Chapter IX

On the Imperfection of the Geological Record

On the absence of intermediate varieties at the present day -- On the

nature of extinct intermediate varieties; on their number -- On the vast

lapse of time, as inferred from the rate of deposition and of denudation --

On the poorness of our palaeontological collections -- On the intermittence

of geological formations -- On the absence of intermediate varieties in any

one formation -- On the sudden appearance of groups of species -- On their

sudden appearance in the lowest known fossiliferous strata.

In the sixth chapter I enumerated the chief objections which might be

justly urged against the views maintained in this volume. Most of them

have now been discussed. One, namely the distinctness of specific forms,

and their not being blended together by innumerable transitional links, is

a very obvious difficulty. I assigned reasons why such links do not

commonly occur at the present day, under the circumstances apparently most

favourable for their presence, namely on an extensive and continuous area

with graduated physical conditions. I endeavoured to show, that the life

of each species depends in a more important manner on the presence of other

already defined organic forms, than on climate; and, therefore, that the

really governing conditions of life do not graduate away quite insensibly

like heat or moisture. I endeavoured, also, to show that intermediate

varieties, from existing in lesser numbers than the forms which they

connect, will generally be beaten out and exterminated during the course of

further modification and improvement. The main cause, however, of

innumerable intermediate links not now occurring everywhere throughout

nature depends on the very process of natural selection, through which new

varieties continually take the places of and exterminate their

parent-forms. But just in proportion as this process of extermination has

acted on an enormous scale, so must the number of intermediate varieties,

which have formerly existed on the earth, be truly enormous. Why then is

not every geological formation and every stratum full of such intermediate

links? Geology assuredly does not reveal any such finely graduated organic

chain; and this, perhaps, is the most obvious and gravest objection which

can be urged against my theory. The explanation lies, as I believe, in the

extreme imperfection of the geological record.

In the first place it should always be borne in mind what sort of

intermediate forms must, on my theory, have formerly existed. I have found

it difficult, when looking at any two species, to avoid picturing to

myself, forms directly intermediate between them. But this is a wholly

false view; we should always look for forms intermediate between each

species and a common but unknown progenitor; and the progenitor will

generally have differed in some respects from all its modified descendants.

To give a simple illustration: the fantail and pouter pigeons have both

descended from the rock-pigeon; if we possessed all the intermediate

varieties which have ever existed, we should have an extremely close series

between both and the rock-pigeon; but we should have no varieties directly

intermediate between the fantail and pouter; none, for instance, combining

a tail somewhat expanded with a crop somewhat enlarged, the characteristic

features of these two breeds. These two breeds, moreover, have become so

much modified, that if we had no historical or indirect evidence regarding

their origin, it would not have been possible to have determined from a

mere comparison of their structure with that of the rock-pigeon, whether

they had descended from this species or from some other allied species,

such as C. oenas.

So with natural species, if we look to forms very distinct, for instance to

the horse and tapir, we have no reason to suppose that links ever existed

directly intermediate between them, but between each and an unknown common

parent. The common parent will have had in its whole organisation much

general resemblance to the tapir and to the horse; but in some points of

structure may have differed considerably from both, even perhaps more than

they differ from each other. Hence in all such cases, we should be unable

to recognise the parent-form of any two or more species, even if we closely

compared the structure of the parent with that of its modified descendants,

unless at the same time we had a nearly perfect chain of the intermediate

links.

It is just possible by my theory, that one of two living forms might have

descended from the other; for instance, a horse from a tapir; and in this

case direct intermediate links will have existed between them. But such a

case would imply that one form had remained for a very long period

unaltered, whilst its descendants had undergone a vast amount of change;

and the principle of competition between organism and organism, between

child and parent, will render this a very rare event; for in all cases the

new and improved forms of life will tend to supplant the old and unimproved

forms.

By the theory of natural selection all living species have been connected

with the parent-species of each genus, by differences not greater than we

see between the varieties of the same species at the present day; and these

parent-species, now generally extinct, have in their turn been similarly

connected with more ancient species; and so on backwards, always converging

to the common ancestor of each great class. So that the number of

intermediate and transitional links, between all living and extinct

species, must have been inconceivably great. But assuredly, if this theory

be true, such have lived upon this earth.

On the lapse of Time. -- Independently of our not finding fossil remains of

such infinitely numerous connecting links, it may be objected, that time

will not have sufficed for so great an amount of organic change, all

changes having been effected very slowly through natural selection. It is

hardly possible for me even to recall to the reader, who may not be a

practical geologist, the facts leading the mind feebly to comprehend the

lapse of time. He who can read Sir Charles Lyell's grand work on the

Principles of Geology, which the future historian will recognise as having

produced a revolution in natural science, yet does not admit how

incomprehensibly vast have been the past periods of time, may at once close

this volume. Not that it suffices to study the Principles of Geology, or

to read special treatises by different observers on separate formations,

and to mark how each author attempts to give an inadequate idea of the

duration of each formation or even each stratum. A man must for years

examine for himself great piles of superimposed strata, and watch the sea

at work grinding down old rocks and making fresh sediment, before he can

hope to comprehend anything of the lapse of time, the monuments of which we

see around us.

