Main image on top: A rip-block till resting on shattered Devonian flagstones at Dunbeath Cemetery

Definition: accumulations of unsorted, unstratified mixtures of clay, silt, sand, gravel, and boulders deposited by glaciers

The till sheets of Caithness are the products of two opposing ice movements, one from inland Sutherland-shire and one from the Moray Firth. Each till sheet has a distinctive composition. The shelly till is dark in colour, muddy and contains far-travelled erratics, a reflection of its derivation in part from the floor of the Moray Firth. The inland till is brown, sandy and contains igneous and metamorphic rocks. Both tills, however, when seen on the plain of Caithness contain mainly stones from the local Devonian rocks. In places, the base of the till can be seen to rest on rubble and these exposures provide a snapshot of glacial erosion and till formation at the very end of the last glacial period.

Tills in the valley of the Dunbeath Water. The ice which deposited the dark grey shelly till on the left was forced to flow over bedrock highs and erode the earlier cover of brown till derived from inland

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