M3 Clonee-North of Kells Motorway Scheme

Lismullin National Monument (A042 & E3074)

Director’s Excavation Progress Report 5

Aidan O’Connell

Archaeological Consultancy Services

11 October 2007

Summary

Quadrant A

The post excavation plan is complete and attached.

Quadrant C

Fifty-four of the sixty-one inner enclosure postholes have been excavated to date. The postholes

vary in diameter between 0.10m-0.30m with an average of 0.22m and between 0.16m-0.28m in

depth. The postpipes vary in diameter between 0.15m-0.26m and in depth between 0.16m-0.28m

in depth. Similar to the outer enclosure, the inner enclosure posts appear to have been driven. In

addition to being slightly larger than the outer enclosure posts it would appear that the

construction of the inner enclosure was more regular than the two outer rings, the spacing

between the posts was closer and there were fewer gaps between posts.

Excavation has commenced on the features inside the inner enclosure. Preliminary indications

are that the features are very shallow c.0.10m in depth. The fills are rich with charcoal flecks and

they contain some tiny fragments of burnt bone. One unworked flint flake was recovered from

one of these pits.

Excavation of the remaining grids in Quadrant C is ongoing. A row of post holes identified in the

pre-excavation planning adjacent the edge of the landtake south-west of the inner enclosure now

appear to be part of a double row. To date very few artefacts have been recovered from Quadrant

C. In addition to a small number of unworked flint flakes from the clean-back, three small

fragments of prehistoric pottery were recovered from a shallow deposit.

Dr Chris Burbidge visited the site on Tuesday 9th October and took samples for OSL dating of the

field ditch that bisects the enclosure, in addition to other features outside the enclosure.

Site Conditions

Conditions on site have been good with light rainfall.

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 and is now complete. Following the same sequence of trowel cleanback,

supplementary pre-excavation planning, magnetic susceptibility survey and control soil

sampling, excavation commenced in Quadrant C on 14 September and is ongoing.

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 postexcavation

plan of Quadrants A (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

pear-shaped 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

Dr. Steven Lancaster (Headland Archaeology Ltd) and Dr. Helen Lewis (School of Archaeology,

UCD) visited the site on the 20th September to review ongoing sampling strategies and to examine

the sectioned palaeosoil over the inner enclosure. They examined a slot-trench excavated through

the palaeosoil in the inner enclosure. Dr Lancaster concluded that the base of an ancient soil

survives in this area, which may contain chemical signatures of activities that were taking place

on the interior. Geoarchaeological samples have been collected from the palaeosoil on a grid

interval of 2m. The section through this soil has been recorded and a kubiena thin section sample

has been collected for further analysis.

Dr. Lancaster also carried out a geoarchaeological assessment of the western landtake section to

ascertain whether or not a greater depth of archaeological deposits may have been present in the

interface between the modern ploughsoil and the archaeological deposits as visible and exposed

on site. His assessment concluded that only the overlying ploughsoil had been removed and that

mechanical stripping has not impacted on the underlying archaeological deposits. A record of Dr

Lancaster’s site visit and findings is provided.

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

Lismullin National Monument, Director’s Progress Report 5 Aidan O’Connell 11 October 2007 4

M3 Clonee-North of Kells Motorway Scheme – Archaeological Investigations

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

Quadrant C

Excavation in Quadrant C is ongoing. Fifty-four of the sixty-one inner enclosure postholes have

been excavated to date. The postholes vary in diameter between 0.10m-0.30m with an average of

0.22m and between 0.16m-0.28m in depth. The postpipes vary in diameter between 0.15m-0.26m

and in depth between 0.16m-0.28m in depth. Similar to the outer enclosure, the inner enclosure

posts appear to have been driven. In addition to being slightly larger than the outer enclosure

posts it would appear that the construction of the inner enclosure was more regular than the two

outer rings, the spacing between the posts was closer and there were fewer gaps between posts.

A further two postholes have been excavated in the area between the inner enclosure and the slot

trench at the end of the funnel shaped avenue. These have smaller dimensions than the inner

enclosure postholes (average 0.11m diameter by 0.09m deep). It is not currently possible to relate

these features to the enclosure.

Excavation has commenced on the features inside the inner enclosure. Preliminary indications

are that the features are very shallow c.0.10m in depth. The fills are rich with charcoal flecks and

they contain some tiny fragments of burnt bone. One unworked flint flake was recovered from

one of these pits.

Excavation of the remaining grids in Quadrant C is ongoing. A range of additional features have

been excavated at the west and south of the inner enclosure. These include five pits, three spreads,

five postholes and seven stakeholes. Currently there are no apparent spatial patterns that could

aid with the interpretation of these features. The spreads are located directly west of the linear

field ditch and one of them contained some small fragments of later Bronze Age pottery. A row

of post holes identified in the pre-excavation planning adjacent the edge of the landtake southwest

of the inner enclosure now appear to be part of a double row. To date very few artefacts

have been recovered from Quadrant C. In addition to a small number of unworked flint flakes

from the clean-back, three small fragments of prehistoric pottery were recovered from a shallow

deposit.

Dr Chris Burbidge visited the site on Tuesday 9th October and took samples for OSL dating of the

field ditch that bisects the enclosure, in addition to other features outside the enclosure.

Quadrant A

Excavation is complete in Quadrant A and a post-excavation plan has been prepared. 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 postholes

forming the arc or ring of the enclosure or are immediately adjacent to it - twenty-two form the

outer ring, forty form the inner ring, 2 postholes are immediately external to the ring, 5 are

immediately inside the rings and 11 are located between the two rings. An additional thirty-two

features 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.

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, the

pattern of postholes is more complex and there are a number of additional features clustered

around 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. The only other artefacts recovered from this phase of works on

the enclosure are unworked flint flakes mainly from the clean-back but also from some of the

features with pottery.

Enclosure Postholes

Excavation of the enclosure postholes in Quadrant A is complete. A total of sixty-two enclosure

postholes have been recorded, sampled and fully excavated in Quadrant A. Twenty-two form the

outer ring and forty form the inner ring. A further eighteen postholes were immediately adjacent

the enclosure rings of posts but not directly on the line of either ring - 2 postholes are

immediately external to the ring, 5 are immediately inside the rings and 11 are located between

the two rings. 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

Lismullin National Monument, Director’s Progress Report 5 Aidan O’Connell 11 October 2007 9

M3 Clonee-North of Kells Motorway Scheme – Archaeological Investigations

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. Samples have been taken for OSL dating of this feature.

Site Conditions

Conditions on site have been very good with in general only light rainfall. The protective features

on site including the sandbag bund, the sump hole, the excavated field ditches and the extensive

use of barrow-runs are protecting the site. There has been no requirement as yet to use the

plastic.

Lismullin National Monument, Director’s Progress Report 5 Aidan O’Connell 11 October 2007 10