Castle Rock, Edinburgh

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Castle Rock
Castle from Princes Street, Edinburgh.JPG
Castle Rock as seen from Princes Street
Elevation 130 m (430 ft)[1]
Prominence c. 80 m (260 ft)
Listing Tump
Location
Location Edinburgh, Scotland
Coordinates 55°56′55″N 3°12′03″W / 55.948611°N 3.200833°W / 55.948611; -3.200833Coordinates: 55°56′55″N 3°12′03″W / 55.948611°N 3.200833°W / 55.948611; -3.200833
Topo map OS Landranger 66
Geology
Type Crag and tail, volcanic plug
Age of rock ~350 million years
Climbing
First ascent Unknown

Castle Rock is a volcanic plug in the middle of Edinburgh upon which Edinburgh Castle sits. The rock is estimated to have risen some 350 million years ago during the lower Carboniferous period. It is the remains of a volcanic pipe which cut through the surrounding sedimentary rock before cooling to form very hard dolerite, a type of basalt. Subsequent glacial erosion was resisted by the dolerite, which protected the softer rock to the east, leaving a crag and tail formation.[2]

The summit of the castle rock is 130 metres (430 ft) above sea level, with rocky cliffs to the south, west and north, rearing up to 80 metres (260 ft) from the surrounding landscape.[1] This means that the only readily accessible route to the castle lies to the east, where the ridge slopes more gently. The defensive advantage of such a site is clear, but the geology of the rock also presents difficulties, since basalt is an extremely poor aquifer. Providing water to the Upper Ward of the castle was problematic, and despite the sinking of a 28-metre (92 ft) deep well, the water supply often ran out during drought or siege,[3] for example during the Lang Siege of 1573.[4]

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