Editing Barra (section)

== Geology ==
In common with the rest of the [[Western Isles]], Barra is formed from the oldest rocks in Britain, the [[Lewisian gneiss]], which dates from the [[Archean|Archaean]] eon. Some of the gneiss in the east of the island is noted as being [[pyroxene]]-bearing. Layered textures or [[Foliation (geology)|foliation]] in this [[metamorphic rock]] is typically around 30° to the east or northeast. [[Palaeoproterozoic]] age [[diorite|metadiorites]] and [[tonalite|metatonalites]] forming a part of the East Barra Meta-igneous Complex occur around [[Castlebay]] as they do on the neighbouring islands of [[Vatersay]] and [[Flodday, Sound of Barra|Flodday]]. A few [[mafic|metabasic]] [[dike (geology)|dykes]] intrude the gneiss in the east.<ref>{{cite web |title=Uist and Barra (South) |url=http://www.largeimages.bgs.ac.uk/iip/mapsportal.html?id=1002541 |website=BGS large map images |publisher=British Geological Survey |access-date=3 February 2020}}</ref>
The island is traversed by a handful of [[normal fault]]s running WNW-ESE and by west-facing [[thrust fault]]s bringing [[nappe]]s of gneiss from the east. [[Machair|Blown sand]] masks the bedrock around [[Borve, Barra|Borve]] and Allisdale as it does west of Barra airport. [[Peat]] deposits are mapped across Beinn Chliaid and Beinn Sgurabhal in the north of the island.<ref>{{cite web |title=Onshore Geoindex |url=https://mapapps2.bgs.ac.uk/geoindex/home.html |website=British Geological Survey |publisher=British Geological Survey |access-date=3 February 2020}}</ref>