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82-621: Sheffield Pike (possibly meaning "the peak above the sheep fold") is a fell in the English Lake District , a prominent intermediate top on one of the eastern ridges of Stybarrow Dodd . It separates and stands high above the Glencoyne and Glenridding valleys, on the eastern side of the Helvellyn range in the Eastern Fells and it looks down onto Ullswater . A broad ridge runs east from

164-582: A dense rock equivalent volume of as much as 1,140 cubic kilometres (270 cu mi). Remarkably, this appears to have had little impact on life. There was vigorous tectonic activity along northwest margin of Gondwana during the Floian, 478 Ma, recorded in the Central Iberian Zone of Spain. The activity reached as far as Turkey by the end of Ordovician. The opposite margin of Gondwana, in Australia, faced

246-587: A biogeographic affinity with Gondwana, and the Alborz margin of Gondwana was linked biogeographically to South China. Southeast Asia's fauna also maintained strong affinities to Gondwana's. North China was biogeographically connected to Laurentia and the Argentinian margin of Gondwana. A Celtic biogeographic province also existed, separate from the Laurentian and Baltican ones. However, tropical articulate brachiopods had

328-465: A burst of volcanic activity that deposited new silicate rocks, which draw CO 2 out of the air as they erode. Another possibility is that bryophytes and lichens, which colonized land in the middle to late Ordovician, may have increased weathering enough to draw down CO 2 levels. The drop in CO 2 selectively affected the shallow seas where most organisms lived. It has also been suggested that shielding of

410-632: A collective rather than a specific location or specific summit (the "s" in til fjells is an old genitive form remaining only in fixed expressions). According to Ivar Aasen, berg refers to cliffs, bedrock and notable elevations of the surface underpinned by bedrock; berg also refers to the substance of bedrock. For all practical purposes, fjell can be translated as "mountain" and the Norwegian language has no other commonly used word for mountain. In Sweden, fjäll generally refers to any mountain or upland high enough that forest will not naturally survive at

492-572: A community; thus the township of Cartmel Fell . In northern England, there is a Lord of the Fells – this ancient aristocratic title being associated with the Lords of Bowland . Groups of cairns are a common feature on many fells, often marking the summit – there are fine examples on Wild Boar Fell in Mallerstang Dale, Cumbria , and on Nine Standards Rigg just outside Kirkby Stephen , Cumbria. As

574-582: A deep embayment between Siberia and the Central Mongolian terranes . Most of the terranes of central Asia were part of an equatorial archipelago whose geometry is poorly constrained by the available evidence. The period was one of extensive, widespread tectonism and volcanism. However, orogenesis (mountain-building) was not primarily due to continent-continent collisions. Instead, mountains arose along active continental margins during accretion of arc terranes or ribbon microcontinents. Accretion of new crust

656-603: A distinct band around the Earth, and that the breakup of the parent body may have formed a ring system for a period of about 40 million years, with frequent falling debris causing these craters. The Ordovician was a time of calcite sea geochemistry in which low-magnesium calcite was the primary inorganic marine precipitate of calcium carbonate . Carbonate hardgrounds were thus very common, along with calcitic ooids , calcitic cements, and invertebrate faunas with dominantly calcitic skeletons. Biogenic aragonite , like that composing

738-464: A given landmass were severely affected. Tropical lifeforms were hit particularly hard in the first wave of extinction, while cool-water species were hit worst in the second pulse. Those species able to adapt to the changing conditions survived to fill the ecological niches left by the extinctions. For example, there is evidence the oceans became more deeply oxygenated during the glaciation, allowing unusual benthic organisms (Hirnantian fauna) to colonize

820-672: A more cosmopolitan distribution , with less diversity on different continents. During the Middle Ordovician, beta diversity began a significant decline as marine taxa began to disperse widely across space. Faunas become less provincial later in the Ordovician, partly due to the narrowing of the Iapetus Ocean, though they were still distinguishable into the late Ordovician. Trilobites in particular were rich and diverse, and experienced rapid diversification in many regions. Trilobites in

