Darwin's Geological diary from the voyage of the Beagle

An introduction by Gordon Chancellor

The Darwin Online project has produced the first complete transcription of Darwin's Geological diary (CUL-DAR32-38) from the voyage of the Beagle (1831-1836). Images of the entire manuscript, donated to Cambridge University Library (CUL) in 1942, appeared on Darwin Online in 2006. The entire Diary has now been transcribed and published here for the first time. The transcriptions can be viewed alongside the images of the manucript at the click of a button.

Various scholars have contributed to the transcription but by far the largest contribution has been that of Kees Rookmaaker. John van Wyhe has edited Kees's transcriptions and added editorial notes and Gordon Chancellor has checked Rookmaaker's transcriptions against the online images and the original manuscripts. Other significant contributions have been Claire Ring's transcription of Chiloe, Gregory B. Estes and K. Thalia Grant's transcription of the Galapagos notes, Guido Chiesura of parts of the Cape Verde, Azores, St Helena and Ascension sections and Maxwell and Doris Banks' of Hobart (published in Banks 1971). The entries for the Geological diary in the Darwin Online manuscripts catalogue have been extensively revised from the Cambridge University Library original as regards place names, transcription errors and dates.

1. Introduction

Darwin's Geological diary is a crucial document for studying his intellectual development during the voyage of the Beagle. It is Darwin's longest single unpublished manuscript from the voyage and records the greater part of his geological work from the Cape Verde islands in January 1832 to the Azores in September 1836. The Geological diary was the foundation on which Darwin built his post-voyage geological career.

As far as is known, Darwin never referred to the manuscript as any sort of 'diary'; this is a name given by scholars to what are now volumes CUL-DAR32-38 in the Cambridge University Library, although this is a somewhat arbitrary limitation as there are closely related materials in CUL-DAR39-44. When Darwin did refer to his geological manuscripts he generally called them his 'notes' or 'memoranda' or on one occasion his 'note-book' (see section 3).

Armstrong (1985), in addition to providing images and transcripts of some of Darwin's geological notes, described very clearly the interrelationships of all Darwin's Beagle materials. He explained how Darwin – usually when back on the Beagle following an expedition on land – used his field notebooks and occasionally loose field notes as the basis for writing up his private journal or Beagle diary, written for his family, as well as his private scientific notes. Darwin placed the greatest importance on  note-taking (Beagle notebooks) and in his chapter in the Admiralty Manual (1849), he advised every travelling naturalist to write 'very copious notes'.

Darwin divided his scientific notes into what have come to be known as his Zoological diary and the Geological diary, so that effectively he had three 'diaries', although this three-way split was not always clear cut. Darwin then re-combined these after the voyage into his published Journal of researches (1839). The Geological diary and related notes were the raw material for two of the three parts of Darwin's Geology of the Beagle (Volcanic Islands of 1844 and South America of 1846) and various articles; the third part was Coral Reefs of 1842 which was based on other manuscripts now in CUL-DAR41. As the Geological diary is derived from the field notebooks it is necessary to have the transcriptions of these, together with Volcanic Islands and South America continuously at hand while studying the Geological diary. Darwin dealt with his fossil discoveries in the Geological diary although in the 1830s fossil mammal specialists tended to regard themselves firstly as zoologists. It is therefore fair to say that the Fossil mammalia volume of the Zoology of the Beagle is also based on the Geological diary. All these materials are available on Darwin Online.

Armstrong, in an indispensable series of books and articles looking at Darwin's Beagle work while actually describing the places Darwin visited, has made extensive use of the Geological diary. Banks (1971) was the first scholar to transcribe and discuss some of the manuscript in any detail. Pearson (1996) provided a useful overview and Herbert has discussed specific parts of all Darwin's geology manuscripts in her book on Darwin's geological career (Herbert 2005). This introduction seeks to build on these earlier studies and the availability of searchable transcriptions on Darwin Online to provide an holistic view of the Geological diary.

In this introduction the Geological diary is placed within the context of all of Darwin's manuscripts from the voyage and presented as a summary of its contents, which are by no means confined to geology. The emphasis is laid here on what the manuscript can tell us about Darwin's development as a geologist and about his changing views on species origins.

The newly transcribed and edited diary reveals new insights into Darwin's theorising such as clear evidence that he was not, as often claimed, an immediate convert to Charles Lyell's gradualistic geology. The view of some (e.g. Brinkman 2010) that Darwin's discovery of fossil mammals in 1832-1834 was pivotal to his emerging views on species is supported, although more emphasis is placed here on a single horse tooth. The view that Darwin's discovery of a fossil forest high in the Andes in 1835 may have been a trigger for his belief in oceanic subsidence which in turn led to his theory of coral atoll formation (Pearn 2009; Sponsel 2009) is also supported.

It is further suggested that there was another crucial stage in Darwin's development which occurred neatly between the fossil bones of 1833 and the fossil forest of 1835, namely his sight of mist in Andean valleys in August 1834. This arguably 'eureka' moment, like his later sight of Eimeo from Tahiti, showed Darwin how one landform can evolve into another, thus providing a geological template for the same kind of dynamic thinking in biology.

Finally, the possibility is raised that some land snails given to Darwin on St Helena near the end of the voyage may have contributed to his emerging doubts on the stability of species.

2. The Beagle manuscripts

In order fully to appreciate the importance of the Geological diary an overview must first be taken of the interrelationships of Darwin's manuscripts from his voyage in HMS Beagle. The best place to start is the summary in Correspondence vol. 1: Appendix II, pp. 545-8. In addition to all Darwin's known Beagle correspondence published in that 1985 volume, the Appendix lists (1) the field notebooks, (2) the Beagle diary, (3) the 'zoological diary', (4) the 'geological diary and notes' and (5) the catalogues of specimens. The terms used for the different manuscripts in the Correspondence have tended to stick and seem likely to become canonical, even though they were not always those used by Darwin himself. The Darwin Correspondence project studied all the Beagle manuscripts in preparing their reconstructed list of the books in the Beagle library (Correspondence 1: 553). (See the newly reconstructed online Beagle Library here.)

Herbert (1987) published the 'Red notebook' and Chancellor and van Wyhe published the field notebooks (1) in their entirety in Beagle notebooks. Beagle notebooks made clear that Darwin always used the 'Red notebook', the first part of which he filled during the voyage, as a theory notebook and never as a field notebook.

Barlow (1933) first published the Beagle diary (2) which has since been republished with minor amendments by Keynes 1988, and transcribed again by Rookmaaker in Darwin Online. Gruber and Gruber (1962) seem to have been the first to look seriously at the zoological and geological materials (3 and 4). They briefly described the 'notes' and pointed out that those for geology greatly outnumber those for zoology, although in the first half of the voyage the ratio was fairly equal. They quoted a total of 1,383 pages of geology as against 368 of zoology, although it is not entirely clear how they arrived at their figures. For geology the figure they quote is 145 higher than the total of pages numbered by the archivist in the Geological diary. It may be that they counted the pages before they had been numbered or included material not now archived as Geological diary such as the 'Coral Islands' material in CUL-DAR41. Keynes (2000) published the zoological diary (3) which he called the 'zoology notes' - and 'primary' biological specimen catalogues (part of 5).

Banks (1971) published a transcription of the Hobart section of the Geological diary (CUL-DAR38.837-857) while Herbert in a series of studies of Darwin's early career (1974, 1991, 1995, 2005, 2007, 2009, 2010) has made many contributions to our understanding of the geological notes (4). Sulloway (1982) analysed some of them in his groundbreaking study of Darwin's voyage spelling habits. Armstrong made extensive use of them in his Darwin publications and Pearson (1996) has used them in his studies of Darwin's work on igneous rocks.

Lyall Anderson in Pearn (2009) summarised the present state of the geological specimens and Herbert (2010) has described Darwin's geological collection methods. Rosen and Darrell (2011) have attempted to pull all the known information concerning Darwin's specimens together and have provided the very useful categorisation, adopted here, of the specimen catalogues (5) into primary and secondary.

The primary biological catalogues consist of two lists of specimens, one for 'dry' specimens, one for 'wet', i.e. specimens preserved in spirits. These are contained in six small brown notebooks and are entirely in Darwin's handwriting, three notebooks for dry specimens and three for wet. In the left margins Darwin added a letter to indicate the type of organism represented by the specimen (e.g. 'I' for insect). The secondary biological catalogues are lists on foolscap paper and are written mainly in the hand of Darwin's amanuensis Syms Covington, with notes added in places by Darwin. Each list deals with a particular group of organisms, such as 'fish' or 'plants' and it is therefore clear that they were copied by Covington from the primary catalogues. Various authors (e.g. Barlow 1963, Porter 1987, Keynes 2005) have published the secondary catalogues but some remain unpublished and some have not yet been found. The most famous are undoubtedly the 'Ornithological notes' published by Barlow (1963) which include Darwin's first written doubts about the 'stability' of species.

The primary geological catalogues for rocks and fossils, which remain unpublished, are in four other notebooks, now CUL-DAR236. A page from one of these notebooks is shown in Herbert (2005, p. 147) and Grant and Estes (2009, fig. 25E) have published a colour photograph of the third notebook. In the four notebooks the specimen numbers are split as follows: 12-1675; 1677-2851; 2864-3742; 3743-[3913]. Harker's transcription of them is available and fully transcribed by Christine Chua in Darwin Online.

The text of the Geological diary is peppered with specimen numbers, after CUL-DAR32.41 usually written in the margins, and there are several secondary lists in Darwin's hand of his geological specimens from specific locations, although the most extensive of these lists are in CUL-DAR39. It is often possible to trace these back via the primary lists to the original field notebook entry and in some cases forward to the published descriptions in the Zoology of the Beagle and the Geology of the Beagle. In the case of some of the fossil mammals there are further important manuscripts which cite these specimen numbers, for example the fossil Macrauchenia in the February 1835 CUL-DAR42.97-99 essay containing the phrase 'gradual birth and death of species' (Hodge 1983, Herbert 2005, p. 310).

DiGregorio and Gill (1990) published the marginalia in Darwin's books and although few of these date from the voyage itself it is helpful that they are becoming available at http://www.archive.org/details/darwinslibrary. Now, with the transcription of the Geological diary on Darwin Online, we have for the first time fully searchable editions of almost all Darwin's Beagle publications and manuscripts.

The value of these manuscripts to historians has now been notably enhanced by Rookmaaker's Concordance between the Beagle diary, the Geological diary and the Beagle notebooks. This concordance provides the dates, locations and page numbers for all Darwin's geological manuscripts throughout the voyage.

The only remaining untranscribed manuscripts are some of those in CUL-DAR39-44 (transcibed by Christine Chua and in Darwin Online since this introduction was first written), the few secondary zoological specimen catalogues and the four primary catalogues of geological specimens.

3. What is the Geological diary?

Although the term 'diary' seems to have stuck, Darwin never himself used it for any of his manuscripts. He generally referred to the Beagle diary as his 'private journal', for example in CUL-DAR34.377, although at the start of the voyage he once referred to it as his 'log Book' (Correspondence vol. 1, p. 202). The earliest use of the term 'diary' seems to have been Horace Darwin's for the transcription he had typed in 1891 of his father's Beagle manuscript which is now CUL-DAR217.3. Horace's daughter Nora Barlow then published a corrected transcription of this, which has ever since been known as the Beagle diary (Barlow 1933, p. ix). Barlow (1933) apparently accepted her father's term 'diary' to distinguish that document from Darwin's easily confusable Journal of researches (1839) which was derived from it, although in her introduction she refers to it as 'the manuscript Journal'.

No contemporary published references to the scientific manuscripts by anyone other than Darwin himself has been found, prior to the appearance of the Handlist of Darwin papers at the University Library Cambridge (1960). Where Darwin referred to his geology manuscripts he generally cited his 'notes', 'geology' (see e.g. Fernando Noronha discussion in section 4; Keynes 2000, p. 372) or 'memoranda' (Correspondence vol. 1, p. 449). In one of his publications ('Erratic Boulders' of 1842, see Shorter publications, p. 151) he mentioned an entry in his 'note-book', which is actually the Geological diary (CUL-DAR32.118), perhaps indicating that the notes were bound at that time. There is physical evidence that at least the earlier sections of the Geological diary were once sewn, as with the zoological diary (Keynes 2000). Paradoxically Darwin seems to have intended his 'private journal' to be read by close family and friends, whereas there is no evidence that he ever showed anyone his scientific notes during the voyage. So far as is known the only exception to this was Darwin's amanuensis Syms Covington's copy of the 'Coral Islands' essay in CUL-DAR41.13-22, annotated by Fitzroy. As leader of the voyage FitzRoy would have been entitled to read any of Darwin's scientific notes and may of course have done so. The Geological diary therefore sits within Darwin's sphere of 'private science', as characterised by Rudwick (1982).

The Handlist divides the Beagle notes into the Diary of observations on zoology of the places visited during the voyage (CUL-DAR30-31) and the geological diary and notes (CUL-DAR32-38). Other zoological material went into CUL-DAR29 and other geological material went into CUL-DAR39-44. These categories are thought to have been more or less those in which Darwin's executors found his papers in 1882. They certainly were not 'a vast accumulation of useless manuscript' as stigmatized by T.H. Huxley in his obituary to Darwin (1888). It is only fair to Huxley to point out, however, that he was probably not talking about the Geological diary and he probably regarded Darwin's Geology of the Beagle as the 'published version' of the Geological diary. The only page which can be assumed lost before the papers arrived at the CUL is the nineteenth page of Darwin's Hobart notes (i.e. the page which should have been after CUL-DAR38.854). He may have simply skipped '19' when he was adding page numbers but it would be an amazing co-incidence if this happened exactly where there appears to be text missing.

The CUL archivists bound the geological notes presumably in the order in which they arrived at the library and further split them into what they hand-listed as Diary of observations on the geology of the places visited during the voyage (CUL-DAR32-33) and Notes on the geology of the places visited during the voyage (CUL-DAR34-38), with other material bound in CUL-DAR39-44. The titles used are written in ink in an unidentified hand on pieces of brown paper now bound in with the notes. These were presumably cut from the wrappers in which the manuscripts arrived at the Library. The archivists numbered the 'Diary' and 'Notes' in pencil as two separate sequences: CUL-DAR32-33, pp. 1-278; CUL-DAR34-38, pp. 1-960; total 1,238. By co-incidence the earlier volume numbers (32-35) are similar to the dates (1832-1835) of the material they contain.

It is not clear why the Geological diary was split between 'Diary' and 'Notes'. It does not reflect any difference in the way Darwin himself treated the manuscript during the voyage. The reason for the split seems to be an archivist's later assumption that the Geological diary was intended to be strictly chronological and a secondary assumption that Darwin departed from this intention a few years into the voyage. In fact there is no evidence that Darwin ever intended a strictly chronological order and early in the voyage he began to arrange the manuscript into geographical and subject-based sections. He did this as he started to revisit places (e.g. Bahia Blanca in Argentina) and as he revised his earlier interpretations of what he had seen. He did, however, tend to number these specific sections, presumably as an insurance against having to re-order the pages should they become jumbled. The most obvious proof that the 'Diary/Notes' split was not of Darwin's making is that the last sheet of his 'Pampas' section at the end of the 'Diary' (i.e. CUL-DAR33.278) was numbered '30' by Darwin himself, while his sheet '31' is in the 'Notes' (i.e. CUL-DAR34.17).

The reader must, therefore, be aware that if Darwin visited a place more than once the notes on that place may be of different dates and this can become very confusing if one expects the Geological diary to be a diary in any strict chronological sense. In the most extreme case, the very first fourteen sheets of the entire Geological diary, describing the Brazilian coast, date from the last few months of the voyage in 1836. A non-specialist might not realise that the Beagle re-visited Brazil and would assume that since these pages were at the front they must date from 1832. There are many other examples of departure from a chronological sequence: CUL-DAR32 ends with Darwin's second visit to the Falklands in March 1834, then CUL-DAR33 starts nine months earlier in Maldonado in May-June 1833 before returning to the Falklands account. These later Falkland notes refer to King George's Sound, Australia so seem to have been written after March 1836 but they are followed by more notes from the 1833 visit to the Falklands in CUL-DAR34. Other examples include the first sheets in CUL-DAR34 which actually date from October 1832 three years earlier than CUL-DAR34.177-178 which date from November 1835.

The Geological diary is characterised by a great range of paper types and writing styles used by Darwin over the course of the five year voyage and against this background it is impossible to point to any consistent difference between the 'Diary' and the 'Notes'. The range of styles is not surprising when one considers that Darwin was using whatever paper was to hand on board ship, or perhaps in a tent on some remote shore. The arbitrary division of 'Diary' from 'Notes' obscures the flow of the manuscript and therefore Darwin Online refers to all Darwin's notes written during the voyage and now in CUL-DAR32-38 as the Geological diary.

Many annotations in the Geological diary date from after the voyage. In almost all cases these are written on the versos (reverse sides) of the diary pages, using a different pen and are obviously, judging from content e.g. literature references, post-voyage additions. Conversely, some geological notes unquestionably dating from the voyage are in other volumes of the Darwin archive (CUL-DAR39-44) and in several cases (e.g. those from January-March 1833 and May 1835 in CUL-DAR39) it is not clear why they are not part of the Geological diary. There are some pieces of the Geological diary excised, presumably by Darwin, and now in these later volumes; CUL-DAR42.75 is part of CUL-DAR33.79 and it is likely that other examples will be discovered.

Perhaps the most significant example of notes being in the 'wrong' volume is that all the notes on Keeling from April 1836 are in CUL-DAR41, although this is obviously because Darwin grouped them with his 'Coral Island' essay. Most importantly, much of the material in CUL-DAR39-44 is integral to understanding the Geological diary and Darwin would not have endorsed any labelling of these manuscripts which would tend to obscure their close relationships. Various sections of these other voyage manuscripts have been published previously and some of the most significant are referred to below. In due course introductions to all this material will be provided.

In this introduction no detailed physical description of the Geological diary has been attempted. The notes themselves are generally written on 20 cm x 25 cm sheets but there is a great variety of paper types, for example some are ruled and margined, others not, and some are formed from 25 cm x 40 cm un-ruled sheets folded in half to make four pages. Some are mere scraps of paper and some are not written by Darwin, for example maps (e.g. CUL-DAR35.405 by Alexander Caldcleugh), drawings (e.g. CUL-DAR35.403 possibly by Zacarias Nixon), letters and memoranda from men Darwin met and corresponded with during the voyage (e.g. CUL-DAR34.14-15 from Charles Hughes, CUL-DAR35.232 from Frederick Eck, CUL-DAR35.329 from Charles Douglas, CUL-DAR36.427 from Robert Alison, CUL-DAR37.685 from Belford Wilson) and in one case some notes by an unknown author in Spanish (CUL-DAR34.10; see Darwin Online for translation by Austin Whittall and Sergio Zagier).

The CUL archivist generally numbered the recto page because Darwin tended to use the verso for later notes, often referring to something specific on the recto and paralleling the approach he used for the zoological diary (Keynes 2000). Departures from this are the July-August 1836 notes on St Helena, from sheets numbered '7' to '36' (CUL-DAR38.926-935), Ascension (CUL-DAR38.936-953) and Bahia (CUL-DAR32.1-8) where Darwin wrote on both sides of the paper, as he did in his Beagle diary, with a large margin for notes and diagrams. Surprisingly he reverted to the 'old style' for part of the Bahia 1836 notes (CUL-DAR32.9-14) and the Azores in September (CUL-DAR38.957-960).

There are many non-matching pieces of paper bound in with the notes, often with hand-drawn diagrams and maps, some not in Darwin's hand. The sketches by Darwin were probably a trial to him as he noted (CUL-DAR32.134v) 'I cannot draw', but some of his coastal views are quite appealing (see for example Pearn 2009, p. 45). Occasional pieces of paper are actually field notes and one section on Chiloe (CUL-DAR35.328) are the field notes for an entire excursion (see section 4). Throughout the manuscript geological specimens are referred to by their numbers, usually added in the margin.

Approximate dates in the Diary:

DAR32      pp. 1-152   Jan 1832-Mar 1834, plus Aug 1836        
CUL-DAR33      pp. 153-278        May 1833-May 1834, plus notes on Falklands written after March 1836
CUL-DAR34      pp. 1-205   Oct 1832-July 1834, plus Tierra del Fuego appendix, pp.177-178 dated Nov 1835
CUL-DAR35      pp. 206-418        July 1834-Mar 1835                             
CUL-DAR36      pp. 419-610        Apr-June 1835                    
CUL-DAR37      pp. 611-811        June-Dec 1835                                   
CUL-DAR38      pp. 812-960        Jan-Sep 1836    

Places covered in the Diary:
(for detail see the itinerary by Rookmaaker)

CUL-DAR32      Cape Verdes and other Atlantic islands, Brazil including notes from second visit to Bahia and Pernambuco in 1836, Uruguay, Tierra del Fuego
CUL-DAR33      Uruguay, Argentina, Falklands
CUL-DAR34      Uruguay, Argentina (includes Santa Cruz expedition), Falklands, Chiloe
CUL-DAR35      Chile (includes Chonos and Chiloe)
CUL-DAR36      Chile and crossing of Andes into Argentina and Copiapo
CUL-DAR37      Northern Chile, Peru, Galapagos, Tahiti, New Zealand
CUL-DAR38      Australia, Mauritius, South Africa, St Helena, Ascension, Bahia, Azores      

4. The importance of the Geological diary

As previous scholars, notably Sandra Herbert (2005), have observed the Geological diary is highly recursive and records how Darwin was from the very start of the voyage deeply concerned with theoretical issues, often re-working his material as his views evolved.

As Darwin recalled many years later in his Autobiography, at his very first landfall, on the Cape de Verde island of St Jago (Santiago) in January 1832, he deduced that the archipelago was volcanic and had emerged from the sea and how marine erosion was responsible for much of the islands' landscape (Vala 2009). As has been suggested by many historians (Secord 1991, Armstrong 2004, Herbert 2005, Pearson and Nicholas 2007, Pasquarè et al. 2009) this episode exemplifies arguably Darwin's most important methodological commitment, right at the start of his geologizing, to the actualism promoted in Charles Lyell's Principles of geology (1830-1833). Henslow, a 'catastrophist', had famously recommended Darwin to take Lyell's first volume of 1830 with him and Captain FitzRoy actually gave Darwin a copy. Henslow told Darwin 'on no account' to believe everything Lyell wrote, meaning presumably that Darwin should not be persuaded by Lyell's Huttonian view of a steady state or cyclical Earth, where everything changes at the same gradual rate today as it has always done.

Darwin was certainly a ready convert to Lyell's parsimonious method of always preferring explanations based on processes currently observable, now called actualism. Lyell was disingenuous, however, in implying that only those who followed his view of gradual (i.e. step-like) change over enormous periods of time were applying actualism, as some geological phenomena certainly required a more 'catastrophic' interpretation.

Declaring that Darwin adopted Lyell's actualism from the start is not to say that from then on he rejected 'catastrophism' where the evidence seemed to demand it. There are several passages in CUL-DAR32 which indicate that early in the voyage Darwin was certainly not entirely a 'gradualist', or 'uniformitarian' as William Whewell would have termed it back at the Geological Society in London. Pearson and Nicholas (2007), for example, have discussed Darwin's early catastrophic interpretations of the valleys of the Cape Verdes which he believed must have been formed by a dramatic flood:

 The surrounding country bespeaks the utmost violence; pieces of rocks torn apart from their beds stand like castles walls erect. — others as wild & jagged in their outlines as mica slate give to the horizon a grand & picturesque appearance. (CUL-DAR32.31-32)

In section 6 of this introduction another distinctly 'catastrophic' passage is quoted in which Darwin is understandably amazed by the immense extent of geological structures in South America and reflects that:

If this remarkable continuity was more satisfactorily proved, it would be a fine instance for those who attribute the present state of the world more to great causes at distinct epochs, that to a succession of smaller ones. (CUL-DAR32.43)

At this early point in the voyage, therefore, Darwin is seeing the structures as possible support for Sedgwick's view (following Élie de Beaumont) that the Andes had been 'risen by one blow' (CUL-DAR36.501). It is possible to trace in the Geological diary Darwin's continuing openness to catastrophic explanations for valley formation at various places throughout the voyage, such as during the Santa Cruz excursion of April 1834, in the Andes in March/April 1835 and in Australia in January 1836. He did, however, revise his interpretation of the deposits containing fossil mammals from the initial somewhat catastrophic view of September 1832 to a more gradualist position a year later (see discussion of CUL-DAR32.73 in section 6).

