Ross - Geology

Geology

The central portion of this county is occupied by the younger highland schists or Dalradian series. These consist of quartzites, mica-schists, garnetiferous mica-schists and gneisses, all with a gentle inclination towards the southeast. On the eastern side of the county the Dalradian schists are covered unconformably by the Old Red Sandstone. The boundary runs southward from Edderton on Dornoch Firth, by Strathpeffer, to the neighborhood of Beauly. These rocks comprise red flags and sandstones, grey bituminous flags and shales. An anticlinal fold with a southwest-northeast axis brings up the basal beds of the series about the mouth of Cromarty Firth and exposes once more the schists in The Sutors (The Sutors of Cromarty) guarding the entrance to the firth. The western boundary of the younger schist is formed by the great pre-Cambrian dislocation line that traverses the county in a fairly direct course from Elphin on the north by Ullapool to Glencarron. Most of the area west of the line of disturbance is covered by Torridonian Sandstone, mainly dark reddish sandstones, grits and shales, resting unconformably on the ancient Lewisian gneiss with horizontal or slightly inclined bedding. The unconformity is well exposed on the shores of Gairloch, Loch Maree and Loch Torridon. These rocks, which attain a considerable thickness and are divisible into three sub-groups, build up the mountain districts of Applecross, Coigach and elsewhere.

Within the Torridonian tract the older Lewisian gneiss occupies large areas north of Coigach, on the east of Enard Bay, between Gruinard Bay and Loch Maree. Between the last named and Gairloch, on both sides of middle Loch Torridon and at many other spots smaller patches appear. The Lewisian gneiss is everywhere penetrated by basic dikes, generally with a northwest-southeast direction; some of these are of great breadth. The Torridonian rocks are succeeded unconformably by a series of Cambrian strata confined to a variable but narrow belt west of the line of main thrusting. This belt of Cambrian rocks has suffered an enormous amount of subordinate thrusting. It is composed of the following subdivisions in ascending order: falsebedded quartzite, Pipe Rock quartzite, fucoid beds and Olenellus band, serpulite grit, Durness dolomite and marble, Durness dolomite and limestone: but these are not always visible at any one spot. So great has been the disturbance in the region of thrusting that in some places, as in the neighborhood of Loch Kishorn and elsewhere, the rocks have been completely overturned and the ancient gneiss has been piled upon the Torridonian.

On the shore of Moray Firth at Rathie a small patch of Kimeridge shale occurs, and beneath the cliffs of Shandwick there is a little Lower Oolite with a thin seam of coal. Glacial striae are found upon the mountains up to heights of 3,300 ft (1,000 m), and much boulder clay is found in the valleys and spread over large areas in the eastern districts. Raised beaches occur at up to 108 ft (33 m) or so above the present sea-level; they are well seen in Loch Carron.

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