Muskeg at Maguiresbridge
Derryvree is important because it preserves a break in a glacial sequence. The lower till indicates that ice had previously reached the locality. Above it, freshwater sediments accumulated in an ice-free or at least locally deglaciated landscape. The upper till shows that glacier ice later returned. This is powerful evidence against any simple picture of Ireland as continuously buried under one uniform ice sheet throughout the later Ice Age. It also does not establish that the whole island was open at once. Ireland’s ice margins, uplands, lowlands and western marine approaches changed at different times, while later ice erosion destroyed much of the evidence that might have clarified the pattern.