Editing Geography of Saint Helena (section)

===Geology ===
[[File:Saint Helena Island.jpg|thumb|Saint Helena Island as seen from space.]]
[[File:SaintHelena2021OSM.png|thumb|Enlargeable, detailed map of Saint Helena.]]

St. Helena exists because of the [[St. Helena hotspot]] which began to produce basaltic lava about 145 million years ago when it was near the [[Divergent boundary|constructive plate margin]] of the [[Mid-Atlantic Ridge]]. The movement of the [[African Plate]] away from the hotspot has left the chain of the St. Helena [[seamounts]], which may connect with the [[Cameroon Volcanic Line]]. St. Helena, the most south westerly point on the chain, is close to the plate margin, but the last volcanic eruptions occurred about 7 million years ago.

The first investigations of St. Helena geology were made when [[Charles Darwin]] visited the island on the voyage of [[H.M.S. Beagle]] in July 1836. He "used the observations on St Helena to formulate an intermediate hypothesis (published in 1844 in his book "Geological Observations on the volcanic islands and parts of South America visited during the Voyage of H.M.S. "Beagle") - volcanoes rise by slow, gradual and episodic events".<ref>David Bressan in [[Scientific American]] July 8, 2013, "8, July 1836: Darwin on St Helena and the Birth of a Volcano"</ref>

====Geological features====
The Barn is a capping of younger lavas upon weaker rocks. The Barn features cliffs on the side that faces the sea. It overlooks the pyroclasts and weak flows of Turk's Cap Valley to the south.

Taking their names from the story of [[Lot (Bible)|Lot]] in the Book of Genesis, "Lot" and "Lot's Wife" are two solitary pillars of rock topping two valleys near Sandy Bay.  The pillars are [[phonolitic]] [[intrusion]]s, which are more resistant to erosion than surrounding volcanic features which have, in time, eroded away.<ref>web|url=http://www.btinternet.com/~sa_sa/st_helena/st_helena_geology.html; The Geology of Saint Helena Island, Reginald A. Daly,Proceedings of the American Academy of Arts and Sciences,Vol. 62, No. 2 (Mar., 1927), pp. 31-92</ref>