Discordant coastline

A discordant coastline occurs where bands of different rock types run perpendicular to the coast.

Durlston Head (limestone) to Handfast Point (chalk), with Peveril Point (limestone) dividing Durlston Bay from Swanage Bay

The differing resistance to erosion leads to the formation of headlands and bays. A hard rock type such as granite is resistant to erosion and creates a promontory whilst a softer rock type such as the clays of Bagshot Beds is easily eroded creating a bay.

Part of the Dorset coastline running north from the Portland limestone of Durlston Head is a clear example of a discordant coastline. The Portland limestone is resistant to erosion; then to the north there is a bay at Swanage where the rock type is a softer greensand. North of Swanage, the chalk outcrop creates the headland which includes Old Harry Rocks.

The converse of a discordant coastline is a concordant coastline.

Examples

• The coastline around Durlston Bay (50°36′24″N 1°57′54″W) is an example of a discordant coastline.

See also

• Concordant coastline