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What Lies Beneath: geoarchaeology at Cotswold Archaeology

Over the years, Cotswold Archaeology has been involved in many projects that have included geoarchaeological investigations, and I’ve picked out a few different sites to demonstrate the range of geoarchaeological work we undertake at CA. While geoarchaeology often forms a component of our archaeological projects, occasionally the geoarchaeological work itself represents the principal focus of the work. For instance, we have recently been working on a site at Saxonvale in Frome, Somerset, where the main aim of the project was to collect data on alluvial sediments and peats associated with the River Frome. The sediments encountered in both boreholes and test pits were logged and sampled in order to create a deposit model for the River Frome catchment and set it within a wider archaeological and environmental context.

Geoarchaeological analysis can contribute significantly to the way we interpret sites, allowing us to distinguish between various site formation processes, such as colluvial (material deposited at the base of slopes) and alluvial (material deposited by running water) sequences. These processes can vary significantly in their complexity. On a recent site at Whitchurch near Bristol, for example, we encountered a relatively simple sequence of slope wash deposits that covered and partially filled all of the archaeological features. The geoarchaeological assessment enabled us to recognise a thick layer of redeposited occupation debris derived from the area upslope, which was then sealed by redeposited oxidized clay derived from the local bedrock, which had eroded from the slope above.

East Challow, Oxfordshire. Excavation on the chalky colluvium to expose the buried soil (courtesy of Nick Watson, ARCA)
Fig. 1. East Challow, Oxfordshire. Excavation on the chalky colluvium to expose the buried soil (courtesy of Nick Watson, ARCA)

One of our most interesting projects involving more complex geoarchaeology was undertaken at East Challow, Oxfordshire. Here, the geoarchaeological investigation conducted by Nick Watson at ARCA revealed that layers initially interpreted as natural bedrock were in fact a thick Devensian solifluction deposit, covered by Early Holocene colluvium which contained a buried soil with mud cracks, filled with the colluvial deposits (Fig. 1). Closer examination of the monolith samples in the laboratory helped to confirm the presence of the buried soil that formed at the very beginning of Holocene (around 9500 cal BC) and developed over 900 years before being buried.

The range of different geologies we work on can be challenging at times and can make the recognition of natural features such as paleochannels and periglacial features tricky. One such site is at Swavesey, Cambridgeshire, where the stripped area was described as being like one massive ‘lava lamp’ landscape by the project leader. The geoarchaeological assessments of these ‘blobs’ allowed us to establish that the features formed under cold conditions during the Devensian period (although they contained some intrusive artefactual material just to confuse the issue!). The periglacial condition affected the top fraction of the bedrock and the overlying braidplain gravels, resulting in the formation of a thermokarstic landscape (an irregular surface of hollows and hummocks) which underlay the entire site (Fig. 2).

Fig. 2. Drone photo showing the periglacial involution features at Swavesey
Fig. 2. Drone photo showing the periglacial involution features at Swavesey

We have also been working on a long term geoarchaeological project, doing some test pitting in Kent. The Swanscombe area in the Ebbsfleet Valley is one of the most important locations for Paleolithic archaeology in Britain; our work there has revealed a rich sequence of deeply buried Pleistocene deposits containing flint tools and paleoenvironmental remains, which is contributing to the research programme led by Francis Wenban-Smith of the University of Southampton.

Fig. 3 Monolith samples being taken from a section of a Roman defensive ditch in Exeter
Fig. 3. Monolith samples being taken from a section of a Roman defensive ditch in Exeter

Although geoarchaeological work is often linked with Pleistocene sediments and buried soils, we also often use it to help answer questions about specific archeological features. Recently, the geoarchaeological examination of sediments in monolith samples from a defensive ditch, thought to be part of an Early Roman fortlet, from St Sidwell’s Point in Exeter aimed to characterise the origin of the ditch`s fills and to determine if there was any evidence for eroded rampart material within them. The examination revealed that the fills derived from a bank, which may have been hardened using turf and stones. It also demonstrated that this bank was situated on the outside of the ditch, not on the inside (Fig. 3).

Agata Kowalska

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Oxford Cotswold Archaeology JV wins a place on England’s first archaeology framework for national road projects

Oxford Cotswold Archaeology

Oxford Archaeology and Cotswold Archaeology, working together as Oxford Cotswold Archaeology JV (OCA JV), are delighted to have won a place on a framework to undertake archaeological investigations associated with new major road projects in England over the next four years.

