Editing Glastonbury Tor (section)

==Location and landscape==
[[File:Street and Glastonbury Tor.jpg|thumb|upright=1.25|left| Glastonbury Tor and [[Street, Somerset|Street]] seen through the mist, as viewed from Walton Hill]]

The Tor is in the middle of the Summerland Meadows, part of the [[Somerset Levels]],{{sfn|Siraut|Thacker|Williamson|2006a|}} rising to an elevation of {{convert|518|ft}}.<ref name=nhlesm/> The plain is reclaimed [[fen]] above which the Tor is clearly visible for miles around. It has been described as an island, but actually sits at the western end of a [[peninsula]] washed on three sides by the [[River Brue]].{{sfn|Hawkins|1989|p=69}}

The Tor is formed from rocks dating from the early [[Jurassic]] Period, namely varied layers of [[Lias Group]] strata. The uppermost of these, forming the Tor itself, are a succession of rocks assigned to the [[Bridport Sand Formation]]. These rocks sit upon strata forming the broader hill on which the Tor stands; the various layers of the [[Beacon Limestone Formation]] and the [[Dyrham Formation]].<ref name="bgs2">{{cite web|url=http://www.bgs.ac.uk/discoveringGeology/geologyOfBritain/viewer.html|title=Geology of Britain viewer &#124; British Geological Survey (BGS)|publisher=bgs.ac.uk|access-date=6 June 2014}}</ref><ref>{{cite web|title=Engineering Geology of British Rocks and Soils&nbsp;— Lias Group|url=http://nora.nerc.ac.uk/17270/1/OR12032.pdf|publisher=British Geological Survey|access-date=16 November 2013|page=2}}</ref> The Bridport Sands have acted as a [[caprock]], protecting the lower layers from erosion. 

The iron-rich waters of [[Chalice Well]], a [[Spring (hydrology)|spring]] at the base of the Tor, flow out as an artesian well impregnating the sandstone around it with [[iron oxide]]s that have reinforced it to produce the caprock.{{sfn|Rahtz|Watts|2003|p=20}} Iron-rich but oxygen-poor water in the aquifer carries dissolved [[Iron#Chemistry and compounds|iron (II) "ferrous" iron]], but as the water surfaces and its oxygen content rises, the oxidised [[Iron#Chemistry and compounds|iron (III) "ferric" iron]] drops out as insoluble "rusty" oxides that bind to the surrounding stone, hardening it.{{sfn|Mann|2011|p=17}}

The low-lying damp ground can produce a visual effect known as a [[Fata Morgana (mirage)|Fata Morgana]] when the Tor appears to rise out of the mist.{{sfn|Young|1807|p=302}} This [[optical phenomenon]] occurs because rays of light are strongly bent when they pass through air layers of different temperatures in a steep [[Inversion (meteorology)|thermal inversion]] where an [[atmospheric duct]] has formed.<ref>{{cite web|last=Young|first=Andrew|title=An Introduction to Mirages|url=http://mintaka.sdsu.edu/GF/mirages/mirintro.html|publisher=San Diego State University|access-date=5 July 2010}}</ref> The Italian term ''Fata Morgana'' is derived from the name of [[Morgan le Fay]], a powerful sorceress in [[Arthurian legend]].<ref>{{cite web|title=Morgan le Fay|url=http://d.lib.rochester.edu/camelot/theme/morgan|work=Camelot Project|publisher=University of Rochester|access-date=28 October 2013}}</ref>

===Terraces===
[[Image:Glastonbury Tor from north east showing terraces.jpg|thumb|Terraces on the Tor]]

The sides of the Tor have seven deep, roughly symmetrical terraces, or [[lynchet]]s. Their formation remains a mystery<ref>{{PastScape|mname=Earthworks Glastonbury Tor|mnumber=196702|access-date=27 October 2013}}</ref> with many possible explanations. They may have been formed as a result of natural differentiation of the layers of Lias stone and [[clay]] or used by farmers during the [[Middle Ages]] as [[Terrace (agriculture)|terraced hills]] to make ploughing for crops easier.{{sfn|Rahtz|Watts|2003|p=67}} Author Nicholas Mann questions this theory. If agriculture had been the reason for the creation of the terraces, it would be expected that the effort would be concentrated on the south side, where the sunny conditions would provide a good yield, but the terraces are equally deep on the northern side, which would provide little benefit. Additionally, none of the other slopes of the island have been terraced, even though the more sheltered locations would provide a greater return on the labour involved.{{sfn|Mann|1986|pp=32–33}}