902-617: A mountain or moor -covered hill. The term is most often employed in Fennoscandia , Iceland , the Isle of Man , parts of northern England , and Scotland . The English word "fell" comes from Old Norse fell and fjall (both forms existed). It is cognate with Danish fjeld , Faroese fjall and fjøll , Icelandic fjall and fell , Norwegian fjell with dialects fjøll , fjødd , fjedd , fjedl , fjill , fil(l) , and fel , and Swedish fjäll , all referring to mountains rising above

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984-528: A set of island arcs. The accretion of these arcs to the eastern margin of Gondwana was responsible for the Benambran Orogeny of eastern Australia. Subduction also took place along what is now Argentina (Famatinian Orogeny) at 450 Ma. This involved significant back arc rifting. The interior of Gondwana was tectonically quiet until the Triassic . Towards the end of the period, Gondwana began to drift across

1066-403: A whole, strictly speaking refers to the summit; the slopes have names such as Tilberthwaite High Fell, Low Fell and Above Beck Fells. The word "fell" is also used in the names of various breeds of livestock , bred for life on the uplands, such as Rough Fell sheep, Fell terriers and Fell ponies . It is also found in many place names across the north of England, often attached to the name of

1148-498: A wide band around the western and northern sides of the Lake District. These sheets were formed by successive eruptions of mobile andesitic lava from shallow-sided volcanoes Between the individual lava flows may be beds of volcaniclastic sandstone, sedimentary deposits formed from the erosion of the volcanic rocks, and the map shows a small deposit of this near the summit of Sheffield Pike. Two minor igneous intrusions occur on

1230-468: A word limited to far-Northern dialects of Finnish and Karelian, is a loan from Sami , compare Proto-Sami *tuontër , South Sami doedtere , Northern Sami duottar , Inari Sami tuodâr "uplands, mountains, tundra", Kildin Sami tūndâr , which means "uplands, treeless mountain tract" and is cognate with Finnish tanner "hard ground". From this Sami word, the word " tundra " is borrowed, as well, through

1312-482: Is marked by a sudden abundance of hard substrate trace fossils such as Trypanites , Palaeosabella , Petroxestes and Osprioneides . Bioerosion became an important process, particularly in the thick calcitic skeletons of corals, bryozoans and brachiopods, and on the extensive carbonate hardgrounds that appear in abundance at this time. Green algae were common in the Late Cambrian (perhaps earlier) and in

1394-515: Is the case with Seathwaite Fell , for example, which would be the common grazing land used by the farmers of Seathwaite . The fellgate marks the road from a settlement onto the fell (see photograph for example), as is the case with the Seathwaite Fell. In other cases the reverse is true; for instance, the name of Wetherlam , in the Coniston Fells , though understood to refer to the mountain as

1476-513: The Cambrian , reef -forming corals appeared in the early Ordovician, including the earliest known octocorals , corresponding to an increase in the stability of carbonate and thus a new abundance of calcifying animals. Brachiopods surged in diversity, adapting to almost every type of marine environment. Even after GOBE, there is evidence suggesting that Ordovician brachiopods maintained elevated rates of speciation. Molluscs , which appeared during

1558-573: The Fairfield horseshoe , although it appears that, by coincidence, both Heron Pikes are exactly the same height.) Standing between two valleys and at the head of a third, the northern slopes of Sheffield Pike are drained by Glencoyne Beck, the southern slopes by Glenridding Beck, and the eastern side by Mossdale Beck. The undulating summit plateau of Sheffield Pike has marshy ground and small tarns in places between rocky outcrops, with rough grass and heather. A broad cairn on top of an outcrop of rock marks

1640-893: The Hirnantian . The Ashgill Epoch, the last epoch of the British Ordovician, is made of four ages: the Hirnantian Age, the Rawtheyan Age, the Cautleyan Age, and the Pusgillian Age. These ages make up the time period from c. 450 Ma to c. 443 Ma. The Rawtheyan, the second last of the Ashgill ages, was from c. 449 Ma to c. 445 Ma. It is in the Katian Age of the ICS's Geologic Time Scale . During

