Editing Islands of the Clyde (section)

== Geology and geography ==
[[File:Firthofclydemap.png|thumb|The [[Firth of Clyde]]]]

The [[Highland Boundary Fault]] runs past Bute and through the northern part of Arran. Therefore, from a geological perspective, some of the islands are in the Highlands and some in the [[Central Lowlands]].<ref>Gillen (2003) p. 28</ref> As a result of Arran's geological similarity to Scotland, it is sometimes referred to as "Scotland in miniature" and the island is a popular destination for [[geologist]]s. They come to Arran to study its [[igneous rock|intrusive igneous landforms]], such as [[Sill (geology)|sill]]s and [[Dike (geology)|dyke]]s, as well as its [[sedimentary]] and metasedimentary rocks, which  range widely in age.<ref name= McK300>McKirdy ''et al.'' (2007) pp. 297- 301</ref> Visiting in 1787, the geologist [[James Hutton]] found his first example of an [[Hutton's Unconformity|unconformity]] there. The spot where he discovered it is one of the most famous places in the history of the study of geology.<ref name=monty>{{cite web|url=http://nagt.org/files/nagt/jge/abstracts/Montgomery_v51n5.pdf |title=Siccar Point and Teaching the History of Geology |access-date=26 March 2008 |last=Montgomery |first=Keith |year=2003 |publisher=University of Wisconsin }}</ref><ref name=Waymarking>{{cite web|url=http://www.waymarking.com/waymarks/WM3F65 |title=Hutton's Unconformity - Lochranza, Isle of Arran, UK - Places of Geologic Significance on Waymarking.com |publisher=Waymarking.com| access-date=20 October 2008}}</ref> The group of weakly metamorphosed rocks that form the [[Highland Boundary Fault#Highland Border Complex|Highland Border Complex]] lie discontinuously along the Highland Boundary Fault. One of the most prominent exposures is along Loch Fad on Bute.<ref>Gillen (2003) pp. 89–90</ref> [[Ailsa Craig]], which lies some {{convert|25|km|mi}} south of Arran, has been quarried for a rare type of [[granite|micro-granite]] containing [[riebeckite]], known as "Ailsite". It is used by [[Kays of Scotland]] to make [[curling]] stones. (As of 2004, 60 to 70% of all curling stones in use globally were made from granite quarried on the island.)<ref>Roch, John (27 October 2004) [https://web.archive.org/web/20041102011535/http://news.nationalgeographic.com/news/2004/10/1027_041027_curling_stones.html "Puffins Return to Scottish Island Famous for Curling Stones"]. National Geographic News. Retrieved 29 August 2010</ref>

Like the rest of Scotland, the Firth of Clyde was covered by ice sheets during the [[Pleistocene]] [[ice ages]], and the landscape has been much affected by [[glaciation]].<ref>Gillen (2003) pp. 174–86</ref> Back then, Arran's highest peaks may have been [[nunatak]]s.<ref>McKirdy ''et al.'' (2007) pp. 297- 301.</ref> Sea-level changes and the [[isostasy|isostatic]] rise of land after the last retreat of the ice created clifflines behind [[raised beach]]es, which are a prominent feature of the entire coastline. The action of these forces has made charting the [[Quaternary glaciation|post glacial]] coastlines a complex task.<ref>McKirdy ''et al.'' (2007) p. 28.</ref><ref>Ritchie, W. [https://archive.today/20120910123631/http://www.snh.org.uk/pubs/detail.asp?id=1291 "Beaches of Cowal, Bute & Arran"] (1975) Scottish Natural Heritage. (Originally published by the Countryside Commission for Scotland). pp. 6–9</ref>

The various soil types on the islands reflect their diverse geology. Bute has the most productive land, and it has a pattern of deposits that is typical of the southwest of Scotland. In the eroded valleys, there is a mixture of [[boulder clay]] and other glacial deposits. Elsewhere, especially to the south and west, there are raised beach- and marine deposits, which in some places, such as Stravanan, result in a [[machair]] landscape inland from the sandy bays.<ref>[http://www.bute-gateway.org/background.html "Bute's Geology & Geomorphology"] Bute-gateway.org. Retrieved 20 January 2011.</ref><ref>[http://www.scapetrust.org/pdf/Clyde_Bute/Bute_map6.pdf "Bute Map 6: Garroch Head to Stravannan Bay"] {{Webarchive|url=https://web.archive.org/web/20110728002227/http://www.scapetrust.org/pdf/Clyde_Bute/Bute_map6.pdf |date=28 July 2011 }} (pdf) scapetrust.org. Retrieved 20 January 2011.</ref>

The Firth of Clyde, in which these islands lie, is north of the Irish Sea and has numerous branching inlets. Some of those inlets, including [[Loch Goil]], [[Loch Long]], [[Gare Loch]], [[Loch Fyne]], and the estuary of the [[River Clyde]], have their own substantial features. In places, the effect of glaciation on the seabed is pronounced. For example, the Firth is {{convert|320|m|ft}} deep between Arran and Bute, even though they are only {{convert|8|km|mi}} apart.<ref>Gillen (2003) p. 177</ref> The islands all stand exposed to wind and tide. Various [[lighthouse]]s, such as those on Ailsa Craig, [[Pladda]], and [[Davaar Island|Davaar]], act as an aid to navigation.<ref>[http://www.nlb.org.uk/LighthouseLibrary/Main/ "Lighthouse Library"] Northern Lighthouse Board. Retrieved 14 July 2007.</ref>