The geology of Ireland consists of the study of the rock formations on the island of Ireland. It includes rocks from every age from Proterozoic to Holocene and a large variety of different rock types is represented. The basalt columns of the Giant's Causeway together with geologically significant sections of the adjacent coast have been declared a World Heritage Site. The geological detail follows the major events in Ireland's past based on the geological timescale.
The oldest known Irish rock is about 1.7 billion years old and is found on Inishtrahull Island off the north coast of Ulster. [1] [2] Outcrops at Annagh Head on the Mullet Peninsula are almost as old. [3] In other parts of Donegal, scientists have discovered rocks that originated as glacial deposits, demonstrating that at this early period, part of what was to become Ireland was in the grip of an ice age. However, because of the effects of later upheavals, it is almost impossible to sequence these early rock layers correctly. [4]
About 600 million years ago, at the end of the Precambrian super-eon, what would later become the Irish landmass was in two parts, with one half on the north-western side of the Iapetus Ocean in Laurentia and the other on the south-eastern side in the micro-continent Avalonia, both at a latitude of around 80° South, close to what is now northwest Africa. [5] From the evidence of the Oldhamia fossils found at Bray Head in Leinster, both parts of Ireland were below sea level at this time. [6]
Over the next 150 million years, these two parts moved towards each other, eventually uniting about 440 million years ago. Fossils discovered near Clogherhead, County Louth, show the coming together of shoreline fauna from both sides of the original dividing ocean. The mountains of northwest Ireland were formed during the collision, as was the granite that is found in locations in Donegal and Wicklow. The Irish landmass was now above sea level and lying near the equator, and fossil traces of land-based life forms survive from this period. These include fossilised trees from Kiltorcan, County Kilkenny, widespread bony fish and freshwater mussel fossils and the footprints of a four-footed amphibian preserved in slate on Valentia Island in Munster. Old Red Sandstone also formed at this time. [7]
Between 400 million and 300 million years ago, parts of Northwest Europe, including much of Ireland, sank beneath a warm tropical sea. Great coral reefs formed in these waters, eventually creating the limestone that still makes up about 65 per cent of the area of the island. As the waters receded, tropical forests and swamps flourished. The resulting vegetation eventually formed coal, most of which was later eroded. This period, known as the Carboniferous period, ended with further tectonic movement which saw Ireland drift further northward. The resulting pressure created those Irish mountain and hill ranges that run in a northeast to southwest direction. [8]
By 250 million years ago, Ireland was at the latitude of present-day Egypt and had a desert climate. It was at this time that most of the coal and sandstone were eroded. The thinner layers of limestone in the south of the country were also partially affected by this erosion. The limestone that was exposed by the disappearance of its sandstone mantle was subject to solution by weakly acidic water resulting in a karstic landscape that can still be seen in the Burren in County Clare. [9] Shortly after this period, organic debris in the seas around Ireland began to form the natural gas and petroleum deposits that now play a role in the economy of Ireland. Then, about 150 million years ago, Ireland was again submerged, this time in a chalky sea that resulted in the formation of chalk over large parts of the surface. Traces of this survive under the basalt lava that is found in parts of the north. [10]
About 66 million years ago, the volcanic activity that formed this lava began. [11] The Mourne Mountains and other mountains in the northern part of the island formed as a result of this activity. [12] Climatic conditions at this time were warm and vegetation thrived. Vegetable debris in the Antrim Depression formed deposits of brown coal or lignite which remain untouched down to the present time. [7] The warm conditions produced high rainfall that accelerated processes of erosion and the formation of karstic landscape forms. [13]
By 25 million years ago, Ireland was close to assuming its present position. From then on, a long period of erosion resulted in considerable soil formation mantling most of the bedrock. In areas with good drainage, the covering consisted of brown or grey soil, while in poorly drained areas, black clay tended to dominate. As the climate cooled, soil formation slowed, and a flora and fauna that would millions of years later be familiar to the first human inhabitants began to emerge. The present landscape of Ireland had more or less formed. [14] Before the Quaternary glaciations affected Ireland the landscape had a thick weathered regolith on the uplands and karst in the lowlands. Pre-Quaternary relief was more dramatic than today's smoothed landforms. [15]
Since about 1.7 million years ago, the Earth has been subjected to a cycle of warm and cold stages and these have, inevitably, affected Ireland. The earliest evidence we have for this effect comes from the period known as the Ballylinian Warm Stage, some half a million years ago. At this time, most of what are now considered to be native Irish trees were already established on the island. The action of the ice during the cold stages was the major factor in bringing the Irish landscape to its current form. [7] [16]
Obvious impacts of the ice on the landscape include the formation of glacial valleys such as Glendalough in Wicklow and of corries, or glacial lakes. The depositing of mounds of debris under the melting ice created drumlins, a common feature of the landscape across the north midlands. [17] [18] Streams also formed under the ice and the material deposited by these formed eskers (Irish eiscir). The greatest of these, the Esker Riada, divides the northern and southern halves of the island and its ridge once served as the main highway connecting the east and west coasts. [19] About one half of the coastline consists of a low-lying dune pasture land known as machair .
