What makes Edinburgh special? Many different factors make a city, but one key feature that most visitors to Edinburgh notice is the dramatic scenery of the city centre. This is a landscape of rocky crags, cliffs and steep slopes surrounded by lower, flatter ground. It is derived from a mix of different kinds of rock – sedimentary and igneous.
Sedimentary rocks form when sediment, such as sand and mud, collects in layers at the Earth’s surface. Lower layers get compressed and heated, gradually being cemented to form solid rock. This rock is quite easy to erode. It is also easy to carve and so makes a good building stone. Edinburgh’s Old and New Towns are built mostly of local sandstone from quarries such as Craigleith.
Sedimentary rocks found in the Lothian area include sandstone, mudstone and coal; they were mostly formed during the Carboniferous Period (359-299 million years ago). These rocks have been useful in different ways to people. As well as building material (sandstone), people in the past used sedimentary rocks to heat their homes (coal) and as a source of light and for transport (oil from West Lothian oil shale).
Most of Edinburgh’s older buildings are made of local sandstone, which was quarried at 20 locations within the city. This is usually a light-coloured or grey quartz sandstone. As demand increased in the 1800s, stone was brought from West Lothian, Fife and eventually further afield. From about 1900, several buildings were constructed using New Red Sandstone from the south-west of Scotland. This red-coloured sandstone was laid down in a desert environment.
Try this …
Are there sedimentary rocks under your school? Use the Geology of Britain viewer to find out.
Tip: Choose ‘Bedrock only’ in the Surface Geology box. Click on the map for a pop-up that tells you about the kind of rock and what age it is.
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Can you spot these different column designs in Edinburgh’s buildings? What are they called?
You can use Google Streetview to look for columns in Edinburgh’s New Town. Here are some examples:
1 Doric – The Royal Scottish Academy, Princes Street, Edinburgh EH2 2EL
2 Ionic – Scottish National Gallery, The Mound, Edinburgh EH2 2EL
3 Corinthian – St Andrew’s and St George’s Church, 13 George St, Edinburgh EH2 2PA
Igneous rocks form when molten rock (magma) cools underground or erupts at the surface as lava. Magma comes from deep beneath the surface, and is created when hot rock in the Earth’s mantle melts. The magma rises into the Earth’s crust, where it can get trapped underground or erupt from volcanoes as molten lava. As magma or lava cools, crystals form, and the interlocking crystals result in a tough rock that is resistant to erosion. Salisbury Crags, Arthur’s Seat and the other six hills of Edinburgh are all made of igneous rocks.
You can find the remains of several volcanoes around Edinburgh, including Edinburgh Castle Rock, Arthur’s Seat, Berwick Law and the Bass Rock. There are also areas where magma got trapped underground and cooled slowly to form a tough igneous rock called dolerite. You can find this at Salisbury Crags and Corstorphine Hill. This rock makes good road stone, because it resists erosion. It was quarried at Salisbury Crags and other locations around Edinburgh, and you can still see it used on Edinburgh’s roads.
Try this …
What are the nearest igneous rocks to your school? What age are they? Are they extrusive rocks (formed by surface volcanic eruptions) or intrusive rocks (formed by magma intrusion underground)?
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Can you find igneous rocks in Edinburgh’s roads? Why would igneous rocks be used to make roads?
Metamorphic rocks, the third category of rock, are formed when existing rock is buried or heated, so that the minerals that make up the rock change. Sometimes this simply involves the formation of some new crystals. But it can involve the complete reorganising of the chemistry and fabric of the rock into bands of new minerals.
Metamorphic rocks do not occur naturally in Edinburgh, but one particular metamorphic rock, slate, has been brought to the city from the Highlands. It makes an ideal roofing material because it is water-resistant, and splits into thin sheets that are light but strong.
The Edinburgh Geological Society is one of the UK’s foremost geological societies and aims to promote public interest in geology and advance geological knowledge. We organise varied programmes of excursions and lectures that bring together everyone from complete beginners to professional geologists interested in exploring the geology of Scotland and beyond. We publish the Edinburgh Geologist and excursion guides. Our geoconservation groups promote sites of local interest, publish leaflets and make sure that local geodiversity is understood and protected.
This web page is published by the Edinburgh Geological Society 2019 under a Creative Commons ‘Attribution Non-commercial’ (CC BY-NC) licence, which permits non-commercial reuse provided the original work is properly cited.