Chris Green1 and Rob Batchelor1
1QUEST (Quaternary Scientific), School of Archaeology, Geography and Environmental Science, University of Reading
Southall Gasworks: multi-purpose urban development context (West London) in a very rich region for Palaeolithic archaeology (Middle Thames), but theoretically promising site highly disturbed due to complicated investigative history.
For West London this is a large site (37ha). It has a history of industrial land-use and associated potential for widespread chemical contamination. The proposed multi-purpose redevelopment incorporated residential, retail and leisure space together with altered and new transport links.
The site is on a remnant of Pleistocene Thames river terrace underlain in part by Langley Silt (‘brickearth’) and in part by Holocene Alluvium of the Yeading Brook, both resting on Lynch Hill Gravel. A few Lower Palaeolithic (Acheulean) artefacts are recorded from the gravel within the site and a few Pleistocene large mammal remains (Wymer 1968, 1999; https://archaeologydataservice.ac.uk/archives/view/terps_eh_2009/ [site ID no. 23365; artefact ID no.s: 31707 and 31708]).
Palaeolithic remains have previously been recorded from similar Langley Silt/Lynch Hill Gravel sequences to the west, around West Drayton (Collins 1978), and to the east, including the important Middle Palaeolithic (Levallois) assemblage at Creffield Road (Brown 1887).
There have been many geotechnical and geoarchaeological investigations of the site resulting in over 500 recorded interventions. During the present investigation, logs from these interventions were used together with historic OS maps to predict the distribution of undisturbed sediment sequences suitable for further field investigation.
Based on the existing Creffield Road evidence, interest in this investigation focused on the Langley Silt and its contact with the Lynch Hill Gravel. However, the evidence from previous interventions combined with the results of new fieldwork by QUEST show that no potential remains for the preservation of significant archaeological or palaeoenvironmental evidence.
- Desk based assessment
- Literature/mapping review (DBA)
Post-determination, Pre/during development
- Test pitting/boreholes (TP)
Post-excavation/research dissemination/HER enhancement
- Post-excavation assessment (and reporting)
- Final Report
- Deposit with HER and museum (and Oasis)
As is quite usual for large urban developments, there had been several investigations, undertaken by different contractors and for different purposes, both geotechnical and geoarchaeological, before the investigation described in this case study.
- Geotechnical investigations took place in 1996, 1998, 1999, 2001, 2013 and 2014 resulting in 529 sediment logs of boreholes and test pits.
- MOLA recorded investigation of the site in an Archaeological DBA in 2008 leading to the preparation of a WSI in 2011, in which the view was expressed that no geoarchaeological interventions would be possible in the western part of the site due to high levels of contamination. MOLA also reported that in large areas truncation associated with industrial land-use had removed any potential for pre-modern archaeology.
- ASE undertook two phases of archaeological investigation in 2016 in the eastern part of the site where industrial land-use, ground disturbance and contamination appear to have had least impact. In Phase 1, following the preparation of a WSI, 20 archaeological trenches and six geoarchaeological test pits were opened and were described in an Archaeological Evaluation (Blinkhorn 2016a). In Phase 2, following the preparation of a second WSI, three large (10m x 10m) trenches were opened, allowing the examination of some 250 cubic metres of sediment and at least 120m of section. The results of post-excavation analyses, including Optically Stimulated Luminescence (OSL) dating and soil micromorphology were reported in a Post-Excavation Assessment (Blinkhorn 2016b).
- QUEST was approached by the client’s consultant late in 2016 and prepared a preliminary assessment of the potential for further investigation early in 2017 and submitted a full report with recommendations in May 2017. The report was commended by the client and by Historic England and seven test pits were opened in October, with a report of the findings submitted in the following month.
This is a large urban site currently earmarked for development over a period of 10 to 20 years. The proposed development comprised demolition of existing housing, remediation and subsequent redevelopment for multiple purposes (including residential, retail, restaurants, hotel, health-care and educational facilities, offices, sports pavilion and associated car-parking and amenity space) as well as new access roads to the site, widening of the railway line and construction of two new bridges over the Grand Union Canal and Yeading Brook. It was important therefore that any recommendations for archaeological oversight should be capable of implementation over this lengthy development period.
