Hence, cross-beds may be used as paleocurrent indicators, or indicators of ancient current flow directions. Cross-beds usually curve at the bottom edge, becoming tangent to the lower bed surface. The upper edge of individual inclined cross-beds is usually at a steep angle to the overlying bedding plane. These are features which form on the surface of a bed of sediment. In a sequence of sedimentary rock, bed forms and surface markings are found on bedding planes.
Ripples are undulations of the sediment surface produced as wind or water moves across sand.
Crests of asymmetrical ripples may be straight, sinuous, or lobe-like, depending on water velocity. Asymmetrical ripples have a steep slope on the downstream side, and a gentle slope on the upstream side. Because of this unique geometry, asymmetrical ripples in the rock record may be used to determine ancient current directions or paleocurrent directions. In waves or oscillating water , symmetrical ripples are produced. These ripples are produced by the interaction of waves and currents in the ridge and runnel system at the beach.