May 2007

Economic Geology

The Basalt Controversy III (Part 17)

By R. J. Cathro

"Having, in the natural history of this earth, seen a succession of worlds, we may from this conclude that there is a system in nature; in like manner as, from seeing revolutions of the planets, it is concluded, that there is a system by which they are intended to continue those revolutions … . The result, therefore, of our present enquiry is, that we find no vestige of a beginning, - no prospect of an end." (Hutton, 1788, p 304)

Most geologists are unaware that Edinburgh played a major role in the history of economic geology. The last of Werner’s disciples to carry the Neptunist flame was a Scot, Robert Jameson (1774-1854), who joined the University of Edinburgh in 1804, two years after studying under Werner for a year, and became Regius Professor of Natural History and Keeper of the Museum until his death.

While many professors have managed to drive outstanding students into other fields of study, none can equal the influence of Jameson. One scientist recalled that he had attended Jameson’s lectures on geology and zoology in 1826, at the age of 17, and found them so dull that he determined "never as long as I lived to read a book on geology or in anyway to study the science." He was also present on a field trip to Salisbury Crags (on the edge of Edinburgh), when the professor showed them "a trap-dyke, with amygdaloidal margins and the strata indurated on each side, with volcanic rocks all around us, and (declared) that it was a fissure filled with sediment from above, adding with a sneer that there were men who maintained that it had been injected from beneath in a molten condition. When I think of this lecture, I do not wonder that I determined never to attend to geology."

Unfortunately for Jameson’s reputation, the student’s name was Charles Darwin, who recalled these events in his autobiography (1887). Fortunately for geology, Darwin went on to make many valuable contributions and even considered himself a geologist (Herbert, 2005). Jameson’s sneer was directed at James Hutton 1726-1797), often referred to as ‘the father of modern geology,’ who laid the scientific foundations of Plutonism. It led to the demise of the Neptunist theory, several years after Hutton’s death, and also resulted in recognition that volcanic and plutonic rocks, and hydrothermal fluids were generated by the melting of rock from the upper crust.

Since both Hutton and Werner were Deists who believed in a God who created the universe and then abandoned it, assuming no control over life and exerting no influence on natural phenomena, their disagreement was not religious. One of the few traits they had in common was that neither was a prolific writer, although Werner’s students disseminated his ideas widely. Otherwise, their scientific careers and personalities could not have been more different. Even though he taught field techniques, Werner did little fieldwork himself because of health problems. He was an expert mineralogist whose experience was limited to the mining districts of Erzgebirge and Harz in Saxony. Hutton, on the other hand, thrived on fieldwork and travelled widely throughout Great Britain, but had no knowledge of mining. Living for much of his life in Edinburgh, which is built on basalt, and being a frequent visitor to Salisbury Crags, Hutton was much more aware of volcanic rocks and had a more worldly view because of his close contact with leading scientists and philosophers. Whereas Werner was an influential professor who spent his career in an academic setting, Hutton used his scientific training to become a self-taught geologist.

Hutton was born in Edinburgh, enrolled at the university at the age of 14, and apprenticed for a year in a law office after graduating in 1743. When he realized that he wasn’t suited for office work, he decided to study medicine because it was the only field that offered to satisfy his growing interest in chemistry. Receiving his degree in 1749, following a year in Paris and three more at Leiden University in Holland, he returned to England and, with a partner, James Davie, perfected a method for manufacturing the metalworking-flux sal ammoniac (NH4Cl) from chimney soot. This proved so successful that it provided him with the financial security to switch his interest in 1752 to a farm he had inherited from his father, located in Berwickshire, 65 kilometres southeast of Edinburgh.

In order to become knowledgeable about animal husbandry, he lived for two years on a farm in Norfolk and travelled widely, during which time he began to recognize the significance of erosion in the formation of soil and the deposition of sediments. This interest continued to grow after he returned to the family farm and he gradually emerged as a leading Scottish geologist. After touring the diverse geology, rugged topography, and abundant outcrop in the Highlands in 1764, he began to think seriously about the origin of different types of rock. That led him to put his thoughts on paper in an unpublished essay titled Natural History of the Earth. It focused on two key observations, neither of which was original - that most rocks are composed of eroded materials and that all surface exposures are subjected to constant erosion. It was linking the two into a cycle that made Hutton’s ideas important. He was beginning to recognize that the earth must be very ancient.

This was an unorthodox, even dangerous, position to take at a time when the age of the earth was generally acknowledged to be about 6,000 years. Using the genealogical chronology laid out in the Bible, Martin Luther had calculated in 1541 that creation had occurred in 3961 BC. By 1650, the calculation had been refined by Bishop James Ussher to give a date of October 23, 4004, which was generally supported by Sir Isaac Newton before his death in 1727. A proposal by Georges-Louis Leclerc, Compte de Buffon, in 1749, that the earth was 75,000 years old aroused little interest. While Hutton accepted the conventional estimate as the age of humanity, he felt that the earth itself must be much older. To be taken seriously, Hutton would have to overcome the accepted wisdom that the earth was quite young, an enormously difficult challenge.

