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

Posts tagged “geophysics

Day 13 – Putting our best foot forward.

Work continued from yesterday with Eimear planning in Area 1 (Cutting 6), Matt excavating features in Area 2 (Cutting 7), Niamh extending the cutting to expose the full extent of the grave cut, and the rest of the team taking down the rest of the base of ploughsoil material in Cutting 8. Kevin, our geophysical surveyor, was also on site again to monitor progress, compare the excavated features to the anomalies identified in the initial surveys and take some additional readings.

Eimear adjusts her planning frame.
The plan in progress.

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In Area 1, Cutting 6, Eimear’s plan is nearing completion. The process is taking some time because of the size of the cutting and the complexity of the features and soils there. However, she is nearly finished and we will be taking levels on the surface tomorrow morning and assigning numbers to each of the separate fills and features. We even made a start this afternoon on one spread of material that seems to be occupation/refuse spread associated with the occupation of the oval enclosure. This appears to overlie the lower north-south ditch fill so we set Igor up to put a section across it to assess its depth. By tomorrow we will hopefully know what its exact relationship is to the other features and fills around it.

Matt examines the burnt stone.

Matt continued to deal with other features in Cutting 7 while Niamh and Sarah excavated the 1m x 0.5m extension to the cutting to fully open up the grave cut. His feature today, numbered F.705, appeared on the surface as a spread of charcoal flecked soil extending over an area c.1m in extent and disappearing beneath the northern baulk. As Matt excavated the feature revealed itself to be small furnace with a number of heat-shattered stones around and in it. The fill is mainly charcoal-rich soil, which we sampled. There was also a stone with a distinct concretion suggestive of some sort of slag, waste material from an industrial process, possibly metalworking. The base of the feature was reddened, baked soil, indicating intense heat. The proximity of this feature to the grave is interesting as it is not unusual to have such industrial features close to burials on non-ecclesiastical sites. Niamh, Sarah and Ciara gradually removed all of the ploughsoil from the extension and revealed the line of the grave cut retrieving a fragment of cranium from the ploughsoil Matt then added this detail to the previously drawn plan and proceeded to tidy up the area and continue to excavate it.

A beautifully trowelled surface!
Lisa and the post hole.

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In Cutting 8 the team there continued to remove, using trowels, the base of ploughsoil/interface layer. At the southern end of the cutting Igor had recovered a number of pieces of human bone and a tooth which indicates that there were probably other graves in that area which are now destroyed by ploughing. There is also a small gully-like feature here which appears to be relatively late in date and may be associated with later agricultural activity. Also at the southern end of the cutting, Lisa found her first feature. It looks at this stage like a very nice post-hole – an area of loose darker soil surrounded by a ring of packing stones. We will take a closer look at it in due course.

Kevin takes MS readings.
The metal detector in action.
Setting up the total station.

Kevin was on hand again to look at how work was progressing. He took additional magnetic susceptibility readings from the excavated surfaces of each of the cuttings and recorded interesting results. The values were all significantly higher than those recorded at the surface prior to excavation. There will be a very useful dataset gathered by the end of the excavation to carry out detailed comparisons between pre-excavation surface readings and post excavation readings as well as surface soil samples and ‘top of archaeology’ soil samples. Kevin also took the opportunity to scan the spoil heaps with a metal detector to ensure that we hadn’t missed anything (I don’t think we have but you never know..!) and he also scanned the unexcavated surfaces around the cuttings. In the afternoon, Kevin used a total station to survey in some of the major features identified on the site so far like the grave cut and the edges of the ditches in Area 1 Cutting 6.

In the afternoon we had a bit of diversion when the group of students currently working a the Blackfriary site in Trim paid us a visit. They are part of the Irish Archaeological Field School and on their way they visited the Bective site. I think the students enjoyed their visit and they told us that it was quite different to the other two sites.


Day 9 – Time to start recording

The Area 1 team.

Today promised to be another fantastic day weatherwise and it was. However, there was a little bit of cloud and a bit of a breeze which made it a bit more bearable. The team in Area 1 continued to clear off the last layer of ploughsoil and expose the surfaces of the features underneath. They have now reached the topmost rows in the trench and the whole surface will have been cleared by tomorrow.

