
North-west Seaboard: geological foundations
Britain’s oldest rocks – the 3,000 million-year-old Lewisian rocks – are found in the foundations of Scotland’s North-west Seaboard.
Britain’s oldest rocks – the 3,000 million-year-old Lewisian rocks – are found in the foundations of Scotland’s North-west Seaboard.
Rocks of three distinct ages form the geological foundations of Scotland’s North-west Seaboard, which includes:
A fault known as the Moine Thrust separates these foundations from those of the neighbouring Northern Highlands.
At up to 3,000 million years old, the Lewisian rocks are the oldest rocks in the North-west Seaboard and in Scotland as a whole. They’re also among the world’s oldest rocks.
The Lewisian rocks formed over a huge span of time (up to 2,000 million years) through the burial, compression, folding and heating of both:
By about 1,000 million years ago, the Lewisian rocks were already ancient and had been eroded down into a hilly landscape.
About 1,200 million to 800 million years ago, huge rivers flowed across this landscape, depositing layers of red sandstone, muds and pebbly conglomerates. This sequence of river sediments is known as the Torridonian, and it once formed a blanket up to 7.5km thick over the Lewisian landscape.
Like the Lewisian rocks, the Torridonian rocks were later partly eroded away. Today, much of the old Lewisian landscape is visible once more, and it is dotted with hills of Torridonian rock, like Slioch and Suilven.
A shallow sea covered the area about 550 million to 500 million years ago (late Cambrian and early Ordovician periods).
Onto the eroded surface of Lewisian and Torridonian rocks were laid down:
These Cambro-Ordovician sediments have largely been eroded away and are now only found:
A Landscape Fashioned by Geology collection