Hutton the Geologist
James Hutton’s early curiosity in geology was awakened by his farming activities coupled undoubtedly with his fascination for chemistry. As early as 1753, while in his mid-twenties and having commenced his farming career, in a letter to Sir John Hall, Hutton is quoted as saying:
“that he was 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 in his way”.
Hutton’s farms are on contrasting terrains – a fact unlikely to have missed his acute sense of observation. He was himself directly involved in clearing, cultivating and draining his lowland farm, providing him with an opportunity to observe the nature of soils and rocks. As a young farmer Playfair tells us, Hutton noticed that:
“a vast proportion of the present rocks are composed of materials afforded by the destruction of bodies, animal, vegetable and mineral, of more ancient formation”.
It is apparent from John Playfair’s biography that Hutton’s ideas began to come together to form a Theory of the Earth in 1760, and while he was still farming, he took a geological tour in 1764 of the north of Scotland with George Clerk-Maxwell.
The Testimony of the Rocks
To Hutton, rocks were:
‘God’s books wrote upon by God’s own finger’.
He consulted the testimony of rocks tirelessly and methodically. His extensive travels in Britain always had a geological purpose. Over a thirty year period of arduous travel and field observation, he was able to gain a detailed and remarkable knowledge of rocks and their distribution in the British Isles and so to formulate an understanding of its geological make-up. This was supplemented by extensive reading of explorers accounts of other countries and continents. Playfair records how Hutton:
‘never ceased to study the natural history of the globe, with a view to ascertaining the changes that have taken place on its surface and of discovering the causes by which they have been produced…’
He was driven in his sense of purpose and great hunger for knowledge such that he describes himself in a letter to George Clerk-Maxwell
‘Lord, pity the arse that’s clagged to a head that will hunt stones’ …‘I begin to be tired of speaking to stones and long for a fresh bit of mortality to make sauce for them’.
The Theory of the Earth
Playfair informs us that Hutton:
“…was in no haste to publish his theory; for he was one of those who are much more delighted with the contemplation of truth, than with the praise of having discovered it”.
It would take some 25 years to the first publication of an abstract to the Royal Society of Edinburgh in 1785, followed by full publication in 1788 and again in 1795.
The basic theme of Hutton’s theory is that the continents are repeatedly being wasted away (eroded), and simultaneously renewed by the operation of earth processes which are as evident now as they were in the past ie the erosion of rocks and soil and the transport of the eroded sediment to the sea; the uplift and subsidence of continents and volcanic activity are visible manifestations of the Earth operating as a machine fired by heat. An important aspect of the theory is that these processes took place over an indefinite space of time:
“…so that with respect to human observation, this world has neither a beginning nor an end”
This is Hutton’s own description of his theory from his abstract (1785):
“The solid parts of the present land appear in general, to have been composed of the productions of the sea, and of other materials similar to those now found upon the shores. Hence we find reason to conclude:
1st, That the land on which we rest is not simple and original, but that it is a composition, and had been formed by the operation of second causes.
2nd, That before the present land was made, there had subsisted a world composed of sea and land, in which were tides and currents, with such operations at the bottom of the sea as now take place. And,
Lastly, That while the present land was forming at the bottom of the ocean, the former land maintained plants and animals; at least the sea was then inhabited by animals, in a similar manner as it is at present.
Hence we are led to conclude, that the greater part of our land, if not the whole had been produced by operations natural to this globe; but that in order to make this land a permanent body, resisting the operations of the waters, two things had been required;
1st, The consolidation of masses formed by collections of loose or incoherent materials;
2ndly, The elevation of those consolidated masses from the bottom of the sea, the place where they were collected, to the stations in which they now remain above the level of the ocean.
Hutton realised that his theory raised two questions the answers to which would provide the proof for it, and in his abstract he continues:
“Thus the subject is considered as naturally divided into two branches, to be separately examined;
First, by what natural operation strata of loose materials had been formed into solid masses;
Secondly, By what power of nature the consolidated strata at the bottom of the sea had been transformed into land
What is remarkable and original about this “new and sublime conclusion” as Playfair described it, is that Hutton perceived the connection or continuity between these processes and on a global scale in terms of space, and a virtually infinite scale in terms of time; ie that rock and soil are eroded, that this eroded material is transported to the sea, where it is deposited, consolidated and elevated to form new land and that this cycle has taken place repeatedly during our planet’s past and will continue to do so into its future. Though the process is immeasurably slow in human terms, the surface of the earth has undergone transformation of gigantic proportions over a gigantic timescale – and continues to do so. Thus he famously concluded when he published his theory in full (1788):
“The result therefore of our present inquiry is that we find no vestige of a beginning – no prospect of an end”.
