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On the absence of intermediate varieties at the present day -- On thenature of extinct intermediate varieties; on their number -- On the lapseof time, as inferred from the rate of denudation and of deposition number-- On the lapse of time as estimated by years -- On the poorness of ourpalaeontological collections -- On the intermittence of geologicalformations -- On the denudation of granitic areas -- On the absence ofintermediate varieties in any one formation -- On the sudden appearance ofgroups of species -- On their sudden appearance in the lowest knownfossiliferous strata -- Antiquity of the habitable earth.

In the sixth chapter I enumerated the chief objections which might bejustly urged against the views maintained in this volume. Most of themhave now been discussed. One, namely, the distinctness of specific formsand their not being blended together by innumerable transitional links, isa very obvious difficulty. I assigned reasons why such links do notcommonly occur at the present day under the circumstances apparently mostfavourable for their presence, namely, on an extensive and continuous areawith graduated physical conditions. I endeavoured to show, that the lifeof each species depends in a more important manner on the presence of otheralready defined organic forms, than on climate, and, therefore, that thereally governing conditions of life do not graduate away quite insensiblylike heat or moisture. I endeavoured, also, to show that intermediatevarieties, from existing in lesser numbers than the forms which theyconnect, will generally be beaten out and exterminated during the course offurther modification and improvement. The main cause, however, ofinnumerable intermediate links not now occurring everywhere throughoutnature depends, on the very process of natural selection, through which newvarieties continually take the places of and supplant their parent-forms. But just in proportion as this process of extermination has acted on anenormous scale, so must the number of intermediate varieties, which haveformerly existed, be truly enormous. Why then is not every geologicalformation and every stratum full of such intermediate links? Geologyassuredly does not reveal any such finely graduated organic chain; andthis, perhaps, is the most obvious and serious objection which can be urgedagainst my theory. The explanation lies, as I believe, in the extremeimperfection of the geological record.

In the first place, it should always be borne in mind what sort ofintermediate forms must, on the theory, have formerly existed. I havefound it difficult, when looking at any two species, to avoid picturing tomyself forms DIRECTLY intermediate between them. But this is a whollyfalse view; we should always look for forms intermediate between eachspecies and a common but unknown progenitor; and the progenitor willgenerally have differed in some respects from all its modified descendants. To give a simple illustration: the fantail and pouter pigeons are bothdescended from the rock-pigeon; if we possessed all the intermediatevarieties which have ever existed, we should have an extremely close seriesbetween both and the rock-pigeon; but we should have no varieties directlyintermediate between the fantail and pouter; none, for instance, combininga tail somewhat expanded with a crop somewhat enlarged, the characteristicfeatures of these two breeds. These two breeds, moreover, have become somuch modified, that, if we had no historical or indirect evidence regardingtheir origin, it would not have been possible to have determined from amere comparison of their structure with that of the rock-pigeon, C. livia,whether they had descended from this species or from some other alliedspecies, such as C. oenas.

So with natural species, if we look to forms very distinct, for instance tothe horse and tapir, we have no reason to suppose that links directlyintermediate between them ever existed, but between each and an unknowncommon parent. The common parent will have had in its whole organisationmuch general resemblance to the tapir and to the horse; but in some pointsof structure may have differed considerably from both, even perhaps morethan they differ from each other. Hence, in all such cases, we should beunable to recognise the parent-form of any two or more species, even if weclosely compared the structure of the parent with that of its modifieddescendants, unless at the same time we had a nearly perfect chain of theintermediate links.

It is just possible, by the theory, that one of two living forms might havedescended from the other; for instance, a horse from a tapir; and in thiscase DIRECT intermediate links will have existed between them. But such acase would imply that one form had remained for a very long periodunaltered, whilst its descendants had undergone a vast amount of change;and the principle of competition between organism and organism, betweenchild and parent, will render this a very rare event; for in all cases thenew and improved forms of life tend to supplant the old and unimprovedforms.

By the theory of natural selection all living species have been connectedwith the parent-species of each genus, by differences not greater than wesee between the natural and domestic varieties of the same species at thepresent day; and these parent-species, now generally extinct, have in theirturn been similarly connected with more ancient forms; and so on backwards,always converging to the common ancestor of each great class. So that thenumber of intermediate and transitional links, between all living andextinct species, must have been inconceivably great. But assuredly, ifthis theory be true, such have lived upon the earth.

ON THE LAPSE OF TIME, AS INFERRED FROM THE RATE OF DEPOSITION AND EXTENT OFDENUDATION.

Independently of our not finding fossil remains of such infinitely numerousconnecting links, it may be objected that time cannot have sufficed for sogreat an amount of organic change, all changes having been effected slowly. It is hardly possible for me to recall to the reader who is not a practicalgeologist, the facts leading the mind feebly to comprehend the lapse oftime. He who can read Sir Charles Lyell's grand work on the Principles ofGeology, which the future historian will recognise as having produced arevolution in natural science, and yet does not admit how vast have beenthe past periods of time, may at once close this volume. Not that itsuffices to study the Principles of Geology, or to read special treatisesby different observers on separate formations, and to mark how each authorattempts to give an inadequate idea of the duration of each formation, oreven of each stratum. We can best gain some idea of past time by knowingthe agencies at work; and learning how deeply the surface of the land hasbeen denuded, and how much sediment has been deposited. As Lyell has wellremarked, the extent and thickness of our sedimentary formations are theresult and the measure of the denudation which the earth's crust haselsewhere undergone. Therefore a man should examine for himself the greatpiles of superimposed strata, and watch the rivulets bringing down mud, andthe waves wearing away the sea-cliffs, in order to comprehend somethingabout the duration of past time, the monuments of which we see all aroundus.

It is good to wander along the coast, when formed of moderately hard rocks,and mark the process of degradation. The tides in most cases reach thecliffs only for a short time twice a day, and the waves eat into them onlywhen they are charged with sand or pebbles; for there is good evidence thatpure water effects nothing in wearing away rock. At last the base of thecliff is undermined, huge fragments fall down, and these remaining fixed,have to be worn away atom by atom, until after being reduced in size theycan be rolled about by the waves, and then they are more quickly groundinto pebbles, sand, or mud. But how often do we see along the bases ofretreating cliffs rounded boulders, all thickly clothed by marineproductions, showing how little they are abraded and how seldom they arerolled about! Moreover, if we follow for a few miles any line of rockycliff, which is undergoing degradation, we find that it is only here andthere, along a short length or round a promontory, that the cliffs are atthe present time suffering. The appearance of the surface and thevegetation show that elsewhere years have elapsed since the waters washedtheir base.

