Author : Dan Boddice B.A. M.Sc.
Client : St Bartholomew's Church, Wilmslow
Report Reference : DB2010.1
Date of Report : November 2010
1. Summary
1.1.
In May 2010, a survey was carried out using ground penetrating radar (G.P.R.) over the parish church of St. Bartholomew’s in Wilmslow, Cheshire, in order to map subsurface features under the floor, both for archaeological interest, and to inform later planning decisions. The survey was to a degree successful in locating a number of features, both archaeological and modern, with interpretations being aided by recent excavations in part of the church. Below are detailed images of these anomalies, along with suggested about what each anomaly may represent.
1.2.
This report has been written to English Heritage guidelines (David et al. 2008).
2. Introduction
2.1.
St. Bartholomew’s church is located in the town of Wilmslow (Grid reference SJ848814. See fig. 1), about 10 miles south of central Manchester , 40 miles north-east of Chester and 1.2 miles south of the county boundary with Greater
Manchester. To the north-west of Wilmslow is the massive conurbation of Manchester, to the east are the foothills of the Pennines, while to the south and west is the Cheshire Plain.
The church is built on a hill, rising above the River Bollin, which flows to the North
2.2.
of the churchyard.
The earliest documentary evidence for the church is dated to 1246, although the ongoing church project by Wilmslow community archaeology has shown a number of different stages in the construction of the church. Although work has been carried out throughout the 19 th
and 20 th
century, much of the original church’s structure is still present in the current structure. The building is currently a grade I listed building, and remains an active Anglican church, holding regular services. The church contains a number of items of furniture, many of which are fixed or built into the church’s structure, which present considerable challenges to surveyors. For this

reason a strategy using a number of irregular shaped areas as opposed to a usual grid or transect approach was employed to obtain the maximum amount of data.
2.3.
The geology of the site consists primarily of sandstone with drift geology of glacial sand and gravel (www.bgs.co.uk and fig. 2) which has low signal attenuation rates due to its low conductivity and water content. This allows a deeper penetration of the signal. The floor of the church itself is constructed from ashlar buff sandstone.
This material is not known to display any major impedance to the passage of the electro-magnetic signal, but should display a significant contrast in comparison to the sandy subsoil and air spaces due to its higher density. Greater signal attenuation may occur due to the proximity of metal objects both in the church floor and in the surrounding furniture, which cause strong signal reflections, and prohibit the passage of radar energy.
3. Aims of the Survey
3.1.
The aims of the geophysical survey were

To locate voids under the church floor which may be indicative of graves or other features of archaeological interest

To find modern heating pipes and features
4. Methodology
4.1.
The site was surveyed during May 2010 by Dan Boddice from the University of
Bradford, assisted by a team of local volunteers from the Wilmslow community archaeology group in a level 2 survey (IFA-Gaffney et al. 2002: table 2). Ground penetrating radar (G.P.R.) was used, as the only geophysical method capable of penetrating the sandstone floor to reveal subsurface information, with other methods being deemed unsuitable for the site.
4.2.
Due to the unusual shape of the survey area, and the presence of several items of immovable furniture, which presented considerable challenges to conventional grid based survey techniques, the survey was conducted by dividing the church into a series of areas shown on figure 3. Each of the areas was surveyed separately using different traverse directions and collection strategies which are discussed below.

Area 1: The Bell Tower
Instrument Sensors and Software pulse Ekko1000
Antenna Peak Frequency 450MHz
Stacking 8
Traverse separation 0.5m
Traverse Length
Traverse direction
4m
West-East
Collection Method
Collection Mode
Area 2: Back of the Nave
Parallel Traverses
Continuous
Instrument Sensors and Software pulse Ekko1000
Antenna Peak Frequency 450MHz
Stacking
Traverse separation
Traverse Length
8
0.5m
12m
Traverse direction
Collection Method
North-South
Parallel Traverses
Continuous Collection Mode
Area 3: Main Nave
Instrument Sensors and Software pulse Ekko1000
Antenna Peak Frequency 450MHz
Stacking 8
Traverse separation
Traverse Length
1m
13m
North-South Traverse direction
Collection Method
Collection Mode
Parallel Traverses
Continuous

