AbstractThe secondary flow and transverse changes of water depth in curved stream channels are exploited to develop a quantitative, partly empirical model of the way lithology varies vertically in deposits accumulated through processes of lateral deposition. According to the model, grain size decreases upward in a lateral deposit and the sedimentary structures change from those denoting large stream powers upward to kinds indicative of small powers. The model also shows that the proportion of flat‐bedded sand‐grade material in a lateral deposit is essentially independent of stream power but controlled by channel curvature and hence general sinuosity. The predictions of the model compare satisfactorily with the characteristics of selected coarse members in fining‐upwards cycles of fluviatile origin from Devonian strata in Britain and North America. The model is thought to have value as a tool for environmental interpreta