We have, however, recently learned from the observations of Ramsay, in thevan of many excellent observers--of Jukes, Geikie, Croll and others, thatsubaerial degradation is a much more important agency than coast-action, orthe power of the waves. The whole surface of the land is exposed to thechemical action of the air and of the rainwater, with its dissolvedcarbonic acid, and in colder countries to frost; the disintegrated matteris carried down even gentle slopes during heavy rain, and to a greaterextent than might be supposed, especially in arid districts, by the wind;it is then transported by the streams and rivers, which, when rapid deepentheir channels, and triturate the fragments. On a rainy day, even in agently undulating country, we see the effects of subaerial degradation inthe muddy rills which flow down every slope. Messrs. Ramsay and Whitakerhave shown, and the observation is a most striking one, that the greatlines of escarpment in the Wealden district and those ranging acrossEngland, which formerly were looked at as ancient sea-coasts, cannot havebeen thus formed, for each line is composed of one and the same formation,while our sea-cliffs are everywhere formed by the intersection of variousformations. This being the case, we are compelled to admit that theescarpments owe their origin in chief part to the rocks of which they arecomposed, having resisted subaerial denudation better than the surroundingsurface; this surface consequently has been gradually lowered, with thelines of harder rock left projecting. Nothing impresses the mind with thevast duration of time, according to our ideas of time, more forcibly thanthe conviction thus gained that subaerial agencies, which apparently haveso little power, and which seem to work so slowly, have produced greatresults.

When thus impressed with the slow rate at which the land is worn awaythrough subaerial and littoral action, it is good, in order to appreciatethe past duration of time, to consider, on the one hand, the masses of rockwhich have been removed over many extensive areas, and on the other handthe thickness of our sedimentary formations. I remember having been muchstruck when viewing volcanic islands, which have been worn by the waves andpared all round into perpendicular cliffs of one or two thousand feet inheight; for the gentle slope of the lava-streams, due to their formerlyliquid state, showed at a glance how far the hard, rocky beds had onceextended into the open ocean. The same story is told still more plainly byfaults--those great cracks along which the strata have been upheaved on oneside, or thrown down on the other, to the height or depth of thousands offeet; for since the crust cracked, and it makes no great difference whetherthe upheaval was sudden, or, as most geologists now believe, was slow andeffected by many starts, the surface of the land has been so completelyplaned down that no trace of these vast dislocations is externally visible.The Craven fault, for instance, extends for upward of thirty miles, andalong this line the vertical displacement of the strata varies from 600 to3,000 feet. Professor Ramsay has published an account of a downthrow inAnglesea of 2,300 feet; and he informs me that he fully believes that thereis one in Merionethshire of 12,000 feet; yet in these cases there isnothing on the surface of the land to show such prodigious movements; thepile of rocks on either side of the crack having been smoothly swept away.

On the other hand, in all parts of the world the piles of sedimentarystrata are of wonderful thickness. In the Cordillera, I estimated one massof conglomerate at ten thousand feet; and although conglomerates haveprobably been accumulated at a quicker rate than finer sediments, yet frombeing formed of worn and rounded pebbles, each of which bears the stamp oftime, they are good to show how slowly the mass must have been heapedtogether. Professor Ramsay has given me the maximum thickness, from actualmeasurement in most cases, of the successive formations in DIFFERENT partsof Great Britain; and this is the result:FeetPalaeozoic strata (not including igneous beds)..57,154Secondary strata................................13,190Tertiary strata..................................2,240

--making altogether 72,584 feet; that is, very nearly thirteen andthree-quarters British miles. Some of these formations, which arerepresented in England by thin beds, are thousands of feet in thickness onthe Continent. Moreover, between each successive formation we have, in theopinion of most geologists, blank periods of enormous length. So that thelofty pile of sedimentary rocks in Britain gives but an inadequate idea ofthe time which has elapsed during their accumulation. The consideration ofthese various facts impresses the mind almost in the same manner as doesthe vain endeavour to grapple with the idea of eternity.

Nevertheless this impression is partly false. Mr. Croll, in an interestingpaper, remarks that we do not err "in forming too great a conception of thelength of geological periods," but in estimating them by years. Whengeologists look at large and complicated phenomena, and then at the figuresrepresenting several million years, the two produce a totally differenteffect on the mind, and the figures are at once pronounced too small. Inregard to subaerial denudation, Mr. Croll shows, by calculating the knownamount of sediment annually brought down by certain rivers, relatively totheir areas of drainage, that 1,000 feet of solid rock, as it becamegradually disintegrated, would thus be removed from the mean level of thewhole area in the course of six million years. This seems an astonishingresult, and some considerations lead to the suspicion that it may be toolarge, but if halved or quartered it is still very surprising. Few of us,however, know what a million really means: Mr. Croll gives the followingillustration: Take a narrow strip of paper, eighty-three feet four inchesin length, and stretch it along the wall of a large hall; then mark off atone end the tenth of an inch. This tenth of an inch will represent onehundred years, and the entire strip a million years. But let it be bornein mind, in relation to the subject of this work, what a hundred yearsimplies, represented as it is by a measure utterly insignificant in a hallof the above dimensions. Several eminent breeders, during a singlelifetime, have so largely modified some of the higher animals, whichpropagate their kind much more slowly than most of the lower animals, thatthey have formed what well deserves to be called a new sub-breed. Few menhave attended with due care to any one strain for more than half a century,so that a hundred years represents the work of two breeders in succession. It is not to be supposed that species in a state of nature ever change soquickly as domestic animals under the guidance of methodical selection. The comparison would be in every way fairer with the effects which followfrom unconscious selection, that is, the preservation of the most useful orbeautiful animals, with no intention of modifying the breed; but by thisprocess of unconscious selection, various breeds have been sensibly changedin the course of two or three centuries.

Species, however, probably change much more slowly, and within the samecountry only a few change at the same time. This slowness follows from allthe inhabitants of the same country being already so well adapted to eachother, that new places in the polity of nature do not occur until afterlong intervals, due to the occurrence of physical changes of some kind, orthrough the immigration of new forms. Moreover, variations or individualdifferences of the right nature, by which some of the inhabitants might bebetter fitted to their new places under the altered circumstance, would notalways occur at once. Unfortunately we have no means of determining,according to the standard of years, how long a period it takes to modify aspecies; but to the subject of time we must return.

ON THE POORNESS OF PALAEONTOLOGICAL COLLECTIONS.

