A straightforward, energetic walk from the Knockan Crag visitor centre along a well defined and maintained geo path, passing rock art and poetry will take you to a clearly exposed section of the Moine Thrust.
So important is this site to geology that it is a UNESCO endorsed Geopark. The structure of the Moine Thrust was not fully understood until the late part of the 19th century, primarily as a result of the work undertaken by Ben Peach and John Horne. Their here work put paid to the Highland Controversy, shattering some reputations in the process. Simply put, the puzzle was: How could older metamorphic rocks form above younger unmetamorphosed rocks below? The answer is that the older metamorphic rocks (Moine Schists) were thrust upward and over the unmetamorphosed rocks (Durness limestone).
It seems so simple, yet this discovery changed forever geological thinking.
The Visitor Centre is open 24 hours a day, although a daylight visit is essential! The centre can be seen from the car park at N58 02.023 W5 04.276 and displays wonderfully the history of this amazing place.
Displays at the Knockan Crag
Visit www.knockan-crag.co.uk for lots of interesting information.
Technical details:
The section at Knockan Crag is deceptive in that it displays an apparently simple upward progression through the foreland Cambro-Ordovician strata into the apparently conformable Moine.
Indeed the entire thrust belt is here represented by the Moine Thrust alone. Within a few metres of the thrust, carbonates of the Durness Group are sheared and cut by cataclastic seams and veins although deformation structures are absent below. In contrast, the overlying Moine is dominated by crystal-plastic deformation mechanisms as displayed by a tract of mylonites over 100m thick.
Within about 1-2m of the thrust surface the mylonites are brecciated and recemented by a fine-grained green phyllonitic gouge. These cataclastic fault rocks are themselves foliated, possibly implying a return to ductile shearing, within a few centimetres of the thrust surface. The thrust surface is sharp, marked by a few cm of dominantly carbonate gouge. It is the ready weathering of the gouge that results in the sharply incut expression of the fault surface at Knockan Crag.
To Log this cache, please perform the following task and include it as an image posted with your log as soon as possible.... Or your find will be deleted.
From the Visitors Centre follow the "Thrust Trail" until you reach the Moine Thrust. Ben Peach, the Victorian geologist who first worked out the relationship between the rocks at this location was famous for the quality of his field sketches. Your first task is to draw your own field sketch of the cliff section, which as every good geologist knows must include plenty of SNOT
- SCALE such as a stick person or metre bar
- NOTES or labels for the Moine metamorphic rocks, Thrust Surface/Plane, Cambrian Limestone [optional]
- ORIENTATION, which direction you are looking
- TITLE for your field sketch
Your sketch can be scanned or photographed and then posted as an image with your log.
Your second (simpler) task is to post a photo of yourself, with GPS at the Thrust section near the "hands".
These educational guidelines must be fulfilled and are laid down by the Earthcaching organisation. Please note: I no longer cache actively, but have kept these caches (Earth and Virtuals) for the enjoyment of those who do. I may not reply, therefore, to your email. If you are really looking for a reply, please don't log this cache.