Читать книгу Walking on Rum and the Small Isles. Rum, Eigg, Muck, Canna, Coll and Tiree онлайн

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The western hills, including Orval and Ard Nev, are predominantly composed of coarse-grained granites formed from magma that crystallised below the Earth’s surface. The Rum Cuillin is mostly composed of layers of pale, hard gabbro interspersed with brown, crumbly peridotite, rocks created from cooling magma at the base of the magma chamber, especially on Hallival and Askival. There are some outcrops of the pre-volcanic Lewisian gneiss near Dibidil in the south-east corner of the island, and extensive Torridonian sandstone is found in the north and east.

Basalt dikes are found on the north-west coast between Kilmory and Guirdil: erosion of the less-resistant rock into which they are intruded has left them exposed as natural walls. They tend to radiate out from a point in Glen Harris, which suggests that this was the centre of volcanic activity. Bloodstone Hill was formed by lava flowing away from this volcanic centre; gas bubbles in the rock filled with heated silica, which cooled to form green agate flecked with red, hence the name ‘bloodstone'.