Although only barely mentioned in the Northwest Highlands memoir, slump structures characterize the Torridonian sandstone (Precambrian) in western Scotland. Two types are described and figured--small, drop-shaped structures in fine sandstone and larger slump foldswith wave lengths of one to seven feet. The origin is considered in the light of experimental work. The smaller structures appear to be somewhat similar to those formed by letting sand sink into a layer of mobilized mud, and it is suggested that an oncoming sediment-laden flood might have generated waves that mobilized the underlying beds. The larger structures are also attributed to liquefaction of beds, but it is noted that this calls for liquefaction in beds of a grain size in excess of 0.2 mm, the figure above which mobilization is not normally supposed to occur.

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