A day-by-day account of the activities of the Rossnaree Archaeological Project 2010-11

Posts tagged “magnetic susceptibility

Day 14: No drama today, just another day’s work

No thunder or lightning today, just one or two light showers of rain. No sun either and the day was a bit cooler than previous but nonetheless was quite pleasant.

Rossnaree excavation

Chris reads some levels

Now with the weather report out of the way we can move on to the work done on site today. In Trench 4 (I always seem to start with this one, possibly because it is the nearest one to the site) Kieran drew a plan of the cutting showing the extent of the ditch, the slopes to the base on each side and the rest of the cutting. This view complements the section he drew yesterday – the section shows the side-view or elevation of all of the layers in the side of the trench while the plan view gives the bird’s-eye-view of the feature excavated. At the same time, I took a series of soil samples from the sides of the trench for magnetic susceptibility analysis. Samples had been taken previously at a higher level and readings have also been taken across the surface of the trench before the trench was desodded so we will end up with a very good record of how magnetic susceptibility varies with depth within the ditch. To remind readers, magnetic susceptibility measures the ability of the soil to become magnetised when a magnetic field is introduced and is a very good indicator of past burning or disposal of organic material like food waste or manure.

Rossnaree excavation Trench 4

Chris and Kieran level the site.

Both of these are of course closely related to settlement. The soil samples will have to be processed at a later stage after the excavation is over before the analysis takes place. They will be dried, sieved to remove stones and weighed to produce equal sized samples. In this way, we will be able to get accurate and directly comparable values for magnetic suceptibility. At the end of Kieran’s planning process, the final job to be carried out is to take levels of the area to give an impression of how undulating the planned surface is and to give a feeling for the relative depths of features. This is done on site with a simple dumpy level, which is being used in the photo by Chris who was visiting the site this morning. Chris was one of the geophysics team who first discovered and mapped the enclosure back in 2008 and he was anxious to see for himself how progress was going. In the photo, Kieran is holding the staff, which is like a giant ruler. He places this on each spot in the trench that he wants measured and Chris takes the reading through the level, which is like a small telescope that has been set up on the level. We know the height of the level in space (this has been established already) so we can calculate the heights of each point measured and recorded by Kieran on the plan.

Rossnaree excavation Trench 3 artefact

Intact flint blade from Trench 3

In Trench 1 the work of the past number of days went on and Darren and Matt removed more of the dark, rich organic layer overlying the cobblestones making up the core of the bank. Lots more animal bone was found, some of which seems to have been burned (this will hopefully be confirmed by our animal bone specialist who is visiting next week). Some nice pieces of flint were also found including various flake fragments, a scraper fragment and a complete blade.

Rossnaree excavation Trench 3

Cobbles in the bank in Trench 3

Beneath this layer the cobble stones were coming up very nicely and the site in this area at least was beginning to feel more than a little like an early medieval cashel. Because these date to between 500 and 1000AD, I wasn’t too happy with this idea! I still believe the site is Neolithic (4,000 to 2,500BC). I believe the staff have a book open on the date; one bet is that it is 850AD. Traitors! Seriously, no artefacts have been found that suggest that this site is anything other than prehistoric (and probably Neolithic) although, as I said before, some pottery would be very nice and would help remove any doubt. The cobbles in the wall do seem to have collapsed a bit over time; they are most intact at the bank end and less distinct moving eastwards away from the bank. There is also a lot of soil in between them which probably filtered down from above over the years too.

Rossnaree excavation Trench 1

Stony fill in Trench 1 ditch

In Trench 1 more progress was made removing one of the ditch fills. Gary and Niamh cleaned up and exposed the layer of stones within this layer and, although at first glance they seem to have a pattern to them and appear to be part of a structure, this is completely coincidental. The excavators are certain that this just happens to be the way the stones settled after rolling or sliding down the slope from above, finally settling at the lowest part of the ditch. We will clean them a bit more and record them in plan anyway, just to be sure.

Rossnaree excavation crew

The team admire their handiwork


Day 9: Soft day, thank God

Rossnaree excavation umbrella

Should we stay or should we go now..? Matt and Kieran are glad of Deirdre's amazing umbrella

We Irish have a ludicrous saying suggesting that we actually like the auld bit o’ rain now and then. Today might have qualified for the ‘soft day’ categorisation but there’s no way any of us on site were particularly pleased with it today. There were numerous heavy showers but the weather couldn’t make up its mind as to whether it was coming or going. The result was a lot of wettings and some very stop-start work. Anyway, the one good thing about the weather today was that some of our crew were not able to make it to site today because of other commitments. So not everybody had to be subjected to a soaking!

