ABSTRACTThe majority of the linear sand banks in the Norfolk Banks area of the southern North Sea are considered to be large‐scale mobile bed forms in dynamic equilibrium with the environment, thus confirming much of the earlier work of Houbolt(1968). Sand streams moving in opposing directions on either side of a bank are shown to be deflected to the right, upslope, and converge at the crestline, whilst the asymmetry of a bank is considered to be a reflection of the dominance of one of these streams. Convergence of sand streams causes an accumulation of sand which is believed to result in the continuing growth of the bank parallel to the direction of flow of the tidal currents. Migration of asymmetric banks is in the direction of the steeper side; the predominant direction is to the northeast, but it is suggested that the opposing movement of sand streams may magnify localized irregularities into a complex “S” shaped bank surrounding a pair of ebb and flood channels. The apices of this bank may eventually disappear, leaving a line of en echelon banks. Confirmatory evidence is forthcoming from a study of a linear sand bank lying off the Belgian coast, and it is suggested that the general sequence of bank development may be of far wider applic