Regarding the creation of the Andes, having by April 1835 experienced earthquakes and traversed the Cordillera himself, Darwin certainly rejected Sedgwick's view of their formation. He was by then convinced that they had arisen by a huge number of gradual steps over an immense period of time. Darwin's Autobiography account of his conversion to gradualism can be taken at face value on this point.

Darwin's realisation that the Cape Verdes had risen from the sea profoundly influenced his interpretation of the geological history of South America and formed the basis for his theory of coral reef evolution, a crucial hydrographical and geological research priority in the 1830s (Sponsel 2009). Moreover, Darwin's theory of coral reefs absolutely requires commitment to gradualistic interpretation of crustal evolution. When later dealing with other continents he became so fixed in his belief in vertical movements of the crust and the erosive power of the sea that he excluded other possible explanations, such as river action in Australia and ice in Scotland (Beagle notebooks). Darwin's growing commitment to a Lyellian position on gradual geological change over time was, however, a pre-requisite for his growing belief in descent with modification in the organic world (i.e. evolution). In section 5 the evidence is presented that the Geological diary reflects Darwin's shifting perspective on the descent issue.

Around Easter 1834 Darwin was already well into what can now be seen to be the second half of his general-interest Beagle diary (manuscript pages around 450 of 780 total). Since this was more or less the voyage mid-point, it seems that by around this time Darwin's scientific writing was already taking precedence over his more general writing. This also supports Gruber and Gruber's (1962) analysis that it was from 1834 that the ratio of Darwin's geological to zoological output increased decisively. It is remarkable that the entire seventh volume of the Geological diary (i.e. CUL-DAR38) deals with places visited in 1836, whereas there are only fourteen pages for these places in the zoological diary.

The Geological diary includes some important thematic or synthetic essays, such as the 'Elevation of Patagonia' (CUL-DAR34.40-60) which Darwin started to write after about two years of the voyage exploring the implications of his conviction that a vast area of South America was emerging step-wise from the Atlantic (see section 5 and Herbert 2005). Through these essays, one of the earliest of which, 'Reflection on reading my Geological notes', dates from around February 1834 and is now in CUL-DAR42.93-96, we see Darwin's growing confidence as a geologist and as Sandra Herbert (1995) has called him 'a prospective author'. The 'Reflection' essay shows Darwin at a critical stage in his thinking, exploring the implications of the elevation of South America for the history of life there and on the surrounding sea bed.

There are several other geological essays which have been archived in CUL-DAR41 and 42, outside the Geological diary, for example in chronological order 'Recapitulation & Concluding Remarks' (CUL-DAR41.23-39; this is Syms Covington's fair copy, Darwin's original is lost), 'Coral Islands' (CUL-DAR41.1-23; 1-13 are Darwin's original; 13-22 Covington's copy) and 'Cleavage' (CUL-DAR41.59-77). It is a mistake to think of the essays not bound in CUL-DAR32-38 as logically separate from the Geological diary. Darwin routinely headed all his notes, and arranged them for clarity, some by place, some by subject and that is how he eventually arranged his chapters in the Geology of the Beagle.

It is certainly significant that around mid-1834, in the southern winter, the Beagle after two years on the Atlantic coast of South America, began to work her way up the Pacific coast. This opportunity to study the largely unexplored southern half of the mighty Andes and to compare the two sides of the continent was seized by the young Darwin with gusto. It allowed his understanding of geological history to mature rapidly as the reams of his manuscript piled ever higher. Alistair Sponsel (2009) has drawn attention to the entry on pp. 39a-40a for 18 August 1834 in Darwin's Valparaiso notebook as the first possible indication that he might have started to consider the possibility of Pacific subsidence: "With respect to great valleys, Mem Pat — pebble bed. — Perhaps in Pacific if seen, wonder would be reversed. —" (Beagle notebooks, p. 352)

Sponsel has pointed out that Darwin wrote a letter to Robert Alison dated 29 May 1835 which, judging from Alison's reply now in CUL-DAR36.427 (Correspondence vol. 1, p. 452), must have mentioned his speculation that Pacific islands might be subsiding. At some point during 1835 Darwin became convinced that the elevation of South America was at least partly balanced by subsidence of the Pacific basin. By one of the first of those imaginative leaps, so characteristic of Darwin in the post-Beagle years, this concept of crustal oscillation provided him with a mechanism for the evolution of coral atolls (see Sponsel 2009). We might wonder whether any of Darwin's discoveries prior to the 29 May letter was especially significant in triggering Darwin's speculations?

Although there is no evidence in the Geological diary as defined here (i.e. CUL-DAR32-38) of Darwin working out his coral reef theory, his mid-1835 notes in CUL-DAR36.523 amply demonstrate how profoundly he was struck by finding a fossil forest high in the Andes on 1 April 1835. Since the trees seemed to be in a life-like standing position he thought they proved massive subsidence to allow them to be covered by water-borne sediment, followed by dramatic elevation to their present altitude: "I must confess however that I myself cannot quite banish the idea of a subsidence, enormous as the extent of movement required assuredly is.”

In a letter to Henslow of 18 April (Correspondence vol. 1, p. 442) Darwin said 'I am quite afraid of the only conclusion which I can draw from this fact, namely that there must have been a depression in the surface of the land to that amount'. Perhaps his clearest statement of his view of the fossil forest was the one he published in South America: "Certainly the upright trees have been buried under several thousand feet in thickness of matter, accumulated under the sea. As the trees obviously must once have grown on dry land, what an enormous amount of subsidence is thus indicated!" (p. 203)

We agree with Pearn (2009, p. 83) that finding the fossil forest may have been the spark which ignited Darwin's belief in crustal oscillation. Darwin actually reported to Henslow in a letter dated 12 August 1835 (Correspondence vol. 1, p. 462) that the mixture of volcanic and sedimentary rocks he had found high in the Cordillera supported his view of the crust 'changing in a circle', perhaps hinting at this idea. Ironically perhaps, recent work shows that the fossil forest was never under the sea and was actually preserved under volcanic ash flows (Poma et al. 2009; Brea et al. 2009; Thomas 2009). If Darwin had realised that, he might not have been so convinced that uplift must be balanced by subsidence.

Certainly by the time the Beagle weighed anchor for the Galapagos in September 1835 Darwin, as recorded in his Santiago notebook, was speculating that the rising of South America was balanced by sinking of the Pacific, although his insight regarding atolls seems to have occurred later, at Tahiti in November (Sponsel 2009). That breakthrough led Darwin to write his 'Coral Islands' essay of late 1835 (CUL-DAR41), crafted almost to publication standard and the basis for his first published monograph (Coral Reefs of 1842). Rob Wesson, a seismologist who has visited many of Darwin's field locations, has described how throughout the Beagle voyage and for some years afterwards Darwin gradually synthesised all the evidence he had seen for oscillations of the Earth's crust. Wesson argues that Darwin's belief that all these oscillations had a single cause deserves to be thought of as his first scientific theory (Wesson 2017).

Sponsel (2009) has shown conclusively that Darwin's interest in coral reefs was driven by a serious commitment to the study of living corals and related groups of organisms. The fact that Darwin knew which genera could only thrive near the surface in warm seas was crucial to his breakthrough. As discussed in section 6 Darwin was deeply interested in the shape and depth of the sea bed and paid great attention to the material brought up attached to the Beagle's sounding lead, noting if it included delicate living animals, or only dead ones. Darwin's possibly unique opportunity on the Beagle to connect his marine zoology with his geology underpinned his understanding of crustal dynamics and its relationship to sedimentology. As is clear from the Santiago notebook this allowed him to anticipate the shape of the sea bed around Pacific islands and whether its depth supported life, thus providing him with a test for his subsidence hypothesis. To quote Sponsel (2009, p. 132): 'Thus [Darwin] used hydrography as a kind of stratigraphy of the present, which he then used, in Lyellian fashion, to decode the history of rocks and organisms.'

From the start of the voyage Darwin divided his geological and zoological notes into separated, dedicated sections.

In a like manner notes should be as simple as possible: I kept one set for geology, and another for zoological and all other observations. It is well to endeavour to write upon separate pages remarks on different specimens; for much copying will thus be saved. My journal was likewise kept distinct from the other subjects. I found an arrangement carried thus far very useful: a traveller by land would, I suppose, be obliged to adopt a still more simple plan. [Journal of researches 1839, p. 600; emphasis added]

The earliest dated zoological note is 6 January 1832 (CUL-DAR30.01) which may have been the first day he felt well enough to write any scientific notes, as his first Beagle diary entry after leaving England was only 5 January. The earliest dated geological note is 17 January which was his first contact with foreign rocks and apparently when he first used a field notebook. He must, therefore, have decided on the 'geology/zoology etc' split before writing a single word of geology. One must always bear in mind that these subject divisions are intellectual constructs and that the words 'geology' and 'zoology' themselves had only been in general use since the late eighteenth century. It is also crucial to remember that when Darwin uses 'zoology' he means 'natural history', including botany, although as mentioned below he recorded some important 'natural history' observations in the 'geology' notes, and vice versa. Famously of course Darwin's published account of the voyage from which the quote is taken uses the terms 'geology' and 'natural history' in its title and Darwin himself probably did more than any other scientist to re-unite these subjects in his Origin of species.

That Darwin split his scientific notes in this way is very significant, as it shows how he intended to focus his efforts and thus how he perceived his career developing. Darwin was pursuing a research programme with two main agendas, the first of which sprang from his Edinburgh work on invertebrate zoology, with an emphasis on those animals apparently closest to plants (see Sloan 1985 and Sponsel 2009 but also Keynes 2000 for an alternative view).

There is little of strictly zoological interest in the Geological diary for the obvious reason that Darwin diverted it into his zoological diary, but there was occasional 'spillage', such as the field notes quoted below, and some of these are of interest in regard to Darwin's views on species (see section 5). There are also references to the remains of beetles in Patagonia (CUL-DAR32.67, the ecology of lagoons in Uruguay (CUL-DAR33.162) and sub-fossil birds' eggs and land snails on St Helena (CUL-DAR38.932). There are also various observations on biogeography (e.g. CUL-DAR32.119, 34.129v,173,195, 35.302). Most importantly, Darwin treated his mammalian fossil work as part of geology rather than zoology, even though vertebrate palaeontologists were more likely then to identify themselves as zoologists rather than geologists, as remains the case today. Perhaps most surprising is a paragraph on global commerce with very little direct relevance to geology or zoology; this was used almost verbatim in Darwin's published Journal and concerns the shipment of Uruguayan cattle bones for soil enrichment to England and of frozen fish from America to the East Indies (CUL-DAR33.261v).

Darwin's second major research agenda of geology was distinctive in that it had a strong historical emphasis stemming partly from his Edinburgh days but mainly from his 1831 field work with Sedgwick in North Wales. Right from the Beagle's first landfall Darwin wanted not just to draw sections and maps and collect specimens; he wanted to understand how the ground under his feet came to be. Not long into the voyage his geological programme split into multifarious new strands, such as structural geology, elevation, erratic boulders, cleavage and metamorphism and the extinction of megafauna. Later in the voyage he focussed on coral reefs and the links between volcanoes and earthquakes (Beagle notebooks). Towards the end of the voyage when his time on land was more constrained by the Beagle's itinerary he had less opportunity to pursue new research topics. As he wrote to his friend W.D. Fox from Hobart in February 1836, revealing much about his scientific philosophy:

I have had little opportunity, for some time past of doing anything in Natural History. I draw up very imperfect sketches of the Geology of all the places, to which we pay flying visits; but they cannot be of much use. Leaving America, all connected & therefore interesting, series of observations have come to an end (Correspondence vol. 1, pp. 491-2)

Although Darwin collected plants pretty assiduously he seems to have lumped botany into the 'General Observations' category. Henslow's remark to William Hooker that Darwin was only collecting plants to please him can be taken at face value (see Porter 1987, p. 149; see also Porter 2009). This in no way contradicts the view of Darwin later in his career becoming more and more interested in plants and eventually becoming one of the world's greatest plant scientists (Beagle notebooks, p. 261). As Porter pointed out Darwin did make botanical references in the zoological diary (though the percentage is closer to 3%-5% than the 20% mentioned by Porter) but it has not generally been noticed that ecological observations are also scattered throughout the Geological diary, as the following examples will show. The first quote is from the tiny Atlantic islands known as St Paul's Rocks in CUL-DAR32.38-38v (16 February 1832):

I will here add the few other observations I made. — The island is entirely destitute of vegetation: it affords a secure a building place for countless numbers of boobys & noddys: They hitherto have had so little cause to dread man, that we killed numbers with my geological hammer. — The Boobys lay their eggs on the bare ground; the noddys make a sort of orpi nest with sea-weed. — By the side of the female noddy on the nest, there generally was lying a small flying fish. It was very amusing to see the large crabs with which the rock is covered, quietly stealing them. — The only other inhabitants were numbers of [Flies] & Ornithomya. the latter on the bodies of the Boobys. — I think it is a new species. — There were several spiders. A Staphylinus in the dung. & a small brown moth. — What this latter isolated little being found to live-on I am quite at a loss even to guess. — I believe what I have mentioned is the whole Fauna of the Island of St Pauls. — Whilst I we were busy in collecting the birds & their eggs. the men in boats caught numbers of fine fish. & had it not been for the vast numbers of sharks they would have soon filled the boat. —

This is followed by a remarkable description of the island of Fernando Noronha (CUL-DAR32.40-41), written less than two months after leaving England, which is actually the lengthiest description left by Darwin of this island and clearly derives from his Cape de Verds notebook entry (Beagle notebooks, p. 24). The passage is worth quoting in full as indicating that at this early stage in the voyage Darwin was prepared to blur the subject boundaries of his manuscripts. He actually recorded this in his private Diary entry for 20 February 1832: 'I have written one account of the island in my geology and it is much too hard work to copy anything when the sun is only a few degrees from the zenith'. This Diary entry is doubly interesting for perhaps showing that writing up his geology was already taking priority. The Geological diary entry is itself highly revealing as it shows how very early in the voyage Darwin was questioning the theistic assumption that where there is prey there will be predators to maintain the 'balance of nature':

Large masses of the columnar rock shaded by laurels & ornament[ed] by a leafless tree covered with fine pink flowers like Dystachis, only of more [delicate] colour, gave to the nearer parts of the scenery a beautiful effect. — & the bright sight of a tropical scene could not fail to render the more distant islands & wild outline of the coast exceedingly striking. — The woo[ds] were full of birds, but not of many sorts. — doves & a bird. like the english willow wren were very common: I was surprised to see Terns settling on the trees in flocks. — Both boobys noddys & a most graceful little tern of a snow-white colour when disturbed from the branches, hovered in great numbers round our heads. like little angels — I did not observe any hawks or ravens; which is curious. considering the number of birds that would serve for prey. & the secure building place the rocks would afford. them: compared to St Jago it is quite inexplicable. Mice & Lizards are in great profusion, as I believe is always the case in a hot dry country. — The commonest animal is a little ant. — which builds a nest often 3 feet high & 2 thick, round the stems of trees. It is formed of tough dark brown substance & is full of irregular cavities, disposed without any order. — from the bottom a broard covered way goes to the ground, & from the top small ones branch off along the boughs of the tree. —

[How can birds of preys catch others in a Wood?! Written in margin]

Then in CUL-DAR33.270-271 there is a delightful description of part of the Pampas, elaborating on Darwin's Beagle diary entry for 14 September 1833:

... the country has the same general features; moist grass, plains with a blank vegetable earth, passing into swamps with coarse herbage & bog earth. —& extensive, but shallow lakes, flanked with great beds of rushes & other aquatic plants, which afford a harbor for innumerable wild fowl.... It is a basin or low tract of country very imperfectly drained & may be likened to the Cambridgeshire fens. —

Of course the Geological diary is mainly of importance as the core record of Darwin's geological work. It is, however, of far greater general interest and several other examples could be quoted which show that the Geological diary should not be overlooked by those interested in Darwin's more general pursuits. Perhaps the most fascinating example are the 'Memoranda for Mr C Darwin' now in CUL-DAR34.14-15 from Charles Hughes dated 2 November 1832. These were to help prepare Darwin for his expedition up the Rio Negro to Mercedes and should be read in entirety, although an extract will give a flavour of their appeal:

The water of the Rio Negro is strongly impregnated with the Sarsaparilla which grows on the banks, and this no doubt is the cause of its dark colour — it has a powerful effect on a stranger when first taken (causing a looseness in the bowels) — it is best not to drink largely of it at first, but mix with it a little wine or spirits —

The wild animals which abound in the country about Mercedes are deer, tigers, carpinchos, nutrias, armadillos and many others whose names I do not remember — of birds you will find great plenty — ostriches, flamingos, wild swans, storks, gausos, eagles both black & white, vultures & kites, ducks, partridges, snipes, teru terus, parroquets- in short the variety of birds it is impossible to detail. — There are some snakes, but not of a large size, tho' generally dangerous — centipedes and spiders grow to a large size & their bite is often fatal-

Occasionally there are in the Geological diary mentions of biological specimens mingled with the geology for no obvious reason. The best examples are these specimens in spirits in CUL-DAR34.129-130:

825 Orchis damp woods

(829) (Fish pale yellowish brown. muscles on sides pale coppery. [sketch] about mouth, branchial covering tips of Pectorals & Ventrals reddish orange. — Hook caught Port Famine first time seen. — iris brown

(830). [crab] back brownish orange with auricula purple" legs mottled "orpiment orange"

Conversely, those interested in Darwin's geological work should bear in mind that as with botanical material the zoological diary contains some items of geological interest, obviously reflecting Darwin's 'Humboldtian' view of organisms and their environments. Examples are the various 'General Observations', often mentioning fossils, some aspect of the sea or the landscape, or the climate such as in Tierra del Fuego (Keynes 2000, pp. 130-133).

Some sections of the Geological diary are obviously field notes (e.g. CUL-DAR35.272-273, 35.328, 38.954-956) and are actually primary records of observations as opposed to later notes derived from those primary records. These field notes are of great importance as they deal with the wide range of subjects observed by Darwin which were normally recorded in his pocket field notebooks. There is the occasional reference to people, including a ship-wrecked sailor, but regrettably only one albeit fascinating mention of the Fuegian Indians (on CUL-DAR34.60v). As the role of the Fuegians in undermining Darwin's belief in the fixity of species has been justly emphasised by scholars (e.g. Browne 1995) we quote the passage here in full:

Conversing with Capt: Fitz Roy, ha concerning the recent elevation of the continent he suggested the following bold hypothesis:

The number of distinct languages in T. del Fuego & the the difference of their habits from surrounding similarity in physical structure suggests an high antiquity to the race of these Indians: — It seems a most strange fact, that any power could have induced a set of men to leave the fertile immense & beautif fertile regions of temperate America & inhabit the miserable country of the South. — May we conjecture that this migration took place, anterior to the last 2 or 3000 ft elevation; when the greater part of America was to be being covered with the sea. necessity want of food might well compel small tribes to follow to the extremity the ridge of mountains? May we venture to enlarge extend this idea — the lofty plains of Mexico & Peru would form fertile regions probably existed as dry land at an immensely remote epoch. — Hence have did they not become to the two centres of civi aboriginal civilization? —

More often than not the field notes were written in pencil on the verso pages of geology notes which are almost always written in ink. Where the ink has come through the paper the pencil is now very difficult to read and it is not surprising that these notes have been previously unremarked by scholars. Some of these field notes add considerably to what we know of Darwin's activities and interests and in some cases provide detail which did not even find its way into the Beagle diary. They also illustrate Darwin's remarkable breadth of vision in constantly seeking interconnections between natural phenomena, a vision he had imbibed largely from reading Humboldt's Personal Narrative.

We quote here a few field entries from Tierra del Fuego to Valdivia on the Chilean coast to illustrate their biogeographical, ecological and human interest CUL-DAR34.185A (February 1833)

Collect together — kelp shells — (from extreme S Fuegian hills)

Label: crust Sphaeromid Hermit
Porcellana do Pelagic color bright red. use of legs. & swimming

[arrange] Stick lice from albatross

Arrange insects & lichens from M: Video

Describe fish

Fistularia smooth

CUL-DAR34.173 (February 1834):

In the Beagle Channel & in the Sts of Magellan the appearances were strong in favor of the land on each having been joined (especially presence of Island of same elevation as sides in mid channel)

In the former we showed the presence of some animals, which do not exist in those Islands, where this formation does not occur. —

In the low country on the East coast, I have found two others, which from their feeble weakness & subterranean habits would be very unlikely to swim across; there are the Toco Toco, & the mouse (or Gerbillus with grooved teeth) (978 spirits): now these animals are quite characteristic of the Patagonian plains & occur all along the North coast of the Sts. — To me these facts are convincing of the former connexion.

CUL-DAR35.259v (December 1834):

Vultur aura. excessively abundant here. 3 fingered island & Port Otway

no animals, sea-birds & otters seals [refuse] of sea. —

        Penguin demersa no nest eggs [under del] in holes under the tussocks or bushes

Barking bird, (large like Junco — sooty brown reddish about abdomen) —Cheucau& Creeper & lastly little Black wren (every one noisy birds) Humming bird & T. del. Thrush not uncommon & last the common black Furnarius on coast in great numbers. (Humming bird in dense forest).

Wonderful to see kelp on the very outside coast. — degradation of rocks. —

Ascended, cone dreadful walking, curious immense rock. ascended like a ladder. saw Hoppner Sound: curiosity to know whether fellow brethren. bit of wood & mansnest. — How strange, a ship-wrecked man! — In the North barren level hills.

CUL-DAR35.272-276 selection, leading into Cape Tres Montes (December 1834-January 1835):

Mem: good sized, but not healthy trees of T. del. Beech

immense quantity of Cryptogam: plants

At S. Pedro Torres Foxes & little deer & mice

This very small island Mice & [Deer del]

Deer on Lemuy on C. Tres Montes

Where plain no trees, but thick peat formed by Bog Plant (specimen of white flower with tufts of coarse grass & sea plant & little stunted Beeches. latter trees 1/5th of wood

No arborescent grasses: T del Fuego creeper

December 18th went to sea

Lat: 45° 18'

Lampyrus prevalent genus [Pselaphus?] & Staphylinus & Cyrus abundant in the forest & cryptogamic flora

20th. [Tacked] to North. — Noon — C Tres Montes. — Weather beaten coast lofty — steep like Wollaston Island. —

remarkable number of trees on windward side, numerous abrupt points. — dangerous

[Furnarius like water wagtail del]

Seals feed on whole food — Terns do — owl — others on squids or sepias —


The otter weighed 9 & 1/2 pounds

Potatoes — long diameter 2 inches

Large Voluta in otters paw.

Goats of Yuche: all more or less (partially uniform ferruginous brown many with white mark in front & some with one on lower jaw. — otherwise very much of one appearance as wild animal. The upper jaw line of forehead in all much [Bombe] for which cause I have preserved it.

Grebe-like petrel in Lat 44°30'. — outside of islands. — Chonos. Archipelago —

CUL-DAR35.349v (January 1835):

Peaches — standing

Strawberr Figs extending few & not & do not ripen well

Olives partially ripen. —

no grapes ripen, but scarcely worth cultivating


Indian corn? Tobacco (poor) in Chiloe Lat. —

Oranges. No —

 (Chiloe very few peaches)

Lat. — Valdivia. — 39° — 53.

