Eday Group

The Eday Group is a Devonian lithostratigraphic group (a sequence of rock strata) in Orkney, northern Scotland. The name is derived from the island of Eday where the strata are exposed in coastal cliffs.

Eday Group
Stratigraphic range: Givetian (Devonian)
Red Head at the north end of Eday. The lower and steeper part of the cliff is formed of Middle Eday Sandstone, whereas the upper less steep part is formed of Eday Marl
Type	Group
Unit of	Old Red Sandstone Supergroup
Sub-units	Upper Eday Sandstone Formation, Eday Marl Formation, Middle Eday Sandstone Formation, Eday Flagstone Formation, Lower Eday Sandstone Formation, Hoy Sandstone Formation
Underlies	not overlain
Overlies	Caithness Flagstone Group
Thickness	over 2000 m
Lithology
Primary	sandstone
Other	mudstone, siltstone, lava
Location
Region	Orkney
Country	Scotland
Extent	Orkney Islands
Type section
Named for	Eday

Outcrops

These rocks are exposed throughout Orkney, notably in coastal cliffs of Eday and western Sanday, South Ronaldsay and the Deerness peninsula of Mainland. 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 during the Givetian stage of the Devonian period. The sediments vary from fluvial to lacustrine to lagoonal. On the island of Hoy, the Hoy Sandstone is a particularly thick formation at whose base is the Hoy Volcanic member.

See also

• List of fossiliferous stratigraphic units in Scotland