2006:585 - COOLDRINAGH: Leixlip Water Treatment Plant, Dublin

Two phases of testing were carried out at Cooldrinagh, Co. Dublin, in advance of a proposed extension of the adjacent water treatment plant. The site was situated just south of Leixlip on a bend in the River Liffey where the Geological Survey of Ireland has identified several palaeochannels of immediately post-glacial date, before the river shifted to its present course. The site was crossed by two sunken fences, or ha-has, dating to the late 18th century, part of the landscaping associated with the adjacent Cooldrinagh House. A golf-course was constructed here in the 1990s, and overgrown bunkers, fairways and greens were still clearly visible.

From the 1990s onwards, the site has been the subject of a series of archaeological investigations. In the early 1990s monitoring of groundworks associated with the golf-course construction took place. Particular attention was paid to the top of the ridges at the north end of the site, but nothing of archaeological significance was noted.

In 1995 archaeological excavation took place on a small mound to the west of the site, directed by Clare Mullins. Prior to excavation, the mound was thought to be a possible ring-barrow, and subsequently became RMP site DU017–075. Excavation revealed the mound to be an 18th- or 19th-century landscape folly, surrounded by a contemporary enclosing ditch. Beneath the mound were found a number of non-associated subsoil-cut features ranging from the late 7th to the early 13th centuries, as well as a large assemblage of Mesolithic worked flints. Other finds include a spiral-ringed pin and a pseudo-pennanular ring-brooch, together with a quantity of medieval and post-medieval debris (Excavations 1995, No. 52, 95E039).

In 1997, a programme of machine test-trenching was carried out under the direction of Martin Byrne, but, apart from some pottery sherds of medieval date and two medieval bronze stick-pins, nothing of archaeological interest was noted (Excavations 1997, No. 90, 97E0027). Following on from this, monitoring of groundworks in the western part of the site by Clare Mullins produced an assemblage of lithic material and some medieval pottery, but no other traces of human activity were noted (Excavations 1997, No. 91, 97E0027 ext.). As a result of these finds the area was added to the RMP files as DU017–79. In 2004, monitoring of a water pipe for the Lucan to Palmerstown water scheme took place. No archaeological material was identified during the course of this work.

A number of investigations were also carried out in 2005. A geophysical survey carried out by Earthsound Archaeological Geophysics identified a number of areas of archaeological potential, which were tested by the excavation of eleven trenches, under the current ministerial consent number and under the direction of Clare Mullins (Excavations 2005, No. 410). No archaeological features were noted, but a number of flints, considered to be evidence of Mesolithic activity, were found in several trenches. A programme of archaeological field-walking and a survey of the plough zone were also carried out.

In the 2006 campaign, the initial phase of this testing was concentrated on the three areas, A, B and C, which would be affected by the proposed development. The testing programme included the digging of 15 hand-excavated and 41 machine-excavated trenches, together with the excavation and sieving of 200 test-pits and the metal detection of all excavated spoil. Forty pieces of flint were recovered from the test-pits, with no particular concentrations noted. Nothing of archaeological interest was found in Areas A and C, to the south and east of the site, apart from some flint in the ploughsoil. In Area B, however, two of the test-trenches revealed what appeared to be the remains of a prehistoric tomb, located in an east–west palaeochannel, close to the southern limit of the site.

Following this discovery, Phase 2 testing was initiated, the object of which was to clarify the nature of the tomb and find its limits, as well as to monitor groundworks along the line of a proposed water mains to Ballycoolen, to the east of the tomb. When the sod was removed from the area around the two former test-trenches, it was revealed that the remains here consisted, in fact, of two adjacent monuments. To the west was what appeared to be a passage tomb. It seemed to have been reduced to ground level at some stage, with only the deeper western side, where the tomb seemed to have been partly dismantled and filled in, surviving to any great depth. Immediately to the east of this was a circular kerb of large stones, within which were a small central cairn and two cists. This monument had also been severely disturbed.