1722-732: The Rheic Ocean between Gondwana and Avalonia. Avalonia collided with Baltica towards the end of Ordovician. Other geographic features of the Ordovician world included the Tornquist Sea , which separated Avalonia from Baltica; the Aegir Ocean, which separated Baltica from Siberia; and an oceanic area between Siberia, Baltica, and Gondwana which expanded to become the Paleoasian Ocean in Carboniferous time. The Mongol-Okhotsk Ocean formed

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1804-579: The Russian language . Hills that are over 50 m high, but do not reach the tree line are referred to as vaara , while the general term for hills including hills of 50 m or less is mäki . In place names, however, tunturi , vaara and vuori are used inconsistently, e.g. Rukatunturi is technically a vaara , as it lacks alpine tundra. The term förfjäll (literally "fore-fell") is used in Sweden and Finland to denote mountainous zones lower and less dissected than

1886-493: The University of Bergen , Anders Lundeberg, has summed up the problem by stating, "There simply is no fixed and unambiguous definition of fjell ." Ivar Aasen defined fjell as a "tall berg ", primarily referring to a berg that reaches an altitude where trees do not grow, lower berg are referred to as "berg", ås (hill, ridge) or hei (moor, heathland). The fixed expression til fjells refers to mountains (or uplands) as

1968-627: The alpine tree line . In northern England, especially in the Lake District and in the Pennine Dales , the word "fell" originally referred to an area of uncultivated high ground used as common grazing usually on common land and above the timberline. Today, generally, "fell" refers to the mountains and hills of the Lake District and the Pennine Dales. Names that originally referred to grazing areas have been applied to these hilltops. This

2050-524: The endocerid cephalopods died out completely, except for possible rare Silurian forms. The Ordovician–Silurian extinction events may have been caused by an ice age that occurred at the end of the Ordovician Period, due to the expansion of the first terrestrial plants , as the end of the Late Ordovician was one of the coldest times in the last 600 million years of Earth's history. On the whole,

2132-506: The Cambrian or even the Ediacaran , became common and varied, especially bivalves , gastropods , and nautiloid cephalopods. Cephalopods diversified from shallow marine tropical environments to dominate almost all marine environments. Graptolites, which evolved in the preceding Cambrian period, thrived in the oceans. This includes the distinctive Nemagraptus gracilis graptolite fauna, which

2214-467: The Cambrian were succeeded by those that dominated the rest of the Paleozoic, such as articulate brachiopods, cephalopods , and crinoids . Articulate brachiopods, in particular, largely replaced trilobites in shelf communities. Their success epitomizes the greatly increased diversity of carbonate shell-secreting organisms in the Ordovician compared to the Cambrian. Ordovician geography had its effect on

2296-865: The Early Eocene Climatic Optimum. Carbon dioxide levels were very high at the Ordovician period's beginning. By the late Early Ordovician, the Earth cooled, giving way to a more temperate climate in the Middle Ordovician, with the Earth likely entering the Early Palaeozoic Ice Age during the Sandbian, and possibly as early as the Darriwilian or even the Floian. The Dapingian and Sandbian saw major humidification events evidenced by trace metal concentrations in Baltoscandia from this time. Evidence suggests that global temperatures rose briefly in

2378-518: The Early Ordovician, leveling off somewhat during the middle of the period. Locally, some regressions occurred, but the sea level rise continued in the beginning of the Late Ordovician. Sea levels fell steadily due to the cooling temperatures for about 3 million years leading up to the Hirnantian glaciation. During this icy stage, sea level seems to have risen and dropped somewhat. Despite much study,

