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TRANSACTIONS
OF THE
EDINBURGH GEOLOGICAL SOCIETY,
SESSION 1888–89.
INAUGURAL ADDRESS.
I.—Darwin's Geological Work. By RALPH RICHARDSON, W.S.,
F.R.S.E., Vice-President of the Society.
(22nd November 1888.)
THE most important and the most charming scientific publication of last winter was the "Life of Charles Darwin." That work divided itself into three parts—Darwin's Autobiography, Darwin's Biography by his son Francis, and the letters which passed between Darwin and his more celebrated correspondents, such as Lyell, Hooker, Huxley, and others. Taken as a whole, the work placed the greatest scientific figure of modern times before us in manner which was not only complete, but as Darwin was never placed before, because, owing to his constant illhealth and his modest retiring nature, he was little known personally beyond the limited band of scientific friends who visited him at his country residence. And what did this work reveal Darwin personally to be? It showed him to be a man of the most sterling and lovable character, a good father, a faithful friend, a hard-working man of science, whom no obstacle could discourage, no fame intoxicate, a man who had but one wish and one resolution—to discover and tell what he conscientiously believed to be the truth. That modesty which is said to be inseparable from true greatness was admirably displayed in all that Darwin wrote or said, whilst that gentleness which is considered to be essential to true Christianity was apparent in all that Darwin thought or did. Taken altogether, the bitterest opponent of Darwin's scientific opinions must, I feel sure, rise from the perusal of this work with the conviction that personally
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Darwin possessed one of the most perfect characters ever displayed. Notably his love of truth, his determination to exhaust every channel in his pursuit of it, and his readiness to fling aside the most cherished theory if he thought it lacked it, stand prominent features in the noble character of Darwin
Darwin is best known as a great naturalist. He was also a great geologist. In the course of his correspondence we find how much, especially when a young man, he loved geology. He thought it was the most attractive and mind-enlarging of all the sciences. He recommended all his young friends to join in its study if they wished to enjoy thoughts of the largest and widest character. "It creates," he wrote, "the same grand ideas respecting this world which astronomy does for the universe." Again: "There is so much larger a field for thought (in geology) than in the other branches of natural history." This enthusiasm for geology Darwin did not, alas! acquire at the University of Edinburgh,1 Where he was, as Prof, Judd says,2 "repelled by the narrow and soulless system of Geognosy taught by Jameson," but it was afterwards, when at Cambridge, he came under the spell of Henslow, a man of most catholic taste, extensive acquirements, and widest sympathy with all branches of natural science, that "Darwin's flagging interest in science was rekindled and kept alive." I pass over his student days at Edinburgh (where he was evidently much busier than he admits) and Cambridge, and proceed to the first official appointment he held.
When quite a young man, Darwin sailed as naturalist on board H.M.S.Beagle for South America and Australasia, and geologised zealously wherever he landed. His "Journal of Remarks" on that voyage, which lasted from 1832–36, was published in 1839, when Darwin, who was only twenty-nine years of age, had attained the proud position of Secretary to the Geological Society of London. I shall, in my address this evening, shortly describe some of the leading features of Darwin's geological work—first when naturalist on board the Beagle, and afterwards when he returned to England.
Darwin's Journal when naturalist on board the Beagle is one of his most interesting works. He was very young then, yet, as truly as "The child is father of the man," we can trace in the enthusiastic young man observing with extraordinary minuteness everything that Nature presented, the future greatest naturalist
1 Still it was, as Mr Grant Allen remarks, at Edinburgh that Darwin "gave the earliest distinct evidence of his definite scientific tastes by contributing to the local academic society a paper on the floating eggs of the common sea-mat, in which he had even then succeeded in discovering for the first time organs of locomotion." The house(No.11 Lothian Street) where Darwin resided when a student at Edinburgh University is now marked by a tablet which I have had erected.—R. R.
2 Presidential Address, Geological Society, London, February 1888.
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of his times. There is a freshness and enthusiasm about the Journal which tells of the youthful Darwin, then possessed of excellent health and high spirits, ranging for the first time amid splendours of Nature of which formerly he had only dreamed. It is a book which should have peculiar claims upon us, for in it he especially records observations on the geology of the places touched at, and also advances and champions several theories of the greatest geological importance. Let me refer first to his theory of the elevation of the land around South America.