Having turned the farm into a model operation, Hutton moved back to Edinburgh in 1767, at a time when it was emerging as the ‘Athens of the North,’ and became part of a circle of Scottish scientists and intellectuals called the ‘Scottish Enlightenment’ that was centred around the university. It included the philosopher David Hume, the economist Adam Smith, the sociologist Adam Ferguson, the historian William Robertson, the chemist Joseph Black, and the inventor James Watt, as well as the polymath Benjamin Franklin and the writers Robbie Burns and Sir Walter Scott. This circle, which was more creative than any group in England at the time, was the moving force behind the creation of the Royal Society of Edinburgh in 1783.

By 1785, Hutton had synthesized his 30 years of observations into a theory about the history of the earth. His two-part paper titled Concerning the System of the Earth, Its Duration, and Stability was delivered to the Royal Society in March and April of that year. Joseph Black, who is recognized as one of the founders of modern chemistry because he isolated carbon dioxide and showed that the atmosphere is actually a mixture of several gases, read the first lecture because Hutton was sick. It described erosion and the formation of strata, while the second paper discussed the elevation of strata from below sea level to form new land, with internal heat and upwelling molten rock and mineral veins postulated as the cause. The conclusion that he left with his audience was "this world has neither a beginning nor an end." In other words, the world was ancient, of immeasurable age, which was a direct challenge to the teachings of the Christian church.

The 1785 lectures generated strong criticism, largely for religious reasons, that was led by the Irish chemist and mineralogist, Richard Kirwan. Deciding that he needed more field evidence to support his theory and answer his critics, Hutton embarked on a series of field trips between 1785 and 1788. Starting at Glen Tilt, a stream northwest of Edinburgh near Blair Athol, he observed many sill-like fingers of reddish granite intruding along the bedding of black micaceous quartzite. The following year, at the age of 60, he went to Galloway, on the west coast south of Glasgow, and found more granitic dykes cutting older sediments. In 1787, he visited the Isle of Arran, in the Firth of Clyde, southwest of Glasgow, where he collected a 270-kilogram specimen from a similar intrusive contact. He also found a poorly exposed unconformity at Loch Ranza, at the north end of the island. Later in the year, he observed another example in the Tweed Basin, on the east coast near the English border.

The most important trip was made by boat in 1788 along the coast southeast of Edinburgh, accompanied by two sceptical friends, John Playfair, a university professor who specialized in Euclidian geometry, and Sir James Hall, a young chemist. At Siccar Point, he found what he was looking for, an excellent exposure showing the unconformity between vertical Silurian greywacke and overlying flat beds of Devonian Old Red Sandstone. He believed that this represented a gap in time separating two cycles of deposition. This was clear evidence that the earth had been elevated, a crucial step in proving his theory.

He had concluded from his field mapping that basalt was derived from volcanoes and granite from magma, that the mechanical and chemical weathering of rocks produced sedimentary particles, and that these were transported by wind, water, and gravity and deposited on the sea floor as sediment in essentially horizontal attitudes. Also, he interpreted steeply inclined beds as evidence of uplift through crustal movement, and suggested that mineral deposits were formed by crystallization from comparatively dry melts. Inexplicably, he still believed that there was a distinction between basalt and lava.

When the 1789 publication of his 1785 lectures failed to stop the criticism, Hutton began to write a more detailed expansion of his theory, including the field evidence collected in the interim. Although he was a great conversationalist, the two-volume, 1,000-page, rambling book published in 1795, two years before his death, has been roundly criticized as virtually unreadable and dense, with endless quotations in French (a third volume was unfinished in manuscript form). It left Hutton with the reputation as “the all-time worst writer among the great thinkers” (Gould, 1987, p.64). He had been in great pain with kidney disease during its preparation, which may have contributed to the problem. It was not translated into other languages until 1815, and Hutton’s ideas were not widely available in Europe for years because of the French Revolution and the Napoleonic wars. Although Hutton’s last book was published at almost the same time as Werner’s main publication, neither referred to the other and they never met or corresponded.

Several of Hutton’s influential champions, notably Archibald Geikie and Charles Lyell, spread the myth that his theories were the result of empirical study and observation. However, the truth is that he formulated most of his important ideas based on general observations and only confirmed them with his field work after the presentation of his 1785 paper (Gould, 1987).

Except where noted, the information on Werner and Hutton is from Adams (1938), Dean (1998), and Repcheck (2003).

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