Cross-bedding is a series of thin, inclined parallel or near parallel layers in a larger body of rock which form a distinct angle to the principal horizontal bedding plane. Cross-bedding is found mainly in sandstones but also in some limestones and conglomerates. It occurs where sediment is being moved as it is being deposited, building sand dunes, sand waves, or ripples. It is useful for interpreting ancient environments as the direction and strength of former currents can be determined from the pattern and type of structure.