Rocks at Dunquin on the Dingle Peninsula

The Blasket Islands are deserted now but at one time the small pier at Dunquin was a lifeline for the small island community. It is hard to imagine the hardships of their existence and the way they would have navigated in all weathers across the short stretch of water to the mainland of the Dingle peninsula in tarred canvas-covered open boats called curraghs. For the islanders wanting to buy or sell goods, needing a doctor, having to attend church, confession, christenings, weddings, or funerals, or to visit mainland friends and family, Dunquin was an important landing place. The very basic, even primitive, life of the islanders is movingly and simply told in The Islandman by Tomás O’Crohan  who lived and died on Great Blasket Island (1856 to 1937). Nowadays, it seems to be mostly small boats that launch from the pier to ferry tourists to the uninhabited islands .

Dunquin harbour not only has this important historical association but it is also a noteworthy geological location. Walking down the steep, zig-zag path from the stone-walled green fields above to the beach and pier below, there are great views of the cliffs to the north and south of the harbour. It is a transition zone between two major geological periods – where a predominantly marine environment changed to a mainly terrestrial one due to vascillating sea level relative to the land. It is the location where yellow marine siltstones belonging to the Drom Point Formation of the Silurian Dunquin Group lie next to the reddish, purplish, and greenish sandstone strata of the Silurian/Devonian Dingle Group which are terrestrial in origin.

The cliff faces seem to be striped in contrasting subtle hues. The rock layers are steeply angled now following earth movements over the many millions of years since they were originally laid down in a horizontal position. Odd circular or spherical formations can be seen in some layers. The bedding plane of one outcrop next to the pier has a roughly polygonal pattern of drying mud cracks preserved in the stone. Curving veins of quartz cut across the strata to the south of the harbour.

Altogether a very good place for rock enthusiasts and well worth a return visit. Next time I would like to take a boat trip to the Blasket Islands where (on Inishvickillane at least) the rocks are mainly volcanic tuffs and lavas.

REFERENCES

O’Crohan, Tomás,  1937 The Islandman, Oxford University Press, ISBN 978-0-19-281233-9, re-issued 2000.

Horne, Ralph R., 1976, Geological Guide to the Dingle Peninsula, Geological Survey of Ireland Guide Series No. 1, Minister for Industry and Energy, Geological Survey Office. Reprinted 1999.

Rocks at Clogher Bay 2

Silurian Period rocks belonging to the Dunquin Group on the Irish Coast.

This is the second in a series of photographs of rocks at Clogher Bay on the Dingle Peninsula in the West Coast of Ireland, and they belong to the Dunquin Group from the Silurian Period. Clogher Bay is just south along the coast from Ferriters Cove which has featured in earlier postings.

Silurian Period rocks belonging to the Dunquin Group on the Irish Coast.

Silurian Period rocks belonging to the Dunquin Group on the Irish Coast.

Silurian Period rocks belonging to the Dunquin Group on the Irish Coast.

Silurian Period rocks belonging to the Dunquin Group on the Irish Coast.

Silurian Period rocks belonging to the Dunquin Group on the Irish Coast.

Silurian Period rocks belonging to the Dunquin Group on the Irish Coast.

Silurian Period rocks belonging to the Dunquin Group on the Irish Coast.

Silurian Period rocks belonging to the Dunquin Group on the Irish Coast.

Silurian Period rocks belonging to the Dunquin Group on the Irish Coast.

Rocks at Ferriters Cove 10

This marks the final post in the series about the rocks at Ferriters Cove. I had spent a happy few hours on the beach and reached the limit of accessible shore at Ferriters Cove. Time to call it a day. At this northernmost part of the shore, the steeply sloping strata in the cliff, with the bedding planes facing outwards as a continuous sheet, at first seem to be buckling under their own weight, as seen in images 55a and 56 in the previous post. Then, just a few metres further on, the strata can be viewed side-on across the bedding planes with the sequence of individual layers revealed. The strata are curved concavely so that the cliff face is like the under-side of a huge wave, the crest of which is curving over and about to crash down and break. You can see this best in images 60 and 61.

