Hutton’s Tercentenary

By John Lewington, RSGS Collections Team 

James Hutton

JAMES HUTTON was born on June 3, 1726, so this year is the tercentenary of his birth. What makes Hutton incredibly important was the contents of his book “Theory of the Earth”, published in 1788, but read to the Royal Society of Edinburgh in 1785. In the book he seeks to disprove the idea that the Earth was just over 6,000 years old, as had been accepted based on timings taken from a study of the Bible, and that it was in fact many millions of years old, which has been accepted as correct since his “Theory” was published.  We now put the age of the Earth as four and a half billion years old.  He has been described as “the Father of Modern Geology” (although the term ‘geology’ was not in use until after his death), a genius and a star of the Scottish Enlightenment. 

His “Theory” was based on the study of rock formations, the first on Arran, the second at Inchbonny, near Allar’s Mill in Jedburgh, and the third, and now world-famous, Siccar Point on the coast of Berwickshire, of what we now know refer to as “an unconformity”.  But what had brought this ageing gentleman, he was 59 years of age when the “Theory” was first heard, to this radical and indeed revolutionary conclusion? 

Hutton was the son of an Edinburgh merchant, William Hutton, who died when his son James was just three years old, leaving a widow, Sarah, and four children (James, Isabella, Jean and Sarah) who were well enough provided for.  James fell heir to two small farms in Berwickshire. After his early years attending the High School of Edinburgh, Hutton went to the University of Edinburgh aged just 14, to study ‘humanities’, although he became interested in chemistry and mathematics – a grounding in formulas and rules.    

However to support his family he became a solicitor’s apprentice, teaching him under Scots Law that reason was more important than precedent, but the law was not for him so he soon turned to medicine. 

Here he became friends with John Clerk of Eldin whose family were wealthy landowners who mined coal in Midlothian, and here can be seen the start of Hutton’s interest in geology. After three years studying medicine in Edinburgh he headed to Paris and then the University of Leiden where he completed his studies and was awarded his degree in 1749. His degree thesis was on the circulation of blood, however Hutton had no interest in practicing medicine so worked with a friend to manufacture ammonium chloride, from the soot of Edinburgh’s chimneys, to supply the dyeing industry.    

A scandal involving a relationship, which produced a child, drove Hutton from the city to his two farms, Slighhouses and Nether Monynut, north of Duns in Berwickshire.   At the time, Scottish agriculture was modernizing so before embarking on actual farming Hutton went on a tour of East Anglia and later the Low Countries to seek out best practice, ostensibly learning about farming but studying the soils and rocks.   It was on these sojourns that his ideas that rocks were composed of animal, vegetable and mineral fragments of more ancient formation began to develop. 

Slighhouses farm was about 100m above sea level and potentially decent arable land, whereas Nether Monynut was 300 m above sea level - a hill farm with poor stony soil.   To both, Hutton applied his new learnings on agriculture in order to make a living from his land – making friends with the Dunglass family, which would later make an impression on rather more than Hutton. As a break from farming, after ten years he went travelling in the Highlands, as usual interested in geology.    

Hutton’s interests widened to include weather and climate, fertility and fertiliser components and how the studies of light, heat and the chemistry of the soil operated together to support life. Surely a model Geographer! All the while, Hutton’s ideas and knowledge of the Earth and its surface developed. Soil he decided was formed from the erosion of the bare rock, of which the planet was formed, but that soil too would be eroded. Thus the “rock cycle” came into understanding. 

In time, using this widely accumulated knowledge, he had turned his farms into reasonable successes so he returned to Edinburgh in December 1767, where he became involved in the construction of the Forth and Clyde Canal.  He built a house at St. John’s Hill facing Salisbury Crags, today marked by a monument to its most famous resident and became involved in driving forward the Scottish Enlightenment. 

Hutton’s journeys to prove his Theory of the Earth took him to Glen Tilt, near Blair Atholl with the purpose of demonstrating that granite was a young, igneous rock and not of ancient origin.  He had such a thorough knowledge of the geology of the British Isles he estimated accurately where to look and found exposed on the River Tilt the contact point between granite and its surrounding rock.  The granite had broken the edges of the surrounding marble and penetrated deeply into it – proving it was both intrusive and younger than the surrounding rock and not of ancient origin. 

The following summer he journeyed south-west to examine the granite of Galloway and its junction with the older sedimentary rocks of the Southern Uplands, then to Arran to study “the nature of granite and the connection of it with the contiguous strata”, observing the power of the sea in eroding whole land-masses.  Later that year, he made a chance, but important, discovery whilst visiting his friend John Davidson of Stewartfield near Jedburgh in the Scottish Borders.  In the exposed sheer banks of the River Jed, across the water from Allars Mill, he noticed the sedimentary sandstone rock-layers lying horizontally over vertical layers of greywackes (and shale), with a thin layer between them of a conglomeration of material from the lower rock-layers of greywackes. The significance of this (now known as an unconformity), was the two different rock layers lying at angles and not parallel to each other. 

Hutton deduced that the greywacke and shale, having been deposited on the sea bed as muds and clays, were than physically folded and elevated above the surface of the sea. This was followed by exposure to erosion, which removed the curve at the apex of the fold, leaving the vertical layers, before the land sank to be re-submerged by the sea. A second phase of sedimentation and compaction of sands, took place on the ocean floor before a second elevation to form a new land-mass took place. This process could only have been possible given a gigantic timescale, proving Hutton’s proposition of the ancient age of the Earth. 

Hutton typically sought verification of this observation through other examples so the following year, he made a journey by boat along the foot of the Berwickshire cliffs not far from his farm at Slighhouses.   “Having taken boat at Dunglass Burn, we set out to explore the coast”, he writes of his trip with his friends John Playfair and James Hall, to find further proof for his theory… and this they did “At Siccar Point”, he wrote “…we found a beautiful picture of this junction washed bare by the sea”.  They found the same junction of the same rock layers as those at Jedburgh; the horizontal sandstone rock-layers extensively eroded by the sea, exposing in parts, the vertical ends of the more resistant greywacke which are left protruding above it. 

Siccar Point validated and clarified the unconformity in Jedburgh, providing the defining proof for Hutton’s Theory of the Earth.   John Playfair, deeply moved by the significance of what they observed wrote later “The palpable evidence presented to us, of one of the most extraordinary and important facts in the natural history of the Earth, gave a reality and substance to those theoretical speculations, which, however probable, had never till now been authenticated by the testimony of the senses… What clearer evidence could we have had of the different formation of these rocks, and of the long interval which separated their formation, had we actually seen them emerging from the bosom of the deep?… The mind seemed to grow giddy by looking so far into the abyss of time”. 

Hutton’s ideas were not then universally accepted. He was seen as a “Plutonist”, believing that the interior of the Earth was hot and rock could emerge from it before being eroded and re-deposited, as opposed to the “Neptunists” who believed that the rocks of the Earth had emerged after a single enormous flood. Over the long time since The Theory of the Earth was published, Hutton has been shown to be absolutely correct.