Chalk quarrying
Chalk is a soft, white, porous form of limestone composed of the mineral calcium carbonate. It is relatively resistant to erosion and slumping compared to the clays that it is usually associated with, and so forms tall steep cliffs where chalk ridges meet the sea. Chalk hills, known as chalk downland, usually form where bands of chalk reach the surface at an angle.
Chalk is formed in shallow waters by the gradual accumulation of the calcite mineral remains of micro-organisms over millions of years. Embedded flint nodules are commonly found in chalk beds.
Because chalk quarrying is porous, chalk downland usually holds a large water table providing a natural reservoir that releases water slowly through dry seasons.
Chalk has been quarried from prehistory, providing building material and marl for fields. In southeast England, deneholes are a notable example of ancient chalk pits.
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