Area 4: Hawthorn Chapel
Instrument Sensors and Software pulse Ekko1000
Antenna Peak Frequency 450MHz
Stacking
Traverse separation
Traverse Length
Traverse direction
Collection Method
Collection Mode
8
0.5m
3.2m
East-West
Parallel Traverses
Continuous
Area 5: Jesus Chapel
Instrument Sensors and Software pulse Ekko1000
Antenna Peak Frequency 450MHz
Stacking
Traverse separation
8
0.5m
Traverse Length
Traverse direction
Collection Method
Collection Mode
5.7m
East-West
Parallel Traverses
Continuous
Area 6: Chancel
Instrument Sensors and Software pulse Ekko1000
Antenna Peak Frequency 450MHz
Stacking
Traverse separation
8
0.5m
4m Traverse Length
Traverse direction
Collection Method
Collection Mode
East-West
Parallel Traverses
Continuous

Area 7: Booth Chapel
Instrument Sensors and Software pulse Ekko1000
Antenna Peak Frequency 450MHz
Stacking 8
Traverse separation 0.5m
Traverse Length
Traverse direction
10m
East-West
Collection Method Parallel Traverses
Collection Mode
Area 8: Altar Step
Instrument
Continuous
Sensors and Software pulse Ekko1000
Antenna Peak Frequency 450MHz
Stacking
Traverse separation
8
0.5m
Traverse Length
Traverse direction
Collection Method
Collection Mode
5.6m
South-North
Parallel Traverses
Continuous
5. Processing and Display
5.1. Results from the G.P.R. data were processed using Reflex W, published by
Sandmeier Scientific Software. The following methods were used.

Rubber Banding

Dewow

Move start time

Bandpass

Background removal

Gain

Running average
Images from the G.P.R. were processed and provided as timeslices which are displayed in figures. A more complete discussion of these processing steps is provided in
Appendix 1.

6. Interpretations
These interpretations should be studies in conjunction with figures(). A diagram of all the archaeological and possible archaeological anomalies is shown in figure ().
Area 1: Tower
A.
Rectangular anomaly showing a significant contrast in relation to the background. Its proximity to the door suggests that this is caused by part of the subsurface foundation structure for the door arch. This seems to suggest that either the West door was rebuilt at some stage in the church’s history, or that a structure was located in front of the doors current location
B.
Shallow low reflection anomaly that is roughly rectangular in shape and close to the
South wall of the tower.
C.
Area of ill defined noisy responses, which show a mixture of high and low reflections at a wide range of different depths which are not easily interpretable but may relate to a subsurface feature. The lack of a clear archaeological shape means this is uncertain, and they may relate to noise caused by local electrical cables.
D.
Relatively deep low reflection feature suggesting a lower density than the surrounding material located roughly in the centre of the tower area. Excavations suggest that this may be the response cause by the previous font location.
Area 2: Back of the Nave
E.
Modern disruption to the survey caused by the location of the current stone font causing an absence of data at this point
F.
Rectangular anomaly showing running in the direction of the aisle. Excavation data from the church would suggest that this is a linear void which runs the length of the aisle. The void is also bordered by strong reflections (G)
G.
Strong reflections forming a roughly rectangular shape around anomaly F. These are most likely to be the walls at the sides of the void which support the floor.
H.
Very large area of low reflection at the greatest depth extent of the survey. The anomalies clear rectangular shape seems to match with the area of the wooden floor

and is likely to have been caused by the different dielectric properties of the wood in comparison to the sandstone
I.
Very large area of low reflection at a great depth, which is very similar in nature to anomaly H. It shows a slightly more irregular L shape which again seems to match the area of the wooden floor, and its cause is likely to be similar to anomaly H.
J.
Noisy response which is most likely to be caused by an electrical wire or metal pipe running along the West wall of the church. The response obscures any other features in this area
K.
Strongly reflecting Semi-circular shaped anomaly, parallel to anomaly L and showing a greater density than the surrounding matrix. It is possible that these two features are walls surrounding a less dense void, although this is uncertain, and the anomaly may simply be part of the support structure for the floor
L.
Strongly reflecting semicircular shaped anomaly, parallel to anomaly K and of a similar size and shape. It may be a buried wall feature or part of the floors support system.
M.
Anomaly roughly the same shape and size as the roof support pillar. It is almost certainly part of the foundations of this pillar.
Area 3: Main Nave
N.
Noisy response, possibly caused by ringing from a metallic response running parallel to the front of the nave. This is most likely to have been caused by a linear metal feature, and in the context, it is most likely to be one of the churches heating pipes.
O.
Very strong and noisy reflections which almost certainly result from nearby metallic objects. The most likely cause for this anomaly is the pipes which supply the radiators. The anomaly obscures any more subtle archaeological anomalies which may exist in this area.
P.
Possible archaeological feature showing as a sub-circular anomaly on the deeper time slices. This may be either a plinth, similar to those seen on the excavations, or part of the floor support system.
Q.
Possible archaeological feature, similar in shape and nature to anomaly P, and showing at a similar depth. This may be either a plinth, similar to those seen on the excavations, or part of the floor support system.

