Darwin and Modern Science Part 29

The second period of Darwin's geological career--the five years spent by him on board the "Beagle"--was the one in which by far the most important stage in his mental development was accomplished. He left England a healthy, vigorous and enthusiastic collector; he returned five years later with unique experiences, the germs of great ideas, and a knowledge which placed him at once in the foremost ranks of the geologists of that day. Huxley has well said that "Darwin found on board the "Beagle" that which neither the pedagogues of Shrewsbury, nor the professoriate of Edinburgh, nor the tutors of Cambridge had managed to give him." ("Proc. Roy. Soc." Vol. XLIV. (1888), page IX.) Darwin himself wrote, referring to the date at which the voyage was expected to begin: "My second life will then commence, and it shall be as a birthday for the rest of my life." ("L.L." I. page 214.); and looking back on the voyage after forty years, he wrote; "The voyage of the 'Beagle' has been by far the most important event in my life, and has determined my whole career;... I have always felt that I owe to the voyage the first real training or education of my mind; I was led to attend closely to several branches of natural history, and thus my powers of observation were improved, though they were always fairly developed." ("L.L." I. page 61.)

Referring to these general studies in natural history, however, Darwin adds a very significant remark: "The investigation of the geology of the places visited was far more important, as reasoning here comes into play. On first examining a new district nothing can appear more hopeless than the chaos of rocks; but by recording the stratification and nature of the rocks and fossils at many points, always reasoning and predicting what will be found elsewhere, light soon begins to dawn on the district, and the structure of the whole becomes more or less intelligible."

("L.L." I. page 62.)

The famous voyage began amid doubts, discouragements and disappointments. Fearful of heart-disease, sad at parting from home and friends, depressed by sea-sickness, the young explorer, after being twice driven back by baffling winds, reached the great object of his ambition, the island of Teneriffe, only to find that, owing to quarantine regulations, landing was out of the question.

But soon this inauspicious opening of the voyage was forgotten. Henslow had advised his pupil to take with him the first volume of Lyell's "Principles of Geology", then just published--but cautioned him (as nearly all the leaders in geological science at that day would certainly have done) "on no account to accept the views therein advocated."

("L.L." I. page 73.) It is probable that the days of waiting, discomfort and sea-sickness at the beginning of the voyage were relieved by the reading of this volume. For he says that when he landed, three weeks after setting sail from Plymouth, in St Jago, the largest of the Cape de Verde Islands, the volume had already been "studied attentively; and the book was of the highest service to me in many ways... " His first original geological work, he declares, "showed me clearly the wonderful superiority of Lyell's manner of treating geology, compared with that of any other author, whose works I had with me or ever afterwards read."

("L.L." I. page 62.)

At St Jago Darwin first experienced the joy of making new discoveries, and his delight was unbounded. Writing to his father he says, "Geologising in a volcanic country is most delightful; besides the interest attached to itself, it leads you into most beautiful and retired spots." ("L.L." I. page 228.) To Henslow he wrote of St Jago: "Here we spent three most delightful weeks... St Jago is singularly barren, and produces few plants or insects, so that my hammer was my usual companion, and in its company most delightful hours I spent." "The geology was pre-eminently interesting, and I believe quite new; there are some facts on a large scale of upraised coast (which is an excellent epoch for all the volcanic rocks to date from), that would interest Mr Lyell." ("L.L." I. page 235.) After more than forty years the memory of this, his first geological work, seems as fresh as ever, and he wrote in 1876, "The geology of St Jago is very striking, yet simple: a stream of lava formerly flowed over the bed of the sea, formed of triturated recent sh.e.l.ls and corals, which it has baked into a hard white rock.

Since then the whole island has been upheaved. But the line of white rock revealed to me a new and important fact, namely, that there had been afterwards subsidence round the craters, which had since been in action, and had poured forth lava." ("L.L." I. page 65.)

It was at this time, probably, that Darwin made his first attempt at drawing a sketch-map and section to ill.u.s.trate the observations he had made (see his "Volcanic Islands", pages 1 and 9). His first important geological discovery, that of the subsidence of strata around volcanic vents (which has since been confirmed by Mr Heaphy in New Zealand and other authors) awakened an intense enthusiasm, and he writes: "It then first dawned on me that I might perhaps write a book on the geology of the various countries visited, and this made me thrill with delight.

That was a memorable hour to me, and how distinctly I can call to mind the low cliff of lava beneath which I rested, with the sun glaring hot, a few strange desert plants growing near, and with living corals in the tidal pools at my feet." ("L.L." I. page 66.)