Now let us turn to our richest museums, and what a paltry display webehold! That our collections are imperfect is admitted by every one. Theremark of that admirable palaeontologist, Edward Forbes, should never beforgotten, namely, that very many fossil species are known and named fromsingle and often broken specimens, or from a few specimens collected onsome one spot. Only a small portion of the surface of the earth has beengeologically explored, and no part with sufficient care, as the importantdiscoveries made every year in Europe prove. No organism wholly soft canbe preserved. Shells and bones decay and disappear when left on the bottomof the sea, where sediment is not accumulating. We probably take a quiteerroneous view, when we assume that sediment is being deposited over nearlythe whole bed of the sea, at a rate sufficiently quick to embed andpreserve fossil remains. Throughout an enormously large proportion of theocean, the bright blue tint of the water bespeaks its purity. The manycases on record of a formation conformably covered, after an immenseinterval of time, by another and later formation, without the underlyingbed having suffered in the interval any wear and tear, seem explicable onlyon the view of the bottom of the sea not rarely lying for ages in anunaltered condition. The remains which do become embedded, if in sand orgravel, will, when the beds are upraised, generally be dissolved by thepercolation of rain water charged with carbonic acid. Some of the manykinds of animals which live on the beach between high and low water markseem to be rarely preserved. For instance, the several species of theChthamalinae (a sub-family of sessile cirripedes) coat the rocks all overthe world in infinite numbers: they are all strictly littoral, with theexception of a single Mediterranean species, which inhabits deep water andthis has been found fossil in Sicily, whereas not one other species hashitherto been found in any tertiary formation: yet it is known that thegenus Chthamalus existed during the Chalk period. Lastly, many greatdeposits, requiring a vast length of time for their accumulation, areentirely destitute of organic remains, without our being able to assign anyreason: one of the most striking instances is that of the Flyschformation, which consists of shale and sandstone, several thousand,occasionally even six thousand feet in thickness, and extending for atleast 300 miles from Vienna to Switzerland; and although this great masshas been most carefully searched, no fossils, except a few vegetableremains, have been found.

With respect to the terrestrial productions which lived during theSecondary and Palaeozoic periods, it is superfluous to state that ourevidence is fragmentary in an extreme degree. For instance, until recentlynot a land-shell was known belonging to either of these vast periods, withthe exception of one species discovered by Sir C. Lyell and Dr. Dawson inthe carboniferous strata of North America; but now land-shells have beenfound in the lias. In regard to mammiferous remains, a glance at thehistorical table published in Lyell's Manual, will bring home the truth,how accidental and rare is their preservation, far better than pages ofdetail. Nor is their rarity surprising, when we remember how large aproportion of the bones of tertiary mammals have been discovered either incaves or in lacustrine deposits; and that not a cave or true lacustrine bedis known belonging to the age of our secondary or palaeozoic formations.

But the imperfection in the geological record largely results from anotherand more important cause than any of the foregoing; namely, from theseveral formations being separated from each other by wide intervals oftime. This doctrine has been emphatically admitted by many geologists andpalaeontologists, who, like E. Forbes, entirely disbelieve in the change ofspecies. When we see the formations tabulated in written works, or when wefollow them in nature, it is difficult to avoid believing that they areclosely consecutive. But we know, for instance, from Sir R. Murchison'sgreat work on Russia, what wide gaps there are in that country between thesuperimposed formations; so it is in North America, and in many other partsof the world. The most skilful geologist, if his attention had beenconfined exclusively to these large territories, would never have suspectedthat during the periods which were blank and barren in his own country,great piles of sediment, charged with new and peculiar forms of life, hadelsewhere been accumulated. And if, in every separate territory, hardlyany idea can be formed of the length of time which has elapsed between theconsecutive formations, we may infer that this could nowhere beascertained. The frequent and great changes in the mineralogicalcomposition of consecutive formations, generally implying great changes inthe geography of the surrounding lands, whence the sediment was derived,accord with the belief of vast intervals of time having elapsed betweeneach formation.

We can, I think, see why the geological formations of each region arealmost invariably intermittent; that is, have not followed each other inclose sequence. Scarcely any fact struck me more when examining manyhundred miles of the South American coasts, which have been upraisedseveral hundred feet within the recent period, than the absence of anyrecent deposits sufficiently extensive to last for even a short geologicalperiod. Along the whole west coast, which is inhabited by a peculiarmarine fauna, tertiary beds are so poorly developed that no record ofseveral successive and peculiar marine faunas will probably be preserved toa distant age. A little reflection will explain why, along the risingcoast of the western side of South America, no extensive formations withrecent or tertiary remains can anywhere be found, though the supply ofsediment must for ages have been great, from the enormous degradation ofthe coast rocks and from the muddy streams entering the sea. Theexplanation, no doubt, is that the littoral and sub-littoral deposits arecontinually worn away, as soon as they are brought up by the slow andgradual rising of the land within the grinding action of the coast-waves.

We may, I think, conclude that sediment must be accumulated in extremelythick, solid, or extensive masses, in order to withstand the incessantaction of the waves, when first upraised and during subsequent oscillationsof level, as well as the subsequent subaerial degradation. Such thick andextensive accumulations of sediment may be formed in two ways; either inprofound depths of the sea, in which case the bottom will not be inhabitedby so many and such varied forms of life as the more shallow seas; and themass when upraised will give an imperfect record of the organisms whichexisted in the neighbourhood during the period of its accumulation. Orsediment may be deposited to any thickness and extent over a shallowbottom, if it continue slowly to subside. In this latter case, as long asthe rate of subsidence and supply of sediment nearly balance each other,the sea will remain shallow and favourable for many and varied forms, andthus a rich fossiliferous formation, thick enough, when upraised, to resista large amount of denudation, may be formed.

I am convinced that nearly all our ancient formations, which are throughoutthe greater part of their thickness RICH IN FOSSILS, have thus been formedduring subsidence. Since publishing my views on this subject in 1845, Ihave watched the progress of geology, and have been surprised to note howauthor after author, in treating of this or that great formation, has cometo the conclusion that it was accumulated during subsidence. I may add,that the only ancient tertiary formation on the west coast of SouthAmerica, which has been bulky enough to resist such degradation as it hasas yet suffered, but which will hardly last to a distant geological age,was deposited during a downward oscillation of level, and thus gainedconsiderable thickness.

All geological facts tell us plainly that each area has undergone numerousslow oscillations of level, and apparently these oscillations have affectedwide spaces. Consequently, formations rich in fossils and sufficientlythick and extensive to resist subsequent degradation, will have been formedover wide spaces during periods of subsidence, but only where the supply ofsediment was sufficient to keep the sea shallow and to embed and preservethe remains before they had time to decay. On the other hand, as long asthe bed of the sea remained stationary, THICK deposits cannot have beenaccumulated in the shallow parts, which are the most favourable to life. Still less can this have happened during the alternate periods ofelevation; or, to speak more accurately, the beds which were thenaccumulated will generally have been destroyed by being upraised andbrought within the limits of the coast-action.

