A Geological History of Lochcarron

A Geological History of Lochcarron
a brief introduction to the geology influencing the scenery of Lochcarron & district.

Continental Drift
The ancient landscape that is Lochcarron and its environs has as its foundation some of the oldest rocks on the planet, the Lewisian Gneiss and Moine Schists (both, much altered, metamorphic rocks) originated when the earliest continents were formed.

One such ‘super’ continent (Gondwanaland), lying about the South Pole region, began to break-up around 600 million years ago. Two of the resulting fragments (Laurentia – comprising of the USA, Canada, Greenland and N.W. Scotland; and Baltica – comprising of Scandinavia and Central Europe) began to drift independently northward towards the equator.

The area of Laurentia which was N.W. Scotland, composed of Lewisian Gneiss and Torridonian Sandstone, was fringed by a shallow sea. As the waters became warmer the deposition of both the intertidal beach sands which were to become the Durness Limestones occurred. By 500 million years ago Lochcarron had crossed the equator in its inexorable northward drift.

Approximately 400 million years ago these two land masses collided with the western edge of the Baltican Moine Schists over-riding the eastern edge of Laurentia, the Moine Thrust Plane indicating the boundary with today’s ‘Highlands’ being the remnants of the resultant mountain chain. Put crudely, if you’re at Strathcarron station you are in ancient Scandinavia, whereas if you’re admiring the view from the top of the Bealach na Bà then you are in ancient North America.

In the ensuing 320 million years nothing much happened to Lochcarron, with only the mountains gradually eroding under the normal elements of rain and frost etc. Then around 80 million years ago the Atlantic Ocean started to form as the continents began to drift apart. Finally 65 million years ago Scotland broke away from North America having been attached for over a billion years.

The Ice Age
The Ice Age began 2,400,000 years ago and lasted until 9,500 BC. It was not, however, one continuous Artic winter as there were at least three periods (called interglacial oscillations) when temperatures rose higher than today’s, indeed southern England was a sub-tropical swamp complete with hippos, crocodiles and elephants etc. on each occasion! Furthermore, as these warm periods lasted tens of thousands of years, it is quite possible that the Ice Age has not actually ended and despite global warming we may still yet be plunged back to those Arctic conditions.

There are various theories as to the cause of the Ice Age, but there is no mistaking its effects. Many of the physical features in today’s landscape have been sculptured by the movement of the glaciers which were up to 1km thick and reached out as much as 100km from the coast. These features include:

  • U-shaped valleys – where glaciers bulldozed their way down a valley creating the characteristic cross-section shape. A good example of this feature being the glen in the which the Bealach na Bà runs, particularly when viewed from the top looking down to Kishorn).
  • Moraines and drumlins – long banks and small hillocks of dumped loose rocks and soil etc. pushed to one side and then left when the glaciers eventually melted. Good examples can be seen around the Achnasheen area.
  • Erratics – huge boulders carried along in or on the ice, sometimes for long distances, before being left stranded when the ice melted.
  • Bedrock striations – scratches and grooves scoured into the exposed bedrock as the glaciers advance. Fine examples of both of these last two features can be found near the top of the ascent into the entrance to Coire Lair on the Coulin circuit walk.

Post-Glacial
Most low-lying areas are now covered by glacial, alluvial and/or peat deposits masking the underlying bedrock. But one striking post glacial feature of lower Glen Carron is the raised beach formed between 6,000 and 3,000 BC, when sea levels were higher from melting ice sheets in North America and Canada. Ever since the huge weight of ice was removed from Scotland, it has been steadily bobbing back up out of the molten underlying Mantle on which all land masses float, hence leaving these beaches high and dry.

by Paul Swan
(Map and images to follow)

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