2460-535: The Glencoyne and Glenridding valleys, rising high above both. Each flank is steep, the Glenridding Screes on the south side particularly so, and the upper slopes on both sides have substantial outcrops of steep crags . East of the summit is a second top named Heron Pike (612 metres / 2,008 ft), a rock turret backed by a couple of tiny tarns . (This should not be confused with the Heron Pike that forms part of

2542-543: The Great Ordovician Biodiversification Event) was no less remarkable; marine faunal genera increased fourfold, resulting in 12% of all known Phanerozoic marine fauna. Several animals also went through a miniaturization process, becoming much smaller than their Cambrian counterparts. Another change in the fauna was the strong increase in filter-feeding organisms. The trilobite, inarticulate brachiopod, archaeocyathid , and eocrinoid faunas of

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2624-474: The Greenside vein, and allowed deeper levels of the vein to be exploited. Over its lifetime the mine produced 2,400,000 tons of ore, finally closing in 1962. Considerable evidence of mining remains with extensive spoil heaps on the lower slopes of Sheffield Pike. Part of the mine buildings have been converted into a Youth Hostel . The mine was still working when Alfred Wainwright prepared his Pictorial Guide to

2706-498: The Hirnantian glaciation. As with North America and Europe , Gondwana was largely covered with shallow seas during the Ordovician. Shallow clear waters over continental shelves encouraged the growth of organisms that deposit calcium carbonates in their shells and hard parts. The Panthalassic Ocean covered much of the Northern Hemisphere , and other minor oceans included Proto-Tethys , Paleo-Tethys , Khanty Ocean , which

2788-426: The Lake District. The richest known lead vein of all was found crossing the south-east shoulder of Green Side, running in a north–south direction. Mining at Greenside Mine began during the eighteenth century by driving levels into the side of Green Side , but in 1853 a new level was begun from the present entrance to the mine at Lucy's Tongue beneath Nick Head. This was driven north and west for 16 years to intersect

2870-677: The Lakeland Fells . Sheffield Pike . This name is unexplained. Its first known use is by the Ordnance Survey in 1859. One possibility is that it reflects the influence of the Howard family at Greystoke, the Dukes of Norfolk, who also owned estates in Sheffield, though there is no direct evidence for this explanation. Another possibility is that the original name was something like Sheepfold Pike, and that

2952-623: The Ordovician System are referred to as coming from the Lower, Middle, or Upper part of the column. The Tremadoc corresponds to the ICS's Tremadocian. The Arenig corresponds to the Floian, all of the Dapingian and the early Darriwilian. The Llanvirn corresponds to the late Darriwilian. The Caradoc covers the Sandbian and the first half of the Katian. The Ashgill represents the second half of the Katian, plus

3034-463: The Ordovician of Wisconsin have been found with an age of about 460 million years ago, a time when the land flora most likely only consisted of plants similar to non-vascular bryophytes . Though stromatolites had declined from their peak in the Proterozoic, they continued to exist in localised settings. The Ordovician came to a close in a series of extinction events that, taken together, comprise

3116-421: The Ordovician were very different from their predecessors in the Cambrian. Many trilobites developed bizarre spines and nodules to defend against predators such as primitive eurypterids and nautiloids while other trilobites such as Aeglina prisca evolved to become swimming forms. Some trilobites even developed shovel-like snouts for ploughing through muddy sea bottoms. Another unusual clade of trilobites known as

3198-768: The Ordovician, the southern continents were assembled into Gondwana , which reached from north of the equator to the South Pole . The Panthalassic Ocean, centered in the northern hemisphere, covered over half the globe. At the start of the period, the continents of Laurentia (in present-day North America ), Siberia , and Baltica (present-day northern Europe) were separated from Gondwana by over 5,000 kilometres (3,100 mi) of ocean. These smaller continents were also sufficiently widely separated from each other to develop distinct communities of benthic organisms. The small continent of Avalonia had just rifted from Gondwana and began to move north towards Baltica and Laurentia, opening

