Editing Benbecula (section)

== Geology ==
In common with the rest of the [[Western Isles]], Benbecula is formed from the oldest rocks in Britain, the [[Lewisian gneiss]] which dates from the [[Archean|Archaean]] eon.  Some around Ruabhal is described as [[Scourian orogeny|Scourian]] gneiss of ortho-[[amphibolite]] composition. The direction of inclination of layered textures or [[Foliation (geology)|foliation]] in this [[metamorphic rock]] varies across the island. [[Pseudotachylite]]s are developed in certain areas whilst [[dike (geology)|dykes]] and [[metasediment]]s are noted at various localities.<ref>{{cite web |title=Uist and Barra (South) |url=http://www.largeimages.bgs.ac.uk/iip/mapsportal.html?id=1002540 |website=BGS large map images |publisher=British Geological Survey |access-date=3 February 2020}}</ref>
The island is traversed by numerous [[normal fault]]s most of which run broadly NW-SE though others run NNW-SSE. The Outer Hebrides Thrust, a legacy of the [[Caledonian orogeny]], lies just off the eastern coast of the island and is seen on neighbouring [[Wiay, Uist|Wiay]] and Marigaidh.  Recent geological deposits include [[Machair|blown sand]] which is found around [[Balivanich]] and the airport and [[peat]] which though widespread in pockets, is found in larger quantities in the centre of the island.<ref>{{cite web |title=Onshore Geoindex |url=https://mapapps2.bgs.ac.uk/geoindex/home.html |website=British Geological Survey |access-date=3 February 2020}}</ref>