The coastline will be made of bands of hard and soft rock to begin with. As the waves erode the coastline, the soft rock will be eroded quicker. This results in the areas of softer rock to retreat, forming bays, whilst the hard rock is eroded slower so will form headlands. Over time, deposition will occur in the bays and so forming beaches. This is because the majority of energy is directed onto the headlands as they now stick out, causing reduced energy to reach the bay areas - resulting in deposition.