The large central lowland is of limestone covered with glacial deposits of clay and sand, with widespread bogs and lakes. The Bog of Allen is one of the largest bogs. [20] The coastal mountains vary greatly in geological structure. In the south, the mountains are composed of Old Red Sandstone with limestone river valleys. Around the Ulster/Connacht border, the mountains are made from Carboniferous sandstones with softer Carboniferous limestones below them. In central Ulster, the mountains are predominantly made from metamorphic rocks. In the west of both Connacht and Ulster, the mountains are mostly metamorphic rocks with some granite. The Mourne and Wicklow Mountains are mainly granite. Much of the northeast of Ireland is a basalt plateau. An area of particular note is the Giant's Causeway on the north coast, a mainly basalt formation caused by volcanic activity between 50 and 60 million years ago. [21] The basalts were originally part of the great Thulean Plateau formed during the Paleogene period. [22]
The soils of the north and west tend to be poorly drained peats and gleys, including peaty podzols. In contrast, in the south and east the soils are free-draining brown earths and brown and grey-brown podzols.
An unusual environment is present in north Clare, in the Burren. This karst landscape consists of limestone bedrock, with little or no soil in the innermost areas. There are numerous sinkholes, where surface water disappears through the porous rock surface, and extensive cave systems have been formed in some areas. Doolin Cave is the site of one of the world's longest known free-hanging stalactites. [23]
Ireland is an island in Northern Europe in the north Atlantic Ocean. The island lies on the European continental shelf, part of the Eurasian Plate. The island's main geographical features include low central plains surrounded by coastal mountains. The highest peak is Carrauntoohil, which is 1,039 metres (3,409 ft) above sea level. The western coastline is rugged, with many islands, peninsulas, headlands and bays. The island is bisected by the River Shannon, which at 360.5 km (224 mi) with a 102.1 km (63 mi) estuary is the longest river in Ireland and flows south from County Cavan in Ulster to meet the Atlantic just south of Limerick. There are a number of sizeable lakes along Ireland's rivers, of which Lough Neagh is the largest.
The geology of Great Britain is renowned for its diversity. As a result of its eventful geological history, Great Britain shows a rich variety of landscapes across the constituent countries of England, Wales and Scotland. Rocks of almost all geological ages are represented at outcrop, from the Archaean onwards.
The geology of the Grand Teton area consists of some of the oldest rocks and one of the youngest mountain ranges in North America. The Teton Range, partly located in Grand Teton National Park, started to grow some 9 million years ago. An older feature, Jackson Hole, is a basin that sits aside the range.
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The geology of Kansas encompasses the geologic history and the presently exposed rock and soil. Rock that crops out in the US state of Kansas was formed during the Phanerozoic eon, which consists of three geologic eras: the Paleozoic, Mesozoic and Cenozoic. Paleozoic rocks at the surface in Kansas are primarily from the Mississippian, Pennsylvanian, and Permian periods.
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The geology of the Isle of Skye in Scotland is highly varied and the island's landscape reflects changes in the underlying nature of the rocks. A wide range of rock types are exposed on the island, sedimentary, metamorphic and igneous, ranging in age from the Archaean through to the Quaternary.
The geology of Lancashire in northwest England consists in the main of Carboniferous age rocks but with Triassic sandstones and mudstones at or near the surface of the lowlands bordering the Irish Sea though these are largely obscured by Quaternary deposits.
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The geology of Estonia is the study of rocks, minerals, water, landforms and geologic history in Estonia. The crust is part of the East European Craton and formed beginning in the Paleoproterozoic nearly two billion years ago. Shallow marine environments predominated in Estonia, producing extensive natural resources from organic matter such as oil shale and phosphorite. The Mesozoic and much of the Cenozoic are not well-preserved in the rock record, although the glaciations during the Pleistocene buried deep valleys in sediment, rechanneled streams and left a landscape of extensive lakes and peat bogs.
The geology of Austria consists of Precambrian rocks and minerals together with younger marine sedimentary rocks uplifted by the Alpine orogeny.
The geology of Utah includes rocks formed at the edge of the proto-North American continent during the Precambrian. A shallow marine sedimentary environment covered the region for much of the Paleozoic and Mesozoic, followed by dryland conditions, volcanism and the formation of the basin and range terrain in the Cenozoic. Utah is a state in the western United States.
The geology of North Dakota includes thick sequences oil and coal bearing sedimentary rocks formed in shallow seas in the Paleozoic and Mesozoic, as well as terrestrial deposits from the Cenozoic on top of ancient Precambrian crystalline basement rocks. The state has extensive oil and gas, sand and gravel, coal, groundwater and other natural resources.
The geology of Thailand includes deep crystalline metamorphic basement rocks, overlain by extensive sandstone, limestone, turbidites and some volcanic rocks. The region experienced complicated tectonics during the Paleozoic, long-running shallow water conditions and then renewed uplift and erosion in the past several million years ago.
Geology of Latvia includes an ancient Archean and Proterozoic crystalline basement overlain with Neoproterozoic volcanic rocks and numerous sedimentary rock sequences from the Paleozoic, some from the Mesozoic and many from the recent Quaternary past. Latvia is a country in the Baltic region of Northern Europe.
The geology of national parks in Britain strongly influences the landscape character of each of the fifteen such areas which have been designated. There are ten national parks in England, three in Wales and two in Scotland. Ten of these were established in England and Wales in the 1950s under the provisions of the National Parks and Access to the Countryside Act 1949. With one exception, all of these first ten, together with the two Scottish parks were centred on upland or coastal areas formed from Palaeozoic rocks. The exception is the North York Moors National Park which is formed from sedimentary rocks of Jurassic age.
The geology of the Gower Peninsula in South Wales is central to the area's character and to its appeal to visitors. The peninsula is formed almost entirely from a faulted and folded sequence of Carboniferous rocks though both the earlier Old Red Sandstone and later New Red Sandstone are also present. Gower lay on the southern margin of the last ice sheet and has been a focus of interest for researchers and students in that respect too. Cave development and the use of some for early human occupation is a further significant aspect of the peninsula's scientific and cultural interest.
