A discordant coastline occurs where bands of different

rock Rock most often refers to: * Rock (geology), a naturally occurring solid aggregate of minerals or mineraloids * Rock music, a genre of popular music Rock or Rocks may also refer to: Places United Kingdom * Rock, Caerphilly, a location in Wales ...

types run

perpendicular In elementary geometry, two geometric objects are perpendicular if they intersect at a right angle (90 degrees or π/2 radians). The condition of perpendicularity may be represented graphically using the ''perpendicular symbol'', ⟂. It ca ...

to the

coast The coast, also known as the coastline or seashore, is defined as the area where land meets the ocean, or as a line that forms the boundary between the land and the coastline. The Earth has around of coastline. Coasts are important zones in ...

. The differing resistance to erosion leads to the formation of headlands and bays. A hard rock type such as

granite Granite () is a coarse-grained ( phaneritic) intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly cools and solidifies under ...

is resistant to erosion and creates a promontory whilst a softer rock type such as the

clay Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4). Clays develop plasticity when wet, due to a molecular film of water surrounding the clay par ...

s of

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 Bags ...

is easily eroded creating a bay. Part of the

Dorset Dorset ( ; archaically: Dorsetshire , ) is a county in South West England on the English Channel coast. The ceremonial county comprises the unitary authority areas of Bournemouth, Christchurch and Poole and Dorset. Covering an area of , ...

coastline running north from the

Portland limestone Portland stone is a limestone from the Tithonian stage of the Jurassic period quarried on the Isle of Portland, Dorset. The quarries are cut in beds of white-grey limestone separated by chert beds. It has been used extensively as a building sto ...

Durlston Head Durlston Bay (also known as Durdlestone Bay) is a small bay next to a country park of the same name, just south of the resort of Swanage, on the Isle of Purbeck in Dorset, England. It has been a renowned site for Lower Cretaceous fossils since th ...

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 Greensand or green sand is 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 co ...

. North of Swanage, the

chalk Chalk is a soft, white, porous, sedimentary carbonate rock. It is a form of limestone composed of the mineral calcite and originally formed deep under the sea by the compression of microscopic plankton that had settled to the sea floor. Ch ...

outcrop creates the headland which includes

Old Harry Rocks Old Harry Rocks are three chalk formations, including a Stack (geology), stack and a stump, located at Handfast Point, on the Isle of Purbeck in Dorset, southern England. They mark the most eastern point of the Jurassic Coast, a UNESCO World H ...

. The converse of a discordant coastline is a

concordant coastline In coastal geography, 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 (for example, granite) provides a prote ...

Examples

*The coastline around

Durlston Bay Durlston Bay (also known as Durdlestone Bay) is a small bay next to a country park of the same name, just south of the resort of Swanage, on the Isle of Purbeck in Dorset, England. It has been a renowned site for Lower Cretaceous fossils since the ...

() is an example of a discordant coastline.

Examples

See also