16 June 2017

Digging Up The Geophysics: Chichester

A couple of years ago, I did some radar surveys in Priory Park, Chichester. After a small test pit dug by CDAS last year, there was an official press release by Chichester District Council, which then led to an awful lot of press coverage (some of them actually managed to spell my name right), and me appearing on South Today briefly. Then this year, there was a bigger excavation run by the council and CDAS that produced even more press coverage. Here are a few more details about it all than you may not have heard about in the press.

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If you look at the above image, the test pit from last year is on the western end of the building marked 'B', targetting the surviving floors, while the larger trench from this year targets the smaller building marked 'C'.

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What is left of the floor fills most of the test pit in the above image, unfortunately with no surviving mosaics. There are walls to the west and north, with a cut representing a robber trench for another wall to the east, over which can be seen part of the remaining floor in the next room

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The above image shows the southern end of the larger trench from this year, looking west. The funny shape of the end of the wall visible in the radar is also visible in plan. The stacks of tile are pilae forming part of a hypocaust heating system, over which would have been an opus floor, part of which is visible sticking out of the baulk at the bottom of the image. That floor, and the pilae, don't appear on the radar data though, so clay products don't seem to have a difference in contrast to the local soil. The building is most likely a small bath house, which despite being built next to the building to the north, is actually attached to the building to the south. This distance is so that if the building goes up in flames because of the under floor heating, the rest of the building is not threatened. Dating seems to suggest a date for the building in the last Roman period.

Congratulations to Chichester on a fantastic dig, and watch this space for more results if they dig more next year.





06 April 2017

NSGG Conference 2016

It's been a few months since the NSGG conference in December 2016, so it's about time I did my usual post about my favourite bits.

Erica Utsi, whose name is on my GPR and is shortly to publish a book recently became a TV star after appearing on a program about William Shakespeare's grave, and given we were a specialist audience rather than the TV viewing public, we got a slightly more in depth explanation of what it was all about, which was that Shakespeare's head may have been nicked due to a fashion for collecting the skulls of famous people.

Adam Booth treated us to some technology not often linked to the sort of geophysics we do, portable x-ray fluorescence, which can be used to identify the elements present in a sample, without having to a lab. His test site was the site of a WWII plane crash. Parts of the plane were visible on magnetometry, so what did the new tech turn up to go with that? In a transect across the site, a spike in copper and zinc from the remains of the plane leaching into the surrounding soil was visible. I've seen a similar talk where the technology was used in industrial sites, where it was suggested that it was useful for identifying prehistoric metal working, which may have been little more than a campfire affair. Always nice to see new tech explained.

My favourite subject, Roman roads, got a mention by Joep Orbons, who had thrown quite a few geophysics techniques (EM, Mag, ER, ERT and GPR) at a section of Roman road in Belgium. The sort of results he got were very familiar to me, with differences in preservation and different soil conditions giving different results of quite a small area, with some techniques (GPR, ER) performing better than others. Sometimes even massive features like this can be hard to find. Not content with one talk on Roman roads, that last talk was immediately followed by Michal Pisz taking about the Roman fort of Tibiscum in Romania with the Roman roads and surrounding vicus being surveyed and excavated.

Already mentioned in this blog, Chris Lockyear has been producing some amazing results on the Roman town of Verulanium here in the UK, with multiple buildings, roads and an aqueduct visible in surveys carried out using ER, Mag and GPR. The preservation is fantastic, and I really hope they find a lot more like it. If you haven't seen it already, check out their blog. Talking of big, pretty surveys, Tomasz Herbich spoke after Chris and has been researching ancient towns in Egypt, with predictably decent results from magnetometry due to the use of fired brick.

H Webber suggested a new avenue of research for archaeologists, using the vast geophysical surveys, such as EM, carried out for the benefit of farmers in modern day precision agriculture. Phosphates present in occupation material may highlight areas of occupation that the archaeological community were not previously aware of. Of course, the farmers would have to be approached in order to get this data, and someone in the audience pointed out that if all of this was explained to the farmers, some of them might deep plough the sites away in order to bring the free fertiliser to the surface.

Petra Schneidhofer gave us a talk about the state of geophysics in Norway and Denmark. Apparently, igneous geologies make our usual favourite, magnetometry, rather pointless, so GPR is commonly used instead. despite that, the natural variation over an area in GPR is quite extreme, and it can be quite difficult to pick out features. Thanks goodness for the boring sedimentary geologies in my part of the world.


All the little geophysical surveys

It's that time of year when the weather is getting a bit warmer and it is time for me to wander once more into the green fields of England, with a machine that goes beep, to find the lost wossnames of times past. It isn't just my own Roman period projects that I work on though, I also do work for various local societies, as many don't have their own geophysics equipment. Here's a selection of projects that I've been involved with recently.

The Pepperpot, Brighton

At the end of Tower Road, Brighton, there is a tower (no surprise there) which apparently used to house pumping equipment for a well that supplied the Attree Villa and estate. There was apparently a water tank and an underground tunnel under what is now the road, and Brighton and Hove Archaeological Society along with the Friends of the Pepperpot asked me to take a look with my radar. There were signs of rubble in the area where the water tank would have been, and very vague signs of the tunnel, but the results weren't all that clear. You can see the full report here.

The interpretation of the GPR survey over an old map of the area around the Pepperpot

Butts Brow Neolithic Enclosure, Eastbourne

Though mostly filled with a combination of car park and a clump of trees, there is a second neolithic enclosure above Willingdon, Eastbourne (the first being the more well known Combe Hill causewayed enclosure). After a season of excavation targetting the surviving sections of bank and ditch by the Eastbourne Natural History and Archaeology Society, I was asked to see if I could find them some internal features to dig up. It's rather difficult to see cuts in chalk with radar, especially with modern tracks and bands of natural flint around, but the ditch was slightly visible as a negative feature cutting through the flint layers. It's the dark band in the image below. The contrast between the ditch and surrounding chalk was very slight though, so smaller internal features were not visible. You can see the full report here and you can see a video of the results here. Details of a dig this summer will be published here at some point.

The neolithic ditch cutting through a band of natural flint

Southborough Post Mill

Just over the border into Kent this time, the Southborough and High Brooms Amateur Archaeological Society asked me to look at a platform in the woods of Southborough Common, the site of a post mill. Geophysics surveys in woodlands are never easy, and while the woods had been cleared, some trees remained. Both earth resistance and magnetometry were used, the results of which are in the channel merge image below. The magnetometry didn't show much apart from a big chunk of metal and some surrounding (no longer visible) fencing, the earth resistance showed a high resistance area on the east side of the platform, which may have been the site of the mill. You can see the full report here.

Earth resistance in green and magnetometry in red.