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Ceiswyn Formation
The Ceiswyn Formation (also known as the Ceiswyn Beds) is an Ordovician lithostratigraphic group (a sequence of rock strata) in Mid Wales. The rock of the formation is made up of interleaved beds of silty mudstones and siltstones with some sandstones and tuffs also present in small amounts. The formation runs diagonally across Mid Wales from close by Bala Lake to Cardigan Bay near Tywyn. Outcrops The formation is exposed in a number of locations in Mid Wales where glacial valleys cut across it. It is especially visible in the cliffs of Graig Goch. Fossil content Harnagian-Soudleyan trilobites have been found in the rocks of the Ceiswyn Formation near Dinas Mawddwy Dinas Mawddwy () is a village in the community of Mawddwy in south-east Gwynedd, north Wales. It lies within the Snowdonia National Park, but just to the east of the main A470, and consequently many visitors pass the village by. Its population is .... References Geologic formations of Wales Ordovician Syste ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Graig Goch
Graig Goch is a 586m high hill in the Gwynedd area in Wales and lying within Snowdonia National Park. The hill falls within the communities of Llanfihangel-y-Pennant and Corris, the summit being located in the former. The hill takes the form of a NE-SW aligned ridge with a broad top which rise to subsidiary tops either side of the main summit. These are the 540m+ top of Mynydd Cedris (OS grid ref SH 707080) and the 504m top of Mynydd Rugog (OS grid ref SH 722092). The hill’s most notable feature is the large cliff which stretches the length of its northwestern face overlooking Tal-y-llyn, in part a major rock-slope failure. Geology The hill is formed from a succession of mudstones and siltstones laid down by turbidity currents during the Ordovician Period. The main ridge is developed in rocks of the Ceiswyn Formation assigned to the Ogwen Group and dating from around 457 to 454 million years ago. A near vertical cleavage is developed in the steeply southeasterly dipping ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Siltstones
Siltstone, also known as aleurolite, is a clastic sedimentary rock that is composed mostly of silt. It is a form of mudrock with a low clay mineral content, which can be distinguished from shale by its lack of fissility.Blatt ''et al.'' 1980, pp.381-382 Although its permeability and porosity is relatively low, siltstone is sometimes a tight gas reservoir rock, an unconventional reservoir for natural gas that requires hydraulic fracturing for economic gas production. Siltstone was prized in ancient Egypt for manufacturing statuary and cosmetic palettes. The siltstone quarried at Wadi Hammamat was a hard, fine-grained siltstone that resisted flaking and was almost ideal for such uses. Description There is not complete agreement on the definition of siltstone. One definition is that siltstone is mudrock (clastic sedimentary rock containing at least 50% clay and silt) in which at least 2/3 of the clay and silt fraction is composed of silt-sized particles. Silt is defined as gr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mudstone Formations
Mudstone, a type of mudrock, is a fine-grained sedimentary rock whose original constituents were clays or muds. Mudstone is distinguished from ''shale'' by its lack of fissility (parallel layering).Blatt, H., and R.J. Tracy, 1996, ''Petrology.'' New York, New York, W. H. Freeman, 2nd ed, 529 pp. The term ''mudstone'' is also used to describe carbonate rocks (limestone or dolomite) that are composed predominantly of carbonate mud. However, in most contexts, the term refers to siliciclastic mudstone, composed mostly of silicate minerals. The NASA Curiosity rover has found deposits of mudstone on Mars that contain organic substances such as propane, benzene and toluene. Definition There is not a single definition of mudstone that has gained general acceptance,Boggs 2006, p.143 though there is wide agreement that mudstones are fine-grained sedimentary rocks, composed mostly of silicate grains with a grain size less than . Individual grains this size are too small to be distinguishe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ordovician System Of Europe
