Main image on top: Thick till sequences at An Dùn. Postglacial erosion is clearing out glacial deposits which fill an older rock-cut valley

The shelly till margin runs roughly from south to north along the western edge of the plain of Caithness. West of this boundary, the glacial deposits are derived wholly from the igneous and metamorphic terrain, and the patches of Devonian cover rocks of western Caithness and Sutherland. Erosion of these materials by ice has created a generally brown, sandy till devoid of fossils. Crampton and Carruthers (1914) noted striated clasts of Moine schist, pink granite, felsite and flags above Strathmore Lodge. Near An Dùn on the Langwell Water, a sequence of three inland tills occurs but at most locations only one till unit is recognised. Aside from SE Caithness, where the inland till locally underlies shelly till, there has been little detailed work on the stratigraphy of these deposits. The most important site is Drumhollistan, where tills derived from inland lie above and below a till with tiny shell fragments.

Thick till sequences at An Dùn. Postglacial erosion is clearing out glacial deposits which fill an older rock-cut valley

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