Archaeology in East Oxford

Archive for the tag “geophysics”


We had a great time earlier this week.  We went to the dig at Damerham in Hampshire county, just South-West(ish) of Salisbury – see the website at the Damerham Archaeology Project.  We stayed in a local pub, the Compasses, which was very comfortable and provided good pub grub and coped beautifully with my inability to eat milk products.

The project itself is a community project led by Helen, Chris, Martyn and Olaf; that’s the same Olaf who is the Project Officer with Archeox. Olaf had suggested that we go down with him and have a couple of days down there to see how he’s been spending his summers for that last few years. As it turned out he couldn’t make it: he wanted to leave going down until the fields had been cultivated and that date seemed rather indeterminate.

One of the main reasons behind the Project is to investigate some aerial photographs, which showed some interesting crop marks, and see how they relate to the geophysics and, ultimately, to invasive (excavation) and non-invasive (field walking) techniques. The field walking has to wait until the land has been cultivated (ploughed and harrowed), so that the ground has been churned up and stuff brought to the surface – hence Olaf’s delayed arrival.

Aerial photo of the site at Damerham. NMR 21271/05 © English Heritage.NMR. Photographer: Damian Grady.

Aerial photo of the site at Damerham.
NMR 21271/05 © English Heritage.NMR. Photographer: Damian Grady.

Four trenches had been opened when we arrived as Chris explained after we had introduced ourselves. From right to left, one trench was across the ditch of the larger circular feature to the right, though no one was actually working there at that time. Below that where there was a circular feature joined to an elongated feature, Jack (Helen’s student from Kingston U.) was supervising a small trench.

Jack's trench, down to the chalk, cleaned up but with a lot of sieving to do!

Jack’s trench, down to the chalk, cleaned up but with a lot of sieving to do!

The largest trench had been put going away from the road across the large feature in the middle of the picture and finally, a small trench across the strange double circular feature to the left of the ‘bite’ out of the field, completed the tour.

The longest trench, gently sloping down the hill. More than one ditch in it.

The longest trench, gently sloping down the hill. More than one ditch in it. Lovely weather, too!

The last feature was especially exciting as it is unique in the British Isles, the only other example being in France, in the Pas-de-Calais.

Explanations over, we set to work with Jack, sieving the spoil which had been removed by the opening of the trench. It was interesting to be excavating – well, sieving – in a completely different geology to the one we are used to. Here we were on the chalk, and only about 30-40 cm down we were down onto solid chalk, showing clearly the grooves cut by deep ploughing – though the farmer says they no longer deep plough, so the archaeology might last a bit longer.

The grooves cut by the deep ploughing can clearly be seen in Jack's trench.

The grooves cut by the deep ploughing can clearly be seen in Jack’s trench.

We sieved away all afternoon – found some flint flakes and some pottery; Medieval and earlier (well, really grotty, anyway). The flint was different – given its age and the environment, the surface changes and goes a milky-whitish colour; nothing like the flint we are accustomed to seeing. One has to look for the bulb of percussion (the little bulbous bit where the flint was struck to split it away from the original core) and the remains of the previous flakes on the dorsal side as the surface change tends to disguise the characteristic ripples that we normally see in flints in our neck of the woods. We had a lot of help as some of the volunteers from previous years had brought along their whole families.

Lots of help with the sieving - this was a quiet  moment - while Helen inspects the trench.

Lots of help with the sieving – this was a quiet moment – while Helen inspects the trench.

At the end of the day we repaired to the pub, the Compasses in Damerham, for a serious relax. We were a bit late in on the next day as we went into Fordingbridge, the nearest town of any size, to do a spot of shopping, but arrived on site at about 10. We had a look at the main trench, where it looked like they had found a couple of post holes at the top of the trench.

The two post holes (?) at the top of the main trench - quite busy by the look of it, a lot of tidying up going on.

The two post holes (?) at the top of the main trench – quite busy by the look of it, a lot of tidying up going on.

