Derryvree’s Sedge Marsh
The best Irish chronological anchor is the Derryvree sequence near Maguiresbridge in County Fermanagh. Roadworks in 1969 cut through a drumlin and exposed organic freshwater silts and fine sands trapped between two substantial layers of till, sediment laid down by ice. This order is crucial. It records glaciation, then an ice-free freshwater environment, followed by another glacial advance. Derryvree is not a record of all Ireland, but it decisively complicates any simple image of an island continuously buried beneath ice.