3280-563: The Ordovician, when at least two volcanic island arcs collided with Laurentia to form the Appalachian Mountains . Laurentia was otherwise tectonically stable. An island arc accreted to South China during the period, while subduction along north China (Sulinheer) resulted in the emplacement of ophiolites. The ash fall of the Millburg/Big Bentonite bed, at about 454 Ma, was the largest in the last 590 million years. This had

3362-428: The Ordovician. The ice age was possibly not long-lasting. Oxygen isotopes in fossil brachiopods show its duration may have been only 0.5 to 1.5 million years. Other researchers (Page et al.) estimate more temperate conditions did not return until the late Silurian. The late Ordovician glaciation event was preceded by a fall in atmospheric carbon dioxide (from 7000 ppm to 4400 ppm). The dip may have been caused by

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3444-557: The Ordovician. Terrestrial plants probably evolved from green algae, first appearing as tiny non- vascular forms resembling liverworts , in the middle to late Ordovician. Fossil spores found in Ordovician sedimentary rock are typical of bryophytes. Among the first land fungi may have been arbuscular mycorrhiza fungi ( Glomerales ), playing a crucial role in facilitating the colonization of land by plants through mycorrhizal symbiosis , which makes mineral nutrients available to plant cells; such fossilized fungal hyphae and spores from

3526-592: The South Pole. This contributed to the Hibernian glaciation and the associated extinction event. The Ordovician meteor event is a proposed shower of meteors that occurred during the Middle Ordovician Epoch, about 467.5 ± 0.28 million years ago, due to the break-up of the L chondrite parent body. It is not associated with any major extinction event. A 2024 study found that craters from this event cluster in

3608-553: The Wuliuan, exploded in diversity during the Tremadocian, quickly becoming globally widespread. Several groups of endobiotic symbionts appeared in the Ordovician. In the Early Ordovician, trilobites were joined by many new types of organisms, including tabulate corals, strophomenid , rhynchonellid , and many new orthid brachiopods, bryozoans, planktonic graptolites and conodonts, and many types of molluscs and echinoderms, including

3690-507: The depths. These organisms were cosmopolitan in distribution and present at most latitudes. At the end of the second event, melting glaciers caused the sea level to rise and stabilise once more. The rebound of life's diversity with the permanent re-flooding of continental shelves at the onset of the Silurian saw increased biodiversity within the surviving Orders. Recovery was characterized by an unusual number of "Lazarus taxa", disappearing during

3772-415: The details remain unresolved. In particular, some researches interpret the fluctuations in sea level as pre-Hibernian glaciation, but sedimentary evidence of glaciation is lacking until the end of the period. There is evidence of glaciers during the Hirnantian on the land we now know as Africa and South America, which were near the South Pole at the time, facilitating the formation of the ice caps of

3854-532: 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 had in

3936-422: The diversity of fauna; Ordovician invertebrates displayed a very high degree of provincialism. The widely separated continents of Laurentia and Baltica, then positioned close to the tropics and boasting many shallow seas rich in life, developed distinct trilobite faunas from the trilobite fauna of Gondwana, and Gondwana developed distinct fauna in its tropical and temperature zones. The Tien Shan terrane maintained

4018-478: The diversity of life. Fish , the world's first true vertebrates , continued to evolve, and those with jaws may have first appeared late in the period. About 100 times as many meteorites struck the Earth per year during the Ordovician compared with today in a period known as the Ordovician meteor event . It has been theorized that this increase in impacts may originate from a ring system that formed around Earth at

4100-568: The earlier Cambrian Period, although the end of the period was marked by the Ordovician–Silurian extinction events . Invertebrates, namely molluscs and arthropods , dominated the oceans, with members of the latter group probably starting their establishment on land during this time, becoming fully established by the Devonian . The first land plants are known from this period. The Great Ordovician Biodiversification Event considerably increased

4182-552: The early Katian (Boda Event), depositing bioherms and radiating fauna across Europe. The early Katian also witnessed yet another humidification event. Further cooling during the Hirnantian, at the end of the Ordovician, led to the Late Ordovician glaciation . The Ordovician saw the highest sea levels of the Paleozoic, and the low relief of the continents led to many shelf deposits being formed under hundreds of metres of water. The sea level rose more or less continuously throughout