Helen reckoned after all that sieving we deserved something a bit more interesting, so introduced us to Angela who was supervising the aptly named Angela’s Anomaly (I like the naming of the trenches – no Invisible Archaeologists here). We had a bit of tidying up to do – surprise, surprise – and then Helen suggested we split the ditch into six parts, so we could excavate three, and get a good number of sections.

The ditch with string already to start excavating - not very easy to see the string, but all will become clear.

The ditch with string already to start excavating – not very easy to see the string, but all will become clear.

While doing this we became aware of another difference from previous excavations; we had to ‘small find’ all finds! At least all we had to do was find Sam, Chris’ son, and he came over with a survey-grade GPS to get the location, so we didn’t have to faff around with tapes and a Dumpy level (though I do quite like doing it the old-fashioned way). We also took some soil samples as we went down, at least after we had got through the disturbed layer caused by ploughing. Another warm day so lunch came as a welcome break.

A bit more cloudy today, but still pretty warm.

A bit more cloudy today, but still pretty warm.

Angela had to leave at lunchtime, so I got promoted to (nominal) trench supervisor – I wondered what Olaf had being saying about us! We kept on going down, assisted by Anthony, a very experienced digger who was familiar with chalk environments. I certainly wouldn’t have recognised the lumps of fire-affected flint which he pounced upon; he says he finds piles of them in the the New Forest where they were used to heat water. When you wet the surface you can see the fracturing caused by the thermal shock as the heated stones are put if the cold water, but dry and out of the ground they just looked like little grey pebbles to me. Gill came across a much softer bit of surface, which turned out to be an animal burrow, which after Helen dug around a bit, seemed to have a bottom layer of much darker material, perhaps an organic-rich layer washed in?

The three sections we were digging, the animal burrow is in the top right.

The three sections we were digging, the animal burrow is in the top right.

We weren’t the only ones to find animal burrows – in the main trench, where it was thought there were a couple of post holes it turned out the ‘complications’ were in fact a badger’s set, so a lot more tidying-up to unpick that one.

The animal burrow, a badger's set by the look of the size, which the post holes morphed into.

The animal burrow, a badger’s set by the look of the size, which the post holes morphed into.

At this point we were being helped by a group of artists from the Isle of Wight who were gathering impressions for future work, as well as experiencing excavating. It made for a busy and entertaining trench, though I rather blew it when, getting up to answer two questions at the same time, twisted and did some serious damage to my knee. Just at the end of the day, so I didn’t miss out on too much, but felt a complete idiot as I limped off to the car. Thankfully I could still drive but was really disappointed to have to miss out on Wednesday – we just drove home so I could get my leg up with cold compresses on the knee in hope that I could recover enough for the journey to the Orkneys.

Apart from the disappointing denouement, it was  great couple of days, and a really big thank you to Chris, Helen, Jack and Martyn (in strict alphabetical order) for making us so welcome, and giving us such an insight into excavating a chalky prehistoric site – we hope to be back in the future.

Leigh & Gill


Topographic survey by tractor, etc

Olaf has done had his first stab at doing the topo survey of South Park (see Geophysics at South Park). After having worked out the best way to attach our GPS unit to the tractor –

The GPS unit strapped to the front of the tractor with gaffer tape

Then Olaf pressed the button and off the tractor went, gathering info as it went. The grass was pretty long, as you can tell from the picture Jo sent me –

The tractor in full flight – you can just see (hopefully) the aerial of the GPS device poking up at the front of the bonnet (?, perhaps engine cover) of the tractor.

Gang mowing in action, in the service of archaeology! Olaf had set the GPS to collect data every 1 second, which gave the following set of collection points –

Each green circle represents a sample point.

Which when he had crunched the numbers gave us the following –

The results of the survey.