Removal of the sod to the west exposed very stony topsoil, around 0.2m thick, containing a lot of modern material and representing ploughed-out cairn material. This was investigated by means of five 2m-wide, hand-excavated sondages, revealing the remnants of an oval cairn, measuring 19.3m by 16m. The greater part of the cairn consisted of a thin, patchy, disturbed layer of blue/grey limestone resting directly upon the bedrock, from which it was derived. There was a discontinuous yet distinct line of angular quartz fragments around the edge of the cairn material, seeming to represent the remains of a quartz facing. Towards the south-east edge of the cairn a large fragment of human skull was discovered, beneath which were a jaw fragment and some long bones. These bones, perhaps representing a secondary inhumation, lay in a loose, stony, loamy deposit with no discernable cut. As well as flint, a number of modern finds were noted amongst the stones of the cairn, further evidence of the degree of disturbance to which it had been subjected.

On the western side of the cairn the bedrock dipped sharply. Several large upright slabs, almost certainly orthostats, had been revealed here during the Phase 1 testing. There was a line of three of these running north–south, with a further two stones opposite and slumped towards them. Two further possible orthostats were also identified on the surface, one partially exposed at the southern end of the test-trench and another towards the north, both at right angles to the other slabs. The slabs measured up to 1m by 0.8m and 0.26m thick and together may have formed a structure some 4.8m by 0.8m, probably a passage or small chamber.

A very stony material, around 0.8m thick, filled the gap between the orthostats. The upper part of this consisted of a very stony, loose, loamy silt containing modern finds, animal bone and shell, but further down this became a more compact, silty clay and a quantity of burnt and unburnt fragments of human bone was encountered, together with more animal bone. A small sondage revealed that, near the base of the tomb sealed by a layer of charcoal, there was human bone, lying on several small, flat stones, perhaps indicating an in situ burial, resting on the floor of the tomb.

Around 2.4m to the east of the cairn were the partly ploughed-out remains of a circular stone kerb with an internal diameter of 14m. This was constructed from large, subrectangular blocks of the local blue/grey limestone, some of which were displaced. The circle was not complete, being best preserved on the western side. Two rounded granite stones were noted just outside the line of the kerb on the southern side, perhaps indicating that there was an entrance here. Outside the kerb to the west was a skirt of densely packed, medium-sized limestone, extending up to 1.2m from it. A small, box-like structure containing some animal bone was noted amongst this stone, suggesting that it may have been largely in situ, perhaps forming an external bank.

With three notable exceptions, the stone within the kerb was generally small and sparsely scattered. Some of the smaller stones were arranged in neat lines running north–south, probably as the result of ploughing. The eastern part of the monument was almost completely devoid of stones, with just a light scatter here. In the centre of the kerb circle was an L-shaped structure of closely packed small stones, with a dense scatter of similarly sized stones spread out to the north of it. This feature may have been a small cairn, with the scattered stones representing its ploughed-out remains. As well as a selection of modern finds, small fragments of burnt bone were found amongst this scattered stone.

Two rectangular cists were discovered in the south-west quadrant of the kerb circle, between the kerb and the central structure, and, on the advice of the DoEHLG, these were fully excavated. The larger of them, Cist 1, was orientated east–west, with two large limestone blocks forming the sides and two smaller end stones within them forming the ends. The two sides of this cist were actually exposed on the ground surface, hidden only by the long grass here. The external dimensions of the cist were 1.2m by 1.2m and the internal dimensions were 0.87m by 0.6m, with a depth of 0.5m. No capstone was present, but the cist was surrounded by a concentration of large to medium-sized pieces of limestone, some of which may have been supports for the side stones.

The upper fill of Cist 1 had been disturbed in recent times, as evidenced by a metal beer can found within it. Below this was fairly loose, orange silty clay, 0.12m thick, which contained a few fragments of quartz and bone and appeared disturbed. The basal fill was a very loose clayey silt and within this layer, lying on the base of the cist, were the partial remains of a human skeleton. The skeleton consisted of a cranial fragment, a few pieces of vertebrae, two crushed pelvic fragments, femurs, tibias, a fibula, a calcaneus and a talus, most of these lower limb bones being articulated. No ribs or upper limb bones were present. The skeleton was in a flexed position, facing south with the head towards the east, the unfused long bones indicating that the individual was a juvenile. The bones rested on the floor of the cist, which was constructed from slabs of limestone, although these appeared disturbed in the centre. It seems that the cist had been robbed at some stage, the culprit digging down straight through the skeleton and floor of the cist.

