Geology of Durness
This map shows the local geology curtsey of the British Geological Survey Natural Environment Research Survey
For the interested amateur the shapes, colours and situations of some of the rocks can only attract curiosity and fascination. The country is a Geologists playground, with rocks displaying 3 billion years of geological time. Major fault and thrust lines, running from northeast to southwest, define the main geological zones. The U-shaped valleys are a legacy of the last Ice Age. The weight and movements of glaciers broke off spurs, deepening and rounding out the existing river valleys.
The parish can be divided into well determined geological regions. Distribution is defined more by faulting than any other single factor. Faults have brought the limestone against the Lower Cambrian and Pre-Cambrian so that there are contrasting adjacent rocks types. Conclusive proof can be found in the area that north west Scotland was divided from the rest of Britain and most of western Europe and lay on the opposite side of the Lower Palaeozoic Proto-Atlantic Ocean . One of Britain 's outstanding earth science sites, it is of essential importance in studies of transatlantic correlation, palaeogeography and faunas.
The area contains rock formations of outstanding geological interest, which span over 2,800 million years and include some of the oldest surface rocks in Britain . TAlong the west coast, the oldest rock in the region, Lewisian gneiss, creates a landscape of low hills and scattered lochans. Rising from this gneiss landscape are huge masses of Torridonian sandstone, capped by quartzite.Much is comprised of schists and granulites of the Moin series named after A' Mhoine near Tongue where they were first described. The softer schists of the series have weathered to produce the level landscape of the peatlands, from which the more resistant rock masses of Ben Hope and Ben Klibreck. The Moine Thrust zone, which lies east of the gneiss and sandstone area, crosses the region from north to south. This zone provides evidence of immense disturbance of the earth's crust some 400 million years ago and has long been an area of study for geologists from all over the world.
The oldest rocks in the area are of the oldest in the world. Three major divisions of the pre - Cambrian system are found. The oldest is Lewisian comprising of rock between one thousand four hundred million years and two thousand six hundred million years old. The other two divisions Moine series and Torridonian, eight hundred to nine hundred million years old, distinguishable by their appearance. The youngest solid rocks are of Cambrian and lower Ordovician, approximately four to six hundred million years. An excellent section through some of the Cambro-Ordovician Rocks can be seen along the south shore of Balnakeil Bay . Limestones and Dolomites are present here and some of the former contains fossils and a large number of Chert Nodules, sub spherical masses of rock with a chemical composition similar to quartz. The compacting of sediment deposited in a low energy marine environment that is on a part of the seabed where there was little or no wave or current action formed these rocks. They are fine-grained (tiny particles) and muddy rocks. At Faraid Head , the rocks are associated with gigantic earth movements, which took place approximately three hundred and seventy five million years ago during the latter stages of the Caledonian Orogeny (mountain building movement). The rocks forming Faraid Head are metamorphosed but they had a different origin from the Lewisian Gneiss and were altered at a much later date. In Sango Bay , there is another small belt of rocks, which have been thrust over from the east and faulted down. The actual fault plane is the steep cliff that forms the eastern end of the bay.
The rocks at the western end of Sangobeg Sands are of the Lower Cambrian age and are known as pipe rocks because of the pipe like markings in the Quartzite (metamorphosed sandstone) of which they are composed. These markings are not true fossils but are called 'trace fossils' because they are impressions left in the original sediment by organisms. Worm like creatures with vertical burrows formed these 'pipes'. The rocks at the eastern end of the sands are Lewisian Gneiss with an age of about fourteen to eighteen hundred million years. Veins substantially thick of biotite and or hornblende can be found as garnets, amethyst, and iron ore minerals. Two or three times a year geology students are brought to Durness for two or three weeks from national and international Universities to study local rocks.
At approximately grid ref. 420650 there is a huge mass of almost pure Feldspar. Three or four vertical Pegmatite veins (very course grained crystalline rock) each approximately three hundred metres long and one hundred metres wide occur in the Lewisian Gneiss . There is a minimum of twelve million tones of pegmatite in about half a square kilometre of ground and the feldspar comprises about seventy percent of this. Feldspar is used in the glass and ceramics industries. Dolomite is utilised for magnesium production