In defence of geophysics

You never know what’s going to catch journalists’ imagination – no matter how hard you try to direct attention to the stories you’d like them to publicise. The new British Archaeology, which hit the shops on Friday, features the Crosby Garrett Roman helmet on the cover. And inside is a great piece on the find, with new information and new photos – and much else besides.

But it is a footnote to a reader’s letter that became a story in today’s Mail on Sunday (and thence to Radio 4’s Broadcasting House, courtesy of a rather confused Sister Wendy Beckett). This shouldn’t get out of hand, so here is the background.

We heard in June from the University of Birmingham that a new feature had been discovered near Stonehenge in a geophysics survey. It was puffed up (something we all might have done with such a find), but as I wrote twice at some length, here and on BBC News, the henge or barrow or whatever it was, was an important new addition to our understanding of the landscape. Exactly what it was, however, would have to await excavation.

Meanwhile at British Archaeology, I received an email from Melvyn P Heyes in New York City, to say that he thought he’d found the “new” site on Google maps – ie, it was an upstanding barrow. That in itself shouldn’t matter, as what the geophysics showed was something below ground we could not have known, barrow rising from the grass or otherwise (though it might support my argument that we are looking at details of an unusual burial mound, rather than a henge).

However, some archaeologist colleagues of mine had noticed that the pits inside the ditch ring seemed to be aligned in straight segments rather than on a continuous curving circle. That is not something we know to be a neolithic or bronze age design feature: but we do see it in recent fences put around barrows to protect them from cattle – not least an octagonal fence around a barrow on a 20th century Ordnance Survey map, close to the site of the geophysics survey (though not there now). In other words, the question was posed, is the prehistoric post circle a modern fence?

Or as I wrote in the new British Archaeology: is the new site “the first major ceremonial monument that has been found [at Stonehenge] in the past 50 years or so”? Or an over-hasty PR embarrassment (at an early stage in what is undoubtedly an important archaeological project)? Full publication and small-scale excavation would clinch the matter.”

I did not, as the Mail on Sunday puts it, say “I am in no doubt that this was a modern fence line”. The truth is I really don’t know. Clearly Vince Gaffney thinks it prehistoric, and he, after all, has the full data on the site, which the rest of us don’t. If it turns out he is right, and that the post ring is set out in straight segments, then the interest of the survey is yet greater, as that in itself is a significant new discovery. If it is a not-so-old fence, most of what the geophys survey shows is likely still to be prehistoric, and is of great interest. This remains, as I wrote in June, “an important discovery whose significance will be fully realised only with excavation”.

And, I think, a discovery whose interest and value has been added to by debates about data and meaning such as this one.

If you’ve got this far, you must like reading about Stonehenge, so here’s a quick update on some other stuff. In November Nova’s latest film about Stonehenge had its first broadcast, with some nice footage of the recent digs at Bluehenge by the river Avon and the Aubrey Hole at Stonehenge (you can see a trailer here). The film also featured Andy Young’s idea that stones were moved on wooden rails holding stone ball bearings. And later in the month we heard about Gary Lavin’s shot at let’s-see-how-complicated-we-can-make-moving-the-stones-to-Stonehenge: wrapping the megaliths in great wicker baskets and rolling them. These things are great fun, but I still think putting the stones on sledges and manipulating them with rollers and levers is the simplest and most effective way of doing it.

Also in November English Heritage, having lost the £10m promised by the previous government for the proposed new visitor centre, regained it from the Heritage Lottery Fund. Hopefully now EH will be able to raise the rest of the money it needs: but Stonehenge won’t be ready for the 2012 Olympics, the politicians’ original claim, and instead if all goes well, at that time Stonehenge will be a bit of a building site.

