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

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.