North West Highlands Geopark (2016) North West Highlands Geopark Geodiversity Audit and Action Plan 2013–2016
Additional notes: These web pages are sourced from the PDF North West Highlands Geopark Geodiversity Audit and Action Plan 2013–2016
NWHG Ref. 025 — Beinn Gharbh
Location, grid reference and photograph
The site occupies the area of Beinn Gharbh which rises above Loch Assynt on its south-west side, Grid Ref.
GCR site reference, block, volume and notified feature of SSSI?
GCR Ref. 1225, Caledonian Igneous Block, Vol. 17. Confirmed GCR site, not SSSI notified feature.
Description and geological significance
The view onto Beinn Gharbh, looking southwards from the north side of Loch Assynt, is one of the most important in British geology and displays the “double unconformity” of basal Lewisian gneisses rising up from the shore of Loch Assynt and being unconformably overlain by horizontally bedded Torridonian sandstone strata, both of which are unconformably overlain and overstepped by Cambrian quartzites dipping at about 15o to the east. The differences in dips of the Torridonian and Cambrian strata are visually highlighted by two parallel major sills of Canisp Porphyry on Beinn Gharbh, both of which clearly follow (and emphasise) the bedding planes of the two different strata, the sills changing dip as they cross the upper unconformity. The site therefore serves to clearly illustrate a double unconformity within the flank of the north-facing slope as well as providing exceptional exposures of Canisp Porphyry, the largest development of Caledonian magmatism in the Foreland terrane.
Accessibility
The main features are easily seen from laybys on the A 894 as it rises northwards from its junction with the A 837 at Skiag Bridge. The site is therefore accessible to all abilities.
Conservation
There are no conservation requirements due to the scale and location of the site.
Visibility and “clarity”
The essential geological features are best seen from a distance from the A 894 to the north. The view is both dramatic and spectacular and also inspirational once the significance of the features is explained to the casual viewer.
Interpretation and interpretation potential
There is currently no interpretation panel but this is certainly one instance where a new panel erected at the layby at the top of the Skiag hill, looking south towards Loch Assynt, would be of significant interest and benefit for the general public. There is considerable potential for development of an appropriate viewpoint as an educational resource for university parties and researchers as well as the public. Certainly, the double unconformity should be listed in a future Geopark guide and the viewpoint from Skiag included in any guided tours.
Key references
PARSONS, I. 1999. Late Ordovician to mid-Silutian alkaline intrusions of the North-west Highlands of Scotland. In Stephenson, D., Bevins, R. E., Milward, D., Highton, A. J., Parsons, I., Stone, P. & Wadsworth, W. J. (eds) Caledonian Igneous rocks of Great Britain. Geological Conservation Review Series, 17, Chapman & Hall, 345–393 (site description page 383).