When the Beagle arrived off the coast of Patagonia, Darwin observed that the line of coast there consisted of a succession of terraces rising one above another. The terraces occasionally numbered from seven to eight, and included heights between 1200 feet and the level of the sea. "When any broad valley enters the country," he adds, "the terraces sweep round and run up on each side, in which case the correspondence on the opposite sides is beautifully illustrated." He gives a representation of them,1 from which we see that the terraces consisted of gravel, &c., reposing on the strata of the coast. One of the terraces figured is 100 feet above the level of the sea, the next is 250 feet, the third is 350 feet, and the highest is 580 feet. Darwin confesses himself at a loss to understand how these terraces were formed until he referred to Lyell's "Principles of Geology," the first edition of which was published in 1833, or one year preceding Darwin's visit to Patagonia. Turning to that edition,2 we find that Lyell notes certain sea-cliffs in Sicily as furnishing proof of successive elevation. Darwin adopted this theory for the sea-terraces of Patagonia. "There are proofs," he says, "that the whole coast has been elevated to a considerable height within the recent period; and on the shores of the Pacific, where successive terraces likewise occur, we know that these changes have latterly been very gradual."3
The theory adopted by Darwin to account for the formation of these successive sea-terraces rising one above the other on the Patagonian coast, is that enunciated by Lyell, viz., periods of elevation followed by periods of quiescence. "These changes," says Darwin, "all result from the assumption of a steady but very gradual elevation extending over a wide area, and interrupted at long intervals by periods of repose." I may remark, parenthetically, that in 1884 I read a paper before this Society, in which I adduced the same theory to account for the formation of River Terraces,4 and I have a letter from
1 "Narrative of Voyage," vol. iii. p. 202. London, 1839. See Plate 1.
2 Vol. iii. p. 111.
3 "Narrative," p.204.
4 "On the Terraces ocurring on the Banks of the Tay and its Tributaries."
"Edin. Geol. Soc. Trans.," vol. v. p. 56.
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Sir Herbert Maxwell, M.P., who says that, in company with Dr John Evans, he examined the raised River gravels1 along the Somme at St Acheul and Amiens, &c.; and he thought it would be hard to account for these terraces except by Lyell's theory.
When the Beagle had rounded Cape Horn, Darwin found the same evidences of elevation on the western as on the eastern coast of South America. At Coquimbo he spent several days examining the step-formed terraces of shingle, first described by Capt. Basil Hall,2 whilst at Guasco the phenomenon of parallel terraces was very strikingly seen, no less than seven perfectly level but unequally broad plains ascending by steps, and occuring on one or both sides of the valley. "The origin of the terraces of Coquimbo," he says, "is precisely the same, according to my view, with that of the plains of Patagonia; the only difference is, that the plains are rather broader than the terraces, and that they front the Atlantic Ocean instead of a valley,—which valley, however, was formerly occupied by an arm of the sea, but now by a fresh-water river. In every case it must be remembered that the successive cliffs do not mark so many distinct elevations, but, on the contrary, periods of comparative repose during the gradual, and perhaps scarcely sensible, rise of the land."
In a paper which he read before the Geological Society of London in 1838,3 Darwin enters into further details regarding the elevation, particularly of the coast of Chili. He showed that recent marine shells are scattered abundantly to the height of about 100 feet, and he thought the land on the coast of Chili has risen, though insensibly, since 1822. In support of this gradual rise, independent of earthquakes, he stated that the eastern coast of South America bordering on the Atlantic, from the Rio Plata to the Strait of Magellan, presents terraces containing recent shells; yet in the provinces near the mouth of the Rio Plata earthquakes are never experienced.
I now come to perhaps the only piece of geological work which Darwin afterwards regretted. I refer to his theory of the formation of the Parallel Roads of Glen Roy. Fresh from abundant evidences of elevation on the coast of South America, it is not surpirsing that when Darwin went (as so many savants have done) to find a theory for the sphinxlike Parallel Roads, he should at once apply the theory which did duty in South America to Glen Roy. Consequently, in a paper which he read before the Royal Society
1 The higher-level alluvium rises to 100 feet above the plain at Amiens. Lyell's "Antiquity of Man," 4th ed., 1873,p. 178.
2 "Narrative," p.423.
3 "Geol. Soc. Pro.," ii.1838, pp. 446.9.
