The northern part is Eocene clay (Barton beds), but where the land rises to the sea there are several parallel strata of Jurassic rocks, including Portland limestone and the Purbeck beds.
The northern part is Eocene clay (Barton beds), including significant deposits of Purbeck Ball Clay. Where the land rises to the sea there are several parallel strata of Jurassic rocks, including Portland limestone and the Purbeck beds.