1998:209 - LAMBAY ISLAND, Dublin

The site shows evidence of two related activities: the working of the porphyritic andesite outcrops that form the sides of the valley for stone axe production; and the occurrence of a number of related features on the valley floor, under and partially truncated by a cultivation soil resulting from 19th-century spade cultivation.

The primary objectives of the 1998 season were:
(1) To evaluate the extent and nature of the pits and associated features in the main area of excavation on the valley floor (Test-pit 2 and associated areas, Cuttings 3 and 5–8). Several additional test-pits were excavated to determine the condition of survival and the extent of archaeological features.
(2) To continue and complete the excavation of the cross-section (Cuttings 1, 1W, 4, 9 and 10) across the valley from the working area out from the west-facing rock face to the low bank forming the east-facing side of the valley at this point. The excavation of Cuttings 1 and 1W had been completed in 1997 (Excavations 1997, 57-9).
(3) To examine spatial variability in the working of the porphyritic andesite by excavating a series of test-pits along the bank of porphyry build-up against the west-facing porphyritic andesite outcrop.
(4) In 1997 a series of test-pits had been dug in the small valley immediately to the west of the valley that has been the focus of the excavation project. One of these (Test-pit 7), close to the west-facing porphyritic andesite outcrop, had revealed the edge of a build-up of porphyritic andesite debitage and associated grinding stones, with little signs of disturbance by cultivation activity. To look at the nature and character of the exploitation an excavation cutting 7.3m (east-west) x 2m in extent (Cutting 11) was opened, with Test-pit 7 lying immediately to the north-west of the cutting.

The main area of excavation on the valley floor
As in previous years, all the cultivation soil that was excavated was removed in spits 0.1m deep and finds were recorded in 1m x 1m units. A distinct difference can be seen in the stratigraphic sequence beneath the cultivation soil within the excavation area. In the western part it was possible to recognise a very thin interface between the cultivation soil and the underlying subsoil. It appears that this interface represents the base of disturbance/truncation of the original palaeosol. In the eastern part of the area underlying the cultivation soil is a brown to dark brown, sandy loam (C707) over subsoil. This appears to be the surviving portion of the palaeosol. The sandy subsoil also slopes down to the east and has numerous rabbit burrows cut into it. It was hoped that C707 would have greater preservation of Neolithic features, and a number had been identified (F8–10, 14 and 15).

In 1998 a further two features were identified in the Cutting 7 area. F16 appeared to be a small segment of a trench with a distinct, loam-textured fill containing occasional charcoal flecks. In the north-east corner of Cutting 7 was a dense spread of stones (F21). Excavation of this feature exemplified the problems of recognising features in this context: there was no sign of a cut or edge and yet it appeared to be a definite feature. C707 had been churned up by rabbit-burrowing activity, and this has resulted in the destruction of the cuts of archaeological features. The stone fills of what appear originally to have been pits (F14, 15 and 21) are all that have survived to a greater or lesser extent intact. In Cutting 8 a dark yellowish/brown, loose, sandy loam with numerous pieces of porphyry underlay C707/807 and overlay the subsoil.

To the west of the edge of C707 Neolithic features only survive as truncated cuts in the subsoil or as spreads of stone above pit features. In Cutting 5 a segment of a very shallow trench, c. 0.8m in surviving length, was discovered cut into the subsoil. In the fill was a small sherd of Neolithic pottery and a flint flake.

At the end of the 1998 season excavation of much of this main area was completed. What remains to be worked on is a 3m x 4.5m strip running north-east to south-west, centred on F11, F2, F7, F8 and F10.

A series of test-pits was excavated to the north and west of this main area of excavation. Test-pits 11 and 22 were immediately to the north, 12 and 13 to the west, and 26-28 at the northern end of the valley in the lowest of the three modern cultivation terraces, or small fields, east of Cutting 2. The character of the stratigraphy was similar in all these pits with the exception of Test-pit 12, which is immediately adjacent to the east-facing outcrop of porphyritic andesite forming the western side of the valley. Here was debitage immediately below the sod and above the subsoil. In all the other test-pits there was clear evidence of intensive spade cultivation. There was Neolithic flint in all, but no surviving archaeological features. The presence of Neolithic pottery and a large projectile point or javelinhead in Test-pit 13 suggests that the southern end of the valley was the main focus of Neolithic activity.

Cuttings 4, 9 and 10
In Cutting 4 what was left to excavate was the major basal layer of the porphyritic andesite material, C408, overlying a palaeosol, C409, which has some smaller porphyritic andesite pieces impressed into the surface. The basal slabs in C408 are quite large and appear to have been deliberately placed to level up the original ground surface, which may have been quite uneven. The build-up over this surface includes non-porphyritic andesite lithic material, such as hammerstones, rubbers and struck flint flakes, some with retouch. Further west in this cutting 19th-century cultivation has truncated the stratigraphic sequence almost to the top of the palaeosol. In addition running east to west through the cutting is a series of intrusive rabbit burrows. On the south side of the main burrow run and truncated by it is a small cut feature, F13 (0.23m x 0.1m with a depth of 0.14m), cut into the palaeosol and subsoil. In this were a number of flint blades and flakes that appear to be part of a cache. This cache was sealed by C408. Excavation in 1998 revealed more disturbed flakes from the cache.

