Near Achonry in County Sligo, a feature that spent years listed as a possible prehistoric enclosure is, in fact, a quarry. The mix-up is a small but telling reminder of how much early archaeological cataloguing depended on reading maps rather than walking the ground.

The confusion arose from a 1941 to 1942 Ordnance Survey six-inch map, on which the site was represented by a semicircle of hachures. Hachures are short lines used on older maps to indicate slopes or changes in elevation, and in many cases a curving arrangement of them does signal an earthwork, a ringfort, or some form of enclosed settlement. When the site was entered into the Sites and Monuments Record in 1989, that semicircular pattern was taken as grounds for classifying it as a possible enclosure. Subsequent investigation, however, established that the hachures were simply depicting the cut face of a modern quarry, an entirely ordinary feature that happened to leave the kind of mark on a map that archaeologists are trained to notice.