Definition: the buried basement terrain beneath the Devonian sandstones

Low granite hills west of Stromness

In the area around Stromness small areas of basement rocks poke through the Devonian cover rocks. Erosion has exhumed a 380 million year old land surface of rounded hills developed in granitic rocks, Brinkies Brae is the largest of these rock islands. 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. No buried soils are known and the hills were probably stripped just prior to burial by breccias, conglomerates and sandstones which contain abundant basement debris. It is remarkable that today we stand at just the same level erosion as in the Devonian – many hundreds of metres, if not kilometres of cover rocks have been deposited, buried, consolidated and then eroded in the meantime.

Steep sub-Devonian slopes south of Yesnaby

Yesneby-01 Devonian rocks

Preglacial Landscapes

  • 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.

  • 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. ...