Voussoirs are the wedge-shaped stones that form the curve of an arch, and their presence here as loose fragments suggests that somewhere in this building's long history, an arched opening, perhaps a doorway or a chancel arch, was dismantled or simply fell, leaving these shaped pieces behind on the floor where the arch once led.

St Finan's is dedicated to one of the early Irish monastic saints associated with this corner of Kerry, and Church Island itself is one of those small lake or coastal islands that early Christian communities chose deliberately, seeking the kind of separation from ordinary life that water naturally provided. The survival of any dressed, purposefully cut stonework in such a remote setting is notable. Voussoirs require a degree of craft; they are not rough field stones but pieces worked to a specific angle so that each one locks against its neighbours under compression. Finding four of them still together in the chancel points to a building that was, at some point, considerably more ambitious than the ruined outline visible today might suggest.