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of London in 1839,1, we find him maintaining that the roads are of marine origin. In fact, his first conclusion is that it is admitted by everyone that the horizontal shelves are ancient beaches. 2nd, No lake theory could be admitted on account' of the overwhelming difficulties in imagining the construction and removal at successive periods of several barriers of immense size, whether placed at the mouths of the separate glens or at more distant points. 3rd, A sheet of water gradually subsiding from the height of the upper shelves to the present level of the sea, occupied for long periods, not only the glens of Lochaber, but the greater number of, if not all, the valleys of this part of Scotland. 4th, The above change of level in Scotland, independently attested by marine remains at considerable heights on both the eastern and western coasts, implies the elevation of the land, and not the subsidence of the surrounding waters. 5th, There would be intervals of rest in the action of the subterranean impulses. 6th, If the land were subjected to the above conditions, it would be found modelled in a manner wholly similar to the structure of the valleys of Lochaber as they now exist, many points detail being explicable on the supposition that the valleys had been occupied by arms of a sea subject to tides, and which had gradually subsided during the rising of the land. Having thus considered the marine origin of the parallel roads demonstrated, he says, "I may add, that in South America I have observed numerous instances of terraces in every respect similar to these, with sea-shells abundantly scattered on their surface, and therefore where there could exist no obscurity regarding their origin.
Until Darwin became a convert to the views of Agassiz regarding the Parallel Roads of Lochaber, he maintained the marine theory which I have just detailed. In doing so he did battle with our President, Mr Milne-Home, who, in 1847 (he was then Mr Milne), criticised Darwin's theory in a paper which he read before the Royal Society of Edinburgh,2 a criticism which affected Darwin considerably, for he wrote to Sir Joseph Hooker that he was very unwell, "Mr Milne having attacked my theory, which made me horribly sick." Another opponent (although certainly not on marine grounds) was Robert Chambres, who had visited Glen Roy with our President. Chambers criticised Darwin's theory in his "Ancient Sea Margins," in a manner which Darwin considered rather arrogant, and which he accordingly resented, as his letters to Lyell show.3
The upshot of the whole affair was that Darwin ultimately
1 "Philosophical Trans.," 1830, pp. 39–82.
2 "Transactions," vol. xvi.
3 "Darwin's Life," vol. i. p. 362.
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abandoned his theory that the Parallel Roads are ancient sea beaches. In his Autobiography1 he tells us that during 1837 and 1838 he acted as one of the Honorary Secretaries of the Geological Society of London. He then continues: "During these two years I took several short excursions as a relaxation, and one longer one to the Parallel Roads of Glen Roy, an account of which was published in the 'Philosophical Transactions.' This paper was a great failure, and I am ashamed of it. Having been deeply impressed with what I had seen of the elevation of the land in South America, I attributed the parallel lines to the action of the sea; but I had to give up this view when Agassiz propounded his glacier-lake theory. Because no other explanation was possible under our then state of knowledge, I argued in favour of sea-action; and my error has been a good lesson to me, never to trust in science to the principle of exclusion."
This was not, however, the only instance of (what Chambers called) the "mobile South American Continent" furnishing Darwin with a theory founded on the mobility of the land surface. We must return to his voyage in the Beagle to witness the origin of his celebrated theory to account for the formation, structure, and distribution of Coral Reefs. When the Beagle arrived in view of the Keeling or Cocos Islands, situated in the Indian Ocean, and about 600 miles distant from the coast of Sumatra, Darwin paid particular attention to the formation of the islands as they were wholly composed of coral. "Such formations," he exclaims, "surely rank high amongst the wonderful objects of this world.… Throughout the whole group of islands, every single atom, even from the smallest particle to large fragments of rock, bears the stamp of having been subjected to the power of organic arrangement. Captain Fitzroy, at the distance of but little more than a mile from the shore, sounded with a line 7200 feet long, and found no bottom. This island is therefore a lofty submarine mountain, which has a greater inclination than even those of volcanic origin on land."2
Darwin then proceeds to give his now well-known theory for the formation of coral reefs, which he briefly recapitulates as follows: "In the first place, reefs are formed around islands, or on the coast of the mainland, at that limited depth at which the efficient classes of zoophytes can live; and where the sea is shallow, irregular patches may likewise be produced. Afterwards from the effects of a series of small subsidences, encircling reefs, grand barriers, or lagoon islands, are mere modifications of one necessary result. Secondly, it can be shown on the above
1 "Darwin's Life," vol. i. p. 68.
2 "Narrative," p. 554.
