Inishtrahull Island - Geology

Geology

The island is formed of a granitic gneiss, a type of metamorphic rock, which is known as Inishtrahull Gneiss. It is dated at 1.7 billion years old, making it Paleoproterozoic in age, and is the oldest known rock on the Irish Islands. The Inishtrahull Gneiss is considered to form part of the Rhinns complex that is also exposed on the islands of Islay and Colonsay. The Rhinns complex is correlated with the Ketilidian metamorphic belt of southern Greenland and the Svecofennian of Scandinavia.