truncated spurs

glacial erratics

A small roche moutonnée north of Brinkies Brae developed in jointed basement rocks. Ice movement L-R.







origins of roches moutonnées

Roches moutonnées

Definition: rock hills shaped by the passage of ice to give a smooth up-ice side and a rough, plucked and cliffed surface on the down-ice side. The upstream surface is often marked with striations.

Ice-moulded bedforms like roches moutonnées are best developed in strong, jointed rocks. It is no surprise therefore that these features appear to be rare on the Devonian sandstone terrains that dominate Orkney. A few examples do occur on the basement rocks around Stromness and Yesnaby and here the whaleback forms are partly inherited from the sub-Devonian surface. Other roches moutonnées may lie concealed beneath drapes of till, especially on East Mainland.