About 0.75m to the north-west of F13 on the north side of the east-west-trending burrow and cut into the subsoil was a roughly circular pit, F00, measuring 0.7m at the mouth and with a depth of 0.3m, which appears to have been sealed by the palaeosol, C409. The top of the pit seems to be disturbed on the southern side by rabbit activity. There was a large stone in the top of the pit, which was lined by small slabs on the southern side. The fill was a homogeneous, soft, dark yellowish/brown loam, with charcoal flecks. There were a number of structured deposits in the pit. In this regard F00 appears to be related in some way to the pits in the main area of excavation to the north.

Excavation revealed what appears to be the top of another pit feature (F19) in the north-west corner of Cutting 4. Here there was a setting of stones with a distinct, curved outer edge, suggesting that it is a segment of what may be a larger feature. On the surface large quantities of flint flakes and beach nodules are visible.

In Cutting 9 the cultivation soil was relatively shallow and was underlain by a compact build-up of porphyritic andesite. This context (C904) is an intact Neolithic surface with spreads of pottery and lithics, apparently corresponding to C408 (and C111) and overlying F19. C904 continues into Cutting 10, where the edge of the context can be seen running in a north- south line close to the eastern edge of the cutting.

Two test-pits (25 and 24) immediately to the south of Cuttings 4 and 9 confirm that the stratigraphic sequence seen in these areas continues to the south. It appears that C904 has a considerable surface expression and that there is a definite modern cultivation cut or truncation into the porphyritic andesite build-up along a north-south line at the east end of Cutting 4.

Test-pits 14–21
Eight test-pits were dug along the north-south line 14.5m east of the site baseline to test the stratigraphy and the character of the porphyritic andesite build-up along the bank abutting the west-facing outcrop, to the north and south of Cutting 1. Test-pit 17 was excavated down to the bottom of the build-up to see how the stratigraphy compared with the stratigraphic sequence found in Cutting 1 to the south.

The results show that there is a recognisable build-up of porphyry debitage stretching from Test-pit 14 to Test-pit 20. Test-pit 20 appears to be close to the northern terminal of this build-up, and in plan the surface of the porphyry debitage deposit curves to the east. In Test-pit 21 there was no sign of the porphyry debitage deposit. The test-pits show that along the line of the bank the porphyry debitage has been disturbed. Test-pits 15 and 17–20 all show signs of a truncation of the surface of the porphyry build-up. However, the stratigraphy in Test-pit 16, with a weathered, compact, porphyry-rich layer over the actual debitage surface, suggests that in this location the debitage build-up is undisturbed. At the southern end of the bank of debitage in Test-pit 14 it appears that what remains of the debitage is all sitting in cultivation soil. Immediately to the east of this test-pit there are also indications of modern quarrying of the porphyry outcrop in the form of what appears to be a well-defined, wedge-shaped cut into the bedrock.

Looking at the character of the surface of the debitage build-up in the test-pits and examining the components of this build-up in Test-pit 17 it seems clear that the bank of debitage is not of uniform composition and is varied along its length. It may be that the apparent regularity of the bank on the field surface is the result of modern clearance and cultivation activity and that before this it was much more amorphous, reflecting debitage from a series of quarrying and production episodes, perhaps spread over a considerable period of time during the Neolithic.

In Test-pit 21, while there is no sign of porphyry debitage, the surface of the bedrock has a ground surface with multiple, parallel, fine striae orientated north-south. These striae are the result of glacial smoothening. The implication of this is that the exposed outcrop surfaces in the valley would all have been striated. It may well be that part of the original attraction of the valley was that it had porphyritic rock outcrop that already had an apparently polished surface.

Cutting 11
In the small valley to the west of the one that has been the focus of the excavation project a cutting 7.3m (east-west) x 2m was opened up, with Test-pit 7 immediately adjacent to the north-west of the cutting. The higher, eastern end of the cutting is actually on the porphyry outcrop.

Removal of the sod revealed a compact, weathered, porphyry debitage surface. Excavation to date suggests that there are a number of distinct layers or contexts representing episodes of quarrying and production. A major spread of debitage forms the current excavation surface. Towards the western end of the cutting a rabbit burrow disturbed the surface of this context, but further west is a zone with a concentration of pieces of porphyry with ground surfaces and small sandstone rubbers.

Within the excavated layers of the debitage are small flakes and chips of flint, some burnt, occasional pieces of rock crystal and small sherds of Neolithic pottery. Most of the last seems to resemble the decorated bowl pottery found elsewhere on the site, but there are also sherds of thin-walled, fine pottery that may come from carinated bowls (Western Neolithic pottery).

Radiocarbon dating
A sample of Prunus charcoal from one of the fill contexts in the large excavated pit feature (F1) on the valley floor was submitted to the Radiocarbon Laboratory, Department of Experimental Physics, UCD. The sample dates to 4930+175 radiocarbon years BP (rounded to the nearest five years). Calibration of the date was carried out using the CALIB programme of Stuiver and Reimer (1993) and was based on the decadal calibration of the dating using the intercept method. The 1-sigma calibrated age range for the sample is estimated as 3965–3383 BC. This provides an indication of the date of activity on the site. Further samples from other contexts are being dated.

The final season of excavation will take place in 1999. Excavation in 1998 was grant-assisted by funding from Dúchas The Heritage Service, Department of Arts, Heritage, Gaeltacht and the Islands, on the recommendation of the National Committee for Archaeology of the Royal Irish Academy.

Belfield, Dublin 4