Rectangular in plan, roughly seven metres by three, it was defined by a shallow ditch about a metre wide with faint traces of an external bank. When archaeologists first recorded it in 1991, they classified it as a barrow, the general term for a burial mound or funerary earthwork. But the classification was never entirely comfortable.

The uncertainty comes down to shape and size. Barrows in Ireland tend toward the circular, and this feature's rectangular footprint and modest dimensions made it look rather similar to something altogether more industrial: the kelp-drying kilns found at several other points along the west Sligo coast. Kelp harvesting was once a significant coastal industry in Connacht, with seaweed gathered and burned in stone-lined trenches or kilns to produce ash rich in alkali, used in glass and soap manufacture. Whether the Lackan feature was a prehistoric burial monument or the remnant of that coastal economy was never resolved. A second possible barrow lies about 150 metres to the south-south-west, which might have tipped the balance toward a funerary interpretation, but the question was left open. By the time a follow-up inspection took place in 2013, land reclamation had removed any visible trace of the feature entirely, leaving the ambiguity permanently unresolved.