In October British Archaeology’s front cover featured what I called a crisis facing the archaeology of human remains in Britain. This is the fact that standard excavation licences now carry a requirement to rebury human remains after two years. This practice was introduced by the Ministry of Justice in 2008, so the practical implications are only now really kicking in. They affect Stonehenge (the Aubrey Hole cremations were recovered in 2008; the MoJ has now amended reburial conditions, extending the stay on reburial until November 2015). But more importantly they affect our ability to research and understand our entire history, from early humans to medieval and more recent people. Robin McKie wrote about this in the Observer, and Duncan Sayer and I talked about it on Radio 4 Material World. Kenneth Clarke, secretary of state for justice, seems to be sympathetic to our cause (see his letter here, “regarding archaeological investigation of human remains”): but we’re not yet convinced that the Ministry of Justice really understands why we are so concerned, and the case continues. I suspect it will be raised at the “Mortuary archaeology and popular culture” session at the Bristol TAG conference on December 18.

4 thoughts on “In defence of geophysics

  1. For most of my life, my mother and I have kept horses, and whenever you do this keeping the animal inside a fence-line is a constant battle. Fence-posts are expensive, so we always recycled old posts as much as we could, and this meant putting up posts with bits and pieces of nails and staples still in them (staples are especially hard to remove, unless you have a special tool and the motivation to try).

    Now, imagine you’re a sheep farmer on Salisbury Plain. Some archaeologists have just come up to you and told you to fence off a bit of the plain that you’ve been grazing all your life, and your father’s life before you. There’s no rhyme nor reason to it, nor any arguing with the archaeologists either. So, what do you do?

    Easy, grab a load of old fence-posts that were earmarked for reinforcing fencing, and which have the usual staples and whatnot already hammered into ’em. You womble out to the place, half-heartedly bash the posts in (give ’em full force and they’ll split; this was probably a job for a mallet and some care) and string pig netting round the circle; has to be pig-netting with mesh smaller at the bottom or lambs’ll get caught inside the ring.

    And then you forget the thing. A decade later, the weather will have rotted the wire and some of the posts, so you drive over with the same old tractor, yank the whole lot out and give it a one-way ride to the farm dump, the posts now being little more than woodworm sanctuaries. In the ground behind you are left post-holes and crumbling debris of fragments of galvanised wire.

    This is the key to the thing: galvanised wire or to you and me, soft steel wire pre-dipped in zinc to delay rusting. When it does rust, it rusts really fast, but the soil-brown fragments are still highly visible to magnetometers, and possibly even to pulse-induction metal detectors. This is what I think was found up on that lonely hillside.

    1. All of that makes sense. The one point of difficulty, in this case, is that there are apparently no metallic objects associated with the ring of pits, so in that respect your argument suports the idea that the pits are in fact ancient and not modern.

  2. The point I was driving at was mostly this: if a farmer unwittingly contaminates a series of stakeholes with old staples, say, then once the wood has decayed then the zinc-coated iron is also going to mostly decay too, but it WILL leave a ferromagnetic trace in the ground.

    I have some experience using metal detectors, including a Scheibel mine detector purchased secondhand. This latter device makes for a wonderful archaeological tool, simply because it picks up on absolutely everything in the soil and especially likes iron (most commercial detectors mask out iron as unwanted trash; it ain’t trash but interesting material).

    The one thing that does mar this machine is what detectorists call “hot rocks”. These aren’t metallic, they often look like soil, but they are detectable by a detector. Coal ash is a frequent source of this; rusted iron is, as well. What makes these things even more infuriating to a detectorist is the halo effect; when buried in soil a hot-rock often “looks” quite big and interesting to the detector; loosen the soil by digging it out and the halo is destroyed and the thing becomes un-findable, or even worse, findable sometimes then non-findable when soil is moved. This leads to huge excavations, cursing and footling about with a pinpoint probe looking for that signal you _know_ you had just a moment ago, but have now lost.

    Halo effects from rusted iron likely have exactly the same effects on magnetometers that they do on pulse-induction metal detectors; the detection system is the same, just a lot more brutal with the detector.

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