The landscape of Orkney before the Ice Age can be reconstructed from the fragments of ancient landforms that have escaped erosion by the great ice sheets. Although no sediments of Tertiary age exist on land, the adjacent submarine shelves on the northern North Sea and the Atlantic carry thick covers of sediments that provide important evidence of events on the intervening land area. Orkney also provides fine examples of structural landforms developed by weathering and erosion of tilted, folded and faulted Devonian sandstones. The oldest land surfaces are those which bare presently emerging through erosion of Devonian cover rocks.

The rolling preglacial terrain of northern Hoy, now truncated and dissected by sea cliffs and glacially-deepened valleys

Image courtesy of Alan Moar

  • Faulting and landforms

    Faulting has two main effects on subsequent erosion. Firstly, the line of fracture and movement is a zone of breakage which is often later exploited by erosion to give a valley. ...

  • Folding and landforms

    Orkney have been flexed into gentle folds with a N-S trend. Inverse relief is widespread (Godard, 1956), where anticlines and synclines now form low and high points in the landscape. The central depression of West Mainland and other 'brays' follow breached anticlines. ...

  • Preglacial drainage

    Godard has reconstructed the drainage system immediately prior to glaciation by combining to valley systems on land with those submerged by sea level rise on the surrounding sea bed. Glacial erosion has cut through low watersheds to form the archipelago of today.

  • Erosion surfaces

    Definition: a land surface of low relief reflecting long term erosion. The surface may now lie well above sea level as a result of uplift or be tilted or deformed as a result of later tectonics.

  • Sub-Devonian landsurface

    Near Yesnaby the ancient surface is more hilly and Devonian conglomerates are seen plastered onto a steep rock wall that now forms the upper part of the sea cliff. ...

  • Tertiary of the northern North Sea

    At the opening of the Tertiary chalk sedimentation continued on the northern North Sea. Starting around 63 Ma, the East Shetland Platform was uplifted and tilted towards the south-east. ...