I’m not quite sure what the drop-outs represent – I’ll have to have a chat with Olaf when he returns from his travels. I do know he plans to have another go when they next mow the park, as they will do it at right angles to the last time, so we’ll get a different set of data-points, which will increase the resolution of the final image.

I had written quite a lot more, but when I tried to save it, I was asked if I was sure I meant to do that (?), and when I said yes – you’ve guessed it – everything I had just typed in disappeared. Thank you, WordPress.

Main point was I’ve finished adding the fields to the Cowley Enclosure map –

All the cultivated areas added to the background details.

I’m now letting my eyes return to normal!

We’ll report on yesterday’s talk on Oxford’s Medieval Farming Landscape and other tings in the next Blog – I will have calmed down by then.


Various Updates

Nothing specific going on, just continuing with this and that, though some interesting stuff has come to light.

First off, Olaf has sent me the following images following on from our morning in South Park.

Olaf’s professionally presented results showing the sample points from when we did the initial test walk. Imagery © Bing Maps/Microsoft Corporation and its data suppliers – this applies to the next 2 images as well.

Pretty slick, eh. Pity it doesn’t reproduce so well at this sort of resolution, though the background image does show up the ridges and furrows rather nicely. I’ve extracted the relevant bit and blown it up a bit – what you are looking at is the processed result of the scan overlayed with a red circle showing each point at which a sample was taken.

The same image, enlarged, so it’s hopefully a bit clearer.

We all did a few back and forth scans, then Olaf did the wander around (this was before opening time, honest!). The next shot is of the processed results, again blown up a bit from the centre of the image Olaf sent me.

The processed results of our wandering around.

The spotty bits are where we bounced a bit while carrying the GPS, but you can clearly see the ridge and furrow – the slightly strange bits at the top right and bottom left are where the software didn’t have enough data to work on and was trying to be creative.

So that was the “proof of concept” trial, and it seems to have worked pretty well, so Olaf went off this morning and met up with Andy to strap the GPS on to the tractor and do the real data collection run. I’ve heard it went OK, and Jo sent me this photo –

The GPS unit strapped to the front of the tractor.

Olaf went back to the gaffer tape, I see – I’m looking forward to the final result, I’m just hoping the tractor didn’t bounce around too much. With no suspension and the bumpiness of the terrain it could be a problem, but we can only wait and see what comes out in the processing.

We’ve also found a lot more about the Enclosure map, or maps. Graeme came across this map http://www.icowley.info/words/15,and started to look into it a bit more. I contacted the web site in question, but they just pointed me at the Oxfordshire History Centre. Graeme eventually found this new map on microfilm at the OHC, which has opened up some new avenues which he and Christopher are looking into. With the help of Carl Boardman, History Services Manager at the OHC, we realised that when the Enclosure award was worked out, the commissioners had their own working copies of the maps, which ended up in London, and are now at The National Archive. They also deposited one copy with the diocese, which is the one at the OHC, and another copy with the parish – this one often got lost. As I said, new avenues to look down.

And talking about maps, the digitising of the Cowley Enclosure map is coming on – I’ve done the rivers and streams, the existing roads (as of 1853) and the roads which were to created after the enclosure, and I’ve made a start on the houses with their surrounding property. Here is a quick glimpse of how far I’ve got.

The whole map.

And a close up –

Temple Cowley

Just as I was about to publish this post, Olaf phoned me up, alerting me to a couple of emails he had sent me about the results of today’s topo survey – they look great – and I’ll do a report about that tomorrow.


Geophysics at South Park

I’ve just got back from a meeting with Olaf & David Pinches at South Park,

South Park, in relation to the rest of East Oxford

where Olaf had arranged to meet up with Chris & Andy from the City Council’s Parks and Leisure Department. Chris (whose background is in archaeology!) is being really helpful towards the project, and has agreed to try a novel form of surveying – we are going to strap the GPS to the side of a tractor so that we can gather a whole load of info while Andy mows the park.