Highways England has announced the organisations that have won places on its new £195m framework which offers the successful suppliers the opportunity to work with them to protect and enhance England’s unique cultural heritage and buried archaeology.

The framework has been divided into three Lots depending upon the value of the projects, and OCA has been awarded a place on Lots 2 and 3 which cover projects with values greater than £2m.

Catherine McGrath of Highways England said: ‘We’re delighted to announce the new framework; it’s the first of its kind in the archaeological sector for Highways England and enables us to develop direct relationships with archaeology contractors, developing greater efficiencies. We look forward to working with the successful suppliers.’

OCA has put together a strong team to deliver the framework, including UK civil engineering market leader Balfour Beatty who are supporting us with industry-leading expertise in health and safety and project management and programming. Other partners include Drapers Civil Engineering who will supply plant and welfare facilities, and specialist geophysicists from Magnitude Surveys.

Oxford Archaeology and Cotswold Archaeology have a proven track record of collaborating successfully on major projects. We are currently working on the proposed Lower Thames Crossing road scheme in Essex and Kent and on the High Speed 2 railway. CEOs Gill Hey and Neil Holbrook said ‘OCA has proven itself to be a highly successful vehicle to deliver major projects, and we look forward to working together and with our partners over the next four years to support Highways England’s road investment strategy’.

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Timeline: Neolithic henge at Vaynor farm, Carmarthenshire

The henge in its landscape setting, with the pipeline traversing the hills and valleys beyond
The henge in its landscape setting, with the pipeline traversing the hills and valleys beyond

As reported in CA’s latest Monograph, Timeline, some of the discoveries made along the South Wales natural gas pipeline were spectacular, not least of which was a previously unknown henge monument located on a ridge overlooking the River Taf.

Surviving as two ‘banana’-shaped rock-cut ditches with post or stone sockets along the interior, this represents the most south-westerly henge discovered in Wales. Statistical modelling of a large number of radiocarbon dates indicated that it was built during the Late Neolithic, before 2600 cal BC. The monument may have been deliberately slighted, perhaps when the high ground was used for burial during the Bronze Age at which time the henge may have been an unwelcome reminder of an earlier religion.

The rock-cut henge ditch, showing a sequence of infilling
The rock-cut henge ditch, showing a sequence of infilling

The henge banks and ditches remained as earthworks however, attracting attention during the Early Roman period, when they may have been the focus of small-scale occupation or religious activity, something captured in a reconstruction drawing of the site created by Mark Gridley (below). The landscape shown in this drawing is based on extensive environmental sampling and analysis undertaken along the entire pipeline route, which allowed changes in climate, fauna and flora across the millennia, and the impact of human land use, to be studied in close detail.

Jon Hart

The henge during the Early Roman period
The henge during the Early Roman period. Reconstruction by Mark Gridley.
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Cribbs Causeway, Bristol

An excavation near Cribbs Causeway, Bristol, which started back in December 2019, came to an end in February 2021 after a long interruption in 2020. Despite the challenging conditions created by a very wet winter, the excavation revealed some very interesting remains of Late Iron Age to Late Roman occupation. These included a Roman building, which truncated a series of Iron Age ditches and pits and was bounded to the north-east and south-east by a ditched enclosure. To the north-east of the enclosure was a small field system created by several field boundaries and at least one small quadrangular enclosure; to the south-east were the remains of a large curvilinear boundary ditch, which is currently undated.

Overall plan of the excavation areas. Roman building to the south, shown in red, surviving walls and surfaces in blue and yellow respectively
Overall plan of the excavation areas. Roman building to the south, shown in red, surviving walls and surfaces in blue and yellow respectively

The Roman building was substantially truncated by later agricultural activity, but the remaining walls and the robbed-out foundation trenches allowed identification of its footprint. The building was aligned north-east/south-west and it continued beyond the south-western and north-western limits of the excavation. The footprint of the structure showed a composite plan; it included four rectangular rooms and an external cobbled surface in its central area. To the east of this surface were two large post-pads, which may have been bases for the pillars of a small portico-like structure.

Photo showing one of the walls and the remains of the cobbled surface
Photo showing one of the walls and the remains of the cobbled surface

The alignment of the building was reflected by the ditches to the north and east: all were perpendicular or parallel to the projected line of a Roman road thought to be below the current Station Road (to the north-west of the site) that connected the Roman port of Abonae (Sea Mills) to other northbound roads running towards Glevum (Gloucester).