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4264-425: The extinction and reappearing well into the Silurian, which suggests that the taxa survived in small numbers in refugia . An alternate extinction hypothesis suggested that a ten-second gamma-ray burst could have destroyed the ozone layer and exposed terrestrial and marine surface-dwelling life to deadly ultraviolet radiation and initiated global cooling. Recent work considering the sequence stratigraphy of

4346-479: The fauna that emerged in the Ordovician were the template for the remainder of the Palaeozoic. The fauna was dominated by tiered communities of suspension feeders, mainly with short food chains. The ecological system reached a new grade of complexity far beyond that of the Cambrian fauna, which has persisted until the present day. Though less famous than the Cambrian explosion , the Ordovician radiation (also known as

4428-462: The fell proper. However, its more pronounced relief, its often higher amount of plateaux, and its coherent valley systems distinguishes the förfjäll also from the undulating hilly terrain ( bergkullsterräng ) and the plains with residual hills ( bergkullslätt ). Generally, the förfjäll do not surpass 1000 m ASL. As a geomorphic unit, the förfjäll extends across Sweden as a 650 km-long and 40 km to 80 km-broad belt from Dalarna in

4510-420: The fell. A basalt dyke of similar age to the volcanic rocks crosses Nick Head, and a later microgranite dyke of Devonian age runs near the top of the crags on the south side of the fell. This was probably associated with the later stages of the emplacement of the granite batholith which underlies the Lake District. Also associated with the granite batholith was the creation of mineral veins in parts of

4592-558: The first rugose corals appeared. The planktonic graptolites remained diverse, with the Diplograptina making their appearance. One of the earliest known armoured agnathan (" ostracoderm ") vertebrates, Arandaspis , dates from the Middle Ordovician. During the Middle Ordovician there was a large increase in the intensity and diversity of bioeroding organisms. This is known as the Ordovician Bioerosion Revolution. It

4674-486: The industrial nightmare that AW Wainwright complained of in his 1955 guide-book when the mine was still working, but the spoil heaps and some of the mine buildings are still there. Sheffield Pike can also be included in walks that take in Glenridding Dodd first, and then proceed either to Hart Side for a circuit of Glencoyne, or to Stybarrow Dodd and Helvellyn for a much longer horseshoe of Glenridding. Virtually all

4756-519: The most mountainous region of England, the Lake District is the area most closely associated with the sport of fell running , which takes its name from the fells of the district. "Fellwalking" is also the term used locally for the activity known in the rest of Great Britain as hillwalking . The word "fell" also enjoys limited use in Scotland; with, for example, the Campsie Fells in central Scotland, to

4838-616: The north-east of Glasgow. One of the most famous examples of the use of the word "fell" in Scotland is Goat Fell , the highest point on the Isle of Arran . Criffel and the nearby Long Fell in Galloway may be seen from the northern Lake District of England. Peel Fell in the Kielder Forest is on the border between the Scottish Borders to the north and the English county of Northumberland to

4920-411: The old Greenside Mine, is Open Access land. Ascents can begin from Glenridding village or from Glencoyne on the track behind Seldom Seen. In either case the route may use either of the two cols, east or west of Sheffield Pike. From Glenridding a track known as The Rake leads to the eastern col, or the track past the former Greenside Mine leads to Nick Head, the western col. The latter route is no longer

5002-505: The old, highly eroded, gently shaped terrain without glaciers, as found in Finland. They are round inselbergs rising from the otherwise flat surroundings. The tree line can be at a rather low altitude, such as 600 m in Enontekiö, owing to the high latitude. The fells in Finnish Lapland form vestiges of the Karelides mountains, formed two billion years ago. The term tunturi is also generally used to refer to treeless plains at high altitudes in far north regions. The term tunturi , originally