But it was when the "Beagle", after touching at St Paul's rock and Tristan d'Acunha (for a sufficient time only to collect specimens), reached the sh.o.r.es of South America, that Darwin's real work began; and he was able, while the marine surveys were in progress, to make many extensive journeys on land. His letters at this time show that geology had become his chief delight, and such exclamations as "Geology carries the day," "I find in Geology a never failing interest," etc. abound in his correspondence.

Darwin's time was divided between the study of the great deposits of red mud--the Pampean formation--with its interesting fossil bones and sh.e.l.ls affording proofs of slow and constant movements of the land, and the underlying ma.s.ses of metamorphic and plutonic rocks. Writing to Henslow in March, 1834, he says: "I am quite charmed with Geology, but, like the wise animal between two bundles of hay, I do not know which to like best; the old crystalline groups of rocks, or the softer and fossiliferous beds. When puzzling about stratification, etc., I feel inclined to cry 'a fig for your big oysters, and your bigger megatheriums.' But then when digging out some fine bones, I wonder how any man can tire his arms with hammering granite." ("L.L." I. page 249.) We are told by Darwin that he loved to reason about and attempt to predict the nature of the rocks in each new district before he arrived at it.

This love of guessing as to the geology of a district he was about to visit is amusingly expressed by him in a letter (of May, 1832) to his cousin and old college-friend, Fox. After alluding to the beetles he had been collecting--a taste his friend had in common with himself--he writes of geology that "It is like the pleasure of gambling. Speculating on first arriving, what the rocks may be, I often mentally cry out 3 to 1 tertiary against primitive; but the latter have hitherto won all the bets." ("L.L." I. page 233.)

Not the least important of the educational results of the voyage to Darwin was the acquirement by him of those habits of industry and method which enabled him in after life to accomplish so much--in spite of constant failures of health. From the outset, he daily undertook and resolutely accomplished, in spite of sea-sickness and other distractions, four important tasks. In the first place he regularly wrote up the pages of his Journal, in which, paying great attention to literary style and composition, he recorded only matters that would be of general interest, such as remarks on scenery and vegetation, on the peculiarities and habits of animals, and on the characters, avocations and political inst.i.tutions of the various races of men with whom he was brought in contact. It was the freshness of these observations that gave his "Narrative" so much charm. Only in those cases in which his ideas had become fully crystallised, did he attempt to deal with scientific matters in this journal. His second task was to write in voluminous note-books facts concerning animals and plants, collected on sea or land, which could not be well made out from specimens preserved in spirit; but he tells us that, owing to want of skill in dissecting and drawing, much of the time spent in this work was entirely thrown away, "a great pile of MS. which I made during the voyage has proved almost useless." ("L.L." I. page 62.) Huxley confirmed this judgment on his biological work, declaring that "all his zeal and industry resulted, for the most part, in a vast acc.u.mulation of useless ma.n.u.script." ("Proc.

Roy. Soc." Vol. XLIV. (1888), page IX.) Darwin's third task was of a very different character and of infinitely greater value. It consisted in writing notes of his journeys on land--the notes being devoted to the geology of the districts visited by him. These formed the basis, not only of a number of geological papers published on his return, but also of the three important volumes forming "The Geology of the voyage of the 'Beagle'". On July 24th, 1834, when little more than half of the voyage had been completed, Darwin wrote to Henslow, "My notes are becoming bulky. I have about 600 small quarto pages full; about half of this is Geology." ("M.L." I. page 14.) The last, and certainly not the least important of all his duties, consisted in numbering, cataloguing, and packing his specimens for despatch to Henslow, who had undertaken the care of them. In his letters he often expresses the greatest solicitude lest the value of these specimens should be impaired by the removal of the numbers corresponding to his ma.n.u.script lists. Science owes much to Henslow's patient care of the collections sent to him by Darwin. The latter wrote in Henslow's biography, "During the five years' voyage, he regularly corresponded with me and guided my efforts; he received, opened, and took care of all the specimens sent home in many large boxes." ("Life of Henslow", by L. Jenyns (Blomefield), London, 1862, page 53.)

Darwin's geological specimens are now very appropriately lodged for the most part in the Sedgwick Museum, Cambridge, his original Catalogue with subsequent annotations being preserved with them. From an examination of these catalogues and specimens we are able to form a fair notion of the work done by Darwin in his little cabin in the "Beagle", in the intervals between his land journeys.

