GEOLOGICAL CONTEMPORANEITY AND PERSISTENT TYPES OF LIFE. 

By Thomas H. Huxley

[1]

MERCHANTS occasionally go through a wholesome, though troublesome andnot always satisfactory, process which they term "taking stock. " Afterall the excitement of speculation, the pleasure of gain, and the pain ofloss, the trader makes up his mind to face facts and to learn the exactquantity and quality of his solid and reliable possessions. 

The man of science does well sometimes to imitate this procedure; and, forgetting for the time the importance of his own small winnings, tore-examine the common stock in trade, so that he may make sure how farthe stock of bullion in the cellar--on the faith of whose existence somuch paper has been circulating--is really the solid gold of truth. 

The Anniversary Meeting of the Geological Society seems to be anoccasion well suited for an undertaking of this kind--for an inquiry, in fact, into the nature and value of the present results ofpaleontological investigation; and the more so, as all those who havepaid close attention to the late multitudinous discussions in whichpaleontology is implicated, must have felt the urgent necessity of somesuch scrutiny. 

First in order, as the most definite and unquestionable of all theresults of paleontology, must be mentioned the immense extension andimpulse given to botany, zoology, and comparative anatomy, by theinvestigation of fossil remains. Indeed, the mass of biological factshas been so greatly increased, and the range of biological speculationhas been so vastly widened, by the researches of the geologist andpaleontologist, that it is to be feared there are naturalists inexistence who look upon geology as Brindley regarded rivers. "Rivers, "said the great engineer, "were made to feed canals"; and geology, someseem to think, was solely created to advance comparative anatomy. 

Were such a thought justifiable, it could hardly expect to be receivedwith favour by this assembly. But it is not justifiable. Your favouritescience has her own great aims independent of all others; and if, notwithstanding her steady devotion to her own progress, she can scattersuch rich alms among her sisters, it should be remembered that hercharity is of the sort that does not impoverish, but "blesseth him thatgives and him that takes. "

Regard the matter as we will, however, the facts remain. Nearly 40, 000species of animals and plants have been added to the Systema Naturae bypaleontologic research. This is a living population equivalent tothat of a new continent in mere number; equivalent to that of a newhemisphere, if we take into account the small population of insects asyet found fossil, and the large proportion and peculiar organization ofmany of the Vertebrata. 

But, beyond this, it is perhaps not too much to say that, except for thenecessity of interpreting paleontologic facts, the laws of distributionwould have received less careful study; while few comparative anatomists(and those not of the first order) would have been induced by mere loveof detail, as such, to study the minutiae of osteology, were it notthat in such minutiae lie the only keys to the most interesting riddlesoffered by the extinct animal world. 

These assuredly are great and solid gains. Surely it is matter for nosmall congratulation that in half a century (for paleontology, thoughit dawned earlier, came into full day only with Cuvier) a subordinatebranch of biology should have doubled the value and the interest of thewhole group of sciences to which it belongs. 

But this is not all. Allied with geology, paleontology has establishedtwo laws of inestimable importance: the first, that one and the samearea of the earth's surface has been successively occupied by verydifferent kinds of living beings; the second, that the order ofsuccession established in one locality holds good, approximately, inall. 

The first of these laws is universal and irreversible; the second is aninduction from a vast number of observations, though it may possibly, and even probably, have to admit of exceptions. As a consequence ofthe second law, it follows that a peculiar relation frequently subsistsbetween series of strata, containing organic remains, in differentlocalities. The series resemble one another, not only in virtue ofa general resemblance of the organic remains in the two, but alsoin virtue of a resemblance in the order and character of the serialsuccession in each. There is a resemblance of arrangement; so that theseparate terms of each series, as well as the whole series, exhibit acorrespondence. 

Succession implies time; the lower members of a series of sedimentaryrocks are certainly older than the upper; and when the notion of age wasonce introduced as the equivalent of succession, it was no wonder thatcorrespondence in succession came to be looked upon as a correspondencein age, or "contemporaneity. " And, indeed, so long as relative age onlyis spoken of, correspondence in succession 'is' correspondence in age;it is 'relative' contemporaneity. 

But it would have been very much better for geology if so loose andambiguous a word as "contemporaneous" had been excluded from herterminology, and if, in its stead, some term expressing similarity ofserial relation, and excluding the notion of time altogether, had beenemployed to denote correspondence in position in two or more series ofstrata. 

In anatomy, where such correspondence of position has constantly to bespoken of, it is denoted by the word "homology" and its derivatives; andfor Geology (which after all is only the anatomy and physiology of theearth) it might be well to invent some single word, such as "homotaxis"(similarity of order), in order to express an essentially similar idea. This, however, has not been done, and most probably the inquiry will atonce be made--To what end burden science with a new and strange term inplace of one old, familiar, and part of our common language?

