has blown over and the resulting hole filled by
the washing-in of the surrounding sediments. Alternatively these
features could be explained by any one of a number of processes:-
solution, subsidence or excavation by frost or by man. Work on
subsoil hollows on the South Downs at Asham and at Cow Gap shows that there is no evidence to distinguish conclusively between any
of these theories.
The general character of the Late-glacial and Postglacial deposits and the processes responsible for their formation are summarised in Table A.
Postglacial slopewash together with creep produces the colluvium characteristic of the chalk dry valley infills. The 45
Table A : Summary of the characteristics of slope deposits and the conditions and processes involved in their formation
DEPOSIT CHARACTERISTICS CONDITIONS PROCESS SITES PRESENT
Coombe deposit Coarse angular and Periglacial, slope >2°, Solifluxion Exceat, Devils subangular chalk fragments. incomplete vegetation Dyke, Hope Gap Unconsolidated, cover, saturated debris. unstratified with stone orientation downslope.
Chalk melt water Sorted and bedded materials Periglacial, slope >2°, Slope wash Asham, Cow deposit much fine sediment, poor vegetation cover, Gap, South overland flow. Heighton, Exceat, Hope Gap
Scree Loosely packed, unsorted Periglacial, slope >350, Frost creep Devils Dyke angular fragments. poor vegetation cover, freezing and thawing cycles.
Strings of small Continuous for many metres Periglacial, wind, snow Niveoaeolian Cow Gap pebbles and can be traced over the and overland flow. Fluvial interfluves.
Loess Distinct buff colour, Periglacial, dry and Aeolian Cow Gap, Hope vertical jointing, silt windy suitable source Deflation Gap fraction 70-80% of total. material.
Brickearth Loess interbedded with Periglacial, presence of Usually Asham, Cow Gap (redeposited chalk meltwater deposits. loess and slope for Slopewash loess) overland flow.
Buried soils Soil containing organic Temperate, stability, in Soil formation Cow Gap, Devils matter and weathered situ weathering, soil Dyke, Asham, minerals. organisms. South Heighton, Exceat
Colluvium Poorly sorted materials Temperate, incomplete Fluvial mass All sites with traces of bedding. vegetation cover, slopes movement Large numbers of small in excess of 20. subangular chalk pellets.
Pebble bands Bands stretching for many Temperate, incomplete Rill and Cow Gap, Hope metres across sections vegetation cover, heavy gulley erosion Gap, South extending back laterally rainfall. Heigh ton into the deposits suggesting pebble sheets.
Subsoil hollows Pockets of sediments Temperate, trees with Uprooted tree Cow Gap, Asham Approximately lm deep large root system and In-washing of containing uniform sufficient soil. sediments sediments of silt and clay sized particles. 46
collective term colluvium includes hillwash and ploughwash
deposits, and has been defined by Avery (1980) as " unstratified or
crudely stratified deposits that have accumulated by slopewash or
downslope creep during the Holocene period ". The sediments tend to
build up by gradual increments to their surface, and accumulate on
dry valley floors or at field boundaries as lynchets.
These processes of erosion and transport are minimal when
conditions are stable and the vegetation cover complete. Erosion
only becomes important when bare unprotected soil or regolith is
present on the hillslopes. This was widespread during the
Late—glacial period, and after forest clearance in the Postglacial
when large areas of land were being cultivated. On an unvegetated
sloping surface, all types of creep would be accelerated, and
during rainstorms particles would be easily entrained by overland
flow. During most of the Postglacial the surface would not have
remained completely bare as weeds quickly colonise cleared ground
but if the land was under cultivation a large surface area would be
unprotected and prone to erosion.
Intensive studies in Luxembourg by Kwaad (1977); Kwaad and
Mucher (1977) have been carried out on the relationship between the
type and percentage vegetation cover and the resulting amount of
colluvium. Their studies have shown that colluviation is greatest
during cultivation but can be substantially reduced by
afforestation. Work by Carson and Kirkby (1972) in South west
England has shown that removal of grassland causes soil erosion to
be accelerated by 400 times. From these studies and those on
, molluscan successions in colluvium it is evident that the large 47
amounts of Postglacial colluvium found in dry valleys on the South
Downs result from forest clearance and cultivation of the slopes. 48
4. METHODS
i. Fieldwork
a. Choice and recording of sections
In the study area of the South Downs, sites were chosen to cover as broad a range of reliefs and environments as possible.
Scarp and dip slope valleys, coastal and inland sites, and valleys with differing aspects were all included. Sections of the valley fills were obtained either from existing man-made or natural exposures, or by cutting trenches with a mechanical digger.
The sections were then cleared to remove loose soil and other debris (including living molluscs), examined and photographed. A horizontal datum line was placed across the section using string, pins and a spirit level and this was used as a reference line from which to measure the section. Details of the section were then plotted onto graph paper (for scale see each diagram), marking in the length and overall height of the section, details of the stratigraphy, location of the sample columns and spot samples and any field finds of pottery, bones or flint artifacts. Finer details of the stratigraphy were also recorded, as for example pebble bands, pockets of fine silt, charcoal layers etc. A key to the symbols used to represent the lithological features is included in each section diagram. The same symbols have also been used in the stratigraphy columns on the molluscan histograms. 49
b. Sampling
The position of the sample columns was usually chosen at a point on the section where the deposits were at their thickest and most complete. For dry valley fills this is usually in the valley axis. It was not always possible to take all the samples in a single vertical sequence and so for all the sites the location of all the sample points were plotted onto the sketch diagram of the section. Sample blocks were marked out on the face of the section at either 5cm or 10cm intervals,depending on the likely rate of formation of the deposits and their textural characteristics. Care was taken to avoid sampling across stratigraphic boundaries, root holes, animal burrows or other disturbances.
Samples of approximately 1.5kg (wet weight) were cut from the section face using a hammer and sharp bolster and were transferred into polythene bags, labelled with the site, section name and the depth below the modern soil surface. Samples were taken from the bottom of the section upwards to avoid contamination, and additional field notes were made of the sediments as they were sampled.
At some sites spot samples were taken prior to the main sampling to ascertain suitable sampling intervals and to get some idea of the molluscan biozones present. In addition bulk samples of about 80kg were taken from suitable layers to obtain charcoal and shells for radiocarbon dating. 50
Laboratory work.
a. Extraction of shells.
In the laboratory the colour of the field wet samples was recorded using the Munsell soil colour charts in daylight conditions. The samples were then oven dried. For ease of comparison between samples and sites, a standard sample size of lkg
(dry weight) was always used and stones larger than 14mm were removed. A weighed and dried sample was then placed in a bowl and water added. Usually the sample disaggregated on contact with the water but sometimes it was necessary to aid the process physically by stirring, or chemically by adding hydrogen peroxide which speeds up disaggregation by oxidizing the organic matter that binds the soil particles together. As the sample collapsed, the mollusc shells floated to the surface and were decanted into a British
.Standards mesh number 30 sieve (0.5mm mesh size). This procedure of adding water and decanting off the shells was repeated usually seven or eight times until no more shells floated to the surface.
The "sinks" remaining in the bowl were then placed in a second BS
Number 30 sieve and washed thoroughly to remove the fine sediment fraction of less than 0.5mm diameter. These two sieves were then placed in the oven to dry at 60°C. A high percentage (>80%) of the molluscan shells in a sample were retained on the sieve as "floats" but any shells that were broken and so unable to trap air, or apical and shell fragments, remained in the other sieve as the
"sinks". These were extracted by dry sieving the "sinks" through a graded series of sieve sizes (BS numbers 8, 12, 16 and 22). These were then picked under a low powered binocular microscope using a 51
black sorting tray marked with white lines so that the field of view could be tracked efficiently. Every shell and any important diagnostic shell fragments were removed using fine forceps and a fine sable—haired paint brush. These shells and shell fragments were sorted into species and then counted. In addition any seeds, charcoal and bones were also extracted at this point.
b. Identification and counting
The nomenclature and taxonomic order of molluscs throughout this thesis follows Walden (1976) and Kerney (1976c).
Identification of the shells was carried out with the aid of reference books and papers (Kerney and Cameron 1979; Evans 1972;
Macan 1977; Preece 1978,1981) and from reference material from
Dr.M.P.Kerney. Ease of identification varied between species and samples. In some of the Postglacial material, the shells were in a poor state of preservation, highly corroded and lacking any surface sculpture. Much of this type of material was very fragmentary with large numbers of individuals based upon the identification of small apical fragments. In addition to poorly preserved materials, some species are difficult to identify as fossils because the identification characteristics are based upon the living animals.
Problems were encountered with the following species —
Succinea oblonga
• This species only occure at Asham Quarry in column A at depth
100-105cm. This is not a definite identification as this species is virtually impossible to tell apart from Catinella arenaria. 52
Cochlicopa lubrica and C.lubricella
Juveniles of these species are impossible to separate and so
have been counted and recorded as Cochlicopa sp.
Slugs
Slug plates were recorded from most samples and have been
recorded as Deroceras / Limax species. No Milax plates could be
determined. Identification of these plates is problematical. It has
been attempted in the past to identify them to the species level
(Phillips and Watson 1930; Sparks and West 1960) but to date the
identification is still highly unsatisfactory. In addition
calcareous granules from species of Anon were present in all the
Postglacial samples and in some of the Late—glacial.
Cochlodina laminata and Clausilia bidentata
These species are hard to separate from apical fragments
especially when they are highly corroded. Identification is more
positive when apertures are preserved.
Helicellids
This group is made up of the species Cernuella virgata,
Helicella itala, Candidula intersecta and C.gigaxii. At some sites all four species were present. The identification of adult shells is fairly straightforward but juveniles are extremely difficult to
separate. Much time was spent studying these juveniles and 53
eventually it became possible to separate the species with some degree of confidence. The main problem was to separate H. itala from C. virgata, and C. intersecta from C. gigaxii.
The Separation of H. itala and C. virgata juveniles
The main character used to separate juveniles of these species was the size of the protoconch (apical whorl of the shell).
C. virgata juveniles have a larger, more bulbous protoconch than H. itala. In well preserved specimens the protoconch of C. virgata has a matt sheen in contrast to the rather glossy appearance of H. itala. These differences are illustrated by the S.E.M. photographs
(Figure 3). An additional identification feature is that the spire of H. itala is flattened on top in contrast to the C. virgata shells which were more globular and higher—spired.
The Separation of C. gigaxii and C. intersecta
These two species were easy to seperate from H. itala and C. virRata because of their distinct transverse ribbing. The difficulty was in separating the juveniles. This was done entirely on the regularity of the ribbing. C. intersecta has irregularly spaced ribbing and C. gigaxii more regular, finer ribbing. An additional feature used to seperate the adult and nearly mature shells is the shape of the umbilicus, which in C. gigaxii is more eccentric than in C. intersecta. These differences are illustrated by the S.E.M. photographs (Figure 3). 54
Cernuella virgta (da Costa) Candidula gigaxii (Pfeiffer)
Cow Gap Cow Gap
Helicella itala (L.) Asham Candidula intersecta (Poiret)
Cow Gap
Figure 3. S.E.M. Photographs of the Helicellids. 55
-, 56
Monachä spp.
Monacha cartusiana occurred fairly frequently at all the
sites. Although fully sized specimens were quite easy to identify,
juveniles were easily overlooked and confused with young Trichia hispida. The characteristics used to identify juveniles and apices are the absence of hair pits which are present even on the protoconchs of Trichia hispida, the smoothness and creamy—whiteness of the shell, a slightly shouldered form and the minuteness of the umbilicus.
Only one example of M. cantiana occured in the samples. This was an adult individual and so there was no problem with identification.
Cepaea and Arianta spp.
Apical fragments of these species are inseparable but the presence of both genera is usually quite clear from the characteristic microsculpture found on the shell fragments. The presence of each species is recorded by a X in the tables but the total numbers based on apical counts are plotted on the diagrams as
Cepaea/Arianta.
For counting purposes, the aim is to obtain the minimum number of individuals in the sample. Therefore with broken shells only the apices are counted, apertures being usually discarded with the exceptions of Clausilia bidentata, Cochlodina laminata, Vertigo spp. and Cepaea spp. where apertures are more diagnostic. At no 57
site were bivalves found so the problem of halving the number of valves was not encountered. For some species, noticeably for Helix aspersa, only a X is shown in the table indicating the presence of diagnostic non-apical shell fragments.
It is probable that an under or over-representation of certain species occurs with this technique. The very robust apices of Pomatias eleRans, Clausilia bidentata, Cochlodina laminata and to a lesser exent Cochlicopa spp. probably means that they are over-represented. It is observed that in some samples, apices range from the beautifully preserved to some that are very badly corroded. An under-representation probably occurs with species such as Trichia striolata whose juveniles are indistinguishable from T. hispida and Carychium tridentatum whose apices are so small that many are lost through the sieve.
Data Presentation
The results from all the samples are presented in a table and in a relative abundance (percentage frequency) histogram. The merits of using relative abundance as opposed to absolute abundance have been discussed by Kerney (1963). The layout of the molluscan diagrams is essentially similar to pollen diagrams. A + sign indicates that the species represents less than 1% of the total fauna. The overall numbers of shells . used for the percentage calculations are shown immediately to the right of the stratigraphical column.
All species, including marine molluscs and Cecilioides 58
acicula, have been recorded in the table. C. acicula has been excluded from the histograms as it burrows and has been recorded living at depths of 2 metres from the soil surface (Evans 1972) and so is not contemporary with the molluscan assemblages.
The species are plotted on the histogram in an order of approximate ecological preference. On the left of the diagram are the watersnails, then shade-demanding species followed by catholic and then open-country genera. This order has been slightly adjusted to try and present the biozones visually. For example Helix aspersa, a species with catholic ecological requirements, is plotted on the far right of the diagrams as it is one of the latest arrivals into the country. The same order of plotting has been used in all the diagrams to ease visual comparison between them.
In the plotting of the diagrams some amalgamation of species has been necessary. Trichia striolata and T. hispida have been plotted as Trichia spp. and the same procedure has been repeated for Cochlicopa lubrica and C. lubricella, and Vitrea contracta and
V. crystallina. With the species Vallonia excentrica and V. pulchella the juveniles are inseparable, and for plotting purposes if adults of both species occur the juveniles are split in the same proportion as the adults. Finally Cepaea and Arianta apices are virtually indistinguishable and so have been combined.
On the far right of the histograms, an ecological summary column has been constructed by totalling the percentages of each ecological group. These groupings are only very approximate as many of the species have the ability to live in other habitats. A 59
similar grouping of species was first used by Evans (1972) in his
studies of archaeological sites. The species have been grouped as:-
WATERSNAILS
Ovatella myosotis, Hydrobia spp, Bithynia tentaculata, Lymnaea
truncatula and Valvata piscinalis
SHADE-DEMANDING
Acicula fusca, Carychium tridentatum, Vertigo pusilla, Lauria
cylindracea, Acanthinula aculeata, Spermodea lamellata, Ena obscura, Discus spp, Vitrea spp, Aegopinella spp, Oxychilus spp,
Zonitoides excavatus, Cochlodina laminata, Clausilia bidentata,
Balea perversa, Helicigona lapicida.
CATHOLIC
Pomatias elegans, Cochlicopa spp, Columella edentula, Punctum pygmaeum, Vitrina pellucida, Nesovitrea hammonis, Deroceras / Limax spp, Euconulus fulvus, Trichia spp, Arianta / Cepaea spp, Helix aspersa
OPEN-COUNTRY
Succinea oblonga, Truncatellina cylindrica, Vertigo pygmaea, Abida secale, Pupilla muscorum, Vallonia spp, Helicella itala, Monacha spp, Candidula spp, Cernuella virgata.
Finally by studying the assemblages and the summary diagram, 60
the molluscan sequences have been assigned to molluscan biozones. 61
5. INTERPRETATION OF THE FOSSIL ASSEMBLAGES
1. Introduction
Buried assemblages of fossil land snail shells have been used for many years to interpret past environments, to indicate climatic change and to provide evidence of the origin of the deposits.
Palaeoenvironmental work, mainly in Southern Britain, has been carried out by Evans (1972); Thomas (1978); Bell (1983); Preece
(1978); Kerney (1963) and Kerney et al (1964).
Evidence of climatic changes can be traced in Late-glacial slope deposits (Kerney 1963) in which the climatic amelioration of pollen zone II is reflected by an increase in the numbers of individuals and species. Work has also been done by Gould (1969) on
Bermudan land snails, tracing the raising and lowering of sea levels during the Pleistocene. Most of the work has been on the
Postglacial period and has been concerned with the impact of man on the landscape as opposed to trying to trace small fluctuations in the climate. It must be said that interpretation of these fossil assemblages is hindered by the lack of appropriate knowledge of some modern faunas.
History of the technique
Documented interest in fossil non-marine molluscs in Britain can be traced back to 1706 when a letter from the Rev. John Morton to Dr. Hans Sloane was published in the Philisophical Transactions 62
of the Royal Society entitled 'a relation of river and other shells digg'd up together with various remains in a bituminous marshy earth near Mears Ashby in Northamptonshire'. He made the first attempt to compare fossil shells with those living today.
Probably the first person to realise the potential value of
Quaternary land snails as chronological indicators was Clement Reid
(1896), who wrote that 'they are likely to prove extremely valuable historic medals for the periods before coins were used or history written'.
On the continent interest was also being shown in fossil
Mollusca. The earliest biostratigraphical work was by A. C.
Johansen (1904) on freshwater molluscan assemblages from
Late-glacial and Postglacial lake sediments in Denmark. He proposed that the molluscan assemblages could be used as climatic indices by relating them to the July isotherms. From this he created five
Late-glacial and three Postglacial zones based upon the different assemblages. He further suggested that as molluscs were widely and uniformly distributed over much of Denmark they could be used to date deposits more accurately than plants, which vary regionally.
There have been many criticisms of the validity of a zoning scheme based upon air temperatures, but it was the first attempt to zone and date deposits using non-marine molluscs.
The majority of the early Continental and British published works were just lists of the species present at each site, making little attempt to link them with the stratigraphy or to compare faunas between sites. An exception was the work of Favre (1927) in 63
the Lake Geneva basin, Switzerland. He recognised two major
divisions of the Postglacial molluscan fauna:-
Lower Niveau, I - based on the occurrence of Discus ruderatus
Upper Niveau, ha - coexistence of the species from zone I with
immigrating species from the south and west
IIb - extinction of Columella columella and Vertigo
genesii
IIc - expansion of grassland genera
Favre attempted to link these biozones with the
Blytt-Sernander subdivisions of the Postglacial.
In Britain most of the early pioneer work was carried out by
A. S. Kennard (1871-1948) who wrote 250 papers on non-marine
molluscs. Many of his early papers were on taxonomy but the later
ones dealt with ecology and palaeoenvironmental interpretations.
Most of his work was carried out during the inter war period on
archaeological sites, mainly in chalk • and limestone areas in
southern Britain.The results were usually published as appendices
to excavation reports (eg. Kennard and Woodward in Peake, 1919;
Kennard in Armstrong, 1934; Kennard in Curwen, 1934). One of
Kennard's main aims was to differentiate between endemic and
introduced species in Britain. He compiled many faunal lists from
sites throughout Britain and Ireland, usually recording whether the
species were common, frequent or rare. His work has been criticised
on several counts. First, his sampling techniques were crude, often analysing only a single sample usually from a visibly rich shell
horizon, as for example the Cyclostoma elegans rainwash zones
recorded from the shaft infills at the Neolithic flint mines in 64
Sussex and Norfolk. He rarely took stratigraphy into account, assuming that the sediments and their fossils were uniform. His deductions from the faunal lists have also been much criticised as the interpretations were made largely in terms of regional climate
(especially rainfall and humidity), disregarding local environmental factors.
The first attempt to present molluscan results graphically was by J. P. T. Burchell who used sector diagrams to show the relative proportions of four selected species (Pupilla muscorum,
Discus rotundatus, Trichia hispida and Pomatias elegans) from
Neolithic and Bronze Age deposits in Kent (Burchell and Piggot
1939). This method of data presentation was very unsatisfactory for palaeoecological studies as only part of the fauna was used and the reconstruction incomplete and plotting all species in this way was so visually complex as to be unhelpful.
In two later papers, Burchell (1957, 1961) divided
Late-glacial and Postglacial assemblages from South-east England into stages, each with a characteristic faunal assemblage. In his earlier paper in 1957 he recognised 12 'phases' based on the occurrence and percentages of certain key shells, whereas in his
1961 paper the 'phases' were increased in number to 32, beginning with deposits belonging to the end of the Devensian full-glacial and continuing to the early medieval period.These stages he presents graphically showing the distribution of the key shells as a percentage for each stage. Burchell assumes that the changes in the composition of the molluscan fauna was due directly to climatic change during the Postglacial. Although a decrease in temperature 65
since the thermal optimum is thought to have caused the contraction in range of Pomatias elegans in Britain (Kerney 1968), it is unlikely that the majority of the faunal changes in the Postglacial can be linked to temperature as local factors are clearly more important than the overall regional climate.
The technique of mollusc analysis in Britain was finally given a sound quantitative base by B. W. Sparks (1957). He serially sampled fossiliferous deposits and presented the results as a histogram. The first histogram was produced from Bobbitshole, the
Ipswichian type site (Sparks 1957) and was in the form of a saw tooth' as used at the time by palynologists. In subsequent diagrams the present-day method of a bar histogram was used, allowing the thickness of each sample to be plotted precisely. The species are usually plotted as relative abundances except when the species and individual numbers are low. Then they are presented as absolute abundances as for example when dealing with periglacial slope deposits (Kerney 1963, 1971).
Once established, this quantitative technique was applied more extensively to interglacial freshwater assemblages by Sparks and West (1968, 1970) and then by Kerney to Late-glacial ' slope deposits in Kent, Surrey and Sussex (Kerney 1963, 1965), to a sequence of slope deposits spanning the Late-glacial and early
Postglacial periods at Brook, Kent (Kerney et al 1964) and to mid
Devensian deposits at Balling, Kent (Kerney 1971). Also in the late
1960's this idea of palaeoenvironmental reconstruction using non-marine molluscs was taken up by environmental archaeologists, most notably J. G. Evans (Evans 1966a, 1966b, 1968, 1972, 1984). He 66
concentrated on archaeological sites in calcareous areas in southern Britain to obtain some idea of the impact of early man on the landscape and the date and extent of forest clearance.
At the same time, similar techniques were being applied by
Lozek to calcareous spring and slope deposits in central Europe
(Lozek 1964, 1972). He sampled many sites throughout
Czechoslovakia, but most of his early work was rather crude, taking only bulk samples from distinct lithological units with no independent dating evidence, as for example from pollen zonation or radiocarbon dating.
Recent Advances
Since the early 1970's the technique of mollusc analysis has become more sophisticated, with interest being shown from fields of study other than Quaternary research. Biologists have become interested in fossil molluscan populations from the point of view of studying the effect of climate on polymorphism. Curry and Cain
(1968) and Jones et al (1977) studied the frequency of shell banding morphs in populations of Cepaea nemoralis from Neolithic,
Iron Age and Romano-British contexts in southern Britain. They compared the frequencies to those of nearly modern populations and found an increase today in the percentages of banded morphs. They interpreted these results in terms of climatic selection, suggesting that the unbanded morphs are more frequent with good summers, for example, at the Devil's Kneading Trough, Kent, 93% of the Cepaea nemoralis extracted from molluscan biozones c and d were bandless (Curry and Cain 1968). 67
Biogeographers have also become interested in fossil molluscs. An atlas of the present day distribution of species in the British Isles includes some maps of fossil distributions
(Kerney 1976b). A species of particular interest is Pomatias elegans. This species has been retracting in range since the mid
Postglacial, as it was once widespread over much of southern and central Britain and is now largely restricted to the southeast corner.
Attempts have also been made by statisticians to gain more insight into the fossil populations. Williamson (1978) used multivariate analysis to demonstrate that the Hoxnian molluscan assemblage at Swanscombe broadly conforms to the same ecological groupings as proposed by Sparks (1961). Thomas (1982) has used the
Chi-squared test to compare the palaeoecological conditions at different sites. Finally Gordon and Ellis (1983) have demonstrated that biological statistics can be applied to fossil molluscan data and used to detect environmental change.
Physical scientists have also become interested in using fossil shells for dating purposes. In addition to radiocarbon dating, which is discussed later on, they have also been used for
Uranium series dating and amino-acid racemisation (Miller et al
1979; Hughes 1984; Hunt et al 1984).
Finally, studies have been made of the metrical variations in the shells between fossil and modern populations. Kerney (1963) notes the difference in size of Pupilla muscorum from Late-glacial 68
and Postglacial deposits. Measurements have also been made of
fossil and modern populations of P. elegans and C. nemoralis and it
was shown that the fossil ones were larger and heavier. This
difference in size was tentatively linked to the thermal decline
since the mid Postglacial thermal optimum (Kerney 1968; Burleigh
and Kerney 1982). Preece (1980) looked at shape and colour
variation in Cernuella virgata from modern and fossil populations.
He found that the fossil shells were significantly smaller (1%
level) than the modern ones and the bandless forms were much more
numerous in the modern sample. But most important to Quaternary
science has been the establishment of Late-glacial and Postglacial
biozones using non-marine molluscs for South-east England (Kerney
1977; Kerney et al 1980) and these are discussed in detail in the
next section.
iv. Biozones
A simple biostratigraphical zonation scheme for Late-glacial
and Postglacial deposits using land Mollusca has been established
from work carried out at Folkestone, Kent (Kerney 1977; Kerney et
al 1980). The zones have been linked to approximate pollen zone
equivalents by pollen, plant macrofossils and radiocarbon dates
from the deposits. The molluscan biozones are based on the ranges
of certain indicator species and their changing dominance. In
biozones y to d inclusive the changes are due to migration from the
continent reflecting climatic and natural vegetatonal changes,
whereas the faunas of biozones e and f result from the influence of
man on the environment by clearing woodland and by the accidental
introduction of alien species. 69
The assemblage zones are listed below:-
Zone y Open ground fauna. Restricted periglacial assemblage
dominated by Pupillasp. and Vallonia
Zone z Open ground fauna. Restricted periglacial assemblage with
Pupilla, Vallonia, Abida and Trichia
Zone a Decline of bare soil species and expansion of catholic
species. Appearance of Carychium, Vitrea and Aegopinella.
Zone b Open woodland fauna. Expansion of Carychium and
Aegopinella. Appearance of Discus ruderatus.
Zone c Closed woodland fauna. Expansion of D. rotundatus. 1 Zone d Closed woodland fauna. Expansion of Oxychilus cellarius. 2 Zone d Closed woodland fauna. Expansion of Spermodea, Leiostyla
and Acicula.
Zone e Open ground fauna. Decline of shade demanding species.
Re-expansion of Vallonia.
Zone f Open ground fauna but with the appearance of Helix
aspersa.
The biozones can also be shown as an idealised diagram
(Figure 4) which has been modified from work in Sussex (Ellis
1983a).
In the Late-glacial period (biozones y and z) there is a restricted open-country assemblage. Biozone z differs from .y by the appearance of the thermophile Abida secale. The early Postglacial biozones a and b are characterised by the decline of the open-country genera and the expansion of woodland species including
Discus ruderatus, a species now extinct in Britain. In biozones 70
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*613 SEIV3A§ § § § - EEEEEE 71
and d the woodland genera predominate until forest clearance, which marks the base of biozone e. These anthropogenic biozones (e and f) are characterised by the re-expansion of the open-country genera and the appearance and subsequent expansion of many of the introduced species. Biozone f is defined by the appearance of Helix aspersa, a Mediterranean species thought to have been introduced into lowland Britain during the Romano-British period (Kerney
1966). Later zone f introductions into Britain include Candidula gigaxii, C. intersecta, Cernuella virgata and Cochlicella acuta.
More recent work in Wales and Lincolnshire (Preece 1984a), the Mendips (Willing unpub.) and Sussex (Ellis 1983a) has shown that these biozones can be applied with modifications to suitable deposits throughout southern Britain. Work by Preece (1984b) in
Glen Avon, Scotland has shown that the molluscan biozones cannot sucessfully be applied to deposits this far north.
Molluscan assemblage biozones have now been established by
Lozek (1982) for the highland belt of Central Europe. Lozek has investigated more than 150 late Vistulian-Holocene depositional sequences from which he has produced a scheme of six zones (A to F) which are summarised here briefly:-
Zone A - Late Vistulian Pleniglacial
Open-country species adapted to very dry, cold conditions
Zone B - Late Vistulian (=Late glacial)
Tolerant open-country and catholic species, including
Discus ruderatus. A more diverse fauna. 72
Zone C - Early Holocene (approximately Preboreal and Boreal)
Discus ruderatusfauna of woodland species with xerothermic
elements. Dominance of open woodland species.
Zone D - (Atlantic)
Closed woodland species predominate.
Zone E - (Epiatlantic
Closed woodland species dominant. Discus ruderatus
disappears and Carychium tridentatum reaches maximum
abundance. Optimum forest fauna.
Zone F - (Sub-boreal)
Re-expansion of open ground and weed species.
These biozones can only be applied to the highland belt in central Europe. They have been correlated with the Holocene stratigraphy by archaeologically dated horizons in the sections.
Lozek's zones can be criticised as they are based on work from many sites, without defined stratotypes. Also they have a restricted application as they cannot be used in the Alpine regions or in the
Chernozerm belt as neither have ever had a forest vegetation.
v. Taphonomy
In order to reconstruct past environments from fossils it is essential to understand the formation of the sediments, and the amount of distortion of the original life assemblages by processes of transport, burial and fossilisation. Taphonomy literally means 73
'the laws of burial' and was originally defined by Efremov (1940).
It is concerned with all aspects of the passage of organisms from the biosphere to the lithosphere as shown in Figure 5.
The sediments described from the South Downs consist of
Late-glacial and Postglacial slope washes which in places include soils. The slope washes contain molluscan assemblages with a large allochthonous component, as the shells represent a wide range of habitats within the catchment area. This is in contrast to the buried soils which contain an autochthonous assemblage of the molluscs living on the soil surface.
