Northern Isles

The Northern Isles (Scots: Northern Isles; Old Norse: Norðreyjar; Norn: Nordøjar) are an archipelago located off the north coast of the Scottish mainland. The climate is cool and temperate and highly influenced by the surrounding seas. There are two main island groups: Shetland and Orkney. There are a total of 36 inhabited islands, with the fertile agricultural islands of Orkney contrasting with the more rugged Shetland islands to the north, where the economy is more dependent on fishing and the oil wealth of the surrounding seas. Both archipelagos have a developing renewable energy industry. They share a common Pictish and Norse history, and were part of the Kingdom of Norway before being absorbed into the Kingdom of Scotland in the 15th century. The islands played a significant naval role during the world wars of the 20th century.

Tourism is important to both archipelagos, with their distinctive prehistoric ruins playing a key part in their attraction, and there are regular ferry and air connections with mainland Scotland. The Scandinavian influence remains strong, especially in local folklore and both island chains have strong, though distinct local cultures. The names of the islands are dominated by the Norse heritage, although some may retain pre-Celtic elements.

The phrase "Northern Isles" generally refers to the main islands of the Orkney and Shetland archipelagos. The Island of Stroma, which lies between mainland Scotland and Orkney, is part of Caithness, so for local government purposes it falls under the jurisdiction of the Highland council area, rather than that of Orkney. It is nevertheless clearly one of the "northern isles" of Scotland. Fair Isle and Foula are outliers of Shetland, but would normally be considered part of Shetland, and thus of the Northern Isles. Similarly, Sule Skerry and Sule Stack, although distant from the main group, are part of Orkney, and therefore technically amongst the Northern Isles. However, the other small islands that lie off the north coast of Scotland are in Highland, and are thus not usually considered to be part of the Northern Isles.

Orkney has 20 inhabited islands and Shetland has 16.

Orkney is situated 16 kilometres (10 mi) north of the coast of mainland Scotland, separated from it by the waters of the Pentland Firth. The largest island of Orkney, known as the "Mainland" has an area of 523.25 square kilometres (202.03 sq mi), making it the sixth largest Scottish island. Its total population in 2001 was 19,245, and its largest town is Kirkwall. Shetland is around 170 kilometres (110 mi) north of mainland Scotland. It covers an area of 1,468 square kilometres (567 sq mi) and its coastline is 2,702 kilometres (1,679 mi) long. Lerwick, the capital and largest settlement, has a population of around 7,500. About half of the archipelago's total population of 22,000 people live within 16 kilometres (10 mi) of the town.

The superficial rock of Orkney is almost entirely Old Red Sandstone, mostly of Middle Devonian age. As in the neighbouring mainland county of Caithness, this sandstone rests upon the metamorphic rocks of the Moine series. This can be seen on the Orkney Mainland, where a narrow strip of the older rock is exposed between Stromness and Inganess, and also on the small island of Graemsay.

Middle Devonian basaltic volcanic rocks are found on western Hoy, on Deerness in eastern Mainland and on Shapinsay. A correlation between the Hoy volcanics and the other two exposures has been proposed, but because of differences in their chemical makeup, this remains uncertain. Lamprophyre dykes of Late Permian age are found throughout Orkney. Glacial striation and the presence of chalk and flint erratics that originated from the bed of the North Sea demonstrate the influence of ice action on the geomorphology of the islands. Boulder clay is also abundant, and moraines cover substantial areas.

The geology of Shetland is quite different from that of Orkney. It is extremely complex, with numerous faults and fold axes. The Shetland Islands are the northern outpost of the Caledonian orogeny, and there are outcrops of Lewisian, Dalriadan and Moine metamorphic rocks whose histories are similar to those of their counterparts on the Scottish mainland. There are also small Old Red Sandstone deposits and granite intrusions. Shetland's most distinctive geological feature is the ultrabasic ophiolite, peridotite and gabbro on Unst and Fetlar, which are remnants of the Iapetus Ocean floor. There are oil-bearing sediments in the surrounding seas, on which much of Shetland's economy depends.