There are also some enigmatic markings on that part of the bedrock on the beach which is covered each day by the tide. I wonder if these are fossils. Photo 73 has a number of rounded shapes that look like they might be gastropods; and Bembexia is a marine snail that is recorded in this locality.

More problematic are the plant-like patterns which occur on a number of rocks (see images 79 – 81). They seem to have a central stem with numerous branchlets along the length. I am not at all certain that these are fossils although they seem to be integral with the surface of the rock and to have a slightly different composition which is reflected in the fact that there is no black biofilm (maybe lichen) growing on them. I am fairly sure that the ‘plants’ are not grazing trails left by the feeding activities of the adjacent limpets and periwinkles. Plants are in fact recorded from the Silurian but I cannot find any illustrations that resemble these Ferriters Cove ‘plants’.

In an article about the Silurian Period on the website of the University of California Museum of Paleontology it says:

Perhaps the most striking of all biological events in the Silurian was the evolution of vascular plants, which have been the basis of terrestrial ecology since their appearance. Most Silurian plant fossils have been assigned to the genus Cocksonia, a collection of branching-stemmed plants that produce sporangia at their tips.

However, drawings of that particular genus show a very different branching system to that exhibited by the Ferriters Cove ‘plants’. Maybe I will get a clearer understanding when I have tracked down some of the specialist research papers on the fossils of this area such as those written by C. H. Holland:

Holland, C. H. (1969) Irish counterpart of the Silurian of Newfoundland. Memoir of the association of Petroleum Geologists 12, 298-308.

Holland, C. H. (1987) Stratigraphical and structural relationships of the Dingle Group (Silurian), County Kerry, Ireland. Geological Magazine 124, 33-42.

Holland, C. H. (1988) The fossiliferous Silurian rocks of the Dunquin inlier, Dingle Peninsula, County Kerry, Ireland. Transactions of the Royal Society of Edinburgh: Earth Sciences 79, 347-360.

Rocks at Ferriters Cove 9

Cliff of Silurian strata at Ferriter CoveBy the time I had reached the northernmost edge of the beach at Ferriters Cove, the Silurian rocks had changed their appearance again. The cliff here is higher and composed of a wonderful patchwork of mainly yellow slabs with purple-grey markings. Many of these slabs have fallen to the shore in a thick loose layer. Among these pieces of stone I found some more fossils, internal casts and impressions of brachiopods, including different species to the one I found earlier (I thought that might be Leptaena sp.). Two particular brachiopods are mentioned on the sign at the entrance to the beach, Holcospirifer (bigugosus?) and Rhipidium (hibernicum?), and it is likely that the fossils in images 57b,c,& d belong to one or both of those species. I am wondering if the much larger regular rounded fossil in image 57a is a species of Atrypa.

REFERENCE

Bassett, M. G., Cocks, L. R. M., and Holland C.H. (1976) The affinities of two endemic Silurian brachiopods from the Dingle Peninsula, Ireland, Palaeontology, Vol. 19, Part 4, pp. 615 – 625, pls. 93-95.

Rocks at Ferriters Cove 8

Natural abstract design in Silurian rock at Ferriters Cove

Water-worn, soft, and stripey Silurian sedimentary rocks make sporadic appearances through the sandy beach at Ferriters Cove and sometimes they can have a strangely sculptural appearance, or even of a landscape in miniature, depending on the perspective from which they are photographed. I also particularly like the pale blue-green colour contrasting with the muted yellow that contributes to the natural abstract striped designs.

You can click on an image to enlarge it.

Silurian rocks on the beach at Ferriters Cove

Silurian rocks on the beach at Ferriters Cove

Silurian rocks on the beach at Ferriters Cove

Silurian rocks on the beach at Ferriters Cove

Silurian rocks on the beach at Ferriters Cove

Silurian rocks on the beach at Ferriters Cove

Silurian rocks on the beach at Ferriters Cove

Beach Stones at Ferriters Cove

View of Ferriters Cove on the Dingle PeninsulaBetween rocky outcrops and promontories at Ferriters Cove lie stretches of sandy beach with patches of water-worn beach stones and smaller pebbles. The stones are derived from a variety of Silurian strata, not only from this cove but also from the coast further to the north which is also composed of Silurian Period rocks.