The distortion of the living assemblage that occurs during fossilisation can be summarised under six headings:-
a) Transport
This causes the removal of biological information from one environment and its addition to another, and is prevalent during the Late-glacial, and in the Postglacial after vegetation clearance. Transport of shells occurs by mass movement, fluvial or aerial processes, although a few shells may be moved by other animals,. as for example by worms mixing up the sediment, by being carried on animal coats and by birds eating them (accidentally or purposely) and excreting the shells elsewhere. In particular thrushes collect Cepaea and deposit them at their anvils. Cranbrook
(1970) has studied the shells in starling droppings from birds feeding on arable land and grassland. He showed that starlings feeding on grassland eat more snails than those feeding on arable 74
Life assemblage (biocoenose or community)
Allochthonous Autochthonous material material
trans,00rtation
Death assemblage (thanatocoenose)
fossilization
Fossil assemblage
Figure 5. Taphonomic Processes. 75
land. Sea birds are also known to eat and excrete molluscs and this can be cited as one explanation for the water molluscs found in these dry valley deposits.
b) Non—preservation
This would happen only if the pH was sufficiently low for solution of the shells. This is unusual in calcareous areas and would only occur in the patches of chalk heath (Perrin 1956) or where drainage and downward water percolation is sufficiently fast for leaching. There is also non—preservation of some of the thin—shelled species such as the Zonitidae. This differential destruction has been discussed at length by Sparks (1964). It is obvious that the large—shelled species are more prone to crushing than smaller ones and thin—shelled than thick. Sparks has also demonstrated that shells with a maximum and minimum dimensions of a ratio of less than 3:1 are less likely to be destroyed, and that the more loosely coiled shells such as Vitrina pellucida are more prone to destruction than the more tightly coiled species such as
Punctum pygmaeum. Finally there is the loss of biological information about species that can only be identified on the characteristics of the living animal as for example slugs, as slug plates are not diagnostic to the species level.
c) Diagenesis
Shell diagenesis can occur either chemically by mineral alteration of the shell, or physically by changes in the sedimentary environment after death. Both types of diagenesis occur 76
within these sediments. Physical diagenesis of the shells occurs as
they are either moved with or buried by the sediments causing them
to break into fragments. Chemical diagenesis by leaching and
solution also occurs and is indicated by the differential
preservation of the shells within samples and also laterally across
the section.
d) Redeposition
This process is dependent on weathering and transportation and creates problems with the interpretation of the Late—glacial, and the Postglacial clearance assemblages because of the large component of allochthonous shells reworked from earlier horizons.
e) Duplication
This can be a problem with assemblages containing bivalves or where shells are highly fragmentory. Care is taken when counting to ascertain only the minimum number of individuals present. Shell fragments of large shelled species such as Helix aspersa are often very numerous, clearly representing more than one individual but often with no identifiable apical remains to count.
f) Contamination
Mixing of the deposits occurs at all the sites but is most easily recognised at the junction between the Late—glacial and
Postglacial sediments as fragments of Pomatias elegans and tiny species such as Carychium tridentatum filter down cracks and root 77
holes and become incorporated into the Late-glacial deposits.
Differential preservation between shells may also be indicative of contamination. Late-glacial shells tend to be well preserved, whereas the Postglacial shells are usually battered and corroded.
Also Pupilla muscorum was larger in size during the Late-glacial so that contamination from Postglacial Pupilla can be spotted. Mixing is increased in the Postglacial sediments by the actions of animals. Worms do the most mixing as they create burrows and they also transport and redeposit fine materials in soil voids or on the soil surface. Finally contamination of the fossil assemblage is caused by living species of mollusc that burrow into the sediments, as for example Ceciliodes acicula which has been recorded living at depths of up to 2 metres (Evans 1972). 78
6. NOTES ON CERTAIN MOLLUSCAN SPECIES
Prior to discussing in detail the study sites, it is useful to examine the status and geological history of some of the main diagnostic species found during this research.
Biozones and z
These Late-glacial zones contain a fauna for which there is no true modern analogue. The species have open-country ecological requirements but are restricted in number, being dominated by
Pupilla muscorum, Vallonia costata, V. pulchella, Abida secale,
Helicella itala and Trichia hispida. These open-country species became suppressed in the Postglacial by the spread of forests but many managed to survive in refuges and to re-expand after deforestation.
Early Postglacial Biozones a-c
Although early Postglacial sediments were absent from the sites studied, one shell of Discus ruderatus, a zone b fossil, was recovered from a subsoil hollow at Cow Gap.
Discus ruderatus. This boreal/alpine species occurred only in the early Postglacial biozones, being replaced by D. rotundatus in biozone c at approximately 8000 B.P. during the mid Postglacial thermal optimum. On the Continent it is found mainly in coniferous woods. It is now extinct in Britain although it is possible that relict populations may exist somewhere in the British Isles. 79
Biozone d
These assemblages were found at the sites within the buried soils and the subsoil hollows. The assemblages are shade-demanding and would be found today in light woodland.
Acicula fusca. This species is characteristic of late biozone d. It can be found today living around damp hollows in sheltered woodland environments but is not very tolerant of human disturbance.
Consequently its distribution is receding and this may have been accentuated by the drop in winter temperatures since the mid
Postglacial.
Vertigo pusilla. This species has shown a marked decline since the
Boreal and Atlantic periods, possibly due to deforestation and the disturbance caused by farming. It is now extinct in a great many counties (including Sussex). There has been much debate as to whether the decline is man-made or climatic.
Spermodea lamellata. Two shells of this species occurred in the subsoil hollows at Asham. This is another late zone d indicator, arriving slightly earlier than A. fusca. It is one of the few species that is diagnostic of ancient woodland that has never been clear-felled. It has declined strongly since the Postglacial thermal optimum due to human pressures and long term climatic changes. It is now almost totally absent from southern Britain, the nearest colony to Asham being at Balcombe, Sussex. 80
Helicigona lapicida. This species is characteristic of biozone d but has now receded from much of southern and eastern England
(including Sussex) partly because of the removal of old hedgerows which formed its principal habitat in many areas.
Pomatias elegans. This species is thought to have arrived in
Britain at about 7000 B.P. It is present in low numbers throughout biozone d and peaks in abundance at biozone d/e boundary just before the expansion of the open-country genera. It favours a loose rubbly substrate such as would occur at clearance.
Zonitoides excavatus. An unusual find from the subsoil hollow at
Cow Gap (biozone d) was two shells of Z. excavatus. This is the only British terrestial mollusc which is truly calcifuge, avoiding neutral or calcareous soils. Its presence on the chalk at Beachy
Head in the mid Postglacial probably indicates pockets of acidification. This species was more widespread in the mid
Postglacial and has been recorded from other calcareous contexts, for example from tufa at Blashenwell, Dorset (Preece 1980a) and at
Totland Bay, Isle of Wight, and Caerwys, North Wales (Preece 1978).
All the species that are characteristic of biozones y-d inclusive migrated into Britain from the Continent in response to vegetational and climatic changes. This is in contrast to many of the species characteristic of biozones e and f which are introductions. 81
iv. Biozones e and f
These biozones result from forest clearance and are preserved within colluvium that formed because of accelerated soil erosion.
Several long depositional sequences provide an excellent opportunity for expanding our knowledge of these biozones.
Weed specie's
The term 'weed' is usually used in a botanical context for plants that invade an area after the removal of the natural vegetation cover. They are usually described as pioneers and form the first part of the new vegetation cover. The term can just as usefully be applied to land snails that colonise areas after clearance. It would include both the introduced alien species from the continent and the Late-glacial open-country forms that were excluded from most areas by the spread of the Postglacial forests.
Many of the Late-glacial relicts are not exclusive to the clearance biozones as they were able to persist in reduced numbers throughout the woodland biozones.
Late-glacial relicts
These are open-country species that were pesent in Britain in the Late-glacial and have managed to survive the spread of forests.
Fossil molluscan studies show that these species gradually became excluded or reduced in number in many areas, but were able to survive in suitable, very local habitats until forest clearance.
Clearance created open-country conditions, similar to those in the 82
Late-glacial, allowing relicts such as Vertigo pygmaea, Pupilla muscorum, Vallonia spp, Abida secale and Helicella itala to recolonise and expand. A few Late-glacial species (e.g. Trochoidea geyeri) have become extinct and others such as Abida secale have been relatively unsuccessful at recolonisation. Other relicts include-
Vallonia pulchella. This species was present in the Late-glacial and is usually associated with damp, marshy conditions. It has turned up consistently in the Postglacial hillwashes in late zone e/early zone f. It suggests the presence of damp, lush grassland within the catchment area but is inconsistent with the rest of the assemblage.
Helicella itala. This species was successful in the Late-glacial and again in recolonising areas after clearance in the Postglacial.
Today it is becoming increasingly local and indeed absent in areas where previously it was widespread. This decline can either be attributed to changes in farming such as a decline in sheep grazing
(it dislikes arable habitats and wet pasture, prefering short, dry grassland), or possibly to the effects of competition from alien helicellids.
Succinea oblonga. This is a relict species, found in Late-Devensian wind-blown sediments, returning to the area only after clearance.
Two shells of this species have been recorded from the Postglacial colluvium at Asham. 83
Truncatellina cylindrica. This species is also included in this
section although it occurrence in the Late—glacial is uncertain. It
has been recorded from several sites associated with cold climate
faunas (Kennard and Woodward 1905; Sparks 1952). It is certainly
absent from the early Postglacial biozones but appears in biozone e
after clearance.
Alien species
These are continental species that have been accidentally or
purposely introduced into Britain after Postglacial forest
clearance, probably in conjunction with the introduction of many
new plants and crops.
Monacha cartusiana. This Mediterranean xerophile occurs at all the
sites after forest clearance in mid zone e. Fossil occurrences show
that its British distribution was formerly greater, and its
recession may be due to the decline in summer temperature since the
Postglacial thermal optimum, possibly accentuated by changes in
farming techniques (Kerney 1970). The arrival of this species at
the Devil's Dyke has been radiocarbon dated to 2315 35 b.p. (BM
2137).
Helix aspersa. This Mediterranean species is thought to have been
introduced into lowland Britain at the begining of the Roman period
(Kerney 1966) and is used to define the begining of biozone f. It
has spread throughout much of Britain with the exception of parts of Scotland, where lack of lime and low winter temperatures prevent
it colonising. It occurs at all the sites studied in Sussex. 84
Cernuella virgata. This Mediteranean species is a post-Roman introduction into Britain, colonising man-made habitats after clearance. Its arrival in Sussex clearly postdates H. aspersa and predates Candidula intersecta, and is roughly synchronous with that of Candidula gigaxii.
Candidula gigaxii. Again a post-Roman introduction, appearing in
Sussex at approximately the same time as C. virgata. This species has recently declined in numbers and has disappeared from some areas, perhaps because of changes in agriculture.
Candidula intersecta. A southern European species for which there are no certain medieval records in Britain. It is probably a relatively modern introduction and certainly in Sussex it is the latest of the helicellids to appear, occurring at the Devil's Dyke,
Exceat and Asham only in the topsoil samples.
Monacha cantiana. A very late introduction into Britain, the earliest well-dated stratified context being from a third century
A.D. occupation level at Lullingstone Roman Villa, Kent (Kerney unpub.). In Sussex it was found only in a topsoil sample at the
Devil's Dyke but in contrast to M. cartusiana it is widespread today as it is well suited to colonising roadside verges and waste ground.
Ceciliodes acicula. The geological history of this species is unknown because it has been recorded living at depths of 2m, making it impossible to date its actual arrival into Britain. 85
7. DEVILS DYKE
Grid Reference: TQ 266103
Location: 3 miles N.W. of Brighton
Introduction
This is one of the most famous chalkland dry valleys due to its frequent citation in the literature and its impressive relief.
Since the early nineteenth century there has been speculation and debate over its origin. In 1828 P.I. Martin regarded the Dyke as a
'good specimen of the manner in which a rent may be enlarged by diluvian and meteoric action' whereas in 1830 Sir Charles Lyell claimed that the escarpment was an ancient sea cliff. It was not until 1887 when Clement Reid's classic paper on the origin of the dry valleys of the chalk was published that a more plausible explanation for its origin was proposed. Reid studied in detail three dry valleys, the Devil's Dyke, Arundel Park and Kingley Vale, and suggested that they formed during periods of permafrost when the ground was frozen causing the summer rains to flow overland and cut valleys. He stated that they could not have formed during the temperate period by normal streams because of the absence of gravel and terrace deposits.
The first advocate of a temperate—fluvial origin for the Dyke was White (1924). He very briefly discusses the origin of the Dyke, suggesting that it was once a branch of the beheaded valley which runs southeastwards to Patcham. He interprets the sharp bend in the valley as an elbow of capture.
In 1929 Sherlock wrote a short paper on the origin of the
Dyke proposing that it was of glacial origin, cut by glacial melt waters from an ice sheet occupying the Weald to the north. This theory was promptly attacked by many of his contemporaries including Wooldridge who wrote a comment at the end of Sherlock's paper stating that there was no evidence that ice sheets extended as far south as the Weald and pointed out the lack of glacial drift in the area. Wooldridge went on to suggest that the Dyke was cut by periglacial fluvial processes from the melting of snow capping the
Downs.
More recently Small (1962) has proposed that a combination of periglacial and temperate fluvial processes formed the Dyke. He suggested that the Dyke originated from spring-sapping along a joint when the water table was higher, and was subsequently modified by periglaciation. He argues strongly that the rainwater hypothesis of Reid is inadequate to explain the formation of the
Dyke because of the small size of the catchment area.
Despite the frequent use in the literature of the Dyke as a good example of a chalk dry valley it is really atypical. Only perhaps does Rake Bottom, Hampshire (Small 1958; Gordon and
Shakesby 1973; Shakesby 1975) match the Dyke in size and form. The
Dyke is a steep-sided valley cut mainly into Middle Chalk. The slopes often exceeding 30°. The upper part of the valley runs parallel to the chalk escarpment and then turns abruptly northwards through a sharp bend, finally breaching the escarpment at the 87
spring line, at 65m O.D. In the floor of the valley are two
pronounced steps (Figure 6). At the present day the lower step
corresponds with the spring head and the upper with the sharp bend.
The origin of this upper step has been explained by Small (1962) as
the notch left by the higher level springs that initiated the
valley. He also stated that the valley inf ill deposits in the Dyke were much less than in other scarp face valleys (although pits
excavated in 1982 and 1983 for the Fourth International Flint
Conference revealed Postglacial and Late-glacial deposits up to 4m
thick).
In addition to work on the geomorphology of the Dyke, archaeologists have studied the remains of the Late Iron Age hill fort on a spur of the Downs above the Dyke. It is described as a large hill fort with an irregular outline and weak defences (Bedwin
1978). Physically it is more like the Early Iron Age hill forts, but a small excavation in the interior revealed a shallow gulley that was interpreted as the foundations of a circular hut (Burstow and Wilson 1936). The associated pottery was dated to between 50
B.C. and A.D. 50, indicating that the fort may have been in use at the time of the Roman invasion of the area. Also in the floor of the Dyke are 'prehistoric' earthworks superimposed on the
Postglacial fill and known as the Devil's Grave. These were excavated at the beginning of the century (Toms 1924) and it was concluded that because of the absence of an old land surface beneath the ramparts and the shallowness of the overlying deposits that they were not of great antiquity. This interpretation of age has been upheld by these excavations which have shown that most of the Postglacial infill is historic in age. 88
r-I
a)
a)
4-) 4-1
a) 1-1 .H
$-4
00 0
if) (1)
00 •r-I rx-o
3 0 0 0 0 I 0 0 I 0 tn 1.0
89
Seven pits were excavated in the floor of the Dyke but only
five were sampled. One was too deep and the deposits could not be
bottomed and the other revealed very recent made ground containing
bricks. The location of these pits is shown in Figure 6, adapted
from Small (1962).
Pit 1 (TO 26641027)
This was the highest pit excavated up the valley at a point
just below the Devil's Grave. The Postglacial deposits reached a
maximum depth of 210 cm in the centre of the valley floor. The
general stratigraphy is recorded in the sketch diagram (Figure 7)
and the detailed stratigraphy from the point on the face where the
samples were taken.
Stratigraphy
This is summarised as follows using Munsell soil colour
notations:
Depth (cm)
0-20 Topsoil: grayish brown (10 YR 3/2) silt.
20-40 Brown (10 YR 5/3) silt with abundant small rounded
chalk fragments.
40-60 Dark brown (10 YR 4/3) silt with scattered rounded
chalk fragments.
60-140 Dark brown (10 YR 4/3) silt with virtually no chalk
fragments. 90
0
2
Et,
T. 0 91
140-160 Dark brown (10 YR 3/3) silt rich in charcoal.
160-180 Dark brown (10 YR 3/3) silt becoming increasingly
clay-rich down profile.
180-200 Brown (10 YR 4/3) silt, clay-rich with abundant
angular chalk fragments.
200+ Shattered chalk.
Mollusca
This pit was sampled at 10 cm intervals as the sediments
appeared to be fairly uniform stratigraphically. Shells were
recovered from all the Postglacial samples but were poorly
preserved being highly corroded and fragmentary. The Mollusca
obtained from the deposits are detailed in Table 1 and presented
graphically in Figure 8.
The shattered chalk at the base of the pit was sampled but
did not contain a periglacial molluscan assemblage. Thirteen shells
of Postglacial species were recovered but they clearly represented
contamination from the overlying Postglacial deposits.
In the basal Postglacial deposits (170-200cm), woodland
species were recovered totalling 39% of the total fauna. These
included Helicigona lapicida, Acicula fusca, Cochlodina laminata and Vertigo pusilla. From these samples open-country species were almost (<1%) totally absent.
At 170 cm there is a marked change in the composition of the
fauna as the open-country genera expand in number, suggesting 92
— —0 6 0 0000 0 000 4t00 00 0 0 • . 0
§1 1 I I gl aoilligi1 110 Oeptn(crns) Nonmer 01 5hel5 r 2 a 2 ACiCul0 fuSCO Corychium tridenlotum
Vertigo pusillo Aconthinuto acvleato
• n•=1/ • Discus rotundatus
Vitreo - I Aegopinetla aura Aegopinella nifidula OxychiluScellorius Cochlodino lominoto pideoteuo Het icigono lopicida
Pomatias elegons n11, •
Cochlicopa NNW
•n=1.1 Punctum pygmaeum Vitrino pellucid° wesovitrea hammonis Trichia
Aria nto I Cepoeo IMO Limo"( I DeroceroS
Vertigo pygmoeo =WM, MN OM Abido Secole • PupillO muscorvm • Aim • MEP NM • IMO Voltania costato
Vollonio Pulchella Vollonia excentrico al 1111
it010 rond,dula intersect° Mona Cha COrtuSicnC U. Alonocha COntiOno NOlor esperse
woe elar.d 102B1 interrnernate -„i1111111 % open Country
(1) —01 mOLLuSC ZONE
Figure 8. Molluscan Histogram of Pit 1. 93
clearance of woodland and the creation of open conditions. The
expansion is most marked in Vallonia costata but also occurs to a
lesser extent with V. excentrica and Pupilla muscorum. Just prior
to the main expansion of the open-country genera Pomatias elegans
peaks in abundance, suggesting the presence of a loose rubbly soil.
Above 170cm the open-country forms increase to become the
dominant ecological group. At 70cm V. excentrica becomes dominant
over V. costata, indicating more stable, damper conditions, which
in turn can be linked to the characteristic late expansion of V.
pulchella at 30cm. In the sample of topsoil there is some
re-expansion of the woodland genera, most obviously Carychium
tridentatum, which suggests some shrub regeneration and a
relaxation of grazing pressures.
Within these deposits the Arrival of the introduced species
into the area can be traced. At 140 cm Monacha cartusiana appears.
Its arrival into this valley has been dated to the late Bronze
Age/early Iron Age. It expands in numbers throughout the deposits
until 50 cm where it disappears. At 100cm the Romano-British
introduction Helix aspersa occurs and remains present throughout
the upper deposits. In this valley it is only in the topsoil that any of the introduced helicellids occur. At this site only
Candidula intersecta is present, coexisting with Monacha cantiana.
Interpretation
• In accordance with the biozone criteria established in Kent
(Kerney 1977; Kerney et al 1980) this molluscan succession has been 94
subdivided into biozones d, e and f.
Pit 2 (TQ 26651029)
This was excavated 15m down valley from Pit 1 for two
purposes: to bulk sample the basal Postglacial deposits to obtain a
radiocarbon date for primary clearance, and to sample in detail the
shattered chalk deposits down to the bedrock.
Stratigraphy
In this pit the Postglacial deposits reached a maximum depth
of 245cm. The stratigraphy was similar to Pit 1 with clay-rich dark brown (10 YR 3/3) silts overlain by 180cm of yellowish brown (10 YR
5/4) silts containing abundant rounded or sub-angular chalk fragments. At one point excavations were made into the shattered chalk to reach the bedrock at 4m.
Mollusca
The shattered chalk was sampled at 10cm intervals but was found to be devoid of shells.
One kilogramme from the bulk sample of the basal clay-rich deposits was analysed to obtain an idea of the molluscan assemblage being dated. The sample contained a mixture of woodland, catholic and open-country genera, and this together with the large number of
Pomatias elegans suggests an approximate correspondance with the clearance horizon. The molluscan assemblage was similar to that 95
described from the basal deposits in Pit 1 and so has been assigned
to biozones d/e. The list from this sample is given in table 2.
iv. Pit 3 (TQ 26671032)
This was excavated 25m down valley from Pit 2. There is a sharp lateral bend between the two pits.
Stratigraphy
In Pit 3 the Postglacial deposits reached a maximum depth of
320cm in the centre of the valley but the stratigraphy was essentially the same as that described from Pit 1, with the exception that there was no charcoal-rich layer or as stony a horizon just beneath the ground surface. Details of the south face of this pit are shown in an idealised diagram (Figure 9).
Three spot samples were taken in this pit to obtain an approximate idea of how the deposits and molluscan succession varied between pits and down valley. Sample 1 was taken from the basal Postglacial deposits which were dark brown (10 YR 3/3) clay-rich silts containing abundant rounded chalk fragments. Sample
2 was taken from the basal lighter coloured colluvium and was of yellowish brown (10 YR 5/4) silt containing abundant rounded chalk fragments. Sample 3 was taken from light yellowish brown (10 YR
6/4) silts with very few chalk fragments. 96
0 0_0 0 0 0 I\ 0 0 0
0
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o 0 0
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00PAII • 0 0 0 & _ • ^ 101,11/n/ 90J0.20.1.13
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Suatela 00.00014i oppidog ouotIpnaff 0 0 00011101>!0 011190013 01120/4001 0111.11,0111300 snY0Ilaa stuAloAr0
0111P1110 0nouldo5ay mold 0,1001006ar 000.11000 &LIM
tnjopuni0J 0n.V0 00•1 r-- mow= 07nuiwuroy
W010100014 tung43A/03
suarl 10 +.0000
Jagtunu aplutin 97
Mollusca
The results from these samples are listed in Table 3 and
presented graphically in Figure 9.
Sample I contained a predominantly woodland fauna, including
Helicigona lapicida, Cochlodina laminata, Clausilia bidentata and
Acanthinula aculeata. It contained no open-country species. Sample
2 was taken from the base of the lighter coloured colluvium and
contained open-country forms including Vallonia spp, Pupilla
muscorum and Vertigo pygmaea, but still with some woodland species
persisting. Sample 3 contained a predominantly open-country fauna
including the early introduction Monacha cartusiana.
Interpretation
These samples have been assigned to molluscan biozones d and
e.
v. Pit 4 (TQ 26621051)
This was excavated much further down valley towards the
valley side. At this point the central part of the valley floor contains a spring.
Stratigraphy
The Postglacial deposits reached a thickness of 210 cm but excavation was continued into the shattered chalk so that a sample 98
of this could be obtained. Four samples were taken to compare the stratigraphy and molluscan succession between pits and down valley.
The general stratigraphy of this pit is recorded in the sketch diagram (Figure 10).
Sample A was taken from the shattered chalk (2.5Y 7/2) and was made up almost entirely of angular chalk fragments with no fine matrix. Sample B was taken at 170 cm and was of light yellowish brown (2.5Y 6/4) silt containing abundant rounded and subangular chalk fragments. Sample C was taken at 100cm and was of light yellowish brown (10 YR 6/4) silt containing a few large chalk fragments. Sample D was of the topsoil which was dark grayish brown
(10 YR 4/2) silt with no chalk fragments.
Mollusca
The Postglacial samples from this pit were fairly rich in
Mollusca although they were poorly preserved.
Sample A contained no shells or shell fragments.
Sample B was taken from the basal colluvium and contained an open-country assemblage dominated by Vallonia costata and V. excentrica, and to a lesser extent by Monacha cartusiana. Woodland species are present only in very low numbers.
In sample C there was a dominance of open-country species, including Abida secale. Helix aspersa fragments were also present and M. cartusiana disappeared.
99
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100
Sample D (the topsoil) contained shells of Candidula gigaxii,
a species not present in samples from the other pits.
Details of the stratigraphy and molluscan results are shown
in Figure 10 and the results detailed in Table 4.
Interpretation
These samples have been assigned to biozones e and f. No
biozone d deposits were present in this pit.
vi. Pits (TQ 26641053)
This pit was dug furthest down the valley below the spring
line. The Postglacial deposits attained a thickness of 245cm. The
general stratigraphy of this pit is recorded in the sketch diagram
(Figure 11) and the detailed stratigraphy is from the point on the
face where the samples were taken.
Stratigraphy
Depth (cm)
0-20 Topsoil; grayish brown (10 YR 3/2) silts.
20-130 Pale brown (10 YR 6/3) silts with abundant rounded chalk
fragments.
130-180 Light yellowish brown (2.5 Y 6/4) silts, very clay rich.
180-205 Brown (10 YR 4/3) silts containing chalk fragments.
205-235 Very dark brown grayish brown (10 YR 3/2) silts with some 101
east face of pit N S samples Depth 1 (cms) 0 KEY 0 - 00 0 0 topsoil - 0 0 o o mil 0 _ 0 o 0 0 0 chalky silt 0 o - 0 0 co 1'11 50 0 0 0 0 a 0 in situ soil - HA o _ Io a 0 0 chalk fragments - 0 a o IV31 0 - 0 0 o 0 100 _ _ 0 0 _ 0 _ 0 150 0 _ _ o - 0 a o - 0 C, 0 0 o a 200 0 a . 0 0 Qt - 0 o _ a I o 1 0 - 0 o 0 _ 1 0 10 0=. c* Co O 0 CI 0 0 cm 911=5 C:2:14=4Eg 0 0 - caC=t=9 C3 9=F:ea:I:I C=)C=1 1:::) I 140cms
Figure 11. Sketch Diagram of Pit 5. 102
iron staining. A few large chalk fragments that increase
in abundance down profile.
235-245 Zone of mixing between the Postglacial deposits and the
shattered chalk.
245+ Shattered chalk.
Mollusca
This pit was sampled at 5cm and 10cm intervals depending on
the stratigraphy. It was not possible to sample the whole sequence
because of lack of time. In the basal Postglacial deposits there
was a complete mixture of woodland, catholic and open—country
species, although the woodland component was the most diverse found
in any of the pits and included Acicula fusca, Helicigona lapicida
and Ena obscura. At 210cm the open—country forms expand slightly in
numbers suggesting patchy clearance. At 165cm Monacha cartusiana appears but by 75cm it has gone and Helix aspersa is present.
Throughout these deposits the catholic genera predominate, namely
Trichia spp, Deroceras spp and Limax spp, making precise
environmental determinations difficult. The Mollusca from these
samples are listed in Table 5 and presented graphically in Figure
12.
Interpretation
These deposits have been assigned to biozones d, e and f.
103
3Noz asmlov4
1..4000, 1..00 N.
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DJI.nuaOra 00,10110A 1n1 oilay.21nd 041011001
INDj ga, DivellOA 11= ••
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voodoo/ Dluquy
^
Mu! 7/511.07.0..a0 puoww04.1 ommosaN op!.7ni1ad otig.mA wnaowatd wmound
Odoampo0 IMM
Sul2671a soaowod
opi.wdol ouodPnaH • • •
DJDJUipq sn010 INDu.swal 0utp0l1P0,2 WyJbllao snIN0,047
Oinp.rpti onauldo5ay cvnd Dl lawde6ay
oa.,191 sn i0W(0110J Snpa ainnqo Djoitruo elnupauCkly wn.IDNapiAl trirmp,4co Onni 011V1.2),
Si 1.6 10 ...0tuunly
( S. ') YlOaa — ,--- — n -0,o -° 0 . 0 -0 0 rip U MNIVn33 — _ U-0 — 'r-----6v070_i /LOn 0 --- 0 — ANd0it911Yill5 _- 0-0-0'0 "U ' 0 U . 104
vii. Other Remains
Marine Mollusca
Fragments of Mytilus edulis were recovered from Pit 1 from the topsoil and at depths 30-40cm, 50-60cm, 70-80cm, 90-100cm, and also from Pit 3 in sample 2. Their origin is uncertain but they may be the result of manuring the land using seaweed (Thomas in Bell
1977), or less probably human food debris.
Vertebrates
Bones and teeth were recovered from Pit 1 (110-120cm,
120-130cm, 140-150cm, 150-160cm, 160-170cm, 170-180cm, 180-190cm,
190-200cm, 200-210cm), Pit 2 (bulk sample), Pit 3 (all 3 samples), and Pit 5 (all the samples with the exception of 210-2156M and
245-255cm). These have been identified by Andrew Currant as remains of the bank vole Clethrionomys glareolus. This species occurs in deposits of Late-glacial age to the present day. It is the dominant microtine in woodland habitats, feeding mainly on fruits and seeds, but on the whole has rather catholic tastes.
viii. Dating
Radiocarbon
Two charcoal samples were submitted to the British Museum
Research Laboratory. 105
The first sample was from Pit 1 at 135-150cm depth. The
charcoal was identified by Rowena Gale as Prunus sp, Rosaceae
(subfamily Pomoideae), Fraxinus sp, Corylus sp and Acer sp.
A date of 2315 ± 35 b.p. (BM 2137) was obtained from near the
base of molluscan biozone e. This corresponds with the first appearance of Monacha cartusiana (Burleigh et al 1984). This Iron
Age date was somewhat later than expected for primary forest
clearance but it should be noted that the actual clearance horizon
(base of biozone e) lies 25cm lower. The plant species represented by the charcoal suggest some secondary regeneration, possibly indicating that primary clearance may have been for shifting settlements and agricultural purposes.
The second sample was from Pit 2 at 190-210cm depth from what was interpreted as the primary clearance horizon. The charcoal extracted was less than was needed for conventional dating techniques. The sample has now been submitted to the radiocarbon accelerator laboratory at Oxford and a result is awaited.
Pottery
Fragments of pottery extracted from the pits were entirely of undiagnostic wall sherds. The majority were recovered from Pit 1 in association with the charcoal-rich layer and were hand-made, flint-gritted pottery, a type most typical of the earlier part of the first millenium B.C. (identified by Valery Rigby and Ian
Kinnes). 106
ix. Discussion and conclusions
The valley will be here considered as a whole and not as individual pits.
