Orkney Islands

The Orkney Islands are one of 32 unitary council regions in Scotland, and form a traditional county and Lieutenancy area. Orkney consists of about 70 small islands 16 km north of Caithness in northern Scotland. The largest island in the group is known as "The Mainland"; about 20 are inhabited in total.

Geology

All the islands of this group are built up entirely of Old Red Sandstone. As in the neighbouring mainland county of Caithness, these rocks rest upon the metamorphic rocks of the eastern schists, as may be seen on The Mainland, where a narrow strip is exposed between Stromness and Inganess, and again in the small island of Graemsay; they are represented by grey gneiss and granite.

Related Topics:
Sandstone - Caithness - Metamorphic - Schist - Gneiss - Granite

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The upper division of the Old Red Sandstone is found only on Hoy, where it forms the Old Man of Hoy and neighbouring cliffs on the northwest coast. The Old Man of Hoy presents a characteristic section, for it exhibits a thick pile of massive, current-bedded red sandstones, resting, near the foot of the pinnacle, upon a thin bed of amygdaloidal porphyrite, which in its turn lies uncomfortably upon steeply inclined flagstones. This bed of volcanic rock may be followed northward in the cliffs, and it may be noticed that it thickens considerably in that direction.

Related Topics:
Old Man of Hoy - Sandstone - Porphyrite - Volcanic

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The Lower Old Red Sandstone is represented by well-bedded flagstones over most of the islands; in the south of The Mainland these are faulted against an overlying series of massive red sandstones, but a gradual passage from the flagstones to the sandstones may be followed from Westray southeastwards into Eday. A strong synclinal fold traverses Eday and Shapinsay, the axis being North and South. Near Haco's Ness in Shapinsay there is a small exposure of amygdaloidal diabase, which is (of course) older than that on Hoy.

Related Topics:
Sandstone - Diabase

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Many indications of ice action are found on these islands; striated surfaces are to be seen on the cliffs in Eday and Westray, in Kirkwall Bay and on Stennie Hill in Eday; boulder clay, with marine shells, and with many boulders of rocks foreign to the islands (chalk, oolitic limestone, flint, etc), which must have been brought up from the region of Moray Firth, rests upon the old strata in many places. Local moraines are found in some of the valleys in The Mainland and Hoy.

Related Topics:
Clay - Chalk - Flint - Moraine

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