Besides writing up his notes, it is evident that he was able to accomplish a considerable amount of study of his specimens, before they were packed up for despatch to Henslow. Besides hand-magnifiers and a microscope, Darwin had an equipment for blowpipe-a.n.a.lysis, a contact-goniometer and magnet; and these were in constant use by him.

His small library of reference (now included in the Collection of books placed by Mr F. Darwin in the Botany School at Cambridge ("Catalogue of the Library of Charles Darwin now in the Botany School, Cambridge".

Compiled by H.W. Rutherford; with an introduction by Francis Darwin.

Cambridge, 1908.)) appears to have been admirably selected, and in all probability contained (in addition to a good many works relating to South America) a fair number of excellent books of reference. Among those relating to mineralogy, he possessed the manuals of Phillips, Alexander Brongniart, Beudant, von Kobell and Jameson: all the "Cristallographie" of Brochant de Villers and, for blowpipe work, Dr Children's translation of the book of Berzelius on the subject. In addition to these, he had Henry's "Experimental Chemistry" and Ure's "Dictionary" (of Chemistry). A work, he evidently often employed, was P.

Syme's book on "Werner's Nomenclature of Colours"; while, for Petrology, he used Macculloch's "Geological Cla.s.sification of Rocks". How diligently and well he employed his instruments and books is shown by the valuable observations recorded in the annotated Catalogues drawn up on board s.h.i.+p.

These catalogues have on the right-hand pages numbers and descriptions of the specimens, and on the opposite pages notes on the specimens--the result of experiments made at the time and written in a very small hand.

Of the subsequently made pencil notes, I shall have to speak later.

(I am greatly indebted to my friend Mr A. Harker, F.R.S., for his a.s.sistance in examining these specimens and catalogues. He has also arranged the specimens in the Sedgwick Museum, so as to make reference to them easy. The specimens from Ascension and a few others are however in the Museum at Jermyn Street.)

It is a question of great interest to determine the period and the occasion of Darwin's first awakening to the great problem of the trans.m.u.tation of species. He tells us himself that his grandfather's "Zoonomia" had been read by him "but without producing any effect," and that his friend Grant's rhapsodies on Lamarck and his views on evolution only gave rise to "astonishment." ("L.L." I. page 38.)

Huxley, who had probably never seen the privately printed volume of letters to Henslow, expressed the opinion that Darwin could not have perceived the important bearing of his discovery of bones in the Pampean Formation, until they had been studied in England, and their a.n.a.logies p.r.o.nounced upon by competent comparative anatomists. And this seemed to be confirmed by Darwin's own entry in his pocket-book for 1837, "In July opened first notebook on Trans.m.u.tation of Species. Had been greatly struck from about the month of previous March on character of South American fossils... " ("L.L." I. page 276.)

The second volume of Lyell's "Principles of Geology" was published in January, 1832, and Darwin's copy (like that of the other two volumes, in a sadly dilapidated condition from constant use) has in it the inscription, "Charles Darwin, Monte Video. Nov. 1832." As everyone knows, Darwin in dedicating the second edition of his Journal of the Voyage to Lyell declared, "the chief part of whatever scientific merit this journal and the other works of the author may possess, has been derived from studying the well-known and admirable 'Principles of Geology'".

In the first chapter of this second volume of the "Principles", Lyell insists on the importance of the species question to the geologist, but goes on to point out the difficulty of accepting the only serious attempt at a trans.m.u.tation theory which had up to that time appeared--that of Lamarck. In subsequent chapters he discusses the questions of the modification and variability of species, of hybridity, and of the geographical distribution of plants and animals. He then gives vivid pictures of the struggle for existence, ever going on between various species, and of the causes which lead to their extinction--not by overwhelming catastrophes, but by the silent and almost un.o.bserved action of natural causes. This leads him to consider theories with regard to the introduction of new species, and, rejecting the fanciful notions of "centres or foci of creation," he argues strongly in favour of the view, as most reconcileable with observed facts, that "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 s.p.a.ce on the globe." ("Principles of Geology", Vol. II. (1st edition 1832), page 124. We now know, as has been so well pointed out by Huxley, that Lyell, as early as 1827, was prepared to accept the doctrine of the trans.m.u.tation of species. In that year he wrote to Mantell, "What changes species may really undergo! How impossible will it be to distinguish and lay down a line, beyond which some of the so-called extinct species may have never pa.s.sed into recent ones"

(Lyell's "Life and Letters" Vol. I. page 168). To Sir John Herschel in 1836, he wrote, "In regard to the origination of new species, I am very glad to find that you think it probable that it may be carried on through the intervention of intermediate causes. I left this rather to be inferred, not thinking it worth while to offend a certain cla.s.s of persons by embodying in words what would only be a speculation" (Ibid.

page 467). He expressed the same views to Whewell in 1837 (Ibid. Vol.