These remarks apply chiefly to littoral and sublittoral deposits. In thecase of an extensive and shallow sea, such as that within a large part ofthe Malay Archipelago, where the depth varies from thirty or forty to sixtyfathoms, a widely extended formation might be formed during a period ofelevation, and yet not suffer excessively from denudation during its slowupheaval; but the thickness of the formation could not be great, for owingto the elevatory movement it would be less than the depth in which it wasformed; nor would the deposit be much consolidated, nor be capped byoverlying formations, so that it would run a good chance of being worn awayby atmospheric degradation and by the action of the sea during subsequentoscillations of level. It has, however, been suggested by Mr. Hopkins,that if one part of the area, after rising and before being denuded,subsided, the deposit formed during the rising movement, though not thick,might afterwards become protected by fresh accumulations, and thus bepreserved for a long period.

Mr. Hopkins also expresses his belief that sedimentary beds of considerablehorizontal extent have rarely been completely destroyed. But allgeologists, excepting the few who believe that our present metamorphicschists and plutonic rocks once formed the primordial nucleus of the globe,will admit that these latter rocks have been stripped of their covering toan enormous extent. For it is scarcely possible that such rocks could havebeen solidified and crystallised while uncovered; but if the metamorphicaction occurred at profound depths of the ocean, the former protectingmantle of rock may not have been very thick. Admitting then that gneiss,mica-schist, granite, diorite, etc., were once necessarily covered up, howcan we account for the naked and extensive areas of such rocks in manyparts of the world, except on the belief that they have subsequently beencompletely denuded of all overlying strata? That such extensive areas doexist cannot be doubted: the granitic region of Parime is described byHumboldt as being at least nineteen times as large as Switzerland. Southof the Amazon, Boue colours an area composed of rocks of this nature asequal to that of Spain, France, Italy, part of Germany, and the BritishIslands, all conjoined. This region has not been carefully explored, butfrom the concurrent testimony of travellers, the granitic area is verylarge: thus Von Eschwege gives a detailed section of these rocks,stretching from Rio de Janeiro for 260 geographical miles inland in astraight line; and I travelled for 150 miles in another direction, and sawnothing but granitic rocks. Numerous specimens, collected along the wholecoast, from near Rio de Janeiro to the mouth of the Plata, a distance of1,100 geographical miles, were examined by me, and they all belonged tothis class. Inland, along the whole northern bank of the Plata, I saw,besides modern tertiary beds, only one small patch of slightlymetamorphosed rock, which alone could have formed a part of the originalcapping of the granitic series. Turning to a well-known region, namely, tothe United States and Canada, as shown in Professor H.D. Rogers' beautifulmap, I have estimated the areas by cutting out and weighing the paper, andI find that the metamorphic (excluding the "semi-metamorphic") and graniterocks exceed, in the proportion of 19 to 12.5, the whole of the newerPalaeozoic formations. In many regions the metamorphic and granite rockswould be found much more widely extended than they appear to be, if all thesedimentary beds were removed which rest unconformably on them, and whichcould not have formed part of the original mantle under which they werecrystallised. Hence, it is probable that in some parts of the world wholeformations have been completely denuded, with not a wreck left behind.

One remark is here worth a passing notice. During periods of elevation thearea of the land and of the adjoining shoal parts of the sea will beincreased and new stations will often be formed--all circumstancesfavourable, as previously explained, for the formation of new varieties andspecies; but during such periods there will generally be a blank in thegeological record. On the other hand, during subsidence, the inhabitedarea and number of inhabitants will decrease (excepting on the shores of acontinent when first broken up into an archipelago), and consequentlyduring subsidence, though there will be much extinction, few new varietiesor species will be formed; and it is during these very periods ofsubsidence that the deposits which are richest in fossils have beenaccumulated.

ON THE ABSENCE OF NUMEROUS INTERMEDIATE VARIETIES IN ANY SINGLE FORMATION.

>From these several considerations it cannot be doubted that the geologicalrecord, viewed as a whole, is extremely imperfect; but if we confine ourattention to any one formation, it becomes much more difficult tounderstand why we do not therein find closely graduated varieties betweenthe allied species which lived at its commencement and at its close. Several cases are on record of the same species presenting varieties in theupper and lower parts of the same formation. Thus Trautschold gives anumber of instances with Ammonites, and Hilgendorf has described a mostcurious case of ten graduated forms of Planorbis multiformis in thesuccessive beds of a fresh-water formation in Switzerland. Although eachformation has indisputably required a vast number of years for itsdeposition, several reasons can be given why each should not commonlyinclude a graduated series of links between the species which lived at itscommencement and close, but I cannot assign due proportional weight to thefollowing considerations.

Although each formation may mark a very long lapse of years, each probablyis short compared with the period requisite to change one species intoanother. I am aware that two palaeontologists, whose opinions are worthyof much deference, namely Bronn and Woodward, have concluded that theaverage duration of each formation is twice or thrice as long as theaverage duration of specific forms. But insuperable difficulties, as itseems to me, prevent us from coming to any just conclusion on this head. When we see a species first appearing in the middle of any formation, itwould be rash in the extreme to infer that it had not elsewhere previouslyexisted. So again, when we find a species disappearing before the lastlayers have been deposited, it would be equally rash to suppose that itthen became extinct. We forget how small the area of Europe is comparedwith the rest of the world; nor have the several stages of the sameformation throughout Europe been correlated with perfect accuracy.

We may safely infer that with marine animals of all kinds there has been alarge amount of migration due to climatal and other changes; and when wesee a species first appearing in any formation, the probability is that itonly then first immigrated into that area. It is well known, for instance,that several species appear somewhat earlier in the palaeozoic beds ofNorth America than in those of Europe; time having apparently been requiredfor their migration from the American to the European seas. In examiningthe latest deposits, in various quarters of the world, it has everywherebeen noted, that some few still existing species are common in the deposit,but have become extinct in the immediately surrounding sea; or, conversely,that some are now abundant in the neighbouring sea, but are rare or absentin this particular deposit. It is an excellent lesson to reflect on theascertained amount of migration of the inhabitants of Europe during theglacial epoch, which forms only a part of one whole geological period; andlikewise to reflect on the changes of level, on the extreme change ofclimate, and on the great lapse of time, all included within this sameglacial period. Yet it may be doubted whether, in any quarter of theworld, sedimentary deposits, INCLUDING FOSSIL REMAINS, have gone onaccumulating within the same area during the whole of this period. It isnot, for instance, probable that sediment was deposited during the whole ofthe glacial period near the mouth of the Mississippi, within that limit ofdepth at which marine animals can best flourish: for we know that greatgeographical changes occurred in other parts of America during this spaceof time. When such beds as were deposited in shallow water near the mouthof the Mississippi during some part of the glacial period shall have beenupraised, organic remains will probably first appear and disappear atdifferent levels, owing to the migrations of species and to geographicalchanges. And in the distant future, a geologist, examining these beds,would be tempted to conclude that the average duration of life of theembedded fossils had been less than that of the glacial period, instead ofhaving been really far greater, that is, extending from before the glacialepoch to the present day.