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5084-548: The ophiuroids ("brittle stars") and the first sea stars . Nevertheless, the arthropods remained abundant; all the Late Cambrian orders continued, and were joined by the new group Phacopida . The first evidence of land plants also appeared (see evolutionary history of life ). In the Middle Ordovician, the trilobite-dominated Early Ordovician communities were replaced by generally more mixed ecosystems, in which brachiopods, bryozoans, molluscs, cornulitids , tentaculitids and echinoderms all flourished, tabulate corals diversified and

5166-429: The pronunciation became corrupted, though again there is no evidence for this. These two explanations need not be mutually exclusive. Heron Pike was called Herring Pike in nineteenth century guide-books; both names seem equally unlikely. Probably a corruption of Old English erne , 'eagle', plus pike. Fell A fell (from Old Norse fell , fjall , "mountain" ) is a high and barren landscape feature, such as

5248-517: The ridge rises 91 m (299 ft) to the top of Sheffield Pike (675 m / 2,215 ft). Two lower ridges descend to the east of Sheffield Pike. The south-east shoulder, below Heron Pike, drops to a grassy col and then rises to Glenridding Dodd , the final top on the ridge before Ullswater. The north-east shoulder drops through Glencoyne Wood and past Moss Crag to Ullswater. The secluded little valley of Mossdale lies between these two lower ridges. Broadly oval in plan, Sheffield Pike separates

5330-410: The rocks of Sheffield Pike are part of the Borrowdale Volcanic Group , formed on the margin of an ancient continent during a period of intense volcanic activity, roughly 450 million years ago in the Ordovician Period. Within that group , nearly all the rocks on the fell belong to the Birker Fell Andesite Formation . These rocks are part of a thick succession of andesite sheets which now outcrop in

5412-400: The sea level dropped, and the vast shallow intra-continental Ordovician seas withdrew, which eliminated many ecological niches. When they returned, they carried diminished founder populations that lacked many whole families of organisms. They then withdrew again with the next pulse of glaciation, eliminating biological diversity with each change. Species limited to a single epicontinental sea on

5494-426: The sea, and about 49% of genera of fauna disappeared forever; brachiopods and bryozoans were greatly reduced, along with many trilobite , conodont and graptolite families. The most commonly accepted theory is that these events were triggered by the onset of cold conditions in the late Katian, followed by an ice age , in the Hirnantian faunal stage, that ended the long, stable greenhouse conditions typical of

5576-403: The second largest of the five major extinction events in Earth's history in terms of percentage of genera that became extinct. The only larger one was the Permian–Triassic extinction event . The extinctions occurred approximately 447–444 million years ago and mark the boundary between the Ordovician and the following Silurian Period. At that time all complex multicellular organisms lived in

5658-425: The shells of most molluscs , dissolved rapidly on the sea floor after death. Unlike Cambrian times, when calcite production was dominated by microbial and non-biological processes, animals (and macroalgae) became a dominant source of calcareous material in Ordovician deposits. The Early Ordovician climate was very hot, with intense greenhouse conditions and sea surface temperatures comparable to those during

5740-411: The south to Norrbotten in the north. Ordovician 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

5822-451: The south. In Norway, fjell , in common usage, is generally interpreted as simply a summit or area of greater altitude than a hill, which leads to a great deal of local variation in what is defined as a fjell . Fjell is mostly used about areas above the forest line . Distinct summits can be referred to as et fjell (a mountain). High plateaus ( vidde landscape) such as Hardangervidda are also regarded as fjell. Professor of geography at

5904-464: The southern and eastern sides of the fell better views may be had from other places. The cairn above Black Crag, or the top of Heron Pike, both give better views of Ullswater, and a well-used sheep path above the crags along the south side of the fell gives the best views of upper Glenridding, backed by Catstye Cam and Helvellyn . Most of the fell, above the Greenside Road and away from the site of