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views, that the intertropical ocean throughout more than a hemisphere, may be divided into linear and parallel bands, of which the alternate ones have undergone, within a recent period, the opposite movements of elevation and subsidence. Thirdly, that the points of eruption seem invariably to fall within areas subject to a propulsion from below."1
The theory thus advanced was elaborated in Darwin's book on the "Structure and Distribution of Coral Reefs," and is well expressed by Professor James Geikie in his "Outlines of Geology,"2 who describes it as follows: "A beautiful theory was advanced by Mr Darwin to account for the existence of such reefs. According to him each atoll (or coral island) has passed through the successive stages of fringing reef and barrier reef. As reef-building corals do not flourish at greater depths than 100 feet, it is evident that the foundations of a coral reef could not have been laid in deeper water. Now, as such moderate depths occur only round islands and off the shores of continents, the reef builders would begin their work by forming at first a fringing reef. Slow subsidence of the sea bottom is supposed to have supervened, but while the foundations were being carried down the corals continued to grow upwards, the building of the reef keeping pace with the sinking of the seabottom. Thus by and by the fringing reef is converted into a barrier reef. We have now only to suppose that the movement of subsidence and the labours of the corals continue until the reef-encircled island disappears below the waves, and a complete atoll will be the final result."
DARWIN'S THEORY OF CORAL ISLANDS.
AB, AB. Fringing Reef encircling an island while the sea level is at S1 S1.
A' B', A' B'. Barrier Reef, with Lagoon C, with the sea level at S2 S2.
A" A", A" A". Atoll with Central Lagoon C' over site of drowned island, the sea level being at S3 S3.
The most prominent opponents of this theory are Dr John Murray of the Challenger Expedition, and Dr Guppy. Dr Murray points out, to quote Professor Geikie again, "that all the islets surrounded by coral reefs are of volcanic origin, and that no trace of any general subsidence, such as Darwin's theory requires, can be detected. If it were true that coral reefs
1 "Narrative," p. 569.
2 "London, 1886, p. 97.
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are monuments marking the site of continental islands or masses of land, surely the islets that still remain unsubmerged, fringed and ringed with reefs, might be expected to contain other kinds of rock than volcanic lavas and tuffs. Dr Murray thinks it most probable therefore that the reefs have simply been built up from the tops and slopes of submerged and partially submerged volcanic banks and mountains." According to him, atolls "have grown upwards from the tops of submarine banks. Fringing reefs, he believes, are converted into barrier reefs by the simple growth of the coral, and do not require any process of subsidence to explain them. They simply grow outwards upon a talus of their own debris, which is forced off from the edge of the reef by the breakers."1 But, says Professor Geikie, "although this theory does away with the necessity of any such widespread subsidence as Mr Darwin desiderated, it does not forbid the probability that some, perhaps many, coral reefs may have originated in the manner supposed by the latter."
Dr Archibald Geikie, in his "Text Book of Geology,"2 also eulogises Darwin's theory as a "simple and luminous explanation of the history of coral reefs," and states that Darwin's views were "universally accepted by geologists" until Dr Murray threw doubts upon a theory which demanded such vast oceanie subsidence. Dr Geikie explains, but does not champion, Dr Murray's theory. It is evident that the two rival theories are at present upon their trial, and that the obvious objection to Dr Murray's theory that it "requires the existence of so many volcanic peaks just at the proper depth for coral growth, and that the number of atolls is so great,"3 may be set against the objection to Darwin's theory, which demands vast oceanic subsidence. Dr Murray's theory was announced in a paper read before the Royal Society of Edinburgh in 1880.4 A most valuable criticism of Darwin's theory of subsidence as affecting coral reefs (with maps) by Dr Guppy, appeared in the "Scottish Geographical Magazine" for March 1888.
At the meeting of the British Association (at which I was present) last September, at Bath, the subject of the formation of coral reefs was discussed at a special and crowded joint meeting of the Geological and Biological Sections. Both Professors Boyd-Dawkins and Seeley championed Darwin's views, whilst the leading speaker, Dr Hickson, who had studied coral reefs in the Pacific, said: "For the present, I must consider myself an adherent of the views of Dr Murray, but feel doubtful about two points—(1) Whether the force
1 Geikie's "Outlines," p. 99.
2 London, 1882, p. 466.
3 Geikie's "Text Book," p. 468.
4 "Pro. Roy. Soc. Edin.," 1880, p. 505.
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The only illustration in his Journal on board the "Beagle" except two small woodcuts.
