The last ice sheet in Snowdonia

In Snowdonia there is a marked contrast between weathered summits, often with well-developed blockfields or tors, and lower ice-moulded terrain. The boundary is interpreted as a trimline marking the upper surface of the last ice sheet. This interpretation is supported by the presence of gibbsite, an end-product of prolonged weathering, at the base of soils above but not below the trimline. The reconstructed ice surface reaches about 850 m above present sea-level along an ice divide running NE-SW through the massif. There is no evidence to support the popular view that ice centred further south extended over Snowdonia, and breaching to form the major glacial troughs can be explained by the action of local ice. The field evidence presented here demonstrates that most models of the southern British and Irish Sea ice sheets are significantly flawed, the earliest being far too thick and the most recent far too thin. Copyright (C) 2000 John Wiley & Sons, Ltd.