II. page 5.), and to Sedgwick (Ibid. Vol. II. page 36) to whom he says, of "the theory, that the creation of new species is going on at the present day"--"I really entertain it," but "I have studiously avoided laying the doctrine down dogmatically as capable of proof" (see Huxley in "L.L." II. pages 190-195.))

After pointing out how impossible it would be for a naturalist to prove that a newly DISCOVERED species was really newly CREATED (Mr F. Darwin has pointed out that his father (like Lyell) often used the term "Creation" in speaking of the origin of new species ("L.L." II. chapter 1.)), Lyell argued that no satisfactory evidence OF THE WAY in which these new forms were created, had as yet been discovered, but that he entertained the hope of a possible solution of the problem being found in the study of the geological record.

It is not difficult, in reading these chapters of Lyell's great work, to realise what an effect they would have on the mind of Darwin, as new facts were collected and fresh observations concerning extinct and recent forms were made in his travels. We are not surprised to find him writing home, "I am become a zealous disciple of Mr Lyell's views, as known in his admirable book. Geologising in South America, I am tempted to carry parts to a greater extent even than he does." ("L.L." I. page 263.)

Lyell's antic.i.p.ation that the study of the geological record might afford a clue to the discovery of how new species originate was remarkably fulfilled, within a few months, by Darwin's discovery of fossil bones in the red Pampean mud.

It is very true that, as Huxley remarked, Darwin's knowledge of comparative anatomy must have been, at that time, slight; but that he recognised the remarkable resemblances between the extinct and existing mammals of South America is proved beyond all question by a pa.s.sage in his letter to Henslow, written November 24th, 1832: "I have been very lucky with fossil bones; I have fragments of at least six distinct animals... I found a large surface of osseous polygonal plates... Immediately I saw them I thought they must belong to an enormous armadillo, living species of which genus are so abundant here,"

and he goes on to say that he has "the lower jaw of some large animal which, from the molar teeth, I should think belonged to the Edentata."

("M.L." I. pages 11, 12. See "Extracts of Letters addressed to Prof.

Henslow by C. Darwin" (1835), page 7.)

Having found this important clue, Darwin followed it up with characteristic perseverance. In his quest for more fossil bones he was indefatigable. Mr Francis Darwin tells us, "I have often heard him speak of the despair with which he had to break off the projecting extremity of a huge, partly excavated bone, when the boat waiting for him would wait no longer." ("L.L." I. page 276 (footnote).) Writing to Haeckel in 1864, Darwin says: "I shall never forget my astonishment when I dug out a gigantic piece of armour, like that of the living armadillo."

(Haeckel, "History of Creation", Vol. I. page 134, London, 1876.)

In a letter to Henslow in 1834 Darwin says: "I have just got scent of some fossil bones... what they may be I do not know, but if gold or galloping will get them they shall be mine." ("M.L." I. page 15.)

Darwin also showed his sense of the importance of the discovery of these bones by his solicitude about their safe arrival and custody. From the Falkland Isles (March, 1834), he writes to Henslow: "I have been alarmed by your expression 'cleaning all the bones' as I am afraid the printed numbers will be lost: the reason I am so anxious they should not be, is, that a part were found in a gravel with recent sh.e.l.ls, but others in a very different bed. Now with these latter there were bones of an Agouti, a genus of animals, I believe, peculiar to America, and it would be curious to prove that some one of the genus co-existed with the Megatherium: such and many other points depend on the numbers being carefully preserved." ("Extracts from Letters etc.", pages 13-14.) In the abstract of the notes read to the Geological Society in 1835, we read: "In the gravel of Patagonia he (Darwin) also found many bones of the Megatherium and of five or six other species of quadrupeds, among which he has detected the bones of a species of Agouti. He also met with several examples of the polygonal plates, etc." ("Proc. Geol. Soc." Vol.

II. pages 211-212.)

Darwin's own recollections entirely bear out the conclusion that he fully recognised, WHILE IN SOUTH AMERICA, the wonderful significance of the resemblances between the extinct and recent mammalian faunas. He wrote in his "Autobiography": "During the voyage of the 'Beagle' I had been deeply impressed by discovering in the Pampean formation great fossil animals covered with armour like that on the existing armadillos." ("L.L." I. page 82.)

