1.1.4

• lithology is the hardness permeability and chemical composition
• Hardness 

  As a result of heating and compression during their formation, igneous rocks (e.g. granite) and metamorphic rocks (e.g. gneiss) are harder and therefore more resistant to erosion. 

  These types of rock form many high cliffs in northwest Britain. 

  In contrast, many of the rocks that form the coastlines of southern and eastern Britain are 'soft rocks' – unconsolidated sand and clays of Tertiary age, as well as deposits of glacial boulder clay and gravels.
• Permeability 

  A further lithological factor is permeability, resulting from, for example, pores in an open-textured limestone or fissures and cracks or joints (e.g. in chalk or limestone). 

  As surface water seeps through the cliffs, it increases the rock's resistance to subaerial processes, thereby adding strength to relatively soft rocks. 

  This explains why chalk invariably forms high, near-vertical cliffs (such as at Beachy Head, Sussex, or the White Cliffs of Dover, Kent) and supports natural arches and stacks.
• Chemical composition 

  Chemical composition includes mineral composition and solubility. Sandstones, are made almost completely from silica, which is chemically inert. The very low rate of chemical weathering adds resistance to the rock. 

  Other rocks are more prone to rapid chemical weathering. Iron compounds oxidise in some sandstones.

  The chemical decomposition of limestones by carbonation (solution) happens even more rapidly. It is caused by saltwater corrosion, leading to accelerated disintegration.
• strata is layers of rock
• bedding planes is horizontal cracks. these are natural breaks in the strata caused by gaps in time during periods of rock formation
• joints are vertical cracks. these are fractures caused either by contraction as sediment dries out or by earth movements during uplift
• folds are formed by pressure during tectonic activity which makes rocks buckle and crumple such as lulworth crumple
• faults are formed when the stress or pressure to which a rock is subjected exceeding its internal strength causing it to fracture. the fault then slips or moves along fault planes
• dip refers to the angle at which rock strata lie horizontally, vertically, dipping towards the sea or dipping inland