Although the basal shattered chalk was sampled at various
places ' in the Devil's Dyke, no contemporary molluscan assemblages were recovered. It is nevertheless likely that the chalk was shattered during the Devensian glaciation.
The overlying Postglacial deposits do not span the entire
Postglacial, but only the later half. Sediments from the early
Postglacial would probably only be preserved in chance subsoil hollows or more likely in tufaceous deposits below the spring line, and sediments of this type were not located. All the Postglacial sediments encountered in this valley are of colluvial origin, with the exception of the stratigraphic layer 205-235cm, Pit 5, which was an in situ soil, buried and hence preserved by colluvium. These colluvial sediments formed as a result of accelerated soil erosion caused by forest clearance and/or cultivation by man, as discussed in chapter 3.
The woodland molluscs found in the basal colluvium and the in situ soil indicate that the Dyke was still wooded in the mid
Postglacial and that clearance had begun by the Iron Age. A charcoal rich layer in Pit 1 has been radiocarbon dated to
2315 ± 35 b.p. (BM 2137). Clearance would probably have been a gradual process, beginning in the valley bottom and progressing up the valley sides. The initial clearance may have been carried out 107
to provide timber to build the Iron Age fort on the spur nearby or more probably just to create open space for settlement and agriculture.
Once clearance had begun on the slopes of the valley, colluvium would begin to accumulate on the valley floor. As a result the molluscan assemblages in the basal colluvium (Pits 1, 3 and 4) are mixed (allochthonous), with molluscan contributions from both the stripped pre-existing woodland soil and the newly created open country habitats. The Mollusca from these basal deposits show differential preservation, the shells of the woodland species being highly corroded and fragmentary, whereas the open-country species are unusually intact and sometimes retain pieces of the periostracum.
The build up of colluvial sediments would have continued for as long as the Dyke was used for arable farming. The cross-sectional form of the valley makes it clear that it was once ploughed, as the junction between the floor and the sides has been undercut so as to increase the flat area of the floor itself.
Ploughing probably continued well into the Romano-British period as at least 90cm of colluvium has built up after the arrival of Helix aspersa (Pit 1).
Once abandoned the land would have reverted to stable grassland. This would have been maintained by grazing pressures exerted by sheep and rabbits. From then onwards colluvium would have ceased to form at the same rate, leaving only the topsoil and turf to represent the greater part of the Christian era. 108
It is only recently that the myxomatosis epidemic and the reduction in sheep grazing has allowed scrub to invade the Dyke.
This has permitted some expansion of shade—demanding forms as found in the topsoil samples (Pits 1 and 4).
At present a 21 acre site has been fenced off within the
Dyke. It is intensively grazed by sheep to try and attract rare plants and other wildlife back into the area. This scheme is supported and funded by the Nature Conservancy Council and the
Countryside Commission. 109
8. ASHAM QUARRY
Grid Reference: TQ 440061
Location: 2.5 miles SE of Lewes, 2 miles NW of South Heighton
i. Introduction
A road cutting in the south-west corner of this quarry has provided sections through the floor of a scarp-slope dry valley running NNE from Itford Hill to the River Ouse floodplain. In the late 1960s Late-glacial deposits of poorly stratified chalk debris were examined by J. G. Evans and R. B. G. Williams (Williams 1971).
These sections have since been destroyed. Further expansion of the quarry in the mid 1970s revealed Late-glacial and Postglacial deposits on the north and south side of the road cutting. This valley is directly north of the dry valley of Itford bottom studied by Bell (1981, 1983) and both are located close to the famous
Bronze Age burial site at Itford Hill (Burstow and Holleyman 1957;
Holden 1972).
The Late-glacial molluscan assemblages at Asham were first examined by Evans and Williams (Williams 1971), and their results are presented in Figure 13. They examined a much longer
Late-glacial sedimentary sequence than is available at the site today. The molluscan histogram has been redrawn and molluscan biozones assigned (Ellis 1983a). It is only at this section that biozone y is preserved, based on the low diversity of the assemblage and the absence of any of the slightly thermophilous 110
70 —
30 —
40
30—
60—
70 — — 110
70
100
00 —
120—,
130 —
'40 —
150 —
170
ISO —
M—
200 —
710 —
220 —
730—
260— — NO FAUNA 730 —
760 —
270 --
750—
0 330 GOO n00 30 0 100 102 100000 ,00 BOO 300 700 12 LLLLJ LJ 1,2 LLL 1.1 Li t.1_1.1.1 E / LI.L.Lci
Figure 13. Molluscan Histogram Redrawn from Williams 1971.
111
species which characterize zone z (e.g. Trichia hispida, Helicella
itala and Abida secale).
South section
Stratigraphy
The deposits at this section are of both Late-glacial and
Postglacial age, with a hiatus of many thousands of years between
them. The Late-glacial deposits consist of poorly stratified chalk
silts and rubbles interbedded with pockets of fine silt,similar to
those described by Evans and Williams (Williams 1971). Overlying
these deposits are Postglacial fine silts which can be subdivided
into the stratigraphical units of a subsoil hollow fill, an in situ
soil, a transported soil and a hillwash.
Two columns of samples were taken from this section (columns
A and B) the positions of which, together with the general
stratigraphy of the section, are shown in Figure 14. The detailed
stratigraphy of the sample columns is as follows-
Column A
Depth (cm)
0-30 Quarry fill.
30-125 Pale brown(10 YR 6/3) silts containing abundant small
subangular chalk pellets and some large chalk
fragments.
125-145 Dark brown (10 YR 3/3) silts containing abundant small
subangular chalk pellets. Presence of charcoal
fragments. 112
•
0
C/)
4—)
0
czt
cr)
4-1
0
$.4
CO •r(
4-) a)
113
145-185 Dark brown (10 YR 3/3) silts with no chalk fragments,
becoming lighter in colour down profile.
185-220 Poorly stratified chalk rubbles and silts.
220+ Shattered chalk and flint.
Column B
Depth (cm)
0-30 Quarry fill.
0-90 Pale brown (10 YR 6/3) silts containing abundant small
subangular chalk pellets and some large chalk fragments.
90-105 Dark brown (10 YR 3/3) silts containing abundant chalk
pellets in the upper levels.
105-225 Brown (10 YR 4/3) silts.
225-230 Poorly stratified chalk rubbles and silts.
230+ Shattered chalk and flint.
Careful field examination of the subsoil hollow (Column B,
Figure 14) was carried out to obtain some idea of its size. During
this three year study the hollow was reduced in size as the face
weathered back. Furthermore by augering horizontally into it
Late—glacial silts were reached at only about 60cm. Clearly then
the hollow is more likely to have been a closed basin than a linear
channel.
Mollusca
To obtain the fullest biostratigraphical detail from this 114
section two columns of samples were taken; one where the deposits
were thickest and most complete and the other through the subsoil
hollow extending into the overlying soil so as to link the
molluscan succession and the stratigraphy between the columns.
Column A
Samples were taken at 5cm intervals from 30 to 220cm depth.
The basal samples (185-220cm) were of the Late-glacial chalky silts
and rubbles, and contained a typical Late-glacial molluscan
assemblage of Trichia hispida, Punctum pygmaeum, Euconulus fulvus,
Abida secale, Pupilla muscorum and Vallonia spp. In the upper
samples there has been contamination by Postglacial species such as
Carychium tridentatum, Clausilia bidentata and Discus rotundatus
the shells of which had probably fallen down root-holes and cracks made by the Postglacial vegetation colonising the Late-glacial surface.
Between the Late-glacial deposits and the overlying
Postglacial silts is a hiatus of several thousand years. The basal
Postglacial deposits (145-185cm) contained a predominantly woodland assemblage, including C. tridentatum, Vertigo pusilla, Acanthinula aculeata, D. rotundatus, Aegopinella pura_ and A. nitidula. Within these samples catholic genera such as Trichia hispida are largely suppressed, together with moderately shade tolerant open-country species such as Vallonia costata.
At 145cm is the clearance horizon. This is marked sedimentologically by a sharp increase in the number of subangular 115
chalk pellets in the deposits, and malacologically by the dramatic expansion of open—country molluscs from 145cm upwards. Also at this level Pomatias elegans peaks in abundance, suggesting a rubbly soil.
At 145cm Vallonia excentrica and Helicella itala rapidly expand in numbers, and are joined at 135cm by Monacha cartusiana which persists throughout the upper deposits. Of particular interest is the appearance and persistance of Vallonia pulchella above 135cm and the occurrence of one shell of Succinea oblonga at
100cm.
The results of the molluscan analyses are shown graphically in Figure 15 and listed in Table 6.
Interpretation
On the basis of the zoning criteria established in Kent these deposits have been assigned to molluscan biozones z, d and e.
Column B
This was taken through the subsoil hollow and the overlying soil. The sediments in the hollow are the earliest Postglacial deposits preserved at this site as they are stratigraphically between the Late—glacial deposits and the overlying soil. They were sampled at 5cm intervals, and sampling was extended into the overlying soil and down into the Late—glacial silts (where no
Mollusca were found).
116
S3NOZ Nvosmiovu CD "0 N
euepnpea etpeuow ++--+ ++—+ + + +
ele)! ellaallaH +
equtuaua eluolleA ++ enAl= MEM
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somptirlio, smsyo ++ + + + + ++—+ uppitity etorip.tiati + + +4 + ++++++ rilyumill lipt1/1/303 + 4+ In1.11:dpIt/ eystulo + +4 + ++—++++ ...-.' i9nasqo i113 01 , !:11117V 1.711(1111J1111V vammpoo.1 ellisixt (''J '3A
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Throughout the subsoil hollow (110-225cm) the fauna is made up mainly of woodland species which reach a maximum dominance at
185-190cm (75% of the total). These sediments have allowed a more detailed examination of the woodland assemblages than those preserved in the basal Postglacial deposits of column A. Although the silts appeared to be lithologically uniform the contained
Mollusca revealed a stratification. The overall assemblage was dominated by Carychium tridentatum and Discus rotundatus, and to a lesser extent by the other common woodland species. In addition
Vertigo pusilla, Ena obscura, Balea perversa and Lauria cylindracea occurred sporadically throughout the deposits.
At 150cm two shells of Spermodea lamellata were recovered.
This species is now virtually extinct in South East England and does not occur in this area of Sussex. At 145cm Acicula fusca appears and it expands up to 105cm in the overlying soil. From work in Kent and elsewhere this species is believed to be a very late immigrant into the mid Postglacial woodland environment and this is supported by the present work in Sussex.
At 110cm, at the top of the hollow, samples were taken into the overlying soil. The Mollusca repeated the same pattern as in column A, with a predominantly woodland assemblage in the basal samples being replaced suddenly by the open-country forms such as
Vallonia spp and H. itala. Monacha cartusiana also appears in the clearance horizon. Just prior to the expansion of the open-country forms, Pomatias elegans peaks in abundance indicating loose rubbly soil conditions as would be expected at clearance. 118
The results of the molluscan analyses are presented graphicaly in Figure 16 and listed in Table 7.
Interpretation
According to the biozone criteria established in Kent these deposits have been assigned to molluscan biozones d and e.
Other remains
Marine Mollusca
Fragments of Mytilus edulis were recovered at column A from samples 30-35cm, 45-50cm, 55-60cm, 65-70cm and from column B from samples 90-95cm.
Vertebrates
Bones and teeth were recovered from column A (140-145cm,
160-165cm, 170-175cm, 175-180cm) and from column B (95-100cm,
115-190cm inclusive, 195-200cm, 200-205cm, 220-225cm). These have all been identified by Andrew Currant as remains of bank vole
Clethrionomys glareolus.
Radiocarbon dating
Charcoal from the clearance horizon (140-150cm) was submitted to the British Museum Research Laboratory and a date of 3580 ± 280
119
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op .H snjopuruoJ silos hg o. nasQ0 0U3 • • • °JO, 1.34101 oapocu „tads
CIJ0a7 li30 op, u! tau 133y • oa.3o. u wfo opno7 0 wsnd otP
Wf'3OWJPIJf Lun !yak:op oinapte
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• • o NIAM110D s • • o 0 _9 -1 0 0 AHdY/1911V/IIS I • of 120
b.p. (BM 2277) was obtained. This suggests early Bronze Age clearance of this valley.
North section
This section is 24.2m further down the valley than the south section and provides a longer and more complete sedimentary sequence. There are over 4 metres of Postglacial silts preserved here including the uppermost silts and topsoil that had been at least in part removed and replaced by quarry fill at the south section.
StratiRranhy
The deposits are of both Late-glacial and Postglacial age with a hiatus of several thousand years between them. The general stratigraphy of the section and the position of the sample columns
(C and D) is shown in Figure 17. The upper diagram is a plan showing the curve of the section, with the letters A-F linking up with those on the general stratigraphy diagram. Two columns of samples were taken, the main one (column C) where the stratigraphical sequence was thickest and most complete (including another subsoil hollow) and the other (column D) through the basal
Postglacial silts where a rich charcoal layer occurred. These charcoal-rich layers appeared to be discrete local burning episodes, possibly to aid clearance of the valley by the removal of large trees. Alternatively they may have been cooking fires as a large bovine bone was found in the centre of the burnt layer at column C.
121 I
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122
The detailed stratigraphy recorded for the two sample columns
is as follows-
Column C
Depth (cm)
0-15 Topsoil. Very dark grayish brown (10 YR 3/2) silts.
15-275 Pale brown (10 YR 6/3) silts containing abundant large
and small subangular chalk and flint fragments.
275-330 Dark brown (10 YR 3/3) silts containing abundant small
subangular chalk pellets.
330-345 Dark brown (10 YR 3/3) silts rich in charcoal fragments.
345-380 Dark brown (10 YR 3/3) silts with very few chalk
fragments.
380-395 Zone of mixing between Late-glacial chalky silts and
Postglacial silts.
395-405 Poorly stratified chalk rubbles and silts.
405+ Shattered chalk and flint.
Column D
Depth (cm)
0-25 Quarry fill.
25-310 Pale brown (10 YR 6/3) silts containing abundant large
and small chalk fragments.
310-370 Dark brown (10 YR 3/3) silts containing abundant small
subangular chalk pellets.
370-420 Dark brown (10 YR 3/3) silts rich in charcoal fragments
(400-410cm).
420+ Shattered chalk and flint. 123
The discrepancy between the actual depths of the two columns and the general stratigraphy diagram has resulted because column C was sampled on a completely vertical face cut by a mechanical
digger whereas column D was measured and sampled where the section was curved with overhanging bulges of soil.
Mollusca
a) Column C
Samples were taken at 5cm intervals, although from 10-325cm
only alternate samples were analysed as the molluscan assemblages recovered were very uniform. A complete vertical sequence was
taken, beginning in the Late—glacial deposits, proceeding through a small subsoil hollow and finally through the overlying 3-5m of mainly colluvial Postglacial deposits. These last can be subdivided
into in situ and transported soil, and a hillwash.
The results of the molluscan analyses are presented
graphically in Figure 18 and listed in Table 8.
The totals from the basal samples (390-405cm) had to be amalgamated as they were very low. Nevertheless it was clear that at least some of the shells were of Late—glacial age, as their
preservation differed markedly from those of the Postglacial woodland species (Pomatias elegans, Carychium tridentatum,
Acanthinula aculeata, Discus rotundatus and Clausilia bidentata)
that are contamination from the overlying deposits. Additional
124
I' III1i 1/111 I ii I ill I I I g 1 Ili It i Hill I III I t t 1 I 11 ' I r r. ' • I NS I I illral IN RR IN El • I • • • OM • • NMI II I • • • • MI • MI NI I III • - II WSW& • • • II IIU • OM INN I IM II I III I I I • MN MINI • I MI O Iii • • • • • O I • • - 1:-:-•
_ . . ON I II III I I I f .. . MI 1•11•1 • • NI • II • I I :. • NI IMIN •I IN I ON NI I u rn _-. • l• MIN I OM l• Il• ,. . I I • • ME II MI 11E01E1 • -_. • •• III En I • MN I • I • • ...... I • 1• • •• •INIIIMI !MI - _... 1 •Ili BM •1•111EN NI • 1 • 1 . • I I MI MIN • I MIN I I. I I I I • SIM • I OM • I I 11:1=1 :3. I . I • IN NM I NMI II • I .",• • I IIII MIN I MI MN I I • I I I O 1 IMO ii MN MI ii I I •III INN I NI . NMI I I =MN - . I • NUM •• I MI MN II . I • IN .110111 •I• • MEI I .,. .. I • • NM • 11E111 ii I • I II• MIi.iu • I • p 1 so mil II. Immo II I I= owl i me 1 1 so•- n am II•e missi• rn MI I . - . I • II NI NMI III ... 011-1 MN III MI OM I • IIII I II 1 • I • II II II I MI MN I • . •1. -k _..,, . : 11 1 • : _::: • • •i i •: — ... 1 ••• f f IA - I •11 ii — NO _LI •••
— 1 200 : i : : - GM Mb 11 •. : II 1 i i 1 1 z/d ;tilt llllll 10 CCM 0 SO I00••
Figure 18. Molluscan Histogram Worth Section, Column C. 125
evidence is provided by the presence of Abida secale as this was found only in the Late-glacial samples and not in the Postglacial colluvium.
The molluscs recovered from samples 350-390cm were predominantly of woodland forms, largely C. tridentatum and D. rotundatus. Acicula fusca was present almost throughout these deposits, suggesting that this hollow was formed and filled slightly later than the one at the south section (column B) where
A. fusca was present only in the upper levels. The open-country and catholic genera are suppressed and persist only in very low numbers through these samples.
At 330cm there is a marked change in the assemblage from a domination by woodland forms to a domination by open-country forms.
This expansion of open-country forms begins with those already present in very low numbers during the forest phase (Vallonia costata, V. excentrica, Pupilla muscorum and Vertigo pygmaea).
Their expansion is preceeded by a peak in the abundance of P. elegans (10%).
From the clearance horizon (350cm) upwards the open-country forms become dominant by further expansion and the gradual exclusion of woodland forms. After the initial expansion of the open-country species already present in low numbers, the introduced species of open-country and waste ground arrive and expand. For example at 315cm Monacha cartusiana appears and from then on is present into the topsoil. At 160cm Helix aspersa appears, allowing an approximate age to be given to the sediments. This is followed 126
somewhat later by Candidula gigaxii (75cm), Cernuella virgata
(35cm) and lastly by Candidula intersecta in the topsoil. Also within the topsoil there is a minor re-expansion of shade-loving forms (e.g. Aegopinella nitidula, Vitrea spp. and Discus rotundatus) suggesting some shrub regrowth. Again in this section can be observed the late expansion of Vallonia pulchella, a species which occurs sporadically throughout the upper silts.
Interpretation
According to the biozone criteria established in Kent, these deposits have been assigned to biozones z, d, e and f. The basal deposits have been labelled z/d as the contamination of the
Late-glacial deposits by the Postglacial sediments and molluscs has been so great that it was virtually impossible to separate the assemblages. This section was the thickest sedimentary sequence studied in this project and has allowed a detailed study of the biozones e and f preserved im 3-5m of sediments.
b) Column D
Samples were taken at 10cm intervals from the basal
Postglacial silts (420cm) up to 340cm in order to provide a molluscan succession linked to the radiocarbon date. These samples also provided an opportunity to compare two vertical sequences taken from the same section but laterally 3.75m apart.
The basal samples (390-400cm, 400-410cm, 410-420cm) contained a predominantly woodland molluscan assemblage, dominated by 127
Carychium tridentatum and Discus rotundatus and to a lesser extent by Clausilia bidentata. Oxychilus alliarius was found at 390cm, a species not present in the other three columns of samples studied.
At 390cm, the clearance horizon, there was an expansion of the open-country forms, first of Vallonia costata and then followed by V. excentrica, Pupilla muscorum, Vertigo pygmaea and Helicella itala. At 350cm Monacha cartusiana appears, providing a useful link between the molluscan sequences. The results of the molluscan analyses are shown graphically in Figure 19 and listed in Table 9.
Interpretation
These deposits have been assigned to molluscan biozones d and e but represent only a short part of the sedimentary and molluscan record preserved elsewhere at this section.
Other remains
Marine Mollusca
Fragments of Mytilus edulis were recovered from 18 samples from column C (0-5cm, 15-20cm, 25-30cm, 35-40cm, 55-60cm, 65-70cm,
85-90cm, 95-100cm, 105-110cm, 115-120cm, 125-130cm, 135-140cm,
145-150cm, 165-170cm, 225-230cm, 235-240cm, 265-270cm, 340-345cm).
Vertebrates
Bones and teeth were recovered from column C (75-80cm, 128
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oioluagpq ongsnoo ojouiumi ou.spolcpoo srvJonio sn1.140Xx0 sn!Jollao snl!LPI4Y0 oinpmu onau./do5av aind oll8Ufd05aV
0,34 M
sniopunioJ sn3sfa oloainao olnumuoav tun jojuapui umNoAJoj
ko S113HS 30 2134111AMN °gD?
(SvviD) H1d30 I ff:rs,
0 Nwn-ioD o 0 0 0 o AtAdV6011Vel1S 0 — 129
95-100cm, 115-120cm, 135-140cm, 155-160cm, 305-310cm, 335-340cm,
340-345cm, 350-355cm, 360-365cm, 365-370cm, 370-375cm, 385-390cm) and from column D (360-370cm, 370-380cm, 380-390cm, 390-400cm).
These were identified by Andrew Currant as cheek teeth and jawbones of Clethrionomys glareolus (bank vole). A large bone present in the radiocarbon sample taken from column C (335-345cm) is most likely part of the innominate bone of a bovine.
Pollen
Dr. Charles Turner examined a sample from 350-355cm (column
C) but reported that no pollen was present. The sample was chosen because the molluscs from this level had, unusually, retained a glassy appearance suggesting slightly acidic conditions.
Seeds
Carbonised seeds were seperated from the charcoal sample
(335-345cm, column C), submitted for radiocarbon assay. They were examined by Dr. David Holyoak. The majority were unidentifiable as they had suffered marked shrinkage and distortion, but he was able to name the following:-
Arrhenatherum elatius 4 root tubers
Atriplex or Chenopodium sp. 8 seeds
Labiatae (cf Stachys or Laumium) 1 nutlet fragment
Leguminose root nodules 2
Leguminosae 1 seed cf Potentilla anselina 1 acheme 130
Veronica hederifolia 4 seeds
Plantago lanceolata 3 seeds
Viola sp. 1 seed
A. elatius and P. lanceolata are late colonisers of chalkland spreading into areas after some vegetation has colonised the bare chalk rubble. Atriplex, V. hederifolia and Viola sp. are all weeds that colonise bare cultivated ground.
All these species are typical of the flora that would be expected to colonise an area shortly after vegetational clearance.
Radiocarbon dating
Two samples of charcoal from the North section were submitted to the British Museum Research Laboratory. The first was from
Column C (335-345cm), immediately above the clearance horizon
(350cm). The following result was obtained:— 2760 ± 120b.p.(BM
2216).
The second sample was from column D (400-410cm), just below the clearance horizon (390cm). The following result was obtained:—
3460 ± 190 b.p.(BM 2217)
These dates suggest that vegetational clearance in this valley and its catchment area had begun by the early Bronze Age period. This is in agreement with the date obtained from the same stratigraphical layer from the south section. 131
iv. Discussion and conclusions
The deposits at Asham again do not span the entire
Postglacial as there is a hiatus of several thousand years between
the Late-glacial and earliest Postglacial sediments. The molluscan
biozones found at this site are y and z (Late-glacial) and d, e and
f (Postglacial).
The interpretation of the Postglacial stratigraphy has been
difficult and the final stratigraphical subdivisions have been based on both the molluscan and the field evidence. The earliest
Postglacial sediments are found in the subsoil hollows, the best example of which is found at the South section (column B). Their origin has been discussed earlier in Chapter 3. They are probably tree root hollows that have become filled in. Overlying these hollows is an in situ woodland soil (A and partial B horizon), containing a woodland molluscan fauna (biozone d). In the centre of the valley axis where the sediments are at their thickest the soil is overlain by similar soil-like material, but containing abundant small subangular chalk fragments and an open-country molluscan fauna. This is interpreted as transported soil (colluvium) that has been moved downslope by accelerated soil erosion in response to vegetational clearance, incorporating with it fragments of bedrock.
It is at the junction between the basal stone-free sediments and the overlying stone-rich colluvium that clearance started, as is indicated by the dramatic expansion of open-country forms together with the more gradual exclusion of the woodland species. Overlying this transported soil is lighter coloured, poorly sorted colluvium forming the more typical hillwash, which lacks humus and contains 132
abundant large and small chalk and flint fragments.
The stratigraphy of these sediments has also been examined in
the field by Dr. John Boardman and Dr. Roger Smith. They are of the
opinion that what has here been interpreted as an in situ woodland
soil has also been transported. The field evidence which they cite
as supporting this hypothesis is that the soil is too thin to be in
situ and has no obvious B horizons and that there is a sharp
boundary between the chalk rubbles and Postglacial silts as opposed
to a smeared weathering front, and finally that the soil thins
laterally very quickly towards the valley sides. Although these
points are true, a B horizon is present where the sediments are
thickest and the contained molluscs and sedimentological
differences between the in situ and the transported soil do support
the first interpretation.
Clearance of this valley and its catchment area would have
been gradual over many years. It would probably have begun on the
floor of the valley and extended slowly up the valley sides,
causing the formation of colluvium as a result of accelerated soil
erosion. The deeper woodland soil would first be stripped from the
valley sides and later the humus—free sediments and chalk rubble.
The three radiocarbon dates from this site suggest that clearance
of this valley had begun by the Bronze Age. This links with the work of Bell (1983) at Itford Bottom and evidence from the Bronze
Age site on Itford Hill (Holden 1972). Cultivation of most of the valley and its catchment probably continued for many centuries into
the Romano—British and Anglo—Saxon periods when much of the Downs reverted from 'arable to pasture. This is indicated by the large 133
amount of colluvium present in the valley floor.
The four molluscan sequences obtained from this site are very simslar in general detail. A biozone d fauna occurs in the earliest
Postglacial deposits in the subsoil hollows and the overlying in situ soil. Towards the end of the biozone Acicula fusca appears. At the junction of the in situ soil and the basal colluvium there is a dramatic expansion of the open-country forms that were present already in low numbers during the forest phase (Vallonia costata,
Helicella itala and to a lesser extent V. excentrica), preceeded by a peak in the abundance of Pomatias elegans. These open-country forms quickly became dominant, with the gradual exclusion of the shade-demanding forms with progressive clearance of the valley.
Within these colluvial sediments the relative order of arrival of the introduced molluscan species has been determined. First in the area was Monacha cartusiana, probably a late Neolithic/early Bronze
Age introduction into Britain, followed by Helix aspersa (a
Romano-British introduction) and last Candidula RiRaxii, Cernuella virRata and C. intersecta. In the most recent colluvial deposits
(column C) there is a slight reexpansion of some of the shade-loving forms, probably due to scrub regrowth. At the present time C. intersecta is abundant living in the quarry, to the virtual exclusion of C. .giRaxii and Helicella itala. Monacha cantiana, a species not found in the molluscan analyses, is also very common today.
The analysis of column B taken through the subsoil hollow on the south section further substantiates the hypothesis that this feature resulted from an uprooted tree leaving behind a cavity that 134
became gradually filled from the surrounding sediments. The contained deposits are fine silts almost totally lacking stones and with a rich woodland assemblage. The molluscan succession suggests that the filling took place gradually as there are distinct changes through the hollow ending with the presence of Acicula fusca in the upper 35cm extending into the overlying soil. It must be noted that the sediments in the hollow underlie the buried soil and that there is a clear junction between them, the hollow sediments being much finer and differing in colour. They probably incorporate much redeposited loess, many metres of which can be found immediately to the south—west.
Minor faunal differences are nevertheless apparent between the molluscan sequences. For example Spermodea lamellata and
Oxychilus alliarius occurred only in single samples from columns B and D respectively, indicating the benefit of-taking more than one vertical sequence through deposits of this kind.
The sediments at Asham (column C) represent the longest snail rich sedimentary sequence found in Sussex with over four metres of
Postglacial silts still preserved. This has allowed detailed study of the anthropogenic biozones e and f, and the determination of the relative order of arrival of the introduced molluscan species into this valley. 135
9. SOUTH HEIGHTON
Grid reference: TQ 450034
Location: 2 miles N.E. of Newhaven
i. Introduction
At a builders yard on the outskirts of the village of South
Heighton excavations for the foundations of a building that was
never erected have provided an exposure of Late-glacial and
Postglacial dry valley infill deposits. This dry valley is on the
dip slope of the South Downs and trends southwestwards towards the
River Ouse floodplain.
This site is about 3 miles south of Asham Quary and is close
to several important archaeological finds __ for example, a
biconical urn of Neolithic grooved wave (Ellison 1978), Iron Age
pottery at Well Bottom and a Saxon burial ground to the North (Bell
1978).
Stratigraphy
The deposits show the typical tripartite sequence of
Late-glacial solifluxion and slope-wash overlain by a mid
Postglacial soil that has been buried in turn by colluvium. A
complete record through these deposits was obtained by cutting down
through the talus. The deposits are shown in an idealised diagram
(Figure 20). The detailed stratigraphy recorded from the sample
column is as follows- 136
SW NE samples
0
0
C=, r 0c3 ° c0c)cz) c=z. c=1 c:D o
o 0 el 0 o o c. o o 0 o 0 0 0 o I 0 o ...... --... --- o • • i. o . o ci.1 • • I- ../". NOT - 0 . ....0"" KEY • • ..0". EXPOSED \ • NOT EXPOSED I I I topsoil 1°.11 chalky silt
in situ soil 1 1111 lm IOC= I 07 I CYO chalk fragments
cmc=x=31
Figure 20. Sketch Diagram of South Heighton.
137
Depth (cm)
0-30 Topsoil and turf.
30-170 Light yellowish brown (10 YR 6/4) silts containing
large fragments of chalk and flint.
170-200 Dark brown (7.5 YR 4/4) silts containing abundant
rounded chalk fragments.
200-250 Dark brown (7.5 YR 4/4) silts with very few chalk
fragments.
250-270 Mixture of Postglacial and Late-glacial deposits.
Mainly gravel sized material, partly calcreted.
270-280 Very pale brown (10 YR 7/3) chalky silt with shattered
chalk fragments.
280+ Shattered chalk.
Mollusca
The deposits were sampled at 10cm intervals from beneath the
turf line down into the shattered chalk. The results are given in
Table 10 and are presented graphically in Figure 21. The basal
sample (270-280 cm) of chalky silt contained a typical restricted
Late-glacial molluscan assemblage of Trichia hispida, Pupilla
muscorum, Vallonia costata and Deroceras/Limax spp. These shells
were all very well preserved and the examples of Pupilla muscorum
were of the large, Late-glacial type.