A. B. C. Land sinking gradually beneath the Sea, the level of which remains constant at X,
Z. Leeberg depositing Boulders on Coast line.
NOTE.—When subsequently the land was raised, the 2d and 3d deposits would probably be high above the sea-level, and possibly be higher than the rock in situ from whence the boulders were originally derived.
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of solution of sea water is sufficient to account for the formation of lagoons; and (2) Whether, in some cases, such as the eastern part of the Fiji Archipelago and the Low Archipelago, the theory of subsidence may not be the correct one. Another speaker, Mr Stephen Browne, stated, from his observation of coral reefs, that he had come to the conclusion that the conditions of coral life were so complicated as to require a great deal of further observation before any theory could be formulated. We thus see that there is still a very great variety of opinion upon this interesting subject.
Although Darwin's memorable voyage in the Beagle influenced his intellectual life ever after (and alas! shattered his health as well), yet, arrived in England, he had to turn his attention to observations of British phenomena. I have already referred to his visit to Glen Roy. He likewise did some excellent palæontological work, his Monograph of Fossil Lepadidæ (barnacles) being printed by the Palæontographical Society in 1851, and his Monograph of Fossil Balanidæ (acorn shells) by the same Society in 1854. Darwin also studied glacial phenomena with success. In 1842 appeared his article on the Ancient Glaciers of Wales,1 occasioned by a paper which Dr Buckland had read before the Geological Society. Darwin describes a series of mounds in North Wales covered with hundreds of large blocks of stone, which he regards as Moraine mounds. He refers to Agassiz's work on Glaciers, and says some of the Welsh phenomena might have served as models for some of the plates in the work. He likewise notices boulders described in the till of Edinburgh by Charles Maclaren,2 and says the Welsh boulders were not, like the Edinburgh ones, "scored on the spot where they are now embedded." In 1848, Darwin read a paper before the Geological Society3 upon the Transport of Erratic Boulders, in which he mentions that in 1838 he had observed many boulders of granite (resembling in character that seen in situ at the head of the Spey) strewed on Ben Erin, on the western side of Glen Roy, up to the height of 2200 feet above the sea, or 900 feet above the granite in situ on Speyside. Similarly Maclaren noticed on Arthur's Seat blocks of sandstone 400 feet above any spot where sandstone now exists in situ. Darwin thought that it was by coast-ice that boulders had been transported from a lower to a higher level. Supposing that during a "long course of years," he says, "the land had subsided one or two hundred feet, is it not almost certain that they (the boulders) would have been landed so many feet higher up with respect to the former level, in the same manner as would have happened
1 "London Phil. Magazine," xxi. 180 (1842).
2 "Geology of Fife and Lothians." p. 212.
3 "Geol. Soc. Journal," iv. p. 315. See Plate I.
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with so much drift timber? It is indeed paradoxical thus to speak of the boulders having been carried up, whilst the land has gone down; for, in fact, the boulders are merely kept up by the floating ice at the same level whilst the land sinks." Darwin adduced evidence to show that during the glacial period the land subsided and afterwards was upraised.
In 1855, Darwin considered in an article1 the power of icebergs in grooving rocks. "Having been induced," he says, "to believe, with many geologists, that certain continuously scored and polished surfaces of rock were due to icebergs and not to glaciers, I have, nevertheless, always felt much difficulty in understanding how long rectilinear scratches, running in a given direction across an undulatory surface, could have been thus formed. The paper is written to explain how he thought the difficulty could be removed. Whilst he had formed these views in favour of coast-ice, icebergs, &c., Darwin read, approvingly, the "Great Ice Age," by Professor James Geikie, and honoured its author with letters which appear in his "Prehistoric Europe," and which are by no means antagonistic to Professor Geikie's own theory. One of these letters was written so lately as 1876, and suggests, with regard to the drift near Southampton, "that during the commencement and height of the glacial period great beds of frozen snow accumulated over southern England, and that during the summer, gravel and stones were washed from the higher land over its surface and in superficial channels." Darwin concludes with the words: "When I viewed the country, I could not persuade myself that any flood, however great, could have deposited such coarse gravel over the almost level platforms between the valleys."