Little Indian girls

Officer at the Fort of Niebla: [I] shot [dirty] cannon stony earth much mortar – cattle path – loose way Good coal at Estagillos

And here recording his first impressions of witnessing the aftermath of the February 1835 earthquake at Concepcion CUL-DAR35.354v:

B. Blanca Bird. Callandra — Thesosoma. Sturnus. Ruber

4th [March 1835] Reached Concepcion (3d earthquake of sea Mocha) Landed

Quiriquina — good geology — Wrecks on coast cotton below roofs chairs tables &c &c &c returned late at night Landed at Talcuana & scarce — Rode to Concepcion. [great cracks]; cheerful slate church

Buttresses dust danger — Ladies in Ponchos — place of town like old cities —

Height of wave — soft pools — escape of child. boat SW & NE (compass); Walls stand better than shore.

Through vibration from Andes; Rode distance of parrapets — Heavy rain. — Rotten. —

deaths owing to time of day [illeg]. Home & man fell down. cattle wild with fright, fell over promontory

Say owing to Indian to open having stopped Anteri[illeg]

: From 4 years : Sea height of — Hot water some spring stopped some flow too much. — immense degradation, solid rock: shivered — wonder referred — villages — fires an appalling sight — bitterness of height — some manufacturers effect on England — Corcovado fine weather. When active: here when northerly wind flocks of gulls. —

repeated subsequent earthquakes. — Scenery of Concepcion

Once Darwin started his epic geological researches in the Andes, broadly speaking covered in CUL-DAR36 and the first half of CUL-DAR37, there is very little of general interest in the Geological diary as the summaries in section 6 will show. For these 'Andean' parts of the voyage the field notebooks and the Beagle diary provide the non-geological raw material.

There are some quasi-field notes from Lima dated 27 July 1835 (CUL-DAR37.704-715). They are mainly geological but seem to contain material never used in any publication and are therefore worthy of further study. Darwin's notes mainly relate to the devastation of the 1746 Lima earthquake on the port of Old Callao. Lyell (1832, p.265) in a footnote had stated that "It is well known that during the great earthquake of Lima, in 1746, part of the promontory south of Callao sank down, and it is a common story at Lima that its former termination became the present isle of San Lorenzo, between which and the main land there is now a navigable channel. The submerged arches of a church, and the present position of other buildings, are said to indicate that the site of Callao underwent, during the earthquakes, a change of level; an interesting fact, the evidences of which we hope will soon be examined by some of our naval officers, and other intelligent persons frequenting that port." Darwin's examination of the evidence had to be brief for political reasons but seems not to have fully convinced him of the subsidence. As he wrote in his Journal "It has been stated that the land subsided during this memorable shock: I could not discover any proof of this; yet it seems far from improbable, for the form of the coast must certainly have undergone some change since the foundation of the old town; as no people in their senses would willingly have chosen for their building place the narrow spit of shingle on which the ruins now stand." (1839, p.451). In the second edition he added that "Since our voyage, M. [Johann Jakob von] Tschudi has come to the conclusion, by the comparison of old and modern maps, that the coast both north and south of Lima has certainly subsided." (1845, p. 369)

Darwin's notes dated 'Saturday' (probably 25 July) in CUL-DAR37.709v are worth quoting here for their historical interest as they go beyond the account in his published Journal. They seem to relate to the atrocities which General José de St Martin inflicted on the surrendering Spanish garrison at Callao in 1821: "Vaults of dead [Rodil?] – 12000 destroyed destruction of Castle, little fort peppered [illeg] New graves probably secretly shot. – Awful spectacle.- Starvation and executions."

Once Darwin leaves South America to cross the Pacific in September 1835 other subjects than geology begin again to appear in the diary.

The final quotes of general interest from the Geological diary are from the field notes from Darwin's return visit to Bahia in Brazil in August 1836. From the very first line it is obvious that the place no longer cast the spell that it did when Darwin first made landfall in South America four long years before (CUL-DAR38.955-956):

Monday, Aug 1t [1836]. Entered, little disappointment, novelty & surprise gone, & circumstance not very favourable in evening took walk & Aug 2d do. — a great untidy hot house, smell, ornamented with houses & artificial gardens (well contrasted to wild luxuriance of nature) — [small sketch] Portugeese architecture. — hills & valleys — nature's menagerie for insects. — magnificent mango Jack Fruit & Orange, Cocoa Nut & Palm. — Splendid greens with bright sun — open epithet upon epithet. Botanic tell you name after name, & a short characteristic of each but that fail to all but the learned traveller. — distant low land across the bay. [Much] of [Boats] country itself a plain 2-300 ft [worn] by valleys (oh what delicious shady spots) but red hillocks [when some view] peep out. —

The next passage must rank amongst the most wistful ever written by a weary traveller about to head for home, never to return:

[sentence interlined] & I stopped & stopped again to gaze on such beauty & to try to fix an impression which alas must die away merely leaving a Banana, a coco nut, [red] fruit trees, but the thousand beauties must perish in one's mind.

Fishing village; — grass hills — fine wild sea — Cocoa nuts — Number of blacks insurrection — women carrying heavy stones — almost wished for it. if without blood-shedding. Every lover of Nature, would do anything to see another planet, but the Tropics are other planet. — long city - churches convents, older & richer look than East coast of America, a marked style of architecture. — long to live some time there to drink deeply of these charms. —

Wednesday [3 August 1836] Pic nic: — Thursday [4 August 1836]. Bonfin — Well wet through vertical sun best tops of trees — greatest pleasure I ever enjoyed; alternate view, all beautiful, structure of country - elements of views — Palms — If England had possessed it.

The field notes in the Geological diary are all available on Darwin Online. There are a few pages excised from the field notebooks in the Geological diary; the two we have identified to date are CUL-DAR35.297A from the Port Desire notebook (pp. 77-8) and CUL-DAR37.642A from the Despoblado notebook (pp. 29b-30b).

5. Evolution in the Geological diary

The Geological diary has been explored by a succession of scholars, starting with Gruber and Gruber (1962), eager to trace Darwin's steps towards his theory of evolution. These scholars have succeeded in illuminating Darwin's development as a geologist and in particular his commitment by the end of the voyage to Lyellian gradualism. This has been seen in itself to have pre-disposed Darwin to a naturalistic explanation of species origins (various authors in Pearn 2009; Hodge 2010). Searching in the Geological diary for clues to Darwin's views on species is not an unreasonable thing to do, given that it is his largest scientific manuscript. We also know from the Origin how important his fossil discoveries were.

As demonstrated in section 4, the Geological diary does contain some natural history observations but none of these has any obvious bearing on species origins. Is there instead any evidence of Darwin's gradual loss of faith in the theistic views he had inculcated from his Cambridge teachers, such as John Henslow, from being charmed as a student by Paley's Natural Theology, or from Lyell? The loss of this faith allowed Darwin to see adaptation of organisms to their environments as relative rather than perfect, removing the barriers to variation beyond limits thought to have been set by the Creator. Did Darwin find evidence that species are not always where they 'should' be, given that species were supposed to be introduced when and where suitable environments existed? Specifically does the Geological diary record any challenge to Lyell on species, since at the start of the voyage Lyell's Principles of geology (1830-1833) stood as the major statement on the subject?

Before the voyage Darwin was aware of his grandfather's publications some of which were distinctly 'evolutionary'. It is also well known that his association with Robert Grant in Edinburgh had probably exposed him to the latest continental views on the transmutation of species. So it is reasonable to suppose that Darwin at the start of the voyage would have been aware of the descent (or 'development') question. It was also touched on in several books in the Beagle library (Herbert 1995).

By the southern summer of 1832/3 Darwin was already a convert to Lyell's actualistic approach to geology. He was avidly reading Lyell's second volume which he obtained in Monte Video in November 1832. In that volume Lyell discussed the extinction and transmutation of species in great detail, so Darwin's discovery of fossils of extinct mammals from September 1832 would certainly have triggered his interest in Lyell's views of how species come and go. In the very first sentence of the Origin Darwin stressed how important 'his' fossils were in convincing him that species had descended with modification, or – to use the last word of that great book - evolved. Lyell, however, concluded that transmutation had never been witnessed and he left the 'creation' of species unexplained, although he did attempt an account of how they might 'endure for an appointed period': "Each species may have had its origin in a single pair, or individual, where an individual was sufficient, and species may have been created in succession at such times and in such places as to enable them to multiply and endure for an appointed period, and occupy an appointed space on the globe." (Lyell 1832, p. 124)

As discussed above Darwin separated his zoological from his geological notes, but the distinction was certainly unclear when Darwin started to describe and speculate on the fossil mammals he encountered in Patagonia. We know from the Rio notebook (p. 79b) that by July 1832 he was aware of Thomas Falkner's (1774) book on Patagonia which mentioned fossils of mammals somehow similar to existing South American species. By October Darwin had no trouble in seeing the similarities between his fossils and living South American creatures such as the armadillo and agouti which he knew well by then, in CUL-DAR32.65-66:

At Punta Alta, the only organic remains I found in the Tosca (excepting mere particles of shells) was a most singular one: it consisted in an extent of about 3 feet, by 7 2 covered with thick osseous. polygonal plates; forming together a tessellated work: it resembles the case of Armadillo on a grand scale 735 ... 739 & 807: 808: these plates were double, on an interval of few inches between them. (a) — With it was only a fragment of joint of extremity. — At present the case of the dead Armadillos are oftener found separate from the body. than connected with any part. — In this case the envelope of the great animal would easily be carried by the water, & by the pressure of Tosca would be doubled up as described. —

This similarity was shown by experts back in London in 1837 indeed to have indicated a genealogical link and Darwin generalised this link in 1839 as the 'law of the succession of types'. This was certainly crucial by early 1837 to his belief in transmutation (Brinkman 2010; Norman in Pearn 2009).

There was, however, an even more intriguing fossil than those of obviously extinct species. This was the horse's tooth which Darwin discovered on 10 October 1833 (see section 6; CUL-DAR33.253). This tooth was immediately important to Darwin for focussing his attention on the causes of the extinction of species, because when he found the tooth he thought there were no horses in South America before the Europeans introduced them in the sixteenth century. How could a fossil tooth be in the same sediment as extinct species? He wrote the following in his Beagle diary entry for 7 September (obviously a retrospective entry):

In N: America bones of horses have been found in close proximity to those of the Mastodon; and I at St Fe Bajada found a horses tooth in the same bank with parts of a Megatherium; if it had not been a horses tooth, I never should have for an instant doubted its being coeval with the Megatherium. — Yet the change of habits, proved by the frequency of the arrow heads, convinces me that the horse was not an original inhabitant. —

At some point between finding the anomalous tooth and writing the following entry in the Geological diary Darwin must have changed his mind after reading Frederick Beechey's Narrative of a voyage to the Pacific and Beering's Strait (1831) CUL-DAR33.253v (probably written around December 1833):

I must re-urge that I have if anything overstated the cause of doubt respecting the position of the Horses tooth. — Equally I might doubt respecting nearly all the fossils; for few were in absolutely vertical cliffs: — Now that I find (appendix to Beechey. P 348) that horses bones have been found with the fossil Elephant. in my own mind I am convinced that a horse coexisted with the Megatherium & Mastodon: How strange that man after an immense epoch should repeople the country with the same genus. — I believe all Historians are agreed that the Spaniards found no Horse in S. America.

The horse's tooth was an enigma because it seemed to be of the same age as the 'Megatherium & Mastodon', creatures certainly no longer living anywhere in the world. Horses on the other hand are obviously still thriving and in fact multiplying by their thousands since re-introduction to South America by the Spanish in the sixteenth century. So what could have wiped out the 'Mastodon' and the other giant mammals Darwin had excavated, but not the horse? Once Darwin was certain that the horse and the extinct mammals had co-existed he realised that the relationship between organisms and their environments was far more complex than Lyell had suggested. Darwin wrote on p. 318 of the Origin that he was 'astonished' when he found the horse's tooth as it was a serious challenge to Lyell's view that extinction of species must occur when the environment is no longer suited to them (Beagle notebooks, p. 171; Gardiner 2004; Brinkman 2010).

Darwin's fossil discoveries are discussed further in section 6. For a modern re-appraisal of Darwin's mammal fossils and their geological context see Quattrocchio et al. (2009), Fernicola et al. (2009) and Vizcaíno et al. (2009).

Having considered Darwin's emerging views on extinction, the next step is to see whether the Geological diary reveals anything about Darwin's views on the 'appearance' (or 'creation') of new species, the area left so vague by Lyell. According to Lyell species will appear when environmental conditions are suitable for them.

The first relevant note probably dates from Tierra del Fuego in February 1833. It shows that Darwin was already noticing how animals were not always found even where there are suitable conditions CUL-DAR32.119v: "It is very remarkable that J. Button says there are no foxes or Guanacoes in Hoste island, which in every way appears equally well adapted for them [as Navarin Island]. I found however one mouse!"

In CUL-DAR34.24v there is a note on the ecology of some salt lakes in Patagonia. Unfortunately this note is undated though it cannot be earlier than November 1833:

Although the water was almost in the state of brine, I saw the marks or burrows of worms or rather Annelidae. — & this is further proved by the number of Flamingoes, which live & breed here, & were then of wading about in search of food. — What becomes of these animals, when the lake is dry; they must actually live in the mud, impregnated in the fullest degree with brine. The bodies of the flamingoes are found, perfectly preserved, in the solid salt. —

Nature has created animals for every circumstance [.] we have seen animals inhabiting brine; & the surrounding banks, without a drop of fresh water are burrowed by numerous Rodentia. [emphasis added]

The last sentence is rephrased in Journal of researches (1839, p. 77): "How surprising it is that any creatures should be able to exist in a fluid, saturated with brine, and that they should be crawling among crystals of sulphate of soda and lime!...Thus we have a little world within itself, adapted to these little inland seas of brine."

'A little world within itself' was a phrase Darwin reserved in Journal of researches for sites of great importance to him from an evolutionary perspective, such as the Galapagos (p. 454) and St Helena (p. 583).

More significant are some notes on St Joseph's Bay, Patagonia, which Darwin visited on 17 April 1833. The notes probably date from a few months after the visit and concern the age of oyster-bearing sediments and the 'Tosca', a red, earthy clay which Darwin encountered along some two thousand kilometres of coastline in CUL-DAR33.226:

All the above conjectures would go to show, that the Patagonian & R. Negro beds are contemporaneous & likewise that of the Tosca (with the oyster beds) or rather that the superior ones in this latter formation were deposited at the same time the gravel was spread over the R. Negro sandstone; which gravel, when it has extended, seems to to have destroyed the inhabitants of the then existing sea & that subsequently a new race appeared. [emphasis added]

Here, probably for the first time, Darwin is guessing that a spread of gravel across the sea bed destroyed the 'inhabitants', some of which became fossilised, then 'a new race appeared'. If that is what happened, thinks Darwin, the sediments at St Fe Bajada to the north may be slightly younger than those in Patagonia.

A few pages but many months later, by CUL-DAR33.239, the notes on Port Desire dated January 1834 have taken on a distinctly discursive tone as Darwin again discusses the affects of the gravel on the sea creatures: "It is curious to observe, how the causes which produced the enormous gravel bed over so many miles of country ocean, appear completely to have destroyed its inhabitants, & thus subsequently to only to have allowed a few shells, which now exist, to be scattered over its bottom. —"

He then seems to speculate on p. 239 that 'the first occurrence' of the species now living on the coast, after the fossils and scallops now found as fossils, would have been a fairly rapid affair:

as I cannot believe the ocean would remain sterile for any great number of years, I must think it probable that not much time elapsed between the deposition of first Porphyry pebble & the upheaval of the plain; & therefore between the existence of another race of organic beings, the great oysters & Pectens &c & the first occurrence of those which now are living. [emphasis added]

It is intriguing that Darwin uses the word 'sterile' as if he envisages 'the first occurrence' to have been a sort of germination process, rather than colonisation from somewhere else. Of course this is conjecture, but it is consistent with the terminology used for 'creation' in some of the books Darwin cited in his Beagle manuscripts, such as Edward Griffith's edition of George Cuvier's Animal Kingdom. The age of the oyster beds was one of the main topics discussed in Darwin's 'Reflection' essay, drafted sometime around February 1834 after reviewing the notes he had written up to that point. In that essay Darwin reworks this discussion, re-using the word 'appeared' for new 'inhabitants' of the sea bed (see below).

Perhaps five or six months later than the St Joseph's Bay notes, Darwin wrote a verso note (CUL-DAR33.257v) in his 'Pampas' section, which is difficult to date but must be later than November 1833. In this note Darwin makes what appears to be perhaps his first ever explicit reference to the 'creation' of species:

On the East coast it is said the country wears the same appearance, till about Lat 31°. - 30° on west side of the Laguna de los Patas, here the granite hills of Port Alepe first begins to shown in altitude & with them the forests of Brazil. — I have conjectured the absence of wood in Banda Oriental as well as in the Pampas. (V Gen Observ. Maldonado) to originate from the modernness of the Tosca covering. — (This will be abundantly shown)

The trees of Brazil would require greater heat, those of Tierra del Fuego more moisture & irregularity of soil. — & no creation has taken place. [emphasis added]

Exegesis of this passage is difficult, but a likely reading seems to be that the ancient rocks of Brazil are covered in trees whereas the soil of the Pampas is too immature for trees, the Tosca under the Pampas in Darwin's view being the result of the recent 'debacles' which wiped out the megafauna he had discovered. Trees must be adapted to their environments to form forests: those of Brazil liking tropical heat, those of Tierra del Fuego thriving in a wet climate (see also CUL-DAR34.158 for Darwin's discussion). As yet there has not been 'creation' of trees suited to Pampas conditions. After the voyage Darwin expanded the argument at some length in his Journal of researches (1839, pp. 53-4).

As Herbert (1995) was the first to demonstrate, Darwin wrote another essay headed 'Reflection on reading my geological notes' (CUL-DAR42.93-96), a few months after the 'Pampas' section. In the 'Reflection' essay he uses almost the same wording: "I have conjectured the absence of trees in the fertile Pampas & rich valleys of B. Oriental. To be owing to no Creation having taken place subsequently to the formation of the superior Tosca beds [emphasis added]"

Herbert also pointed out that Darwin uses a nearly identical phrase, 'no creation having taken place since this country was elevated', perhaps a month or two later in his zoological diary in connection with the Santa Cruz expedition of April 1834 (CUL-DAR31.260v; Keynes 2000, p. 230). He also used it in the Beagle diary for 5 August 1834: 'It seems a not very improbable conjecture that the want of animals may be owing to none having been created since this country was raised from the sea.'

Since the 'Reflection' essay was drafted after reviewing the parts of the Geological diary written up to that time, it is not surprising that similar wording occurs in both places. Another significant example of this is in 'Reflection' (CUL-DAR42.96) where Darwin generalises the discussion quoted above from CUL-DAR33.239 concerning the age of the oyster beds:

...that rocks from seas too deep for life were rapidly elevated & that immediately when within a proper depth life commenced...the elevations continued; and was produced on which great quadrupeds lived: the former inhabitants of the sea perished...the present ones appeared. [emphasis added]

Here the narrative is being refined into a coherent geological history, whereby the elevation of the sea bed goes hand in hand with spreads of sediment derived from the rising Andes; these wipe out the creatures living on the sea bed, but before long new inhabitants 'appear' on the sea bed while mammals colonise the newly emerged land.

By the time Darwin wrote the 'Reflection' essay he had read all the key books bearing on the 'birth and death of species' and was maturing into a confident naturalist on the lookout for theoretical questions to tackle. A few months later, by April 1834, he had also visited the Falklands twice and had been told that the foxes on East and West Falkland were different, a fact which made little sense if they had been created, as the islands seemed so similar. Darwin may have assumed the Falkland foxes had somehow reached the islands from the mainland. If he thought about it he might have wondered whether the foxes had diverged after somehow becoming isolated from each other. This idea certainly occurred to him after visiting the Galapagos the following year.

There is another 1834 episode featured in the Geological diary which had deep significance for Darwin's emerging views on species. The Valparaiso notebook shows that in late August 1834 he saw the valleys near Santiago in Chile filled with mist and as he recorded in CUL-DAR35.404 this convinced him that Tierra del Fuego will eventually by elevation become a mountain range. In this case Darwin is seeing 'with the eye of reason' how a typological series (islands – mountains) interpreted historically can be seen as an evolutionary series (Ghiselin 1969; Gould 1986). Of course it was exactly the same method which Darwin used to such triumphant effect in the Origin to convince his readers that similar organisms may have descended with modification from a common ancestor, in other words that biological evolution has occurred. This crucial methodological point is explored further in the summary of CUL-DAR35 below.

In February 1835 Darwin wrote the essay on the Macrauchenia skeleton he had found in January 1834 at Port St Julian (CUL-DAR42.97-99) in which he used Lyell's phrase 'the gradual birth and death of species' (see Kohn 1983; Hodge 2010). There is nothing else of relevance except perhaps a reference on CUL-DAR37.661 to the 'intermediate zoological character' of a stratum of fossiliferous sediment at Coquimbo in Chili, although there is nothing in this phrase to indicate a transmutationist interpretation of the fossil sequence.

In the last year of the voyage and specifically after visiting the Galapagos Islands Darwin was certainly viewing species as entities which might be capable of 'instability'. He also thought that islands were populated by species generally derived from the nearest pre-existing mainland, rather than created de novo to suit the islands, as Lyell had suggested. Unfortunately none of the voyage manuscripts prove that he also understood that island organisms will sometimes descend with modification from their mainland ancestors. It is therefore very interesting that around that time Darwin noted the possible linkage between the age of Tahiti and the peculiarities of its organic life in CUL-DAR37.801v (after November 1835):

From the same facts, I deduce, that the Isd of Tahiti has existed as dry land for a long period.
Does this agree with any conclusion, which might be drawn from the geographical kinds of its flora or Fauna? Does such indicate a distinct & ancient origin? [emphasis added]

This note is impossible to date accurately as it is written on the verso and although the first section may date from soon after the Tahiti visit, the second section appears to have been written with a different pen and could even be of post-voyage date.

The final episode from the Geological diary which is worth recounting here is from the St Helena section. The Beagle visited that South Atlantic island for five days from 8-14 July 1836 and the notes probably date from just after the visit. This is significant because it was in June or July that Darwin was sorting out his bird specimens, a process which led to his famous note in CUL-DAR29.74 on the stability of Galapagos mockingbird species (Barlow 1963; Hodge 2010).

As Hodge (2010) has elucidated, although Darwin had spotted the varieties of Galapagos mockingbirds while on the islands he would have assumed that they were varieties of a species also found on the nearest mainland, which he had never visited. We know from his notes that he quickly perceived the 'American' character of the land birds. It was not until he was sorting his bird specimens in June-July 1836 and perhaps pondering the divergence from a common ancestor of the Myothera species on parts of the mainland he had visited, that Darwin realised that isolation alone seemed to account for the mockingbird varieties. This was a novel conclusion about varieties which reinforced the more fundamental point about the species of Myothera, thus provoking the observation that archipelagos were where one might look for divergence due to isolation. The transmutationist 'clincher' for Darwin came in early 1837 when Gould pronounced that several Galapagos land birds were new species related to mainland species, meaning that species and not just varieties would arise by isolation. The fact that Gould went further and identified divergence into new land bird species within the Galapagos islands was the final proof Darwin needed that descent with modification is a fact.

An encounter with an apparently extinct land snail at the time Darwin was pondering these issues may well have a played a small role in his thinking on this crucial topic.

On 9 July Darwin wrote to Henslow that St Helena was a 'little centre of a distinct creation' (Correspondence 1:500), apparently paraphrasing Lyell (1832, p. 126) who had speculated that the island under certain circumstances would give an appearance of being a centre or focus of creation. In the fifth edition of Lyell's Principles which appeared the following year Darwin wrote in his copy 'All this agrees perfectly with my theory' (Lyell 1837, p. 81; see Marginalia). On the first page of the Geological diary notes Darwin used almost the same wording as in his letter to Henslow in CUL-DAR38.920: "The Beagle only staid five days at St. Helena, in this limited time I endeavoured to make out the structure of this Isd. which is so very remarkable as being a centre of distinct creation. [emphasis added]"

At some point on the 'sea-side of Flagstaff Hill' Darwin found some Bulimus land shells in a 'black earth' deposit which occurred in the higher parts of the Island (CUL-DAR38.934). This find cannot be dated precisely but there is a mention of 'black bed' on 13 July in the Despoblado notebook, p. 82b. A parcel of shells from the same deposit at a different locality on Flagstaff Hill was given to him by Robert Seale which contained specimens differing slightly but noticeably from Darwin's, which clearly puzzled him. No-one Darwin met had ever seen any of these species of snails alive on the Island.

