2004:0161 - ISLANDMAGRATH/BALLYGIRREEN/BOARLAND ROCK, Fergus Estuary, Clare

An intertidal survey/excavation was carried out in May 2004 on several archaeological sites on the Fergus estuary, Co. Clare, on the foreshores adjacent to Islandmagrath and Ballygirreen townlands and beside an intertidal feature known as Boarland Rock. The Fergus estuary was previously surveyed (between 1992 and 1997) as part of the Discovery Programme's North Munster Project, leading to the discovery of Late Bronze Age and early medieval structures on the mudflats (O'Sullivan 2001). The present investigations were carried out by the Palaeoenvironmental Research Unit, NUI Galway, and the School of Archaeology, UCD, and aimed to investigate the rate of erosion and destruction of the known wooden structures at Islandmagrath and Ballygirreen and to further sample them for wood species identification and tree-ring studies, as part of a research programme being carried out by Mary Dillon on woodlands and wood species selection in early Ireland.

Late Bronze Age structure, Islandmagrath
The Late Bronze Age structure at Islandmagrath is located on the Fergus estuary, on the west bank of the river, on an eroding bend (O'Sullivan 2001, 107–20). It is exposed for approximately two hours at every low tide on the lower foreshore. The site consists of two rows of uprights, less then 1m apart, which run together for 32m. The structure is linear and curves at the northern end to an S shape. Horizontal posts, varying in size, are woven around the uprights. It was originally thought to be a trackway across the muds, giving access to the water. This project has revealed that the site has been considerably eroded since the 1995–7 survey and much of the wood previously recorded, especially on the northern part of the site, has been washed away. A large amount of previously unrecorded wood on the southern side of the structure has been exposed. Two small wattle panels protrude from the mud to the west of the site.

The uprights ranged in diameter from 30mm to 100mm, with the majority measuring about 50mm in diameter. The uprights were at a 45 degree angle, leaning eastwards towards the water. This is probably as a result of erosion of the bank, as a number of upright posts to the south-west, further back from the water erosion front, were vertical. The horizontal timbers were 20–30mm in diameter and were up to 30mm long. These were woven around the uprights. The two rows of uprights seem to merge into one, 10m from the southern end. It is possible that the top row of posts is buried beneath the higher muds, as these are not yet subject to erosion. Five uprights to the south-east of the site were noted and are likely to belong to the same structure. A large post 0.1m in diameter and 3m in length was located at the north end of the structure, just beside the creek. It was sharpened to a point at one end, while the other end had a single axe mark. The bark was still visible, indicating that the post was not converted but used whole. Most of the uprights and horizontals also had bark still attached.

A box section was dug 0.3m by 0.3m at one of the uprights on higher ground to the south-west of the structure to establish the depth of the posts. This upright was 0.1m in diameter and one of the more substantial posts present. A hole was dug 1m into the ground. The cross-section of mud revealed a homogeneous stratigraphy, with no notable difference between the uppermost and lowermost mud. At least ten horizontal woods were removed from around the upright. At 1m depth the upright continued into the muds. The moisture content of the mud made digging any deeper impossible, as the deposits became unstable. As the upright protruded 0.2m above the mud, this gave a minimum height of 1.2m for the post. The depth of the posts lower down on the foreshore was also investigated. A number of posts were less than 0.3m in total height. These had cut marks on the end that was buried in the mud. Another small box section was dug at the northern end of the structure, near the lowest water level, to determine the original height of the posts. Two posts, each 0.6m in length, were crossed over each other in the mud. It can be concluded, therefore, that the posts had presumably originally been much higher but had been worn down to 0.3-0.6m in height by the eroding water.

The site was cored in two places using a gouge corer to a depth of 2m. This revealed rather uniform stratigraphy, consisting of blue-grey estuarine mud that had short intervals of high silt content. This indicates that the environment of the site has been unchanged since before the structure was built until the present day. The structure was built in an environment that was similar to that of today (i.e. it was built on estuarine muds). This is important when considering the original function of the structure.

