This is a fully guided tour based on Raasay, and included hotel accommodation and food. Chris is a born teacher and loves to share his encyclopaedic knowledge: he not only knows his geology, but the local history as well. It goes without saying that, for these trips, you need to like walking, some of it is up and down, and a geology hammer helps!

The west coast summer weather in Scotland can be variable, but Chris made sure we got the best of every day, moving round in advance of rainstorms – some of us even came back with suntans! The midgies and horseflies were a nuisance to some, but my tried and tested method is to buy a Scottish brand of insect repellant. It seems to work for me, at any rate. Some days we took the ferry to Skye (once Chris had cast the weather forecast runes of course). Most evenings were spent companionably going over the day’s excursion notes after an excellent dinner in the Isle of Raasay hotel sitting watching the colours shift on the Cuillins of Skye across the bay. Long evening sunshine is an added bonus in this beautiful part of the world.

The Raasay Ferry and the Red Cuillin

The geology of Skye and Raasay is that of a truncated geological column starting with a thick basement of continental Lewisian gneiss, fractured early by plate tectonic activity.

Following this came river deposits from the Canadian locality laid down as Diabeg, the earliest Torridonian. At the next stage, Raasay lay on a shallow ocean margin. This was when the Applecross Torridonian was deposited, the Brochel locality being an example. This is a fascinating exposure that is marked on the geological map as vent activity, but observation in the field suggests something different. What it actually resembles is a collapse of an ancient landscape over an existing cliff, backing up the theory that the Torridonian had two main stages. In Raasay House, we bumped into a final year Paisley geology mapping student who we took back to Brochel to look at parts of his map. As we walked through a cleared forestry plantation, an added bonus for him was spotting a new exposure in a cleared forestry plantation that no one had yet mapped. We decided that it was a rotting dyke with yellow clay minerals and onion skin weathering of granophyre boulders.

Raasay escaped the Moine thrust activity, so we went across to Skye to sample an exposure hands on. The Moine thrust was the result of the collision of the ancient continents of Baltica and Laurentia. We collected some specimens of phyllonite and mylonite in a damp and gloomy stream bed on the Broadford to Elgol road, but were beaten back by the fully paid up geological conservationists – midgies with razors for teeth. These rocks resemble a shaly sandstone, but are actually Lewisian gneiss ground to a fine powder.

We spent an enjoyable afternoon hacking rocks at the old quarry above the Old Manse at Kilchrist on the Broadford to Elgol road. I thoroughly recommend a bit of violence to vent your feelings after an intensive midgie biting session. The marbles in this quarry are thermally metamorphosed Durness limestones, (Cambro-Ordivician age) yielding colourful purple streaked brucite, and Serpentine green stripes with white quartz bands. This metamorphism occurred along the contact zone of the Tertiary intrusive rocks (Cuillin Hills).

The Silurian to Permian is missing in Skye and Raasay, being probably an erosional phase here with some faulting. To view Triassic sediments, we drove to SE Raasay and walked along the coastal path around the slumps to Rudha na Leac. This is a Triassic platform of red lumpy rock formed quickly from coarse debris raining down in flash floods. It is a beautiful coastal spot with views inland to the highest point, Dun Caan, a hill topped with a dolerite sill. (There is another similar Triassic exposure just south of the ferry near the high water mark – not marked on the geological maps).

Dun Caan

For a view of the Lower Jurassic, we visited the disused Raasay iron mine south of the jetty. This mine, sunk in sedimentary rock, exploited the iron carbonate deposits. On Raasay this bed is over 2m thick, consisting of green chamosite (hydrous iron silicate) and siderite (iron carbonate) in a limestone matrix. It yielded up to 25% iron. Magnificent belemnite rich rocks lie under foot on the slopes, and we spent a short time clearing mossy mats from their exposures.

We set off for Skye again to view the Middle Jurassic, on the NE coast where the Sgurr Loch HEP dams empty into the sea. This is a steep climb down, but worth it for the views across to Kilt Rock formation, a doleritic intrusion in the Jurassic, showing vertical columnar jointing (hence the resemblance to a kilt). The predominant rock on the seashore here is the Bearreraig sandstone formation, lying unconformably on the Raasay ironstone formation. It is rich in belemnites, with the occasional big ammonite. I found some horsetail fern and worm tube fossils. After that we rushed back to catch the last ferry, passing lovely views of the further western isles. We also viewed the Bearreraig sandstone at Elgol, in the sea cliffs showing honeycomb weathering where calcareous cement in the sandstone has leached out. Every view in Skye is scenic (weather permitting) but the view across the sea from Elgol is stunning.

The Kilt Rock	The Kilt Rock and a be-hatted Janice

It is impossible to describe the geology of Skye and Raasay without mentioning the Tertiary volcanics which have done much to shape the area’s forbidding beauty during probably the most extensive volcanic episode ever in N. Europe. It is too complex however to do justice to it here, other than to say that there may have been a hot spot under the Cuillins making it arch and erupt basalt, as there is under Iceland at the present day. Kilt Rock in Northern Skye is a basic sill igneous intrusion, and the Cuillin Centre is a basaltic magma, with granite masses in the Red Cuillins. In fact, almost every road in Skye has magnificent views of the formations that make up this episode.

One of our trips to Skye was to the Quiraing landslip on the Trotternish ridge. Spectacular pillars and pinnacles have formed where tertiary lavas lie on buckled rocks. It is the largest landslip in Britain and five successive movements have been identified, extending over 2km from the scarp slope to the coast. Although features such as the Storr and the Quirang are currently stable, other areas remain active.

The Quirang

Below the Quirang, on the Uig to Staffin, road there is an interesting quarry (now being used as a dump). Foraging around, we found some rare zeolites complete with fur, & laterites with occasional twigs. Unfortunately my specimens evaporated overnight leaving holes where the fur was!

All in all our trip to Skye and Raasay was a fascinating and informative trip through geological time and one that I would not hesitate in recommending to the beginner and experienced amateur alike.

REFERENCES:

http://www.bambi.demon.co.uk/skyedata/geology.html