29 August 2011

Latest Results: Pond Field at Barcombe

As part of the Culver Project, I've been working with Rob Wallace to track his Roman road across the fields. We surveyed a new field this bank holiday weekend, and the results are great! The road takes a strange curve, and there is settlement on both sides of it, partly obscured by a metal pipe. The other annoying thing about this metal pipe is that it carries on over the stream to the north, where my nice line of Roman iron-workings has turned into a modern metal pipe with some sections removed. I imagine this was a water pipe that once supplied a trough for animals, as it suddenly stop in the field to the north.

Rob has already dug up a section of the road in this field, and found burning and evidence of industry on site, which is why the ditch features show so clearly. I'm sure Rob will be excavating some more of this at some point, so if you are interested in getting involved, contact him at the Culver Project. Many thanks to Rob, John and my long suffering wife Merryn for helping out this weekend.

26 August 2011

Annoying Geology 1

So there you are, doing a nice little resistivity survey on the chalk hills, and you get this :

Wow, you think. Look at all those lovely features. There must be a lot of big pits there, and so you dig them up... and wish you hadn't. Even as you excavate them, you find what looks like an obvious cut and fill in the chalk, but it is only a ruse, for this is a particular form of geology called clay-with-flints. At one time, there used to be a layer of tertiary geology on top of all that chalk, mostly sandy or clay, for example, The Reading Beds. Most of this has been washed away over time, but some layers are still intact. In other places, these tertiary layers, being acidic, have eaten down into the chalk below, creating pit like features filled with clay and flints, hence the name.

This is of course intensely annoying when you are trying to find archaeology, because these features show up particularly strongly compared to any weaker looking archaeology next to it. This cloud does have a silver lining though. You wont find any features with a magnetometer on chalk, as it can't tell the difference between the soil and the bedrock, but if there is clay-with-flints in the area, the clay in the soil will help show up those cut features. You just have to spot them amongst all of the geology.

I have learnt a fair amount about the local geology from doing geophysics, and I will be sharing some of the quirks in this blog.

25 August 2011

Iron-Age Enclosure?

Let's start the blog off with a pretty picture. I did this survey with the Independent Historical Research Group a while back, and it's been one of my favourite surveys, despite it not being Roman. It was initially spotted by someone from the Hastings group as a crop mark on Google Earth, and as IHRG were already working next door at Bardown, they decided to get permission from the landowner. My initial thoughts from the aerial photographs were that we might have a henge, but that doesn't look like that is the case now we have the geophysics results.

As you can see from the magnetometer survey results, there is a double ditched enclosure, but not perfectly circular as you would expect a henge to be. There is a single entrance to the east through both ditch circuits, whereas you would normally expect two from a henge. The ditch circuits disappear to the south and north as the enclosure is built on an east-west ridge, burying these sections under colluvium. The nice strong readings from the ditches are due to charcoal, which was discovered in the fill using an auger. There weren't any finds on the surface, and no coins found with metal detectors, so probably not Roman, so we are going with Iron-age until it is dug. You can see the full survey report here.

The blog begins

I've been doing archaeological geophysics for a long time now. I haven't had any formal training in it, I just picked it up as I went along. I have bought a TR systems resistivity meter (with tomography kit) and a Bartington GRAD601-2, and I borrow a total station. I'd like to share with you some of the prettier survey results I've had, along with some of the things I have learned about archaeological geophysics over the years, to help those who are just starting to get into the field (pun intended). I will also, of course, be talking about the geophysics software I wrote, Snuffler.