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Ciara with a mattock.
Jamie’s blue glass bead.

It is looking very well and, as outlined yesterday, major features are visible. It will be very interesting to record these and then begin to dig them one-by-one. Some nice finds came up again today – several pieces of flint and a fragment of another blue glass bead, probably dating to the early medieval phase of occupation. The bead was not complete like the previous one and Jamie, who found it,  did very well to spot it. The fragment is so small it wouldn’t have been picked up in the sieve either. It seems to have been more delicate and thin than the one from last week.

‘It could be a feature…’
A flint scraper from Area 2.

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In Area 2 the same questions dogged the team there – have we got base of ploughsoil or is there a spread of occupation material? It seems clear now that there is, in fact, a spread of material below the base of ploughsoil which has frequent large pieces of animal bone – a good indicator that it is undisturbed by ploughing as this would cause a relatively delicate material like bone to break down into smaller pieces. We took the decision to expose this layer as fully as possible and then record it by taking photographs the surface and then drawing a scale plan of it.

Spot the post hole!
Matt starts the plan.

While this final clean-back was being completed, a couple of possible features became apparent. These are small circular or sub-circular areas of slightly darker soil with charcoal flecking, and may be something like post holes. When the planning is finished, we will take a closer look at them. Matt set up to draw the plan using a long tape to orient himself relative to the site grid and a planning frame to help draw the detail on the surface, metre square by metre square. You don’t have to be an artist to do this – it is a technical rather than an artistic process – but, like so much in archaeology, it requires time, patience and a thorough meticulous approach.

Area 2 cleaned surface.

Cutting 8 soil sampling.

The others in the Area 2 team were now redundant – as Matt was busy planning, they couldn’t dig in that cutting or they would be in the way. Also, as the trowelers began to finish their strips in Area 1 they came across to Area 2 to join the diggers there. They started work on a third cutting which will ultimately join with Cutting 7. This is a 2m x 7m trench extending southwards and will investigate further anomalies identified in the magnetic gradiometry there. As with the previous trenches, we used long tapes set out between the site grid pegs to position the trench relative to the grid and set out a line to define the edges. This time we cleared off the loose stalks from the surface to help with the digging and sieveing process. The first step, however, before the digging could begin, was to take a series of magnetic susceptibility soil samples, to keep a consistent record. By late afternoon the first square had been almost completely dug and sieved. More of the same tomorrow; hopefully the weather will hold up, although the forecast is not good. We’ll take it as it comes.


Day 7 – Those wascally wabbits

Rabbit hole 1.
The neighbours.

Our nocturnal visitors had been back again to the site and this time they seem to have tried to set up residence in the Area 1 spoil heap. When we arrived down to the site this morning there were several burrows dug into the heap with a series of cute little footprints all around. They seem to have given up, however, as the holes weren’t too deep and were apparently unoccupied. As long as they confine themselves to the spoil heap I don’t mind too much – on some other sites I have dug on rabbit burrows had done a lot of damage to the archaeology. For some reason they don’t seem to be interested in the Area 2 spoil heaps.

Sophie and Sarah taking soil samples in Area 1.
Troweling down in Area 1.

On the work front the last of the ploughsoil was taken down – two half squares and one full square. This was easily achieved before the morning break and there was a certain air of proud satisfaction at the final moment. 30 square metres of ploughsoil removed and sieved since the start of the dig. After the break we took a second series of magnetic susceptibility samples from the base of ploughsoil using plastic implements in order to reduce the possibility of contamination. One sample was taken from each metre square and duly brought up to the cabin at lunch time. Once this was done we were ready to start troweling the surface to remove the last skim of ploughsoil and start identifying the features. Working from east to west in column I squares 1-5, we uncovered a band of hard, compact, yellowish soil which gradually gave way to darker slightly less compact, more fill-like soil with frequent flecks and larger pieces of charcoal and animal bone, also with occasional pieces of flint. This looks like the top of the fill of the north-south ditch identified in the geophysics. We will continue tomorrow and see what emerges.

The sondage in Area 2.
Matt and Eimear in Area 2.

