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

The Ancient Crust

Rocks dating back 3 billion years are to be found in the Western Isles, on Coll, Tiree, lona and the Rhinns of Islay, and along a coastal strip of the Northwest Highlands from Cape Wrath to Kyle of Lochalsh. These banded rocks, called Lewisian 'gneiss' (pronounced 'nice'), were formed many kilometres down in the crust and were gradually exposed at the surface as earth movements pushed them upwards. Over time, wind, water and ice wore away the covering rocks and this ancient crust was exposed at the surface. These are the oldest known rocks in Scotland and are among the most ancient to be found anywhere in the world.

The imposing glens around Applecross and Torridon are built of red sandstones which were dumped in vast thicknesses on top of this primordial crust of Lewisian gneiss. Large rivers flowed eastwards from higher ground, depositing layer upon layer of sand and pebbles at the edge of the continent of Laurentia which lay at that time, south of the Equator. These Torridonian strata are largely restricted to the Northwest Highlands with smaller occurrences on Skye, Rum, lona, Colonsay and Islay. The Durness Limestones lie on top of the Torridonian sandstones, and also form part of the ancient crust. These limestones and associated sandstones are interpreted as beach deposits marking the coastal fringe of Laurentia. Beneath tranquil seas, sands, silts and limy muds were deposited, containing evidence of early life. This, the Cambrian period, is characterised by a profusion of new life-forms world-wide, some of which are preserved in the Durness Limestones.

The foundations for the Scottish Highlands were also being laid at this time. Thick sequences of sandstone, shales and limestones were deposited, later to be altered or metamorphosed by heat and pressure related to subsequent earth movements - primarily those generated when continents collided. These Dalradian (named after the ancient Scots Kingdom of Dalriada) and Moine rocks occupy much of the ground north of the Highland Boundary Fault. Despite their turbulent origins, the Dalradian rocks provide evidence for some of the earliest life-forms in Scotland, indeed in the world. Small pellet-like features found on Islay are dung pellets produced by soft-bodied creatures, such as worms, which inhabited these ancient sediments.

next