 There is a tillite bed near Port Askaig that provides evidence of an ice age in the Precambrian.In comparatively recent times the island was ice-covered during the Pleistocene glaciations save for Beinn Tart a' Mhill on the Rinns, which was a nunatak on the edge of the ice sheet.The complex changes of sea level due to melting ice caps and isostasy since then have left a series of raised beaches around the coast.