NT2772 : Hutton's Section
taken 10 years ago, near to Edinburgh, Scotland
Although the Salisbury Crags form a familiar and prominent part of the view of Arthur's Seat, they are not, geologically speaking, related to the rest of Arthur's Seat at all!
They are the remnants of a sill of analcime-dolerite, formerly termed teschenite, which was intruded deep underground into the sandstones which underlie the Arthur's Seat volcano, long after the volcano had become extinct. Later again, earth movements tilted the whole structure so that the sill, like the lava flows that make up the volcano, now dips at 25º towards the east. The exposed scarp is up to 46 metres high, but it was quarried from about 200 years ago, and in places the present line of the scarp is well back from its original line.
The slope below is talus or scree, that is, loose pieces of rock which have fallen from the rock face and rolled downhill.
The crags, and especially the faces in the quarried parts, have been popular for climbing, but climbing is now controlled by the ranger service, and mostly takes place in the form of bouldering, resulting in trails of white chalk dust across the quarry faces.
The broad path round the foot of the crags is called the Radical Road. It is said to have been so named because it was paved by unemployed weavers after the 'Radical War' of 1820, a spell of strikes and unrest among artisans and skilled craftsmen seeking improved working conditions.
There is some doubt about the origin of the name Salisbury Crags. It has been suggested that they were named after the Earl of Salisbury, who accompanied King Edward III of England on an expedition to Scotland, but a more likely explanation is Lord Hailes' suggestion that is it from Anglo-Saxon and means a waste or dry settlement.
James Hutton (3 June 1726 - 26 March 1797), pioneer of the science of geology, was one of the extraordinary men of science and learning who flourished in Edinburgh in the latter part of the 18th century, in a period called the Scottish Enlightenment.
He was born in Edinburgh, and after briefly studying law, and then medicine, achieving an MD degree in Holland in 1749, he took up farming. In 1768 he turned to scientific investigation.
There are several localities known as 'Hutton's Locality', where Hutton observed features in the rocks that were counter to the prevailing view of the time.
Geologically, the conventional wisdom was that all the rocks on Earth had precipitated out of sea water at the time of the Flood. The part played by igneous rocks was entirely unrecognised.
On Arthur's Seat in Edinburgh Hutton noted that the sedimentary strata had been deformed, and that the deformation resulted from molten rock being intruded into the pre-existing rocks. The evidence for that is that the deformed sediments had been baked, both above and below, by the heat of the magma as it forced its way through the sediments. Therefore Hutton could demonstrate that the magma post-dated the sandstone, and that it had been molten or semi-molten when it was intruded.
In Glen Tilt, Hutton observed pink crystalline rock interfingering with grey schists, again showing that the crystalline material must have been intruded in a molten state into pre-existing rocks, and hence that not all rocks were of the same age, or formed by precipitation from sea water.
The Irish archbishop James Ussher (1581-1656) had counted back the generations listed in the Book of Genesis and calculated the time and date of the Creation as 'the entrance of the night preceding the 23rd day of October... the year before Christ 4004'; that is, around 6 pm on 22 October 4004 BC, by the Julian calendar.
At Siccar Point, on the Isle of Arran, and at Jedburgh, Hutton observed rock layers at a sharp angle to overlying horizontal sedimentary strata. He deduced that the underlying layers must have been deformed and tilted, and that for this to take place meant that the process of rock formation must have been going on for an inconceivable length of time.
These ideas were totally revolutionary when Hutton published his findings in a series of papers under the title 'Theory of the Earth', presented to the Royal Society of Edinburgh in the 1780s. The basis of his theory was that all geological phenomena could be explained by observable processes, and that these processes had been operating since time immemorial and would continue operating in all time to come.
Although fiercely opposed by the churches and by the geological establishment, Hutton's theory, termed uniformitarianism, is now accepted as the fundamental principle of the scientific study of geology.
- Grid Square
- NT2772, 480 images (more nearby 🔍)
- Anne Burgess (more nearby)
- Date Taken
- Sunday, 9 June, 2013 (more nearby)
- Monday, 10 June, 2013
- Subject Location
OSGB36: NT 2719 7283 [10m precision]
WGS84: 55:56.5786N 3:10.0371W
- Camera Location
- OSGB36: NT 2719 7283
- View Direction
- NORTH (about 0 degrees)