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Geophysical Survey Results

Data from the geophysical survey was downloaded onto a computer during our lunch break and at the end of the day. This allowed us to begin to ‘see’ the site as it unfolded very quickly, as well as allowing us to identify any problems with our survey technique, and in the case of any technical difficulties would could limit the amount of data loss. I for one, couldn’t wait to download the data! This blog post will briefly describe the process we undertook after the data was downloaded.

Raw Data

fieldbscrnshot

Field B showing grid (raw data)

Survey data downloaded from the magnetometers is considered ‘raw’. The data for each grid is stored separately and has to be compiled using software. Computer programmes do not know how to put each grid together, so you have to keep accurate notes when surveying!

We used GEOPLOT 3.0 to work with our data. Because we ended up grid-ing out each of the fields separately, we created compiled images for each individual field. That way, we could take the fences into account.

Data Processing

Once the grids for each field were compiled, we then had to ‘process’ the data. Processing corrects for the slight (but unavoidable) inaccuracies caused by the field slope, different gaits from different surveyors, and even very slight inaccuracies in the grid layout. It also helps to smooth out some of the data. Then the files are exported from GEOPLOT 3.0 and imported into GIS software (I used QGIS for this project). You can see a comparison of the raw data and the processed data below.

SWALL14 raw data

2014 Swallowcliffe Down, Wiltshire Geophysical Survey (Raw Data)

 

SWALL14 processed data

2014 Swallowcliffe Down, Wiltshire Geophysical Survey (Processed Data)

Interpretation

Based on the fully processed data and our understanding of the site from visits and the 1920s excavation report, we then began to interpret the survey.

Field A

2014 Swallowcliffe Down, Wiltshire Geophysical Survey (Field Names)

2014 Swallowcliffe Down, Wiltshire Geophysical Survey (Field Names)

Despite the visible earthwork in Field A, which is only faintly visible in the geophysical survey results (marked in blue), no other features of archaeological interest were visible. Dr Clay described this ring earthwork as an amphitheatre or ‘circus’ and considered it to be part of the settlement enclosure visible in Field B. It is unfortunate that the road that separates the two sites cuts through anything that may have indicated the relationship between the two features. However, given the other known dated evidence for both prehistoric and historic features in the immediate vicinity, there is no reason for this earthwork to be directly related to the Iron Age activity.

Field B, C, Ca

The linear features forming the ditch enclosure (marked in green) is particularly strong to the west (were it is visible on the surface), but also on the eastern side. The eastern portion of the ditch visible in field Ca may continue into the south-eastern corner of field C. It is possible that originally both ditches were connected along the southern side, but the road later cut through the site. Another, disconnected, linear feature far to the west of the enclosure ditch is also faintly visible on the survey results.

A number of roughly circular negative features (marked in red) are visible in the area that appears to be the inside of the enclosure. Many of these are likely to be the pits that Clay previously excavated, but it is not possible to exactly identify each pit.

There also seem to be several possible curvilinear features that may indicate round-structures (marked in purple). Clay was unaware that Iron Age people lived in roundhouses at the time of his excavations and instead believed that they lived in pits, so he didn’t know to look for evidence of roundhouses.

2014 Swallowcliffe Down, Wiltshire Geophysical Survey (Interpretation)

2014 Swallowcliffe Down, Wiltshire Geophysical Survey (Interpretation: Green=Visible Ditches, Blue=Visible Banks, Red=Negative Features, Purple=Ring?)

A full report with technical details about the survey is available here. 


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Finds while geophysing – a flint blade from Swallowcliffe Down

While we were only conducting geophysical survey during the 2014 field season at Swallowcliffe Down, we did manage to find a single artefact; a small flint blade lying on the ground surface of Field B. While this particular kind of stone tool is not considered to be diagnostic of a specific period, it does indicate the potential for earlier occupations of the site to have taken place.

Small blade

The small blade recovered from Field B (photo by Frederick Foulds).

The presence of flint is ubiquitous within the chalk downloads of Wiltshire, occurring as nodules within the chalk bedrock. As a result, worked flint is commonly found throughout the area and Wiltshire has produced a wide range of flint artefacts, encompassing much of human and early hominin prehistory. Everything from Lower Palaeolithic Acheulian handaxes (750,000-300,000 years ago), to Neolithic (4, 000-2,500 BCE) and Bronze Age (2,500-800 BCE) flint blades have been discovered in this archaeologically rich region.

The site at Swallowcliffe Down is no different. The presence of flint in the area is provided by the abundant natural debris on the ground surface where it has eroded out or been cast up by agricultural processes. Therefore, it was no great surprise to find some evidence of prehistoric flintwork. However, given the amount of natural debris, we had to be certain that this was an actual humanly worked artefact. Fortunately, we have a number of different characteristics to look for when trying to determine if human hands created it.

Swallfinal

Some of the characteristics that indicate worked flint (illustration by Frederick Foulds).

In the picture above, you can see some of these characteristics. Many of these are the result of the way that flint fractures, as well as the method of manufacture employed by the flintknapper who produced the tool. On one side we see scars, which is evidence of previous flakes or blades that were removed from the original flint nodule, or core, prior to this one. The other side is relatively smooth and would originally have been inside the core. However, it also displays evidence that this was worked by human hands. We can clearly see a striking platform, where the nodule was struck to remove this blade. There is also a bulb of percussion – a raised area caused by the application of force when the flint was struck. In this case, the bulb is small and diffuse, which shows that the blade was produced using a ‘soft hammer’ technique; possibly using an antler hammer, or a punch. We can also see ripple marks – undulcations in the surface of the flint that expand from the point of percussion and show the direction that the flaking energy took when the flake was removed.