In Area 2 Matt, Tomás and Ciara continued to take down the last skim of ploughsoil using a combination of troweling and mattocking. As described yesterday, a number of possible features had been identified yesterday along the northern side of the cutting. However, there were no similar features visible elsewhere in the cutting that might correspond the the geophysical anomalies. Matt carried out a sondage, or test area, in the extreme southwest corner of the trench to determine exactly where subsoil was located and it emerged that there was another 10 to 15cm to be taken down. Thus, although the northern edge was relatively clear, there seems to be a shallow wedge of ploughsoil thickening towards the southern side of the cutting. There is usually an occasionally disturbed zone at the very base of the ploughsoil which is transitional between fully disturbed ploughsoil and never disturbed natural/subsoil with archaeological features. When ploughing takes place in a field, it doesnt necessarily plough to exactly the same depth as previous years with the result that there is no clear ‘line’ or interface between ploughsoil and ‘unploughed’ soil. Sometimes, depending on local soils, it is difficult to easily distinguish between regularly ploughed ploughsoil, occasionally ploughed base of ploughsoil and subsoil and it takes a bit of deliberation to establish where each ends and the next begins. Tomorrow they will remove this and trowel the surface back and hopefully we will see some more features.


Day 6 – Moving up a gear.

Magnetic gradiometry, Area 1.

We all arrived down to the site hut revitalised, reinvigorated and ready for the new week. We were close to being completely free of the monotony of mattocking, shoveling and sieving through ploughsoil, although the finds we are coming across are nice. In Area 1 at the start of the day there were still 10 square metres to be dug away and throughout the day the team there got through seven and two half squares. Tomorrow, there are only two half-squares and one full one to go. Once they are gone, we will be nearly ready to begin to search for the features identified in the geophysical surveys carried out by Kevin before the dig started up. In the plot the cutting itself is made up of columns G, H and I and extends from row 1 to row 10. This takes in two very distinct features: one, a possible ditch running from north to south (from previous geophysical surveys this seems to be the innermost enclosure defining the knoll of high ground) and the second, at a higher level and cutting the other feature curving in from the middle of the right side to the bottom of the panel (this seems to be a separate oval enclosure superimposed on the other ditch. See the original plot HERE). This cutting will investigate the exact relationship between these two separate features and hopefully will yield material for dating.

Lisa, Mags and Sarah.
Sophie on the sieve.
Darren gets to trowel.
Magnetic gradiometry, Area 2.

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In Area 2, they started the day with just two metre squares to go and these were quickly removed and sieved. Once this was completed, we took another series of soil samples for lab magnetic susceptibility measurements using the same grid as before. Thus we will be able to compare values taken from the field surface to those at the base of ploughsoil. Once this was done the cutting was ready to be troweled back. There was still a layer of ploughsoil over the cutting – we deliberately didn’t remove everything when we were mattocking off the ploughsoil partly to protect the site from being open too long and from the impact of people crossing over and back as they work. Trowelling, with the help of some light mattocking where necessary, is the next step taken to remove any remaining layer of disturbed ploughsoil and begin to identify the features underneath. We are lucky in that we have a very detailed set of geophysical plots to guide us as to what to expect. However, the picture here is less clear with a series of features that are unfortunately less identifiable than those in Area 1. The excavation here is to explore the nature of these possible features – our hunch is that they may be houses because of their location within the innermost enclosure on the highest point in the site – but we will be scratching our heads if we don’t end up finding the features indicated on the geophysical plots. The cutting itself measures 5m x 4m and is located between squares Q10-13 and U10-13 although this will probably be extended southwards at a later stage.

Eimear searches for the feature in square U13.
All hard at work in Area 2.

The plan for 2011

Based on the geophysics carried out in August 2010 immediately after last summer’s excavations, I put in an application to the Royal Irish Academy for further funding to return to the site and excavate in the core area on the top of the knoll. This appears to have been the focus of all the activity on the site. The lithic scatter is clearly centered on this feature and the later enclosures all encircle it. Standing on top of the knoll, it is not hard to see why it would have been an attractive spot for a settlement, whatever the period, dominating the land to the south and with a good view over the river while being out of the reach of the winter floods. Happily, the application to the RIA was successful and work will start again on the site on 4th July.

