The Eureka Moments

Dr. Hutton made several excursions into different parts of Scotland, with a view of comparing certain results of his theory of the earth with actual observation.

John Play/air, 1805

T he fellows of the Royal Society of Edinburgh left their offices, studies, laboratories, and court chambers in the early afternoon of March 7, 1785, and started walking toward the university library for that day's meeting. Adam Smith closed his office at the Custom House early and walked down High Street with his trademark cane, turning right at Nicholson Street on his way to the university. Professors Playfair, Cullen, Robison, and Robertson were already at the university, so they had the briefest of strolls across the courtyard. There was great anticipation for this gathering because this was the day of the long-awaited formal presentation of James Hutton's theory of the earth. Almost everyone attending the talk knew Hutton personally, and they were aware of his decades-long fascination with minerals and the surface of the earth. But almost no one knew what kind of general theory this fascination had led to. They were in for quite a surprise.

No record remains of precisely who sat in the library that day to hear the first of two scheduled lectures. There were over 150 members of the society, but many—such as James Watt and Benjamin Franklin—did not live in Edinburgh. The society was also divided into two groups, the Physical Class and the Literary Class. The latter convened on a different day and may have been less motivated to listen to a talk on a topic outside its main interests. For the members of the Physical Class, though, this was going to be a riveting session, and everyone who was not ill or out of town would have found a way to attend. So at least fifty of the most learned men in Scotland assembled to hear the "famous fossil philosopher" address them. The person Hutton was probably most eager to impress, however, was Professor John Walker.

Walker had been professor of natural history at the university since 1779, and was instrumental in the founding of the Royal Society. As secretary of the Physical Class, he must have been involved in soliciting Hutton to give his talks. Walker was born in Edinburgh in 1731; like Hutton, he came from a comfortable family. He attended the University of Edinburgh in the 1740s, where he developed an interest in chemistry. Afterward, he became enthusiastic about mineralogy. In 1764, he toured the Highlands (Hutton's Highland tour was the same year) as a min eralogist assessing forfeited estates, just as Hutton did with George Clerk-Maxwell. Unlike Hutton, though, Walker was a Christian and became a minister in the Church of Scotland in the 1750s. As a young man, he had cultivated ties to prominent citizens of Edinburgh, especially William Cullen, and these connections eventually helped him to gain his appointment to the university.

As a professor at the university and Keeper of the Natural History Museum (which had a large mineral collection), Walker introduced the first known geology course in the English-speaking world, which started in 1781. Copies of his course notes make it clear that he believed in the biblical age of the earth, and that he generally followed the teachings of the most influential geologist of the day, Abraham Gottlob Werner. Because Werner's theory of the history of the earth was so well-known and accepted, it is important to describe it in some detail. The specter of Werner would haunt Hutton and his supporters for years.

Abraham Gottlob Werner (1749-1817) was twenty-three years younger than Hutton, and by 1785, he was known throughout Europe. Werner had spent his youth surrounded by rocks and ores—his father was the inspector of the Duke of Solm's ironworks—and had emerged as a fine mineralogist at a young age. In 1774, he published what was essentially the first rigorous field guide for identifying and analyzing minerals. On the strength of this book, Werner was given a professorship at the Freiburg School of Mines (in the German province of Saxony) in

1775, at the age of twenty-six. He was a gifted lecturer, and, much like Joseph Black's, his international fame rested on a few publications, a renowned course, and the small army of inspired students who had heard his lectures and then spread the Wernerian vision as they scattered throughout the universities of Europe. He started teaching his historical geology class in 1779, making it the first of its kind in Europe. Many of Werner's students drafted informal manuscripts based on lecture notes, which were then circulated among the international mineralogy community. By the time Hutton delivered his lectures to the Royal Society of Edinburgh, Werner's view of the history of the earth was accepted in most scholarly circles.

The Wernerian model was a synthesis of several precursors. He started with Buffon's theory of the earth, found in his thirty-four-volume Histoire Naturelle (1749). As described earlier, Buffon's theory was complex, but in essence argued that the earth formed when a comet collided with the Sun and the ejecta re-formed into a planet. Buffon believed that the earth had once been as hot as the Sun, but that it was now slowly cooling off and would someday stop supporting life. As it cooled, according to Buffon, the earth became covered by a universal ocean, and the features of the continents were formed as the ocean receded and evaporated. This meant that all the rocks on the earth had precipitated out of the universal ocean.

