The earthwork at Cloghonan, on a north-north-west to south-south-east ridge beneath the southern slope of Knockadiggeen, belongs firmly to the second category. It is not visible at ground level. What draws attention to it now is its absence, the fact that something was once there and is no longer.

The first edition Ordnance Survey six-inch map, surveyed in 1843, recorded a small, circular enclosure on this ridge, the kind of feature that might represent the remains of a ringfort, a type of enclosed farmstead common across Ireland from the early medieval period, typically defined by one or more earthen banks and ditches. By the time the revised edition was published in 1904, the enclosure had disappeared from the map entirely, suggesting it had been levelled sometime in the intervening decades, most likely cleared to improve agricultural land. That a gap of sixty years could swallow a feature so completely is not unusual for lowland pasture, where ploughing and drainage schemes gradually erased many such remains across the nineteenth century. What remains at Cloghonan is, in effect, a cartographic ghost.