20Fergusson, James. Rude Stone Monuments in All Countries Their Age and Uses. London: J. Murray, 1872. 294. Quoting W. Hackett.
Another source has further accounts of the natural features in folklore attributed to the Black Pig: "In Co. Monaghan, in the townland of Knocknacran, there is a field called 'Poll na muic' which has indentations said to have been made when the pig rolled there or when he lay there to rest. The field is three cornered and fields of an unusual shape like this tend to attract attention. In addition to having made indentations the Black Pig is also believed to have caused certain lakes and rivers." (Williams, Fionnuala. "The Black Pig's Dyke and Linear Earthworks." Emania: Bulletin of the Navan Research Group 3 (1978): 15-18.)