The Fabric of the Globe: Chemistry and Geology in Enlightenment Edinburgh

By Matthew D. Eddy

During the 18th century, geology was closely linked to chemistry via medical and industrial experiments that sought to identify the composition of stones that formed the surface and foundations of the globe. Over the past two centuries this connection has been largely overshadowed as historians have sought to identify how early modern notions of geological strata led to 19th-century evolutionary ideas. However, if one digs into the dusty articles and dissertations of Enlightenment chemistry, it becomes quite evident that the practice of “chemical mineralogy,” a forerunner of geology, was pursued in most universities across Europe. In Britain the leading center during this time was the University of Edinburgh. Its professors were keenly interested in geological matters, and this article explains how their chemical knowledge framed the emergence of the discipline of geology in Scotland.

Chemical Principles

In 18th-century Scotland the leading chemists taught in the University of Edinburgh’s medical school. Chemistry had played a central role in the curriculum ever since the school had been founded in 1726 by students who had trained in Leiden with the renowned Dutch chemist Hermann Boerhaave. Although chemistry was also taught in Glasgow and Aberdeen throughout the century, by 1750 the professors of Edinburgh’s medical school set the standard in Scotland for chemical experimentation and patronage. For the next 50 years it was predominantly University of Edinburgh students who lectured in the city’s Royal College of Physicians and edited Scotland’s internationally acclaimed Essays Physical and Literary, the Scottish Pharmacopoeia, and, later, the Transactions of the Royal Society of Edinburgh. Edinburgh’s medical school also had an impact abroad. Its students held positions in the Russian court, traveled on British naval vessels, obtained professorships in America, and maintained lucrative practices in London.

As in most Enlightenment chemical communities, when creating the smells and bangs of their experiments, Edinburgh’s professors and students used a form of chemical nomenclature based on six basic types of matter: Earths, Salts, Metals, Inflammables, Airs, and Water. Each of these categories was called a “principle,” and each was treated as both a primary substance and (save for Metals and Earths) an agent of material change. Using these principles, chemists performed experiments both on the human body and in vitro in the laboratory. To generate extra money for themselves, chemistry students were taught how to apply their knowledge to pharmaceutical production or to the industries of mining, bleaching, brewing, ceramics, and metallurgy. Some students met with considerable success. John Roebuck, for example, founded the first sulfuric acid plant in Scotland and became a captain of industry, and the agriculturalist James Anderson went on to write successful books that addressed the chemical foundations of farming.

Such an interest in practical application made Edinburgh’s chemists less interested in the armchair speculation offered by more gentlemanly institutions like the Royal Society of London or even the early theories offered by the chemical reformer Antoine-Laurent Lavoisier during the 1780s. From the 1750s until around 1800 the Scottish canon of chemistry textbooks drew heavily from authors who lived in Germany and Scandinavia. William Cullen (1710–1790), Edinburgh’s professor of chemistry during the 1750s and 1760s, strongly recommended the work of the Dutch Boerhaave, the German Georg Ernst Stahl, and the Swede Axel Cronstedt. His successor, Joseph Black (1728–1799), promoted these authors and added the names of two more Swedes: Torbern Bergman and Johan Gottschalk Wallerius. Key to almost every single one of the chemical experiments explained by Cullen, Black, and the books they promoted were minerals. This was mainly because mineralogy supplied the raw material for the acidic and alkaline Salts that they used as solvents in most of their experiments. Additionally, Scotland was by no means lush country, and if its physicians wanted indigenous sources for drugs, they had to turn to minerals rather than plants. These minerals usually came from the Salts, Earths, and Metals extracted from Scotland’s many moors, mines, and mineral wells.

Venues of Experimentation

Although chemistry was taught primarily n the medical school, chemically related subjects were frequently discussed in other venues in and around the city of Edinburgh. Overall, there were three types of places where experiments were discussed. The first and most obvious venue was the laboratory, which was then less rigorously defined than the modern concept. In Edinburgh one sees the word applied to rooms in the university, the Royal Infirmary, or even a professor’s home.

