Added to this complex interaction of pre-volcanic and volcanic activity, the area was subject to the action of glaciers during successive Ice Ages. Deep valleys were formed as glaciers exploited weaknesses in the rocks (faults and softer rocks) while hills were scoured leaving craggy outcrops, boulder strewn slopes and rocky ridges and hollows and rounded drumlins were formed in valley floors. The 'tail' of Slieve Gullion, which itself forms the 'crag', is seen at Dromintee, and is a ridge of boulder clay deposited in the wake of Slieve Gullion as it was overrun by ice moving from the north.