In conclusion, the recent archaeological investigation of this site revealed that the structure had been considerably eroded since the 1995–6 survey. As a result, much previously unrecorded wood has become visible, and this will be radiocarbon dated and analysed for species and age. This will give more information about the woodlands in this area during the late Bronze Age and may indicate selective use of wood practices. Coring revealed that the structure was built in an estuarine environment, similar to what it is like today. The function of this enigmatic structure still eludes us. It could feasibly be a trackway, providing access to the water at low tide. It may be a fence of some kind. It is also possibly an unusual fish trap. It is hoped that further dates obtained for the structure, detailed wood analysis and comprehensive comparison between previous plans and photos and the new information gathered will yield some more information regarding the function of this site.

Medieval fish traps, Boarland Rock
The project also carried out intertidal surveys further south on the Fergus estuary, 4km to the south of Islandmagrath, at the point were the river widens into a full estuary and where a number of wooden structures were recorded. They were situated on the west bank of the channel, opposite a point named Boarland Rock (OS 50:7:3; NGR 132520 166504). Three structures were visible at low tide for c. two hours. Two large well-defined structures, Boarland Rock 1 and 2, ran perpendicular to each other. The structures consisted of rows of uprights protruding 0.2m above the estuarine muds. The uprights were 50-80mm in diameter. Horizontal rods, 20–30mm in diameter, lay between these.

Boarland Rock 1 was an L-shaped fish trap, stretching 65m east-west and 130m north-south. The two lines of posts met at a narrow point c. 1m in width and ran together for c. 5m to form a funnel-like end. For the most part, the structure consisted of two to four rows of uprights. However, at some points along the structure five or six rows of uprights were apparent. This is probably a sign of repair and rebuilding. Two large post-and-wattle panels were found near the funnel end of the construction. The largest of these was c. 2m in width by c. 5m in length. A sample of wood from the Boarland Rock 1 fish trap has produced a calibrated radiocarbon date of AD 1410–1460.

Boarland Rock 2 was smaller in size and ran across Boarland Rock 1. It was slightly different in type, as the lines were curved rather than straight and more V-shaped than L-shaped. It is likely that the two are broadly contemporary but were not in use at the same time. Boarland Rock 3 is another structure, 300m south of 1 and 2. This is smaller than both 1 and 2 but is similar in construction. It consisted of c. 80 uprights in a V-shaped arrangement, with little or no horizontal woods visible. In all three structures it was noted that many of the uprights were oak. To the north and south of these Boarland Rock structures, and on the same side of the river, were several post alignments, which were viewed from the water but not investigated. It is considered likely that they too are probably fish traps.

Previous archaeological investigations of fish traps on the Shannon and Fergus estuary have shown that they date from the early medieval period to modern times, with the majority probably being post-medieval in date (Sullivan 2001, 193–233). Previous intertidal surveys on the Fergus estuary also produced a fish trap fence of 5th-6th century AD date at Ballygirreen, but this current project's surveys have revealed that this site may now be eroded out. The structures at Boarland Rock had not been previously documented but were known to the local fishermen, who referred to them as 'old eel traps'.

Boarland Rock 1 has now been shown to date to the 15th century AD, the first such discovery on the Irish coastline and a useful addition to late medieval rural archaeology and economy. It is likely that the Boarland Rock fish trap complex as a whole dates from across the medieval period. The Boarland Rock 1 fish trap at least may have been built and used by the monks of the Augustinian Abbey on Canon Island, which is situated c. 3km further to the south and clearly visible from the site. This was founded by Donal M—r Ua Briain in the 12th century, but there is also architectural and historical evidence for the abbey's expansion through the 15th century, when its inhabitants were presumably making use of the diverse resources of the field and shoreline.

Reference
O'Sullivan, A. 2001 Foragers, farmers and fishers in a coastal landscape: an intertidal archaeological survey of the Shannon estuary. Dublin.

School of Archaeology, UCD and Palaeoenvironmental Research Unit, Department of Botany, NUI Galway