It is good to wander along lines of sea-coast, when formed of moderately

hard rocks, and mark the process of degradation. The tides in most cases

reach the cliffs only for a short time twice a day, and the waves eat into

them only when they are charged with sand or pebbles; for there is reason

to believe that pure water can effect little or nothing in wearing away

rock. At last the base of the cliff is undermined, huge fragments fall

down, and these remaining fixed, have to be worn away, atom by atom, until

reduced in size they can be rolled about by the waves, and then are more

quickly ground into pebbles, sand, or mud. But how often do we see along

the bases of retreating cliffs rounded boulders, all thickly clothed by

marine productions, showing how little they are abraded and how seldom they

are rolled about! Moreover, if we follow for a few miles any line of rocky

cliff, which is undergoing degradation, we find that it is only here and

there, along a short length or round a promontory, that the cliffs are at

the present time suffering. The appearance of the surface and the

vegetation show that elsewhere years have elapsed since the waters washed

their base.

He who most closely studies the action of the sea on our shores, will, I

believe, be most deeply impressed with the slowness with which rocky coasts

are worn away. The observations on this head by Hugh Miller, and by that

excellent observer Mr. Smith of Jordan Hill, are most impressive. With the

mind thus impressed, let any one examine beds of conglomerate many thousand

feet in thickness, which, though probably formed at a quicker rate than

many other deposits, yet, from being formed of worn and rounded pebbles,

each of which bears the stamp of time, are good to show how slowly the mass

has been accumulated. Let him remember Lyell's profound remark, that the

thickness and extent of sedimentary formations are the result and measure

of the degradation which the earth's crust has elsewhere suffered. And

what an amount of degradation is implied by the sedimentary deposits of

many countries! Professor Ramsay has given me the maximum thickness, in

most cases from actual measurement, in a few cases from estimate, of each

formation in different parts of Great Britain; and this is the result:-

  Feet

Palaeozoic strata (not including igneous beds)..57,154

Secondary strata................................13,190

Tertiary strata..................................2,240

--making altogether 72,584 feet; that is, very nearly thirteen and

three-quarters British miles. Some of these formations, which are

represented in England by thin beds, are thousands of feet in thickness on

the Continent. Moreover, between each successive formation, we have, in

the opinion of most geologists, enormously long blank periods. So that the

lofty pile of sedimentary rocks in Britain, gives but an inadequate idea of

the time which has elapsed during their accumulation; yet what time this

must have consumed! Good observers have estimated that sediment is

deposited by the great Mississippi river at the rate of only 600 feet in a

hundred thousand years. This estimate may be quite erroneous; yet,

considering over what wide spaces very fine sediment is transported by the

currents of the sea, the process of accumulation in any one area must be

extremely slow.

But the amount of denudation which the strata have in many places suffered,

independently of the rate of accumulation of the degraded matter, probably

offers the best evidence of the lapse of time. I remember having been much

struck with the evidence of denudation, when viewing volcanic islands,

which have been worn by the waves and pared all round into perpendicular

cliffs of one or two thousand feet in height; for the gentle slope of the

lava-streams, due to their formerly liquid state, showed at a glance how

far the hard, rocky beds had once extended into the open ocean. The same

story is still more plainly told by faults,--those great cracks along which

the strata have been upheaved on one side, or thrown down on the other, to

the height or depth of thousands of feet; for since the crust cracked, the

surface of the land has been so completely planed down by the action of the

sea, that no trace of these vast dislocations is externally visible.

The Craven fault, for instance, extends for upwards of 30 miles, and along

this line the vertical displacement of the strata has varied from 600 to

3000 feet. Prof. Ramsay has published an account of a downthrow in

Anglesea of 2300 feet; and he informs me that he fully believes there is

one in Merionethshire of 12,000 feet; yet in these cases there is nothing

on the surface to show such prodigious movements; the pile of rocks on the

one or other side having been smoothly swept away. The consideration of

these facts impresses my mind almost in the same manner as does the vain

endeavour to grapple with the idea of eternity.

I am tempted to give one other case, the well-known one of the denudation

of the Weald. Though it must be admitted that the denudation of the Weald

has been a mere trifle, in comparison with that which has removed masses of

our palaeozoic strata, in parts ten thousand feet in thickness, as shown in

Prof. Ramsay's masterly memoir on this subject. Yet it is an admirable

lesson to stand on the North Downs and to look at the distant South Downs;

for, remembering that at no great distance to the west the northern and

southern escarpments meet and close, one can safely picture to oneself the

great dome of rocks which must have covered up the Weald within so limited

a period as since the latter part of the Chalk formation. The distance

from the northern to the southern Downs is about 22 miles, and the

thickness of the several formations is on an average about 1100 feet, as I

am informed by Prof. Ramsay. But if, as some geologists suppose, a range

of older rocks underlies the Weald, on the flanks of which the overlying

sedimentary deposits might have accumulated in thinner masses than

elsewhere, the above estimate would be erroneous; but this source of doubt

probably would not greatly affect the estimate as applied to the western

extremity of the district. If, then, we knew the rate at which the sea

commonly wears away a line of cliff of any given height, we could measure

the time requisite to have denuded the Weald. This, of course, cannot be

done; but we may, in order to form some crude notion on the subject, assume

that the sea would eat into cliffs 500 feet in height at the rate of one

inch in a century. This will at first appear much too small an allowance;

but it is the same as if we were to assume a cliff one yard in height to be

eaten back along a whole line of coast at the rate of one yard in nearly

every twenty-two years. I doubt whether any rock, even as soft as chalk,

would yield at this rate excepting on the most exposed coasts; though no

doubt the degradation of a lofty cliff would be more rapid from the

breakage of the fallen fragments. On the other hand, I do not believe that

any line of coast, ten or twenty miles in length, ever suffers degradation

at the same time along its whole indented length; and we must remember that

almost all strata contain harder layers or nodules, which from long

resisting attrition form a breakwater at the base. Hence, under ordinary

circumstances, I conclude that for a cliff 500 feet in height, a denudation

of one inch per century for the whole length would be an ample allowance.