The function of our building has not been determined yet but its proximity to an important trade route should be considered. Surrounded as it was by agricultural fields, our building might have been the core of a farmstead, although it may have been used at some point as a road-side inn. One isolated inhumation burial was identified to the north-east of the main Roman enclosure, but its association with other features at the site remains to be understood.

A selection of copper alloy coins
A selection of copper alloy coins

The site seems to have been occupied between the end of the Iron Age and the 4th century AD, with activity perhaps intensifying towards the end of this period. A collection of coins, three brooches, an iron knife with a copper handle and several fragments of samian ware are among the most remarkable of the finds produced by the excavation.

Paolo Guarino

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Timeline: prehistoric occupation and burnt mound activity in Pembrokeshire

Recording along the South Wales natural gas pipeline, detailed in CA’s latest Monograph, Timeline, revealed many significant remains, including a Neolithic henge, but there were many more features that, although less spectacular, collectively transform our understanding of early occupation in South Wales. At Upper Neeston, Pembrokeshire, the archaeological remains fell into both categories.

The early prehistoric cove feature
The early prehistoric cove feature

These discoveries were made possible by the vigilance of the watching brief team who were monitoring the crossing of a small stream. Here, they spotted part of a wooden object just below the marshy surface. Given its shallow depth, the object was initially presumed to be of relatively recent date, but a priority radiocarbon date and further excavation demonstrated that it was in fact a trough belonging to the Middle Bronze Age. A decision to extend the excavation was taken and further remains were revealed.

The earliest of these included an enigmatic cove feature and many pits, dating from the Early Neolithic through to the Early Bronze Age. Such pits, typically small and unspectacular, were found with unexpected regularity along much of the western section of the pipeline. An intensive programme of radiocarbon dating, one of the largest ever undertaken in Wales, has made it possible to demonstrate the density of human occupation along the route during those millennia, revealing that early prehistoric South Wales was at times well settled, but with distinct pulses of activity.

A Middle Bronze Age burnt mound: the wooden trough and hearth are visible in the centre of the photograph
A Middle Bronze Age burnt mound: the wooden trough and hearth are visible in the centre of the photograph
First minister Rhodri Morgan (second from left) and the Bronze Age trough
First minister Rhodri Morgan (second from left) and the Bronze Age trough

Some 2000 years after Neolithic occupation began on the site, a stream became a focus of activity, where hot stones were used to generate steam or hot water, which resulted in the formation of a burnt mound. Water contained in the wooden trough was heated by stones placed in an adjoining hearth. While this process is well understood, the purpose of such features remains a matter of ongoing debate, with use for cooking, craft activities, brewing and saunas all suggested. Over 40 such mounds were found along the pipeline, with radiocarbon dating at one site indicating reuse over a remarkably long timespan of over 1500 years.

The findings generated much interest, including a visit from the then First Minister for Wales, Rhodri Morgan.

The same site was later used for Roman food production, with small paddocks and crop-processing ovens reflecting intensified agricultural production following the conquest of Wales (c. AD 47–78), something evidenced at several other sites along the route.

Jon Hart

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Glass artefacts from Jesus College, Cambridgeshire

grozed quarry
Grozed glass piece

Nothing indicated wealth and comfort in medieval England more than beautifully glazed windows. Continuing work on the finds coming out of excavations at Jesus College, Cambridge, has identified moderate amounts of post-medieval glass, most commonly pieces from discarded bottles. Amongst the earliest pieces of glass, however, are two fragments of attractive medieval window .

Likely to date to the 13th century, the first fragment is decorated with a red/brown painted border, while the second has been grozed, or ‘nibbled’ along its outer edges, creating a characteristic diamond shape. Grozing irons were used for this cutting process on medieval window glass until the diamond cutter was introduced in the 15th century.

painted window glass
Painted glass fragment

The two fragments are both of a type of glass sometimes referred to as ‘forest glass’ because the small glasshouses that produced it were usually situated in woodland; woods were an ideal location for glass manufacture as large quantities of wood were required as fuel to fire the furnaces, and wood ash was needed as a flux in glass production. Although both fragments now appear opaque due to weathering, they would originally have been translucent.

While the Jesus College glass may have been produced in the 13th century, it is possible that it was recycled in windows of a later date.  It is not uncommon to find early glass re-used in later buildings for political and ideological reasons, or to assert the antiquity of a building. Following the Dissolution of the monasteries in the 16th century, glass may have been resold or appropriated. Second-hand glass from wealthy religious establishments may have been a good buy for secular homes owned by those with money and influence.

Ruth Beveridge

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