One of Mr Seale's types had been assumed from its size and appearance to be a sea shell and on that assumption had been used to indicate the elevation of the find spot. As Darwin wrote to his sister Caroline four days after leaving the Island, he had found this to be 'a monstrous mistake' which had led to the false conclusion that 'this Isd though possessing an entirely unique Flora, must have been raised, within a late period, from beneath the Ocean.' (Correspondence vol. 1, p. 502).

The significance of the variability of the snails has previously been overlooked. The following is from CUL-DAR38.934v-935:

 [Mr Seale's] shells were all perfect & had been picked with care out of a black mould. — In general form they resemble my Bulimus but differ from it in possessing a very thickly incressated lip; in examining the specimens I see (3728) this is a character which varies; moreover, in those I collected the margin in some is broken, but in one specimen the traces of the thick lip are sufficiently clear [emphasis added].

I confess it is strange that all mine should be in this state; it must however be recollected that perhaps with those presented to me by Mr Seale such might have existed in the earth, but from this same cause were not collected. — N.B. Mr Seal's shells appear more elongated, some few are less so than mine; that is on the supposition of the thick lip having being removed [state normal condition written in pencil in margin]

I believe it is a Land shell; but whatever it may be, there is no question, but what in this Isld it is an extinct species. —

In Volcanic islands Darwin explained that the introduction of pigs and goats after 1502 had led to the decimation of the Island's forests, probably explaining the land snail extinctions. Darwin also drew attention to Mr Sowerby's naming of his snail specimens as a new subspecies Cochlogena auris-vulpina var. It is significant that Darwin was struck by the variation in the snails as he particularly noted the high variability of the shape of the lip. He was later to stress that variation among individuals is a necessary precondition for natural selection to form new species, as explained in the Origin (e.g. p. 51-52):

Hence I look at individual differences, though of small interest to the systematist, as of high importance for us, as being the first step towards such slight varieties as are barely thought worth recording in works on natural history. And I look at varieties which are in any degree more distinct and permanent, as steps leading to more strongly marked and more permanent varieties; and at these latter, as leading to sub-species, and to species.

It is impossible to date the St Helena pages of the Geological diary with any accuracy, although there are stylistic similarities to the Ascension notes for which there is some internal evidence of a post-voyage date. All that is certain is that Darwin encountered the snails around the time that he wrote the note on the varieties of Galapagos mockingbirds.

There is a further twist to this tale in that some land snails on oceanic islands were discovered several decades later to be highly important examples of adaptive radiation. John Gulick collected snails as a boy on Hawaii and inspired by Darwin's Origin was able to show in 1873 that species of snails can have extremely small geographical ranges, in some cases confined to individual valleys. Darwin was sufficiently interested in endemism in land snails on islands that he discussed them alongside Galapagos mockingbirds in the Origin (Origin, pp. 402-3). He also corresponded with and met Gulick in 1872.

The introduction of non-native species to St Helena, as so often on oceanic islands, was very damaging as the remaining flora showed that many plants were endemic, an observation Darwin stressed in the Beagle diary and his published Journal. His last sentence on St Helena in the Geological diary follows from his enumeration of the geological evidence for the Island's 'high antiquity': "A conclusion in harmony with the extinct species of land shell & probably also with that most singular feature in the Natural history of St Helena, its unique Flora." (DAR38.935v)

These entries in the Geological diary do not record Darwin's path to natural selection, although CUL-DAR36.605 does contain Darwin's earliest known use of the word 'evolution', albeit in a non-biological context. Alongside other key manuscripts, however, notably the 'Reflection' essay of early 1834 (CUL-DAR42.94-96), the notes on the fossil Macrauchenia of February 1835 (CUL-DAR42.97-99) and the 'Ornithological Notes' of June-July 1836 (CUL-DAR29.2) the development of Darwin's mindset recorded in the Geological diary can be seen to have laid the foundations for his decisive move towards biological evolution. This radical shift occurred during the last few months of the voyage and was confirmed within six months of Darwin's disembarkation back in England (Hodge 2010).

6. Summary of the Geological diary sections

This following is a summary of the contents of the Geological diary, volume by volume, focussing on passages of more general interest and explaining Darwin's geological interpretations where possible. Lengthy and detailed descriptions of rocks and strata have largely been ignored; instead instances are selected for discussion where they illustrate Darwin's working methods and his constant tendency to generalise from particulars. Material already quoted in sections 4 and 5 is referred to but not repeated.

In order to follow Darwin's progress it is necessary to have to hand a chart showing the track of the Beagle, such as those available on Darwin Online (here for the track, and here for a detailed map of South America) or reprinted in van Wyhe (2008) or a map of the southern part of South America. The place names used here are those used by Darwin and not always those appearing on modern maps.


The first fourteen sheets of CUL-DAR32 are out of chronological sequence and concern Darwin's return to Bahia on the Brazilian coast in August 1836. After leaving Ascension Darwin had expected to keep sailing north back to England but Captain FitzRoy needed instead to return to Bahia, first visited in March 1832. Most of these sheets seem to represent three separate drafts, probably written on the Beagle's run further up the coast to Pernambuco, although the first two sheets were written after leaving Pernambuco. They need to be considered along with Darwin's 1832 notes on Bahia (CUL-DAR32.41-48).

There is little of general interest here and the Bahia 1836 notes are mainly concerned with the detection of evidence that the coast of South America has been rising relative to the Atlantic Ocean. As is discussed in full throughout this summary of the Geological diary, this subject of the ups and downs of the Earth's crust relative to sea level became an obsession for Darwin throughout the voyage. He usually assumed that where he found, say, a horizontal bed of sea shells above the present sea level it proved that the land had been elevated by subterranean forces, rather than that the sea had fallen. There is a good example of this in CUL-DAR38.886. This was a reasonable assumption at the time Darwin was writing as the fluctuations of the oceans' surface were then poorly understood, although he was aware of this possibility. Some of the evidence of elevation he recorded in these first pages of the Geological diary found its way into South America. There are also abundant literature references (e.g. to Humboldt) and later annotations.

The 'correct' chronological sequence of the Geological diary commences on p. 15 dated January 1832 at St Jago (Santiago) in the Cape de Verdes islands, off the northwest coast of Africa. It is striking that Darwin seems even at this early point in the voyage to be concerned with geological process and time rather than with description alone. He is fascinated by the baobab tree which (p. 36) he thinks must have existed for much of the biblical age of the Earth which he quotes as 6,000 years, straight away realising that the valley in which it sits must pre-date this by some vast interval. Pasquarè et al. (2009) have provided an excellent modern re-appraisal of the geology of St Jago in the context of Darwin's work.

Gruber and Gruber (1962) were the first to discuss the baobab passage and the associated discussion of the 'long disputed Diluvium', part of which Darwin scored through and wrote 'I have drawn my pen through those parts which appear absurd' (p. 20). They tentatively dated that statement to Darwin's return visit to the Cape Verdes in September 1836. This dating has been accepted by subsequent scholars who have analysed Darwin's work at St Jago in detail (Pearson and Nicholas 2007, p. 252; Beagle notebooks, p. 5) although Herbert (1991, p. 169) was non-committal on this point. It seems to have been written at or soon after the return visit.

'Diluvium' was already a slightly antiquated term by 1832; it had been coined by geologists in northern Europe as a label for the somewhat chaotic deposits of sand and coarser material found overlying older rocks over, for example, much of the English midlands. Its origin was obscure, hence the etymological link to the Biblical Flood which seemed one possible explanation. Darwin had seen classic 'diluvium' during his early training in England and he encountered many and various deposits which reminded him of it in his travels especially in Patagonia. Herbert (2005, especially p. 397 note 60) has traced Darwin's changing use of the term throughout the Geological diary, showing how he wrestled with the question of whether it was the result of one 'debacle', such as a catastrophic rise of sea level or – more likely in his view – repeated deposition by the sea or by rivers flowing from the rising Andes. Darwin stopped using the term 'diluvium' soon after the Beagle voyage when it became obvious that classic 'diluvium' had been dumped by retreating glaciers during ice ages (Herbert 2005).

On p. 37 there begins a short section on the islands known as St Paul's Rocks (February 1832) which includes colourful descriptions of the fish and birdlife (see section 4). These rocks are today Brazilian territory and are of great geological interest because they are one of only two places in the world where mantle rocks are exposed above sea level (Armstrong 2004). Almost all other oceanic islands are composed of crustal volcanic rocks. Darwin realised their special character straight away: 'Is not this the first Island in the Atlantic which has been shown not to be of Volcanic origin?' (CUL-DAR32.38v). Several of his specimens are illustrated in an essay by Lyall Anderson in Pearn (2009, pp. 35-36).

The notes on the Brazilian island of Fernando Noronha (see lengthy quote in section 4) begin on p. 39. Considering how early in the voyage this location was and the fact that by his own admission he only spent seven hours there, the vehemence of Darwin's dismissal of the geological description provided by Dr Webster of HMS Chanticleer is surprising. On p. 39v Darwin uses his comparative method to great effect in speculating that the reason this island is so much more lushly vegetated than the Cape Verdes, even though he believes they are of similar age, is the more moisture-laden winds which bless the Brazilian island (see also Armstrong 2004).

Darwin's chronologically earliest notes on the Brazilian coast begin at the end of February 1832 on p. 41 and this is reproduced by Pearson (1996, p. 61). On p. 41v there is a diagram copied from Darwin's Cape de Verds notebook p. 72b. Darwin tells us immediately that 'Owing to my being lame I was only able to examine a small part of the adjoining country'. He follows this directly, however, with a confident assertion that the rocks are all igneous, or what Lyell the following year would term 'metamorphic' in the third volume of his Principles. A few pages later Darwin realises that these are in fact in places covered by conglomerates and other sediments, sometimes containing fossils.

There is a remarkable paragraph on p. 43 showing that Darwin at this stage in the voyage was not a convinced gradualist:

As far as the eye could reach the dip of beds was most regular. — Humboldt mentions that in gneiss-granitic formations in Columbia the dip for 300 hundred miles is exactly N 50° W: Now this agrees most curiously with the greater number of my observations. — From this fact & from the rocks of Bahia well agreeing in their mineralogical character with those of Columbia, I should consider them, although separated by the great distance of 1380 miles, as the same formation. If this remarkable continuity was more satisfactorily proved, it would be a fine instance for those who attribute the present state of the world more to great causes at distinct epochs, that to a succession of smaller ones. —

Darwin's last sentence indicates that if anything he was rejecting Lyell's gradualism in favour of the catastrophism of authors such as Jean Baptiste Élie de Beaumont, who for example believed the Andes to have been raised in one 'revolution'. Darwin may have been immediately charmed by Lyell's brand of actualistic methodology but he clearly still had Robert Jameson's and Adam Sedgwick's catastrophism ringing in his ears.

There is a delightful reference to the 'wild luxuriance' of the Brazilian vegetation on p. 44.

Notes on the five rocky Abrolhos Islets, seven or eight days sail north of Rio de Janeiro, start on p. 49 (29 March 1832), with a traced map on p. 49v. Unusually Darwin dated (as 1834) his verso note concerning the possible age of the islands. Since they were sedimentary and metamorphic they could not easily be described in Volcanic islands so Darwin added them in a footnote to South America (Armstrong 2004).

Page 51 is the start of the Rio notes. On the verso Darwin wonders whether signs of elevation might in fact be due to falling sea level and reminds himself strictly to follow the 'philosophical' method he learnt in Cambridge:

The valley of Botofago from its flatness & from the hard mud injected into crags in the gneiss. has evidently been leveled by water. — Having one sufficient cause, it is unphilosophical to theorize on another. — But have not reasons been advanced to show the Atlantic is falling? Some geological facts would tend to render it more probable.

Darwin commented in his Beagle diary at the end of June that he found the geology of Rio 'uninteresting', at least in comparison with the many other distractions of that City. On pp. 58-59 there is discussion of the enormous fragment of gneiss at Botofogo Bay described in Volcanic islands (in the context of Australia) and illustrated in South America. Darwin's enigmatic field sketch, which seems to be overlain by a drawing of two figures, is reproduced in Beagle notebooks (2009, p. 48). The fair copy in CUL-DAR39.200 was the basis for the published woodcut. Katherine Antoniw's short essay on Darwin's Rio geology in Pearn (2009, pp. 44-45) is useful background.

From Rio the Beagle had a tempestuous cruise down to the River Plate during July, anchoring at Monte Video on the 25th. She remained there for three weeks before setting off on her first southward surveying cruise. On p. 61 Darwin began a section entitled 'Coast of Patagonia'. Over the course of the next two years he had many adventures on that coast and came to a deep understanding of its geology. On the verso of p. 61 he made a deliberate change to his method for linking notes to the main text of the diary:

N. B. For the future. the marginal letters will refer to the notes on the back of page & not on the opposite one:

Darwin's exceptionally interesting notes on Bahia Blanca, made in September, begin on p. 62. This is the bay where he first discovered the fossil bones which were to prove so important (see section 5 for quote from pp. 65-6):

Punta Alta. projects into the bay & is formed of a mile of low cliffs. — it possesses great interest to the geologist from containing numerous organic remains. — (p. 62)

In his field notebook Darwin made several drawings of the section at Punta Alta, a fair copy of which is in CUL-DAR44.22 (see Herbert 2005, p. 69), which he later published (e.g. South America, p. 82). On p. 63 Darwin starts to describe the geology in detail but these notes are dated October 1832 after he had also visited the Monte Hermoso site where he had found fossil remains. On p. 65 he states his impressions of the conglomerate containing the fossil shells and bones:

This mixture of such quantities of bones of land animals with shells, must be explained by supposing a body of water sweeping over the plain & bringing with them the bones strewed on the surface & the living animals; & that in this place these & the pebbles were deposited together; the finer particles being carried on by the stream. —

On p. 66 Darwin identified some of his fossils as the bones of the Megatherium and makes the following extraordinary statement:

In connection with the Megatherium I may mention a curious fact. — It is a common report in all these parts of S America that there exists in Paraguay, an animal larger than a bullock, & which goes by the name of "gran bestia"

Whether or not reports of the 'gran bestia' were believable, it is now known from finds such as those at 'Mylodon Cave' in Chile that some species of ground sloth and Macrauchenia were living up to 5,000 years ago after people had arrived in Patagonia from Asia.

On p. 67v Darwin notes the remains of insects lying on the sand dunes which could easily be fossilised:

 It is curious how very perfectly. the dry nature of this sandy soil preserves insects, when we first arrived there at B. Blanca no insects were yet moving about: the spring was not far enough advanced, on the surface however I found the remains of the greater number of Heteromerous insects & Lamellicorna. in such a perfect state that I had intended keeping them: it is probable these had been exposed to all the changes of the winters climate: How easily would these have been preserved in any geological strata. —

On pp. 71-72 Darwin is intrigued by the remains of extant species of sea shells he finds embedded with the extinct mammals and realises that no simple environmental explanation will account for this:

Some geologists have been surprised that the extinction of land-animals, has not occurred, without destroying the inhabitants of the sea; this would seem to be a case in point. —

In a note on p. 71v clearly added months later and possibly after finding the horse tooth in October 1833, Darwin reflects on the meaning of the rodents he found at Monte Hermoso:

It is interesting to observe that this tribe of animals. the Agoutis which are now peculiar to the Americas, should in the epoch, when the Megatherium flourished, also be present. — Showing that with the extinction of one genus, that of others did not follow.

Page 73 is dated October 1833 so is about a year later than the previous entries and covers Darwin's second visit to Punta Alta in August of that year. Here Darwin dismisses his earlier interpretations and concludes that the fossil beds at Monte Hermoso are not the same age as Punta Alta:

Having revisited P. Alta, seeing the neighbouring country. my opinion respecting its geology is completely altered (a) — & renders superfluous the greater part of the following pages. —The P. Alta bed is not coeval with the great Tosca formation.................many other phenomena. require are best explained by small modern upheaval: —

Darwin's shift of opinion reveals his adoption of a noticeably more 'Lyellian' gradualistic interpretation, having moved from 'a body of water sweeping over the plain' in September 1832 to 'small modern upheaval' in October 1833. By the time he published his detailed account in ­1846 in South America he was certain that Punta Alta was younger than Monte Hermoso and that the sediments represented different palaeoenvironments, with Punta Alta being shallower water. His numerous uncertainties reflect the highly complex microstratigraphy of the Pampean deposits and geologists today still praise his careful descriptions. Quattrocchio et al. (2009) provide a modern appraisal of the geology at Bahia Blanca and explain that the earliest Monte Hermoso rocks date from the late Miocene to early Pliocene (c. 4 million years ago) while Punta Alta represents the late Pleistocene to Holocene (c. 1 million years ago). They show remarkable photographs of Megatherium and human footprints, the latter dated c. 7,000 years before present.

Pages 75-76 are a short section on the geology of Buenos Ayres in November 1832. Pp. 77-84 concern the other side of the river at Montevideo where there were metamorphic rocks displaying strong cleavage, overlain by various sediments (the bottom of p. 79 is now CUL-DAR42.75). Darwin's description of his rock specimen 852 (now in the Sedgwick Museum) gives a flavour of his views on the geology: 'Gneiss on which M. Video is built'. On p. 80 he struggles to understand how the rocks display vertical cleavage and yet the country is so flat; this is a more refined version of the notes now in CUL-DAR34.1-6 which are discussed further below. Pages 83-84 are some material added as an appendix after Darwin's excursion of November 1833. He probably received the second volume of Lyell's Principles at Monte Video on 24 November.

Page 85 is the start of extensive notes on Tierra del Fuego, which Darwin first had the chance to explore on 16 September 1832 (Armstrong 2004). There are many other notes on Tierra del Fuego, often covering the same subjects and best read together, of which the most extensive are in CUL-DAR34.The notes here are dated January-February 1833 and go into great detail concerning the slate formations and especially their cleavage, this being a subject Darwin had been advised by Henslow and Sedgwick to pay particular attention to. Cleavage is a characteristic of rocks which have been subject to great pressure which has forced the re-alignment of minerals in the rock in such a way that the rock will split along flat planes. These planes are often at high angles and even perpendicular to the original sedimentary bedding of the rock, potentially confusing the geologist who might mistake the cleavage for bedding and so seriously misinterpret the rock structures.

On p. 111 Darwin starts on the first of his thematic (as opposed to geographical) mini-essays, headed 'Cleavage' and concerned with this sometimes confusing relationship between cleavage and original bedding. Later in the voyage, probably around May 1836, Darwin wrote one of his 'synthetic' essays on this subject, now CUL-DAR41.59-77. Here in the Tierra del Fuego notes he is beginning to see that cleavage is often parallel to major structural features such as 'lines of elevation', a theme he was to explore at great length in his major 1840 paper on earthquakes and volcanoes.

It is worth reflecting that fieldwork conditions were rarely ideal in Tierra del Fuego, even in the summer, and that it was around this time that all on the Beagle narrowly escaped drowning when she nearly capsized in January 1833. (See Sorely tried) For a recent study of some aspects of the solid geology of Tierra del Fuego see Olivero et al. (2009).

On p. 117 there is an essay titled 'alluvium' which includes the reference to the 'debacle' on p. 118 which Darwin (mis)quoted in his 1842 'Erratics' paper (see section 4). It also contains the following zoological (and anthropological) remarks on p. 119 (the note on 119v is quoted above in section 5):

In Navarin Isd, we find Guanaco. foxes & Mice; it is highly probable that these animals passed over from the mainland, before the Beagle channel had broken through the bed of Alluvium. —

In Wollaston Isd I saw the skull of a Guanaco on the beach. but not much rotted; was it brought over by the Fuegians? or is it an inhabitant? thus by the wasting of a few more centuries or even less time, we might have had islands where animals lived & where boulders of foreign rock were lying on the beach, & the presence of each equally inexplicable excepting by vague conjectures. —

It is tempting to see here the first suggestion of Darwin's interest in island biogeography which was to be such an important clue to the process of speciation after his visits to the Falklands and the Galapagos in 1834 and 1835 (see section 5). As Keynes (2000, p. 171) observed, Darwin a few months after the Navarin note (May-June 1833) wondered in his zoological diary whether a rat from Goriti Island near Maldonado was 'an aboriginal'. Already in February 1834 (see quote in section 5 from CUL-DAR34.173) he was interested in the varying abilities of animals to swim between islands.

The next mini-essay is on 'glaciers' starting on p. 121. Ice was a new geological agency to Darwin and seeing it in action triggered a whole new field of interest to him, although he thought the erratic boulders he found in eastern Tierra del Fuego were too far from the Andes to have been dropped by glaciers. Darwin explained the erratics as having been dropped to the sea bed from icebergs probably inspired by Lyell's enthusiasm for this agency (1830, p. 299). Darwin was not to know that glaciers had actually extended much further east in the past and that the erratics were dumped when the ice melted (Evenson et al. 2009).

Back in Britain at this time the power of ice was just beginning to be appreciated by geologists who had seen the Alpine glaciers. When returning in 1842 to Snowdonia, a landscape Darwin had examined carefully with Sedgwick just before joining the Beagle ten years earlier, he immediately realised that they had both missed the clearest evidence that the valleys had been carved by glaciers. (see further discussion under CUL-DAR34.169 below).

Page 123 starts the discussion on the sandstones and slates of the Falklands and is dated March 1833 (Armstrong 1992, 2004). It is clear how excited Darwin was by finding fossils, mainly moulds of brachiopod shells, which he soon realised were among the oldest known fossils from anywhere in the world (they are now known to be of Devonian age; see Stone and Rushton 2013). He was certainly puzzled by the 'streams' of quartz boulders, wondering if they were caused by earthquakes, and he was impressed by discovering that the general cleavage direction was the same as in Tierra del Fuego. On p. 148v he notes that a gaucho two years later told him that he had never felt any tremors in the Falklands, although he had lived there for several years. A variant of this note occurs in the later draft of the notes, on CUL-DAR33.208v. It is now thought that the 'streams of stones' are the result of solifluxion, that is the down slope movement of frozen ground or tundra as it freezes and thaws.

The last section of CUL-DAR32 is an 'appendix' on the Falklands and is in fact dated March 1834 so also deals with Darwin's second visit to the islands. It is mainly a lengthy account of the structural geology with speculations on the forces which caused the folds in the sandstone, starting on p. 133 and ending on p. 152. The impression left by these pages, which lack general interest, is that Darwin was by now deeply interested in the mountain building process and he is starting to link what he is seeing with what he has read in Humboldt and others concerning the great Cordillera, which he will soon see for himself. On pp. 146-146v his speculations begin to run wild, rather in the way that they were to do five years later in his Transmutation notebooks:

It is important to observe, that the power which causes cleavage is so far of a mechanical nature. as to bend & stretch the strata of quartz. — ؟ Is it a Vibration??. — Are the lines of mineral change, owing to lines of electrical intensity, or difference??! & therefore of heat!!??? —

There is no harm in conjectures: do the electrical currents which circulate at the surface & are supposed to cause polarity: act with such intensity beneath the surface as to melt & alter rocks?!!!!!!

The Falklands are returned to at great length in CUL-DAR33.165-212 and again in CUL-DAR34.67-86, so it is clear that these are various drafts which ought all to be considered together. This emphasises the point that the Geological diary is more a series of descriptions of places arranged in approximately the order they were visited, rather than a diary in any strict sense.