The reply to this question will become obvious as the inquiry into theresults of paleontology is pushed further. 

Those whose business it is to acquaint themselves specially with theworks of paleontologists, in fact, will be fully aware that very few, if any, would rest satisfied with such a statement of the conclusions oftheir branch of biology as that which has just been given. 

Our standard repertories of paleontology profess to teach us far higherthings--to disclose the entire succession of living forms upon thesurface of the globe; to tell us of a wholly different distribution ofclimatic conditions in ancient times; to reveal the character of thefirst of all living existences; and to trace out the law of progressfrom them to us. 

It may not be unprofitable to bestow on these professions a somewhatmore critical examination than they have hitherto received, in order toascertain how far they rest on an irrefragable basis; or whether, afterall, it might not be well for paleontologists to learn a little morecarefully that scientific "ars artium, " the art of saying "I don'tknow. " And to this end let us define somewhat more exactly the extent ofthese pretensions of paleontology. 

Every one is aware that Professor Bronn's 'Untersuchungen' and ProfessorPictet's 'Traite de Paleontologie' are works of standard authority, familiarly consulted by every working paleontologist. It is desirable tospeak of these excellent books, and of their distinguished authors, with the utmost respect, and in a tone as far as possible removed fromcarping criticism; indeed, if they are specially cited in this place, it is merely in justification of the assertion that the followingpropositions, which may be found implicitly, or explicitly, in the worksin question, are regarded by the mass of paleontologists and geologists, not only on the Continent but in this country, as expressing some of thebest-established results of paleontology. Thus:--

Animals and plants began their existence together, not long afterthe commencement of the deposition of the sedimentary rocks; and thensucceeded one another, in such a manner, that totally distinct faunaeand florae occupied the whole surface of the earth, one after the other, and during distinct epochs of time. 

A geological formation is the sum of all the strata deposited over thewhole surface of the earth during one of these epochs: a geologicalfauna or flora is the sum of all the species of animals or plants whichoccupied the whole surface of the globe, during one of these epochs. 

The population of the earth's surface was at first very similar in allparts, and only from the middle of the Tertiary epoch onwards, began toshow a distinct distribution in zones. 

The constitution of the original population, as well as the numericalproportions of its members, indicates a warmer and, on the whole, somewhat tropical climate, which remained tolerably equable throughoutthe year. The subsequent distribution of living beings in zones is theresult of a gradual lowering of the general temperature, which firstbegan to be felt at the poles. 

It is not now proposed to inquire whether these doctrines are trueor false; but to direct your attention to a much simpler though veryessential preliminary question--What is their logical basis? what arethe fundamental assumptions upon which they all logically depend? andwhat is the evidence on which those fundamental propositions demand ourassent?

These assumptions are two: the first, that the commencement of thegeological record is coeval with the commencement of life on theglobe; the second, that geological contemporaneity is the same thing aschronological synchrony. Without the first of these assumptionsthere would of course be no ground for any statement respecting thecommencement of life; without the second, all the other statementscited, every one of which implies a knowledge of the state of differentparts of the earth at one and the same time, will be no less devoid ofdemonstration. 

The first assumption obviously rests entirely on negative evidence. Thisis, of course, the only evidence that ever can be available to prove thecommencement of any series of phenomena; but, at the same time, it mustbe recollected that the value of negative evidence depends entirely onthe amount of positive corroboration it receives. If A B wishes to provean 'alibi', it is of no use for him to get a thousand witnesses simplyto swear that they did not see him in such and such a place, unless thewitnesses are prepared to prove that they must have seen him had hebeen there. But the evidence that animal life commenced with theLingula-flags, 'e. G. ', would seem to be exactly of this unsatisfactoryuncorroborated sort. The Cambrian witnesses simply swear they "haven'tseen anybody their way"; upon which the counsel for the other sideimmediately puts in ten or twelve thousand feet of Devonian sandstonesto make oath they never saw a fish or a mollusk, though all the worldknows there were plenty in their time. 

But then it is urged that, though the Devonian rocks in one part of theworld exhibit no fossils, in another they do, while the lower Cambrianrocks nowhere exhibit fossils, and hence no living being could haveexisted in their epoch. 

To this there are two replies: the first, that the observational basisof the assertion that the lowest rocks are nowhere fossiliferous is anamazingly small one, seeing how very small an area, in comparison tothat of the whole world, has yet been fully searched; the second, thatthe argument is good for nothing unless the unfossiliferous rocks inquestion were not only 'contemporaneous' in the geological sense, but 'synchronous' in the chronological sense. To use the 'alibi'illustration again. If a man wishes to prove he was in neither of twoplaces, A and B, on a given day, his witnesses for each place must beprepared to answer for the whole day. If they can only prove that he wasnot at A in the morning, and not at B in the afternoon, the evidence ofhis absence from both is 'nil', because he might have been at B in themorning and at A in the afternoon. 

