That is, in a sense, the whole point. Somewhere beneath the surface of a field in north Cork, a circular ditch traces the outline of an enclosure that has left no mark on the landscape visible to the naked eye. The only evidence it exists at all is a faint cropmark caught in a single aerial photograph taken in July 1975.

Cropmarks appear when buried features such as ditches or foundations influence how crops or grass grow above them. A filled-in ditch retains moisture differently from the surrounding soil, and in dry conditions the vegetation overhead responds in kind, producing subtle variations in colour and height that become readable from altitude but disappear at ground level. The photograph in question, taken as part of the Geological Survey of Ireland's aerial programme, shows the fosse, or outer ditch, of a small circular enclosure on the western side of what was once a field boundary, since levelled. Ring-ditches of this kind are generally understood to be the remains of prehistoric funerary or ceremonial monuments, sometimes the eroded remnants of burial mounds whose earthen cores have long since been ploughed or weathered away. Whether that is the case here, the aerial image alone cannot confirm.

What the photograph preserves is a moment of legibility that no longer exists on the ground. The field boundary that once marked the enclosure's western edge is gone. The cropmark may not recur in the same way. The site persists only in the archive and, just below the soil, in the difference between one kind of earth and another.