Geology of the Dingle
Peninsula
Geolaíocht leithinis Chorca Dhuibhne
Underlying the spectacular, rugged beauty of Corca Dhuibhne, the Dingle Peninsula, a stony core of rock records a fascinating saga of earth history going back at least 410 million years to the Silurian Period. The earliest chapters in this story reveal the presence of a shallow sea where small colonial corals, brachiopods and trilobites lived on a soft bottom of fine sand and mud. Nearby, active volcanoes made life difficult for this early marine life by periodically blanketing the region in fine deposits of volcanic ash and an occasional lava flow.
After a few million years, shifts in the earth's crust uplifted Corca Dhuibhne, and the sea withdrew. Following a period of crustal instability, erosion, and volcanic activity, Corca Dhuibhne next emerged as a vast inland valley basin bordered by uplands and mountains. Slowly, during the ensuing Devonian Period from 400 to 350 million years ago, these mountains eroded as rivers carried coarse gravel, sand and mud into the valley of Corca Dhuibhne where it accumulated in shallow fresh water lakes, river bottoms, and dunes of wind-blown sand.
Not much is known about the life that existed in this inland valley, for only a few tracks and burrows are preserved where unidentified amphibians and other organisms crawled over the soft sands and mud. The lakes were quite shallow most of the time, as is revealed by the numerous wave-formed ripple-marked surfaces preserved in the layers of sediment. Periodically, the lakes dried up completely, cracking the red muds and fine sands into polygonal patterns. Crustal uplift also continued at intervals throughout this long period, causing faulting and erosion within the valley itself and resulting in pulsations of eroded gravel, including abundant pebbles of jasper, which washed down from the mountains to the south.
Towards the end of the Devonian Period, the sea once again encroached over Corca Dhuibhne, and by the Lower Carboniferous Period 345 million years ago, soft lime muds and skeletal debris produced by corals, molluscs, algae and bryozoa were now accumulating in a shallow, warm and crystal clear sea, far from the influence of land.
At the end of the Upper Carboniferous Period 290 million years ago, major mountain building occurred, folding, faulting and contorting the sandstones, mudstones, volcanics, and limestones of Corca Dhuibhne into the striking patterns we see today.
Little is known about the next 280 million years of geologic evolution that occurred here. There are signs that the seas returned, and that more sediment was deposited, along with more volcanic activity and periods of mountain building. But we will never know for sure, because that record has been totally stripped away.
We do know that during the Pleistocene Epoch between 200,000 and 10,000 years ago,
Corca Dhuibhne was repeatedly scoured by glacial ice. High in the mountains, repeated
advances of the ice carved out beautiful mountain lakes and shaped the striking landscape
we see today. Eventually, the last of these glaciers melted away, leaving a blanket of
rock debris, clay, sand and gravel over the hillsides and valleys.
Throughout much of Corca Dhuibhne this glacial debris eventually weathered into
thick rich soil which has supported the farming communities of Corca Dhuibhne
for over a 100 generations. Or, as you will find in other areas, the landscape
was again covered over, this time in the form of thick blankets of peat bog,
which began to advance as the climate gradually became wetter about 4,000 years ago.
For the casual visitor and professional alike, Corca Dhuibhne presents a fascinating array of geological history and geology in action. Almost anywhere you stop, the rich geological past is displayed. A visit to the beaches and cliffs during an North Atlantic gale is an awsome spectacle to behold.
Where should a visitor go first? Comparisons are difficult, but some of the exceptional stops to include are these listed here.
The Sand Dunes of Inch
The 5km long dune-covered sandy spit at Inch is one of the largest dune fields
in Ireland. To walk eastward from the crashing waves of the Atlantic surf of Dingle
Bay through these large active dunes to the quiet lagoons and mud-flats behind in
Cromane Bay is to witness nature caught in a dynamic, yet harmonic, tension of wind,
sea, and sand. Magnificent!
The Boulder Beach at Minard
If as a child you have ever wondered what a beach might look like to an ant,
Kilmurray Bay at Minard is a Liliputian dream come to life. Here in the hulking
shadow of Minard Castle giant sausage-shaped sandstone boulders form a beach
unlike anything you have ever seen! Definitely not a place for bathing, but a
wonderful place for a surrealistic picnic lunch.
Sea Sculpture at Trabeg Bay
Like Minard, the beach at Trabeg faces the southwest storms of the Atlantic. Here, on an ebbing tide, you will find exquisite wave-sculptured maroon sandstone forms marching seaward from sheer rock cliffs and small sea caves lined with veins of crystalline quartz, silent momentos of Corca Dhuibhne's turbulent past. An incessant symphony of texture, colour and sound.
