Directory

Abstract

The following chapter is intended to provide a comprehensive field description of the Torridonian, replacing that given in the Geological Survey's NW Highlands memoir of 1907, and citing all relevant literature. Stratotypes and palaeocurrents are described, along with the section lines used to construct the regional stratigraphic sections (Figs 4&23), but detailed consideration of topics such as geochemistry, diagenesis, sediment source areas, palaeomagnetism and basin tectonics is contained in Chapters 2-5. for convenience the rocks are described under thirty-three compact subareas, most of which are shown on Plate 2. This plate also locates all figured maps and sections. The Directory starts with Cape Wrath and continues with sub-areas progressively farther south. The Geological Survey divided the Cape Wrath succession into three stratigraphic units, without definitely correlating any of them with the formations of the Torridon Group that they had established farther south (Peach et al. 1907, p. 292). They described the lowest unit (30 m thick) as coarse pebbly sandstone or basal conglomerate; the middle unit (300m thick) as coarse red sandstone with pebble bands, and the uppermost unit (75 m thick) as finegrained mottled purple and yellow sandstones. Remapping by Williams (1966a, 1969a, 2001) enabled him to subdivide the sequence stratigraphically into five main lithological units, which he called facies associations (FA) even though they always appear in the same order (cf. the definition of facies given on p. 2). Each successive facies is finer than the one below, as shown by the representative logs in Figure