Derryvree Organic Silt Layer
Archived: 5 October 2026
Around 30,243 BCE, Ireland lay within the climatically unstable later Marine Isotope Stage 3, not a dated historical year. Derryvree, County Fermanagh, preserves organic wetland silts between glacial tills, demonstrating local ice-free intervals with cold freshwater pools, tundra vegetation and severe seasonal conditions. Castlepook Cave, County Cork, contains a complex MIS 3 fauna, including reindeer, mammoth, giant deer, predators and Arctic species, indicating intermittent ecological links with Britain and continental Europe. A marked reindeer femur may indicate early human butchery, but cannot prove settlement. Lower sea levels altered routes, while advancing ice repeatedly reshaped and erased landscapes across the island.