Dress code: non-magnetic options

Mike, Clare and I took the third year students on our ‘Introduction to Professional Practice’ module up to the summit of New Laund Hill yesterday so that they could learn how to use the Bartington fluxgate gradiometer. This is the instrument that measures minute fluctuations in the earth’s magnetic field and, hopefully, reveals buried archaeology in the process. This is the same machine that Olaf and Mike used to find the New Laund enclosure in 2011. One of the quirks of this sort of survey is that the operator has to be completely non-magnetic. They must have no metal about their person at all: no watches, rings, boot eyelets, zips, metal fasteners and no phones, keys or glasses in their pockets.

This is harder to achieve than it sounds. Wellies (but of course no steel toecaps) or trainers are about your only footwear options. Clothing tends to be fleecy and baggy and drawstring waists feature a lot. Sartorially speaking, non-magnetic is not a structured look. The photos of the survey will give you an idea of what a dashing bunch we all were in the car park yesterday morning. If you imagine  members of an obscure religious group who refuse to wear zips or buttons, but embrace high-tech survey, then you will get the picture: techno-Amish perhaps describes the look best.

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Of course the purpose of all this was to carry out the survey over the summit of the hill. We had chosen this point because it is a particularly visible bit of the local landscape. It overlooks both the New Laund Enclosure to the north-east and Fairy Holes cave to the east. This photo shows how the person doing the survey must walk a prescribed path backwards and forwards across a marked 30 x 30 m square on the ground. In the background you can see Damien measuring in the corners of the square with the Leica GPS so they can be located on the OS National Grid. This photo shows Caitlin walking across the grid square taking a reading every 25 cm with each of the two detectors on the frame she is wearing.  This means that as the machine logs the changes in magnetic response they can then be fitted into their correct place on the surface of the site. The computer can then draw up a plot of where the responses change and, hopefully, where the archaeology is.

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Here you can see the survey continuing on the summit with the New Laund Enclosure visible on the spur of the hill behind the team. I had chosen to survey the summit of the hill on the highly rigorous grounds that I felt like there should be something there. It overlooks the enclosure, Fairy Holes and Mouse Hole cave and is the highest point on the farm. The surface is quite irregular but there was no real sign of anything that couldn’t be explained as natural fissures in the limestone. Still, I thought it was worth a go.

new laund basic interpretation

I am feeling very smug about this now because Mike has processed the data and there is archaeology there. This is his quick interpreted version of the results (North is at the top) showing that there seem to be quite a few pits or postholes, possible in two lines, on the top of the hill as well as two faint linear responses. These are probably small ditches as they look a lot like the trace for the inner ditch in the New Laund Enclosure. One of our jobs next week will be to get some resistivity survey on this bit of the hill too, so we can compare the results from the two different techniques.

Rick

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