I, a Geologist (Part 2): The geology of Charles Darwin

“When he returned from his voyage, Darwin was already known to its leaders [of all the scientific societies of the metropolis] as a young geologist of great promise, owing to the geological letters he had sent home from South America” (Rudwick 1982, p. 190)

This is the second of two articles examining aspects of Charles Darwin as a geologist. In the first part (see I, a Geologist (Part 1): The geology of Charles Darwin), we discussed his early influences produced by natural historians at the universities of Edinburgh and Cambridge, Darwin’s field education and experience, and his ideas on

crustal dynamics. In this final part, we will discuss the application of this geological knowledge after his return from this voyage on The Beagle.

Darwin as a palaeontologist

“There is nothing like geology; the pleasure of the first day’s partridge-shooting or first day’s hunting cannot be compared to finding a fine group of fossil bones, which tell their stories of former times with almost a living tongue” (Darwin in Parodiz 1981, p. 43)

In South America, Darwin collected mainly fossil mammals, which he gave to Sir Richard Owen (1804-1893) to describe. Hunting fossil remains of gigantic quadrupeds, such as Mylodon (Fig. 1), along the Argentinean coast from Buenos Aires to Bahia Blanca, Darwin (1838) was struck by three remarkable facts:

1. The bizarre and monstrous proportions of animals, which became extinct almost in recent times.
2. Their peculiar geographical distribution.
3. The simultaneous, almost incomprehensible disappearance of the whole fauna.

Together with the fossil mammals, he found shells identical to some existing in an adjoining bay, testifying that the gigantic animals became extinct in a very recent epoch. This also corroborated Lyell’s rule that the longevity of mammal species was shorter than that of mollusc species. However, there appeared to be no obvious reason for the sudden extinction of the complete fauna, since the elevation of the area had been slow and there were no signs of a catastrophe.

After his return to Britain, Darwin carried out a major biological and palaeontological research programme of his own. He commenced a study, in minute detail, of all barnacles (both fossil and extant) – a laborious project that took him eight years to complete (Stott 2003). The result was a series of authoritative monographs that threw a new light on the cirripedes and which are still important references for barnacle researchers over 150 years after publication. The scrupulously careful anatomical investigations of the living species (Darwin 1851b, 1854b) gave him a deeper understanding of the fossil forms (Darwin 1851a, 1854a), which often existed only as minute loose parts of their shells.

In this way, Darwin could determine, on a sound basis, which parts belonged together (Fig. 2) and which of the many existing names were synonyms.

He was also able to fit the fossil forms into his systematic scheme. In addition, he tried to find out how the very distinct forms had adapted themselves to their different modes of life, and how organs had degenerated and eventually disappeared altogether when they no longer had a function. This research formed part of the solid base for On the Origin of Species, for which Darwin had already written an elaborate resume (just in case of his demise). However, he wanted to substantiate his ideas further before eventually publishing an expanded, but still provisional form, in 1859. As is generally known, his great work, comparable to Lyell’s three-volume Principles, was never completed to his satisfaction.

It is an interesting aside that, through his study of fossil barnacles, Darwin came into contact with the Dutchman, Joseph Augustin Hubert de Bosquet (1814-1880), a pharmacist and naturalist from Maastricht (Crouzen, 1994; Jagt 2004), whom he highly regarded. He donated to Darwin a magnificent collection of Upper Cretaceous barnacles from the surroundings of Maastricht and Darwin was really delighted when de Bosquet found, in the Maastrichtian, a sessile barnacle, Chthamalus darwini Bosquet, 1856 (Fig. 3).

He had previously been convinced that these had started suddenly at the beginning of the Tertiary and were immediately quite diverse, which he found difficult to explain with his theory of evolution. A Cretaceous ancestor was just what he needed and he remarked that he would never again put any trust in negative geological evidence.

The geological roots of Darwin’s On the Origin of Species

“Darwin’s theory of evolution by natural selection was presented as a biological application of geological principles (specifically Lyell’s)” (O’Connor 2008, p. 437)

Darwin’s geological knowledge formed a solid base for the development and critical testing of his theory on the origin of species. He had a flair and personal preference for arranging facts in an all-embracing theory, like the combination of earthquakes, volcanism and the elevation of the South American continent in his theory of vertically moving plates (see Part 1 of this article). His theories, including ideas on icebergs and glaciation (see below), were not always successful, but the impact of his theory of evolution by means of natural selection greatly outweighed these failures.

First of all, the geological sense of time – thinking in terms of hundreds of millions of years instead of centuries – was of critical importance for Darwin to envisage the gradual development of life to its present-day, highly evolved state. Darwin even over-estimated the duration of the Tertiary as lasting 300Ma, several times in excess of modern radiometric dating (Rudwick 2008, p. 385, footnote 8; see also Burchfield 1974). The fossil record had proved, through the work of William Smith (1769-1839), to be a good tool to date the layers of the Earth relatively. This meant that life had clearly changed through time, the living beings becoming gradually more ‘complicated’ when approaching present times, as is to be expected according to Darwin’s theory of evolution.