At this rate, on the above data, the denudation of the Weald must have

required 306,662,400 years; or say three hundred million years.

The action of fresh water on the gently inclined Wealden district, when

upraised, could hardly have been great, but it would somewhat reduce the

above estimate. On the other hand, during oscillations of level, which we

know this area has undergone, the surface may have existed for millions of

years as land, and thus have escaped the action of the sea: when deeply

submerged for perhaps equally long periods, it would, likewise, have

escaped the action of the coast-waves. So that in all probability a far

longer period than 300 million years has elapsed since the latter part of

the Secondary period.

I have made these few remarks because it is highly important for us to gain

some notion, however imperfect, of the lapse of years. During each of

these years, over the whole world, the land and the water has been peopled

by hosts of living forms. What an infinite number of generations, which

the mind cannot grasp, must have succeeded each other in the long roll of

years! Now turn to our richest geological museums, and what a paltry

display we behold!

On the poorness of our Palaeontological collections. -- That our

palaeontological collections are very imperfect, is admitted by every one.

The remark of that admirable palaeontologist, the late Edward Forbes,

should not be forgotten, namely, that numbers of our fossil species are

known and named from single and often broken specimens, or from a few

specimens collected on some one spot. Only a small portion of the surface

of the earth has been geologically explored, and no part with sufficient

care, as the important discoveries made every year in Europe prove. No

organism wholly soft can be preserved. Shells and bones will decay and

disappear when left on the bottom of the sea, where sediment is not

accumulating. I believe we are continually taking a most erroneous view,

when we tacitly admit to ourselves that sediment is being deposited over

nearly the whole bed of the sea, at a rate sufficiently quick to embed and

preserve fossil remains. Throughout an enormously large proportion of the

ocean, the bright blue tint of the water bespeaks its purity. The many

cases on record of a formation conformably covered, after an enormous

interval of time, by another and later formation, without the underlying

bed having suffered in the interval any wear and tear, seem explicable only

on the view of the bottom of the sea not rarely lying for ages in an

unaltered condition. The remains which do become embedded, if in sand or

gravel, will when the beds are upraised generally be dissolved by the

percolation of rain-water. I suspect that but few of the very many animals

which live on the beach between high and low watermark are preserved. For

instance, the several species of the Chthamalinae (a sub-family of sessile

cirripedes) coat the rocks all over the world in infinite numbers: they

are all strictly littoral, with the exception of a single Mediterranean

species, which inhabits deep water and has been found fossil in Sicily,

whereas not one other species has hitherto been found in any tertiary

formation: yet it is now known that the genus Chthamalus existed during

the chalk period. The molluscan genus Chiton offers a partially analogous

case.

With respect to the terrestrial productions which lived during the

Secondary and Palaeozoic periods, it is superfluous to state that our

evidence from fossil remains is fragmentary in an extreme degree. For

instance, not a land shell is known belonging to either of these vast

periods, with one exception discovered by Sir C. Lyell in the carboniferous

strata of North America. In regard to mammiferous remains, a single glance

at the historical table published in the Supplement to Lyell's Manual, will

bring home the truth, how accidental and rare is their preservation, far

better than pages of detail. Nor is their rarity surprising, when we

remember how large a proportion of the bones of tertiary mammals have been

discovered either in caves or in lacustrine deposits; and that not a cave

or true lacustrine bed is known belonging to the age of our secondary or

palaeozoic formations.

But the imperfection in the geological record mainly results from another

and more important cause than any of the foregoing; namely, from the

several formations being separated from each other by wide intervals of

time. When we see the formations tabulated in written works, or when we

follow them in nature, it is difficult to avoid believing that they are

closely consecutive. But we know, for instance, from Sir R. Murchison's

great work on Russia, what wide gaps there are in that country between the

superimposed formations; so it is in North America, and in many other parts

of the world. The most skilful geologist, if his attention had been

exclusively confined to these large territories, would never have suspected

that during the periods which were blank and barren in his own country,

great piles of sediment, charged with new and peculiar forms of life, had

elsewhere been accumulated. And if in each separate territory, hardly any

idea can be formed of the length of time which has elapsed between the

consecutive formations, we may infer that this could nowhere be

ascertained. The frequent and great changes in the mineralogical

composition of consecutive formations, generally implying great changes in

the geography of the surrounding lands, whence the sediment has been

derived, accords with the belief of vast intervals of time having elapsed

between each formation.

But we can, I think, see why the geological formations of each region are

almost invariably intermittent; that is, have not followed each other in

close sequence. Scarcely any fact struck me more when examining many

hundred miles of the South American coasts, which have been upraised

several hundred feet within the recent period, than the absence of any

recent deposits sufficiently extensive to last for even a short geological

period. Along the whole west coast, which is inhabited by a peculiar

marine fauna, tertiary beds are so scantily developed, that no record of

several successive and peculiar marine faunas will probably be preserved to

a distant age. A little reflection will explain why along the rising coast

of the western side of South America, no extensive formations with recent

or tertiary remains can anywhere be found, though the supply of sediment

must for ages have been great, from the enormous degradation of the

coast-rocks and from muddy streams entering the sea. The explanation, no

doubt, is, that the littoral and sub-littoral deposits are continually worn

away, as soon as they are brought up by the slow and gradual rising of the

land within the grinding action of the coast-waves.