Rocks at Ferriters Cove 1

View of the beach at Ferriters Cove

The wide sandy beach that you see as soon as you get to Ferriters Cove, gives way to a broad expanse of olive green seaweeds at mid tide level that conceals an uneven pavement of low-lying and jagged rocks to which they are attached. These rocks are the first signs of the incredible ancient fossil-bearing Silurian strata for which this cove is famous. Walking around the cove in a northerly direction reveals, one-by-one, a series of strata, each with a character of their own in terms of colour, texture, and shape, and terminating in the massive flat shining slabs of rock that face the cliffs in the distance below Ferriters Castle.

This is the first in a series of posts illustrating the changing nature of the Silurian strata in the sequence exposed at this location.

Seaweed covered rocks on the sandy beach at Ferriters Cove

Close-up of fucoid seaweeds on the seashore

seaweeds and Silurian rocks on the beach

Low-lying and upstanding sharp edges of Silurian strata and flat slabs lying loose on the shore at Ferriters Cove

Smerwick Harbour on the Dingle Peninsula

View looking due east across Smerwick Harbour showing outcrop of Silurian rock topped by rip-rap boulders

Smerwick Harbour on the north shore of the Dingle Peninsula in Ireland has a wide sandy beach overlooked on one side by mist-covered slopes of hills  and mountains, with Ballydavid Head and Pointe Bhaile Na NGall projecting into the sea, and the village of Murreagh nestling at the water’s edge. While on the other side lies the scalloped horizon of the Three Sisters with Smerwick Village in their hinterland. From the parking spot close to Na Cluainte, the sand stretches for about three kilometres, forming part of the extensive Dingle Way footpath, and the length is delineated by a small slipway at the northwest end, and a small promontory called Traigh an Fhiona at the southeast end.

The geology is so varied in this area that the two ends of this sandy beach are composed of entirely different rocks, with older compact and fractured layers of green and yellow Silurian siltstones of the Clogher Head Formation belonging to the Dunquin Group to the north – and younger coarser-grained, purple and red coloured Devonian conglomerates of the Trabeg Member of the Trabeg Conglomerate Formation of the Dingle Group to the south.

The differences in the two types of rocks are very obvious. They make an interesting contrast visually, and they afford a variation of habitat for seashore creatures, seaweeds, and lichens that colonise them. Between the two kinds of strata at the separate ends of this beach, the wide and mainly yellow sandy shore is subtlly coloured in some areas with shades of purple or pale green, reflecting the constituent grains derived from the local rocks. Pebbles exposed in wet patches at mid tide level exhibit many petrologies of which bright red stones of jasper are the most remarkable.

Some pictures illustrating these features are shown below.

Don’t forget, you can click on any photograph to enlarge the image.

Ferriters Cove on the Dingle Peninsula

Layers of upstanding Silurian rock on the beach

The mountains look down on the golden crescent of sand at Ferriters Cove. It is isolated and peaceful – where the sound of gently lapping waves is only occasionally broken by raucous calls when flocks of oyster catchers or herring gulls suddenly take flight.

Rock layers here stand up like stacked tombstones with wide knife edges, or stumps of strata with sharp points protrude from the surface like nails on a fakir’s bed. The rocks are fossiliferous marine Silurian sediments, from the Ferriters Cove Formation in the Dunquin Group, dating from between 423 and 395 millions of years ago. They are composed of pale brown, yellow, grey and red siltstones, mudstones, and sandstones. They were deposited in a shallow sea with active volcanoes on its shore and hinterland, which produced volcanic deposits such as lava and tuffs.  The character of the rocks changes as you walk along the beach. Fossils such as brachiopods, corals, and trilobites are found in the mudstones.

Some pictures illustrating these features are shown below.

Don’t forget, you can click on any photograph to enlarge the image!