From 210 to 270 cm the molluscs were predominantly of
woodland species, including Acicula fusca, Acanthinula aculeata, 138
3NO2 "3sn-1o4 V 11 IN 7 6
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01015173 op.10110A
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DAP/Ji 2 XDUJI7/CDJ.730J80 immo.1•1111•111111Mr=16.1•11111.11111111.11
sluowumq oanfriogaN • • -11.1 opyannad ou.o19I • tuneow6Xd tunpund • • • • odo3mpoo
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(Su.,) (Ada() IV II 2111
0 o 04 9 o 0 NINMOD 0° ° AHd‘1191 /NMI s o 00 139
Helicigona lapicida and Clausilia bidentata, comprising about 30%
of the fauna. These shells were poorly preserved, often broken and
fragmentary. In these deposits, open-country forms were virtually absent, with only Vallonia costata and Pupilla muscorum present in very low numbers; the former species is able to tolerate shade to some extent. From 200 to 250 cm Pomatias elegans is very numerous, suggesting broken ground.
At 210 cm there is a marked expansion of the open-country forms, namely P. muscorum, Vallonia spp, Helicella itala and, to a lesser extent, Monacha cartusiana, together with occasional shells of Vertigo pygmaea and Truncatellina cylindrica. From here on the woodland forms decrease, with only a few shells or fragments persisting.
Helix aspersa first occurs at 100 cm and is present throughout the rest of the deposits. At this site M. cartusiana also persists throughout. At 60 cm Vallonia pulchella occurs, showing its characteristic late expansion.
Although the broad changes in the molluscan assemblages are similar to those described from the other sites, there are certain peculiarities worth noting. At 180 cm Pupilla muscorum peaks in abundance with 643 specimens (62% of the fauna). This is unusual in this type of environment. Also at 130 cm Oxychilus alliarius occurs and persists until 60 cm, a feature not seen at any other site.
Finally there are no introduced helicellids in the upper colluvial deposits. Within these deposits were shells of brackish molluscs:
Hydrobia ulvae, H. ventrosa and Ovatella myosotis. These are 140
clearly exotics and were probably brought to the valley from the
tidal floodplain of the River Ouse by birds or on plants used as
fertilizers.
iv. Interpretation
According to the biozone criteria established in Kent these
molluscan assemblages have been assigned to biozones z
(Late-glacial) d, e and f (Postglacial).
V. Other remains
Marine Mollusca
Fragments of Mytilus edulis were recovered from samples 30-40
cm, 40-50 cm, 60-70 cm, 100-110 cm, 160-170 cm, 180-190 cm and
190-200 cm. These may be the result of manuring with seaweeds or
less probably are human food debris.
Vertebrates
Bones and teeth were recovered from samples 190-200 cm,
210-220 cm, 220-230 cm, 230-240 cm and have been identified by
Andrew Currant as the remains of bank vole, Clethrionomys glareolus.
vi. Dating
A charcoal sample from 190-210 cm was submitted to the 141
British Museum Research Laboratory for radiocarbon dating. A date
of 3450 ± 150 b.p. (BM 2219) was obtained for the base of biozone e, the clearance horizon. This falls within the middle Bronze Age.
viii. Discussion and conclusions
The sequence of deposits at South Heighton do not span the entire Postglacial period and represent only the later half, with a hiatus of several thousand years between the Late—glacial and the earliest Postglacial deposits.
The molluscs recovered from the shattered chalk and silts are clearly Late—glacial in age. They are well preserved and the
Punilla muscorum shells are of the large type characteristic of
'cold' deposits.
The deposits at 210-250 cm depth contained a predominantly woodland assemblage, representing the fauna that was living on the soil surface in the mid Postglacial forest. The presence of calcreted sediments towards the base suggests waterlogging and inadequate drainage.
Clearance of this forest began in the Bronze Age and has been radiocarbon dated to 3450 ± 150 b.p. (BM 2219). Clearance would probably have begun on the floor of the valley and progressively moved up the valley sides, creating open spaces for settlement and arable farming.
Deforestation would have led to the onset of colluviation, 142
beginning with the erosion of the pre-existing forest soil and incorporating chalk fragments during transport. The subsequent colluvium was nearly humus-free, but contained abundant small sub-angular chalk pellets (30-170 cm). Colluvium would have continued to build up until the cessation of arable farming lead to the development of stable grassland maintained by grazing. At this section the uppermost colluvium and the original turf line has probably been removed, perhaps artificially, as no introduced helicellids are preserved. 143
10. HOPE GAP
Grid reference: TV 509974
Location: 4 Km S.E. of Seaford_
i. Introduction
Hope Gap is the access point to the beach from the chalk
cliffs at Seaford Head where a dip slope dry valley trending SSE
through the nature reserve has been truncated by a cliff retreat.
This has left the Late-glacial and Postglacial inf ill deposits
naturally exposed. The site is unique in that all the other valleys
to the east that dissect the chalk to form the Seven Sisters have
infills only of Late-glacial and earlier Devensian deposits, as for
example at Birling Gap (TV 553960).
Capping the clif top to the east of this valley are several metres of redeposited loess. This was sampled at a place where masses had slumped to beach level and was found to contain calcium
carbonate concretions (loess dolls) and a characteristic 'loess' molluscan fauna dominated by Pupilla muscorum and Trichia hispida .
These sediments have been examined by David Gordon who has confirmed by particle size analysis and scanning electron
microscopy (SEM) that the material is indeed predominantly loess.
Stratigraphy
The Late-glacial and Postglacial deposits are over six metres
thick and represent one of the thickest sedimentary sequences found 144
in this area of the South Downs. Due to the inaccesible nature of the section it was impossible to obtain a closely spaced column of samples, but spot samples were taken at various points which could be reached from the steps to the beach. A total of seven samples were taken (Figure 22).
The Late-glacial deposits consisited of about two metres of shattered chalk and flints interbedded With pockets of fine silt. A sample (Sample 1) of this silt was taken for molluscan analysis.
Six samples were taken from the overlaying Postglacial deposits and the stratigraphy was as follows-
Depth (cm)
0 - 30 Topsoil. Dark brown (10YR 3/3) silts (sample 7).
30 - 300 Yellowish brown (10YR 5/4) silts containing
abundant angular and subangular chalk fragments and
strings of large rounded chalk pebbles (samples 5
and 6)
300 - 500 Dark yellowish brown (10YR 4/4) non-calcareous
silts. Occurrence of several struck flakes.
(samples 2, 3 and 4).
Mollusca
Shells were common in the Late-glacial deposits (sample 1) and in the upper Postglacial colluvium (samples 5 and 6) and 145
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topsoil (sample 7). The samples from the non-calcareous silts
(samples 2,3 and 4) lacked shells. This was either due to decalcification or because of primary non-preservation. The mollusca are listed in Table 11 and presented graphically (Figure
22).
a. Late-glacial fauna
Sample 1 contained Cochlicopa spp, Punctum pygmaeum,
Helicella itala, Deroceras Limax spp, Pupilla muscorum, Trichia hispida and Vallonia spp. These have been assigned to biozone z rather than y on the basis of the occurrence of H. itala, a thermophilous species, and the relative diversity of the assemblage. These forms indicate open-country conditions with a dry, grassy substrate.
b. Postglacial fauna
The mollusca from the Postglacial deposits are predominantly open-country and include P. muscorum, Vallonia spp, Vertigo pygmaea and H. itala. Fragments of Helix aspersa were found in samples 6 and 7 and on this basis sample 5 has been assigned to biozone e and samples 6 and 7 to biozone f. The occurrence of woodland species including Carychium tridentatum, Aegopinella nitidula, Lauria cylindracea, and Clausilia bidentata in samples 5 and 6 suggest that there were some patches of scrub providing shade in the valley.
Fragments of the marine mollusc Mytilus edulis were recovered 147
from the topsoil sample.
iv. Discussion and conclusions
The deposits in this dry valley provide a thick sedimentary
sequence of the Late-glacial and later Postglacial. All of the
Postglacial deposits are of colluvial origin resulting from
accelerated soil erosion due to agriculture. The thickness of the
colluvium suggests that there was prolonged agricultural activity
in this valley.
The basal two metres of the colluvium are non-calcareous.
This is not surprising as many metres of loess have been recorded
immediately to the east of this valley, providing a substrate
favouring the development of deeply leached soils. Analysis of
samples 2,3 and 4 from these sediments showed that they were made
up almost entirely of fine silt sized particles suggesting a large
loess component. Basal non-calcareous Postglacial deposits appear
to be a common feature of some dry valley inf ills on the South
Downs and have been described in detail by Bell (1983) at Kiln
Combe, Bullock Down (TV 573964).
These basal deposits have not been interpreted as an in situ woodland soil because they are too deep and show no evidence of soil horizons. Instead they are thought to be the initial colluvium produced at the onset of woodland clearance, representing the stripping of the previously acidified woodland soil from the valley sides and redepositing it on the valley floor. Woodland Mollusca would have lived on the surface of this soil but because of the low 148
pH have not been preserved.
The upper colluvium is lighter in colour and contains abundant chalk fragments. It originated as soil which developed directly on top of the stripped chalk bedrock and was then quickly moved down valley, incorporating with it chalk fragments and the shells of open—country molluscan species. Large scale erosion would have continued until arable farming stopped and the valley was allowed to revert to pasture, hence restoring stability to the slopes.
Today the vegetation of the valley is artificially maintained as grassland, by mowing and by the annual burning of scrub. Sheep do not graze the valley but rabbits are very common. 149
11. EXCEAT
Grid Reference: TV 520989
Location: 2 miles East of Seaford
i. Introduction
Two exposures of slope deposits were examined at Exceat in the Seven Sisters Country Park near Seaford. The sections are 346 metres apart and are on the eastern side of the River Cuckmere floodplain. a
The village of Exceat (Esceat) was founded in the early
Anglo—Saxon period at the same time as many of the other villages in the area including Birling, East Dean, West Dean and Friston, probably because of economic reasons resulting from population growth (Drewett 1982). The establishment of these medieval villages and farnmsteads occurred at a time when most of the chalk downlands was being ploughed for arable farming.
All that remains of the village today is a stone set on the hilltop marking the position of the church and the strip lynchets on the side of the Cuckmere valley.
Formation of strip lynchets
In contrast to the other slope deposits studied, those at
Exceat were not dry valley inf ills but positive lynchets. Lynchets form on steep hillslopes (up to 20°) in response to ploughing 150
across the slope. They develop when soil moving downhill as a
result of ploughing accumulates against a field boundary, such as a
wall, fence, ditch or hedge. A positive lynchet forms upslope from
the boundary where soil accumulates and a negative lynchet forms
downslope where soil is lost (Figure 23). The land surface prior to
ploughing is often preserved as a buried soil beneath the positive
lynchet.
Work has been carried out on the dating and origin of strip
lynchets by Curwen (1939) and Wood (1961), and on their contained
fossil Mollusca by Fowler and Evans (1967), Evans (1972) and Thomas
in Bell (1977). Work at Fyfield Down, Wiltshire (Fowler and Evans
1967) revealed the presence of a pre—lynchet soil that contained
woodland molluscs. This was in contrast to the main body of the
lynchet which contained open—country molluscs. At Overton Down,
Wiltshire, a line of post holes was found preserved beneath the
lynchet, probably marking the original field boundary above which
the positive lynchet developed (Fowler and Evans 1967).
In contrast to the other published fossil molluscan studies
from lynchets, the present samples were taken from longitudinal
sections through lynchets (Figures 24 and 26).
Exceat 1
Stratigraphy
This was a longitudinal section through a lynchet in part naturally exposed through recent landslipping. The general
151
F— al IA l) 1 0 C.) t 0 Z (1) >- D / C >LI 0 / -0 / F-- L>1 < 0 0 4:7_ "0 / 11.1 (.) C Z n c 0 / 0 n /
0 C 0 -0 47-;
an0 152
stratigraphy is shown in Figure 24 and the detailed stratigraphy for the sample column is given below. An additional spot sample was taken from the pre-lynchet land surface, the position of which is marked on the diagram (Figure 24).
Depth (cm)
0-20 Topsoil: dark brown (10 YR 3/3) silts.
20-125 Light yellowish brown (10 YR 6/4) silts.
125-200 Yellowish brown (10 YR 5/4) silts becoming increasingly
clay-rich down profile.
200-220 Dark brown (10 YR 3/3) silts containing abundant
sub-angular chalk fragments.
220-230 Zone of mixing.
230+ Shattered chalk showing solution features.
-Mollusca
Samples were taken at 5cm intervals down to 230cm depth.
Molluscs were present only to 80cm and the basal three samples
(65-70cm, 70-75cm, 75-80cm) had to be amalgamated to make the totals large enough to be plotted as percentages. All samples below
80cm were devoid of shells or shell fragments despite an abundance of sub-angular broken chalk. Samples 65-80cm yielded very low counts and preservation was very poor. The species recovered included Pomatias elegans, Discus rotundatus, Cepaea spp, and
Vallonia spp; all of which are fairly resistant to physical and chemical destruction. None of the more delicate zonitidae (for exampleVitrea spp) were present in these samples suggesting that
there has been destruction of some of the thinner-shelled species. 153
0
00
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0 — 154
Within these slope deposits open-country species predominate, including Pupilla muscorum, Vertigo pygmaea, Abida secale, Vallonia spp and Helicella itala. At 65cm Vallonia excentrica appears and by
50cm has become dominant over V. costata. Also at 65cm P. elegans peaks in abundance, suggesting a rubbly soil such as would be expected from clearance or ploughing. Present also within these deposits is the characteristic late expansion of V. pulchella. At
55cm Monacha cartusiana and Helix aspersa appear, followed by
Cernuella virgata and Candidula intersecta within the topsoil.
Mollusca recovered from the spot sample from the buried soil were predominantly of open-country forms, suggesting that forest clearance had taken place before the onset of ploughing.
A few shells of brackish and freshwater Mollusca occur throughout these deposits (Valvata piscinalis, Anisus leucostoma,
Hydrobia ulvae and Lymnaea truncatula). These species represent a miscellany of aquatic habitats. Their origin is uncertain. They could be the result of manuring using plants from the floodplain.
Alternatively they may have been derived from bird droppings, or have been blown in from the floodplain.
The results of the molluscan analyses are presented graphically in Figure 25 and listed in Table 12.
Interpretation
According to the biozone criteria established in Kent, these 155
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deposits have been assigned to biozones e and f.
Marine Mollusca
Fragments of marine species were recovered from many of the samples and are recorded below.
75 70 65 60 55 50 45 40 35 30 25 20 15 10 5
80 75 70 65 60 55 50 45 40 35 30 25 20 15 10
Mytilus edulis L. - -X- -X- -X-XXXXX
Patella vulgata L. X 1 2 -
Littorina littorea L. 1
They may be the result of manuring using seaweeds or less probably are human food debris.
iv. Exceat 2
Stratigraphy
This was another longitudinal section through the body of a positive lynchet, from a position rather further upslope from the projected field boundary than Exceat 1. This exposure was due to a road cutting. The sample column was not taken through the thickest part of the colluvium as this was inaccessible. The general stratigraphy is shown in Figure 26 and the detailed stratigraphy for the sample column is as follows:- 157
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Depth (cm)
0-10 Topsoil: dark brown (10YR 3/3) silts.
10-110 Dark yellowish brown (10YR 4/4) silts containing
subangular chalk pellets which increase in number down
profile.
110-120 . Dark brown (10YR 3/3) silts containing abundant
subangular chalk fragments.
120+ Shattered chalk and flints.
Samples were not taken from the shattered chalk and flints at
either section because of the lack of fine chalk silt matrix or
other suitable sediments in which molluscs would be preserved.
Mollusca
Samples were taken at 10cm intervals through the Postglacial
deposits and shells were found to be present in all the samples.
Within these deposits the molluscs were predominantly open-country
species, mainly Pupilla muscorum, Vallonia costata, V. excentrica and Helicella itala. In the basal samples (80-120cm) Pomatias elegans was very abundant and was associated with a few shells of
the woodland species Clausilia bidentata, Discus rotundatus,
Aegopinella nitidula and Helicigona lapicida.
At 70cm Helix aspersa and Cernuella virgata appear, followed by Candidula .gigaxii at 60cm, Monacha cartusiana at 10cm and
Candidula intersecta in the topsoil. Of particular interest was the occurrence of Truncatellina at 40cm as there are few living or fossil records of this snail. All the examples of Pupilla muscorum 159
from 40cm upwards were of the small toothed variety (form biRranata) and this with Truncatellina suggests that the valley sides presented some areas of dry stable grassland not being ploughed. Shells of the brackish-water snail Hvdrobia ulvae were present throughout these deposits and have probably come from the
River Cuckmere estuary.
The results of the molluscan analyses are presented graphically in Figure 27 and listed in Table 13.
Interpretation
According to the biozone criteria established in Kent, these deposits have been assigned to the open-country biozones e and f.
Marine Mollusca
Fragments of Mvtilus edulis were recovered from three samples
(70-80cm, 50-60cm and 40-50cm).
v. Discussion and conclusions
These molluscan sequences are from the positive bodies of two
lynchets at different distances from the field boundaries. The
sedimentary sequence preserved at Exceat 1 represents a longer
period of time than that at Exceat 2 but they both provide a very much shorter record of the Postglacial than the dry valley inf ill
deposits studied. This is because the colluvium would only have begun to accumulate after ploughing and the erection of field 160
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boundaries. From local archaeological evidence the date of formation of these particular lynchets is thought to have been between 700 and 1000 A.D.
These sequences of molluscs found preserved in the lynchet bodies can be used to relatively date the lynchets and to compare and contrast them between sites. The amount of colluvium preserved at these sites will depend on the position of the lynchet, the steepness of the slope, the amount of land being ploughed and the length of time it is kept under cultivation.
There is no real evidence from either section of a woodland cover prior to ploughing. The open—country molluscs recovered from the sample of the buried soil at Exceat 1 suggests that clearance must have occured considerably earlier than the onset of ploughing.
Subtle differences are apparent between the two diagrams.
Truncatellina is present only at Exceat 2. At the same section
Helix aspersa and Cernuella virgata appear together, but at Exceat
1 they are seperated by 50cm of sediments. This shows that the fossil mollusca within the deposits may reflect some quite local variations such as differences in scrub cover, aspect or steepness of slope. This emphasises the value of taking several vertical sequences from a section. 162
12. COW GAP
Grid Reference: TV 595957
Location: 2 miles west of eastbourne.
1. Introduction
The section of the South Downs chalk escarpment from
Eastbourne to Beachy Head is indented by a series of arm-chair shaped hollows. These were first described by Bull (1940) who thought that they were the result of nivation in an arctic climate.
All that would be necessary for them to form would be sufficient precipitation, a climate cold enough to maintain snow patches and a suitable hillside.
Debris produced by periglacial processes has been moved out of these hollows and redeposited in front of the escarpment. Kerney
(1963) studied in detail the Late-glacial deposits from one such hollow at Cow Gap and described a sequence of shattered chalk and chalk rubble overlain by fine silts, forming a fossil soil. This was in turn buried by chalk silts interbedded with coarse rubble.
These deposits were analysed for molluscan remains (Figure 28).
The archaeology of this area of the South Downs, including
Cow Gap, has been extensively investigated over the past five years
(1976-1981) by the Sussex Archaeological Field Unit and the
Institute of Archaeology (Drewett 1982). This area, Bullock Down, forms the south-east corner of the Downs, bounded by the cliffs of 163
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Beachy Head to the south, the scarp slope to the east and Birling
Gap to the west. This archaeological investigation provided evidence of extensive occupation from the Neolithic to the post-Medieval period. Work at Kiln Combe, a dry valley within the field area (Bell 1981a, 1983) and on the adjacent medieval farmstead (Drewett 1982), showed that the economy was self sufficient, based on sheep and corn, supplemented by local resources. There was much evidence of the use of marine shells as a food source (e.g. mussels, limpets, oysters) at all periods and it is likely that Cow Gap and Birling Gap were the nearest access points to the beach even after taking into account probable alterations in the coastline by erosion.
• Bell (1981a) also investigated the deposits at Cow Gap.
(central section of infill described in this study) and recovered a sherd of finger-impressed beaker pottery from the basal Postglacial deposits (see Figure 30).
All the way along this section of the coast from Eastbourne to Beachy Head deposits of Late-glacial and Postglacial age can be seen naturally exposed at cliff top level. At Cow Gap these are exposed at several levels in a series of terraced landslips. These multiple deep seated rotational slips reach down to beach level and are the result of the sea eroding the weaker Gault clay underlying the Chalk t this point (Bromhead 1979). The geological situation here has been compared to the landslips at Folkestone Warren, Kent
(Bull 1937; Hutchinson 1965; Bromhead 1979).
These landslips provide useful access from the beach to the 165
cliff top deposits. They are thickest and most complete opposite the centres of the hollows. The stratigraphy of the Late-glacial and Postglacial fill of one hollow, at Cow Gap, is described here in detail together with that of an additional section 200 metres east along the cliff. This allows a useful comparison between the deposits at the hollow interfluve with those in the centre.
Central infill section
Stratigraphy
The stratigraphical sequence preserved in the centre of this hollow is exposed at several heights in the terraced landslips from the cliff top to the beach. The deposits studied by Kerney (1963) were in a slip at mid-cliff level and appear now to have been eroded by the sea. The most accessible and complete section at present was found in situ at the cliff top. Here full glacial,
Late-glacial and Postglacial deposits were present but with a hiatus of several thousand years between the Late-glacial and earliest Postglacial deposits.
The Late-glacial deposits were extremely variable along the section and have been extensively cryoturbated in places. The stratigraphy consists of a basal loessic layer of uncertain age, but probably early to mid Devensian, lying directly on top of shattered bedrock. This is overlain by several metres of chalk rubble interbedded with pockets of fine silt, within which are pebble and mollusc strings that can be traced for many metres along the section and over the interfluves. The origin of these strings 166
is discussed in detail elsewhere (Chapter 3) but they probably result from niveofluvial processes. These rubbles and silts are in turn overlain by a fossil soil of fine humic silts containing a few unidentifiable charcoal fragments. This soil was buried by another layer of loess of Late-glacial age. In places, cutting through the upper loess, fossil soil, and chalk silts and rubbles, are melt water channels flowing out of the hollow. These are delineated by water-sorted pebbly gravels. A sample column was taken through these cold deposits (column C) at a position where the deposits were relatively undisturbed. The stratigraphy at this column was as follows-
Column C
Depth (cm)
200-220 Pale yellow (2.5Y 7/4) silts.
220-230 Light gray (2.5Y 7/2) fine silts containing occasional
charcoal fragments (fossil soil).
230-300 White (2.5Y 8/2) silts and chalk rubbles. Very
variable, with pockets of gravel and very coarse
rubble.
300-340 Pale yellow (2.5Y 7/4) silts becoming increasingly
gravelly towards the base.
340+ Shattered chalk and bedrock.
In the basal loessic deposit at 320cm depth a docimeter was placed in order to obtain the calibration necessary to date the loess by thermoluminesence. This is to be carried out by Dr. Helen
Rendell.
167
The earliest Postglacial deposits at this section were found
in the subsoil hollow (column B), 15 metres north-east of column A.
The hollow was filled with stratigraphically uniform dark yellowish
brown (10 YR 4/4) silts with very few chalk fragments. These were
overlain by several metres of colluvium, reaching a maximum
thickness of about four metres at one point on the section. Due to
the inaccessibility of the deposits at this point they were sampled
where they were only two metres thick (column A). The stratigraphy
at this point is as follows-
Column A
Depth (cm)
0-10 Topsoil: dark brown (10YR 3/3) silts.
10-70 Brown (10YR 5/3) silts with large numbers of chalk and
flint fragments. Pronounced pebble band at 40cm.
70-100 Dark brown (10YR 3/3) silts containing large numbers of
subangular chalk fragments.
100-140 Brown (10YR 5/3) silts.
140-190 Dark brown (10YR 3/3) silts containing charcoal
fragments.
Particularly noticeable at this section were the prominent
bands of rounded large chalk and flint pebbles within the
Postglacial colluvium. When removed, other similar pebbles were
found behind suggesting a pebble sheet. The origin of these pebble
bands is discussed in detail in Chapter 3. 168
The general stratigraphy, the position of the sample columns
(A, B and C) and the location of the pottery found by Dr. Martin
Bell are shown in Figure 29 and 30.
Mollusca
Three columns of samples were taken through the deposits and samples were taken at 10cm intervals throughout. The results of the analyses are presented graphically in Figure 31 and listed in
Tables 14, 15 and 16.
Late-glacial deposits (Column c)
The basal 140cm (14 samples) contained no mollusca with the excception of one shell of Trichia hispida at 350cm, and two shells of Pupilla muscorum and one of Punctum pygmaeum at 330cm. Within the chalk silts and rubbles the Mollusca were preserved only in the pockets of fine silt, not in the coarse rubbles. Mollusca were most abundant within the fossil soil. The fauna was a typical
Late-glacial open-country assemblage dominated by P. muscorum,
Abida secale, Vallonia costata and V. pulchella and to a lesser extent by P. pygmaeum, Cochlicopa spp and Nesovitrea hanmonis. All the shells of P. muscorum were of the large size typical of
Late-glacial assemblages. The overlying loess contained an almost identical assemblage. There was no obvious contamination from the overlying Postglacial silts.
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Postglacial subsoil hollow (Column a
These sediments were extremely fine silts and the sieve residues were almost entirely made up of shell fragments, mainly from Pomatias elegans. The molluscs from within this hollow formed rotu.n a a. a woodland assemblage dominated by Discus redea-t-tis and Aegopinella nitidula. The sediments appeared to be stratigraphically uniform but the molluscs indicated some stratification. For example,
Acicula fusca was present in significant numbers only in the basal samples (330-360cm) as were Vertigo pusilla and Lauria cylindricea.
Of particular interest was the occurrence of Zonitoides excavatus in samples 270-280cm and 340-350cm from the subsoil hollow. Z. excavatus is a calcifuge and its presence suggests that there were local patches of acidification, probably due to the deeper forest soils developed on loess covering the chalk bedrock becoming leached. This species is discussed in more detail in Chapter 6.
Also of interest was the occurrence of one shell of Discus ruderatus, a species that apparently became extinct in southern
Britain in the early Postglacial, being replaced by D. rotundatus at approximately 8000 B.P. It is clearly out of context with the fauna in the hollow which is dominated by D. rotundatus and C. tridentatum. This hints at some reworking of earlier Postglacial deposits that may have existed in the vicinity, possibly in an older hollow upslope when this particular hollow was being filled.
Throughout the hollow the open-country species are almost totally suppressed with the exception of V. costata, which is able to withstand some light shade. At 280cm V. excentrica and P. muscorum slightly increase in numbers, indicating that small clearances may have existed. At 230cm in the basal colluvium undoubted clearance 173
occurs, indicated by the rapid expansion of the already present but supressed open-country species (V. excentrica, V. costata,
Helicella itala and P. muscorum) and by a slightly earlier peak in the abundance of Pomatias elegans. At the same time C. tridentatum declines abruptly. This species is intolerant of human disturbance.
At 220cm the first of the introduced species, Monacha cartusiana, arrives. Its presence enables the top of column B to be linked with the basal samples of column A.
Postglacial colluvium (Column Fa
In the basal samples (180-190cm) a woodland fauna was preserved, essentially similar to that from the uppermost samples of the hollow, dominated by D. rotundatus and C. tridentatum. At
180cm vegetational clearance occurs, indicated by the expansion of the open-country genera. The first species to expand are V. costata and V. excentrica and this is accompanied by a decline in the woodland forms, espcially C. tridentatum. This again coincides approximately with a peak in the numbers of Pomatias elegans, a species favouring a loose rubbly soil such as would be found at clearance.
The woodland forms persist in low numbers throughout the colluvium, reflecting isolated patches of shade, but the open-country forms quickly become dominant. These include Abida secale, an open-country species common in the Late-glacial but usually less successful at recolonising after clearance compared with Vallonia spp, H. itala and P. muscorum. Also within the colluvium is the characteristic late expansion of V. pulchella 174
together with two shells of Truncatellina cylindrica, very rare as a Postglacial fossil. Monacha cartusiana is present sparodically through much of the coluvium, but disappears from the uppermost deposits. At 50cm Helix aspersa appears, followed later by
Candidula gigaxii and Cernuella virgata. The expansion of the
Candidula/Cernuella group occurs at the same time as a decline in the numbers of H. itala. Although Candidula intersecta is widespread over this area today, it was not present in the topsoil samples.
Interpretation
According to the criteria established for the molluscan biozones in Kent, the Late-glacial deposits (190-280cm) have been assigned to biozone z, the subsoil hollow and basal colluvium to woodland biozone d, and the remaining colluvium to the open-country biozones e and f.
Marine Mollusca
Fragments of marine species were recovered from the
Postglacial silts (column A). Fragments of Mytilus edulis were recovered from all the samples and entire shells of Patella vulgata, Nucella lapillus and Littorina littorea from the basal four samples (150-190cm). These may be the result of manuring using seaweeds or alternatively represent human food debris.
175
Dating
A charcoal sample from the basal colluvium (170-190cm) was
submitted to the British Museum Research Laboratory, with the
following result:- 4820 ± 350 b.p. (BM 2220).
This dates , the onset of clearance and falls within the
Neolithic period. This is in agreeement with the finger impressed
sherd of beaker pottery found from the same level.
Interfluve deposits
Stratigraphy
A section of posible Late-glacial and of Postglacial deposits
was examined at the interfluve between Cow Gap and the next hollow
northeastwards along the coast. The glacial deposits consisted of
30cm of chalk rubble and silt lying directly on shattered chalk
bedrock. The overlying Postglacial deposits consisted of 90cm of
colluvium and topsoil, with a pronounced pebble band at 40cm depth
(a continuation of the one at the central section). The
stratigraphy at the sample column is as follows-
Depth (cm)
0-10 Topsoil: dark brown (10YR 3/3) silts.
10-90 Brown (10YR 5/3) silts containing abundant small
subangular chalk pellets and a pronounced pebble band
at 40cm.
90-120 Chalk silts and rubble. 176
120+ Shattered chalk and bedrock.
Details of these sediments are shown in the sample column on the left of the molluscan histogram (Figure 32).
Mollusca
The cold deposits contained no indigenous Mollusca as the few shells recovered were definitely due to contamination from the overlying Postglacial silts (eg. Ceciliodes acicula, Cernuella virgata).