The impression made on Darwin's mind by the discovery of these fossil bones, was doubtless deepened as, in his progress southward from Brazil to Patagonia, he found similar species of Edentate animals everywhere replacing one another among the living forms, while, whenever fossils occurred, they also were seen to belong to the same remarkable group of animals. (While Darwin was making these observations in South America, a similar generalisation to that at which he arrived was being reached, quite independently and almost simultaneously, with respect to the fossil and recent mammals of Australia. In the year 1831, Clift gave to Jameson a list of bones occurring in the caves and breccias of Australia, and in publis.h.i.+ng this list the latter referred to the fact that the forms belonged to marsupials, similar to those of the existing Australian fauna. But he also stated that, as a skull had been identified (doubtless erroneously) as having belonged to a hippopotamus, other mammals than marsupials must have spread over the island in late Tertiary times. It is not necessary to point out that this paper was quite unknown to Darwin while in South America. Lyell first noticed it in the third edition of his "Principles", which was published in May, 1834 (see "Edinb. New Phil. Journ." Vol. X. (1831), pages 394-6, and Lyell's "Principles" (3rd edition), Vol. III. page 421). Darwin referred to this discovery in 1839 (see his "Journal", page 210.))

That the pa.s.sage in Darwin's pocket-book for 1837 can only refer to an AWAKENING of Darwin's interest in the subject--probably resulting from a sight of the bones when they were being unpacked--I think there cannot be the smallest doubt; AND WE MAY THEREFORE CONFIDENTLY FIX UPON NOVEMBER, 1832, AS THE DATE AT WHICH DARWIN COMMENCED THAT LONG SERIES OF OBSERVATIONS AND REASONINGS WHICH EVENTUALLY CULMINATED IN THE PREPARATION OF THE "ORIGIN OF SPECIES". Equally certain is it, that it was his geological work that led Darwin into those paths of research which in the end conducted him to his great discoveries. I quite agree with the view expressed by Mr F. Darwin and Professor Seward, that Darwin, like Lyell, "thought it 'almost useless' to try to prove the truth of evolution until the cause of change was discovered" ("M.L."

I. page 38.), and that possibly he may at times have vacillated in his opinions, but I believe there is evidence that, from the date mentioned, the "species question" was always more or less present in Darwin's mind.

(Although we admit with Huxley that Darwin's training in comparative anatomy was very small, yet it may be remembered that he was a medical student for two years, and, if he hated the lectures, he enjoyed the society of naturalists. He had with him in the little "Beagle" library a fair number of zoological books, including works on Osteology by Cuvier, Desmarest and Lesson, as well as two French Encyclopaedias of Natural History. As a sportsman, he would obtain specimens of recent mammals in South America, and would thus have opportunities of studying their teeth and general anatomy. Keen observer, as he undoubtedly was, we need not then be surprised that he was able to make out the resemblances between the recent and fossil forms.)

It is clear that, as time went on, Darwin became more and more absorbed in his geological work. One very significant fact was that the once ardent sportsman, when he found that shooting the necessary game and zoological specimens interfered with his work with the hammer, gave up his gun to his servant. ("L.L." I. page 63.) There is clear evidence that Darwin gradually became aware how futile were his attempts to add to zoological knowledge by dissection and drawing, while he felt ever increasing satisfaction with his geological work.

The voyage fortunately extended to a much longer period (five years) than the two originally intended, but after being absent nearly three years, Darwin wrote to his sister in November, 1834, "Hurrah! hurrah!

it is fixed that the 'Beagle' shall not go one mile south of Cape Tres Montes (about 200 miles south of Chiloe), and from that point to Valparaiso will be finished in about five months. We shall examine the Chonos Archipelago, entirely unknown, and the curious inland sea behind Chiloe. For me it is glorious. Cape Tres Montes is the most southern point where there is much geological interest, as there the modern beds end. The Captain then talks of crossing the Pacific; but I think we shall persuade him to finish the coast of Peru, where the climate is delightful, the country hideously sterile, but abounding with the highest interest to the geologist... I have long been grieved and most sorry at the interminable length of the voyage (though I never would have quitted it)... I could not make up my mind to return. I could not give up all the geological castles in the air I had been building up for the last two years." ("L.L." I. pages 257-58.)

In April, 1835, he wrote to another sister: "I returned a week ago from my excursion across the Andes to Mendoza. Since leaving England I have never made so successful a journey... how deeply I have enjoyed it; it was something more than enjoyment; I cannot express the delight which I felt at such a famous winding-up of all my geology in South America. I literally could hardly sleep at nights for thinking over my day's work.