In order to get a perfect gradation between two forms in the upper andlower parts of the same formation, the deposit must have gone oncontinuously accumulating during a long period, sufficient for the slowprocess of modification; hence, the deposit must be a very thick one; andthe species undergoing change must have lived in the same districtthroughout the whole time. But we have seen that a thick formation,fossiliferous throughout its entire thickness, can accumulate only during aperiod of subsidence; and to keep the depth approximately the same, whichis necessary that the same marine species may live on the same space, thesupply of sediment must nearly counterbalance the amount of subsidence. But this same movement of subsidence will tend to submerge the area whencethe sediment is derived, and thus diminish the supply, whilst the downwardmovement continues. In fact, this nearly exact balancing between thesupply of sediment and the amount of subsidence is probably a rarecontingency; for it has been observed by more than one palaeontologist thatvery thick deposits are usually barren of organic remains, except neartheir upper or lower limits.

It would seem that each separate formation, like the whole pile offormations in any country, has generally been intermittent in itsaccumulation. When we see, as is so often the case, a formation composedof beds of widely different mineralogical composition, we may reasonablysuspect that the process of deposition has been more or less interrupted.Nor will the closest inspection of a formation give us any idea of thelength of time which its deposition may have consumed. Many instancescould be given of beds, only a few feet in thickness, representingformations which are elsewhere thousands of feet in thickness, and whichmust have required an enormous period for their accumulation; yet no oneignorant of this fact would have even suspected the vast lapse of timerepresented by the thinner formation. Many cases could be given of thelower beds of a formation having been upraised, denuded, submerged, andthen re-covered by the upper beds of the same formation--facts, showingwhat wide, yet easily overlooked, intervals have occurred in itsaccumulation. In other cases we have the plainest evidence in greatfossilised trees, still standing upright as they grew, of many longintervals of time and changes of level during the process of deposition,which would not have been suspected, had not the trees been preserved: thus Sir C. Lyell and Dr. Dawson found carboniferous beds 1,400 feet thickin Nova Scotia, with ancient root-bearing strata, one above the other, atno less than sixty-eight different levels. Hence, when the same speciesoccurs at the bottom, middle, and top of a formation, the probability isthat it has not lived on the same spot during the whole period ofdeposition, but has disappeared and reappeared, perhaps many times, duringthe same geological period. Consequently if it were to undergo aconsiderable amount of modification during the deposition of any onegeological formation, a section would not include all the fine intermediategradations which must on our theory have existed, but abrupt, thoughperhaps slight, changes of form.

It is all-important to remember that naturalists have no golden rule bywhich to distinguish species and varieties; they grant some littlevariability to each species, but when they meet with a somewhat greateramount of difference between any two forms, they rank both as species,unless they are enabled to connect them together by the closestintermediate gradations; and this, from the reasons just assigned, we canseldom hope to effect in any one geological section. Supposing B and C tobe two species, and a third, A, to be found in an older and underlying bed;even if A were strictly intermediate between B and C, it would simply beranked as a third and distinct species, unless at the same time it could beclosely connected by intermediate varieties with either one or both forms. Nor should it be forgotten, as before explained, that A might be the actualprogenitor of B and C, and yet would not necessarily be strictlyintermediate between them in all respects. So that we might obtain theparent-species and its several modified descendants from the lower andupper beds of the same formation, and unless we obtained numeroustransitional gradations, we should not recognise their blood-relationship,and should consequently rank them as distinct species.

It is notorious on what excessively slight differences manypalaeontologists have founded their species; and they do this the morereadily if the specimens come from different sub-stages of the sameformation. Some experienced conchologists are now sinking many of the veryfine species of D'Orbigny and others into the rank of varieties; and onthis view we do find the kind of evidence of change which on the theory weought to find. Look again at the later tertiary deposits, which includemany shells believed by the majority of naturalists to be identical withexisting species; but some excellent naturalists, as Agassiz and Pictet,maintain that all these tertiary species are specifically distinct, thoughthe distinction is admitted to be very slight; so that here, unless webelieve that these eminent naturalists have been misled by theirimaginations, and that these late tertiary species really present nodifference whatever from their living representatives, or unless we admit,in opposition to the judgment of most naturalists, that these tertiaryspecies are all truly distinct from the recent, we have evidence of thefrequent occurrence of slight modifications of the kind required. If welook to rather wider intervals of time, namely, to distinct but consecutivestages of the same great formation, we find that the embedded fossils,though universally ranked as specifically different, yet are far moreclosely related to each other than are the species found in more widelyseparated formations; so that here again we have undoubted evidence ofchange in the direction required by the theory; but to this latter subjectI shall return in the following chapter.

With animals and plants that propagate rapidly and do not wander much,there is reason to suspect, as we have formerly seen, that their varietiesare generally at first local; and that such local varieties do not spreadwidely and supplant their parent-form until they have been modified andperfected in some considerable degree. According to this view, the chanceof discovering in a formation in any one country all the early stages oftransition between any two forms, is small, for the successive changes aresupposed to have been local or confined to some one spot. Most marineanimals have a wide range; and we have seen that with plants it is thosewhich have the widest range, that oftenest present varieties, so that, withshells and other marine animals, it is probable that those which had thewidest range, far exceeding the limits of the known geological formationsin Europe, have oftenest given rise, first to local varieties andultimately to new species; and this again would greatly lessen the chanceof our being able to trace the stages of transition in any one geologicalformation.

It is a more important consideration, leading to the same result, as latelyinsisted on by Dr. Falconer, namely, that the period during which eachspecies underwent modification, though long as measured by years, wasprobably short in comparison with that during which it remained withoutundergoing any change.

It should not be forgotten, that at the present day, with perfect specimensfor examination, two forms can seldom be connected by intermediatevarieties, and thus proved to be the same species, until many specimens arecollected from many places; and with fossil species this can rarely bedone. We shall, perhaps, best perceive the improbability of our beingenabled to connect species by numerous, fine, intermediate, fossil links,by asking ourselves whether, for instance, geologists at some future periodwill be able to prove that our different breeds of cattle, sheep, horses,and dogs are descended from a single stock or from several aboriginalstocks; or, again, whether certain sea-shells inhabiting the shores ofNorth America, which are ranked by some conchologists as distinct speciesfrom their European representatives, and by other conchologists as onlyvarieties, are really varieties, or are, as it is called, specificallydistinct. This could be effected by the future geologist only by hisdiscovering in a fossil state numerous intermediate gradations; and suchsuccess is improbable in the highest degree.

