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  • David Quick

Geophys - planning for Colemore in the autumn

Updated: Aug 21, 2021

I have long been curious about some features on Peter Page's original low-resolution geophys plot (resistivity) just to the north of where we put our tents and marquees at Colemore, and just west of Trench L where the square room of our Romano-British building was discovered in 2012. I asked Carl and Juliet whether, during our CM519 dig, we could scan this area in high resolution, i.e. with readings every half-metre instead of every 1 metre, which gives 4 times the detail. Juliet too was interested for the same reasons as me and because she is looking for some target areas for test pits during the smaller-than-usual Autumn Dig.

We did a lot of scanning during the actual dig and the results were very interesting - so much so that with permission from Rem, the landowner, Juliet and Carl decided to stay on until Thurs 23 May to continue doing as much as possible aided by whichever volunteers were prepared to assist at short notice. By the end of Thursday we had scanned 43 grid squares, each 20 x 20 metres, taking 1600 readings per square = 68,800 readings in total! That's a lot of lifting up and down of the RM85 and Carl is having to order a new battery for it.

However, the results seen below are fascinating - to me at any rate!

To understand this plot from QGIS you need to know that:

  • The background is drone imagery;

  • The green dashed lines are where hedgerows used to exist until dug up in the 1960s, shown to avoid confusion with archaeology on the geophys;

  • The magenta rectangle is the main Iron Age enclosure ditch;

  • The yellow outlines are all our past trenches and the little white squares our previous test pits;

  • The grey and pinks blobs and lines are features appearing on the low-resolution resistivity and magnetometry respectively.

The monochrome plot is the new high-resolution data. It was done very quickly from Snuffler before we went home on Thursday, so I apologise that I have not 'edge-matched' some of the grid squares. Have a look for yourself to see what features you can spot. Just a few of the features that I notice are:

  • A rhombus-shaped feature about 20 metres west of Trench L;

  • Possible tracks coming from near Test Pit 38 (bottom-left) towards Trench O;

  • A dark area just inside the south-west corner of the rectangular enclosure, near Test Pit 33;

  • A very dark area on the top edge of the area scanned, just west of Test Pit 06;

  • An incredibly straight feature running almost due north from the north-west corner of the enclosure ditch at Trench A;

  • Various other 'tracks' and an interesting circular feature.

You can incidentally see the foundations of the building we found, most notably in Trenches L and LA. We are going to be sitting down together in the near future to select the most interesting candidate areas for the autumn test pits. It looks as though we won't have as far to walk from the tents next time!

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