Buckland Rings, Lymington, Hampshire

Report on Geophysical Survey, April 1993


INTRODUCTION

A geophysical survey was carried out in the interior of Buckland Rings - a 3 hectare later Iron Age hill-fort at NGR SZ 31 96 in the New Forest. The survey was commissioned for the purpose of informing the interpretation and future management of the site, which is in the curatorship of Hampshire County Council and is a scheduled ancient monument (HA 34). The extreme western edge of the fort is occupied by two 20th-century houses with gardens, the remainder is open and under grass. The fortifications consist of two banks and ditches with a counterscarp bank. These are presently fenced off from the interior and wooded, except at the east end where the ditches have been filled in and the ramparts slighted, forming a large break in the otherwise well preserved defensive circuit. The site was partially excavated (see below) in 1935 by C. F. C. Hawkes (Hawkes 1936a).

Geology and soils

The site is situated at 30m OD overlooking the valley of the Lymington River. It is situated on mixed superficial deposits of Pleistocene plateau and river terrace gravels1 (Soil Survey of England & Wales 1983) overlying Tertiary (Eocene) deposits of Bagshot Bed sands (British Geological Survey 1976).

METHOD

Magnetometry was chosen as the most appropriate method of geophysical exploration on the basis of previous successful investigations of Iron Age settlement sites. In this case time limitations also dictated the use of magnetometer survey due to its advantages of speed and ease of ground coverage. The entire area enclosed by the ramparts was covered by the survey except for the areas occupied by the modern houses and gardens. The survey was also extended to the east to cover the degraded eastern defences of the fort. In addition, a large scale area survey of the variation of magnetic susceptibility (MS) in the topsoil was carried out in order to provide information in support of the interpretation of the magnetometer data.

Magnetometry

The survey was conducted over a grid consisting of 30m squares, with grid north aligned parallel to the eastern boundary of Buckland Rings Cottage (see PLAN 1). A Geoscan FM36 fluxgate gradiometer was carried across the grid squares along 30m traverses orientated N-S, spaced at 1.0m intervals. The magnetometer signal (sensitive to changes of 0.1 of a nanotesla) was sampled at 0.25m intervals along each traverse and stored on a portable micro-computer. The resulting reconstructed data is illustrated in raw and enhanced versions in the form of X-Y traceplots and greytone images (PLANS 2 and 3).

Magnetic Susceptibility (MS)

Readings of the topsoil MS were taken at 15m intervals across the magnetometer survey grid using a Bartington Instruments MS2-D search loop connected to a MS2 susceptibility meter. At each station point the sensor was first zeroed in the air, then four successive measurements were taken to produce an average reading for the locality (see PLAN 4) in order to avoid the spurious effects of intrusive ferrous items in the topsoil and poor surface contact.

RESULTS

Magnetometry

Capital letters in bold type refer to anomalies marked in white upper case on PLAN 2.

Features detected by the survey that have an obvious archaeological source chiefly relate to the degraded east circuit of the defences. Two parallel sections of ditch have been located as slight anomalies ( A and B ), at the margin of detectability, in squares 15-16, 23-24 and 31-32. These appear to turn inward at a right angle to form the south side of a deeply inturned entrance corridor up to 75m long ( C ). An anomaly on the west edge of square 09, may represent the opposite side of the entrance approach, in which case a gap in the defences up to 20m wide is suggested. Several intermittent narrower linear features ( D and E ) are also present (in the west of grid squares 09 and 22). These run parallel to and inside the line of the main ditches. That a feature as substantial as a hill-fort ditch is near to the margin of detectability suggests that conditions at the site for magnetic detection of archaeology are poor (see below). A weak horse-shoe shaped anomaly approximately 5m wide at G near the western end of feature C may also be archaeologically significant.

An area of very strong magnetic disturbance at F crossing the line of the eastern defences (square 23) represents a former archaeological cutting through the ramparts no doubt dating from Hawkes's excavations in 1935. Some more localised areas of similar disturbance ( H ) in the interior of the enclosure (south-east corners of squares 03, 08 and 28) can perhaps also be attributed to former excavation trenches or other features of ancient or modern date associated with degraded ferrous material.

With the exception of the above, anomalies that may be related to archaeological remains in the interior are all but absent. Such a lack of anomalies cannot necessarily be taken to imply a genuine absence of archaeological features: soil magnetic susceptibility values (see below) are low and not favourable for the detection of features such as pit fills. Also, smaller features such as post-hole structures are unlikely to be detectable, even in favourable circumstances. Despite the unpromising geophysical evidence, the records of sparse amounts of pottery recovered from excavation suggest that some activity is nevertheless present.

Magnetic Susceptibility

Magnetic susceptibility values are low (range 5-31, mean 16.21 x 10-5 SI Units - volume specific) but the distribution appears to show some patterning. Higher susceptibility values are concentrated in the north-west of the fort and this may suggest increased burning (?settlement) activity in this area or more mundanely a geological transition (perhaps the boundary of the plateau gravel - see above). The area of higher MS does not coincide with anomalous activity in the magnetometer data, but if the source is archaeological activity, previously in-situ features such as hearths could have been destroyed by past cultivation and therefore may only survive as diffused traces in the topsoil. Although both sets of data are not demonstrative for this area, it should nevertheless be considered as potentially archaeologically sensitive. Readings are generally low around the inner ramparts of the enclosure probably due to accumulation of stoney material eroded from the banks or thinner topsoil build up against the banks.

CONCLUSIONS

The results of the survey are of limited value for informing future management strategy for the site. While the survey has sucessfully traced the course of the missing defences, located the position of Hawkes's excavations and partly defined the entrance features, it has not provided conclusive evidence of the nature of the utilisation and occupation of the hill-fort. The results as they stand indicate an absence of internal occupation features, but, given the suspect geological conditions, some uncertainty as to the status of the fort interior must remain.

ARCHAEOMETRY BRANCH,
Ancient Monuments Laboratory,
Science & Conservation Services, RPS.

NOTES

1. Plateau gravel is defined as the denuded remnants of fluvio-marine formations that occur in patches generally forming cappings to flat-topped hills. They are believed to mark pauses in the upward movement and accumulation of flood-plain deposits.

REFERENCES

Hawkes, C F C, 1936a The Excavations at Buckland Rings, Lymington 1935,
Proceedings of the Hampshire Field Club, 13 , 124-64.

Institute of Geological Sciences, 1976 1:50,000 Geological Survey of Great Britain, Sheet 330,331,344,345 - Drift.

Soil Survey of England and Wales, 1983 1:250,000 Soil Map of England and Wales, Sheet 6 South East England.

PLANS ENCLOSED

1) Location of survey (1:2500 scale)

2) Linear greyscale plot of enhanced data (interpolated and smoothed using a 1m radius Gaussian low-pass filter) superimposed on 1:2000 plan of the hillfort (by permission of the controller of the Ordnance Survey)

3) X-Y traceplot and interpolated linear grey-scale plot of raw magnetometer data (1:1000).

4) Linear non-interpolated grey-scale plot of magnetic susceptibility data in locational context (1:2500).

Ordnance Survey maps reproduced under licience from the controller of Her Majesty's Stationary Office, Crown Copyright


Surveyed by: M Cole, A Payne
Date of survey: 23-24 April 1993
Reported by: A Payne
Date of report: 20th August 1993
Plans revised: February 1995
Ancient Monuments Laboratory report number: 80/93


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Paul Linford (P.Linford@eng-h.gov.uk),
Copyright © 1995 Historic Buildings & Monuments Commission for England.