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Edinburgh is said to have been built on seven hills, the first to be developed being the Castle Rock on which the Edinburgh castle sits. The development of the ‘New Town’in the 19th and 20th centuries saw Calton Hill followed by the other six hills being absorbed into the city. Most of these landforms are volcanic in origin and were subsequently affected by erosion, in particular owing their current form to glacial moulding.
The rocks underlying the Edinburgh area are typical example of those found in the geological heartland of Scotland, the Midland Valley. These belong to two main geological periods : the Devonian and the Carboniferous, covering a time span from about 415 million years ago to about 300 million years ago. The area has also been affected by Quaternary glacial activity (2 million years to present).
The oldest rocks in the Edinburgh area are Devonian age (ca. 415 M years old). Lower Devonian lavas including basalts, andesites and acid lavas and tuffs were produced by volcanoes.
Most of the rocks in the Edinburgh area are Carboniferous in age (365-290 m years old). The region was volcanically active during the early Carboniferous period, around 350 million years ago. The small volcanoes of Arthur’s Seat and Calton Hill, Castle Rock and West and East Craiglockhart were briefly active, laying down lava flows and volcanic ash. At various times subsequently, molten rock was also intruded between layers of sedimentary rock to form igneous sills of dolerite.
And what happened here million years ago?
Deep below the Earth´s surface molten magma around 1000°C is forced upwards, erupting in violent volcanic explosions which spread ash and lava across the region. Lava and ash produced by the vents of the volcano formed Calton Hill and after the last volcanic eruption this area was buried deep beneath hundreds of meters of mud, sand and silt.
At interval ice sheets (2.5 million years to 18,000 ago), hundreds of meters thick, cover the land. The weight of moving ice erodes the softer rocks and many millions of years later, glacier carved out and revealed many of the features you can see here (see the picture below).
Calton Hill is protected by Scottish Natural Heritage as a Site of Special Scientific Interests as part of the Arthur’s Seat volcano complex which also includes Edinburgh Castle Rock.
To the south lies Arthur’s Seat Volcano. The top part of the tilted volcano has been lost, and only fragments are left. The double summit is the remnant of the two central vents where the molten rock came to surface. The ridges of Whinny Hill, to the left, are the remaining part of the cone built up by lava flows from many eruptions, with layers of volcanic ash, or tuff, thrown out during explosive episodes. Each rocky ridge is formed of one lava flow, each grassy hollow hides tuff. Salisbury Crags is a quite different geological formation called a sill, formed where the molten rock did not reach the surface, but was squeezed between sedimentary layers.
Calton Hill lies to the east of Princes Street and gives access to the panoramic views. It is easily reached by bus or on foot from the city center.
Source: EDINBURGH & West Lothian - A Landscape Fashioned by Geology by David McAdam, Calton Hill – Geological Walk by Lothian and Borders RIGS Group
To claim this cache you must fulfill following tasks and send answers to my profile gogo CZ.
a) At the starting coordinates, take a look at the information board and find what happened here 285 million years ago.
b) Look in the western direction from the information board. Can you see the Castle Rock (under the Edinburgh castle)?
c) Look at the pictures in the listing. Try to explain (make your own theory) why Calton Hill lies just in the N-W direction from the Arthur’s Seat Volcano.
d) You can attach a photo with GPS on the hill - this task is OPTIONAL.
You can log the cache without my confirmation but you should send me answers before the logging. If there is anything wrong with your answers I will let you know. Logs without sending answers will be deleted.
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Coordinates are in the WGS84 datum