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Archived News ~ Week ending Friday 19th March 2004.
Ladybridge Farm Evaluation - Soil Resistance Survey
A recent soil resistance geophysical pilot study demonstrated that resistivity is a more effective geophysical technique than standard magnetometry in defining buried archaeological features at Ladybridge Farm (see archived news, 12th March 2004). Subsequently, it has been decided to undertake a soil resistance survey, as the favoured geophysical technique, in the southwest field of the evaluation area, which until recently had been inaccessible due to the presence of a beet crop. The survey was undertaken within two 30metre wide transects (one north-south, one east-west and crossing one another), representing a 20% sample of the field and maximising the likelihood of identifying buried boundary features.
Little archaeological information existed for this part of the evaluation area which represents approximately 10 hectares. Due to the presence of a beet crop, no fieldwalking has as yet been undertaken in the field. The existence of two linear cropmarks plotted from aerial photographs provided the only background information for the geophysical survey.
The soil resistance pilot study was carried out using a RM15 advanced soil resistance meter fitted with a multiplexer and multiple probe array. The survey methodology was identical to that used for the pilot study producing two sets of data, a high resolution image of shallow soil resistance features, and a lower resolution image of deeper features.
Once again, the two data sets produced similar results suggesting that most of the features are relatively deep. The results of the survey were, however, disappointing compared to those of the pilot study areas, although it was noted that the topsoil, and possibly the underlying geology, were harder since the topsoil at least appeared to contain a higher proportion of gravel.
Results of the high resolution 0.5m probe survey
Results of the low resolution 1.0m probe survey
A group of low resistance features defined in the northern part of the survey area formed the most convincing features of possible archaeological origin (see interpretation plan, below). A broad east-west linear feature with an intersection, together forming a Y-shaped anomaly, may well represent the buried remains of a former boundary or enclosure, although the possibility that this anomaly represents a relatively recent field drain should not be discounted. The northern half of the survey area contains a number of high and low resistance anomalies that may indicate archaeological activity.
It is interesting to note that the cropmark identified by aerial photography was not defined by the soil resistance survey. However, the alignment of the cropmark within the survey area corresponds with the eastern side of the possible palaeo-channel which suggests that, in some cases, cropmarks may represent a change in the underlying geology or the edges of large natural features rather than archaeology.
The most striking feature defined by the survey is a 10 to 20metre wide curvilinear anomaly running approximately north-south through the survey area. This apparent feature may be caused by variation in the underlying geology, such as a band of gravel, although it is equally possible that it represents a former watercourse or palaeo-channel.
The results of this survey have been used to agree a scheme of evaluation excavation for this area including hand-excavated trial pits to detect lithic distributions within the topsoil, and a series of evaluation trenches to identify and characterise any archaeological remains within the area.
Interpretation of the survey results