Evidence and Explanation
Having first presented his theory in public as an abstract in 1785 to the Royal Society of Edinburgh, Hutton set-out to prove it over the next three years on four epic journeys throughout Scotland with John Clerk of Eldin, who recorded their findings in skilfully executed geological drawings. Hutton was in his late fifties. He had utmost faith in the evidence of rocks and what they tell us:
“Let us therefore open the book of Nature and read in her records”.
He was able to prove his theory through accurate observation of them, and acute interpretation.
The surface of the Earth is composed mainly of rocks in layers. Detailed examination of what composed these rock layers led Hutton to conclude that they were the sediments derived from the weathering and erosion of an earlier surface. As he describes:
“From the top of the mountain to the shore of the sea, everything is in a state of change; the rock dissolving, breaking and decomposing for the purpose of becoming soil; the soil travelling along the surface of the earth, in its way to the shore; and the shore wearing and wasting by the agitation of the sea…”
In hardened and compacted rock-layers or strata (the word first coined by Hutton), he recognised particles of sand and grit identical to that which he had observed in soil and also on the sea shore. Likewise larger pieces of gravel and pebble. He realised that the collection of sediment at the bottom of the sea would rest in layers and also there must be an uplifting of these layered compressed sediments to bring them above the surface of the oceans to form dry land:
“We are led to conclude that all the strata of the earth have had their origin at the bottom of sea by collection of sand and gravel, of shells, and of earths and clays… consolidating those collections in various degrees and either elevating those consolidated masses or lowering the level of that sea. The spoils of wreck of an older world are everywhere visible in the present. The strata which now compose our continents are all formed out of strata more ancient than themselves”
Hutton recognised more than one cycle of erosion and uplift.
Hutton also needed to explain how rock layers beneath the surface of the ocean became uplifted so that they than became the surface of land. This he did through another leap of his imagination, that the Earth was a heat engine; that its internal heat fuses loose eroded debris into hard rock layers and raises them from the ocean floor to make new land. Hutton sought his evidence for the Earth’s internal heat from rock which had been melted and was once fluid. He found his evidence in igneous intrusions ie solidified melted rock (or magma) which has been forced under pressure from below, into fissures and cracks of other solid sedimentary rock layers, where it cools and solidifies. He gathered many examples of intrusions in his travels to prove his theory, eg the Salisbury Crags and the Castle rock – on his doorstep in Edinburgh.
As evidence of the uplifting power of the Earth’s heat engine, Hutton looked again to the nature of sedimentary rock layers and observed that they were often
“broken, twisted and counfounded, as might be expected from the operation of subterranean heat and violent expansion”.
Had there been no uplift they would have remained as they had been deposited at the bottom of the sea – in undisturbed horizontal layers. He also cited the scale and power of volcanic activity with the widespread occurrence of igneous rocks as supporting evidence.
Having dealt with the issues of sedimentation, consolidation and uplift of rock layers, what of time? As these processes are barely measurable on a human timescale they were certainly impossible to demonstrate. Hutton postulated that they happened very slowly over a long period of time and that the earth was very ancient “with no vestige of a beginning”. He was able intellectually to conceptualise and argue his case because of his theory on time.
Hutton’s Journeys to Prove his Theories
Hutton’s journeys to prove his theory took him to Glen Tilt, Southwest Scotland and Arran with the purpose of demonstrating that granite was 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 find what he was looking for. He 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 they journeyed south-west to examine the granite of Galloway and its junction with the older sedimentary rocks of the Southern Uplands. The following year in 1787, Hutton went to Arran to study “the nature of granite and the connection of it with the contiguous strata”. Here he made additional observations to strengthen proof of this theory, that of the power of the sea to erode 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 in other places. The following year, knowing what he was looking for, 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”, writes James Hutton of his trip with his friends John Playfair and James Hall from nearby Dunglass, to find further the 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”. Here Hutton and his colleagues 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 Theory of the Earth Accepted?
John Playfair informs us that not much notice was taken initially of Hutton’s theory:
‘Yet the truth is that it drew their attention very slowly, so that several years elapsed before anyone showed himself publicly concerned about it…’
By way of explanation he suggests that:
‘The world was tired out with unsuccessful attempts to form geological theories…’
He also adds:
‘…that other reasons certainly contributed not a little to prevent Dr Hutton’s theory from making a due impression’.
Though when expounding on his theories, Hutton was articulate and convincing, his writing style was laborious and complicated:
‘…producing a degree of obscurity astonishing to those who knew him, and heard him…’
Not having a teaching post, Hutton was not able to expound his theory with generations of students; however, John Playfair (who held the chair of Professor of Natural Philosophy at Edinburgh), and James Hall (chemist and geologist), who both accompanied him to Siccar Point, took up the cause of Hutton’s theory. James Hall’s experimental work on igneous rocks and limestone was decisive in further demonstrating proof for Hutton’s theory. Playfair elucidated and popularised Hutton’s theory in ‘Illustrations of the Huttonian Theory’ (1802), making it more widely acceptable.