Werner next looked to Italian mineralogist Giovanni Arduino, who in 1759 published a classification scheme for all visible rock groups. "Primary" rocks were formed at Creation and had no fossils in them; they were still visible among the highest mountains, such as the Alps. "Secondary" rocks were the earliest stratified rocks and they were represented by limestone and shale; "Tertiary" rocks were fossil-filled clays and sandstones. The youngest rocks in the world were volcanic rocks, from recent eruptions. Arduino was probably influenced by the German mineralogist Johann Lehmann, who had first presented this classification but had explicitly correlated the categories with the Bible; thus, Primary rocks were formed at Creation, Secondary during the Deluge, and Tertiary after the Deluge. Arduino's scheme was less biblically oriented.

Werner embraced the idea of the universal ocean coupled with the distinctive rock groups of Lehmann and Arduino. Werner's universal ocean had been slowly receding since its inception. As time went on, different types of rocks were revealed. Primary rocks were the oldest; they were the earth's highest and were found in mountain ranges. These rocks contained no fossils because they were formed before living organisms appeared. The next group of rocks was called Transition (a group that Werner inserted into Arduino's scheme), and they were the oldest and most distorted stratified rocks, made of eroded Primary rocks and primitive dead organisms. They were often vertical and broken because they had formed on the surface of the chaotically shaped Primary rocks, or because ancient caverns had collapsed under the weight of these early sediments. The universal ocean was stormy during this stage, a condition that contributed to the extreme shapes of the layers and the many dead organisms now manifested as fossils. Secondary rocks were more recent stratified rocks, formed from eroded Primary and

Transition rocks and normally found in horizontal beds. The final type of rock was Alluvial, formed by such recent events as volcanoes or floods. Of particular significance, Werner argued that granite, a very common rock in mountain ranges, was a Primary rock, the first to precipitate from the universal ocean and therefore the oldest type of rock. Werner's theory was embraced by most of the scientific community because it seemed to explain all the rock formations found around the world. The Christian community accepted it, too, because Werner did not openly dispute the biblical time frame (although privately he had his doubts), and the universal ocean could be interpreted either as Noah's Flood or the original waters of Creation.

When the scholars started arriving at the library, they were surprised to see Joseph Black, not James Hutton, sitting near the front of the room. Whether it was because of nerves or a genuine illness that afflicted him at an inopportune time, Hutton was so sick on this important day that he could not even deliver his own lecture. It is possible that he was not even in the room. Luckily, the rules of the Royal Society had forced Hutton to draft the lecture so that it could be published; thus, it was available to be read by someone else if the need arose. In a way, Hutton's incapacitation worked in his favor. Joseph Black, his best friend, agreed to deliver the talk in his place. Black was reputed to have a marvelous baritone voice and a cadence that enticed listeners, and his years of classroom experience made him relaxed and polished in front of an audience. More important, he was a lionized scientist and his agreeing to read the lecture gave it his implicit approval.

Once the fellows and guests had found their seats, Black took his place behind the lectern and began. The title was intriguing: "Concerning the System of the Earth, Its Duration, and Stability." Black's opening line immediately commanded the audience's attention: "The purpose of this Dissertation is to form some estimate with regard to the time the globe of this earth has existed, as a world maintaining plants and animals; to reason with regard to the changes which the earth has undergone; and to see how far an end or termination to this system of things may be perceived, from the consideration of that which has already come to pass." On that first day, Black described Hutton's observation that most of the land on which people now live is made up of the waste of past land, that is, stratified rocks. We know that two things have happened—"collections of loose or incoherent materials" have been consolidated, and those "consolidated masses" have been somehow elevated above the sea to form new land. Black continued by saying that the present inquiry was aimed at learning how these two related processes occurred. The rest of the first lecture focused on the formation of strata, Hutton/Black in the end discounting aqueous causes and instead proposing that heat and pressure were the reasons for consolidation.