Throughout the Postglacial colluvium there was an open—country molluscan assemblage dominated in the basal samples
(70-80cm, 80-90cm) by Vallonia excentrica and in the upper deposits by the introduced helicellids, C. virgata and Candidula gigaxii.
Helix aspersa and C. virgata were present throughout the deposits with C. gigaxii appearing at 60cm. Also in the colluvium was the characteristic late expansion of Vallonia pulchella and the slight re—expansion of Abida secale. At this section C. virgata clearly preceedes C. .gigaxii and again coincides with a decline in the numbers of Helicella itala. Absent from these deposits was
Candidula intersecta, although widespread in the area today.
The results of these analyses are presented graphically in
Figure 32 and listed in Table 17. 177
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Interpretation
According to the biozone criteria established in Kent these
Postglacial deposits can all be assigned to biozone f.
Marine Mollusca
Fragments of marine species were recovered from the
Postglacial silts and are recorded below:-
80 70 60 50 40 30 20 10
90 80 70 60 50 40 30 20
Mytilus edulis L. XXXXXXXX
Patella vulgata L. - - - - - 1
Nucella lapillus (L) 1
These may be the result of manuring using seaweeds or
represent human food debris.
iv. Discussion and conclusions
The deposits at Cow Gap are of both Late-glacial and
Postglacial age and are at their thickest and stratigraphically most complete opposite the centre of the hollow. The Late-glacial deposits were produced by periglacial processes. The sediments were
transported out of the hollow and redeposited in front of the
escarpment by a combination of mass movement and fluvial processes.
The Late-glacial molluscan assemblages recovered from these
sediments are essentially similar to those described by Kerney 179
(1963)with the exception of Columella columella, which was not refound. Mollusc shells were absent from the lower glacial deposits, suggesting an earlier Devensian ('Full Glacial') age when environmental conditions were largely unsuitable for Molluscs
(Kerney 1977).
The overlying Postglacial sediments were not examined by
Kerney but were studied by Burchell (unpub. M. S.). The sediments provide a good record of the molluscan biostratigraphy of the later part of the Postglacial, preserving faunas of biozones d, e and f in the subsoil hollow and the overlying colluvium.
At the central infill section, the sedimentary sequence is at its most complete. The earliest Postglacial sediments are found in the subsoil hollow (column B) and preserve a rich woodland fauna including Acicula fusca, Vertigo pusilla, Discus rotundatus, Lauria cylindracea, Aegopinella nitidula and Aegopinella pura (biozone d).
These suggest that the Downs were covered by dense woodland with local patches of acidification as indicated by the presence of
Zonitoides excavatus.
Overlying this hollow are several metres of colluvium, resulting from accelerated soil erosion due to forest clearance and agriculture. The basal colluvial deposits have been radiocarbon dated, demonstrating a Neolithic age for the onset of clearance.
Within the colluvium (column A), the open—country molluscan biozones (e and f) are preserved, with the record of the arrival of the introduced helicellids into the area. None of these Postglacial deposits reflect purely the immediate environment. The sediments in 180
the hollows have been derived from the surrounding area and the
colluvium originates from the entire catchment area under cultivation.
In addition to the evidence of human activity from the
Neolithic onwards at Cow Gap, it is known that this area of the
South Downs was occupied at this time from the work at Bullock Down
(Drewett 1982), Forest clearance of this area would have been gradual and for the purpose of providing land for settlement and
farming. The economy was that of self sufficiency supplemented by local natural resources such as marine molluscs. The basal colluvium at Cow Gap is rich in marine shells confirming their exploitation by man in the Neolithic.
The interfluve section was sampled in addition to the central infill section in order to compare and contrast the sedimentary sequence and molluscan succession from the centre to the edge of the catchment. No Late-glacial molluscan faunas were recovered from the interfluve section suggesting an earlier Devensian age for the basal cold deposits, and the Postglacial sediments contained only a biozone f assemblage. Clearly only the very late Postglacial deposits are preserved here, originating during a period when colluviation was at its most active.
The molluscan succession at the interfluve section is essentially the same as in the equivalent deposits at the central infill section except that biozone f spans 90cm of sediments at the interfluve in contrast to 50cm in the centre. This has allowed a more detailed examination of this biozone. In the central deposits 181
Cernuella virgata and Candidula gigaxii appear approximately together, but at the interfluve it is clear that C. virgata precedes C. gigaxii. The rest of the molluscan succession is very similar at both sites with the re—expansion of Abida secale, the late expansion of Vallonia pulchella, and the decline of Helicella itala corresponding to the expansion of the Cernuella/Candidula group.
The Postglacial sediments at Cow Gap preserve a long molluscan sequence (biozones d, e and 0, including the exciting finds of shells of Discus ruderatus and Zonitoides excavatus in the subsoil hollow. Woodland clearance at this site occurred much earlier than at the other study sites, which suggests that this area was important in the Neolithic for settlement, agriculture and as an access point to the shore. 182
13. ARION GRANULES
These are small ovoid calcareous granules ranging in size
from between 0.5mm and 1.5mm in maximum diameter. They are the
rudimentary internal shells of arionid species of slug, several
granules being present in each individual. It is not possible from
the granules to identify them to species level but it is clear that
the very large granules come from the Anon ater group whereas the
smaller granules come partly from the smaller species of Anon,
e.g. A. hortensis or A. circumscriptus.
Anon granules from freshly killed slugs have been compared
with those from fossil deposits by Kerney (1971). He was able to
show by XRD analysis that they were made of low magnesium calcite
but was unable to pinpoint differences in the structure of the
granules between the species.
At all the sites studied in Sussex Anon granules were
present in large numbers throughout the Postglacial sediments. At
Asham and at Cow Gap they also occurred in the Late-glacial chalky
silts.
In order to obtain an idea of the number of Anon granules in a sample and the variation between stratigraphical layers at Cow
Gap, the granules present in 20g of sediment were counted from each sample from column A (Postglacial colluvium) and also from column B
(subsoil hollow). Numbers were then plotted as an absolute frequency histogram and compared with the total number of shells 183
per kg (Figure 33). The absolute totals of shells and of Anon granules are given in Table 18.
It was hoped to show that:-
1. - the numbers of Anon granules were positively correlated with the total numbers of shells and slug plates, indicating that there had been little loss of shells by solution as the aragonite shells would be lost before the calcitic slug granules.
2. - the granules and shells would peak in abundance at any stability levels in the colluvium, as a stable soil surface would accumulate shells and granules in larger numbers than the colluvial increments.
As can be seen from the absolute frequency histograms the numbers of shells and Anon granules are closely linked, for example at depths 30-40cm, 110-120cm, 250-260cm. These data were also plotted as a scattergram which shows that there is a good positive correlation between the two data sets from column B (the subsoil hollow) but a much smaller correlation with the colluvium
(column A). This suggests that within the colluvium there has been some loss or segregation of shells by taphonomic processes, or less probably that conditions were better for arionid slugs than for snails.
From comparing the shell and granule totals with the stratigraphy there appears to be little correlation between stability horizons and peaks in abundance. In the topsoil (0-10cm) 184
Depth Total number of Arlon granules from cms shells from 1Kg 20g 0
50
C I
100
150
220
250
Cr 300
0
350
1 1 1 1 1 1 1 I 1 1 1 I 0 500 1000 0 300 600 Figure 33. Histogram of Shells and Anon Granules from Cow Gap,
Central Infill Section. 185
and the top of the subsoil hollow (220-230cm) there were no peaks.
Much more information could be obtained from these granules if they could be identified to species level and if the number of granules per slug was constant. But at present they can only be used to indicate levels where a substantial loss of shells has occurred. 186
14. DATING OF THE DEPOSITS
Typical Postglacial deposits found in chalk dry valleys include a woodland soil that has been buried by several metres of colluvium. Finds of stratified artifacts provide one method of dating these deposits and their associated molluscan assemblages, but layers that contain charcoal are immensely preferable as they can be dated by radiocarbon. Charcoal is usually only present in the buried soils and in the basal colluvium, and is associated with clearance. It is nearly always absent from the upper colluvium
(ploughwash). Charcoal extracted from buried soils has been successfully dated from elsewhere, for example Pitstone,
Buckinghamshire (Evans and Valentine 1974) and Brook, Kent
(Burleigh and Kerney 1982), but there are inherent problems in the dating of such deposits. The charcoal occurs usually only in very small amounts, necessitating the washing of large sediment samples.
Also, as charcoal is extremely stable, the fragments may not be of the same age, but represent more than one burning episode. It is safe to assume that one clearance episode is being dated only if the fragments are concentrated in one thin well—defined layer.
During this work in Sussex six radiocarbon dates from four sites have been obtained by the British Museum Research Laboratory from charcoal taken from the basal colluvium and from the top of the buried soil, thereby dating the onset of clearance. It was only in these lower deposits that charcoal was present in sufficient quantity to make dating possible. Nevertheless often 60-80 kg of sediment taken from a discrete layer needed to be washed to obtain 187
sufficient charcoal. The fragments were also usually very small, making species identification difficult if not impossible.
These uncalibrated radiocarbon dates have been put into a local cultural context by comparing them with other radiocarbon dates on charcoal or bone obtained from archaeological and palynological sites in Sussex (Table 19).
The date from the basal colluvium at Cow Gap is much the earliest obtained in this study and demonstrates a Neolithic age for the onset of woodland clearance of the adjacent Downs. This agrees satisfactorily with the find by Bell (1981a) of a finger impressed Beaker sherd from the same layer. Many of the dated
Neolithic sites in Sussex show that forest clearance at that time was very local. For example the dated layer from the Harrow Hill flint mines (4670 ± 60 b.p. BM 2071) contains a molluscan assemblage of pure woodland character (Kerney 1983). This indicates that only a small area of woodland was cleared for mining not large enough to allow open-country species to colonise.
The dates from Asham and South Heighton fall within the
Bronze Age period, i.e. considerably later than the clearance at
Cow Gap. These dates agree well with that obtained for clearance nearby at Itford Bottom (Bell 1983). The date obtained from the
Devil's Dyke is even later and is of the Iron Age period.
These differences between the sites suggest that the location and form of the valleys may have had a great influence on the date of clearance. It can be postulated that because of the importance 188
of Cow Gap as an access point to the beach it was cleared at an
early date. In contrast the Devil's Dyke is a very steep-sided dry
valley not offering much space on the valley floor for cultivation.
It may have been cleared much later for this reason or just
possibly to provide timber for the construction of the Iron Age
hill fort on the escarpment above.
An alternative method of dating these deposits is by directly
radiocarbon dating the mollusc shells. The British Museum Research
Laboratory is currently carrying out a long term research project
on the suitability of non-marine molluscs for dating.
The problems of using non-marine molluscan shells are:-
1. Over estimation of age due to the primary incorporation of
'dead' carbon.
2. Secondary recrystallisation and carbonate replacement of the
shell.
3. 'Industrial' and 'bomb effect' making modern shells unsuitable
as standards.
Living shells incorporate 'dead' carbon in their shells.
Rubin at al (1963) show from tracer studies that some species can
incorporate up to 12% ancient carbon into their shells in a highly calcareous environment. 'Dead' carbon incorporation can occur from
the dissolution of limestone, forming bicarbonates in soil water.
This error due to 'dead' carbon becomes relatively less important
with older shells. Goodfriend and Stipp (1983) illustrate this
'dead' carbon effect. They compare radiocarbon dates from modern
land snails from limestone and non-limestone areas in Jamaica. The 189
shells from the limestone areas produced dates as old as 3120 b.p., 12 attributed to the incorporation of C from the limestone into the shell. The rock-scraping species produced the largest dating anomalies compared with the litter-feeding species. They suggest that by selecting ecologically appropriate species in the limestone areas this dating error could be minimised.
After death the shells can recrystallise and there may be some carbonate replacement. If the shells are aragonite the replacement and regrowth as calcite can be detected by X-ray diffraction (XRD). This problem is worse for some species such as
Cochlicopa spp, Acanthinula aculeata and Pomatias elegans, where visible secondary accretions are common, especially on interior surfaces.
In order to validate a radiocarbon date from fossil shells it is necessary to establish a satisfactory modern standard, preferably based on the same species. Due to the depletion in the 14 amount of C in the atmosphere due to the combustion of fossil fuels since the nineteenth century ('industrial effect' or 'Suess 14 effect') and the enhancement of the amount of C due to artificial 14 C released by thermonuclear weapon testing in the 1950's ('bomb effect') such standards are difficult to establish.
Work carried out in Britain on the direct dating of non-marine molluscs is very limited. Burleigh and Kerney (1982) published a series of dates from fossil shells extracted from a radiocarbon dated charcoal layer of Neolithic Age at Brook, Kent
(Kerney et al 1964). Dates were obtained from fossil P. elegans and 190
Cepaea, nemoralis, and from living specimens collected from the site in 1976. An additional sample of P. elegans collected ca 1930 was also dated to eliminate the 'bomb effect'. The charcoal was dated to 4540 ± 105 b.p. (BM 254), whereas the fossil shell dates were
400-500 radiocarbon years older. This discrepancy suggests that P. elegans and C. nemoralis incorporate about 5-6% 'dead' carbon into their shells giving a dating error of a similar order. The shells collected in 1976 gave future dates, demonstrating the radiocarbon enhancement due to the 'bomb efect', whereas the 'old' date from the P. elegans collected ca 1930 exemplifies the depletion in 14 natural C activity due to the 'industrial effect'.
Shells of Cernuella virgata from the slope deposits of Roman or later age at Gore Cliff, Isle of Wight, were also submitted for radiocarbon dating (Preece 1980b). The slope deposits are thought nd to have begun to accumulate not earlier than the 2 century A.D. because of the presence of pottery fragments and a bronze trapeze—shaped brooch at their base (Mew 1932). There was insufficient charcoal for direct dating. Shells of C. virgata were therefore used. The dates obtained proved anomalous, as living specimens from the site yielded a date of 130 ± 50 b.p. (BM 1481) and the fossil shells 3940 ± 65 b.p. (BM 1482). Both dates were much older than expected, suggesting that large amounts of primary
'dead' carbon are incorporated by this species into their shells.
Dating has also been carried out on the freshwater mussel
Margaritifera auricularia, a species now extinct in Britain, dredged from the River Thames at several sites between Mortlake and
Battersea (Preece et al 1983). Three radiocarbon dates of Neolithic 191
age were obtained from these shells. To validate these dates and to calculate the 'dead' carbon content, it is necessary to assay a modern specimen. Unfortunately the species is now extremely rare living and no suitable material has yet been obtained.
From the four non-marine molluscan species that have been radiocarbon dated (jL:elegans, C. nemoralis, C. virgata and M. auricularia) it seems that reliability varies between species, with even the better species yielding dates 5-10% too old. Some species are obviously preferable for dating for practical reasons. The large-shelled species are easier to clean and fewer shells are needed.
Many more dates are needed from shells of these and other selected species from different sites and from a range of ages.
Ideally all the dates should be coupled with a reliable date from wood or charcoal from the same layer. With the advent of the accelerator very small amounts of carbon will be usable
(milligrammes as opposed to grammes). It has also been suggested that it might be possible to date the remains of the periostracum found preserved on fossil shells in some environments (although unfortunately rarely in slope deposits). This protein coat is in isotopic equilibrium with the plants on which the snails feed. As the periostracum is not calcareous, it eliminates the primary
'dead' carbon effect entirely (Burleigh and Kerney 1982).
Dating of Pomatias elegans from Asham and Cow Gap
P. elegans from the radiocarbon dated layers at Asham (column 192
D) and Cow Gap were dated by the British Museum Research
Laboratory. In addition to the adult specimens that were used first in the biometric study (Chapter 15), immature specimens were added to increase the weight of shell.
The shells were carefully washed and cleaned, aided by an ultrasonic bath and were then lightly crushed. The fragments were examined under the microscope and dirty pieces or fragments with calcite encrustations were removed. In addition the opercula were discarded as these are calcitic not aragonitic. Removal of any fragments contaminated by organic material or secondary calcite was necessary as they would have the effect of increasing the age of the sample.
As both shell samples were from already dated layers, this provided a rare opportunity for direct comparison between charcoal and shell dates. The dates obtained from the sites are :-
Asham charcoal 3460 ± 190 b.p. (BM 2217) shell 4590 ± 110 b.p. (BM 2296)
Cow Gap charcoal 4820 ± 350 b.p. (BM 2220) shell 5860 ± 130 b.p. (BM 2295)
The shell dates were evidently approximately 1000 radiocarbon years older than the charcoal dates, suggesting that at these sites
P. elegans incorporates significant amounts of 'dead' carbon into 193
their shells. This is a considerably larger error than that obtained from Brook, Kent (Burleigh and Kerney 1982). These shells from Sussex were considerably more encrusted with calcite than those from Kent, with about a third of the shell material having to be discarded. Although every care was taken, residual undetected calcite could well be an important source of contamination.
These pairs of dates from Asham and Cow Gap have provided more data on radiocarbon dating of P. eleRans. It is hoped that further dates may be obtained from other species present in the dated layers. 194
15. NOTES ON POMATIAS ELEGANS
Pomatias elegans is a Mediterranean species at the northern limit of its range in Britain. It is an obligatory calcicole, its distribution reflecting strongly the outcrops of chalk and limestone, and the occurrence of chalky boulder clay and shell sands (Figure 34 taken from Kerney 1976a). Its general biology and ecology have been discussed at length by Kilian (1951). Briefly it favours sheltered banks with a scrubby vegetation, together with a loose, friable soil in which to burrow. As it is a southern
European species it begins to hibernate at the end of September. It is frost sensitive, being killed by harsh winters. In Europe the main body of its distribution is approximately bounded by the mean
January isotherm of 2°C.
The geological history of this species is fairly well known.
It occurred in previous interglacials in Britain and reappeared in southern Britain in the Flandrian at approximately 7500 b.p., in biozone d (Kerney 1977; Kerney et al 1980).
The distribution of this species today in northwest Europe can be described as disjunct with isolated colonies many miles to the north of the main distribution, for example on the Danish
Islands, Zealand and Funen (Schlesch 1961), and in Britain in Forge
Valley, Scarborough (Kerney 1968). These sites are all south or south—west facing habitats providing favourable microclimates.
Kerney (1972, 1976a) has published evidence that P. elegans was formerly more widespread in Britain than it is today. There are 195
0 1 2 3 4 • - ANT HY 7. N2. POMATIAS ELEGANS , (Willer) Ni —1 • 1950 onwards 0 before 1950 Only + flandrian fossils 8 i ioo q7, -k, mn
I
, -___.--114,0111111 r
C.-7 .1 5
\,,,,,b4 • - ‘ 0 0 se
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o Nii, c"- 1 o '. N,L.,,A, + 3 +8+ v, ( 1 o o i oo f § 4 :•.2°•1 i* !,i •• + ° 0041.11 +ii+Q – - • . ••• ••••• • •••0•10 V6."--/ -71..es 01; q .:11ti + 131%1 ..,.._.--j • • •• +0+0 .110 --,--4 • r (1,- .41• • • rollr •• • •Onjir_l e•Cr•••• • • •44 0---d0.---4 .0 .1. ++,441:0• ...• .. •.:: . + ** ; ** .:ii:w::: j 4.0, 1.0:iot-11 _.;_...„..• ...,•••1•040 * * * * * II. / OYINEL GL .05 , r: 'leo : 4::* .1.01 ND OM 4.+ .... 1.1.W10 • .. tZ) 6C.,:( 1 • '4 0
Figure 34. Distribution of Pomatias elegans in the British Isles
taken from Kerney 1976a. 196
records of nineteenth century colonies which are marked today only by empty shells on the ground surface. This is very common in the
East Midlands, East Anglia and Lincolnshire. Lozek (1964) also has shown that this species once occurred in Czechoslovakia and
Schlesch (1961) that it once lived in North Jutland. The fossil records of this species from earlier Postglacial deposits show that this species was formerly more widespread over Britain than today
(Kerney 1976a), suggesting that past environmental conditions were more suitable for this species.
Kerney (1968, 1972) has suggested that this shrinkage in distribution may be related to the temperature decline since the mid Postglacial thermal optimum when the mean annual temperature was 2-3°C higher than today. This idea is based upon the observation that the now isolated northern colonies of P. elegans are all found in sheltered microhabitats and that the main European distribution closely follows the "frost line". As P. elegans is intolerant of frost, increasing severity of the winters may well be a contributary factor in its recession.
Additional support comes from the work of Burleigh and
Kerney (1982) and Preece (1978) on the sizes of fossil and living species of P. elegans. These authors demonstrate that mid
Postglacial fossil shells were considerably larger and heavier than ones living in the same area today. This suggests that conditions were better for Pomatias elegans, enabling it to grow larger and probably to extend its breeding season.
A decline in temperature by a couple of degreees centigrade 197
is enough to make a species at the edge of its range lose ground and perhaps also to decrease in size. There is also some evidence
that the decline of P. elegans can be attributed to man's activities, as agriculture and especially ploughing destroy the habitats that P. elegans favours. This is particularly true of East
Anglia, an area of relatively low winter temperatures where the scattered colonies are at risk through intensive farming.
It has long been known that fossil examples of P. elegans are larger than living specimens. Bourguignat (1869) recorded a specimen 17mm X 9.5mm in S.E. France. This he considered a distinct species, Cyclostoma lutetianum. Germain (1912) studied a series of specimens of P. elegans from a Postglacial tufa in the Rhone valley and concluded that C. lutetianum was only an extreme form of P. elegans and not a seperate species. More recently work has been carried out on the size of P. elegans from Brook, Kent (Burleigh and Kerney 1982) have been studied. 150 living and 150 fossil shells were measured, the fossils being from a layer dated by radiocarbon to 4540 ± 105 b.p. (BM 254). A graph showing the distribution of sizes is given by Burleigh and Kerney (1982). It is clear from their graph that the Neolithic shells are on average much larger than the modern shells. The shells were also weighed and found to be on average 0.0223g heavier. A similar study was also caned out by Preece (1978) on fossil shells from tufas at
Wateringbury, Kent, and at Blashenwell, Dorset. He also demonstrated that the fossil shells were considerably larger than their modern equivalents.
P. elegans is a sexually dimorphic species (Boycott 1909), 198
females being on average lmm taller and broader thad the males. But it can be assumed within the present study that the numbers of males and females are approximately equal.
As no P. elegans shells have previously been measured from
Postglacial deposits in Sussex, this was carried out on shells from the dated layers at Asham and Cow Gap. Adult shells (le. those with a thickened peristome) were selected from the radiocarbon 'floats' and measured using a micrometer screw gauge. Two measurements were taken, the height being measured from the apex to the most distant part of the peristome on a line parallel to the axis of coiling, and the breadth measured at right angles to the axis. At Asham 96 fossil individuals were measured and at Cow Gap 69 (Tables 20 and
21, Figures 35 and 36).
Shells from the two sites were, as expected, larger than those of living populations of P. elegans from southern England.
However, none of the shells exceeded 17mm in height, unlike at
Brook, Blashenwell and Wateringbury. The largest shell at Cow Gap was 16.77mm X11.14mm and at Asham 15.72mm X 11.35mm. These shells are still considerably larger than modern British specimens which very rarely exceed I5mm in height. At Cow Gap, 17 individuals
(24.5%) exceeded this measurement as did 9 (9%) at Asham.
From analysis of all the data sets available it is clear that shells dating from around the mid Postglacial are larger in size than modern equivalents in southern England. However, there are differences between the fossil data sets. The fossil shells from
Asham are the most recent in age and on average smaller than the 199
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shells from the other, older sites. It can be postulated that these size differences can be related to the decline in temperature since the thermal optimum, ie. the shells nearest in age to the thermal optimum will be the largest. The average heights and breadths of the measured specimens are given in Table 22. 202
16. OPTIMUM SAMPLE SIZE
(by David Gordon and Caroline Ellis)
Although quantitative molluscan analysis has been carried out on Holocene deposits for the past 30 years no work has been done on the optimum sample size necessary to obtain ecologically meaningful results. In Britain a variety of sample weights have been employed from 200g (Preece 1978) to 2kg dry weight (Kerney et.al 1964). In 3 contrast on the continent volumetric samples of 10000 cm have been analysed (Piechocki 1977), a time-consuming but statistically more accurate method. The problems associated with using samples of insufficient size have long been recognised in sedimentological and palaeontological studies. Grayson (1981) has shown that by using small samples containing vertebrate remains incorrect ecological conclusions have been drawn, and Uries (1970) has shown that small samples have caused incorrect sedimentological interpretation.
Until now no work has been carried out on the optimum sample size for Quaternary non-marine Mollusca although de Caprariis et al
(1976) have developed a statistical method for determining the optimum sample size for modern Marine Mollusca in contemporary beach sediments. This method is applicable to this study of
Flandrian slope deposits.
A large quantity of soil from the south section at Asham from between 140-150cm was dried and samples of 100g, 250g, 500g, 750g, lkg, 1.5kg, 2.5kg and 5kg extracted. Stones over 16mm in diameter 203
were excluded. This soil was considered to be typical of the deposits studied in this research project and contained an average number of shells per unit weight of sediment compared with other samples and other sites. The soil was treated by the procedure detailed in Chapter 4. The molluscs were extracted, identified and counted, and the results are listed in Table 23.
From theoretical considerations it would be expected that the number of shells recovered would increase linearly with sample size. As can be seen from Figure 37 this is precisely what occurs.
The regression of the number of molluscs against sample size may be expressed as the ordinary least squares regression equation of y 73 + 606x which has an r 2 value of 98.3% adjusted for degrees of freedom. This is highly significant. From this result it can be concluded that no large operator errors have occurred during the tedious technique of counting and extracting 7634 molluscs.
Theoretically it would also be expected that the number of molluscan species found would increase in a hyperbolic manner, that is the number of species found would at first rapidly increase with increased sample size and then slowly tail off as only one or two additional rare species were found. A smooth curve would thus be expected. However although a smooth curve is present, as can be seen from Figure 38, obvious clumping can be observed within the
500g to lkg samples. There is no reason to believe that this is an artifact of the regression analysis. It is quite common to find clustered data of this nature in species area studies, as for example in the study by Korstian and Cole (1938) on forest stands. 204
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El) CU L 0(1- CL CU 0.1 (A 206
Unfortunately, the simple hyperbolic model of de Caprariis et al (1976) which fits the curve y ax/l+bx to the data leads to incorrect estimations of the number of species present because of the irregular nature of the curve (Heck et al 1975; de Caprariis and Lindeman 1978).
De Caprariis and Lindeman (1978) have suggested a change to allow meaningful optimum sample size results to be obtained from clustered data in non—uniform environments. They suggest converting a species area curve into a species range curve. This is a complex and somewhat subjective method that was thought to be inappropriate to this study. Instead cumulative species were plotted against sample weights in order to obtain a smoothed curve and the de
Caprariis hyperbolic model was fitted (Figure 39). The same regression is plotted on Figure 38 which is the raw data. It provides a good fit if the clumping is ignored between the 500g and lkg samples, thus showing the effectiveness of the cumulative percentage transformation. The maximum number of species predicted by this method that are likely to occur in the soil at Asham is
29.4. This is in good agreement with the number recovered from the largest sample (5kg) which was 28. Only 30 species were found in the entire sample series of which one Ceciliodes acicula was due to contamination.
In view of this good agreement between the predicted and actual maximum number of species present it was possible to calculate the percentage error expected when using different sample weights. For example, the model equation of
y = ax/l+bx (1)
▪
207
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I 41 •C I O ..I. •Cl- ••-C•1 at I 3t I CU I .--e 1. CL E I CI I O 1 6 .1.. CT) > t 1 co cu 1 * U O I o_ 1 co I 0 1 I 6 C t In • >- I e-4 ..-4 I 4.) 0 I .--• 1 ,-4 D t1/4 t E \ \ D 1 O , * I Oi 1 m i o) s._ I D I U) ------IF- Ir- 1...... __ ..4- -- .... _4_ 0 lf) 1.11 tn o In tn tn o In in u-t o (r)( \ I •CV .--n .--• N ('J.I. C-: CV r--"- o3 N c\i .-.
OD ED --4 0 41 --4 > CU 0 CL 0 o— 0 0 208
it can be transformed into a linear equation if you let
w = 1/y
z = 1/x then equation (1) will become
(2) w = K + K2z 1
where: K = b/a 1 K = 1/a 2
The regression equation for the transformed data is 2 0.0341+0.00455x which has an r value of 95.47 adjusted for degrees of freedom.
The coefficients of regression and model equation for the soil at Asham are
K K a a/b 1 2 0.0341 0.00455 219.79 7.49 29.4
From the limiting value (a/b) of y, it is possible to calculate the maximum amount of material needed to ensure that all the species are found from the expression (1/(a/b)}((a/b)-axc/(1+bxc)) = E
One can then solve the equation for a critical sample size x c x = (1-E)/b c where E = the percentage error with respect to the number of species found.
By solving x c for different values of the percentage error the results can be plotted graphically and are summarised in Figure 40.