Second, chemical discourse was also conducted in polite society. The university not only allowed its own students to sign up for courses outside their official degree program but also permitted professionals, merchants, and gentlemen to audit classes. Thus a variety of people could attend medical school courses on chemistry and mineralogy, and many of them aspired to be naturalists—whether professional or amateur. Moreover, between 1750 and 1800 a wide range of clubs and societies were founded in Edinburgh. Many of them focused on “natural philosophy” and were therefore attended not only by university professors but also by students who had audited the chemistry course. The associations that most frequently discussed chemistry were the Philosophical Society (renamed the Royal Society of Edinburgh in the 1780s), the Medical Society, the Highland Society, the Society of Antiquaries, and the student-run Chemistry Society. As with other European clubs and societies (in London and Paris, for example), chemistry played a central role in their discussions, not only in relation to medicine, but also in reference to topics like agriculture, mining, industry, weather, and—inevitably—the structure and composition of the globe. For the most part, a paper as read at each meeting and then debate ensued. Discussion often spilled over into coffeehouses, pubs, and private homes. If the topic proved especially interesting, members wrote letters to each other, or even to other experts, on the subject. For the benefit of the public, summaries of some of their papers were often printed in the Caledonian Mercury and the Scots Magazine.

A third chemical venue was the natural world itself. Many of Edinburgh’s students went on to pursue careers that took them to various corners of Scotland and to posts in the British colonies. This created a network of chemically trained naturalists interested in collecting a wide variety of minerals and plants that could be used to make drugs. Most of these objects could be obtained only in rural areas or in the wilderness. Since traveling naturalists did not have the space to carry back items that might prove useless, they performed their own chemical tests in situ to determine whether the object was worth taking back to Edinburgh. Their observations can be found in the letters written back to Edinburgh’s Philosophical Society and in articles printed in the city’s magazines and newspapers. Many of these travelers went on to write about their experiments in essays and treatises on mining, alkali production, and mineral-well analysis.

From Chemistry to Mineralogy

In Enlightenment Europe there were primarily two ways to classify minerals. The first was to use physical characters like shape, color, and texture. The main promoter of this approach was the Swede Carl Linnaeus. Trained as a physician, he originally developed the method to classify plants, but he then used the same characters to classify minerals. His method spread quickly among the 18th-century dilettantes, gentlemen, and professionals who maintained their own collections of natural “curiosityes.” There was, however, another way to classify minerals, one based on chemical characters like Salts, Earths, and Metals. Although numerous early modern chemists had proposed chemically founded mineralogical arrangements, it was the Berlin chemist Johann Heinrich Pott who eventually argued that stones were made up of different types of Earth. He performed hundreds of experiments in which he used water, fire, and acids to reduce stones to what he thought to be the most basic “primary” Earths: Vitrescible, Calcareous, Argillaceous, and Talky. He published his results in Lithogéonosie (1745) and so laid the foundation for a chemical understanding of stones. Thus when Cullen began to teach chemistry at Edinburgh in the 1750s, he taught his students to base their systems on the four Earths of Pott.

After Pott, the chemical classification of minerals was dominated by the medically and industrially orientated experiments of Cronstedt, Wallerius, and Bergman, each of whom proposed a different number of primary Earths. All these men published their thoughts in books, and the Scots followed their publications with great interest—so much so that, when Cullen found out about Cronstedt’s new mineralogical system, he immediately commissioned a translation of the classification categories so that he could give copies to his students. The Scots, however, being proficient chemists themselves, did not accept these systems blindly, and their independence engendered a wide variety of personalized arrangements influenced by the experiments or mineralogical collections of the chemists creating them.

