Abstract

DR. R. G. PARK congratulated both authors on their interesting accounts of the very complex geology of the southern Outer Hebrides. Lacking first-hand knowledge of that area, he was tempted, despite his sceptical approach to structure correlation in general, to try to match the structural sequence proposed by the authors with the sequence obtained by the speaker and others in their recent work on the southern Laxfordian belt of the Scottish mainland, but found considerable difficulty in doing so. A superficial similarity existed between the f3 folds of the authors and the large-scale second Laxfordian folds on the mainland with a NW–SE trend and steep axial planes. The distribution of these structures showed a marked heterogeneity of deformation with narrow intensely deformed synformal belts (e.g. the Gairloch schist belt) separated by wide, relatively little-deformed zones. A characteristic feature of the Scourie dyke margins in the highly deformed zones was the presence of tight small-scale folds with relatively sharp antiformal and synformal hinges suggesting fairly ductile behaviour of dykes and gneiss, whereas no small-scale folding of dyke margins has been observed in the antiformal zones. In contrast, during the earlier Laxfordian deformation, small-scale folding of dyke margins is apparently absent throughout the region investigated and the dykes have developed a foliation only which is absent from the enclosing gneisses. In the light of these observations, could Dr. Coward comment on the role of small-scale f1 and f2 folding of the dyke margins in his area and on the physical conditions

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