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34-519: The Glarus thrust crops out over a relatively large area in the cantons Glarus , St. Gallen and Graubünden , due to its horizontal orientation and the high local relief . Famous outcrops include those at Lochsite near Glarus (the town) and in a mountain cliff called Tschingelhörner between Elm and Flims (in the same cliff is a natural hole called the Martinsloch ). Thrust faults of this kind are not uncommon in many mountain chains around

68-668: A continuous line along the top edge with lines protruding down; outcrops have a continuous line around each area of bare rock. An outcrop example in California is the Vasquez Rocks , familiar from location shooting use in many films , composed of uplifted sandstone . Yana is another example of outcrops, located in Uttara Kannada district in Karnataka , India . Variscan orogeny The Variscan orogeny , or Hercynian orogeny ,

102-450: A full-scale reconstruction of the Glarus thrust. The first naturalist to examine the Glarus thrust was Hans Conrad Escher von der Linth (1767–1823). Escher von der Linth discovered that, contradictory to Steno's law of superposition , older rocks are on top of younger ones in certain outcrops in Glarus. His son Arnold Escher von der Linth (1807–1872), the first professor in geology at

136-563: A land mass, which has been named Gondwana (present day South America, Africa, Antarctica, Arabia , the Indian subcontinent , Zealandia and Australia), straddled the space between the South Pole and the Equator on one side of the globe. Off to the west were three other masses: Laurentia , Siberia and Baltica , located as if on the vertices of a triangle. To the south of them was a large archipelago,

170-632: A rare green mineral first discovered in the Vogtland district of Saxony in Germany, which is in the Variscan belt, has the same etymology.) Hercynian , on the other hand, derives from the Hercynian Forest . Both words were descriptive terms of strike directions observed by geologists in the field, variscan for southwest to northeast, hercynian for northwest to southeast. The variscan direction reflected

204-539: A record of relative changes within geologic strata . Accurate description, mapping, and sampling for laboratory analysis of outcrops made possible all of the geologic sciences and the development of fundamental geologic laws such as the law of superposition , the principle of original horizontality , principle of lateral continuity , and the principle of faunal succession . On Ordnance Survey maps in Great Britain , cliffs are distinguished from outcrops: cliffs have

238-590: A similar shift in meaning. Today, Hercynian is often used as a synonym for Variscan but is somewhat less used than the latter in the English speaking world. In the United States, it is used only for European orogenies; the contemporaneous and genetically linked mountain-building phases in the Appalachian Mountains have different names. The regional term Variscan underwent a further meaning shift since

272-668: A wide belt north of the Algarve and extending into the northernmost part the autonomous region of Andalusia and southern Extremadura . In the Czech Republic and southwestern Poland the Bohemian Massif is the eastern end of the unmodified Variscan belt of crustal deformation in Europe. Further Variscan developments to the southeast are partly hidden and overprinted by the Alpine orogeny . In

306-475: Is a visible exposure of bedrock or ancient superficial deposits on the surface of the Earth and other terrestrial planets . Outcrops do not cover the majority of the Earth's land surface because in most places the bedrock or superficial deposits are covered by soil and vegetation and cannot be seen or examined closely. However, in places where the overlying cover is removed through erosion or tectonic uplift ,

340-677: The Alps a Variscan core is built by Mercantour , Pelvoux , Belledonne , Montblanc and Aar Massif . Dinaric , Greek and Turkish mountain chains are the southeastern termination of the Variscan proper. The Variscan was contemporaneous with the Acadian and Alleghenian orogeny in the United States and Canada, responsible for forming the Ouachita and Appalachian Mountains . North American areas with Variscan foldbelts include New England , Nova Scotia and Newfoundland and Labrador . The Moroccan Meseta and

374-902: The Anti-Atlas in northwestern Africa show close relations to the Appalachian Mountains and used to form the eastern part of the Appalachian orogeny before the opening of the Atlantic Ocean in Jurassic times. 'Variscan' mountains in a broad chronological sense include the Urals , the Pamir , the Tian Shan and other Asian foldbelts. The Variscan orogeny involved a complicated heterogeneous assembly of different microplates and heterochronous collisions, making

