Arran Walk: 600 Million Years of Earth’s History

History of Earth unfolds on scenic walk around Scotland’s Isle Arran

Known as Scotland in miniature, the Isle of Arran is a geological wonder, and a compact tour through the long history of the Earth in a comparatively small space. An excursion over its various scenery is a journey of millions of years, back to the early collisions of continents, and the comparatively recent force of glaciers. After recently becoming a UNESCO Global Geopark, Arran boasts a world-class outdoor classroom because of its rare geology.

We start our walk at the north where the steep hills of Goatfell and the adjacent mountains prevail in the skyline. These dramatic structures are made of granite, hard, igneous rock which formed deep inside the earth surface about 60 million years ago. The granite is a part of the North Atlantic Igneous Province, which alludes to the immense volcano action that was connected with the splitting of the Atlantic Ocean. These mountains bear sculptured, stark forms testifying to the power of ice erosion over these rocks in successive glacial periods to produce the U-shaped valleys and corries that we observe today.

Passing southwards across the island we cross the well-known Highland Boundary Fault, a great geological line of demarkation actually separating the ancient geology of the Highlands of the north with that of the Lowlands of the south. The fault line is a solid evidence of the tremendous crustal forces that formed Scotland.

The lower half of Arran is different, with sedimentary rocks forming the main part of it. We find here immense areas of Old Red Sandstone, which is Devonian in age (about 400 million years old). These colourful red rocks tell the story of when Scotland existed as a portion of a large desert continent, and huge rivers carried sand and gravel. Still farther south we come to Carboniferous rocks (about 360-286 million years ago), whilst Arran was close to the equator, with a warm, tropical climate.

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The fossils of trees and the ancient coal seams are indicators of a previously lush landscape with dense forests. Coastal walks at this part of the island sometimes expose layers of evidence representing an ancient climatic trajectory across Arran – this evidence takes the form of layers of rocks showing the transition from desert, to tropical swamps, and back again where some of the coastal walks, such as Corrie Shoreline walk would present the layers.

Travelling a little further to the west coast in the Arran area of Machrie Moor, we encounter the Permian desert sandstones, and evidence of a return to aridity in the landscape, the associated aeolian (commonly wind-blown) dune structures provide a stark example of an ancient landscape 270 million years ago. The Machnie Moor Standing Stones are also located in this area; archaeology is another layer of geological exploration and ancient societies employed the island’s robust stone for their megalithic structures,

One of the most important geological sites on Arran which is accessible from the north (near Lochranza), is Hutton’s Unconformity, which relates the steeply tilted older metamorphic rocks (the Dalradian schists which were formed in the Cambrian time, over 540 million years ago)-in direct contact with younger, and relatively horizontally deposited sedimentary rocks (the Devonian Old Red Sandstone).

Hutton was able to see this incredible junction of rock types in the late 18th century, and it provided him with the concept of time, as the introduction of two extreme designs (the dramatically tilted orientation of the metamorphic rocks, and the horizontal deposition of the sedimentary) required an immense contour of time, much greater than the date that was proposed.

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