Quinag

Quinag is one of the great mountain massifs of Assynt. It forms a roughly Y-shaped range with the two northern prongs containing the high peaks of Sail Gharbh (808m) and Sail Gorm (776m). The highest of these is capped by the thin skin of Cambrian quartzites, These form an outlier to the dip slope of quartzites that forms the eastern flank of Spidean Coinich. Apart from this quartzite skin, Quinag is made of a pile of Torridonian sandstone, resting on the substrate of Lewisian gneisses. So the massif is an excellent place to appreciate the relationship between these three major rock units of NW Highland geology, exposed ahead of the complexities of the Moine Thrust Belt.

Spidean Coinich and Sail Gharbh are frequently ascended. They give dramatic views of northern Assynt and beyond to the craggy mountains of Foinaven and Arkle. This ascent, with a return down Bealach a'Chornaidh, passing the eponymous lochan is highly recommended. But it also gives a great insight into the recent glacial modification of the landscape.

It was once thought that Quinag, along with the other western Assynt hills, were over-run by ice during the most recent regional glaciation (Late Devensian). However, in the past ten years or so the top of Spidean Coinich has been found to contain deep weathering and boulder rings indicative of having been poking out of the ice sheet. It was a nunatak. An ascent up the dip-slope of Cambrian quartzite illustrates this superbly. Low on the mountain the quartzites are scraped clean. The bedding is smoothed and striated. Erratics including rare Moine and Lewisian boulders decorate the surface. So Late Devensian ice ran over this ground, carrying off the loose bed rock and leaving behind erratic blocks. The preservation of deeply weathered bed-rock on the summit says that it was not over-run by ice. The effect of Quinag on ice flow can be checked by measuring glacial striae on the quartzites.

By about 13,000 years ago there was a rapid improvement in climate and the ice quickly melted from the valleys. We know this because the oldest sediment in lakes such as Cam Loch in southern Assynt are of this age. When the ice was there, the lake wouldn't have been and no lake sediments would have been deposited. However, the same lake sediments record a short return to cold conditions (not enough to grow back huge glaciers) at about 11,000 years ago. This is the Loch Lomond "re-advance". On Quinag ice returned, but only to its north-facing corries. The tell-tale signs are quartzite boulders found in the low ground north of Spidean Coinich. Rock-fall today from high on the hill is building small scree cones, piles of quartzite blocks on the underlying Torridonian. But a line of quartzite blocks lies hundreds of metres ahead of the hillside too. These can't have reached their current position by simply falling down a scree slope. The intervening ground must have been partially banked up by snow and ice. At this stage rock fall high the mountain sends blocks onto the snow and then they continue to skim out building a so-called "rampart". And there are other signs of ice in the corrie. The bed rock is fresher around the head wall - the upper edge of this is called a "trim line".

There are further signs of glacial environments around Quinag. Just west of the A894, down valley from the corrie with its headwall at Spidean Coinich, there are plenty of indicators. Great blocks of Torridonian have been toppled slightly from their bed-rock positions, rather like a giant child's wooden brick set. This would have happened as the ice retreated during the end of the Late Devensian glaciation. Low moraine ridges mark the retreat. On the north side of Bealach a'Choraidh there are spectacular terraces of boulders formed by large-scale soil creep enhanced by freeze-thaw action (solifluction). Melt-water from this retreat and the melting of the smaller Loch Lomond re-advance corrie glaciers have carved the ravines that carry the Unapool Burn today. The most dramatic melt-water channel drains the modern Loch na Gainmhich, that crosses the A 894 before joining the Unapool Burn.

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