Significance: the presence of chalk and flint in the tills of Orkney provides important evidence of the direction of ice flow across the bed of the outer Moray Firth.

For well over a century fragments of chalk and flint have been recovered from the shelly tills of Orkney and Caithness. Rae (1976) plotted the known distribution in Orkney, demonstrating a marked concentration on the eastern side of the islands. The till at Banks of Runabout, Shapinsay, also contains chalk. In Caithness, chalk erratics occur from Wick northwards (Crampton and Carruthers, 1914).

The outcrop of the chalk on the floor of the Moray Firth has been mapped by the British Geological Survey. Whilst it is possible that unknown small outliers exist, the known outcrop is quite restricted in area and confined to a N-S oriented linear zone some 10-20km across. To carry erratics directly to eastern Orkney, the flow of ice must have moved between SSE-NNW to ESE to WNW. To carry erratics to northern Caithness the flow is from the E or SE. Against a background of multiple ice advances and of ice margins across the Moray Firth, more complex flow patterns are possible, with pick up and carry of erratics by successive glaciers. Transport by icebergs from calving glacier margins may also have occurred.

  • 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. ...

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  • 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 ...

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  • 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. ...

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  • 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.

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