Among the site's surviving stonework is a roughly cross-shaped slab, modest almost to the point of invisibility, set into the south-western side of the Monks' Graveyard. It measures just 46 centimetres high, 40 centimetres wide, and 3 centimetres thick; a thin, weathered piece of stone that could easily be passed without a second glance.

Described in a 1996 archaeological survey of the Iveragh Peninsula by A. O'Sullivan and J. Sheehan, the slab is recorded simply as "roughly cross-shaped", a phrase that says a good deal in a small space. It is not a finely carved high cross of the kind found on the Irish mainland, with its elaborate knotwork and figurative panels. It is instead the kind of grave marker that speaks to the practical and austere conditions under which the Skellig community lived, probably between the sixth and twelfth centuries. The monks who occupied this crag off the Kerry coast, some 12 kilometres from the Iveragh Peninsula, cut and shaped what was available to them, and what they produced was functional, direct, and built to last in some of the most punishing maritime weather in Ireland. The graveyard in which the slab stands formed part of that same compact monastic complex of dry-stone cells, oratories, and terraced paths that clings to the upper reaches of the rock.