Glastonbury Tor: Difference between revisions - Wikipedia

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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}}