The second lecture was delivered exactly four weeks later, on April 4. This time, James Hutton was well enough to do his own talking. Having deduced how stratified rocks formed, Hutton's next inquiry concerned the elevation of the new strata from below the seas to form new land. Once again, Hutton called on the power of heat—subterranean heat—as the causal force. Simply put, the elevation could not be the result of receding water; if it were, all stratified rocks would be horizontal, just as they had formed on the floor of lakes, seas, and oceans. Instead, it was well known that many strata were found in every degree of "fracture, flexure, and contortion"; therefore some force was pushing the strata upwards. The only available force was hot liquid rock, created by the same heat that caused the consolidation of stratified rocks. His proof of this phenomenon was "mineral veins, those great fissures of the earth, which contain matter perfectly foreign to the strata they traverse." Because these veins clearly came from below the strata, hot liquid rock must have been pushing from beneath, lifting the new stratified rocks above the sea. Hutton argued that we knew the earth had experienced this cycle of regeneration in the past because we could see fossils of "every manner of vegetable production . . . in the strata of our earth." This meant that dry land containing plants had eroded to form underwater sediments, and those sediments had later been raised as new land, where people could later find the evidence of the long-dead organisms in fossils dug from the new dry land.

At last, Hutton arrived at his remarkable conclusion, one that was based on simple logic and observation. Thus, "a question naturally occurs with regard to time; what has been the space of time necessary for accomplishing this great work?" He urged his listeners to reflect on erosion, of which they were all aware: "As there is not in human observation proper means for measuring the waste of land upon the globe, it is hence inferred, that we cannot estimate the duration of what we see at present, nor calculate the period at which it had begun; so that, with respect to human observation, this world has neither a begin ning nor an end." It is important to note that Hutton was arguing that the earth is unknowably old, not eternal; the phrase "with respect to human observation" is critical in this context.

Like Charles Darwin, whose best friends did not know the full extent of his views until his paper on natural selection was first presented, Hutton had dropped a bombshell. By 1785, many theories of the earth had been put forth, so Hutton's was just one more. But nearly all previous theories had worked within the biblically prescribed 6,000 years, or they had sidestepped the issue entirely. Only one noted scholar had been as bold as Hutton. A few years before Hutton's talk, Buffon had revised his famous 1749 book, arguing that the age of the earth was 75,000 years (he arrived at this number by estimating how quickly the earth had cooled from its original molten state). However, because many features of Buffon's original hypothesis were no longer accepted, and Werner's theory was gaining popularity, the 1778 revision did not have nearly the same impact as the original. But even if it had, Buffon's 75,000 years were a simple multiple of 6,000. The earth was still very young. Hutton's idea, on the other hand, was revolutionary; simple observation of the land forced one to acknowledge that the earth was profoundly ancient, so old that one could not even hazard a guess as to its age.

Joseph Black had discovered carbon dioxide and the nature of the atmosphere; Adam Smith had properly analyzed how economies work; William Cullen had devised many important medical procedures and practical chemical discoveries for the textile industry; John Playfair was working on a text about Euclid's geometry. These were important contributions. But if

Hutton was right, his theory made the others pale before it. His would challenge the very place of humans in the cosmos.

No account exists of how Hutton's lectures were received in the early months of 1785. Playfair states that "the truth is, that [the theory] drew their attention very slowly, so that several years elapsed before any one showed himself publicly concerned about it, either as an enemy or a friend." Playfair was probably referring to written reaction because it was not until 1788 that the first published reviews appeared. The only other reference to the lectures before 1788 comes from Adam Ferguson, who in a 1787 letter to a famous French geologist, Horace de Saussure, wrote, "His (Hutton's) ideas are magnificent and, what is more precious and more difficult in science, formed with a scrupulous regard for reality."

Still, there must have been some reaction from the members of the Royal Society who sat in the library those two Fridays. Walker surely voiced his objections, since he disagreed with so many of Hutton's assertions. All that is known for sure, though, is that immediately after giving the lectures, Hutton set out on a series of field trips designed to provide evidence for his positions. Just as a teacher needs to give a lecture at least once to learn what the students do and do not grasp, Hutton learned by the audience's reaction which parts of his theory "worked" and which ones cried out for proof.

Hutton must have realized that his critics did not much care about the claim that the mineralizing process was caused by heat. However, they did care about his contention that the earth behaved in a cyclical fashion. The only way such a cycle could exist was if subterranean heat had caused hot rocks to push upward toward the surface. Thus, the major controversy was over Hutton's argument that heat was the engine that caused submerged stratified rocks to rise above the sea. Hutton's proof was that mineral veins could be found permeating stratified rocks: "In many places those consolidated strata had been broken and invaded by huge masses of fluid matter similar to lava, but, for the most part, perfectly distinguishable from it."