The GPS has a setting whereby you can get it to take readings at specified time intervals, say once every second, so in theory, we could get a complete survey of the park done in the time it takes to mow it. It is going to need a bit of fiddling with the attaching of the GPS to the tractor – the two main problems are going to be vibration, as a tractor has no suspension. The only thing that stops (barely, at that, from experience) the driver getting shaken to death is a sprung seat. The other one is the actual way of attaching the GPS – both Chris & Andy suggested cable ties rather than gaffer tape, which had been our first idea. The main point is avoiding a horribly expensive sound as the GPS drops off and promptly gets mowed, with extreme prejudice!

Olaf is going to meet up again with them when Andy brings the tractor and gang-mower along to have a go at sorting out the practicalities. After they had gone off to carry on working (this is about the busiest time of year for them, everything growing like mad and with the school hols, the parks being used like mad) we had a go at using the GPS in this automatic data collection mode. First we started off by doing an area near where we were (the entrance on Headington Road), all taking turns to do a bit, then we set off up the hill to so some more serious work.

David’s area of interest is (rather imprecisely) Oxford during the Civil War, which ties in nicely with doing a survey of South Park, as there are, hopefully, the remains of the earth-works the Parliamentarians set up to bombard the city which was the Royalist capital. You can see why – you get a marvellous view of the “dreaming spires” up there. After a little confab –

David and Olaf working out which area to walk to get a representative sample.

Dave set off at a brisk pace, walking up and down the hill, to get a mini survey covering a section of the ramparts. In the above photo you can also just about pick out the medieval ridge-and-furrow field system – the yellow Plantain is flowering along the tops of the ridges which you can see stretching diagonally across the photo. Cycling across the park must almost make you sea-sick, the ridge-and-furrows are so well preserved.

David treading boldly!

The purpose of all this hard work was to get some representative samples of the sort that the tractor might gather, so that Olaf can play around with it a bit, to see how it comes out. He is also going to look into if there is any LIDAR data for the park – but it’s a bit random as the main amount of data collection has been by the Environmental Agency for compiling flood-risk maps. Whether areas off to the side get looked at depends on flight paths, which rivers, and streams are their responsibility, and all sorts of other factors, so it’s a bit of a lottery, but worth looking at as the data is very high quality. You can manipulate it in all sorts of ways to bring out detail which might not be noticed under ordinary viewing.

We finished up and I gave David a lift back to Rewley House with the GPS (it packs into a rather unwieldy large red flight case) while Olaf went off to a meeting with Jane.

I’m carrying on preparing for a Test Pit which Gill and I are running, just off Cowley Road, tomorrow and Friday, which I think is going to be interesting – regardless of what finds turn up, the location is in the area of Cowley Marsh. We have been thinking about what precisely “Marsh” might mean. When we did a test pit in the Elder Stubbs allotments we came down onto sandstone after about 0.40 metres which doesn’t seem all that marshy. But do we know it is pretty damp around Bartlemas, so more information is going to be useful. As an aside, I was talking to Christopher Franks, who lives in the Farmhouse opposite Bartlemas Chapel the other day and he says that the trench around the Chapel, which was our “excuse” for last year’s dig there, is a great success. During the downpours earlier on this year, the chapel stayed dry throughout!

I’ll be back with what happens at the test pit this weekend and what Olaf comes up with from the survey.


Geophysics Week

A while ago (apologies for the gap in posts, I’ve been getting my head around a new GIS package, ESRI ArcGIS, and working on the Cowley Enclosure map – more about that in a later blog) Olaf organised a geophysics week. We knew it was in the pipeline, but he has had to do a lot of work behind the scenes to get all the necessary permissions for access; some sites were public recreations grounds and one was a school, so a lot of negotiation was in order.

I missed the first few days as my car had given up the ghost (Oh Woe, Oh decreased bank account)

The first site to be surveyed

Olaf started off by surveying the public recreation ground next to the sports field at Rose Hill Primary School that I talked about in an earlier blog (09 May – Geophysics Weekend) – this was done while I was busy. I met up with everyone after lunch on Wednesday at Donnington Sports Ground.

