DESCRIPTION: Ripple Marks are ridges of sediment that form in response to a fluid (water or wind) moving across a layer of sediment. They form generally perpendicular to fluid movement. Fluid movement can be in the form of waves, currents or wind. Ripple Marks that are symmetrical commonly indicate periodic water movement in opposite directions such as occurs in tidal areas (oscillation ripples). In areas of unidirectional currents, ripples are asymmetrical with the leeward slopes being steeper than the opposite slopes.