Chalk comprises of a sequence of mainly soft, white, very fine-grained extremely pure limestones which are commonly 300-400 m thick. These rocks consist mainly of the remains of skeletal bits of planktonic green algae, associated with varing proportions of larger microscopic fragments of bivalves, foraminifera and ostracods.
Flints are a well known component of Chalk and they are present as nodular seams, tabular beds ann linings to fractures. The silica was derived from the dissolution of the siliceous skeletons of sponges and other organisms and has been redistributed in the form of nodules during several stages of crystallisation.
Both the English and French shores are mainly formed by chalk cliffs i.e. 'White Cliffs of Dover'. This is perhaps THE classic location of chalk.
Flamborough Head on the east Yorkshire coast.
Cliffs of Dover, Kent.