Finally, we can tell that this flake is archaeologically meaningful due to its patination. This is the colouration of the flint surface. Flint is usually a black or grey colour when freshly knapped. However, chemical changes to the flint surface can occur in the ground that can change its colour. In this case, much of the flint in the Swallowcliffe area displays a white patina. As the blade retains this patina, and does not show the black or grey expected of a fresh break, we can be confident that the tool is a product of the past.

The blade itself is rather small and slightly wider than expected. The typical classification of a flint blade is a flake that is “twice as long as it is wide”. However, its shape and the characteristic crest that runs down its centre, coupled with the evidence that it was humanly worked, make us confident in classifying it as this particular tool type. Its small size may also allow us to narrow this definition to what is commonly referred to as a ‘bladelet’.

As already mentioned, this particular tool type is relatively undiagnostic and it is hard to place this artefact within a specific period. Despite this, there have been finds from the area around Swallowcliffe village that have been dated to the Mesolithic (10,000-5,500 years ago) and later periods. In addition, evidence of lithic materials from the earlier Upper Palaeolithic , when blades first appeared in increased frequencies, are generally sparse within Wiltshire. Therefore, we can limit our understanding of when this tool may have been created, although we are still left with a rather extensive period of time. Nevertheless, the fact that human occupation and use of the landscape around Swallowcliffe Down may extend beyond the Bronze and Iron Age is a very exciting prospect and one that we hope to be able to explore in further detail as the New Lights on Old Sites project continues.

If you are interested in lithic analysis and want to find out more, we can recommend the following basic texts:

Flintknapping: making and understanding stone tools by John C. Whittaker

The nature and subsequent uses of flint by John Lord

Prehistoric flint work by Chris Butler

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The pictures within this post are licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.


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Swallowcliffe Down Project

Hello, and welcome to the ‘New light on old sites’ blog where we will chronicle our fieldwork adventures. The name of our project reflects our interest in re-evaluating sites that were excavated/explored early in the history of archaeology that became intrinsic for defining the Iron Age period in Britain (c. 800 BC – AD 43). We are currently looking at Swallowcliffe Down in Wiltshire where many Early Iron Age period artefacts were recovered. The following is an excerpt from our project proposal:

The Early Iron Age settlement at Swallowcliffe Down, Wiltshire, was excavated in the 1920s by Dr RCC Clay1,2. He uncovered a rich assemblage of artefacts including pottery, glass beads, and an assortment of other domestic material. Clay’s technique for finding archaeological features relied on striking the ground and listening for changes in the vibrations, which located a total of 93 pits. Today, we would recognise the pits as only one type of feature that is often present at settlements and we would interpret the finds within them as acts of structured deposition3. However, as the study of the British Iron Age was still in its infancy, Clay recognised that only some of the pits were used for storage, while he interpreted most of them erroneously as Iron Age domestic structures. As a consequence of the ambiguity of the deposits, the material found was considered to be solely the result of domestic life. Due to his excavation methodology and the state of knowledge at the time of these excavations, other, smaller features, such as post-holes for roundhouses or 4-post structures, may well be present on the site, but remain unidentified.

The lack of structural evidence at this site renders discussions of settlement impossible; as a consequence the artefactual evidence has been the focus of subsequent study. This has led to some interesting results. Amongst the material found in pits was evidence for iron smelting, bronze working, and pottery manufacture. Interestingly, the artefactual evidence suggests that there was an exceptional level of continental connectivity. For example, although much of the pottery falls within the Early Iron Age types (i.e. bucket with slightly everted rims) that bear similarity to the All Cannings Cross type, two unusual forms have been suggested to be local copies of continental La Tène types4. In addition, the five glass beads have continental parallels. As settlements within Wiltshire have traditionally been seen within the Wessex hillfort-dominated approach, the range of artefacts and the continental affiliations found at Swallowcliffe Down (a non-hillfort site) suggests that the situation is much more complex, which has wider implications for our understanding of social organisation during this period5.

 

More about our project in the next blog post!

 

Bibliography

1. R. C. C. Clay, An Inhabited Site of La Tene I date, on Swallowcliffe Down. Wiltshire Archaeology and Natural History Society 43, 59 (1925).

2. R. C. C. Clay, Supplementary Report on the Early Iron Age Village on Swallowcliffe Down. Wiltshire Archaeology and Natural History Society 43, 540 (1927).

3. J. D. Hill, Ritual and rubbish in the Iron Age of Wessex: a study of the formation of a specific archaeological record.  (BAR British Series no. 242, Oxford, 1995).

4. B. Cunliffe, Iron Age Communities in Britain: An Account of England, Scotland and Wales from the Seventh Century BC until the Roman Conquest, Fourth Edition.  (Routledge, London, 2005).

5. J. D. Hill, in The Iron Age in Britain and Ireland: Recent Trends, T. C. Champion, J. R. Collis, Eds. (J.R. Collis Publications, Sheffield, 1996),  pp. 95-116.