Donnington Sports Ground (to the west) & Larkrise sports ground (to the East of Iffley road

I found a couple of things had changed since the Geophysics Weekend, both for the better.

First Olaf had sorted out the GPS; it turns out that you have to explicitly log on to the OS network. Survey grade GPS works by being basically the same as your off-the-shelf satnav, but it has a built-in mobile which dials up a network of stations maintained by the Ordnance Survey which give the unit a whole load of extra data to refine the information coming down from the satellites. Why anyone would spend about £12,000 and then not want to log on, which then drops the accuracy back to a £150 satnav, is beyond me – but that’s the way it goes. This was why we were getting such a lot of problems with the GPS on the previous weekend.

The second change was that we have upgraded the gradiometer to the two tube version.

Two tube gradiometer.

This has two advantages – first, the obvious one, is that you collect the information twice as fast, or to put it another way, you walk half the distance to collect the same amount of info. The other is that being quite a bit heavier, it comes with a harness, which makes it a lot easier to use.

So while the gradiometers were settling down (the first thing that happens when we arrive on site is that the gradiometers are assembled and left to come up to ambient temperature) we went and marked up the grid of squares to be surveyed – with the GPS now working properly this is pretty quick; we marked the vertices of the squares with an aerosol as the sports ground is a public space, we didn’t want bamboo sticks sprinkled around (Health & Safety).

We had two gradiometers with us, the upgraded Project one, and another one which we had had lent to us by the Continuing Education department at Rewley House. This meant we were able to run two teams (it takes three people in a team – one to do the actual survey and two others to move the trapeze) so we could really get going! Well, in theory, but as this was a training exercise, not all of us were zipping along at the same speed as Olaf, even when Olaf, David Griffiths and Jane were doing the tricky bits – it’s bad enough doing the grid squares, but doing the odd, non-square bits round the edge need a bit more confidence. You have to have the basics down pat before starting on the bells-and-whistles.

We ran into another problem then, also to do with it being a public open space – a load of guys turned up to use the football pitch. We will have to come back really early to finish off the remaining grid points, though I’m not sure what sort of results we are going to get around the goal posts as the gradiometer is thrown out by large lumps of iron (Olaf said it could have an effect as much as 10m away).

Next day we went off to the Larkrise Sports Ground – this was a different kettle of fish as it was part of (confusingly) Gregory the Great school so we had to sign in and get issued with ID tags – in fact, as we thought we might have some of the sixth-form students coming along, we had to have one person with a CRB (Criminal Records Bureau) check present; though as it turned out, they had something else to do so never turned up.

Olaf left Tim, Steve and I to do the GPS part of the survey – setting up the grid squares – so we each did about 6 grid points each. You really start to get the hang of it with a bit of repetition! I had to shoot off at that point (I was booked in on the next Animal Bones workshop) but Jane arrived just as I left to take over and make up the numbers, so they were going to have no problems with finishing off.

Slightly depressingly, one of Olaf’s next-door neighbours turned up and was telling us that he had planted the hedge and assorted trees around the edge of the field – he said the digging was awful;it looked like the level had been made up with some modern “soil”, so we weren’t at all confident of finding anything. This was a bit of a blow as we knew that this was part of the medieval field system, and I had found a couple of marker stones shown on the Cowley Enclosure map, but with a load of modern stuff laid on top of the older surface, any archaeology was most probably going to be masked.

Saturday turned out to be the last day; Olaf had planned on doing Sunday as well, but it looked like we were going to finish off so he felt like cancelling Sunday and having a bit of a (well deserved) lie-in. I managed to set up the GPS and check if we could set up another grid point – we couldn’t; trees caused me to lose the signal about 6 metres away from the grid point – but it was good experience doing it from scratch on my own.