Thus everything depends upon the validity of the second assumption. And we must proceed to inquire what is the real meaning of the word"contemporaneous" as employed by geologists. To this end a concreteexample may be taken. 

The Lias of England and the Lias of Germany, the Cretaceous rocksof Britain and the Cretaceous rocks of Southern India, are termed bygeologists "contemporaneous" formations; but whenever any thoughtfulgeologist is asked whether he means to say that they were depositedsynchronously, he says, "No, --only within the same great epoch. " And if, in pursuing the inquiry, he is asked what may be the approximate valuein time of a "great epoch"--whether it means a hundred years, or athousand, or a million, or ten million years--his reply is, "I cannottell. "

If the further question be put, whether physical geology is inpossession of any method by which the actual synchrony (or the reverse)of any two distant deposits can be ascertained, no such method can beheard of; it being admitted by all the best authorities that neithersimilarity of mineral composition, nor of physical character, nor evendirect continuity of stratum, are 'absolute' proofs of the synchronismof even approximated sedimentary strata: while, for distant deposits, there seems to be no kind of physical evidence attainable of a naturecompetent to decide whether such deposits were formed simultaneously, orwhether they possess any given difference of antiquity. To return to anexample already given: All competent authorities will probably assent tothe proposition that physical geology does not enable us in any way toreply to this question--Were the British Cretaceous rocks deposited atthe same time as those of India, or are they a million of years youngeror a million of years older?

Is paleontology able to succeed where physical geology fails? Standardwriters on paleontology, as has been seen, assume that she can. Theytake it for granted, that deposits containing similar organic remainsare synchronous--at any rate in a broad sense; and yet, those who willstudy the eleventh and twelfth chapters of Sir Henry De La Beche'sremarkable 'Researches in Theoretical Geology', published now nearlythirty years ago, and will carry out the arguments there most luminouslystated, to their logical consequences, may very easily convincethemselves that even absolute identity of organic contents is no proofof the synchrony of deposits, while absolute diversity is no proof ofdifference of date. Sir Henry De La Beche goes even further, and adducesconclusive evidence to show that the different parts of one and the samestratum, having a similar composition throughout, containing the sameorganic remains, and having similar beds above and below it, may yetdiffer to any conceivable extent in age. 

Edward Forbes was in the habit of asserting that the similarity of theorganic contents of distant formations was 'prima facie' evidence, notof their similarity, but of their difference of age; and holding ashe did the doctrine of single specific centres, the conclusion was aslegitimate as any other; for the two districts must have been occupiedby migration from one of the two, or from an intermediate spot, andthe chances against exact coincidence of migration and of imbedding areinfinite. 

In point of fact, however, whether the hypothesis of single or ofmultiple specific centres be adopted, similarity of organic contentscannot possibly afford any proof of the synchrony of the deposits whichcontain them; on the contrary, it is demonstrably compatible withthe lapse of the most prodigious intervals of time, and with theinterposition of vast changes in the organic and inorganic worlds, between the epochs in which such deposits were formed. 

On what amount of similarity of their faunae is the doctrine of thecontemporaneity of the European and of the North American Siluriansbased? In the last edition of Sir Charles Lyell's 'Elementary Geology'it is stated, on the authority of a former President of this Society, the late Daniel Sharpe, that between 30 and 40 per cent. Of the speciesof Silurian Mollusca are common to both sides of the Atlantic. By way ofdue allowance for further discovery, let us double the lesser numberand suppose that 60 per cent. Of the species are common to the NorthAmerican and the British Silurians. Sixty per cent. Of species in commonis, then, proof of contemporaneity. 

Now suppose that, a million or two of years hence, when Britain hasmade another dip beneath the sea and has come up again, some geologistapplies this doctrine, in comparing the strata laid bare by the upheavalof the bottom, say, of St. George's Channel with what may then remain ofthe Suffolk Crag. Reasoning in the same way, he will at once decide theSuffolk Crag and the St. George's Channel beds to be contemporaneous;although we happen to know that a vast period (even in the geologicalsense) of time, and physical changes of almost unprecedented extent, separate the two. 

But if it be a demonstrable fact that strata containing more than 60 or70 per cent. Of species of Mollusca in common, and comparativelyclose together, may yet be separated by an amount of geological timesufficient to allow of some of the greatest physical changes the worldhas seen, what becomes of that sort of contemporaneity the sole evidenceof which is a similarity of facies, or the identity of half a dozenspecies, or of a good many genera?

