Basal Quartzite at Clais Lobhta

Poorly sorted, granule-rich and feldspar bearing beds become rarer within the younger beds and the member gradually becomes whiter in appearance.

Sedimentary features are abundant, the most common being medium-thick bedded units with fining-upwards features typically 0.25m thick. These are seen in beds that have low levels of messy ‘vein-like’ bioturbation features which become more common in younger beds. Graded bedding (pebble-sized up into medium sand) are also seen within abundant cross-laminated beds. Nearer the top of the member, further cross-stratification is seen with herring-bone features present but less abundant. Dark-pink beds containing thin, light-pink coloured lenticles, truncated by pinch-out features indicate westwards & eastwards bimodal palaeocurrents. Fine, colourless detrital feldspars are also scattered throughout

This small gully marks a large fault that seperates the Lewisian Gneiss (south) and a hillock (north) formed of the Basal Quartzite and Pipe Rock. The Basal Quartzite is the lowermost part of the Eriboll Sandstone Formation and is generally poorly exposed in the Durness area, although small outcrops are found along the northern sides of this gully.

Abundant cross-bedding and some herring-bone bedding implies that these are ancient beach deposits. These beaches were formed during the Cambrian period c.500 Ma during a worldwide sea-level rise that occurred at that time.

The Basal Quartzite consists of a very pale to dark beige coloured quartzite composed of colourless to beige coloured, well-rounded quartz grains and minor feldspar granules. Where individual grains have been preserved, a grainsize of medium to coarse sand can be seen with the coarsest beds having as much as 10% porosity, otherwise a white coloured intercrystalline matrix is all that can be seen with a lack of pebbles.