Kilchiaran to Ardnave Point, Islay

Geological Conservation Review site | GCR #2679 | Structural and Metamorphic Geology | Dalradian

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Summary

This site provides a complete, and almost continuous cross-section of the lower part of the Colonsay Group.

Together with their continuation in Colonsay and Oronsay, this group is at least 4km in thickness. The succession is founded upon a slide, which separates it from the Islay Lewisian. Above this are ten formations named after their type areas in this site (Eilean Liath Grit, Kilchiaran Phyllite, Rubha Gaidhealach Grit, Rubha na h-Airde Moire Phyllite, Crosprig Grit, Kilchoman Phyllite, Smaull Greywacke, Sanaigmore Phyllite, Sanaig Greywacke, Ardnave Phyllite). There are also another seven formations exposed on Colonsay. One of these, the Colonsay Limestone has been tentatively correlated with the Ballachulish Limestone of the Appin Dalradian. This would presumably make the lower part of the Colonsay Group in this site the Lochaber Subgroup and/or the Grampian Group. Clearly the rocks in this site have a crucial role to play in the geotectonic evolution of Late Proterozoic Scotland if and when their true stratigraphic affinities are established.

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