A discordant coastline occurs where bands of differing rock

Rock (geology)

In geology, rock or stone is a naturally occurring solid aggregate of minerals and/or mineraloids.The Earth's outer solid layer, the lithosphere, is made of rock. In general rocks are of three types, namely, igneous, sedimentary, and metamorphic...

 type run perpendicular

Perpendicular

In geometry, two lines or planes are considered perpendicular to each other if they form congruent adjacent angles . The term may be used as a noun or adjective...

 to the coast

Coast

A coastline or seashore is the area where land meets the sea or ocean. A precise line that can be called a coastline cannot be determined due to the dynamic nature of tides. The term "coastal zone" can be used instead, which is a spatial zone where interaction of the sea and land processes occurs...

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The differing resistance to erosion leads to the formation of headlands and bays

Headlands and bays

Headlands and bays are two related features of the coastal environment.- Geology and geography :Headlands and bays are often found on the same coastline. A bay is surrounded by land on three sides, whereas a headland is surrounded by water on three sides. Headlands are characterized by high,...

. A hard rock type such as granite

Granite

Granite is a common and widely occurring type of intrusive, felsic, igneous rock. Granite usually has a medium- to coarse-grained texture. Occasionally some individual crystals are larger than the groundmass, in which case the texture is known as porphyritic. A granitic rock with a porphyritic...

 is resistant to erosion and creates a promontory

Promontory

Promontory may refer to:*Promontory, a prominent mass of land which overlooks lower lying land or a body of water*Promontory, Utah, the location where the United States first Transcontinental Railroad was completed...

 whilst a softer rock type such as the clay

Clay

Clay is a general term including many combinations of one or more clay minerals with traces of metal oxides and organic matter. Geologic clay deposits are mostly composed of phyllosilicate minerals containing variable amounts of water trapped in the mineral structure.- Formation :Clay minerals...

s of Bagshot Beds

Bagshot Beds

In geology, the Bagshot Beds are a series of sands and clays of shallow-water origin, some being fresh-water, some marine. They belong to the upper Eocene formation of the London and Hampshire basins, in England and derive their name from Bagshot Heath in Surrey. They are also well developed in...

 is easily eroded creating a bay.

Part of the Dorset

Dorset

Dorset , is a county in South West England on the English Channel coast. The county town is Dorchester which is situated in the south. The Hampshire towns of Bournemouth and Christchurch joined the county with the reorganisation of local government in 1974...

 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

Swanage

Swanage is a coastal town and civil parish in the south east of Dorset, England. It is situated at the eastern end of the Isle of Purbeck, approximately 10 km south of Poole and 40 km east of Dorchester. The parish has a population of 10,124 . Nearby are Ballard Down and Old Harry Rocks,...

 where the rock type is a softer greensand

Greensand

Greensand or Green sand is either a sand or sandstone, which has a greenish color. This term is specifically applied to shallow marine sediment, that contains noticeable quantities of rounded greenish grains. These grains are called glauconies and consist of a mixture of mixed-layer clay...

. North of Swanage

Swanage

Swanage is a coastal town and civil parish in the south east of Dorset, England. It is situated at the eastern end of the Isle of Purbeck, approximately 10 km south of Poole and 40 km east of Dorchester. The parish has a population of 10,124 . Nearby are Ballard Down and Old Harry Rocks,...

, the chalk

Chalk

Chalk is a soft, white, porous sedimentary rock, a form of limestone composed of the mineral calcite. Calcite is calcium carbonate or CaCO3. It forms under reasonably deep marine conditions from the gradual accumulation of minute calcite plates shed from micro-organisms called coccolithophores....

 outcrop creates the headland which includes Old Harry Rocks

Old Harry Rocks

The Old Harry Rocks are two chalk sea stacks located at Handfast Point, on the Isle of Purbeck in Dorset, southern England.- Location :Old Harry Rocks lie directly east of Studland, about 4 kilometres northeast of Swanage, and about 10 kilometres south of the large towns of Poole and...

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The converse of a discordant coastline is a concordant coastline

Concordant coastline

A concordant, longitudinal, or Pacific type coastline occurs where beds, or layers, of differing rock types are folded into ridges that run parallel to the coast. The outer hard rock provides a protective barrier to erosion of the softer rocks further inland...

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Examples

• The coastline around Swanage
  Swanage
  Swanage is a coastal town and civil parish in the south east of Dorset, England. It is situated at the eastern end of the Isle of Purbeck, approximately 10 km south of Poole and 40 km east of Dorchester. The parish has a population of 10,124 . Nearby are Ballard Down and Old Harry Rocks,...
  
  (50°36′24"N 1°57′54"W) is an example of a discordant coastline.