James Hutton (1726-1797) was one of the most celebrated thinkers of the Scottish Enlightenment, and is generally considered to be the first man to form a sensible theory of geology.
He was born into a middle-class home in Edinburgh and attended the city's High School (at that time located between Infirmary Street and The Pleasance), where he showed particular promise in mathematics and chemistry. At age 14 he began studying the humanities at Edinburgh University, but it was always clear that the young Hutton was far more interested in science. At age 18 he became a physician's assistant and attended lectures in medicine at the university. he went on to study medicine at the University of Paris and took the degree of doctor of medicine at Leyden in 1749. His thesis was on blood circulation.
Hutton returned to Edinburgh in 1750, but not to take up a doctor's practice. With his friend James Davie he conducted successful experiments in the production of sal ammoniac from soot. This was a crystalline form of ammonium chloride, used at that time in considerable quantities in dye works and in metalworking and until then only available by import from Egypt. Perfecting their technique, the two men set up in business and contracted the city's chimney sweeps to supply the basic raw material; the business prospered. Using some of the profits, Hutton purchased shops and houses in the city and rented them out, employing a factor to do so. He also inherited farmlands in Berwickshire which he tried to improve. It was on his farms that the young James Hutton developed an interest in agricultural improvement and in the study of the earth.
In 1753 Hutton confessed to a friend that he had "become very fond of studying the surface of the earth, and was looking with anxious curiosity into every pit or ditch or bed of a river that fell his way". Some of the geology he studied seemed to him to contradict the then-current theory of how and when the earth was formed, namely that all rocks had precipitated out of a single enormous flood. Hutton proposed that the centre of the earth was hot, and that this heat was the engine which drove the formation of new rocks, a process that had been going on for very much longer than had ever been imagined. He had seen Salisbury Crags on Arthur's Seat, which overlooked his house in Edinburgh, and noted that volcanic rock had intruded through sedimentary layers, and near Jedburgh in the Scottish Borders he found an eroding cliff face showing sedimentary layers tilted almost vertically, below a layer of conglomerate, with horizontal layers of sandstone above all. In Berwickshire he noted at Siccar Point on the coast more stratigraphical evidence that the earth was far, far older than anyone had previously guessed. Hutton reasoned there must have been innumerable cycles, each involving deposition on the seabed, uplift with tilting and erosion, followed by re-immersion, further deposition, and so on. Looking at the thickness of these rock layers and the time required by current geological processes, his inescapable conclusion was that the earth was many, many millions of years old.
Hutton's ideas were first printed in his Theory of the Earth in 1788. They received a very mixed reception, as may be imagined. He was not popular with many Kirk (Church of Scotland) ministers, some of whom thought his conclusions were essentially atheistic; their hostility led Hutton to a number of barbed comments, such as "the volcano was not created to scare superstitious minds and plunge them into fits of piety and devotion. It should be seen as the vent of a furnace." Some scientists of the day called his theory atheistic, some plainly ludicrous, and others failed to understand them at all, for although a highly gifted man his book is so densely and awkwardly worded that it is clear that writing was not his strongest suit. Yet to those who cared to make the effort it was clear that Hutton had revolutionised the study of geology and that he had been the first to understand the forces at work in the earth.
James Hutton died in his beloved Edinburgh in 1797, but his ideas were championed by Charles Lyell in the 1830s and reached a wide readership, including the young Charles Darwin who read them with enthusiasm on his voyage on the Beagle. Today James Hutton is seen as one of the truly great pioneers of modern science, and the founder of modern geology.