Summer School Week 3 has been really successful with the training of volunteers in geophysics and excavation. We returned to the Baillie area that we first visited on the very first day of fieldwork back in June. We had already discovered 2 hut circles and a possible burnt mound using the LiDAR data and walkover survey but we wanted to see what else we could find.
Monday’s work was carried out in the Castlehill Heritage Centre where some more time was spent looking at the LiDAR data, which everyone is getting pretty good at, and the volunteers were introduced to the techniques of geophysics and testpitting that they were to use during the week.
Tuesday in the field saw the beginning of transects of 50cm testpits laid across the hut circles by volunteers Winnie, Paul and Terry and AOC workers Graeme and Jamie. The volunteers saw the difference between different soils at different levels and sampled the deposits from the section, or side, of the testpit. Graeme even found a sherd of pottery-what a professional! Also, an excavation trench was opened up over the possible burnt mound to try and prove the interpretation. However, when two wall faces appeared from the ground it was found that it is actually a hut circle instead.
Meanwhile volunteers Jonie, Richard and Vanessa were taken off by AOC worker, Gemma, to carry out some geophysical survey. After being previously told to be magnetically clean the volunteers had accordingly worn suitable clothing, however, Jonie was banished after discovering her nail varnish was magnetic! Jonie and Richard laid out 30m grids using their school memories of Pythagoras Theorem while Vanessa practiced walking in a straight line at a set pace. Together the team managed 30 testpits and 5 gradiometer survey grids-amazing work!
Wednesday saw the continuation of the gradiometer survey with Jonie returning, with clean nails(!), and carrying out the first grid of the day. Gradiometer survey measures the earth’s magnetic field and how it is disturbed by features on the earth’s surface such as archaeology or magnetic items such as wire fences. To sense the change in magnetic field the surveyor must walk systematically across grids holding the gradiometer and walking at a set pace. It’s quite frustrating when the ground isn’t flat which is what volunteers Jonie and Carol found out as they tried to walk straight through ditches and long rushes. Volunteer Richard took over in the afternoon and successfully managed a few more grids.
Over in the excavation team, work continued on the hut circle trench with its exposed wall faces. The team carefully dug down decayed turf layers sampling the different soil types, or contexts, as they went down. Work also continued on testpitting, but this time the whole site was investigated with the diggers positioning their testpits at the corner of each geophysics grid with their handy 30m spacing. A second trench was also opened up by volunteers Murial, Paul and Winnie over the southernmost hut circle that had been identified from the LiDAR and walkover survey.
Volunteers Paul, Murial and Winnie showed volunteer Jonie their trench. Meanwhile volunteer Richard takes a well deserved rest from geophysics while desperately trying to not look like he’s wearing a rugby goalpost fancy dress costume.
Thursday saw more of the same with the testpits, excavation trench and geophysics. Volunteer Terry kept the testpits across the site going and discovered in one area that he hit bedrock and couldn’t even get the three required deposits. Unfortunately when downloading the gradiometer survey at the end of the day Jonie and Richard discovered their handywork was marred by a white glow across one edge of the grids. This was due to a metal pole being used as a sight line being left too close to the grid edge so was detected by the gradiometer. Geophysics is very unforgiving!
Friday it rained, and rained and rained! But, we would not be discouraged. The team were back out on site excavating their hut circle trench and volunteer Murial was rewarded for her wet efforts when she happened upon some ard marks in the bottom of the trench. Ard marks are scored lines in the natural level of soil from a plough, showing that the area was farmed. The interesting thing about these ard marks is that they were found to go under the wall of the hut circle meaning that they are associated with an earlier use of the site, perhaps a hut circle that we are yet to discover!
Meanwhile AOC worker Jamie had opened up a trench to purposefully look for ard marks and found nothing. Sometimes a bit of luck is needed in archaeology!
The second hut circle trench was finally finished on Friday and an inner and outer wall of the hut circle were identified along with a spread of rubble further to the north and south.
Special mention to Vanessa for her gradiometer survey work, with no waterproof clothing to ensure that she was magnetically clean! She redid a couple of Richard’s grids to remove the white line marring the data and then expanded the entire grid area to the west to include the area of bedrock that Terry found during the testpitting.
Saturday morning brought much better weather and the finishing up of work on site. Volunteer Paul took some kubiena samples from the second hut circle trench to be used for thin section analysis, which looks at the microstructure of the soil particles, and then it was backfilled.
Meanwhile geophysicist volunteers Vanessa, Rona and Terry carried out a grid of resistivity survey over a third hut circle that is on site. Resistivity survey measures the current through the ground which is affected by buried archaeological remains giving different results to gradiometer survey. The fourth week of the summer school may focus on excavating this hut circle so extra geophysics can be used to identify the best location for the excavation trenches.
And finally, the geophysics results from the week of gradiometer survey:
The 2nd and 3rd bottom rows show the three hut circles that we identified on site. The one is the centre is the best preserved and the bright black and white pixels show that there is a lot of stone in its bank. Also to the right of these rows you can see our “possible burnt mound” which turned out to be a hut circle, and can be seen on the plot above to be oval in shape. The second excavation trench was put over the hut circle to the far left of the picture. Can you spot a possible fourth hut circle between the centre and left hut circles? Also to the right of the central hut circle is a possible enclosure which is much subtler so may be entirely built from turf as opposed to stone. In the right hand column and 3rd grid down from the top is another feature which is showing up as strongly magnetic and there is a diagonal striping effect in the upper area grids. It could be rig and furrow or it could be bedrock ridges, only excavation will tell… Further to the hut circles are two long wide lines leading down from them and general disturbance all around which could be related to the structures. The above plot is only the raw data so it will be further processed and interpreted. Please comment with what you can see!
Thank you so much to all our volunteers this week: Terry, Carol, Winnie, Muriel, Rona, Paul, Jonie, Richard, Vanessa, Chris, Ian and anyone else that I might have forgotten! You are now all trained diggers and geophysicists, and more importantly a lot of fun to work with. See you at week 4!