[[File:Glastonbury-tor-ST5129638553.png|thumb|upright=1.0|LIDAR topography]]

Other explanations have been suggested for the terraces, including the construction of defensive ramparts.{{sfn|Vallins|2013|}} Iron Age hill forts including the nearby [[Cadbury Castle, Somerset|Cadbury Castle]] in Somerset show evidence of extensive [[fortification]] of their slopes. The normal form of ramparts is a bank and ditch, but there is no evidence of this arrangement on the Tor. South Cadbury, one of the most extensively fortified places in early Britain, had three concentric rings of banks and ditches supporting an {{convert|18|ha|adj=on|order=flip}} enclosure. By contrast, the Tor has seven rings and very little space on top for the safekeeping of a community.{{sfn|Mann|1986|p=32}} It has been suggested,{{By whom|date=January 2020}} that a defensive function may have been linked with [[Ponter's Ball Dyke]], a linear [[Earthworks (archaeology)|earthwork]] about {{convert|1|mile}} east of the Tor.<ref>{{Google maps|url=https://www.google.com/maps/place//@51.1437815,-2.6701305,14z|title=Ponter's Ball Dyke |access-date=20 January 2020}}</ref>{{sfn|Allcroft|1908|p=496}}<ref name=SHER23564/> It consists of an embankment with a ditch on the east side.<ref name=SHER23564>{{cite web|title=Ponters Ball (linear earthwork), Havyatt|url=http://www.somersetheritage.org.uk/record/23564|work=Somerset Historic Environment Record|publisher=South West Heritage Trust|year=2002|access-date=12 April 2011}}</ref> The purpose and provenance of the dyke are unclear. It is possible that it was part of a longer defensive barrier associated with [[New Ditch]], three miles to the south-west, which is built in a similar manner. It has been suggested by [[Ralegh Radford]] that it is part of a great Celtic sanctuary, probably 3rd century BC, while others, including [[Philip Rahtz]], date it to the post-Roman period and link it to the [[Dark Ages (historiography)|Dark Age]] occupation on Glastonbury Tor. The 1970 excavation suggests the 12th century or later.<ref>{{PastScape|mname=Ponters Ball|mnumber=196694|access-date=12 April 2011}}</ref> The historian [[Ronald Hutton]] also mentions the alternative possibility that the terraces are the remains of a medieval "spiral walkway" created for pilgrims to reach the church on the summit,{{sfn|MacLaran|Scott|2009}} similar to that at [[Whitby Abbey]].{{sfn|Hutton|2006|p=79}}

[[File:glastonbury tor (the final climb) arp.jpg|thumb|left|The last few yards of the concrete path up the Tor.]]

Another suggestion is that the terraces are the remains of a three-dimensional labyrinth,{{sfn|Ivakhiv|2001|p=135}} first proposed by Geoffrey Russell in 1968. He states that the classical [[labyrinth]] ([[Caerdroia]]), a design found all over the Neolithic world, can be easily transposed onto the Tor so that by walking around the terraces a person eventually reaches the top in the same pattern.{{sfn|Bowden-Pickstock|2009|p=107}}{{sfn|MacQueen|2005|p=106}} Evaluating this hypothesis is not easy. A labyrinth would very likely place the terraces in the Neolithic era,{{sfn|Mann|1986|p=24}} but given the amount of occupation since then, there may have been substantial modifications by farmers or monks, and conclusive excavations have not been carried out.{{sfn|Hutton|2006|p=79}} In a more recent book, Hutton writes that "the labyrinth does not seem to be an ancient sacred structure".{{sfn|Hutton|2013|p=354}}

[[File:Glastonbury_Tor,_View_From_Main_Path.jpg|thumb|right|alt=Imposing tower as viewed on the main approach|View from the main approach]]