Cross-stratification or cross-bedding are sedimentary structures that form as ripples and dunes are deposited and eventually migrate. The movement of dunes causes the foreset laminae to dip and the mobile grains accumulate on the lee side of the bedform. The inclined foreset laminae makes contact with the horizontal bottomset laminae around the angle of repose. This process is responsible for the crossing appearance of sedimentary layers. Cross beds are distinguished from each other by the shape of their bounding surfaces. When the bounding surfaces appear to be planar, the bed is a tabular cross-bed. If the bounding surfaces appear to be curved, it is called a trough cross bed. This image is an example of tabular cross-bedding. Cross bedding is one of the most commonly preserved sedimentary structures found in ancient rocks. This type of structure is formed in a flowing medium and either a fluvial, eolian or marine environment.