Firstly, in differential erosion alternating bands of hard and soft rock are eroded at different rates. For example, chalk is a soft rock and is eroded backwards to make bays e.g, Swanage bay.

On the other hand, basalt is a hard rock and is more resistant to erosion so erosional rates are slower. This makes headlands e.g. Peveril Point.

Secondly, headlands and bays are formed by wave refraction.
-As the waves approach the shores of the headland they begin to slow down and increase in height as they meet the shallow water.

The wave crests attempt to align themselves with the shore which causes them to bend – wave refraction.

In the bays, the waves move unimpeded so move ahead of the rest of the waves approaching the headland.