We may, I think, safely conclude that sediment must be accumulated in

extremely thick, solid, or extensive masses, in order to withstand the

incessant action of the waves, when first upraised and during subsequent

oscillations of level. Such thick and extensive accumulations of sediment

may be formed in two ways; either, in profound depths of the sea, in which

case, judging from the researches of E. Forbes, we may conclude that the

bottom will be inhabited by extremely few animals, and the mass when

upraised will give a most imperfect record of the forms of life which then

existed; or, sediment may be accumulated to any thickness and extent over a

shallow bottom, if it continue slowly to subside. In this latter case, as

long as the rate of subsidence and supply of sediment nearly balance each

other, the sea will remain shallow and favourable for life, and thus a

fossiliferous formation thick enough, when upraised, to resist any amount

of degradation, may be formed.

I am convinced that all our ancient formations, which are rich in fossils,

have thus been formed during subsidence. Since publishing my views on this

subject in 1845, I have watched the progress of Geology, and have been

surprised to note how author after author, in treating of this or that

great formation, has come to the conclusion that it was accumulated during

subsidence. I may add, that the only ancient tertiary formation on the

west coast of South America, which has been bulky enough to resist such

degradation as it has as yet suffered, but which will hardly last to a

distant geological age, was certainly deposited during a downward

oscillation of level, and thus gained considerable thickness.

All geological facts tell us plainly that each area has undergone numerous

slow oscillations of level, and apparently these oscillations have affected

wide spaces. Consequently formations rich in fossils and sufficiently

thick and extensive to resist subsequent degradation, may have been formed

over wide spaces during periods of subsidence, but only where the supply of

sediment was sufficient to keep the sea shallow and to embed and preserve

the remains before they had time to decay. On the other hand, as long as

the bed of the sea remained stationary, thick deposits could not have been

accumulated in the shallow parts, which are the most favourable to life.

Still less could this have happened during the alternate periods of

elevation; or, to speak more accurately, the beds which were then

accumulated will have been destroyed by being upraised and brought within

the limits of the coast-action.

Thus the geological record will almost necessarily be rendered

intermittent. I feel much confidence in the truth of these views, for they

are in strict accordance with the general principles inculcated by Sir C.

Lyell; and E. Forbes independently arrived at a similar conclusion.

One remark is here worth a passing notice. During periods of elevation the

area of the land and of the adjoining shoal parts of the sea will be

increased, and new stations will often be formed;--all circumstances most

favourable, as previously explained, for the formation of new varieties and

species; but during such periods there will generally be a blank in the

geological record. On the other hand, during subsidence, the inhabited

area and number of inhabitants will decrease (excepting the productions on

the shores of a continent when first broken up into an archipelago), and

consequently during subsidence, though there will be much extinction, fewer

new varieties or species will be formed; and it is during these very

periods of subsidence, that our great deposits rich in fossils have been

accumulated. Nature may almost be said to have guarded against the

frequent discovery of her transitional or linking forms.

From the foregoing considerations it cannot be doubted that the geological

record, viewed as a whole, is extremely imperfect; but if we confine our

attention to any one formation, it becomes more difficult to understand,

why we do not therein find closely graduated varieties between the allied

species which lived at its commencement and at its close. Some cases are

on record of the same species presenting distinct varieties in the upper

and lower parts of the same formation, but, as they are rare, they may be

here passed over. Although each formation has indisputably required a vast

number of years for its deposition, I can see several reasons why each

should not include a graduated series of links between the species which

then lived; but I can by no means pretend to assign due proportional weight

to the following considerations.

Although each formation may mark a very long lapse of years, each perhaps

is short compared with the period requisite to change one species into

another. I am aware that two palaeontologists, whose opinions are worthy

of much deference, namely Bronn and Woodward, have concluded that the

average duration of each formation is twice or thrice as long as the

average duration of specific forms. But insuperable difficulties, as it

seems to me, prevent us coming to any just conclusion on this head. When

we see a species first appearing in the middle of any formation, it would

be rash in the extreme to infer that it had not elsewhere previously

existed. So again when we find a species disappearing before the uppermost

layers have been deposited, it would be equally rash to suppose that it

then became wholly extinct. We forget how small the area of Europe is

compared with the rest of the world; nor have the several stages of the

same formation throughout Europe been correlated with perfect accuracy.

With marine animals of all kinds, we may safely infer a large amount of

migration during climatal and other changes; and when we see a species

first appearing in any formation, the probability is that it only then

first immigrated into that area. It is well known, for instance, that

several species appeared somewhat earlier in the palaeozoic beds of North

America than in those of Europe; time having apparently been required for

their migration from the American to the European seas. In examining the

latest deposits of various quarters of the world, it has everywhere been

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 absent

in this particular deposit. It is an excellent lesson to reflect on the

ascertained amount of migration of the inhabitants of Europe during the

Glacial period, which forms only a part of one whole geological period; and

likewise to reflect on the great changes of level, on the inordinately

great change of climate, on the prodigious lapse of time, all included

within this same glacial period. Yet it may be doubted whether in any

quarter of the world, sedimentary deposits, including fossil remains, have

gone on accumulating within the same area during the whole of this period.

It is not, for instance, probable that sediment was deposited during the

whole of the glacial period near the mouth of the Mississippi, within that

limit of depth at which marine animals can flourish; for we know what vast

geographical changes occurred in other parts of America during this space

of time. When such beds as were deposited in shallow water near the mouth

of the Mississippi during some part of the glacial period shall have been

upraised, organic remains will probably first appear and disappear at

different levels, owing to the migration of species and to geographical

changes. And in the distant future, a geologist examining these beds,

might be tempted to conclude that the average duration of life of the

embedded fossils had been less than that of the glacial period, instead of

having been really far greater, that is extending from before the glacial

epoch to the present day.

