Climbing-ripple cross-lamination, Sorby’s (1859, 1908) ripple-drift bedding, is an important and significant sedimentary structure resulting from the action of unidirectional currents. The importance of the structure lies in its worldwide distribution and frequent occurrence in such diverse sediments as river channel and levee sands and in turbidity current deposits. Its significance is that, of all sedimentary structure, it stands alone in giving information on short-term rates of sediment deposition (Sorby 1908; Kuenen 1967; Walker 1969; Allen 1970,, 1971,, 1972). Hence the study of this structure may lead to a deeper understanding of aspects of the character of past events—river floods and turbidity currents—of an intrinsically brief and catastrophic nature.

This goal will not however be achieved until the nature of climbing-ripple cross-lamination is clearly perceived and defined within the framework of an unambiguous field classification. The most widely used existing classification of the structure is now recognized to be confused, because some of the criteria adopted for the definition of its categories relate to the individual cross-laminated set (and the set with its immediate neighbours) perceived at some station in a coset, whereas others properly describe the coset of which the individual cross-laminated set is generally a very subordinate part. Set and coset are here used in the well-known sense of McKee & Weir (I953). The consequence is that aspects of the structure at the level of the set and its immediate neighbours are not sharply enough distinguished from aspects of the structure at the level of the

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