Two areas of potential were identified. This was a difficult process firstly because of the huge overall size of the site. The time or the resources are not available to dig everything or even a large sample of the site so positioning cuttings is like playing ‘pin the tail on the donkey’. However, the geophysics are a big help. Choosing areas to focus was also difficult because it is almost impossible to identify features in the geophysics that are more likely to be early (ideally prehistoric and preferably neolithic). You normally get very little indication of the date of features from geophysical plots unless they are very recognisable. The chance that all such early features are long gone, destroyed by over zealous and unwitting early medieval remodelling, is constantly at the back of my mind.

Figure 1: Areas 1 and 2 superimposed on the detailed magnetic gradiometry plot.

Area 1

This is located over the junction between the oval enclosure and the innermost D-shaped enclosure lying beneath it. See the last post for a discussion of these features. The innermost D-shaped enclosure  feature appears to define the top of the knoll or topographic high and appears to be quite different in character to the other ditches. The character of the feature on the magnetometry plot shows it to be narrower and less magnetic than the other enclosures. The magnetometry plot also shows that it is clearly cut by the oval enclosure suggesting a relative chronological relationship between the features. The earth resistance plot (Figure 2, last post) shows that the inner enclosure feature encloses an area of high resistance with a sharp delineation between the high-resistance inner area and the low resistance area immediately outside. The junction between the two areas appears to be particularly sharp and suggests a possible stone facing/revetment feature. This again suggests that the method used to construct the inner enclosure is different to that of the other enclosures. The area chosen lies well within the area defined by the lithic scatter. It is proposed to open a trench over the junction between the two ditches on the western side of the oval enclosure in order to examine the relationship between these features. Hopefully, it will be possible to retrieve material suitable for dating from the earlier enclosure. Given the apparent relationship between the oval enclosure and this inner enclosure, it is possible that the inner enclosure is early in date and possibly prehistoric.

Area 2

The second area of potential is also in the core area close to the highest point on the knoll. It shows up in the magnetic data as a circular cut feature of slightly positive magnetic gradient, c. 6m in diameter and possible with a centrally placed posthole and there are other possible pits or postholes immediately outside it. There is an area of lower resistance in the same location on the earth resistance plot (Figure 2, last post) and the magnetic susceptibility plot also indicates an almost discrete area of enhanced magnetic susceptibility to the north of the main area of enhancement (Figure 2, below). The feature lies at the north-eastern corner of the area defined by the lithic scatter. Given that this feature appears to be relatively well preserved and that it is potentially prehistoric in date based on its position and morphology, it is proposed to excavate a cutting over this feature to establish its date.

Figure 2: Magnetic susceptibility plot with superimposed features from magnetic gradiometry survey


Geophysical Survey 2010

Following the surprise development in the excavation last year where it was conclusively established that the enclosures on the site are likely to be early medieval in date (and probably between 7th-11th century AD), it was decided to carry out further geophysical survey over the core area of the site on the top of the knoll within the tillage field. This was clearly a focus of activity in prehistoric times because of the extensive lithic (flint) scatter found there. It also seems to have been a focus during the early medieval period as this is the area central to all of the enclosures.

Because of the lithic scatter, this area remained the best candidate area for identifying prehistoric activity. However, because of the apparent intensity of activity in the early medieval period, there is a chance that any prehistoric features that may once have existed are completely destroyed and disturbed.

With these problems in mind, a second programme of geophysical survey was carried out in August 2010 at a higher resolution than the original geophysical surveys. The hope was to identify more clearly any features that might be earlier than the early medieval enclosures. Three high resloution surveys were carried out: magnetic gradiometry (Figure 1), earth resistance (Figure 2) and magnetic susceptibility (Figure 3). See the following figures for the results of each of these.

