It has to be remembered that at the end of the last Ice Age, this region was on the edge of the Solent river valley and several miles from the sea. As sea levels rose and the chalk hills stretching from Purbeck to the Needles were eroded, the sea finally broke through and flooded the estuarine system.
Ian West site for geology and much more
The cliffs of Hordle and Barton have been famous for their fossils since the 18th century. Barton-on-Sea is the type-site for the Bartonian formation of the upper Eocene period and covers the period from about 44M to 37M BP. It was a marine environment, believed to be similar to that in southeast Asia today. In later stages it became more estuarine as the sea silted up leaving marshes and lagoons. Remains of 2 genera of whale, Prozeuglodon and Basilosaurus,have been found here. In the last century, Hordle cliffs became known as 'Crocodile valley' due to the large number of reptilian remains obtained from there. The nine kilometre stretch of cliff between Friar's Cliff, Highcliffe and Paddy's Gap, Milford is an SSSI for its fresh exposures of the Barton and Headon beds as well as their capping of Plateau gravels.
Museums -Gosport : St Barbe Museum Natural history museum