In order to get a perfect gradation between two forms in the upper and

lower parts of the same formation, the deposit must have gone on

accumulating for a very long period, in order to have given sufficient time

for the slow process of variation; hence the deposit will generally have to

be a very thick one; and the species undergoing modification will have had

to live on the same area throughout this whole time. But we have seen that

a thick fossiliferous formation can only be accumulated during a period of

subsidence; and to keep the depth approximately the same, which is

necessary in order to enable the same species to live on the same space,

the supply of sediment must nearly have counterbalanced the amount of

subsidence. But this same movement of subsidence will often tend to sink

the area whence the sediment is derived, and thus diminish the supply

whilst the downward movement continues. In fact, this nearly exact

balancing between the supply of sediment and the amount of subsidence is

probably a rare contingency; for it has been observed by more than one

palaeontologist, that very thick deposits are usually barren of organic

remains, except near their upper or lower limits.

It would seem that each separate formation, like the whole pile of

formations in any country, has generally been intermittent in its

accumulation. When we see, as is so often the case, a formation composed

of beds of different mineralogical composition, we may reasonably suspect

that the process of deposition has been much interrupted, as a change in

the currents of the sea and a supply of sediment of a different nature will

generally have been due to geographical changes requiring much time. Nor

will the closest inspection of a formation give any idea of the time which

its deposition has consumed. Many instances could be given of beds only a

few feet in thickness, representing formations, elsewhere thousands of feet

in thickness, and which must have required an enormous period for their

accumulation; yet no one ignorant of this fact would have suspected the

vast lapse of time represented by the thinner formation. Many cases could

be given of the lower beds of a formation having been upraised, denuded,

submerged, and then re-covered by the upper beds of the same

formation,--facts, showing what wide, yet easily overlooked, intervals have

occurred in its accumulation. In other cases we have the plainest evidence

in great fossilised trees, still standing upright as they grew, of many

long intervals of time and changes of level during the process of

deposition, which would never even have been suspected, had not the trees

chanced to have been preserved: thus, Messrs. Lyell and Dawson found

carboniferous beds 1400 feet thick in Nova Scotia, with ancient

root-bearing strata, one above the other, at no less than sixty-eight

different levels. Hence, when the same species occur at the bottom,

middle, and top of a formation, the probability is that they have not lived

on the same spot during the whole period of deposition, but have

disappeared and reappeared, perhaps many times, during the same geological

period. So that if such species were to undergo a considerable amount of

modification during any one geological period, a section would not probably

include all the fine intermediate gradations which must on my theory have

existed between them, but abrupt, though perhaps very slight, changes of

form.

It is all-important to remember that naturalists have no golden rule by

which to distinguish species and varieties; they grant some little

variability to each species, but when they meet with a somewhat greater

amount of difference between any two forms, they rank both as species,

unless they are enabled to connect them together by close intermediate

gradations. And this from the reasons just assigned we can seldom hope to

effect in any one geological section. Supposing B and C to be two species,

and a third, A, to be found in an underlying bed; even if A were strictly

intermediate between B and C, it would simply be ranked as a third and

distinct species, unless at the same time it could be most closely

connected with either one or both forms by intermediate varieties. Nor

should it be forgotten, as before explained, that A might be the actual

progenitor of B and C, and yet might not at all necessarily be strictly

intermediate between them in all points of structure. So that we might

obtain the parent-species and its several modified descendants from the

lower and upper beds of a formation, and unless we obtained numerous

transitional gradations, we should not recognise their relationship, and

should consequently be compelled to rank them all as distinct species.

It is notorious on what excessively slight differences many

palaeontologists have founded their species; and they do this the more

readily if the specimens come from different sub-stages of the same

formation. Some experienced conchologists are now sinking many of the very

fine species of D'Orbigny and others into the rank of varieties; and on

this view we do find the kind of evidence of change which on my theory we

ought to find. Moreover, if we look to rather wider intervals, namely, to

distinct but consecutive stages of the same great formation, we find that

the embedded fossils, though almost universally ranked as specifically

different, yet are far more closely allied to each other than are the

species found in more widely separated formations; but to this subject I

shall have to return in the following chapter.

One other consideration is worth notice: with animals and plants that can

propagate rapidly and are not highly locomotive, there is reason to

suspect, as we have formerly seen, that their varieties are generally at

first local; and that such local varieties do not spread widely and

supplant their parent-forms until they have been modified and perfected in

some considerable degree. According to this view, the chance of

discovering in a formation in any one country all the early stages of

transition between any two forms, is small, for the successive changes are

supposed to have been local or confined to some one spot. Most marine

animals have a wide range; and we have seen that with plants it is those

which have the widest range, that oftenest present varieties; so that with

shells and other marine animals, it is probably those which have had the

widest range, far exceeding the limits of the known geological formations

of Europe, which have oftenest given rise, first to local varieties and

ultimately to new species; and this again would greatly lessen the chance

of our being able to trace the stages of transition in any one geological

formation.

It should not be forgotten, that at the present day, with perfect specimens

for examination, two forms can seldom be connected by intermediate

varieties and thus proved to be the same species, until many specimens have

been collected from many places; and in the case of fossil species this

could rarely be effected by palaeontologists. We shall, perhaps, best

perceive the improbability of our being enabled to connect species by

numerous, fine, intermediate, fossil links, by asking ourselves whether,

for instance, geologists at some future period will be able to prove, that

our different breeds of cattle, sheep, horses, and dogs have descended from

a single stock or from several aboriginal stocks; or, again, whether

certain sea-shells inhabiting the shores of North America, which are ranked

by some conchologists as distinct species from their European

representatives, and by other conchologists as only varieties, are really

varieties or are, as it is called, specifically distinct. This could be

effected only by the future geologist discovering in a fossil state

numerous intermediate gradations; and such success seems to me improbable

in the highest degree.