Page 153 is dated May-June 1833 and is headed 'Maldonado', the Uruguayan port. The account is based on 'a short ride' which must be the 'Maldonado excursion' featured in the Falkland notebook of 9-21 May. The geology was varied although Darwin described it as 'simple' in his Journal (1839, p. 45). He was inclined to view the Uruguayan bedrocks as of 'Transition' date (p. 159), much older than Patagonia but perhaps not as old as some of the rocks he had seen in Brazil. On p. 161 there is a paragraph on the 'alluvium' covering the older rocks, then a section on the 'laguna' on p. 162. Darwin is fascinated by the dramatic change in the ecology of the lake after it was breached by the sea:

From the same cause there were many marine shells, mingled with immense numbers of large Ampullaria 1339 the animals of the latter dying & dead from the effects of the salt. — By the sinking of the lake, a large surface before covered with water was exposed; in the mud the number of Ampullariae Limniae &c. Fish. Craw fish was exceedingly great. —

He says many of the shells are the same as he found living at Bahia Blanca and he thinks the alternation of marine and freshwater deposits at the lake might help to explain similar deposits he had seen at Rio. He extends this discussion in a section dated July 1833 on p. 164, on the verso of which he makes a comparison with the Paris Basin deposits described in Lyell's third volume (1833). Darwin started to read this around May 1834.

Page 165 returns to the Falklands and the account continues to p. 222. These pages are undated but obviously cannot be earlier than Darwin's second visit to East Falkland in March-April 1834 (see Armstrong 1992 for a detailed account with many references to the Geological diary). The inclusion of a mention on p. 175 of King George's Sound, Australia, visited in March 1836, indicates that the notes must actually have been written several years after the Falkland visits. There is considerable repetition of the notes in CUL-DAR32 and as explained in section 3 they should all be considered together as successive drafts of the Falkland account. There is little of general interest in this account, which was eventually published as a separate paper (Shorter publications, p. 196) except Darwin's speculation that the fossils he found might indicate that the climate had been much warmer at that latitude when those creatures were living.

 On p. 198 Darwin refers to the 'Plutonian Theory'; this is the view promoted by geologists such as James Hutton in the late eighteenth century that crystalline rocks (granite, for example) were formed by the cooling of molten rocks. The alternative view, 'neptunism', that these rocks had precipitated out of a primeval ocean had been promoted by Abraham Werner, then by Robert Jameson while Darwin was in Edinburgh. Darwin had been persuaded in Edinburgh by Thomas Hope that 'neptunism' was incorrect so on the Beagle he believed  the Falklands rocks demanded a 'plutonian' explanation. On p. 214 he goes so far as to suggest that if more heat were applied to the Falklands sandstone it might by metamorphic processes become granite. We recur to the 'neptunism' debate when considering p. 234 below.

On p. 209v Darwin makes an aide memoir to ask Sedgwick about some rocks Darwin had seen at Barmouth, probably on their field trip of 1831, a memory triggered by comparable structures on the Falklands. It is worth noting that on p. 209 Darwin describes his notes on the Falklands as a 'chapter' so they obviously represent a draft of a book on the 'Geology of the Beagle'. Again on p. 212 he talks of a 'proper chapter'. These may be the earliest reference to such a book, which he tells us in his Autobiography he first thought of writing while in the Cape Verdes in January 1832. Actually by the time Darwin had been to Australia he envisaged two books, one on volcanic and coral islands, the other on South America. Back in England he decided to split the first book into two and at some point while preparing South America he decided to publish his Falklands geology separately (Darwin 1846).

Pages 217-222 concern comparisons between the Falklands and the geology of Anglesea as described by Henslow (1822). Darwin is respectful of his mentor's 'admirable memoir' but is  highly critical on pp. 221-222 of his view that 'crystalline force assisted by moisture & pressure, is an agent of sufficient power to have produced the similar but still more perfect texture of the oldest stratified rocks', Darwin being convinced that heat metamorphism is the real agent. In fairness to Henslow, by the mid 1830s he too would probably have repudiated his earlier view published as it was in a pioneering and highly regarded report. In Darwin's published version he refers to the 'admirable paper' in a footnote but tactfully omits any reference to Henslow's 'agent of sufficient power' (Shorter publications, p. 203). The tone of these notes is very close to the account in the Journal (1839) which we know Darwin wrote sometime between January and September 1837.

The account of St Joseph's Bay in Patagonia, visited for half an hour on 17 April 1833, begins on p. 223. On approaching the bay in the Beagle Darwin had expected the horizontal strata to contain abundant fossils; he called it in his diary 'an El Dorado to a geologist'. He found that up to one fifth of the bed was fossil shells, mainly large oysters, and the age of this bed was an issue which provoked Darwin into a long series of discussions with himself. As we have seen in section 5 these discussions triggered a burst of thinking on the 'appearance' of new 'races' on the sea floor. It is significant that the issue of the age of the oyster bed was one of the main topics discussed in the 'Reflection' essay, written around February 1834, in which Darwin uses the phrase 'no Creation having taken place'(Herbert 1995).

On p. 223v Darwin refers to some information about the locality sent to him by 'a Spaniard'; this item is now CUL-DAR34.10. On p. 225 he assesses the age of the oyster bed as about the same as a similar bed at St Fe Bajada and by extension the same as that at the Rio Negro. Pages 227-228 are geological notes from the Beagle surveyors from their run down the coast to Port Desire (Puerto Deseado). Page 228A is an exceptionally nice view of the coast, perhaps by John Lort Stokes.

Pages 229-242 are dated January 1834 and deal with Port Desire where Darwin famously rescued the remains of the lesser rhea at Christmas 1833 (Beagle notebooks, p. 66). Darwin's Beagle diary for Port Desire is unusually rich in geological comment, for example on Boxing Day: 'here the usual geological story, of the same great oyster-bed being upheaved in modern days, was very evident', and this from 29 December: 'the red porphyry rock rises from the water in perpendicular cliffs, or forms spires & pinnacles in its very course'. Page 230 is reproduced by Herbert (2005, p. 99) to illustrate Darwin's use of specimen numbers in the Geological diary. For a detailed recent study of the geology around Port Desire see Casadío and Griffin (2009). For discussion of what Darwin called the 'Gravel Formation' or 'Great Shingle Formation' of Patagonia, for example in the first chapter of South America, see Martínez et al. (2009).

The notes refer frequently to specimens Darwin has collected and on p. 234 he mentions 'this most Wernerian doctrine of dykes', a reference to the 'neptunism' of Abraham Werner (see section 4 and discussion of p. 198 above). Here Darwin deduces that he has found dykes where sediment has filled cracks in the sea bed, hence 'neptunian' as opposed to the more usual dykes which are injected as molten ('plutonic') from beneath (see diagram on p. 232A). This probably reminded Darwin of the dispute over a dyke on Salisbury Crags while he was a student in Edinburgh. Darwin tells us in his Autobiography (p. 53) that being lectured by Robert Jameson 'with a sneer' that this obviously plutonic dyke was in fact neptunian was one of the reasons why he had determined 'never as long as I lived to read a book on Geology or in any way to study the science'! It is a little surprising that in a recently published 1870 letter Darwin seems to have completely dismissed his Edinburgh geological education, implying to his correspondent W.T. Pryer that he was ignorant of the subject before the trip with Sedgwick (Correspondence 18:42).

Darwin was certainly puzzled by the Port Desire dykes, and he devoted several pages of South America to discussing them under a special heading 'Pseudo-Dikes'. Darwin discusses this issue further under CUL-DAR34.33v (see below).

On p. 235 Darwin has written 'Tertiary' in pencil in the margin; this is an example of where he has been re-reading his notes and adding headings to break up the narrative. On p. 236 Darwin refers in connection with the levels at Port Desire to 'a set of notes on the subject', which is probably his essay on the 'Elevation of Patagonia', now in CUL-DAR34.40-60. The issues treated on p. 239 are discussed in section 5 and increasingly echo themes discussed in Darwin's 'Reflection' essay, drafted around February 1834 (Herbert 1995).

Page 243 begins an 'Appendix' on Port Desire, dated May 1834 and probably written on the run down to Port Famine which the Beagle reached on 1 June. The notes start with the important information that Darwin has 'read Mr Lyells 3d Vol', the third volume of the Principles (1833). Darwin probably received this book on arrival in the Falklands on 1 March 1834 but 'deferred' reading it until after the St Cruz river expedition, which ended 8 May. It is known from the Banda Oriental notebook (Beagle notebooks, p. 285) that Darwin had probably read Lyell's treatment of the 'metamorphic' rocks by mid May.

Darwin says on p. 243 that having read Lyell and seen the proofs of elevation on the river expedition 'many facts are now much more easily explicable than they formerly were' and this mid-point in the voyage is marked by a new confidence in his writing. Darwin's enormous debt to Lyell is well documented (e.g. Herbert 2005) but this was not just a case of Darwin deriving his thinking from Lyell. The third volume of the Principles reached Darwin at just the right stage in the voyage for him to pit his own rapidly maturing views against the master. As he wrote to Henslow on 24 July 1834:

"I had deferred reading the third volume till my return, you may guess how much pleasure it gave me; some of his woodcuts came so exactly into play, that I have only to refer to them, instead of redrawing similar ones." (Correspondence vol. 1, p. 399)

During the Santa Cruz expedition Darwin became convinced of the truly continental scale of the elevation he was witnessing. In this he was for the first time seriously challenging Lyell, who saw elevation as something far more localised, caused by earthquakes, although the step wise elevation along the Santa Cruz did support Lyell's view that mountain ranges are not raised in single events. Thus Darwin by the voyage mid-point realised that he was no longer the student and was starting seriously to question his geological masters.

In his third volume Lyell applied the actualistic methodology, which he had developed in the previous two volumes, to the rocks and fossils then known from around the world. In his first volume Lyell had described physical processes observable today and in the second he did the same for the living world, so the third volume was an attempt at a geological history of the world, starting with the most recent rocks. Lyell's history is understandably sketchier the further he is from the present, but as a whole it is a masterful account underpinned by his theistic concept of an essentially cyclical or steady state world.

Lyell envisaged sea level and temperature oscillating gradually throughout time in a fundamentally balanced way, with no overall direction and certainly no support for biological evolution as espoused by men like Erasmus Darwin, Lamarck or Grant. Less forgivably to contemporary geologists, Lyell was at such pains to deny direction that he over-extended his own methodology in interpreting the fossil record. By the 1830s most geologists saw directional signals in the order of appearance of the major groups of organisms, as for example mammals succeeding reptiles. Lyell, however, argued that this appearance was largely an artefact of the imperfection of the fossilisation process. He went further, arguing that because reptiles today like warm climates, whereas mammals thrive in temperate zones, the dominance of reptiles in the Mesozoic and then of mammals in the Cenozoic only confirmed that the world had been warmer in the Mesozoic. Some geologists lampooned Lyell's suggestion that if the climate warms sufficiently the dinosaurs might return (Rudwick 2008).

Symbolically perhaps, the reason for the St Cruz excursion had been to prepare the Beagle before she entered Pacific waters and no doubt Darwin was preparing himself for the geology of the Cordillera. In the 'Appendix' Darwin reflects on the 'neptunian' dykes and on the ravines he had examined at Port Desire, which he suspects are based on faults linked to earthquakes.

Pages 245-248 returns to January 1834 at Port St Julian, perhaps 200km down the coast from Port Desire. It was there that Darwin discovered the famous Macrauchenia skeleton which he starts to report on p. 246 (Beagle notebooks, p. 290). This creature which Darwin thought might be a 'Mastodon' was of extraordinary importance because it was the subject of the 'Feb. 1835' note (CUL-DAR42.97-99) in which Darwin first discussed explicitly the 'birth and death of species' (Brinkman 2010). Darwin must have drafted the Geological diary notes by the end of March as he added this dated paragraph at the end of p. 248:

March After some reflection I have come to this conclusion: so many facts require repeated elevations & then we certainly should have as at Port Desire, the oyster bed & the Porphyry in places denuded & again recovered & as in this instance interstratified with the very substance the sea has been denuding. I never-the-less think that the gravel & last regular bed were not long separated from each other. — Indeed, why should they? the sea never lies idle! —

The notes then become a long section on the 'Pampas' which is split between CUL-DAR33 and CUL-DAR34. The opening sentence on p. 249 of this section, which derives from Darwin's extraordinary expeditions over vast distances, was obviously written after November 1833:

In the months of August to November, I made three excursions in the Pampas North & South of B: Ayres, from Latitude 31.47 to 41 South. I will begin with the most northern point St Fe. & so proceed: but there will be many inversions of time, from having seen the country & written my notes in a different order.

The field notebooks on which the essay is based are Falkland (August), B. Blanca (September), St. Fe (October) and Banda Oriental (November). As Darwin says, his account goes from north to south, so is broadly in reverse time sequence. He begins by describing the Tosca and gives a geological section for St Fe, then on p. 251 he reports with some credence how the locals believe the rivers can petrify bones and other organic items. This topic was the subject of several memoranda, now CUL-DAR34.12-15, from people with whom he had discussed his travel plans in November 1832. He gives an account of the fossil mammals he discovered at the start of October, including on p. 253 the horse tooth discussed in section 5. Iriondo and Kröhling (2009) provide an excellent modern assessment of Darwin's work on the Rio Parana up to St Fe.

On p. 257 Darwin cross-refers to other manuscripts (e.g. 'Maldonado (P 123)' which is CUL-DAR33.161) and adds sub-headings, such as 'B Ayres' and 'Gran Seco'. The latter heads a detailed account of the terrible drought of 1827 which caused the deaths of at least one million cattle and other animals. Darwin is intrigued as having witnessed (and smelled) the rotting carcasses he understood how future geologists might miss-interpret the masses of bones washed into the rivers as the result of a great flood. On p. 257v he makes what may be his earliest recorded use of the word 'creation' (see section 5). His researches in Uruguay have been the subject of a recent study by Martinez and Veroslavsky (2000).

On p. 261v there is a very un-geological addendum which was written back in England and printed verbatim, except for the last sentence, as a footnote in Darwin's Journal (1839, p. 157):

In the neighbourhead of the great towns on the shores of the Plata, the number of bones strewed over the ground, is truly astonishing. — Since our return, I have been informed. that ships have been freighted to England this country with with a cargo of bones. to grind for manure. — The turnip fields in Great Britain being manured That cattle in England should be fattened for on turnips, manured with the ground bones of animals, that lived on in the plains southern hemisphere, is a curious fact in the commerce of the world. — In the East Indies, the luxurious drink wine cooled with North American ice, which in its journey has twice crossed the equator. — The same people may have at their table, fish fresh as when caught taken from the waters of the same country.

On pp. 270-271 Darwin likens parts of the Pampas to the Cambridgeshire fens. We have quoted in section 4 how in South America (p. 147) he mentioned finding gneiss in the Guitru-gueyu which, if correct, would be surprising. There is no mention of gneiss from this location in the Geological diary and the specimens Darwin refers to on pp. 273-274, now in the Sedgwick Museum, are varieties of sandstone, so it appears he made an uncharacteristic error in his published description. The Pampas notes continue to p. 278 which is numbered '30' by Darwin. They continue at CUL-DAR34.17.


As explained previously, CUL-DAR34 is the first volume labelled 'Notes' as opposed to 'Diary', so its pagination is re-set to 1, although as discussed in section 3 it is best treated as  a continuation of the Geological diary.

CUL-DAR34 starts at the Uruguayan port of Monte Video with scrappy notes dated 27-28 October 1832. The notes describe the geology of Rat Island and the Mount (the hill which gives the City its name). There is one remarkable passage on p. 6:

It may be observed how strange it is that in a country which has suffered so remarkably little from the convulsions of nature that this stratification should be vertical. – How is it possible that horizontal plates, deposited beneath water should be elevated through a space of 90˚ - and yet the country be one of the most unbroken on the face of the globe.

Judging from his discussion in the chapter on cleavage and foliation in South America, Darwin must at some point after writing this note have decided that the 'stratification' at Monte Video was in fact cleavage. Original sedimentary bedding ('stratification') can be very difficult to distinguish from cleavage even when, as is often found, they are at right angles to each other. As Darwin wrote to Henslow in March 1834 he had:

not one clear idea about cleavage, stratification, lines of upheaval...I draw my own conclusions & most gloriously ridiculous ones they are...Can you throw any light into my mind, by telling me what relation cleavage and planes of deposition bear to each other? (Correspondence vol. 1, p. 370)

Perhaps tactfully, Henslow omitted this section of Darwin's letter from the extracts he published in November 1835 (Darwin 1835)!

Pages 7-9 jump to St Matthias Bay and St Josephs Bay and are dated 17-18 April 1833 and their brevity reflects the entry in the Beagle diary that Darwin's 'visit was so short that there was only time to see how much was missed'. 34.10-11 is in Spanish by an unknown hand and has been translated for Darwin Online by Austin Whittall. It was mentioned under CUL-DAR33.223v.

Pages 12-13 are remarkable lists of 'Scattered facts, communicated to me by different people: Novemb: 1832' and written in Buenos Ayres or Monte Video. The informants' names are Meggett, Hughes, Morris, Tweedie, Lumb and Oakley (see Ollerton et al. 2012). Pages 14-15 are 'Memoranda for Mr C Darwin' from his Shrewsbury acquaintance Charles Hughes (Beagle notebooks, p. 60). The latter are listed as 'Notes for a trip along the Rio Negro to Mercedes' in Correspondence vol. 1, p. 282 from which an extract is given in section 4. Taken together these four sheets are among the most interesting in the entire Geological diary.

Page 16 is on the slate country of Good Success Bay, Tierra del Fuego, dated 20 December 1832. Pages 17-24 jump to the Rio Negro in Patagonia, visited in early August 1833, although the notes were written no earlier than November. This is not the Rio Negro mentioned in the last paragraph. Since p. 17 is numbered '31' in Darwin's hand and headed 'B. Ayres' these notes are obviously a continuation of the Pampas description which ends at '30' on CUL-DAR33.

In addition to geology there is some general interest here. On p. 20v Darwin notes the differences in vegetation at equivalent latitudes in the northern and southern hemispheres:

It has been stated (b), that the climate (s. productions) in the Southern hemisphere in any latitude corresponds to one 10 degrees higher in the northern. —

R. Negro is situated in Lat: 41°. — the following vegetable productions are raised there. Peaches, Nectarines (of course standard) Quinces, Apples, Grapes, Pumpkin, Water & musk melon, Cherries; Patacas dulces (sweet potatoes), olive, Fig, Oranges (only lately tried) & Indian corn. — Could such trees be raised in Sussex in Lat: 51°. —

On p. 21 Darwin makes an early reference in the Geological diary to Lyell:

If we apply the theory of numerous successive elevations, which Dr Lyell has so strongly supported, it will perhaps so well explain various appearances, as to render it highly probable [that the Tosca was elevated recently]

There are long descriptions of the saline deposits, including their ecology on p. 24v, from which a 'creationist' note has been quoted in section 5. The descriptions end on p. 28, numbered '42' by Darwin, signifying the end of the 'Pampas' section. Zárate and Folguera (2009) provide a very useful modern account of the geology along Darwin's route across the Pampas from Buenos Ayres down to the Rio Negro.

Page 29 concerns Port Desire and has the appearance of being notes drafted prior to the more polished accounts in CUL-DAR33, and are dated January 1834. Again, on p. 33v, we have Darwin wondering about the 'neptunian' dykes as on CUL-DAR33.234 (see above):

The following facts are I think proved by geology of Port Desire viz that earthy & crystalline porphiries were formed, were covered by conglomerates & other mechanical rock; that rocks partaking of both character of mechanical & chemical passed into each other & alternated[,] an argument for the Wernerians....

Darwin's first true thematic essay, on the 'Elevation of Patagonia' begins on p. 40 and runs to p. 60. The reader is referred to the full analysis provided by Herbert (2005, pp. 160-166), but suffice here to say that in this essay Darwin is synthesising his understanding of the stepwise elevation of the south-eastern part of South America. Using barometric altitudes for the various plains he had surveyed on the St Cruz expedition and elsewhere he creates a diagram , variations of which he eventually published in his Journal and in South America, as he believes proving '7 or 8 successive elevations' (p. 57). It is possible to give date brackets to the composition of this essay. Darwin refers in the later pages of the essay to Lyell's third volume which he started to read after 8 May, so there is overlap in timing here with the Port Desire 'Appendix' in CUL-DAR33.243-244. Because he says on p. 47 that he hopes to prove elevation of the Andes, we can assume that the essay was written before Darwin 'found beds of recent shells' at Valparaiso by 5 August (Beagle diary).

The note on the Fuegians on p. 60v has been discussed by Herbert (1974, p. 231) and we have quoted it in full in section 4. Pages 61-65 continue Darwin's account of the elevation of Patagonia.

Pages 67-86 are from the Falklands and are dated March 1833 so link back to notes which first appear in CUL-DAR32.123. Darwin comments on p. 74 that he 'hammered every inch of this mile of coast' and it is worth noting perhaps the earliest reference in the Geological diary to 'Mr Lyell's theory of many elevations' on p. 85.

Pages 87-92 are headed 'April 1834. Observations on the Bottom of the sea between the Falkland Islands & St. Cruz', although notes were added to this in May when the Beagle was looking for L'Aigle rock and Darwin was still adding notes a year later. He was especially interested to understand how far from the Andes the sands and gravels had spread eastwards, and to determine the gradient of the sea bed. He concludes from the fact of delicate creatures living there that even in shallow depths there was not enough agitation to move gravel (p. 89), although he contradicts himself strongly two pages on. In his specimen notebook against no. 1947 Darwin has written: 'Interesting to geologists: 10 fathoms water, 3 miles from shore, where most rapid tides, yet living corallines posses most delicate spines, showing how little pebbles are moved at the bottom.' Sponsel (2009) has demonstrated that Darwin's serious interest in the sea bed was driven as much by his fascination with marine invertebrates as by hydrography. Darwin's novel synthesis of information from both directions, sketched in his Santiago notebook in 1835, led directly to his prediction that the Pacific might be subsiding.

Page 93 begins Darwin's long account of the St Cruz river expedition which extends with interruptions for over fifty pages. The circumstances of the expedition have been described in Beagle notebooks and Strelin and Malagnino (2009) have discussed Darwin's work on erratic boulders on this expedition in some detail. One of Darwin's main concerns on the expedition was to test Lyell's theory of gradual ('gradus', Latin for step) elevations, so the first pages are taken up with barometric altitude measurements of the plains, taken as the party slogged its way westwards towards the Andes.

Page 99 has Darwin's diagram of the successively higher and older plains based on Banda Oriental notebook p. 103 and published in South America. Darwin is clearly concerned to understand how the river could be effective in carving its valley and is happier on p. 106 to believe that the sea did this as the land emerged:

Taking all these facts into consideration there cannot be any doubt, but that the sea has excavated this great valley & that by the successive elevation of the the step-like plains were deposited in its bosom & the escarpements being its former coasts. —

This is followed by more barometer readings and on p.110 by a reference to the drawings of Basalt Glen and the main valley made by the Beagle's artist Conrad Martens. These were eventually published and are available on Darwin Online and Wesson (2017) provides several fine photographs of the same scenes as they appear today. Then there are various notes and lists of specimens, followed by a section titled 'Hypothesis' on p. 115 which encapsulates Darwin's imagined geological history for the St Cruz valley. Pages 118-119 skip to 12 May when the Beagle was back at sea and Darwin is recording depth soundings and details of the material found attached to the tallow on the sounding lead, but pp.120-124 return to notes made on land in mid-April. There are more notes on St Cruz starting on p. 130.

Pages 125-129 deal with Port Famine in Tierra del Fuego, visited by the Beagle in early February 1834. The map on p. 126 and the diagram on p. 128 of a hornblende boulder are from p. 22 of the Port Desire notebook. Darwin reports some interesting fossil discoveries from Mount Tarn on p. 126v (p. 127 appears to be missing). Pages 129-130 are lists of specimens from Mount Tarn; the ecological entries from these pages are quoted in section 4. In several rather telegraphic notes Darwin is interested to know how elevation may stop the free movement of animals between the Pacific and Atlantic: 'Straits were certainly once connected & allowed animals to pass.' (p. 129v). Notes on Port Famine resume on p. 153.

