in the Canna Lava Formation (Harker 1908; Emeleus 1996) and in the .... mainland, NW Scotland. ..... volcanic rocks of Eigg, Muck and Canna, N.W Scotland.
Red tuffs in the Palaeocene lava successions of the Inner Hebrides C. H.
EMELEUS',
E. A.
ALLWRIGHT',
A. C.
KERR~ and
I. T. WILLIAMS ON^
Department of Geological Sciences, University of Durham, South Road, Durham DHl 3LE Department of Geology, University of Leicestex; University Road, Leicester LEI 7RH British Geological Survey, Keyworth, Nottingham, NG12 5GG Synopsis Thin, sharply defined red deposits in the Palaeocene lava successions of the Inner Hebrides are interpreted as tuffs. They commonly contain plagioclase and augite, or in some instances, sanidine, aegirine-augite, amphibole, biotite and titanite; lithic fragments include basalt and, less commonly, trachyte and pumice, and even rarer glass. They contrast with the contemporaneously weathered and deeply decomposed, reddened lateritized, tops of lava flows that grade down into dark-coloured lava. The tuffs provide stratigraphical markers of at least local use and at some localities their distinctive petrography and mineralogy records magmatism not preserved in the contiguous lavas. The recognition that some of the inter-lava red beds are tuffs rather than laterites may imply a reduction in the time required for the lava successions to form.
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The subaerial Palaeocene lava successions of the Hebrides and NE Ireland are well exposed in cliffs of darkweathering lava flows interspersed with thin beds of strongly coloured (commonly red, but also purple, brown, yellow and intermediate shades), fine-grained, clay-rich rock. These distinctive deposits, which are generally
