The Isle of Arran, located in the Firth of Clyde on Scotland’s south-west coast, is often called ‘Scotland in miniature’. Arran’s oldest rocks, in the north of the island, akin to those of Highland Scotland, are separated from younger rocks in the south by the Highland Boundary Fault. Hence the ‘Scotland in miniature’ moniker echoing the mainland’s Highland and Lowland topography and geology.
The Geological Society considers Arran to be “one of the best locations for fieldwork in Europe”.
Rocks that once were on the ocean floor between the areas we know as Scotland and England are testimony to the tectonic movements that brought together the foundations of the island. As part of the North Atlantic Igneous Province, some 50% of the island is igneous in origin. A large granite pluton, shot through by smaller dykes, makes up the core of the north of the island. Large sill intrusions at Drumadoon in the south-west and the dyke swarm at Kildonnan in the south testify to continental crust being split apart with the opening of what is now the Atlantic Ocean.
Half of the island is a National Scenic Area, recognised as having outstanding scenic value of national importance.
The sheer variety of rock types and structures on Arran has for many years provided an excellent teaching ground used by students of Geology as part of their secondary education or degree-level studies. However, the stories of shifting continents and ancient environments and the cultural association with James Hutton, who used now-classic features of the island’s geology to help develop his Theory of the Earth, transcend academic research and teaching, and are there for all to explore and enjoy.
Nearly one third of the island is designated as a Site of Special Scientific Interest for its geology.
For details of all of the island’s protected sites, please see our interactive map.
This brief introduction to the island’s geology is adapted from Stuart Blake’s article in Earth Heritage 48 Autumn 2017.
- Visit one of our interpretation centres, follow one of our geotrails, or join us on a guided walk!
- Arran, Landscapes in Stone, written by Alan McKirdy, is a great place to begin to understand Arran’s landscape and its geology. Buy using this link to help support local bookshops – Arran Geopark will be given 10% too.
- The Geological Society of Glasgow provides detailed and informative “excursion itineraries” to three locations: Corrie Shore, Drumadoon, and Lochranza. These are free to download and are updated chapters from the now out-of-print MacGregor’s Excursion Guide to the Geology of Arran (ISBN: 090289207X).
- The British Geological Survey’s “Special Sheet” S21 & S13 provides the definitive record of the island’s bedrock i.e. “solid” geology – and it looks great on the wall! (ISBN: 0751810401)
- The British Geological Survey’s GeoIndex provides a free, online, interactive map of the UK’s geology.
Don’t visit Arran’s hills and wild coastline without an Ordnance Survey map! The whole island fits satisfyingly on to one sheet of an OS Landranger map, buy one here. Or for even more detail purchase an OS Explorer map. Buy using these links to help support local bookshops – Arran Geopark will be given 10% too.