The Eday Group is a

Devonian The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, wh ...

lithostratigraphic Lithostratigraphy is a sub-discipline of stratigraphy, the geological science associated with the study of strata or rock layers. Major focuses include geochronology, comparative geology, and petrology. In general, strata are primarily igneou ...

group A group is a number of persons or things that are located, gathered, or classed together. Groups of people * Cultural group, a group whose members share the same cultural identity * Ethnic group, a group whose members share the same ethnic ide ...

(a sequence of

rock strata In geology and related fields, a stratum ( : strata) is a layer of rock or sediment characterized by certain lithologic properties or attributes that distinguish it from adjacent layers from which it is separated by visible surfaces known as e ...

) in

Orkney Orkney (; sco, Orkney; on, Orkneyjar; nrn, Orknøjar), also known as the Orkney Islands, is an archipelago in the Northern Isles of Scotland, situated off the north coast of the island of Great Britain. Orkney is 10 miles (16 km) north ...

, northern

Scotland Scotland (, ) is a country that is part of the United Kingdom. Covering the northern third of the island of Great Britain, mainland Scotland has a border with England to the southeast and is otherwise surrounded by the Atlantic Ocean to ...

. The name is derived from the island of Eday where the

strata In geology and related fields, a stratum ( : strata) is a layer of rock or sediment characterized by certain lithologic properties or attributes that distinguish it from adjacent layers from which it is separated by visible surfaces known as e ...

are exposed in coastal cliffs.

Outcrops

These rocks are exposed throughout Orkney, notably in coastal cliffs of Eday and western Sanday,

South Ronaldsay South Ronaldsay (, also , sco, Sooth Ronalshee) is one of the Orkney Islands off the north coast of Scotland. It is linked to the Orkney Mainland by the Churchill Barriers, running via Burray, Glimps Holm and Lamb Holm. Name Along with No ...

and the Deerness peninsula of

Mainland Mainland is defined as "relating to or forming the main part of a country or continent, not including the islands around it egardless of status under territorial jurisdiction by an entity" The term is often politically, economically and/or dem ...

. There are spectacular exposures of the Hoy Sandstone Formation and particularly the Trowie Glen Sandstone Member in the precipitous cliffs of Hoy's west coast.

Lithology and stratigraphy

The Group comprises the Upper Eday Sandstone Formation, Eday Marl Formation, Middle Eday Sandstone Formation, Eday Flagstone Formation, Lower Eday Sandstone Formation and the Hoy Sandstone Formation laid down in the shallow

Orcadian Basin The Orcadian Basin is a sedimentary basin of Devonian age that formed mainly as a result of extensional tectonics in northeastern Scotland after the end of the Caledonian orogeny. During part of its history, the basin was filled by a lake now known ...

during the

Givetian The Givetian is one of two faunal stages in the Middle Devonian Period. It lasted from million years ago to million years ago. It was preceded by the Eifelian Stage and followed by the Frasnian The Frasnian is one of two faunal stages in the ...

stage of the Devonian period. The sediments vary from fluvial to lacustrine to lagoonal. On the island of

Hoy Hoy ( sco, Hoy; from Norse , meaning "high island") is an island in Orkney, Scotland, measuring – the second largest in the archipelago, after Mainland. A natural causeway, ''the Ayre'', links the island to the smaller South Walls; the two ...

, the Hoy Sandstone is a particularly thick formation at whose base is the Hoy Volcanic member.British Geological Survey 1:100,000 scale geological map (Scotland) ''Orkney Islands'' (special sheet)

References

{{Reflist Geological groups of the United Kingdom Geologic formations of Scotland Devonian System of Europe Devonian Scotland Givetian Stage

Outcrops

Lithology and stratigraphy

See also

References