Although it was once described as "extremely uninteresting" (Macculloch, "A Description of the Western Isles of Scotland" 1819), the geology of Colonsay is now known to be quite exciting.  In a nutshell, the Great Glen faultline which runs down from Inverness and along the Firth of Lorne splits northeast of Colonsay.  One fault continues towards Donegal, running between Colonsay and the Ross of Mull; whilst the other runs between Colonsay and Jura before splitting Islay in two, via Loch Gruinart and Loch Indaal.  Thus Colonsay, Oransay, the Rhinns of Islay and the tiny, northernmost islands of Ireland are geologically connected and are rather different to the surrounding area.  The little islands are called Inishtrahull and, together with Colonsay and the rest of the group, broke away from what is now Greenland some 1,800 million years ago; tectonic plate movements led to their being transposed by some 800 miles.

Incidentally, there is a differing and as yet unsubstantiated suggestion that the area outlined above might in fact have no connection with Greenland; by this reasoning, it forms a tiny and quite discrete independent tectonic platelet of its own!  Time, as they say, will tell.

As far as we know, the oldest rocks in Colonsay are rather more ancient - in fact, they may be 1,700 billion (i.e. million million) years old; and even the youngest of our rocks predate conventional life on earth, so there are no native fossils to be found locally. Naturally enough, much of the geological structure is only appreciated by specialists, but even the lay person can appreciate the effects of glaciation, can easily identify the raised beaches and can recognise the igneous rocks around Scalasaig.  There are also some remarkable dykes, and there is always the chance of a gentle undersea earthquake as the faultlines are eased - usually about strength 3 on the Richter scale and about ten years apart.  The most recent episodes took place in early 2012, in the vicinity of Loch Gruinard and Loch Indaal. 

Note: The Lovatt family recently (2016) discovered two fossils, evidently brought to Colonsay by glaciation. Apparently they were lycopsids, part of the root structure of the tree-like plants that produced coal seams, dating to the Carboniferous period (350 - 290 m.y. ago).

For further information on local material, please refer to the geological notes attached below.

File Attachments: 

Colonsay Moorings Development

A Marine License Application for the 10 moorings due to go into Queen’s Bay was submitted to the Crown Estate in March. CCDC also submitted an application to Marine Scotland in late April. Both these applications have had a considerable amount of input from MOWI who are one of our key match-funders for this development. We hope to hear if our applications are successful in the next six to eight weeks. MOWI would like to see the moorings installed as soon as possible, but as you would expect, COVID-19 has impacted many of the administrative and physical processes required to see the 2 tonne anchor blocks put in place. Similarly, the Path Development has been delayed due to an inability to source materials. Our funder, Paths for All, are understanding of the situation and are willing to work with us on this. Colonsay Estate has agreed in principle to the path up to the church and we are working through the details with them.  
In the meantime, CCDC have been corresponding with other marine establishments, and are working on a management plan which incorporates an online booking system for the moorings.  
If anyone has any thoughts or questions about the moorings. Please contact Roz Jewell: