Geology and Cuisine of Ireland

The island of Ireland lies at the wind and wave-swept western edge of Europe, where warm Atlantic rain and a diverse geology combine to create high-quality agricultural produce and, of course, pure water for a drop of the ‘black stuff’. But Ireland’s proximity to oceanic margins extends back over time, leading to a long and complex geological history and range of rocks and landscapes.

Ireland is often described as ‘saucer-shaped’, with the uplands around the edge enclosing a flat-lying area in the middle. The combination of bedrock and Quaternary geology, its influence on topography and soil development, and climatic variations across the island of Ireland, influence different land uses and agriculture type.

Upland areas underlain by very poorly transmissive rocks such as igneous rocks, Old Red Sandstones, Namurian sandstones and mudstones, and Precambrian metamorphic rocks, as well as areas with thin soil horizons underlain by very well-drained karstified limestone and extensive gravels, tend to be occupied by sheep farms. Lamb or mutton is an essential component of Irish Stew. Ewe’s milk is also turned into specialist cheeses such as Creeny (County Clare), Knockalara (Waterford), Millhouse (Offaly) and Knockdinna (Kilkenny).

Dairy and beef farming takes place across much of Ireland, typically in the flat-lying Midlands, which are underlain by shelf and basinal limestones, on hillsides and in valleys of the ‘Southern Synclines’, where Old Red Sandstone and Carboniferous strata have been folded during the Variscan Orogeny, and in the North, where sub-glacial drumlin landforms resembling an upside-down eggbox are carefully drained to give lush pastures. Both industries are economically important, with mass-produced and craft cheeses being produced from dairy products, and

Potatoes are also an intrinsic component of Irish Stew and although potatoes were a subsistence crop in Ireland for centuries and grown everywhere, potatoes are commercially grown mainly in the east and southeast of the country. Here, the gently rolling lowland landscape with large fields, well-drained soils derived from Ordovician and Silurian greywackes, and a generally warmer and drier climate than the west combine to create optimal conditions for growing crops of all types, including wheat, corn, and barley.

Although tea is probably the most popular drink in Ireland, followed closely by coffee, to accompany a meal, or to drink on their own, stout – a dark, black ale (most famously brewed by Guinness), beer and cider are produced – and drunk – in Ireland. The vast majority of production is undertaken at a commercial scale and exported around the world. There is also, however, a burgeoning craft beer movement, with small-scale breweries producing bespoke ales, beers, lagers and stouts. Whiskey is produced at several distilleries across Ireland. Stouts, beers and whiskeys are predominantly made of wheat, barley, hops and water. The character of some whiskeys depends on the peaty signature of the water used in their production.


A short geological history of Ireland

Oldest rocks
The oldest rocks in Ireland occur on a small island at the very north of Ireland, and in the West. These are coarsely crystalline banded gneisses produced by strong metamorphism of Palaeoproterozoic igneous rocks. Most Precambrian rocks of northwestern Ireland are part of a belt of rocks called the Dalradian Supergroup. This extends from the west of Ireland into Scotland and is composed mainly of metamorphosed marine sedimentary rocks, but includes volcanic rocks and metamorphosed glacio‑marine deposits from the Precambrian glaciations known as “Snowball Earth”. The Dalradian rocks were deposited during the fragmentation of Rodinia, which rifted apart about 600 million years ago to form the Iapetus Ocean.

Iapetus
The Iapetus Ocean began to close in the early Ordovician. The axis of Iapetus ran through central Ireland, approximately from the present day Shannon Estuary to Dundalk Bay. Present day northwest and southeast Ireland lay along the margins of separate continents – Laurentia in the north, and micro-continents peripheral to Gondwana in the south – with the Iapetus Ocean several thousand kilometres wide in between. Lower Palaeozoic sedimentary rocks were deposited on these continental margins.
Iapetus suture

Subduction gradually closed the Iapetus, with volcanic arcs building up along both margins and within the ocean. Thick successions of Ordovician volcanic arc rocks are preserved in the West and Southeast of Ireland, with large gabbroic to granitic plutons in the West representing the deep intrusive level of a magmatic arc. Lower Palaeozoic sediments preserved in an accretionary prism that is the geological continuation of the Southern Uplands of Scotland – that today forms a wide band of greywacke and shale that spans the border between the North and the Republic.

As the ocean narrowed, several separate Silurian sedimentary basins were formed. Final closure of Iapetus occurred during late Silurian to early Devonian times, amalgamating the foundations of Ireland on the southern, equatorial margin of Laurussia. The resulting Caledonian Orogeny raised a composite mountain chain which runs from the Appalachians of North America, through Ireland and Britain, to the Arctic Circle in Norway. Continental collision was accompanied by voluminous granite emplacement, creating large batholiths around Ireland.

Tropics
During the Devonian Period, Ireland was located on landmass in which the climate was semi-arid with seasonal rainfall. Erosion of the Caledonian Mountains supplied sediment via south-flowing rivers to extensive alluvial plains. Present-day southwest Ireland was the site of the thickest non-marine Devonian sequence in Europe, with more than 6km of sedimentary rocks deposited.

Fossil footprints forming several trackways are preserved in Devonian siltstones on Valentia Island in Southwest Ireland. They were made by the first known tetrapod, a primitive amphibian, as it walked across a fluvial plain. As the first discovery of this type in Europe and the oldest in situ record of an amphibian animal, the site is now protected as an important part of Ireland’s heritage.
 Fossil footprints

By the end of the Devonian, Ireland lay near the equator. Global sea-level rises caused a northwards transgression, depositing coastal and shallow marine early Carboniferous sediments. These siliciclastics were followed by extensive shelly limestone deposits in a shallow water shelf sea. Early Variscan extensional tectonics caused block-and-basin faulting; shallow shelf areas were sites of relatively pure biogenic limestones and deeper basins were filled with fine-grained muddy limestones and calcareous mudstones.

One of the best places to see the Carboniferous limestones is the Burren, Co. Clare. Here the limestones are extensively exposed at the surface and have hardly been disturbed by earth movements; individual bedding surfaces can be traced for kilometers. The Burren limestones are one of the best places in the world to study karst landscapes. Caves, dolines, turloughs, sink holes and disappearing rivers can all be found in abundance in the Burren and surrounding limestone areas.

The Upper Carboniferous in Ireland saw a return to siliciclastic depositon related to global sea level changes. Deep-water basinal sediments and marginal coal measures were followed by shallow water deltaic sandstones and shales. The best places to see these rocks are on the coast of Co. Clare, from the Shannon Estuary to the Cliffs of Moher. Irish coalfields have thin coal seams which are relatively uneconomic to work.

At the end of the Carboniferous, Ireland was on the northern edge of the Variscan orogenic belt and its effects were relatively slight, except for the south where the rocks were folded into broad open anticlines and synclines with a wavelength of several kilometres. The anticlines are now ridges underlain by Devonian Old Red Sandstone, while the synclines are now valleys floored by Carboniferous limestone.

Ireland lay just north of the equator by the beginning of the Permian on the new supercontinent of Pangaea. Rocks of this Permian “New Red Sandstone” desert and succeeding Cretaceous chalks are preserved on land mainly in the northeast where they have been protected from erosion by the covering of Palaeogene basalt lavas (part of which forms the Giant’s Causeway). Later in the Triassic, great thicknesses of sediment and evaporites accumulated a subsiding basin, including more than 400m of rock salt, which is commercially extracted. Early Jurassic mudstones over 100m thick and rich in ammonite fossils are visible along the foreshore 30km northeast of Belfast. At the time of writing, this section is being considered for the global stratotype section for the base of the Jurassic.

Giant’s Causeway

Late Cretaceous and early Palaeogene plate movements caused widespread emergence of northern land areas from the Cretaceous chalk sea. The combined effects of crustal stretching, which preceded North Atlantic rifting, and a localised ‘hot spot’ created great volumes of magma that intruded and erupted to form the North Atlantic Igneous Province. In Ireland, voluminous basalt flows issued from NW-SE trending fractures, creating great lava fields across northeastern Ireland and the Inner Hebrides of Scotland, and extending northwards to the Faroe Islands. In northeast Ireland, repeated basalt flows built up an extensive plateau (the ‘Lower Basalts’). Between eruptions, the hot and wet climate caused deep weathering of the basalt, resulting in a red soil layer of laterite which is 15m thick in places. Thicker flows of basalt were ponded in localised hollows in the Giant’s Causeway area. The resulting Giant’s Causeway basalt architecture, a geological UNESCO World Heritage Site, is due to a combination of this great flow thickness and the striking regularity of the famous columnar jointing formed from slow cooling of the lava. 

 Giant's Causeway

Following the extrusion of the fissure lavas, further magmatism was centralised and built up large volcanoes. Erosion of the volcanoes has revealed the gabbro to granophyre roots in mountains of Slieve Gullion the Cooleys in the northeast of the island of Ireland, either side of the border. Granites intruded at this time form the nearby Mourne Mountains.

Ireland was terrestrial during the Palaeogene and the rocks underwent tropical weathering to clays. These clays were washed into depositional basins near Belfast, where they contain significant lignite deposits.

Ice Age
Global temperatures began to fall during Neogene times and the Arctic ice sheets spread across most of northern Europe at the beginning of the Quaternary Period. During the last 1.7 million years or so, there were several periods of ice advance and retreat, with warmer inter-glacial periods between. In Ireland, there is good evidence preserved for only the last two glaciations, which took place during the last 500,000 years. Dramatic ice-carved corries and U-shaped valleys give the Irish mountains grandeur beyond their relatively low height. In the lowlands, the rocks are mostly obscured by unconsolidated deposits left behind by the retreating ice sheets. Drumlin fields are well developed across the northern part of the island, with drowned drumlin fields giving hundreds of small islands in inland waters and sheltered marine environments in the West (Clew Bay) and Northeast (Strangford Lough). The Irish language gave the word Esker to the long ridges of gravels deposited by sub-glacial rivers. Extensive post-glacial peats occupy the flat interior, where they are harvested for fuel, and the upland areas around the perimeter of the island.

For more information on Ireland's climate through time and to download the 'Climate Through Time' poster click here.

You can download a simplified geology map of Ireland here.
 

Selected Irish cuisine

Irish Stew
Recipe from the Irish Food Board, Bord Bia.

Ingredients to serve 4-6 people

  • 1-1½ kg neck or shoulder of lamb
  • Bouquet of parsley, thyme and bayleaf (tied together with twine)
  • 3 large onions, finely chopped
  • Salt and freshly ground black pepper
  • 3-4 carrots, chopped into bite-sized pieces
  • 1 small turnip, chopped into bite-sized pieces
  • Some small new potatoes, peeled and quartered, or large potatoes, peeled and chopped
  • 75-100g cabbage, shredded
  • Finely chopped parsley and dash of Worcester Sauce

Irish stew

To Cook
Remove the meat from the bone, trim off all the fat and cut into cubes. Keep the bones, place the meat in a pot, cover with cold salted water. Bring to the boil, drain and rinse the lamb.

In a fresh pot, put the meat, bones, bouquet of herbs, onions, seasoning, carrots, leeks and turnip and cover with water. Simmer gently for one hour. Skim off the foam as it rises. (This is very important for the final flavour and appearance of the stew.) Add the potatoes and continue cooking for 25 minutes. For the last 5 minutes add in the cabbage. When the meat and vegetables are cooked remove the bones and bouquet for herbs. Stir in the chopped parsley and a dash of Worcester sauce. Serve in deep bowls with soda bread.
 

Rhubarb Tart with Whiskey Cream
Recipe from the Irish Food Board, Bord Bia.

Rhubarb grows very easily in Ireland and has always been a staple of country gardens. The whiskey sauce lifts this pretty dessert from its more usual everyday role.

Ingredients to serve 4 people

  • 350g (12 oz) prepared puff pastry
  • 450g (1 lb) rhubarb, washed and thinly sliced
  • 150g (6 oz) melted butter
  • 150g (6 oz) caster sugar
  • 250ml (½ pint) cream
  • 100g (4 oz) caster sugar
  • Dash of Irish whiskey

Rhubarb tart


To Cook
Preheat a moderate oven, Gas Mark 4, 180°C (350°F). Roll the pastry out to make four 10cm (4") diameter discs, then pleat the pastry all round the edge. Carefully arrange the sliced rhubarb on top of each pastry disc, making sure there are no gaps, then brush with the melted butter and sprinkle the sugar over. Cook in the preheated oven for 30 minutes. To make the sauce, whip the cream then whisk in the sugar and whiskey. When the rhubarb is tender and nicely caramelised on top, serve on heated plates with the whiskey cream and a sprig of fresh mint to garnish.


Cheeseboard

  • Leave the cheese at room temperature for approximately 2-3 hours before serving
  • Avoid too much choice, better to have two or three good size pieces of cheese than a lot of smaller bits. It looks better and the cheese will keep better.
  • A semi-soft, a hard and a blue are guides but there are no rules – choose what you prefer. Try:
  1. Cais Dubh is a hard cheese made from raw cow’s milk from the farm’s own Freisan Holstein herd at Strawhill, Fermoy, County Cork. The cheese comes in black-waxed 5 kg wheels, is made using traditional rennet and a mixture of morning and evening’s milk. Buttery with a mild tang, the cheese pairs well with beer, cider and Rioja.
  2. Cashel Blue is Ireland’s original farmhouse blue cheese, and is on made on the farm at Beechmount, near Fethard, in County Tipperary since 1984. It is a natural-rinded blue cheese made from pasteurised cow’s milk and vegetarian rennet. Depending on condition, the cheese has a chalky to soft yellow paste and a distinctive blue/green mould. Young cheeses are chalky, lactic and mildly blue whereas more mature versions are rich and buttery with a well-rounded blue flavour. Cashel is a blue cheese which relies more on balance, elegance and finesse than sheer power. Young wheels pair well with Gewurztraminer, medium aged wheels prefer Sauternes and New World Botrytis Semillion, very mature wheels can stand up to LBV Port.
  3. Milleens is Ireland’s longest established farmhouse cheese, made on the Beara Peninsula, County Cork since 1976. Made from pasteurised cow’s milk, formed in 1.2 kg rounds and aged from 4-12 weeks, it is semi-soft, smooth, with pungent farmyard aromas with creamy paste and earthy. Suggested pairings are: off-dry Gewurztraminer, still cider.

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