Islands in the Making at Coumeenoole Strand and Dunmore Head
Facing the hauntingly beautiful Blasket Islands, the strand at Coumeenole and cliffs of Dunmore Head can be a raging monster with jagged, sandstone teeth jutting from the frothing foam, to a placid crystal-clear bather's pool lined with golden sands and towering vertical slabs of ancient water-polished stone tile. A 400-year old graveyard for more than one Spanish ship, this section of the coast stands in not-so-mute testimony as to how crashing waves on a rising sea continue to carve away bits of Corca Dhuibhne, spitting out islands in the wake, like so many icebergs in stone.
A Stroll through Time at Dunquin Pier
The rocks are melting at Dunquin Pier. Evidence of erosion falls away on every side as you walk down the steep, narrow, winding tarmac ramp to small pier below. In many ways, your short walk down is like an inverted elevator ride through time, as you pass through layers of soft, yellow and brown Silurian siltstones into the overlying red, flaggy Devonian sandstones and mudstones below. What a story these red rocks could tell, with upturned bedding surfaces flaunting tell-tale mud-cracks of ancient seas gone dry, and now once more awash in an encroaching sea. The Blasket Islanders knew this ramp well, as their ancestors before them knew other ramps now almost eroded away, their traces still visible in the time-worn cliffs.
The Fiery Past of Clogher Head
In 79 AD, Mt. Vesuvius awoke from a fitful slumber to devastate the silence and bury alive the residents of Pompeii within a time-encapsulating tomb of fiery ash and cinders. It happened at Clogher Head, too, but this time it was only the likes of trilobites and brachiopods which were left to scream in silence as the molten ash and cinders boiled their juices and clogged the shallow seaways of their watery home. But, still, as all good stone lovers know, it's an ill ignimbrite that doesn't blow some life form some good.
Just as the Neolithic Irish treasured Clogher Head for the axeheads they could make from its fire-begat stone, you too will treasure Clogher Head for the marvelous view of the Blasket Islands, and for the view from Minnaunmore Rock of the sea beyond, emblazened by the afternoon sun.
The Lava Cave at Ferriter's Cove
Stealthily their naomhógs crept through the dark along the narrow-steep walled cut of Coosglass inlet beneath the now pitch-black overhang of coarse reddish Devonian conglomerates. At last, they rested bobbing on the swell in the dark recesses of the large sea cave. Over their heads, the crystalline phenocrysts of feldspar glowed almost with an inner light of their own against the Silurian lava flow host rock, the oldest rock of Corca Dhuibhne. The fault-of-all-faults had now been crossed, and Piaras smiled slightly knowing that only a few more kilometres of treacherous cliff and cave-lined coast remained before they would reach the safety of the secret sea cave entrance to the Castle. It had been a long pull from Smerwick through the tumultuous seas off Sybil Head, but they had made it... at least for the time being, thought Piaras Ferriter, they were safe. He chuckled to himself, certain in his knowledge that they would still be waiting for them at the Cove, nestled down behind those jagged up-turned ledges of Silurian silstones along the shore. He could see them now, their fingers tracing chain-linked doodles over the stoney Halysites corals, and peering through the pre-dawn gale with eyes big as those of the rock-bound Phacops beside them on the wave-washed ledge ...
The Valley Glaciers of the Brandon Mountains
Looking down into the Ownenmore Valley from the carpark at the top of the Conor Pass, the villages of Cloghane and Brandon nestle peacefully where a mighty glacier once flowed out into Brandon Bay. Rising up from this bog-covered valley interspersed with shimmering lóchs (lakes) a fractal pattern of smaller valleys, many beset with their own smaller lochs, branch ever-upward into the surrounding mountains.
It's been only 10,000 years since the last of the ice melted here, and the signs of alpine glaciation are everywhere, from the mega-scale classic U-shape valley of the Glenahoo to the micro-striations on the corrie walls surrounding Peddlars Lake. Hiking further into the high country, the evidence is even more breathtaking – matterhorn-type peaks, arrete-shaped ridges and cascading waterfalls. There are also the mysterious bogs of the Coumanare Upland, a pristine tangle of glaciated valleys, crystal clear lakes, and streams that disappear into 4 metre thick eroded bog and then resurface a few hundred metres away. Not a place for inexperienced or boot-less hikers, but very rewarding for those who make the effort.
Thanks to Michael P. O'Connor of Dingle for contributing this article.