And yet there is no better evidence for the contemporaneity assumedby all who adopt the hypothesis of universal faunae and florae, of auniversally uniform climate, and of a sensible cooling of the globeduring geological time. 

There seems, then, no escape from the admission that neither physicalgeology, nor paleontology, possesses any method by which the absolutesynchronism of two strata can be demonstrated. All that geology canprove is local order of succession. It is mathematically certainthat, in any given vertical linear section of an undisturbed series ofsedimentary deposits, the bed which lies lowest is the oldest. Inmany other vertical linear sections of the same series, of course, corresponding beds will occur in a similar order; but, however great maybe the probability, no man can say with absolute certainty that the bedsin the two sections were synchronously deposited. For areas of moderateextent, it is doubtless true that no practical evil is likely to resultfrom assuming the corresponding beds to be synchronous or strictlycontemporaneous; and there are multitudes of accessory circumstanceswhich may fully justify the assumption of such synchrony. But the momentthe geologist has to deal with large areas, or with completely separateddeposits, the mischief of confounding that "homotaxis" or "similarity ofarrangement, " which 'can' be demonstrated, with "synchrony" or "identityof date, " for which there is not a shadow of proof, under the one commonterm of "contemporaneity" becomes incalculable, and proves the constantsource of gratuitous speculations. 

For anything that geology or paleontology are able to show to thecontrary, a Devonian fauna and flora in the British Islands may havebeen contemporaneous with Silurian life in North America, and with aCarboniferous fauna and flora in Africa. Geographical provinces andzones may have been as distinctly marked in the Paleozoic epoch asat present, and those seemingly sudden appearances of new genera andspecies, which we ascribe to new creation, may be simple results ofmigration. 

It may be so; it may be otherwise. In the present condition of ourknowledge and of our methods, one verdict--"not proven, and notprovable"--must be recorded against all the grand hypotheses of thepaleontologist respecting the general succession of life on theglobe. The order and nature of terrestrial life, as a whole, areopen questions. Geology at present provides us with most valuabletopographical records, but she has not the means of working them into auniversal history. Is such a universal history, then, to be regarded asunattainable? Are all the grandest and most interesting problems whichoffer themselves to the geological student essentially insoluble? Is hein the position of a scientific Tantalus--doomed always to thirst fora knowledge which he cannot obtain? The reverse is to be hoped; nay, itmay not be impossible to indicate the source whence help will come. 

In commencing these remarks, mention was made of the great obligationsunder which the naturalist lies to the geologist and paleontologist. Assuredly the time will come when these obligations will be repaidtenfold, and when the maze of the world's past history, through whichthe pure geologist and the pure paleontologist find no guidance, will besecurely threaded by the clue furnished by the naturalist. 

All who are competent to express an opinion on the subject are, atpresent, agreed that the manifold varieties of animal and vegetableform have not either come into existence by chance, nor result fromcapricious exertions of creative power; but that they have taken placein a definite order, the statement of which order is what men ofscience term a natural law. Whether such a law is to be regarded as anexpression of the mode of operation of natural forces, or whether itis simply a statement of the manner in which a supernatural power hasthought fit to act, is a secondary question, so long as the existence ofthe law and the possibility of its discovery by the human intellect aregranted. But he must be a half-hearted philosopher who, believingin that possibility, and having watched the gigantic strides of thebiological sciences during the last twenty years, doubts that sciencewill sooner or later make this further step, so as to become possessedof the law of evolution of organic forms--of the unvarying order of thatgreat chain of causes and effects of which all organic forms, ancientand modern, are the links. And then, if ever, we shall be able to beginto discuss, with profit, the questions respecting the commencement oflife, and the nature of the successive populations of the globe, whichso many seem to think are already answered. 

The preceding arguments make no particular claim to novelty; indeedthey have been floating more or less distinctly before the minds ofgeologists for the last thirty years; and if, at the present time, it has seemed desirable to give them more definite and systematicexpression, it is because paleontology is every day assuming a greaterimportance, and now requires to rest on a basis the firmness of which isthoroughly well assured. Among its fundamental conceptions, theremust be no confusion between what is certain and what is more or lessprobable. [2] But, pending the construction of a surer foundation thanpaleontology now possesses, it may be instructive, assuming for thenonce the general correctness of the ordinary hypothesis of geologicalcontemporaneity, to consider whether the deductions which are ordinarilydrawn from the whole body of paleontologic facts are justifiable. 