The Palaeolithic potential of the site relates to its location on the Lynch Hill Terrace of the Thames, underlain by Langley Silt resting on Lynch Hill Gravel (Figure 1). These sediments have been an important source of Palaeolithic remains in the surrounding area (see Archaeological Context for details).
The scope for investigation at Southall Gasworks has been severely constrained by the impacts of past land-use (Figure 2). OS maps show that the site was in agricultural use until the mid-19th century but that during the second half of the century much of the site was occupied by brickfields working the Langley Silt ‘brickearth’ or by workings exploiting the Lynch Hill Gravel.
Between the 1890s and 1935 the site was progressively occupied by industrial premises, including chemical works and Southall Gasworks, involving the creation of a dense pattern of buildings and associated roads and railway sidings across all but the eastern end of the site which remained in recreational use as playing fields and allotments.
In initial geoarchaeological investigations within this eastern part of the site material seen overlying the Lynch Hill Gravel was largely interpreted as the product of either mass movement or the colluvial reworking of fluvial sediment. Thin (0.5–0.85m) remnants of the Langley Silt were recorded but no artefacts or identifiable fossil remains were observed (Blinkhorn 2016a).
These findings no doubt reflect the fact that although the eastern part of the site was never occupied by industrial buildings and infrastructure, it was occupied in the 19th century by brickfields. It is likely therefore that any economically workable brickearth (Langley Silt) will have been removed.
Within a few kilometres of the site the Langley Silt and Lynch Hill Gravel stratigraphic units have been a prolific source of Lower and Middle Palaeolithic artefacts and Pleistocene mammalian remains. Most of the Palaeolithic artefacts are handaxes found as isolated examples in abraded condition in the Lynch Hill Gravel (Collins 1978). However, at Creffield Road an important Levallois assemblage was recovered in the 19th century containing evidence of artefacts in primary context (Brown 1887; Figure 1).
This assemblage occurred on a probable land surface at the contact between the Lynch Hill Gravel and the overlying Langley Silt. There is therefore potential for remains of national importance, according to the criteria outlined in the Historic England guidance document ‘Sites of Early Human Activity: Scheduling Selection Guide‘.
The importance of this discovery has strongly influenced the choice of priorities in schemes of archaeological investigation at Southall Gasworks.
Methodology & Research Questions
An archaeological desk-based assessment (DBA) for the site was prepared in 2008 (MOLA 2008) and fieldwork and post-excavation work was undertaken on the eastern part of the site in 2016 (Blinkhorn 2016a; 2016b). The following account outlines the methodology for a subsequent desk-based geoarchaeological deposit model report and fieldwork (Green 2017a; 2017b).
The aims of the exercise were: (1) to clarify the nature of the deposits across the site, in particular the presence and thickness of any Langley Silt across the site, and (2) to provide a rational basis for the ongoing watching brief programme in terms of geoarchaeological and archaeological potential.
The investigation described here is divided into five stages leading to the preparation of the deposit model report and recommendations for further geoarchaeological investigation.
1. Literature Review: Review of published and grey literature to establish with reference to the site and to nearby areas with topographic conditions and underlying geology similar to the site, (a) the stratigraphy, structure and sedimentology of the Pleistocene deposits, including the characteristic features of well-preserved Langley Silt (Gibbard 1985); and (b) the amount, condition and stratigraphic distribution of Palaeolithic and palaeoenvironmental remains.
2. Data Evaluation: Standardised tabulation of data from borehole and test pit sediment logs (n = 529), to provide the basis for deposit modelling of the principal stratigraphic units:
- Made Ground
- Silt/Clay (Holocene Alluvium)
- Silt/Clay (Langley Silt)
- Lynch Hill Gravel
- London Clay
Recording focused upon OD height, depth below ground surface (bgs) of contacts between the principal stratigraphic units, and notes on significant details, e.g. organic remains, stone content, charcoal.