But Darwin was destined to be called away from the geological field and to acquire world-wide fame in another. It is not as a geologist but as a naturalist, as a biologist, as the perfecter of the greatest life-theory ever announced, that the name of Darwin will go down to posterity. His famous work on the "Origin of Species," in which he first announced his theory, appeared in 1859, and when I have referred briefly to the geological chapters it contains, I shall bring this address to a conclusion; for Darwin henceforth devoted himself almost entirely to biological studies. His youth saw him an enthusiastic geologist, his old age an equally ardent naturalist. The study of biology is often but a development of the study of geology. "All geological science," said Professor Judd in his presidential address to the Geological Society of London in February 1888, "is based on the principle that the past can only be interpreted by the study of the present; Darwin was the intellectual child of Lyell, and the 'Origin of Species' was the logical outcome of
1 "Philosophical Magazine," x., 1855, p. 96.
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the 'Principles of Geology.'" And again: "The grand secret of Darwin's success in grappling with the great problem of 'the origin of species' is found in the fact that he was at the same time a geologist and a biologist. The concentration of the later years of his life upon zoological and botanical researches has led many to forget the position occupied by Darwin among geologists. Not only are his geological writings of the highest value for the wealth of accurate observations which they contain, and the important generalisations which they put forward, but in his more purely biological works the value of his geological training and experience are constantly exemplified."
In his "Origin of Species," Darwin candidly admits that the most obvious and gravest objection to his theory that species have descended from species by insensibly fine gradations, is that geology assuredly does not reveal any such finely graduated organic chain. If his theory be true, he asks, why is not every geological formation and every stratum full of intermediate links showing how one species was gradually developed from another? The explanation lies, he believes, in the extreme imperfection of the geological record.
Darwin proceeds to explain this imperfection by reference to 1st. The lapse of time.—He remarks that whoever can read Lyell's "Principles of Geology" and not realise how incomprehensibly vast have been the past periods of time may at once close his volume upon the "Origin of Species." He advises the student to examine great piles of superimposed strata, and watch the sea at work grinding down old rocks and making fresh sediment; to wander along lines of sea-coast and mark the process of degradation; or to examine beds of conglomerate many thousand feet in thickness, and then he will perhaps feebly comprehend the lapse of time. But the amount of denudation which the strata have in many places suffered probably offers, in his opinion, the best evidence of the lapse of time. He instances faults as affording evidence of, as in Merionethshire, a downthrow of 12,000 feet, yet the surface of the land has been so completely planed down by denudation that there is nothing to show the vast dislocations which have taken place, the pile of rocks on the one or other side of the vault having been smoothly swept away. "The consideration of these facts impresses my mind," he adds, "almost in the same manner as does the vain endeavour to grapple with the idea of eternity."
2nd. The poorness of our palœontological collections.—"Now turn to our richest geological museums," he exclaims, "and what a paltry display we behold!" He repeats Edward Forbes' remark that numbers of our fossil species are known and named from single and often broken specimens or from a few
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specimens collected on some one spot. No organism wholly soft can be preserved. Shells and bones will decay and disappear when left on the bottom of the sea, where sediment is not accumulating. He suspects that few of the very many animals which live on the beach betwen high and low water mark are preserved. The imperfection in the geological record mainly results, in his opinion, from the several formations being separated from each other by wide intervals of time. From books or a cursory glance at nature we fancy they are closely consecutive, but we know from observation what wide gaps there are between the superimposed formations, and that during periods absolutely blank and barren in one country great piles of sediment charged with new and peculiar forms of life were being accumulated in another country. He is convinced that all our ancient formations which are rich in fossils have been formed during subsidence. Thus the geological record will almost necessarily be rendered intermittent; indeed each separate formation, like the whole pile of formations in any country, has generally been intermittent in its accumulation.
Again, he reminds us that at the present day, with perfect specimens for examination, two forms can seldom be connected by intermediate varieties and thus proved to be the same species until many specimens have been collected from many places; and in the case of fossil species, this could rarely be effected by palæontologists. He says we shall perhaps best perceive the improbability of our being enabled to connect species by numerous fine intermediate fossil links, by asking ourselves whether, for instance, geologists at some future period will be able to prove that our different breeds of cattle, sheep, horses, and dogs have descended from a single stock or from several aboriginal stocks. This could only be effected by the future geologist discovering in a fossil state numerous intermediate gradations; and such success seems to Darwin improbable in the highest degree. In our geological formations, he thinks, we ought to look for a few links, some more closely, some more distantly related to each other, and we have no right to expect an infinite number of fine transitional forms.
3rd. On the sudden appearance of whole groups of allied species.—Darwin admits that if numerous species belonging to the same genera or families have really started into life all at once, the fact would be fatal to the theory of descent with slow modification through natural selection. But he thinks we continually overrate the perfection of the geological record, and falsely infer that, because certain genera or families have not been found beneath a certain stage, they did not exist before that stage.
