The countryside around Charlton Down this April is a landscape of rolling hills covered by a brightly coloured patchwork of flowering oilseed rape fields contrasting with spring wheat, each patch separated from the next by boundaries of ancient field hedgerows and trees with branches just springing into life.
Textures and patterns in chalk cliffs at Studland Bay – showing white strata and darker flint nodule layers; different degrees of weathering, fracturing and smoothing of the rock surfaces; subtle inherent variations in colouring; greyscale shading brought about by dirt and biological encrustations; and more dramatic green algal coatings on the wave-washed cliff base.
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.
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.
The sand looks black from a distance as you descend to the shore at Trá Chathail near An Trá Bheag (Short Strand) – otherwise known as Trabeg. The path cuts down deep through the stratified red rocks to get to the beach which is strewn with pebbles, mostly shades of red, maroon, green, grey, and white.
Trabeg is on the south coast of the Dingle Peninsula in Ireland, and is the “type section” of the Trabeg Conglomerate Formation which is exposed in the cliffs on the beach. This is place where that particular rock type was first described. The rock layers constitute part of the Dingle Group and were formed in the Devonian period between 345 and 395 million years ago. The conglomerates are composed of fairly well rounded pebbles of red sandstones and mudstones, with white vein quartz and chert. A few pebbles of volcanic rock and of grey limestone are also present.
The way in which the conglomerate rock has formed from the mass movement and subsequent accumulation of debris from terrestrial locations during, for example, river flood events, means that the pebbles are derived from a wide area covering many different geological types. The pebble beds or conglomerates are inter-bedded with layers of red sandstones and mudstones, the finer sediments of which were deposited normally by rivers during non-storm/flood times. The alternating layers are now tilted from the original horizontal orientation in which they were first deposited, and are clear to see dipping south at about 70 degrees.
As the cliffs at Trá Chathail are worn away by the action of waves and weathering, the pebbles contained in the conglomerate matrix are freed up and remain the shore below – an instant pebble beach. Added to these are pieces of other rock or matrix that became rounded into pebbles after they arrived on the beach. Some pebbles and rocks may have been transported by wave action from further along the coast were the geology is quite different: from the Eask Formation, West Cork Sandstone, Bulls Head Formation, and the earlier Silurian rocks of the Dunquin Group.
Horne, Ralph R. (1976) Geological Guide to the Dingle Peninsula, Geological Survey of Ireland Guide Series No. 1, reprinted 1999.
Ancient Acadian Forest cloaks the slopes right down to the shore along the trail from Louisbourg Lighthouse to Big Lorraine on Cape Breton Island. This unique forest is one of six identified for protection by the World Wildlife Fund because, here, the northern boreal forest blends with the southern hardwood forest to create a diverse habitat supporting a wide range of plant and animal life. The forest is mostly home to balsam fir with some black spruce and tamarack. Many of the trees are stunted and twisted from exposure to severe weather conditions, salt spray and poor soil in this coastal stretch. The bare sun-bleached branches on stands of dead trees are frequently covered with thick layers of pale branching lichens.
Amongst the trees are wetland areas of bog with shallow pools of open water which transition to fen with thick mats of sphagnum mosses, ground juniper, cotton grass, crowberry, and carnivorous pitcher plants. Despite the beautiful blue skies it was a particularly late and cold spring at the time of my visit (2 June 2016) and flowers were scarce but rare alpine species are known to occur in this location.
The forest, bogs, and fens sit on top of very old rocks responsible for the spectacular scenery along the coast beside the trail. All are derived from extensive volcanic activity in Precambrian (Neoproterozoic) times and belong to the Main-à-Dieu sequence. They include layered volcanic ash in the form of tuff, and varying kinds of conglomerates and breccias from pyroclastic flows down the sides of an arcing series of volcanoes where two land masses collided.
We stayed at the most excellent Louisbourg Harbour Inn while we explored this part of Cape Breton Island.
