Geology of the Dingle Peninsula

Silurian Trilobites. These fossil arthropods are preserved as fragments in the Ballynane Limestone. This remote mountain-side outcrop and its fossils were first discovered and described by Jukes and Du Noyer in 1863. The Caherconree Fault is a major fracture that can be traced southwards for 25km to Minard Head.

During the Silurian period Ireland was divided into two portions separated by the lapetus Ocean. As this closed on account of plate tectonics a series of volcanic islands developed in western Ireland. On the Dingle Peninsula these volcanoes produced ash, myolitic lava and pyroclastic deposits which are now found associated with fossil-bearing sediments in the Dunquin district.

At Ferriter’s Cove are found purple to buff-coloured siltstones of Silurian age in which fossils including corals, trilobites and brachiopods, are preserved.These animals all lived in a shallow sea close to the volcanic islands once near Clogher Head.

Much of the western end of the Dingle Peninsula is composed of terrestrial sediments such as conglomerate and fine to coarse-grained sandstone that make up the Dingle Group. These were deposited in river systems during the late Silurian and early Devonian. There is a distinctive gap between them and the overlying red sandstone best seen at Bull’s Head. While Inishvickillane is made of older volcanic rocks the remaining Blasket Islands are composed of Dingle Group rocks.

Kilmurry Bay is of great geological interest for two main reasons.Here 380 million year old fossilised sand dunes can be seen in the cliffs and it contains one of the finest storm beaches in Ireland. In the Devonian period rivers flowed south across a large desert and carried sands and coarse sediments. Today the coarser material forms conglomerates now seen at Inch while the sand that formed crescent-shaped sand dunes in the desert makes up the pale yellow coloured Kilmurry sandstone. This is a unit of the Old Red Sandstone that forms much of the Slieve Mish mountains and those seen on the Iveragh Peninsula opposite. Blocks of sandstone have become rounded by the action of the waves and from knocking against each other. Storms have thrown them towards the back of the beach where they have form a ridge called a storm beach.

This is a rare sedimentary rock type whose coarsest portion contains cobbles of metamorphic rocks gneiss and schist 1.38 to 3034 billion years old. The Inch Conglomerate sucession is exposed in the foreshore west of Inch beach beyond the defensive boulder wall at Coosarone.

The low lying narrow Maharees Peninsula is an excellent example of a tombola, a depositional landform in which a rocky island is connected to the mainland by a long narrow spit. The beaches along either side of the tombola show the complex patterns of recent sand deposition and erosion by both wind and marine currents. The limestone bedrock exposed only at the northern end (at Kilshannig) represents the youngest sedimentary bedrock seen in the Dingle Peninsula.

The climbing route on the north east of Mount Brandon from Cloghane brings you to a series of corries and lakes on the north-east side of Brandon Peak. The string of lakes are known as paternoster lakes. Ice from the corries fed the valley glacier below that flowed from south to north. The imposing east-facing cliffs of Mount Brandon are composed of sandstone beds and show the large and shallow folding of the lower Devonian Dingle Group Strata.

Lough Doon (locally known as Pedlar’s Lake) is a glacial corrie that was once full of ice that fed the Owenmore valley glacier.This location is accessed from a small car park beside the waterfall on Conor Pass and provides the most accessible place in the Dingle Peninsula to study glaciated mountain scenery. You can see the glacially striated rock lip of the corrie lake and boulder strewn moraines, a moraine-dammed lake and a kettle hole lake in the wide U shaped valley below. 

The cliffs at Kilgobbin are composed of glacial till (boulder clay) that was deposited when the ice of the last Ice Age melted. By mapping bedrock one can determine the direction that glaciers and ice sheets flowed by looking at the rock types left behind in the glacial till. These were picked up by the ice as it passed over the bedrock.

Geological Survey Ireland (GSI) have launched a new field guide book and 1:50,000 geological map of the Dingle Peninsula  This beautifully produced 246 page full colour publication meticulously and engagingly guides the geologist and non-geologist through the sites of importance in the story of the Dingle Peninsula.  
Geology of the Dingle Peninsula – a field guide was written by two internationally renowned geologists, Emeritus Professor Ken Higgs, University College Cork, and Emeritus Professor Brian Williams, University of Aberdeen, both of whom have worked for many years in the area, and have taught and inspired many of their students on the beaches, coves and headlands of the Dingle Peninsula. The book is dedicated to Ralph Horne, former Assistant Director of Geological Survey Ireland, who contributed enormously to promoting the modern geological understanding of the Dingle Peninsula. Speaking at the launch Koen Verbruggen, GSI Director said, "This book is amazing, it captures the beauty of the Dingle Peninsula, the importance of the geology, and explains the origin and science of the rocks in a way that is accessible to both geologists and non-geologists."
Geological Survey Ireland was founded in 1845 to map the geology of Ireland and to gain an understanding of the mineral resources. Early mapping was carried out by people walking the length and breadth of the island, marking every rock on the newly produced Ordnance Survey 6-inch maps, making drawings, sketches, and detailed descriptions of the rocks. That early work is the basis of our work today but we now use boats, planes, drones and drills to enhance that knowledge.  GSI is part of the Department of Communications, Climate Action and Environment. The Dingle Peninsula was first mapped for the Geological Survey in the 1850s by George Victor Du Noyer. His maps are works of art as well as science.