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. 039 — Loch Ailsh Intrusion
Location, grid reference and photograph
The site covers an area of about 10 km2 extending from within 750 m of the northern shore of Loch Ailsh and on either side of the Oykel valley for some 3 km, Grid Ref.
GCR site reference, block, volume and notified feature of SSSI?
GCR Ref. 1221, Caledonian Igneous Block, Vol. 17. Notified as feature of Ben More Assynt SSSI.
Description and geological significance
The Loch Ailsh intrusion is important because it includes a suite of unusually sodium- rich syenites considered to be unique in the British Isles. It is internationally important as it includes the type-locality for alkali feldspar syenite, or “perthosite”. The radiometric age and structural relationships are important for the timing of movements in the Moine Thrust Zone.
Accessibility
The intrusion occupies a huge area of about 10 km2 and can be accessed to some extent via unsurfaced forestry tracks within Glen Oykel. A considerable amount of walking over rough terrain and within forestry areas is required. There is no all abilities access.
Conservation
Low conservation requirement due to the scale and location of the site area.
Visibility and “clarity”
General views only of the associated terrain and mountainous landscape can be had from the north-east side of Loch Ailsh. Specialist knowledge is required in order to associate individual landscape features to the particular rock-types occurring within the intrusion.
Interpretation and interpretation potential
The Loch Ailsh intrusion lies in a very remote area and is unlikely to be of interest to the general public as it requires specialist knowledge to interpret it. Nonetheless, it does represent an important locality for petrological studies and for examining the detailed timing of movements in the Moine Thrust Zone. There may be some potential, therefore, for developing the area as a teaching resource for geology students. The area should be listed in a future Geopark guide but guided walks specifically to see the key features would be inappropriate.
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 366).