The Ordovician ( ) is a geologic period and system, the second of six periods of the Paleozoic Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start of the Silurian Period Mya. The Ordovician, named after the Welsh tribe of the Ordovices, was defined by Charles Lapworth in 1879 to resolve a dispute between followers of Adam Sedgwick and Roderick Murchison, who were placing the same rock beds in North Wales in the Cambrian and Silurian systems, respectively. Lapworth recognized that the fossil fauna in the disputed strata were different from those of either the Cambrian or the Silurian systems, and placed them in a system of their own. The Ordovician received international approval in 1960 (forty years after Lapworth's death), when it was adopted as an official period of the Paleozoic Era by the International Geological Congress. Life continued to flourish during the Ordovician as it did in the earlier Cambrian Peri ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Geologic Formations Of Wales
Geology () is a branch of natural science concerned with Earth and other astronomical objects, the features or rocks of which it is composed, and the processes by which they change over time. Modern geology significantly overlaps all other Earth sciences, including hydrology, and so is treated as one major aspect of integrated Earth system science and planetary science. Geology describes the structure of the Earth on and beneath its surface, and the processes that have shaped that structure. It also provides tools to determine the relative and absolute ages of rocks found in a given location, and also to describe the histories of those rocks. By combining these tools, geologists are able to chronicle the geological history of the Earth as a whole, and also to demonstrate the age of the Earth. Geology provides the primary evidence for plate tectonics, the evolutionary history of life, and the Earth's past climates. Geologists broadly study the properties and processes of Eart ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dinas Mawddwy
Dinas Mawddwy () is a village in the community of Mawddwy in south-east Gwynedd, north Wales. It lies within the Snowdonia National Park, but just to the east of the main A470, and consequently many visitors pass the village by. Its population is roughly 600. The village marks the junction of the unclassified road to Llanuwchllyn which climbs up through the mountains to cross Bwlch y Groes at its highest point, the second highest road pass in Wales. This minor road also provides the closest access to the mountain Aran Fawddwy and is the nearest settlement to Craig Cywarch. Geography Dinas Mawddwy stands at the confluence of three rivers. The Afon Cywarch flows from the mountains to the north and the Afon Cerist flows from the west, both joining the River Dyfi here. The Dyfi flows south to Cemmaes Road where it turns west to head past Machynlleth to the Irish Sea. The mountains to the north are the Aran Fawddwy range of high, rocky peaks. To the south and the west stand the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Trilobites
Trilobites (; meaning "three lobes") are extinct marine arthropods that form the class Trilobita. Trilobites form one of the earliest-known groups of arthropods. The first appearance of trilobites in the fossil record defines the base of the Atdabanian stage of the Early Cambrian period () and they flourished throughout the lower Paleozoic before slipping into a long decline, when, during the Devonian, all trilobite orders except the Proetida died out. The last extant trilobites finally disappeared in the mass extinction at the end of the Permian about 252 million years ago. Trilobites were among the most successful of all early animals, existing in oceans for almost 270 million years, with over 22,000 species having been described. By the time trilobites first appeared in the fossil record, they were already highly diversified and geographically dispersed. Because trilobites had wide diversity and an easily fossilized exoskeleton, they left an extensive fossil record. The stud ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
British Geological Survey
The British Geological Survey (BGS) is a partly publicly funded body which aims to advance geoscientific knowledge of the United Kingdom landmass and its continental shelf by means of systematic surveying, monitoring and research. The BGS headquarters are in Keyworth, Nottinghamshire, England. Its other centres are located in Edinburgh, Wallingford, Cardiff and London. The current motto of the BGS is: ''Gateway to the Earth''. History and previous names The Geological Survey was founded in 1835 by the Board of Ordnance as the Ordnance Geological Survey, under Henry De la Beche. This was the world's first national geological survey. It remained a branch of the Ordnance Survey for many years. In 1965, it was merged with the Geological Museum and Overseas Geological Surveys, under the name of Institute of Geological Sciences. On 1 January 1984, the institute was renamed the British Geological Survey (and often referred to as the BGS), a name still carried today. Competenc ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tywyn
