Definition: accumulations of unsorted, unstratified mixtures of clay, silt, sand, gravel, and boulders deposited directly from glacier ice.

Much of the low ground of Orkney is blanketed by a layer of glacial deposits left directly by the last ice sheet. Termed boulder clay in the 19th century on account of its common mix of boulders in a matrix of sand, mud and clay, this material is now referred to as till. Till content and structure provides evidence of the formation of landforms of glacial deposition and of former directions of ice flow. Till is also of interest where it occurs within sequences of other sediments as it provides evidence of glacial conditions within the stratigraphy.

The character and content of a till depends on the rocks over which the ice has passed and the distance of travel. Many tills contain erratics, ranging in size from boulders to sand grains. Locally-derived tills are dominated by local material and often can be traced to nearby outcrops of glacially-disturbed and dragged bedrock. The direction of over-turning and dragging of blocks can often indicate the direction of ice flow.

Thin, locally-derived till with many angular sandstone clasts. Birsay.

In Orkney, till is generally only thinly developed on high ground and tends to be thickest on lee slopes where it can be as much as 10 m thick. The till colour depends on the matrix material. In eastern and northern Orkney the till is red due to the passage of ice across the marls and sandstones of the Eday Beds. Further west the red hues are replaced progressively by browns and greys as more material from the Rousay and Stromness Flags is incorporated. Locally-derived debris dominates but a range of far travelled erratics is also present. Shell debris also occurs, especially in eastern areas.

Till capping low cliffs in NW Westray

  • 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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