Mammoth Cave, Derryvree Silts
This was long before the Last Glacial Maximum, when the British–Irish Ice Sheet reached its greatest known extent, broadly around 27,000–23,000 years ago. Around 33,800 years ago, ice did not simply cover all of Ireland in one uniform mass. The extent, thickness and timing of ice changed across the island and through time. Geological evidence indicates that north-central Ireland was ice-free until at least roughly 34,000 years ago, while other evidence points to glacier growth and fluctuating ice margins in the wider Irish and British region. That distinction matters: an ice-free district was not a mild refuge, but a severe periglacial environment beyond or between advancing ice.