5986-446: The summit of Stybarrow Dodd , across a grassy saddle to the subsidiary top of White Stones, the summit of Green Side (795 m / 2,608 ft), where it turn to the north-east to Hart Side and Watermillock Common . The south-east shoulder of Green Side drops about 200 m (660 ft) down a slope which has been quarried and damaged by mining activities beneath to the depression of Nick Head (584 m / 1,916 ft). From here

6068-484: The summit. Two iron posts, one on Heron Pike and the other above Nick Head, are inscribed “H 1912” on one side and “M 1912” on the other. These mark the boundary between the Howard estate of Greystoke and the Marshall estate of Patterdale. The summit cairn also carries an old stone boundary marker with the H and M initials as well as a cryptic E.R. and the date 1830. The summit overlooks Glencoyne, but being set back from both

6150-484: The sun's rays from the proposed Ordovician ring system, which also caused the Ordovician meteor event , may have also led to the glaciation. As the southern supercontinent Gondwana drifted over the South Pole, ice caps formed on it, which have been detected in Upper Ordovician rock strata of North Africa and then-adjacent northeastern South America, which were south-polar locations at the time. As glaciers grew,

6232-643: The time. In 2008, the ICS erected a formal international system of subdivisions for the Ordovician Period and System. Pre-existing Baltoscandic, British, Siberian, North American, Australian, Chinese, Mediterranean and North- Gondwanan regional stratigraphic schemes are also used locally. The Ordovician Period in Britain was traditionally broken into Early (Tremadocian and Arenig ), Middle ( Llanvirn (subdivided into Abereiddian and Llandeilian) and Llandeilo ) and Late ( Caradoc and Ashgill) epochs. The corresponding rocks of

6314-672: The top, in effect a mountain tundra . Fjäll is primarily used to describe mountains in the Nordic countries, but also more generally to describe mountains shaped by massive ice sheets, primarily in Arctic and subarctic regions. There are however dialectal differences in usage, with comparatively low mountains or plateaus, sometimes tree-covered, in Bohuslän and Västergötland (e.g. Safjällets nationalpark  [ sv ] and Kynnefjäll  [ sv ] ) being referred to as "fjäll", similar to how

6396-399: The trinucleids developed a broad pitted margin around their head shields. Some trilobites such as Asaphus kowalewski evolved long eyestalks to assist in detecting predators whereas other trilobite eyes in contrast disappeared completely. Molecular clock analyses suggest that early arachnids started living on land by the end of the Ordovician. Although solitary corals date back to at least

6478-479: The word is used in Norwegian In Finnish, the mountains characteristic of the region of Lapland are called tunturi (plural: tunturit ), i.e. "fell". A tunturi is a hill high enough that its top is above the tree line and has alpine tundra . In Finnish, the geographical term vuori is used for mountains recently uplifted and with jagged terrain featuring permanent glaciers, while tunturi refers to

6560-532: Was closed off by the Late Ordovician, Iapetus Ocean , and the new Rheic Ocean . For most of the Late Ordovician life continued to flourish, but at and near the end of the period there were mass-extinction events that seriously affected conodonts and planktonic forms like graptolites . The trilobites Agnostida and Ptychopariida completely died out, and the Asaphida were much reduced. Brachiopods , bryozoans and echinoderms were also heavily affected, and

6642-543: Was distributed widely during peak sea levels in the Sandbian. Some new cystoids and crinoids appeared. It was long thought that the first true vertebrates (fish — Ostracoderms ) appeared in the Ordovician, but recent discoveries in China reveal that they probably originated in the Early Cambrian . The first gnathostome (jawed fish) may have appeared in the Late Ordovician epoch. Chitinozoans, which first appeared late in

6724-490: Was limited to the Iapetus margin of Laurentia; elsewhere, the pattern was of rifting in back-arc basins followed by remerger. This reflected episodic switching from extension to compression. The initiation of new subduction reflected a global reorganization of tectonic plates centered on the amalgamation of Gondwana. The Taconic orogeny , a major mountain-building episode, was well under way in Cambrian times. This continued into

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