This is a midden, the archaeological term for a refuse deposit left by people who gathered, prepared, and ate shellfish, sometimes over generations. The shells are not scattered at random but built up in a distinct stratum, the kind of accumulation that only happens when people return to the same place repeatedly, leaving behind the remnants of meals that, taken together, form an unintentional archive.

The island itself is roughly oblong, measuring approximately fifty-five metres from north to south and twenty metres across, and lies about seven hundred and seventy metres east of Killala town in the inner reaches of the bay. Killala is already well known in Irish historical memory as the landing point for the French expeditionary force under General Humbert in August 1798, but this deposit belongs to a far older pattern of coastal life, one defined not by military strategy but by the slow, practical rhythms of harvesting what the tidal flats provided. The midden layer is not always visible; exposure depends on the tides and the slow erosion of the island's eastern face, which means the shells appear in section only intermittently.