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408-566: The ETH at Zürich , mapped the structure in more detail and concluded that it could be a huge thrust . At the time, most geologists still accepted the theory of geosynclines , which states that mountains are formed by vertical movements within the Earth's crust . Escher von der Linth had therefore difficulty with explaining the size of the thrust fault. In 1848, he invited the British geologist Roderick Murchison , an international authority, to come and look at

442-523: The Rhine Massif (Ardennes, Eifel , Hunsrück , Taunus and other regions on both sides of Middle Rhine Valley), the Black Forest and Harz Mountains remain as testimony. In southern Iberia it is marked by a classic strike-slip suture zone between very distinct suspect terranes, and clear evidence can be seen of ductile shearing between high-grade metamorphic rocks and lower grade sedimentary rocks in

476-558: The Surselva , Linthtal and Walensee . In the arena are a number of peaks higher than 3000 meters, such as Surenstock (its Romansh name is Piz Sardona , from which the name comes), Ringelspitz and Pizol . In 2006, the Swiss government made a first proposal to declare the region World Heritage to the International Union for Conservation of Nature (IUCN). The IUCN then did not find

510-726: The terrane Avalonia , rifted off the north Gondwana margin in early Ordovician . By the end of the Silurian and in Early Devonian times, Baltica and Laurentia drifted towards each other, closing the Iapetus Ocean between them. They collided in the Caledonian orogeny and formed the Caledonide mountains of North America, Greenland , the British Isles and Norway . Seafloor spreading to

544-541: The 1960s. Geologists generally began to use it to characterize late Paleozoic fold-belts and orogenic phases having an age of approximately 380 to 280 Ma. Some publications use the term Variscan for fold belts of even younger age, deviating from the meaning as a term for the North American and European orogeny related to the Gondwana-Laurasia collision. The North American and European Variscan Belt includes

578-671: The British Isles, northern Germany, Scandinavia and western Russia). In late Devonian and in the Carboniferous the archipelago Armorica of southern Europe, which had rifted off Gondwana after Avalonia later in the Ordovician, was pushed into Avalonia, creating a second range, the North American/European Variscan, to the east of the Caledonide/Appalachian. The collision of Gondwana proper with Laurussia followed in

612-447: The Earth's soft asthenosphere causes horizontal forces within the crust . Presently, geologists explain the formation of most mountain chains by the convergent boundary evolving between tectonic plates accompanied by a subduction process in which the heavier plate dives beneath the less dense plate and sinks into the Earth's mantle . Outcrop An outcrop or rocky outcrop

646-423: The Earth's surface due to human excavations such as quarrying and building of transport routes. Outcrops allow direct observation and sampling of the bedrock in situ for geologic analysis and creating geologic maps . In situ measurements are critical for proper analysis of geological history and outcrops are therefore extremely important for understanding the geologic time scale of earth history. Some of

680-554: The Highlands are a thrust system. Swiss geologists Hans Schardt and Maurice Lugeon then discovered in 1893 that in western Switzerland, Jurassic rock layers are on top of younger molasse too, and argued that the structure of the Alps is a large stack of nappes , large sheets of rock that had been thrust on top of each other. At the turn of the century, Heim was also convinced of the new theory. He and other Swiss geologists now started mapping

714-586: The area to have an extraordinary or universal value and denied the proposal. The Swiss made a new, this time successful proposal in March 2008. The region was declared a World Heritage Site in July 2008, because "the area displays an exceptional example of mountain building through continental collision and features excellent geological sections through tectonic thrust." The American Museum of Natural History in New York exposes

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748-590: The direction of ancient fold belts cropping out throughout Germany and adjacent countries and the meaning shifted from direction to the fold belt proper. One of the pioneers in research on the Variscan fold belt was the German geologist Franz Kossmat , establishing a still valid division of the European Variscides in 1927. The other direction, Hercynian , for the direction of the Harz Mountains in Germany, saw

782-478: The early Carboniferous, when the Variscan belt was already in place and actively developing. By the end of the Carboniferous, Gondwana had united with Laurussia on its western end through northern South America and northwestern Africa. Siberia was approaching from the northeast, separated from Laurussia only by shallow waters. Collision with Siberia produced the Ural Mountains in the latest Paleozoic and completed

