Subdivisions
The Chalk Group is now divided into a White Chalk Subgroup and a Grey Chalk Subgroup, both of which are further subdivided into formations. These modern divisions replace numerous earlier divisions, references to which occur widely on geological maps and in other geological literature. Previously no subgroups were defined but three formations were identified; the Upper Chalk, Middle Chalk and Lower Chalk. Different formations are defined within the 'northern' and 'southern' provinces, from Norfolk northwards and south of the Thames valley respectively. A 'transitional province' between the two and covering much of East Anglia and the Chiltern Hills is also recognised. A different approach again is taken as regards the succession beneath the North Sea.
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