The evidence on which such conclusions are based is of two kinds, negative and positive. The value of negative evidence, in connectionwith this inquiry, has been so fully and clearly discussed in an addressfrom the chair of this Society [3], which none of us have forgotten, that nothing need at present be said about it; the more, as theconsiderations which have been laid before you have certainly not tendedto increase your estimation of such evidence. It will be preferable toturn to the positive facts of paleontology, and to inquire what theytell us. 

We are all accustomed to speak of the number and the extent of thechanges in the living population of the globe during geological timeas something enormous: and indeed they are so, if we regard only thenegative differences which separate the older rocks from the moremodern, and if we look upon specific and generic changes as greatchanges, which from one point of view, they truly are. But leavingthe negative differences out of consideration, and looking only at thepositive data furnished by the fossil world from a broader point ofview--from that of the comparative anatomist who has made the study ofthe greater modifications of animal form his chief business--a surpriseof another kind dawns upon the mind; and under 'this' aspect thesmallness of the total change becomes as astonishing as was itsgreatness under the other. 

There are two hundred known orders of plants; of these not one iscertainly known to exist exclusively in the fossil state. The wholelapse of geological time has as yet yielded not a single new ordinaltype of vegetable structure. [4]

The positive change in passing from the recent to the ancient animalworld is greater, but still singularly small. No fossil animal is sodistinct from those now living as to require to be arranged even in aseparate class from those which contain existing forms. It is only whenwe come to the orders, which may be roughly estimated at about a hundredand thirty, that we meet with fossil animals so distinct from those nowliving as to require orders for themselves; and these do not amount, onthe most liberal estimate, to more than about 10 per cent. Of the whole. 

There is no certainly known extinct order of Protozoa; there is but oneamong the Coelenterata--that of the rugose corals; there is noneamong the Mollusca; there are three, the Cystidea, Blastoidea, andEdrioasterida, among the Echinoderms; and two, the Trilobita andEurypterida, among the Crustacea; making altogether five for thegreat sub-kingdom of Annulosa. Among Vertebrates there is no ordinallydistinct fossil fish: there is only one extinct order of Amphibia--theLabyrinthodonts; but there are at least four distinct orders ofReptilia, viz. The Ichthyosauria, Plesiosauria, Pterosauria, Dinosauria, and perhaps another or two. There is no known extinct order ofBirds, and no certainly known extinct order of Mammals, the ordinaldistinctness of the "Toxodontia" being doubtful. 

The objection that broad statements of this kind, after all, restlargely on negative evidence is obvious, but it has less force than mayat first be supposed; for, as might be expected from the circumstancesof the case, we possess more abundant positive evidence regarding Fishesand marine Mollusks than respecting any other forms of animal life;and yet these offer us, through the whole range of geological time, nospecies ordinally distinct from those now living; while the far lessnumerous class of Echinoderms presents three; and the Crustacea two, such orders, though none of these come down later than the Paleozoicage. Lastly, the Reptilia present the extraordinary and exceptionalphenomenon of as many extinct as existing orders, if not more; thefour mentioned maintaining their existence from the Lias to the Chalkinclusive. 

Some years ago one of your Secretaries pointed out another kindof positive paleontologic evidence tending towards the sameconclusion--afforded by the existence of what he termed "persistenttypes" of vegetable and of animal life. [5] He stated, on the authorityof Dr. Hooker, that there are Carboniferous plants which appear to begenerically identical with some now living; that the cone of the Oolitic'Araucaria' is hardly distinguishable from that of an existing species;that a true 'Pinus' appears in the Purbecks, and a 'Juglans' in theChalk; while, from the Bagshot Sands, a 'Banksia', the wood of which isnot distinguishable from that of species now living in Australia, hadbeen obtained. 

Turning to the animal kingdom, he affirmed the tabulate corals of theSilurian rocks to be wonderfully like those which now exist; while eventhe families of the Aporosa were all represented in the older Mesozoicrocks. 

Among the Molluska similar facts were adduced. Let it be borne in mindthat 'Avicula', 'Mytails', 'Chiton', 'Natica', 'Patella', 'Trochus', 'Discina', 'Orbicula', 'Lingula', 'Rhynchonella', and 'Nautilus', allof which are existing 'genera', are given without a doubt as Silurianin the last edition of 'Siluria'; while the highest forms of the highestCephalopods are represented in the Lias by a genus, 'Belemnoteuthis', which presents the closest relation to the existing 'Loligo'. 

The two highest groups of the Annulosa, the Insecta and the Arachnida, are represented in the Coal, either by existing genera, or by formsdiffering from existing genera in quite minor peculiarities. 

Turning to the Vertebrata, the only Paleozoic Elasmobranch Fish ofwhich we have any complete knowledge is the Devonian and Carboniferous'Pleuracanthus', which differs no more from existing Sharks than thesedo from one another. 

