25 October 2011

Latest Results: Steyning

Working on the theory that large scale Roman occupation is common where Roman roads cross large rivers, I worked with the Independent Historical Research Group to try to find such settlement where the Sussex Greensand Way crosses the River Adur. Initially, to the west of the river, the results were promising. The magnetometer showed some Roman settlement next to the road, but the road was 80m north of where it was supposed to be. The red line shows Ivan Margary's course for the road, with the corrected line shown in green. The strange course for the road may have something to do with the steep slope that the road climbed up.

We were looking for something more substantial though, and there was plenty of pottery on the other side of the river, where the ground was not as steep. Unfortunately, due to very heavy contamination with metal, the area on the east side of the river was a complete mess on the results, so the Roman remains here will remain a mystery for a while longer. The plot is below anyway. Eeewwwwww! You can see the full report here.

13 October 2011

Magnetometry Junk

Interpreting geophysics results is like sorting wheat from chaff, and you have to be able to recognise a lot of different chaff, otherwise you end up digging it up. A while ago, I had the dubious fortune of surveying an area that contained pretty much all the types of chaff you are likely to come across in a magnetometry survey. The site is in a valley that runs roughly north-south down the centre of the image.

A is the actual archaeology we are looking for. It's a small Roman period iron bloomery that was excavated by Henry Cleere in the 1960's*.

B is a water pipe. An off-shoot of this leads to a water trough. These are easily recognised by their stripey character and high readings.

C is an electricity cable, leading to the house at the northern end.

Covering the survey are are land drains, such as at D. They are generally ceramic pipe, and help drain the land of excess water. Modern land drains may be plastic and less easy to spot.

Just to the right of E is a small feature, half black and half white. This is known as a dipole, and is generally indicative of modern metal junk. You tend to get these more on arable land as bits break off tractors as they work.

F is a plastic pipe dug into the centre of the valley to take the small stream underground. Whilst the magnetometer does not pick up the plastic, it does pick up the cut into the underlying geology in which the pipe sits.

Just in the corner at G, we surveyed close to the metal fence. Fences tend to show up as negative readings.

The two blobs at H are actually down to the landowners landrover pulling up as I neared the end of the survey line. Be sure to make a note of such things as you survey, otherwise you might mistake them for features

*Cleere, H.  The Romano-British industrial site of Bardown, Wadhurst. Sussex Archaeological Society occasional papers no. 1

12 October 2011

Writing a Geophysics Report

Compared to excavation reports, geophysics reports are really quite simple, and fairly quick to write. If you were to look at standard grey literature geophysics reports, it may seem otherwise, for two reasons. Firstly, commercial units like to pad out reports with unnecessary waffle, to make the customer feel like they are getting their money's worth. Much of this will be copied and pasted between reports with little alteration. Secondly, geophysics reports may also include a wider desk-based evaluation of the surrounding area as part of the contracted work, which may not be necessary otherwise. So what is the minimum required of a geophysics report? Here are a few things to include :

  1. A bit of background about what is already known about the archaeology of the site, and why the survey is being undertaken.
  2. A short statement about the equipment used and how it is being used.
  3. Notes on the positioning of the survey grids, in such a form that those grids can be re-established by someone else.
  4. A plot of the results.
  5. Interpretation of those results.
After you have finished your report, what do you do with it? Giving a copy to the landowner is always a nice thing to do, as well as the county archaeologist (if you are in the UK) or equivalent in your country. There are several options if you want to publish your results in some way. Local archaeological societies will be quite happy to publish surveys in their area in their newsletter or journal. Some of the larger county or national journal may not be interested in pure geophysics in their own right, and will probably charge you for the privilege if they do. The other option is to publish on-line. I use a site called scribd, which allows sharing of documents on the web for anyone to download. You can see a list of my already uploaded reports here, which will give you some examples of geophysics reports if you intend to write one yourself.