Freezing fog has lately covered all the vegetation in my village with a transparent icy coat bearing fringes of needle-like crystals. As the sun comes out to burn off the mist, the rising temperature begins to melt this hoar frost. As I walked along beside tall beech trees on one such frosty morning, an unexpected heavy rain of icy water began to fall from the thawing ice in the highest boughs, cascading down through the understorey of saplings where drops accumulated on the twigs and leaves, shining like diamonds in the low-slanting winter sun. Difficult to capture with the camera the brilliance of the eye-dazzling effect of reflections from the melt water rain and droplets.
These photographs of the hazy horizons of successive hilltops in the Tuscan countryside are views looking southwards from the top of Brunelleschi’s dome on the cathedral of Santa Maria del Fiori, the Florence Duomo. Spectacular vistas of the city and its surrounding countryside are the reward for climbing 463 steep steps in claustrophobic narrow passageways of herringbone brickwork through the interior of the dome.
The Landscape of Inishowen
The beautiful countryside around Inishowen is featured in many articles and fantastic images by Aidymcglynn: Landscape, hillwalking and nature photography around Ireland. Adrian’s photographs of the hills, beaches, and seascapes most effectively capture and reflect the incredibly interesting geology of the region. It is the shores around Inishowen that are the source of the wonderful beach stones collected and photographed by Noel Tweedie which were mentioned in the earlier posting.
The route known as the Cabot Trail in the Cape Breton Highlands National Park cuts right through some of the oldest rocks in the world as it passes round the northern perimeter of the park between North Mountain and the Grande Anse Valley. These rocks belong to the Blair River Inlier and are up to one and a half billion years old (Donahoe et al. 2005). They were pushed up from deep down in the earth’s crust by two major fault lines during the Appalachian mounting building episode so that they now lie adjacent to much younger rocks. The road is steep and winding as it passes through the territory, affording no opportunity to get a closer look at this isolated portion of the Canadian Shield and the ancient supercontinent of Rodinia.
It is, however, possible to pull off the road at a site called The Lone Shieling where a replica shepherd’s hut has been built to commemorate the Scottish heritage of the people who first settled the area after being expelled from the highlands of the Isle of Skye. Contained within the walls of this building and its boundary wall are local rocks, some of which come from the nearby Blair River Inlier. They include pink-grey granulite, banded quartz-feldspar gneiss, and also igneous rocks like the white anorthosite, and dark pink syenite that have been zircon dated to 1,100 to 980 million years ago when they intruded into even older rocks that formed about 1,500 million years ago (Hickman Hild and Barr 2015).
The Lone Shieling shepherd’s hut lies within the only accessible part of an undisturbed 4,000 acres of protected hardwood forest, the largest of its kind in the Canadian Maritimes, and marking the northern limit of growth for many of its plant species. Within the sheltered Grande Anse River Valley 97% of the trees occupying the rich moist soil of lower slopes are deciduous sugar maples (some are 350 years old and 25 metres high) with lower numbers of other species like elm, red spruce, hemlock, yellow birch, white ash, striped maple, red oak. White spruce grows on the stony river banks. Wild flowers, twenty species of ferns, and millions of hardy sugar maple seedlings cover the forest floor. Bracket fungi colonise old wood of trees left to fall. Melting snow from mountains to the south floods the river each year and strips soil from the river bed while bringing down rocks of all kinds. Angular stones of a multiplicity of types, colours, textures, patterns, and geological periods are strewn over the river bed.
Atlantic Geoscience Society (2001) The Last Billion Years – A Geological History of the Maritime Provinces of Canada, Atlantic Geoscience Society Special Publication No. 15, Nimbus Publishing, ISBN 1-55109-351-0.
Canadian Confederation of Earth Sciences (2014) Four Billion Years and Counting- Canada’s Geological Heritage, Nimbus Publishing, pp 93-97, ISBN 978-1-55109-996-5.
Donohoe, H. V. Jnr, White, C. E., Raeside, R. P. and Fisher, B. E, (2005) Geological Highway Map of Nova Scotia, Third Edition. Atlantic Geoscience Society Special Publication #1.
Hickman Hild, M. and Barr, S. M. (2015) Geology of Nova Scotia, A Field Guide, Touring through time at 48 scenic sites, Boulder Publications, Portugal Cove-St. Philip’s, Newfoundland and Labrador. ISBN 978-1-927099-43-8, pp 30-35.