816-463: The exact reconstruction of the plate tectonic processes difficult. Plate convergence that caused the Caledonian orogeny in the Silurian continued to form the Variscan orogeny in the succeeding Devonian and Carboniferous Periods. Both orogenies resulted in the assembly of a super-continent, Pangaea , which was essentially complete by the end of the Carboniferous. In the Ordovician Period,

850-896: The formation of Pangaea. Eastern Laurussia was still divided from Gondwana by the Paleotethys Ocean. In the Triassic Period of the Mesozoic Era, animals could move without oceanic impediment from Siberia over the North Pole to Antarctica over the South Pole. In the Mesozoic Era, rifting and subsequent opening of the Atlantic split Pangaea. As a consequence, the Variscan Belt around the then periphery of Baltica ended up many hundreds of miles from

884-597: The idea of a thrust. One of them was Marcel Alexandre Bertrand (1847–1907), who interpreted the structure as a thrust in 1884, after reading Heims observations. Bertrand was familiar with the Faille du Midi ( Variscan orogeny ), a large thrust fault in the Belgian Ardennes . Meanwhile, British geologists began to recognize the nature of thrust faults in the Scottish Highlands . In 1883, Archibald Geikie accepted that

918-867: The mountains of Portugal and Spain ( Galicia , and Pyrenees ), southwestern Ireland (i.e. Munster ), Cornwall , Devon , Pembrokeshire , the Gower Peninsula and the Vale of Glamorgan . Its effects are present in France from Brittany , below the Paris Basin to the Ardennes , the Massif Central , the Vosges and Corsica . The Variscan Belt reappears in Sardinia in Italy and in Germany where

952-403: The nappes of Switzerland in more detail. From that moment on, geologists began recognizing large thrusts in many mountain chains around the world. However, it was still not understood where the huge forces that moved the nappes came from. Only with the arrival of plate tectonic theory in the 1950s an explanation was found. In plate tectonics, the horizontal movement of tectonic plates over

986-509: The rock may be exposed, or crop out . Such exposure will happen most frequently in areas where erosion is rapid and exceeds the weathering rate such as on steep hillsides, mountain ridges and tops, river banks, and tectonically active areas. In Finland , glacial erosion during the last glacial maximum (ca. 11000 BC), followed by scouring by sea waves, followed by isostatic uplift has produced many smooth coastal and littoral outcrops. Bedrock and superficial deposits may also be exposed at

1020-566: The south of Avalonia pushed the latter into north Laurentia and thrust up the northern Appalachian Mountains in the acadian phase of the Caledonian orogeny. Contemporaneously the Tornquist Sea between Avalonia and Baltica was entirely closed. Thus Avalonia formed the southern coast of the new continent Euramerica ( Laurussia , the Old Red Sandstone continent in present-day North America,

1054-600: The structure. Murchison was familiar with larger thrust faults in Scotland and agreed with Escher's interpretation. However, Escher himself felt insecure about his idea and when he published his observations in 1866 he instead interpreted the Glarus thrust as two large overturned narrow anticlines . This hypothesis was rather absurd, as he admitted himself in private. Escher's successor as professor at Zürich, Albert Heim (1849–1937), initially stuck to his predecessor's interpretation of two anticlines. However, some geologists favoured

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1088-468: The types of information that cannot be obtained except from bedrock outcrops or by precise drilling and coring operations, are structural geology features orientations (e.g. bedding planes, fold axes, foliation ), depositional features orientations (e.g. paleo-current directions, grading, facies changes), paleomagnetic orientations. Outcrops are also very important for understanding fossil assemblages, and paleo-environment, and evolution as they provide

1122-463: The world, but the Glarus thrust is a well accessible example and has as such played an important role in the development of geological knowledge on mountain building . For this reason the area in which the thrust is found was declared a geotope , a geologic UNESCO World Heritage Site , under the name "Swiss Tectonic Arena Sardona." The area of this "tectonic arena" encompasses 32,850 hectares of mainly mountainous landscape in 19 communities between

1156-581: Was a geologic mountain-building event caused by Late Paleozoic continental collision between Euramerica (Laurussia) and Gondwana to form the supercontinent of Pangaea . The name Variscan comes from the Medieval Latin name for the district Variscia , the home of a Germanic tribe, the Varisci ; Eduard Suess , professor of geology at the University of Vienna , coined the term in 1880. ( Variscite ,

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