The chemical differences which exist between the Moine and Torridonian rocks of the Scottish Highlands are of the same nature and order of magnitude as those between extreme end members of the Norwegian Sparagmite Formation. It is concluded that in Scotland, as in Norway, a unilateral trend of sedimentary differentiation operated from north-west to south-east across the direction of the Caledonian geosyncline and led to chemical grading of the arenaceous sediments transverse to the trend of the late Pre-Cambrian depositional basin.