A dense band of shells, twenty to thirty centimetres thick, sits roughly thirty centimetres below the present land surface and about a metre above the stony shoreline below. Cockles, limpets, mussels, and periwinkles are packed into the layer, the compressed remains of countless meals eaten by people who once worked or lived along this stretch of coast.

A midden, in archaeological terms, is essentially a refuse heap, most often composed of shell, bone, and other food waste discarded by coastal communities over time. They can represent anything from a single season of activity to accumulations built up across generations, and they are among the more reliable indicators of where people actually ate, camped, or settled along a shoreline. This particular example on Inishbiggle was only noticed in September 2018, brought to attention by Moira Heery and Michael Heery. The midden layer is visible in section where the cliff face has partially eroded, though vegetation partly obscures the exposure. The traceable length runs to approximately two metres, though the full extent of the deposit is not yet known.

Inishbiggle is a small, sparsely populated island in Achill Sound, off the coast of County Mayo, accessible by a small ferry. The inlet at Clúideog on the island's south-eastern side is narrow, and the midden sits on the north-western bank of that inlet. Because the deposit is eroding out of a cliff face rather than being excavated in a controlled way, the layer is fragile and its visible extent may change over time. Anyone approaching the shoreline here should be aware that what looks like an unremarkable line of pale debris in a low cliff could be a material record of shellfish gathering that goes back an unknown number of centuries.