R.
Another roughly sub-circular anomaly, with possible archaeological origins but shallower than P and Q. This may be either a plinth, similar to those seen on the excavations, or part of the floor support system.
S.
Another anomaly with possible archaeological origins but more rectangular than P, Q and R. It is most likely to be a wall round the aisle void, similar to G at the back of the nave, although it may also be part of an archaeological feature.
T.
Unknown reflective anomaly which may be caused either by a floor support foundation feature, or a plinth. It is similar to anomalies P, Q, R and S
Area 4: Hawthorn Chapel
U.
Reflective anomaly forming a U shaped feature. The shape of this feature may suggest a wall surrounding a void feature although this is far from certain.
V.
Two reflective anomalies which are most likely to have been caused by parts of the churches foundations and floor supports.
Area 5: Jesus Chapel
W.
Metallic anomaly caused by a metal grill in the floor.
X.
Faintly contrasting rectangular shaped anomaly showing on depth 2 time-slice. The cause of this anomaly is unknown. It is possibly that these are either the walls of a buried void or part of the floor support structure.
Y.
Sub rectangular reflective anomaly showing at a substantial depth (25-30ns). It position in the centre of anomaly V may suggest a relationship with this feature and it is possible this represents a burial plinth, similar to those found during the excavations, although this is far from certain.
Z.
Very strong reflection which is likely to result from the presence of metal. Its proximity to the north wall of the chapel suggests that it may be part of a modern pipe system.
AA.
Linear metal response running north-south and showing a very strong reflection. This is almost certainly one of the pipes using in the churches heating system

BB.
Sub-circular reflective anomaly which is most likely to part of a foundation or wall support
Area 6: Chancel
CC.
Highly reflective interface with no clear shape or archaeological pattern. This is most likely to be part of the floor support structure
DD.
Highly reflective interface with no clear shape or archaeological pattern. This is most likely to be part of the floor support structure
Area 7: Booth Chapel
EE.
Area of noise. This is most likely to be the result of a metal response, possibly caused by brass on one of the tombstones in the floor.
Area 8: Altar Step
FF.
Low reflection anomaly which is roughly L shaped, with one part of the anomaly going in the direction of the crypt before disappearing from the image. The anomaly is located in the centre of the altar step, in front of the altar on the deeper timeslices.
The precise cause of this anomaly is unknown, although it seems to represent a less dense medium than the surrounding matrix.
GG.
Strong reflections which seem to show no clear archaeological patterning.
These seem most likely to have been caused by an electrical wire or similar modern source.

7. Conclusions
The survey was successful in locating a series of different subsurface features in the church floor, including modern heating systems, possible coffin plinths and possible foundation structures. However a combination of factors, including electrical interference from nearby wires and nearby furniture, has meant that the data is difficult to interpret, with a combination of modern and archaeological effects combining to produce highly complex responses. The use of previous excavation data has been used in order to allow interpretations to be made with a greater degree of accuracy and the results are displayed above. It is recommended that future work on the church build should avoid those anomalies with a suggested archaeological provenance.
Further information on the subsurface features of the church may be possible by conducting a further survey using an antenna with a lower peak frequency. This will allow a greater depth of penetration, albeit with a loss of resolution, particularly at greater depths. The nature of the church and its furniture however may make such a survey difficult, due to the increased size of low frequency antenna.
8. Statement of Indemnity
8.1.
Whilst every effort has been taken to provide an accurate interpretation of the geophysical anomalies in an archaeological context, it should be noted that archaeological features may be undetectable and interpretations provided are a subjective assessment of the data. All interpretations are supplied in good faith and in compliance with professional standards, and the author takes no responsibility for errors of fact or opinion resulting from data supplied to a third party, or their consequences.