This shows the percentage error versus sample weight. 209
— — — — -- __ _A __ — —4 --
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cri
N As can be seen by using the lkg sample you would expect an error of just over 10%. This is acceptable for most ecological interpretations. However this error is only true if the number of species are randomly distributed throughout the sediment as the percentage error calculations are based upon the cumulative species graph (Figure 39). This is clearly not the case with this data as the 500g to lkg samples are clumped. It would therefore be necessary when using soil samples of this type where clumping can be expected either to use a sample larger than lkg or alternatively, if errors of less than 25% are required to use sub-sampling techniques designed to reduce the effects of clumping. The reason for clumping is obvious. In slowly forming sediments such as soils microenvironmental conditions and ped formation cause the shells to be irregularly distributed. This is in marked contrast to the slope-wash deposits where mass movement and fluvial processes cause taphonomic mixing. This presents a problem when sampling Flandrian slope deposits for molluscan analysis since they often include both slow and fast forming sediments (soil and slope-wash deposits). From the statistical point of view it is highly desirable to keep sample size constant (Williamson 1978; Gordon and Ellis 1984). Yet in heterogeneous sediments such as soils very large samples (in excess of 5kg) may be statistically desirable. An obvious method of overcoming this dilemma is to take initially larger samples in the field and then split samples down to the desired size using a suitable method to randomise the natural clumping. Allen and Khan (1970) have shown that this can be done adequately by using a Chute riffler or a spinning riffler. The use of a scoop in order to sub-sample, a procedure used by most 211 molluscan workers, can be expected to lead to an error greater than 20%. It would seem advisable that more controlled sampling techniques be used when a detailed ecological molluscan analysis is required. Since Sparks (1957) the standard method of presenting quantitative non-marine molluscan data has been in the form of a percentage histogram. Though crude, this technique has been favoured by most workers because of its robustness. However until this present study no quantitative analysis has been undertaken to determine the possible effects of insufficient sample size upon the percentage histograms. Figure 41 shows the 100g to 5kg samples plotted in the form of a percentage histogram. Despite the fact that there is a theoretical 60% error for the 100g sample, there is hardly any change in the histogram between the 100g and 5kg sample or with respect to the number of species present (Figure 41). This graphically illustrates the strength of the percentage histogram method for palaeoecological studies where detailed sedimentology is not known. However, if a detailed ecological study is desirable in order to reconstruct palaeoenvironmental conditions to a higher degree of accuracy, then the percentage histogram method in isolation maybe too crude a method to show subtle environmental changes. Other methods of biological statistics such as described by Gordon and Ellis (1984); Williamson (1978) may be necessary. 212 D11)31,30 sapy)!)!oao DLIDISNJO3 OCIODUON 0101! DIlaallaki MIN sem =NI mum oo.olueoxa oru0110/1 1 1 1 1 1 .oloisoo • Ill • • • wn.JoosnW Ojj!cind 1 1 II 1 1 II II II aioDas opiqv oaow5Xd 05n..iaA 11111 MN NMI =NMI MEN oluD.I.JV/ oandap OMB WM lima EMI op!dsp.i • I II II III Z2 0 srminj snInuoon3 I. xow!7/ soJaoo.Jaa • is al • II • • • s!trowwoy oaiirnosaN 4 opionilad ou.IJPA 4- 4- wnaow54d wniound In 0c/0311(003 III IN. so NO al ow am su0591e sonowod 111 11•1111 •• —0 opfordoi ou05.13.tiati 4- 4- 4- 4- oioluapiq oflisnolo MIN DIDU rwoi ouipoitiooa snponao sniNoXxo Dinmpu oilaurdo5av mind oli3tpdo53v 4- oaJim sniopunioJ snos.la ain3sqo 0u3 oppa)noo oinufyluoav wniolueoui wniciokioj 4- oosnj Dinp!OV 0 0 000 0 10 0 0 (st.u6) ILIEHam 8 10 0 0 to 0 213 17. DISCUSSION AND GENERAL CONCLUSIONS In these studies of dry valley inf ill deposits a characteristic tripartite sequence of sediments was repeatedly found. This consisted of Late-glacial chalky slope-washes (silts and rubbles) below, and Postglacial colluvium above, with an in situ forest soil between them at some sites. A clear parallel can be drawn between the wide of formation of the Late-glacial deposits and the Postglacial colluvium: they both formed in open-country environments where instability of the slopes resulted in soil being eroded from the valley sides and redeposited on the valley floor. The Late-glacial and Postglacial deposits resulted from a combination of mass movement and fluvial processes. In the Late-glacial the sediments were transported by both fluvial action (slope-wash, ruling and gulleying) and by mass movement (solifluxion), whereas in the Postglacial, after forest clearance, sediment movement down valleys occured mainly as small increments due to soil creep (mass movement) and only partly to occasional overland flow as sheet wash or gulleying (fluvial processes). The forest soil found between these Late-glacial and Postglacial slope deposits represents a period of stability with very little erosion or deposition. There would only be the gradual chemical, physical and biological weathering of the bedrock together with the incorporation of organic matter, producing a soil. Of the earliest Postglacial soils probably all that would remain would be the more resistant mineral fraction. Carbonates (including shells) of that period would have been destroyed by 214 chemical solution, accelerated by the probable presence of acid humus (mor) on the soil surface. There seems to be very little evidence to support the alternative hypothesis that early Postglacial slope sediments have been eroded. It is unlikely that water flowed in the upper and middle reaches of these now dry valleys during the earlier Postglacial although there is abundant evidence of flow in the lower reaches in modern times. It has become clear from this work in Sussex that the early Postglacial molluscan biozones a—c inclusive are not represented in soils or colluvium. The only deposits so far found to preserve faunas of this period are calcareous tufas and other biogenic spring deposits as studied by Preece (1978) and Kerney et al (1980) because suitable slope sediments were not generally forming at this time. Subsoil hollows are a special case . As discussed earlier their most probable mode of formation is by the uprooting of a tree, leaving behind a depression which is then filled with soil from the surrounding area. It is in these hollows that the earliest Postglacial deposits were found during this study, lying stratigraphically below the in situ forest soils and basal colluvium. The hollows studied were all found to contain relatively late, biozone d molluscan assemblages. There are two likely reasons for this. First, any hollows fills formed early in the Postglacial are likely to have been destroyed by natural weathering and a general lowering of the surface by the time of the forest optimum. 215 Secondly, early Postglacial forests on the Downs would probably consist of shallow-rooted trees (birch, pine etc.) growing over thin soils. Their uprooting would leave shallow hollows only and there would not be much weathered sediment available to fill them. It has become apparent from these studies on slope deposits that they preserve well stratified biological remains, in this case Molluscs, which provide an excellent source of environmental information. By comparing fourteen molluscan histograms from the eastern end of the South Downs it is obvious that there are clear biostratigraphical similarities between the sites, as well as smaller, subtle differences. It has therefore been possible to separate the very local molluscan changes specific to single sites from the regional pattern of the entire area and hence establish a general molluscan succession for this region of the South Downs stretching from Hove to Eastbourne. In order to facilitate comparison between the sites, biozone boundaries have been drawn on the histograms. The ease with which this could be done varied between sites and between biozones. The biozone boundaries that were defined by the appearance of a single species, for example biozone f (Helix aspersa), were easy to draw, but the base of biozone e was often difficult to place because the expansion of the open-country forms was not always very abrupt. To aid drawing the d/e boundary the ecological summary histogram to the far right of the diagrams was also used and this boundary was drawn where the most rapid increase in the open-country species occurred. 216 A clear pattern of the molluscan succession in Sussex during the Late-glacial and Postglacial has emerged from this study and supports the work of Evans and Williams (Williams 1971) and Bell (1981, 1983). The present studies of slope deposits have allowed a further amplification of the standard biozones of Kerney (1977) and Kerney et al (1980). The earliest preserved Mollusca are of Late-glacial age. These were found only at Asham, Cow Gap, South Heighton and Hope Gap. The periglacial molluscan assemlages recovered at these sites all contained some of the slightly thermophilous species, for example Trichia hispida and Abida secale, and have therefore all been assigned to biozone z. At none of the sites studied were any extinct British species found, with the exception of Columella columella recovered at Cow Gap in the earlier study by Kerney (1963). Between these Late-glacial deposits and the earliest Postglacial sediments there is a hiatus of several thousand years. At none of the sites were any of the early Postglacial biozones (a-c inclusive) found and the only indication that these assemblages occurred in this area of South-east England was the presence of one shell of Discus ruderatus (characteristic of biozone b) in the subsoil hollow at Cow Gap. A biozone d fauna was found preserved at all the sites with the exception of Exceat. These woodland molluscan assemblages were found preserved in the subsoil hollows at Cow Gap and Asham, in the buried soil at Asham, and in the buried soil and overlying basal 217 colluvium at the Devil's Dyke pits. The fauna of this biozone is characterised by Discus rotundatus, Aegopinella pura., A. nitidula, Oxychilus cellarius and the Clausiliidae, together with the very late appearance and expansion of Acicula fusca at the end of the biozone. This is seen most clearly at Asham, Cow Gap and South Heighton. The base of biozone e occurs in the colluvium and is defined by the expansion of the open-country forms. These were mostly already present in the area throughout the woodland biozones, but only in low numbers. Expansion usually begins with Vallonia costata and is then followed quickly by V. excentrica and Helicella itala. This is accompanied by the more gradual decline and eventual exclusion of the woodland forms although some managed to persist, probably living in small isolated patches of shade. Corresponding approximately to the base of zone e is a peak in the abundance of Pomatias elegans. This usually occurs just before the main expansion of the open-country forms, when the broken soil suitable for P. elegans would precede the development of a grassland cover, allowing the open-country genera (Pupilla, Vallonia etc.) to expand in turn. Also consistently present in biozone e in Sussex is Monacha cartusiana. This was a very early introduction, present at Asham, Cow Gap, Exceat and South Heighton. Its arrival at the Devils Dyke has been dated to 2315 ± 35 b.p., a date which falls within the Iron Age. At all the sites in Sussex the open-country genera continue to expand in numbers within the colluvium, making up the dominant ecological group. Woodland forms now total only between 216 1-2% of the assemblages. Deposits containing Helix aspersa (biozone 0 were preserved at all sites, usually within the upper metre of colluvium and in the topsoil. This species is a Romano-British introduction which is known to have spread very rapidly across lowland England. It is later joined by the introduced helicellid species, first by Cernuella virgata and Candidula gigaxii (which seem to appear approximately together) and then by Candidula intersecta (which occurs only in the topsoil samples). At most sites Monacha cantiana is also present in the topsoil. This species was usually not picked up by sampling, but only by collecting dead shells from the ground surface. In contrast to biozone f, which is based upon the appearance of an introduced species which spread quickly, the base of biozone e is strongly diachronous. This is because clearance of the valleys occurred at widely different times. A Neolithic date for clearance was obtained at Cow Gap compared to an Iron Age date at the Devil's Dyke. So, unlike the other biozones, which are based upon climatic and vegetational changes or by the introducion of alien species, the onset of biozone e is dependent purely on the actions of man in clearing the valleys. Hypothetically if clearance did not occur until the Romano-British period the bases of biozones e and f could well be synchronous. Another feature of the general molluscan succession of the South Downs is the late expansion of Vallonia pulchella. This species, unlike the xerophilic V. excentrica, usually lives in 219 marshes or on river floodplains. Nevertheless it consistently occurs within the colluvial deposits in Sussex, as well as in comparable dry valley fills on the North Downs (Kerney et al 1964) and in Wiltshire (Kerney unpub.). As its appearance is so constant, it must be concluded that either changes in the climate or in the vegetation must have allowed it to colonise the hillsides. It is possible that its expansion can be related to an increase in rainfall during the sub—Atlantic period, but it seems more likely that it is linked in some way to the vegetational succession on the Downs. Possibly it appeared when a rich stable grass sward developed, providing suitable damp microhabitats. Another interesting feature of the molluscan succession is the decline in numbers of Helicella itala. This has been discussed by Preece (1980) who with others has suggested that it can be related to a decline in sheep grazing and hence a loss of the typical chalk grassland ecosystem coupled with an increase in the amount of land being ploughed. An alternative or additional explanation is that the decline of H. itala may be linked with the introduction of alien helicellids (Candidula, Cernuella) into the area as its depletion occurs at approximately the same time as these species appeared. This decline could therefore possibly result from competition by these species with the result that H. itala was progressively excluded from the few suitable habitats available. No ecological work is however available to test this hypothesis. This molluscan sequence has been based upon the expansion or contraction of certain forms in response to climatic and 220 environmental change, and on the introduction of alien species into the area. The faunal sequence during the late Postglacial can also be related to the biological concept of succession. An ecological model applicable to chalk downland has been constructed based upon the molluscan changes (Figure 42). The natural climax vegetation of the South Downs is a mixed oak forest. This is associated with a molluscan fauna (biozone d) of D. rotundatus, A. nitidula, A. pura, 0. cellarius and A. fusca, the last occuring only where the most shaded, stable habitats are available. This forest was cleared by man creating at first areas of loose broken soil that were quickly colonised by P. elegans. Then, as the pioneering weed species of plants became established, molluscs such as T. hispida and V. costata were able to expand in numbers. These two species are the first of the catholic and open—country forms to expand after woodland clearance, being already present in the area in low numbers during biozone d. They are pioneers able to withstand the harsh conditions of exposed, dry and only partially vegetated habitats which occur immediately after clearance. The expansion of V. costata is seen most clearly at the Devil's Dyke, (Pit 1) where it totals 557 of the assemblage. The pioneering plants (ragworts, nettles and dandelions) are followed by the later colonisers of grasses, plantains and thistles, which create more humid and less exposed micro—habitats. This change enables the open—country species V. excentrica, H. itala and V. pygmaea to migrate in and expand in numbers. Evans (1972) has shown that V. excentrica prefers slightly moister habitats than V. costata even though this species is better able to 221 Succession on Chalk in Sussex (Figure 42) Environment Flora Mollusca Late-glacial open- Grasses, sedges, T. hispida, A. secale, ground. Solifluxion. willow, birch. V. costata, P. muscorum, P. pygmaeum. Postglacial closed Mixed deciduous D. rotundatus, forest. woodland. Clausiliidae, Soil formation and Climax vegetation. Zonitidae, slope stability. C. tridentatum. CLEARANCE Open ground, soil Pioneering species: V. costata, P. muscorum, erosion. ragworts, dandelions, T. hispida. nettles. Open ground, Late colonisers: V. excentrica, increasing stability. grasses, plantains. V. pygmaea, H. itala, M. cartusiana. Slope stability. Grassland plagio- Decline of climax. M. cartusiana. Re-expansion of C. tridentatum and Zonitidae, expansion of V. pulchella. 222 withstand shade. The later plant colonisers, which are mainly grasses, create an almost complete ground cover forming in time the typical chalk grassland sward (grassland plagioclimax). This provides stable and evenly humid microclimates. Although this is a climax community it is not the natural climax vegetation of the Downs, which is forest, but this has been removed by man. This grassland community is ecologically unstable and needs to be maintained by the grazing of sheep and rabbits. Once this pressure is removed or even reduced the grass quickly becomes invaded by scrub species such as hawthorn. This change allows the re-expansion of many of the woodland (shade-demanding) molluscs as seen in the topsoil or uppermost colluvium at several sites. The environmental change from woodland to broken soil and the subsequent invasion by weed species leading to the development of a chalk grassland community is reflected in the molluscan succession. But the appearance in biozone e and f of the introduced molluscs (M. cartusiana, H. aspersa, C. intersecta, C. gigaxii, C. virgata and M. cantiana) is not directly related to the ecological succession but to the activities of man and the ability of these species to act as 'weeds', ie. they are able to live in artificially maintained environments. Other characteristics of the molluscan succession can be linked with the ecological model proposed above (Figure 42). The characteristic late expansion of V. pulchella can be explained in terms of the establishment of a grassland climax. This species 223 prefers wetter habitats than V. excentrica or V. costata, and is probablyonly able to colonise areas where the grassland is sufficiently thick and lush. Future studies of the molluscan biostratigraphy of slope deposits will yield greater information. The minute charcoal fragments which occur at most levels within these deposits are insufficient for dating by present conventional methods. 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Institute British Geographers, Publication No. 10. WOOLDRIDGE, S. W. and LINTON, D. L. 1955. Structure Surface and Drainage in South-east England. London : George Philip. 