A shore zone may be subject to the same range of physical and chemical weathering processes that occur on land, but the presence of seawater and the cycle of wetting and drying produced by tides introduces additional significant factors. The tidal cycle of wetting and drying is instrumental in a variety of weathering processes. The zone affected extends from low water mark to the furthest limit reached by waves and spray at high tide. Its areal extent is therefore controlled largely by tidal range, but tidal type and meteorological factors are also important because these affect, respectively, the time available for drying between tides and the rate of evaporation. The most aggressive regime for shoreline weathering probably occurs along coasts characterized by high evaporation rates and mixed or diurnal tides (Summerfield 1991).