The ‘Snowball Earth’ deposits of Islay and the Garvellachs are one of the ‘51 Best Places to see Scotland’s Geology’. Together the islands record a thick, well-exposed, and complete section through a major glacial episode which is correlated with the global ‘Sturtian’ event that occurred some 720 million years ago. The Garvellachs section is proposed as a ‘golden spike’ to mark the definitive base of the Cryogenian Period of the Precambrian; and in northern Islay there are several candidates for a cap-carbonate which mark the termination of the glacial cycle.

Image (courtesy Tony Spencer): Drone photograph of A’Chuili and Eilean an Naoimh in the Garvellachs. Jura and Islay in the distance.