259 APPENDIX I This section contains tables of the results of the molluscan analyses carried out at the six sites in Sussex. The species are listed in taxonomic order with the exception of the water snails. These are listed at the top of the table. The depths from the surface are given in centimetres across the top of the table and the shell totals at the bottom. The dry weights of all the samples were 1 kg. Table 1 : Devils Dyke, Pit 1 Depth (cm) 200 190 180 170 160 150 140 130 120 110 100 90 70 50 30 0 210 200 190 180 170 160 150 140 130 120 110 100 80 60 40 20 Pomatias elegans (Muller) - 15' 41 66 41 39 31 26 13 9 12 11 13 7 7 5 Acicula fusca (Montagu) - - - 1 Carychium tridentatum (Risso) 1 18 8 7 3 2 12 1 1 - 1 - - - - 85 Cochlicopa lubrica (Muller) 2 9 4 3 3 2 - - 16 _ Cochlicopa lubricella (Porro) - 1 - - - Cochlicopa sPP. 1 14 48 52 33 36 25 9 14 5 8 7 - 13 4 17 Vetigo pusilla (Muller) - 1 1 Vertigo pygmaea (Draparnaud) 1 - 1 - 2 13 10 2 6 2 1 1 2 12 8 45 Abida secale (Draparnaud) - 1 2 2 2 1 Pupills muscorum (L.) 3 - 1 - 4 20 21 3 - 5 3 6 10 39 3 118 Vallonia costata (Muller) - - - 9 3 24 38 70 72 81 151 89 42 13 34 33 Vallonia pulchella (Muller) 2 - Vallonia excentrica (Sterki) -----2 4 - - 1 - - 5 31 4 68 Vallonia pulchella/excentrica - 2 1 2 8 3 6 2 1 - 2 3 77 27 84 Acanthinula aculeata (Muller) - 4 16 7 2 3 6 - 1 Punctum pygmaeum (Draparnaud) - 1 - 2 - 1 3 1 - 1 - - - 2 1 9 Discus rotundatus (Muller) 2 5 21 24 4 8 1 3 6 1 - 1 1 - _ Vitrina pellucida (Muller) - 1 - - 1 3 3 3 2 3 1 - - 1 - Vitrea crystallina (Muller) 1 1 - - - - 5 Vitrea contracta (Westerlund) - - 5 - 2 3 - - 5 8 Nesovitrea hammonis (Strom) - - 1 - 1 2 1 - - - - 2 3 10 Aegopinella pura (Alder) - 8 8 7 2 - - 2 1 1 Aegopinella nitidula (Draparnaud) 1 8 11 13 6 4 5 4 2 - 2 2 2 - 1 6 Ox chilus cellarius (Muller) - 7 10 5 5 2 - 1 - - - - 1 - - 1 Limax/Deroceras spp. 2 18 80 104 82 101 84 49 37 33 39 37 30 31 22 39 Cecilioides acicula (Muller) 5 9 19 29 1 Cochlodina laminata (Montagu) - 1 10 10 4 3 4 - 1 Clausilia bidentata (Strom) - 2 19 21 8 8 4 2 2 2 5 2 - 1 2 2 Candidula intersecta (Poiret) - 1 Helicella itala (L.) - - - - 1 - 1 4 4 6 10 6 13 17 5 1 Monacha cartusiana (Muller) 3 4 5 11 4 12 2 - - Monacha cantiana (Montagu) 1 Trichia striolata (Pfeiffer) - 1 - - - 1 4 8 2 - - - - 2 6 1 Trichia hispida (L.) 2 24 89 71 39 35 19 17 14 11 16 28 11 46 59 117 Helicigona lapicida (L.) - X 2 3 2XXXXXXXX - - - Arianta arbustorum (L.) - -X-X-XX - - X Cepaea/Arianta spp. - 12 21 23 13 7 11 9 4 4 2 3 5 2 2 - CAEMI sPP. - - XXXXXXX XXXXXX - Cepaea hortensis (Muller) - X X - - - - Cepaea, nemoralis (L.) X Helix aspersa (Muller) XXXXX Total Shells 13 144 393 419 257 321 294 233 194 174 271 214 162 320 228 676 Table 2 : Devil's Dyke, Pit 2 Pomatias elegans (Muller) 31 Cochlicopa spp 37 Vallonia costata (Muller) 1 Vallonia excentrica /pulchella 1 Acanthinula aculeata (Muller) 3 Discus rotundatus (Muller) 11 Vitrina pellucida (Muller) 1 Aegopinella nitidula (Draparnaud) 13 Oxychilus cellarius (Muller) 2 Deroceras /Limax spp 72 Cochlodina laminata (Montagu) 3 Clausilia bidentata (Strom) 9 Trichia hispida (L.) 41 Arianta arbustorum (L.) X Cepaea spp X Arianta /Cepaea spp 14 Helicigona lapicida (L.) 2 Total shells 241 Table 3 : Devil's Dyke, Pit 3 Depth (cm) 285-290 250-255 130-135 Pomatias elegans (Muller) 29 3 1 Carychium tridentatum (Risso) 10 5 2 Cochlicopa lubrica (Muller) - - 6 Cochlicopa spp 31 8 25 Vertigo pygmaea (Draparnaud) - 4 6 Pupilla muscorum (1.) - 6 11 Vallonia costata (Muller) - 11 41 Vallonia exentrica Sterki - 7 21 Acanthinula aculeata (Muller) 5 3 - Punctum pygmaeum (Draparnaud) - 1 - Discus rotundatus (Muller) 18 2 - Vitrea contracta (Westerlund) - - 3 Aegopinella pura (Alder) 11 2 - Aegopinella nitidula (Draparnaud) 16 10 5 Oxychilus cellarius (Muller) 5 1 - Deroceras/Limax spp 50 26 93 Cecilioides acicula (Muller) - - 3 Cochlodina laminata (Montagu) 6 - - Clausilia bidentata (Strom) 11 1 1 Helicella itala (L.) . - - 8 Monacha cartusiana (Muller) - - 17 Trichia hispida (L.) 44 8 48 Trichia striolata (Pfeiffer) - - 1 Cepaea spp - X X Arianta/Cepaea spp 12 6 4 Helicigona lapicida (L.) X - X Total Shells 249 104 297 Table 4 : Devils Dyke, Pit 4 Sample A Pomatias elegans (Muller) - 3 15 1 Carychium tridentatum (Risso) - - 1 - Cochlicopa lubrica (muller) - 4 1 - Cochlicopa spp - 10 13 7 Vertigo pygmaea (Draparnaud) - 8 40 13 Abida secale (Draparnaud) - - 7 1 Pupilla muscorum (L.) - 11 48 6 Vallonia costata (Muller) - 39 71 36 Vallonia excentrica Sterki - 10 7 17 Vallonia spp - 15 20 29 Acanthinula aculeata (Muller) - 1 - - Punctum pygmaeum (Draparnaud) - - 1 6 Discus rotundatus (Muller) - X 1 - Vitrina pellucida (Muller) - - 2 1 Vitrea contracta (Westerlund) - - 3 1 Nesovitrea hammonis (Strom) - - - 2 Aegopinella pura (Alder) - 1 - 1 Aegopinella nitidula (Draparnaud) - 2 - 3 Deroceras/Limax spp - 52 36 40 Cecilioides acicula (Muller) - 1 9 3 Clausilia bidentata (Strom) - - 3 - Candidula gigaxii (Pfeiffer) - - - 3 Helicella itala (L.) - 6 12 - Monacha cartusiana (Muller) - 20 - - Trichia hispida (L.) - 21 43 50 Trichia striolata (Pfeiffer) - 1 - 2 Arianta/Cepaea spp - 4 - - Helix aspersa (Muller) - - 5 - Total shells 0 210 338 223 Table 5 : Devils Dyke, Pit 5 Depth (cm) 245 235 230 225 220 215 210 205 200 195 190 185 180 175 165 155 145 75 255 245 235 230 225 220 215 210 205 200 195 190 185 180 175 165 155 SO Pomatias elegans (Muller) - 1 4 X 1 8 16 19 17 11 10 16 12 6 8 2 7 2 Acicula fusca (Montagu) ------1 - - - - Carychium tridentatum (Risso) - - 4 - - - 1 1 - 1 - - - - 2 X Cochlicopa app. - 6 13 12 3 14 4 8 7 11 16 15 10 4 6 7 2 3 Vertigo pygmaea (Draparnaud) ------1 2 - 4 4 5 1 4 1 Abida secale (Draparnaud) - 1 1 1 ----- 1 1 ------1 Pupilla muscorum (L.) - - 2 - - - 1 3 1 3 8 2 3 11 2 - 1 - Vallonia costata (Muller) - - 4 - - 1 10 5 3 6 9 3 4 5 11 8 3 Vallonia pulchella (Muller) ------1 Vallonia excentrica Sterki - - 1 - - - 1 - 4 - 1 - 1 2 1 2 1 2 Vallonia spp. - 5 5 3 - 1 2 6 5 3 14 3 4 4 3 4 3 - Acanthinula aculeata (Muller) - - 4 - - - 4 2 - - 1 - - - - 1 - - Ena obscura (Muller) ------1 ------_ - Punctum pygmaeum (Draparnaud) _ 2 3 _ - _ _ _ 1 - 1 - 1 1 1 _ - Discus rotundatus (Muller) - 1 3 1 - 2 - - - 3 2 1 6 X X X 1 X Vitrina pellucida (Muller) - 1 ------1 - - 1 - 3 - - Vitrea crystallina (Muller) - X Vitrea contracts (Westerlund) ------1 6 Nesovitrea hammonis_(Strom) - - 1 ------1 AeRopinella pure (Alder) ' - 1 - - - 1 1 1 1 3 - 1 - - - - - AeRopinella nitidula (Draparnaud) - 2 5 2 - - 7 1 2 1 - 5 1 1 2 2 Oxychilus cellarius (Muller) - - - 2 ------2 - 3 - - - Deroceras/Limax spp. - 1 9 10 3 16 20 15 25 19 27 30 29 8 21 43 26 42 Ceciliodes acicula (Muller) ------1 46 Cochlodina laminata (Montagu) - - 3 - - 2 2 2 1 2 1 ------ Clausilia bidentata (Strom) - 1 5 1 - 6 5 6 1 4 4 1 7 4 5 - 1 - Helicella itala (L.) ------1 - - - 1 4 Monacha cartusiana (Muller) ------1 2 - Trichia hispida (L.) - 4 30 8 - 13 11 9 6 4 10 12 14 6 11 8 3 34 Trichia striolata (Pfeiffer) - - X X - - - 1 ------1 1 2 Arianta arbustorum (L.) - X - X ------ff_PILe.g_ s PP- - - - XXX- X - - XXXXXXX - Arianta/Cepaea app. - - 12 - 4 2 3 9 1 3 6 4 3 4 1 1 4 - Helicigona lapicida (L.) - - - X - X X - - X - XXXXXX - Helix asperse Muller ------1 Total shells 0 24 111 40 11 64 79 94 76 73 112 99 103 59 79 85 69 149 Table 5 : Devils Dyke. Pit 5 Depth (cm) 245 235 230 225 220 215 210 205 200 195 190 185 180 175 165 155 145 75 255 245 235 230 225 220 215 210 205 200 195 190 185 180 175 165 155 80 Pomatias eleRans (Muller) - 1 4 X 1 8 16 19 17 11 10 16 12 6 8 2 7 2 Acicula fusca (Montagu) ------1 - - - Carychium tridentatum (Risso) - - 4 - - - 1 1 1 - - - - 2 X - Cochlicopa spp. - 6 13 12 3 14 4 8 7 11 16 15 10 4 6 7 2 3 Vertigo pyRmaea (Draparnaud) ------1 2 - 4 4 5 1 4 1 Abida secale (Draparnaud) - 1 1 1 - - - - 1 1 ------1 Pupilla muscorum (L.) - - 2 - - - 1 3 1 3 8 2 3 11 2 - 1 - Vallonia costata (Muller) - - 4 - - - 1 10 5 3 6 9 3 4 5 11 8 3 Vallonia pulchella (Muller) ------1 Vallonia excentrica Sterki - - 1 _ _ - 1 - 4 - 1 - 1 2 1 2 1 2 Vallonia spp. - 5 5 3 - 1 2 6 5 3 14 3 4 4 3 4 3 - Acanthinula aculeata (Muller) - - 4 - - - 4 2 - - 1 - - - - 1 - - Ens obscura (Muller) ------1 ------ Punctum pyRmaeum (Draparnaud) - 2 3 - - - 1 - 1 - 1 1 1 - - Discus rotundatus (Muller) - 1 3 1 - 2 - - - 3 2 1 6 X X X 1 X Vitrina pellucida (Muller) - - 1 ------1 - - 1 - 3 - - - Vitrea crystallina (Muller) - x - _ _ ------ Vitrea contracta (Westerlund) ------1 6 Nesovitrea hammonis (Strom) - - 1 ------1 AeRopinella pura (Alder) - - 1 - - 1 1 1 1 3 1 - - - - AeRopinella nitidula (Draparnaud) 2 5 2 - - 7 1 2 1 - 5 1 1 2 2 1 - Oxychilus cellarius (Muller) - - - 2 ------2 - 3 - - - Deroceras/Limax app. - 1 9 10 3 16 20 15 25 19 27 30 29 8 21 43 26 42 Ceciliodes acicula (Muller) ------1 46 Cochlodina laminata (Montagu) - - 3 - - 2 2 2 1 2 1 ------ Clausilia bidentata (Strom) - 1 5 1 - 6 5 6 1 4 4 1 7 4 5 - 1 - Helicella itala (L.) ------1 - - - 1 4 Monacha cartusiana (Muller) ------1 2 - Trichia hispida (L.) 4 30 8 - 13 11 9 6 4 10 12 14 6 11 8 3 34 Trichia striolata (Pfeiffer) - - X X - - - 1 ------1 1 2 Arianta arbustorum (L.) - - x ------f_tata sPP . - - - X X X - X - - XXXX-XXX Arianta/Cepaea app. - - 12 - 4 2 3 9 1 3 6 4 3 4 1 1 4 - HeliciRona lapicida (L.) - - - x - x x _ - x - xxxxxx - Helix asperse Muller ------1 Total shells 0 24 111 40 11 64 79 94 76 73 112 99 103 59 79 85 69 149 Table 6 : Asham -Column A Depth (cm) 215 210 205 200 195 190 220 215 210 205 200 195 Ovatella myosotis (Draparnaud) - - - - Hydrobia ulvae (Pennant) - - - - Bithynia tentaculata (L.) - 1 - - Pomatias elegans (Muller) - - - - Carychium tridentatum (Risso) - - - 2 5 1 Succinea oblonga Draparnaud - - - - Cochlicopa lubrica (Muller) - - - - Cochlicopa lubricella (Porro) - - - - - Cochlicopa spp. - - 1 3 3 2 Vertigo pusilla Muller ------Vertigo pygmaea (Draparnaud) ------Abida secale (Draparnaud) 10 15 6 6 6 25 Pupilla muscorum (L.) 15 18 11 4 4 - Lauria cylindracea (da Costa) ------Vallonia costata (Muller) 1 1 - - 12 - Vallonia pulchella (Muller) - - 1 - - - Vallonia excentrica Sterki ------Vallonia spp. - 1 2 2 - 6 Acanthinula aculeata (Muller) - - - - 1 - Ena obscura (Muller) ------Punctum pygmaeum (Draparnaud) 7 11 6 4 - 1 Discus rotundatus (Muller) - - - - 4 2 Vitrina pellucida (Muller) - - - - - 2 Vitrea crystallina (Muller) ------Vitrea contracta (Westerlund) - - - - 1 - Nesovitrea hammonis (Strom) 2 3 2 • 1 1 1 Aegopinella pura (Alder) ------Aegopinella nitidula (Draparnaud) - - - - 3 1 Oxychilus cellarius (Muller) ------Limax/Deroceras spp. 2 - - - 2 1 Euconulus fulvus (Muller) 1 1 1 - 4 7 Ceciliodes acicula (Muller) ------Cochlodina laminata (Montagu) ------Clausilia bidentata (Strom) - - 1 2 - Helicella itala (L.) ------Monacha cartusiana (Muller) ------Trichia hispida (L.) 31 '29 28 16 30 37 Trichia striolata (Pfeiffer) ------Arianta arbustorum (L.) - X X X X X X Cepaea spp. ------Arianta/Cepaea spp. 1 1 1 1 1 1 Helicigona lapicida (L.) ------ Total Shells 70 81 59 40 79 82 Table 6 cont.: Asham-Column A Depth (cm) 185 180 175 170 165 160 155 150 190 185 180 175 170 165 160 155 O. myo ------H. ulv ------B. ten ------P. ele 5 2 22 56 71 126 79 56 C. tri 4 10 21 24 20 7 4 14 S. obi ------C. ica ------1 C. lla ------Coch - 6 16 14 14 26 14 13 V. pus - 1 - - 1 - - - V. pyg - - - 1 - 1 1 A. sec 20 9 1 - - 3 - - P. mus 3 4 5 1 2 2 4 4 L. cyl - - - - 1 - - V. cos 12 25 10 5 5 3 9 9 V. pul 2 ------V. exc 1 3 - 1 - - 2 1 Vall 3 4 - 1 1 - 4 4 A. acu - - 8 7 16 12 5 4 E. obs - 1 - - - - - P . PYg 2 2 - - 2 - 2 - D. rot 2 13 20 34 64 37 16 14 V. pel - - - - 1 1 - - V. cry - - 1 2 1 - V. con - 2 4 3 2 - - - N. ham 5 6 - 1 17 - 2 1 A. pur - 1 8 19 7 5 - 1 A. nit 2 10 7 19 19 17 13 4 O. cel - 1 2 6 2 9 1 4 Limx 2 5 20 24 38 55 42 28 E. ful - 2 - 2 2 1 - - C. aci ------C. lam - - - - - 1 1 - C. bid - 6 10 19 20 19 18 15 H. ita ------M. car ------T. his 50 44 30 40 42 70 44 23 T. str - - - 1 - - - A. arb X X - X X - - - Cep - XXXXXXX A/C 1 3 4 11 19 20 20 10 H. lap - - XX3XXX Total Shells 14 160 190 291 369 416 283 207 Table 6 cont.: Asham-Column A Depth (cm) 145 140 135 130 125 120 115 110 150 145 140 135 130 125 120 115 O. myo ------H. ulv ------B. ten ------P. ele 53 49 40 37 60 53 46 35 C. tri 1 ------S. obi ------C. ica - 1 - 1 1 - 1 - C. lla - 1 - - - 1 1 1 Coch 14 13 10 19 12 16 13 17 V. pus ------V. pyg - 3 11 5 - 7 3 - A. sec ------P. mu's 2 7 45 82 65 53 72 62 L. cyl - - - - - V. cos 7 17 33 35 53 58 67 60 V. pul 1 - - 3 4 -. 1 V. exc - 9 16 44 29 43 19 20 Vail 2 22 46 77 88 95 53 69 A. acu - 1 ------E. obs ------P. PYg - 1 - - - - - D. rot 11 1 4 1 3 - - 1 V. pel - - - 1 3 2 - 1 V. cry. ______V. con ------N. ham ------1 - A. pur - 1 - - - - - A. nit - 5 1 1 2 - - - O. cel - 2 1 - 1 - 1 - Limx 4 10 18 14 27 33 35 33 E. ful - 2 ------C. aci ------C. lam - 1 ------C. bid 5 4 3 3 5 2 4 5 H. ita - 10 7 9 5 18 15 23 M. car - - - 1 1 3 - 2 T. his 16 14 38 96 146 176 129 137 T. str ______A. arb ------Cep. X X - XXXXX A/C 9 7 11 7 11 7 11 4 H. lap - - - - X - - X Total Shells 125 178 285 435 516 566 469 471 Table 6 cont.: Asham-Column A Depth (cm) 105 100 95 90 85 80 75 70 100 105 100 95 90 85 80 75 O. myo - 1 1 - - - - - H. ul y 1 ------B. ten ------P. ele 30 8 9 18 9 4 10 3 C. tri - - 1 - 2 1 - 1 S. obl - 1 ------C. ica - 1 1 1 1 1 1 - C. ha - - - 1 - 1 - - Coch 5 9 5 20 21 10 10 3 V. pus ------V. pyg. 4 6 14 40 38 37 14 14 A. sec ------P. mus 35 20 24 42 47 41 24 14 L. cyl - - - - V. cos 50 66 78 139 143 161 160 127 V. pul 3 2 4 2 - 5 6 V. exc 22 21 50 121 88 65 52 39 Vail 56 70 123 280 283 181 162 152 A. acu ------E. obs ------P . PYg - - 2 2 1 4 5 3 D. rot 1 2 - - - - 1 - V. pel 1 - - 3 3 4 2 2 V. cry ------V. con - - 3 3 2 2 1 1 N. ham 1 1 1 3 - 3 1 - A. pur - - - - - A. nit - - - - 3 7 4 5 O. cel ------1 - Limx 18 16 15 54 68 49 62 36 E. ful ------C. aci ------C. lam ------C. bid 2 2 - - 1 - - - H. ita 23 27 17 34 20 36 22 19 M. car 5 3 2 6 12 7 7 6 T. his 152 192 140 260 313 230 236 179 T. str ------A. arb ------Cep X X X - XXXX A/C 7 2 1 1 2 5 1 1 H. lap X ------ Total Shells 417 449 490 1028 1056 850 775 611 Table 6 cont.: Asham-Column A Depth (cm) 65 60 55 50 45 40 35 30 70 65 60 55 50 45 40 35 0. myo, ------H. uly ------B. ten ------P. ele 7 4 5 7 7 9 5 8 C. tri ------S. obl ------C. ica 1 ------C. Ila ------Coch 7 6 5 3 2 3 - 1 V. pus ------V. pyg 8 13 5 4 5 2 3 - A. sec ------1 P. mus 6 4 9 1 3 5 1 7 L. cyl ------V. cos 97 102 74 100 71 103 98 62 V. pul, - 4 2 2 - 1 1 - V. exc 32 23 24 22 28 25 16 7 Vall 134 123 125 83 74 70 58 51 A. acu ------E. obs ------1 - - 1 - 1 - D. rot - - 2 1 - - - - V. pel, 2 1 1 1 - 1 1 - V. cry. ------V. con - - - - - 2 1 2 N. ham - 2 ------A. pur - - - - - 1 - - A. nit 2 1 - 1 - 2 - - O. cel - - 1 - - - - - Limx 25 53 68 54 36 56 45 39 E. ful ------C. aci - - - 1 - 2 2 4 C. lam ------C. bid 1 - 1 1 - - - - H. ita 15 21 18 13 22 17 21 42 M. car 11 26 12 13 10 10 13 8 T. his 172 155 137 173 137 134 104 56 T. str 1 - - - - 1 - - A. arb ------XX - - - X - - A/C 1 1 3 3 2 2 - - H. lap - 1 - - - 1 - - Total Shells 522 541 493 483 399 447 370 289 Table 7 : Asham-Column B Depth (cm) 225 220 215 210 205 200 195 190 185 180 175 170 165 230 225 220 215 210 205 200 195 190 185 180 175 170 Pomatias elegans (Muller) 4 16 19 19 23 23 25 22 34 32 28 46 36 Acicula fusca (Montagu) ------Carychium tridentatum (Risso) 5 42 44 48 35 52 92 172 173 116 70 91 84 Cochlicopa lubrica (Muller) ------Cochlicopa lubricella (Porro) ------Cochlicopa spp. 2 3 6 3 2 - 3 13 8 8 5 4 3 3 Columella edentula (Draparnaud) ------1 - - Vertigo pusilla (Muller) ------2 - - 1 - Vertigo pygmaea (Draparnaud) - 2 1 - - - - 1 - - - - - Abida secale (Draparnaud) - 4 - 2 1 2 1 1 8 4 4 3 7 Pupilla muscorum (L.) 1 5 2 2 2 - 4 2 7 3 - 2 2 Lauria cylindracea (da Costa) - - - - - 1 - - - - - Vallonia costata (Muller) 6 9 12 7 4 6 8 6 14 2 8 3 6 Vallonia pulchella (Muller) ------Vallonia excentrica (Sterki) 1 ------Valloniaspp. ------Acanthinula aculeta (Muller) - 2 5 3 3 3 5 9 19 16 14 7 8 Spermodea lamellata (Jeffreys) ------Ena obscura (Muller) ------Punctum pygmaeum (Draparnaud) - 2 1 - 1 1 5 2 2 - 2 1 Discus rotundatus (Muller) 1 15 15 14 25 12 15 25 32 35 45 69 58 Vitrina pellucida (Muller) ------1 4 - 1 2 Vitrea contracta (Westerlund) - 3 2 1 2 1 1 8 17 9 10 9 16 Nesovitrea hammonis (Strom) - 1 1 ------Aegopinella pura, (Alder) - 4 2 3 2 2 5 13 21 8 17 5 14 Aegopinella nitidula (Draparnaud) - 3 2 4 3 5 8 14 6 8 - 6 7 Oxychilus cellarius (Muller) 2 15 6 8 13 9 12 15 12 16 18 32 31 Limax/Deroceras spp. - 7 4 12 7 19 15 10 12 10 14 22 17 Euconulus fulvus (Muller) - - - 2 ----- 1 - - 1 Ceciliodes acicula (Muller) - - - - _ _ _ _ 1 - - - Cochlodina laminata (Montagu) - 1 2 ----- 1 - - - 3 Clausilia bidentata (Strom) - 5 9 6 3 3 4 6 8 - 8 3 11 Balea perversa (L.) ------1 - - 1 1 Helicella itala (L.) ------Monacha cartusiana (Muller) ------Trichia hispida (L.) 2 15 14 20 5 26 19 20 13 26 16 27 19 Trichia striolata (Pfeiffer) ------1 3 6 - - 4 4 Arianta arbustorum (L.) X - - - 1 - - - 1 - _ _ Helicigona lapicida (L.) XX2XXXX - XXX2 X Cepaea spp. XXXXXXXXXXXXX Arianta/Cepaea app. 2 5 4 5 11 5 7 9 7 3 6 16 5 Total Shells 27 160 153 160 143 172 238 350 404 304 265 355 336 Table 7 cont.: Asham-Column B Depth 160 155 150 145 140 135 130 125 120 115 110 105 100 95 90 (cm) 165 160 155 150 145 140 135 130 125 120 115 110 105 100 95 P. ele 38 39 29 31 39 39 28 24 35 40 61 47 41 58 61 A. fus - _ _ - 2 8 15 3 6 5 4 2 - - - C. tri 65 37 29 25 23 35 49 48 30 33 18 3 2 1 - C. ica - _ _ - - - - - _ _ _ _ - - 5 C. lla _ _ _ - - - - - 1 _ _ _ - - Coch 9 7 5 5 4 5 5 - 2 5 9 2 8 9 21 C. ede _ _ - _ - - 1 ______- V. pus 2 1 - - 1 - 1 - 1 1 - - - - - _ _ _ - - - - - 2 1 2 1 1 14 a.,... sec 5 1 1 1 - 6 5 7 9 2 1 1 - 1 - 11, mus 4 - 1 1 3 - 2 5 2 4 4 1 5 30 63 L.c10. _ _ _ - - 1 _ _ _ _ - - - y, cos 2 3 1 3 5 11 4 3 2 4 9 7 12 22 37 V. 211 _ _ _ _ _ - _ _ _ - 2 - - 3L exc _ _ _ - - - - - 1 2 3 6 5 18 47 Vail - - 1 - - _ - - 1 - 7 10 13 56 81 A. aca 11 7 6 1 11 9 10 4 2 2 6 2 2 1 - S. lam - _ _ 2 - - - - _ _ _ - _ _ - E. obs - _ _ - - 1 1 1 1 - - _ _ - P. piA 1 1 2 - - 3 4 3 1 1 2 1 _ _ _ D. rot 46 23 13 15 12 25 42 50 36 50 53 21 7 6 3 V. itel _ _ - _ _ 1 1 - 1 - _ _ - - 1 y, con 7 1 - - 2 2 4 8 1 8 2 - - 1 - N. ham - _ _ ------1 - - 1 A. pur 7 4 - 4 2 8 14 8 9 9 5 - 2 - 2 A. nit 8 1 2 8 2 - 4 3 6 6 5 4 3 - 1 O. cel 34 18 9 7 1 15 12 15 9 15 6 4 1 _ _ Limx 22 19 17 25 23 27 13 20 8 24 20 10 14 12 22 E. ful - 1 1 - 1 1 1 - - - 2 2 1 - - C. aci _ _ ------_ .. - - - C. lam - 1 - 2 1 2 - 3 2 - 1 1 - - - C. bid 10 9 7 9 10 13 7 5 9 6 11 3 7 10 B. E.E1 _ _ _ ------_ _ _ - - - H. ita _ _ ------_ _ _ - - 12 13 M. car - _ - _ _ - - _ _ _ _ _ - 1 4 T. his 22 21 20 21 16 23 26 40 19 16 23 13 12 37 79 T. str 1 1 - - 4 - 1 1 1 - - 1 - - A. arb X - 1 _ _ - - - - _ _ - - - - H. 1A2 X X X X X X X XXXXX - X X Cep X X X X X X X XXXXX X X X ALq 10 4 6 1 5 5 7 1 4 2 6 14 8 13 5 Total 305 200 151 172 164 243 258 252 199 240 260 158 147 290 462 Shells Table 8 : Asham-Column C Depth (cm) 400 395 390 385 380 375 405 400 395 390 385 380 Hydrobia ulvae (Pennant) ------Ovatella myosotis (Draparnaud) ------Pomatias elegans (Muller) - - 1 32 22 24 Acicula fusca (Montagu) - - - - 3 39 Carychium tridentatum (Risso) - - 3 20 21 61 Cochlicopa lubrica (Muller) - - - 3 - 1 Cochlicopa lubricella (Porro) ------Cochlicopa spp. - - - 5 11 7 Vertigo pygmaea (Draparnaud) - - - 2 4 2 Abida secale (Draparnaud) - - 1 - - 2 Pupilla muscorum (L.) ------Vallonia costata (Muller) 2 4 3 36 27 30 Vallonia pulchella (Muller) - - - - Vallonia excentrica Sterki - - - 2 6 5 Vallonia spp. - - - 10 9 6 Acanthinula aculeata (Muller) - - 1 - 1 1 Ena obscura (Muller) ------Punctum pygmaeum (Draparnaud) 1 - - 1 - 2 Discus rotundatus (Muller) - - 1 0 13 25 Vitrina pellucida (Muller) - - - 1 - 3 Vitrea crystallina (Muller) - - - - - 16 Vitrea contracta (Westerlund) - - - 4 9 16 Nesovitrea hammonis (Strom) - - - 1 - 2 Aegopinella pura (Alder) - - - - 3 35 Aegopinella nitidula (Draparnaud) - - - 4 8 27 Oxychilus cellarius (Muller) - - - 2 3 12 Deroceras/Limax spp. - - - 10 6 18 Euconulus fulvus (Muller) - - 1 - - 1 Ceciliodes acicula (Muller) ------Cochlodina laminata (Montagu) - - - - 1 2 Clausilia bidentata (Strom) - - 1 4 4 1 Balea perversa (L.) ------Candidula intersecta (Poiret) ------Candidula gigaxii (Pfeiffer) ------Cernuella virgata (da Costa) ------Helicella itala (L.) - - - - - 1 Monacha cartusiana (Muller) ------Trichia hispida (L.) 1 - 1 15 20 15 Trichia striolata (Pfeiffer) - - - - - 1 Arianta arbustorum (L.) X - - - X - Cepaea spp. - - X X 3 X Arianta/Cepaea spp. 1 - 1 5 5 3 Helicigona lapicida (L.) - 1 - 1 - - Helix aspersa (Muller) ------ Total Shells 5 5 14 168 179 360 Table 8 cont.: Asham-Column C Depth (cm) 370 365 360 355 350 345 340 335 330 375 370 365 360 355 350 345 340 335 H. ulv ------O. myo, ------P. ele 40 48 59 56 104 84 60 32 34 A. fus 113 33 36 34 6 2 2 1 C. tri 131 197 200 281 247 112 69 71 14 C. ica 3 1 4 4 6 6 10 5 2 C. lla - 1 2 1 11 15 6 9 - Coch 7 16 19 31 55 71 79 55 27 V. PYg 2 8 6 4 7 19 46 32 26 A. sec ------P. mus 2 - - 1.4 10 36 20 16 V. cos 39 58 72 34 185 544 763 296 157 V. pul ------9 3 - V. exc 22 19 18 9 9 70 99 56 11 Vail 12 10 15 8 5 71 105 257 37 A. acu 5 3 7 7 10 - - - 1 E. obs - - - - 1 2 - - - P. AYR 1 3 1 1 3 11 7 10 2 D. rot 59 59 65 111 139 77 22 124 V. pel 2 1 5 1 11 11 24 17 5 V. cry 16 17 22 25 15 10 13 1 2 V. con 27 18 31 48 25 27 24 6 7 N. ham 4 2 2 3 25 11 4 7 2 A. pur 33 19 28 28 28 8 16 3 - A. nit 56 56 39 45 69 37 29 24 4 O. cel 17 22 41 40 17 12 9 - - Limx 7 15 19 12 53 45 64 36 14 E. ful 1 ------C. adi ------C. lam 2 4 1 1 1 - 1 - - C. bid 4 4 10 7 5 5 3 3 2 B. per - 1 1 ------C. int ------C. gig ------C. vir ------H. ita 1 - - - 2 6 21 11 11 M. car ------T. his 23 33 56 56 60 47 103 95 50 T. str -- 2 1 5 - - - - - A. arb 2 3 - 2 2 -- - 2.22.C XXX1X3X3 X A/C 5 7 19 17 13 7 10 6 3 H. lap. - 4 1 1 1 - 1 - - H. asp_ ------ Total Shells 636 663 778 880 1119 1324 1629 1076 431 Table 8 cont.: Asham-Column C Depth (cm) 325 315 305 295 285 275 265 255 245 330 320 310 300 290 280 270 260 250 H. ulv - - - 1 - - - - - O. myo ------1 P. ele 34 24 44 56 32 17 9 8 10 A. fus ------C. tri 16 32 10 4 1 2 - - - C. ica 1 1 - - 4 - - 3 - C. lla ------1 - Coch 20 16 21 19 17 6 4 11 1 V. pyg 15 6 8 13 7 2 4 42 21 A. sec ------P. mus 25 18 15 64 45 34 8 33 21 V. cos 101 70 69 30 14 22 24 75 112 V. pul. - - - - - 1 3 1 1 V. exc 18 33 25 64 6 26 17 73 67 Vail 72 65 52 138 136 85 115 257 308 A. acu ------E. obs ------P. pyg 3 1 2 1 1 - 1 12 5 D. rot 3 4 5 1 4 1 1 - - V. pel 4 12 2 3 3 1 - 4 1 V. cry - 5 3 - - 1 1 - - V. con 6 12 8 1 - 2 1 2 - N. ham 1 2 - 1 - - 1 1 5 A. pur 4 2 1 ------A. nit 12 5 5 - - 1 - 3 4 O. cel 3 4 1 - - - 3 1 - Limx 10 27 14 20 31 13 21 39 83 E. ful ------C. aci ------C. lam - - 2 2 - - - - - C. bid 1 4 2 4 4 - - 2 - B. per. ------C. int ------C. gig ------C. vir ------H. ita 28 6 10 4 11 14 14 14 15 M. car - 1 1 2 4 5 4 16 T. his 21 42 86 65 141 98 82 141 216 T. str - 1 ------1 - Cep X X 2 X X X X 1 X A/C 10 5 12 9 5 1 1 5 7 H. lap ------1 H. asp ------ Total Shells 408 397 401 502 516 332 311 734 895 Table 8 cont.: Asham-Column C Depth (cm) 235 225 215 205 195 185 175 165 155 240 230 220 210 200 190 180 170 160 H. ulv ------O. myo ------P. ele 9 5 9 7 2 2 2 7 - A. fus ------C. tri - - 1 - - - - - C. ica - - - 1 2 5 - 4 '6 C. ha - 1 ------Coch 4 2 7 3 6 5 7 10 2 V. PYg 5 2 4 4 - - - - 14 A. sec ------P. mus 3 8 14 17 4 5 3 13 63 V. cos 50 61 63 148 65 124 72 104 100 V. pul - - - 1 - V. exc 39 35 26 23 9 2 2 4 17 Vall 137 90 92 57 67 20 32 12 57 A. acu ------E. obs ------P. Ug - 1 1 ------D. rot ------V. pel - - - 1 - - - - - V. cry - - - 4 1 2 5 4 - V. con - - 3 4 1 5 9 2 2 N. ham - - - - - 1 - - - A. pur ------1 1 A. nit - - - 2 - - - 1 3 O. eel ------Limx 56 97 44 30 44 46 51 51 60 E. ful ------C. aci - 4 - 15 12 12 37 49 116 C. lam ------C. bid - 1 ------B. per ------C. int ------C. vir ------H. ita 2 19 5 18 10 30 8 6 4 M. car 10 9 12 8 10 1 8 8 5 T. his 161 120 88 121 95 111 92 123 109 T. str - - - - 1 -. - - - A. arb ------_ICY.C XXXXXXXX - A/c 2 - 1 2 2 2 1 1 1 H. lap - X ------H. asp ------ Total Shells 489 457 369 466 331 373 330 402 563 Table 8 cont.: Asham-Column C Depth (cm) 145 135 125 115 105 95 85 75 65 150 140 130 120 110 100 90 80 70 H. ulv ------O. myo ------P. ele 4 1 4 1 - 1 2 2 1 A. fus ------C. tri ------2 C. ica 2 - - 1 - 1 - - - C. lla ------Coch 7 4 4 3 1 - 2 1 - V. PYg 23 12 8 2 1 1 2 1 1 A. sec ------P. mus 100 38 7 8 4 8 4 - 2 V. cos 120 115 124 91 38 36 21 28 33 V. pul 3 2 3 4 2 1 - - - V. exc 38 13 24 6 5 3 1 2 1 Vail 125 76 138 40 36 28 19 13 14 A. acu ------E. obs ------P. PYg - - - 1 - - - - - D. rot ------1 1 V. pel 1 1 ------V. cry 1 - 4 ------V. con 2 2 2 2 - - 1 - N. ham - - , 1 ------A. pur 2 ------A. nit 4 1 5 ------O. cel - - 1 ------Limx 70 81 59 44 48 37 64 31 57 E. ful ------C. aci 205 201 256 224 190 194 168 100 98 C. lam ------C. bid - 1 ------B. per ------C. int ------C. .gig ------2 2 C. vir ------H. ita 13 8 23 11 13 6 11 9 8 M. car 3 4 5 10 8 6 8 22 11 T. his 140 163 191 106 68 72 156 134 85 T. str ------1 - - A. arb ------Cep X - - X - X - - - A/C 2 1 - 1 - 1 - - - H. lap ------H. asp 1 1 2 3 4 3 5 1 1 Total Shells 798 726 861 559 418 399 464 348 317 Table 8 cont.: Asham-Column C Depth (cm) 55 45 35 25 15 5 0 60 50 40 30 20 10 5 H. ulv ------O. myo ------P. ele 1 1 2 2 1 1 1 A. fus ------C. tri 1 ------C. ica - - - - - 5 7 C. lla ------Coch - 2 - - 2 9 9 V. PYg - 2 2 1 1 - - A. sec ------P. mus 3 2 3 1 2 5 6 V. cos 29 30 115 161 50 25 16 V. pul 6 1 12 7 - 1 - V. exc 4 3 3 7 8 28 5 Vail 10 81 47 16 31 34 23 A. acu ------E. obs ------P. pyg ------D. rot - - - - - 1 - V. pel - - X _ _ 1 9 V. cry _ _ _ _ _ - 3 V. con .1 - 1 - - - 5 N. ham ------1 A. pur - _ _ _ _ _ A. nit 1 - X - - 11 14 O. cel - - - - - 3 - Limx 42 29 41 52 53 34 20 E. ful - - - - C. aci 142 87 162 124 93 20 12 C. lam ------C. bid - - - - - 1 1 B. per. ------C. int - - - - - 4 2 C. gig 6 17 28 30 38 33 10 C. vir - - 2 1 - 1 1 H. ita 5 - 2 - 1 - 2 M. car 29 9 50 16 6 2 1 T. his 69 107 99 117 88 95 55 T. str ------3 A. arb ------Cep. ------X A/C ------H. lap ------H. asp 4 1 1 1 1 1 1 Total Shells 353 309 573 537 376 315 209 Table 9 : Asham - Column D Depth (cm) 410 400 390 380 370 360 350 340 420 410 400 390 380 370 360 350 Pomatias elegans (Muller) 5 30 27 35 49 35 51 39 Carychium tridentatum (Risso) 1 8 13 18 6 1 - - Cochlicopa lubrica (Muller) - - 1 1 - - - 4 Cochlicopa lubricella (Porro) - - - 1 - - - - Cochlicopa spp 2 6 12 14 17 3 13 15 Vertigo pygmaea (Draparnaud) 1 1 - - 1 6 6 18 Pupilla muscorum (L.) 2 2 1 1 3 2 18 41 Vallonia costata (Muller) 7 4 9 45 49 14 49 61 Vallonia excentrica Sterki 1 1 1 - 6 6 23 40 Vallonia spp 5 9 3 6 25 22 49 87 Acanthinula aculeata (Muller) - - 1 3 2 1 - - Punctum pygmaeum (Draparnaud) - - 1 - - - 2 1 Discus rotundatus (Muller) 3 5 11 7 10 4 5 3 Vitrea crystallina (Muller) - - - - - 1 - - Vitrea contracta (Westerlund) - 2 1 - - - - - Nesovitrea