As the General Preface accompanying Volume I contains an introduction to the work as a whole, it is only necessary for me here to outline the scope of the second volume. Volume I1 is about sedimentary structures found in relatively complex physical settings, where groupings or hierarchies of features are often of most interest, and more emphasis is placed than in the first volume on cohesive as opposed to cohesionless beds. Secondary currents can exist for a number of reasons in boundary-layer flows, giving rise to flow-parallel sedimentary structures on both kinds of bed. A type of secondary flow arises where river or tidal streams occupy curved channels, with the result that definite vertical and horizontal sequences of sedimentary structures are formed.