On the hillside near Austwick there is a large collection of glacial erratics consisting of Silurian slate boulders that were brought here by the last Ice age ~15,000 years ago. These erratic boulders are about 400 million years ago, whilst the younger limestone they rest on is only about 300 million years old.
Many of these erratics stand upon little limestone pedestals. Over many years the boulders have protected the limestone beneath from the weathering, but the other surrounding limestone has been worn away.
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