Pages 130-156 return to St Cruz with what appear to be more polished versions of earlier drafts, although unusually the entries from p. 134 are individually dated, starting 24 April. This is presumably because Darwin was able to link the dates to other correlated measurements such as barometric altitudes as the expedition went further and further west until turning round on 5 May. We refer the reader to the introduction to the Banda Oriental notebook for more discussion. The map on p. 134v is based on notebook p. 60 and the section on p. 143 was published in South America,p. 114. In part of the entry for 1 May on p. 140 Darwin strove to trace the source of the lavas:

The valley here widened considerably, & I never was able to reach the lava; I could see it on the north side, gradually rising in a broken, irregular plain, to very near the snowy cones of the Andes: it was much traversed by large valleys: [a crater for such deluges probably large written in margin]

Then on p. 141v he makes a startling comparison:

In England we should hesitate in attributing any step of trap rock in the counties of Nottinghamshire or Leicestershire to the highest mountains in Wales; yet the distance is not greater. —

We have commented above under p. 93 on Darwin's fascination with the erratic blocks he encountered. On p. 143v he reflects on what might have transported them:

...there were endless numbers of two, three, & four feet square. — generally but little rounded. They are at present at least 55 miles from their original site. — What a vast tumult in the waters must have carried them this far; their shapes preclude the idea of rolling by degrees along the bottom of the ocean. —

A few lines later he considers the possibility, prompted by Lyell's work in Europe and clearly dismissing the possibility that the present river was an adequate agent, that the boulders were dropped from icebergs. We now know that they were in fact deposited by various glacial processes, but not from icebergs (Strelin and Malagnino 2009). On p. 145 Darwin groups his thoughts under a general 'boulders' heading, then broadens the discussion under 'gravel' from p. 147 to reflect on the effects of the gravel covering the sea bed on p. 149:

A sudden change in the nature of the bottom, must destroy many animals, & when of great extent, if the species are not in proportion more extended, they must perish from the world.

The remainder of the St Cruz notes show Darwin struggling to understand where the boulders and gravel came from. On p. 150v he seems baffled: 'The subject is to me full of difficulty.' By p. 151 (there appear to be two pages so numbered) Darwin seems to have regained his composure: 'Let us try another hypothesis':

During the long succession of years, when sediment was gradually forming at the bottom of the S. Atlantic ocean a great mass of beds, an enormous accumulation of gravel must have been piled up at the Eastern submarine foot of the Andes. — When the land elevations took place, & one of the first or highest plains took place was found, the remodelling action of the [illeg] & powerful sea would remove the finer sediment & leave only a thick bed of gravel; when, this other plane was exposed to in its turn, part of it would be destroyed & the gravel spread out in a thinner layer over another plain (or for seas bottom). — this process being repeated, the gravel would at length be carried far to sea-ward by the action of the sea near to a beach; but necessarily the thickness & quantity must be greatly diminished in each time successive plain. —

This hypothesis is supported by two diagrams on p. 151v which show how the gravel at the foot of the Andes could be spread by marine action and this was an idea which Darwin kept returning to in his Red notebook and A notebook (Transmutation notebooks). Today the origin of the gravel is attributed to a range of fluvio-glacial processes in different regions of Patagonia and not to marine processes (Martinez et al. 2009). On p. 152v Darwin wonders if the processes he envisaged might have transported the famous giant erratic in the Alps, such as the 'great block at Geneva' mentioned in the Galapagos notebook on p. 10a in connection with Chiloe.

There now follows a long series of notes relating to Tierra del Fuego spanning three years and all Darwin's time in that region. In one case (p. 196) the notes go back to December 1832 and at the other extreme an 'Appendix' on pp. 177-178 probably mis-dated November 1835 (see below). These notes in many cases deal with the same subjects as in CUL-DAR32 so that both sets should be considered together.

Pages 153-156 return to Port Famine with notes dated June 1834 but covering much the same ground as pp. 125-129 from February, so this is an example of Darwin reworking earlier material. Pages 157-176 are twenty pages headed 'E coast of T. del Fuego' apparently dated May 1834, but with later verso notes up to December 1834. The account first takes the reader broadly on the route of the Beagle into the Straits of Magellan, descending geologically in a south-westerly direction through the Tertiary rocks into Darwin's 'Clay Slate' of Cretaceous age, with occasional older rocks outcropping.

On p. 166 Darwin switches back to the Atlantic at San Sebastian Bay where he reports fossil plants, crustacea and molluscs found in February 1834. He also describes large erratics, always a source of fascination to him and now known to have been dropped by glaciers (Evenson et al. 2009). On p. 169 Darwin makes it clear that he sees the boulders as of great theoretical importance and referring to Lyell's keen interest he  reminds the reader of who is in charge on the voyage:

But this subject is intimately connected with the transportation of boulders, to which I turned my attention, from some queries sent by Mr Lyell to Capt. FitzRoy. —

The discussion becomes a complicated hypothetical history, broadening to include the southernmost parts of Tierra del Fuego. After the voyage Darwin in his Journal which, because of its delayed publication, gave him time to add a lengthy appendix on the subject on glaciers, icebergs and erratics (1839, pp. 615-625). At the same time, the gradual acceptance of Louis Agassiz's 'Ice Age theory' provoked Darwin to attempt to blend his belief in elevation with Agassiz's proof of the power of ice on land to deposit erratics. Darwin was converted to Agassiz's theory in 1841 but still believed that most erratics were carried by icebergs.

Darwin's elucidation of South American elevation reflected that continent's unique geological history and did not translate easily to Europe. As Roberts (2012) has shown, once Darwin had revisited Snowdonia in 1842 he become convinced that ice had shaped the British mountains. However, he still concluded that at Moel Tryfan, on the northwest fringe the National Park, there was evidence for marine deposits, proving massive uplift. This allowed him to explain some erratics in the Shrewsbury area as iceberg transports but delayed by decades abandonment of his 1839 uplift explanation for the 'parallel roads' of Glen Roy (see Rudwick 1974). Ironically, much of the Welsh evidence was well known to him from his pre-voyage explorations, but at that time his 'eye of reason' could not see this evidence for want of a glacial theory with which to understand it.

On p. 173 there is a series of zoological observations from which we quoted in section 4, with Darwin using the presence of poorly-swimming mammals as evidence that the islands they inhabit must have formerly been joined. He ends on pp. 175-176 by saying that the Beagle Channel is easier to understand:

We have here no such curious forms of land, as we see at the narrows in the Sts of Magellan. to cause puzzles & hypotheses. —

Pages 177-178 are an 'Appendix' bearing the extraordinarily late date of November 1835, which is when the Beagle visited Tahiti and Darwin was pre-occupied with coral islands! It is presumably a mistake for 1834 but, if not, it is a remarkable instance of Darwin focussing on several different subjects at once. The page is headed 'P. 94' and it may relate to CUL-DAR32.112 which is also numbered '94'. It describes a chart coloured by Darwin which is obviously the geological map in CUL-DAR44.13 which has 'P. 94' on the verso (Herbert 2007; Pearn 2009; Zappetini and Mendía 2009). It is a great shame that this was never published in South America.

Pages 179-198 complete Darwin's 'copious notes' on Tierra del Fuego, with sections varying from relatively polished general discussions on stratification, cleavage and other general topics (pp. 179-180, 193, 197-198), to relatively scrappy detailed descriptions. Examples of these concern Orange Bay pp. 181-182; Gregory Bay p. 183, this being dated 28 May and therefore among the latest from the Atlantic side; Wollaston Island and Goree Sound pp. 184-185, these being dated January- February 1833 so among the earliest; Cape Virgins pp. 186-187, 192; Magdalen Island and Cape Negro pp. 188-189; 'East coast' and Straits of Magellan pp. 190-191; Cape Espirito Santo pp. 194-195; St Sebastian to St Pauls Head p. 196. There is little of general interest here, save for mentions of Beagle crew members (e.g. Bynoe on p. 182), the field notes on p. 185A and the occasional reference to Darwin's favourite indicators of former land connections: 'There were heads, dung, immense numbers & holes of Toco Toco. excellent connecting animal' on p. 195v.

The sheets pp. 199-200 deal with the Pacific Coast with notes written in San Carlos on Chiloe Island starting 29 June 1834. These notes concern the local mainly volcanic geology but bear the somewhat enigmatic heading 'The Andes created all S. America', perhaps added later. At this point the Geological diary has reached a major milestone, with all the notes in the remaining volumes relating to the Pacific coast and beyond. The notes on Chiloe continue on pp. 201-205 with Darwin on p. 204 already collecting evidence of dramatic recent uplift: 'Capt Williams. says about 4 feet. land has risen or water fallen during the last four years. — Knows by building a vessel.'(see also p. 213). On p. 205 he mentions being 'on the road to Castro' which was probably in the first week of July 1834 (see also pp. 208-208v for the same phrase).


Pages 206-17 continue the description of Chiloe for the winter fortnight the Beagle was there in July 1834 before heading north to Valparaiso. The notes are numbered '1' to '12' by Darwin, confirming that they are more finished versions than those in CUL-DAR34. Curiously there is a two-page 'appendix' to p. 212 dated 1835 and now in CUL-DAR37.796-797 and p. 217 is also numbered 'P. 182'.The first page has '35' added near the date which may refer to the note on p. 210v dated January 1835, reflecting the fact that the Beagle revisited Chiloe in 1835. Darwin's field notes for the January 1835 expedition are on p. 328 and several other Chiloe field notes are quoted in section 4 (e.g. 259v, 272). His coloured geological map of Chiloe is on p. 306. Darwin's main interest in these notes is finding evidence of uplift and he pays particular attention to beaches and sea caves now above high water mark (Armstrong 2004).

Page 218 is dated 24 July [1834] and concerns Valparaiso. Darwin was based there until November, making an expedition to Santiago (the capital of Chile) in August-September before falling seriously ill. 24 July was the day Darwin wrote a famous letter to Henslow who published the following delightful extract (Darwin 1835, p. 19):

We arrived here the day before yesterday; the views of the distant mountains are most sublime and the climate delightful: after our long cruise in the damp gloomy climates of the South, to breathe a clear dry air, and feel honest warm sunshine, and eat good fresh roast beef, must be the summum bonum of human life. I do not like the looks of the rocks half so much as the beef, there is too much of those rather insipid ingredients, mica, quartz, and feldspar.. . . .

As so often, Darwin focuses in the Valparaiso notes on signs of elevation, especially sea shells on the hills proving either that the land has risen or the sea retreated since the animals were alive. The notes continue to p. 226, then pp. 227-229 are lists of specimens. Pages 230-231 are altitude calculations and p. 232 is related information supplied by Frederick Eck. It is odd that Darwin used various spellings for Santiago, for example 'St Jago' on p. 226v (see Beagle notebooks, p. 175 note 403).

Pages 233-258 are a twenty-four page section on 'Chonos and Tres Montes' and concern the many islands off the west coast south of Chiloe, several still today bearing the names given them by Captain FitzRoy. Darwin was there from 14 December 1834 to 14 January 1835, in the southern summer. The geology was relatively complex and Darwin chose to  summarise it, not in the Geological diary,but with reflections on granite and a philosophical flourish in his Beagle diary entry for 31 December 1834:

...the chief part of the range is composed of grand solid abrupt masses of granite, which look as if they had been coeval with the very beginning of the world. — The granite is capped with slaty gneiss, & this in the lapse of ages of time has been worn into strange finger-shaped points......I took much delight in examining the structure of these mountains. — The complicated & lofty ranges bore a noble aspect of durability — equally profitless however to man & to all other animals. Granite to the Geologist is a classic ground: from its wide-spread limits, its beautiful & compact texture, few rocks have been more anciently recognised. Granite has given rise perhaps to more discussion concerning its origin than any other formation. — We see it generally the fundamental rock, & however formed, we know it to be the deepest layer in the crust of this globe to which man is able to penetrate. The limit of mans knowledge in every subject possesses a high interest, which is perhaps increased by its close neighbourhood to the realms of imagination.

Darwin in the Geological diary begins with the Tertiary rocks then moves down to the predominant 'Primitive' on p. 235. On p. 237 he is struck by the regularity of the north-south strike of the mica slate and he considers this comparable to what Humboldt termed 'loxodromism', that is the parallelism of geological structures over huge distances, especially down mountain chains like the Andes. Darwin discusses loxodromism at length in the 'Cleavage' essay (CUL-DAR41.59-77). He also mentions on this page the 'grand dykes' he encounters and invents an arresting culinary simile:

At a point 3 miles East of the anchorage the mica slate is traversed to a most extraordinary degree by grand dykes. One simile will better explain the appearance than a thousand descriptions; it is that the crust of a tart, broken in by the pressure of the knife, & where the syrup & fruit represent the rock of the dykes.

[the earlier draft on p. 321 is given here for comparison: The word example simile will more truly explain appearance, than a thousand explanations. it is the thin crust of a tart broken in & the fruit & syrup mingling with it. —]

On p. 244 Darwin is so convinced of the 'original' north-south strike that when he finds some rocks at Tres Montes striking east-west he attributes this difference to the more recent intrusion of granite pushing the rocks aside. This was radical thinking in 1834 as not all geologists followed Lyell's view that 'primitive' granite could be young enough to do this (see Beagle diary quote above). In the sixth chapter of South America Darwin has a long section on this and explains how he enlisted William Hopkins to explain the geometry of the rocks. On p. 245A there is an impressive diagram of the north dipping slates of Tres Montes.

Page 259 starts eight pages on Cone Harbour dated 21-23 December 1834 which are obviously early drafts. Page 259v is quoted in section 4 as of considerable ornithological interest, representing Darwin's field notes for this location. There then follows a collection of Chonos notes in chaotic chronological order: pp. 272-273 are dated 16-20 December and are partly zoological field notes of great interest (see section 4), pp. 270-271 are 25-29 December, pp. 268-269 are 6 January 1835 from Lemoos and p. 267 is 16 January from Huafo. Pages 274-275 are 4-5 January, then pp. 277-285 revert to 31 December-2 January and deal mainly with Anna Pink Harbour and pp. 286-287 are 28 December at Cone Harbour.

Pages 288-303 are 15 sheets dated November 1834-January 1835 on the complex geology of Chiloe archipelago. On p. 300 Darwin refers to information sent him by Charles Douglas in February 1835 so these notes span several months. Page 297A is a page excised from the Port Desire notebook and has some general observations on earthquakes in the early 1830s (Beagle notebooks, p. 326). On p. 297 Darwin makes use of the Indian language as evidence of geological elevation:

In my notes to S. Carlos, I have attempted to show the land to this day as rising, a proof of it exists in the names of the places. — "Huapi" in the Indian language means islander; now many peninsulas, joined by low land have at the present day the affix Huapi affixed to them. — The inhabitants state they were formerly islands. — Suitras Huapi Laing & Huapilinao &c &c

Darwin then starts a long discussion of the angular boulders he finds on the west of the Island and he enlists Lyell as authority that they have not got there by tidal action. On p. 302 Darwin is describing a bed of shells which today would be called a 'raised beach' and he mentions a deer's antler found embedded in the soil overlying these deposits. He believes the peninsula on which this was found was an island and notes that puda deer are common today on the islands, noting the 'absolute proof this affords the time of elevation'. Darwin ends by noting that the genera of shells in the raised beach are the same as living on the beach today, leading to this reflection on p. 303v:

To what an epoch does this consideration lead the [mind] when in the older strata, not only is the local habitation of species altered; but the species & even genera are changed.

Page 304 concerns Lacuy Peninsula, p. 305 is a map of San Carlos, p. 306 a coloured geological map of Chiloe and pp. 307-9 are various diagrams. Pages 310-318 follow on from p. 304. On pp. 316-317 we have an interesting insight into Darwin's method of reasoning: he seems to say that geological phenomena are rarely simple:

In almost every geological question; facts of an opposite tendency can be brought forward. — It is right to state that occasionally a doubt crossed my mind...

So in Darwin's view the most satisfying explanation is likely to be the one consistent with the longest list of facts. This rule of thumb is perhaps something Darwin learnt from John Herschel's Preliminary discourse on the study of natural philosophy (1830), a book he certainly admired as a student in Cambridge. It is of course a rule Darwin applied to great effect in the Origin. Interestingly on p. 317 Darwin uses Conybeare and Phillips's (1822) account of the geology of the Isle of Wight in Britain to help him understand just such a geological problem (see also p. 338).

Pages 319-327 concern Lowes Harbour, then p. 328 contains a long series of field notes from Darwin's Chiloe excursion starting 22 January 1835, two days after the eruption of Mt Osorno. These notes are written on notebook-sized pieces of paper, but are perhaps cut from larger sheets. The reader is referred to the separate introduction to these notes (Chancellor and van Wyhe). Pages 329-330 comprise a letter from Charles Douglas (Correspondence vol. 1, pp. 430-1).

Pages 331-340 are a separate ten page section on Lacuy, starting 19 January, then pp. 341-342 are from Chiloe and dated 1 February. Notes from this month have the added interest that they may have been drafted at the same date as the famous 'Feb. 1835' (CUL-DAR44.97-99) notes on Macrauchenia which speak for the first time of 'the gradual birth and death of species' and were probably written before Darwin arrived in Valdivia on 7 February. It was also in this month that Darwin experienced the terrible Chilean earthquake of 20 February 1835, while 'lying down in the wood to rest myself' in Valdivia as he tells us in the Beagle diary. In his first letter to Henslow following the earthquake, Darwin told him in an extract later published by Henslow (Darwin 1835, p. 21) that 'we felt the shock very severely'.

Valdivia is the subject of pp. 343-346 but there is no mention of the earthquake. The port is shown on a fine fold-out coastal view on p. 344A by Midshipman Philip Gidley King. On p. 347v Darwin notes 'Surly manner of the people' and on p. 349v from Niebla Fort on 10 February he makes some fascinating notes on fruits growing there, quoted in section 4. Pages 351-353 continue with Valdivia, but again there is no mention of the earthquake.

Page 354v is dated 4 March and records in telegraphic style Darwin's first sight of the devastation wrought around Concepcion by the earthquake and ensuing tsunami. His jottings are quoted in full in section 4. The earthquake made a profound impression on Darwin, as it confirmed his view of South America being raised by subterranean forces which it was obvious from co-incident timing were also causing eruption of the great Andean volcanoes. After the voyage he chose to publish his views in a separate paper to the Geological Society, the full version of which (Darwin 1840) was a major theoretical contribution and included additional material from William Hopkins (Shorter publications).

Pages 357-370 are a fourteen page section on Concepcion. Darwin is concerned to date the sandstone there. He refers on p. 358 to Captain Beechey's 1832 report on the geology of the coast but is clearly sceptical of his dating:

Capt. Beechey appears to have found a greater abundance of shells & bones of cetaceous animals — I hope they are in the collection of the Geological Society: — I know not what reasons he has to call the sandstone secondary. —

It is obvious from Darwin's post-voyage note of giant ammonites on p. 357v that Beechey was correct. In South America Darwin eventually published an illustration of a 'Secondary' (in fact Cretaceous) age Nautilus from Concepcion collected by Mr Kent of the Beagle but not mentioned in these notes.


The Geological diary has now reached the start of the longest single section which stretches across CUL-DAR35 to CUL-DAR37 and amounts to 192 pages numbered by Darwin. Although it goes by several headings it is generally labelled 'Chili' and concerns the coast ranges from Valparaiso to Copiapo. As will be shown, it covers the year from July 1834 to July 1835 and is interrupted by some thematic essays (e.g. 'Valleys', CUL-DAR36.452-465) and a massive 84 pages on the Santiago-Mendoza Andean traverse (CUL-DAR36.466-549).

Pages 371-376 concern Valparaiso and are dated 1834, so relate mainly to the July-November period. At this time Darwin made his August-September excursion northwards via Quillota and Jajuel. He then went south via Santiago and San Fernando before returning via Navidad up the coast and back to Valparaiso to recover from what seems to have been a fairly serious illness. These pages describe Darwin's observations of the complex geology of the Andean coast ranges, with the emphasis on the gneisses and other 'hard' rocks, although breccias and other sedimentary rocks also feature. Pages 377-418 continue the series but are headed 'Chili' rather than 'Valparaiso' even though Darwin's page numbering is continuous. The note from near Quillota dated 18 August 1834 is quoted in section 4 and appears to be Darwin's first mention of possible Pacific subsidence.

On p. 382A Darwin has drawn a section which he has worked up from the two page field sketch in the Valparaiso notebook, pp. 66a-67a dated 23 August 1834, showing a large greenstone dyke in the Aconcagua valley near San Felipe cutting across jaspery rocks and breccia-conglomerate. He goes into great detail describing this section and on p. 383 was seriously puzzled by greenstone sitting above the breccias which seemed obviously derived from the dyke:

I had at first no doubt it had flowed through the main dyke, but upon close examination, I found the semi-porphyritic breccia & the greenstone were united (however odd it may sound) by the most gradual transition in nature & [mere] color. — There can be no doubt the main dyke crosses this conformable mass: (I could not see it owing to nature of ground). How strange thus to see the two rocks, so alike, one which has flowed, the other been merely altered in situ!

In his field notebook (p. 71a) he despaired: 'I see no way of distinguishing greenstone produced in situ & ones that have flowed'.

According to a note dated January 1980 by the archivist Peter Gautrey, p. 386 was obviously incorrectly positioned, according to Darwin's page numbers, and was moved to be part of p. 410 and so is discussed in the correct place below. Page 387 continues with Santiago then to p. 388 on the famous hot baths of Cauquenes (Beagle notebooks, p. 370). On p. 390 Darwin uses the heading 'Volcanic' for the first time, for a discussion of the relation between extruded (i.e. volcanic) trachytic lavas he found and the intruded greenstones. On p. 393 he describes the Porphyritic Breccia, which proved to be one of the most important rock formations Darwin encountered in the Andes and a constant feature in his notes from March-April 1835. It leads him into a reflection on p. 395 on the possible history of the Cordilleras:

Does it not almost demonstrate, that the nucleus of the Cordilleras then existed at this remote period, (anterior to the deposition of Transition beds?) as a chain of mountains, washed by a sea, where the debris were collection during a succession of ages. It is impossible to detect conjecture, what could have caused the subterranean fire (literally according to the Huttonian theory) to have broken these deposits & then elevated them by an elevation in the line of the former chain to have given them a corresponding tilt. — If this reasoning is correct, it makes the Cordilleras of the Andes nearly as old as the world is as interpreted by geology, — & this surely is no more consonant to its magnificent dimensions, than a sudden outbursting in the Tertiary period. —

By p. 400 Darwin is starting to mention the gold and copper mines, which feature prominently in his published descriptions of the Andes. The verso of that page is covered with an extraordinary range of later notes, for example cross-references to the Red notebook. Page 403A and 403Av are diagrams of mines, not drawn by Darwin but perhaps by Zacarias Nixon who owned the mines Darwin was visiting.

On p. 404 Darwin begins with a cross-reference to the Beagle diary entry for 15 August 1834 where he wrote an unusually detailed description of the geomorphology. He is concerned to link what he had seen as the emerging archipelago of Tierra del Fuego with what he now sees as the already emerged archipelago of the coast ranges between Valparaiso and Santiago. In the Valparaiso notebook in late August on p. 61a he wrote that 'The mist well represents the sea in the basin & showed probability' and in the immediately following Santiago notebook in mid September on p. 35 'Had often wondered how Tierra del F. Would appear if elevated'. Now in the Geological diary he expands on this:

Often when sailing about the intricate bays & channels in the South I had tried to picture to myself, what appearance this country, when elevated, would assume. — it was no ordinary satisfaction to have seen find in Chili answers to all my conjectures.

In South America (p. 61) he presents the argument more fully:

It is hardly possible to state too strongly the perfect resemblance in outline between these basin-like, long, and narrow plains of Chile, (especially when in the early morning the mists hanging low represented water,) and the creeks and fiords now intersecting the southern and western shores of the continent. We can on this view of the sea, when the land stood lower, having long and tranquilly occupied the spaces between the mountain-ranges, understand, how the boundaries of the separate basins were breached in more than one place; for we see that this is the general character of the inland bays and channels of Tierra del Fuego; we there, also, see in the sawing action of the tides, which flow with great force in the cross channels, a power sufficient to keep the breaches open as the land emerged.