Tywyn (Welsh: ; in English often ), formerly spelled Towyn, is a town, community, and seaside resort on the Cardigan Bay coast of southern Gwynedd, Wales. It was previously in the historic county of Merionethshire. It is famous as the location of the Cadfan Stone, a stone cross with the earliest known example of written Welsh, and the home of the Talyllyn Railway. Toponymy The name derives from the Welsh ''tywyn'' ("beach, seashore, sand-dune"): extensive sand dunes lie to the north and south of the town. In Middle Welsh, the spelling was generally ''Tywyn''. In the Early Modern period, however, the spelling ''Towyn'' became common in Welsh in order to reflect a slight change in pronunciation at that time. That also came to be the usual spelling in English up to the latter part of the twentieth century. The modern spelling ''Tywyn'' better reflects the current pronunciation in modern Welsh as spoken in north Wales. With the standardisation of the orthography of the Welsh ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cardigan Bay
Cardigan Bay ( cy, Bae Ceredigion) is a large inlet of the Irish Sea, indenting the west coast of Wales between Bardsey Island, Gwynedd in the north, and Strumble Head, Pembrokeshire at its southern end. It is the largest bay in Wales. Geography Cardigan Bay has numerous beaches, and marine life. Much of the coast surrounding the bay is fertile farmland, dotted with towns and seaside resorts such as Fishguard Fishguard ( cy, Abergwaun, meaning "Mouth of the River Gwaun") is a coastal town in Pembrokeshire, Wales, with a population of 3,419 in 2011; the community of Fishguard and Goodwick had a population of 5,407. Modern Fishguard consists of two p ..., New Quay, Aberaeron, Llanon, Aberystwyth, Borth, Aberdyfi, Tywyn, Barmouth, Porthmadog, Criccieth and Pwllheli on the Cambrian Coast. Smaller coastal villages include Cwmtydu, Nanternis and Llangrannog. Major rivers flowing into the bay include the Afon Glaslyn, Glaslyn, River Mawddach, Mawddach, River Dysynni, Dysynni, Ri ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bala Lake
Bala Lake ( cy, Llyn Tegid ) is a large freshwater glacial lake in Gwynedd, Wales. The River Dee, which has its source on the slopes of Dduallt in the mountains of Snowdonia, feeds the long by wide lake. It was the largest natural body of water in Wales before its level was raised by Thomas Telford to provide water for the Ellesmere Canal (later Llangollen Canal). The town of Bala, which was once an important centre for the North Wales woollen trade, is located on the north-eastern end of the lake. The narrow gauge Bala Lake Railway, between the town and Llanuwchllyn (whose name means "church llan'above uwch'the lake llyn'), runs along the lake's south-eastern shore using a section of former trackbed from the former Ruabon–Barmouth line. Toponyms Previous names Gerald of Wales records the lake in his 12th century ''Itinerarium Cambriae'' under the name ''Penmelesmere''. In his 1804 translation of Gerald's work, Sir Richard Colt Hoare states that the lake was a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tuffs
Tuff is a type of rock made of volcanic ash ejected from a vent during a volcanic eruption. Following ejection and deposition, the ash is lithified into a solid rock. Rock that contains greater than 75% ash is considered tuff, while rock containing 25% to 75% ash is described as tuffaceous (for example, ''tuffaceous sandstone''). Tuff composed of sandy volcanic material can be referred to as volcanic sandstone. Tuff is a relatively soft rock, so it has been used for construction since ancient times. Because it is common in Italy, the Romans used it often for construction. The Rapa Nui people used it to make most of the ''moai'' statues on Easter Island. Tuff can be classified as either igneous or sedimentary rock. It is usually studied in the context of igneous petrology, although it is sometimes described using sedimentological terms. Tuff is often erroneously called tufa in guidebooks and in television programmes. Volcanic ash The material that is expelled in a volcanic e ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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