The cliff face of Salisbury Crags looks down on Edinburgh like a grand fortress. Situated in Holyrood Park, less than a half-mile (1 km) southeast of Princes Street, the Crags represent the glaciated remains of a Carboniferous sill, injected between sedimentary rocks which formed in a shallow sea some 340 million years ago. Glaciers sweeping outwards from the centre of Scotland have left a classic crag-and-tail, descending gently towards Arthur's Seat and Whinny Hill in the East. Salisbury Crags are of great significance in the development of modern geology. At Hutton's Section, the Edinburgh geologist James Hutton (1726-97) recognised that the rock now forming the Crags had been injected in a molten state. He was able to use this evidence to disprove the suggestion of the influential German, Abraham Werner, that all rocks had crystallised from a supposed primordial sea.
The hard dolerite which forms the crags was quarried for use as street cobble stones from the mid-17th C. on the authority of the Earls of Haddington who were hereditary keepers of Holyrood Park. However, the use of explosives from the beginning of the 19th C. increased the level of extraction to the point that the citizens of the city complained the landmark was beginning to disappear. Legal action was taken in 1819, but it was not until 1831 that the matter was resolved when the House of Lords decreed that no more stone should be removed. In 1845, Thomas Hamilton, the 9th Earl of Haddington (1780 - 1858), was paid the astronomical sum of £30,000 to relinquish his office as Keeper of the Royal Park.
Gentlemen of the Scottish Enlightenment would walk along a track around the base of the crags to gain inspiration. Around 1820 this was formed into a good road, known as the Radical Road, so-named after Sir Walter Scott (1771 - 1832) promoted its creation to provide jobs for unemployed radical weavers.