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Project launch
Geophysics surveys
Geological survey Downley Common
Archaeology of Downley Common - photos
Downley School excavation
Bricks and brick-making
Events next in the programme
Art and archaeology on Downley Common
Poetry at Downley School
Maps and archaeology
The 'Big Dig'
Art workshop on Downley Common
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Geophysics surveys
Location: Buckinghamshire
Resistivity
The resistance surveys proved tricky with rain, brambles and nettles growing quickly during the spring and summer! However, the results soon showed two areas that showed good potential to be the site of the kiln with perhaps an accessory building. These features showed up as high resistance signals - because masonry does not conduct the electrical current well. They also coincided with very high magnetometer values.
The first part of Downley Common surveyed with this technique was north of the cricket pitch and is that area indicated on the ancient Manorial Map of 1767 as being the location of the brick kiln, so the evidence at this stage was looking good! Permissions were sought from the County Archaeologist Sandy Kidd, who gave the thumbs up for a series of investigative trenches across the areas that looked positive from the resistance survey and magnetometer results. See the 'Big Dig' page to discover what happened!
After the Big Dig we continued with the resi survey on the south side of the road (adjacent to the cricket pitch, which we named 'Downley Common south'). These results are shown below and indicate substantial archaeology.
The wide linear feature running NW-SE is highly likely to be a Prehistoric land boundary. This could be the Bronze Age-Iron Age Grims Ditch or similar feature, or perhaps Romano-British field boundary.
The thinner dark lines, all marked 'F' are the facilities such as water mains, sewers, etc.
The white lines are the footpaths. Footpaths show up as white areas as they have sparse vegetation or are worn bare, have compacted soil and dry out quicker than adjacent vegetated areas. The paths are therefore very high resistance, which shows up white on the plot.
A document detailing the 'how to do it' of resistivity is available as a word file below, if you would like more information on this topic.
The features of interest are labelled 1, 2 and 3.
No. 1 is a circular feature around 18 to 20 metres in diameter. The northern edge is fairly clear on this plot, but not all the feature was covered in the survey work as brambles, a post and the track get in the way (where the number 1 is positioned).
No. 2 Is a very long, linear feature which is c. 4 metres wide. It is dark in colour and therefore a very low resistance feature. This has caused us much head-scratching, as it mysteriously follows a footpath. However, the footpath cannot be creating the low resistance feature as these are consistently high resistance and much narrower - only half to 1 metre wide. In places, on a good quality printout the white trace of the high resistance footpath can be seen overprinting the wider low resistance feature. The only interpretation for this feature is a wide and deep ditch. In this area these would usually be ancient field or other land boundaries which is enticingly hinting at an Iron Age or Roman-British date!
No. 3 is a much more diffuse feature, very difficult to see on the poorer quality plots of the website image here, but it is circular and around 10 m in diameter. There may be a second one adjacent to it.
I shall be requesting permission to excavate these three features from the County Archaeologist and hopefully the work can start in the spring. Keep looking at the events page to find out when.
 Resisitivity - more about it [29 kb] 
Magnetometer survey
The magnetometer is a very useful machine for finding sites such as kilns. It was therefore essential that we have this machine for the first part of the survey on the north side of the Common in the hunt for the kiln.
Its success is due to the fact that it detects the magnetic properties of the sediments or artefacts below the ground surface. Kilns, due to the extreme high heat processes involved, provide a very high magnetic signal.
The results were largely inconclusive for this survey as there is such a large amount of strewn rubble and metallic items within the soil layers.
However, one area gave particularly high values - and this is, not surprisingly, where the resistibility is indicated a structure beneath the surface.
One of these magnetometer 'hot spots' also coincided with the 1767 Manorial Map location for the kiln which (see the pdf file below for the results).
This area was selected for an exploratory trench during the 'Big Dig' during August 2005. See the Big Dig page to discover what happened!
Magnetometer results, north common [308 kb] 
Magnetic susceptibility
This is an excellent technique for showing where people have been 'active' in an area (see the photo). It does not rely on distinctive features such as walls or ditches, but detects human occupation or activity. They have a poor penetration depth compared to the magnetometer, but usefully show variations in the topsoil.
The technique relies on the fact that materials with a positive susceptibility can become magnetised by a magnetic field. But unlike permanent magnetism is is only measurable in the presence of the magnetic field. When the mag sus instrument is taken over the area to be investigated a value is given. Three readings were taken in a 1 metre square and averaged to give a value for that area of the grid. This showed extremely high values in just one corner of our test area - an area which has been highlighted by the magnetometer and by map research as the potential 18th century kiln site.
Geophysics Workshop
The workshop held in May was very successful. We demonstrated several items of equipment: magnetometers, resistance meters, magnetic susceptibility, gps, as well as the use of the laptop in field processing. Alister Bartlett and Roger Ainsley, both professional geophysicists, undertook the training day.
I have added several photographs from the day's fieldwork which followed our indoor training.
Lots more photographs are can be seen in the image bank under 'Archaeology of Downley Common - Photos'
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