4th. On the sudden appearance of groups of allied species in
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the lowest known fossiliferous strata.—This is a much graver difficulty, in his opinion. If Darwin's theory be true, it is indisputable that before the lowest Silurian stratum was deposited, long periods elapsed, as long as, or probably far longer than, the whole interval from the Silurian age to the present day; and that during these vast, yet quite unknown, periods of time, the world swarmed with living creatures. To the question, Why we do not find records of these vast primordial periods, Darwin admits he can give no satisfactory answer. Yet whilst inexplicable at present, the question may hereafter receive some explanation. Darwin points out that from the nature of the organic remains large islands or tracts of land (whence the sediment which formed the rocks of the various formations was derived) seem to have occurred in the neighbourhood of Europe and North America; but we do not know what was the state of things in the intervals between the successive formations, whether Europe and the United States existed as dry land or were submerged.
Looking at the difficulties caused by the imperfection of the geological record, Darwin considers that we possess the last volume only of that record, relating only to two or three countries. Of this volume only here and there a short chapter has been preserved, and of each page only here and there a few lines. Each word of the slowly-changing language in which the history is supposed to be written being more or less different in the interrupted succession of chapters, may represent the apparently abruptly changed forms of life contained in our consecutive but widely separated formations. On this view, the difficulties above discussed are, in his opinion, greatly diminished, or even disappear.
In the next chapter Darwin discusses the geological succession of organic beings, and arrives at the conclusion that all the leading facts in palæontology simply follow on the theory of descent with modification through natural selection. The extinction of old forms is the almost inevitable consequence of the production of new forms. When a group has once wholly disappeared, it does not reappear, for the link of generation has been broken. We can understand, he says, how it is that all the forms of life, ancient and recent, make together one grand system, for all are connected by generation. "If, then," he concludes, "the geological record be as imperfect as I believe it to be, and it may at least be asserted that the record cannot be proved to be much more perfect, the main objections to the theory of natural selection are greatly diminished or disappear. On the other hand, all the chief laws of palæontology plainly proclaim, as it seems to me, that species have been produced by ordinary generation, old forms having been supplanted by new
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and improved forms of life, produced by the laws of variation still acting round us, and preserved by natural selection."
In a subsequent chapter, Darwin explains how the glacial period to which, he says, "Agassiz and others called vivid attention," affords a simple explanation of the identity of many plants and animals on mountain summits separated from each other by hundreds of miles of lowlands. He says it is perfectly evident that within a very recent geological period Central Europe and North America suffered under an Arctic climate. "The ruins of a house burned by fire do not," in his opinion, "tell their tale more plainly than do the mountains of Scotland and Wales with their scored flanks, polished surfaces, and perched boulders, of the icy streams with which their valleys were lately filled. So greatly has the climate of Europe changed, that in Northern Italy gigantic moraines, left by old glaciers, are now clothed by the vine and maize. Throughout a large part of the United States, erratic boulders and rocks scored by drifted icebergs and coast-ice plainly reveal a former cold period."
It will be observed from this passage that whilst Darwin associated "icy streams" (glaciers), "icebergs," and "coast-ice," with the glacial period of Agassiz, he did not, like Agassiz, assert the existence of an ice-cap, or vast moving field of ice many thousand feet thick. At the same time, he says, "We have good evidence in almost every case that the (glacial) epoch was included within the latest geological period. We have also excellent evidence that it endured for an enormous time, as measured by years, at each point." In fact he considers that during at least a part of the glacial period the cold was actually simultaneous throughout the world. Thus a universal Alpine flora flourished, and to this day on the lofty mountains of equatorial America a host of peculiar species belonging to European genera occur. On the mountains of the Cape of Good Hope some few representative European forms are found, whilst on the Himalayas and the heights of Ceylon, and on the volcanic cones of Java, many plants occur representing plants of Europe not found in the intervening hot lowlands.
