Isle of Arran - Geography and Geology

Geography and Geology

The island lies in the Firth of Clyde between Ayr and Kintyre. The profile of the north Arran hills as seen from the Ayrshire coast is a well-known sight referred to as the "Sleeping Warrior" due to its resemblance to a resting human figure. The highest of these hills is Goat Fell at 873.5 metres (2,866 ft). There are three other Corbetts, all in the north east: Caisteal Abhail, Cìr Mhòr and Beinn Tarsuinn. Beinn Bharrain is the highest peak in the north west at 721 metres (2,365 ft).

The largest valley on the island is Glen Iorsa to the west, whilst narrow Glen Sannox (Gaelic: Gleann Shannaig) and Glen Rosa (Gaelic: Gleann Ròsa) to the east surround Goat Fell. The terrain to the south is less mountainous, although a considerable portion of the interior lies above 350 metres (1,150 ft), and A' Chruach reaches 512 metres (1,680 ft) at its summit. There are two other Marilyns in the south, Tighvein and Beinn Bhreac.

Arran is sometimes referred to as "Scotland in miniature", as it is divided into "Highland" and "Lowland" areas by the Highland Boundary Fault which runs northeast to southwest across Scotland. Arran is a popular destination for geologists, who come to see intrusive igneous landforms such as sills and dykes as well as sedimentary and metasedimentary rocks ranging in age from Precambrian to Mesozoic.

Most of the interior of the northern half of the island is taken up by a large granite batholith that was created by substantial volcanic activity around 60 million years ago in the Paleogene period. There is an older outer ring of coarse granites and an inner core of finer grained material. Sedimentary rocks dominate the southern half of the island, especially Old and New Red Sandstone. Some of these sandstones contain fulgurites - pitted marks that may have been created by Permian lightning strikes. Sand dunes are preserved in Permian sandstones near Brodick, there are localised outcrops of Triassic rocks and even a rare example of Cretaceous chalk. During the 19th century barytes was mined near Sannox. First discovered in 1840, nearly 5,000 tons were produced between 1853 and 1862. The mine was closed by the 11th Duke of Hamilton on the grounds that it "spoiled the solemn grandeur of the scene" but was reopened after the First World War and operated until 1938 when the vein ran out.

Visiting in 1787, the geologist James Hutton found his first example of an unconformity to the north of Newton Point near Lochranza, which provided evidence for his Plutonist theories of uniformitarianism and about the age of the Earth. This spot is one of the most famous places in the study of geology.

The Pleistocene glaciations almost entirely covered Scotland in ice, and Arran's highest peaks may have been nunataks at this time. After the last retreat of the ice at the close of the Pleistocene epoch sea levels were up to 70 metres (230 ft) lower than at present and it is likely that circa 14,000 BP the island was connected to mainland Scotland. Sea level changes and the isostatic rise of land makes charting post-glacial coastlines a complex task, but it is evident that the island is ringed by post glacial raised beaches. King's Cave on the south west coast is an example of an emergent landform on such a raised beach. This cave, which is over 30.5 metres (100 ft) long and up to 15.3 metres (50 ft) high, lies well above the present day sea level. There are tall sea cliffs to the north east including large rock slides under the heights of Torr Reamhar and at Scriden (An Scriodan) at the far north end of the island. North Arran is one of 40 National Scenic Areas in Scotland.