The dots represent a boulder circle with a central megalithic structure, probably a passage tomb of the kind that makes Carrowmore one of the most significant prehistoric cemeteries in Ireland. By the time the map was printed, the monument was already partly gone. Today, there is no trace of it whatsoever at ground level.

The antiquarian George Petrie visited the site and recorded what he found: twenty-four large stones surviving from a circle whose cromleac, the capstone and uprights of the central chamber, had been destroyed roughly three years before his visit. His description was later published by Margaret Stokes in 1868. The destruction was deliberate and almost certainly agricultural, the stones broken up or shifted to clear land or build field walls, a fate that befell dozens of prehistoric monuments across Ireland during the nineteenth century. What Petrie saw was already a ruin of a ruin, and whatever he estimated of its original form was based on those remaining stones and the outline still faintly legible on the ground.

Carrowmore as a whole still contains a remarkable concentration of surviving megalithic tombs, some excavated and interpreted, others still unexcavated. But this particular monument sits in a different category entirely: present on the earliest detailed mapping of the landscape, documented by one of Ireland's foremost antiquarians, and then gone. Its absence is itself a kind of record.