The Sleat Group

Abstract

The group consists of up to 3500 m of coarse, grey fluviatile sandstones, with subordinate grey shales, resting unconformably on the Lewisian basement complex. Although the beds have been thrust tens of kilometres from the east as part of the Caledonian Kishorn nappe (Ramsay 1969) their stratigraphic position is secured by a conformable relationship with the overlying Torridon Group, presumed to be only slightly younger (Fig. 19). The Stoer Group does not form part of the Kishorn nappe and its relationship to the Sleat Group is unknown. Lithostratigraphic correlation of the two groups is thought unlikely, however, for reasons given later. Slight Caledonian deformation and very low grade metamorphism have had little effect on sedimentary structures in the Sleat Group between Loch na Dal and Kylerhea, in Skye. The metamorphism has, however, dissuaded attempts at isotopic dating. The lithology, framework mineralogy of the sandstones, palaeocurrents and stratigraphic nomenclature of the Sleat Group are summarized in Figure 20. No formal facies nomenclature is proposed. The present outcrop is shown in Plate 1. Stratigraphy Sleat Group lithostratigraphy was originally established by the Geological Survey (Peach et al . 1907, p. 349) and revised by Sutton & Watson (1964). Stratotypes are described in detail on pp. 109-112. The dominant feature of the group is an upward decline in grain size, from very coarse sandstones in the basal Rubha Guail Formation to very fine sandstone in the Kinloch. The two lowest formations are easily distinguished by their coarse grain size, shale content, relatively thin bedding