Isle of Skye - Geology

The Isle of Skye has a long geological history, illustrated by a Geology Excursion Guide that has 21 detailed itineraries, the majority are of 8 - 10 hours in duration. Located on the Atlantic coast of Scotland there is the prospect of some changeable weather, which means there is the opportunity for making a landscape photograph with a narrative of the geology and/or geomorphology.

View from the western slopes of Marsco  ~ 2013

One particular geological feature has played on my mind, since my last visit to Skye, in late November 2013.  I had followed an excursion in a geology guide book, down Glen Sligachan and ended up in Harker's Gully on Marsco, that has exposures of intrusive rocks in a composite ring dyke. In lieu of typing verbatim the geology guide description, there is a description of the ring dyke and its context within the western Red Hills (volcanic) centre on the BGS Earthwise blog or Geological Conservation Review. The ring fracture was differentially weathered into a gully and a distinctly verdant flora compared to that growing over the thinner soils on the adjacent granite bedrock. That geology excursion was compromised by the distraction of the views over Glen Sligachan to the Black Cuillins, glacial geomorphology and the course of the River Sligachan, that in places delineates the boundary of the gabbro and granite intrusions.

Screen shot taken from http://mapapps.bgs.ac.uk/geologyofbritain/home.html to illustrate Marsco hybrids of the western Red Hills Centre

For those curious about Britain's bedrock, the British Geological Survey has an excellent Geology viewer application to investigate the landscape. Below is a satellite image taken in late winter of Marsco, judging by the snow lying on the Black Cuillin, shadows and the drab brown foliage. Clearly visible are stripes and patches of green foliage.

Screen shot taken from http://mapapps.bgs.ac.uk/geologyofbritain/home.html to illustrate Marsco hybrids of the western Red Hills Centre

 Clicking on a green strip reveals the underlying geology as mapped by field geologists, which is the Marsco Hybrids.

Changing the geology transparency layer reveals the underlying geology and the green foliage correlates with the outcrop of the Marsco Hybrids.

On the visit to Skye in late October 2016 and in the itinerary under 'iffy weather' there were a list of geology excursions and two in particular explored the nature of the ring dyke further. First up was an impromptu geology excursion to the John Muir Trusts, Sconser estate, that proved interesting, but probably best visited after some drier weather, with lower water flows to make crossings easier and when the Sligachan 'peatlands' are less saturated. The plateau basalts, Glaimaig granite and the composite ring dyke of Marsco Hybrids are revealed in the stream exposures of bedrock and also on the north spur of Druim na Ruiage the Marsco Hybrids are revealed by verdant green flora against the autumnal russet flora of the sedges and grasses. Sadly by the time I had got to grips with the geology exposures, the weather had really deteriorated and dusk arrived. Nevertheless, I was impressed with the potential of the area and the backdrop of the Red Cuillins.

After arriving on Skye, Nic booked a kayaking trip on the day before we departed Skye and at the time the plan was to drop me off somewhere and then pick me up somewhere else at at dusk. The weather forecast deteriorated, with a weather front spreading in from the north around midday and so the plan changed, to me dropping off Nic and picking her up from the kayaking offices, giving me a window between 09.00 - 16.00 hrs. The leading edge of a weather front can deliver some atmospheric weather, so I decided on a walk up into Coire nam Bruardaran,  which was also covered by a geology excursion I could cherry pick from and if the opportunity arose, wander up a hill summit if the weather held. After dropping Nic off in Lower Breaknish, I parked up at Loch Ainort and the weather was pretty good, a few wisps of hill fog over Glaimaig, but the higher summit of Gharb-bheinn clear. A beeline was made for Gharbh-bheinn, the geology could wait until the descent. An hour later and the summit of Gharb-bheinn was 'clagging' up, sigh. I was passed by two local hillwalkers, who in view of the dire weather forecast, were heading up Gharbh-bheinn for a shorter hill day in preference to the Black Cuillin. In view of the hill fog I decided to concentrate on the geology and views from Druin Eadar Da Choire and Point 489.

Topographic expressions of weathering and erosion.

Where the ring dyke crosses the ridge of Druin Eadar Da Choire, its presence is revealed by a gully, the ground vegetation is less convincing, although the signature of the verdant flora corresponding with the Marsco Hybrids is readily apparent on the eastern flank. The view across Coire na Seilg, juxtaposes the weathering and erosion profiles of differing lithologies : granite of Glas-Bheinn Mhor and assorted intrusive/extrusive basic rocks of Belig.

Onwards to point 489, which for a modest elevation has extensive views. Any lingering hopes I had of taking in more elevated views were dispelled by incoming cloud and orographic fog. I should add that the western summits of the Black Cuillin appeared to be largely free of cloud/fog, whilst the lower tops of the Red Hills were afflicted by cloud/fog. A 'wee blether' with the two hillwalkers on their return journey, revealed that they did get a brief view from Gharb-bheinn's summit.

I did chance upon a Hard fern nestled in an outcrop of granite accompanied by some Fir clubmoss.

The western slopes of point 489 had extensive granite block fields against a backdrop of Marsco and the Black Cuillin. I did keep an eye out for any glacial erratics, but didn't notice anything, which suggests the block fields are autochthonous and generated under periglacial conditions, some areas of the slopes had distinct banded pattern of vegetation and block stripes, landforms indicative of periglacial mass movement.


The dark basic rocks of Garbh-bheinn, provided a contrasting backdrop to the granite block slope. The name given to this area is the Red Hills, I somehow arrived in an area where the geology comprised either dark basic rock or granites that were blue/green/gray when fresh and gray/brown when weathered. The weather as forecast deteriorated and I made my way back to the car, not a bad excursion and an area to return to again one day. I'll cover other excursions on the Isle of Skye in the next post.