Even though Edinburgh’s chemists were keen to observe stones and rocks in their natural habitat, most of them maintained some sort of mineralogical collection. The largest belonged to the University of Edinburgh, but other no notable collections were maintained by aristocrats like John Stuart, third Earl of Bute, and “chemical philosophers” like Black and the natural historian John Walker. The landed classes often kept collections of the minerals from their own estates and from other areas around the world. Such collections allowed them to compare chemically the economic potential of their land (mainly fields, quarries, and mines) to that of other properties. Many relied on the university professors as authoritative scientific advisers; thus Cullen, for example, taught John Campbell, Duke of Argyll, how to use chemical apparatus during the 1750s. A decade later, Black assayed minerals for John Hope, second Earl of Hopetoun, and some of Cullen’s other students surveyed the mineralogical potential of Lord Bute’s family estates.

From Mineralogy to Geology

One of the side effects of using chemical names to classify minerals into systems was that the language of chemistry was firmly transferred into the nascent discipline of mineralogy. Evidence for this linguistic overlap exists in most of Edinburgh’s chemically related courses, but a good example can be seen in Black’s use of the word gluten in his chemistry lectures. Early modern medical circles had previously used this word to describe the sticky material often produced by putrefaction experiments conducted on both animal and plant remains. During the early 18th century gluten was also used to describe the material that held bladder stones together. However, in his 1767 lectures on how limestone can be turned into limewater (a cure for bladder stones), Black transferred the word gluten into the mineral realm by using it to describe the substance that held limestone together. That Black should transfer this word to limestone is not surprising, since he believed that the “calcareous” Earth of limestone came from compressed shells. Such a transfer allowed him to apply what had been an organic term to an inorganic stratigraphical formation. Black was not alone in this practice: several chemically trained naturalists of his generation followed his lead in using chemistry to understand geology. One good example is John Walker (1731–1803), who was appointed regius professor of natural history at Edinburgh in 1779.

Even though mineralogy had been taught in the medical school from the start, the first geology lectures were not given there until Walker made them part of the natural history course that he started in 1782.Walker was one of Cullen’s star students, and when investigating the layers of the earth, he approached the topic via the same chemical principles used by Black, Wallerius, and Bergman. Like most naturalists in the 18th century, Walker taught his students that “the Fabric of the Globe itself” was made of three “classes” of strata: primary, secondary, and tertiary. He held that primary strata, the base on which all other strata rested, contained high concentrations of indurated (hardened) Earths and demonstrated strong bonds of chemical affinity. More specifically, he thought that the rocks of primary strata were formed by a prehistoric chemical solution present at the time of the world’s formation. Taking Black’s use of gluten even further, Walker employed the term to describe the cemented matter that held together the oldest rocks of the earth, thereby firmly transplanting the term into geology. The most common types of minerals found in Scottish primary strata were granite and jasper. On the basis of experiments on these rocks, Walker concluded that the prehistoric solution was not the same as the biblical flood but rather a mix of Earth and Salts similar to liquid cement. Walker felt that secondary strata had been formed by a large aqueous flood, quite possibly the same one as described in the Bible and other ancient texts. They therefore had weaker bonds of chemical affinity than those in primary strata and could be dissolved either by water or acids. Examples of secondary strata were limestone, shell marl, marble, sandstone, and coal. Tertiary strata, the topmost level, consisted of pieces of eroded primary or secondary strata or other deposits like river silt, shell marl, peat bogs, and lava.

The Huttonian Theory

Whereas Walker and his medical school colleagues felt that the strata of the globe were made by different types of aqueous solutions, another theory began to gain attention in the 1780s. James Hutton (1726–1797) used his knowledge of chemistry and mineralogy to argue that the world was shaped by both water and fire. Although Hutton had studied chemistry as a medical student in Edinburgh and Paris, he was independently wealthy and thus free to pursue a career as gentleman farmer, experimental industrialist, and intellectual. In all three areas he was keen to push chemical knowledge into the service of utilitarianism and theism. His theories of material composition sometimes differed from the practically orientated chemistry of the medical school, especially the static view of geological strata promoted by most of the professors, but his Theory of the Earth (1795) was firmly anchored in medical chemistry. Hutton argued that the earth’s crust was continually being broken down and reformed. This idea was closely related to the chemical concepts of blood circulation that he had originally contemplated in his 1749 medical thesis. His Theory presented the earth as one colossal act of material circulation, with strata and stones being recycled as they were pushed into the ocean or into the earth’s fiery core. In the ocean, secondary strata hardened in a cementation process similar to that taught in the lectures of Walker and Black. However, Hutton’s theory differed in that heat, or fire, played a more active role. In particular, he suggested that primary strata could only become indurated via the application of intense heat and that all new strata (whether from the ocean floor or from the magmatic core) could only be raised to the surface via heat.