It has been asserted over and over again, by writers who believe in theimmutability of species, that geology yields no linking forms. Thisassertion, as we shall see in the next chapter, is certainly erroneous. AsSir J. Lubbock has remarked, "Every species is a link between other alliedforms." If we take a genus having a score of species, recent and extinct,and destroy four-fifths of them, no one doubts that the remainder willstand much more distinct from each other. If the extreme forms in thegenus happen to have been thus destroyed, the genus itself will stand moredistinct from other allied genera. What geological research has notrevealed, is the former existence of infinitely numerous gradations, asfine as existing varieties, connecting together nearly all existing andextinct species. But this ought not to be expected; yet this has beenrepeatedly advanced as a most serious objection against my views.

It may be worth while to sum up the foregoing remarks on the causes of theimperfection of the geological record under an imaginary illustration. TheMalay Archipelago is about the size of Europe from the North Cape to theMediterranean, and from Britain to Russia; and therefore equals all thegeological formations which have been examined with any accuracy, exceptingthose of the United States of America. I fully agree with Mr. Godwin-Austen, that the present condition of the Malay Archipelago, with itsnumerous large islands separated by wide and shallow seas, probablyrepresents the former state of Europe, while most of our formations wereaccumulating. The Malay Archipelago is one of the richest regions inorganic beings; yet if all the species were to be collected which have everlived there, how imperfectly would they represent the natural history ofthe world!

But we have every reason to believe that the terrestrial productions of thearchipelago would be preserved in an extremely imperfect manner in theformations which we suppose to be there accumulating. Not many of thestrictly littoral animals, or of those which lived on naked submarinerocks, would be embedded; and those embedded in gravel or sand would notendure to a distant epoch. Wherever sediment did not accumulate on the bedof the sea, or where it did not accumulate at a sufficient rate to protectorganic bodies from decay, no remains could be preserved.

Formations rich in fossils of many kinds, and of thickness sufficient tolast to an age as distant in futurity as the secondary formations lie inthe past, would generally be formed in the archipelago only during periodsof subsidence. These periods of subsidence would be separated from eachother by immense intervals of time, during which the area would be eitherstationary or rising; whilst rising, the fossiliferous formations on thesteeper shores would be destroyed, almost as soon as accumulated, by theincessant coast-action, as we now see on the shores of South America. Eventhroughout the extensive and shallow seas within the archipelago,sedimentary beds could hardly be accumulated of great thickness during theperiods of elevation, or become capped and protected by subsequentdeposits, so as to have a good chance of enduring to a very distant future. During the periods of subsidence, there would probably be much extinctionof life; during the periods of elevation, there would be much variation,but the geological record would then be less perfect.

It may be doubted whether the duration of any one great period ofsubsidence over the whole or part of the archipelago, together with acontemporaneous accumulation of sediment, would EXCEED the average durationof the same specific forms; and these contingencies are indispensable forthe preservation of all the transitional gradations between any two or morespecies. If such gradations were not all fully preserved, transitionalvarieties would merely appear as so many new, though closely alliedspecies. It is also probable that each great period of subsidence would beinterrupted by oscillations of level, and that slight climatical changeswould intervene during such lengthy periods; and in these cases theinhabitants of the archipelago would migrate, and no closely consecutiverecord of their modifications could be preserved in any one formation.

Very many of the marine inhabitants of the archipelago now range thousandsof miles beyond its confines; and analogy plainly leads to the belief thatit would be chiefly these far-ranging species, though only some of them,which would oftenest produce new varieties; and the varieties would atfirst be local or confined to one place, but if possessed of any decidedadvantage, or when further modified and improved, they would slowly spreadand supplant their parent-forms. When such varieties returned to theirancient homes, as they would differ from their former state in a nearlyuniform, though perhaps extremely slight degree, and as they would be foundembedded in slightly different sub-stages of the same formation, theywould, according to the principles followed by many palaeontologists, beranked as new and distinct species.

If then there be some degree of truth in these remarks, we have no right toexpect to find, in our geological formations, an infinite number of thosefine transitional forms, which, on our theory, have connected all the pastand present species of the same group into one long and branching chain oflife. We ought only to look for a few links, and such assuredly we dofind--some more distantly, some more closely, related to each other; andthese links, let them be ever so close, if found in different stages of thesame formation, would, by many palaeontologists, be ranked as distinctspecies. But I do not pretend that I should ever have suspected how poorwas the record in the best preserved geological sections, had not theabsence of innumerable transitional links between the species which livedat the commencement and close of each formation, pressed so hardly on mytheory.

ON THE SUDDEN APPEARANCE OF WHOLE GROUPS OF ALLIED SPECIES.

The abrupt manner in which whole groups of species suddenly appear incertain formations, has been urged by several palaeontologists--forinstance, by Agassiz, Pictet, and Sedgwick, as a fatal objection to thebelief in the transmutation of species. If numerous species, belonging tothe same genera or families, have really started into life at once, thefact would be fatal to the theory of evolution through natural selection. For the development by this means of a group of forms, all of which aredescended from some one progenitor, must have been an extremely slowprocess; and the progenitors must have lived long before their modifieddescendants. But we continually overrate the perfection of the geologicalrecord, and falsely infer, because certain genera or families have not beenfound beneath a certain stage, that they did not exist before that stage. In all cases positive palaeontological evidence may be implicitly trusted;negative evidence is worthless, as experience has so often shown. Wecontinually forget how large the world is, compared with the area overwhich our geological formations have been carefully examined; we forgetthat groups of species may elsewhere have long existed, and have slowlymultiplied, before they invaded the ancient archipelagoes of Europe and theUnited States. We do not make due allowance for the enormous intervals oftime which have elapsed between our consecutive formations, longer perhapsin many cases than the time required for the accumulation of eachformation. These intervals will have given time for the multiplication ofspecies from some one parent-form: and in the succeeding formation, suchgroups or species will appear as if suddenly created.

I may here recall a remark formerly made, namely, that it might require along succession of ages to adapt an organism to some new and peculiar lineof life, for instance, to fly through the air; and consequently that thetransitional forms would often long remain confined to some one region; butthat, when this adaptation had once been effected, and a few species hadthus acquired a great advantage over other organisms, a comparatively shorttime would be necessary to produce many divergent forms, which would spreadrapidly and widely throughout the world. Professor Pictet, in hisexcellent Review of this work, in commenting on early transitional forms,and taking birds as an illustration, cannot see how the successivemodifications of the anterior limbs of a supposed prototype could possiblyhave been of any advantage. But look at the penguins of the SouthernOcean; have not these birds their front limbs in this precise intermediatestate of "neither true arms nor true wings?" Yet these birds hold theirplace victoriously in the battle for life; for they exist in infinitenumbers and of many kinds. I do not suppose that we here see the realtransitional grades through which the wings of birds have passed; but whatspecial difficulty is there in believing that it might profit the modifieddescendants of the penguin, first to become enabled to flap along thesurface of the sea like the logger-headed duck, and ultimately to rise fromits surface and glide through the air?