Here is classic Darwin reasoning: take a typological series (islands to mountains) and an ongoing process across the series for which there is abundant evidence (emergence from the sea) and given time one end of the series will transform into the other. This is the exact reverse of the series from volcanic islands fringed with reefs to atolls formed by subsidence. On CUL-DAR35.404 perhaps Darwin is guessing that elevation and emergence ought to be balanced by subsidence and drowning, unless the world is expanding. He took the fossil forest he found in April 1835 to be evidence of massive subsidence.

At this time some geologists believed the world to be cooling and saw mountain ranges such as the Andes as 'wrinkles' proving this contraction. Lyell, always opposed to directional earth history, cited Pierre Simon Laplace as disproving contraction, so Darwin was well aware of the literally global significance of his South American findings.

This episode in August 1834 had even deeper significance for Darwin than has hitherto been appreciated and it is mentioned in section 5. The phrase in the field notebook 'showed probability' is as close as historians are ever likely to get to seeing a scientist making a brilliant leap of the imagination and emerging with real new understanding. In this case Darwin is seeing with his physical eyes the mist in the valleys and seeing 'with the eye of reason' how islands can become mountains. In other words Darwin is realising how a typological series interpreted historically can become an evolutionary series, although in this case the word 'evolutionary' does not imply self-replication as it does in biology. Although the  island which becomes a mountain changes its relation to the sea and may alter its shape by eruption, erosion or the accretion of reefs, it is always the same piece of rock.

Darwin's method of  demonstrating an evolutionary series is the same one he  used in the Origin to explain the similarities between species by descent with modification from a common ancestor, in other words biological evolution. Darwin of course did not know that in the biological case it is DNA which remains almost constant by self-replication and is therefore analogous to the island-mountain series (Ghiselin 1969; Gould 1986). Rather in the way that the island will change shape over time, DNA will change by differential rates of survival, by the process of natural selection which was Darwin's greatest discovery.

Pages 405A-405 (parts 1-3) are a beautiful manuscript map drawn by Alexander Caldcleugh of the country between Santiago and San Fernando, with notes on people and places to visit (see Pearn 2009, pp. 82-83). Pages 406 onwards describe the geology near and to the south of Santiago. On pp. 409-410 Darwin makes a surprising observation about a limestone:

Beyond Padaguel, (on road to Valparaiso, in same direction) such sand is capped by a horizontal thin bed of aluminous limestone, which is worked, in order to procure lime. This substance is precisely similar to the Tosca rock of the Pampas of La Plata. — I could not tell, if I had seen two was shown specimens from both localities, from which side of the Andes either came! —

Darwin continues expending many words explaining how he believes the landscape has evolved by gradual emergence from under the sea. By p. 415 even he realises that he is getting repetitive:

I have been this tedious in my proofs: because it appears to me an important fact to show, that all the principal valleys & level plains even in any one country have been once occupied & modeled by the sea. —

On the next page Darwin makes a rare comparison between a South American landscape and one he is familiar with from home:

Reflecting on the effect, which centuries of weathering, would have on one of these step-like countries, it appears to me, from what I have seen, that where the lines of escarpements were not far apart, an undulatory country would be produced, such as most of the secondary districts of England. —

As he returns to the Pacific Darwin begins to note signs of elevation. He remarks on p. 418 how the shells are more different from those living on the coast than they are on the Atlantic side of the Andes. By applying the 'statistical' approach to shells advocated by Lyell in his third volume of the Principles Darwin would normally date the Pacific deposits as older than the Atlantic ones, as fossils are almost always better for dating than minerals. Instead, he makes a startling deduction based on the similarity of the deposits and their elevations and his reluctance to admit differential uplift:

The shells certainly appear to be more distinct from the recent ones, than those in the great Patagonian formation: yet the mineralogical resemblance, especially at S. Cruz between these two formations is strikingly similar. — This formation, although apparently older, than the Patagonian & therefore more time has elapsed for its elevation, yet is on the same level with it. — This can be accounted for, without supposing a less force of upheaval has acted on this side the Andes than the other; viz by the greater depth, as at the present day. of the Pacific ocean on this coast than on the other. —

Page 418 is the last in CUL-DAR35. It was numbered '46' by Darwin.


The Chili notes continue without interruption from CUL-DAR35, as p. 419 is numbered '47' by Darwin and he cites the sea shells above Valparaiso as proofs of elevation. Page 420 is an appendix to '47', on 'Elevation'. Darwin is at pains to eliminate the possibility that the shells were taken there by human agency and after the voyage he was quick to publish this evidence (Darwin 1837). Pages 423 and 425-427 are letters from Robert Alison (p. 427 is referred to in section 4), although p. 424 continues on the shells. Page 424v has a note added in 1835 concerning the exact time of the 20 February earthquake. Page 428 is interesting in that Darwin is using the dates of buildings as indices of the amount of elevation, then p. 429 resumes the 'Chili' notes at '48'. By p. 433 he concludes that notwithstanding the tremendous power of the mountain torrents he has witnessed, they are impotent compared with the ocean surf and tides to excavate the valleys they flow through. Thus on p. 435 he arrives at his model of landscape evolution, driven by elevation:

... primarily the lines of elevation determine the figure of a continent; secondarily that a gradually retreating ocean models the elevated points, smooths with so called Diluvium some of its asperities, determines the directions of the great slopes. — & sometimes not infrequently sometimes excavates even the [mount] valleys — Thirdly we have rivers with aid of floods & subterranean movements modifying altering & generally deepening those lines of depression left by the preexisting ocean.

Page 438 resumes the main series of notes as '55' and its verso presents a simple diagram (reproduced in Herbert 2005, p. 224) of how Darwin saw the north-south 'crevices of upheaval' in the coast ranges. As Herbert points out, Darwin here has no truck with any idea of the Andes as a mountain range elevated 'at one blow', as Sedgwick might have paraphrased the orogenic theories of Élie de Beaumont as part of Darwin's pre-Beagle tutoring.

Although there are later notes on the versos of these pages, they were probably written in the closing months of 1834, perhaps while Darwin was convalescing in Valparaiso. The first  page referring to the Concepcion earthquake of 20 February 1835 is near the end (p. 448, that is Darwin's '63') while on his last numbered page before going north from Valparaiso (i.e. p. 451, Darwin's '66'; '67' is p. 550) he realises that this was exactly a month after the Osorno eruption. This fact was crucial to his great 'Connexion' paper of 1840:

This time is interesting, as it is of such rare occurrence that many travellers have doubted whether this peak, which is 23,000 ft high, is a volcano. This eruption took place took place at night on the 19th of Jany, the very same night as we saw Osorno, 600 miles distant, in activity. I only discovered this by referring to my Journal (a). Was this most curious coincidence accidental: — Or has the one volcanic power acted at these two remote points stretching across that basin, which a month subsequently at Concepcion was so violently agitated.

There is in fact no evidence in the notes before about p. 463 that Darwin had seen anything of the Andes east of Santiago so they were probably finished before he set out from there for Mendoza in mid March. It is worth remembering that while writing them he cannot have been sure he would have further opportunities to explore the Cordillera. In the event of course he made a full recovery and spent the southern summer in Chiloe and surrounding areas, returning to Valparaiso in March 1835, then spending almost four more months making the most detailed study of the range ever attempted.

Page 452 begins a fourteen page section headed 'Valleys-Cordillera' with a diagram of a bifurcating valley on p. 453v which was eventually published as part of a general discussion of valleys, in South America (p. 63). From the evidence of places mentioned this, like most of his Chile notes, must have been written after Darwin finished exploring the Cordillera. Some of the pages are very hard to read as the ink has migrated through the paper from the versos. From here on there are also several pages such as p. 642 with sections cut out, presumably by Darwin. Unfortunately we have only located a few of the removed sections.

Page 466 is the start of the 84page section dealing with Darwin's traverses across the Andes from Santiago to Mendoza and back again. The outward leg was via the Piuquenes or Portillo Pass (South America plate 1, section 1) between 18 March and 28 March 1835. The return leg was via the Uspallata Pass (plate 1, section 2) between 30 March and 10 April, total 24 days. Darwin's work on these traverses which was recorded in his St. Fe notebook, by far the longest of any of his field notebooks, is discussed in Beagle notebooks, pp. 175-182. As usual verso notes are not discussed in this summary which is confined to matters of general interest in the Geological diary. Note the important appraisals of Darwin's work on the Portillo Pass by Giambiagi et al. (2009) and by Aguirre-Urreta and Vennarí (2009), and on the Puente del Inca by Ramos (2009). Wesson (2017) provides an excellent modern geologist's description of Darwin's traverses and some fine photographs alongside Darwin's published sections.

Page 466 is exceptionally hard to read as it has become very dirty and smudged over the years, presumably as it probably served as a 'front cover' for the section. It has the following marginal comment in very small ink writing: 'Urge clearness of atmosphere, no vegetation steepness. I learnt more than in as many months on the [illeg]'. A more readable version of this occurs on p. 496 and it was the basis for the following sentence at the start of Darwin's published account of the Portillo traverse in South America (p. 175-176):

Although I crossed the Cordillera only once by this pass, and only once by that of the Cumbre or Uspallata (presently to be described), riding slowly and halting occasionally to ascend the mountains, there are many circumstances favourable to obtaining a more faithful sketch of their structure, than would at first be thought possible from so short an examination. The mountains are steep and absolutely bare of vegetation; the atmosphere is resplendently clear; the stratification distinct; and the rocks brightly and variously coloured: some of the natural sections might be truly compared for distinctness to those coloured ones in geological works. Considering how little is known of the structure of this gigantic range, to which I particularly attended, most travellers having collected only specimens of the rocks, I think my sketch-sections, though necessarily imperfect, possess some interest.

Page 490v illustrates the way Darwin builds up or 'stitches together' his sections. That page shows the view looking west up the valley from below Mal Paso and corresponds to field sketch 'No. 9' dated 21 March in the St. Fe notebook p. 128a (Beagle notebooks, p. 214). As Darwin wrote in the notebook the atmosphere that day was 'Respendently clear' and he was feeling the lack of oxygen, but the view at that point, approaching half way to Mendoza, was 'something inexpressibly grand'. The section is vaguely recognisable in Pearn (2009, p. 78) in the middle of the published section.

There is an interesting statement of Darwin's methodology on pp. 495-496 (Darwin's '30-31') as he descends to Mendoza past 'mere mole-hills from 3-600 ft' height:

Reviewing the sections of the Cordillera; represented in papers (a.b.c.d) I must distinctly remark they pretend to little or no accuracy; they are merely drawn to give a general idea of the structure. – It will be sufficient to state, that I only once (but not quickly) crossed this pass; Day by Day I made partial sketches and here they are all united.

By p. 501 Darwin has reached Mendoza and on p. 502 he is beginning his return to Santiago. As has been mentioned, however, these notes are retrospective and pp. 500-501v show that he had already returned to Santiago and seen northern Chile. He makes an explicit prediction that if granite continues to be intruded in the central Chilean ranges they will come to look like those in northern Chile. He also explains that the Portillo ranges post-date the Piuquenes ranges, thus disproving at a stroke the theory of Élie de Beaumont (1829-30) that the Andes were all raised in one 'paroxysm of elevation'. Darwin also adds that Elie de Beaumont's doctrine that rocks in mountain ranges are all parallel is also incorrect, as the outer ranges of the Andes are oblique to the central ranges.

This critique is interesting as one more example of Darwin siding with Lyell against Sedgwick, as Lyell criticised Élie de Beaumont in the Principles for speculating that the elevation of the Andes might have caused the 'diluvium' of Europe. Darwin surely knew that Sedgwick had praised Élie de Beaumont's theory, albeit with qualification, in his Anniversary Address to the Geological Society in 1831. As he recalled in his Autobiography (p. 102) Darwin himself heard Sedgwick lauding Elie de Beaumont at the Society 'to the skies', but there seems no way of knowing if this was in 1831 or after the voyage.

Herbert (2007, p. 317) has chosen p. 508 to illustrate Darwin's method of combining his sketches with his text and his specimen numbers. That page corresponds to St. Fe p. 164a dated 1 April (actually 31 March). Herbert points out that Darwin's method follows that advocated by William Fitton in his 'Instructions for collecting geological specimens' of 1827.

On p. 518 Darwin begins his account of the '11 silicified trees and about 40 columns of crystallised Carb: of Lime' (i.e. calcite) at Agua de la Zorra (see quote from CUL-DAR36.523 in section 4). The trees were 'very perfect' and the calcite, which he was quite certainwere former trees 'reminded me of Lot's wife turned into a pillar of Salt'.

As discussed in section 4, finding the trees was hugely significant as it convinced Darwin that they had been buried under 'Subaqueous' sediment (p. 521) so that parts of the Andes which had once been dry land must, he thought, have later subsided under the sea then returned to their present high altitude. This was the first time in South America that Darwin had (incorrectly) recognised subsidence on a grand scale and it may well have been the trigger for his (correct) guess that parts of the Pacific sea bed were subsiding, giving him an understanding of how some limestones may have formed and a mechanism for the all important question of coral atolls.

The rest of the 84page Andes section is an account of the Uspallata Range, some pages with pieces missing (pp. 541, 546), ending with this speculation on the cause of its upheaval on p. 549:

I cannot help admiring the beautiful symmetry of the Uspallata Range: the granitic peaks may be considered rather as accidents, which serve however to point out the cause in an arch of the same substance at a greater depth.

Page 550 marks a resumption of the 192-page section on the coastal ranges and is numbered '67' by Darwin, his '66' being CUL-DAR35.451. This continuation covers Darwin's longest ever horseback expedition up the arid coast (number eight of Barlow 1933) starting 27 April and ending eight weeks later (see Beagle notebooks for a general account). Darwin went aboard the Beagle in Valparaiso on 23 April to catch up on news, then back on shore set out for Coquimbo on the 27 April. He took lodgings there with FitzRoy on 16 May before continuing to Copiapo. The expedition is covered by two consecutive field notebooks, Coquimbo and Copiapò, before Despoblado takes over for the Despoblado Valley, Iquique and Callao in June-July, followed by Galapagos in July and August for Lima. Page 550 sets the scene with the following introduction:

I travelled from Valparaiso to Coquimbo thence to Guasco and Copiapò. I resume the account of my geological observations from the North side of the Cerro of Chili Cauquen. From this point, for a considerable extent of coast to beyond Longostomo all the rocks are granitic, they occur chiefly in a very decomposed slate, amongst which syenite and some very quartzose granites can be discovered.

Then a few pages later (p. 552) Darwin extends the now familiar image of a submerged continent gradually emerging from the sea, albeit by a fall in sea level:

If the Pacifick was lowered a hundred yards I believe we should see the very same form of land which now extends above its beach. – And in the course of time it is probable such will take place.

The map on p. 555A shows the road north of Illapel taken by Darwin and is worked up from the one dated 7 May in the Coquimbo notebook, p. 27. It shows the northeast-dipping porphyritic breccia, gypseous formation and siliceous strata with petrified wood near the mines of Los Hornos. Darwin later had the wood identified by Robert Brown as coniferous. This is followed by page after page of details of the geology and mining for metals such as gold and copper, until Darwin reaches Coquimbo around p. 574 where he focuses on the Arquerros silver mines before off-loading his specimens onto the Beagle.

Beagle notebooks, p. 450 describes how the description of Darwin's specimen 2940 listed on pp. 575-576 is a remarkable case where all his documentation of the specimen can be traced, from the original field note (Coquimbo, p. 102) right through to the published citation (South America, p. 236). To that account can now be added the photograph of the specimen at the Sedgwick Museum (Pearn 2009, p. 68).

While staying at Coquimbo Darwin paid special attention to the famous 'parallel roads' which he had read about in Lyell's book and which he took to be obvious proof of elevation (see Beagle notebooks, pp. 445-446). These are dealt with in a dedicated section of the notes around CUL-DAR37.662-670. Small pieces of pages 581 and 586 are excised.

The next part of the notes covers the trek north from Coquimbo, which Darwin left on 2 June towards Guasco. He was not to see the Beagle again until rendezvous in Lima on 5 July. The notes headed 'Copiapò' [sic] start on p. 598. On p. 602v he adds a long note which he seems to have "omitted” by mistake and which includes the following:

The higher mountains which bound the valley rise like islands from it.— The plain slopes to Seaward is clearly of marine origin & must be one of the highest which I have seen in Chili

The note on p. 605v contains what may be Darwin's first ever written uses of the word 'evolution', but in this case it refers to volcanic gasses as a possible cause of rounded porphyry pebbles and has nothing to do with the living world. There is no other recorded use of this word by Darwin before 1859 where 'evolved' is famously the last word in the Origin, the book which unintentionally changed its meaning forever. Darwin himself begrudged Herbert Spencer's appropriation of 'evolution' for what Darwin called descent with modification (Gould 1977). The last page in CUL-DAR36 is p. 610, that is Darwin's '126'.


The first page in CUL-DAR37 is p. 611, Darwin's '127', and continues the 'Copiapò' headed part of the 192page Chile coast notes without interruption. There are another forty-odd pages of highly technical geology as Darwin arranges the observations he made in June 1835 to support his third published section (South America, plate 1, section 3; see Pearn 2009, pp. 80-81 for the manuscript fair copy now in CUL-DAR44.19).

Darwin seems surprised on p. 620 that two species of 'the prevailing shells' he finds in two formations he takes to be separated by a 'considerable epoch' still 'continue the same'. Thus, like geologists up to the present day, he expects to see fossils change either in the details of their morphology or as Lyell argued, in the proportions of the species. He does not expect stasis or equilibrium over time.

Sometimes Darwin appears defeated by the dangers of the mountains and the geological complexity he observes, a very long way in every sense from his training under Sedgwick four years previously (p. 630):

I followed the road to the first main ridge beyond which it was not prudent to venture.— I will not attempt to give a section of the line of road, the excessive confusion in the stratification would render this no easy task & the geological structure is so similar to that of the main valley that it would not have been worth the trouble.

For the reader uninterested in geology the monotony is relieved by an excised page from one of the field notebooks. This is at p. 642A and is from the Despoblado notebook pp. 29b-30b, dated 1 July but referring to observations made the previous day. Darwin's text for the field sketch is on pp. 641-642 and was condensed into South America p. 232. Page 648 is an undated copy by Darwin of a letter to him from Charles Lambert which he referred to in South America, p. 211.

Page 649 begins the last part of the Chile section and is mainly concerned with elevation of the coast. The lines of evidence are the usual ones: the shape of the land, raised beaches and shells found at altitudes where human agency would be an implausible explanation. Darwin is naturally attentive to the parallel roads of Coquimbo which he had examined on 18 May. The fair copy of his Coquimbo notebook p. 88 field sketch is on p. 662A and is on pp. 662-670. The top of p. 669 has been sheared off and the last page (p. 677, Darwin's '192') is a mini-essay on valleys. One of Darwin's last references to the 'Diluvium' of Europe is on p. 675.

It is not certain when Darwin compiled and numbered his Chile coast section. From the absence of any reference to anywhere north of Copiapo, a July 1835 date seems reasonable but it would be surprising if he could have written so many pages in the six days sailing north to Iquique, arriving 12 July (notes starting on p. 678). Darwin spent two days there before the Beagle weighed anchor again for Callao, the port of Lima, where she arrived on 20 July, sailing for the Galapagos on 7 September.

Darwin had almost certainly finished the notes before reaching the Galapagos in mid September and he wrote in the Beagle diary some time before 6 September that 'My occupation has been writing up Geological notes about Chili'. Before that date he also wrote his 'Recapitulation and Concluding Remarks' which starts with the sentence 'Before finally leaving the shores of South America...' Darwin's original manuscript of that essay is lost, but Syms Covington's elegant 39-page fair copy survives (CUL-DAR41.23-39).

Iquique in 1835 was part of Peru so it is not covered by Darwin's notes on Chili even though the City was seceded to Chile in the 1880s. His Peruvian notes have a very different feel from those on Chili and many are given a precise date so almost count as field notes, perhaps reflecting the political instability in Peru which restricted his field work. There are also several pages of telegraphic notes for July-August in the Despoblado notebook, and the Galapagos notebook (pp. 81a, 17a, 25a) has a short section on Lima.

The Iquique notes start on p. 678 and are written on poorer quality, larger sheets than the Chile notes. The predominant rock is no longer granite, rather it is a porphyritic conglomerate. By now Darwin's dry specimens are numbered in the 3000s and he is hoping to link his own work with that of his hero: 'Perhaps through the means of these sections I can connect Humboldt's geology of Peru with what I have seen in Chili' (p. 681). Page 685 lists figures on the export of nitrate in the hand of Consul General Belford Wilson, previously aide-de-camp to Simon Bolivar. Pages 686-687 are notes on FitzRoy's specimens from Peru, reinforcing the Captain's claim that perhaps Darwin did not sufficiently acknowledge the Navy's support in his publications from the voyage.

Darwin's 16 pages of notes from Lima commence on p. 688 and are dated 21 July. His notes on the Indian mounds are worth quoting here as evidence for extreme rates of elevation of Peru (p. 694):

Together with the shells there were birds bones, bits of roots of sea weeds, corallines, ovules of molluscous animals, heads and flower of Indian corn, other vegetable matter and lastly a piece of rotten cotton string & another of woven rush such as I have seen taken from the Huacas (or burial grounds of the Indians). This however only proves they might be [older del.] (but not that they are) [older del.] of an age anterior to the arrival of the Spaniards.

This found its way into a lengthy section on 'Fossil Remains of Human Art' in South America which is all the more interesting as South America is now known only to have been peopled for about 11,000 years. On p. 703 Darwin has to eliminate the possibility that some littoral material was transported up the slopes by the tsunami of 1747 (a misdated reference to the Lima earthquake of 1746).

Page 704 is an 'Appendix to 27th [July]' and the remainder of the Lima notes are effectively a bundle of scraps of notes from which the main notes were derived. Page 706 is virtually a field note, although in ink so presumably not written on the move. We have quoted from p. 708v in section 3. Page 711 is dated 27 July from San Lorenzo Island and p. 713 is the field note on which p. 694 is based. Darwin is clearly struggling to understand the Indian remains: 'I cannot feel sure about the relics'. Page 715 is the last from the South American mainland.

Pages 716-795 are 121 pages on the Galapagos. K. Thalia Grant and Gregory B. Estes have contributed an introduction to the notes, prepared as part of their reconstruction of Darwin's seminal visit to the Islands in September-October 1835. They have also published a definitive account of the visit which includes as their fig. 21A an image of CUL-DAR37.753 and a summary of Darwin's geological work (Grant and Estes 2009). As they point out (Grant and Estes 2009, p. 187) some of the notes have been archived in the incorrect chronological order and some were apparently written while Darwin was actually on James Island, rather than later on board ship.

Herbert et al. (2009) have also published exhaustive accounts of Darwin's Galapagos geology which show how important the Archipelago was in forming his advanced views on magma fractionation. Pearson (1996) has likened these views, explained in Volcanic islands but largely ignored by Darwin's contemporaries, to Darwin's biological theory of natural selection. Sponsel (2009) has also discussed the Galapagos notes at length.

The present introduction does not supercede what these authors have already written and instead mentions three issues where perhaps further information can be added. Firstly, Estes and Grant in their introduction state that the Geological diary is CUL-DAR34-38 whereas here it is defined as including CUL-DAR32-33. Secondly, the opportunity is taken to correct an error in the introduction to the Galapagos notebook (Beagle notebooks, p. 418) where it was assumed that Darwin's description of the lavas on Albemarle as 'a lake ruffled by a breeze' was his own. In fact the simile originated with John Stokes of the Beagle (FitzRoy 1839, p. 493). Finally, attention is drawn to Darwin's comment on p. 791 that he 'is no believer in the theory of Lagoon Isds [resting del.] being based on the circular ridges of submarine craters'. He writes this in support of his observation that Galapagos crater rims are rarely horizontal, making it hard to see how they could become coral atolls, such as those he had seen in the South Pacific before he wrote this section of the notes. Sponsel (2009, p. 114 and footnote) has discussed this note and shows that when it was written Darwin had already left Tahiti. He was correct to endorse FitzRoy's view on p. 792 that the scarcity of coral reefs in the Galapagos is due to the sea there being too cold for them, so here there is a clear demonstration of the connection between Darwin's zoology and his geology (Sponsel 2009). As is well known Darwin had been extremely keen to test the crater rim 'theory of Lagoon Isds' expounded in Lyell's Principles so it is interesting to see him emphatically dismissing it in favour of his own theory as laid out in the 'Coral Islands' essay.

