1996:129 - LAMBAY ISLAND, Dublin

The site is in a small valley which runs in a north-west to south-east direction at a height of 183m OD. Two cuttings (1 and 2), each 4m x 1.5m, had been opened to examine the junction of the porphyritic andesite (porphyry) outcrop with deposits of loose porphyritic pieces and to analyse the stratigraphic sequence. Cutting 1 is at the south-east end of the valley and Cutting 2 is at the north-west end. Cutting 1 was subsequently extended to the south-west by opening two additional areas; Cutting 1W (3m x 1.5m), separated from Cutting 1 by a 1m baulk, and Cutting 4 (4.3m x 1.5m), separated from Cutting 1W by a 0.5m baulk.

In 1994 a series of five 1m2 test-pits (TP 1–5) were opened along the floor of the valley to assess the extent and survival of archaeological features. The results led to the expansion of excavation in the area around TP2, 6.5m to the north of Cutting 4. This can be treated as comprising two areas of excavation: firstly the area immediately to the southwest of TP2–TP2W/SW/Curting 3- and secondly Cuttings 5 and 6 to the north-west.

Cutting 1W
Here nineteenth-century agricultural disturbance had led to the truncation of the porphyry debitage build-up. But at a depth of only 50–100mm below the surface a dense mass of porphyry occurred. In the south-west corner of the excavation area there was a sandstone grinding slab and three polishing slabs of porphyry in situ. The base of these slabs rested directly on a spread of decorated Neolithic pottery in a yellow-brown clay matrix. Below this matrix there was a compact blocky surface of porphyritic andesite pieces, which in turn overlay small pieces of porphyritic andesite set in a dark reddish-brown/dark brown matrix with a depth of 0.12–0.15m over the subsoil, which was exposed in a number of rabbit burrows. It appears that this dark reddish-brown/dark brown matrix represents the surface of the soil/palaeosol at the beginning of the build-up of porphyritic andesite debitage over it.

Through the stratigraphic sequence were quantities of struck flint, hammerstones, cobbles and sandstone rubbers. A broken polished porphyry axe was found in this cutting. All the material, with the exception of a small quantity of modern pottery in the cultivation zone, in both disturbed and in situ contexts appears to be Neolithic in date.

Cutting 4
The removal of a very stony topsoil revealed the presence of a dense build-up of porphyritic andesite at the east end of the cutting. Further to the west there was a cultivation soil with furrows and rabbit burrows. Below the dense porphyry mass was a surface composed of very compact porphyritic blocks of variable size. This was underlain by a matrix of small porphyry pieces in a dark reddish-brown/dark brown layer overlying subsoil. A rabbit burrow cut into this context revealed a large cache of Neolithic flint flakes and blades, some clearly in situ. The stratigraphic sequence of the burrow also suggested that there was a distinct thin palaeosol over the subsoil. To the west excavation has revealed the surface of a large mass of porphyritic andesite. From the stratigraphy in the side of the rabbit burrow it would appear that this was the top of the fill of a feature cut into the palaeosol and the subsoil. In the porphyritc build-up hammerstones, rubbers and grinding slabs occurred. Struck flint was also common.

TP2/TP2W/SW/ Cutting 3
In Test-pit 2 (TP 2), lying 6.5m to the north-west of Cutting 4, sherds of a Neolithic pot of Carrowkeel ware occurred in a stony spread in the lowest part of the cultivated soil and above what appeared to be part of a truncated feature cut into the subsoil. This consisted of a shallow trench running to the north-east and with a return to the south-east. Excavation to the west of this test-pit (TP2W/SW/Curting 3) revealed a large, roughly circular spread of stones in the base of the cultivation soil. Below this stone spread there was a large stone-filled pit, 1.6m x 1.4m, dug into the subsoil. It appears that originally there would have been a low ‘cairn’ of stone over this pit, which has been truncated and spread owing to modern cultivation.

In the pit there were a series of deliberate surfaces with careful arrangements of stone and placed deposits. A central and early feature in the pit was a slab setting, apparently deliberately placed on a step or ledge which was made when the pit was dug. The earliest deposit in the pit was a basal sediment containing comminuted cremated bone, charcoal and flint chips. In association with this sediment were Carrowkeel sherds. Around the edge of the pit there appears to have been a ‘packing’ of sediment, while the main part of the fill was dominated by pieces of porphyritic andesite and hammer-stones, cobbles and rubbers associated with the working of this stone. There were a series of pottery deposits both in the stony central fill and in the ‘packing’ sediment. It appears that the arrangement of the stone fill itself was deliberate. One of the last acts of formal deposition may have been the placement, close to the top of the pit, of a flint core, a broken sandstone rubber and granite hammerstone.

Cutting 5/Cutting 6
Initially an area measuring 5m x 3m (Cutting 5) was opened to the north-west of TP2, as this appeared to be an area with significant Neolithic activity; this was later extended to the south-east (Cutting 6). The cultivation soil was excavated in spits 0.1m in depth and in 1m x 1m units. Again struck flint, hammerstones and rubbers and the occasional small sherd of Neolithic pottery occurred throughout the cultivation soil without any obvious patterning. At a low level in the cultivation soil a couple of fragments of porphyritic andesite with ground and polished surfaces were revealed. There was also clear evidence of rabbit-burrowing right through the cultivation soil and into the subsoil. Sealed under the cultivation soil were a number of truncated features cut into the subsoil, These consisted of two lengths of truncated shallow trenches and two truncated pit features.

Extension of the excavation to the east and south-east revealed the presence of three distinct stone concentrations which appeared to be similar in form. In all cases the features appeared to extend into unexcavated areas and rabbit-burrowing had disturbed the stratigraphic sequence. One of these features, 1.3m x 0.6m in extent, survived as an actual cairn to a height of 0.2m above the surrounding level, while the surfaces of the other two (1.2m x 1m and 1m x 0.5m in extent) were at the same level as the base of the cultivation soil. A sharply defined V-shaped trench at least 0.2m deep ran north-west to south-east into an unexcavated section.

The significance of the excavation to date is that it appears to confirm the quarrying of porphyritic andesite during the Neolithic and the use of the quarried rock for axe production. It seems clear that a range of other activities were raking place on the site, including the deliberate placement of porphyritic andesite debitage and other material in large pits.

Excavation in 1996 was grant-assisted by funding from the Heritage Services, Department of Arts, Culture and the Gaeltacht, on the recommendation of the National Committee for Archaeology of the Royal Irish Academy.