Again, vast as is the number of undoubtedly Ganoid fossil Fishes, andgreat as is their range in time, a large mass of evidence has recentlybeen adduced to show that almost all those respecting which we possesssufficient information, are referable to the same sub-ordinal groupsas the existing 'Lepidosteus', 'Polypterus', and Sturgeon; and that asingular relation obtains between the older and the younger Fishes;the former, the Devonian Ganoids, being almost all members of the samesub-order as 'Polypterus', while the Mesozoic Ganoids are almost allsimilarly allied to 'Lepidosteus'. [6]

Again, what can be more remarkable than the singular constancy ofstructure preserved throughout a vast period of time by the familyof the Pycnodonts and by that of the true Coelacanths; the formerpersisting, with but insignificant modifications, from the Carboniferousto the Tertiary rocks, inclusive; the latter existing, with still lesschange, from the Carboniferous rocks to the Chalk, inclusive?

Among Reptiles, the highest living group, that of the Crocodilia, is represented, at the early part of the Mesozoic epoch, by speciesidentical in the essential characters of their organization with thosenow living, and differing from the latter only in such matters as theform of the articular facets of the vertebral centra, in the extent towhich the nasal passages are separated from the cavity of the mouth bybone, and in the proportions of the limbs. 

And even as regards the Mammalia, the scanty remains of Triassic andOolitic species afford no foundation for the supposition that theorganization of the oldest forms differed nearly so much from some ofthose which now live as these differ from one another. 

It is needless to multiply these instances; enough has been said tojustify the statement that, in view of the immense diversity of knownanimal and vegetable forms, and the enormous lapse of time indicated bythe accumulation of fossiliferous strata, the only circumstance to bewondered at is, not that the changes of life, as exhibited by positiveevidence, have been so great, but that they have been so small. 

Be they great or small, however, it is desirable to attempt to estimatethem. Let us, therefore, take each great division of the animal world insuccession, and, whenever an order or a family can be shown to have hada prolonged existence, let us endeavour to ascertain how far the latermembers of the group differ from the earlier ones. If these latermembers, in all or in many cases, exhibit a certain amount ofmodification, the fact is, so far, evidence in favour of a general lawof change; and, in a rough way, the rapidity of that change will bemeasured by the demonstrable amount of modification. On the other hand, it must be recollected that the absence of any modification, whileit may leave the doctrine of the existence of a law of change withoutpositive support, cannot possibly disprove all forms of that doctrine, though it may afford a sufficient refutation of any of them. 

The PROTOZOA. --The Protozoa are represented throughout the whole rangeof geological series, from the Lower Silurian formation to the presentday. The most ancient forms recently made known by Ehrenberg areexceedingly like those which now exist: no one has ever pretended thatthe difference between any ancient and any modern Foraminifera is ofmore than generic value, nor are the oldest Foraminifera either simpler, more embryonic, or less differentiated, than the existing forms. 

The COELENTERATA. --The Tabulate Corals have existed from the Silurianepoch to the present day, but I am not aware that the ancient'Heliolites' possesses a single mark of a more embryonic or lessdifferentiated character, or less high organization, than the existing'Heliopora'. As for the Aporose Corals, in what respect is the Silurian'Paleocyclus' less highly organized or more embryonic than the modern'Fungia', or the Liassic Aporosa than the existing members of the samefamilies?

The 'Mollusca'. --In what sense is the living 'Waldheimia' lessembryonic, or more specialized; than the paleozoic 'Spirifer'; or theexisting 'Rhynchonellae', 'Craniae', 'Discinae', 'Lingulae', than theSilurian species of the same genera? In what sense can 'Loligo' or'Spirula' be said to be more specialized, or less embryonic, than'Belemnites'; or the modern species of Lamellibranch and Gasteropodgenera, than the Silurian species of the same genera?

The ANNULOSA. --The Carboniferous Insecta and Arachnida are neither lessspecialized, nor more embryonic, than these that now live, nor are theLiassic Cirripedia and Macrura; while several of the Brachyura, whichappear in the Chalk, belong to existing genera; and none exhibit eitheran intermediate, or an embryonic, character. 

The VERTEBRARA. --Among fishes I have referred to the Coelacanthini(comprising the genera 'Coelacanthus', 'Holophagus', 'Undina', and'Macropoma') as affording an example of a persistent type; and it ismost remarkable to note the smallness of the differences between any ofthese fishes (affecting at most the proportions of the body and fins, and the character and sculpture of the scales), notwithstanding theirenormous range in time. In all the essentials of its very peculiarstructure, the 'Macropoma' of the Chalk is identical with the'Coelacanthus' of the Coal. Look at the genus 'Lepidotus', again, persisting without a modification of importance from the Liassic to theEocene formations inclusive. 