It is difficult to imagine the impact of changing the unquestioning acceptance of time and the earth’s age held by entire societies in the ‘old world’ from a mere 6,000 years to one of ‘…no prospect of an end’. As Hutton argues; How shall we acquire the knowledge of a system calculated for millions, not of years only, nor of ages of man, but of the races of men and the succession of empires?
Once people had taken notice of Hutton’s theory, it soon became well known and circulated through the academic network in Britain and Europe. There was considerable opposition to it, both on religious and scientific grounds. In particular the final sentence of his 1788 paper ‘The result therefore of our present inquiry is, that we find no vestige of a beginning, no prospect of an end’, was taken as directly flouting the bible – still at the time considered heresy, and he was accused of atheism. This was a curious contradiction of his frequent references to the work of God in the evidence of rocks, benevolent in creating ‘a world beautifully calculated for the growth of plants and nourishment of men and animals’.
Scientific opposition to his theory was especially vehement and prolonged, and much of it came after he died. Most opposition arose from those who believed that part of the earth’s crust was composed of ‘primitive mountains’ which had been precipitated from a primeval ocean – or the seas created during the Flood. This ‘neptunist’ system was in complete opposition to Hutton’s theory dubbed the ‘plutonic’ system. There was also objection to his belief in the relative constancy of geological time and processes (later termed ‘uniformitarianism’), which was in direct opposition to the more popular ‘catastrophist’ explanations for geological events. The debates raged into the early nineteenth century, being tested at scientific meetings, publications, laboratories and even at social occasions.
Arguing his theory, involved dismissing and refuting some deeply held convictions and introducing some original concepts:
On time
The Earth was believed to be only 6,000 years old; a date rooted in the bible and which was considered heresy to question.
On consolidation of sediments into rock
Rocks it was believed, were precipitated from solutions of sediments in the sea.
On the igneous and ‘recent’ origins of granite
Granite was believed to be of ancient origin.
On the changeability of the earth’s surface
The earth was considered by most geologists to be composed of its original rock surface or ‘primitive’ rock that had never changed.
On igneous rock including granite being ‘young’
Igneous rocks were considered primitive (ie pre-life), because they contained no fossils.
On the earth as a ‘heat engine’
which caused uplift and consolidation
On the constancy of geological time and processes
This opposed the popularly held belief that the earth was formed by sudden and catastrophic geological events such as earthquakes and floods.
Legacy
Hutton’s empirical details have stood the test of time. It is now known that the greywacke layer which underlies much of the Scottish Southern Uplands is more than 400 million years old, and the sandstone is more than 300 million years old – ancient indeed. Hutton was also right about the Earth’s internal heat and its power to elevate. Only as recently as 1960 have geophysicists known that the Earth’s internal heat engine drives convection in the earth’s mantle causing it to move and elevate. This is the basis of one of the most important discoveries of the last century – plate tectonics. Hutton’s supposition that igneous rocks had once been fluid was also correct.
His greatest contribution to science and philosophy, was his recognition of ‘deep time’, which was an essential forerunner to Darwinian evolution. His theory was popularised both by his biographer John Playfair and the nineteenth century geologist Sir Charles Lyell. Through Lyell, Hutton influenced Darwin (also a geologist), who in his Origin of Species wrote “It is hardly possible for me to recall to the reader who is not a practical geologist, the facts leading the mind feebly to comprehend the lapse of time… which the future historian will recognise as having produced a revolution in natural science” Both Lyell and Darwin owe this concept to Hutton. Hutton himself recognised natural selection, describing it as ‘a beautiful contrivance’.
His disciplined methodology has also been invaluable to the development of geology as a science; it is simply that any conjecture must be tested and refuted through verifiable predictions, with supportive accurate observations, and deductions guided by field evidence. Hutton was not the first to propose geological theories, but he was the first to make systematic use of refutation, enabling him to reliably prove his theory.
Hutton’s approach to geology and natural philosophy came from a very broad base of knowledge and experience of living systems as an innovative farmer and a medical doctor. He had a remarkably modern ‘holistic’ sense of our dynamic and habitable Earth “Here is a compound system of things, forming together one whole living world”. He claimed that sedimentary rocks are evidence of ‘a succession of worlds’, believing that this system was designed to maintain our ‘habitable earth’.
Hutton’s thinking was apparently influenced by his belief in deism, ie the habitable Earth as a connected system. However, we now know particularly through the science of ecology, that we do indeed live in an interconnected and interdependent world. This is not just in terms of the habitable surface of the earth, but all of the earth as a planet and the planet as a small part of our universe.