3. Preparation of Deposit Model: The spatial and stratigraphic data were imported into RockWorks 16. Topographic and surface plots and thickness models were generated for each of the main stratigraphic units, using an Inverse Distance Weighted algorithm. The modelling procedure was manually adjusted so that only those areas for which sufficient stratigraphic data are present are modelled. Due to the high number of truncated sequences therefore, a ‘maximum distance cut-off filter’ equivalent to 10m was applied around each record containing Silt/Clay units.
4. Data analysis: Evaluation of data, including sediment logs, deposit models, topographic, geological and archaeological setting of the site and its land-use history, taking account of former quarrying, the footprints of former industrial buildings, plant and services, and existing records of ground contamination and deposit truncation. The aim was to identify areas in which undisturbed and uncontaminated sediment sequences seemed likely to have survived, comprising Lynch Hill Gravel overlain by Langley Silt and potentially including Middle Palaeolithic contexts.
Potential for survival was assessed on the basis of three criteria:
(a) Areas where there were boreholes/test pits recording fine-grained sediment units overlying the Lynch Hill Gravel and where there were no or few boreholes/test pits from which such units were missing (Figure 3).
(b) Areas where fine-grained sediment units more than 1.0m in thickness were recorded overlying the Lynch Hill Gravel (Figure 4a).
(c) Areas where stoneless fine-grained sediment units were recorded overlying the Lynch Hill Gravel (Figure 4b).
The results were presented as a plan showing where fine-grained sediment was present overlying the Lynch Hill Gravel, i.e. areas meeting criterion (a) above; and plans showing the distribution of boreholes/test pits recording sediment sequences that met criteria (b) and/or (c) above (Figure 5). These results formed part of a detailed report on the geoarchaeology of the site.
5. Written Scheme of Investigation (WSI): On the basis of the above report a WSI for Geoarchaeological Fieldwork was prepared and seven locations were identified as having potential for the preservation of fine-grained sediments overlying the Lynch Hill Gravel (Figure 5). Four sites (TP4, TP5, TP6, TP7) were in areas where the presence of the Langley Silt was predicted, and three sites (TP1, TP2, TP3) where the alluvium of the Yeading Brook was predicted.
Click to view the full image and then zoom in for more detail
- Field Investigations: Seven test pits were dug as planned. Five were within 5m of the intended locations, but two (TP6 and TP7) had to be relocated due to the presence of active services. In all seven test pits contamination was recognised, mainly hydrocarbons but cyanide was highlighted as a risk near test pits TP5 and TP6. Of the three test pits in the alluvium of the Yeading Brook, one proved Made Ground resting directly on Lynch Hill Gravel and the other two were stopped when pipework and basement structures were encountered at shallow depths. In all four test pits planned to investigate the Langley Silt, fine-grained sediment units were present overlying the Lynch Hill Gravel. In three of these test pits these units were thin (0.5-0.7m) and gravelly but in test pit TP6 1.2m of brown silty sand was present. Small grab samples of the fine-grained units were collected in test pits TP4 to TP7.
- Laboratory investigations: Four grab samples were inspected for evidence of typical Langley Silt features (Gibbard 1985). None of the samples displayed these features.
- Recommendations: On the basis of the findings of the DBA, including the archaeological context of the site on the Lynch Hill Gravel and the results of previous geoarchaeological work in the eastern part of the site, and having regard to the results of fieldwork in the western part of the site and the examination of sediment samples from this area, the recommendation was that no further work should be carried out on the Southall Gasworks site. Not only has previous development truncated or disturbed the natural sequence across most of the site, there was also evidence of widespread contamination, often severe, particularly in the western part of the site.
The work at the Southall Gasworks site over many years and recorded in a succession of geotechnical and geoarchaeological reports, culminating in the investigation reported in this case study, illustrates in particular the problematic relationship between long-term industrial land-use and the survival (or not) of Pleistocene/Holocene sediment sequences and related archaeological remains.