Or among the Teleostei--in what respect is the 'Beryx' of the Chalkmore embryonic, or less differentiated, than 'Beryx lineatus' of KingGeorge's Sound?

Or to turn to the higher Vertebrata--in what sense are the LiassicChelonia inferior to those which now exist? How are the CretaceousIchthyosauria, Plesiosauria, or Pterosauria less embryonic, or moredifferentiated, species than those of the Lias?

Or lastly, in what circumstance is the 'Phascolotherium' moreembryonic, or of a more generalized type, than the modern Opossum; or a'Lophiodon', or a 'Paleotherium', than a modern 'Tapirus' or 'Hyrax'?

These examples might be almost indefinitely multiplied, but surely theyare sufficient to prove that the only safe and unquestionable testimonywe can procure--positive evidence--fails to demonstrate any sort ofprogressive modification towards a less embryonic, or less generalised, type in a great many groups of animals of long-continued geologicalexistence. In these groups there is abundant evidence of variation--noneof what is ordinarily understood as progression; and, if the knowngeological record is to be regarded as even any considerable fragmentof the whole, it is inconceivable that any theory of a necessarilyprogressive development can stand, for the numerous orders and familiescited afford no trace of such a process. 

But it is a most remarkable fact, that, while the groups which havebeen mentioned, and many besides, exhibit no sign of progressivemodification, there are others, co-existing with them, under the sameconditions, in which more or less distinct indications of such a processseems to be traceable. Among such indications I may remind you of thepredominance of Holostome Gasteropoda in the older rocks as comparedwith that of Siphonostome Gasteropoda in the later. A case less opento the objection of negative evidence, however, is that afforded by theTetrabranchiate Cephalopoda, the forms of the shells and of the septalsutures exhibiting a certain increase of complexity in the newer genera. Here, however, one is met at once with the occurrence of 'Orthoceras'and 'Baculites' at the two ends of the series, and of the fact that oneof the simplest Genera, 'Nautilus', is that which now exists. 

The Crinoidea, in the abundance of stalked forms in the ancientformations as compared with their present rarity, seem to present uswith a fair case of modification from a more embryonic towards a lessembryonic condition. But then, on careful consideration of the facts, the objection arises that the stalk, calyx, and arms of the paleozoicCrinoid are exceedingly different from the corresponding organs of alarval 'Comatula'; and it might with perfect justice be argued that'Actinocrinus' and 'Eucalyptocrinus', for example, depart to the fullas widely, in one direction, from the stalked embryo of 'Comatula', as'Comatula' itself does in the other. 

The Echinidea, again, are frequently quoted as exhibiting a gradualpassage from a more generalized to a more specialized type, seeingthat the elongated, or oval, Spatangoids appear after the spheroidalEchinoids. But here it might be argued, on the other hand, that thespheroidal Echinoids, in reality, depart further from the general planand from the embryonic form than the elongated Spatangoids do; and thatthe peculiar dental apparatus and the pedicellariae of the former aremarks of at least as great differentiation as the petaloid ambulacra andsemitae of the latter. 

Once more, the prevalence of Macrurous before Brachyurous Podophthalmiais, apparently, a fair piece of evidence in favour of progressivemodification in the same order of Crustacea; and yet the case will notstand much sifting, seeing that the Macrurous Podophthalmia depart asfar in one direction from the common type of Podophthalmia, or from anyembryonic condition of the Brachyura, as the Brachyura do in theother; and that the middle terms between Macrura and Brachyura--theAnomura--are little better represented in the older Mesozoic rocks thanthe Brachyura are. 

None of the cases of progressive modification which are cited fromamong the Invertebrata appear to me to have a foundation less open tocriticism than these; and if this be so, no careful reasoner would, I think, be inclined to lay very great stress upon them. Among theVertebrata, however, there are a few examples which appear to be farless open to objection. 

It is, in fact, true of several groups of Vertebrata which have livedthrough a considerable range of time, that the endoskeleton (moreparticularly the spinal column) of the older genera presents a lessossified, and, so far, less differentiated, condition than that of theyounger genera. Thus the Devonian Ganoids, though almost all members ofthe same sub-order as 'Polypterus', and presenting numerous importantresemblances to the existing genus, which possesses biconcave vertebrae, are, for the most part, wholly devoid of ossified vertebral centra. TheMesozoic Lepidosteidae, again, have, at most, biconcave vertebrae, whilethe existing 'Lepidosteus' has Salamandroid, opisthocoelous, vertebrae. So, none of the Paleozoic Sharks have shown themselves to be possessedof ossified vertebrae, while the majority of modern Sharks possesssuch vertebrae. Again, the more ancient Crocodilia and Lacertiliahave vertebrae with the articular facets of their centra flattenedor biconcave, while the modern members of the same group have themprocoelous. But the most remarkable examples of progressive modificationof the vertebral column, in correspondence with geological age, arethose afforded by the Pycnodonts among fish, and the Labyrinthodontsamong Amphibia. 