He explained the general absence of transitional forms, apart from exceptions such as Archaeopteryx with its characteristics of both reptile and bird (“a grand case for me”; Darwin in a letter to Dana, 7 January, 1863; see Herbert 2005, p. 333), in the following way:

• On the one hand, these transitional forms would have been rare, since the development would have gone quickly towards a complete adaptation to the new circumstances (from fluttering from one tree to the next, towards good flying capacities).
• On the other hand, he was also fully aware that only a very small proportion of the diversity of animals and plants had been preserved as fossils, since most had decayed to unrecognisable fragments, and the rare fossil remains of animals without shells and bones were largely unknown (for a different perspective, see Donovan & Paul 1998). However, the enigmatic traces of Precambrian life required by Darwin are now much better known.

The large South American mammals, which had become recently extinct and which Darwin (1838) had immediately recognised as being related to forms still alive and restricted to that continent, suggested a close relationship. That is, the fossil forms were the direct ancestors of the living representatives. Also, as previously mentioned, Darwin’s research on both living and fossil barnacles formed a solid basis for his evolutionary ideas, as the modification or even loss of organs due to changing living conditions pointed to the importance of natural selection.

As far as sudden extinctions were concerned, Darwin assumed that the faunas (and floras) could have survived elsewhere in unexplored areas and the extinction could, therefore, have been more gradual. Nowadays, it is clear that there have been periods of geologically rapid mass extinction (which, incidentally, pose no problem for Darwin’s theory of evolution by means of natural selection, as the driving mechanisms are large scale physical processes). However, he was right that presumably extinct animals have survived in hidden corners, the coelacanth found in the deep water of the Indian Ocean being an excellent example.

This view was quite popular in the nineteenth century and was admirably expressed in The Lost World (Conan Doyle 1912). The influence of Lyell, advocating that geological processes in the past had not been different from the present ones, not even in intensity, made Darwin an opponent of theories of catastrophism, although it is now recognised not to have been in contradiction with his evolutionary ideas. It is remarkable that Lyell only reluctantly adhered to Darwin’s evolutionary theory and was not completely convinced until 1869 (Simpson 1970, p. 54). This was despite the fact that his ideas had been a great influence on Darwin and formed an excellent explanation, completely according to his views of gradual changes, for the changes of species over time.

Darwin on icebergs and ancient glaciations

“… many glaciers beryl blue most beautiful contrasted with snow” (Darwin in field notebook, in Patagonia)

Darwin’s (1842) last serious fieldwork was in Snowdonia in North Wales, describing boulder deposits on a striated basement. This was in accordance with the views of, among others, the Reverend William Buckland (1784-1856), that they had been formed by glaciers. However, other boulders did not show the features typical for glaciers, but appeared to have been deposited in the sea on gently dipping surfaces before these had been elevated.

Distortion of the beds could have been caused by icebergs grating over the surface, shattering the soft slate in the same way as they appear to have contorted the sedimentary beds on the east coast of England (Lyell 1840). Darwin compared these with deposits of till he had seen in Tierra del Fuego, which were formed by icebergs calved off from glaciers coming down from the Andes to the coast. The Welsh deposits of irregularly stratified gravel and boulders looked rather similar to beds with marine shells in Shropshire and Staffordshire. The remote origin of some of the pebbles supported Darwin’s opinion that they had been transported by icebergs and he compared the situation with present day Spitsbergen (Svalbard).

Darwin assumed that the British Isles had been lower and partly covered by a sea in which the icebergs would have floated. However, he was reluctant to accept the glacial origin of the “parallel roads” since it made his publication on Glen Roy almost ridiculous (see Part 1). Although he considered that a cooler climate was the reason for glaciers on local hills and the forming of icebergs, he – like Lyell – was against the land ice theory of Agassiz or, rather, that of Venetz and Charpentier (Rudwick 2008, pp. 518, 536-537).

Conclusion

When we celebrated 200 years since his birth and 150 years since publication of On the Origin of Species in 2009, Darwin the biologist received ample public exposure. Yet, when he sailed on HMS Beagle, Darwin travelled as an aspiring geologist. That he attained his aspiration may be judged, not least, by the award of the Wollaston Medal to Darwin in 1859, the greatest accolade of the Geological Society. If Darwin’s geological enquiries waned as his biological research waxed, it did not make them any less remarkable.

Rather, Darwin was a geologist whose attainments in that field were notable and comparable with those of his illustrious contemporaries such as Lyell, De la Beche, Murchison and Phillips.

About the authors

Stephen Donovan is a researcher in fossil invertebrates at the Department of Geology at the National Centre for Biodiversity – Naturalis, Leiden, The Netherlands. Cor Winkler Prins is a retired researcher at Naturalis with a particular interest in Upper Palaeozoic Brachiopoda and Carboniferous stratigraphy. The authors share an interest in the history of geology.

References

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Burchfield, J.D. 1974. Darwin and the dilemma of geological time. Isis 65, 301-321.

Conan Doyle, A. 1912. The Lost World: Being an Account of the Recent amazing adventures of Professor George E. Challenger, Lord John Roxton, Professor Summerlee, and Mr. E.D. Malone of the “Daily Gazette.” Hodder and Stoughton, London, 319 pp.

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