9. Acknowledgements
9.1.
Special thanks go to the University of Bradford for the use of the G.P.R.
Equipment and to the volunteers of Wilmslow Community Archaeology for their assistance during data collection
9.2.
Maps are reproduced from Ordnance Survey material with the permission of
Ordnance Survey on behalf of the Controller of Her Majesty’s Stationary Office
(Crown Copyright). Unauthorised reproduction infringes Crown copyright and may lead to prosecution or civil proceedings.
10. Bibliography
Conyers, L. 2004. Ground Penetrating Radar for Archaeology . Lanham: Altramira
David, A. P. Linford and N. Linford . 2008. Geophysical Survey in Archaeological Field
Evaluation , English Heritage Research & Professional Services Guidelines No. 1, English
Heritage, London.
Gaffney, C., Gater, J. and Van Ovenden, S. 2002. The Use of Geophysical Techniques in
Archaeological Evaluation . IFA technical paper
Jol, H. M. 2009. Ground Penetrating Radar: Theory and Applications . London : Elsevier
Science
11. Figures
11.1 List of Figures
Figure 1: Location of the Survey
Figure 2: Geology map of the survey area
Figure 3: Areas of the Survey
Figure 4: Time-slice 10-15ns window
Figure 5: Time-slice 15-20ns window
Figure 6: Time-slice 20-25ns window
Figure 7: Time-slice 25-30ns window
Figure 8: Time-slice showing the back of the nave 30-40ns window
Figure 9: Interpretation plan of the anomalies

Figure 1: The location of Wilmslow

Figure 2: The geology of the Site

Figure 3: The Areas of Survey

Figure 4: Time-slice 10-15ns window

Figure 5: Time-slice 15-20ns window

Figure 6: Time-slice 20-25ns window

Figure 7: Time-slice 20-30ns window

Figure 8 : Time-slice showing the back of the nave 30-40ns window

Figure 9: Interpretation Plan of Anomalies

Appendix 1: Processing Steps
Ground Penetrating Radar Processing Steps
Further details of these methods are described by Conyers (2004) and Jol (2009).
Processing Step Description
Bandpass A combined high and low pass filter which filters out undesirable
Background
Removal frequency “noise” from outside the antenna’s peak frequency
Removes horizontal “banding” effects caused by naturally occurring interfaces and “ringing”.
Dewow Removes the bow in the received signal baseline resulting from electrostatic and inductive fields decreasing the time variation in response.
Counters the effects of attenuation of the signal from deeper traces and Gain allows deeper traces to be emphasised and become more visible
Move Start Time Removes the fast travelling airwave component of the signal and makes the top of the radargram equate to the interface with the earth.
Rubber Banding Corrects the different number of readings between fiducal markers due to inconsistencies in transect speed and located traces horizontal position correctly
Running Average Averages and smoothes out reflections measured along the traces by combining a series of traces arithmetically

Appendix 2: Interpretation Categories used
GPR responses are produced by differences in the amount of the wave which is reflected over different surfaces. Dense materials display as high reflections. These include features such as walls and stone floors. By contrast, less dense materials or voids reflect less of the
Electromagnetic wave and show as lighter low reflections. These include features such as metal. An additional complex response can be observed if the wave makes contact with metal as the wave cannot pass through the material and is rapidly attenuated. This creates a series of strong and weak reflections which continue below the object (known as ringing).
The length of time for a reflection to reach the receiver antenna is related to the depth of the interface. These interfaces have been divided into a number of different depths displayed on the figures. The interpretation categories used are discussed below.
Interpretation
Category
Archaeology
Explanation
Archaeology?
Responses which are almost certainly archaeological in nature, because of a combination of their strength, shape and patterning
Responses which have a possible archaeological origin but their identification is far from certain
Metal response A response characteristic of a metallic object causing rapid attenuation of the signal and a “ringing” effect in the profile. These may or may not be part of an archaeological feature and further identification is given in the discussion
Unknown A response which clearly stands out from the background but cannot be said to be clearly modern or archaeological in nature and may result from either of these causes.
Modern/Structural a response which is likely to have resulted from a modern feature, part of the churches structure or a piece of furniture causing distortions or attenuation of the signal
Electromagnetic
Noise
Responses from nearby sources of electricity such as wires and cables which emit electromagnetic causing spurious responses as it is picked up by the receiving antenna

Appendix 3: Instruments Used
Sensors and Software Pulse Ekko 1000 G.P.R.: This instrument is a modular system consisting of both a transmitting and receiving antennae linked to a laptop via a console which controls data collection. Interfaces in the ground produce different reflections of the electromagnetic waves and the time for these to return is logged in a digital format.
Positioning along the trace is recorded using a trigger system and fiducial marks (Conyers
2004, 83). A 450MHz antenna was used for this survey, as it was thought to give enough depth of penetration, while still providing adequate resolution to see small features, as well as being small enough to manoeuvre around tight spaces.
The existence of a reflection depends upon the physical properties of the reflecting material and the contrast, if any with the surrounding materials. Responses from materials such as metal are extremely intense whereas other materials such as stone and sand are less strong.
Any material is only visible if it displays different geophysical properties to the materials which surround it. The presence of furniture may also have had a significant effect on the signal, causing distortions in the reflection and attenuation of the signal, which creates responses which are complicated to interpret.