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

Archive for June 29, 2011

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.