INTRODUCTION Island Eddy is a small uninhabited island in the inner reaches of Galway Bay (Map 1). It was home to a small but stable community until the Second World War. Thereafter the population declined rapidly until 1980, when the last two inhabitants left the island.The island ‘village’, now an overgrown cluster of ruined houses, stands at the eastern end. The site of a castle in its vicinity indicates that human settlement there extends back to medieval times. The island is composed of a string of low drumlins, ranged east–west, which are connected today by a series of shingle isthmuses and spits. The latter define two large inlets or ‘malluirs’, 1 one on the north-eastern side and the other on the south-west (Map 2).These give the island a deceptively large footprint: approximately 3km east–west and 1km north–south. The maximum elevation is 8m. As part of the Discursive Survey of Island Eddy (Roden 2010), a three-day expedition was undertaken to the island in August 2010. During this visit, several oblong cut stones engraved with numbers were recorded. Most of these had been noted in passing by one of the authors (PG) on previous visits. One was built into a house wall, two were in use as mooring stones at the harbour in the north malluir where the islanders once drew up their boats (Gosling, MacMahon et al. 2010), and six were set in line along the foreshore in the south malluir. The last-mentioned stones were spaced at equal distances and positioned just below the maximum height of the brown seaweed. A former islander, Pat Bermingham (pers. comm.), confirmed that they were used to mark out seaweed rights. Some six months later two similarly numbered stones were discovered by another of the authors (MSS) on the mainland some 2km to the north-east of Island Eddy. These were on the foreshore of Carrowmore townland at Ballinacourty. A survey of the rest of the shoreline of the townland by MSS and NES revealed many more such engraved stones, most of them set in a similar position to those on the foreshore of Island Eddy (Map 2). Several older local farmers confirmed that these stones also marked the seaweed rights which had been used when they were children. Many also said that the rights were originally administered by the local landlord. Seaweed-collecting was once of great economic importance in the west of Ireland, reaching a peak in the first quarter of the nineteenth century (Hardiman 1820; Evans 1957; Wilkins 1989; O’Sullivan and Downey 2010). Seaweed always had value as manure for the improvement of land, but in the seventeenth century it began to be used in Ireland for the production of kelp (McErlean et al. 2002). Kelp is the term given to the remnant left after the slow burning of plant material; it was used in glass-making, linen production and gunpowder, principally for its alkali but also for salt and potassium. Previously alkali had come from wood ashes (potash), but with the increasing deforestation of Europe this had been replaced in the seventeenth and eighteenth centuries by the use of kelp and barilla (produced in southern Europe from the ashes of salt-marsh plants, especially Salsola soda) (Clow The Journal of Irish Archaeology Volume XXII, 2013 93–109 Numbered seaweed mearing stones on Island Eddy and the adjoining mainland at Carrowmore townland, Ballinacourty, Galway Bay M. Sheehy Skeffington, N.E. Scott and P. Gosling Numbered stones are described from Island Eddy and the adjacent shore of Carrowmore, inner Galway Bay. Six of the nine on Island Eddy are along the southern shoreline, just below the upper limit for brown seaweeds. These are said to have marked out seaweed rights, but the numbers and stones are of disparate style and are not all in sequence. Stones in Carrowmore are numbered in sequence (with gaps of missing stones) and are more uniform in style. Local farmers confirmed that these demarcated seaweed rights, which the landlord administered until 1912, auctioning them every year.The Carrowmore stones were probably erected to control seaweed harvest at the time it became most lucrative, i.e. at the end of the eighteenth century, for the production of kelp principally for its alkali content. One kelp kiln is reported here and it is suggested that a large storehouse in Ballinacourty village may have been used for storing kelp. It is further proposed that kelp production ceased on these shores after the early nineteenth century, when seaweed was no longer used for alkali. The Laminaria seaweed species continued to be harvested for iodine but probably not at Carrowmore, as no large stands of Laminaria occur along this shore. It is also suggested here that the numbered stones on Island Eddy have been moved there from other shores since the cessation of their use for demarcating kelp rights.