The Ardnamurchan Volcano - 5

Volcanic activity moved to the west for the next phase, producing a second Caldera centred where the small village of Achnaha now stands. Centre 2 produced the great Ring Dykes (red) which form the western tip of the Ardnamurchan Peninsula, including the hills around the Lighthouse ('L' on map), Portuairk, and to the north and south of Sanna Bay.

Centre 2 also produced volcanic rocks such as lavas, ashes and agglomerates (purple), but these are not distinguished on the map from those of Centre 1.

A good example of the features produced by the Centre 2 Ring Dyke complex is this hill, Beinn Bhuidhe, which dominates the skyline to the west of Achosnich. Further to the south and east, Beinn na Seilg, the mountain which stands behind Ormsaigbeg, is also part of a Ring Dyke of this phase.

All the rock around the Lighthouse is formed of the Ring Dykes of Centre 2. The rocks vary in composition, though all belong to the basalt family; being coarse-grained because they cooled slowly, they are termed Gabbros.

This phase probably produced the most prolific swarms of Cone Sheets, these being particularly well exposed in the hillsides and coast around Ormsaigbeg and Kilchoan ('K' on map). The photograph above shows lines of Cone Sheets picked out by the rising tide along the Ormsaigbeg shore....

....and this sheet, exposed in the coast below Coilum, shows one of the Cone Sheets cutting the Jurassic sedimentary rocks into which it was intruded.