A few of Hutton’s close friends were impressed with the theory. For instance, Hutton’s traveling companion John Clerk (1728–1812) sketched a cutaway view of a volcano while on one of his many field trips with Hutton. However, though Clerk may have been inspired by the theory, most of the chemists in Edinburgh’s medical school would have considered this sketch conjecture, since it was in practice impossible to get mineralogical samples from the hypothetical dormant lava pool pictured at the base of the mountain. A closer look at more of Clerk’s drawings shows that he often blended the static strata model of the medical school with the renewable strata of Hutton’s theory and failed to include one of Hutton’s central premises, the earth’s fiery core. Instead, he most often depicted primary strata as the bottommost geological level, as in his hypothetical side view of southern Scotland from about 1787. Moreover, his depictions of secondary and tertiary strata were also consistent with the chemical mineralogy that undergirded the classification of geological strata in the medical school—a fact that suggests he was to some degree reluctant to engage in the full breadth of the theory.

In reality, although Hutton’s contemporaries viewed his theory as entertaining, few accepted it at first, and even those who promoted it tended to modify it to fit into the chemical conception of minerals and geology that dominated the intellectual scene in Edinburgh. The reason for this reluctance was that the heart of the theory—the fiery core of the earth—was viewed as an improvable premise, a fanciful piece of conjecture. Thus, Black, who was Hutton’s close friend, courteously mentioned Hutton’s theory in his chemistry lectures on minerals, but he did not explicitly support it. It was the same for Walker’s lectures on natural history.

Mechanics and Medicine

The 1790s were a time of upheaval in Edinburgh. Britain was at war with France, which restricted the exchange of ideas with continental Europe. Locally, there were serious, wide-ranging disagreements between professors who sought to direct the intellectual paths of the university and the Royal Society of Edinburgh. In the midst of these events, the principle-based chemistry employed by the medical school was slowly being changed over to the new nomenclature promoted by Lavoisier. This conversion was not a smooth process. Using a new system of chemistry was potentially dangerous, as untested propositions about matter could prove harmful if rashly applied to long-standing notions of health and disease. Established medical professors and older intellectuals, in particular, were not keen to revamp their lectures or theories at the end of their careers. Cullen, Black, Walker, and even Hutton never brought themselves to accept fully the new chemical nomenclature. The transition to this system was engineered by the next generation of chemists, like Sir James Hall, Robert Jameson, and Thomas Charles Hope.

Ironically, even though Hutton’s theory diverged from the dominant, static view of strata promoted by the medical school, it is his work that is most often discussed in history books that address 18th-century science, largely because his theory became embroiled in a complex dispute over experimental method that ended up dividing Edinburgh’s scientific community for nearly two decades. Within the Royal Society of Edinburgh there was a group keen to extend the mathematical mechanics of physics into chemistry. The leader of this group, John Playfair (1748–1819), Edinburgh’s professor of natural philosophy, emphasized the parts of Hutton’s theory that used heat to explain the earth’s formation. Opposing this view was a group dominated by Robert Jameson (1774–1854), who replaced Walker as professor of natural history. Its members promoted the methods of medical chemistry and followed the teachings of Abraham Werner, a German mineralogist who built on the works of Bergman and Wallerius to argue that the world as shaped by water. The debates between these groups soon transcended Hutton’s theory, and bitter divisions formed within the Royal Society of Edinburgh. At one point the society’s Transactions were in effect suspended, and Jameson closed the mineralogical collection of the university’s natural history museum. One of the most significant results of the “Huttonian debates” (as they were later called) was that Playfair completely rewrote the theory after Hutton died. Hutton’s original work was written in a narrative style, used chemical examples of minerals familiar to the professors of the medical school, and comprised two volumes. Playfair’s edition, on the other hand, cut the thesis down to one volume. Entitled Illustrations of the Huttonian Theory of the Earth (1802), his version played up the sections on heat and played down the parts on water. The result was a theory that had more in common with the mechanics Playfair taught in his natural philosophy course and less in common with chemical notions of mineralogy and geology familiar to the students trained in the medical school during the last half of the 18th century.

