Derryvree’s Silted Tundra
The most important Irish archive for this broad interval lies at Derryvree near Maguiresbridge in County Fermanagh. Roadworks in 1969 cut through a drumlin and exposed organic silts and fine sands trapped between two separate beds of glacial till. Such a sequence matters because it records a time when water, plants and animals occupied ground that was later overridden or enclosed by ice-derived sediment. The organic layer produced a radiocarbon determination of 30,500 years before present, with a large original uncertainty of roughly a millennium either side. The deposit is not a diary entry for a single season, still less for a single calendar year; it accumulated over time and its date must be calibrated against changing atmospheric radiocarbon levels.