I will now give a few examples to illustrate the foregoing remarks, and toshow how liable we are to error in supposing that whole groups of specieshave suddenly been produced. Even in so short an interval as that betweenthe first and second editions of Pictet's great work on Palaeontology,published in 1844-46 and in 1853-57, the conclusions on the firstappearance and disappearance of several groups of animals have beenconsiderably modified; and a third edition would require still furtherchanges. I may recall the well-known fact that in geological treatises,published not many years ago, mammals were always spoken of as havingabruptly come in at the commencement of the tertiary series. And now oneof the richest known accumulations of fossil mammals belongs to the middleof the secondary series; and true mammals have been discovered in the newred sandstone at nearly the commencement of this great series. Cuvier usedto urge that no monkey occurred in any tertiary stratum; but now extinctspecies have been discovered in India, South America and in Europe, as farback as the miocene stage. Had it not been for the rare accident of thepreservation of footsteps in the new red sandstone of the United States,who would have ventured to suppose that no less than at least thirtydifferent bird-like animals, some of gigantic size, existed during thatperiod? Not a fragment of bone has been discovered in these beds. Notlong ago, palaeontologists maintained that the whole class of birds camesuddenly into existence during the eocene period; but now we know, on theauthority of Professor Owen, that a bird certainly lived during thedeposition of the upper greensand; and still more recently, that strangebird, the Archeopteryx, with a long lizard-like tail, bearing a pair offeathers on each joint, and with its wings furnished with two free claws,has been discovered in the oolitic slates of Solenhofen. Hardly any recentdiscovery shows more forcibly than this how little we as yet know of theformer inhabitants of the world.

I may give another instance, which, from having passed under my own eyeshas much struck me. In a memoir on Fossil Sessile Cirripedes, I statedthat, from the large number of existing and extinct tertiary species; fromthe extraordinary abundance of the individuals of many species all over theworld, from the Arctic regions to the equator, inhabiting various zones ofdepths, from the upper tidal limits to fifty fathoms; from the perfectmanner in which specimens are preserved in the oldest tertiary beds; fromthe ease with which even a fragment of a valve can be recognised; from allthese circumstances, I inferred that, had sessile cirripedes existed duringthe secondary periods, they would certainly have been preserved anddiscovered; and as not one species had then been discovered in beds of thisage, I concluded that this great group had been suddenly developed at thecommencement of the tertiary series. This was a sore trouble to me,adding, as I then thought, one more instance of the abrupt appearance of agreat group of species. But my work had hardly been published, when askilful palaeontologist, M. Bosquet, sent me a drawing of a perfectspecimen of an unmistakable sessile cirripede, which he had himselfextracted from the chalk of Belgium. And, as if to make the case asstriking as possible, this cirripede was a Chthamalus, a very common,large, and ubiquitous genus, of which not one species has as yet been foundeven in any tertiary stratum. Still more recently, a Pyrgoma, a member ofa distinct subfamily of sessile cirripedes, has been discovered by Mr.Woodward in the upper chalk; so that we now have abundant evidence of theexistence of this group of animals during the secondary period.

The case most frequently insisted on by palaeontologists of the apparentlysudden appearance of a whole group of species, is that of the teleosteanfishes, low down, according to Agassiz, in the Chalk period. This groupincludes the large majority of existing species. But certain Jurassic andTriassic forms are now commonly admitted to be teleostean; and even somepalaeozoic forms have thus been classed by one high authority. If theteleosteans had really appeared suddenly in the northern hemisphere at thecommencement of the chalk formation, the fact would have been highlyremarkable; but it would not have formed an insuperable difficulty, unlessit could likewise have been shown that at the same period the species weresuddenly and simultaneously developed in other quarters of the world. Itis almost superfluous to remark that hardly any fossil-fish are known fromsouth of the equator; and by running through Pictet's Palaeontology it willbe seen that very few species are known from several formations in Europe. Some few families of fish now have a confined range; the teleostean fishesmight formerly have had a similarly confined range, and after having beenlargely developed in some one sea, have spread widely. Nor have we anyright to suppose that the seas of the world have always been so freely openfrom south to north as they are at present. Even at this day, if the MalayArchipelago were converted into land, the tropical parts of the IndianOcean would form a large and perfectly enclosed basin, in which any greatgroup of marine animals might be multiplied; and here they would remainconfined, until some of the species became adapted to a cooler climate, andwere enabled to double the southern capes of Africa or Australia, and thusreach other and distant seas.

>From these considerations, from our ignorance of the geology of othercountries beyond the confines of Europe and the United States, and from therevolution in our palaeontological knowledge effected by the discoveries ofthe last dozen years, it seems to me to be about as rash to dogmatize onthe succession of organic forms throughout the world, as it would be for anaturalist to land for five minutes on a barren point in Australia, andthen to discuss the number and range of its productions.

ON THE SUDDEN APPEARANCE OF GROUPS OF ALLIED SPECIES IN THE LOWEST KNOWNFOSSILIFEROUS STRATA.

There is another and allied difficulty, which is much more serious. Iallude to the manner in which species belonging to several of the maindivisions of the animal kingdom suddenly appear in the lowest knownfossiliferous rocks. Most of the arguments which have convinced me thatall the existing species of the same group are descended from a singleprogenitor, apply with equal force to the earliest known species. Forinstance, it cannot be doubted that all the Cambrian and Siluriantrilobites are descended from some one crustacean, which must have livedlong before the Cambrian age, and which probably differed greatly from anyknown animal. Some of the most ancient animals, as the Nautilus, Lingula,etc., do not differ much from living species; and it cannot on our theorybe supposed, that these old species were the progenitors of all the speciesbelonging to the same groups which have subsequently appeared, for they arenot in any degree intermediate in character.

Consequently, if the theory be true, it is indisputable that before thelowest Cambrian stratum was deposited long periods elapsed, as long as, orprobably far longer than, the whole interval from the Cambrian age to thepresent day; and that during these vast periods the world swarmed withliving creatures. Here we encounter a formidable objection; for it seemsdoubtful whether the earth, in a fit state for the habitation of livingcreatures, has lasted long enough. Sir W. Thompson concludes that theconsolidation of the crust can hardly have occurred less than twenty ormore than four hundred million years ago, but probably not less thanninety-eight or more than two hundred million years. These very widelimits show how doubtful the data are; and other elements may havehereafter to be introduced into the problem. Mr. Croll estimates thatabout sixty million years have elapsed since the Cambrian period, but this,judging from the small amount of organic change since the commencement ofthe Glacial epoch, appears a very short time for the many and greatmutations of life, which have certainly occurred since the Cambrianformation; and the previous one hundred and forty million years can hardlybe considered as sufficient for the development of the varied forms of lifewhich already existed during the Cambrian period. It is, however,probable, as Sir William Thompson insists, that the world at a very earlyperiod was subjected to more rapid and violent changes in its physicalconditions than those now occurring; and such changes would have tended toinduce changes at a corresponding rate in the organisms which then existed.