I did a couple of grids and then I had to do one of these partial grids. Instead of walking the full 30 metres, one stops short at, say, 28 metres, then starts again at 28 metres to go. Sounds simple, but you do have to be fairly confident of walking at a steady pace to do the return walk and get to the end marker at the correct time.

I’ve been chatting to Olaf about getting the results to show here – we’re having problems emailing it (we don’t know which end is limiting the file size) – so I’m going to call it a day now and do another blog when we have managed get the files across, and when I’ve worked out how to display them!

Geophysics Weekend

We have just spent the weekend – well the days, at least! – attending a geophysical survey weekend at Iffley’s Rose Hill Primary School. Olaf Bayer, our project officer, has negotiated permission to do a survey of the playing field at the back of the school, and decided to use the opportunity to familiarize more people with the kit involved.

Location of Rose Hill Primary School

He intends to start a programme of doing surveys on as many of the open spaces as he can get access to, and this weekend was a start on building up a team to carry out the work. We turned up on Saturday morning, being really thankful for the fact that it wasn’t raining (after all, we do have a hosepipe ban), though up on the top of the hill, with allotments to one side (North West) and a recreation ground to the East, the wind cut right through us – and in the morning it was bitter.

The kit all laid out, gradiometer out of its box, signing-in sheet ready for action, with our wellies, lunch etc.

Olaf started off, after the obligatory signing-in and confirmation of having read the Health & Safety info (easy to take the mickey about, but not so funny when things go wrong), by explaining about the preparation needed before we started doing any geophysics and the equipment we would we using. Initially we got the piece of kit – the gradiometer – out of its box to settle down to ambient temperature, and then he started to talk about the need for laying out a grid. This is laid out in squares of 30 metres a side over the area to be surveyed – the size of the squares being a compromise between large (less faffing about surveying but bigger gaps fitting the squares into an irregular shape) and smaller (more surveying, more turning around and toing-and-froing during the survey but fewer gaps around the edges of the survey). We needed to lay it out accurately in the sense of accurate squares (obviously) but also in terms of position as we want to extend the survey into the recreation ground to the East of the Primary School – it’s separated by a tall, painted steel fence – and we need to be able to marry up the future survey with the one we’re doing this weekend.

The area we could survey in and a rough idea of where the grid was laid out

The idea was to use the projects survey-grade GPS (it’s like a sat-nav but works to centimetre accuracy, instead of the 3-5 metre accuracy of your normal off-the -shelf device – you pay a fortune for the precision, though) to fix the points where the squares meet. Not all of them, just along two lines at right angles to form a cross, and then use tapes and ranging rods to fix the other points from that base-line. The GPS has a neat facility where you can input the co-ordinates in the comfort of your own home or office, and then it’s just a matter of selecting the right co-ordinates and up pops a screen like this:-

Screen on the GPS device

The two arrows on the right of the screen show how far – in metres –  that you have to move the device to get to the exact position that you had earlier keyed in, get the numbers down to the sort of precision you are interested in and there you are; change to a different Point ID and do the next position. The trouble was the numbers kept on jumping around, even when we held the device totally still! At first we thought it was because we were right next to a big sycamore – survey-grade GPS relies on a direct line-of-sight link to the various satellites – its major draw back; but when we had done four positions in a line, we noticed that they were definitely not in a line! Much head-scratching and re-checking ensued. Olaf has used this sort of kit a lot, and has never come across this sort of problem, but he said he has never used this particular make and model before. I think it’s down to the perennial problem with modern technology, the more functionality you pack into one device, the more details you have to get spot-on or you get problems down the line; and I think we have all had experience with struggling to wrest information from manuals. So we decided to cut our losses and go back to the old way of doing it – tapes, right-angled triangles and using an optical square and Olaf would sort out the device at a later date.

