M3 Clonee-North of Kells Motorway Scheme

Lismullin National Monument (A042 & E3074)

Director’s Excavation Progress Report 3

Aidan O’Connell

Archaeological Consultancy Services

17 September 2007

Summary

Excavation in Quadrant A is complete in 18 of 20 grid squares and recording is being completed

in the remaining two. The post excavation plans are currently being digitized.

Excavation in Quadrant C (the NW quadrant in which the inner enclosure is located) has now

commenced following the completion of a series of works including trowel back, magnetic

susceptibility survey, supplementary pre-excavation planning, and geoarchaeological control

sampling.

Following the trowel back a sump hole was excavated in order to allow for pumping should the

site flood in the future. Excavation of the later field ditch which bisects the site is being

prioritized in order to assist in keeping water away from the inner enclosure.

The interim results of the magnetic susceptibility survey have been provided by Earthsound, and

are attached. The combined surveys to date appear to suggest that there is a moderate degree of

MS enhancement around the outside of the Outer Enclosure. In Quadrant C to the south of the

later field ditch another zone of high MS data corresponds to previous magnetometer responses

which suggest burning. This area corresponds to a number of pit features surrounded by an arc of

postholes as visible pre-excavation. The inner enclosure contains some moderate MS

enhancement with a concentration in the northern half which corresponds with the previous

magnetometer survey responses and the features visible on the ground pre-excavation. There is

strong MS enhancement just outside the inner enclosure on its NE side which corresponds very

well with the enhanced patch identified in the magnetometer data. This may be associated with

the slot trench identified on site which curves around this part of the inner enclosure. The

enhancement funnels out in a NE direction. This may represent human activity on this axis or

enhanced material may have been ploughed out in this direction.

Introduction

Site works commenced on 7 August 2007, following approval to commence from the Minister’s

Advisory Committee on 2 August.

As per standard procedure all works on site are recorded by reference to a grid which divides the

site into 10m2 areas. In addition the site has been divided into four separate areas or quadrants:

Quadrant A at NE, Quadrant B at SE, Quadrant C at NW and Quadrant D at SW (Fig 11).

The initial site clean-back and supplementary pre-excavation plan was carried out from 7–13

August in Quadrant A. Following additional geophysical survey and soil sampling for

geoarchaeological study, as described below, excavation of the planned features in Quadrant A

commenced on 15 August. Excavation is now nearing completion in Quadrant A. Excavation

commenced in Quadrant C on 14 September.

The excavation is being carried out by twenty-eight archaeologists divided into four teams, each

led by a senior supervisor. Supervisory staff attend weekly site meetings to review the ongoing

works.

Topographic Survey

Prior to excavation an aerial topographic survey was carried out by BKS. The results of this

survey have been produced as digital terrain models onto which the motorway landtake has been

superimposed along with the preliminary excavation plan of the enclosure, the souterrain and the

ringditch, and the new ringditch identified by geophysical survey outside the landtake to the SW

of the enclosure.

1 Figure 1 Site grid and quadrant layout with preliminary pre-excavation plan of site (in blue) and

supplementary pre-excavation plan of Quadrants A & C (in black), ACS Ltd.

Geophysical Survey

Magnetic Gradiometer Survey

The magnetic gradiometer survey identified a pear-shaped anomaly in Quadrant A which is

labeled ‘A’ on the interpretive drawing. It was interpreted as being likely to represent a ditch

which appears to act as an enclosure adjacent to a large linear ditch. The potential pear-shaped

enclosure measures 31m N-S and 23m E-W. In addition a small number of isolated circular

anomalies which could represent pits or postholes were identified at the southern end of the pearshaped

enclosure.

No trace of a pear-shaped or similar enclosure has been identified through excavation in this area.

Following post excavation recording it is proposed to excavate a box section through the edge of

the identified geophysical anomaly in an attempt to identify the origin of this anomaly. The

correlation between the anomalies identified on the magnetic gradiometer survey and the features

confirmed as archaeological during excavation is ongoing, however excavators have reported that

in general features close to the anomalies identified by the gradiometer survey have tended to be

slightly richer in charcoal.

Magnetic Susceptibility Survey

A magnetic susceptibility survey of Quadrant A was undertaken by Earthsound on 13 August.

This detected a number of discreet zones which appear to relate to natural geology.

Under examination on site in the northeastern corner the high readings appear to relate to an area

of underlying boulder clay, while at the northwestern corner and along the eastern side of

Quadrant A the low readings refer to underlying gravels and sand respectively. At the

southwestern corner, the high reading may be due to the presence of the palaeosoil that is located

around the inner enclosure. This soil has been left in situ to be excavated and recorded as part of

the ‘key area’ identified around the inner enclosure.