Figure 1: Detailed magnetic gradiometry plot with topography, August 2010

The magnetic gradiometry has shown up more detail than was apparent on the original survey. For example, the second enclosure from the outside clearly deviates from its curvilinear path as we move northwards towards the terrace slope. This may be a modification of an earlier version of the enclosure as there are hints of an earlier, less definite enclosure continuing northwards. The other feature of interest is the relationship between the inner complete oval enclosure and the D-shaped enclosure beneath it. The oval enclosure looks like it cuts through the other enclosure and thus is later in date. Furthermore, there is a difference in the quality of the magnetic response between the two features suggesting that they are constructed differently. The oval enclosure is more similar in the character of its response to the other, outer, enclosures. There seems to be a contrast between the innermost D-shaped enclosure and the rest of the enclosures, possibly suggesting different construction techniques which may be due to their being constructed at different dates. Clearly, the innermost D-shaped enclosure is earlier than the oval one. The question is how much earlier. Are we looking at a possible prehistoric enclosure?

Figure 2: Detailed earth resistance plot with topography, August 2010

The contrast between the different enclosures noticed in the magnetic gradiometry is replicated to some degree in the earth resistance plot in Figure 2 so what we are seeing is likely to be real and reflect the real character of the features themselves. The innermost D-shaped enclosure is almost invisible on this plot, especially along its western side. At the southern end of this inner enclosure feature there is an area of high resistance with a sharp delineation between the high-resistance (light coloured in the plot above) inner area and the low resistance area immediately outside (dark coloured). The junction between the two areas appears to be particularly sharp and suggests a possible stone facing/revetment feature.

Figure 3: Detailed magnetic susceptibility plot with topography, August 2010

The magnetic susceptibility plot shows an area where the soils have been strongly altered by activities like burning and the disposal of organic waste. It shows a clear and distinct focus of activity which seems to be contained to the west by the third enclosure from the edge. It extends a lot further to the south than the line of this ditch and continues on outside the survey area. There is a band of low values running in a north-south direction through the middle of the zone of enhancement which may be due to the way the space was utilised in the past, or it may be due to sampling or post-depositional processes. There seems to be a slightly separate elongated area of enhancement running east-west along the northern boundary of the field which may be a secondary activity focus. It may be significant that this is focused on the southern side of the highest point of the topographic knoll.


2010 Season Report

This interim report describes the work undertaken during the 2010 excavation season at Rossnaree Co. Meath. The excavation took place over a four-week period between Monday 5th July and Friday 30th July and targeted a series of topographical and geophysical anomalies identified in previous survey work. The site was first discovered as a dense scatter of lithic (chipped stone) artefacts systematically recovered from the surface of a tilled field during a major extensive surface collection undertaken some years previously in the Brú na Bóinne area (National Museum of Ireland collection number C97.2).

magnetic gradiometry survey Rossnaree Excavation

Mark carrying out the magnetic gradiometry survey

Subsequent multi-method geophysical survey funded by the Heritage Council and undertaken by Kevin Barton of Landscape and Geophysical Services revealed the presence of a large multi-vallate enclosure on the banks of the River Boyne which is roughly D-shaped and is bounded on the north and east sited by the River Boyne at the point where the famous ‘Bend of the Boyne’ begins. The enclosure cordons off an area of approximately 3.5 hectares and measures c.250m east-west by c. 150m north-south. This enclosure was reported to the Archaeological Survey of Ireland and an RMP number was subsequently issued (ME019-080—).

Excavation funding was granted for a dig in 2010 by the Royal Irish Academy Committee for Archaeology and four trenches in total were opened and excavated during the season. Two of these trenches focused on extant low bank-and-ditch features located to the north of the tillage field close to the riverbank. A third trench (Trench 4) examined the continuation of the line of the outer enclosure in the low floodplain to the east of the core area of the site and a fourth trench (Trench 5) investigated the area around a semi-buried greywacke slab close to the field boundary in the pasture field to the east of the core area of the site.

While flint flakes and tools were frequently recovered, the major features on the site, especially the bank feature in Trench 3, was dated to the early medieval period on the basis of the recovery of a double-sided bone or antler comb fragment. A fragment of a copper-alloy strap was also recovered from the same context. A fragment of a lignite bracelet was also recovered from topsoil in Trrench 5, also indicative of activity during the early medieval period.

The interim report may be downloaded in PDF format here. Rossnaree_Report_2010(lowres)


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