Geography and Geology
The Dingle Peninsula, in County Kerry, is the northernmost of the series of peninsulas which form Ireland's south-west coast. It stretches 30 miles westwards from the Vale of Tralee towards the Atlantic Ocean, the Blasket islands off its western tip forming the westernmost part of Ireland and of Europe. The Barony of Corca Dhuibhne occupies almost the whole of the peninsula, its eastern boundary running south from Tralee Bay to the summit of Glanbrack mountain in the Slieve Mish range, then west along the summit of the range to Caherconree mountain, and then south again to Castlemaine Harbour. Caherconree inland promontory fort (259) forms part of this boundary. The remainder of the peninsula is occupied by part of the Barony of Trughanacmy (not included in this survey).
Corca Dhuibhne is comprised of an area of about 217 square miles (562 square kilometres) or 138,990 acres (56,247 hectares), of which 888 acres are taken up by water. The area is dominated by a mountainous spine which extends westwards along the centre of the peninsula from the Slieve Mish range to Brandon Mountain, and thence as a less pronounced ridge to Mount Eagle and the Blasket islands. The transverse Brandon mountain range, including Ireland's highest mountain outside the Macgillycuddy's Reeks, extends northwards from Dingle Town to the precipitous sea-cliffs at Brandon Head, isolating the western part of the peninsula. The road through Dingle Town provides the only means of access to the west by road. The central ridge similarly creates an almost continuous barrier between the north and south sides of the peninsula, east of Brandon, modern roadways crossing the ridge at only three points over a distance of about 20 miles.
On the north side of the central ridge, to the east of Brandon, a series of generally north-south valleys have been cut deep into the mountains by glacial action. These open northwards onto a low-lying coastal strip, bordered by almost continuous sandy beaches. A sandy spit, projecting northwards between Tralee Bay and Brandon Bay, joins two of the Magharee islands to the mainland. A similar spit projects 3 miles southwards into Dingle Bay at Inch.
To the south of the mountains lie the longitudinal Emlagh and Anascaul valleys, and the broad crescent-shaped valley that surrounds the Trabeg inlet. The former are bounded along their south sides by the coastal mountain ridge that extends between Minard Head and Knockbrack.
The physical landscape of the western part of the peninsula is characterised by generally gently sloping hills and broad open valleys. The coastline here, as along much of the south coast of the peninsula, is marked by steep sea-cliffs, interrupted occasionally by small inlets and coves, and by the three major drowned valleys that form Smerwick, Ventry and Dingle harbours.
The geological history of the peninsula begins in the Silurian period of the Palaeozoic Era, when the area was submerged beneath a shallow sea with active volcanoes on its shores and hinterland. The oldest rocks, known as the Dunquin Group, accumulated on the floor of this sea about 410 million years ago. The sedimentary and volcanic rocks which make up this group occur at the western tip of the peninsula and in a long narrow strip from Minard Bay, along the Anascaul valley, to Derrymore Glen. They include the rhyolites from near Dunquin which were utilised for the manufacture of stone tools at Ferriter's cove during the 4th millenium B.C.. The Silurian period in Ireland was characterised by elements of the Caledonian upheaval which caused volcanic activity and gradual uplift of rocks in the Dingle Peninsula area. By the end of the Silurian, there was major uplift and folding of rocks into the Caledonide mountains, more to the north of the region. The Dingle Peninsula area became a continental margin, with steep mountain slopes at first; as the Caledonide mountains were denuded, it became a low-lying coastal plain. Great thicknesses of conglomerates, sandstones and mudstones were deposited and accumulated in a deepening basin which underlay this continental margin. These largely red-coloured rocks are named the Old Red Sandstone. The Dingle Group which forms much of the mountainous backbone of the peninsula, including Brandon mountain, is the oldest of the Old Red Sandstone groups. There are no rocks of Middle Devonian age in the Dingle Peninsula region, this period being represented by an unconformity where the sequence of Silurian and Lower Devonian rocks were uplifted and folded. This unconformity represents the end of the Caledonian upheaval. Rocks of Upper Devonian age outcrop at the eastern end of the peninsula, consisting of the upper Old Red Sandstone of the Slieve Mish range which disappears under the Lower Carboniferous limestone of the Vale of Tralee. The carboniferous limestone, deposited on the floor of the shallow sea which reinvaded the area of Ireland about 350 million years ago, formerly covered the Old Red Sandstone. However, about 270 million years ago, the sediments of south-west Ireland were raised and folded along their present east-west axis, and the limestones were exposed to the elements and gradually eroded. On the Dingle Peninsula, they are now confined to the Magharee and Inch peninsulas and a narrow coastal strip to the north of the Slieve Mish range. Further periods of sedimentation, volcanicity and mountain-building movements followed, but erosion has removed all trace of these from the Dingle Peninsula. About 2 million years ago, the climate of Europe deteriorated severely. During the ensuing Pleistocene period, popularly known as the Ice Age, the climate seems to have alternated between cold stages, during some of which ice formed, and warm stages when the climate improved sufficiently to allow deciduous woodland to become established. During the cold stages, active glaciers carved out the deep valleys and spectacular corries of the central ridge and Brandon mountain, putting the final touches to the physical landscape of the peninsula. The amelioration of the climate about 10,000 years ago was followed by the return of the modern vegetation, and in early post-glacial times Ireland was densely wooded. Extensive woodlands existed as recently as the 17th century along the north coast of the peninsula, between Tralee and Brandon mountain (McCracken 1971, 45). The stumps of trees preserved under the blanket bogs, and place-names such as An Doire M6r, Baile na gCrann and An Choill Mh6r, are the only reminders of this former wooded landscape, the peninsula now being almost devoid of pre-reafforestation trees. (For a general guide to the geology of the Dingle Peninsula see Horne, 1983).