The rocks beneath our feet not only shape the ground we live on, they can also tell us about the long geological history of a place and the wider world. Here, the story is of the ancient Iapetus Ocean, from its opening 700 million years ago dividing the supercontinent Rodinia and the sediments deposited on its floor, to its closing 450 million years ago. The associated collision of the two continents Laurentia and Gondwana formed a massive mountain range and transformed the previously formed sedimentary rocks. Throughout this 250 million year period, north west Ireland was part of the continent Laurentia, as was Scotland, Greenland, western Scandinavia and north eastern America (USA and Canada). This connection is celebrated by the International Appalachian Trail, of which the Western Way is now a part of.

This part of the Mám Éan trail will take you walking over metamorphic rocks, namely quartzite, marble and schist. These rocks were formed by the transformation of earlier rocks due to extreme heat and pressure linked with the collision of tectonic plates and the formation of a large mountain range called the Caledonides during the closure of the Iapetus Ocean. Quartzite was originally sandstone, marble was limestone and schist was mudstone. The intense conditions have also deformed the rocks after their formation and you will be able to see many examples of folded quartzite on the way up to Mám Éan (see picture). The ancient Caledonides mountain range has been completely worn down since its formation and these rocks would have been deep within.

Our connection to North America ended only about 100 million years ago at the opening of the North Atlantic Ocean. We currently understand that the early phase of the opening released enough pressure to uplift some of the bedrock of the West of Ireland by at least 700 metres and create the mountains we see today, like the 12 Bens and the Maumturks. These were since eroded and shaped by the moving ice of the glaciers in the ice ages of the last 2 million years.