Limestone Pavement, bare limestone rock surfaces composed of slabs of rock (clints), separated by variable-width vertical cracks (grikes) that have developed by weathering and enhanced solution along joints. Composed principally of calcite, limestone is vulnerable to chemical weathering by water (solution) and dissolves easily (see Limestone Features). The outer parts of the pavements, which have been exposed longest to the atmosphere, often have quite sharp and fretted surface-weathering features. At the back of the pavements where they emerge from the soil the clints are generally smaller and have a much more rounded and smooth appearance. In some areas, for example, in the northern Pennines of England, exposure of very extensive pavements may be partly an example of the stripping of soil by moving ice during the last glaciation period. In other areas they may be exposed by the washing of soil down joints or by wind erosion.
Where the surface of the clint is relatively level it often displays small solution features related to either flowing or standing water. Features that look like river channels are known as solution runnels (or rinnenkarren) and can be up to 0.5 m (1.5 ft) across, of similar depth, and in excess of 10 m (33 ft) long. Where they develop under the soil they are of similar dimensions but much more rounded and are known as rundkarren. Standing water on flat limestone surfaces can produce small, almost circular depressions that are known as solution pans. Limestone pavements are common on the carboniferous limestone areas throughout the Arnside / Silverdale AONB, the northern Pennines of England, the Burren in the Republic of Ireland, the Causses of France, and the Karst Plateau of the former Yugoslavia.