Geological Conservation Review
There are sixteen GCR sites in Orkney; the following twelve GCRs are also designated as Sites of Special Scientific Interest (SSSI):
- Bay of Skaill.
- Central Sanday.
- Cruaday Quarry.
- Ward Hill, Enegar’s Corrie and Dwarfie Hamars (Hoy SSSI).
- Old Man of Hoy Coast (Hoy SSSI).
- Too of the Head (Hoy SSSI).
- Mill Bay.
- West Coast of Orkney (Stromness Heaths & Coast SSSI).
- Yesnaby & Gaulton Coast Section (Stromness Heaths & Coast SSSI).
- South Stromness Coast Section (Stromness Heaths & Coast SSSI)
- Muckle Head and Selwick.
Information on the qualifying features of these SSSIs/GCRs is available under the Related Sites section; the GCRs which haven’t been designated as SSSIs are included as Local Nature Conservation Sites, which can be found in Annexe 1 of the Natural Heritage Planning Policy Advice, available under Related Links.
The remaining four GCR sites are located at:
Greenan Nev Coast
A section through the Eday Marls can be clearly seen on the western coast of Eday at Greenan Nev, where over 100m of bright red and pale green siltstones are exposed in the shore platform and low fringing cliffs. To the south the marls pass down into the Middle Eday Sandstones, to the north they give way to the Upper Eday Sandstone. These sediments were formed from fine grained material and dissolved salts which were deposited as overbank material and in floodplain lakes.
Precipitation of calcium carbonate led to the formation of harder, more resistant siltstone bands, while periods of intermittent exposure to the air produced sun cracks up to 150mm deep. Burrowing organisms which became established in the muds during periods of flood produced parallel-sided straight burrows of up to 500mm long.
South Fersness Bay
The southern shores of Fersness Bay provide an excellent section through the western limb of one of the major structural units of Orkney - the Eday Syncline - whose axis trends north-south through the Sands of Mussetter, a short distance to the east. The cliffed coastline includes good exposures of the Rousay Beds, Lower Eday Sandstones, Eday Flags and Middle Eday Sandstones in their type area.
At the south end of a large disused quarry, previously worked for building stone, a vertical face exhibits over 25m of sandstone and shows large-scale planar cross-bedding.
Point of Ayre
The Deerness Peninsula lies over a gentle, symmetrical north-south trending syncline whose limbs expose Rousay Flags, Lower Eday Sandstones, Eday Flags and Middle Eday Sandstones with intrusive and contemporaneous igneous rocks. Exposures can be seen in an extensive rock platform which skirts the south-eastern corner of the peninsula, as well as in the cliffs to the north of the Point of Ayre.
At Point of Ayre a 7m thick outcrop of basaltic lava is visible; in its top portion many of the gas bubbles in the volcanic lava have become infilled by carbonate minerals, while its lower part shows well-developed spheroidal weathering creating rounded rocks. This is an unusual feature in Orkney.
Taracliff Bay to Newark Bay
The cliffed coast between Taracliff Bay and Newark Bay exposes a fairly continuous, eastwardly dipping succession of strata showing the transition from the Rousay Beds to Passage beds and Lower Eday Sandstones and including the most extensive section through the Eday Flags in Orkney. The major part of the Middle Eday Sandstones is also exposed. Near the Muckle Castle the junction of the Sandstones with the Eday Flags is faulted and obscured by a volcanic intrusion of olivine dolerite.