Geological research, though it has added numerous species to existing and

extinct genera, and has made the intervals between some few groups less

wide than they otherwise would have been, yet has done scarcely anything in

breaking down the distinction between species, by connecting them together

by numerous, fine, intermediate varieties; and this not having been

effected, is probably the gravest and most obvious of all the many

objections which may be urged against my views. Hence it will be worth

while to sum up the foregoing remarks, under an imaginary illustration.

The Malay Archipelago is of about the size of Europe from the North Cape to

the Mediterranean, and from Britain to Russia; and therefore equals all the

geological formations which have been examined with any accuracy, excepting

those of the United States of America. I fully agree with Mr.

Godwin-Austen, that the present condition of the Malay Archipelago, with

its numerous large islands separated by wide and shallow seas, probably

represents the former state of Europe, when most of our formations were

accumulating. The Malay Archipelago is one of the richest regions of the

whole world in organic beings; yet if all the species were to be collected

which have ever lived there, how imperfectly would they represent the

natural history of the world!

But we have every reason to believe that the terrestrial productions of the

archipelago would be preserved in an excessively imperfect manner in the

formations which we suppose to be there accumulating. I suspect that not

many of the strictly littoral animals, or of those which lived on naked

submarine rocks, would be embedded; and those embedded in gravel or sand,

would not endure to a distant epoch. Wherever sediment did not accumulate

on the bed of the sea, or where it did not accumulate at a sufficient rate

to protect organic bodies from decay, no remains could be preserved.

In our archipelago, I believe that fossiliferous formations could be formed

of sufficient thickness to last to an age, as distant in futurity as the

secondary formations lie in the past, only during periods of subsidence.

These periods of subsidence would be separated from each other by enormous

intervals, during which the area would be either stationary or rising;

whilst rising, each fossiliferous formation would be destroyed, almost as

soon as accumulated, by the incessant coast-action, as we now see on the

shores of South America. During the periods of subsidence there would

probably be much extinction of life; during the periods of elevation, there

would be much variation, but the geological record would then be least

perfect.

It may be doubted whether the duration of any one great period of

subsidence over the whole or part of the archipelago, together with a

contemporaneous accumulation of sediment, would exceed the average duration

of the same specific forms; and these contingencies are indispensable for

the preservation of all the transitional gradations between any two or more

species. If such gradations were not fully preserved, transitional

varieties would merely appear as so many distinct species. It is, also,

probable that each great period of subsidence would be interrupted by

oscillations of level, and that slight climatal changes would intervene

during such lengthy periods; and in these cases the inhabitants of the

archipelago would have to migrate, and no closely consecutive record of

their modifications could be preserved in any one formation.

Very many of the marine inhabitants of the archipelago now range thousands

of miles beyond its confines; and analogy leads me to believe that it would

be chiefly these far-ranging species which would oftenest produce new

varieties; and the varieties would at first generally be local or confined

to one place, but if possessed of any decided advantage, or when further

modified and improved, they would slowly spread and supplant their

parent-forms. When such varieties returned to their ancient homes, as they

would differ from their former state, in a nearly uniform, though perhaps

extremely slight degree, they would, according to the principles followed

by many palaeontologists, be ranked as new and distinct species.

If then, there be some degree of truth in these remarks, we have no right

to expect to find in our geological formations, an infinite number of those

fine transitional forms, which on my theory assuredly have connected all

the past and present species of the same group into one long and branching

chain of life. We ought only to look for a few links, some more closely,

some more distantly related to each other; and these links, let them be

ever so close, if found in different stages of the same formation, would,

by most palaeontologists, be ranked as distinct species. But I do not

pretend that I should ever have suspected how poor a record of the

mutations of life, the best preserved geological section presented, had not

the difficulty of our not discovering innumerable transitional links

between the species which appeared at the commencement and close of each

formation, pressed so hardly on my theory.

On the sudden appearance of whole groups of Allied Species. -- The abrupt

manner in which whole groups of species suddenly appear in certain

formations, has been urged by several palaeontologists, for instance, by

Agassiz, Pictet, and by none more forcibly than by Professor Sedgwick, as a

fatal objection to the belief in the transmutation of species. If numerous

species, belonging to the same genera or families, have really started into

life all at once, the fact would be fatal to the theory of descent with

slow modification through natural selection. For the development of a

group of forms, all of which have descended from some one progenitor, must

have been an extremely slow process; and the progenitors must have lived

long ages before their modified descendants. But we continually over-rate

the perfection of the geological record, and falsely infer, because certain

genera or families have not been found beneath a certain stage, that they

did not exist before that stage. We continually forget how large the world

is, compared with the area over which our geological formations have been

carefully examined; we forget that groups of species may elsewhere have

long existed and have slowly multiplied before they invaded the ancient

archipelagoes of Europe and of the United States. We do not make due

allowance for the enormous intervals of time, which have probably elapsed

between our consecutive formations,--longer perhaps in some cases than the

time required for the accumulation of each formation. These intervals will

have given time for the multiplication of species from some one or some few

parent-forms; and in the succeeding formation such species will appear as

if suddenly created.

I may here recall a remark formerly made, namely that it might require a

long succession of ages to adapt an organism to some new and peculiar line

of life, for instance to fly through the air; but that when this had been

effected, and a few species had thus acquired a great advantage over other

organisms, a comparatively short time would be necessary to produce many

divergent forms, which would be able to spread rapidly and widely

throughout the world.

