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Sron Uladail – 250m of overhanging Lewisian gneiss with the ‘cnoc and lochan’ terrain of Morsgail Forest in the distance (Walk 14)

The rugged and desolate landscape of Lewis and Harris today dates from the most recent ice age that scoured away loose rock and deepened and widened pre-existing valleys, leaving the fjord-like lochs and sea lochs such as Loch Sìophort (Loch Seaforth). Many of the basins formed by the ice are now filled with either water or peat and surrounded by ice-sculpted crags. This ‘cnoc and lochan’ landscape is best seen in the Bays area on the east coast of Harris: cnoc meaning hillock, lochan meaning a little loch. Further north in Lewis the retreating ice laid down smooth, undulating layers of glacial rubble called till. Subsequently peat formed on top of this layer which, being rich in clay, is poorly drained. From about 11,500 years ago, when the sea level was 50m below today's level, the dry Arctic climate was gradually replaced by a relatively warm maritime climate dominated by the Gulf Stream. As the ice withdrew back to the poles the seas rose, changing the coastline and reducing the landmass. Around 6000 years ago it was 20m below current levels and it continues to rise, the east coast region of the Bays in South Harris being typical of a recently drowned landscape.