Scotland: The Creation of its Natural Landscape

Landscape Fashioned by Geology

• Introduction
• Geological Pioneers
• Drifting Continents
• The Ancient Crust
• Continents Collide
• Devonian Lakes and Hot Springs
• Coal Swamps and Volcanoes
• Deserts and Dinosaurs
• The Atlantic Ocean Opens
• Filling the North Sea
• Rocks Disintegrate
• The 'Ice Age'
• Beyond the Ice
• After the Ice
• The Coast
• Landscape Cameos

Rocks Disintegrate

In many parts of the Highlands, rocks of different types began to disintegrate at different speeds under the humid climatic conditions. In the early part of the Tertiary period, Scotland experienced warm humid climates similar to the sub-tropics of today, resulting in chemical disintegration of the rocks. Kaolin, a clay material, was formed. Deposits of this type are found at Pittodrie, Aberdeenshire, for instance. With the gradual cooling of the climate to more temperate conditions towards the end of the Tertiary period, chemical disintegration became less significant and physical disintegration of rocks increased to create gravelly material known as 'grus'. Weathered material often stayed in place.

Indeed, in parts of Aberdeenshire and Buchan, for example, faces of apparently solid granite rock crumble to the touch; a handful of gravel rather than a solid piece of rock.

Smooth erosion surfaces of relatively uniform altitude are found all around the drainage basins of eastern Scotland. Below these, river valleys often open out into wider basins and it is there that the chemically weathered and physically altered rocks are to be found.

More singular and dramatic features in the landscape, especially in the granites of the Cairngorms and Aberdeenshire, are the 'tors'. These represent remnants of harder, more resistant rocks, standing sentinel-like on the high mountains. The weaker rocks which had surrounded them disintegrated and were removed by ice and solifluction, leaving the tors upstanding at the surface.

The classic theory of tor formation involves a number of steps. We start with a level or gently sloping surface of crystalline granite rocks which have vertical and horizontal cracks as a result of their shrinking on cooling and the unloading that followed the removal of the overlying rocks. Rainwater of a warm, mildly acidic type during the early Tertiary period penetrated these cracks gradually exploiting the weaknesses. Through time, core stones of the stronger and more resistant rocks were left surrounded by weathered rock debris. Later, during the period of the ice ages, the loose debris was finally removed to reveal the tors as we see them today.

next