I will now give a few examples to illustrate these remarks; and to show how

liable we are to error in supposing that whole groups of species have

suddenly been produced. I may recall the well-known fact that in

geological treatises, published not many years ago, the great class of

mammals was always spoken of as having abruptly come in at the commencement

of the tertiary series. And now one of the richest known accumulations of

fossil mammals belongs to the middle of the secondary series; and one true

mammal has been discovered in the new red sandstone at nearly the

commencement of this great series. Cuvier used to urge that no monkey

occurred in any tertiary stratum; but now extinct species have been

discovered in India, South America, and in Europe even as far back as the

eocene stage. The most striking case, however, is that of the Whale

family; as these animals have huge bones, are marine, and range over the

world, the fact of not a single bone of a whale having been discovered in

any secondary formation, seemed fully to justify the belief that this great

and distinct order had been suddenly produced in the interval between the

latest secondary and earliest tertiary formation. But now we may read in

the Supplement to Lyell's 'Manual,' published in 1858, clear evidence of

the existence of whales in the upper greensand, some time before the close

of the secondary period.

I may give another instance, which from having passed under my own eyes has

much struck me. In a memoir on Fossil Sessile Cirripedes, I have stated

that, from the number of existing and extinct tertiary species; from the

extraordinary abundance of the individuals of many species all over the

world, from the Arctic regions to the equator, inhabiting various zones of

depths from the upper tidal limits to 50 fathoms; from the perfect manner

in which specimens are preserved in the oldest tertiary beds; from the ease

with which even a fragment of a valve can be recognised; from all these

circumstances, I inferred that had sessile cirripedes existed during the

secondary periods, they would certainly have been preserved and discovered;

and as not one species had been discovered in beds of this age, I concluded

that this great group had been suddenly developed at the commencement of

the tertiary series. This was a sore trouble to me, adding as I thought

one more instance of the abrupt appearance of a great group of species.

But my work had hardly been published, when a skilful palaeontologist, M.

Bosquet, sent me a drawing of a perfect specimen of an unmistakeable

sessile cirripede, which he had himself extracted from the chalk of

Belgium. And, as if to make the case as striking as possible, this sessile

cirripede was a Chthamalus, a very common, large, and ubiquitous genus, of

which not one specimen has as yet been found even in any tertiary stratum.

Hence we now positively know that sessile cirripedes existed during the

secondary period; and these cirripedes might have been the progenitors of

our many tertiary and existing species.

The case most frequently insisted on by palaeontologists of the apparently

sudden appearance of a whole group of species, is that of the teleostean

fishes, low down in the Chalk period. This group includes the large

majority of existing species. Lately, Professor Pictet has carried their

existence one sub-stage further back; and some palaeontologists believe

that certain much older fishes, of which the affinities are as yet

imperfectly known, are really teleostean. Assuming, however, that the

whole of them did appear, as Agassiz believes, at the commencement of the

chalk formation, the fact would certainly be highly remarkable; but I

cannot see that it would be an insuperable difficulty on my theory, unless

it could likewise be shown that the species of this group appeared suddenly

and simultaneously throughout the world at this same period. It is almost

superfluous to remark that hardly any fossil-fish are known from south of

the equator; and by running through Pictet's Palaeontology it will be seen

that very few species are known from several formations in Europe. Some

few families of fish now have a confined range; the teleostean fish might

formerly have had a similarly confined range, and after having been largely

developed in some one sea, might have spread widely. Nor have we any right

to suppose that the seas of the world have always been so freely open from

south to north as they are at present. Even at this day, if the Malay

Archipelago were converted into land, the tropical parts of the Indian

Ocean would form a large and perfectly enclosed basin, in which any great

group of marine animals might be multiplied; and here they would remain

confined, until some of the species became adapted to a cooler climate, and

were enabled to double the southern capes of Africa or Australia, and thus

reach other and distant seas.

From these and similar considerations, but chiefly from our ignorance of

the geology of other countries beyond the confines of Europe and the United

States; and from the revolution in our palaeontological ideas on many

points, which the discoveries of even the last dozen years have effected,

it seems to me to be about as rash in us to dogmatize on the succession of

organic beings throughout the world, as it would be for a naturalist to

land for five minutes on some one barren point in Australia, and then to

discuss the number and range of its productions.

On the sudden appearance of groups of Allied Species in the lowest known

fossiliferous strata. -- There is another and allied difficulty, which is

much graver. I allude to the manner in which numbers of species of the

same group, suddenly appear in the lowest known fossiliferous rocks. Most

of the arguments which have convinced me that all the existing species of

the same group have descended from one progenitor, apply with nearly equal

force to the earliest known species. For instance, I cannot doubt that all

the Silurian trilobites have descended from some one crustacean, which must

have lived long before the Silurian age, and which probably differed

greatly from any known animal. Some of the most ancient Silurian animals,

as the Nautilus, Lingula, &c., do not differ much from living species; and

it cannot on my theory be supposed, that these old species were the

progenitors of all the species of the orders to which they belong, for they

do not present characters in any degree intermediate between them. If,

moreover, they had been the progenitors of these orders, they would almost

certainly have been long ago supplanted and exterminated by their numerous

and improved descendants.

Consequently, if my theory be true, it is indisputable that before the

lowest Silurian stratum was deposited, long periods elapsed, as long as, or

probably far longer than, the whole interval from the Silurian age to the

present day; and that during these vast, yet quite unknown, periods of

time, the world swarmed with living creatures.

