Boat trip on Loch Glencoul

Duration — 2 hours there and back

Difficulty — none

Ascent — none

Start — grid reference NC 230 338

This boat trip takes you along scenic Loch Glencoul, visiting seal islands and the highest waterfall in Britain. It also provides an excellent view of the outcrop of the Glencoul Thrust, which is one of the most famous thrust localities in the world. The trip on the ‘Statesman’ leaves from the jetty outside Kylesku Hotel, and at the time of writing summertime departures are twice a day, five days a week. Tickets can be bought just before boarding the boat. While you’re waiting, have a look at the rocks beside the jetty; these striped, pink and grey rocks are good examples of Lewisian Gneiss.

The boat leaves the jetty and heads east towards Loch Glendhu and Loch Glencoul. These steep-sided sea-lochs are fjords, similar to those in Norway. They were formed during the Ice Age when large glaciers flowed down from the mountains in the east, gouging out deep valleys. Rounding the point below the village of Unapool, the boat enters Loch Glencoul to pay a visit to the islands on which seals bask during the summer [1] [NC 24356 32057]; young common seals can often be seen swimming and diving here. The islands are composed of striped Lewisian Gneiss.

Heading onwards up Loch Glencoul, you can see a prominent hill at the head of the loch. This is the Stack of Glencoul, which is composed of mylonite, a rock formed by intense deformation of the Moine Rocks as they were moved along the Moine Thrust. The Moine Thrust lies below the prominent cliff near the top of the Stack.

The boat is an excellent vantage point from which to view superb exposures of the Glencoul Thrust, a major thrust lying below the Moine Thrust. On the northern shore of the loch [2] [NC 25875 31554] are prominent cliffs, which form a wall of orange-coloured rocks that slope down to the water. They are composed of Cambrian Quartzite, which here lies on top of the Lewisian Gneiss that forms the rocky, hummocky ground below the cliffs. Torridonian Sandstone is missing in this area, having been entirely eroded away before the quartzite was laid down.

Above the quartzite cliffs is a gentle green slope that gives way to rocky, hummocky ground on the hill of Beinn Aird da Loch; like the ground below the cliffs, this rocky hill is composed of Lewisian Gneiss. In other words, the ancient Lewisian Gneiss has been forced on top of the quartzite. The surface along which this movement occurred is known as the Glencoul Thrust, and here the thrust lies at the top of the green grassy slope above the quartzite cliffs.

On the southern shore of the loch [3] [NC 26313 30321], the Glencoul Thrust runs through the cliffs, and there is often an opportunity to view it closely from the boat. The grassy slopes coming down to the loch shore are underlain by quartzite, and above these is a cliff of Fucoid Beds, marked by a line of rowan trees. This cliff is overshadowed by the rocky crags of Cnoc na Creige. As with Beinn Aird da Loch on the north shore, this hill is formed of Lewisian Gneiss above the Glencoul Thrust. The thrust itself can be seen in a dark, overhanging cliff above a line of trees, where dark grey Lewisian Gneiss lies on top of pale yellow Durness Limestone. The sharp boundary between the two rock types is the Glencoul Thrust, and it is estimated that the Lewisian Gneiss moved some 30 kilometres along the thrust plane to its present position.

From there, the boat continues on into Loch Beag, passing cliffs of Lewisian Gneiss within the Glencoul Thrust Sheet. From the head of Loch Beag you can see the waterfall, Eas a’ Chùal Aluinn, the splendid waterfall of Coul. At 200 metres high this is the highest waterfall in Britain. A local legend is that a local maiden threw herself off the cliff to avoid being married to a man she did not love, and that as she fell, her tresses spread out behind her, forming the waterfall. The waterfall cascades from the side of the glen, rather than its head. As glaciers gouged out the glen during the Ice Age, they cut through an existing river channel, leaving the river to fall over the steep cliff to the floor of the glen.

From the waterfall, the boat returns to Kylesku, with the red-brown Torridonian Sandstone peaks of Quinag as a backdrop. If you stop at the Kylesku Hotel for refreshment after your trip, make sure you look out for the geological map that forms the top of one of the tables!

Figures

(Figure 92) Boat trip on Loch Glencoul. Painting of excursion by Elizabeth Pickett.

(Figure 93) The Statesman.

(Figure 94) Quinag from the seal islands.

(Figure 95) The Stack of Glencoul towering above hills of Lewisian Gneiss.

(Figure 96) The Glencoul Thrust on the north shore of Loch Glencoul.

(Figure 97) View of the Glencoul Thrust on the south shore of Loch Glencoul.

(Figure 98) Simplified cross-section from Kylesku to the Stack of Glencoul, along the north shore of Loch Glencoul, showing the main thrusts.

(Figure 99) Eas a’ Chùal Aluinn waterfall.