The bands of soft rock, such as sand and clay, erode more quickly than those of more resistant rock, such as chalk. This leaves a section of land jutting out into the sea called a headland. The areas where the soft rock has eroded away, next to the headland, are called bays. Sandy beaches are often found the sheltered bays where waves lose energy, and their capacity to transport material decreases resulting in material being deposited.
A discordant coastline and the landforms created as the result of different rates of erosion
The image below shows Selwicks Bay at Flamborough.
Selwicks Bay, Flamborough
Where the geology alternates between strata (bands) of soft and hard rock are called discordant coastlines. A concordant coastline is where the same rock runs along the length of the coast. Concordant coastlines tend to have fewer bays and headlands.
Along the coastline of Dorset, there are concordant and discordant coastlines. The concordant coastline runs from west to east along the south coast. The discordant coastline runs from Studland Bay to Durlston Head as the geology changes from clay and sands, to chalk, to clay and sands again to limestone.
Discordant and concordant coasts in Dorset