The scenery was so new, and so majestic; everything at an elevation of 12,000 feet bears so different an aspect from that in the lower country... To a geologist, also, there are such manifest proofs of excessive violence; the strata of the highest pinnacles are tossed about like the crust of a broken pie." ("L.L." I. pages 259-60.)

Darwin antic.i.p.ated with intense pleasure his visit to the Galapagos Islands. On July 12th, 1835, he wrote to Henslow: "In a few days' time the "Beagle" will sail for the Galapagos Islands. I look forward with joy and interest to this, both as being somewhat nearer to England and for the sake of having a good look at an active volcano. Although we have seen lava in abundance, I have never yet beheld the crater."

("M.L." I. page 26.) He could little antic.i.p.ate, as he wrote these lines, the important aid in the solution of the "species question" that would ever after make his visit to the Galapagos Islands so memorable.

In 1832, as we have seen, the great discovery of the relations of living to extinct mammals in the same area had dawned upon his mind; in 1835 he was to find a second key for opening up the great mystery, by recognising the variations of similar types in adjoining islands among the Galapagos.

The final chapter in the second volume of the "Principles" had aroused in Darwin's mind a desire to study coral-reefs, which was gratified during his voyage across the Pacific and Indian Oceans. His theory on the subject was suggested about the end of 1834 or the beginning of 1835, as he himself tells us, before he had seen a coral-reef, and resulted from his work during two years in which he had "been incessantly attending to the effects on the sh.o.r.es of South America of the intermittent elevation of the land, together with denudation and the deposition of sediment." ("L.L." I. page 70.)

On arriving at the Cape of Good Hope in July, 1836, Darwin was greatly gratified by hearing that Sedgwick had spoken to his father in high terms of praise concerning the work done by him in South America.

Referring to the news from home, when he reached Bahia once more, on the return voyage (August, 1836), he says: "The desert, volcanic rocks, and wild sea of Ascension... suddenly wore a pleasing aspect, and I set to work with a good-will at my old work of Geology." ("L.L." I. page 265.) Writing fifty years later, he says: "I clambered over the mountains of Ascension with a bounding step and made the volcanic rocks resound under my geological hammer!" ("L.L." I. page 66.)

That his determination was now fixed to devote his own labours to the task of working out the geological results of the voyage, and that he was prepared to leave to more practised hands the study of his biological collections, is clear from the letters he sent home at this time. From St Helena he wrote to Henslow asking that he would propose him as a Fellow of the Geological Society; and his Certificate, in Henslow's handwriting, is dated September 8th, 1836, being signed from personal knowledge by Henslow and Sedgwick. He was proposed on November 2nd and elected November 30th, being formally admitted to the Society by Lyell, who was then President, on January 4th, 1837, on which date he also read his first paper. Darwin did not become a Fellow of the Linnean Society till eighteen years later (in 1854).

An estimate of the value and importance of Darwin's geological discoveries during the voyage of the "Beagle" can best be made when considering the various memoirs and books in which the author described them. He was too cautious to allow himself to write his first impressions in his Journal, and wisely waited till he could study his specimens under better conditions and with help from others on his return. The extracts published from his correspondence with Henslow and others, while he was still abroad, showed, nevertheless, how great was the ma.s.s of observation, how suggestive and pregnant with results were the reasonings of the young geologist.

Two sets of these extracts from Darwin's letters to Henslow were printed while he was still abroad. The first of these was the series of "Geological Notes made during a survey of the East and West Coasts of South America, in the years 1832, 1833, 1834 and 1835, with an account of a transverse section of the Cordilleras of the Andes between Valparaiso and Mendoza". Professor Sedgwick, who read these notes to the Geological Society on November 18th, 1835, stated that "they were extracted from a series of letters (addressed to Professor Henslow), containing a great ma.s.s of information connected with almost every branch of natural history," and that he (Sedgwick) had made a selection of the remarks which he thought would be more especially interesting to the Geological Society. An abstract of three pages was published in the "Proceedings of the Geological Society" (Vol. II. pages 210-12.), but so unknown was the author at this time that he was described as F. Darwin, Esq., of St John's College, Cambridge! Almost simultaneously (on November 16th, 1835) a second set of extracts from these letters--this time of a general character--were read to the Philosophical Society at Cambridge, and these excited so much interest that they were privately printed in pamphlet form for circulation among the members.