To the question why we do not find rich fossiliferous deposits belonging tothese assumed earliest periods prior to the Cambrian system, I can give nosatisfactory answer. Several eminent geologists, with Sir R. Murchison attheir head, were until recently convinced that we beheld in the organicremains of the lowest Silurian stratum the first dawn of life. Otherhighly competent judges, as Lyell and E. Forbes, have disputed thisconclusion. We should not forget that only a small portion of the world isknown with accuracy. Not very long ago M. Barrande added another and lowerstage, abounding with new and peculiar species, beneath the then knownSilurian system; and now, still lower down in the Lower Cambrian formation,Mr Hicks has found South Wales beds rich in trilobites, and containingvarious molluscs and annelids. The presence of phosphatic nodules andbituminous matter, even in some of the lowest azotic rocks, probablyindicates life at these periods; and the existence of the Eozoon in theLaurentian formation of Canada is generally admitted. There are threegreat series of strata beneath the Silurian system in Canada, in the lowestof which the Eozoon is found. Sir W. Logan states that their "unitedthickness may possibly far surpass that of all the succeeding rocks, fromthe base of the palaeozoic series to the present time. We are thus carriedback to a period so remote, that the appearance of the so-called primordialfauna (of Barrande) may by some be considered as a comparatively modernevent." The Eozoon belongs to the most lowly organised of all classes ofanimals, but is highly organised for its class; it existed in countlessnumbers, and, as Dr. Dawson has remarked, certainly preyed on other minuteorganic beings, which must have lived in great numbers. Thus the words,which I wrote in 1859, about the existence of living beings long before theCambrian period, and which are almost the same with those since used by SirW. Logan, have proved true. Nevertheless, the difficulty of assigning anygood reason for the absence of vast piles of strata rich in fossils beneaththe Cambrian system is very great. It does not seem probable that the mostancient beds have been quite worn away by denudation, or that their fossilshave been wholly obliterated by metamorphic action, for if this had beenthe case we should have found only small remnants of the formations nextsucceeding them in age, and these would always have existed in a partiallymetamorphosed condition. But the descriptions which we possess of theSilurian deposits over immense territories in Russia and in North America,do not support the view that the older a formation is the more invariablyit has suffered extreme denudation and metamorphism.

The case at present must remain inexplicable; and may be truly urged as avalid argument against the views here entertained. To show that it mayhereafter receive some explanation, I will give the following hypothesis. >From the nature of the organic remains which do not appear to haveinhabited profound depths, in the several formations of Europe and of theUnited States; and from the amount of sediment, miles in thickness, ofwhich the formations are composed, we may infer that from first to lastlarge islands or tracts of land, whence the sediment was derived, occurredin the neighbourhood of the now existing continents of Europe and NorthAmerica. This same view has since been maintained by Agassiz and others. But we do not know what was the state of things in the intervals betweenthe several successive formations; whether Europe and the United Statesduring these intervals existed as dry land, or as a submarine surface nearland, on which sediment was not deposited, or as the bed of an open andunfathomable sea.

Looking to the existing oceans, which are thrice as extensive as the land,we see them studded with many islands; but hardly one truly oceanic island(with the exception of New Zealand, if this can be called a truly oceanicisland) is as yet known to afford even a remnant of any palaeozoic orsecondary formation. Hence, we may perhaps infer, that during thepalaeozoic and secondary periods, neither continents nor continentalislands existed where our oceans now extend; for had they existed,palaeozoic and secondary formations would in all probability have beenaccumulated from sediment derived from their wear and tear; and would havebeen at least partially upheaved by the oscillations of level, which musthave intervened during these enormously long periods. If, then, we mayinfer anything from these facts, we may infer that, where our oceans nowextend, oceans have extended from the remotest period of which we have anyrecord; and on the other hand, that where continents now exist, largetracts of land have existed, subjected, no doubt, to great oscillations oflevel, since the Cambrian period. The coloured map appended to my volumeon Coral Reefs, led me to conclude that the great oceans are still mainlyareas of subsidence, the great archipelagoes still areas of oscillations oflevel, and the continents areas of elevation. But we have no reason toassume that things have thus remained from the beginning of the world. Ourcontinents seem to have been formed by a preponderance, during manyoscillations of level, of the force of elevation. But may not the areas ofpreponderant movement have changed in the lapse of ages? At a period longantecedent to the Cambrian epoch, continents may have existed where oceansare now spread out, and clear and open oceans may have existed where ourcontinents now stand. Nor should we be justified in assuming that if, forinstance, the bed of the Pacific Ocean were now converted into a continentwe should there find sedimentary formations, in recognisable condition,older than the Cambrian strata, supposing such to have been formerlydeposited; for it might well happen that strata which had subsided somemiles nearer to the centre of the earth, and which had been pressed on byan enormous weight of superincumbent water, might have undergone far moremetamorphic action than strata which have always remained nearer to thesurface. The immense areas in some parts of the world, for instance inSouth America, of naked metamorphic rocks, which must have been heatedunder great pressure, have always seemed to me to require some specialexplanation; and we may perhaps believe that we see in these large areasthe many formations long anterior to the Cambrian epoch in a completelymetamorphosed and denuded condition.

The several difficulties here discussed, namely, that, though we find inour geological formations many links between the species which now existand which formerly existed, we do not find infinitely numerous finetransitional forms closely joining them all together. The sudden manner inwhich several groups of species first appear in our European formations,the almost entire absence, as at present known, of formations rich infossils beneath the Cambrian strata, are all undoubtedly of the mostserious nature. We see this in the fact that the most eminentpalaeontologists, namely, Cuvier, Agassiz, Barrande, Pictet, Falconer, E.Forbes, etc., and all our greatest geologists, as Lyell, Murchison,Sedgwick, etc., have unanimously, often vehemently, maintained theimmutability of species. But Sir Charles Lyell now gives the support ofhis high authority to the opposite side, and most geologists andpalaeontologists are much shaken in their former belief. Those who believethat the geological record is in any degree perfect, will undoubtedly atonce reject my theory. For my part, following out Lyell's metaphor, I lookat the geological record as a history of the world imperfectly kept andwritten in a changing dialect. Of this history we possess the last volumealone, relating only to two or three countries. Of this volume, only hereand there a short chapter has been preserved, and of each page, only hereand there a few lines. Each word of the slowly-changing language, more orless different in the successive chapters, may represent the forms of life,which are entombed in our consecutive formations, and which falsely appearto have been abruptly introduced. On this view the difficulties abovediscussed are greatly diminished or even disappear.