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The use of a nomogram constructed by J. T. Andrews (I970) has allowed an approximate chronology of deglaciation to be established for the Island of Arran. The last ice cover of the area began to build up about 25 000 years BP, and reached a maximum about 18 000 BP, after which a retreat began. It is thought that the Aberdeen- Lammermuir readvance and the Perth readvance were not major readvances but stillstands or minor oscillations of the ice front. The south of Arran became free of ice by 13 000 BP and the island was totally free of Highland ice by 12 500 BP, although there was still a local ice centre in the northern hills. There was a quite extensive ice cover during the Loch Lomond readvance, though there was no ice in the south of the island at this time. The ice retreated gradually, and there is some evidence that there was either a stillstand or a minor readvance after the glaciers had shrunk into the high corries. The last ice on the island disappeared about 10 300 BP. THE Island of Arran is located in the Firth of Clyde some 30 km west of the Ayrshire coast and 5-10 km east of Kintyre. The island has an area of about 400 km2, and has long been noted for its variety of relief. In the north of the island there is a group of hills, cut in granite, which present a rugged appearance and display many features such as glacial troughs, horns and hanging valleys normally associated with Alpine glaciation. The highest point on the island is Goatfell (Fig. i), 873 m, while several other peaks exceed 700 m. The overall plan of these hills is in the form of three north-south ridges separated from one another by glacial troughs (Fig. i). The hills are surrounded by a well developed surface, the so called 'iooo foot platform' bounded by steep slopes descending to the coast. Much of the south of the island consists of rolling upland covered with moorland vegetation, the hills rarely rising above 450 m. Lowlands are limited in Arran, the largest being in the south west, while smaller lowlands are found at the mouths of the major valleys. Though the island has been overwhelmed by ice from the Scottish Highlands at various times (J. Geikie, I894), it is evident from local relief that the north of the island has also been subjected to glaciation from a local mountain ice centre. The study of the relics of these glaciations has helped to elucidate the sequence of deglaciation for the island and, by extension, for the lower Firth of Clyde. Arran is a key area in the study of the deglaciation of the Firth of Clyde for its geomorphology has been influenced by all the major glacial events in the area. Indeed, Arran might well be considered to contain a microcosm of the entire Scottish late glacial sequence (Table I). It lies completely within the limits of all but the Loch Lomond readvance, and deposits relating to these earlier glaciations are to be found in the southern part of the island (A. M. D. Gemmell, I971). Moreover, the Loch Lomond glaciation affected only the northern hills in Arran, thus helping to preserve the older deposits in the south of the island. It is therefore possible to |