I have now dwelt at some length upon Darwin's geological work. I admit that it does not compare in amount or in value with his biological work, and that it was his original researches in natural history that gave him his world-wide fame. Still, in geology as in natural history he occupies a proud position. He stands there in our geological Walhalla as one of the pioneers of geology who, taking the burning torch from the hands of Lyell, carried it down faithfully to our own day. He exhibited in his geological as in his natural history researches, the same indefatigable industry, the same keen-eyed observation, the
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same constant love of truth that were the leading characteristics of his mind the life. When he made a mistake he at once admitted it. Witness his abandonment of his theory to account for the Parallel Roads of Glen Roy. When a new theory was launched, he was not prejudiced against it because it was a new theory, for he knew too much of the riddles of Nature to think that man would decipher them until many and many a theory had been adopted and discarded. In all things he exhibited a broad-mindedness, a modesty, a patience, which make him personally one of the most admirable men of science that ever lived; and it will be to all those who tell the story of his lif, as it has certainly been to me, a labour of love to dwell upon the high personal character of Darwin: there is no need for anyone to extol his peerless intellectual position.
DARWIN'S GEOLOGICAL WRITINGS.
(Selected and arranged from the Appendix to Darwin's Life,
vol. iii. p. 362.) Books have * prefixed.
1. General.
Geological Notes made on board the Beagle. Geological Society's Proceedings, ii. 1838, pp. 210-212. (Incorrectly described as by F. Darwin.)
* Journal of Researches on board the Beagle, 2nd edition, 1845. (In the original narrative Darwin's Journal was vol. iii., published 1839.)
* Geological Observations on South America (being third part of Geology of Beagle Voyage). 1846.
*Origin of Species, containing Geological chapters. 1859.
2. Coral Reefs.
Areas (Coral) of Elevation and Subsidence in Pacific. Geological Society's Proceedings, ii. 1838, pp. 552-4.
* Structure and Distribution of Coral Reefs (being first part of Geology of Beagle Voyage). 1842.
Letter on Coral Islands to Charles Maclaren, Edinburgh. Edinburgh New Phil. Journal, xxxiv. 1843, pp. 47-50.
* Structure and Distribution of Coral Reefs, 2nd edition, 1874.
3. Volcanic Phenomena.
Volcanic Phenomena. Geological Society's Proceedings, ii. 1838, pp. 654-60; Geological Society's Transactions, v. 1840, pp. 601-632.
* Geological Observations on Volcanic Islands visited by Beagle (being second part of Geology of Beagle Voyage.) 1844.
Volcanic Rocks and Glaciers. Proceedings Royal Society, Edinburgh, ii. 1851, pp. 17-18.
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4. Palæontology.
Deposits containing extinct Mammalia. Geological Society's Proceedings, ii.1838, pp. 542-4.
* Monograph of Fossil Lepadidæ. Palæontographical Society. 1851.
* Monograph of Fossil Balanidæ. Palæontographical Society, 1854.
5. Formation of Mould.
Formation of Mould. Geological Society's Proceedings, ii. 1838, pp. 574-576; Geological Society's Transactions,v. 1840, pp. 505-510.
* Formation of Vegetable Mould. 1881.
6. Stratigraphy.
Saliferous Deposits in Patagonia. Geological Society's Journal, ii. part ii., 1838, pp. 127-8.
Sandstone off Pernambuco. Phil. Mag., xix. 1841, pp. 257-60.
Geology of Falkland Islands. Geological Society's Journal, ii. 1846, pp. 267-274.
Pampean Formation, Buenos Ayres. Geological Society's Journal, xix. 1863, pp. 68-71.
7. Elevation.
Proofs of Elevation of Coast of Chili. Geological Society's Proceedings. ii. 1838, pp. 446-9.
Areas (Coral) of Elevation and Subsidence in Pacific. Geological Society's Proceedings, ii. 1838, pp. 552-4.
Parallel Roads of Glen Roy. Phil. Transactions, 1839, pp. 39-82.
8. Glaciation.
Rock seen on Iceberg. Geographical Society's Journal, ix. 1839, pp. 528-9.
Erratic Boulders of South America. Geological Society's Proceedings, iii. 1842, pp. 425-430; Geological Society's Transactions, vi. 1842, pp. 415-432.
Ancient Glaciers of Wales. London Phil. Mag., xxi. p. 180, 1842.
Erratic Boulders' transportal. Geological Society's Journal, iv. 1848, pp. 315-323.
Volcanic Rocks and Glaciers. Proceedings Royal Society, Edinburgh, ii. 1851, pp. 17-18.
Icebergs' power of grooving. Phil. Mag., x. 1855. pp. 96-8.
Letter (dated 1876) on Drift near Southampton in Professor James Geikie's "Prehistoric Europe."
9. Dust.
Fine Dust in Atlantic. Geological Society's Journal, ii.1846, pp. 26-30.