The reuse is striking not because it is unusual in Irish ecclesiastical history, where ancient stonework was frequently repurposed, but because the stone itself carries enough carving to make its earlier life very legible.

The slab is sandstone, just over two metres long and a little more than half a metre wide, and its upper surface was smoothly dressed before a carver set to work on it. The decoration is carefully composed: a Latin cross rises from a double-outline square base, and the four quadrants of that base each contain a small crosslet in relief. The cross-head is ringed, a form common in early medieval Irish stonework, and its angles are recessed rather than flush. Above it sits a peltaform, a crescent-shaped motif borrowed from classical ornament that appears occasionally on early Christian carved stones in Ireland. Below the cross, the surface shows evidence of unfinished methodical pocking, suggesting the carver began a further area of decoration and stopped, for reasons the stone cannot explain. The whole thing was reputedly associated with St Finan, whose name is attached to the island and its monastic remains, though how old that attribution is and how securely it was ever grounded is difficult to say with certainty.