Conclusion

Chemistry was a popular and practical subject in Enlightenment Edinburgh. Although it was taught in the medical school, it was also applied to many topics. From the 1750s onward, its principles were employed to create mineralogical classification systems and this in turn allowed chemists to transfer chemical terms and concepts into geology. The interaction between chemistry and geology continued to thrive into the 19th century via works like Jameson’s books on mineralogy and crystallography and Playfair’s Huttonian Theory. But, as scientific disciplines began to become more specialized, the work of these two scholars increasingly appealed to different audiences.

Jameson’s books were more popular with physicians and chemists, while Playfair’s text often influenced natural philosophers who did not want to get their hands dirty in the laboratory. In Victorian times chemistry remained firmly connected to mineralogy and geology, but that connection was often overlooked in the popular press, where interest concentrated instead on how the classification of strata was related to fossils and evolution. Although many histories of the earth sciences focus on the “forerunners” of Darwinian interpretations of geology and paleontology, we must remember that the early modern notion of the “fabric of the globe” was very much a chemical affair.

For Further Reading

Donovan, Arthur L. Philosophical Chemistry in the Scottish Enlightenment: The Doctrines and Discoveries of William Cullen and Joseph Black. Edinburgh: Edinburgh University Press, 1975.

Eddy, M. D. “Scottish Chemistry, Classification and the Early Mineralogical Career of the ‘Ingenious’ Rev. Dr. John Walker.” British Journal for the History of Science 35 (2002), 382–422.

———.“Set in Stone: Medicine and the Vocabulary of the Earth in 18th-Century Scotland.” In Science and Beliefs: From Natural Philosophy to Natural Science, 1700–1900, ed. David M. Knight and Matthew D. Eddy (Aldershot, UK: Ashgate, 2005), pp. 77–94.

Emerson, R. L. “The Philosophical Society of Edinburgh 1768–1783.” British Journal for the History of Science 18 (1985), 255–303.

Hutton, James. Abstract Of A Dissertation Concerning The System of the Earth, Its Duration And Stability: The 1785 Abstract of James Hutton’s Theory of The Earth. Edinburgh: Edinburgh University Press, 1997.

Laudan, Rachel. From Mineralogy to Geology: The Foundations of a Science, 1650–1830. Chicago: University of Chicago Press, 1987.

Oldroyd, David R. Sciences of the Earth: Studies in the History of Mineralogy and Geology. Aldershot, UK: Ashgate, 1998.

Porter, Roy. The Making of Geology: Earth Science in Britain 1660–1815. Cambridge: Cambridge University Press, 1977.

Torrens, Hugh. The Practice of British Geology, 1750–1850. Aldershot, UK: Ashgate, 2002.

Walker, John. Lectures on Geology: Including hydrology, mineralogy, and meteorology with an introduction to biology, ed. Harold W. Scott. Chicago: University of Chicago Press, 1966.

Wood, Paul; Charles Withers. “Introduction: Science, Medicine and the Scottish Enlightenment: An Historiographical Overview.” In Science and Medicine in the Scottish Enlightenment, ed. C.W. J.Withers and P.Wood (East Linton, UK: Tuckwell Press, 2002), pp. 1–16.