<P> The chalk of Old Harry Rocks used to be part of a long stretch of chalk between Purbeck and the Isle of Wight , but remained as a headland after large parts of this seam were eroded away . As the headland suffered hydraulic action ( a process in which air and water are forced into small cracks by the force of the sea , resulting in enlarging cracks ) , first caves , then arches formed . The tops of the arches collapsed after being weakened by rainfall and wind , leaving disconnected stacks . One of these stacks is known as Old Harry . Old Harry 's Wife was another stack which was eroded through corrosion and abrasion , until the bottom was so weak the top fell away , leaving a stump . Hydraulic action is the main cause of erosion ( sheer force of the wave ) that damaged the rock and caused it to fall away . </P>
<P> The chalk of Old Harry Rocks used to be part of a long stretch of chalk between Purbeck and the Isle of Wight , but remained as a headland after large parts of this seam were eroded away . As the headland suffered hydraulic action ( a process in which air and water are forced into small cracks by the force of the sea , resulting in enlarging cracks ) , first caves , then arches formed . The tops of the arches collapsed after being weakened by rainfall and wind , leaving disconnected stacks . One of these stacks is known as Old Harry . Old Harry 's Wife was another stack which was eroded through corrosion and abrasion , until the bottom was so weak the top fell away , leaving a stump . Hydraulic action is the main cause of erosion ( sheer force of the wave ) that damaged the rock and caused it to fall away . </P>
what type of rock is old harry made from
what type of rock is old harry made from
chalk
chalk