From work on two Upper Carboniferous formations in southwest England, three morphologically distinct types of ripple-drift cross-lamination have been recognised. Type 1 is characterised by strong erosion of laminae on the stoss (or up-current) side of the ripples, and absence of grading. Type 3 is characterised by an absence of erosion on the stoss sides, concentration of mud in the ripple troughs and an upward gradual decrease in grain size and amplitude of rippling. Type 2 is an intermediate form with some characteristics in common with types 1 and 3. An examination of the illustrated literature has shown that types 1 and 3 occur frequently, and that type 2 has not pre- viously been recorded.
It is suggested that type 1 is formed in fluvial and shallow water environments at times of net deposition of sediment, and that type 3 is formed by deposition from a tur- bidity current. Type 2 suggests hydrodynamic conditions intermediate between fluvial or shallow water traction currents, and turbidity currents.
Since all current ripples move forwards, or “drift”, it is suggested that the term “ripple-drift” should be used to describe ripple cross-lamination where the ripples can be seen to climb onto the stoss slope of the ripple immediately downstream, there having been a net deposition, and not merely a forward drift of sediment.