Definition: scratches and grooves cut in rock parallel to ice flow by granules and stones embedded in the moving sole of the glacier

Caithness is one of the best parts of Scotland in which to use striae to reconstruct the changing patterns of flow of the last ice sheet. The soft Devonian flagstones of the Caithness plain were easily scored by the debris of the last sheet, although postglacial weathering of exposed rock surfaces has often been sufficient to remove their traces. Many soil- and till-covered surfaces retain striations. A few show crossing striae, with, for example, an older set of SW-NE striae over-printed with a set of oriented to 340º (Peach and Horne, 1881). Crossing striae are particularly common around Watten (Crampton and Carruthers, 1914) and Loch Stemster [ND 187422](Omand, 1972). The low relief of the plain mean that deflection of the basal layers of ice by hills and valleys has been modest. The plain can be seen as a tabula stria where the striae provide an unambiguous record of the direction of the last ice flow to cover an area.

It is surprising therefore that there has been little detailed work on striations in Caithness for over 90 years. The existing data stems from the pioneering work of Peach and Horne (1881) and Crampton and Carruthers (1914). Whilst this provides a clear picture of the flow of the last ice sheet in general it leaves some specific questions unanswered:

  • do the occasional SW-NE striae found between Wick and Dunnet Bay relate to an early or late movement of inland ice or to the withdrawal of ice towards the Moray Firth?
  • is there a set of SSW-NNE striae parallel to the coast between Dunbeath and Wick that relate to a late movement of Moray Firth ice along the present coast? (Flinn, 1981)?
Striated flagstones at Mid-Clyth after rain
Crossing striae at Gills Bay. The older set trend 126-136º. The finer, younger set trend 139-154º.

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