Pages 796-797 are an 'appendix' to p. 212, the latter being a page on Chiloe in CUL-DAR35 from July 1834. There is no obvious reason why this appendix is now in CUL-DAR37. Page 798 begins the four pages of notes on Darwin's November 1835 visit to the northwest part of Tahiti (Armstrong 2004). Although the island was obviously a volcano, Darwin could find no crater. A fine Darwin specimen of olivine basalt with amygdaloids from the island is shown in Pearn (2009, p. 104).

In some paragraphs headed 'conjectural' Darwin seems to assume that Tahiti was once submerged but can find no evidence of recent elevation, leading him to speculate on p. 801v that 'the Isd of Tahiti has existed as dry land for a long period.' His verso note on what this might imply for the island's biological history is quoted in section 5. Darwin's Beagle diary entry for 18 November includes the following note which makes his views very clear:

I believe a group of the interior mountains stood as a smaller island in the sea, & around their steep flanks streams of Lavas & beds of sediment were accumulated in a conical mass under water. This after having been raised was cut by numerous profound ravines, which all diverge from the common centre; the intervening ridges thus belonging to one slope & being flat-topped.

This appeared almost verbatim in the published Journal, although significantly the word 'underwater' was dropped. In Coral reefs and Volcanic islands Darwin stressed the lack of evidence of recent elevation and on his chart of coral islands of the world he classed the reefs of Tahiti as barrier reefs. He probably wrote the 'Coral Islands' essay at sea in December, between Tahiti and New Zealand.

Pages 802-811 are on the Bay of Islands, North Island, New Zealand, the last place visited by the Beagle in 1835 (see Laurent and Campbell 1987 and Armstrong 2004 for summaries of Darwin's scientific work on the island). New Zealand being one of the most geologically active countries on Earth, it is no surprise that Darwin found volcanic rocks there, but it is odd that all he ever published on the geology was a footnote in Volcanic islands listing the rocks he collected. On p. 802v he notes what seems to be a 'ledge' on the coast at the extreme high tide level which reminds him of something similar in South America. Herbert (1980, p. 88 note 49) points out that Darwin refers to this note in the Red notebook, p. 38 alongside a series of jottings on coastal erosion. This feature in New Zealand may be a raised beach. On p. 804 Darwin mentions his walk inland to Waimate and as usual Darwin notes 'positive proof' (p. 807) of elevation. He is confident that New Zealand is a volcanic country and on p. 810-811 observes:

On the mainland there are many springs of hot water & I heard of one of Pitch. — These volcanic districts of in the Northern Island of New Zealand, may from its position & direction of its coast. be with propriety described as the SE termination of the great band of volcanic action, which contains the parallel lines of New Caledonia, New Hebrides, New Zealand & New Guinea. —

New Zealand is indeed the south western end of the 'Pacific Ring of Fire', more properly perhaps a horseshoe than a ring, with Chile at the other end. Darwin was right to spot New Zealand's relationship, without of course knowing the tectonic cause, to other points of friction between the Indo-Australian and Pacific plates. He would have been intrigued to know that New Zealand is only the small exposed part of a submerged continent, now known as Zealandia.


Pages 812-836 cover Darwin's excursion from Sydney to Bathurst, New South Wales, Australia between 16 January and 27 January 1836. Although Branagan and Townley's (1976) review of Australian geological research does not even mention Darwin's now appreciated contribution, there are other excellent accounts of his visit: see Laurent and Campbell (1987), Armstrong (2004) and Nicholas and Nicholas (1989). The published version of Darwin's notes is in Volcanic islands.

Page 812 opens with a general outline of the sandstones which continues on p. 814, as pp. 813-813v seem to be a list of places visited on the journey, quoting distances in miles from Sydney and heights in feet for some of them. These barometric heights were courtesy of Captain Phillip Parker King, who had been commander of the Beagle's first voyage. There is a diagram on p. 814 of what is obviously cross-bedding, which Darwin calls 'Pseudo Stratiform Structure' derived from the Sydney notebook, p. 12a. He reports pebbles of 'trap' from Emu Ferry on p. 815 and immediately jumps to the (erroneous) conclusion that they could not have been brought there by rivers, 'the retiring sea' being the assumed agent. On p. 820 Darwin reports a 'beautiful' granite with very large feldspar crystals at the Vale of Clwyd, then on p. 822 there are coals in the sandstone and a few miles from Bathurst there is slate (p. 824). Captain King told Darwin that the north-south strike of the slate is so regular that 100 miles to the south it is used by the locals to guide their travels through forests, another example, notes Darwin, of Humboldt's loxodromism. On p. 826 Darwin employs the antiquated term 'Diluvium' for the sands and gravels which conceal the bedrock around Bathurst, which again he attributes to the 'retiring sea'.

By pp. 827-828 Darwin is summarising his view that there is an older granite, slate and marble formation overlain by the sandstones and slates derived from erosion of the granite, interstratified with coals formed from trees once growing on the granite. He is puzzled that in places the younger rocks have a higher altitude than the ones he considers older but suggests this may be due to differential uplift (unlikely on such an ancient, stable continent as Australia). On p. 829 Darwin raises what is for him 'the most interesting part of the Geology of this Colony, namely the structure of the valleys in the elevated sandstone platform'. He explains that tourists are encouraged to visit the 'immense precipices' at places such as Govett's Leap of which his old shipmate Conrad Martens is making money selling watercolours, such as the one in Nicholas and Nicholas (1989, p. 37). Darwin recounts how throwing a stone off the edge he saw it hit the trees in the valley '800 or 1000 ft' (300m) below:

The geologist is immediately astonished at the enormous amount of matter, which the corresponding horizontal stratification on each side of the grand valley seems to prove to have been removed. (pp. 830-831)

Since the river below is 'an insignificant rivulet or mere chain of pools' Darwin is confident that anyone would conclude that the valleys are the work of the sea. He says that 'more than one person' has told him they always imagine the valleys were once occupied by the sea, but even if this were the case Darwin doubts the power of the sea to form such stupendous cliffs. He concludes that the sandstone never did evenly fill the space now occupied by the valleys (p. 834) and that this is because the sediment was never of uniform thickness (p. 835). He ends the notes by hoping that some future Australian geologist will settle the question. In fact, as discussed by Armstrong (1993), the very next geologist to visit the valleys believed –correctly – that they were caused by river action. The geologist was Darwin's near contemporary the American James Dwight Dana who followed in many of Darwin's footsteps just a few years after him. These two men, though disagreeing on this and other scientific issues over the years, came to acquire great mutual respect.

Pages 837-857 continue the Australian story in Van Diemen's Land (Tasmania) which the Beagle reached on 5 February, leaving on the 17th. The notes have been transcribed and discussed by Maxwell and Doris Banks with an illustration of p. 844 (Banks 1971; see also Armstrong 2004). Hobart is one of the Beagle locations not covered in any field notebook. The field notes, which were transcribed by Chancellor have been used in detail by Nicholas and Nicholas (1989) and by Banks and Leaman (1999) and are instead on loose sheets in CUL-DAR40.97-101. The last page of the field notes (p. 101v) is of exceptional interest.

Darwin's nine day visit to Hobart and the Derwent Valley in south east Tasmania was remarkable from the number of Permian fossils he collected there, namely brachiopods, some of them 'new', some 'new' corals (actually bryozoans), both mentioned on p. 843 and some Tertiary plant material (p. 851). The brachiopods and bryozoans were described without illustration in Volcanic islands by G.B. Sowerby and William Lonsdale respectively. The frequency with which George Frankland is mentioned in the notes is a reminder that wherever he went Darwin sought out the local experts to assist his researches (see Rudwick 1982). It is also worth noting that Darwin turned twenty seven on the day he dined with Frankland, one of 'the most agreeable evenings since leaving England', in a house that is now the Maritime Museum of Tasmania.

The CUL-DAR38 notes begin with an immediate mention of the ubiquitous igneous rocks; in fact the eastern half of Tasmania is basically the world's largest exposure of dolerite (Darwin's 'greenstone'), dating from Jurassic times. At the risk of oversimplifying, pp. 837-842 describe various sandstones cut by dolerites and overlain by Tertiary basalts, then on p. 843 Darwin details the fossiliferous mudstones in the Barossa Road area. On p. 846 Darwin deduces for the very first time that the dolerite post-dates the Permian strata, as is obvious from the succession on Mt Wellington (p. 847). Mr Frankland (p. 849) provides enough knowledge for Darwin, ever keen to generalise, to sketch 'a general outline of the Geology' of Tasmania. The plant bearing travertine is described on pp. 851-853, with the first record of a 'Neptunian' dyke from Australia on p. 852.

We see Darwin on p. 853, as so often, focusing on evidence of raised beaches as proofs of elevation. He then resumes his 'shadowy outline' geological history of Tasmania including comparison with New South Wales (pp. 855-857). Darwin's p. 19 seems to be the only case of a page missing from a sequence numbered by himself.

On the last sheet Darwin makes the remarkable suggestion that the fossiliferous 'second series' rocks might 'correspond' to the 'Limestones of Argyl', which if this means Argyll in Scotland is on the other side of the world (the same name occurs on CUL-DAR40.7). As when comparing his Falklands fossils to those he knew from Britain, Darwin rightly saw fossils as globally reliable means of correlating rocks. Banks and Leaman (1999, pp. 35, 41-43) cite no evidence to support their suggestion that Darwin had visited Argyll as a student, so perhaps 'Argyl' is a mis-transcription of some other place where Darwin had seen Limestone containing similar fossils, perhaps in North Wales? Darwin had certainly seen the 'Mountain Limestone' around Shropshire and Edinburgh and this is probably the rock he had in mind but there is no obvious place name in any of these areas which could be confused with 'Argyl'. If it is found that Darwin did geologise in Argyll this would force a revision of what is known of his Edinburgh days which he implied were worse than useless for his geological education. That matter is for future scholars, like Darwin's parting challenge to future geologists:

With respect to the absolute age of the second series of this place, I fear the fossils are far too scanty even to offer a conjecture. The subject remains a field open to the examination of the rising Geologists of Tasmania.—

Pages 858-881 are Darwin's notes on the geology of King George's Sound on the southwest extremity of Australia, visited by the Beagle in March 1836 after a three week sail from Hobart (Armstrong 1985, 2004). The notes fall into two distinct sections: pp. 858-863 being rough drafts, while  pp. 864-881 are a more polished version consistently numbered by Darwin. Unusually there is a sheet in CUL-DAR40.92 in Syms Covington's hand which appears to be a fair copy of some of these notes. Armstrong (1985) illustrates p. 858 which, as increasingly in notes from the later stages of the voyage, bears a specific date, in this case apparently for Darwin's visits to Vancouver Peninsula and Bald Head. Pages 859v, 861v and 863v are in pencil and bearing in mind that there are no field notebooks for the February to April 1836 these pencil notes can be regarded as field notes (Chancellor and van Wyhe, in preparation). Armstrong (1985) reproduces pp. 867-868 which also deal with Bald Head, where the dyke-riddled granitic bedrocks are overlain by the calcareous sands discussed at considerable length in ­Volcanic islands. Armstrong also reproduces and transcribes p. 864. Perhaps because Bald Head had been described by previous navigators, Darwin went with FitzRoy to determine the nature of the 'peculiar calcareous cylindrical projections' found there (p. 875). Their joint conclusion, summarised in the Beagle diary that the structures were casts of rotted plants, is broadly correct.

There is no section in the Geological diary devoted to Keeling Island as all Darwin's geological notes from his visit of April 1936 are in CUL-DAR41 (Armstrong 1991, 2004).

Pages 882-901 are twenty, rather small numbered sheets on the Indian Ocean island of Mauritius, visited by the Beagle in May 1836 (Armstrong 1988, 2004). The notes begin with a 'slight sketch' of the geology, but Darwin seems anxious to get on with what really excites him, namely examining the coral reefs and testing out his theory. He cites René Primevère Lesson's view that the island is the remains of a crater 'five leagues in diameter' and on p. 884 suggests that this was like some of the 'so called craters of elevation'. Herbert (2005, p. 241-244) has discussed Darwin's modified support in Volcanic islands for the 'craters of elevation' theory which was opposed by Lyell, who finally disproved the original version in the 1850s (see Correspondence vol. 3). At some point after visiting Mauritius, probably in 1838, Darwin was struck by its similarities to St Jago, and to a lesser extent St Helena. Having been convinced that elevation and vulcanicity are expressions of the same forces, he concluded that the form of such islands was due to relief of pressure in the central parts of the crater, resulting in differential elevation (Chancellor 1990).

By p. 885 Darwin is reporting coral rock now lying high and dry and is already convinced that the slopes 10-15m above the present sea level at 'no very distant period were covered by the waters of the sea.' He never seriously considers the possibility of sea level fall, always assuming it is the Earth's crust which oscillates:

Near the mouth of a small brook, but yet some distance within the running fresh water, several of the rounded blocks of were coated with serpulae, it would appear from this that the rise of the land had been very recent, but as earthquakes are said never to be experienced here, the epoch probably goes back to beyond historical records. (p. 886)

From p. 890 Darwin focuses in detail on the fringing reefs which more or less surround the Island, indicating that he was taking depth soundings, no doubt with others from the Beagle (p. 894):

Pulling out to seaward the water gradually deepened; to the depth of 8 fathom I sounded repeatedly with a lead, the face of which was formed like a saucer with a diameter of four inches.

Further down that page he says 'As at each cast especially where I could see the bottom we pounded the bottom with the lead...' suggests the sounding was done together with others. His finds did not contradict his view that Mauritius was gradually rising, unlike the many sinking islands of the South Pacific, and that island reefs are generally more substantial on the windward coast (Sponsel 2009). Perhaps surprisingly, his field notes for this work are in the Despoblado notebook rather than the Sydney notebook which contains most of the Mauritius notes.

Pages 902-919 are eighteen un-ruled sheets on the Cape of Good Hope, the Beagle's only African landfall, visited in early June 1836. Stepping ashore at Simonstown, Darwin took a gig to Cape Town, then on a four day ride via the granite hills to the east, then back to the ancient 'clay slates' and sandstones of Cape Town, where he spent a very cultured ten days with 'long geological rambles' before departing for St Helena. His account of the Cape's geology is given in Volcanic islands.

Armstrong (1999) has given an excellent account of Darwin's Cape studies, showing that Darwin may have been the first to explain how weathering along joints has caused the peculiarly rounded granite boulders characteristic of the area (p. 903). Darwin also focused (pp. 906-909) on the relations between the ancient 'clay slates' and the granites intruded into them, previously described by Basil Hall, the whole capped unconformably by the Transition age Karoo Sandstone (pp. 909-911). Darwin describes the 'beautiful junction' between the sandstone and the underlying rocks on p. 912 and on pp. 913-914 he discusses the horizontal sandstone which gives rise to the 'well known form of Table Mountain'. On the remaining pages Darwin sketches the 'curious' geology he merely saw 'in riding past' (p. 916) in the eastern hills, and on pp. 917-920 he describes the geologically recent ferruginous sands with plant traces which on the last page he compares with those he examined in Australia (p. 919v).

Pages 920-935 are twenty six pages dealing with the South Atlantic island of St Helena, visited briefly from 8 to 14 July 1836, which as Darwin immediately states 'is so very remarkable as being a centre of distinct creation' (see section 5). Darwin in the notes defers to the geology previously published by Robert Seale but manages in Volcanic islands to devote a substantial chapter to his own work on the island, ending with his essay on 'Craters of Elevation'.

The first three pages sketch out Darwin's impressions of the overall structure of the island, which he says later is an old crater broken through by the sea on the south side. As Darwin explained to his sister Caroline just after leaving the Island its structure 'is complicated & its geological history rather curious' (Correspondence vol. 1, p. 502). As an old man, Darwin recalled in his Autobiography that his geological work on the Island gave him 'high satisfaction'.

In the notes Darwin moves on to describe the parts he examined in detail, starting in the north east with Flagstaff Hill and the Barn where there are submarine basalts overlain by strata rich in feldspar apparently filling the central parts, the whole cut by dykes implying stretching and dislocation (pp. 924-927). As noted in section 3, the layout of the notes changes on p. 926, with Darwin adopting a wide margin for notes, the versos used as numbered pages for text.

Darwin next describes the north eastern coast around Prosperous Hill, with a small view drawn in the margin on p. 928. A few pages on (p. 929, Darwin's '13') he tries to make sense of St Helena by imagining that it might once have resembled Mauritius (aka 'Isle of France'):

This structure & the removals of large portions, can I think be only understood on the supposition that formerly these black masses formed parts of one of those immense craters such as yet now may be seen traced in the circular range of mountains in the Isle of France (a) or in Santorini &c &c . — In the former of these Islands, if eruptions or so of variously coloured lavas, were to take place from the Pitou du Milieu, on so a great a scale, as fill up the central plains & the spaces between the coast mountains, the original structure would very closely resemble (with the exception of the dislocation) that of St. Helena.—

On the same page he writes a long marginal note in very small handwriting illustrated by a diagram showing how eruptions in the centre of a crater might stretch the crater and wonders 'May not this partly account for the so called craters of Elevation?' At some point, perhaps years later, he has scrawled an emphatic 'NO' over the entire note.

By p. 929v Darwin has reached the southern half of the island and his increasingly ragged style suggests that he is in a hurry to finish. He describes the 'semioval' of mountains with Diana's Peak at the eastern end and Sandy Bay Ridge in the middle and by his page '15' he is certain this as the northern rim of what was once the central crater:

To this view, the structure of the Amphitheatre, included within the horns of the ridge (Sandy Bay valley & its branches) perfectly corresponds.

On p. 931 Darwin has drawn a diagram in the margin showing a dyke in the central ridge cutting through tuff, both unconformably and with an undulating junction overlain by the feldspar-rich lava. This implies a significant time interval when much rock must have been eroded away. The diagram first appears on p. 81b of the Despoblado notebook and eventually became woodcut no. 10 in Volcanic islands. There is a small pencil annotation to 'V[ide] Model' which is Darwin's instruction to himself to have another look at Robert Seale's 'gigantic model' of the Island (Beagle notebooks, p. 523).

The notes close with discussion of the superficial deposits. Firstly, there is 'calcareous sand' sometimes containing fragments of land shells and birds eggs. Darwin also found in the uppermost layers of this deposit some whole land shells and even bird bones and eggs (p. 932v). Some of the shells were later described as previously unknown extinct forms by G.B. Sowerby in an appendix to Volcanic islands. Secondly, there is a 'black earth' (p. 934v) which contains abundant shells of land snails apparently no longer found living on the Island. These shells told an intriguing story, related in section 5.

Pages 936-953 are thirty-five of Darwin's numbered pages dealing with the mid-Atlantic island of Ascension, reached by the Beagle on 19 July 1836. Ascension is one of those locations for which Darwin's field notes from his three-day visit are not in any notebook; instead they are at CUL-DAR40.93-96 (Chancellor and van Wyhe, in preparation). It is obvious from the Beagle diary entry for 20 July that Darwin did not much care for Ascension: 'The Isld is entirely destitute of trees, in which & in every other respect it is very far inferior to St Helena.' This did not stop him writing perhaps the highest 'page per day' of any location he visited and devoting the longest chapter of Volcanic islands to Ascension, including in it a detailed map of the Island. There is internal evidence that at least the later pages were written in England.

The Geological diary notes continue in the style of those from St Helena with text on both sides. The notes commence with a general description on p. 936 then focus on the petrology of the basalts and trachytes. It is clear that Darwin suspected from its few sea cliffs and few visible dykes that Ascension has been far more recently active than St Helena. On p. 937 he mentions the incrustations on the coast which are illustrated by woodcuts in Volcanic islands and which he thought had some similarities to Peruvian guano. In passing, Darwin makes notes on volcanic bombs (p. 939), also figured in the book and featured in the 'Catalogue of the Museum of Practical Geology' (Ramsay et al. 1862, p. 225). On p. 944 Darwin describes strange upstanding veins:

Sometimes the veins although so thin project upwards although two or three feet & extend in length for a few yards. They are, in such cases, both to extremely sonorous, emitting, when struck, a sound like a big drum

Perhaps it was the striking of these veins that he referred to in his Autobiography pp. 81-82:

Towards the close of our voyage I received a letter whilst at Ascension, in which my sisters told me that Sedgwick had called on my father and said that I should take a place among the leading scientific men. I could not at the time understand how he could have learnt anything of my proceedings, but I heard (I believe afterwards) that Henslow had read some of the letters which I wrote to him before the Philosophical Soc. of Cambridge and had printed them for private distribution. My collection of fossil bones, which had been sent to Henslow, also excited considerable attention amongst palæontologists. After reading this letter I clambered over the mountains of Ascension with a bounding step and made the volcanic rocks resound under my geological hammer!

Darwin weighs the evidence that the veins might have been deposited in fissures on the sea bed and at first concludes 'all seem to declare on the side of Neptune'. On reflection, however, he decides there 'are too many facts grounds, which appear to me scarcely controvertible for the an igneous theory.' (p. 944v). Similarly, after describing a range of rocks with at first sight little in common (pp. 946v-947):

In conclusion, I may remark, that on laying by the side of each other pieces of the black obsidian, the white fibrous pumice, the flinty like slate, the homogeneous blueish grey stone, the earthy & crystalline thinly laminated rocks, it was with astonishment that I came to the conclusion, that all formed part of one series (whatever might be causes of variation) which could not be separated; & that they were all equally the products of volcanic heat.

As so often with Darwin, on p. 949 he stresses the dependence of life on geology:

These porous layers, on the Green Mountain collect the water, & by a most fortunate circumstance, a continuous but very thin layer of clay-iron stone 3750, throws out in the form of a spring. — It may be asserted, that the existence of all the larger animals on the Isld. depends entirely on the occurrence of this seam of compact stone.

On the next page Darwin describes a specimen 'which I bought home' (p. 949v), the phrasing suggesting that the note was written in England, bearing sphraerulites, no doubt one of the ones published as woodcuts. On p. 953v there is a curious note about a nail from an animal's stomach and this relates to Darwin's speculation that the sphaerulites might have some connection to Bezoar stones (stones formerly in the digestive systems of animals). Finally, he describes calcareous deposits used for building, and incrustations (p. 951v) which seem to be somewhat ephemeral, coming and going each year, apparently depending on the sea conditions.

Pages 954-956 are Darwin's field notes from his return visit to Bahia in Brazil in August 1836. As noted previously, the 'worked up' notes from Bahia are out of chronological sequence as the very first pages of the Geological diary (CUL-DAR32.1-14). The field notes are in pencil and hard to decipher, but contain much of general interest and are gems of travel writing. They are quoted extensively in section 4.

Pages 957-960 complete the Geological diary and cover Darwin's last ever visit to foreign soil on the mid-Atlantic island of Terceira in the Azores, from 20 to 24 September 1836 (Armstrong 1992, 2004; Pereira and Neves 2009). He made three excursions: to see the steam vents of Furnas do Enxofre on the 20th, to examine Monte Brasil on the 21st and a circuit of almost the whole island on the 22nd. On p. 960v although he says 'We visited [the island of] St Michael' it is clear from the Beagle diary that he never went ashore there. Armstrong (1992) has given a thorough account of Darwin's geology on Terceira. Armstrong draws attention to Darwin's by now ingrained habit of comparison, in this case with the Galapagos, and states that it was at the Furnas that Darwin probably came closest to an active volcano of any place visited on the Beagle voyage.

Gordon Chancellor



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