Hutton hypothesized that the "fluid matter" intrusions were made of granite, and that they were formed when fresh hot magma from within the earth, "the mineral region," welled up and forced its way into older stratified rocks. They then raised the strata above the sea. Werner and his followers thought exactly the opposite: that those granite veins were Primary rocks, formed at the earliest stage of the earth's history and precipitated from the universal ocean, and that the stratified rocks surrounding these Primary rocks had formed around them at some later stage. They had their unusual shape because of ancient movements that were now impossible to re-create.

James Hutton resolved to go into the field and find proof that granite intrusions formed from within the earth and were therefore younger than the overlaying strata. He enrolled one of his friends, Sir John Clerk of Eldin, the younger brother of George Clerk-Maxwell and himself a talented mineralogist and artist, to accompany him in an effort to find strata cut by granite. They were looking for an exposure in which the shape and direction of the veins demonstrated that it came from below. Hutton knew from his 1764 trip to the Highlands with George Clerk-Maxwell that what he called "veined granite" was common there. In a later paper describing his search for granite, Hutton stated that "this question could only be determined by the examination of that species of granite upon the spot, of where it is to be found in immediate connection with those bodies which are evidently stratified." This was likely a line directed at John Walker, who stressed the need to see rocks in the field, not in the lab.

Hutton had become acquainted with the Duke of Athol, whose estate was in the town of Blair in the eastern Highlands north of Dundee and west of Aberdeen. The estate was just south of the Grampian Mountains in the part of the Highlands where the granite of the mountains often mixed with the stratified rock. Hutton remembered that the area contained many streams and rivers, which would create vivid exposures. Hutton mentioned his goal to the duke, who then invited Hutton and Clerk to visit during hunting season, when his party would be traveling to Glen Tilt. As Playfair described it, "The Tilt is, according to the seasons, a small river, or an impetuous torrent, which runs through a glen of the same name."

Playfair went on to relate what happened next:

When they reached the forest lodge, about seven miles up the valley, Dr. Hutton already found himself in the midst of the objects which he wished to examine. In the bed of the river, many veins of red granite, (no less indeed than six large veins in the course of a mile), were seen traversing the black mica ceous schistus, and producing, by contrast of color, an effect that might be striking even to an unskillful observer. The sight of objects which verified at once so many important conclusions in his system, filled him with delight; and his feelings, on such occasions, were always strongly expressed, the guides who accompanied him were convinced that it must be nothing less than the discovery of a vein of silver or gold, that could call forth such strong marks ofjoy and exultation.

The formation "most clearly demonstrates the violence with which the granitic veins were injected among the schistus." Hutton later commented about seeing the Glen Tilt veins for the first time: "I here had every satisfaction that it was possible to desire."

The next summer, Hutton and Clerk again headed into the field. Hutton was now sixty years old and Clerk fifty-eight. This time they went to Galloway, a region at the extreme southwest of Scotland, and found more evidence of granite invading strata from below. In Hutton's words:

We therefore left the chaise . . . while we ran with some impatience along the bottom of the sandy bay to the rocky shore which was washed by the sea. .. . But breaking through the bushes and briars, and climbing up the rocky bank . . . we saw something that was much more satisfactory. . . . For here we found the granite interjected among the strata, in descending among them like a mineral vein, and terminating in a thread where it could penetrate no farther. . . [this] will convince the most skeptical with regard to this doctrine of the transfusion of granite.

The following summer, this time assisted by Clerk's son, Hutton visited the island of Arran, which lies in the Firth of Clyde, southwest of Glasgow. Once again, he was looking for granite meeting with stratified rock. And again, he was successful: "Having once got hold of the clue or caught the scent, we traced back (with more animation than could have been expected from such an innocent chase) the object of our investigation all the way to the Cataract rock. Great veins of granite may be seen traversing the schistus, and ramifying in all directions. I procured a specimen, which I have had conveyed to Edinburgh, though weighing above 600 pounds." Indeed, Hutton did ship a huge boulder from Arran back to his house.

