Purbeck Monocline

The term 'fold' is used in geology when one or more originally flat sedimentary strata surfaces are bent or curved as a result of plastic (i.e. permanent) deformation.

The Purbeck Monocline was formed during the late Oligocene and early Miocene epochs, about 30 million years ago.

This chalk band runs from Swyre Head via Flower's Barrow to Old Harry Rocks.

From here the fold continues under the sea to The Needles and forms the central spine of the Isle of Wight.

These features also include the polygonal thrust ridges developed in the harder rock bands at Kimmeridge Bay and related to the growth of the monocline is the fault at Ballard Down.