The Quaternary Period of the last 1.6m years has been marked by Ice Ages which were punctuated each 100,000 years or so by inter-glacials like the one we are presently in.
At the peak of the last glaciation about 18,000 years ago the Antarctic ice-sheet would have been double its present size and ice covered most of Ireland, as well as the greater fraction of the Northern Hemisphere. In parts it was up to 3km thick [or high] and scoured out wide U-shaped valleys in its advance. The most dramatic examples are in Donegal [Glengesh, Glenveagh] and Antrim [Glenariff] though there are numerous examples in the High Mournes, and in our own area, the wide U-shaped Kilbroney valley climbs northwards out of fair Rostrevor. Besides the U-shaped valleys and sculpted mountain tops and sides, the principal relics of the last retreating Ice Age are the numerous lakes, the drumlins and the boulder clays and tills scoured out elsewhere and deposited randomly across our countryside. A minor relic is the occasional ‘erratic” – like the Cloughmore Stone in Rostrevor – carried from distant parts and dumped sometimes in the most unlikely of places. The ‘Big Stone’ was carried from an island in Strathclyde bay and deposited on the edge of a hilltop many hundreds of feet above beautiful Carlingford Lough.
Towards the end of the last Ice Age the greatest thickness of ice, after its retreat from the Mournes, spread over the Lough Neagh and Sperrin Mountains area. The climate warmed and the ice began to melt. The low-lying and scoured-out area in the centre of the north of Ireland filled to overflowing with the melted ice. The clays and other solids beneath the ice sheets became the covering of the rock strata in the whole Lough Neagh basin and south well into North Armagh. The deluge flooded south towards the sea at Carlingford Lough, carving out – and depositing along its length – the Poyntzpass drainage channel. Although most drumlins – from ‘dromn