The late able ichthyologist Heckel pointed out the fact, that, whilethe Pycnodonts never possess true vertebral centra, they differ in thedegree of expansion and extension of the ends of the bony arches ofthe vertebrae upon the sheath of the notochord; the Carboniferous formsexhibiting hardly any such expansion, while the Mesozoic genera presenta greater and greater development, until, in the Tertiary forms, theexpanded ends become suturally united so as to form a sort of falsevertebra. Hermann von Meyer, again, to whose luminous researches weare indebted for our present large knowledge of the organization of theolder Labyrinthodonts, has proved that the Carboniferous 'Archegosaurus'had very imperfectly developed vertebral centra, while the Triassic'Mastodonsaurus' had the same parts completely ossified. [7]

The regularity and evenness of the dentition of the 'Anoplotherium', ascontrasted with that of existing Artiodactyles, and the assumed nearerapproach of the dentition of certain ancient Carnivores to the typicalarrangement, have also been cited as exemplifications of a law ofprogressive development, but I know of no other cases based on positiveevidence which are worthy of particular notice. 

What, then, does an impartial survey of the positively ascertainedtruths of paleontology testify in relation to the common doctrines ofprogressive modification, which suppose that modification to have takenplace by a necessary progress from more to less embryonic forms, orfrom more to less generalized types, within the limits of the periodrepresented by the fossiliferous rocks?

It negatives those doctrines; for it either shows us no evidence of anysuch modification, or demonstrates it to have been very slight; and asto the nature of that modification, it yields no evidence whatsoeverthat the earlier members of any long-continued group were moregeneralized in structure than the later ones. To a certain extent, indeed, it may be said that imperfect ossification of the vertebralcolumn is an embryonic character; but, on the other hand, it would beextremely incorrect to suppose that the vertebral columns of the olderVertebrata are in any sense embryonic in their whole structure. 

Obviously, if the earliest fossiliferous rocks now known are coevalwith the commencement of life, and if their contents give us any justconception of the nature and the extent of the earliest fauna and flora, the insignificant amount of modification which can be demonstratedto have taken place in any one group of animals, or plants, is quiteincompatible with the hypothesis that all living forms are the resultsof a necessary process of progressive development, entirely comprisedwithin the time represented by the fossiliferous rocks. 

Contrariwise, any admissible hypothesis of progressive modification mustbe compatible with persistence without progression, through indefiniteperiods. And should such an hypothesis eventually be proved to be true, in the only way in which it can be demonstrated, viz. By observationand experiment upon the existing forms of life, the conclusion willinevitably present itself, that the Paleozoic, Mesozoic, and Cainozoicfaunae and florae, taken together, bear somewhat the same proportion tothe whole series of living beings which have occupied this globe, as theexisting fauna and flora do to them. 

Such are the results of paleontology as they appear, and have for someyears appeared, to the mind of an inquirer who regards that study simplyas one of the applications of the great biological sciences, and whodesires to see it placed upon the same sound basis as other branches ofphysical inquiry. If the arguments which have been brought forward arevalid, probably no one, in view of the present state of opinion, willbe inclined to think the time wasted which has been spent upon theirelaboration. 

[Footnote 1: The Anniversary Address to the Geological Society for1862. ]

[Footnote 2: "le plus grand service qu'on puisse rendre a la science estd'y faire place nette avant d'y rien construire. "--CUVIER]

[Footnote 3: Anniversary Address for 1851, 'Quart. Journ. Geol. Soc. 'vol. Vii. ]

[Footnote 4: See Hooker's 'Introductory Essay to the Flora of Tasmania', p. Xxiii. ]

[Footnote 5: See the abstract of a Lecture "On the Persistent Types ofAnimal Life, " in the 'Notices of the Meetings of the Royal Institutionof Great Britain'. --June 3, 1859, vol. Iii. P. 151. 

[Footnote 6: "Memoirs of the Geological Survey of the UnitedKingdom. --Decade x. Preliminary Essay upon the Systematic Arrangement ofthe Fishes of the Devonian Epoch. "]

[Footnote 7: As the Address is passing through the press (March 7, 1862), evidence lies before me of the existence of a new Labyrinthodont('Pholidogaster'), from the Edinburgh coal-field, with well-ossifiedvertebral centra. ]