hammonis (Strom) - - 2 1 1 1 1 - Aegopinella pura (Alder) - - 6 2 - - - - Aegopinella nitidula (Draparnaud) - 7 4 4 5 4 - Oxychilus cellarius (Muller) - 2 2 - 1 2 2 1 Oxychilus alliarius (Muller) - - 1 - - - - - Deroceras/Limax spp 7 2 6 24 36 13 19 37 Euconulus fulvus (Muller) 1 - 1 - - - - - Cecilioides acicula (Muller) 3 - - 1 - - - 2 Cochlodina laminata (Montagu) - - 4 - - - - - Clausilia bidentata (Strom) 3 5 8 5 11 9 7 5 Helicella itala (L.) - - - - - 2 12 37 Monacha cartusiana (Muller) ------3 2 Trichia hispida (L.) 9 7 10 15 28 20 32 71 Trichia striolata (Pfeiffer) - - - - 1 - - - Cepaea spp 4 6 9 13 14 19 11 8 Helicigona lapicida (L.) XXXXXXXX Total Shells 55 91 138 197 265 171 308 473 Table 10 : South Heighton Depth (cm) 270 260 250 240 230 220 280 270 260 250 240 230 Hydrobia ulvea (Pennant) - - - - - 1 Hydrobia ventrosa (Montagu) ------Ovatella myosotis (Draparnaud) ------Pomatias elegans (Muller) - 2 5 44 89 130 Acicula fusca (Montagu) - - - - - 2 Carychium tridentatum (Risso) - 1 2 15 19 35 Cochlicopa lubrica (Muller) - - - - 2 Cochlicopa lubricella (Porro) - - - - - 2 Cochlicopa spp. - - 1 1 3 13 Truncatellina cylindrica (Ferussac)------Vertigo pygmaea (Draparnaud) - - - - 1 - Abida secale (Draparnaud) - 1 3 - - - Pupilla muscorum (L.) 18 4 3 2 4 9 Vallonia costata (Muller) 3 2 1 2 8 38 Vallonia pulchella (Muller) ------Vallonia excentrica Sterki - - 1 - 2 3 Vallonia spp. ------Acinthinula aculeata (Muller) - 1 1 2 2 3 Punctum pygmaeum (Draparnaud) - 1 - - - 3 Discus rotundatus (Muller) - 1 4 2 22 16 Vitrina pellucida (Muller) ------Vitrea crystallina (Muller) - 2 2 1 - 2 Vitrea contracta (Westerlund) - - - 1 1 1 Nesovitrea hammonis (Strom) - 2 2 - - - Aegopinella pura (Alder) - - - 1 2 2 Aegopinella nitidula (Draparnaud) - - 2 4 2 12 Oxychilus cellarius (Muller) - - 3 3 3 2 Oxychilus alliarius (Muller) - - - - Deroceras/Limax spp. 2 - 11 6 39 , 40 Ceciliodes acicula (Muller) - - - - Cochlodina laminata (Montagu) - - - 1 1 2 Clausilia bidentata (Strom) - - X 5 9 6 Helicella itala (L.) - - 1 - - - Monacha cartusiana (Muller) - - - - Trichia hispida (L.) 7 6 5 7 10 29 Trichia striolata (Pfeiffer) - - - - - Arianta arbustorum (L.) - - - - - X Cepaea spp. - - XXXX Arianta/Cepaea spp. - - - 10 12 19 Helicigona lapicida (L.) - - XXXX Helix asprsa Muller ------ Total Shells 30 23 50 108 230 373 Table 10 cont.: South Heighton Depth (cm) 210 200 190 180 170 160 150 140 130 220 210 200 190 180 170 160 150 140 H. ul y - - - - - 1 - - - H. yen ------O. myo ------P. ele 156 99 65 47 34 23 10 9 3 A. fus 4 2 2 - - - - - C. tri 54 13 11 1 2 1 1 - - C. ica 3 3 - 1 - - - - - C. lla 1 ------Coch 24 17 8 6 5 7 2 3 - T. cyl - - 1 2 - - - 1 - V. pyg 8 3 4 1 - 1 - 1 - A. sec ------P. mus 14 111 244 221 643 156 99 74 47 V. cos 53 85 64 23 52 68 65 46 53 V. pul ------V. exc 4 15 26 12 15 29 25 19 8 Vail 11 38 57 25 44 63 81 55 41 A. acu 5 - 1 ------P . PYR - 2 1 1 - - - 1 - D. rot 8 9 2 2 3 1 - 1 - V. pel 1 1 - - - - 2 - - V. cry 2 2 1 ------V. con 1 - 2 ------N. ham - - 1 1 - - - - - A. pur 2 ------A. nit 15 - 2 ------O. cel 2 2 - - - - - 1 - O. all ------Limx 50 51 42 17 19 24 18 14 9 C. aci - - - - - 1 - - - C. lam 2 1 ------C. bid 13 5 1 1 5 1 - 1 - H. ita 4 13 12 11 22 12 23 10 10 M. car - 6 3 5 11 6 1 3 4 T. his 41 39 55 52 177 237 138 128 97 T. str ------A. arb ------Cep X X X X X X X X X A/C 20 9 11 7 6 3 6 1 1 H. lap. X 2 X X X - X - - H. asp ------Total Shells 499 528 615 439 1039 635 472 368 273 Table 10 cont.: South Heighton Depth (cm) 120 110 100 90 80 70 60 50 40 30 130 120 110 100 90 80 70 60 50 40 H. ulv 2 2 1 1 H. ven 1 0. myo 1 1 1 P. ele 1 8 10 9 7 5 5 1 2 A. fus C. tri C. ica C. ha - 2 ------Coch - 1 1 7 - - 1 - 1 - T. cyl - - - 3 - - - - 1 - V. pyg 1 2 8 2 - - - - 1 - A. sec ------P. mus 22 65 121 64 17 27 47 70 85 39 V. cos 48 73 70 67 38 36 61 131 167 114 V. pul ------2 1 - V. exc 11 18 43 25 16 19 24 34. 31 24 Vail 41 59 111 75 41 48 68 125 115 90 A. acu ------P. PYg - - 5 ------D. rot X V. pel 1 V. cry 1 1 2 5 8 V. con 2 1 4 1 3 13 N. ham 1 A. pur 1 A. nit 0. cel I- 0. all 10 15 4 2 2 3 1 - Limx 7 9 24 20 10 9 10 17 13 17 C. adi 1 - 4 - 6 4 55 39 C. lam C. bid 2 1 H. ita 18 21 16 19 14 23 26 28 31 37 M. car 9 6 2 1 4 12 5 3 T. his 93 123 169 84 76 126 139 178 162 148 T. str - 2 2 A. arb X X X X X A/C 1 2 4 3 3 ^ H. lap H. asp, X X X X X 2 1 Total Shells 258 394 595 388 235 306 402 615 679 538 Table 11 : Hope, Gap Sample Number 1 2 3 4 5 6 7 Pomatias elegans (Muller) - - - - 1 2 - Carychium tridentatum (Risso) - - - - 7 - - Cochlicopa lubrica (Muller) 2 - - - 3 - - Cochlicopa spp 9 - - - 12 3 1 Vertigo pygmaea (Draparnaud) - - - - 2 - 7 Pupilla muscorum (L.) 33 - - 12 6 3 Lauria cylindracea (da Costa) - - - - 1 - - Vallonia costata (Muller) 111 - - - 141 90 25 Vallonia pulchella (Muller) 3 ------Vallonia excentrica Sterki - - - - 37 29 8 Vallonia spp - - - - 67 56 9 Punctum pygmaeum (Draparnaud) 23 - - - 2 1 - Vitrina pellucida (Muller) 18 - - - - 1 - Vitrea crystallina (Muller) - - - - 2 5 - Vitrea contracta (Westerlund) - - - - 3 8 - Nesovitrea hammonis (Strom) - - - - 3 - - Aegopinella nitidula (Draparnaud) - - - - 9 - - Oxychilus cellarius (Muller) - - - - 3 - - Deroceras/Limax spp 11 - - - 8 13 1 Euconulus fulvus (Muller) 1 Cecilioides acicula (Muller) - - - - - 8 2 Clausilia bidentata (Strom) - - - - - 1 - Helicella itala (L.) 1 - - 1 10 9 - Trichia hispida (L.) 1 - - X 201 252 14 Arianta arbustorum (L.) - - - - X - - Helix aspersa (Muller) - - - - - X X Total Shells 213 0 0 3 522 485 70 Table 12 : Exceat 1 Depth (cm) 75 70 65 60 55 50 80 75 70 65 60 55 Valvata piscinalis (Muller) ------Hydrobia ulvae (Pennant) - - - X 2 - Lymnaea truncatula (Muller) ------Anisus leucostoma (Millet) - - - - - 1 Pomatias elegans (muller) X X 10 16 27 11 Carychium tridentatum (Risso) - - - - 2 1 Cochlicopa lubrica (Muller) ------Cochlicopa spp. - - - - - 2 Vertigo pygmaea (Draparnaud) - - - - 3 3 Abida secale (Draparnaud) 2 1 2 - - - Pupilla muscorum (L.) - 1 3 4 4 22 Vallonia costata (Muller) 3 3 2 4 11 38 Vallonia pulchella (Muller) ------Vallonia excentrica Sterki - - - 1 1 7 Nrallonia spp. - - - - 1 18 Punctum pygmaeum (Draparnaud) - 1 - - 1 - Discus rotundatus (Muller) - X X 1 3 1 Vitrina pellucida (Muller) ------Vitrea crystallina (Muller) - - - - - 1 Vitrea contracta (Westerlund) - - - - - 2 Nesovitrea hammonis (Strom) - 1 - - - Aegopinella pura (Alder) ------Oxychilus cellarius (Muller) - - 1 1 - 2 Deroceras/Limax spp. - - - - 3 10 Ceciliodes acicula (Muller) - 2 - 2 12 15 Clausilia bidentata (Strom) - - X - 1 2 Candidula intersecta (Poiret) ------Cernuella virgata (da Costa) ------Helicella itala (L.) - 1 - 1 3 9 Monacha cartusiana (Muller) - - - - - 1 Trichia hispida (L.) X 8 4 11 28 98 Trichia striolata (Pfeiffer) - - - - 1 - Arianta arbustorum (L.) - - - X X - Cepaea spp. - X X X X - Arianta/Cepaea spp. - - 1 - 2 - Helix aspersa Muller - - - - - 3 Total Shells 7 21 25 44 105 247 Table 12 : Exceat 1 cont. Depth (cm) 45 40 35 30 25 20 15 10 5 Spot 50 45 40 35 30 25 20 15 10 Sample V. pis ------1 - H. ulv 1 1 1 2 2 - - - 2 - L. tru 1 - ______- A. leu - ______- P. ele 12 10 9 8 14 8 12 2 6 15 C. tri 1 - 2 2 - - 1 1 - - C. lub - 1 ------Coch 1 - 1 2 1 1 2 1 1 1 V. pyg 5 2 4 2 1 3 2 2 7 - A. sec 2 - 2 - - 4 2 1 5 - P. mus 27 27 12 21 21 6 15 18 58 23 V. cos 28 31 25 33 18 23 18 14 28 - V. pul 1 - - 1 2 3 1 4 2 - V. exc 18 14 21 22 13 10 2 4 18 8 Vail 32 40 62 80 36 46 40 31 34 12 P. P_YR - - - - 1 1 - - 1 - D. rot - 1 ------1 V. pel. ------1 - V. cry. 3 1 1 - ______V. con 1 - 1 1 - - - - 2 - N. ham ------_ A. pur - 1 2 ------O. cel - 2 ------Limx 17 12 25 22 35 20 41 22 37 - C. adi 31 26 35 45 32 44 37 25 32 1 C. bid - 2 - - 1 1 - 1 - _ mint------2 - C. vir ------1 5 - H. ita 11 12 24 26 33 60 50 39 36 7 M. car 2 1 2 - - - - 1 1 T. his 156 155 147 241 177 208 170 179 216 35 T. str ------A. arb ------CepX ------X A/C ------2 H. asp 2 X 2 3 2 2 2 1 4 - Total 353 340 378 511 389 441 395 347 499 44 Shells Table 13 : Exceat 2 Depth (cm) 110 100 90 80 70 60 50 40 30 20 10 0 120 110 100 90 80 70 60 50 40 30 20 10 Hydrobio ulvae (Pennant) 1 3 1 - 2 2 1 2 - - - 3 Pomatias elegans (Muller) 22 48 51 61 34 60 41 26 42 27 30 33 Cochlicopa app. 1 4 3 3 3 6 4 4 3 4 1 Truncatellina cylindrica (Ferussac)- - - - - 1 - - - - Vertigo Pvgmaea (Draparnaud) 1 - - - 2 8 6 5 4 3 6 13 Abida secale (Draparnaud) - - - - - 1 - 1 - - - Pupilla muscorum (L.) 20 24 24 46 118 169 89 35 29 24 49 156 Vallonia costata (Muller) 8 6 8 37 100 126 79 34 65 50 44 35 Vallonia excentrica Sterki 13 11 18 18 31 54 43 30 34 28 18 51 Punctum pygmaeum (Draparnaud) - - - - - 1 ------ Discus rotundatus (Muller) 3 - - - X - - X X - - - Vitrea contracta (Westerlund) ------1 Aegopinella pura (Alder) ------1 - - - - - Aegopinella nitidula (Draparnaud) - - - 4 2 ------ Oxychilus cellarius (Muller) ------1 - Deroceras/Limax app. 1 11 12 23 33 44 44 68 32 39 27 38 Cecilioides acicula (Muller) - - - - - 1 1 4 4 4 2 Clausilia bidentata (Strom) 4 4 5 5 2 4 3 - 2 4 Candidula intersects (Poiret) ------12 Candidula sigaxii (Pfeiffer) - - - - - 1 - - - - 1 Cernuella virgata (da Costa) - - - - 2 1 1 4 5 2 15 48 Helicella itala (L.) 7 31 50 55 54 59 49 50 40 49 50 28 Monacha cartusiana (Muller) ------1 - Trichia hispida (L.) 45 47 53 53 94 130 108 73 83 60 87 172 Cepaeo app. 7 10 7 9 7 4 7 5 3 4 5 5 Helicigona lapicida (L.) X X - - X X - - - - Helix asperso Muller - - - - XXXXXXXX Total Shells 134 200 232 314 488 670 480 348 350 295 340 604 Table 14 : Cow Gap, Central Infill Section - Column C Depth (cm) 340 320 270 260 210 200 190 350 330 280 270 220 210 200 Cochlicopa lubrica (Muller) - - - - - 1 - Cochlicopa lubricella (Porro) - - - 1 3 - - Cochlicopa spp - - 3 8 14 2 6 Abida secale (Draparnaud) - - 93 42 43 29 48 Pupila muscorum (L.) - 2 - 5 14 15 13 Vallonia costata (Muller) - - 21 14 43 15 46 Vallonia pulchella (Muller) - - 12 31 30 3 20 Punctum pygmaeuth (Draparnaud) - 1 28 7 26 3 16 Vitrina pellucida (Muller) - - 1 2 3 1 2 Nesovitrea hammonis (Strom) - - 3 1 13 1 3 Deroceras/Limax spp - - - 1 7 1 3 Euconulus fulvus (Muller) - - - - - 1 2 Helicella itala (L.) - - 1 17 1 2 4 Trichia hispida (L.) 1 - 1 8 31 11 58 Total Shells 1 3 93 119 228 85 221 Table 15 : Cow Gap, Central Infill Section-Column B Depth (cm) 350 340 330 320 310 300 290 280 270 260 250 240 230 220 360 350 340 330 320 310 300 290 280 270 260 250 240 230 Pomatias elegans (Muller) 25 22 26 38 17 6 16 15 4 2 12 31 63 44 Acicula fusca (Montagu) 16 15 18 2 - - - 1 - - 1 1 - - Carychium tridentatum (Risso) 19 28 25 10 16 27 16 24 23 6 13 47 90 52 Cochlicopa spp. 18 32 42 45 54 62 47 42 35 12 6 14 14 13 Vertigo pusilla Muller 1 ------ Vertigo pygmaea (Draparnaud) ------5 1 - 5 Abida secale (Draparnaud) 2 - - - - 2 - - - 8 - 1 Pupilla muscorum (L.) 2 2 2 - 1 3 4 4 5 2 3 3 - 11 Lauria cylindracea (da Costa) 11 3 ------ Vallonia costata (Muller) 12 2 6 8 15 19 17 18 12 5 8 14 46 116 Vallonia excentrica Sterki - - - - 1 - 2 3 19 17 5 11 50 86 Acanthinula aculeata (Muller) 16 22 32 27 26 25 36 27 11 2 1 2 3 - Ens obscura (Muller) X - - - 3 - - - 2 1 - - - - Punctum pygmaeum (Draparnaud) 1 - 1 1 1 1 1 - 5 3 3 1 - 2 Discus ruderatus (Ferussac) ------1 ------ Discus rotundatus (Muller) 57 84 85 69 53 64 65 41 17 11 14 25 31 15 Vitrina pellucida (Muller) 2 1 1 - 1 - - - 1 1 - - 1 4 Vitrea crystallina (Muller) - - 3 3 - 4 6 8 2 6 1 4 2 3 Vitrea contracta (Westerlund) 3 4 2 3 4 3 - - - 2 1 2 4 5 Nesovitrea hammonis (Strom) - - - - 4 7 4 11 10 6 1 1 - - AeRopinella pura (Alder) - 2 6 6 5 6 8 7 1 - 2 3 1 2 Aegopinella nitidula (Draparnaud) 17 30 53 35 55 44 49 45 38 22 18 36 44 22 Zonitoides excavatus (Alder) - 1 ------1 - - - - - Oxychilus cellarius (Muller) 11 16 7 6 17 3 2 6 2 4 5 2 12 6 Deroceras/Limax app. 39 114 103 144 101 90 119 90 63 23 25 62 80 119 Euconulus fulvus (Muller) ------1 ------ Cochlodina laminata (Montagu) 2 4 3 5 2 1 2 X - 7 - - - 1 Clausilia bidentata (Strom) 25 24 40 37 33 28 24 27 17 12 4 15 9 7 Balea perversa (L.) 3 ------ Helicella itala (L.) - - - - - 1 - 1 - 1 - - 10 40 Monacha cartusiana (Muller) ------1 Trichia hispida (L.) 63 55 100 112 82 121 106 116 76 37 38 29 34 63 Trichia striolata (Pfeiffer) 3 3 5XXXX2XX - 1 - - Arianta arbustorum (L.) XXXX - XXXXXXXXX Cepaea app. XX1XXXXXXXXXXX Arianta/Cepaea spp. 9 23 18 16 11 13' 18 9 7 7 5 17 16 17 Helicigona lapicida (L.) XXXXXXX - - - XXXX Total Shells 359 488 580 569 504 532 545 499 352 190 180 323 511 636 Table 16 : Cow Gapj Central Infill Section-Column A Depth (cm) 180 170 160 150 140 130 190 180 170 160 150 140 Pomatias elegans (Muller) 44 48 33 18 17 6 Carychium tridentatum (Risso) 106 101 25 6 6 21 Cochlicopa lubrica (Muller) 2 - 1 - X 3 Cochlicopa lubricella (Porro) ------Cochlicopa spp. 20 15 11 5 3 2 Truncatellina cylindrica (Ferussac)- - 2 - - - Vertigo pygmaea (Draparnaud) - - 1 2 1 - Abida secale (Draparnaud) - 1 - - - 1 Pupilla muscorum (L.) 1 - 4 1 2 8 Vallonia costata (Muller) 57 91 119 74 92 147 Vallonia pulchella (Muller) ------Vallonia excentrica Sterki 10 25 26 20 16 33 Vallonia spp. 38 62 85 70 66 106 Acanthinula aculeata (Muller) 4 5 1 1 2 - Punctum pygmaeum (Draparnaud) - 1 - - 1 1 Discus rotundatus (Muller) 20 14 2 3 - 1 Vitrina pellucida (Muller) - - - - - 1 Vitrea crystallina (Muller) - 4 - - - 1 Vitrea contracta (Westerlund) 18 13 2 - 1 2 Aegopinella pura. (Alder) 4 2 1 1 - - Aegopinella nitidula (Draparnaud) 10 13 10 2 1 4 Oxychilus cellarius (Muller) 22 5 8 - 1 4 Deroceras/Limax spp. 52 56 52 38 19 29 Cecilioides acicula (Muller) - - - - - Cochlodina laminata (Montagu) - 2 2 1 - - Clausilia bidentata (Strom) 8 7 5 3 3 2 Candidula gigaxii (Pfeiffer) - - - - - Cernuella virgata (da Costa) ------Helicella itala (L.) 3 2 5 12 6 18 Monacha cartusiana (Muller) - 2 2 1 - - Trichia hispida (L.) 55 57 93 60 46 72 Trichia striolata (Pfeiffer) 1 4 6 - - 3 Arianta arbustorum (L.) XXXX X X Cepaea spp. X 2 X X X X Arianta/Cepaea spp. 10 8 11 6 4 5 Helicigona lapicida (L.) X X X - X Helix aspersa Muller ------ Total Shells 486 541 508 325 287 471 Table 16 cont.: Cow Gap, Central Inf ill Section-Column A Depth (cm) 120 110 100 90 80 70 60 50 40 30 130 120 110 100 90 80 70 60 50 40 P. ele 5 7 3 4 6 3 3 1 5 2 'C. tri 13 26 - 1 1 1 1 3 7 - C. ica 1 ------C. lla ------Coch 3 6 - 3 - - 1 - - 2 T. cyl ------V. pyg 1 2 1 2 6 1 2 5 24 42 A. sec - - - 1 1 2 1 2 7 15 P. mus 17 12 4 7 3 2 3 11 32 53 V. cos 230 134 95 85 94 58 93 93 141 127 V. pul - 2 1 6 - - - - - 9 V. exc 75 56 46 49 43 14 21 14 33 71 Vail 191 223 204 133 109 106 75 65 84 97 A. acu ------P. PYR - 2 - 1 1 - - - D. rot 1 3 - - X - 1 1 1 - V. pel - 1 ------V. cry - - - - 8 - 6 3 6 1 V. con 3 5 1 1 2 9 10 3 4 - A. pur ------A. nit 6 2 ------O. cel 8 9 - - 1 - - - 1 - Limx 58 54 32 32 50 25 38 31 27 67 C. aci - - 3 4 13 12 54 142 173 C. lam ------C. bid 1 2 1 1 1 - 1 1 3 1 C. gig ------1 - - - C. vir ------1 - 92 H. ita 31 17 18 22 26 29 25 21 15 57 M. car - 1 - 4 9 3 3 1 4 - T. his 195 263 137 102 89 45 33 37 117 184 T. str 3 5 - - A. arb XXXX - X Cep. XXXXX - - X A/C 3 - 1 2 3 2 ^ H. lap. - - - - -7 H. asp. - - - - X X X X 1 2 Total Shells 845 883 544 459 459 314 331 349 654 925 Table 16 cont.: Cow Gap, Central Inf ill Section-Column A Depth (cm) 20 10 0 30 20 10 P. ele 6 2 1 C. tri - - - C. ica - - - C. lla - - - Coch 1 1 5 T. cyl - - - V. pyg 8 5 2 A. sec 8 4 3 P. mus 46 16 9 V. cos 26 29 19 V. pul 10 12 5 V. exc 27 21 11 Vail 99 63 39 A. acu - - - D. rot X - _ V. pel - - _ V. cry 4 6 1 V. con - - - A. pur - - - A. nit 2 - - O. cel - - - Limx 67 71 49 C. aci 200 237 109 C. lam - - - C. bid 1 - 2 C. gig. 6 36 58 C. vir 86 76 61 H. ita 24 11 8 M. car - - - T. his 104 108 45 T. str - - - A. arb - - - Cep. - - - A/C - - - H. lap - - - H. asp 2 X 7 Total Shells 728 699 434 Table 17 : Cow Gap, Interfluve Section Depth (cm) 120 110 100 90 80 70 130 120 110 100 90 80 Pomatias elegans (Muller) - - - - 1 4 Carychium tridentatum (Risso) - - - - 1 - Cochlicopa lubrica (Muller) - - - - - Cochlicopa spp. - - - - - 2 Vertigo pygmaea (Draparnaud) - - - - 3 3 Abida secale (Draparnaud) - - - - - 2 Pupilla muscorum (L.) - - - - - 39 Vallonia costata (Muller) - - - - 2 27 Vallonia pulchella (Muller) - - - - - 1 Vallonia excentrica Sterki - 1 - - 3 20 Vallonia spp. - - - - 5 35 Punctum pygmaeum (Draparnaud) ------Vitrea contracta (Westerlund) _ _ - - - Limax/Deroceras spp. - - - - 1 12 Cecilioides acicula (Muller) - - 1 25 64 279 Clausilia bidentata (Strom) - - - - 1 4 Candidula gigaxii (Pfeiffer) ------Cernuella virgata (da Costa) - - - 1 3 16 Helicella itala (L.) - - - - 2 14 Trichia hispida (L.) 1 - 1 - 6 39 Trichia striolata (Pfeiffer) - - - X - - Cepaea spp. - - - X - X Helix aspersa Muller - - - - X 6 Total Shells 1 1 2 28 93 503 Table 17 cont. : Cow Gap, Interfluve Section Depth (cm) 60 50 40 30 20 10 70 60 50 40 30 20 P. ele 2 12 3 2 7 - C. tri ------C. ica - - - 1 - - Coch - 1 - - 3 5 V. pyg 4 2 1 3 2 - A. sec - 1 1 1 - 1 P. mus 20 1 1 4 5 - V. cos 19 12 7 4 6 3 V. pul 2 3 5 1 - _ V. exc 17 19 13 5 1 3 Vail 48 93 44 16 8 13 P. PYR L.., - - - - 1 V. con - - - 1 - 1 Limx 20 14 30 31 25 26 C. aci 179 236 134 147 80 40 C. bid - 2 - - - 1 C. gig, - 8 19 30 34 14 C. vir 104 73 65 45 34 14 H. ita 16 13 9 1 6 1 T. his 39 36 19 34 35 21 T. str ------Cep------H. asp 5 6 5 2 6 5 Total Shells 475 532 356 328 252 149 APPENDIX II Table 18 : Shell and Anon granule totals from Cow Gap_ Column A Depth (cm) Absolute Number of Absolute number of Shells per Kg Anon granules per 20g 0-10 434 174 10-20 699 147 20-30 728 178 30-40 925 312 40-50 654 206 50-60 349 156 60-70 331 154 70-80 314 181 80-90 459 177 90-100 459 227 100-110 544 274 110-120 883 312 120-130 845 310 130-140 471 177 140-150 287 201 150-160 325 245 160-170 508 365 170-180 541 320 180-190 486 268 Column B 220-230 636 281 230-240 511 304 240-250 323 265 250-260 180 179 260-270 190 286 270-280 352 358 280-290 499 544 290-300 545 457 300-310 532 483 310-320 504 486 320-330 569 500 330-340 580 442 340-350 488 466 350-360 359 353 Table 19 : Selected Radiocarbon Dates from Sussex MESOLITHIC Vale of Brooks (Lewes I) 6290 ± 180 b.p. (Birm-168) Vale of Brooks (Lewes II) 5674 ± 167 b.p. (Birm-167) NEOLITHIC Court Hill 5420 ± 180 b.p. (I-12, 893) Church Hill 5340 ± 150 b.p. Trundle 5240 ± 140 b.p. (I-11, 615) Blackpatch 5090 ± 130 b.p. - Harrow Hill 4930 ± 150 b.p. Offham Hill 4925 ± 80 b.p. (BM 1414) Trundle 4860 ± 100 b.p. (I-11, 612) Cow Gap*ap 4820 ± 350 b.p. (BM 2220) Offham Hill 4740 ± 60 bp. (BM 2790) Cissbury 4730 ± 150 b.p. Cissbury 4720 ± 150 b.p. Bury Hill 4680 ± 80 b.p. (Har-3596) Harrow Hill 4670 ± 60 b.p. (BM 2071) Combe Hill 4590 ± 110 b.p. (I-11, 613) Bury Hill 4570 ± 80 b.p. (Har-3593) Bishopstone 4460 ± 70 b.p. (Har-1662) Alfriston 4310 ± 150 b.p. Rackham 3900 ± 140 b.p. Table 19 cont.: Selected Radiocarbon Dates from Sussex BRONZE AGE Itford Bottom 3770 ± 120 b.p. (BM 1545) Kiln Combe 3630 ± 90 b.p. (Har-5469) Asham 3580 ± 280 b.p. (BM 2277) Asham 3460 ± 190 b.p. (BM 2217) South Heighton 3450 ± 150 b.p. (BM 2219) Vale of Brookes (Lewes II) 3190 ± 125 b.p. (1-4454) Hove 3189 ± 46 b.p. Itford Hill 2950 ± 35 b.p. Asham 2760 ± 120 b.p. (BM 2216) Amberley 2620 ± 100 b.p. (0-690) IRON AGE Devils Dyke 2315 ± 35 b.p. (BM 2137) Bishopstone 2220 ± 80 b.p. (Har-1086) * sites studied in this thesis Table 20 : Measurements of mature Pomatias elegans from Asham-Column D (400-410cm) HEIGHT BREADTH HEIGHT BREADTH HEIGHT BREADTH 15.03 10.42 12.51 9.60 13.54 10.05 14.88 10.06 13.81 10.17 14.52 9.72 15.51 10.84 14.04 10.63 14.74 10.55 13.51 10.21 13.52 10.14 13.11 9.97 14.93 10.84 13.48 9.76 14.19 10.04 15.21 10.71 13.02 9.54 14.03 10.58 14.48 10.68 14.49 10.33 13.97 9.60 15.70 11.26 13.58 10.31 13.82 10.06 14.66 10.20 13.25 9.67 13.60 9.94 15.53 10.73 13.91 10.07 13.47 9.13 14.82 11.46 15.61 10.98 13.48 9.55 14.04 11.37 13.71 10.09 14.46 9.76 15.05 10.50 14.70 10.54 13.01 9.43 14.28 10.33 14.23 10.13 12.10 8.17 15.16 10.53 13.17 9.81 14.29 10.81 13.28 9.09 14.94 10.83 13.83 10.12 15.72 11.35 13.07 10.32 14.89 10.67 12.37 9.04 13.45 10.07 12.62 9.09 13.71 9.88 12.79 9.26 13.97 10.01 14.16 9.97 14.10 10.43 13.00 9.15 14.22 10.85 14.20 10.49 13.71 10.37 14.47 10.28 14.16 10.67 13.64 9.87 12.88 9.60 13.25 9.39 13.63 10.11 12.53 9.37 13.41 9.98 14.17 9.68 13.63 9.99 13.79 10.03 14.49 11.16 12.34 8.39 14.79 10.40 13.53 9.19 13.00 9.94 14.84 10.53 13.57 9.80 12.88 9.23 13.78 9.61 13.47 9.53 13.05 9.70 12.97 9.59 13.30 9.72 13.86 9.88 14.49 10.47 13.17 9.68 14.19 10.34 12.88 9.33 14.24 10.45 14.63 9.81 14.49 10.18 13.59 9.54 Table 21 : Measurements of mature Pomatias elegans from Cow Gap (170-190cm) HEIGHT BREADTH HEIGHT BREADTH HEIGHT BREADTH 15.23 10.63 14.41 10.84 15.36 10.47 14.12 10.57 16.43 11.33 13.90 9.76 16.17 11.29 14.61 10.04 16.66 11.53 13.65 9.97 16.62 10.43 13.29 9.67 14.44 10.36 15.98 10.97 15.24 10.25 14.60 10.03 14.32 10.74 14.43 9.61 15.87 11.71 14.73 10.15 14.73 10.77 12.47 9.02 14.82 10.38 14.47 10.24 14.67 10.34 13.81 10.02 15.02 10.55 14.00 10.11 16.22 11.09 14.61 10.25 14.93 10.51 13.87 9.75 15.92 11.43 14.16 10.17 14.51 10.02 14.48 10.59 14.78 10.27 14.01 9.85 14.79 10.43 12.80 9.58 15.86 11.17 14.04 9.98 16.77 11.14 13.83 10.17 14.99 10.81 14.66 9.88 14.48 10.44 13.78 9.76 14.45 9.88 13.63 10.10 14.92 10.97 14.74 10.42 14.39 10.48 13.42 9.76 15.11 10.77 13.28 10.00 14.50 10.02 12.62 9.47 13.71 10.06 13.07 9.48 15.46 11.26 13.64 9.68 14.96 9.96 13.49 9.87 14.22 10.11 14.91 10.46 15.48 10.47 14.38 9.72 14.71 10.21 Table 22 : Summary of the morphometric data available from Pomatias eleans FOSSIL SPECIMENS LIVING SPECIMENS HEIGHT BREADTH HEIGHT BREADTH Brook 14.70 10.60 13.29 9.72 Wateringbury 14.89 10.53 13.27 9.93 Blashenwell 15.10 10.59 13.43 9.82 Asham 13.90 10.06 not available Cow Gap 14.58 10.30 not available Table 23 : Results of the Optimum Sample Size Analyses, Asham-Column A ' Dry Weight ( kg ) 0.05 0.1 0.25 0.5 0.75 1.0 1.5 2.5 5.0 Pomatias elegans (Muller) 4 11 21 64 45 85 119 208 332 Acicula fusca (Montagu) - - - '- - - - 1 - Carychium tridentatum (Risso) 1 1 3 2 4 5 11 12 Cochlicopa lubrica (Muller) - - - , 3 3 5 6 9 Cochlicopa lubricella (Porro) - 1 - - 1 3 3 4 6 Cochlicopa spp. X 3 3 21 14 38 40 72 121 Vertigo pygmaea (Draparnaud) - 3 4 12 9 21 28 44 77 Abida secale (Draparnaud) - - - 2 - 1 2 3 5 Pupilla muscorum (L.) 4 11 21 62 82 93 137 281 408 Vallonia costata (Muller) 3 6 10 34 50 70 126 193 310 Vhlonia excentrica Sterki 5 9 21 98 104 150 198 363 616 Acanthinula aculeata (Muller) - - - 1 2 6 4 Ena obscura (Muller) ------2 1 Punctum pygmaeum (Draparnaud) - - - 1 1 1 1 4 Discus rotundatus (Muller) 1 2 - 4 9 3 8 21 32 Vitrina pellucida (Muller) - - - 2 1 - 1 2 5 Vitrea contracts (Westerlund) - - - 1 - - - - 1 Nesovitrea hammonis (Strom) - - - - - 1 4 2 Aegopinella pura (Alder) - - - - - 1 2 3 6 Aegopinella nitidula (Draparnaud) - 1 - 8 - 4 18 22 40 Oxychilus cellarius (Muller) - - - 1 1 2 4 5 Deroceras/Limax spp. 3 7 10 30 48 65 115 202 293 Euconulus fulvus (Muller) - - - 1 - - - - Cecilioides acicula (Muller) - - - - - 1 - - Cochlodina laminata (Montagu) - - - - - 2 3 5 4 Clausilia bidentata (Strom) - - 4 5 8 10 13 28 30 Hellicella itala (L.) 1 1 3 11 10 16 35 38 60 Monacha cartusiana (Muller) - - 1 - 1 2 4 15 17 Trichia hispida (L.) 2 7 18 65 78 88 145 250 507 Arianta arbustorum (L.) - - - - - X X X Cepaea spp. X X X X X X X X X Arianta/Cepaea spp. - 2 4 11 10 6 17 44 63 Helicigona lapicida (L.) X - X X X X X 1 2 Total Shells 26 65 122 439 479 666 1029 1834 2972 Number of Species 11 13 14. 21 20 20 27 28 28