The magnetic susceptibility survey of Quadrant C was undertaken by Earthsound on 13

September and the preliminary results are attached. In summary the combined surveys to date

appear to suggest that there is a moderate degree of MS enhancement around the outside of the

Outer Enclosure. In Quadrant C to the south of the later field ditch another zone of high MS data

corresponds to previous magnetometer responses which suggest burning. This area corresponds

to a number of pit features surrounded by an arc of postholes as visible pre-excavation. The inner

enclosure contains some moderate MS enhancement with a concentration in the northern half

which corresponds with the previous magnetometer survey responses and the features visible on

the ground pre-excavation. There is strong MS enhancement just outside the inner enclosure on

its NE side which corresponds very well with the enhanced patch identified in the magnetometer

data. This may be associated with the slot trench identified on site which curves around this part

of the inner enclosure. The enhancement funnels out in a NE direction. This may represent

human activity on this axis or enhanced material may have been ploughed out in this direction.

Geoarchaeological sampling

Geochemical sampling

Dr Steven Lancaster (Headland Archaeology Ltd) is due to visit the site on 20th September to

review the ongoing sampling, to examine the sectioned palaeosoil over the inner enclosure and to

carry out a geoarchaeological assessment of the western landtake section.

On completion of the clean-back and geophysical survey in Quadrant A and in advance of the

commencement of excavation, geoarchaeological samples of approximately 200g (1 small bag)

were collected from the subsoil at 5m grid intervals, on 14-15 August. Approximately 100

samples were collected from Quadrant A. The grid samples are registered in a separate

geoarchaeological sample register and are being retained on site for future assessment and

analysis.

Dr Lancaster visited the site on 21 August to review the sampling methodology. A supervisor has

been assigned to specifically coordinate sampling on site in accordance with the methodology

agreed with Dr Lancaster, to ensure consistency of approach. In addition to grid samples, small

sub-samples of all excavated archaeological deposits are being retained for geo-chemical

analysis. The sampling strategy was reviewed to ensure that sufficient and appropriate samples

were being retained for each requirement.

During this visit the excavated features in Quadrant A were examined. This included a box

section excavated through two enclosure postholes, described below. This section had revealed a

thin deposit layer between the postholes which was interpreted as a thin layer of palaeosoil and

subsoil which had survived in a natural hollow. It was proposed that this palaeosoil would be

sampled using a kubiena tin.

Additionally, a proportion of half-sectioned enclosure postholes were examined in order to

establish their formation process. It was proposed that post-hole F3323 would be box-sectioned

and sampled using a kubiena tin to include subsoil, primary and secondary posthole fills for geochemical

analysis.

The potential buried soil within the interior is located around the inner enclosure and has not been

cleaned back yet although a small portion of it extends into the quadrant currently under

excavation. This soil will be sampled at a smaller grid interval of 2m. Some additional localized

patches or areas of darker soil were noted in Quadrant A and it was agreed on site that these

would be planned and sampled for geo-chemical analysis.

The control geoarchaeological sampling of Quadrant C took place between 13-17 September.

The methodology was identical to that in Quadrant A except over the inner enclosure where the

sampling frequency was reduced from 5m to 2m intervals.

Palaeonenvironmental sampling

In accordance with the method statement, a sample of all deposits and 100% of the fill material

from each cut feature in Quadrant A is being retained for dating and palaeoenvironmental

purposes. These samples will be processed through a flotation tank and sieves to extract suitable

material for analysis.

Due to the large quantity of material being generated as a result of this extensive sampling

exercise, a supervisor has been appointed, in addition to two assistants, to supervise the archiving

of samples and finds.

Excavation

To date two hundred and forty features or possible features have been excavated in Quadrant A.

One hundred and three of these have been found to be non-archaeological including a modern

geotechnical pit. One hundred and thirty-seven features are interpreted as archaeological - eighty

are enclosure postholes, thirty-two are postholes off the line of the enclosure, fourteen are small

pits inside the enclosure, eight are small pits outside the enclosure, one field ditch, one hearth,

and one furrow.

Quadrant C

The following works have taken place in Quadrant C (the NW quadrant in which the inner

enclosure is located): trowel back, magnetic susceptibility survey, supplementary pre-excavation

planning, and geoarchaeological control sampling. Excavation in Quadrant C has now

commenced. Excavation of the later field ditch which bisects the site is being prioritized in order

to assist in keeping water away from the inner enclosure.

Quadrant A

Excavation is nearing completion in Quadrant A. Excavation is complete in 18 of 20 grid squares

and recording is being completed in the remaining two. The completed post-excavation plans are

currently being digitized.

Part of this quadrant corresponds with ‘the northwestern segment of the outer enclosure’ which

was identified as one of three key excavation areas in the Supplemental Method Statement for

Lismullin National Monument (02 August 2007).

In the northwestern segment key area, thepattern of postholes is more complex and there are a number of additional features clusteredaround the outer enclosure. Excavation of these features is complete and analysis is ongoing. No stratigraphic relationship has been recorded between the enclosure and these features. Their size, shape and fills are broadly similar to the range of size, shape and fills of the enclosure postholes, however these are not distinctive enough for this to be meaningful. One of these features however, in Grid 12, has produced sherds of what has been preliminarily identified as later Bronze Age coarse ware pottery (Eoin Grogan pers comm.).