Rossnaree excavation Trench 4

Trench 4 in the rain

The work that we did manage to get done was limited but it nonetheless pushes us a little further towards our ultimate goal. In Trench 4, Kieran, Eamonn and Deirdre continued to peel the cultivation sol off the top of the fill of the enclosure ditch. Very few finds were coming out of the material being removed but Deirdre’s sharp eyes picked out a fragment of a rock crystal flake (sorry no photo). This is very small-less than half the size of your little fingernail-but is distinctive and unusual. Although more difficult to work into tools than flint (and harder for us archaeologists to recognise) it is clear that materials other than flint were often used by people in the Neolithic. In some cases it seems simply that where there was a shortage of good quality flint, people used other materials like chert and quartz as ‘second best’ alternatives. However, it is also possible that the materials chosen for toolmaking reflected the intended functions of the tools or reflected the identities of the people making the tools. We all have the good crockery at home for when visitors call. Similarly, craftspeople today often use unusual or distinctive materials as a sort of trademark. Perhaps this was going on in the Neolithic as well. The flake fragment we found is distinctive because it is a type of quartz which is almost transparent, like glass. This quality would not have been lost on the Neolithic people.

In Trench 1 we continued to take out the fill of the gully and we also drew the north-facing section exposed when we excavated the enclosure ditch. We also plotted the locations of the magnetic susceptibility soil samples we took yesterday. We managed to complete these various jobs by lunchtime between showers and then we transferred over to Trench 3 where there is also a bank and ditch feature. The plan was to start to take down the material filling the ditch in the same was as in Trench 1. We unfortunately didn’t get much done because of the rain but we did notice a larger number of bone fragments compared to Trench 1, reflecting the position of Trench 1 closer to the ‘core’ of the site.

Rossnaree excavation

Soft day...!

Can’t decide whether the weather forecast was accurate; I think it was today. A blustery day is forecast tomorrow with scattered passing showers. I think we may be able to cope with that.

Day 8: Every cloud has a silver lining.

The day got off to a very unpromising start weatherwise. There had been rain overnight and when we reached the site at 9am, light drizzle was gradually becoming more persistent. We suited up in our wegear, hoping this was only a shower, and walked down to the site. The rain got heavier as we went and stopped us getting stuck in to the work. We sheltered under a combination of hawthorn trees in the hedge, taking time to speculate on their age, and Deirdre’s very functional fishing umbrella. This should perhaps become standard issue on all archaeological sites!

Rossnaree excavation trench 4

Kieran and Eimear in Trench 4

However, just as we were saying ‘five more minutes and we’ll go up and stick on the kettle’ the sky brightened a bit and the rain actually stopped. We split into our teams and started. In Trench 4 the team began to take down the next spit of cultivation soil overlying the ditch which we had identified in the geophysics. It seems that the cultivation soil is relatively deep in this area because there is a very distinctive corrugated pattern to the field surface indicating ridge-and-furrow cultivation with the ridges set about 5m apart from each other.

Rossnaree excavation Trench 4

Deirdre and Eamonn working the sieve

Additionally, the geophysics from this area is a lot less distinct than that for the field to the west where the main part of the enclosure is located, perhaps suggesting a lot of agricultural disturbance.

Rossnaree excavation

Deirdre proves the sieve works.

The Trench 4 team was joined by our new recruit, Eimear, and experienced digger and research student based in UCD, who is very welcome.

Rossnaree excavation Trench 1

Ditch fills section face, Trench 1.

In Trench 1 the other team cleaned up the section face of the ditch that was exposed yesterday and took a close look at the various fills of the ditch. Six separate fills were identified, indicating the various stages involved in the gradual silting up of the ditch to its present surface level. While it was once almost 1m deep, it now is only about 15cm deep. A lot of material washed down the slope and off the tops of the adjacent banks over time. We also took another series of soil samples from the section faces for magnetic susceptibility analysis.

Rossnaree excavation Trench 1

A find in situ in Trench 1

Matt began to look at a smaller ditch to the west of the main enclosure ditch. This shows up in the geophysics for the area but appears to be a much less substantial feature and it also follows a slightly different line to the main ditch. Our feeling at the moment is that it may be a much later drainage gully which was coincidentally placed close to the prehistoric ditch. The fill is very clean silty clay with no finds of any kind.

Rossnaree Excavation Trench 4

Eimer trowelling in Trench 4

Meanwhile, by the afternoon, real progress was being made in Trench 4. The diggers there had found the base of cultivation soil. Disturbed soil gave way to a layer of more gravelly soil which in turn gave way to more compact clean gravelly material. They now have a good understanding of the depth of disturbed soil that must be removed from the top of the trench before the first intact ditch fills are encountered.

So, no dramatic finds or discoveries made today, but despite the unpromising start, a good solid productive day followed.