LANDSCAPES AND GEOLOGY
The oldest rocks in the Geopark formed around 895 million years ago and can be seen on the northern shores of Lower Lough Erne in Tullychurry Forest. These rocks are completely different from any others in the Geopark and are linked to the rugged and often bleak landscapes found in the Sperrin Mountains or the Donegal Highlands. The types of rock found at Tullychurry Forest are known as metamorphic rocks and it is from here that the original raw materials for the nearby Belleek Pottery were sourced.
The island of Ireland as we know it didn’t exist for much of geological time as it was part of much larger continents and when our story began, the island of Ireland was literally split in half. The northern half and the southern half were part of two huge supercontinents that were separated by an ocean many thousands of kilometres wide.
Vanished Oceans and Mountain Building
The location of the Earth’s continents and oceans has constantly changed through geological time. The huge ocean that lay between the two huge supercontinents containing either half of the island of Ireland slowly began to diminish approximately 500 million years ago as the landmasses moved closer together. Remnants of this vast ocean are preserved as mudstones beneath Lough Oughter in County Cavan and in some of the surrounding countryside on the southern shore of the lake. When two huge supercontinents eventually collide, the results are often spectacular. This is what is currently happening between India and the rest of Asia where the Himalayas, the highest mountains on Earth, are being pushed up by enormous pressures as two huge land masses push into each other. Exactly the same thing happened in Ireland around 450 million years ago when the two landmasses, home to either half of what we now know as Ireland collided. The uplands of the Sperrin Mountains and the Donegal Highlands are the remnants of this vast mountain chain.
By now the two halves of Ireland were joined together but were still part of one huge continent. Around 400 million years ago, the land that was to become the island of Ireland lay approximately ten degrees south of the equator, roughly in the same place as the Sahara Desert is now. This barren, inhospitable desert landscape was periodically inundated with flash floods forming rivers and small lakes. The resulting rocks make up the red sandstones that can be found in and around Castle Archdale Forest. Most of the rocks are hidden but if you look closely at some of the boulders on the lake shore you might just find some of this preserved desert landscape.
Limestone is by far the most dominant rock in the Geopark and it formed around 330 million years ago during the Carboniferous geological period, when Ireland lay on or just slightly south of the equator. Located on the edge of a supercontinent, where sea-levels were higher, the area that we now call Ireland was covered by a shallow, tropical sea. The limestones formed by the accumulation of lime-mud on the bottom of this ancient sea floor and from the remains of millions of dead sea creatures that would have thrived in these waters. Limestone forms the bedrock of most of the middle slopes of Cuilcagh Mountain and it is in these rocks that the large number of caves in the Geopark, including the Marble Arch Caves, are found. The limestone is often full of fossils, representing sea creatures that lived in these shallow seas all those millions of years ago.
Coral fossils in Limestone
Deltas and Coal Swamps
A fall in sea-level around 320 million years ago meant that the shallow tropical seas disappeared, gradually replaced by a massive river delta. Similar in size to the Amazon River delta, this huge system started somewhere in the region of present day south Donegal, bringing with it huge amounts of sand and silt. This was also a time of coal formation across Europe due to the tropical conditions and the vast amounts of large land plants. The resulting rocks in the Geopark are mostly sandstone, which makes up the plateau tops of hills such as Cuilcagh Mountain, Belmore Mountain and Slieve Rushen.
A New Ocean
The next period in Earth history represented in the Geopark is from around 65 million years ago, when the land that eventually became Ireland had moved much further north to somewhere similar to the present day Mediterranean region. The Atlantic Ocean was a young ocean, still in its infancy after opening up between what we now know as America and Europe. Earth movements had a dramatic impact on the Irish landscape, such as the volcanic eruptions that formed the Giant’s Causeway in County Antrim. The Geopark was not without its share of the action as the resulting stresses forced molten rock up through cracks in the Earth’s surface. However, the molten rocks did not reach the surface, they cooled and hardened to form vertical sheets of solid rock within other rock types. These features are known as dykes and some of these, exposed by weathering, can be seen at Lough Navar Forest as well as in Cuilcagh Mountain Park.
The Big Freeze
The single biggest influence on the present day landscapes of the Geopark came from the huge ice sheets that ravaged much of northern Europe, including Ireland, during the last glaciation. The ice sheets which were up to 600 metres thick finally melted 13,000 years ago but before that they crept across the region, sculpting the landscape and forming beautiful u-shaped valleys such as the valley occupied by Lough MacNean, or shaping drumlins and ribbed moraines such as the spectacular ones that make up the Lough Oughter lake system. The ice sheets left behind vast amounts of glacial debris such as the large sand and gravel deposits outside Ballyconnell or the hundreds of huge boulders known as glacial erratics left scattered across the countryside when the ice sheets melted.
Lough MacNean & Drumlin Islands (Copyright Tourism Northern Ireland)
After the ice sheets melted the climate gradually began to warm up and Ireland was covered by grasses, willow, birch and other such heath plants. It was home to the famous Giant Irish deer along with reindeer, wolves and brown bears. As the ice melted, enormous quantities of water were released across the land forming the many lakes of the Geopark, including Lower Lough Erne, Lough Melvin and Lough MacNean. Temperatures were about two degrees warmer than today and precipitation was lower, so eventually most of Ireland was covered in dense forest causing the extinction of larger mammals such as the Giant Irish deer, which was adapted to open countryside. A pocket of post glacial forest can be seen at the Cladagh Glen, where the damp ash woodland represents the typical type of woodland that grew up after the glaciation ended. As human settlers began to take hold of the landscape, deforestation, burning and grazing provided ideal conditions for peat growth creating much of the internationally important blanket bog that now covers parts of the Geopark.
Underground Worlds and Water Worn Landscapes
The landscapes of the Geopark are constantly changing and nowhere is this more evident than in the many caves that lie hidden in the region. All of these caves have been carved by water flowing in the limestone that was deposited over 330 million years ago, but no one is really sure when all of the caves actually formed. Caves form as the limestone is slowly dissolved by weakly acidic water, such as rain water, but this is not just evident below ground. In certain areas of the Geopark much of the surface limestone has been water worn giving it a rugged, rocky appearance; a landscape that is often referred to as limestone pavement. This is best seen in Cuilcagh Mountain Park and at Corratirrim along the Cavan Way. There are numerous caves within the Geopark, the most famous being the Marble Arch Caves which are open for guided tours from March to September. Cave entrances in the Geopark that are safe to view but not to enter include Whitefathers Cave outside Blacklion and Pollnagollum Cave in Belmore Forest at Boho.