Geog 4

Most of the interior of the Northern Half of the island is taken up by large granite batholith, that domed the sandstone surface about 60 million years ago as Greenland sperated from Scotland during the creation of the Atlantic Ocean. The fractured sandstone and metamorphic schists have been weathered and eroded to expose the resistant granite.

A series of dykes 2-3m wide are exposed across Kildonan beach. At Drumadoon a sill has been exposed on the coast forming a 50m cliff.

The centre of the range comprises of Devonian granitre outcrop surrounded by Sulurian and Devonian andesite lava flow on each side. In turn intruded by igneous dykes arranged radially around the Cheviot Pluton. The formation of the hills was a result of the Avalana-Laurentia collision during the Ordivican which subducted Avalonian crust underneath the Laurentian plate. Creating some of the large caledonian igneous provinces.

A large batholith forming the core of the Sierra Nevada mountain range in California, USA. Exposed at the surface as granite. The batholith is composed of many individual masses of rock called plutons which formed underground during seperate epsiodes of magma intrusion millions of years before the Sierra itself started to rise. The extremley hot more buoyant plutons, intruded through denser rock and sediment. The batholith became exposed as tectonic forces initiated the formation of the basin and range geological province. As the mountain rose the forces of erosion eventually wore down the material which ahd covered the batholoth. The exposed parts became known as Sierra including half dome. Most of the batholiths remains below the surface.

Arthurs seat is an extinct volcano-the largets of a number which gave this region its shape. Thin layers of calcareous mud and sand were deposited in shallow tropical seas and lakes fringed by forested coastlines. The castle volacno erupted to form a cone, and a lava flow spread towards the east. The Arthur's Seat Volcano pushed through the sediments and early lavas. A cone of basaltic lavas and ash beds built up around the vents finally filling with intrusions.