The trips to Glen Tilt, Galloway, and Arran supplied ample proof of Hutton's contention that granite was formed by subterranean heat, that it often flowed underground, and that it forced its way into overlaying strata. More important, it showed that subterranean heat could indeed be a force that raised the land. This finding went a long way toward buttressing his theory. However, the other revolutionary idea in his scheme, that the earth recycles itself, was not necessarily proved by the granite discoveries. It was critical to find evidence that a cycle had actually occurred. That was what the breathtaking discovery at Siccar Point in 1788 provided. After that successful excursion along the North Sea coast, Hutton at last felt that his theory was secure.

In 1788, the full-length paper based on the 1785 lectures finally appeared in print. The ninety-five-page document was published in the first volume of the Proceedings of the Royal Society. Though published three years—and four productive field trips—after the original lectures, the printed version did not mention the discoveries at Glen Tilt and Siccar Point. Hutton must have finished the manuscript in 1785, and the printers for the Royal Society of Edinburgh must have been extraordinarily slow.

Three reviews of Hutton's paper appeared in 1788, just months after the publication of the Royal Society's volume. The first appeared in the widely read Monthly Review, a journal that culled news and findings from recent publications. In two pages, the anonymous article summarized Hutton's argument, but then dismissively pointed out that Hutton argued for "a regular succession of Earth from all eternity! And that the succession will be repeated for ever!!" Because Hutton had not ventured a guess about the actual age of the earth, confusion was created among many of his reviewers, for they thought that he was arguing for an eternal earth, which he was not. In the previous articles the editors of the Review had stated their agreement with the "allegiance between Nature and Revelation, which the wisest men of all ages have discerned and admired, and which the minute philosophers of the present times have made many important efforts to destroy."

One paragraph was all it took for the Analytical Review to dismiss Hutton as simply another grand theorist with few facts to support his "philosophical romances."

But the Critical Review gave Hutton's paper a four-page critique that accurately described Hutton's positions. It did not embrace the theory, but it did not reject it, either, and it recognized the rigorous scholarship found in it.

In 1789, a new book appeared: The Natural History of the Mineral Kingdom by John Williams. It included a forty-page addition that was written and printed quickly to respond to Hutton. The inserted chapter summarized Hutton's arguments, refuting each in turn, and concluded with a comment about Hut-ton's proposed eternal earth (which he had not claimed): "The wild and unnatural notion of the eternity of the world leads first to skepticism, and at last to downright infidelity and atheism."

These essentially negative reviews seemed to have had very little effect on Hutton, who was confident in his theory, and secure with the knowledge that Black, Playfair, and Hall—and no doubt many others in the Royal Society—supported him.

However, one review did goad him into action. The hurtful critique was by Richard Kirwan (1733-1812), who published a thirty-page paper on Hutton's theory in the Transactions of the Royal Irish Academy (1793). Kirwan was a respected scientist who as a young man had trained to be a Jesuit priest. In 1787, after living in London for ten years, he returned to Ireland and helped found the Royal Irish Academy. At one point in his review he attacked Hutton for proposing cycles, which were "contrary to reason and the tenor of the mosaic (Book of Moses) history." He also essentially accused Hutton of being an atheist and blasphemer.

In the summer of 1793, the same year that Kirwan's paper was published, James Hutton suffered a serious illness. He was retaining urine, which could have been caused by kidney failure. He was so ill that he needed surgery, which in the late eighteenth century was anything but routine. Though very weak from the illness and surgery, Hutton resolved to write a major expansion of the 1788 paper the "very day after Mr. Kirwan's paper was put into his hands." Unfortunately, Hutton never really recovered his strength, and he suffered terribly while working on his book. This no doubt helps to explain why The Theory of the Earth, published in 1795, has always been regarded as poorly written (though the 1788 paper and the 1785 abstract of the Royal Society of Edinburgh lectures are both accessible and clear).

After the book came out, the sixty-nine-year-old Hutton again fell seriously ill from the same ailment. He was confined to his house, and during the winter of 1796-1797 "he became gradually weaker, was extremely emaciated, and suffered much pain." Playfair describes his last day:

On Saturday, the 26th of March he suffered a good deal of pain; but nevertheless, employed himself in writing, and particularly in noting down his remarks on some attempts which were then making towards a new mineralogical nomenclature. In the evening he was seized with a shivering, and his uneasiness continuing to increase, he sent of his friend Mr. Russel, who attended him as his surgeon. Before he could possibly arrive, all medical assistance was in vain: Dr. Hutton had just strength left to stretch out his hand to him, and immediately expired.

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