It was the first time any of us had come across an optical square; a little hand-held optical device for locating you on a straight line between two points, and then working out a right angle from that base-line (you can get some more details about the principles involved here). But first we had to establish straight lines which we did by sighting along the ranging rods and using tapes to work out the 30 metre grid points. We then used a combination of the optical square and good old Pythagorus (3-4-5 triangles, and a new one Olaf told us – if the two sides are 10 each, the hypotenuse is 14.14) to lay out the complete grid. If it looks like there are a lot of gaps from the diagram above, it was because there was a lot of rough ground around the edge of the playing ground proper, as well as a small pavilion and some vegetable beds planted out (I don’t think we would have been flavour of the month for stomping over them in our wellies).

After a break for lunch and, more importantly, something warm to drink, we started on actual surveying. First we had to divest ourselves of anything ferrous; the gradiometer is incredibly sensitive. It works by detecting tiny variations in magnetism so anything magnetic near it throws out its data; so no zips, eyelets, metal buttons, watches, mobiles, steel-toecaps, etc.. It basically means wellies, track-suit bottoms and tee-shirts – though Olaf had some waterproofs he has customized by cutting out all the zips and other metal work and then sewing in Velcro. The sensitivity is why we had to take it out of its case to settle down and why it has to be calibrated – the tube which you can see in the photo has a magnetometer at either end.

Calibrating the gradiometer

By subtracting the reading from the one at the bottom of the tube from the reading from the top one, you “edit out” the effect of the Earth’s magnetic field and are left with any magnetism caused but stuff buried in the ground; archaeology hopefully but just as probably services, old nails or any old iron. To do the calibration Olaf had to wander around a lot to find a relatively “clean” area – a place with as little magnetic noise as possible; you can set the device so it beeps when the magnetic field changes so you aim for as quiet an area as possible. Then you go through a routine of facing the points of the compass and turning the device upside-down (basically you are following the instructions  on the screen that you can just see being peered at above). Once it is calibrated we were almost ready to get stuck in – just one more thing before we started; we all had to checked to make sure no stray ferrous items had crept in by accident!

Queuing up to be checked for unknown metal bits

Then we could start. The basic procedure is that one has to walk up and down in lines in the 30 metre square, a metre apart at a time until the whole square has been covered. To make this easier, we use a “trapeze”; two poles with holes a metre apart through which are threaded cords 30 metres long – you can see where the name trapeze comes from – and the mid-point of each pole is marked with tape. Then, on opposite sides of the square we stretch measuring tapes which have marks along their lengths at every other metre. You lay the trapeze down lined up with marks on the tape, the operator walks up one cord then back down the other one, the trapeze is moved up to the next mark, operator walks up the cord and so-on. The cords have marks every metre and the gradiometer beeps every metre so that when you are the operator, you aim to get the beep happening when the tube is directly over one of the marks; you set the device with a speed you are comfortable with for that to occur – fast for Olaf and embarrassingly slowly for the rest of us.

Gill taking readings – you can see the trapeze (the blue cords) with the spacing pole at my feet in the distance. Thanks to Olaf for the photo.

You would think that just walking up and down a laid-down cord at a steady pace would dead easy, wouldn’t you? Just goes to prove that you have to try something before you can pass judgement. It really does take a bit of getting used to – quite a bit of deleted and repeated lines, and later on in the day Olaf stepping in finish in a reasonable time! We did the southern most three squares (North is at the top in both maps, sorry Jane, as usual I’ve forgotten to put in the North arrow) on Saturday and finished off the rest on Sunday. At the end of the day on Sunday, Olaf got out his laptop and did an initial pass through the data we had collected – a fairly obvious services pipe at the North end of the field and some rather symmetrical oddities dotted around – but at first glance, no henges! Early days, though, and a valuable learning exercise for all involved – a big thank-you to Olaf for being so patient with us, especially as he is more used to the speed at which the pressures of commercial archaeology force one to. I know Gill and I are both looking forward to putting our experience to use in the future.


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