Allt Cracaig Coast
Also within
Condition (NatureScot)
| Unit | Feature | Condition | Area (ha) | Assessed |
|---|---|---|---|---|
| F1 | Moine | Unfavourable No Change | — | 2015-07-28 |
Climate exposure
This is about exposure to a nationwide pressure this habitat type carries — not a verdict on this site's own management.
Coastal habitats are exposed to sea-level rise and storm erosion. Where hard sea defences sit behind them, there's nowhere landward to retreat to — a squeeze that keeps compressing the habitat no matter how well it's managed.
Geology & landscape
Rock Type: Conglomerate
Landscape processes: Coastal, Volcanic / Igneous
Description
ALLT CRACAIG COAST Allt Cracaig Coast Site of Special Scientific Interest (SSSI) lies about 2km to the south of Glenelg Bay on the eastern shore of the Sound of Sleat. Exposures of an area of rock called the Glenelg Inlier are found here. The Glenelg Inlier consists of ancient rocks called Lewisian gneisses (up to 3000 million years old), surrounded by much younger (800 – 1000 million year old) metamorphic rocks belonging to the Moine Supergroup, which are the rocks that underlie much of the central Northern Highlands. The site contains the contact between these two groups of rocks and is of national importance as one of the few places where this contact can be convincingly demonstrated to be an unconformity. There are a number of Lewisian inliers within the Moine of northern Scotland, but where the contact between Moine and Lewisian rocks is visible, the rocks are often so deformed and metamorphosed that the original nature of the contact is impossible to determine. At Allt Cracaig Coast, however, the rocks are deformed relatively little and the following can be seen: 1. the Lewisian rocks have been cut by bodies of molten rock and fluid (seen now as amphibolite and pegmatite) which do not cut the Moine rocks; 2. the layering in the Moine rocks is not parallel to that in the Lewisian rocks; 3. sedimentary structures in the Moine rocks show that they become younger in a downwards direction, away from the Lewisian; 4. and the oldest unit of the Moine is a conglomerate containing clasts of Lewisian rock. This is all crucial evidence indicating that the Lewisian rocks have an extensive early history of intrusion, deformation and metamorphism which pre-dates formation of the Moine and that, though now inverted by later folding, the Lewisian-Moine contact is an unconformity with the Moine rocks originally constituting a sedimentary sequence deposited onto a surface eroded into the ancient Lewisian rocks.