Significance: a glacial deposit containing many shell fragments derived in part from the bed of the North Sea

In a few parts of Scotland, including northern Lewis, Berwickshire, Buchan, Caithness and Orkney, the last ice sheet flowed across marine sediments before moving on to the current land area. In Caithness and Orkney, ice moved out of what is now the Moray Firth and carried with it large amounts of debris derived from erosion of pre-existing marine sediments. In northeast Scotland some of this material was transported as huge rafts and so retains much of its original bedding. In Orkney however the original sediment was much more thoroughly mixed to form part of the matrix of lodgement till.

The most obvious clue to the passage of ice across the former sea bed is the presence of shell debris. This is often fragmented and abraded but occasionally whole or nearly whole valves may be found, especially in sections in the eastern parts of the islands. The greater distance of glacial transport at sites in the western and northern areas means that shell here has been ground up and is usually present only a tiny flakes and chips. Shell is also absent from the top 2 m of exposures due to postglacial weathering and associated decalcification. The shells comprise mainly cold water species and include Arctica islandicaAstarte sp, Mya truncata and mussels.

  • During the periods of maximum cold in the Quaternary, major ice sheets covered Scotland. An ice stream hundreds of metres thick curved out from the Moray Firth to cross the plain of Caithness and flow over Orkney towards ice limits close to the edge of continental shelf.

  • In the gently-dipping sandstone terrain of Orkney, it is often difficult to pick out classic landforms of glacial erosion. Low-lying areas often show a pronounced SW-NE grain to the topography, parallel to the main direction of ice sheet flow. ...

  • Glacial deposition is largely confined to low-lying areas on Orkney, where thicknesses of till may exceed 10 m. The glacial deposits drape the landscape, smoothing its outlines. Ice-marginal features are largely unrecognised outside Hoy ...

  • Westray is the furthest northwest of the Orkney islands. The total area is 47 square kilometres, not huge but the irregular shape gives it a long coastline of almost 80 kilometres, a good place to look for glacial striations. The bedrock of the whole of the island is made up of the cyclical Rousay Flagstone Formation. ...