Cist 2, just east of Cist 1, was a smaller, slighter structure, of similar basic design, with external dimensions of 0.85m by 0.62m and internal dimensions of 0.56m by 0.44m, with a depth of 0.33m. It was also orientated east–west and lacked a capstone. The sides of the cist were supported externally by supplementary limestone blocks packed against them. Upon excavation, two sandy silt fills were noted, containing a few small fragments of charcoal and bone, but no skeletal remains were found. The base of this cist was formed from the natural bedrock.

A small sondage was excavated between Cist 1 and the central cairn. A layer of burnt, reddish-brown silty clay was noted running under the cairn, but no clear stratigraphical relationship could be established between the two features. There did not appear to be a cut associated with the cists, which were probably built at ground level and may have been covered with a small cairn of stones.

No new archaeology was discovered along the route of the pipeline, but a pit and adjacent hearth, discovered during Phase 1, were fully excavated. The hearth was rectangular in plan, measuring 1.1m by 2.2m, and had been cut into the bedrock and clay to a depth of 0.25m. The base of the hearth was formed from very compact, fire-reddened clay containing occasional charcoal flecks. A sondage through this clay showed that it was burnt to a depth of up to 0.04m. Above this was a deposit of grey/brown/orange silty clay containing large amounts of charcoal and ash. The upper fill consisted of loose stones derived from the bedrock, which seemed to have been deliberately placed over the hearth. Two burnt flints were found within these stones.

The pit, 2.4m to the south, was subcircular in plan, measured 1.44m by 1.26m and was up to 0.56m deep, the base sloping sharply from north-east to south-west, following the natural slope of the bedrock. It had been cut into the bedrock on three sides and into the natural clay at the southern end. The basal layer of the pit was a very clean, soft, grey clay up to 0.3m thick. This clay covered the base of the pit and the rock-cut sides but was less extensive where the pit had been cut through clay. Above this was a succession of charcoal-rich clay or clayey silt deposits, with evidence for a possible recut of the pit. A number of finds were recovered, including burnt and unburnt animal bone, antler, a disc-shaped granite hammerstone, flint flakes, blades and scrapers, a large, water-rolled granite pebble, as well as a quantity of burnt quartz and granite.

Weathering marks, evident in the central part of the limestone base of the pit, displayed characteristics of those formed from water percolating through subterranean rock and the fact that this weathering was absent from the rock at the margins of the base suggests that there was originally a natural damp hollow here that was enlarged by chipping away the rock from its sides. The rock was very porous and the basal clay layer was probably laid down in order to make the pit waterproof. This interpretation is strengthened by the fact that this clay layer covered the rock but was less in evidence where the side of the pit was cut through clay. The burnt fill of this pit and the great quantity of bone and antler recovered from it indicated that cooking was taking place here. The large amount of burnt quartz and granite found in this deposit, taken together with the waterproof clay lining, suggested that this cooking was by means of water heated with stones and that the stones had been fired in the nearby hearth. These two features, a hearth and waterproof cooking pit, are typical of fulachta fiadh, but no burnt material was found in the surrounding area and it may be that the pit was in use for only a short time.

The presence of burnt quartz and granite in the pit is of interest, since these stones do not occur naturally in the vicinity of the site, although granite pebbles may have been available along the bed of the nearby River Liffey. The naturally occurring limestone would not be suited to this type of cooking process, especially since it readily absorbs water. It would not be a practical proposition to import quartz on site for this purpose and the obvious inference is that it has been robbed from the nearby cairn.

The tombs, which were not further affected by the development, were covered by geotextile and two low mounds of earth were raised over them in order to mark their position and provide protection. At the time of writing, post-excavation analysis of bone and lithics is ongoing and samples have been sent for radiocarbon dating. It is hoped that this will allow a closer dating of the various elements of the site and allow the broad sequence of events to be reconstructed.

Windsor House, 11, Fairview Strand, Dublin 3