The record shows that in this case the presence of significant Lower Palaeolithic remains in the Lynch Hill Gravel is unlikely; and that sediment sequences that might include nationally important Middle Palaeolithic contexts (cf. Creffield Road) have been so comprehensively damaged by truncation, disturbance and contamination that the potential for the preservation of significant Middle Palaeolithic archaeological or palaeoenvironmental remains is for practical purposes vanishingly small.
There is therefore no realistic scope for further field investigation at the Southall Gasworks site.
The London Archaeological Research Framework (Museum of London 2002) highlighted the potential for palaeo-landsurfaces with Lower Palaeolithic occupation beneath surviving Langley Silt (brickearth) deposits across West London. This large contaminated brownfield site illustrates the challenges of actually implementing a strategy to investigate this research agenda.
The project’s long time-scales and commercial factors meant that no one archaeologist in any role saw the project through from start to finish. The original mitigation strategy envisaged a watching brief but on review some years later this seemed impractical.
The initial test pit strategy instead aimed to use geoarchaeology to establish if a palaeo-landsurface existed and also sought evidence of human presence. If both were positive then there would be a clear demonstrable case for further investigation. This strategy was successful in that micromorphological analysis indicated that the brickearth was a product of a variety of different depositional processes that included a coarse brickearth unit representing a former land surface, sealed by finer silts and clays deriving from mass movement and subject to pedogenesis. The latter was OSL-dated to c. 80 kya. No lithics or faunal remains were identified in this investigation.
Overall, the detailed desk-based assessment and test-pitting exercise demonstrated the site had very limited Palaeolithic potential due to historic land-use and contamination. A similar strategy, albeit streamlined, is now being applied at other major development sites on Langley Silt. Hunting for Lower Palaeolithic sites in West London will always resemble searching the proverbial haystack but at least we now have a rational approach to doing so which can be refined as our understanding of the brickearth improves.
The successive implementation of several separate archaeological/geoarchaeological investigations seems inefficient. It is probably not unique to Southall Gasworks and cannot be in the best interest of any of the parties involved. It should be possible to reach definitive recommendations for a site through a single well-focused investigation, and this should always be the aim of local authorities, developers and their consultants.
It is also important to highlight that a pragmatic approach and flexibility is often necessary when on-site works are taking place. On this site for example, despite using all available resources to locate the test-pits in the optimal position prior to fieldwork, the presence of unmarked services meant that these had to be moved to alternative locations that would still satisfy the aims and objectives of the exercise.
Brown, J.A. 1887. 'Palaeolithic Man in NW Middlesex'. Macmillan & Co: London.
Collins, D. 1978. 'Early Man in West Middlesex'. HMSO and London Museum Archaeological Report: London.
Gibbard, P.L. 1985. 'The Pleistocene History of the Middle Thames Valley'. Cambridge University Press: Cambridge.
Gibbard, P.L., Wintle, A.G. and Catt, J.A. 1987. 'Age and origin of clayey silt ‘brickearth’ in west London, England'. Journal of Quaternary Science 2: 3–9.
Green, C.P. 2017a. 'Southall Gasworks, Southall, London Borough of Ealing: desk-based geoarchaeological deposit model report'. Quaternary Scientific (QUEST) Unpublished Report August 2017; Project Number 185/16.
Green, C.P. 2017b. 'Southall Gasworks, Southall, London Borough of Ealing: geoarchaeological fieldwork report'. Quaternary Scientific (QUEST) Unpublished Report November 2017; Project Number 185/16.
Museum of London 2002. A research framework for London archaeology 2002. Museum of London and English Heritage: London.
MOLA 2008. 'Southall Gasworks site'. Unpublished DBA.
MOLA 2011. 'Southall Gasworks site'. Unpublished WSI.
Wymer, J.J. 1968. 'Lower Palaeolithic Archaeology in Britain'. John Baker: London.
Wymer, J.J. 1999. The Lower Palaeolithic Occupation of Britain. Wessex Archaeology and English Heritage: Salisbury.