To the question why we do not find records of these vast primordial

periods, I can give no satisfactory answer. Several of the most eminent

geologists, with Sir R. Murchison at their head, are convinced that we see

in the organic remains of the lowest Silurian stratum the dawn of life on

this planet. Other highly competent judges, as Lyell and the late E.

Forbes, dispute this conclusion. We should not forget that only a small

portion of the world is known with accuracy. M. Barrande has lately added

another and lower stage to the Silurian system, abounding with new and

peculiar species. Traces of life have been detected in the Longmynd beds

beneath Barrande's so-called primordial zone. The presence of phosphatic

nodules and bituminous matter in some of the lowest azoic rocks, probably

indicates the former existence of life at these periods. But the

difficulty of understanding the absence of vast piles of fossiliferous

strata, which on my theory no doubt were somewhere accumulated before the

Silurian epoch, is very great. If these most ancient beds had been wholly

worn away by denudation, or obliterated by metamorphic action, we ought to

find only small remnants of the formations next succeeding them in age, and

these ought to be very generally in a metamorphosed condition. But the

descriptions which we now possess of the Silurian deposits over immense

territories in Russia and in North America, do not support the view, that

the older a formation is, the more it has suffered the extremity of

denudation and metamorphism.

The case at present must remain inexplicable; and may be truly urged as a

valid argument against the views here entertained. To show that it may

hereafter receive some explanation, I will give the following hypothesis.

From the nature of the organic remains, which do not appear to have

inhabited profound depths, in the several formations of Europe and of the

United States; and from the amount of sediment, miles in thickness, of

which the formations are composed, we may infer that from first to last

large islands or tracts of land, whence the sediment was derived, occurred

in the neighbourhood of the existing continents of Europe and North

America. But we do not know what was the state of things in the intervals

between the successive formations; whether Europe and the United States

during these intervals existed as dry land, or as a submarine surface near

land, on which sediment was not deposited, or again as the bed of an open

and unfathomable sea.

Looking to the existing oceans, which are thrice as extensive as the land,

we see them studded with many islands; but not one oceanic island is as yet

known to afford even a remnant of any palaeozoic or secondary formation.

Hence we may perhaps infer, that during the palaeozoic and secondary

periods, neither continents nor continental islands existed where our

oceans now extend; for had they existed there, palaeozoic and secondary

formations would in all probability have been accumulated from sediment

derived from their wear and tear; and would have been at least partially

upheaved by the oscillations of level, which we may fairly conclude must

have intervened during these enormously long periods. If then we may infer

anything from these facts, we may infer that where our oceans now extend,

oceans have extended from the remotest period of which we have any record;

and on the other hand, that where continents now exist, large tracts of

land have existed, subjected no doubt to great oscillations of level, since

the earliest silurian period. The coloured map appended to my volume on

Coral Reefs, led me to conclude that the great oceans are still mainly

areas of subsidence, the great archipelagoes still areas of oscillations of

level, and the continents areas of elevation. But have we any right to

assume that things have thus remained from eternity? Our continents seem

to have been formed by a preponderance, during many oscillations of level,

of the force of elevation; but may not the areas of preponderant movement

have changed in the lapse of ages? At a period immeasurably antecedent to

the silurian epoch, continents may have existed where oceans are now spread

out; and clear and open oceans may have existed where our continents now

stand. Nor should we be justified in assuming that if, for instance, the

bed of the Pacific Ocean were now converted into a continent, we should

there find formations older than the silurian strata, supposing such to

have been formerly deposited; for it might well happen that strata which

had subsided some miles nearer to the centre of the earth, and which had

been pressed on by an enormous weight of superincumbent water, might have

undergone far more metamorphic action than strata which have always

remained nearer to the surface. The immense areas in some parts of the

world, for instance in South America, of bare metamorphic rocks, which must

have been heated under great pressure, have always seemed to me to require

some special explanation; and we may perhaps believe that we see in these

large areas, the many formations long anterior to the silurian epoch in a

completely metamorphosed condition.

The several difficulties here discussed, namely our not finding in the

successive formations infinitely numerous transitional links between the

many species which now exist or have existed; the sudden manner in which

whole groups of species appear in our European formations; the almost

entire absence, as at present known, of fossiliferous formations beneath

the Silurian strata, are all undoubtedly of the gravest nature. We see

this in the plainest manner by the fact that all the most eminent

palaeontologists, namely Cuvier, Owen, Agassiz, Barrande, Falconer, E.

Forbes, &c., and all our greatest geologists, as Lyell, Murchison,

Sedgwick, &c., have unanimously, often vehemently, maintained the

immutability of species. But I have reason to believe that one great

authority, Sir Charles Lyell, from further reflexion entertains grave

doubts on this subject. I feel how rash it is to differ from these great

authorities, to whom, with others, we owe all our knowledge. Those who

think the natural geological record in any degree perfect, and who do not

attach much weight to the facts and arguments of other kinds given in this

volume, will undoubtedly at once reject my theory. For my part, following

out Lyell's metaphor, I look at the natural geological record, as a history

of the world imperfectly kept, and written in a changing dialect; of this

history we possess the last volume alone, relating only to two or three

countries. Of this volume, only here and there a short chapter has been

preserved; and of each page, only here and there a few lines. Each word of

the slowly-changing language, in which the history is supposed to be

written, being more or less different in the interrupted succession of

chapters, may represent the apparently abruptly changed forms of life,

entombed in our consecutive, but widely separated formations. On this

view, the difficulties above discussed are greatly diminished, or even

disappear.