Dryas Octopetala Silts
The principal Fermanagh evidence was exposed during road works in 1969, when a cut through a drumlin at Derryvree revealed freshwater silts and fine sands between two distinct sheets of till: unsorted sediment deposited by glacier ice. Organic material from the intervening deposits produced a conventional radiocarbon determination of 30,500 years BP, with an uncertainty of approximately a thousand radiocarbon years. That measurement cannot be converted honestly into one precise BCE date. Radiocarbon years and calendar years differ because atmospheric carbon levels have varied; calibration produces probability ranges, not a single historical timestamp.