31 March 2012

Latest Results: Rocky Clump

For those of you who haven't heard of Rocky Clump (i.e. not Sussex archaeologists), it's a Roman farming settlement near the city of Brighton that has been under excavation by the Brighton and Hove Archaeological Society for the past billion years (or so it seems). Not quite as rich as a villa, but interesting nevertheless. The site is famous for a vast array of ditches that seem to make no sense, and some sarsen stones in a clump of trees after which the site is named. After several years digging up ditches to the north of the clump, BHAS started digging to the south in 2011. Many, many years ago, I did a large resistivity survey in the south field which showed up a large number of features, which you can see the results of below. Click the image for a larger version.

Whilst there is a lot going on in the image, a lot of it is geological. Readers of this blog may remember a post I wrote about an annoying form of geology known as clay-with-flints. This nasty stuff will make you think you have features everywhere, until you dig them up. There is an upside though. Normally magnetometry will not work on chalk, as there are no magnetic particles in the soil to form a contrasting reading when a ditch cuts the geology. The presence of the clay-with-flints introduces those magnetic particles, allowing magnetometry to work. I resurveyed part of the field today, to see if I could work out which of the features were geology and which were archaeology. You can see the results below.

Just look at all those lovely ditches. There is a small settlement enclosure in the middle, possibly within the corner of a field boundary. The ditch to the north that was visible on the resistivity is also visible on the magnetometry, but the large low resistance area that it passed through is now looking like geology, but I can't be sure about that. Further to the west are three ditches, one of which takes a curve to the south, and a possible east-west trackway formed by two further ditches. Of the two large low resistance features near the clump, the north-west one has transformed itself into a series of small ditch features and is most likely archaeological. The south-east one is a bit of a mess and is most likely geological, but again I can't be sure. There are plenty of dark blobs that represent the clay-with-flints, which stand in stark contrast to the fainter archaeology. One particular faint feature to take note of is just to the north-west of the settlement enclosure. It is about 6m x 4.5m, and could well be part of the settlement. BHAS have stripped the topsoil for a new excavation this year, which shows up well as a giant white reverse L shaped feature.

16 March 2012

Walking Around Your Geophysics Results II

Hello everybody,

Do you remember me writing this long and complicated blog post about how to walk around your geophysics results using a mobile device? Well you can forget about all that. I recently saw this blog post from Google, which suggested that you can now open kml files directly using the mobile version of Google Earth. "That's really great", I thought, "but I wonder if it also does kmz and image overlays?". Well the answer is yes it does! All you have to do is upload your kmz to a website somewhere, then point the browser on your mobile to it, and it will give you the option to load the file using Google Earth.  It may not immediately fly to the file which you have just loaded, but up will pop your image overlay. This is, of course, more awesome than I can properly explain. Thankyou Google, you are the best. That is the killer app I needed for me to buy an android tablet.

09 March 2012

Latest Results: Barcombe

The geophys season has started again, and here are the first batch of results. For some strange reason, I took a week off of work to do this survey. It must be some sort of winter induced madness. I've done a lot of surveying at Barcombe, and this time it is on the site of the Roman villa itself. The villa has already been excavated over the course of many years, but I wanted to see if there was anything else that had been missed, especially as there was an adjacent bath house and Roman road. My thanks go to members of MSFAT for helping out with this survey. Click on the image to see a bigger version.

To get you oriented on what is where, the Roman road runs broadly along where the green line is to the east, and the villa is to the west, with the bath house being in the field to the north, which you can see under excavation on the image. The most obvious features on the results are unfortunately rubbish. The zebra like line is a metal pipe, and the dark blobs are most likely geological. There are a couple of old field boundaries near the centre of the image showing as dark lines, with a paleo-channel in the north east, where the current stream that flows between the fields used to cross directly through the field. Most of the ditches that you can see in the north-west are already known about from the excavations, though there are a few on the periphery which were not excavated. It seems that the original excavation took in most of what was available archaeologically, and there is not additional occupation associated with the villa, bath-house and road, at least in this field.

This survey also shows how magnetometry and resistivity complement each other. The above survey shows the ditches only, whereas the resistivity only shows the walls, as you can see below.