Ireland’s Weird Geology

For a small island, Ireland sure does have some odd, interesting, varied and fascinating geology.

From basalt columns to dramatic cliffs to exposed limestone landscapes, explore some of Ireland’s strangest geological wonders with us. 

A bit of geological Irish history

Ireland is made up of bits of two today non-existent continents – Laurentia and Gondwana, who collided some 420 million years ago. Other parts of Laurentia went on to create parts of North America, hence why we see geological similarities between the mountains of Donegal and northwest Ireland and the Appalachian Mountains. From 450 million years ago, Ireland was under the sea, resulting in limestone, mudstone, and of course, plenty of fossils.

The bedrock – deeply embedded hard rock – of Ireland is made up of a wide variety of rock types, each with different ages, though the oldest rock is found in Donegal, formed some 1750-1780 million years ago, though Kerry’s Valentia Island is also quite old (and home to dinosaur footprints!). Sections of quartzite are also quite old, and found on the mountains of a few regions.

Ireland has a good bit of sedimentary rocks as well, most notably the exposed limestone landscape of the Burren region, as well as the rocky, mountainous terrain of the southwest. Learn more here.

Read on to discover a few of Ireland’s most iconic geological features.

Coumshingaun Lake, Wexford

A good example of a corrie lake is Coumshingaun Lake in the Comeragh Mountains of southeast County Wexford. There is a great 7.5 km walk (which takes about 4 hours) following the ridge of the mountains that form a horseshoe around the lake. The cliffs stand 365 m (1,200 feet high) above Coumshingaun Lake, though the highest point above sea level is 793 metres. So expect great views! At the the beginning or end of the path, there is an optional side track leading to the lake’s shore.

The Eglone Stone, Sligo

A glacial erratic is a stone deposited in a landscape via glacial movement. There are many such stones throughout Ireland, though a good example of the geological wonder is on the Moyrura Plateau in County Sligo. Outside the wee village of Highwood on the Historical Trail, find the huge monolith, the Eglone Stone. Once thought to be carved by Neolithic peoples, we now know that it, like many other the huge boulders strewn throughout this region, is a glacial erratic. (Though there are plenty of other Neolithic monuments in this region too!)