Geology
The area of Poole Bay was predominantly created during the Pleistocene period, when the Solent river ran across the whole of South East Dorset and West Hampshire, out past the Isle of Wight The solid geology of the cliffs, and the seabed beneath Poole Bay, is composed of rocks of the Tertiary Bracklesham Group, consisting of a sequence of fine, medium and coarse sands. At Hengistbury Head there are younger rocks of the Bartonian group, forming an outlier . The Barton Clay here is made up of a series of sands and interbedded clays, with four distinct bands of ironstone nodules. These formations dip eastwards and are cut out by a north-west to south-east trending fault. This defines the eastwards boundary of Christchurch Ledge, which is a seawards continuation of the resistant ironstone strata exposed in Hengistbury Head.
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