One of the additional features identified in this key area included a pit from the surface of which

numerous sherds of what has been identified as middle Bronze Age domestic cordoned urn

pottery (Eoin Grogan pers comm.) have been collected. Preliminary investigations indicated that

this pit did not appear to be stratigraphically related to the outer enclosure. Considering the early

Iron Age C14 date received for the stakeholes, it was considered important to verify this and

attempt to establish the relationship between this pit and the site as a whole. Excavation of the pit

has been completed and has confirmed that it is not possible to stratigraphically relate the pit

 to the post enclosure. The excavated feature is an extremely shallow depression from the

fill of which further sherds of identical pottery have been recovered. It would appear that this

feature had been heavily truncated.

A range of dispersed small features including fourteen pits or postholes and a hearth have been

recorded inside the enclosure. No distinct spatial patterns have been identified. Three small

shallow pit features in Grid 3 have produced sherds of what has been preliminarily identified as

later Bronze Age pottery (Eoin Grogan pers comm.). In addition a furrow and a modern squareshaped

geotechnical pit have been excavated inside the enclosure in this quadrant.

Eight small pits or postholes have been excavated outside the enclosure.

To date none of the enclosure postholes have produced any artefacts, however their fills remain to

be sieved. The current evidence of a number of apparently dispersed features producing bronze

age pottery of different periods, and the early iron age C14 dates from a selection of enclosure

postholes appears to indicate that these dispersed features represent earlier activity and are not

directly related to the enclosure.

Enclosure Postholes

Excavation of the enclosure postholes in Quadrant A is complete. A total of eighty enclosure

postholes have been recorded, sampled and fully excavated in Quadrant A. A further thirty-two

postholes off the line of the enclosure ring have been excavated. The postholes have dimensions

ranging between 15-23cm in diameter and between 15-23cm in depth. The postholes are

generally arranged at 0.4-1m intervals and the enclosing rings 1.5-2.5m apart with apparent

localized variations in their spacing.

Preliminary examination of the half sectioned postholes on site by Dr Steven Lancaster, as

described above, concurs with the excavator’s interpretation that the posts were most likely

driven into the ground (rather than being placed into a prepared posthole) and that the clay fill

surrounding the postpipe has resulted from half driven posts being manually moved to gain more

purchase in the ground before being driven further. As described above, a thin section sample

from a specific posthole has been proposed in order to investigate this theory further.
 

A thin clay layer c. 2cm deep was recorded in the box section, between the two postholes. Three

possible interpretations were initially considered for this deposit:

• That it is the remains of an earthen bank, revetted by the two concentric outer rings of

posts – this might imply that there was a timber facing between the posts.

• That it is a trampled ground surface - this might imply that the outer concentric rings

delineated a processional routeway.

• That it is a localized concentration of buried topsoil/palaeosoil similar to the layer

recorded around the inner enclosure.

However, preliminary examination of this deposit on site by Dr Steven Lancaster, as detailed

above, suggests that it is unlikely to be a trampled surface or bank material. A thin section

sample of both this deposit and the underlying subsoil is to be taken for further analysis. An

additional box section has been excavated through two postholes in Grid 12 in order to test if the

palaeosoil recorded in Grid 11 extends through this area. No evidence of a similar deposit has

been identified.

Linear Ditch (F3611)

Excavation of the east-west aligned ditch is complete in Quadrant A. The ditch is cut by a figureof-

eight cereal drying kiln outside the enclosure on the basis of which a date range of late Iron

Age to early medieval is currently suggested. Within Quadrant A it is 33m long by 0.95m wide

by 0.4m deep and contains between 2 and 4 fills. The basal fills appear to have silted up over

time indicating that this feature may have functioned as a drain. A ditch terminal has been

identified adjacent to the eastern boundary of Quadrant A in Grid 11 representing a short break or

causeway. A corresponding terminal is visible in Quadrant B where the ditch continues its

course. The intersection between this ditch and a north-south aligned linear feature (F2724) in

Grid 2 are being investigated. Quarter sections have been excavated at the point of intersection

between these features however the stratigraphic relationship has not yet been confirmed due to

the similarity of the fills. The quarter sections have been left open to the elements in an attempt

to improve their visibility.

Site Conditions

In general, conditions on site have been good since works recommenced. The sandbag cordon

has assisted in keeping excessive silt from accumulating on the enclosure during heavy rainfall

and this has been monitored and supplemented where necessary.

A sheet of plastic has been unrolled and positioned close to the enclosure for speedy deployment

should it be deemed necessary.

A water bowser and hoses have also been provided on site and have been used to maintain

optimum moisture levels in dry sunny conditions.

Following trowel back of Quadrant C a sump hole was excavated in order to allow for pumping

should the site flood in the future. In addition excavation of the later field ditch which bisects the

enclosure has been prioritized in order to assist in keeping excess water away from the inner

enclosure.

Lismullin National Monument, Director’s Progress Report 1 Aidan O’Connell 17 September 2007 9